Day 8 - Web Access for Home

Transcription

Week 2 Topics
Day 6:
Remainder of Week 1
Day 6:
Includes Chemistry
Day 7:
Material & Energy Balances
Thermodynamics (done week 1)
Fluid Mechanics (done week 1)
Heat Transfer (done week 1)
Day 7:
Mass Transfer
AFTERNOON EXAM
Day 8:
Day 8:
Day 9:
Day 9:
Day 9:
Day 10:
Process Design & Economics
Ethics, Health, Safety & Environment
Chemical Reaction Engineering
Computers
Process Controls
Summary & Send-off
BEGINNING OF MASS AND
ENERGY BALANCES AND MASS
TRANSFER
Refrigeration
•
•
•
•
•
Material, Energy Balances
Thermodynamics
Heat Exchanger Sizing
Capital & Operating Cost
http://dc178.4shared.com/doc/UXTK3tk7/pre
view.html
Reaction, Recycle, Purge Reaction
http://193.146.160.29/gtb/sod/usu/$UBUG/repositorio/10300047_Aitani.pdf
END OF MASS AND
ENERGY BALANCES
Chemical Discipline‐Specific Review Course for the FE/EIT Exam
Process Design & Economic
Optimization
DSCHRC
© 2011, Professional Publications, Inc. (PPI)
© Professional Publications, Inc. (PPI)
1b‐1
Topics Covered
• Process Flow Diagrams (PFD)
• Piping and Instrumentation Diagrams (P&ID)
• Scale‐up
DSCHRC
• Economic Optimization
–
–
–
–
Net Present Value
Discounted Cash Flow
Rate of Return
Cost Estimation
1b‐2
Process Flow Diagrams
• Contains data for design of process
• No universally‐accepted standards
• Contains:
– Major equipment with description (unique ID)
– Process streams (ID)
– Utilities supplied to major equipment
– Control loops & strategy
DSCHRC
1b‐3
PFD Markings
•
•
•
•
•
•
•
P‐101A/B
C: compressor/turbine
E: heat exchanger
H: fired heater
P: pump
R: reactor
T: tower
DSCHRC
TK: storage tank
V: vessel
Y: within the plant
ZZ: number for each item in a class
• General Format: •
•
•
•
– XX‐YZZ A/B
• XX ID letters for equipment classification
1b‐4
PFD Utility Streams
• lps: low‐pressure steam
• mps: medium‐pressure steam
• hps: high‐pressure steam
• htm: heat transfer media (organic)
• cw: cooling water
• rw: refrigerated water
• rb: refrigerated brine
DSCHRC
• wr: river water
• cs: chemical wastewater with high COD
• ss: sanitary waste water with high BOD
• el: electrical service
• ng: natural gas
• fg: fuel gas
• fo: fuel oil
• fw: fire water
1b‐5
PFD Example
From Analysis, Synthesis, and Design of Chemical Processes, 2nd Ed., Turton
DSCHRC
1b‐6
Piping & Instrumentation
Diagram
• P&ID
• Each PFD requires many P&IDs
• Mechanical aspects of the plant except:
– operating conditions
– steam flows
– equipment locations
– pipe routing (lengths & fittings)
– supports, structures, & foundations
DSCHRC
1b‐7
P&ID Conventions
• Equipment
• Instruments
– spares
– parallel units
– summary details
• Lines/Drains
–
–
–
–
DSCHRC
– indicators
– recorders
– controllers
• Utilities
size
schedule
materials of construction
insulation
– entrance & exits
– waste treatments
1b‐8
P&ID Instrumentation
Conventions—First Letters
•
•
•
•
•
•
•
•
•
•
A: analysis
B: burner flame
C: conductivity
D: density
E: voltage
F: flowrate
H: hand initiated
I: current
J: power
K: time
DSCHRC
•
•
•
•
•
•
•
•
•
•
L: level
M: moisture/humidity
P: pressure
Q: quantity
R: radioactivity/ratio
S: speed/frequency
T: temperature
V: viscosity
W: weight
Z: position
1b‐9
P&ID Example
From Analysis, Synthesis, and Design of Chemical Processes, 2nd Ed., Turton
DSCHRC
1b‐10
Economic Analysis
DSCHRC
© 2011, Professional Publications, Inc.
(PPI)
1b‐11
Net Present Value Example
EFPRB (Economics‐9)
Consider a project that involves the investment of $100,000 now and $100,000 at the end of year 1. Revenues of $150,000 will be generated at the end of years 1 and 2. What is most nearly the net present value of this project if the effective annual interest rate is 10%?
A) −$65,000 B) −$50,900 C) $43,300 D) $78,500
DSCHRC
1b‐12
NPV Solution
P  A P / A, i , n
 $100,000  $50,000 P / F ,10%,1  $150,000 P / F ,10%,2
 $100,000  $50,000 0.9091  $150,000 0.8264
 $78,505
The answer is D.
DSCHRC
1b‐13
Profit Example
A company invests $10,000 today to be repaid in 5 years in one lump sum at 12% compounded annually. If the rate of inflation is 3% compounded annually, approximately how much profit, in present day dollars, is realized over the 5 years?
A) $3200 B) $5200 C) $5630 D) $7620
DSCHRC
1b‐14
Profit Solution
F  P (F / P , i , n )
 $10,000(F / P,12%,5)
  $10,000 1.7623 
 $17,623
PV  $17,623(P / F ,3%,5)
  $17,623  0.8626 
 $15,202
Profit  $15,202  $10,000
 $5202
The answer is B.
DSCHRC
1b‐15
Discount Rate Example
Given that the discount rate is 15%, what is the equivalent uniform annual cash flow for the following stream of cash flows?
Year 0: ‐$100k
Year 1: ‐$200k
Year 2: ‐$50k
Year 3: ‐$75k
DSCHRC
1b‐16
Discount Rate Solution
EUAC  P A / P , i , n
 A / P , i , n F P / F , i , n
 A / P ,15%,3 $100,000  $200,000 P / F ,15%,1
 $50,000 P / F ,15%,2  $75,000 P / F ,15%,3

  0.4380 $100,000   $200,000 0.8696   $50,000 0.7561   $75,000 0.6575
 $158,200
DSCHRC

1b‐17
Depreciation Example
The purchase of a motor for $6000 and a generator for $4000 will allow a company to produce its own energy. The configuration can be assembled for $500. The service will operate for 1600 h/yr for 10 yr. The maintenance cost is $300/yr, and the cost to operate is $0.85/h for fuel and related costs. There is $400 in salvage value for the system at the end of 10 yr. Using straight‐line depreciation, what is the annual cost for operation?
DSCHRC
1b‐18
Depreciation Solution
Initial Cost  $6000  $4000  $500
 $10,500
C  S $10,500  $400
Dj 

n
10 yr
 $1010/yr
operation cost  ($0.85/h)(1600 h/yr)
 $1360/yr
annual cost  D j  maintenance  operation
 $1010  $300  $1360
 $2670 / yr
DSCHRC
1b‐19
Conclusion
• Be familiar with manipulating equations • Be comfortable reading and evaluating PFDs and P&IDs
• Review the Economics section of the FERM to understand economic relationships fully
DSCHRC
1b‐20
FE Review Course
FE
Review
Course
Engineering Economics
FERC
© Professional Publications, Inc.
4‐1
FE Review Course
4-1
Cash Flow
Cash flow is the sum of money recorded
as receipts or disbursements in a
project’s financial records.
A cash flow diagram presents the flow of
cash as arrows on a time line scaled to
the magnitude of the cash flow, where
expenses are down arrows and receipts
are up arrows.
Year-end convention ~ expenses
occurring during the year are
assumed to occur at the end of the
year.
Example (FEIM):
A mechanical device will cost $20,000
when purchased. Maintenance will cost
$1000 per year. The device will generate
revenues of $5000 per year for 5 years.
The salvage value is $7000.
Professional Publications, Inc.
FERC
4‐2
FE Review Course
4-2a
Discount Factors and Equivalence
Present Worth (P): present amount at t = 0
Future Worth (F): equivalent future amount at t = n of any present
amount at t = 0
Annual Amount (A): uniform amount that repeats at the end of each year
for n years
Uniform Gradient Amount (G): uniform gradient amount that repeats at
the end of each year, starting at the end of the second year and
stopping at the end of year n.
FERC
4‐3
FE Review Course
4-2b
NOTE: To save time,
use the calculated
factor table provided
in the NCEES FE
Handbook.
FERC
4‐4
FE Review Course
4-2c
Example (FEIM):
How much should be put in an investment with a 10% effective annual
rate today to have $10,000 in five years?
Using the formula in the factor conversion table,
P = F(1 + i) –n = ($10,000)(1 + 0.1) –5 = $6209
Or using the factor table for 10%,
P = F(P/F, i%, n) = ($10,000)(0.6209) = $6209
FERC
4‐5
FE Review Course
4-2d
Example (FEIM):
What factor will convert a gradient cash flow ending at t = 8 to a future
value? The effective interest rate is 10%.
The F/G conversion is not given in the factor table. However, there are
different ways to get the factor using the factors that are in the table. For
example,
(F/G,i%,8) = (P/G,10%,8)(F/P,10%,8)
= (16.0287)(2.1436)
or
= 34.3591
(F/G,i%,8) = (F/A,10%,8)(A/G,10%,8)
= (11.4359)(3.0045)
= 34.3592
NOTE: The answers arrived at using the formula versus the factor table
turn out to be slightly different. On economics problems, one should not
worry about getting the exact answer.
FERC
4‐6
FE Review Course
4-3
Nonannual Compounding
Effective Annual Interest Rate
An interest rate that is compounded more than once in a year is
converted from a compound nominal rate to an annual effective rate.
Effective Interest Rate Per Period
Effective Annual Interest Rate
Example (FEIM):
A savings and loan offers a 5.25% rate per annum compound daily over
365 days per year. What is the effective annual rate?
 r 
 0.0525 
ie  1   1 1
  1 0.0539
365 
 m 

m
365
FERC
4‐7
FE Review Course
4-4
Discount Factors for Continuous Compounding
The formulas for continuous compounding are the same formulas in the
factor conversion table with the limit taken as the number of periods, n,
goes to infinity.
FERC
4‐8
FE Review Course
4-5a
Comparison of Alternatives
Present Worth
When alternatives do the same job and have the same lifetimes,
compare them by converting each to its cash value today. The superior
alternative will have the highest present worth.
Example (CORE):
FERC
4‐9
FE Review Course
4-5b
Capitalized Costs
Used for a project with infinite life that has repeating expenses every
year.
Compare alternatives by calculating the capitalized costs (i.e., the
amount of money needed to pay the start-up cost and to yield enough
interest to pay the annual cost without touching the principal).
NOTE: The factor conversion for a project with no end is the limit of the
P/A factor as the number of periods, n, goes to infinity.
FERC
4‐10
FE Review Course
4-5c
Example (CORE):
FERC
4‐11
FE Review Course
4-5d
Annual Cost
When alternatives do the same job but have different lives, compare the
cost per year of each alternative.
The alternatives are assumed to be replaced at the end of their lives by
identical alternatives. The initial costs are assumed to be borrowed at
the start and repaid evenly during the life of the alternative.
Example (CORE):
FERC
4‐12
FE Review Course
4-5e
Cost-Benefit Analysis
Project is considered acceptable if B – C ≥ 0 or B/C ≥ 1.
Example (FEIM):
The initial cost of a proposed project is $40M, the capitalized perpetual
annual cost is $12M, the capitalized benefit is $49M, and the residual
value is $0. Should the project be undertaken?
B = $49M, C = $40M + $12M + $0
B – C = $49M – $52M = –$3M < 0
The project should not be undertaken.
FERC
4‐13
FE Review Course
4-5f
Rate of Return on an Investment (ROI)
The ROI must exceed the minimum attractive rate of return (MARR).
The rate of return is calculated by finding an interest rate that makes the
present worth zero. Often this must be done by trial and error.
FERC
4‐14
FE Review Course
4-6a
Depreciation
Straight Line Depreciation
The depreciation per year is the cost minus the salvage value divided by
the years of life.
FERC
4‐15
FE Review Course
4-6b
Depreciation
Accelerated Cost Recovery System (ACRS)
The depreciation per year is the cost times the ACRS factor (see the
table in the NCEES Handbook). Salvage value is not considered.
FERC
4‐16
FE Review Course
4-6c
Depreciation
Example (FEIM):
An asset is purchased that costs $9000. It has a 10-year life and a salvage
value of $200. Find the straight-line depreciation and ACRS depreciation
for 3 years.
$9000  $200
10
 $880 / yr
Straight-line depreciation/year 
ACRS depreciation
First year
($9000)(0.1) = $ 900
Second year ($9000)(0.18) = $1620
Third year
($9000)(0.144) = $1296
FERC
4‐17
FE Review Course
4-6d
Depreciation
Book Value
The assumed value of the asset after j years. The book value (BVj) is the
initial cost minus the sum of the depreciations out to the j th year.
Example (FEIM):
What is the book value of the asset in the previous example after 3 years
using straight-line depreciation? Using ACRS depreciation?
Straight-line depreciation
$9000 – (3)($880) = $6360
ACRS depreciation
$9000 – $900 – $1620 – $1296 = $5184
FERC
4‐18
FE Review Course
4-7a
Tax Considerations
Expenses and depreciation are deductible, revenues are taxed.
Example (CORE):
FERC
4‐19
FE Review Course
4-7b
Tax Considerations
Tax Credit
A one-time benefit from a purchase that is subtracted from income taxes.
Example (CORE):
FERC
4‐20
FE Review Course
4-7c
Tax Considerations
Gain or loss on the sale of an asset:
If an asset has been depreciated and then is sold for more than the book
value, the difference is taxed.
FERC
4‐21
FE Review Course
4-8
Bonds
Bond value is the present worth of payments over the life of the bond.
Bond yield is the equivalent interest rate of the bond compared to the
bond cost.
Example (CORE):
FERC
4‐22
FE Review Course
4-9
Break-Even Analysis
Calculating when revenue is equal to cost, or when one alternative is equal to
another if both depend on some variable.
Example (FEIM):
How many kilometers must a car be driven per year for leasing and buying to cost
the same? Use 10% interest and year-end cost.
Leasing: $0.15 per kilometer
Buying: $5000 purchase cost, 3-year life, salvage $1200,
$0.04 per kilometer for gas and oil, $500 per year for insurance
EUAC (leasing) = $0.15x, where x is kilometers driven
EUAC (buying) = $0.04x + $500 + ($5k)(A/P,10%,3) – ($1.2k)(A/F,10%,3)
= $0.04x + $500 + ($5k)(0.4021) – ($1.2k)(0.3021)
= $0.04x + $2148
Setting EUAC (leasing) = EUAC (buying) and solving for x
$0.15x = $0.04x + $2148
x = 19,527 km must be driven to break even
FERC
4‐23
FE Review Course
4-10
Inflation
Inflation-Adjusted Interest Rate
FERC
4‐24
FE Review Course
4-11a
Additional Examples
Example 1 (FEIM):
What is the uninflated present worth of $2000 in 2 years if the average
inflation rate is 6% and i is 10%?
d = i + f + if = 0.06 + 0.10 + (0.06)(0.10) = 0.166
P = ($2000)(P/F,16.6%,2) = ($2000)(1 + d)–n
= ($2000)(1 + 0.166)–2 = $1471
FERC
4‐25
FE Review Course
4-11b
Additional Examples
Example 2 (FEIM):
It costs $75 per year to maintain a cemetery plot. If the interest rate is
6.0%, how much must be set aside to pay for maintenance on each plot
without touching the principal?
(A) $1150
(B) $1200
(C) $1250
(D) $1300
P = ($75)(P/A,6%,) = ($75)(1/0.06) = $1250
Therefore, (C) is correct.
FERC
4‐26
FE Review Course
4-11c
Additional Examples
Example 3 (FEIM):
It costs $1000 for hand tools and $1.50 labor per unit to manufacture a
product. Another alternative is to manufacture the product by an
automated process that costs $15,000, with a $0.50 per-unit cost. With
an annual production rate of 5000 units, how long will it take to reach the
break-even point?
(A) 2.0 yr
(B) 2.8 yr
(C) 3.6 yr
(D) never
Cumulative cost (hand tools) = $1000 + $1.50x, where x is the number
of units.
Cumulative cost (automated) = $15,000 + $0.50x
Set cumulative costs equal and solve for x.
$1000 + $1.50x = $15,000 + $0.50x
$1x = $14,000
x = 14,000 units
tbreak-even = x/production rate = 14,000/5000 = 2.8 yr
Therefore, (B) is correct.
FERC
4‐27
FE Review Course
4-11d
Additional Examples
Example 4 (FEIM):
A loan of $10,000 is made today at an interest rate of 15%, and the first
payment of $3000 is made 4 years later. The amount that is still due on
the loan after the first payment is most nearly
(A) $7000
(B) $8050
(C) $8500
(D) $14,500
loan due = ($10k)(F/P,15%,4) – $3000
= ($10k)(1 + 0.15)4 – $3000
= ($10k)(1.7490) – $3000
= $14,490 ($14,500)
Therefore, (D) is correct.
FERC
4‐28
FE Review Course
4-11e
Additional Examples
Example 5 (FEIM):
A machine is purchased for $1000 and has a useful life of 12 years. At
the end of 12 years, the salvage value is $130. By straight-line
depreciation, what is the book value of the machine at the end of 8
years?
(A) $290
(B) $330
(C) $420
(D) $580
BV = $1000 – ($1000 – $130)(8/12) = $1000 – $580 = $420
FERC
4‐29
FE Review Course
4-11f
Additional Examples
Example 6 (FEIM):
The maintenance cost for an investment is $2000 per year for the first 10
years and $1000 per year thereafter. The investment has infinite life.
With a 10% interest rate, the present worth of the annual disbursement is
most nearly
(A) $10,000
(B) $16,000
(C) $20,000
(D) $24,000
The costs or benefits for a cash flow that repeat should be broken into
different benefits and costs that all start or finish at the time of interest.
Take the $2000 cost that repeats for 10 years and break it into two
$1000 costs to have one $1000 cost that goes on infinitely and one
$1000 cost that goes on for 10 years.
P = ($1000)(P/A,10%,10) + ($1000)(P/A,10%,)
= ($1000)(6.1446) + ($1000)(1/0.10)
= $6144.6 + $10,000 = $16,144.6 ($16,000)
FERC
4‐30
FE Review Course
4-11g
Additional Examples
Example 7 (FEIM):
With an interest rate of 8% compounded semiannually, the value of a
$1000 investment after 5 years is most nearly
(A) $1400
(B) $1470
(C) $1480
(D) $1800
ie = (1 + r/m)m – 1= (1 + 0.08/2)2 – 1 = 0.0816
F = ($1000)(F/P,8.16%,5) = ($1000)(1 + 0.0816)5
= ($1000)(1.480) = $1480
FERC
4‐31
FE Review Course
4-11h
Additional Examples
Example 8 (FEIM):
The following data applies for example problems 8.1 through 8.3. A company is
considering the purchase of either machine A or machine B.
initial cost
estimated life
salvage value
other costs
machine A
$80,000
20 years
$20,000
$18,000 per year
machine B
$100,000
25 years
$25,000
$15,000 per year for the first 15 years
$20,000 per year for the next 10 years
Example 8.1 (FEIM):
The interest rate is 10%, and all cash flows may be treated as end-of-year cash
flows. Assume that equivalent annual cost is the value of the constant annuity
equal to the total cost of a project. The equivalent annual cost of machine B is
most nearly
(A) $21,000
(B) $21,500
(C) $23,000
(D) $26,500
FERC
4‐32
FE Review Course
4-11i
Additional Examples
The $15,000 cost for 15 years and the $20,000 cost for the next 10 years
can be broken into a $20,000 cost for the full 25 years and a $5000 benefit
that is present for the first 15 years.
The present worth of $20k for 25 years is
P($20,25) = ($20k)(P/A,10%,25) = ($20k)(9.0770) = $181.54k
The present worth of $5k for 15 years is
P($5,15) = ($5k)(P/A,10%,15) = ($5k)(7.6061) = 38.03k
Pother costs = $181.54k – $38.03k = $143.51k
Aother costs = Pother costs(A/P, 10%, 25) = ($143.51k)(0.1102) = $15,815
EUAC
= ($100k)(A/P,10%,25) – ($25k)(A/F,10%,25) + $15,815
= ($100k)(0.1102) – ($25k)(0.0102) + $15,815
= $11,020 – $255 + $15,815 = $26,610 ($26,500)
FERC
4‐33
FE Review Course
4-11j
Additional Examples
Example 8.2 (FEIM):
If funds equal to the present worth of the cost of purchasing and using
machine A over 20 years were invested at 10% per annum, the value of
the investment at the end of 20 years would be most nearly:
(A) $548,000
(B) $676,000
(C) $880,000
(D) $1,550,000
P(A) = – $80k + ($20k)(P/F,10%,20) – ($18k)(P/A,10%,20)
= – $80k + ($20k)(0.1486) – ($18k)(8.5136)
= – $80k + $2.972k – $153.245k
= – $230,273, or simply $230,273
F(A,10%,20) = ($230,273)(F/P,10%,20) = ($230,273)(6.7275)
= $1,549,162 ($1,550,000)
FERC
4‐34
FE Review Course
4-11k
Additional Examples
Example 8.3 (FEIM):
How much money would have to be placed in a sinking fund each year to
replace machine B at the end of 25 years if the fund yields 10% annual
compound interest and if the first cost of the machine is assumed to
increase at a 6% annual compound rate? (Assume the salvage value does
not change.)
(A) $2030
(B) $2510
(C) $2540
(D) $4110
F = P(F/P,6%,25) – salvage value = ($100,000)(4.2919) – $25,000
= $404,190
A = F(A/F,10%,25) = ($404,190)(0.0102)
= $4123 ($4110)
FERC
4‐35
Health, Safety
& the Environment
DSCHRC
2b‐1
NCEES Reference Book
• Environment, Health & Safety throughout
• Environmental Engineering—Noise, Toxicology, Waste Treatment, Storage & Handling, & MSDS
• Industrial Engineering—Ergonomics & Noise
• Chemical Engineering—Toxicology, Risk Assessment, Flammability
DSCHRC
2b‐2
Material Safety Data Sheets
& Hazard Assessment
Toxicology, Flammability, Corrosivity
DSCHRC
(PPI)
2b‐3
Material Safety Data Sheets
• “MSDS”
• Important for determining chemical information
• Sheet must be provided on exam—examinee must know how to read MSDS
• Important information will be toxicological information, protective measures, storage & handling, disposal, transportation, & reactivity
DSCHRC
2b‐4
Information on an MSDS
•
•
•
•
•
•
•
•
Material identification
Reactivity data
Spill procedures
Melting point
Boiling point
Flash point
Other physical data
Special precautions & comments
DSCHRC
• Chemical abstract series number
• First aid
• Reactivity
• Storage information
• Disposal information
• Personal protective equipment
• Health hazard information & toxicity © 2011, Professional Publications, Inc. (PPI)
2b‐5
Hazard Assessment
• Fire hazard diamonds appear on the MSDS
• Also shown on chemical labels
• “Flammable:” any solid, liquid, vapor, or gas that ignites with ease and burns quickly
DSCHRC
B
A
C
D
2b‐6
Hazard Analysis
• Requires analyzing processing using appropriate planning (checklist, fault‐tree analysis, hazards & operability study)
• Checklists: specific & focused
• Fault‐tree analysis: – Identify catastrophic failures
– Identify contributing failures
• Hazards & Operability Study:
– Allows for ignoring failures that would not affect system
– Identifies human factors
DSCHRC
2b‐7
Toxicology
• Evaluate based on exposure pathway
– Absorption
– Inhalation
– Ingestion
– Eyeway
• Dose‐Response Relationships
• Safe Human Dose
DSCHRC
2b‐8
Organ Effects Terminology
•
•
•
•
•
•
•
•
Pulmonary toxicity: effects on respiratory system
Cardiotoxicity: effects on the heart
Hematoxicity: effects on blood supply
Hepatoxicity: effects on liver
Nephrotoxicity: effects on kidneys
Neurotoxicity: effects on nervous system
Immunotoxicity: effects on immune system
Reproductive toxicity: effects on reproductive system
DSCHRC
2b‐9
Dose Response Curves
• Environmental Engineering section of NCEES Reference Handbook
• Lethal Dose/Lethal Concentration
– Particulate concentration = mg particulate/m3 of air
– Concentration for LDxx = mg toxicant/kg body mass at which XX% of the test animals died
DSCHRC
2b‐10
Dose Response Example
Chemical A has an LD50 of 3 mg/kg. Chemical B has an LD50 of 9mg/kg. Chemical A is
(A) 1/3 as toxic as Chemical B
(B) 3 times as toxic as Chemical B
(C) Not comparable to Chemical B because no pathway is specified
(D) Not comparable to Chemical B because it is not clear which organs are targeted
The correct answer is B.
DSCHRC
2b‐11
Human Health Risk
• Carcinogens
Risk  dose  toxicity  CDI  CSF
CDI  chronic daily intake
CSF  cancer slope factor
• Noncarcinogens
mass of toxicant
body weight  exposure time
chronic daily intake
HI 
RfD
Dose 
DSCHRC
2b‐12
Human Health Risk (2)
• Reference Dose
RfD 
NOAEL
UF
SHD  RfD  W 
• Exposure
NOAEL  W
UF
– Must be calculated based on the pathway
– Be familiar with the pathway equations and variables
DSCHRC
2b‐13
Exposure Question
The town of Franklin receives its water from a city water supply. If the maximum contaminant level of benzene of the city’s drinking water is 0.003 mg/L, what is the ingestion chronic daily intake for a child 3 years old who swims in a city pool 1 hour a day, 4 days per month?
A) 1.4*10‐9 mg/kg*d
B) 1.1*10‐6 mg/kg*d
C) 1.4*10‐6 mg/kg*d
D) 5.2*10‐9 mg/kg*d
DSCHRC
2b‐14
Exposure Question (2)
• From the problem statement and NCEES reference book:
CW  0.003mg/L
BW  14kg NCEES
ET  1hr/d
CR  50mL/hr NCEES
EF  4d/mo  12mo/yr  48d/yr
ED  70years NCEES
CW*CR*ET*EF*ED
AT  ED * 365d/y NCEES CDI 

BW*AT
0.003mg/L 50mL/h 1L/1000mL 1hr/d 48d/yr 70yr
14kg 70yr 365d/yr
‐6 mg
 1.4*10
kg*d
• The correct answer is C
DSCHRC
2b‐15
Waste Minimization &
Treatment
Air, Water & Solids
DSCHRC
(PPI)
2b‐16
Wastewater Treatment
• Typically related to municipal wastewater treatment systems
• Systems must support bacteria to process organic matter, colloids and nitrogen/phosphorus compounds
DSCHRC
2b‐17
Wastewater Treatment (2)
• Activated Sludge
XA 
θ c Y(So  Se )
θ(1  k d θ c )
θ c  solids residence time 
• Aerobic Digestion
Vol 
DSCHRC
Vol(X A )
Q w X w  Qe X e
Q i (X i  FSi )
1
X d (k d Pv  )
θc
2b‐18
Wastewater Treatment (3)
• Anaerobic Digestion
– Standard Rate
Vol reactor
Vol1  Vol 2

t r  Vol 2 t s
2
– High Rate
Vol reactor firststage  Vol1t r
Vol reactor secondstage 
DSCHRC
Vol1  Vol 2
t t  Vol 2 t s
2
2b‐19
Wastewater Technologies
•
•
•
•
•
•
•
•
•
Activated Carbon Adsorption
Air Stripping
Clarifier
Electrodialysis
Filtration
Lime‐Soda Softening
Flocculators
Reverse Osmosis Settling
DSCHRC
2b‐20
Reverse Osmosis Example
The osmotic pressure of sodium hydroxide of a 0.1M NaOH solution at 25oC with an osmotic coefficient of 0.5 is most nearly:
A) 124,000 Pa
B) 90,000 Pa
C) 124,000 kPa
D) 124 Pa
DSCHRC
2b‐21
Reverse Osmosis Solution
n
  v
RT
Vol

0.1mol
1000L/m3 1kmol/1000mol 8312Pa*m3 /kmol*K
L
  124,000Pa
0.5 1
25oC  273.15 K
The answer is A
DSCHRC
2b‐22
Air Pollution Treatment
• Atmospheric dispersion modeling
• Cyclone collection
– Use collection efficiency chart based on particle size ratio
• Baghouse design
– NCEES provides Air‐to‐Cloth ratios for Shakers/Reverse Air/Woven and Pulse Jet/Felt
• Electrostatic precipitators
• Incineration
DSCHRC
2b‐23
Safety Control & Design
DSCHRC
(PPI)
2b‐24
Pressure Relief Systems
• Designed to provide multiple systems in case of simultaneous failure
• Devices must operate under undesirable conditions and flow may be one‐ or two‐phase
• Relief valves or rupture disks
DSCHRC
2b‐25
Additional Safety Evaluations
• Not in NCEES FE Reference Handbook
• May be asked to calculate mixtures and given flammability limits to determine if mixture would be an explosion hazard
DSCHRC
2b‐26
Explosion Hazard Example
Lean and rich flammability limits for a propane and air mixture at atmospheric pressure are 51% and 283%, respectively. Which of the following, stored in a vessel, presents an explosion hazard?
A) 6.7 mol% C3H8, 93.3 mol%air
B) 34 mol% C3H8, 66 mol% air
C) 72 mol% C3H8, 28 mol% air
D) both (b) and (c)
DSCHRC
2b‐27
Explosion Hazard Solution
• First write a balanced equation
C3H 8  5O 2  3CO 2  4H 2 O
• Evaluate stoichiometry of air
 molair
(5 molO 2 )
 0.21 molO
2


  23.8 molair


• Evaluate stoichiometry of propane

1 molC3H8

 23.8 molair  1 molC H
3 8

DSCHRC

(100%)  4.03%


2b‐28
Explosion Hazard Solution
(cont.)
• Calculate flammability limit
UL  (2.83)(4.03%)  11.4% C3 H 8
LL  (0.51)(4.03%)  2.06% C3 H 8
• The Answer is A
DSCHRC
2b‐29
Personal Protection
Personal Protective Equipment, Ergonomics, Auditory Protection
DSCHRC
(PPI)
2b‐30
Personal Protection
•
•
•
•
Wide range of subjects
Personal Protective Equipment (“PPE”)
Ergonomics
Noise/Auditory Harm
– Noise pollution
– Workplace noise
DSCHRC
2b‐31
Personal Protective Equipment
• Protects against inhalation and dermal hazards
– Respirators protect against inhalation hazards (require proper filters to protect)
– Protective Clothing
•
•
•
•
DSCHRC
Aprons
Face shields
Gloves*
Goggles
2b‐32
Ergonomics
• Work‐rest cycles
• Manual load handling
• Cumulative trauma disorders (“CTDs”)
– Carpal Tunnel Syndrome
– Tendonitis
– Pronator Syndrome
DSCHRC
2b‐33
Ergonomics (2)
• Recommended weight limit
W  51(10/H)(1  0.0075 | V  30 |)(0.82 
1.8
)(1  0.0032A)(FM)(CM)
D
• Anthropometric Measurements—how to measure provided in the NCEES reference book
• Civilian body dimensions table in NCEES reference book
• Facility planning & locating equations
DSCHRC
2b‐34
Workplace Noise
• Hearing charts in NCEES Reference Book
• Permissible Noise Exposure (OSHA)
Ci
D  100%  
Ti
C i 8h
 105  SPL 
80  SPL  130dBA,Ti  2
 hours
5


DSCHRC
2b‐35
Noise Example
A woman works in a power plant where she spends 2 hours per day in an area which measures 98 dBA and 6 hours per day in an area which measures 81 dBA each day. Her noise dose:
A) Exceeds by 135% B) Under by 33%
C) Exceeds by 33% D) Under by 135%
DSCHRC
2b‐36
This image cannot currently be display ed.
Noise Solution
• Calculate the T values
• Calculate the noise dose
 105  81 
T81  2
 hours
5


 105  98 
T98  2
 hours
5


C
C 
6 
 2
D  100% 98  81   100%

  133%
 2.8 9.6 
 T98 T81 
• The answer is C
DSCHRC
2b‐37
Noise Pollution
SPL (dB)  10 log10 (P 2 /P02 )
SPL total  10 log10 10
DSCHRC
SPL/10
2b‐38
Storage & Handling
DSCHRC
(PPI)
2b‐39
Storage & Handling
• Important not to store incompatible chemicals together
• Hazardous waste compatibility chart
• Labels are required in storage areas
DSCHRC
2b‐40
FE Review Course
FE
Review
Course
Ethics & Business
Practices
FERC
© Professional Publications (PPI)
18‐1
FE Review Course
Ethics & Business Practices
18-1
FE Exam Information
The ethics questions test students on reading comprehension and
elementary logic.
• Assumptions are necessary since exam problems may not give
complete information.
• Answers that require large leaps in logic are almost always wrong.
• Answers that relate to professional societies are probably wrong.
• There will likely be nonsense answers that are irrelevant to the
problem statement, engineering, or ethics.
• Beware of true statements about ethics that are not germane to
the problem.
Read the Ethics pages in the NCEES FE Handbook at least four times
and read FERM Chapter 54.
FERC
18‐2
FE Review Course
18-2a
Obligation to Society
An engineer’s first obligation is always to society. This obligation takes
precedence over all others.
A registered engineer’s obligations to society are summarized as
follows:
• Be a guardian of the public safety.
• Submit truthful and complete reports, statements, and testimonies.
• Don’t abuse credibility.
• Don’t be involved in fraud.
• Inform state board of possible ethics violations.
FERC
18‐3
FE Review Course
18-2b
Obligation to Society
Example (FEIM):
A registered engineer is being interviewed for television on a matter
relating to his expertise that affects the public safety. The interviewer
asks a question about the chances for a cure for AIDS. The engineer
should
(A) express his opinion honestly and completely
(B) decline to comment
(C) recount what he read in a magazine article on the subject
(D) suggest everyone get an AIDS test
The engineer’s credibility with the public should not be abused. The
public could attribute too much credibility to the engineer’s opinion
because of his perceived expertise. Or the public might have less
confidence in the engineer’s expertise on the matter of public safety
if they disagree with his opinion on AIDS. Protecting his credibility on
matters of public safety is all the engineer should care about, so he
should decline to comment.
FERC
18‐4
FE Review Course
18-3a
Obligation to Employers and Clients
Registered engineers’ obligations to employers or clients are secondary
to their obligation to society. Where there is a conflict, the interests of
society (especially regarding safety) take precedence.
Obligations to employers or clients are summarized as follows:
• Only accept assignments the engineer is qualified to complete.
• Don’t sign and seal plans or documents on something the
engineer is not competent in, or that were not prepared under
his/her direct supervision.
• Coordinate projects that include segments in which they are not
competent only if a qualified registered engineer signs and seals
plans and documents for those segments of the project.
• Protect facts, data, and information belonging to the employer
or client.
FERC
18‐5
FE Review Course
18-3b
• Don’t accept anything of value for work from any other parties
except the employer or client, unless agreed to by all parties.
• Make prior disclosure of any actual or perceived conflicts of
interest.
• Don’t contract with a government body if a member of the
engineer’s organization has influence on the government body’s
contracting decisions. Conversely, if the engineer is part of a
government body and can influence contracting decisions, the
engineer should not contract with any outside organization to
which he/she belongs.
FERC
18‐6
FE Review Course
18-3c
Example 1 (FEIM):
Under what circumstances can a registered engineer sign and seal
plans or documents he/she did not prepare?
(A) Registered engineers can coordinate projects that include
segments that they are not competent in if a qualified registered
engineer signs and seals plans or documents for those segments
of the project.
(B) Under no circumstances.
(C) If the plans or documents were prepared by someone under the
registered engineer’s direct supervision and the registered
engineer is an expert in the subject matter.
(D) When practicing in a state different than the one in which the
engineer is registered.
Answer (A) is a true statement, but it has nothing to do with the
problem statement. Plans or documents prepared under the direct
supervision of a registered engineer where the engineer is an expert
can be signed and sealed by the engineer, assuming he or she has
reviewed the plans or documents.
FERC
18‐7
FE Review Course
18-3d
Example 2 (FEIM):
You and your design group are competing for a multidisciplinary concept project.
Your firm is the lead group in the design professional consortium formed to
compete for the project. Your consortium has been selected to be the first to enter
fee negotiations with the project owner. During negotiations, the amount you have
to cut from your fee to be awarded the contract will require dropping one of the
consortium members whose staff has special capabilities not found in the staff of
the remaining consortium members.
Is your consortium response in the negotiations ethical?
(A) No, not if the owner is left with the impression that the consortium is still fully
qualified to perform all the required tasks.
(B) Yes, if your remaining consortium members hire a few new, lower cost
employees to do the special work originally intended to be provided by the
consortium member dropped.
(C) No, because an engineer may not accept a contract to coordinate a project
with other professional firms providing capabilities and services not under
the engineer’s direct control.
(D) Yes, if in accepting an assignment to coordinate a project, a single person
will sign and seal all the documents in the entire consortium work.
FERC
18‐8
FE Review Course
18-3e
It is never ethical to accept a contract if you or the organization you are
negotiating for cannot complete the work. Answer (A) does not tell us if
the scope of the contract will be reduced so the consortium can
complete the work without the eliminated partner, or if the consortium
has some other way of completing the work without the special skills of
the eliminated partner, so we can’t really say that answer (A) is correct,
but it is the best option provided.
Therefore, the answer is (A).
FERC
18‐9
FE Review Course
18-4a
Obligation to Other Registrants
A registered engineer’s obligation to other registrants is less important than the
obligation to society. Where there is a conflict, the interests of society (especially
as regards safety) take precedence.
A registered engineer’s obligations to other registrants are summarized as follows:
• Don’t falsely represent one’s qualifications or the qualifications of associates.
• Don’t solicit, accept, or give anything of value to secure work.
• Don’t give a political contribution to influence the award of a contract by a
public authority.
• Don’t try to damage the careers of other registrants falsely. There are specific
circumstances where one can act against another registrant’s career without it
being a violation of this obligation. These circumstances are summarized as
follows:
- When one registrant has reason to suspect something another registrant
has done, or will do, threatens the public safety.
- When one registrant has reason to suspect another registrant has violated,
or will violate, their ethical code.
- When one registrant has reason to suspect another registrant has
committed, or will commit, fraud.
FERC
18‐10
FE Review Course
18-4b
Obligation to Other Registrants
Example (FEIM):
A registered engineer has applied for a promotion at a firm she has been working
at for several years. During an interview for the new position, she is asked to
contrast her qualifications with other registered engineers at the firm who have
applied for the same position. She should
(A) withdraw her application for the position.
(B) give a full accounting of all the ways her ability and experience are superior
to those of the other applicants.
(C) demand to speak to the interviewer’s supervisor.
(D) decline to compare her qualifications but offer to describe them.
It is not a violation of a registered engineer’s obligation to other registrants to
promote their own qualifications. However, one can’t help but speak negatively
about another registrant when comparing qualifications in a circumstance like
this. The engineer in this situation can discuss her qualifications for the position
but cannot ethically compare qualifications with other registrants applying for the
position. The other registrants can then discuss their qualifications, and the
employer can make the comparisons.
FERC
18‐11
FE Review Course
18-5a
Expert Witness
An expert witness has only one obligation:
• To give a complete and objective analysis of the facts pertaining
only to his or her area of expertise.
Before and after a registered engineer testifies as an expert witness,
he/she has the same obligations as any other registered engineer.
An expert witness is not a character witness or material witness. Expert
witnesses only have knowledge of evidence in the case or data relevant
to the case. They can express their opinions, and are not limited to
stating the facts only.
FERC
18‐12
FE Review Course
18-5b
Expert Witness
Example (FEIM):
A registered engineer is retained as an expert witness by one of the
parties in a civil case where the public safety is not involved. In
investigating the technical data in the case, the engineer makes
findings that are not favorable to the side of the party who retained her.
The engineer should
(A) inform the party who retained her of the findings.
(B) inform the judge of the findings.
(C) inform the opposing party of the findings.
(D) say nothing about the findings until called to testify.
In this case, the engineer has only an obligation to her client until she is
called to the stand, so she should report her findings to the party who
retained her and that party will decide whether or not to call the engineer
to testify.
Therefore, (A) is correct.
FERC
18‐13
FE Review Course
18-6a
Consultants
Consultant:
A registered engineer acting as a consultant must be fully qualified as an
expert in the subject matter.
Registered Engineer:
A registered engineer may be hired for a regular position requiring
expertise in some area where the engineer is not an expert, as long as the
employer knows this and arrangements are made for the hired engineer to
be trained in those areas. This is not so, however, for a consultant.
Consultants have the same obligations to clients that registered engineers
who are regular employees have to their employers. They are obliged to
protect data, processes, and information belonging to the client and not
share these with other clients. There are exceptions, however.
For example, if the consultant develops analysis techniques, special skills,
experience, etc., working for one client, he/she can use this when working
for another client as long as it doesn’t involve something deliverable under
a contract with the former client (e.g., a software algorithm).
FERC
18‐14
FE Review Course
18-6b
Consultants
Example (FEIM):
A professional engineer, originally licensed 30 years ago, is asked to act
as a consultant on a newly developed computerized control system for a
public transportation system. The engineer may accept this project if
(A) he or she is competent in the area of modern control systems.
(B) his or her professional engineering license has not lapsed.
(C) his or her original area of specialization was in transportation
systems.
(D) he or she has regularly attended annual meetings of a professional
engineering society.
By definition, if he or she is a professional engineer, his or her license
cannot have lapsed, so (B) is wrong. All that matters is that the
professional engineer is competent.
Therefore, (A) is correct.
FERC
18‐15
MASTER SET OF
30 CASES !
(PART 1)
(updated 4/3/08)
Engineering Ethics: You Be The Judge
Real Life Fact Base Case Studies
Case #1
The Situation
The attorney for a plaintiff involved in a legal action orally retains N.D.
Middle, P.E., a principal in a private practice firm, to provide accident
reconstruction consultation. The plaintiff is suing a defendant allegedly
responsible for a traffic accident. Middle sends a letter of agreement to the
plaintiff's attorney, but it is never returned. No additional information is
exchanged between Middle and the plaintiff's attorney. About two years
later, the law firm representing the defendant contacts Middle and seeks to
retain his services in connection with the same legal action. Middle,
assuming that the plaintiff and his attorney have decided to retain the
services of another expert, agrees to provide his services to the law firm
representing the defendant. Later, the plaintiff's attorney contacts Middle
with the expectation that Middle will provide accident reconstruction
consultation per their earlier oral agreement.
What Do You Think?
Was it ethical for Middle to agree to provide his services to the law firm
representing the defendant?
MASTER SET OF 30 CASES! – April 2008
Part I – Pg. 1
Case #2
The Situation
Will K. Neckted, P.E., is a principal in a consulting engineering firm. He is
appointed by the governor of a state to serve as secretary of commerce
and subsequently resigns from the engineering firm. While Neckted was a
principal in the engineering firm, the firm had performed work for a major
developer that is planning to build a major project in the state. As secretary
of commerce, Neckted has been asked by the governor to spearhead the
state's campaign to bring the major development project to the state. The
project has been the subject of controversy on account of its potential
environmental impact and the effect it could have on historic areas of the
state.
Although Neckted resigned from the engineering firm, he maintained a
$250,000 retirement fund, which is administered by, and includes a very
small amount of stock in, the firm. The firm has recently indicated that it
might be interested in pursuing additional engineering work for the
developer as part of the major development project. Neckted has also
indicated to members of the media that upon the conclusion of his services
as secretary of commerce, he could very well return to his consulting
engineering firm. Neckted has fully disclosed all pertinent information to the
state.
What Do You Think?
Was it ethical for Neckted to maintain a retirement fund administered by his
former engineering firm while serving as secretary of commerce? Was it
ethical for Neckted, as secretary of commerce, to participate in the
discussions surrounding the development project?
Part I – Pg. 2
Case #3
The Situation
E.E. Most, a PE in the electrical engineering field, is employed by a state
agency as a computer systems engineer with some management
responsibilities. Educated and trained to perform customary engineering
services, Most's work experiences have never involved technical and
design issues concerning environmental services.
As part of a restructuring of the agency, his direct supervisor, Felix A. Ball,
recommends that Most accept a position the Department of Environmental
Services has offered him. The position requires a PE and involves
engineering analysis and design responsibilities, and Most would be
working as part of a team of engineers.
Most refuses to accept the position, citing state board regulations requiring
him to perform work only in his area of competence and his lack of
expertise to perform the work. Thereafter, Most is terminated.
During an administrative hearing involving Most's reinstatement to his
former position and back pay, Ball testifies that Most was qualified to
accept the position offered in the Department of Environmental Services.
What Do You Think?
Was it ethical for Most to decline the position? And did Ball act ethically in
testifying that Most was qualified to accept the position?
Part I – Pg. 3
Case #4
The Situation
Earnest N. Steadfast, P.E., is a research professor at a major engineering
college. He performs important research in connection with certain new
technologies in the transportation field. As part of his work, the university
has received a number of grants from major corporations and the federal
government.
As the principal investigator, Steadfast routinely meets with representatives
of government agencies and private funding groups, reports on the status
of his research, and publishes the results in professional journals and at
technical conferences.
Steadfast meets with the major commercial sponsor about his
transportation research and presents the results of his research in a paper,
including charts, graphs, and other illustrative material. The commercial
sponsor clearly has a significant interest in the research report and its
conclusions and, subsequently, makes certain changes in the report
bearing Steadfast's name without his knowledge and approval. The
changes include altering report text and removing figures.
What Do You Think?
Would Steadfast be ethical in taking action against the sponsor? Did the
sponsor act ethically in altering Steadfast's report?
Part I – Pg. 4
Case #5
The Situation
Hardy N. Strong, P.E., serves as a member of the board of trustees of a
college in a medium-sized city. The U.S. Department of Housing and Urban
Development (HUD) has awarded money to the city, and the city has
agreed to use the money to construct a new library at the college. Strong
would like to be considered for providing engineering services on the
project.
What Do You Think?
Would it be ethical for Strong to offer his engineering services on the
project?
Part I – Pg. 5
Case #6
The Situation
Vera City, P.E., is a volunteer chairman of a university search and screening
committee. As part of the search and screening guidelines of the university,
she is asked by the administration to do the following:
 Recommend strategic areas for the college, keeping in mind the
objectives of the university, including the enhancement of horizontal
and interdisciplinary connections among faculty and its affirmative
action commitments;
 Recommend strategic areas where there is proven need to support the
state and the nation as evidenced by continuing and new federal and
state programs, such as affirmative action;
 Look for candidates who provide the opportunity for initial leverage of
funding and positions supported by specific campus, state, and federal
initiatives, such as affirmative action programs.
Under the university procedure, a pool of candidates from underrepresented
minorities will be recruited first, and only then will non-minority candidates
be solicited.
Although the university publicly maintains that "all qualified candidates will
be equally considered," the university has a strong financial incentive in
selecting individuals from underrepresented minorities in order to continue to
receive federal, state, and local financial support. City believes the university
is misrepresenting the process to all candidates.
What Do You Think?
Is it ethical for City to participate in the screening and selection process of
the university under these conditions?
Part I – Pg. 6
Case #7
The Situation
Dee Duction is a principal in XYZ Company, a firm that performs utility
audits for large corporations. As part of the services, Duction's firm reviews
the corporations' activities, budget, business forecast, needs, requirements,
and other factors; and makes recommendations concerning the most
appropriate use of equipment and utilities in the performance of its services.
Generally, Duction recommends an approach that includes a request for
proposals and a list of potential service providers who generally prepare a
proposal and bid to perform services for the firm.
In recent years, utility service providers have established a custom of
providing a "rebate" to utility audit firms that perform the audits for the
corporation. The rebate is calculated to reflect the savings the audit firm has
provided for its clients. As a business practice, when Duction receives a
copy of a rebate check from one of the service providers, Duction makes a
copy of the check and sends the copy with half the amount of the check to
the client with a note reading "Another benefit provided to you by XYZ
Company." The general practice among many other utility audit firms is to
keep the check and provide nothing to the client.
What Do You Think?
Is it ethical for Duction to accept the rebate check? Is it ethical for Duction to
send a portion of the rebate check to the client in the manner indicated?
Part I – Pg. 7
Case #8
The Situation
N. X. Perryanst, P.E., is starting out as a consulting engineer. Perryanst
responds to a notice in the newsletter of a local chapter of an engineering
society asking for volunteers to help organize a consultant's referral
network. Avery Mature, P.E., a society officer, asks Perryanst to help
organize the network.
Some time later, Mature calls to ask Perryanst if he would look at an
engineering problem. Perryanst goes to Mature's office expecting to get the
particulars of a referral, since some members of the developing network are
in the habit of giving one another referrals. Mature then accompanies
Perryanst to the potential client's office, but because the referral process is
new, Perryanst does not discuss arrangements with Mature. In the middle of
the client's description of the engineering problem, the client asks about the
contractual relationship. Mature replies that Perryanst will subcontract to
Mature on the project.
What Do You Think?
Was it ethical for Mature to indicate that Perryanst will subcontract to Mature
on the project? What were Perryanst's ethical obligations under the
circumstances?
Part I – Pg. 8
Case #9
The Situation
Duane Etright, P.E., is employed by a software company and designs
specialized software used in the operation of facilities affecting the public
health and safety, such as air quality control, and water quality control
facilities. As part of the design of a particular software system, Etright
conducts extensive testing, and although the tests show that the software is
safe to use under existing standards, Etright is aware of new draft standards
that are about to be released by a standard-setting organization-standards
that the new software might not meet. Testing is very costly and the
company's clients are eager to move forward. The software company wants
to satisfy its clients and protect its finances and employees' jobs; but at the
same time, wants to be sure that the software will be safe to use under the
new standards. Tests proposed by Etright will likely result in a decision on
whether to move forward with the use of the software. The tests are costly
and will delay the use of the software by at least six months, which will put
the company at a competitive disadvantage and cost it money. Also,
delaying implementation will cause the state public service commission
utility rates to rise significantly. The company requests Etright's
recommendation on the need for further software testing.
What Do You Think?
Under the Code of Ethics, does Etright have a professional obligation to
inform his company of the reasons for additional testing and recommend
that it be undertaken?
Part I – Pg. 9
Case #10
The Situation
Hy Caliber, P.E., serves as a peer reviewer for an organized peer review
program developed to help engineers improve their professional practice.
When originally selected as a peer reviewer, Caliber is asked to sign a
"confidentiality agreement" whereby Caliber agrees not to disclose
confidential information involving peer-reviewed firms.
As part of a peer review visit, Caliber visits the firm of Ondi Edge, P.E.
Following a review of technical documentation connected to a series of
recent design projects involving Edge's firm, Caliber discovers that Edge's
work may be in violation of state and local safety code requirements and
could endanger public health, safety, and welfare.
What Do You Think?
What are Caliber's ethical responsibilities under the circumstances?
Part I – Pg. 10
Case #11
The Situation
Hayes A. Dualpro is both an attorney and an engineer. Dualpro is retained
by client Ben Hurt on a contingency basis to perform legal services in
connection with an accident that Hurt alleges was caused by a
manufactured product. Dualpro interviews a number of experts familiar with
the product and the reasons for similar accidents, and hires Arthur Eddie,
P.E., an expert on the product in question. No written agreement is executed
between Dualpro and Eddie for the services in question. Eddie reviews the
facts and circumstances surrounding the accident, conducts and completes
a study, and issues a report to Dualpro. Dualpro reviews Eddie's report and
informs Hurt that it appears that no basis exists for a lawsuit. Eddie bills
Dualpro for his professional services. Dualpro refuses to pay, indicating that
since Dualpro was not paid for his services, Dualpro has no obligation to pay
Eddie.
What Do You Think?
Was it ethical for Dualpro to refuse to pay Eddie for Eddie's services?
Part I – Pg. 11
Case #12
The Situation
Dewitt Wright, P.E., is a mechanical engineer employed by Designco, a company
responsible for the design of liquid chillers to be used in a nuclear power plant operated
by the PowerCo. The pressure vessels used are manufactured in accordance with
mechanical engineering standards. The design parameters are specified to
ManufactureCo by Wright.
A utilities quality assurance program specifies that, for their records, a pressure vessel
code report stamped and signed by a professional engineer must accompany each
vessel.
Wright receives an initial code report from ManufactureCo entitled "Revision 0" for
submission to PowerCo for review. This code report contains numerous errors and is not
stamped or generated by a professional engineer. Wright returns it to ManufactureCo,
authorizing ManufactureCo to "Proceed with manufacture with exceptions noted."
Wright's engineering superiors support Wright's actions in requiring ManufactureCo to fix
the errors and to hire a consulting professional engineer to review and rewrite the report
as necessary.
Thereafter, ManufactureCo submits Revision 1 of the code report to Designco for
submission to PowerCo, but the report is returned to ManufactureCo because the text on
the drawing contained in the code report was not entirely legible. The drawing insert of
the code report is clearly titled with the code report number.
The vice president of Designco requests that Wright replace the text on the drawing with
more legible text and resubmit the code report to PowerCo. Wright responds that this
would not be proper. Following a contentious discussion, Wright calls the director of
engineering and leaves a voicemail message that he needs to discuss with him the fact
that he was being asked to do an improper act. Thereafter, Wright is called into the vice
president's office. After another contentious discussion, the vice president acknowledges
that "it was technically improper to substitute text." He also explains that this was "only
text on a drawing so that a department secretary would do it" if Wright continued to
refuse to prepare text on the drawing. The vice president indicates that he does "not want
to put ManufactureCo through the exercise of rewriting another code report requiring a
minor correction."
What Do You Think?
Would it be ethical for Wright to make the text in the code report legible and resubmit the
code report to PowerCo?
Part I – Pg. 12
Case #13
The Situation
Industraco is involved in the manufacturing of consumer products, including
certain industrial tools. Cy Lanced, P.E., who has performed research and is
experienced in the design and manufacture of these specialized industrial
tools, is now an engineering faculty member at a private university. Lanced
also owns an independent consulting engineering practice. Industraco
contacts Lanced and requests that he agree to a consulting contract
designed to prevent him from speaking out in public or testifying in any
future litigation involving industrial tools manufactured by Industraco.
What Do You Think?
Would it be ethical for Lanced to agree to a consulting contract (with
Industraco) with the sole purpose of preventing Lanced from speaking out in
public or testifying in any future litigation involving industrial tools
manufactured by Industraco?
Part I – Pg. 13
Case #14
The Situation
Engineer A is a graduating senior with excellent credentials from X
University. Engineer A has had a series of job interviews with engineering
companies from around the U.S. Following interviews with several industrial
companies, Engineer A decides to accept an offer with ABC Incorporated
located in his hometown of Townville and plans to notify ABC the following
week. In the interim period, Engineer A receives a call from Engineer B, an
executive with XYZ Incorporated, a potential employer with whom Engineer
A interviewed. On behalf of XYZ, Engineer B offers Engineer A, a position
with XYZ and invites Engineer A, at XYZ's expense, to visit XYZ's
headquarters in Mountainville, a city located near a resort area following
Engineer A's graduation. Engineer A had earlier decided he would not
accept a position with XYZ if offered a position by ABC because Engineer A
wanted to live near Townville to be close to family and friends, and also
because ABC provided better long-term professional opportunities.
However, after receiving the call from XYZ, Engineer A decides to accept
the invitation to visit XYZ's headquarters and combine the trip with a postgraduation vacation, believing that the visit to XYZ will broaden his
knowledge of the employment market, as well as future professional
opportunities with XYZ. A week after the trip, Engineer A calls ABC and
informs the company that he will accept the position with ABC.
What Do You Think?
Was it ethical for Engineer A to accept the invitation to visit XYZ
headquarters?
Part I – Pg. 14
Case #15
The Situation
Hy Standards, P.E., was an engineer with a local government. Standards learned about a
critical situation involving a bridge 280 feet long, 30 feet above a stream. This bridge was
a concrete deck on wood piles that was built by the state in the 1950s. It was part of the
secondary roadway system given to the counties many years ago.
In June 2000, Standards received a telephone call from the bridge inspector stating that
this bridge needed to be closed due to the large number of rotten piling. Standards had
barricades and signs erected within the hour on a Friday afternoon, and residents in the
area were required to take a 10-mile detour.
On the following Monday, the barricades were in the river and the "Bridge Closed" sign
was in the trees by the roadway. More permanent barricades and signs were installed.
The press published photos of some of the piles that did not reach the ground and the
myriad of patch work over the years.
Within a few days, a signed and sealed, detailed inspection report prepared by a
consulting engineering firm indicated that seven pilings required replacement. Within
three weeks, Standards had obtained authorization for the bridge to be replaced. Several
state and federal transportation departments needed to complete their reviews and tasks
before the funds could be used.
A rally was held, and a petition with approximately 200 signatures asking to reopen the
bridge to limited traffic was presented to the County Commission. Standards explained
the extent of the damages and the efforts under way to replace the bridge. The County
Commission decided not to reopen the bridge.
Preliminary site investigation studies then began. Environmental, geological, right-of-way,
and other studies were also performed. A decision was made to use a design-build
contract to avoid a lengthy scour analysis for the pile design.
A non-engineer public works director decided to have a retired bridge inspector, who was
not an engineer, examine the bridge, and a decision was made to install two crutch piles
under the bridge and to open the bridge with a five-ton limit. No follow-up inspection was
performed.
Standards now observes that traffic is flowing and the movement of the bridge is
frightening. Log trucks and tankers cross it on a regular basis. School buses go around it.
What Do You Think?
What is Standards's ethical obligation under these circumstances?
Part I – Pg. 15
Case #16
The Situation
Juan Anoyd, P.E., is a small business owner. Filching N. Pilfering, a
licensed engineer formerly employed by Anoyd's firm, makes calls to
Anoyd's employees (at home and at work) requesting that they make him
copies of their company's proprietary schematics. Pilfering's request
specifically instructs these individuals to not mention these conversations to
Anoyd. Anoyd's employees alert Anoyd to the problem. However, Anoyd is
concerned about Pilfering's activities and the potential threat these requests
could have on the health of Anoyd's company (if their proprietary information
were to fall into competitor's hands).
Anoyd confronts Pilfering at a seminar and, in front of many other engineers,
architects, contractors, clients, and others, makes several accusations and
angry comments to Pilfering. Pilfering denies the accusations, and both
exchange a series of derogatory comments. Following this exchange, Anoyd
and Pilfering both leave the seminar.
What Do You Think?
Was it ethical for Pilfering to contact Anoyd's employees? Was it ethical for
Anoyd to confront Pilfering in the manner described?
Part I – Pg. 16
Case #17
The Situation
Bill LeVard, P.E., performs a traffic study for HighYield Enterprises as part of
the client's permit application for traffic flow for the development of a store.
LeVard invoices HighYield for a complete traffic study.
Later, HighYield learns that LeVard created part of the traffic study earlier for
a developer, ProfitTech Industries. High Yield also learns that LeVard
invoiced ProfitTech for the complete traffic study. The second study on a
new project for HighYield used some of the same raw data that was in the
report prepared for ProfitTech. The final conclusion of the engineering study
was essentially the same in both studies.
What Do You Think?
Was it ethical for LeVard to charge HighYield for the complete traffic study?
Part I – Pg. 17
Case #18
The Situation
Dee Sine, P.E., prepares a set of drawings for a client for the design and
construction of a building. The client, N. A. Fixx, contracts with Strongwill
Contracting, who is not an engineer, for construction. Fixx does not retain
Sine for construction phase services. Sine is paid in full for his work. Sine's
drawings are filed with town code officials and a building permit is issued.
Strongwill builds the building, but does not follow Sine's design, relying upon
Strongwill's own experience in construction. Following construction,
Strongwill, with the assistance of Tractor, prepares a set of record "as built"
drawings, based upon the actual construction of the building as reported by
Strongwill. Because the design and the construction drawings are not
reconciled, the building official refuses to issue an occupancy permit to the
client. Fixx asks Sine to "reconcile" the original design and the record
drawings. Sine, not wanting to conduct an in-depth study of the work, agrees
to perform the "reconciliation."
What Do You Think?
 Was it ethical for Sine to perform the design reconciliation?
 Was it appropriate for Tractor to prepare a set of record drawings based
on the construction without notifying Sine?
Part I – Pg. 18
Case #19
The Situation
Avery Trusting, P.E., a CEO of a small engineering corporation, teams up
with another small firm in the development and delivery of highway/rail
intersection database management systems for various public and private
enterprises. Trusting is the co-author and the program is patented and
copyrighted.
Abe Using, P.E., a principal in a private firm from State X calls Trusting and
informs Trusting that State X's Department of Transportation is interested in
the highway/rail system and has asked Using to evaluate the system. Using
requests and Trusting agrees to visit with Using in State X. Prior to the visit,
Using requests that Trusting prepare a project proposal, which Trusting
submits. Later, at Using's request, Trusting visits Using's offices and
demonstrates the systems. Project managers, as well as programmers, from
Using's firm are present at the meeting. Trusting describes in great detail the
technical aspects of the system. Following the meeting, Using requests that
Trusting prepare a new proposal with a detailed breakdown of all costs.
Later, Trusting receives a phone call from a subordinate of Using, advising
that Using will not need Trusting's firm's services because Using's firm now
has the capability to design their own system.
What Do You Think?
Was it ethical for Using to obtain Trusting's technology in the manner
described in this case?
Part I – Pg. 19
Case #20
The Situation
Acton Haste, P.E., is employed by SPQ Engineering, an engineering firm in
private practice involved in the design of bridges and other structures. As
part of its services, SPQ Engineering uses a CAD software design product
under a licensing agreement with a vendor. Under the terms of the licensing
agreement, SPQ Engineering is not permitted to use the software at more
than one workstation without paying a higher licensing fee. SPQ
Engineering ignores this restriction and uses the software at a number of
employee workstations. Haste becomes aware of this practice and calls a
hotline publicized in a technical publication and reports his employer's
activities.
What Do You Think?
Was it ethical for Haste to report his employer's apparent violation of the
licensing agreement on the hotline without first discussing his concerns with
his employer?
Part I – Pg. 20
Case #21
The Situation
B.A. Worthy, P.E., receives the following letter from a contractor:
Dear Mr. Worthy:
If you have not already heard of us, please allow me to introduce myself. My name is Y.
Worry, owner of X Construction Company. We are a medium-sized general contractor
firm with 20 years of experience. One of my company's strengths is our ability to interpret
a blueprint or drawing and properly execute the construction of the project as it was
conceived.
This year, I would like to associate my company with an engineering firm that we can
refer clients to and receive clients from. I understand that there is a necessary ethical
distance that must be maintained between an engineer and a contractor. I also know that
it is not unethical for an engineer to provide their clients with a list of a few qualified
contractors.
As an incentive to include my company on such list or as a referral to your clients, I am
prepared to offer you a flat $500, plus 3% of the total contract price, as a finder's
fee/commission for every contract I sign as a result of your referral. Once a client has
called for an estimate of proposal, we work directly with them. I will in no way use your
good name or any association with your firm as a sales tool.
All I ask for is the opportunity for my firm's proposal to be included in the client's decisionmaking process. We both work from different ends of the same field. If it is possible for
our firms to establish an arm's-length relationship, it could be very beneficial to both of us.
We are fully licensed, insured, and registered with the Better Business Bureau, and can
provide a long list of satisfied clients. Please call or write if you would like to discuss this
further and take full advantage of the new season.
Sincerely yours, Y. Worry
What Do You Think?
Is it ethical for Worthy to associate with Worry and the X Construction Company under
the circumstances being proposed in this letter?
Part I – Pg. 21
Case #22
The Situation
Avery Global, P.E., is a consulting engineer who works in the U.S. and
abroad. Global is contacted by the government of Country A and asked to
submit a proposal for a major water project being constructed there. As part
of the project, Global is encouraged to associate with and retain Engineer B,
a local engineer in Country A, with whom Global has worked on private
projects in that country. One of the accepted "customs" in Country A is for
consultants, such as engineers, to give substantial gifts to public officials in
connection with the awarding of public works contracts. Global recognizes
that the giving of such gifts may be a violation of U.S. law-although it may
not technically violate the law in Country A. Engineer B proposes to Global
that if the project is awarded to Global's firm, Engineer B will handle
"business arrangements" in Country A and that Global will be involved in
overall project management as well as all technical matters.
What Do You Think?
Would it be ethical for Global to proceed with the project under these
circumstances?
Part I – Pg. 22
Case #23
The Situation
Benny Fitting, P.E., and Hy Returnto, P.E., are in a joint venture in an
engineering and construction management practice that is hired by a
developer to design a 90-lot subdivision in Township A. Township A officials
determine that a second road will be needed to access the subdivision;
however, the second road exits into Township B, which is adjacent to
Township A. Fitting and Returnto's joint venture owns undeveloped property
in Township B, and their joint venture also serves as municipal engineer in
Township B. It is clear that the property owned by Fitting and Returnto will
be positively affected by the construction of the new road. The joint venture
of Fitting and Returnto discloses its relationship with the developer to
Township B, but does not disclose its ownership of the property in Township
B. On this basis, Township B does not object to Fitting and Returnto making
a recommendation regarding the feasibility of the construction of the
proposed road. Thereafter, as municipal engineer for Township B, Fitting
and Returnto's joint venture recommends that Township B approve
construction of the proposed road.
What Do You Think?
Was it ethical for Fitting and Returnto to serve as the engineers for the
developer and also serve as municipal engineer for Township B under the
circumstance described? Was it ethical for Fitting and Returnto to
recommend approval of the road under the circumstances described?
Part I – Pg. 23
Case #24
The Situation
Hy A. Cheever, P.E., works for ABC Engineering Company and has a good
working relationship with a major client, Clover City, which is a neighboring
city. ABC is currently under contract with Clover City for the preparation of a
report on an expansion of the city's water treatment plant. As an employee
of ABC, Cheever develops the report and includes a section dealing with
funding for an elevated storage tank, which was not part of the scope of
work originally negotiated between ABC and Clover City. No contract exists
between the city and ABC for the design of the elevated storage tank.
Clover City is impressed by Cheever's initiative on this project. The city has
paid ABC for this report.
Recently, officials in Clover City suggested that Cheever open his own
engineering company in Clover City, indicating that they would consider a
city retainer contract and also a contract for the design of the elevated
storage tank. Six months later, Cheever decides to establish his own firm in
Clover City without soliciting work from ABC's clients, including Clover City,
for a period of time. However, after a year has passed, Cheever begins
soliciting work from ABC's clients, including Clover City. There was no "noncompete agreement" between Cheever and ABC Engineering Company.
What Do You Think?
Was it ethical for Cheever to establish his own firm in Clover City? Was it
ethical for Cheever to begin soliciting work from ABC's clients, including
Clover City, after a year had passed?
Part I – Pg. 24
Case #25
The Situation
Manny Hatz, P.E., a licensed professional engineer and land surveyor,
works 35 hours per week on a flex-time basis for a state governmental
agency. In addition, Hatz is associated with XYZ Engineering and Surveying
firm as the PE in charge under the state's certificate of authorization
requirement.
Hatz provides about twenty hours per week supervising engineering
services at the firm, plus an additional twelve hours of work on the
weekends, and is available for consultation twenty-four hours a day. XYZ
grants Hatz 10% share of the stock in the firm, and as compensation for his
engineering services, Hatz will receive 5% of the gross billings for
engineering work for which the seal of a licensed engineer in responsible
charge of engineering is required. This agreement is contingent on the
understanding that if any one of the three principals of XYZ becomes
licensed as a PE in the state, the agreement will become void and the 10%
stock will be returned to XYZ.
Both the state governmental agency and the engineering firm are aware of
Hatz's activities as a dual employee and do not object to these activities.
What Do You Think?
Is it ethical for Hatz to be associated with XYZ Engineering and Surveying in
the manner described?
Part I – Pg. 25
Case #26
The Situation
Ben D. Truth, P.E., is the principal in an engineering firm that has been in
existence for approximately 18 months. All of the engineers in the firm have
come from other engineering firms. Truth develops a firm promotional
brochure that contains a "list of clients," implying that the companies on the
list are clients of the firm, and a "list of projects of the firm," implying that the
projects were performed by the new firm. In fact, the client list is actually the
companies for whom the engineers performed work where they were
previously employed. Similarly, the project list is a series of projects
performed by the new firm's engineers for their former firms.
What Do You Think?
Was it ethical for Truth to produce a promotional brochure for his new firm
containing this type of information?
Part I – Pg. 26
Case #27
The Situation
A public agency retains the services of VWX Architects and Engineers to
perform a major scheduled overhaul of a bridge. VWX retains the services of
"Spec" U. Lating, P.E., a civil engineer, to perform bridge inspection
services. Lating's scope of work is solely to identify any pavement damage
on the bridge and report the damage to VWX for further review and repair.
Before the scheduled overhaul begins, Police Officer Truly loses control of
his patrol car while traveling across the bridge, and the vehicle crashes into
the bridge wall. The wall fails to restrain the vehicle, and it falls to the river
below, killing Truly.
While Lating is conducting the bridge inspection, he notices an apparent
pre-existing defective condition in the wall close to the accident site,
although such an inspection was not part of the scope of services for which
Lating was retained. Lating surmises that the defective condition may have
contributed to the wall failure and notes this in his engineering notes. He
verbally reports this information to his client, who then verbally reports it to
the public agency. The public agency contacts VWX Architects and
Engineers, which then contacts Lating and asks Lating not to include this
additional information in his final report since it was not part of his scope of
work. Lating states that he will retain the information from his engineering
notes but not include it in the final report, as requested. Lating does not
report this information to any other public agency or authority.
What Do You Think?
Was it ethical for Lating to retain the information in his engineering notes but
not include it in the final report as requested? Was it ethical for Lating not to
report this information to any other public agency or authority?
Part I – Pg. 27
Case #28
The 1999 NSPE Board of Ethical Review Ethics Contest challenged all NSPE Chapters, student chapters, and current
NSPE individual members to match their wits against experienced professional engineers and chapters throughout the
U.S. NSPE's BER provided a situation based on actual experiences involving a structural engineer, an architect, a city
engineer, and a client, and presented the entrants with an ethical question to analyze. A panel of judges from the NSPE
BER judged the entries and selected this year's winner, the Kansas State University Student Chapter of the Kansas
Society of Professional Engineers, submitted by Angela Forrest, of Manhattan, Kansas. The chapter received a $500
award and was recognized at the annual meeting in Spokane, Washington, in July. A condensed version of the entry is
presented here.
The Situation
Engineer A, a structural designer of a large commercial building,
incorporates new and innovative design concepts. After construction is
complete and the building is occupied, he finds an omission in the
calculations that could result in the building's collapse under severe, but not
unusual, wind conditions. The collapse would not only jeopardize the
occupants and their immediate surroundings, but could possibly cause a
"domino" effect threatening a much larger area. After consultation, the
architect, the client, and the city engineer all agree upon remedial
construction, which can be accomplished over the next few months. A storm
monitoring system and contingency evacuation plan for the building and
surrounding neighborhood are developed for the time before construction is
complete. Both the client and architect strongly agree that the situation
should be kept secret, with construction accomplished during the evening
hours when the building is unoccupied. Engineer A is confident that the
construction will completely rectify any structural concerns and that the
evacuation plan has a reasonable chance of success. Engineer B, the city
engineer, has concern for the public, especially the office workers in the
building and their right to know, but the architect and the client maintain that
right is superseded by the consequences of a possible public panic resulting
from any notification.
What Do You Think?
Is it ethical for Engineer A to comply with the client's and the architect's
desire for secrecy? It is ethical for Engineer B to maintain the secrecy?
Part I – Pg. 28
Case #29
The Situation
N. A. Fixx, P.E., who is the director of a building department in a major city,
has been concerned that, as a result of a series of budget cutbacks and
more rigid code enforcement requirements, the city has been unable to
provide a sufficient number of qualified individuals to perform adequate and
timely building inspections. Each code official member of Fixx's staff is often
required to make as many as 60 code inspections per day. Fixx believes
that there is no way even the most conscientious code official can make 60
adequate, much less thorough, inspections in one day, particularly under the
newer code requirements for the city.
Fixx meets with the chairman of the local city council, who says he would be
willing to issue an order to permit the hiring of additional code officials for the
building department. At the same time, the chairman notes that the city is
seeking to encourage more businesses to relocate into the city in order to
provide more jobs and a strengthened tax base. In this connection, the
chairman seeks Fixx's concurrence on a city ordinance that would permit
certain specified buildings under construction to be "grandfathered" under
the older existing enforcement requirements and not the more rigid
requirements now in effect. Fixx agrees to the chairman's proposal, and the
chairman issues the order to permit the hiring of additional code officials for
the building department.
What Do You Think?
Was it ethical for Fixx to agree to the chairman's proposal under the facts?
Part I – Pg. 29
Case #30
The Situation
Izzy A. Candid, P.E. was requested by client, Hope and Trusting (H&T), to
prepare specifications for a curtain wall system. Candid immediately makes
H&T aware that he is a minority shareholder in a curtain wall manufacturing
company and that if H&T agrees, Candid would be pleased to prepare a set
of generic specifications for a curtain wall system. H&T agrees but is silent
on the point of having Candid's firm submit a proposal. Later, Candid
provides H&T with the names of three manufacturers that prepare curtain
wall systems for bidding purposes. Candid includes the name of his firm
among the three manufacturers, but does not include the full specifications
and other supporting material about Candid's curtain wall manufacturing firm
with the bidding material provided to the client. Candid's reasoning is that he
could answer any questions that H&T might have about the curtain wall
manufacturing system in his company. After evaluating the proposals
solicited through documentation prepared by Candid, and upon Candid's
recommendation, H&T selects Candid's company.
What Do You Think?
Was it ethical for Candid to prepare bidding criteria, bid, evaluate bids, and
recommend his company for owner selection?
Part I – Pg. 30
NSPE Code of Ethics for Engineers
Preamble
Engineering is an important and learned profession. As members of this profession, engineers are expected to exhibit the highest
standards of honesty and integrity. Engineering has a direct and vital impact on the quality of life for all people. Accordingly, the
services provided by engineers require honesty, impartiality, fairness, and equity, and must be dedicated to the protection of the public
health, safety, and welfare. Engineers must perform under a standard of professional behavior that requires adherence to the highest
principles of ethical conduct.
I. Fundamental Canons
Engineers, in the fulfillment of their professional duties, shall:
1.
Hold paramount the safety, health, and welfare of the public.
2.
Perform services only in areas of their competence.
3.
Issue public statements only in an objective and truthful manner.
4.
Act for each employer or client as faithful agents or trustees.
5.
Avoid deceptive acts.
6.
Conduct themselves honorably, responsibly, ethically, and lawfully so as to enhance the honor, reputation, and usefulness
of the profession.
II. Rules of Practice
1.
2.
3.
Engineers shall hold paramount the safety, health, and welfare of the public.
a.
If engineers’ judgment is overruled under circumstances that endanger life or property, they shall notify their
employer or client and such other authority as may be appropriate.
b.
Engineers shall approve only those engineering documents that are in conformity with applicable standards.
c.
Engineers shall not reveal facts, data, or information without the prior consent of the client or employer except as
authorized or required by law or this Code.
d.
Engineers shall not permit the use of their name or associate in business ventures with any person or firm that
they believe is engaged in fraudulent or dishonest enterprise.
e.
Engineers shall not aid or abet the unlawful practice of engineering by a person or firm.
f.
Engineers having knowledge of any alleged violation of this Code shall report thereon to appropriate professional
bodies and, when relevant, also to public authorities, and cooperate with the proper authorities in furnishing such
information or assistance as may be required.
Engineers shall perform services only in the areas of their competence.
a.
Engineers shall undertake assignments only when qualified by education or experience in the specific technical
fields involved.
b.
Engineers shall not affix their signatures to any plans or documents dealing with subject matter in which they lack
competence, nor to any plan or document not prepared under their direction and control.
c.
Engineers may accept assignments and assume responsibility for coordination of an entire project and sign and
seal the engineering documents for the entire project, provided that each technical segment is signed and sealed
only by the qualified engineers who prepared the segment.
Engineers shall issue public statements only in an objective and truthful manner.
a.
Engineers shall be objective and truthful in professional reports, statements, or testimony. They shall include all
relevant and pertinent information in such reports, statements, or testimony, which should bear the date indicating
when it was current.
Part I – Pg. 31
4.
5.
b.
Engineers may express publicly technical opinions that are founded upon knowledge of the facts and competence
in the subject matter.
c.
Engineers shall issue no statements, criticisms, or arguments on technical matters that are inspired or paid for by
interested parties, unless they have prefaced their comments by explicitly identifying the interested parties on
whose behalf they are speaking, and by revealing the existence of any interest the engineers may have in the
matters.
Engineers shall act for each employer or client as faithful agents or trustees.
a.
Engineers shall disclose all known or potential conflicts of interest that could influence or appear to influence their
judgment or the quality of their services.
b.
Engineers shall not accept compensation, financial or otherwise, from more than one party for services on the
same project, or for services pertaining to the same project, unless the circumstances are fully disclosed and
agreed to by all interested parties.
c.
Engineers shall not solicit or accept financial or other valuable consideration, directly or indirectly, from outside
agents in connection with the work for which they are responsible.
d.
Engineers in public service as members, advisors, or employees of a governmental or quasi-governmental body
or department shall not participate in decisions with respect to services solicited or provided by them or their
organizations in private or public engineering practice.
e.
Engineers shall not solicit or accept a contract from a governmental body on which a principal or officer of their
organization serves as a member.
Engineers shall avoid deceptive acts.
a.
Engineers shall not falsify their qualifications or permit misrepresentation of their or their associates’ qualifications.
They shall not misrepresent or exaggerate their responsibility in or for the subject matter of prior assignments.
Brochures or other presentations incident to the solicitation of employment shall not misrepresent pertinent facts
concerning employers, employees, associates, joint venturers, or past accomplishments.
b.
Engineers shall not offer, give, solicit, or receive, either directly or indirectly, any contribution to influence the
award of a contract by public authority, or which may be reasonably construed by the public as having the effect
or intent of influencing the awarding of a contract. They shall not offer any gift or other valuable consideration in
order to secure work. They shall not pay a commission, percentage, or brokerage fee in order to secure work,
except to a bona fide employee or bona fide established commercial or marketing agencies retained by them.
III. Professional Obligations
1.
2.
Engineers shall be guided in all their relations by the highest standards of honesty and integrity.
a.
Engineers shall acknowledge their errors and shall not distort or alter the facts.
b.
Engineers shall advise their clients or employers when they believe a project will not be successful.
c.
Engineers shall not accept outside employment to the detriment of their regular work or interest. Before accepting
any outside engineering employment, they will notify their employers.
d.
Engineers shall not attempt to attract an engineer from another employer by false or misleading pretenses.
e.
Engineers shall not promote their own interest at the expense of the dignity and integrity of the profession.
Engineers shall at all times strive to serve the public interest.
a.
Engineers are encouraged to participate in civic affairs; career guidance for youths; and work for the
advancement of the safety, health, and well-being of their community.
b.
Engineers shall not complete, sign, or seal plans and/or specifications that are not in conformity with applicable
engineering standards. If the client or employer insists on such unprofessional conduct, they shall notify the
proper authorities and withdraw from further service on the project.
c.
Engineers are encouraged to extend public knowledge and appreciation of engineering and its achievements.
Part I – Pg. 32
d.
3.
4.
5.
6.
7.
8.
1
Engineers are encouraged to adhere to the principles of sustainable development in order to protect the
environment for future generations.
Engineers shall avoid all conduct or practice that deceives the public.
a.
Engineers shall avoid the use of statements containing a material misrepresentation of fact or omitting a material
fact.
b.
Consistent with the foregoing, engineers may advertise for recruitment of personnel.
c.
Consistent with the foregoing, engineers may prepare articles for the lay or technical press, but such articles shall
not imply credit to the author for work performed by others.
Engineers shall not disclose, without consent, confidential information concerning the business affairs or technical
processes of any present or former client or employer, or public body on which they serve.
a.
Engineers shall not, without the consent of all interested parties, promote or arrange for new employment or
practice in connection with a specific project for which the engineer has gained particular and specialized
knowledge.
b.
Engineers shall not, without the consent of all interested parties, participate in or represent an adversary interest
in connection with a specific project or proceeding in which the engineer has gained particular specialized
knowledge on behalf of a former client or employer.
Engineers shall not be influenced in their professional duties by conflicting interests.
a.
Engineers shall not accept financial or other considerations, including free engineering designs, from material or
equipment suppliers for specifying their product.
b.
Engineers shall not accept commissions or allowances, directly or indirectly, from contractors or other parties
dealing with clients or employers of the engineer in connection with work for which the engineer is responsible.
Engineers shall not attempt to obtain employment or advancement or professional engagements by untruthfully criticizing
other engineers, or by other improper or questionable methods.
a.
Engineers shall not request, propose, or accept a commission on a contingent basis under circumstances in
which their judgment may be compromised.
b.
Engineers in salaried positions shall accept part-time engineering work only to the extent consistent with policies
of the employer and in accordance with ethical considerations.
c.
Engineers shall not, without consent, use equipment, supplies, laboratory, or office facilities of an employer to
carry on outside private practice.
Engineers shall not attempt to injure, maliciously or falsely, directly or indirectly, the professional reputation, prospects,
practice, or employment of other engineers. Engineers who believe others are guilty of unethical or illegal practice shall
present such information to the proper authority for action.
a.
Engineers in private practice shall not review the work of another engineer for the same client, except with the
knowledge of such engineer, or unless the connection of such engineer with the work has been terminated.
b.
Engineers in governmental, industrial, or educational employ are entitled to review and evaluate the work of other
engineers when so required by their employment duties.
c.
Engineers in sales or industrial employ are entitled to make engineering comparisons of represented products
with products of other suppliers.
Engineers shall accept personal responsibility for their professional activities, provided, however, that engineers may seek
indemnification for services arising out of their practice for other than gross negligence, where the engineer’s interests
cannot otherwise be protected.
a.
Engineers shall conform with state registration laws in the practice of engineering.
b.
Engineers shall not use association with a nonengineer, a corporation, or partnership as a “cloak” for unethical
acts.
Part I – Pg. 33
9.
Engineers shall give credit for engineering work to those to whom credit is due, and will recognize the proprietary interests of
others.
a.
Engineers shall, whenever possible, name the person or persons who may be individually responsible for designs,
inventions, writings, or other accomplishments.
b.
Engineers using designs supplied by a client recognize that the designs remain the property of the client and may
not be duplicated by the engineer for others without express permission.
c.
Engineers, before undertaking work for others in connection with which the engineer may make improvements,
plans, designs, inventions, or other records that may justify copyrights or patents, should enter into a positive
agreement regarding ownership.
d.
Engineers’ designs, data, records, and notes referring exclusively to an employer’s work are the employer’s
property. The employer should indemnify the engineer for use of the information for any purpose other than the
original purpose.
e.
Engineers shall continue their professional development throughout their careers and should keep current in their
specialty fields by engaging in professional practice, participating in continuing education courses, reading in the
technical literature, and attending professional meetings and seminars.
Footnote 1 “Sustainable development” is the challenge of meeting human needs for natural resources, industrial products, energy,
food, transportation, shelter, and effective waste management while conserving and protecting environmental quality and the natural
resource base essential for future development.
—As Revised July 2007—
“By order of the United States District Court for the District of Columbia, former Section 11(c) of the NSPE Code of Ethics prohibiting
competitive bidding, and all policy statements, opinions, rulings or other guidelines interpreting its scope, have been rescinded as
unlawfully interfering with the legal right of engineers, protected under the antitrust laws, to provide price information to prospective
clients; accordingly, nothing contained in the NSPE Code of Ethics, policy statements, opinions, rulings or other guidelines prohibits
the submission of price quotations or competitive bids for engineering services at any time or in any amount.”
Statement by NSPE Executive Committee
In order to correct misunderstandings which have been indicated in some instances since the issuance of the Supreme Court decision
and the entry of the Final Judgment, it is noted that in its decision of April 25, 1978, the Supreme Court of the United States declared:
“The Sherman Act does not require competitive bidding.”
It is further noted that as made clear in the Supreme Court decision:
1.
Engineers and firms may individually refuse to bid for engineering services.
2.
Clients are not required to seek bids for engineering services.
3.
Federal, state, and local laws governing procedures to procure engineering services are not affected, and remain in full
force and effect.
4.
State societies and local chapters are free to actively and aggressively seek legislation for professional selection and
negotiation procedures by public agencies.
5.
State registration board rules of professional conduct, including rules prohibiting competitive bidding for engineering
services, are not affected and remain in full force and effect. State registration boards with authority to adopt rules of
professional conduct may adopt rules governing procedures to obtain engineering services.
6.
As noted by the Supreme Court, “nothing in the judgment prevents NSPE and its members from attempting to influence
governmental action . . .”
NOTE: In regard to the question of application of the Code to corporations vis-à-vis real persons, business form or type should not
negate nor influence conformance of individuals to the Code. The Code deals with professional services, which services must be
performed by real persons. Real persons in turn establish and implement policies within business structures. The Code is clearly
written to apply to the Engineer, and it is incumbent on members of NSPE to endeavor to live up to its provisions. This applies to all
pertinent sections of the Code.
Part I – Pg. 34
MASTER SET OF
30 CASES !
(PART 2)
(Updated 4/3/08)
ENGINEERING ETHICS: YOU BE THE JUDGE
REAL LIFE FACT BASE CASE STUDIES
Case #1
What the Board Said
Middle acted ethically in agreeing to provide those services. He was never
involved substantively in the accident analysis and was apparently provided
with only a general and perfunctory description of the nature of the accident
and the issues involved in the case. From the facts, it appears that the only
exchange that took place between Middle and the plaintiff's attorney was
an oral agreement by Middle to provide the requested services. The written
letter of agreement prepared by Middle was never signed by the plaintiff or
his attorney. Because no one discussed "particular, specialized knowledge"
with Middle and no actual, substantive facts and circumstances of the case
were revealed to him, it is plausible to conclude that Middle never became
privy to any information that could cause a conflict of interest.
While he did not have a conflict of interest per se, Middle, as a courtesy,
should have asked whether his professional services would be required by
the plaintiff's attorney as part of the litigation, before agreeing to be
retained by the defendant's attorney. Moreover, although the plaintiff and
his attorney acted improperly in their failure to respond to Middle's letter of
agreement, Middle should not have assumed that the plaintiff and his
attorney had sought consulting services elsewhere. Because of the delicate
nature of the matter at hand and the danger of misperception of Middle's
actions, he should have made inquiries before agreeing to provide services
to the defendant.
Part II – Pg. 1
Case #2
What the Board Said
It was unethical for Neckted to maintain the retirement fund while serving
as secretary of commerce, but he acted ethically-with on proviso-in
considering issues relating to the major development project. When such
consideration specifically and directly related to the professional services
provided by his former engineering firm, the NSPE Code of Ethics does not
allow his participation.
Neckted's disclosure of the facts and circumstance surrounding his
retirement fund and his relationship with his engineering firm constituted a
disclosure of the possible conflict of interest. But that did not come within
the ethical guidelines of the Code and was not a proper course in dealing
with the appearance of conflict. An engineer can only avoid such a conflict
either by disposing of his land and holdings prior to undertaking the
commission or by declining to perform the services if it is not feasible or
desirable for him to dispose of his land at the particular time; in this case, a
minimum amount of stock in his former firm. Such an approach would not
constitute an unfair and unreasonable financial hardship for Neckted and
would not go beyond the requirements of the Code.
Neckted's role as secretary of commerce presumably involves a broad
range of commercial, business, and related issues involving the financial
well-being of the state, so the development project would be an appropriate
topic for his involvement. However, when it comes to issues involving his
engineering firm, one may assume that Neckted's judgment and knowledge
would be influenced by his ongoing relationship with the firm. As a principal
in the consulting firm, Neckted's relationship with the developer should
require that, as secretary of commerce, he remove himself from
consideration of these development project issues.
Mere disclosure of a potential conflict of interest to a client or employer
does not, in and of itself, eliminate the conflict of interest issue (contrast
Code of Ethics Section II.4.a. with Section III.5). A greater level of ethical
commitment is required of professional engineers.
Part II – Pg. 2
Case #3
What the Board Said
The NSPE Board of Ethical Review interpreted the Code of Ethics as
prohibiting Most from accepting the new assignment if he truly believed that
he lacked the competence to perform the work. The Board believes that the
Code does not aim to prohibit engineers from accepting new and different
tasks and duties and thereby grow professionally. Nevertheless, the Board
could not ignore the practical realities of engineering and infringe upon the
autonomy, judgment, and professional discretion of an individual practicing
engineer.
The Board, therefore, must take Most at his word that the reason for
declining the position offered was because he believed that he lacked the
competence to perform the work-even though he would be performing the
services as part of a team. As a professional engineer in an environmental
agency, Most at some point would probably be put in responsible charge of
activities for which he lacked the necessary education, training, and
experience.
Having concluded that Most could ethically decline the position, the Board
also decided that it was ethical for Ball to testify as to Most's qualifications
to accept the position. The Board based its decision on the assumption that
Ball had a reasonable and good-faith belief that Most could perform the
services in question.
Part II – Pg. 3
Case #4
What the Board Said
Several aspects of this case need to be considered in order to evaluate appropriate
courses of action and ethical implications. For example, did the changes improve the
report quality? Did the changes modify or change the results inappropriately? Did the
changes make the report clearer or more confusing? Was the report published by the
sponsor or just used in-house?
One could argue that the "changed" report will be used specifically and only by the
sponsor in their internal decision-making process. The sponsor paid for the research
and it is theirs to use as they see fit, as long as they do not modify the results to serve a
purpose not intended by the research engineer. However, the report remains the
responsibility of the author and should not be changed. The sponsor could ethically
write another report using Steadfast's information with appropriate references. The
Code requires that the engineer's name not be affixed to any document not prepared
under their direction and control.
If the "changed" report is to be published by the sponsor or if the "certain changes"
made by the sponsor did change the actual conclusions of the engineer's report, one
could question the ethics of the sponsor. The sponsor is obligated to notify the engineer
of the changes and seek his permission. Under these circumstances, the engineer
should, at a minimum, request the removal of his name from the changed report. At a
maximum, the engineer should take the sponsor to court. Of course, several actions
between these extremes are possible and should be explored.
According to the NSPE Code of Ethics, engineers should be objective and truthful in
reports. They should also include all relevant and pertinent information. Furthermore,
the Code states that engineers must not permit the use of their names in business
ventures with any person that they have reason to believe is engaging in fraudulent or
dishonest business or professional practice. A fundamental canon of the Code states
that the engineer shall act in professional matters for each employer or client as faithful
agents or trustees. Assuming that the sponsor involved in this case was an engineer, he
should also be aware of and adhere to the profession's ethics code.
The Board of Ethical Review therefore concluded that the sponsor acted unethically
toward Steadfast and that Steadfast would be ethical in taking action against the
sponsor.
Part II – Pg. 4
Case #5
What the Board Said
The NSPE Board of Ethical Review (BER) has considered similar issues in
previous cases, and provided a context for understanding this situation.
In one case, an engineer serving on a community-service corporation was
responsible for obtaining money to construct a courthouse and office. The
engineer was instrumental in getting the federal government to spend the
money on the project, but his service corporation had no influence in
determining who would design or build the project. The engineer wanted to
be a subconsultant to a larger design firm, and submitted proposals to the
responsible federal government agency. The BER found no violation of the
ethical code.
In another case, an engineer served on the board of directors of a private
health care provider that had contracted with the county hospital board to
operate a health care facility where some engineering work was needed.
The engineer received a contract from the private provider to perform the
work. The decision was made by the private board, of which the engineer
was a member, and the engineer participated in the decision. The BER
concluded that the engineer could not ethically seek the work or participate
in the decision of selecting himself.
In the present case, the city will award the library contract using HUD
funds. The college trustees and city fathers must have a very close
relationship. Although Strong will not be involved in the decision, he is too
close to the city and could influence its decision. According to the BER, it
would be unethical for Strong to be considered for providing engineering
services on this project.
Part II – Pg. 5
Case #6
What the Board Said
Under the NSPE Code of Ethics, it is not ethical for City to knowingly
participate in a program that uses deceptive advertisement, regardless of
whether the engineer is acting in a volunteer or paid position. Furthermore,
it is unethical for the university as a whole to misrepresent to the public
information that leads to deception.
The key in this case is that the engineer has advanced knowledge of
possible deception. The ethical approach for the engineer would be to
address the wording of the advertised program in the presence of the
university authorities and suggest corrective wording.
It is incumbent upon engineers who know of "deceptive practices" being
used in their work environment to bring these to the attention of the
responsible parties and to advise the administration that the use of
deceptive practices is not in the best interest of the institution. In fact,
deception in the advertising could cause the university to have to defend its
intentions in court. However, regardless of the possible court actions,
engineers must at all times be truthful. Thus, if the advertisement indicates
that minorities will be considered first, then there should not be a problem
in serving on the committee. However, if the advertisement does not state
this, then all candidates should be treated equally.
Part II – Pg. 6
Case #7
What the Board Said
The actions in each instance were unethical. The facts bring together a
reality of certain practices that are on a collision course with the ethical
constraints of many practicing professionals. The issue of rebates,
bonuses, kickbacks, gifts, and other "emoluments" raises the specter of
conflicts of interest, with few mitigating circumstances. The NSPE Code of
Ethics is unequivocal in stating that "engineers shall not . . . accept
financial or other valuable consideration, directly or indirectly, from outside
agents in connection with the work for which they are responsible."
The Code also specifically states that "engineers shall not accept
commissions or allowances, directly or indirectly, from contractors or other
parties dealing with clients or employers of the Engineer in connection with
work for which the Engineer is responsible."
Business practices have changed significantly in recent years, making for
more competitive operations less tightly bound to old and customary
practices. Nevertheless, it was unethical for Bates to accept any "rebate"
check, despite the conditions created by the customary trade practice.
Under such circumstances, the client could very well question whether the
work XYZ Company did was in any way compromised and thus reflected in
the amount of the part remitted to the client.
Part II – Pg. 7
Case #8
What the Board Said
It was unethical for Mature to indicate that Perryanst will subcontract to
Mature on the project without Perryanst's prior knowledge. Perryanst's
ethical obligations under the circumstances were to advise the client that
final arrangements had not been completed.
Mature's notification to the client that Perryanst would be subcontracting
from Mature appears to have been caused by a misunderstanding or
miscommunication, or an absence of communication that occurred
between Mature and Perryanst. It is not clear from the facts what the nature
of the referral was. It is possible that Perryanst may have been under the
impression that Mature would merely be providing Perryanst with an
introduction to a client and that Perryanst would simply take it from there.
However, it is evident from the facts that a contractual relationship between
Perryanst and Mature was discussed.
In view of the fact that Perryanst was a new engineer starting out as a
consultant, it may be argued that Perryanst should have expected that
Mature would play a significant role in the work being performed. However,
a burden of responsibility falls on Mature to more clearly define his role with
the client. For that reason, Mature was deceptive in using the chapter
referral network as a means of enhancing his personal business interests.
In addition, it is critical that all of these factors be balanced with the
interests of the client.
This apparent unmet expectation could have been minimized had
Perryanst and Mature had a more open discussion concerning the referral,
or if the detailed procedures of the chapter referral program had had more
time to become established.
Part II – Pg. 8
Case #9
What the Board Said
Etright has a professional obligation under the Code of Ethics to recommend the
additional testing and explain why it should be done. Then, the company can
make an informed decision about the need for more testing and its effects on the
public health, safety, and welfare.
One of the most difficult questions for engineers is how much testing is enough.
This issue always depends on a careful assessment of all facts and
circumstances in each case. Each engineer must determine this based on
reasonable professional judgment.
Etright must balance a variety of factors. He generally believes that the software
designed by his company is safe but has become aware of a new test that is
likely to produce results that could cast a cloud over the software's viability. The
financial pressures that exist, including the potential impact on his company, the
client, and the public, as well as the delays and potential loss of jobs if additional
testing is pursued, are clearly important factors that need to be addressed.
However, it would seem that these nontechnical considerations should be given
weight separate and apart from Etright's decision whether to recommend the
additional testing.
Etright would be well advised to prepare a technical report that explains both the
current testing analysis and results as well as the new testing procedure that was
recently reported in the professional literature, so that his employer can make an
informed decision regarding additional testing (see Code Sections III.6.b and
II.4.a). The nature of the industries using the software-water, air, and nuclearobviously have an enormous impact upon the public health, safety, and welfare,
and Etright should be certain, therefore, that the information imparted to his
employer and the client is clear and accurate. Under the facts in this case, it is
apparent that the employer wants to have a significant degree of certainty that
the products designed and manufactured have a high degree of reliability. Etright
is in a strong position to assist his employer, and ultimately his employer's client,
in carefully evaluating all of the pertinent facts and deciding on a course of
action.
Part II – Pg. 9
Case #10
What the Board Said
If Caliber determines that Edge's work is or may be in violation of state and local safety
requirements and endangers public health, safety, and welfare, Caliber should
immediately discuss these issues with Edge in an effort to clarify and resolve this issue
quickly. If Caliber and Edge are unable to resolve the issue, Caliber must inform Edge
that as a professional engineer, his only alternative is to notify the proper authorities.
In recent years, various professions, including engineering groups, have successfully
developed peer review programs. These voluntary programs have been immensely
successful in creating a mechanism for professionals to work together in a collegial
atmosphere to understand and improve professional practice. This can be accomplished
by analyzing and evaluating the actions, decisions, and techniques of the professional
and offering constructive and, at times, critical feedback. Peer review enhances
professional practice.
However, such programs are built on a foundation of confidentiality-an individual
agreeing to serve as a peer reviewer must sign a confidentiality agreement—and for
good reason. Firms under peer review should be encouraged to provide as much
pertinent, detailed information to the peer reviewer as possible to allow a thorough
evaluation of the firm. Confidentiality ensures a maximum amount of disclosure. In
addition, confidentiality helps build trust between the parties involved in the peer review
process and promotes an atmosphere that will improve production and guarantee
success.
While the merits of confidentiality are clear, in Caliber's case, the NSPE Board of Ethical
Review was faced with the discovery that the Edge may be in violation of state and local
safety code requirements and could endanger public health and welfare. This ethical
dilemma appears to involve two separate provisions of the NSPE Code of Ethics-Section
III.4. and Section II.1.e. The BER has considered at least one case involving an engineer
gaining knowledge of information damaging to a client's interest and affecting the public
health and safety (see BER Case 76-4). On one hand, the engineer has an obligation not
to disclose confidential information concerning the business affairs or technical processes
of any present or former client without the client's consent. On the other hand, Caliber,
having knowledge of any alleged violation of the Code of Ethics, has an obligation to
cooperate with the proper authorities in furnishing such information or assistance as may
be required.
Part I – Pg. 10
Case #11
What the Board Said
It was not ethical for Dualpro to refuse to pay Eddie for his services.
The facts in this case illustrate a frequently encountered situation often
presented within the engineering profession—payment disputes that occur
between client and engineer that ripple into disputes between engineers and
other consultants. In this case, the fact that Dualpro is a lawyer is not
relevant to his obligation as an engineer dealing with another engineer,
although this could be a factor in other cases.
The Board believes that Dualpro's failure to have informed Eddie in advance
about the nature of Dualpro's contingency fee arrangement with Hurt was at
best misleading. If Dualpro intended that compensation to Eddie would be
on a contingency fee basis, Dualpro should have negotiated this up front
with Eddie. Having not done so, Dualpro had a clear obligation to
compensate Eddie in full.
Part I – Pg. 11
Case #12
What the Board Said
Obviously, this situation involves sensitive circumstances, requiring the
engineer to exercise great skill and prudent judgment in dealing with the
employer. Wright may be viewed by management as a "can't do'er" and
damage his promotional prospects. One alternative in this type of situation is
for Wright to obtain a copy of the state engineering licensure board's rules
and discuss them with the employer. Under those rules, the engineer is
legally bound under the rules of professional conduct. In this connection, it
appears that the actions the engineer is being requested to take would be in
direct violation of the state law and rules. Wright might have suggested that
the applicable provisions be reviewed by the company's legal counsel for a
legal opinion.
In sum, ethics should not be a matter of what might be convenient for the
engineering firm, a vendor, or a client. Instead, engineering ethics is
intended to provide guidance to practicing engineers to help navigate
through professional obligations and restrictions. Moreover, a corporate
official who ignores a mandate of licensure laws is acting irresponsibly, and
it would seem as though higher-ranking corporate officials, particularly those
with engineering backgrounds, as well as shareholders, would presumably
be interested in being made aware of that fact.
It would not be ethical for Wright to substitute text in a code report that
supports the design of a component prepared by another engineer. This
conclusion rests on the presumption that the text was too illegible to discern
with certainty the substance and wording.
Part I – Pg. 12
Case #13
What the Board Said
Various provisions in the NSPE Code of Ethics result, at times, in competing
ethical values. One of the more prominent competing values relates to the
ethical obligation of the engineer to maintain the confidentiality of information
provided to Lanced, the engineer's client, or derived as a result of the
professional services rendered by the engineer. There are occasions in
which this basic and straightforward ethical responsibility conflicts with the
duty of the engineer to hold paramount the public health and safety.
However, in this case there do not appear to be any overriding or legitimate
ethical reasons for Lanced to agree to a consulting contract with the sole
purpose of preventing him from speaking out in public or testifying in any
future litigation involving industrial tools manufactured by Industraco. By
signing the contract, Lanced would compromise his professional judgment
and play the role of a "hired gun" bound by "golden handcuffs" without
regard to the individual facts and circumstances involved in a particular
case. In potential future situations, it would be in the public's interest for
Lanced to speak out publicly concerning information that could have an
important bearing on the public health, safety, and welfare. As a professional
engineer with an affirmative obligation to hold paramount the public health
and safety, the Board cannot see how Lanced is serving this ethical value by
executing an agreement that prevents Lanced from prospectively performing
this basic ethical obligation.
It would not be ethical for Lanced to knowingly agree to a consulting contract
(with Industraco) with the sole purpose of preventing Lanced from speaking
out in public or testifying in any future litigation involving industrial tools
manufactured by Industraco.
Part I – Pg. 13
Case #14
What Iowa Engineering Society's Northwest Chapter Said
A majority of the difficulty that we had with Engineer A is that he was not up front with XYZ
Incorporated in that he had decided to accept an offer with ABC Incorporated.
Engineer A's acceptance of the interview trip to XYZ's mountain headquarters was deceptive in
that he had already decided to commit to ABC, and did not offer that information to XYZ. He tries
to justify the trip to himself reasoning that it will "broaden his knowledge of the employment
market, as well as future professional opportunities." This is in direct conflict with the reasoning
for his decision to go with ABC because "ABC offered better long-term professional
opportunities." He had decided to go with ABC because of the long-term opportunities, so future
opportunities with XYZ should not have been a factor. We felt that Engineer A was not being true
to himself by trying to justify the trip this way.
Though Engineer A was opportunistic in combining the ski trip with the interview with XYZ
Incorporated, XYZ may have not have had a problem with his interest in skiing. Given that the trip
was scheduled after graduation, XYZ may have even expected and encouraged a ski trip
depending on how interested in they were in Engineer A. Being near a resort is an amenity for
XYZ Incorporated and a positive factor in the decision making process to work for their company.
A company recruiting engineers has some degree of risk and sunk cost in bringing them to the
headquarters without a commitment from the recruit. They do have an expectation though, that
they have a reasonable (or better if this is a second interview) chance that the recruit will commit
to their company. XYZ incorporated was not afforded this chance because Engineer A had made
his decision to go with ABC Inc. If Engineer A would had communicated his decision to go with
ABC Inc. to the XYZ executive after the offer of the trip, XYZ Inc. could have determined if it was
worth it to still fly him out and try to sway his decision. Seeing that he had "excellent credentials,"
it may have been worth the risk to XYZ Inc. to bring him to their headquarters. Though he had
decided on ABC Inc. he had not officially accepted the position with them and was "still on the
table."
The Fact situation does not discuss the size of XYZ Inc. If it is a small company, flying one recruit
that has no interest in the company may use up the recruiting budget for the year, making the
deception egregious. Where if it is a large company recruiting numerous individuals and flying
them out to the headquarters, they know they are taking the chance and will not get all the
recruits they go after. This is a point that Engineer A should have considered prior to accepting
the offer of the trip.
Ultimately, we felt that because Engineer A was not honest and up front with the XYZ executive,
he was deceptive and took advantage of XYZ Incorporated. It was unethical for Engineer A to
accept the invitation to visit XYZ headquarters.
Part I – Pg. 14
Case #15
What the Board Said
The obligation of a professional engineer to take action when faced with a
situation involving a direct threat to the public health and safety has been
addressed by the Board on several other occasions. The Board believes
much of the same reasoning in the earlier cases applies to the case at hand.
The facts and circumstances facing Standards involve fundamental issues of
public health and safety, which are at the core of engineering ethics. For an
engineer to bow to public pressure or employment situations when the
engineer believes that great dangers are present would be an abrogation of
the engineer's most fundamental responsibility and obligation. Standards
should take immediate steps to contact the county governing authority and
county prosecutors, state and/or federal transportation/highway officials, the
state engineering licensure board, and other authorities.
Standards should immediately approach his supervisor to press for strict
enforcement of the five-ton limit, and if this is ineffective, contact state and/or
federal transportation/highway officials, the state engineering licensure
board the director of public works, county commissioners, state officials, and
such other authorities as appropriate. Standards should also work with the
consulting engineering firm to determine if the two crutch pile with five-ton
limit design solution would be effective and report this information to his
supervisor. In addition, Standards should determine whether a basis exists
for reporting the activities of the retired bridge inspector to the state board as
the unlicensed practice of engineering.
Part I – Pg. 15
Case #16
What the Board Said
Clearly, Pilfering's conduct is well beyond the pale of ethical conduct and he
should be condemned for his actions. To make calls to Anoyd's employees
at home and at work requesting that they make him copies of their
company's proprietary schematics is more than an ethical violation—it is a
legal violation.
There can be no doubt that Anoyd had justification for being angry and upset
over Pilfering's actions. And it is easy to see how, at the seminar, Pilfering
would have taken the actions he took under the circumstances presented.
However, it is the Board's view that Anoyd's actions in confronting Pilfering
in the manner indicated were not ethical or professional. It is clear that there
were other reasonable options for Anoyd to explore, such as a direct
conversation with Pilfering over his actions and, if necessary, a letter from
Anoyd (or Anoyd's attorney) demanding that Pilfering cease and desist from
continuing his improper actions, or else face legal consequences.
Engineers are often confronted by unprofessional and unethical conduct by
non-engineers and from other engineers. However, all engineers need to be
mindful that their actions and conduct—good and bad—in response to such
unprofessional and unethical conduct reflect upon the entire profession, and
help to shape the public's image and impression of engineers and
engineering.
It was not ethical for Pilfering to contact Anoyd's employees. It was not
ethical or professional for Anoyd to confront Pilfering in the manner
described. Also, it was not professional for Pilfering to engage in derogatory
language at the seminar.
Part I – Pg. 16
Case #17
What the Board Said
This case relates to the direct obligations of truth and honesty that all
engineers owe to their clients in the performance of their services. Under the
facts presented in the case, LeVard was performing the same basic service
for two separate clients and billing HighYield for data that LeVard had
already developed and billed ProfitTech. In this connection, the Board
believes that at some point, HighYield, ProfitTech, or the local code officials
would become aware of LeVard's action, which could ultimately reflect upon
LeVard and potentially the engineering profession in general.
However, the Board does not believe that an ethical violation exists under
the facts. The Board believes that it would have been appropriate for LeVard
to inform HighYield that a similar study had been done for another client,
and that LeVard would contract to review the study to determine whether
any modifications, updates, or other changes would be necessary. LeVard
would then say that HighYield would be charged for full value of the report.
LeVard's intellectual property, expertise, knowledge, and professional
judgment are contained in the report, and LeVard had the ethical right to be
fully compensated for such services. Such an approach would be in accord
with the language and intent of the NSPE Code and demonstrate good will
on the part of LeVard.
It was ethical for LeVard to charge HighYield for a complete traffic study. It
was unethical for LeVard not to disclose the use of propriety data developed
for another client.
Part I – Pg. 17
Case #18
What the Board Said
The facts and circumstances go beyond anything that would be permitted under the letter
or the spirit of the NSPE Code of Ethics. The Board interprets the facts to suggest that
Sine is being asked to adopt a design that was not prepared by Sine, was not under
Sine's direct control or supervision, and does not reflect the professional judgment and
intent of Sine. Instead, it appears that Fixx is seeking to have Sine seal the drawings in
question merely to satisfy the requirements of the building official, without regard to
actual responsibility for the contents of the drawings. The work to be "reconciled" was
clearly not performed under the responsible charge (direct control or personal
supervision) of Sine. In fact, the work that was prepared by Sine was essentially ignored
or rejected by Strongwill, in favor of another solution chosen by the Strongwill. Since Sine
was not retained for construction-phase services, Sine never had the opportunity to
observe the work, nor did she provide guidance to Fixx or Strongwill on the relationship of
the work to the original design and construction documents she prepared.
It is critically important that an engineer actually prepares the work or in responsible
charge of the work that she ultimately seals. By contrast, the facts in this case illustrate
an example where an engineer is being asked to sign and seal work for which she was
neither in responsible charge, nor which she was involved in preparing. In essence, it can
be argued that the facts present the appearance that Sine's services were used by the
Fixx merely to gain approval for the project, with no intent on the part of the client or
Strongwill to follow Sine's design intent.
It is not entirely clear under the facts whether Fixx knew or chose to accept Strongwill's
decision to ignore Sine's designs. In unilaterally altering Sine's design, Strongwill may
have engaged in the unlicensed practice of engineering. However, since Sine's design
was approved by the building official, and Strongwill's approach was at variance with the
approved design, Fixx may now find that Strongwill's approach will result in additional
design and/or construction costs to obtain the building official's approval. Clearly, there is
a lesson here for clients who fail to appreciate the importance of publicly approved design
drawings.
It was not ethical for Sine to reconcile his original design documents without an extensive
investigation to ensure that all original design intent was followed. It was not appropriate
for Tractor to prepare a set of record drawings based on the construction without notifying
Sine. Moreover, there is a possibility that Tractor was aiding and abetting the unlicensed
practice of engineering.
Part I – Pg. 18
Case #19
What the Board Said
The Board is of the view that this case involves much more than a failure on
the part of one engineer to give proper credit to another engineer for work
performed. Instead, this case appears to suggest an outright
misrepresentation and possible misappropriation on the part of Using.
Without addressing the copyright, patent, and other legal issues that are
raised by the facts, it is clear that Using appears to have carelessly or
intentionally created the misimpression that Using's firm was planning to use
Trusting's firm on the project in question. Moreover, it appears that Using
carelessly or intentionally induced Trusting's cooperation and support in
furtherance of this objective. In truth, the Board finds it difficult to believe that
Using's actions were careless because Using solicited and received a
project proposal from Trusting for the project.
While it is clear that in today's highly competitive environment, engineering
firms and companies need to be on guard and protective of trade secrets
and other intellectual property that provide a competitive advantage,
relations among engineers must continue to be based on mutual trust and
cooperation. Where one engineer is asked to cooperate with another
engineer in an activity for their mutual benefit and the benefit of a client, the
cooperating engineer should not have his support and good will be
subjected to abuse and exploitation by the other engineer. As with other
professions, engineering is a collegial enterprise based on mutual respect
and trust. A profession that fails to recognize this basic principle will cease to
be a profession.
It was not ethical for Using to obtain and share details of Trusting's
technology in the manner herein described.
Part I – Pg. 19
Case #20
What the Board Said
Haste has an obligation to pursue this matter with SPQ Engineering. If a
satisfactory ethical resolution cannot be reached, he is obligated to report
the violation to the vendor. In addition, Haste should reconsider his further
association with a firm that has shown itself engaged in fraudulent and
dishonest enterprise. The Board recognizes the right and the obligation of
the engineer to report such violations as appropriate. At the same time, the
Board believes that as a professional, an engineer should always exercise
judgment and discretion when confronting a situation such as the one
presented under the facts. Depending on all of the facts and circumstances,
an engineer should take reasonable steps to exhaust all appropriate
alternatives before taking an extreme action, such as reporting an employer
or a client for their actions, particularly where such actions do not appear to
result in physical harm or danger to the public health or safety. At the same
time, engineering managers acting for an employer who knowingly act in an
unlawful manner or who take retaliatory actions against another engineer
who brings such matters to their attention are ignoring the basic principles
contained in the NSPE Code of Ethics and are acting unethically.
It was not ethical for Haste to report his employer's apparent violation of the
licensing agreement on the hotline without first discussing his concerns with
his employer. Engineering firms acting through engineering managers who
willfully ignore licensing agreement restrictions are in violation of the NSPE
Code of Ethics.
Part I – Pg. 20
Case #21
What the Board Said
It would be unethical for Worthy to carry out the contractor's proposal. It is
essential that engineers maintain a truly arms-length relationship with such
entities as contractors and vendors having, or potentially having, contractual
arrangements with engineers employers or clients. The case involves two
primary issues: First, Worthy would be referring clients to the contractor and
for that receiving a commission-a clear conflict of interest. Moreover, the
Code specifically prohibits the receiving of commission or other valuables
from a contractor. Second, the contractor makes no suggestion that Worthy
disclose to his client his conflict of interest as required by the Code. Further,
a broad interpretation of the Code's provision on political contributions would
indicate that an engineer receiving contributions (commissions) or other
valuable considerations would also constitute an ethical violation.
Part I – Pg. 21
Case #22
What the Board Said
It would be unethical for Global to proceed. Clearly, Global is being asked to
participate in a project under circumstances that may involve a violation of
U.S. law as well as the NSPE Code of Ethics. While being respectful of all
the parties involved in this matter, Global should diplomatically indicate that,
although he would be interested in participating in the project and offering
professional services, it would be illegal and unethical for him to do so under
the described arrangement. He should further explain that he would be
willing to consider an alternative arrangement under circumstances that
were consistent with U.S. law and engineering ethics.
In the 1970s, the NSPE Board of Ethical Review determined that the socalled "When in Rome . . ." rule, whereby engineers could engage in the
legal and ethical practices of the host country, is not consistent with the
NSPE Code of Ethics (see BER Case 76-6). The BER's decision was proper
at that time and continues to be so today.
The BER noted that the facts in case 76-6 involved a direct "kickback"
between the engineer and a public official, while the present case involved
the "encouragement" by a foreign official that Global "associate" with a local
engineer. "Situational ethics" is no less wrong in the professional practice
area than it is in the technical practice area. If the Board decided otherwise,
it would not be much of a leap to suggest that engineers practicing in
another country could engage in unsafe engineering practices simply
because that country allows it. The Board believes that such an approach is
wholly unacceptable and refuses to follow that path. Earlier and subsequent
BER cases support this view.
Part I – Pg. 22
Case #23
What the Board Said
Fitting and Returnto acted unethically in serving both as the engineers for
the developer and as municipal engineer for Township B, and in
recommending approval of the road.
By failing to disclose their ownership of undeveloped property in Township
B, the engineers did not provide Township B with a full range of all known or
potential conflicts of interest or other circumstances that could have
influenced, or appear to have influenced, their judgment or the quality of
their services. It is not clear to the NSPE Board of Ethical Review why the
engineers did not provide a full and complete disclosure, but it appears that
had the engineers done so, it is at least possible that Township B may have
objected to the engineers' making a feasibility recommendation regarding
the new road.
It must be assumed that the engineers' recommendation to Township B
regarding the new road was based on a review of documents and
information involving the professional services they had provided for the
developer in connection with the subdivision project in Township A. There is
nothing in this case to indicate that Fitting and Returnto had solicited or
reviewed any other plans, drawings, documents, reports, recommendations,
or alternatives that were prepared by unrelated or disinterested parties. On
that basis, there appears to be a clear violation of NSPE Section II.4.d.,
which prohibits engineers in public service as advisors or employees of a
governmental body to participate in decisions involving such information.
Part I – Pg. 23
Case #24
What the Board Said
Balancing the interests of all parties involved in this matter, the NSPE Board
of Ethical Review believes that Cheever's actions and conduct were ethical.
The Board can find no general ethical proscription limiting Cheever's
decision to establish an engineering firm, particularly because Cheever was
not a partner or principal of ABC. It is not unusual for engineers to break off
from their employer and go into business for themselves at some point. This
is a fundamental principle of the U.S.'s free enterprise system and generally
should not be discouraged.
Regarding Cheever's solicitation of business, while Clover City may have
expressed preliminary interest in Cheever's future services, there was no
formal agreement between Cheever and the city and no guarantee that once
Cheever was independent, his solicitations for work would be positively
received by the city. In fact, Cheever declined an offer of work by Clover City
and waited for more than a year before deciding to go into competition with
ABC. Also, it appears that ABC's business with Clover City was related
strictly to the presence of Cheever in the firm, and Cheever apparently did
not obtain any particular specialized knowledge as an employee of ABC that
would restrict his ability to establish his own firm and eventually compete
with ABC.
Part I – Pg. 24
Case #25
What the Board Said
The NSPE Board of Ethical Review considers Hatz's actions ethical. The circumstances
Hatz faces in this case are not unlike circumstances occasionally faced by other
engineers who seek to explore career opportunities beyond a "full-time" position. A key
question involved in such activities is whether the engineer can devote sufficient attention
to the responsibilities involved in an ethical manner.
Hatz's responsibilities are limited to professional engineering services and appear to be
consistent with the state's certificate of authorization requirements. Hatz has a flexible
schedule with his other employer and presumably is able to adjust his schedule to meet
the needs of his employers. While it appears that Hatz may be stretching his role as an
engineer in responsible charge for the firm, without more evidence to suggest improper
activity, the BER is hesitant to conclude that Hatz was violating the NSPE Code of Ethics.
The manner in which Hatz is compensated does not appear to contain any specific
provision that would necessarily run afoul of the Code. Although it could be argued that
Hatz's receiving 5% of the gross billings for engineering work for which the seal of a PE is
required could potentially compromise Hatz's judgment, the BER believes that would
stretch this provision of the Code beyond its actual intent. In addition, the BER does not
view the transfer provision as one that would compromise Hatz's judgment. Instead, the
board views this provision as a way for the firm's principals' to maintain control over
management of the firm.
With regard to Hatz's dual role as a government and private employee, both the state
government agency and the engineering firm are aware of Hatz's activities and do not
object to these activities. However, the BER notes that should a conflict-of-interest arise,
Hatz will need to carefully address those activities consistent with NSPE Code Sections
III.6.b., II.4.d., II.4.e. and other applicable provisions of the Code.
As has been noted in similar cases, while the actions of Hatz may be consistent with the
NSPE Code of Ethics, it is critical for an engineer under these circumstances to perform a
careful review of all pertinent material before signing and sealing appropriate plans and
drawings. In addition, Hatz must carefully review and understand all state requirements
regarding "responsible charge" activities, including possible local office and employment
restrictions.
Part I – Pg. 25
Case #26
What the Board Said
It was unethical for Truth to produce a promotional brochure for his new firm that
contained a "list of clients" that implied they were clients of his firm and a "list of
projects" that implied they were performed by his firm.
It is clear that these situations frequently present delicate and sometimes difficult
issues, particularly where long-established business relationships exist between
engineering firms, engineers, and their clients. Obviously, no engineer or
engineering firm "owns" a client, as clients are free to determine for themselves
which engineer or engineering firm is appropriate for their present and future
needs and requirements.
However, the NSPE Board of Ethical Review is deeply troubled by the manner in
which Truth undertook to promote his new engineering firm. The board believes
there was a clear effort on the part of Truth to engage in misleading and deceptive
acts. To imply that certain companies are "clients" of the new firm and apparently
take credit for projects that were performed by other engineering firms is wholly
improper.
The board cannot identify any context in which Truth could have accurately used
the term "client" to describe the new firm's relationship with the companies listed
on the brochure. A "client" implies some past or present business relationship
between an engineer, the engineer's firm, and a company. To use the term "client"
when referring to a relationship that existed when an engineer was employed
elsewhere is misleading, deceptive, and a violation of the NSPE Code of Ethics.
The Board cannot think of any clarification that could have been included in the
brochure that would have made the reference to "client" less misleading or
deceptive (see Code Sections II.3.a., II.5.a., III.3.a).
For similar reasons, the reference to the "projects of the firm" is misleading,
deceptive, and a violation of the Code. Depending upon all of the facts and
circumstances, however, if the promotional brochure had contained a clarification
specifically stating that the projects were performed by the firm's employees when
they were employed by other, named firms, the board may have reached a
different result.
Part I – Pg. 26
Case #27
What the Board Said
According to the facts of this case, Lating acted reasonably by properly
balancing the obligation to be faithful to the client and not disclose what the
client might consider to be confidential information with the obligation to hold
paramount the public health and safety. Lating's observation appears to be
based on a visual inspection without anything more, and there is nothing
noted in the facts to indicate that Lating has expertise in structural
engineering. While it may be appropriate for Lating to note such information
in his field notes, to place this information in a final report would not be
responsible and could unnecessarily inflame the situation. However, under
no circumstance would it be appropriate for Lating to alter his field notes.
The NSPE Board of Ethical Review believes that Lating has an obligation to
follow through to see that correct follow-up action is taken by the public
agency. Only if the public agency does not take corrective action should
Lating consider alternatives.
Part I – Pg. 27
Case #28
What the KSU Chapter Said
The facts presented in this case highlight the ethical dichotomy facing
engineers today—their obligation to be faithful to the client and their
obligation to hold paramount the safety, health, and welfare of the public.
Engineer A realized that, because the structure carried a risk of collapse, the
safety and welfare of the public were in jeopardy. Therefore, Engineer A
suggested that remedial construction should begin, in accordance with the
number one canon of a professional engineer. The moment that the client
and architect suggested accomplishing the remedial construction in secret,
without even alerting the workers in the building, Engineer A had an ethical
obligation to take additional steps to address the situation, including a
"paramount professional obligation to notify the appropriate public authority if
his/her professional judgment is overruled under circumstances where the
safety of the public is endangered." Because the safety of the public should
be held in higher regard than the desire of the client and architect to keep
the remedial construction secret, Engineer A is obligated to notify the public
authority and to not comply with the client's and architect's request for
secrecy. Furthermore, it is Engineer A's ethical responsibility to refuse to
continue to work on the project unless the public is alerted about the risk of
collapse.
The same professional obligation holds for Engineer B as for Engineer A.
Not only should Engineer B realize that the safety of the public supersedes
the wishes of the client and architect, but he or she invariably understands
that if the building does collapse, and any person is injured, all peoples
involved in misleading the public will be held legally liable. As a public
official, Engineer B is obligated to inform all those at risk of injury from the
possible collapse of the structure, despite the protests of the client and
architect.
Part I – Pg. 28
Case #29
What the Board Said
In this case, Fixx is faced with a predicament with a variety of options and
alternatives. First, Fixx could interpret the situation as one involving "tradeoffs," in which he could arguably rationalize a decision to permit the
inconsistent application of a building code in order to accomplish the larger
objective of obtaining the necessary resources to hire a sufficient number of
code enforcement officials to provide proper protection to the public health
and safety. On the other hand, Fixx's decision to permit developers to avoid
compliance with the updated building code enforcement requirements might
potentially cause a real danger to the public health and safety if the failure of
a new facility to comply with those requirements causes harm to the public.
As concluded in earlier BER cases, the engineer must hold the public health
and safety paramount and has a responsibility to insist that public officials
and decision-makers take steps-corrective steps if necessary-to see that this
obligation is fulfilled. The Code of Ethics makes it clear that engineers have
an obligation to advise their clients or employers when they believe a project
will not be successful. In this case, Fixx should make it clear to the chairman
that "righting a wrong with another wrong" does grave damage to the public
health and safety. Fixx should insist that public safety will be seriously hurt in
either case and, that if the integrity of the building code enforcement process
is undermined for short-term gain, the city, its citizens, and its businesses
will be harmed in the long term.
Part I – Pg. 29
Case #30
What the Board Said
It was not ethical for Candid to prepare bidding criteria, bid, evaluate bids, and
recommend his company for owner selection. Candid would have been better advised to
avoid this conflict of interest.
Engineers are always cautioned by the NSPE Code of Ethics to disclose all known or
potential conflicts of interest by promptly informing clients of any business association,
interest, or other circumstances which could influence or appear to influence their
judgment or the quality of their services. Under the facts of this case, it is not entirely
clear why and on what basis H&T selected Candid to provide the curtain wall
specifications on behalf of H&T. It could be that in the rendering of consulting services,
Candid performed professional services to the satisfaction of H&T and this fact may have
persuaded H&T to select Candid's curtain wall company to manufacture the required
equipment. At the same time, the Board believes the early and complete disclosure by
Candid needs to be balanced against Candid's later inclusion of his firm on the list of
potential curtain wall manufacturers without the client's prior affirmative approval. The
Board believes this point is instructive because it demonstrated Candid's recognition of
the potential for a conflict of interest in connection with the services provided to H&T and
the actions he took in regard to that potential conflict.
While it is difficult to speculate what H&T's thinking and considerations were in
connection with its selection of Candid's company, we do have a concern over H&T's
selection of Candid's curtain wall manufacturing company under the facts. The Board is
also concerned that the decision to select Candid's firm was made without H&T
affirmatively approving in the early stages Engineer's A's firm's participation in the bidding
process. The Board's opinion is that Candid's actions could be interpreted as being
calculated to result in the selection of his firm from the beginning, despite the fact that
Candid provided early partial notice of the potential conflict of interest.
In addition, the Board is troubled that Candid did not provide H&T with initial complete
and appropriate information about the products available from Candid's firm, the
manufacturing process, services provided, warranty information, operation and
maintenance, and other important issues. In this connection, the Board believes that
once Candid made the decision to include his firm in the bidding process, Candid should
have provided H&T with the same information and under the same circumstances that
Candid provided H&T with the information about the two other competing firms so that
H&T would have complete information upon which to make a decision, review with other
H&T representatives, and compare the information objectively with the other proposals.
Part I – Pg. 30
Fitting Michaelis-Menten directly to
substrate concentration data
Murray Hannah & Peter Moate
Outline
Enzyme Kinetics
Outline
Enzyme Kinetics
Michaelis−Menten equation
Outline
Enzyme Kinetics
Traditional parameter estimation methods
Outline
Enzyme Kinetics
More direct estimation strategies
Direct fit to rate data
Numerical solutions
Semi-parametric
Outline
Enzyme Kinetics
More direct estimation strategies
Direct fit to rate data
Numerical solutions
Semi-parametric
A GenStat procedure, MICHAELIS
Enzymes
‘Little’ molecular machines that catalize biochemical reactions
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Product P
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Scientists wish to
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predict reaction rate as a function of substrate
concentration
Enzyme kinetics
Scientists wish to
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concentration
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predict concentration as function of time
Enzyme kinetics
Scientists wish to
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concentration
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predict concentration as function of time
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predict reaction rate as a function of time
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dt = −k1 SE0 + k−1 E1
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dt = −k1 SE0 + k−1 E1 + k2 E1
dE1
dt = k1 SE0 − k−1 E1 − k2 E1
k1
k
2
S + E0 E1 −→
E0 + P
k−1
dS
dt = −k1 SE0 + k−1 E1
dE0
dt = −k1 SE0 + k−1 E1 + k2 E1
dE1
dt = k1 SE0 − k−1 E1 − k2 E1
dP
dt = k2 E1
k1
k
2
S + E0 E1 −→
E0 + P
k−1
dS
dt = −k1 SE0 + k−1 E1
dE0
dt = −k1 SE0 + k−1 E1 + k2 E1
dE1
dt = k1 SE0 − k−1 E1 − k2 E1
dP
dt = k2 E1
Constraints . . .
dE
ET = E0 + E1 ⇒ dtT = 0,
k1
k
2
S + E0 E1 −→
E0 + P
k−1
dS
dt = −k1 SE0 + k−1 E1
dE0
dt = −k1 SE0 + k−1 E1 + k2 E1
dE1
dt = k1 SE0 − k−1 E1 − k2 E1
dP
dt = k2 E1
Constraints . . .
dE
ET = E0 + E1 ⇒ dtT = 0,
dE1
dt ' 0
... which give...
(k2 ET ) S
dS
Vmax S
=
=
k−1 +k2
dt
Km + S
+S
k1
... which give...
(k2 ET ) S
dS
Vmax S
=
=
k−1 +k2
dt
Km + S
+S
k1
k1
k
2
S + E0 E1 −→
E0 + P
k−1
... which give...
(k2 ET ) S
dS
Vmax S
=
=
k−1 +k2
dt
Km + S
+S
k1
k1
k
2
S + E0 E1 −→
E0 + P
k−1
Km =
k−1 +k2
k1
= substrate-enzyme "affinity"
... which give...
(k2 ET ) S
dS
Vmax S
=
=
k−1 +k2
dt
Km + S
+S
k1
k1
k
2
S + E0 E1 −→
E0 + P
k−1
Km =
k−1 +k2
k1
Vmax = k2 ET = maximal reaction rate
... which give...
(k2 ET ) S
dS
Vmax S
=
=
k−1 +k2
dt
Km + S
+S
k1
k1
k
2
S + E0 E1 −→
E0 + P
k−1
Km =
k−1 +k2
k1
Vmax = k2 ET = maximal reaction rate
dS
→ Vmax , S → ∞,
dt
S = Km ⇔
dS
Vmax
=
dt
2
The Michaelis-Menten equation.
v=
Vmax S
Km + S
Maud Menten and Leonor Michaelis, 1913
How good is the steady-state approximation?
http://online.redwoods.cc.ca.us/...
MM approx compared to actual DE
Traditional estimation of Vmax and Km
Linearize v =
Vmax S
, Linear regression, or graphical
Km + S
Linearize v =
I
1
v
=
1
Vmax
+
Vmax S
Km + S
Km 1
Vmax S
Lineweaver Burk, 1939
Linearize v =
Vmax S
Km + S
I
1
v
=
1
Vmax
+
Km 1
Vmax S
I
v
S
=
Vmax
Km
−
1
Km v
Scatchard, 1949
Linearize v =
Vmax S
Km + S
I
1
v
=
1
Vmax
+
Km 1
Vmax S
I
v
S
=
Vmax
Km
−
1
Km v
I
S
v
=
Km
Vmax
+
1
Vmax S
Scatchard, 1949
Woolf (Haldane, 1957)
Linearize v =
Vmax S
Km + S
I
1
v
=
1
Vmax
+
Km 1
Vmax S
I
v
S
=
Vmax
Km
−
1
Km v
I
S
v
=
Km
Vmax
+
1
Vmax S
I
Scatchard, 1949
or by non-linear regression. (e.g. FITCURVE [CURVE=ldl])
Linearize v =
Vmax S
Km + S
I
1
v
=
1
Vmax
+
Km 1
Vmax S
I
v
S
=
Vmax
Km
−
1
Km v
I
S
v
=
Km
Vmax
+
1
Vmax S
I
Scatchard, 1949
or by non-linear regression. (e.g. FITCURVE [CURVE=ldl])
vi and Si derived from experiment i = 1 . . . k
Fit directly to concentration data, S vs t?
Require S(t), the solution to
dS
Vmax S
=
dt
Km + S
Require S(t), the solution to
dS
Vmax S
=
dt
Km + S
But no closed form solution for S(t) exists!
Solution to S(t)
S0
S(t) = Km W
exp
Km
S0 − Vmax t
Km
Solution to S(t)
S0
S(t) = Km W
exp
Km
S0 − Vmax t
Km
where Lambert’s W : y = W (x) such that ye y = x
Solution to S(t)
S0
S(t) = Km W
exp
Km
S0 − Vmax t
Km
(Fig. from Barry et al., Math Comp Sim, 2000.)
Estimation strategies using (S, t) data:
I
Transform (S, t) to rate data, (v , S)
I
I
Purely numeric solution to S(t)
I
I
I
Analytic expansion for Lamberts W
I
I
I
Analytic expansion for Lamberts W
I
A semi-parametric method
Transform (S, t) to (v , S ∗ )?
vi = −
Si+1 − Si
ti+1 − ti
and
Si∗ =
Si + Si+1
2
Transform (S, t) to (v , S ∗ )?
vi = −
Si+1 − Si
ti+1 − ti
and
Si∗ =
Si + Si+1
2
Note that
2σ 2
Si+1 − Si
= 2 ,
Var(Vi ) = Var
ti+1 − ti
δi
where δi = ti+1 − ti
Note that
2σ 2
Si+1 − Si
= 2 ,
Var(Vi ) = Var
ti+1 − ti
δi
where δi = ti+1 − ti
Unequal time intervals δi ⇒ unequal variance.
Fitting v =
Vmax S ∗
Km +S ∗ ,
with weights = δi2
Transforming (S, t) to (v , S ∗ ) data:
Allows us to fit MM directly, but ...
I
Heteroscedasticity, due to unequal δi .
I
I
Correlated errors, MA(1), induced by differencing:
Vi = −
Si+1 − Si
, ⇒
δi
Cov(Vi , Vi+1 ) = −
σ2
δi δi+1
I
I
Correlated errors, MA(1), induced by differencing:
Vi = −
I
Si+1 − Si
, ⇒
δi
Cov(Vi , Vi+1 ) = −
Errors in variables:
Var(S ∗ ) =
σ2
2
σ2
δi δi+1
Direct fit to (S, t) data: S(t) numeric solution?
I
E.g., S(t) by Euler’s method:
I
I
Note, the slope at t is
v (t) = −
Vmax S(t)
Km + S(t)
I
I
v (t) = −
I
Vmax S(t)
Km + S(t)
Estimate S(t +h) ' S(t) + v (t) × h
I
I
v (t) = −
I
I
Vmax S(t)
Km + S(t)
Start with initial value, S(0)
I
I
v (t) = −
I
I
I
Vmax S(t)
Km + S(t)
Iterate, gives S̃(t) for t = 0, h, 2h, ...
I
I
v (t) = −
I
I
I
I
Vmax S(t)
Km + S(t)
interpolate S̃(ti )
I
I
v (t) = −
I
I
I
I
Vmax S(t)
Km + S(t)
interpolate S̃(ti )
Minimize
n h
X
i=1
Si − S̃(ti ; Vmax , Km )
i2
w.r.t Vmax , Km
Euler’s solution to S(t)
Simple to program, fits MM directly to (S, t), but ...
I
Computationally intensive
I
I
Uncertain accuracy
I
I
Uncertain accuracy
I
Runge-Kutta methods
Analytic numeric solution for S(t)?
I
S0
S(t) = Km W
exp
Km
S0 − Vmax t
Km
I
S0
S(t) = Km W
exp
Km
S0 − Vmax t
Km
I
Expansion to give (approximate) Lambert’s W :
I
S0
S(t) = Km W
exp
Km
S0 − Vmax t
Km
I
I
See Golicnik, Analytic Biochemistry (2010), and
references therein.
maximum error < 0.02% (Barry et al., 2000)
I
S0
S(t) = Km W
exp
Km
S0 − Vmax t
Km
I
I
See Golicnik, Analytic Biochemistry (2010), and
references therein.
maximum error < 0.02% (Barry et al., 2000)
Minimize
n h
X
i=1
Si − Š(ti ; Vmax , Km )
i2
w.r.t Vmax , Km
"
Fit Michealis-Menten (following Golicnik)
"
SCALAR Vm,Km,K1,W0
SCALAR epsilon; VAL=0.4586887
CALC d1=12/5
EXPRESSION mm[1]; VALUE=!e(x=(W0-K1-Vm*TIME)/Km)
& mm[2]; VALUE=!e(x=(W0-K1)*exp(x)/Km)
& mm[3]; VALUE=!e(d2=x/log(1+d1*x))
& mm[4]; VALUE=!e(d2=5*log(d1*d2))
& mm[5]; VALUE=!e(d3=(1+epsilon)*log(6*x/d2))
& mm[6]; VALUE=!e(d4=log(1+2*x))
& mm[7]; VALUE=!e(d4=epsilon*log(2*x/d4))
& mm[8]; VALUE=!e(W=Km*(d3-d4)+K1)
Semi-parametric method?
Represent S(t) by f (t) = Φ(t)β,
e.g. beta spline
e.g. beta spline
Require
f 0 (t) '
Vmax f (t)
.
Km + f (t)
e.g. beta spline
Require
f 0 (t) '
Vmax f (t)
.
Km + f (t)
Minimize
n
n X
X
Vmax f (ti ) 2
2
0
{si − f (ti )} + λ
f (ti ) −
Km + f (ti )
i=1
i=1
e.g. beta spline
Require
f 0 (t) '
Vmax f (t)
.
Km + f (t)
Minimize
n
n X
X
Vmax f (ti ) 2
2
0
{si − f (ti )} + λ
f (ti ) −
Km + f (ti )
i=1
or
n
X
i=1
i=1
{si − f (ti )}2 + λ
Z f 0 (t) −
Vmax f (t)
Km + f (t)
2
dt
Nested minimization
2 #
Z n
X
V
f
(t)
max
min
{si −f (ti )}2 +λ
f 0 (t)−
dt
β
Km + f (t)
"
min
{Vmax ,Km }
i=1
where f (t) = Φ(t)β, B-spline
(Cao et al., Biometrics, 2011)
Semi-parametric method
Fit spline to (S, t) data, conforming to MM, but ...
I
Large number of non-linear parameters.
I
I
Need expressions for gradients (Ramsay et al., JRSS,
2007.)
I
I
2007.)
I
Arbitrary tuning parameter, λ,
I
I
2007.)
I
I
Estimate λ by cross-validation
I
I
2007.)
I
I
Estimate λ by cross-validation
I
Programming
A GenStat procedure
Procedure MICHAELIS
M.C. Hannah (May, 2011)
1.
Purpose
Fits Michaelis-Menten curve to substrate concentration vs time data
2.
Description
The Michaelis-Menten non-linear curve, for biochemical reaction rate versus substrate
concentration,
v (t ) =
dS (t ) Vmax S (t )
=
,
dt
K m + S (t )
can be fitted in GenStat using FITCURVE [CURVE=ldl]. However, in practice, data are
available only for substrate concentration, S, at time t, and not for the reaction rate, v. The
function S(t), that is the solution to this differential equation, has no closed form expression.
The procedure MICHAELIS fits the curve S (t ) versus t, obtaining parameter estimates for
Vmax, Km and, if required, S0 (the initial substrate) and, also if required, an additive constant
K1 representing the quantity of non-reactive substrate. This generalized Michaelis-Menten
curve is thus,
dS (t ) Vmax [ S (t ) − K1 ]
=
.
dt
K m + S (t ) − K1
4.
Options
PRINT = string
PLOT = string
WINDOW = scalar
TITLE = text
XTITLE = text
YTITLE = text
WEIGHTS = variate
5.
I: strings {model, deviance, summary, estimates,
correlations, fittedvalues, monitoring;
default mode, summ, esti printed output (same as for
FITNONLINEAR)
I: requests graphs, strings {fitted, rate }; default
fitted.
I: scalar
I: Title of S vs t graph; default, ‘Fitted MichaelisMenten solution’
I: Title for x-axis; default the TIME identifier
I: Title for y-axis; default the CONCENTRATION identifier
I: weights for use in FITNONLINEAR
Parameters
CONCENTRATION = variate I: Substrate concentration data
TIME = variate
I: Times at which substrate concentration data were measured
INITIAL = variate
I: optional initial values for parameters !(Vm, Km, K1, W0).
Generally not required, but must be in correct order, if supplied.
STEP = variate
I: optional step lengths for parameters (see GenStat directives
RCYCLE and FITNONLINEAR). If supplied, these must be in
correct order, !(Vm, Km, K1, W0). A zero will hold the
corresponding parameter at its initial value.
O: Final parameter estimates; !(Vm, Km, K1, W0)
FINAL = variate
VCOV = symmetric
O: matrix, vcov for estimates
FITTED = variate
O: Fitted concentration
FRATE = variate
O: Fitted reaction rate
MICHAELIS CONC=S; TIME=ElapsDays
357
Initial parameter values
Vm_i
4.511
Km_i
447.5
K1_i
34.88
S0_i
2627
Nonlinear regression analysis
Response variate:
Weight variate:
Nonlinear parameters:
Model calculations:
S
Wts
Vm, Km, K1, S0
mm[1], mm[2], mm[3], mm[4], mm[5], mm[6], mm[7], mm[8]
Summary of analysis
Source
Regression
Residual
Total
d.f.
4
48
52
s.s.
137399158.
14762.
137413920.
m.s.
34349789.5
307.5
2642575.4
v.r.
111690.71
Percentage variance accounted for 100.0
Standard error of observations is estimated to be 17.5.
Message: the following units have large standardized residuals.
Unit
1
Response
2589.4
Residual
-2.41
Estimates of parameters
Parameter
Vm
Km
K1
S0
estimate
5.1627
293.2
200.7
2635.97
s.e.
0.0980
28.3
10.6
5.48
RGRAPH INDEX=ElapsDays
RCHECK
RCHECK
MICHAELIS [PLOT=#,Rate] CONC=SubConc; \
TIME=ElapsDays
Fix K1 = 0 (original Michaelis-Menten.)
MICHAELIS CONC=SubConc; TIME=ElapsDays; \
INITIAL=!(*,*,0,*); STEP=!(*,*,0,*)
Fix K1 = 0 (original Michaelis-Menten.)
MICHAELIS CONC=SubConc; TIME=ElapsDays; \
INITIAL=!(*,*,0,*); STEP=!(*,*,0,*)
Estimates of parameters
Parameter
Vm
Km
K1
S0
estimate
6.550
850.3
0
2648.2
s.e.
0.322
99.7
*
12.7
Leonor Michaelis Maud Menten, 2011
3
HETP Evaluation of Structured and
Randomic Packing Distillation Column
Marisa Fernandes Mendes
Chemical Engineering Department, Technology Institute,
Universidade Federal Rural do Rio de Janeiro
Brazil
1. Introduction
Packed columns are equipment commonly found in absorption, distillation, stripping, heat
exchangers and other operations, like removal of dust, mist and odors and for other
purposes. Mass transfer between phases is promoted by their intimate contact through all
the extent of the packed bed. The main factors involving the design of packed columns are
mechanics and equipment efficiency. Among the mechanical factors one could mention
liquid distributors, supports, pressure drop and capacity of the column. The factors related
to column efficiency are liquid distribution and redistribution, in order to obtain the
maximum area possible for liquid and vapor contact (Caldas and Lacerda, 1988).
These columns are useful devices in the mass transfer and are available in various
construction materials such as metal, plastic, porcelain, ceramic and so on. They also have
good efficiency and capacity, moreover, are usually cheaper than other devices of mass
transfer (Eckert, 1975).
The main desirable requirements for the packing of distillation columns are: to promote a
uniform distribution of gas and liquid, have large surface area (for greater contact between
the liquid and vapor phase) and have an open structure, providing a low resistance to the
gas flow. Packed columns are manufactured so they are able to gather, leaving small gaps
without covering each other. Many types and shapes of packing can satisfactorily meet these
requirements (Henley and Seader, 1981).
The packing are divided in random – randomly distributed in the interior of the column –
and structured – distributed in a regular geometry. There are some rules which should be
followed when designing a packed column (Caldas and Lacerda, 1988):
a. The column should operate in the loading region (40 to 80% flooding), which will
assure the best surface area for the maximum mass transfer efficiency;
b. The packing size (random) should not be greater than 1/8 the column diameter;
c. The packing bed is limited to 6D (Raschig rings or sells) or 12D for Pall rings. It is not
recommended bed sections grater than 10m;
d. Liquid initial distribution and its redistribution at the top of each section are very
important to correct liquid migration to the column walls.
A preliminary design of a packed column involves the following steps:
1. Choice of packing;
2. Column diameter estimation;
www.intechopen.com
42
Mass Transfer / Book 1
3. Mass transfer coefficients determination;
4. Pressure drop estimation;
5. Internals design.
This chapter deals with column packing efficiency, considering the main studies including
random and structured packing columns. In packed columns, mass transfer efficiency is
related to intimate contact and rate transfer between liquid and vapor phases. The most
used concept to evaluate the height of a packed column, which is related to separation
efficiency, is the HETP (Height Equivalent to Theoretical Plate), defined by the following
equation:
Z   HETP    N 
(1)
in which Z is the height of the packed bed necessary to obtain a separation equivalent to N
theoretical stages (Caldas and Lacerda, 1988).
Unfortunately, there are only a few generalized methods available in the open literature for
estimating the HETP. These methods are empirical and supported by the vendor advice. The
performance data published by universities are often obtained using small columns and with
packing not industrially important. When commercial-scale data are published, they usually
are not supported by analysis or generalization (Vital et al., 1984). Several correlations and
empirical rules have been developed for HETP estimation in the last 50 years. Among the
empirical methods, there is a rule of thumb for traditional random packing that says
HETP  column diameter
(2)
That rule can be used only in small diameter columns (Caldas and Lacerda, 1988).
The empirical correlation of Murch (1953) cited by Caldas and Lacerda (1988) is based on
HETP values published for towers smaller than 0.3 m of diameter and, in most cases,
smaller than 0.2 m. The author had additional data for towers of 0.36, 0.46 and 0.76 m of
diameter. The final correlation is
  
HETP  K1GK2 DK3 Z1 3  L 
 L 
(3)
K1, K2 and K3 are constants that depend on the size and type of the packing.
Lockett (1998) has proposed a correlation to estimate HETP in columns containing
structured packing elements. It was inspired on Bravo et al.’s correlation (1985) in order to
develop an empirical relation between HETP and the packing surface area, operating at 80%
flooding condition (Caldas and Lacerda, 1988):
 4.82  
HETP 
in which

L
 G 


0.5
r0.06

0.25 

0.00058 ap  G 
  ap  1  0.78e

 

 L  

www.intechopen.com
(4)
2
(5)
HETP Evaluation of Structured and Randomic Packing Distillation Column
43
According to the double film theory, HETP can be evaluated more accurately by the
following expression (Wang et al., 2005):
HETP 
u 
ln   uGs
  Ls 

  1  kG ae
kL a e 
(6)
Therefore, the precision to evaluate HETP by equation (6) depends on the accuracy of
correlations used to predict the effective interfacial area and the vapor and liquid mass
transfer coefficients. So, we shall continue this discussion presenting the most used
correlations for wetted area estimation, both for random and structured packed columns.
Wang et al. (2005) also presented a complete discussion about the different correlations
mostly used for random and structured packing.
2. Literature review
The literature review will be divided in two sections, treating and analyzing separately
random and structured distillation columns as the correlations for the effective area and
HETP evaluation.
2.1 Part A: performance of random packing
Before 1915, packed columns were filled with coal or randomly with ceramic or glass shards.
This year, Fredrick Raschig introduced a degree of standardization in the industry. Raschig
rings, together with the Berl saddles, were the packing commonly used until 1965. In the
following decade, Pall rings and some more exotic form of saddles has gained greater
importance (Henley and Seader, 1981). Pall rings are essentially Raschig rings, in which
openings and grooves were made on the surface of the ring to increase the free area and
improve the distribution of the liquid. Berl saddles were developed to overcome the Raschig
rings in the distribution of the liquid. Intalox saddles can be considered as an improvement
of Berl saddles, and facilitated its manufacture by its shape. The packing Hypac and Super
Intalox can be considered an improvement of Pall rings and saddles Intalox, respectively
(Sinnott, 1999). In Figure 1, the packing are illustrated and commented.
The packing can be grouped into generations that are related to the technological advances.
The improvements cited are from the second generation of packing. Today, there are
packing of the fourth generation, as the Raschig super ring (Darakchiev & Semkov, 2008).
Tests with the objective to compare packing are not universally significant. This is because
the efficiency of the packing does not depend, exclusively, on their shape and material, but
other variables, like the system to be distilled. This means, for example, that a packing can
not be effective for viscous systems, but has a high efficiency for non-viscous systems.
Moreover, the ratio of liquid-vapor flow and other hydrodynamic variables also must be
considered in comparisons between packing. The technical data, evaluated on packing, are,
generally, the physical properties (surface area, free area, tensile strength, temperature and
chemical stability), the hydrodynamic characteristics (pressure drop and flow rate
allowable) and process efficiency (Henley and Seader, 1981). This means that Raschig rings
can be as efficient as Pall rings, depending on the upward velocity of the gas inside the
column, for example. These and other features involving the packing are extensively
detailed in the study of Eckert (1970).
www.intechopen.com
44
Ref: Henley & Seader (1981)
Fig. 1. Random packing: (a) plastic pall rings. (b) metal pall rings (Metal Hypac). (c) Raschig
rings. (d) Intalox saddles. (e) Intalox saddles of plastic. (f) Intalox saddles
In literature, some studies on distillation show a comparison between various types of
random and structured packing. Although these studies might reveal some tendency of the
packing efficiency for different types and materials, it is important to emphasize that they
should not generalize the comparisons.
Cornell et al. (1960) published the first general model for mass transfer in packed columns.
Different correlations of published data of HL and HV, together with new data on industrial
scale distillation columns, were presented to traditional packing, such as Raschig rings and
Berl saddles, made of ceramic. Data obtained from the experimental study of HL and HV
were analyzed and correlated in order to project packed columns. The heights of mass
transfer for vapor and liquid phases, are given by:
HV 
  SCV 0 ,5
 GL  f1  f 2  f3 n
 d   Z 3
 C   
 12   10 
Z
H L    C fL   
 10 
which:
www.intechopen.com
m
0 ,15
 SCL 0 ,5
1
(7)
(8)
45
  
f1   L 
 W 
0 ,16
(9)
 
f2   W 
 L 
1, 25
SCV 
SCL 
(10)
G
G  DG
(11)
L
 L  DL
(12)
In the f factors, the liquid properties are done in the same conditions of the column and the
water properties are used at 20 ºC. The parameters n and m referred to the packing type,
being 0.6 and 1.24, respectively, for the Raschig rings. CfL represents the approximation
coefficient of the flooding point for the liquid phase mass transfer. The values of φ and Ψ are
packing parameters for the liquid and vapor phase mass transfer, respectively, and are
graphically obtained. In this correlation, some variables don’t obey a single unit system and
therefore need to be specified: dc(in), Z(ft), H(ft), G(lbm/h.ft2).
Onda et al. (1968 a, b) presented a new model to predict the global mass transfer unit. In
this method, the transfer units are expressed by the liquid and vapor mass transfer
coefficients:
HV 
GV
kV  aW  P  MV
HL 
(13)
GL
kL  aW  L
(14)
In which:
 R T 
 GV 
kV  
  

a
D

 P V
 aP  V 
0 ,7
  SCV  3   aP  dP 
1
2
(15)
1
  3
 GL  3

0,4
kL   L   0 , 0051  
   SCL  2   aP  dP 
 aw   L 
 g  L 
1
2
(16)
where Γ is a constant whose values can vary from 5.23 (normally used) or 2, if the packing
are Raschig rings or Berl saddles with dimension or nominal size inferior to 15 mm.
It can be noted, in these equations, the dependence of the mass transfer units with the wet
superficial area. It is considered, in this model, that the wet area is equal to the liquid-gas
interfacial area that can be written as
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46
0 , 75  


 

 
aW  ap  1  exp  1, 45  ReL 0 ,1 FrL 0 ,05  WeL 0 , 2  




 C



(17)
where:
Re L 
WeL 
FrL 
GL
aP   L
(18)
GL 2
aP     L
(19)
aP  GL 2
g  L 2
(20)
The ranges in which the equation should be used are: 0.04 < ReL < 500; 1.2x10-8 < WeL < 0.27;
2.5x10-9 < FrL < 1.8x10-2; 0.3 < (σc/σ) < 2.
The equation for the superficial area mentioned can be applied, with deviations of,
approximately, 20% for columns packed with Raschig rings, Berl saddles, spheres, made of
ceramic, glass, certain polymers and coatted with paraffin.
Bolles and Fair (1982) compiled and analyzed a large amount of performance data in the
literature of packed beds, and developed a model of mass transfer in packed column.
Indeed, the authors expanded the database of Cornell et al. (1960) and adapted the model to
new experimental results, measured at larger scales of operation in another type of packing
(Pall rings) and other material (metal). The database covers distillation results in a wide
range of operating conditions, such as pressures from 0.97 to 315 psia and column diameters
between 0.82 to 4.0 ft. With the inclusion of new data, adjustments were needed in the
original model and the values of φ and Ψ had to be recalculated. However, the equation of
Bolles and Fair model (1982) is written in the same way that the model of Cornell et al.
(1960). The only difference occurs in the equation for the height of mass transfer to the vapor
phase, just by changing the units of some variables:
HV 
  SCV 0 ,5
 3600  GL  f1  f 2  f3 n
 Z 3
 d 'C m   
 10 
1
(21)
In this equation, d’C is the adjusted column diameter, which is the same diameter or 2 ft, if
the column presents a diameter higher than that.
Unlike the graphs for estimating the values of φ and Ψ, provided by Cornell et al. (1960),
where only one type of material is analyzed (ceramic) and the percentage of flooding,
required to read the parameters, is said to be less than 50% in the work of Bolles and Fair
(1982), these graphics are more comprehensive, firstly because they include graphics for
Raschig rings, Berl saddles and metal Pall rings, and second because they allow variable
readings for different flooding values.
The flooding factor, necessary to calculate the height of a mass transfer unit in the Bolles and
Fair (1982) model, is nothing more than the relation between the vapor velocity, based on
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47
the superficial area of the column, and the vapor velocity, based on the superficial area of
the column at the flooding point. The Eckert model (1970) is used for the determination of
these values. The authors compared the modified correlation with the original model and
with the correlation of Onda et al. (1968 a, b), concluding that the lower deviations were
obtained by the proposed model, followed by the Cornell et al. (1960) model and by the
Onda et al. (1968 a, b) model.
Bravo and Fair (1982) had as objective the development of a general project model to be
applied in packed distillation columns, using a correlation that don’t need validation for the
different types and sizes of packing. Moreover, the authors didn’t want the dependence on
the flooding point, as the model of Bolles and Fair (1982). For this purpose, the authors used
the Onda et al. (1968 a, b) model, with the database of Bolles and Fair (1982) to give a better
correlation, based on the effective interfacial area to calculate the mass transfer rate. The
authors suggested the following equation:
ae 
 ae  HV    ae  HL 
(22)
HOV
Evidently, the selection of kV e kL models is crucial, being chosen by the authors the models
of Shulman et al. (1955) and Onda et al. (1968a, b), since they correspond to features
commonly accepted. The latter equation has been written in equations 23 and 24. For the
first, we have:
 d 'p  GV 
kV  V  RT
 1.195  

GV
 V  1    
kL  d ' p
DL
 d 'p  GL 
 25.1  

 L 
0.45
0.36
  SCV 
  SCL 
0.50

2
3
(23)
(24)
The database used provided the necessary variables for the effective area calculation by the
both methods. These areas were compared with the known values of the specific areas of the
packing used. Because of that, the Onda et al. (1968 a, b) model was chosen to provide
moderate areas values, beyond cover a large range of type and size packing and tested
systems.
The authors defined the main points that should be taken in consideration by the new
model and tested various dimensional groups, including column, packing and systems
characteristics and the hydrodynamic of the process. The better correlation, for all the
systems and packing tested is given by:
  0.5 
ae
0.392
 0.498   0.4   CaL  ReV 
ap
Z 
which:
CaL 
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 L  GL
L    gC
(25)
(26)
48
ReV 
6  GV
aP  V
(27)
Recently, with the emergence of more modern packing, other correlations to predict the rate
of mass transfer in packed columns have been studied. Wagner et al. (1997), for example,
developed a semi-empirical model, taking into account the effects of pressure drop and
holdup in the column for the Nutter rings and IMTP, CMR and Flaximax packing. These
packing have higher efficiency and therefore have become more popular for new projects of
packed columns today. However, for the traditional packing, according to the author, only
correlations of Cornell et al. (1960), Onda et al. (1968a, b), Bolles and Fair (1982) and Bravo
and Fair (1982), presented have been large and viable enough to receive credit on
commercial projects for both applications to distillation and absorption.
Berg et al. (1984) questioned whether the extractive distillation could be performed in a packed
distillation column, or only columns with trays could play such a process. Four different
packing were used and ten separation agents were applied in the separation of ethyl acetate
from a mixture of water and ethanol, which results in a mixture that has three binary
azeotropes and a ternary. A serie of runs was made in a column of six glass plates, with a
diameter of 3.8 cm, and in two packed columns. Columns with Berl saddles and Intalox
saddles (both porcelain and 1.27 cm) had 61 cm long and 2.9 cm in diameter. The columns
with propellers made of Pyrex glass and with a size of 0.7 cm, and Raschig rings made of flint
glass and size 0.6 cm, were 22.9 cm long and 1.9 cm in diameter. The real trays in each column
were determined with a mixture of ethyl benzene and m-xylene. The cell, fed with the mixture,
remained under total reflux at the bubble point for an hour. After, the feed pump was
switched on and the separating agent was fed at 90 °C at the top of the column. Samples from
the top and bottom were analyzed every half hour, even remain constant, two hours or less.
The results showed, on average, than the packed column was not efficient as the columns of
plates for this system. The best packing for this study were, in ascending order, glass helices,
Berl saddles, Intalox saddles and Raschig rings. The columns with sieve plates showed the best
results. Propellers glass and Berl saddles were not as effective as the number of perforated
plates and Intalox saddles and Raschig rings were the worst packing tested. When the
separating agent was 1,5-pentanediol, the tray column showed a relative volatility of ethyl
acetate/ethanol of 3.19. While the packed column showed 2.32 to Propeller glass, 2.08 for Berl
saddles, 2.02 for Intalox saddles and 2.08 for Raschig rings.
Through the years, several empirical rules have been proposed to estimate the packing
efficiency. Most of the correlations and rules are developed for handles and saddle packing.
Vital et al. (1984) cited several authors who proposed to develop empirical correlations for
predicting the efficiency of packed columns (Furnas & Taylor, 1940; Robinson & Gilliand,
1950; Hands & Whitt, 1951; Murch, 1953; Ellis, 1953 and Garner, 1956).
According to Wagner et al. (1997), the HETP is widely used to characterize the ability of
mass transfer in packed column. However, it is theoretically grounded in what concerns the
mass transport between phases. Conversely, the height of a global mass transfer, HOV, is
more appropriate, considering the mass transfer coefficient (k) of the liquid phase
(represented by subscript L) and vapor (represented by subscript V) individually. Thus, the
knowledge of the theory allows the representation:
HOV  HV    HL
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(28)
49
HV 
GV
kV  ae  P  MV
HL 
(29)
GL
kL  a e   L
(30)
The effective interfacial mass transfer area, in a given system, is considered equal to the
liquid and vapor phases, as is the area through which mass transfer occurs at the interface. It
is important to also note that ae is not composed only by the wet surface area of the packing
(aW), but throughout the area that allows contact between the liquid and vapor phases
(Bravo and Fair, 1982). This area can be smaller than the global interfacial area, due to the
existence of stagnant places, where the liquid reaches saturation and no longer participate in
the mass transfer process. Due to this complicated physical configuration, the effective
interfacial area is difficult to measure directly. The authors proposed a new model using
high-efficiency random packing as IMTP, CMR, Fleximac and Nutter. The final model
became
.
∈
4
.
.
1
1 ∈
1
1
(31)
After the test using 326 experimental data, the predicted values of HETP showed a deviation
less than 25% from the experimental results. It was observed that physical properties have a
little effect on mass transfer.
Four binary systems were tested (cyclohexane-heptane, methanol-ethanol, ethylbenzenestyrene and ethanol-water) from different database and different packing types and sizes.
The only packing parameter needed was a packing characteristic which has a value of 0.030
for a 2 in Pall and Raschig rings and about 0.050 for 2 in nominal size of the high efficiency
packing investigated.
The theoretical relations between the mass transfer coefficient and a packing efficiency
definition, are not easily obtained, in a general manner. This is due to the divergence
between the mechanisms of mass transfer in a packed section and the concept of an ideal
stage. The theoretical relation deduced, applied in the most simple and commonly situation
is described as:
HETP  HOV 
ln 
 1
(32)
Although validated only for the cases of dilute solutions, constant inclination of the
equilibrium line, constant molar flow rates, binary systems and equimolar countercurrent
diffusion, this equation has been applied to systems with very different conditions from
these, and even for multicomponent systems (Caldas & Lacerda, 1988).
The design of packed columns by the method of the height of a global mass transfer unit is
an established practice and advisable. For this, it is necessary to know the height of the mass
transfer unit for both liquid and for vapor phases.
HL values are usually experimentally obtained by absorption and desorption of a gas,
slightly soluble, from a liquid film flowing over a packed tower, in a countercurrent mode
with an air stream. Under these conditions, changes in gas concentration are neglected and
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50
no resistance in the gas film is considered. The variables that affect the height of the liquid
transfer unit are the height of the packed section, gas velocity, column diameter, the
physical properties of liquid and the type and size of the packing.
The values of the height of a transfer unit of a gas film, HV, need to be measured under the
same conditions as the resistance of the liquid film is known. This can be done by the
absorption of a highly soluble gas. An alternative method to determine HV involves the
vaporization of a liquid, at constant temperature, within a gas stream. In this case, the
resistance of the liquid film is zero and HV is equal to HOV. The variables that affect the
height of transfer unit of a gas film are the gas and liquid velocities, the physical
properties of the gas, column diameter, the height, type and size of the packing (Cornell et
al., 1960).
Linek et al. (2001) studied the hydraulic and mass transfer data measuring pressure drop,
liquid hold-up, gas and liquid side volumetric mass transfer coefficients and the interfacial
area for Rauschert-Metall-Sattel-Rings (RMSR) with 25, 40 and 50 mm. The shape and
characteristics of the studied packing corresponded with the metal Pall rings and Intalox
packing of Norton. The distillation experiments were performed using the systems
methanol-ethanol, ethanol-water and isooctane-toluene at atmospheric pressure in a column
of diameter 0.1 m and a height of packing 1.67 m, operated under total reflux. The measured
values of HETP were compared with those calculated for the different sizes of RMSR
packing for the distillation systems. The calculated values differ by less than ± 15% from the
experimental values, with the exception for the data obtained at extremely low gas flow
rates in the system ethanol-methanol for which the respective difference reached 46%.
Figure 2, from the paper of Linek et al. (2001), shows the comparison of measured values of
HETP with those calculated from absorption mass transfer data using the model described
in Linek et al. (1995) cited by Linek et al. (2001).
Fig. 2. Comparison of measured values of HETP with those calculated from absorption mass
transfer data (Linek et al., 2001)
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51
Senol (2001) studied the performance of a randomly packed distillation column depending
on the effective vapor-liquid interfacial area and the flood ratio. The analysis were mainly
focused optimizing HETP and effective interfacial areas as function of the flood ratio
estimated by Eckert flooding model (Eckert, 1970 cited by Senol, 2001). The experiments
were done in a pilot scale column of 9 cm inside diameter randomly filled to a depth of 1.90
m with Raschig-type ceramic rings under atmospheric pressure. The runs were conducted to
determine the capacity and efficiency at total reflux for several pressure drops. The
efficiency tests were made using three packings of 6.25, 9 and 10.8 mm nominal sizes and
binary
systems
like
trichloroethylene/heptane,
methylcyclohexane/toluene,
heptane/toluene and benzene/toluene. The HETP was obtained by the Fenske equation.
The efficiency results gave evidence of two critical factors, the flood ratio and the packing
geometry that affects significantly the magnitude of effective interfacial area.
A working database of 2350 measurements (under total molar reflux), in the work of Piché
et al. (2003), were extracted from the open literature to generate height equivalent to a
theoretical plate (HETP) calculations, essential for the design of randomly packed
distillation columns. According to the authors, the HETP approaches more a rule of thumb
concept than an exact science and can be calculated as:
ln
´⁄ ´
´⁄ ´
1
(33)
The database used included 325 measurements on the interfacial area, 1100 measurements
on the liquid-film coefficient (kLaw), 361 measurements on the gas-film coefficient (kGaw),
1242 measurements on the liquid-overall coefficient (KLaw) and 742 measurements on the
gas-overall coefficient (KGaw). The distillation database constituted 2357 HETP
measurements taken from 22 different references, conducted at total molar reflux with
standard binary mixtures (chlorobenzene-ethylbenzene, ethylbenzene-styrene, benzenetoluene, methanol/ethanol, trans-decalin/cis-decalin, ethanol-water, hexane-heptane,
isopropanol-water,
iso-octane-toluene,
toluene-methylcyclohexane,
cyclohexanecyclohexanol, o-xylene-p-xylene, benzene-1,1-dichloroethylene, trichloroethylene-n-heptane,
n-heptane-toluene). All the systems were distilled using 24 varieties of packing. After the
construction of a new model based on a neural network, the deviations were calculated and
were better than the original model of Piche et al. (2002) cited in Piche et al. (2003). The
minimum deviation of HETP was 21.3%, including all the systems studied.
Darakchiev & Semkov (2008) studied the rectification of ethanol with three types of modern
random packings, IMTP, Raschig Super Rings and Ralu Flow, in conditions close to real
conditions of industrial operation. The experiments were performed in high and medium
concentrations. The experimental unit consisted of a column of internal diameter of 21.3 cm,
made of stainless steel, with reboiler of 80000 cm3 of capacity and maximum resistance of 45
kW, condenser, pipes, devices for monitoring and measurement and a control panel. The
column was built in separated sections and assembled by flanges. The packed section has a
height of 2.8 m. To limit the damaging effect of preferential channels, reflectors rings were
willing on 20 cm distance between the height of the packing. One type of disperser, a type of
liquid distributor, with 21 holes of 3 mm with Teflon nozzle of 1.7 mm, was attached to the
upper spine. To prevent clogging, a filter was placed before the distributor.
A diaphragm and a differential manometer were used to measure the discharge flow, which
may be total or partial. The column was insulated by a layer of 50 mm glass fiber. The
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52
experimental runs were done feeding 60000 cm3 of the solution to reboiler. The minimum
liquid flow rate in the distributor needed to ensure good distribution of liquid in the column
was obtained, experimentally, in 58000 cm3/h, which required a minimum output of 13 kW.
After equilibrium, samples were taken before and after the packing. A densimeter was used
to determine the concentration of the samples, applying temperature corrections. Eight
types of random packings were studied: four metal Raschig Super Rings, with dimensions
of 1.27, 1.52, 1.78 and 2.54 cm, a Raschig Super Ring, made of plastic, of 1. 52 cm, two kinds
of IMTP packing and a Ralu Flow of plastic. The results showed good efficiency of the
packing in ethanol dehydration. The best packing tested was Raschig Super Ring in the
smaller dimension, producing a HETP with 28 cm. Comparing metal to plastic, there was a
6% lower efficiency for plastic packing.
Larachi et al. (2008) proposed two correlations to evaluate the local gas or liquids side mass
transfer coefficient and the effective gas-liquid interfacial area. The study was done using
structured and random packing, testing 861 experiments for structured packings and 4291
experiments for random packings. In order to reconstruct HETP values from the mass
transfer parameters, 1192 HETP experiments for random packings and 127 experiments for
structured packings were evaluated. All the distillation experiments were done at total
molar reflux with standard binary mixtures as chlorobenzene/ethylbenzene,
ethylbenzene/styrene, benzene/toluene, methanol/ethanol, etc. All the physical chemical
properties unavailable were predicted according to the rules of Reid et al. (1987). According
to the neural network weights, the relative deviation was 29.2% for the random packing and
18.2% for the experiments done with structured packings.
Soares (2010) studied the ethanol concentration using different salts, NaCl, CaCl2, Ca(NO3)2,
sodium acetate and potassium acetate, in a packed column, with 5.9 cm of internal diameter
and 37 cm of packed section height, with Raschig rings (0.73 cm) made of glass. The HETP
was evaluated operating the distillation column at total reflux ratio. Despite of the less
efficiency compared with the more modern packing, this type of packing presented the
lowest costs. The correlations used in this work were Bravo & Fair (1982), Bolles and Fair
(1982) and Onda et al. (1968 a, b). The Cornell et al. (1960) correlation was not adopted, due
to the fact that the model of Bolles and Fair (1982) is its improvement. All the physicalchemical properties were estimated by the different methods present in Reid et al. (1987).
The thermodynamic modeling was done based on the work of Macedo et al. (1990), that
introduced the Debye-Hückel term in UNIQUAC, to calculate the phase equilibrium for
electrolytes. Two systems with different ethanol concentration were studied, 7 and 52 ºGL.
The better results of predicted HETP were obtained using the Onda et al. (1968 a, b) and
with the Bolles and Fair (1982) correlations. The results predicted by the correlation of Bravo
and Fair (1982) modified by Onda et al. (1968 a, b) were much higher than the experimental
HETP. According to Caldas and Lacerda (1988), the maximum deviation is 27% using
Raschig rings made of ceramic.
The choice for a distillation column is based on the cost and on the properties of the studied
system. In the past, except for the columns with small diameters, the trays are adopted in
the most of the distillation columns. However, the development of high efficient packing
and the need for the improvement of the capacity, efficiency, and to reduce the pressure
drop, has led to a more use of the packing columns in a large wide of applications in an
industrial scale (Perry and Green, 1999).
The difference in cost and height, between the tray and packed columns, are not significant,
if operating conditions are providing efficiency close to maximal. In general, trays are used
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53
in large diameter columns and in columns that need 20 to 30 stages. The packing are widely
applied in the gas absorption, vacuum processes and pilot scale units (Henley and Seader,
1981). This can be explained, considering that: the packed columns can contain packing
made of ceramic or plastic, desirable characteristics required for corrosive systems (very
common in gas absorption processes), show characteristics of efficiency and pressure drop,
critical factors in the vacuum distillation (often used to separate thermally sensitive
mixtures, suffering decomposition and/or polymerization at high temperatures) are cheaper
than the tray columns when employed less than 76 cm diameter. Another recommendation,
for the preferential use of packed column, is made when you want separate systems with a
tendency to form foams, since the tray columns have a higher degree of agitation (Perry and
Green, 1999).
According to Perry & Green (1999), the main restrictions on the use of packed columns are:
1) when multiple feeds and/or multiple side streams and condensers and/or intermediary
reboilers are required (tray valves are desirable in these cases); 2) when a periodic cleaning
must be done inside the column due to certain characteristics of the system to be distilled
(trays are easier to clean), 3) when data for the design of packed distillation columns are not
available for certain mixtures (projects of tray columns are better established than for
packed columns).
None of the three restrictions limit the use of packing to obtain anhydrous ethanol by
extractive saline distillation. Doubts could arise with respect to the periodic cleaning of the
interior of the column, needed for the alleged deposition of salt. This would not be
necessary because the salt would tend strongly to remain in solution. Side devices are not
required and the project data can be obtained through studies on a pilot scale, emphasizing
the importance of this work.
The packed distillation columns must be fitted with a good distribution of liquid through
the interior of the packing, to promote fluid turbulence and mass transfer by liquid
dispersion. This allows for a greater contact between the liquid and vapor phases, increasing
the efficiency of separation. At low flow rate of steam and/or liquids, or if the feeding of the
liquid is not regular distributed over the packing, the liquid will tend to descend the walls of
the column, forming preferential channels. Thus, the upward flow of steam is bypassed by
the middle column, without a proper contact between the phases. In very small flow rates,
the liquid may be insufficient to wet the packing surface. Therefore, it is strongly
recommended an adjusted flow condition and the use of distributors, what can improve the
wettability of the interior of the column (Henley and Seader, 1981).
The proposal of a generalized correlation for the HETP is a difficult task, because packed
columns are equipments of continuous contact, so that the modeling of the phenomenon is
more powerful when done by balances in the differential element of the packing. However,
the use of HETP in specific situations provides reliable results and, in many cases, is the
only possible systematic (Caldas & Lacerda, 1988).
2.2 Part B: performance of structured packing
In the field of distillation, structured packings have been established for several decades.
They are preferred where liquid loads are acceptable, a high separation performance is
required and low pressure drop is of importance (Fischer et al., 2003).
The first generation of structured packing was brought up in the early forties. In 1953, it was
patented a packing named Panapak ™, made of a wavy-form expanded metal sheet, which
was not successful may due to maldistribution or lack of good marketing (Kister, 1992).
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The second generation came up at the end of 1950’s with the highly efficient wire mesh
packings, as Goodloe ™, Hyperfil ™ and Koch-Sulzer. Until the 70’s, those packings were
the most used in vacuum distillation due to their low pressure drop per theoretical stage.
However, high cost, low capacity and high sensitivity to solids have prevented the
utilization of wire mesh packings, except in vacuum distillation.
The corrugated structured packings, introduced by Sulzer by the end of the 70’s, have
initiated the third generation of structured packed columns. High capacity, lower cost, less
sensitivity to solids while keeping a high performance, have made them competitive in
relation to other column internals. The 1980’s have perceived a growing popularity of those
packings, especially on revamps in oil and petrochemical plants (Nicolaiewsky, 1999).
Those structured packings, made of corrugated metal sheets, had their surfaces treated,
chemical or mechanically, in order to enhance their wettability and, consequently, their
wetted area, improving their performance. The way wetted area is created, maintained and
renewed, related to different surface geometry, has a remarkable effect not only on packing
efficiency, but also on the performance of packed columns (Nicolaiewsky et al., 1999).
Spiegel and Meier (2003) summarized in the Figure 3 the evolution of the structured
packings, concluding that no better performance was achieved with various packings of
similar geometry. In 1994, a new geometry was developed and called as Optiflow and, in
1999, an improved structure of corrugated sheet packings, the MellapackPlus was
developed based on CFD simulations and experimental tests. This new structure, compared
with conventional Mellapak, has the pressure drop remarkably lowered and the maximum
useful capacity could be extended uo to 50%.
Fig. 3. History of structured packings (Spiegel and Meier, 2003)
According to Shi and Mersman (1985), the effective interfacial area includes not only films
on the packing surface but also drops, jets and sprays which flow through the voids of the
packed bed. In truth, wetted area can be divided into two parts: one occupied by the liquid
film flowing over the surface of the packing and the other, the stagnant liquid. In gas
absorption, the fraction of the wetted area occupied by the stagnant liquid soon becomes
saturated with gas, and as renewal of that liquid is insignificant; it does not contribute to
mass transfer. However, in distillation, these portions of stagnant liquid are also effective in
the separation (Puranik and Vogelpohl, 1974).
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The first fundamental model for structured packing efficiency is attributed to Bravo et al.
(1985), applied to Sulzer gauze packings, in which the effective interfacial area should be
considered equal to the nominal packing area. The pressure effect was not included in that
model, due to the vacuum conditions on the tests, involving low liquid flow rates and films
with lower resistance to mass transfer (Orlando Jr. et al., 2009).
Later, in 1987, Fair and Bravo proposed the following equations to predict the wetted area of
corrugated structured packings:
ae= .ap (34)
where = 0.50 + 0.0059 (% flood) and = 1.0 for above 85% flood. The above equations
mean that the effective interfacial area is always lower than the nominal packing area.
Based on measurements of widths of liquid films flowing over inclined surfaces, Shi and
Mersmann (1985) have established a correlation for the estimation of wetted area. For the
liquid film thickness, they used Nusselt’s equation. The authors’ correlation for the wetted
area took into account the influence of physical properties like viscosity, surface tension and
contact angle, with a great influence of the latter. The authors found out that a small
variation on contact angle would cause a large influence on the wetted area, which is not
reasonable according to findings of Nicolaiewsky et al. (1999), in which work correlations
for the estimation of liquid film width and thickness were proposed to be used on a wetted
area model in packed columns containing structured packing.
Shi and Mersmann’s (1985) correlation for sheet metal structured packings can be written:
29.12  WeL FrL  S 0.359
ae
 FSE
(35)
0.3
0.2 0.6
ap
 1  0.93 cos  sin  
ReL
0.15
in which FSE accounts for variations in surface enhancements and the contact angle θ
accounts for surface material wettability. For sheet metal packing, the authors stated that:
cos θ = 0.9
for σ ≤ 0.055 N/m
cos  5.211x1016.835
ReL 
for σ ≥ 0.055 N/m
4 uLe L
FrL 
WeL 
L
(36)
uL2
Sg
(37)
uL2 LS
 gc
(38)
Henriques de Brito and coworkers (1994) measured the effective interfacial area of sheet
metal structured packings such as Mellapak 125Y, 250Y and 500Y. Their results have
demonstrated that the effective area can be much higher than the packing surface area due
to instabilities in liquid flow, such as ripples, waves, detachment of the film into liquid
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showers, etc. The resulting correlation for all measurements is a function of the Reynolds
number for the liquid phase, as follows:
ae
0.30
 0.465ReL
ap
(39)
It must be pointed out that the authors have not checked the correlation with fluids with
different densities and viscosities.
Later on, Rocha et al. (1993, 1996) developed a mechanistic model aiming the design and
optimization of CSSP (continuous separation structured packing) distillation columns of the
metallic corrugated type, also applied to absorption and stripping processes. Liquid holdup
prediction was the key to the development of correlations to measure pressure drop, capacity
and mass transfer efficiency in the packing. In their model, Rocha and coworkers used Shi and
Mersmann’s (1985) correlation in order to evaluate the interfacial area available for mass
transfer and the liquid holdup present in the packing. Those correlations involved parameters
related to surface treatment, as contact angle on the packing surface, as well as packing
geometry, liquid and vapor flow rates and physical properties of the system (Orlando Jr. et al.,
2009). For the estimation of the liquid side mass transfer coefficient, Rocha et al. (1996) used a
correlation developed by Brunazzi and coworkers (1995) for the evaluation of effective areas in
absorption columns containing Mellapak 250Y and Sulzer BX.
Rocha et al. (1993) studied correlations to calculate flooding velocity and mass transfer
efficiency by using the concept of HETP for distillation columns filled with structured
packings. The authors observed that there are few correlations to predict HETP values amd
most of them need empirical constants or exponents for their calculation. The disadvantage
is that these values are not reported for all the packings and all the sizes available. It was
used the Billet (Billet, 1987), Spiegel and Meier (Spiegel & Meier, 1987) and Bravo et al.
(1985) correlations for the HETP calculation and the deviation between them was 11%.
Billingham and Lockett (1999) studied very small modifications to structured packing in
order to increase the capacity. It was tested the air-water system and the cryogenic
distillation. It was done three bricks of aluminum Flexipac 1Y in the initial experiments and
in the other experiments, the packing was removed and the bricks disassembled and
repinned together with each alternate sheet staggered in a vertical direction. For the
cryogenic distillation, a larger specific surface area packing than Flexipac was used. The
authors observed that the key is to reduce the pressure drop associated with vapour entry
into the bricks, facilitating the passage of liquid from the bricks. Although the modified
packings have increased capacity, HETP is about 25% higher than that the unmodified
packings. To overcome this problem, another packing was used with the bricks having a flat
top and a staggered base and were made from sheets of two different lenghs arranged
alternatively. The modified packing had about 15% more capacity and the HETP has the
same value of the unmodified packings.
None of those models mentioned so far considered the effect of vapor flow and thus can
only be used with low vapor rates. However, since industrial columns often operate above
the loading point, it was necessary to develop a correlation for effective interfacial area
which was valid for a wide range of vapor rates (Xu et al., 2000). Using Billet and Schultes’
model (1993) for effective interfacial area (which is very similar to Shi and Mersmann’s
model, but at least was validated with experimental data), Xu et al. (2000) introduced in that
model the Marangoni effect. The authors considered that the surface tension positive
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systems should have a higher interfacial area than the neutral and negative systems because
the liquid films are more stable. This result is in agreement with measurements of contact
angles formed by liquid films of diverse properties, in flat or textured surfaces
(Nicolaiewsky and Fair, 1999), in which it was clear that texturing of surfaces would
enhance wetting characteristics of positive systems. Xu et al’s model (2000) was validated
for three structured packing (Gempak 2.5A, AW7 and AW12), with three test systems
(methanol-isopropanol, water-acetic acid and methanol-water), at two operating pressures
(710 and 260 mmHg), having achieved an average 10.2% deviation of model prediction. The
deviations are 20% approximately for 90% of the data points.
Olujic et al. (2003) made experimental studies in a distillation column at total reflux to report
the capacity of a new generation of Montz structured packing. According to the authors, the
major feature of Montz B1 is a smooth bend in the bottom third of the corrugation with
continuously increasing corrugation base width. The experiments were done using a bed
height of approximately 3.3 m and the system cyclohexane/heptanes was utilized, under
different conditions of pressure, 0.17, 0.33, 1.03 and 4.14 bar. Five different dimensions of
structured packing were investigated with ap (m2/m3) of 244, 247, 250, 346 and 350. The
number of equilibrium stages was calculated from the distillate and bottom compositions
using the Fenske equation and an average relative volatility. Among the various results
published by the authors, Figure 4 shows the dimensionless product of the specific surface
area and HETP as a function of the operational pressure for both packing sizes. The figure
concludes that larger surface area packing appear to use their available surface less
efficiently. The performance enhancement in case of 350 series packings is 21% with respect
to the standard size. The relatively high efficiency is similar as the original packing in its
range of application. Because of that characteristic, columns equipped with B1-250 packing
can be revamped with B1-250M packing.
Fig. 4. Relative surface utilization efficiency as a function of operating pressure (total reflux)
In 2006, results from continuous feed and total reflux distillation experiments, carried out
with a common type and size structured packing using two- and three-component mixtures
of common alcohols and water, were published (Mori et al., 2006). The composition profiles
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measured with the three component mixture were used to validate the rate-based (nonequilibrium) model developed at the Nagoya Institute of Technology (NIT), which appeared
to be highly accurate, but also sensitive to the choice of the predictive method for the
interfacial area. The rate-based, non-equilibrium (NEQ) approach adopted at NIT (Mori et
al., 1996, 1999, 2002) includes Bravo et al. (1985) correlations for vapor and liquid side mass
transfer coefficients that differ to some extent from those employed in the Delft model
(Olujic et al., 1999). Two simple empirical models for effective specific area were considered
in this work. First one is that introduced by Olujic and coworkers (1999) for Montz B1-250
packing and the other one is proposed by Henriques de Brito et al. (1994), for Mellapak
packings. The authors concluded that the Delft model overpredicts the measurements at
higher F factors to such an extent that it may be considered as safe or conservative. The NEQ
model developed at NIT, in conjunction with Henriques de Brito et al. (1994) correlation for
effective area, proved to be capable of reproducing all the measured composition profiles
very well, regardless of the water content of the feed.
Also, in 2006, Mori et al. presented results of continuous feed and total reflux distillation
experiments carried out with a common type and size structured packing, Montz-pack B1250, using two (methanol-water) and three (methanol/ethanol/water) component mixtures
of common alcohols and water. The packing is a conventional corrugated sheet metal
structured packing with a regular shallow embossed unperforated surface, a corrugation
inclination angle of 45º and an element height of 0.196 m. The experiments were done in a
210 mm diameter distillation column, with a total packed height of 2.156 m and the packed
bed consisted of four sections. The experimental packing efficiency, expressed as HETP,
under total reflux conditions, was calculated using the Fenske equation to estimate the
number of equilibrium stages. The rate-based, non-equilibrium (NEQ) model was used
because it does not require any empirically determined packing specific constant, just the
main dimensions of corrugated sheets as well as the corrugation inclination angle. The
model includes Bravo et al. (1985) correlations for vapor and liquid side mass transfer
coefficients that differ from the Delft model. Two simple empirical model for the calculation
of the effective specific area was considered: the first one, by Olujic et al. (1999) for B1-250
packing (equation 40) and the other one was proposed by Brito et al. (1994) for Mellapack
packings (equation 41).

ae
1

ap 1  0.000002143u1.5
Ls
ae
 0.465 Re0.3L
ap

(40)
(41)
Equation 40 was originally developed for Mellapak and is assumed here to be valid for
other similar sheet metal packings, including Montzpak B1-250. The results, at total reflux
conditions, is presented in Figure 5, that shows the mass transfer efficiency (the average
HETP of B1-250) as a function of vapor load factor (F-factor). In the figure, Feed 1 refers to a
low water content and the Feed 2 to a feed with relatively high water content. In both cases,
the efficiency slowly decreases with increasing F-factor. According to the authors, a
pronounced trend was observed with the B1-250 packing because is it an inherent
characteristic of the Delft method (Olujic et al., 1999 cited by Mori et al., 2006).
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Fig. 5. Comparison of calculated and measured packing efficiencies at total reflux conditions
Ceramic foam packing has been known for many years and has a wide range of applications
due to its low density and attractive thermal, mechanical, electrical, and acoustical
properties. In a recent paper (Lévêque et al., 2009), its performance was evaluated as a
distillation packing material. The hydraulic characteristics of the foam were experimentally
determined for gas–liquid countercurrent flow using an air–water system. The performance
in terms of pressure drop per unit height and flooding behavior was quite low compared
with classical distillation packing materials (Sulzer M250Y, Sulzer CY and Pall rings). The
liquid hold-up of the foam packing increased with increased liquid–gas loading in the
loading zone, and the liquid hold-up was greater than other classical packing materials.
Mass transfer efficiency was determined over the entire operating range using a
cyclohexane/n-heptane system at atmospheric pressure under total reflux. The foam
packing performance was very good, with a HETP of 0.2 m and increasing mass transfer
with increasing gas and liquid superficial velocities inside the packing (Lévêque et al., 2009).
Last year, a French group from Université de Toulouse (Bessou et al., 2010), sponsored by
Sulzer and Snecma Propulsion Solide, has developed a new structured packing, made of
carbon, named The Sepcarb 4D packing, presenting its performance characteristics. The
advantages of the packing rest on being inert, corrosion-resistant; has very low density (40
kg/m3), with tubes of small thickness (0.2 mm). The separation efficiency has been
determined using the HETP concept on distillation experiments with cyclohexane/nheptane system at atmospheric pressure and total reflux. The best results were obtained
with wall wipers, which improved liquid redistribution between packing cylinders and
involved low wall effects. HETP calculated was 0.2 m, which corresponds to a good transfer
performance when compared to classical packings such as Mellapak 250Y, Mellapak 425Y
and Pall rings.
Performance of a distillation column, operating continuously with a mixture of known
composition (C8-C14), containing Sulzer DX SS structured packing, has been evaluated. Prior
to the experimental tests, simulation studies using commercial software PRO/II® were
performed in order to establish the optimum operational conditions for the distillation,
especially concerning operating pressure, top and bottom temperatures, feed location and
reflux ratio. The results of PRO/II® were very similar to the analysis of the products
obtained during continuous operation, therefore permitting the use of the properties
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calculated by that software on the theoretical models investigated. Five theoretical models
available in the literature (Bravo, Rocha and Fair, 1985; Rocha, Bravo and Fair, 1993, 1996;
Brunazzi and Pagliant, 1997; Carlo, Olujić and Pagliant, 2006; Olujić et al., 2004) and an
empirical model (Carrillo and coworkers, 2000) have been compared. Modifications
concerning calculation of specific areas were performed on the correlations in order to fit
them for gauze packing HETP evaluation. As the laboratory distillation column was
operated continuously, different HETP values were found by the models investigated for
each section of the column. The low liquid flow rates in the top section of the column are a
source of error for HETP evaluation by the models; therefore, more reliable HETP values
were found in the bottom section, in which liquid flow rates were much greater. Among the
theoretical models, Olujić et al. (2004) has shown good results relatively to the experimental
tests. In addition, the former model by Bravo, Rocha and Fair (1985) underestimates HETP
values; however, with the modifications proposed in this work, it has achieved more
realistic performance prediction, remaining a good choice for gauze packing HETP
evaluation. Having the advantage of avoiding the calculation of effective area and mass
transfer coefficients, an empirical model proposed by Carrillo and coworkers (2000) was also
investigated, showing low deviations compared to the theoretical models tested.
Among the short-cut methods for the estimation of column efficiency, Carrillo and
coworkers (2000) have proposed a modification of the Lockett equation (1998) to be used for
HETP estimation of Sulzer BX packing. The correlation was proposed to be a function of the
gas flow factor, densities of the liquid and vapor phases and the system pressure. The HETP
values calculated by the modified equation have shown a good fit, compared to the
published experimental data available.
Later, Carlo, Olujić and Pagliant (2006) used the absorption column studies developed by
Brunazzi and Pagliant (1997), and made some modifications on the liquid side mass transfer
coefficient, to adapt those correlations for HETP evaluation of distillation columns. Olujić’s
model (1997) was developed to predict hydraulic and separation performance of corrugated
sheet structured packing in distillation systems. Since 1997, until its last version (Olujić et al.
(2004), the model, named the Delft model, has been enhanced through tests using Montz B1
and BSH packings. A complete evaluation of Delft’s model has been accomplished by Fair
and coworkers (2000), showing that it overestimates the effective superficial area for
structured packing column design. In order to compensate for that deviation, Olujić et al.
(2004) have adapted Onda’s correlation (1968) apud Olujić et al. (2004) to be used with
structured packing columns.
In 2009, two works deal with the HETP evaluation using distinct base lube oil mixtures in a
lab-scale distillation column, of 40 mm of nominal diameter, having 4 sections of 550 mm
each containing Sulzer DX (gauze) structured packing, as the contacting device (Machado et
al. and Orlando Jr. et al., 2009). Orlando Jr. et al. (2009) made several tests with a
hydrocarbon mixture (C8-C14) to evaluate HETP using six HETP correlations to find out
which is the most appropriate for structured packed columns with medium distillates. The
theoretical models investigated are: Bravo et al. (1985), Rocha et al. (1993, 1996), Brunazzi
and Pagliant (1997), Carlo et al. (2006) and Olujic et al. (2004). As the laboratory distillation
column was operated continuously, different HETP values were found by the models for
each section of the column. Olujic et al. (2004) was the best method, showing good results,
together with the correlation of Carrillo et al. (2000), in which low deviations were obtained.
The average deviation varied from 8 to 47%. The deviations can be explained by the fact that
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most of the models have been proposed from testes using corrugated sheet structured
packing elements, which performs differently from gauze type packing.
In the work of Machado and coworkers (2009), the authors worked with two mixtures, a
heavier one composed of neutral medium and bright stock and another composed of
spindle and neutral light. Simulation studies using the PRO II software had been performed
in order to establish the best operating conditions in the distillation unit. Concerning the
empirical models, a comparison between the Lockett (1998) and Carrillo et al. (2000) models
was done. Among the theoretical models, Olujic et al. (2004) was chosen for being one of the
most recent and robust. According to the authors, unfortunately, neither mass transfer
model was able to properly describe the base lube oil distillation. Olujic et al. (2004) model
yielded underestimated area values, by using Onda´s correlation (Onda et al., 1968), but a
modified version proposed by Orlando Jr. et al. (2009) provided more realistic values for the
effective areas. It was concluded that the nature of the mixtures had no influence on HETP
deviations, pointing out that the low vapor flowrate inside the column was the most
influential variable. Large deviations varying from 27 to 70% were obtained for all the
mixtures and using all the methods.
Finally, Li et al. (2010) used a special high-performance structured packing, PACK-13C, with
a surface area of 1135 m2/m3 and the first stable isotope pilot-scale plant using structured
packing was designed. The height and inner diameter of the distillation column were 20 m
and 45 mm, respectively, and the height of the packing bed was 18 m. The raw materials
utilized were only high purity CO gas and liquid notrogen. When the F-factor changes from
0.18 to 0.90 m/s, the number of theoretical plates per meter decreases from 30 to 20. The new
structured packing was a combination of the advantages of structured and random packing,
as showed in Figure 6. The inclination angle was 45º, the height of corrugation was 2.5 mm,
the porosity was 0.77 and the silk diameter was 0.085 mm.
Fig. 6. Illustration of the structured packing PACK-13C (Li et al., 2010)
The minimum theoretical plates, at total reflux, was calculated by the Fenske equation. The
authors concluded that the PACK-13C structured packing exhibits very high performance in
isotope separation, combining the advantages of high theoretical plate numbers of the
random packing and the excellent hydrodynamic properties of structured packing. Figure 7
confirms the characteristics of the structured packing relating the theoretical plates number
and factor F.
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Fig. 7. The theoretical plates of PACK-13C (Li et al., 2010)
3. Conclusions
The use of packed columns for continuous contacting of vapors and liquids is well
established in the chemical industry, nowadays. The design of the columns require a
knowledge of the height of a transfer unit and this chapter had as main objective the
description of the present correlations, relating their advantages and disadvantages, for
random and structured packing.
Among the researches encountered in the literature and cited in this chapter, it is important
to have a model that describes the fluid dynamic relationships in packed columns with
countercurrent flow of the gas and liquid phases to describe up the flood point. It is so
important because above this point, the liquid accumulates to such an extent that column
instability occurs. The disadvantage of some correlations relies on the fact that many
parameter characteristics is only obtained graphically, what introduces deviations in the
calculation of areas and HETP.
For the distillation in packed columns, it was ascertained that the resistance in both phases,
liquid and vapor phases, should be taken into account in the HETP evaluation.
About the packing, new random and structured packing have been studied, but the
difficulty in HETP representation remains the problem, due to the fact that it is so difficult to
find a correlation that covers all systems with different physical properties and different
nominal sizes of the packing.
Moreover, normally, HETP is substantially constant over a wide range of vapor flows; on
the other hand, vapor flow varies increasing or decreasing the mass transfer depending on
the liquid phase. Because of that, HETP is not constant along the column and it is convenient
to define one value that which may be used for design purposes. Due to these factors, the
correlations proposed, empirical or theoretical, do not reach the real value of HETP for any
system studied.
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Finally, to better evaluate HETP, it is also important to choose a thermodynamic model that
can represent the behavior of the liquid-vapor equilibrium and complex methodologies to
calculate the theoretical number of stages.
4. Nomenclature
dP – nominal size of the packing
– inclination ratio between the equilibrium and operation straight
– fraction of surface used for mass transfer
P – pressure of the system
G – mass flow of the phase
GL – liquid mass flow
GV – vapor mass flow
G - V – gas or vapor rate
L – liquid rate
M – molecular mass
ML – molecular weight of liquid
MV – molecular weight of vapor
ρ – density
H – height representation of the mass transfer unit
HG – HV – height of gas-side phase transfer unit (m)
HL – height of liquid-side phase transfer unit (m)
HOG - HOV – height of an overall gas phase transfer unit (m)
gC - conversion factor between strengh and mass
CaL – capilar number
CfL – coefficient for effect of approach of flood point on liquid-phase mass transfer
Cpk – packing characteristic
h – operating holdup - m3/m3
c – void fraction
– corrugation angle
γ – angle with the horizontal for falling film or corrugation channel
 - contact angle
g – gravity acceleration
R – universal constant of the gases
T – absolute temperature
S – side dimension of corrugation – m
uLs - liquid phase superficial velocity – m / s
uGs – vapor phase superficial velocity – m / s
L – liquid viscosity – kg / m.s
v – G – vapor viscosity – kg / m.s
w – water viscosity - kg / m.s
ρL - liquid density – kg / m3
ρv – vapor density - kg / m3
ρw – water density - kg / m3
ε – void fraction of packing
 - packing parameter (function of packing type, size and GL)
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 - ratio (density of water/density of liquid)
d’p – diameter of a sphere with the same superficial area of the packing element
dc – column diameter
SC – Schmidt number
SCV - Schmidt number of the vapor phase
SCL - Schmidt number of the liquid phase
D – diffusivity
DL – liquid diffusion coefficient – m2/s
DV – vapor diffusion coefficient - m2/s
σ - liquid surface tension - N/m
σc – critical surface tension – N/m
Z – height of the packed bed
N – number of theoretical stages
m – slope of equilibrium line
ae – effective interfacial area (m2 / m3)
aw – wetted surface area of packing (m2 / m3)
ap - specific surface of the packing (m2 / m3)
kG - kV – gas-phase mass transfer coefficient
kL – liquid-phase mass transfer coefficient
r – relation between liquid viscosity at the packing bed temperature and viscosity of the
water at reference temperature of 20 oC
4 uLe L
ReL 
(Reynolds number for liquid)
FrL 
L
uL2
Sg
WeL 
(Froude number for liquid)
uL2 LS
 gc
(Weber number for liquid)
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www.intechopen.com
Mass Transfer in Chemical Engineering Processes
Edited by Dr. Jozef MarkoÅ¡
ISBN 978-953-307-619-5
Hard cover, 306 pages
Publisher InTech
Published online 04, November, 2011
Published in print edition November, 2011
This book offers several solutions or approaches in solving mass transfer problems for different practical
chemical engineering applications: measurements of the diffusion coefficients, estimation of the mass transfer
coefficients, mass transfer limitation in separation processes like drying, extractions, absorption, membrane
processes, mass transfer in the microbial fuel cell design, and problems of the mass transfer coupled with the
heterogeneous combustion. I believe this book can provide its readers with interesting ideas and inspirations
or direct solutions of their particular problems.
How to reference
In order to correctly reference this scholarly work, feel free to copy and paste the following:
Marisa Fernandes Mendes (2011). HETP Evaluation of Structured and Randomic Packing Distillation Column,
Mass Transfer in Chemical Engineering Processes, Dr. Jozef MarkoÅ¡ (Ed.), ISBN: 978-953-307-619-5,
InTech, Available from: http://www.intechopen.com/books/mass-transfer-in-chemical-engineeringprocesses/hetp-evaluation-of-structured-and-randomic-packing-distillation-column
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MCB 137
M ICHAELIS -MENTEN K INETICS
W INTER 2002
Lesson 6. MICHAELIS-MENTEN KINETICS
Objective
1. To learn how to reduce the complexity of a system by separating “fast” and “slow” variables.
2. To model ‘saturating’ Michaelis-Menten kinetics.
Saturating kinetics
Many kinetic systems obey the same reaction scheme:
Enzyme kinetics:
k1
k2
ææ
æÆ
E+S¨
æ ES ææÆ E + P
k -1
k1
k2
ææ
ææ
Æ CmembS ææ
Membrane Transport Carrier, C:C memb + Sin ¨
ÆC memb + Sout
k
(1)
(2)
-1
k1
k2
ææ
ææ
Æ RS ææ
Ligand-Receptor Binding: R + S ¨
Æ Action
k -1
(3)
All of these lead to the same rectangular hyperbola that describes Michaelis-Menten kinetics (c.f.
Appendix):
Y=
YmaxS
KM + S
where Y = k2 (ES)
(4)
k2 (ES) represents the velocity of the enzyme catalyzed reaction, rate of transport, or action of
1
drug/hormone. Ymax = the maximum value of Y, and Km = the value of S when Y = ⁄2 Ymax. The
equation and its properties are derived in most biochemistry texts1 ; the derivation is sketched in the
Appendix. The constant Km is given by
Km =
k -1 + k 2
k1
(5)
If we assume that the overall reaction rate is limited by the second reaction, i.e. the second reaction
is a bottleneck (i.e. k1 >> k2 ) then
Km =
k -1
k1
(6)
i.e. Km is a dissociation constant: Km = krelease/kcapture. One can interpret Vmax/Km as an effective
rate of capture of substrate by the enzyme.2
1
See, for example: Stryer, L. (1995). Biochemistry. New York, W. H. Freeman. pp 192-195.
2
Northrop, D. (1998). On the meaning of Km and V/Km in enzyme kinetics. J. Chem. Edu. 75(9): 1153-1157.
1
MM KINETICS
Exercises
Use Madonna to plot Equation (1) by writing the equation for Y directly into the Equation
Window and setting S = TIME. Use the BATCH mode so that you can plot several different
curves with different parameters. Start by holding Km constant at 10 mM for different values of
Ymax, and show that Y = Ymax/2 only when S = Km.
Next hold Ymax fixed at 10 and allow Km to vary. The higher the Km the slower the rise in Y—i.e.
the longer it takes to get half way. In fact, Km = Y1/2.
S Shaped (sigmoidal) Curves
The reaction
k1
k
ææ
æÆ
nS + R ¨
æ Sn R ææ2 Æ Action
k -1
(7)
leads to
Y=
YmaxSn
n
(K m ) + Sn
(8)
Exercises
1. Plot this equation for different values of the parameters. Show that Ymax and Km retain the same
significance as before(Ymax = the maximum value of Y, and Km = the value of S when Y =
1
⁄2 Ymax), and that the larger the exponent, n, the larger the initial delay and the steeper the rise
once it starts.
2. An inhibitor reacts with the with a mediator (enzyme, carrier, or receptor) and deactivates it. This
reduces the total number of available mediators and leads to:
YmaxK nm
Y= n
Km + Sn
(9)
Plot this equation as before for different values of the parameters.. Show that Ymax and Km
retain their significance as before (Ymax = the maximum value of Y, and Km = the value of S
when Y = 1/2 Ymax), and that larger the n the larger the initial delay and the steeper the fall
once it starts.
-2 -
MM KINETICS
‘Stiff’ systems
One of the most important methods of simplifying a
complicated system is to separate the processes into
‘fast’ and ‘slow’ variables. The term arose from
mechanical systems where ‘stiff’ springs respond
very fast, while weak springs respond much more
slowly. Then the displacement, z(t), can be broken into
an initial ‘fast’ regime, followed by a long-time
‘slow’ regime. In many situations, we don’t care
about the initial transient, but only on the long-time
behavior. This is frequently the case in biochemical
systems, where some reactions are fast and others are
slow. The classical example is the Michaelis-Menten
system, which we study below.
Consider the simple system:
d/dt (X) = Y - 2*X,
INIT X = 1
d/dt (Y) = -100*(Y - X),
INIT Y = 0
(10)
Y(t) settles to its final value very fast, while X(t)
decays much more slowly.
Exercise
Use the Rosenbrock “Stiff solver” with DT = 0.01
and DTMAX = 0.5 to solve the system (10).
Notice that y(t) rises very fast at the beginning (zoom in and see!), and thereafter changes slowly,
along with x(t). Suppose y changed so rapidly that it was always near its steady state: dy/dt = 0.
They you could solve the second equation for y = x and substitute it into the first equation for x, so
that it became dx/dt = -2x+x = -x. To see how good this approximation is, define a third variable, z
by dz/dt = -x and plot it along with x and y.
Now solve the same system using the Euler method. Turn on the data points with the button (•) and
see how many more steps Madonna has to take to get a solution.
Derivation of Michaelis-Menten Kinetics
Transformation of a substrate, S, into a product, P, by an enzyme, E, proceeds by first forming an
‘activated complex’ C which then dissociates (almost irreversibly) into free enzyme and product, P:
(Notation change: let C ≡ E⋅S denote the enzyme-substrate complex.)
k1
k
ææ
æÆ
E +S ¨
æ C ææ2 Æ E + P
k -1
-3 -
MM KINETICS
These reactions can be written as the following set of differential equations:3
dE
= k -1C + k 2 C - k1E ⋅S
dt
dS
= k -1C - k1E ⋅S
dt
dC
= k1E ⋅S - k -1C - k 2C = k1E ⋅S - (k -1 + k 2 )C
dt
(11)
dP
= k 2C
dt
An important common situation is when the enzyme, E, is saturated; i.e. it is working as fast as it
can, so that k-1 >> k2, so that k2 is the ‘bottleneck’. Then the concentration of the E•S complex is
nearly constant, so that we can set dC/dt ª 0, and C can be eliminated so that the system reduces to
a single equation for the velocity of the reaction, V = -dS/dt:
V =-
dS
V S
= - max
dt
Km + S
(12)
Vmax!S
k -1 + k 2
. The function V = Km!+!S is the Michaelis-Menten
k1
hyperbola. Km is the value of S when the velocity of the reaction is half its maximum, Vmax, and the
slope of the V(S) curve is Vmax/Km.
where Vmax = k 2E Total K m =
Exercise
Simulate the Michaelis-Menten equations (11) in Madonna using
k1 = 0.005, k2 = 0.005, k3 = 0.1
INIT S = 100, INIT P = 0, INIT E = 10, INIT C = 0
First use the Euler method with DT < 0.01. Then switch to the Rosenbrock (stiff) solver with
DTMIN = 1e-6, DTMAX = 1, DTOUT = 0, and TOLERANCE = 1e-4. Use the Show Data button
(•) on the graph to compare how efficient this integration method is to the Euler and Runge-Kutta.
Use the Chemical Reaction Module (Menu: Model > Modules > Chemical Reactions…) to
simulate the Michaelis-Menten system.
3
Not all of the differential equations are independent: adding the first two equations yields: E + C = ETotal (the total
amount of enzyme is constant). Also, the last equation for P(t) is completely determined once C is known.
Therefore, the four differential equations (11) can be reduced to only two independent differential equations.
-4 -

Day 8 - Web Access for Home

Transcription

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