Operating Costs

Review of Capital Costs
Cp = Purchased equipment cost = f(capacity variable)
Bare module cost (CBM)= Cp x FBM(materials, pressure)
Cost of Process Unit = (CBM )CE Index fcurr  floc
Location
Time Currency
Total Project Cost = Process Units + Offsites + Contingency
+ Contractor’s Fee
Contingency = 5 to 40% depending on class of estimate
Utility Costs
GD Ulrich, Chemical Engineering, 1992, Vol 2, pp 110
• Updated costs using same calculation method as text
Cu = Cost of utility per unit, e.g. $/kWh or $/kJ cooling
Cu = Capital equipment and labor expenses + Energy related
expenses
Cu = a·CE Index + b·Cf
Cf = Price of fuel, $/GJ
EXAMPLE PROCESS
• Deutsche Texaco AG Isopropanol Process
Unit
(Hydrocarbon Processing, November,
1981)
• Application: Process for the manufacture of
99.9% min. purity isopropanol (IPA) from
90-99% propylene
IPA Process Description
• The direct hydration of isopropylene to isopropanol is
carried out in a trickle-bed reactor using an ion exchange
catalyst
• Liquid propylene is mixed with preheated water, then
charged as a supercritical mixture to the top of a fixed-bed
reactor, and allowed to trickle downward over a bed of ion
exchange resin
• Intensive mass transfer occurs between the liquid and
vapor phases in the reactor at 130-160C and 1200-1500
psig
IPA Process Description (Cont.)
• Aqueous alcohol and unconverted propylene are separated
in a high-pressure separator
• The liquid phase is passed to a low-pressure separator, then
charged to a distillation column. Di-isopropyl ether (a byproduct) is removed from the top of the column.
• The bottom stream is sent to a second column, which
removes isopropanol as an azeotropic mixture in the
overhead stream
• The water from the bottom of the column is desalted by ion
exchange and recycled to the reactor. Azeotropic
isopropanol is further purified by distillation, after adding
benzene to break the azeotrope
Raw Materials
• Raw Material Consumption: 0.746 ton propylene/ton IPA
• Conversion:93.4% wt of propylene to IPA
5.0% wt of propylene to di-isopropyl ether
1.6% wt of propylene not reacted or lost
• Conversion per pass = 75%
• Costs: A 100,000 tonne/yr plant requires battery limits
investment of $13.8 million (1981) and uses 1 supervisor
and 4 operators
Utilities for IPA
• Utility requirements per tonne of IPA (99.9% purity) are:
–
–
–
–
–
–
–
Cooling water, USG T 7 C
Process water, USG
Low pressure steam, GJ
Electricity, kWh
Med. pressure steam, GJ
Chemicals + catalysts, $
Catalyst life, months
1000
80
7.4
115
0.525
2.8
8
• Calculate the cost per unit product for a 60,000 t/yr
plant.