Comparison of Dewatering Technologies

HWEA Biosolids:
Dewatering Processes and Practices
Sustainable Sludge Treatment Systems
Presented by:
Mack McPherson
Mike Elhoff
Hawaii Engineering Services
Dry Solids!
Dewatering of
digested sludge
>30% w/w
Introduction
•
•
•
•
Centrifuge Design
S
Screw
P
Press Design
D i
Sludge Performance
Conclusion
History - Centrifuge
•
Continuously operated screw press:
– Pulp and Paper
– Other applications with fibrous material involved:
e.g. Cardboard compaction
What Does Mechanical Liquid-SolidSeparation Mean?
Sedimentation
Filtration (gravity/pressure)
Centrifugal
Centrifugal Force
Centrifugal force Fz grows with:
 longer distance r to the rotating axis
g
speed
p
 higher
m: mass; c: centrifugal acceleration
: angular speed
Fz = m · c
c = r ·2
Bowl and Scroll Design Features
State-of-the-art rotor design
 steep bowl cone, d:l = 1:4
 deep pond (for large volume)
 double cone scroll (for intensive compacting)
 spin element at the end of feed pipe
Centrifuge Advancements
1975
•Hydraulic scroll drives allow independent scroll and bowl operation
•Eddy current drives allow for differential scroll speed adjustment
•Steep cone designs increase capacity
•PLC
PLC control
t l system
t
allows
ll
for
f fully
f ll automatic
t
ti control
t l
•VFDs are used on scroll drives but require bowl and scroll linkage due to
gear box braking
•Independent bowl and scroll gearbox not utilizing braking
•Planetary gearbox allows totally independent bowl and scroll operation
•Centrifuge can run in either leading or lagging mode
•Less energy loss by elimination of braking
•Scroll can operate independently at maximum speed for cleanout
•Energy recovery and deep pond designs
for higher capacity and drier solids
2014
Decanter Drive Systems
Hydraulic Scroll Drive
 Instead
stead o
of a gea
gear bo
box there
t e e is
s
a rotating hydraulic motor
supplied with pressurized oil
via a rotary feedthrough.
 The differential speed is
continuously adjustable
 The oil pressure is directly
proportional to the torque
moment in the scroll drive.
Independent Bowl & Scroll Variable Speed
Dual VFD
Dual VFD Control
 Independent scroll and
bowl operation
 Automatic
A t
ti and
d unattended
tt d d
operation via torque control
 Highest efficiency and
reliability
 Small space requirement
Dual VFD Control
Bowl Drive
Bowl
VFD
Bowl
motor
Scroll
Drive
Bowl speed set point
Scroll
motor
Scroll
VFD
Control loop
PLC
Dual VFD efficiency
Example: energy losses (kw) at scroll drive:
Where is the energy
primarily lost?
9
8
By braking.
7
6
5
4
High
g torque
q
3
Normal use
2
1
By belt drive losses
at a tremendous
circulating power.
By poor efficiency
of the hydraulic
pump and motor.
0
SIMPDRIVE
Backdrive Hydraulic
2-Gear
EddyBrake
By braking and
refeeding.
Only moderate
gearbox
losses.
Typical Control Panel Interior
Flottweg new C-series
Centrate Energy Recovery
Traditional design
New design
Centrate is discharged straight
into the housing.
Centrate is redirected and
tangentially discharged into the
housing.
g
Rotational energy of the centrate
is lost!
Rotational energy is recovered!
Advancements in Centrifuge Design
• Deep Pond Technology reduces Energy
Consumption by 25-30%
• Centrate Energy Recovery reduces Consumption by
an additional 20%
• Dual VFD has lower installed HP and reduces
energy consumption by eliminating “braking the
bowl”
• Optimized Solids Discharge (1-2% added cake
solids)
Wear
S
Scroll
ll with
ith TC tiles
til and
d ceramic
i paste
t
• Optional: Hard metal wear plates (with backing plate)
• Optional: CXL paste on scroll blades
Wear
Feed Zone
Replaceable Wear Protection
Solids Discharge Zone
showing
s
o
g TC
C de
deflectors
ecto s a
and
d so
solids
ds po
portt liners
es
Quality centrifuge - critical features:
Central lubrication
system
Wear protection
Field replacable
Bowl removal
vertical
Sound insulated
Drive system
outside separation
area
Separate scroll
bearing
All high grade
stainless steel
Scroll interchange
program
Municipal Dewatering Centrifuges
Flottweg Model
C3E C4E
C5E
Z6E
C7E
Z8E
Z92
Max. Bowl
M
B lS
Speed
d (rpm)
(
)
G-Force
4000
3300
3400
3000
3100
3000
3200
3500
2770
3000
2650
3000
2250
2600
Capacity (varies by application) (lbs
dry/hour)
y
)
750
2500
3500
4000
6000
7000
8000
075
50150
125225
150250
225400
250450
300500
14
18
22
24
27.5
30
36
3800
7000
000
20
5
40
10
Dewatering Range
(GPM , typical)
Mechanical
Bowl Diameter (inch)
Machine Weight (lbs typical))
Electrical
Motors: Main Drive (HP)
Scroll Drive (HP)
12000 20000 20000 35000 50000
75
20
150
30
150
40
200
40
350
60
C4E
Type
C4E
Bowl Speed
Bowl Power
Scroll Power (SIMP®
Drive)
Dimensions (mm)
RPM
HP
HP
L
W
H
5000
40
10
3520
1140
1030
History – Screw Press
• Screw Press: ancient world
– Oil mill: edible oil
•
•
•
•
Oil seeds
Palm fruit
Olive Oil
Coconut Oil
• Screw Press: Biosolids Dewatering
– Existing Screw press designs applied from other
industries
– Modifications
M difi ti
tto optimize
ti i operation
ti and
d allow
ll
dewatering of different types of sludge
– Special design for sewage sludge dewatering:
Inclined…
Inclined Screw Press
Design Features
auger
pressure
cone
pneumatic
cylinders
filter basket
pressure
monitoring
auger
bearing
auger
drive
i d
pressurized
sludge feed
filtrate
fil
outlet
cake
discharge
• O&M advantages: Screw Press
– Labor: unattended operation, high automation level already
built in
– Dewatering process starts immediately even with empty
screw press
– Spare
p
Parts: minimal cost factor – slow turning
g device,,
minimal number of turning parts
– Wear Parts: wiper to clean basket on the inside – located at
tip of the auger flight; crucial for sludge with very little or no
fibrous material and no self cleaning. No major off site
overhaul and inspection like for centrifuges
Performance
• Screw Press’
Press have proven to be competitive with centrifuges:
anaerobically digested sludge
Sludge Evaluation and Equipment Selection
• Cake Solids: project specific
–
–
–
–
–
Bench
B
hT
Tests
t
Pilot Tests
Scale Up
p
Basket design: drainage, thickening, dewatering
Sludge characteristics
Sample Analysis
• Dewaterability
• Polymer
screening
• Pilot Go I No
Go
40
35
30
cake solids [% DS
S]
Effect of Volatile
Solids % on
Dewatering
Performance
25
20
15
an
WAS
blend
Log. (an)
Power (blend)
10
5
0
40
50
60
70
VSS [%]
80
90
100
Dry Solids vs.
% Residue on Ignition(100-%VS)
50
Dry Solids Content [%wt.]
45
Raw- and mixed sludge
Raw
40
35
Digested sludge
30
25
20
15
Activated sludge
10
5
0
0
10
20
30
40
50
Residue on ignition [%wt.]
60
70
80
Polymer Use - Demonstration and Pilot Tests
Blend
# off plants
l t
19
WAS
17
Aerobically
digested
Anaerob.
digested
26
29
Polymer Consumption in lbs active / ton DS
Avg.
Min - Max
15.5
20.3
25.1
31.5
8.1 – 24.9
9.6 - 27.2
8.5 - 40
10 - 75
29.5%
18.2%
19.8%
22.1%
18 - 38%
14 - 24%
14 - 27%
16 - 35%
Cake Solids (DS) in %
Avg.
Min - Max
Performance
Site tests: cake solids for anaerobically digested sludge
• BFP: 14
14.8
8 to 18
18.5
5%
• Centrifuge: 22.2 to 23.7 %
• Screw Presses: 17.3 to 24.1 %
Evaluation Criteria
•
•
•
•
•
Cake Solids
Polymer Consumption
Wash Water Requirements
Energy Consumption
O&M costs:
– Labor: unattended operation, automation
– Spare parts
– Wear parts
• Indirect O&M costs:
– Nutrients
N i
lload
d returned
d to treatment plant
l
– Capture rate
– Hauling Costs: highly affected by cake solids
Evaluation
Screw Press 20 Year LCC Breakout
Power Cost
1%
Chemical Cost
1%
3%
9%
4%
1%
Operating Cost (manpower)
Maintenance Cost (parts &
labor)
Disposal Cost
Major Rework
81%
Equipment Cost
Evaluation $0 Disposal
Screw Press 20 Year LCC Breakout
Power Cost
Chemical Cost
4%
17%
Operating Cost (manpower)
8%
0%
3%
47%
21%
Maintenance Cost (parts &
labor)
Major Rework
Equipment Cost
Cost Per Dewatering Technology
Dover, NH Pilot Study (Centrifuge, BFP, and Screw Press)
Dewatering Cost
Total
Disposal
Water
Electrical
Polylmer
Operations Labor
Maintenance
$0
$50,000
$100,000
$150,000
BFP
Reference AECOM Pilot Testing Results – Dover, NH
$200,000
$250,000
Screw Press
$300,000
Centrifuge
$350,000
$400,000
$450,000
$500,000
Energy
Energy Consumption: the installed HP clearly favor
BFP and screw presses at similar throughput
• Centrifuge: 37.5 kW (50 hp)
• BFP: drive unit 4 kW(5
( hp)
p)
• Screw Press: 4 kW (0.5 - 5 hp)
Dewatering Technologies
Belt Filter Press
Centrifuge
Belt Filter Press
•
•
•
•
•
•
•
•
Oldest Technology
Low to Med Cake Solids
High Water Consumption
Low to High Polymer
Consumption
High Operator Attention
Low Maintenance
Low Electrical Loads
Low to Med Capture Rate
Inclined Screw Press
Centrifuge
•
•
•
•
•
•
•
•
Older Technology
Medium to High Cake Solids
No Water Consumption
Med/High Polymer
Consumption
Low Operator Attention
High Maintenance
High Electrical Loads
Med to High Capture Rate
Screw Press
•
•
•
•
•
•
•
•
Newer Technology
Medium to High Cake Solids
Low Water Consumption
Med/High Polymer
Consumption
Low Operation Attention
Low Maintenance
Low Electrical Loads
Med to High Capture Rate
Energy
• Energy
gy Consumption:
p
– Mid size plant: processing 25 ton DS/week
centrifuge: 78,000 kWh/yr
screw press: 8,000 kWh/yr
annual savings: $ 22,400.00 at $0.32/kWh
– Large
g p
plant: p
processing
g 200 ton DS/week
annual savings: $ 180,000.00 at $0.32/kWh
Conclusion
Overall evaluation needs to be tailored for site specific
conditions: treatment plant process and biosolids
handling affect the importance of each parameter in the
cost analysis
Dry Solids!
Dewatering of
digested sludge
>30% w/w