HWEA Biosolids:HWEA Biosolids: Dewatering Processes and Practices

Sustainable Sludge Treatment Systems

Presented by:Mack McPhersonMike Elhoff

Hawaii Engineering Services

Dry Solids!

Dewatering of digested sludge

>30% w/w

Introduction

• Centrifuge DesignS P D i• Screw Press Design

• Sludge Performance • Conclusion• Conclusion

History - Centrifuge

• Continuously operated screw press: Pulp and Paper– Pulp and Paper

– Other applications with fibrous material involved: e.g. Cardboard compaction

What Does Mechanical Liquid-Solid-Separation Mean?

Sedimentation Filtration (gravity/pressure) CentrifugalSedimentation Filtration (gravity/pressure) Centrifugal

Centrifugal Force

Centrifugal force Fz grows with:

longer distance r to the rotating axis

higher speed Fz = m · cg p

m: mass; c: centrifugal acceleration

: angular speedc = r ·2

Bowl and Scroll Design Features

State-of-the-art rotor design steep bowl cone, d:l = 1:4 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 spin element at the end of feed pipe

Centrifuge Advancements

•Hydraulic scroll drives allow independent scroll and bowl operation

1975

•Eddy current drives allow for differential scroll speed adjustment

•Steep cone designs increase capacity

PLC t l t ll f f ll t ti t l•PLC control system allows for fully automatic control

•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•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 of a gear box there is stead o a gea bo t e e sa 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 torqueproportional to the torque moment in the scroll drive.

Independent Bowl & Scroll Variable Speed

Dual VFD

Dual VFD Control

Independent scroll and bowl operation

A t ti d tt d d Automatic and unattendedoperation via torque control

Highest efficiency and reliability

Small space requirement

Dual VFD Control

Bowl

Bowl DriveScroll Drive

Bowl VFD

motor

DriveBowl speed set point

Scroll motor

Scroll VFD PLCControl loop

Dual VFD efficiency

Example: energy losses (kw) at scroll drive:

Where is the energyWhere is the energy primarily lost?

By braking.7

8

9

4

5

6

High torque

By belt drive lossesat a tremendouscirculating power.

1

2

3g q

Normal use By poor efficiency of the hydraulic pump and motor.

0SIMP-DRIVE

Backdrive Hydraulic 2-Gear Eddy-Brake

By braking and refeeding.

Only moderategearbox losses.

Typical Control Panel Interior

Flottweg new C-seriesCentrate Energy RecoveryCentrate Energy Recovery

Traditional design New designTraditional 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• 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 ll ith TC til d i tScroll with TC tiles and ceramic paste

• Optional: Hard metal wear plates (with backing plate)• Optional: Hard metal wear plates (with backing plate)• Optional: CXL paste on scroll blades

Wear Feed ZoneFeed Zone

Replaceable Wear Protection

Solids Discharge Zone showing TC deflectors and solids port linerss o g C de ecto s a d so ds po t e s

Quality centrifuge - critical features:

Central lubricationsystem

Wear protectionField replacable

Bowl removal vertical

Sound insulated

Drive system outside separation

area

Separate scrollbearing

All high grade stainless steel

Scroll interchangeprogram

Municipal Dewatering Centrifuges

Flottweg Model

M B l S d ( )

Z6EC4EC3E Z8E Z92C5E C7E

Max. Bowl Speed (rpm)G-Force

Capacity (varies by application) (lbsdry/hour)

32003500

4000

34003000

2500

40003300

750

26503000

7000

22502600

8000

31003000

3500

27703000

6000y )

Dewatering Range(GPM , typical)

Mechanical

4000

150-250

2500

50-150

750

0-75

7000

250-450

8000

300-500

3500

125-225

6000

225-400

Mechanical

Bowl Diameter (inch)Machine Weight (lbs typical))

24

20000

18

7000

14

3800

30

35000

36

50000

22

12000

27.5

20000

ElectricalMotors: Main Drive (HP)

15030

000

4010

3800

205

20040

35060

7520

15040Motors: Main Drive (HP)

Scroll Drive (HP)30105 40 6020 40

C4E

Type Bowl Speed Bowl Power Scroll Power (SIMP® Drive)

Dimensions (mm)Drive)

RPM HP HP L W H

C4E 5000 40 10 3520 1140 1030

History – Screw Press

• Screw Press: ancient world– Oil mill: edible oil

• Oil seeds• Palm fruit• Olive OilOlive Oil• Coconut Oil

• Screw Press: Biosolids Dewatering– Existing Screw press designs applied from other

industriesM difi ti t ti i ti d ll– Modifications to optimize operation and allow dewatering of different types of sludge

– Special design for sewage sludge dewatering:Special design for sewage sludge dewatering: Inclined…

Inclined Screw Press

Design Featurespressurecone

augerpneumaticcylindersfilter basket

pressuremonitoring auger

bearingaugerdrive

cakei d fil cakedischarge

pressurizedsludge feed

filtrateoutlet

• O&M advantages: Screw Press

– Labor: unattended operation, high automation level already built in

– Dewatering process starts immediately even with empty screw press

– Spare Parts: minimal cost factor – slow turning device, p g ,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 notip 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’ have proven to be competitive with centrifuges:Screw Press have proven to be competitive with centrifuges:anaerobically digested sludge

Sludge Evaluation and Equipment Selection

• Cake Solids: project specificB h T t– Bench Tests

– Pilot Tests– Scale Upp– Basket design: drainage, thickening, dewatering– Sludge characteristics

Sample AnalysisSample Analysis

• Dewaterability

• Polymerscreening

• Pilot Go I No GGo

Effect of Volatile 35

40

Solids % on Dewatering Performance

30

35

S]20

25

solid

s [%

DS

10

15

cake

anWAS

0

5

blendLog. (an)Power (blend)

40 50 60 70 80 90 100

VSS [%]

Dry Solids vs. % Residue on Ignition(100-%VS)

45

50

Raw- and mixed sludge

30

35

40

tent

[%w

t.]

Digested sludge

Raw and mixed sludge

15

20

25

Solid

s C

on

Activated sludge

0

5

10

Dry

Activated sludge

0 10 20 30 40 50 60 70 80

Residue on ignition [%wt.]

Polymer Use - Demonstration and Pilot Tests

Blend WAS Aerobically Anaerob. digested digested

# f l t 19 17 26 29# of plants 19 17 26 29

Polymer Consumption in lbs active / ton DSAvg. 15.5 20.3 25.1 31.5Min - Max 8.1 – 24.9 9.6 - 27.2 8.5 - 40 10 - 75

Cake Solids (DS) in %Avg. 29.5% 18.2% 19.8% 22.1%Min - Max 18 - 38% 14 - 24% 14 - 27% 16 - 35%

Performance

Site tests: cake solids for anaerobically digested sludge

• BFP: 14 8 to 18 5 %• BFP: 14.8 to 18.5 % • Centrifuge: 22.2 to 23.7 %• Screw Presses: 17.3 to 24.1 %

Evaluation Criteria

• Cake Solids• Polymer Consumption• Wash Water Requirements• Energy ConsumptionEnergy Consumption• O&M costs:

– Labor: unattended operation, automationSpare parts– Spare parts

– Wear parts• Indirect O&M costs:

N i l d d l– Nutrients load returned to treatment plant– Capture rate– Hauling Costs: highly affected by cake solids

Evaluation

Screw Press 20 Year LCC BreakoutPower Cost

Chemical Cost1%

9%

4% 1%

1%

3%

Chemical Cost

Operating Cost (manpower)

Maintenance Cost (parts & labor)

Disposal Cost

81%Major Rework

Equipment Cost

Evaluation $0 Disposal

Screw Press 20 Year LCC Breakout

Power Cost

Chemical Cost4%

8%

17%

Operating Cost (manpower)

47%

3%0% Maintenance Cost (parts &

labor)

Major Rework21%

Major Rework

Equipment Cost

Cost Per Dewatering Technology

Dover, NH Pilot Study (Centrifuge, BFP, and Screw Press)

Total

Dewatering Cost

Disposal

Electrical

Water

Operations Labor

Polylmer

$0 $50,000 $100,000 $150,000 $200,000 $250,000 $300,000 $350,000 $400,000 $450,000 $500,000

Maintenance

BFP Screw Press Centrifuge

Reference AECOM Pilot Testing Results – Dover, NH

BFP Screw Press Centrifuge

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 Inclined Screw Press

Belt Filter Press Centrifuge Screw Press• Oldest Technology• Low to Med Cake Solids• High Water Consumption• Low to High Polymer

• Older Technology• Medium to High Cake Solids• No Water Consumption• Med/High Polymer

• Newer Technology• Medium to High Cake Solids• Low Water Consumption• Med/High Polymer• Low to High Polymer

Consumption• High Operator Attention• Low Maintenance• Low Electrical Loads

• Med/High Polymer Consumption

• Low Operator Attention• High Maintenance• High Electrical Loads

• Med/High Polymer Consumption

• Low Operation Attention• Low Maintenance• Low Electrical Loads• Low Electrical Loads

• Low to Med Capture Rate• High Electrical Loads• Med to High Capture Rate

• Low Electrical Loads• Med to High Capture Rate

Energy

• Energy Consumption:gy p– Mid size plant: processing 25 ton DS/week

centrifuge: 78,000 kWh/yrscrew press: 8,000 kWh/yrannual savings: $ 22,400.00 at $0.32/kWh

– Large plant: processing 200 ton DS/weekg p p gannual savings: $ 180,000.00 at $0.32/kWh

Conclusion

Overall evaluation needs to be tailored for site specific conditions: treatment plant process and biosolidshandling affect the importance of each parameter in thehandling affect the importance of each parameter in the cost analysis

Dry Solids!

Dewatering of digested sludge

>30% w/w