POLYMER OPTIMIZATION FORCENTRIFUGE DEWATERINGCENTRIFUGE DEWATERING

CWEA SeminarMath, Operations, and Maintenance for

Biosolids Systems

Steve Walker

September 13, 2011

Senior Operations Specialist

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Learning Objectives• Why optimize

• Dewatering basics

• Centrifuge basics• Centrifuge basics

• Polymer considerations

• Sludge considerations

• Optimization approach

P tti ti i ti i ti

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• Putting optimization in action

DewateringSludge Dewatering • The removal of a portion of the water contained in sludge

by means of a filter press, centrifuge, or otherby means of a filter press, centrifuge, or other mechanism.

Process optimizationProcess optimization • The discipline of adjusting a process so as to optimize a

set of parameters without violating a constraint

• The most common goals are minimizing cost, maximizing throughput, and/or efficiency

• The goal is to maximize one or more of the process paramrters, while keeping all others within their constraints

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constraints

WHY OPTIMIZEWHY OPTIMIZE

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Polymer Costs

57%57%

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Dewatering Polymer Costs

$16,222

$465,220 $15,701 $130,014

$137,038

$206,715 $466,391

57%$1,911,634

Liquid Oxygen Ferric Chloride DAF Polymer Cent Polymer

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Polymer – Raw Material Costs40

20

25

30

35

ntag

e Ch

ange

Producer Price Index for Plastics Material and Resins Manufacturing

Source: Bureau of Labor Statistics http://stats.bls.gov/ppi

5

10

15

20

Mont

hly P

erce

Index includes:PropyleneAcrylonitrileEpichlorhydrinMethyl acrylateMethyl methacrylateFormaldehyde

0

Month

6

4

5 US No. 2 DieselRetail Sales

1

2

3

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01/1/2001 1/1/2002 1/1/2003 1/1/2004 1/1/2005 1/1/2006 1/1/2007 1/1/2008 1/1/2009 1/1/2010 1/1/2011

$/gal

DEWATERINGDEWATERING

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Dewatering Considerations

• Centrifuge components

• Centrifuge adjustments

• Operational targets• Operational targets

• Throughput

• Sludge makeup

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Water in SludgeGallons of Water in 10 tons of Sludge

600 000

500,000

600,000

er

300,000

400,000

ns o

f Wat

e

100,000

200,000

Gal

lo

Focus Area

0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35

Percent Solids

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Percent Solids

Centrifuge Components

Sludge Feed Weir PlatesScrollBowl

SIEBTECHNIK GmbH

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Solids DischargeLiquid Discharge

Centrifuge FactorsBowl speed

Adj t d th h th PLC• Adjusted through the PLC

• The faster the speed, the greater the shear f t fl l t d l dfactor on flocculated sludge

• Can impact cake dryness, centrate quality, and polymer dose

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Centrifuge FactorsConveyor (scroll) speed

• Controlled by the PLC• Controlled by the PLC

• Modern centrifuges are controlled using a %torque setpoint%torque setpoint

• To obtain the desired torque, the PLC adjusts th ll dthe scroll speed

• Can impact cake dryness, centrate quality, and polymer dose

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Centrifuge FactorsDifferential

Th diff b t th b l d d th• The difference between the bowl speed and the scroll speed

Th diff ti l h th PLC hi• The differential changes as the PLC achieves the desired torque

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Centrifuge FactorsWeir depth

M h i l dj t t t l t t th d f• Mechanical adjustment to plates at the end of the bowl

S t th l d th ithi th b l• Sets the pool depth within the bowl

• Can impact cake dryness, centrate quality, and polymer dose

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Operational TargetsCriteria Units Importance

Cake dryness %TS Disposal costs y

Water equals weight and takes up volume

Centrate quality %TS Impact on liquid treatment processesCentrate quality %TS or TSS, mg/L

Impact on liquid treatment processes

Re-treatment of solids (thickening, digestion and dewatering)

Impact of inert solids on activatedImpact of inert solids on activated sludge mass calculations

Throughput Pounds per How centrifuges are sized and soldhour

Polymer dose Active pounds per

Operating costs

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pounds per dry ton

Throughput Calculationgallon x 8.34 pounds x %TS x 60 minutes = pounds

min gallon hour hour

gpm 100 150 200%TS0.020 1001 1501 20020.022 1101 1651 22020.024 1201 1801 24020.026 1301 1952 26020.028 1401 2102 28020.030 1501 2252 3002

Notice the large change in throughput ith ll h i d it fl

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with small change in density or flow

Impact of Sludge Density

4000

4500

3000

3500

n lb

/hr 2250 lb/hr

2000

2500

roug

hput

in

1000

1500Thr

1500 lb/hr

0

500

100 125 150 175 200 225 250 275

0.02 0.022 0.024 0.026 0.028 0.03

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100 125 150 175 200 225 250 275

gpm

SLUDGE CONSIDERATIONSSLUDGE CONSIDERATIONS

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Primary To Secondary Sludge Ratio• The ratio is determined by primary solids in pounds

divided by secondary solids in pounds – Do not use gallons / gallonsDo not use gallons / gallons

• There is a direct correlation between primary solids to secondary solids (P/S) ratio and polymer required forsecondary solids (P/S) ratio and polymer required for dewatering

• A reduced P/S ratio reduces centrate and cake quality• A reduced P/S ratio reduces centrate and cake quality

• An increased P/S ratio reduces the amount of polymer required to meet centrate and cake qualityrequired to meet centrate and cake quality

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Primary to Secondary Solids Blend sw

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Economic Impact

Product Unit Cost Usage I t

$ per 1,000 d tImpact dry tons

Emulsion A $2.50/active lb 7.5 lb/ton $18,750

Emulsion B $2.30/active lb 8.0 lb/ton $18,400

Dry A $2 20/lb 9 5 lb/ton $20 900Dry A $2.20/lb 9.5 lb/ton $20,900

Dry B $2.00/lb 10.5 lb/ton $21,000

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Primary to Secondary Solids Blend Suggested operational considerations

• Optimize primary sludge removal efficiencyOptimize primary sludge removal efficiency

• Optimize primary BOD removal efficiency

• Plan for impacts when taking activated sludge basins or primary clarifiers out of servicep y

• Understand impacts of secondary wasting adjustmentsadjustments

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POLYMERPOLYMER

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Polymer Factors• Polymer types

• Polymer solution strength• Polymer solution strength

• Batching considerations

• Mixing considerations

• Solution injection point• Solution injection point

• Purchasing flexibility

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Polymer Characteristics

Type Appearance Primary Ingredients

Active Content

Liquid - emulsion Opaque Polymer, oil, inverting

surfactant, water

25% - 40%

su ac a , a e

Liquid - dispersion White Polymer, oil, inverting surfactant

40% - 75%

Liquid - mannich Clear, highly viscous

Polymer, water 3% - 8%viscous

Dry White granules, spheres, or

Polymer, dry surfactant

50% – 98%

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powder

Polymer CharacteristicsType Charge Typical Molecular Weight

Cationic Positive Medium to very highy g

Anionic Negative Medium to very high

Non-ionic Neutral Medium to very high

• Higher charge = more active sites on a molecule

• Molecular weight dictates the length of the molecule; higher = longer

• Higher molecular weight = harder to get into solution and more viscous when in solution

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Polymer Characteristics

Solution Strength 0.3% +/- 0.1

• Calculated by dividing the pounds of polymer added to a batch by the sum of pounds of polymer + pounds ofbatch by the sum of pounds of polymer + pounds of water in a batch

• Downstream dilution water increases the surface contact• Downstream dilution water increases the surface contact area

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Batching • Aging time• Aging time

– Need enough time to allow the polymer molecules to uncoil

– Water temperature can impact aging time

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Potable or Non-Potable Water

• During aging, solids in non-potable water take up charge sites and can decrease polymer performance

• Expense of potable water likely offsets the lossExpense of potable water likely offsets the loss of polymer performance

M k d t t t• Makedown water temperature– Warmer is better

• Chlorine residual– High chlorine content can decrease performance

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Polymer Mixing SystemsI ffi i i i l l d• Insufficient mixing energy causes polymer to gel, and prevents effective polymer activation

Excessive high mixing energy causes polymer to shear• Excessive high mixing energy causes polymer to shear

- Increased polymer dosage

- Decreased process performance

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Solution Injection Point

• Before centrifuge feed pump– Blended with sludge feed

– Mixed through travel time, in piping and elbows

Can shear molecules going through the pump– Can shear molecules going through the pump

• Upstream of rotating assembly– Allows for some mixing

• Inside the rotating assembly• Inside the rotating assembly– Injected at the splash plate and diffuses into sludge

S t t ti lt t i t i ll

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Suggest testing alternate points occasionally

Contract Flexibility• Establish Primary and Alternate supplies

– Use two different suppliers rather than two different ppproducts from the same supplier

• Determine if seasonal constraints supportDetermine if seasonal constraints support alternatives– An emulsion polymer may be more cost effective in

winter months

– A dry polymer may be more cost effective in the y p y yother months

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APPROACHAPPROACH

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Putting It All Together

• Centrifuge adjustments

• Throughput

• Polymer batchingPolymer batching

• Polymer solution feed rates

• Operational targets

Operational planning• Operational planning

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Optimization - Premise• The readily apparent visual clue is centrate

quality

• Within an operating range, optimum dosage results in quality centrate

• When in the optimal dosing range, the driest cake will be producedcake will be produced

• With excessive dosages, both cake dryness and t t lit ill d licentrate quality will decline

Goal is to determine guidelines to achieve the optimal range

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for a variety of conditions

Test Methodology – Phase 1• Batch polymer at preferred solution strength

• Set sludge feed rate

• Enter typical torque setpoint and bowl speed

• Set lowest polymer feed rate• Set lowest polymer feed rate

• Run for a standard time (i.e., 45 minutes)

S l f d t t d k f TSS F d TSS• Sample feed, centrate and cake for TSS. Feed TSS is used to calculate throughput.

• Run through sequence for at least 5 polymer feed• Run through sequence for at least 5 polymer feed rates

• Plot results

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Plot results

Performance Curve

98

10035Dose v. % Recovery

94

9630

S

88

90

92

20

25

ton

or %

TS

24 lb/ton

84

86

88

15

20

lb/t

80

82

101 2 3 4 5 6

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Test Methodology – Phase 2S f• Set sludge feed rate

• Set polymer solution feed rate for the “ideal” polymer dose

• With sludge and polymer feed rates “locked in”, g yadjust % torque setpoint

• Run for a standard time (i.e., 45 minutes)( , )

• Sample feed, centrate and cake for TSS. Feed TSS is used to calculate throughput.g p

• Run through sequence for at least 5 torque setpoint

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Performance Curve 2

98

100

45

50Torque v. % Recovery

94

96

35

40

45

ue

88

90

92

30

35

S o

r Tor

qu

84

86

88

20

25

%TS

39% Torque

80

82

10

15

1 2 3 4 5 6

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Outcome• Determine what dose is effective under what

conditions

• Determine what torque is effective at what throughput

• Provide general guidelines to “dial in” centrifuges

If i th l d t i d• If using more than one polymer, determine under what conditions each is most effective

• Forecast usage to establish budget projections

C id h d li f ll f t ti t l t 6

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Consider scheduling full range of testing at least every 6 months

Operating Rangesw

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Throughput Rangesw

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Polymer Dose Ratesw

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Guidelines With Budgetary Impacts

Polymer Projected Throughput

Cake Dryness Centrate Capture

Emulsion Greater than X Consistently falls Consistently falls belowEmulsion Greater than X lb/hr per machine

Consistently falls below target

Consistently falls below target

Dry Less than X Consistently stays Consistently stays aboveDry Less than X lb/hr per machine

Consistently stays above target

Consistently stays above target

or seasonally

Polymer Time of YearEmulsion ~Dec 15 – Apr 15

Dry ~ April 16 – Dec 14

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Dry April 16 Dec 14

Dewatering – Operating Targetssw

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What Was Covered• Why optimize dewatering polymer use

f• What impacts centrifuge output

• What impacts polymer batchingy g

• The impact of P/S blend

A th d l t d fi ti• A methodology to define operating ranges

• Putting optimization in action

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Polymer Optimization for Centrifuge Dewatering

Thank you for being a wastewater treatment professional. Be proud of your contributions.

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professional. Be proud of your contributions.