Creating Digester Capacity Creating Digester Capacity Through Improved Mixing

PNCWA 2010 – Bend, OregonOctober 26, 2010

Michelle Burkhart CH2M HILLMichelle Burkhart, CH2M HILLSteve Prazak, City of Bend

AcknowledgementsAcknowledgements

Drexell Barnes Jeff Buystedt

Lizzy EnglishAdrienne Menniti Jeff Buystedt

Matt HansenScott ThompsonGreg Mooney

d e e e tJohn KabourisBob Forbes

Jason KrumsickGreg MooneyJason SuhrJim Wodrich

Jason Krumsick Dave Green

2

OverviewOverview

• Design ProcessDesign Process

• Mix System Details

S d O i• Tracer Study Overview

• Testing and Sampling

• Results

• Conclusions and next stepsConclusions and next steps

3

Design Process hSystem Characteristics

• Digester 3 • Digester 2g– Primary Digester

– 50’ diam.

52’ SWD

g– Dewatering feed tank 

– 50’ diam.

18 28’ SWD– 52  SWD

– 820,000 gallons

– Fixed Cover

– 18‐28  SWD

– 409,000 gallons

– Fixed Cover

• Digester 1– Secondary Digester

– 50’ diam50  diam.

– 26‐28’ SWD

– 409,000 gallons

d– Fixed Cover

4

Design Process ( )Existing Mix System(s)

• Digesters 1 and 2Digesters 1 and 2– Gas Mixing (Compressors with(Compressors with spargers)

– Limited solidsLimited solids concentration

• Digester 3Digester 3– External Pump Mix

– Inverted ConeInverted Cone

5

Design Process lProject Goals

• Increase solids concentration (up to 4%) inIncrease solids concentration (up to 4%) in digestion system by providing better mixing – Put off Digester #4 for 20 years– Put off Digester #4 for 20 years

– Eliminate mixing limitations

M it th h di ti• Move grit through digestion process

• Minimize maintenance

• Internal city evaluation defined pump mix as preferred approach

6

Design Processl

V d 1 P V d 2 P C t P

Mix System Evaluation

Vendor 1 Pump Mix System

Vendor 2 Pump Mix System

Custom Pump Mix System

Number of Pumps 1 per Vessel 1 per Vessel 1 per VesselT f P Ch Ch S C t if lType of Pump Chopper Chopper Screw Centrifugal

Inverted Cone No No YesCapital Costs $320,000 $430,000 $624,000Annual Operating Costs $26,200 $24,200 $16,100

20-Year Present Worth $736,000 $814,000 $880,000

Custom External Pump Mix with Inverted Cone

• Energy savings are very important

• Ability to manage grit

7

• Ability to manage grit

• Compatibility with existing equipment

Design Process hOptimizing the Design

• Computational FluidComputational Fluid Dynamics (CFD) Modeling used toModeling used to– Confirm effectiveness of inverted coneinverted cone

– Confirm mix rate

– Define number of nozzles– Define number of nozzles

– Define nozzle placement

8

Mix System DetailsMix System Details

• External Pump Mix Systemp y– Dedicated pump per digester

– Screw Centrifugal, variable speed

4 000 gpm max 3 000 gpm each– 4,000 gpm max, 3,000 gpm each

– Typ. Operating Horsepower ‐ 30 hp

– Mixing Design Criteria‐ 10‐14 turnovers/day

9

Mix System DetailsMix System Details

• Inverted ConeInverted Cone– Prevents grit deposition

– Eliminates costly excavation

• Two nozzles/tank

10

Mix System DetailsMix System Details

• HDPE internal pipingHDPE internal piping– Reduces mixing impacts

Reduces opportunities– Reduces opportunities for ragging

11

Tracer Study Overview’ lCity’s Goals

• Verify design goalsVerify design goals– Entraining/moving grit– Maximize active volume– Allow for thicker solids concentration

• Understand short circuiting so Digester 1 canUnderstand short circuiting so Digester 1 can be utilized as Primary Digester

• Perform test at varying solids concentrationsPerform test at varying solids concentrations– 2%– 4%

12

Tracer Study OverviewTracer Study Overview

What is a tracer study?What is a tracer study?• Inject a known quantity of Tracer (LiCl)• Track washout (dilution)Track washout (dilution)

13

Tracer Study Overviewf fProof of Concept

What do we expect to see?What do we expect to see? 

5) 5)

33.54

4.5

tion (m

g/l)

33.54

4.5

tion (m

g/l)

11.52

2.5

Concen

trat

11.52

2.5

Concen

trat

00.5

0 5 10 15 20 25 30

Li C

00.5

0 5 10 15 20 25 30

Li C

14

Time (days)Time (days)

Tracer Study Overviewf fProof of Concept

What do we expect to see?

55

What do we expect to see? 

33.54

4.5

ion (m

g/l)

33.54

4.5

ion (m

g/l)

11.52

2.5

Concen

trat

11.52

2.5

Concen

trat

00.5

0 5 10 15 20 25 30

Li C

00.5

0 5 10 15 20 25 30

Li C

Time (days)Time (days)

15

Tracer Study OverviewSteps

• Inject a known quantity of Tracer (LiCl)• Inject a known quantity of Tracer (LiCl)

• Sample Digester Outlet for 2‐3 HRTs

• Analyze for Li ion

• Fit to a washout curve• Fit to a washout curve–Determine active volume

– Identify short circuiting

• Methodology Assumes Idealized CSTRMethodology Assumes Idealized CSTR

16

Testing and SamplingTesting and Sampling

• Detailed Test PlanDetailed Test Plan

• 100 lb LiCl

• Bend staff performed allBend staff performed all test activities

• Contract lab performedContract lab performed all Li analysis of sludge samples

• Test lasted 26 days

17

Testing and SamplingTesting and Sampling

18

Testing and SamplingTesting and Sampling

• Sampler at Digester Overflow BoxSampler at Digester Overflow Box– Every 30 minutes initially

– Once per day

• ISCO automatic sampler 

19

Testing and SamplingTesting and Sampling

• EPA Method 200.7 (ICP‐MS)EPA Method 200.7 (ICP MS)

• ~ $30 per sample

20

Resultsd hConditions During the Testing

Consistency during Testing is ImportantConsistency during Testing is Important25,000

4,000

4,500

)

25,000

4,000

4,500

)

15,000

20,000

2 500

3,000

3,500

tration (m

g/L

Rate (gpm

)

15,000

20,000

2 500

3,000

3,500

tration (m

g/L

Rate (gpm

)

10,000

1,500

2,000

2,500

olids C

oncent

x Pum

p Flow

 R

10,000

1,500

2,000

2,500

olids C

oncent

x Pum

p Flow

 R

Mixing and Total Solids C i t t!

0

5,000

0

500

1,000

Total SMix

0

5,000

0

500

1,000

Total SMix Consistent!

00

0 5 10 15 20 25

Time (days)Mix Pump Flow Rate Solids Concentration

00

0 5 10 15 20 25

Time (days)Mix Pump Flow Rate Solids Concentration

21

Resultsd hConditions During the Testing

Consistency during Testing is ImportantConsistency during Testing is Important

390,000

400,000

100

120

390,000

400,000

100

120

360,000

370,000

380,000

80

100

me (gallons)

ure (˚F)

360,000

370,000

380,000

80

100

me (gallons)

ure (˚F)

330,000

340,000

350,000

40

60

igester V

olum

Tempe

ratu

330,000

340,000

350,000

40

60

igester V

olum

Tempe

ratu

Temperature and V l C i t t!

300,000

310,000

320,000

0

20

Di

300,000

310,000

320,000

0

20

DiVolume Consistent!

0 5 10 15 20 25

Time (days)

Temp (F) Digester Volume

0 5 10 15 20 25

Time (days)

Temp (F) Digester Volume22

Resultsd hConditions During the Testing

Consistency during Testing is ImportantConsistency during Testing is Important

10

12

55

60

ays)

10

12

55

60

ays)

8

10

40

45

50

etical HRT

 (da

ed (gpm

)

8

10

40

45

50

etical HRT

 (da

ed (gpm

)

4

6

25

30

35

aneo

us The

or

Digester Fee

4

6

25

30

35

aneo

us The

or

Digester Fee

Feed Rate Not Ideal

0

2

10

15

20

Instan

ta

0

2

10

15

20

Instan

taFeed Rate Not Ideal, But Not Bad

0 5 10 15 20 25

Time (days)

Digester Feed Theoretical HRT

0 5 10 15 20 25

Time (days)

Digester Feed Theoretical HRT23

ResultshWashout Curve

Lithium Concentration vs Time

8.0

9.0

8.0

9.0

Lithium Concentration vs. Time

5.0

6.0

7.0

ratio

n (m

g/L)

5.0

6.0

7.0

ratio

n (m

g/L)

3.0

4.0

hium

 Con

centr

3.0

4.0

hium

 Con

centr

0.0

1.0

2.0

Lith

0.0

1.0

2.0

Lith

0.00 5.00 10.00 15.00 20.00 25.00

Time (days)

Reported Background

0.00 5.00 10.00 15.00 20.00 25.00

Time (days)

Reported Background

ResultshWashout Curve

Data Tracks Theoretical Curve Well

8.0

9.0

8.0

9.0

Data Tracks Theoretical Curve Well

5 0

6.0

7.0

ation (m

g/L)

5 0

6.0

7.0

ation (m

g/L)

3.0

4.0

5.0

um Con

centr

3.0

4.0

5.0

um Con

centr

0.0

1.0

2.0

Lithi

0.0

1.0

2.0

Lithi

0.00 5.00 10.00 15.00 20.00 25.00

Time (days)

Reported Theoretical Background

0.00 5.00 10.00 15.00 20.00 25.00

Time (days)

Reported Theoretical Background25

ResultshWashout Curve

Slope of line defines HRTSlope of line defines HRTa

1 5

2

1 5

2

A ti V l 96 7%y = ‐0.1341x + 1.7867

0.5

1

1.5

og C

y = ‐0.1341x + 1.7867

0.5

1

1.5

og C

Active Volume = 96.7%

‐0.5

0

0.00 5.00 10.00 15.00 20.00 25.00

atural Lo

‐0.5

0

0.00 5.00 10.00 15.00 20.00 25.00

atural Lo

‐1.5

‐1N

‐1.5

‐1N

‐2time, days

‐2time, days

ResultshWashout Curve

Methodology to determine short circuiting

8.0

9.0

8.0

9.0

Methodology to determine short circuiting

5 0

6.0

7.0

ation (m

g/L)

5 0

6.0

7.0

ation (m

g/L)

3.0

4.0

5.0

um Con

centr

3.0

4.0

5.0

um Con

centr

0.0

1.0

2.0

Lithi

0.0

1.0

2.0

Lithi

0.00 5.00 10.00 15.00 20.00 25.00

Time (days)

Reported Theoretical Background

0.00 5.00 10.00 15.00 20.00 25.00

Time (days)

Reported Theoretical Background27

ResultshShort Circuiting

Li Conc. on Day 1 of testing defines short circuiting

8.0

9.0

Li Conc. on Day 1 of testing defines short circuiting

6.0

7.0

n (m

g/L)

% bypass = 0.62%

3.0

4.0

5.0

Concen

tration

1.0

2.0

Li C

0.0

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90

Time (days)28

ConclusionsConclusions

• Digester is behaving as a completely mixedDigester is behaving as a completely mixed reactor– 11 turnovers / day– 11 turnovers / day

• Standard criteria is 10‐14 turnovers/day

– 0 5 hp/ 1000 gallons0.5 hp/ 1000 gallons • MOP 8: 0.2 – 1.5 hp/1000 gallons

• Minimal Short circuiting – use of Digester 1 as• Minimal Short circuiting – use of Digester 1 as a primary digester is appropriate

N i t i !• New mix system is a success!

29

Next StepsNext Steps

• Test again at thicker solids• Test again at thicker solids

• Compare results

• Consider operational changes

• Report out• Report out

30

Questions?Questions?

Michelle Burkhart, P.E.CH2M HILLCH2M HILL Michelle.Burkhart@ch2m.com

Steve PrazakCity of BendCity of Bendsprazak@ci.bend.or.us

31