creating digester capacity through improved mixing · 2016. 7. 14. · l vd 1pvd 2pct p mix system...
TRANSCRIPT
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 [email protected]
Steve PrazakCity of BendCity of [email protected]
31