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20-WMWDPre-6-07.ppt
Maximizing Secondary ClarifierCapacity with Three-dimensional Modeling
Randal Samstag and Ed Wicklein
Carollo Engineers
20-WMWDPre-6-07.ppt
Presentation Outline
• Introduction to the problem
• Comparison of models
• Case studies:
Center feed circular radial flow
Center feed square radial flow
Peripheral feed square countercurrent flow
Rectangular lamella clarifiers
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The Clarifier
• Used for both primaryand secondaryseparation of solids
• Efficiency depends on Settling
characteristics
Tank geometry
• The good news: Both settleability and
tank geometry canoften be improved
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Settleability Can be Improved
• Analysis of thebiologicalpopulations iscrucial
• Selectorsencouragepopulations thatsettle well
• Depends on:
Configuration
SRT
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Geometry Can Be Improved
Old Geometry New Geometry
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Why do Modeling?
• Thirty years of development usingcomputational fluid dynamics (CFD) foranalysis of sedimentation has proven thatCFD can
1) Capture the main features of clarifierbehavior
2) Model detailed features of hydraulic behavior
3) Efficiently predict performance of noveldesigns
4) Be more cost effective than full-scaleprototypes
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Types of Sedimentation Models
• Solids flux models (state point analysis)
• One-dimensional dynamic models(Biowin, Sedtank, Takacs, Vitasovic,Stenstrom)
• Two-dimensional dynamic models (UNO,TANKXZ, Carollo Fluent UDF)
• Three-dimensional dynamic models(Zhou/McCorquodale, Carollo Fluent UDF)
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State Point Analysis(Clariflux®)• Developed by Vesilind.
Implemented by CarolloEngineers (amongothers)
• Solves solids fluxequations based onmeasured settlingvelocity coefficients (orSVI)
• Calculates state pointfor steady stateoperation SOR Line MLSS Line RAS line
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One-dimensional (1D) DynamicModels
• Developed byStenstrom, Tracy,Vitasovic, Takacs,Sedtank, Biowin
• Simulate averageupward velocityversus downwardsettling velocity
• Solved dynamically
• Layered model
• Used for long-termdynamic simulations
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Two-dimensional (2D) Models
• Incorporate 2D tankhydraulics Boundary effects
Turbulence
Density effects
• Used for geometricoptimization ofsymmetricalelements
• Proprietary codes orpublic domainprograms
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Three-dimensional (3D) Models
• Resolution and detaillimited only bycomputing power
• Very detailed grids canbe used to capturegeometric features assmall as several inches
• Crucial for modeling ofnon-symmetric features
• Implemented inproprietary code orcommercial CFDpackages with specialadd-ons
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Each Type of Model Has itsPlace
• State Point Analysis – Steady StateCapacity Analysis
• 1D Dynamic Models – Long-termDynamic simulations
• 2D Models – Simple design evaluations
• 3D Models – For design problems that arenot simple
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Examples of 3D Problems
• Analysis of inlet conditions
Almost all inlet flow is three-dimensional
• Analysis of tank shapes that are notsimple
Square radial flow tanks
Circular peripheral feed tanks
Circular or square peripheral feed andwithdrawal tanks
Tanks with eccentric baffles or effluenttroughs
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Case Studies
• Center feed square radial flow
• Center feed circular radial flow
• Square peripheral feed / withdrawal
• Rectangular lamella clarifiers
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Center-feed, Radial-flow SquareClarifiers
• Case study for useof models
State PointAnalysis
2D Model
3D Model
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State Point Comparison
33% RAS 66% RAS
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2D Model – UNO Model
• Developed by J. A.McCorquodale andassociates at theUniversity of NewOrleans for EPA
• Two-dimensionalmodel based on Vorticity / stream
function model (2Donly)
Turbulent hydraulics Radial flow
coordinates (axi-symmetric)
Solids transport Composite settling
model Flocculation
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2D Model ResultsTest Calibration Results
FieldUNOModel
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2D Model ResultsSummary of Model Runs
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3D Model (Zhou CFD)
• Developed by SipingZhou and J. A.McCorquodale
• Three-dimensionalsolution based on Control volume
model Turbulent hydraulics Generalized
coordinates Solids settling Solids transport No flocculation or
compressionmodeling
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Inlet Comparison
Existing
Multilayer EnergyDissipating InletColum (MEDIC)
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3D Model ResultsSummary of Model Runs
Clarifier Configuration
Operational Conditions Clarifier Performance
ClarifierFlow (mgd)
SOR(gpd/sf)
RAS Ratio(%)
MLSS(mg/L) SVI (mL/g)
TheoreticalRAS
PredictedESS (mg/L)
PredictedRAS
(mg/L)(mg/L)Test Calibration 3.5 714 33 3,600 126 14,509 15 11,000
Existing Clarifier 2.5 510 33 3,250 110 13,000 7.1 10,821
Existing Clarifier 3.5 714 33 3,250 110 13,000 13.1 10,773
Existing Clarifier +Perimeter Effluent Weir
and Baffle
3.5 714 33 3,250 110 13,000 14.5 10,772
Existing Clarifier 4.5 918 33 3,250 110 13,000 83 10,183
Existing Clarifier 3.5 714 66 3,250 190 8,100 428 6,234
Existing Clarifier 3.5 714 100 3,250 190 6,500 1017 5,167
3-Layer MEDIC +Middle Feed Well
2.5 510 33 3,250 110 13,000 5.2 10,943
3-Layer MEDIC +Middle Feed Well
3.5 714 33 3,250 110 13,000 5.7 11,025
3-Layer MEDIC +Middle Feed Well
4.5 918 33 3,250 110 13,000 6.7 10,904
3-Layer MEDIC +Middle Feed Well
3.5 714 33 3,250 190 13,000 10.5 8,482
3-Layer MEDIC +Middle Feed Well
3.5 714 66 3,250 190 8,100 7.9 6,985
3-Layer MEDIC +Middle Feed Well
3.5 714 100 3,250 190 6,500 7.8 6,015
20-WMWDPre-6-07.ppt
3D Model ResultsInlet Improvements (SVI 110)
Figure 16 Performance comparison between the existing and optimized clarifiers under a peakflow condition (Clarifier flow = 4.5 MGD, RAS = 33.3%, MLSS = 3250 mg/L and SVI = 110)
1) Existing Clarifier
2) OptimizedClarifier
a) Inlet jets entering clarifier [2.45 ft/s (73.4 cm/s)]
a) Inlet jets entering MEDIC (2.45 ft/s) and ones entering clarifier [0.13 ft/s (3.88 cm/s)]
b) Strong turbulenceinduced by intensiveclarifier influent flow
b) Significantlydamped turbulencedue to substantiallyreduced clarifierinfluent flow intensity
c) Dispersed sludge blanket
c) Dispersed sludge blanket
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3D Model ResultsInlet Improvements (SVI 190)
Figure 20 Performance comparison between the existing and optimized clarifiers under a poorSVI combined with a low RAS of 33.3% (Clarifier flow = 3.5 MGD, MLSS = 3250 mg/L and SVI= 190)
1) ExistingClarifier
2) OptimizedClarifier
Significant solids inventory due to poor SVIcombined with limited RAS capacity
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Conclusions from 3D Modeling
• Optimized inlet would allow increase ofsafe operating flow from 3.5 to 4.5 mgdper clarifier with good SVI (110 mL/g)
(30% Increase)
• Optimized inlet would allow safeoperation at 3.5 mgd per clarifier withpoor SVI (190 mL/g) compared to 2.5mgd with existing inlet
(40% increase)
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Center-feed Circular Radial Flow TankComparison of Tangential to Puzzled Inlets
Tangential Inlet Puzzled Inlet
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Carollo Fluent UDF Model
• 2D or 3D• Sophisticated grid
generation andvisualization tools
• Choice ofturbulence models
• User definedfunctions (UDF) toimplement Solids transport Density coupling Solids settling
velocity
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Calibration of 2D Model toField Test
Field Test
Model
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Comparison of Tangential toPuzzled InletsInlet Velocities
Tangential Inlet Puzzled Inlet
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Comparison of Tangential toPuzzled Inlets (3D Model)
Inlet Velocity Intensity
Tangential Inlet Puzzled Inlet
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Optimization of InletInlet Geometry (3D Model)
Existing Inlet Optimized Inlet
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Optimization of InletSolids and Velocity Profiles
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Optimization of InletComparison of Inlet Velocity and
Energy
Existing Inlet Optimized Inlet
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Square Peripheral Feed / Withdrawal TankOverall Geometry and Grid
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Square Peripheral Feed / WithdrawalOverall Solids Profiles
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Square Peripheral Feed / WithdrawalVelocity and Solids Profiles
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Square Peripheral Feed / WithdrawalSludge Blanket Level Topography
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Rectangular Lamella Clarifier
• Carollo Fluent UDFModel
• 2D and 3D flow inand around thelamella platemodules
• Activated sludgeclarifiers
• Two differentsettling models: Vesilind Vesilind with
Boycott in lamellazone
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Detailed Grid
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Vesilind Model of Low SVICondition
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Vesilind Model with Moderate SVI
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Vesilind Model with No Lamellas
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Vesilind/Boycott Model ofModerate SVI
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Vesilind Model of Inlet Baffle
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Conclusions
• CFD models are well developed forevaluation of sedimentation tanks
• Each level of model has its place
• Several important problems can only beadequately evaluated using 3D models Inlet design
Radial flow / square shape
Non-symmetrical elements
• Commercial 3D CFD codes can beproductively used but only with customadd-ons
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Questions?
Randal W. Samstag([email protected])
Ed A. Wicklein([email protected])
