Maximizing Secondary Clarifier Capacity with Threedimensional

Transcription

1 Maximizing Secondary Clarifier Capacity with Threedimensional Modeling Randal Samstag and Ed Wicklein Carollo Engineers

2 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

3 The Clarifier Used for both primary and secondary separation of solids Efficiency depends on Settling characteristics Tank geometry The good news: Both settleability and tank geometry can often be improved

4 Settleability Can be Improved Analysis of the biological populations is crucial Selectors encourage populations that settle well Depends on: Configuration SRT

5 Geometry Can Be Improved Old Geometry New Geometry

6 Why do Modeling? Thirty years of development using computational fluid dynamics (CFD) for analysis of sedimentation has proven that CFD can 1) Capture the main features of clarifier behavior 2) Model detailed features of hydraulic behavior 3) Efficiently predict performance of novel designs 4) Be more cost effective than full-scale prototypes

7 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)

8 State Point Analysis (Clariflux ) Developed by Vesilind. Implemented by Carollo Engineers (among others) Solves solids flux equations based on measured settling velocity coefficients (or SVI) Calculates state point for steady state operation SOR Line MLSS Line RAS line

9 One-dimensional (1D) Dynamic Models Developed by Stenstrom, Tracy, Vitasovic, Takacs, Sedtank, Biowin Simulate average upward velocity versus downward settling velocity Solved dynamically Layered model Used for long-term dynamic simulations

10 Two-dimensional (2D) Models Incorporate 2D tank hydraulics Boundary effects Turbulence Density effects Used for geometric optimization of symmetrical elements Proprietary codes or public domain programs

11 Three-dimensional (3D) Models Resolution and detail limited only by computing power Very detailed grids can be used to capture geometric features as small as several inches Crucial for modeling of non-symmetric features Implemented in proprietary code or commercial CFD packages with special add-ons

12 Each Type of Model Has its Place State Point Analysis Steady State Capacity Analysis 1D Dynamic Models Long-term Dynamic simulations 2D Models Simple design evaluations 3D Models For design problems that are not simple

13 Examples of 3D Problems Analysis of inlet conditions Almost all inlet flow is three-dimensional Analysis of tank shapes that are not simple Square radial flow tanks Circular peripheral feed tanks Circular or square peripheral feed and withdrawal tanks Tanks with eccentric baffles or effluent troughs

14 Case Studies Center feed square radial flow Center feed circular radial flow Square peripheral feed / withdrawal Rectangular lamella clarifiers

15 Center-feed, Radial-flow Square Clarifiers Case study for use of models State Point Analysis 2D Model 3D Model

16 State Point Comparison 33% RAS 66% RAS

17 2D Model UNO Model Developed by J. A. McCorquodale and associates at the University of New Orleans for EPA Two-dimensional model based on Vorticity / stream function model (2D only) Turbulent hydraulics Radial flow coordinates (axisymmetric) Solids transport Composite settling model Flocculation

18 2D Model Results Test Calibration Results Field UNO Model

19 2D Model Results Summary of Model Runs

20 3D Model (Zhou CFD) Developed by Siping Zhou and J. A. McCorquodale Three-dimensional solution based on Control volume model Turbulent hydraulics Generalized coordinates Solids settling Solids transport No flocculation or compression modeling

21 Inlet Comparison Existing Multilayer Energy Dissipating Inlet Colum (MEDIC)

22 3D Model Results Summary of Model Runs Operational Conditions Clarifier Performance Theoretical Clarifier SOR RAS Ratio MLSS RAS Predicted Predicted Clarifier Configuration Flow (mgd) (gpd/sf) (%) (mg/l) SVI (ml/g) (mg/l) ESS (mg/l) RAS (mg/l) Test Calibration , , ,000 Existing Clarifier , , ,821 Existing Clarifier , , ,773 Existing Clarifier , , ,772 Perimeter Effluent Weir and Baffle Existing Clarifier , , ,183 Existing Clarifier , , ,234 Existing Clarifier , , ,167 3-Layer MEDIC , , ,943 Middle Feed Well 3-Layer MEDIC + Middle Feed Well , , ,025 3-Layer MEDIC + Middle Feed Well 3-Layer MEDIC + Middle Feed Well 3-Layer MEDIC + Middle Feed Well 3-Layer MEDIC + Middle Feed Well , , , , , , , , , , , ,015

23 3D Model Results Inlet Improvements (SVI 110) a) Inlet jets entering clarifier [2.45 ft/s (73.4 cm/s)] c) Dispersed sludge blanket 1) Existing Clarifier b) Strong turbulence induced by intensive clarifier influent flow a) Inlet jets entering MEDIC (2.45 ft/s) and ones entering clarifier [0.13 ft/s (3.88 cm/s)] c) Dispersed sludge blanket 2) Optimized Clarifier b) Significantly damped turbulence due to substantially reduced clarifier influent flow intensity Figure 16 Performance comparison between the existing and optimized clarifiers under a peak flow condition (Clarifier flow = 4.5 MGD, RAS = 33.3%, MLSS = 3250 mg/l and SVI = 110)

24 3D Model Results Inlet Improvements (SVI 190) 1) Existing Clarifier Significant solids inventory due to poor SVI combined with limited RAS capacity 2) Optimized Clarifier Figure 20 Performance comparison between the existing and optimized clarifiers under a poor SVI combined with a low RAS of 33.3% (Clarifier flow = 3.5 MGD, MLSS = 3250 mg/l and SVI = 190)

25 Conclusions from 3D Modeling Optimized inlet would allow increase of safe operating flow from 3.5 to 4.5 mgd per clarifier with good SVI (110 ml/g) (30% Increase) Optimized inlet would allow safe operation at 3.5 mgd per clarifier with poor SVI (190 ml/g) compared to 2.5 mgd with existing inlet (40% increase)

26 Center-feed Circular Radial Flow Tank Comparison of Tangential to Puzzled Inlets Tangential Inlet Puzzled Inlet

27 Carollo Fluent UDF Model 2D or 3D Sophisticated grid generation and visualization tools Choice of turbulence models User defined functions (UDF) to implement Solids transport Density coupling Solids settling velocity

28 Calibration of 2D Model to Field Test Field Test Model

29 Comparison of Tangential to Puzzled Inlets Inlet Velocities Tangential Inlet Puzzled Inlet

30 Comparison of Tangential to Puzzled Inlets (3D Model) Inlet Velocity Intensity Tangential Inlet Puzzled Inlet

31 Optimization of Inlet Inlet Geometry (3D Model) Existing Inlet Optimized Inlet

32 Optimization of Inlet Solids and Velocity Profiles

33 Optimization of Inlet Comparison of Inlet Velocity and Energy Existing Inlet Optimized Inlet

34 Square Peripheral Feed / Withdrawal Tank Overall Geometry and Grid

35 Square Peripheral Feed / Withdrawal Overall Solids Profiles

36 Square Peripheral Feed / Withdrawal Velocity and Solids Profiles

37 Square Peripheral Feed / Withdrawal Sludge Blanket Level Topography

38 Rectangular Lamella Clarifier Carollo Fluent UDF Model 2D and 3D flow in and around the lamella plate modules Activated sludge clarifiers Two different settling models: Vesilind Vesilind with Boycott in lamella zone

39 Detailed Grid

40 Vesilind Model of Low SVI Condition

41 Vesilind Model with Moderate SVI

42 Vesilind Model with No Lamellas

43 Vesilind/Boycott Model of Moderate SVI

44 Vesilind Model of Inlet Baffle

45 Conclusions CFD models are well developed for evaluation of sedimentation tanks Each level of model has its place Several important problems can only be adequately evaluated using 3D models Inlet design Radial flow / square shape Non-symmetrical elements Commercial 3D CFD codes can be productively used but only with custom add-ons

46 Questions? Randal W. Samstag Ed A. Wicklein