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McGill Ozone Contactor Design Project

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McGill Ozone Contactor Design Project

  1. 1. Analysis of an Ozone Contactor Tank Presented by: Nadera Nawabi, Henk Williams & Nick Mead-Fox
  2. 2.  Nadera Nawabi – Data Analyst  Henk Williams – CFD Modeller  Nick Mead-Fox – CFD Modeller Meet our team…
  3. 3.  Determine geometry of the ozone contactor tank at the San Andreas Water Treatment Plant (SAWTP)  Develop a computational fluid dynamics (CFD) model of the ozone contactor to determine flow characteristics  Compare CFD simulations to the tracer test results obtained from the SAWTP report Project Overview
  4. 4. Scope  Develop a 3-D 2-phase model (air & water) that predicts the hydraulic processes of an ozone contactor Objective  Maximize ozone contact time in SAWTP ozone contactors  Qualitative: analyze “dead spots” in velocity contours before and after the addition of gas bubblers  Quantitative: use particle tracking to calculate the average retention time of particles in the system Scope & Objective
  5. 5.  Ozone has been used for water treatments for almost 100 years  It is a very strong oxidizing agent and a powerful disinfectant  Ozone is very effective against almost all microorganisms Ozone Disinfection
  6. 6. Source: (Rakness, 2005) Giardia and Virus Removal and Inactivation Requirements
  7. 7. Source: (Camp Dresser & McKee, 1994) CT concept was developed by EPA to quantify disinfection effectiveness CT Requirements for Various Disinfectants
  8. 8. Contactor Flow (mgd) Total Air Flow (scfm) Simulated Ozone Dose (mg/l) T10 /T HDT (mins) T10 (mins) 20.00 0 0 0.52 10.38 5.35 29.40 0 0 0.61 7.07 4.31 45.00 0 0 0.66 4.62 3.05 20.00 120 1.4 0.66 10.38 6.85 29.40 120 1.0 0.69 7.07 4.88 45.00 120 0.6 0.71 4.62 3.28 20.00 350 4.0 0.68 10.38 7.06 29.40 350 2.8 0.78 7.07 5.51 45.00 350 1.8 0.80 4.62 3.69 Tracer Results from Report
  9. 9.  ‘San Francisco Water Department: San Andreas Water Treatment Plant Ozone Contactor Tracer Tests’ → used to determine the dimensions of the tank and compare simulation results Source of Data
  10. 10.  Reducing dead zone regions (areas with very low velocity) in the ozone contactor tank will improve the disinfection efficiency of the contactor Source: (University of Waterloo, 2014) Why improve hydraulics of an ozone contactor?
  11. 11. Hence, a more purified, safe and clean water! Source: (Water Liberty Research Center)
  12. 12. Learn Software •Complete ANSYS Fluent tutorials 2D, 1 Phase Prototype •Achieve proper flow through system – water only •Extract velocity profile and learning about basic boundary conditions Geometry of Tank •Determine dimensions of ozone contactor using fluid flow relationships and basic geometry 2D, 2 Phase Tank Prototype •Visualize flow in filled container 3D, 2 Phase Tank Prototype •Replicate 2D results •Experiment with bubblers – full tank bottom vs discrete inlet- mass balance 3D, 2 Phase Tank Real Design •Remove air pocket include ozone bubbler •Model inlets and outlets •Achieve steady state •Extract particle data, and velocity/phase animations Design Approach
  13. 13. Timeline Dates Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8 Week 9 Week 10 Week 11 Week 12 Week 13 Week 14 Tasks Design Team Formation Assignment of Project Meet with Advisor Design Brief Team Presentation Build Simple 2D Figure in Ansys Build 1-Phase of Model Build Simple 2D structure with 2 Phase Build 2D of Model with 2 Phase Build 3D Model with 2 Phase Mid-Term Presentation Remove Air Pocket in 3D Model and Include Ozone Bubbler Model Inlets and Outlets Achieve Steady State Extract Particle Data and Velocity/Phase Animations Final Presentation Written Report
  14. 14. CFD Theory Numerical Models and Considerations
  15. 15. Continuity Equations  1st order upwind scheme - Finite Differencing Scheme → Tracks changes by using the mesh element directly upstream of the point being calculated, solves continuity equations relatively stable and has good convergence properties, loses some accuracy due to numerical diffusion  Other schemes: QUICK, 2nd order, WENO more accurate, but greatly increases computation time of simulatins and increases divergence probability
  16. 16.  Continuity equations being solved for mass, momentum, and energy  Energy is the critical parameter in a turbulent system, requiring a more complicated energy equation
  17. 17. Turbulence Models Two primary models were used: k-epsilon  Tracks changes in k: the turbulent kinetic energy  Tracks changes in e: the rate of energy dissipation, or change in kinetic energy (turbulence)  Relatively stable and converges easily  Inaccurate when simulating rotating flow, or flow with strong curvature → Transferred to omega once had working models in k-epsilon omega - w  specific energy dissipation  Increases accuracy rotating flow, but is less stable, more dependent on initial conditions.
  18. 18. Turbulence Model: k-omega k: → change with time, change with distance (convection) = velocity change with (shear and viscous elements), current energy, change with dissipation w: similar to above then where µt is turbulent viscosity- actual term used to fit continuity
  19. 19. Prototypes with ANSYS Fluent Modelling and Data Presetation
  20. 20. The Importance of Pipe Prototypes Refining Data Presentation  Steady vs. Transient Modelling  Velocity Profiling  Phase Profiling  Uniformity Indices  Residence Time Boundary Condition Properties Multiphase Modelling
  21. 21. The Importance of Pipe Prototypes Identifying Boundary Condition Properties Inlet  Pressure Inlets  Velocity Inlets  Mass Flow Inlets  Inlet Vent  Intake-Fan Outlet  Pressure outlets  Outflow  Outlet Vents  Degassers  Velocity Outlets  Exhaust Fan
  22. 22. Multiphase Models - VOF For two immiscible fluids; uses a single set of momentum equations and the volume fraction in each cell is tracked. Applications  Stratified Flows  Free Surface Flows  Filling, Sloshing  Large Bubbles  Tracking Interfaces
  23. 23. Multiphase Models - Mixture For two or more phases; phases treated as interpenetrating continua. Solves for the mixture momentum equations, prescribes relative velocities to dispersed phases. Applications  Low Load Particle-laden Flows  Bubbly Flows  Sedimentation  Cyclone Separators
  24. 24. Multiphase Models - Eulerian Eulerian - Most complex multiphase model. Solves a set of n momentum and continuity equations for each phase. Applications  Bubble columns  Risers  Particle suspension  Fluidized beds
  25. 25. Ensuring Model Convergence  Incompatible Boundary Conditions  Turbulence Errors  Boundary Backflow  Vertical Outlets  Mass Balance
  26. 26. Multiphase Mass Balance Tracer 1: Qw = 45 MGD = 1.972 m^3/s, Qa = 350 SCFM = Inlet Area = 1.52 m^2, inlet velocity = 0.6485526 m/s, Q = 0.9858m^3/s Outlet Area = 3.23 m^2, volume fraction = 0.25, effective outlet area = 2.42 m^2 Outlet Flow = Q = 0.9858m^3/s , outlet velocity = -0.4069 Air vent Area = 14.6612, Qair = 350 SCFM = 0.1652 m^3/s, Vair = 4 m/s Effective area = Q/v = 0.0413 Volume fraction = 0.0413/14.6612 = 0.002817
  27. 27. Diffuser Modelling  Velocity, Area, and Flow: The problems with surface outlets  Square Inlets: Not representative  Striped Inlets: Successful, but can’t be placed adjacent to walls  Volume fraction more appropriate and versatile than re-modelling area changes.  In all Cases: Inlet Area >>> Mesh Size
  28. 28. The Final Product Particle Pathlines: 350 SCFM
  29. 29. Final Contactor Geometry Depth = 6.55m Length = 25.6 m Width = 3.81 m
  30. 30. Final Mesh
  31. 31. Phase Modelling
  32. 32. Velocity Profiling
  33. 33. Final Phase Distribution
  34. 34. Trace 1: Design Flows Inlet Area = 1.52 m^2, inlet velocity = 0.6485526 m/s, Q = 0.9858m^3/s Outlet Area = 3.23 m^2, volume fraction = 0.25, effective outlet area = 2.42 m^2 Q = 0.9858m^3/s , outlet velocity = -0.4069 Air vent Area = 14.6612, Qair = 350 SCFM = 0.1652 m^3/s, Vair = 4 m/s Effective area = Q/v = 0.0413 volume fraction = 0.0413/14.6612 = 0.002817 Tracer 1: Qw = 45 MGD = 1.972 m^3/s, Qa = 350 SCFM = 0.16518
  35. 35. Air Flow vs. Phase Profiles Qair = 350 SCFM Qair = 700 SCFM Qair = 1400 SCFM t = 1000 Seconds
  36. 36. Pathlines of Residence Time Qair = 700 SCFM Qair = 1400 SCFM
  37. 37. Tracer Tests and Residence Times Scenario Water inlet velocity (m/s) Ozone Outlet Area (m^2) Ozone injection velocity (m/s) Average residence time (s) Tracer Residence Time Control 0.6485 0 0 3.95 3.05 Trace 1 (350 SCFM) 0.6485 0.0413 4 9.3 3.69 Air 2 (700 SCFM) 0.6485 0.0826 4 11 NA
  38. 38. Air Flow vs Velocity Profiles   Scale: 0 - 1.24 m/s Scale: 0 – 4m/s  Qair = 0 SCFM  Qair = 350 SCFM  Qair = 700 SCFM
  39. 39. Qualitative Conclusions  The relationship between air flow, residence time and disinfection capacity is nonlinear and poorly understood.  Air flows required for disinfection and appropriate residence time are too low to induce turbulence and decrease the presence of hydraulic dead zones within the contactor.  The disinfection process is far from homogenous.  The calculation of CT-values has a significant margin of error. → Calculated vs. “True” contact times. → Any amount of air flow increases contactor residence time, but does not necessarily improve the contactors disinfection capacity.
  40. 40. A Reference for Further Analysis  Ozone contactor performance optimization.  Simulating disinfection scenarios: Injector surface area and velocity, flow composition, interior surface effects, and gas extraction methods.  Dual media injectors - liquid water injection with high ozone concentrations to mix water and eliminate dead zones.  The chemistry of ozone disinfection by incorporating CFD-based CT-calculations
  41. 41. Acknowledgements  Paul Rodrigue, PE Environmental Engineer at CDM Smith  Shawn McCollum, McGill IT Services
  42. 42. Works Cited  Stenmark, E. (2013, November 1). On Multiphase Flow Models in ANSYS CFD Software. Retrieved November 27, 2014, from http://publications.lib.chalmers.se/records/fulltext/182902/182902.pdf  24.4.1. Discrete Phase Boundary Condition Types. (n.d.). Retrieved November 27, 2014, from http://www.arc.vt.edu/ansys_help/flu_ug/flu_ug_sec_discrete_bctypes.html  24.4.1. Discrete Phase Boundary Condition Types. (n.d.). Retrieved November 27, 2014, from http://www.arc.vt.edu/ansys_help/flu_ug/flu_ug_sec_discrete_bctypes.html  24.4.1. Discrete Phase Boundary Condition Types. (n.d.). Retrieved November 27, 2014, from http://www.arc.vt.edu/ansys_help/flu_ug/flu_ug_sec_discrete_bctypes.html  Ma, J., & Srinivasa, M. (2008, January 1). Particulate modeling in ANSYS CFD. Retrieved November 27, 2014, from http://www.ansys.com/staticassets/ANSYS/staticassets/resourcelibrary/confpaper/2008-Int-ANSYS-Conf-particulate-modeling-in-ansys-cfd.pdf  25.3.2. Modeling Open Channel Flows. (n.d.). Retrieved November 27, 2014, from http://www.arc.vt.edu/ansys_help/flu_ug/flu_  24.4.1. Discrete Phase Boundary Condition Types. (n.d.). Retrieved November 27, 2014, from http://www.arc.vt.edu/ansys_help/flu_ug/flu_ug_sec_discrete_bctypes.html  17.2.1. Approaches to Multiphase Modeling. (n.d.). Retrieved November 27, 2014, from http://www.arc.vt.edu/ansys_help/flu_th/flu_th_sec_mphase_approaches.html  Rakness, K. L., Ozone in Drinking Water Treatment - Process Design, Operation, and Optimization (1st Edition). American Water Works Association (AWWA): 2005.  Camp Dresser & McKee. San Francisco Water Department: San Andreas Water Treatment Plant Ozone Contactor Tracer Tests. 1994.  WaterLiberty.com - Ancient Water Purification System - Black Mica. (2013, January 1). Retrieved November 27, 2014, from http://www.waterliberty.com/presentation-dd.php  Full-Scale Water Treatment Facilities. (2014, January 1). Retrieved November 27, 2014, from http://www.civil.uwaterloo.ca/watertreatment/facilities/full.asp
  43. 43. THANK YOU! QUESTIONS?

Hinweis der Redaktion

  • C is usually defined as the ozone residual concentration at the outlet of a chamber and T is the residence time of microorganisms in the chamber
  • T10 is the residence time of the first 10% of the water to travel from the contactor inlet to outlet, to ensure a minimum exposure time for 90% of the water and microorganisms entering a disinfection contactor.
  • http://www.civil.uwaterloo.ca/watertreatment/facilities/full.asp
  • http://www.waterliberty.com/presentation-dd.php

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