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Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions

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Fume re-entry is an important concern for many types of facilities such as hospitals and laboratories that emit pathogens and toxic chemicals that may impact public health by being re-entrained into the building though nearby air intakes. Numerical methods can be used to evaluate dispersion of pollutants from stacks at sensitive receptors. However, numerical methods have limitations and simplifications that can significantly affect its predictions. An alternate way of analyzing stack re-entrainment is with physical modeling in a wind tunnel. In such a study, a scale model that accounts for buildings, topography, and vegetation is used with planned and alternate stack designs to determine the toxic emission impacts on air intakes and other sensitive locations. In a wind tunnel study different stack designs and possible mitigation options can be evaluated. This method is superior to numerical methods (e.g., dispersion models) because it accounts for the immediate structures, topography, and vegetation that is often ignored or oversimplified in numerical methods.
This presentation will show a hypothetical case study evaluating a site with toxic air emissions using AERMOD and physical modeling.

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Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions

  1. 1. Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions Pacific Northwest International Section of the A&WMA 2017 Annual Conference Boise, ID Sergio A. Guerra, PhD Ron Petersen, PhD, CCM November 2, 2017
  2. 2. Outline 1. Background on re-entrainment studies 2. Two case studies comparing predicted impacts from using: – AERMOD – Wind tunnel testing 3. Benefits of using WT testing instead of AERMOD Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions2
  3. 3. Public Concern Business Weekly - May 2, 1988 3
  4. 4. Health & Liability Chicago Daily Herald - April 17, 1998 • Study finds that rare cancer in Amoco employees is probably work related • Incidence in 503 wing was four times that of general population • Incidence of the second and third floors was seven times that of general population • The incidence of such tumors on the rest of Amoco’s campus was actually lower than that of the general population Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions4
  5. 5. • Chloroform fumes from capped stacks • Fumes reenter building roof top units • High incidence of miscarriages • Litigation Petrochem lab Capped Stack Air Intake Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions5
  6. 6. Air quality - why the concern in labs? Accidental Spill Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions6
  7. 7. Why the concern? Fume Re-entry Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions7
  8. 8. Design Guidelines http://www.i2sl.org/documents/toolkit/bp_modeling_508.pdf Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions8
  9. 9. ( ) 0* ** * * = ∂ ∂ + ∂ ∂ i i x U t ρρ )( 2 */*/ *** *2 3 ** 2* * ** * * * * * ji kkk i oo o i oo ooo i kjijk o oo j i j i UU xxx U LU v gT UT gLT x U U L x U U t U −+ ∂ ∂ + ∂∂ ∂       +∆     ∆ − ∂ ∂ − =Ω∈      Ω − ∂ ∂ + ∂ ∂ δ ρ φ ρ         ∆       +− ∂ ∂ + ∂∂ ∂             = ∂ ∂ + ∂ ∂ opo o oo o i ikkoo o ooPo o i i TC U LU v UT xxx T UL v vC K x TU t T )( )( *//* *** *2 * ** * * Wind Tunnel Modeling Starts With the Basic Equations of Motion (Navier Stokes Equations) Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions9
  10. 10. • Used to validate CFD and analytical methods • Compares well with the atmosphere • Analogous to a field study • Controlled meteorological conditions • Results sensitive to site specific features • Accurate for near-field applications Wind Tunnel Modeling Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions10
  11. 11. Accuracy From EPA Fluid Modeling Guideline, 1981 • Basic equations are solved by simulating the flow at a reduced scale, then measuring the desired quantity • An analog computer with near infinitesimal resolution and near infinite memory • If a mathematical model cannot simulate the results of an idealized laboratory experiment, how can it possibly be applicable to the atmosphere Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions11
  12. 12. 12 Compliance? BPIPBuilding Geometry Meteorological Data Terrain Data AERMET AERMAP Operating Parameters AERMOD OtherInputs Building Inputs AERMOD Modeling Approach Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions
  13. 13. Building Downwash 13 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions Image from Lakes Environmental Software
  14. 14. Building Profile Input Program (BPIP) Figure created in BREEZE ® Downwash Analyst BREEZE is a registered Trademark of Trinity Consultants, Inc. 14 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions
  15. 15. 15 PRIME AERMOD’s Building Downwash Algorithm • Used EPA wind tunnel data base and past literature • Developed analytical equations for cavity height, reattachment, streamline angle, wind speed and turbulence • Developed for specific building dimensions • When buildings outside of these dimensions, theory falls apart Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions
  16. 16. Evaluation Investigate the effect on nearby air intakes from: 1. Combustion sources at a hospital and 2. A laboratory stack at a university Evaluated with: – AERMOD v16216r (screening mode) – Wind tunnel testing Compared to normalized concentration thresholds for: – National Ambient Air Quality Standards – The National Institute of Occupational Safety and Health recommended exposure limit for NO2. – Occupational Safety and Health Administration permissible exposure limit for NO2. Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions16
  17. 17. Case Study 1 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions17 Boiler Stack Diesel Engine Stack Co-gen Stack Rec1 Rec4 Rec18 Rec7
  18. 18. Model of Site Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions18
  19. 19. Stack Parameters Source Q (g/s) Hs (m) T (K) Vs (m/s) D (m) Boiler 1 28.45 414.8 12.29 0.60 Diesel Generator 1 28.45 414.8 31.67 0.60 Co-Gen 1 28.35 599.8 22.15 0.76 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions19
  20. 20. Boiler Stack Comparison Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions20 Boiler Stack Rec1 Rec4 Receptor AERMODv16216r (µg/m3 / g/s) Wind Tunnel Testing (µg/m3 / g/s) AERMOD/ WT Factor Receptor 1 2066 560 3.7 Receptor 4 1608 508 3.2 Health Thresholds µg/m3 / g/s NO2 NAAQS 540 NIOSH 5169 OSHA 25,843
  21. 21. Boiler Stack: Receptor 1 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions21
  22. 22. Boiler Stack: Receptor 1 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions22
  23. 23. Boiler Stack: Receptor 4 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions23
  24. 24. Boiler Stack: Receptor 4 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions24
  25. 25. Diesel Generator Comparison Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions25 Diesel Engine Stack Rec4 Rec7 Receptor AERMODv16216r (µg/m3 / g/s) Wind Tunnel Testing (µg/m3 / g/s) AERMOD/WT Factor Receptor 4 1159 204 5.7 Receptor 7 1186 242 4.9 Health Thresholds µg/m3 / g/s NO2 NAAQS 38 NIOSH 363 OSHA 1,817
  26. 26. Diesel Generator: Receptor 4 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions26
  27. 27. Diesel Generator: Receptor 4 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions27
  28. 28. Diesel Generator: Receptor 7 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions28
  29. 29. Diesel Generator: Receptor 7 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions29
  30. 30. Co-Gen Stack Comparison Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions30 Co-gen Stack Rec1 Rec18 Receptor AERMODv16216r (µg/m3 / g/s) Wind Tunnel Testing (µg/m3 / g/s) AERMOD/WT Factor Receptor 1 1328 483 2.7 Receptor 18 665 244 2.8 Health Thresholds µg/m3 / g/s NO2 NAAQS 34 NIOSH 326 OSHA 1,632 Odor (1:4000 dilution) 25
  31. 31. Co-Gen Stack: Receptor 1 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions31
  32. 32. Co-Gen Stack: Receptor 1 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions32
  33. 33. Co-Gen Stack: Receptor 18 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions33
  34. 34. Co-Gen Stack: Receptor 18 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions34
  35. 35. Case Study 2 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions35 Laboratory Fume Hood Stack Rec1
  36. 36. Model of Site Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions36 Source Q (g/s) Hs (m) T (K) Vs (m/s) D (m) Fume Hood Exhaust 1 20.5 294.3 20.33 0.77
  37. 37. Lab Stack Comparison Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions37 Laboratory Fume Hood Stack Rec1 Receptor AERMODv16216r (µg/m3 / g/s) Wind Tunnel Testing (µg/m3 / g/s) AERMOD/WT Factor Receptor 1 267 321 0.8 Health Thresholds µg/m3 / g/s Phosphine 7803-51-2 264 Ethylamine 75-04-7 298 Carbon disulfide 75-15-0 306 Methyl Hydrazine 60-34-4 320
  38. 38. Lab Stack: Receptor 1 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions38
  39. 39. Lab Stack: Receptor 1 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions39
  40. 40. Conclusions • Numerical methods like AERMOD have limitations when used in re-entrainment studies • Building created by BPIP and used by AERMOD is not actual building • BPIP’s artificial building may over or under estimate concentrations when used by AERMOD • Effects from building structures and nearby terrain are best characterized with a wind tunnel study Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions40
  41. 41. Sergio A. Guerra, PhD Ron Petersen, PhD, CCM sguerra@cppwind.com rpetersen@cppwind.com Mobile: + 612 584 9595 Mobile:+1 970 690 1344 wwww.SergioAGuerra.com CPP, Inc. 2400 Midpoint Drive, Suite 190 Fort Collins, CO 80525 + 970 221 3371 www.cppwind.com @CPPWindExperts Questions? 41 Using Physical Modeling to Evaluate Re-entrainment of Stack Emissions

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