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Use of Wind Tunnel Refinements in the Dispersion Modeling Analysis of the Alaska LNG Gas Treatment Plant

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The proposed Alaska LNG GTP project includes the construction of a natural gas treatment plant on the Alaska North Slope. The Gas Treatment Plant (GTP) is proposed to be located on the west coast of Prudhoe Bay and would treat natural gas produced on the North Slope.
Initial dispersion modeling of the Alaska LNG Gas Treatment Plant (GTP) found results inconsistent with local and regional measurements when evaluating compliance with the 1-hour NO2 National Ambient Air Quality Standard (NAAQS) due in part to two adjacent nearby sources. These existing sources include the Central Gas Facility (CGF) and Central Compression Plant (CCP) located immediately east of the GTP. The prevailing winds at the site are east-northeast and west-southwest which align with the arrangement of the facilities.
The building downwash inputs generated by the Building Profile Input Program for PRIME (BPIPPRM) were evaluated for the CGF and CCP facilities. This analysis confirmed that the building dimension inputs for numerous wind directions were outside of the tested theory used to develop the building downwash algorithms in AERMOD. Previous studies2,8,11,12,13 suggest that AERMOD predictions are biased to overstate downwash effects for certain building input ratios.
Wind tunnel determined equivalent building dimensions (EBD) were conducted for the most critical stacks and wind directions to refine AERMOD-derived predicted concentrations. The current paper covers the EBD method used to refine the building inputs for the CGF and CCP facilities. The regulatory process and benefits from this physical modeling method is also discussed.

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Use of Wind Tunnel Refinements in the Dispersion Modeling Analysis of the Alaska LNG Gas Treatment Plant

  1. 1. Sergio Guerra, PhD | GHD Ron Petersen, PhD, CCM | CPP Jim Pfeiffer | BP/Alaska Gasline Development Corporation June 28, 2018 Use of Wind Tunnel Refinements in the Dispersion Modeling Analysis of the Alaska LNG Gas Treatment Plant A&WMA's 111th Annual Conference & Exhibition, Hartford, CT
  2. 2. Abstract The proposed Alaska LNG GTP project includes the construction of a natural gas treatment plant on the Alaska North Slope. The Gas Treatment Plant (GTP) is proposed to be located on the west coast of Prudhoe Bay and would treat natural gas produced on the North Slope. Initial dispersion modeling of the Alaska LNG Gas Treatment Plant (GTP) found results inconsistent with local and regional measurements when evaluating compliance with the 1-hour NO2 National Ambient Air Quality Standard (NAAQS) due in part to two adjacent nearby sources. These existing sources include the Central Gas Facility (CGF) and Central Compression Plant (CCP) located immediately east of the GTP. The prevailing winds at the site are east- northeast and west-southwest which align with the arrangement of the facilities. The building downwash inputs generated by the Building Profile Input Program for PRIME (BPIPPRM) were evaluated for the CGF and CCP facilities. This analysis confirmed that the building dimension inputs for numerous wind directions were outside of the tested theory used to develop the building downwash algorithms in AERMOD. Previous studies2,8,11,12,13 suggest that AERMOD predictions are biased to overstate downwash effects for certain building input ratios. Wind tunnel determined equivalent building dimensions (EBD) were conducted for the most critical stacks and wind directions to refine AERMOD-derived predicted concentrations. The current paper covers the EBD method used to refine the building inputs for the CGF and CCP facilities. The regulatory process and benefits from this physical modeling method is also discussed. Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  3. 3. Outline 1. Introduction 2. WT Study 3. Regulatory Review Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  4. 4. Alaska LNG Project From: https://agdc.us/alaskas-lng-project/project-overview/ Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  5. 5. Locations of the existing CCP and CGF facilities with respect to the proposed GTP facilities Figure 1-1 from the Alaska LNG 7 Oct 2016 air modeling report.
  6. 6. Initial Screening Assessment The following ratios are analyzed: 1. Hs/Hb ratios below 3.5 2. Width/height ratio (Wb/Hb) or the length/height ratio (Lb/Hb) and compare to ratio of 3.5 3. Wb/Hb and Lb/Hb ratios below 3.5 can also produce overpredictions Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  7. 7. Aerial views of Central Gas Facility (left) and the Central Compression Plant (right) at Prudhoe Bay, Alaska Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  8. 8. Justification for Wind Tunnel Refinements • Used for over two decades in regulatory permit modeling (ISC and AERMOD). • Source characterization technique used in lieu of BPIP, not subject to alternative modeling requirements from Section 3.2.2 of Appendix W. • The theoretical basis derived from the basic equations of motion in dimensionless notation. • Uses established methodology in EPA’s Fluid Modeling Guideline. Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  9. 9. Wind Tunnel vs BPIP-Derived Building Dimensions • BPIPPRM uses simplifications to determine bdg dimensions used by PRIME to calculate downwash effects. • Wind tunnel-derived building dimensions can be used to refine the traditional way of obtaining building dimension inputs with BPIPPRM. Figure created in BREEZE® Downwash Analyst BREEZE is a registered trademark of Trinity Consultants, Inc. Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  10. 10. Model Design and Construction Obtain source/site data Specify test wind speeds and directions Compute model operating conditions Construct scale model
  11. 11. CGF facility looking northeast and corresponding photograph of 3D printed model Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  12. 12. CCP facility looking northeast and corresponding photograph of 3D printed model Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  13. 13. Identify Wind Tunnel Determined EBD that Match Dispersion with Site Structures Present Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  14. 14. Acceptance Criteria Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  15. 15. Regulatory Review • The ADEC requested the technical assistance of the Environmental Protection Agency Region 10’s Office of Air and Waste technical staff (EPA Region 10) in reviewing this project. • Review from EPA Region 10: • (1) found that the use of EBDs was justified due to the complex building arrangements of the nearby sources evaluated (CGF and CCP); • (2) found that the methodology used in the study was in compliance with current EPA guidance and recommendations for EBD studies and wind tunnel modeling; • (3) recommended that ADEC allow the use of the EBDs for the GTP project as presented in the final EBD report; and • (4) identified possible issues when the lateral displacement of a stack from the building center (YBADJ) is significant. Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  16. 16. Regulatory Review • EPA R10 suggested a criterion where the use of the EBD method is most appropriate when applied to Wb/Hb ratios that are outside the limits specified in Equation 2 (less than 0.5 and more than 8.0). However, cases that fall within the range of Equation 2 may still qualify for an EBD analysis, but must be evaluated on a case-by-case basis. • EPA R10 was concerned that using a different YBADJ from BPIPPRM could create a realignment of near source plumes that could misrepresent the concentration field and may prevent plume overlapping. Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  17. 17. Example of Plume Distortion due to YBADJ Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  18. 18. PRIME Cavity and Wake Sources Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  19. 19. Cavity Plume Unrealistic Concentration Amplification Issue Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  20. 20. Conclusions • Downwash effects were evaluated for the two adjacent facilities (CGF and CCP) next to the Alaska LNG GTP. • This case study is unique because of the highly complex and elongated arrangement of the two facilities. • The EBD refinements obtained from the wind tunnel studies were reviewed and approved by the regulatory agency. The predicted concentrations for key receptors were significantly reduced when running AERMOD with the building input refinements obtained from the wind tunnel study. • As a result, AK LNG GTP is able to demonstrate that operation of these nearby facilities will not cause an exceedance of the ambient air quality standards. Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant
  21. 21. Sergio A. Guerra, PhD Ron Petersen, PhD, CCM sergio.guerra@ghd.com rpetersen@cppwind.com Mobile: + 612 584 9595 Mobile:+1 970 690 1344 Questions?
  22. 22. www.ghd.com Use of Wind Tunnel Refinements in the Analysis of the Alaska LNG Gas Treatment Plant

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