www.cppwind.com www.cppwind.com Strategies to Deal with Monitored Exceedances When AERMOD Can’t be Used Ron Petersen, PhD, CCM Sergio Guerra, PhD Cell: 970 690 1344 Cell: 612 584 9595 [email protected][email protected]CPP, Inc. 2400 Midpoint Drive, Suite 190 Fort Collins, CO 80525 www.cppwind.com @CPPWindExperts
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Strategies to deal with monitored exceedances when AERMOD can’t be used
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Strategies to Deal with Monitored Exceedances When AERMOD Can’t be Used
Overview • Monitored SO2 concentrations exceed the new 1-hour SO2
NAAQS at nearby Water Tower Monitor (WTM)
• Monitored design concentration is 151 ppb (2009-2011) relative to 75 ppb NAAQS; background is about 8 ppb
• For attainment, maximum hourly SO2 concentration needs to be reduced by at least 55%
• AERMOD is showing compliance at the monitoring station with predicted concentrations a factor of two lower than monitored
• Rhinelander Mill Boiler Stack S09 has been identified as the primary contributor
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Rhinelander Mill and Monitor
Looking Northeast SO2 Monitor
Stack S09
Corner Vortex Problem
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Rhinelander Mill and Critical Features
Cyclone Boiler(S09)
Stack Height
63 m
207 ft
Boiler
Building
38 m
125 ft
Looking South
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Monitored SO2 Concentrations for 2009 Highest concentrations for wind speeds around 5 m/s for 200 degree wind direction (toward Water Tower monitor)
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AERMOD Corner Vortex Issue
• Current building wake equations do not account for corner vortex
• Corner vortex causes higher concentrations than currently predicted in AERMOD due to increased downdraft and plume rise suppression
• AERMOD and PRIME downwash model do not even have input for approach flow relative to building corners – model assumes flow toward broad side of buildings and is totally oblivious to corner effects
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Corner Vortex Issues – EPA Research
Note increased effect for 45º approach flow
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Possible Solutions • Reduce emission rate by 50% based on monitored
results >> not a good solution
• Extend stack to formula GEP stack height of 75 m plus emission control: how do you determine since AERMOD doesn’t work?
• Extend stack to actual GEP stack height plus emission control if needed: how to determine since AERMOD doesn’t work?
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Issues for Consideration
• Two problems for consideration:
– The need to find a tool other than AERMOD to correlate reductions in SO2 emissions from the Mill to SO2 concentrations at the Water Tower monitor to show compliance with the 1-hour SO2 standard, and
– The need to develop a site-specific GEP stack height given the topography of the Mill and monitor and the excessive downwash caused by the corner vortex.
• Fluid modeling in a wind tunnel using HYWINMOD allows for correlation of mill emissions to monitor results, as well as development of site-specific GEP determination.
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Overall Plan • Determine actual GEP stack height using wind
tunnel modeling
• Demonstrate compliance for final design configuration – HYWINMOD (CPP model utilizing output from wind tunnel +