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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
www.cppwind.com www.cppwind.com
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 +
AERMOD) >> complete but EPA approval pending
– AERMOD w/o downwash plus wind tunnel downwash factor >> likely approval soon
10
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GEP Study Plan • Test protocol developed and reviewed by WDNR and
EPA – tentatively approval received
• Constructed scale model (1:240) and setup
• Wind tunnel testing – documentation tests
• Wind tunnel testing – GEP stack height tests
– Tests with buildings present
– Tests without building present
• Specify the GEP stack height (40% and NAAQS test)
• Report submission and approval – January, 2015
11
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40 CFR 51.110 (ii) Defines GEP stack height to be the greater of:
• 65 meters;
• the formula height (Hb+1.5 L), or – For a 40 m cube, GEP = 100 m > 65 m!!!
• The height determined by a wind tunnel modeling study – Will be taller than the formula!! – Up to 3.25 times the building height versus 2.5 for the
formula
– Typically 2 times the nearby terrain height
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GEP Stack Height Criteria for Wind Tunnel
• 40% maximum concentration difference with and without the buildings or terrain
• With buildings in Max Concentration must exceed NAAQS or PSD increment
• Easy test since approved wind tunnel method does not include plume buoyancy.
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Example 1 • Kennecott Smelter
mid 80s
• 1200 ft stack justified as GEP using wind tunnel modeling
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Example 2: • Titus Generating Station, Schuylkill River about 3 km south of
Reading, Pennsylvania
• 175 m stack height justified as GEP using wind tunnel
modeling, 1995
175m
100m
65m
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Basic Wind Tunnel Modeling Methodology
•Specify model operating conditions
•Construct scale model (3D printing)
• Install model in wind tunnel and measure desired quantity
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Source Parameters
Stack
Height
Source Source Above Exit Exit Volume Exit
Description ID Base Diameter Temp. Flow Rate Velocity
(m) (m) (K) (m3/s) (m/s)
S09 - Maximum Load S09 max 62.09 2.13 430.4 47.23 13.25
S09 - Nominal Load S09 nom 62.09 2.13 422.0 34.21 9.60
S09 - Minimum Load S09 Mmin 62.09 2.13 422.0 26.50 7.44
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Wind Tunnel Testing 1:240 Scale Model Installed in Wind Tunnel
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Measure Ground-level Concentrations
Tracer
from stack
Max ground-level concentrations measured versus x
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Measure Ground-level Concentrations
Data taken until good fit and max
obtained Automated Max GL Concentration Mapper
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Buildings in
Buildings out
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Plume rise with and without the building
Buildings in
Buildings Out
CORNER VORTEX EFFECT
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All GEP Testing Results
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GL Concentration Profile W and W/O Buildings at 90 m GEP Stack Height
90 m stack height,
190 degree WD,
8 m/s wind speed
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Final Result
Actual GEP = 90 m
Formula GEP = 75 m
Creditable GEP = 90 m > formula > 65 m
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NAAQS Compliance Demonstration Using HYWINMOD • Test protocol development and approval
• HYWINMOD validation
• Surface Roughness
– 0.49 m for Water Tower Direction
– 0.25 m for Airport
• Scale model setup and instrumentation
• Wind tunnel testing of final design configuration for S09
• HYWINMOD analysis to demonstrate compliance at monitor and at least 55% reduction in concentrations from baseline emission conditions
• Report submission – approval pending
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HYWINMOD • CPP developed a practical method where wind
tunnel modeling can be used to predict hourly concentrations for all stabilities and can account for plume buoyancy
• Previously validated against EPA database: Bowline Point
• Will account for corner vortex
Wind tunnel
predicted
concentration
(neutral)
Data post
processing
and
correction
Hourly concentrations
incl. plume buoyancy
for all stabilities
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HYWINMOD Validation Rhinelander Mill WT Monitor
HYWINMOD
AERMOD
”Raw” wind tunnel
prior to HYWINMOD
processing
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HYWINMOD Results
4th highest max daily SO2
concentration (μg/m3)
Description/Source Configuration
Maximum
Load
Scenario
Nominal
Load
Scenario
Minimum
Load
Scenario*
5-year
average
5-year
average
5-year
average
Supporting Information
1-hour NAAQS NAAQS 196.5 196.5 196.5
Water Tower Monitor SO2 Design Value
(2009-2011) Co,DV (WTM) 395.6 395.6 395.6
Estimate Design Value Based on
HYWINMOD Scaling Plus BG at 90 m
GEP Stack Height
Cp,DV
(WTM,GEP,S09)+
BG
136.8 152.4 195.7
% Emission Reduction Required -52% -34% 0%
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AERMOD Compliance Demonstration
• Run AERMOD w/o building downwash in approved manner
• Use wind tunnel determine downwash factor, R, to adjust emission rate
• R is a only a function of wind speed
R = 1 @ <= 2 m/s
R = 1.5 @ 10.8 m/s
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AERMOD Emission Factor to account for downwash
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AERMOD Compliance Demonstration
• Protocol prepared: reviewed and approved by agency
• Report submitted: approval should be forthcoming this month.
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Ron Petersen, PhD, CCM Sergio A. Guerra, PhD
[email protected] [email protected]
Mobile: +1 970 690 1344 Mobile: + 612 584 9595
CPP, Inc.
2400 Midpoint Drive, Suite 190
Fort Collins, CO 80525
+ 970 221 3371
www.cppwind.com @CPPWindExperts
Questions?