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Utility MACT Working Group

Utility MACT Working Group. Addressing Variability. OAQPS/ESD August 8, 2002. Purpose. To review possible methods for addressing variability in setting a MACT floor and standard Focus on the methods – not the results

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Utility MACT Working Group

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  1. Utility MACT Working Group Addressing Variability OAQPS/ESD August 8, 2002

  2. Purpose • To review possible methods for addressing variability in setting a MACT floor and standard • Focus on the methods – not the results • Would prefer not to provide numbers for various scenarios – tendency is to focus on numbers and select method based on what results it will give • Have not done analyses on all available methods

  3. Background • Current data base contains a significant number of emission tests at a variety of plants – but still represents only “snapshots” in time • Variability must be accounted for in floor analyses and in ultimate standard • Presumption is that data are adequate

  4. Approaches to addressing variability • Worst-case performance • Averaging time • Control technology parameters • Format of standard • Correlation of mercury and…something else • Statistical approach(es)

  5. Worst-case performance • Base emission limit on worst-case performance within floor facilities based on analysis of actual performance or good engineering judgment

  6. Averaging time • Establish compliance averaging period to account for variability over time • 12-month rolling average • 365-day rolling average • 30-day rolling average

  7. Control technology parameters • Base emission limit on control technology which employs • Parameters which can be adjusted to deal with variety of input concentrations (e.g., lime feed rate) • Inherent characteristics which inhibit variability or dampen inlet variability (e.g., fabric filters)

  8. Format of standard • Base standard on either-or approach • Percent reduction OR emission rate

  9. Correlation of mercury and… something else • Plot potential mercury emissions based on (good) correlation with another coal constituent • Select emission value based on desired confidence limit • Similar to approach presented by Ralph Roberson at December 2001 Working Group meeting using ICR data and EPRI algorithm • Uses coal mercury vs. chlorine contents to establish mercury emissions estimate

  10. Statistical approach • Uses standard SAS program • Equation MACT floor level = Mean of top 12% + (standard deviation of 3-run average for single plant * t value for “x” percent confidence interval) • Results different from those presented in July • Variability for the MACT from only the data used to obtain the MACT • Variability much less in the best units than in all of the data • Caution: Do not focus on the numbers – they may not be final

  11. Sample results – no subcategorization DRAFT Values in lb/TBtu

  12. Sample results – subcategorization by fuel DRAFT Values in lb/TBtu Waste coals not included

  13. Sample results – subcategorization by fuel, no FBC DRAFT Values in lb/TBtu Waste coals not included

  14. So where does this leave us... • Multiple approaches have been, and can be, used to address variability • More analyses on each potential approach warranted • Approaches may be combined • Advice/recommendations from the members on the approach to be taken are welcomed

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