An Empirical Approach to Estimate Trace Metal Emissions from Combination Boilers

Transcription

1 An Empirical Approach to Estimate Trace Metal Emissions from Combination Boilers by Arun V. Someshwar, NCASI NCASI Northern Regional Meeting May 8, 2014 Wausau, WI

2 Rationale For Seeking Alternate Methodology To Estimate Trace Metal Emissions From Combination Boilers Current methodology is to take published emission factors and proportion them according to fuel input This does not take into account the increasingly low PM emissions measured from boilers currently Neither does it account for the geographical variability of trace metal content among wood, coal and other fuels What is required is a predictive equation that uses the real time information on PM emissions measured during a test and the real time fuel metal and fuel ash concentrations measured during the test 2

3 EPA s Predictive Equation for Trace Metal Emissions From Coal Combustion Table of AP-42 Chapter 1.1 provides predictive emission factor equations for 9 of the 11 trace metal HAPs pertaining to coal combustion (all except Hg & Se) For example As (lb/10 6 Btu) = 3.1 * (C/A * PM) 0.85 where C = conc. of metal in the coal, parts per million by weight (ppmwt) A = weight fraction ash in the coal (e.g.; 10% = 0.1) PM = site-specific EF for total particulate matter, lb/10 6 Btu 3

4 Trace Metal Emissions From Coal Combustion - Table of AP-42 Pollutant Emission Equation (lb/10 12 Btu heat input) Antimony 0.92 * (C/A * PM) 0.63 Arsenic 3.1 * (C/A * PM) 0.85 Beryllium 1.2 * (C/A * PM) 1.1 Cadmium 3.3 * (C/A * PM) 0.5 Chromium 3.7 * (C/A * PM) 0.58 Cobalt 1.7 * (C/A * PM) 0.69 Lead 3.4 * (C/A * PM) 0.80 Manganese 3.8 * (C/A * PM) 0.60 Nickel 4.4 * (C/A * PM)

5 lb/mmbtu Measured or Predicted 1.0E E E E E-05 Predicted Vs Measured Arsenic Emissions For Coal-Fired Boilers - Boiler MACT Data AP-42 Eqn (Table ); X = 3.10 * (C/A * PM) 0.85 AP-42 Equation Prediction Measured Values AP-42 Emission Factor = 1.64E-05 lb/mmbtu 0.0E+00 5

6 Developing Predictive Equations For Trace Metal Emissions From Wood-Fired Boilers Using Boiler MACT fuel and emissions data, predictive equations for 100% wood combustion are developed similar to the ones developed by EPA for coal Y (trace metal emissions in lb/10 6 Btu) = a * (C * PM) b -log (Y) = - log (a) + b * -log (X1 * X2) Boiler MACT data for PM emissions (X2) and wood trace metal concentrations (X1) for 15 boilers firing ~100% wood are used to obtain the coefficients a and b for the 9 trace metals (all except Se and Hg) 6

7 -log (Y) Estimating Coefficients a and b for Predicting Trace Metal Emissions From WFBs - Arsenic Y - As Emissions in lb/mmbtu X1 - FPM in lb/mmbtu X2 - ppm As in Wood Fuel y = x R² = a= = 3.42E-05 b = log (X1 * X2) 7

8 NCASI Predictive Equations for Trace Metal Emissions From Wood Combustion Pollutant Emission Equation (lb/10 6 Btu heat input) Antimony 8.14E-06 * (PM * C) 0.53 Arsenic 3.42E-05 * (PM * C) 0.71 Beryllium 6.30E-08 * (PM * C) 0.19 Cadmium 7.16E-06 * (PM * C) 0.46 Chromium 1.38E-05 * (PM * C) 0.42 Cobalt 1.00E-05 * (PM * C) 0.63 Lead 2.50E-05 * (PM * C) 0.48 Manganese 2.38E-05 * (PM * C) 0.67 Mercury E-06* (PM * C) 0.08 Nickel 5.62E-06* (PM * C) 0.29 Selenium E-07* (PM * C)

9 lb/mmbtu Measured or Predicted 1.6E E E E E E E E E+00 Predicted Vs Measured As Emissions For Wood-Fired Boilers - Boiler MACT Data Y = 3.42E 05 * (PM * C) 0.71 TB 1013 Mean = 1.88E 06 lb/mmbtu Actual Emissions Predicted Emissions 9

10 Applying the Predictive Equations Developed for Coal-Wood Combination Boilers Using the measured PM emissions during a test and simultaneously analyzed coal/wood trace metal concentrations, the predictive equations developed for coal and wood combustion are used to develop coal and wood trace metal EFs for that boiler, for that test Based on the fraction coal/wood fired in each boiler, the individual EFs are then combined to predict emissions Predicted and actual emissions for ten combination coalwood boilers (Boiler MACT data), 6 with dry PM control and 4 with wet PM control, are then compared 10

11 Arsenic Emissions, lb/mmbtu 2.0E E E E-06 Predicted Vs Measured As Emissions For Six Bark-Coal Combination Boilers with ESP/FFs - Boiler MACT Data Actual Emissions Predicted From Coal/Wood EFs Predicted Based on Fuel Metals Concns & Measured PM 0.0E Percent of Wood/Bark in Coal/Wood Fuel Mix 11

12 Arsenic Emissions, lb/mmbtu 8.0E E E E E E E E-05 Predicted Vs Measured As Emissions For Four Bark-Coal Combination Boilers with WSs - Boiler MACT Data Actual Emissions Predicted From Coal/Wood EFs Predicted Based on Fuel Metals Concns & Measured PM 0.0E Percent of Wood/Bark in Coal/Wood Fuel Mix 12

13 Applying the Alternate Method To Predict Metal Emissions From Other Combination Boilers Boilers burning wood and/or coal with gas or oil Combine published trace metal EFs for oil or gas with predicted EFs for coal &/or wood based on relative fuel fractions Boilers burning small amounts of an alternative fuel with no published trace metal EFs, e.g., TDF, OCC rejects, sludge along with wood and/or coal Estimate within-boiler trace metal capture efficiency for coal or wood fuel combustion Apply this efficiency to the trace metal input from the alternate fuel(s) to estimate emissions from this fuel(s) 13

14 Conclusions NCASI derived equations to predict trace metal emissions from wood combustion in FPI boilers. Along with similar equations derived by EPA for coal combustion, they allow one to predict trace metal emissions from all coal-wood boilers using realtime PM emissions and fuel metal content data. These predictive equations can also be used to estimate trace metal emissions from boilers burning gas, oil, TDF, OCC rejects, etc. with coal/wood. For gas/oil, published EFs for oil/gas are used. For TDF & OCCR (no published EFs), the calculated in-boiler trace metal capture efficiency for coal or wood is assumed same for TDF & OCCR. 14