a Data from EPA, Compilation of Air Pollutant Emission Factors, AP-42, Fifth ed., U.S. Environmental Protection Agency, U.S. Government Printing Office, Washington, D.C., January 1995. Factors represent uncontrolled emissions, unless otherwise specified, and should be applied to coal feed, as fired. Tons are short tons.

^Expressed as SO2, including SO2, SO3, and gaseous sulfates. The factor in parentheses should be used to estimate gaseous SOX emissions for subbituminous coal. In all cases, S is weight percent (wt.%) sulfur content of coal as fired. Emission factor would be calculated by multiplying the wt.% sulfur in the coal by the numerical value preceding S. For example, if a fuel is 1.2% sulfur, then S = 1.2. On average, for bituminous coal, 95% of fuel sulfur is emitted as SO2, and only about 0.7% of fuel sulfur is emitted as SO3 and gaseous sulfate. An equally small percent of fuel sulfur is emitted as particulate sulfate. Small quantities of sulfur are also retained in bottom ash. With subbituminous coal, about 10% more fuel sulfur is retained in the bottom ash and particulate because of the more alkaline nature of the coal ash. Conversion to gaseous sulfate appears about the same as for bituminous coal.

cExpressed as NO2. Generally, 95 vol% or more of NOX present in combustion exhaust will be in the form of NO, the rest NO2. To express factors as NO, multiply factors by 0.66. All factors represent emissions at baseline operations (i.e., 60 to 110% load and no NOX control measures). d Nominal values achievable under normal operating conditions; values 1 or 2 orders of magnitude higher can occur when combustion is not complete.

eEmission factors for CO2 emissions from coal combustion should be calculated using pounds CO2 per ton coal = 72.6C, where C is the wt.% carbon content of the coal. For example, if the carbon content is 85%, then C equals 85.

f Wall-fired includes front and rear-wall-fired units, as well as opposed-wall-fired units. gPre-NSPS boilers are not subject to any NSPS. NSPS boilers are subject to Subpart D or Subpart D(a). Subpart D boilers are boilers constructed after August 17, 1971, and with a heat input rate greater than 250 million Btu per hour (MM Btu/hr). Subpart D(a) boilers are boilers constructed after September 18, 1978, and with a heat input rate greater than 250 MMBtu/hr. ^Includes traveling-grate, vibrating-grate, and chain-grate stokers.

1SO2 emission factors for fluidized-bed combustion are a function of fuel sulfur content and calcium-to-sulfur ratio. For both bubbling-bed and circulating-bed design, use pounds SO2/ton coal = 39.6(S)(Ca/S)-19. In this equation, S is the wt.% sulfur in the fuel and Ca/S is the molar calcium-to-sulfur ratio in the bed. This equation may be used when the Ca/S is between 1.5 and 7. When no calcium-based sorbents are used and the bed material is inert with respect to sulfur capture, the emission factor for underfeed stokers should be used to estimate the SO2 emissions. In this case, the emission factor ratings are E for both bubbling- and circulating-bed units.



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