OCR Text |
Show 15 where i is a given HAP (e.g., benzene) and N is the total number of HAPs (benzene + toluene + carbon disulfide + xylene, etc.). Results from this calculation do not support the hypothesis that staged-combustion, which is designed to minimize NOx formation, exacerbates VOC and PAH emissions. VOC data reproducibility was fairly good (for the A - 1.9 case, the total emissions factors were 8.2E-04 and 8.5E-04 IblMBtu; and for A - 0.9 case, the results were 1.2E-04 and 5.6E-04 IblMBtu). The total Semi-VOCs and PAHs were conSistently in very low concentrations compared to the VOCs (9.2E-07 to 1.3E-04 IblMBtu and 1.1 E-07 to 2.2E-07 IblMBtu, respectively). Miller, et al. (1994) conducted the coal combustion studies in the EPA's 100 kW downfired furnace under baseline and low NOx conditions. Respective maximum Title III values were 2.9E-05 and 3.3E-05 Ib/MBtu for VOCs, and 3.4E-06 and 6.5E-06 Ib/MBtu for semi-VOCs. They, thus, cautiously concluded that low NOx firing may lead to increased emissions of organic air toxics. Schmidt and Brown (1994) recently summarized US Department of Energy (DOE) results on air toxies emissions from eight power plants. While this summary does not provide enough details to assess the impact of low NOx firing on organic air toxies emissions, it provides all emission factor ranges found. Benzene emissions, for example, were found to fall in the 3.4E-06 - 1.7E-04 IblMBtu). The comparisons indicate that the results presented in this paper are of the same orders of magnitude as those reported by others. Practical Application. As an exercise, one case of the emissions factors found in this study was expressed in terms "ton/year" as a function of an electrical power plant's generation, efficiency and capacity factor. Figure 8 illustrates the worst case VOC emission factor scenario obtained from this study (Le., 8.5E-04lbIMBtu). The follOwing assumptions were made: (1) power generation-25 - 400 MWe ; (2) boiler efficiency- 34, 38 and 42%; and (3) capacity factor- 0.50, 0.65 and 0.85. Estimated results for these scenarios fall in the range of -0.5 to 11 .5 ton/year. |