OCR Text |
Show 4.0 Formation of Airborne Emissions Airborne emissions of consequence include opacity, S02, and NOx. These are the regulated airborne emissions. Fossil CO2 also is of consequence, particularly for utilities making voluntary commitments to the global climate challenge. 4.1 Opacity Emissions Opacity emissions have been unaffected by cofiring and trifiring practices. All tests have shown that the plant is capable of meeting regulatory requirements when firing with all coal from either eastern or western sources, when cofiring wood waste or TDF with coal, and when trifiring wood waste and TDF with coal. Of significance is the fact that the wood waste and TDF have low ash percentages, and this makes the impact of cofiring and trifiring on opacity inconsequential. 4.2 Sulfur Dioxide Emissions Emissions of S02 are a function of the sulfur content in the fuel. Between 90 and 100 percent of the fuel sulfur is converted to S02 in a normal system. As shown in Table 1, cofiring wood waste reduces the sulfur content of the fuel. While TDF can raise the sulfur content of a blended fuel slightly when cofiring with western coal, trifiring has the ultimate impact of essentially holding the fuel sulfur content of the blend at a level equal to that of the western coal, with the wood waste offsetting the TDF. Cofiring wood waste with coal has the impact of reducing S02 emissions, and the reduction is proportional to the fuel sulfur content expressed in lb. SII 06 Btu fuel. Trifiring wood waste and TDF with coal holds S02 emissions at a level equal to those associated with coal-only firing as long as the mass ratio ofwood:TDF exceeds 3:1. 4.3 Oxides of Nitrogen Emissions The parametric testing suggests that emissions of NOx may be reduced significantly as a function of cofiring and trifiring wood waste and coal. The data indicate that such reductions could occur, as is shown in Table 3. The mechanisms governing NOx control also can be determined from the test data. It is important to note that the NOx reductions occurred during parametric testing, and that significant additional testing must proceed if these reductions are to be confirmed. At the same time, however, it is important to note that both the reductions and the fundamental mechanisms driving those reductions can be observed from the tests conducted to date. Mechanisms associated with reducing NOx from fuel characteristics include reducing the fuel nitrogen content, expressed in lb. Nil 06 Btu; increasing the fuel volatility and thereby altering the consequent combustion pathways; and decreasing the lb-m O2 required in the combustion air to achieve a stoichiometric ratio (SR) of 1.0. Figure 3 shows the impact offuel nitrogen content on NOx emissions for Boiler #2 at ALF. 10 .- |