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Show 2.2 Ash Compositions of the Various Fuels The ash compositions of the various fuels changes dramatically as a function of the base coal and the alternate fuel. The wood ash, while containing significant quantities of dirt, also brings substantial calcium oxide (CaO) to the total fuel. The TDF brings both iron in the form of wire, and zinc in both the rubber and the wire. The CaO in the wood, and the iron in the TDF, can serve as fluxing agents to some extent. However they are introduced in such minor quantities that the practical fluxing characteristics of these fuels can be minimal. What is significant, for cyclone firing, is the fact that the wood and TDF do not increase the T 250 temperature of the slag formed by high temperature combustion. Rather, calculations demonstrate that both the wood and the TDF have the potential to modestly reduce the T250 temperature. 3.0 Operational Impacts of Cofiring and Trifiring Alternate Fuels Operating issues of significance include the impact of cofiring and trifiring on the ability of the boiler to achieve 100 percent capacity, the influence of cofiring and trifiring on boiler stability, the impact of cofiring and trifiring on boiler efficiency and the primary determinants of efficiency, and the impact of cofiring and trifiring on operating temperatures. Table 2 summarizes the operational results from the cofiring and trifiring tests conducted at the Allen Fossil Plant. This table presents fuel blend, load, firing rate, efficiency, and furnace exit temperature data. These data can be used to evaluate operational impacts of cofiring. 3.1 Boiler Capacity and Stability As shown in Table 2, co firing and trifiring at the Allen Fossil Plant did not compromise the ability of the units to achieve the firing rates associated with MCR. When trifiring a blend of 80 percent western coal, 15 percent green sawdust, and 5 percent TDF, the boiler was fired at 100 percent of MCR. Routinely, the tests involving 15 to 20 percent wood were conducted with firing rates >97 percent of MCR. It is recognized that the data taking portions of these tests were on the order of 2.5 tc 4.5 hrs in duration. However the actual operating times at any given blend ranged from 12 to 16 hrs due to the boiler and bunker configuration. Stability was evaluated by calculating the standard deviation as a percentage of the mean, and by calculating the 95 percent confidence interval as a percentage of the mean. For virtually all operating parameters, the standard deviation was <2.5 percent of the mean, and in most cases it was 0.1 to 0.2 percent of the mean. From an operations perspective, the boiler was as stable when cofiring and trifiring alternate fuels as when it was operating on all coal. 6 |
