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Show 4.4 Fossil Carbon Dioxide Emissions Fossil fuel-based CO2 emissions are considered to be critical concerns for the global climate challenge, and many utilities have signed up for voluntary reductions of these emissions. Programs are many and varied. Cofiring has some significant potential as a low-cost method for achieving such reductions. Fossil CO2 reductions are largely a function of the Btu replacement of coal with biofuels, accommodating the differences in efficiency as noted above. For a boiler the size of ALF Unit #2, for example, the fossil C02 displacement can be on the order of 5 to 7.5 tonlhr of fossil carbon, or 18 to 28 tonlhr of CO2 depending upon the level of cofiring, the efficiency penalty involved, and the type of coal displaced. Over the course ofa year this represents about 35,000 to 52,000 tons offossil carbon, or about 125,000 to 195,000 tons of fossil-based CO2. Currently the CO2 has no economic value; however utilities may place their own value on greenhouse gases depending upon alternative programs and the extent of their voluntary commitment. 5.0 Conclusions Cofiring and trifiring unconventional fuels with coal significantly impacts the performance of cyclone boilers, based upon the data developed from parametric testing at the Allen Fossil Plant. While these data are preliminary in "nature, they indicate that biofuels do not reduce boiler capacity, however they can impact boiler efficiency. They depress flame temperatures slightly, and significantly impact furnace exit temperatures. The practices of cofiring and trifiring do not impact opacity emissions from boilers, and impact S02 emissions expressed in Ib SOjl06 Btu fuel input to the extent that fuel sulfur content is altered. Biofuels, being sulfur-free, reduce S02 emissions. TDF reduces S02 emissions when cofired with interior province coal, but increases S02 emissions when cofired with western coal. The combination of wood waste and TDF can be used to displace western coal while leaving S02 emissions unchanged. The practices of cofiring and trifiring biofuels and other alternate energy sources have the potential to reduce NOx ewjssions from cyclone boilers, and this potential relates both to fuel NOx and thermal NOx. Biofuels and TDF can reduce the fuel nitrogen content of the fuel and increase the fuel volatility, thereby impacting NOx emissions. Biofuels increase the oxygen content of the fue~ and decrease the oxygen required from combustion air, expressed in lb-m Ojl06 Btu fuel. Finally, biofuels reduce furnace exit temperatures, thereby impacting fonnation ofthennal NOx. The practices of cofiring or trifiring have some potential to impact unit perronnance. Their economic impact depends upon the relative prices of coal and alternate fuels in any given market, the specifics of plant configuration and logistics, and the consequent relative costs of both coal and alternate fuels at the burner entrance of the cyclone boiler. The technical relationship between alternate fuels and specific coals, and the availability and price of alternate fuels in immediate proximity to a given power plant, must be assessed on a site-specific basis. Further, the long tenn potential for cofiring and trifiring must also be assessed on a plant-specific basis if the process is to move forward. 15 |
