Cofiring waste biofuels and coal for emissions reduction

Combustion tests have been performed in two pilot-scale combustion facilities to evaluate the emissions reduction possible while firing coal blended with several different biofuels. Two different boiler simulations, pulverized coal fired boilers and stoker coal fired boilers, were simulated. The pc-fired studies investigated the use of waste hardwood, softwood and sludge as potential reburning fuels and compared the results with coal and natural gas. The use of these wood wastes is attractive because: wood contains little nitrogen and virtually no sulfur; wood is a regenerable biofuel; wood utilization results in a net reduction in CO{sub 2} emissions; and, since reburning accounts for 10-20% of the total heat input, large quantities of wood are not necessary. The results of this program showed that a reduction of 50-60% NO was obtained with approximately 10% wood heat input. Reburn stoichiometry was the most important variable. The reduction was strongly dependent upon initial NO and only slightly dependent upon temperature. The stoker program investigated barriers for the successful blending of coal with waste railroad ties. Parameters evaluated included blending firing rate, chip size, optimum feed location, overfire/underfire air ratio, and natural gas addition. The results of this study demonstrated that NO emissions can bemore » reduced by more than 50% without any significant increase in CO or THC emissions by the proper use of zoned reburning. Both programs demonstrated several benefits of biofuel blends, including: (1) lower operating costs due to reduced fuel prices; (2) reduced waste disposal; (3) reduced maintenance costs; (4) reduced environmental costs; and (5) extension of the useful life of existing equipment.« less