Co-Firing of Coal and Feedlot Biomass (FB) in a Laboratory Scale Boiler Burner

摘要

The use of biomass as a fuel source has the potential to both solve biomass disposalproblems, and reduce CO_2 emissions. Previous attempts to utilize biomass as a sole fuel sourcemet with only limited success due to the higher ash and moisture of biomass and inconsistentproperties. Thus, co-firing technology is proposed where cattle manure (henceforth called feedlotbiomass, FB) is ground, mixed with coal, and then fired in existing pulverized coal fired boilerburner facilities. The coal having higher BTU content enables the low quality FB to burn.Thermogravimetric analyses (TGA) were performed on coal, FB, and 90:10 coal: FB blend. TheTGA studies found that biomass will release volatiles at a lower temperature, about 100 K lowerthan that of coal, and more rapidly than coal. While the single parallel reaction model seems tofit the pyrolysis of coal, a bimodal parallel reaction model appears to fit the pyrolysis curve ofbiomass. Coal and coal: FB blends were first fired in a stainless steel combustor unit and byusing gas analyses, transient combustion and pollutant emission characteristics were obtained.Subsequently, the combustor unit was modified with a cast ceramic liner and a commercialfeeding system for firing coal and then blends. The boiler burner experiments revealed that the90:10 blend burns more completely in the boiler, due to the earlier release of biomass volatiles.The Nox emission data in the transient experiments indicate that biomass more readily releasesNox even at lower temperatures. However, when the furnace reached higher temperatures, theblend released less Nox than coal despite the higher N content of FB; but CO emission increased.The long duration experiments in the modified facility confirm Nox reduction with the firing ofblend. Large scale pilot plant tests performed at the DOE National Energy TechnologyLaboratory, Pittsburgh confirm improved combustion, but Nox emission are the same for both thecoal and blend.