Effects of blending, staging and furnace temperature on co-firing of coal and biomass-bagasse

Abstract

This manuscript reports on emissions generated from laboratory-scale batch combustion of a high-volatile content bituminous coal, sugar-cane bagasse, and blends thereof. The average bulk equivalence ratio during the volatile combustion phase was calculated to be sub-stoichiometric. Characterization and quantification of major fixed gases, light volatile hydrocarbons, semi-volatile polycyclic aromatic hydrocarbons (PAH) and particulate matter are reported. The work consists of two parts. The first part of the thesis investigated the effects on emissions generated for increasing the amount of bagasse in the coal-bagasse blend at furnace temperature of 1000 °C in atmospheric pressure air. Coal emitted two times more CO2 and particulate ass than bagasse. In contrast, coal emitted half the amounts of CO, light hydrocarbons and PAH than bagasse. The fuel blends experienced synergistic ombustion behavior during their volatile matter combustion phase. As biomass was added to coal, CO2 and articulate yields were curtailed in linear proportion to the amount of iomass. CO and PAH yields from the blends showed little change, although linear additivity predicted that these emissions would have been much higher. Light hydrocarbons emissions from blends showed no clear trend. The second part of the thesis studied batch combustion of fixed beds of oal, bagasse and blends thereof in a two-stage laboratory furnace. The rimary and secondary furnace temperatures were varied from 800oC to 1000oC. The effects of the fuel blending, the combustion staging, and of the operating furnace temperatures on emissions of pollutants were assessed. Total CO2 emissions from coal were the highest, whereas CO emissions from bagasse were the ighest. Combustion of the volatile matter of the blend resulted in lower yields of PIC, than combustion of its neat constituents, suggesting synergistic behavior. Though carbon monoxide (CO) and unburned volatile and semi-volatile hydrocarbons from the coal and the blend did not exhibit a clear trend with temperature, such emissions from bagasse experienced increasing trends with temperature. The secondary stage typically reduced CO, light hydrocarbons and PAH by further oxidation of effluents coming from the primary furnace. Overall, minimum yields of PIC were obtained when the fuels were burned blended, in staged furnace, operated around 900 °C.