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Abstract: Combustion experiments of two Chinese coals were conducted in a 50kWth circulating fluidized bed (CFB) combustor in air and O2/CO2 atmospheres, and the effects of atmosphere and O2 staging on combustion characteristics including temperature distribution profiles, combustion efficiency, gaseous pollutant emission and desulfurization efficiency were investigated. Results show that O2 enrichment in the atmosphere elevates the temperature level in the riser and improves the combustion efficiency. Without limestone addition, O2 enrichment in the atmosphere augments SO2 and NO emission and reduces CO emission. The desulfurization efficiency under higher O2 concentration is higher with the same Ca/S molar ratio in O2/CO2 atmosphere. O2 staging provides more operation flexibility for oxy-fuel CFB combustion. As O2 concentration in the primary gas increases, combustion efficiency and desulfurization efficiency are improved. O2 staging can reduce the NO emission to a large extent in O2/CO2 atmosphere. [Copyright &y& Elsevier]

Abstract: The present paper is addressed toward the impact of O2 concentration and combustion temperature on emission and chemical composition of particulate matter with aerodynamic diameters less than 2.5μm (PM2.5) derived from a circulating fluidized bed (CFB) under O2/CO2 atmosphere. A Chinese bituminous coal was burned in the 50kW CFB. The ash samples collected by the Electrical Low Pressure Impactors (ELPI) were characterized in details to study the ash formation behaviors. Enhancing the oxygen concentration and the temperature of combustion increases the emission of PM2.5 in the O2/CO2 atmosphere. Enrichment of S, Na and K is observed in PM1, but Si, Fe and Ca do not enrich in PM1. The particle size distributions (PSDs) of PM2.5 appear in two modes, one in the submicron region around 0.2μm and the other around 2.0μm. Comparing the fly ashes formed in O2/CO2 combustion and air combustion at the same temperature with a mixture ratio of 21:79, less PM2.5 is generated in O2/CO2 combustion than in air combustion. Vaporization and condensation mechanism are the primary cause of formation and growth of submicrometer particles, while the fine fragmentation mode is believed to form through fragmentation and coalescence mechanisms. [ABSTRACT FROM AUTHOR]