Abstract
The present paper is addressed toward the impact of O 2 concentration and combustion temperature on emission and chemical composition of particulate matter with aerodynamic diameters less than 2.5 μm (PM 2.5) derived from a circulating fluidized bed (CFB) under O 2/CO 2 atmosphere. A Chinese bituminous coal was burned in the 50 kW 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 PM 2.5 in the O 2/CO 2 atmosphere. Enrichment of S, Na and K is observed in PM 1, but Si, Fe and Ca do not enrich in PM 1. The particle size distributions (PSDs) of PM 2.5 appear in two modes, one in the submicron region around 0.2 μm and the other around 2.0 μm. Comparing the fly ashes formed in O 2/CO 2 combustion and air combustion at the same temperature with a mixture ratio of 21:79, less PM 2.5 is generated in O 2/CO 2 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.
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