Emission of Particulate Matters from Coal Combustion and Its Correlation WithCoal Mineral Properties

摘要

Four Chinese coals were ground to smaller than 125 μm and subjected to combustion ina laboratory-scale drop tube furnace to investigate the relation between coal mineralproperties with the emission of particulate matters (PM). The combustion conditionswere selected at 1200℃, 2.4 seconds and an oxygen content of 20%. All the carbon wasburnt out. The metallic elements in raw coals were divided into three parts: organicallybound, included inorganic particles and excluded. The properties of PM wereinvestigated including its concentration, particle size distribution and elementalcomposition. Two typical sizes of PM were also subjected to CCSEM analysis toquantify the chemical species within them. The results indicate that, during coalcombustion, about 0.5 to 2.5wt% of inherent minerals changed into PM, with the coalash content increases, PM concentration was increased linearly. The emitted PM has abimodal distribution having two peaks around 2.5 and 0.06 μm respectively. SiO2 andAl2O3 dominate PM larger than 1.0 μm having the peak around 2.5 μm, mainly formedby the direct transferring of inherent minerals. Meanwhile, SO3 and P2O5 are prevalentin PM smaller than 1.0 μm having the peak around 0.06 μm, formed by vaporization ofthese two elements. The excluded refractory elements undergo direct transferring toform PM larger than 1.0 μm, their concentration in PM is proportional to their contentsin raw coal. On the other hand, both the organically bound and included mineralsundergo vaporization to form PM smaller than 1.0 μm, and their vaporization rates areproportional to their contents in raw coals as well. PM of 2.5 μm is rich inaluminosilicate and its salts, whereas PM of 0.06 μm is dominated by both sulfates andphosphates of alkali elements, which fairly agrees with the thermodynamic equilibriumcalculation.