Role of exhaust gas recycle on submicrometer particle formation during oxy-coal combustion

During oxy-coal combustion, recycled exhaust gas is used as a diluent to replace nitrogen in pulverized coal-fired boilers to moderate boiler temperatures. The effect of recycle (upto recycle ratios of 60%) on combustion of Powder River Basin (PRB) coal related submicrometer particle formation was investigated in a drop-tube furnace system. The recycled exhaust gas containing lower O-2 concentration and higher CO2 concentration suppressed submicrometer particle formation. However, it was found that water vapor in recycled exhaust gas greatly enhanced the formation of submicrometer particles. The gas composition changes that result with exhaust-gas recycle significantly affected the size distribution of submicrometer particles at the exit of the combustor. Differences in the particle size distribution with and without filtration of recycled exhaust gas was insignificant. The composition of the resultant particles in oxy-coal combustion and conventional coal-air combustion as determined by X-ray diffraction was similar. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.