Size distributions of major elements in residual ash particles from coal combustion

Combustion experiments for three coals of different ranks were conducted in an electrically-heated drop tube furnace. The size distributions of major elements in the residual ash particles (>0.4μm) such as Al, Si, S, P, Na, Mg, K, Ca and Fe were investigated. The experimental results showed that the concentrations of Al and Si in the residual ash particles decreased with decreasing particle size, while the concentrations of S and P increased with decreasing particle size. No consistent size distributions were obtained for Na, Mg, K, Ca and Fe. The established deposition model accounting for trace element distributions was demonstrated to be applicable to some major elements as well. The modeling results indicated that the size distributions of the refractory elements, Al and Si, were mainly influenced by the deposition of vaporized elements on particle surfaces. A dominant fraction of S and P vaporized during coal combustion. Their size distributions were determined by surface condensation, reaction or adsorption. The partitioning mechanisms of Na, Mg, K, Ca and Fe were more complex. Supported by the National Natural Science Foundation of China (Grant Nos. 50706013, 50721005 & 50720145604)