Studies on Enrichment Mechanics of Trace Elements in Particulate Matter After Pulverised Coal Combustion

Three kinds of pulverized coals were burnt in a laboratory-scale drop tube furnace, and an 8-stage Andersen particle impactor was employed for separating and sampling the ash particles after the pulverized coals combusting, in order to study the enrichment characteristics of trace elements in primary particulate matter during coal combustion. The PM samples were analysed by ICP-AES, the concentration values of Cr, Ni, Pb, Cu, and Zn are acquired. Then relative enrichment ratio (R_ER) is defined to compare the concentration variation in ash PM deposited on grading filters. The results have been shown that the trace elements concentration present increasing trend with the PM size minimize. The R_ER values of these five trace elements present principles as Pb>Zn>Cu>Ni in turn, which lines in the sequence of the metal melting point from lower to higher, the case of Cr differed from coal to coal. The result of theoretical analysis was that in the continuum medium region (Kn<<1), the concentration of the condensed species (C_m) follows a trend prop 1/d_p ², and the better the correlation relation of C_m and 1/d_p ² is, the greater the value of R_ER is, the stronger the volatility of trace element is. But the enrichment extent of trace elements is different from various coals combustion, accordingly, the extent of vaporized trace elements homogeneous condensation to submicron PM or heterogeneous condensation on existing particles is different, which is also illustrated and demonstrated by the SEM images of submicron PM.