The fate of trace elements and bulk minerals in pulverized coal combustion in a power station

Abstract

The behaviour of 15 trace elements (As, Ba, Cr, Cu, Mn, Mo, Nb, Ni, Pb, Rb, Sr, V, Y, Zn and Zr) and 10 major and minor elements (Al, Ca, Fe, K, Mg, Na, P, S, Si and Ti) in coal during combustion in a power station has been studied. Synchronized sampling of pulverized coal, bottom ash and fly ash was undertaken over a limited time period. Fly ash morphology was studied by SEM and the mineral composition was studied by EDX and XRD. Major, minor and trace elements were determined by XRF and AAS. Differences between the composition of the ashes of pulverized coal, bottom ashes and fly ashes have been observed. As, Cu, Mo, Pb and Zn were concentrated in the fly ash. The relationship between the composition of the fly ashes and their particle size was studied. Enrichment factors were calculated for each element in different size fractions. As the particle sizes of fly ash decrease, the concentrations of As, Cu, Mo, Pb and Zn increase. From the different composition of bottom ashes and fly ashes (and relying on the results of the characterization of the feed coal carried out in previous work), it can be assumed that pyrite and carbonates make a greater contribution to the furnace bottom ashes. Quartz carries through into the fly ash. This mineral is almost absent in the finest fractions, reflecting the absence of small quartz particles in the feed coal.