Trace elements in Chinese coals and their partitioning during coal combustion

This paper gives a detail investigation about the trace elements (TEs) in typical Chinese coals, TEs partitioning during combustion and their different environment impacts. Firstly, it is determined that the contents of 9 TEs (As, Be, Cd, Co, Cr, Cu, Ge, Ni, Pb) and 3 sulfur species (sulfate SO42-, sulfide S2- and Organic S-0) in 7 density fractions of Qingshan bituminous coal, and the TEs occurrence mode is studied with Solari (1989) model. Moreover, the contents of 12 TEs (including above-mentioned 9 TEs and Mn, V, Zn) in 7 Chinese typical coals are determined and chemometric methods (factor and cluster analysis) are used to investigate the TEs combination in these coals. Secondly, 8 fly ashes with 4 sizes are sampled during Qingshan bituminous coal combustion in a thermal power plant. Higher temperature and reducing atmosphere are found to enhance greatly the metals enrichment in the submicron and micrometer particles. An enrichment coefficient is used to describe the TEs partitioning in the fly ash size-fractions and the results are discussed according to three factors: TEs combination in coals, combustion condition in a combustor, and fly ashes size. Finally it is also studied, by the sequential extraction analysis, that the TEs speciation in ashes (dregs and fly ashes) from Qingshan bituminous coal combustion, in order to assess reasonably the TEs environmental impacts.