Effects on enrichment characteristics of trace elements in fly ash by adding halide salts into the coal during CFB combustion

Abstract

The effects on enrichment characteristics of trace elements (TEs) in fly ash by adding halide salts into the coal during coal combustion were conducted on a 6 kWth circulating fluidized bed (CFB) experimental device. Results show that unburn carbon content in fly ash has little relationship with the concentration of TEs namely Hg, As, Pb, Cr and Mn. All the TEs are enriched in fly ash for the raw coal CFB combustion. Concentration of Hg and Mn increases with increasing the addition amount of CaCl2, NH4Cl and NH4Br. As, Pb and Cr enrich in fly ash more strongly when adding more CaCl2 into the coal while more addition of NH4Cl and NH4Br leads to the decrease of their enrichment compared to addition amount of 0.1 wt%. On the whole, putting halide salts into the coal results in the TEs enriched in fly ash, which benefits for TEs removal during the coal combustion. Combining this method with the chemical sequential extraction or thermal treatment of the fly ash will be a promising way to realize the TEs removal and their recovery.