Heavy metals migration and ash slagging/fouling behaviors during co-combustion of coal slime and biomass

Abstract

This study investigated the migration characteristics of heavy metals (Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb) during the co-combustion of coal slime (CS) and biomass. The effects of combustion temperature, blending ratio, biomass types, and mineral additives on heavy metal behavior were examined in detail. Additionally, the risk of ash slagging and fouling was predicted, and the influence relationship of various factors on heavy metal retention rates was studied by correlation analysis. Data indicated that the co-combustion of CS and moso bamboo (MB) at high temperatures (≥1050 °C) facilitated the enrichment of Cr, Ni, and As in bottom ash but hindered that of Zn, Pb, and Cd. Interactions among heavy metal migration were observed during CS-MB co-combustion, with all different ratio samples promoting the enrichment of Cr, Ni, As, and Cd in bottom ash. A CS: MB ratio of 5:5 was recommended based on heavy metal retention rates and interaction effects. The influence of biomass types on the migration of Ni, Cu, Zn, As, Cd, and Pb was insignificant. Adding Fe₂O₃ or CaO minerals effectively increased the Cr retention rate, and 10 % Fe₂O₃ or CaO addition was recommended to enrich heavy metals in bottom ash. CS-MB co-combustion effectively mitigated the ash slagging and fouling risks associated with MB combustion, and an MB ratio of less than 70 % was recommended to avoid ash slagging and fouling. Moreover, the combustion temperature exhibited an extremely strong negative correlation with Zn and Pb retention rates.