Effects of Gaseous Agents on Trace Element Emission Behavior during Co-combustion of Coal with Biomass

The speciation characterizations of toxic elements (TEs) under air and oxy-fuel combustion of bituminous coal/biomass blends were determined via laboratory simulation experiments. The experiments were performed in a fluidized bed reactor with different combustion temperatures (800, 900, and 1000 °C) and combustion atmospheres (21% O2+ 79% N2, 21% O2+ 79% CO2, 30% O2+ 70% CO2, and 35% O2+ 65% CO2). The concentrations of the selected TEs (As, Cr, Cu, Pb, V, Sb, Se, and Zn) in feedstock, bottom ash, and fly ash were determined using inductively coupled plasma mass spectrometry. The results showed that the redistribution characterizations of the selected TEs were greatly proportional to the reactivity of TE, association of TE, and combustion temperature and atmosphere. The selected gaseous TEs could be captured effectively by adding biomass for the chemical reactions with alkali and alkaline earth metals (Ca, Mg, Fe, K, and Na). The volatile TEs (As, Cu, Pb, Sb, Se, and Zn) were favored to enrich in gaseous and fine particles with the increase of the combustion temperature and oxygen concentration. The non-volatile TEs (Cr and V) were mainly associated with bottom ash and fly ash. More critical measures should be adopted to clean up fly ash and atmospheric pollutants during oxy-fuel combustion.