Migration characteristics of heavy metals during co-combustion of dehydrated sludge with straw

Abstract

Sludge incineration technology has significant advantages such as capacity reduction and energy utilization, but it will cause heavy metal pollution. Therefore, the co-combustion of dewatered sludge with corn straw at 700–850 °C was studied in a laboratory scale internal circulating fluidized bed. The effects of different temperature, sludge mixing ratio and secondary air ratio on the NO emission and the migration of different heavy metals in bottom ash, fly ash and flue gas after co-combustion were examined. The results show that under the experimental conditions, with the increase in temperature, the NO emission concentration increases, and the concentrations of V, Cr, As, Sb and Hg first increase and then decrease in the bottom ash, while the concentrations of Zn, Cu, Se and Cd vary to the contrary. The turning point of most heavy metals concentration is at 800 °C. However, with the increase in the sludge mixing ratio, the NO emission concentration first decreases and then increases, and the Cu, Hg and Tl concentrations all increase first and then decrease in the bottom ash, while the Cr concentration change is the opposite, with turning points all at the sludge mixing ratio of 10%. Also, with the increase in the secondary air ratio, the NO emission concentration decreases, and the Zn, Cu, Se and Hg concentrations in bottom ash decrease, on the contrary, the As and Cd concentrations increase.