Release characteristics of semi-volatile heavy metals during co-combustion of sewage sludge and coal under the O2/CO2 atmosphere

Abstract

Co-combustion of sewage sludge and bituminous coal in O2/CO2 atmosphere was carried out in a horizontal electric heating tube furnace. The effects of incineration temperature, mass ratio of sewage sludge to coal (Xs) and incineration atmosphere on the release characteristics of heavy metals (HMs, such as As, Cr, Ni and Pb) were investigated. The results indicated that incineration temperature can promote the release of As and Pb significantly, but it has little effect on the release of Cr and Ni. The release fractions of As, Cr, Ni and Pb in 21%O2/79%CO2 atmosphere are less than that in air atmosphere due to higher specific heat of CO2. With increasing O2 content in O2/CO2 atmosphere, the release fractions of Cr, Ni and Pb increase, but As release fraction decreases. With the increase in Xs, the release fractions of As and Pb increase, Cr release fraction decreases, but Ni release fraction is almost stable. It is infeasible to predict the release fractions of different HMs under co-combustion based on sewage sludge addition and their release fractions of mono-combustion. The co-combustion condition of sewage sludge with coal is suggested as: temperature of 800–900 °C, 30%O2 in O2/CO2 atmosphere, and about 30% sludge addition.