Co-combustion of Shenmu coal and pickling sludge in a pilot scale drop-tube furnace: Pollutants emissions in flue gas and fly ash

Co-combustion of Shenmu coal and pickling sludge was carried out in a pilot scale drop-tube furnace. The effect of different pickling sludge amounts on the NOx, SO2, HCl, HF, PCDD/Fs and gaseous heavy metals emissions and fly ash behaviors was studied. The burnout section furnace temperature was 1250 degrees C, and the pickling sludge amount ranged from 0 to 20 wt%. The result indicates that the co-combustion of < 20 wt% pickling sludge did not reduce the combustion efficiency. With increasing pickling sludge amount in the blended fuels, NOx and HCl emission concentrations were basically stable; however, those of SO2 and HF increased obviously. The total TEQ of PCDD/Fs emission was basically positively correlated to the sludge amount in the blended fuels, and the gaseous heavy metals emissions also increased obviously with the addition of sludge. To meet the national standard (GB18484-2001) on heavy metals emissions, the pickling sludge amount used in co-combustion must be < 10 wt%. According to national standard (GB 16889-2008), because of the high leaching concentrations of heavy metals Cr, Ni, Cu and Pb, the co-combustion fly ash needs further treatment before being landfilled disposal as common waste.