Characterization and analysis of sludge char prepared from bench-scale fluidized bed pyrolysis of sewage sludge

Abstract

Pyrolysis of sewage sludge (SS) was performed in a bench-scale fluidized bed pyrolyzer. Addition of kaolin at 850 °C resulted in minimum sludge char (SC) yield of 54.64 wt%. The maximum condensate yield of 17.07 wt% was obtained at 650 °C with Ca-bentonite addition. The H/C ratio of SC significantly decreased with increasing temperature, indicating the greater stability of high temperature SC in the soil environment. CaO obtained the largest carbon content of 12.91% in the form of carbonates, which was related to the intensive adsorption of CO2 by CaO. Meanwhile, CaO achieved prominent retention of sulfur in SC. CaO had a considerable ability to retain Cu and As at 850 °C and all catalysts had a good retention effect on As at 650 °C. X-ray diffraction (XRD) analysis implied that relatively stable ZnO and SiAs2 in SC inhibited volatilization of Zn and As. The maximum energy yield (88.66%) of the condensate was obtained when kaolin was added, while the addition of CaO resulted in the highest energy yield (18.27%) of non-condensable gas.