Blended torrefaction of combustible construction solid wastes and paper sludge on its combustion characteristics and migration of heavy metals and Cl

Combustible construction solid wastes (CCDW) and paper sludge (PMS) are important components of combustible solid waste (CSW), which are also important ingredient in waste-to-energy system. Torrefaction experiments of CCDW, PMS and their blends in equal proportion (C50S50) were conducted in a tubular furnace reactor at torrefaction temperature (T) of 200–400 °C for 30 min. The fuel properties and migration of heavy metals and Cl of torrefied CCDW, PMS and C50S50 were investigated based on proximate analysis, ultimate analysis, caloric value determination, and the measurement of heavy metals and Cl in solid, liquid and gaseous products. Combustion characteristics of CCDW, PMS, C50S50 and their torrefied solid products were evaluated by TG-FTIR analyzer. The obtained results indicated that torrefaction can improve fuel performance of CCDW, PMS and C50S50. The fixed carbon, higher heating value (HHV) of torrefied solid products increased and volatile matter decreased gradually while T < 250 °C; however, the HHV and energy yield of blended torrefied solid products obviously decreased while T > 250 °C. The combustible index (Cn) and burnout index (S) of blended torrefied products at 250 °C were the largest, achieving 111.26 × 10−6 and 0.49 × 10−6. Torrefaction can effectively remove Zn, Hg, As in CCDW, PMS and C50S50. More than 50 % of Cl was released from torrefied C50S50 when T > 300 °C. High torrefaction temperature (T > 300 °C) can remove more heavy metals and Cl, but it has an adverse effect on fuel properties of torrefied products, so the suggested torrefaction temperature is 250 °C.