Pyrolysis experiment of municipal sewage sludge and characteristics of fractions

At 250-700°C and under normal pressure, pyrolysis experiments of sewage sludge were performed by using an externally heated fixed-bed reactor. The characteristics of solid, liquid and gas products as fuel from different experiments were investigated. The results indicate that the volatile fractions decrease while the fixed carbon and ash increase as the final pyrolysis temperature increases. The volatile decreases faster at 250°C-450°C than 450°C-700°C. The calorific value of the solid products is relatively high at low temperature, and reaches the highest level, which is about 32475.6 kJ/kg at 350°C, and then decreases as the pyrolysis temperature increases. The quality of liquid products can meet the fuel oil standard (SH 0536-95) except that the sulfur and nitrogen contents exceed the limit. According to the analysis of gas phase chromatography, the main component of the gas at 250°C-450°C is CO2 and the content of the gas, such as H2, CH4 and CO, increases gradually as the temperature increases from 450°C to 700°C. The calorific value of the gas reaches the highest level of 15530 kJ/m3 at 600°C. In practice, the suitable final pyrolysis temperature is between 450°C and 600°C.