Effects of carbonization and solvent-extraction on change in fuel characteristics of sewage sludge

Urban sewage sludge was carbonized at 300–500 °C for 1 h, and combustible components were extracted through the solvent-extraction process. N-methyl-2-pyrrolidinone (NMP) was used as the solvent for extraction, and the extraction temperature was fixed at 360 °C. The atomic ratios of the solvent-extracted sludge of CS300 (ECS300) were shown to be 1.04 for H/C and 0.11 for O/C, which represented the characteristics of its coal band. Thus, its coal band was similar to that of a high-rank fuel such as bituminous coal. FT-IR analysis showed that the absorbance band of ECS300 was considerably different from that of dried sludge (RS) or the carbonized sludge at 300 °C (CS300) but similar to that of coal, although the ash content absorbance band of 800–1200 cm−1 was of very low intensity. The combustion profile showed that combustion of ESC300 occurred at a temperature higher than the ignition temperature (Ti) or maximum weight loss rate (DTGmax) of coal.