Kinetic study of the energetic reuse from torrefied sewage sludge and urban pruning blends

Abstract

Disposal of solid waste demands a high cost and causes significant environmental impacts. However, this waste can be converted into fuels by thermochemical processes due to the high content of the volatile materials and can be reused to produce energy. This study evaluated the production of renewable energy from solid waste such sewage sludge, urban pruning, and a blend composed of 50% urban pruning and 50% sewage sludge, after subjecting the samples to a torrefaction at 260 degrees C. The experiments were carried out using approximately 7mg of each sample, under nitrogen atmosphere, at different heating rates (5, 10 and 20 degrees C min(-1)), and the temperature ranged from room temperature to 700 degrees C in simultaneous TG-DTA. For the determination of kinetic parameters, a local linear integral isoconversional method analogous to the Wanjun-Donghua method was used. From approximate and ultimate analysis, the higher heating values of the samples were determined. The results indicated that the blend presented a reduction in the moisture content (5.93-3.68%), 50% in volume and 31.8% in mass. Moreover, the sample became more hydrophobic because it incorporated 33.8% less humidity after torrefaction. The higher heating value increased from 20.36 to 32.15MJkg(-1). The kinetic study showed that the average activation energy of the blend (138kJmol(-1)) was lower than the individual samples due to the synergism effect between them. The blend is converted to renewable fuel, minimizing environmental impacts and giving a noble destiny to the waste.