Torrefaction of municipal solid waste to enhanced hydrophobic solid fuel: parametric optimisation and optimised torrefied solid products characterisation, grindability, and pyrolysis behaviour

Rapid population growth has led to more municipal solid waste (MSW), which can be turned into energy. But direct MSW utilisation generates tar in gasification, produces water and acid contents in pyrolysis bio-oil, and releases secondary pollutants during combustion. Torrefaction solves the issues associated with direct MSW utilisation. This work optimised torrefaction process parameters (T: 220-300 degrees C and t: 10-50 min) for torrefied solid fuels (TSF) production using response surface methodology and studied the characteristics, grindability, and pyrolysis behaviour of the optimised TSF. Temperature and time influenced the TSF calorific value (CV) and mass yield (YS), with temperature effect more compared to time. The CV increased with torrefaction severity. 25.94 MJ/kg and 17.94 MJ/kg CV were obtained at T300-50 (300 degrees C, 50 min) and T222-13 (222 degrees C, 13 min), respectively. YS gave an opposite trend with 97.52% and 51.58% at T222-13 and T300-50, respectively. The optimum condition was achieved at T282-19 with 21.97 MJ/kg CV and 70.10% YS. T300-50 and T282-19 CV and carbon content increased, while O/C and H/C ratios reduced. The removal of the OH group hindered H bond formation, consequently improving MSW hydrophobicity. T300-50 and T282-19 pyrolysis kinetics activation energy decreased from 240.44 to 104.34 and 195.46 kJ/mol, respectively, confirming optimised TSF pyrolysis reactivity improvement. The Criado and Coats Redfern models showed that all the samples followed the second-order reaction mechanism. Torrefaction improved the thermal, reactivity, and grindability properties of MSW. These findings showed the potential of torrefaction to transform MSW into a renewable and sustainable energy source.