Thermochemical conversion of waste into energy: a review

The increasing global energy demand, the decline in fossil fuels and the growing amount of municipal solid waste are major environmental and socioeconomic issues, calling for advanced techniques to recycle waste into energy. Here, we review the thermochemical valorization of household, industrial and agricultural waste, with focus on municipal solid waste composition, fuel production, fuel characteristics, legislation and standards. Processes include pyrolysis, gasification, and incineration, e.g. in cement kilns. We found that refuse-derived fuel has a calorific value of 8–20 MJ kg⁻¹, a moisture content of 8–40% and an ash content of 4–20%. Optimized refused-derived fuel pyrolysis can yield up to 67.9 wt% liquid oil, while gasification produces syngas with heating values up to 10.9 MJ m⁻³. In cement kilns, co-processing achieves thermal substitution rates of 50–60% in rotary kilns and 80–100% in calciners. Limitations comprise variability in the composition of the feedstock, tar formation and control of emissions.