Review of numerical studies on thermal treatment of municipal solid waste in packed bed combustion

Municipal solid waste (MSW) is increasingly considered a source of energy and materials rather than an environmental and socioeconomic problem. Incineration using the grate-firing technique is one of the best available technologies for thermal treatment of non-recyclable MSW with energy recovery. The transition to a circular economy brings a new challenge to the Waste to Energy (WtE) industry. Due to advanced waste management schemes, the calorific value of the input waste is likely to decrease. Nevertheless, WtE plant designers and operators have aimed to increase the energy and material recovery efficiency of their installations, while maintaining or even decreasing operation and maintenance costs. For these reasons, there is a need for better understanding of the chemical and physical phenomena involved in the MSW incineration process. Accurate numerical modelling of MSW packed bed combustion can substantially contribute to this objective.The literature on similar fields such as coal and biomass combustion has delineated many crucial aspects of modelling solid fuel combustion in grate-firing applications. However, the know-how obtained in these fields cannot be one on one transferred to MSW incineration because MSW is much more inhomogeneous in composition and thermophysical properties. This paper first presents an overview of MSW's chemical and thermophysical properties. Then, the heterogeneous nature of MSW and its complex thermal degradation behaviour are used as a basis to discuss the suitability of the available numerical methodologies. Finally, current challenges in the modelling of waste beds are identified, with relevance to improving the performance of industrial WtE plants