Pyrolysis mechanism and gasification characteristics of actual municipal solid waste: A kinetic study through two-stage reaction models

Abstract

Municipal solid waste (MSW) gasification technologies represent a novel approach to waste management, while research on the kinetic characteristics and gasification behavior of actual MSW remains limited. In this paper, a new two-step kinetic model combining the segmentation of the main pyrolysis stages of MSW with Coats-Redfern (C-R) method which was more suitable for describing the pyrolysis process of actual MSW was established. Then the pyrolysis mechanism, tar generation process and the interactions among components, were thoroughly investigated based on this kinetic model. The results show the two-stage approach can effectively improve the accuracy of the MSW pyrolysis kinetic model (R² > 0.989). The first stage of MSW pyrolysis conforms to the reaction order model, while the second stage aligns with the geometric contraction model. The average activation energies of the two pyrolysis stages are 70.49 and 120.62 kJ/mol, which demonstrated that the two-stage reaction follows different types of reactions. Gasification experiments of MSW, guided by the kinetic model, indicate that higher temperature (T > 700 °C) and equivalence ratios (ER) can promote the gasification of MSW and tar, under the optimized conditions, the H₂ yield increased from 0.08 to 1.82 mmol/g, and the CO yield increased from 0.26 to 1.92 mmol/g. Further increasing the ER (ER > 0.5) can inhibit the conversion of benzene and polycyclic aromatic hydrocarbons (PAHs) by promoting the generation of CO₂. Increasing the ER and employing flue gas combustion to raise the CO₂ concentration during the gasification process is an ideal method for suppressing the formation of benzene and PAHs.