Laboratory-scale simulation study of pyrolysis process in a fixed-bed gasifier for municipal solid waste pellets: Effects of temperature distribution and residence time

In this study, stepwise heating pyrolysis was designed to simulate the pyrolysis process of municipal solid waste (MSW) pellet in an updraft fixed bed gasifier at a laboratory scale. Differences in pyrolysis product between fixed bed stepwise heating pyrolysis (FBS, ranging from 300 °C to 800 °C) and continuous heating pyrolysis (FBC, maintained at 800 °C) were revealed. The impact of residence time at various temperature ranges on MSW pyrolysis was also investigated. Results indicated that compared to FBC, the gas yield of FBS decreased by 30.74 %, while its liquid yield increased by 11.96 %. It was primarily due to the lower heating rate reduced the secondary conversion of aliphatic hydrocarbons, oxygenated compounds, and monoaromatic hydrocarbons (MAHs) within liquid products. In addition, the composition of MSW pyrolysis products was changed by adjusting the residence time. Maintaining a uniform residence time of 5 min for MSW pellets at each temperature was considered optimal for gas yield, which was mainly attributed to the enhanced cracking of long-chain aliphatic and polycondensation of MAHs and polycyclic aromatic hydrocarbons (PAHs). Besides, the volatiles (C- and O-containing compounds) of the char were almost completely released. The underlying influence mechanism of residence time on the pyrolysis behavior of MSW was also proposed, which could provide insights for the implementation of MSW gasification.