Effect of heat transfer model on the prediction of refuse-derived fuel pyrolysis process

Abstract

Heat transfer models using to estimate the effective thermal conductivity have been developed and included in a model for the pyrolysis of refuse-derived fuel or solid recovered fuel particles composed of cardboard and polyethylene. Both the predictions from the Kunii and Smith model and the Breitbach and Barthels model were presented and compared with the experimental data. The possible mechanisms of heat transfer in the porous solid particles were discussed. Compared to the conduction mode by solid matrix and gas phase, radiation heat flux between the neighboring voids and from particle surface and neighboring particle surface are considered as the main mechanisms at the temperatures presented in this paper. The porosity has been reported to serve as an important role in the accurate estimation of the radiation exchange factor for the radiation term in heat transfer model in a highly porous medium. Refuse-derived fuel particle with a high plastic concentration exhibits a rapid increase of porosity with the continuous thermal conversion of plastic. Thus, a coefficient as a function of porosity was applied to the radiation exchange factor in the Kunii and Smith model, which was constructed and based on a simplified model of heat transfer in packed bed. Moreover, the effect of the contact surface area between solid particles on the heat transfer of conduction mode was also considered in the Breitbach and Barthels model. Both modified models were further validated with experimental results obtained at different temperature, with different PE content and initial porosity.