Modelling of the pyrolysis of low-rank-coal briquettes in an industrial-scale gas heat carrier pyrolyzer

Abstract

Pyrolysis is an effective coal-upgrading method by converting low rank coals (LRCs) to thermal-efficient and environmentally friendly fuels together with many other valuable products. Compared to wall heat pyrolyzer, gas heat carrier pyrolyzer is expected to be more stable in performance. In this paper, a mathematical model is used to describe the multiphase flow related to the pyrolysis of LRC ellipsoidal briquettes in a gas heat carrier pyrolyzer at industrial-scale. The model is validated against the practical measurements in terms of components distribution of gas products. The comprehensive in-furnace phenomena during the pyrolysis are illustrated, in terms of flow, temperature, gas composition, and pyrolysis characteristics. The simulation results indicate that the opposite-positioned gas inlets lead to weak gas flow along chamber centreline, and results in the non-uniform temperature distribution in the bed. The ellipsoidal briquettes in the lower part of bed show a better pyrolysis performance compared to the upper part because of the stronger interphase heat transfer. Then the effects of particle shape on pyrolysis efficiency are examined by comparing ellipsoidal and spherical particles. It is indicated that in the upper bed where the gas velocity is relatively low, the spherical raw coal particles show better pyrolysis efficiency compared to ellipsoidal briquettes. This model provides a cost-effective way to understand and optimise the pyrolysis practice of gas heat carrier pyrolyzers.