A combined experimental and numerical study of coal briquettes pyrolysis using recycled gas in an industrial scale pyrolyser

Abstract

Low-rank coal pyrolysis plays a significant role in clean coal utilisation in various coal-based industries. Using recycled gas or exhaust gas as heat carrier in the pyrolyser is a promising way for improving its energy efficiency and reducing carbon emission. In this study, an experimental and numerical combined study is conducted to cost-effectively investigate the effect of utilising the recycled gas on coal pyrolysis in an industrial scale gas-heat-carrier pyrolyser. First, a lab-scale two-stage pyrolyser is employed to pyrolyze the low-rank coal samples to obtain the gas products composition. The experimental results are subsequently used in the CFD pyrolyser model as operating conditions to simulate the pyrolysis process of utilising the recycled gas as the heating carrier gas in an industrial scale pyrolyser. The comprehensive in-furnace phenomena evolution during the pyrolysis are illustrated, in terms of flow, temperature, gas composition, and pyrolysis characteristics. The effects of two carrier gases – hydrocarbon-rich recycled gas and CO2-rich exhaust gas are examined and compared on the pyrolysis performance. The results indicate that compared to the exhaust gas, the employment of the pre-heated recycled gas as the heat carrier could significantly reduce the direct carbon emission (58%); improve pyrolysis efficiency (33%) and produce more valuable hydrocarbon gases (71.4%).