Effects of Dewatering on the Pyrolysis and Gasification Reactivity of Victorian Brown Coal

摘要

This study aims to investigate the effects of dewatering on the primary pyrolysis behavior and gasification reactivity of Victorian brown coal. Dewatered brown coal samples were prepared by dewatering/drying of the brown coal in steam and by means of mechanical thermal expression (MTE). The primary pyrolysis behavior and gasification reactivity of these dewatered coal/char samples were evaluated in a wire-mesh reactor and in a thermogravimetric analyzer (TGA), respectively. It was found that changes in the physical structure of the brown coal and the loss of NaCl during dewatering at low temperatures did not significantly affect the char and tar yields. However, dewatering/drying at temperatures > 250℃ not only reduced the volatile yield but also shifted the normalized derivative thermogravimetric (DTG) peak to a higher temperature during pyrolysis in the TGA under constant heating rates. The analysis of the pyrolysis kinetics of dewatered brown coal samples using a distributed activation energy model indicates that dewatering/drying at elevated temperatures partially degraded the brown coal structure, leading to stronger covalent bonds formed during pyrolysis that require higher temperature to break down. It was also found that changes in pore structure and chemical structure in the brown coal during dewatering had little effect on the char reactivity. However, the loss of inorganics (mainly NaCl) during dewatering led to decreases in char reactivity.