The characteristic of Shengli brown coal fractions from heavy medium separation and its influence on CO₂ gasification

CO₂ gasification offers a relatively economical means for coal utilization while minimizing CO₂ emission. Coal ash may play an important catalytic role; however, undesirable ash also causes troublesome problems in the process of CO₂ gasification, especially for that of brown coal featuring high gasification activity and ash content. Therefore, it is necessary to remove the undesirable ash from the brown coal prior to the gasification. Heavy medium separation, one of the most popular ash removing clean technologies, could successfully separate coal fractions with various ash contents according to specific gravity. Consequentially, these coal or char fractions produced from pyrolysis in a newly designed quartz reactor were distinct in certain characteristics, such as ash and maceral compositions, specific surface area as well as carbon structure determined by Raman spectrum in this study, which, in turn, influenced the CO₂ gasification of different char fractions both in the novel fixed-bed quartz reactor and Thermogravimetric Analyzer (TGA). Specifically, experimental results show that the heavier coal/char fractions had less vitrinite and exinite while more inertinite, leading to higher aromatization determinated by Raman spectrum. Carbon structure and content of exchangeable metal ion were the dominant contributors to the different behavior of coal fractions during the isothermal CO₂ gasification, except at high conversion (more than 60 wt.%, daf) of char fractions where ash content played a major role. For the non-isothermal CO₂ gasification in TGA, heavier char fraction presented higher gasification reactivity due to its well-ordered pores.