Combustion Behavior of Low-Rank Coal Upgraded by Degradative Solvent Extraction

The authors have recently separated one lignite and one subbituminous coal into several fractions at around 350 degrees C by a degradative solvent extraction. The main products obtained are solvent-soluble fractions (extracts) and insoluble fraction which we call "upgraded coal (UC)." The UCs, with the yields of around 75 %, have rather lower moisture content, lower oxygen content, and higher energy content, compared with the raw coals. In this work, the combustion behaviors of the UCs and their raw coals were investigated preliminarily by a thermogravimetric analyzer. The results showed that the comprehensive combustibility index S of the UC was slightly improved by the degradative solvent extraction. For the lignite, the temperature of ignite temperature (T-ig) and burnout temperature (T-bo) of the lignite were increased slightly, while the maximum weight loss rate (R-max) was slightly increased. But for the subbituminous coal, the T-ig and T-bo were decreased by about 20 degrees C. The mechanism of the changes was also primarily investigated.