Upgrading Effects of Supercritical Carbon Dioxide Extraction on Physicochemical Characteristics of Chinese Low-Rank Coals

摘要

The effects of supercritical carbon dioxide (SCCO2) extraction on coal composition, coal rank, pore structure, and combustion reactivity of three typical Chinese low-rank coals (LRCs) were investigated in this study. The results show that the SCCO2 extraction process has significantly reduced the moisture content and increased the fixed carbon content of LRCs. The oxygen/carbon atomic ratio of upgraded LRCs decreases, indicating that the coal rank of upgraded LRCs improves after SCCO2 extraction, which is consistent to the findings from Fourier transform infrared spectroscopy. The specific surface area and total pore volume of upgraded Hu Lun Bei Er (HLBE) and Zhao Tong (ZT) lignite increase significantly with extraction time and temperature. Thermogravimetric analysis shows that the combustion process of upgraded LRCs is moving toward the high temperature region and its burnout temperature (T-b) increases. The average reactivity rate (k(mean)), maximum reactivity rate (k(max)), and comprehensive reactivity parameter (S) increase obviously for upgraded HLBE and ZT lignite, whereas they decrease slightly for upgraded Xin Jiang sub-bituminous coal, indicating that the combustion reactivity of upgraded lignite is enhanced by the SCCO2 extraction process.