Effects of hydrothermal upgrading on the physicochemical structure and gasification characteristics of Zhundong coal

It is difficult to directly use Zhundong (ZD) coal because of its high alkali metal content and the associated slagging and fouling problems. Therefore, in this study, hydrothermal (HT) treatment was introduced to remove the alkali metals and upgrade ZD coal at 150-350 °C. The physicochemical structure and gasification characteristics of ZD coal were investigated. The results showed that the properties of the upgraded coal were effectively improved and the coal rank increased after HT upgrading. Additionally, alkali metals Na and K were notably removed, reaching approximately 98% and 82% at 350 °C, respectively. BET analysis indicated that the pore structure was initially enriched at 150-300 °C and then deteriorated at 300-350 °C. The XRD and Raman results revealed that the microcrystalline structure tended to be more aromatic and graphitized, and the chemical structure became dense, orderly and stable. In addition, the CO2 gasification reaction curve shifted to the high-temperature region as the HT temperature increased. The gasification reactivity exhibited a decreasing trend, and the results were verified by dynamic analysis. Moreover, the comprehensive influence of different factors on the gasification reactivity was explored via a potential mechanism analysis, and a multiple linear regression model of gasification reactivity was established.