Abstract
Low rank coals are deposited abundantly in several regions throughout the world and they will continue to be significant resources for both energy and chemicals. However, they have not been utilized to the same extent as higher rank coals because of their high water contents (40-70wt%) and low calorific values. Developments of dewatering and upgrading processes are necessary to utilize the coals on a large scale. Hydrothermal treatment has generally been conducted by adding extra water to the coal prior to treatment, leading to a decrease in the efficiency of the process. In this study hydrothermal treatment of a brown coal was performed by utilizing the water inherent in coal. An Australian brown coal, Loy Yang, was solely loaded in an autoclave and treated at 200∼350°C for 30 and 180 min. Measured temperature vs. pressure relationship closely followed the vapor pressure curve during treatment of the coal, revealing that hydrothermal conditions are maintained throughout the experiments with only the inherent water. The water content of the treated coals decreased with increasing temperature. The oxygen content of the treated coal decreased above 250°C, which successfully increased the calorific value of the treated coal. FTIR analysis revealed that the carboxyl groups were selectively decomposed through these treatments.
