Change in Properties and Combustion Characteristics of an Indonesian Low-Rank Coal Due to Hydrothermal Treatment

An Indonesian low-rank coal, Adaro, was hydrothermally treated at 200-350°C in an autoclave. The raw and treated coals have been subjected to several analyses which include hygroscopicity, the content of oxygenic functional groups, FTIR spectrum, and specific surface area. When the coal is hydrothermally treated, the hygroscopicity of coal remarkably decreases. The content of carboxyl group in coal greatly decreases as the heat treatment temperature (HTT) is raised. From FTIR analysis, the methyl/methylene ratio in coal somewhat increases, especially when the coal is treated at 350°C; while the aromaticity of coal is enhanced a little. Due to the hydrothermal treatment, the ignition temperature (T i ) shifts to a high temperature; whereas the temperature, at which the maximum combustion rate occurs (T m ), is not so changed. The change in the properties of coal and the combustion characteristics is discussed.