Enhanced combustion processes of liquid carbon dioxide (LCO2)–low rank coal slurry at high pressures

It is difficult to evaporate water and burn volatile content at high pressures owing to the conflict in boiling temperatures of two components in the coal. The evaporation of water is critical for low rank coal with water content exceeding 20 %. However, the hydrophobicity of liquid carbon dioxide (LCO2) can release water from inner coal, which in turn can solve the problem of evaporation and the subsequent combustion process. However, there is a paucity of studies that examine such water removal and evaporation/combustion behaviors of LCO2–low rank coal slurry. In this study, the effect of LCO2 on the combustion behavior of low rank coal at high pressure is examined and compared with that of raw coal and water–coal slurry. A visualization technique is introduced to observe the evaporation and combustion of coal slurry under the high-pressure fixed-bed condition. The bed temperature is measured at two different temperatures, and the char, gas, and liquid yield are simultaneously determined. Enhanced volatile combustion is observed at 650 °C for the LCO2–coal slurry, which is due to the rapid release and evaporation of water. The water removal phenomenon by LCO2 in high moisture coal are supported by both data from forward scattering and thermogravimetric analysis measurement.