Combustion characteristics of liquid carbon dioxide-dried coal at different pressures of CO2–O2 mixture

Abstract

In this study, the coal combustion behavior was determined at different combustion pressures, including supercritical CO2–O2 conditions. The coal mass and mass ratio of oxygen-to-coal remained constant. The drying impact of liquid carbon dioxide (LCO2) on supercritical combustion was investigated using raw coal with a high moisture content (20%). The extent of combustion (i.e., coal conversion) and particle temperature were measured using a weighing method and a two-color pyrometer, respectively. The effects of oxygen diffusion and volatile release on the extent of combustion were explored as pressures varied from subcritical to supercritical conditions. The temperature was further increased at the same supercritical pressure to study the effect of oxygen diffusivity on combustion. The phase change behavior of CO2–O2 mixture is identified and visualized. The kinetic and diffusion data were used to determine the Thiele modulus and the resultant effectiveness factor. The role of the hydrophobic surface groups in coal in the LCO2 drying process was investigated using Fourier Transform Infrared (FTIR) spectroscopy. In addition, the time-resolved water contact angle with the LCO2-treated coal sample was determined using the in-situ pendent drop method at atmospheric pressure.