Coal char characteristics variation in the gasification process and its influencing factors

Abstract

Underground coal gasification is a burgeoning coal exploitation technique that coal is directly converted into gaseous fuel by controlled combustion. In this paper, the gasification experiments of Inner Mongolia lignite, Xinjiang subbituminous coal, and Hancheng medium volatile bitumite were conducted respectively by using the tube furnace coal gasification experiment system. The gasification process was conducted under 3°C/min increment within the range of 600–900°C. The gas composition was analyzed by gas chromatography and the pore structure of the coal char was detected by low-temperature N2 adsorption. The results show that the gasification temperature, gasification agent, and coal type have an important influence on the gasification reaction. With the increase of gasification temperature, the effective component, gas calorific value, and gas production rate increase. When CO2 is used as the gasifying agent, the effective components in the gas are mainly CO. When H2O(g) is used as the gasifying agent, the effective component of gas is H2. The coal gasification performance with low thermal maturity is obvious better than the high rank coal with higher coalification. N2 adsorption–desorption experiments show that the pore is mainly composed by transition pore and the micropores, the specific surface area is chiefly controlled by a pore size of 2–3 nm. With the increase of coalification degree, the adsorption amount, specific surface area, and total pore volume show a decreasing trend. The gasifying agent has a great influence on the pore structure of the coal char. The gasification effect of H2O (g) is significantly better than that of CO2. Analyzing the gasification characteristics and pore changes of different coal rank coals under different gasification agents, we found that Inner Mongolia lignite is more conducive to the transport of gasification agents and gaseous products in coal.