Research on the main control factors of gas desorption in middle and low rank coals based on orthogonal testing

To study the factors influencing gas desorption by middle rank and low rank coal, gas adsorption and desorption experiments of middle rank and low rank coal samples were designed with the orthogonal test method by considering the particle sizes, adsorption equilibrium pressures, temperatures and water contents of the coal samples, and the main factors affecting gas desorption from the middle rank and low rank coal samples were investigated. The results showed that there were obvious differences in the desorption capacity of the middle rank and low rank coals in the designed experimental scheme, and the maximum cumulative amounts of gas desorbed were 6.11 ml/g for Xinjiang low rank coal and 6.50 ml/g for Hebi middle rank coal. The relative sensitivities to the factors affecting gas desorption by Xinjiang low rank coal decreased in the order adsorption equilibrium pressure > particle size > water content > temperature, which the effect of adsorption equilibrium pressure on gas desorption from Xinjiang low rank coal was the most obvious and main controlling factor for gas desorption from Xinjiang low rank coal. The relative sensitivities to the factors affecting gas desorption by Hebi middle rank coal decreased in the order particle size > adsorption equilibrium pressure > temperature > water content, which the effect of particle sizes on gas desorption from Hebi middle rank coal was the most obvious and main controlling factor for gas desorption from Hebi middle rank coal. The cumulative amounts of gas desorbed from Xinjiang low rank coal first increased and then decreased with increasing coal grain sizes, and the cumulative amounts of gas desorbed from the Hebi middle rank coal gradually decreased with increasing coal grain size. The cumulative amounts of gas desorbed from both Xinjiang low rank coal and Hebi middle rank coal gradually increased with increasing adsorption equilibrium pressure.