Safety evaluation of combustion-prone longwall mining gobs induced by gas extraction: A simulation study

Underground methane-rich and combustion-prone longwall mining gobs are usually subjected to the symbiotic threat of spontaneous coal combustion and gas explosion, resulting in significantly economic and environmental impacts. Inappropriate methods or control parameters of gas extraction in combustion-prone longwall mining gobs may trigger a series of secondary accidents, such as the formation of excessive carbon monoxide, and even a gas explosion. Although gob coal-gas interactions induced by gas extraction have been comprehensively investigated previously, few studies are able to quantitatively predict how the symbiotic hazard of gas explosion and spontaneous coal combustion is formed, and guide how to change the design or control parameters for safety and efficiency. In this work, the formation criteria of the coal combustion-gas explosion hazard and a new index of gas extraction safety are proposed to make up for these knowledge gaps. Furthermore, gob gas migration, coal self-heating and their symbiotic risk evolution induced by gas extraction under the different gas control, face mining and ventilation parameters were investigated. The results show that although gas extraction can significantly reduce gob gas emission into the workface, it simultaneously exerts great influence on coal self-ignition and gob safety. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.