A comprehensive gas extraction system coupling high-level suction roadway and boreholes for gas disaster prevention in closely-spaced multiple coal seams

Abstract

ABSTRACT Mining a protective layer is an effective way to prevent coal and gas outbursts in underground coal mines; this method has been used widely. However, when mining closely spaced multiple coal seams (CMCS), gas from adjacent coal seams flows into the working face through fractures in the goaf. This is caused by pressure relief and consequently gas overruns occur, a significant problem that negatively affects efficient mine production. This study analyzes the reasons that gas overruns occur at a working face during the mining of CMCS protective layers. A comprehensive gas extraction system coupling a high-level suction roadway and boreholes was introduced and applied to prevent and control gas overruns at the working face. Gas extraction rates and the amount of gas in the air return system were monitored and the results used to evaluate the effectiveness of the system. The results show that gas desorption caused by pressure relief of the adjacent coal seams was the main cause of the gas overruns at the working face. After the system started working, the average extraction rate increased from 2390 m3/d to 16200 m3/d with average gas concentration in the extracted gas rising from 6% to 41.21%. After using the gas extraction system, the average gas concentrations in the tailgate roadway, working face upper corner, and return airway were reduced by 45%, 30%, and 13%, respectively. Gas overrun accidents have apparently been eliminated. At the time of this writing, there have been no new gas overrun accidents. In addition to solving the gas problem, the gas extraction system has allowed average coal production from the working face to increase 46.7% per month and in 9 months, 4.4 million cubic meters of gas, which could be directly used to generate electricity, was extracted. The tests indicated that an appropriately configured high-level gas extraction system in the fractured zone can effectively solve the working face gas overrun problem in mines exploiting CMCS. This study can be used as a valuable example for other coal deposits being mined under similar geological conditions.