Date Published: March 1, 2019
Publisher: Public Library of Science
Author(s): Kun Wang, Haibo Tang, Fengqi Wang, Yong Miao, Dapeng Liu, Hongbo Zhao.
Spontaneous combustion of coal is one of the major hazards threatening production safety during longwall mining. Mining-induced voids, which provide passages for air leakage, are the key factor triggering spontaneous combustion of coal in longwall goafs. In this study, a comprehensive method, which combined pressure balance, grouting injection, and filling fissures, was proposed to prevent spontaneous combustion of coal in longwall goafs with complex air leakage. Field engineering practice was carried out in Sitai Coal Mine in China. The results demonstrated that with the application of the proposed method, in the working face, the concentration of CO was decreased from 31ppm to 0 and the air leakage quantity was decreased from 261 to below 80 m3min-1. The gas samples analysis from the gob areas also indicated that concentrations of O2 and CO were successively decreased, indicating that the risk of spontaneous combustion of coal in goafs was eliminated. The above mentioned analysis indicates that, the method proposed in this study is useful and efficient. Successful application of this technology could provide reference for the treatment of other coal mines.
China is the largest coal-producing and consuming country in the world, and 90% of coal comes from the longwall mining faces [1, 2]. During longwall mining, the underground coal fires are a major hazard threatening production safety [3–5]. Majority of underground coal fires are caused by spontaneous combustion of coal, and the longwall gob area is one of the main places that is prone to spontaneous coal combustion . Coal fires occurring in goafs not only produce large amounts of toxic and harmful gases but also cause production interruption on the working face . Therefore, the research on spontaneous combustion in longwall goafs has always been an important global issue .
Sitai Coal Mine is located at the western Datong Basin of Shanxi province in China. It covers an area of 65.45 km2. The coal production is 4.2Mt/a. The mine belongs to high gassy coal mine and the negative pressure ventilation has was adopted. The main minable coal seam was the 14# coal seam. The 12# coal seam is the overlying seam and the distance between them is only 8.3–15.7m, thus the gobs of two coal seams interconnect with each other. Large amounts of harmful gases were gathered in 12# coal seam gob areas, which brought danger of spontaneous combustion of coal to 14# coal seam. In order to prevent fresh air from entering the gob areas and to detect the harmful gases, all gob areas of 14# coal seam were sealed with fire-proof closed walls, and seven gas monitoring points were set up, as presented in Fig 1.
The pressure balance measurement was carried out on the third day of mining, whereas the slurry grouting and fracture filling methods were conducted on the 20th day of mining.
Table 3 lists the cost of comprehensive method.
In this study, the analysis of mining-induced air leakage passages was presented, while the method to prevent spontaneous combustion of coal in longwall gob areas with complex air leakages was proposed. The field engineering practice was carried out in the Sitai Coal Mine in China.