Comprehensive Gas Prevention and Control Technique for Mining the First Seam in Short-Distance Outburst Coal Seam Groups.

Coal and gas outbursts are a phenomenon whereby broken coal and gas suddenly erupt from the coal body into the mining space under pressure. The Diandong mining area is a group of close-range outburst coal seams in which the gas content is up to 20 m3/t and gas pressure can reach 3 MPa. Research has been conducted on engineering challenges such as advanced detection and prevention of interlayer excavation in close-range coal seam groups, improvement of gas extraction quality and efficiency in low-permeability coal seam groups, and traceability and evaluation of joint extraction of coal seam groups. Through this study, advanced detection technology with full coverage in front of the excavation working face has been constructed as well as advanced pre-extraction technology for adjacent coal seams and this coal seam in ultraclose layers. We have developed a method for achieving the standard of cross-layer fixed-point hole expansion and permeability enhancement for the first mining of coal seams in a coal seam group. A combined process of graded enhanced pre-extraction and segmented regulation and extraction was proposed, which included "fixed-point control section sealing pre-extraction of coal seam groups and secondary sealing and extraction of mining pressure relief orifice."

Assessment of coal spontaneous combustion index gas under different oxygen concentration environment: an experimental study.

Oxygen plays a crucial role in coal spontaneous combustion (CSC), and the magnitude of oxygen concentration determines the oxidation reaction intensity of CSC. This work is aiming to investigate the contribution of oxygen concentration to CSC and to predict the spontaneous combustion stage of coal at different oxygen concentrations. Firstly, experiments on the spontaneous combustion of coal samples at six oxygen concentrations (6%, 9%, 12%, 15%, 18%, and 21%) were carried out combined with a temperature-programmed system. Then, the gas products at different temperature stages were extracted to provide detailed classification and assessment of the indicator gasses for coal spontaneous combustion at different oxygen concentrations. The results show that the oxygen concentration and the crossing point temperature (CPT) are inversely proportional. The higher the oxygen concentration, the more intense the coal-oxygen complex reaction and the greater the gas product concentration. The critical temperature of some stages in high oxygen concentration environment is lower than that in low oxygen concentration environment. The oxidation process can be slowed down by reducing the oxygen concentration as much as possible. Indicator gasses are different for different oxygen concentration environments and should be selected reasonably and optimally to match the specific environment for judging natural coal fires in order to effectively prevent coal spontaneous combustion fire disasters.

Investigating the effect of coal particle size on spontaneous combustion and oxidation characteristics of coal.

As a key parameter, the particle size of residual coal contributes greatly to its oxidation characteristics, so it is a significant and far-reaching topic to explore the role of different particle sizes in coal spontaneous combustion disaster. In this work, temperature-programmed system (TPS) was applied to analyze the oxygen consumption rate and CO and C2H4 production rules of six groups of coal samples with different particle sizes in the process of oxidation heating. The critical temperature (CT) and xerochasy temperature (XT) of different coal samples were obtained, and the coal oxidation process was divided into three stages (S1, slow oxidation stage; S2, fast oxidation stage; and S3, combustion stage). Then, the apparent activation energy (E) and pre-exponential factor (A) in three stages were regressed combined with Arrhenius formula. The results show that the smaller the coal particle size is, the larger the specific surface area is, the stronger the adsorption capacity of coal molecules and oxygen molecules is, resulting in the larger oxygen consumption rate. The values of CT and XT with particle size of 0.125-0.18 mm and 2-4 mm are the smallest and largest. For coal samples with the same particle size, the maximum values of E and A occur in stage S3 and the minimum values appear in stage S1. This is mainly due to the higher temperature of stage S3, which allows the activation of functional groups with higher apparent activation energy, stronger collisions between activated molecules, and more intense oxidation reactions.