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In the goaf of the high gas and spontaneous combustion coal seam, the gas drainage is mutually contradictory and restrictive to the prevention and control of coal spontaneous combustion. For this, we analyzed the disaster mechanism of gas and coal fire coupling disaster, determined the main factors affecting the coupling disaster, and identified the potential ethical risks of the existing gas and coal spontaneous combustion prevention technology. Based on analytic hierarchy process, the ethical risk assessment model of gas and coal fire coupling disaster was established and applied in 7436 working face of Kongzhuang Coal Mine. The results show that the weight of the coal spontaneous combustion during the mining of 7436 working face is 0.262 3, the weight of the gas disaster is 0.205 4, and the weight of the gas and coal fire coupling disaster is 0.529. Special attention should be paid to the occurrence of the gas and coal fire coupling disaster during mining. The probability of coal spontaneous combustion disaster is higher than that of gas disaster when coal spontaneous combustion disaster and gas disaster are treated respectively.

With the increasing mining depth of the mine, the high temperature and heat damage of the mining face is becoming more and more serious, and the phenomenon of spontaneous combustion of residual coal is particularly obvious, which seriously affects the safety production of the mine. In order to study the heat transfer law of fluid in porous media in goaf and analyze the influencing factors of porous media heat transfer, a porous media model of goaf is established by taking the 7271 working face of Yaoqiao Coal Mine as an example, and Fluent numerical simulation method is used to simulate the changes of gas concentration and temperature field in goaf under different wind speeds and different heat source positions. The results show that with the increase of wind speed, the range of “three zones” of spontaneous combustion in goaf moves to the depth of goaf, and the influence range of “three zones” of spontaneous combustion in air inlet side is larger than that in air return side. The closer the heat source is to the air inlet tunnel, the higher the overall temperature of the goaf. Increasing the air inlet tunnel wind speed can effectively reduce the internal temperature of the goaf and reduce the fluid heat transfer efficiency in porous media.

In order to solve the problems of unreasonable node distribution and complex connection of pressure energy lines in the current mine ventilation network pressure energy distribution diagram, a new method with independent disjoint roads as the main skeleton, and the node distribution method of the mine ventilation network pressure energy graph distributed on both sides of the remaining connected nodes is proposed. According to the spatial relationship between independent disjoint roads and the remaining nodes and the remaining nodes, the drawing method of the branch shape between the nodes is analyzed and the drawing algorithm is designed. The drawing results of the drawing algorithm show that the algorithm can use the existing data to reasonably convert the mine ventilation network diagram into the pressure energy distribution diagram of the mine ventilation network, and the nodes in the pressure energy distribution diagram are distributed in an orderly manner, and the pressure energy lines between the nodes are connected normally, which can not only reflect the network relationship between nodes, but also reflect the pressure energy distribution of nodes. The algorithm can provide a reference for intelligent mine ventilation and underground fire prevention and risk avoidance.

Aiming at the shortcomings of the current coal mine explosion venting devices, a new explosion venting door is designed, and its structure, explosion venting mechanism and beneficial efficiency enhancement are discussed. FLUENT software was used to simulate gas explosion under different working conditions and the change laws of explosion pressure, flame temperature and flame speed were analyzed by monitoring, and the explosion venting effect of the explosion vent door was verified. The results show that when the gas mass fraction is 9.5%, it is found that the explosion pressure peak generated by the explosion-proof wall is the largest, and the pressure is maintained at 0.29 MPa after attenuation, and the surrounding rock and equipment in the roadway are continuously damaged under high-pressure environment. The explosion venting door can quickly release the pressure, so that the fire area can be closed without fresh air, and reduce the occurrence of secondary explosions and secondary disasters. Under the working condition of gas mass fraction 5.5%-11.5%, the overall change law of gas explosion characteristic parameters is the same. As the gas volume fraction increases, the gas explosion characteristic parameters first increase and then decrease. The explosion venting capacity of the explosion venting door has nothing to do with the gas volume fraction, however the gas volume fraction changes, the pressure is released and the fire area is closed at the same time.

In view of problems such as excessive dust concentration in working face and deterioration of working environment in mines caused by wide application of mechanized mining. We put forward technical means to optimize technical parameters of water injection and dust control in coal seam so as to increase water content of coal seam to be exploited. Using the simulation software COMSOL, the relationship between the process parameters such as water injection pressure and time and the infiltration effect of coal seam was studied. The third-order polynomial fitting function curve of wetting radius and water injection time under the condition of medium pressure water injection is obtained. The research results show that the infiltration effect of coal seam with medium pressure water injection is better. When the water injection pressure is 5 MPa, the optimal water injection duration is 5 h.

To accurately analyze the spontaneous combustion mechanism of coal seams in western Inner Mongolia area of China and the microscopic characteristics of coal spontaneous combustion, Jurassic experimental coal samples and Carboniferous comparative coal samples were selected to reveal the moisture in coal through industrial analysis of coal, static oxygen uptake and temperature programmed experiments. The influence of water, volatiles, ash, oxygen consumption and coal organic gas generation rate on coal spontaneous combustion tendency was studied. After measuring and finishing, it is known that the spontaneous combustion tendency of the Jurassic coal seam is positively correlated with the moisture and volatile matter content in the coal sample, but negatively correlated with the ash content. The static oxygen uptake of Jurassic coal samples exceeded 0.70 cm3/g and was higher than that of Carboniferous coal samples. At about 130 °C, the formation rates of CO and CO2 in Jurassic coal samples were 0.08 t/°C and 0.1 t/°C, CH4 is derived from the coal body itself, and the temperature rises to 120 °C to generate C2H6, and 150 °C precipitates C2H4. It indicates that the oxidation of the western Inner Mongolia Jurassic coal in the low-temperature oxidation stage is more severe.

The utilization of CO 2 is extremely important to solve the environmental problems and coal spontaneous combustion in goaf. There are three kinds of CO 2 utilization in goaf: adsorption, diffusion, and seepage. Since adsorption will consume CO 2 in goaf, the optimization of CO 2 injection amount is very critical. A self-developed adsorption experimental device was used to determine the CO 2 adsorption capacity of three different particle sizes of lignite coal samples at 30-60 °C and 0.1-0.7 MPa. The factors affecting CO 2 adsorption by coal and its thermal effect were studied. In the coal and CO 2 system, the CO 2 adsorption characteristic curve is not affected by temperature, but there are differences in that with different particle sizes. The adsorption capacity increases with the increase of pressure, while it decreases with the increase of temperature and particle size. Under atmospheric pressure, the adsorption capacity of coal is a logistic function relationship with temperature. Furthermore, the average adsorption heat of CO 2 on lignite shows that the interaction force between CO 2 molecules has a stronger effect on CO 2 adsorption than the effect of heterogeneity and anisotropy on the coal surface. Finally, the existing gas injection equation is improved theoretically with CO 2 dissipation, which provides a new idea for the work of CO 2 prevention and fire suppression in goaf., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The mining technology of gob-side entry retaining without a coal pillar is gradually becoming a mature and increasingly important mining technology. As it maintains the roadway near goaf, the air leakage should be greater than a U-type ventilation system in goaf, so it is prone to cause coal spontaneous combustion problems. CO 2 is an inert gas, and it is usually used to prevent spontaneous combustion and extinguish coal fire. However, there is a lack of research on characteristics and safety of CO 2 for the mining technology of gob-side entry retaining without the coal pillar. In this paper, the indexes of influencing factors were proposed on gas, pipelines, and mining technical parameters. Using a three-dimensional physical model of coal stope, the gas migration law of CO 2 , the relationship between gas injection rate and the oxidation zone area, and the safety of the CO 2 inerting technology were analyzed. The results indicate that the O 2 concentration is diluted between the working face and the injection port, especially in the air intake side. Furthermore, the CO 2 injection rate is an important parameter to the fire prevention and extinguishing technology. When the gas injection rate ranges from 240 to 720 m 3 /h, the oxidation zone area varies from 7380 to 14 760 m 2 , and the gas injection rate grows exponentially with the area of the oxidation zone. Moreover, the redundant CO 2 gas flows to the retaining roadway, and it reduces the O 2 concentration, resulting in asphyxia accidents of miners. The research results are helpful to balance the relationship between inert gas injection and production safety and provide guidance for the practical application of the inert gas fire prevention technology., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)