Mechanism of Fire Prevention with Liquid Carbon Dioxide and Application of Long-Distance Pressure-Holding Transportation Technology Based on Shallow Buried and Near-Horizontal Goaf Geological Conditions

Abstract

Shallow burial, very close coal seam groups, and spontaneous combustion are typical characteristics of most coal seams in the Shendong mining area, China. With the continuous extension of the production level of various mines, some mining areas have gradually shown complex production conditions including multiple types of fire forms such as those in coal fields, small kilns, and multilayer mined-out and hidden high-temperature areas, resulting in fire control difficultly and posing threats to safety. With the aim of limiting the above problems, in this work, the liquid carbon dioxide fire prevention technology is focused on. Phase change and migration law of CO2 in the goaf are studied. Through the study on the influence of the use of liquid CO2 on the cooling law of high-temperature coal and on its spontaneous combustion characteristics and through thermal analysis experiments, it was observed that the porosity of loose coal has a significant impact on the cooling effect of carbon dioxide. Moreover, it was emphasized that the higher the CO2 concentration, the higher the rise in temperature of coal oxidation, and the increase of CO2 concentration was able to affect apparent activation of coal oxidation, leading to a theoretical basis to explain the effect of CO2 in inhibiting coal spontaneous combustion. The utilization of Fluent numerical modeling allowed us to simulate the diffusion radius of liquid CO2 injected into the goaf, to study the effective inerting radius of liquid CO2 on the left coal in the goaf. After comprehensive analysis of experiments and numerical simulations, appropriate equipment and process flow are selected and designed. Taking the Huojitujing well of Daliuta Coal Mine in Shendong mining area as the industrial test site, an intelligent pressure-holding transportation of liquid CO2 in the 1000 m transportation pipeline was developed. The surface liquid CO2 infusion capacity was 20 t/h, and the pressure-holding interval at the end of the transportation pipeline was determined to be 1.0–2.3 MPa. The maximum diffusion radius of the mined-out area is 300 m under the effect of positive air flow and self-expansion and diffusion of CO2 gas in the roadway. Under the influence of reverse wind flow and self-expansion and diffusion, the diffusion radius of the goaf is 150 m, and the maximum storage time of gaseous CO2 in the goaf is 27 h. Liquid CO2 was injected into the area with relevant presence of CO, an indicator of possible fires. Practice has proved that, after 65 hours and two perfusion processes, the CO concentration dropped from 790 ppm to 41 ppm, which indicates that liquid CO2 has a significant effect on fire prevention.

Study on Spontaneous Combustion “Three Zones” of the Distribution Law and Integrated Fire Prevention Technology in Mined-Out Area of Lingquan Mine

“…According to the simulation results of the SCTZ range in the goaf, when the air supply is 1,000 m 3 /min, the suffocation zone is 75 m away from the inlet side of the work face, and the CO in the return airflow corner is excessive, which indicates that there is serious air leak in the mined-out area. The main feature of air leak in the goaf is that the air enters from the inlet side and then flows out near the return airflow side, therefore, in order to stop the leakage in the goaf, it is necessary to seal the inlet and return airflow side, the air inlet tunnel and the connection tunnel [ 15 ]. The sealing measures adopted are as follows: at the corner of the return airway, a mixture of sodium polyacrylate, polyacrylamide, additives and water in a ratio of 3 : 1:2 : 3 is used to make a new polymer colloid material for sealing, and the connection tunnel is sealed at the same time.…”

Study on Inerting Characteristics of Gas Coal by the Inerting Concentration and Ratio of an Inert Gas Mixture

“…Li et al improved the existing gas injection equation using CO 2 dissipation theory, providing new ideas for CO 2 prevention and fire extinguishing work in goaf. Through practice, it has been proven that liquid CO 2 has a significant fire prevention effect. Liu et al , used chemical deposits generated by the reaction of two-phase aerosols (CO 2 and hydroxide) to prevent coal spontaneous combustion in underground goaf areas.…”

Investigating Critical Parameters for the Application of Liquid Carbon Dioxide in Fire Prevention and Extinguishing in Goaf

“…Yu and Gao [17] designed a suitable liquid carbon dioxide delivery scheme and injection quantity for solving the spontaneous combustion problem of residual coal in the goaf of Long'an Coal Industry, arranged the tunnels reasonably, and ultimately suppressed the spontaneous combustion of residual coal in the goaf through field implementation. Cao and Liang [18] studied the cooling law of liquid carbon dioxide on high-temperature coal and used numerical simulation methods to determine the cooling equipment and process flow that are more suitable for the coal mine under study. Practice has proved that liquid carbon dioxide has a more significant fire prevention effect.…”