Research on the Law of Coal Pillar Spontaneous Combustion and Fire Prevention and Control Technology.

In coal pillar fires, the fire source is hard to be detected and the adjacent goaf is extremely likely to be affected. Such fires would give rise to thermal and dynamic disasters in mines, further causing casualties and environmental disruption. In this study, with the coal pillar spontaneous combustion (CPSC) accident in Chahasu Coal Mine taken as the research object, the oxygen uptake and limit of oxygen concentration of CPSC were explored. Based on the research results, a similar model was constructed, where a control group was used to simulate the hazardous area of CPSC in a bid to investigate the law of CPSC. Moreover, the polymer colloid perfusion system was constructed and the drilling parameters and perfusion process parameters were determined, and practices concerning spontaneous fire control were carried out. Here are the conclusions: First, air leakage in the coal pillar may lead to coal spontaneous combustion due to the impact of rib spalling, threatening 2-6 m above the middle of the coal pillar at a shallow position. Second, coal pillar grouting, injecting polymer colloids for cooling, and coal pillar cement reinforcement prove to be effective ways to prevent CPSC fires and combat recombustion.

Detection and management of coal seam outcrop fire in China: a case study.

The outcrop fire area in Rujigou Coal Mine in Ningxia, China has been burning continuously for over 100 years. This not only results in wastage of resources but also poses significant damage to the ecological environment. Previous research on open fire detection has mainly focused on coalfield fire areas, using single method such as infrared remote sensing or surface temperature measurement, magnetic method, electrical method, radon measurement and mercurimetry. However, the outcrop fire area has migrated to deeper parts over the years, conventional single fire zone detection methods are not capable of accurately detecting the extent of the fire zone, inversion interpretation is faced with the problem of many solutions. In fire management, current research focuses on the development of new materials, such as fly ash gel, sodium silicate gel, etc., However, it is often difficult to quickly extinguish outcrop fire areas with a single technique. Considering this status quo, unmanned aerial vehicle (UAV) infrared thermal imaging was employed to initially detect the scope of the outcrop fire area, and then both the spontaneous potential and directional drilling methods were adopted for further scope detection in pursuit of more accurate results. In addition, an applicable fire prevention and extinguishing system was constructed, in which three-phase foam was injected for the purpose of absorbing heat and cooling. Furthermore, the composite colloid was used to plug air leakage channels, and loess was backfilled to avoid re-combustion. The comprehensive detection and control technologies proposed in this study can be applied to eliminating the outcrop fire area and protecting the environment. This study can provide guidance and reference for the treatment of other outcrop fire areas.

Detection of Spontaneous Combustion Areas of Coal Gangue Dumps and Comprehensive Governance Technologies: A Case Study.

Spontaneous combustion of coal gangue dumps not only releases toxic and harmful gases, polluting the environment, but also leads to explosion accidents and casualties due to improper handling. This paper focuses on delineating the fire area, constructing a comprehensive fire prevention and extinguishing system, and restoring the ecological environment. Infrared thermal imaging was used to detect the shallow fire area, while intensive drilling was conducted to detect the deep fire area. The stability of the coal gangue dump was enhanced by perfusing three-phase foam for cooling and using a curing material to fill the cracks. Land reclamation was then performed to restore the ecological environment. The results indicate that spontaneous combustion of coal gangue dumps can trigger the spread of the fire area from the outside to the inside, gradually expanding due to the 'stack effect'. The sources of spontaneous combustion in gangue fire areas are mainly located 3-5 m below the flat surface, and the shallow and deep fire areas are interconnected, posing a significant danger. These research findings can serve as a reference for detecting fire areas in coal gangue dumps and controlling environmental pollution.

Influence of Temperature Change on the Change Law of Free Radicals in Coal.

This study investigates changes in the concentration and types of free radicals in the process of coal heating, first rising and then falling. Hailar lignite, Panjiang bituminous coal, and Yangquan anthracite were selected as coal test samples. The results show that the lignite's concentration of free radical changes during heating is greater than that of bituminous coal or anthracite. It clearly shows that lignite is more prone to spontaneous combustion. In the heating and cooling portion of the experiment, the concentration of free radicals during the cooling process was much more than that of free radicals at the same temperature during the heating process. These results obtained from this research study can provide a reference for the prevention and control of the spontaneous combustion of coal with changes in temperature. This study provides a theoretical basis for the prevention and control of spontaneous combustion of coal and the selection of retarding agents and methods in the process of flame retarding by testing the free radical changes of coal at different temperatures. Also, it provides a reference for preventing and controlling coal oxidation with the change in temperature, first rising and then falling.

Pyrolysis Characteristics of Jet Coal and Oxidation of Residues in Zhundong Coalfield Fires.

Coalfield fire area reburning is one of the serious disasters in fire prevention and safety production. In this study, a synchronous thermal analyzer was used to conduct isothermal pyrolysis of jet coal at different temperatures, and the reaction characteristic parameters of different pyrolysis residual structures were analyzed. FTIR was used to measure group contents in raw coal and different pyrolysis residues. Programmed oxidation thermogravimetric experiments were carried out on the residues to obtain their oxidation characteristic parameters. The results demonstrated that the reaction characteristic parameters of the residual structures changed at 450 °C. The pyrolysis reaction mainly affected the variation of hydroxyl, aliphatic hydrocarbon, and aromatic hydrocarbon groups. The increase in pyrolysis temperature resulted in the decline in hydroxyl and aliphatic hydrocarbon groups as well as the increase in the aromatic hydrocarbon group. After pyrolysis, the ignition point temperature of the coal sample decreased, which causes the coal more likely to spontaneously ignite. It indicated that the pyrolysis residue at 450 °C is most likely to reburn. Compared with raw coal, the maximum combustion intensity of the pyrolysis residue was greatly increased, which reached the peak at 500 °C.

Coupling Relation between the Location of Cross-Cut Negative Pressure and Injecting Nitrogen into Coal Mine Goaf.

Injecting nitrogen into goaf has been widely adopted for preventing fire hazards in coal mines. In this paper, the coupling relation between different locations of negative pressure of cross-cut drainage and nitrogen injection was investigated. The minefield data collection was carried out by an in situ beam tube system on the intake airway and return airway of the mine goaf. The validated Computational Fluid Dynamics (CFD) model that was secondarily modified by on-site collected data was applied for further research. It is demonstrated that the area of the spontaneous combustion zone generally shows a sharp decline first, then tends to stabilize, and finally has a slight drop and rise with the increasing nitrogen injection time. It is obvious that the location of the negative pressure of cross-cut exerts a significant influence on the optimal nitrogen injection location and time. When the cross-cut is located in the center of the air leakage zone, spontaneous combustion zone, and asphyxiation zone of goaf, the optimal nitrogen injection location and time correspond to the P2 (25 m, 1200 min), P3 (30 m, 120 min), and P4 (35m, 1800 min), respectively. According to the simulation result, the specific relation between the optimal nitrogen injection point N(x) and the distance from the working distance of the cross-cut (x) by Newton interpolation polynomial analysis was figured out and verified that N(x) = 24.70808 + 0.293356x - 0.001436x 2. It is hoped that the result can provide scientific guidance for coal mine fire prevention and control with nitrogen injection.

Reaction Mechanism of Aldehyde Groups during Coal Self-Heating.

In order to further understand the mechanism of coal self-heating in the initial stage, the aldehyde group was analyzed by using the quantum chemistry methods. The charge distribution, structural parameters, and molecular orbital were analyzed to determine the active sites existing in the structure of aldehyde group. Then, a chemical reaction model including five elementary reaction sequences was established. In elementary reaction E1, the hydrogen of the aldehyde group is captured by hydroxyl to form the aldehyde radical, which provides the reactant and accumulates heat for the subsequent reaction. In elementary reaction E2, the aldehyde radical further reacts to form a carbon-free radical (R·) and CO, which is the main source for CO generation during coal spontaneous combustion. In elementary reaction E3, the aldehyde radical is oxidized to a carboxyl radical, providing the reactant for elementary reaction E4, which is directly related to CO2 generation during coal spontaneous combustion. The thermodynamic parameters of the elementary reactions were further analyzed and confirmed by quantum chemistry methods. The results are helpful for further understanding the pathways of CO generation in the initial stage of coal spontaneous combustion, which provides theoretical support for prediction of coal spontaneous combustion.