Coal Spontaneous Combustion Research Articles

Study on the preparation and characteristics of thickened slurry to prevent coal spontaneous combustion

In response to the problems of small diffusion area, short solidification time, and poor flowability of existing fire extinguishing materials in preventing coal spontaneous combustion in goaf areas of western mining areas, this paper studies a thickened slurry with good flowability and fast diffusion ability. The optimal ratio of thickened slurry was determined through orthogonal experiments, and the rheological properties, impregnation characteristics, and wall hanging characteristics of the material were studied. The results showed that when the water to soil ratio was 8:1, and the concentrations of sodium alginate (SA) and apigenin were 0.6 % and 0.5 %, the flowability and suspension performance of the thickened slurry were the best. When the soaking time is 14 days, the best soaking degree of the material can be achieved, with a soaking depth of 0.93 mm. Through wall hanging tests, it was found that the thickened slurry can naturally air dry on the surface of vertically placed coal pillars with a small sliding distance, which has good adhesion and retention characteristics. Further on-site experiments have shown that by injecting thickened slurry, the CO concentration at the return air corner is significantly reduced, indicating that thickened slurry can cover a large area of residual coal in the goaf, prevent contact between coal and O2, and effectively prevent the composite reaction between coal and oxygen.

Thermodynamic characteristics and mechanism of low-rank coal oxidation in oxygen-poor environment

Aiming at the restricted oxygen environment of coal mine, this paper focus on the whole process from physical adsorption to chemical reaction between coal and oxygen, and quantum chemical calculations investigate the potentiating or inhibiting effects of different active groups on the amount of oxygen adsorbed and thermally released from the main coal structure, and experimentally investigate the effect of oxygen concentration (OC) on the transformation relationship between active functional groups and active sites. The results showed the coal side-chain structure has an effect on the heat release characteristics of the aromatic ring in the process of oxygen adsorption, and the heat of adsorption of the aromatic ring with alkyl and aldehyde side-chains reaches 422.706 kJ/mol. The relationship between carbon oxide release and temperature at different OC all conformed to the exponential function model, and the apparent activation energy was positively correlated with the OC. The increase of OC narrows the gap between the production and consumption rates of active sites, which is helpful for the further understanding of the coal spontaneous combustion (CSC).

Experimental Study on Spontaneous Combustion Monitoring in Coal Mine Airspace Based on Distributed Fiber Optic Temperature Measurement

ABSTRACT Spontaneous combustion fires in the mining airspace seriously affect safety at mines. It is crucial to accurately predict the location of fire sources and forecast spontaneous combustion disasters. This study, therefore, proposes an intuitive, accurate, and efficient distributed fiber optic temperature measurement technique for detecting spontaneous coal combustion. To overcome the limitations of using traditional optical fibers in the complex environment of the goaf, this study independently developed an enhanced armored distributed optical fiber for coal mines through experiments. Aiming at the possible influence of the armoring material on the accuracy of temperature measurement, the temperature of the armored distributed optical fiber was corrected through calibration experiments of the armored optical fiber and the heat transfer simulation study of the enhanced temperature measurement optical fiber, to improve the accuracy of the measurement. Based on COMSOL’s simulation study of the spontaneous combustion temperature field and fiber optic detection in the extraction zone, a method of laying optical fibers in parallel at 15-meter intervals to achieve accurate detection of the fire source location in the extraction zone. To explore the feasibility of this technology, a field test was carried out in the 22,117 working faces of Shanxi Lu’an Group Luning Coal Co. Ltd. in the hollow area. The temperature analysis results are consistent with the results of the beam pipe monitoring. The results show that the distributed fiber optic temperature measurement technology can produce a graded warning of spontaneous coal combustion and achieve an accurate detection of the fire source.

Study on optimization of preparation and liquid content of thermo-responsive inhibitor for preventing coal spontaneous combustion

To address the issue of fast failure of salt inhibiting liquid in preventing coal spontaneous combustion, our team proposed the use of a thermo-responsive secundina sphere inhibitor (TRSSI). This agent involved wrapping the salt inhibiting liquid with phase change materials (PCMs). The previous experimental results were proven. However, subsequent observations revealed surface cracks in the TRSSI upon room temperature cooling, leading to internal liquid leakage and a low rate of complete formation. To address this, this paper conducted a thermal analysis of the TRSSI preparation process. Through range analysis, three factors affecting the thickness of the shell were determined: notably, the ice-ball radius exhibited a significant positive correlation, while the initial temperature of the PA-SA had a substantial negative impact. Conversely, the initial temperature of the ice-ball showed relatively minimal influence on thickness. By combining the regression analysis equation and mechanical conditions, the optimal volume ratio, ice-ball radius, and shell thickness under varying compressive strengths were obtained. Water retention tests showed that the TRSSI exhibited a mere 3.67% water loss rate over nine months at room temperature. The adiabatic heating test of coal demonstrated that the TRSSI, when applied to coal seam surface, accurately targeted the heat source center and swiftly reduced its temperature. Ineffective TRSSIs absorbed heat, stacked on each other, and formed a tight water-retaining layer on coal seam surface, effectively prolonging the coal’s self-heating oxidation period.

Reaction mechanism of antioxidant inhibition of hydroxyl radical in coal oxidation.

To solve the problem of unclear targeted inhibition of key free radicals by antioxidants, this paper took the hydroxyl radical with the highest oxidation activity of coal as the inhibition target and selected five antioxidants such as ethylene diamine tetraacetic acid, tea polyphenol, citric acid, vitamin C, and proanthocyanidins. Based on the theory of quantum chemistry, the characteristics and oxidation pathway of antioxidants inhibiting coal oxidation of hydroxyl radical were analyzed. Analyze the influence characteristics of antioxidants on the evolution of free radicals in coal through an electron paramagnetic resonance experiment (ESR). The results showed that the electron density of antioxidants was mainly distributed in the functional groups of carboxyl and hydroxyl, which played a key inhibitory role, and the vicinity of carboxyl and hydroxyl and other functional groups was positive potential, which was the active site of inhibiting hydroxyl radical. The order of inhibitory capacity of the five antioxidants was determined as GTP > PC > EDTA > CA > VC. It is concluded that the energy barrier of hydroxyl radical inhibition by citric acid is much lower than that of EDTA. For the hydrogen extraction reaction, VC inhibited the hydroxyl radical pathway with a higher energy barrier than the other three antioxidants. The mechanism of five antioxidants inhibiting •OH reaction was comprehensively analyzed. It was found that tea polyphenols have more active sites that can react with •OH to quench it, so the inhibition of tea polyphenols should be the most significant. When antioxidants inhibit coal spontaneous combustion, the type, complexity, concentration, and linewidth of free radicals in coal molecules are lower than those in raw coal, with GTP antioxidants having the best inhibitory effect. The research results have important theoretical and practical significance for revealing the mechanism of coal spontaneous combustion inhibition and developing directional coal spontaneous combustion inhibition technology.

Comparative study on oxidation reaction characteristics of different forms of hydroxyl‑containing coal molecules

Hydroxyl groups in coal contain a variety of forms. It is very important to study the reaction characteristics of different forms of hydroxyl‑containing coal molecules for revealing the mechanism of coal spontaneous combustion and the development of inhibitor. Therefore, this study focuses on the influence and reaction mechanism of the molecular oxidation reaction stage of different forms of hydroxyl‑containing coal by molecular dynamics, quantum chemistry and FTIR. The results show that there are two paths in the reaction of different hydroxyl structure: dehydrogenation and hydroxyl addition. The consumption rate of polyhydroxyl coal molecules (88 %) is higher than that of monohydroxyl (18 %), and the consumption rate of 2-methylphenol (58 %) is higher than that of other positions. The reaction of monohydroxyl coal is mainly influenced by aliphatic hydrocarbon, and the reaction of polyhydroxyl coal is mainly influenced by hydroxyl group. Quantum chemical calculation shows that the reactivity difference of different forms of hydroxy‑containing coal molecules is due to the active sites. Furthermore, the free energy barrier of hydroxyl addition reaction is 73–89 KJ /mol and the heat release is 52–56 KJ /mol, which can increase the trend of benzene ring-opening reaction.

Low reaction threshold of ambient temperature oxidation of coal: Perspective from oxygen concentration and airflow rate

Coal spontaneous combustion remains a significant hazard in mining operations. In this study, the temperature rise characteristics of sub-bituminous coal were investigated using an air stream of varying concentration and airflow rate. The chemical structure changes under various oxygen contents were analyzed using the FTIR technique. The findings demonstrate that ambient temperature oxidation can occur even under low oxygen and airflow rate conditions, emphasizing the need for vigilance. Although oxygen enrichment in the atmosphere promotes the coal-oxygen complex and increases the total temperature rise (TTR), TTR can still reach 0.31 °C with 6 vol% oxygen. There exists an optimum ventilation rate to maximize the TTR. TTR at the flow rate of 25 mL/min is 47 %, 36 %, 165 % and 308 % higher than at the 10, 50, 75 and 100 mL/min. Moreover, FTIR experiments indicated the difference of active groups under different oxygen concentrations is slight. The low reaction threshold for ambient temperature oxidation complicates the prevention of coal spontaneous combustion during latency periods.

Analysis of stage parameters of low-temperature oxidation of water-soaked coal based on kinetic principles

Mine fires caused by spontaneous coal combustion are major disasters in coal mines. The staged oxidation kinetic parameters of various coal samples at oxygen concentrations of 21 %, 15 %, 10 %, 5 %, and 3 % were analyzed using a programmed temperature testing system. Herein, the temperature increase rate of coal, the temperature difference between the furnace and coal, and the oxygen consumption characteristics were obtained. Based on the amount of CO produced and the temperature sensitivity coefficient, three characteristic temperatures and four stages of low-temperature oxidation (LTO) were identified. The results showed that at a critical temperature (TC), the amount of CO gas released from the coal samples increased with increasing oxygen concentration, and the difference in the oxygen consumption rate increased. After the limit temperature (Tu), the amount of CO gas increased steadily, and the increase in the oxygen consumption rate stagnated. CO production, the maximum heating rate, and the maximum heat release rate were positively correlated with the oxygen concentration. As the oxygen concentration increased, the activation energy during the oxygen absorption stage gradually decreased. The average reaction enthalpy (ΔH) of pre-oxidized water-immersed coal was 19.37 kJ/kg greater than that of raw coal. The equation for the conservation of energy of the coal oxidation warming process was normalized. The theoretical values of the awakening stage and the stable stage were τν and τν (1-B), respectively. When B was >1, pre-oxidized water-immersed coal at a low oxygen concentration was prone to crossover points during the oxygen absorption stage, which increased the risk of coal spontaneous combustion (CSC). The research results could provide a theoretical basis for the staged control of the spontaneous combustion of water-immersed coal in goaf areas.

Research Progress and Visualization Analysis of Spontaneous Combustion of Water-Immersed Coal

ABSTRACT One of the most catastrophic events that can occur during coal mining is a fire triggered by spontaneous combustion of the coal. Due to complex geological conditions, some coal mines in China have the characteristics of shallow burial and small spacing between coal seams. With the increase of mining depth, there will be many cracks in the overlying goaf. Surface water and groundwater flow into the goaf along these fissures. After long-term water immersion, the increase of ground temperature will lead to the spontaneous combustion of coal. A thorough analysis of the impact of water immersion on the spontaneous combustion of coal necessitates a review of the most recent findings in this field. The review will promote the further development of the theory and prevention of spontaneous combustion of water-immersed coal and provide theoretical help for monitoring and preventing spontaneous combustion of water-immersed coal. The creation of water-immersed coal and the reason for spontaneous combustion is investigated, as are the characteristics of the water accumulation in the goaf and their origins. The research status of spontaneous combustion of water-immersed coal is presented and illustrated domestically and internationally. On this basis, the theoretical and experimental research directions, problems, and prospects of spontaneous combustion of water-immersed coal are put forward. This study can provide a theoretical basis for monitoring, preventing, and controlling the spontaneous combustion of water-immersed coal, and provide a reference for reducing energy waste.

CFD Characterization and Field Test Study on Plugging Air Leakage with Time-Varying Viscosity Solidified Foam to Prevent Coal Spontaneous Combustion

ABSTRACT From the perspective of plugging air leakage paths and preventing coal spontaneous combustion in the goaf of coal mines, filling and plugging the ends of the working face is crucial. Generally speaking, rapidly solidified foam slurry is beneficial to plugging air leakage paths. However, researchers have not yet clarified the accumulation and diffusion rules of rapidly solidified foam, resulting in low efficiency in plugging air leakage paths. To solve the above problems, this study takes the goaf of 1301 working faces of the Shandong Lilou Coal Industry as the research object, uses the computational fluid dynamics modeling method to construct a physical model of pressure injection foam slurry, and optimizes the on-site application process parameters of plugging the end of the working face. The numerical simulation results show that coagulant can improve the accumulation characteristics and plugging efficiency of foam slurry, and the optimal addition amount is 3 wt%. In addition, as the perfusion flow increases from 5 to 15 m3/h, the airflow rates on the working face gradually increases and the oxidation zone gradually shrinks. Therefore, the grouting flow is preferably 15 m3/h. Field test results show that rapid-setting inorganic solidified foam blocks the airflow at the air inlet corner from leaking into the goaf and weakens the composite reaction of coal and oxygen. The temperature at each monitoring point first decreased, then stabilized, and the final temperature was maintained at 27-28°C. The CO concentration gradually decreased and finally remained below 20 ppm. The CO concentration of the mine’s total return airflow is stable below 10 ppm. This study can provide theoretical guidance for the technological design of using solidified foam to rapidly plug the air leakage paths at the end of the fully mechanized caving working face.

Investigation on the Tea Polyphenol/Swelling Gels to Inhibit Coal Spontaneous Combustion: An Experimental Study

ABSTRACT Developing new fire-fighting material is most significant for effective prevention and control of coal spontaneous combustion. To enhance the flame-retardant performance of the gel, the tea polyphenol/swelling gels are developed using a water-soluble polymerization method. Thermogravimetric analysis, programmed temperature experiments, and Fourier-transform infrared spectroscopy are used to reveal the structural characteristics, microscopic morphology, and thermal stability of the gel. Experimental testing the tea polyphenol/swelling gels’ water absorption, water retention, and reusability as well as their inhibitory effect on coal spontaneous combustion. The results showed that the prepared tea polyphenol/swelling gels exhibited a porous three-dimensional network structure, with a maximum swelling ratio of 607.2 g/g and a salt absorption rate of 121.4 g/g. After the testing coal sample is treating by the tea polyphenol/swelling gels, its CO production rate is sharply decreased, but the corresponding ignition point temperature and flame-retardant rate are significantly increased. The activation energy in the first stage is increased by 32.2 kJ·mol−1, in the second stage by 4.0 kJ·mol−1, and in the third stage by 23.2 kJ·mol−1. Additionally, the active functional groups such as hydroxyl and methyl in the coal are also reduced by the treatment of tea polyphenol/swelling gels. Correlation analysis indicate that the inhibition effect of coal spontaneous combustion can be achieved by reducing -OH, CH3/CH2 groups, while the increasing of C = C, C- O, C- H functional groups in the coal. Moreover, the tea polyphenol/swelling gels performing the characteristics of excellent water absorption, inhibiting coal spontaneous combustion by absorbing heat, covering the coal microstructure, and inhibiting the oxidative activity of coal molecules. This study can provide theoretical guidance for the application of swelling gels in inhibiting coal spontaneous combustion.

Geochemical Characteristics of Soil Rare Earth Elements within Spontaneous Combustion Coalfields of Rujigou Coal Mine

(1) Background: The spontaneous combustion of coal (SCC) not only consumes huge amounts of coal resources but also causes environmental degradation. Rare earth elements (REE) can be taken as an effective indicator to evaluate the environmental effects of SCC. Coal in the Rujigou Mine has been spontaneously combusting for hundreds of years. (2) Methods: The geochemical properties of REE and major elements in the soil of the Rujigou coal mine are methodically examined to reveal the environmental effects of SCC. (3) Results: Soil REE concentration in the Rujigou mine is 216.09 mg/kg, and there is an enrichment of light rare earth elements (LREE) and a depletion of heavy rare earth elements (HREE), LREE/HREE in Rujigou mine was 5.52. The spontaneous combustion of coal could change the vertical distribution of REE, which is conducive to the enrichment of LREE. According to the Eu anomaly and δCe/δEu, the source of material in this mine may be derived from the terrigenous clastic rock controlled by weak reduction. Aluminum and titanium have similar geochemical behavior to REE, especially LREE. The concentration of sulfur is negatively correlated with REE, especially HREE. Calcium, sodium, and magnesium all had a negative correlation with LREE. (4) Conclusions: The spontaneous combustion of coal can lead to the fractionation of light and heavy rare earth elements, resulting in the enrichment of LREE and depletion of HREE.

Research on the spontaneous combustion of the goaf at different advancing distances based on the dynamic evolution of porosity

Spontaneous combustion of residual coal in the goaf is one of the main disasters in coal mines. Understanding the law of spontaneous combustion of residual coal can effectively prevent coal mine fires. This paper establishes a dynamic evolution model of overburden caving and porosity in the goaf using PFC numerical simulation software, and compares and analyzes the dynamic changes in porosity and the spontaneous combustion zone at advancing distances of 50 m, 70 m, and 100 m. The results show that when the working face advances 100 m, the porosity in the caving zone of the goaf decreases from 0–0.6 to 0.16–0.3. The range of the spontaneous combustion zone on the return air side expands from 42m-50 m to 39m–61 m, and on the inlet side, it expands from 0 to 22m–50 m. With increased exposure time, the spontaneous combustion zone range shifts slightly forward to 32m–55 m on the inlet side and 21m–49 m on the return side. This study reveals the dynamic evolution law of the spontaneous combustion zone in the goaf under the influence of different advancing distances and exposure times, which can assist in preventing goaf fires.

Exploration and Frontier of Coal Spontaneous Combustion Fire Prevention Materials

Mine fires have always been one of the disasters that restrict coal mining in China and endanger the life safety of underground workers. The research and development of new fire prevention materials are undoubtedly important to ensure the safe and efficient production of modern mines. At present, the main inhibiting materials used are grout material, inert gas, retarding agent, foam, gel, and so on. In order to explore the current situation of coal spontaneous combustion (CSC) fire prevention, the existing fire prevention materials were reviewed and prospected from three aspects: physical, chemical, and physicochemical inhibition. The results show that, at present, most of the methods of physicochemical inhibition are used to inhibit CSC. Antioxidants have become popular chemical inhibitors in recent years. In terms of physical inhibition, emerging biomass-based green materials, including foams, gels, and gel foams, are used to inhibit CSC. In addition, CSC fire-fighting materials also have shortcomings, including incomplete research on the mechanism of material action, poor stability of inhibitory properties, low efficiency, and economic and environmental protection to be improved. The future research direction of fire-fighting materials will be based on theoretical experiments and numerical simulation to study the mechanism and characteristics of CSC and develop new directional suppression materials with physicochemical synergies. These findings have extremely important implications for improving materials designed to prevent CSC.

Preparation of Thermal Controlled Deoxygenation Inhibitor and Its Inhibition of Coal Spontaneous Combustion

ABSTRACT The purpose of this study was to prepare a new type of thermal controlled deoxygenation inhibitor successfully. By adding a particular inorganic salt hydrate, this new deoxidizing inhibitor effectively slows down the oxidative-exothermic reaction that may occur during the action of the original deoxidizing inhibitor, improving the efficiency of preventing coal from spontaneous combustion. The heat shielding approach was employed, using the inorganic salt hydrate’s high heat capacity to absorb and decelerate heat transport during the phase change process. To assess the heat shielding effect of inorganic salt hydrates like Na2CO3·10 H2O, MgSO4·7 H2O, Na2SO4·10 H2O, MgCl2·6 H2O, and CaCl2·6 H2O, we conducted tests using thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). With a heat shielding effect of 171.2 J/g, which is much superior to that of other hydrates, the testing results demonstrate that Na2CO3·10 H2O has the best thermal control performance. In addition, we verified the effective inhibition of coal spontaneous combustion by the thermal controlled deoxygenation inhibitor, especially under the condition of increasing temperature, and the blocking effect of the inhibitor was enhanced with the increase of temperature. The findings of this study provide a new strategy for spontaneous combustion prevention during coal mining and storage and provide a scientific basis for further industrial application and optimization.

Preparation and Experimental Research of Temperature Sensitive Expansion Gel Material for Fire Prevention and Extinguishing in Coal Mines

ABSTRACT In order to solve the problems of high viscosity at room temperature, easy dehydration and shrinkage of phase change gel, and poor plugging effect of traditional mine gel, a new type of temperature-sensitive expansion gel was developed by using hydroxypropyl methyl cellulose, chitosan, guar gum and sodium bicarbonate as raw materials, using orthogonal test and response surface analysis. The structural characterization, characteristics, fire prevention, and extinguishing performance of the temperature-sensitive expansion gel were tested. The experimental results show that the optimal ratio of temperature-sensitive swelling gel is 0.75 wt % chitosan, 0.5 wt % acetic acid, 2.5 wt % hydroxypropyl methyl cellulose, 0.4 wt % sodium bicarbonate, and 0.15 wt % guar gum. The phase transition temperature (LCST) of this ratio is 67°C. After standing at room temperature for 6 h, the gel viscosity is 5852 mpa·s, the expansion ratio is 0.846, and the strength is 319.525 N/m2. During the heating process of the coal sample after adding the temperature-sensitive expansion gel, the gel will undergo phase change and expansion in the high-temperature area of the coal, and the viscosity will increase. It can stay in the high-temperature area, wrap the coal block, and isolate the oxygen from entering, thus effectively inhibiting the coal spontaneous combustion process. In addition, the gel also produces inert gas carbon dioxide, which effectively suffocates the flame. Therefore, compared with the conventional inhibitor solution, the temperature-sensitive expansion gel has better fire extinguishing effect.

Online CO Monitoring During Low Temperature Oxidation of Zonguldak Coals

ABSTRACT During low temperature oxidation of coals, due to half reaction of carbon with oxygen, concentration of CO is readily being increased and it is monitored by the field operators via gas detectors. In this study, low temperature oxidation tests were carried out for 26 samples, which were collected from Zonguldak hardcoal basin. In order to have observation CO concentrations levels during low temperature oxidation, a complete experimental set up was established. The experimental set up abovementioned includes two gas chromatographs (GC HP 5890 and GC HP 6890), one of which (HP 5890) is employed for oven purposes. As in the case of low temperature oxidation testing procedure, a starting temperature and the ramp is defined as 30°C and 0.5 °C/min, respectively. Every 15 minutes, (7.5°C increase) gas sample produced from coal via the process of low temperature oxidation was taken and analyzed by the gas chromatograph. Based on the results obtained, the amount of CO generated at low temperature (at 37.5 °C) was found to be a significant measure for the coal spontaneous combustion liability. As for the indicator gas for the spontaneous combustion of coal, results implied the fact that increase in the amount of CO generated during spontaneous combustion was observed. Due to the abovementioned fact in terms of indicator gas for spontaneous coal combustion, it was found out the fact that the increase in the amount is significant. CO (ppm) result at early temperature was found out to be in very strong relationship with corresponding spontaneous combustion liability test results. The correlation between CPT and CO (ppm) at 37.5°C for 26 coal samples was found out to have a correlation coefficient of 0.82, i.e. R2 = 0.8224. Increase in CO (ppm) was observed with the increase in the environment temperature for each of 26 coal samples studied. Based on the FCC index values (coal spontaneous combustion liability index) calculated for each of 26 coal samples, the correlation between CO (ppm) and the corresponding FCC index values yielded a correlation coefficient of 0.86, (R2 = 0.8585).

Spatiotemporal Evolution and Frontier Focus Analysis Based on Coal Fire Control Body of Knowledge

Mine fire accidents frequently constitute a major threat to mining safety, and their potential consequences are extremely severe, which highlights the urgency of fire prevention and control research. In this study, the CiteSpace software was used to conduct a metrological analysis of 717 relevant studies in the field of mine fire prevention and control (MFPC), aiming to reveal the research trends and trends in this field. This analysis found that the annual number of MFPC articles showed a significant upward trend, indicating that it is in rapid development during the active period. China, the United States, and Australia are the main contributors in this field, and the institutional contribution of China University of Mining and Technology is particularly outstanding, reflecting the regional concentration of research activities. The analysis of cooperation networks reveals the close cross-regional collaboration among European countries. The inhibition effect and evaluation criteria and the inhibition technology under different coal characteristics have become the focus of research. Activation energy, release, and quantum chemistry have become recent hot spots, reflecting the research on the mechanism of forward physicochemical synergistic inhibition and the in-depth exploration of the molecular level. It indicates that future research will focus on the development of temperature-responsive retardant materials, the application of quantum chemistry theory, and the exploration of the microscopic mechanism of coal spontaneous combustion through molecular simulation technology to further optimize the fire prevention strategy. In summary, the findings of this study not only provide a comprehensive picture of current research activities in the MFPC field but also indicate potential directions for future research and have important guiding significance for promoting the development of this field.

Influence of composite chloride salt retardant on the characteristics of coal spontaneous combustion and comprehensive evaluation methodology

ABSTRACT In this study, we aimed to improve the efficacy and longevity of single inhibitors. NaCl, CaCl2, MgCl2, and layered double hydroxides (LDHs) were selected as the inhibitory components for experimental study. The impact of the composite inhibitors on the spontaneous combustion characteristics of the coal was studied through temperature programmed experiment, thermal analysis experiments, thermogravimetric mass spectrometry and entropy weight method, and the optimal inhibitor was determined. The findings indicate that the apparent activation energy (E a ) of the coal sample, with the addition of inhibitors during the oxidation stage, was improved. E a of MgCl2 +1.0 LDHs + Coal was the highest (127.28 kJ/mol), i.e. 35.99 kJ/mol higher than that of the original coal. The inclusion of the inhibitor increased the characteristic ignition temperatures of the coal samples compared with the original coal. The highest ignition temperature was observed for MgCl2 +0.5 LDHs + Coal, reaching (323.98°C), i.e. 11.42°C higher than that of the original coal. The addition of inhibitors significantly inhibited the production of CO. Among the three chloride salts, MgCl2 exhibited the strongest inhibitory effect on CO production. According to the entropy weight method, MgCl2 +0.5 LDHs showed the best inhibitory effect. The results show that the composite halogen inhibitor can effectively inhibit the spontaneous combustion of coal.

Quantum chemistry study on inhibition of coal spontaneous combustion based on anti-gastric acid bionics: Na+, Mg2+ inhibition and CO2 inerting

In view of the limitations of single means of inhibiting coal spontaneous combustion and the lack of research on the joint mechanism of different inhibition means, this paper constructed a joint oxygen shielding structure based on the bionic principle that gastric mucosa and gastric mucus cooperate with each other to resist gastric acid and prevent gastric acid from eroding the gastric wall, and studied the microscopic mechanism of joint inhibition of coal spontaneous combustion by using Na+, Mg2+ blocking and CO2 inerting at the same time. In this paper, the change of CO2 adsorption strength before and after ionic inhibition is used to demonstrate that the two have a synergistic effect of inhibiting coal spontaneous combustion, and the micro-mechanism of the combination of these two means is not seen in related studies. In addition, this paper also made detailed quantum chemistry simulation calculations on the water absorption of ions, the existence of coordination bonds, and the chemical stability of coal molecules after inhibition, which is a refinement and supplement to the theory of coordination inhibition. The results showed that the coal molecules themselves were attractive to water, with an adsorption energy of -12.43 kJ/mol; the adsorption strength of coal molecules to water after Na+ inhibition was more than four times of that before the inhibition, at -53. 65 kJ/mol, and the effect of Mg2+ was even better, with the adsorption energy to water increasing to -180.98 kJ/mol, and from the point of view of adsorption of water, the ions exhibited a positive coal spontaneous combustion inhibition effect. The inhibitory effect of Na+ on aldehyde group is stronger than that of Mg2+; the initial adsorption energy between CO2 and coal molecules was -12.34 kJ/mol, and the adsorption energy between the coal molecular structure and CO2 after ionic inhibition was -18.12 kJ/mol ∼ -28.62 kJ/mol, which was significantly enhanced compared with that before the inhibition, suggesting that the combination of the two means can synergistically inhibit spontaneous combustion of coal, and the synergistic effect of Mg2+ with inert gases is stronger than that of Na+.