Coal Spontaneous Combustion Research Articles

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+.

Effect of axial stress-induced coal particle breakage on the evolution laws of coal spontaneous combustion characteristics and limit parameters of loose broken coal

Coal particles are broken to varying degrees under the axial stress, thereby affecting the particle size distribution, which has an essential impact on coal spontaneous combustion (CSC). This work investigated the evolution behavior of the characteristic parameters and limit parameters of the coal oxidation process under different breakage degrees. Results showed that as the axial stress increased, the breakage degrees of coal gradually increased, while the permeability gradually declined. The increase in the breakage degree of particle induced by axial stress would promote the CSC process and increase the risk of CSC. The promotion effect reached the most prominent at 12 MPa and began to decrease at 15 MPa. Particle breakage and increasing specific surface area caused by stress were responsible for the change in CSC characteristic parameters. The reduction in permeability caused by stress dominated the changes in CSC limit parameters.

Migration and cooling characteristics of low-temperature gaseous CO2 in high-temperature loose coal

To investigate the extinguishing effect of low-temperature gaseous CO2 on coal spontaneous combustion, a similar simulation experiment was designed and conducted to test its migration and cooling characteristics in high-temperature loose coal. During the injection of low-temperature gaseous CO2, the temperature along the central axis of the release port decreases rapidly. The size of the cooling range and the diffusion rate of the cooling area are inversely proportional to the distance from the center axis and directly proportional to the injection time. The injection time plays a dominant role in the cooling effect of the high temperature coal, followed by the injection position. Gaseous CO2 diffuses inside the loose coal body rapidly, filling the vicinity of the release port within 5s and the container within 30s. The average diffusion velocity of CO2 within the loose coal is 0.051 m/s. The results of this study provide a theoretical basis for the application of low-temperature carbon dioxide to combat coal fire disasters.

Experimental and mesoscopic simulation study of size effect on splitting tensile performance of spontaneous combustion coal gangue concrete

The spontaneous-combustion coal gangue concrete (SCGAC) demonstrates different mechanical behavior compared to ordinary concrete owing to its distinct porous structure and the presence of fibrous materials in its coarse aggregates. Presently, research on the macroscopic mechanical properties of SCGAC is reasonably comprehensive; however, it falls short of fully understanding its size effect. This study examines the splitting tensile strength of cubic SCGAC specimens with three strength grades, i.e., C30, C35, and C40, and three sizes, i.e., 100 mm, 150 mm, and 200 mm; proposes a mesoscopic modeling approach based on the computer vision; analyzes the intrinsic mechanisms of splitting failure and the size effect of different strength grades on the SCGAC by utilizing mesoscopic simulation methods. Subsequently, an analysis of the size effect on the splitting tensile strength of SCGAC is conducted based on classical size effect laws. The results reveal the following: The method proposed in this study for mesoscopic modeling is recognized for its low cost, high efficiency, and accurate simulations, fulfilling the required standards for mesoscopic mechanical analysis. SCGAC, as a heterogeneous material, demonstrates significant size effect phenomena that become more pronounced with enhancements in strength grades. The Carpinter fractal size effect law is ideally suited to characterize the size effect patterns in SCGAC. This paper enhances the comprehension of the size effect of SCGAC through a combination of macroscopic experiments and mesoscopic simulations, thereby facilitating its engineering applications.

Effects on environmental conditions and limiting parameters for spontaneous combustion of residual coal in underground goaf

This study collected coal from the Meihuajing Coal Mine, Ningxia, China, and employed a temperature-programmed experimental setup to investigate the characteristics of coal spontaneous combustion (CSC) and determine the primary parameters influencing coal temperature in the goaf of this underground mine. The obtained results indicated that positive correlations existed between CO concentration, CO2 concentration, oxygen consumption rate, exothermic intensity, and coal temperature. Principal component analysis (PCA) was employed to examine the correlations of three limiting parameters—namely maximum air leakage intensity (Qmax), minimum oxygen volume fraction (Cmin), and minimum thickness of residual coal (Hmin)—with coal temperature (30–170 °C) during coal oxidation. The results of a PCA indicated that among these parameters, Qmax was most strongly correlated with coal temperature. In addition, gray correlation analysis (GCA) was adopted to examine the primary parameters influencing the occurrence of CSC during different stages. The results of GCA indicated that the primary parameter influencing the occurrence of CSC varied with the coal oxidation stage. At coal temperatures between 80 and 90 °C, Cmin and Hmin were the primary parameters influencing coal temperature. The correlation curves of Cmin and Hmin with respect to coal temperature fit well with the GaussMod model. The findings of this research provide a theoretical foundation for mitigating CSC in underground goafs.

Study on the Explosion Characteristics of CH4 with the Addition of Coal Spontaneous Combustion Gases

Study on the Explosion Characteristics of CH₄ with the Addition of Coal Spontaneous Combustion Gases

Dynamic prediction of high-temperature points in longwall gobs under a multi-field coupling framework

Spontaneous coal combustion (SCC) in longwall gobs is a serious disaster and requires prediction tools to accurately and reliably predict the temperature in gobs, but currently, there has been a lack of simple and efficient predictors. To address this issue, the temperature distributions in a longwall gob under different mining state parameters were simulated using a multi-fields coupled model. The temperature distribution and the mining state parameters were extracted to serve as input variables for prediction. Two machine learning models, integrating parameter optimization and ensemble learning strategies, respectively, were proposed to establish the functional relationships between the dynamic change boundary temperature and the maximum temperature in the gob. The results show that these two models have good prediction accuracy on the high-temperature points in longwall gobs, indicating that the ensemble learning has improved prediction accuracy. There is a positive correlation between the number of measuring points and the prediction accuracy, and three measurement points at the key locations can deliver reliable predictive performance.

Experimental study on inhibition of coal spontaneous combustion by carbon dioxide and nitrogen

ABSTRACT Injecting CO2 and N2 to reduce the concentration of O2 in the air is a commonly used measure to prevent coal spontaneous combustion (CSC). To study the difference in inhibitory effects of CO2 and N2 on coal oxidation, experiments in this study were conducted using a setup of self-developed gas-bath coal oxidation for low temperatures. The oxidation process of the coal-oxygen system was then analyzed using reaction kinetics. Two different coal samples were tested in experiments under two inert gas environments, i.e. CO2 and N2 with various O2 concentrations, respectively. The changes in O2 and CO concentrations were measured during the oxidation process. By studying the standard oxygen consumption rate (SOCR) and the apparent activation energy of the coal-oxygen reaction system, inhibitory effects of CO2 and N2 on CSC were analyzed and compared. The results showed that the SOCR of the same coal sample remained consistent and independent of the O2 concentration within the same inert gas environment although under different O2 levels. In both CO2-O2 and N2-O2 environments, the SOCR of the coal sample exhibits exponential growth with temperature. The SOCR was found to have a functional connection with temperature, it can be represented as y = a ⋅ e bT , and the R 2 (determination coefficients) of the fitting formulas are all greater than 0.94. In the correlation, the inert gas environment has minimal impact on coefficient “b,” while in the CO2-O2 environment, reducing the value of coefficient “a” can effectively lower the coal sample’s SOCR. The GBMK sample and YMWK sample have an “a” value that is 20% of the value in the N2-O2 environment when oxidizing in the CO2-O2 environment. The SOCR in the CO2-O2 environment showed a decrement of between 26.0% and 52.1% when compared to that in the N2-O2 environment, whereas the activation energy showed an increment between 1.4% and 18.6%. The findings in this work provide an in-depth understanding of the prevention of CSC in the gob for risk mitigation.

Research Status and Development Trend of Coal Spontaneous Combustion Fire and Prevention Technology in China: A Review.

Coal seam spontaneous combustion fire is not only one of the main forms of the five major mine disasters, but also the main cause of secondary disasters such as mine gas and coal dust explosions. In recent years, with the advancement of mechanization, automation, and intelligent mine construction, spontaneous coal fires in mines have presented a series of new characteristics, and the prevention and control of spontaneous coal fires are also facing new challenges. On the basis of literature research, this paper summarizes and discusses the basic theory of coal spontaneous combustion, monitoring and early warning methods, and prevention and control technology, summarizes the development process of coal spontaneous combustion theory, reviews the research progress of coal spontaneous combustion monitoring and early warning methods and prevention and control technologies, and discusses the future development direction. In terms of the basic theory of spontaneous combustion of coal, from the initial hypothesis of spontaneous combustion of multielement coal to the unified understanding of coal-oxygen composite theory, a complete set of theoretical systems have been established, and a lot of macro and micro studies have been carried out and analyzed from multiple perspectives. In terms of coal spontaneous combustion monitoring and early warning, from the initial single indicator gas early warning to the construction of gas index system, the hierarchical early warning system is studied, and gradually tends to be perfect. With the development of automation and intelligence technology, the monitoring of coal spontaneous combustion disasters has also formed a new monitoring technology with beam tube monitoring as the traditional method, distributed optical fiber, wireless AD hoc network temperature measurement, and a coal spontaneous combustion multiparameter wireless monitoring system. In terms of fire prevention and control, the traditional "prevention" and "treatment" have changed to the "prevention-control-extinction" technical system based on hierarchical early warning, and the focus has gradually shifted to "prevention", and a large number of antifire materials have been developed, including blocking materials and fire-fighting materials. However, the precise inhibition and control of coal spontaneous combustion disasters, the evolution model of coal spontaneous combustion under the conditions of multifactor coupling in the field, the reliability and stability of intelligent monitoring system, the noncontact detection method of fire source, and the collaborative adaptation of multiple prevention and control techniques are not yet clear. In the future development, the mechanism of spontaneous coal combustion and its evolution process and other basic theories should be deeply studied. On the basis of the mechanism optimization early warning method of spontaneous coal combustion process, flame retardant and fire prevention materials should be targeted and developed. On the basis of the spatiotemporal evolution of spontaneous coal combustion, monitoring and monitoring system equipment with high speed, high precision, and high stability should be developed, which should accelerate the realization of accurate dynamic sensing and intelligent early warning of coal spontaneous combustion, and form an active hierarchical collaborative prevention and control system based on the trinity of "prevention-control-extinction" of coal spontaneous combustion. The conclusions and prospects of this paper can be used for reference in the future research direction, and have a certain role in promoting the exchange of research results of coal science and technology workers.

Preparation of complex physicochemical synergistic inhibitors and study on inhibition of spontaneous combustion of coal

ABSTRACT To efficiently isolate oxygen and block free radical reactions， sodium alginate (SA), sodium polyacrylate (PAAS), attapulgite (ATP), and melatonin (MLT) were selected to develop an oxygen-insulating physicochemical synergistic inhibitor. The water loss experiment, EPR experiment, and programmed temperature rise experiment were used to characterize the performance of the inhibitor. The results show that the optimal ratio of the oxygen barrier physicochemical synergistic inhibitor is 2.5 wt% SA, 1.5 wt‰ PAAS, 9 wt% ATP, 6 wt% MLT, and 3 wt% CaCl2. In the oxygen-insulating physicochemical synergistic inhibitor, the MLT can react with oxidizing radicals in the coal to slow down the process of the oxidation reaction of the coal, and the SA gel can fill the pore space to prevent oxygen adsorption on the coal surface, the inhibition rate of the inhibitor reaches 70% at 120°C. Compared with the original coal, the CO concentration of the treated coal samples is reduced by 253.9ppm compared with that of the original coal, the generation rate is reduced by 1. 13 × 10−11 mol·cm−3·s−1, and the rate of oxygen consumption is reduced by 90. 65 × 10−11 mol·cm−3·s−1 at 120°C. The above results show that the oxygen-insulating physicochemical synergistic inhibitor developed in this paper can effectively improve the fire extinguishing efficiency is environmentally friendly and pollution-free, and has good application prospects.