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In recent years, abnormal CO gas overruns have often occurred in coal mining workings. CO overruns were thought to be caused by the underground blasting work or spontaneous combustion of coal seams; however, minimal attention has been given to the causes of the desorption and release of adsorbed CO in the coal seams. Additionally, insufficient research has been conducted on the generation, distribution and adsorption and desorption characteristics of protogenetic CO in coal seams. Therefore, a self-built comprehensive testing system for coal seam adsorption and desorption was used to study the characteristics of the depressurization desorption and thermal desorption of coal with different degrees of metamorphism during coal seam mining. The results showed that under isothermal conditions, the amount of CO adsorption and desorption of coal samples increased with increasing pressure; under temperature rise conditions, the gas adsorption-desorption was in a dynamic equilibrium process under certain conditions. When the temperature increased, the equilibrium was beneficial to the desorption direction. The initial temperature range of CO production at different equilibrium pressures was 45–55°C. With increasing pressure, the initial temperature point of CO gas production moves forward and was significantly lower than the initial temperature of coal spontaneous combustion. Our research results further supplement the source of underground protogenetic CO gas and provide theoretical support for the accurate prediction of CO coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

The shallow coal seam resources are gradually reduced, the depth of coal seam mining is increased, and the underground temperature is increased, which makes the risk of residual coal fire increase year by year. In order to explore the transformation path of functional groups during oxidation and the caloric release characteristics of residual coal in deep coal mine, the microcosmic changes of coal oxidation process in deep mine were analyzed by in situ diffuse reflectance (In situ FTIR) and electron spin resonance (EPR) experiments, and macroscopic characteristics such as characteristic temperature of residual coal were tested by synchronous thermal analysis experiment. In FTIR results, it is observed that hydroxyl groups, active aliphatic hydrocarbon structures, and active oxygen-containing groups are key chemical structures involved in the oxidation process of residual coal, displaying a strong correlation transformation phenomenon. This can be described as follows: oxygen absorption led to a negative correlation between aliphatic hydrocarbon structures and hydroxyl groups, while the conversion of aliphatic hydrocarbon structures into carboxyl and aldehyde groups resulted in a negative correlation between aliphatic hydrocarbons, carboxyl groups, and aldehyde groups. Active oxygen-containing functional groups showed a positive correlation. With the increased of free radical concentration, the type of free radicals increased and the linewidth (ΔH) increased. The high-temperature environment intensified thermal behavior tendencies, increased the number of active structures, and raised the risk of spontaneous combustion. The research results provided a theoretical basis for understanding the process of coal spontaneous combustion, and had important reference value for ensuring the safe mining of deep coal seams and implementing effective disaster prevention measures. [ABSTRACT FROM AUTHOR]

Given the shortcomings of existing fire-extinguishing materials, a new type of fire-retarding foam material with composite foaming agents and antioxidants as raw materials was developed. The formula of the composite foaming agent was determined by screening and compounding surfactants. Then, the inhibition characteristics of different antioxidants were tested using a cone calorimeter to determine the best antioxidant. Next, the inhibition characteristics and fire-extinguishing and cooling characteristics of fire-retarding foam were measured by a temperature programmed apparatus and a fire-extinguishing test bench. Results show that the prepared fire-retarding foam achieves the best performance when the mass ratio of the surfactants CAB-35 and MES is 2:3, the mass concentration is 0.4%, and the mass concentration of the tea polyphenols is 1%. In the aspect of low-temperature inhibition, the cross-point temperature of the fire-retarding foam increases from 119.4°C of raw coal to 142.7°C, which is 15.4°C and 6.5°C higher than that of ordinary foam and MgCl2 solution, respectively. At 180°C, the CO concentration is only 1613 ppm, which is about 67.3% of that of raw coal, 78.3% of that of coal treated with ordinary foam, and 85.8% of that of coal treated with MgCl2 solution. The fire-extinguishing times of common foam, MgCl2 solution, and fire-retarding foam are 1780 s, 1350 s, and 820 s, respectively, indicating that fire-retarding foam has the highest fire-extinguishing efficiency. [ABSTRACT FROM AUTHOR]

The research in this paper focuses on the development of a recyclable, efficient and environmentally friendly fireproofing material for mining applications. Therefore, we formulated a novel composite gel named sodium alginate composite gel (PBSL-3) with sodium alginate, alkali lignin and polyvinyl alcohol as raw materials and borax as cross-linking agent. The success of the synthesis of PBSL gel material was verified by scanning electron microscopy and infrared spectroscopy experiments. The good self-healing and ability of PBSL-3 was verified by self-healing, thermal stability and rheological performance experiments; The material has a moderate viscosity and exhibits suitable rheological properties at different shear rates, making it suitable for pipeline transportation; In addition, the weight loss of the gel material was only 64.43% at the programmed warming to a temperature of 160°C, presenting a lesser rate of weight loss, and the material lost only 58% of its weight at temperatures up to 800°C. The flame retardancy of the PBSL-3 gel material was verified by programmed warming experiments and small-scale fire extinguishing experiments. The experimental results showed that the material critical temperature of the coal samples treated with the material was delayed from 100°C to 130 °C, and the CO and C2H4 gas inhibition was 41.98% and 58.12%, respectively, and the flame retardancy was 56.41% at a temperature of 200°C. Small-scale fire extinguishing experiments show that the overall fire extinguishing effect of PBSL gel material is better, and it can effectively extinguish spontaneous coal combustion fires. [ABSTRACT FROM AUTHOR]

To overcome the problem of poor biocompatibility of inorganic gel foam, a biomass gel foam was prepared using carboxymethyl chitosan, tannic acid, and ammonium ferric citrate as raw materials. The results indicated that the gel foam exhibited optimal comprehensive performance when the mass concentrations of foaming agent, stabilizer, gelling agent, and crosslinking agent were 0.8, 0.2, 0.9, and 0.6 wt%, respectively. At this point, the foaming multiple was up to 8 and the half-life was 7.79 days. Compared to pure foam, the gel foam demonstrated excellent water retention and film-forming properties. After continuous heating at 80°C for 10 hours, its water retention rate remained as high as 49.34%. The foam film formed after 120 hours of room temperature drying reached a thickness of 1 cm without any liquid separation phenomenon. The gel foam exhibited a good inhibition effect on the spontaneous combustion and oxidation process of coal. The CO inhibition rate reached 67.43% at 100°C, and the cross-point temperature was effectively delayed by 18.2°C. Moreover, the gel foam exhibited excellent burn resistance properties. [ABSTRACT FROM AUTHOR]

An efficient, environmentally friendly, and economical polyphosphate/nitrogen-containing composite inhibitor (APNI) has been developed to prevent coal spontaneous combustion (CSC) disasters. Using temperature rise experiments during coal spontaneous combustion, mercury pressure experiments, and Fourier transform infrared spectroscopy (FTIR), the samples treated with the APNI were compared with those treated with MgCl2 and NH4H2PO4 inhibitors, and the inhibitory effects of the three inhibitors on CSC were studied. The results showed that the APNI effectively limited the reactions between the coal and oxygen, reduced the amount of CO gas generated, sealed most of the cracks, large pores and mesopores in the coal, and reduced the number of active functional groups in the coal. The APNI was more effective in preventing CSC than MgCl2 and NH4H2PO4. [ABSTRACT FROM AUTHOR]

The study aimed to explore the influence of pre-oxidation oxygen concentration on the mass variation and microstructure of coal oxidation using TG and FTIR experiments. The objective was to comprehend the thermal effects and mechanisms of coal oxidation under distinct pre-oxidation conditions. Employing fuzzy mathematics and multiple linear regression equations, the study sought to elucidate the influence mechanism of pre-oxidation oxygen concentration on the thermal effect. The findings reveal that pre-oxidation did not alter the overall weight loss pattern during the spontaneous combustion process of coal, yet significantly accelerated the rate of weight loss. Furthermore, the dry cracking temperature experienced a notable advancement. Through FTIR experiments, it was observed that pre-oxidation activated the reactivity of C=O, -CH2-, and aromatic hydrocarbons, thus leading to more intense reactions. The key functional groups influencing the mass change were identified as aromatic hydrocarbons and hydrogen bonds. Notably, the pre-oxidation effect on the thermal impact was most pronounced when the pre-oxidation oxygen concentration reached 15%. [ABSTRACT FROM AUTHOR]

Dry water is a green fire extinguisher agent with good cooling and fluidity that is composed of hydrophobic silica and tiny liquid droplets. However, the structure of dry water is unstable and easily broken during production, transportation and storage. In this study, a lignin-based hydrogel was employed as the core material and hydrophobic silica as the wall material to develop a hydrogel reinforced dry water suitable for preventing coal spontaneous combustion. The bulk density, fluidity, stability and particle size distribution of the synthesized hydrogel reinforced dry water were all measured. Compared to traditional dry water, the lignin-based hydrogel reinforced dry water had a better angle of repose and outflow velocity, measuring 19.53° and 9.40 mL/s, respectively. Additionally, the bulk density and water retention in an open environment were 2.6% and 5.2% higher than traditional dry water, respectively. The particle size distribution of the lignin-based hydrogel reinforced dry water is likewise more uniform. Thermal analysis was used to examine the effect of the reinforced dry water on coal oxidation. The results showed that the reinforced dry water reduced the mass increase caused on by oxygen adsorption, hence inhibiting coal oxygen chemisorption. Further investigation revealed that addition of reinforced dry water improved the inhibitory performance of coal spontaneous combustion by decreasing coal oxidation heat release by 4.2% and 11.2%, respectively, in comparison to raw PING and YZ coal, and by increasing coal oxidation activation energy, with maximum increases of 23 and 265 kJ/mol for PING and YZ, respectively. [ABSTRACT FROM AUTHOR]

Coalfield fires have become a major hidden danger in mining operations. In order to analyze the laws of coal oxidation and combustion under stress, a uniaxial pressurized experiment was conducted on briquettes. The results show that as the temperature rises, the oxygen consumption rate of the oxidative combustion of the coal sample increases. This rate is higher in the active stage (120–200°C). CO and CO2 gases begin to be generated in the awakening stage (60–70°C), while hydrocarbon gases are gradually generated in the active stage. Additionally, the index gas escape rate is relatively high under a specific axial pressure (4MP). The cross point temperature of the coal sample at 4MP is lower (86.9°C), and the maximum heating rate is higher (0.117°C/s) compared to other coal-oxygen samples with axial pressure applied. The application of axial pressure has two functions including opening pore channels and compacting particle space, which affect the oxidative spontaneous combustion of coal samples. The research results provide a strong scientific basis and theoretical guidance for the detection and prevention of coalfield fires. [ABSTRACT FROM AUTHOR]

Free radicals and metal ions are key factors causing coal spontaneous combustion. In order to effectively suppress coal spontaneous combustion, experiments were conducted using luteolin as an inhibitor, luteolin is abbreviated as LUT. The influence of different concentrations of LUT on the spontaneous combustion heat characteristics of coal was tested using a C600 high-precision microcalorimeter, and the inhibition mechanism was inferred by FTIR. The experimental results show that LUT is an effective coal oxygen inhibitor, under the same action conditions, different concentrations of LUT can absorb heat to different degrees, delay the initial exothermic temperature of coal, prolong the heat absorption phase of coal. Compared with raw coal, 6 wt% LUT absorbs the most heat, the starting exothermic temperature is delayed by 46°C, and the activation energy is increased by 47.89 kJ/mol, the functional group -OH content decreased by 43.4%, -CH3 decreased by 32.1%, -CH2-decreased by 37.76%. Based on this, the mechanism of inhibition is inferred, LUT not only removes free radicals (ROO•) during the chain initiation stage and captures free radicals (•OH) in the reaction chain but also chelates metal ions to inhibit the catalytic effect of metal ions during the free radical reaction, which can play a dual role in preventing free radical generation and interrupting the free radical chain reaction. The results of the study can provide a novel, environmentally friendly and effective way to prevent the spontaneous combustion of coal. [ABSTRACT FROM AUTHOR]

The exposure to spontaneous combustion of coal subjected to high ground temperatures increases as the depth of mine excavation increases. To research the oxidative heat release characteristics of deep coal, a study was carried out to characterize the oxidation kinetics and thermal effects on coal in deep thermal environments; deep coals (heat-treated coals) in 30°C (T30), 45°C (T45) and 60°C (T60) environments were prepared using a simultaneous thermal analysis, and the thermal weight characteristics (TG) and thermal release characteristics (DSC) of heat-treated coals were tested by simulating coal samples in different deep thermal environments; the thermal effects of heat-treated coals were analyzed by oxidation kinetic theory. The findings indicated that the characteristic point temperature of the coal gradually reduces (T60 has the lowest oxidation characteristic temperature) as the heat treatment temperature increases, and the maximum mass loss (63.76%) during thermal treatment coal oxidation occurs in the combustion stage. The oxidation reaction mechanism function for the low-temperature oxidation phases of the deep coal conforms to the Z-L-T equation with a three-dimensional diffusion reaction mechanism. As the temperature of the thermal environment is increased, the apparent activation energy of the coal decreases and the exothermic heat increases. This increases the tendency for oxidation of the deep coal, making it more amenable to spontaneous combustion as the ambient temperature at depth rises. The results contribute to a theoretical framework for monitoring and preventing coal spontaneous combustion fires in deep mine excavations. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion disasters frequently appear in the process of coal mining, which brings great-hidden danger to mine safety production. To effectively inhibit coal spontaneous combustion, HPMC/PEG/CS thermosensitive hydrogels with quick phase-transition response times and excellent thermal stability have been developed in this study. Then, the effects of HPMC/PEG/CS thermosensitive hydrogel on microscopic groups of coal molecules at the corresponding temperature and coal spontaneous combustion heating processes are analyzed by using Fourier transform infrared spectrometry, temperature-programmed and thermogravimetric experiments. The results reveal that the gel skeleton shows porous structure and connects with each other, which improves the thermal stability and endothermic cooling capacity of the system. Compared with raw coal, the oxygen-containing groups and aliphatic hydrocarbon active groups of HPMC/PEG/CS thermosensitive hydrogel treated coal are decreased. In addition, the characteristic temperature point of CO rapid release is postponed, and its inhibition rate is 74.48%. Simultaneously, the apparent activation energy of different oxidation stages is increased. The characteristic temperature point of coal spontaneous combustion oxidation process is delayed, thus improving the difficulty of coal spontaneous combustion reaction. HPMC/PEG/CS thermosensitive hydrogels can inhibit coal spontaneous combustion reactions by reducing the activity of coal molecules and delaying the process of coal spontaneous combustion reactions through releasing water, absorbing heat, cooling, and covering oxygen. [ABSTRACT FROM AUTHOR]

In order to improve the environmental friendliness of inhibiting coal spontaneous combustion, a new environmentally friendly biomass gel foam was successfully prepared by using xanthan gum (XG), aluminum citrate (Alcit), gluconate-δ-Lactone (GDL), alkyl glycoside (APG), and tea saponin (TS). When the concentrations of XG, Alcit, GDL and biomass composite foaming agent were 4, 4, 0.4, and 0.3 wt%, respectively, the gel foam had a half-life of up to 27 days. The gel foam water retention study showed that the water loss rate of its was 60% lower than that of water and 58.6% lower than that of foam after heating at 60°C for 10 h. The temperature-programmed experiment showed that the gel foam could delay the accelerated oxidation temperature of coal from 90°C to 140°C. The fire extinguishing experiment showed that the gel foam could extinguish coal fire quickly, the temperature of coal rapidly dropped from 960°C to 121°C within the first 20 min and the reburning of coal fire was not observed after the extinguishment. This study is useful for the development of environmentally friendly gel foams for inhibiting coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

The alpha cup method was employed to delineate spontaneous combustion areas in three coal mines. Following this, cores were drilled to measure radon concentration at various depths using the RAD7 radon detector. Subsequently, the results were then combined with the equation of radon concentration distribution with depth in a semi-infinite medium, demonstrating the equation's suitability for shallow coal seams. Thereafter, numerical models of radon migration were constructed. The study found that the upward migration of radon is weakened and adsorbed by rock formations, and faults, altering the migration path of radon. [ABSTRACT FROM AUTHOR]

In order to prevent and control the spontaneous combustion phenomenon of rectangular coal pile under the coal storage and transportation scenario, the spontaneous combustion process of rectangular coal pile was simulated based on the experimental platform, the spontaneous combustion temperature change characteristics of rectangular coal pile were obtained, a coal spontaneous combustion prediction model was constructed based on the proposed prediction method. The results show that the height of the coal pile of 30 cm is a demarcation line, the temperature change of the upper measurement point is more consistent, but the lower measurement point has a greater variability, and reaches the ignition point in a shorter time, the peak temperature is higher, which further exacerbates the spontaneous combustion of the coal pile; At 3 h the coal pile formed an initial high-temperature region, and at about 14 h the pile was in a state of complete spontaneous combustion; The prediction method using temperature data from surface measurement points as model inputs is more feasible; All three models have good robustness and generalization, and the specific order of merit is GA-BP > GA-RF > GA-SVR. The study has an important guide for the safe, green and economical development of coal transportation and storage. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shenyang Ligong University is the property of Journal of Shenyang Ligong University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Shenyang Ligong University is the property of Journal of Shenyang Ligong University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The occurrence of coal spontaneous combustion has a significant impact on both the safety of personnel and mine recovery. In order to establish an early warning system for combustion, it is crucial to develop a mathematical model that characterizes indicator gases and coal temperature. In this study, we investigated the O2, CO, and CO2 characteristics of data collected from a goaf beam pipe in the Mengcun mine. Our findings demonstrate a linear decrease in O2 concentration with goaf depth and a strong negative correlation between CO and O2. We observed that CO/∆O2 and CO/CO2 increased to a maximum and then decreased as the goaf depth increased. Furthermore, we found that the peaks of these parameters at the same sampling point corresponded to the same goaf depth, and both occurred at the junction between the air-leakage and oxidation zones. By using a logistic model to fit the CO and C2H4 data, we developed a model that characterizes the relationships among CO, C2H4, and coal temperature based on statistical laws. The model provides direct information about the inflection point temperatures of C2H4 and CO, with the former being slightly lower within the same coal sample. The overall difference between the inflection point temperatures is relatively small, about 10°C. The initial temperature ratio of C2H4 and CO remains essentially constant at 3.8. C2H2 concentrations are low and irregular, and the presence of this gas can be used to assess when coal enters the accelerated oxidation stage. This research result provides a new research view for elucidating the distribution characteristics of coal spontaneous combustion index gas. [ABSTRACT FROM AUTHOR]

When mining deep coal seams, the overlying mined-out area must be pumped and drained, and the remnant coal in the mining void area is vulnerable to spontaneous combustion via water immersion and air drying. To investigate the effect of soaking time on the spontaneous combustion characteristics of lignite, low-temperature N2 adsorption experiments and Fourier transform infrared spectroscopy (FTIR) experiments were used in this study to investigate the changes in pore structure and functional group content of coal samples by increasing the soaking time. Based on programmed warming experiments, macroscopic characteristic indicators of coal spontaneous combustion (CSC) oxidizability, such as the oxygen consumption rate and index gas, were derived. Results showed that the effect of soaking caused the total pore volume and specific surface area of lignite to increase to different degrees, which enhanced the adsorption capacity of coal to oxygen and improved the effective contact of oxygen with the active sites on the coal surface. However, there was no consistency in the effect of different soaking times on the content of reactive functional groups of the coal, with higher methyl and methine contents after 60 days of soaking (S60) and 120 days of soaking (S120) than in the raw coal (RC), and less in 90 days of soaking (S90). The propensity of coal to spontaneously combust is determined by both the pore structure and reactive functional groups, which shows the propensity of spontaneous combustion S60>S120>RC>S90. Results from this study are important in understanding the mechanism of CSC of water-soaked lignite in mined-out areas and can provide theoretical guidance to prevent CSC in mining areas. [ABSTRACT FROM AUTHOR]

The production practices in Shendong mining area show that the CO concentration at the return air corner of shallow coal seams often exceeds the limit, but the temperature of the residual coal in the goaf has not significantly increased, and no other indicative gas of spontaneous combustion in coal seams has been detected. In order to provide scientific basis for CO management at the return air corner of the fully mechanized mining face in Shendong mining area and the prevention and control of coal seam spontaneous combustion fires, based on the "three zones" distribution parameters of spontaneous combustion of coal in goaf and the characteristic parameters of spontaneous combustion of coal, and based on the mechanism of CO production in shallow buried mining area, the source and influencing factors of CO in working face were analyzed, and the calculation model of CO concentration at the return air corner in working face was established. The concentrations of CO at the return air corner in different working faces in Shendong mining areas were calculated by using the model. The results showed that the relative error between the observed and measured values remained between 0.32% and 6.92%. The quantitative analysis of the proportion of CO production from each source to the total production of CO in the return air corner is of great significance to the effective control of CO concentration in the air return corner of the working face. [ABSTRACT FROM AUTHOR]

CO2 is injected into coal bodies in advance so that CO2 is fully adsorbed in the crack pores of the coal. It can inhibit the combination of coal and oxygen, so as to prevent and control the natural combustion of coal left in goaf. However, domestic and foreign scholars have little research on the low temperature oxidation characteristics and functional group changes of coal after CO2 pre-injection. In this article, a temperature programmed experimental device is used to analyze the formation of the macro-combustion index gas; a Fourier transform infrared spectroscopy experimental analyzer was determined the content of active functional groups of each component. The results showed that when the coal-sample pre-adsorbed CO2, the generation trend of CO2 formed an approximate "V" shape, the oxygen consumption decreased by about 4%. The initial generation temperature of CO and alkane gases is lagged, and the lag temperature is 20 ~ 30°C. CO2 occupied the surface of the coal surface, and inhibiting the oxidation response of oxygen-containing functional groups. The content of hydroxyl group increases, the oxidative decomposition rate of aliphatic hydrocarbon slows down, and the content of aromatic hydrocarbon increases, which can effectively slow down the course of coal oxidation and spontaneous combustion. [ABSTRACT FROM AUTHOR]

This study aims to compare and analyze the coal tendency to undergo coal spontaneous combustion (CSC) oxidation, thereby providing theoretical guidance for predicting and controlling CSC in goafs. Experimental research was conducted to investigate the oxygen absorption characteristics during the pressure-increasing stage of 0–0.1 MPa and to examine the differences in macro- and microcharacteristic parameters during the oxidation process of coal with varying metamorphic degrees at temperatures ranging from 30 to 250 °C. The experimental data were comprehensively analyzed. The results of the experiments and analysis indicate that high-rank anthracite exhibits the highest physical oxygen absorption capacity. At 30 °C, the O2 adsorption (Qmax) maximum values of anthracite is 1.186 cm3 g−1 when the maximum equilibrium pressure (Pmax) is attained. Low-rank lignite, on the other hand, demonstrates high rates of oxygen consumption and gas generation, with the lowest crossing-point temperature (CPT) observed during the CSC oxidation process. The CPTs for lignite, bituminous coal, and anthracite are 138.2 °C, 167.9 °C, and 185.5 °C, respectively. Additionally, the linewidth (ΔH) and g-values for lignite surpass those of bituminous coal and anthracite. The free radical concentrations (Ng) of coal exhibit a significant increase with rising temperature, with high-rank anthracite demonstrating the highest Ng throughout the experimental oxidation process. However, the oxygen adsorption per unit specific surface area (QBET) is greatest, and the rate of increase in free radical concentration (ΔNg) for low-rank lignite is substantially higher than that of bituminous coal and anthracite. The active structure of lignite possesses a strong capacity to convert physiosorbed oxygen into chemisorbed oxygen, indicating that coal samples with a low degree of metamorphism exhibit a pronounced oxidation self-heating ability, which facilitates the initiation and acceleration of the free radical chain reaction. This study conducts a comprehensive analysis comparing the CSC oxidation capabilities of various types of coal. The findings provide relevant methodologies for assessing the spontaneous combustion characteristics of different metamorphic coals, which is significant for elucidating the mechanism of CSC and offering guidance for its prevention and control. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion (CSC) is a major issue in the coal mining industry and poses a significant threat to the safety of coal production. To address this problem, various technologies for CSC prevention and extinguishing have been developed. Despite this, a bibliometric and systematic review of CSC prevention and extinguishing technologies (PAETs) is currently lacking. To bridge this gap, a scientometric analysis of the bibliographic data in this field is conducted to identify current popular technologies and challenges, including statistics and analysis of the number of publications, institutions, journals, and research hotspots. Also, the paper divides CSC-PAET into two categories: wind flow control methods and fire prevention and extinguishing medias. It also provides detailed information on the research status, fire extinguishing principle, application effect, advantages, and disadvantages of each category. Finally, based on the findings and limitations of the published literature, this paper recommends that future research should focus on the microscopic mechanism of CSC reaction, strengthening the development of fire prevention and extinguishing medias and intelligent equipment, and realizing the dynamic identification, analysis and control of the whole mine fire prevention and extinguishing system, which is helpful for researchers and engineers in the field. [ABSTRACT FROM AUTHOR]

To explore the inhibiting effect of ionic liquids (ILs) on coal spontaneous combustion (CSC), the long-flame coal was treated by [BMIM][BF4], [BMIM][NO3], [BMIM][I], [EMIM][BF4], and [BMIM][AcO], the thermogravimetric analyzer and FTIR spectrometer were adopted, and they were used to analyze functional groups and mass loss properties of each sample. The combustion and thermokinetic characteristics were obtained at four heating rates, and the relation between each functional group and apparent activation energy was received. The results indicated that, the content of -OH, -CO-O-, -COO-, and aromatic hydrocarbon -CH in ILs-treated coals reduced conspicuously, and the content of C-O and aromatic ring C=C enhanced. Meanwhile, the mass maximum temperature and ignition temperature for ILs-treated coals was delayed, their reaction capacity was weakened markedly. In addition, their apparent activation energy enhanced, in which [BMIM][BF4] showed a higher apparent activation energy. The active group for -COO-, aromatic hydrocarbon -CH, and hydroxyls were main parameters affecting the CSC characteristics by Pearson correlation coefficient method. Those findings guidance for the efficient application of ILs on field of CSC. [ABSTRACT FROM AUTHOR]

After a coal seam is mined, the oxidized coal left in its goaf is prone to water immersion, and spontaneous combustion accidents involving water-immersed coal may easily occur when mining the underlying coal seam. Using scanning electron microscopy and nitrogen adsorption experimental methods, the physical structure of high-temperature pre-oxidized water-immersed coal samples was characterized. By means of infrared spectroscopy, electron spin resonance (ESR) and simultaneous thermal analysis, the microscopic characteristics of the coal samples and the endothermic and exothermic characteristics of the oxidative combustion process were studied. The results showed that a specific pre-oxidation soaking time generated more oxidation pores in the coal sample, causing more water to become trapped in the pores and increasing the secondary oxidation heat absorption. High-temperature oxidation promoted the conversion of coal sample functional groups (FG) and free radical active sites, Water immersion led to the formation and loss of FG, and the longer the water immersion time was, the greater the loss. The larger average pore size of the pre-oxidized water-immersed coal sample provided more coal-oxygen contact sites, and the breaking of chemical bonds in the FG during the secondary oxidation process accelerated the heat release and promoted the oxidative re-ignition of the coal sample. The spontaneous combustion of water-immersed coal in the goaf can be prevented by controlling the high oxidation temperature and water immersion time. [ABSTRACT FROM AUTHOR]

The index gas analysis is an important method of predicting coal spontaneous combustion (CSC). The temperature programmed experiment was used to simulate the CSC process in goaf, and the characteristics of each index gas and coal temperature change were investigated. The corresponding relationship between the target center distance and the coal temperature was determined using the multi-index weighted gray target decision theory. The findings indicate that the selected gases (CO, C2H4, C2H6) and gas combination (format fire coefficient (R), φ(CO)/φ(CO2), φ(C2H4)/φ(CH4), φ(C2H4)/φ(C2H6)) can be used as index gases for CSC prediction. The critical temperature was 70°C and the dry cracking temperature was 110°C. The combined action of coal and oxygen is divided into three stages: slow oxidation (30–70°C), accelerated oxidation (70–110°C), and strong oxidation (after 110°C). The combination of the programmed temperature experiment and the weighted gray target decision theory model determines the relationship between the off-target distance and the coal temperature. The lower the degree of CSC, the better the decision scheme, and the smaller the off-target distance. The results of Xiaobaodang's experimental analyses are applied to the field, and the actual coal temperature in the goaf is predicted to be between 37–62°C. The risk level of CSC in the goaf is determined more intuitively and precisely, providing a theoretical foundation for improving the mining area's fire prevention and extinguishing scheme. [ABSTRACT FROM AUTHOR]

In order to improve efficiency when preventing and controlling spontaneous combustion of coal, a type of compound inhibitor with tea polyphenol and vitamin E as the chemical inhibitor, grafted on a copolymer hydrogel, was prepared. The oxidation resistance of the compound inhibitor to coal was analyzed by thermogravimetric test, Fourier infrared spectroscopy, and quantum chemistry theory. The experiment results showed that: The optimum ratio of tea polyphenols and vitamin E was 1:0.05; tea polyphenols and vitamin E inhibited the oxidation of coal by capturing the decomposition products of hydroperoxides and finally forming stable ether structures, and slowing down the hydrogen supply reaction between aliphatic hydrocarbons and carboxyl groups; the antioxidant properties of vitamin E (VE) and tea polyphenols (EGCG) were mainly due to the presence of active hydroxyl groups in the ring; H22 of VE and H38 of EGCG were able to inhibit the chain reaction of coal effectively. This study provides a new technical method for development of comprehensive fire prevention technology to address spontaneous combustion of coal, and provides a reference for the research into the inhibition mechanism of spontaneous combustion of coal. [ABSTRACT FROM AUTHOR]

The minerals in coal contain a certain amount of metal ions, among which transition metal ions have a catalytic effect on coal spontaneous combustion (CSC). Therefore, the addition of metal ion chelating agent to coal will weaken this catalytic effect, thereby inhibiting CSC. As a class of highly effective metal ion chelating agent, two kinds of organic phosphonic acid compounds (OPAC), 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP) and 2-Hydroxyphosphonoacetic Acid (HPAA), were investigated for their inhibitory effect on CSC. First, the low-temperature oxidation experiment was performed on coal samples before and after OPAC treatment. The experimental results show that HEDP and HPAA could reduce CO generation during spontaneous combustion of coal with different metamorphic degrees. Besides, the inhibiting efficiency of HEDP on CSC is higher than that of HPAA. Then, the effects of HEDP and HPAA on the thermal properties of CSC were investigated using synchronous thermal analysis experiment. The experimental results show that HEDP and HPAA could significantly weaken the oxygen adsorption, mass loss, and heat release during the high-temperature oxidation stage of CSC and exhibit the same result that HEDP is better than HPAA. Finally, the reasons for the difference in the inhibitory effects of HEDP and HPAA were analyzed and the inhibition mechanism of them on CSC was revealed via quantum chemical calculation. The results can provide new ideas for preventing CSC and developing new inhibitors. [ABSTRACT FROM AUTHOR]

The coal pillar along the goaf of the completely mechanized caving face of "Isolated Island" is severely damaged, with complex air leakage and a high risk of coal spontaneous combustion. In order to research the law of goaf air leakage in "Isolated Island" working face and effectively control the hidden threat of coal spontaneous combustion in goaf, it is necessary to investigate the goaf air leakage law. In this work, the 3302 "Isolated Island" entirely mechanized caving face of Jining No. 2 Coal Mine in Shandong province, China, served as an example. SF6 tracer gas air leakage measurement was utilized to identify the air leaking route in the goaf. In conjunction with the numerical modeling, the air leakage route surrounding the goaf was evaluated to establish the coal spontaneous combustion risk region, and the targeted prevention and controlled ways of coal spontaneous combustion were proposed. The results indicated that the primary source of air leakage was the seepage of air flow through the working face to the rear goaf and the diffusion to the adjacent goaf through the broken coal pillar. The risk area for coal spontaneous combustion was 40–80 m behind the rear goaf and 50 m within the coal pillar of the adjacent goaf. Regarding this region, the comprehensive prevention and control strategies of plugging and oxygen reduction, inerting and cooling, monitoring and forecasting were proposed. In addition, the fire prevention and extinguishing system combining slurry spraying, sodium silicate, and liquid CO2 injection was designed at both ends of the 3302 track and haulage roads. Using field measurements during the working face mining process, the corresponding methods for reducing the CO volume fraction in 3302 return air roadway and air return corner effectively prevented and controlled the hidden danger of coal spontaneous combustion in the goaf and ensured the safety of working face mining. This research developed a new technology for the prevention and management of coal spontaneous combustion in the goaf of the "Isolated Island" working face. [ABSTRACT FROM AUTHOR]

The preparation of gel foams with high stability for inhibiting coal spontaneous combustion remains a huge challenge. In this paper, a highly stable gel foam (SCTH) was developed by introducing nano-hydroxyapatite (HAP) into gel foam system (sodium alginate/calcium L-lactate/tannic acid/composite forming agent). The effects of HAP on the foam performances of SCTH were analyzed. The results showed that HAP could improve the stability of SCTH by forming hydrogen bonds, metal ion bonds with the system and interfacial barriers. After 100 days, SCTH without HAP had only 44.8% of the foam volume remaining. The SCTH with 1.2 wt% HAP had 80% of the volume remaining. In addition, the SCTH had better safety. Thermogravimetric analysis showed that the SCTH could improve the maximum weight loss rate temperature, and increase the residual weight of the coal after thermal decomposition. The coal temperature-programmed oxidation experiment showed that the SCTH could increase the temperature of coal entering the rapid oxidation stage from 120 to 190°C, and the CO inhibition rate was 85.3% at 200°C. Fire suppression experiment showed that the SCTH could reduce the temperature of burning coal by 81.9% within 10 min, thus achieving rapid fire suppression. X-ray photoelectron spectroscopy analysis showed that the SCTH could more effectively reduce the total content of C=O and -COO in coal and block the chain cycle reaction of coal. This work presents a new design idea for using multifunctional nanoparticles to prepare highly stable gel foams with excellent inhibition performance of coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

Transition metal ions in coal can catalyze the oxidation of coal, reduce the activation energy of the coal-oxygen reaction, and promote spontaneous combustion. Adding a metal chelating agent to coal can form chelates with metal ions so that the metal ions lose their catalysis. A green metal chelating agent, L-malic acid (L-MA), was proposed in this study. A C600 microcalorimeter was used to study the inhibitory effect of L-MA on spontaneous coal combustion. The results show that under the same temperature-programmed conditions, the heat absorption capacity of coal treated with L-MA solution is higher than that of raw coal, but the heat release capacity of treated coal is lower. With increase in the concentration of the L-MA solution, the inhibitory effect first increased and then decreased. The maximum heat flow of raw coal is 292 mW, and the maximum heat flow of coal samples treated with malic acid is 246 mW, 237 mW, 232 mW, 240 mW and 255 mW, respectively. The maximum heat flow of 15 wt% coal sample is 20.55% lower than that of raw coal. Based on the thermal analysis, kinetic theory, and experimental data, the activation energy of each coal sample can be calculated. The activation energy of raw coal is the lowest, and the activation energy of each group first increases and then decreases with increasing L-MA concentration, which is in agreement with the law of heat flow data. Combined with the microscopic process of coal oxidation at different temperature stages, the mechanism of L-MA inhibiting spontaneous coal combustion was explored. In summary, L-MA can effectively reduce the concentration of related free radicals in the chain reaction of spontaneous coal combustion and inhibit spontaneous coal combustion. [ABSTRACT FROM AUTHOR]

To study the effect of air leakage on the risk of spontaneous combustion of close coal seam clusters, the heat release characteristics and microstructural evolution of coal samples during primary and secondary oxidation at different air volumes were compared with the help of a high precision calorimeter and an X-ray diffractometer. The Arrhenius formula was applied to calculate the effect of different air volumes on the activation energy. The results show that: The effect of air volume on coal spontaneous combustion is found to have stage adaptation, low airflow is more conducive to coal self-ignition in the pre-heat storage, and the effect of high air volume on coal spontaneous combustion becomes increasingly significant after the temperature rises to a certain degree. The effect of air volume on secondary oxidation and primary oxidation has high affinity. The risk of spontaneous combustion of secondary versus primary oxidation is not absolute, but there is a critical temperature, and secondary oxidation has a higher risk of spontaneous combustion only when the temperature is higher than the critical temperature. The effect of wind volume on the morphological characteristics of the aromatic layer structural unit is achieved mainly by changing the side chain structure. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion (the term is hereafter abbreviated as CSC) is an important problem facing by China to achieve carbon peak and carbon neutrality. CSC affects the mining process of mining for a long time, not only causing a large amount of waste of coal resources, but also severely destroying the ecological environment. At present, filling & plugging materials (the term is hereafter abbreviated as F&P materials) is widely welcomed and developed rapidly because of its advantages of wide application, obvious performance and low price. Based on the research of the prevention and control of CSC and the materials applying for it, this paper creatively puts forward an application system of materials used for the prevention and control of CSC. The types of F&P materials are systematically summarized. According to the form of materials, the F&P materials are divided into slurry, colloid and foam. The performance and effect of three kinds of F&P materials are analyzed in detail. On this basis, the cost and environmental protection characteristics of F&P materials in China were compared and evaluated. Finally, this paper predicts the development of F&P materials. This paper provides an effective reference for Chinese coal mining enterprises to select suitable F&P materials, which is of great significance for the prevention and control of CSC and environmental protection. [ABSTRACT FROM AUTHOR]

The spontaneous combustion and gas explosion induced by crushed small coal pillars and the residual coal of adjacent goaf will cause a large amount of coal loss and casualties of workers. Moreover, it also seriously pollutes the environment and aggravates the greenhouse effect. To effectively block small coal pillars and fracture zones of adjacent old workings is the key to prevent gas and coal spontaneous combustion in small coal pillars. However, the commonly used blocking materials at present are easy to shrink and chap after air drying, and they have no chemical inhibitory property. Thus, these materials cannot realize the coordinated prevention of gas and coal spontaneous combustion. In this paper, a low-cost and eco-friendly Synergistic Inhibiting and Sealing Material (SISM)with strong inhibitory properties is proposed. The optimal ratio of the material was determined by experiments. The inhibitory properties of the material are analyzed by testing and comparing the generation rate of free radical and CO generation rate. The experimental results showed that the optimal molar ratio of main antioxidant and auxiliary antioxidant was 5:2, and the optimal mass ratio of synergistic antioxidant and high water material was 1:8. Secondly, SISM can prevent or delay the production of new free radicals during coal spontaneous combustion, significantly reduce the concentration of free radicals in coal and finally delay the process of coal spontaneous combustion. Thirdly, both physical and chemical inhibitory properties are taken into account when preparing SISM. Hence, it can maintain both high inhibitory properties in the whole temperature range and the inhibition effect on coal-oxygen compound reaction, which is significantly better than MgCl2 and yellow mud (YM) with only physical inhibition. [ABSTRACT FROM AUTHOR]

Traditional coal spontaneous combustion (CSC) inhibitors, while effective, have limitations such as frequent application or short-term efficacy. To this end, we developed a slow-release and water-soluble synergistic inhibitor (SWSI) to achieve long-term CSC inhibition. The SWSI was formulated by integrating synergistic antioxidants (SA) composed of ascorbic acid (AsA) and Fe-superoxide dismutase (Fe-SOD) dissolved in a super absorbent polymer (SAP) encapsulated within hydrogel microcapsules. The effectiveness of SWSI was evaluated through simultaneous thermal analysis and in-situ free radical tests. The formulation optimization demonstrated that AsA and Fe-SOD had the maximum synergistic inhibition effect at a 1:1 molar ratio. The optimal SA: SAP ratio of 3:1 achieved the lowest oxygen consumption rate and highest inhibition rate. The encapsulation formulation, consisting of 3% SA, 6% PAM, 1% CaCl2, and 0.5% citric acid, generated the highest swelling ratio. Simultaneous thermal analysis and in-situ free radical tests indicated that SWSI greatly increased feature temperatures and the apparent activation energy, lowered reaction heat, and substantially reduced free radical concentration in the full oxidation process. The newly developed SWSI offers a significant advancement in long-term CSC prevention by integrating physical and chemical inhibition, which provides sustained and effective inhibition throughout the entire oxidation process. [ABSTRACT FROM AUTHOR]

Air leakage rates are a crucial factor affecting the oxygen supply and heat storage capacity of coal spontaneous combustion (CSC) in goaf in underground coalmines. A suitable airflow rates in goaf can significantly promote CSC. To accurately reveal the effect of airflow rate on CSC, a bituminous coal was selected, and the thermogravimetric and differential scanning calorimetry were used to receive the mass loss characteristics and enthalpy changes for sample. Six characteristic temperatures and five reaction stages were identified under multiple airflow rates, the combustion characteristics were calculated, and apparent activation energy was obtained by Coats–Redfern, FWO and Starink methods. The results indicate that with the increasing airflow rate, the characteristic temperatures decreased firstly and then rose, of which all characteristic temperatures at 150 mL min−1 were the lowest. Meanwhile, the stability and combustion capability of sample were prominently enhanced, and its exothermic ability and heat release enlarged, and the reaction capability with oxygen was the highest at 150 mL min−1. Then, the Avrami–Erofeev equation (n = 3/2) was verified to be the most appropriate mechanism of the coal sample. In addition, apparent activation energy of sample was the lowest at 150 mL min−1, and the CSC ability was sensibly strengthened. The findings will serve as a theoretical basis for the initial stage on CSC in underground coalmines. [ABSTRACT FROM AUTHOR]

CO, H2, and other combustible gases will be produced during coal oxidation in coal mines, which will increase the risk of explosion when mixed with methane. Therefore, it is very important to understand the production characteristics of combustible gas during coal oxidation. In this paper, a programmed temperature gas test system is built to study the impact of lignite on the production of gases at different particle sizes and temperatures, and the release characteristics of gases are also analyzed. The result shows that the production of combustible gas is influenced by the coal particle size significantly when the temperature is above 200 °C, and it decreases as the particle size increases. CO is the main gas during the early stage of coal spontaneous combustion, and the release of CH4 and H2 increases after 300 °C. The fitted equations of gas generation and temperature are consistent with the experimental results. The research results are helpful in understanding the hazards of coal spontaneous combustion and have a certain guiding significance for coal mine monitoring and prevention of coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

The oxidation characteristic parameters of residual coal in working face change with the advance of coal seam. To explore the influence of dynamic oxygen-consuming environments, we examined the influence of reducing the oxygen concentration on the formation characteristics and characteristic parameters of coal oxidation products, conducted with temperature-programmed experiments under staged oxygen consumption. The correlation between the characteristic oxidation parameters was determined, and the critical oxygen concentration that determined the gas yield was obtained. The results show that after staged oxygen-consumption, the oxidation of coal is stronger than that under constant low oxygen, the oxidation products are greatly affected, and the influence of pyrolysis gas is small. The oxidation characteristic parameters such as gas product volume fraction, production rate, and heat release intensity are positively correlated with the oxygen-consumed temperature. We found that the oxidation reaction heat of coal is 180~330 kJ·mol−1, and the maximum and minimum exothermic intensities are significantly linearly correlated with the oxygen consumption rate. Finally, the critical oxygen concentrations for gas production rate under oxygen-consumed conditions were 17, 9, and 5%. These results have practical significance for strengthening the prevention and control of spontaneous combustion disasters in goafs. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion (CSC) is a multifaceted research domain that has been widely explored in the literature, ranging from analytical and numerical modeling to the development of fire suppression materials and methods. A comprehensive review of the literature has revealed several distinct research trajectories, or "roadmaps", identified through criteria such as the volume of studies addressing each theme, the presence of review papers dedicated to a specific roadmap, and the explicit mention of coal spontaneous combustion in the title or keywords. This classification framework has outlined six primary roadmaps: (1) spread, quantification, and impact; (2) mechanisms, models, factors, and parameters; (3) experimental studies and models; (4) detection, monitoring, and prediction; (5) prevention and control; and (6) applications. While interconnections exist between these roadmaps, and all ultimately converge towards roadmap 5 (prevention and control), each roadmap constitutes a distinct research cluster. The focus of this review is on roadmap 4, specifically addressing the methods and technologies for detection, monitoring, and prediction of CSC events. This review encompasses studies published from 2010 to the present, providing a thorough examination of the various detection techniques employed, with particular emphasis on their limitations and the strategies proposed to overcome these challenges. A critical analysis highlights the key advantages and disadvantages of each category of techniques, offering insights into their practical applications and the potential for future advancements in this field. The present review aims to contribute to the refinement of detection and monitoring methods for CSC, with the goal of enhancing early detection capabilities and improving fire management strategies. [ABSTRACT FROM AUTHOR]

Spontaneous coal combustion adversely affects coal mine safety and restricts safe, efficient, and green coal mining. Inert gas fire prevention and extinguishing technology is a widely used fire prevention and extinguishing method in coal mines. CO2 is often used as the primary raw material for inert gas fire prevention and extinguishing, owing to its good inerting and cooling characteristics. However, the lack of data on the physical and chemical properties and fire extinguishing mechanism of CO2 by field personnel has limited the efficient application of CO2 in coal mine fire prevention and extinguishing. To explore the practical application effects of CO2 fire prevention and extinguishing technology on coal mine sites, this paper summarised and analysed the research and development status of CO2 fire prevention and extinguishing technology and expounded the physical and chemical properties, phase characteristics, and fire prevention and extinguishing mechanisms of CO2. The CO2 pipeline, CO2 pipeline intelligent monitoring and control system, CO2 inerting mechanism, and comprehensive gas fire prevention and extinguishing technology are summarised and discussed. This study provides a systematic theoretical basis for the field application of CO2 fire prevention and extinguishing technology. [ABSTRACT FROM AUTHOR]

To study the effect of pyrite on coal spontaneous combustion characteristics in low-rank coal under an oxygen atmosphere in goaf, this paper selected PZ brown coal impregnated with pyrite and its reaction products and monitored the changes in the generation of characteristic gases CO and CO2 during the programmed heating process of coal samples. The experiment found that oxygen concentration has the greatest impact on the spontaneous combustion characteristics of coal with added Fe3+. When the oxygen concentration in goaf coal increases to 9%, the promotion rate of high sulfur coal spontaneous combustion is the highest, which easily increases the range of goaf spontaneous combustion risk areas. When the temperature rises to 60°C, the catalytic effect of pyrite reaction products on coal spontaneous combustion is greatly enhanced. Through FTIR testing, it was found that Fe3+ ions, as strong oxidative free radicals, promote the reaction of –CH2–, –COOH, and –OH in coal at low oxygen concentrations, leading to a further increase in the tendency of coal to self ignite at low oxygen concentrations. [ABSTRACT FROM AUTHOR]

In order to study the effect of particle size on the thermodynamic characteristics and limiting parameters of coal spontaneous combustion, the oxidation process of coal samples of five different particle sizes (0-

Abstract Traditional coal spontaneous combustion (CSC) inhibitors, while effective, have limitations such as frequent application or short-term efficacy. To this end, we developed a slow-release and water-soluble synergistic inhibitor (SWSI) to achieve long-term CSC inhibition. The SWSI was formulated by integrating synergistic antioxidants (SA) composed of ascorbic acid (AsA) and Fe-superoxide dismutase (Fe-SOD) dissolved in a super absorbent polymer (SAP) encapsulated within hydrogel microcapsules. The effectiveness of SWSI was evaluated through simultaneous thermal analysis and in-situ free radical tests. The formulation optimization demonstrated that AsA and Fe-SOD had the maximum synergistic inhibition effect at a 1:1 molar ratio. The optimal SA: SAP ratio of 3:1 achieved the lowest oxygen consumption rate and highest inhibition rate. The encapsulation formulation, consisting of 3% SA, 6% PAM, 1% CaCl2, and 0.5% citric acid, generated the highest swelling ratio. Simultaneous thermal analysis and in-situ free radical tests indicated that SWSI greatly increased feature temperatures and the apparent activation energy, lowered reaction heat, and substantially reduced free radical concentration in the full oxidation process. The newly developed SWSI offers a significant advancement in long-term CSC prevention by integrating physical and chemical inhibition, which provides sustained and effective inhibition throughout the entire oxidation process.

In this paper, CaCl2 solution was used as an inhibitor. Raw coal was soaked in CaCl2 solution with a mass concentration of 20%, and inhibited coal samples were prepared at different temperature conditions (30 ℃, 50 ℃, 70 ℃ and 90 ℃) for different periods of time. The inhibition effect of CaCl2 solution on coal spontaneous combustion was studied through temperature programmed tests and infrared spectrum experiments. It was found that the content of surface active groups (−CH3, −CH2, −COOH, −C=O) and coal oxygen consumption rate decreased significantly with the increase of pre-inhibition temperature and pre-inhibition time. The inhibition rate and cross point temperature also increase significantly. The results show that increasing the pre-inhibition temperature and the pre-inhibition time can obviously improve the inhibitory effects on the spontaneous combustion characteristics of coal.

In light of the escalating global energy imperatives, mining of challenging-to-access resources, such as steeply inclined extra-thick coal seams (SIEC), has emerged as one of the future trends within the domain of energy advancement. However, there is a risk of gas and coal spontaneous combustion coupling disasters (GCC) within the goaf of SIEC due to the complex goaf structure engendered by the unique mining methodologies of SIEC. To ensure that SIEC is mined safely and efficiently, this study conducts research on the GCC within the goaf of SIEC using field observation, theoretical analysis, and numerical modeling. The results demonstrate that the dip angle, the structural dimensions in terms of width-to-length ratio, and compressive strength of the overlying rock are the key factors contributing to the goaf instability of SIEC. The gangue was asymmetrically filled, primarily accumulating within the central and lower portions of the goaf, and the filling height increased proportionally with the advancing caving height, the expansion coefficient, and the thickness of the surrounding rock formation. The GCC occurs in the goaf of SIEC, with an air-return side range of 41 m and an air-intake side range of 14 m, at the intersection area of the “”-shaped gas concentration distribution (gas explosion). The optimal nitrogen flow rate is 1000 m3/h with an injection port situated 25 m away from the working face for the highest nitrogen diffusion efficacy and lowest risk of gas explosion, coal spontaneous combustion, and GCC. It has significant engineering applications for ensuring the safe mining of SIEC threatened by the GCC.

In order to investigate the influence mechanism of temperature on the permeability of loose coal body in the process of spontaneous combustion of residual coal in the gob, the mathematical model of the permeability of coal body under different temperature conditions was established by considering the effects of temperature-induced adsorption deformation, thermal expansion deformation, thermal fission deformation and sliding effect, etc., and the parameters of the single influencing factors of the mathematical model of the permeability were controlled by the method of controlling variables to investigate the influence mechanism of the temperature change on the permeability of the loose coal body. Based on the principle of physical similarity, an experimental platform for loose coal seepage was designed and constructed, and anthracite coal from Chengzhuang Mine in Shanxi Province was selected as the experimental object, and air was used as the seepage gas to simulate the underground environment, so that gas transport experiments were carried out in the loose coal body under different temperature conditions (40-100 ℃), different injection pressures (0.3-0.5 MPa), and different permeability pressures (0.04-0.08 kPa). The mechanism of the influence of temperature change on the permeability of the loose coal body was investigated by mutual verification of the experimental and modeling results. The results show that: the permeability of loose coal body increases exponentially with the increase of gas pressure gradient; under the condition of the same pressure gradient, the permeability decreases gradually with the increase of temperature; the influence of the temperature on the permeability is small when it is from 40 ℃ to 60 ℃, and the change of the permeability is not obvious, and the permeability starts to decrease after 60 ℃, and the decrease of the permeability is more significant when it is from 90 ℃ to 100 ℃; under the influence of the slippage effect, the increase of the injection pressure inhibits the permeability of the coal body. Under different osmotic pressure conditions (0.04-0.08 kPa), the model values of the permeability of the loose coal body and the experimental values of the seepage flow are in high agreement. With the increase of temperature, adsorption deformation has an inhibitory effect on the permeability of the loose coal body, thermal cracking deformation and the slipping effect have a promotional effect on the permeability of the loose coal body, and the effect of the deformation of the thermal expansion on the permeability of the loose coal body is weak. Temperature affects the permeability of loose coal body through the combined effect of adsorption deformation, thermal cracking deformation and sliding effect.

Fly ash grouting is a common method for mine fire prevention and control. Aiming at the problems of fly ash slurry which is prone to water-loss cracking, poor stability and low fire prevention efficiency, fly ash colloids were prepared by adding high molecular polymer xanthan gum (XG) and hydroxypropyl methyl cellulose (HPMC) to fly ash slurry, and the gel formation time, water-retaining property and thermal stability of fly ash colloids with different water-cement ratios were tested. The effect of colloid on the inhibition of coal spontaneous combustion was studied by programmed temperature. The results showed that when the water-cement ratio of fly ash slurry was 10∶1, the glue formation time was 9.52 min, and the water-retaining property and static stability were good. The fly ash colloid exhibited the shear dilution phenomenon of non-Newtonian fluid, and the energy storage modulus G′ was higher than the loss modulus G″. It was a pseudo-plastic fluid conforming to the power law model, and exhibited the properties of elastic solid. The weight loss process of fly ash colloidal heating can be divided into three stages (30-100 ℃, 218-380 ℃ and 380-800 ℃), and the total mass loss was about 6.17%. Fly ash colloid had the function of high moisture content, oxygen isolation and fissure sealing. The inhibition rate of coal sample after inhibition was 75.86%, and the corresponding temperature point of CO and C2H4 gas generation were 30 ℃ and 20 ℃ later than that of raw coal. The spontaneous combustion process of coal had been effectively inhibited.

In order to investigate the influence of gas mixture (O2/N2 and O2/N2/CO2) on the spontaneous combustion characteristics of coal, synchronous thermal analyzers, temperature programmed gas chromatography/infrared spectrometers were used to study the characteristic temperature, thermal effect/indicator gas, and functional group changes of coal under gas mixture. The results show that under O2/N2 atmosphere, with the increase of N2 volume fraction, the characteristic temperature point lags behind, TG, DTG, DSC all shift towards high temperature, heat release decreases, activation energy during combustion stage increases, final oxygen consumption and CO volume fraction of coal decrease, hydroxyl groups in coal increase, and the content of aliphatic hydrocarbons, oxygen-containing functional groups, and aromatic hydrocarbons shows a decreasing trend; under O2/N2/CO2 atmosphere, as CO2 increases, the characteristic temperature point shifts backward, the heat release decreases, the activation energy during the combustion stage decreases, the oxygen consumption and CO volume fraction both decrease, hydroxyl and fatty hydrocarbons increase, and the content of oxygen-containing functional groups decreases; when the volume fraction of O2 is the same, the peak weight loss rate, oxygen consumption, and CO volume fraction in the O2/N2/CO2 mixture are all lower than those in O2/N2; −OH is easily oxidized and undergoes dehydration reaction. Coal releases less heat in the initial stage of the reaction, but rapidly increases in the later stage. CO is mainly generated by −C=O.

In order to study the changes of oxidation characteristics of coal with different degrees of metamorphism, the oxidation process of non-sticky coal (BN), gas-fat coal (QF) and 1/3 coking coal (1/3JM) was tested and analyzed by temperature programmed experiment system, the apparent activation energy of different oxidation stages was determined, and the change characteristics of spontaneous combustion limit parameters of coal were quantitatively calculated. The results show that the apparent activation energy of coal with low metamorphism is lower than that of coal with high metamorphism. The average apparent activation energy of BN, QF and 1/3JM coal samples is 39.90, 65.28 and 69.43 kJ/mol, respectively. The apparent activation energy of coal is positively correlated with its metamorphism, and the spontaneous combustion risk of coal with low metamorphism is higher; the apparent activation energy of the same coal at different stages is also different. The apparent activation energy of BN, QF and 1/3JM coal samples at stage 1 is 55.28, 75.05 and 80.79 kJ/mol, respectively, and that of stage 3 is 23.23, 59.07 and 61.50 kJ/mol, respectively, which decreases with the depth of oxidation reaction; the extreme temperature points of the three coal spontaneous combustion limit parameters are 50.3, 61.5 and 59.7 ℃, respectively. The extreme point temperatures of low-metamorphic coals are lower than those of high-metamorphic coals; under the same conditions, the minimum floating coal thickness and lower oxygen volume fraction of low metamorphism coal are smaller, the upper air leakage intensity is larger, and the spontaneous combustion is more likely to occur.

Accurately grasping the distribution and evolution law of coal spontaneous combustion temperature in goaf is a prerequisite for improving the prevention and control effect of coal spontaneous combustion. Taking the 15103 working face of Wenzhuang Coal Mine as the prototype, a similar experimental platform for heterogeneous goaf was established to explore the evolution law of temperature distribution in goaf under different flow field conditions, and the influence of different wind speed and unsteady wind flow conditions on the evolution of temperature distribution in goaf was analyzed. The results show that both porosity and wind flow have a certain influence on the temperature distribution, and the temperature distribution will be biased towards the large porosity area and the downwind area of the wind flow. Under the condition of unsteady flow field, the high temperature area of goaf will expand, resulting in the increase of coal spontaneous combustion danger area. The migration phenomenon of high temperature area and high temperature point under the action of airflow was found, and the migration principle was revealed.