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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]

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]

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]

To explore the spontaneous combustion characteristic stages of active ferrous sulfide (FeS) and its inhibition effect by gas-phase passivation. Active FeS samples were prepared and then the spontaneous combustion characteristics of active FeS and commercial FeS samples were compared. The active FeS spontaneous combustion process was divided into several characteristic stages from the perspective of spontaneous combustion kinetics. Furthermore, the inhibition effect of gas-phase passivation on the characteristic stages and the kinetics and thermal effects of active FeS spontaneous combustion process were investigated to further reveal the inhibition mechanism. The results indicate that spontaneous combustion process of active FeS is divided into the room temperature (RT) spontaneous combustion, oxygen-adsorption-induced weight gain, high-temperature combustion and burnout stages, while the spontaneous combustion process of commercial FeS excludes the RT spontaneous combustion stage. Active FeS presents greatly advanced characteristic stages, stronger spontaneous combustion reactivity and more intense reaction in the RT spontaneous combustion and high-temperature combustion stages, which agrees more with the sulfur corrosion products under actual on-site working conditions. The spontaneous combustion tendency of passivated FeS weakens gradually with the increase of passivation time until it loses its RT spontaneous combustion reactivity after 6 h passivation. After the oxide film formed on the surface of passivated FeS is destroyed, its high-temperature combustion reaction becomes relatively intense. The activation energy of passivated FeS in the spontaneous combustion reaction is much higher than that of active FeS, and their activation energies both soar with the deepening of passivation, indicating that the gas-phase passivation technology can effectively inhibit the FeS spontaneous combustion process. The gas-phase passivation time must be maintained for over 6 h despite the weakening inhibitory effect of passivation treatment on the FeS spontaneous combustion process. [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]

Coal in high-temperature deep mines or igneous intrusion mines is prone to complicated spontaneous combustion in the mining process, because it has occurred in a pyrolysis state for a long time. In order to investigate the effect of initial pyrolysis on coal oxidation, in this study, the coal samples were first pyrolyzed to different temperatures in the nitrogen atmosphere and then oxidized in the dry air atmosphere. Meanwhile, the changes in radical parameters (linewidth of ESR spectra, g factor and radical concentration), CO release and O2 content in the process of changing the states of coal samples from pyrolysis to oxidation at 70°C, 110°C, 150°C and 190°C were determined through experiments. The following conclusions were drawn: When the coal samples change from the pyrolysis state to the oxidation state, their linewidths of ESR spectra increase suddenly, and such an increase is more obvious when the change is made at a lower temperature. The linewidth increases by more than 0.066 mT after the change at a temperature lower than 110°C. Initial pyrolysis promotes the turning point temperature of g factor, and the turning point temperatures of g factor of coal after the gas atmosphere is changed from nitrogen to dry air at 70°C, 110°C, 150°C and 190°C are 160°C, 180°C, 190°C and 200°C, respectively. The growth rate of radical concentration surges after the change from the pyrolysis state to the oxidation state, and the radical concentrations of the coal samples whose states are changed after 150°C grow faster than that of the coal sample oxidized in dry air. When the temperature is lower than 110°C, the CO release under the pyrolysis and oxidation conditions is low, the maximum value being only 105 ppm. At the final temperature of 230°C, when the gas atmosphere is changed from nitrogen to dry air at 70°C, 110°C, 150°C and 190°C, the CO produced by coal is 14,386 ppm, 13220 ppm, 11836 ppm and 10,287 ppm, respectively. The mode of the effect of initial pyrolysis on coal spontaneous combustion was discussed in the end, and the conclusions are of guiding significance for coal spontaneous combustion control. [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]

A WG/C/XG (water glass/sodium carboxymethyl cellulose/xanthan gum) gel was created in this study by incorporating a tracer indicator into the fire protection material. The gel is both a tracer and flame retardant. First, scanning electron microscopy, UV spectrophotometer, and chromatography-mass spectrometer was used to characterize the samples. The microstructure of the WG/C/XG gel was investigated, as well as its impact on high-temperature response. The average rate of tracer gas release varies significantly before and after 55°C. Moreover, the release patterns of the two tracer gases are similar, indicating that the WG/C/XG gel is suitable for the solid loading of tracer gases. A thermal analyzer and programmed warming oxidation experiment analysis were used to investigate the inhibitory effect of WG/C/XG gel on the oxidation of spontaneous coal combustion. The experimental results demonstrated that the WG/C/XG gel improved the thermal stability of coal samples and inhibited spontaneous coal combustion. In mined areas, WG/C/XG gel is an excellent tracer material. [ABSTRACT FROM AUTHOR]

To investigate the influence of gangue left in goafs on the low-temperature oxidation characteristics of coal, the variations of gas products and free radical parameters of coal-gangue mixed samples with different gangue contents were tested. The results show the concentration of gas products is directly proportional to temperature and inversely proportional to gangue content (except the sample with 20% gangue content (G(20))). In addition, the oxygen consumption rate and heat release intensity follow a variation trend similar to that of gas product. Pure gangue corresponds to the highest apparent activation energy, 57.6 kJ/mol, and G(20) has the lowest value, 48.8 kJ/mol. With the rise of temperature, the free radical concentration of the mixed samples decreased slowly when it was lower than 90°C and higher than 210°C, and increased between 90°C and 210°C. Compared with the theoretical calculation results, the mixed samples all possess higher gas product, oxygen consumption rates, heat release intensities, free radical concentrations and lower apparent activation energy in the experiments, which indicates that gangue can remarkably promote the reaction of coal during low-temperature oxidation. As a result, the gangue left in goafs may promote the risk of coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

The spontaneous combustion of coal gangue hills is accompanied by the release of toxic gases and the infiltration of metal elements, posing a serious threat to the global ecological environment. The current temperature monitoring methods for coal gangue hills have certain limitations, hence advanced and timely temperature monitoring is crucial for the management of coal gangue hills. This paper takes Guojiahe coal gangue hill as an example, thousands of visible light and thermal infrared images are obtained by using an unmanned aerial vehicle, and the 3-D model of the surface temperature of the gangue hill is established with Gaussian kernel technique and Random Sampling Consensus Method (RANSAC). Furthermore, the high-temperature zone in the gangue hill is measured by handheld thermocouples. The results indicate that high-temperature areas are distributed in a circular pattern and mostly concentrated on the slope surface and the boundary line between the slope and the bench. The thermal images can reflect the temperature inside the gangue hill by comparing the results of thermocouple temperature measurement and UAV detection. Further, it is analyzed that the air leakage cracks formed on the slope of the gangue hill provide a channel for the combination of coal gangue and oxygen, accelerating the heat accumulation, and the three-field coupling mechanism of coal gangue spontaneous combustion is proposed. This study can provide technical and methodological support for the prevention and control of spontaneous combustion in coal gangue hills. [ABSTRACT FROM AUTHOR]

Existing research has found that the number, insertion depth and angle, filling rate, and working fluid of heat pipe (HP) can affect the distribution of temperature field inside coal gangue dumps. However, there is relatively little research on the optimal arrangement of heat pipes (HPs) in coal gangue dumps. In response to the above issues, based on the theoretical model of HP heat transfer, the influence of HPs layout on the temperature field of coal gangue dumps is analyzed through a combination of numerical simulation and experiments, and the optimal layout of HPs is obtained. The results show that the presence of HPs can change the heat conduction path in a coal gangue dump and help the coal gangue dumps to dissipate heat in time. As the insertion spacing of the HPs decreases and the insertion depth of the HPs increases, the area of the spontaneous combustion danger zone (SCDZ) decreases, the maximum temperature value (Tmax) decreases, and the better the cooling effect. The influence of the insertion spacing of HPs on the spontaneous combustion volume of coal gangue dumps is greater than the influence of the insertion depth of HPs. When the insertion spacing of HPs is 3 m and the insertion depth of HPs is 7 m, the spontaneous combustion volume and the highest temperature point respectively decrease by 11755m3 and 302.57 ℃, and the cooling effect of coal gangue dumps is the best. Consequently, this study provides a reference for the design and optimization of coal gangue fire fighting engineering with HP application in the future. [ABSTRACT FROM AUTHOR]

The majority of a coal mine's goaf is semi-closed complex porous medium space, which is a critical place for coal spontaneous combustion disasters. To investigate the flow diffusion pattern of inorganic compounds in fractured coal in the goaf, as well as the capacity to put out coal fires. It examine the viscosity properties of an inorganic material slurry as a function of water/material ratio and time. By building a three-dimensional grouting test platform in the lab, simulating the broken coal body with sand and gravel, designing orthogonal tests to run multiple groups of grouting tests, and analyzing the effects of factors besides grouting pressure, water/material ratio, and air space ratio on the slurry diffusion radius. The effect of grouting pressure on the pattern of slurry diffusion radius of inorganic material and the water/material ratio under the action of grouting pressure is studied. The test of inorganic materials to extinguish coal pile fire is done, and the fire extinguishing and cooling ability is assessed in comparison to mud of the same grade, based on a prior research of inorganic materials to suppress CO formation in coal oxidation warming. According on the findings, the three-dimensional grouting test platform can pass the grouting test of loose sand and gravel bodies at various grouting pressures. The effects of grouting pressure, water/material ratio, and air space ratio on slurry dispersion are discovered to be multivariate power function relationships rather than linear correlations. The related slurry diffusion radius equation is established, and the variables impacting the parameters of the slurry diffusion range are evaluated, with the grouting pressure and water/material ratio having a substantial impact on slurry diffusion. Inorganic materials, as opposed to mud, require less time to extinguish coal pile fires and are less prone to scatter. It can form an oxygen barrier through continually covering the surface of coal. The study's findings might give a solid foundation for the avoidance of slurry and fire suppression of inorganic materials in the goaf. [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 solve the problem of early warning of coal spontaneous combustion (CSC) caused by abnormal continuous CO overrun in the tailgate corner of low metamorphic coal seam, this paper takes 1306 working face of Dananhu No. 1 coal mine in Hami, Xinjiang as an example. Field measurement, experimental research and numerical simulation were used to study the sources of CO in the tailgate corner and its overrun mechanism, and a CO early warning limit calculation method suitable for CSC oxidation of low metamorphic coal seam is proposed. The results show that the ambient temperature oxidation is the most important source during non-production periods. When ambient O2 concentration is ≥7.7%, the coal sample can undergo ambient temperature oxidation to release CO, and the CO production rate has a good quadratic function fitting relationship with the ambient O2 concentration. The average CO production rate of the dissipation zone in the goaf is 3.3 times that of the oxidation zone, and the CO output proportion is 1.1. The CO early warning limit calculated can indicate the phenomenon of CSC oxidation well. The relevant research work is significant for the safety management of CSC in low metamorphic coal seam mining. [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]

Gob is one of the most serious areas of coal spontaneous combustion. With the continuous increase of mining depth, the residual coal in gob bears increased axial stress, the rise of ground temperature, and the degree of fragmentation of mining coal and rock continues to increase, the external water in the mining process changes the water content of broken residual coal, under the influence of multiple factors, the prevention and control situation of coal spontaneous combustion in gob is becoming more serious. Based on the actual accumulation environment of residual coal in gob, this paper carried out the oxidation and temperature rise experiment of broken coal under the condition of water bearing and pressure. The variation laws of oxidation characteristic parameters such as outlet oxygen concentration, oxidation derived gas, oxygen consumption rate and heat release intensity were obtained. It is found that with the increase of water content of coal sample, the water content first promotes and then inhibits the oxidation process of coal. It is found that after water molecules form a relatively stable hydrogen bond with oxygen-containing functional groups, the total energy of the two-phase materials decreases, and the reason for the decrease of wetting heat release is analyzed. The influence mechanism of axial stress loading on coal spontaneous combustion oxidation process is studied. It is found that the increase of axial stress first promotes and then inhibits the process of coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

Affected by the occurrence conditions, the inclination angle of the goaf and the ground temperature change the caving structure and temperature rise environment of the goaf, which in turn affects the distribution range of the spontaneous combustion zone in the goaf. During the process of inert gas injection, the cooling and diffusion range of the inert gas determines the its inerting effect. In this paper, the temperature-programmed experiment was used to obtain the oxygen consumption rate of coal at different temperatures. Fluent simulation showed that when no inert gas was injected, the scope of the spontaneous combustion zone on the inlet side moved backward and expanded, while the gas in the gob on the return air side overflowed, and the spontaneous combustion zone The range becomes smaller; when inert gas is injected at low temperature, the influence of different inert gases (N2, CO2) on cooling and diffusion distribution is quite different, CO2 accumulates at the bottom of the goaf, and the influence range is larger; And the space inerting effect is better; the spontaneous combustion area is affected by the injection of inert gas, and there is a risk of secondary re-ignition when the inert gas injection ends. [ABSTRACT FROM AUTHOR]

In order to study the influence of the mechanical crushing process on the low-temperature oxidation characteristics of coal, the programmed heating experiments of coal samples with different particle sizes were carried out using a programmed heating device. By comparing and analyzing the changes in CO and CO2 emission, cross-point temperature, heat release intensity, and apparent activation energy of coal samples with different particle sizes during temperature heating, the influence of particle sizes on the spontaneous combustion characteristics of coal samples was obtained. On the basis of the infrared spectrum experiment and ESR (electron paramagnetic resonance) experiment of coal samples with different particle sizes, the changes of functional groups and free radicals were further compared, and the deep-seated reasons that the mechanical crushing process affected the spontaneous combustion characteristics of coal were explored. The results showed that with the decrease in particle size, more alkyl side chains are dehydrogenated to produce alkyl radicals during mechanical crushing, and the alkyl radicals are oxidized with oxygen to form more oxygen-containing functional groups. These oxygen-containing functional groups can accelerate the low-temperature oxidation process of coal in the subsequent secondary low-temperature oxidation process, release more heat, and increase the heat release intensity. In the process of mechanical crushing, the coal sample not only changes in physical structure but also changes in chemical structure. With the decrease in particle size of coal samples, more CO and CO2 are produced in the process of low-temperature oxidation of coal, and the time to reach the cross-point temperature is advanced. However, the cross-point temperature and the apparent activation energy decreases, and the spontaneous combustion characteristics of coal are enhanced. [ABSTRACT FROM AUTHOR]

To control spontaneous combustion of sulfide ores, the compound inhibitor was prepared by selecting physical resistance raw materials(Na2CO3), chemical resistance raw materials(Melatonin), Cetyltrimethylammonium bromide(CTMAB) and hydroxyethyl cellulose(HEC). With the help of the simultaneous thermal analyzer, different concentrations of inhibitors were prepared and the thermal behavior of the ore samples with 10, 15, and 20 wt% inhibitor at four heating rates of 5, 10, 15, and 20 K/min was determined. The Flynn-Wall-Ozawa method was applied to calculate the activation energy of sulfide ores with different concentrations. The results showed that: Gradually increasing the heating rate will increase the reaction intensity of each ore sample in the first weight loss stage of thermal decomposition, and then reduce the mass of the ore samples involved in the second weight loss stage; The thermal stability of each resisted ore sample is better than that of the original ore sample; The increase in the concentration of inhibitor can inert the reaction process of ore samples in the thermal decomposition stage, weakening the exothermic effect of ore samples; The inhibitor with 15 wt% had a better effect on preventing spontaneous combustion of sulfide ores, and its property value is higher than other concentrations. [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]

Passive daytime radiative cooling (PDRC) achieves cooling by simultaneously reflecting sunlight and radiating heat to outer space, without consuming any external energy. Traditional PDRC designs use organic materials that are prone to aging and secondary pollution under solar illumination. Here, a flexible alumina fiber membrane (FAFM) is prepared using electrospinning technology. The fiber‐membrane hierarchical structure ensures macroscopic flexibility, allowing this inorganic material to be assembled on complex surfaces just like organic materials. It can efficiently dissipate heat by emitting infrared radiation that matches the atmospheric window and scattering sunlight. Importantly, it is notable that no aging phenomenon occurs even under prolonged ultraviolet irradiation, which brings additional benefits to its green energy‐saving properties. As a result, its outstanding fire resistance and thermal insulation prevent the possibility of spontaneous combustion in extremely hot weather during the summer and may serve as a multifunctional insulation layer for buildings. This preparation method promotes surface design based on more inorganic structural materials in the future, enabling the design of more low‐cost, highly flexible inorganic PDRC materials. [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]

Combustible gases, such as CO, CH4, and H2, are produced during spontaneous coal combustion in goaf, which may cause an explosion under the stimulation of an external fire source. It is of great significance to study the influence of combustible gases, such as CO and H2, on the characteristics of a gas explosion. In this study, CHEMKIN software (Version 17.0) and the GRI-Mech 3.0 reaction mechanism were used to study the influences of different concentration ratios between CO and H2 on the ignition delay time, free radical concentration, and key reaction step of a gas explosion. The results show that the increase in the initial CH4 and CO concentrations prolonged the ignition delay time, while the increase in the H2 concentration shortened the time and accelerated the explosion reaction. The addition of H2 promoted the generation of free radicals (H·, O·, ·OH) and accelerated the occurrence of the gas explosion. CO generated ·OH free radicals and dominated the methane consumption through the R119 and R156 reactions. As the concentrations of CO and H2 increased, the R38 reaction gradually became the main driving factor of the gas explosion. [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]

Coal-to-liquid technology is a key technology to ensuring national energy security, with the Fischer–Tropsch synthesis process at its core. However, in actual production, Fischer–Tropsch wax residue exhibits the characteristics of spontaneous combustion due to heat accumulation, posing a fire hazard when exposed to air for extended periods. This significantly threatens the safe production operations of coal-to-liquid chemical enterprises. This study primarily focuses on the experimental investigation of the oxidative spontaneous combustion process of three typical types of wax residues produced during Fischer–Tropsch synthesis. Differential Scanning Calorimetry (DSC) was used to test the thermal flow curves of the three wax residue samples. Kinetic analysis was performed using the Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods to calculate their apparent activation energy. This study analyzed the thermal behavior characteristics, exothermic properties, and kinetic parameters of three typical wax residue samples, exploring the ease of reaction between wax residues and oxygen and their tendency for spontaneous combustion. The results indicate that Wax Residue 1 is rich in low-carbon chain alkanes and olefins, Wax Residue 2 contains relatively fewer low-carbon chain alkanes and olefins, while Wax Residue 3 primarily consists of high-carbon chain alkanes and olefins. This leads to different thermal behavior characteristics among the three typical wax residue samples, with Wax Residue 1 having the lowest heat release and average apparent activation energy and Wax Residue 3 having the highest heat release and average apparent activation energy. These findings suggest that Wax Residue 1 has a higher tendency for spontaneous combustion. This research provides a scientific basis for the safety management of the coal chemical industry, and further exploration into the storage and handling methods of wax residues could reduce fire risks in the future. [ABSTRACT FROM AUTHOR]

Fires originating from coal spontaneous combustion within coalfields result not only in substantial coal resource depletion but also producing residual low-activity pyrolysis coal chars exhibiting varying degrees of oxidation. These chars develop progressively through successive heat penetration at the fire front and post-fire extinguishment phases. This paper focuses on the alkaline earth metal-activated catalytic gasification of residual oxidized coal in fire zones, constructs a carbon-based model of oxidized coal in fire zones. The results show that the reaction active sites of the oxidized coal carbon matrix model are mainly concentrated on the carbon atoms at the end of the aromatic ring. During catalytic gasification, the calcium-based catalyst engages with these active sites, forming a preliminary catalyst. The transformation of oxidized coal into CO primarily occurs through two distinct routes. Calcium attaches to the surface of the oxidized coal's carbon-based structure, establishing active sites. Acting as a facilitator, it aids the movement of CO2 to the carbon-based surface, leading to its further breakdown into CO. The catalytic species containing calcium persistently amalgamates with active sites on coal coke surface, fostering the release of additional CO. Moreover, these catalytic species with calcium also bind CO2 and unite with active coal coke sites, generating carbon–oxygen complexes on the surface. These complexes are thermally unstable and decompose, yielding CO and initiating the formation of fresh active sites on the coal coke surface. Consequently, they interact further with calcium-based catalytic species, culminating in the creation of catalyst precursors, which drive a recurrent catalytic reaction process. [ABSTRACT FROM AUTHOR]

Coal is a crucial energy source globally, but it poses environmental challenges due to high temperatures and harmful missions during combustion. This study investigates bituminous coal's oxidation combustion in low-oxygen environments using thermogravimetry and differential thermogravimetry tests. We explore the thermal behavior and kinetic properties of three coal samples during combustion. Our findings reveal that, as oxygen concentration decreases, the combined combustion index of the coal samples also decreases during the oxygen-absorption stage. Additionally, the apparent activation energy of coal increases with its conversion rate (temperature). We observe a shift in the reaction mechanism from three-dimensional dissipation mode to two-dimensional as the oxygen concentration decreases. Notably, the activation energy initially rises and then decreases with increasing conversion (temperature) during the pyrolysis combustion stage, with a shortened phase of increased activation energy at lower oxygen concentrations. Furthermore, the kinetic mechanism transitions from stochastic nucleation and growth to one-dimensional phase-boundary mode with decreasing oxygen concentration. These insights enhance our understanding of coal oxidation combustion in low-oxygen environments, contributing to strategies for mitigating coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion (CSC) events pose hazards to miners, infrastructure, and the environment. To mitigate some of the risk of CSC, this study explored the influence of airflow rate (AFR), oxygen concentration (OxyC), and heating rate (HR) on CSC. A temperature programmed experiment was used to examine a coal sample under different AFRs, OxyCs, and HRs. The characteristic temperature was determined using index gas growth rate analysis, and the characteristic parameters were shown. The apparent activation energy (Ea) of the sample was computed by the Arrhenius equation, and variance analysis was employed to quantitatively characterise the impact of different environmental factors on the characteristic parameters of the coal samples. The experimental results show that the critical temperature of the coal samples ranges between 65 and 75 °C, and the cracking temperature ranges between 115 and 130 °C, dividing the low-temperature oxidation process of coal into three stages: before the critical temperature, between the critical temperature and the cracking temperature, and after the cracking temperature. An AFR of 120 mL min−1 was identified as the optimal level; exceeding or falling below this value inhibits the coal-oxygen reaction. Increasing OxyC and reducing HR improves coal oxidation. Compared to the same samples under AFR and HR conditions, the Ea of coal under oxygen conditions is lower, ranging between 20 and 35 kJ mol−1, while under AFR and HR conditions, the Ea is not less than 30 kJ mol−1, indicating a stronger tendency for spontaneous combustion under oxygen conditions. AFR substantially affects the oxygen consumption rate, CH4, and exothermic intensity at all stages, with a partial η2 of 0.6. Before the critical temperature, OxyC has the greatest impact on CO2; between the critical temperature and the cracking temperature, OxyC has the greatest impact on CO; and after the cracking temperature, OxyC has the greatest impact on CO, CO2, C2H4, and C2H6, with partial η2 values of 0.51, 0.59, 0.278, and 0.45, respectively. [ABSTRACT FROM AUTHOR]

The effect of different oxygen concentration conditions on the heat release behaviour of bituminous coal during spontaneous combustion was investigated. Thermal analysis experiments were conducted using differential scanning calorimetry (DSC) and laws governing feature peak changes. Heat flow curves were utilised to identify thermal reaction stages, and the impact of oxygen concentration on heat flows during spontaneous coal combustion (SCC) was assessed. The determinants of heat release rates according to temperature and different oxygen concentration conditions were shown. The heat release process exhibited varying heat proportions at distinct stages. Using the feature point analysis method, the DSC curves could be used to show the apparent activation energy of the total SCC process for different oxygen concentrations. Findings showed a noteworthy influence of oxygen concentration on the overall SCC process. As oxygen concentration increased, the characteristic peak of the heat flow curve appeared earlier, the range of heat release and its heat release temperature rose, and the apparent activation energy also increased. A critical oxygen concentration range, between 7 and 12%, was identified, causing fluctuations in the development process of SCC. This article provided a theoretical basis for further investigation into the SCC process and mechanisms. [ABSTRACT FROM AUTHOR]

The phenomenon of spontaneous combustion during the release of high-pressure H 2 is critical to the safe storage and transportation. Besides physical methods to suppress self-ignition, the approach of mixing low-reactivity gases has gained increasing attention. Previous work has mainly focused on the flow, physical heating effects, and boundary conditions of self-ignition in mixed gases, while the intrinsic chemical reaction mechanisms of spontaneous combustion remain underexplored. To clear this issue, this work uses the ReaxFF MD simulation method to study the spontaneous combustion process of H 2 /CO and H 2 /CH 4 mixtures with various concentrations. The results indicate that: (1) in pure H 2 , H 2 /CO, and H 2 /CH 4 systems, the primary initial reaction mechanism is H 2 +O 2 HO 2 +H. Additionally, in some mixed systems, CO + O 2 CO 2 +O and CH 4 +O 2 CH 3 +HO 2 may also serve as initial reaction mechanisms. (2) Under fuel-lean combustion conditions, the RIDTs of the systems decrease, supporting the viewpoint that self-ignition typically occurs first in fuel-lean regions. The addition of CO and CH 4 increases the RIDTs, which helps inhibit the development of self-ignition. (3) In H 2 -rich environments, CO combusts to CO 2 through the formation of HOCO, while CH 4 undergoes dehydrogenation and oxidation processes through intermediates such as CH 3 , CH 3 O, and HCHO, leading to the formation of CO and CO 2. The combustion of H 2 is also influenced by these processes. (4) The addition of CO and CH 4 increases the activation energy of H 2 combustion, raising the reaction energy barrier that must be overcome for spontaneous combustion. This effectively helps to suppress the occurrence and development of self-ignition during the release of high-pressure gases. • Clear initial reaction mechanism of pure H 2 , H 2 /CO, and H 2 /CH 4 combustion systems. • RIDTs of H 2 , H 2 /CO, and H 2 /CH 4 systems are statistically analyzed and compared. • Reaction pathways of H 2 , CO, and CH 4 in mixed systems have been identified. • Combustion activation energies of H 2 in mixed systems are calculated. • Explained the inhibition of self-ignition from a molecular reaction perspective. [ABSTRACT FROM AUTHOR]

To investigate the influence of moisture on the exothermic properties of coal oxidation, this study investigated the variation in thermal effect and radical parameters in the oxidation process of coal under different moisture content. This was achieved through thermogravimetric–differential thermal experiments and electron spin resonance experiments. Additionally, the study analyzed the impact of free radicals on the characteristics of the thermal effect of coal at different oxidation stages using the product–moment correlation method. The results indicate that the moisture content of 8% is a critical point for promoting or inhibiting the oxidation reaction of coal. Below this threshold, it promotes the oxidation reaction, while above it, it plays an inhibitory role. The most significant promotional effect was observed at 8% moisture content, which increased both the weight loss and heat release by 8.61% and 1567.04 J/g, respectively, while also significantly enhancing free radical species and complexity. Conversely, when the moisture content of coal reached 20%, there was a notable inhibition effect, with a reduced weight loss and exothermic capacity by 4.94% and 2705.03 J/g, respectively, along with decreased free radical species and complexity. The free radical species and heat effect parameters in coal showed a strong correlation at all stages of low-temperature oxidation, thus indicating that g-factor can characterize the coal oxidation process to some extent. [ABSTRACT FROM AUTHOR]

To investigate the influence of imidazole ionic liquids (IILs) on the whole process of coal spontaneous combustion (CSC). Three IILs, [EMIm][BF4], [BMIm][BF4], and [BMIm][NO3], were selected to carry out thermogravimetry and differential scanning calorimetry (TG–DSC) thermal analysis experiments on long-flame coal. The mass change curve (TG) and enthalpy change curve (DSC) of the coal oxidation process were determined. The characteristic temperatures and stages of the whole process of CSC were also divided by TG and DSC curves, respectively. The influence of IILs on the mass and enthalpy changes were analyzed. Then, the inhibition effect of different IILs on the whole process and each stage of CSC were calculated based on the thermal release, and the inhibition strength of anion and cation was discriminated. From the TG curve, the characteristic temperatures (except T2) and stages of the treated coal moved toward the high-temperature region of the CSC process compared with the raw coal, the whole mass loss behavior lags behind the raw coal significantly, and the mass loss in the combustion stage is smaller than that of the raw coal. From the DSC curve, the characteristic temperatures (except TD4) of the treated coal are higher than that of the raw coal, and the thermal release at each stage is lower. Although IILs have a slight facilitating on the accelerated oxidation stage of CSC. However, in general, IILs not only inhibit the occurrence and development of CSC mass loss behavior, but also cause the thermal behavior to end earlier and thermal release reduced. The inhibition effect of the three IILs on spontaneous combustion of long-flame coal is as follows: [EMIm][BF4] > [BMIm][NO3] > [BMIm][BF4], with inhibition effects of 26.5%, 19.4%, and 4.8%, respectively. The inhibition effect on CSC of cation [EMIm]+ is better than that of [BMIm]+, anion [NO3]– is better than that of [BF4]–, and the inhibition strength of cation was superior to the anion. [ABSTRACT FROM AUTHOR]

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Air humidity has a significant effect on the characteristic parameters and heat changes of the coal spontaneous combustion process. In this study, a self-built precision humidity-generating device with adjustable humidity was used to investigate the effect of different humidity conditions on the spontaneous combustion process of coal. The release of indicator gases was determined by a humidity-generating unit in conjunction with a temperature-programmed device for coal oxidation, and the effect of air humidity on coal spontaneous combustion was studied from a macroscopic perspective. A quantitative study of the effect of air humidity on the heat released during the spontaneous combustion of coal was carried out by obtaining data for exothermic heat release intensity by conducting thermal analysis. Meanwhile, the numerical simulation method was used to study the influence of air humidity on the heat released during the coal spontaneous combustion process. The experimental results indicated that the introduction of moist air could significantly increase the oxygen consumption rate of the coal samples and promote the production of CO and CO2. In the slow oxidation stage, the air humidity has a greater effect on the heat release than that in the accelerated and fast oxidation stages. The simulated results of heat release in the slow oxidation phase are consistent with the experimental data, verifying that the moisture in the air can increase the amount of heat release and promote the coal-oxygen reaction. When the moisture in the air first came into contact with the coal, it released a large amount of adsorption heat in a short time, which increased the coal temperature. [ABSTRACT FROM AUTHOR]

Due to the influence of high ground stress, high ground temperature, high water inflow and other problems in deep mines, coal spontaneous combustion (CSC) is seriously harmful. This paper studied the variation law of three kinds of indicator gases in the process of coal heating in deep mines, and established a multi-parameter gas indicator prediction system for CSC. Secondly, in view of the shortcomings of the negative pressure bundle tube. A positive pressure beam tube monitoring system for early warning of CSC was developed, the accuracy of sampling data was verified on site, and the high temperature area in the well was further identified by isotope radon measurement. Combined with the positive pressure beam tube monitoring system, to realize the joint detection of uphole and downhole. Finally, according to the detection results of the fire area, the fire prevention methods for small space fire area, multi-coal seam and multi-source air leakage complex fire area and large-area concealed fire area are determined. The above-mentioned CSC early warning and prevention system was applied in Dongtan (DT) Coal Mine, and a good fire prevention effect was achieved. In this paper, the CSC prevention and extinguishing system established has important significance in the prevention and control of mine fires. [ABSTRACT FROM AUTHOR]

The risk of coal spontaneous combustion in goaf is one of the disasters in coal mining, ventilation and extraction often aggravate air leakage from the goaf. Due to the unclear rule of expansion law and air leakage, the risk space for coal spontaneous combustion continues to occur. To investigate the influence of ventilation and extraction on the evolution of the risk space of coal spontaneous combustion (CSC) in goaf, further reveal the characteristics of air leakage and extraction in goaf and obtain the expansion law of CSC risk space. A three-dimensional model of goaf under surface drilling and gas extraction was developed. Using FLUENT numerical simulation software, taking a coal mine in Anhui Province, this study analyzes the influence factors, evolution law, and influence characteristics of CSC through field observations and numerical simulation. The research indicates that ventilation keeps the risk space of CSC expanding. The extraction of single drilling showed a local space expansion, while the extraction of double drilling shows the overall space expansion of the goaf. The air leakage flow path in goaf, air flow velocity vector in working face, gas concentration loss, and gas extraction characteristic parameters are determined. The loss of air leakage along the working surface meets four-stage: "strong in – flow - mixed flow – steady inflow – sudden outflow." It can be determined that the extraction intensity of single drilling should be greater than 34.8 m3/min, and the double drilling should be greater than 18.7 m3/min. The relationship between the coupling influence of ventilation and extraction and the expansion law of CSC risk space is determined, and the maximum risk space width of CSC can be predicted. The research results are of guiding significance for CSC prevention and gas efficient extraction. [ABSTRACT FROM AUTHOR]

Insufficient handling of spontaneous combustion in coal piles arises from the influence of natural wind during the piling process, resulting in the displacement of the heat source. To investigate the impact of wind flow on heat source movement in simulated coal piles under varying wind velocities, an experimental stage was established. The research findings elucidate that both normal and tangential winds exert an influence on the heat source position, with normal winds exhibiting a greater effect than tangential winds. The relationship between heat source position speed and wind speed magnitude follows a common fitting function under both wind conditions. Specifically, the speed of the heat source at the edge position demonstrates a linear correlation with the magnitude of wind speed, while the speed of the heat source at the center position conforms to a quadratic function with the wind speed magnitude. The heat source moves at a distance of 0.8 cm to 5.3 cm on the Y = 0 tangent, corresponding to a moving speed of 0.03 cm/min to 0.18 cm/min. On theY = −20 tangent, the heat source moves at a distance of 2.1 cm to 8.1 cm, corresponding to a moving speed of 0.07 cm/min to 0.27 cm/min. Moreover, the study reveals that the influence on heat source movement at the center of the simulated coal pile diminishes as wind speed decreases under both wind conditions. These research findings provide a theoretical foundation for managing spontaneous combustion in coal piles and offer insights into precise management of heat source positions within coal piles. [ABSTRACT FROM AUTHOR]

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 address the environmentally friendly issue of fire prevention and extinguishing materials in coal mines, a new biomass gel material was prepared using sodium carboxymethyl cellulose (CMC) as the matrix, ferro aluminum citrate (Fe-AlCit) as the cross-linking agent, and gluconic acid-δ-lactone (GDL) as the pH modifier. Through performance tests of gel micromorphology, thermal stability, viscoelasticity and yield stress, it was found that the CMC-3 gel material with a ratio of 2.5% CMC + 4% Fe-AlCit +2% GDL had a dense surface structure, good thermal stability and moderate viscosity, which was the most suitable for pipeline transport. A metal coordination bond favorable to the stability of CMC-3 gel is formed by the carboxylate ion in CMC and the double high-valent metal ions Fe3+ and Al3+ dissociated by Fe-AlCit. CMC-3 gel exhibits excellent fire prevention and extinguishing properties. The results of the programmed warming experiments showed that the inhibition rate of the coal sample treated with CMC-3 gel against CO and C2H4 gases reached 44.84% and 46.57% at 220°C, respectively, and the growth rate of the activation energy in the first and second stage reached 17.63% and 22.68%, respectively, which plays a significant inhibitory role. The infrared spectroscopy test showed that after adding CMC-3 gel, the content of -OH and Ar-C-O in the coal samples was reduced by 49.58% and 40.82%, respectively, and the content of stable C=C in the aromatics was increased by 6.14%, which effectively blocked the coal-oxygen chain reaction and reduced the tendency of coal spontaneous combustion. The thermogravimetric test showed that the characteristic temperature points of the coal sample treated with CMC-3 gel were all increased to different degrees. The fire extinguishing test showed that CMC-3 gel could significantly reduce the temperature of coal sample and extinguish the coal fire quickly. Moreover, the CMC-3 gel material also has excellent self-healing properties, which can self-repair the damaged network through the abundant reversible hydrogen and ionic bonds inside the gel in only 90 s. The study has certain guiding significance for the development of efficient and environmentally friendly self-healing mining fire prevention and extinguishing materials. [ABSTRACT FROM AUTHOR]