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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]

This study employed the in-situ infrared experiment (In-situ FTIR) to investigate the content changes of key active functional groups during the low-temperature oxidation process so as to obtain the transformation patterns between functional groups. Based on the quantum chemistry theory, we conducted structural optimization, transition state configuration analysis, thermodynamic parameter calculations and intrinsic reaction coordinate (IRC) computations on the constructed coal molecular models by using GaussView 6.0 and Gaussian 16. This serves for a comprehensive understanding of the evolution patterns and reaction pathways of active functional groups during coal low-temperature oxidation at both macroscopic and microscopic levels. Results reveal that —CH3, —CH2— in coal could transform into oxygen-containing functional groups such as —CHO, —COOH, —OH during low-temperature oxidation. The reactions of key active functional groups in coal with O2 were found to be endothermic, requiring external heat input, while those with ·OH were exothermic, albeit initial dependance on the original ·OH in coal. This research contributes to the further understanding of the mechanism underlying low-temperature oxidation of coal.

Magma intrusion into coal seams is widely existed in China, and the structure and components of the coal body are changed after intrusion to form a high-order metamorphic coal, but its spontaneous combustion characteristics are not clear. It is a great significance to explore the effect of magma intrusion on the low-temperature oxidization characteristics of coal, and to prevent and control spontaneous combustion disasters in mining magma-eroded coal seams. Taking the −350 working face in the second mining area of the Xin'an Coal Mine as the engineering background, the coal samples were collected at different distances from the magma intrusion on the spot. By testing the industrial composition and analyzing the differences in the surface morphology of the samples, it was concluded that magma intrusion metamorphosed the raw coal and increased the number of pores and fissures on the surface, mainly through contact thermal evolution. The metamorphic coals were categorized into strongly eroded coals, weakly eroded coals, and high rank coals of the homogeneous group. Based on fixed carbon, ash, specular group reflectance, and paleo temperature, the distribution range of different intrusive metamorphic coals was calculated by curve backpropagation, and the influence range of magmatic intrusion was predicted to be about 172.34%−234.68% of the width of the intrusive body. A comparative study of the oxidative thermal effect of magma intrusion on metamorphic coal and raw coal was carried out by using C80 microcalorimeter. And the results showed that under different air supply conditions, compared with the original coal, the initial exothermic and thermal equilibrium temperature points in the low-temperature oxidation stage were advanced by 0.2−3.4 ℃ and 1.9−18.2 ℃ for strongly eroded, weakly eroded, and homogeneous high-order coals, the total exothermic capacity was increased by 1.72%−135.75%, and the apparent activation energy was reduced by 1.62%−69.02%, and the closer the metamorphic coal was to the magma intrusion, the more oxidizing and exothermic it was, and the shorter the natural ignition period was. Under the condition of sufficient oxygen supply, magma intrusion enhanced the exothermic capacity of oxidation reaction of the strongly eroded coal within the range of 1.01−2.68 m from the magma intrusion, and its mining volume only accounted for about 6.23%−12.15% of the influence range of the magma intrusion. Therefore, when mining back into the magma intrusion area, the prevention and control of spontaneous combustion of strongly eroded coal should be strengthened, and the critical value of the coal spontaneous combustion forecast index in this area should be corrected in time, so as to guarantee the safe mining of coal seams.

The determination of the influence law of coal molecular active structure on its oxidation and exothermic characterization parameters is one of the keys to effectively prevent coal spontaneous combustion, but it is difficult to quantify the influence of specific group structure on coal spontaneous combustion, and solvent extraction technology can peel the structure of coal molecular active group to explore effective coal spontaneous combustion reduction technology. In this paper, the coal sample from Caojiatan Coal Mine was treated by solvent extraction technology. The extracted coal sample was tested by STA 8000-Spectrum thermal analysis instrument, and the influence of coal sample extraction on the characterization parameters of oxidation thermal physical properties was studied. The results show that the thermal physical properties of the raffinate coal sample are different from the original coal group. The mass of the raffinate coal sample decreases in the mass gain stage on the TG curve, the mass loss rate decreases in the combustion stage on the DTG curve, and the absolute area of heat release decreases on the DSC curve. The extraction reagent mainly reduces the coal mass entering the combustion stage by weakening the early reactivity of coal, and then inhibits the thermal release power of coal spontaneous combustion reaction to prevent the effect of coal spontaneous combustion. This study will provide a new idea for the development and innovation of coal spontaneous combustion active prevention and control technology. [ABSTRACT FROM AUTHOR]

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Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology 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.)

In order to study the “three zones” of spontaneous combustion in gob under different gas treatment conditions of high gas prone to spontaneous combustion and the change law of temperature field distribution, combined with the actual conditions of a high gas prone to spontaneous combustion working surface, a physical model of spontaneous ignition in goaf with “one face and four lanes” was constructed. The oxidation oxygen consumption and heat release parameters of coal samples obtained from temperature programmed experiment were applied to numerical simulation. The influence of different air supply, low and high pumping flow on the “three zones” of spontaneous combustion and temperature field distribution in goaf was studied. The variation of parameters such as maximum width of oxidation zone, area of oxidation zone and maximum temperature point of goaf with air supply, low and high pumping flow was quantitatively analyzed. The results show that in the range of simulation test, increasing air supply, low pumping flow and high pumping flow will cause the increase of air leakage in goaf, which is not conducive to the prevention and control of spontaneous combustion of coal left in goaf. The maximum temperature point does not change significantly (only within the range of 1K), and the influence of the change of high pumping flow rate on the width and area of the oxidation zone and the maximum temperature of the goaf is greater than that of the air supply volume and low pumping flow rate. The maximum width of oxidation zone increases with the increase of air supply, and the maximum temperature of goaf and the area of oxidation zone decrease with the increase of air supply. When the air supply increases from 1600 m3/min to 1900 m3/min, the maximum width of oxidation zone increases by 2 m (74−76 m), and the maximum temperature decreases by 0.1 K (315.38−315.28 K). The oxidation zone area decreased by 180.08 m2 (8 669.49−8 489.41 m2). The maximum width of oxidation zone increases with the increase of low extraction flow rate, the maximum temperature of goaf and the area of oxidation zone increase with the increase of extraction flow rate. When the low extraction flow rate increases from 200 m3/min to 300 m3/min, the maximum width of oxidation zone increases by 2 m (75−77 m). The maximum temperature increased by 0.152 K (315.34−315.492 K), and the oxidation zone area expanded by 51.56 m2 (8 553.79−8 605.35 m2). When the high pumping rate increased from 80 m3/min to 240 m3/min, the maximum width of the oxidation zone remained at about 75 m, and the maximum temperature increased by 0.76 K (315.13−315.89 K).

For the situation that coal is still capable of oxidative spontaneous combustion under different oxygen conditions, we choose three coals with different metamorphic degrees: lignite, gas coal and fatty coal, selected as experimental samples to carry out programmed temperature gas chromatography(TPGC) experiments and molecular dynamics simulations based on ReaxFF force fields at oxygen concentrations of 3%, 5%, 10%, 14% and 18%, to investigate the characteristics of changes in the oxygen influence of groups under oxygen-poor conditions in coals with different degrees of metamorphosis according to the production patterns and pathways of CO and CO2, etc. The results show that coal is easily affected by temperature and oxygen to produce indicator gases such as CO and CO2, and when the indicator gas tends to increase exponentially, the lower the degree of coal deterioration and the lower the temperature at which the indicator gas is produced at the same oxygen concentration. The simulations show that the reaction of coal with oxygen under oxygen-poor conditions is likely to be an active intermediate fragment reaction between oxygen and coal affected by temperature, rather than a direct attack on the main structure of the coal. The coal structural groups are not directly altered when the coal is subjected to temperature, but undergo structural adjustments for bond twisting, breaking and atomic transformations to produce reactive intermediate fragments suitable for reaction with oxygen. The higher the degree of metamorphosis, the more stable the molecular structure of the coal and the less likely it is to be affected by temperature to produce reactive intermediate fragments, and when oxygen is introduced, the rate of reaction of oxygen with the reactive intermediate is lower than the rate at which the coal is affected by temperature to produce the reactive intermediate, therefore, oxygen under depleted conditions is generally reacted with reactive intermediates to produce indicator gases such as water, CO, rather than with the main structure of the coal among them. A combination of experimental and simulation analysis reveals that the amount of water and oxygen containing gases increases significantly at 3%-5% oxygen concentration for lignite, 10%-14% oxygen concentration for gas coal and 14%-18% oxygen concentration for fat coal compared to the other stages, indicating that these three coals with different degrees of deterioration are more affected by oxygen in this oxygen-poor concentration range and accelerated the process of coal oxidation reaction.

Coal spontaneous combustion (CSC) is one of the main disasters in the process of coal mining. In this paper, the important role of high-latent heat phase change material CH3COONa·3H2O (SAT) in controlling CSC was studied and compared with common inhibitors (NaCl, CaCl2, ascorbic acid (VC)). The thermal performance characteristics of SAT were revealed by the C80 micromanometer, and the effects of different inhibitors on the thermal behavior of Shengli lignite were analyzed and compared. Furthermore, the gas–solid coaxial fixed bed measurement system was used in conjunction with the Pfeiffer online mass spectrometer, to design the natural temperature rise experiment of coal after the heating interruption in the same programmed temperature rise interval, investigating the effects of different inhibitors on the temperature and gas production in the process of coal oxidation. The results show that the heat absorption effect of SAT is more significant than common inhibitors, which not only improves the heat absorption rate of the samples but also increases the total heat absorption of the sample by 236.6 J·g−1 compared with the raw coal. In the programmed temperature rise experiment, the maximum temperature point of the SAT-inhibited coal sample is reduced by 15.5% compared with raw coal, the time to reach the maximum temperature point is delayed by 20.5%, and the SAT inhibitor effectively inhibits the production of CO and CO2 gases. The method described in this paper provides a new idea for the prevention and control of CSC. [ABSTRACT FROM AUTHOR]

Abstract To explore the mechanism of inhibiting spontaneous combustion of coal by mixed gases, the low-temperature oxidation characteristics of coal under different components of mixed gases were analyzed. ESR and FTIR experiments were used to investigate the effects of different gas mixtures on the activity of coal during low-temperature oxidation and the oxidation reaction of coal surface functional groups. The mechanism of chemical oxygen inhibition of mixed gas was studied by density functional theory. The results show that the larger the CO2 component in the mixed gas, the higher the ability to inhibit coal oxidation. The concentration of free radicals in coal under dry air condition is higher than that under inert mixed gas condition during oxidation heating at 30–230 °C. The oxidation ability of –CH3, –OH and oxygen-containing functional groups in the mixed gas reaction is inhibited. Through quantum chemistry calculation, it is found that the mixed gas increases the activation energy of free radicals and reduces the heat release of the reaction. This study provides theoretical reference for coal mine thermal disaster.

In order to study the changes of spontaneous combustion characteristics of bituminous coal with different degrees of metamorphism, according to the order of metamorphism degrees from low to high, four types of bituminous coal with different degrees of metamorphism were selected: Ningxia Lingwu non-stick coal, Ningxia Lingwu gas coal, Shanxi Huozhou 1/3 coking coal and Liaoning Shenyang lean coal, and liquid nitrogen adsorption experiments, Fourier infrared spectroscopy experiments and TG-DSC simultaneous thermal analysis experiments were conducted respectively. The results showed that the specific surface area of internal pores of bituminous coal gradually increased with the increase of the degree of metamorphism, and the pore volume changed in the same trend; the proportion of active functional groups in coal samples gradually decreased, and the proportion of chemically stable functional groups gradually increased; the critical temperature T1 and ignition point temperature T4 of bituminous coal gradually increased with the increase of the degree of metamorphism, and the heat release in the combustion stage of coal samples gradually decreased. In summary, the chemical properties of bituminous coal become more stable with the increase of deterioration, and it is more difficult to spontaneously combust; the influence of active functional groups in coal samples is greater than that of pore structure.

Coal is one of the primary energy sources in China, and the hazard of mine spontaneous combustion is severe. With the development of technology and environmental protection requirements, liquid carbon dioxide fire prevention technology has been widely applied in the prevention and control of spontaneous combustion in goaf. The technical key to the application of liquid carbon dioxide fire prevention and extinguishing technology is how to determine the injection parameters. This paper, combining the law of heat conservation and the laser flash method, tests the thermal diffusivity, specific heat capacity, and thermal conductivity of coal at different temperatures. It also establishes the relationship functions of specific heat capacity and thermal conductivity with changes in coal sample temperature. Furthermore, by combining the laws of mass and heat transfer, the required amount of liquid carbon dioxide injection for the oxidation heating of goaf is calculated. This provides key parameters for the injection of liquid carbon dioxide in mines and constructs a mathematical model, offering a theoretical basis for the technology of fire prevention and extinguishing with liquid carbon dioxide. [ABSTRACT FROM AUTHOR]

To explore the mechanism of inhibiting spontaneous combustion of coal by mixed gases, the low-temperature oxidation characteristics of coal under different components of mixed gases were analyzed. ESR and FTIR experiments were used to investigate the effects of different gas mixtures on the activity of coal during low-temperature oxidation and the oxidation reaction of coal surface functional groups. The mechanism of chemical oxygen inhibition of mixed gas was studied by density functional theory. The results show that the larger the CO2 component in the mixed gas, the higher the ability to inhibit coal oxidation. The concentration of free radicals in coal under dry air condition is higher than that under inert mixed gas condition during oxidation heating at 30–230 °C. The oxidation ability of –CH3, –OH and oxygen-containing functional groups in the mixed gas reaction is inhibited. Through quantum chemistry calculation, it is found that the mixed gas increases the activation energy of free radicals and reduces the heat release of the reaction. This study provides theoretical reference for coal mine thermal disaster. [ABSTRACT FROM AUTHOR]

In order to study the effect of magnesium salt (magnesium chloride hexahydrate + magnesium hydroxide) on the retarding characteristics of coal spontaneous combustion, the effects of inhibitor dosage and silane coupling agent on the characteristic temperature and thermal effect of coal spontaneous combustion were studied by synchronous thermal analysis and programmed heating-gas chromatography. The results of simultaneous thermal analysis showed that the inhibitory effect was relatively best when the magnesium salt inhibitor was added at 30%, the pyrolysis temperature T3 was delayed by 40 °C compared with the raw coal sample, and the total heat release was reduced by 165.14 J/mg. F@M30%·G resisted coal sample adding silane coupling agent mainly delayed the occurrence of coal pyrolysis and ignition, in which the pyrolysis temperature T3 was 49 °C higher than that of raw coal, and the ignition temperature T4 was increased by 26 °C. F@M30% inhibited coal samples can reduce the volume fraction of CO, and the effect of inhibiting spontaneous combustion of coal is gradually enhanced with the increase of temperature. After adding silane coupling agent, the volume fraction of CO of inhibited coal samples can be reduced by about 4×10-6. The inhibition rate of F@M30% inhibited coal samples is 30.87%, and that of F@M30%•G inhibited coal samples is as high as 91.57%.

The early warning of coal spontaneous combustion is difficult to solve the perception of fire information. The acoustic emission (AE) signal generated by thermal damage and destruction on coal rock can perceive the temperature, and then issue a warning on the evolutionary state of coal spontaneous combustion. In order to study the change of AE signal in the process of coal heating and combustion, we explore the difference of and the time and frequency changes of the AE signals released by coal in different temperatures in the process of coal spontaneous combustion, and study the generation mechanism of the AE signal, so as to provide a theoretical basis for the inversion of coal temperature and for monitoring coal spontaneous combustion. The AE signal test system is constructed. By choosing the bituminous coal from Dongtan coal mine as the research subject, we test and analyze the change of the AE signal during coal heating process, analyze the evolutionary process of coal deformation and cracking under the influence of temperature and the change of coal composition, and examine the generation mechanism of AE signal in the process of coal heating. The results show that the ringing counts of coal increase sporadically from heating to combustion, and the correlation coefficient exceeds 0.87 by linear fitting, indicating that the frequency of coal deformation and cracking increases during the heating process. With the increase of temperature, the growth rate of ringing counts and the average frequency (AF value) of AE signal generated by coal are lower in the initial heating stage, but are higher when the temperature rises rapidly. The cumulative damage parameters show an inflection point when the coal temperature exceeds 80°C, and the main damage mode changes from rapid expansion damage to progressive damage. By analyzing the macro- and microscopic changes of coal structure and composition at different temperatures, we find that the mineral conversion rate in coal affects the main damage mode inside the coal body with the increase of temperature, and that the high mineral conversion rate corresponds to the rapid expansion damage inside the coal body, which promotes the derivative expansion of coal pores and cracks, and produces gradually increasing AE signals.

In order to solve the problem of spontaneous combustion of coal in U-shaped stope during dynamic advance, a multiphysical field coupled mathematical model including the inlet and return airway, working face and goaf is established, and the reasonableness of the model is verified by field measurement data. The simulation analyzed the law of temperature field and oxygen concentration field in the goaf with the dynamic advance of working face, and further studied the influence of surrounding rock temperature, air flow temperature and working face advance speed on the self-heating of coal oxidation in the mining area. The results indicate that the temperature field on the inlet side of the goaf forms the phenomenon of high temperature region tailing in the shape of “wing section” in the process of advancing the working face, and the temperature of the high-temperature area gradually decreases under the effect of compaction of the goaf and heat dissipation of the surrounding rock; the temperature in the goaf continues to rise after the stoppage of mining, but the high-temperature area migrates to the working face; in the early stage of mining, different ventilation temperature has almost no effect on the maximum temperature in the mining area, while in the later stage of mining, the higher the ventilation temperature, the higher the maximum temperature in the mining area; the faster the working face advances, the lower the maximum temperature in the mining area.

To investigate the impact of stratified mining on the spontaneous combustion characteristics of lower coal in thick coal seams, an analysis was conducted on the macro pore structure, temperature rise, oxygen consumption characteristics, chemical structure, surface chemical properties, and functional group distribution of the upper and lower stratified coal samples (LSC, LSR) from the LinSheng Mine 1202 re-mining face. Post re-mining, the specific surface area, average pore diameter for adsorption, micropore volume, and mesopore volume of LSR showed a significant increase compared to LSC. The maximum mass loss rate for LSR was approximately three times that of LSC, and the characteristic temperature of LSR was lower. When the volumetric fraction of oxygen exceeded 12%, the oxygen consumption rate and CO generation rate of LSR surpassed those of LSC. The alkyl carbon content in LSR was 2% lower compared to LSC, while the oxygenated carbon content was higher by 4.37%. The oxygen content in LSR and the O/C ratio were higher than those in LSC. The structural order of LSR was lower by 11.3%, and the oxygen-containing functional groups were higher by 1.15%. These findings suggest that stratified mining increases the spontaneous combustion risk of lower coal layers. This study underscores the need for careful consideration of mining strategies to mitigate potential risks.

The moisture content of coal tends to have a significant impact on the occurrence of spontaneous combustion. In the present study, both molecular simulation and experimental investigation are performed to examine the interaction among water-containing coal and O2 in the goaf atmosphere, with the following conclusions drawn. Firstly, the presence of water and methane impedes the physical adsorption of coal and oxygen at a temperature of 298K. Methane mainly hinders the contact between coal and oxygen through the reduced concentration of oxygen and competitive adsorption. The increase in water content reduces the adsorption density of each gas but makes no difference to their relative proportions in the amounts of adsorption. At the initial stage of coal oxidation (30°C-80°C), the rate of oxygen consumption declines with a rise in water content. However, it is observed immediately after entry into the rapid oxidation stage (80°C-230°C) that the coal sample with a water content of 9.05% is the highest in the intensity of reaction. A higher concentration of methane in the initial atmosphere produces an inhibitory effect on both oxygen adsorption and chemical reaction, which is effective in reducing spontaneous combustion. [ABSTRACT FROM AUTHOR]

Mine fires are one of the common major disasters in underground mining. In addition to the external fire sources generated by mining equipment and mechanical and electrical equipment during operations, coal is exposed to air during mining, and spontaneous combustion is also the main cause of mine fires. In order to reduce the hidden danger of coal mines caused by spontaneous coal combustion during lignite mining, the microbial inhibition of coal spontaneous combustion is proposed in this paper. Via SEM, pore size analysis, and NMR and FT-IR experiments, the mechanism of coal spontaneous combustion is discussed and revealed. The modification of lignite before and after the addition of retardants is analyzed from the perspective of microstructure, and the change in flame retardancy of the lignite treated with two retardants compared with raw coal is explored. The results show that, compared with raw coal, a large number of calcium carbonate particles are attached to the surface of the coal sample after bioinhibition treatment, and the total pore volume and specific surface area of the coal sample after bioinhibition treatment are decreased by 68.49% and 74.01%, respectively, indicating that bioinhibition can effectively plug the primary pores. The results of NMR and Fourier infrared spectroscopy show that the chemical structure of the coal sample is mainly composed of aromatic carbon, followed by fatty carbon and carbonyl carbon. In addition, the contents of active groups (hydroxyl, carboxyl, and methyl/methylene) in lignite after bioretardation are lower than those in raw coal, and methyl/methylene content is decreased by 96.5%. The comparison shows that the flame-retardant performance of biological retardants is better than that of chemical retardants, which provides an effective solution for the efficient prevention and control of spontaneous combustion disasters in coal mines. [ABSTRACT FROM AUTHOR]

The gases evolution during the low-temperature oxidation of coal is an essential parameter used to assess the state of coal oxidation and to estimate the gaseous pollutants. However, the current semi-quantitative method, which employs gas concentration as the measurement standard, is flawed. This paper presents a quantitative calculation method for gas products during coal oxidation. N2 is used as the tracer gas in the experiment, because nitrogen is an inert gas that will not participate in the reaction, and the amount of matter will not change in the reaction. According to the formula M i = X i X N 2 × V N 2 × ρ i , the corresponding mass flow rates of each gases component were calculated, and the gas yields during the reaction period were determined by comprehensive calculation. To this end, experiments were conducted on the low-temperature oxidation of coal using a flow reactor. After undergoing quantitative calculations, the main gas products' mass flow rates, yields, and energies, including CO, CO2, CH4, C2H4, C2H6, C2H2, and C3H8 between 30 and 180 °C were obtained. The findings showed that CO2 > CO > CH was generated in all the coal samples. The amount of gases produced in the low-temperature oxidation of coal is proportional to the level of oxygen concentration. When the oxygen concentration ranges from 0 to 21%, the gaseous production of MTH coal ranges from 381.44 g/ton to 8562.80 g/ton. The results of gaseous energy calculations showed that the energy loss for low temperature oxidation of the four coal samples ranged from 4334.14~26,772.73 kJ/ton under air atmosphere. Energy loss is also significantly affected by the oxygen concentration, and the energy loss of MTH coal increases significantly from 520.52 kJ/ton at 0% oxygen concentration to 26,772.73 kJ/ton at 21% oxygen concentration, an increase of about 50 times. Significantly, this method not only reflects the real gas evolution during low-temperature oxidation of coal but also computes the gas emission and energy loss, which is crucial for studying the mechanism of coal spontaneous combustion and assessing gases pollutants. [ABSTRACT FROM AUTHOR]

The gas explosion induced by the high-temperature surface of coal spontaneous combustion in goaf will cause a devastating blow to personnel and equipment in the process of coal mining. Secondary explosion may be induced by the high-temperature surface of coal spontaneous combustion after primary explosion with the continuous emission of gas and the ventilation of goaf. This will lead to new disasters for the ongoingrescue operation. A high-temperature source explosion experimental system consistent with the similarity and unity of goaf was designed and developed based on the similarity criterion in this study. A CH4/air explosion experiment was carried out with the high-temperature surface as an ignition source. The characteristics of secondary explosion were studied, and chemical kinetics was analyzed. It is of great significance to the safety of the process of mining production. The results show that the secondary explosion limit (6.5–14%) is less than the primary explosion (5.5–14.5%). Its explosion risk (F) is reduced by 15.6%. The key parameters Pmax, Tmax, and (dP/dt)max of secondary explosion at each concentration are lower than those of primary explosion. The te of secondary explosion is higher than primary explosion. The most dangerous concentration of primary and secondary explosions induced by the high-temperature surface is 11.5%. Carbon oxides (CO2 and CO) and C2 hydrocarbon gases (C2H2, C2H4, and C2H6) are generated after primary explosion. The chemical kinetics of secondary explosion was analyzed with CHEMKIN Pro 2021. When the CH4 concentration is <11.5%, the formation of the key free radicals ·H, ·O, ·OH, and CH2O is inhibited due to the formation of CO2. When the CH4 concentration is ≥11.5%, the formation of the key free radicals ·H, ·O, ·OH, and CH2O is inhibited due to the generation of combustible gases (C2H2, C2H4, C2H6, and CO) and inert gas (CO2). As a result, the limit range of secondary explosion and the explosion hazard characteristics are reduced. R156 and R158 played major roles in the process of secondary explosion with the analysis of reaction sensitivity. [ABSTRACT FROM AUTHOR]

In order to find out the key causes of changes in spontaneous combustion characteristics of igneous intrusive coal seams, this paper took the Daxing Coal Mine in Tiefa Coalfield as example for analysis, which was widely invaded by igneous and had serious coal spontaneous combustion disasters.Metamorphic coal and unaffected primary coal were collected from the study area.Specifically, this paper studied the patterns of heat production and temperature rise, gas production rules, and microscopic structure parameters of coal samples by synchronous thermal analyzer and coal spontaneous combustion characteristic measuring device.The experimental results show that the igneous intrusion caused the mutation in the spontaneous combustion characteristics of the coal.Compared with the primary coal, there was significantly higher oxidation heat release of the metamorphic coal at the low temperature stage.Also, the crossing point temperature of metamorphic coal was reduced by 13.2 ℃, and it entered the stage of oxidation and weight gain earlier than the primary coal.When the environment temperature exceeded 90 ℃, the oxidation heat generation and reaction rate of metamorphic coal increased rapidly, which showed higher oxygen consumption rate and faster generation rate of oxidative gas products such as CO and CO2.This demonstrated higher oxidation activity of metamorphic coal than that of primary coal.The analytic results of physicochemical microstructure showed that the high temperature and pressure of igneous intrusion changed the pore structure of coal, which reduced the pore volume and specific surface area of micropores/mesopores in metamorphic coal, and the pore volume of macropores was three times higher than that of primary coal.The average pore size and porosity increased significantly, which was conducive to the transport, migration and adsorption reaction of oxygen molecules in the coal structure.At the same time, igneous intrusion reduced the oxygen-containing functional groups of metamorphic coal, and the content of aliphatic hydrocarbons with higher activity increased from 27.98 % to 29.07 %, which enhanced the oxidative activity of metamorphic coal.Moreover, igneous intrusion caused problems such as increased air leakage, long oxidation time of left coal, and wide oxidation zone during the mining, eventually leading to severe coal spontaneous combustion disasters.

The paper used thermogravimetric experiments to study the spontaneous combustion characteristics of coal samples with different pre-oxidized temperatures during the secondary oxidation process and focused on the calculation of kinetic parameters during the oxygen-absorbing and weight-increasing stage. The results showed that the total reaction course of spontaneous combustion of raw coal and pre-oxidized coal were similar; the difference in pre-oxidized temperature only had a greater impact on the critical temperature and dry cracking temperature of the coal sample, and then had a greater impact on the water evaporation and desorption stage and the oxygen-absorbing and weight-increasing stage. And the oxygen-absorbing and weight-increasing stage had a more violent reaction than the water evaporation and desorption stage. In the oxygen-absorbing and weight-increasing stage, the difference of pre-oxidized temperature had little effect on the reaction mechanism of each coal sample. The reaction functions all followed the Jander equation, and the mechanism was three-dimensional diffusion. The energy of activation of pre-oxidized coal samples was smaller than that of raw coal, and decreased with the rise of pre-oxidized temperature. When the pre-oxidized temperature was less than 160°C, the pre-factor of the pre-oxidized coal was larger than that of the raw coal, and when the pre-oxidized temperature was greater than 160°C, the pre-exponential factor of the pre-oxidized coal was smaller than that of the raw coal. The research results can lay a foundation for the subsequent prediction of coal spontaneous combustion reaction process, determination of critical spontaneous combustion conditions and evaluation of inhibitory effect. At the same time, it can also be used as a reference and supplement for the existing research on coal oxidation kinetic parameters. [ABSTRACT FROM AUTHOR]

In order to study the microstructure and heating characteristics of water-soaked air-dried bituminous coal, the bituminous coal samples from a coal mine in Shaanxi Province were selected. Using low temperature liquid nitrogen adsorption instrument and thermogravimetric analyzer, the specific surface area, pore volume and thermogravimetric and derivative thermogravimetric tests were carried out on the coal samples soaked for 30 days, 60 days and 90 days and raw coal samples after constant temperature drying at 25 ℃ for 72 h. The influence mechanism of long-term soaking and air-drying on the physical characteristics and activation energy of bituminous coal during heating process was explored. The results show that the specific surface area and total pore volume of coal samples change with the increase of soaking time. After soaking for 90 days and drying, the contribution proportion of micropore contrast surface area and total pore volume was the largest, and the contribution proportion was larger than that of other pore sizes. It is speculated that the coal sample soaked in water for 90 days after drying, the faster the coal oxygen reaction rate, the higher the coal spontaneous combustion tendency. In the process of heating up, the characteristic temperature difference and characteristic temperature point change of coal samples at different soaking time are different.

In order to effectively prevent and control coal spontaneous combustion disasters in Tangjiahui Mine, thermogravimetric experiments were used to analyze the thermal reaction kinetics characteristics of coal samples at different heating rates and different oxygen volume fractions. The results showed that at the same oxygen volume fraction, the apparent activation energies of coal at heating rates of 2 ℃/min, 5 ℃/min, 10 ℃/min were 150.27 kJ/mol, 131.97 kJ/mol, 106.86 kJ/mol, respectively; in addition, at the same heating rate, the apparent activation energies of coals with oxygen volume fraction of 6%, 9%, 12%, 15%, 18%, 21% are 106.86, 120.61, 127.31, 131.58, 135.26 and 136.82 kJ/mol, respectively. The apparent activation energies decrease with the increase of heating rate and oxygen volume fraction, and the change law is basically in line with the increase of logarithmic function. The calculation results of activation energy kinetics reveal that the degree of coal-oxygen composite reaction is different under different heating rates and different oxygen volume fractions.

In order to prevent spontaneous coal fire, the effect of copper compounds on coal oxidation and heating process was studied. Six compounds containing copper were selected and mixed with Xinjiang lignite for synchronous thermal analysis. Based on TG and DSC data, the variation of characteristic temperature points of coal before and after the addition of copper compounds was analyzed, and the variation of ignition activation energy and heat release characteristics of coal before and after the addition of copper compounds was clarified. The results show that the characteristic temperature points of coal with copper compound are lower than that of raw coal. The weight loss before ignition point increased compared with raw coal. The ignition activation energy decreases to 0.66-0.85 times of raw coal. Compared with raw coal, the oxidative heat release peak and combustion heat release peak moved forward, and the oxidative heat release increased to 1.14-2.48 times of raw coal. These results indicate that these copper compounds have catalytic effect on spontaneous combustion of coal.

Spontaneous combustion of coal is a phenomenon that often occurs in open coal mining activities, especially strip mining and open pit mining systems which are detrimental to mining companies, the economy, the environment, and society. This phenomenon causes coal mining activities to contribute to CH4 gas emissions in global warming by 11% of total global emission. The purpose of this study was to analyze the role of organic sulfur in the formation of CH4 gas emissions in the spontaneous combustion of coal in the TAL area. The approach is based on a literature review and field survey. The literature review was intended to examine the influence of geological factors, maceral analysis, and depositional environment on the rank and form of coal sulfur, while the field survey was conducted by measuring CH4 gas emissions in 36 samples of spontaneous combustion hotspots. Literature review shows that coal in the TAL area belongs to low rank (sub-bituminous/sub-bituminous B) which has high organic sulfur content in the form of thiother bonds (C-S), especially carbon disulfide (CS2). The average CH4 emission measurement in the field is 6,989 mg/m3, which is still within the limits set by other researchers, between 3,700-34,098 mg/m3. The role of organic sulfur from C-S bonds especially CS2 in the formation of CH4 gas emissions, is very dominant at 93.10% or 6,507 mg/m3 of the total coal sulfur in the TAL area. The emission of CH4 gas in the spontaneous combustion of coal is strongly influenced by geological factors, maceral analysis, and the depositional environment related to the rank and form of coal sulfur. Further, detailed, and comprehensive research on the form of organic sulfur needs to be carried out to mitigate CH4 gas emissions in the spontaneous combustion of coal in the TAL area. [ABSTRACT FROM AUTHOR]

In order to study the transformation law of the most essential active groups in the process of coal spontaneous combustion and low-temperature oxidation, the Fourier in-situ infrared measurement technology was used to obtain the distribution of the main functional groups of the raw coal, and the key active groups in the coal were obtained by peak fitting. The content changes during the heating process under different atmospheres were compared, and the active group conversion curve representing the intrinsic coal-oxygen recombination reaction was obtained by using the subtraction map. The results show that the content of -CH3 and -CH2- in the air atmosphere decreases overall, and the content conversion rate of -COOH with the increase of temperature is less than that of C=O; the net difference of the content change of -COOH under pyrolysis in nitrogen atmosphere is the largest; in the coal-oxygen recombination reaction, the overall decrease in the content of active groups is due to the fact that the consumption rate of the oxidation reaction is greater than the production rate; the coal oxidation reaction rate began to increase gradually from 60 ℃to 70 ℃, and it was found that the decrease of the overall content of four key active groups provided conditions for the low-temperature oxidation reaction of coal samples.

The intensity of air leakage not only increases the risk of spontaneous combustion of coal, but also is the cause of coal fire disasters caused by spontaneous combustion of coal left in the goaf. Aim to find the influence of the air leakage intensity on the spontaneous combustion characteristics of the remaining coal when the fire zone is opened, the coal spontaneous combustion characteristics measuring device is used to conduct a temperature-programming experiment on the coal samples, and then Fourier transform infrared spectroscopy(FTIR) is used for analysis to obtain different gas environments. The relative content of functional groups changes at each characteristic temperature point. The results show that in the oxygen-containing groups, the content of -COOH increases as the temperature rises. Although the change range of -C-O- is not obvious with the rise of the temperature point, its content is relatively high; in the functional groups of -OH, it is present at all temperature stages. It exists and the peak intensity is obvious; among the aliphatic hydrocarbons, the peak areas of -CH3 and -CH2 are both large, and both dry air and nitrogen atmosphere participate in the reaction at various temperature points, and the activity is high. Through structural parameter value analysis, T120 is the key active point temperature. In the coal sample that is naturally cooled under dry air or nitrogen atmosphere, the functional groups of the raw coal react more violently in T120, and the functional groups change more. As a whole, the increasing and decreasing trend of functional group changes in nitrogen atmosphere is smaller than that in dry air atmosphere, and the risk of coal re-ignition is also reduced.

In this paper, polymer colloid and fly ash colloid fire extinguishing materials are selected. Through experimental preparation and water precipitation characteristics research, colloid fire extinguishing materials and optimal concentration ratio suitable for Binchang mining area are selected to effectively control the fire area. The results show that, the higher the concentration of polymer colloidal powder mixed with water, the shorter the gelling time. After the fly ash is mixed with the gelling agent and water, when the concentration ratio of fly ash to water remains the same, the greater the concentration of the gelling agent, the shorter the gelling time. After the colloid is left standing for 24 h, the smaller the concentration is, the more water is precipitated, and the higher the water precipitation rate is. Through comparison, it was found that when the polymer colloid was selected as the fire extinguishing material, with the concentration ratio of polymer colloid material to water being 3.5%–4%: 96.5%–96%, effective control could be achieved over the fire zones in the goaf of Binchang mine. The research is of great reference value for the control of mine fires.

To improve the fire extinguishing efficiency and reduce the re-combustion risk, a novel approach to fire extinguishing using sodium pyrotechnic aerosol (SPA) was adopted for controlling underground mine fires. Physical simulation experiments of 1 m3 in size show that the extinguishing effect of aerosol consisting of NaNO3 and dicyandiamide is better than that of 0.2 MPa nitrogen, in which the cooling rate peaks at 32.6 °C min−1. Experiments result prove that the N2 and CO2 yield of aerosol reach about 10 mol s−1 m−3 and 5 mol s−1 m−3, respectively. As an additive, phenol–formaldehyde resin embodies advantages compared with agents such as K2C2O4, CH4Mg2O6, and potassium hydrogen phthalate. According to TG/DTG tests, characteristic temperature points of coal with SPA can be increased significantly, and the apparent activation energy of coal also increases to 18.8–80.5%. Theoretically, Na-salt generated by aerosol reaction consumes the O-contained groups in coal and creates an alkaline environment. Abundant N2 and CO2 also carry ultra-fine Na-salt residue continuously suppressing fire. As a new fire extinguishing technique for use in underground coal mines, SPA shows potential for underground fire prevention. [ABSTRACT FROM AUTHOR]

In view of the high cost of the gel fire-fighting technology in the field and the difficulty of large-scale use, the relatively cheap coal chemical solid waste gasification ash is used as the base material and hydroxypropyl methylcellulose gelling agent (HPMC) is added. Later, a new type of gasification ash gel material was prepared. Meanwhile, taking lignite as the research object, the coal spontaneous combustion retardant properties of CaCl2 inhibitor and gasification ash gel were compared and analyzed by temperature-programmed gas chromatography combined experiment and FTIR Fourier transform spectrometer. The results show that with the increase of coal temperature, the release concentrations of CO and C2H4 in the coal samples with the addition of CaCl2 inhibitor and gasification ash gel are significantly lower than those in the raw coal, and the CO inhibition rates reach 46% and 67.5% at 110 ℃, respectively; gasification ash gel can increase the oxygen activation energy of coal by 25.2% in the temperature range of 30 ℃ to 200 ℃; the gasification ash gel can reduce the content of C-O, C=C functional group, effectively inhibit the free radical chain reaction, and its inhibition effect is better.

In order to study the effect of silicification on low temperature oxidation characteristics of coal, scanning electron microscopy(SEM) was used to observe the difference of pore structure between silicified coal and non-silicified coal; the temperature programmed test system of spontaneous combustion of coal was used to test the characteristics of low temperature oxidation of two coal samples at different temperatures and the variation rule of indicator gas. On this basis, the oxygen consumption rate at different temperatures in the process of low temperature oxidation was analyzed. The results show that silicification enlarges the pores and increases the specific surface area of coal, on the one hand, it is beneficial to the occurrence of gas in coal, on the other hand, the composite reaction between coal and oxygen is more sufficient, and the silicified coal is easier to oxidize and spontaneous combustion; the volume fraction of the marker gas generated in the oxidation process of silicified coal is always higher than that of non-silicified coal, and when the temperature rises to 110 ℃, the difference in the volume fraction of the gas products of the two coal samples gradually becomes larger, which may be because silicification causes physical and chemical changes in coal body and its molecular structure, leading to oxidation cracking of silicified coal more easily; the rate of oxygen consumption and CO formation of silicified coal is always higher than that of non-silicified coal, indicating that silicification enhances the low temperature oxidation characteristics of coal.

Spontaneous combustion of coal remains an important problem for coal mines, which can lead to an explosion of methane and coal dust. Accidents associated with spontaneous combustion of coal can cause significant economic losses to coal mining companies, as well as entail social damage – injuries and loss of life. Accidents are known at the Kuzbass mines, which occurred as a result of negligent attitude to the danger of spontaneous combustion of coal, the victims of which were dozens of people. The analysis of emergency situations associated with spontaneous combustion of coal shows that the existing wide range of means of preventing endogenous fires does not provide complete safety when working out coal seams prone to spontaneous combustion, therefore, spontaneous combustion places continue to occur in mines. The consequences that may arise as a result of a methane explosion initiated by a self-ignition place indicate the need to improve the used technologies. The purpose of the work is to determine the impact of modern technological solutions used in functioning mines during underground mining of flat-lying coal seams prone to spontaneous combustion, and to develop new solutions that reduce endogenous fire hazard. Conclusions on the influence of leaving coal pillars in the developed space, isolated air removal from the stoping face through the developed space, the length of the stoping face and the excavation pillar, and other factors on the danger of the formation of spontaneous combustion places are presented. Conclusions about the possibility of using modern technological solutions in future are also drawn.

• Inhibition of spontaneous coal combustion is best when the wall-to-core ratio of microencapsulated inhibitors is 4:1. • Reduction of free hydroxyl groups in coal samples after addition of microencapsulated inhibitor. • The addition of inhibitors increases the interaction energy of the system. • The hydroxyl group in the inhibitor interacts with the oxygen atoms in the water molecule more strongly. In order to solve the shortcomings of traditional inhibitors, which are easy to be interfered by the outside world during the inhibition process and the active ingredients are easy to be oxidized and invalidated, microencapsulated inhibitors were developed. In this study, we prepared microencapsulated inhibitors of varying wall-to-core ratios using a composite phase of polyethylene glycol 20,000 (PEG-20000) and octenyl amyl succinate (OSAS) as the wall material and a lauryl glucoside (APG-12) and butyl hydroxyanisole (BHA) phase as the core material. After thoroughly mixing the microcapsule inhibitor with coal samples, simultaneous thermal analyzer (TG/DSC) and a temperature-programmed system were used to evaluate the resisting qualities of the produced microencapsulated inhibitors. The results of the temperature programmed experiment showed that the overall CO release from the blocked coal samples was less than that of the original coal. According to thermogravimetric results, the most effective inhibition occurred when the wall/core ratio of the microcapsule inhibitor was 4:1. This also resulted in a reduction of the maximum coal weight loss rate from 1.34 to 0.96 %/min and an increase in the maximum coal weight loss temperature from 477.4 to 507.6 °C. The microencapsulated inhibitor melts in the wall at 57.4 °C, enabling temperature-sensitive intelligent control of core release. Following heating the raw and inhibited coal samples to 100 and 200 °C, respectively, Fourier infrared spectroscopy was conducted. At these temperatures, the amounts of ether bonds increased by 20.4 and 22.6 %, and the number of free hydroxyl groups decreased by 12.8 and 2.7 %, respectively, in the inhibited coal samples. Finally, molecular dynamics theory was applied to investigate the inhibitory mechanism. The prepared microcapsule retardant effectively inhibited the spontaneous combustion reaction of coal, suggesting this microcapsule inhibitor could be manufactured as a novel inhibitor for coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

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Underground mining operations are subject to a number of natural hazards. Events resulting from these hazards are difficult to predict, and if they occur, they disrupt the entire mining process and pose a great danger to the crew. Some of the most dangerous include ventilation hazards involving methane explosions and fires caused by the spontaneous combustion of coal. The complex state of the underground environment means that these hazards oftentimes occur simultaneously, making mining conditions even worse. The following paper addresses this issue by developing the methodology for determining areas endangered by methane explosions and spontaneous coal combustion in goaves. The reference to goaves results from the fact that this particular area is most frequently affected by spontaneous coal combustion and the accumulation of dangerous amounts of methane. The developed methodology was based on model tests with the use of the CFD method and data necessary to develop a numerical model. The research encompassed a real longwall in one of the hard coal mines, ventilated with the Y system during its exploitation, which is beneficial in the case of the methane hazard but worsens the safety in terms of the self-ignition of coal. As a result of the conducted research, for the exploitation conditions, dangerous zones were specified due to the potential possibility of methane explosion and self-heating of coal. The basis for determining dangerous zones was the criteria of occurrence of the examined phenomena. In this study, the zones were identified for each of the investigated hazards separately and for their simultaneous occurrence. Thus, the aim of the study, which involved the determination of potentially hazardous zones by applying modern methods of modelling in the mining area, was achieved. The results are an immensely important source of information for activities aimed at improving safety in the studied area in relation to the studied threats. [ABSTRACT FROM AUTHOR]

To prevent coal fire disaster, a precision grading warning method was previously proposed for coal seams that are susceptible to spontaneous combustion. The uncertainty in the reaction mechanism of the spontaneous combustion of coal greatly restrains the in-depth understanding of the fine division theory in the course of coal combustion. In this paper, further research has been conducted to study the mechanism of this method. In this study, thermogravimetric analysis was carried out on the Jurassic coal of three different metamorphic grades. The variations of the TG/DTG curves of the coal samples at four heating rates were compared to examine their kinetic model and kinetic compensation effect. For the three samples of the Jurassic coal, a similar trend was obtained for the TG and DTG curves at the different heating rates. With an increase in the heating rate, the hysteresis phenomenon appeared in the TG/DTG curves. In the low-temperature coal oxidation stage, the most probable mechanism function of Coal A and Coal B was obtained to be No.9 (G(α) = [1-(1-α)1/2]2, f(α) = (1-α)1/2[1-(1-α)1/2]−1), and that of Coal C was No.14 (G(α) = [-ln(1-α)]2, f(α) = (1-α)[-ln(1-α)]−1/2). A significant kinetic compensation effect was also observed in the oxidation stage. Despite the difference in the metamorphic grade, the reaction process of the low-temperature oxidation, as well as the rate-determining step was the same for the three samples. [ABSTRACT FROM AUTHOR]

CO gas, as a marker gas in the whole process of coal spontaneous combustion, plays a very important role in the prediction of coal spontaneous combustion. However, a large amount of CO gas can be generated under normal conditions of low-metamorphic coal, which interferes with the prediction of coal spontaneous combustion in low-metamorphic coal seam mining area. Coal samples were collected from five typical mines in Gushan Mine in Pingzhuang, Bulianta Coal Mine in Shendong, Daliuta Coal Mine in Shenmu Mining Area in Shaanxi, Zaoquan Mine in Lingwu Mining Area in Ningxia, and No.1 Mine in Dananhu Mine in Dananhu Mining area in Xinjiang. After oxygen isolation crushing treatment, the CO generation law of coal samples in 5 mining areas during oxygen isolation heating process was studied by using oxygen isolation program heating and Fourier optical interference experiment, and the types of active functional groups on coal molecules with or without oxygen separation heating were analyzed. It was believed that carbonyl (C=O), carboxyl (-COOh), ether (-O-CH3) and other oxygen-containing groups on coal molecules were directly related to the generation of CO gases in low-metamorphism coal at room temperature.

In order to solve the spontaneous combustion in the places such as coal storage heaps and gangue dump, which causes huge waste and serious pollution to resources and environment, the method of extracting heat from loose high-temperature medium with heat-conducting rod to prevent spontaneous combustion is proposed. The method of optimizing working medium is given, and an experimental system for studying the heat-extracting rate of heat conducting rod is set up. On this basis, the experiment of heat dissipation of the heat-conducting rod is carried out. The results show that the efficiency and the cooling rate of extracting heat from high temperature loose medium are the highest when methanol is used as the heat-conducting rod.

Spontaneous coal combustion (SCC) is one of the significant hazardous phenomena in underground coal mines. The tendency of spontaneous coal combustion is an intrinsic property, due to the presence of the maceral content. Unlike its importance, this matter has not been discussed in detail among the researchers. Therefore, it is necessary to investigate the effect of this parameter on SCC. Maceral content is defined by the original vegetation from which coal is formed. The present study examines the role of maceral content on SCC, based on 51 coal samples with different maceral contents. These samples were collected from several Iranian underground coal fields, and the R70 test was carried out on each coal sample. By examining the results and comparing the R70 values, it was found that with an increase in the vitrinite and liptinite contents and a decrease in the inertinite content, the coal samples showed to have more tendency of spontaneous combustion.

The negative pressure of high level roadway extraction is one key factor which can influence coal spontaneous combustion and the gas extraction, to determine the reasonable negative pressure of extraction, combined with the actual situation of gas over-limit and spontaneous ignition in 401102 fully mechanized caving face of a mine, ANSYS numerical simulation and field measurement method were adopted to study the influence of negative pressure of extraction in high level roadway on gas extraction effect and “three zones” distribution of coal spontaneous combustion, and engineering practice was carried out. The results show that negative pressure can result in coal spontaneous combustion. When negative pressure increases from 0.5 kPa to 3.5 kPa, gas extraction scalar increase by 21.02 m3/min, compared with the “U” ventilation mode, when the negative pressure of the high roadway was 3 kPa, the width of the oxidation heating zone increased by 17 m on the inlet side, and decreased by 14 m in the middle and 11 m on the return side; the method of defining the range of reasonable negative pressure of extraction was proposed, and the fluctuation range of negative pressure was determined between 0.951 6 and 2.558, and the optimal point was 2.558 kPa. When high level roadway is adopted in coal seam, the reasonable setting of negative pressure can ensure the coupling prevention and control of gas and coal spontaneous combustion in goaf.

Organic elastomers such as polyurethane are widely used as a filling material in underground coal mines. However, the risk of fire hazard in coal seams is increased due to the flammability of polyurethane. Laboratory tests illustrate that in a thermostatic reactor with initial temperature of 25 °C, the temperature during the production of polyurethane increases up to > 140 °C. Adiabatic oxidation experiments and TG–DTG analysis showed that the heating rate of the mixed samples of polyurethane and coal was higher than that of any single component in the initial oxidation stage. From the initial temperature to 100 °C, increasing the proportion of polyurethane was conducive to the acceleration of temperature rise. From 0.180 to 0.850 mm, the self-heating rate was inversely proportional to the particle size. At the initial stage, the low ventilation rate promoted the spontaneous combustion of mixed samples, but when the temperature is > 70 °C, an opposite trend was seen. Kinetic parameters suggested that the activation energy decreases with the introduction of polyurethane. According to the mathematical model, the variation of the spontaneous combustion period of coal and polyurethane was predicted. [ABSTRACT FROM AUTHOR]

The characteristic parameter test is the basis for the prevention and control of the spontaneous combustion of coal; however, there are some deficiencies in many test methods at present, such as large amounts of experimental coal, long testing periods, and not being able to fully reflect the oxidation and exothermic characteristics of coal itself. This study has independently designed and developed a test device to determine the characteristic parameters of the spontaneous combustion of coal based on the isothermal difference leading method. Through experimental testing of different coal samples using 3, 7, 10, 15, and 20°C as the leading values, it was determined that the lead error was less affected by the lead value, and that it had a direct relationship with the temperature control program. The difference in the lead value did not change the linearity; however, it changed the periodicity. The optimal leading temperature difference was determined as 15°C. In a comparison experiment using a large-scale spontaneous combustion test bench, the heating law of the spontaneous combustion of coal was consistent. The experimental system based on isothermal difference leading achieved the adiabatic oxidation of coal up to a maximum point, which could better reflect the low-temperature oxidization of coal, reduce the amount of experimental coal needed, and improve the experimental periodicity. Additionally, it considerably improved experimental efficiency and provided a new technical approach for the prevention and control of the spontaneous combustion of coal. [ABSTRACT FROM AUTHOR]

Coal kept in the coal storage yard spontaneously catches on fire, which results in wastage and can even cause a massive fire to break out. This phenomenon is known as the spontaneous combustion of coal. It is a complex process that has non-linear relationships between its causing variables. Preventive measures to prevent the fire from spreading to other coal piles in the vicinity have already been implemented. However, the predictive aspect before the fire occurs is of great necessity for the power generation sector. This research investigates various prediction models for spontaneous coal combustion, explicitly selecting input and output parameters to identify a proper clinker formation prediction model. Feed-Forward Neural Network (FFNN) is proposed as a proper prediction model. Two Hidden Layers (2HL) network is found to be the best with 5 minutes prediction capability. A sensitivity analysis study is also conducted to determine the influence of random input variables on their respective response variables. [ABSTRACT FROM AUTHOR]

Gas and spontaneous combustion of coal have seriously threatened the production safety and efficiency during the process of mining. Gas drainage can reduce the risk of gas while it may intensify the self-ignition of coal. In order to study the certain relationship between these two issues, the south 906 working face of Dalong Coal Mine was taken into research. The physical geometrical and mathematical model was established. Numerical investigation based on Fluent was conducted to identify the gas concentration distribution and air leakage field under four different gas drainage methods, such as high drill holes drainage (HDHE), buried pipe drainage (BPE), adjacent roadway drainage (ARE), and tail roadway drainage (TRE). The simulation results show that all these four gas drainage methods are able to control the gas concentration in the air return corner, so as not to exceed the certain limit (1%). However, these methods have also enlarged the area of spontaneous combustion zone with 1.11, 1.30, 1.61, and 2.10 times, respectively. According to the comprehensive analysis on simulation results, HDHE has the minimal influence under the same gas drainage amount. This gas drainage method was then applied in the aforementioned working face. The follow-up monitoring data proved our research results, with CO concentration in the drainage pipes always keeping lower than 0.0024% and gas concentration in the air return corner maintaining no more than 0.70%. The study provides significant references for managing the gob where exists symbiosis disaster of gas explosion and spontaneous combustion of coal. [ABSTRACT FROM AUTHOR]