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• The thermogravimetric experiments of acid-base pretreated coals were studied. • Acid treatment can observably inhibit coal spontaneous combustion. • Alkali treatment promote CSC at low temperature but inhibit it at high temperature. • The effect of acid-base pretreatment on coal spontaneous combustion was discussed. The effect of inorganic salt ions on coal spontaneous combustion has been well revealed. However, the effect of organic metals on coal self-heating process has been paid little attention, which deserves further study. In this study, coals with different content of carboxylate were prepared by acid treatment, alkali treatment and re-acid treatment. The effect of acid-base pretreatment on the generation and oxidation of active sites was measured by pyrolysis-room temperature oxidation experiments. Thermal analysis and kinetic calculation, SEM-EDX, XPS, ESR were used to analyze the internal mechanism. The results show that the increase of free radicals (ΔNg) for the acid -pretreated coal during pyrolysis is 14.52 × 1018 spins/g, less than that of raw coal. The conversion of carboxylate structures to carboxylic acid structures by acid treatment significantly reduced the production of active sites, thus inhibiting coal self-heating behavior. The activation energy of alkali treated coal was 33.57 kJ/mol lower than that of raw coal, attributing to the conversion of carboxylic structures to carboxylate structures. The carboxylate structures can form coal matrix and Na binding structures (CM-Na) during the thermal decomposition process. The structure was able to constantly break and recombine due to its weak stability at low temperatures, accompanied by the generation of active sites, resulting in higher free radical concentration of 20.66 × 1018 spins/g. The research results have great value for investigating the mechanism of coal spontaneous combustion and providing an effective pathway to restrain the coal self-heating process. [ABSTRACT FROM AUTHOR]

Terahertz technology holds promise for monitoring coal fires and assessing associated risks, relying on the dielectric response of coal during the oxidation process. Besides, unraveling the response mechanism is crucial for enhancing the application's reliability. In light of these, this study focused on investigating the terahertz complex permittivity of lignite with different oxidation temperatures through microstructure analysis. Results indicated that oxidation temperature dependencies in the real and imaginary parts of lignite's permittivity, exhibiting a pattern of initial decrease followed by an increase. The decrease in permittivity during the dehydration and weight loss stage is primarily attributed to moisture content. In the oxygen absorption and weight gain stage, pore development and scattering effects contribute to the continuous decrease in real permittivity and rise in imaginary permittivity. During the oxidative decomposition stage, the hydroxyl group initiates an increased real permittivity. Upon reaching the combustion temperature, there is a sudden surge in permittivity, driven by the dominance of minerals in coal dielectric properties. The conclusions offer theoretical support for terahertz technology in monitoring coal fires, which can contribute to the sustainable development of the coal industry, mineral processing, and safety production. • Evolution and mechanism for THz permittivity of coal during oxidation were studied. • THz permittivity of coal exhibits distinctive dependence on oxidation temperature. • Evolution for THz permittivity of coal is linked to microstructural transformation. • THz technology can be used to identify the oxidation degree of coal. [ABSTRACT FROM AUTHOR]

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

The low-temperature oxidation of coal involves multiple gas production paths including desorption, pyrolysis and oxidation. These paths interfere with each other, resulting in unclear kinetic characteristics of CO and CO 2 production in coal oxidation and incomplete mechanism of gas production. Therefore, this paper proposed a method that can effectively exclude the effects of desorption and pyrolysis on gas production and adopted this method to explore the kinetic characteristics of CO and CO 2 production under different paths. Besides, with the aid of microscopic characterization methods, the kinetic steps controlling gas production and the mechanism of gas production were analyzed. The experimental results demonstrate that the proposed method can effectively eliminate the effects of desorption and pyrolysis, and can obtain the kinetic characteristics of gas production under the oxidation path that can reflect the intrinsic characteristics of low-temperature oxidation of coal. Based on the difference method, the activation energies of CO and CO 2 produced under the oxidation path are 59.49 kJ/mol and 60.09 kJ/mol, which activation energies are almost the same, suggesting that CO and CO 2 are likely to be produced from the same precursor. The gas production in low-temperature oxidation is a process in which methylene groups in coal react with oxygen to generate oxygen-containing intermediates which then decompose to produce CO and CO 2. The reaction of methylene groups with oxygen is the control step of gas production kinetics in coal spontaneous combustion, resulting in the same apparent activation energies of CO and CO 2 production in the stable phase under the oxidation path. • A method was established to exclude the effect of physical desorption and pyrolysis gas production. • The activation energies of CO and CO 2 produced in the oxidation path are equal. • The reaction of methylidene with oxygen to form the same intermediate is a key control step to control oxidation. [ABSTRACT FROM AUTHOR]

• pH responsiveness of HMDS terminated m-Cresol inhibitor is studied. • The stronger the acidity, the higher the conversion rate of HTMC to m-Cresol. • HMDS terminated m-Cresol remarkably improve the inhibition efficiency. • Inhibition mechanism of HTMC in different-rank coals is proposed. In this study, pH responsiveness of 1, 1, 1, 3, 3, 3-hexamethyldisilazane terminated m-Cresol (HTMC) in different-rank coals was investigated, and its inhibition performance regarding the spontaneous combustion of coal was explored. First, color changes in the deprotection reaction of HTMC under different acidic conditions were analyzed. Then, surface microstructures of these coals and pH values of their filtrates were tested. Subsequently, experiments were performed on different coal samples for grasping their low-temperature oxidation characteristics, weight loss rates, pore characteristics, and free radical variations. The experimental results show that HTMC can effectively protect phenolic hydroxyl groups in inhibitors, and the acidity of coal can promote the conversion rate of its deprotection reaction. For instance, in XAM coal (pH ≈ 6), sufficient H+ stimulates HTMC to release massive m-Cresol which contains highly reactive phenolic hydroxyl, thereby effectively suppressing increases of the concentration and type of free radicals. The crossing point temperature (177.2 °C) and inhibition rate at 110 °C (75.9 %) of the HTMC-inhibited XAM sample are 33.1 °C and 17.9 % higher than those of the m-Cresol-inhibited one, respectively. This study confirms the applicability of pH-responsive HTMC to different-rank coals and may lay a theoretical foundation for the design of efficient reactive inhibitors. [ABSTRACT FROM AUTHOR]

In view of the shortcomings of pure hydrogels, such as a single inhibition effect and poor stability at high temperatures, this study aims to develop a new composite hydrogel inhibitor and to study its inhibition mechanism. To this end, gallic acid and lignin were added to modify the hydrogel, and a gallic acid/lignin-modified hydrogel (GA/LG-PAA) inhibitor was prepared. By scanning electron microscope, it was discovered that inhibited coal samples treated with gallic acid hydrogel (GA-PAA) and GA/LG-PAA had bigger particles. By using thermogravimetric analysis, it was found that after the inhibition treatment with GA/LG-PAA, the coal samples' characteristic temperature points have increased to different degrees. Among these, the dry cracking temperature was increased by 53.87 °C, the ignition temperature was increased by 20.23 °C, and the burnout temperature was increased by 19.79 °C. Thermogravimetric experiments therefore showed that GA/LG-PAA had the best inhibition effect. Through infrared diffuse reflection experiments, it was found that the peak areas of methylene, carbonyl, carbon-carbon double bond, ether bond and other functional groups were all increased in coal samples after inhibition. The GA/LG-PAA inhibited spontaneous combustion by forming ether bonds. The results show that GA/LG-PAA can effectively inhibit coal spontaneous combustion. • This article mainly studies a novel compound inhibitor based on hydrogel. • The grafting of the material was verified by infrared spectrum experiment. • The inhibition performance of the materials were studied by scanning electron microscopy and thermogravimetry. • The mechanism of preventing coal spontaneous combustion was studied. • The compound inhibitor has obvious performance in inhibiting Spontaneous combustion of coal. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion (CSC) occurs with the change of temperature and gas concentration which is useful for early warning. To explore the intrinsic correlation between temperature evolution and gas distribution, a Back Propagation Neural Network (BPNN) model of coal temperature - gas composition - spatial distance was constructed, which is based on the gas characteristics and spatial distribution of coal temperature in large-scale coal spontaneous combustion experiments. The results showed that the O 2 concentration reached the lowest value (8.058%) at 45 cm on Day 52 with the time. CO and CO 2 also formed concentration peaks at 45 cm, and the gas distribution continuously moved towards the inlet position. The hydrocarbon gas components showed periodic increases, with values below 100 ppm. When the supply air time increased, the temperature rise rate in the initial stage of oxidation was slow but relatively uniform. Affected by ventilation conditions and coal density, two high-temperature zones were observed at 45 cm and 85 cm in the experimental furnace. With the inclusion of spatial distance parameters in coal temperature prediction, the BPNN model exhibits accurate predictive capability, with a total error of 0.94997. This can provide a method for predicting temperature changes in coal mine. [Display omitted] • The temperature and gaseous product exhibit a nonlinear relationship during CSC. • After 100 °C, the gas generation rate spikes notably in coal near the inlet. • CSC temperature is predicted by gas concentrations and distance from air inlet. • The temperature prediction model proposed achieves accuracy of 0.94997. [ABSTRACT FROM AUTHOR]

The use of coal combustion inhibitors, which are mostly sprayed on the surface of the coal that remains in the mining region (post-mining inhibition), has a significant effect on preventing spontaneous burning of coal, although their duration of action is limited. Pre-inhibition (pre-mining inhibition) prolong the inhibition duration and offers the chance to change the temperature of the inhibition fluid. This results in the suggestion of a hydrothermal inhibition strategy that emphasises the influence of inhibition fluid temperature on the inhibitory effect in order to achieve accelerated inhibition. Infrared tests and temperature-programmed oxidation are used to explore the inhibition law and mechanism of inhibition temperature on the spontaneous combustion of different coal orders. The findings demonstrated that when the inhibition temperature increased to 30 °C, 40 °C, 50 °C, 60 °C and 70 °C, the average inhibition rate and cross point temperature increased dramatically while the rates of oxygen consumption, exothermic rate, and CO production continuously dropped. Simultaneously, the coal's content of more reactive groups, such methyl and methylene, dropped, and the coal's risk to self-heat reduced. At the 70 °C inhibition temperature, the lignite coal showed the maximum inhibition rate (65.28%). This research is crucial to advancing the inhibitor's application technology and efficiency of inhibition. • A method for hydrothermal fluid inhibition to actively prevent coal spontaneous combustion was proposed. • Increasing inhibition temperature significantly reduces oxygen consumption rate and CO production. • Increasing inhibition temperature significantly increases the cross point temperature and the inhibition rate. • Increasing inhibition temperature can further reduce the key active groups on coal surface. [ABSTRACT FROM AUTHOR]

• Release of CO and CO 2 at constant temperature with time follows two different rules. • C–H in side chains is oxidized into precursors of carbon oxides, C = O and –COO. • CO and CO 2 can be produced by stepwise decomposition at ambient temperature. • Production of CO and CO 2 by direct decomposition occurs only at high temperatures. Precursors of carbon oxides in coals are considered to be related to aldehyde group(–CHO) and carboxyl group (–COOH), but the way of decomposition of precursors to produce carbon oxides is not clear. Through theoretical analysis, experimental research and quantum chemical calculation at molecular scale, this paper explores the decomposition mode and products of carbon oxide precursors during coal spontaneous combustion (CSC). A programmed heating device was used to investigate the change rule of gas product concentration during the constant temperature oxidation of coals, and the microstructure of the coals was characterized by low-temperature nitrogen adsorption experiments (BET), X-ray Diffraction (XRD) and X-ray photoelectron spectrometer (XPS). The results of the study show that during coal oxidation, the inhomogeneous energy exchange between the coals and the external heat source results in the change of gas product concentration with time following two rules. BET experiments reveal that oxidation leads to the evolution of fine mesopores to macropores and an increase in the number of pores with diameters larger than 20 nm in the coals, which facilitates the transport of oxygen molecules through the pore structure. Within 200 °C, the microcrystalline structure of coals is basically unchanged, and the active structure C–C/C–H on the side chain is converted to –CHO and –COOH and then decomposed to produce carbon oxides. Quantum chemical calculation shows that the reaction energy barrier of carbonyl group and carboxyl group decomposed step by step to form carbon oxides is much smaller than that of direct decomposition, and carbon oxides and alkyl radicals can be produced even at room temperature by step decomposition. The research results provide theoretical guidance for the formation mechanism of carbon oxides during low temperature oxidation of coals. [ABSTRACT FROM AUTHOR]

• CaCl 2 inhibited the participation of C H bonds in the oxidation reaction. • The inhibition effect of the inhibitor was most obvious at a 20 % concentration. • A coal molecular model with 20 % inhibitor concentration at 50 °C was constructed. • By utilizing a coal structural model, a point of reference is provided for the study of the inhibitory effects of inhibitors. The aim of this work is to use the changes in coal molecular structure to study the effect and mechanism of inhibitors, and to provide a reference for better preventing and controlling coal spontaneous combustion. In this study, Xinjiang Zhundong coal was used to construct the macromolecular structure. The changes in the molecular structure of the coal under different inhibitor concentrations and temperature conditions were analyzed by Fourier infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis. ChemDraw and Materials Studio were used to construct a coal molecular structure model with an inhibitor concentration of 20 % at 50 ℃. Results showed that the molecular formula of the ZD2–1 is C 222 H 123 O 39 N. The coal molecule contained a higher number of aliphatic hydrocarbon branches and a lower degree of aromatic ring condensation. When heated to 300 ℃, the proportion of adsorbed oxygen in raw coal decreased obviously, while the reduction of adsorbed oxygen was inhibited under inhibitor conditions. The change of functional groups of coal samples was obvious under 20 % inhibitor concentration, and the dosage was less than that of 30 % inhibitor concentration, revealing the optimal inhibitory effect on coal samples of Zhundong with this concentration. [ABSTRACT FROM AUTHOR]

• A porosity evolution model is developed to provides theoretical foundation for studying the diffusion of slurry. • Rock strata in the caving zone primarily fracture due to pressure from 'O' ring characteristics and key layers. • Numerical simulations is applied to determine the optimal flow rate, water-cement ratio and drill hole spacing for ground and underground grounding. These findings validate the proposed grout diffusion radius prediction formula. • In the in-situ test, the effect of grouting in actual engineering high temperature treatment and the mechanism of inhibiting high temperature are analyzed based on numerical simulation findings. The pores formed by spontaneous combustion of coal in goaf and the damage of surrounding rock caused by high temperature roasting may result in the surface to settle or even collapse, and produce crisscross pores. Porosity is an important influence index of oxygen supply by air leakage, smoke and heat escape, as well as seepage and diffusion of anti-fire media, and is the core influence factor of coal-oxygen composite, heat storage and heating, and high temperature prevention. Hence, a specialized porosity evolution model is developed, tailored to the context of high-intensity mining in high-temperature coal seams. Using this model, grouting simulations were conducted with the working face 12,315 of Huojitu Mine as the engineering basis. The results revealed that grout flow rates of 300 and 85 m3/h, water-cement ratios of 4:1 and 5:1, and drill hole spacing of 40 and 48 m exhibited notably effective grouting performance for surface and underground applications, respectively. The simulation and optimization outcomes have demonstrated favorable results for practical engineering applications. Signature gases, such as carbon monoxide and acetylene, were effectively reduced to 0 ppm, ethylene concentrations fell below 36 ppm, and oxygen levels stabilized at or below 8%. Furthermore, the sealing temperature within the goaf was maintained at approximately 16 ℃, effectively mitigating the high-temperature zone. [ABSTRACT FROM AUTHOR]

Most researches on coal spontaneous combustion characteristics under different oxygen concentration only consider different oxygen nitrogen ratio atmosphere, but low temperature oxidation law of coal under different methane atmospheres is seldom studied. In view of the above problems, index gas and activation energy of coal spontaneous combustion under different methane atmospheres were researched by temperature-programmed oxidation experiment and thermogravimetric analysis experiment. The results show that initial temperature of CO and CO2 production increase significantly with the increase of methane volume fraction. In initial stage of coal oxidation, production quantity of CO and CO2 under different methane atmospheres increase slowly with the increase of temperature. In accelerated oxidation stage of coal, production quantity of CO and CO2 increase exponentially with the increase of temperature, and the lower the methane volume fraction (the higher the O2 volume fraction) is, the larger the production quantity of CO and CO2 is, indicating that the higher the temperature is, the more obvious the inhibition effect of methane on coal oxidation is. With the increase of methane volume fraction, oxidation activation energy of coal at low temperature increases and index factor decreases, indicating that the increase of methane volume fraction has a good inhibition effect on coal spontaneous combustion.

A self-developed experimental system for high-temperature source-induced flammable gas explosion was used to simulate methane explosion induced by high-temperature source. Similarities and differences of methane explosion characteristic parameters between high-temperature source induction mode and electric spark induction mode were compared. The results show that methane explosion limit range under high-temperature source induction mode is 5.5%-14.5%, and that under electric spark induction mode is 5%-15.5%. It is more difficult for high-temperature source to detonate methane at explosion limit boundary. The methane explosion induced by electric spark has a more obvious temperature gradient than that induced by high-temperature source. The maximum explosion pressure of methane explosion induced by temperature source is higher than that induced by electric spark at different methane concentration. Methane concentration of the maximum explosion pressure under high-temperature source induction mode is 14.5%, while that under electric spark induction mode is 9.5% and 14.5%. Pressure boosting time of methane explosion induced by high-temperature source is larger than that induced by electric spark at each methane concentration.

In view of goaf spontaneous combustion prevention of 12401 fully mechanized working face with large mining height in Shangwan Coal Mine, CO is determined as prediction index gas of coal spontaneous combustion and C2H4 is used as auxiliary index gas to master coal spontaneous combustion through temperature programmed oxidation experiment. Gas in goaf is monitored by laying beam tubes on air return side in goaf of the working face, and spontaneous combustion 'three zones' in goaf were divided according to monitoring results. Heat dissipation zone is 0-32 m away from the working face, spontaneous combustion zone is 32-225 m away from the working face, and suffocation zone is 225 m away from the working face. According to total length of heat dissipation zone and spontaneous combustion zone and the minimum coal spontaneous combustion period, the minimum safe advancing speed of the working face is about 6.4 m/d. The research results can provide reliable basis for formulation of fire prevention measures on the working face.

In view of problems of poor fluidity, unsatisfactory fire-extinguishing effect and high cost of existing mine-used anti-fire extinguishing resistant material,inorganic clay composite superabsorbent resin was synthesized by aqueous solution polymerization method, and its structural characterization and thermal stability were measured. The resistive properties were studied combined with heating process of coal spontaneous combustion. The results of infrared spectrum and thermal stability analysis show that the prepared composite superabsorbent resin has main functional group with high water absorption characteristics and high thermal stability. The coal samples were treated with CaCl2, ascorbic acid and composite superabsorbent resin to resist the oxidation, and the oxidation kinetics and index gas tests were carried out on the coal samples after the inhibition. The results show that compared with the raw coal, CaCl2 and ascorbic acid resistant coal sample, composite superabsorbent resin resistant coal sample has the smallest oxygen consumption when the temperature of coal sample reaches 70 °C, and its intersection temperature is the highest, the initial temperature required to produce CO and CO2 is higher, which indicates that the composite superabsorbent resin has better inhibition effect on coal spontaneous combustion.

The problem of coal spontaneous combustion prediction is very complex, and there are many factors that affect the prediction results. In order to solve the issues of high dimension and redundancy among features and limited samples in the prediction of coal spontaneous combustion, this paper proposes a prediction algorithm of coal spontaneous combustion based on least squares support vector machine and adaptive particle swarm optimization (APSO-LSSVM). The adaptive PSO algorithm is used to solve the problems such as high computational complexity and slow calculation speed of the LS-SVM model for large-scale samples, so that it can always obtain the optimal solution, and its training speed and accuracy are improved. This method adjusts the inertia weight based on the convergence degree of group and the adaptive value of an individual for accelerating the training speed of swarm. After that, the improved PSO is used to iteratively solve the matrix equations in LS-SVM. APSO-LSSVM avoids the matrix inversion, saves the internal memory and obtains the optimum solution. The experiment results show that this method simplifies the training sample, accelerates the training speed, and also offers superior classification accuracy, fast convergence speed and good generalization ability.

At present，there are few researches on coal spontaneous combustion with different metamorphic degree under environment conditions of simulated gradually heated goaf. Taking 4 kinds of metamorphic coal samples, such as coke lean coal, gas-fat coal, anthracite coal and fat coke coal as example, the experiment of coal spontaneous combustion was carried out by using simulation system of coal spontaneous combustion to study combustion characteristics of coal and generation rules of spontaneous combustion gas under goaf environment. Experiment results show that when coke lean coal, gas-fat coal, anthracite and fat coke coal are warmed up, the temperature will rise 'S' type. The early temperature will have a slow accumulation process at first and then start to heat up quickly, and finally tend to balance at 300 ℃, and then slowly rising. Different coal samples produce volatile gases such as hydrocarbons and carbon oxides during the spontaneous combustion process and the rate of formation is affected by temperature, as well as the maximum and minimum two inflection points are present. The temperature rise curve of anthracite coal is similar to a straight line, and the gas curve does not fluctuate obviously with temperature. Large amounts of CO and CH4 are produced in spontaneous combustion of gas-fat coal and fat coke coal, the rate of CO production of gas-fat coal is the fastest, the maximum volume fraction of CO can reach 8%; and the rate of CH4 production of fat coke coal is the fastest, the maximum volume fraction of CH4 can reach 14%. The volume fraction of CO and CO2 produced by coke lean coal and anthracite is about 2% and 4% respectively.

Among fossil fuels, coal is the most widely used all over the world for generating power and electricity and it is a stable source of energy. Despite all these benefits, coal mining has serious hazards, such as coal spontaneous combustion. There are many factors that influence the tendency for coal to spontaneously combust in coal mines. Pyrite can promote the risk of this phenomenon. This promotion is accelerated by the combination of pyrite and moisture content at the same time. This combination is very rarely discussed in literature. So, in this research, the accelerating effect of reactive pyrite and moisture content on coal spontaneous combustion was measured experimentally using crossing point temperature (CPT) and R70 test methods. For this purpose, a new experimental apparatus was assembled and made in Iran. Reaction rate data obtained from the experimental results showed that pyrite has a twofold action. It first catalyzes the oxidation reaction. Then, in a moist environment, pyrite is itself oxidized, which provides a secondary heat source, and so accelerates the process of coal spontaneous combustion. Since the pyrite oxidation reaction consumes moisture, there is a mutual effect of accelerated heating as less heat is used up in moisture evaporation. The results show that pyrite content can linearly accelerate the coal spontaneous combustion process, while moisture content under 20% increases it, and if the moisture exceeds 20%, the rate of this process is reduced. The results of this research are helpful in the assessment and management of coal spontaneous combustion issues in coal mines.

Coal spontaneous combustion (CSC) in gob causes notorious safety issues to workers, especially during withdrawal period. Withdrawal period was normally divided into three stages (initial stage, expanding back channel stage and equipment returning stage) when evaluating and preventing the risk of CSC. This study first analyzed the characteristics of ventilation system at each stage, such as oxidized zone movement, local fire wind pressure and air leakage. Then, principles and specialized measurements were applied to minimize the ranges and effects of CSC in gob. In detail, this includes reducing the total air volume flow of mining face in initial stage, adding windscreen in outlet way and local fan in inlet way to increase the pressure of working face, and lowering external air leakage. Considering the working face ventilation area shrinks at equipment returning stage, keeping it bigger than windscreen’s areas can help to reduce air leakage. Further, foamed gel was grouted into gob to narrow and stop the moving forward of oxidized zone. Field application was applied in Zhang Shuang-lou coal mine. Findings of these studies could be used in other coal mine with similar conditions during withdrawal period.

Coal spontaneous combustion (CSC) is a disaster that seriously threatens safe production in coal mines. Revealing the mechanism of CSC can provide a theoretical basis for its prevention and control. Compared with experimental research is limited by the complexity of coal molecular structure, the quantum chemical calculation method can simplify the complex molecular structure and realize the exploration of the mechanism of CSC from the micro level. In this study, toluene and phenylacetaldehyde were used as model compounds, and the quantum chemical calculation method was adopted. The reaction processes of the methyl and aldehyde groups with oxygen were investigated with the aid of the Gaussian 09 software, using the B3LYP functional and the 6-311 + G(d,p) basis set and including the D3 dispersion correction. On this basis, the generation mechanisms of CO and CO2, two important indicator gases in the process of CSC, were explored. The calculation results show that the Gibbs free energy changes and enthalpy changes in the two reaction systems are both of negative values. Accordingly, it is judged that the reactions belong to spontaneous exothermic reactions. In the reaction processes, the activation energy of CO is less than that of CO2, indicating that CO is formed more easily in the above-two reaction processes. In addition, the variations in concentrations of important oxidation products (CO and CO2) and main active functional groups (such as methyl, carboxyl and carbonyl) with temperature were revealed through a low-temperature oxidation experiment. The experimental results verify the accuracy of the above quantum chemical reaction path. Moreover, it is also found that the generation mechanisms of CO and CO2 in coal samples with different metamorphic degrees are different. To be specific, for low-rank coal (HYH), CO and CO2 mainly come from the oxidation of alkyl side chains; for high-rank coal (CQ), CO is produced by the oxidation of alkyl side chains, and CO2 is attributed to the inherent oxygen-containing structure.

To enhance the stability of biomass gel foam used for inhibiting coal spontaneous combustion (CSC), a novel highly stable biomass gel foam (SA-Ca2+@TA-GF) based on a double cross-linked structure was prepared by introducing tannic acid (TA) into a gel form (sodium alginate/calcium L-lactate/composite foaming agent). FT-IR confirmed the formation of the double cross-linked structure. The effects of TA concentration on the performance of SA-Ca2+@TA-GF were analyzed, considering gelation time, half-life, film microstructure, and strength. With the addition of 1.6 wt% TA, SA-Ca2+@TA-GF forms a dense foam structure with a gelation time of 10 min. The half-life of the gel foam improves from 0.4 to 30 days and the strength increases by 72.9% compared to that of foam without TA. The inhibition experiments show that SA-Ca2+@TA-GF can asphyxiate coal, thus effectively inhibiting coal oxidation. Additionally, it can increase the temperature of coal at the rapid oxidation stage by 60 °C, and the CO inhibition rate is up to 79.6% at 200 °C. The fire-fighting experiment shows that SA-Ca2+@TA-GF can effectively cool coal and quickly extinguish fires. This study provides a simple method to prepare highly stable biomass gel foams, which is useful for improving the efficiency of gel foams in inhibiting CSC.

In order to prevent spontaneous combustion in the goaf of the ZF1801 working face in the lower layer of the Xiagou coal mine, the oxygen volume fraction and air leakage speed at the actual air supply of the working face at 1 026 m³/min were monitored on site. According to the "three zones" division standard of coal spontaneous combustion in goafs and numerical simulation method, the dynamic changes of the spontaneous combustion zone in the goaf of the stratified ZF1801 face were studied by using Fluent software, then the range of spontaneous combustion zone was determined, and the fitting curve of spontaneous combustion zone in goaf was obtained. Finally, the combined fire prevention and extinguishing technology of "plugging and reducing oxygen-inert replacement" was put forward. The results show that the numerical simulation of the spontaneous combustion "three zones" fits well with the on-site monitoring, and the numerical simulation is reliable. The oxidation heating zone is 40~150 m on the inlet side of the goaf and 35~130 m in the middle. When the distance between air flow separation walls in goaf is 50m and the distance between nitrogen injection through sieve tube is kept at 40 m, the extinguishing effect is better, the maximum width of the oxidation heating zone of air flow separation wall is reduced from 110m to 80 m, and the maximum width of the oxidation heating zone of nitrogen injection through sieve tube is reduced from 110 m to 25 m. With on-site application of a combination of air flow separation wall and nitrogen injection through sieve tube to prevent and extinguish the fire, the CO volume fraction of the air return tunnel side bundle tube in the lower layer goaf is reduced from 476×10-6 to 32×10-6, and the upper corner CO volume fraction is reduced from 300×10-6 to 11×10-6. In the upper layer goaf, the CO volume fraction in the goaf above the transport roadway side was reduced from 700×10-6 to 37×10-6, and the air return tunnel side was reduced from 528×10-6 to 19×10-6. The treatment effect is remarkable. [ABSTRACT FROM AUTHOR]

In order to study the mechanism of delaying coal spontaneous combustion through CaCl2 and improve inhibition effect, the chemical reactions between CaCl2 and coal have been studied. This research includes the study of ligand structure, formed by combination of Ca2+ and phosphorus (P)-contained active structure of coal, molecular frontier orbital, stabilization energy, natural bond orbital, Mulliken population, and charge transfer. All the calculations are performed with the Gaussian03 program. The calculation results indicate that bidentate, tridentate, and quadridentate ligands can be formed through the chemical reaction between Ca2+ and P-contained active groups in coal. During the generation of the complexes, stabilization energy becomes higher and the energy gap of frontier molecular orbital becomes lower, making a stable complex formed. After the formation of those complexes, the contribution of -PH2 group in the P-contained active structure is greatly reduced in the molecular frontier orbital. The orbital energy level increases dramatically, improving the stability of the active structure and retarding oxidation reaction. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion and coal fire accidents always lead to a large number of coal resource losses and casualties of workers. Moreover, the environment is polluted and the greenhouse effect is aggravated at the same time. At present, it is difficult for commonly used fire extinguishing materials like water and ordinary foam to suppress the coal spontaneous combustion effectively for a long time and to put out fire quickly. In this paper, a pollution-free fire-retardant foam with high foam expansion and good stability was proposed. The concentrations of SDBS, Guar and MgCl 2 were determined as 2%, 0.5% and 1% respectively by the orthogonal test. In addition, the flame retardant property was investigated from three aspects, namely free radical, functional group and CO generating rate. Meanwhile, the fire extinguishing property was investigated through the rate and time of reducing the coal temperature when putting out fire. The results show that the new fire-retardant foam is more effective than water and ordinary foam in inhibiting free radical production and coal‑oxygen composite reaction. Thus, it can inhibit coal spontaneous combustion and the spread of coal fire better. In the low temperature stage, the new fire-retardant foam mainly relies on physical inhibition methods such as water evaporative cooling and isolation of coal and oxygen contact. In the high temperature stage, it mainly relies on chemical inhibition methods such as MgCl 2 inhibiting coal‑oxygen complex reaction. Compared with water and ordinary foam, fire-retardant foam can extinguish coal fire and prevent smolder. [Display omitted] • Adding inhibitor to ordinary foam to make fire-retardant foam. • Obtain the optimal ratio of Fire-retardant foam through orthogonal test. • Fire-retardant foam can inhibit the generation of coal free radicals. • Fire-retardant foam is more effective than ordinary foam and water. [ABSTRACT FROM AUTHOR]

Gas and coal spontaneous combustion (CSC) compound disasters have become a common mode of serious accidents in coal mines. This study is aimed at revealing the characteristics of such compound disasters in the gob of Y-type ventilation fully mechanized top coal caving face with a high-level drainage roadway (HLDR) (hereafter referred to as "Y+HLDR" working face) and providing a theoretical basis for disaster prevention and control. With the W1310 fully mechanized working face of Gaohe Coal Mine taken as the research background, the distribution law of gas concentration field in the gob of the "Y+HLDR" ventilation mode under different air supply conditions was numerically simulated with the aid of COMSOL, and the area of gas and CSC compound disaster in the gob was divided quantitatively. The results show that data obtained from the field experiment coincide with the simulation results, which verifies the effectiveness of the simulation; Meanwhile, with the increase of air supply volume, the gas concentration near the working face is significantly reduced, and high-concentration gas is transferred to the deep part of the gob. The area where CSC induces gas explosions is divided by superimposing the gas and oxygen concentration fields that meet the conditions of compound disaster occurrence on the gob floor. It is concluded that the range of area with compound disaster risk is positively correlated with the air supply volume. The results of the simulation provide important theoretical guidance for the prevention and control of gob disasters. [ABSTRACT FROM AUTHOR]

Hydroxyl groups are one of the key factors for the development of coal spontaneous combustion. Although the reaction mechanism has been studied by many scholars, the effects of their positions in the molecule on the reaction characteristics have not been considered. In this paper, Ph−CH 2 −CH 3 was selected as the basic unit to construct small coal molecule models with one hydroxyl at different positions. The microscopic parameters of each model were calculated by density functional theory (DFT), and the elementary reaction pathways and thermodynamic parameters of hydroxyl groups were explored. It was found that the hydrogen of OH is the active site of nucleophilic reaction, the C α H bond of α-phenethyl alcohol and the O H bonds of the other molecules are most vulnerable to oxygen. All the models can generate H 2 O in the process of oxidation, other products of alcoholic hydroxyl groups are highly active oxygen-containing free radicals, while that of phenolic hydroxyl groups are quinones or ketones. The results of intrinsic reaction coordinate (IRC) indicated that hydrogen captured by oxygen is endothermic, while the ·OH free radical capturing hydrogen is exothermic. The activation energy of oxygen capturing hydrogen is 98–182 kJ/mol, which shows that the reaction can occur in the middle stage of coal spontaneous combustion (70–120 ℃), and the reaction rate gradually accelerate with the increase of temperature. In the same conditions, the order of the oxidation reaction rates is 2-ethyl phenol > 3-ethyl phenol > 4-ethyl phenol > α-phenethyl alcohol > β-phenethyl alcohol, which is the same as the order of reaction activities but opposite to that of activation energies. The research is helpful to strengthen the judgment of coal spontaneous combustion risk and the development of flame retardant. [ABSTRACT FROM AUTHOR]

There is a change in both the quantity and type of functional groups due to the fact that they become oxidized and pyrolyzed during the spontaneous coal combustion process. In order to study the oxidation and pyrolysis mechanisms that are at play during the evolution of these functional groups, in situ Fourier transform infrared (FTIR) spectroscopy was employed to test the real‐time evolution of these functional groups in both air and argon atmospheres. The differences found between functional groups when under an oxygen oxygen‐free environment were analyzed. The results show that when the temperature exceeds 200 °C, the changes in functional groups steadily increase and that regardless of whether the atmosphere is made up of argon or air, the oxygen‐containing functional groups change significantly. In this situation, −OH, −CH3, and −CH2‐ are important reactants in the whole heating process; −COOH and −C=O are reactants during the low temperature oxidation stage, but when reaching the high temperature stage, they become the products; C‐O‐C and C=C is a stable reaction product. During the coal spontaneous combustion process, oxidation and pyrolysis work as two coupling reactions: The heat released by the oxidation reaction pyrolyzes the macromolecular structure and coal‐oxygen complexes, while a large number of active groups are produced during pyrolysis, which then provides the reactants for the oxidation reaction. These results reveal the changes that functional groups go through during the process of oxidation and pyrolysis, and provide a theoretical basis for the development of efficient fire‐fighting materials. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Due to high gas content and a low permeability coefficient in deep coal seam mining, the spontaneous combustion of coal around the wellbore can easily occur, leading to difficulties in extracting gas during the mining process. To determine the dangerous area around the borehole and conduct advanced prevention and control measures are the keys to preventing spontaneous combustion in boreholes. However, the dangerous area around the borehole is not clear, the sealing parameters lack scientific basis, and the key prevention and control measures are not clear, which have caused great harm to coal mines. This study took the 24,130 working face of Pingdingshan No. 10 Mine as an example, using numerical simulation, theoretical analysis, and field tests to classify the risks of studying the surrounding area of the wellbore. The dangerous area variations under different lengths of shotcrete in the roadway were analyzed, the optimal plugging parameters were studied, and the current “two plugs and one injection” plugging device was optimized. Based on the oxygen concentration and air leakage rate, a method was proposed to divide the dangerous area of fissure coal spontaneous combustion around the borehole induced by gas extraction. The dangerous area of spontaneous combustion around the borehole was defined as having an oxygen concentration larger than 7% and an air leakage rate less than 0.004 m/s. The comprehensive control measures of the grouting length at 2–4 m, hole-sealing parameter at 20-13 (hole-sealing depth 20 m, hole-sealing length 13 m) and the “two plugs, one injection and one row” device were determined.

Much of the residual coal in a goaf was immersed in water for extended periods of time, which leads to complicated coal spontaneous combustion (CSC) characteristics that are difficult to predict. In this work, five kinds of coal samples with different moisture content (MC) of 4%, 11%, 18%, 25% and 32% were prepared by soaking, and a temperature programmed test was carried out. The gas produced by the oxidation of coal samples with different moisture contents and its concentration variation law were analyzed during temperature rise, and the index gas suitable for predicting CSC was selected. The concentration of gas generated by coal sample heating increased with increasing temperature. We also found that CO, C2H6, C2H4 and C3H8 can be used as the single auxiliary index gas for CSC prediction, and the composite gases CO/CO2 (ω) and C2H4/C2H6 (ξ) can be used to predict the CSC oxidation stage comprehensively and reliably under different degrees of water immersion. The process of coal oxidation was divided into three stages: oxygen absorption and thermal storage (ω ≤ 0.133), slow oxidation stage (0.758 ≤ ξ ≤ 0.919) and accelerated oxidation stage (ω ≥ 0.401 or ξ ≥ 0.919). Combined with the actual conditions at different coal mines, timely parameter index correction can improve the CSC prediction index and provide guidance for preventing and controlling coal spontaneous combustion and safety management of coal mines. [ABSTRACT FROM AUTHOR]

• Variation of atomic ratio and microcrystalline structure with temperature under nitrogen atmosphere were explored. • Abrupts of H/C and O/C occured as rising the temperature of coal samples. • Correlation was established by thermal property with atomic ratio and microcrystalline structure. To explore the main influencing factors of atomic ratio (O/C, N/C, and H/C) as well as microcrystalline structure (d 002 , L a , L c , and M c) on thermal properties (specific heat capacity, thermal conductivity, and thermal diffusivity) at certain temperatures within 30.0–300.0 °C, three coal samples were collected from coal mines of Dafosi, Yangjiaping, and Hujiahe in Binchang coalfield, Shaanxi Province, PR China. Thermal properties of coal samples were determined by laser-flash apparatus in nitrogen atmosphere. After temperature treated at 30.0, 60.0, 90.0, ..., 300.0 °C in nitrogen atmosphere, the atomic ratio and microcrystalline structure of samples were measured by proximate analyser and X-ray diffractometer. The results indicated that with an increment in the temperature, the value of H/C for three coal samples diminished slightly and then promptly, whereas O/C diminished slightly and then increased before 120.0 °C, as well as finally increasing, and the N/C had no obvious change. Concurrently, the microcrystalline structure of coal samples became more orderly and complete. Furthermore, the TD decreased with temperature, the SHC and TC showed an opposite trend with TD. Based upon grey correlation analysis, the major influencing factors of atomic ratio and microcrystalline structure on thermal property were approached. The results provided insight into the physicochemical properties of the coal of interest for predicting the progress of coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

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

Copyright of 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.)

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department 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.)

Electromagnetic radiation (EMR) is an optimal non-contact and directional geophysical detection method, which has been applied in geotechnical engineering, monitoring and giving early warning about the coal and rock dynamic disaster. In this paper, the different frequencies EMR signals generated in the process of coal heating and spontaneous combustion are tested and analyzed, and the detection criterion of locating anomalous heating areas by EMR is illustrated. During the spontaneously-heating process of coal, the EMR signals are detected by antennas with frequencies of 30 kHz, 100 kHz, 300 kHz and 1 MHz, covering both low and high frequencies. In the process of coal spontaneous combustion, the spectrum of EMR signal changes with the increase of coal temperature. The amplitude of EMR also fluctuates, showing the characteristics of high frequency and high amplitude, and the corresponding thermal damage of coal occurs in different degrees (intensities). Further, in order to use EMR as an effective detection method of coal fire, the relationship between the intensity of EMR and coal size, test distance and temperature is discussed. With the dominant spectrum of EMR determined by field tests, researchers can employ different EMR frequency to detect the fire risk based on the concrete conditions of coal field. This study provides a meaningful method for improving the level of safety and environmental protection during mining process. [ABSTRACT FROM AUTHOR]

To solve the problem of unclear targeted inhibition of key free radicals by antioxidants, this paper took the hydroxyl radical with the highest oxidation activity of coal as the inhibition target and selected five antioxidants such as ethylene diamine tetraacetic acid, tea polyphenol, citric acid, vitamin C, and proanthocyanidins. Based on the theory of quantum chemistry, the characteristics and oxidation pathway of antioxidants inhibiting coal oxidation of hydroxyl radical were analyzed. Analyze the influence characteristics of antioxidants on the evolution of free radicals in coal through an electron paramagnetic resonance experiment (ESR). The results showed that the electron density of antioxidants was mainly distributed in the functional groups of carboxyl and hydroxyl, which played a key inhibitory role, and the vicinity of carboxyl and hydroxyl and other functional groups was positive potential, which was the active site of inhibiting hydroxyl radical. The order of inhibitory capacity of the five antioxidants was determined as GTP > PC > EDTA > CA > VC. It is concluded that the energy barrier of hydroxyl radical inhibition by citric acid is much lower than that of EDTA. For the hydrogen extraction reaction, VC inhibited the hydroxyl radical pathway with a higher energy barrier than the other three antioxidants. The mechanism of five antioxidants inhibiting •OH reaction was comprehensively analyzed. It was found that tea polyphenols have more active sites that can react with •OH to quench it, so the inhibition of tea polyphenols should be the most significant. When antioxidants inhibit coal spontaneous combustion, the type, complexity, concentration, and linewidth of free radicals in coal molecules are lower than those in raw coal, with GTP antioxidants having the best inhibitory effect. The research results have important theoretical and practical significance for revealing the mechanism of coal spontaneous combustion inhibition and developing directional coal spontaneous combustion inhibition technology., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

To explore the spontaneous combustion characteristics and hazards of the low-temperature oxidation (LTO) stage in the process of spontaneous combustion of coal and mudstone, the pore structure, spontaneous combustion characteristic parameters, and exothermic characteristics of coal and mudstone were tested and studied, and the oxidation kinetic parameters were calculated. The results show that mudstone has a larger specific surface area and pore volume than coal. From the fractal characteristics, the pore structure of mudstone is more complex than that of coal. According to the comparison of theoretical and actual gas generation and oxygen consumption rate curves, it is found that there is an interaction between coal and mudstone in the LTO process. With the increase of mudstone mass ratio, gas production, and its oxygen consumption rate increase. Among them, CM-4 (Coal:Mudstone = 1:1) has the highest exothermic intensity and the exothermic factor (A) and fire coefficient (K) increase with the increase of mudstone content. The apparent activation energy of the mudstone sample is lower than that of the raw coal, indicating that the sample after adding mudstone is more likely to have spontaneous combustion in the LTO stage., (© 2024. The Author(s).)

In order to study the effect of temperature on the structure and mechanical properties of coal with different metamorphic degree. Three coal samples with varying degrees of metamorphism were chosen for analysis. The discrete element software PFC2D is used to simulate the heat treatment and compression of coal. The findings indicate that during the heating process, low-order coal exhibits noticeable thermal cracks at an early stage, while thermal crack development in middle-order coal is concentrated in the later stages. In contrast, high-order coal demonstrates a more stable macroscopic structure. The strength and stiffness of low rank coal show the lowest value and decrease significantly within 135 °C. However, the strength and stiffness of medium rank coal decrease significantly after 135 °C. The changes of mechanical properties and damage modes of coal caused by thermal damage are often ignored, which may lead to the deviation of design and research results from the actual situation. Therefore, this study is of great significance to the prevention and control of coal mine disasters., (© 2024. The Author(s).)

In order to explore the micro structure variation features of coal after pre-oxidation, the liquid nitrogen adsorption experiment was adopted to measure the specific surface area and pore structure of Liujia lignite, Sitai lignite, Tongxin bituminous coal and Baijigou anthracite, the variation laws of specific surface area, pore size distribution and pore volume with coal sample pre-oxidation temperature and pre-oxidation time were obtained. The results show that the specific surface area of oxidized coal samples from different coal mines has the same change law: pre-oxidized coal samples at 50 ℃>original coal samples >pre-oxidized coal samples at 120 ℃> pre-oxidized coal samples at 200 ℃, and the longer the pre-oxidized time is, the smaller the specific surface area will be. The pore size of pre-oxidized coal samples from four coal mines is concentrated in the range of 2-10 nm. Coal samples 50-6（pre-oxidized at 50 ℃ for 6 h） have the highest cumulative pore volume value, while coal samples 200-24（pre-oxidized at 200 ℃ for 24 h） have the lowest cumulative pore volume final value. The internal pore network of coal sample 50-6 is the most developed, it is easier to react with oxygen under the same conditions, thus has the highest spontaneous combustion risk, while the coal sample 200-24, on the contrary, has the lowest spontaneous combustion risk.

To solve the problem that the sublimation of dry-ice is too slow when it was used for fire prevention in goaf, a new device, dry-ice phase transformation generator, has been designed, which can improve the speed of dry-ice sublimation by the heat supply of water. In order to make the device successfully applied to underground coal mines, its performance was tested. Through the laboratory experiments, its hydraulic characteristics of the hot water supply part and gas production change were analyzed, the heat transfer was calculated, and the risk of copper tube freezing was evaluated. The results show that the device can produce CO2 stably and efficiently for 4 hours, and the water in the copper pipe does not have the risk of freezing under normal conditions. Finally, it is concluded that the device has good fire-fighting performance and can be used in goaf fire-fighting.

In view of problem of natural fire on 1078 working face of Qingdong Coal Mine, through a combination of laboratory research and on—site testing, the main and auxiliary indicators of spontaneous combustion index gases were optimized: CO and C2H4 can be used as main indexes of oxidation and spontaneous combustion of coal in 10 coal seam, olefin ratio and alkane ratio are used as auxiliary indexes of oxidizing spontaneous combustion index gas of coal in 10 coal seam. The spontaneous combustion 'three zones' in goaf were divided by two indicators of oxygen concentration variation law and temperature change trend in goaf: the heat dissipation zone is 0～31 m from the working face, the spontaneous combustion zone is 31～78 m from the working face, and the suffocation zone is 78 m far away from the working face. The research results provide scientific basis and theoretical guidance for natural fire control on 1078 working face.

Changing rule of composite gas indexes under different dry air flow and oxygen concentration was analyzed through coal temperature-programmed experiment. The experimental results show that φ(O2)/(φ(CO)+φ(CO2)) should be selected as gas indexes for coal spontaneous combustion prediction in the case of uncertain dry air flow. φ(O2)/(φ(CO)+φ(CO2)) can be used as gas indexes for coal spontaneous combustion prediction when coal temperature is below 100 °C. φ(C2H4)/φ(CH4) and φ(CO)/φ(CO2) can be used as gas indexes for coal spontaneous combustion prediction when coal temperature exceeds 100 °C. φ(C2H4)/φ(CO) can also be used as gas indexes for coal spontaneous combustion when coal temperature exceeds 160 °C and oxygen volume fraction is approximately 5%.

Summary: Aiming at the problems that the existing coal spontaneous combustion physical inhibitor has the disadvantages of short retarding time and low blocking efficiency, the novel super‐absorbent polymer‐grafted tea polyphenol composite inhibitor is prepared based on analyzing the advantages and disadvantages of various kinds of inhibitors. The orthogonal test was carried out with the water‐absorbent as the assessment index, and the optimum formulation of the composite inhibitor was obtained: the degree of neutralization was 90%, the amount of initiator was KPS (Potassium peroxydisulfate)/AA (Acroleic acid) = 1.2%, and the amount of cross‐linking agent was MBA (N,N' Methylene diene amide)/AA = 0.4%. The experimental results show that the temperature of the cross‐point of the coal sample treated by obtained composite inhibitor increased by 18°C compared with the raw coal, and the crossing point temperature delayed by 37 minutes, the activation energy increased by 38.552 kJ/mol. The further mechanism analysis shows that the inhibitor has good water‐retaining and water‐absorbing property. The function of cooling by absorbing heat, covering coal and insulating oxygen, and also inhibiting the oxidation activity of the coal molecule can effectively inhibit the spontaneous combustion of the coal. [ABSTRACT FROM AUTHOR]

• Microstructure of the coal sample was quantitatively characterized. • Inhibiting effects of ILs on coal occurred during low-temperature oxidation. • The kinetic characteristics of the sample were determined. • Changes in the kinetic characteristic were illustrated using microstructures. Coal spontaneous combustion (CSC) has become a safety topic and has been widely debated. This study investigated the inhibiting effect on CSC by using a series of novel ionic liquids (ILs) as chemical inhibitors. The microstructure and thermokinetic characters were observed and evaluated by Fourier transform infrared spectroscopy and synchronous thermal analyser. The results indicated that ILs could destroy reactive groups on relatively active coal surfaces, such as OH, aliphatic C H, and O-containing groups. However, as aromatic CH is the main chain of coal molecule, damaging it is difficult. Different anions and cations found in ILs exhibited different abilities for destroying the groups on the surface of coal molecules. The damage was caused by the properties of anions and cations by affecting the chain length, number of chains of the anion and cations, and electronegativity strength. The changes in microstructure increased the physical adsorption capacity of inhibitive coal samples during low-temperature oxidation, which changed the characteristic temperature points. In stages of water evaporation and desorption mass loss (stage 2) and the thermal decomposition (stage 3), the apparent activation energy of coal samples increased. The kinetic characteristics of the obstructed coal sample were predicted using the Flynn–Wall–Ozawa method. The development ability was delayed and the risk level was reduced of CSC in stages 2 and 3. Therefore, ILs should be utilised at relatively low-temperatures (<230.0 °C) to control CSC. [ABSTRACT FROM AUTHOR]

• The spontaneous combustion tendency of coal was determined. • The evolution of functional groups was derived. • The addition of 2.0 mass% FeS 2 exerted a prominent promoting effect on coal oxidation. • The influence mechanism of FeS 2 on coal oxidation was determined. Spontaneous combustion of coal has become an important disaster that threatens the safety of coal mines. FeS 2 is the main component of pyrite, which is suspected to be a major contributor to coal spontaneous combustion (CSC). So, it has important significance to FeS 2 on the characteristics of coal oxidation for prevention and treatment. This study used coal samples mixed with different proportions of FeS 2 (2.0 mass%, 4.0 mass%, and 6.0 mass% mass percentage) were tested to investigate the characteristics of spontaneous combustion, as compared with the fresh sample. The CO and CO 2 production rates, critical temperature, and dry cracking temperature during oxidation were analyzed. The temperature-programmed experiments was conducted to simulate low-temperature oxidation processes realistically. In-situ infrared spectroscopy was used to appraise the evolution of low-temperature (< 200.0 °C) oxidation of aromatic hydrocarbons, aliphatic hydrocarbons, and oxygen-containing functional groups on the surfaces of the samples. Experimental results showed that FeS 2 exhibited a strong influence as the temperature exceeded the dry cracking temperature. Adding 2.0 mass% and 4.0 mass% FeS 2 showed a promoting effect on low-temperature oxidation; however, FeS 2 became an inhibitor which reached 6.0 mass%. Furthermore, adding 2.0 mass% FeS 2 showed the strongest promoting effect. From a microscale perspective, the promoting effect of FeS 2 on coal oxidation was due to thermal release from FeS 2 oxidation, enhancing the reaction between aliphatic hydrocarbons, such as methyl groups and methylene, and oxygen. Due to the reaction of FeS 2 , the acidic environment was conducive to the hydrolyzation of lipid structures into highly active alcohol or phenol structures, which in turn promoted the oxidation of the coal sample. These results are crucial for understanding the mechanism underlying the influence of FeS 2 on CSC and mine safety protocols. [ABSTRACT FROM AUTHOR]

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

• The effects of ionic liquids on physicochemical structure and oxidation characteristic of coal were studied. • N 2 adsorption and FTIR analyses showed the changes of pore structure and functional groups of the treated coals. • The thermogravimetric kinetics of the raw coal and treated coal with ionic liquids were investigated comparatively. • Ionic liquid delayed the oxidation process of coal. Ionic liquids (ILs) including [BMIm][NTf 2 , [BMIm][BF 4 and [HOEtMIm][NTf 2 were used to inhibit coal spontaneous combustion (CSC) in this study. The effects of three Ionic liquids (ILs) on the physical and chemical structure of coal including surface morphology, pore structure and functional groups were analyzed by Scanning electron microscope, N 2 adsorption, Fourier transform infrared spectroscopy (FTIR). Subsequently, thermodynamic analysis and oxidation kinetics experiment were utilized to investigate the influence of ILs on the oxidation process. Pore structure analyses indicated that ILs could dissolve the minerals in coal, causing the collapse and blocking of pore structure and resulting in lower specific surface area and pore volume of the treated coals by ILs compared to the raw coal (RC). FTIR results showed the enhanced apparent aromaticity and more stable chemical structure of the treated coals, and this increased the difficult of chemical functional group on the coal surface reacting with oxygen. The thermodynamic and oxidation kinetics experiments revealed that ILs delayed the oxidation process of the treated coals obviously, and the treated coals demonstrated less mass loss ratio and oxygen consumption, as well as lower heat release and carbon monoxide products than the RC. Moreover, [HOEtMIm][NTf 2 showed the best inhibition effect on coal spontaneous combustion as verified by minimum heat release and highest activation energy E a for the treated coal sample. [ABSTRACT FROM AUTHOR]

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.)