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A pressurized inhibition method is proposed based on the pre-inhibition process to study the inhibition law and mechanism of the pre-inhibition pressure on the coal spontaneous combustion, with a purpose of enhancing the inhibiting effect of chloride salt inhibitors. In this work, inhibited coal samples were prepared by immersing raw coal in high-temperature and high-pressure reactor at 1 MPa, 2 MPa, 3 MPa, 4 MPa, and 5 MPa, respectively, using MgCl 2 solution with a mass concentration of 20 %. The variation rules of the characteristic parameters, such as the indicator gas concentration, inhibition rate, surface microscopic morphology, and reactive groups, of various coal samples with the elevation of the pre-inhibition pressure were investigated using the programmed temperature-raising oxidation system, infrared spectroscopy, and SEM. It was found that the pre-inhibition pressure was in the range of 1–4 MPa, and with the increase of pre-inhibition pressure, the gas-producing concentration and the content of active groups of coal decreased, and the inhibition rate increased significantly. Increasing the pre-inhibition pressure can significantly improve the inhibition effect, and the optimum pre-inhibition pressure is 4 MPa. Continuing to increase the pre-inhibition pressure will destroy the pore structure of the coal and reduce the inhibition effect. [ABSTRACT FROM AUTHOR]

• Sound waves travel mainly through voids in the loose coal. • Influence of humidity on acoustic coal temperature measurement can not be ignored. • Acoustic temperature measurement technology can be applied to loose coal. Spontaneous coal bunker combustion disasters not only cause a waste of resources, but also cause huge economic losses and heavy casualties. The existing coal spontaneous combustion detection technology has obvious limitations, and there is an urgent need for new coal spontaneous combustion high temperature point detection technology. This paper constructs a model for measuring the temperature of loose coal using acoustic wave method that takes humidity into account. By measuring the mechanical properties of coal, it is found that when sound waves propagate in loose coal, they mainly propagate through the air in the gaps of loose coal. By analyzing the relationship between sound speed and temperature in free atmospheric pressure, a loose coal acoustic temperature measurement model considering humidity was constructed, and a correction factor was introduced to modify the temperature measurement model. Using the frequency sweep signal as the sound source signal, the temperatures of loose coal with three different degrees of metamorphism were measured. The results show that the temperature measurement of loose coal considering gas environment relative humidity is more accurate. The measured long flame coal temperature is closest to the real temperature, with a maximum absolute error of 1.68 °C and a maximum relative error of 5.44 %. Error analysis shows that the temperature measurement error is mainly caused by changes in the gas composition of the voids in the loose coal, the functional relationship between the characteristic factor and temperature, and errors in sound wave flight time measurement. This study can provide certain theoretical support for the acoustic method to measure the temperature of high temperature points in coal bunkers, and provide a new temperature detection method for coal fire disaster prevention and control. [ABSTRACT FROM AUTHOR]

[Display omitted] • DOPO-MMT nanomaterials are prepared by a solvent-free method and introduced into the gel foam. • Proposes a DOPO-MMT co-stabilized gel foam (D-M/CSGF) mining extinguishing material, based on the assembly effect of hydrophobic nanoparticles (DOPO-MMT) and hydrophilic macromolecules. • D-M / CSGF can effectively inhibit coal spontaneous combustion by covering, oxygen insulation, wetting and inhibiting coal-oxygen chemical reaction. To improve the inhibitory effect of gel foam on coal spontaneous combustion, this paper proposes a DOPO-MMT co-stabilized gel foam (D-M/CSGF) mining extinguishing material composed of a foaming system, stabilizing system, gel system, and DOPO-MMT based on the assembly effect of hydrophobic nanoparticles (DOPO-MMT) and hydrophilic macromolecules. The optimal ratio of D-M/CSGF is determined through single-factor experiments and orthogonal experiments. The microstructure of D-M/CSGF is characterized using stereomicroscopy, and the foaming properties, foam stability, and water retention of the gel foam are investigated. The inhibitory effects of DOPO-MMT co-stabilized gel foam (D-M/CSGF), ordinary gel foam (GF), and water-based foam (OF) on coal spontaneous combustion are compared through temperature-programmed experiments and infrared spectroscopy. The results show that when the mass fractions of the foaming system, foam stabilization system, gel system, and nanoparticles are 0.9 wt%, 0.3 wt%, 1.7 wt%, and 0.5 wt%, respectively, D-M/CSGF exhibits better foam properties, with small bubble size, long retention time, and uniform distribution, and a half-life of over 12 h. At 100 °C, OF, GF and D-M/CSGF reach 90 % moisture loss after 5 h, 8 h, and 10 h, respectively. Comparing with OF and GF, the water retention time of D-M/CSGF increases by 50 % and 20 %, respectively. The CO inhibition rate of D-M/CSGF at 150 °C is 93.7 %, the oxygen consumption rate is reduced by 46.64 % at 100 °C, and the inhibition rate is 87.6 %, which can effectively slow down the low temperature oxidation process of coal. Meanwhile, the content of active functional groups such as–OH and aliphatic hydrocarbons in the coal molecules is reduced by 40.92 % and 64.13 %, respectively, comparing with the original coal, which effectively reduces the oxidative activity of coal molecules. This study provides a D-M/CSGF with good foam properties and inhibitory effects, which can effectively isolate oxygen, reduce temperature, and heat radiation during the inhibition process, achieve efficient inhibition of coal spontaneous combustion, and have excellent fire extinguishing performance. [ABSTRACT FROM AUTHOR]

The limit parameters of coal spontaneous combustion are important indicators for determining the risk of spontaneous combustion in coal seams. By analyzing the limit parameters of coal spontaneous combustion, the dangerous areas of coal spontaneous combustion can be determined, and corresponding measures can be taken to avoid the occurrence of fires. In order to accurately predict the limit parameters of coal spontaneous combustion, the prediction model of coal spontaneous combustion limit parameters based on GA-SVM was constructed by coupling genetic algorithm (GA) and support vector machine (SVM). Meanwhile, the GA and particle swarm optimization algorithm (PSO) were used to optimize the back propagation neural network (BPNN) to construct the GA-BPNN and PSO-BPNN prediction models, respectively. To predict the intensity of air leakage of the upper limit of coal spontaneous combustion in the goaf, the prediction results of the models were compared and analyzed using MAE, MAPE, RMSE, and R2 as the prediction performance evaluation indexes. The results show that the MAE of the GA-SVM model, the PSO-BPNN model, and the GA-BPNN model are 0.0960, 0.1086, and 0.1309, respectively; the MAPE is 2.46%, 3.11%, and 3.69%, respectively; the RMSE is 0.1180, 0.1789, and 0.2212, respectively; and the R2 is 0.9921, 0.9818, and 0.9722. The prediction results of the GA-SVM model are the most optimal in four evaluation indexes, followed by the PSO-BPNN and the GA-BPNN models. Applying each model to the prediction of minimum residual coal thickness in the goaf of a coal mine in Shanxi, the GA-SVM model has higher accuracy, which further verifies the universality and stability of the model and its suitability for the prediction of coal spontaneous combustion limit parameters.

Due to high stress, high ground temperature, high moisture, and other factors in deep mines, the risk of coal spontaneous combustion (CSC) is enhanced, seriously affecting the safety of coal mining. To achieve early prediction of spontaneous combustion in the No. 3 coal seam at the Juye coalfield in the deep mine, this paper employs a temperature-programmed device to analyze the changing pattern of single-index gases and composite gas indices with temperature derived from the gas produced during csc. It also optimizes the index gas of coal sample spontaneous combustion. Simultaneously, the characteristics of coal temperature and a four-level warning indicator system for CSC are determined based on the analysis of indicator gas growth rate method, carbon-to-oxygen ratio, and the characteristics of the indicator gas. The composite index gases of the No. 3 coal seam in Juye coalfield are selected in the initial oxidation stage (Rco), accelerated oxidation stage (R1, G1), intense oxidation stage (R2, G1, G3), and oxidative decomposition stage (G3). This leads to the construction of a six-level warning system consisting of initial warning value, blue, yellow, orange, red, and black levels. Meanwhile, warning thresholds are also established.

To explore the hazard zone of coal spontaneous combustion in the adiacent goaf at different stages of the roadway driving face, the 2202 working face and the 2201 adjacent goaf of Yingpanhao Coal Mine were taken as examples. The large-scale experiment was conducted to analyze the coal spontaneous combustion limit parameters of the 2201 goaf. The conditions for identifying the hazard zone of coal spontaneous combustion in the adjacent goaf were proposed. Monitoring the gas concentration and temperature in 2201 adjcent goaf by the drilling holes through coal pillar, and the numerical simulation was conducted to study the oxygen concentration distribution in 2201 adjcent goaf, and the hazard zone of coal spontaneous combustion in the adjacent goaf was obtained. The results show that during the mining period of the 2202 working face, the coal pillar was broken by the stress concentration, and the oxygen volume fraction of the adjacent goaf was in the range of 10.1% to 13.8%. The oxygen volume fraction of the adjacent goaf before the stop mining period was between 10.3% and 15%. During the mining period, a narrow area on the coal pillar side with width 55 m from the front 45 m and behind 119 m of 2202 working face in the adjacent goaf was the coal spontaneous combustion hazard zone. Before the stop mining period, a narrow area on the coal pillar side with width 42 m from the front 63 m and behind 107 m of 2202 working face in the adjcent goaf was in an oxidizing environment.

The orthogonal experiment method was used to investigate the heat transfer performance of the gravity heat pipe under the influence of multiple factors such as types of working fluid, filling rate, and the aspect ratio. The Multi-index weighting method and rescaled range analysis were introduced to analyze the experimental results to propose an appropriate combination scheme of factors for the best heat transfer performance of the gravity heat pipe. The results show that gravity heat pipe can effectively reduce the internal temperature of the coal pile, thereby inhibiting the increase of the temperature of the coal pile. Moreover, the cooling capacity and effective pore radius of gravity heat pipe are positively correlated with the temperature of the coal pile. Specifically, when the coal pile temperature is about 70 ℃, the most appropriate combination of various factors is as follows, the working fluid is Al2O3-water nanofluid, the liquid filling rate is 15%, and the aspect ratio is 25.0. When the temperature of the coal pile rose to 210 ℃, the most appropriate combination of each factor is as follows, the working fluid is Al2O3-water nanofluid, the liquid filling rate is 25%, and the aspect ratio is 25.0.

In order to reveal the influence of air leakage on oxygen concentration in goafs of fully mechanized caving mining with a shallow buried and high mining height, the air leakage of No.122108 working face in Caojiatan coal mine in different seasons was tested by the SF6 tracer gas test method. Based on the result of the air leakage test, the “three zones” of spontaneous combustion in the goaf were simulated using Ansys Fluent fluid dynamics software, and the simulated result was compared with that of the field test. The result shows that the vertical air leakage of the working face is serious, the wind speed is high, and the air leakage rate is up to 86.96%. The air leakage rate is higher in winter and lower in summer. The air leakage intensity decreases from the air inlet side to the air return side through the middle of the goaf. The range of the oxidation heating zone of the goaf is 98–245 m on the air inlet side and 33–96 m on the air return side. The numerical simulation result is well consistent with the field test data. The research conclusion can guide fire prevention and the extinguishing of No.122108 working face and lay a foundation for the prevention and control of spontaneous fire in goafs of fully mechanized caving mining with a shallow buried and high mining height.

Most of the existing coal spontaneous combustion temperature prediction models are based on relatively complete index gas sample data. However, the index gas data are affected by instruments or human factors. There are often data missing phenomena, resulting in low accuracy and over-fitting of coal spontaneous combustion temperature prediction. In order to solve the above problems, the paper proposes to apply filling algorithms such as K-nearest neighbor algorithm (KNN), random forest algorithm (RF), decision tree algorithm (DT) and support vector regression algorithm based on particle swarm optimization (PSO-SVR) to fill in the missing values. The missing data and the filled data are trained by RF, SVR and extreme gradient boosting (XGBoost) algorithm respectively. The parameters are optimized by the PSO algorithm. The RF, XGBoost and SVR coal spontaneous combustion temperature prediction models based on data filling are constructed. CO, CO2, CH4, C2H6 and O2 are selected as index gas in coal spontaneous combustion experiment, and six kinds of random data missing are designed. The overall missing rates are designed as 10%, 20% and 30%. The missing rates of CO and CO2 are designed as 40%, 50% and 60%. The average absolute error percentage (MAPE) is used as the filling effect evaluation index. The MAPE, the judgment coefficient R2 and the root mean square error (RMSE) are used as the model performance evaluation index. Four filling algorithms and three prediction models are compared. The results of the comparative analysis show the following points. The DT filling algorithm has better filling effect than the other three algorithms in six kinds of missing data cases. When there are more missing values of CO and CO2, the MAPE between the filling value and the actual values of the RF algorithm is large. The XGBoost model works extremely well in the training set without adjusting the parameters, but it is very prone to overfitting. The prediction effect of SVR model is very poor and the model cannot meet the prediction requirements. In the case of six kinds of data missing, the MAPE of PSO-SVR, RF and PSO-RF coal spontaneous combustion temperature prediction models based on the DT filling algorithm are about 4%. The RF model based on the DT filling algorithm can predict the coal spontaneous combustion temperature without optimization and has good stability.

In view of the problem of coal spontaneous combustion and re-ignition by reducing the oxidation of coal with inert gas, most of the existing studies are related to the coal low-temperature oxidation process and the coal re-ignition process. The spontaneous combustion characteristics of coal secondary oxidation after reducing inert gas temperature are less covered. In order to solve the above problems, taking coking coal as an example, the spontaneous combustion characteristics of coking coal oxidized at different temperatures after CO2 cooling and secondary oxidation are explored through the low-temperature oxidation experiment. The coking coal is pre-oxidized by GC-4000A temperature-programmed equipment at 70, 110, 150 ℃ respectively. The oxygen consumption rate, CO production rate, CO2 concentration and apparent activation energy of coking coal during the secondary oxidation process are analyzed after cooling to 30 ℃ with CO2 gas and dry air respectively. The experimental results show that at the same pre-oxidation temperature, compared with the dry air cooling, the change rule of related parameters of coking coal cooled by CO2 is basically the same. In the early stage of secondary oxidation, because of coking coal absorbs a lot of CO2, CO2 hinders the contact between coal and O2, the oxygen consumption rate and CO production rate decrease. The apparent activation energy increases, and the oxidation of coking coal decreases. As the CO2 resolves, CO2 cooling also affects the later reaction of pre-oxidized coking coal, which reduces the spontaneous combustion risk of pre-oxidized coking coal during the whole reaction process. When the pre-oxidation temperature is different, the pre-oxidation coking coal at 70 ℃ and 110 ℃ has a small amount of CO2 adsorption in the early stage. This leads to no change in oxygen consumption rate, CO production rate and apparent activation energy. When the pre-oxidized coking coal at 150 ℃ is cooled to 30 ℃, the coking coal has more CO2 adsorption, resulting lower the oxygen consumption rate and CO production rate. With the increase of activation energy, more energy is required. The coal oxygen reaction is more difficult. The risk of spontaneous combustion is also reduced. Therefore, when there is a danger of oxidation and spontaneous combustion of coal in the coal mine, it is necessary to inject CO2 for a long time to reduce the possibility of secondary oxidation and re-ignition when the mining area is reopened.

The gas extraction in the low-level roadway in the coal seam roof is an important technical measure to solve the problem of gas concentration exceeding the limit in the upper corner of the working face. But the high-flow mixed extraction in the low-level roadway causes serious air leakage in goaf and increases the risk of spontaneous combustion of residual coal. At present, there are few studies on the synergistic effect of low-level roadway layout and extraction flow on the spontaneous combustion of residual coal in goaf. According to the actual situation of gas extraction in existing goaf with the low-level roadway in 10106 working face of Jiajiagou Coal Mine, a three-dimensional fluid-solid-thermal multi-field coupling numerical model of heterogeneous goaf is established by COMSOL software. The spontaneous combustion law of residual coal in goaf induced by gas extraction in the low-level roadway is analyzed by numerical simulation. The results show that gas extraction in the low-level roadway can reduce the gas concentration in the upper corner of the working face. The gas extraction flow rate is proportional to the maximum width of the spontaneous combustion oxidation zone and the maximum temperature of goaf. With the increase of gas extraction flow rate, the maximum width of the spontaneous combustion oxidation zone and the maximum temperature of goaf will increase. But too high gas extraction pressure will cause the air near the upper corner to 'flow back' to the goaf. This will increase the risk of spontaneous combustion of residual coal in goaf. When the gas extraction flow rate of low-level roadway is constant, the smaller the dislocation distance is, the larger the maximum width and the maximum temperature of the spontaneous combustion oxidation zone in goaf are. Combined with the numerical simulation results and engineering practice, it is determined that the dislocation distance in the low-level roadway of Jiajiagou Coal Mine is 15 m. The gas extraction flow rate is 45 m3/min. The gas volume fraction in the upper corner is 0.875% and the maximum width of the spontaneous combustion oxidation zone in goaf is 59.14 m. The scheme effectively solves the problem of gas concentration exceeding the limit in the upper corner. The risk area of spontaneous combustion of residual coal in goaf is not significantly increased.

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.)

Mine fire has always been a serious disaster in coal industry; many academic achievements have poured out in the past two decades for solving this problem. In this study, visual analysis was conducted to grasp the hotspots and development trend of mine fire research. Papers that published in 1999–2020 were retrieved as the data basis from Web of Science, and CiteSpace was used to carry out knowledge map analysis. The results shown that number of papers has increased steadily since 2005 and achieved explosive growth since 2014. Deng J is the first published author among many scholars. China, the USA, and Australia are active areas in mine fire research and China University of Mining and Technology ranks first in this field. The highest co-occurrence frequency keyword is "spontaneous combustion." International Journal of Coal Geology and Fuel provide guidance for mine fire research. Fire prevention technology, low carbon, ecology, and sustainable development are the hot research in recent years. The prevention and control of mine fire from combustion mechanism should be further strengthened. [ABSTRACT FROM AUTHOR]

The mined-out space in underground coal mines increases due to the mining face advances. The airflow continuously could enter the mine gob via the air leakage channels, which may cause the coal in gob spontaneously ignite and combust. The gob is not accessible for personal direct gas composition measurement due to rock collapses and blockages. Thus, it is difficult to monitor its spontaneous combustion condition timely, which leads to the blindness of developing spontaneous combustion prevention measures. Therefore, it is important to understand the status of spontaneous combustion of residual coal in the gob in time. To more accurately predict the coal spontaneous combustion in gobs, this paper proposes a new model to predict the burning state of coal in the gob by using the gas-CO generated by coal spontaneous combustion with considering the action of air leakages in the gob. Then the reflected CO critical value in the corner of the longwall face in return airflow side can be derived. An example application is also presented in this paper, which shows that the proposed method could better reflect the spontaneous combustion state of gob, and the derived critical value can be used as an early warning message to prevent the coal spontaneous ignition in the gob and reduce the probability of coal spontaneous combustion accidents. [ABSTRACT FROM AUTHOR]

In the process of coal formation at deep coal seam, the coal quality changes by geological environment. Under the influence of high-temperature and surrounding heat storage conditions, the combined capacity of coal and oxygen is enhanced, and the risk of coal spontaneous combustion is enhanced. Based on the spontaneous combustion law of coal in deep high-temperature and thermal environment, industrial analysis and correlation analysis of coal samples with different buried depth in the same coal seam were carried out. The low-medium temperature oxidation laws of different coal samples were studied by infrared spectroscopy (IR) and thermogravimetric analysis. Industrial analysis and correlation analysis showed that the buried depth of coal samples was significantly correlated with protolith temperature and water content. The infrared spectrum analysis of coal samples showed that with the increase in buried depth, the oxygen-containing functional groups in coal structure increased so the tendency of spontaneous combustion of deep coal seam was greater. Thermogravimetric analysis showed that the low medium temperature oxidation process of coal samples could be divided into three stages. Compared with the shallow coal seam, the deep coal seam changes smoothly in the first two stages, and dramatically in the last stage. [ABSTRACT FROM AUTHOR]

The spontaneous combustion of coal storage piles and gangue piles in coal mines has been resulting in significant resource waste and serious environmental pollution. To solve spontaneous combustion problems, the use of gravity heat pipes to extract internal heat from piles of coal has been proposed. In this paper, a method for selecting the optimum working medium for a heat pipe is presented. In addition, an experimental system was set up to study a gravity heat pipe's heat extraction rate, and a gravity heat pipe heat dissipation experiment was conducted. The experimental results showed that compared with using ethanol or hexane as the working medium, a methanol gravity heat pipe had the highest efficiency and provided the fastest cooling rate. [ABSTRACT FROM AUTHOR]

During a heating experiment, there are two sources of heat that increase the temperature of a coal sample: the heat released by the oxidation reaction of the coal itself, and the heat provided by the experimental system. Here, we propose a method for measuring the thermal effect of oxidation and self-ignition through a reference experiment conducted with a material that is physically similar to coal but does not combust. The reference material used was an aggregate of alumina, fly ash, and concrete, and experiments were conducted on both materials simultaneously. The temperature of the coal sample was obtained under self-heating conditions, and compared with that of the non-combusting material. The relationship of temperature as a function of time for both materials was determined from the data, the comparison of which allowed for the thermal effect of oxidation and coal spontaneous combustion (CSC) to be calculated. The reliability of the thermal effect data obtained by the experiment was verified by chemical bond energy estimation. These results provide theoretical guidance for on-site fire prevention and extinguishing in coal mines, and are important for the further development of the understanding of CSC. [ABSTRACT FROM AUTHOR]

Immediately and accurately assessing the risk of coal spontaneous combustion and taking targeted action are crucial steps in coal spontaneous combustion prevention and control. A new model, AEM-AHP-LSTM, was proposed to solve the weight calculation problem of multiobjective evaluation in the process of coal spontaneous combustion. Firstly, the key indicators of coal spontaneous combustion were analyzed and used as risk factors to establish an evaluation system. Next, the objective and subjective weights were calculated using AEM and AHP, respectively. The objective and subjective weights were then combined, and TOPSIS was used to calculate the score of the evaluation sample. Finally, the obtained evaluation samples were trained with the BP, RBF, and LSTM model to resolve the problem of model overdependence on historical data and achieve the auto-adapt adjustment of weight with data change. Additionally, data from 15 typical Chinese coal mines were applied to the model. The results indicate that, compared with the BP and RBF neural networks, the LSTM model has higher prediction accuracy, stronger generalization ability, and stronger practicability. The modeling and application findings show that the AEM-AHP-LSTM model was better appropriate for the risk assessment of coal spontaneous combustion. This method can potentially be further applied as reliable approach for the assessment of mine disaster risk. [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.)

Understanding the influence of high ground temperatures on the characteristics of the spontaneous combustion of coal is important for increasing safety in deep mines, where high temperatures are encountered. In this experimental study, long flame coal samples were treated at a constant temperature of 30, 40, and 50°C to simulate the high ground temperatures found in deep mines. By Fourier transform infrared spectroscopy, thermogravimetry, and gas chromatography, changes to the functional groups, gas generation, and characteristic temperatures resulting from the exposure to elevated temperatures were reported. The results demonstrate that as the ground temperature rises, the abundance of hydroxyl groups and oxygen-containing functional groups increases, and the coal becomes more reactive. Results from gas chromatography show that the quantity and rate of production of CO, C2H4, and C2H2 during oxidation all increased with increasing pretreatment temperature. Additionally, results from the thermal analysis indicate that the critical temperature, dry cracking temperature, and ignition temperature all decreased with increasing pretreatment temperature. These results all suggest that high ground temperatures can regularly increase the risk of spontaneous combustion of coal by enhancing the activity of functional groups. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion (CSC) is a disaster associated with coal mining that leads to loss of coal resources and environmental and human health issues. To investigate kinetic characteristics for oxidation of coal, three coal samples were collected from different coal mining areas in the Southern Junggar coalfield. Subsequently, the collected coal samples were ground into different particle sizes and tested using microscopic and macroscopic methods, including thermal gravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, and temperature-programmed oxidation. The results obtained are as follows: the sharpest absorption peak (002) indicates that graphitization is high. Furthermore, the results show that the SKS coal sample is prone to spontaneous combustion; the greater the aromatic hydrocarbon content is, the more difficult it is for CSC to occur, while the opposite is true for oxygen-containing functional groups. The SKS data confirmed this conclusion; the rate for generation of CO and CO2 controlled the possibility of SKS oxidation at 110 °C and provided an indication of the temperature. During the dehydration stage, the WD sample had the lowest activation energy, indicating that it was most susceptible to spontaneous combustion. During the combustion stage, the lowest activation energy was found for the SKS sample with particle sizes < 0.075 mm, indicating that particle size was one of the factors affecting spontaneous combustion. The activation energy for dehydration was significantly lower than that for combustion, which showed that the coal oxygen reaction was more likely to occur in the dehydration stage. Based on DSC curves, the SKS sample had the largest exothermicity, indicating that it would ignite more readily. [ABSTRACT FROM AUTHOR]

In order to investigate P-containing flame retardant on coal spontaneous combustion, trisodium phosphate, sodium hexametaphosphate, and ammonium polyphosphate were selected. Raw coal and inhibitor solution (10 wt%) were mixed at weight ratio 4:1. Coal (raw coal, inhibited coals) oxidation reaction was measured by own designed temperature-programming device. Simultaneous TG-DSC was carried out. Evolution of CO with increasing temperature and cross point temperature (CPT) were obtained of coal oxidation reaction; these results showed that the addition of (NaPO3)6 and ammonium polyphosphate (APP) to raw coal had an obvious suppression effect during low-temperature oxidation. CPT of APP-inhibited coal was 16°C higher than that of raw coal. TG-DTG curve results revealed that characteristic temperatures and mass fraction (ω) of APP-inhibited coal were significantly higher than other coal samples. Initial exothermal temperatures, thermal peak temperatures, and inhibition ratio were obtained from DSC curves. The results all demonstrated that APP had obvious inhibition effects on the whole coal oxidation. Infrared spectrograms of release gases showed that temperatures of the maximum release value and the whole quantity of gas products (CO2, CH4, CO, and H2O) were decreased due to the addition of APP by eliminating free radicals and diluting the amount of oxygen in the surrounding coal sample. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion (CSC) is a complex physical and chemical process. Numerical simulation is an efficient method for visualizing and quantifying CSC. However, in previous models, the property parameters of coal are frequently assumed to be constant and hence cannot be used to predict accurately the thermodynamic behaviors during CSC. In this study, a fully coupled porous media model considering water migration, heat transfer, and thermal deformation was developed to investigate the thermal kinetics of CSC. The porosity and thermal strain during CSC in the model were consistent with the experimental results. Moreover, a method based on nuclear magnetic resonance (NMR) was used to calculate the residual saturation of fluids in porous media during heat treatment. The results showed that porosity increased with temperature during CSC, and the NMR transverse relaxation cutoff values of coal depended nonlinearly on temperature. In the initial stage of CSC, moisture was the dominant factor affecting CSC. As time progresses, moisture and temperature exhibited a synergistic effect. Temperature was the leading factor contributing to CSC in the final stage. The temperature increase during CSC exhibited a 'slow and then fast' trend. In addition, the deformation of coal during CSC caused thermal shrinkage, and its magnitude depended on the temperature increase rate. The results can be used to identify the thermodynamic behaviors during CSC and contribute to a better understanding of the mechanism of CSC. [ABSTRACT FROM AUTHOR]

Traditional coal spontaneous combustion (CSC) inhibitors, while effective, have limitations such as frequent application or short-term efficacy. To this end, we developed a slow-release and water-soluble synergistic inhibitor (SWSI) to achieve long-term CSC inhibition. The SWSI was formulated by integrating synergistic antioxidants (SA) composed of ascorbic acid (AsA) and Fe-superoxide dismutase (Fe-SOD) dissolved in a super absorbent polymer (SAP) encapsulated within hydrogel microcapsules. The effectiveness of SWSI was evaluated through simultaneous thermal analysis and in-situ free radical tests. The formulation optimization demonstrated that AsA and Fe-SOD had the maximum synergistic inhibition effect at a 1:1 molar ratio. The optimal SA: SAP ratio of 3:1 achieved the lowest oxygen consumption rate and highest inhibition rate. The encapsulation formulation, consisting of 3% SA, 6% PAM, 1% CaCl 2 , and 0.5% citric acid, generated the highest swelling ratio. Simultaneous thermal analysis and in-situ free radical tests indicated that SWSI greatly increased feature temperatures and the apparent activation energy, lowered reaction heat, and substantially reduced free radical concentration in the full oxidation process. The newly developed SWSI offers a significant advancement in long-term CSC prevention by integrating physical and chemical inhibition, which provides sustained and effective inhibition throughout the entire oxidation process., (© 2024. The Author(s).)

To investigate the oxidation combustion heat effect and thermokinetic behavior of lean coal, the pulverized coal samples were tested using C80 micro caloric system and thermogravimetric experimental device, respectively. The thermal effects of lean coal samples during the low-temperature oxidation and oxidation combustion were analyzed, and the influence of the heating rate on the combustion process of lean coal was also studied. In addition, the apparent activation energy and the most probable mechanism function of the coal sample during the combustion process were analyzed. The results indicated that the low-temperature oxidation process of lean coal pulverized coal could be divided into slow oxidation, accelerated oxidation and fast oxidation stages. Moreover, the five characteristic temperature points during the oxidation combustion of pulverized coal were determined by the variations of TG/DTG curves; with the increase of the heating rate, the TG and DTG curves of the coal sample shifted to the high temperature zone, and the peak value of the DTG curve increased with the ignition temperature increased; the apparent activation energy of coal sample in the pyrolysis combustion stage described a trend of first increasing and then decreasing with the increase in the conversion rate. The maximum apparent activation energy were observed when the conversion rate is 0.2, which was 32.4 kJ/mol; heating rates had tiny effect on the most probable mechanism function of the oxidation reaction. The most probable mechanism functions of the reaction under the four heating rates were all basically in line with the A-E equation random nucleation and subsequent growth model, and the peak value of the function curve increased with the heatingrate increased.

In order to study the effect of moisture content on the combustion characteristics of coal, taking the bituminous coal from Zhujixi Coal Mine as the research object, the method uses cone calorimeter to test the parameters of ignition time, heat release rate, total heat release, smoke generation rate, total smoke release and CO generation rate of coal samples with different moisture content and analyzes the combustion efficiency of coal samples. The experimental results show the following points. ① The ignition time of coal samples decreases first and then increases with the increase of moisture content. The order of moisture content of coal samples corresponding to ignition time from long to short is 17.82%>13.82%>1.82%>5.82%>9.82%. The peak heat release rate of the coal sample decreases first, then increases and then decreases with the increase of water content. The order of moisture content of coal samples corresponding to peak heat release rate from large to small is 9.82%>1.82%>5.82%>13.82%>17.82%. The total heat release, smoke generation rate, and total smoke release of coal samples decrease first, then increase and then decrease with the increase of water content. The order of the moisture content of coal samples corresponding to the total heat release, smoke generation rate, and total smoke release from large to small is 1.82%>9.82%>5.82%>13.82%>17.82%. In the late stage of combustion process, the coal sample with 5.82% moisture content has the lowest CO generation rate, and the coal sample with 17.82% moisture content has the highest CO generation rate. The high moisture content will increase the CO yield. The order of the moisture content of coal samples corresponding to the combustion efficiency from high to low is 9.82%>5.82%>1.82%>13.82%>17.82%. ② Appropriate moisture content can improve the combustion performance of coal. It is suggested to choose the coal with moisture content of 5.82% to 9.82% so as to shorten the coal ignition time, reduce the smoke generation rate, total smoke release and CO generation rate, and improve the heat release rate and combustion efficiency.

Coal spontaneous combustion seriously restricts the safe production of coal mines, and adding an inhibitor is one of the effective methods to prevent coal spontaneous combustion. To improve the pertinence and high efficiency of the inhibitor, this paper considered the intrinsic properties and external conditions that affect the occurrence of coal spontaneous combustion, combined with the characteristics that the rare earth hydrotalcite can effectively improve the thermal stability, coupling, and flame retardancy of the coal and the halide inhibitor. The halide inhibitor can enhance the permeability, dispersion, and uniformity of the rare earth hydrotalcite as a carrier. The halide carrier inorganic salt inhibitor was prepared. To study the inhibition mechanism and performance of the halide carrier inorganic salt inhibitor on coal spontaneous combustion, differential scanning calorimetry (DSC) was used to test the variation law of parameters, such as stage characteristics, characteristic temperature, thermal effect, and apparent activation energy in the process of coal spontaneous combustion under the action of a rare earth hydrotalcite, MgCl2 and a halide carrier inorganic salt inhibitor. Test results reveal that the OH of the rare earth hydrotalcite laminate can generate a weak hydrogen bond with acidic functional groups such as −COOH in coal molecules so that the activity of the acidic functional groups is weakened. Mg2+ complexes with −COO− in coal molecules to form −COOMg−, resulting in the weakening of the C=O activity in −COO−, which is the main mechanism of the halide carrier inorganic salts inhibiting coal spontaneous combustion. The endothermic peak of the DSC curve appears as a double peak or multi-peak after the addition of halide carrier inorganic salts to the coal sample. Compared with the raw coal, the peak temperature is shifted back by 50–60 ℃, the T1 temperature is shifted back by 90–100 ℃, and the total heat release decreased by 19–27 kJ·g−1. Furthermore, the apparent activation energy of each stage of the coal body is effectively improved. Results revealed that the halide carrier inorganic salt inhibitor could effectively inhibit the reaction process of coal spontaneous combustion.

To explore the influence of the oxidation and spontaneous combustion process of fractured coal at different burial depths under uniaxial stress, the spontaneous combustion characteristics of coal under loading was studied within the testing device of coal spontaneous combustion and loading. Bituminous coal from the Liuhuanggou mining area in Xinjiang was selected and oxidized in the oxygen-lean environment loaded at the range of 0–8 MPa. Based on the relationship between the gas generated in the experiment and the temperature, we calculated the apparent activation energy and oxygen consumption rate of coal samples under uniaxial stress. We combined the oxidation kinetics and pyrolysis parameters of spontaneous coal combustion to describe the nonlinear development of coal from slow to rapid oxidation under uniaxial stress. Based on catastrophe theory, the catastrophic temperature and critical temperature of bituminous coal oxidation-combustion process under test conditions were calculated, and four characteristic parameters were determined: catastrophic temperature \begin{document}$ {T}_{\mathrm{C}\mathrm{O}} $\end{document} (characterization of CO) and \begin{document}$ {T}_{\mathrm{H}\mathrm{Y}} $\end{document} (characterization of oxygen consumption rate), and critical temperature \begin{document}$ {T}_{\mathrm{C}\mathrm{O}}^{'} $\end{document} (characterization of CO) and \begin{document}$ {T}_{\mathrm{H}\mathrm{Y}}^{'} $\end{document} (characterization of oxygen consumption rate), and analyzed the variation of different characteristic parameters with uniaxial stress. The analysis results show that the pyrolysis gas concentration, apparent activation energy, and oxygen consumption rate follow a cubic function law that first increases, then decreases, and then increases with increases in the uniaxial stress (the critical axial pressures at 1.8 and 5.5 MPa). At 1.8 MPa, the apparent activation energy and various parameter values are lowest, the oxygen reaction rate of coal is fastest, and the oxygen consumption rate is the highest. When the uniaxial stress is 5.5 MPa, the oxygen consumption rate is the highest, the greatest number of new cracks is created, and the characteristic \begin{document}$ {T}_{\mathrm{C}\mathrm{O}} $\end{document} parameters have the greatest impact. The temperature index of spontaneous coal combustion slowly transitions to rapid oxidation, and the catastrophic temperature \begin{document}$ {T}_{\mathrm{C}\mathrm{O}} $\end{document} characterized by the CO concentration is the most accurate. The research results have important theoretical guiding significance for the early warning and prevention and control of spontaneous combustion of coal at different buried depths.

In order to solve the problem of coal spontaneous combustion in the goaf, this paper used multi-component polymers as materials, and determined the optimal concentration of polyethylene glycol, carbonate and sodium polyacrylate was 13.7 wt%, 14.1 wt%, 0.03 wt% by response surface method. The water loss rate and surface tension of PAS-W were tested. The effect of PAS-W on functional groups was analyzed by infrared experiments. Thermogravimetric experiment was used to test the thermodynamic properties of PAS-W. The research showed that PAS-W had good applicability and stability. After treated with PAS-W, the content of aliphatic hydrocarbon and aromatic hydrocarbon in coal decreased by 49.5% and 39.7%, respectively. The oxidation rate of coal slowed down, and the ignition temperature also increased significantly. By analyzing the flame retardant mechanism of PAS-W, it was found that PAS-W had good flame retardant effect in physical and chemical properties.

This study aimed to further explore the adsorption properties of different gases (CO2, O2, and CH4) on the coking coal surface by establishing a molecular model. Changes in the absolute adsorption capacity and the isosteric heat of adsorption of gases under different temperatures, pressures, and compositions were simulated using grand canonical Monte Carlo (GCMC) and molecular dynamics simulations. Interaction energy and energy distribution were used to analyze the adsorption behavior of gases, and the diffusion properties were investigated using the diffusion coefficient and diffusion activation energy. The absolute adsorption results fit well with the Langmuir–Freundlich model. The absolute adsorption capacity had a significant positive correlation with pressure and the corresponding mole fraction, and a significant negative correlation with temperature. The competitiveness, based on binary adsorption selectivity, was in the order of CO2 > O2 > CH4. The isosteric heat of adsorption of CH4 was slightly higher than that of O2, and that of CO2 was 1.49–1.64 times that of O2 and CH4. The isosteric heat of the adsorption of gases was also barely influenced by temperature and pressure. The interaction energy between CO2 and coal was greater than that of O2 or CH4, but the high pressure and high content were not conducive to the adsorption of O2 by CO2. The preferred adsorption site for CO2 was stronger than that for O2 and CH4, and its peak value negatively correlated with the molar fraction. The diffusion coefficient for single component gases initially increased and then decreased with increased pressure, showing a positive correlation with temperature. A close inverse correlation existed between diffusion activation energy and pressure. These results revealed the microscopic adsorption and diffusion regularities of CO2, O2, and CH4 in the coal model, indicating great significance in accurately predicting coal fires.

Coal spontaneous combustion (CSC) is a serious threat to the safe mining of coal resources, and the selection of suitable gas indicators to predict the CSC state is crucial for the prevention and control of coal mine fires. In this paper, the temperature-programmed experiment of CSC was first carried out to analyze the gas components and compositions in the oxidative pyrolysis process of three coal samples (lignite, long-flame coal, and lean coal) with different coalification degrees. Subsequently, the spontaneous combustion tendency of these three coal samples was evaluated. Finally, through the variation of gas concentration, gas concentration ratio, and fire coefficient with coal temperature, the indicators suitable for predicting the spontaneous combustion of coal were preferred, and a multi-parameter indicator system was established to make a comprehensive judgment on the spontaneous combustion status of coal. The results show that coal rank is negatively correlated with oxygen consumption rate. The higher the coalification degree of coal, the slower the oxidation reaction and the later the characteristic temperature point appears. The lignite selected in this experiment is a type of coal that is more prone to spontaneous combustion than long-flame coal and poor coal, and the CO concentration, C2H6/CH4, and second fire coefficient R2 can be used as the main indicators for predicting CSC, while the other gases, olefin-alkane ratio and fire coefficient can be used as auxiliary indicators. To some extent, the research content can effectively and accurately determine the stage and degree of coal spontaneous combustion, which has a certain guiding role in predicting CSC.

In order to solve the defects of traditional coal spontaneous combustion prevention technology in a closed goaf, a strain of aerobic endogenous bacteria was isolated from coal and used as a blocking raw material. Based on the metabolic and reproductive characteristics of microorganisms, the experimental study on the inhibition of coal spontaneous combustion by microorganisms was carried out. The colonies were isolated and purified by the dilution concentration plate method and the scribing plate method. The growth morphology of microorganisms was analyzed, and the growth curve was determined. The strains were identified by seamless cloning technology for high-throughput sequencing. The surface morphology of coal was analyzed by SEM, the differences of oxidation characteristic temperature points were analyzed by TG–DTG–DSC images, a programmed heating experiment was used to analyze the concentration of the indicator gas CO, and the changes in microscopic groups before and after microbial action were analyzed by FTIR and XPS spectra. Therefore, the inhibition of coal oxidation by endogenous bacteria was verified from macroscopic and microscopic perspectives. The results show that the coal bacteria isolated from the coal is Lysinibacilus sp. After the culture of Lysinibacilus sp., the surface of the coal demonstrated less detritus, and was relatively smooth. In the early stage of low temperature oxidation of coal spontaneous combustion, the characteristic temperature point of coal oxidation and the reaction between coal and O2 could be delayed by Lysinibacilus sp., and the total heat release was reduced in the combustion process. Not only that, Lysinibacilus sp. could also reduce the CO concentration during coal heating. After the coal was decomposed by Lysinibacilus sp., the C=C thick ring skeleton structure had little effect; however, the aromatic substitution pattern changed. This bacterium had an effect on the C-O bond, reducing the percentage of -CH2- and increasing the percentage of -CH3. It might also use the crystalline water in coal for life activities. The carboxyl carbon in coal changed the most, with a decrease of 12.03%, so it might become the carbon source required for microbial growth. The reproductive metabolism of microorganisms also affected the form of nitrogen, and the percentage of pyridine nitrogen in coal was reduced. The ratio of single-bond carbon to double-bond carbon in raw coal was about 3:2, but after this bacterial action, the ratio of the two was about 1:1. The analytical conclusions of XPS and FTIR spectra were consistent, and the results supported each other.

The functional group structures of coal molecules are one of the most important factors affecting spontaneous combustion. However, it is difficult to determine the exact effects of such structures. Extraction technology is able to modify the functional groups in coal as a means of inhibiting spontaneous combustion reactions. The present work extracted coal from the Caojiatan mine in northern Shaanxi, China, with various solvents. The extraction effectiveness of these solvents was found to decrease in the order of dioctyl sulfosuccinate (AOT) > water > n-hexane > cyclohexane + AOT + ethanol > cyclohexane > ethanol > methanol. With the exception of the AOT, the concentration of functional groups in the extracted coal was decreased compared with that in a control specimen extracted using only water. Ethanol, n-hexane, and methanol provided the optimal extraction efficiencies in terms of capturing coal molecules with aromatic structures, aliphatic structures, and oxygen-containing groups, respectively. The results of this work are expected to assist in future research concerning the extraction of coal molecules with specific functional groups. This work also suggests new approaches to the active prevention and control of spontaneous combustion during the mining, storage, and transportation of coal.

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When a shallow-buried close-distance coal seam group is mined, the residual coal in the goaf of the upper coal seam is immersed in water for a prolonged period of time, increasing the risk of coal spontaneous combustion (CSC). In this study, the macroscopic characteristics of water-soaked coal (WSC) during low-temperature oxidation were analyzed using a temperature-programmed device. The microstructure changes at different oxidation temperatures (40, 80, 120, 160, and 200 °C) were investigated through liquid nitrogen adsorption and X-ray diffraction. The results revealed that, during low-temperature oxidation, macroscopic characteristic parameters such as the oxidation gas product concentration, temperature, and oxygen consumption rate of WSC changed, indicating higher oxidizability and lower apparent activation energy. The average pore size and macropore volume of the coal surface gradually increased during low-temperature oxidation. The mesopore volume increased at first and then tended to stabilize. The mineral content on the surface of the coal markedly diminished, but the mineral content did not participate in the oxidation process. Water leaching enhanced the interlayer spacing of the aromatic lamellae of the coal samples, curtailed the degree of coalification, and condensed the aromatic ring of the coal sample during the oxidation process. This analysis of the oxidation and macroscopic characteristics of WSC from micro- and macroperspectives is valuable for the prevention and containment of CSC. [ABSTRACT FROM AUTHOR]

In order to restrain the spontaneous combustion of coal and ensure the safety of coal mine, an environment-friendly whole-processinhibiting hydrogel-tea polyphenols-halloysite nanotubes (HNTs) physicochemical composite inhibitor was prepared. The optimal ratio was determined by response-surface experiment, namely, tea polyphenol 2.42%, neutralization degree 80%, initiator dosage 1.68%, crosslinking agent 1%, and crossing point temperature 159.74°C. Compared with pure hydrogel inhibitor and tea polyphenol hydrogel inhibitor, the composite inhibitor performed superior whole-process inhibition effect, with the lowest oxygen consumption rate, CO, and CO2 production rate. The overall inhibition rate was stable at approximately 55% and its highest value was 58%, which indicated that tea polyphenols and HNTs effectively improved the thermal stability. The radical concentration treated with composite inhibitor was the lowest with the reduction of 2.784 × 1017/g lower than that of raw lignite, which proved that the composite inhibitor improved the inhibiting effect microscopically. Finally, inhibition mechanisms of the composite inhibitor were proposed. The results of this work suggest that composite inhibitor is an effective inhibitor of coal oxidation. [ABSTRACT FROM AUTHOR]

Acetaldehyde is one of the crucial gases with odor released during the early stage of spontaneous combustion of coal, and it is essential for predicting the spontaneous combustion tendency of coal. In this study, we systematically investigated the effects of coal metamorphic degree, coal temperature, coal particle size, and oxygen concentration on the release of acetaldehyde using three coal samples with different metamorphic degrees and a combination of oxidation and warming processes as well as gas and liquid chromatography. The results showed that with the increase in temperature, the amount of acetaldehyde released first increased and then stabilized or slightly decreased. The amount of acetaldehyde released at low temperatures was linearly related to oxygen consumption. The higher the degree of coal deterioration, the lower the amount of acetaldehyde released. As the particle size decreased, the amount of acetaldehyde released increased and then decreased. Finally, four warning levels were established based on the concentrations and trends of acetaldehyde together with other index gases. [ABSTRACT FROM AUTHOR]

It is of great significance to study the characteristics of lowtemperature oxidation of coal in an adiabatic environment for the prediction and control of coal spontaneous combustion. Coal spontaneous combustion experimentation can better simulate the field conditions and reflect and test the actual process underlying the spontaneous combustion of coal. Numerical simulation methods can provide a systematic solution for research on the dynamic evolution process of coal spontaneous combustion. In this study, a large-scale coal spontaneous combustion test bench was employed to test the oxidation heating characteristics and gas generation laws of Huangling coal samples from 303-443 K, revealing the spatiotemporal evolution characteristics of the gas concentration and temperature fields. Based on the theory of computational fluid dynamics (CFD), a mathematical model of the spontaneous combustion of coal in the adiabatic state is therefore constructed. The evolution law and distribution characteristics of the temperature and gas concentration fields of coal in the experimental furnace are simulated by Fluent. The results indicate that the position of the highest coal temperature in the experimental furnace mainly changed along the central axis and gradually moved down toward the air inlet as the coal temperature continued to rise. Above the critical temperature (353 K), the hightemperature point mobility was high, and only one-tenth of the ignition period could be utilized to travel along with more than one-third of the original distance from the intake side. In the furnace, O2, CO, and CO2 were distributed in the upper and lower layers at different concentration values. The concentration of O2 gradually decreased from the inlet side along the gas flow direction, but the concentrations of CO and CO2 demonstrated the opposite behavior. When the temperature exceeded 120°C, the consumption of O2 and the production of CO and CO2 gases were mainly distributed in the furnace body below 0.65 m. The simulation results are in line satisfactorily with the experimental results. This study provides theoretical support for field index gas and three zone division. The development of the model can improve the existing theory of coal spontaneous combustion and find a more systematic and reasonable criterion for judging coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

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The low-temperature oxidation of coal includes processes such as coal-oxygen reactions and pyrolysis. As heat generated from coal-oxygen reaction is the fundamental driver of coal spontaneous combustion, the thermokinetic studies of coal spontaneous combustion should be focused on that. However, the pyrolysis path will impact the coal-oxygen reaction, resulting in limited capability of characterizing the t accurate hermokinetic parameters of coal-oxygen reaction process. Therefore, this paper proposed a new method to test the heat generation characteristics of coal-oxygen reaction path and the theoretical model of the method was established. The experimental results show that the method can achieve successful experiments within a short period of time, and exclude the impacts from heat absorption of water evaporation and pyrolysis, and well characterize the nature of coal spontaneous combustion. Meanwhile, the thermokinetic parameters such as heat generation rate and heat production can be obtained quickly and accurately. The coal-oxygen reaction path is divided into three stages by using the heat generation characteristics. By analyzing in-situ FTIR results, it is concluded that the gradual participation of different active groups is the main reason for the three stages. There are two main factors affecting the starting and heat generation of each stage, one is the activity of active groups which can participate in the initial reaction, and the other one is the number and activity of active groups that can participate in the reaction. [ABSTRACT FROM AUTHOR]

Due to the concealment of the fire source in the gob, the fire prevention and extinguishing work in the gob is facing great difficulties. This study is made in order to realize the real-time monitoring of gob temperature and the accurate positioning of high temperature area, so that the fire prevention and extinguishing work in gob can be targeted. In this study, the previously developed COMBUSS-3D software was used to predict the high temperature area in the gob of 85001 working face of Yangmeiwu Coal Mine and II830 working face of Zhuxianzhuang Coal Mine in China, and the continuous monitoring system of gob temperature was independently developed to realize the real-time monitoring of gob temperature, achieving the purpose of accurate positioning of high temperature area in gob. The results show that the high temperature area of the gob of 85001 working face of Yangmeiwu Coal Mine was in the range of approximate circle centered on the point (36.6, 30), and the maximum temperature was 31.7 °C. The high temperature area of the gob of II830 working face in Zhuxianzhuang Coal Mine presented an approximate ellipse centered on (28.2, 25), and the long axis was parallel to the working face, and the maximum temperature was 43.9 °C. The research results are expected to provide reference for the early prediction of spontaneous combustion in gob. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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To mitigate coal spontaneous combustion in the fully mechanized caving face at the boundary of Jining No. 2 coal mine, the accurate prediction of the location and degree of coal spontaneous combustion was realized through theoretical analysis, experimental prediction, and field observations. The concentration changes of CO, C2H6, and C2H4 during coal oxidation and heating were analyzed. By combining a mathematical prediction model with CO generation rates for different temperature thresholds, the CO concentration in the return air corner was predicted to assess the coal spontaneous combustion degree in the goaf. Through the analysis of the coal spontaneous combustion oxygen concentration limit and three zones, the spontaneous combustion position in the goaf was obtained and verified by drilling. Moreover, based on the mine's existing glue injection system, we proposed a new system with long-distance and large-flow transportation, flowrate control, and precise slurry concentration control. The results showed that the remaining coal temperature in the goaf reached the critical temperature (60–80 C). The highest temperature point in the goaf was located 12 m behind support #10. The proposed glue injection system increased the efficiency of coal spontaneous combustion prevention and control. [ABSTRACT FROM AUTHOR]

The high temperature area of coal spontaneous combustion in coal mine goaf may cause methane/coal dust explosion. Therefore, it is necessary to carry out research on coal spontaneous combustion induced methane/coal dust explosion. The current research on the characteristics of methane/coal dust explosion based on the electric spark induced method cannot fully reflect the characteristics of methane/coal dust explosion induced by coal spontaneous combustion in the goaf. In order to solve this problem, the self-developed 40 L gas explosion equipment is used to study methane/coal dust explosion characteristics under the high temperature surface ignition of heat source. The results are showed as follows. ① The methane/coal dust explosion process obtained by the surface ignition method of the high-temperature heat source is consistent with that of methane/air explosion, which can be divided into 3 stages. ② The three explosion parameters of methane/coal dust (explosion pressure, pressure rise rate and explosion temperature) are consistent with the change law of methane concentration, that is, the parameters first increase with the increase of methane concentration, reach a peak and then decrease with the increase of methane concentration. When the methane concentration is less than the turning concentration, the three explosion parameters of methane/coal dust are greater than the corresponding explosion parameters of methane/air respectively. When the methane concentration is greater than the turning concentration, the three explosion parameters of methane/coal dust are less than the corresponding explosion parameters of methane/air respectively. Due to the addition of coal dust, the turning concentrations of the three explosion parameters of methane/air decrease from 11.5% to 9.5%, 10.5% and 9.5% respectively, and the peak values increase by 0.8%, 6.9% and 0.8% respectively, and decrease regularly. ③ Due to the different ignition methods, the explosion temperature change law is different. The explosion temperature rises again in the falling stage (stage III) after the methane/coal dust is detonated by the electric spark. The explosion temperature change law after detonation of methane/coal dust on the surface of high-temperature heat source remains the same as that before the addition of coal dust. ④ The coal dust ignition temperature prediction function is corrected, and the goodness of fit is improved by 20.05% after correction. Combined with the experimental data, the ignition temperature prediction function of coal dust in the ignition mode of the high temperature heat source surface is obtained.

The existing researches do not consider that coal of different particle sizes in the goaf is affected by the axial stress generated by the collapsed coal rock and the residual coal pillars, which will cause major changes in the coal permeability, fracture structure and other parameters, thereby affecting the temperature rise process of coal spontaneous combustion and oxidation. In order to study the temperature rise characteristics of spontaneous combustion and oxidation of coal with different particle sizes under the effect of thermal-stress coupling, the change law of the temperature rise rate, oxygen consumption rate and heat production rate of coal with different particle sizes is measured by using load-and-pressure coal spontaneous combustion characteristic parameter measuring device and a gas chromatograph. The experiment show the results as follows. ① The temperature rise rate of coal samples of different particle sizes under different uniaxial stresses has a consistent trend with the increase of temperature, and the overall trend is to increase first and then decrease. When the uniaxial stress is 2, 4, 6, 8 MPa, as the particle size of the coal sample increases, the maximum temperature rise rate first increases and then decreases. When the uniaxial stress is 10 MPa, the maximum temperature rise rate increases with the increase of particle size. ② The oxygen consumption rate of coal samples with different particle sizes increases rapidly and then increases slowly during the temperature rise process. The oxygen consumption rate of coal samples with different particle sizes generally tends to increase with the increase of uniaxial stress. ③ The overall heat production rate of coal samples with different particle sizes tends to remain stable first and then increase and then decrease during the temperature rise process. As the particle size of coal samples increases, the maximum heat production rate of coal samples under appropriate uniaxial stress is greater than that without uniaxial stress.

In order to reveal the effect of different inert gases in preventing coal spontaneous combustion and the law of flame retardation, the experiment of isothermal dynamic displacement of oxygen by inert gas in coal with different particle sizes is carried out, and the concentration of oxygen, displacement time, displacement volume, displacement rate and other parameters that characterize the displacement process of He, N2 and CO2 are analyzed. The experimental results are showed as follows.① The concentration change of oxygen displaced by inert gas can be divided into three stages. Firstly, the inert gas displaces the oxygen in the pipeline of the gas detector, and the volume fraction is about 21%. Secondly, the inert gas displaces free and partially adsorbed oxygen in the coal sample tank, and the oxygen concentration remains stable. Thirdly, the inert gas has completely replaced the free oxygen in the coal sample tank, and the oxygen concentration shows a negative exponential change. ② The time for different inert gases to displace oxygen in coal generally decreases as the particle size increases. The total time for CO2 to displace oxygen is the longest, followed by He, and N2 is the shortest. ③ For the same particle size, the amount of oxygen displacement shows an obvious inflection point. Before the inflection point, the amount of oxygen displacement basically increases linearly. After the inflection point, the amount of oxygen displacement increases slowly with time and finally remains stable. The accumulative amount of oxygen displacement under different inert gases decreases with the increase of particle size. The accumulative displacement of CO2 to oxygen is the largest, followed by He, and N2 is the smallest. ④ The oxygen displacement rate under the effects of different inert gases is characterized by first disorder and then stable decrease. Among them, the disorder stage of CO2 displacement is especially obvious. In the stable decrease stage of oxygen displacement rate, the rate of oxygen displacement basically decreases with the increase of particle size at the same time.

In order to investigate the evolution law of the functional groups of pre-oxidized coal samples, lignite from Liujia and Sitai, bituminous coal from Tongxin and anthracite from Baijigou were pre-oxidized at 50 ℃, 120 ℃ and 200 ℃ for 6 h. Fourier transform infrared spectrometer was used to test the infrared spectrum of both original and pre-oxidized coal samples. The evolution law of functional groups on the coal surface was obtained. the results showed that: pre-oxidation did not change the type of functional groups, which only changed the amounts of functional groups; The higher is the pre-oxidation temperature, the more functional groups of -OH were involved in the reaction. The absorbance of the -OH decreased 51.43% after the pre-oxidization at 200 ℃, which suggested that the pre-oxidation had more effects on the low metamorphic degree coal; as the pre-oxidation temperature increased, the functional groups of -CH2-, -CH3 and -C=O increased first, and then decreased. For coal samples pre-oxidized at 50 ℃, the amounts of -CH2-, -CH3 and -C=O increased after pre-oxidation; for coal samples pre-oxidized at 120 ℃ and 200 ℃, the amounts of -CH2-, -CH3 and -C=O decreased after pre-oxidation. When the pre-oxidized coal samples were re-oxidized, compared with the original coal samples, the coal samples pre-oxidized at 50 ℃ generated more gases of CO, CO2, C2H4 and C2H6 at a lower temperature, while the coal samples pre-oxidized at 120 ℃ and 200℃ generated less gases at ahigher temperature.

It is difficult to fully reflect the distribution of O2 concentration field of coal spontaneous combustion in goaf by using theoretical analysis and experimental research methods to study the impact of high ground temperature on coal spontaneous combustion in goaf. Fluent numerical simulation software is used to analyze the distribution law of O2 concentration field in the inlet air side, return air side and the middle section of the high ground temperature goaf. The results are listed as follows. ① When the temperature increases from 24.8 ℃ to 40 ℃ with the same ventilation volume, O2 flows into the whole goaf with the wind, and the O2 concentration decreases with the increase of goaf depth. When the air volume increases from 1 800 m3/min to 2 700 m3/min with the same temperature, the air leakage range in goaf increases significantly, the O2 concentration field in goaf changes obviously, and O2 almost fills the whole goaf. Moreover, the existence range of high concentration O2 increases, then the temperature of goaf increases due to heat accumulation, and the temperature of the residual coal inside goaf also continues to increase, the coal-oxygen reaction accelerates, and the possibility of spontaneous combustion of the residual coal increases. ② As the distance between goaf and the working face increases, the O2 concentration decreases. The O2 concentration on the inlet air side is greater than the O2 concentration on the return air side, indicating that the risk of coal spontaneous combustion on the inlet air side is greater than that on the return air side. ③ As the depth of goaf increases, the volume fraction of O2 on the inlet air side and the middle section of goaf continues to decrease, and the slope of the curve increases first and then decreases. The volume fraction of O2 on the return air side decreases with the increase of goaf depth. A large amount of high concentration O2 exists before 150 m of goaf, and the risks of coal spontaneous combustion in the inlet air side and the middle section of the whole goaf are greater than in the return air side. ④ When the temperature is 40 ℃ and the ventilation volume is 2 700 m3/min, the maximum width of the oxidation zone is 126 m. This maximum width is regarded as the maximum theoretical width of mining. Further calculation of the safe advancing speed can provide a theoretical basis for coal mining.