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The occurrence of surface strata movement in underground coal mining leads to the generation of numerous ground fissures, which not only damage the ecological environment but also disrupt building facilities, lead to airflow and easily trigger coal spontaneous combustion, induce geological disasters, posing a serious threat to people's lives, property, and mining production. Therefore, it is particularly important to quickly and accurately obtain the information of ground fissures and then study their distribution patterns and the law of spatial-temporal evolution. The traditional field investigation methods for identifying fissures have low efficiency. The rapid development of UAVs has brought an opportunity to address this issue. However, it also poses new questions, such as how to interpret numerous fissures and the distribution law of fissures with underground mining. Taking a mine in the Shenfu coalfield on the semi-desert aeolian sand surface as the research area, this paper studies the fissure recognition from UAV images by deep learning, fissure development law, as well as the mutual feed of surface condition corresponding to the under-ground mining progress. The results show that the DRs-UNet deep learning method can identify more than 85% of the fissures; however, due to the influence of seasonal vegetation changes and different fissure development stages, the continuity and integrity of fissure recognition methods need to be improved. Four fissure distribution patterns were found. In open-cut areas, arc-shaped fissures are frequently observed, displaying significant dimensions in terms of depth, length, and width. Within subsidence basins, central collapse areas exhibit fissures that form perpendicular to the direction of the working face. Along roadways, parallel or oblique fissures tend to develop at specific angles. In regions characterized by weak roof strata and depressed basins, abnormal reverse-"C"-shaped fissures emerge along the mining direction. The research results comprehensively demonstrate the process of automatically identifying ground fissures from UAV images as well as the spatial distribution patterns of fissures, which can provide technical support for the prediction of ground fissures, monitoring of geological hazards in mining areas, control of land environmental damage, and land ecological restoration. In the future, it is suggested that this method be applied to different mining areas and geotechnical contexts to enhance its applicability and effectiveness. [ABSTRACT FROM AUTHOR]

To improve the accuracy of early warning on coal spontaneous combustion (CSC), this paper, on the basis of the principle of preferential selection of index gases in CSC process, carries out fitting analysis of the variation curve of index gas data with coal temperature by combining logistic fitting model, then establishes a CSC graded warning system based on positive pressure beam tube monitoring, and determines CO, O2, φ(CO)/φ(O2), C2H4, C2H6, φ(C2H4)/φ(C2H6) as the index gases for predicting and forecasting CSC, and accurately divides the CSC process into seven levels of early warning: safe, gray, blue, yellow, orange, red, and black. Applying the CSC positive pressure beam tube monitoring system to Dongtan coal mine and analyzing the error by manual sampling and sampling by positive pressure beam tube system, we find that the error is less than 0.1%. Monitoring of several working faces, we get that the CO and CH4 concentrations of 14,320 working face are higher than the normal level at the beginning of mining, and the 100 × CO/ΔO2 value is higher than the gray warning threshold of 0.1, and the warning level is gray warning. After taking timely preventive measures against coal oxidation and warming, the CO and CH4 concentrations return to the normal level and the warning level drops to the safe level. This paper improves the monitoring, identifying and early warning capabilities of underground CSC in its early stage. [ABSTRACT FROM AUTHOR]

This paper aims to study the law of pressure behavior and the characteristics of mutual influence in the process of steeply inclined coal seam mining. Based on the geological and engineering conditions of the B8 coal seam in Nanshan coal mine, this paper explores the law of mine pressure behavior in the process of steeply inclined coal seam mining by means of theoretical analysis and FLAC3D numerical simulation. Based on this, this paper also examines the influence of the interaction range between coal seams, the reasonable setting size of the section coal pillar, and the mining distance of the working face on the return air roadway. The results suggest as follows: (1) With an increase in the coal seam dip angle, the difference in the abutment pressure plastic zone between upper and lower coal pillars increases, and when mining in steeply inclined coal seams, the stress concentration in the lower and upper part of the working face deviates to the roof and floor respectively, which is obviously different from that of gently inclined coal seams. (2) The vertical stress above the section coal pillar changes in three stages with an increase in the width of the coal pillar, and the width of the coal pillar in the second stage can be taken as the reasonable size of the width of the coal pillar. The numerical simulation results are consistent with the theoretical calculation results, which indicate the high reliability of this method in determining the reasonable coal pillar size. (3) With an increase in the mining distance in steeply inclined coal seams, the maximum pressure around the working face and above the return air roadway has gone through three stages. When the distance between the working face and the adjacent return air roadway is close, the pressure above the return air roadway increases sharply, and disturbance is stronger. [ABSTRACT FROM AUTHOR]

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

Understanding the molecular structure characteristics of coal at the molecular level is of great significance to realize the rational utilization and efficient conversion of coal. This paper gives insights into the acquisition of characterization parameters of coal molecular microstructure by testing and analyzing the long flame coal from Qinggangping (QGP) Coal Mine through proximate analysis, ultimate analysis, vitrinite reflectance determination, fourier transform infrared Spectroscopy test (FTIR), X-ray photoelectron epectroscopy test (XPS), carbon nuclear magnetic resonance (13C-NMR) and X-ray diffraction (XRD). The results show that benzene rings in the QGP coal are mainly connected in a disubstituted way, accounting for 36.48%. Oxygen atoms mainly exist in the oxygen-containing functional groups such as the ether C–O, C=O and –COO. Aliphatic hydrocarbons in the aliphatic group are mainly of symmetrical -CHx stretching vibration. Hydroxyl groups are mainly composed of OH–OH and OH–O hydrogen bonds, accounting for 29.21% and 21.53%, respectively. Nitrogen atoms exist in the form of C4H5N. The coal molecular is mainly of aromatic carbon structure, where the ratio of bridge aromatic carbon to peripheral carbon is 0.198. There are benzene, naphthalene and anthracene in the coal molecular structure, and the former two chemicals play a dominating role. According to the analysis results, the molecular formula of the QGP coal is finally determined as C205H181O29N3S. On this basis, the two-dimensional and three-dimensional macromolecular models are constructed with the assistance of simulation software. In addition, the 13C-NMR spectra and densities of the constructed molecular models are calculated, which verifies the rationality of the models. The macromolecular structure model of bituminous coal constructed in this study provides a theoretical model basis for the optimal surfactant. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper summarizes the results of determination of the washability characteristics of anthracite coal from Vrska Cuka coal mine, Serbia. The effect of different coal size fractions has been studied through washability studies. In this study, float-sink experiments were carried out with the anthracite coal samples on (−19 + 9.5) mm, (−9.5 + 4.75) mm, (−4.75 + 2.36) mm, and (−2.36 + 0.6) mm size fractions. Two washability parameters, Index of Washability (IW) and Near Gravity Material Index (NGMI), were calculated and the results were compared. The IW and NGMI values indicated that the washability of different size fractions of anthracite coal was easy to relatively difficult to wash. The obtained values of IW showed that the order of coal washing ability by size fractions was as follows: (−9.5 + 4.75) mm, (−4.75 + 2.36) mm, (−2.36 + 0.6) mm, and (−19 + 9.5) mm. The NGMI values decreased with increasing specific gravity and decreasing particle size fractions. The minimum values of NGMI were achieved at density of 1650 kg/m3 and these values were 0.1322, 0.0695, 0.0677, and 0.0240, respectively. The results presented in this study indicate that washability of the anthracite coal is relatively easy and should be washed at a specific density of 1650 kg/m3. [ABSTRACT FROM AUTHOR]

Coal is the main energy source in China, and spontaneous combustion of coal is one of the main disasters in coal mines. Fully mechanized caving top coal mining technology is widely used in coal mines. Under the comprehensive action of multiple factors, gas generated by coal oxidation and low oxygen gas in goaf is easy to rush to working face, resulting in lower oxygen concentration in upper corner and exceeding harmful gas concentration. It seriously threatens the health of underground workers and the normal operation of production. If the oxygen concentration in the upper corner is changed, it is bound to cause the change of the oxygen concentration in the goaf and aggravate the threat of spontaneous combustion of coal in the goaf. In order to solve the double threat of low oxygen in upper corner and coal spontaneous combustion in goaf, based on Coulomb model, this paper uses command flow to conduct numerical simulation tests on the failure law of overlying strata, and obtains the influence of mining of the lower 1 coal seam and the lower 5 coal seam on the overlying strata subsidence and surface penetration. Based on the comprehensive consideration of atmospheric pressure, ore pressure activity, external air leakage and other factors, the mixed model of the source and emission of low oxygen gas in goaf was established, and the formation mechanism of low oxygen problem in the corner of return air of working face was defined. The use of pressure air belt to deal with low oxygen in return air corner is proposed creatively. The comprehensive fire prevention measures such as corner plugging, nitrogen injection and grouting are used to inhibit the oxidation of the left coal and the influx of low oxygen gas to the corner in the goaf, so as to achieve the goal of collaborative prevention and control of low oxygen in the corner of return air and coal spontaneous combustion. The research results have important reference significance for the mine with the risk of spontaneous combustion or the problem of low oxygen in the return air corner. [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.)

High-temperature coal oxidation generates a substantial amount of CO and CO2, especially CO, rapidly, which is a primary factor leading to casualties. The oxygen concentration is the predominant factor affecting the high-temperature oxidation of coal, particularly in the generation of CO and CO2. Understanding the generation patterns and relationship characteristics of CO and CO2 under various oxygen concentrations is important for predicting high-temperature coal oxidation and ensuring personnel safety. The paper used TG–MS and FTIR to study the formation characteristics of isothermal oxidation of CO and CO2 in long-flame coal under different oxygen concentrations. The results indicate that there exists an optimal threshold for CO production when the oxygen concentration is about 9% during the isothermal temperature oxidation process at 200.00–350.00 °C. When the oxygen concentration is less than 13%, the influence of oxygen on CO2 production is weakened. As the temperature increases, the pattern of CO + CO2 production and CO/CO2 is reversed, with CO + CO2 increasing and CO/CO2 decreasing. The relationship between the total production of CO and CO2 and the loss of coal mass follows the function y = a + bx at the isothermal temperatures of 300.00 °C and 350.00 °C. An increase in oxygen concentration does not alter the linear relationship. In the isothermal oxidation process of coal, carbonyl and carboxyl groups are the key groups for CO and CO2 production. At 200.00 °C and 250.00 °C, carbonyl and carboxyl groups increase, and other groups are being converted to carbonyl and carboxyl groups while decomposing into CO and CO2. At 300.00 °C and 350.00 °C, the relative content of carboxyl groups decreases. The research findings play a fundamental role in coal mine disaster prevention and control. [ABSTRACT FROM AUTHOR]

Long-term accumulation of coal gangue hill has a high risk of spontaneous combustion, and the toxic and harmful gases emitted by spontaneous combustion seriously pollute the atmosphere. The key to managing the spontaneous combustion fire of coal gangue hill lies in the accurate measurement of fire source location. However, measuring the fire source location of surface coal gangue hill lacks experimental and empirical research. In this paper, an oxidation warming experiment was conducted on the coal gangue samples, and the law of radon gas exhalation from coal gangue under different temperatures was analyzed. At the same time, surface thermometry and isotope radon measurement were applied to measure the high-temperature areas inside the gangue hill, and the measurement results were compared. The experimental results show that as the temperature of gangue increases, the amount of radon gas exhalation in gangue shows a changing trend of rising first and then decreasing. The radon exhalation from coal gangue can be divided into three stages. In the I stage (30 ~ 100°C), the evaporation of pore water in coal gangue leads to the exhalation of radon in water, causing the increase of radon concentration; in the II stage (100 ~ 350°C), the coal gangue is pyrolyzed at high temperature, and a large amount of radon is exhalated from the closed pores; in the III stage (350 ~ 450°C), after the first two stages of radon release, the number of radon atoms in this stage decreases, leading to a rapid decrease of radon concentration. The field measurement results show that compared with the surface thermometry method, the isotope radon measurement method is less disturbed by external conditions, and the circled fire area is more accurate, which has essential theoretical significance and practical application value for the accurate measurement of fire source location in coal gangue hill. [ABSTRACT FROM AUTHOR]

As coal mining continues to progress to deeper levels, the temperature of the coal and rock continues to rise, causing coal spontaneous combustion disasters to become increasingly prominent. This paper studies the spontaneous combustion characteristics of coal in a high temperature environment before and after coal seam mining. The results were as follows: 1) Before mining, under the action of a constant ground temperature, the deep coal seam continuously and slowly released heat, and the higher the ground temperature was, the more heat was released. 2) During mining, after air entered, the coal samples initially maintained the continuous slow heat release. With the continuous entry of air, the coal samples were in an endothermic state. Higher ground temperature provides favorable conditions for coal sample heat absorption and coal spontaneous combustion. 3) When the local temperature rises, the associated hydroxyl groups in the coal sample are gradually activated and become free hydroxyl groups that are more prone to chemical reactions; the methyl groups are destroyed to generate more methylene groups; the aromatic hydrocarbons change significantly after oxygen supply. The long-term high ground temperature environment could lead to an increase in the chemical activity of coal. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion is a common problem faced by many coal mines. Spontaneous combustion in goaf releases a large amount of harmful gases, polluting the environment while causing a large amount of wasted resources, and even endangering the lives of workers. Due to the collapse of the interior of the mining area, it is impossible to measure the internal gas composition directly. In order to more accurately predict the spontaneous combustion state inside the mining airspace, this paper obtains the CO generation law and the main source of the working face through the combination of laboratory experiments and on-site monitoring. The CO concentration prediction model of the return corner is established with CO as the index gas. Finally, the safe concentration and warning concentration of the working face are calculated according to the example, which provides theoretical basis for the prediction of spontaneous combustion of coal. [ABSTRACT FROM AUTHOR]

Kilometer-deep mines have become the new norm in coal mining. To study the influence of high stress-high ground temperature coupling conditions in deep mines on the oxidative exothermic characteristics of coal, this paper pre-treats coal samples under different stress and different temperature coupling conditions, and then conducts oxidation temperature tests on coal samples. By analyzing the parameters of initial exothermic temperature, exothermic heat and apparent activation energy of coal, the influence law of stress-temperature coupling on the oxidative exothermic properties of coal was obtained. The results show that when the initial temperature is 313 K, the initial exothermic temperature of coal decreases first and then increases with increasing initial stress. The exothermic heat and activation energy change trends in the initial exothermic stage are the same, both show atrend of first decreasing and then increasing, and both reach their minimum values at 10 MPa. When the initial stress is 5 MPa, the initial exothermic temperature of coal first increases and then decreases with increasing initial temperature. Both the exothermic and apparent activation energy of coal in the initial exothermic stage showed atrend of increasing and then decreasing, and reached the inflection point at the initial temperature of 323 K. The research results provide theoretical support for the prevention and control of spontaneous combustion in deep mines. [ABSTRACT FROM AUTHOR]

Residual coal in mine goafs will be oxidized in the presence of air leakage, which can be well tracked through the radical reaction. This study aimed to explore the changes in radical parameters and the reactivity and persistence of newly produced radicals of coal at different temperature stages. To this end, an in situ electron spin resonance (ESR) spectrometer was adopted to measure changes in radical parameters at the heating, maintaining and cooling stages in real time. The following conclusions were drawn. At the heating stage, the radical concentration first rises slowly and then surges; the g factor remains small initially and increases rapidly later; the linewidth falls continuously. At the maintaining stage (230 °C), the radical concentration keeps increasing, while the g factor and the linewidth remain stable. At the cooling stage, the radical concentration first decreases and then stabilizes at a relatively high level, and both the g factor and the linewidth nearly return to the initial values. Based on the changes in radical parameters at different oxidation stages, the radicals in coal are divided into transient radicals and persistent radicals according to their survival times. Transient radicals, which are strongly reactive, are quickly consumed, while persistent radicals, which is of weak reactivity, can exist in the system for a long time. That is, the active radicals in coal are transient, while the stable ones are persistent. In addition, this paper gives insight into the changes in contents of active radicals and stable radicals at these stages. Finally, the changes in indicator gas and oxygen concentrations at these stages were analyzed. The research finding further explains the mechanism of radical reactions during coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

Spontaneous coal combustion is a serious hazard that affects mining safety. Since the coal seams are thin and their resistivity dramatically changes during spontaneous combustion, locating the burned cavities or caving zones using electromagnetic (EM) methods is challenging. The conventional transient electromagnetic (TEM) method with a loop transmitter is ineffective, as the main targets are mostly horizontal and resistive. We propose in this paper to apply TEM with an electrical source to detect the resistive targets of spontaneous coal combustion. Considering that its areas generally have very complex geometry, we adopt the unstructured finite-element method for accurate EM forward modeling. For the time discretization, we choose the unconditionally stable backward Euler scheme. Numerical experiments for typical spontaneous combustion models show the high sensitivity of TEM for an electrical source to the burned cavities, and based on this we further use the limited-memory BFGS method to do 3D inversions. To obtain high-resolution imaging results, we bound the resistivity based on the measurements to the coal mine. The inversion results show that the 3D TEM inversions can effectively recover the locations and resistivities of the burned cavities, implying TEM is a valid tool for detecting spontaneous coal combustion. [ABSTRACT FROM AUTHOR]

For further understanding the coal spontaneous combustion in goaf, the dynamic evolution of the oxygen concentration field influenced by the condition of negative pressure of cross-cut were analyzed. Based on the on-site testing results, the range of the oxidation zone on the headentry and tailentry side is determined as 30 ~ 75 m and 15 ~ 65 m respectively. This paper adopts a new method called "fixed grid, dynamic attribute" to dynamically describe the spatial change of goaf caused by working face advancing. The validated model which developed by field measured data is used to study the dynamic evolution of negative pressure impact of cross-cut on oxygen concentration field in goaf. The results demonstrate that when the cross-cut is located at different positions of three zones of coal spontaneous combustion, the negative pressure of the cross-cut has different impact rules on the distribution of oxygen concentration field. The results are hopeful for providing effective guidance for coal mine fire prevention in goaf. [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.)

The methane contained in a coal seam is closely related to the oxidative properties of the coal and serves as an important basis for accurately evaluating the coal spontaneous combustion (CSC) behavior. In this paper, programmed temperature rise experiments were conducted on three coal samples with different methane contents. The sensitivity of oxidation products, olefin products, and their production rates to methane content were investigated. Also, the contribution made by methane content to the characteristic temperature point and CSC limit parameters were qualitatively assessed. When the methane content is 2.7 cm3/g, 4.5 cm3/g, and 6.8 cm3/g, the critical temperatures (CT) are 70°C, 80°C, and 100°C, respectively, and the dry cracking temperatures (DCT) are 100°C, 110°C, and 130°C, respectively. The higher the methane content, the greater the CT and DCT points during coal oxidation, which is because high concentration of methane will inhibit coal oxygen chemical reaction. The methane content is positively correlated with the minimum floating coal thickness (hmin) and the lower limit oxygen concentration (Cmin), while the upper limit air leakage intensity (Qmax) decreases with the increasing methane content. Coal samples with high methane content can withstand higher safe float thicknesses and oxygen concentrations and require less air leakage to carry away the heat accumulated by the residual coal in the mining area, making the CSC risk lower. [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]

The productivity of coal mines is seriously threatened by the combined disasters of gas and coal spontaneous combustion, which have become a common disaster mode. It is unclear how the gas and coal spontaneously combusted in the roof cutting along gob working face. The goal of this study is to identify the distinctive features of combined disasters in gob from two different types of roof cutting along working faces. In these two different types of roof cutting along gob working faces, the paper constructs the permeability model of the gob. The findings demonstrate that the data from the field experiment and the simulation results agree, which validates the simulation's reliability. In contrast to single sided roof cutting along gob working faces, double sided roof cutting along gob working faces clearly has a thinner oxidation zone. Moreover, the oxidation zone of the double side roof cutting along gob working faces is closer to the working face, which is located in the shallow area of the gob 50 m behind the working face. The gas explosion area and the coal spontaneous combustion area are divided by the double side roof cutting along gob working face, which reduces the risk of compound disasters. Important theoretical direction for the prevention and control of gob disasters in the roof cutting along gob working face is provided by the simulation results. [ABSTRACT FROM AUTHOR]

To accomplish various and efficient inhibitions of coal spontaneous combustion (CSC) and solve the safety hazards of CSC encountered in the production and operation of coal mining enterprises, inhibitors play an important role in the prevention and management of CSC. Herein, we report quercetin, which is selection as an antioxidant to prepare a composite solid lipid inhibitor. The concentration of the composite solid lipid inhibitor with the best inhibition effect on the active groups is selected by Fourier pressure infrared experiments, the change pattern of gas content and characteristic temperature released from coal samples during an oxidation process warming process was tested by using a programmed warming test system and simultaneous thermal analysis experiments, and finally, the inhibitory rate and combustion characteristic index were calculated. The results of the research showed that 10 mass% of quercetin had the most impact on the various groups, the highest inhibitor rate of the composite solid lipid inhibitor is 80.67% in the coal low-temperature oxidation process, compared to the raw coal, the heat release of coal treated with the composite solid lipid inhibitor was decreased by 507.65 J g−1, the maximum amount of heat emitted was lowered by 60%, and the flammability index was reduced by 56.4. A composite solid lipid inhibitor containing quercetin developed in this paper indicated high effectiveness in inhibiting CSC, which is vital for coping with the safety management of coal mine production. [ABSTRACT FROM AUTHOR]

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

In coal mining operations, coalbed methane is one of the potential hazards that must be extracted to prevent an explosion of the accumulated gas and environmental pollution. One of the mechanisms is using microwave irradiation so that the thermal stress caused by microwave heating generates fractures. In this research, we investigated the most important parameters affecting the electric and thermal fields' distribution in coal in order to identify the effective parameters that achieve the highest temperature increase rate and to reach the highest impact and efficiency of the system with the least amount of consumed energy. In this paper, using Maxwell equations, heat transfer, mass transfer and coupling them by COMSOL, we have simulated the radiation of electromagnetic field and heat in the cavity and coal, and we have also shown the temperature dispersion inside the coal. The parameters studied included the amount of coal moisture (type of coal), operating frequency, input power and heating time, location of the waveguide, the size of the waveguide and the location of the coal, and finally the parameters were re-examined in a secondary standard cavity to separate the parameters related to the size of the environment and the cavity from the independent parameters. The results of this study show that the most effective parameter on the electric and thermal fields' distribution within coal is the size of the resonance chamber. Additionally, the results show that the moisture of 5%, the highest input power and cutoff frequency close to the operating frequency cause the highest average temperature inside the coal, but many parameters such as operating frequency, waveguide location and coal location should be selected depending on the chamber size. [ABSTRACT FROM AUTHOR]

Conventional longwall layout (CLL) for mining coal, trona, etc. is still fraught with problems including low resource recovery, wavy ground surface subsidence, bumps or rockbursts, gateroad support and maintenance, poisonous air hazard, spontaneous combustion in coal mines, instability of equipment at inclined, or steeply inclined working face, etc. In order to improve longwall mining, a novel alternate longwall panel layout that has been employed for over 20 years in China, Australia, and Russia, etc. is proposed termed "split-level longwall layout" (SLL). Gateroads on either end of the same SLL panel are split level, i.e., placed in different levels. This paper provides a review of existing research literature and insights on the problems encountered in CLL and the improvement of the new approach. Theoretical, numerical analysis, and field observation results of the new strategy demonstrate that the problems mentioned above in CLL are mitigated, and the development entries using the improved longwall system have a better stress environment with associated reduction in large roadway convergence, coal bumps or outbursts, and many other issues on ground control. Based on the current development of SLL and the future requirement of mining industry, the prospects as well as its applications, limitations, and concerns for SLL are presented. [ABSTRACT FROM AUTHOR]

In view of the complexity and concealment of goafs, numerical simulations have become an important means for studying the coupling disasters of spontaneous coal combustion and gas. Porosity is an important parameter in the numerical simulation, but this is difficult to detect directly on site, as the current porosity model does not fully reflect the characteristics of "three horizontal areas" and "three vertical zones" in the goaf. To establish a more accurate porosity model which is based on a theory of overlying strata movement, the Sigmoid function was introduced to reflect the distribution characteristics of the "three horizontal areas" in the goaf, and subsidence models of the main roof and overlying strata were established. A model that measures the porosity of the goaf was formulated, which reflects its O-shaped circle characteristics. The accuracy of the theoretical model was verified by obtaining experimental data. The results showed that the main roof subsidence in the natural accumulation area was approximately zero, there was an exponential decrease in the load-affected area, and the maximum subsidence appeared in the compacted area. The descending displacement was very small around the impacted area along the roadway wall. The movement of overlying strata in the fractured zone was controlled by the main roof, and the subsidence of the strata near the roadway wall and the working face was very small. In the vertical direction, the subsidence of the overlying strata decreased as the distance from the mining coal seam increased. The distribution of porosity in the goaf was shaped like a dustpan. In the horizontal direction, the porosity of the natural accumulation area and the impacted area of the roadway wall was the largest. Deep within the goaf, the porosity gradually decreased. The porosity in the fractured zone decreased in the vertical direction in a logarithmic manner. The porosity model proposed in this paper fully reflects the characteristics of the goaf, and provides a more accurate porosity model for the numerical simulation of spontaneous coal combustion and gas coupling disasters in the goaf. [ABSTRACT FROM AUTHOR]

During the mining of coal seam groups, the physical and chemical properties of the residual coal in goaf will be changed after undergoing water leaching and air-drying, affecting the oxidation characteristics of the coal. To examine the effect of the water immersion and air-drying times on the oxidative combustion characteristics of long-flame coal, this paper uses thermal gravimetric (TG) analysis and infrared spectral analysis to analyze coal samples with different immersion and air-drying times. The change in activation energy (AE), which is associated with the change in the functional groups, was analyzed for the coal-oxygen chain reaction process under coal immersion and air-drying conditions. The results show that coal samples soaked in air-dried for 10 days after water for 20 days have a lower AE (39.14 kJ/mol) than coal samples that underwent other treatment times and have a higher oxygen absorption rate and a higher tendency to undergo spontaneous combustion. According to the TG-DSC test, a range of weight loss and exothermic strengths are observed during the longest immersion and air-drying times. Additionally, during the longest immersion and air-drying times, the variations in the different functional groups are more obvious, the aliphatic hydrocarbon chain breaks and the coal rank is lower. The period of immersion and air-drying can change the spontaneous combustion oxidation characteristics of coal. After being soaked in water for 20 days and air-dried for 10 days, the coal sample was looser and the chain reaction process was accelerated, which promoted the oxidation and spontaneous combustion of coal. [ABSTRACT FROM AUTHOR]

Large amounts of fine coal are produced during coal mining as a result of the extensive deployment of the mechanized mining technology and should be cleaned with the consideration of energy source conversation and environment protection, Urgent need for fine coal (especially high sulfur content fine coal) sorting desulfurization technology. On the basis of an analysis of raw coal, the use of a compound dry separator is proposed in this paper to separate high-sulfur coal across the full-size range of 6–0 mm. The relationship between the change of bed structure and the distribution of bed sulfur content and the force law of the particles is analyzed emphatically. The effect of the change of the backboard angle and the change of the clapboard length and height on the migration trajectories and vibration energy distribution of the material during the sorting process was studied systematically. The results showed that when the backboard angle was 45°, the clapboard length and height were 250 mm and 55–60 mm, respectively. The materials are sufficiently stratified, the sulfur content distribution regularity significantly. The law of vibration energy distribution is significant, and the maximum values of the particles force in the clean coal and gangue are 12.3 mN and 14.1 mN, the vibration acceleration of the clean section and the gangue section are 33.5m/s2, 20.6m/s2, the high sulfur content materials are mainly concentrated in the gangue section. The yields of the clean coal and gangue were 71.45% and 28.55%, respectively, with corresponding sulfur contents of 0.93% and 25.24%. The probable error (E) was 0.14g/cm3. [ABSTRACT FROM AUTHOR]

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Accurately determining the risk level of coal spontaneous combustion (CSC) in goaf is very important for coal mine safety production. In this paper, bituminous coal in Shanjiaoshu Coal Mine (SJS) was used as the research object to conduct a simulated spontaneous combustion experiment of coal with programmed heating. The results show that according to the characteristic temperature of CSC combined with the Graham R2 coefficient and the degree of spontaneous combustion and oxidation, the risk level of CSC in SJS Coal Mine is classified into four risk levels: low risk, general risk, greater risk, and major risk. Based on the grey target theory and grey entropy correlation analysis method, the equilibrium function is introduced to determine the variable weight of evaluation indexes and the risk grade judgment method of CSC in goaf. Based on the variable weight grey target model is established. The bull's-eye distance corresponding to each risk level were 0 ~ 0.0052, 0.0052 ~ 0.1455, 0.1455 ~ 0.9554, and >0.9554, respectively. The verification results of the model based on the data of 6 groups of 12 measuring points of the beam tube monitoring system in SJS are consistent with the actual risk level. [ABSTRACT FROM AUTHOR]

Coal is a principal source of energy and the combustion of coal supplies around one-third of the global electricity generation. Coal mines are also an important source of CH4 emissions, the second most important greenhouse gas. Monitoring CH4 emissions caused by coal mining using earth observation will require the exact location of coal mines. This paper aims to determine surface coal mines from satellite images through deep learning techniques by treating them as a land use/land cover classification task. This is achieved using Convolutional Neural Networks (CNN) that has proven to be capable of complex land use/land cover classification tasks. With a list of known coal mine locations from various countries, a training dataset of "Coal Mine" and "No Coal Mine" image patches is prepared using Sentinel-2 satellite images with 13 spectral bands. Various pre-trained CNN network architectures (VGG, ResNet, DenseNet) are trained and validated with our prepared coal mine dataset of 3500 "Coal Mine" and 3000 "No Coal Mine" image patches. After several experiments with the VGG network combined with transfer learning is found to be an optimal model for this task. Classification accuracy of 98% has been achieved for the validation dataset of the pre-trained VGG architecture. The model produces more than 95% overall accuracy when tested on unseen satellite images from different countries outside the training dataset and evaluated against visual classification. [ABSTRACT FROM AUTHOR]

Spontaneous combustion of oxidized coal was one of the serious hazards during coal mining and utilization. However, spontaneous combustibility of oxidized coal affected by the first oxidation of coal was still unclear. In this paper, the influence of pre-heating with different oxygen concentrations on coal secondary spontaneous combustion behaviors was studied. Temperature-programmed heating experiments were carried out to prepare pre-heated coal samples by heating at the preset temperature of 80 °C in mixture atmosphere of N2 and O2 with different oxygen proportions of 0%, 5%, 10%, 15%, 20%. Pre-heated and raw coals were heated programmatically in an air atmosphere of 120 mL min−1 with a heating rate of 0.33 °C min−1. The gaseous compounds of O2, CO and CO2 were analyzed to identify spontaneous combustion behaviors of pre-heated and raw coals. The results showed that pre-heating at 80 °C promoted oxygen physisorption at low temperatures and lowered oxidability at high temperatures in the coal secondary oxidation process. Pre-heating at 80 °C with higher oxygen content reduced oxidability and exothermicity of coal secondary spontaneous combustion, but had no obvious effect on oxygen physisorption of coal low-temperature oxidation. [ABSTRACT FROM AUTHOR]

The frequency conversion ventilation has achieved good results in the practical application of preventing the gas concentration of the coal mining face exceeding the limit. However, its impact on the spontaneous combustion of coal in the goaf is uncertain. Therefore, this paper studies the spontaneous combustion of three types of coal samples at different ventilation rates under frequency conversion ventilation. The results show that frequency conversion ventilation can reduce the average CO concentration compared with constant ventilation, and the inhibiting effect will weaken with the average ventilation rate increased. In three variable frequency ventilation rates, the rate of 10-30-50cm3/min has the best inhibiting effect. At this condition, the inhibiting effect is related to the type of coal, the inhibition rate on anthracite and lignite is proportional to the temperature, while the inhibition rate on bituminous coal is inversely proportional to the temperature. During one cycle around 120°C, the heat released by the oxidation reaction of bituminous coal, lignite, and anthracite decreased by 0.030 J/g, 0.144 J/g, and 0.034 J/g, respectively. Thus, the frequency conversion ventilation can affect the elementary reaction of coal, resulting in a reduction in the heat release from the coal oxidation reaction. [ABSTRACT FROM AUTHOR]

Copyright of Scientific Bulletin of National Mining University is the property of National Mining University, State Higher Educational Institution 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.)

Summary: To reduce the pressure on underlying coal seam and maximize the mining efficiency of coal resource, narrow coal pillar mining technology is often used. However, for coal mines with high gas and spontaneous combustion, this technology can cause gas and coal spontaneous combustion composite disaster easily. In this paper, we adopted a new type of inorganic fire‐extinguishing material (IFEM) to prevent and control gas and coal spontaneous combustion composite disaster. The result shows that the destruction of narrow pillar caused by stress extrusion and mining disturbance is the internal cause of gas and coal spontaneous combustion composite disaster. IFEM can go deep into the cracks of coal mass to seal up the cracks and reduce gas exchange between roadway and adjacent goaf. Meanwhile, it is full of moisture in the interior, which can reduce the temperature of coal mass through evaporation and heat absorption. The IFEM has the characteristics of high water retention, strong fluidity, and strong flame retardant, which can inhibit the generation of free radicals in coal mass at both physical and chemical levels, prevent the spontaneous combustion of coal mass, and reduce the occurrence of composite disasters of gas and coal spontaneous combustion. Highlights: The crack inside the narrow coal pillar develops, and the gas permeability is good.The combined disaster in the narrow coal pillar working face is serious.IFEM can seal cracks and increase the strength of narrow coal pillars.IFEM can inhibit the generation of free radicals in coal and prevent coal from contact with oxygen. [ABSTRACT FROM AUTHOR]

The spontaneous combustion of residual coal in coal mine gob has long been a problem and poses a threat to the safe production of coal. Therefore, it is of great significance to conduct an in-depth study of the oxidation and self-heating progress of residual coal in the gob. Considering that the geometric dimensions and physical characteristics of the gob will change during the advance of the working face, the purpose of the present paper is to determine how the coal self-heating develops during and after coal mining. A fully coupled transient model including gas flow, gas species transport, and heat transfer in the gob and the butt entries, as well as heat transfer in the surrounding strata, is developed to quantify the evolution of coal self-heating in gob during and after mining. The model was solved by COMSOL Multiphysics package and then verified by comparing the field data with the simulated data. On this basis, parametric studies including the influences of the surrounding strata temperature, airflow temperature, coal-rock particle size, and advance rate of the working face on coal oxidation and self-heating in the gob were conducted. The results show that a tailing phenomenon of the high-temperature area is formed on the air inlet side of the gob during mining, and the temperature in the high-temperature zone decreases gradually due to the accumulation and compaction of the gob and heat dissipation to the surrounding strata. Also, although the temperature in gob increases gradually after the stopping of mining, the high-temperature area migrates towards the working face. Moreover, when the temperature of the surrounding strata is consistent, different ventilation temperatures have no obvious effect on the maximum temperature of the gob at the initial mining stage, whereas the higher ventilation temperature results in the higher self-heating temperature after several days of mining. Finally, the smaller average particle size or faster advance rate results in a lower maximum temperature of gob. [ABSTRACT FROM AUTHOR]

Unusual methane emission and spontaneous combustion of coal induced by the air leakage are both hazards during mining. The most common practice has been to improve mine safety is sealing the mining fractures. In this paper, the methane and geology, coal spontaneous combustion characteristics and the coexistence of methane emission and spontaneous combustion of coal were analyzed. The preparation system of inorganic solidified foam (ISF) in field applications is studied and the working principle of generating device consists of foam generator and mixer was expounded. The technical plan of site construction is that the foam fluid was injected to respectively seal the mining fractures behind hydraulic supports, the cavities of air return corner, and the fractures nearby the coal pillar. After the foam fluid injection, the two stress values in the coal pillar eventually maintained above 15.5 Mpa and 13 Mpa, respectively. It indicated that the ISF can enhance the bearing stress ability of the coal pillar by transforming the stress state from two dimensional to three dimensional. The methane concentration in the air return corner and air return roadway declined significantly to 0.63% and 0.25%. The differential pressure inside and outside of the 4301(1) goaf fluctuated between −100 pa and 150 pa and the concentration of CO and O2 declined to 9 ppm and 6%. The CO concentration in the air return corner finally reached a stable level of 6 ppm. What that all means, the foam fluids can seal the air leakage and inhibit spontaneous combustion of coal effectively. [ABSTRACT FROM AUTHOR]

Coal and gas outbursts have occurred in the Zhaozhuang coal mine (a high gas coal mine) since its construction, and these outbursts pose a great threat to lives and property. Therefore, the combination of methane desorption experiments and molecular simulations was adopted to investigate the effects of moisture on the methane desorption characteristics of the Zhaozhuang coal, and the microscopic mechanism was analyzed in this paper. The aim of this work is to provide a method for predicting the effect of moisture on coal seam methane desorption, and quantitatively evaluating the control effect of hydraulic measures on coal and gas outbursts from a molecular perspective. The experimental data (methane desorption amount) were measured under various adsorption equilibrium pressures (0.3 MPa, 0.4 MPa, and 0.5 MPa) and moisture contents (0%, 5%, and 9.8%). Based on the Zhaozhuang coal molecular model, the molecular simulation process was conducted using Materials studio software, which can better match the experimental conditions by setting various pressure parameters (0.3 MPa, 0.4 MPa, and 0.5 MPa) and calculating various numbers of H2O molecules (0, 8, and 16) on the coal molecule. The results show that methane desorption decreases with the increasing moisture content in the experiment. The number of CH4 molecules adsorbed on the coal molecule decreases with the increasing number of H2O molecules in the simulation. This phenomenon can be explained by the competitive adsorption between CH4 and H2O molecule: the interaction between coal molecule and H2O molecules is stronger. The affinity between CH4 molecules and the coal molecule is reduced, and CH4 molecules are less aggregated around the coal molecule because of the presence of H2O molecules. [ABSTRACT FROM AUTHOR]

• Frequent occurrence of composite disasters of gas and coal spontaneous combustion in deep mining. • Inner fracture development of narrow coal pillars under the stress. • Composite disasters caused by gas exchange between two sides of narrow coal pillars. • Dangerous area division based on the gas concentration and safety principles. In order to reduce the stress on the underlying coal seam and improve mining efficiency in deep coal mining activities, narrow coal pillars are often used. They are the main factor that increases the risk of coal spontaneous combustion in the goaf. Based on the on-site experiment and the experimental analysis in the laboratory, this paper adopted correlation coefficient criteria and safety principles to research the disaster-causing mechanism of such risk. It also classified and divided the studied area into different risk levels to effectively manage it. The results show the coal mass fractures generated by the movement of stress concentration points on the narrow coal pillars is the main factor that contribute to the increased spontaneous combustion in the goaf. The two main forms are gas explosion caused by CH 4 flowing into the roadway and spontaneous combustion of residual coal caused by O 2 flowing into the nearby goaf. By adopting correlation coefficient criteria and safety principles, this paper selected two indicators, gas-impermeability of narrow coal pillars and risk degree of residual coal spontaneous combustion in the goaf to divide the whole narrow coal pillars and goafs into three areas, namely "Safe Area", "General Area" and "Dangerous Area". This can maximize safety benefits with the lowest cost and guarantee safe and efficient coal mining. [ABSTRACT FROM AUTHOR]

Safety and environmental problems caused by coal mining and utilization are becoming increasingly serious. Studies in the coal spontaneous combustion characteristics based on constant temperature difference guidance method, which is of great significance for mine safety prevention and environmental protection. In this paper, a new method, Constant Temperature Difference Guidance Method, was developed in this paper for studying coal spontaneous combustion characteristics. By creating a constant temperature difference between coal temperature and ambient temperature, self-heating of coal is guided in this new method, which largely improves the efficiency and success rate of coal spontaneous combustion testing. Through analysis, this method was proved capable of providing a comprehensive description of coal's low-temperature oxidation characteristics. Besides, through changing different values of the temperature difference, various factors of low-temperature coal oxidation under adiabatic environment can be calculated. Additionally, spontaneous combustion point and ignition point can be obtained by analyzing time-temperature curve of coal oxidation. These two points along with the duration to achieve these two points were used in this paper to develop a risk index for evaluating coal spontaneous combustion propensity. [ABSTRACT FROM AUTHOR]

• The wetting characteristics of coals with different degrees of metamorphism and different particle sizes were elucidated. • The correlation of LF-NMR parameters, surface contact angle and FTIR, LTNA structural parameters was revealed. • The LF-NMR method for quantitative characterization of wettability was proposed for physicochemical properties of the coal. Water injection in coal seams is an effective technique for preventing and controlling dust disasters in coal mines. However, there is a lack of quantitative evaluation of water transport in coal and its wetting effect. In this paper, the wetting experiments of coal samples with different coal rank and particle size at a given water volume were characterized using low-field nuclear magnetic resonance (LF-NMR) tests. Additionally, the physicochemical properties of coal were investigated by Fourier transform infrared (FTIR) and low temperature N 2 adsorption (LTNA) experiments, establishing quantitative relationships between these properties and contact angle, T 2 -weighted average value (T 2g), and peak area of adsorbed water (A Total). The relationships reveal the dynamic transport process of water in coal samples and its wettability law. The results show that the relaxation time of free state water in porous media decreases with stronger wetting of coal samples, resulting in a faster relaxation rate of free state water and a leftward shift of corresponding peaks. In the range of coal particle sizes from 0.18 to 2 mm (10–80 mesh), the wettability of coal deteriorates with the increasing degree of deterioration of coal samples, with larger particles of lower rank coal samples exhibiting better wettability. The better the wettability of the coal, the shorter the relaxation time of the corresponding peaks, the larger the total area of the adsorption peaks, and the smaller the T 2g,24h values. The FTIR structural parameters of hydroxyl (–OH) and carboxyl (–COOH) groups have the greatest influence on the hydrophilicity of the coal. Correlations of factors affecting the wettability of the coal body were analyzed, and three equations for quantitative characterization of the wettability of the coal body were constructed. Overall, the low-field NMR method presented in this paper provides an efficient means of quantitatively characterizing coal wettability and revealing the macro and microscopic mechanisms underlying the interaction between coal and water, as well as the associated wettability patterns. [ABSTRACT FROM AUTHOR]

Coal fire disasters generally occur in major coal-producing countries. They destroyed many coal resources and triggered various environmental problems. The identification and state assessment of coal fire areas are paramount to coal fire management. In this paper, a method for identifying coal fires by integrating land surface temperatures (LSTs) from multitemporal thermal infrared remote sensing and subsidence information from multitemporal interferometric synthetic aperture radar (MT-InSAR) is proposed. The method primarily consists of estimating the LSTs and subsidence values, normalizing and equidistantly partitioning the LSTs, estimating the thermal anomaly frequency (TAF), extracting high-subsidence areas, determining the thermal anomaly frequency threshold (TAFT), and identifying coal fire areas according to the TAFT. The coal fire ratio index (CRI) was developed to quantitatively evaluate the severity of coal fires and its variations. Midong District, Urumqi, Xinjiang, China, was selected as the study area. Forty-five Landsat 8 images and sixty-one Sentinel-1 SAR images were used to retrieve LST and subsidence time series, respectively. The proposed method and CRI were applied to identify and evaluate coal fires in the study area. The results demonstrate the satisfactory reliability of these methods compared with field surveys. The maximum CRI was 6.145 × 10-4 (July 28, 2019), and the minimum CRI was 2.685 × 10-5 (January 13, 2020). Coal fires in summer were more severe than those in winter. The CRI profile presented seasonal and annual periodicities and was affected by the local climate. The soil cohesion and humidity are higher in winter due to possible snowmelt, which weakens the interaction between oxygen and coal seams and the subsequent combustion of coal. The LST, thermal anomaly, and deformation information were combined in a time series overlay analysis to reveal the differences in the LSTs and subsidence values among mining areas, coal fire areas, and areas with both mining and coal fires. The results verify the applicability and reliability of the proposed method. [ABSTRACT FROM AUTHOR]

Mine fires have always been one of the disasters that restrict coal mining in China and endanger the life safety of underground workers. The research and development of new fire prevention materials are undoubtedly important to ensure the safe and efficient production of modern mines. At present, the main inhibiting materials used are grout material, inert gas, retarding agent, foam, gel, and so on. In order to explore the current situation of coal spontaneous combustion (CSC) fire prevention, the existing fire prevention materials were reviewed and prospected from three aspects: physical, chemical, and physicochemical inhibition. The results show that, at present, most of the methods of physicochemical inhibition are used to inhibit CSC. Antioxidants have become popular chemical inhibitors in recent years. In terms of physical inhibition, emerging biomass-based green materials, including foams, gels, and gel foams, are used to inhibit CSC. In addition, CSC fire-fighting materials also have shortcomings, including incomplete research on the mechanism of material action, poor stability of inhibitory properties, low efficiency, and economic and environmental protection to be improved. The future research direction of fire-fighting materials will be based on theoretical experiments and numerical simulation to study the mechanism and characteristics of CSC and develop new directional suppression materials with physicochemical synergies. These findings have extremely important implications for improving materials designed to prevent CSC. [ABSTRACT FROM AUTHOR]

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Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study explores the influence of a repeated mining process on an upper coal pillar in a close coal seam group. The pillar's breaking and instability processes are emphasized, and the influence of fracture development on the oxidation and spontaneous combustion of coal pillars is revealed. A numerical simulation is used to simulate the dynamic evolution characteristics of stress, displacement of the upper coal pillar, and the numerical results elucidate that the mining of the lower adjacent coal seam is a pressure relief process for the upper coal pillar. The theoretical length of the fracture along the strike of the upper coal pillar is also obtained for the upper coal pillar. [ABSTRACT FROM AUTHOR]

Coal is a material which has many features deciding about its quality. Among them, the decisive ones are mainly ash contents, sulfur contents and combustion heat. The paper presents the investigation of coal characteristics of three selected coal types in the context of their energetic value. For this purpose samples were collected from three different Polish mines: coal types 31, 34.2 and 35 (Polish classification of coals). Each of these materials was separated into particle size fractions (9 fractions) and then into 8 density fractions by separation in heavy liquids. For each size-density fractions obtained in this way, chemical analyses were performed which allowed for determination of such features as combustion heat, sulfur contents, ash contents, volatile parts contents and analytical moisture. Altogether, seven dimensions of grained material characteristics were obtained. The data prepared in this way was subsequently analyzed for correlation with the purpose of determining significant relations between investigated features. It was stated that the most correlated coal features are density, combustion heat, ash contents and volatile parts contents. For multidimensional analysis and identification of coal type, the modern image visualization technique, the Observational Tunnels Method, was applied. After performing seven-dimensional analysis aimed at the proper recognition of coal type, it was decided to determine the minimum amount of random variables, which describe a particular material in order to identify its type. It was stated that the crucial coal identification parameter is "analytical moisture". Due to existing correlation between individual features, three of them were selected for testing: analytical moisture, sulfur contents and volatile parts contents. On the basis of the obtained images, it was stated that it was possible to obtain a view with the data concerning each type of coal being located in other part of the space. Subsequently, it was checked if a similar result is possible when the parameter "volatile parts contents" is replaced with highly correlated parameters "combustion heat" and "ash contents". In both cases the exchange of these variables did not produce good enough results. This can be explained by a different scale of empirical data making it impossible to obtain a clear multidimensional image for which all three types of coal would be located in other parts of space. However, it was proved that the modern graphical and computer methods can be successfully applied to identify the types of particulate materials. [ABSTRACT FROM AUTHOR]

Due to its strong fluidity and easy evaporation characteristic, high water-cut physical inhibitors (HWPIs) cause the decrease in moisture content of coal, so that its inhibitory effect on coal spontaneous combustion weakens or even fails. Aiming at solving the problem, this paper proposes to inhibit coal spontaneous combustion using thermo-responsive inhibitors (TRIs). These inhibitors are sensitive to specific temperatures and can retain their effects as long as the temperatures have not been reached. Besides, when the temperatures are reached, they are able to absorb heat and undergo physical and chemical changes to release H 2 O and inert gases (defined as gases that are not involved into the coal oxidation reaction in this paper) such as NH 3 and CO 2 , so as to inhibit the low-temperature oxidation of coal. Based on the temperature-programmed experiment of coal spontaneous combustion, this paper analyzed the effects of types and amounts of TRIs on coal spontaneous combustion by using differential scanning calorimetry (DSC), scanning electron microscope (SEM), thermogravimetry-derivative thermogravimetric analysis-differential scanning calorimetry (TG-DTG-DSC) and nitrogen adsorption test methods. The results show that CaCl 2 •6H 2 O achieves the most stable inhibitory effect, as its inhibiting rate rises steadily in the heating process to reach a maximum value of 79.9% at 200 °C. [ABSTRACT FROM AUTHOR]