Spontaneous Combustion Research Articles

Comparative analysis of permeability model construction and risk fields evaluation by roof cutting along the gob in a coal mine.

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 50m 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.

Study on the inhibitory effect of inhibitor based on the coal molecular structure analysis: A case study of Zhundong coal, Xinjiang, China

The aim of this work is to use the changes in coal molecular structure to study the effect and mechanism of inhibitors, and to provide a reference for better preventing and controlling coal spontaneous combustion. In this study, Xinjiang Zhundong coal was used to construct the macromolecular structure. The changes in the molecular structure of the coal under different inhibitor concentrations and temperature conditions were analyzed by Fourier infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis. ChemDraw and Materials Studio were used to construct a coal molecular structure model with an inhibitor concentration of 20 % at 50 ℃. Results showed that the molecular formula of the ZD2–1 is C222H123O39N. The coal molecule contained a higher number of aliphatic hydrocarbon branches and a lower degree of aromatic ring condensation. When heated to 300 ℃, the proportion of adsorbed oxygen in raw coal decreased obviously, while the reduction of adsorbed oxygen was inhibited under inhibitor conditions. The change of functional groups of coal samples was obvious under 20 % inhibitor concentration, and the dosage was less than that of 30 % inhibitor concentration, revealing the optimal inhibitory effect on coal samples of Zhundong with this concentration.

Research on prediction model of coal spontaneous combustion temperature based on SSA-CNN

To predict the coal spontaneous combustion temperature accurately and efficiently, this study proposes a model based on the Sparrow Search Algorithm (SSA) and Convolutional Neural Network (CNN). Firstly, the study analyzes the main gas reactions during the coal oxidation to pyrolysis process. Six gas indicators, namely O2, CO, C2H4, CO/ΔO2, C2H4/C2H6, and C2H6, are closely related to coal temperature. Subsequently, a prediction indicator system is established. Then, the excellent data mining capabilities of CNN are leveraged through deep learning, along with their unique advantages in local perception and weight sharing, and a CNN prediction model framework is constructed. Moreover, the comparison between the algorithm performances is executed and SSA is selected for optimization. Utilizing its exceptional global search capability and adaptability, SSA optimizes the seven hyper-parameters of the model, significantly enhancing prediction accuracy. In the final step, SSA-CNN is compared with five reference models on test samples. The SSA-CNN model showcases a maximum relative error of 0.155, outperforming other models. Moreover, the RMSE of this model yields 8.4500, which is also lower than other models. The results suggest that the combination of the selected gas indicators with the SSA-CNN model can accurately predict the spontaneous combustion temperature of coal.

Investigation of the physicochemical inhibitors on coal spontaneous combustion based experimental and quantum chemical methods

Investigation of the physicochemical inhibitors on coal spontaneous combustion based experimental and quantum chemical methods

Experimental evaluation of the effect of sulfur content on the spontaneous combustion characteristics parameters of coal

The coal spontaneous combustion (CSC) is the main hazard threatening the coal safety production. In this work, the CSC characteristic, CSC tendency and limit parameters with different sulfur were measured and discussed using temperature-programmed experiment. The results show that the cross-point temperature (CPT) decreases first and then increases with the increasing sulfur content. The CSC tendency of coal with sulfur content in the range of 3.28–5.13 % is greater than that with sulfur content of 2.57 % and 7.59 %. When sulfur content is less than 5.13 %, sulfur and its unstable compounds in coal have strong reactivity and can promote oxidation reaction. When sulfur content is greater than 5.13 %, a large number of sulfur-containing substances reduce the contact area of coal oxygen molecules, which inhibits the oxidation reaction of coal. The sulfur content of coal sample has a significant effect on the limit parameters of coal spontaneous combustion.

Stability Improvement of the TDLAS-Based CO Monitoring Module in a Coal Mine by Using a Spectral Denoising Algorithm Based on SVR

CO gas is not only lethal but also a significant forecasting indicator for the spontaneous combustion of coal mines. It is imperative that monitoring modules for CO gas that work well in the coal mine environment are available. A feasible solution is the detection of CO by using monitoring modules based on tunable diode laser absorption spectroscopy (TDLAS) over a mid-infrared waveband near 4.6 μm. However, in most cases, the mid-infrared TDLAS-based CO monitoring module tends to introduce severe interference fringe noise into the TDLAS spectral backgrounds which is difficult to filter out using traditional spectral filtering methods, reducing the detection performance of the module. In order to filter out the noise and improve the stability of the module in complex coal mine environments, this work proposed an algorithm based on support vector regression (SVR) to extract the TDLAS spectral backgrounds. Spectral analysis indicates that the TDLAS spectral background can be predicted over the entire scanning spectrum range by using this algorithm, and the noise in the spectral background can be effectively filtered out when calculating the absorbance spectrum based on the Lambert–Beer law. Compared to extracting spectral backgrounds using the traditional least square polynomial fit, the obtained correlation coefficients between regression models of spectral backgrounds and corresponding training point datasets were increased from below 0.998 to above 0.999. The peak-to-peak value of the obtained N2 absorbance spectrum was suppressed below 0.022 from nearly 0.045. The signal-to-noise ratio of the obtained 25 ppm CO absorbance spectrum was increased to 13.35 from 6.95. A CO monitoring module polluted by dust was used to conduct experiments to further test the SVR-based algorithm. The experiment results showed that after programming the SVR-based algorithm to the module, the estimated limit of detection of the module was reduced to 5.46 ppm from 29.08 ppm, and all the absolute measuring errors of the standard CO gases with different low concentrations were reduced to less than 4 ppm from a majority of the errors of more than 10 ppm, compared to least square polynomial fit. The CO monitoring module could still maintain the performance of high-precision quantitative detection when using the SVR-based algorithm even if it had been polluted severely. So, the CO monitoring module has good adaptability to harsh field environments, and its operation stability can be effectively improved by using the algorithm proposed in this work.

Research on slurry seepage law and in-situ test based on the 3-D of goaf porosity in CFD modelling

The pores formed by spontaneous combustion of coal in goaf and the damage of surrounding rock caused by high temperature roasting may result in the surface to settle or even collapse, and produce crisscross pores. Porosity is an important influence index of oxygen supply by air leakage, smoke and heat escape, as well as seepage and diffusion of anti-fire media, and is the core influence factor of coal-oxygen composite, heat storage and heating, and high temperature prevention. Hence, a specialized porosity evolution model is developed, tailored to the context of high-intensity mining in high-temperature coal seams. Using this model, grouting simulations were conducted with the working face 12,315 of Huojitu Mine as the engineering basis. The results revealed that grout flow rates of 300 and 85 m3/h, water-cement ratios of 4:1 and 5:1, and drill hole spacing of 40 and 48 m exhibited notably effective grouting performance for surface and underground applications, respectively. The simulation and optimization outcomes have demonstrated favorable results for practical engineering applications. Signature gases, such as carbon monoxide and acetylene, were effectively reduced to 0 ppm, ethylene concentrations fell below 36 ppm, and oxygen levels stabilized at or below 8%. Furthermore, the sealing temperature within the goaf was maintained at approximately 16 ℃, effectively mitigating the high-temperature zone.

Experimental study on the displacement effect and inerting differences of inert gas in loose broken coal

The pre-injection of inert gas before coal self-ignition is a common key measure for preventing and controlling spontaneous coal combustion in a goaf. Previous studies have mainly considered inerting to reduce the concentration of ambient gas components and explored the influence of oxygen or inert gas concentration on the inerting effect of loosely broken coal, but seldom considered the replacement of oxygen by an inert gas, especially the replacement of adsorbed oxygen. Here, we quantitatively investigated the difference in room-temperature inerting of loosely broken coal by N2 and CO2 by conducting one-factor experiments on replacing oxygen in coal with an inert gas at room temperature and pressure. The results reveal that the replacement process can be divided into three stages and that the different adsorption capacities of coal for N2 and CO2 are the main reasons for the asynchrony of each replacement stage. The stronger the adsorption capacity, the stronger the displacement of adsorbed oxygen in the adsorbed state by the inert gas. CO2 exhibits an inerting strength 2.3–2.6 times higher than N2 and 5.7–8.8 times higher than He. The experiments also revealed that optimizing the key parameters of inert fire protection technology should consider the adsorption effect.

Preparation and study of a sodium alginate film for preventing spontaneous combustion of water-soaked coal in goaf

Considering the high risk of spontaneous combustion of soaked coal compared to raw coal and the limitations of existing technology in preventing spontaneous combustion of coal in goaf water, a sodium alginate film has been developed which can effectively solve the problem of preventing spontaneous combustion of soaked coal by oxygen insulation, heat absorption and inhibition. The optimum composition ratio and the properties of the film are evaluated by film formation and thermogravimetric experiments. The results show that the film properties are best when the ratio of sodium alginate to gelatin is 8:2, the sodium tripolyphosphate concentration is 0.5 %, the ammonium polyphosphate concentration is 0.2 %, and the concentration of CaCl2 for the first and second cross-linking is 0.01 % and 0.2 %, respectively. The combination of sodium alginate and CaCl2 forms a stable and compact spatial network structure that can reduce the temperature of the covered coal by approximately 36 °C. Throughout the field trials, the temperature change of the goaf treated with sodium alginate film is opposite to that of the untreated area, showing a downward trend, with a total decrease of 0.4 °C in 20 days. This study provides a new idea for preventing spontaneous combustion of soaked coal.

Comprehensive evaluation of spontaneous combustion phenomenon from asphaltite perspective: Comparison with coal and clues of a universal process

Asphaltite holds importance as an energy raw material for Turkey. This study explores the potential for spontaneous combustion during underground mining production of Şırnak Üçkardeşler vein asphaltites and describes a generalized process by highlighting similarities and differences with self-heating of coal. Incubation tests, gas composition analysis, and infrared spectroscopy were conducted. Additionally, thermal analysis, surface area measurements, pore diameter analysis, mechanical testing, proximate analysis, and ultimate analysis were performed on the samples. The results reveal key differences in the spontaneous combustion behavior of asphaltites compared to low-rank coals. Melting, occurring between 60 and 80 °C, replaces the moisture-related stagnation observed in coals. The role of different functional groups, such as OH, CH, and CH2, in fueling the initial oxidation processes and other radicals initiating thermal runaway is identified. The reduction in surface area and pore diameters of asphaltites at higher temperatures limit their oxidation capacity. The compressive and tensile strengths of asphaltites significantly decrease with temperature. Similar to coals, carbon dioxide and carbon monoxide are indicative of spontaneous combustion, with carbon monoxide exhibiting a regular increase in temperature. The Arrhenius form confirms the occurrence of homogeneous reactions in asphaltite spontaneous combustion after 75 °C. These findings provide valuable insights into a universal mechanisms and warning signs of spontaneous combustion, aiding in the development of effective prevention strategies.

Mechanisms of CO and CO2 Production during the Low-Temperature Oxidation of Coal: Molecular Simulations and Experimental Research

The spontaneous combustion of coal caused by oxidation often leads to catastrophic fires. However, the understanding of oxidized carbon gas as a predictor of coal’s spontaneous combustion is still in its infancy. To better study the characteristics of CO2 and CO generation during low-temperature coal oxidation, the chemical reactions and activation energies during the formation of oxidized carbon gases within coal molecules were investigated using the molecular simulation method, and the reaction characteristics at different temperatures were determined. In addition, TG was used to experimentally analyze the variations in coal weight, exothermic conditions, and gas generation patterns. The results show that the low-temperature oxidation process consists of four different phases, each of which is characterized by unique CO and CO2 generation. The results of this study are important for the prevention and prediction of the spontaneous combustion of coal.

Research Progress of Gel Foam Extinguishing Agent in Coal Mines

Gel foam extinguishing agent (gel foam) has promising applications in the prevention and management of mine coal spontaneous combustion. Based on the research on coal spontaneous combustion and prevention technology, this article discusses recent studies on using gel foam to extinguish coal mines. The structural properties and principles of gel foam are described briefly. The research developments of three significant varieties of gel foam are then presented in detail, including silicate gel foam, acrylamide copolymer gel foam, and natural polymer gel foam. Meanwhile, the research status of gel foam anti-fire technology’s rheological properties, stability property, plugging property, and inhibitory properties are introduced. Furthermore, in conjunction with the research state, the prospects of the research direction of gel foam are proposed, which serve as a reference for future research on gel foam.

Experimental study on the effect of room temperature pre-oxidized time on spontaneous combustion characteristics of coal

The presence of different types of coal at room temperature can lead to self-heating of coal, potentially resulting in spontaneous combustion. To investigate the effect of ambient temperature pre-oxidation (BL) time on the self-combustion characteristics of different coal types, synchronous thermal analysis (STA) and Fourier-transform infrared spectroscopy (FTIR) experiments were conducted. The results of the synchronous thermal analysis experiments indicate that ambient temperature pre-oxidation for 3 months (BL3), BL6, and BL9 coals exhibit faster oxidation reactions compared to the original coal, while BL12 coal shows slower oxidation than the original coal. Among these, BL9 coal demonstrates the most significant changes in oxidation reaction characteristics, with the fastest oxidation reaction time being 35.36 min, which is 1.38 min faster than the original coal. To support this observation, a comparison was made between the relative content of active functional groups in the original coal and BL coal. The study revealed that the BL process affects the relative content of hydroxyl groups, aromatic hydrocarbons, aliphatic hydrocarbons, and oxygen-containing functional groups, thereby influencing the coal-oxygen reaction process. This suggests that pre-oxidized coal, compared to the original coal, has a larger pore structure, which plays a dominant role in promoting coal self-combustion in the first 9 months of the BL process. As BL time continues to increase, the continuous reaction of active functional groups at room temperature leads to excessive consumption, resulting in a more significant role in inhibiting coal self-combustion. The research results provide valuable insights for predicting the spontaneous combustion risk of oxidized coal.

Surface characteristics and re-ignition law of water-soaked coal in a coal mine closed fire area

There are different degrees of oxidized coal samples in the gobs of coal mines, and there will be hidden dangers of re-ignition of water-soaked coal after the fire zone is closed. Using an atomic force microscope (AFM) and a simultaneous thermal analyzer, the re-ignition properties of coal samples and the pore dynamic evolution in different water-immersed areas of the goaf were studied. The results show that the IO (oxidation after water immersion) coal sample has a more microporous structure and larger fractal dimension when oxidized at 300 °C. The roughness of OI (water immersion after oxidation) coal samples decreases as the oxidation temperature increases. The re-ignition temperature points of the IO300 and O200I coal samples are lower, and the combustion heat release is greater. Before reaching 311 °C, the oxidation kinetics curve conforms to the cubic polynomial ln[-ln(1-a))/T2] =A(1/T)3-B(1/T)2 + C(1/T)-D. After reaching 311 °C, the activation energy of IO300 and O200I coal samples is smaller and more prone to oxidation and re-ignition, which conforms to ln [- ln (1-a))/T2] =A (1/T) – B. Different control measures can be taken in different areas and points based on the oxidized degree and different immersion methods to prevent coal spontaneous combustion (CSC) in closed fire areas.

Effect on the oxidation characteristic at lignite of two types of endogenous microorganisms from coal

In recent years, coal biotechnology has gained considerable popularity due to its economic, eco-friendly, and sustainable advantages, which offer a novel perspective and pathway for the development of green technologies aimed at preventing and controlling coal spontaneous combustion (CSC). Two endogenous microorganisms from lignite were succeeded in extracting in this work, namely Aspergillus and Bacillus velezensis. Subsequently, the effect of these microorganisms on the microscopic structure and macroscopic oxidation characteristics of coal was investigated by X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The results revealed that both Aspergillus and Bacillus velezensis treatments altered the microcrystalline structure of the coal, disrupting the aliphatic hydrocarbon structure and oxygen-containing functional groups of the coal molecules. Particularly, the OH − O hydrogen bond of two kinds of microbial treatment coal samples content respectively decreased significantly by 17.29 % and 11.06 % compared to the raw coal sample. However, the effects of different microorganisms on coal varied. Thermodynamic behavior demonstrated that the critical temperature of the two treated coal samples was delayed by 29.44 °C and 26.62 °C, and the ignition temperature was delayed by 11.31 °C and 5.18 °C. Overall, all characteristic temperature points of the Aspergillus group were delayed, but the maximum weight loss rate temperature and the burn-out temperature of the Bacillus velezensis group exhibited slight advancement. The thermal mass loss characteristics also changed during the oxidation combustion stage. In addition, the average activation energies of oxidized combustion stage calculated by the Kissinger-Akahira-Sunose method were 74.26 kJ/mol and 78.61 kJ/mol, respectively, and 82.41 kJ/mol and 86.15 kJ/mol for the Friedman method, which were both increased compared to the raw coal. The results indicate that both Aspergillus and Bacillus velezensis have effects with varying degrees on the coal oxidation characteristics. It can be observed that the effect of treatment with Aspergillus is better than Bacillus velezensis from the overall changes in characteristic temperature points. This work lays the foundation for investigating the effect of microbial action on the oxidative properties of CSC.

Study on the bond properties between basalt fiber-reinforced spontaneous combustion coal gangue concrete and BFRP bars

Microstructural characterization of spontaneous combustion coal gangue (SCCG), the hydration products and mechanism of spontaneous combustion coal gangue concrete (SCCGC) were discerned through microscopic analysis. The bond performance was assessed employing a central pull-out test on samples variably substituted with SCCG (0%, 25%, 50%, 75%, and 100%) and augmented with basalt fiber (BF) (0%, 0.1%, 0.15%, and 0.2%). The failure mode and bonding mechanism were also revealed by this test. The bond-slip curves were fitted by various bond-slip constitutive models and a suitable model was found for each section. As indicated by the results, SCCGC possessed a lower carbon content and higher Al and Si element contents. These elements would undergo secondary hydration reactions with CH, which could enhance the strength of the ITZ and the compactness of the bond interface between BFRP bars and concrete. The failure modes were splitting and pull-out. An inverse correlation was observed between bond strength and the increment in SCCG aggregate substitution, ranging from a decline of 2.6% to 23.1%. As the BF content increased, the bond strength and peak slip increased by 3.9% ∼ 19.7% and 4.0% ∼ 14.6%, respectively. Furthermore, the reinforcing effect of BF on bond strength increased from 3.9% ∼ 10.3% to 8.8% ∼ 19.7% as the SCCG replacement rate increased, which was noticeable. The Malvar model and the Continuous Curve model were the best fitting models for the ascending and descending sections of bond-slip curves, respectively, while the residual stage was well fitted by the Hao Qingduo model.

Study on the catalysis of copper-based compounds on coal spontaneous combustion and its mechanism

ABSTRACTTo study the effect of the copper element in coal on the spontaneous combustion process of coal, corresponding copper-containing compounds were added to the coal-based on their occurrence state, and thermodynamic experiments and in-situ diffuse reflectance infrared spectroscopy experiments were conducted. Thermodynamic oxidation experiments have shown that the catalytic effects of Cu (NO3)2, CuCl2, CuCl, and Cu2O on three types of coal with different degrees of metamorphism are mainly reflected in the accelerated oxidation stage. After adding copper-containing compounds, the ignition temperature of coal decreased by 22.1°C to 134.4°C, the heat release increased by 1.33 to 3.19 times, and the CO emission and oxygen consumption rate also increased. CuCl has the greatest impact on the ignition point temperature of coal and increases the oxygen consumption rates of DNH and TS by 2.32 and 1.51 times that of raw coal. CuCl2 has the strongest catalytic effect on coal oxidation heat release. Through in-situ diffuse reflectance infrared spectroscopy experiments, it was found that the reaction rate of fatty hydrocarbons in the oxidation process of three types of coal with the addition of copper-containing compounds increased to 1.3–3 times that of raw coal, and the oxidation rate of oxygen-containing functional groups also significantly increased, while the cracking temperature of aromatic structures significantly decreased. This is because copper ions, as strong free radicals, induce free radical chain reactions in coal and exhibit a strong promoting effect on the coal oxygen reaction process.

Detection of Spontaneous Combustion Areas of Coal Gangue Dumps and Comprehensive Governance Technologies: A Case Study.

Spontaneous combustion of coal gangue dumps not only releases toxic and harmful gases, polluting the environment, but also leads to explosion accidents and casualties due to improper handling. This paper focuses on delineating the fire area, constructing a comprehensive fire prevention and extinguishing system, and restoring the ecological environment. Infrared thermal imaging was used to detect the shallow fire area, while intensive drilling was conducted to detect the deep fire area. The stability of the coal gangue dump was enhanced by perfusing three-phase foam for cooling and using a curing material to fill the cracks. Land reclamation was then performed to restore the ecological environment. The results indicate that spontaneous combustion of coal gangue dumps can trigger the spread of the fire area from the outside to the inside, gradually expanding due to the 'stack effect'. The sources of spontaneous combustion in gangue fire areas are mainly located 3-5 m below the flat surface, and the shallow and deep fire areas are interconnected, posing a significant danger. These research findings can serve as a reference for detecting fire areas in coal gangue dumps and controlling environmental pollution.

Effect of Resveratrol on physicochemical structure evolution of lignite during spontaneous combustion

Studying the evolution of the physicochemical structure of coal during coal spontaneous combustion (CSC) by antioxidants is of great significance for revealing the mechanism of CSC and preventing it. The effects of three concentrations of Resveratrol (RES) on the physicochemical structure evolution of coal during the low-temperature oxidation (L-TO) process of CSC were comprehensively analyzed through low-field nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) experiments. The results showed that the pore cracks in the coal develop more fully with the increase in oxidation temperature. Besides, there was an increase in porosity and permeability, and a full development of pore throat. Based on the T1-T2 2D fluid identification results, it was found that as the oxidation temperature increased, the adsorption capacity and permeability of the coal were stronger. RES can effectively inhibit the CSC process of coal, with a maximum reduction of 23 % in porosity and a maximum reduction of 82 % in permeability. The hydroxyl groups and CH3/CH2 of coal samples treated with RES decreased by a maximum of 42 % and 43 %, respectively. The oxygen-containing functional groups increased by a maximum of 77 %. RES can not only cover on the coal surface to prevent oxygen from seeping into the coal, but also infiltrate into the pores of coal to inhibit the combination of the active functional groups and oxygen molecules.

A Review on Mine Fire Prevention Technology and Theory Based on Bibliometric Analysis

Of all mine disasters, fires are very threatening to mine safety and often lead to the most serious consequences. Research on mine fire prevention technology and theory has experienced significant growth and is attracting escalating academic interest and attention. However, dedicated literature reviews on this topic are scarce. For the purpose of uncovering the research characteristics and trends on mine fire prevention technology and theory, this paper employs bibliometric analysis using the Web of Science Core Collection database. This study presents a detailed analysis of relevant articles published between 2010 and 2022. An assessment of the influences of journals, countries, institutions, and authors was conducted through a citation analysis. Furthermore, this paper describes co-authorship networks among different countries, institutions, and authors. Lastly, a review of the mine fire prevention techniques and theories researched during this period was carried out through a keyword clustering analysis. Four main research topics in mine fire prevention research were identified: “mine fire control technology”, “mine fire occurrence mechanism”, “mine fire prediction technology”, and “mine fire monitoring technology”. Additionally, the theory study of spontaneous combustion and its underlying mechanisms may represent a potential focus for future research. These findings contribute to providing a solid foundation for future research endeavors in this field of fire prevention.