Coal Mine Gas Research Articles

Sound Identification Method for Gas and Coal Dust Explosions Based on MLP.

To solve the problems of backward gas and coal dust explosion alarm technology and single monitoring means in coal mines, and to improve the accuracy of gas and coal dust explosion identification in coal mines, a sound identification method for gas and coal dust explosions based on MLP in coal mines is proposed, and the distributions of the mean value of the short-time energy, zero crossing rate, spectral centroid, spectral spread, roll-off, 16-dimensional time-frequency features, MFCC, GFCC, short-time Fourier coefficients of gas explosion sound, coal dust sound, and other underground sounds were analyzed. In order to select the most suitable feature vector to characterize the sound signal, the best feature extraction model of the Relief algorithm was established, and the cross-entropy distribution of the MLP model trained with the different numbers of feature values was analyzed. In order to further optimize the feature value selection, the recognition results of the recognition models trained with the different numbers of sound feature values were compared, and the first 35-dimensional feature values were finally determined as the feature vector to characterize the sound signal. The feature vectors are input into the MLP to establish the sound recognition model of coal mine gas and coal dust explosion. An analysis of the feature extraction, optimal feature extraction, model training, and time consumption for model recognition during the model establishment process shows that the proposed algorithm has high computational efficiency and meets the requirement of the real-time coal mine safety monitoring and alarm system. From the results of recognition experiments, the sound recognition algorithm can distinguish each kind of sound involved in the experiments more accurately. The average recognition rate, recall rate, and accuracy rate of the model can reach 95%, 95%, and 95.8%, respectively, which is obviously better than the comparison algorithm and can meet the requirements of coal mine gas and coal dust explosion sensing and alarming.

Theoretical Basis and Technical Method of Permeability Enhancement of Tectonic Coal Seam by High Intensity Acoustic Wave In Situ

Tectonic coal seams are characterized by soft, low permeability and high gas outburst. The traditional gas control method is the intensive drilling and extraction in this seam, which is not only large in engineering quantity, high in cost, difficult to form holes and low in extraction efficiency, but also easy to induce coal and gas outburst, which is a difficult problem for global coal mine gas control. To solve this difficult problem, the controllable shockwave equipment developed by the author’s team and successfully applied in the practice of permeability enhancement of coal seam, combined with the principles of shock vibration sound wave generation and shock wave attenuation and evolution in the rock stratum, a new idea of loading a controllable shock wave in the roof and floor of coal seam is proposed. The shock wave first attenuates and evolves into a high-strength sound wave in the roof and floor rock stratum, and then enters and loads into the coal seam to achieve the purpose of increasing permeability without damaging the physical properties of the tectonic coal seam and facilitating the opening of the original fractures. According to the new technical ideas, the implementation scheme and key parameters of the gas pre-extraction models in tectonic coal seam are designed, including the penetration drilling, roof and floor horizontal holes, shield tunneling and the high-strength acoustic wave of the working face, which provides a new technical approach to solve the problem of high efficiency and low cost gas extraction in the tectonic coal seam.

A novel temperature compensation approach of IR gas sensors in coal mines

Infrared spectrum analysis is a technical method for quantitative analysis of coal mine gases. However, current infrared (IR) gas sensors are significantly affected by the change of ambient temperature. In this study, experimental research was carried out in the hope of improving the accuracy and applicability of IR gas sensors. Firstly, a test platform whose functions could support sensor temperature compensation experiments was built. The accuracy of sensors without temperature compensation was calculated under the concentrations CO2 of (0.5%, 1%, and 2.43%), CH4 concentrations of (0.1%, 1%, and 4.0%), and CO concentrations of (10 × 10−6, 100 × 10−6, and 500 × 10−6). The calculation results show that the errors are 1.4%∼2.0%, (3,000∼5,000) × 10−6, and (50∼160) × 10−6, respectively, which fail to meet the requirements for error ranges. Secondly, the constant temperature heating test of sensors was carried out in the temperature range of (25–55)℃, and the optimal heating temperature was determined to be 45℃. Then, the accuracy of sensors after temperature compensation was calculated again under the same CO2, CH4 and CO concentrations at 45℃. The results reveal that the errors are only 0∼0.045%, 0∼900 × 10−6, and 0∼9 × 10−6, respectively, which are better than the results before temperature compensation. Thirdly, with the temperature in the high-low temperature test chamber set as (-20∼45)℃, it is found that the errors remain huge. Considering the highly variable temperature conditions in underground coal mines, the genetic algorithm-back propagation (GA-BP) neural network model was established for error analysis. For CO2, CH4, and CO, the mean absolute errors (MAEs) of the GA-BP neural network model are 62.7%, 26.9% and 29.1% lower than those of the back propagation (BP) neural network model, respectively. In summary, this study obtained the appropriate heating range of IR gas sensors, established the error optimization model under different ambient temperature conditions, and provided a technical foundation for the construction of the in-situ on-line monitoring system for coal mine gases.

Risk assessment of coal mine gas explosion based on cloud integrated similarity and fuzzy DEMATEL

The risk of coal mine gas explosion seriously threatens the continuous safe production of coal mines, which in turn affects the national energy security, so it is important to prevent and control the coal mine gas risk. Current risk assessment methods are difficult to fully express the uncertainty in the assessment process, and calculating index weights is easy to deviate from reality. This study introduces Decision-making Trial and Evaluation Laboratory (DEMATEL) as well as the cloud model, and proposes a new coal mine gas explosion risk assessment model based on cloud integrated similarity and fuzzy DEMATEL. The model fully expresses the uncertainty in the whole risk assessment process and makes the index weights assignment more reasonable. It also combines the calculation of cloud integrated similarity to more accurately determine the risk level based on the advantage that the cloud model can visually display the risk status of the assessment object. An example study was conducted on a mine of a large state-owned coal mine enterprise in Shaanxi Province, China. The results show that the method helps coal mine enterprises to accurately assess gas explosion risks, identify weak links in risk prevention and control, and provide a powerful means for continuous improvement of risk management level.

Effect of chemical structure on mechanical-seepage characteristics of briquette under different heating temperatures

Based on the low strength and high permeability of briquette coal (BC) used in physical simulations of coal mine disasters, we propose a new briquette production method that can improve the mechanical strength and reduce the permeability of BC. The reduction of physical simulation experiments of coal and gas outburst was improved, which is of significance for the prevention and control of coal mine gas disasters. Based on this method, we developed a set of briquette hot-pressing systems and optimized the proportion of coal powder used in the briquette formation process. Mechanical property and seepage tests of the briquettes were carried out under uniaxial and triaxial compression. The effects of different temperatures on the physical (size, density, ignition loss rate) and mechanical (Poisson's ratio, elastic modulus and compressive strength) coal parameters and the effect of the permeability were analyzed using scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analyses. The morphology and pore, crystallite, and molecular structures were used to determine the cause of the increase in the mechanical strength of BC. Based on the packing density theory, the optimal ratio of the 40–60, 100–120, and 180–200 mesh particle sizes is 91.77:5.87:2.35. With the increase in the temperature from 150 to 450 °C, the microstructure changes from loose to compact, the number of pores and cracks increase, the degree of order of the microcrystalline structure gradually increases, the distance between the microcrystalline layers d002 continuously decreases, aliphatic chains shorten, and the aromaticity increases. The rate of the change of the loss rate and density of the hot-pressed briquette first increase, then decrease, and then increase again. The mechanical parameters (strength and elastic modulus) first increase and then decrease, whereas the Poisson's ratio first decreases and then increases, and the permeability increases. Considering the density, strength, and permeability of hot-pressed briquettes, the optimal heating temperature at which the similarity between the hot-pressed BC and raw coal is the highest at 300 °C.

MoS2 based dual mine gas disaster sensor that operates at room temperature

It is urgent to design a dual mine gas disaster sensor that operates at room temperature, including methane (CH4) and carbon monoxide (CO). Here, molybdenum sulfide (MoS2) nanoflowers was modified on the Quartz Crystal Microbalance (QCM), a sensing platform without heating, to fabricate a dual gas disaster sensor. The sensor exhibited dual sensitivity to CH4 and CO with ppm concentration at room temperature. Additionally, the sensor exhibits good short-term repeatability and long-term stability over a period of two months. This sensor demonstrates its potential in monitoring coal mine gas.

Research on gas emission quantity prediction model based on EDA-IGA

In order to accurately predict the possible gas emission quantity in coal mines, it is proposed to use the multi-thread calculation of the Immune Genetic Algorithm (IGA) and injection of vaccines to improve the accuracy of prediction and combine the Estimation of Distribution Algorithm (EDA) to the distribution probability of excellent populations. Calculating, and selecting excellent populations for iteration, optimize the population generation process of the Immune Genetic Algorithm, so that the population quality is continuously optimized and improved, and the optimal solution is obtained, thereby establishing a gas emission quantity prediction model based on the Immune Genetic Algorithm and Estimation of Distribution Algorithm. Using the 9136 mining face with gas emission hazards in a coal mine from Shandong Province in China as the prediction object, the absolute gas emission quantity is used to scale the gas emission quantity, and it is found that the model can accurately predict the gas emission quantity, which is consistent with the on-site emission unanimous. In the prediction comparison with IGA, it is found that the accuracy of the prediction results has increased by 9.51%, and the number of iterations to achieve the required goal has been reduced by 67%, indicating that the EDA has a better role in optimizing the population update process such as genetic selection of the IGA. Comparing the prediction results of other models, it is found that the prediction accuracy of the EDA-IGA is 94.93%, which is the highest prediction accuracy, indicating that this prediction model can be used as a new method for the prediction of coal mine gas emission. Accurately predicting the gas emission quantity can provide guidance for safe mining in coal mines. The gas emission quantity can also be used as a safety indicator to reduce the possibility of coal mine accidents, ensure the personal safety of coal miners and reduce economic losses in coal mines.

Prediction method of coal mine gas occurrence law based on multi-source data fusion

To improve the prediction accuracy and time-consuming of coal mine gas occurrence law (OL), a new prediction method based on multi-source data fusion is proposed in this paper. Firstly, the method obtains the data of coal mine gas OL, determines the key data required in prediction through decision matrix, and preprocesses the data to reduce the influence of regular noise data. This paper analyzes the basic principle of multi-source data fusion, constructs the prediction model of coal mine gas OL with this technology, takes the optimal value of weighting factor as the input value of the model, and completes the design of coal mine gas OL prediction method based on multi-source data fusion. The experimental results show that the accuracy of this method can reach 98%, while that of the other two traditional methods is lower than the existing methods. This method has high accuracy and efficiency in predicting the coal mine gas OL.

Performance and application of new inorganic retarding sealing material suitable for multi-scale fractures

Gas extraction is an important way to solve coal mine gas in China. At present, the development of new and more efficient gas sealing materials is an urgent problem in China's coal mining industry. In order to improve the gas extraction efficiency and promote the development and utilization of coalbed methane, we developed a new inorganic slow setting material which used bentonite as main material. We added two kinds of organic modified materials and two kinds of inorganic modified materials to optimize the sealing performance, and analyzed the viscosity, sealing and particle size changes after modification. The rheological properties and diffusion properties of sealing materials was studied. Meanwhile, field experiments were carried out to verify that it has more efficient sealing performance than traditional cement materials and could improves the efficiency of gas drainage and reduces mine gas disaster accidents.

Coal mine gas migration model establishment and gas extraction technology field application research

Gas drainage is the main technical measure to prevent and control coal and gas disasters. Reasonable extraction parameters can improve extraction efficiency and reduce the risk of gas accidents. In order to further study the influence of extraction parameters on gas drainage effect, this paper combines COMSOL Multiphysics numerical simulation and field experiment to optimize the two parameters of intubation spacing and extraction negative pressure in goaf of 42,201 working face in Buertai Coal Mine, Inner Mongolia. The three-dimensional gas distribution model in goaf was established, and the COMSOL numerical simulation software was used for calculation. Combined with the field experiment, the influence of intubation spacing and extraction negative pressure on the extraction effect was obtained. The results show that in the range of 50 m-70 m, the drainage effect is ideal when the negative pressure is 12–18 kPa.

New insight into efficient CH4/N2 separation based on Ni-decorated porous carbon functional composites

Separation of CH4/N2 mixture in coal-mine gas with low CH4 concentration is still challenging due to similar physical properties between CH4 and N2. Herein, we construct quantitative relationships between the pore distribution and CH4 adsorption capacity of porous carbon, exploring the specific role of micropores and meso-/macropores in the accommodation of CH4. Then, nickel (Ni) species selected on account of density functional theory (DFT) were employed for accurately regulating the size and surface properties of the pore structure, targeted to enhance the separation of CH4 against N2. The results indicate that 10 %Ni/C adsorbent achieved the highest CH4 adsorption (28.3 cm3/g) as well as CH4/N2 selectivity (5.29), compared to 20.0 cm3/g and 3.67 of the porous carbon. Additionally, a deep understanding of the synergistic effect between porous sizes and adsorption potentials provided by Ni species is triggered by the obtained results, which indicated Ni-decorated porous carbon as promising adsorbents and provided new insight for the improvement of CH4/N2 separation.

Research progress of methane purification from coal mine gas by variable pressure adsorption

Research progress of methane purification from coal mine gas by variable pressure adsorption

Explosion and vented explosion behaviors of low-concentration gas in large-scale pipes

The extraction, transmission, and use of low-concentration gas in coal mines are often challenged by potential accidents due to proximity to the combustion and explosion concentration limit. Water sealing of fire barriers and explosion venting devices guarantee the safe transmission of low-concentration gas. The propagation and venting of gas explosion under different concentrations are experimentally investigated in a DN500 mm pipe explosion propagation test system. The water sealing of fire barrier vented explosion field evolution of methane-air mixture at the stoichiometric concentration (9.5 vol%) is examined through Fluent numerical simulation to reveal the water sealing of fire barrier further vented explosion pattern of gas transmission pipelines under low concentrations. The explosion overpressure and flame propagation of low-concentration gas in pipes are observed and correlated. Based on their coupling relationship, the design basis for the installation location of the explosion venting device is derived. The vented explosion characteristics of low-concentration gas during pipe transmission are summarized, proving that this explosion venting technique enhances both the explosion venting device and explosion parameters. Our observations and analysis can offer useful clues to underground gas explosion and prevention in coal mines.

Studying the Favorable Zone for Pressure-Relief Gas Extraction by Combining Numerical Investigation and On-Site Application

Gas extraction in the pressure-relief area using the depressurization effect of seam mining is an effective way to solve coal-mine gas problems. In this paper, we performed numerical modelling of the 204 working face via FLAC 3D, by which the stress variation of the rock mass and associated permeability evolution during the working face advancement were investigated. Furthermore, the favorable gas extraction zone for pressure relief was proposed based on the gas extraction performance of the on-site boreholes. The results show that: (1) gas extraction varies with the evolution of the three zones of the overlying rock and the associated permeability variation, which becomes stable when the height of the three zones remains unchanged; (2) the favorable zone for gas extraction of the 204 working face ranges from 13 m to 19 m of Dv, in which the gas extraction of on-site boreholes are located, presents better performance than other areas; (3) the gas extraction volume of the optimized gas extraction scheme rises to 77.46 m3/min with a 77.26% gas extraction rate, eliminating gas overrun in the working face and upper corner and increasing the advancement speed to 6.4 m/d. The on-site verification confirms the numerical simulation scope, more accurately determining the favorable zone for gas extraction. This may provide a reliable approach for improving the pressure-relief gas extraction performance and reducing the associated engineering costs.

Characterization and field application of a novel dual-liquid gas leakage material: Mechanical properties and microscopic hydration mechanism.

Gas drainage materials are one critical aspect of preventing coal mine gas explosions. Here, a novel dual-liquid gas sealing material was developed to improve gas extraction. The mechanical properties and hydration mechanism of the proposed material were determined. The novel dual-liquid gas sealing material's performance was verified experimentally and with field testing, with practical application explored in the YunGaiShan 2 coal mine. The results showed that the main factor responsible for gas drainage leakage was the poor sealing effect of the sealing materials on the cracks around the borehole. The novel dual-liquid gas sealing material reduced damage to the rock surrounding the borehole and significantly improved the gas drainage performance. The initial and final setting times of the novel dual-liquid material were shown to be controllable, and the slurry exhibited good fluidity, with a 28-day uniaxial compressive strength of 11.06 MPa. The analysis of the microscopic hydration mechanism showed that the production of ettringite (AFt) in the dual-liquid material increased significantly, forming a denser network interlace that functioned as a network skeleton, improving the compressive strength of the material and achieving the characteristics of plastic deformation. Field-based analysis was performed to verify the practical applicability of the proposed material, showing that the gas drainage concentration increased by 200.5% compared to the original sealing material. Moreover, the average gas drainage negative pressure increased from 7.8 kPa (using the conventional sealing technique) to 16.6 kPa using the proposed material. Overall, the proposed materials are suitable for sealing materials for effective gas drainage performance and can help control gas disasters.

An Impacting Factors Analysis of Unsafe Acts in Coal Mine Gas Explosion Accidents Based on HFACS-ISM-BN

With the development of intelligent coal mine construction, China’s coal production safety has been greatly improved, but coal mine gas explosion accidents still cannot be completely avoided and the unsafe acts of miners are an important cause of the accidents. Therefore, this study firstly collected 100 coal mine gas explosion cases in China, improved the framework of human factors analysis and classification system (HFACS) and used it to identify the causes of miners’ unsafe acts in detail. A hierarchy of the impacting factors is established. Then, combining with the interpretive structural model (ISM), the correlation between the impacting factors among different levels, especially among non-adjacent levels, is qualitatively analyzed through expert judgment. Then, the correlation among the contributing factors was quantitatively tested by chi-square test and odds ratio (OR) analysis. On this basis, a Bayesian network (BN) is constructed for the impacting factors of miners’ unsafe acts. The results show that the probability of coal mine gas explosion accident is 20% and 52%, respectively. Among the leading factors, the government’s insufficient crackdown on illegal activities had the greatest impact on miners’ violations, with a sensitive value of 13.2%. This study can provide reference for evaluating the unsafe acts of miners in coal mine gas explosion accidents by the probabilistic method.

Kinetic evaluation of hydrate-based coalbed methane recovery process promoted by structure II thermodynamic promoters and amino acids

Coalbed methane recovery is crucial to coal mine safety, greenhouse gas emission reduction and economic benefits. Gas hydrate technology can be employed to separate CH4 from the N2-rich coal mine gas. To enhance hydrate formation kinetics, separation performance and CH4 recovery, we examined the synergistic effect of structure II (sII) hydrate promoters and amino acids on hydrate formation of 30 mol% CH4/70 mol% N2 mixture, involving three thermodynamic promoters (tetrahydrofuran (THF), cyclopentane (CP) and propane) and four amino acids (l-cysteine, l-methionine, l-tryptophan and l-lysine). Amino acids exhibited extraordinary promotion effects on the propane system with over 10 times improvement in kinetics. CP-amino acid systems excelled in separation performance by enriching CH4 content from 30 mol% to 70 mol%. THF-amino acid systems showed moderate performance on kinetics and separation but achieved the highest CH4 recovery up to 50.27%. The impacts of amino acids were system-dependent: they did not alter the hydrate growth pattern of the THF system but completely changed the hydrate morphology of CP and propane systems. Two possible mechanisms were discussed including interfacial tension alteration and hydrophobicity of amino acids. These insights would provide a basis for further optimizing the hydrate process promoted by sII promoters and amino acids for applications including coalbed methane recovery and beyond.

Effect of new modified materials on the microscopic pore structure and hydration characteristics of sealing materials in coal seam boreholes

To improve the efficiency of coal mine gas extraction, it is necessary to optimize the performance of sealing materials. In this paper, fly ash, nano-silica, and triethanolamine was selected to optimize the pore structure of the sealing materials. The qualitative and quantitative analysis of the seal material was performed by low-temperature liquid nitrogen adsorption experiments, scanning electron microscopy, and combined with fractal theory. The results show that the pores of common sealing materials are mainly mesoporous, accounting for 52.19%, and the volume of micropores is the smallest, accounting for 9.88%. The single doping of fly ash made the pore volume of the material decrease by 9.5%, and the percentage of mesopores increased by 1.3%, but the percentage of micropores decreased by 0.9%. Co-doping with nano-silica and fly ash increased the microporous percentage of the material by 0.77% and the peak stress by 17.43%. The synergistic effect of fly ash, nano-silica, and triethanolamine was most effective in optimizing the pore structure of the sealing material. The pore volume was reduced to 0.08198 cm3/g, and the fractal dimensions D1 and D2 were increased by 2.88% and 2.48%, respectively. The microscopic morphology of the material was also flatter and denser, and the hydration of fly ash was also more complete.

Numerical Simulation of Effective Extraction Radius of Pre-Drainage Borehole Based on Coal Damage Model

Borehole pre-drainage is an important technical means to control a coal mine gas disaster. In order to determine the optimal pre-drainage parameters of Dashucun mine, a coal damage permeability evolution model was established based on coal damage deformation, considering gas adsorption and desorption and the Klinkenberg effect, and a damage fluid-structure coupling model of coal seam containing gas was established by combining the coal seam deformation equation and the mass conservation equation. COMSOL software was used to simulate the influence of factors such as the initial permeability of coal seam, negative pumping pressure, aperture and pumping time on the effective pumping radius of pre-drainage borehole. The results show that the effect of negative pressure on the effective extraction radius can be ignored. The effect of borehole aperture, initial permeability of coal seam and extraction time on effective extraction radius is great, which conforms to the power function relationship, and the coefficient correlation value is high. The optimal extraction parameters of Dashucun mine are determined as borehole diameter 113 mm, coal seam permeability 1 × 10−17 m2, negative extraction pressure 30 kPa and extraction time 180 d. The research results can provide theoretical reference for the pre-drainage of gas in Dashucun mine.

Study on time effect of acidified pulverized coal micro components and discussion on mathematical correlation of influencing factors

In this paper, 3 % HCl + 3 % CH3COOH + 3 % HF + 2 % KCl complex acid is used to dissolve pulverized coal, and the industrial analysis method, XRD and SEM experiments were used for testing. The results show that the relative contents of M, Fc, and V in coal samples increase with the dissolution time, the A decreases, the content of elements C and O increases, and the content of elements H, N, and S decreases. The effect of composite acid on the surface morphology of coal is significant. It can effectively remove the particles on the coal surface. According to the theory of factor analysis, the industrial component and element is reasonably analyzed, and the weight coefficient of industrial parts is greater than the element factor. This study provides theoretical support for the time effect of coal mine gas drainage and coal seam water injection.