Driven by the global transition toward carbon neutrality and the increasing demand for clean coal utilization, underground coal gasification (UCG) has emerged as a promising technology. Its advantages lie in the characteristics of in situ conversion and surface utilization, which enhance the recovery efficiency of deep coal resources. The operational stability of the injection-production process in UCG largely depends on the internal organization of pores, fractures, and matrix within the coal body, as well as their control over seepage pathways. However, the multiscale complexity of the coal microstructure and the intertwined distribution of pore-fracture systems introduce uncertainties in both grayscale representation and spatial resolution in CT imaging, thereby limiting its effectiveness in the quantitative analysis of seepage behavior and mechanical properties. To address these challenges, a "pattern-domain representation + unsupervised clustering" framework based on sparse representation and K-SVD dictionary learning is proposed. For CT slice data of anthracite subjected to different pyrolysis temperatures, the complex imaging information is transformed into sparse coefficients that encode structural features through dictionary learning, followed by unsupervised clustering to achieve effective separation of pore-fracture structures from the matrix. This approach yields classification results that are more robust and physically interpretable than conventional threshold-based segmentation. In addition, multifractal singularity spectrum analysis is incorporated to quantitatively characterize the multiscale heterogeneity of the pore-fracture system and its temperature-dependent evolution from a statistical perspective. The results demonstrate that, compared with traditional threshold segmentation, the proposed method enables more stable and structurally meaningful discrimination between pore-fracture networks and matrix phases. With increasing temperature, the area fraction of the dominant matrix cluster decreases from approximately 90% to 66%, while clusters associated with low-gray-value regions (pores/fractures) increase in proportion and exhibit greater spatial dispersion. Meanwhile, fracture connectivity and network complexity are significantly enhanced, indicating a transition of the pore-fracture system from a compact structure toward a multiscale channel-dominated configuration under high-temperature conditions. These findings provide a quantitative foundation for characterizing pore-fracture networks and inferring seepage behavior in UCG scenarios.

Studying the thermal deformation characteristics of coal under thermo-hydro-mechanical-chemical coupling is crucial for analysing roof stability, surface subsidence, and heat injection channel formation during the in situ pyrolysis mining of coal. Therefore, in this study, the deformation characteristics, gas production characteristics, and pore structure evolution as well as strength of bituminous coal during carbonisation and steam pyrolysis were explored. The results show that: 1) coal sample deformation can be divided into two stages: softening and pyrolysis deformation. Softening deformation depends solely on temperature, and pyrolysis deformation is affected by the severity of coal pyrolysis; 2) the deformation of bituminous coal and the evolution of pore and crack structures influence each other. Deformation promotes changes in pore and crack structures, and these structural changes serve as the internal drivers of deformation; 3) below 400 degrees C, steam injection accelerates the softening deformation of bituminous coal. Meanwhile, above 400 degrees C, deformation intensifies considerably under steam pyrolysis conditions owing to increased gas production of the coal sample compared to that during carbonisation. [Received: August 12, 2024; Accepted: April 9, 2025]

Coal contains complex and tortuous micropores that serve as the primary occurrence sites for gases. Coal seams at different burial depths show varied storage characteristics of H2 and CO2 owing to differences in temperature and pore structure. In this study, an anthracite macromolecular model was processed via compression and quenching, and ten amorphous supercells with diverse micropore structures were generated by configuration sampling. Gas storage molecular simulations were conducted at temperatures ranging from 273.15 to 408.15 K. The results indicate that H2 exists in both adsorbed and free states, with interaction energies between −1.637 and 0.594 kJ/mol. In contrast, CO2 is solely present in the adsorbed state, with interaction energies ranging from −55.38 to −13.19 kJ/mol. As temperature increases, the most probable interaction energy decreases and the dispersion of energy distribution declines. The storage capacity and adsorption density of both H2 and CO2decrease exponentially, and this decreasing trend is more remarkable for CO2. Meanwhile, the free density of H2 also decreases synchronously. An increase in volume-specific surface area reduces gas storage capacity and adsorption density following a negative power-law relationship, and linearly decreases the free density of H2 by reducing the effective storage space. Pores with high tortuosity lead to the loss of effective storage space, and high temperature further exacerbates this phenomenon. The critical Connolly radii are 1.1 Å for H2 and 1.3 Å for CO2, and the accessible spaces corresponding to these radii contribute the most to gas storage. This study quantitatively characterizes gas storage behaviors and clarifies the underlying mechanisms, which provides a theoretical reference for temperature control, pore structure optimization and storage capacity assessment in coalbed hydrogen storage and carbon sequestration.

The complex tortuous micropores in coal are the main sites for gas occurrence. Coal seams at different burial depths exhibit distinct H2 and CO2 storage behaviors due to variations in temperature and pore structure. In this work, an anthracite macromolecular model was compressed and quenched, and 10 amorphous supercells with different micropore structures were obtained through configuration sampling. Molecular simulations of gas storage were then performed at 273.15-408.15 K. Results show that H2 coexists in adsorbed and free states with a potential energy range of -1.637~0.594 kJ/mol, while CO2 exists only in the adsorbed state with a range of -55.38~-13.19 kJ/mol. With rising temperature, the most probable interaction energy shifts to lower levels and the energy dispersion weakens. H2 and CO2 storage and adsorption density decrease exponentially, with a more obvious reduction for CO2, accompanied by a synchronous decline in H2 free density. Increased volume specific surface area reduces gas storage and adsorption density via a negative power law and linearly lowers H2 free density by regulating effective storage space. Highly tortuous pores waste effective space, and high temperature aggravates this effect. The critical Connolly radii are 1.1 Å for H2 and 1.3 Å for CO2, with the maximum storage contribution corresponding to the accessible space at these radii. This study accurately quantifies gas storage and reveals the mechanism, providing a theoretical basis for temperature regulation, pore structure optimization, and capacity evaluation in coalbed hydrogen storage and carbon sequestration.

In order to investigate the influence of water-gas domain distribution on the relative permeability of water and gas during the injection of hot water into coal, we establish a two-dimensional pore cavity throat model based on fractal theory, and use the water gas dynamic equilibrium equation as the judgment condition for seepage calculation. The water and gas balance control equation of the cavity throat network was derived, and the distribution law of the water-gas domain during coal seam thermal injection and drainage gas production process was clarified. Finally, the relationship between water injection pressure, fractal dimension, temperature and relative permeability was obtained. In the study of constant temperature water injection process, it was found that as the injection pressure increases, the gas chamber is constantly occupied by water, the saturation of water continuously increases, and the relative permeability of water significantly increases. The injection pressure is positively correlated with the relative permeability of water. During the constant pressure heating and drainage process, the increase of free methane leads to an increase in gas pore pressure in the model, overcoming capillary forces to discharge water. The temperature is higher, the water chamber is occupied by the gas chamber, and the distribution of the gas domain is wider. When percolation occurs, the relative permeability of the gas increases sharply, which is positively correlated with temperature and conducive to the discharge of water.

In terms of the phenomenon of nonuniformity adsorption energy between methane and a natural heterogeneous coal surface, a heterogeneous potential well model is established in this study based on adsorption science and molecular dynamics theories. This model describes the methane adsorption positions in coal pores as a three-dimensional space composed of adsorption equipotential surfaces with varying depths of potential well, which emphasizes the heterogeneous distribution of methane adsorption potential well depths in coal and accurately describes the spatial distribution and energy states of methane molecules during methane adsorption and desorption in naturally heterogeneous coal. By taking the residual sum of squares (RSS) and Pearson correlation coefficient as indicators, the fitting accuracies of the Langmuir model and the heterogeneous potential well model for isothermal adsorption and desorption curves are compared so that the superiority of the heterogeneous potential well model in describing the adsorption and desorption of methane in natural coal is confirmed. According to this new model, a method to calculate the potential well distribution of coal by using isotherm adsorption and desorption curves was proposed. Taking the number of potential wells, the average potential well depth, and the variance of potential well depth as statistical indicators, the potential well distribution characteristics of coal in different ranks in the processes of methane adsorption and desorption under different temperatures were analyzed. In addition, the effects of temperature increase on the changes of the occupation rate of potential wells and methane desorption amount of coal with different potential well depth distributions are studied, which confirmed the necessity of evaluating the thermal recovery rate of coalbed methane based on the potential well depth distribution of coal seams.

Coal seam hydrogen storage has garnered significant attention due to its potential for large-scale, long-term, low-cost, and safe hydrogen storage. This study selected coal samples of three different ranks: long-flame coal (CYM), coking coal (JM), and anthracite (WYM). Utilizing a combined approach of physical experiments and molecular simulations, the thermodynamic and kinetic characteristics along with energy mechanisms of H-2 adsorption were investigated over a temperature range from 313.15 to 353.15 K and a pressure range from 0 to 2.5 MPa. The results indicate that the adsorption of H-2 on coal is predominantly governed by van der Waals forces (-4.358 to -3.298 kJ/mol), accounting for only 1.18% of the adsorption energy of CH4. With increasing temperature, the adsorption process conforms to the Langmuir-Freundlich model, while the saturated adsorption capacity exhibits a decreasing trend. The isosteric heat of adsorption during H-2 adsorption (1.78 to 3.47 kJ/mol) is merely 12.5% of that of CH4, resulting in a significantly weaker thermal response compared to CH4. Both the adsorption heat and temperature change for H-2 across different coal ranks follow the order: WYM > JM > CYM. The adsorption kinetics of H-2 on coal conform to the pseudo-second-order kinetic model. The adsorption rate constant k(2) increases with temperature, decreases with higher diffusion activation energy, and shows no significant correlation with pressure variations. The diffusion activation energy of H-2 (5.54 to 8.09 kJ/mol) is regulated by the combined effects of coal pore structure and interaction energy, with the order of activation energy being JM > WYM > CYM. Compared to CH4, the diffusion activation energy of H-2 is reduced by approximately 33.33%, enabling efficient and low-energy hydrogen charging/discharging cycles in coal. Therefore, hydrogen storage engineering requires comprehensive evaluation and optimization of coal rank and temperature parameters based on storage capacity and injection/withdrawal flexibility requirements.

Permeability rebound and recovery are pivotal in determining the efficacy of coalbed methane (CBM) extraction and the impact of superheated water injection during thermally enhanced CBM extraction. Existing research predominantly focuses on the roles of effective stress and methane desorption shrinkage, often neglecting the critical influence of the temperature. Therefore, our study introduces a mathematical model incorporating heat-fluid-solid coupling and a permeability evolution model considering temperature variations. The model was used to analyze the phenomenon of permeability rebound and recovery during CBM extraction and the effects of various factors on it. The results show that the permeability rebound and recovery time increase with initial gas pressure but decrease with initial diffusion coefficient and permeability. Initial coal seam temperature has little effect on the permeability rebound time, which increases the recovery time. The permeability rebound value rises with the initial diffusion coefficient but falls with the initial gas pressure and permeability, and the coal seam temperature has little impact on it. In addition, whether to consider the temperature on the permeability evolution is compared. The results reveal that temperature impact causes an elevation in permeability rebound, prolongs rebound and recovery time, and reduces postrecovery permeability ratio compared to the scenario without temperature influence. Inspired by the law of permeability evolution, this paper discusses the impact of injection pressure and temperature on the effectiveness of superheated water injection in the initial stage of enhanced CBM recovery engineering practice. The findings offer valuable insights into selecting optimal injection parameters tailored to various coal seams.

Before the occurrence of rock instability and failure, the deformation field in rockmass often undergo pronounced and uneven fluctuations. Investigating effective short-term precursor methods to identify and capture events preceding rock instability based on limited displacement information is of significance and practical importance for successfully predicting dynamic hazards in rock masses. In this study, to explore displacement precursors preceding instability in different lithologies, uniaxial compression tests were conducted on six types of rocks: red sandstone, coarse-grained yellow sandstone, bituminous coal, marble, granite, and basalt. By monitoring surface displacements and internal acoustic emission signals during specimen loading, we examined surface deformation characteristics before rock instability and introduced a rock instability precursor indicator, namely displacement coordination coefficient (DCC). Results show that DCC can capture precursor information leading to rock instability, with a sharp increase observed as a crucial precursor feature. For various rock types, the DCC abrupt change point appears at 95

In order to further reveal the dynamic characteristics of coal with different degrees of metamorphism under different adsorption pressures, the self-developed TQY-2 precision adsorption instrument and infrared thermal imaging device were used to conduct macroscopic adsorption tests on lignite, coking coal and anthracite coal samples with a diameter of 8.5 mm at different pressures (0.2, 0.4, 0.6, 0.8, 1.0 MPa) and the adsorption test of the mesoscopic structure of the coal body with adsorption pressures of (0.3, 0.6, 0.9, 1.2, 1.5 MPa), using quasi-primary and quasi-secondary adsorption kinetic models such as intra-particle diffusion, Elovich and double constant analyze the law and mechanism of adsorption gas. The results show that compared with five adsorption kinetics models, the quasi-secondary adsorption kinetics model is suitable for characterizing the adsorption gas process of lignite and coking coal, while the optimal model for anthracite is the intra-particle diffusion model; with the increase of adsorption pressure, the quasi-secondary adsorption rate constant k2 of lignite and coking coal gradually increased, and the intra-particle diffusion rate constant kp of anthracite coal also gradually increased, all of which were positively correlated; adsorption pressure has little effect on the dynamic model suitable for coal samples; under the macroscopic adsorption experiment and the mesoscopic structure adsorption experiment of coal body based on infrared thermography, the dynamic models suitable for different degrees of metamorphism are consistent.

A self-made triaxial testing machine with thermal–hydraulic–mechanical–chemical (THMC) coupling and a tubular heating furnace, combined with in situ (IS) micro-computed-tomography technology was utilized in this study. The evolution of pore-fissure (PF) structure parameters (porosity, PF scale distribution, effective PF volume ratio, and permeability) of bituminous coal under stress-free (SF) and IS conditions with temperature was investigated, and then the mechanism of experimental results was analyzed. Results showed that (1) under SF conditions, at 300–550 °C, the coal samples after pyrolysis are dominated by elongated large fissures, with PF structure parameters positively correlating with temperature. After 400 °C, the number of PFs increases, with most PFs having equivalent diameter (R) ≤ 100 μm. (2) Under IS conditions, coal sample fissures are dominated by elongated large fissures at 300–350 °C and by holes at 350–600 °C. (3) Under IS conditions at 300–600 °C, the PF structure parameters of coal samples initially decrease with temperature and subsequently increase. The number of PFs fluctuates within a certain range, and the PF scale distribution dynamically shifts with temperature. (4) After 300 °C, the PF structure parameters of bituminous coal under SF and IS conditions show a bipolar distribution with temperature. Therefore, the weakening effect of stress on the PF structure of coal samples should not be overlooked during IS pyrolysis mining of coal bodies.

Underground in situ pyrolysis mining of coal will be a new trend for utilizing coal resources in the future. Steam heating is a feasible and key technology used in this process. Investigating the evolution mechanism of microstructural parameters during coal in situ steam pyrolysis is essential. The influence of external stress on microstructural parameters of coal has not been considered in previous studies. Herein, the permeability and fracture structure parameters of bituminous coal subjected to in situ steam pyrolysis were studied using a high-temperature and high-pressure triaxial testing machine combined with in situ micro-computed tomography (micro-CT) technology. Moreover, the advantages of steam pyrolysis were revealed by comparing it with the natural pyrolysis process. Results showed that (1) the evolution law of fracture ratio and the proportion of large fractures (equivalent fracture diameter R >100 mu m) with temperature is consistent. The proportion of large fractures has a considerable impact on the fracture ratio. (2) From 25 degrees C to 600 degrees C, the permeability and fracture structure parameters of bituminous coal exhibit an "increase - decrease-increase" trend with increasing temperature. The threshold temperature points for changing fracture structure parameters are 300 degrees C and 400 degrees C. The promoting effect of pyrolysis on fracture structure parameters competes with the inhibition effect of external stress on fracture development, determining the evolution law of fracture structure parameters with temperature. (3) The threshold temperature zone where the microstructural parameters change considerably is 400 degrees C-600 degrees C. The fracture ratio, proportion of large fractures, and permeability of coal increase considerably. (4) Unlike natural pyrolysis, steam pyrolysis promotes the advancement of threshold temperature point. After 450 degrees C, steam pyrolysis promotes the development of large fractures (R >100 mu m) and the fracture ratio is about twice that observed in case of natural pyrolysis. These findings provide theoretical support for the engineering practice of coal in situ underground pyrolysis mining and are of great importance to the development of micromechanics.

The permeability evolution of bituminous coal under in situ steam pyrolysis was studied combing with in situ CT technology. The results showed that: 1) Permeability varied negatively logarithm with pore pressure, which is related to adsorption expansion; 2) Permeability changed in a "V" shape with temperature. In a range of 300-400 degrees C, the coal sample continues to soften under hydrothermal action, the external stress closed the crack, and permeability decayed; 3) At 400-600 degrees C, the hydrothermal action promoted the pyrolysis of the coal samples and generated more seepage channels. The continuous compression by the external stress on the coal body suppressed the expansion of the pores and fissures. However, the former played a leading role in promoting permeability, and permeability showed a piecewise linear growth. CT results showed that the porosity trend of the coal samples was consistent with that of permeability; 4) Above 400 degrees C, superheated steam promotes the pyrolysis of the coal samples and improved permeability due to its excellent convection and thermal conduc-tivity, drive effect, and participation in chemical reactions.

Because of the strong adsorption characteristics of methane and the low permeability of coal seams, the extraction efficiency of coalbed methane (CBM) is very low. Here, based on the energy conservation equation, we propose the theory of heat injection-enhanced CBM extraction. We developed a device for heat injection-enhanced CBM extraction and performed an on-site heat injection test in the Chengzhuang coal mine. The results showed that when the water injection rate was 0.5 m3/h, the heat injection temperature was 145 °C, with two heat injections, yielding the best CBM extraction effect. This could fully utilize the heat injection equipment and achieve a fast, safe, and efficient extraction. The gas production law of the intermittent heat injection-enhanced CBM extraction method had obvious stages; the CBM concentration and daily gas production were very low during the heat injection stage but were greatly improved during the extraction stage after heat injection. The highest CBM concentration reached 100%, and the maximum daily gas production of CBM increased by 1269 times. The variation law of the cumulative gas production with time was fitted using Wang's empirical formula. Comparative analysis showed that, compared to traditional extraction, intermittent heat injection shortened the extraction time by 6.6 years. Compared with other enhanced CBM extraction methods, the intermittent heat injection method had obvious technical advantages and greater improvements in concentration and CBM extraction speed. Therefore, the results are of great significance for improving the recovery rate of CBM and for reducing greenhouse gas emissions.

The low permeability of coal seams and strong adsorption of methane considerably inhibit gas drainage; thus, developing a method for efficient gas drainage is crucial. The heat injection-enhanced gas drainage tests were carried out in the laboratory and coal mine, and the gas drainage effect and mechanism of heat injection method were studied. Then, through numerical simulation, the gas production law of heat injection method was analyzed from the perspective of water and gas migration. Indoor experiments demonstrated that heat injection strengthened methane desorption and relieved the inhibitory effect of water on gas. The gas drainage effect of field tests was remarkable, and the gas concentration and daily gas production increased by over 10 and 100 times, respectively. During heat injection, water occupied the migration channel of gas, and the inhibition of water on gas was greater than the promotion of temperature, resulting in the reduction of gas production; After heat injection, high temperature promoted gas desorption and relieved the inhibition of water on gas, resulting in a significant increase in gas production. The gas production law obtained from the numerical simulation showed a high degree of consistency with field tests. The results can provide a reference for gas control.

Underground in-situ pyrolysis of coal is a new trend in the utilization of coal resources in the future. It is especially critical to investigate the coal pore-fissure structure, its spatial distribution and connectivity under different pyrolysis methods, and the existing studies on the pore-fissure structure parameters of coal after pyrolysis are in non-stress condition and lack of the comparison of pore-fissure structure parameters under different pyrolysis methods. Based on the above deficiencies, using the self-made triaxial testing machine of thermo-fluid-mechanical-chemical coupling at high temperature and pressure, combined with the micro-CT technology, the fissure structure differences of bituminous coal under the conditions of natural and steam in-situ pyrolysis (600 ℃) were investigated, and then the mechanism of the differences was explored. The results show that ① After the natural and steam in-situ pyrolysis at 600 °C, the fissure forms generated inside the coal sample are mainly slender cracks and holes, and the fissure scale is further improved after steam pyrolysis. The fissure network is more abundant and complex. ② Under the stress condition of 5 MPa axial pressure and 3 MPa confining pressure, after natural pyrolysis, the fissure rate is 2.68 times of the original fissure rate. However, after steam pyrolysis, the fissure rate is 3.65 times of the original fissure rate, and the fissure rate of each layer is more uniform. ③ Steam pyrolysis makes the bituminous coal heated evenly, with large heat exchange area and more adequate pyrolysis of organic matter. The displacement effect ensures the continuous production of pyrolysis products. The local stress effect of pore pressure not only expands the original pore-fissure volume, but also destroys the weak surface of pore wall, which greatly increases the pore connectivity. The steam denudation effect will “scour and transport” the tar with high viscosity attached to the blind fissures out of the coal body. Hydrogen-rich environment promotes the cracking of heavy tar and enhances the fluidity of oil. ④ There are large differences in the fissure rate and fissure morphology between in-situ and non-stress of coal pyrolysis. Steam pyrolysis is the optimal heating method for the engineering practice of in-situ thermal injection coal mining.

Studies on coal permeability at high temperatures (> 300 ℃) under the thermo–hydro–mechanical–chemical (THMC) coupling effect are few and their conclusions are divergent. Herein, the influence of different volumetric stresses (12, 24, and 36 MPa) on bituminous coal permeability is discussed. Moreover, the permeability evolution law of bituminous coal under different pore pressures (0.2–0.8 MPa) and temperatures (300 ℃–600 ℃) are studied using a self-made triaxial test machine with the THMC coupling effect. The experimental findings and micro-computed tomography (micro-CT) test results of coal samples under different temperatures in situ are reported. The obtained results show that (1) bituminous coal permeability underwent a negative logarithmic change with pore pressure (0.2–0.8 MPa) at different temperatures because of gas adsorption–expansion, gas slippage, and shear deformation. (2) Bituminous coal permeability varied with temperature in stages; this result differs from traditional research results. At 300 ℃–450 ℃, the permeability continuously decreased and slightly increased at 450 ℃–600 ℃; however, it was still lower than that at 300 ℃. The micro-CT results show consistent porosity evolution with permeability. (3) At 300 ℃–450 ℃, the permeability attenuation of bituminous coal mainly resulted from coal softening deformation. The continuous increase in the coefficient of linear thermal expansion increased the permeability decay rate. With the increasing temperature from 450 ℃ to 600 ℃, the accelerated pyrolysis of the coal sample enhanced the permeability, the coefficient of linear thermal expansion exhibited a negative correlation with temperature, and the inhibition effect of coal compression on permeability was weakened, slightly increasing the permeability at this stage. However, the continuous compression accumulation effect of stress still played a principal role, inducing low permeability. (4) Under the same temperature and pore pressure, the correlation between the permeability and volumetric stress of the coal samples decreased exponentially.

Coalbed methane (CBM) is strongly adsorbed to coal, with over 95% existing in an adsorbed state, making it difficult to effectively extract using traditional borehole drainage or drainage gas methods, particularly in low permeability and under pressure CBM reservoirs. This study proposes thermal-enhanced CBM extraction by superheated water injection. Laboratory experiments were first conducted to examine deformation and temperature change during coal adsorption/desorption, to quantify adsorption heat at low (room temperature-150 ?) and high (150-240 ?) temperature ranges, and to elucidate the potential physical mechanisms of temperature modulation on coal adsorption of methane. Further experiments studied two-phase methane-water flow under elevated temperature and thermal-induced methane drainage affected by the water lock effect. Pilot field tests then validated the feasibility and effectiveness of this thermal extraction technology based on the theoretical findings. The results demonstrate that (1) energy conversion occurs during coal adsorption/desorption of methane, absorbing heat and causing matrix shrinkage during desorption. (2) Heterogeneous coal adsorption potential requires increased temperature to desorb methane from deep wells into the free state. Under isobaric conditions, adsorption heat is significantly higher at 150-240 ? versus room temperature-150 ? due to potential well depth effects. (3) The gas-driving-water process involves liquid flow, gas-liquid two-phase flow, and gas flow stages. Elevated temperature facilitates water and gas flows, accelerates gas breakthrough, and improves the production rate. (4) High temperature eliminates the water lock effect and increases the desorption rate to around 80% regardless of adsorption pressure, greatly shortening equilibrium time. (5) Further field tests show that the drainage period after thermal injection is only 1/46-1/31 that of the conventional method given the same production volume. Thus, thermal-enhanced CBM extraction is disruptive, with this study providing theoretical and engineering basis.

在井下煤炭开采和瓦斯抽采过程中,裸露的煤壁以及煤柱长期处于瓦斯气体环境中,不断地进行着吸附—解吸过程.本文采取实验方法,利用自主研发设计的恒温定容煤体吸附—解吸实验装置,进行煤体循环吸附—解吸实验,分析了煤体循环吸附/解吸气体的特性规律.实验结果表明:在循环吸附—解吸过程中,煤体的吸附量逐渐减少并趋于平稳;随着吸附—解吸循环次数的增加,吸附罐在吸附前后的压降变化逐渐减小,吸附速率减缓;煤体的解吸量以及解吸率均随着循环次数的增加而逐渐增加,最后趋于平稳;吸附平衡压力越高,解吸率越大,两者呈线性关系.

The heat injection mechanism for improving gas desorption, coal seam gas pressure, and coal seam permeability in the Yangquan mining area was investigated via theoretical analysis. This analysis was conducted to address the problems of poor permeability, difficult gas extraction, and low extraction efficiency of 15# coal seam. An underground heat injection-enhanced gas extraction technology was proposed; accordingly, a heat injection-enhanced gas extraction system was developed and appropriate extraction methods were devised. The findings of an industrial test on 15# coal seam in the coal mine show that the proposed technology not only increased the amount of gas extracted but also halved the extraction time and realized efficient gas extraction. Two mature underground heat injection-enhanced gas extraction methods were established. These methods have similar gas production principles in that the gas production speed and gas concentration in the heat injection stage are relatively low, while the average degree of improvement in the extraction stage after heat injection can reach more than 50 times. The average degree of improvement in gas production speed and gas concentration after the second heat injection is greater than that after the first.