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Based on the generalized gradient approximation (GGA) under the density functional theory system,the first-principles method was used to investigate the effect of gas molecule adsorption on the adsorption energies,energy band structures and optical properties of the V-doped graphene.The band structure calculation showed that the band gap of V-doped graphene adsorbing NO2gas molecule is increased from 0 eV to 0.368eV,and its material property has also changed from metal to semiconductor.However,the band gaps of V-doped graphene adsorbing CO and NH3 molecules are almost unchanged.The adsorption energies of the three adsorption (NO2,CO,NH3) configurations are-8.499 eV,-2.05 eV and-2.01 eV, respectively, indicating that V-doped graphene has the best adsorption effect on NO2gas molecules.Furthermore,the optical properties of intrinsic and doped graphene when adsorbing NO2gas molecules were calculated.The results displayed that the dielectric absorption peak value of graphene is increased with V doping and adsorbing NO2gas,and the dielectric peak position is moved to the low energy region;Intrinsic graphene can only absorb ultraviolet light,and V-doped graphene can significantly improve the spectral range of light absorption after absorbing NO2molecules.The photoconductivity of graphene can be significantly enhanced by the doping and adsorption,and the photocurrent can be generated in the infrared and visible light regions.The above research results show that the electronic structures and optical properties of V-doped graphene adsorbing NO2have been significant changed,and it can be applied as an optical gas sensing material to detect NO2gas. [ABSTRACT FROM AUTHOR]

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The pore structure has a significant impact on the capability of coal seams to adsorb methane. But there is currently limited research on the features of adsorption pore structure in high-rank coal and its influence on methane adsorption capability. Taking the high-rank coal samples from Nuodong Coal Mine of Guizhou Xing'an Coal Industry Co., Ltd. as the research object, low-temperature N2 adsorption and low-temperature CO2 adsorption experiments are conducted. Combined with fractal theory, this paper studies the pore structure features of high-rank coal adsorption pores. Through high-pressure isothermal methane adsorption experiments, the influence of coal reservoir properties, pore structure features, and fractal dimension on methane adsorption capability is analyzed. The results show the following points. ① The pore morphology of high-rank coal reservoirs is relatively simple, mostly consisting of parallel plate pores and narrow slit pores with open ends. Micro pores dominate the pore structure of coal, with pore volume and pore specific surface area accounting for more than 98%, providing space for gas enrichment. ② The method calculates the comprehensive fractal dimension of high-rank coal pores based on the proportion of pore volume in different aperture segments, with micropore fractal dimension dominating the comprehensive fractal dimension. The pore structure of coal samples has obvious fractal features and strong heterogeneity of pores. ③ The Langmuir model can describe the adsorption behavior of high-rank coal. The physical properties, pore structure, and fractal dimension of coal reservoirs have a significant impact on methane adsorption capability. Langmuir volume is linearly positively correlated with maximum vitrinite reflectance, vitrinite content, ash content, and moisture content. It is linearly negatively correlated with inertinite content. The Langmuir volume is linearly positively correlated with the pore specific surface area and pore volume of the adsorption pores. The Langmuir volume is weakly linearly correlated with the fractal dimension. The research results can provide theoretical guidance for the exploration and development of high-rank coalbed methane and the prevention and control of coal mine methane disasters in southwestern Guizhou.

Based on the generalized gradient approximation（GGA) under the density functional theory system, the first-principles approach was used to investigate the ability of SiGe nanowires along the [112] crystallographic orientation as molecular sensors to detect CO, CO2 and Cl2. The adsorption energies, energy band structures and optical properties before and after adsorption of gas molecules were mainly calculated. The calculation of geometric structure optimization shows that the absolute values of adsorption energy of CO, CO2 and Cl2 molecules on the [112] crystal orientation of SiGe nanowires with different SiGe compositions are between 0.001 eV and 1.36 eV, and the adsorption energy of Si24Ge36H32 for CO2 gas is maximum and gas sensing performance is the best. The energy band structure calculation shows that the energy band degeneracy of the [112] crystal-oriented SiGe nanowires adsorbed by CO and CO2 molecules is significantly reduced, and the band gap change is small. The impurity energy level is generated between the top of the valence band and the bottom of the conduction band after adsorption of Cl2 molecules, which reduces the band gap. The calculation of optical properties shows that the optical properties of Si24Ge36H32 nanowires after adsorptions of CO, CO2 and Cl2 molecules are obviously different, which is mainly reflected in the range of the absorption spectrum and the amplitude of the absorption peak. The above research results provide a theoretical basis for [112] Si24Ge36H32 nanowires as a sensitive material for gas sensors. [ABSTRACT FROM AUTHOR]

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

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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.

In order to study the evolution mechanism of microfracture apparent permeability under the effect of effective stress, gas adsorption and slip effect during shale-gas extraction, the fractal theory was used to characterize the total gas flow in microfracture, and an apparent permeability model of the combined effects of microfracture deformation and slip effect based on the Hagen-Poiseuille second-order slip equation was established. Meanwhile, the influence of effective stress and gas adsorption on the slip coefficient was quantified by combining with the functional relationship between the slip coefficient and intrinsic permeability, the dynamic evolution of the slip coefficient during shale-gas seepage was explored, and the reliability of the model was verified. In addition, the effects of microfracture compressibility coefficient, fractal dimension and internal expansion coefficient on slip coefficient were explored in conjunction with sensitivity analysis. The results shown that, (1) Under the conditions of constant external and effective stress, the apparent permeability tended to decrease with the gradual increase of pore pressure, which was influenced by the coupling of gas adsorption and slip effect. (2) When the external stress was constant, the average free range of gas molecules decreased with increasing pore pressure, the slip effect was weakened, the first-order and second-order slip coefficients C1 and C2 decreased, and the overall slip coefficient B increased. When the effective stress was constant, the shale-gas seepage channel was subject to gas adsorption and gradually reduced, and C1, C2 and B gradually increased. (3) Based on the model sensitivity analysis, the reciprocal feedback mechanism between microfracture compressibility coefficient, fractal dimension, internal expansion coefficient and slip coefficient was explored, in which the microfracture compressibility coefficient and fractal dimension led to an increase in intrinsic permeability, and a decrease in C1, C2 and B decrease. The increase of internal expansion coefficient led to an decrease in the intrinsic permeability, and an increase in C1, C2 and B. The findings of this study will provide some theoretical support for shale-gas extraction.

Micro-pore structure affects the fluid storage and seepage in coal seams.In this paper, six samples from the Jurassic Yan'an Formation coal seam in the Shenmu area of the Ordos Basin were taken as the object of study.The pore distribution characteristics of coal seams were jointly characterized by NMR, CO2 adsorption and N2 adsorption at multiple scales, and the connectivity and homogeneity of microscopic pores were investigated by combining multi-scale joint characiterization with CT scanning.Results show that the micro-pores of coal are the main contributors to the specific surface area and pore volume, followed by meso-pores.There is a good uniformity in the pore size distribution of the micro-pores and meso-pores by combing NMR and adsorption, while considerable differences are found in the macro-pores.Displacement NMR and CT excel in reflecting the degree of connectivity, both of which are consistent in the characterization of connectivity.Parameters such as coordination number and seepage pore ratio can effectively reflect the degree of connectivity of the sample, whose patterns of connectivity is M6>M2>M12>M15>M10>M4.The saturation of bound water shows a satisfactory positive correlation with pore-throat ratio of coal samples.It can be seen that the pore structure has a great influence on the degree of fluid migration, which is the basis for studying and evaluating gas occurrence and seepage.

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Information on SF6 decomposition components can be detected using gas-sensitive sensor methods to assess the operational status of GIS equipment and detect the insulation defects early. Metal-doped SnP3 monolayer has good adsorption properties, which makes it promising for gas detection applications. Based on the first-principles, the parameters of adsorption energy, density of states, energy gap and desorption time of the system after the adsorption of SO2, H2 S, SOF2 and SO2 F2 by Pd-SnP3 monolayer were calculated and analyzed to explore the possibility of using this material for gas sensors. The results show that, in terms of adsorption performance, Pd-SnP3 monolayer only chemisorb SO2 F2. Combined with the results of density of states, differential charge density and transfer charge analysis, it is verified that the adsorption of SO2 F2 is significantly better than that of SO2, H2 S and SOF2. In terms of sensing characteristics, only the adsorption of SO2 F2 causes significant change in the energy gap of the system, and desorption of SO2 F2 from the Pd-SnP3 monolayer surface rapidly occur at temperature of 398 K and above. Therefore, the Pd-SnP3 monolayer has the potential to become a gas-sensitive material for the detection of SO2 F2 for its high selectivity and detectability to SO2 F2. This study provides a theoretical basis for the application of Pd-SnP3 monolayers in the field of gas-sensitive materials. [ABSTRACT FROM AUTHOR]

With the development of coal seam fracturing technology, promote the gas extraction by liquid nitrogen cold soaking fracturing coal has attracted widespread attention. In order to study the effect of liquid nitrogen cold soaking on the microstructures of different coals (lean coal, fat coal and anthracite) before and after liquid nitrogen cold soaking, the scanning electron microscopy (SEM), pore size distribution instrument and physical adsorption instrument were jointly characterized. The influence of liquid nitrogen cold soaking on the distribution of pore volume and specific surface area of different coal samples was comparatively analyzed. The results show that the thermal stress generated during the liquid nitrogen cold soaking destroys the microstructure of the coal or causes the initiation of micro-cracks, After liquid nitrogen cold soaking, the total pore volume and specific surface area of coal samples increase. The total pore volume growth rate of fat coal is the lowest, followed by anthracite, and the lean coal’s is the highest. The volume of micropores, micropores, meso-pores and macropores/fractures in the coal samples increase. cold leaching of liquid nitrogen causes macropores to pass through and form macropores/fissures in coal samples, resulting in the reduction of pore volume of macropores. After liquid nitrogen cold soaking, the pore specific surface area of each coal sample concentrate in the range of 10 − 100 nm, and has obvious peak characteristics. Liquid nitrogen cold soaking can increase the adsorption capacity of lean coal, fat coal and anthracite coal samples, and the adsorption capacity difference is the largest in the middle high pressure region (0.4 < p/p0 < 1.0). Liquid nitrogen cold soaking can effectively transform the internal microstructure of different coals. The research results are helpful to reveal the spatial expansion and connectivity of macroscopic and microscopic pore fractures in coal reservoirs during liquid nitrogen cracking.

In this work, a steam-assisted method is used to prepare bimetallic organic framework materials （bimetallic MOFs). Co, Fe, Mn, Zn, and Ni as the secondary metals are exchanged in the structure of PCN-6 which has large specific surface area and high porosity, and a series of PCN-6（M）（M=Co/Fe/Mn/Zn/Ni） bimetallic materials are obtained. Their structure, morphology, composition, and adsorption properties are characterized by powder X-ray diffraction（PXRD), scanning electron microscopy（SEM), energy dispersive spectroscopy（EDS), inductively coupled plasma-atomic emission spectroscopy（ICP-OES), and gas adsorption methods. The results show that the diffraction peaks and morphology of the PCN-6（M） series bimetallic materials are consistent with the parent material PCN-6, and the exchanged metals content reaches 12. 1% for Co, 22. 0% for Fe, 16. 1% for Mn, 17. 5% for Zn, and 16. 8% for Ni, respectively, which is much higher than the metal exchange capacity of solvothermal method （about 5. 0%） under the same conditions. In terms of gas adsorption performance, PCN-6（Zn), PCN-6（Ni） and PCN-6（Co） have better adsorption capacity for CH4 and CO2 than the parent material, especially at low pressure. In addition, the adsorption selectivity of V（CO2 ）∶V（CH4 ）=50∶50, PCN-6 （Fe） is superior to the parent material by theoretical ideal adsorption solution theory （IAST） calculation. The preparation of bimetallic MOFs by steam-assisted method can improve the exchange capacity of metals and change the affinity of MOFs to different gas molecules, thereby improving the gas adsorption performance and selectivity of materials. The steam-assisted method provides a new idea for the preparation of bimetallic MOFs, which is expected to be used in the preparation of other materials. [ABSTRACT FROM AUTHOR]

In order to obtain the energy change rule in coal adsorbing methane process, methane adsorption experiments were carried out with the temperature of 30 ℃, 15 ℃, 0 ℃, -15℃, -30 ℃, -45 ℃ and the initial adsorption pressure of 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa by the high and low temperature intelligent adsorption experiment chamber. The results show that increasing the gas injection pressure and decreasing the adsorption temperature are two important factors that affect the increase of temperature variation in the process of methane adsorption; the surface free energy of coal samples with a certain mass decreases and the heat increases before and after methane adsorption, and the difference increases gradually due to the increase of methane pressure; in the process of coal adsorbing methane, either pressure boost or temperature drop will increase the coal temperature variation, it is essentially a phenomenon that methane molecular potential energy of coal surface free energy is converted into heat value to maintain the overall energy balance.

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In order to accurately measure the coal gas adsorption capacity and gas content under the influence of water content, soft and hard anthracite is taken as the research object, and molecular adsorption module is used to establish the coal macromolecular structure model of four coal samples under the conditions of 0%, 1%, 3% and 5% water content. The applicability of linear equation, traditional linear equation, power function equation and exponential equation in quantitative characterization of water content was further compared. The results show that the isothermal adsorption curves of soft and hard coals under different moisture content conform to the characteristics of type I isotherm, and the Langmuir volume of soft coal is higher than that of hard coal, and the Langmuir volume of the four anthracite coals is most sensitive to the change of water content when the moisture content is 0%-1%. The water influence coefficient of soft and hard anthracite gas adsorption capacity under water effect is more suitable for linear equation characterization. At the same time, the influence degree coefficient a of water content of soft coal is small, that is, the change of water content has a more significant influence on the gas adsorption capacity of soft coal.

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

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Copyright of Journal of Petrochemical Universities / Shiyou Huagong Gaodeng Xuexiao Xuebao is the property of Journal Editorial Department Of Liaoning Shihua University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to deeply understand the control mechanism of gas adsorption on coal permeability, based on the seepage experiment, the variation of coal permeability of helium, nitrogen and carbon dioxide under different pressures and effective stress was studied by using triaxial percolation apparatus. The conclusions are follows: under the same conditions, the permeability of the three gases is helium>nitrogen>carbon dioxide, and the permeability of carbon dioxide is most significantly affected by adsorption deformation. The relationship between gas adsorption and effective stress is competitive on coal permeability under the constant external stress. The gas adsorption is stronger than the effective stress in low pressure stage, but on the contrary in high pressure stage, the coal permeability firstly decreases and then increases. When the pressure is constant, the permeability of three kinds of gas decreases with the increase of effective stress. Under the same effective stress, the permeability damage rates of nitrogen and carbon dioxide are higher than that of helium. At the same time, the decline of permeability at 2 MPa can reach up to 30.98% than that at 1 MPa, and the average compressibility is about 15%.

In order to explore the application of acidizing technology in coal seam permeability enhancement, the paper carried out the research on gas adsorption performance and micro-mechanism of acidizing modified coal samples. Ten groups of modified coal samples of lignite and coking coal were prepared by hydrochloric acid solution with different pH values. The industrial analysis, gas adsorption test and low temperature nitrogen adsorption test of modified coal and raw coal were carried out respectively. The results of gas adsorption test show that acid modification can change the adsorption properties of coal samples. When the pH value is equal to 3, the adsorption properties of modified coal samples decrease, while the adsorption properties of other modified coal samples are higher than that of raw coal. Analysis of low temperature nitrogen adsorption test results shows that lignite is dominated by pores of 10-100 nm, while coking coal is dominated by pores of 2-10 nm. The specific surface area of modified coal samples with pH value of 3 decreases and the pore volume of samples more than 100 nm increases. Fractal dimension of each group of coal samples is calculated by fractal theory, and the fractal dimension of coking coal is positively correlated with lignite pores and mesopores and gas adsorption constant a. The modification of coal with suitable acid can change the adsorption property of coal and increase the permeability of coal.

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

To grasp the difference of different inert gas flame retardancy in different oxidation stages of coal, in this paper, an adiabatic oxidation device is used, and non-adsorbable helium is used as the reference gas to design inert （N2、CO2） flame retardant experiments with different initial temperatures （70、110、150℃）. Taking the temperature and oxygen concentration of the coal sample after inert gas injection as assessment indicators, the flame-retardant effects of different inert gases were compared and studied. The results show that the apparent activation energy of the experimental coal sample is 47 kJ/mol, and the critical temperature of spontaneous combustion is 83 ℃. The higher the initial temperature, the longer it takes to cool down to 30 ℃. After injecting different inert gases at the same initial temperature, helium has the best flame retardant effect, followed by nitrogen, and carbon dioxide is the worst. The replacement rate of nitrogen and carbon dioxide for oxygen increases with the increase of temperature. When the initial temperature is the same, the cooling rate and relative displacement of nitrogen injected are larger than those of carbon dioxide injected, and the flame retardant efficiency of nitrogen is better than that of carbon dioxide.

The degree of coal pulverization leads to the difference of gas adsorption state in coal, which has an important impact on the gas migration time in coal pores. The research results play an important role in improving the accuracy of gas content determination in coal. In this paper, coal samples from Machang Mine were chosen as the research object to observe the relationship between particle size and the equilibrium time, the adsorption isotherms and the adsorption equilibrium time of coal with four degrees of particle sizes are measured in the laboratory. The conclusions are as follows: the smaller the degree of particle sizes is, the larger the gas adsorption capacity of coal sample is. The isotherms can be divided into four parts: “micron, ten microns and small particle size hundred microns, large particle size hundred microns and millimeter”. With the increase of particle size degree, coal sample adsorption equilibrium time is rapidly increasing, in which, the adsorption equilibrium time for the coal sample with the minimum particle size was only 5 min, but for the largest particle size was more than dozens of days, which means that the impact of diffusion path will increase rapidly with the increase of degree of particle sizes. Comprehensive analysis shows that the adsorption equilibrium time of coal sample with 100 μm particle size can be significantly shortened and the gas content determination accuracy can be improved.

To study the physicochemical structure characteristics of coal and its effect on the thermodynamic of gas adsorption, the physicochemical structure of coal was characterized by low pressure nitrogen adsorption and FTIR experiment. The gas adsorption curves of lean coal and long-flame coal at different temperatures were measured using isothermal adsorption experiment. Langmuir model and Freundlich model were used to fit the empirical data and the thermodynamic parameter △G° based on two models was calculated. The results show that Freundlich model is suitable to describe the thermodynamic process of gas adsorption and the gas adsorption process is characterized by spontaneous at different temperatures. It was found that the pore structure of long flame coal is more beneficial to the adsorption process, while the surface chemical structure of lean coal benefits the adsorption process more. The joint action of pore structure and functional groups affects the adsorption capacity of gas. Besides, △G° obviously shows the different characteristics of pore structure of coal. Thus, the adsorption amount and △G° should be considered together for comprehensive evaluation on the adsorption performance of gas with different metamorphic degrees coals.

In order to clarify the mapping law of adsorption capacity, porosity and deformation of gas bearing coal, the influence of adsorption amount on porosity and deformation of coal sample under different gas pressures was analyzed theoretically based on the process of testing isothermal curve of coal adsorbing gas by high pressure volumetric method; the adsorption capacity of gas bearing coal was studied by combining industrial CT technology and high pressure capacity method. The results show that with the increase of adsorbed gas, the porosity of coal gradually decreases and tends to a stable value; the higher the coal metamorphism degree is, the slower the porosity evolution trend is; the volume strain of coal presents approximate linear growth.

In this paper, multifractal analysis from low-temperature nitrogen adsorption isotherm was employed to analyze the heterogeneity of pore distribution of low-volatile bituminous coal, and the effect of macreal composition on the distribution of pore heterogeneity was discussed. The results show that the generalized dimension Dq decrease as q increases, demonstrating a multifractal behavior of pore distribution of coal derived from low-temperature nitrogen adsorption. However, the degree of multifractality shows differences among coal with various maceral composition. In comparison of vitrinite-rich coals, the Dq values of the width of left side D-5-D0 of inertinite-rich coals decrease while the values of information dimension D1 and Hurst exponent H increase. The above results show that with the increasing inertinite, the pore structure becomes simple, the clustering of pores decreases, the pore connectivity increases, resulting in the reductionin heterogeneity of pore distribution. For the same rank coal, the D1, H and D-5-D0 are the major indexes to differentiate between heterogeneity of pore distribution of coal with different maceral composition.

In order to study influence of temperature and pressure on gas adsorption and desorption characteristics of coal sample, adsorption capacity, isosteric heat of adsorption, Langmuir adsorption constant, initial effective diffusion coefficient and diffusion kinetic parameter under different temperatures(20,25,30,35,40,45,50 ℃) and pressure(0-5 MPa) were analyzed by use of gas adsorption and desorption experimental device. The results show that adsorption capacity decreases with the increase of temperature and increases with the increase of pressure. When adsorption capacity is constant, the higher the temperature is, the greater the gas adsorption pressure is, and isosteric heat of adsorption increases with the increase of adsorption capacity. Langmuir adsorption constant a decreases firstly, and then rises and decreases again with the increase of temperature, and reaches peak value at 45 ℃, while Langmuir adsorption constant b decreases with the increase of temperature. Initial effective diffusion coefficient and diffusion kinetic parameter increase with the increase of temperature, and increase amplitude is most obvious at 35-40 ℃.

To explore the rules of the expansion of blasting cracks in coal under different gas pressures, based on the research results that the mechanical properties of gas-containing coal are different from those of ordinary coal, the strength modification is carried out on the basis of the physical and mechanical parameters of ordinary coal to determine the mechanical parameters of gas-containing coal. LS-DYNA finite element software is used to simulate the expansion of coal blasting cracks under different gas pressures, and the propagation and attenuation law of stress field in ordinary and gas-containing coal are analyzed. The results show that the radius of coal crushing zone and fracture zone increases with the increase of gas pressure, and the distribution of fracture is denser. In the near area of blasting, the peak pressure of gas-containing coal unit decreases slightly with the increase of gas pressure; in the far area of blasting, the peak pressure of unit increases, and the attenuation rate of stress field in gas-containing coal is lower than that of ordinary coal, and the stress action time increases, which causes the coal to break.

In order to explore and select the appropriate acid solution to improve the permeability of coal, experiments were carried out to study on the adsorption characteristics of coal samples modified by acid solution at different pH values. Through collecting coking coal samples, eight groups of raw coal and acidification modified coal samples with different pH values were prepared. The industrial analysis and physical parameters test of the samples were carried out, and then the isothermal gas adsorption test was carried out. The experimental results show that: compared to the raw coal sample, acidification modified can reduce the ash content of coal sample without changing volatile coal sample; the true density of the modified sample is similar to that of the raw coal sample, but the apparent density decreases slightly. With the increase of pressure, the gas adsorption capacity of the modified coal sample is obviously greater than that of the raw coal sample. The adsorption constant a decreases with the increase of pH value（except pH=1）, while the adsorption constant b generally decreases with the increase of pH value. The results show that the pore structure of coal body can be changed and the adsorption capacity of coal body can be increased by selecting appropriate pH value solution to modify the specific coal seam, realize the effect of coal seam permeability enhancement finally.

In order to study the effect of the fractal characteristics of gas coal pores on gas adsorption, the pore structure of Fukang gas coal was tested by the low temperature liquid nitrogen adsorption method, the FHH model was used to calculate the fractal dimension of experimental coal samples, the adsorption characteristics of coal samples were determined by high pressure volumetric method, the relationship between the fractal dimension of gas coal and the gas adsorption performance was analyzed. It is shown through the experimental results that the surface fractal dimension D1 is positively correlated with Langmuir volume VL and negatively correlated with Langmuir pressure pL, but the correlation between the structural fractal dimension D2 and the Langmuir volume VL and Langmuir pressure pL of coal samples is not obvious. It is shown through the analysis that pore structure distribution and pore type of the gas coal affect the gas migration of the coal pores.

Aiming at the methane adsorption dynamics characteristics of tectonic coals, Yuwu Coal Mine of Lu’an Group in Shanxi Province was chosen as the engineering background. Four tectonic coal samples with different degrees of destruction were selected for high-pressure mercury intrusion porosimetry and methane isothermal adsorption experiments, and the pore distribution characteristics in coal and methane adsorption dynamics curves were obtained. The changing laws of adsorption pressure, adsorption volume and adsorption speed with time were analyzed. The research result shows that the adsorption pressure is decreased with the increase of time. At the initial 20 min of the adsorption, pressure sharply declines with the decreasing amplitude, more than 60%. As the increase of adsorption time, the methane adsorption volume experiences a nonlinear changing process: dramatical increase-slow rise-reaching equilibrium. The adsorption speed curves indicate that both the methane adsorption speed and adsorption capacity are enhanced with the increase of the degree of destruction. The pore distribution characteristics of tectonic coals with different destruction types vary a lot, further affecting the methane adsorption dynamics, which should be considered in the engineering practice for coalmine gas control and methane exploitation.

To study the cause of abnormal CO emission in coal seams at igneous rock intrusion sites, and quantitatively describe the effects of thermal effects and time of magma intrusion on coal seam pore structure and gas adsorption capacity, the raw coal samples were treated with different temperature and time by anaerobic heating method, and the vitrinite reflectance experiment, mercury intrusion experiment and adsorption experiment were carried out. The results show that under the temperature and time conditions of this experiment, the effect of heat on the pore structure of coal sample is stronger than time; the thermal action increases the number of pores, total pore volume and large pore volume of coal samples, and the pores of coal samples change from semi-closed to fully open, and the connectivity between the voids is enhanced; the adsorption amount of CH4 and CO in coal samples is proportional to the heat application temperature, and the thermal action changes the pore structure of the coal sample to improve the adsorption capacity of the coal sample for the two gases.

Coal strongly adsorbs methane and during the adsorption process there is always a thermal effect that leads to some changes in the coal structure and temperature. These changes have an electrical effect, such as a change in coal resistivity. The investigation of the thermoelectric effect of the adsorption process of coal has long been a hot research issue to industry experts and scholars. It is important that this thermoelectric effect be well understand with respect to the energy transfer and translation in the adsorption process, as well as to support geophysical electrical prospecting and disaster prediction. Both domestic and international scholars have conducted many studies on this issue. The heating and electrical effects in the process of coal adsorption are interrelated. Previous research has primarily addressed the single characteristic of gas adsorption or its application, with little attention being paid to their correlation. Most studies have used adsorption quantity to reflect the coal adsorption ability, and few have focused on the thermoelectric effect to study coal adsorption. Studies regarding coal particle size and the thermoelectric effect are even rarer. In this study, we investigated the temperature change and the current vs. time curves of three different metamorphic grade briquette coals, which consist of five different coal particle sizes, at a temperature of 25℃ and pressure of 3 MPa in the coal gas adsorption process. To do so, we used a SH-X multi-channel temperature tester and CHI660E electrochemical workstation. To determine the adsorption ability of coal with respect to the thermoelectric effect, we used the Clausius-Lapeyron equation to analyze the thermoelectric effect mechanism of coal and its correlation in the coal gas adsorption process of different particle sizes. The results show that an obvious thermoelectric effect accompanies the coal gas adsorption process. The temperature of the coal increases from 0.93℃ to 8.74℃ and the resistivity of the coal decreases 0.14-0.16 times from that of its stability when it reaches adsorption equilibrium. We found the temperature of the coal to increase as the particle size decreased and the gas adsorption quantity increased, but the coal resistivity change was the opposite. Coal temperature and resistivity change are strongly correlated with the gas adsorption quantity, with the correlation coefficients rd and rw ranging between 0.9502-0.9899 and -0.9316 to -0.9916, respectively, which are close to±1. Therefore, the heat adsorption process can reflect the adsorption ability of coal. When reaching equilibrium, the greater the temperature change, the higher the temperature and the lower the resistivity, which means that the adsorption capacity is greater, and in contrast, the adsorption capacity is weaker.

In order to study influence of adsorption pressure and grain size of coal sample on coal gas desorption, the No.3 coal in Sihe Coal Mine was selected as samples, and variety characteristics of gas desorption amount and desorption speed of coal samples with 0.17-0.25, 0.25-0.50, 1-3 mm grain sizes were analyzed at 1, 1.5, 3 MPa adsorption pressure by use of a gas isothermal adsorption and desorption experiment system. The experimental results show that under different adsorption pressure conditions, the gas desorption amount of the coal samples and initial desorption speed increase with the increase of adsorption on the whole. However, the influence of adsorption pressure on gas desorption amount and desorption speed of coal samples with 0.25-0.50 mm grain size is smaller than the other two grain sizes. The initial gas desorption amount of coal samples with smaller grain sizes is more than the one of the coal sample with bigger grain size under different adsorption pressure conditions, and the initial desorption speed is faster. But the gas desorption amount of the coal sample with 1.0-3.0 mm grain size is more than the one of the others under 1.5, 3 MPa adsorption pressure condition. Therefore, increasing adsorption pressure of coal sample or reducing grain size would cause increase of gas desorption amount and desorption speed.

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

Coal samples of six outburst coal seams in coal-rich areas in Guizhou province were taken as research objects to analyze size grade of pore, fractal dimension, fractal characteristics and relationship between the fractal characteristics and gas adsorption or coal permeability by use of liquid nitrogen adsorption experiment and mercury intrusion experiment. The experimental results show that pores of the coal samples with different grades have good fractal characteristics, which can show porosity and pore distribution characteristics. The fractal dimension can be used to quantitatively analyze pore characteristics of coal samples. There is a positive correlation between the fractal dimension of micro pore of the coal samples and gas adsorption value. Gas adsorption capacity of coal samples in different coals is quite different. The fractal dimension of small pore reflects simple pore structures of coal samples and pore similarity among coal samples. The fractal dimensions of medium pore, large pore, pore fracture and micro fracture show that pore distribution trend of each coal sample is similar. Pores with some size grades develop badly, so measure for increasing the permeability of coal seam are needed to improve gas drainage effect.

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The gas adsorption process of coal is an exothermic process and the desorption process is an endothermic process.The extent of temperature and energy changes is related to the degree of coal metamorphism, and the equilibrium pressure of gas adsorption, etc. The data of gas adsorption were obtained by using isothermal adsorption experiments, and the influencing factors of coal adsorption gas was analyzed through its pore structure and interaction force.However, few scholars have explored the mechanism of coal adsorbing gas from the perspective of the change of surface Gibbs function.Therefore, the calculation formulas of relevant characteristic parameters of the change of Gibbs function of coal specific surface in gas adsorption process were studied.Isothermal adsorption experiments were carried out using two coal samples from Fenghuangshan Mine and Qigou Mine in China.The data of isothermal adsorption experiment at four different temperatures( 20, 30, 40 and 50 C°) and six different pressures( 0.2, 1.2, 1.5, 2.5, 3.0 and 4.0 MPa)were obtained.The specific surface Gibbs functions during the gas adsorption of different coal samples were calculated by using single-layer adsorption and multi-layer adsorption models. Studies showed that the specific surface Gibbs function of methane adsorbed on coal samples was calculated in two different ways, the change of Gibbs function of specific surface decreases with the increase of temperature and increases with the increase of pressure. The results of single-layer adsorption and multi-layer adsorption were quite different and this phenomenon was analyzed.The heat of the gas adsorption and desorption process was calculated.It can be seen from the calculation of heat that the specific surface Gibbs function obtained by using the multi-layer BET adsorption model is closer to the actual situation. The mechanism of energy change in gas adsorption was discussed.The results show that the change of gas adsorption energy affects the change of adsorption capacity, and the change of energy is also affected by the microstructure and internal chemical structure of coal samples.Therefore, the adsorption and desorption of coal samples is a complex and changeable process.To explore how to influence gas desorption can improve the gas extraction effect from the perspective of changing energy. [ABSTRACT FROM AUTHOR]

In order to analyze influence of coal particle size on initial speed of methane diffusion, the relationship of particle size and initial speed of methane diffusion of coal samples with different moisture content was tested by use of WT-1 type initial speed of methane diffusion tester. The coal samples were collected in No.4 coal seam in a coal mine with different particle sizes of less than 7 mesh, 7-10 mesh, 10-18 mesh, 18-35 mesh and different moisture content of natural drying, drying, 3%, 5% and 7%. And the initial speed of methane diffusion of coal samples of natural drying and drying for 5 h were tested, which were with different particle sizes of less than 7 mesh & 35-60 mesh,7-10 mesh & 35~60 mesh, and 10-18 mesh & 35-60 mesh under different proportion of 6∶1,5∶2,4∶3,3∶4,2∶5 and 1∶6. The experimental results show that initial speed of methane diffusion of coal samples with different moisture content increases as the particle size decreases, and the particle size smaller, the increasing trend is more obvious; the proportion of coal particles with small particle size in coal seam larger, the initial speed of methane diffusion of coal samples is larger.

In order to verify the influence law of water content in coal to gas adsorption and desorption characteristics, gas adsorption and desorption experiments were carried out in different equilibrium pressure conditions with different water content in coal. The experiment results show that the gas adsorption capacity decreases with increasing of water content in coal, it could be corrected by use of water content influence coefficient in practical application. With the water content increasing, the gas desorption became slower and the amount of gas remaining was greater. The water filled in the coal gap has inhibitory effect to gas adsorption and desorption.

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

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

In order to verify the universality of Darcy law in coal particle gas flow，the coal particle gas adsorption experiment in enclosed space under variable pressures was designed on the basis of the constant pressure adsorption and desorption and variable pressure desorption experiments of different coal particles shapes. And the gas accumulative adsorption amount with time variation of 42.976，11.600~13.800，3.350~4.000 and 1.180~1.400 mm coal particles under 0.5，1，2 and 4 MPa initial pressures were obtained.Based on Darcy and Fick law，the gas adsorption mathematical models were proposed separately. The use of finite difference method，combined with the computer program coded in Visual Basic，enabled to solve the equations. And the gas accumulative adsorption amount of two models at different times and different initial gas pressures were obtained.By comparing and analyzing ln[1-(Qt/Q∞)2]vs.t diagrams from experiment and numerical simulation，it is found that the gas adsorption process of coal particles in the enclosed space also follows Darcy's law. This conclusion is consistent with a series of previous researches，namely whether the adsorption or desorption process，and the coal particle external pressure and the coal particle shape change or not，it is concluded that Darcy law is the basic rule of coal particle gas flow. [ABSTRACT FROM AUTHOR]

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

While 3D stress or strain measurement in coals is significant for understanding the mechanism of rock burst, gas adsorption, coal and gas outburst,few experimental techniques exist that can really provide full field 3D strain distribution inside a coal specimen in lab. By using a newly developed digital volumetric speckle photography (DVSP) combined with Micro-focus industrial computed tomography (ICT), the interior deformation fields of coal specimen under uniaxial compression and in CO, sorption were measured respectively, and then the 3D strain fields were calculated. The results prove that the internal natural structure of coal specimens can be seen as speckle structure carrying deformation information, and be applied to measure the deformation. Wilh the help of the visual distributions of equivalent strain and volumetric strain,the onset and development of strain localizations are displayed directly. There are obvious strain localization characteristics in the deformation and failure process of coals,and the strain localization zones are consistent with the final position of failure surface in the specimen. 3D strain fields in the coal specimen under CO, sorption were obtained by using DVSP,and the results were consistent with the strain by the gages. From the volumetric strain distributions under different lime, it directly indicates that there are expanded areas as well as shrunk areas in the specimen, and the deformation is not uniform because of heterogeneity. [ABSTRACT FROM AUTHOR]