Gas Diffusion Characteristics Research Articles

Diffusion process simulation and ventilation strategy for small-hole natural gas leakage in utility tunnels

The utility tunnel provides enough spaces, dry environment, better monitoring and maintenance for municipal pipelines. When gas pipelines are incorporated into the utility tunnel, the flammability and explosion property of the natural gas would threaten its safe operation. At present, the safety prevention technology and the safety design specifications for gas pipeline in utility tunnels are not mature. To investigate the gas diffusion characteristics in the utility tunnel, and to propose an emergency accident ventilation strategy, in this paper, the mechanism of small-hole gas leakage diffusion under natural and mechanical ventilation is studied, and the influential factors are simulated and analyzed in detail using the Fluent software. The results indicate that under the natural ventilation, the gas spreads to the whole compartment at the leakage time of 300 s, while under the normal ventilation scheme, the leaked natural gas fills the downstream half of the compartment at the time of 120 s. When the leak size and pressure increase, the alarm response time shortens, the concentration of test point increases, and the danger zone expands. To prevent alarm failure and gas gathering for the near-outlet leakage, it is recommended that the last detector and the air outlet should be placed as close as possible to the fireproof wall. In addition, when a leak occurs, increasing the air change rate can greatly reduce the overall gas concentration. When the leak size is no more than 5 mm, and the pipeline pressure is lower than 0.4 MPa, the minimum accident ventilation scheme could guarantee the safe operation of the utility tunnel. When the pipeline pressure grows to 0.8 MPa, the effective air change rates of the emergency accident ventilation are 15 times/h, 18 times/h, and 24 times/h, respectively for the leak sizes of 4 mm, 5 mm, and 6 mm. Moreover, for the pipeline pressure of 1.6 MPa, the effective air change rates are 21 times/h, 30 times/h, and 36 times/h, respectively for the leak sizes of 4 mm, 5 mm, and 6 mm.

A Study of the Differences in the Gas Diffusion and Migration Characteristics of Soft and Hard Coal in High Gas Coal Seams

At the present time, it is of major significance to examine the differences in the gas diffusion and migration characteristics of soft and hard coal in order to prevent and control safety hazards in high gas coal seams. In this study, the differences in the gas diffusion and migration characteristics between soft coal and hard coal were examined in detail using macrostructural, mesostructural, and microstructural research methods. The root causes of the differences in the gas diffusion and migration between soft coal and hard coal were revealed in the obtained research results. The study shows that, in terms of the macrostructures, the soft coal particle grains were flakey and with shapes resembling fingernails. Meanwhile, the hard coal particle grains were observed to be in the shapes of complete blocks. In addition, in terms of the mesostructures of the different coal types, it was found that the proportion of granular coal below the particle size limit of 6 mm in the soft coal was much higher than that of the hard coal. Also, from the aspect of the characteristics of the microstructures, the pores and fissures on the soft coal surfaces were observed to be better developed, and the BJH specific surface areas of the soft coal were more than twice those of the hard coal. That is to say, the gas diffusion and migration conditions of the soft coal were better than those of the hard coal. At the same time, the increments of the specific surface areas and volumes of the pores of soft coal were above 100 nm, which provided channels for gas diffusion and migration at rates of more than twice those of the hard coal. Therefore, the soft coal was more conducive to gas emissions. This study conducted gas desorption experiments on both soft and hard coal samples and found that the initial gas desorption speed of the soft coal was significantly higher than that of the hard coal. Since the instantaneous gas emissions of the soft coal were significantly higher than those of the hard coal, it was considered to be more likely that gas outbursts and transfinite accidents could potentially occur in the soft coal layers of a project site. This study’s results provided a foundation and basis for effective gas control measures in coal seams composed of soft coal layers, which will be of major significance to the safety of coal mining activities in the future.

Effects of pulse wave on the variation of coal pore structure in pulsating hydraulic fracturing process of coal seam

Coal pore structure is not only closely related to gas adsorption, but also affect the dynamic characteristics of gas desorption and diffusion. In order to understand the influence of pulsating hydraulic fracturing on the variation of coal pore structure, in this paper, the mercury intrusion method and liquid nitrogen adsorption method were used to quantitatively analyze the changes of coal porosity and pore size distribution under the action of pulse wave. And combined with scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) test to study the variation of minerals on the surface of coal samples. The results show that the influence of pulsating load on coal porosity is greater than that of static pressure load. The cumulative volume of micropores and their proportion decrease with the increase of pulsating frequency and pressure; the cumulative volume and proportion of macropores show an increasing trend; the cumulative volume of mesopores increases with increasing frequency, but the proportion increases in the low frequency phase, and decreases in the high frequency phase. There are two types of pores in the coal sample affected by the pulse waves: one is the expansion of the original pores, and the other is the new pores because the mineral crystals embedded in the coal body are washed out. The results have an important theoretical basis for the analysis of gas microscopic dynamics during pulsating hydraulic fracturing.

Molecular Transport Behavior of CO2 in Ionic Polyimides and Ionic Liquid Composite Membrane Materials.

Ionic polyimides (i-PI) are a new class of polymer materials that are very promising for CO2 capture membranes, and recent experimental studies have demonstrated their enhanced separation performance with the addition of imidazolium-based ionic liquids (ILs). However, there is very little known about the molecular-level interactions in these systems, which give rise to interesting gas adsorption and diffusion characteristics. In this study, we use a combination of Monte Carlo and molecular dynamics simulations to analyze the equilibrium and transport properties of CO2 molecules in the i-PI and i-PI + IL composite materials. The addition of several different common ILs are modeled, which have a plasticization effect on the i-PI, lowering the glass transition temperature (Tg). The solubility of CO2 strongly correlates with the Tg, but the diffusion demonstrates more unpredictable behavior. At low concentrations, the IL has a blocking effect, leading to reduced diffusion rates. However, as the IL surpasses a threshold value, the relationship is inverted and the IL has a facilitating effect on the gas transport. This behavior is attributed to the simultaneous contributions of the increased i-PI plasticization at higher IL concentrations (facilitating gas hopping rates from cavity-to-cavity) and the increased IL continuity throughout the system, enabling more favorable transport pathways for CO2 diffusion.

Diffusion and Flow of CO2 in Carbon Anode for Aluminium Smelting

Using a well-made carbon anode with the right porosity characteristics is essential to the successful operation of a Hall–Heroult cell. Bubble generation at this carbon anode and its contribution to the overall voltage drop in aluminum production holds significant potential for reducing overpotential and improving energy savings. This voltage drop is believed to be greatly influenced by the gas diffusion in the anode carbon, for which there are a limited number of measurements to correlate with the carbon anode properties. In the present study, the CO2 gas diffusion characteristics were first investigated via measuring anode porosity using mercury intrusion porosimetry (MIP) for different samples with different permeability. Second, diffusion experiments were conducted by flowing CO2 gas into the anode sample at elevated temperatures (up to 960 °C). The impact of temperature, average pore size, and permeability on the diffusion coefficient was investigated. The diffusion coefficient was consequently calculated by curve fitting using diffusion theories. The value obtained varied from 1.38 × 10−6 to 7.89 × 10−6 m2/s. A high diffusion coefficient was measured in the carbon sample with larger average pore size and higher permeability. It was found that anomalous diffusion behavior in the temperature range 600 °C to 960 °C was caused by convective flow effects, different diffusion mechanisms, and the Boudouard reaction for these carbon anode samples. Furthermore, by plotting the measured diffusion coefficient against average pore size and permeability, an increasing trend of diffusivity with an increase in pore size and permeability was observed.

The air-flow structure and gas dispersion behavior in gas tunnel construction through bench cut method

The inability to accurately predict the in rush of gas increases the fear of field workers security and unnecessary investments in tunnel ventilation. In this study, a 3-D numerical model was established to investigate the air-flow structure and gas diffusion characteristics of a gas tunnel during construction. The result showed that the flow inside the bottom bench mainly came from the re-circulation zone of the upper bench. Mutation in the tunnel section due to bottom bench excavation would cause the formation of some air circulation in the bottom bench. The circulation air in the bottom bench came from the re-circulation zone of the upper bench, while the air-flow in the considered zone was a polluted air. Based on the obtained results, there was no accumulation of CH4 inside the bottom bench. Nevertheless, gas gushing will still appear during the construction of the bottom bench surface, which can possibly lead to gas disaster. This study aims to provide some guidance for tunnel engineers on safety monitoring systems.

Characteristics of methane desorption and diffusion in coal within a negative pressure environment

To study the characteristics of gas diffusion and changes in the dynamic parameters of coal under a negative pressure environment, experiments were performed to constrain the desorption process under different negative pressures in coal samples at (0.5, 1.5 and 2.5) MPa adsorption equilibrium pressures. The experimental results demonstrate that the relation curves between time and the desorption quantities of coal samples with different negative pressures have shapes similar to that of Langmuir’s adsorption isotherm. In addition, all coal samples with different negative pressures have a maximum regarding methane desorption. As the negative pressure increases from 10 kPa to 40 kPa, the limitation gas desorption amount increases from 8.73 to 10.93 mL/g, from 14.91 to 17.75 mL/g, and from 18.30 to 23.27 mL/g, respectively, under 0.5 MPa, 1.5 Mpa and 2.5 Mpa adsorption equilibrium pressure. Moreover, under the same adsorption pressure, the larger the negative pressure becomes, the greater the gas desorption velocity of the first minute (V1) is. The change of gas desorption velocity with negative pressure during the first minute is an exponential function. The performance under different adsorption equilibrium pressures demonstrates the same regularity. With the increase of negative pressure, interfacial mass transfer resistance also decreases, and the diffusion coefficient and Fourier’s criterion of mass transmission increase. This indicates that the negative pressure environment changes the desorption kinetic-parameters of the coal mass and increases the amounts of methane desorption and desorption velocity, which are advantageous for desorption and diffusion of coal methane.

Gas diffusion characteristics as criteria of nonequilibrium state of amorphous glassy polymers

Three amorphous glassy polymers (polyetherimide Ultem-1000, polyhexafluoropropylene and poly(3,4-bis(trimethylsilyl)tricyclonon-7-ene) were subjected to different physical treatments (biaxial stretching, removal of residual solvent (drying), annealing, aging, etc.). This work summarizes the observations made earlier in the papers of the same group of authors but also presents some new results. The treatments were shown to produce various changes of gas permeability and diffusivity. In all the cases with good accuracy the diffusion coefficients followed a well-known equation logD=a−b∙d2, here d is the kinetic diameter of gas molecules. The parameters a and b were shown to be sensitive to the treatments of the polymers and, in addition, linearly correlate with each other. By combining equations of Eyring and Meares, it was demonstrated that the parameters a and b can characterize the deviation from equilibrium state of polymers after particular treatment.

Methane Adsorption Rate and Diffusion Characteristics in Marine Shale Samples from Yangtze Platform, South China

Knowledge of the gas adsorption rate and diffusion characteristics in shale are very important to evaluate the gas transport properties. However, research on methane adsorption rate characteristics and diffusion behavior in shale is not well established. In this study, high-pressure methane adsorption isotherms and methane adsorption rate data from four marine shale samples were obtained by recording the pressure changes against time at 1-s intervals for 12 pressure steps. Seven pressure steps were selected for modelling, and three pressure steps of low (~0.4 MPa), medium (~4.0 MPa), and high (~7.0 MPa) were selected for display. According to the results of study, the methane adsorption under low pressure attained equilibrium much more quickly than that under medium and high pressure, and the adsorption rate behavior varied between different pressure steps. By fitting the diffusion models to the methane adsorption rate data, the unipore diffusion model based upon unimodal pore size distribution failed to describe the methane adsorption rate, while the bidisperse diffusion model could reasonably describe most of the experimental adsorption rate data, with the exception of sample YY2-1 at high pressure steps. This phenomenon may be related to the restricted assumption on pore size distribution and linear adsorption isotherm. The diffusion parameters α and β/α obtained from the bidisperse model indicated that both macro- and micropore diffusion controlled the methane adsorption rate in shale samples, as well as the relative importance and influence of micropore diffusion and adsorption to adsorption rate and total adsorption increased with increasing pressure. This made the inflection points, or two-stage process, at higher pressure steps not as evident as at low pressure steps, and the adsorption rate curves became less steep with increasing pressure. This conclusion was also supported by the decreasing difference values with increasing pressures between macro- and micropore diffusivities obtained using the bidisperse model, which is roughly from 10−3 to 100, and 10−3 to 10−1, respectively. Additionally, an evident negative correlation between macropore diffusivities and pressure lower than 3–4 MPa was observed, while the micropore diffusivities only showed a gentle decreasing trend with pressure. A mirror image relationship between the variation in the value of macropore diffusivity and adsorption isotherms was observed, indicating the negative correlation between surface coverage and gas diffusivity. The negative correlation of methane diffusivity with pressure and surface coverage may be related to the increasing degree of pore blockage and the decreasing concentration gradient of methane adsorption. Finally, due to the significant deviation between the unipore model and experimental adsorption rate data, a new estimation method based upon the bidisperse model is proposed here.

Determining the diffusion coefficient of gas diffusion in coal: Development of numerical solution

Determining gas diffusion coefficient from experimental data is a key step of reproducing and predicting the diffusion process in coal. Previously analytical solution, including the unipore diffusion model and the bidisperse diffusion model, has been used extensively to estimate the gas diffusion coefficient(s) in coal. The utilization of analytical solution is convenient, however, there are some defects which may affect the accuracy of the results. For example, it is not suitable for fitting manometric sorption data, and the assumption of linear adsorption isotherm is not true.In this paper, we present a numerical solution to determine the gas diffusion coefficients. Three models were developed based on different assumptions of pore system and diffusion forms, i.e., unipore model assuming one kind of pore and diffusion, bidisperse model I (BM I) assuming independent macropore diffusion and micropore diffusion, bidisperse model II (BM II) assuming dependent macropore diffusion and micropore diffusion. Nitrogen diffusion experiment was conducted and the adsorption isotherm was measured. Sphere geometry was built for numerical simulation and the proposed models were used to fit the experimental data to determine the diffusion coefficients. Results show that neither the analytical unipore model nor the numerical unipore model can describe the diffusion process perfectly. By giving the same diffusion coefficient, the modelled fractional uptake ratio of numerical unipore model is smaller than the result of analytical unipore modeling at early stage while greater at later stage, which is due to the different assumptions of adsorption isotherm. Both BM I and BM II can describe the diffusion process well. The determined macropore diffusion coefficients of the two models are similar, while the micropore diffusion coefficient and the macropore adsorption ratio of BM II are greater than that of BM I. These can be explained by the different roles of the macropore diffusion in the two models. The gas pressure change at the center of the coal sphere was examined, from the modeling result of BM I, the macropore pressure increases sharply and then drops along with the external gas pressure, while the initial increasing rate of macropore pressure of BM II is much smaller and tends to be stable at later stage. No apparent impacts of initial gas pressures on diffusion coefficients can be observed, the change of diffusion coefficients and macropore adsorption ratio are actually small with increasing gas pressure.The numerical solution of determining gas diffusion coefficients can easily relax the assumptions and restrictions of the analytical solution. It can be used to test different kinds of coal samples, investigate different diffusion mechanisms and match all kinds of experimental data. The measured sorption isotherm and coal properties can also be incorporated into the modeling, which makes the determined diffusion coefficients more reliable. This paper is a preliminary attempt and we hope it can bring the researchers some new ideas about studying the gas diffusion characteristics in coal.

Flue gas diffusion for integrated dry-cooling tower and stack system in power plants

For the integrated dry-cooling tower and stack, the flue gas diffusion characteristics are of great concerns for the pollutant control and tower anticorrosion. In this work, the computational models of flue gas diffusion for the integrated dry-cooling tower and stack system are developed and experimentally validated. By means of numerical simulations, the flue gas diffusions inside and outside the dry-cooling tower are investigated and the flue gas concentrations at different heights of the inner tower shell and on the ground level are obtained. The rising height of flue gas is studied and compared with the separate stack. The total mass flow rate of cooling air and heat rejection of air-cooled heat exchanger for both the dry cooling system with and without the stack inside the dry-cooling tower are also obtained. The results show that not only the thermo-flow performances of the natural draft dry cooling system with the integrated stack can be improved, but also the air pollution alleviation can be guaranteed. At high wind speeds, the inner tower shell faces corrosion risks due to the flue gas deposition, so the anticorrosion measures for the tower should be taken.

Development on Measuring Methods of Catalyst Layer Structure Parameters Under Operating Condition of PEFCs

In order to familiarize fuel cell vehicles (FCV), its system cost reduction is a critical issue. High current density operation is an effective approach, but it is necessary to reduce activation overvoltage, IR loss and concentration overvoltage. In particular, the concentration overvoltage must be decreased to increase oxygen flux at high current density. In order to reduce concentration overvoltage, oxygen gas diffusion characteristics in gas diffusion layer (GDL) and microporous layer (MPL), oxygen dissolution and diffusion characteristics in ionomer, reduction of oxygen local flux to platinum and influence analyses of water retention in MEA to PEFC performance have been researched by various approaches. In recent years, not only water retention in GDL / MPL but the effect of water retention in catalyst layer (CL) on cell performance has been reported by advancement of MEA inside visualization technique. However, relationship between the catalyst layer structure parameters and liquid water retention characteristics has not been found out yet. In this study, to find out this relationship and influence of water retention in CL to oxygen transport resistance and PEFC performance, porosity/tortuosity (ε/τ) measuring method has been developed under operating condition of PEFC as first step. The ε/τ of CL did not change with temperature (25-80 deg.C) under dry environment, which is reasonable due to low thermal expansion coefficient of each CL material. Currently, we are planning this technique to humidity control and the results will be reported. AcknowledgmentsThis research was financially supported by New Energy and Industrial Technology Development Organization (NEDO), Japan.

Pulverization characteristics of coal from a strong outburst-prone coal seam and their impact on gas desorption and diffusion properties

Coal seams that are prone to strong outbursts have low strength and cause heavy structural damage to the seam. Their outburst risk is highly related to the release of the adsorbed coalbed gas, which is controlled by the gas desorption and diffusion characteristics of coal. In the Haizi Coal Mine, China, an extremely high gas outburst risk was detected, and the coals from this area were found to have an unprecedented high degree of fragmentation and were present in the pulverized state. To explain the pulverization characteristics of the pulverized coal, the related physical parameters were investigated; the gas desorption and diffusion properties of the pulverized coal were analyzed and compared with those of the unpulverized coal. The results indicated that the pulverized coal could easily reach the required degree of fragmentation for a coal and gas outburst to occur. Furthermore, the pore volume and specific surface area of the pulverized coal differed according to the coal particle size. Compared with the unpulverized coal, the gas desorption and diffusion properties of the pulverized coal were largely varied, and the pore structure of the pulverized coal was much simpler. The formation of pulverized coal is believed to be closely related to complex geological conditions.

Synthesis, characterization and performance of robust poison-resistant ultrathin film yttria stabilized zirconia – nickel anodes for application in solid electrolyte fuel cells

We report on the synthesis of undoped ∼5 μm YSZ-Ni porous thin films prepared by reactive pulsed DC magnetron sputtering at an oblique angle of incidence. Pre-calcination of the amorphous unmodified precursor layers followed by reduction produces a film consisting of uniformly distributed tilted columnar aggregates having extensive three-phase boundaries and favorable gas diffusion characteristics. Similarly prepared films doped with 1.2 at.% Au are also porous and contain highly dispersed gold present as Ni-Au alloy particles whose surfaces are strongly enriched with Au. With hydrogen as fuel, the performance of the undoped thin film anodes is comparable to that of 10–20 times thicker typical commercial anodes. With a 1:1 steam/carbon feed, the un-doped anode cell current rapidly falls to zero after 60 h. In striking contrast, the initial performance of the Au-doped anode is much higher and remains unaffected after 170 h. Under deliberately harsh conditions the performance of the Au-doped anodes decreases progressively, almost certainly due to carbon deposition. Even so, the cell maintains some activity after 3 days operation in dramatic contrast with the un-doped anode, which stops working after only three hours of use. The implications and possible practical application of these findings are discussed.

A study of gas diffusion characteristics on a micro porous composite silica ceramic membrane

The purpose of this study is to investigate gas permeation behaviour of five gases (CO2, He, H2, N2 and Ar) across two silica modified ceramic membranes, Membrane Y and Membrane Z. An examination of the variations in their layer thickness and flow rate was determined. Solution-dip coating process was used for the modification process specifically for pore size reduction. This resulted in some level of modifications in the layer thickness after a successive dipping time as well as flow rate in relation to pressure drop. The effect of number of dips generally influenced the layer thickness of both membranes. Membrane Y layer thickness through five successive dipping was in the range of 89.2–36μm while Membrane Z ranges between 150.72 and 43.69μm. Gas permeability as a function of mean pressure for Membrane Z was calculated using data obtained experimentally. The permeation tests confirmed the contribution of both Knudsen and viscous flow mechanism with an estimation and prediction of the membrane pore radius.

Experimental investigation on the characteristics of gas diffusion in shale gas reservoir using porosity and permeability of nanopore scale

Abstract The aim of this study is to investigate the diffusion characteristics of nanoscale gas flow in a shale gas reservoir. An experimental apparatus was designed and set up to measure porosity and permeability at the nanopore scale. The measured properties have been used to determine a diffusion coefficient by classification standard of gas flow regime. To investigate the impact of pressure and pore size, the analysis of diffusion flow was conducted using Knudsen and Fick diffusion coefficients. From the results, it was revealed that Knudsen diffusion coefficient gradually increased with the growth of pressure and pore radius and Fick diffusion coefficient was dependent on the gas molecular diameter and temperature. It was also found that Knudsen diffusion coefficient was equal to Fick diffusion coefficient if pore radius is too small. The study implied that the characteristics of gas diffusion should be implemented by using the diffusion coefficient theory based on gas flow regime in shale gas reservoirs.

Effect of an electrostatic field on gas adsorption and diffusion in tectonic coal

The characteristics of adsorption, desorption, and diffusion of gas in tectonic coal are important for the prediction of coal and gas outbursts. Three types of coal samples, of which both metamorphic grade and degree of damage is different, were selected from Tongchun, Qilin, and Pingdingshan mines. Using a series of experiments in an electrostatic field, we analyzed the characteristics of gas adsorption and diffusion in tectonic coal. We found that gas adsorption in coal conforms to the Langmuir equation in an electrostatic field. Both the depth of the adsorption potential well and the coal molecular electronegativity increases under the action of an electrostatic field. A Joule heating effect was caused by changing the coal–gas system conductivity in an electrostatic field. The quantity of gas adsorbed and ΔP result from competition between the depth of the adsorption potential well, the coal molecular electronegativity, and the Joule heating effect. ΔP peaks when the three factors control behavior equally. Compared with anthracite, the impact of the electrostatic field on the gas diffusion capacity of middle and high rank coals is greater. Compared with the original coal, the gas adsorption quantity, ΔP, and the gas diffusion capacity of tectonic coal are greater in an electrostatic field. In addition, the smaller the particle size of tectonic coal, the larger the ΔP.

Effects of Organic Micromolecules in coal on its Pore Structure and Gas Diffusion Characteristics

Coal has complex pore structures including micro-, meso-, and macropores and cracks, and contains organic micromolecules. To in-depth study the effects of organic micromolecules in coal on the pore structure and gas diffusion characteristics, organic micromolecules were extracted by tetrahydrofuran using microwave-assisted method from anthracite and bituminous coal samples to obtain the residual coal samples at 50 \(^{\circ }\)C and atmospheric pressure. Changes in raw and residual coal samples were explored using a series of methane desorption and low-temperature nitrogen adsorption experiments and their pore structure parameters were compared using samples with same granule size (0.180–0.250 mm). The results showed that (1) although the micropores of both raw and residual coal granules are characterized by fractal, residual coal has lower fractal dimension than raw coal; (2) residual coal samples have higher gas emission amount and rate than the raw coal samples and lower gas diffusion resistance, indicating that gas in residual coal is easier to flow from micropores through mesopores into macropores and cracks. Based on the fractal theory and the diffusion model, extraction of organic micromolecules increased the number and diameter of pores and cracks and dredged the rawly clogged pores and cracks, all of which decreased the resistance of gas diffusion in the coal matrix. In addition, extraction of organic micromolecules has the most obvious effect on diffusion pores. After extraction, the proportion of meso-/macropores increased, while that of micropores reduced, thereby reducing the resistance of gas flowing from micropores through mesopores into macropores and cracks, and subsequently increasing the amount and rate of gas emission. The study is of great significance for pushing forward the boundary of our recognition of the influences exerted by micromolecules on gas diffusion.

Impact of pore structure on gas adsorption and diffusion dynamics for long-flame coal

The pore structure of coal has a “U-shaped” relation with coal rank. Adsorption pores (pore size smaller than 2 nm) and seepage pores (2 nm < pore size<50 nm) greatly influence gas adsorption and diffusion. Thus, the pore structure of five coal samples (Ro between 0.57% and 0.62%) from eastern China was investigated in this study. Scanning electron microscopy was used for the qualitative analysis of the pore structure. Additionally, mercury porosimetry and the adsorption of CO2 at 273 K were used for the quantitative analysis of the pore size distribution. #15 and #16 coal samples were used to study gas adsorption properties at different temperature, while #12, #13, #14 and #16 coal samples were used to study gas diffusion characteristics. The results show that the micropores of long-flame coal are well developed and that micropores (pore size smaller than 2 nm) greatly affect gas adsorption properties, whereas mesopores (2 nm < pore size<50 nm) affect gas diffusion characteristics. The adsorption ability of long-flame coal increases with the microinvasion capacity and specific surface area. From the perspective of adsorption dynamics, VL increases with temperature, whereas PL does not change appreciably. Methane's effective diffusion coefficient, obtained from adsorption data based on Fick's laws of diffusion, was observed to increase with the development of mesopore structure and decrease with time. Initially, the effective diffusion coefficient decreased sharply and stabilized after 15 min. The results may have significant implications for the control of methane in coal.

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