Pore Structure Of Coal Research Articles

Impact of Microbially Enhanced Coalbed Methane on the Pore Structure of Coal

Microbially enhanced coalbed methane (MECBM) has important theoretical and practical significance for reforming coal reservoir structure, alleviating greenhouse effects and energy crises and developing new sources of clean energy. In this study, No. 3 coal seams in Qinshui Basin were taken as research objects to analyze the pore structure characteristics after microbial treatment by means of low-temperature nitrogen adsorption (LTNA), mercury porosimetry (MP), and isothermal adsorption/desorption experiments. The results showed that after bioconversion, the specific surface area and pore volume increased from 1.79 m2/g and 0.0018 cm3/g to 4.01 m2/g and 0.0051 cm3/g respectively under liquid nitrogen testing; however, the specific surface area was reduced from 5.398 m2/g to 5.246 m2/g and the pore volume was increased from 0.053 cm3/g to 0.0626 cm3/g under MP. The fractal dimension based on the LTNA data indicated that the fractal dimension of micropores and minipores was increased from 2.73 to 2.60 to 2.89 and 2.81, however the fractal dimension of meso-macropores was decreased from 2.90 to 2.85. The volatile matter and fixed carbon were both reduced from 6.68% to 78.63%–5.09% to 75.63%, and the Langmuir volume and Langmuir pressure were increased from 34.84 cm3/g and 2.73 MPa to 36.34 cm3/g and 3.28 MPa, respectively. This result indicated that microorganism participated in the degradation of coal reservoir and promoted the production of methane gas, the meso-macropores were more obviously modified by microorganism, so that the pore diameter stabilized, the pores became smoother, the specific surface area decreased, and the pore volume increased. These are more beneficial to the adsorption and production of coalbed methane (CBM) after microbial treatment.

Experimental Investigation on the Pore Structure Evolution of Coal in Underground Coal Gasification Process

Underground coal gasification (UCG) has been shown to be a promising method for deep coal resources. A series of complicated chemical reactions can induce a considerable change in the pore structure of coal and thus promote the UCG process in turn. Currently, most studies on the effect of elevated temperature on the pore structure of coal were not involved in an air atmosphere, bringing a series of difficulties to understanding the pore structure evolution of gasified coal in the UCG process. The objective of this work was to investigate the pore structure evolution of coal heated in nitrogen and air atmospheres at elevated temperatures. Thermogravimetry tests were first conducted to gasify coal samples, and then, the method scanning electron microscopy was used to observe the microscopic morphology of the pore structure. Besides, the effect of final temperature, atmosphere, pressure, and residence time on the thermal dynamics of coal at elevated temperatures was comprehensively discussed. Results indicated that the temperature range of a heating process of coal can be classified into three stages, 25–320 °C, 320–750 °C, and 750–1000 °C. For the three temperature ranges, drying, primary pyrolysis, and secondary pyrolysis can dominate, respectively, under a nitrogen atmosphere, while the combustion and gasification process will prevail at a high temperature under an air atmosphere. Because of mass loss, the coal was becoming porous during the heating process. Compared with the intact structure of coal when the temperature is lower than 300 °C, the pore space can interconnect under moderate-temperature conditions (500 °C) like a honeycomb, and then, only an ash framework remained under a higher-temperature condition (700 °C) under an air atmosphere. In comparison, the coal heated in a nitrogen atmosphere can gradually turn into a porous char. This investigation can provide some new insights into the pore structure evolution of gasified coal and contribute to the mechanisms of a UCG process.

Study on Pore Structure Change Characteristics of Water-Immersed and Air-Dried Coal Based on SEM-BET

ABSTRACT The pore structure of coal affects spontaneous combustion to a certain extent. The pore structure of the coal body will be altered after prolonged waterlogging and is highly susceptible to spontaneous combustion in the presence of elevated ground temperatures. To study the pore structure changes in the coal body after immersion and drying. The coal samples from the Jinjitan coal mine in Yulin, Shaanxi Province, the Tangkou coal mine in Jining, Shandong Province, and the Gaojiapu coal mine in Shaanxi Province were scanned by electron microscopy and low-temperature nitrogen adsorption experiments. This study indicates that after water immersion, the fracture pores of the coal body are developed, the morphology changes, and the percentage of pore fracture area increases significantly. With the increase in immersion time, the pore types of Coal samples A and C did not change, being delicate necked bottle-shaped pores and open, permeable pores, respectively. Coal sample B pore type developed from impermeable pores to open pores. The cumulative pore volume of coals from all three areas increased for the same pore size. The contribution of micropores to the BET specific surface area and total BJH pore volume was more significant than the original coal samples. The specific surface area of A90, B30, and C60 was larger than that of the other coal samples for the soaking time, so it can be assumed that A90, B30, and C60 have a higher propensity for spontaneous combustion. Underwater immersion, the pore type of coal samples from coal mines in Northwest China did not change, but the pore types of coal samples from coal mines in East China changed. Therefore, the pore structure of gas coal was easily changed underwater dissolution.

High Rank Coal Pore Fracture Structure and its Impact on Reservoir Characteristics in the Southern Qinshui Basin

Although the southern Qinshui Basin is the most successful area for coalbed methane (CBM) development in China, the production of CBM wells in different blocks in the area is significantly different. One of the key reasons is the difference in pore structure in various-ranked coal. In this study, No. 3 coal seam of Sihe and Zhaozhuang blocks in southern Qinshui Basin was selected as the research object to investigate the high rank coal pore fracture structure and its impact on reservoir characteristics. Mercury intrusion porosimetry (MIP), low-temperature liquid nitrogen adsorption (LTN2A), scanning electron microscopy (SEM), and isothermal adsorption tests were conducted. The results show that the Sihe No.3 coal seam was mainly composed of open cylindrical and flat pores with a high proportion of transition pores (10–100 nm), large specific surface area, good connectivity, strong adsorption capacity, high gas content, and reservoir energy. Zhaozhuang No.3 coal had high proportion of mesopores (100–1,000 nm), small specific surface area, poor pores connectivity, weak adsorption capacity, poor gas content, low reservoir energy, and critical desorption pressure. The proportion of cylindrical pores, parallel plate pores, and wedge-shaped pores closed at one end was high. The anomalies in pore morphology and pore structure characteristics of coal reservoir were the main factors that caused variation in gas production of No.3 coal seam in Sihe and Zhaozhuang blocks.

Effects of cyclic freeze-thaw by liquid nitrogen on the coal breakage properties and fragment size distribution

Transforming intact coal seams into broken coals that are convenient to transport is one of the technical problems of fluidized coal mining. In this paper, cyclic freeze-thaw by liquid nitrogen (CFT-LN2) was adopted to improve the fragmentation degree of coal seams. The coal pore structure evolutions and coal breakage properties were explored using the acoustic emission (AE) parameter method (the kernel density estimation method), the fractal theory, and the nuclear magnetic resonance spectra. The main factors discussed include the number of freeze-thaw cycles, the LN2freezing time and the moisture content of the coal sample. Variations of these factors alter the mechanical and physical characteristics and pore structures of coal samples treated with CFT-LN2. The results reveal that the kernel density estimation method can distinguish the density region determined based on the rise angle (RA) and average frequency (AF) values and visualize the rupture modes of coal samples formed after CFT-LN2. As the number of freeze-thaw cycles grows, the tensile rupture mode gradually transits to shear rupture mode; the fractal dimension gradually increases; the equivalent average size gradually decreases; and the mass of different fragment sizes tend to be more uniform. Only freezing in LN2without CFT-LN2cannot notably change the rupture mode or fragmentation degree of a coal sample. During CFT-LN2, the coal matrix is subjected to repeated action of contraction in LN2and expansion at room temperature. As a result, new micro-pores are formed easily in the matrix, and micro-pores incline to connect into larger pores. Meanwhile, increasing the moisture content is conducive to coal fracturing through CFT-LN2.

Investigations on the mechanism of the microstructural evolution of different coal ranks under liquid nitrogen cold soaking

ABSTRACT Liquid nitrogen (LN2) is an important means to improve the permeability of coal reservoirs. The LN2 soaking method has a wide range of application prospects. However, not enough studies exist to highlight the effect of increasing the permeability of different coal samples using LN2. Hence, this investigation was carried out to examine the effect of cold soaking in LN2 using different coal ranks such as fat coal, lean coal and anthracite coal, on their pore structures and fractal characteristics. Frenkel-Halsey-Hill (FHH) fractal theory was used to understand the fractal dimension characteristics of pores in these different coals before and after cold soaking in LN2. Furthermore, the relationship between the fractal dimensions and pore parameters was also studied. The results show that low-temperature nitrogen adsorption curves of fat coal, lean coal and anthracite before and after cold soaking in LN2 are “S” type. An increase in the total pore volume and pore surface area of coal after LN2 cold soaking is noted. LN2 cold soaking is found to transform the internal pore structure of different coals effectively. Moreover, the heterogeneity of the porous structure of coal is enhanced after LN2 cold soaking along with an increase in the fractal dimension. The growth also decreases with an increase in the metamorphism. The uneven shrinkage of coal occurred during LN2 cold soaking, and the thermal stress generated is greater than the tensile strength of coal, which promotes the development of the porous structure of coal. These results are beneficial in revealing the macroscopic and microscopic pore fissure space expansion and connectivity law of coal seam during the process of LN2 cracking.

Effect of high-temperature treatment on the desorption efficiency of gas in coalbed methane reservoirs: Implication for formation heat treatment

Formation heat treatment has been considered as a potential stimulation technology for the enhanced recovery of coalbed methane. However, the influence of heat treatment on the desorption efficiency of coalbed methane has not been clarified. In this study, isothermal adsorption experiments of a cylindrical anthracite coal treated at 25 °C, 200 °C, 400 °C, 600 °C, and 800 °C were conducted to investigate the variation in the methane adsorption potential and desorption efficiency. The pore structure of coal was characterized by nuclear magnetic resonance measurements and scanning electron microscopy. Changes in the organic matter and functional group content of coal were monitored by proximate analysis and Fourier transform infrared spectroscopy. Results reveal that pore structure and composition are the main factors that affect the coal adsorption potential. With the increase in the temperature to 200–600 °C, the maximum adsorption potential of coal increased by 7% due to the increase in the pore volume and the functional group content. At a heat-treatment temperature of 800 °C, the functional group content decreased, which in turn reduced the maximum adsorption potential by 76%. Comparison of isothermal adsorption data of coals with different ranks reveals that the Langmuir parameter of bituminous coals is more easily affected by heat treatment in comparison with that of anthracite coal. Based on the reversible theory of coalbed methane isothermal adsorption and desorption process, weighted pressure was proposed, which could comprehensively evaluate the desorption efficiency of coal after heat treatment at different temperatures, and the heat treatment temperature for the optimal desorption efficiency can be determined by the weighted pressure.

Nanopore Structure and Mechanical Properties in Brittle Tectonically Deformed Coals Explored by Atomic Force Microscopy

Tectonically deformed coals (TDCs) are of great importance to coalbed methane exploitation and coal mining safety. Compared to primary coals, reservoir properties of TDCs have been transformed greatly by tectonic stress. Here, the pore structure and mechanical properties of primary coal and brittle TDCs were obtained with atomic force microscopy and software. The results showed that tectonic stress generally promotes pore development and Young’s modulus of brittle TDCs. According to the variation in pore structure and Young’s modulus, two stages were identified: weak brittle deformation stage (primary coal–cataclastic coal–schistose coal–mortar coal) and strong brittle deformation stage (mortar coal–granulitic coal–flaky coal). The extent of tectonic impact varies greatly between these two stages. In weak brittle deformation stage, tectonic stress has little impact on coal pore structure. The mean pore number increases slowly, and the mean pore size decreases slowly. In this stage, half of the pore number increment is provided by macropores of 100–200 nm diameter. In strong brittle deformation stage, tectonic stress has a major impact on coal pore structure. The mean pore number increases quickly, and the mean pore size decreases quickly. Most of the pore number increment comes from mesopores of 10–50 nm diameter and macropores of 50–100 nm diameter. In addition, the Young’s modulus of primary coal and different brittle TDCs varies from 1.5 to 2.0 GPa. In weak brittle deformation stage, the Young’s modulus of different samples levels off. While in strong brittle deformation stage, the Young’s modulus increases gradually. Combined with former studies, it is inferred that tectonic stress can influence coal’s Young’s modulus by transforming its chemical structure.

Advances in Liquid Nitrogen Fracturing for Unconventional Oil and Gas Development: A Review

Liquid nitrogen (LN2) fracturing is an anhydrous fracturing technology that enhances coal permeability and supports unconventional oil and gas exploitation. In this Review, we provide a systematic review of five aspects of LN2 fracturing. They are the history of the technology’s development, research topics, factors influencing fracturing efficiency, fracturing mechanism, and engineering processes and systems. Liquid nitrogen fracturing transforms coal and rock pore structure through mechanisms such as low temperature, freeze–thaw damage, and gas expansion. It changes coal and rock mechanical properties and improves the pore penetration and efficiency of unconventional oil and gas extraction. However, in-depth studies are still required in many areas. They include theoretical studies of two-phase nitrogen flow in coal and rock, development of technical equipment to support field operations, and plans to monitor and evaluate fracturing efficiency. On the basis of the advances in LN2 fracturing research and the challenges, we conclude that future research should focus on multiphase flow and field equipment and technology.

Effect of pore structure on competitive sorption and diffusion of mixed methane and carbon dioxide in anthracite, South Qinshui Basin, China

A deep understanding of the competitive adsorption and diffusion of methane (CH4) and carbon dioxide (CO2) in coal is significant for implementing the CO2-ECBM project. For three high-rank coal samples, industrial analysis, coal maceral, and vitrinite reflectance (RO) determination, mercury injection test, and low-temperature nitrogen/carbon dioxide specific surface test were carried out, and the composition and pore structure of coal samples were studied systematically. Meanwhile, through the three mixed gases (75%CH4 + 25%CO2, 50%CH4 + 50%CO2, 25%CH4 + 75%CO2) adsorption and desorption test, the absolute adsorption amount, free phase and adsorption phase of CH4 and CO2 under different equilibrium pressures, and the equivalent diffusion coefficients of gas migration in the process of adsorption/desorption equilibrium were calculated. Finally, the relationship among the coal composition, pore structure, and the competitive adsorption and diffusion characteristics of methane and carbon dioxide mixture in coal were studied. The results show that: (1) the composition of coal has an important influence on the development of coal pore structure and the adsorption and transport of gas in coal. Supermicropore (<2 nm in size) is the prominent adsorption place. Furthermore, its development, which essentially determines the adsorption capacity of coal samples, is positively correlated with fixed carbon content, vitrinite content, and vitrinite reflectance. (2) When the pores >100 nm in size relatively developed, the coal samples have higher porosity, lower micropore diffusion, and a smaller desorption hysteresis index. Because the pore's connectivity is limit, its content has no apparent correlation with the permeability of coal samples and most of the adsorption and diffusion parameters. (3) The desorption hysteresis is mainly caused by the opposite migration direction of gas in the process of adsorption and desorption and the resulting dislocation of coal matrix swelling and shrinkage. The competitive adsorption of CH4 or CO2 and their separation index (SCO2/CH4) in coal samples decreases with the increase of adsorption equilibrium pressure. Also, the desorption process often shows a higher SCO2/CH4 value than that of the adsorption process. (4) During the adsorption process, the equivalent macro-diffusivities of the coal sample decrease as a power function with increasing pressure and increase with the carbon dioxide content increasing in the mixed gas. However, the equivalent micro-diffusivities change little with the different CH4 and CO2 mixtures migration in different coal samples. The equivalent diffusion coefficient of coal is positively correlated with macropore, mesopore, transitional and micropore content in coal samples.

Effect of coalification and maceration on pore differential development characteristics of high-volatile bituminous coal

The coal type of high-volatile bituminous coal (HBC) is an important component of coalbed methane (CBM) reservoirs in China. Moreover, the accurate characterization of pore structures of coal is crucial to the exploration and development of CBM. In this work, the pore structure of vitrain and durain in high-volatile bituminous coals was detected using a scanning electron microscope, mercury intrusion porosimetry, low-temperature N2 adsorption, and low-temperature CO2 adsorption across multiple length scales and the effect of coalification and maceral on pore differential development law of HBC was analyzed. The findings reveal that at different pore size scales and the pore characteristics of different coal lithotypes under the influence of coalification are clearly different. In the same sample, the specific surface area (SSA) and total pore volume (TPV) of supermicropores in vitrain are higher than those of durain but the SSA and TPV of micropores and transition pores in vitrain are lower. The fractal results reveal that with the increase in pore size, the complexity of pore structure of coal increases. The relationship between the vitrain and durain pore fractal dimensions in different scale sections will change. At different pore size scales, the difference in pore structure in the vitrain and durain exhibits a trend of initially increasing and then decreasing with pore size. The inertinite content is positively correlated with the adsorption pore volume and SSA of vitrain and durain, and the vitrinite content is negatively correlated. Physical compaction considerably reduces the pore volume of vitrain during the early evolution stage of HBC but has no effect on durain. The pore parameters of vitrain and durain initially increase and subsequently decrease with the increase in vitrinite reflectances. The maximum value is obtained near the first coalification jump point. The evolution trend of the pore volume of vitrain and durain is consistent at different pore size scales; however, the total variation range of durain is higher than that of vitrain. The adsorption pore structure is mainly affected by asphaltification and polycondensation, whereas physical compaction has a greater impact on the seepage pore structure.

Influence of particle size on pore structure and multifractal characteristics in coal using low-pressure gas adsorption

Understanding pore heterogeneity is essential to obtain insights into the gas storage, transport, and recovery from coal. The pore structure in analytical sample particles of different sizes varies significantly, leading to inaccurate pore characterization. In this study, we discuss the effect of particle size on the pore structures and multifractal characteristics of two samples with six particle sizes using low-pressure gas adsorption. The results show that, with decreasing particle size, the mesopore and macropore volumes and specific surface areas (SSAs) of the two samples fluctuate. The variations of micropores that contribute to most of the total pore volume and SSA (>90%) are different. Multifractal analysis shows that the subsamples with the smallest particle size have the most homogeneous pore structures and the highest pore connectivity. We reveal a negative power function relationship among particle size and pore volume, and SSA, indicating that crushing opens up more pores that were initially closed. The differences between the two coal samples may be caused by the combined effects of crushing and associated impacts (e.g., pore collapse), coalification, incomplete equilibration of N2 adsorption, and mineralogical inhomogeneity. Our results demonstrate that in the range of test particles, the finer the particle size used, the more accurate the evaluation of highly mature coal adsorption properties.

Effect of Liquid Nitrogen Freeze-Thaw Cycles on Pore Structure Development and Mechanical Properties of Coal.

To improve the mining efficiency of coalbed methane, liquid nitrogen freeze–thawing experiments were performed to improve coal seam permeability and to study its influence on coal pore structure development and mechanical properties. Mechanical properties and nuclear magnetic resonance tests of coal samples were performed with 0, 5, 10, and 15 freeze–thaw cycles of liquid nitrogen. The results show that the number of freeze–thaw cycles caused the change of uniaxial compressive strength and elastic modulus of coal, and the change effect decreased significantly after 11–15 freeze–thaw cycles. Between 0 and 5 freeze–thaw cycles, the base growth rate of the transverse relaxation time T2 spectral area of the full pore of coal is 44.1%, and that of the transverse relaxation time T2 spectral area of adsorption pore is 71.5%. After 6–10 freeze–thaw cycles, the fixed base growth rate of the transverse relaxation time T2 spectral area of the full hole of coal is 269.0%, and the chain growth rate is 156.2%. In this stage, the chain growth rate of the transverse relaxation time T2 spectral area of the seepage hole is 198.4%, which is mainly the growth of seepage hole volume. After 11–15 freeze–thaw cycles, the chain growth rate of the full pore of coal transverse relaxation time T2 spectrum area is 20.1%, the chain growth rate of adsorption pore is 4.8%, the chain growth rate of seepage pore is 22.2%, and the growth rate of the pore volume is greatly reduced. Comparing the changes of pore and coal mechanical properties in different pore sizes, it can be seen that the change of adsorption pore volume has a greater impact on coal mechanical properties.

Study on the Evolution of Pore Structure of Anthracite Coal under Liquid-Nitrogen Freeze-Thaw Cycles.

To analyze the evolution characteristics of the internal pore structure of anthracite by liquid-nitrogen (LN2) freeze–thaw cycles, nuclear magnetic resonance was used to test the water-saturated samples, which were frozen–thawed with LN2 for 0–9 exposure. The pore size distribution, development degree, and variation characteristics of different pores were examined from the changes of parameters related to T2 spectra, which increased the macropore frequency: First, LN2 freeze–thaw cycles are beneficial to the development of cracks and have the greatest promoting effect on macropores. Second, the crack development rate of coal samples decreased with the increase of the number of freeze–thaw cycles. The crack development rate was the fastest in the first freeze–thaw cycle, and the crack development did not increase significantly after the third freeze–thaw cycle. Third, the pore structure of anthracite is under the influences of thermal stress and frost heaving force (the force caused by the expansion of water as it freezes). Therefore, it can be determined that three times of LN2 freeze–thaw cycles has the best effect in the LN2 injection to increase coal permeability and recover coalbed methane. The results provide theoretical support for the field application of coal freezing cracking and antireflection promotion pumping.

Evolutions of Pore and Crack Structure of Coal under Hot Steam Heating

Evolutions of Pore and Crack Structure of Coal under Hot Steam Heating

Water adsorption characteristic and its impact on pore structure and methane adsorption of various rank coals.

Coalbed methane not only is a new clean energy source, but also has potential damage to ecological environment. Water and methane coexist in coal reservoir; understanding the adsorption of water on coal and its impact on pore structure and methane adsorption of coal is vital to evaluate the reserves and productivity of coalbed methane. In the paper, water adsorption characteristics of various rank coals are firstly investigated by ten mathematical models. The modified Dent model provides a best fit, followed by GAB and Dent models. For GAB model, the primary site adsorption is more difficult to reach saturation, and the contribution rate of the secondary site adsorption is surprisingly high at P/P0 approaching 0, which can be attributed to the possible overestimation of GAB monolayer adsorption capacity and secondary site adsorption. Besides, the low-rank coal sample YZG2 exhibits more prominent hysteresis than middle- to high-rank coals. The low-pressure hysteresis can be attributed to the water-water interactions over the primary site and the strengthened binding forces of water molecules in the water desorption process. In contrast, the high-pressure hysteresis largely depends on pore structure of coal such as ink-bottle pores, especially for the studied sample YZG2. Besides, pore analyses by low-temperature nitrogen adsorption method show that the pre-adsorbed water has remarkable influence on micropores smaller than 10 nm, and the micropores smaller than 4 nm almost disappear for water-equilibrated coals, which is closely related to the formed water clusters and capillary water in pore throats. This finding reveals that more methane gas can only be adsorbed in the larger pores of moist coal, and provides an explanation for water weakening methane adsorption capacity.

Effect of Analytical Particle Size on Pore Structure of High Volatile Bituminous Coal and Anthracite Using Low-Pressure N2 and CO2 Adsorption

To investigate the effect of analytical particle size on pore structure, mesopore (2-50 nm) and micropore (&lt;2 nm) characteristics of high volatile bituminous coal and anthracite with different particle size were determined using low-pressure N2/CO2 adsorption analyses. Mesopore structure parameters in the two coals increase with decreasing particle size, which are attributed to the opening of closed mesopores during the pulverization process. The closed mesopores with different pore size ranges are opened with a certain percentage in high volatile bituminous coal, but opened irregularly in anthracite during pulverization. Micropore structure parameters of the two coals show different variations with decreasing particle size, which are not related to the reconstituted micropore structure. Mineral matter contributes more mesopores than organic matter in anthracite and exerts the negative effect on micropore in the two coals. An evolution model is established to elaborately describe the change of pore structure during the pulverization process, where mineral matter plays a mediating role in the effect of particle size on pore structure.

Effect of Acidification on Microscopic Properties and Pore Structure of Coal

Effect of Acidification on Microscopic Properties and Pore Structure of Coal

Pore structure characterization and its significance for gas adsorption in coals: A comprehensive review

The coal reservoir has multifaceted and hierarchical characteristics influenced by heterogeneity of the pore and fracture networks. The coal pore including micropore, mesopores and macropores determines the critical migrate processes of gas molecules, especially for adsorption. Normally, coal pore structure refers to the pore shape, size distribution and interconnection of variable pores. Together with pore volume, pore size distribution, specific surface area and porosity. For coalbed methane, pore structure is the storage place, which largely controls the methane adsorption capacity of coal. Fluid injection, microscope observation and X-ray and spectroscopic analysis can be used to explore coal pore structure. Understanding the pore structure in varied rank coals is very challenging mostly due to the complex pore system leading to ambiguous petrophysical properties and gas performance. Among several important factors controlling the performance of coalbed methane, adsorption is the most crucial one, which affected by the pore aspects including pore volume, specific surface area, pore size distribution, pore shape and porosity. Therefore, accurate characterization of pore structure is coupled with advanced technologies, which resulted in the development of a wide range of methods. In this work, all the necessary technologies from imaging, segmentation, and modeling of the pores to various methods of gas adsorption evaluation are reviewed. This paper presents a critical review of all of the existing relevant and significant techniques and compares their performances together with their limitation with special reference to pore structure characterization. And the impacts of pore structure are thus reviewed. Finally, this review work proposes the current challenges and possible future research. • The coal pore classification scheme is systematically reviewed. • The pore characterizing techniques are summarized. • The influence of coalification on pore structure and its impact on CH 4 adsorption is analyzed. • The challenges and prospects on coal pore research are proposed.

A small furnace for in-situ SAXS/WAXS study on medium temperature carbonisation of coal

The medium temperature carbonisation of coal refers to the process of decomposition of coal by heating to 700°C in absence of air. It is one of the important ways of coal utilisation. Small/wide angle X-ray scattering (SAXS/WAXS) can be used to study the pore and carbon matrix structure of coal. Recently, a small furnace for in-situ study of medium temperature carbonisation of coal by simultaneous or respective SAXS and WAXS was developed and integrated into the SAXS instrument at the 1W2A station of Beijing Synchrotron Radiation Facility (BSRF). A test on a kind of non-caking coal shows that the furnace works well, and the experimental result is reasonable. [Received: January 5, 2021; Accepted: March 2, 2021]