scholarly journals Effect of Mechanical Vibration with Different Frequencies on Pore Structure and Fractal Characteristics in Lean Coal

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Maoliang Shen ◽  
Xuexi Chen ◽  
Yong Xu
Keyword(s):  
Coalbed Methane ◽  
Gas Adsorption ◽  
Mechanical Vibration ◽  
Total Pore Volume ◽  
Nitrogen Adsorption ◽  
Gas Diffusion ◽  
Microscopic Mechanism ◽  
Fractal Characteristics ◽  
And Diffusion ◽  
Nitrogen Adsorption Data

The mechanical vibrations caused by underground operations can easily lead to coal and gas outbursts in coal mines. Using the MVGAD-I experimental platform that we designed, the raw coal (0 Hz) was treated with vibration frequencies of 25, 50, 75, and 100 Hz, and the coal samples with different frequency vibrations were obtained. The total pore volume (TPV), specific surface area (SSA), pore size distribution, and the pore fractal dimension (PFD) of five coal samples were analyzed by mercury intrusion porosimetry and low-pressure nitrogen adsorption data. We found that the TPV, SSA, and PFD of the coal samples fluctuate with the increase of vibration frequency. The changes of the TPV and SSA of coal samples treated with 25 and 75 Hz vibrations were significantly greater than those subjected to vibrations of 50 and 100 Hz. Compared with the raw coal (0 Hz), the TPV and SSA of macropores, mesopores, and micropores increased the most in 75 Hz vibration coal sample. Therefore, the 75 Hz vibration excitation can improve the permeability of a body of coal mass and is conducive to the diffusion and seepage of coalbed methane and its production.. The influence of 25 Hz vibration on the TPV and SSA of macropores and mesopores is not obvious, but the TPV and SSA of minipores and micropores decrease significantly, which is not conducive to gas diffusion and adsorption. In addition, 25 and 75 Hz vibrations obviously damaged the fractal characteristics of both mesopores and micropores, resulting in the change of gas adsorption and diffusion ability. The rational use of a 75 Hz vibration is beneficial to both the production of gas and the prevention of outbursts, while a 25 Hz vibration should be avoided. The results are expected to reveal the microscopic mechanism of a vibration-induced outburst and provide theoretical guidance for employing the appropriate frequency of vibration to improve the rate of gas drainage and reduce the risk of outbursts.

Fractal Characteristics and Its Controlling Factors of Nanopore of Coal from Shanxi Province, North China

2021 ◽  
Vol 21 (1) ◽  
pp. 727-740
Author(s):  
Zhi Xu ◽  
Ming Li ◽  
Yu Xu ◽  
Luwei Sun
Keyword(s):  
Fractal Dimension ◽  
Coalbed Methane ◽  
Correlation Coefficients ◽  
Fractal Dimensions ◽  
Total Pore Volume ◽  
Nitrogen Adsorption ◽  
Fractal Model ◽  
Shanxi Province ◽  
Fractal Characteristics ◽  
Permian Coal

Much attention has been recently paid to the Carboniferous-Permian coal-bearing strata in Shanxi Province, now the largest producing coalbed methane field in China. In this study, a comprehensive approach of mercury injection, low-temperature liquid nitrogen adsorption, and permeability experiments was adopted to investigate the structure and fractal characteristics of nanopores in the Carboniferous-Permian coal (with 0.77%˜3.04% Ro,ran). Based on the fractal model, two fractal dimensions D1 and D2 corresponding to diffusion pore (<65 nm) and seepage pore (pore size ≥65 nm), respectively, were calculated, and the relationships between the fractal dimensions with the pore structure parameters and permeability are discussed here. The results indicate that the studied coal samples have good fractal characteristics and that the calculated linear correlation coefficients are higher than 0.80. The fractal dimension D1 of the diffusion pores ranges from 2.3777 to 2.4624, with an average of 2.4173, while the fractal dimension D2 of the seepage pores is between 2.5844 and 2.6256, with an average of 2.5990. The fractal dimensions D1 of the diffusion pores increases with an increase in the BET specific surface area, vitrinite content, and Ro,ran while it decreases with an increase in the permeability, and has a weak correlation with the total pore volume. The correlation coefficients R2 for the fractal dimension D2 of the seepage pores, pore parameters, permeability, and maceral composition ranges from 0.0357 to 0.2551. These results indicate that uncertain relationships exist among these parameters.

scholarly journals Experimental research on desorption characteristics of gas-bearing coal subjected to mechanical vibration

2020 ◽  
Vol 38 (5) ◽  
pp. 1454-1466
Author(s):  
Xuexi Chen ◽  
Liang Zhang ◽  
Maoliang Shen
Keyword(s):  
Coalbed Methane ◽  
Gas Adsorption ◽  
Mechanical Vibration ◽  
Particle Diameter ◽  
Reference Value ◽  
Desorption Rate ◽  
Gas Desorption ◽  
Adsorbed Gas ◽  
Vibration Parameters ◽  
Adsorption Desorption

Mechanical vibration can induce coal and gas outburst accidents, and can also promote the exploitation of coalbed methane. In this paper, a vibration-adsorption-desorption experiment system was established, the effects of coal sample particle diameter, gas pressure, and vibration frequency on gas desorption were studied. Mechanical vibration can generate a shear force in the adsorbed gas and promote gas desorption, but there are appropriate vibration parameters. Within the range of experimental parameters, the larger the amplitude, the more favorable for gas desorption. The change rules of gas desorption rate and desorption quantity under different conditions are basically the same, showing a power function shape with time increase, and most of the desorption quantity was completed within the first 5 minutes. The gas desorption rate and desorption quantity were positively related to the gas adsorption pressure. The results have great reference value for preventing gas outbursts and promoting gas exploitation.

scholarly journals Study on the Effect of Soft and Hard Coal Pore Structure on Gas Adsorption Characteristics

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Xun Zhao ◽  
Tao Feng ◽  
Ping Wang ◽  
Ze Liao
Keyword(s):  
Pore Structure ◽  
Adsorption Capacity ◽  
Residence Time ◽  
Coalbed Methane ◽  
Gas Adsorption ◽  
Nitrogen Adsorption ◽  
Hard Coal ◽  
Research Results ◽  
Adsorption Characteristics ◽  
Soft Coal

In order to grasp the effect of soft and hard coal pore structure on gas adsorption characteristics, based on fractal geometry theory, low-temperature nitrogen adsorption and constant temperature adsorption test methods are used to test the pore structure characteristics of soft coal and its influence on gas adsorption characteristics. We used box dimension algorithm to measure the fractal dimension and distribution of coal sample microstructure. The research results show that the initial nitrogen adsorption capacity of soft coal is greater than that of hard coal, and the adsorption hysteresis loop of soft coal is more obvious than that of hard coal. And the adsorption curve rises faster in the high relative pressure section. The specific surface area and pore volume of soft coal are larger than those of hard coal. The number of pores is much larger than that of hard coal. In particular, the superposition of the adsorption force field in the micropores and the diffusion in the mesopores enhance the adsorption potential of soft coal. Introducing the concept of adsorption residence time, it is concluded that more adsorption sites on the surface of soft coal make the adsorption and residence time of gas on the surface of soft coal longer. Fractal characteristics of the soft coal surface are more obvious. The saturated adsorption capacity of soft coal and the rate of reaching saturation adsorption are both greater than those of hard coal. The research results of this manuscript will provide a theoretical basis for in-depth analysis of the adsorption/desorption mechanism of coalbed methane in soft coal seams and the formulation of practical coalbed methane control measures.

Small Angle X-ray Scattering Test of Hami Coal Sample Nanostructure Parameters with Gas Adsorbed Under Different Pressures

2021 ◽  
Vol 21 (1) ◽  
pp. 538-546
Author(s):  
Baisheng Nie ◽  
Kedi Wang ◽  
Yu Fan ◽  
Junsheng Zhao ◽  
Letong Zhang ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Small Angle ◽  
Coalbed Methane ◽  
Gas Adsorption ◽  
Gas Diffusion ◽  
X Ray ◽  
X Ray Scattering ◽  
Surface Dimension ◽  
Nanopore Structure ◽  
Ray Scattering

The complexity and multiscale structure of coal pores significantly influence the gas diffusion and seepage characteristics of coal. To apply small angle X-ray scattering (SAXS) to study the coal pore structure parameters within the scale of 1–100 nm in the methane adsorption process, the X-ray window was optimized and a gas adsorption chamber was designed to interface with the small angle X-ray scattering platform. The fractal dimension and porosity of Hami coal samples under different methane pressures were studied using the small angle X-ray scattering platform and adsorption chamber. The surface and nanopore fractal information of the nanopores in coal were distinguished. The variation trends of the pores and surface fractal dimension with time under the same methane pressure were compared. The results indicate that the surface dimension changes from 2.56 to 2.75, and the extremum point may indicate that the primary nanopore structure is crushed by the adsorbed gas after approximately 15 minutes. This work clarifies that the fractal dimension can characterize the changes in nanopores in the process of gas adsorption by using SAXS. According to the fractal characteristics, the adsorption of gas in coal nanopores is summarized as four steps: expansion from adsorbance, deformation, crushing and recombination. The minimum porosity is 0.95% and the extreme value point is 1.47%. This work also shows that decrease in surface energy affect the porosity changes in nano-size pores. This work is of some significance to coalbed methane permeability improvement and gas extraction.

scholarly journals Fractal characteristics and significances of the nanopores in oil shales during hydrous pyrolysis

2019 ◽  
Vol 10 (2) ◽  
pp. 557-567
Author(s):  
Lina Sun ◽  
Deliang Fu ◽  
Shunqi Chai ◽  
Wenxia Yang ◽  
Kai Zhou ◽  
...  
Keyword(s):  
Gas Adsorption ◽  
Fractal Dimensions ◽  
Nitrogen Adsorption ◽  
Average Diameter ◽  
Relative Pressure ◽  
Thermal Maturity ◽  
Adsorption Method ◽  
Pore Structures ◽  
Hydrous Pyrolysis ◽  
Fractal Characteristics

Abstract In order to explore the pore characterizations in shales during organic matter evolution, a series of simulation experiments were conducted. The artificial hydrous pyrolysis was conducted on the same seven columned oil-shale samples at 250 °C, 300 °C, 350 °C, 375 °C, 400 °C, 450 °C and 500 °C, respectively. To obtain the characteristics of pore structures in shales, the unheated and the residual solid samples were analyzed by low-pressure nitrogen adsorption method. Based on the nitrogen adsorption isotherms, fractal dimensions were calculated by the model of Frenkel–Halsey–Hill, which also contained the fractal dimension of D1 and D2 before and after the relative pressure P/Po = 0.5, respectively. And then the relationships of simulation temperatures (thermal maturity), total-, macro-, meso- and micro-pores volumes, specific surface areas and diameters to fractal dimensions were investigated. The results showed that the average value of D2 (2.6110) was higher than D1 (2.4147) and there was a positive relationship between them (R2 = 0.9237), which indicated that though D2 and D1 were more related to pore structures and surfaces, the better linear relationships suggested that both of them could be used in the representation of pore structures and surfaces in shales. With the thermal maturity increasing, the obvious fractal characteristics were, the complexity of pore structures were, which may be associated with the following cause-and-effect relationships. During the pyrolysis, the generation of hydrocarbons increased, as well as the consumption of TOC may increase the volume and surface area of total-, macro-, meso- and micro-pores but decrease the corresponding average diameter and then the quantities of smaller pores occurred and led to the strengthening of pore heterogeneity in shales. Based on the fractal characteristics, we also found the higher thermal maturity would result in the better connections among pores but worse permeability in shale, which further increased the gas adsorption quantity. Therefore, analyzing the fractal characteristics in shales could provide help for clarifying the characteristics of reservoirs as well as the comprehensive exploration and development of shale gas.

scholarly journals Comparison of fractal dimensions from nitrogen adsorption data in shale via different models

RSC Advances ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 2298-2306
Author(s):  
Kouqi Liu ◽  
Mehdi Ostadhassan ◽  
Ho Won Jang ◽  
Natalia V. Zakharova ◽  
Mohammadreza Shokouhimehr
Keyword(s):  
Adsorption Isotherm ◽  
Gas Adsorption ◽  
Fractal Dimensions ◽  
Nitrogen Adsorption ◽  
Adsorption Data ◽  
Nitrogen Adsorption Data

Comparison of the fractal dimensions from different fractal theories by using the same sample gas adsorption isotherm.

scholarly journals Pore-Scale Lattice Boltzmann Simulation of Gas Diffusion–Adsorption Kinetics Considering Adsorption-Induced Diffusivity Change

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4927 ◽  
Author(s):  
Zhigao Peng ◽  
Shenggui Liu ◽  
Yingjun Li ◽  
Zongwei Deng ◽  
Haoxiong Feng
Keyword(s):  
Coalbed Methane ◽  
Gas Adsorption ◽  
Fluid Velocity ◽  
Gas Diffusion ◽  
Gas Production ◽  
Pore Scale ◽  
Desorption Process ◽  
Gas Diffusivity ◽  
Isotherm Adsorption ◽  
Adsorption Desorption

The diffusion–adsorption behavior of methane in coal is an important factor that both affecting the decay rate of gas production and the total gas production capacity. In this paper, we established a pore-scale Lattice Boltzmann (LB) model coupled with fluid flow, gas diffusion, and gas adsorption–desorption in the bi-dispersed porous media of coalbed methane. The Knudsen diffusion and dynamic adsorption–desorption of gas in clusters of coal particles were considered. Firstly, the model was verified by two classical cases. Then, three dimensionless numbers, Re, Pe, and Da, were adopted to discuss the impact of fluid velocity, gas diffusivity, and adsorption/desorption rate on the gas flow–diffusion–adsorption process. The effect of the gas adsorption layer in micropores on the diffusion–adsorption–desorption process was considered, and a Langmuir isotherm adsorption theory-based method was developed to obtain the dynamic diffusion coefficient, which can capture the intermediate process during adsorption/desorption reaches equilibrium. The pore-scale bi-disperse porous media of coal matrix was generated based on the RCP algorithm, and the characteristics of gas diffusion and adsorption in the coal matrix with different Pe, Da, and pore size distribution were discussed. The conclusions were as follows: (1) the influence of fluid velocity on the diffusion–adsorption process of coalbed methane at the pore-scale is very small and can be ignored; the magnitude of the gas diffusivity in macropores affects the spread range of the global gas diffusion and the process of adsorption and determines the position where adsorption takes place preferentially. (2) A larger Fickian diffusion coefficient or greater adsorption constant can effectively enhance the adsorption rate, and the trend of gas concentration- adsorption is closer to the Langmuir isotherm adsorption curve. (3) The gas diffusion–adsorption–desorption process is affected by the adsorption properties of coal: the greater the pL or Vm, the slower the global gas diffusivity decay. (4) The effect of the gas molecular adsorption layer has a great impact on the kinetic process of gas diffusion–adsorption–desorption. Coal is usually tight and has low permeability, so it is difficult to ensure that the gas diffusion and adsorption are sufficient, the direct use of a static isotherm adsorption equation may be incorrect.

Synthesis of dispersed mesoporous powders solid solution Zr0.88Ce0.12O2 for catalyst carrier of the conversion of methane to synthesis –gas

2020 ◽  
pp. 73-83
Author(s):  
L. V. Morozova ◽  
◽  
I. A. Drozdova ◽  
Keyword(s):  
Solid Solution ◽  
Total Pore Volume ◽  
Nitrogen Adsorption ◽  
Primary Crystal ◽  
X Ray ◽  
Catalyst Carrier ◽  
Conversion Of Methane ◽  
Deposition Processes ◽  
Zirconia Oxide ◽  
Coprecipitation Of Hydroxides

The xerogels in the system 0.88 mol.% ZrO2 − 0.12 mol.% CeO2 were obtained by the method of coprecipitation in a neutral (pH = 7) and slightly alkaline (pH = 9) medium under the influence of ultrasound with the size of the agglomerates 70 – 230 nm. It is shown that the coprecipitation of hydroxides of zirconium and cerium at pH = 9 with the use of ultrasonic treatment facilitates the formation of a primary crystal is symbolic of the particles in the xerogel, whose size is ~ 5 nm, whereas the xerogel synthesized in a neutral environment consists only of the x-ray amorphous phase. The effect of pH-precipitation on deposition processes of dehydration of the xerogels and crystallization solid solution based on zirconia oxide in the metastable pseudocubic modification (с′-ZrO2) was discovered. It was found that in the temperature range 500 – 800 °C there is a phase transition с′-ZrO2 → t-ZrO2, the size of the crystallites of the formed tetragonal solid solutions is 8 and 11 nm. The method of low-temperature nitrogen adsorption were investigated dispersion properties and characteristics of the pore structure of the powders of the solid solution Zr0.88Ce0.12O2. It is determined that the specific surface area of t-ZrO2 samples obtained after firing at 800 °C is 117 and 178 m2/g, the total pore volume reaches 0.300 − 0.325 cm3/g, the pore size distribution is monomodal and is in the range of 2 − 8 nm. The effect of thermal “aging” at a temperature of 800 °C (40 h) on the structure and dispersion of the solid solution t-ZrO2 powders was studied.

Influence of tectonic evolution on pore structure and fractal characteristics of coal by low pressure gas adsorption

2020 ◽  
pp. 103788
Author(s):  
Xiaolei Wang ◽  
Yuanping Cheng ◽  
Dongming Zhang ◽  
Zhengdong Liu ◽  
Zhenyang Wang ◽  
...  
Keyword(s):  
Pore Structure ◽  
Tectonic Evolution ◽  
Gas Adsorption ◽  
Low Pressure ◽  
Fractal Characteristics

scholarly journals Nanometer Pore Structure Characterization of Taiyuan Formation Shale in the Lin-Xing Area Based on Nitrogen Adsorption Experiments

Minerals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 298
Author(s):  
Chenlong Ding ◽  
Jinxian He ◽  
Hongchen Wu ◽  
Xiaoli Zhang
Keyword(s):  
Specific Surface ◽  
Pore Structure ◽  
Surface Area ◽  
Specific Surface Area ◽  
Shale Gas ◽  
Pore Volume ◽  
Ordos Basin ◽  
Total Pore Volume ◽  
Nitrogen Adsorption ◽  
Taiyuan Formation

Ordos Basin is an important continental shale gas exploration site in China. The micropore structure of the shale reservoir is of great importance for shale gas evaluation. The Taiyuan Formation of the lower Permian is the main exploration interval for this area. To examine the nanometer pore structures in the Taiyuan Formation shale reservoirs in the Lin-Xing area, Northern Shaanxi, the microscopic pore structure characteristics were analyzed via nitrogen adsorption experiments. The pore structure parameters, such as specific surface area, pore volume, and aperture distribution, of shale were calculated; the significance of the pore structure for shale gas storage was analyzed; and the main controlling factors of pore development were assessed. The results indicated the surface area and hole volume of the shale sample to be 0.141–2.188 m2/g and 0.001398–0.008718 cm3/g, respectively. According to the IUPAC (International Union of Pure and Applied Chemistry) classification, mesopores and macropores were dominant in the pore structure, with the presence of a certain number of micropores. The adsorption curves were similar to the standard IV (a)-type isotherm line, and the hysteresis loop type was mainly similar to H3 and H4 types, indicating that most pores are dominated by open type pores, such as parallel plate-shaped pores and wedge-shaped slit pores. The micropores and mesopores provide the vast majority of the specific surface area, functioning as the main area for the adsorption of gas in the shale. The mesopores and macropores provide the vast majority of the pore volume, functioning as the main storage areas for the gas in the shale. Total organic carbon had no notable linear correlation with the total pore volume and the specific surface area. Vitrinite reflectance (Ro) had no notable correlation with the specific surface area, but did have a low “U” curve correlation with the total pore volume. There was no relationship between the quartz content and specific surface area and total pore volume. In addition, there was no notable correlation between the clay mineral content and total specific surface area and total pore volume.

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