scholarly journals Effects of Particle Size on Diffusion Kinetics in Chinese Anthracites during CH4 Desorption

Processes ◽  
2020 ◽  
Vol 8 (5) ◽  
pp. 514
Author(s):  
Jie Zang ◽  
Kai Wang ◽  
Yanbin Yu
Keyword(s):  
Particle Size ◽  
Coalbed Methane ◽  
Gas Flow ◽  
Hard Coal ◽  
Diffusion Kinetics ◽  
Methane Recovery ◽  
Coal Matrix ◽  
Matrix Blocks ◽  
Reported Data ◽  
Coalbed Methane Production

Diffusion kinetics is widely acknowledged to dominate gas flow in coal matrix blocks. Knowledge of this topic is important for ongoing coalbed methane recovery and CO2-enhanced coalbed methane production. Because laboratory diffusivity measurements are normally conducted on powdered coals, it is unclear how representative the results are for coalbeds. Investigations into the effects of particle size on gas diffusivity can provide insights into the in situ diffusivity of the coal matrix. This paper presents measured CH4 desorption data in two Chinese anthracites (one brittle, one hard) having different particle sizes, to investigate the effects of particle size on diffusion kinetics. The experimental data were fitted by both the unipore (UP) and bidisperse (BD) models. The BD model agreed better with the measured data than the UP model, especially for the brittle coal. This indicated that the brittle coal was more abundant in macropores than the hard coal. Diffusivity in the hard coal decreased with increasing particle size but varied stochastically within a small value range in the brittle coal as the particle size increased. The diffusivity of the brittle coal, with its higher vitrinite content and lower inertinite content, was greater compared with the hard coal. This was inconsistent with reported data in which vitrinite had a smaller diffusivity than inertinite. This anomalous phenomenon may be caused by the generation of comparatively more macropores during grinding in the brittle coal. These results indicate that the effects of particle size on diffusivity may be coal-dependent, and further, the effects of particle size are influenced by other factors, including coal structure.

Application of Hydraulic Flushing in Coal Seams To Reduce Hazardous Outbursts in the Mengjin Mine, China

2018 ◽  
Vol 24 (4) ◽  
pp. 425-440 ◽  
Author(s):  
Jingyu Jiang ◽  
Weihua Yang ◽  
Yuanping Cheng ◽  
Baomin Lv ◽  
Kai Zhang ◽  
...  
Keyword(s):  
Field Test ◽  
Coalbed Methane ◽  
Gas Flow ◽  
Average Diameter ◽  
Gas Production ◽  
Hard Coal ◽  
Gas Extraction ◽  
Coal Seams ◽  
Influence Radius ◽  
Borehole Camera

Abstract Hydraulic fracturing and waterjet slotting fracturing have been demonstrated to be effective in creating artificial fractures and stimulating gas production in hard coal seams. However, these methods are inefficient for soft-outburst coal seams because these created fractures are short and easy to close. To eliminate the outburst risk of soft coals, a novel enhanced coalbed methane under-panel cross-strata drainage technique via hydraulic flushing was proposed in this work. The hydraulic flushing effects of boreholes of different sizes in the coal seam were also pre-evaluated by a simulation approach. The modeling results indicate that as the radius of the borehole increases, the plastic and stress-decreasing zone expands. A field test was also conducted in the Minjin mine, China, that investigated the gas pressure variation between three monitoring boreholes at different distances from a hydraulic flushing borehole. Test results indicate that the effective influence radius of gas extraction is approximately 5.5 m. Based on the results of the field test and borehole camera observation, the unloaded coal quantity and the average diameter of the boreholes were estimated to be 8.0 t and 942 mm, respectively. The borehole diameter expanded up to 10 times larger than its original size. The average gas extraction concentration and gas flow rate increased by approximately 2 and 3.5 times, respectively, demonstrating the effectiveness of the proposed hydraulic flushing in improving the gas extraction efficiency. The hydraulic flushing technique therefore is proved to be efficient in eliminating the outburst risk of coal and reducing greenhouse gas emissions.

scholarly journals Influence of Coal Particle Size on Coal Adsorption and Desorption Characteristics

2014 ◽  
Vol 59 (3) ◽  
pp. 807-820 ◽  
Author(s):  
Lei Zhang ◽  
Naj Aziz ◽  
Ting Ren ◽  
Jan Nemcik ◽  
Shihao Tu
Keyword(s):  
Particle Size ◽  
Sorption Capacity ◽  
Coalbed Methane ◽  
Coal Particle ◽  
Sorption Isotherms ◽  
Ash Content ◽  
Methane Recovery ◽  
Adsorption And Desorption ◽  
Coal Particles ◽  
Desorption Hysteresis

Abstract Accurate testing coal isotherm can play a significant role in the areas of coal seam gas drainage, outburst control, CO2 geo-sequestration, coalbed methane (CBM) and enhanced coalbed methane recovery (ECBM) etc. The effect of particle size on the CO2 and CH4 sorption capacity of bituminous coal from Illawarra, Australia was investigated at 35°C and at pressure up to 4 MPa. A unique indirect gravimetric apparatus was used to measure the gas adsorption and desorption isotherms of coal of different particle sizes ranging from around 150 urn to 16 mm. Langmuir model was used to analysis the experimental results of all gases. Coal particle size was found to have an apparent effect on the coal ash content and helium density results. Coal with larger particle size had higher ash content and higher helium density. The sorption isotherm was found to be highly sensitive with helium density of coal which was determined in the procedure of testing the void volume of sample cell. Hence, coal particle size had a significant influence on the coal sorption characteristics including sorption capacity and desorption hysteresis for CO2 and CH4, especially calculated with dry basis of coal. In this study, the 150-212 um (150 um) coal samples achieved higher sorption capacity and followed by 2.36-3.35 mm (2.4 mm), 8-9.5 mm (8 mm) and 16-19 mm (16 mm) particle size samples. However, the differences between different coal particles were getting smaller when the sorption isotherms are calculated with dry ash free basis. Test with 150 um coal samples were also found to have relatively smaller desorption hysteresis compared with the other larger particle size samples. The different results including adsorption/desorption isotherm, Langmuir parameters and coal hysteresis were all analysed with the CO2 and CH4 gases.

The Influences of the Rank of Coal on Methane Sorption Capacity in Coals/Wpływ Rzędu Węgla Na Pojemność Sorpcyjną Metanu W Węglach

2014 ◽  
Vol 59 (2) ◽  
pp. 509-516
Author(s):  
Andrzej Olajossy
Keyword(s):  
Sorption Capacity ◽  
Coalbed Methane ◽  
Vitrinite Reflectance ◽  
Sorption Isotherms ◽  
Volatile Matter ◽  
Low Rank ◽  
Hard Coal ◽  
Petrographic Composition ◽  
Methane Sorption ◽  
Indian Coals

Abstract Methane sorption capacity is of significance in the issues of coalbed methane (CBM) and depends on various parameters, including mainly, on rank of coal and the maceral content in coals. However, in some of the World coals basins the influences of those parameters on methane sorption capacity is various and sometimes complicated. Usually the rank of coal is expressed by its vitrinite reflectance Ro. Moreover, in coals for which there is a high correlation between vitrinite reflectance and volatile matter Vdaf the rank of coal may also be represented by Vdaf. The influence of the rank of coal on methane sorption capacity for Polish coals is not well understood, hence the examination in the presented paper was undertaken. For the purpose of analysis there were chosen fourteen samples of hard coal originating from the Upper Silesian Basin and Lower Silesian Basin. The scope of the sorption capacity is: 15-42 cm3/g and the scope of vitrinite reflectance: 0,6-2,2%. Majority of those coals were of low rank, high volatile matter (HV), some were of middle rank, middle volatile matter (MV) and among them there was a small number of high rank, low volatile matter (LV) coals. The analysis was conducted on the basis of available from the literature results of research of petrographic composition and methane sorption isotherms. Some of those samples were in the form (shape) of grains and others - as cut out plates of coal. The high pressure isotherms previously obtained in the cited studies were analyzed here for the purpose of establishing their sorption capacity on the basis of Langmuire equation. As a result of this paper, it turned out that for low rank, HV coals the Langmuire volume VL slightly decreases with the increase of rank, reaching its minimum for the middle rank (MV) coal and then increases with the rise of the rank (LV). From the graphic illustrations presented with respect to this relation follows the similarity to the Indian coals and partially to the Australian coals.

IDENTIFYING THE SOURCE, PATHWAYS, AND RATES OF ENHANCED MICROBIAL COALBED METHANE PRODUCTION

2016 ◽  
Author(s):  
Katherine J. Davis ◽  
◽  
Robin Gerlach ◽  
H.D. Schweitzer ◽  
Al Cunningham ◽  
...  
Keyword(s):  
Methane Production ◽  
Coalbed Methane ◽  
Coalbed Methane Production

scholarly journals Experimental Analysis of the Mechanical Properties and Resistivity of Tectonic Coal Samples with Different Particle Sizes

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2303
Author(s):  
Congyu Zhong ◽  
Liwen Cao ◽  
Jishi Geng ◽  
Zhihao Jiang ◽  
Shuai Zhang
Keyword(s):  
Mechanical Properties ◽  
Particle Size ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Uniaxial Compressive Strength ◽  
Coalbed Methane ◽  
Coal Sample ◽  
Fine Particles ◽  
Particle Sizes ◽  
Tectonic Coal

Because of its weak cementation and abundant pores and cracks, it is difficult to obtain suitable samples of tectonic coal to test its mechanical properties. Therefore, the research and development of coalbed methane drilling and mining technology are restricted. In this study, tectonic coal samples are remodeled with different particle sizes to test the mechanical parameters and loading resistivity. The research results show that the particle size and gradation of tectonic coal significantly impact its uniaxial compressive strength and elastic modulus and affect changes in resistivity. As the converted particle size increases, the uniaxial compressive strength and elastic modulus decrease first and then tend to remain unchanged. The strength of the single-particle gradation coal sample decreases from 0.867 to 0.433 MPa and the elastic modulus decreases from 59.28 to 41.63 MPa with increasing particle size. The change in resistivity of the coal sample increases with increasing particle size, and the degree of resistivity variation decreases during the coal sample failure stage. In composite-particle gradation, the proportion of fine particles in the tectonic coal sample increases from 33% to 80%. Its strength and elastic modulus increase from 0.996 to 1.31 MPa and 83.96 to 125.4 MPa, respectively, and the resistivity change degree decreases. The proportion of medium particles or coarse particles increases, and the sample strength, elastic modulus, and resistivity changes all decrease.

scholarly journals Stress-Dependent Deformation and Permeability of a Fractured Coal Subject to Excavation-Related Loading Paths

2021 ◽  
Author(s):  
Wenzhuo Cao ◽  
Qinghua Lei ◽  
Wu Cai
Keyword(s):  
Coal Mining ◽  
Coalbed Methane ◽  
Axial Stress ◽  
Equilibrium Phase ◽  
Natural Fracture ◽  
Equivalent Permeability ◽  
Coal Matrix ◽  
Bedding Planes ◽  
Fractured Coal ◽  
Stress Dependent

AbstractThe deformation and permeability of coal are largely affected by the presence and distribution of natural fractures such as cleats and bedding planes with orthogonal and abutting characteristics, resulting in distinct hydromechanical responses to stress loading during coal mining processes. In this research, a two-dimensional (2D) fracture network is constructed based on a real coal cleat trace data collected from the Fukang mine area, China. Realistic multi-stage stress loading is designed to sequentially mimic an initial equilibrium phase and a mining-induced perturbation phase involving an increase of axial stress and a decrease of confining stress. The geomechanical and hydrological behaviour of the fractured coal under various stress loading conditions is modelled using a finite element model, which can simulate the deformation of coal matrix, the shearing and dilatancy of coal cleats, the variation of cleat aperture induced by combined effects of closure/opening, and shear and tensile-induced damage. The influence of different excavation stress paths and directions of mining is further investigated. The simulation results illustrate correlated variations among the shear-induced cleat dilation, damage in coal matrix, and equivalent permeability of the fractured coal. Model results are compared with results of previous work based on conventional approaches in which natural fracture networks are not explicitly represented. In particular, the numerical model reproduces the evolution of equivalent permeability under the competing influence of the effective stress perpendicular to cleats and shear-induced cleat dilation and associated damage. Model results also indicate that coal mining at low stress rates is conducive to the stability of surrounding coal seams, and that coal mining in parallel to cleat directions is desirable. The research findings of this paper have important implications for efficient and safe exploitation of coal and coalbed methane resources.

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