scholarly journals Multi-fractal characteristics of pore structure for coal during the refined upgrading degassing temperatures

2021 ◽  
Author(s):  
Jianjun Wang ◽  
Lingli Liu ◽  
Zehong Cui ◽  
Hongjun Wang ◽  
Teng Li ◽  
...  
Keyword(s):  
Low Temperature ◽  
Pore Structure ◽  
Fractal Theory ◽  
Dynamic Change ◽  
Ordos Basin ◽  
Nitrogen Adsorption ◽  
Low Rank ◽  
Low Rank Coal ◽  
Adsorption Measurement ◽  
Fractal Spectrum

AbstractThe low-temperature nitrogen adsorption measurement is commonly used to describe the pore structure of porous medium, while the role of degassing temperature in the low-temperature nitrogen adsorption measurement does not attract enough attention, various degassing temperatures may lead to the different pore structure characterization for the same coal. In this study, the low-rank coal collected from Binchang mining area, southwest of Ordos Basin was launched the low-temperature nitrogen adsorption measurement under seven various degassing temperatures (120 °C, 150 °C, 180 °C, 210 °C, 240 °C, 270 °C and 300 °C), respectively, the dynamic change of the pore structure under refined upgrading degassing temperatures are studied, and it was also quantitative evaluated with the multi-fractal theory. The results show that the pore specific surface area and pore volume decrease linearly with the increased degassing temperatures, ranges from 12.53 to 2.16 m2/g and 0.01539 to 0.00535 cm3/g, respectively. While the average pore aperture features the contrary characteristics (various from 4.9151 to 9.9159 nm), indicating the pore structure has been changed during the refined upgrading degassing temperatures. With the upgrading degassing temperatures, the sizes of hysteresis loop decrease, and the connectivity of pore structure enhanced. The multi-fractal dimension and multi-fractal spectrum could better present the partial abnormal of pore structure during the refined upgrading degassing temperatures, and the quality index, Dq spectrum, D−10–D10 and multi-fractal spectrum could describe the homogeneity and connectivity of the pores finely. The degassing temperatures of 150 °C, 180 °C and 270 °C are selected as three knee points, which can reflect the partial abnormal of the pore structure during the refined upgrading degassing temperatures. Under the lower degassing temperature (< 150 °C), the homogeneity and connectivity of the pore feature a certain increase, following that it presents stable when the degassing temperatures various from 150 to 180 °C. The homogeneity and connectivity of the pore would further enhanced until the degassing temperature reaches to 270 °C. Because of the melting of the pore when the degassing temperature exceeds 270 °C, the complexity of pore structure increased. In this study, we advise the degassing temperature for low-temperature nitrogen adsorption measurement of low-rank coal should not exceed 120 °C.

scholarly journals The dynamic change of pore structure for low-rank coal under refined upgrading pretreatment temperatures

2020 ◽  
Author(s):  
Teng Li ◽  
Cai-Fang Wu ◽  
Zi-Wei Wang
Keyword(s):  
Pore Structure ◽  
Pore Volume ◽  
Dynamic Change ◽  
Total Pore Volume ◽  
Nitrogen Adsorption ◽  
Volatile Matter ◽  
Low Rank ◽  
Low Rank Coal ◽  
Pore Collapse ◽  
Pretreatment Temperature

AbstractPore structure characteristics are significant factor in the evaluation of the physical characteristics of low-rank coal. In this study, three low-rank coal samples were collected from the Xishanyao Formation, Santanghu Basin, and low-temperature liquid-nitrogen adsorption (LP-N2A) measurements were taken under various pretreatment temperatures. Owing to the continuous loss of water and volatile matter in low-rank coal, the total pore volume assumes a three-step profile with knee temperatures of 150 °C and 240 °C. However, the ash in the coal can protect the coal skeleton. Pore collapse mainly occurs for mesopores with aperture smaller than 20 nm. Mesopores with apertures smaller than 5 nm exhibit a continuous decrease in pore volume, whereas the pore volume of mesopores with apertures ranging from 5 to 10 nm increases at lower pretreatment temperatures (<150 °C) followed by a faint decrease. As for mesopores with apertures larger than 10 nm, the pore volume increases significantly when the pretreatment temperature reaches 300 °C. The pore structure of low-rank coal features a significant heating effect, the pretreatment temperature should not exceed 150 °C when the LP-N2A is used to evaluate the pore structure of low-rank coal to effectively evaluate the reservoir characteristics of low-rank coal.

scholarly journals The Dynamic Change of Pore Structure for the Low-Rank Coal with Various Pretreatment Temperatures: A Case Study from Southwestern Ordos Basin

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Teng Li
Keyword(s):  
Coal Sample ◽  
Dynamic Change ◽  
Ordos Basin ◽  
Hysteresis Loops ◽  
Low Rank ◽  
Low Rank Coal ◽  
Mesopore Volume ◽  
Pore Characteristics ◽  
Pattern Distribution ◽  
The Right

The pore characteristics of the low-rank coal are different from medium- and high-rank coals. The low-temperature N2 adsorption (LP-N2A) measurements with a single low-rank coal were launched, and the dynamic change of pore structures under various pretreatment temperatures from 120°C to 300°C was studied. The isothermal curves of the DFS coal sample feature IV type, the hysteresis loops convert from H4 type to H2 type, and the hysteresis loops tend to be closed with the increased pretreatment temperatures. The mesopores are dominant in the DFS coal. The dynamic of pore volume (PV) and pore specific surface area (SSA) features the three-step-style change with the cut-off temperature points at 150°C and 240°C, and this has a relationship with the loss of the moisture and volatiles in the DFS coal sample. The pores with an aperture below 10 nm are the dominant mesopores in the DFS coal, and the mesopore volume features bimodal pattern distribution with a higher left peak of approximately 1.7 nm and a lower right peak of approximately 3-5 nm, and the right peak continuously right shift with the increase pretreatment temperatures. The total mesopore volume decreases with the upgrading temperatures, while the ratio of pores greater than 5 nm increases. Finally, the mesopore evolution model with the increased pretreatment temperatures was summarized.

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.

scholarly journals Fractal Characterization of Nanopore Structure in Shale, Tight Sandstone and Mudstone from the Ordos Basin of China Using Nitrogen Adsorption

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 583 ◽  
Author(s):  
Xiaohong Li ◽  
Zhiyong Gao ◽  
Siyi Fang ◽  
Chao Ren ◽  
Kun Yang ◽  
...  
Keyword(s):  
Pore Structure ◽  
Pressure Range ◽  
Ordos Basin ◽  
Fractal Dimensions ◽  
Nitrogen Adsorption ◽  
Relative Pressure ◽  
Tight Sandstone ◽  
Porosity And Permeability ◽  
The Ordos Basin ◽  
Nanopore Structure

The characteristics of the nanopore structure in shale, tight sandstone and mudstone from the Ordos Basin of China were investigated by X-ray diffraction (XRD) analysis, porosity and permeability tests and low-pressure nitrogen adsorption experiments. Fractal dimensions D1 and D2 were determined from the low relative pressure range (0 < P/P0 < 0.4) and the high relative pressure range (0.4 < P/P0 < 1) of nitrogen adsorption data, respectively, using the Frenkel–Halsey–Hill (FHH) model. Relationships between pore structure parameters, mineral compositions and fractal dimensions were investigated. According to the International Union of Pure and Applied Chemistry (IUPAC) isotherm classification standard, the morphologies of the nitrogen adsorption curves of these 14 samples belong to the H2 and H3 types. Relationships among average pore diameter, Brunner-Emmet-Teller (BET) specific surface area, pore volume, porosity and permeability have been discussed. The heterogeneities of shale nanopore structures were verified, and nanopore size mainly concentrates under 30 nm. The average fractal dimension D1 of all the samples is 2.1187, varying from 1.1755 to 2.6122, and the average fractal dimension D2 is 2.4645, with the range from 2.2144 to 2.7362. Compared with D1, D2 has stronger relationships with pore structure parameters, and can be used for analyzing pore structure characteristics.

Low-temperature co-pyrolysis of a low-rank coal and biomass to prepare smokeless fuel briquettes

2003 ◽  
Vol 70 (2) ◽  
pp. 665-677 ◽  
Author(s):  
M.J Blesa ◽  
J.L Miranda ◽  
R Moliner ◽  
M.T Izquierdo ◽  
J.M Palacios
Keyword(s):  
Low Temperature ◽  
Low Rank ◽  
Low Rank Coal

Variation in Pore Structure Characteristics with Composition in the High Volatile Bituminous Coal of Binchang Area

2014 ◽  
Vol 962-965 ◽  
pp. 890-898
Author(s):  
Jin Ping Li ◽  
Da Zhen Tang ◽  
Ting Xu Yu ◽  
Gang Sun
Keyword(s):  
Low Temperature ◽  
Pore Structure ◽  
Parallel Plate ◽  
Bituminous Coal ◽  
Nitrogen Adsorption ◽  
Bet Surface Area ◽  
Test Results ◽  
Structure Characteristics ◽  
Desorption Isotherms ◽  
Adsorption Desorption

Pore structure characteristics and the effect of lithotype and maceral on pore for three types of high-volatile bituminous coals from Binchang area were investigated by combined low-temperature nitrogen adsorption/desorption, nuclear magnetic resonance (NMR), scanning electron microscope (SEM) and maceral analysis. The low temperature N2 adsorption/desorption test results show that: micropores are more abundant than transitional pores with high BET surface area; two types of pore structures can be identified by adsorption/desorption isotherms; Pore morphology is mainly represented by well-connected, ink-bottled, cylindrical and parallel plate pores. NMR T2 distributions at full saturated condition are apparent or less obvious trimodal and three types of T2 distributions are identified; Seepage pores are better developed when compared with the middle-high rank coal. Further research found that the three coal lithotypes are featured by remarkably different pore structure characteristics and maceral contents of coal are linearly correlated to some of pore structure parameters.

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