International Journal of Coal Science & Technology最新文献

In this study, the installation of an airlift pump with inner diameter of 102 mm and length of 5.64 m was utilized to consider the conveying process of non-spherical coal particles with density of 1340 kg/m³ and graining 25–44.5 mm. The test results revealed that the magnitude of increase in the solid transport rate due to the changes in the three tested parameters between compressed air velocity, submergence ratio, and feeding coal possibility was not the same, which are stand in range of 20%, 75%, and 40%, respectively. Hence, creating the optimal airlift pump performance is highly dependent on submergence ratio. More importantly, we measured the solid volume fraction using the method of one-way valves in order to minimize the disadvantages of conventional devices, such as fast speed camera and conductivity ring sensor. The results confirmed that the volume fraction of the solid phase in the transfer process was always less than 12%. To validate present experimental data, the existing empirical correlations together with the theoretical equations related to the multiphase flow was used. The overall agreement between the theory and experimental solid delivery results was particularly good instead of the first stage of conveying process. This drawback can be corrected by omitting the role of friction and shear stress at low air income velocity. It was also found that the model developed by Kalenik failed to predict the performance of our airlift operation in terms of the mass flow rate of the coal particles.

To study the dynamic mechanical properties and failure characteristics of intersecting jointed rock masses with different joint distributions under confining pressure, considering the cross angle α and joint persistence ratio η, a numerical model of the biaxial Hopkinson bar test system was established using the finite element method–discrete-element model coupling method. The validity of the model was verified by comparing and analyzing it in conjunction with laboratory test results. Dynamics-static combined impact tests were conducted on specimens under various conditions to investigate the strength characteristics and patterns of crack initiation and expansion. The study revealed the predominant factors influencing intersecting joints with different angles and penetrations under impact loading. The results show that the peak stress of the specimens decreases first and then increases with the increase of the cross angle. When α < 60°, regardless of the value of η, the dynamic stress of the specimens is controlled by the main joint. When α ≥ 60°, the peak stress borne by the specimens decreases with increasing η. When α < 60°, the initiation and propagation of cracks in the cross-jointed specimens are mainly controlled by the main joint, and the final failure surface of the specimens is composed of the main joint and wing cracks. When α ≥ 60° or η ≥ 0.67, the secondary joint guides the expansion of the wing cracks, and multiple failure surfaces composed of main and secondary joints, wing cracks, and co-planar cracks are formed. Increasing lateral confinement significantly increases the dynamic peak stress able to be borne by the specimens. Under triaxial conditions, the degree of failure of the intersecting jointed specimens is much lower than that under uniaxial and biaxial conditions.

The Pabdeh Formation represents organic matter enrichment in some oil fields, which can be considered a source rock. This study is based on the Rock–Eval, Iatroscan, and electron microscopy imaging results before and after heating the samples. We discovered this immature shale that undergoes burial and diagenesis, in which organic matter is converted into hydrocarbons. Primary migration is the process that transports hydrocarbons in the source rock. We investigated this phenomenon by developing a model that simulates hydrocarbon generation and fluid pressure during kerogen-to-hydrocarbon conversion. Microfractures initially formed at the tip/edge of kerogen and were filled with hydrocarbons, but as catagenesis progressed, the pressure caused by the volume increase of kerogen decreased due to hydrocarbon release. The transformation of solid kerogen into low-density bitumen/oil increased the pressure, leading to the development of damage zones in the source rock. The Pabdeh Formation’s small porethroats hindered effective expulsion, causing an increase in pore fluid pressure inside the initial microfractures. The stress accumulated due to hydrocarbon production, reaching the rock’s fracture strength, further contributed to damage zone development. During the expansion process, microfractures preferentially grew in low-strength pathways such as lithology changes, laminae boundaries, and pre-existing microfractures. When the porous pressure created by each kerogen overlapped, individual microfractures interconnected, forming a network of microfractures within the source rock. This research sheds light on the complex interplay between temperature, hydrocarbon generation, and the development of expulsion fractures in the Pabdeh Formation, providing valuable insights for understanding and optimizing hydrocarbon extraction in similar geological settings.

This study aimed to investigate the effects of ammonia addition on ethylene counter-flow diffusion flames with different diluents on the fuel or oxidizer side, using kinetic analyses. A special emphasis was put on assessing the coupled chemical effects of NH₃ and CO₂ on C₂H₄ combustion chemistry. The chemical effects could be evaluated by comparing fictitious inert NH₃ or CO₂ with normal active NH₃ or CO₂. The results revealed that the addition of NH₃ decreased the mole fractions and production rates of key soot precursors, such as acetylene, propynyl, and benzene. When CO₂ was used as the dilution gas, the coupled chemical effects of NH₃ and CO₂ were affected by the chemical effects of CO₂ to varying degrees. With the oxidizer-side CO₂ addition, the coupled chemical effects of NH₃ and CO₂ reduced the mole fractions of H, O, OH radicals, acetylene, propynyl, and benzene, while the effects differed from the fuel-side CO₂ addition. The coupled chemical effects of NH₃ and CO₂ also promoted the formation of aldehyde contaminants, such as acetaldehyde, to some extent, particularly with CO₂ addition on the oxidizer side.

The objectives of this study were to explore the changes in soil stoichiometry and enzyme activities at different distances from an opencast coal mine in the Hulun Buir Grassland of China. Four transects were established on north and east sides of the opencast coal mining area, and samples were collected at 50 m, 550 m, and 1550 m from the pit on each transect. Control samples were collected from a grassland station 8 km from the opencast coal mining area that was not disturbed by mining. Four replicate soil samples were collected at each point on the four transects. Soil physicochemical properties and enzyme activities were determined, and correlations between soil properties and stoichiometric ratios and enzyme activities were explored using redundancy analysis. The increase in distance from mining did not significantly affect soil properties, although soil urease activity was significantly lower than that of the control area. Soil properties 1550 m from the mine pit were similar to those at the grassland control. In addition, soil total nitrogen had the greatest effect on soil stoichiometry, and soil total potassium had the greatest effect on soil enzyme activities. Coal dust from opencast mining might be the main factor affecting soil stoichiometry and enzyme activities. The results of this study provide direction for the next step in studying the influence of mining areas on soil properties and processes.

In order to study the problems of unreasonable airflow distribution and serious dust pollution in a heading surface, an experimental platform for forced ventilation and dust removal was built based on the similar principles. Through the similar experiment and numerical simulation, the distribution of airflow field in the roadway and the spatial and temporal evolution of dust pollution under the conditions of forced ventilation were determined. The airflow field in the roadway can be divided into three zones: jet zone, vortex zone and reflux zone. The dust concentration gradually decreases from the head to the rear of the roadway. Under the forced ventilation conditions, there is a unilateral accumulation of dust, with higher dust concentrations away from the ducts. The position of the equipment has an interception effect on the dust. The maximum error between the test value and the simulation result is 12.9%, which verifies the accuracy of the experimental results. The research results can provide theoretical guidance for the application of dust removal technology in coal mine.

Recent studies have indicated that the injection of carbon dioxide (CO₂) can lead to increased oil recovery in fractured shale reservoirs following natural depletion. Despite advancements in understanding mass exchange processes in subsurface formations, there remains a knowledge gap concerning the disparities in these processes between the matrix and fractures at the pore scale in formations with varying permeability. This study aims to experimentally investigate the CO₂ diffusion behaviors and in situ oil recovery through a CO₂ huff ‘n’ puff process in the Jimsar shale oil reservoir. To achieve this, we designed three matrix-fracture models with different permeabilities (0.074 mD, 0.170 mD, and 0.466 mD) and experimented at 30 MPa and 91 °C. The oil concentration in both the matrix and fracture was monitored using a low-field nuclear magnetic resonance (LF-NMR) technique to quantify in situ oil recovery and elucidate mass-exchange behaviors. The results showed that after three cycles of CO₂ huff ‘n’ puff, the total recovery degree increased from 30.28% to 34.95% as the matrix permeability of the core samples increased from 0.074 to 0.466 mD, indicating a positive correlation between CO₂ extraction efficiency and matrix permeability. Under similar fracture conditions, the increase in matrix permeability further promoted CO₂ extraction efficiency during CO₂ huff ‘n’ puff. Specifically, the increase in matrix permeability of the core had the greatest effect on the extraction of the first-cycle injection in large pores, which increased from 16.42% to 36.64%. The findings from our research provide valuable insights into the CO₂ huff ‘n’ puff effects in different pore sizes following fracturing under varying permeability conditions, shedding light on the mechanisms of CO₂-enhanced oil recovery in fractured shale oil reservoirs.

Rock bolts are extensively utilized in underground engineering as a means of offering support and stability to rock masses in tunnels, mines, and other underground structures. In environments of high ground stress, faults or weak zones can frequently arise in rock formations, presenting a significant challenge for engineering and potentially leading to underground engineering collapse. Rock bolts serve as a crucial structural element for the transmission of tensile stress and are capable of withstanding shear loads to prevent sliding of weak zones within rock mass. Therefore, a complete understanding of the behavior of rock bolts subjected to shear loads is essential. This paper presents a state-of-the-art review of the research progress of rock bolts subjected to shear load in three categories: experiment, numerical simulation, and analytical model. The review focuses on the research studies and developments in this area since the 1970s, providing a comprehensive overview of numerous factors that influence the anchorage performance of rock bolts. These factors include the diameter and angle of the rock bolt installation, rock strength, grouting material, bolt material, borehole diameter, rock bolt preload, normal stress, joint surface roughness and joint expansion angle. The paper reviews the improvement of mechanical parameter setting in numerical simulation of rock bolt shear. Furthermore, it delves into the optimization of the analytical model concerning rock bolt shear theory, approached from the perspectives of both Elastic foundation beam theory coupled with Elastoplasticity theory and Structural mechanic methods. The significance of this review lies in its ability to provide insights into the mechanical behavior of rock bolts. The paper also highlights the limitations of current research and guidelines for further research of rock bolts.

Abstract

Deep shale reservoirs (3500–4500 m) exhibit significantly different stress states than moderately deep shale reservoirs (2000–3500 m). As a result, the brittleness response mechanisms of deep shales are also different. It is urgent to investigate methods to evaluate the brittleness of deep shales to meet the increasingly urgent needs of deep shale gas development. In this paper, the quotient of Young’s modulus divided by Poisson’s ratio based on triaxial compression tests under in situ stress conditions is taken as SSBV (Static Standard Brittleness Value). A new and pragmatic technique is developed to determine the static brittleness index that considers elastic parameters, the mineral content, and the in situ stress conditions (BIEMS). The coefficient of determination between BIEMS and SSBV reaches 0.555 for experimental data and 0.805 for field data. This coefficient is higher than that of other brittleness indices when compared to SSBV. BIEMS can offer detailed insights into shale brittleness under various conditions, including different mineral compositions, depths, and stress states. This technique can provide a solid data-based foundation for the selection of ‘sweet spots’ for single-well engineering and the comparison of the brittleness of shale gas production layers in different areas.

Excessive emissions of nitrogen oxides from flue gas have imposed various detrimental impacts on environment, and the development of deNO_x catalysts with low-cost and high performance is an urgent requirement. Iron oxide-based material has been explored for promising deNO_x catalysts. However, the unsatisfactory low-temperature activity limits their practical applications. In this study, a series of excellent low-temperature denitrification catalysts (Ha-FeO_x/yZS) were prepared by acid treatment of zinc slag, and the mass ratios of Fe to impure ions was regulated by adjusting the acid concentrations. Ha-FeO_x/yZS showed high denitrification performance (> 90%) in the range of 180–300 °C, and the optimal NO conversion and N₂ selectivity were higher than 95% at 250 °C. Among them, the Ha-FeO_x/2ZS synthesized with 2 mol/L HNO₃ exhibited the widest temperature window (175–350 °C). The excellent denitrification performance of Ha-FeO_x/yZS was mainly attributed to the strong interaction between Fe and impurity ions to inhibit the growth of crystals, making Ha-FeO_x/yZS with amorphous structure, nice fine particles, large specific surface area, more surface acid sites and high chemisorbed oxygen. The in-situ DRIFT experiments confirmed that the SCR reaction on the Ha-FeO_x/yZS followed both Langmuir-Hinshelwood (L-H) mechanism and Eley-Rideal (E-R) mechanism. The present work proposed a high value-added method for the preparation of cost-effective catalysts from zinc slag, which showed a promising application prospect in NO_x removal by selective catalytic reduction with ammonia.