International Journal of Coal Science & Technology最新文献

Utilizing energy storage in depleted oil and gas reservoirs can improve productivity while reducing power costs and is one of the best ways to achieve synergistic development of "Carbon Peak–Carbon Neutral" and "Underground Resource Utilization". Starting from the development of Compressed Air Energy Storage (CAES) technology, the site selection of CAES in depleted gas and oil reservoirs, the evolution mechanism of reservoir dynamic sealing, and the high-flow CAES and injection technology are summarized. It focuses on analyzing the characteristics, key equipment, reservoir construction, application scenarios and cost analysis of CAES projects, and sorting out the technical key points and existing difficulties. The development trend of CAES technology is proposed, and the future development path is scrutinized to provide reference for the research of CAES projects in depleted oil and gas reservoirs.

Graphical abstract

The cyclic hydrogenation technology in a direct coal liquefaction process relies on the dissolved hydrogen of the solvent or oil participating in the hydrogenation reaction. Thus, a theoretical basis for process optimization and reactor design can be established by analyzing the solubility of hydrogen in liquefaction solvents. Experimental studies of hydrogen solubility in liquefaction solvents are challenging due to harsh reaction conditions and complex solvent compositions. In this study, the composition and content of liquefied solvents were analyzed. As model compounds, hexadecane, toluene, naphthalene, tetrahydronaphthalene, and phenanthrene were chosen to represent the liquefied solvents in chain alkanes and monocyclic, bicyclic, and tricyclic aromatic hydrocarbons. The solubility of hydrogen X (mol/mol) in pure solvent components and mixed solvents (alkanes and aromatics mixed in proportion to the chain alkanes + bicyclic aromatic hydrocarbons, bicyclic saturated aromatic hydrocarbons + bicyclic aromatic hydrocarbons, and bicyclic aromatic hydrocarbons + compounds containing heteroatoms composed of mixed components) are determined using Aspen simulation at temperature and pressure conditions of 373–523 K and 2–10 MPa. The results demonstrated that at high temperatures and pressures, the solubility of hydrogen in the solvent increases with the increase in temperature and pressure, with the pressure having a greater impact. Furthermore, the results revealed that hydrogen is more soluble in straight-chain alkanes than in other solvents, and the solubility of eicosanoids reaches a maximum of 0.296. The hydrogen solubility in aromatic ring compounds decreased gradually with an increase in the aromatic ring number. The influence of chain alkanes on the solubility of hydrogen predominates in a mixture of solvents with different mixing ratios of chain alkanes and aromatic hydrocarbons. The solubility of hydrogen in mixed aromatic solvents is less than that in the corresponding single solvents. Hydrogen is less soluble in solvent compounds containing heteroatoms than in compounds without heteroatoms.

The residual subsidence caused by underground mining in mountain area has a long subsidence duration time and great potential harm, which seriously threatens the safety of people's production and life in the mining area. Therefore, it is necessary to use appropriate monitoring methods and mathematical models to effectively monitor and predict the residual subsidence caused by underground mining. Compared with traditional level survey and InSAR (Interferometric Synthetic Aperture Radar) technology, GNSS (Global Navigation Satellite System) online monitoring technology has the advantages of long-term monitoring, high precision and more flexible monitoring methods. The empirical equation method of residual subsidence in mining subsidence is effectively combined with the rock creep equation, which can not only describe the residual subsidence process from the mechanism, but also predict the residual subsidence. Therefore, based on GNSS online monitoring technology, combined with the mining subsidence model of mountain area and adding the correlation coefficient of the compaction degree of caving broken rock and the Kelvin model of rock mechanics, this paper constructs the residual subsidence time series model of arbitrary point on the ground in mountain area. Through the example, the predicted results of the model in the inversion parameter phase and the dynamic prediction phase are compared with the measured data sequence. The results show that the model can carry out effective numerical calculation according to the GNSS monitoring data of any point on the ground, and the model prediction effect is good, which provides a new method for the prediction of residual subsidence in mountain mining.

Abstract

This study aims to investigate the effects of different mapping unit scales and study area scales on the uncertainty rules of landslide susceptibility prediction (LSP). To illustrate various study area scales, Ganzhou City in China, its eastern region (Ganzhou East), and Ruijin County in Ganzhou East were chosen. Different mapping unit scales are represented by grid units with spatial resolution of 30 and 60 m, as well as slope units that were extracted by multi-scale segmentation method. The 3855 landslide locations and 21 typical environmental factors in Ganzhou City are first determined to create spatial datasets with input-outputs. Then, landslide susceptibility maps (LSMs) of Ganzhou City, Ganzhou East and Ruijin County are produced using a support vector machine (SVM) and random forest (RF), respectively. The LSMs of the above three regions are then extracted by mask from the LSM of Ganzhou City, along with the LSMs of Ruijin County from Ganzhou East. Additionally, LSMs of Ruijin at various mapping unit scales are generated in accordance. Accuracy and landslide susceptibility indexes (LSIs) distribution are used to express LSP uncertainties. The LSP uncertainties under grid units significantly decrease as study area scales decrease from Ganzhou City, Ganzhou East to Ruijin County, whereas those under slope units are less affected by study area scales. Of course, attentions should also be paid to the broader representativeness of large study areas. The LSP accuracy of slope units increases by about 6%–10% compared with those under grid units with 30 m and 60 m resolution in the same study area's scale. The significance of environmental factors exhibits an averaging trend as study area scale increases from small to large. The importance of environmental factors varies greatly with the 60 m grid unit, but it tends to be consistent to some extent in the 30 m grid unit and the slope unit.

Graphic abstract

Oil transport is greatly affected by heterogeneous pore–throat structures present in shale. It is therefore very important to accurately characterize pore–throat structures. Additionally, it remains unclear how pore–throat structures affect oil transport capacity. In this paper, using finite element (FE) simulation and mathematical modeling, we calculated the hydrodynamic resistance for four pore–throat structure. In addition, the influence of pore throat structure on shale oil permeability is analyzed. According to the results, the hydrodynamic resistance of different pore throat structures can vary by 300%. The contribution of additional resistance caused by streamline bending is also in excess of 40%, even without slip length. Furthermore, Pore–throat structures can affect apparent permeability by more than 60% on the REV scale, and this influence increases with heterogeneity of pore size distribution, organic matter content, and organic matter number. Clearly, modeling shale oil flow requires consideration of porous–throat structure and additional resistance, otherwise oil recovery and flow capacity may be overestimated.

The article presents the results of experimental studies on the gasification of mixtures of brown coal and polyethylene (up to 20 wt% fraction) in a laboratory reactor. The work aims to study the agglomeration process during the heating and oxidation of the mixtures. The measurement results (gas composition, pressure drop) provide indirect information on the dynamics of thermal decomposition and structural changes in the fuel bed. We have shown that the interaction between polyethylene and a coal surface leads to the formation of dense agglomerates, in which the molten polymer acts as a binder. Clinkers form as a result of interfacial interactions between components and filtration flow rearranging. The hydrogen/carbon ratio in the solid residue of coal-polyethylene co-gasification increases from 0.07–0.2 to 1.11, indicating the formation of stable hydrocarbon compounds on the carbon surface. The conducted research makes it possible to identify possible interactions between chemical reactions and transfer processes that lead to agglomeration in mixtures of coal with polyethylene.

This study focuses on CO₂ capture by pressure swing adsorption (PSA), with modified clinoptilolite as the adsorbent. Natural clinoptilolite is modified by roasting, by acid pickling, by a combination of acid pickling and roasting, and by ion exchange. Modification by acid pickling–roasting and by ion exchange are found to give the highest CO₂ adsorption capacities, of 730 mL/g and 876.7 mL/g, respectively. It is found that regeneration of clinoptilolite by a combination of vacuum desorption and heating enables recovery of as much as 89% of its previous CO₂ adsorption capacity. To examine the CO₂ adsorption capacity of clinoptilolite when applied to mixed gas, a simulated coking exhaust containing 12% CO₂ and 4% O₂ is used, and it is found that ion exchange modified clinoptilolite achieves a CO₂ removal efficiency of 92.5%. A BET test reveals that acid pickling–roasting and Na⁺ modification enhance the porosity of clinoptilolite, thereby improving its adsorption capacity. This work demonstrates the feasibility of applying modified clinoptilolite as an effective adsorbent for CO₂ capture, providing a promising tool for dealing with greenhouse gases.

The crack initiation stress threshold is widely used in excavation industries as rock spalling strength when designing deep underground structures to avoid unwanted brittle failures. While various strain-based methods have been developed for the estimation of this critical design parameter, such methods are destructive and often requires subjective interpretations of the stress–strain curves, particularly in rocks with pre-existing microcracks or high porosity. This study explore the applicability of non-destructive ultrasonic through-transmission methods for determining rock damage levels by assessing the changes in transmitted signal characteristics during loading. The change in velocity, amplitude, dominant frequency, and root-mean-square voltage are investigated with four different rock types including marble, sandstone, granite, and basalt under various stress levels. Results suggest the rate of signal variations can be reliably used to estimate crack closure and crack initiation stress levels across the tested rocks before failure. Comparison of the results between the conventional techniques and the new proposed methods based on ultrasonic monitoring are further discussed.

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.