International Journal of Coal Science & Technology最新文献

This study investigates the impact of different water coupling coefficients on the blasting effect of red sandstone. The analysis is based on the theories of detonation wave and elastic wave, focusing on the variation in wall pressure of the blasting holes. Using DDNP explosive as the explosive load, blasting tests were conducted on red sandstone specimens with four different water coupling coefficients: 1.20, 1.33, 1.50, and 2.00. The study examines the morphologies of the rock specimens after blasting under these different water coupling coefficients. Additionally, the fractal dimensions of the surface cracks resulting from the blasting were calculated to provide a quantitative evaluation of the extent of rock damage. CT scanning and 3D reconstruction were performed on the post-blasting specimens to visually depict the extent of damage and fractures within the rock. Additionally, the volume fractal dimension and damage degree of the post-blasting specimens are calculated. The findings are then combined with numerical simulation to facilitate auxiliary analysis. The results demonstrate that an increase in the water coupling coefficient leads to a reduction in the peak pressure on the hole wall and the crushing zone, enabling more of the explosion energy to be utilized for crack propagation following the explosion. The specimens exhibited distinct failure patterns, resulting in corresponding changes in fractal dimensions. The simulated pore wall pressure–time curve validated the derived theoretical results, whereas the stress cloud map and explosion energy-time curve demonstrated the buffering effect of the water medium. As the water coupling coefficient increases, the buffering effect of the water medium becomes increasingly prominent.

Fine slag (FS) is an unavoidable by-product of coal gasification. FS, which is a simple heap of solid waste left in the open air, easily causes environmental pollution and has a low resource utilization rate, thereby restricting the development of energy-saving coal gasification technologies. The multiscale analysis of FS performed in this study indicates typical grain size distribution, composition, crystalline structure, and chemical bonding characteristics. The FS primarily contained inorganic and carbon components (dry bases) and exhibited a "three-peak distribution" of the grain size and regular spheroidal as well as irregular shapes. The irregular particles were mainly adsorbed onto the structure and had a dense distribution and multiple pores and folds. The carbon constituents were primarily amorphous in structure, with a certain degree of order and active sites. C 1s XPS spectrum indicated the presence of C–C and C–H bonds and numerous aromatic structures. The inorganic components, constituting 90% of the total sample, were primarily silicon, aluminum, iron, and calcium. The inorganic components contained Si–O-Si, Si–O–Al, Si–O, SO₄²⁻, and Fe–O bonds. Fe 2p XPS spectrum could be deconvoluted into Fe 2p_1/2 and Fe 2p_3/2 peaks and satellite peaks, while Fe existed mainly in the form of Fe(III). The findings of this study will be beneficial in resource utilization and formation mechanism of fine slag in future.

Abstract

Opencast coal mining produces trash of soil and rock containing various minerals, that are usually dumped nearby the abandoned sites which causes severe environmental concern including the production of acid mine drainage (AMD) through oxidation pyrite minerals. The current study entailed assessing the potential production of AMD from an opencast coal mining region in Northeast part of India. In order to have a comprehensive overview of the AMD problem in Makum coalfield, the physico-chemical, geochemical, and petrological characteristics of the coal and overburden (OB) samples collected from the Makum coalfield (Northeast India) were thoroughly investigated. The maceral compositions reveal that coal features all three groups of macerals (liptinite, vitrinite, and inertinite), with a high concentration of liptinite indicating the coal of perhydrous, thereby rendering it more reactive. Pyrite (FeS₂) oxidation kinetics were studied by conducting the aqueous leaching experiments of coal and (OB) samples to interpret the chemical weathering under controlled laboratory conditions of various temperature and time periods, and to replicate the actual mine site leaching. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) was operated to detect the disposal of some precarious elements from coal and OB samples to the leachates during our controlled leaching experiment. The Rare earth element (REE) enrichment in the samples shows the anthropogenic incorporation of the REE in the coal and OB. These experiments reveal the change in conductivity, acid producing tendency, total dissolved solid(TDS), total Iron(Fe) and dissolved Sulfate(SO₄²⁻) ions on progress of the leaching experiments. Moreover, the discharge of FeS₂ via atmospheric oxidation in laboratory condition undergoes a significant growth with the rise of temperature of the reaction systems in the environment and follows pseudo first order kinetics. A bio-remediative strategies is also reported in this paper to mitigate AMD water by employing size-segregated powdered limestone and water hyacinth plant in an indigenously developed site-specific prototype station. Apart from neutralisation of AMD water, this eco-friendly AMD remediation strategy demonstrates a reduction in PHEs concentrations in the treated AMD water.

Novel coal gangue-based persulfate catalyst (CG-FeCl₂) was successfully synthesized by the means of calcinating under nitrogen atmosphere with the addition of ferrous chloride tetrahydrate (FeCl₂·4H₂O). The phase transformation of the prepared materials and gas products during the heating process are thoroughly investigated. It is suggested that ferrous chloride participated in the phase transformation and formed Si-O-Fe bonds. And the main gaseous products are H₂O, H₂, and HCl during the heating process. Besides, the ability of CG-FeCl₂ to activate peroxymonosulfate (PMS) for catalytic degradation of polycyclic aromatic hydrocarbons (PAHs) and phenol was deeply studied. More than 95% of naphthyl, phenanthrene and phenol were removed under optimizied conditions. In addition, ¹O₂, ^·OH, and SO₄^·− were involved in the CG-FeCl₂/PMS system from the free radical scavenging experiment, where ¹O₂ played a major role during the oxidation process. Furthermore, CG-FeCl₂/PMS system exhibited superior stability in a relatively wide pH range and the presence of common anion from related degradation experiments. Overall, the novel CG-FeCl₂ is an efficient and environmentally friendly catalyst, displaying potential application prospect in the field of PAHs and phenol-contaminated wastewater treatment.

Indirect fracturing in the roof of broken soft coal seams has been demonstrated to be a feasible technology. In this work, the No. 5 coal seam in the Hancheng block was taken as the research object. Based on the findings of true triaxial hydraulic fracturing experiments and field pilot under this technology and the cohesive element method, a 3D numerical model of indirect fracturing in the roof of broken soft coal seams was established, the fracture morphology propagation and evolution law under different conditions was investigated, and analysis of main controlling factors of fracture parameters was conducted with the combination weight method, which was based on grey incidence, analytic hierarchy process and entropy weight method. The results show that “士”-shaped fractures, T-shaped fractures, cross fractures, H-shaped fractures, and “干”-shaped fractures dominated by horizontal fractures were formed. Different parameter combinations can form different fracture morphologies. When the coal seam permeability is lower and the minimum horizontal principal stress difference between layers and fracturing fluid injection rate are both larger, it tends to form “士”-shaped fractures. When the coal seam permeability and minimum horizontal principal stress between layers and perforation position are moderate, cross fractures are easily generated. Different fracture parameters have different main controlling factors. Engineering factors of perforation location, fracturing fluid injection rate and viscosity are the dominant factors of hydraulic fracture shape parameters. This study can provide a reference for the design of indirect fracturing in the roof of broken soft coal seams.

Abstract

To analyze the relationship between macro and meso parameters of the gas hydrate bearing coal (GHBC) and to calibrate the meso-parameters, the numerical tests were conducted to simulate the laboratory triaxial compression tests by PFC3D, with the parallel bond model employed as the particle contact constitutive model. First, twenty simulation tests were conducted to quantify the relationship between the macro–meso parameters. Then, nine orthogonal simulation tests were performed using four meso-mechanical parameters in a three-level to evaluate the sensitivity of the meso-mechanical parameters. Furthermore, the calibration method of the meso-parameters were then proposed. Finally, the contact force chain, the contact force and the contact number were examined to investigate the saturation effect on the meso-mechanical behavior of GHBC. The results show that: (1) The elastic modulus linearly increases with the bonding stiffness ratio and the friction coefficient while exponentially increasing with the normal bonding strength and the bonding radius coefficient. The failure strength increases exponentially with the increase of the friction coefficient, the normal bonding strength and the bonding radius coefficient, and remains constant with the increase of bond stiffness ratio; (2) The friction coefficient and the bond radius coefficient are most sensitive to the elastic modulus and the failure strength; (3) The number of the force chains, the contact force, and the bond strength between particles will increase with the increase of the hydrate saturation, which leads to the larger failure strength.

The post-peak characteristics of coal serve as a direct reflection of its failure process and are essential parameters for evaluating brittleness and bursting liability. Understanding the significant factors that influence post-peak characteristics can offer valuable insights for the prevention of coal bursts. In this study, the Synthetic Rock Mass method is employed to establish a numerical model, and the factors affecting coal post-peak characteristics are analyzed from four perspectives: coal matrix mechanical parameters, structural weak surface properties, height-to-width ratio, and loading rate. The research identifies four significant influencing factors: deformation modulus, density of discrete fracture networks, height-to-width ratio, and loading rate. The response and sensitivity of post-peak characteristics to single-factor and multi-factor interactions are assessed. The result suggested that feasible prevention and control measures for coal bursts can be formulated through four approaches: weakening the mechanical properties of coal pillars, increasing the number of structural weak surfaces in coal pillars, reducing the width of coal pillars, and optimizing mining and excavation speed. The efficacy of measures aimed at weakening the mechanical properties of coal is successfully demonstrated through a case study on coal burst prevention using large-diameter borehole drilling.

Abstract

One of the most dangerous safety hazard in underground coal mines is roof falls during retreat mining. Roof falls may cause life-threatening and non-fatal injuries to miners and impede mining and transportation operations. As a result, a reliable roof fall prediction model is essential to tackle such challenges. Different parameters that substantially impact roof falls are ill-defined and intangible, making this an uncertain and challenging research issue. The National Institute for Occupational Safety and Health assembled a national database of roof performance from 37 coal mines to explore the factors contributing to roof falls. Data acquired for 37 mines is limited due to several restrictions, which increased the likelihood of incompleteness. Fuzzy logic is a technique for coping with ambiguity, incompleteness, and uncertainty. Therefore, In this paper, the fuzzy inference method is presented, which employs a genetic algorithm to create fuzzy rules based on 109 records of roof fall data and pattern search to refine the membership functions of parameters. The performance of the deployed model is evaluated using statistical measures such as the Root-Mean-Square Error , Mean-Absolute-Error, and coefficient of determination ( (R_2) ). Based on these criteria, the suggested model outperforms the existing models to precisely predict roof fall rates using fewer fuzzy rules.

In China, coal miners are the primary workforce in coal mining, and among all patients with occupational diseases, 90% suffer from pneumoconiosis. Therefore, the psychological problems resulting from the dual pressures of occupational stress and the high risk of occupational diseases among coal miners are significant factors that affect the development of physical and mental health and even production safety. The Crown–Crisp Experience Index (CCEI) is a multidimensional questionnaire that assesses the psychological state of patients. This study aims to test reliability and validity of Chinese version of the CCEI questionnaire using factor analysis, and apply it to coal miners. We recruited a total of 900 participants from different occupational stages in coal mining, including active miners, Coal Workers’ Pneumoconiosis (CWP) patients, and retired miners, to evaluate the reliability and validity of the Chinese version of the CCEI questionnaire. A questionnaire survey was conducted on three groups of 1000 individuals each, including active coal miners, retired coal miners, and pneumoconiosis patients, to determine the detection rate of psychological problems in each group. An analysis was performed for each group to explore the primary factors influencing anxiety. The exploratory factor analysis yielded six principal components that accounted for a total of 79.389% of variances. The confirmatory factor analysis showed that the Chi-square freedom ratio (χ²/df) was 1.843, the root mean square error approximation was less than 0.044, and the comparative fit index was 0.938 and Tucker–Lewis index (TLI) was 0.934. The Cronbach's alpha coefficient was 0.948, and the scale-level content validity index (S-CVI) was 0.88. Effective questionnaires were obtained from 98.5%, 96.9%, to 91.0% of pneumoconiosis patients, active miners, and retired miners, respectively, with the incidence rates of psychological problems being 21%, 35.8%, and 13.6%, respectively. Compared with retired miners, active miners showed higher levels of psychological problems in the dimensions of depressive symptoms, free-floating anxiety and somatic symptoms, whereas pneumoconiosis patients had higher levels of psychological problems in the dimensions of phobic anxiety and somatic symptoms. This study demonstrates that the Chinese version of the CCEI is highly reliable and valid and can be used as a screening tool to measure patients' anxiety and fear levels in coal minders. Miners face distinct psychological challenges at different stages and require targeted screening and interventions.

Nano-to-micron-sized coal dust can cause coal workers’ pneumoconiosis (CWP), and cutting and drilling are the main coal dust-generating processes. Based on a self-developed simulated coal cutting and drilling dust generation system, the effects of cutting parameters (tooth tip cone angle, impact angle, roller rotary speed, cutting speed) and drilling parameters (drill bit diameter, drilling speed) on the mass concentration distribution, number concentration distribution and fractal dimension of 10 nm – 10 μm coal dust were investigated. Results show that the mass concentration of 10 nm – 10 μm coal dust generated by cutting/drilling peak at 5.7 – 7.2 μm, while the number concentrations during cutting and drilling respectively peak at 60 – 90 nm and 20 – 30 nm. During both cutting and drilling processes, the generated coal dust particles in 10 – 300 nm account for > 90% of the total 10 nm – 10 μm coal particles, while PM2.5 in PM10 is generally below 18%. It is also found that smaller tooth tip cone angle, larger impact angle, lower roller rotary speed, smaller drill bit diameter, or lower drilling speed can reduce the generation of 10 nm – 10 μm coal dust with a fractal dimension of 0.94 – 1.92. This study reveals the distribution characteristics of nano- to micron-sized coal dust particles under different cutting and drilling parameters, and the research results can serve as reference for adjusting cutting and drilling parameters to lower down the 10 nm – 10 μm coal dust generation and thus prevent the CWP.