Coal Mining Process Research Articles

Prospects for vortex hydrodedusting in coal mines

Efficiency of coal mining and mineral processing is restricted by imperfection of the technology of blasting-generated dust control and mine safety. Using the mechanism of circulating inertia hetero-coagulation in the liquid–solid system, the authors propose the method of vortex high-pressure hydrodedusting. Furthermore, the contact interaction model is adjusted, and the relations are derived for the Stokes and Reynolds criteria, minimized total dust absorption energy, effective wetting angle and minimum diameter of water drops as function of their rotation speed. It is shown that the reduction in the particle size distribution in dispersed dust improves efficiency of dust explosion localization and silicosis control. It is proved that the patented vortex nozzles scale-down both minimum size of absorbed dust by times and water flow rate by 20%.

Long-term stacking coal promoted soil bacterial richness associated with increased soil organic matter in coal yards of power plants

Coal exploitation inevitably brings a chain of ecological problems, e.g., land destruction and biodiversity decrease. Most previous studies have investigated the ecological effect of coal mining process and the ecological restoration after coal mining practice. However, no study has concerned about the potential influence of long-term stacking coal process on soil microbial communities, the pivotal components to maintain the health of terrestrial ecosystems. This study aims to investigate the influence of long-term stacking coal on soil microbial communities, as well as the time effect. We collected soil samples from coal yards of four power plants (representing four stacking time: 10, 28, 31, and 71 years) in Huainan city. Soils in the lawn near each coal yard were also selected as control at four sites. Soil microbial communities were analyzed via 16S and 18S rRNA gene sequencing. Our results showed that long-term stacking coal significantly (P < 0.05) increased soil organic matter (SOM), and thus facilitated soil bacterial richness and the shifts of bacterial community composition. We also detected significant (P < 0.05) increase of SOM, bacterial richness, and community dissimilarity with stacking time, indicating a substantial time effect. Meanwhile, predicted functional data implied that stacking coal activated anaerobic microbial communities by forming an anaerobic environment in soils. Together, these data provide basic knowledge of the potential influence of long-term stacking coal on soil microbial communities and reinforce the role of SOM in shaping bacterial community composition and richness.

The role of gangue on the mitigation of mining-induced hazards and environmental pollution: An experimental investigation

Gangue, produced from coal mining and washing process, is a serious threat to the ground environment. Gangue backfilling mining method can solve this problem and reduce mining-induced hazards, e.g., controlling surface subsidence and preventing water inrush from seeping into goaf by cracks in overlying strata. In this paper, effects of the original particle size distribution (PSD) and water content on the particle crushing behavior and seepage properties of granular gangues were investigated. Experimental results show that the crushing behavior can promote the compaction of gangue particles; the variation of PSD after crushing reveals distinct fractal characteristics. With the increasing compression stress, the particle crushing ratio and fractal dimension increase, while the permeability decreases. Due to the rearrangement of particles and newly generated fine particles filled the gap among larger particles, it is difficult to reduce the permeability by increasing the compressive stress. In addition, the variation of fractal dimensions is similar to the crushing ratio, so the particle crushing can be illustrated by fractal dimensions. The relationship between porosity and permeability established by the Kozeny-Carman equation can model the effect of particle crushing in this research. The reliability of the equation is verified by the comparison of model result and experimental data. To increase the mitigation rate of mining-induced hazards and environmental pollution by GBM method, granular gangues can be crushed into smaller particles and dehydrated before backfilling.

Better accounting of greenhouse gas emissions from Indian coal mining activities — A field perspective

Fugitive methane emissions from coal mining activities have been frequently talked about in the literature due to concerns about climate change. However, indirect and direct CO2 emissions may also result from coal mining processes. The indirect CO2 emissions include those from diesel combustion from equipment while direct CO2 emissions are a relatively new area of research and have been recently brought into the purview of the Intergovernmental Panel on Climate Change (IPCC) inventory guidelines. We discuss some of the preliminary results which can give some directions into the potential research areas for better accounting of greenhouse gas emissions from coal mining activities. These have been derived from practical studies undertaken at selected coal mines in India.

Study on the mechanism of water inrush in the arid western mining area

The analysis found that the coal mining process in the western mining area has the mining loss and disaster effect of the water-rich aquifer of the coal seam roof, which is mainly manifested by the overburden water in the roof. On this basis, the formation and development of the separation water of the roof is proposed, and the mechanism of the water inrush from the layer is revealed. It is found that there is hydrostatic pressure and hydrodynamic pressure in the separated water, under the combined action of bed separation water pressure, the mining-induced fracture and water-isolation layer tension fracture are connected, which causes water inrushing in the coal working face of the mine, and provides a theoretical guarantee for the large-scale development of coal resources in western mining areas.

Structural analysis of Greek and Bulgarian coals by solid-state &lt;SUP align="right"&gt;13&lt;/SUP&gt;C nuclear magnetic resonance spectroscopy

In this study, 32 peat, xylite-rich and matrix lignites, and sub-bituminous coal samples from representative lignite and sub-bituminous coal basins of Greece and Bulgaria were used to investigate how their NMR differences reflect the organic matter origin, genesis conditions and coalification process in each one of these basins. The evolution of the major organic structural units in the samples was identified by using high-resolution, solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, using a spectrometer with cross-polarisation and magic angle spinning. Solid-state 13C CP/MAS NMR is considered as a very powerful method for determining the chemical structure of complex organic substances such as coals of various ranks. To investigate a possible influence of paramagnetic species on the CPMAS-NMR spectra of the samples, electron paramagnetic resonance (EPR) spectroscopy was also applied. Similarities were observed between the spectra of coals of similar rank or of similar forming conditions. The peat-lignite and lignite-sub-bituminous coal transition is marked by pronounced differences in the NMR spectra, as do the different lithotypes of lignite, i.e., matrix and xylite-rich. Determination of the coal organic constituents offers valuable knowledge about the chemical and thermal behaviour of coals in order to investigate major issues associated with coal mining, combustion, and post-combustion processes.

Experimental study of the effects of stacking modes on the spontaneous combustion of coal gangue

Coal gangue is a solid waste material which is generated during coal mining processes. Due to its low utilization value, it is normally discarded on gangue fields where it is stacked into very large hill formations. Spontaneous combustion is one of the major hazards which frequently occur during the long-term stacking of coal gangue. This study targeted the coal gangue stacks of the Chengzhuang Coal Mine, located in China’s Shanxi Province. The results of programmed heating tests helped determine that CO and C2H4 could be used as the index gases in the predictions of the self-heating degrees of coal gangue. Four of the typical coal gangue stacking modes which were often adopted by the Chengzhuang Mine were selected as the experimental objects of this study. The corresponding coal gangue models were piled in a field, and the self-heating degrees were measured with the passage of time. The entire experiment lasted for 60 days. The results showed that the loess isolation and loess stratified stacking methods could effectively suppress the self-heating processes. Also, the CO production and O2 consumption of the coal gangue were consequently reduced. The study also indicated that in the loess stratified stacking, the inhibitory effects on the spontaneous combustion of the coal gangue had increased with the increased thicknesses of the loess layers.

Cutting Pattern Identification for Coal Mining Shearer through Sound Signals Based on a Convolutional Neural Network

Recently, sound-based diagnosis systems have been given much attention in many fields due to the advantages of their simple structure, non-touching measurement style, and low-power dissipation. In order to improve the efficiency of coal production and the safety of the coal mining process, accurate information is always essential. It is indicated that the sound signal produced during the cutting process of the coal mining shearer contains much cutting pattern identification information. In this paper, the original acoustic signal is first collected through an industrial microphone. To analyze the signal deeply, an adaptive Hilbert–Huang transform (HHT) was applied to decompose the sound to several intrinsic mode functions (IMFs) to subsequently acquire 1024 Hilbert marginal spectrum points. The 1024 time-frequency nodes were reorganized as a 32 × 32 feature map. Moreover, the LeNet-5 convolutional neural network (CNN), with three convolution layers and two sub-sampling layers, was used as the cutting pattern recognizer. A simulation example, with 10,000 training samples and 2000 testing samples, was conducted to prove the effectiveness of the proposed method. Finally, 1971 testing sound series were recognized accurately through the trained CNN and the proposed method achieved an identification rate of 98.55%.

Development law of air leakage fractures in shallow coal seams: a case study in the Shendong Coalfield of China

Continuous air leakage from ground mining-induced cracks is a significant cause of coal spontaneous combustion, low oxygen at the working face and other disasters in shallow coal seams. This paper studies mining-induced cracks and air leakage caused by the repeated mining of shallow coal seams at the Bulianta coal mine, Shendong Coalfield, China. A similar simulation experiment was carried out in the laboratory, and then the ground mining-induced cracks were observed and the crack air leakage was detected. The results showed that the surface air flowed into the composite goaf before the fractures redeveloped to the surface during the process of lower coal seam mining. Due to the different development processes of vertical fractures in various regions, the width of the vertical fractures in the boundary area of the overlying goaf increases significantly after the repeated mining of coal seams, while the vertical fractures in the central area of the overlying goaf experience almost no change. The distribution of the surface air leakage cracks is in the shape of “回”. Graben-type cracks and half-graben-type cracks are surface air leakage cracks, which are the focus of surface air leakage problems, especially the half-graben-type cracks. The results are important in engineering for reducing air leakage from surface mining-induced cracks.

Determination of geological conditions of gassy coal seams on the basis of seismic acoustic profiling in underground mine workings

The article views the experience of mine geophysical prospecting using a seismic screening method of roof rocks from mine workings. The possibility of recording coal seams structural disturbances is estimated based on the analysis of seismic signals velocity fluctuation. The results of coal seam conditions assessment and their influence on the technological process of coal mining are presented.

Experimental Investigation on Seepage Stability of Filling Material of Karst Collapse Pillar in Mining Engineering

In northern China, groundwater inrush of Karst collapse pillar (KCP) often affects the coal mining process. Current studies rarely consider the seepage stability of filling materials of KCP, especially through experimental investigations. This study is to quantify the impacts of variable initial porosity and cementing strength on the seepage properties of filling material. For this purpose, we designed and fabricated a test system. This system can offer high water pressure and abundant water flow rate. We tested three types of specimens which were cemented by clay, gypsum, and cement, respectively. The seepage properties were obtained under the initial porosity of 0.11, 0.13, 0.15, and 0.17, respectively. The change mechanism of seepage properties was measured through the comparison between mass loss and mass gain. The results showed the followings findings: (1) The permeability-time curves have two types: the first type is that permeability gradually increases up to the occurrence of seepage instability and the second type is that permeability gradually decreases and approaches to a stable value. No seepage instability is observed. (2) Initial porosity and cementing material significantly affect the water flow properties of filling material. In general, larger initial porosity has larger permeability. For clay as cementing material, seepage instability occurs soon and higher initial porosity has shorter time to reach seepage instability. For gypsum, seepage instability occurs after a period of time when initial porosity is large enough. For cement, the permeability decreases gradually and approaches to a stable value. The permeability-time curves have rapid decrease and slow decrease. (3) The permeability has a magnitude of 10−15–10−13 m2 and varies with initial porosity and cementing materials. The permeability is the largest for clay cementing and is the smallest for cement cementing.

Enrichment Law of Hazardous Chemicals Enrichment under Dangerous Chemical Environment of Coal Mining

During the process of coal mining, the CH4 produced by the coal will be released in the workspace. With the movement of the working face, the overlying strata will be moved or destroyed, resulting in the continuous development of mining cracks and thus the forming a methane enriched area. The study of methane enrichment law is helpful for methane extraction and utilization, and at the same time reduces the risk of workspace. The development of the mining fracture field in overlying strata is determined by the process of overlying strata movement. Since there are many factors affecting the migration of overlying strata, the migration process of the rock strata is complex and the field is limited by many conditions, it is difficult to detect the distribution of the fractured field in the overlying strata. In this paper, the evolution law of mining fracture field will be studied by similar material model test. Based on the geological conditions of the 12# coal seam in Nanzhuang coal mine, Yangquan, the paper uses the similar model test to analyze and discuss the evolution law of the mining fracture field in the overlying strata of the coal seam, which provides a theoretical basis for the design of the mining scheme for the mining in the adjacent layer of the coal seam of the 12# coal seam.

Way of Carbon Emission Reduction in Coal Mines Based on Carbon Balance Method and B-Wilson Method

This study is to analyze carbon balance method and B-Wilson method in carbon emission reduction in coal mines. The carbon balance method and B-Wilson method are studied in four open-pit coal mines in Yimin River, Anjialing, Heidaigou and Buzhaoba. It is found that continuous process can effectively improve the unit production capacity, and has positive effect on unit coal emission. It is also found that the production process system has certain effect on the carbon emission in open-pit coal mines. Conclusion has been drawn that the coal mining process system has certain application and research value in the research on way of carbon emission reduction in open-pit coal mines.

Climate change mitigation in the coal mining industry: low-carbon pathways and mine safety indicators

As China’s major energy source, the coal sector contributes to a significant portion of China’s greenhouse gas emissions, and the industry faces huge pressure in relation to saving energy and reducing carbon emissions. Considering Chinese National Knowledge Infrastructure database as the basic retrieval source, this paper presents the status and hot spots reported in studies on the carbon emissions of the coal mining industry. The results reveal that the scientific outcomes of these studies in this field have increased sharply in the last 5 years. China University of Mining and Technology and the China Coal Research Institute are outstanding research institutes regarding this research topic. The subject distribution suggested the studies on the carbon emissions of the coal mining sector have developed into an interdisciplinary field, which includes the coal mining technology, industrial economy, management and environment. The related hot spots indicate that the energy consumed during the mining process, coal mine gas, sustainable plans for abandoned coal mines and utilization of coal gangue are the indexes for low-carbon development of the coal mining industry, which is also significant for mine disaster prevention. It should be highlighted that the coal spontaneous combustion during the coal mining process and the coal production structure represented by the number of coal mines and the minimum capacity requirement could be important factors for achieving future carbon emission reductions in the coal mining sector.

Permeability enhancement of deep hole pre-splitting blasting in the low permeability coal seam of the Nanting coal mine.

To solve the hidden danger of high methane and low permeability gas in the coal mining process, potentially affecting the safety production in an orderly way, we propose the use of deep hole blasting technology to improve the permeability of the coal seam gas drainage, increase the quantity and rate of extraction, and reduce methane output. Taking the geological conditions of the 201 working surface of Tingnan Coal Mine as an example, it is calculated that the single drilled fracture crack extension range is 3.11~5.24 m according to the coal seam deep-hole pre-splitting blasting joint mechanism and fracture propagation mechanics model, providing a theoretical basis for choosing the appropriate hole spacing. Using COMSOL simulation software to simulate the effective gas drainage radius of a coal seam from a two-dimensional perspective on a single borehole radial, the least squares fitting method was used to analyze the simulated data, and obtained the effective drilling extraction radius after pre-split blasting in a deep hole that is 3.6 m, which is in accordance with the theoretical calculations. In order to obtain accurate and scientific calculations, Fast lagrangian analysis of continua (FLAC3D) numerical simulation software was used. After simulating the distribution of plastic zone between two blast holes at different intervals from a three-dimensional angle, and evaluating the development of cracks in the blasting hole, the white zone of the blasting space was completely eliminated when the interval between blasting holes was 7 m, and the cracks could be propagated throughout the surroundings. Therefore, a blasting hole spacing of 7 m is optimal. On-site monitoring in the Nanting coal mine showed that the quantity and rate of extraction of the single hole after pre-splitting blasting were 2.36 times and 1.62 times as much as before. By integrating the borehole drainage amount and the optimized calculation equation, it could be concluded that the permeability coefficient of the coal seam after blasting was 7.78 times as much as before. The function of time-variated drilling methane emission was obtained using multivariate statistical regressions based on the on-site monitored borehole methane emission (qt), and the drilling limit after pre-splitting blasting revealed that the limitation of methane extraction volume was 5.27 times as much as before.

Analysis of Prediction Model of Failure Depth of Mine Floor Based on Fuzzy Neural Network

To obtain the law of failure depth of mine floor and its influencing factors during coal mining process, a large amount of field measured data of floor failure depth was collected, and five influencing factors were summarized based on the analysis of data and years of field experience. The five main influencing factors were the length of working face, mining depth, mining height, dip angle and floor anti-sabotage ability. Based on fuzzy math membership and membership function, the five factors were preliminarily processed, then the sensitivity ranking was obtained according to the weight of influencing factors, and the prediction model of failure depth of mine floor was established based on the fuzzy neural network. It was shown that the order of the weight of the five factors was the length of working face > dip angle > floor anti-sabotage ability > mining depth > mining height. The maximum weight of the length of working face was 0.3678. The accuracy of the model was high and the prediction results were in good agreement with the engineering practice according to verification results. To ensure the maximum economic benefit of mine, some measures and methods through human intervention to reduce the failure depth of floor and ensure mine safety were suggested.

Changes in woodland cover in the Karviná district from the second half of the 18th century to the beginning of the 21st century

Abstract This study analyses the changes in woodland cover from the mid-18th century to the turn of the 21st century in a distinctive region of the Czech Republic – the Karviná district. This region has been substantially affected by the process of industrialisation during the 19th and 20th centuries, which transformed a formerly agricultural landscape into a landscape heavily impacted by underground coal mining and related landscape processes. The occurrence of woodland cover in the Karviná district was determined from historical military maps (second half of the 18th century, first half of the 19th century, second half of the 19th century, first half of the 20th century) and from a colour orthophoto (2017) verified with reference to a contemporary map. The article interprets the occurrence of woodland cover depicted in the abovementioned sources and presents an interpretative key. The vectorisation of the woodland cover and the analysis of temporal–spatial changes in woodland cover were conducted using ArcGIS 10 software.

Experimental investigation on spontaneous imbibition of water in coal: Implications for methane desorption and diffusion

During the process of coal mining and coalbed methane extraction, the application of hydraulic techniques generally leads to the spontaneous imbibition of water in coal seams. To study spontaneous imbibition of water in coal and evaluate its influence on methane desorption and diffusion, experiments of spontaneous imbibition in coal containing methane were conducted under different adsorption equilibrium pressure and water imbibition ratios. The displacement effect of water during imbibition was investigated, and methane desorption was also tested under atmospheric-pressure conditions. Imbibition test results show that adsorbed methane can be displaced by water. The displacement amount and its efficiency increase with water imbibition ratio, but an upper limit on the displacement amount exists because of the limited imbibition capacity. Desorption test results show an inhibitory effect of water blocking on methane desorption and diffusion. The desorption time increases and diffusivity decreases with the imbibition ratio. However, the time-dependent characteristics of desorption ratio indicate that the desorption process is temporarily delayed rather than completely stopped by water blocking. Moreover, the residual methane amount decreases with the water imbibition ratio based on long-time-scale desorption, suggesting that spontaneous imbibition of water can promote methane desorption on the whole. The scale effects of coal samples and actual conditions on methane adsorption, desorption and imbibition are also discussed. These findings show the multiple effects of spontaneous imbibition on methane desorption in coal and help in better understanding the overall effects of water-based treatment techniques on coalbed methane extraction and coal seam gas control for mining safety.

Effects of Water and Brine Saturation on Mechanical Property Alterations of Brown Coal

The adsorption of moisture or brine into coal causes the coal mass mechanical properties to be significantly altered, which can greatly affect the coal mining and coal seam gas extraction process. A study was therefore initiated to investigate the influence of moisture and brine saturations (5–25%) on brown coals’ strength through a series of unconfined compressive strength tests, with the aid of acoustic emission, optical 3-D deformation analysis and scanning electron microscopy. According to the results, the coal mass is weakened by up to 26% upon the adsorption of moisture and water saturated samples show no crack propagation, whereas brine saturation enhances coal strength by up to 21% and delays crack propagation due to the crystallization of sodium chloride. Besides, a high brine concentration (25%) greatly improves coal mass strength but impairs the increase of Young’s modulus due to its corrosive nature, which is consistent with the values of maximum strain at failure of the tested samples (3.9%, 3.1% and 3.6% for 5%, 15% and 25% brine saturated samples, respectively). In addition, because of the precipitation of sodium chloride in coal and the increase of conductivity of pore fluid, more acoustic emission signals are detected for brine saturated samples, while water saturated samples exhibit mush less acoustic release compared to the unsaturated samples.

Measurement of the Strong Pressure Appearance Laws with Hard Roof and Full Mechanized Mining Extra Thick Coal Seam

To master the laws of strong strata behavior of Tashan coal mine under Carboniferous coal mining process, the laws of strong strata behavior in 8107 working face was measured and analyzed. It was shown that the average initial weighting step of 8107 working face was 59.4 m. The average periodic weighting step of main roof was 16.2 m. The maximum working resistance during periodic weighting was 14,711.1 kN. The maximum working resistance during non-periodic weighting was 11,339.9 kN. The average dynamic load factor K during periodic weighting was 1.31. The stress of coal column on the side of the goaf could be divided into four zones (stress stabilization zone, stress slow-increasing zone, significant—increasing stress zone, stress reduction zone) along the strike of 8107 working face. There was a peak of lateral support pressure along the trend of 8107 working face. And the peak position was biased to the side of return airway roadway. With the increase of the distance from the down-side of return airway, the pressure peak of the inner coal body along the strike of 8107 the working face increased and the peak position decreased from the coal wall. The peak stress of coal column tended to be close to the up-side of return airway. And the distance from the down-side of return airway for the peak of inner coal was larger than that for the peak of coal pillar. The peak position of abutment pressure of hard roof was in the range of 10–25 m in front of 8107 working face under full mechanized mining extra thickness coal seam conditions. The relative stress concentration coefficient of k was 1.3–6.5. The range of 10–25 m from the front of the working face to coal wall was stress reduction zone. And the influence range of abutment pressure was about 80 m. It was of great significance to the control and practice of the surrounding rock of the stope for the mining of the hard extra-thick coal seam.