Coal Process Research Articles

Experimental study on the mechanism of coal spontaneous combustion inhibition by degradation of white-rot fungus

To investigate the mechanism of inhibition of spontaneous combustion of coal by degradation of white-rot fungus, the changes of macroscopic oxidizing characteristics and microstructure of the degraded coal were investigated by the programmed temperature-raising test and the in situ Fourier-transform infrared spectroscopy experiments. The difference in gas production between the degraded coal and the blank samples indicated that the degradation inhibited the oxidation process of coal, and the intensity of the inhibition effect was different at different oxidation stages. The strongest inhibition effect was found in the accelerated oxidation stage, i.e. 80–140 °C. To further analyze the micro-mechanism of the degradation of Phanerochaete chrysosporium affecting the spontaneous combustion of coal, the relative contents of active functional groups in coal samples were compared. The results showed that the degradation affected the relative contents of hydroxyl, aliphatic hydrocarbon, and oxygenated functional groups in coal. Among them, the most significant changes of –OH and –CO- were observed at 80–140 °C. Thus, it was analyzed that Phanerochaete chrysosporium could degrade the macromolecular structure of coal by generating biological enzymes to reduce the number of oxidizable functional groups such as –OH, –CH2, –CH3, –CO-, and so on, thus reducing the risk of spontaneous combustion of coal.

A novel coal purification-combustion system: Product and efficiency of coal purification process

A novel coal purification-combustion technology is presented to realize the efficient and clean utilization of coal under carbon peaking and carbon neutrality goals. Central to this technology is the implementation of a purification process, the product characteristics, and energy properties of which are the focus of this study. An experimental test of coal purification was conducted using Shenmu coal. The results demonstrate increased coal reactivity following the moderate temperature activation (MTA) process. The high temperature reduction (HTR) phase promotes the production of higher amounts of amorphous carbon, reduces aromatic carbon content, and further decreases fuel particle size. The composite combustion characteristic index(S) of the purified fuel reaches its peak when the excess air coefficient of secondary air (λ2) is 0.36. As λ2 increases from 0.1 to 0.36, the energy in the gas product of the purification system increases from 13700 kJ/kg coal to 25351 kJ/kg coal, while exergy increases from 6530 kJ/kg coal to 11030 kJ/kg coal. The energy efficiency of the purification process ranges from 74.74 % to 80.88 %, with exergy efficiency varying between 60.51 % and 70 %. These findings offer significant insights into refining the coal purification process, ultimately contributing towards maximizing the utility of coal resources.

Study on Ultra-Long-Distance Transportable Concentration Gradient of Coal Gangue Slurry with Different Gradations

Coal gangue, the primary solid waste generated during the coal mining process, is typically disposed of on the surface, where it gradually accumulates to form gangue piles that significantly contaminate the surrounding environment. Filling technology has been widely employed for the safe and efficient disposal of coal gangue due to its sustainability, safety, and efficiency. However, there is still a lack of theoretical research on the concentration of gangue slurry in long-distance filling pipeline transportation. Therefore, a calculation model of the ultra-long-distance transportable concentration of coal gangue slurry with different grades was constructed based on the static anti-segregation performance and Bingham model. In addition, the relevant parameters of the calculation model of the ultra-long-distance transportable concentration of coal gangue slurry in this mine were determined using the 8 km pipeline transport of coal gangue slurry in one mine as the technical background. It was subsequently demonstrated that the yield stress, plastic viscosity, and mass concentration of the various grades of gangue slurry in this mine exhibit an increasing exponential function, while the slurry density and mass concentration exhibit an increasing linear function, and the mass concentration and actual flow rate correspond to a quadratic polynomial increment. Finally, the minimum and maximum concentrations for different grades of gangue slurry that can be transported over long distances in this mine were determined. This work provides theoretical and practical guidance on how to select the concentration of gangue slurry for long-distance pipeline transport.

Coal-derived char for durability improvement of cement stabilized soil under freeze–thaw, wet–dry, and sulfate attack

Cement soil stabilization is widely used in civil engineering to improve the performance of soils subjected to freeze–thaw (F–T), wet–dry (W–D), and sulfate attack (SA). Due to the negative impacts associated with manufacturing cement, the development of eco-friendly and sustainable additives is highly desirable. Coal-derived char is a cost-effective byproduct of the coal pyrolysis process. In this study, the influence of coal char on mineralogical, microstructural, physical, and mechanical properties of cement stabilized soils (with cement contents of 0%–20% and char contents of 0%–30%) subjected to F–T cycles, W–D cycles, and SA is investigated. Compared to cement stabilized soils, char-cement stabilized soils exhibit up to 60.8% fewer volume changes during F–T cycles and 31.6% fewer during W–D cycles. The compressive strength of char-cement stabilized soils with cement contents of 5%, 10%, and 20% are on average 7.9%, 17.6%, and 11.0%, respectively, higher than that of cement stabilized soil subjected to F–T cycles, W–D cycles, or SA. The inclusion of char promotes cement hydration and results in the formation of more amorphous hydration products that fill voids or cover soil minerals. The findings indicate the promising potential of coal char in enhancing soil performance under a range of challenging environmental conditions.

Research on coal gangue size calibration based on perspective correction-parameter calibration synergy

The size calibration of coal gangue can help to determine the size range of coal gangue, which has a great influence on the grabbing strategy of coal gangue in the process of coal gangue sorting. However, at present, the size calibration of coal gangue has not been effectively studied. Based on this, this paper innovatively proposes a gangue size calibration method based on perspective correction-parameter calibration. Firstly, a coal gangue image acquisition and processing system was built to collect coal gangue images and preprocess the images. Secondly, the size calibration system model is established, including mathematical model and operation model. Finally, the influence of different heights and tilt angles on the accuracy and stability of the size calibration results were compared. The results show that when the camera height and the coal gangue height are 600 mm and the camera is perpendicular to the ground, the calibration accuracy and stability are the best, and the accuracy rate is more than 97 %. The research content of this paper provides theoretical support for the accurate positioning and precise sorting of coal gangue in the process of belt transportation.

Research on prediction of coal water medium separation effect based on multi-models

To improve the separation efficiency of raw coal and ensure clean use, the accurate calculation of the partition coefficients (PCs) in coal water medium sorting is required. Single models have been used to predict the partition coefficient (PC) for decades, but their accuracy remains constrained. This study proposes a multi-model (MM) calculation method based on the Gompertz model (GM), the Logistic model (LM), the Arctangent model (AM), and the Approximate formula (AFM) to improve the accuracy of the predicted coal water medium sorting PCs. Four groups of coal samples and two specific cases were used to verify the accuracy of the MM calculation method. The PCs of the MM method had a minimal Ef (0.91–8.84), a maximal R2 (0.9648–0.9994), a maximal F-value (199.17–11352.31), and the highest significance of all the models. The MM method was found to be the most suitable of all the models for predicting any coal water medium separation process. Further, when calculating the PC for cleaned coal ash, the separation density of MM is closer to the actual separation density than that of either the GM, LM, AM, or AFM models. The MM method, therefore, produces more accurate results compared to a single model. MM is expected to predict the PC based on the required cleaned coal ash, and then regulate the sorting density to improve the production efficiency.

Surface deformation of moving droplets of slurry fuels

Experimental research findings are reported on the characteristics of surface transformation of droplets of promising fuel slurries in the air, as they move at subsonic velocities typical of combustion chambers of power plants. The main components of the fuels were water, coal processing waste, and coal. Typical shapes of droplets and the duration of their deformation cycles were identified. Droplets containing more than 70% of the solid phase remained practically undeformed. The lowest relative velocities of droplets leading to their fragmentation were determined. The key characteristics of secondary droplets (their number, sizes, velocities, and surface area of liquid) were calculated on the basis of the experimental findings. These characteristics were compared with those of initial droplets. Disruption conditions in the chosen range of the gas jet pressure (P ≤ 6 bars) can only be provided for fuel slurry droplets containing less than 60% of a coal component. The effect of a group of factors on deformation characteristics was identified. These include air jet and droplet velocities, droplet sizes, temperature, concentration, and type of components and additives. Approximation equations were derived for the mathematical description of the experimental data. Using certain criteria, the conditions necessary and sufficient for the disruption of water–fuel slurries on impact with an air jet were estimated.

Additional Power Losses Under Non-Sinusoidal Conditions in a 22 kV Overhead Power Line

Non-sinusoidal conditions in the electrical networks cause active power losses at the fundamental frequency, corresponding to the first harmonic, and at harmonic frequencies, which are a multiple of the fundamental frequency. Non-sinusoidal currents flow through network components and create additional active power losses. One of the non-sinusoidal current sources is electronic equipment used in industrial plants to control process equipment. In Vietnam, coal mines use frequency-controlled induction motors when processing coal. The induction motors consume non-sinusoidal current, which creates additional active power losses in the supply network. The harmonic active power does not perform useful work. It causes economic damage to both the supply network and industrial enterprises. The power supply systems in industrial areas of Vietnam, where coal is mined, are characterized by low power quality. Companies engaged in coal mining and processing are forced to pay for additional losses of active power due to the low power quality under non-sinusoidal conditions, which reduces the economic efficiency of the companies' operations. The paper presents a review of the literature on the assessment of additional active power losses in overhead power lines at harmonic frequencies. An example of calculating additional losses of harmonic active power is given for a 22 kV overhead power line, through which electrical energy is supplied to the coal grading plant of the Kua Ong-Vinacomin company. Additional losses are calculated using the measurements of harmonic voltage and current at the point of the supply network connection to the 22 kV overhead power line, through which electrical energy is supplied to the coal mine and the coal grading plant. To assess the influence of the electrical equipment of the coal grading plant on the power quality in the supply network, measurements were carried out on 0.4 kV buses of electrical substation of the coal mine.

Transforming Waste into Wealth: Advanced Carbon-Based Electrodes Derived from Refinery and Coal By-Products for Next-Generation Energy Storage.

This comprehensive review addresses the need for sustainable and efficient energy storage technologies against escalating global energy demand and environmental concerns. It explores the innovative utilization of waste materials from oil refineries and coal processing industries as precursors for carbon-based electrodes in next-generation energy storage systems, including batteries and supercapacitors. These waste-derived carbon materials, such as semi-coke, coal gasification fine ash, coal tar pitch, petroleum coke, and petroleum vacuum residue, offer a promising alternative to conventional electrode materials. They present an optimal balance of high carbon content and enhanced electrochemical properties while promoting environmental sustainability through effectively repurposing waste materials from coal and hydrocarbon industries. This review systematically examines recent advancements in fabricating and applying waste-derived carbon-based electrodes. It delves into the methodologies for converting industrial by-products into high-quality carbon electrodes, with a particular emphasis on carbonization and activation processes tailored to enhance the electrochemical performance of the derived materials. Key findings indicate that while higher carbonization temperatures may impede the development of a porous structure, using KOH as an activating agent has proven effective in developing mesoporous structures conducive to ion transport and storage. Moreover, incorporating heteroatom doping (with elements such as sulfur, potassium, and nitrogen) has shown promise in enhancing surface interactions and facilitating the diffusion process through increased availability of active sites, thereby demonstrating the potential for improved storage capabilities. The electrochemical performance of these waste-derived carbon materials is evaluated across various configurations and electrolytes. Challenges and future directions are identified, highlighting the need for a deeper understanding of the microstructural characteristics that influence electrochemical performance and advocating for interdisciplinary research to achieve precise control over material properties. This review contributes to advancing electrode material technology and promotes environmental sustainability by repurposing industrial waste into valuable resources for energy storage. It underscores the potential of waste-derived carbon materials in sustainably meeting global energy storage demands.

Experimental Investigation on Gallium and Germanium Migration in Coal Gangue Combustion

Gallium (Ga) and germanium (Ge) critical elements have a wide range of applications and market value. Extracting critical elements from coal gangue and combustion products can alleviate pressures on primary mining resources. Understanding the transformation behavior of Ga and Ge during coal gangue combustion processes is significant for resource utilization and environmental protection. Coal gangue from Xing’an League, Inner Mongolia, was chosen to explore how combustion temperatures (600 °C to 1000 °C) and particle sizes (50, 80, 10, 140, and 200 mesh) influence Ga and Ge migration during combustion. Techniques such as ICP-MS, XRD, XRF, SEM, TG-DSC, and sequential chemical extraction were employed to analyze the transformation of minerals and to quantify the contents and occurrence forms of Ga and Ge. Smaller gangue particle sizes were associated with higher concentrations of Ga and Ge. Approximately 99.19% of Ga and Ge in coal gangue were found in the residual, organic/sulfide-bound, and metal-oxide-bound modes. High temperatures promoted element volatilization and changed the reactions and interactions between elements and minerals. As combustion temperatures rose from 600 °C to 1000 °C, Ga and Ge contents in the products declined progressively. Under high temperatures, minerals like kaolinite, illite, and pyrite in gangue converted to silicate glass phases, mullite, and hematite. Minerals like kaolinite, calcite, and pyrite melted, leading to increased cohesion and agglomeration in the products. Over 90% of Ga and Ge in the combustion products existed in the residual, organic/sulfide-bound, and metal-oxide-bound forms. Moreover, Ga was enriched in combustion products, with its content exceeding critical extraction levels. The results may provide a useful reference for developing critical elements enrichment, extraction, and separation technologies from coal gangue.

Process Optimization and Robustness Analysis of Ammonia–Coal Co-Firing in a Pilot-Scale Fluidized Bed Reactor

A computational fluid dynamics (CFD) model was coupled with an advanced statistical strategy combining the response surface method (RSM) and the propagation of error (PoE) approach to optimize and test the robustness of the co-firing of ammonia (NH3) and coal in a fluidized bed reactor for coal phase-out processes. The CFD model was validated under experimental results collected from a pilot fluidized bed reactor. A 3k full factorial design of nine computer simulations was performed using air staging and NH3 co-firing ratio as input factors. The selected responses were NO, NH3 and CO2 emissions generation. The findings were that the design of experiments (DoE) method allowed for determining the best operating conditions to achieve optimal operation. The optimization process identified the best-operating conditions to reach stable operation while minimizing harmful emissions. Through the implementation of desirability function and robustness, the optimal operating conditions that set the optimized responses for single optimization showed not to always imply the most stable set of values to operate the system. Robust operating conditions showed that maximum performance was attained at high air staging levels (around 40%) and through a balanced NH3 co-firing ratio (around 30%). The results of the combined multi-optimization process performance should provide engineers, researchers and professionals the ability to make smarter decisions in both pilot and industrial environments for emissions reduction for decarbonization in energy production processes.

Experimental Study on Ultra-Low Concentration Methane Regenerative Thermal Oxidation

As a major coal country, China faces the issue of significant gas emissions during the coal mining process. This study aims to improve the utilization efficiency of mine gas, reduce greenhouse gas emissions, and promote the low-carbon and green transformation of the coal industry. A 10 kW gas regenerative thermal oxidizer (RTO) experimental system was constructed. The effects of initial methane concentration, low-temperature flue gas proportion, and operating load on combustion temperature, methane oxidation rate, high-temperature flue gas energy, and system thermal efficiency were studied. The results show that when the combustion temperature is below 600 °C, the CH4 combustion reaction cannot proceed effectively, and the system temperature continuously decreases and cannot be maintained stably. The experiment determines the stable operating methane concentration range of the RTO. In this experimental system, the lower limit of the initial methane concentration is 0.28%, corresponding to an 86% methane oxidation rate. As the initial methane concentration decreases, the combustion temperature also decreases, and the methane oxidation rate follows suit. The higher the low-temperature flue gas proportion, the higher the combustion temperature, and the system’s thermal efficiency and output heat decrease with the increase in the low-temperature flue gas proportion. This experiment explores multiple factors affecting regenerative thermal oxidation, providing a basis for ensuring the safe and stable operation of the system and its optimization. Improving the thermal insulation and heat exchange performance of the storage body can expand the lower limit of the initial methane concentration, thereby increasing the stability and thermal efficiency of the system.

WASTEWATER TREATMENT OF COAL TAR PROCESSING PROCESS FROM PHENOL

The coal tar processing process provides the chemical industry with valuable products: naphthalene, cresol, xylenols, phenol, technical oils and lubricants. The most significant product of coal tar processing is anthracene, which is a raw material for the production of carbon black. The prospects for the implementation of the coal tar processing process entail a danger to the environment and public health.Wastewater formed during the processing process has a complex chemical composition, mainly represented by organic aromatic compounds. Wastewater pollutants significantly exceed discharge standards permissible for discharge into the Centralized Wastewater Disposal System of Settlements and Urban Districts. Phenol, which has the third hazard class according to the standards of maximum permissible concentrations of harmful substances in the waters of water bodies of fishery importance, is particularly dangerous. The toxic effect of phenol leads to the suppression of biocenoses, a decrease in the number of living organisms, negatively affects human health, and can lead to death. Based on the above, in order to reduce the anthropogenic load on the environment and maintain the quality of water resources, it is necessary to carry out a set of environmental measures aimed at wastewater treatment.The article presents methods of wastewater purification from phenol, describes complex purification methods and formulates proposals for the technology of wastewater treatment of the enterprise. Spectral and quantitative chemical analysis were performed to determine the composition of wastewater. Regenerative cleaning methods are proposed. Methods for wastewater treatment have been formulated and implemented. Methods for wastewater treatment of the coal tar processing process are proposed.The aims of research are to reduce the concentration of phenol in wastewater to the standard values permissible for discharge into the Centralized Wastewater Disposal System of Settlements and Urban Districts, based on experimental data; formulate a proposal for the wastewater treatment of the coal tar processing process from phenol.Objectives of the work are to study the composition of the source wastewater; to consider methods of wastewater treatment from phenols; to carry out wastewater treatment, based on the results of the study, to propose a wastewater treatment scheme.The object of the study is the wastewater of the enterprise after the coal tar processing process.

Numerical Multifield Coupling Model of Stress Evolution and Gas Migration: Application of Disaster Prediction and Mining Sustainability Development

At present, coal mining is gradually shifting towards deep areas, and coal mines under deep mining conditions are more prone to coal and gas outburst accidents. In this research, we aim to explain the causes and mechanisms of dynamic disasters, which are caused by the combined action of static load, gas, and dynamic load on tectonic regions in complex stress field environments. Through numerical simulation using COMSOL Multiphysics software, based on the geological conditions of a mine in Jilin Province, it was found that faults lead to abnormal stress in tectonic regions. The combined action of dynamic and static loads results in excessive stress, causing the fragmentation and displacement of the coal body, leading to coal mine disasters, thus disrupting sustainability. Additionally, the coal matrix gas entering fractures raises the gas pressure and leads to the accumulation of methane near earthquake sources. Dynamic loads accelerate gas desorption in coal and increase porosity and permeability, facilitating rapid gas migration. This influx of gas into the roadways exceeds safety limits. Then, based on these findings and on-site conditions, a set of sustainable measures for coal mines has been proposed. This research offers theoretical guidance for enhancing safety, stability, and sustainability in coal mining processes.

Rare earth element enrichment in coal and coal-adjacent strata of the Uinta Region, Utah and Colorado

This study aims to quantify rare earth element enrichment within coal and coal-adjacent strata in the Uinta Region of central Utah and western Colorado. Rare earth elements are a subset of critical minerals as defined by the U.S. Geological Survey. These elements are used for a wide variety of applications, including renewable energy technology in the transition toward carbon-neutral energy. While rare earth element enrichment has been associated with Appalachian coals, there has been a more limited evaluation of western U.S. coals. Here, samples from six active mines, four idle/historical mines, four mine waste piles, and seven stratigraphically complete cores within the Uinta Region were geochemically evaluated using portable X-ray fluorescence (n = 3,113) and inductively coupled plasma-mass spectrometry (n = 145) elemental analytical methods. Results suggest that 24%–45% of stratigraphically coal-adjacent carbonaceous shale and siltstone units show rare earth element enrichment (>200 ppm), as do 100% of sampled igneous material. A small subset (5%–8%) of coal samples display rare earth element enrichment, specifically in cases containing volcanic ash. This study proposes two multi-step depositional and diagenetic models to explain the enrichment process, requiring the emplacement and mobilization of rare earth element source material due to hydrothermal and other external influences. Historical geochemical evaluations of Uinta Region coal and coal-adjacent data are sparse, emphasizing the statistical significance of this research. These results support the utilization of active mines and coal processing waste piles for the future of domestic rare earth element extraction, offering economic and environmental solutions to pressing global demands.

Chemical reaction process and dynamic characteristics of urea pyrolysis products in inhibiting gas explosion

During the coal mining process, gas explosions pose significant hazards, causing casualties and property losses. In order to develop new types of inhibitors for gas explosions, this paper explores the reaction mechanisms of urea pyrolysis products NH3 and HNCO inhibiting gas explosions based on density functional theory (DFT), transition state theory, and grand canonical ensemble Monte Carlo method (GCMC). It analyzes the reaction processes and kinetic characteristics of urea pyrolysis products with key radicals and gas molecules involved in explosions from a microscopic dynamic perspective. The results show that urea pyrolysis products exhibit good inhibition effects on active radicals involved in explosion reactions·NH3 and HNCO show stronger van der Waals forces in electrostatic attraction towards O2 and *H, respectively, and faster rate advantages in reaction rate constants. The lower Gibbs free energy barrier indicates higher reaction activity of pyrolysis products, thereby diluting the concentration of key radicals involved in explosion reactions and effectively inhibiting explosion key elementary reactions (R32, R38, R53, R57, R156, and R170). This study provides new insights into the microscopic inhibition mechanism of urea pyrolysis products on gas explosions, offering a new approach for designing more targeted modified inhibitors, which helps reduce the hazards of gas explosions during coal mining and provides scientific support and technical guidance for safe coal mining production.

Exploring barriers towards effective coal supply-A non-core perspective using ISM-DEMATEL

While other energy sources are becoming more popular, India is expected to continue to depend on coal in the coming years. This study aims to identify and assess barriers to the efficient supply of coal to non-core industries reliant on this energy source. Employing a hybrid approach combining Interpretive Structural Modeling (ISM) and Decision-Making Trial and Evaluation Laboratory (DEMATEL), we analyse the hierarchical structure and causal relationships among barriers affecting the coal sourcing process. The hybrid model emphasizes that the 'biased government approach' and 'lack of mining technology and infrastructure' are crucial barriers. These key barriers exert a substantial influence on other factors within the scope of our study. Unlike earlier studies, this research enhances theoretical understanding by thoroughly exploring barriers to effective coal sourcing strategies. Policymakers engaged in decision-making for the non-core coal-dependent sector in India can benefit from this research. Attention should be directed towards addressing key barriers influencing effective coal sourcing, specifically focusing on ‘biased approach by the government’, ‘lack of mining technology and infrastructure’, ‘social and political constraints’, ‘low research and development’, and ‘lack of skilled personnel’.

Study on time–frequency features of induced charge signals during the damage and failure process of coal medium

Monitoring and preventing coal-rock dynamic disasters are vital for safe mining. To investigate the time–frequency features of induced charge signals with coal damage and failure of roadways, the generation mechanism of free charge in loaded coal is analyzed and the induced charge monitoring test is conducted. According to the stress-induced charge-time curves, the time-domain features of charge signals at each loading stage are obtained. The wavelet threshold denoising approach and generalized Morse wavelet transform method are applied to denoise the raw signals and study the frequency-domain features. Further, the quantitative relationship between the de-noised induced charge signals and the degree of coal damage is established. The results show that the event number, amplitude and fluctuation degree of available induced charge signals are all at a low level in the compaction and elastic stages of the coal, which are mainly generated by the piezoelectric effect and predominantly represent discreteness. When entering the plastic and failure stages, the available signals are primarily produced by the crack propagation and triboelectric effects, with a significant increase in the event number, amplitude, and fluctuation degree. Then the induced charge signals gradually transit from discrete to continuous. Generally, the dominant frequency of the available induced charge signals during the coal damage process is concentrated at 0 ~ 11 Hz. The available induced charge is positively correlated with the degree of coal damage, which can perform the damage degree of coal mass, providing a new approach to evaluate the stability of roadway surrounding rocks.

Investigation of surrounding rock stability during proximal coal seams mining process and feasibility of ground control technology

The goaf formation of upper seam stope in proximity coal seams mining would influence the stability of the surrounding rock mass due to mining stress redistribution, which will seriously threaten the subsequent mining process and even ground environmental protection. Therefore, developing safe and efficient mining techniques, robust support strategies, and comprehensive safety evaluation systems is crucial for ensuring the overall safety of the mining process. Drawing upon on-site data, this study conducted a detailed feasibility analysis of the mechanized caving method. We developed a simulation model using similar materials, tailored for scenarios with overlying goaf, to demonstrate how lower seam mining was affected by the caving zone of the upper seam, leading to the progressive evolution of fracture networks. Furthermore, we employed numerical simulation models to juxtapose the simulated deformation areas with the actual potential deformation zones in the mining area. The mine seismic prediction (MSP) technique was utilized for the precise identification of unfavorable geological formations ahead of the working face, thereby preempting potential fractures or irregularities due to the presence of overlying goaf. In addition, a comprehensive support strategy was designed and implemented to bolster the stability of the roadways, thereby reinforcing the safety measures within the mining process. This study presents an integrated approach to investigate mining activities in the lower layers during stratified extraction, particularly how the overlying goaf of the upper seam affects the mining of the lower seam, leading to the progressive evolution of fracture networks. The findings and methodologies outlined in this work hold substantial practical significance, offering a pathway to enhance the reliability and safety of the mining process.

Numerical simulation study on chemical ignition process of underground coal gasification

Underground coal gasification (UCG) is a process that produces combustible gas by the in-situ gasification of coal seams. For a steady and efficient gasification project, the ignition of coal seam is a prerequisite. The heating method and reacting process of coal seam play an essential role to the ignition. A coal seam ignition model coupled with heptane combustion was created to simulate the deep UCG ignition stage employing the chemical ignition method. A 1700 K heptane jet flame and a U-shaped pyrolysis gas flame formed the heat source. The flame temperature of pyrolysis gas was around 1300 K. The effective heating length of the flame increased with the heating time, which reached 600 mm at 400 s. The coal seam reaction process was divided into four stages: (1) heptane flame stabilization, (2) coal seam heating, (3) pyrolysis gas release, and (4) pyrolysis gas flame stabilization. It was the third stage when the coal seam ignited. The coal seam would ignite faster with a lower excess air coefficient, and the ignition time ranged from 225 to 275 s when the excess air coefficient was 1.39. The outlet carbon dioxide concentration increased by about 5 %–17 % when the coal seam ignited.