Experimental investigations of stress-gas pressure evolution rules of coal and gas outburst: A case study in Dingji coal mine, China

Coal and gas outburst is a potentially fatal risk during the mining of gassy coal seams, which seriously threatens the safe mining of collieries. To understand the outburst mechanism and evolution rules, a new apparatus (LSTT) was developed to conduct simulated experiment. In the context of an outburst accident in Dingji coal mine, the authors launched an authentic outburst experiment to replay the outburst accident. Experimental apparatus, similar criterion, coal‐like materials and gas sources, and experimental design were discussed systematically in this paper. Experimentally, the study analyzed the geo‐stress has significant influence on the outburst evolution. At the driving face, the stress concentration possibly caused gas outburst, under the influence of mining‐induced stress. After the outburst occurred, the stress balance of the coal changed, resulting in the instability of the coal. Furthermore, the elastic energy, gas enthalpy, and gravitational potential energy were released rapidly. The experimental result stated that outburst coal has the sorting characteristics, in line with the field outburst law. The intensity prediction model has been built based on the energy model. Moreover, the factors that impact outburst intensity were analyzed. In the process of coal and gas outburst, the gas enthalpy of gas and the elastic potential of coal are the main energy sources. This study provides guidance for the development of the outburst mechanism and outburst mine management

Three-Dimensional Physical Similarity Simulation of the Deformation and Failure of a Gas Extraction Surface Well in a Mining Area

Surface well deformation and failure in a mining area are a key issue challenging the surface well gas extraction technique. To provide information for the design of gas extraction surface wells in mining areas, the deformation and failure of surface wells with different materials under the influence of mining-induced rock movement were analyzed based on a three-dimensional physical similarity simulation and key strata theory. The research findings reveal that the fractures in the overlying strata had an elliptic-parabolic shape. The stope center was the highest point in the fracture zone. Horizontal shear deformation was most likely to occur in the thick strata (horizontal shear deformation could be larger if they were key strata) with large strength and stiffness near the intersection between the fracture surface of the overlying strata and the surface well. Due to the shear force and bending moment of the key strata, the surface well deformed into an S-shape. In addition, the surface well was vulnerable to shear deformation in the key strata. The surface well deformation did not weaken from bottom to top due to rock movement. Instead, it was subject to the influence of the rupture strength of the key strata. The surface well above the key strata was prone to tensile strain-compressive strain transition. In contrast, an abrupt change in the compressive strain occurred in the surface well below the key strata where tensile failure may occur. Moreover, a mechanical model of the surface well during the movement of the key strata was established according to the characteristics of the surface well deformation. The test results provide important information on the design optimization of surface wells and high-risk area protection in mining areas

Experimental Study of the Pore Structure and Permeability of Coal by Acidizing

The permeability of coal reservoirs prominently determines methane flow in reservoirs. A large amount of coal reservoirs containing methane, however, have low permeability because pores in reservoirs are sealed. To solve this issue, we investigated the pore structure and permeability law of coal through contrastive analysis of the microstructure and macrostructure before and after acidizing, using ASAP 2020 and triaxial servo-controlled seepage equipment. An analysis of the experimental data revealed the mechanism and the key parameters of acidizing, such as acid mass fraction and acidizing time. In addition, we hold that the optimal mass fraction for the test specimens is about 12~15%. Furthermore, the acid reaction is divided into three stages according to characteristics of the reaction progress. An analysis of the reaction kinetics of “HCl-HF” states that the significant factors will impact the process of reaction, like the composition of coal, surface area of the acid-coal reaction, mass fraction of acids, and environment of the reaction system. The results provide a new idea and research method for further enhancing permeability and gas extraction

Experimental Investigation on Influence Factors of Acoustic Emission Activity in Coal Failure Process

Stress-dominated coal and gas outburst disaster has become one of the main safety problems in deep coal mines. Acoustic emission (AE) or microseismic technology has been viewed as a promising method that can effectively reflect the stress and stability status of rock mass. The AE activity precursor of coal failure is the theoretical basis of this technology. In this study, AE experiments in failure process of coal specimens with different properties and under different stress conditions were performed in laboratory to explore influence factors and their effect of AE activity, and AE activity pattern classification was proposed based on the failure type of coal. The results indicate that the AE activity of different coals under loading are associated with the failure phase, and the evolution pattern of AE activity depends on the failure type of stressed coal. Both the mechanical property and the external stress condition have an important influential effect on the failure type and AE activity pattern in coal failure process. The internal mechanical property decides the inherent tendency of stressed coals to perform brittle or ductile behavior, and the responded AE activity pattern. The contrast of fissure distribution of specimens suggested that fissure structure in coal significantly affects the fracturing mode of coal in uniaxial compression and the AE activity pattern. The external stress condition has a transition effect on AE event energy distribution and AE activity pattern. Under the effect of external stress condition, the energy distribution of AE events was transforming between relative disperse and relative concentration, the failure type and AE activity evolution pattern of coal could appear the brittle-ductile transition. Based on the view of failure type, the pattern of AE activity of coal failure can be classified into three types, i.e., ductile, brittle, and semi-brittle pattern. It is suggested that the high-level AE activity can be viewed as the precursor of brittle instability of coal, and relative quiet phenomenon of AE activity as the precursor of ductile or semi-brittle instability. The research achievement can provide a theoretical base for the prewarning criteria establishment of coal and rock dynamic disasters at depth and improve the insight of AE activity in the coal failure process

An Experimental Study on the Particle Size and Shape Distribution of Coal Drill Cuttings by Dynamic Image Analysis

Particle size and shape distribution can be measured in great detail by dynamic image analysis (DIA). The narrow dispersion of repeated experiment results indicates that the particle size distribution can be obtained with high reliability. Particle size distribution can be better fitted to Rosin-Rammler equation than Gaudin-Schuhmann distribution and the lognormal distribution. The spread parameter (m) and the location parameters (d0) of the Rosin-Rammler equation can be calculated precisely. We analyzed the similarities and differences between the different particle shape distributions. The distributions of form factor and circularity are right-skewed distributions, while the distributions of ellipse ratio, irregularity, and aspect ratio obey a normal distribution. By studying the relation between particle size and shape, we find a linear relationship between the ellipse ratio and the Legendre ellipse diameter on the logarithmic scale

Combustion of Low-Concentration Gas in a Porous Media Burner: Reactor Design and Optimization

In order to utilize the low-concentration gas directly discharged into the atmosphere from 1.1% to 1.50% in coal mine production, the heat storage and oxidation equipment of gas was improved, and the heat storage and safety of gas under high-temperature environment were tested. The experimental results show that the regenerative oxidation system could provide a high-temperature oxidation environment of 1000°C for gas oxidation after changing the heating mode and enhancing the sealing property. The pressure curves of air and gas in the burner were similar. With the increase of gas concentration, the pressure difference between inlet and outlet tended to increase linearly with a minimum pressure differential of 4 kPa (air) and a maximum pressure differential of 11 kPa (1.50% gas). The internal pressure was relatively stable without an instantaneous pressure surge or explosion. The result of this study provides a reference for further research on the low-concentration gas regeneration oxidation unit at high temperatures

Distribution characteristics of pulverized coal and stress–gas pressure–temperature response laws in coal and gas outburst under deep mining conditions

Abstract Deep mining will increase the likelihood of coal and gas outburst accidents and do harm to the safety of coal mining. In this study, a coal and gas outburst experiment under deep high‐stress conditions was carried out and stress–gas pressure–temperature response laws in coal and rock surrounding the burst hole were evaluated. The experimental results showed that the stress response around the burst hole was intense and stress variation decreased as distance from the position to burst port increased. The gas pressure in the coal decreased sharply and oscillated several times during the burst process. The maximum rebound range was 0.05 MPa during this process. The decreasing rate of gas pressure reduced with the increase of the position‐burst port distance. The temperature response near the burst port was stronger than peripheral area. The gas internal energy was still the main energy source of coal and gas outbursts, accounting for 75% of the total energy, and played a key role in the burst process. The contribution of elastic potential energy was 22% under deep high‐stress conditions in this study. Based on the analysis of burst energy, the gas and stress were key factors of an outburst

Numerical Simulation Study on the Multi-Physical Field Response to Underground Coal and Gas Outburst under High Geo-Stress Conditions

Based on thermal–fluid–solid coupling law in coal and gas outburst, a multi-physical field numerical analysis model is built for the whole outburst process. The response laws of stress, gas pressure, temperature, and seepage in different areas and different time nodes around coal and rock mass in the coal and gas outburst under high stress condition are discussed. Research results show: Firstly, the stress response law of the coal and rock mass around the burst hole is initial vibration–sudden attenuation–late stability. Secondly, the gas pressure response law in different areas is that the gas pressure response rate decreases gradually with the increase of the distance from the outburst. Thirdly, the adsorbed gas contained in the broken coal near the outburst port is desorbed rapidly and expands to do work, and the temperature changes dramatically after outburst occurs. In contrast, with the increase of stress, the proportion of elastic potential in total coal and gas outburst energy increases, and the proportion of elastic potential is positively correlated with stress. The critical gas pressure under the energy condition of coal and gas outburst decreases with the increase of stress. It illustrates that the lower gas pressure can also meet the energy condition of coal and gas outburst under high stress

Multiorgan failure caused by Chinese herbal medicine Xanthii Fructus poisoning: a case report

Abstract Background Xanthii Fructus was used in the treatment of rhinitis and related nasal disease. It is the most commonly used chemically active component in compounds formulated for the treatment of rhinitis. However, poisoning, resulting in serious consequences, can easily occur owing to cocklebur overdose, improper processing, or usage without processing. Case presentation We reported on a 55-year-old man who experienced allergic rhinitis for 2.5 years. He ingested unprocessed Xanthii Fructus for 2 months as treatment. However, he developed anorexia; nausea; abdominal pain; general weakness; hiccups; oliguria and anuria; significantly elevated serum alanine aminotransferase, aspartate aminotransferase, and creatinine levels; and abnormalities in blood coagulation series. Nutritional support; daily drugs for liver protection, gastric protection, inflammation reduction; fresh plasma; and cryoprecipitate infusion were administered. Continuous venovenous hemodialysis (Prismaflex ST100) was also administered. However, the patient’s multiple organ failure gradually worsened, ultimately leading to death. Conclusion Xanthii Fructus poisoning affects multiple systems, and its clinical manifestations are complex. Therefore, it is easily misdiagnosed and missed. Along with careful inquiry of medical and medication history, early diagnosis and intervention are vital for a successful treatment. It is also important to educate people and create awareness about this poisoning. Therefore, this intractable case has great clinical significance

Numerical Simulation Study on the Multi-Physical Field Response to Underground Coal and Gas Outburst under High Geo-Stress Conditions

Based on thermal–fluid–solid coupling law in coal and gas outburst, a multi-physical field numerical analysis model is built for the whole outburst process. The response laws of stress, gas pressure, temperature, and seepage in different areas and different time nodes around coal and rock mass in the coal and gas outburst under high stress condition are discussed. Research results show: Firstly, the stress response law of the coal and rock mass around the burst hole is initial vibration–sudden attenuation–late stability. Secondly, the gas pressure response law in different areas is that the gas pressure response rate decreases gradually with the increase of the distance from the outburst. Thirdly, the adsorbed gas contained in the broken coal near the outburst port is desorbed rapidly and expands to do work, and the temperature changes dramatically after outburst occurs. In contrast, with the increase of stress, the proportion of elastic potential in total coal and gas outburst energy increases, and the proportion of elastic potential is positively correlated with stress. The critical gas pressure under the energy condition of coal and gas outburst decreases with the increase of stress. It illustrates that the lower gas pressure can also meet the energy condition of coal and gas outburst under high stress