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International Journal of Coal Science & Technology
Journal Prestige (SJR): 2.063  Citation Impact (citeScore): 3 Number of Followers: 3  Open Access journalISSN (Print) 2095-8293 - ISSN (Online) 2198-7823 Published by SpringerOpen  [229 journals]
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- Comparative study on the flame retardancy of CO2 and N2 during coal
adiabatic oxidation process
Abstract: Abstract To test the effectiveness of N2 and CO2 in preventing coal from spontaneously combusting, researchers used an adiabatic oxidation apparatus to conduct an experiment with different temperature starting points. Non-adsorbed helium (He) was used as a reference gas, and coal and oxygen concentration temperature variations were analyzed after inerting. The results showed that He had the best cooling effect, N2 was second, and CO2 was the worst. At 70℃ and 110℃, the impact of different gases on reducing oxygen concentration and the cooling effect was the same. However, at the starting temperature of 150℃, CO2 was less effective in lowering oxygen concentration at the later stage than He and N2. N2 and CO2 can prolong the flame retardation time of inert gas and reduce oxygen displacement with an initial temperature increase. When the starting temperature is the same, N2 injection cools coal samples and replaces oxygen more effectively than CO2 injection. The flame retardancy of inert gas is the combined result of the cooling effect of inert gas and the replacement of oxygen. These findings are essential for using inert flame retardant technology in the goaf.
PubDate: 2023-11-25
- Influence analysis of complex crack geometric parameters on mechanical
properties of soft rock
Abstract: Abstract Soft rocks, such as coal, are affected by sedimentary effects, and the surrounding rock mass of underground coal mines is generally soft and rich in joints and cracks. A clear and deep understanding of the relationship between crack geometric parameters and rock mechanics properties in cracked rock is greatly important to the design of engineering rock mass structures. In this study, computed tomography (CT) scanning was used to extract the internal crack network of coal specimens. Based on the crack size and dominant crack number, the parameters of crack area, volume, length, width, and angle were statistically analyzed by different sampling thresholds. In addition, the Pearson correlation coefficients between the crack parameters and uniaxial compression rock mechanics properties (uniaxial compressive strength UCS, elasticity modulus E) were calculated to quantitatively analyze the impact of each parameter. Furthermore, a method based on Pearson coefficients was used to grade the correlation between crack geometric parameters and rock mechanical properties to determine threshold values. The results indicated that the UCS and E of the specimens changed with the varied internal crack structures of the specimens, the crack parameters of area, volume, length and width all showed negative correlations with UCS and E, and the dominant crack played an important role both in weakening strength and stiffness. The crack parameters of the angle are all positively correlated with the UCS and E. More crack statistics can significantly improve the correlation between the parameters of the crack angle and the rock mechanics properties, and the statistics of the geometric parameters of at least 16 cracks or the area larger than 5 mm2 are suggested for the analysis of complex cracked rock masses or physical reproduction using 3D printing. The results are validated and further analyzed with triaxial tests. The findings of this study have important reference value for future research regarding the accurate and efficient selection of a few cracks with a significant influence on the rock mechanical properties of surrounding rock mass structures in coal engineering.
PubDate: 2023-11-25
- Water–rock two-phase flow model for water inrush and instability of
fault rocks during mine tunnelling
Abstract: Abstract Water inrush hazard is one of the major threats in mining tunnel construction. Rock particle migration in the seepage process is the main cause of water inrush pathway and rock instability. In this paper, a radial water–rock mixture flow model is established to study the evolution laws of water inrush and rock instability. The reliability of the proposed model is verified by the experimental data from a previous study. Through the mixture flow model, temporal-spatial evolution laws of different hydraulic and mechanical properties are analysed. And the proposed model’s applicability and limitations are discussed by comparing it with the existing water inrush model. The result shows that this model has high accuracy both in temporal evolution and spatial distribution. The accuracy of the model is related to the fluctuation caused by particle migration and the deviation of the set value. During the seepage, the porosity, permeability, volume discharge rate and volume concentration of the fluidized particle increase rapidly due to the particle migration, and this phenomenon is significant near the fluid outlet. As the seepage progresses, the volume concentration at the outlet decreases rapidly after reaching the peak, which leads to a decrease in the growth rate of permeability and porosity, and finally a stable seepage state can be maintained. In addition, the pore pressure is not fixed during radial particle migration and decreases with particle migration. Under the effect of particle migration, the downward radial displacement and decrease in effective radial stress are observed. In addition, both cohesion and shear stress of the rock material decreased, and the rock instability eventually occurred at the outlet.
PubDate: 2023-11-20
- Elimination mechanism of coal and gas outburst based on geo-dynamic system
with stress–damage–seepage interactions
Abstract: Abstract Coal and gas outburst is a complex dynamic disaster during coal underground mining. Revealing the disaster mechanism is of great significance for accurate prediction and prevention of coal and gas outburst. The geo-dynamic system of coal and gas outburst is proposed. The framework of geo-dynamic system is composed of gassy coal mass, geological dynamic environment and mining disturbance. Equations of stress–damage–seepage interaction for gassy coal mass is constructed to resolve the outburst elimination process by gas extraction with boreholes through layer in floor roadway. The results show the occurrence of outburst is divided into the evolution process of gestation, formation, development and termination of geo-dynamic system. The scale range of outburst occurrence is determined, which provides a spatial basis for the prevention and control of outburst. The formation criterion and instability criterion of coal and gas outburst are established. The formation criterion F1 is defined as the scale of the geo-dynamic system, and the instability criterion F2 is defined as the scale of the outburst geo-body. According to the geo-dynamic system, the elimination mechanism of coal and gas outburst—‘unloading + depressurization’ is established, and the gas extraction by boreholes through layer in floor roadway for outburst elimination is given. For the research case, when the gas extraction is 120 days, the gas pressure of the coal seam is reduced to below 0.4 MPa, and the outburst danger is eliminated effectively.
PubDate: 2023-11-18
- Evaluation of roof cutting by directionally single cracking technique in
automatic roadway formation for thick coal seam mining
Abstract: Abstract Automatic roadway formation by roof cutting is a sustainable nonpillar mining method that has the potential to increase coal recovery, reduce roadway excavation and improve mining safety. In this method, roof cutting is the key process for stress relief, which significantly affects the stability of the formed roadway. This paper presents a directionally single cracking (DSC) technique for roof cutting with considerations of rock properties. The mechanism of the DSC technique was investigated by explicit finite element analyses. The DSC technique and roof cutting parameters were evaluated by discrete element simulation and field experiment. On this basis, the optimized DSC technique was tested in the field. The results indicate that the DSC technique could effectively control the blast-induced stress distribution and crack propagation in the roof rock, thus, achieve directionally single cracking on the roadway roof. The DSC technique for roof cutting with optimized parameters could effectively reduce the deformation and improve the stability of the formed roadway. Field engineering application verified the feasibility and effectiveness of the evaluated DSC technique for roof cutting.
PubDate: 2023-11-18
- Numerical analysis of water-alternating-CO2 flooding for CO2-EOR and
storage projects in residual oil zones
Abstract: Abstract Residual oil zones (ROZs) have high residual oil saturation, which can be produced using CO2 miscible flooding. At the same time, these zones are good candidates for CO2 sequestration. To evaluate the coupled CO2-EOR and storage performance in ROZs for Water-Alternating-CO2 (WAG) flooding, a multi-compositional CO2 miscible model with molecular diffusion was developed. The effects of formation parameters (porosity, permeability, temperature), operation parameters (bottom hole pressure, WAG ratio, pore volume of injected water), and diffusion coefficient on the coupled CO2-EOR and storage were investigated. Five points from the CO2 sequestration curve and the oil recovery factor curve were selected to help better analyze coupled CO2-EOR and storage. The results demonstrate that enhanced performance is observed when formation permeability is higher and a larger volume of water is injected. On the other hand, the performance diminishes with increasing porosity, molecular diffusion of gas, and the WAG ratio. When the temperature is around 100 °C, coupled CO2-EOR and storage performance is the worst. To achieve optimal miscible flooding, it is recommended to maintain the bottom hole pressure (BHP) of the injection well above 1.2 minimum miscibility pressure (MMP), while ensuring that the BHP of the production well remains sufficiently high. Furthermore, the tapered WAG flooding strategy proves to be profitable for enhanced oil recovery, as compared to a WAG ratio of 0.5:1, although it may not be as effective for CO2 sequestration.
PubDate: 2023-11-18
- Apparent activation energy of mineral in open pit mine based upon the
evolution of active functional groups
Abstract: Abstract This study aimed to investigate the mechanism of mineral spontaneous combustion in an open pit. On the study of coal and mineral mixture in open pit mines, as well as through the specific surface area and Search Engine Marketing (SEM) experiments, the specific surface area and aperture characteristics of distribution of open pit coal sample and pit mineral mixture samples were analyzed. Thermal analysis experiments were used to divide the oxidation process was divided into three stages, and the thermal behavior characteristics of experimental samples were characterized. On the basis of the stage division, we explored the transfer law of the key active functional groups of the experimental samples. The apparent activation energy calculation of the key active groups, performed by combining the Achar differential method with the Coats–Redfern integral method, microstructural and oxidation kinetic properties were revealed. The resulted showed that the mixed sample had high ash, the fixed carbon content was reduced, the specific surface area was far lower than the raw coal, the large aperture distribution was slightly higher than the medium hole, the micropore was exceptionally low, the gas adsorption capacity was weaker than the raw coal, the pit coal sample had the exceedingly more active functional groups, easy to react with oxygen, more likely to occur naturally, and its harm was relatively large. The mixed sample contained the highest C–O–C functional group absorbance. The functional groups were mainly influenced by the self-OH content, alkyl side chain, and fatty hydrocarbon in the sample. The main functional groups of the four-like mixture had the highest apparent activation energy, and the two reactions were higher in the low-temperature oxidation phase.
PubDate: 2023-11-18
- Effect of CO2 dilution on laminar burning velocities, combustion
characteristics and NOx emissions of CH4/air mixtures
Abstract: The laminar combustion characteristics of CH4/air premixed flames with CO2 addition are systemically studied. Experimental measurements and numerical simulations of the laminar burning velocity (LBV) are performed in CH4/CO2/Air flames with various CO2 doping ratio under equivalence ratios of 1.0–1.4. GRI 3.0 mech and Aramco mech are employed for predicting LBV, adiabatic flame temperature (AFT), important intermediate radicals (CH3, H, OH, O) and NOx emissions (NO, NO2, N2O), as well as the sensitivity analysis is also conducted. The detail analysis of experiment and simulation reveals that as the CO2 addition increases from 0% to 40%, the LBVs and AFTs decrease monotonously. Under the same CO2 doping ratio, the LBVs and AFTs increase first and then decrease with the increase of equivalence ratio, and the maximum of LBV is reached at equivalence ratio of 1.05. The mole fraction tendency of important intermediates and NOx with equivalence ratio and CO2 doping ratio are similar to the LBVs and AFTs. Reaction H + O2 ⇔ O + OH is found to be responsible for the promotion of the generation of important intermediates and NOx under the equivalence ratios and CO2 addition through sensitivity analysis. The sensitivity coefficients of elementary reactions that the increasing of CO2 doping ratio promotes or inhibits formation of intermediate radicals and NOx decreases. Graphical abstract
PubDate: 2023-11-13
- Simulation study of hydrogen sulfide removal in underground gas storage
converted from the multilayered sour gas field
Abstract: Abstract A simulation study was carried out to investigate the temporal evolution of H2S in the Huangcaoxia underground gas storage (UGS), which is converted from a depleted sulfur-containing gas field. Based on the rock and fluid properties of the Huangcaoxia gas field, a multilayered model was built. The upper layer Jia-2 contains a high concentration of H2S (27.2 g/m3), and the lower layer Jia-1 contains a low concentration of H2S (14.0 mg/m3). There is also a low-permeability interlayer between Jia-1 and Jia-2. The multi-component fluid characterizations for Jia-1 and Jia-2 were implemented separately using the Peng-Robinson equation of state in order to perform the compositional simulation. The H2S concentration gradually increased in a single cycle and peaked at the end of the production season. The peak H2S concentration in each cycle showed a decreasing trend when the recovery factor (RF) of the gas field was lower than 70%. When the RF was above 70%, the peak H2S concentration increased first and then decreased. A higher reservoir RF, a higher maximum working pressure, and a higher working gas ratio will lead to a higher H2S removal efficiency. Similar to developing multi-layered petroleum fields, the operation of multilayered gas storage can also be divided into multi-layer commingled operation and independent operation for different layers. When the two layers are combined to build the storage, the sweet gas produced from Jia-1 can spontaneously mix with the sour gas produced from Jia-2 within the wellbore, which can significantly reduce the overall H2S concentration in the wellstream. When the working gas volume is set constant, the allocation ratio between the two layers has little effect on the H2S removal. After nine cycles, the produced gas’s H2S concentration can be lowered to 20 mg/m3. Our study recommends combining the Jia-2 and Jia-1 layers to build the Huangcaoxia underground gas storage. This plan can quickly reduce the H2S concentration of the produced gas to 20 mg/m3, thus meeting the gas export standards as well as the HSE (Health, Safety, and Environment) requirements in the field. This study helps the engineers understand the H2S removal for sulfur-containing UGS as well as provides technical guidelines for converting other multilayered sour gas fields into underground storage sites.
PubDate: 2023-11-04
- An efficient 3D cell-based discrete fracture-matrix flow model for
digitally captured fracture networks
Abstract: Abstract Complex hydraulic fracture networks are critical for enhancing permeability in unconventional reservoirs and mining industries. However, accurately simulating the fluid flow in realistic fracture networks (compared to the statistical fracture networks) is still challenging due to the fracture complexity and computational burden. This work proposes a simple yet efficient numerical framework for the flow simulation in fractured porous media obtained by 3D high-resolution images, aiming at both computational accuracy and efficiency. The fractured rock with complex fracture geometries is numerically constructed with a cell-based discrete fracture-matrix model (DFM) having implicit fracture apertures. The flow in the complex fractured porous media (including matrix flow, fracture flow, as well as exchange flow) is simulated with a pipe-based cell-centered finite volume method. The performance of this model is validated against analytical/numerical solutions. Then a lab-scale true triaxial hydraulically fractured shale sample is reconstructed, and the fluid flow in this realistic fracture network is simulated. Results suggest that the proposed method achieves a good balance between computational efficiency and accuracy. The complex fracture networks control the fluid flow process, and the opened natural fractures behave as primary fluid pathways. Heterogeneous and anisotropic features of fluid flow are well captured with the present model.
PubDate: 2023-11-01
- Building 3D CityGML models of mining industrial structures using
integrated UAV and TLS point clouds
Abstract: Abstract Mining industrial areas with anthropogenic engineering structures are one of the most distinctive features of the real world. 3D models of the real world have been increasingly popular with numerous applications, such as digital twins and smart factory management. In this study, 3D models of mining engineering structures were built based on the CityGML standard. For collecting spatial data, the two most popular geospatial technologies, namely UAV-SfM and TLS were employed. The accuracy of the UAV survey was at the centimeter level, and it satisfied the absolute positional accuracy requirement of creating all levels of detail (LoD) according to the CityGML standard. Therefore, the UAV-SfM point cloud dataset was used to build LoD 2 models. In addition, the comparison between the UAV-SfM and TLS sub-clouds of facades and roofs indicates that the UAV-SfM and TLS point clouds of these objects are highly consistent, therefore, point clouds with a higher level of detail and accuracy provided by the integration of UAV-SfM and TLS were used to build LoD 3 models. The resulting 3D CityGML models include 39 buildings at LoD 2, and two mine shafts with hoistrooms, headframes, and sheave wheels at LoD 3.
PubDate: 2023-10-30
- Experimental study on the slip evolution of planar fractures subjected to
cyclic normal stress
Abstract: Abstract The frictional rupture mechanisms of rock discontinuities considering the dynamic load disturbance still remain unclear. This paper investigates the transitional behaviors of slip events happened on a planar granite fracture under cyclic normal stress with different oscillation amplitudes. The experimental results show that the activations of fast slips always correlate with unloading of normal stress. Besides, the intensive normal stress oscillation can weaken the shear strength which is recoverable when the normal stress return to constant. The rupture patterns are quantified by stress drop, slip length and slip velocity. With the effect of small oscillation amplitudes, the slip events show chaotic shapes, compared to the regular and predictable style under constant normal stress. When the amplitude is large enough, the big and small slip events emerge alternately, showing a compound slip style. Large amplitude of the cyclic normal stress also widens the interval differences of the slip events. This work provides experimental supports for a convincible link between the dynamic stress disturbance and the slip behavior of rock fractures.
PubDate: 2023-10-27
- Time-shift effect of spontaneous combustion characteristics and
microstructure difference of dry-soaked coal
Abstract: Abstract The physical and chemical properties of the air-dried residual coal after soaking in the goaf will change, resulting in an increase in its spontaneous combustion tendency. This study aimed to look into the features and mechanism of soaked-dried coal's spontaneous combustion. Five samples of coal were dried to various degrees, and the weight loss features during thermal processing were examined. Based on this, the pore structure and chemical structure characteristics of the coal samples with the highest tendency to spontaneous combustion were quantitatively examined, and the mechanism by which soaking-drying affected the spontaneous combustion heating process of the remaining coal in goaf was investigated in turn. The results show that T1 decreases with the increase of drying time, T2–T6 shows a fluctuating change, and the ignition activation energy of 36-S-Coal is smaller than that of other coal samples. The pore type of 36-S-Coal changes from a one-end closed impermeable pore to an open pore, and the pore group area is large. During the 36 h drying process, the internal channels of the coal were dredged, and a large number of gravels and minerals were precipitated from the pores with the air flow. A large number of gravels were around the pores to form a surface structure that was easy to adsorb various gases. Furthermore, infrared spectroscopy was used to analyze the two coal samples. It was found that soaking and drying did not change the functional group types of coal samples, but the fatty chain degree of 36-S-Coal was reduced to 1.56. It shows that the aliphatic chain structure of coal is changed after 36 h of drying after 30 days of soaking, which leads to the continuous shedding of aliphatic chain branches of residual coal, and the skeleton of coal is looser, which makes the low-temperature oxidation reaction of 36-S-Coal easier. Based on the above results, the coal-oxygen composite mechanism of water-immersed-dried coal is obtained, and it is considered that the key to the spontaneous combustion oxidation process of coal is to provide oxygen atoms and accelerate the formation of peroxides.
PubDate: 2023-10-27
- Influence of nanosized magnesia on the hydration of borehole-sealing
cements prepared using different methods
Abstract: Abstract Gas drainage is an effective technology for gas control in coal mines. A high borehole-sealing quality is the fundamental precondition for efficient gas drainage. The expansibilities of cement pastes used in borehole-sealing processes are critical for the borehole-sealing effect. Nanosized magnesia expansive agents are used to improve the expansibilities of cement pastes and improve the borehole-sealing effect. Nuclear magnetic resonance spectrometry and scanning electron microscopy were adopted to study the effects of nanosized magnesia on the hydration of borehole-sealing cements used with different preparation methods. The results showed that an increase in the mass fraction of the nanosized magnesia promoted cement hydration, and the mass fraction was positively correlated with the promotion effect. The use of different preparation methods did not change the water-phase distribution in the cement. When using the wet-mixing preparation method, nanosized magnesia promoted the induction, acceleration, and deceleration periods of hydration; when using the dry-mixing preparation method, the nanosized magnesia promoted the induction period of cement hydration, and the promotion effect was less obvious than that seen when using the wet-mixing method. When using the wet-mixing preparation method, the nanosized magnesia was uniformly dispersed, thus enlarging the surface area of the reaction, which provided more nucleation sites for the hydration products of the cement and therefore accelerated the hydration reaction. When using the dry-mixing preparation method, the nanosized magnesia powders were dispersed nonuniformly and aggregated. Under these conditions, only a few nanosized magnesia particles on the surfaces of the aggregated clusters took part in hydration, so only a small number of nucleation sites were provided for the hydration products of cement. This led to inconsistent hydration of cement pastes prepared using the dry-mixing method. The surface porosity of the cement prepared with the wet-mixing preparation method first decreased and then increased with increases in the mass fraction of the nanosized magnesia. The cement surface exhibited compact hydration products and few pores, and the surface was relatively smooth. In comparison, the surface porosity of the cement prepared using the dry-mixing method fluctuated with increasing mass fraction of the nanosized magnesia, resulting in a rough cement surface and microfractures on some surfaces. The two preparation methods both reduced the surface porosity of the cement. The wet-mixing preparation was more effective and consistent in improving the compactness of the cement than the dry-mixing preparation. These results provide important guidance on the addition of nanosized magnesia in borehole-sealing engineering and the selection of cement preparation methods, and they also lay a solid foundation for realizing safe and efficient gas drainage.
PubDate: 2023-10-26
- Spoil characterisation using UAV-based optical remote sensing in coal mine
dumps
Abstract: Abstract The structural integrity of mine dumps is crucial for mining operations to avoid adverse impacts on the triple bottom-line. Routine temporal assessments of coal mine dumps are a compliant requirement to ensure design reconciliation as spoil offloading continues over time. Generally, the conventional in-situ coal spoil characterisation is inefficient, laborious, hazardous, and prone to experts' observation biases. To this end, this study explores a novel approach to develop automated coal spoil characterisation using unmanned aerial vehicle (UAV) based optical remote sensing. The textural and spectral properties of the high-resolution UAV images were utilised to derive lithology and geotechnical parameters (i.e., fabric structure and relative density/consistency) in the proposed workflow. The raw images were converted to an orthomosaic using structure from motion aided processing. Then, structural descriptors were computed per pixel to enhance feature modalities of the spoil materials. Finally, machine learning algorithms were employed with ground truth from experts as training and testing data to characterise spoil rapidly with minimal human intervention. The characterisation accuracies achieved from the proposed approach manifest a digital solution to address the limitations in the conventional characterisation approach.
PubDate: 2023-10-26
- Stability analysis of a slope containing water-sensitive mudstone
considering different rainfall conditions at an open-pit mine
Abstract: Abstract Mudstone, as a typical soft rock with wide distribution, has been endangering the slopes containing mudstone by its water-sensitivity of swelling and weakening strength when encountering water. To comprehensively understand the water-sensitivity of mudstone and reveal its influence on slope stability, we took the working slope containing water-sensitive mudstone of Shengli No.1 open-pit coal mine in Xilinhot, Inner Mongolia, China, as an example. Mudstone samples taken from the working slope were remodeled and saturated, and then triaxial tested to obtain the effective cohesion and effective internal friction angle. The filter paper method was used to obtain the soil–water characteristic curve of unsaturated mudstone. The pore structure of mudstone samples with different water contents were analyzed using the mercury intrusion porosimetry tests combined with the fractal dimension. The total pore content of the mudstone sample with lower water content is greater than that of the mudstone sample with higher water content. The mesopores are more in the mudstone sample with lower water content, while the small pores are more in the mudstone sample with higher water content. The variation of water content will change the complexity of mudstone pore structure. The higher the water content, the simpler the mudstone pore structure and the smoother the pore surface. Numerical calculations were conducted on the stability of the working slope under different rainfall conditions. The effective saturation on the mudstone layer surface changed and the plastic strain all occurred on the mudstone steps under different rainfall conditions. The key to preventing landslide of the slope containing water-sensitive mudstone in Shengli No.1 open-pit coal mine is to control the deformation and sliding of the mudstone layer.
PubDate: 2023-10-06
- Environmental performance assessments of different methods of coal
preparation for use in small-capacity boilers: experiment and theory
Abstract: Abstract The purpose of this article is to receive environmental assessments of combustion of different types of coal fuel depending on the preparation (unscreened, size-graded, briquetted and heat-treated) in automated boilers and boilers with manual loading. The assessments were made on the basis of data obtained from experimental methods of coal preparation and calculated methods of determining the amount of pollutant and greenhouse gas emissions, as well as the mass of ash and slag waste. The main pollutants from coal combustion are calculated: particulate matter, benz(a)pyrene, nitrogen oxides, sulfur dioxide, carbon monoxide. Of the greenhouse gases carbon dioxide is calculated. As a result of conducted research it is shown that the simplest preliminary preparation (size-graded) of coal significantly improves combustion efficiency and environmental performance: emissions are reduced by 13% for hard coal and up to 20% for brown coal. The introduction of automated boilers with heat-treated coal in small boiler facilities allows to reduce emissions and ash and slag waste by 2–3 times. The best environmental indicators correspond to heat-treated lignite, which is characterized by the absence of sulfur dioxide emissions.
PubDate: 2023-10-05
- In-situ gas contents of a multi-section coal seam in Sydney basin for coal
and gas outburst management
Abstract: Abstract The gas content is crucial for evaluating coal and gas outburst potential in underground coal mining. This study focuses on investigating the in-situ coal seam gas content and gas sorption capacity in a representative coal seam with multiple sections (A1, A2, and A3) in the Sydney basin, where the CO2 composition exceeds 90%. The fast direct desorption method and associated devices were described in detail and employed to measure the in-situ gas components (Q1, Q2, and Q3) of the coal seam. The results show that in-situ total gas content (QT) ranges from 9.48 m3/t for the A2 section to 14.80 m3/t for the A3 section, surpassing the Level 2 outburst threshold limit value, thereby necessitating gas drainage measures. Among the gas components, Q2 demonstrates the highest contribution to QT, ranging between 55% and 70%. Furthermore, high-pressure isothermal gas sorption experiments were conducted on coal samples from each seam section to explore their gas sorption capacity. The Langmuir model accurately characterizes CO2 sorption behavior, with fit coefficients (R2) greater than 0.99. Strong positive correlations are observed between in-situ gas content and Langmuir volume, as well as between residual gas content (Q3) and sorption hysteresis. Notably, the A3 seam section is proved to have a higher outburst propensity due to its higher Q1 and Q2 gas contents, lower sorption hysteresis, and reduced coal toughness f value. The insights derived from the study can contribute to the development of effective gas management strategies and enhance the safety and efficiency of coal mining operations.
PubDate: 2023-10-01
- Online coal dust suppression system for opencast coal mines
Abstract: Abstract Coal is the major source of power in India and world over. Coal mining is an essential industry which has a major role in the economic development of the country. Most major mining activities contribute directly or indirectly to air pollution. Coal dust is a major air pollutant which affects the personal working in the mines and also people residing in villages near the mines. Air pollution due to coal particulates can affect human health and cause damages to the environment. Hence effective pollution control mechanisms are needed to keep the pollution levels within permissible levels. The easiest and most common method employed for dust suppression worldwide is sprinkling of water. In majority of mines, water sprinklers are operated manually and can lead to wastage of water due to over sprinkling. It can also prove to be ineffective in dust suppression if sprinkling is not done properly. The paper proposes a system which can be deployed to automate the dust suppressions sprinklers. The system will monitor the concentration of PM10 and PM2.5 in the air and initiate sprinkling operation when the particulate matter content exceeds preconfigured limits.
PubDate: 2023-10-01
- A developed dual-site Langmuir model to represent the high-pressure
methane adsorption and thermodynamic parameters in shale
Abstract: Abstract Comprehending the mechanism of methane adsorption in shales is a crucial step towards optimizing the development of deep-buried shale gas. This is because the methane adsorbed in shale represents a significant proportion of the subsurface shale gas resource. To properly characterize the methane adsorption on shale, which exhibits diverse mineral compositions and multi-scale pore sizes, it is crucial to capture the energy heterogeneity of the adsorption sites. In this paper, a dual-site Langmuir model is proposed, which accounts for the temperature and pressure dependence of the density of the adsorbed phase. The model is applied to the isothermals of methane adsorption on shale, at pressures of up to 30 MPa and temperatures ranging from 40 to 100 °C. The results show that the proposed model can describe the adsorption behavior of methane on shale more accurately than conventional models, which assume a constant value for the density of adsorbed phase. Furthermore, the proposed model can be extrapolated to higher temperatures and pressures. Thermodynamic parameters were analyzed using correctly derived equations. The results indicate that the widely used, but incorrect, equation would underestimate the isosteric heat of adsorption. Neglecting the real gas behavior, volume of the adsorbed phase, and energy heterogeneity of the adsorption sites can lead to overestimation of the isosteric heat of adsorption. Furthermore, the isosteric heat evaluated from excess adsorption data can only be used to make a rough estimate of the real isosteric heat at very low pressure.
PubDate: 2023-10-01
