Special Issue "Advanced Technologies for Energy Exploitation of Coals"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "Geo-Energy".

Deadline for manuscript submissions: closed (28 April 2020).

Special Issue Editors

Dr. Manoj Khandelwal
Website SciProfiles
Guest Editor
School of Engineering, Information Technology and Physical Sciences, Federation University, Ballarat VIC 3353, Australia
Interests: rock engineering, rock blasting, soft computing, ground control, coal technology
Special Issues and Collections in MDPI journals
Prof. Dr. P.G. Pathegama Ranjith
Website
Guest Editor
Deep Earth Energy Laboratory, Department of Civil Engineering, Monash University, Melbourne, Australia
Interests: geomechanics; CO2 sequestration; shale gas; coal seam gas; geotherml energy
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

Energy, water, and food are three major elements to ensure human existence. The whole world has entered into a new historical period, where clean and low-carbon energy is undoubtedly required. Coal is definitely an indispensable source of energy necessary for the techno-economic progress of any country. The burning of coal releases numerous nitrous, carobon and sulphur oxides vis-à-vis organic and inorganic compounds, which are hazardous for the environment. It is a fact that these emissions result in air contamination, including climate change and local acid rain problems. Coal has been widely studied by various researchers to explore the possibilities of economical and eneviormental freiendly energy sources, and viable metals. Coal has also been used comprehensively to fabricate new nanomaterials in laboratories, as well as waste treatment and clean-coal technologies. So, this Special Issue aims to encourage researchers to address the technological advancements that have led to more efficient combustion of coal with reduced emissions of sulfur, carbon and nitrogen oxide. We are looking for contributions in the following areas:

  1. Coal as sustianable energy sources,
  2. Underground coal gassifications,
  3. Advanced coal mining technology.

Dr. Manoj Khandelwal
Prof. Dr. P.G. Ranjith
Guest Editors

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Keywords

  • Energy
  • Coal
  • Environmental hazards
  • Gasification
  • Mining
  • Sustainability

Published Papers (11 papers)

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Research

Open AccessArticle
Influence Analysis and Stepwise Regression of Coal Mechanical Parameters on Uniaxial Compressive Strength Based on Orthogonal Testing Method
Energies 2020, 13(14), 3640; https://doi.org/10.3390/en13143640 - 15 Jul 2020
Abstract
Uniaxial compressive strength (UCS) and peak strain (PS) are essential indices for studying the mechanical properties of coal and rock masses, and they are closely related to mechanical parameters such as the elastic modulus (E), Poisson’s ratio (υ), cohesion (C) and internal friction [...] Read more.
Uniaxial compressive strength (UCS) and peak strain (PS) are essential indices for studying the mechanical properties of coal and rock masses, and they are closely related to mechanical parameters such as the elastic modulus (E), Poisson’s ratio (υ), cohesion (C) and internal friction angle (Φ) of coal and rock masses. This study took the No. 2-1 coal seam of Zhaogu No. 2 Mine, in Henan Province, China, as the research object. An RMT-150B servo testing machine was used to test all mechanical parameters, including the E, υ, C and Φ of coal and rock masses. Based on the principle of orthogonal testing, Three Dimensions Fast Lagrangian Analysis of Continua (FLAC3D) was used to select E, υ, C, Φ, tensile strength (Rm) and dilation angle (Ψ) as initial participation factors. Using these six parameters and a five-level combination scheme (L25 (56)), the influence of coal mechanical parameters on UCS and PS was investigated, using the software SPSS for stepwise regression analysis, and a uniaxial pressure-resistant regression prediction equation was established. The research showed that, under uniaxial compression conditions, the main parameters controlling UCS of coal masses are C and Φ; conversely, the main parameters controlling PS are E and C. UCS and PS exhibit significant linear relationships with these main controlling parameters. Here, a stepwise regression prediction equation was established through reliability verification analysis using the main controlling parameters. This prediction method produces very small errors and a good degree of fit, thus allowing the rapid prediction of UCS. The precision of the stepwise regression model depends on the number of test samples, which can be increased in the later stages of a design project to further improve the precision of the projection model. Full article
(This article belongs to the Special Issue Advanced Technologies for Energy Exploitation of Coals)
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Open AccessArticle
A Modified Bursting Energy Index for Evaluating Coal Burst Proneness and Its Application in Ordos Coalfield, China
Energies 2020, 13(7), 1729; https://doi.org/10.3390/en13071729 - 05 Apr 2020
Cited by 2
Abstract
Coal burst is a type of dynamic geological hazard in coal mine. In this study, a modified bursting energy index, which is defined as the ratio of elastic strain energy at the peak strength to the released strain energy density at the post-peak [...] Read more.
Coal burst is a type of dynamic geological hazard in coal mine. In this study, a modified bursting energy index, which is defined as the ratio of elastic strain energy at the peak strength to the released strain energy density at the post-peak stage, was proposed to evaluate the coal burst proneness. The calculation method for this index was also introduced. Two coal mines (PJ and TJH coal mines) located in Ordos coalfield were used to verify the validity of the proposed method. The tests results indicate that modified bursting energy index increases linearly with increasing uniaxial compressive strength. The parameter A, which is used to fit relation between total input and elastic strain energy density, has a significant effect on the modified bursting energy index. A large value of parameter A means more elastic strain energy before the peak strength while a small value indicates most of input energy was dissipated. Finally, the coal burst proneness of these two coal mines was evaluated with the modified index. The results of modified index are consistent with that of laboratory tests, and more reasonable than that from original bursting energy index because it removed the dissipated strain energy from the total input strain energy density. Full article
(This article belongs to the Special Issue Advanced Technologies for Energy Exploitation of Coals)
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Open AccessArticle
Research on Mechanism and Control of Floor Heave of Mining-Influenced Roadway in Top Coal Caving Working Face
Energies 2020, 13(2), 381; https://doi.org/10.3390/en13020381 - 13 Jan 2020
Cited by 1
Abstract
The stability of the surrounding rock is the key problem regarding the normal use of coal mine roadways, and the floor heave of roadways is one of the key factors that can restrict high-yield and high-efficiency mining. Based on the 1305 auxiliary transportation [...] Read more.
The stability of the surrounding rock is the key problem regarding the normal use of coal mine roadways, and the floor heave of roadways is one of the key factors that can restrict high-yield and high-efficiency mining. Based on the 1305 auxiliary transportation roadway geological conditions in the Dananhu No. 1 Coal Mine, Xinjiang, the mechanism of roadway floor heave was studied by field geological investigation, theoretical analysis, and numerical simulation. We think that the surrounding rock of the roadway presents asymmetrical shrinkage under the original support condition, and it is the extrusion flow type floor heave. The bottom without support and influence of mining are the important causes of floor heave. Therefore, the optimal support scheme is proposed and verified. The results show that the maximum damage depth of the roadway floor is 3.2 m, and the damage depth of the floor of roadway ribs is 3.05 m. The floor heave was decreased from 735 mm to 268 mm, and the force of the rib bolts was reduced from 309 kN to 90 kN after using the optimization supporting scheme. This scheme effectively alleviated the “squeeze” effect of the two ribs on the soft rock floor, and the surrounding rock system achieves long-term stability after optimized support. This provides scientific guidance for field safe mining. Full article
(This article belongs to the Special Issue Advanced Technologies for Energy Exploitation of Coals)
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Open AccessArticle
Mechanical Properties and Consolidation Performances of High-Polymer Material in Coal
Energies 2020, 13(1), 270; https://doi.org/10.3390/en13010270 - 05 Jan 2020
Abstract
Roof collapse and wall spalling in mines commonly occurred. Grouting in the rock mass of a collapsed zone is one of the most effective technologies for solving this problem. Through grouting, the rock mass of a collapsed zone can be cemented into continuous [...] Read more.
Roof collapse and wall spalling in mines commonly occurred. Grouting in the rock mass of a collapsed zone is one of the most effective technologies for solving this problem. Through grouting, the rock mass of a collapsed zone can be cemented into continuous and stable blocks, and the physical and mechanical parameters of the rock mass can be significantly improved. In order to investigate the mechanical properties and damage of rock samples after the injection of a high-polymer material, we conducted uniaxial compression tests in a laboratory on grouted specimens. A high-polymer material is commonly used to address the gangue stacking that is caused by large roof collapse and wall spalling accidents in the mining face and the cracking of coal walls. Research has shown that a high-polymer material effectively solidifies gangues. The results indicate a micromechanics effect of the grouted specimens under uniaxial compression. The compressive strength, fracture propagation, damage mode, and other specimen behaviors are related to the amount of injected high-polymer materials. A high-polymer material substantially improves the mechanical strength of the prefabricated fractured coal and rock mass via strong material adhesion. The vertically- and horizontally-consolidated coal/rock masses exhibit different properties. The use of a high-polymer material results in distinct properties of the consolidated coal and rock masses. Full article
(This article belongs to the Special Issue Advanced Technologies for Energy Exploitation of Coals)
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Open AccessArticle
Tests to Ensure the Minimum Methane Concentration for Gas Engines to Limit Atmospheric Emissions
Energies 2020, 13(1), 44; https://doi.org/10.3390/en13010044 - 20 Dec 2019
Cited by 2
Abstract
During the extraction of hard coal in Polish conditions, methane is emitted, which is referred to as ‘mine gas’. As a result of the desorption of methane, a greenhouse gas is released from coal seams. In order to reduce atmospheric emissions, methane from [...] Read more.
During the extraction of hard coal in Polish conditions, methane is emitted, which is referred to as ‘mine gas’. As a result of the desorption of methane, a greenhouse gas is released from coal seams. In order to reduce atmospheric emissions, methane from coal seams is captured by a methane drainage system. On the other hand, methane, which has been separated into underground mining excavations, is discharged into the atmosphere with a stream of ventilation air. For many years, Polish hard coal mines have been capturing methane to ensure the safety of the crew and the continuity of mining operations. As a greenhouse gas, methane has a significant potential, as it is more effective at absorbing and re-emitting radiation than carbon dioxide. The increase in the amount of methane in the atmosphere is a significant factor influencing global warming, however, it is not as strong as the increase in carbon dioxide. Therefore, in Polish mines, the methane–air mixture captured in the methane drainage system is not emitted to the atmosphere, but burned as fuel in systems, including cogeneration systems, to generate electricity, heat and cold. However, in order for such use to be possible, the methane–air mixture must meet appropriate quality and quantity requirements. The article presents an analysis of changes in selected parameters of the captured methane–air mixture from one of the hard coal mines in the Upper Silesian Coal Basin in Poland. The paper analyses the changes in concentration and size of the captured methane stream through the methane capturing system. The gas captured by the methane drainage system, as an energy source, can be used in cogeneration, when the methane concentration is greater than 40%. Considering the variability of CH4 concentration in the captured mixture, it was also indicated which pure methane stream must be added to the gas mixture in order for this gas to be used as a fuel for gas engines. The balance of power of produced electric energy in gas engines is presented. Possible solutions ensuring constant concentration of the captured methane–air mixture are also presented. Full article
(This article belongs to the Special Issue Advanced Technologies for Energy Exploitation of Coals)
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Open AccessArticle
Study on Rule of Overburden Failure and Rock Burst Hazard under Repeated Mining in Fully Mechanized Top-Coal Caving Face with Hard Roof
Energies 2019, 12(24), 4780; https://doi.org/10.3390/en12244780 - 15 Dec 2019
Cited by 3
Abstract
The dynamic disasters caused by the failure of hard roof in the process of mining coal seriously affect the safe production in coal mines. Based on the W1123 mining coal working face of Kuangou coal mine, the physical similar material simulation experiment and [...] Read more.
The dynamic disasters caused by the failure of hard roof in the process of mining coal seriously affect the safe production in coal mines. Based on the W1123 mining coal working face of Kuangou coal mine, the physical similar material simulation experiment and acoustic emission (AE) monitoring method are used to study the failure law and AE characteristics of overburden in the process of coal mining. The stress evolution law is revealed through numerical simulation, the dangerous areas and rock burst hazard under the repeated mining with hard roof are studied combined with microseismic monitoring on site. The results show that the energy of W1123 working face released by the overburden damage under B4-1 solid coal is higher than that of the gob, and the peak value of the AE energy appears near the W1145 open-off cut. Through the statistics of the AE data, the large energy rate of AE event is defined, and the AE events with large energy rate appear in the scale of 82.4–231.2 cm within the model. This area is shown as a stress superposition area according to the numerical simulation. On the basis of comparing with the characteristics of energy distribution in the field, it is considered that the main control factors of rock burst in this area are hard roof of the working face and the stress concentration caused by the repeated mining. It provides a scientific guidance for the prevention and control measures of rock burst in this type of mining condition. Full article
(This article belongs to the Special Issue Advanced Technologies for Energy Exploitation of Coals)
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Open AccessArticle
Study on the Evolution Law of Overburden Breaking Angle under Repeated Mining and the Application of Roof Pressure Relief
Energies 2019, 12(23), 4513; https://doi.org/10.3390/en12234513 - 27 Nov 2019
Cited by 3
Abstract
Aiming at the serious problems caused by coal mine mining activities causing the rock burst accidents, this paper is based on rock mechanics and material mechanics to establish the key layer breaking by the double-key layer beam breaking structural mechanics model of a [...] Read more.
Aiming at the serious problems caused by coal mine mining activities causing the rock burst accidents, this paper is based on rock mechanics and material mechanics to establish the key layer breaking by the double-key layer beam breaking structural mechanics model of a single working face and double working face under repeated mining. The theoretical calculation formula of the angle was used as the theoretical basis for the elevation angle of the pre-reloading hole of the hard roof. The rationality and reliability of the formula were verified by the physical similarity simulation experiment and the 3 Dimension Distinct Element Code numerical simulation experiment, revealing the rock formation under the influence of repeated mining. The results show that the derived key layer breaking angle formula is suitable for the theoretical calculation of the breaking angle of the key layer of a single coal seam when the repeated disturbance coefficient is λ = 1; when it is λ = 2, it is suitable for the repeated mining of the short-distance double-coal mining. The rationality and reliability of the theoretical formula of the breaking angle of the double key layer of single coal seam and double coal seam were verified by the physical similarity simulation experiment. Through the 3DEC numerical simulation results and theoretical calculation results, the W1123 working face hard top pre-cracking pressure relief drilling elevation angle was 78°. The drilling peeping method was used to verify the results. The results show that the theoretical formula of the critical layer breaking angle is well applied in engineering practice. Full article
(This article belongs to the Special Issue Advanced Technologies for Energy Exploitation of Coals)
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Open AccessArticle
Study on Deformation and Energy Release Characteristics of Overlying Strata under Different Mining Sequence in Close Coal Seam Group Based on Similar Material Simulation
Energies 2019, 12(23), 4485; https://doi.org/10.3390/en12234485 - 25 Nov 2019
Cited by 2
Abstract
For the characteristics of overburden deformation and energy release under different mining sequences of close-distance coal seam groups, physical material similar simulation experiments were carried out, and comprehensive monitoring methods such as dial gauge, total station, micro-seismic monitor, and pressure sensor were used [...] Read more.
For the characteristics of overburden deformation and energy release under different mining sequences of close-distance coal seam groups, physical material similar simulation experiments were carried out, and comprehensive monitoring methods such as dial gauge, total station, micro-seismic monitor, and pressure sensor were used to test the Guangou Coal Mine. The comparative analysis of the initial mining and the upward recovery of the B4-1 coal seam is carried out to study the migration law, mine pressure distribution, and energy release characteristics of the overlying strata during W1145 mining face mining and residual coal mining. The results show that the maximum subsidence of surface and rock formation caused by re-mining of B4-1 residual coal is 0.96 m and 2.57 m respectively, which is 0.42 m and 0.47 m lower than that of W1145 working face. The boundary angle, moving angle, and rock stratum formed by the upward recovery of the remaining coal seam are 79.3°, 81.1°, and 67.5° respectively, which are smaller than the 80.9°, 82.3°, and 75.8° formed by the first mining. The cumulative development height of the fracture zone caused by upward mining is 115.7 m, which is 8.0% smaller than the cumulative development height of the downstream fracture zone of 125.8 m. When the up-level mining is carried out, the fragmentation effect of the rock layer below the key layer is strong, which makes the loosely broken rock block have a better supporting effect. Therefore, the residual coal mining time is longer than that of the first mining. The initial pressure step of the residual coal recovery is 139.2 m, and the average step of the cycle is 34.2 m, which is significantly larger than the 128.0 m and 26.0 m of the first mining. The loose rock strata that are disturbed by the upward recovery are more likely to be broken. Therefore, there are more micro-seismic events during the re-mining of the remaining coal. The B4-1 residual coals have a total of 945 incidents of re-seismic micro-seismic events, which is 292 more than the W1145 working face. After the B2 coal seam mining disturbance, the energy of some rock layers above the B4-1 coal seam is released, so that the micro-seismic energy caused by re-mining of the remaining coal seam is small. Through microseismic monitoring, it can be concluded that the accumulated energy in the process of upward re-mining of remaining coal seam is less than that in the process of downward mining of W1145 working face. Upward recovery is more likely to cause damage in the disturbed loose rock formation. Therefore, the frequency of micro-seismic events during the upward recovery is higher, and the partial energy release of the rock after the disturbance is caused, so that the source energy generated in the unit length of the upward recovery is smaller than the initial one. Full article
(This article belongs to the Special Issue Advanced Technologies for Energy Exploitation of Coals)
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Open AccessArticle
Study on Thermal Energy Conversion Theory in Drilling Process of Coal and Rock Mass with Different Stresses
Energies 2019, 12(22), 4282; https://doi.org/10.3390/en12224282 - 10 Nov 2019
Cited by 1
Abstract
In view of the problem that the evolutionary mechanism of bit temperature during the drilling process is still unclear and the influencing factors are complex, this paper analyzes the causes of heat generation and the factors of heat production when the drill bit [...] Read more.
In view of the problem that the evolutionary mechanism of bit temperature during the drilling process is still unclear and the influencing factors are complex, this paper analyzes the causes of heat generation and the factors of heat production when the drill bit interacts with the coal and rock mass. Considering the stress field distribution of coal and rock mass and the dynamic characteristics of drilling, a three-dimensional mechanical structure model of bit drilling is established in this paper, based on the energy conservation theory and introducing the friction heat micro-distribution mechanism. The corresponding relationship between coal stress and the bit temperature variation rate is obtained in this paper. Therefore, the temperature rise condition model and the coal stress identification model can be verified, combined with the existing experimental data. The result shows that the temperature of bit drilling is affected by factors such as bit geometry and drilling parameters, as well as the strength and stress state of the coal and rock. Without considering other factors, the rate of increase in bit temperature is proportional to the stress of the coal and rock mass. Based on the research results, the temperature rate of the drill bit can be used as an index to identify the stress areas of coal and rock mass. Research results provide a theoretical basis for the identification of high-stress risk areas in coal mines. Full article
(This article belongs to the Special Issue Advanced Technologies for Energy Exploitation of Coals)
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Open AccessFeature PaperArticle
Numerical Analysis of Roadway Rock-Burst Hazard under Superposed Dynamic and Static Loads
Energies 2019, 12(19), 3761; https://doi.org/10.3390/en12193761 - 30 Sep 2019
Cited by 6
Abstract
Microseismic events commonly occur during the excavation of long wall panels and often cause rock-burst accidents when the roadway is influenced by dynamic loads. In this paper, the Fast Lagrangian Analysis of Continua in 3-Dimensions (FLAC3D) software is used to study the deformation [...] Read more.
Microseismic events commonly occur during the excavation of long wall panels and often cause rock-burst accidents when the roadway is influenced by dynamic loads. In this paper, the Fast Lagrangian Analysis of Continua in 3-Dimensions (FLAC3D) software is used to study the deformation and rock-burst potential of roadways under different dynamic and static loads. The results show that the larger the dynamic load is, the greater the increase in the deformation of the roadway under the same static loading conditions. A roadway under a high static load is more susceptible to deformation and instability when affected by dynamic loads. Under different static loading conditions, the dynamic responses of the roadway abutment stress distribution are different. When the roadway is shallow buried and the dynamic load is small, the stress and elastic energy density of the coal body in the area of the peak abutment stress after the dynamic load are greater than the static calculations. The dynamic load provides energy storage for the coal body in the area of the peak abutment stress. When the roadway is deep, a small dynamic load can still cause the stress in the coal body and the elastic energy density to decrease in the area of the peak abutment stress, and a rock-burst is more likely to occur in a deep mine roadway with a combination of a high static load and a weak dynamic load. When the dynamic load is large, the peak abutment stress decreases greatly after the dynamic loading, and under the same dynamic loading conditions, the greater the depth the roadway is, the greater the elastic energy released by the dynamic load. Control measures are discussed for different dynamic and static load sources of rock-burst accidents. The results provide a reference for the control of rock-burst disasters under dynamic loads. Full article
(This article belongs to the Special Issue Advanced Technologies for Energy Exploitation of Coals)
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Open AccessArticle
On the Kaiser Effect of Rock under Cyclic Loading and Unloading Conditions: Insights from Acoustic Emission Monitoring
Energies 2019, 12(17), 3255; https://doi.org/10.3390/en12173255 - 23 Aug 2019
Cited by 4
Abstract
The Kaiser effect reflects the memory of the loaded rock to the irreversible damage and deformation. The stress level, loading rate and lithology are the main factors affecting the Kaiser effect of the rock. To identify the accurate stress point of the Kaiser [...] Read more.
The Kaiser effect reflects the memory of the loaded rock to the irreversible damage and deformation. The stress level, loading rate and lithology are the main factors affecting the Kaiser effect of the rock. To identify the accurate stress point of the Kaiser effect, the MTS 816 rock mechanics testing system and the DS5-A acoustic emission testing and analysis system were adopted. The uniaxial cyclic loading–unloading and acoustic emission characteristic test of 90 rock specimens from three types of rocks under different stress level and loading rate was carried out. The evolution of acoustic emission under uniaxial compression of the rock corresponds to the compaction stage, elastic stage, yield stage and post-peak stress drop stage of the rock deformation and failure process and is divided into the quiet period, transition period, active period and decay period of the acoustic emission. The larger the hardness of rock is, the earlier the stress point of the Kaiser effect appears. The loading stress level (σA) has appreciable influence on the Kaiser effect of the rock. When σA ≥ 0.7σc, the Kaiser effect disappears. Usually, the dilatancy stress (crack initiation stress) does not exceed 70% of the uniaxial compressive strength (σc) of the rock, and the stress point can be the threshold to determine whether the Kaiser effect occurs. The influence of loading rate (lr) on Felicity rate (FR) is relatively large when lr < 0.01 mm/s, and FR rapidly grows with increase of the loading rate. When lr ≥ 0.01 mm/s, the influence of the loading rate on FR is relatively small. The findings facilitate the future application of the Kaiser effect and improvement of the accuracy of the acoustic emission data interpretation. Full article
(This article belongs to the Special Issue Advanced Technologies for Energy Exploitation of Coals)
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