Search

Cocrystallization integrates the merits of high energy and insensitivity between energetic molecules to obtain energetics with satisfying performance. However, how to obtain supramolecular synthons accurately and rapidly for predicting the structure and property of cocrystal remains a challenging problem. In this research, an efficient systematic search approach to predict CL-20/2,4-DNI cocrystal has been proposed that 2,4-DNI revolves around CL-20 with a stoichiometric ratio of 1:1 in accordance with the specified rules (hydrogen bond length: 2.2–3.0 A; search radius: 6.5 A; the number of hydrogen bond: 1–3). Eight possible supramolecular synthons were obtained by combining quantum chemistry with molecular mechanics. Crystal structure prediction indicated that there are four structures in cocrystal, namely P21/c, P212121, Pbca and Pna21, and CL-20/2,4-DNI cocrystal is likely to be P21/c and the corresponding cell parameters are Z = 4, a = 8.28 A, b = 12.17 A, c = 20.42 A, α = 90°, β = 96.94°, γ = 90°, and ρ = 1.9353 g/cm3. To further study the intermolecular interaction of CL-20/2,4-DNI cocrystal, a series of theoretical analyses were employed including intermolecular interaction energy, electrostatic potential (ESP), Density of State (DOS), Hirshfeld surface analysis. The C–H⋯O hydrogen bonds are demonstrated as the predominant driving forces in the cocrystal formation. The mechanical properties and detonation properties of CL-20/2,4-DNI cocrystal implies that the cocrystal shows better ductility and excellent detonation performances (9257 m/s, 39.27 GPa) and can serve as a promising energetic material. Cocrystal structure predicted was compared with the experimental one to verify the accuracy of systematic search approach. There is a less than 8.8% error between experiment and predict results, indicating the systematic search approach has extremely high reliability and accuracy. The systematic search approach can be a new strategy to search supramolecular synthons and identify structures effectively and does have the potential to promote the development of energetic cocrystal by theoretical design.

This research reviewed the mechanics and gas desorption properties of intact coal, and tested the crushing work ratios of different intact coals, and then, studied the stress conditions for the failure or crushing of intact coal and the gas demand for the pulverization of intact coal particles. When a real-life outburst case is examined, the required minimum stress for intact coal outburst is estimated. The study concludes that the crushing work ratios of three intact coal samples vary from 294.3732 to 945.8048 J/m2. For the real-life case, more than 2300 MJ of transport work is needed, and 10062.09, 7046.57 and 5895.47 m3 of gas is required when the gas pressure is 1, 2 and 3 MPa, respectively. The crushing work exceeds the transport work and even reaches 13.96 times of the transport work. How to provide such an enormous crushing work is an energy-limiting factor for the outburst in intact coal. The strain energy is needed for the crushing work, and the required minimum stress is over 54.35 MPa, even reaching 300.44 MPa. These minimum stresses far exceed the in-situ vertical and horizontal stresses that can be provided at the 300–700 m mining depth range.

Outburst energy is a major factor influencing coal and gas outbursts, albeit its estimation is difficult owing to the lack of amenable means for quantification of gas desorption. In the past decades, determining the mechanism of outbursts is one of the most challenging issues in rock mechanics. In this study, a triaxial coal and gas outburst simulation system was employed to perform simulated experiments using He (to rule out the influence from gas ad-desorption), N2, and CO2. This facilitated understanding of the energy principle underlying the said outbursts and evaluation of the effects of gas desorption on outburst development. Results of this study indicate that outburst energy and energy consumption are influenced by several factors, including outburst pressure, outburst intensity, ejection distance, and particle size of ejected coal. Among these, gas desorption demonstrates the greatest influence when performing controlled tests (using He). Considering the effects of gas desorption, the total outburst energy can be increased by 1.35–2.95 times, thereby causing an enormous increase in the destructive potential of outbursts. Additionally, values of the coal crushing and transport energies can be enhanced by the order of 118.9–206.6% and 157.8–406.6%, respectively, thereby resulting in a stronger conveying capacity of outburst coal–gas flow along with severe coal fragmentation. A further analysis of the energy distribution indicated that in the development stage, gas desorbed from coal acts as the force driving coal transport, whereas free gas energy is mainly consumed during coal crushing. Findings of this study highlight the importance of quantifying contributions of coal gas towards effective interpretation of outburst-causing mechanisms.

Deep mining and drilling activities typically trigger significant deformation of coal/rock roadway and even coal/rock dynamic hazards, which has attracted considerable attention. Hence, in this article, the mechanics and failure properties of intact coal are examined through triaxial compression tests and creep tests. First of all, triaxial compression experiments demonstrated that the complete stress–strain curves of intact coal are characterised by Class-I behaviour; and the post-peak modulus is negative. Second, with increasing confining pressure, peak strength and residual strength rise linearly, whereas elasticity modulus and peak strain increase as a power function form. Thirdly, compared with conventional triaxial load, tiered cyclic load can stiffen the strength of intact coal. Moreover, the data of creep tests are successfully fitted to the Burgers model. Maxwell elasticity modulus is significantly smaller than other creep parameters; Maxwell viscosity coefficient shows a positive correlation with deviatoric stress. Contrarily, Kelvin elasticity modulus and Kelvin viscosity coefficient drop with the rise in deviatoric stress. Additionally, with increasing deviatoric stress, single-step creep strain and average creep strain rate, proposed in this study, increase in a power function form. Finally, failure characteristics of intact coal under triaxial stress could be classified into four types (mainly shear failure and multiple shear fractures). The failure-plane angle generally linearly increases with the rise in confining pressure applied.

The intrinsic exothermic reaction of coal with oxygen during low-temperature oxidation is the main heat source responsible for the self-heating and spontaneous combustion of coal. Due to the comple...

It is imperative to have an in-depth understanding of CO overrun at the air return corner not only for pre-warning concentrations of safety and spontaneous combustion but also for providing scienti...

Solar energy driven cerium dioxide (CeO2) thermochemical cycle based fuel production is considered to be a promising technology that can integrate with a combined cooling, heating and power (CCHP) system owing to the pollution free property and favorable chemical reaction kinetics characteristics. In this study a combined cooling, heating, power and fuel (CCHPF) distributed energy system is devised to improve the energy utilization efficiency and reduce the dependence on conventional fossil fuels. To realize the efficient and cost-effectively operations of the system, a constrained multi-objective optimization problem with aims of maximizing primary energy saving ratio (PESR) and minimizing CO2 emission and energy cost is proposed to search for the optimal operation strategy and schedule. A potent optimization method that capitalizes on the advantages of the non-dominated sorting genetic algorithm-II (NSGA-II) and the random walk with directional exploitation (RWDE) algorithm is developed to solve the proposed optimization problem more effectively. The fuzzy decision making method is tailored to determine the final operation strategies of the CCHPF system from the obtained Pareto front according to the decision maker preferences. Numerical results show that the proposed system realizes the supply-demand balance, the optimal dispatch of the energy and the efficient economic operation. In comparison with existing CCHP systems, the energy utilization efficiency of the developed CCHPF system increases by 0.60% and 17.65%, CO2 emission decreases by 13.79% and 3.77%, as well as economic cost reduces 0.29% and 6.33% on a typical winter and summer days, respectively. The research findings provide new insights for improving the coordinated operation of distributed renewable energy system and alleviating energy crisis and environmental pollution.

A series of efficient and stable Z-scheme LaCoO3/g-C3N4 heterojunction photocatalysts with different weight contents of g-C3N4 had been first successfully fabricated by a facile one-step impregnation method. The crystal structure, surface state, element distribution and photoelectronic properties of the as-prepared samples were characterized by XRD, FT-IR, XPS, SEM, TEM, UV–Vis DRS, PL, photocurrent testing and EPR technique. The results show that Z-scheme heterostructures have formed on the interfaces between the perovskite-type oxides LaCoO3 and the flake-like g-C3N4, which enhance the visible-light absorption, separation of the photogenerated electron-hole pairs and transformation of the photogenerated electrons. Moreover, the LaCoO3/g-C3N4-60 wt% composite photocatalyst presented the highest photocatalytic activity for the degradation of phenol under visible light, whose phenol degradation rate is 85% after 5 h under visible light irradiation, which is about 5.2 and 7.5 times higher than that of bare LaCoO3 and g-C3N4, respectively. What's more, the LaCoO3/g-C3N4-60 wt% composite also shows an excellent stability. The highest photocatalytic activity can mainly attribute to high charge carrier separation efficiency as well as the improved dispersity via the Z-scheme LaCoO3/g-C3N4 heterostructure and a possible mechanism for photodegradation process over the Z-scheme LaCoO3/g-C3N4 heterojunction photocatalysts has been proposed.

The bottleneck for large-scale application of Nickel-rich layered LiNi0.6Co0.2Mn0.2O2 (NCM) cathode material for lithium-ion batteries is their severe capacity fading, especially at high voltage. Herein, we modify the NCM cathode materials by substituting the boracic polyanion to suppress capacity degradation and improve power performance. The crystal structure, morphology, elemental states and surface elemental composition of the cathode materials are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM), respectively. Compared to the bare NCM, the I(003)/I(104) ratio of the B3-NCM sample increases from 1.58 to 1.66, and the cation mixing declines from 4.65% to 3.21%, as known by XRD and Rietveld refinement. The results of electrochemical tests indicate that the B1-NCM exhibit superior rate property at the high current density (131.02 mAh g−1 at 5 C), and the higher capacity retention (76.07% after 100 cycles at 1 C). Further electrochemical impedance spectra (EIS) and galvanostatic intermittent titration technique (GITT) demonstrate that boracic polyanion doping decreases impedance value and enhances lithium ion diffusion coefficient. These consequences reveal that the boracic polyanion modified LiNi0.6Co0.2Mn0.2O2 cathode material has better electrochemical performance.

A series of catalysts with p-LaFeO3/n-ZnO heterostructure were designed and prepared by hydrothermal method. The structure, surface topographies, optical properties and interfacial interactions of these photocatalysts were analyzed by XRD, SEM, TEM, PL, Uv-vis DRS, XPS, COD, TOC etc., indicating that p-n heterojunction formed at the interface between p-LaFeO3 and n-ZnO, which enhanced the photocatalytic activity. Among them, the 20%-p-LaFeO3/n-ZnO composite exhibits the best activity for the phenol degradation under visible light. The superior photocatalytic activity of the heterojunction photocatalyst is mainly attributed to the formation of p-n heterojunction which leads to an efficient separation of photogenerated electron-hole pairs. Besides, the 20%-p-LaFeO3/n-ZnO heterojunction photocatalyst shows the excellent photocatalytic stability after 4 cycles. And from the free radical capture experiment, the degradation of phenol is dominated by the oxidation reaction of hydroxyl radicals and direct hole oxidation. What's more, certain intermediates were detected by HPLC and 3D-EEMs. Therefore, a photocatalytic mechanism of the 20%-p-LaFeO3/n-ZnO p-n heterojunction catalyst for phenol degradation under visible light irradiation was proposed.

Coal mine fire often occurs in lean-oxygen environments caused by methane. In order to clarify the characteristics and mechanisms of coal-oxygen reaction under these conditions, the coal-oxygen reaction experiments were carried by using thermogravimetric analysis (TGA)-gas chromatograph (GC) combined technology in the range of 30-800°C. The thermogravimetric-subtraction/derivative thermogravimetric-subtraction (TG-S/DTG-S) curves which can more accurately reflect the coal-oxygen process were obtained by subtracting the TG/DTG curve of coal pyrolysis under the condition of pure N2. Through TG-S/DTG-S curves, the coal-oxygen reaction was divided into low temperature oxidation stage, accelerated oxidation stage and combustion stage. In the low temperature oxidation and accelerated oxidation stages, methane delayed the coal-oxygen reaction as an inert gas. Under the same oxygen concentration, the effect of methane on reducing CO, CO2 production and increasing ignition temperature (Ti) of coal was obvious than...

La/Y-codoped microporous organosilica membranes were successfully fabricated by sol-gel procedure with 1,2-bis(triethoxysilyl)ethane (BTESE) as silica precursor for efficient desalination. The rare earth elements were confirmed to be doped into silica frameworks during the sol-gel procedure by various characterizations, which would decrease particles size and size distribution of BTESE-derived sols and form hydrothermally stable Si–O–RE (RE for La and Y) bonds. It could significantly influence membrane surface morphology, microstructure properties and hydrophilcity of La/Y-codoped membranes, and then improve their desalination performance. Under the optimized preparation conditions, La25Y75-SiO2 (La:Y = 25:75, mol%) membranes exhibited the highest water flux of 10.3 kg m−2 h−1 and NaCl rejection of nearly 100% towards 3.5 wt% NaCl feed solution even at room temperature of 25 °C. It was attributed to strongest hydrophilcity, finest microstructure, and lowest mass resistance of water permeation for La25Y75-SiO2 membranes. Moreover, such these organosilica membranes demonstrated good stability for 200 h simulated seawater desalination tests without any significant changes of separation performance and promising hydrothermal durability under various salts solutions with different concentrations at 25–60 °C.

Coal and gas outbursts are small-scale geological disasters controlled by tectonic movement, and tectonic coal is widespread in outburst zones. In this study, we compare tectonic and intact coal specimens to examine the basic properties of tectonic coal. We estimate the different energies and limits of the crushing work ratio of coal from five typical outburst cases using on-site outburst data, and discuss the relationship between outbursts and tectonic coal. The results show that tectonic coal is a product of tectonic movement and its original primary structure is destroyed during the tectonic process. Compared with intact coal, tectonic coal shows low strength properties and a crushing work ratio of 22.11 J/m2. The specific surface area and total pore volume of the minipores, mesopores, and macropores of the coal strongly increase under conditions of intense tectonism, which indicates that tectonic coal has a very high capacity for rapid initial gas desorption. An adequate supply of gas is required to transport outburst coal, such that the existence of coal particles smaller than the critical diameter is important. Our calculations indicate that the crushing work ratio of coal from the five outburst case ranges from 22.19 to 78.67 J/m2. Only the crushing work ratio of tectonic coal satisfies the requirement for these cases. Therefore, the properties of the tectonic coal and crushing work ratio for the five cases indicate that the widespread occurrence of tectonic coal plays a crucial role in outbursts.

Hard carbon is the most common carbon-based material with abundant raw material resources, low cost, high reversible capacity and reliable safety performance, it is the most suitable sodium-ion batteries (SIBs) anode material for commercial production, which attracts the interest of the researchers. Unfortunately, the electrochemical performances of hard carbon are still underestimated in the previous reports. In this research, we use a simple process flow to obtain carbonized oatmeal as a kind of hard carbon. It can deliver initial reversible capacity of 272.4 mAh g−1 at 20 mA g−1, the capacity retention rate is 93.3% after 100 cycles, exhibits a good electrochemical performance. Simultaneously, the transport properties of sodium-ion in carbonized oatmeal material are also characterized by electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). The measurement results show that the low potential platform region of the oatmeal-derived hard carbon is attributed to the insertion/extraction characteristics of sodium-ion in the graphitic microcrystallites sheets.

LaFeO3 is introduced as an ideal protective coating layer with excellent conductivity to enhance LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode material for use at higher operating voltage (especially 4.6 V). Various material characterization methods are employed to characterize the structural and morphological characteristics of the pristine and modified samples, including x-ray diffraction analysis, field-emission scanning electron microscopy, transmission electron microscopy, and x-ray photoelectron spectroscopy. The electrode with 2 wt.% LaFeO3 coating showed capacity retention of 80% at current density of 1 C after 200 charge/discharge cycles at 25°C, compared with 63% for the pristine electrode. Cyclic voltammogram results indicated that the LaFeO3 coating reduced the cell polarization during extended cycling. The results therefore show that LaFeO3 has potential for coating of NCM523 for use even at high voltage.

Investigating independent active materials is inadequate to settle the technological challenges involved in the booming lithium ion battery industry. The further development of energy-storage properties with both high energy density and superior cycling lifespan are highly dependent on the overall system optimization, which highlights the study of the interface between different components in a system. Herein, a system-level strategy of engineering MnO-based anode build on the plentiful electrolytic manganese dioxide are developed via a microwave-assisted carbothermic reduction, combined with a succeeding in-situ aggregation of polydopamine (PD) onto MnO along with chemical binding with polyacrylic acid (PAA) binder. Fourier transform IR spectra, X-ray photoelectron spectroscopy spectra validate the formation of cross-linking reaction between the PD buffer and PAA binder. Benefited from the prominent structure stability which endowed by well-connected three-dimensional porous structure, as well as two steady interfaces between MnO and PD buffer and between PD buffer and PAA binder, the cross-linked MnO anode exhibit a reversible capacity of 687 mAh g−1 at 300 mA g−1 and high Coulombic efficiency of 99% over 500 cycles and impressive rate capability of 320 mAh g−1 at 3000 mA g−1.

Respirable dust pollution at an underground heading face driven with continuous miner was detected during a ventilation survey. In order to obtain fundamental understandings of the airflow patterns and the respirable dust dispersion characteristics within the heading face, three dimensional Computational Fluid Dynamics (CFD) models were developed according to field condition. The continuous miner (JOY 12CM27), which significantly impacts the ventilation and respirable dust flow behaviour, was embedded into the model. The inappropriate ventilation arrangement, lack of effective dust control measures, as well as insufficient maintenance of equipment (e.g. blunt picks, missing nozzles etc.) were identified as the main reasons causing the high dust exposure levels (greater than 500 mg/m3). Based on the CFD model results, a new ventilation arrangement together with dust mitigation strategy were proposed. And an evaluation of the proposed system demonstrated a high respirable dust mitigation effect (90%) could be achieved. Therefore, it is highly recommended these control strategies to be implemented immediately to address the extremely high dust levels in the underground working environment. The proposed strategy will be also suitable for headings with similar conditions and could provide guidance for mining operators to refer.

Spontaneous combustion of coal has long been a thermal dynamic hazard during coal mining, storage, and transport, posing a great threat to coal mine safety. Especially coal spontaneous combustion in longwall goaf poses a great threat to underground working crew. To investigate such a mine safety issue with more insights and “what if” scenarios, this study employs CFD technique to develop a proactive inertisation plan in a longwall goaf. Based on real on-site conditions of the longwall goaf, a three-dimensional transient non-equilibrium thermal CFD model was developed to study heating evolution and proactive inertisation plans of the longwall goaf. The theoretical model incorporated a set of governing equations including low temperature kinetics of coal oxidation, energy and mass conservation, momentum balance, and continuity equation. After the base model (1000 m) was validated and calibrated with field gas monitoring data, another model (500 m model) was studied to obtain an optimum inertisation plan. Both steady state and transient simulations were conducted to study the flow dynamics of air velocity, oxygen ingress, dispersion of gaseous products and heating evolution in the longwall goaf. Based on the flow dynamics field, proactive inertisation plans using nitrogen to suppress the onset and development of goaf heatings were then developed and studied.

Extensive studies have been conducted on the use of fibre-reinforced polymer (FRP) as a confining material in hybrid tubular columns for civil construction, where the design of columns is often controlled by the stiffness and/or strength requirements. By contrast, the capacity of sustaining large deformation without losing structural integrity can be critical in some applications such as the standing supports for underground mines. This paper presents the conceptual development of a novel column form with large deformation capacity. The novel column consists of an outer FRP tube, and an infill made of coarse lumps/aggregates, which can be from coal rejects or other waste/recycled materials, as well as calcium sulfoaluminate (CSA)-based cementitious material with high water content. In addition to its large deformation capacity, the new column allows the extensive, direct and easy use of waste materials and eliminates the need for mixing concrete on site or transporting commercial concrete. This paper also presents the results from a series of compression tests on the new columns as well as two similar column forms. These tests demonstrate the very large deformation capacity of the new column and show that an existing stress-strain model for FRP-confined normal concrete can be used to provide reasonable predictions of the behaviour of the confined infill material in the new column. The potential applications of the new column and the needs for future research are also discussed.

Reinforced s-shaped bellows, which can withstand high pressure, is a kind of typical reinforced metal bellows. The reinforced s-shaped bellows mainly uses the hydroforming process, and the forming process is a severe plastic deformation process. The hydroforming process and its effects on the fatigue life of reinforced s-shaped bellows were discussed in the present study. Different levels of plastic strain and wall thickness thinning were detected in the hydroforming process. The maximum plastic strain can reached 32%, while the maximum wall thickness thinning ratio is 20%, which occurs on the wave peak. Mechanical characteristics of reinforced s-shaped bellows were discussed considering the effects of hydroforming process. The maximum stress appears on the upper and lower ends, which is the weak part of the structure. Fatigue life of the reinforced s-shaped bellows was analyzed based on the modified Manson-Coffin method. Mechanical properties of related materials, which can be more accurate consideration the effects of hydroforming process, were tested under the pre-plastic deformation. Fatigue life analysis of reinforced s-shaped bellows was carried out and the effects of hydroforming process were discussed. The hydroforming process will lead to a decline in fatigue life, which needs to be considered well in the structural design and analysis. Keywords: Reinforced s-shaped bellows, Hydroforming process, Fatigue life, Mechanical characteristics.

The massive rural-to-urban migration has been one of the most important features of China’s labour market in recent decades. The recent pattern of return migration and migrant wages has increased the costs of firms in urban areas and has negatively affected urbanisation. Therefore, it is important to understand the determinants of settlement intention of migrants. Using data from Rural Urban Migration in China (RUMiC), we find that migrants express higher settlement intention in a city after receiving training that is provided by firms. The effect is larger for females, high school graduates and dropouts, and wage earners. These findings suggest that training may complement migrants’ human capital and upgrade their skills. Therefore, training in cities may act as an instrument that facilitates the migration decisions and transforms a temporary migrant to a permanent resident in an urban area.

Dust management at longwall faces has always been a concern for mine operators. Recent respirable dust monitoring at a longwall top coal caving (LTCC) face indicated that extremely high dust exposure levels have been experienced at the face. Dust contamination from intake ventilation and the incorrect use of ventilation arrangements (i.e. curtains) at maingate (MG) area were identified as the main cause of this issue. Computational Fluid Dynamics (CFD) modelling studies were therefore conducted to investigate the impact of different ventilation arrangements on the dispersion behaviour of respirable dust at the LTCC face, with a special focus on the airflow patterns and the aerodynamics of fugitive dust at the intersection of MG and face. Field investigation was first carried out to observe the dust issue and obtain essential data for the development and validation of base model. Then parametric studies were conducted to evaluate the effectiveness of two different curtain configurations at MG considering the worst scenario of intake dust contamination to face (dust from travel road and beam stage loader (BSL) discharge point flows towards face) with the shearer cutting into the MG. Model results demonstrate that the occurrence of flow separation and incorrect use of curtains account for the main reasons of high dust exposure level at the intersection of MG and face, especially when the shearer is cutting into the MG. Ventilation arrangements at the MG and face entry are critical to minimise the impact of flow separation on the dust flow patterns at the intersection. Based on model results, new ventilation arrangements at the MG and face entry have been proposed and evaluated through which significant dust mitigation effect can be achieved at face entry, contributing to the overall reduction of dust exposure levels along the face.

Coal and gas outburst is the extreme instability caused by stress, gas, and coal. In this review article, dominant factors and inducing factors of outburst were summarized; geologic features of typical outburst cases and the effects of tectonic movement on outbursts were analyzed; the outburst stages with considerations to geologic factors were divided. It was found that inducing factors, including buried depth, tectonic movement, gas composition, coal seam conditions, overlying/underlying rock conditions, and mining mode, control the outburst by influencing the dominant factors (stress, gas, and coal). Among them, tectonic movement is the key of outburst. Influenced by tectonic movement, the primary structure of coals is damaged/pulverized due to the tectonic stress and unique tectonic mode, resulting in the formation of tectonic coals. When external dynamic factors are changed, tectonic coals are crucial to outburst control for its evolution of porous structure as well as the unique mechanical behaviors and gas flowing responses. Besides, the preparation stage of outburst includes the tectonic process and mining process. The former one refers to the restructuring process of the original coal-bearing strata by tectonic movement, while the mining process is the prerequisite of outburst and it refers to the disturbance of human mining activities to the initial coal seams. It is suggested that more work is required on geological factors of outburst, and a few research areas are proposed for future research.

Hard rock Tunnel Boring Machines (TBMs) engaging disc cutters as cutting tools have been employed in considerable underground coal mines to accommodate the requirement of more stone drivage as operations are going deeper. This study conducted a set of disc cutter indentation tests to explore the influence of confining stresses on rock fragmentation, thrust force, and penetration energy on sandstone, which is commonly encountered in underground coal mines. The test results show that there exists a critical confining stress, under which the maximum thrust force and penetration energy keep increasing with confining stress mounting while the maximum thrust force and penetration energy will decrease or flatten if it is surpassed. By combining with previous studies and comparing the critical confining stress values to the rock mechanical properties’ values, the critical value is most likely to be of cohesion. For subsurface rock fragmentation, the Constant Cross Section (CCS) disc cutter indentation has denser cracks and their orientations are more lateral than those under the V shape one; the V shape disc cutter indentation is less sensitive to confining stresses, with no notable increase of crack number and crack reorientation with increasing confinement. Thus, the CCS disc cutter is more favorable than the V shape one from the perspective of rock fragmentation under confining stresses.

Groundwater is the dominant source of freshwater in many countries around the globe, and the deterioration in its quality by contaminants originating from anthropogenic sources raises serious concern. In this study, a scenario where groundwater is contaminated by acid mine drainage (AMD) from mining activities and/or sewage was envisaged, and the performance of a direct contact membrane distillation (DCMD) system was investigated comprehensively for different compositions of the AMD- and sewage-impacted groundwater. Regardless of the composition, MD membrane achieved 98-100% removal of metals and bulk organics, while the removal of the selected micropollutants ranged between 80 and 100%. Effective retention of contaminants by the MD led to their accumulation over time, which affected the hydraulic performance of the MD membrane by reducing the permeate flux by 29-76%. When persulfate (PS)-mediated oxidation process was integrated with the DCMD, degradation of bulk organics (50-71%) and micropollutants (50-100%) by PS reduced their accumulation. Characterisation of the fouling layer revealed the occurrence of membrane scaling that was mainly due to the deposition of iron oxide or oxyhydroxide precipitates. For an identical composition of the AMD- and sewage-impacted groundwater, flux decline was 10% less in PS-assisted DCMD as compared to that in the standalone DCMD. However, this did not prevent the formation of iron oxide scales on MD membrane during the operation of PS-assisted DCMD. This study demonstrates the long-term performance of a standalone and PS-assisted DCMD operated in continuous-flow mode to treat AMD- and sewage-impacted groundwater for the first time.

Coal burst is the violent failure of overstressed coal, and it is often accompanied by sound, coal ejection and seismic events. It is subsequently recognized as a serious safety risk of Australia after double fatalities coal burst happened at Austar Coal Mine. Considering the increasing trend of coal burst severity and frequency with mining depth, it is an urgent task to develop the coal burst risk assessment methods for Australia underground coal mines. Coal burst propensity index method is a widely used method of burst risk evaluation of coal as it is summed up from the coal burst research and practice of many countries. This paper presents the experimental and theoretical research of coal burst propensity index method for coal burst risk assessment in Australia. The definition of four indexes including elastic strain energy index (WET), bursting energy index (KE), dynamic failure time (DT) and uniaxial compression strength (RC) is introduced in the first part. Then, the standard laboratory test process and test parameter of coal burst propensity index is presented. DT test is conducted with 0.3 mm/min displacement control loading rate while other test is with 0.5 mm/min. Besides, modified data processing and risk classification method of test are proposed. Differentiate analysis of stress-strain curve is adopted in the data processing of DT and KE index. A four level risk classification form of burst risk is recommended for Australian underground coal mines. Finally, two likely improvement methods of WET test, including volumetric strain indicator method and theoretical calculation method, are discussed. Keywords: Coal burst, Coal burst propensity, Risk evaluation, Underground mining

To investigate the bedding influence on coal mechanical behaviour in underground environments such as coal or rock burst, simulations of dynamic SHPB tests of pre-stressed coal specimens with different bedding angles were carried out using a particle flow code 2-dimensional (PFC2D). Three impact velocities of 4, 8 and 12 m/s were selected to study dynamic behaviours of coal containing bedding planes under different dynamic loads. The simulation results showed that the existence of bedding planes leads to the degradation of the mechanical properties and their weakening effect significantly depends on the angle θ between the bedding planes and load direction. With θ increaseing from 0° to 90°, the strength first decreased and subsequently increased and specimens became most vulnerable when θ was 30° or 45°. Five failure modes were observed in the specimens in the context of macro-cracks. Furthermore, energy characteristics combined with ultimate failure patterns revealed that maximum accumulated energy and failure intensity have a positive relation with the strength of specimen. When bedding planes were parallel or perpendicular to loading direction, specimens absorbed more energy and experienced more violent failure with increased number of cracks. In contrast, bedding planes with θ of 30° or 45° reduced the specimens’ ability of storing strain energy to the lowest with fewer cracks observed after failure. Keywords: Static–dynamic coupled loads, SHPB, Coal bedding angle, Strain energy, PFC2D

Strata movement control during backfill mining of coal seam is dependent on the goaf filling rate, which is much related to the mechanical properties of the backfill bodies in goaf. A main roof mechanics model of the inclined backfill stope was established to investigate the factors that influence the overburden stability of an inclined coal seam during backfill mining. The proposed model was based on the results of laboratory tests on the compressive mechanical properties of crushed coal gangue and the key strata theory of ground control, which considers the nonlinear elastic mechanical properties of backfill bodies under a linearly increasing overlying strata load. The deformation characteristics of the main roof of the inclined backfill stope were analyzed in reference to the elastic thin-plate theory. The stability criterion of the main roof of the inclined backfill stope was inferred by introducing the Mohr–Coulomb yield criterion. And factors that influenced the overburden stability control of the inclined backfill stope were investigated. These factors included the elasticity modulus and thickness of the main roof, the overlying strata load, the advancement distance and workface width, the strata pitch of inclined stope, and the linear and the nonlinear foundation coefficients of the goaf backfill body. The results can provide crucial theoretical bases for determination of the sizes and filling rates of the goaf backfill body and the overburden stability control of an inclined backfill mining workface in coal seam under the actual engineering geological conditions.

Spontaneous heating of coals continues to be a major environmental, safety and economic concern in coal storage, preparation and firing systems in power plants. Coal handling plants mitigate spontaneous heating in coal stockpiles by stacking in layers and compaction. This study was focused on investigating self-heating behaviour of compacted and loosely stacked stockpiles commonly used in a coal handling plant. Experimental stockpiles, each having 2500–3000 ton of coal, were built: compacted and loosely stacked. Temperature changes within the stockpiles were measured over a test period. Hot coals from loosely stacked stockpile were spread out to cool and re-stacked to form a third experimental stockpile.

The performance of pre-gas drainage in low permeable seams especially in CO2 abundant coal seams is not satisfactory. Due to the high affinity of coal to CO2, much lead time is needed for gas drainage boreholes to reduce the coal seam gas content below the threshold limit value (TLV), thus meeting the demand of the scheduled mining activities. In this study, simulations of N2 injection enhanced gas drainage were carried out for CO2-rich coal seams. A binary gas migration model was developed to illustrate gas migration in coal seam. The simulation results matched well with the laboratory test results, indicating that this model could be used to investigate the mechanism of N2 flushing coal seam gas. The parameters affecting the flushing performance were then studied using this model, including coal seam permeability, gas diffusion coefficient, N2 injection pressure andin-situ gas content. These results suggest that coal seam permeability and CO2 diffusion coefficient are the key parameters having significant impacts on the drainage performance whilst N2 diffusion coefficient only has negligible effect. A critical parameter theory was developed to describe the correlation between these parameters (especially coal seam permeability and the diffusion coefficient of coal seam gas). Specifically, in low permeable coal seams, permeability was the critical parameter and the effects of other parameters were insignificant. Similarly, if the diffusion coefficient of coal seam gas was very low, it could become a critical parameter.

In this study, BCPS-1, a polysaccharide previously isolated and characterized from Bupleurum chinense was chemically modified to yield two sulfated derivatives, which we designated as S-BCP1-4 and S-BCP1-8. The physicochemical properties of these sulfated derivatives were then determined by high performance liquid chromatography (HPLC), Fourier transform infrared spectrometry (FT-IR), and gas chromatography (GC), and then compared with those of BCPS-1. Furthermore, the antioxidant activities of all three polysaccharides were also evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay, superoxide radical assay and hydroxyl radical assay, while their effects against H2O2-induced cellular senescence were determined using senescence-associated β-galactosidase (SA-β-gal) staining, cell cycle assay and immunoblotting in H2O2-induced mouse lung endothelial cells (MLECs). Compared to BCPS-1, S-BCP1-4 and S-BCP1-8 exhibited remarkable antioxidant effect, and in a concentration-dependent manner. They also provided stronger protection against H2O2-induced cellular senescence in MLECs. These results indicated that the sulfate group in the modified B. chinense polysaccharides might play an important role in radical scavenging and resistance to H2O2-induced senescence. These sulfated polysaccharides could be considered as novel pharmaceutical products with potential antioxidant and anti-senescence effects.

Coalbed gas content measurement is important for both unconventional gas recovery and mining safety. This study experimentally discussed factors affecting coalbed gas content measurement. It is found that small coal particles demonstrated high desorption rate at the early stage of desorption tests. However, the difference in methane desorption rate reduces when the coal particle size is more than 1.0 mm, indicating that a threshold of coal particle size exists in methane desorption in coal. Also, the particle size distribution tends to be stable when coal sample mass is over 15 g, stabilizing at around 1.75 mm. Therefore, the coal sample over 15 g is recommended to use in desorption tests of coalbed gas content measurement. The temperature and gas pressure can enhance the desorption rate, especially at the early stage of desorption. This temperature effect, however, mainly occurred in the first 15 min of desorption test. After 30 min, the desorption rate tends to be stable, slightly changing from around 0.35 mol/kg/min to 0.75 mol/kg/min. Due to endothermic process, absolute isothermal condition does not exist in desorption test, but this temperature variation mainly occurred in the first 15 min. The results also show incorporating the desorption data from the time of exposure to 13 min of desorption tests is essential to typically reflect methane desorption kinetics in coal. The study also shows that the measurement difference in gas content between the case with sample being air-puffed and -flushed and the case with sample exposed to the air is small. Therefore, the air-puffing and flushing during the sample collection has an insignificant effect the gas contact measurement result. This study can help to advance the understanding of impact factors on coalbed gas content measurement method.

As the one of the most catastrophic hazards in underground mining, coal and gas outburst seriously threatens the safe mining of collieries. To understand the formation and transport mechanism of outburst coal-gas flow in roadway as well as evaluate the effects of gas desorption on its development, a new apparatus was developed to conduct simulated experiments with different gases of CO2 and N2. Results indicated that the outburst coal-gas flow was a high-speed (up to 41.02 m/s during tests) gas-solid two phases flow with extreme complexity, its transport/destructiveness characteristics were significantly influenced by a number of factors including the outburst pressure, coal sample composition, ejection distance and so on. Among these factors, the gas desorption showed the greatest impact when compared to the controlled tests which only considered the effect of free gas expansion. With the effect of gas desorption, especially the rapid gas desorption from powdered coal, the total outburst energy could be promoted by 1.30–2.43 times; the peak values of outburst shockwave could be enhanced by at least 13.67%–63.22%; the transport type of coal-gas flow could be changed from dynamic pressure pneumatic conveying to the static pressure conveying which providing higher capability for outburst coal/rock conveying; the motion of ejected coal flow could have higher speed, longer transport duration and could suffer secondary acceleration. As the result, the destructiveness of outburst coal-gas flow would be remarkably intensified. A further analysis for the energy consumption during the outburst coal-gas flow transport indicated that the free gas expansion energy was insufficient for the conveying of ejected coal (only accounting for less than half of the total energy), the difference of which was made up by the gas desorption, especially the rapid gas desorption from powdered coal (the average contribution ratio reached 56.0%, while the maximum reached 64.1%). Thus, it can be concluded that the rapid gas desorption from powdered coal played a decisive role on the promotion of outburst.

Spontaneous combustion of residual coal in longwall goaf is a long standing hazard. Airflow leakage into goaf is a major driver to the hazard and this issue deteriorates where longwalls are operating in multiple seams and shallow covers because mining-induced cracks are very likely to draw fresh airflow into goaf due to presence of pressure differential between longwall face and surface. To study the problem more critically, a ventilation simulation package “Ventsim” is used to conduct a case study from Bulianta colliery. It was found that isolating and pressurizing active longwall panel can mitigate the problem and the pressure differential can be adjusted by varying performance of auxiliary fan and resistance of ventilation regulator. A booster ventilation system can also mitigate the problem by adjusting fan duties. Ventilation simulation is a powerful tool to study spontaneous combustion control in underground coal mine. Keywords: Ventilation simulation, Spontaneous combustion, Longwall operation, Pressure differential, Ventsim

Seam gas pre-drainage, is widely used as an effective method to control gas and coal outburst in underground coal mines. However, in CO2 abundant low permeable seams, this technology seems to be less efficient due to the CO2 sorption characteristics and the lower safe mining threshold limit for CO2 applied in many outburst risk management plans. This paper presents the experimental investigations of the applicability of nitrogen (N2) injection to improve gas drainage in CO2 rich seams. Core specimens were obtained from Bulli coal seam, Sydney Basin and N2 flood tests were conducted under different permeability conditions (0.3 mD and 0.06 mD). A triaxial permeability test rig equipped with a back pressure regulator was used to conduct the test. The variation of gas composition, gas outlet flow rate, N2 flushing efficiency, and permeability variation were analyzed. In addition, a comparative study between N2 flushing coal seam CO2 and N2-ECBM was conducted and it was observed that CO2 was much more difficult to drain out and with longer time compared with CH4. Based on the test results, a two-stage flushing mechanism was obtained. In the first stage, the original free phase coal seam gas accounted for the large percentage and this stage last for a shorter time. In the second stage, desorption time governed the flushing efficiency and desorbed gas was the primary gas. It took much longer time than the first stage. The final recovery rate in 0.3 mD and 0.06 mD scenarios were 90.5% and 87.7%, and the N2 consumption/CO2 production ratios were 15 and 11.2, respectively. Through these laboratory experiments, we concluded that N2 injection can significantly decrease coal seam CO2 content level and increase gas drainage efficiency.

Gas management at longwall faces has always been a challenging issue to mine operators. Along a longwall face of an Australian colliery where CO2 is the dominant coal seam gas, frequent power trip off occurred due to the high goaf gas (CO2) emission, which significantly affected the normal longwall production and brought about safety threats to the longwall crew. CO2 fringe fluctuation changes close to tailgate (TG) was identified as a major concern. To better understand the CO2 fringe behaviour on the longwall face and develop the corresponding effective control measures, Computational Fluid Dynamics (CFD) model was developed and validated based upon field data collected from the colliery. General gas flow characteristics on the longwall face were obtained based on which parametric studies were then carried out to investigate the impact of ventilation system and gas drainage options on goaf gas fringe behaviour. The use of a back-return ventilation system was demonstrated to be an effective approach to control the CO2 fringe at TG; however, it was not practical due to the restriction of existing panel layout. As a compromise of the back-return system, a new gas drainage option using TG borehole which was more practical and cost effective was proposed and assessed by the CFD models. Model results indicated that goaf gas fringe at TG can be effectively controlled when a suction pressure between − 1500 Pa and − 2000 Pa was applied to the TG borehole. Therefore, it can be concluded from this study that gas drainage conducted through TG borehole can be an effective approach to solve the CO2 accumulation at TG on a longwall face, especially when the back-return system is not applicable on site.

An amino acid-functionalized protic ionic liquid (IL), monoethanolamine glycinate ([MEA][GLY]), was used as a CO2 absorbent. Its performance was evaluated by a membrane gas absorption (MGA) process. Various effect factors including both absorbent aspect and operational parameters were investigated in MGA for CO2 capture. Performance of [MEA][GLY] IL was also compared with that of an amino acid salt and an amine. Liquid CO2 loading of the functional protic IL was the largest in three absorbents, presenting an order of [MEA][GLY]>PGLY>MEA. [MEA][GLY] IL obtained a high membrane flux and a low gas outlet CO2 concentration in MGA process. It could reach 3.25 × 10−4 mol m−2 s−1 of membrane flux. The IL could achieve higher initial and instantaneous membrane fluxes and the maximal membrane flux with a range of optimum concentration of 3.5–4.5 mol L−1. Change of operational parameters, especially gas CO2 mole fraction, can significantly affect and enhance the membrane flux of MGA on a limited scale. [MEA][GLY] IL is a more environmentally-friendly and efficient CO2 absorbent.

Carbon dioxide (CO2) enhanced coalbed methane (ECBM) is an effective method to improve methane (CH4) production and this technology has already been used to increase gas production in several field trials worldwide. One major problem is the injection drop in the later period due to permeability decrease caused by coal matrix swelling induced by CO2 injection. In order to quantify the swelling effect, in this work, coal samples were collected from the Bulli coal seam, Sydney Basin and adsorption tests with simultaneous matrix swelling measurement were conducted. The adsorption and swelling characteristics were analyzed by measuring the adsorption mass simultaneously with the strain measurement. Then experiments were conducted to replicate the ECBM process using the indirect gravity method to obtain the swelling strain change with CO2 injection. The results show that the coal adsorption capacity in CO2 is almost two times greater than that in CH4, and nitrogen adsorption is the least among these gases. A Langmuir-like model can be used to describe the strain with the gas pressure and the swelling strain induced by gas adsorption has a linear relationship with gas adsorption quantity. Moreover, swelling strain increase was observed when CO2 was injected into the sample cell and the swelling strain was almost the sum of the strains induced by different gases at corresponding partial gas pressure.

In this study, complex variable theory was employed to study the stress distribution for rock mass containing a hole with complex shapes. The method of mapping function calculation using optimization technique was investigated and improved. The shape-related mapping function was defined for parameter analysis. A new objective function for mapping function determination was developed to calculate related parameters without the consideration of restrictive conditions between boundary points in z-plane and ζ-plane, which significantly simplified the calculation process. In addition, the mapping function for planes containing a rotated hole was deducted to simplify analytical stress solution process for holes under complex stress conditions. Finally, for six kinds of holes with typical shapes in practical rock engineering, the mapping functions were determined, and the external analytical stress distribution were further presented. The analytical solutions combined with numerical and experimental results show that holes with arched boundaries suffer less stress concentration compared with those with corners. Hole shape mainly affects the stability of rock containing a hole via its influence on stress concentration extent around the hole.

The Jigongcun Re-rich quartz vein-type Mo deposit is located in the Gangdese porphyry Cu belt, southern Tibet, China. The stratiform and lenticular orebodies are hosted within the quartz veins and are controlled by the NW-/EW-trending faults. In this study, we have identified four hydrothermal stages, namely the (1) pre-ore stage (stage Ⅰ) characterized by the development of thick Mo-free quartz veins; (2) stage Ⅱ, mainly forming thick quartz veins with Re-rich massive molybdenite (Mo1-type; mean = 1811 ppm) and bladed molybdenite (Mo2-type; mean = 1312 ppm); (3) stage III, mainly forming quartz veins with Re-barren bladed molybdenite (Mo3-type) and abundant galena and pyrite; (4) the post-ore stage (stage Ⅳ) characterized by formation of thick ore-barren quartz–calcite veins. Both electron probe micro-analysis and in situ laser ablation–inductively coupled plasma–mass spectrometry analysis of different types of molybdenite show that high Re concentrations are due to isovalent Re substitution for Mo in molybdenite. Fluid evolution during the four stages of mineralization was constrained by a detailed fluid inclusion study. Fluid inclusions during the formation of the early pre-ore stage indicate relatively high-temperature (311–337 °C), high-pressure (1300–1600 bars), low-salinity (0.2–2.6 wt% NaCl-equiv.), and CO2-rich hydrothermal fluids. Fluid immiscibility assemblages in CO2-rich inclusions coexisting with aqueous inclusions occur in quartz–K-feldspar veins of stage Ⅱ, and likely record phase separation at a temperature of 262–300 °C and pressure of 900–1100 bars, with the precipitation of Re-rich molybdenite. The subsequent fluid mixing occurs at a temperature of 220–271 °C, with the precipitation of Re-barren molybdenite at stage III. H–O–S isotope compositions show that sulfur and ore-forming fluids are derived from a deep-seated igneous source. Re-Os dating of molybdenite samples yielded an isochron age of 22.0 ± 0.4 Ma, indicating that the Jigongcun deposit formed in the Early Miocene, which is earlier than most of the porphyry Cu deposits in the Gangdese porphyry Cu belt. Combined our new geochemical and isotopic results with previous regional investigations, we suggest that the Re-rich Mo mineralization of Jigongcun deposit may be related to the Early Miocene northward subduction of the Indian continental plate.

The purpose of this study was to investigate the effect of ultrasound combined with microbbules (SonoVueTM) on the potency of methylprednisolone in attenuating the renal injury induced by adriamycin in rats. Animal model was established by two intravenous injections of 4 mg/kg adriamycin with a 2-week interval in rats. One week later, the adriamycin injected rats were randomly divided into 7 groups, receiving various treatments daily for 2 weeks. Two doses of methylprednisolone (20 or 40 mg/kg) were administrated alone or 20 mg/kg methylprednisolone and 100 µL SonoVueTM microbbules (1–5 × 108 bubbles/mL; mean diameter of bubbles: 2.5 µm) was co-administrated by intravenous injections from the tail vein. The ultrasound was applied at a frequency of 0.8 MHz and a spatial average temporal average intensity of 2.79 W/cm2 for 5 min at a 50% duty cycle (1 s on 1 s off) on the back skin of the anatomic position of the kidney in rats of two groups combined with ultrasound. Renal injury were analyzed using immunohistochemical staining, real-time PCR, light and transmission electron microcopies. The kidney function related biochemical indexes were measured by automatic biochemistry analyzer. The results showed that adriamycin induced a typical renal injury and 40 mg/kg methylprednisolone injection significantly ameliorated the abnormality of key parameters such as proteinuria, renal mRNA and protein expression levels of nephrin, collagens III and IV as well as podocyte impairment, glomerulosclerosis and tubulointerstitial injury indexes. However, a sub-dose of methylprednisolone at 20 mg/kg was ineffective when administered intravenously, but its potency at this dosage was enhanced by co-administration with 100 µL SonoVueTM microbubbles plus ultrasound irradiation. In conclusion, ultrasound combined with microbubbles can significantly increase local renal drug delivery leading to enhanced therapeutic effect of low dose methylprednisolone in ameliorating adriamycin-induced nephropathy in rats.

The relatively low strength and brittleness are believed to be two main factors restricting the widely use of coal reject concrete (i.e. CRC) in practical applications. This paper presents a concept of the novel hybrid concrete column incorporating fibre-reinforced polymer (i.e. FRP), termed FRP-confined CRC (i.e. FCCR) columns, to widen the use of CRC. The systematic compression tests on natural aggregates concrete (i.e NAC) and CRC with the large range replacement ratios of natural aggregates in volume (i.e. 0%, 25%, 50%, 75% and 100%) were firstly carried out, followed by the compressive tests on FCCR columns. Test variables covered the thickness of FRP jacket (i.e.0-ply, 2-ply and 4-ply), the replacement ratio of natural aggregates and the particle size of coal reject. In parallel, the FRP-confined NAC columns (i.e. FCNA) columns have been prepared and tested for comparison. Test results showed that the compressive strength of CRC decreases with the increased replacement ratio of natural aggregates. When the CRC is confined by the exterior FRP jacket, both the compressive strength and the ductility of which have been significantly enhanced. Furthermore, these FCCR columns with a thicker FRP jacket generally exhibited the superior compressive behaviour. The analysis-oriented model developed by Jiang and Teng for FCNA was adopted to predict the compressive behaviour of FCCR. The feasibility of Jiang and Teng’s model for predicting the behaviour of FCCR with the replacement of fine aggregate was verified.

Lean-oxygen environment caused by methane in high gassy coal mine goaf has a significant influence on the prediction index gases of residual coal spontaneous combustion. The coal sample from Xishan coalfield in China was used to conduct the low-temperature oxidation experiments under different lean-oxygen environments. The experimental results show that different lean-oxygen environments had a significant delay effect on the formation of CO, CO2, H2 and C2H6, and the lower the O2 concentration, the more obvious the delay effect, and the delay effect of methane was greater than that of N2. A lean-oxygen environment caused by methane also had a significant influence on the values of CO/ΔO2 ratio and CO2/ΔO2 ratio. However, when the temperature was T can be accurately expressed by exponential function. The absolute amount of CO, CO2 and C2H6 generated by 1 k g residual coal ( C CO , C CO 2 and C C 2 H 6 ), which can reduce the influence of air leakage and residual coal mass on prediction index gases, were introduced to predict the spontaneous combustion in high gassy coal mine goaf. Then, the distribution diagrams of C CO , C CO 2 and C C 2 H 6 with temperature and O2 concentration were obtained, so as to accurately predict the degree of spontaneous combustion in high gassy coal mine goaf. The research results are of great significance to the prevention of spontaneous combustion in goaf of high gassy mine.

The definition of “residual gas” can be found in different scenarios, such as the “fast” and “slow” desorption methods of measuring gas content and the sorption hysteresis test and gas management of coal mines, however, its meaning varies a lot in different contexts. The main aim of this paper is to discuss the existence of truly undesorbable residual gas in coal seam conditions and its impacts on sorption model and gas drainage efficiency. We believe the undesorbable residual gas does exist due to the observation of the extended slow desorption test and the sorption hysteresis test. The origin of undesorbable residual gas may be because of the inaccessible (closed or semi-closed) pores. Some gas molecules produced during coalification are stored in these inaccessible pores, since the coal is relatively intact in the coal seam condition, these gas molecules cannot escape during natural desorption and then create the undesorbable residual gas. Based on the existing adsorption models, we propose the improved desorption versions by taking into consideration the role of residual gas. By numerically simulating a gas drainage case, the gas contents after different drainage times are studied to understand the influence of residual gas content on gas drainage. The results indicate that the influence starts to be obvious even when the total gas content is at a high level, and the impact becomes more and more apparent with increasing drainage time. Our study shows that the existence of residual gas will impede the gas drainage and the total amount of recoverable coal seam methane may be less than expected. Keywords: Residual gas, Inaccessible pores, Desorption model, Gas drainage

Sodium dithionite and thiourea dioxide are two typical reducing agents commonly used in industry. This paper compared the thermal hazards of sodium dithionite and thiourea dioxide based on DSC-TG (Differential Scanning Calorimetry and Thermogravimetry) thermal analysis, small-scale self-heating experiments and FTIR smoke gas analysis. From the thermal analysis (DSC-TG), sodium dithionite starts to lose crystal water at the temperature around 60 °C which makes the sodium dithionite very unstable at relatively lower temperature. The decomposition of sodium dithionite has a close correlation with oxygen while the decomposition of thiourea dioxide has little relationship with oxygen. Small-scale self-heating experiments were designed to reflect the self-heating and spontaneous combustion properties of the characteristic dimension 20 cm. The small-scale self-heating experiments show that there is a little gap between the Critical Ambient Temperature (CAT) of sodium dithionite and thiourea dioxide. From FTIR smoke gas analysis, the smoke of thiourea dioxide (decomposition or combustion) is far more dangerous than sodium dithionite. Although the risk of spontaneous combustion for sodium dithionite is higher than thiourea dioxide, the thermal hazards of thiourea dioxide are far higher than sodium dithionite as the decomposition and combustion of thiourea dioxide would release far more heat and dangerous smokes.

Large scale open cut coal mining operations have significant impacts to groundwater in surrounding areas in both active and post-mining phases. The prediction of water inflows into a surface mine excavation is one of the many components involved in mine design phase. Groundwater performance also reacts to mining activities from the operational, economic and safety implications perspective. Under NSW planning legislation, as part of the comprehensive risk assessment, a groundwater impact assessment has to be conducted for a coal project to predict and mitigate the impacts in consideration of the government requirements. In this paper, the groundwater assessment modelling of mine pits was discussed in predicting of groundwater inflows and reviewing analytical and numerical approaches. A methodology of groundwater impact assessment for an open cut mine in NSW with a three-dimensional groundwater flow model Modflow Surfact demonstrated its functions in simulating the project’s impacts on the groundwater regime. The key findings with mitigations are discussed and recommended in the paper to reduce impacts on groundwater and fulfil regulation requirements in NSW. Keywords: Open cut coal mine, Groundwater impact assessment, Mining exposure area, Groundwater modelling methodology

Coal exhibits different creep behaviours when filled with different amounts of gas. Creep tests of coal filled with 0 and 0.5 MPa gas were performed, and strain under different axial stress was compared. The three creep constitutive models which were analysed using the method fitting experimental data for determining which creep model can reflect the creep process of the test best. The results show that the deformation of coal filled with 0.5 MPa gas is more higher than that of coal filled with 0 MPa gas under the same axial stress. Gas plays a positive effect on the deformation of coal process and will accelerate creep process. And gas will reduce coal intensity and change coal creep properties. Compared with Nishihara Model and Extensional Nishihara Model, Burgers Model can reflect the three stages of creep process of coal filled with gas better. The research results can contribute to reveal coal and gas outburst mechanism. Keywords: Coal, Gas, Creep, Constitutive model

The management of methane gas has always been a challenging issue for longwall operations. To improve the understanding of methane dispersion and flow characteristics on a longwall face, Computational Fluid Dynamics (CFD) modelling studies were conducted employing the longwall models developed recently. As a prerequisite of the CFD study, the methane emission rate was determined firstly taking advantage of a mathematical model whilst considering the decay of methane emission from different positions along the face, which was capable of estimating the methane emission from individual sources on the longwall face. Taking into account the impact of shearer position and cutting sequence on gas flow behaviour, calculations were carried out on the six CFD models representing six typical longwall operating scenarios respectively. Model results indicate that: 1) the methane concentration around the drums increases gradually as the shearer cuts from the maingate (MG) to tailgate (TG), and decreases as the shearer cuts back towards the MG; 2) the methane concentration at the TG drum is higher than it is at the MG drum in both cutting directions; 3) the monitored methane concentration at the tail end of the shearer body can be approximately two or three times lower than the maximum concentration around the TG drum; 4) the source of methane causing accumulation at TG is identified, i.e., the majority of methane trapped in the inner TG corner comes from the face emission while the methane accumulated at the upper TG corner is caused by goaf methane emission.

To further understand methane flow characteristics on a longwall face, this study focuses on the investigation of methane flow behaviour under six different operating and mining conditions, namely, the impact of ventilation in terms of both flow rate and the ventilation scheme, coal seam gas content, adjacent gas bearing strata, drum sprays and the maingate (MG) curtain. Modelling results obtained from the parametric studies were compared with the corresponding base model results, through which the impact of single parameter on the methane distribution characteristics along the longwall face was investigated. Modelling results indicate that: 1) flow rate has major impact on the methane concentration around the shearer and at the inner tailgate (TG) corner while the impact is minor at the upper TG corner; 2) methane emission from adjacent gas bearing strata significantly affects the methane distribution at the immediate goaf and at the upper TG corner of the face; 3) the use of a TG cut through behind the face is very effective in diluting the methane accumulated at the upper TG corner; 4) methane levels in the vicinity of drums and downstream is reduced greatly with the operation of drum sprays.