160 research outputs found

    A Methodology For Determining Gob Permeability Distributions And Its Application To Reservoir Modeling Of Coal Mine Longwalls

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    Methane can be a significant hazard in coal mine longwalling operations and extensive methane mitigation techniques are employed by coal mine operators. Reservoir modeling techniques are used to better understand the liberation and migration of methane from the surrounding rocks towards the mine ventilation system. The caved rock behind the advancing longwall face, known as the gob, can contain high void ratios, providing high permeability flow paths to the methane. The gob is progressively compacted by the weight of the overburden, resulting in a reduction in the void ratio and associated permeability. Estimating the permeability distribution within the gob poses challenges due to its complexity. The authors have developed a new methodology to determine both horizontal and vertical variations in the permeability of the gob. Variations of the permeability in the vertical direction are based on a model of caving and block rotation, which considers the effect of block dimensions and fall height on the void ratio. Gob compaction by the overburden and associated permeability changes are determined from a three-dimensional geo-mechanical model which simulates the gob as a strain hardening granular material. The resulting three-dimensional permeability distribution in the gob is then transferred to a reservoir model. The paper demonstrates the application of the method and shows that reasonable results are obtained when compared to empirical experience and measurements.2007736

    Coupling Simulation Model Between Mine Ventilation Network and Gob Flow Field

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    Many numerical simulation studies of coal spontaneous combustion have focused on the leakage flow field in the mine gob. However, most of these studies isolate the gob from the mine ventilation system, failing to consider the effects of air leakage on gob boundary conditions. A novel model coupling the mine ventilation network (MVN) and gob flow field (GFF) has been developed to simulate the overall mine ventilation system. The concept of network boundary node was proposed and the corresponding air flow rate balance equations were developed based on the node pressure method for MVN calculation and the finite element method for GFF simulation. These equations, containing the rate of air flow not only from the branches but also from the gob, revealed the coupling relationship between 1D MVN and 2D/3D GFF. An iterative solution technique was developed to solve the coupling model, which has been incorporated into a program i-MVS. An illustrative example with coarse mesh is used to verify the stability and convergence of the model. Results of an application case show that the coupling model has sufficient precision and the developed software is efficient in implementing the computations

    Applications of Advanced Computational Modelling for Principal Underground Mining Hazards Management and Control

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    Underground coal mining is facing increased threats from the hazards of spontaneous combustion and heating of coal, abnormal mine gas emissions, and harmful dust concentrations in underground workings, due to increased production outputs and extraction depth of cover. To control and mitigate these engineering problems, there is a need to gain critical knowledge of spontaneous heating in the longwall (LW) goaf, gas migration patterns onto the LW face, and ventilation dynamics and dust dispersion in complex underground environments. Advanced Computational Fluid Dynamics (CFD) modelling can be used to simulate various scenarios portraying these hazards that may occur in underground LWs and provide much-needed knowledge and fundamental science that can be used to develop robust and effective control and mitigation strategies against these hazards. A comprehensive literature review has been conducted to understand these principal mining hazards (PMH), with a particular emphasis on the applications of CFD modelling in the prevention management and control of those PMH arising during coal extraction process. The insufficiencies and gaps in research on spontaneous combustion in active LW goaf, gas migration onto the LW face, and dust dispersion and transport in the development heading were identified. In addition, several field studies were carried out in underground coal mines in Australia to gain a better understanding of these mining issues and collate essential data for the CFD modelling studies. In recent years, goaf heating and spontaneous combustion incidents have been reported in several Australian underground coal mines during normal production cycles. The onset of these heating incidents was dictated by many operational and environmental parameters. Based on the site-specific conditions of an underground coal mine, where the coal seam gas is of approximately 80% carbon dioxide (CO2) and 20% methane (CH4) with a gas emission rate of 2000 l/s, CFD models were developed and validated with field gas monitoring data collected from the Tube Bundle System. The CFD models incorporated a user defined function (UDF) of gas emission and permeability variations in a three-dimensional (3D) space of computational domain representing the LW panels and goaf areas. Simulation results indicated that better goaf inertisation could be achieved when nitrogen (N2) was injected via cut-throughs (C/T) at about 250 m behind the LW face on the maingate (MG) side and surface boreholes at 100 m and 700 m on the tailgate (TG) side, with a total injection rate greater than 1750 l/s. The oxygen concentration on the MG and TG side dropped below 5% at distances of 120 m and 75 m behind the LW face, with a confined oxidation zone area of 35375 m2, which was approximately one-third of the oxidation zone area without inert gas injection. The impact of geological variations (i.e., coal seam orientations and goaf gas composition) on spontaneous combustion prevention and management was further studied using CFD models. The influence of ventilation design and operational parameters (e.g., tightness of the goaf seals) on spontaneous combustion control was also investigated by additional CFD models based on field data. During LW sealing-off, the ventilation flow dynamics change within the goaf, which considerably increases the risk of spontaneous combustion and gas explosion. To prevent these hazards, CFD models were developed and calibrated with field gas monitoring data to simulate a range of operational scenarios of different ventilation arrangements. The modelling studies indicated that at least six gas sensors should be employed and positioned appropriately to ensure effective goaf atmosphere monitoring for risk management during the LW sealing-off process. Extensive CFD-DPM (Discrete phase model) coupling modelling studies were conducted to investigate dust-related issues in LW gateroad development panels. Based on site-specific conditions, a CFD model incorporating a Continuous Miner (CM), Shuttle Car (SC) and exhausting ventilation tube was established and validated with onsite dust monitoring data. Three scenarios of CM cutting at the middle, floor and roof positions were considered and simulated. In all cases, the simulation results indicated that high levels of dust exposure would occur to left-hand-side (LHS) operators and consequently they should be equipped with high-quality personal protective equipment and stay behind the ventilation duct inlet during coal cutting process, while miners standing at the right-hands-side (RHS) of the CM for roof and/or rib bolting and machine operation should stay immediately behind the bolting rig where dust concentration was relatively low. The studies conducted in this thesis provided new insights into the current goaf inertisation practices to effectively manage and control spontaneous heating in LW goaf by considering geological variations and mining design. Furthermore, the CFD modelling study of gas flow dynamics during the panel sealing-off process provides new knowledge of ventilation and goaf gas dynamics, which is critical to the positioning of gas monitoring sensors to reliably measure goaf atmosphere changes, thus minimizing spontaneous heating and gas explosion risks with much-improved mine safety. The research work also shed light on the dust and ventilation behaviour in gateroad development panels, and provided several recommendations for operators’ locations and dust mitigation strategies to improve the health and safety of miners. The research outcomes from this study contribute to the improvement of current practices and guidance for PMH management and control in underground mines and tunnelling projects

    Master of Science

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    thesisStoppings and other control devices used in underground mines can be viewed as air paths with high resistance. The amount of air that leaks through these devices depends on various factors including the type of construction materials used, workmanship, and stopping inspection and maintenance. Improperly constructed and poorly maintained structures will significantly lower this resistance and cause undue leakage. The circumstances of a real-world mine rarely exhibit the ideal conditions needed to obtain the most accurate measurements. The airflows and pressure drops in an underground mine are subject to considerable variation due to movement of equipment, opening of vent doors, and other changes. In addition, mine layouts are often extremely complex and may be such that the airflow profile at the location where a measurement is required is not fully developed. This can make it so that fluid-flow laws are not truly applicable. Nevertheless, a practical effort must be made. In ventilation planning, resistance values are often measured in the field or in an experimental lab. These measurements were used in a simulated model which was calibrated to match the field conditions. This calibrated model was then used to further evaluate the pressure/quantity requirements for future mining scenarios. Experimental tests conducted at the University of Utah's coal mine model indicate that for a set of similar stoppings, the trend of pressure drop across the stoppings decreases with distance from the main fan. The trend resembles an exponential decay curve more than a linear one. The resistance values measured in the lab are directly correlated to real world measurements by a physical scale factor of 1:625. A CFD model was calibrated to within 5% of the lab measurements. Additional analyses with the CFD model also indicated that with increasing distance from the fan, both pressure drop and leakage flow through the stoppings exhibit an exponential decay function. A single main fan system was compared with a system having a main fan plus a booster fan. The results indicate that the booster fan creates a substantial reduction in pressure drop across the stoppings and a reduction in leakage as well. A VNETPC model of a two-entry development section was used to further characterize leakage flow in terms of progressive mine development, building materials used, and engineering design strategies. From these analyses, a recommended method of prioritizing life of mine engineering designs and leakage reduction methods to be focused in the critical leakage areas was developed. These critical leakage areas are identified as a proportional distance from the main fan. This method is applicable to existing large or extensive mines as well as future projects

    Master of Science

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    thesisMine fires and explosions associated with spontaneous combustion (sponcom) can be the cause of mines closings temporarily or permanently. The risk of fatalities and production losses are also associated with the hazards of sponcom. Over the last 175 years, nearly 13,000 deaths have been recorded and are attributed to mine fires or explosions in the United States coal mines. Some of these fires could have been prevented with proper ventilation precautions. Ventilation is a primary tool used to prevent fires and explosions in an underground mining environment. Removing contaminants with proper air flow rate is the general method for preventing fires and explosions. Another method for fire prevention is pressure balancing. Pressure balancing is a technique of redistribution of the air pressure in areas where there is potential for sponcom. The implementation of passive and dynamic pressure balancing methods can be used to reduce the risk of spontaneous combustions and accumulation of explosive gas mixtures in confined areas. These methods have been applied in mines outside of the United States, mostly practiced in Australia, India, and some European countries. Pressure balancing, when applied correctly, may reduce or eliminate the flow of air through caved areas, thus reducing the possibility of self-heating of coal in critical areas where sponcom is more prevalent. Each mine in the United States will have different ventilation designs that are either classified as Bleeder or Bleederless with multiple variations in design. Passive and active pressure balancing designs were engineered for two underground longwall mines, one ventilated by a bleeder system and the other by a bleederless system. The study includes pressure quantity surveys in these coal mines, computer simulation exercises, and laboratory tests performed at the University of Utah. The simulations of surveyed coal mine models have been compared with field data and model data to produce results of potential pressure balancing implementations. The results have been analyzed and compared to each other, and used to develop strategies to prevent spontaneous combustion, create safe working conditions, and minimize ventilation requirement

    Numerical study on effects of coal properties on spontaneous heating in longwall gob areas

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    A computational fluid dynamics (CFD) study was conducted to model effects of coal properties on the potential for spontaneous heating in longwall gob (mined out) areas. A two longwall panel district using a bleeder ventilation system was simulated. The permeability and porosity profiles for the longwall gob were generated from a geotechnical model and were used as inputs for the three dimensional CFD modeling. The spontaneous heating is modeled as the low temperature oxidation of coal in the gob using kinetic data obtained from previous laboratory scale spontaneous combustion studies. Heat generated from coal oxidation is dissipated by convection and conduction, while oxygen and oxidation products are transported by convection and diffusion. Unsteady state simulations were conducted for three different US coals and simulation results were compared with some available test results. The effects of coal surface area and heat of reaction on the spontaneous heating process were also examined
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