Numerical simulation of ventilation air flow in underground mine workings

In recent years, Computational Fluid Dynamics, CFD, has been commonly utilized in the mining industry to model the fluid flow behavior in underground mine workings. This paper uses CFD modeling to simulate the airflow behavior in underground crosscut regions, where brattice sails are used to direct the airflow into these regions. Brattice sails are cost effective ventilation control devices for temporary or permanent use in underground mining. They can be used to deflect air into the unventilated areas such as crosscut regions. Their design and installation is a fundamental issue for maintaining a sufficient supply of fresh air and achieving effective air circulation and contaminant removal. At the same time, they should have little impact on the mine ventilation system. This paper presents the results of a two-dimensional CFD model, which examines the effects of brattice length on fluid flow behavior in the crosscut regions. The results of this study will assist in understanding the ventilation air behavior and in determining the optimum size of brattice curtain (sails), which provide a highly effective contaminant removal from the unventilated mine areas. This, in turn, helps the mine ventilation designers to meet the mine safety requirements

Monetary Savings Opportunities of Electronic Blast Initiation Systems

There are several blast initiation systems available on the market; these form a large component of the performance of each blast. Each available system has its own advantages and disadvantages which can affect the fragmentation of each blast, which in turn can affect downstream processes such as digging and hauling of material. This study was conducted to determine if there were monetary savings opportunities due to an increase in fragmentation (and hence downstream productivity) due to the use of an electronic blast initiation system over a pyrotechnic blast initiation system. It was completed using data collected from an open cut metallurgical coal mine in Queensland that agreed to be used as a case study. Statistical analysis of data was completed in order to identify if downstream productivity had increased, with the results from this being used to calculate potential savings opportunities. The results of this study suggest that there are increases in productivity during loading and hauling, which lead to significant savings opportunities when using an electronic blast initiation system

Large-scale study of the effect of wellbore geometry on integrated reservoir-wellbore flow

Extraction of coal seam gas (CSG) prior to mining is crucial for reducing the potential risks of gas outburst and explosions during underground coal mining as well as gas production purposes. Many numerical and experimental studies have been carried out to identify the factors affecting the gas productivity. These factors include coal properties, gas content and wellbore geometries. Two different flow conditions determine the gas production efficiency: The gas flow inside the wellbore injected from wall, and the flow through porous coal medium. The full understanding of simultaneous flow of fluids through reservoir and wellbore is critical for analysing the reservoir behaviour. However, previous studies examined the flow of these fluids separately. In this research, a large scale three-dimensional model for simulation of integrated reservoir-wellbore flow is developed to study the effect of wellbore geometry on flow characteristics and wellbore productivity. Four different wellbore diameters of 0.075, 0.10, 0.125 and 0.15 m as well as three different lengths of 50, 100, and 150 m were chosen to accomplish the parametric study of wellbore geometry. It is assumed that the wellbores were in a steady-state condition for two different single phase scenarios of water and methane gas flow. The simulation results were validated against the pressure drop models for internal single phase gas and water flow reported in the literature. The obtained results revealed that increasing the wellbore diameter led to reduction of fluid pressure in the coal seam. Regarding the effect of wellbore length, it was observed that at a specific distance from wellbore outlet, the pressure distribution is independent of the wellbore length and upstream effects. It is also shown that wellbore production could be enhanced by increasing the diameter and the length of wellbore for both gas and liquid flow. The developed integrated framework can be used further for study of any enhanced gas recovery method by changing the boundary conditions based on the physical model

A Review of patents in tyre cooling

A number of patents on tyre cooling have been reviewed with a focus on those which can be applied to earthmoving tyres for the mining industry. The mechanisms of heat transfer within the tyre carcass are introduced as well as the basic tyre structure and effects of overheating on tyre operation. The tyre cooling patents are separated into five functional groups and reviews are made based on practicality and potential for significant heat transfer. This analysis has made it evident that potential cooling effectiveness is often compromised by practicality of an invention. The patents deemed to have the most potential for cooling are those which incorporate a working fluid which undergoes a phase change to transfer heat between different regions of the wheel assembly. Finally, these inventions are also related to current research projects which aim to develop a new cooling technique and extend the working life of earthmoving tyres

Current developments and challenges of underground mine ventilation and cooling methods

The mining industry has experienced a dramatic change over the past 20 years in terms of methods and equipment as well as human resource policies. These changes have had impacts on the design of mine ventilation systems. Although feasible developments have been implemented to some extent, in some other areas ventilation planning still requires further improvements to provide a healthy work environment at a reasonable cost. The boom in energy costs has also encouraged mine ventilation designers to seek for efficient use of energy and optimization strategies. The electricity consumption by mine refrigeration plants should be reduced possibly without any adverse effects on the safety of workers. This study presents an overview of the latest techniques used by the experts to address these issues. A revision of the novel ventilation strategies and mine refrigeration methods, and their ultimate effect on efficiency and mining costs would be identified. Finally, likely future developments in the area of mine cooling are outlined

Development and utilisation of fibre optic-based monitoring systems for underground coal mines

The continuous economic growth and depleting shallow reserves have increased the number of deeper mining operations worldwide which has made safety and productivity more challenging due to the higher stresses, heat and increased gas contents. Any major improvements in safety and productivity require a reliable and real-time monitoring system that provides more comprehensive information about various processes. The current monitoring systems suffer from lack of reliability, accuracy and high capital and operating costs. Recent advancements in fibre-optic based sensing technology have introduced unique solutions for various underground coal mine applications such as health and safety, geotechnical, ventilation, borehole, mine environment and condition monitoring. This paper presents recent research, development and utilisation of this technology by a group of researchers at the University of Queensland (UQ) and CRCMining in Australia and Shandong Academy of Science in China

Development of an integrated reservoir-wellbore model to examine the hydrodynamic behaviour of perforated pipes

Perforated pipes are used widely in vertical and horizontal production wellbores. Understanding the fluid flow behaviour through perforated pipes by taking into consideration the wall inflow is crucial for determining the wellbore frictional characteristics. Accurate prediction of pressure drop along the perforated pipes is a key step in completion design of production wellbores. Many empirical and theoretical models have been reported in the literature to predict pressure drop and friction factor along perforated pipes. However, these models show contradictory findings which is resulted from variations in the wall inflow configuration and modelling assumptions. The fluid flow through the surrounding formation and its interactions with wellbore have been simplified in the previous models which limits their range of applicability. In this study, a three-dimensional integrated reservoir-wellbore model of fluid flow through a perforated pipe surrounded by porous media is developed via Computational Fluid Dynamics (CFD) simulation. The model is used to investigate the effect of perforation parameters including perforation density, diameter and phasing angle on the wall friction factor and the pressure drop along the perforated pipe. The simulations are carried out for pipe inlet velocities of 0.5, 2.5, and 5 m/s with inflow to pipe flow rate ratios of 0, 7.5, 15, 30%. The results from this study show that the friction factor varies linearly with the perforation density but does not change remarkably with the perforation diameter or phasing. The observed trends of wall friction factor with perforation parameters are further explained and confirmed by studying the local wall shear stress results. Increasing the number of perforations leads to a higher friction factor as well as a larger pressure drop along the pipe. It is also observed that for perforation phasing angle of 90°, the overall pressure drop has the highest value compared to other phasing angles due to intensified influence of mixing pressure drop. For turbulent flows with high Reynolds number, the accelerational pressure drop is more dominant than the frictional and mixing pressure drop for the same inflow to pipe flow rate ratios. The developed model provides an alternative solution to experimental studies of perforated pipes, while delivering more details on friction factor behaviour and overall pressure drop components

Recent developments in fibre optic shape sensing

This paper presents a comprehensive critical review of technologies used in the development of fibre optic shape sensors (FOSSs). Their operation is based on multi-dimensional bend measurements using a series of fibre optic sensors. Optical fibre sensors have experienced tremendous growth from simple bend sensors in 1980s to full three-dimensional FOSSs using multicore fibres in recent years. Following a short review of conventional contact-based shape sensor technologies, the evolution trend and sensing principles of FOSSs are presented. This paper identifies the major optical fibre technologies used for shape sensing and provides an account of the challenges and emerging applications of FOSSs in various industries such as medical robotics, industrial robotics, aerospace and mining industry

Experimental investigation on the impact of coal fines generation and migration on coal permeability

Measurements of the coal fines production and the impact of these fines on the permeability of two coals from the Bowen Basin, Australia, were performed at different flow conditions (single-phase water or gas, two-phase water and gas) and pressure conditions. The fines collected from each coal samples ranged in size from 1 mu m to 14 mu m. For both coal samples, during the first 50 h, the permeability decreases from 0.005 mD and 0.048 mD by 60.9% and 85%, respectively, followed by gradual decline with fluctuations. By the end of water injection, the permeability drops by 88% and 89%, respectively. This phenomenon is attributed to the counteraction between formation damage (cleats plugging and coal fines settlement) and breakthrough of coal fines from the samples (widened cleats). It was found that coal fines volumetric production is proportional to the third power of flow velocity once the flow paths for coal fines are established. The critical flow velocities of coal fines production for both samples were also obtained. For hydrophobic coal, water-drive-gas two-phase flow introduces abrupt permeability loss due to coal fines generation and migration. Furthermore, pauses (well shut-in) in the experiments cause slight permeability drops. A comparison between the two samples indicates that narrower and less connected cleating system results in more frequent coal fines generation and migration, resulting in significant permeability fluctuations with general decreasing trend. Tortuosity of the cleats can enhance the deterioration in permeability by coal fines behaviours. This study delivers fundamental understandings of coal fines generation and migration during the CSG production process, and useful guidelines are suggested to be implemented in the field to minimize production loss induced by coal fines behaviours

Characterization of coal fines generation: a micro-scale investigation

Coal fines are commonly generated as by-product during coalbed methane production mainly due to the interaction of coal with inseam water flow. A portion of the created coal fines may settle and plug the coal cleats and hydraulic fractures due to the gravity and coal pore size constraint. This could result in the reduction of coal permeability and blockage of coalbed methane wells or gas drainage boreholes. Despite the increasing awareness of the importance of understanding coal fines, limited research has been carried out on the characterization of coal fines creation. This study aimed to numerically characterize the generation process of coal fines in micro-scale coal cleats. The Scanning Electron Microscopy (SEM) images for a coal sample from Bulli Seam of the Sydney Basin in Australia were obtained and analysed to determine the actual cleat geometries and the characteristics of coal fines distribution. Then a fully coupled fluid-structure numerical model was developed to identify the creation process of coal fines at micro-scale. The impact of pertinent production conditions on coal fines generation was studied, including production pressure drawdown, temperature, coal fines Young's modulus and strength. The SEM images revealed that the particle size distributions of the coal fines in the examined cleats were in the order of hundreds of nanometres to several microns. The results of the numerical studies showed the coal fines production increased with pressure build-up, and decreased with increasing coal fines strength with more sensitivity compared with pressure. Critical values for production pressure drawdown were obtained, above which failure area began to expand; threshold values were also determined, below which remarkable reduction of coal fines production was achieved. Coal cleat geometry plays an important role in determining coal fines production. It was noted that exposed microstructures, cleat elbow regions and micro-fracture tips are more likely to generate coal fines. Based on these findings, guidance can be provided on the control of production conditions to mitigate coal fines issue, and new insight into where and how coal fines are created by inseam water flow can be achieved. (C) 2015 Elsevier B.V. All rights reserved