Numerical and experimental study of geothermal energy extraction from underground mines

Underground mines are valuable sources of geothermal energy. The present study aims to understand the heat transfer phenomenon that takes place during heat extraction from underground mines using two distinctive techniques. In the first technique, geothermal heat is extracted from abandoned mine tunnels by circulating water through the tunnels, which are usually flooded after the mine is decommissioned. The second technique is based on the novel idea of installing geothermal heat exchange tubes in backfilled mine stopes prior to backfill placement in the stope. This second technique is patented by researchers at McGill University. To study geothermal heat extraction from abandoned mine tunnels, a numerical heat transfer model is developed, which takes into account forced convection inside the tunnel, conduction in the rock mass surrounding the tunnel and heat load intermittency. After development, the heat transfer model is validated by comparing its results against results from existing heat transfer models. Effects of various geometric and physical parameters on heat extraction from mine tunnels are studied using the newly developed heat transfer model, and the parameters that have the first-order effect are identified. To investigate the feasibility of the novel technique of heat extraction from backfilled mine stopes, numerical and experimental heat transfer studies are conducted. To assess the performance of a stope-coupled geothermal heat exchanger system, a numerical model is developed. The model is capable of considering the effect of heat conduction as well as natural convection. The results of the developed model are compared with those from existing ground-coupled heat exchanger models. To further validate the developed numerical model, a series of experimental tests are conducted using a small-scale laboratory test setup built for this purpose. By introducing information gathered from a number of Canadian mines into the developed heat transfer model, effects of hydraulic conductivity, thermal conductivity, rate of heat extraction and arrangement of heat exchanger tubes are investigated.Les mines souterraines sont des sources précieuses d'énergie géothermique. Cette étude vise à comprendre le phénomène de transfert de chaleur qui a lieu lors de l'extraction de chaleur à partir des mines souterraines, en utilisant deux techniques distinctes. Pour la première technique, la chaleur géothermique est extraite à partir des tunnels des mines abandonnés. Le mécanisme d'extraction est fait par la circulation d'eau à travers ces tunnels qui sont habituellement submergés après que la mine est déclassée. La deuxième technique est basée sur l'idée nouvelle de l'installation des tubes qui peut échanger la chaleur géothermique dans les chantiers miniers remblayés avant le placement du remblai. Cette technique est brevetée par des chercheurs de l'Université McGill. Un modèle numérique de transfert de chaleur a été développé pour étudier l'extraction de chaleur géothermique des tunnels de mines abandonnés. Ce modèle tient compte de la convection forcée à l'intérieur du tunnel, la conduction dans la masse rocheuse qui entour le tunnel et l'intermittence de la charge thermique. Après son développement, le modèle est validé en comparant ses résultats aux ceux des modèles existants. Les effets de plusieurs paramètres géothermiques et physiques sur l'extraction de la chaleur à partir des tunnels des mines sont étudiés en utilisant le nouveau modèle développé. Les paramètres qui ont l'effet du premier-ordre sont ainsi identifiés. Pour étudier la faisabilité de la technique nouvellement développé pour l'extraction de chaleur par des chantiers des mines remblayés, les études numériques et expérimentales sont menées. Un modèle numérique a été développé pour évaluer la performance d'un chantier couplé avec un système d'échangeur de chaleur géothermique. Le modèle est capable de tenir compte l'effet de la conduction ainsi que la convection naturelle. Les résultats du modèle développé sont comparés à ceux des modèles d'échangeurs de chaleur géothermique existants. Pour une validation plus concrète sur le modèle numérique développé, une série de tests expérimentaux est effectuée en utilisant une configuration dans le laboratoire à petite échelle construite à cet effet. En introduisant l'information recueillie à partir de nombreux mines canadiennes dans le modèle de transfert de chaleur, les effets de la conductivité hydraulique, la conductivité thermique, la vitesse d'extraction de chaleur et la disposition des tubes de l'échangeur de chaleur sont étudiés

Hybrid Renewable Hydrogen Energy Solution for Remote Cold-Climate Open-Pit Mines

Contemporary off-grid mining operations rely on diesel fuel for the provision of their total energy including electricity, heat, and haulage. Given the high cost of diesel and its imposed greenhouse gas emissions, mining companies are looking for more affordable and cleaner sources of energy for their operations. Although renewable energy systems, such as solar photovoltaic and wind provide efficient solutions to address this challenge, full decarbonization has shown to be very challenging, mainly due to the high cost of battery storage along with the inability to meet total site energy demand. Integrating hydrogen and thermal storage with battery banks can facilitate a full transitioning off diesel. In this sense, the present study intends to offer an innovative decarbonized solution by integrating wind turbines with a multi-storage system (battery, hydrogen, and thermal storage) to supply the total energy (electricity, heat, and haulage) for remote open-pit mines. Among the different proposed fully decarbonized configurations in this study, it is shown that a renewable system with a hydrogen-powered fleet and hybridized battery/hydrogen storage configuration can present the most economically viable case for open-pit mines with a considerably less life-of-mine cost

Hybrid Renewable Hydrogen Energy Solution for Remote Cold-Climate Open-Pit Mines

Contemporary off-grid mining operations rely on diesel fuel for the provision of their total energy including electricity, heat, and haulage. Given the high cost of diesel and its imposed greenhouse gas emissions, mining companies are looking for more affordable and cleaner sources of energy for their operations. Although renewable energy systems, such as solar photovoltaic and wind provide efficient solutions to address this challenge, full decarbonization has shown to be very challenging, mainly due to the high cost of battery storage along with the inability to meet total site energy demand. Integrating hydrogen and thermal storage with battery banks can facilitate a full transitioning off diesel. In this sense, the present study intends to offer an innovative decarbonized solution by integrating wind turbines with a multi-storage system (battery, hydrogen, and thermal storage) to supply the total energy (electricity, heat, and haulage) for remote open-pit mines. Among the different proposed fully decarbonized configurations in this study, it is shown that a renewable system with a hydrogen-powered fleet and hybridized battery/hydrogen storage configuration can present the most economically viable case for open-pit mines with a considerably less life-of-mine cost.Applied Science, Faculty ofMining Engineering, Keevil Institute ofReviewedFacult

Hybrid Renewable Hydrogen Energy Solution for Application in Remote Mines

Mining operations in remote locations rely heavily on diesel fuel for the electricity, haulage and heating demands. Such significant diesel dependency imposes large carbon footprints to these mines. Consequently, mining companies are looking for better energy strategies to lower their carbon footprints. Renewable energies can relieve this over-reliance on fossil fuels. Yet, in spite of their many advantages, renewable systems deployment on a large scale has been very limited, mainly due to the high battery storage system. Using hydrogen for energy storage purposes due to its relatively cheaper technology can facilitate the application of renewable energies in the mining industry. Such cost-prohibitive issues prevent achieving 100% penetration rate of renewables in mining applications. This paper offers a novel integrated renewable–multi-storage (wind turbine/battery/fuel cell/thermal storage) solution with six different configurations to secure 100% off-grid mining power supply as a stand-alone system. A detailed comparison between the proposed configurations is presented with recommendations for implementation. A parametric study is also performed, identifying the effect of different parameters (i.e., wind speed, battery market price, and fuel cell market price) on economics of the system. The result of the present study reveals that standalone renewable energy deployment in mine settings is technically and economically feasible with the current market prices, depending on the average wind speed at the mine location.Applied Science, Faculty ofNon UBCMining Engineering, Keevil Institute ofReviewedFacult

Energy Efficiency of Microwave-Induced Heating of Crushed Rocks/Ores

The interaction between electromagnetic waves and heat transfer phenomena due to microwave treatment is of utmost importance for an energy-efficient microwave-integrated grinding circuit. In this study, the effect of microwave irradiations on the heat absorptions of crushed particles is carried out by developing a numerical model. Crushed particles are simulated as diced-shaped geometries with different sitting arrangements but similar size distributions. The energy efficiency of the microwave treatment process is studied by introducing temperature-dependent dielectric properties and accounting for the convective heat loss from the particle boundaries to the surrounding environment. The simulations are quantitatively validated with the experimental results for heat over microwave efficiency. Heat absorption of larger particles is found to be significantly higher, and the arrangement of particles exerts a negligible effect on overall energy absorption. It is also found that ores with a larger average diameter can yield higher energy efficiencies, and the maximum absorption can be achieved by placing the particles at certain distances from the waveguide of the microwave.Applied Science, Faculty ofMining Engineering, Keevil Institute ofReviewedFacult

Techno-Economic Trade-Off between Battery Storage and Ice Thermal Energy Storage for Application in Renewable Mine Cooling System

This paper performs a techno-economic assessment in deploying solar photovoltaics to provide energy to a refrigeration machine for a remote underground mine. As shallow deposits are rapidly depleting, underground mines are growing deeper to reach resources situated at greater depths. This creates an immense challenge in air-conditioning as the heat emissions to mine ambient increases substantially as mines reach to deeper levels. A system-level design analysis is performed to couple PV with a refrigeration plant capable of generating 200 tonne of ice per day to help to mitigate this issue. Generated ice can directly be used in cooling deep underground mines via different types of direct heat exchangers. State-of-the-art technology is used in developing the model which aims to decrease the size and cost of a conventional refrigeration system run on a diesel generator. Costs associated with deploying a solar system are computed as per the recent market value. Energy savings, carbon emissions reduction, and net annual savings in employing the system are quantified and compared to a diesel-only scenario. In addition, two different energy storage strategies: an ice storage system and a battery storage system, are compared. A detailed economic analysis is performed over the life of the project to obtain the net cash flow diagram, payback period, and cumulative savings for both systems. Moreover, a sensitivity analysis is proposed to highlight the effect of solar intensity on solar system size and the area required for installment. The study suggests that the use of solar PV in mine refrigeration applications is technically feasible and economically viable depending on the sun-peak hours of the mine location. Additionally, the economics of deploying an ice storage system compared to the battery storage system has a better payback period and more cumulative savings.Applied Science, Faculty ofMining Engineering, Keevil Institute ofReviewedFacult

Techno-Economic Analysis of Waste Heat Utilization in Data Centers: Application of Absorption Chiller Systems

Modern data centers are playing a pivotal role in the global economic situation. Unlike high-quality source of waste heat, it is challenging to recover the decentralized and low-quality waste heat sourced from data centers due to numerous technological and economic hurdles. As such, it is of the utmost importance to explore possible pathways to maximize the energy efficiency of the data centers and to utilize their heat recovery. Absorption chiller systems are a promising technology for the recovery of waste heat at ultra-low temperatures. In fact, the low temperature heat discharged from data centers cannot be retrieved with conventional heat recovery systems. Therefore, the present study investigated feasibility of waste heat recovery from data centers using an absorption chiller system, with the ultimate goal of electrical energy production. To fulfill this objective, a techno-economic assessment of heat recovery using absorption chiller (AC) technique for the data centers with power consumption range of 4.5 to 13.5 MW is performed. The proposed AC system enables saving electricity for the value of 4,340,000 kWh/year and 13,025,000 kWh/year leading to an annual reduction of 3068 and 9208 tons CO₂ equivalent of greenhouse gas (GHG) emissions, respectively. The results of this study suggest an optimum change in the design of the data center while reducing the payback period for the investors.Applied Science, Faculty ofNon UBCMining Engineering, Keevil Institute ofReviewedFacult

Designing a Large-Scale Lake Cooling System for an Ultra-Deep Mine: A Canadian Case Study

Subsurface mining operations are continuously getting deeper and more complex due to depletion of shallow deposits. This fact inevitably brings more expensive, high-tech oriented and most importantly energy intensive subsurface mining operations to come alive. Accordingly, while big mining companies are developing sensible extraction methods to exploit orebodies located at great depths, they are also seeking to cut down their costs and carbon footprint. A large percentage of the energy needed by a subsurface mine is due to the mine ventilation and air conditioning reasons. In fact, for mines deeper than 2 km, mine air conditioning becomes a must. Yet, as there are not many alternatives developed, most of the modern mines are subjected to deploy tens of megawatts worth of cooling plants using massive refrigeration units. This does not only create a large financial burden during the project stage but also results in heavy energy demands during the operation. This paper aims to investigate a natural, alternative deep-mine lake cooling system by providing a detailed ‘front-end-loading’ design conducted for a real-life, Canadian example.Applied Science, Faculty ofNon UBCMining Engineering, Keevil Institute ofReviewedFacult

A Reduced-Order Fluid Flow Model for Gas Injection into Porous Media: For Application in Carbon Sequestration in Mine Tailings

One method to accelerate carbon sequestration within mine tailings from remote mines involves the injection of diesel generator exhaust into dry stack tailings. The techno-economic feasibility of this approach heavily depends on understanding the flow characteristics inside the perforated injection pipes embedded within the tailings. Two distinctive yet dynamically coupled transport phenomena were identified and evaluated: (i) gas transport inside the pipe and (ii) gas injection into the porous body of the tailings. This paper presents two models to investigate these transport phenomena, a three-dimensional (3D) and a one-plus-one-dimensional (1 + 1)D model. An experimental investigation of the pressure profile through the injection pipe was carried out to validate the models at the experimental scale. To apply the (1 + 1)D model to larger scales, the results were compared with those of the 3D model, as the (1 + 1)D model required significantly less computational resources and time. To include the effect of the perforations in the pipe on the pressure profile of the (1 + 1)D model, an analytical fluid velocity profile was developed in relation to geometric and physical parameters. The performance of the (1 + 1)D model with an impact factor was then evaluated against the 3D model results for the inlet pressure, pressure profile and gas outflow distribution under various conditions than those investigated experimentally. The developed (1 + 1)D model can be used to design an energy-efficient approach for large-scale implementation with a wide range of desired operating parameters.Applied Science, Faculty ofScience, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofMining Engineering, Keevil Institute ofReviewedFacult