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Durjoy Baidya
Doctor of Philosophy in Mining Engineering (PhD)
Research Topic
Numerical and experimental investigation of fluid flow and heat transfer of flue gas carbon sequestration in mine wastes
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Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
Decarbonization of heat and electricity generation through geothermal energy is increasing, thanks to its universal availability and base load capacity. Although geothermal energy has several advantages compared to other renewable energy sources, more research is necessary to understand the fluid flow and heat transfer processes in diverse geological formations. These geological formations can be complex due to the variability of rock/soil properties, fluid presence, and fluid movement. Heat exchangers employed in such systems can reach thousands of meters, posing challenges for field-test experiments. In addition, mathematical modeling of such systems is a challenging task.This dissertation is based on two geothermal projects; one focused on power generation and the other on heating. Both projects employ either a coaxial borehole heat exchanger (a single coaxial borehole) or a system of coaxial borehole heat exchangers. For geothermal power, a field-test experiment is carried out in a high-temperature resource well with a thermal gradient of 0.4°C/m. Experimental results are analyzed and rock properties are measured. In addition, a numerical model is developed to replicate the 500-meter deep field-test experiment. The developed numerical model is validated with the experimental data and is used to understand the subsurface behavior of the geothermal reservoir. Additionally, the performance of the heat exchanger under the complex geological formation, accounting for the presence of subsurface fluid flow, is evaluated.For geothermal heating, a numerical model is developed to study the heat transfer characteristics of a solar-geothermal heating system. The developed numerical model solves the heat and mass transfer process in a rectangular array of 450 coaxial boreholes. It also accounts for energy generation in solar thermal collectors and thermal demand on buildings. The numerical model is used to study energy injection into boreholes, energy extraction from boreholes, thermal interactions between boreholes, thermal losses from the system, and the performance of the solar-geothermal heating system.The results showed that subsurface fluid flow has a significant impact on the energy output from geothermal systems. Solar-geothermal heating systems have good potential to decarbonize space and water heating applications in Canada.
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Efficient carbon capture within mine tailings on an industrial scale holds the potential to make substantial strides in providing permanent solutions for carbon removal from the environment. This dissertation studies the feasibility of carbon sequestration in mine tailings by injecting flue gas. Its investigations revolve around exploring the large-scale implementation, assessing operational feasibility in cold climates, and addressing techno-economic aspects of the concept of diesel exhaust injection in mine tailings for carbon sequestration.Following the delineation of the research scope, the investigation embarks on conceptualizing a design for large-scale CO₂ sequestration within dry stack mine tailings through the utilization of embedded perforated pipes at remote mining operations. The core contribution of this dissertation involves the conception and validation of a novel (1+1)D Reduced Order Model (ROM) designed to predict the pressure phenomenon of the perforated pipes installed in the tailings. This ROM efficiently predicts injection pressures, outflow rates through the perforations, and pressure profiles with a level of precision comparable to commercial numerical solvers while demanding significantly less computational resources and time. The developed model showed the potential to be an asset in the decision-making process by furnishing a strategy for the design of energy-optimal injection scenarios.This research advances the development and validates a numerical model that assesses the feasibility of harnessing the thermal energy from flue gas to avert freezing in tailings beds, thus showcasing the possibility of year-round operation in cold climates. The study quantifies several crucial parameters, including injection rate, temperature, and other operating factors, emphasizing the flexibility of carbon sequestration approaches in frigid environments. A comprehensive array of sensitivity analyses scrutinizes the adaptability of the proposed concept across various operational and climatic conditions.Furthermore, the study develops a techno-economic cost model, accounting for factors such as piping infrastructure and energy operational expenditures. This model informs decision-making by identifying the critical balance between power costs and piping expenditures necessary for optimal operational expenses. Notably, the study emphasizes that carbon capture within mine tailings can be managed efficiently at a reasonable operating cost, reinforcing the practicality of greenhouse gas sequestration.
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For underground mining operations in cold climates, such as Canada and Arctic regions, mine intake air heating is a significant energy- and carbon-intensive activity. The high thermal energy demand is commonly met by burning fossil fuels, particularly for mining operations in remote locations with limited grid access. This dependence on fossil fuels not only has an adverse environmental impact, but also incurs high costs. Mining companies are also facing increased pressure from society, investors, and the governments to address their carbon footprint. To overcome this energy–environmental challenge, mining companies are exploring innovative solutions for decarbonizing their operations. One potential solution is the implementation of a mine exhaust heat recovery system for intake air heating. This approach can reduce the high energy reliance of underground mine heating systems. In this study, two different mine exhaust heat recovery systems are proposed - an indirect capture-indirect delivery system and a direct capture-indirect delivery system - and their performances are evaluated using numerical models. Two fully-coupled thermodynamic models are developed to assess the potential economic and environmental implications of the proposed heat recovery systems. Furthermore, to evaluate the direct capture-indirect delivery system, two numerical models with different one-dimensional and three-dimensional approaches are developed to examine the performance of the direct heat capture unit under various design and operational conditions and to determine its ideal configuration for heat recovery applications. An experimental test setup is also designed and constructed to verify the concept of such heat exchanging systems at a lab scale and validate the results of the numerical models. Once the ideal design is identified, the developed thermodynamic code is populated with the operating and climate data from the mining operation being studied. This allows for the calculation of the potential cost savings and carbon emission reduction. The results of the study show that although both proposed heat recovery systems help mitigating the economic-environmental problem of mine intake air heating, the direct heat recovery system is found to be more efficient in terms of both carbon footprint reduction and energy cost savings.
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Depletion of shallower resources is challenging modern mining industry to reach deeper deposits to maintain global mineral and raw material demand. As mines grow deeper and get more complex, heat loads associated with production, air compression and geology become an important issue for the health and safety of underground workers. For this purpose, mining industry uses water-based bulk-air spray cooling systems. However, design of these systems is reliant on semi-empirical models that were developed based on restricted empirical data collected from limited chamber size and geometry. Therefore, they often fail to respond when the granularity of the operating parameters such as droplet size, air velocity or chamber geometry is challenged by the application. To mitigate this issue, numerical models can be used effectively. Nevertheless, mining literature is missing an extensive study of these cooling chambers with numerical methods. Moreover, mine air conditioning systems are energy intensive, and their energy performance is highly related to their design. To fill this gap, first, the energy problem associated with conventional mine cooling systems were raised and examined with different case studies. These case studies have shown that, there are alternative cooling solutions for deep-mines, and they could offer similar cooling performances with relatively less capital investment. Then, a fully coupled numerical model that can replace conventional design methods was introduced and validated with series of lab experiments. Literature survey done on similar concepts with applicable scales has shown that earlier studies are mainly investigating evaporative cooling of spray cooling systems without offering a relevant condensation criterion to capture the two-way multiphase physics seen in bulk-air cooling applications. In these terms, this study provided a more inclusive approach by introducing a saturation criterion to Lee’s mass transfer model used in multiphase modelling. Finally, once validated with experimentation, the lab-scale solution was scaled up to an industry compliant, full-scale, multistage bulk air cooler model to benchmark the conventional methods. The studies have shown that; numerical models presented here agreed with the experimental work and semi-empirical models within a reasonable error and promised higher granularity when it comes to understanding the system merit and effectiveness.
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Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Dilution is an important factor affecting the profitability and operational costs of mining activities, leading to a potential discrepancies between design intentions and actual operations, commonly referred to as reconciliation. This discrepancy may result in an increase in the tonnage of material to be milled while reducing its value. Despite variations influenced by deposit characteristics, location, and mining practices, dilution is often treated as a fixed value in open-pit mining operations. This study introduces a computer program designed to read and analyze extensive block model datasets. The program automates the computation of dilution, arising from operational errors, empowering users to assess its impact on mine productivity by generating a diluted block model under varied Cut-off Grade (COG) and dilution scenarios. Established for application in an initial phase of mine design and optimization in open pit mining, the program significantly expedites time-intensive dilution calculations. In this study, the program is applied through nine different COG scenarios and four diluting skin percentage applications. The results underscore the value of the program in comprehending the response of the ore body to variations in COG and dilution. It is noteworthy to state that the flexibility of the developed program in modifying conditions, saving time through automated computation, and capturing changes on the block model caused by operational dilution. This is an innovative program in terms of applicability before mine design, the substantial reduction in computation time from days to hours, and the providing of specific insights such as island scenarios. This innovative program offers a computationally affordable and practical solution for mining operations seeking to improve efficiency and accuracy in dilution calculations. By providing a dynamic tool for evaluating and visualizing the impact of dilution under different scenarios, it equips mining professionals with valuable insights in the early stages of mine planning, contributing to more informed decision-making processes.
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Remote, off-grid mining operations in cold climate regions, like northern Canada, exclusively depend on diesel generators for power generation. Even with the best available technology, a typical diesel generator converts only one-third of its diesel fuel thermal capacity into electricity. The rest of this valuable heat is commonly discarded as waste heat. This research exhibits that the amount of energy discarded as heat through the exhaust of a diesel generator is almost the same as the amount of electrical energy generated by the generator. All the while, remote mines in cold regions, like those of Canada’s North, have a high demand for heating throughout most of the year which is generally met by burning fossil fuels. Aiming to provide this necessary heating in a greener way, the quantity and the quality of the thermal energy discarded from different types and sizes of generators have been analyzed thoroughly in the present thesis. A shell and tube heat exchanger-based heat recovery system for the exhaust of a small-scale diesel generator has been designed numerically with ANSYS Fluent and validated with appropriate experimental results. Various parametric studies have been conducted to evaluate the benefits of deploying the proposed system in both underground (pre-heating the mine intake air) and surface (space and process heating) applications. The results project significant savings for all evaluated remote locations and suggest that considerable reductions of carbon footprint can be achieved by using the proposed system. The equivalent carbon emission assessments show that employment of the proposed combined heat and power generation system can help remote mining operations with transitioning towards less carbon intensity.
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Remote mines operating in cold areas of Canada and other Arctic countries are often subjected to subfreezing temperatures that can get as low as -40°C. When those mines are underground, they need to heat their intake airflow up to a comfortable temperature for the adequate operation of machinery and personnel. Remote mines are also frequently not connected to the electrical power grid and need to depend on diesel generators to produce their electric power. As it has been demonstrated by several authors in literature, these commercial diesel generators consistently discard almost 70% of the total energy that is input as fuel. Such energy being neglected mostly in the form of heat through exhaust and other means. Knowing so much energy exists in the exhaust, usually in high grade, a system is proposed to recover thermal energy from the exhaust of the diesel generators, transport it and deliver it to the cold intake airflow of a remote underground mine. The overall alternative heating system is modeled analytically (with MATLAB) using real climate history data from a Canadian remote mine to evaluate its performance. Also, a pilot-test scale experimental setup is designed, constructed and tested and the heat exchanger utilized for intake air heating is further numerically modeled with computational fluid dynamics (using Ansys Fluent) to investigate its behavior in detail. Results from all the models created point to the system effectively recovering a significant part of the waste heat and delivering it to the cold airflow. It is also shown that due to the high temperature gradients created by the subfreezing temperatures the intake air heating unit holds the potential to deliver most of the recovered heat, with the exhaust heat recovery unit mostly driving the performance of the system.
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