Ali Madiseh

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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