Doctor of Philosophy in Mining Engineering (PhD)
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.
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.
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.
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
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.
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.