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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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.