Environmental and ventilation benefits for underground mining operations using fuel cell-powered production equipment

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Over the last few years, a multi-faceted feasibility study evaluated the introduction of hydrogen fuel cell-powered equipment into underground mines to replace diesel engine-powered equipment. The analysis has shown that under normal operating conditions, fuel cells could at the very least be an environmental and health benefit by eliminating combustion engines and their unwanted by-products.
They could also generate significant reductions in the amount of ventilation a mine needs to supply when compared to dieselized operations; this would further decrease a mine’s energy consumption, its associated greenhouse gas impact, and also reduce a mine’s significant ventilation-associated costs. Fuel cell-powered equipment also has the advantage of lower noise and heat production compared to its equivalent diesel-powered counterpart. The degree to which fuel cells can generate ventilation benefits in underground mines depends upon a number of operational parameters and mine- specific qualifiers, such as current ventilation control or management, mine depth, inherent dust conditions, and minimum velocity requirements.
However, another major consideration in the introduction of fuel cells in underground mines will be the safety requirements associated with diluting and removing the potentially explosive hydrogen in the event of a gas leak. In outside surface applications, it is possible to use dispersion, buoyancy, time, and lack of ignition sources as mitigating factors in deriving a low risk of an explosion.  In underground operations these factors change. Dispersion and buoyancy are limited, time may not be available, and in non-coal mines, ignition sources are not typically controlled. When a hydrogen leak occurs, the availability of sufficient ventilation to dilute and effectively remove the gas will be critical; consequently, ventilation may be the prime risk controlling factor.
This paper evaluates the potential benefits of replacing diesel engines with fuel cells in powered production equipment, discusses the mitigating qualifiers that could limit ventilation savings, and evaluates solutions to retain and maintain an additional ventilation capacity in the event of an emergency situation such as a hydrogen leak from the fuel cell stack or its distribution system.
This study has shown that if fuel cells were to replace the diesel engine of the primary production equipment in Canadian underground metal mines, less ventilation would be required. The degree of ventilation reductions in the six mines analyzed range from 9% for a future deep scenario to 25% for current metal mining scenarios. On combining all the ventilation cost components, primary and auxiliary fans, heating and cooling, the cost reductions varied from 20% for a future deep scenario to 38% for the same mine under its current conditions.
It has also been shown that similar order savings may be achieved by other means for specific mines, such as changing the heating fuel, ventilation demand controls, or as a result of changing to quality-based diesel regulations. However, this does not negate the advantages of fuel cells. The savings can be incremental but other limitations imposed by such considerations as a minimum air velocity, blast clearance, or dust conditions may be reached before the full combined potential benefit is reached.
One of the most dramatic benefits was the reduction in GHG emissions, which range from 27% for a future deep scenario  to 41% to 43% for current operations. A major component of these lowered emissions is the reduced consumption of diesel fuel.
One particular challenge to the introduction of fuel cells underground is the delivery, storage, and dispensing of hydrogen to fuel the mining equipment at underground refuelling stations. Large financial commitments may be required in order to provide and maintain a spark-free environment along the hydrogen distribution lines, refuelling stations, development and production workings, as well as throughout the entire mine. Failing this, large volumes of air would be required, potentially larger than that currently supplied for the dilution of diesel fumes, to ensure leaks are quickly diluted to 50% of the LEL. These volumes could be technically impractical and uneconomical.
Keywords: Mine ventilation, Mine plan, Diesel emissions, Ventilation savings, Hydrogen safety
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