The Underground (Hydrogen) Economy
For all the talk of ‘hydrogen highways’ linking suburban Ontario and the future Olympic infrastructure in the Vancouver area, the mining sector has come relatively late to the game in adopting the fuel cell and its related technologies. This is all the more surprising when the mechanics are taken into consideration–the low speed, low centre of gravity and sensitive emissions criteria of underground mining vehicles working in confined zones are perfectly suited to fuel cells powered by on-board hydrogen.
A recent U.S. Department of Energy survey estimated that there is a total market for fuel cells in underground mining of approximately 3,600 MWe. There are currently over 10,000 diesel-powered haulage vehicles operating in the global coal mining industry alone, and an annual conversion rate of 1,200 vehicles that could be converted to fuel cell power. Hydrogen’s attraction as the most abundant naturally-occurring element on Earth, however, has always been tempered by its ‘Hindenberg factor’–no minor consideration for any subsurface application.
Following a five-year period of design, proving and trial, the first on-site productivity tests of a fuel-cell-powered underground vehicle (a locomotive) will be made in 2005 at a Nevada site. The locomotive project has been managed by the Denver-based Fuelcell Propulsion Institute (FPI) with input from Natural Resources Canada’s CANMET division and with the provision of the base locomotive design from RA WarrenEquipment Ltd. of North Bay, Ont. The designs have undergone trial at CANMET’s experimental mine at Val d’Or, Que., and at a number of Ontario mine sites. Many of the other consortium partners were in attendance at the MINExpo exhibition in Las Vegas in September.
Mining work is particularly well-suited to vehicles powered by the hydrogen fuel cells used in the locomotive project. Zero emissions (other than pure water), low noise, high power density, low temperature and pressure operation and component durability are well matched to underground applications. Although hydride storage is heavy, weight is of no consequence in counter-balanced vehicles such as loaders or in steel-wheeled locomotives. In fact it is the nature of the application that has driven much recent research activity into hydrogen storage for the cell operation.
Montreal’s McGill University has been at the forefront of work that has made feasible the use of reversible reactions based on ‘alanates’–compounds that have the capacity to store and release hydrogen from its substrate in a workable 6 wt% ratio. Hydro Quebec has pioneered leading edge research into nanocrystalline magnesium-based hydrides. Hydrogen refueling systems made by Toronto-based Stuart Energy Systems Inc. are integral to the locomotive project, using infrastructure designs that are currently used in ongoing commercial passenger fleets across Europe.
U.S. Mine Safety & Health Administration criteria have been in place for years to regulate hardware installed in gassy environments such as mines, where methane has been of greatest concern. The need for a comparative evaluation of any additional risk presented by hydrogen-powered vehicles was recognized by the U.S. Department of Energy in a recently-commissioned independent survey undertaken by Westinghouse Safety Management Solutions Inc. In this study, the performance of prototype fuel cell vehicles and refueling infrastructure was referenced to existing diesel technologies.
The recommendations of the report appear to justify the design of the FPI locomotive in deploying hydrogen generation from removable on-board fuel beds rather than an ‘energy bus’ (a hypothetical refueling transporter at surface that would refuel vehicles before they went underground). Quantitative evaluations of the risks attached to each aspect of operation in typical mine site conditions concluded that a vehicle in an underground coal mine can be designed to have a ‘moderate risk’–the same risk level determined for diesel-powered equipment in coal mines.
The only truly unacceptable risk derived through calculations based on transportation/refueling/operation cycle for a 13-vehicle fleet operating on a 20-hour day (two 10-hour shifts) over a 360-day year, was the likelihood of a critical threshold 3-kg leak of hydrogen while the energy bus option was deployed. Safety design criteria including hydrogen leak detectors, fuel bed strengthening, temperature and pressure interlocks, excess flow valves and cylinder relief protection could be built in to ensure that a 1-kg leak would not be exceeded during normal operation. The report further recommends that, in the event of hydrogen leakage, it is statistically unlikely that the ‘event consequences’ would be worse than those that are acceptable for mine face methane ignitions (i.e., flashes with no subsequent damage).
The presence of as little as 2% methane (40% of its lower flammability limit), however, would reduce the hydrogen concentration needed to reach the composite flammability limit of the two gases. Large leaks during refueling episodes are most likely to trigger the deflagration to detonation transition (DDT) level (the subsonic to supersonic expansion of combustion gases characterizing explosive rates of oxidization).
Hydrogen storage costs are a critical component of the overall system efficiency. Large scale underground storage of hydrogen in a fuel-cell-compatible form is not viable at present although controlled injection of hydrogen sulphide practised by the Alberta Geological Survey, amongst others, suggests that subsurface storage in some form may be a viable option in the future. On-site production of hydrogen from hydrocarbon compounds as a feedstock for mine vehicles is not likely in the short term. Despite this, when viewed in terms of the annualized capital costs and annual recurring costs, the fuel cell mine vehicle is cost-competitive even while the capital cost of its hydride fuel cell power plant is high.
The Fuelcell Propulsion Institute’s own industry-independent analyses suggest that when the cost of the powerplant (generating the hydride feedstock) is as high as US$3,800/kW, compared with about US$500/kW for the equivalent diesel model, the fuel cell model will compete–largely attributable to lower operations and maintenance costs over its projected lifetime. Recent survey data presented at the 7th Greenhouse Gas Technology Conference in Vancouver in September 2004, confirm that regulatory and mass-production constraints are a greater limiting factor on commercialization of fuel cell technologies than operational factors.
Hydrogen has always been perceived as something of a paradox. It possesses one of the highest energy densities (higher than methanol, propane, octane) and with a low physical density that ensures its buoyancy–its flammability perception only marginally aided by the ease with which it escapes confined zones. Those not old enough to remember the Hindenburg (or unaware that the disaster was attributable to the surface coating of the balloon) are unlikely to forget the Challenger explosion. Institutionalized fear was behind the refusal of planning permission for BP’s proposed first hydrogen refueling station in London this year.
There are probably as many misperceptions about the use of hydrogen as a fuel in mining applications as those surrounding the capture and storage of carbon dioxide in current geo-sequestration projects. Public aversion either to the physical injection or to paying for the costs of underground CO2 storage was recently found to be statistically greater than that for additional nuclear power generation. Once these reservations have been overcome, hydrogen as a viable mine vehicle fuel is not as far removed from reality as many would believe.
The work presented here is the product of research work undertaken by the author ([email protected]) in connection with a fuel cell design project in 2002 funded through the European Commission (Framework 5 Program). This involved the design of an operational polymer electrolyte membrane (PEM) fuel cell of a similar type to that deployed in the mine vehicle project in progress at the Fuelcell Propulsion Institute. It builds on his emissions-reduction project work at the Emissions Trading Group, which was the basis for some of the material in his Kyoto Protocol piece in CMJ June 2004. Some of the material draws upon previous career experience in Applications Engineering of alternative fuel technologies.