March/April 2007

Extracting geothermal heat from mines

By H. Ednie

Throughout the last two decades, much concern has mounted about the environmental impacts of traditional and develop-ing energy resources. In response to this, research and development is underway to finesse alternative methods of generating energy.

One resource under development is the use of low-temperature geothermal heat from mines. Generally regarded as a benign energy source, particularly when compared to today’s most popular sources such as nuclear, oil, and coal, it is, however, a sustainable and environmentally sound solution to some energy requirements.

The Earth/Mine Energy Resource Group (EMERG) at McGill University, headed by Professor Ferri Hassani [pictured above], was formed to investigate and advance the sustainable development of alternative energies from both active and abandoned surface and underground mines. Efforts underway are focused on employing the physical characteristics and properties of different types of mines, such as thermal heat, its potential energy, and its enclosure capacity.

Hassani said there is much potential for ground heat to be extracted and used, either for commercial purposes for mining applications, such as heating deep oil sands deposits, or district heating of buildings in the communities, or employing this heat for drying of food products. In some cases, such energy has been used for heating the water for fish farming.

The goal of EMERG is clear: to make the mining operations truly sustainable by developing an integrated alternate energy during the life of the mine, as well as after mine closure. It will enable local communities to use this sustainable and inexpensive source of energy to attract other businesses to sustain the existing communities.

EMERG aims to promote the use of abandoned mines to generate sustainable energy and encourage the sustainable development of mine energy resources such as low-temperature geothermal energy resources in an economic and environmentally responsible manner.

The use of active or abandoned mines as a source of geothermal energy is not rocket science - there are already productive examples of such technology. Mines, particularly underground mines, are ideal locations for geothermal systems.

The first 100 metres or so underground is well suited for supply and storage of thermal energy. In fact, climatic temperature change over the seasons is reduced to a steady temperature at 10 to 20 metres deep, with future depth temperature increasing according to the geothermal gradient, which is about 1° to 3°C for each 100 metres down.

Geothermal energy is the energy produced internally by radiogenic heat production and long-term cooling of the planet. Various applications can be used from this energy, including direct use for heating and electricity generation.

Due to the steady temperatures deep down, geothermal sources are excellent fuels for heating and cooling systems. For a mean surface air temperature of 15°C, the ground temperature at a depth of 1,000 metres will be about 30° to 45°C - therefore, in the winter, when the surface air temperature drops to -10°C, there will be a temperature difference of 40 to 55 degrees.

The potential to use abandoned mine sites for geothermal energy production is well recognized today - work and development is now underway at many sites. Heat pump systems are already at work in Canada, Germany, and Scotland at flooded, abandoned mines as low-temperature geothermal reservoirs for heating and cooling purposes.

One example of such a system can be found in Springhill, Nova Scotia, where Ropak Can Am Ltd. is using floodwater from abandoned mines to heat and cool the company’s facility at the site. It’s an efficient and economic project that produces annual savings of $45,000, or the equivalent of about 600,000 kWh, when compared to conventional systems.

At Springhill, the warm water supply well is tapped into the No. 2 mine, which extends four kilometres into the earth at a 32 degree angle. Mine water is pumped from the No. 2 mine at a depth of 140 metres, with a flow rate of 4 litres per second. The water is then cooled down from 18 degrees to 13 degrees in heat pumps, then re-injected into the No. 3 mine at the 30 metre level.

In the summertime, the system is reversed to produce a cooling effect, and the mine water is used as a heat sink instead. Ten heat pumps in the plant provide the heating and cooling of the facility.

The Springhill example proves geothermal energy from abandoned, or existing, mines is a feasible alternative energy source. Further efforts could result in it becoming a more effective and attractive option for the reclamation of abandoned mines. In fact, Hassani envisions such systems integrated into the reclamation plans from the time of mine development, so that any necessary infrastructure could be added during the production stages.

With some patent-pending technologies, EMERG’s vision of such energy projects as one more step in the typical mine plan could be tomorrow’s reality.

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