The exploitation of underground deposits require a lot of sweat, and not only because of the ‘hard task’ of extracting and transporting the ore, but also because the tunnels are full of natural heat from the rock.
A group of researchers from McGill University in Canada systematically examined how heat could be tapped when mines get closed. They calculated that each kilometer of a typical deep mine would be able to generate 150 kilowatts of heat, enough calories to heat 5 to 10 Canadian households during peak periods.
A number of communities in Canada and Europe already use geothermal energy from abandoned mines. Taking this into account, the research team has endeavored to develop a general model that could be used by engineers to predict the potential for geothermal energy present in other underground mines.
In a paper accepted by the American Institute of Physics and published shortly in the “Journal of Renewable and Sustainable Energy”, the researchers say they have analyzed the heat flow through mine tunnels flooded by water. In such a situation, the hot water inside the mine will be pumped to the surface, then once the heat extracted, the water cools will be returned to the basement. However, for the system to be sustainable, the heat should not be extracted faster than it can be powered by the rock itself. The model can be used to analyze the thermal behavior of a mine under different scenarios of heat extraction.
“Abandoned mines require constant monitoring and more costly rehabilitation. The use of the mine in a geothermal process will offset these costs and help the mining industry to become more sustainable,” said Seyed Ali Ghoreishi Madiseh, lead author of the article. The team estimated that about 1 million Canadians could benefit from geothermal energy from mine, with an even greater potential for dense populations.
The first geothermal plant in the world of this type was commissioned in October 2008 in Heerlen, the Netherlands. The latter includes two sites based in the center and north of the city. Work began in 2005, Heerlerheide, with the drilling of two wells with a depth of 825 meters to access water from the mine where the temperature reached 35°C. Three other wells were then drilled (Stadpark Oranje-Nassau), ranging from 250 to 500 m depth. These deep well waters in Heelerheide recover after they have been used for heating before being finally stored until it cools.
The British Geological Survey estimates that the use of approximately 1% of the available heat in deep mines of Glasgow could contribute up to 40% on annual heating demand of the city.