The UK Coal Authority posits that water from flooded coal mines has the potential to be used in the heating of UK homes and industry as a source of lower-carbon energy.
In a December 2020 report, the authority states that mines are warmed by natural geothermal processes and, where the mines are flooded, they hold the potential to heat up to a quarter of the UK’s population which live above abandoned coal mines.
On average, the water available in such mines is between 12 oC and 20 oC. These temperatures will only need to be slightly increased to make the water suitable for use in central heating systems in the UK.
The UK Coal Authority posits that heat pumps could be used for such an application.
At the time of publishing its report, the UK Coal Authority, together with the British Geological Survey (BGS), released an interactive map showing where the mines are and the extent to which the temperatures of water increase with depth.
They explained that the mapping tool would be freely available for use by developers, planners and researchers to identify opportunities to investigate the use of mine water as a sustainable heat source.
BGS geoscientist and project leader Gareth Farr said the culmination of the map was the first time visualisation of Britain’s coalfields had been achieved. “We have found records of heat temperatures going back more than 100 years and compared them to temperatures in the mines now, and found them to be quite similar.”
He said this was a clear indication that geothermal processes that create this heat would exist for many years to come.
LOW COST HEAT SOURCE
The UK government has a target to increase the number of homes on heat networks from 2% to 18% by 2050.
The UK Coal Authority recognises that geothermal energy from mines, combined with heat pump technology, could provide a sustainable energy source for these networks that is both local and low cost.
In addition, the authority’s technical specialists suggest there is potential to kickstart a new renewable industry, creating employment, tackling climate change and attracting investment to the coalfield communities previously disadvantaged by mine closures.
UK Coal Authority innovation head Jeremy Crooks says, “when miners were working in hot, dusty conditions, they would not have known that their efforts and the heat they worked in would one day create a sustainable source of energy for hundreds of years to come.”
He adds that the authority is currently reviewing more than 30 potential heat network opportunities using geothermal mine energy. Seaham Garden Village and Gateshead are the first two such schemes to secure funding from the government’s £320-million Heat Network Investment Programme, with others to follow.
BACK AT HOME
In South Africa, African Source Markets CEO Bevan Jones tells Mining Weekly that because South Africa’s underground coal mines are a lot shallower than those in the UK, they do not enjoy the same geothermal gradient as that of the UK.
Nonetheless, he says other potential uses for disused coal mines are available.
One such use could be for industrial heat generators to use disused mines as a heat storage facility for later use when heat is required, such as the application of warming local homes in winter, thereby replacing the need of such homeowners to burn coal and wood in fireplaces, suggests Jones.
In addition, using disused mines in such an instance, combined with the treatment of associated acid mine drainage (AMD) water could present a “useful revenue opportunity”, he says. Doing so will also help clean up underground water sources over time, thereby addressing the legacy issue of AMD in applicable situations.
Jones also suggests that disused mines could perhaps be used in the short term as a testing ground for circular economy solutions that may lead to other potential future uses.
Further, he says flooded mines can be used on a hydro-electric power generation model, where underground water from the mines is pumped using cheap renewable energy during the day and later released, for instance during peak evening demand periods, back down the mine shaft and into turbines to generate electricity.
Furthermore, Jones says entrained air bubbles could also be sucked down the shaft with the water to provide underground compressed air power generation. “This is probably the oldest form of power generation known, such as the classic Roman Trompe.”
This, combined with a super-efficient air-powered Tesla turbine, for instance, he says, will result in abundant free energy.
“There is so much potential just staring us in the face as part of the just transition,” enthuses Jones.