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Mine water heat under the PhD spotlight

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World Coal,

A potential new energy resource for coalfield areas is being researched by a PhD student in conjunction with the Coal Authority to gain a better understanding of the topic.

University of Edinburgh student Mylène Receveur is being partly-sponsored by the Coal Authority to expand its understanding of the geothermal warming of mine waters.

Mylène’s thesis, titled ‘Investigating geothermal heat resources of legacy mine workings, why are some mine waters hotter than others?’ will explore the key controls that create variations between different sites.

When mines are abandoned and the pumps which kept them dry are switched off, the roadways, galleries and fractures fill with ground water, which is heated by geothermal energy from the earth’s core to temperatures of 11 to 20°C close to the surface, and up to 46°C in deeper coal seams.

This difference in temperatures between mines has always been known, and a recent Scottish government study on the geothermal potential of Scotland showed that there is a significant variation down to a depth of approximately 1500 m.

Temperature gradients ranging from 37°C/km to 45°C/km were recorded in 61 boreholes, but understanding why mine waters reach a certain temperature is critical to being able to estimate the heat resource and storage potential.

The Coal Authority is particularly interested in understanding this thermal energy resource better, including how quickly mine water heats up and how it could be used on a large scale for heating homes and businesses for decades to come.

The Coal Authority is particularly interested in better understanding this resource because it is progressing a large number of district heating schemes that will use mines as their source of energy. Dr Ian Watson, technical lead on water for the Coal Authority and Mylène’s industry partner, said: “A quarter of UK homes and businesses sit on the former coalfields, where the flooded underground workings contain vast amounts of renewable thermal energy. The authority wants to work with Mylène to improve its understanding of what the main sources of energy are, and how new energy extraction, or energy storage schemes using mine water, will be able to make the best use of the vast underground workings left behind after mining stops. Several factors are considered to contribute to the temperature profile, and the purpose of Mylène’s PhD is to determine what they are and understand the subsurface ‘plumbing’ and heat distribution of mine workings.”

French-born Mylène has a master’s degree in geology from the UniLasalle Beauvais Engineering School in Beauvais, Paris (France) and has also achieved a research master’s in geology, specialising in geothermal sciences, from the University of Iceland.

She will be collating data from the Coal Authority and spending time at the Mansfield headquarters in the UK.

Hoping to develop hydrogeological conceptual models before interpreting the results to ascertain the temperature resources that are available over the long term, Mylène said: “It is a great challenge to understand what factors control the temperature distribution and the heat recharge rate in systems as hydrogeologically complex as coal mines, but this is essential to assess their geothermal potential. Hopefully, being able to develop a numerical approach that faithfully reproduces heat flow processes in mines could be used to support the dimensioning of heat extraction schemes, first in the UK and something that is ideally reproducible abroad. This is the key to ensure a sustainable heat production from low-temperature geothermal resources.”

Jeremy Crooks, head of innovation for the Coal Authority, on the repurposing of abandoned mines to provide a sustainable energy source added: “Mines are a constant source of sustainable energy, protected from the energy price fluctuations, which will help remove people from fuel poverty and provide business with cheap, low-carbon energy, giving them a commercial advantage and leading to more employment. To make best use of this asset, more about the temperature behaviour and flows within mines needs to be known - Mylène’s work on this will be invaluable.”

Christopher McDermott, Mylène’s principle supervisor at the University of Edinburgh (Scotland) emphasises that it is important to understand the heat resource and distribution to help ensure its sustainability: “There is always the temptation to extract more heat out of the system than is available by recharge, thereby depleting the resource. Mylène’s work is important in helping to balance the heat use and also to investigate ways of enhancing the heat in mines through storage.”

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