Clean coal is a myth. Clean heat from coal mines isn’t! Corinna Abesser and Ashley Patton

Coal is often referred to as the dirtiest of fossil fuels. It produces 40% of the world’s electricity demand, is responsible for 39% of CO2 emissions and causes big problems with air pollution worldwide. In 2012, the use of fossil fuels, in general, has resulted in 34.5 billion tonnes of carbon dioxide being emitted. These emissions need to be dramatically reduced. Earlier this month, we were reminded by the UN’s Intergovernmental Panel on Climate Change (IPCC) of the urgency of this task to reduce emissions and to end coal-fired electricity by 2050 in order to cut the risk of experiencing extreme heat, drought, floods and poverty in the future.

Therefore, alternative, low-carbon  sources of energy are urgently needed for the world to be able to reduce CO2 emissions and limit global warming temperature rises as well as to increase energy security and eliminate fuel poverty.

Coalmines are just the place to help with this, despite their ‘dirty’ past. They can provide a low carbon alternative for heat production, and here is how.

Heat beneath our feet

There are vast amounts of energy stored in the Earth beneath our feet, which are ultimately provided from two sources: the earth and the sun. Decay of radioactive elements in the Earth’s core provides a constant supply of heat within the earth that dissipates up to the crust. As a result, the deeper we drill into the earth the warmer it gets, with temperatures rising by about 2.5°C for every 100m of depth.

At the same time, the insulating effect of the shallow subsurface is able to store heat from sunlight as well as that lost to the subsurface from the basements of buildings and from other subsurface infrastructure in cities, such as sewers or tunnels . This heat resource is typically distributed by natural groundwater systems and through man-made structures such as the abandoned coal-mines that underlie many of the UK’s cities and towns.

Abandoned coal mines comprise networks of flooded voids with water flowing at depths of a few tens of metres to several hundred of metres below the surface.  Even in the shallower mines, temperatures of mine water are elevated, typically around 12-16°C and often higher, especially where mines are deep.

It is this resource that can be exploited for space heating through use of a simple, but ingenious piece of technology:  Ground Source Heat Pump systems. These systems take the  energy from the thermally-enhanced mine water and upgrade it to higher temperatures, e.g., around 40-50°C, for use in domestic heating.

How is geothermal energy stored?

How does it work?

The “heart” of the ground source heat pump system is the actual heat pump.  It works in the same way as a fridge that cools your food by absorbing heat from the food in the fridge and, using a heat exchanger, releases it to the surrounding air via the condenser coils at the back of the fridge (which are always warm because of this). Heat pumps do exactly the same. They absorb the heat from the mine water, upgrade it and release the “concentrated” heat via the home heating system.

Heat pumps require a small amount of external power to accomplish the work of transferring energy. However, for each unit of energy input, the heat pump provides 3-4 units of heat energy output, and hence these systems are much more efficient than conventional gas- or oil-burning heating systems. Because of this high efficiency, minewater-based heating is almost carbon-neutral, especially when the pumps are powered by “green” electricity, e.g. generated by wind turbines or solar panels.

How to extract heat from mine water to heat houses.

The future of Minewater heating in the UK

Small minewater heating schemes have already been successfully developed at different locations in the UK, e.g. at the Markham Colliery, Derbyshire, for heating the offices of Alkane Energy and at Dawdon, County Durham, where heat from mines is extracted for heating buildings at an existing Coal Authority pumping station. The potential for building a heating network for 150 homes using the minewater   from the former Caerau colliery, in the Llynfi valley, South Wales, is currently being investigated by Bridgend County Borough Council and the BGS. Similar investigations are underway in NE England, involving Durham University and local councils, looking at the potential of abandoned mines in for heating homes near Bishop Auckland and Spennymoor, County Durham.

BGS is also in the process of delivering the research infrastructure for the UK Geoenergy Observatory in Glasgow – a research facility equipped with the newest scientific technologies for investigating the potential of mines for heating homes and buildings. Glasgow was once home to some of Scotland’s biggest coalmines, which, post closure, have flooded with water of around 12°C in temperature. Scientists from across the UK will have access to the observatory and their research and experiments will yield a better understanding of how to harvest the heat in abandoned mines in the UK and elsewhere.

Considering that many UK towns and cities grew up around areas where coal was mined, there are many parts of the country that could benefit from this research and from further developing and applying this technology in the UK.