Geothermal district heating network in Mieres
Overview
Mieres, a municipality of around 46,000 inhabitants in the autonomous community of Asturias, northwest Spain, has a rich history deeply related to coal mining. However, the closure of coal mines in recent years posed significant challenges for the community.
The Hunosa Group, a Spanish company based in Asturias, has risen to the challenge of transforming from a mining-focused entity to a champion of sustainable energy generation, with a strong emphasis on local renewable resources.
One of the standout initiatives in this transformation is the Pozo Barredo geothermal project. Born from the closure of the Barredo shaft in 1995, this project addresses the high economic and environmental costs associated with maintaining water pumping activities in inactive wells. By harnessing geothermal energy from these old mines, the project not only mitigates these costs but also provides a sustainable energy solution for the future.
From coal mines to geothermal plant: innovative solutions to old problems
The Asturian coal mines serve as a vast underground reservoir, filled with water from over a century of intensive extraction activities in the Central Carboniferous Basin of Asturias. This extensive mining infrastructure created a network of fissures and cavities that increased water infiltration, necessitating continuous pumping to manage the flow.
When mining operations ceased and pumping stopped, natural flooding occurred, filling the created spaces, fissures, and pores with water. Controlled flooding continues until a minimum safety level is reached, after which constant water pumping is essential to prevent potential issues.
Collaborative studies with the University of Oviedo led Hunosa to discover the geothermal potential of these mine waters. This innovative approach exemplifies the circular economy by transforming a challenge into a sustainable resource, generating new employment opportunities and economic benefits for the entire community.
Investment history
Initial Phase:
The commencement of the geothermal project utilizing water from the Barredo Well, spearheaded by Hunosa, commenced in 2006 with preliminary studies and the establishment of the first two geothermal facilities. These facilities were dedicated to providing both heating and cooling to two key structures: the Vital Álvarez Hospital and the Research Building of the University of Oviedo on the Barredo Campus. Operational since 2014, these installations marked the onset of the project's implementation. Subsequently, in 2016, a third facility was introduced at the headquarters of the Fundación Asturiana de la Energía (FAEN), repurposing a renovated building that once served as the compressor room for the same well. Each of these three installations, developed independently, entailed an investment of approximately €1.5 million, collectively yielding a total power output of 4 MW.
Subsequent Phase:
At the end of 2018, construction commenced on the new geothermal heating district, "Pozo Barredo," leveraging water sourced from the Barredo Colliery. By May 2019, the construction concluded, marking the conclusion of the project's second phase. The newly established geothermal facilities are capable of servicing three distinct circuits: two operating at high temperatures, serving the Escuela Politécnica de Mieres and the Bernaldo de Quirós high school building, alongside another circuit operating at lower temperatures, catering to buildings M9 and M10 Vasco Mayacina, collectively accommodating 245 dwellings. In this subsequent phase, the newly installed facilities boast a capacity of 2 MW. When combined with the 4 MW output from the preceding installations, this brings the total power of the entire network to 6 MW.
In 2018, to ensure the feasibility of the second phase, Hunosa secured €500,000 in grants through its successful participation in a call for proposals co-funded by the European Union via the European Regional Development Fund (ERDF). The aim of this initiative was to promote the transition to a low-carbon economy across all sectors, with backing from the Ministry of Employment, Industry, and Tourism of the Principality of Asturias. The total expenditure for this second phase amounted to approximately €1.4 million.
To further solidify the project's sustainability, Hunosa directly negotiated billing rates with clients, offering a compelling 10-15% discount compared to their previous rates when using natural gas.
Technical details
The extraction of mine water is facilitated through two submersible pumps, collectively boasting a capacity of 2 MW, situated within the vertical shaft of the mine. Leveraging the temperature of the water pumped at 23°C, the heat pumps have the capability to elevate water temperatures to as high as 85°C with favorable COP ratios, thereby enabling seamless integration across diverse building types. Each pump is equipped with a nominal flow of 330 m3/h and a power capacity of 83 kW.
These newly established facilities operate devoid of greenhouse gas emissions, resulting in an annual reduction of 653 tons of CO2 emissions. Notably, this project stands as Spain's largest geothermal district heating initiative and represents the inaugural endeavor to implement a centralized generation system utilizing geothermal mine water within a heat network framework.
The positive impact on the historical heritage
The Pozo Barredo geothermal project has also served as an opportunity to preserve and renovate a building of great industrial heritage and historical value, without modifying the architectural typology of the original construction and maintaining also the old equipment. This old building, that was previously hosting the coal extraction machines of Barredo Colliery, is now being used as the generation room where the heat pumps are placed.
Summary
Total length of wells: 350-meter flooded well
Geothermal power: 6 MW (4 MW for the first three buildings + 2 MW for the district heating network extension of 2018)
Temperature of the water drawn: 23 degrees
Units covered: Two units from 2014: Vital Álvarez Hospital and the Research Building of the University of Oviedo on the Barredo Campus. One additional unit from 2016: the headquarters of the Fundación Asturiana de la Energía (FAEN). Four additional units from 2019: the Polytechnic School of Mieres of the University of Oviedo, the Bernaldo de Quirós Secondary Education Institute and the buildings M-9 and M-10 (totalling 248 dwellings) of the new Vasco Mayacina residential area.
Total amount of investments: €2.9 million circa (€1.5 million for the first phase + €1.4 million for the second phase)
Public contribution: €500.000 of grants (ERDF competition in 2018 in relation to the second phase of the project)
CO2 emissions avoided: 653 tons of CO2 per year
Savings in customers’ bills: 10/15% difference in comparison to the prices the clients previously had using natural gas.
Sources:
“Barredo Colliery” District Heating | Mieres, Asturias, Spain
Noel Canto Toimil, Head of Department Innovation at Hunosa, during the online webinar Large heat pumps in district heating: a winning team to REPower EU!, organised by Euro Heat & Power on 13 December 2022.