1 31 2. POST-MINING ASSET VALORISATION AND CIRCULAR-ECONOMY LOGIC MINE-TO-H2 is designed around a circular-economy logic that treats mine-closure “problems” as inputs for new energy services (Krzemień et al., 2023). The project explicitly leverages the competitive advantages of underground and open-pit mining environments, proposing that mine water and reclaimed land can serve as resources for hydrogen and photovoltaic energy generation, respectively. Beyond H2 production, the project emphasises sector coupling as a pathway to maximising local value creation, as noted by Ramsebner et al. (2021). Two coupling routes are embedded in the design: (i) hybridisation with an existing geothermal district heating system through electrolyser heat recovery, and (ii) partial blending of hydrogen into existing natural gas infrastructure, enabling a gradual and modular transition with reduced need for new pipelines, following the synergies pointed out by Brown et al. (2018). The concept is complemented by supporting measures intended to strengthen regional capabilities and facilitate replication: benchmarking other coal mines, developing business cases, and training and re-skilling programmes for former miners and coal-region stakeholders. 3. CASE STUDY: MINE-TO-H2 DEMONSTRATOR AT POZO FONDÓN 3.1 Site and strategic location The demonstrator is located at the Pozo Fondón mine site in Sama (Langreo, Asturias, Spain), a central position where a high share of the regional population and industrial activity are concentrated within a radius of approximately 60 km. This site supports the intended mobility application and reduces distribution distances for early hydrogen uptake. 3.2 Process configuration and design bases The plant is designed as an integrated process chain consisting of: raw mine-water extraction and intermediate storage; water treatment; PEM electrolysis; hydrogen purification; multi-stage compression; and storage/distribution in 500 bar tube trailers. The electrolysis package is specified at 2.5 MW and designed to deliver approximately 500 Nm³/h of high-purity hydrogen (99.998%, UNE-EN 17124:2022) at an outlet pressure of around 30 bar. A process simulation has been used to validate the design's internal consistency. The model represents a 2.5 MW PEM system operating at 550 V with 289 cells in series, assuming an overall efficiency of 90%. Hydrogen production is estimated at approximately 49.5 kg/h at 30 °C and 30 bar after purification, while a substantial fraction of input power is dissipated as heat, requiring cooling. 3.3 Mine water as feedstock and treatment requirements
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