1334 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 Mine water is extracted from the La Nalona mine drainage. The project reports that sufficient flows have been available for decades, and an intermediate storage tank is included to stabilise the water supply. Indicative raw-water characteristics include pH 7.8–8, conductivity above 1,000 µS/cm, iron concentrations up to 7 mg/L, and notable dissolved ions (e.g., sulphates around 350 mg/L and magnesium around 55 mg/L), indicating the need for dedicated pre-treatment and purification before electrolysis. To meet the electrolyser manufacturer's requirements, the selected treatment train comprises preliminary solid filtration followed by reverse osmosis and electrodialysis (EDI). Annual mine-water consumption is estimated at 3,780 m³/year (approximately 630 l/h), with a nominal water requirement of about 1 m³/h to support electrolysis and associated operations. 3.4 Hydrogen storage, distribution and refuelling concept Hydrogen is compressed and stored at 500 bar to enable high-capacity distribution by tube trailers (a ‘virtual hydroduct’ approach). The project positions 500 bar distribution as an innovation in the Spanish context, enabling materially higher transported hydrogen volumes per trip compared with the prevalent 200 bar logistics chain. The engineering design includes fixed and mobile storage units at 500 bar, with two mobile and two fixed units, each sized at approximately 1,073 kg H₂. A 350-bar hydrogen refuelling station (HRS) is designed for heavy vehicles, with a minimum sizing for the consecutive filling of three buses per day. Hydrogen is supplied directly from 500 bar tube trailers; due to the pressure difference, neither on-site compression nor pre-cooling is considered necessary. 3.5 Sector coupling: district heating integration and gas-grid blending Heat recovery is implemented via a closed electrolyser cooling circuit. The cooling water demand is continuous, with a peak flow of approximately 75 m³/h and a maximum delta-temperature of 10 °C, enabling a thermal jump suitable for integration with the existing district heating chillers. A project study estimates total annual energy benefits of 3.9 MWh/year from the combined effect of recoverable heat, improved chiller performance and avoided electrolyser refrigeration. . In parallel, the concept includes blending a portion of the produced hydrogen into the existing natural gas grid, addressing both technical and regulatory learning needs in a context where harmonised
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