Removal of salt from seawater (desalination) is used to produce drinking water and water for irrigation in the Canary Islands, Spain. This is an energy intensive process.

The article ‘La importancia de los sistemas de recuperación de energía en la desalación de aguas en Canarias’ (The importance of energy recovery systems in water desalination in Canary Islands) by Baltasar Peñate Suarez and Sigrid Arenas (both of Departamento de Agua del Instituto Tecnológico de Canarias, ITC) on the IAGUA blog (in Spanish) describes how existing reverse osmosis (RO) salt removal systems with Francis turbines were retrofitted to be more energy efficient.

The two Sankey diagrams in the blog post visualize the energy flows before and after the retrofit. Energy consumption per cubic metre of water desalinated could be reduced from 3.65 kWh/m³ to 3.05 kWh/m³ by installing isobaric energy recovery devices and last generation membranes.

Check out the blog post to see both Sankey diagrams.

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