Within the framework of the lead project H₂-Mare and its subproject PtX-Wind, the theoretical electrolysis of water and the subsequent synthesis of hydrogen into a chemical energy carrier are being investigated. The overarching objective is to convert the generated hydrogen into a compound that is easier to transport and can later be used either for re-electrification or for industrial purposes. The energy required for the process is to be provided entirely from renewable sources, with the project focusing exclusively on offshore wind power due to its high availability and reliability in the North Sea.
One of the central challenges associated with offshore hydrogen production is the continuous supply of freshwater. Since seawater cannot be fed directly into electrolyzers, appropriate desalination processes must be implemented. For this reason, different desalination technologies are considered within the project. Alongside the state-of-the-art process of reverse osmosis, more recent approaches such as membrane distillation are also evaluated. Particular emphasis is placed on air gap membrane distillation (AGMD) and reverse osmosis, which are not only studied experimentally but are also intended to be represented through mathematical modeling and simulation. In addition, electrodeionization (EDI) is highlighted, providing chemical-free, continuous water purification and ensuring a stable supply of high-purity water to the electrolyzers.
The interdependence of the management of water and energy is noted to date but not specifically addressed. While fresh water resources worldwide are already being overexploited, the global (green) energy transition will place additional stress on their recharge ability due to an increased application of PtX technologies. By deriving open-access models for various applications of the green hydrogen value chain, we aim to secure a fast but water-smart and sustainable energy transition.
DECHEMA has bundled various aspects of the energy transition with regard to water management in the Water-for-X roadmap.
An Electrodeionization (EDI) system is a technology for producing high-purity water that combines ion exchange and electrodialysis. In this process, dissolved ions are captured by mixed-bed ion exchange resins and continuously removed through selective cation and anion exchange membranes under an applied electric field. This electrical regeneration allows the resins to function continuously without the need for chemical regeneration using acids or caustic solutions. EDI units are typically installed downstream of reverse osmosis systems to polish water to ultrapure levels, achieving conductivities as low as 18.2 MΩ·cm. They are widely used in industries requiring ultrapure water, such as semiconductor manufacturing, pharmaceuticals, and power generation, due to their efficiency, environmental friendliness, and ability to operate continuously.
Figure 1: Schematic of an EDI cell [1]
src/Electrodeionization_R2024b.slx (MATLAB/Simulink Ver. 2024b)
[1] Numerical simulation of the electrodeionization (EDI) process for producing ultrapure water, Lu et al. (2010), doi:10.1016/j.electacta.2010.07.054
[2] Continuous Electrodeionizatio, Jonathan H. et al. (2019), Desalination 2nd Edition, (287–328)
[3] Production of ultrapure water by continuous electrodeionization, Jonathan Wood (2009), doi:10.1016/j.desal.2009.09.084
[4] Electrodeionization: Principles, Strategies and Applications, Lucia Alvarado(2014), doi:10.1016/j.electacta.2014.03.165