Ongoing global efforts to reduce greenhouse gas emissions and the associated need to enable the decarbonisation of most sectors of the economy are expected to lead to a significant increase in demand for renewable hydrogen, or green hydrogen. At the same time, current production capacities are very limited, as the economy and consumers need to be supplied with electrical energy from renewable sources in parallel. To meet this challenge, the ProHyGen project aims to develop a prototype floating hydrogen production unit for offshore areas outside the potential locations for conventional offshore wind farms. A wind turbine will generate the energy to split hydrogen from desalinated seawater directly on the floating platform. An innovative method of pressureless storage of the hydrogen, based on a liquid organic hydrogen carrier (LOHC), enables non-hazardous transport with slightly modified conventional tankers. This will create a self-sufficient, integrated green hydrogen production and storage facility that does not compete with locations for electric grid connected energy production and yet offers cost advantages over hydrogen production from other renewable energy sources.

LOHC technology allows the existing logistics of the petroleum industry, tankers, tank barges, tank farms and filling stations, to be used - and with lower hazard class standards. The hydrogen-rich LOHC is only hardly flammable, non-explosive, and classified in German water hazard class 2. On land, the hydrogen is separated from the LOHC again and is available as pure hydrogen.

 The TUHH sub-project aims to optimise the hydrostatic and hydrodynamic behaviour of the platform and to investigate the behaviour of the LOHC in the moving system.

 For the optimisation, the simulation method panMARE will be extended. This is a panel method in which the plant is represented by surface elements. Of particular interest in the investigation is the displacement of the LOHC between the tanks, which can have an influence on the motion behaviour of the whole plant. Based on the simulation results, recommendations for the layout of the LOHC tanks will be developed in order to optimise the floating position and stability. The dynamic behaviour of the entire system under extreme conditions and the influence of damage events will also be investigated. During the refuelling process with LOHC, large and relatively rapid changes in the floating position can occur, under which the system must continue to operate. With the help of the numerical model to be developed, the system will be scaled up to a nominal power of 15 MW from a hydrodynamic point of view.

In the second part of the project, which will run in parallel, the flow processes in the LOHC hydrogenation reactor will be investigated, including the movements of the platform in the seaway. The results will make it possible to evaluate the efficiency of the LOHC hydrogenation reactor on the floating platform. The results of the project will provide further impulses for research.

CRUSE Offshore GmbH (COG) is involved in the design of the entire facility and the integration of the individual components. The development, for which the company has applied for a patent, is being supported by the Technical University of Hamburg in the field of offshore technologies, and by the Friedrich-Alexander University of Erlangen-Nürnberg for the storage of hydrogen in the LOHC. All installed series components of the suppliers have at least Technology Readiness Level (TRL) 7 for onshore operation. CRUSE Offshore GmbH has compleaded TRL 4 for the floater and plans to build a 5 MW prototype with components optimised for offshore use, followed by a 15 MW version for GW offshore H2 farms. The technologies have been adopted from the offshore oil industry and offer the possibility of a smooth transition from fossil to renewable energy using a liquid energy source in an industrial scale. COG is planning several GW offshore H2 farms at suitable European and international locations.

LOHC hydrogen storage technology is a well-studied and now commercialised field of knowledge. However, the LOHC hydrogen storage plants currently in operation are all designed and built for onshore operation, usually stationary. Operating these plants on a floating, moving platform in offshore conditions requires adjustments to the plant design, which CRT is undertaking. Further development of LOHC technology is therefore taking place in the following areas:

• Movement of the plant, in particular influencing fluid flows in the reactor.

• Thermal integration of hydrogenation with other plant components, e.g. desalination

• Fault-tolerant and low-maintenance plant design

The current state of research on fluid flow over a tilted or moving catalyst bed shows significant negative effects on reactor performance. In this project, performance data will be recorded on a moving reactor as a function of the type and magnitude of movement. If necessary, countermeasures will be derived from the results. This experimental work will be supported by CFD simulations performed at the TUHH. In further work packages, the basic parameters (e.g. reactor size, cooling requirements, etc.) of a hydrogen storage system with LOHC for the targeted power range of an offshore wind power plant will be determined. Based on these key findings, the rough design of the LOHC plant will be carried out and finally the system integration of the hydrogenation reactor with the other components such as seawater desalination and electrolysis will be performed.

The offshore hydrogen generator to be developed in the joint project is intended to convert the electrical energy generated by wind power into green hydrogen while being decoupled from the power grid on the mainland. For this purpose, an electrical system is required on the platform that is capable of supplying all connected consumers with electrical power according to their requirements. This electrical system will be developed and planned in the subproject of the partner RENK.

Since the wind turbine supplies electrical energy with variable frequency and the electrolyser, as the largest consumer, requires direct current, an on-board power supply system with a DC intermediate circuit is suitable for the platform. This concept, which has been tested on ships, has to be further developed for the offshore H2 generator in order to take into account the aspects of fluctuating power supply from the wind turbine and autonomous operation. Subsequently, the electrical system will be adapted for scaling up to 15 MW nominal power as planned in the joint project.