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Hydrogen-based fuels – the path to a clean future?

Why do we need hydrogen?

Climate change represents one of the greatest challenge humanity is facing. We need to find ways to reduce and, in perspective, eliminate CO2 emissions. Apart from extracting carbon dioxide from the exhaust gas of conventional fossil fuel plants, the only way to do this is to completely abandon fossil fuels. The potential of globally usable renewable energy sources easily exceeds the combined global energy demand of all sectors many times over. However, it is problematic that the distribution of renewable generation capacities only corresponds to a limited extent to the distribution of the places of use. The direct connection between the place of generation and the place of use is only possible to a limited extent, in some cases it is not even feasible or involves extreme losses.

One possible solution to this problem is the storage of electrical energy in the form of chemical energy. The simplest and at the same time cleanest variant is the electrolysis of water to obtain hydrogen and oxygen. The hydrogen can then be transported directly or preferably in the form of a substance produced from it (e.g.: ammonia, LOHC) to its destination, where it can be used in a variety of ways. Transport by pipelines or special ships can offer advantages over direct transmission of electrical energy by high-voltage direct current or alternating current lines even for medium distances of a few 1,000 kilometers, and also enables worldwide distribution of the bound green energy from the production sites to the consumption centers.

Current situation and challenges of H2 production, storage and use

Hydrogen is an important raw material in many industrial and chemical processes and as such is already in use worldwide. However, production is currently usually carried out using fossil fuels, predominantly natural gas, as the associated costs are currently much lower than in the case of production using renewable energy. A large part of the hydrogen produced is manufactured in close proximity to the location where it is used; accordingly, there are only local distribution networks and practically no infrastructure for long-distance transport. The only exception are some pilot projects, in which the validity of pipeline systems for distances < 100 - 200 km is investigated. The project "Lingen - GET H2" in Emsland can be mentioned as an example. The maritime transport of hydrogen is also limited to some pilot projects. One of these projects is the "SUISO FRONTIER" to be completed in 2020 by Kawasaki Heavy Industries, which will transport about 1,250 m³ LH2 at - 253 °C (~ 90 t) from Australia to Japan.

Basically, it must be stated that the transport of hydrogen is associated with considerable challenges. Small-scale solutions, as in the case of road vehicles, face major challenges, due to considerable losses in range or utility value and, in addition, permanent boil-off losses in the case of cryogenic storage.

Currently, the use of hydrogen-based fuels is a niche solution. After several attempts by the automotive industry to use hydrogen in combination with fuel cells and combustion engines over the past decades, only a few models from Asian manufacturers are currently available on the market. Market penetration is extremely low and the filling station network, most of which offers compressed hydrogen is very thin. In addition, besides some efforts to convert gas-fired power plants and steel mills, pure hydrogen is used in the energy and transportation sectors only in some military submarines and small ships. In personal transportation, direct use of electrical energy, using battery storage, has almost completely taken over the green mobility market.

Future scenarios

Does the future belong to liquid hydrogen, compressed hydrogen, ammonia, LOHC or synthetic fuels? In which form is uncertain, but it is certain that hydrogen-based fuels will play a decisive role on the way to CO2 neutrality. The fundamental difficulties of direct hydrogen use are already known and face such obstacles that the use in individual and air traffic does not appear to make sense at least in the short term. It is in these areas that synthetic fuels represent a drop-in solution as a replacement for existing fossil-based fuels such as gasoline, diesel and kerosene. Using green hydrogen and carbon dioxide extracted from exhaust gases, CO2-neutral operation of these sectors is possible and already technically feasible. Only the currently still high production costs prevent a rapid increase in market share.

Due to its simple production and relatively low costs and requirements in the areas of storage and use, ammonia is suitable for propulsion in marine applications in the short and long term. Ammonia is capable of completely eliminating carbon dioxide emissions from this sector. Furthermore, especially in comparison to the currently predominantly used heavy fuel oil, practically all other emissions can be eliminated completely or in large parts.

One of the biggest tasks is the long-distance transport of green energy from the predestined production regions, for example Australia, North Africa and the windy regions of southern South America, to the consumer regions in Asia, Europe and North America. LOHCs and ammonia are candidates for this task because of their relatively high volumetric energy density, low transport loss, and ease of storage.

Liquid and compressed hydrogen are only suitable for local applications and niche solutions with special framework conditions due to their low volumetric energy density, high technical requirements and, in the case of liquid hydrogen, transport and storage losses. Individual transport, aviation and shipping as well as energy transport are not sensible areas of application for compressed or cryogenic hydrogen.

Plans of FVTR and the University of Rostock

The Chair of Technical Thermodynamics (LTT) and FVTR GmbH do not see this change as a threat to the comprehensive, existing expertise, but primarily as an opportunity to open up new research fields and to help shape the future of mobility and energy supply.

With Prof. Dr.-Ing. habil. Karsten Müller, who has been in office since October 2020, the LTT has been able to recruit an absolute expert in the field of hydrogen-based energy carriers as chair. In his scientific career, Professor Müller has dealt extensively with the subject area and is one of the leading researchers in Europe, particularly in the field of LOHC (liquid organic hydrogen carriers). Accordingly, LOHC as a safe and technically manageable energy carrier will be a focus of the planned activities. How does the energy get from the source to the end user? Is a combination of different energy carriers a valid option for different links in the supply chain to combine the respective benefits? Which fuel is best for personal transportation and which for shipping? The LTT team and its partners will be working intensively on these and other questions in the coming years. Currently, initial investigations are already being carried out with regard to thermophysical material data in order to create a reliable basis for later applications. Further steps are in various planning phases and will form a solid basis for working on this complex of topics.

The FVTR GmbH is currently working together with the sister chair of the LTT, the Chair of Piston Engines and Combustion Engines (LKV) on several projects for the use of hydrogen and ammonia in engine applications. For this purpose, a corresponding hydrogen infrastructure has already been installed. Further measures, such as the conversion of an engine to pure hydrogen operation, are being implemented or are in advanced planning stages. The theoretical aspects of the overall complex of hydrogen-based fuels have already been examined in detail in several studies for customers from industry and research. In addition, there are very concrete intentions to build and operate an ammonia-capable single-cylinder research engine. This work will be undertaken by LKV, and FVTR will contribute to this step by developing design tools for ammonia combustion processes.

Conclusion (need for action, financing scenarios, etc.)

Global emissions of carbon dioxide, and in particular those from fossil sources, must be significantly reduced. Fuels and chemical energy storage systems based on regeneratively produced hydrogen can make an important contribution to this. While the use of pure hydrogen is only relevant in niche areas, LOHCs and ammonia, as well as synthetic fuel, can replace fossil fuels in virtually all applications and also act as chemical storage systems to transport renewable energy from producer regions to the world's main energy markets. While the future of the use of green hydrogen and the secondary materials produced from it is already considered a safe scenario in some cases, the necessary need for research in wide areas between the scientific fundamentals and industrial application must not be underestimated. Only through timely and targeted funding in this field can Germany and Europe be at the technological forefront of hydrogen-based fuels and energy carriers and, on the basis of the newly developed technologies, achieve the CO2 reduction targets they have set themselves.