© istock.com / Le Manna
The energy transition and the nitrogen oxide problem do not stop at the railways. Many lines in Germany are not electrified, especially in local traffic. Therefore, diesel locomotives cannot easily be replaced by electric locomotives on these routes.
More than 40 per cent of the German railway network is not yet electrified1 and even on some electrified sections diesel vehicles run due to the line layout. In many other European countries, such as Switzerland or Austria, diesel trains are almost extinct or the exception. A large part of the non-electrified rail network in Germany will not be passable by electric locomotives in the future, especially since a collective electrification is very cost- and time-intensive. Battery-electric locomotives, on the other hand, do not achieve the required range. For these routes, hydrogen-powered trains are the obvious choice. These run completely pollution-free - and even CO2-neutral if the hydrogen comes from renewable sources.
But for refuelling the trains with compressed hydrogen or cryogenic liquefied hydrogen, a completely new infrastructure would have to be built at the supply stations. This is where the advantage of LOHC technology comes into play.
Advantages of LOHC technology
LOHC stands for "Liquid Organic Hydrogen Carrier", a liquid organic hydrogen carrier. A LOHC is an oil-like liquid that can be charged with hydrogen and also discharged again. The hydrogen released during discharge can then be converted into electricity using a fuel cell. With this organic carrier fluid, it is possible to maintain the existing infrastructure of diesel tank containers as far as possible. The storage and delivery of larger quantities of fuel would also be possible without restriction with LOHC technology, irrespective of safety aspects that need to be taken into account with elemental hydrogen.
How does LOHC technology work?
The organic carrier liquid ("Liquid Organic Hydrogen Carrier") serves the researchers as a kind of liquid deposit bottle for hydrogen. Just one litre binds over 650 litres of hydrogen.
In terms of its handling and physical properties, the oily substance is quite similar to conventional fuels and can be easily transported by tankers and trains. In principle, hydrogen filling stations can also be supplied with hydrogen, which can then be used to refuel hydrogen trains, such as the Coradia iLint from Alstom, which is approved for public transport in Germany.
HI ERN researchers go one crucial step further in this project
"While the LOHC technology is already successfully operated in laboratory setups and has been scientifically published, the operation on the mobile platform is now to be demonstrated," explains sub-project leader Julian Kadar. "For this purpose, a LOHC system in ISO container design is being developed, which achieves the release of hydrogen and its conversion into electricity in a fuel cell during driving operation in conjunction with a commercially available electric locomotive." The aim is not only to achieve a high power density. For mobile use, release devices are needed that react well to dynamic load changes, for example before starts and climbs, when particularly high power - and correspondingly high amounts of hydrogen - are needed.
Direct LOHC fuel cell in focus
In addition to catalytic on-board dehydrogenation, the researchers are also pursuing a particularly innovative approach: the development of a direct LOHC fuel cell for mobile applications. The direct fuel cell generates electrical energy directly from loaded LOHC. An additional apparatus for the catalytic release of the hydrogen gas on board the train would then be unnecessary. The first prototypes of direct LOHC fuel cells are already being operated in the HI ERN laboratories, and the results are very promising.
The research project aims to further develop the direct LOHC fuel cell, to develop a mobile train demonstrator based on LOHC technology and to develop a pathway for the production of the fuel additive OME (oxymethylene ether) from biogenic raw materials.
The large development project is intended to deepen the scientific-technological basis for new technologies such as the direct LOHC fuel cell and to develop all essential process steps for a mobile train demonstrator. This train demonstrator is to show technological options for emission-free rail transport in Bavaria based on hydrogen as a fuel, but without having to store and handle hydrogen in elementary form under high pressure or at very low temperatures and in expensive special infrastructures at Bavarian railway stations.
The project builds on the findings of a small research project ("New options for the economic operation of hydrogen trains using LOHC technology", 2017) and a separate preliminary project ("Operation of hydrogen trains in the Bavarian Oberland using on-board LOHC technology", 2018-2020). It deepens the successful preliminary work carried out there and transfers the fundamental findings obtained into a targeted technological development for the planned train demonstrator. The demonstrator project started in January 2019 with a duration of five years. The train project also aims for intensive cooperation with industry, which is already showing great interest in HI ERN's new concepts. At the beginning of January 2018, the Bavarian state government adopted the Bavarian Electromobility Strategy Rail - known as BESS for short - which envisages testing the practical suitability of these trains in the state's local rail passenger transport with a pilot project if the approval is successful.
The Bavarian State Ministry for Economic Affairs, Energy and Technology has provided funding of 28,6 million euros for the project.
1 Source: https://www.allianz-pro-schiene.de/themen/infrastruktur/elektrifizierung-bahn/ (11.05.2023)