High-Purity Hydrogen Obtained Directly From Biogas for First Time

Green hydrogen is seen as a beacon of hope for the energy and mobility transition, but it is not yet suitable for the masses. There are mutliple reasons for this. Hydrogen is currently mainly produced centrally from fossil raw materials. It then has to be compressed or liquefied in an expensive and energy-intensive process in order to be delivered to petrol stations, for example. There, an expensive infrastructure with high investment costs is required to store large amounts of hydrogen.

For a nationwide hydrogen supply, decentralized production will therefore be indispensable in the future, ideally climate-neutral from locally available renewable energy sources. In 2020, researchers at the Graz University of Technology (TU Graz) led by process engineer Viktor Hacker and the Graz start-up Rouge H2 Engineering presented a sustainable process for decentralized hydrogen production, the so-called "chemical looping hydrogen method". The research results, which have received multiple awards, have resulted in a compact on-demand system on site that can produce hydrogen from biogas, biomass or natural gas.

Hacker and his team are now causing a stir again. This time with regard to the concrete results from the ongoing Biogas2H2 project. In one of the world's largest industrial demonstration plants, they produce high-purity hydrogen directly at an existing biogas plant from real biogas, which contains all of the impurities contained in the gas. The project is funded by the Austrian Research Promotion Agency FFG.

Hydrogen from biogas in southern Styria

“We show that a chemical looping system can be integrated into an existing biogas plant. High-purity hydrogen for fuel cells is produced from real biogas not only in the laboratory, but even on an industrial scale, ”explains Viktor Hacker from the Institute for Chemical Engineering and Environmental Technology at Graz University of Technology. The actual biogas - methane gas from pig manure, glycerine phase, silage maize and grain residues - comes from the South Styrian Ökostrom Mureck GmbH. There they are very interested in this additional mainstay. The option of generating green hydrogen for sustainable mobility in addition to electricity from biogas is of course very exciting, says Managing Director Karl Totter.

Rouge H2 Engineering and Graz University of Technology installed the demonstration system on the company premises in Mureck in the summer of 2021 and it will be in operation for test purposes until the end of October. The 10 kilowatt system diverts around one percent of the biogas flow (around 30 liters per minute) and mixes it with steam. The mixture flows into the plant's reactor. There the biogas is reformed and synthesis gas is produced. This gas then reduces iron oxide to iron. Steam then enters the reactor which reoxidizes the iron back to iron oxide. This releases hydrogen with a purity of 99.998 percent.

Ready for commercial use

This iron-steam process achieves an efficiency of 75 percent. "If we were to use the entire biogas flow from the Mureck biogas plant (approx. We are therefore open to orders from the biogas industry with immediate effect, "emphasizes Rouge H2 project manager Gernot Voitic.

This type of decentralized production also has a positive effect on the production price and thus on the purchase price of hydrogen. Hacker adds: “At the moment, hydrogen is offered at the filling station for 10 euros / kg. The technical-economic analyzes as part of our research project forecast a competitive hydrogen price of 5 euros / kg for decentrally produced hydrogen from our process, making the process competitive compared to other technologies such as electrolysis (5-12 euros / kg hydrogen).

The problem of pressure

The technology has proven itself and can also be easily integrated into an existing biogas plant. However, important questions about nationwide availability are still open. These include: What should happen to the hydrogen in the future? And: who takes the first step?

The idea of ​​installing a hydrogen filling station in addition to the system for generating hydrogen from biogas is obvious. The crux of the matter, however, is that hydrogen vehicles currently have to be refueled at 700 bar pressure "in order to get as much hydrogen as possible in the smallest possible tank and thus achieve an attractive range," explains Viktor Hacker. The chemical looping system produces hydrogen at a pressure of up to 100 bar, which is comparatively high, but not sufficient for refueling. Compressing the hydrogen to 700 bar is tricky and expensive. “This compression has to take place somewhere, either directly at the production site or at the latest at the filling station, which of course could also be supplied with bottled hydrogen. There are costs, and that brings us back to the pump price. "

This compression is not technically necessary: ​​In principle, fuel cell vehicles can also drive with a pressure of only 2 bar - just not very far. Decentralized hydrogen generation directly at biogas plants is ideal for shorter distances, for example for hydrogen tractors (which are currently not even available on the market) or for hydrogen-powered storage vehicles such as forklifts.

Further options for using hydrogen “from the biogas plant” would be filling it into gas bottles for onward transport, laying hydrogen lines directly in apartments equipped with fuel cells or using it in industrial processes. For Karl Totter, senior and junior, the path for Ökostrom Mureck GmbH is very clear: “We could very well imagine using our biogas to produce hydrogen and expanding our location with a corresponding plant. But someone has to buy the hydrogen from us. The demand side still has to move a little so that we can take this investment step. "

For hydrogen research at TU Graz, it is no longer about the specific application of the technology - this is where Rouge H2 Engineering comes into play - but about its further development. Specifically, the Acceptor project (funded by the Austrian Science Fund FWF) started in September 2021, in which Hacker and his team will focus on the extendable service life of the iron-based material in the reactor.

This article was republished from the following materials. Note: The material may have been edited for length and content. For more information, please refer to the source cited.

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