Green hydrogen is considered to be an important energy carrier of the future, but its production lags behind the requirements. A demonstration plant is now showing that biogas from liquid manure and plant residues can also be a worthwhile starting material for high-purity hydrogen. Thanks to a special chemical process, this conversion achieves an efficiency of 75 percent and is also competitive in terms of costs, as researchers report.
Hydrogen produced on the basis of renewable energies is considered to be a beacon of hope in the energy and mobility transition, but is currently not yet suitable for the masses. The production of the gas by electrolysis of water with the help of electricity from wind or sun is only in its infancy. Most of the hydrogen required has so far been obtained almost exclusively from fossil fuels – three-quarters from steam reforming from natural gas, but also from coal or petroleum components.
Steam, biogas and iron oxide
But there is another way of doing things, as a team led by Viktor Hacker from Graz University of Technology and employees of the Graz start-up Rouge H2 Engineering found out. You have developed and optimized a chemical process by means of which high-purity hydrogen can be generated from biogas. In this chemical looping process, the methane-rich biogas from liquid manure, plant residues and other biomass is first mixed with water vapor. So-called steam reforming produces synthesis gas – a mixture of carbon monoxide and hydrogen. Iron oxide as a reaction aid increases the proportion of hydrogen obtained. The result of the process is hydrogen with a purity of 99.998 percent.
The research team has been testing how efficient this looping process is in practice since summer 2021 with one of the world’s largest industrial demonstration systems on the site of the South Styrian Ökostrom Mureck GmbH. “The option that our biogas also generates green hydrogen for sustainable mobility in addition to electricity is of course extremely exciting for us,” says Managing Director Karl Totter. The ten kilowatt system branches off around one percent of the biogas flow – around 30 liters per minute and uses it to generate hydrogen.
Efficient and comparatively cheap
“We are showing that a chemical looping system can be integrated into an existing biogas plant. High-purity hydrogen for fuel cells is produced from real biogas, and not just in the laboratory, but actually on an industrial scale, ”explains Hacker. The first results of the test operation are promising: the iron-steam process achieves an efficiency of 75 percent. “If instead of the one percent we were to route the entire biogas flow from the Mureck biogas plant through a correspondingly scaled-up chemical looping plant, we would even have a three-megawatt hydrogen production plant,” explains Rouge H2 project manager Gernot Voitic.
According to the research team, the technology is now ready for commercial use. “We can also produce decentralized hydrogen from real biogas on a large scale. All it takes is a little space for our system, ”says Voitic. According to the researchers, this decentralized production of hydrogen could also help to make hydrogen cheaper. “Hydrogen is currently offered at the filling station at ten euros per kilogram. The techno-economic analyzes that are part of our research project forecast a competitive hydrogen price of five euros per kilo for decentrally produced hydrogen for our process. This makes the process competitive with other technologies such as electrolysis, ”says Hacker.
Source: Graz University of Technology