So far, green waste and sewage sludge have mostly been composted or burned. It would make more sense to obtain the valuable energy carrier hydrogen from this. This is the goal pursued by a team of researchers at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA. The CO2 produced during the production of hydrogen from waste is captured and used, for example, as a raw material in the chemical industry. In this way, the researchers produce hydrogen with a negative CO2 footprint from the biowaste using different processes. CO2 is thus removed from the atmosphere.
Organic waste is available in large quantities in this country. According to the Federal Environment Agency, Germans collected around 4.6 million tonnes last year in their brown tonnes alone. In addition, there is waste from public parks and gardens, from agriculture and food production, as well as sewage sludge and food residues from canteens – a total of a good 15 million tonnes. The majority ends up in composting plants or is burned to generate heat and electricity. This produces carbon dioxide (CO)2-)Emissions that harm our climate. “But the biowaste is far too bad for that,” says Johannes Full, head of the “Sustainable Development of Biointelligent Technologies” group at Fraunhofer IPA in Stuttgart. It would make more sense to produce hydrogen from the material and the resulting CO2 to be separated, stored or used in the long term.« Hydrogen is considered the clean energy carrier of the future. When burned, only water is released. However, hydrogen is currently produced to a large extent from natural gas. Like electrolysis with renewable electricity, production from plant residues would be much more climate-friendly.
Reducing carbon dioxide levels in the atmosphere
Various processes for the conversion of biomass into hydrogen have been developed in recent years. Johannes Full and his colleagues have analyzed which processes are technically mature and can be operated economically in the future. The new methods are also intended to iron out a weakness of conventional bio-waste management: No matter whether biomass is composted or incinerated, carbon dioxide is always released, which the plants have previously absorbed from the air via photosynthesis. It would make more sense to collect the greenhouse gas from the plants and use it as a raw material in the chemical industry or to store it in the soil in disused natural gas fields. “That’s how we kill two birds with one stone,” says Full. “We help to reduce the carbon dioxide content in the atmosphere and produce green hydrogen from the plant residues.”
Making full use of biomass
A project carried out by Fraunhofer IPA at a company in the metal industry shows how this works. There, waste from fruit and wine growers from the surrounding area, cardboard boxes and waste wood as well as canteen waste can be converted into hydrogen. This is then used directly in metal processing. For this purpose, the fruit residues and canteen waste are first fermented with the help of bacteria in dark containers, producing hydrogen and carbon dioxide. Subsequently, the fermented mass can be fermented into methane in a conventional biogas plant, which also leads to hydrogen and CO2 is converted. Wood and paper fibres, on the other hand, are difficult to ferment. You can use CO in a wood gasifier2 and hydrogen. Fraunhofer IPA compares the various process options in order to support the selection of suitable and as efficient as possible technologies and derives technical optimization approaches in order to save costs and produce as environmentally friendly as possible.
Purple bacteria as producers of hydrogen
Purple bacteria produce hydrogen from fruit and dairy waste particularly diligently. Researchers at the University of Stuttgart have succeeded in modifying the bacterium in such a way that it hardly needs any more light, which makes hydrogen production energy-saving. Together with Fraunhofer IPA, they are investigating how the production of hydrogen with the purple bacterium can be operated economically on a larger scale in the future. In the H2Wood – BlackForest project, the Fraunhofer IPA team is also working together with the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB on how wood waste can be microbially broken down into hydrogen and other valuable molecules for the chemical industry. Further project partners are Campus Schwarzwald and the University of Stuttgart, Institute for Industrial Manufacturing and Factory Operation IFF.
Study »Industrial Hydrogen Hubs in Baden-Württemberg«
The fact that green hydrogen has the potential to cover the energy needs of industry and heavy transport regionally is demonstrated by the study “Industrial Hydrogen Hubs in Baden-Württemberg” – I-H2-Hub-BW for short – by Fraunhofer IPA. The result: Decentralized hydrogen production and use pay off if the distribution centers, English hubs, are strategically placed correctly. The green electricity is used to operate the electrolysers in the hubs, which split water into hydrogen and oxygen. In order to avoid transport costs, the hubs must be close to the consumers. The second important criterion for the choice of location is therefore the demand of the local industry for process heat, high-temperature processes and hydrogen gas, for example for the production of nitrogen fertilizers. The infrastructure is also crucial: “Ideal locations are located near busy roads with truck depots where hydrogen filling stations can be set up,” says Dr. Jürgen Henke, scientist at Fraunhofer IPA. With the help of the location criteria, the research team around Henke in Baden-Württemberg was able to identify possible locations – above all the Rhine-Neckar metropolitan region and the greater Karlsruhe area. Computer simulations at Fraunhofer IPA show that regionally produced green hydrogen can replace 30 percent of fossil energy within ten years, and only if the state’s own open spaces are used.