P2G takes a step forward in Germany
In a pilot exercise, the Fraunhofer Institute for Wind Energy and Energy System Technology has succeeded in utilizing the power-to-gas process in small biogas plants. Biogas with a methane content of over 90 percent can be produced specifically for power production, with the elimination of complicated steps in the process.
In the past year, the power-to-gas process developed by the Fraunhofer IWES wind power research center, the Stuttgart Center for Solar Energy and Hydrogen Research, and the SolarFuel company became well-known as a source of hope for the storability of notably wind and solar power. Especially wind energy, for instance, should feed gas into the gas network when wind turbines produce surplus energy.
The wind power created during the process is used for the electrolysis of water (the splitting into hydrogen and oxygen). In a second process step, the hydrogen reacts with carbon dioxide in a separate reactor, forming methane. This synthetic gas can be fed into the natural gas network and be used, for example, in gas-fired power plants to generate power or as fuel. The states of Hessen and Thüringen also participated in the pilot exercise at the Hessian biogas research center. They tested the combined operation of a biogas plant (with a 25-kilowatt output) and a power-to-gas plant. With this method, they were able to directly methanize the biogas.
Biogas consists of about two thirds methane, one third carbon dioxide, and small amounts of water, hydrogen sulfide, and other gases depending on the substrate. In order to make the biogas useable for generating electricity, multiple process steps are usually necessary – among other things, the separation of carbon dioxide and methane. In the IWES process, the carbon dioxide in the biogas can be utilized for methanization directly.
“With this process, we can generate a gas with a stable methane content of more than 90 percent”, stated Bernd Krautkremer, IWES division manager for Energy System Technology. Further measures are necessary (such as increasing the pressure and conditioning the biomethane), however, for sale to the natural gas network. Therefore the researchers do not want to sell the gas to the natural gas network so they save on costs and technology. Instead, the biomethane is to be stored temporarily or returned to the biogas storage tanks in order to increase the total methane content. As Krautkremer puts it, “We have successfully tested both possibilities.”
The experts say this makes the application especially interesting for smaller biogas plants (with an output of around 250 kilowatts) that generate their electricity directly. In a preliminary study of the project, 34 percent of the Hessian biogas plants had been found to be suited for the economic use of the process.
The project was started just last December, and the researchers now want to refine the process after the initial success. “The potential of direct methanization is great, but there is still quite a bit of research to be done before we can think of a wide range of applications”, stated the IWES institute director Hoffmann. (Craig Morris)