MIL-OSI Translation: Fraunhofer process increases methane yield from biogas plants


MIL OSI translation. Region: Germany/Germany –

Source: Fraunhofer-GesellschaftGermany is on the way to climate neutrality. By 2030, carbon dioxide emissions are expected to fall by 65 percent compared to 1990 levels. One element of defossilization are biogas plants: in them, bacteria build biomass to biogas with the exclusion of oxygen which consists on average of about 60 percent methane and 40 percent CO2. While the biogas generates electricity and heat in combined heat and power plants or can be fed into the natural gas grid after being processed to natural gas quality, the CO2 has so far escaped unused into the air.Using biogas to the fullResearchers at the Fraunhofer IMM now want to change this. “We convert the CO2 into methane with the help of green hydrogen,” explains Dr. Christian Bidart, scientist at the Fraunhofer IMM, the approach of the new process. The resulting biogas can not only be used up to about 60 percent as before, but in its entirety. The underlying reaction has been known for about a hundred years, but so far has mostly remained at laboratory level. Only the forthcoming energy transition will focus on possible applications, so the researchers are converting the reaction into an industrial process for the first time. The research team has already developed a demonstration plant in the ICOCAD I project: This converts one cubic meter of biogas per hour into one cubic meter of methane, its thermal output is ten kilowatts. In the follow-up project ICOCAD II, the researchers are currently scaling this system to five times its size, i.e. to a thermal output of 50 kilowatts. One of the challenges that is on the agenda: the highly dynamic process. Because the amount of electricity generated from wind and photovoltaic systems fluctuates greatly – and with it the amount of green hydrogen that is obtained from water using electricity in electrolysers. The system must therefore be able to react quickly to fluctuating amounts of hydrogen. Storage of hydrogen would also be possible, but complex and expensive. “We are therefore working on making the system flexible in order to avoid storing hydrogen as much as possible,” says Bidart. This includes, among other things, CO2 storage: Because the amount of CO2 that flows out of the biogas plants is constant. Development of efficient catalysts Another challenge lay in the development of efficient catalysts for the reaction. The researchers at Fraunhofer IMM used a micro-coating made of precious metals for this. The principle: Hydrogen and carbon dioxide flow through numerous micro-channels in which they can react with each other and whose walls are coated with the catalyst. “In this way, we can increase the contact surface of the gases with the catalyst material and reduce the amount of catalyst required,” says Bidart. Numerous such microstructures are stacked on top of each other in the reaction reactor.Further scaling plannedThe researchers are currently working on implementing the larger system and realizing dynamic operation. In 2023, the team hopes, this could then go into operation and be tested in a real biogas plant. However, this is by no means the end of the upscaling – after all, the amounts of CO2 produced by the biogas plants are large. The researchers are therefore planning to scale this up to 500 kilowatts by 2025, and by 2026 the system should even generate one to two megawatts of power.


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