How leftover food will power airplanes in the future

researcher

This scientist researches the recycling of biological waste. ©Fraunhofer IKTS

Due to their flexibility, biogas plants help to compensate for fluctuations in the power grid of renewable energy sources. However, if they are not used very often or the feed-in tariffs are low, the systems have so far hardly been worthwhile financially. However, this gap can be filled with a technical extension, as researchers report. In their first pilot plant, the biogas can be converted into biogenic waxes and synthetic fuels such as e-kerosene – depending on what the market needs at the moment.

Over 9,000 biogas plants are currently in operation in Germany. Leftovers from agriculture as well as organic waste from industry and private households are fermented into biogas in them. These are then used in combined heat and power plants or fed into the natural gas grid. In addition to being used directly to generate energy, the products from the biogas plants can also be used further – to make synthetic fuels and biowax. “Such expanded biogas plants open up considerable opportunities to create new value creation and jobs in the central German region for the time after the coal phase-out,” says Erik Reichelt from the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS).

A team led by Reichelt has now put the world’s first biogas plant into operation, which produces fuel and biogenic waxes from old fats from the catering and food industry. The original objective of the project was to make biogas plants more resilient to market fluctuations by being able to switch production to biowax using a switchable technology. These could then be sold to the lubricants and cosmetics industry, which should make it worthwhile to operate the plant even when electricity prices are low. Along the way, however, the researchers found that other products could also be extracted from the process.

Three extensions – many possibilities

In their project, the scientists added three components to an existing biogas plant in Thallwitz near Leipzig: a reformer, an electrolyzer and a so-called Fischer-Tropsch reactor. In the first step, the system feeds the biogas produced together with steam into the reformer, which uses it to generate synthesis gas – a mixture of hydrogen and carbon monoxide. The Fischer-Tropsch unit then converts this synthesis gas into methane, liquid hydrocarbons and wax. The methane is returned directly to the process, where it helps heat the plant. Wax and liquid products remain in a one-to-one ratio. The latter can then be further processed in refineries into synthetic diesel or kerosene.

If little biogas is available or a particularly large amount of electricity from solar or wind power plants is available, the electrolyser can finally be switched on. This is located in a separate container and breaks down water vapor and carbon dioxide into hydrogen and carbon monoxide, i.e. synthesis gas. In this way, it ensures the continuous supply of the Fischer-Tropsch plant, which can only work efficiently with sufficient synthesis gas. Thanks to the installed extensions, the system can now react particularly flexibly to different market situations. If, for example, the electricity purchase prices are particularly high, the operator can convert the biogas into electricity in the conventional way. However, if the feed-in tariffs are low, the plant can be converted to produce biogenic wax and synthetic fuels. If there is also a particularly large amount of electricity from renewable energies available, it is worth switching on the electrolyser.

Demand for e-fuels and organic wax is increasing

Even if the biogas plants become significantly more efficient as a result of the expansion, the petroleum-free fuels and waxes obtained are still more expensive than corresponding fossil-based products. However, the current energy price crisis has already greatly reduced the formerly immense cost differences to petroleum-based products. According to the scientists, however, the demand for sustainably obtained energy sources and materials in many branches of industry continues to increase. The airlines in particular are under pressure because of more restrictive environmental protection laws, since the federal government has announced that from 2026 it will introduce significant admixtures of electrically generated kerosene with conventional aviation fuel as a mandatory quota.

Further demand could also come from other areas in the future, such as the paint and coatings industry, which could use the wax obtained for the production of additives. Erik Reichelt believes that there will also be enough buyers in the cosmetics and lubricants industries in the future. Biogas plant operators who quickly equip their operations with the new technology could therefore be the first to serve this market demand for biogenic waxes. And if this sub-market should become oversaturated, the wax can also be liquefied into fuel using additional plant technology. A facility on an industrial scale is now on the scientists’ agenda. This should be able to produce several hundred liters of synthesis products per hour.

Source: Fraunhofer Institute for Ceramic Technologies and Systems IKTS

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