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Highly Efficient Ammonia-Based Systems for Climate-Friendly Energie Supply

In the future, ammonia could play a decisive role in the transition from fossil fuels to climate-friendly alternatives — as long as it is produced from green hydrogen, for example, using renewable energy sources. Ammonia is easy to store and transport. Researchers at the Fraunhofer Institute for Microengineering and Microsystems IMM/DE are developing ammonia-based systems for a mobile, decentralized energy supply in the infrastructure, transportation and industry sectors. Implementing the energy transition is a huge challenge for all sectors of industry that use large amounts of fossil fuels, such as transport, logistics and the production industry. Currently, the energy requirements of these sectors are mainly met by fossil fuels, which need to be replaced with regenerative electricity or regenerative fuels.

Researchers at Fraunhofer IMM in Mainz are working on the mobile, decentralized provision and storage of electrical energy from sustainable sources. Dr Gunther Kolb, Head of the Energy Division and Deputy Institute Director at Fraunhofer IMM, explains: “An alternative to fossil fuels is power-to-X fuels, which are synthesized from electrolysis-based hydrogen. The most important power-to-X fuel is currently hydrogen itself. However, before hydrogen can be utilized as an energy source on a widespread basis, there are still some considerable hurdles that need to be overcome in terms of its transportation and storage. These include either high space requirements for its storage or other energetically unfavorable conditions. Ammonia (NH3) could become an alternative solution to allow the required hydrogen to be stored and transported with ease.

To date, ammonia has primarily been known as a source material for agricultural fertilizers. However, it is also a high-quality energy carrier, particularly as a storage medium for hydrogen. “Because ammonia can be liquefied at a moderate temperature of –33 °C, its volumetric hydrogen content is significantly higher than that of compressed hydrogen at 700 bar. In comparison to hydrogen, liquefied ammonia makes it easier to transport large volumes to wherever it is needed. Because hydrogen produced from ammonia does not contain any carbon oxides or methane, it is also free from greenhouse gases,” explained Dr Kolb.

The conversion of hydrogen into ammonia is a viable option for using it as an energy source both on-site for industrial processes on a large scale as well as on a decentralized basis in the logistics sector. However, ammonia is not very suitable for generating energy through combustion as it is virtually incombustible in the air. “In a cracking reactor ammonia can be split into nitrogen and hydrogen when suitable catalysts are applied. A mixture of ammonia, hydrogen and nitrogen is suited for homogeneous combustion and can be used as an energy source, known as Spaltgas,” said Dr Kolb. As part of the Spaltgas project, researchers at Fraunhofer IMM and their project partners are developing a combustion technology for this gas mixture that will be used in the brick firing process. In this way, ammonia from hydrogen produced via electrolysis can be used to make the entire brick manufacturing process chain carbon dioxide-free. The Spaltgas project is funded by the German Federal Ministry of Education and Research (BMBF) as part of the KlimPro-Industrie Program.

Ammonia can also be used for supplying hydrogen to land vehicles. It can be converted into hydrogen right at the filling station using decentralized plants. This eliminates the need to transport compressed and liquefied hydrogen — a costly and complex process. To this end, Fraunhofer IMM is developing a cracking reactor based on innovative catalyst technology and microstructured reactor technology. In this reactor, pure hydrogen is produced from ammonia through cracking and subsequent purification, which is then injected into PEM fuel cells. Hydrogen for use in fuel cell vehicles can therefore be produced sustainably from ammonia right at the filling station.

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