Germany funds air cycle cooling of steel

GERMANY: The German Federal Environment Ministry (BMUV) is providing €200,000 in funding for an environmentally-friendlier cooling process for steel hardening that promises substantial energy savings.

The innovative cold chamber using an air chiller, a collaboration between induction hardening company Rudolf Rieker GmbH and Refolution Industrie Kälte GmbH, an industrial refrigeration specialist based in Karlsruhe.

Rudolf Rieker GmbH, based in Leingarten (Baden-Württemberg), is one of the largest induction hardening shops in Europe. The hardening process is an important step in steel production. It involves heating steel to a high temperature, then cooling it down very quickly. This transforms the austenitic structure into a martensitic structure to give the desired hardness.

The cooling process currently uses liquid nitrogen, which is sprayed in a cold chamber. However, liquid nitrogen is associated with not inconsiderable energy expenditure in its production, transport and storage as well as with risks in operation.

The new system from Refolution is based on the air cycle technology developed by Swiss manufacturer Mirai Intex. It dispenses with the traditional use of liquid nitrogen, achieving temperatures of -80ºC for the first time with an air chiller.

Although there are significantly higher investment costs compared to conventional processes, these are offset by significant potential savings in energy and greenhouse gas emissions. The newly developed process only has to consider the energy requirement for operating the air chillers on site, which is reduced by around 30% through heat recovery within alternating cooling chambers. Overall, an energy saving of approximately 410MWh is anticipated, which corresponds to a saving of approximately 60-68% compared to the conventional process.

"The innovative process being funded can make an important contribution to reducing greenhouse gas emissions – as well as to avoiding nitrogen emissions," commented Christian Kühn, parliamentary state secretary of the German environment ministry. "Such a climate and environmental protection innovations in steel production not only benefit the future viability of the German economy, but can also become an export hit."

Air cycle technology is not new, being used on board ships over a hundred years ago. It is still used today in aircraft air conditioning systems. The technology has a number of benefits and recent advances in high-speed compressor design and materials have made the air cycle machine a rival to established vapour compression technology.

The Mirai air cycle machine solves the problems of refrigeration supply in the temperature range of -40ºС to –80°С and lower. In the air cycle machine, the air is heated up with compression and is cooled down in the process of expansion. According to Mirai Intex, this enables the temperature to be regulated with high precision at the outlet and to reach ultra low temperatures for the processes of freezing or storing.

Refolution was founded in 2019 with the aim of implementing the challenges of climate change using only "natural" refrigerants. Amongst a diverse range of projects, it has had great success providing systems for freeze drying for pharmaceutical applications.