Fraunhofer ILT: recycling refractory materials cuts 800,000 tons of CO₂ emissions…

31 Aug 2023

…and Fraunhofer IWS develops new underwater metal laser cutting method.

In the European research project ReSoURCE, experts from nine different companies and institutes are working together to develop sustainable solutions for the recycling of refractory materials. The German project partners are primarily providing laser know-how.

Refractory materials withstand high temperatures beyond 1,500°C. They are indispensable for industrial furnaces that produce glass or ceramics, non-ferrous metals and steels, for example.

The service life for refractory products ranges from a few days to many years – depending on the materials, the temperature in the melting vessel and other operating parameters. As a result, about 32 million tons of used refractory materials are produced worldwide every year, of which only a fraction is recycled.

The production of refractory materials from primary raw materials causes considerable amounts of CO₂, mainly because carbon dioxide has to be removed from carbonate-type raw materials. In addition, the raw materials are largely imported into Europe. There are currently no significant alternatives.

Automatic sorting – by laser

“Refractory products are precisely adapted to the customers’ requirements,” explained ReSoURCE project coordinator Alexander Leitner from RHI Magnesita. The optimal composition of the high-temperature resistant materials depends on the intended application, the manufacturing processes, and the related chemical properties of the process media. “This means that our products have very different compositions. Before recycling, we therefore have to separate them as precisely as possible,” said Leitner.

The project therefore centers on an automatic sorting system for spent refractory materials. A laser unit will be used to identify the constituents of the used material on a conveyor belt without contacting them. The laser technology comes from Laser Analytical Systems & Automation (LSA) from Aachen, a spin-off of the Fraunhofer Institute for Laser Technology ILT. LSA specializes in the development and production of real-time laser analysis systems for industrial applications.

“At Fraunhofer ILT, we have already developed an inline measurement technique that performs a direct analysis of metal scrap on a conveyor belt and detects the composition of each piece of scrap,” said Dr. Cord Fricke-Begemann, Head of the Materials Analysis Group at the ILT. “With this multi-element analysis, we can detect a large number of alloys. We are now transferring the findings to refractory materials.”

The research partners expect they can increase the industry's potential recycling share from the previous 7 to 30 percent up to 90 percent as a result of the project findings. “We are combining the latest analysis technology with state-of-the-art software to solve a current societal problem. We can probably reduce European CO₂ emissions by up to 800,000 tons per year,” says Cord Fricke-Begemann.

A new way to use lasers as metal cutting tools underwater

The need for modern dismantling technologies for underwater use is also growing. For example, to bring a wind power plant in the sea up to more power, old steel frames must first be dismantled below sea level to rebuild them later in a larger size.

The Fraunhofer Institute for Material and Beam Technology (IWS) in Dresden< Germany, has now found a technological approach to use lasers as efficient, environmentally-friendly, and energy-saving cutting tools in water.

To cut steel and other metals below the water surface, the IWS researchers use short-wavelength green lasers with the ability to cut even in water. At the same time, the water serves as a tool to expel the resulting melt from the kerf with pressure. This eliminates power losses, extra gas lines, and other disadvantages. In the laboratory, this already works.

In September, 2023, the IWS will present the innovative process at the Schweißen & Schneiden (Welding & Cutting) trade show in Essen, Germany.

Cutting metal with lasers is not a fundamentally new approach. However, it usually occurs in a dry environment. Infrared or other rather long-wave laser radiation cuts the metal.

The IWS engineers use green lasers with much shorter wavelengths than most industrial lasers today. However, this is only possible since green lasers in the more than one kilowatt class have become available to achieve the necessary cutting power.

In the future, shorter-wavelength versions with blue lasers are conceivable. Such short-wave lasers penetrate even water without significant losses and can thus also be used in bodies of water. This medium abundantly available in the sea can replace the cutting gas required in a dry environment: This eliminates the need for gas pipelines.