Niels Ludwig: In the project, we are developing an economically feasible disposal strategy that achieves the highest possible recycling rate - we hope for up to 80 percent - and thus enables a sustainable circular economy. We are a cross-group and cross-institute recycling initiative comprising eight engineers and technicians from the fields of lightweight construction, plastics technology and aircraft construction.
Why is the focus on wind turbine rotor blades of all things?
Ludwig: To date, almost 30,000 wind turbines with a total output of over 50 gigawatts have been installed in Germany. The German government has announced that it wants to achieve climate neutrality by 2045. This is accompanied by new expansion targets for wind energy: By 2045, around 70 gigawatts are to be added offshore alone. At the same time, the EEG subsidies for some onshore turbines that have already been built ended last year, and some of them will be taken out of operation. We would like to optimize or further develop the recycling concepts currently available on the market for these end-of-life wind turbines (EoL turbines) and all subsequent ones.
What happens to the rotor blades of a wind turbine so far?
Ludwig: They are sawn into small pieces on site. Then the different materials are separated, as they have to be disposed of differently. Rotor blades consist - in addition to metal parts - in the main chord and skin of fiber-reinforced plastics (FRP) with carbon (CFRP) and glass fibers (GFRP), as well as sandwich components made of balsa wood with plastic foams. At present, the FRP and sandwich components are shredded and burned in the cement plant mixed with so-called rejects. The heat is used as energy and the ash is also utilized, as burned glass fiber is used to produce quartz sand, which is urgently needed in the cement industry. The process is well established. But as soon as CFRP is in the rotor blade instead of GFRP, it does not work. The carbon fibers are not wanted and are sent to another disposal route: They are recycled using large-scale pyrolysis, in which the plastic they contain is thermally decomposed and the fibers can be recovered. The fibers can be processed into new nonwovens or even used ground in injection molding.
But how do you know what is installed?
Ludwig: That's not so easy. Sometimes it is no longer possible to find out what the rotor blade is made of - for example, because the company that built it 25 years ago is no longer on the market. That's why an important practical investigation, to which we are devoting ourselves intensively in the project, is the detection of the materials. We have therefore also disassembled an 83-meter rotor blade on our farm, among other things. Firstly, to see how this can be done effectively in terms of handling, given the size of the blade. And secondly, to clarify via thermal camera what the rotor blade is made of. Based on this and other data, we can design an automated initial treatment for the rotor blade.
What else are you working on?
Ludwig: Together with our partner, Bremen University of Applied Sciences, we are working in a test facility on the approach of recovering the high-quality carbon fibers from the thick-walled flange and belt materials by means of a so-called slow-batch pyrolysis. This is a process in which large pieces of the material, not the shredded material, are pushed into the pyrolysis furnace and heated. In the process, epoxy resin gasifies and oil is separated out. The oil can be used in the chemical industry, and the synthesis gases generated during the process can be used for energy or hydrogen production. What remains is the pure fiber. In principle, this could be reused, but it only has a small part of its original strength and is therefore not stable enough for a new rotor blade. What is being considered in terms of sustainability, however, and is already being developed, is to turn it into foamed glass that can be used as insulating glass. A large European glass manufacturer, which already produces insulating glass from its own glass waste, would support us in the follow-up project for implementation in developing the industrial application of our pyrolysis glass. This would actually give us a path of acceptance already.
What is your next big milestone?
Ludwig: The implementation phase with the establishment of a recycling center, which is divided into different parts. One part - the research part, where we establish detection with incoming and outgoing product knowledge - will be with us, a second part, the dismantling center, with one of our partners, a company in Bremerhaven, and the third part, slow-batch pyrolysis, with the Institute for Energy and Circular Economy at Bremen University of Applied Sciences. We would like to bundle all areas in one place in a project after next at a location in Bremerhaven or northern Germany. To this end, we are looking for an investor for the recycling center from industry in the next three to five years. We can prove to him through our research results that the recycling paths and technologies we have designed work and that the rotor blade market is there. After all, we are talking about billions of euros in investment.
The KoReNaRo project is funded with 150,000 euros as part of the "Research for Sustainable Development - FONA3" program of the German Federal Ministry of Education and Research (BMBF) and started in October 2021. Funding is being provided for the conceptual design of a demonstration plant. A decision will subsequently be made on whether to fund implementation in a second phase.