Fraunhofer Institute for Wood Research RE_SORT:
Sustainable and economic recycling of wind turbine rotor blades using pyrolysis of fiber composites
After 20 to 30 years, wind turbines have reached the end of their service life and need to be dismantled. In future, up to 75,000 tons of waste from rotor blades will be produced every year, including large quantities of fibre-reinforced plastics. Up to now, they have been used to generate energy (incinerated) or shredded and recycled as cement aggregate. Together with research and industry partners, we are developing a resource-efficient solution: using pyrolysis, the fiber composite plastic from the rotor blades is broken down into its components to recover the fibers used. Both these »recyclate fibers« and the pyrolysis oils and pyrolysis gases produced at the same time can be used industrially. The focus of the Fraunhofer WKI is on the wet-chemical processing of the recyclate fibers for the renewed production of materials. In this way, we are helping to reduce the raw material requirements of the wind industry.
The rotor blades of the wind turbines currently awaiting recycling consist of over 85 percent (by mass) glass and carbon fiber-reinforced thermosets (GRP/CFRP). Pyrolysis is a suitable process for separating fibers from a thermoset plastic matrix. However, previous pyrolysis processes have not been able to establish themselves in the recycling of rotor blades. This is also due to their design: in order to withstand the high tensile and compressive forces, the shells are reinforced in the longitudinal direction by thick »belts« made of multi-layer fiber composite plastic. There are also multilayer reinforcements in the flange and root area. A large proportion of the fiber-reinforced plastics used are therefore in the form of thick-walled laminates with wall thicknesses up to 150 mm.
The aim of the project is to develop new pyrolysis technologies that make the recycling of thick-walled fiber composite structures economically viable. Two different pyrolysis processes are being considered:
Quasi-continuous batch pyrolysis
In this process, the thermosetting plastic matrix is slowly decomposed into oily and, above all, gaseous hydrocarbon compounds by external heating in the absence of air.
Continuous microwave pyrolysis
In this process, energy is supplied through the absorption of microwave radiation, resulting in rapid internal heat generation.
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