The carbon fiber in wind turbine blades can be recycled. As the global number of decommissioned wind turbine blades surges, the traditional disposal methods like landfilling and incineration are not only environmentally harmful but also a waste of high-value carbon fiber. The industry has developed three mainstream recycling technologies, which can realize the reuse of carbon fiber with different value levels. Here are the details:

1. Mechanical recyclingThis is a low-cost physical recycling method. First, decommissioned blades are disassembled into fragments of 10 - 20cm by hydraulic shearing. Then, the resin is embrittled by low-temperature freezing at -80°C before high-speed crushing. Finally, short-cut carbon fibers with lengths ranging from 5mm to 50mm are separated by air classification according to the density difference between carbon fiber and resin. The tensile strength retention rate of the recycled fiber is about 60% - 70%, and it is mainly used as low-end fillers, such as concrete reinforcement. For example, Goldwind Science & Technology has applied recycled fibers obtained by this method to tower concrete reinforcement, which reduces costs significantly while enhancing the concrete performance.

2. Pyrolysis recyclingIt is the current mainstream technology for high-value recycling of wind power carbon fiber. The carbon fiber components of the blades are placed in an oxygen-free furnace at 600 - 800°C. The resin is pyrolyzed into small-molecule gas (which can be recovered as fuel), and the carbon fiber filaments are retained. After surface cleaning and sizing treatment, the interface bonding ability of carbon fiber is restored. When the process parameters are optimized (such as a pyrolysis temperature of 750°C and a heating rate of 5°C/min), the tensile strength retention rate of the recycled carbon fiber can exceed 85%, and the elastic modulus retention rate is over 90%. Mingyang Smart has used such recycled carbon fiber to make the web of 16MW blades, which meets the 25-year service life requirement after passing the wind power industry certification.

3. Chemical depolymerizationThis is a cutting-edge technology that achieves molecular-level separation of carbon fiber and resin. It uses supercritical ethanol or organic acids as depolymerizing agents to break the chemical bonds in the resin under mild conditions, with a resin degradation rate of over 95%. The solvent can also be recycled with a recovery rate of more than 80%. This method maximizes the retention of the crystal structure and filament form of carbon fiber, with the tensile strength retention rate exceeding 90%. The recycled carbon fiber can be directly used in high-value fields such as the main beam of wind power blades. For instance, the Institute of Process Engineering of the Chinese Academy of Sciences has developed a supercritical fluid depolymerization process, which has achieved pilot-scale mass production and is cooperating with Dongfang Electric to develop applications for the main beam of 12MW blades.

The recycled carbon fiber not only can be reused in the wind power industry but also has been applied in fields such as automobile parts, building reinforcement materials, and sports equipment. For example, some foreign enterprises have successfully made high-performance ski boards using carbon fiber recycled from Vestas wind turbine blades, which are as good as those made of traditional raw materials. These recycling technologies not only solve the problem of solid waste from decommissioned blades but also reduce the carbon emissions and costs associated with the production of virgin carbon fiber, providing strong support for the green development of the wind power industry.