Page 38 - North American Clean Energy July/August 2020 Issue

38
JULY•AUGUST 2020 /// www.nacleanenergy.com
wind power
End of Life Options
Wind turbine blade recycling
FOR NEARLY FOUR DECADES, WIND POWER
has been increasingly adopted in the U.S., but it has accelerated rapidly in the last decade. Cumulative wind power generating capacity surpassed 100 gigawatts in 2019, representing almost 8 percent of total electricity generated. Moreover, wind now comprises about 30 percent of new capacity being added nationwide. The U.S. Department of Energy projects that, in an aggressive scenario, total wind generating capacity could reach more than 400 gigawatts by 2050.
Given that the service life of wind turbines ranges from 20 to 25 years, some of the earliest megawatt-scale wind turbines are just now being decommissioned. A wind turbine assembly includes the rotor (typically with three blades), nacelle (turbine generator
and housing), tower, and foundation (Figure 1). A significant part of a turbine includes recyclable materials: the foundation is concrete; the tower is steel; and the nacelle components are primarily steel and copper. That is not the case for the blades, which are comprised primarily of glass fiber or carbon fiber reinforced polymer composites (GFRP or CFRP) - along with foam, balsa, metal, adhesive, paint, and other materials. At up to 100m in length, these blades are difficult and expensive to recycle due to both their size and the nature of the tough glass and carbon fibers. Since these materials also are non-hazardous, most decommissioned blades are currently sent to landfills for disposal.
The volume of decommissioned blades is currently low, less than 25 thousand tons per year. However, due to expanding use of wind power and increasing numbers of turbines being decommissioned or re-powered each year, managing wind turbine blade end-of-life issues is a growing long-term concern. The annual amount of blade waste is expected to increase 10 times by 2050, ranging between 200,000 tons per year to almost 400,000 tons per year, depending on turbine service life and total capacity deployed.
Blade management technologies
There are many technologies being developed for managing wind turbine blades nearing the end of their useful life. These include:
• Life Extension: Exposure to sunlight, freezing temperatures, and precipitation can degrade or erode blade materials. Blade monitoring, coatings, and repair technology is improving rapidly for life extension beyond 20 years. This is an environmentally friendly means of reducing wind turbine blade waste, and often economically favorable.
• Pyrolysis: Pyrolysis is a process used to recover fibers, char, and/or gases for energy generation. Blades are reduced to small pieces and then decomposed using conventional heating (ovens), in an inert atmosphere to prevent combustion, at temperatures of 450-700°C. Although pyrolysis can be costly, the process may allow the glass and carbon fibers to be recovered and potentially reused. Pyrolysis has been used for other carbon fiber composite material, and glass fiber blades have been tested at a pilot facility in Germany.
• Cement Kilns: Cement kilns use a high temperature combustion process (>1000°C) to produce about 80 million tons of cement per year in the U.S. Size reduced glass fiber composite wind turbine blades can be mixed with the raw kiln feed. The glass fibers replace other raw materials needed for the cement, and the other blade components serve as fuel to offset coal or natural gas normally used in the process, thereby reducing the CO2 footprint of the kiln. Cement
kilns, which can accommodate a large volume of composite waste materials, are being used commercially for blades in Germany, and are under consideration in the U.S.
• Grinding and Re-use: Blades can be processed to produce chunks, needles, or powders that can be used in a variety of products, such as decking, insulation, and building materials. The processed blade materials have a relatively low market value, and a significant portion of the material may require disposal due to paints and other contaminants. Grinding and re-use is being done commercially at pilot scale in the U.S.
Rotor
(Blade assembly)
Nacelle (Turbine housing)
Tower Foundation
by Brandon Fitchett