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The dark side of a green industry

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mandag 14. november 2011
Even though technologies to reuse or recycle wind turbine blades exist they are rarely utilized.

By Karsten Prinds

The wind turbine is a green technology, as everybody agrees. But turbines are not recycled as much as one might like to think. The blades pose a challenge – so far, most of them are dumped on landfills, even though the technologies to reuse or even recycle them do exist.

There are different forecasts of the size of the problem. By 2025 it is expected that Europe will be disposing of 200,000 tonnes of blades every year, according to the Danish research institute Force Technology. Worldwide, the predicament is 225,000 tonnes per year by 2034, says Professor Henning Albers of the environmental institute in Hochschule Bremen, Germany, according to National Wind Watch.

Wind turbine blades are made of composite materials. This makes recycling difficult. Typically, blades are made as hollow structures with shells of glass reinforced plastic. The glass reinforced plastic consists of approximately 60 percent fiberglass, i.e. long threads of glass, and 40 percent plastic, i.e. polyester or epoxy.

So far, landfill is the cheapest solution. But technology offers other methods.

Decommissioning the wind farm Syltholm in Denmark. Photo: Lars Havn Eriksen/Scanpix

Mechanical

Method: The blade is cut to pieces e.g. in a shredder like the ones used for large trees or cars. The rubble can be used in several ways:

  • For cement production as a partial replacement for real glass used in the manufacture. This demands that the rubble is cut into 3.5 cm pieces. The epoxy from the blades acts as fuel and will burn up in the process as it takes place at 2,000 °C. This method is today used by the German disposal company Zajons Logistics EmbH.
  • Incinerated traditionally along with other combustible waste. The slag is used as filler material under roads. This method is performed e.g. by the Danish disposal company H. J. Hansen Deconstruction A/S.
  • For reinforcement of concrete. This demands that the blades are crushed to very fine pieces so that the fibers are no longer than 4 cm. However, there are still problems with getting the fibers clean enough – there is too much epoxy on the fibers.

Advantages: The strength and stiffness of the fibers is kept.
Disadvantages: Fibers are not re-used. It is not recycling, but downcycling

Thermal

Method: Pyrolysis. The blade, cut up in suitable pieces, is placed in a kiln with a non-oxygen atmosphere at 500 °C. Gasification of the epoxy or polyester takes place, leaving the glass fibers clean and separated after the process. The gas is lead from the kiln to a combustion chamber and burned at 1100 °C for power production, heating of the kiln, and surplus heat is sold for district heating.The fiberglass can then be reused for insulation mats, but not recycled for blades. This is because the strength of the fibers is reduced to about half due to the pyrolysis. However, the stiffness is still the same.
The pyrolysis is performed by the Danish company ReFiber ApS.
Advantages: Effective separation of the two components in the glass reinforced plastic. 
Disadvantages: Expensive process, the strength of fibers is reduced. Not cost-effective in the summer, when surplus heat sells at a low price.

Chemical

Method: This is called Solvolysis and it is a chemical reaction where the plastic is dissolved and the fibers remain. This is more a theoretical possibility, as it is expensive and might not be very friendly to the environment. Solvolysis would leave the fiberglass virtually without reduction in strength and could thus be recycled, but not in new blades. This is because the orientation of the fibers is important when producing a new blade. The recycled fibers are too messy in their orientation and often too short. The dissolved plastic would also be recycled.
Advantages: Separation of the components and recyclability of the fibers. 
Disadvantages: Expensive, possibly hazardous chemicals, and the whole process could create another recyclability issue.

Thermal and chemical

Method: Supercritical water oxidation. This is perhaps the most sophisticated and complicated method. It must also be seen as more of a theoretical possibility than actually useful for blades – because of the large difference between the cost of the method and the saved expense for new raw materials. In short, the method is incineration under very high pressure ? 600 atm. ? and in water. The chemical reactions take place under lower temperatures than normal incineration, thus the strength and stiffness of the glass fibers is retained. The plastic is dissolved.
Supercritical water oxidation is mostly used for destroying hazardous waste and polluted water, where the high costs are acceptable.
Advantages: Fibers keep their strength and stiffness. 
Disadvantages: Fibers still have to be cut to small pieces. The orientation of fibers is messed up, and this limits its use. The method is very expensive.

Read more:

Recycling Wind Blades, National Wind Watch
Danish Competence Center for Waste (Dakofa)

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