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Industry Perspective Preview: What to do with "Spent" wind turbine blades?


George Marsh

Given that there are already an estimated 345,000 utility scale wind turbines installed around the world (based on Global Wind Energy Council statistics) and that most are designed for service lives of 20 to 25 years, there is a looming issue; what should happen to large fibre reinforced plastic (FRP) blades when their service lives have expired?

This is a preview of an article that will appear in a future Volume of Renewable Energy Focus Journal...

10-15 tonnes of FRPs are associated with each Megawatt of rated wind turbine power. This illustrates the scale of the emerging challenge when it comes to disposing of turbine blades at end-of-life (eol).

Clearly, this is no small matter. Most turbine rotors have three blades, ranging in size from 12-15 metres long, typical of the early machine generations, to 80 metres today, an example of the latter being the MHI-Vestas blades now spinning on thirty-two 8MW offshore turbines forming the Burbo Bank extension project off Liverpool Bay in the UK. Although it should be many years before these latter become end-of-life (eol) items, the significant numbers of early-generation blades now reaching or approaching this point will soon require careful disposal, or else some form of second life.

This is not to dismiss the eol issue presented by a wind turbine as a whole, but techniques for recycling concrete and steel elements are well established and the main challenge lies with the composite plastics that most blades are made from. These bi-phase FRP materials have been selected for their weight, structural and aerodynamic (when formed into blades) advantages - not for recyclability. Unfortunately, it is difficult to separate the fibres from the polymer resins in which they are embedded, but only by achieving such separation can the highest value recycling options be secured. Techniques for accomplishing this are in their infancy so majority practice to date has been to adopt options that do not require separation.

Second life

One possibility is to recycle blades that have become surplus as a result of re-powering operations, into new installations. A secondary market could develop for original blades which, refurbished as necessary, could be welcomed in territories that have only embarked on the wind power journey more recently. Here less powerful turbines on smaller-scale wind farms, often off-grid, are likely to pertain for some time and pre-used blades with life left in them may prove useful for these. Both Denmark and Germany, wind power pioneers, have experience in this area. Intermediaries already exist that hold stocks of old wind turbines for export and more business opportunities are likely to arise in both blade reclamation and logistics. 

However, recycling complete blades is not the only option; parts of blades can be utilised too. Blade sections have been used for bus shelters and public seating in the Netherlands, and for children’s playground items in a number of countries. Marine structures and art installations are among other potential applications.

Denmark was in the vanguard of wind energy adoption and is naturally becoming one of the first countries to face the bulk disposal challenge. There, a working party has been formed to combine the expertise of several significant players and bring it to bear on blade recycling development. Coordinated by the Danish Wind Energy Association, the body has some 20 participants including such luminaries as MHI-Vestas, LM Wind Power and Siemens. The presence of these blade manufacturers is important given the growing influence of the ’producer responsibility’ principle as a driving force in European waste strategy. 

Landfill

In terms of disposal, while volumes are low and blade sizes remain modest, landfill is the dominant option. Blades may be cut up into manageable fragments, but there is rarely more pre-treatment than this. However, plastics in general are problematic due to their low or negligible degradability and the issue is most pronounced with reinforced plastics. With WT blades likely to account for some 50,000 tonnes of waste annually by 2020, rising four-fold by 2034 (according to research quoted by the European Wind Energy Association), landfill is hardly a viable long-term solution. Already access to permissive facilities is becoming limited.

In Germany, authorities have been banning the use of landfill for blade (and other items) disposal for some time and elsewhere punitive charges are levied; landfill tax in the UK, for instance, can already reach over £80/tonne. Moreover, as public awareness of the volumes of landfill involved grows, reputational damage could become worrying for an industry that prides itself on its green credentials.

Incineration

Landfill can be avoided by disposing of FRPs by incineration, an option that is reasonably accessible and affordable. However, the ash residue from the process, though much reduced in bulk, itself then needs to be disposed of in landfill or used in other manufactures such as cement. Some demand can be anticipated for rotor blade ash because it contains high amounts of silica and calcium, two main components of high-grade clinker.

Combustion processes need to be efficiently controlled to avoid troublesome emissions. Moreover, most incinerators cannot accommodate such large items, so rotor blades would generally have to be cut up into sizes that would fit. 

Material re-use

An attractive alternative to outright disposal is to use recovered material in secondary products such as aggregate and cement. There is considerable potential for reducing decommissioned blades into smaller fragments or particles that can be used to bulk out and enhance the properties of such products used in construction and related industries. Alternatively, they can be utilised as a fuel. Fibreglass fragments derived from rotor blades, boats and other eol composite items are already being so used in concrete furnaces, the ensuing ash being assimilable into concrete as a bulking agent in which short fibres may also have some reinforcement benefit.

A Danish large-scale manufacturer of pultruded fibreglass profiles, Fiberline Composites A/S, points out that there is a natural link between cement and fibreglass. Both, it says, contain sand (silica), so glass fibre fragments make a compatible addition to natural sand used in cement while resin content can be useful as fuel in the energy-intensive cement making process.

Pursuing a zero landfill, zero energy goal, Fiberline is part of a collaboration in which it sends its waste to German companies Zajons Logistik and Neocomp GmbH, where large fibreglass fragments are reduced to granules in giant crushers. Calorific value is adjusted by adding other types of recyclate. The resulting granular material is sent to cement manufacturer Holcim AG, which includes it in the feed to its cement making kilns. Holcim claims that recycling 1,000 tonnes of fibreglass waste into cement in this way saves up to 450 tonnes of coal, 200 tonnes of chalk, 200 tonnes of sand and 150 tonnes of aluminium oxide in a process that produces minimal dust, ash or other residues.   

In another avenue, source material can be further ground into a powder that can then be used in other ways, for example in the production of thermoformed moulds.

The rest of this Industry Perspective article will appear in Volume 22-23 of Renewable Energy Focus Journal...
 

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