Wind blade coatings Challenges in impingement protection of wind turbines

Transcription

1 Wind blade coatings Challenges in impingement protection of wind turbines

2 Outline Wind blades The big picture Leading edge erosion What s the problem? Predictive model Theoretical approach Coatings selection New concepts Preliminary results from EU funded projects Conclusions and future work

3 Wind energy The big picture Follows sustainable energy roadmap Wind will supply 33% of global energy demand in 2050 High yield compared to other sustainable energy sources

4 Wind energy Bigger and bigger Behemoth Larger blades up to 90 m. Less maintenance costs necessary

5 Challenges for wind blades Reduce (off-shore) maintenance costs Weight reduction Droplet impingement resistance Leading edge erosion Tendency for larger blades increases erosive pressure on coating And Increasing market High energy yield Capital intensive Recycling becomes important

6 Main parts of the wind blade Tailoring performance by design: - lift, - rotation, - weight, - materials, - processability Recycling opportunities

7 Impact at leading edge Wind direction is nearly perpendicular to blade surface. => mainly perpendicular impact of particles. Particles: sand, rain drops. For rain drops: 4 to 5 wear rate ~v Blade size v at 20 rpm Wear rate 50 m 100 m/s 90 m 180 m/s x 15

8 Leading edge erosion a b c a) Leading edge erosion at an early stage b) Severely damaged coating and c) Leading edge erosion starts to wear away the shell material.

9 Predictive model surface waves Edge of loaded area Rayleigh wave front Longitudinal wave front Coating Transverse wave front Figure 4 Plot of the normalized stress S RR as a function of radial distance (r) and depth (z) s adapted from [22] Damage results from water-hammer concept: pressure wave is faster than droplet can compensate for Fig. 3 The variation of radial stress component due to the Rayleigh surface wave as a function of radial distance in Polymethylmetacrylate PMMA, for a water drop diameter d d = 1.8 mm and impact H.M. Slot, velocity E.R.M. v d Gelinck, = 222 m/s C. at Rentrop 5 μm depth, and E. adapted van der from Heide, [30]. Leading edge erosion of coated wind turbine blades: review of coating life models, Renewable Energy

10 Hard and soft materials both damage Soft - polymer - coatings Hard and brittle materials (Low cycle fatigue)

11 Relative Impact pressure, p wh /v d (MPa.s/m) Reduce normalized stress Resilience: Acoustic properties: General trend Metals Ceramics Polymers Elastomers & Rubbers Dynamic impedance of material, Z m = r.c (MPa.s/m) minimize: (E.r) 1/2

12 Thermoplast selection

13 Sand erosion angle of impact

14 Erosion rate Sand soft erosion and hard angle properties of impact required Solid particle erosion Brittle facture α max Sliding abrasion Angle with maximum erosion rate for sliding abrasion (α max ) depends on coefficient of friction between particle and coating Impact fatigue Angle of particle impact, a ( )

15 Coating selection Create recyclable thermoharder Properties Thermoplast Thermoharder Anisotropic Nano-particles Introduce Impingement Optimise mechanical stability Scratch resistance (N)OK UV-resistance OK Optimise resilience and acoustic properties NOK Introduce Scavengers Ionomeric coatings Creep NOK OK Solvent resistance NOK OK State of the art Improvements are welcome OK Optimise crosslinking OK Introduce Scavengers Recycling OK NOK (N)OK OK Vitrimers anisotropic nanoparticles to boost performance OK Literature reports mechanical improvements by the use of anisotropic nanoparticles

16 Ionomers

17 Vitrimers Thermo-reversible polymer network based on Diels Alder curing chemistry

18 Diels-Alder chemistry Thermoplastic at high temperature so potential recycle ablility Thermoset properties at low temperature High temperature Low temperature Various methods to introduce in coating (Grafting to resin, (partially) replacing traditional curing, use as and additive.

19 Diels-Alder chemistry selection of materials Diels-Alder Diels-Alder Furfuryl and Maleimide Simple / commercially available Aromatic / rigid structures Furfuryl alcohol Bismaleimide Solid Poor solubility Prone to side reactions State of the art windblade coating systems Poly urethane (Epoxy)

20 Diels-Alder chemistry selection of materials Activate selective reactions, but Avoid side reaction at high temperatures Careful consideration Order of reactions Conditions for each step HO R - OH Isocyanante polyol

21 Diels-Alder chemistry additive synthesis R 1 O O O N R N O >T <T O O R 2 Solid Liquid Additive to introduce self-healing Can be incorporated in traditional paints Combine with novel resins to enable thermoplastic behaviour

22 Rheology Viscosity response Coating without additive Modified coating Diels- Alder additive Temperature cycle

23 Coating without additive Additive

24 How about the impingement results?

25 Sand erosion test set-up Coating area: 30 x 30 mm 2 Abrasive: Sand particles, rounded, μm, mean 250 μm, hardness 950 ± 50 HV Amount of abrasive: 0.6 g/min Angle of impact: 45 and 90 Impact velocity: 65 ± 5 m/s (p a = 4 atm) Time duration: 75 min

26 Conclusions Wind energy is a challenge for coatings & materials development Impingement Wear resistance Recycling Market requires different approach beyond state of the art: Vitrimers (combining thermoset and thermoplastic behaviour) Rheology modification using a DA additive Clay addition to improve impingement Ionomeric coatings show superior resistance to particle impingement

27 Future work Optimise clay and DA additive loading Determine resistance against droplet impingement Understand the droplet impingement Extrapolate DA additive to other applications with industrial partners

28 Droplet impingement test set-up

29 Acknowledgements