As a clean new energy source, wind power is developing rapidly. And the leaves are getting longer.
Currently more than 100 meters of blades have appeared. For example, at the LM Wind Power plant in Cherbourg, France, the first blade produced for GE's Haliade-X12 MW offshore wind turbine is 107 meters long, and it is the world's first wind turbine blade to exceed 100 meters.
The increase of impeller diameter puts forward lighter and higher requirements for the quality and tensile strength of the blade. The blade is an elongated force-bearing structure. This is a bit similar to Liang.
The main beam bears most of the bending load and is the main bearing structure of the blade. The commonly used forms are D-type, 0-type, rectangular and double-split channel steel. With the improvement of technology maturity, the double-slot channel steel structure has gradually become the main body. At present, the structure of large-scale wind power blades is in the form of a skin main beam (see the figure below). The skin is mainly reinforced by a biaxial composite layer, which provides aerodynamic shape and bears most of the shear load. The trailing edge cavity is wide, and the sandwich structure is adopted to improve its anti-stability. The main beam of the structure is mainly reinforced by a unidirectional composite material layer, which is the main bearing structure of the blade. The web is a sandwich structure that supports the main beam.
Blade material and process design changes
Wind power has developed rapidly for more than 100 years. Not only has its shape and structure changed a lot, but its materials have also changed a lot. Starting with the original wooden blades and cloth skin blades, they have experienced steel beam glass fiber skin blades, aluminum alloy blades, FRP blades, and FRP composite blades. High-strength and lightweight carbon fiber reinforced composite materials have been used. FRP composite blades have high strength, light weight, and age resistance, so they are widely used in large and medium-sized wind turbine blades. The performance of FRP blades can also be improved by surface modification, sizing and coating.
However, with the increase of the power of the fan, the blade length continues to increase, and its own weight continues to increase, which can no longer meet the requirements in many occasions. In this case, carbon fiber composite materials with high strength, high modulus, and low density have become the focus of people's consideration.
Technicians have attempted to apply carbon fiber composites to multiple parts of the blade. As the length of the blade increases, stiffness is a very important indicator. In order to strengthen the blade stiffness and reduce the weight of the blade, carbon fiber reinforced composite materials are gradually adopted in local high stress areas in large and very large wind turbine blades. Beam of the blade. The beam of the blade is equivalent to the backbone of a human, and the long blade is supported by the beam!
For example, the 61.5m long large wind turbine blade developed by LM Company for use on a 5MW wind turbine has a weight of 17.7t, and carbon fiber reinforced materials are used in the beams and ends. Vestas also uses carbon fiber on the 44m blade main beam of its 3MW model, which reduces the blade weight to 6t, which is the same mass as the 39m blade used by the 2MW model. Sinoma Blade successfully developed the longest domestic 6MW wind turbine blade in 2014. The blade has a total length of 77.7m and a mass of 28t. The main beam is made of 5t of domestic CFRP. If GFRP design is used, the blade quality will be about Up to 36t. The 83.6-meter-long fan blade launched by Jilin Zhongtong in February 2018 adopted a carbon fiber beam made by the infusion process. The blade weighed 25.2 tons, which reduced the weight by nearly 11 tons.
At present, there are three main processes of carbon fiber main beams: prepreg process, carbon cloth infusion process and pultrusion carbon plate process. This is based on the characteristics of traditional wind power technology and carbon fiber technology. The prepreg process is the most traditional carbon fiber composite material processing process, so prepregs were also used to make blade girders at first. The carbon cloth infusion process is currently used by many fan and blade manufacturers, and the glass fiber beams of ordinary blades adopt this process. The process is relatively mature. The pultrusion process is a traditional process of composite materials. It has been newly developed for wind power beams in recent years.
Because the leaves are very long, there is no way to adopt traditional high temperature curing. The carbon fiber prepreg used for making the blade girders in this way is a low-temperature curing prepreg. The vacuum bagging method adopted in the processing process requires high manual operation and long curing time. The prepreg process is used to prepare carbon fiber beams and lay them by hand. It is an ideal process for producing structural components with complex shapes. The process and equipment are also mature. The labor environment is relatively poor, the efficiency is low, and the cost is high. It is currently used in prototypes and cannot be satisfied. Requirements for batch use. The infusion process does not require high molds, the molds are simple to make, and even existing molds can be used. The product quality is high, the repeatability is good, the apparent quality of the product is good, the thickness of the same layer is thin, and the strength is high. However, this process has higher requirements for carbon cloth, and the production efficiency is not high, and the cost is also high. Once problems occur, the entire carbon beam will be scrapped, which limits its promotion.
The pultrusion process has the highest efficiency and the lowest cost in the composite material process, and has high fiber content, stable quality, continuous molding and easy automation, which is suitable for mass production.
The rapid growth of carbon fiber in the field of wind power can be said to be the biggest success in the application field these years, which has greatly promoted the progress of the industry. We reflect on the reasons for success, and its design progress is the focus. Carbon fiber has superior performance, but high cost and complex and diverse processing technology, which are well known in the industry. But how to better use carbon fiber has always been a recognized problem in the industry. The successful application of carbon fiber in the field of wind power first stems from the design innovation of wind power and persistence. Initially, carbon fiber prepreg was used for wind power blades, followed by carbon cloth infusion process, and finally carbon fiber pultrusion process was selected. As you can imagine, there must be many problems and troubles in this process. If you are really picky or impatient, you may be yellow. And persistence, coupled with design innovation, make the carbon fiber pultrusion process with high efficiency and low cost available. It is this kind of design innovation, driving material innovation and process innovation that standardizes and modularizes the application of carbon fiber in wind power, and simplifies the post-processing process.