foreword
Solar thermal power generation is a clean energy technology that uses heat collectors to convert solar radiation energy into heat energy and generate electricity through a thermodynamic cycle process. The existing solar power generation systems in the world can be roughly divided into three categories according to the heat collection temperature: trough line focusing system, tower system and dish system. Some advanced ceramic materials can be applied to the heat absorber of the tower solar thermal power generation system.
1. The operating principle of trough, dish and tower solar thermal power generation systems:
The trough solar thermal power generation system is an energy power system that uses a trough-shaped parabolic mirror to focus the solar fiber onto the heat collector to heat the heat transfer medium, and the steam generated by the heat exchange drives the steam turbine to drive the generator to generate electricity.
Figure 1 Trough solar thermal power generation system
The dish system, also known as the dish system, mainly uses a dish-shaped parabolic mirror concentrating heat collector, and its structure is similar to a large parabolic radar antenna in appearance. Since the disc-shaped parabolic mirror is a point-focused collector, its concentration ratio can be as high as hundreds to thousands, so it can generate extremely high temperatures. The dish solar power generation system can connect multiple devices in parallel to form a small solar power station to provide electricity for users.
Figure 2. Dish concentrated solar thermal power generation system
The tower system is also called a centralized system. Its concentrating device is composed of many large reflectors (usually called heliostats) installed on the site. Each heliostat has the ability to track the sun in two axes and can accurately Concentrate sunlight reflection on a heat absorber at the top of a high tower, and solar heat heats the heat transfer medium on the heat absorber; the superheated steam generated by the steam generating device enters the power subsystem to realize heat work conversion, thus completing computer output.
Figure 3. Tower solar thermal power plant system
2. Which ceramic materials can be used in solar power generation systems:
Tower-type solar thermal power generation system is highly recommended in solar power generation because of its high concentration ratio (200~1000kW/㎡), high thermal cycle temperature, low heat loss, simple system and high efficiency. As the core device of tower-type solar thermal power generation, the heat absorber needs to withstand the radiation intensity 200-300 times stronger than natural light, and the working temperature can be as high as above 1,000 °C, so its performance is very important for the stable operation and working efficiency of the thermal power generation system. important. The working temperature of traditional metal heat absorbers is limited, which makes porcelain heat absorbers a new research hotspot.
2.1 Due to the inhomogeneity and instability of the concentrated energy flow density of solar energy, there are the following requirements for the ceramic heat absorber material:
(1) High-temperature oxidation resistance, the material will not be oxidized and damaged in a long-term high-temperature working environment;
(2) Good high-temperature mechanical properties and thermal shock resistance can avoid material hot spot damage;
(3) High solar radiation absorption rate, so that the material can fully absorb solar radiation energy;
(4) It has a three-dimensional or two-dimensional connected structure, ensuring high permeability of the material, making the air flow resistance small, and conducive to the uniform and stable distribution of air flow;
(5) High specific surface area ensures that the material has a large heat exchange area and ensures sufficient heat exchange with air.
2.2 The following ceramic materials can be used as heat sink materials:
① Alumina ceramics: can withstand high temperatures above 1000 ° C, high mechanical strength and chemical stability, and acid and alkali resistance, good thermal conductivity, dielectric strength, resistivity, and wear resistance; the disadvantage is that the working temperature is high but the thermal conductivity and The solar radiation absorption rate is low, and its color is white so that it must be coated on the surface when it is used as a heat absorber, thereby increasing the solar radiation water absorption rate. During high-temperature use, the substrate and coating of the product are prone to cracking, and the shock resistance is not good, which limits the actual use.
② Cordierite ceramics: It has the characteristics of low thermal expansion coefficient, good thermal shock resistance, and large specific surface area, but because of its low strength, it is usually necessary to add second phases such as mullite and zirconia to improve its strength. However, the cordierite porcelain heat absorber material has the same problem as the alumina ceramic heat absorber material, and is only suitable for medium temperature heat absorber materials.
Experimental studies have shown that mullite-cordierite composite ceramics prepared by normal pressure sintering using synthetic mullite and synthetic cordierite as raw materials, waste glass powder and aluminum titanate as sintering aids can also be used for solar power generation Heat transfer piping materials used.
③Silicon carbide ceramics: It has excellent characteristics such as high strength, large specific surface area, corrosion resistance, oxidation resistance, good heat insulation, thermal shock resistance and high temperature resistance. Compared with alumina and cordierite porcelain heat absorber materials Has better high temperature performance.
Research results have shown that the heat absorber made of sintered silicon carbide can make the heat absorber obtain an outlet air temperature as high as 1200 °C without material damage.
epilogue
Our country is relatively late in the application research of solar thermal power generation technology, and the substantive application research did not begin until the "Tenth Five-Year Plan" period. But it does not affect China's current status as the world's largest photovoltaic and solar thermal energy market. Advanced ceramics may not be widely used in the solar energy market due to technical cost and other reasons. However, with technological innovation, product upgrading, and production efficiency improvements, ceramic products that can be reasonably and efficiently adapted to solar thermal power generation systems are also available. It will be fully launched on the market, it is only a matter of time.
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