Solar photovoltaic power generation, as the cutting-edge technology of new energy utilization in the world, has the advantages of zero consumption, zero emission, zero pollution and long life cycle. The main heat exchange equipment of solar boiler photovoltaic power generation steam generation system includes steam bag, evaporator, reheater, superheater and preheater.

The principle of solar thermal power generation system and the main heat exchanger equipment composition

Principle of Solar Thermal Power Generation System

In the open ground with good light intensity, a solar collector tower (concentrator tower) stands at a height of 100 m. The collector tower is equipped with a heat absorber. The sun mirror automatically tracks the sun to obtain the maximum radiation from the sun, and the sun mirror reflects the sunlight to the heat carrier (thermal oil or molten salt) in the heat absorber on the collector tower, which heats up the heat carrier, exchanges heat between the heat-absorbing heat-exchanged heat carrier and the water in the steam generator to generate high-temperature and high-pressure saturated steam or superheated steam, which drives a conventional turbine to generate electricity.

Solar photovoltaic power generation steam generation system main heat exchanger equipment composition

The high-pressure steam generator system consists of a superheater, an evaporator unit (two evaporation cylinders and a steam packet) and a preheater, with the reheater operating as a separate heat exchanger in parallel with the former.

The working principle and structure of heat exchanger equipment

1.Superheaters

Principle of operation of superheaters

Saturated steam is extracted from above the steam space (ladle) and contains a small amount of moisture, a small amount of concentrated salt impurities, and other unknown components.

The boiler superheater is a part of the boiler that further heats saturated steam to superheated steam. The role of the superheater is to make the boiler out of the steam is heated again, into a higher temperature dry steam, improve the steam in the turbine's ability to do work, is conducive to improving the thermal efficiency of the boiler, but also conducive to the turbine to avoid water strikes.

Structure of the superheater

The heat exchange section of the superheater is designed as a serpentine tube without a tube sheet. The heat exchange surface consists of tube bundles, which are placed in a circular pressure vessel containing the heat carrier (thermal oil or molten salt). The tube bundle is welded on top of the header box, which passes through a heat sleeve in the shell to reduce thermal stress. The serpentine heat exchanger tube bundle has many bends and is highly flexible. In the same shell stroke, the heat carrier flows countercurrently through the tube bundle without changing direction. The pressure drop of the heat carrier in this configuration is relatively small and the heat transfer coefficient is high.

2. Carburetor

The working principle of the steam packet

The steam bag is an important component of the solar boiler equipment, is the boiler heating, vaporization, superheating of the three processes of the connecting hub, play the role of the upper and lower.

Demineralized water in the boiler into qualified superheated steam, after heating, vaporization, superheating three processes. Heating from water into saturated water is the heating process; saturated water vaporized into saturated steam is the vaporization process; saturated steam is heated into steam process is the superheating process. The above three processes are completed by the preheater, evaporator, superheater.

The steam bag and the above three processes are linked, it should accept the water from the preheater, and evaporator constitutes a circulating loop, saturated steam should be sent to the superheater by the steam bag. The steam bag is both heating, vaporization, superheating three processes of the intersection, but also heating, vaporization, superheating three processes of the demarcation point. Therefore, the steam bag is known as the boiler heating, vaporization, superheating three process connection hub.

The vapor drum is connected to the evaporator by an ascending and descending tube to form the water cycle of the vapor drum. Tank water cycle is convection heat cycle. Boiler generated by the hot water (steam) from the rising tube into the steam bag, hot water quality light to go up in the process of heat exchange, part of the water into a gaseous state; boiler cold water under the action of gravity through the descending tube to supplement to the boiler. Water in the siphon effect in the steam bag and the boiler between the circulation is the steam bag of the self-circulation.

3. Evaporator

The working principle of the evaporator

The serpentine evaporator uses a circular header box to distribute high-temperature thermal oil to the heat transfer tube bundle, and the high-temperature thermal oil heats the water in the evaporator's pot barrel to produce steam. The steam pot barrel of the evaporator and the evaporator are connected with external upper and lower coupling boxes. The cycle of the evaporator is a natural cycle, based on the principle that the difference between the density of the saturated liquid in the lower coupling box, and the density of the vapor-liquid mixture in the evaporator and in the upper coupling tube, which is less dense, carries out a natural cycle under the action of gravity.

 Structure of the evaporator

The serpentine evaporator includes pot cylinder, head, heat transfer tube bundle, collecting box, tube platform, manhole and so on. Heat transfer tube pairs are welded and bent, and welded to the collection box on both sides according to different lengths to form heat transfer tube bundles, which are placed in the evaporation cylinder. The heat transfer tube bundle is placed inside the evaporation cylinder. The tube platform on top of the evaporation cylinder and the steam bag are connected with each other through the rising tube and the falling tube.

4. Preheater

Preheater working principle

High temperature thermal oil (temperature 393 ℃) through the superheater tube bundle, evaporation cylinder tube bundle heat absorption, and then through the preheater, the preheater in the boiler feed water heating. It plays an active role in improving the heat exchange performance of the boiler and reducing energy consumption.

Structure of the preheater

The structure of the preheater mainly consists of the pot barrel, header, heat exchanger tube bundle (heat exchanger tube and collector box assembly), and the structural form is similar to that of the superheater.

5. Reheaters

Principle of operation of reheaters

The process of reheating steam up to a certain temperature and pressure (steam temperature 200 °C, pressure 20 bar) by means of high-temperature thermal oil (temperature 393 °C) through the heat exchanger tube bundle of the reheater. The main function of the reheater is to further increase the thermal efficiency of the cycle, reduce the humidity of the water vapor and help protect the turbine blades.

Structure of the reheater

The structure of the reheater mainly consists of the pot barrel, header, heat exchanger tube bundle (heat exchanger tube and collector box assembly), and the structural form is similar to that of the superheater.

Conclusion

Solar energy, as a major clean energy source at present, has great potential for development. The article provides experience for the design and manufacture of solar boilers by studying the working principle and structural characteristics of the heat exchange equipment of the steam generation system of solar boilers. The development trend of solar boilers moves towards more efficient, intelligent, multi-functional and environmentally friendly. With the continuous progress of technology and the popularization of application, solar boilers will be able to play a more important role in the future and contribute to sustainable energy development.