CN209145784U - A supercritical carbon dioxide Brayton cycle tower solar thermal power generation system - Google Patents

Abstract

The utility model relates to a kind of supercritical carbon dioxide Brayton cycle tower-type solar thermal power generating systems.Including tower light and heat collection system, supercritical carbon dioxide Brayton cycle electricity generation system, heat reservoir and steam Rankine cycle electricity generation system；Supercritical carbon dioxide Brayton cycle electricity generation system is recycled as top-level cycle, steam Rankine cycle electricity generation system as bottom；Heat reservoir is located at bottom circulation；When working by day, supercritical carbon dioxide Brayton cycle electricity generation system is run under stable operating condition, and the waste heat from tail gas of turbine gas-turbine is used to heat the steam Rankine cycle electricity generation system of steam drive bottom；Fuse salt is stored in the hot tank of fuse salt of heat reservoir after molten salt thermal absorber heat temperature raising；When night or cloudy day, steam drive bottom steam turbine power generation is generated in fuse salt steam generator using the fuse salt in the hot tank of fuse salt, fuse salt after cooling is back in the cold tank of fuse salt, and the Brayton cycle at top is in shutdown status at this time.

Description

A supercritical carbon dioxide Brayton cycle tower solar thermal power generation system

technical field

The utility model belongs to the technical field of solar thermal power generation, in particular to a supercritical carbon dioxide Brayton-steam Rankine cascade cycle tower solar thermal power generation system.

Background technique

Compared with photovoltaic power generation, solar thermal power generation is a power generation technology that can be matched with an inexpensive heat storage system, can output power stably and continuously, and is a flexible and adjustable power source. In order to maintain the stability of the power grid, the flexibility to adjust the installed capacity needs to be maintained at a certain ratio, and solar thermal power generation has attracted widespread attention. In order to improve the overall efficiency of the system, the next-generation CSP system has a tendency to develop towards a higher collector temperature. The tower solar thermal power generation adopts the point focusing method, which has a higher concentration multiple and is easier to achieve a higher heat collection temperature. As the temperature rises above 700°C, the chemical reaction between the water vapor and the metal material intensifies significantly, so the traditional steam Rankine cycle can no longer meet the above conditions. The supercritical carbon dioxide Brayton cycle has the advantages of high operating temperature, high cycle efficiency and compact structure. At the same time, carbon dioxide is an inert gas, which has little corrosion to the equipment of the system. However, based on supercritical carbon dioxide Brayton cycle tower solar thermal power generation system, there are still some technical problems and challenges:

1) In the circulating system of the same installed capacity, the working fluid flow of the supercritical carbon dioxide Brayton cycle is several times that of the traditional steam Rankine cycle. The pressure loss of the supercritical system pipeline increases sharply, which seriously reduces the circulation efficiency of the system, and requires a heat exchanger with a larger volume.

2) The system using single-stage supercritical carbon dioxide Brayton cycle cannot maintain an optimal working state throughout the wide operating temperature range of 200~700°C. The supercritical carbon dioxide Brayton cycle can only show more obvious advantages in the higher operating temperature range, and its performance may not have obvious advantages over the traditional steam power cycle in the low temperature range. In addition, the exhaust gas temperature of the supercritical carbon dioxide Brayton cycle gas turbine is relatively high. After the gas turbine exhaust gas is reheated by the regenerator, it is directly cooled by the cooler, causing a large amount of heat loss and reducing the thermal efficiency of the system.

3) Due to the instability of molten salt above 600 °C, traditional molten salt cannot meet the requirements of higher temperature heat storage. At present, there is no mature heat storage solution for higher temperature heat storage, which also limits the application of supercritical carbon dioxide in tower solar thermal power plants.

Utility model content

In order to combine the advantages of the two cycles of Brayton and steam Rankine, to realize the supercritical carbon dioxide Brayton cycle as the top cycle and the traditional steam Rankine cycle as the bottom cycle, the utility model provides a supercritical carbon dioxide Brayton cycle tower solar energy Thermal power generation system.

A supercritical carbon dioxide Brayton cycle tower solar thermal power generation system includes a tower concentrating heat collection system 2, and the tower concentrating heat collecting system 2 includes a tower heliostat and a heat absorption tower;

Also includes supercritical carbon dioxide Brayton cycle power generation system 1, heat storage system 3 and steam Rankine cycle power generation system 4;

The supercritical carbon dioxide Brayton cycle power generation system 1 includes a compressor 11, a turbo turbine 12, a first generator 13, a supercritical carbon dioxide steam generator 14, a regenerator 15, a cooler 16, and a supercritical carbon dioxide working medium Pump 17 and supercritical carbon dioxide heat absorber; the working medium in Brayton cycle power generation system 1 is supercritical carbon dioxide working medium;

The heat storage system 3 includes a molten salt cold tank 31, a molten salt hot tank 32, a second molten salt pump 34, a first molten salt pump 35, a molten salt side of a molten salt steam generator 45, and a molten salt heat sink; The heat storage system 3 has the functions of energy storage and peak regulation;

The supercritical carbon dioxide heat absorber and the molten salt heat absorber constitute a dual working medium parallel heat absorber, and are located at the heat-absorbing end of the heat-absorbing tower;

The steam Rankine cycle power generation system 4 includes a steam turbine 41, a second generator 42, a steam condenser 43, a feed water pump 44 and a steam side of a molten salt steam generator 45;

The supercritical carbon dioxide Brayton cycle power generation system 1 is used as the top circulation, the steam Rankine cycle power generation system 4 is used as the bottom circulation; the heat storage system 3 is located at the bottom circulation;

In the supercritical carbon dioxide Brayton cycle power generation system 1, the inlet temperature of the turbine gas turbine 12 is 550-750°C, the inlet pressure is 20-35MPa, the exhaust gas temperature at the outlet of the turbine gas turbine 12 is 400-600°C, and the exhaust gas temperature is 400-600°C. The gas pressure is 5-15MPa; in the steam Rankine cycle power generation system 4, the main steam temperature of the steam turbine 41 is 350-550°C, the main steam pressure is 8-13MPa, the reheat steam temperature is 350-550°C, and the reheat steam pressure is 350-550°C. It is 1～3MPa, the feed water temperature is 150～300℃; the working temperature of the molten salt hot tank 32 is 290～550℃;

When working during the day, the supercritical carbon dioxide Brayton cycle power generation system 1 operates under stable working conditions, and at the same time, the exhaust heat of the turbine gas turbine 12 is used to heat the steam to drive the bottom steam Rankine cycle power generation system 4; After the heat absorber is heated and heated, it is stored in the molten salt heat tank 32 of the heat storage system 3;

At night or on cloudy days, the molten salt in the molten salt hot tank 32 is used to generate steam in the molten salt steam generator 45 to drive the bottom steam turbine to generate electricity, and the cooled molten salt is refluxed and stored in the molten salt cold tank 31. At this time, the Brayton at the top is The cycle is stopped.

Further limited technical solutions are as follows:

The output shaft of the turbine gas turbine 12 of the supercritical carbon dioxide Brayton cycle system 1 is respectively connected with the first generator 13 and the drive shaft of the compressor 11; The mass pump (17), the carbon dioxide side of the supercritical carbon dioxide steam generator 14, the high temperature side of the regenerator 15 and the cooler 16 are connected to the inlet of the compressor 11, and the outlet of the compressor 11 passes through the low temperature of the regenerator 15 in series. The side and the supercritical carbon dioxide heat absorber are connected to the inlet of the turbine gas turbine 12;

The output shaft of the steam turbine 41 of the steam Rankine cycle power generation system 4 is connected to the drive shaft of the second generator 42, and the outlet of the steam turbine 41 is connected in series with the steam condenser 43, the feed water pump 44, the first valve 46, the melting The steam side inlet of the salt steam generator 45; the steam side outlet of the molten salt steam generator 45 and the steam working medium side outlet of the supercritical carbon dioxide steam generator 14 are connected in parallel, and then connected in series with the inlet of the steam turbine 41; the molten salt steam The steam side outlet of the generator 45 is connected in series with the fourth valve 49, and the steam working medium side inlet of the supercritical carbon dioxide steam generator 14 is connected in series with the second valve 47; the steam working medium side of the supercritical carbon dioxide steam generator 14 is connected in series The outlet is connected in series with the third valve 48;

The inlet of the molten salt cold tank 31 of the heat storage system 3 is connected to the molten salt side outlet of the molten salt steam generator 45, and the outlet pipeline of the molten salt cold tank 31 is connected in series with the first molten salt pump 35 and the first molten salt. The valve 36 and the inlet end of the molten salt heat absorber; the inlet of the molten salt heat tank 32 is connected to the outlet end of the molten salt heat absorber, and the outlet pipeline of the molten salt heat tank 32 is connected in series with the second molten salt pump 34, the second The molten salt valve 33 and the molten salt side inlet of the molten salt steam generator 45.

The supercritical carbon dioxide heat absorber and the molten salt heat absorber are both heat absorber heat absorbers, which are connected in parallel to form a dual working medium parallel heat absorber.

The supercritical carbon dioxide Brayton cycle is a simple basic Brayton cycle or a regenerative Brayton cycle or a reheated Brayton cycle or an intercooled reheated regenerative Brayton cycle.

The steam condenser 43 is a water-cooled condenser or an air-cooled condenser.

The steam turbine 41 is a multi-cylinder steam turbine.

The tower heliostat is a tracking tower heliostat, comprising a high reflectivity mirror surface, a mirror surface support bracket, a servo control system and a tracking transmission mechanism.

The beneficial technical effect of the present utility model is embodied in the following aspects:

1. The tower solar thermal power generation technology scheme of supercritical carbon dioxide Brayton-steam Rankine cascade cycle and double-tank molten salt heat storage has not been reported yet. Compared with the traditional tower-type solar thermal power generation technology based on the double-tank molten salt heat storage based on the steam Rankine cycle, the technical solution of the present utility model uses the supercritical carbon dioxide Brayton as the top cycle, which overcomes the problem of the steam Rankine cycle. The temperature limit can effectively improve the photoelectric conversion efficiency of solar energy when there is solar radiation (such as more than 300W/m ² ). Compared with the traditional tower-type solar thermal power generation technology based on supercritical carbon dioxide Brayton cycle, the technical solution of the present utility model utilizes water vapor Rankine as the bottom cycle of the supercritical carbon dioxide Brayton cycle to effectively carry out two types of thermodynamic cycles. combined to achieve complementary advantages. Taking advantage of the high efficiency of the Brayton cycle at high temperature and the characteristics of low temperature in the steam Rankine cycle, it also reduces the heat loss of the exhaust gas of the turbine gas turbine, making up for and significantly improving the power generation efficiency of the system.

2. The technical scheme of the parallel absorption of heat by the dual working medium of carbon dioxide and molten salt has not yet been reported. Compared with the single supercritical carbon dioxide heat absorption scheme, the technical scheme of the present utility model can ensure stable working parameters such as the inlet and outlet temperature, pressure and flow rate of carbon dioxide under a wide range of solar irradiation conditions (such as greater than 300W/m ² ). , so as to ensure the stability of supercritical carbon dioxide Brayton cycle power generation at the top. When the solar irradiation intensity changes, the flow rate of the molten salt can be adjusted. At the same time, the operating temperature of the molten salt, such as the outlet temperature, can remain unchanged.

3. The working mode of the technical solution of the present invention is innovative. When there is solar irradiation (eg greater than 300W/m ² ), the supercritical carbon dioxide Brayton cycle and the water vapor Rankine cycle work together to improve the heat-to-power conversion efficiency of the system. At night or when there is no solar radiation, the energy stored in the double-tank molten salt system is used to drive the bottom water vapor Rankine cycle to work. This unique working mode effectively improves the solar energy utilization efficiency and shortens the investment recovery period while ensuring the technical reliability of the system.

4. The technical scheme of the present utility model adopts molten salt as the energy storage medium of the bottom steam Rankine cycle power generation system, which effectively solves the problem of difficulty in selection of heat storage materials for conventional Brayton cycle. At the same time, the use of molten salt as the heat transfer working medium in some pipelines of the heat absorber can effectively reduce the flow of supercritical carbon dioxide, significantly reduce the pressure loss in the pipeline, improve the circulation efficiency of the supercritical carbon dioxide system, and reduce the heat exchange of the system. size and cost of the device.

Description of drawings

1 is a schematic diagram of a supercritical carbon dioxide Brayton cycle tower solar thermal power generation system of the present invention.

FIG. 2 is a schematic diagram of the supercritical carbon dioxide Brayton cycle power generation system of the present invention.

FIG. 3 is a schematic diagram of the heat storage system of the present invention.

4 is a schematic diagram of the steam Rankine cycle of the present invention.

The serial number in the above picture: Brayton cycle power generation system 1, tower concentrating heat collection system 2, heat storage system 3, steam Rankine cycle power generation system 4, compressor 11, turbine gas turbine 12, first generator 13 , supercritical carbon dioxide steam generator 14, regenerator 15, cooler 16, molten salt cold tank 31, molten salt hot tank 32, second molten salt valve 33, second molten salt pump 34, first molten salt pump 35 , the first molten salt valve 36, the steam turbine 41, the second generator 42, the steam condenser 43, the feed water pump 44, the molten salt steam generator 45, the first valve 46, the second valve 47, the third valve 48, the first Four-valve 49.

Detailed ways

In order to further illustrate the features and functions of the present utility model, the present utility model will be described in further detail below with reference to the drawings and embodiments.

Specific embodiment 1:

Referring to Figure 1, a supercritical carbon dioxide Brayton-steam Rankine cascade cycle tower solar thermal power generation system includes a tower concentrating heat collection system 2, a Brayton cycle power generation system 1, a heat storage system 3 and a steam Rankine cycle power generation system 4.

The tower concentrating heat collecting system 2 includes a tower heliostat and a heat absorption tower. The tower heliostat is a tracking tower heliostat, including a high reflectivity mirror, a mirror support bracket, a servo control system and a tracking transmission mechanism.

2, the Brayton cycle power generation system 1 includes a compressor 11, a turbo turbine 12, a first generator 13, a supercritical carbon dioxide steam generator 14, a regenerator 15, a cooler 16 and a supercritical carbon dioxide heat absorber ; The working fluid in Brayton cycle power generation system 1 is supercritical carbon dioxide working fluid.

The output shaft of the turbo-turbine 12 is respectively connected with the drive shaft of the first generator 13 and the compressor 11; the outlet of the turbo-turbine 12 passes through the supercritical carbon dioxide working medium pump 17 and the supercritical carbon dioxide steam generator 14 in series in sequence. The carbon dioxide side, the high temperature side of the regenerator 15 and the cooler 16 are connected to the inlet of the compressor 11, and the outlet of the compressor 11 is connected to the turbine gas through the low temperature side of the regenerator 15 and the supercritical carbon dioxide heat absorber in series. Inlet of turbine 12.

The supercritical carbon dioxide Brayton cycle is a simple basic Brayton cycle.

4, the steam Rankine cycle power generation system 4 includes a steam turbine 41, a second generator 42, a steam condenser 43, a feed water pump 44 and a molten salt steam generator 45; the steam turbine 41 is a multi-cylinder steam turbine, and the steam condenser 43 It is a water-cooled condenser. The output shaft of the steam turbine 41 is connected with the drive shaft of the second generator 42, and the outlet of the steam turbine 41 is connected in series with the steam condenser 43, the feed water pump 44, the first valve 46, and the steam side inlet of the molten salt steam generator 45; The steam side outlet of the molten salt steam generator 45 is connected in parallel with the steam working medium side outlet of the supercritical carbon dioxide steam generator 14, and is connected in series with the inlet of the steam turbine 41; the steam side outlet of the molten salt steam generator 45 is connected in series The fourth valve 49, the second valve 47 is connected in series with the steam working medium side inlet of the supercritical carbon dioxide steam generator 14; the third valve 48 is connected in series with the steam working medium side outlet of the supercritical carbon dioxide steam generator 14.

3, the heat storage system 3 includes a molten salt cold tank 31, a molten salt hot tank 32, a second molten salt valve 33, a second molten salt pump 34, a first molten salt pump 35, a first molten salt valve 36, a molten salt The molten salt side of the salt steam generator 45 and the molten salt heat absorber; the heat storage system 3 has the functions of energy storage and peak regulation.

Both the supercritical carbon dioxide heat absorber and the molten salt heat absorber are endothermic tube heat absorbers, which are connected in parallel to form a duplex parallel heat absorber. The inlet of the molten salt cold tank 31 of the heat storage system 3 is connected to the molten salt side outlet of the molten salt steam generator 45, and the outlet pipeline of the molten salt cold tank 31 is connected in series with the first molten salt pump 35 and the first molten salt valve 36 and the inlet end of the molten salt heat absorber; the inlet of the molten salt heat tank 32 is connected to the outlet end of the molten salt heat absorber, and the outlet pipeline of the molten salt heat tank 32 is connected in series with the second molten salt pump 34 and the second molten salt Valve 33, molten salt side inlet of molten salt steam generator 45.

In the Brayton cycle power generation system 1, the inlet temperature of the turbine gas turbine 12 is 700°C, the inlet pressure is 23.86MPa, the exhaust gas temperature at the outlet of the turbine gas turbine 12 is 560°C, and the exhaust gas pressure is 8.96MPa; the steam Rankine In the cycle power generation system 4, the main steam temperature of the steam turbine 41 is 540°C, the main steam pressure is 13MPa, the reheat steam temperature is 540°C, the reheat steam pressure is 1.8MPa, and the feed water temperature is 222°C. The operating temperature range of the molten salt cold tank 31 and the molten salt hot tank 32 is 290 to 550°C.

The specific working principle is as follows:

Referring to FIG. 2, in the Brayton cycle power generation system 1, supercritical carbon dioxide is pressurized and transported to the supercritical carbon dioxide heat absorber through the compressor 11, and the carbon dioxide absorbs heat in the heat absorption tube to heat up, and the output of supercritical carbon dioxide at 700 ° C enters the permeable carbon dioxide. The flat gas turbine 12 completes the expansion work, the first generator 13 and the compressor 11. The exhaust gas that has completed the expansion work in the turbine gas turbine 12 enters the supercritical carbon dioxide steam generator 14 to generate superheated steam with a temperature of 540° C. and a pressure of 13 MPa. Machine 11 completes a complete cycle. At night or under cloudy and rainy conditions, the Brayton cycle power generation system 1 is in a shutdown state;

4, in the steam Rankine cycle power generation system 4, the superheated steam generated by the supercritical carbon dioxide steam generator 14 enters the steam turbine 41 to complete the expansion work, and the exhaust gas of the steam turbine 41 enters the steam condenser 43 to condense into water. Under the conditions of better daytime irradiation, the first valve 46 and the fourth valve 49 are closed, the second valve 47 and the third valve 48 are opened, and the condensed water is transported to the supercritical carbon dioxide steam generator 14 through the feed water pump 44 to generate steam, and the completion of Circulation; under night or rainy weather conditions, the first valve 46 and the fourth valve 49 are opened, the second valve 47 and the third valve 48 are closed, and the condensed water is transported to the molten salt steam generator 45 through the feed pump 44 to generate steam;

Referring to FIG. 3 , in the heat storage system 3, under better conditions of irradiation during the day, the second molten salt valve 33 is closed, the first molten salt valve 36 and the first molten salt pump 35 are opened, and the molten salt cooling tank 31 is closed. The molten salt at 290 °C is transported to the molten salt circuit of the molten salt heat absorber through the first molten salt pump 35, the molten salt absorbs heat in the heat absorption tube and increases the temperature, and the molten salt at 550 °C is output from the molten salt heat absorber and returns. into the molten salt hot tank 32. At night or under rainy weather conditions, close the first molten salt valve 36, open the second molten salt valve 33 and the second molten salt pump 34, and the molten salt at 550°C in the molten salt hot tank 32 is transported through the second molten salt pump 34. To the molten salt side of the molten salt steam generator 45, the molten salt is returned to the molten salt cold tank 31 after the temperature of the molten salt is lowered on the molten salt side of the molten salt steam generator 45.

Specific embodiment 2:

Refer to the specific embodiment 1 for the system schematic diagram. Compared with specific embodiment 1, the difference is:

In Brayton cycle power generation system 1, the inlet temperature of the turbine gas turbine 12 is 600 °C, the inlet pressure is 20 MPa, the exhaust gas temperature at the outlet of the turbine gas turbine 12 is 450 °C, and the exhaust gas pressure is 5 MPa; steam Rankine cycle The main steam temperature of the steam turbine 41 in the power generation system 4 is 425°C, the main steam pressure is 8.33MPa, the reheat steam temperature is 425°C, the reheat steam pressure is 1.6MPa, and the feed water temperature is 195°C. The operating temperature range of the molten salt cold tank 31 and the molten salt hot tank 32 is 290 to 435°C.

For other functions and features, please refer to Embodiment 1.

The present utility model has been described above in conjunction with the accompanying drawings, but the present utility model is not limited to the above-mentioned specific embodiments. Improvement and fine-tuning all belong to the protection of the present invention.

Claims (7)

1. A supercritical carbon dioxide Brayton cycle tower solar thermal power generation system, comprising a tower concentrating heat collecting system (2), the tower concentrating heat collecting system (2) comprising a tower heliostat and an endothermic tower; characterized by: Also includes a Brayton cycle power generation system (1), a heat storage system (3) and a steam Rankine cycle power generation system (4); The Brayton cycle power generation system (1) comprises a compressor (11), a gas turbine (12), a first generator (13), a supercritical carbon dioxide steam generator (14), a regenerator (15), a cooler (16), a supercritical carbon dioxide working medium pump (17) and a supercritical carbon dioxide heat absorber; the working medium in the Brayton cycle power generation system (1) is a supercritical carbon dioxide working medium; The heat storage system (3) includes a molten salt cold tank (31), a molten salt hot tank (32), a second molten salt pump (34), a first molten salt pump (35), and a molten salt steam generator (45) ) of the molten salt side and the molten salt heat absorber; the heat storage system (3) has the functions of energy storage and peak regulation; The supercritical carbon dioxide heat absorber and the molten salt heat absorber constitute a dual working medium parallel heat absorber, and are located at the heat-absorbing end of the heat-absorbing tower; The steam Rankine cycle power generation system (4) comprises a steam turbine (41), a second generator (42), a steam condenser (43), a feed water pump (44) and a steam side of a molten salt steam generator (45) ; The supercritical carbon dioxide Brayton cycle power generation system (1) is used as the top circulation, the steam Rankine cycle power generation system (4) is used as the bottom circulation; the heat storage system (3) is located in the bottom circulation; In the supercritical carbon dioxide Brayton cycle power generation system (1), the inlet temperature of the turbine gas turbine (12) is 550-750°C, the inlet pressure is 20-35MPa, and the exhaust gas temperature at the outlet of the turbine gas turbine (12) is 400～600℃, the exhaust pressure is 5～15MPa; in the steam Rankine cycle power generation system (4), the main steam temperature of the steam turbine (41) is 350～550℃, the main steam pressure is 8～13MPa, and the reheat steam temperature is 350～550℃. is 350～550℃, the reheat steam pressure is 1～3MPa, the feed water temperature is 150～300℃; the working temperature of the molten salt hot tank (32) is 290～550℃; During daytime work, the supercritical carbon dioxide Brayton cycle power generation system (1) operates under stable conditions, while the exhaust heat from the turbine gas turbine (12) is used to heat the steam to drive the underlying steam Rankine cycle power generation system (4) ; The molten salt is stored in the molten salt hot tank (32) of the heat storage system (3) after being heated and heated by the molten salt heat absorber; At night or on cloudy days, the molten salt in the molten salt hot tank (32) is used to generate steam in the molten salt steam generator (45) to drive the bottom steam turbine to generate electricity, and the cooled molten salt is refluxed and stored in the molten salt cold tank (31), At this point the Brayton cycle at the top is in a shutdown state. 2. A supercritical carbon dioxide Brayton cycle tower solar thermal power generation system according to claim 1, characterized in that: the output of the turbo gas turbine (12) of the supercritical carbon dioxide Brayton cycle system (1) The shafts are respectively connected with the drive shafts of the first generator (13) and the compressor (11); the outlet of the gas turbine (12) passes through the supercritical carbon dioxide working fluid pump (17), the supercritical carbon dioxide steam generator in series in sequence The carbon dioxide side of (14), the high temperature side of the regenerator (15) and the cooler (16) are connected to the inlet of the compressor (11), and the outlet of the compressor (11) passes through the low temperature of the regenerator (15) in series. The side and the supercritical carbon dioxide heat absorber are connected to the inlet of the turbo gas turbine (12); The output shaft of the steam turbine (41) of the steam Rankine cycle power generation system (4) is connected with the drive shaft of the second generator (42), and the outlet of the steam turbine (41) is connected in series with the steam condenser (43), Feed water pump (44), first valve (46), steam side inlet of molten salt steam generator (45); steam side outlet of molten salt steam generator (45) and water of supercritical carbon dioxide steam generator (14) The outlet of the steam working medium is connected in parallel with the inlet of the steam turbine (41); the outlet of the steam side of the molten salt steam generator (45) is connected in series with a fourth valve (49), and the supercritical carbon dioxide steam generator (14) A second valve (47) is connected in series with the water vapor working medium side inlet of the supercritical carbon dioxide steam generator (14); a third valve (48) is connected in series with the water vapor working medium side outlet of the supercritical carbon dioxide steam generator (14); The inlet of the molten salt cold tank (31) of the heat storage system (3) is connected to the molten salt side outlet of the molten salt steam generator (45), and the outlet pipeline of the molten salt cold tank (31) is connected in series with the first molten salt. The salt pump (35) is connected with the first molten salt valve (36) and the inlet end of the molten salt heat absorber; the inlet of the molten salt heat tank (32) is communicated with the outlet end of the molten salt heat absorber, and the molten salt heat tank (32) ) are connected in series with the second molten salt pump (34), the second molten salt valve (33), and the molten salt side inlet of the molten salt steam generator (45). 3. a kind of supercritical carbon dioxide Brayton cycle tower solar thermal power generation system according to claim 1, is characterized in that: described supercritical carbon dioxide heat absorber and molten salt heat absorber are both heat absorption pipe heat absorbers . 4. a kind of supercritical carbon dioxide Brayton cycle tower solar thermal power generation system according to claim 1, is characterized in that: described supercritical carbon dioxide Brayton cycle is simple basic Brayton cycle or regenerative Brayton cycle or regenerating Hot Brayton cycle or intercooling reheating reheating Brayton cycle. 5 . The supercritical carbon dioxide Brayton cycle tower solar thermal power generation system according to claim 1 , wherein the steam condenser ( 43 ) is a water-cooled condenser or an air-cooled condenser. 6 . 6 . The supercritical carbon dioxide Brayton cycle tower solar thermal power generation system according to claim 1 , wherein the steam turbine ( 41 ) is a multi-cylinder steam turbine. 7 . 7. a kind of supercritical carbon dioxide Brayton cycle tower type solar thermal power generation system according to claim 1, is characterized in that: described tower type heliostat is a tracking type tower type heliostat, comprising high reflectivity mirror surface, Mirror support bracket, servo control system and tracking transmission mechanism.