Cold end anti-freezing back pressure reducing system of photo-thermal steam turbine and operation method

Abstract

The invention discloses a photo-thermal steam turbine cold end anti-freezing back pressure reducing system which comprises a photo-thermal power station light and heat gathering system, the photo-thermal power station light and heat gathering system is connected with a photo-thermal steam turbine, the photo-thermal steam turbine is connected with a steam exhaust device, the steam exhaust device is connected with an air cooling island through a steam exhaust pipeline, the steam exhaust pipeline is connected with a heat exchanger, and the heat exchanger is connected with a high-temperature heat storage tank. The high-temperature heat storage tank is connected with the auxiliary machine cooling tower which is connected with the heat exchanger and the low-temperature tank. The invention further discloses an operation method of the system, in the low-load working condition at night in winter, the surplus of the auxiliary machine cooling tower is used for cooling dead steam of the photo-thermal steam turbine; in the unit late peak top load stage, partial waste steam is shunted to pass through the heat exchanger, and heat is stored in the high-temperature heat storage tank; in the night low-load working condition stage in summer and winter, high-temperature water in the high-temperature heat storage tank is cooled into low-temperature water through the surplus of the auxiliary machine cooling tower; the freezing problem of the cold end air cooling island of the photo-thermal steam turbine is solved, and the reliability and safety of equipment are guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of solar thermal power generation equipment, and specifically relates to a cold-end anti-freezing and back-pressure reduction system for a solar thermal steam turbine, and also relates to an operation method of the cold-end anti-freezing and back-pressure reduction system for a solar thermal steam turbine. Background Art

[0002] As a regulating power source integrating power generation and energy storage, solar thermal power generation has the advantage of long-term energy storage. It can generate electricity continuously for 24 hours, or can adjust the peak according to the needs of the power grid at any time. During peak load periods, the steam turbine generator set needs to output 100% power, and during low load periods, the steam turbine generator set needs to reduce the power to 15%. In addition, with the change of the positioning of solar thermal power plants, the main function of solar thermal power generation is energy storage + peak regulation. Therefore, in the design concept of the unit, it is mainly to adapt to the characteristics of frequent and rapid start-stop of the unit. During this process, while ensuring the safe and stable operation of the unit, the economy of the unit in a wider load range should be improved.

[0003] Solar thermal power plants are mainly concentrated in areas with sufficient solar resources in the northwest. At night without sunlight, the solar thermal steam turbine needs to operate under low load conditions to ensure non-stop operation at night. In addition, the northwest region is relatively cold in winter. When the solar thermal steam turbine operates at low load, the cold-end heat load is relatively low, which is extremely likely to cause the risk of freezing of the air-cooled island. At present, the anti-freezing of the air-cooled island at the cold end of the solar thermal steam turbine mainly adopts the methods of closing some air-cooled island units, blocking the inlet of the air-cooled unit, and reversing the suction of the counter-flow fan to draw warm air to heat the air-cooled island. Its disadvantages are high operating costs and poor flexibility of the unit. Summary of the Invention

[0004] The purpose of the invention is to provide a cold-end anti-freezing and back-pressure reduction system for a solar thermal steam turbine, which solves the problem of freezing of the air-cooled island at the cold end under the low load operating condition of the solar thermal steam turbine in winter in the existing system.

[0005] Another purpose of the invention is to provide an operation method of the cold-end anti-freezing and back-pressure reduction system for a solar thermal steam turbine.

[0006] The technical solution adopted by the invention is that the cold-end anti-freezing and back-pressure reduction system for a solar thermal steam turbine includes a solar thermal power plant concentrating and heat-collecting system. The solar thermal power plant concentrating and heat-collecting system is connected to the solar thermal steam turbine through a first pipeline. The bottom of the solar thermal steam turbine is connected to an exhaust device. The exhaust port of the exhaust device is connected to an exhaust pipeline. The exhaust pipeline is connected to the inlet of the air-cooled island through an eighth pipeline. The bottom outlet of the air-cooled island is connected to the exhaust device through a pipeline. The exhaust pipeline is also connected to a heat exchanger through a first pipeline. The heat exchanger is connected to a high-temperature heat storage tank through a fourth pipeline. The high-temperature heat storage tank is connected to the upper part of the auxiliary machine cooling through a sixth pipeline. The heat exchanger is connected to the inlet of the auxiliary machine cooling tower through a fifth pipeline. The bottom of the auxiliary machine cooling tower is connected to the inlet of the steam turbine auxiliary machine heat exchanger through a circulating pump pipeline. The auxiliary machine cooling tower is also connected to a low-temperature tank through a seventh pipeline.

[0007] The low-temperature tank is connected to the inlet of the first circulating water pump through the second pipeline, and the outlet of the first circulating water pump is connected to the heat exchanger; the heat exchanger is connected to the bottom of the exhaust steam device through the condensate pipe; a second valve is provided on the second pipeline.

[0008] The auxiliary cooling tower is connected to the inlet of the first circulating water pump through the third pipeline, and a third valve is provided on the third pipeline; the outlet of the steam turbine auxiliary heat exchanger is connected to the inlet of the auxiliary cooling tower.

[0009] A third circulating water pump is provided on the circulating pump pipeline; a seventh valve is provided on the seventh pipeline; an eighth valve is provided on the eighth pipeline, and a fifth valve is provided on the fifth pipeline; a fourth valve is provided on the fourth pipeline, and a first valve is provided on the first pipeline; a second circulating water pump and a sixth valve are provided on the sixth pipeline.

[0010] Another technical solution adopted by the present invention is a method for operating a cold-end anti-freezing and back-pressure reducing system of a solar thermal steam turbine, specifically: 1) During the low-load condition at night in winter, the exhaust steam of the solar thermal steam turbine is less, lower than the minimum anti-freezing flow rate of the air-cooled island. At this time, the surplus of the auxiliary cooling tower is used to cool the exhaust steam of the solar thermal steam turbine. 2) During the peak load stage of the unit in the evening, a part of the exhaust steam is diverted through the heat exchanger and stored in the high-temperature heat storage tank. 3) During the low-load condition at night in summer, the high-temperature water in the high-temperature heat storage tank is cooled to low-temperature water through the surplus of the auxiliary cooling tower to reserve a heat storage space for the next heat storage; during the low-load condition at night in winter, the high-temperature water in the high-temperature heat storage tank is cooled to low-temperature water through the surplus of the auxiliary cooling tower. On the one hand, it reserves a heat storage space for the next heat storage, and on the other hand, it prevents the risk of freezing of the auxiliary cooling tower.

[0011] The characteristics of the present invention also lie in that In case 1), specifically: open the first valve, the third valve and the fifth valve, close the eighth valve, the second valve, the fourth valve, the seventh valve and the sixth valve. The exhaust steam of the solar thermal steam turbine does not flow to the air-cooled island, but flows through the first valve to the heat exchanger, and after passing through the heat exchanger, it becomes condensate and flows to the exhaust steam device; the cooling water in the auxiliary cooling tower flows through the third valve and the first circulating water pump and then to the heat exchanger, and after cooling the exhaust steam, it is heated to high-temperature water and then flows through the fifth valve to the auxiliary cooling tower for heat dissipation. Another path of cooling water in the auxiliary cooling tower flows through the third circulating water pump and then to the steam turbine auxiliary heat exchanger, and then flows back to the auxiliary cooling tower for heat dissipation.

[0012] In case 2), specifically: Open the first valve, the eighth valve, the second valve and the fourth valve, and close the third valve, the fifth valve, the seventh valve and the sixth valve. Part of the exhaust steam of the solar thermal steam turbine flows through the eighth valve to the air-cooled island, is condensed into condensate water after heat exchange and flows back to the exhaust steam device. Another part flows through the first valve and the heat exchanger, is condensed into condensate water after heat exchange and flows to the exhaust steam device. The low-temperature water in the low-temperature tank flows through the second valve and the first circulating water pump and then flows to the heat exchanger, is heated into high-temperature water after passing through the heat exchanger, and flows to the high-temperature heat storage tank through the fourth valve.

[0013] In case 3), specifically: Open the eighth valve, the sixth valve and the seventh valve, and close the first valve, the second valve, the third valve, the fourth valve and the fifth valve. The exhaust steam of the solar thermal steam turbine flows through the eighth valve to the air-cooled island, is cooled into condensate water and flows back to the exhaust steam device. The high-temperature water in the high-temperature heat storage tank flows through the second circulating water pump and then flows to the auxiliary cooling tower for heat dissipation, and is cooled into low-temperature water and flows to the low-temperature tank.

[0014] The beneficial effects of the present invention are as follows: The cold-end anti-freezing system of the solar thermal steam turbine of the present invention adds a heat storage device to prevent freezing and heat preservation of the auxiliary cooling tower and the air-cooled island in case of shutdown of the solar thermal steam turbine in winter, and shunts part of the exhaust steam for heat storage during the peak period of the unit in summer evenings, reducing the back pressure of the unit and improving the load-carrying capacity of the unit. On the one hand, the present invention can solve the problem of freezing of the air-cooled island at the cold end of the solar thermal steam turbine, ensure the reliability and safety of the equipment, and at the same time make full use of the surplus cooling capacity of the auxiliary cooling tower in winter to improve the effective utilization rate of the equipment. On the other hand, when the solar thermal steam turbine is shut down in winter, it prevents the auxiliary cooling tower from freezing, reduces the use of system electric tracing, and improves the overall economy of the unit. Description of the Drawings

[0015] Figure 1 is a schematic structural diagram of the cold-end anti-freezing and back-pressure reducing system of the solar thermal steam turbine of the present invention.

[0016] In the figure, 1. Concentrating and heat-collecting system of the solar thermal power station, 2. Solar thermal steam turbine, 3. Exhaust steam device, 4. Exhaust steam pipeline, 5. Air-cooled island, 6. Condensate water pipe, 7. Heat exchanger, 8. Low-temperature tank, 9. High-temperature heat storage tank, 10. Auxiliary cooling tower, 11. Turbine auxiliary heat exchanger, 12. First circulating water pump, 13. Second circulating water pump, 14. Third circulating water pump, 15. First valve, 16. Second valve, 17. Third valve, 18. Fourth valve, 19. Fifth valve, 20. Sixth valve, 21. Seventh valve, 22. Eighth valve. Detailed Embodiments

[0017] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0018] Embodiment 1 The cold-end anti-freezing and back-pressure reducing system for a solar thermal steam turbine of the present invention is as follows Figure 1 As shown in the figure, it includes a solar thermal power plant concentrating and heat-collecting system 1, a solar thermal steam turbine 2, an exhaust device 3, an air-cooled island 5, a low-temperature tank 8, a high-temperature heat storage tank 9, an auxiliary cooling tower 10, and a steam turbine auxiliary heat exchanger 11; The solar thermal power plant concentrating and heat-collecting system 1 is connected to the solar thermal steam turbine 2 through a first pipeline. The bottom of the solar thermal steam turbine 2 is connected to the exhaust device 3. The exhaust port of the exhaust device 3 is connected to an exhaust pipeline 4. The exhaust pipeline 4 is connected to the inlet of the air-cooled island 5 through an eighth pipeline. An eighth valve 22 is provided on the eighth pipeline. The bottom outlet of the air-cooled island 5 is connected to the exhaust device 3 through a pipeline. The exhaust pipeline 4 is also connected to a heat exchanger 7 through a first pipeline. A first valve 15 is provided on the first pipeline. The heat exchanger 7 is connected to the bottom of the exhaust device 3 through a condensate pipeline 6. The heat exchanger 7 is connected to the high-temperature heat storage tank 9 through a fourth pipeline. A fourth valve 18 is provided on the fourth pipeline. The high-temperature heat storage tank 9 is connected to the upper part of the auxiliary cooling tower 10 through a sixth pipeline. A second circulation pump 13 and a sixth valve 20 are provided on the sixth pipeline. The heat exchanger 7 is connected to the inlet of the auxiliary cooling tower 10 through a fifth pipeline. A fifth valve 19 is provided on the fifth pipeline; The low-temperature tank 8 is connected to the inlet of a first circulation pump 12 through a second pipeline. A second valve 16 is provided on the second pipeline. The outlet of the first circulation pump 12 is connected to the heat exchanger 7; The auxiliary cooling tower 10 is connected to the inlet of the first circulation pump 12 through a third pipeline. A third valve 17 is provided on the third pipeline. The bottom of the auxiliary cooling tower 10 is connected to the inlet of the steam turbine auxiliary heat exchanger 11 through a circulation pump pipeline. A third circulation pump 14 is provided on the circulation pump pipeline. The outlet of the steam turbine auxiliary heat exchanger 11 is connected to the inlet of the auxiliary cooling tower 10. The auxiliary cooling tower 10 is also connected to the low-temperature tank 8 through a seventh pipeline. A seventh valve 21 is provided on the seventh pipeline.

[0019] Embodiment 2 The operation method of the cold-end anti-freezing and back-pressure reducing system for a solar thermal steam turbine of the present invention is specifically as follows: 1) During the low-load operation at night in winter, the exhaust steam of the solar thermal steam turbine is less, lower than the minimum anti-freezing flow rate of the air-cooled island. At this time, the surplus capacity of the auxiliary cooling tower 10 is used to cool the exhaust steam of the solar thermal steam turbine 2. Specifically: Open the first valve 15, the third valve 17, and the fifth valve 19, and close the eighth valve 22, the second valve 16, the fourth valve 18, the seventh valve 21, and the sixth valve 20. The exhaust steam of the solar thermal steam turbine 2 does not flow to the air-cooled island 5, but flows through the first valve 15 to the heat exchanger 7, and after passing through the heat exchanger 7, it becomes condensed water and flows to the exhaust steam device 3; The cooling water in the auxiliary cooling tower 10 flows through the third valve 17 and the first circulating water pump 12 and then flows to the heat exchanger 7. After cooling the exhaust steam, it is heated to high-temperature water and then flows through the fifth valve 19 to the auxiliary cooling tower 10 for heat dissipation. Another path of the cooling water in the auxiliary cooling tower 10 flows through the third circulating water pump 14 and then flows to the turbine auxiliary heat exchanger 11, and then flows back to the auxiliary cooling tower 10 for heat dissipation; 2) During the peak load stage of the unit in the evening peak, a part of the exhaust steam is diverted through the heat exchanger 7 and stored in the high-temperature heat storage tank 9. Specifically: Open the first valve 15, the eighth valve 22, the second valve 16, and the fourth valve 18, and close the third valve 17, the fifth valve 19, the seventh valve 21, and the sixth valve 20. A part of the exhaust steam of the solar thermal steam turbine 2 flows through the eighth valve 22 to the air-cooled island 5, and after heat exchange, it becomes condensed water and flows back to the exhaust steam device 3. Another part flows through the first valve 15 and the heat exchanger 7, and after heat exchange, it becomes condensed water and flows to the exhaust steam device 3. The low-temperature water in the low-temperature tank 8 flows through the second valve 16 and the first circulating water pump 12 and then flows to the heat exchanger 7. After being heated by the heat exchanger 7, it becomes high-temperature water and then flows through the fourth valve 18 to the high-temperature heat storage tank 9.

[0020] 3) During the low-load operation at night in summer, the high-temperature water in the high-temperature heat storage tank 9 is cooled to low-temperature water by the surplus capacity of the auxiliary cooling tower 10 to reserve a heat storage space for the next heat storage; During the low-load operation at night in winter, the high-temperature water in the high-temperature heat storage tank 9 is cooled to low-temperature water by the surplus capacity of the auxiliary cooling tower 10. On the one hand, it reserves a heat storage space for the next heat storage, and on the other hand, it prevents the risk of freezing of the auxiliary cooling tower 10. Specifically: Open the eighth valve 22, the sixth valve 20, and the seventh valve 21, and close the first valve 15, the second valve 16, the third valve 17, the fourth valve 18, and the fifth valve 19. The exhaust steam of the solar thermal steam turbine 2 flows through the eighth valve 22 to the air-cooled island 5, is cooled to condensed water and flows back to the exhaust steam device 3. The high-temperature water in the high-temperature heat storage tank 9 flows through the second circulating water pump 13 and then flows to the auxiliary cooling tower 10 for heat dissipation. After cooling, it becomes low-temperature water and flows to the low-temperature tank 8.

[0021] Example 3 Through the heat balance diagrams of the solar thermal steam turbine under 100% rated load condition, 75% rated load condition, 50% rated load condition, 40% rated load condition, 30% rated load condition and 20% rated load condition, the interpolation method is used to calculate the exhaust steam volume under any load condition, and it is compared with the minimum anti-freezing flow rate of the air-cooled island. When the winter ambient temperature reaches below zero degrees Celsius and the solar thermal steam turbine operates under low load conditions, if the exhaust steam volume is less than the minimum anti-freezing flow rate of the air-cooled island at this time, the air-cooled island stops operating, and the surplus of the auxiliary cooling tower is used to cool the exhaust steam to maintain the back pressure of the unit and ensure safe and reliable operation.

[0022] Example 4 After using the system of the present invention, on the one hand, it can solve the freezing problem of the air-cooled island at the cold end of the solar thermal steam turbine, ensure the reliability and safety of the equipment, and at the same time make full use of the surplus cooling capacity of the auxiliary cooling tower in winter to improve the effective utilization rate of the equipment; on the other hand, during the winter shutdown or low load operation of the solar thermal steam turbine, it can prevent the freezing of the auxiliary cooling tower, reduce the use of system electric tracing, and improve the overall economy of the unit; at the same time, during the summer peak period of the unit, part of the exhaust steam is diverted for heat storage to reduce the back pressure of the unit and improve the load-carrying capacity of the unit.

[0023] Example 5 For the cold end system of a 100MW direct air-cooled solar thermal power station, the design temperature: 13.17°C; the design back pressure (at the steam exhaust port of the steam turbine): 12.0 kPa; after calculation, the summer operating back pressure of the main engine is about (at the steam exhaust port of the steam turbine) 35.0 kPa; the dry bulb temperature for the summer condition calculation is taken as 33.50°C; the number of cooling units of the air-cooled condenser: each unit is equipped with 3 rows of cooling unit groups, each row consists of 3 cooling units, and each unit has a total of 3x3 = 9 cooling units; the radiator area: 240000m 2 ; The cold end heat load under 100% THA condition: 125MW; the cold end heat load under 5% THA condition: 12MW.

[0024] The auxiliary equipment cooling system adopts a dry-wet combined cooling system with mechanical ventilation. Its cooling method is the series operation of dry air cooling and evaporative cooling. When the ambient air temperature is lower than the critical spraying water temperature of the combined cooling (set at 25°C in this project), pure air cooling operation is adopted; when the air temperature is higher than the critical spraying water temperature, the spray water pumps (softened water) of several evaporative air coolers are gradually started to meet the cooling requirements of the cooled medium under the condition of relatively high ambient air temperature. The hot water after the auxiliary equipment is cooled is transported through a pipeline to the radiator of the dry-wet combined cooling tower for cooling. After the cooled water is boosted by the auxiliary equipment cooling water pump, it is transported through a pipeline to the auxiliary equipment cooling water system of the main power building. This system is a closed-loop cooling system, and the cooling medium is demineralized water. Three composite dry-wet combined cooling units are set up. Each unit includes a dry part and a wet part. Each composite dry-wet combined cooling unit is equipped with a fan system with a diameter of 6m. The dry cooling part is provided with 4 dry cooling tube bundle heat exchange units; the wet cooling part is equipped with 1 set of tubular (without fins) heat exchange units and 2 sets of spray water pumps (1 used and 1 standby).

[0025] Example 6 On the basis of Example 5, further, the design parameters of each composite dry-wet combined cooling tower: the design dry bulb temperature in summer of the air cooling part: 25.0°C; the cooling water volume of the auxiliary equipment: 1000 m 3 / h; the design inlet water temperature of the cooling water of the dry cooling tower in summer: 43°C; the design outlet water temperature of the cooling water of the dry cooling tower in summer: 38°C; the number of sections of the composite dry-wet combined cooling tower: 3 sections; the total heat dissipation area of the radiator in the dry cooling part: 24500m 2 ; the total heat dissipation area of the wet cooling part: 600m 2 ; the design heat load of the auxiliary equipment cooling tower under 100%THA condition: 16MW; the heat load of the auxiliary equipment cooling system under 5%THA condition: 3MW.

[0026] Based on the analysis of the above parameters, in winter, at night, the unit operates at a low load under 5%THA condition. The heat load at the cold end of the unit is 12MW, the heat load of the auxiliary equipment cooling system is 3MW, and the surplus of the auxiliary equipment cooling tower is 13 MW, which can meet the heat dissipation requirements of the heat load at the cold end of the unit. The air-cooled island valve above the exhausted steam of the unit can be closed, and the exhausted steam of the unit can be cooled by the auxiliary equipment cooling tower to achieve the anti-freezing requirement of the air-cooled island at the cold end of the unit, and at the same time avoid the freezing of the auxiliary equipment cooling tower due to insufficient heat.

Claims

1. A photothermal steam turbine cold end anti-freezing and back pressure reduction system, characterized in that It includes a concentrating and heat-collecting system (1) of a solar thermal power station. The concentrating and heat-collecting system (1) of the solar thermal power station is connected to a solar thermal steam turbine (2) through a first pipeline. The bottom of the solar thermal steam turbine (2) is connected to an exhaust steam device (3). The exhaust port of the exhaust steam device (3) is connected to an exhaust steam pipeline (4). The exhaust steam pipeline (4) is connected to the inlet of an air-cooled island (5) through an eighth pipeline. The bottom outlet of the air-cooled island (5) is connected to the exhaust steam device (3) through a pipeline. The exhaust steam pipeline (4) is also connected to a heat exchanger (7) through a first pipeline. The heat exchanger (7) is connected to a high-temperature heat storage tank (9) through a fourth pipeline. The high-temperature heat storage tank (9) is connected to the upper part of an auxiliary cooling tower (10) through a sixth pipeline. The heat exchanger (7) is connected to the inlet of the auxiliary cooling tower (10) through a fifth pipeline. The bottom of the auxiliary cooling tower (10) is connected to the inlet of a steam turbine auxiliary heat exchanger (11) through a circulating pump pipeline. The auxiliary cooling tower (10) is also connected to a low-temperature tank (8) through a seventh pipeline.

2. The photothermal steam turbine cold-end anti-freezing and back pressure reduction system according to claim 1, characterized in that, The low-temperature tank (8) is connected to the inlet of a first circulating water pump (12) through a second pipeline. The outlet of the first circulating water pump (12) is connected to the heat exchanger (7); the heat exchanger (7) is connected to the bottom of the exhaust steam device (3) through a condensate pipe (6); a second valve (16) is arranged on the second pipeline.

3. The photothermal steam turbine cold end anti-freezing and back pressure reduction system according to claim 2, characterized in that, The auxiliary cooling tower (10) is connected to the inlet of the first circulating water pump (12) through a third pipeline. A third valve (17) is arranged on the third pipeline; the outlet of the steam turbine auxiliary heat exchanger (11) is connected to the inlet of the auxiliary cooling tower (10).

4. The photothermal steam turbine cold end anti-freezing and back pressure reduction system according to claim 3, characterized in that, A third circulating water pump (14) is arranged on the circulating pump pipeline; a seventh valve (21) is arranged on the seventh pipeline; an eighth valve (22) is arranged on the eighth pipeline, and a fifth valve (19) is arranged on the fifth pipeline; a fourth valve (18) is arranged on the fourth pipeline, and a first valve (15) is arranged on the first pipeline; a second circulating water pump (13) and a sixth valve (20) are arranged on the sixth pipeline.

5. The operating method of the photothermal steam turbine cold end anti-freezing and back pressure reduction system according to claim 4, characterized in that Specifically: 1) In the low-load condition at night in winter, the exhaust steam of the solar thermal steam turbine is less, lower than the minimum anti-freezing flow rate of the air-cooled island. At this time, the surplus of the auxiliary cooling tower (10) is used to cool the exhaust steam of the solar thermal steam turbine (2); 2) In the peak-load stage of the evening peak of the unit, a part of the exhaust steam is shunted through the heat exchanger (7) and stored in the high-temperature heat storage tank (9); 3) In the low-load condition at night in summer, the high-temperature water in the high-temperature heat storage tank (9) is cooled to low-temperature water through the surplus of the auxiliary cooling tower (10) to reserve a heat storage space for the next heat storage; in the low-load condition at night in winter, the high-temperature water in the high-temperature heat storage tank (9) is cooled to low-temperature water through the surplus of the auxiliary cooling tower (10). On the one hand, it reserves a heat storage space for the next heat storage, and on the other hand, it prevents the risk of freezing of the auxiliary cooling tower (10).

6. The operating method of the photothermal steam turbine cold end anti-freezing and back pressure reduction system according to claim 5, characterized in that, In case 1), specifically: open the first valve (15), the third valve (17), and the fifth valve (19), close the eighth valve (22), the second valve (16), the fourth valve (18), the seventh valve (21), and the sixth valve (20). The exhaust steam of the solar thermal steam turbine (2) does not flow to the air-cooled island (5), but flows through the first valve (15) to the heat exchanger (7), and after passing through the heat exchanger (7), it becomes condensed water and flows to the exhaust steam device (3); the cooling water in the auxiliary cooling tower (10) flows through the third valve (17) and the first circulating water pump (12) and then flows to the heat exchanger (7). After cooling the exhaust steam, it is heated to high-temperature water and then flows through the fifth valve (19) to the auxiliary cooling tower (10) for heat dissipation. Another path of the cooling water in the auxiliary cooling tower (10) flows through the third circulating water pump (14) and then flows to the auxiliary heat exchanger of the steam turbine (11), and then flows back to the auxiliary cooling tower (10) for heat dissipation.

7. The operating method of the photothermal steam turbine cold end anti-freezing and back pressure reduction system according to claim 5, characterized in that, In case 2), specifically: open the first valve (15), the eighth valve (22), the second valve (16), and the fourth valve (18), close the third valve (17), the fifth valve (19), the seventh valve (21), and the sixth valve (20). Part of the exhaust steam of the solar thermal steam turbine (2) flows through the eighth valve (22) to the air-cooled island (5), and after heat exchange, it becomes condensed water and flows back to the exhaust steam device (3). Another part flows through the first valve (15) and the heat exchanger (7), and after heat exchange, it becomes condensed water and flows to the exhaust steam device (3). The low-temperature water in the low-temperature tank (8) flows through the second valve (16) and the first circulating water pump (12) and then flows to the heat exchanger (7). After being heated by the heat exchanger (7), it becomes high-temperature water and flows through the fourth valve (18) to the high-temperature heat storage tank (9).

8. The operating method of the photothermal steam turbine cold-end anti-freezing and back pressure reduction system according to claim 5, characterized in that, In case 3), specifically: open the eighth valve (22), the sixth valve (20), and the seventh valve (21), close the first valve (15), the second valve (16), the third valve (17), the fourth valve (18), and the fifth valve (19). The exhaust steam of the solar thermal steam turbine (2) flows through the eighth valve (22) to the air-cooled island (5), is cooled to condensed water and flows back to the exhaust steam device (3). The high-temperature water in the high-temperature heat storage tank (9) flows through the second circulating water pump (13) and then flows to the auxiliary cooling tower (10) for heat dissipation. After cooling, it becomes low-temperature water and flows to the low-temperature tank (8).

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