A nuclear power once-through evaporator water-vapor condition switching system and method

Abstract

The present invention discloses a water-vapor condition switching system and method for a nuclear power once-through evaporator, which includes a main feed pump group, a once-through evaporator, a superheater, a flash tank, a main steam header and a flash tank discharge system; the outlet of the main feed pump group is communicated with the water-side inlet of the once-through evaporator, the water-side outlet of the once-through evaporator is communicated with the inlet of the superheater, the water-side outlet of the once-through evaporator is communicated with the inlet of the flash tank, the water-side outlet of the once-through evaporator is connected to the main steam header, the outlet of the superheater is communicated with the main steam header, and the outlet of the flash tank is connected to the flash tank discharge system. This system and method can effectively solve the problems that occur during the water-vapor condition switching of the nuclear power once-through evaporator.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy and energy conservation, and relates to a water-vapor condition switching system and method for a nuclear power once-through evaporator. Background Art

[0002] At present, there are two types of steam generators in nuclear power plants. One is a saturated steam generator with a steam-water separator, and the other is a once-through steam generator. Most pressurized water reactor units use saturated steam generators with steam-water separators, while high-temperature gas-cooled reactors and sodium-cooled fast reactors use once-through steam generators.

[0003] The conversion of the water-vapor condition of the evaporator refers to the switching of the evaporation point from the water condition to the steam condition as the nuclear island heat load increases, which is the most important control point. In the water condition, both the saturated steam generator with a steam-water separator and the once-through steam generator are under cycle control; in the steam condition, there is no water in the storage tank of the saturated steam generator with a steam-water separator, and the steam-water separator is only a steam channel, and the feed water flow rate is equal to the steam flow rate. The once-through evaporator has no steam-water separator, so special attention should be paid to strengthening the adjustment during the conversion from the water condition to the steam condition, and it is particularly important to maintain the matching of the heat load and the feed water flow rate.

[0004] For high-temperature gas-cooled reactors and sodium-cooled fast reactors that use once-through evaporators, during the water-vapor condition switching stage in the conventional island, the control systems and methods for the feed water flow rate and pressure are very different from those of the saturated steam generator with a steam-water separator. Since the once-through evaporator has no storage tank as a flow buffer, the influence of the flow rate and pressure on the conversion during the water-vapor condition conversion process is very large. Although the conversion from the water condition to the steam condition has little impact on the nuclear island heat load and the unit load, it has the following two aspects of influence on the entire unit: First, if the adjustment is not good during the conversion from the water condition to the steam condition, the two states will be repeatedly converted, sometimes in the water condition and sometimes in the steam condition, affecting the safety of the unit. Second, if the conversion from the water condition to the steam condition takes too long, excessive heat loss will occur. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned disadvantages of the prior art, and provides a water-vapor condition switching system and method for a nuclear power once-through evaporator, which can effectively solve the problems that occur during the water-vapor condition switching of the nuclear power once-through evaporator.

[0006] To achieve the above purpose, the water-vapor condition switching system for a nuclear power once-through evaporator described in the present invention includes a main feed pump group, a once-through evaporator, a superheater, a flash tank, a main steam header, and a flash tank discharge system;

[0007] The outlet of the main feed water pump group is connected to the water side inlet of the once-through evaporator. The water side outlet of the once-through evaporator is connected to the inlet of the superheater. The water side outlet of the once-through evaporator is connected to the inlet of the flash tank. The water side outlet of the once-through evaporator is connected to the main steam header. The outlet of the superheater is connected to the main steam header. The outlet of the flash tank is connected to the flash tank discharge system.

[0008] The water side outlet of the once-through evaporator is connected to the inlet of the superheater through the superheater inlet isolation valve group.

[0009] The water side outlet of the once-through evaporator is connected to the main steam header through the first electric valve group.

[0010] The outlet of the superheater is connected to the main steam header through the second electric valve group.

[0011] It also includes a nuclear island heat source loop for providing heat source for the once-through evaporator.

[0012] The water side outlet of the once-through evaporator is connected to the inlet of the flash tank through the flash tank inlet regulating valve group.

[0013] A method for switching the water-vapor working condition of a nuclear power once-through evaporator includes the following steps:

[0014] Switch the flash tank inlet regulating valve group to manual and keep the opening degree unchanged; put the speed of the main feed water pump group into automatic, set the speed of the main feed water pump group to track the feed water flow into the once-through evaporator, and gradually reduce the flow set value of the main feed water pump group. Since the heat provided by the nuclear island heat source loop remains unchanged, as the feed water flow decreases, the feed water temperature gradually rises until the water in the once-through evaporator approaches the saturated steam temperature, and set the flow set value of the main feed water pump group to the current flow value;

[0015] Manually and gradually increase the opening degree of the flash tank inlet regulating valve group. At this time, the pressure in the once-through evaporator gradually decreases. Since the feed water flow into the once-through evaporator increases when the opening degree of the flash tank inlet regulating valve group increases, the main feed water pump group automatically reduces the speed, thereby further reducing the pressure in the once-through evaporator. Manually increase the opening degree of the flash tank inlet regulating valve group, the pressure in the once-through evaporator gradually drops, the feed water temperature gradually rises, and the feed water in the once-through evaporator gradually turns into superheated steam with a certain degree of superheat. Open the first electric valve group, and the superheated steam enters the main steam header for preheating. Open the superheater inlet isolation valve group and the second electric valve group, and the steam temperature is further increased through the superheater and then enters the main steam header;

[0016] As the thermal power of the heat source circuit in the nuclear island gradually increases, the main feed pump group tracks and adjusts the feed water flow rate into the once-through evaporator to ensure that the once-through evaporator generates steam with a certain degree of superheat and enters the superheater. Manually and gradually close the regulating valve group at the inlet of the flash tank and the first electric valve group until the water condition of the once-through evaporator switches to the steam condition.

[0017] The present invention has the following beneficial effects:

[0018] For the once-through evaporator water-vapor condition switching system and method of the present invention, by adjusting the feed water flow rate into the once-through evaporator through the main feed pump group, the feed water temperature rises rapidly, shortening the transition time and reducing heat source waste. At the same time, a single variable is adopted to indirectly control the superheat degree of the working medium in the once-through evaporator, preventing the repeated progress of the water-vapor switching process, reducing the impact on the unit operation, and improving the safety and stability of the unit. In addition, the regulating valve group at the inlet of the flash tank is used to directly reduce the pressure in the once-through evaporator, causing the saturation temperature point of the working medium in the once-through evaporator to drop, achieving the shortening of the transition time, and then effectively solving the problems that occur in the water-vapor condition switching of the nuclear power once-through evaporator. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the water-vapor condition switching system of the present invention.

[0020] Wherein, 1 is the main feed pump group, 2 is the heat source circuit of the nuclear island, 3 is the once-through evaporator, 4 is the isolation valve group at the inlet of the superheater, 5 is the first electric valve group, 6 is the regulating valve group at the inlet of the flash tank, 7 is the superheater, 8 is the second electric valve group, 9 is the flash tank, 10 is the main steam header, and 11 is the flash tank discharge system. Detailed Embodiments

[0021] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments, and are not intended to limit the scope of the present invention disclosure. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessarily confusing the concepts disclosed in the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0022] The structural schematic diagrams according to the disclosed embodiments of the present invention are shown in the accompanying drawings. These drawings are not drawn to scale, where for the purpose of clear expression, some details are enlarged and some details may be omitted. The shapes of various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary. In practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art can design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0023] The steam-water condition switching system of the nuclear power once-through evaporator according to the present invention includes a main feed pump group 1, a nuclear island heat source loop 2, a once-through evaporator 3, a superheater inlet isolation valve group 4, a first electric valve group 5, an expansion vessel inlet regulating valve group 6, a superheater 7, a second electric valve group 8, an expansion vessel 9, a main steam header 10, and an expansion vessel discharge system 11;

[0024] The outlet of the main feed pump group 1 is communicated with the water side inlet of the once-through evaporator 3. The water side outlet of the once-through evaporator 3 is communicated with the inlet of the superheater 7 through the superheater inlet isolation valve group 4. The water side outlet of the once-through evaporator 3 is communicated with the inlet of the expansion vessel 9 through the expansion vessel inlet regulating valve group 6. The water side outlet of the once-through evaporator 3 is connected to the main steam header 10 through the first electric valve group 5. The outlet of the superheater 7 is communicated with the main steam header 10 through the second electric valve group 8. The outlet of the expansion vessel 9 is connected to the expansion vessel discharge system 11. The nuclear island heat source loop 2 is connected to the heat source side of the once-through evaporator 3.

[0025] The method for switching the steam-water condition of the nuclear power once-through evaporator according to the present invention includes the following steps:

[0026] Switch the expansion vessel inlet regulating valve group 6 to manual and keep the opening unchanged; put the speed of the main feed pump group 1 into automatic, set the speed of the main feed pump group 1 to track the feed water flow entering the once-through evaporator 3, and gradually reduce the flow set value of the main feed pump group 1. Since the heat provided by the nuclear island heat source circuit 2 remains unchanged, as the feed water flow decreases, the feed water temperature gradually increases until the water in the once-through evaporator 3 approaches the saturated steam temperature, and set the flow set value of the main feed pump group 1 to the current flow value; then gradually open the expansion vessel inlet regulating valve group 6 manually. At this time, the pressure in the once-through evaporator 3 gradually decreases. Since the increase in the opening of the expansion vessel inlet regulating valve group 6 will instantaneously increase the flow entering the once-through evaporator 3, the main feed pump group 1 automatically reduces its speed, thereby further reducing the pressure in the once-through evaporator 3. Manually increase the opening of the expansion vessel inlet regulating valve group 6, the pressure in the once-through evaporator 3 gradually decreases, the feed water temperature gradually increases, and the feed water in the once-through evaporator 3 gradually turns into superheated steam with a certain degree of superheat. Open the first electric valve group 5, and the superheated steam enters the main steam header 10 for preheating. Open the superheater inlet isolation valve group 4 and the second electric valve group 8, and further increase the steam temperature through the superheater 7 and then enter the main steam header 10; finally, as the thermal power of the nuclear island heat source circuit 2 gradually increases, the main feed pump group 1 tracks the feed water flow entering the once-through evaporator 3 to ensure that steam with a certain degree of superheat is generated at the outlet of the once-through evaporator 3 and enters the superheater 7. Manually gradually close the expansion vessel inlet regulating valve group 6 and the first electric valve group 5 until the water condition in the once-through evaporator 3 is switched to the steam condition.

Claims

1. A method for switching the water-vapor condition of a nuclear power once-through evaporator, characterized in that, Nuclear power once-through evaporator water-vapor condition switching system. The nuclear power once-through evaporator water-vapor condition switching system is characterized by comprising a main feed water pump group (1), a once-through evaporator (3), a superheater (7), a flash tank (9), a main steam header (10) and a flash tank discharge system (11); The outlet of the main feed water pump group (1) is communicated with the water side inlet of the once-through evaporator (3), the water side outlet of the once-through evaporator (3) is communicated with the inlet of the superheater (7), the water side outlet of the once-through evaporator (3) is communicated with the inlet of the flash tank (9), the water side outlet of the once-through evaporator (3) is connected with the main steam header (10), the outlet of the superheater (7) is communicated with the main steam header (10), and the outlet of the flash tank (9) is connected with the flash tank discharge system (11); The water side outlet of the once-through evaporator (3) is communicated with the inlet of the superheater (7) through a superheater inlet isolation valve group (4); The water side outlet of the once-through evaporator (3) is connected with the main steam header (10) through a first electric valve group (5); The outlet of the superheater (7) is communicated with the main steam header (10) through a second electric valve group (8); It further comprises a nuclear island heat source loop (2) for providing heat source for the once-through evaporator (3); The water side outlet of the once-through evaporator (3) is communicated with the inlet of the flash tank (9) through a flash tank inlet regulating valve group (6); It includes the following steps: Switch the flash tank inlet regulating valve group (6) to manual and keep the opening degree unchanged; the speed of the main feed water pump group (1) is put into automatic, set the speed of the main feed water pump group (1) to track the feed water flow rate entering the once-through evaporator (3), and gradually reduce the flow rate setting value of the main feed water pump group (1). The heat provided by the nuclear island heat source loop (2) remains unchanged. As the feed water flow rate decreases, the feed water temperature gradually increases until the water in the once-through evaporator (3) approaches the saturated steam temperature, and set the flow rate setting value of the main feed water pump group (1) to the current flow rate value; Manually gradually increase the opening degree of the flash tank inlet regulating valve group (6). At this time, the pressure in the once-through evaporator (3) gradually decreases. Since the feed water flow rate entering the once-through evaporator (3) increases when the opening degree of the flash tank inlet regulating valve group (6) increases, the main feed water pump group (1) automatically reduces the speed, thereby further reducing the pressure in the once-through evaporator (3). Manually increase the opening degree of the flash tank inlet regulating valve group (6), the pressure in the once-through evaporator (3) gradually decreases, the feed water temperature gradually increases, and the feed water in the once-through evaporator (3) gradually turns into superheated steam with a certain degree of superheat. Open the first electric valve group (5), and the superheated steam enters the main steam header (10) for preheating. Open the superheater inlet isolation valve group (4) and the second electric valve group (8), and further increase the steam temperature through the superheater (7) and then enter the main steam header (10); As the thermal power of the heat source loop (2) in the nuclear island gradually increases, the main feed water pump group (1) tracks the feed water flow rate into the once-through evaporator (3) to ensure that the once-through evaporator (3) generates steam with a certain degree of superheat and enters the superheater (7). Manually and gradually close the flash tank inlet regulating valve group (6) and the first electric valve group (5) until the water condition of the once-through evaporator (3) is switched to the steam condition.

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