A hydrodynamic mechanical seal system for a nuclear primary pump

Abstract

The present application relates to a kind of fluid dynamic pressure mechanical seal systems for nuclear main pump, comprising multiple sealing assemblies arranged in series, each sealing assembly comprises dynamic pressure seal ring, each dynamic pressure seal ring is fixedly connected on the rotor assembly of nuclear main pump pump shaft, the rotor assembly is connected with stator assembly by the dynamic pressure seal ring with fluid dynamic pressure mechanical seal mode;Parking sealing assembly is further provided above the top sealing assembly. Each dynamic pressure seal ring is provided with periodically arranged groove on the sealing surface connected with the stator assembly, and the area of groove is larger on the back pressure side of sealing surface, which helps to reduce cavitation phenomenon during operation, thus reducing the risk of wear of sealing surface;Sealing surface uses silicon carbide material to improve service life.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nuclear main pump mechanical seal, in particular to a fluid dynamic pressure mechanical seal system for nuclear main pump. BACKGROUND

[0002] Nuclear main pump (RCP) is a key equipment in nuclear power plant system. As a part of pressure boundary, nuclear main pump is the only active equipment with high rotating speed, which drives the reactor coolant to circulate in the reactor primary loop, thereby continuously taking away the heat generated in the core.

[0003] After nearly half a century of technological development, almost all existing nuclear main pump mechanical seals in the world adopt a three-stage pressure reduction structure, and the mechanical seal is the key component existing in each stage. The main function of the nuclear main pump mechanical seal is to prevent the reactor coolant from flowing out along the shaft to cause serious leakage. In operation, a pair of sealing surfaces are closed face to face by the pressure of the spring and the fluid. The nuclear main pump mechanical seal finally forms a fluid dynamic pressure seal from the packing seal, the ring seal and the static pressure seal, and has been used until now.

[0004] The sealing surface of the fluid dynamic pressure mechanical seal has periodic local feature structures along the circumference, such as fluid dynamic grooves. The fluid dynamic pressure seal has the technical characteristics of thin liquid film, low leakage rate and strong resistance to pressure changes. In the test of resisting the station blackout (SBO) condition of the nuclear power plant, the fluid dynamic pressure mechanical seal has been verified to meet the safety requirements of the third generation of nuclear power.

[0005] Based on the research findings, the shape of the local feature structures along the circumference of the sealing surface of the existing fluid dynamic pressure mechanical seal affects its sealing performance, and the sealing effect of different materials has a large difference. The existing main pump seal adopts a corrugated surface structure, and the grinding surface adopts dissimilar materials, which has a significant hardness difference, thereby being prone to wear. Wear is generated by local contact on the solid surface, and the corrugated surface seal cannot supplement fluid on the back pressure side, which is prone to cavitation and wear. Therefore, it has great market value to provide a sealing surface with good sealing effect and long service life. SUMMARY

[0006] To achieve the above-mentioned purpose, the present application provides a fluid dynamic pressure mechanical seal system for nuclear main pump, which comprises a plurality of sealing assemblies arranged in series, each sealing assembly comprising a dynamic pressure seal ring, each dynamic pressure seal ring being fixedly connected to a rotor assembly on the pump shaft of the nuclear main pump, and the rotor assembly being connected to a stator assembly in a fluid dynamic pressure mechanical seal manner through the dynamic pressure seal ring.

[0007] Further, a plurality of grooves are arranged in a periodic manner on the sealing surface of each dynamic pressure seal ring connected to the stator assembly, and the width of one end of the groove is greater than that of the other end.

[0008] Further, two adjacent grooves are connected end to end to form a ring.

[0009] Further, each of the grooves comprises a straight groove which is located outside the dynamic pressure sealing ring and arranged along the tangential direction of the dynamic pressure sealing ring.

[0010] Further, each of the grooves further comprises a wedge-shaped compensation groove which is arranged close to the inner side of the dynamic pressure sealing ring and connected with the corresponding straight groove.

[0011] Further, each of the wedge-shaped compensation grooves extends from one end of the corresponding straight groove to the other end of the straight groove.

[0012] Further, the number of the grooves is 12, which are arranged in a ring shape on the dynamic pressure sealing ring.

[0013] Further, the pointed end of any one of the wedge-shaped compensation grooves is connected with the flat end of another wedge-shaped compensation groove adjacent thereto.

[0014] Further, the material of the pair of sealing surfaces of the dynamic pressure sealing ring connected with the stator assembly is silicon carbide.

[0015] Further, a parking sealing assembly is arranged above the sealing assembly at the top, the parking sealing assembly is provided with a locking pin structure, the pump shaft of the nuclear main pump is provided with a lock hole matched with the locking pin structure, and the locking pin structure and the lock hole are movably connected.

[0016] The present application has the following beneficial effects:

[0017] 1. The grooves are located at the back pressure side of the sealing surface with a larger area, which helps to reduce the cavitation phenomenon during operation, thereby reducing the risk of wear of the sealing surface;

[0018] 2. The sealing surface adopts silicon carbide material to improve the service life. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the mechanical seal of the nuclear main pump of the present application;

[0020] Figure 2 It is a structural schematic diagram of the dynamic pressure sealing ring of the present application;

[0021] Figure 3 It is a local enlarged view of the dynamic pressure sealing ring of the present application. DETAILED DESCRIPTION

[0022] The present application will be further described in detail below in combination with the drawings and specific embodiments. According to the following description, the advantages and features of the present application will be more apparent.

[0023] As shown in the accompanying drawings, the application provides a hydrodynamic mechanical seal system for a nuclear main pump, comprising a nuclear main pump shaft 4, a rotor assembly 41 connected to the nuclear main pump shaft 4, and three seal assemblies 3 arranged axially around the nuclear main pump shaft 4 and connected in series from top to bottom, each seal assembly 3 comprising a dynamic pressure seal ring 1 fixedly connected to the rotor assembly 41 on the nuclear main pump shaft 4, and the rotor assembly 41 is connected to a stator assembly 42 in a hydrodynamic mechanical seal manner through the dynamic pressure seal ring 1. Figure 1

[0024] The seal assembly 3 at the top is further provided with a parking seal assembly 2 for brake control of the nuclear main pump shaft 4, the parking seal assembly 2 is provided with a locking pin structure, after injecting coolant into the parking seal assembly 2, the locking pin structure on the parking seal assembly 2 is pushed into the locking hole of the nuclear main pump shaft 4 through the pressure of the coolant to brake; the brake is released after the coolant in the parking seal assembly 2 is discharged.

[0025] Further, the coolant enters the seal assembly 3 through a throttling member 31 arranged inside the seal assembly 3 to cool and lower the temperature, and each seal assembly 3 is provided with one throttling member 31, and the pressure of the coolant is reduced after passing through the throttling member 31 once.

[0026] Figure 2 In the application, each dynamic pressure seal ring 1 on the rotor assembly 41 is provided with periodically arranged grooves 11 on the sealing surface connected to the stator assembly 42, the two adjacent grooves 11 are connected end to end, and the width of one end of the groove 11 is greater than that of the other end. When the rotor assembly 41 rotates, the periodically distributed grooves 11 will produce a hydrodynamic pressure effect, so that the fluid pressure in the liquid film is increased to reduce the mechanical contact between the sealing surfaces, and the groove 11 with a larger width can also effectively reduce the fluid cavitation phenomenon. Each pair of sealing surfaces (including the sealing surface on the dynamic pressure seal ring 1 and the sealing surface on the stator assembly 42) connected by the dynamic pressure seal ring 1 and the stator assembly 42 adopts the same or different silicon carbide materials (different silicon carbide materials refer to different carbon-silicon ratios in the material), and the silicon carbide material has a very low wear rate in a water environment, which can effectively prolong the service life of the sealing surface.

[0027] Preferably, the number of grooves 11 is 12, which are arranged in a ring shape on the dynamic pressure seal ring 1 in sequence and end to end.

[0028] As shown in the accompanying drawings, the application provides a hydrodynamic mechanical seal system for a nuclear main pump, comprising a nuclear main pump shaft 4, a rotor assembly 41 connected to the nuclear main pump shaft 4, and three seal assemblies 3 arranged axially around the nuclear main pump shaft 4 and connected in series from top to bottom, each seal assembly 3 comprising a dynamic pressure seal ring 1 fixedly connected to the rotor assembly 41 on the nuclear main pump shaft 4, and the rotor assembly 41 is connected to a stator assembly 42 in a hydrodynamic mechanical seal manner through the dynamic pressure seal ring 1. Figure 3 ​As shown, the groove 11 in each single period in the embodiment mainly consists of a straight groove 111 and a wedge-shaped compensation groove 112, and the area, position and size parameters of the wedge-shaped compensation groove 112 in the groove 11 will affect the sealing effect of the sealing surface. The straight groove 111 is located on the outside of the dynamic pressure sealing ring 1 and is arranged along the tangential direction of the dynamic pressure sealing ring 1; each wedge-shaped compensation groove 112 is arranged close to the inside of the dynamic pressure sealing ring 1 and is connected with a corresponding straight groove 111. Specifically, each wedge-shaped compensation groove 112 extends along one end of the corresponding straight groove 111 to the other end of the straight groove, and according to the above two grooves 11, the tip part of the wedge-shaped compensation groove 112 is connected with the flat head part of the adjacent another wedge-shaped compensation groove 112. The flat head part of the wedge-shaped compensation groove 112 is located on the back pressure side b during rotation, and the tip part is located on the pressure side a. In this example, a larger area of local groove structure (i.e. the flat head part of the wedge-shaped compensation groove 112) is introduced on the back pressure side b, so that the fluid can be fully introduced in the back pressure side b area, and the risk of fluid liquefaction is reduced. Considering the absolute value of the leakage rate, the fluid leakage rate in this example is about 100 mL / h, which meets the working condition requirements of the main pump.

[0029] According to the experiment, it is shown that the sealing effect of the sealing surface can be improved by adjusting the parameters (such as area, position, size parameters, etc.) of the wedge-shaped compensation groove 112. The larger the area of the wedge-shaped compensation groove 112, the closer the position to the high pressure area, and the larger the linear size, the more obvious the static pressure effect of the sealing surface, the lower the wear rate, and the higher the leakage rate.

[0030] In summary, the present application has the following beneficial effects:

[0031] 1. The larger area of the groove on the back pressure side of the sealing surface helps to reduce the cavitation phenomenon during operation, thereby reducing the risk of wear of the sealing surface;

[0032] 2. The sealing surface adopts silicon carbide material to improve the service life.

[0033] Although the content of the present application has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present application. After reading the above content, various modifications and alternatives of the present application will be obvious to those skilled in the art. Therefore, the protection scope of the present application should be defined by the appended claims.

Claims

1. A hydrodynamic mechanical seal system for a nuclear primary pump, characterized by, The application relates to a nuclear main pump, which comprises a plurality of sealing assemblies arranged axially around a pump shaft of the nuclear main pump and connected in series, each sealing assembly comprising a dynamic pressure sealing ring, each dynamic pressure sealing ring being fixedly connected to a rotor assembly on the pump shaft of the nuclear main pump, and the rotor assembly being connected to a stator assembly in a fluid dynamic pressure mechanical sealing mode through the dynamic pressure sealing ring. Each dynamic pressure sealing ring is provided with periodically arranged grooves on a sealing surface connected to the stator assembly, and the width of one end of each groove is greater than that of the other end; two adjacent grooves are connected end to end to form a ring shape. Each groove further comprises a wedge-shaped compensation groove, and each wedge-shaped compensation groove is arranged close to the inner side of the dynamic pressure sealing ring and connected to a corresponding straight groove. Each wedge-shaped compensation groove extends along one end of the corresponding straight groove to the other end of the straight groove. The tip of any wedge-shaped compensation groove is connected to the flat head of another wedge-shaped compensation groove adjacent to the wedge-shaped compensation groove. Each groove comprises a straight groove, and the straight groove is arranged along the tangential direction of the dynamic pressure sealing ring and located on the outer side of the dynamic pressure sealing ring.

2. The hydrodynamic mechanical seal system for a nuclear primary pump of claim 1, wherein, The number of grooves is 12.

3. The hydrodynamic mechanical seal system for a nuclear primary pump of claim 1, wherein, The materials of a pair of sealing surfaces, where the dynamic pressure sealing ring is connected to the stator assembly, are both silicon carbide.

4. The hydrodynamic mechanical seal system for a nuclear primary pump of claim 1, wherein, A parking sealing assembly is further arranged above the sealing assembly at the top, the parking sealing assembly is provided with a locking pin structure, the pump shaft of the nuclear main pump is provided with a lock hole matched with the locking pin structure, and the locking pin structure and the lock hole are movably connected.

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