Axial force balancing device for multi-stage vertical molten salt pump and multi-stage vertical molten salt pump

Abstract

Provided in the present invention are an axial force balancing device for a multi-stage vertical molten salt pump, and a multi-stage vertical molten salt pump. An axial force balancing device is provided between a space guide vane and an impeller; the axial force balancing device has a third balancing cavity and a first balancing cavity, wherein a labyrinth clearance is provided between the first balancing cavity and a pressure cavity of the impeller; the third balancing cavity is located inside the space guide vane, and an elastic damping element is provided between the first balancing cavity and the third balancing cavity, thereby balancing the axial force acting on the impeller. The present invention can realize real-time response to the axial force acting on a pump rotor, dividing the main axial force on the impeller into two parts; the axial force acting on the multi-stage vertical molten salt pump is balanced by the joint action of two clearances in front of the first balancing cavity, the bidirectional effect of a spring and the low-pressure state of the third balancing cavity, thereby ensuring the stable operation of the multi-stage vertical molten salt pump.

Description

An axial force balancing device for a multi-stage vertical molten salt pump and the multi-stage vertical molten salt pump Technical Field

[0001] This invention relates to the field of molten salt pumps, and particularly to an axial force balancing device for a multi-stage vertical molten salt pump and a multi-stage vertical molten salt pump. Background Technology

[0002] Vertical multistage molten salt pumps are the core power unit of concentrated solar power (CSP) plants. In actual operation, due to the asymmetry of the impeller's front and rear cover plates, the differences in the flow channels of the impeller's front and rear chambers, and the influence of the rotor's own weight, axial forces are generated during operation. The molten salt pump of the CSP system adopts a multistage impeller arrangement in the same direction and a vertical installation method, so that the axial force on its rotor structure gradually increases from top to bottom along the pump shaft, accumulating at the first-stage impeller on the lower section of the shaft.

[0003] Axial force causes the rotor to move axially, leading to contact between the rotor assembly and stationary parts, resulting in wear, increased vibration and noise, and reduced pump efficiency. Excessive axial force can cause the impeller to move towards the inlet, increasing friction between the impeller and pump casing, increasing motor load, and potentially damaging the sealing structure, leading to increased leakage and power consumption. For multistage pumps, the impact of axial force is even more pronounced; excessive axial force can cause overheating and damage to the support bearings, and may even lead to serious problems such as shaft breakage, threatening the safe and stable operation of the pump. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an axial force balancing device for a multi-stage vertical molten salt pump and a multi-stage vertical molten salt pump. The device has a novel structure and can balance the axial force on the pump rotor, effectively improving the safety and reliability of the multi-stage molten salt pump operation.

[0005] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0006] An axial force balancing device for a multi-stage vertical molten salt pump is provided, wherein an axial force balancing device is provided between a spatial guide vane and an impeller. The axial force balancing device has a third balancing chamber and a first balancing chamber. A labyrinth gap is provided between the first balancing chamber and the pressure chamber of the impeller. The third balancing chamber is located inside the spatial guide vane. An elastic damping is provided between the first balancing chamber and the third balancing chamber to balance the axial force on the impeller.

[0007] Furthermore, the axial force balancing device includes a cylinder, elastic damping, and an adjusting slide plate; the cylinder includes an end cap and an outer cylinder wall, one end of which is fitted with an end cap located inside a spatial guide vane and connected to the spatial guide vane; the other end of the outer cylinder wall is clearance-fitted with an impeller; the adjusting slide plate is located inside the cylinder and is connected to the rear cover plate of the impeller, the adjusting slide plate divides the cylinder into a first balancing chamber and a third balancing chamber, and elastic damping is provided between the adjusting slide plate and the cylinder; one side of the adjusting slide plate, the outer cylinder wall, and the rear cover plate constitute the first balancing chamber; the area between the other side of the adjusting slide plate and the end cap constitutes the third balancing chamber.

[0008] Furthermore, a sealing structure is provided between the adjusting slide plate and the inner wall surface of the outer cylinder wall.

[0009] Furthermore, the sealing structure is an annular metal brush, and one end of the adjusting slide plate is provided with several spaced grooves, with the annular metal brush located within the grooves.

[0010] Furthermore, a first gap is provided between the rear cover plate and the space guide vane, and a second gap is provided between the rear cover plate and the outer cylinder wall. The first gap and the second gap constitute a labyrinth gap between the first balance chamber and the pressure chamber.

[0011] Furthermore, the inner wall of the outer cylinder wall is provided with a protrusion, and a spring is provided between the protrusion and the adjusting slide plate.

[0012] Furthermore, a second balance chamber is provided between the first balance chamber and the pressure chamber. The second balance chamber is the area enclosed by the space guide vane, the cylinder and the rear cover plate.

[0013] A multi-stage vertical molten salt pump includes multiple impellers, and at least one impeller and its corresponding spatial guide vane are provided with the aforementioned axial force balancing device.

[0014] The beneficial effects of this invention are as follows:

[0015] The axial force balancing device for a multi-stage vertical molten salt pump described in this invention includes an axial force balancing device located between the spatial guide vane and the impeller. An elastic damper is provided between the first and third balancing chambers, enabling rapid response to changes in the axial force acting on the pump rotor. When the pump rotor is subjected to different axial forces, the pressure chamber, labyrinth gap, third balancing chamber, and elastic damper automatically balance the axial force acting on the pump rotor. Simultaneously, an infrared ranging device within the balancing device enables real-time monitoring of the pump body's axial force during operation, improving the operational safety of the multi-stage vertical molten salt pump. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are some embodiments of the present invention. For those skilled in the art, it is obvious that other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 is a schematic diagram of the multi-stage vertical molten salt pump described in this invention.

[0018] Figure 2 is a schematic diagram of the installation of the axial force balancing device of the present invention.

[0019] Figure 3 is a magnified view of a portion of Figure 2.

[0020] Figure 4 is a schematic diagram of the installation of the sealing structure described in this invention.

[0021] Figure 5 is a three-dimensional diagram of the axial force balancing device of the present invention.

[0022] Figure 6 is a force comparison diagram between the installation of the axial force balancing device and the existing technology.

[0023] Figure 7 shows a comparison of flow rates under different flow conditions with the balancing device installed.

[0024] Figure 8 is a comparison of the external characteristic parameters of a single-stage pump with this balancing device installed, without balancing measures installed, and in the prior art.

[0025] In the diagram: 1-Inlet section; 2-First stage impeller; 3-Second stage impeller; 4-Space guide vane; 5-Pump shaft; 6-Intermediate section; 7-Outlet section; 8-Balancing device; 9-Rear cover plate; 10-Fixing module; 11-Adjusting slide plate; 12-Spring; 13-End cover; 14-Outer cylinder wall; 15-Infrared ranging device; 16-Sealing structure; 17-Balancing hole; 18-Sliding bearing; a-First clearance; b-Second clearance; 101-Pressure chamber; 102-Second balancing chamber; 104-First balancing chamber; 103-Third balancing chamber. Detailed Implementation

[0026] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0027] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "axial," "radial," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0028] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0029] As shown in Figure 1, the multi-stage vertical molten salt pump of the present invention consists of five impellers, with each impeller connected in series in the same direction on the pump shaft 5. The axial force balancing device of the multi-stage vertical molten salt pump of the present invention can be arranged on one side of a certain impeller or several impellers according to the actual model of the multi-stage pump. Generally, an axial force balancing device 8 is provided between the spatial guide vane 4 of a certain stage and the corresponding impeller. The axial force balancing device has a third balancing chamber 103 and a first balancing chamber 104. A labyrinth gap is provided between the first balancing chamber 104 and the pressure chamber 101 of the impeller. The third balancing chamber 103 is located inside the spatial guide vane 4. An elastic damping is provided between the first balancing chamber 104 and the third balancing chamber 103 to balance the axial force on the impeller.

[0030] As shown in Figures 2, 3, and 5, a sliding bearing 20 is provided between the spatial guide vane 4 and the pump shaft 5. The axial force balancing device 8 includes a cylinder, elastic damping, and an adjusting slide plate 11. The cylinder includes an end cap 13 and an outer cylinder wall 14. The end cap 13 is installed at one end of the outer cylinder wall 14 and is located inside the spatial guide vane 4. The end cap 13 is connected to the spatial guide vane 4. A mechanical seal is provided between the sliding bearing 20 and the end cap 13. The other end of the outer cylinder wall 14 is clearance-fitted with the impeller. The adjusting slide plate 11 is located inside the cylinder and is connected to the rear cover plate 9 of the impeller through a fixing module 10. The adjusting slide plate 11 divides the cylinder into a first balancing chamber 104 and a third balancing chamber 103. Elastic damping is provided between the adjusting slide plate 11 and the cylinder. One side of the adjusting slide plate 11, the outer cylinder wall 14, and the rear cover plate 9 constitute the first balancing chamber 104. The area between the other side of the adjusting slide plate 11 and the end cap 13 constitutes the third balancing chamber 103. The end cap 13 is fixedly mounted on the first-stage space guide vane 4 by bolts. The end cap 13 is also fixedly connected to the outer cylinder wall 14 by bolts. A first gap a is provided between the rear cover plate 9 and the space guide vane 4, and a second gap b is provided between the rear cover plate 9 and the outer cylinder wall 14. The first gap a and the second gap b constitute a labyrinth gap between the first balance chamber 104 and the pressure chamber 101 of the impeller. The second gap b is between 0.5 mm and 0.6 mm, and its axial length can change with the axial force. A second balance chamber 102 is provided between the first balance chamber 104 and the pressure chamber 101. The second balance chamber 102 is the area partially enclosed by the space guide vane 4, the cylinder body, and the rear cover plate 9.

[0031] The rear cover plate 9 and the fixing module 10 are connected by a key to synchronize the position changes during the operation of the molten salt pump. The fixing module 10 and the adjusting slide plate 11 are locked in the axial direction but move freely in the radial direction through corresponding concave-convex structures. That is, rotation of the fixing module 10 will not cause rotation of the adjusting slide plate 11, but axial movement of the fixing module 10 will cause axial movement of the adjusting slide plate 11. A spring 12 is installed between the adjusting slide plate 11 and the outer cylinder wall 14. An infrared ranging device 15 is installed on the corresponding surface of the adjusting slide plate 11 and the end cover 13 to monitor the axial force during rotor operation, thereby monitoring the actual operating status of the entire molten salt pump.

[0032] As shown in Figure 4, a sealing structure 16 is provided between the adjusting slide plate 11 and the inner wall surface of the outer cylinder wall 14. The sealing structure 16 is an annular metal brush. One end of the adjusting slide plate 11 is provided with several spaced grooves, and the annular metal brush is located in the grooves to minimize the leakage of liquid in the first balance chamber 104 to the third balance chamber 103 through the gaps.

[0033] The axial force balancing principle of this invention utilizes the relatively low pressure of the pressure chamber 101, the labyrinth gap, and the third balancing chamber 103, as well as the bidirectional action of the spring 12, to balance the axial force when the pump rotor is subjected to different axial forces. Specifically:

[0034] The axial force on the impeller can be mainly divided into two parts: the axial force exerted by the pressure chamber 101 on the upper part of the impeller rear cover plate 9, and the axial force exerted by the first balance chamber 104 on the lower part of the impeller rear cover plate. The former part of the axial force can be balanced with the axial force exerted on the impeller front cover plate, so the force situation of the lower part of the impeller rear cover plate needs to be focused on.

[0035] When the pump rotor is subjected to an axial force to the right, the fixed module 10 moves synchronously to the right with the impeller, driving the adjusting slide plate 11 to move to the right, and the spring 12 is compressed, generating a force to the left. Furthermore, due to the presence of the first gap a and the second gap b, some of the high-pressure fluid in the pressure chamber 101 leaks into the second balance chamber 102, and some of the fluid in the second balance chamber 102 leaks into the first balance chamber 104. The fluid flow process conforms to the law of conservation of mass. When the flow channel surface decreases, the fluid velocity increases. Simultaneously, according to Bernoulli's equation, for incompressible fluids in a steady flow state, as the velocity increases, the fluid pressure decreases to maintain energy conservation during the flow process. Therefore, under the above effects, the pressure in the first balance chamber 104 will always be lower than that in the second balance chamber 102, and the pressure in the second balance chamber 102 will always be lower than that in the pressure chamber 101. Under the action of the two radial gaps, the pressure in the first balance chamber 104 is always at a lower level compared to the pressure chamber 101. Within the first balancing chamber 104, the axial force on the lower left side of the impeller rear cover plate 9 cancels out the force on the right side of the adjusting slide plate 11. The main source of axial force in the impeller is converted to the force on the left side of the adjusting slide plate 11 and the force on the lower front section of the impeller rear cover plate. Since the lower front section of the impeller rear cover plate is close to the impeller's suction area, the suction inlet of the impeller is a low-pressure area, and the axial force of this fluid on the structure is very small. The left side of the adjusting slide plate 11 is located within the third balancing chamber 103. Part of the fluid in the chamber originates from the liquid in the first balancing chamber 104 leaking from the sealing structure 16, and another part originates from the liquid in the first balancing chamber 104 seeping in through the gap between the lower fixed module 10 and the adjusting slide plate 11. This chamber is essentially a static chamber, and due to the conservation of mass energy when the fluid flows through the seal and gap, the pressure is always lower than the pressure in the first balancing chamber 104. At this time, through the action of the two gaps and the sealing structure, the third balancing chamber 103 will maintain a lower pressure state, significantly reducing the rightward axial force on the lower section of the impeller rear cover plate.

[0036] When the pump rotor is subjected to an axial force to the left, the fixed module 10 and the impeller move to the left, causing the adjusting slide plate 11 to move to the left. At this time, the spring 12 is pulled, generating a force to the right. The pressure state of the three balance chambers is similar to that when the rotor is subjected to an axial force to the right. However, due to the leftward movement of the impeller, and the fact that the space guide vane 4 and the outer cylinder wall 14 of the balancing device are fixed structures, the axial lengths of the first gap a and the second gap b increase. This leads to an increase in the friction loss of the fluid passing through these gaps, resulting in an increase in the pressure difference between the second balance chamber 102 and the pressure chamber 101, and between the first balance chamber 104 and the second balance chamber 102. This makes the pressure in the first balance chamber 104 and the second balance chamber 102 lower than the pressure in the chambers when the impeller is not subjected to a leftward force, thus reducing the force of the liquid on the impeller rear cover plate. At the same time, the presence of the third balance chamber 103 also plays a certain role in inhibiting the leftward movement of the adjusting slide plate 11 (i.e., the impeller).

[0037] The multi-stage vertical molten salt pump of the present invention includes multi-stage impellers, and at least one stage impeller and its corresponding spatial guide vane 4 are provided with the axial force balancing device.

[0038] Example

[0039] This multi-stage vertical molten salt pump has a design flow rate of 950 m³ / h. 3 / h, rated speed of 1450r / min, one stage was selected for comparison between the model equipped with the axial force balancing device 8 of this invention and the model without balancing means. For a smaller flow rate (759m 3 / h), design flow rate (950 m³ / h) 3 / h) and larger flow rates (1141m) 3 The operating conditions of the impeller with 25℃ clean water as the conveying medium were calculated under three operating conditions ( / h). The turbulence model used was the standard k-ε model, and the boundary conditions were total pressure inlet and mass flow rate outlet. The impeller calculation domain was a rotating domain, while the guide vanes, inlet pipe and outlet pipe were stationary domains. The interface between the dynamic and static calculation domains used a frozen rotor model, and the wall surface was a smooth wall condition.

[0040] The magnitudes of the axial forces of both components under different working conditions were calculated using numerical simulation, and the results are as follows:

[0041] As shown in Figure 6, after installing the axial force balancing device 8 described in this invention, the axial forces on the front and rear cover plates of the impeller both decreased significantly, and the variation in the axial force on the blades was relatively small. A significant source of the pump's axial force is the asymmetry in the structure of the front and rear cover plates of the impeller; that is, the force difference between the two cover plates is the main component of the pump's axial force. During the gradual increase in flow rate, the force differences on the impeller cover plates with this balancing device were 11503 N, 1157.7 N, and 1914.5 N, respectively. Without balancing measures, the force differences were 25447 N, 15216 N, and 10729 N. After installing this balancing device, the force differences on the two cover plates decreased by 54.8%, 92.3%, and 82.2% compared to the unbalanced model. Simultaneously, the corresponding total axial force decreased by 40.7%, 56.9%, and 61.5% compared to the model without the balancing device. This indicates that the balancing device provided by this invention can effectively reduce axial force under different operating conditions.

[0042] Currently, there are two main methods for balancing the axial force of multi-stage pumps in engineering: one is a balancing disc, and the other is a combination of a sealing ring and a balancing hole. The former can only be installed after the last stage impeller, its position cannot be changed, and it requires a pipeline to connect to the pump inlet. Therefore, the axial force balancing device 8 of this invention is compared with the second method. The calculation model still uses the aforementioned single-stage pump model. The calculation results are shown in Figure 7. It can be seen that the axial force balancing device 8 provided by this invention has a significantly better ability to balance axial force under different flow conditions than traditional balancing measures. At a flow rate of 759 m³ / h... 3 / h, 950m 3 / h、1141m 3 Under the condition of / h, the axial force balancing device of the present invention reduces the balancing capacity of the device by 24.47%, 44.60% and 49.42% respectively compared with the balancing scheme using the traditional sealing ring and balancing hole structure, and the balancing capacity increases with the increase of flow rate.

[0043] Considering that the axial force balancing device 8 should not significantly affect the pump's hydraulic performance, efficiency, head, and shaft power are the main characteristic parameters for evaluating pump performance. As shown in Figure 8, the external characteristic parameters of a single-stage pump with this balancing device, without balancing measures, and using traditional balancing measures are compared. Regarding the impact on pump hydraulic performance, under multi-flow conditions, the pump's head and efficiency are similar when using the balancing device of this invention and when using traditional balancing measures, while the shaft power is lower. The higher the head and efficiency, the lower the shaft power, and the better the pump performance. Comparing the pump's axial force and hydraulic performance parameters comprehensively, the balancing device of this invention provides good axial force balance while having a smaller impact on pump performance. It can be seen that this balancing device has virtually no impact on the pump's hydraulic performance and can be directly installed on existing pumps without adjusting the hydraulic design, reducing design costs.

[0044] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0045] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. An axial force balancing device for a multi-stage vertical molten salt pump, characterized in that, An axial force balancing device is provided between the space guide vane (4) and the impeller. The axial force balancing device has a third balancing chamber (103) and a first balancing chamber (104). A labyrinth gap is provided between the first balancing chamber (104) and the pressure chamber (101) of the impeller. The third balancing chamber (103) is located inside the space guide vane (4). An elastic damping is provided between the first balancing chamber (104) and the third balancing chamber (103) to balance the axial force on the impeller.

2. The axial force balancing device for a multi-stage vertical molten salt pump according to claim 1, characterized in that, The axial force balancing device includes a cylinder, elastic damping, and an adjusting slide plate (11); the cylinder includes an end cap (13) and an outer cylinder wall (14), one end of the outer cylinder wall (14) is fitted with the end cap (13), the end cap (13) is located inside the spatial guide vane (4), and the end cap (13) is connected to the spatial guide vane (4); the other end of the outer cylinder wall (14) is clearance-fitted with the impeller; the adjusting slide plate (11) is located inside the cylinder, and the adjusting slide plate (11) is connected to the rear cover plate (9) of the impeller, the adjusting slide plate (11) divides the cylinder into a first balancing chamber (104) and a third balancing chamber (103), and elastic damping is provided between the adjusting slide plate (11) and the cylinder; one side of the adjusting slide plate (11), the outer cylinder wall (14), and the rear cover plate (9) constitute the first balancing chamber (104); the area between the other side of the adjusting slide plate (11) and the end cap (13) constitutes the third balancing chamber (103).

3. The axial force balancing device for a multi-stage vertical molten salt pump according to claim 2, characterized in that, A sealing structure (16) is provided between the adjusting slide plate (11) and the inner wall surface of the outer cylinder wall (14).

4. The axial force balancing device for a multi-stage vertical molten salt pump according to claim 3, characterized in that, The sealing structure (16) is an annular metal brush, and the adjusting slide plate (11) has several spaced grooves at one end, with the annular metal brush located in the grooves.

5. The axial force balancing device for a multi-stage vertical molten salt pump according to claim 2, characterized in that, A first gap (a) is provided between the rear cover plate (9) and the space guide vane (4), and a second gap (b) is provided between the rear cover plate (9) and the outer cylinder wall (14). The first gap (a) and the second gap (b) constitute a labyrinth gap between the first balance chamber (104) and the pressure chamber (101).

6. The axial force balancing device for a multi-stage vertical molten salt pump according to claim 2, characterized in that, The inner wall of the outer cylindrical wall (14) is provided with a protrusion, and a spring (12) is provided between the protrusion and the adjusting slide plate (11).

7. The axial force balancing device for a multi-stage vertical molten salt pump according to claim 2, characterized in that, A second balance chamber (102) is provided between the first balance chamber (104) and the pressure chamber (101). The second balance chamber (102) is the area enclosed by the space guide vane (4), the cylinder and the rear cover plate (9).

8. A multi-stage vertical molten salt pump, comprising multi-stage impellers, characterized in that, At least one impeller and its corresponding spatial guide vane (4) are provided with an axial force balancing device as described in any one of claims 1-7.

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