Multistage pump with optimized axial thrust

Abstract

A multi-stage pump (100) for optimizing axial thrust is disclosed. The multi-stage pump (100) includes a pump discharge nozzle (101) and a bypass system (102) connected to the pump discharge nozzle (101). The bypass system (102) includes a throttle valve (104) operatively coupled to the pump discharge nozzle (101) and a bypass line (106) within the multi-stage pump (100) connected to the throttle valve (104) and a clearance ("Se"), the clearance ("Se") configured to receive a balancing flow through the bypass line (106) to increase pressure within the clearance ("Se") for optimizing axial thrust.

Description

Technical Field

[0001] The subject matter described in this specification relates to pumps, and more particularly to the cancellation of axial thrust in a multistage centrifugal pump.

Background Art

[0002] Axial thrust is the resultant of all axial forces (F) acting on the rotating element of a pump. In the case of a single-stage centrifugal pump, the axial forces acting on the rotating element include the axial impeller force, which is the difference between the axial forces acting on the discharge-side impeller shroud and the suction-side impeller shroud; the force due to the momentum constantly acting on the fluid contained in the defined space; the force due to the pressure acting on the relevant shaft cross-section resulting from the static pressures upstream and downstream of the shaft seal; special axial forces, for example, when a change to a vortex state occurs in the clearance (side gap) between the impeller and the casing during startup; other axial forces such as the force of the weight of the rotating element in a non-horizontal centrifugal pump or the magnetic attraction force in an electric motor in a direct-acting pump.

[0003] In the case of a multistage pump with a diffuser (for example, a boiler feed pump), the axial impeller force is greatly influenced by the axial position of the impeller relative to the diffuser. The rotation of the fluid handled within the discharge-side and suction-side clearances between the impeller and the casing strongly affects the axial force due to pressure. The average angular velocity of the rotating fluid handled (refer to the rotational speed) reaches approximately half of the impeller speed. In addition, due to the Coriolis acceleration, the inward clearance flow in the suction-side (i.e., outer) clearance (side gap) between the impeller and the casing further increases the turbulence in the side gap. In the discharge-side (i.e., inner) side gap of a multistage pump where the impeller is not hydraulically balanced, an outward gap flow results, and the process is reversed. The vortex motion is decelerated, and as a result, the axial force, and thus the axial impeller force, increases.

[0004] There are various forms of balancing the axial thrust, including mechanical ones that completely absorb the axial thrust via thrust bearings (such as tilting pad bearings, rolling element bearings, etc.), design-based ones where the impeller or stages are arranged back-to-back (refer to back-to-back impeller pumps), ones that balance or reduce the axial thrust of individual impellers via balance holes, ones that balance the entire rotating assembly via a balance device with an automatic balance function (such as a balance disk or balance disk sheet) or partially balance it via a balance drum or double drum, and ones that reduce it with individual impellers by back vanes.

[0005] Normally, a multistage pump is equipped with a balance piston to balance the axial thrust generated by the impeller. The residual thrust is received by the thrust bearing. The residual axial thrust is minimized at the BEP flow rate and maximized in the minimum flow rate state. For this reason, in multistage pumps, heat generation in the minimum flow rate state becomes excessive, so the use of antifriction bearings (rolling bearings) is restricted. Therefore, in applications with higher pressure and speed, tilting pad bearings that are forcibly lubricated with oil are used. However, the cost of tilting pad bearings and the corresponding lubricating oil facilities is very high compared to antifriction bearings lubricated with sump oil (stored oil).

Summary of the Invention

[0006] The main object of the present invention is to provide a bypass system for a multistage pump that reduces the residual axial thrust in a partial load state.

[0007] Another object of this subject is to enable the use of antifriction bearings (rolling bearings) in higher pressure applications of multistage pumps.

[0008] Another object of this subject is to reduce the size of tilting pad thrust bearings and the corresponding lubricating oil pump / lubricating oil facilities for pumps using bearings forcibly lubricated with oil (forced lubrication bearings).

[0009] Another object of the present subject matter is to provide a bypass system for a multistage pump that is simply designed, cost-effective, and efficient, and is different from conventional designs.

[0010] In one embodiment, the present invention relates to a multistage pump (100) in which axial thrust is optimized. The multistage pump (100) includes a pump discharge nozzle (101) and a bypass system (102) connected to the pump discharge nozzle (101). The bypass system (102) includes a throttle valve (104) operatively coupled to the pump discharge nozzle (101) and a bypass line (106) provided within the multistage pump (100) and connected to the throttle valve (104) and a gap ("Se"). The gap ("Se") is configured to receive a balanced flow flowing through the bypass line (106) in order to increase the pressure within the gap ("Se") for optimization of the axial thrust.

[0011] In another embodiment, the present invention relates to a multistage pump (500) in which axial thrust is optimized. The multistage pump (500) includes a bypass system (502) configured to optimize the axial thrust. The bypass system (502) includes a throttle bush (504) provided in proximity to the gap ("Se"). The throttle bush (504) defines a bypass line (506), and the gap ("Se") is configured to receive a balanced flow flowing through the bypass line (506) in order to increase the pressure within the gap ("Se") for optimization of the axial thrust.

[0012] To further understand the features and technical content of the present subject matter, the related description is made with reference to the accompanying drawings. However, the drawings are merely illustrative and are not used to limit the scope of the present subject matter.

[0013] The accompanying drawings merely illustrate typical embodiments of the present subject matter and should not be regarded as limiting its scope. It should be noted that the present invention can admit other equally effective embodiments. The detailed description will be described with reference to the accompanying drawings. In the drawings, the leftmost digit of the reference number indicates the drawing in which this reference number is first presented. The same reference number throughout the drawings is used to indicate similar functions and components. Hereinafter, by way of example, some embodiments of a system or method according to an embodiment of the present subject matter will be described with reference to the accompanying drawings.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0015] The drawings show embodiments of the present subject matter for illustrative purposes only. Those skilled in the art will readily understand from the following description that alternative embodiments of the structures and methods shown herein can be adopted without departing from the principles of the disclosure described herein.

[0016] The present disclosure presents embodiments of multistage pumps (100, 500) in which the axial thrust is optimized.

[0017] In one embodiment, a multistage pump (100) is presented in which the axial thrust is optimized. The multistage pump (100) includes a pump discharge nozzle (101) and a bypass system (102) connected to the pump discharge nozzle (101). The bypass system (102) includes a throttle valve (104) operatively coupled to the pump discharge nozzle (101) and a bypass line (106) provided within the multistage pump (100) and connected to the throttle valve (104) and a gap ("Se"), where the gap ("Se") is configured to receive a balance flow flowing through the bypass line (106) to increase the pressure within the gap ("Se") for optimization of the axial thrust.

[0018] In other embodiments, a multistage pump (500) is presented in which the axial thrust is optimized. The multistage pump (500) includes a bypass system (502) configured to optimize the axial thrust. The bypass system (502) includes a throttle bush (504) provided in proximity to the gap ("Se"), where the throttle bush (504) defines a bypass line (506) and the gap ("Se") is configured to receive a balance flow flowing through the bypass line (506) to increase the pressure within the gap ("Se") for optimization of the axial thrust.

[0019] It should be noted that the description and drawings merely explain the principles of the present subject matter. Those skilled in the art will understand that the disclosed concepts and specific embodiments can be readily utilized as a basis for modifying or designing other structures to achieve the same objectives of the present subject matter. Also, although not explicitly described or illustrated herein, those skilled in the art will understand that various arrangements can be devised to embody the principles of the present subject matter and that they are included within the spirit and scope of the invention. Furthermore, all examples described herein are clearly intended for educational purposes to assist the reader in understanding the concepts provided by the inventors for the principles of the present subject matter and the development of the technology, and should not be construed as being limited to such specifically described examples and conditions. The novel features considered to be characteristics of the present subject matter, both in terms of its configuration and operating method, will be better understood from the following description, together with the accompanying drawings, which will also disclose further objectives and advantages.

[0020] These and other advantages of the present subject matter will be described in more detail with reference to the following drawings. It should be noted that the description merely explains the principles of the present subject matter. Therefore, those skilled in the art will understand that, although not explicitly described herein, various arrangements can be conceived to embody the principles of the present subject matter and that they are included within the scope of the invention.

[0021] The centrifugal pump is based on the operating principle of transferring energy to the fluid by changing the angular momentum of the fluid by the torque transmitted from a uniformly rotating impeller (impeller) to the fluid flowing in the centrifugal pump. The centrifugal pump can be described as a driving machine considering the direction of energy flow, a turbomachine considering the characteristics of energy conversion, or a hydraulic turbomachine considering the characteristics of the fluid. The centrifugal pump can continuously pump a high flow rate at high pressure or ultra-high pressure. In the case of a high flow rate, the centrifugal pump is clearly more cost-effective and reliable than a positive displacement pump.

[0022] Examples of centrifugal pumps include axial flow pumps, mixed flow pumps, radial flow pumps, and side channel pumps. Further, the centrifugal pump can have a single-stage structure or a multi-stage structure, and bearings are provided in the centrifugal pump. Bearings are elements frequently used in centrifugal pump structures and enable movable parts to slide within fixed parts. Further, the bearing can be either a radial sliding bearing or an axial thrust bearing. In the case of a radial sliding bearing, the movable part is a pin or journal of a rotating shaft (axel) or transmission shaft (shaft), the stationary part is a bearing shell, and the movable part of an axial (thrust) sliding bearing is a thrust collar or thrust plate. Depending on the design, the axial (thrust) sliding bearing is subdivided into a hydrodynamic sliding bearing, a hydrostatic sliding bearing, and a combined sliding bearing of hydrostatic and hydrodynamic for special applications. Both basic design types need to ensure sufficient axial shaft (shaft) movement to accommodate the lubricant film thickness, which varies with load, lubricant viscosity, and sliding speed.

[0023] All rotating bodies are supported by bearings arranged within a bearing housing. The forces generated by the rotating body are transmitted to the bearing housing via the bearings and then to the structure to which the bearing housing is attached or connected. Bearings receive forces acting in both the radial (radial direction) and axial (axial direction) with respect to the rotating shaft. The bearing is either of the antifriction (rolling) type or the sliding bearing type. The antifriction (rolling) bearing system is a more simple self-contained unit and has a lower load-bearing capacity at high speeds compared to sliding bearings (the term load is used to represent the force transmitted through the bearing). As described above, sliding bearings require an external lubricating oil system. On the other hand, rolling bearings function without such an external lubricating system.

[0024] The axial thrust generated in a multi-stage pump usually becomes minimum at the best efficiency point (BEP) and maximum in the part load (minimum flow rate) state. The magnitude of the axial thrust in a high-speed centrifugal pump limits the use of antifriction (rolling) bearings. Usually, a balance device is provided in a multi-stage centrifugal pump. The balance device of a centrifugal pump is designed to cancel out the axial thrust generated by the pump rotor entirely or partially. A design incorporating a single balanced drum or a double drum requires a thrust bearing to absorb the residual axial thrust.

[0025] During the operation of a centrifugal pump, the balance device requires a certain amount of balance flow that flows through the clearance (clearance gap) between the rotating part and the non-rotating part of the balance device. The balance flow is significantly constricted while passing through the clearance. Due to this pressure loss, an axial force acts on the balance device, thereby canceling out the axial thrust of the impeller and performing the necessary balance adjustment. The balance device is used when the involved axial thrust is very large, such as in the case of an ultra-high pressure pump.

[0026] Figure 1 shows a standard axial thrust balance system composed of double pistons for balance. The pressure drops at various positions of the balance piston are shown in Figure 1. Approximately 90% of the thrust load of the impeller is balanced by the balance piston, and the remaining 10% of the load is absorbed by the thrust bearing. A balance flow is provided to the balance piston. The balance flow is the volume flow required to operate the balance device of the centrifugal pump. It increases the loss in the clearance but still constitutes an efficient and cost-reducing design for balancing the axial thrust. Since the diameter of the balance piston is fixed, it can only be designed for one operating point. The axial thrust of the impeller becomes minimum at the best efficiency point (BEP) and maximum in the part load (minimum flow rate state). Figure 2 shows the characteristics of the unbalanced axial thrust at different flow rates.

[0027] FIG. 3 is a schematic view of a multistage pump (100) in which the axial thrust according to an embodiment of the present disclosure is optimized. In one embodiment, the multistage pump (100) is provided with a bypass system (102) for optimizing the axial thrust. The term bypass means to circumvent or bridge. In centrifugal pump technology, it refers to a line that plays an important role in closed-loop control or as a balancing device. Under the circumstances of closed-loop control, it is possible to operate a centrifugal pump at a higher flow rate (large flow rate) than the flow rate available in the piping.

[0028] For this reason, the bypass flow can either be branched and returned directly from the pump discharge nozzle (101) through a narrow loop to the pump suction nozzle, or be reintegrated into the suction-side flow (after a delay) via another device such as a condenser or a cooling unit. When functioning as a balancing device, the bypass is used to cancel out the axial thrust in a boiler feed pump.

[0029] There are various reasons for integrating the bypass system (102) into the multistage pump (100). First, it is for stopping further operation of the pump in the low flow rate range. Second, it is for pumps (such as propeller pumps and vortex (cascade) pumps) whose pump input power curve slopes downward at high flow rates. And finally, it is for preventing the fluid being handled from heating in the low flow rate range. The bypass flow is usually branched through an automatic recirculation valve attached to the discharge nozzle of a high-pressure pump or an ultra-high-pressure pump (for example, a boiler feed pump).

[0030] According to an embodiment of the present disclosure, the bypass system (102) is configured to increase the pressure P1' (see FIGS. 3 and 5) only in the minimum flow state, thereby reducing the unbalanced axial thrust acting on the multistage pump (100). Further, the bypass system (102) is configured to maintain an inactive state at the rated flow rate / BEP flow rate.

[0031] In one embodiment, as shown in FIG. 3, the bypass system (102) connected to the pump discharge nozzle (101) includes a throttle valve (104) operatively coupled to the pump discharge nozzle (101), and a bypass line (106) provided within the multistage pump (100), the bypass line (106) being connected to the throttle valve (104) and a gap ("Se"), wherein the gap ("Se") is configured to receive a balanced flow flowing through the bypass line (106) in order to increase the pressure P1' within the gap ("Se") for optimization of the axial thrust.

[0032] In one embodiment, the throttle valve (104) can operate manually, automatically or semi-automatically. Also, the throttle valve (104) operates at a desired part-load flow rate, and the pressure P1' in the gap ("Se") rises to a predetermined calculated value that leads to a reduction in the residual axial thrust.

[0033] FIG. 4 is a graph (graph result) showing the results related to the multistage pump (100). In one example, the graph result includes a plot of the bearing temperature versus time for the multistage pump (100). In one example, the multistage pump (100) is a CHTR 4 / 1 + 6 pump using antifriction bearings (rolling bearings). In one example, the pressure P1' in the gap ("Se") is about 60 m of the minimum flow rate 3It is about 24 bar at about / hr. In another example, the throttle valve (104) of the bypass line (106) operates stepwise until the pressure P1´ in the gap (“Se”) rises to a predetermined calculated value of 40 bar. As is apparent from FIG. 4, the bearing temperature has decreased by 7° C., which indicates that the axial load applied to the bearing of the multistage pump (100) has decreased.

[0034] FIG. 5 is a schematic view of a multistage pump (500) in which the axial thrust according to another embodiment of the present disclosure is optimized. In another embodiment, the multistage pump (500) includes a bypass system (502) configured to optimize the axial thrust. In another embodiment, the bypass system (502) includes a throttle bush (504) provided close to the gap (“Se”), where the throttle bush (504) defines a bypass line (506), and the gap (“Se”) is configured to receive a balance flow flowing through the bypass line (506) in order to increase the pressure P1´ in the gap (“Se”) for the optimization of the axial thrust.

[0035] In another embodiment, the throttle bush (504) includes a flow control device (508) disposed at one end side of the bypass line (506) close to the gap (“Se”), and an orifice plate (510) disposed at the other end side of the bypass line (506) opposite to the flow control device (508). In one example, the flow control device (508) is a spring loaded device and is configured to operate in a partial load state. During operation of the pump, the flow control device (508) operates when the pressure P1´ is at a predetermined calculated value and does not operate when the multistage pump (500) is operating at optimal efficiency / rated flow. Also, in another embodiment, the orifice plate (510) is configured to reduce the discharge pressure and increase the pressure P1´ in the gap (“Se”) to a predetermined calculated value.

[0036] With the bypass system (102, 502), the multistage pumps (100, 500) can adopt antifriction bearings (rolling bearings) instead of tilting pad bearings that are force-lubricated with oil, thereby providing a cost-effective solution. Also, the overall length and bearing span of the multistage pumps (100, 500) are reduced. Further, expensive lubricating oil facilities, corresponding piping, and accessories can be eliminated.

[0037] In some cases, it may be desirable for the pump to be equipped with sliding bearings or tilting pad thrust bearings that are force-lubricated with oil. Here, when using the bypass system (102, 502), the net thrust load acting on the tilting pad bearings is reduced, so the size of the tilting pad thrust bearings and the lubricating oil pumps / facilities can be significantly reduced.

[0038] Although the embodiments of the present subject matter have been described in terms of words specific to structural features, it should be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous variations and applications of the systems / components of the present invention will be apparent to those skilled in the art, and accordingly, all such variations and applications that fall within the scope of the present subject matter are intended to be encompassed by the appended claims. Note that the description of the claims in the original application was as follows. Claim 1: A multistage pump (100) in which the axial thrust is optimized, a pump discharge nozzle (101), a bypass system (102) connected to the pump discharge nozzle (101), comprising the bypass system (102) a throttle valve (104) operatively coupled to the pump discharge nozzle (101), a bypass line (106) provided in the multistage pump (100) and connected to the throttle valve (104) and a gap (“Se”), comprising the gap (“Se”) is configured to receive a balance flow flowing through the bypass line (106) to increase the pressure in the gap (“Se”) for optimization of the axial thrust, multistage pump (100). Claim 2: The multistage pump (100) according to claim 1, wherein the throttle valve (104) is operable manually, automatically or semi-automatically. Claim 3: The multistage pump (100) according to claim 1, wherein the throttle valve (104) operates at a desired partial load flow rate and the pressure in the gap (“Se”) rises to a predetermined calculated value that leads to a reduction in the residual axial thrust. Claim 4: The multistage pump (100) according to claim 1, wherein the multistage pump (100) is a CHTR 4 / 1 +6 pump using antifriction bearings. Claim 5: The pressure in the gap (“Se”) is 24 bar at a minimum flow rate of 60 m 3 / hr. The multistage pump (100) according to claim 1. Claim 6: The throttle valve (104) of the bypass line (106) operates stepwise until the pressure in the gap (“Se”) rises to a predetermined calculated value of 40 bar. The multistage pump (100) according to claim 1. Claim 7: A multistage pump (500) in which the axial thrust is optimized, comprising a bypass system (502) configured to optimize the axial thrust, the bypass system (502) including a throttle bush (504) provided in proximity to the gap (“Se”), the throttle bush (504) defines the bypass line (506), and the gap (“Se”) is configured to receive a balance flow flowing through the bypass line (506) to increase the pressure in the gap (“Se”) for optimization of the axial thrust, multistage pump (500). Claim 8: The throttle bush (504) of the multi-stage pump (500) according to claim 7 includes a flow control device (508) disposed at one end side close to the gap ("Se") of the bypass line (506), and an orifice plate (510) disposed at the other end side opposite to the flow control device (508) of the bypass line (506). Claim 9: The flow control device (508) of the multi-stage pump (500) according to claim 8 is a spring-biased device. Claim 10: The flow control device (508) of the multi-stage pump (500) according to claim 8 is configured to operate in a partial load state. Claim 11: The orifice plate (510) of the multi-stage pump (500) according to claim 8 is configured to reduce the discharge pressure and increase the pressure in the gap ("Se") to a predetermined calculated value. Claim 12: The flow control device (508) of the multi-stage pump (500) according to claim 11 operates when the pressure is at the predetermined calculated value and does not operate when the multi-stage pump (500) is operating at optimal efficiency / rated flow rate.

Claims

1. A multistage pump (100) using an antifriction bearing in which the axial thrust is optimized, a pump discharge nozzle (101), a bypass system (102) connected to the pump discharge nozzle (101), and includes the bypass system (102) a throttle valve (104) operatively coupled to the pump discharge nozzle (101), a bypass line (106) provided within the multistage pump (100) and connected to the throttle valve (104) and a gap (“Se”), and includes the gap (“Se”) is configured to receive a balance flow flowing through the bypass line (106) via the throttle valve (104) in order to increase the pressure within the gap (“Se”) for optimization of the axial thrust, the bypass system (102) is configured to increase the pressure within the gap (“Se”) in a minimum flow state, the throttle valve (104) is configured to operate stepwise until the pressure within the gap (“Se”) rises to a predetermined calculated value. Multistage pump (100).

2. The multistage pump (100) according to claim 1, wherein the throttle valve (104) is operable manually, automatically or semi-automatically.

3. The multistage pump (100) according to claim 1, wherein the multistage pump (100) is a multistage centrifugal pump.

4. The pressure within the gap (“Se”) is 24 bar at a minimum flow rate of 60 m ３ / hr. The multistage pump (100) according to claim 1.

5. The predetermined calculated value is 40 bar. The multistage pump (100) according to claim 1.

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