JPH0511238B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a multi-stage centrifugal pump, and particularly to a multi-stage centrifugal pump that has an improved final stage differential user, although the axial position of the final stage differential user does not coincide with the pump discharge port. It concerns centrifugal pumps.

[Prior Art] For example, in a barrel-type multistage diffuser pump such as a boiler feed water pump, the pump discharge port is located on the suction side of the final stage diffuser.

A conventional multistage centrifugal pump will be explained with reference to FIGS. 3 to 7.

Here, FIG. 3 is a vertical cross-sectional view showing the main structure of the first stage of a general multi-stage centrifugal pump, FIG. 4 is a vertical cross-sectional view showing the vicinity of the final stage of the multi-stage centrifugal pump, and FIG. , shows a differential user part employing conventional two-dimensional blades, a is a vertical cross-sectional view,
b is a cross-sectional view taken along the Z-Z arrow in a; FIG. 6 is a flow path cross-sectional view showing the fluid flow in a typical stage flow path; FIG. 7 is a diffuser blade employing a conventional three-dimensional blade. In this figure, a is a cross-sectional view of the blade corresponding to the cross section taken along the line E-E in FIG. 4, and b is a view taken along the line Y-Y of a.

As shown in FIGS. 3 and 4, a conventional multistage centrifugal pump pumps liquid sucked from a suction channel 1 into a centrifugal impeller (fitted onto a main shaft 2 and rotating together with the main shaft 2). (hereinafter simply referred to as an impeller), the pressure is raised by the impeller 3, and the pressure is discharged to the differential user 4 provided on the outer periphery of the impeller 3, and the flow is caused to flow into the curved channel 5 provided on the outer periphery of the differential user 4. The flow path of the stage is configured by changing the flow direction by approximately 180 degrees to an inward flow, and then guiding the flow exiting from the curved flow path 5 to the inlet of the next stage impeller 3' through the return flow path 6. Similarly, impellers, differential users, curved channels, and return channels are arranged in multiple stages in the axial direction, and the flow from the final stage differential user 7 is collected at the pump discharge port and discharged to the outlet channel 8.
The flow path is configured such that the fluid is discharged from the pump discharge port 9.

Conventional differential user 4 and final stage differential user 7
As shown in FIGS. 3 and 4, the flow path is connected to the side wall 4 of the differential user on the impeller side plate 3a side (suction side).
a, 7a, differential user side walls 4b, 7b on the impeller core plate 3b side (discharge side), and differential user blades 4c, 7c. A radial diff user is generally used, which is formed in a plane perpendicular to the center and allows the radial flow of liquid pressurized by the impeller 3 to flow out in the radial direction.

Further, the shape of the diffuser blade 4c is a two-dimensional blade having the same shape from the side walls 4a to 4b, as shown in FIG. 5b.

On the other hand, a curved flow path 5 is provided downstream of the differential user 4, and in order to downsize the pump, it is formed in a shape close to a rectangle with almost no curvature immediately around the outer circumference of the differential user 4, as shown in FIG. be done.

In this case, as shown in Figure 6, a force acts in the F direction due to the change in momentum when the radial flow v ₁ changes to the axial flow v ₂ , and the pressure at the X point changes to Y.
Since the pressure is higher than that at the point, the flow near the outlet inside the diff user tends to flow in an inclined direction toward the side wall 4b as indicated by the broken line arrow _v'd .

As a result, the boundary layer along the side wall 4a is significantly developed, and the boundary layer is less developed on the side wall 4b side.
This tendency becomes more pronounced as the pump discharge rate is reduced from the design point, causing separation on the side wall 4a side and causing instability of the pump (indentation in the head curve) in the low flow rate region.

In order to prevent this, to suppress the increase in size of the pump, and to prevent a decrease in pump efficiency, a conventional diff user is formed as shown in FIG. 7.

In FIG. 7, 4ca is the blade profile at a position close to the side wall 4a of the diffuser blade;
4cb shows the blade profile at a position close to the side wall 4b.

That is, as shown in FIG. 7, in the enlarged channel portion where adjacent blades 4c' of the differential user 4 overlap, the expansion angle between the blades is made smaller on the side wall 4a side, and the expansion angle between the blades is made smaller on the side wall 4b side. The shape of the diffuser blade is determined to increase the size of the blade.
However, as shown in FIG. 4, on the downstream side of the final stage differential user 7, there is no curved channel 5 having a shape close to a rectangular shape as shown in FIG. 3, and the flow of liquid discharged in the radial direction v ₁ In the outlet passage 8, the flow becomes an axial flow v ₃ , that is, a flow directed in the opposite direction to the flow v ₂ shown in FIG. 6, and flows out from the pump discharge port 9.

Therefore, if the final stage differential user 7 is made to have the same shape as the differential user 4, the flow out to the pump discharge port 9 will be obstructed, which will not only increase the loss but also reduce the flow velocity at the outlet of the final stage differential user 7. If it is too large, there will be a problem that the inner wall of the casing 10 located downstream of the differential user outlet will be significantly eroded due to erosion.

The general pumps shown in Figures 3 to 5 are shown in "Thermal and Nuclear Power Generation" July 1975 issue.
There is one listed on page 99. Furthermore, the differential user shown in FIG. 7 is related to the present invention, as disclosed in Japanese Patent Application No. 60-99563 entitled ``Diff User for Multistage Centrifugal Pump''.
is given as an example.

[Problems to be Solved by the Invention] As described above, the two-dimensional radial differential user shown in FIGS. 3 to 5 and the three-dimensional differential vane shown in FIG. After the flow at the final stage differential user outlet flows out in the radial direction, a flow component v ₃ flows from the discharge side to the suction side in the outlet flow path 8 as shown in FIG.
Since no consideration was given to the fact that the flow component of V3 must be maintained, the flow component of _V3 was canceled out and the flow was obstructed. For this reason, the outlet flow path 8 from the outlet of the final stage differential user 7 to the pump discharge port 9
There was a problem in that internal losses increased and pump efficiency decreased.

Furthermore, when the differential user having the three-dimensional blades shown in FIG. 7 is applied to the final stage differential user,
Since the flow at the differential user outlet tends to flow out to the side wall 7b (discharge side) on the impeller core plate side rather than the side wall 7a (suction side) on the impeller side plate side, erosion occurs when the flow velocity at the differential user outlet becomes excessive. There is a problem.

Generally, in large-capacity multistage centrifugal pumps, the impeller, differential user, and inner casing (stage) are made of high-quality materials to maintain erosion resistance due to cost considerations, but the outer casing is made of carbon steel. is common. Therefore, when the above-mentioned erosion problem occurs, a material with high erosion resistance such as stellite must be deposited, resulting in an increase in processing costs.

The present invention was made in order to solve the problems of the prior art described above, and it minimizes loss by smoothing the flow of fluid from the outlet of the diffuser to the pump discharge port in the final stage differential user, and also The object of the present invention is to provide a multistage centrifugal pump that can prevent erosion inside the casing by directing the axial component of the flow toward the pump discharge port.

[Means for Solving the Problems] In order to achieve the above object, the configuration of the multistage centrifugal pump according to the present invention includes a centrifugal impeller that is fitted onto the main shaft and rotates together with the main shaft, and a centrifugal impeller that is attached to the outer periphery of the centrifugal impeller. A diff user is located at the center of the centrifugal impeller and guides the flow out from the centrifugal impeller outward to restore static pressure, a curved channel guides the outward flow from the diffuser into an inward flow, and a curved channel directs the flow out of the curved channel inward. Multiple stages are arranged in the axial direction, each consisting of a return flow path that collects the flow and guides it to the inlet of the centrifugal impeller at the next stage. A flow path and a pump discharge port are formed, and the shape of the blades of a plurality of stages of differential users is changed to the shape of the blades of the multiple stages of the diffuser in the flow path close to the side wall of the differential user on the side plate of the impeller in the enlarged flow path portion where adjacent blades of the differential user overlap. In a multi-stage centrifugal pump, the expansion of the side wall of the inter-vane flow passage is reduced, and the expansion of the inter-vane flow passage is increased in the flow passage near the side wall of the differential user on the impeller core plate side. Only the blade shape is changed, and in the enlarged flow path portion where adjacent blades of the relevant differential user overlap, the expansion of the inter-blade flow path is increased in the flow path close to the differential user side wall on the impeller side plate side, and the expansion of the flow path between the blades is increased, and The passages close to the blades are formed so as to reduce the expansion of the passages between the blades.

[Function] In the enlarged flow path section where adjacent blades of the final stage differential user outlet overlap, the expansion of the flow path between the blades is increased near the differential user side wall on the impeller side plate side (suction side), and By reducing the expansion of the inter-vane flow path near the diffuser side wall (on the discharge port side), the main flow of the flow at the diffuser outlet can be directed toward the suction side.

In this case, the shape from the differential user inlet to the flow path where adjacent differential blades overlap is the same as that of a normal two-dimensional blade radial differential user, so the differential user decelerates the flow pressurized by the impeller and restores static pressure. functionality is not impaired.

Due to this, the final stage differential user,
The flow at the differential user outlet can be directed smoothly toward the pump discharge port without deteriorating the differential user performance, and the flow velocity near the inner surface of the casing installed on the discharge side downstream of the differential user outlet is reduced to improve erosion resistance. This makes it possible to improve performance.

[Embodiments] Hereinafter, each embodiment of the present invention will be described with reference to FIGS. 1 to 4 and FIG. 8.

First, FIG. 1 shows a final stage differential user of a multi-stage centrifugal pump according to an embodiment of the present invention, a is a cross-sectional view of the blade corresponding to the cross-section taken along the line E-E in FIG.
is a GG arrow view of a.

The general component configuration and flow path configuration of a multistage centrifugal pump that employs the final stage differential user of this embodiment are shown in FIGS. 3 and 4, which were previously explained in the prior art section.

In Fig. 3, 1 is a suction flow path, 2 is a main shaft, and 3
is a centrifugal impeller (hereinafter simply referred to as an impeller) fitted to the main shaft 2; 4 is a differential user located on the outer periphery of the impeller 3; It has a function of decelerating the rotor while guiding it in the direction (the direction in which the radial direction from the center of the main shaft 2 is larger) and recovering the static pressure.

Reference numeral 5 designates a curved flow path that guides an outward flow into an inward flow, and reference numeral 6 designates a return flow path that collects the flow that has passed through the curved flow path 5 inward and guides it to the inlet of the next-stage impeller 3'.

In FIG. 4, 3'' is the final stage impeller, 7 is the final stage differential user, 7a is the differential user side wall (hereinafter simply referred to as side wall) on the side of the impeller side plate 3a (suction side), and 7b is the impeller core plate 3b. The differential user side wall (hereinafter simply referred to as side wall) 8 on the side (discharge side) is
An outlet flow path that collects the flow from the final stage diff user 7 to a pump discharge port, 9 is a pump discharge port, and 10 is a casing.

That is, from the first stage shown in FIG. 3 to the final stage shown in FIG. A multi-stage pump is constructed from the suction port to the pump discharge port.

The multistage centrifugal pump of this embodiment differs from conventional pumps in the shape of the final stage diffuser vane.

FIG. 1 shows the shape of the differential user blade 7c of the final stage differential user 7. As shown in FIG.

In FIG. 1, 7ca is a blade profile at a position where the differential user blade 7c is close to the side wall 7a, and 7cb is a blade profile at a position where the differential user blade 7c is close to the side wall 7a.
The blade profile is shown in close proximity to b.

As previously shown in FIG. 5, conventional diffuser blades are two-dimensional blades having the same cross-sectional shape from the side wall 4a on the side of the impeller side plate to the side wall 4b on the side of the impeller core plate.

On the other hand, in this embodiment, for the differential users in multiple stages other than the final stage differential user, the seventh
As shown in the figure, adjacent differential user blades 4
The shape of the diffuser vane is determined so that the expansion of the inter-vane passage is small on the side wall 4a side in the enlarged passage part where c' overlaps, and the expansion of the inter-vane passage is made large on the side wall 4b side. As shown in FIG. 2, for the final stage differential user 7, in the enlarged channel portion where adjacent differential user blades 7c overlap, the inter-blade flow path is greatly enlarged on the side wall 7a side, and the inter-blade flow path is enlarged on the side wall 7b side. The shape of the diffuser blade is determined so that it is small. In other words, the adjacent differential user blades 7c
In the enlarged channel portion where the blades overlap, the shape of the blades is determined so that the expansion angle between the blades is large on the side wall 7a side, and the expansion angle between the blades is small on the side wall 7b side.

More specifically, as shown in FIG.
The width d ₁ of the inter-blade flow path at the point is equal on both the side wall 7a side and the side wall 7b side. On the other hand, the outlet of the enlarged channel is at point Na on the side wall 7a side, and the outlet channel width is
d _2a , the flow path length between M and _Na is _la . Also side wall 7
The outlet of the expanded channel on the b side is at point N _b , the outlet channel width is d _2b , and the channel length between M and N _b is l _b .

If the expansion angle of the inter-blade flow path is θ, then the expansion angle θ _a of the inter-blade flow path on the side wall 7a side and the expansion angle θ _b of the inter-blade flow path on the side wall 7b side are given by the following equations.

θ _a 2tan ^-1 (d _2a - _{d 1} /2l _a ) θ _b 2tan ^-1 (d _2b - _{d 1} /2l _b ) As shown in Figure 1, d _2b < d _2a , l _b > l _a Therefore, θ _a > θ _b .

Next, the operation of the multistage centrifugal pump configured as described above will be explained.

When the main shaft 2 is driven and the impeller 3 rotates, liquid is sucked into the impeller 3 from the suction channel 1 . After being pressurized by the impeller 3, it flows into the differential user 4, where it is decelerated, and after the static pressure is restored, it flows into the curved flow path 5. In the curved flow path 5, the direction of the outward flow from the differential user 4 is changed to an inward flow and is discharged to the return flow path 6. In the return flow path 6, this flow is further collected inward and sent to the centrifugal impeller 3 of the next stage. ′
leading to the entrance. After repeating the pressure increase several times in this way, the fluid pressurized by the final stage impeller 3'' is sent to the final stage differential user 7, and after the static pressure is restored, it flows out from the pump discharge port 9 through the outlet flow path 8. be done.

In the embodiment shown in FIG. 1, the area from the entrance of the final stage differential user blade 7c to the position (point M) where the concave surface of the blade overlaps the next differential user blade is formed into a two-dimensional shape, that is, when the differential user blade is viewed from the axial direction, the side wall 7a to the side wall 7b, and from the point M where the concave surface of the blade starts to overlap with the adjacent diff user blade to the exits Na and Nb, the expanded flow path between the adjacent diff user blade is
The blades are inclined so that the expansion is large on the side wall 7a side and small on the side wall 7b side, and since the flow path length is l _b > l _a , the flow at the outlet of the differential user is relatively small on the side wall 7a side. The radial velocity is high, and the circumferential velocity is high on the side wall 7b side. In addition, as shown in Figure 1b, due to the shape effect that the blade shape of the differential user outlet is three-dimensional,
From the side wall 7b to the side wall 7 for the flow coming out of the differential user
The force directed toward a acts not only to smooth the flow from the final stage differential user 7 to the pump discharge port 9, but also to direct the direction of the mainstream from the discharge side to the suction side. has a circumferential velocity in the outlet channel 8 and flows outward, with an axial component v ₃ towards the suction side. Thereby, flow loss from the final stage differential user 7 to the pump discharge port 9 can be reduced.

Furthermore, in the wake of the conventional final stage differential user with two-dimensional blades, if the flow velocity in the radial direction with the velocity in the circumferential direction is excessive, erosion occurs on the inner circumference of the casing 10. By adding a velocity component from the discharge side to the suction side due to the shape of the differential user vanes as in the example, to the differential user outlet flow, erosion of the inner surface of the casing is suppressed, and an efficient and reliable multistage centrifugal pump can be created. Obtainable.

Next, FIG. 2 shows a final stage differential user of a multistage centrifugal pump according to another embodiment of the present invention, a
is a cross-sectional view of the blade corresponding to the cross section taken along line E-E in FIG. 4, and b is a view taken along line H-H in a.

In the figure, the same reference numerals as those in FIG. 1 indicate the same parts, so the explanation thereof will be omitted.

The embodiment shown in FIG. 2 differs from the embodiment shown in FIG. 1 in the blade wall thickness distribution at the outlet of the final stage differential user 7A.

In the embodiment shown in FIG. 1, the blade wall thickness near the differential user exit is determined to be approximately equal between both side walls 7a and 7b, and the blade shape is such that the exit angle is large on the side wall 7a side and the exit angle is small on the side wall 7b side. It is tilted so that

On the other hand, in the embodiment shown in FIG. 2, the convex side of the blade has a two-dimensional shape, the exit angle is made equal on the side wall 7a side and the side 7b, and the thickness of the blade near the exit is set on the side wall of the side plate 3a on the impeller side. Thin on the 7a side, impeller core plate 3b
By tapering across the flow path so that it becomes thicker on the side wall 7b side, the outlet angle on the concave side of the blade can be set such that the outlet angle is large on the side wall 7a side and small on the side wall 7b side. I'm trying to make it happen. h _a shown in FIG. 2 is the thickness of the blade on the side wall 7b side at the outlet of the differential user 7A, and h _b > _ha .

In addition, in this embodiment, as shown in FIG. 2b,
The shape of the outlet of the final stage diff user flow path is such that the blade is concave and the outlet length on the side wall 7b side is smaller than that on the side wall 7a side, and the blade shape is tapered. 7b
An axial flow is generated from the side) to the suction side (side wall 7a side).

Therefore, according to the embodiment shown in FIG. 2, the same effects as those of the embodiment shown in FIG. 1 can be expected.

Next, FIG. 8 is a longitudinal sectional view showing the vicinity of the final stage of a multistage centrifugal pump according to still another embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 4 are the same parts as those of a general multistage centrifugal pump, so a description thereof will be omitted.

In the embodiment shown in FIG. 8, the final stage differential user 7B
The side walls 7B _a and 7B _b have a flat surface perpendicular to the main axis 2 near the differential user inlet, and are bent and inclined by α° in the axial direction from the discharge side to the suction side.

In the embodiment shown in FIG. 8, after the flow flowing out from the final stage impeller 3'' flows into the final stage differential user 7B, the flow flowing out in the radial direction at the time of pressure increase is sucked by inclining the flow path. Since a velocity component toward the side is provided, the same effects as the embodiments shown in FIGS. 1 and 2 described above are expected.

In the embodiment shown in FIG. 8, the differential user side wall is bent by α° in the axial direction from the discharge side to the suction side, but it goes without saying that it may be curved with a curved surface. .

[Effects of the Invention] As described above, according to the present invention, the flow of fluid from the diffuser outlet to the pump discharge port in the final stage diffuser is smoothed to minimize loss, and the flow after the diffuser outflows is reduced. By directing the axial component toward the pump discharge port, it is possible to provide a multistage centrifugal pump that can prevent erosion inside the casing.

[Brief explanation of the drawing]

FIG. 1 shows a final stage diffuser of a multistage centrifugal pump according to an embodiment of the present invention, a is a cross-sectional view of the blade, b is a view taken along the line GG of a, and FIG. 2 shows the final stage diff user of the multistage centrifugal pump according to the embodiment, a is a cross-sectional view of the blade, and b is the H of a.
-H arrow view, Figure 3 is a vertical sectional view showing the main structure of the first stage of a general multistage centrifugal pump, and Figure 4 is
The figure is a vertical cross-sectional view showing the area around the final stage of the multi-stage centrifugal pump, FIG. 6 is a flow path cross-sectional view showing the flow of fluid in a general stage flow path, FIG. 7 is a differential user blade employing a conventional three-dimensional blade, and a is a blade cross-sectional view. ,b
FIG. 8 is a longitudinal sectional view showing the area around the final stage of a multistage centrifugal pump according to still another embodiment of the present invention. 2... Main shaft, 3... Impeller, 3a... Impeller side plate, 3
b... Impeller core plate, 4... Diff user, 5... Curved flow path, 6... Return flow path, 7, 7A, 7B... Final stage differential user, 7a, 7Ba, 7b, 7Bb... Side wall, 7
c... Diffuser vane, 8... Outlet channel, 9... Pump discharge port.

Claims (1)

[Scope of Claims] 1. A centrifugal impeller that is fitted onto the main shaft and rotates together with the main shaft; a diff user that is located on the outer periphery of the centrifugal impeller and that guides the flow exiting from the centrifugal impeller outward to restore static pressure; There are multiple stages in the axial direction, each consisting of a curved channel that guides the outward flow from the differential user into an inward flow, and a return channel that collects the flow exiting from the curved channel inward and guides it to the inlet of the centrifugal impeller at the next stage. A flow path and a pump discharge port are formed to collect the flow from the final stage differential user to the pump discharge port located on the suction side of the final stage differential user, and the blade shape of the multiple stage differential user is In the expanded flow path portion where adjacent blades of the differential user overlap, the expansion of the inter-blade flow path is reduced in the flow path close to the differential user side wall on the side of the impeller side plate, and in the flow path close to the differential user side wall on the impeller core plate side. In the multi-stage centrifugal pump formed to increase the expansion of the flow path between the blades, only the blade shape of the final stage differential user is changed to the diffuser on the side of the impeller side plate in the enlarged flow path portion where adjacent blades of the differential user overlap. In the flow path near the side wall, the expansion of the flow path between the blades is increased,
A multi-stage centrifugal pump characterized in that a flow path close to a diffuser side wall on the impeller core plate side is formed so as to reduce expansion of the inter-blade flow path. 2. In the product described in claim 1, the blade shape of the final stage differential user blade has a two-dimensional shape from the inlet of the differential user blade to the position where the negative pressure surface of the blade overlaps an adjacent diffuser blade,
Regarding the shape of the blades on the downstream side from this position, the enlarged flow path between the adjacent differential user blades has a large expansion at the differential user side wall on the side of the impeller side plate, and a small expansion on the differential user side wall on the side of the impeller core plate. A multi-stage centrifugal pump characterized by a three-dimensional blade shape. 3. In either of claims 1 or 2, the shape of the final stage differential user blade is such that the blade wall thickness near the outlet of the differential user blade is thinner near the differential user side wall on the side of the impeller side plate, A multi-stage centrifugal pump characterized in that the thickness is formed near the differential user side wall on the impeller core plate side. 4 In what is stated in claim 1,
The final stage diff user has a diff user side wall on the impeller side plate side and a diff user side wall on the impeller core plate side, and the area near the inlet of the diff user is a plane perpendicular to the main axis, and the area near the outlet of the diff user is in the axial direction from the discharge side to the suction side. A multistage centrifugal pump characterized by being formed to be curved or curved.