JPH11153097A - Single shaft multistage centrifugal compressor and turbo refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the structure of the interstage inflow part of a single shaft multistage centrifugal compressor and to prevent the increase of length in the direction of a rotary axis according to structure or complication of the structure. SOLUTION: An opening 7 is formed in the outermost peripheral position of the return flow passage 3 of a main flow 2A and the opening 7 is one or a plurality of the openings in number in a peripheral direction. This constitution prevents enlargement of structure in an axial direction to form an inflow passage for an injection flow 2B and eliminates a need for arrangement of a partition part to partition a main flow 2A and the injection flow 2B from each other. Further, a swirl blade 8 is arranged at the opening 7 and incurring of a loss due to confluence is reduced in a way that the flow directions of the main flow 2A and the injection flow 2B are caused to coincide with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-shaft multi-stage centrifugal compressor having an inter-stage inflow, and more particularly to a single-shaft multi-stage centrifugal compressor whose structure is simple and inexpensive, and in which additional loss due to inter-stage inflow is small. About the machine.

[0002]

2. Description of the Related Art FIG. 2 is a system diagram of a two-stage compression centrifugal chiller with an economizer as an example of a system using a single-shaft multi-stage centrifugal compressor having an inflow between stages. In the figure, the refrigerant vapor that has exited the two-stage compressor 21 is condensed by a condenser 22 to become a liquid refrigerant, and then reduced to the pressure of an economizer 24 by a high-pressure expansion valve 23. At this time, the flash gas generated in the economizer 24 flows into the two-stage impeller 5 of the two-stage compressor 21. The liquid refrigerant accumulated in the economizer 24 is reduced in pressure to the pressure of the evaporator 26 by the low-pressure expansion valve 25, evaporated in the evaporator 26, and
It is drawn into the first stage impeller 1 of the stage compressor 21 and is compressed to the pressure of the condenser 22 by two-stage compression of the first stage and the second stage impeller. In this type of single-shaft, multi-stage centrifugal compressor, various structures are realized.In particular, the structure of the interstage inflow section that allows gas to flow into the interstage and merges it with the gas flow from the preceding stage includes:
Many attempts have been made to improve the operation of the compressor.

FIG. 3 shows an example of a conventional structure of an interstage inflow section of the single-shaft multistage centrifugal compressor described above.
No. 44698. In FIG.
In a casing 10, a main flow 2 </ b> A pressurized by a preceding impeller 1 attached to a rotating shaft 11 and an intermediate suction port 3.
The injection flow 2 </ b> B supplied from 0 merges with the return vane 32 in the return passage 31 and is sent to the next impeller 5. When the merging position is set downstream of the front edge 34 of the return vane 32 by installing the partition wall 33, the merging position due to the difference between the flow direction and the speed of the main flow 2A and the injection flow 2B is reduced. Structure to reduce the loss of

A single-shaft, multi-stage centrifugal compressor having a more complicated interstage inflow section has been disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 09-144698.
And JP-A-6-257590. As shown in FIG. 4, an interstage suction nozzle 41 partitioned by a partition plate 43 into which the injection flow 2 </ b> B flows is provided, and the tip of the nozzle extends near the center of the stationary blade 42 in the radial direction. Here, it merges with the main stream 2A. Further, the interstage suction nozzle 41 of the stationary blade 42 up to this confluence point
The portion above the tip (the portion outside in the radial direction) is cut off, and a guide vane 44 is provided here. According to this structure, the loss at the time of merging can be further improved by making the shapes of the stationary blades 42 and the guide vanes 44 suitable for the flow velocity and direction of the main flow 2A and the injection flow 2B, respectively.

[0005]

In the case of the above-described structure of the interstage inflow portion of the prior art, the return flow from the front stage impeller (FIG. 3) is performed in order to merge the interstage inflow near the entrance of the next stage impeller. Then, a flow path for guiding the injection flow is required between the return passage 31) and the next stage impeller. That is, in the case of FIG. 3, it is necessary to provide the partition wall 33 so as to bite in a part of the return vane 32 in the radial direction, and it is necessary to process not only the partition wall 33 but also the shape of the return vane 32. Become. This is the same in the case of FIG. 4, and it is necessary to further provide the guide vanes 44. Further, in the case of FIG. 3, the injection flow is injected from the entire circumferential direction, but since the intermediate suction port 30 is only a part in the circumferential direction, the annular passage 35 for guiding the flow in the entire circumferential direction. Is also formed. This is the same in FIG. However, since many components constituting the return flow path are manufactured by casting or welding of machined products, such processing and addition of components impair the compactness of the compressor and increase the cost. In addition, the space between the previous and next stages becomes longer due to the formation of the flow path for the injection flow, and the natural frequency of the shaft system is reduced accordingly.If the shaft diameter is increased to prevent the decrease, the weight of the rotating body increases. However, there has been a problem that the capacity of the bearing is increased, the diameter of the impeller hub is increased, and the fluid efficiency is reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a single-shaft multi-stage centrifugal compressor which has a simple structure, can be realized with a small number of steps and components, and has an interstage inflow portion which can be configured without increasing the length of a shaft system. It is to realize.

[0007]

In order to achieve the above object, the present invention provides a method for compressing a gas sequentially by a plurality of compression stages, and a method for inter-stage compression of a gas flowing into a second or subsequent compression stage. In the single-shaft multi-stage centrifugal compressor configured to merge the injection flows from the injection section, the interstage injection section may include one or more of the injection flows on the outermost periphery of the main flow return flow path, the main flow path Disclosed is a single-shaft multi-stage centrifugal compressor characterized by having an opening for leading to a shaft.

Further, the present invention is characterized in that, in the single-shaft multistage centrifugal compressor, a swirl vane is provided at the opening so that the injection flow has a swirl component in the same direction as the diffuser outlet in the preceding stage. Is disclosed.

Further, the present invention provides the single-shaft multi-stage centrifugal compressor, wherein the plurality of openings are provided, and at least two of the plurality of openings have different opening areas. A centrifugal compressor is disclosed.

Further, the present invention provides the single-shaft multi-stage centrifugal compressor, wherein the single-shaft multi-stage centrifugal compressor has a plurality of openings, and all of the plurality of openings have the same opening area. Disclose.

Further, the present invention provides the single-shaft multi-stage centrifugal compressor, wherein the opening is formed so as to face a swirl-preventing blade provided in the return flow passage. Disclose machine.

The present invention also provides the uniaxial multistage centrifugal compressor, wherein the opening is formed on an extension of the diffuser of the front compression stage on the side plate side, and the opening is located on a side closer to the impeller of the front compression stage. A single-shaft multi-stage centrifugal compressor characterized in that a guide plate for separating a main flow flowing out of a diffuser of a preceding compression stage from the injection flow is provided outside a periphery of the compressor.

Further, according to the present invention, in the single-shaft multistage centrifugal compressor, when there are a plurality of the openings, a valve is provided in a gas passage for guiding an injection flow to at least one of the plurality of openings, A control means for closing the valve in an operating state in which the driving power of the single-shaft multistage centrifugal compressor is small and adding the control means for opening the valve in an operating state in which the driving power of the single-shaft multistage centrifugal compressor is large is added. A single-shaft, multi-stage centrifugal compressor is disclosed.

[0014]

Embodiments of the present invention will be described below. FIG. 1 is a diagram showing a configuration example of an interstage inflow section of a single-shaft multistage centrifugal compressor according to the present invention, and FIG. 5 is a cross-sectional view taken along the line AA ′ of FIG. Here, for the sake of simplicity, the centrifugal compressor will be described as a two-stage type, but this may be generally a multi-stage type. In FIG. 1, the main flow 2 </ b> A that has been compressed by the first-stage impeller 1 attached to the rotating shaft 11 and has flowed out enters the return passage 3 through the first-stage diffuser 2. The return flow path 3 is provided with a swirl prevention blade 4 for guiding the swirl flow flowing out of the diffuser 2 in the radial direction, and in addition to a two-stage impeller 5.
Into the tank.

An opening 7 connected to the interstage inflow channel 6 and facing the swirl-preventing blade 4 is provided at a part of the outermost position of the return channel 3. The inflow 2 </ b> B is guided into the return channel 3. As shown in the cross-sectional view of FIG. 5, four openings 7 are provided at the lower part, and the wall surfaces 9 at both ends of the openings 7 have the same direction as the swirling flow of the main flow 2A flowing out of the diffuser 2 into the injection flow 2B. In addition to providing a tilt for giving a swirl and providing a swirler vane 8 near the center of the opening 7, a loss at the time of combining the injection flow and the main flow is reduced. For example, in the case of a two-stage compression centrifugal chiller equipped with an economizer, the flow rate of the flash gas as the injection flow is one of the total flow rate sucked by the two-stage impeller.
This is because, in order to reach 0 to 20%, it is necessary to reduce the loss at the time of merging.

According to this configuration example, the main flow and the injection flow are not combined after flowing in the axial direction along two surfaces perpendicular to the axial direction as in the related art, but are combined at the axial direction. They are synthesized while flowing together along one surface in the axial direction.
Therefore, the length in the axial direction does not increase due to the formation of the inflow portion between the stages, and a partition plate or the like for separating the main flow and the injection flow until the merging is not required, thereby simplifying the structure. Also, since there is only one opening 7 at the outermost periphery of the return flow path 3, there is no need for a flow path for guiding the injection flow to the entire circumference unlike the conventional configuration. Further, since the injection flow guides the swirl flow at the diffuser outlet, there is also an effect of suppressing the propagation of the stall cell of the swirl stall that occurs when the compressor flow rate decreases. With this operation, the compressor in which the rotation stall occurrence limit is the operation limit has the effect of expanding the operation range on the low flow rate side.

FIG. 6 shows another configuration example of the single-shaft multi-stage centrifugal compressor according to the present invention, and shows only the interstage injection section. In the present configuration example, the opening 7 into which the injection flow 2B flows,
A guide for separating the main flow 2A and the injection flow 2B flowing out of the first-stage diffuser 2 on the extension of the side plate side 12 of the first-stage diffuser 2 and outside the opening 7 near the first-stage impeller 1. A plate 13 is provided. The main plate 2A flowing out of the diffuser 2 by the guide plate 13
Collision loss between the gas and the injection flow 2B is reduced.

According to this structure, the main flow and the injection flow are merged in a portion where the main flow becomes an axial flow in the return flow path 3, and in particular, an axial component is enlarged for the injection flow. It is neither structural nor complicated. Also,
The opening 7 is located at the outermost peripheral portion of the return channel 3 as in the case of FIG.
If there are only three locations, the flow path of the injection flow can be easily formed. In the present configuration example, since the injection flow flows from immediately downstream of the diffuser 2, the guide action is strong and the effect of suppressing the turning stall is large, but there is no collision loss between the main flow 2 A flowing out of the diffuser 2 and the injection flow 2 B. Therefore, this configuration is suitable for a compressor in which the expansion of the operating range is important.

FIG. 7 shows another example of the configuration of the single-shaft multi-stage centrifugal compressor according to the present invention, in which the interstage inflow portion is shown in a sectional view similar to FIG. In the configuration example of FIG. 1 or FIG. 6, the opening 7 is provided at one place. In this case, although the structure is simple, there is a large difference in density between the injection flow and the main flow. The unevenness in the circumferential direction of the flow increases, which causes noise and vibration. Therefore, in this configuration example, two openings are provided in the circumferential direction as shown in FIG. 5 so that the circumferential inhomogeneity of the flow flowing into the two-stage impeller approaches a symmetrical shape. However, if the size of the two openings 7 and 7 'is the same, the resistance to the flow instability phenomenon decreases, so that one of the openings 7 and 7' is configured to be wider than the other.

FIG. 8 shows another example of the configuration of the single-shaft multi-stage centrifugal compressor according to the present invention, in which the interstage inflow portion is shown in a sectional view similar to FIG. In this configuration example, three openings are provided. In particular, the opening area of the opening 7 is made equal to the sum of the opening areas of the other openings 7 'and 7 ". Thus, the number of openings is increased. However, there is a disadvantage in that the structure of the flow path for guiding the inter-stage inflow to each opening becomes complicated, but the unevenness in the circumferential direction of the inflow of the two-stage impeller is further improved as compared with the case of FIG.

FIG. 9 shows still another example of the configuration of the single-shaft multi-stage centrifugal compressor according to the present invention. The interstage injection section is shown in a cross section similar to FIG. In this configuration, two openings are provided, and the opening areas of the openings 7 and 7 'are equal. This configuration is suitable for a model of an application in which it is important to improve the circumferential nonuniformity of the inflow of the two-stage impeller due to the effect of suppressing the flow instability phenomenon.

Further, with the configuration shown in FIG. 9, the resistance to inflow in the circumferential direction of the inflow of the two-stage impeller is not reduced, and the unevenness in the circumferential direction can be improved. FIG.
Is a system configuration diagram of a two-stage compression centrifugal chiller with an economizer in which such measures are taken. A single-shaft multi-stage centrifugal compressor 21 ′ having the structure of FIG. 9 is used. In this system, the gas flow path of the economizer is connected to two flow paths 16, 1 and 2 respectively connecting to two openings 7, 7 'in FIG.
6 ′, one of which is provided with a shutoff valve 15, a valve controller 17 for controlling the opening and closing thereof, and a drive power detector 18 for detecting the drive power of the two-stage compressor 21 ′. .
The drive power detected by the drive power detector 18 is
The valve controller 17 controls the shut-off valve 15 so that the shut-off valve 15 is opened at, for example, 50% or more of the design rated value, and the shut-off valve 15 is closed at less than 50% of the designed rated value.

According to this configuration, when the amount of gas passing through the two-stage compressor 9 is large, the driving power of the two-stage compressor 9 is large, and the closing valve 15 is opened to open the two openings, that is, the openings 7, 7 '.
Since the flash gas flows into the two-stage impeller, unevenness in the circumferential direction of the flow flowing into the two-stage impeller is improved, and generation of noise or the like which is a problem particularly when the gas amount is large is prevented. In addition, since the flow instability does not occur when the amount of gas passing through the compressor is large, the reduction in the effect of suppressing the flow instability when two openings having the same opening area are provided does not matter.
On the other hand, in a state where the amount of gas passing through the compressor is small, since the driving power of the compressor is small, the closing valve 15 is closed, and only one opening is operated as in FIG. The flow instability that is a problem is suppressed. In this case, the unevenness in the circumferential direction becomes large, but since the gas amount is small, there is no need to worry about problems such as noise. In the configuration of FIG. 8, when the driving source of the compressor 21 ′ is an electric motor, the driving power detector 18 measures the electric motor driving current to provide the most accurate and high reliability. The control can be performed with. Although the compressor shown in FIG. 9 having a plurality of openings having the same opening area is used as the compressor, if there are a plurality of openings, the configuration in FIG. 10 is the same even if the opening areas are not necessarily the same. The effect can be expected.

[0024]

According to the present invention, the interstage inflow structure of a single-shaft multistage centrifugal compressor having an interstage inflow can be realized with a short interstage distance and a simple structure, so that the shaft diameter increases and the shaft diameter increases. Thus, there is an effect that the loss can be prevented from increasing and the compactness of the compressor can be improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration example of a single-shaft multi-stage centrifugal compressor according to the present invention.

FIG. 2 is a diagram schematically showing an apparatus of a two-stage compression turbo refrigerator with an economizer.

FIG. 3 is a longitudinal sectional view showing an example of a conventional single-shaft multi-stage centrifugal compressor.

FIG. 4 is a longitudinal sectional view showing an example of a conventional single-shaft multi-stage centrifugal compressor.

FIG. 5 is a cross-sectional view of a return flow channel in the configuration example of FIG. 1;

FIG. 6 is a longitudinal sectional view showing another configuration example of the single-shaft multi-stage centrifugal compressor according to the present invention.

FIG. 7 is a cross-sectional view of a return passage showing another example of the configuration of the single-shaft multistage centrifugal compressor according to the present invention.

FIG. 8 is a cross-sectional view of a return flow path showing another configuration example of the single-shaft multistage centrifugal compressor according to the present invention.

FIG. 9 is a cross-sectional view of a return flow path showing another configuration example of the single-shaft multi-stage centrifugal compressor according to the present invention.

10 is a diagram schematically showing a two-stage compression centrifugal chiller equipped with an economizer using the single-shaft multi-stage centrifugal compressor shown in FIG. 9;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 First stage impeller 2 Diffuser 3 Return flow path 4 Rotation prevention blade 5 Two-stage impeller 6, 6 'Inter-stage inflow flow path 7, 7', 7 "opening 8 Rotating blade 12 Side plate side 13 Guide plate 15 Closing valve 16, 16 'Flash gas flow path 17 Valve controller 18 Drive power detector 2A Main flow 2B Injection flow

Claims (8)

[Claims] 1. A single-shaft multi-stage centrifugal compressor in which a gas is sequentially compressed by a plurality of compression stages and an injection flow from an interstage injection portion is merged with a main flow flowing into a second or subsequent compression stage. The interstage injection unit is provided on the outermost periphery of the main flow return channel.
A single-shaft multi-stage centrifugal compressor having one or a plurality of openings for guiding the injection flow to a main flow passage. 2. The single-shaft multi-stage centrifugal compressor according to claim 1, wherein a swirl vane is provided at the opening so that the injection flow has a swirl component in the same direction as the diffuser outlet in the preceding stage. A single-shaft multi-stage centrifugal compressor. 3. The single-shaft multi-stage centrifugal compressor according to claim 1, wherein the plurality of openings are provided, and at least two of the plurality of openings have different opening areas. Centrifugal compressor. 4. The single-shaft multi-stage centrifugal compressor according to claim 1, wherein the plurality of openings are provided, and all of the plurality of openings have the same opening area. 5. The single-shaft multi-stage centrifugal compressor according to claim 1, wherein the opening is formed so as to face a swirl-preventing blade provided in the return flow passage. Machine. 6. The single-shaft multi-stage centrifugal compressor according to claim 1, wherein the opening is formed on an extension of a diffuser of a front compression stage on a side plate side, and a side of the opening close to an impeller of the front compression stage. A single-shaft multi-stage centrifugal compressor, wherein a guide plate for separating the main flow flowing out of the diffuser of the preceding compression stage from the injection flow is provided outside the periphery of the compressor. 7. The single-shaft multi-stage centrifugal compressor according to claim 1, wherein when there are a plurality of the openings, a valve is provided in a gas passage for guiding an injection flow to at least one of the plurality of openings. A control means for closing the valve in an operating state in which the driving power of the single-shaft multistage centrifugal compressor is small and adding the control means for opening the valve in an operating state in which the driving power of the single-shaft multistage centrifugal compressor is large is added. A single-shaft multi-stage centrifugal compressor characterized by the following. 8. A centrifugal chiller using the single-shaft multi-stage centrifugal compressor according to one of claims 1 to 7.