JPH11303797A - Multistage compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To downsize a compressor in a multistage centrifugal or a mixed flow compressor, and attain a wide operation range and high efficiency. SOLUTION: Number of diffuser blades 3a to 3e arranged on a downstream side of an impeller composing a multistage centrifugal compressor is decreased from the front stage side ones 3a to the rear stage side ones 3e. In addition, a chord-pitch ratio of the blade is increased for intensifying deceleration as a load of the diffusers in whole of the multistage centrifugal compressor. The number of diffuser blades is also decreased from the front side to the rear side within a set range of specific speed, even when partially high blades are adapted to the diffusers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-stage compressor, and more particularly to a multi-stage compressor having a centrifugal type or mixed flow type impeller.

[0002]

2. Description of the Related Art In a centrifugal compressor, a flow is decelerated in a radially extending diffuser provided downstream of an impeller to convert velocity energy given from the impeller into pressure energy. If this energy conversion can be realized with a small loss, that is, with high efficiency, the efficiency of the entire compressor can be improved. And if it is realized with a short flow path, that is, a small radius, the compressor can be downsized.

A diffuser of a centrifugal compressor includes a bladeless diffuser 3 having no blades in a diffuser portion as shown in FIG. 8 and a plurality of blades provided in a circumferential direction of the diffuser portion shown in FIGS. 9 to 11. It is broadly divided into diffusers.

[0004] The vaneless diffuser has an advantage that a wide operating flow rate range (hereinafter, referred to as an operating range) can be obtained, but the diffuser efficiency is low. On the other hand, the vaned diffuser shown in FIG. 11 generally has an advantage that a high diffuser efficiency can be obtained as compared with a vaneless diffuser, but when applied to all stages of a multi-stage compressor, the operating range becomes extremely large. There is a risk of narrowing.

By the way, a diffuser as shown in FIG. 10 has a chord ratio σ which is a ratio of a chord length L of a blade to a blade pitch p.
Is small. Therefore, it is possible to obtain higher efficiency than the bladeless diffuser while securing a relatively wide operating range. An example of such a diffuser is disclosed in JP-A-53-11941.
It is described in No. 1 gazette. In the following description, a bladed diffuser having a chord ratio of less than 1 will be referred to as a small string ratio diffuser. This small string ratio diffuser has a lower maximum efficiency than the diffuser having a large string ratio shown in FIG.
In the present invention, a value at the center radius between the diffuser blade leading edge radius and the trailing edge radius is adopted as the blade pitch, and a straight line connecting the leading edge and the trailing edge of the diffuser blade is used as the chord length. Is used.

Further, Japanese Patent No. 1347983 (Japanese Patent Publication No. Sho 6)
No. 0-8359), there is a diffuser in which the height of the diffuser is less than half of the height of the flow path (partial height diffuser). This example is shown in FIG.

[0007] As described above, the vaneless diffuser or the diffuser with small chord ratio vanes has the advantage that a wide operating range can be ensured, and is therefore widely used in multistage centrifugal compressors. In addition, a partial height diffuser may be used for the purpose of improving performance in a high specific speed region.

Further, as a more efficient multistage centrifugal compressor, there is a diffuser described in Japanese Patent Application Laid-Open No. Hei 8-159909. In this publication, the chord ratio of the diffuser on the rear stage side is made smaller than the chord ratio of the diffuser at the first stage of the multistage centrifugal compressor, thereby improving the efficiency of the entire compressor and securing a wide operating range. ing.

[0009]

In a vaneless diffuser which has been widely used in the past, the speed reduction in the diffuser portion is insufficient, and there is a limit in improving the efficiency.
In order to obtain a large deceleration in the diffuser section, the flow path length of the diffuser must be increased, and FIG.
As shown in (2), the diffuser outlet diameter R increases. For this reason, the compressor casing 7 must be enlarged, and the production cost increases.

On the other hand, a small string ratio diffuser can provide higher efficiency than a bladeless diffuser, but is somewhat inferior in efficiency to a normal bladed diffuser.
In order to increase the deceleration at the diffuser, a bladeless diffuser is required downstream of the diffuser. As shown in FIG. 9, when the small string ratio diffuser is used, the diffuser outlet diameter R also becomes large, and the compressor casing must be large, thus increasing the manufacturing cost. If the diffuser with blades having a large chord ratio shown in FIG. 10 is applied to all stages of the multi-stage centrifugal compressor, the operation range may be extremely narrowed due to a slight design error.

Furthermore, the one described in Japanese Patent Publication No. 60-8359 is effective in a relatively high specific speed region, but in a multistage centrifugal compressor, the specific speed is different for each stage, so that higher efficiency is achieved. In order to realize this, it is necessary to devise a method for obtaining a rectification effect corresponding to the impeller of the specific speed of each stage.

Japanese Patent Application Laid-Open No. 8-159,094 in which a bladed diffuser is applied to a multi-stage centrifugal compressor is disclosed in Japanese Patent Application Laid-Open No. H8-159094, in which the first stage has a large chord ratio and the second stage has a small chord ratio. The aim is to improve efficiency and secure the operating range.
However, as shown in FIG. 5, the inflow angle to the diffuser is large on the front side having the impeller having a large specific speed, and the inflow angle is small on the rear side having a small specific speed. Since deceleration by the blades increases the flow angle, the former stage having a large flow angle has little room for turning the flow, and the effect is small even if a diffuser having a large chord ratio is used. Therefore, there is a problem that, although the operation range can be secured, a large improvement in efficiency cannot be obtained.

In any of the above, there is a limit in improving the efficiency of the multistage centrifugal compressor by the diffuser. Further, in order to maintain the current efficiency, there is a disadvantage that the compressor cannot be downsized.

The present invention has been made in view of the above-mentioned disadvantages of the related art, and has as its object to achieve a wide operating range and high efficiency in a multi-stage compressor. Another object of the present invention is to reduce the size of a multi-stage compressor and increase the efficiency thereof. Still another object of the present invention is to achieve the above object in a compressor having a multi-stage centrifugal or mixed flow impeller. Still another object of the present invention is to provide a diffuser for a multi-stage compressor having a high efficiency centrifugal or mixed flow impeller with a simple structure and reduced manufacturing cost of the compressor.

[0015]

A first feature of the present invention to achieve the above object is that a rotary shaft having a plurality of centrifugal or mixed flow impellers mounted thereon and an outer diameter side of each of the impellers are provided. In a multi-stage compressor including a diffuser formed, supporting means for rotatably supporting the rotating shaft, and a casing for accommodating the rotating shaft, the diffuser and the supporting means, each diffuser has a circumferential distance. The number of blades of the diffuser at each stage is the same as or larger than the number of blades at the front stage between two adjacent stages, and the first stage at the suction side of this compressor Is greater than the last stage on the discharge side.

Preferably, the chord ratio of the diffuser of each stage is smaller than that of the front stage between two adjacent stages; the axial height of the blades provided in the diffuser of each stage is the flow path of the diffuser of the stage. The height difference is almost the same as the height, and the difference between the entrance and exit angles of the blades in each stage is smaller in the front stage than in the rear stage between two adjacent stages; the axial height of the blades provided in the diffuser in each stage is the flow path of the diffuser in the stage. It is less than half the height. More preferably, the diffuser has a blade ratio of 1 or more in the first stage.

Preferably, the axial height of the blades provided in the diffuser in each stage is such that when the front side of two adjacent stages is less than 1/2 of the flow path height of the diffuser in the adjacent stage, the rear stage has the same height. When the height of the diffuser is less than half of the height of the diffuser of the above-mentioned diffuser or almost the same as the height of the flow of the diffuser of this stage, and the front of the two adjacent stages is almost the same as the height of the diffuser of this stage, the rear stage Is also substantially the same as the channel height of the diffuser in this stage.

[0018] More preferably, the diffuser of each stage has blades in which two adjacent stages have a greater chord ratio than the preceding stage.

A second feature of the present invention for achieving the above object is that a rotary shaft on which a plurality of centrifugal impellers are mounted, a diffuser formed on the outer diameter side of each of the impellers, In a multi-stage compressor comprising a supporting means for rotatably supporting the rotating shaft, a diffuser and a casing accommodating the supporting means, each diffuser includes a plurality of blades arranged at a distance in the circumferential direction. And the number of diffuser blades in each stage is at least one adjacent
Between the two stages, the number of the former stage is larger than the number of the latter stage, and the chord ratio is smaller in the former stage than in the latter stage.

In the multistage centrifugal compressor, the number of blades is increased on the front stage side where the inflow angle to the diffuser is large, and a predetermined deceleration is achieved with a short flow path. The inflow angle is relatively smaller than that of the front stage, and the rear stage, where there is much room for turning and deceleration of the flow by the blades, reduces the number of diffuser blades, while conversely increasing the blade chord ratio increases the diffuser. Is exerted more, and the work of the diffuser, that is, the turning angle of the flow (Δα in FIG. 4) is increased. Also, in the case of partial height blades used in the high specific speed region, the number of blades is increased toward the front stage and reduced toward the rear stage.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of one embodiment of a multistage centrifugal compressor, in which one casing contains five impellers. FIG. 1 shows only the upper half. The rotary shaft 1 is provided with five impellers 2a to 2e. The working gas 8 flowing from the suction pipe 5 is the impeller 2
a, and sequentially flows out of the discharge casing 6 through the respective impellers 2b to 2e. Impeller 2a of each stage
A diffuser 3 having a plurality of blades 3a to 3e and return channels 4a to 4d are provided downstream of .about.2e.

FIG. 2 shows the shape of the diffuser used in the multistage centrifugal compressor shown in FIG. First stage (first stage),
It is a top view of the diffuser of the 3rd stage (middle stage) and the 5th stage (final stage). In this example, the entrance radius ratio r ₂ / r ₁ of all stages of the diffuser to the same. Then, the number of blades is reduced and the blade length is increased from the front stage toward the rear stage. In a multi-stage centrifugal compressor that handles gas, the inflow angle α ₁ into the diffuser is closer to the front in the design of the impeller,
As shown in FIG. 2 or FIG. 5, the inflow angle α ₁ decreases on the subsequent stage.

When the inflow angle α1a is large as in the first stage, the blade length becomes short, as is apparent from FIG. As the blade length decreases, the flow path length also decreases, and the diffuser must slow down the flow in the short flow path. Further, when the inflow angle _α1a is large, even if the flow is turned on the blades of the diffuser, the circumferential component of the absolute speed becomes relatively small, and the absolute speed does not decrease so much.

When the inflow angle α _1a is large, it is difficult to reduce the flow by the diffuser blades. In this embodiment, in order to achieve more effective deceleration even under such conditions, the number of blades of the front diffuser is increased. Thereby, the flow is restricted by the short flow path, and a predetermined deceleration can be achieved.

On the other hand, as shown in FIG. 2, the inflow angle α _1e of the latter stage, for example, the fifth stage, becomes smaller. Therefore, if the inlet / outlet radius ratio r ₂ / r ₁ of the diffuser is made the same as that of the former stage, the flow path length Becomes longer. Therefore, the number of blades on the rear stage is smaller than that of the diffuser on the front stage, and the chord ratio is conversely larger than that on the front stage. That is, in a region where the inflow angle is small and there is a large room for deceleration due to the turning of the flow by the diffuser blades, the friction loss is reduced by reducing the number of blades. Further, a predetermined throat area is secured, and sufficient deceleration is enabled.

FIG. 3 shows the relationship between the number of blades of each stage diffuser and the chord ratio in this embodiment. The number of blades of the diffuser is gradually reduced from the front stage to the rear stage, and the chord ratio of the blades is sequentially increased toward the rear stage. By setting the diffuser specifications of each stage in this way,
For example diffuser flow angle, as shown in FIG. 5, turning angle Δα flow is decelerated by the diffuser may be larger as the rear stage of alpha ₁ is reduced. That is, according to the diffuser of the present invention, the maximum deceleration can be achieved in each stage in consideration of the operation range.

As described above, according to the present embodiment, the diffuser efficiency is higher at all stages than the conventional diffuser, and the efficiency of the compressor can be improved. In addition, a large deceleration can be realized with a diffuser diameter smaller than before,
The compressor can be downsized.

When the size is reduced, not only the manufacturing cost can be reduced, but also the strength design of the high-pressure compressor becomes advantageous. In a large-capacity compressor, there is also an effect that the transportation cost can be reduced by reducing the weight.

When the diffuser having a large chord ratio is used for all stages of the multi-stage compressor as described above, the operating range may be narrowed. Therefore, it is necessary to avoid excessively increasing the chord ratio, and in the present invention, the chord ratio of the bladed diffuser is 1 to 2. Further, when the entrance / exit angle difference Δβ of the blade is increased on the subsequent stage side, FIG.
As shown in (1), the turning angle Δα by the blade, that is, the deceleration increases, and the operating range may be narrowed due to the blade stall. However, when viewed in terms of angle of incidence on the diffuser, when the flow rate changes are the same as shown in FIG. 6, the angle of incidence of the first-stage + [delta], compared to - [delta, the second-stage of design inflow angle alpha ₁ is smaller The incident angles + δx and -δx become smaller.
Therefore, the latter stage is more advantageous in terms of the incident angle.
Thus, in the present invention, the chord ratio on the rear stage side is increased, but the value is kept within an appropriate range to secure a predetermined operating range.

As shown in FIG. 4, the number of blades of the diffuser is gradually reduced from the entire stage to the rear stage, but may be the same in adjacent stages.

FIG. 7 shows another embodiment of the present invention in which partial height blades 9a, 9b, 9c are provided in the diffuser section from the front stage to the rear stage, corresponding to FIG. . As a result, the flow of the impeller outlet flow is greatly distorted, and the number of blades is increased at the high specific speed stage having a short flow direction length, that is, on the front stage side, so that the rectification effect is enhanced by a short flow path. On the other hand, at the intermediate stage or the rear stage where the distortion of the impeller outlet flow is reduced, the number of blades is gradually reduced to reduce the friction loss, and the diffuser efficiency is increased by a corresponding rectifying effect.

In the present embodiment configured as described above, since the specific speed of the entire multi-stage compressor is high, it is possible to solve the problem that the diffuser efficiency is not improved even if the blade having the same height as the flow path is provided. That is, in the present embodiment, the number of blades at the partial height is appropriately selected, so that the diffuser efficiency is improved, and high efficiency as a whole multistage centrifugal compressor can be realized.

In the case of a diffuser of a multi-stage compressor used in a region where the specific speed is slightly lower than the high specific speed region described above, a blade having a partial height is provided in the front stage and a blade having the same height as the flow passage height is provided in the rear stage. Provide wings. Then, each diffuser group is set to have the relationship between the number of blades and the chord ratio as described in FIG. 7, FIG. 1, and FIG. As described above, the diffuser efficiency in the multistage compressor can be improved by selectively using the partial height blade diffuser and the full height blade diffuser in the wide specific speed range of the multistage centrifugal compressor.

The present invention is not limited to the above embodiments, but includes a combination of a centrifugal type or mixed flow type impeller, a bladeless diffuser, a partial height blade diffuser, a full height blade diffuser, and a small string ratio diffuser. All modifications that come within the true spirit and scope of the invention, such as combinations with, are included within the scope of the claims.

[0035]

According to the present invention, in a multistage centrifugal compressor, high efficiency can be realized while securing a predetermined operation range. In addition, the diameter of the diffuser outlet can be greatly reduced as compared with the conventional multi-stage centrifugal compression, so that the compressor can be downsized and the manufacturing and transportation costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of one embodiment of a multistage centrifugal compressor according to the present invention.

FIG. 2 is a partial plan view of a diffuser used in the multi-stage centrifugal compressor shown in FIG.

FIG. 3 is a view for explaining the relationship between the number of blades at each stage and the chord ratio.

FIG. 4 is a view for explaining the relationship between the number of blades at each stage and the chord ratio.

FIG. 5 is a view for explaining a flow angle of a diffuser section at each stage.

FIG. 6 is a view for explaining the flow angle of the leading edge of the diffuser blade in each stage.

FIG. 7 is a front view and a plan view of a diffuser of each stage according to another embodiment of the present invention.

FIG. 8 is a longitudinal sectional view of the multi-stage centrifugal compressor for explaining the multi-stage centrifugal compressor.

FIG. 9 is a longitudinal sectional view of another multi-stage centrifugal compressor for explaining the multi-stage centrifugal compressor.

FIG. 10 is a view for explaining diffuser specifications.

FIG. 11 is a diagram illustrating a diffuser with blades.

[Explanation of symbols]

1 ... rotating shaft, 2, 2a, 2b, 2c, 2d, 2e ... impeller
3 diffuser, 3a, 3b, 3c, 3d, 3e diffuser blade, 4, 4a, 4b, 4c, 4d return channel, 5 suction pipe, 6 discharge casing, 7 casing, 8 main flow direction, 9a, 9b, 9c ... Partial height blades.

Claims (8)

[Claims] 1. A rotating shaft on which a plurality of centrifugal or mixed flow impellers are mounted, a diffuser formed on the outer diameter side of each of the impellers, and support means for rotatably supporting the rotating shaft. In a multi-stage compressor including a rotating shaft, a diffuser, and a casing accommodating a supporting means, each of the diffusers has a plurality of blades arranged at a distance in a circumferential direction, and the blades of the diffuser at each stage are provided. A multi-stage compressor characterized in that the number of sheets in the preceding stage is equal to or greater than the number of sheets in the succeeding stage between two adjacent stages, and the first stage on the suction side of the compressor is larger than the last stage on the discharge side. 2. The multi-stage compressor according to claim 1, wherein the chord ratio of the diffuser of each stage is smaller in the front stage than in the rear stage between two adjacent stages. 3. The height of the blades provided in the diffuser of each stage in the axial direction is substantially the same as the height of the flow path of the diffuser of the stage, and the difference between the entrance and exit angles of the blades in each stage is between two adjacent stages. The multi-stage compressor according to claim 1, wherein the first stage is smaller than the second stage. 4. The multi-stage compressor according to claim 1, wherein the height of the blades of the diffuser of each stage in the axial direction is equal to or less than 流 路 of the flow passage height of the diffuser of the stage. . 5. The multi-stage compressor according to claim 2, wherein the blades of said diffuser have a chord ratio of 1 or more in a first stage. 6. The axial height of the blades provided in the diffuser of each stage is such that when the front side of two adjacent stages is less than half the flow path height of the diffuser of the adjacent stage, the rear side of the diffuser is located at the rear side of the stage. When the flow passage height of the diffuser is less than or equal to 1/2 or less than the flow passage height of the diffuser of this stage, and the front stage of two adjacent stages is almost the same as the flow passage height of the diffuser of this stage,
2. The multi-stage compressor according to claim 1, wherein the downstream side has substantially the same flow passage height as that of the diffuser in the downstream side. 7. The blade provided in the diffuser of each stage,
7. The multi-stage compressor according to claim 6, wherein the chord ratios of two adjacent stages are larger in a latter stage than in a preceding stage. 8. A rotating shaft on which a plurality of centrifugal impellers are mounted,
A multi-stage compressor comprising: a diffuser formed on the outer diameter side of each of the impellers; support means for rotatably supporting the rotary shaft; and a casing for accommodating the rotary shaft, the diffuser and the support means. In each of the diffusers has a plurality of blades arranged at a distance in the circumferential direction, the number of blades of the diffuser of each stage is at least one between two adjacent stages, the number of the front stage is smaller than the number of the rear stage. A multi-stage compressor characterized by a large number of chord ratios in the front stage and smaller than the rear stage.