JPH08159094A - Multistage centrifugal compressor - Google Patents

Abstract

PURPOSE: To improve efficiency and obtain a wide usable range by connecting centrifugal compressors serially, and reducing the solidity of a vane of a diffuser of a centrifugal compressor on a rear stage compared to that of a vane of a front side centrifugal compressor. CONSTITUTION: In a two-stage centrifugal compressor 3, solidity of a vane of a diffuser 15a of a first stage centrifugal compressor 1 is larger than that of a vane of a diffuser 15b of a second stage centrifugal compressor 2. Efficiency of the diffuser 15a on the first stage has high peak and a narrow usable range. Efficiency of the diffuser 15b on the second stage has low peak and a wide usable range. Efficiency improvement is attained mainly by the front side diffuser 15a. As a result, peak is highered and the usable range is narrowed, which is eliminated by the rear side diffuser 15b. The efficiency is improved accordingly, while the usable range is widened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multistage centrifugal compressor.

[0002]

2. Description of the Related Art FIG. 1 shows an outline of a two-stage centrifugal compressor 3 in which a first-stage centrifugal compressor 1 and a second-stage centrifugal compressor 2 are connected in series. As shown in the figure, the impeller 4 of the first-stage centrifugal compressor 1 and the impeller 5 of the second-stage centrifugal compressor 2 are connected back to back via a rotary shaft 6. The rotating shaft 6 is provided with a small diameter gear 7. The small diameter gear 7 is meshed with the idle gear 8. The idle gear 8 is meshed with a large-diameter gear 11 provided on a drive shaft 10 of a motor 9.
With this configuration, when the motor 9 is driven, the impellers 4 and 5 rotate at high speed in synchronization.

The impellers 4 and 5 are housed in housings 12a and 12b, respectively. Housing 12
Is the intake pipe 13, the impeller case 14, and the diffuser 1.
5 and the spiral chamber 16. The swirl chamber 16a of the first-stage centrifugal compressor 1 is connected to the intake pipe 13b of the second-stage centrifugal compressor 2 via a connecting pipe 17. Connecting pipe 17
An intercooler 18 is installed in the. A discharge pipe 19 is connected to the spiral chamber 16b of the second-stage centrifugal compressor 2. An aftercooler 20 is interposed in the discharge pipe 19. According to this configuration, the air is sucked into the intake pipe 13a of the first-stage centrifugal compressor 1, is accelerated radially outward by the impeller 4, is decelerated by the diffuser 15a, and the speed is converted into pressure, whereby the swirl chamber 16a. Be led to. The air in the swirl chamber 16 a is cooled by the intercooler 18, is then sucked into the intake pipe 13 b of the second-stage centrifugal compressor 2, and similarly flows to the impeller 5 → diffuser 15 b → swirl chamber 16 b → aftercooler 20. , Is discharged from the discharge pipe 19.

The diffusers 15a and 15b are shown in FIG.
As shown in FIG. 5, the plurality of vanes 21 are arranged radially in a diagonal direction along the rotation direction of the impellers 4 and 5.
The number of vanes 21 and the mounting angle thereof are set according to the flow rate around a certain design point. When the number of vanes 21 is increased, the efficiency at the flow rate around the design point is increased, but the efficiency is remarkably lowered at the flow rate outside the design point, and the usable flow rate range is narrowed. Conventionally, the vanes 21 of the diffuser 15 have the same solidity in the first-stage centrifugal compressor 1 and the second-stage centrifugal compressor 2. The solidity means a value obtained by dividing the code of the vane by the pitch of the vane, as shown in FIG.

[0005]

In the two-stage centrifugal compressor 3 as described above, the air sucked from the intake pipe 13a is compressed by the first-stage centrifugal compressor 1 and its volume is reduced. After that, it is sucked into the second stage centrifugal compressor 2. Therefore, if the vanes 21 of the diffuser 15 are similar to each other in the first-stage centrifugal compressor 1 and the second-stage centrifugal compressor 2 (the same solidity), as shown in FIG. There is a problem that the usable flow rate range of the machine 2 becomes narrow.

For example, the choke point 22 of the first-stage centrifugal compressor 1 matches the choke point 23 of the second-stage centrifugal compressor 2, and the stall point 24 of the first-stage centrifugal compressor 1 is the second-stage centrifuge. Match the stall point 25 of the compressor 2. Therefore, the usable flow range of the second-stage centrifugal compressor 2 is narrowed, and the usable flow range of the entire two-stage centrifugal compressor 3 (this range depends on the second-stage centrifugal compressor 2 exclusively). ) Was getting narrower.

When the vanes 21 of the diffuser 15 are similar between the first stage side and the second stage side, the solidity of the vanes 21 is adjusted so as to obtain a moderate performance (efficiency and use range) as a whole. Because the design is done,
The efficiency of the diffuser 15a on the first stage side is insufficient,
The use range of the diffuser 15b on the step side was narrow.

An object of the present invention, which was devised in view of the above circumstances, is to provide a multistage centrifugal compressor which can improve the efficiency as a whole and can obtain a wide range of use.

[0009]

In order to achieve the above object, the present invention has a plurality of centrifugal compressors connected in series, and the vane solidity of the diffuser of the centrifugal compressor of the latter stage is changed to the centrifugal compressor of the former stage. It is smaller than the diffuser vane solidity.

[0010]

According to the above construction, since the vane solidity of the diffuser of the centrifugal compressor on the upstream side is large, a high efficiency is obtained around a predetermined design point, and the solidity of the vane of the diffuser of the centrifugal compressor on the downstream side is small. Get a wide range of use. That is, the improvement in efficiency is achieved by the diffuser on the front stage side, and as a result, even if the peak is increased and the use range is narrowed, it is eliminated by the diffuser on the rear stage side. Therefore, the efficiency is improved as a whole and the usage range is widened.

[0011]

An embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 2 is a diagram showing the diffusers 15a and 15b at the respective stages of the two-stage centrifugal compressor 3 shown in FIG. As shown, the solidity of the vanes 21 of the diffuser 15 a of the first-stage centrifugal compressor 1 is larger than the solidity of the vanes 21 of the diffuser 15 b of the second-stage centrifugal compressor 2. Specifically, the number of vanes 21 of the diffuser 15a on the first stage side is 13, and the number of vanes 21 of the diffuser 15b on the second stage side is 8. The number of vanes 21 of the first-stage diffuser 15a (13) is larger than that of the conventional one (10) shown in FIG. 3, and the number of vanes 21 (8) of the second-stage diffuser 15b is 8 in FIG. It is less than the conventional one (10 sheets) shown in.

Therefore, the diffuser 15a on the first stage side
Has a high peak and a narrow use range, and the efficiency of the diffuser 15b on the second stage side has a low peak and a wide use range. Specifically, as shown in FIG. 2, the choke point 26 on the first stage side matches the choke point 27 on the second stage side, and the stall point 28 on the first stage side coincides with the stall point 29 on the second stage side. Thus, the solidity (the pitch and chords of the vanes 21, that is, the number and chord length) of the diffusers 15a and 15b in each stage is set. Therefore, even if air is compressed by the first-stage centrifugal compressor 1 and introduced into the second-stage centrifugal compressor 2, the use range on the second-stage side is not narrowed unlike the conventional one shown by the broken line in the figure. . That is, the improvement in efficiency is achieved only by the diffuser 15a on the front stage side, and as a result, even if the peak is increased and the usage range is narrowed, it is eliminated by the diffuser 15b on the rear stage side. Therefore, the efficiency is improved as a whole and the usage range is widened.

The vane 2 of the diffuser 15a on the first stage side
How much the solidity of 1 is increased and how much the solidity of the vane 21 of the diffuser 15b on the second stage side is decreased depends on the individual machine and whether the priority is given to the efficiency or the usage range.

It is needless to say that the present invention may be applied not only to the two-stage centrifugal compressor as in this embodiment, but also to the three-stage four-stage centrifugal compressor. In this case, the number of vanes in the diffuser gradually decreases from the first stage side toward the second stage side and the third stage side. Further, instead of changing the number of the vanes 21, the code of the vanes 21 may be changed to change the solidity. In this case, the cord of the vane 21 of the front diffuser 15a is made longer than the cord of the vane 21 of the rear diffuser 15b. Further, both the pitch and the chord may be changed.

[0016]

As described above, according to the multi-stage centrifugal compressor of the present invention, the efficiency as a whole can be improved and a wide range of use can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a two-stage centrifugal compressor.

FIG. 2 is an explanatory diagram of a diffuser showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a diffuser showing a conventional example.

FIG. 4 is a schematic view of a diffuser for explaining solidity.

[Explanation of symbols]

 1 First Stage Centrifugal Compressor 2 Second Stage Centrifugal Compressor 3 Two Stage Centrifugal Compressor 15a First Stage Diffuser 15b Second Stage Diffuser 21 Vane

Claims (1)

[Claims] 1. A multi-stage, wherein a plurality of centrifugal compressors are connected in series and the vane solidity of the diffuser of the latter centrifugal compressor is made smaller than the vane solidity of the diffuser of the former centrifugal compressor. Centrifugal compressor.