JPH0630498U - Shroud casing for centrifugal compressors - Google Patents

Abstract

(57) [Abstract] [Purpose] In the high speed range, the efficiency drop on the operating line can be reduced, and in the low speed range, the surging limit can be shifted to a smaller flow rate side than the operating line, which is economical. In addition, the shell casing of the centrifugal compressor, which is excellent in operability, is aimed at. [Structure] As a surging countermeasure, in a shell casing of a centrifugal compressor in which a plurality of circulation holes and a circulation flow path for returning a part of the main flow as a circulation flow to the shell casing are formed, The shroud casing 07 is provided with a plurality of circulation holes 1 and a plurality of variable flow passage restrictors 4 attached to an outlet of the circulation flow passage 5 connected to the plurality of circulation holes 1.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a shell casing of a centrifugal compressor.

[0002]

[Prior art]

For example, as a vaneless diffuser centrifugal compressor, conventionally, as shown in a vertical sectional view of FIG. 4 and a partial plan view of FIG. 5, a working fluid of a working fluid is generated by a blade 03 of an impeller 02 rotated by a drive shaft 01. It is known that the pressure and velocity energy are increased, the velocity energy is converted into pressure by the vaneless diff user 04, and the pressure is discharged to the outside of the machine from a discharge part (not shown) through a scroll 05. In this type of compressor, for example, for three rotational speeds N ₁ , N ₂ , and N ₃ , the ratio of the suction pressure P _s and the discharge pressure P _d when the flow rate Q ₀ is changed, that is, the pressure ratio. When π _C is obtained, it becomes as shown by the broken line in the diagram of FIG. Here, at each rotational speed N ₁ , N ₂ , N _3, each operable minimum flow point is connected by a one-dot chain line, and this is defined as a surging limit I. Therefore, in order to shift the surging limit I toward the smaller flow rate side, as shown in the longitudinal sectional view of FIG. 6 and the partial plan view of FIG. 7, a shroud casing 07 corresponding to the front and rear range of the throat portion 06 of each blade 03 is provided. It is also known that a plurality of circulation holes 08 are bored along the circumferential direction in the range. In this type of compressor, when the discharge flow rate Q ₀ is small, a part of the flow rate ΔQ flows backward from the circulation hole 08 in the direction of arrow 09, so the impeller inlet flow rate Q ₁ is Q ₁ = Q ₀ + ΔQ Then, the inlet flow rate Q ₁ increases and the pressure ratio π _C becomes as shown by the solid line in FIG. Here, at each rotational speed N ₁ , N ₂ and N ₃ , the minimum operable flow rate point is connected by a two-dot chain line, and this is referred to as surging limit II.

However, such a structure has the following drawbacks as shown in FIG. (1) At high rotation speed N ₃ , the pressure rise to the circulation hole is large and the circulation flow is large, so the surging limit II is largely shifted to the small flow rate side, but the efficiency at large flow rate is reduced and it is not so large. The pressure ratio decreases. (2) At a low rotation speed N ₁ , the pressure rise to the circulation hole is small and the circulation flow is small, so that the surging limit is hardly improved.

[0004]

[Problems to be solved by the device]

 The present invention has been proposed in view of such circumstances, and it is possible to reduce the efficiency decrease on the operating line in the high rotation speed range, and to reduce the surging limit to a smaller flow rate than the operating line in the low rotation speed range. An object of the present invention is to provide a shell casing of a centrifugal compressor that can be displaced to the side and is therefore excellent in economy and drivability.

[0005]

[Means for Solving the Problems]

 Therefore, as a countermeasure against surging, the present invention employs a centrifugal compressor shroud casing having a plurality of circulation holes and a circulation flow path for returning a part of the main flow as a circulation flow to the shroud casing. It is characterized by comprising a plurality of circulation holes formed in the rear shroud casing and a plurality of variable flow passage restrictors attached to the outlet of the circulation flow passage connected to the plurality of circulation holes. To do.

[0006]

[Action]

 According to such a configuration, the following actions are performed. (1) Since there are multiple circulation holes drilled in the shell casing behind the throat of the impeller, the flow rate ratio of the circulation flow separated from the main flow becomes large, especially when the rotation speed of the impeller is low. , The surging limit line can be shifted to the smaller flow side than the operation line. (2) Since a plurality of variable flow path restrictors attached to the outlet of the circulation flow path connected to the above plurality of circulation holes are provided, the flow rate ratio of the circulation flow separated from the main flow can be adjusted relatively freely. Especially, when the rotation speed of the impeller is low, the flow restrictor can be fully opened to increase the circulation flow, and the surging limit line can be shifted to the smaller flow side from the operation line. (3) Further, especially when the rotation speed of the impeller is high, the flow restrictor can be throttled to reduce the circulation flow, and the efficiency reduction on the operating line can be reduced.

[0007]

【Example】

 An embodiment in which the present invention is applied to the known shroud casing shown in FIG. 4 will be described with reference to the drawings. The same reference numerals as those in FIGS. 4 to 8 respectively denote the same members, and first, FIG. In the longitudinal sectional view and the partial plan view of FIG. 2, 1 is a surging countermeasure to return a part of the main flow 2 to the main flow as the circulation flow 3, so that the shroud casing 07 on the downstream side of the throat portion 06 of the impeller 02 is opened. A plurality of circulation holes that are provided and extend in the radial direction, and 4 are a plurality of variable flow passage restrictors attached to the outlet of the circulation flow passage 5 connected to the plurality of circulation holes 1.

In such a structure, when the rotation speed of the impeller 02 is low, the flow passage restrictor 4 is fully opened so that the flow rate of the circulation flow 3 becomes larger than the flow rate of the main flow 2. To do. When the rotation speed of the impeller 02 is high, the flow passage restrictor 4 is throttled so that the flow rate of the circulation flow 3 becomes smaller than the flow rate of the main flow 2.

According to such a structure of the embodiment, the following effects can be obtained. (1) Since there are multiple circulation holes bored in the shell casing behind the throat of the impeller, the flow rate ratio of the circulation flow separated from the main flow becomes large, and as shown in Fig. 3, especially the impeller When the rotation speed of is low, the surging limit line can be shifted to the smaller flow rate side than the operating line, thus lowering the lower limit of the operating range of the compressor and improving drivability. (2) Since a plurality of variable flow path restrictors attached to the outlet of the circulation flow path connected to the above plurality of circulation holes are provided, the flow rate ratio of the circulation flow separated from the main flow can be adjusted relatively freely. As shown in FIG. 3, especially when the rotating speed of the impeller is low, the flow restrictor is fully opened to increase the circulation flow, and the surging limit line is set to the small flow side from the operation line. Therefore, the lower limit of the operating range of the compressor is lowered and the drivability is improved. Further, as shown in FIG. 3, particularly when the number of rotations of the impeller is high, the flow restrictor can be throttled to reduce the circulation flow, and thus the decrease in efficiency on the operation line can be reduced. The economical efficiency of the compressor is improved.

[0010]

[Effect of device]

 In short, according to the present invention, as a countermeasure against surging, an impeller throat is provided in a shell casing of a centrifugal compressor in which a plurality of circulation holes and a circulation flow path for returning a part of the main stream as a circulation flow to the shell casing are formed. By providing a plurality of circulation holes formed in the shroud casing at the rear of the section and a plurality of variable flow passage restrictors attached to the outlet of the circulation flow passage connected to the plurality of circulation holes, In the high rotation speed range, the efficiency reduction on the operating line can be reduced, and in the low rotation speed range, the surging limit can be shifted to the smaller flow rate side than the operation line. Therefore, the centrifugal compression has excellent economical efficiency and drivability. The present invention is extremely useful industrially because it obtains a shroud casing for a machine.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment in which the present invention is applied to the shroud casing of the known centrifugal compressor shown in FIG.

FIG. 2 is a partial plan view taken along line II-II of FIG.

FIG. 3 is a diagram showing a flow rate pressure ratio characteristic of the centrifugal compressor of FIG.

FIG. 4 is a vertical cross-sectional view showing a shroud casing of a known centrifugal compressor.

5 is a plan view taken along line VV of FIG.

FIG. 6 is a vertical sectional view showing a shroud casing of a known centrifugal compressor with circulation holes.

7 is a plan view taken along line VII-VII of FIG.

FIG. 8 is a diagram showing flow rate pressure ratio characteristics of the centrifugal compressors of FIGS. 4 and 6;

[Explanation of symbols]

 1 circulation hole 2 main flow 3 circulation flow 4 flow restrictor 5 circulation flow path 01 shaft 02 impeller 03 blades 04 vaneless diff user 05 scroll 06 throat 07 shroud casing

Claims (1)

[Scope of utility model registration request] 1. In a shell casing of a centrifugal compressor in which a plurality of circulation holes and a circulation flow path for returning a part of the main flow as a circulation flow to the shell casing are formed as a surging countermeasure, the impeller throat rear portion is provided. Of the shroud casing, and a plurality of variable flow passage restrictors attached to the outlet of the circulation flow passage connected to the plurality of circulation holes. Type shroud casing for compressors.