CN218266395U

CN218266395U - Centrifugal compressor

Info

Publication number: CN218266395U
Application number: CN202222138512.7U
Authority: CN
Inventors: 林文凯; 李训安
Original assignee: Fusheng Co Ltd
Current assignee: Fusheng Co Ltd
Priority date: 2022-07-15
Filing date: 2022-08-15
Publication date: 2023-01-10
Anticipated expiration: 2032-08-15
Also published as: TW202405312A; TWI827145B; CN117432637A

Abstract

The utility model provides a centrifugal compressor, spout the passageway including air inlet, runner, first order impeller, second level impeller, backward flow stator base and energy-saving appliance. The flow channel is provided with a first diffusion section, a first turning section, a backflow section, a second turning section, a second diffusion section and a volute flow channel. The volute flow passage is connected with the second diffusion section. The first-stage impeller is arranged between the air inlet and the first diffusion section. The second-stage impeller is arranged between the second turning section and the second diffusion section. The backflow guide vane base is provided with a plurality of backflow wings positioned in the backflow section and a plurality of injection holes communicated with the backflow section. Each backflow wing is provided with a first wing part, a second wing part and a slit positioned between the first wing part and the second wing part. The plurality of injection holes fall within the plurality of slits, respectively. The economizer injection channel is communicated with the injection holes. The utility model provides a centrifugal compressor helps reducing the turbulent flow production between the backward flow stator base to promote compression efficiency.

Description

Centrifugal compressor

Technical Field

The utility model relates to a centrifugal compressor especially relates to a second grade centrifugal compressor.

Background

A typical two-stage centrifugal compressor includes a first stage impeller and a second stage impeller, where the first stage impeller is located upstream of the flow passage and the second stage impeller is located downstream of the flow passage. First, a first fluid (e.g., gaseous refrigerant, air, or carbon dioxide) flows from the inlet guide vane toward the first-stage impeller along the longitudinal axis of the drive shaft, and then the first-stage impeller pressurizes the first fluid and drives the first fluid into the flow channel in a centrifugal direction. Then, the first fluid turns at the first turning section of the flow passage and flows to the second-stage impeller along a centripetal direction. In detail, the second-stage impeller is disposed corresponding to the second turning section of the flow channel, and the injection channel of the economizer is communicated with the second turning section of the flow channel to inject a second fluid (such as a gaseous refrigerant, air or carbon dioxide) into the second turning section of the flow channel, so that the first fluid and the second fluid form a third fluid in the second turning section of the flow channel. The third fluid then flows to the second stage impeller and is pressurized by the second stage impeller to flow in a centrifugal direction to the volute flow channel

Generally, a return guide vane base may be disposed between the first-stage impeller and the second-stage impeller, and the second fluid from the economizer is guided by a plurality of return vanes on the return guide vane base to be injected into the second turning section of the flow passage. Furthermore, a backflow channel is formed between any two adjacent backflow wings, and turbulence is easily generated in the backflow channel by the second fluid, so that the first fluid and the second fluid cannot be uniformly mixed, and problems of increased fluid pressure loss, sliding of aerodynamic efficiency and the like are derived, thereby affecting the performance of the centrifugal compressor.

SUMMERY OF THE UTILITY MODEL

The utility model relates to a centrifugal compressor helps reducing the turbulent flow production between the backward flow stator base to promote compression efficiency.

According to the utility model discloses an embodiment, centrifugal compressor includes that air inlet, runner, first order impeller, second stage impeller, backward flow stator base and energy-saving appliance spout the passageway. The flow channel is communicated with the air inlet and is provided with a first diffusion section, a first turning section connected with the first diffusion section, a backflow section connected with the first turning section, a second turning section connected with the backflow section, a second diffusion section connected with the second turning section and a volute flow channel connected with the second diffusion section. The first-stage impeller is arranged between the air inlet and the first diffusion section. The second-stage impeller is arranged between the second turning section and the second diffusion section. The backflow guide vane base is arranged between the first-stage impeller and the second-stage impeller and is provided with a plurality of backflow wings positioned in the backflow section and a plurality of injection holes communicated with the backflow section. Each backflow wing is provided with a first wing part, a second wing part and a slit for separating the first wing part from the second wing part. The plurality of injection holes fall in the plurality of slits respectively. The injection channel of the economizer is communicated with the injection holes.

In an embodiment of the present invention, the slit of the backflow wing has two opposite outlets, and a distance between the two outlets is D. The distance between the injection hole and one outlet is between 1/4D and D.

In an embodiment of the present invention, the first wing portion of the backflow wing has an outer end portion opposite to the slit, and the second wing portion of each backflow wing has an inner end portion opposite to the slit. The distance between the outer end of the first wing part and the inner end of the second wing part is S, and the distance between the slit and the inner end of the second wing part is between 3/4S and 1/2S.

In an embodiment of the present invention, the wing section of the above-mentioned backflow wing includes a concave-convex wing section, a flat-convex wing section, a symmetrical wing section, an S-shaped wing section, and a flat wing section.

In an embodiment of the present invention, the centrifugal compressor further includes a driving shaft, and the first-stage impeller and the second-stage impeller are sleeved on the driving shaft.

In an embodiment of the present invention, the center axis of the injection hole is parallel to the driving shaft.

In an embodiment of the present invention, the central axis of the injection hole is perpendicular to the reflow section.

In an embodiment of the invention, the injection hole includes a taper hole, a straight hole, or a combination of the taper hole and the straight hole.

In an embodiment of the present invention, the slit of the backflow wing includes an arc slit or a linear slit.

In an embodiment of the present invention, the backflow guide vane base has a first surface located in the backflow section and a second surface opposite to the first surface, and the plurality of injection holes penetrate through the first surface and the second surface.

In an embodiment of the present invention, the first wing portion and the second wing portion of the backflow wing protrude from the first surface.

In an embodiment of the invention, the injection hole has a first opening communicated with the slit and a second opening opposite to the first opening, and an aperture of the first opening is smaller than an aperture of the second opening.

In an embodiment of the present invention, the injection hole is located at the reflow section adjacent to the first turning section.

In an embodiment of the present invention, the injection hole is located at the second turning section away from the reflow section.

In an embodiment of the present invention, the centrifugal compressor further includes an economizer, which is connected to the economizer injection passage and disposed outside the centrifugal compressor.

The embodiment of the utility model provides an in, centrifugal compressor still includes inlet guide vane, disposes in the air inlet.

In an embodiment of the present invention, the above-mentioned backflow guide vane base has a third surface located in the first diffusion section and a fourth surface opposite to the third surface, and the plurality of injection holes penetrate through the third surface and the fourth surface.

In an embodiment of the present invention, the first wing portion and the second wing portion of each of the backflow wings protrude from the third surface.

Based on the above, in the centrifugal compressor of the present invention, the injection position of the second fluid falls in the backflow section of the flow channel, so that the first fluid and the second fluid have a longer flow path before flowing to the second-stage impeller to be uniformly mixed. On the other hand, the second fluid injected into the backflow section of the flow channel is divided and rectified for the first time in the slit, and then flows from the backflow section to the second turning section along the outer periphery of the second wing part of the backflow wing, and is rectified for the second time, so that the flow direction of the second fluid in the backflow section is consistent with that of the first fluid, and the generation of turbulence is reduced, so that the first fluid and the second fluid can be uniformly mixed in the flow channel, the pressure loss of the fluid is reduced, the aerodynamic efficiency is improved, and the compression efficiency of the centrifugal compressor is improved.

In order to make the aforementioned and other features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

Drawings

Fig. 1A is a schematic cross-sectional view of a centrifugal compressor according to an embodiment of the present invention;

FIG. 1B is an enlarged schematic view of region R of FIG. 1A;

fig. 2A to 2C are schematic views of a return guide vane base according to an embodiment of the present invention at different viewing angles;

fig. 3 to 7 are schematic top views of return guide vane bases according to other embodiments of the present invention;

fig. 8 is a partially enlarged schematic view of a centrifugal compressor according to another embodiment of the present invention;

fig. 9 is a partially enlarged schematic view of a centrifugal compressor according to still another embodiment of the present invention.

Detailed Description

Fig. 1A is a schematic cross-sectional view of a centrifugal compressor according to an embodiment of the present invention. Fig. 1B is an enlarged schematic view of the region R of fig. 1A. Referring to fig. 1A and 1B, in the present embodiment, the centrifugal compressor 100 may be a two-stage centrifugal compressor, and includes an air inlet 110, a flow passage 120, inlet guide vanes 140, a drive shaft 150, a first stage impeller 160, a second stage impeller 170, a return guide vane base 180, and an economizer injection passage 190. The inlet 110 is connected to the flow channel 120, wherein the inlet guide vane 140 is disposed in the inlet 110, and the first stage impeller 160, the second stage impeller 170, the return guide vane base 180, and the economizer injection channel 190 are disposed along the flow channel 120. In addition, the first-stage impeller 160 and the second-stage impeller 170 are sleeved on the driving shaft 150 to rotate synchronously and in the same direction with the driving shaft 150.

In detail, the flow channel 120 includes a first diffuser section 121, a first turning section 122, a backflow section 123, a second turning section 124, a second diffuser section 125 and a volute flow channel 130, and the first diffuser section 121, the first turning section 122, the backflow section 123, the second turning section 124 and the second diffuser section 125 are sequentially arranged between the gas inlet 110 and the volute flow channel 130.

The gas inlet 110 is communicated with the first diffuser section 121, and the first stage impeller 160 is disposed between the gas inlet 110 and the first diffuser section 121. The first turning section 122 is connected to the first diffuser section 121, and the return section 123 is connected to the first turning section 122. The second turn section 124 is connected to the return section 123, and the second diffuser section 125 is connected to the second turn section 124. The second-stage impeller 170 is disposed between the second turning section 124 and the second diffuser section 125, and the volute flow channel 130 is connected to the second diffuser section 125.

During operation of the centrifugal compressor 100, a first fluid F1 (e.g., a gaseous refrigerant) is directed by the inlet guide vanes 140 to the inlet 110 and flows in an axial direction (e.g., parallel to the long axis of the drive shaft 150) toward the first stage impeller 160. The first stage impeller 160 then pressurizes the first fluid F1 and forces the first fluid F1 to flow into the first diffuser 121 in a centrifugal direction (e.g., away from the long axis of the drive shaft 150). The first fluid F1 then flows from the first diffuser section 121 into the first turning section 122 and is diverted to flow in a centripetal direction (e.g., close to the long axis of the drive shaft 150) into the return section 123. In another aspect, the centrifugal compressor 100 further includes an economizer (not shown) in communication with the economizer injection passage 190 and disposed outside the centrifugal compressor 100. The economizer injection channel 190 is connected to the return section 123 to inject a second fluid F2 (e.g., a gaseous refrigerant) into the return section 123, so that the first fluid F1 and the second fluid F2 form a third fluid F3 in the return section 123. Then, the third fluid F3 flows from the return segment 123 into the second turn segment 124. Thereafter, the second-stage impeller 170 pressurizes the third fluid F3, and drives the third fluid F3 in a centrifugal direction into the second diffuser section 125, and then flows from the second diffuser section 125 into the volute flow channel 130.

In succession, the injection position of the second fluid F2 is located in the backflow section 123 of the flow channel 120, so that the first fluid F1 and the second fluid F2 have a longer flow path for uniform mixing before flowing to the second-stage impeller 170, thereby improving the compression efficiency of the centrifugal compressor 100. The first fluid F1 and the second fluid F2 may be gaseous refrigerant, air, carbon monoxide, carbon dioxide, oxygen, hydrogen, or related mixed gas.

Fig. 2A to fig. 2C are schematic views of a return guide vane base according to an embodiment of the present invention at different viewing angles. Referring to fig. 1B, fig. 2A and fig. 2B, in the present embodiment, the backflow guide vane base 180 is disposed between the first-stage impeller 160 and the second-stage impeller 170, and has a plurality of backflow wings 181 located in the backflow section 123 and a plurality of injection holes 182 communicated with the backflow section 123. The plurality of backflow wings 181 are radially arranged, and each backflow wing 181 is correspondingly provided with an injection hole 182. In detail, each of the backflow wings 181 has a first wing 183, a second wing 184, and a slit 185 between the first wing 183 and the second wing 184, and the first wing 183 and the second wing 184 are separated by the slit 185. In addition, the injection hole 182 is located in the slit 185, wherein the economizer injection channel 190 is connected to the injection hole 182, and the injection hole 182 is connected to the reflow section 123 through the slit 185, so that the second fluid F2 can be injected into the reflow section 123 through the injection hole 182 and the slit 185.

As shown in fig. 1A and 1B, the injection hole 182 has a central axis parallel to the driving shaft 150 and substantially perpendicular to the return section 123, so that the second fluid F2 can be directly injected into the return section 123 in the axial direction. In other embodiments, the central axis of the injection hole 182 is inclined to the backflow section 123, so that the second fluid F2 can be obliquely injected into the backflow section 123.

Referring to fig. 1B, fig. 2A, fig. 2B and fig. 2C, in the present embodiment, the wing shape of the backflow wing 181 is a concave-convex wing shape, and the slit 185 of each backflow wing 181 is an arc-shaped slit. On the other hand, the return guide vane base 180 has a first surface 186 located in the return section 123 and a second surface 187 opposite to the first surface 186, and the plurality of injection holes 182 penetrate the first surface 186 and the second surface 187. Specifically, the first wing portion 183 and the second wing portion 184 of each of the backflow wings 181 protrude from the first surface 186, and when the second fluid F2 flows into the slit 185 from the filling hole 182, the second fluid F2 can be divided and rectified for the first time in the slit 185 to flow along the two opposite wing portions of the second wing portion 184 respectively, and the second rectification effect is achieved by a near-wall effect (near-wall effect), and flows from the backflow portion 123 to the second turning portion 124.

As shown in fig. 1B, 2B and 2C, each injection hole 182 has a first opening 188 communicating with the slit 185 and a second opening 189 opposite to the first opening 188, wherein the first opening 188 connects with the first surface 186 and the second opening 189 connects with the second surface 187. In detail, the second fluid F2 from the economizer injection passage 190 flows from the second opening 189 to the first opening 188 and from the first opening 188 to the slot 185. Since the aperture diameter A1 of the first opening 188 is smaller than the aperture diameter A2 of the second opening 189, it is helpful to improve the pressure loss of the second fluid F2 when the second fluid F2 is injected into the slit 185 or the return section 123.

As shown in fig. 1B, in the present embodiment, the injection hole 182 may be a tapered hole, and the diameter of the hole decreases from the second surface 187 to the first surface 186. In another embodiment, the injection hole 182 may be a straight hole with a uniform diameter from the second surface 187 to the first surface 186. In yet another embodiment, the injection hole 182 may be a combination of a tapered hole and a straight hole, wherein the tapered hole connects the second surface 187 and the straight hole connects the first surface 186.

As shown in fig. 2C, in the present embodiment, the slit 185 of each backflow wing 181 has two opposite outlets 185a, wherein a distance between the two outlets 185a is D (i.e., a length of the slit 185), and a distance D1 between the injection hole 182 (e.g., the first opening 188 of the injection hole 182) and one outlet 185a is between 1/4D and D. For example, the position of the injection hole 182 may be at the center of gravity of the backflow wing 181.

As shown in fig. 1B and 2C, the first wing portion 183 of each of the return wings 181 is farther from the second turning section 124 than the second wing portion 184, wherein the first wing portion 183 has an outer end 183a opposite to the slit 185, and the second wing portion 184 has an inner end 184a opposite to the slit 185. The slit 185 of each return wing 181 is located between the outer end 183a of the first wing 183 and the inner end 184a of the second wing 184, and the inner end 184a is closer to the second turning section 124 than the slit 185. The distance between the outer end 183a of the first wing part 183 and the inner end 184a of the second wing part 184 of each return wing 181 is S (i.e., the length of the return wing 181), and the distance S1 between the slit 185 and the inner end 184a of the second wing part 184 is between 3/4S and 1/2S, i.e., the slit 185 is disposed at the center of gravity of the return wing 181. In addition, the first fluid F1 is rectified between the two adjacent return fins 181 in the return section 123, and the second fluid F2 injected into the return section 123 is split and rectified for the first time in the slit 185, and then the second fluid F2 is rectified for the second time along the outer periphery of the second fin 184 of the return fin 181 and merged with the first fluid F1. The injection hole 182 in the backflow wing 181 is located at the backflow segment 123 adjacent to the first turning segment 122 and away from the second turning segment 124, so that the first fluid F1 and the second fluid F2 have a longer flow path before flowing to the second-stage impeller 170 to be uniformly mixed, thereby improving the compression efficiency of the centrifugal compressor 100.

As shown in fig. 1B and fig. 2A, the second fluid F2 is injected into the flow channel 120 along an axial direction (e.g., parallel to the long axis direction of the driving shaft 150), and the injection position of the second fluid F2 is located in the backflow segment 123 of the flow channel 120. After the second fluid F2 is injected into the backflow segment 123, the second fluid F2 is split and rectified for the first time in the slit 185, and then the second fluid F2 flows from the backflow segment 123 to the second turning segment 124 along the outer periphery of the second wing 184 of the backflow wing 181 to be rectified for the second time and converged with the first fluid F1, so that the flow direction of the second fluid F2 in the backflow segment 123 is consistent with that of the first fluid F1, and the generation of turbulence is reduced, so that the first fluid F1 and the second fluid F2 can be uniformly mixed in the flow channel 120 to form the third fluid F3, thereby reducing the fluid pressure loss and improving the aerodynamic efficiency, and further improving the compression efficiency of the centrifugal compressor 100.

Referring to fig. 1B, the second surface 187 of the return guide vane base 180 is adjacent to the sealed space 101, wherein the economizer injection passage 190 communicates with the injection hole 182 through the sealed space 101, and a sealing member 102 is disposed between the return guide vane base 180, the second stage impeller 170 and the casing to prevent the second fluid F2 from leaking.

Fig. 3 to 7 are schematic top views of the return guide vane base according to other embodiments of the present invention. As shown in fig. 3, the slit 185 of the return wing 181 shown in fig. 2C is an arc-shaped slit, but the slit 1851 of the return wing 181a of the present embodiment is a linear slit extending in a tangential direction of the center circle. As shown in fig. 4, the return wing 181 shown in fig. 2C has a concave-convex wing profile, and the return wing 181b of the present embodiment has a flat-convex wing profile. As shown in fig. 5, the wing profile of the return wing 181 shown in fig. 2C is a concave-convex wing profile, and the difference is that the wing profile of the return wing 181C of the present embodiment is an S-shaped wing profile. As shown in fig. 6, the wing profile of the return wing 181 shown in fig. 2C is a concave-convex wing profile, and the difference is that the wing profile of the return wing 181d of the present embodiment is a symmetrical wing profile. As shown in fig. 7, the wing profile of the return wing 181 shown in fig. 2C is a concave-convex wing profile, and the difference is that the wing profile of the return wing 181e of the present embodiment is a flat wing profile.

For example, the slits of the return wing shown in fig. 2C to 7 may be arc slits, linear slits or a combination of arc slits and linear slits, and the airfoil shape of the return wing on the return guide vane base may be one of the airfoil shapes shown in fig. 2C to 7 or a combination of at least two thereof, according to different design requirements. In addition, the injection hole can be designed to be a straight hole, a tapered hole or a combination of the straight hole and the tapered hole according to the requirement of actual working conditions.

Fig. 8 is a partially enlarged schematic view of a centrifugal compressor according to another embodiment of the present invention. Referring to fig. 1B, the return guide vane base 180 of the present embodiment includes a first return guide vane base 180a and a second return guide vane base 180B, wherein the first return guide vane base 180a is located between the second-stage impeller 170 and the second return guide vane base 180B, and the second return guide vane base 180B is located between the first return guide vane base 180a and the first-stage impeller 160. The first surface 186 of the first return guide vane base 180a faces the first surface 1861 of the second return guide vane base 180b, and the first surface 186 of the first return guide vane base 180a and the first surface 1861 of the second return guide vane base 180b are both located within the return section 123. The return wing 181 protrudes from the first surface 186 of the first return guide vane base 180a and contacts the first surface 1861 of the second return guide vane base 180 b.

Next, referring to fig. 8, unlike the above embodiments, the return wing 181 of the present embodiment protrudes from the first surface 1861 of the second return guide vane base 180b and contacts the first surface 186 of the first return guide vane base 180 a. On the other hand, the injection hole 182 is located at the first return guide vane base 180a and is aligned with the slit 185 of the return wing 181 located at the second return guide vane base 180 b.

Fig. 9 is a partially enlarged schematic view of a centrifugal compressor according to still another embodiment of the present invention. Referring to fig. 9, similarly, according to different working condition requirements, the backflow wing 181 'and the injection hole 182' may be disposed in the first diffusion section 121, so that the backflow wing 181 'protrudes from the third surface 186' of the second backflow guide vane base 180b away from the first surface 1861, and is disposed corresponding to the first diffusion section 121 and the first-stage impeller 160. Specifically, the second return guide vane base 180b has a third surface 186 'located within the first diffuser section 121 and a fourth surface 187' opposite the third surface 186', and the plurality of injection holes 182' pass through the third surface 186 'and the fourth surface 187'. In addition, the first wing portion 183 'and the second wing portion 184' of each backflow wing 181 'protrude from the third surface 186'.

The injection position of the second fluid F2 is located in the first diffuser section 121 of the flow channel 120, after the second fluid F2 is injected into the first diffuser section 121, the second fluid F2 is split and rectified for the first time in the slit 185', and then the second fluid F2 flows from the first diffuser section 121 to the first turning section 122 along the outer periphery of the second wing 184' of the backflow wing 181', so as to be rectified for the second time and converged with the first fluid F1, so that the flow directions of the second fluid F2 and the first fluid F1 in the first diffuser section 121 are the same, and the generation of turbulence is reduced, so that the first fluid F1 and the second fluid F2 can be uniformly mixed in the flow channel 120 to form the third fluid F3, thereby reducing fluid pressure loss and improving aerodynamic efficiency, thereby improving compression efficiency of the centrifugal compressor 100.

In summary, in the centrifugal compressor of the present invention, the injection position of the second fluid falls within the front end of the return section (or the first diffuser section) of the flow passage, so that the first fluid and the second fluid have a long flow path before reaching the second stage impeller to be uniformly mixed. On the other hand, the second fluid injected into the backflow section (or the first diffuser section) of the flow channel is split and rectified for the first time in the slit, and then flows from the backflow section to the second turning section along the outer periphery of the second wing part of the backflow wing, and is rectified for the second time, so that the flow directions of the second fluid in the backflow section (or the first diffuser section) and the first fluid are consistent, the generation of turbulence is reduced, the first fluid and the second fluid can be uniformly mixed in the flow channel, the fluid pressure loss is reduced, the aerodynamic efficiency is improved, and the compression efficiency of the centrifugal compressor is improved.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present invention.

Claims

1. A centrifugal compressor, comprising:

an air inlet;

the flow channel is communicated with the air inlet and is provided with a first diffusion section, a first turning section connected with the first diffusion section, a backflow section connected with the first turning section, a second turning section connected with the backflow section, a second diffusion section connected with the second turning section and a volute flow channel connected with the second diffusion section;

a first stage impeller disposed between the gas inlet and the first diffuser section;

a second-stage impeller disposed between the second turning section and the second diffuser section;

a backflow guide vane base disposed between the first-stage impeller and the second-stage impeller, wherein the backflow guide vane base has a plurality of backflow wings located in the backflow section and a plurality of injection holes communicated with the backflow section, each backflow wing has a first wing portion, a second wing portion and a slit separating the first wing portion from the second wing portion, and the plurality of injection holes respectively fall in the plurality of slits; and

and the economizer injection channel is communicated with the injection holes.

2. The centrifugal compressor according to claim 1, wherein the slit of each of the backflow wings has two opposite outlets at a distance D, and the distance between the injection hole and one of the outlets is between 1/4D and D.

3. The centrifugal compressor of claim 1, wherein the first wing of each of the return wings has an outer end with respect to the slit and the second wing of each of the return wings has an inner end with respect to the slit, a distance between the outer end of the first wing and the inner end of the second wing is S, and a distance between the slit and the inner end of the second wing is between 3/4S and 1/2S.

4. The centrifugal compressor according to claim 1, wherein the airfoil of each of the return vanes includes a concave-convex airfoil, a flat-convex airfoil, a symmetrical airfoil, an S-shaped airfoil, and a flat-plate airfoil.

5. The centrifugal compressor of claim 1, further comprising:

the first-stage impeller and the second-stage impeller are sleeved on the driving shaft.

6. The centrifugal compressor of claim 5, wherein a central axis of the plurality of injection holes is parallel to the drive shaft.

7. The centrifugal compressor of claim 1, wherein a central axis of the plurality of injection holes is perpendicular to the return section.

8. The centrifugal compressor of claim 1, wherein the plurality of injection holes comprise tapered holes, straight holes, or a combination of tapered and straight holes.

9. The centrifugal compressor according to claim 1, wherein the slit of each of the return wings includes an arc-shaped slit or a linear slit.

10. The centrifugal compressor of claim 1, wherein the return guide vane base has a first surface located within the return section and a second surface opposite the first surface, and the plurality of injection holes pass through the first surface and the second surface.

11. The centrifugal compressor of claim 10, wherein the first and second wings of each return wing are raised above the first surface.

12. The centrifugal compressor according to claim 1, wherein each of the injection holes has a first opening communicating with the corresponding slit and a second opening opposite to the first opening, and a bore diameter of the first opening is smaller than a bore diameter of the second opening.

13. The centrifugal compressor of claim 1, wherein the injection hole is located at the return section adjacent to the first turn-around section.

14. The centrifugal compressor of claim 13, wherein the injection hole is located at the return section away from the second turn section.

15. The centrifugal compressor of claim 1, further comprising:

and the economizer is communicated with the economizer spraying channel and is arranged outside the centrifugal compressor.

16. The centrifugal compressor of claim 1, further comprising:

and an intake guide vane disposed at the intake port.

17. The centrifugal compressor of claim 1, wherein the return guide vane base has a third surface located within the first diffuser section and a fourth surface opposite the third surface, and the plurality of injection holes pass through the third and fourth surfaces.

18. The centrifugal compressor according to claim 17, wherein the first wing portion and the second wing portion of each of the return wings are protruded from the third surface.