Centrifugal compressor and method of operating a centrifugal compressor

Abstract

The present application discloses a centrifugal compressor and a method for operating a centrifugal compressor. The centrifugal compressor includes: an impeller for sucking gas to be compressed; a diffuser arranged downstream of the impeller to pressurize the gas, the diffuser including a movable ring, a main channel through which gas flows through the ring, and an openable branch channel; a circulation loop, the circulation loop including an inlet and an outlet, the outlet being connected to the inlet of the impeller; wherein the branch channel is arranged so that when the ring moves into the main channel, the branch channel connects the main channel and the circulation loop, so that a portion of the gas in the main channel returns to the impeller via the circulation loop to be sucked, and when the ring exits the main channel, the branch channel is closed. The present application can circulate part of the gas flowing through the diffuser.

Description

Technical Field

[0001] The present application belongs to the field of compressors, and in particular relates to a centrifugal compressor and a method for operating a centrifugal compressor. Background Art

[0002] Compressors are widely used in industry. A good compressor provides excellent gas compression performance. In the refrigeration industry, the compressor is a particularly critical component of the refrigeration system. Centrifugal compressors, as a type of compressor, are widely used in commercial refrigeration due to their high efficiency and high-capacity gas compression capabilities. Centrifugal compressors utilize an impeller that rotates about an axis to draw gas into the compressor and compress it to the outlet. The gas is directed radially outward from the axis through a diffusion channel that increases the gas pressure to a collector area.

[0003] A compressor map is a well-known way of plotting compressor operating conditions, with the Y-axis representing pressure ratio and the X-axis representing the mass of flow through the compressor. The left-hand boundary of the compressor map represents the surge boundary, and operation to the left of this boundary represents a region of flow instability. Operation in this region is undesirable because it can cause pressurized gas to flow back into the compressor.

[0004] Variable diffuser technology is used to reduce noise near surge conditions. The surge margin may or may not be improved, depending on whether the surge is triggered by the diffuser. Summary of the Invention

[0005] A technical problem to be solved by the present application is to provide a centrifugal compressor capable of circulating the gas in the diffuser.

[0006] The centrifugal compressor involved in this application includes:

[0007] an impeller, the impeller being used to pump the gas to be compressed;

[0008] a diffuser disposed downstream of the impeller to pressurize the gas, the diffuser comprising a movable ring, a main channel through which the gas flows, and an openable branch channel;

[0009] a circulation loop, the circulation loop comprising an inlet and an outlet, the outlet being in communication with the inlet of the impeller;

[0010] The branch channel is configured such that when the ring moves into the main channel, the branch channel connects the main channel and the circulation loop, so that a portion of the gas in the main channel returns to the impeller via the circulation loop to be sucked in, and when the ring exits the main channel, the branch channel is closed.

[0011] In addition to one or more of the above features, or as an alternative, other embodiments may include: the main channel is defined by partitions opposing each other, wherein one of the partitions is provided with a groove to fit the ring into the groove, and the branch channel is provided between at least one surface of the ring and the wall of the groove, or provided inside the groove, or provided inside the ring, or a combination of two or three of the foregoing.

[0012] In addition to or as an alternative to one or more of the features described above, other embodiments may include that at least one surface of the ring is a rear surface and / or a side surface of the ring facing away from the main channel.

[0013] In addition to or instead of one or more of the above features, other embodiments may include: the ring having a protruding portion extending into one of the partitions, the branch channel being formed as an additional flow passage passing between a front surface and a rear surface of the protruding portion.

[0014] In addition to or as an alternative to one or more of the features described above, other embodiments may include: the circulation loop being integrated into the partition and located adjacent to a drive mechanism, wherein the ring is driven by the drive mechanism.

[0015] In addition to or instead of one or more of the above features, other embodiments may include: the circulation loop includes at least one flow channel for guiding gas, the at least one flow channel is made by machining a hole in the partition, and at least one wall of the groove is connected to the at least one flow channel.

[0016] In addition to or as an alternative to one or more of the features described above, other embodiments may include: the side surface of the ring being configured to include at least one segment, with different segments having different surface shapes.

[0017] In addition to or as an alternative to one or more of the above features, other embodiments may include: at least a portion of the circulation loop is formed by a chamber in the centrifugal compressor near the impeller, and the outlet of the circulation loop is the outlet of the chamber.

[0018] In addition to or instead of one or more of the features described above, other embodiments may include the chamber being an injection chamber of an economizer.

[0019] In addition to or instead of one or more of the features described above, other embodiments may include: the ring having at least one protruding head, the head being configured to have a shape that gradually increases toward the main channel, so that when the branch channel is open, the head controls the flow of gas to the circulation loop.

[0020] Another aspect of the present application is to provide a method for operating the centrifugal compressor described above, the method comprising: when the centrifugal compressor is operating close to a surge state, moving the ring into the main channel so that the branch channel is open between the main channel and the circulation loop, thereby allowing a portion of the gas from the main channel to return to the impeller via the circulation loop to be drawn in.

[0021] The present application can circulate the gas flowing through the diffuser. This circulation operation can be actively controlled. That is, when gas circulation is required, the ring is moved into the main channel, the branch channel is opened, and the gas can return to the impeller through the circulation loop; when circulation is not required, the ring is withdrawn or the ring is not moved, and the branch channel is closed.

[0022] The ring of the present application, as a component of the diffuser, can not only change the gas flow in the main channel to reduce the noise and vibration of the compressor, but also circulate part of the gas by opening the branch channel to improve the surge of the compressor.

[0023] The ring movement in this application is achieved by a drive mechanism. Therefore, there's no need for a separate controller within the compressor to control the ring's movement. Furthermore, unlike passive control methods that require set conditions, this application is not limited to those conditions; the timing, speed, duration, and distance of the ring's movement can be controlled by commanding the drive mechanism.

[0024] The branch channel of the present application is openable, and the closed and open states of the branch channel are achieved by moving the ring. The branch channel can be formed by means of the ring and the groove on the partition plate provided with the ring. This eliminates the need for additional channels in the compressor.

[0025] The circulation loop of the present invention is integrated into the partition or at least partially utilizes an existing chamber within the compressor, so the gas circulation of the present invention is internal. Compared with external circulation or setting up a separate circulation loop inside or outside the compressor, the present invention can save costs and does not increase the complexity of the compressor system.

[0026] The ring can be locally processed to obtain a ring with a certain shape, which can control the circulation flow.

[0027] This application establishes a gas recirculation mechanism to address compressor stall or surge. Insufficient air intake to the impeller can trigger surge. This application recirculates a portion of the gas in the diffuser back to the impeller to supplement the impeller's intake volume, thereby improving the surge boundary curve in the compressor characteristic diagram depicting compressor operating conditions and enhancing compressor efficiency.

[0028] Other aspects and features of the present application will become apparent from the following detailed description, which proceeds with reference to the accompanying drawings. It should be understood, however, that the drawings are designed for illustrative purposes only and are not intended to limit the scope of the present application, as reference should be made to the appended claims. It should also be understood that the drawings are intended only to conceptually illustrate the structures and processes described herein and, unless otherwise indicated, are not necessarily drawn to scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present application will be more fully understood by referring to the following detailed description of specific embodiments in conjunction with the accompanying drawings, in which the same reference numerals in different drawings refer to the same features, wherein:

[0030] Figure 1 is a simplified schematic diagram of a centrifugal compressor according to the present application;

[0031] Figure 2 is a partial cross-sectional view of an embodiment of a centrifugal compressor according to the present application, wherein arrows indicate the movement direction of the ring;

[0032] Figure 3 for Figure 2 Schematic diagram of a centrifugal compressor in FIG. 1 when the ring moves into the main channel, wherein the arrows indicate the gas circulation path;

[0033] Figure 4 for Figure 3 A partial enlarged view of

[0034] Figure 5 is a partial cross-sectional view of another embodiment of a centrifugal compressor according to the present application, wherein arrows indicate gas circulation paths;

[0035] Figure 6 is a schematic diagram of a ring of a centrifugal compressor according to yet another embodiment of the present application;

[0036] Figure 7 for Figure 6 Schematic diagram of the ring after installation on the centrifugal compressor;

[0037] Figure 8 for Figure 7 Schematic diagram of the ring moving into the main channel, where the arrows indicate the gas circulation path. DETAILED DESCRIPTION

[0038] In order to help those skilled in the art to accurately understand the subject matter for which protection is sought in this application, the specific implementation methods of this application are described in detail below with reference to the accompanying drawings.

[0039] The centrifugal compressor involved in this application can be used in a wide range of industrial fields. The compressed object can be gas such as air or nitrogen, or gaseous refrigerant such as used in refrigeration compressors. In the application of refrigeration compressors, ideally, liquid refrigerant and / or lubricating oil are not expected to enter the refrigeration compressor. However, in reality, the compressor "inhales liquid" and therefore the "gas" mentioned in this application will carry a small amount of liquid in actual situations. See Figure 1 The compressor includes an impeller 12, which is used to draw in the compressed object, such as the aforementioned refrigerant. A diffuser 13 is located between the impeller 12 and a volute 14. The volute 14 is located radially outward from the impeller 12 and serves as a collection area for the compressed and expanded refrigerant gas. After leaving the impeller 12, the compressed gas first passes through the diffuser 13 before entering the volute 14. In the diffuser 13, the compressed gas is pressurized by converting kinetic energy into pressure energy, and is further pressurized within the volute 14.

[0040] Figure 2-4 The figure shows a partial cross-sectional view of an embodiment of a centrifugal compressor according to the present application. The refrigerant is still used as the compression object. The diffuser includes a first partition plate 16, a ring 22, a second partition plate 18, a main channel 24, a branch channel 26 (see FIG. Figure 3 ) and a drive mechanism 28. In the illustrated embodiment, the first partition 16 and the second partition 18 are opposite to each other. A main channel 24 through which the refrigerant gas passes is defined between the first partition 16 and the second partition 18. The main channel 24 gradually increases in width in the radial direction to pressurize the refrigerant gas. It should be appreciated that the main channel 24 can be an annular cavity. Here, the term "partition" refers to a component in the compressor that divides the space inside the compressor into subspaces. The partition can also be used to accommodate parts in the compressor, such as the rings to be introduced below. The refrigerant gas from the impeller flows to the volute, not shown, via the main channel 24. The ring 22 is arranged on any one of the partitions, such as the first partition 16, and is movable relative to the first partition 16, and the refrigerant gas can pass in front of the ring 22.

[0041] The ring 22 is connected to a drive mechanism 28. The drive mechanism 28 may include at least one actuator-piston system. The actuator may be hydraulically driven, pneumatically driven, electrically driven, etc. The piston head 29 is embedded in the ring 22 to be linked with the ring 22. The actuator-piston system can be implemented in a manner known in the art and will not be further described here. Under the action of the actuator, the ring 22 can be moved along the Figure 2. As the ring 22 is moved into the main channel 24, the width of the main channel 24 changes, thereby changing the flow rate and flow rate of the refrigerant gas flowing therethrough. Although only one drive mechanism is shown, it is contemplated that multiple drive mechanisms 28 may be disposed on the ring 22 to drive the movement of the ring 22, such as, but not limited to, three drive mechanisms disposed on the ring at 120° intervals.

[0042] Figure 2 The ring 22 is shown in its original position. Figure 3 The ring 22 is shown moving into the main channel 24. A branch channel 26 extends from the main channel 24 to receive a portion of the refrigerant gas in the main channel 24. The gap between the side surface 35 of the ring 22 and the surface of the first separator 16 forms the branch channel 26, through which the refrigerant gas can pass. A circulation loop 42 is connected downstream of the branch channel 26. The circulation loop 42 includes an inlet 43 and an outlet 44, with the outlet 44 connecting to the inlet of the impeller 12. Therefore, when the ring 22 moves into the main channel 24, the branch channel 26 is open, and a portion of the refrigerant gas in the main channel 24 can flow into the circulation loop 42 through the branch channel 26, and eventually be discharged along the circulation loop 42 to the inlet of the impeller 12, where it is again sucked into the impeller 12. The specific details of the circulation loop 42 will be described below. The branch channel 26 connects the main channel 24 and the inlet 43 of the circulation loop 42. When the branch channel 26 is open, it is opened between the main channel 24 and the circulation loop 42. The circulation loop 42 can circulate a portion of the refrigerant gas flowing through the main channel 24 back to the impeller 12 to supplement the suction capacity of the impeller 12. When the ring 22 is in the original position, the branch channel 26 is closed and the circulation loop 42 is not working.

[0043] The opening and closing of the branch channel 26 is achieved by moving the ring 22, which is moved by the aforementioned drive mechanism 28. In the closed state, the ring 22 rests within the groove 52 of the mating first baffle 16, with no gap between the side of the ring 22 and the wall of the groove 52. Therefore, the inlet 43 of the circulation loop 42 is blocked by the closure of the branch channel 26. Drive mechanism 28 causes the ring 22 to move toward the main channel 24, creating a gap between the side of the ring 22 and the wall of the groove 52, thereby opening the branch channel 26. When the ring 22 moves out of its original position, the gap between the side surface 35 of the ring 22 and the inner wall 54 of the groove 52 allows the refrigerant gas flowing in the main channel 24 to be diverted. A portion of the diverted gas flows through this gap into the groove 52 and then into the circulation loop 42, where it flows back to the impeller 12.

[0044] Once the ring 22 starts to move, an axial and / or radial gap will appear between the ring 22 and the groove 52, and the side surface 35 of the ring 22 and / or the rear surface 36 of the ring 22, as well as part of the groove 52, can form a branch channel 26. Therefore, it is not difficult to understand that the branch channel 26 is non-permanent, and this gap can be eliminated when the ring 22 is returned to its original position. Therefore, it is possible to determine whether the refrigerant gas in the main channel 24 undergoes partial circulation by controlling the action of the ring 22, and there is no need to set a valve or an additional controller in the branch channel 26 or the circulation loop 42. Furthermore, multiple cycle parameters such as the start time of the cycle, the cycle time and the flow rate can also be determined by controlling the movement of the ring 22. For example, Figure 4 As shown, the side surface 35 of the ring 22 can be designed so that the shape of the side surface 35 conforms to the expected cycle parameters. Figure 4 In the illustrated embodiment, the side surface 35 of the ring 22 includes a first section 37, a second section 38, and a third section 39. The first section 37, located near the front surface of the ring 22, has an inclination (or a relatively large curvature) to reduce resistance to the ring 22 during movement. The second section 38 is flat and, when the ring 22 is in its original position, contacts the inner wall 54 of the groove 52, thereby sealing the groove 52. The third section 39 gradually widens toward the circulation loop 42, directing gas entering the circulation loop 42 and increasing flow. When the ring 22 moves until the second section 38 exits the groove 52, the branch channel 26 opens between the main channel 24 and the circulation loop 42. It should be understood that the design of the side surface 35 of the ring 22 is not limited to the shape described above; the side surface 35 may have other shapes. Other designs on the ring's side surface are also possible, such as, but not limited to, embedding a seal in the second section to enhance sealing. Similarly, the rear surface 36 of the ring may also be designed as a branch channel 26 or a portion thereof. The figure shows that the branch channel 26 is formed on the side of the ring 22 close to the impeller 12, but it may also be formed on the other side opposite to the side.

[0045] The circulation loop 42 is integrated into the interior of the compressor. The circulation loop 42 is arranged in the first partition 16 and in the vicinity of the drive mechanism 28. The inlet 43 of the circulation loop 42 is connected to the groove 52, such as the inlet 43 is arranged at the junction of the bottom wall 53 and the inner wall 54 of the groove 52. The inlet 43 of the circulation loop 42 can also be arranged only on the bottom wall of the groove 52 to form a branch channel with the rear surface 36 of the ring 22, or only on the inner wall of the groove 52 to form a branch channel with the side surface 35 of the ring 22. The circulation loop 42 is realized by punching holes inside the first partition 16 to form a flow channel, so there is no need to set up additional flow channels outside the diffuser, which includes at least one flow channel passing through the first partition 16. The circulation loop 42 includes a first flow channel 45 and a second flow channel 46 that are interconnected, wherein the second flow channel 46 will continue to pass through the sealing ring 15 located between the impeller cover 11 and the impeller 12. First flow channel 45 and second flow channel 46 guide the refrigerant gas through first baffle 16. After exiting second flow channel 46, the refrigerant gas flows through the radial passage between impeller cover 11 and sealing ring 15 to the inlet of impeller 12. The flow channel design of circulation loop 42 is not limited to the above-described configuration. For example, but not limitation, the outlet of circulation loop 42 may be connected to the center of impeller 12, or the outlet of circulation loop 42 may be connected upstream of impeller 12, allowing the refrigerant gas in circulation loop 42 to re-enter the impeller.

[0046] Figure 5 FIG. 1 is a partial cross-sectional view of another embodiment of a centrifugal compressor according to the present application. Figure 2-4 The similarities between the embodiments are not repeated here. The compressed object is still refrigerant. In the illustrated embodiment, the ring 22 has a protruding portion 23 that extends radially into the first partition 16. An additional flow channel 27 is defined in this protruding portion 23 to form a portion of the branch channel 26. When the ring 22 moves into the main channel 24, a portion of the refrigerant gas in the main channel 24 first enters the additional flow channel 27, then into the groove 52, and then flows through the circulation loop 42 to the inlet of the impeller 12. When the ring 22 is in its original position, the rear surface 36 of the ring 22 abuts against the bottom wall 53 of the groove 52, preventing gas from flowing from the additional flow channel 27 into the groove 52. If the gap between the side surface 35 of the ring 22 and the inner wall 54 of the groove 52 is too small to allow refrigerant gas in the main channel to pass through, the additional flow channel 27 can be defined in the ring 22 to introduce the diverted refrigerant gas into the circulation loop 42. In the illustrated embodiment, the additional flow channel 27 is opened on the protruding portion 23 of the ring 22. It should be understood that the protruding portion may not be provided. For example, but not limited to, the additional flow channel may be opened directly on the main body of the ring that is not connected to the drive mechanism or on the partition.

[0047] In the illustrated embodiment, the design of the circulation loop 42 is different from Figure 2-4The inlet 43 of the circulation circuit 42 is set on the inner wall 54 of the groove 52, and the circulation circuit 42 includes more sections of flow channels, and the outlet 44 is still connected to the inlet of the impeller 12. When the ring 22 moves out and enters the main channel 24, part of the refrigerant gas in the main channel 24 flows along the Figure 5 The flow direction indicated by the arrow in the figure circulates back to the inlet of the impeller 12. It should be understood that the number of circulation loops 42 is not limited to the one shown in the figure, and more circulation loops can be set on the partition, wherein the size of the flow channel, the number of sections and other related designs depend on the expected circulation parameters.

[0048] Figure 6-8 A schematic diagram showing yet another embodiment of a centrifugal compressor according to the present application is shown. Figure 6 is a schematic diagram of the ring 22 in this embodiment, Figure 7 for Figure 6 A perspective view of a centrifugal compressor after the ring 22 is assembled, wherein the ring 22 is in its original position. Figure 8 for Figure 6 A partial cross-sectional view of a centrifugal compressor, in which the ring 22 is moved into the main channel 24. The compressed medium is still the refrigerant. Unlike the previous embodiment, the circulation loop 42 is not formed within the first partition, but rather utilizes other existing housing components within the compressor, such as a chamber. By utilizing the chamber near the impeller, a portion of the refrigerant gas in the main channel is returned to the impeller through this chamber, replenishing the impeller's suction capacity.

[0049] In the illustrated embodiment, the chamber near the impeller 12 serves as the economizer's injection chamber 62. When the branch passage 26 is open, a portion of the refrigerant gas from the main passage 24 enters the economizer's injection chamber 62 through the branch passage 26, mixes with the refrigerant from the injection chamber 62, and then returns to the inlet of the impeller 12.

[0050] The branch channel 26 is opened and closed by the movement of the ring 22. A protruding head 63 is provided on the ring 22 and the head 63 is staggered with the driving mechanism not shown. Accordingly, a hole 64 is drilled at a position of the first partition 16 corresponding to the head 63 to communicate with the injection chamber 62 of the economizer. The head 63 is inserted into the hole 64, and the design of the head 63 will be described below. The ring 22 is returned to the groove 52 on the first partition 16 that matches it. The side surface 35 of the ring 22 contacts the inner wall 54 of the groove 52. There is no gap between the two, and the branch channel is closed. The ring 22 moves into the main channel 24 under the action of the driving mechanism not shown. The ring 22 leaves the groove 52 to create a gap, and a branch channel 26 is formed in the groove 52. As a result, a portion of the refrigerant gas in the main channel 24 can enter the groove 52 through the gap, and then flow along the hole 64 to the injection chamber 62 of the economizer, and circulate back to the impeller 12 with the help of the power of the injection chamber 62, as shown Figure 8 shown.

[0051] Figure 6-Figure 8 The illustrated embodiment cleverly utilizes existing compressor casing, allowing at least a portion of the recirculation loop 42 to be shared with the compressor, reducing the need for additional component processing and thus not increasing the complexity of the compressor system. It should be appreciated that the recirculation loop 42 can utilize any chamber within the compressor, as long as the recirculated gas is ultimately returned to the impeller.

[0052] The protruding head 63 is configured to have a shape that gradually decreases toward the injection chamber 62 (i.e., the circulation loop 42), that is, it gradually increases toward the main channel 24 and is configured to be cone-shaped. During the movement of the ring 22 toward the main channel 24, the gap area between the ring 22 and the groove 52 gradually expands due to the gradually decreasing shape, thereby gradually increasing the flow rate of the refrigerant gas. Therefore, the circulation effect can be controlled by designing the head 63, especially when it is desired to circulate the refrigerant gas in a relatively gentle manner. In addition, the side surface 35 of the ring 22 can also be designed in combination to control the cycle start time, cycle time, flow rate and other cycle parameters. The head 63 can have other shapes that are not limited to the above-mentioned shapes. Figure 6 In the embodiment shown, there is one head 63 , but it is contemplated that there may be more than one head. The number of holes 64 is the same as the number of heads 63 . Once the number of heads 63 is determined, the same number of holes 64 is provided on the first separator 16 .

[0053] It should be understood that the present invention is not limited to the embodiments described above and is capable of various modifications and improvements without departing from the concepts described herein. Except in the case of mutual exclusion, any of the features may be applied alone or in combination with any other feature, and the present application extends to and includes all combinations and subcombinations of one or more features described herein. For example, but not by way of limitation, the present application may be used in conjunction with a vaned diffuser, i.e., variable vanes are provided on the second baffle, and the present application provides a ring on the first baffle, with the ring being radially offset from the variable vanes.

[0054] The rings described in this application can be used in a variety of operating conditions. When it is desired to circulate a portion of the refrigerant gas within the main channel 24, the ring 22 can be moved to open the branch channel 26, thereby circulating the diverted refrigerant gas. Alternatively, when the centrifugal compressor is operating near the surge boundary in the compressor characteristic diagram, the ring 22 can be moved into the main channel 24 to circulate a portion of the refrigerant gas to the impeller 12 to supplement the impeller 12's suction capacity. When circulation is no longer required, the ring 22 is returned to its original position.

[0055] The present application is applicable to various compressors, which may or may not include an economizer. These compressors may be single-stage or multi-stage compressors. When the drive mechanism 28 moves the ring 22 into the main passage 24, a portion of the refrigerant gas in the main passage 24 is circulated back to the impeller 12, thereby reducing compressor noise and vibration.

[0056] While specific embodiments of the present application have been shown and described in detail to illustrate the principles of the present application, it will be appreciated that the present application may be embodied in other ways without departing from such principles.

Claims

1. A centrifugal compressor, characterized in that include: an impeller (12) configured to draw in the gas to be compressed; a diffuser (13) disposed downstream of the impeller (12) to pressurize the gas, the diffuser (13) comprising a movable ring (22), a main channel (24) through which the gas flows, and an openable branch channel (26); and a circulation loop (42), the circulation loop (42) comprising an inlet (43) and an outlet (44), the outlet (44) being in communication with the inlet of the impeller (12); wherein the branch channel (26) is configured such that when the ring (22) moves into the main channel (24), the branch channel (26) connects the main channel (24) and the circulation loop (42), so that a portion of the gas in the main channel (24) returns to the impeller (12) via the circulation loop (42) to be sucked in, and when the ring (22) exits the main channel (24), the branch channel (26) is closed; The main channel (24) is defined by partitions (16, 18) facing each other, wherein one of the partitions (16) is provided with a groove (52) to fit the ring (22) into the groove (52), and the branch channel (26) is provided between at least one surface of the ring (22) and a wall of the groove (52); as well as The at least one surface of the ring (22) is a rear surface (36) of the ring (22) facing away from the main channel.

2. The centrifugal compressor according to claim 1, wherein: The branch channel (26) is further arranged inside the groove (52), or inside the ring (22), or a combination of all the aforementioned methods.

3. The centrifugal compressor according to claim 2, wherein: The at least one surface of the ring (22) further comprises a side surface (35) of the ring (22).

4. The centrifugal compressor according to claim 2, wherein: The ring (22) has a protruding portion (23) that protrudes into one of the partitions (16), and the branch channel (26) is formed as an additional flow passage (27) passing between the front and rear surfaces of the protruding portion (23).

5. The centrifugal compressor according to claim 2, wherein: The circulation loop (42) is integrated into one of the partitions (16) and is located in the vicinity of the drive mechanism (28), and the ring (22) is driven by the drive mechanism (28).

6. The centrifugal compressor according to claim 5, characterized in that: The circulation loop (42) includes at least one flow channel (45, 46) for guiding the gas, the at least one flow channel (45, 46) being formed by machining a hole in one of the partitions (16), and at least one wall of the groove (52) being in communication with the at least one flow channel (45, 46).

7. The centrifugal compressor according to claim 3, wherein: The side surface (35) of the ring (22) is configured to include at least one segment (37, 38, 39), and different segments (37, 38, 39) have different surface shapes.

8. A method of operating a centrifugal compressor according to any one of claims 1 to 7, It is characterized by The method includes, when the centrifugal compressor is running close to a surge state, moving the ring (22) into the main passage (24) so ​​that the branch passage (26) is open between the main passage (24) and the circulation loop (42), so that a portion of the gas from the main passage (24) returns to the impeller (12) via the circulation loop (42) to be sucked.

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