Centrifugal compressors and their control methods

Abstract

This application relates to the field of compressor equipment technology, and more particularly to a centrifugal compressor and its control method. The centrifugal compressor includes a housing, within which a drive motor, a first impeller, a second impeller, a first diffuser, a second diffuser, and a return flow device are disposed. The return flow device is connected to the outlet of the first diffuser and the inlet of the second impeller. The first variable diffuser reciprocates axially under the drive of a first drive mechanism to adjust the axial width of the first flow channel; the second variable diffuser reciprocates axially under the drive of a second drive mechanism to adjust the axial width of the second flow channel. By adjusting the axial width of the first flow channel through the first variable diffuser and the axial width of the second flow channel through the second variable diffuser, the airflow can be rationally regulated, effectively improving the performance of the centrifugal compressor under low-load conditions and broadening the operating range of the centrifugal compressor.

Description

Technical Field

[0001] This application relates to the field of compressor equipment technology, and in particular to a centrifugal compressor and its control method. Background Technology

[0002] When centrifugal compressors are used for refrigeration and other applications, they cannot operate at full load under rated conditions for extended periods. They often need to work under various low-load conditions. However, centrifugal compressors inevitably experience surge when operating at low loads, especially with the new generation of environmentally friendly refrigerant R1233ZDE, which has a low density and high specific volume, resulting in more severe surge phenomena. At the same time, due to the significant airflow loss during low-load operation, its performance is greatly reduced. Summary of the Invention

[0003] To address the aforementioned technical problems, this application provides a centrifugal compressor and a control method for the centrifugal compressor.

[0004] In a first aspect, embodiments of this application provide a centrifugal compressor, which includes a housing. A drive motor, a first impeller, a second impeller, a first diffuser, a second diffuser, and a return flow device are disposed within the housing. The return flow device is connected to the outlet of the first diffuser and the inlet of the second impeller, respectively. The centrifugal compressor further includes:

[0005] A first variable diffuser and a first drive mechanism, wherein the first variable diffuser is disposed in a first flow channel between the outlet of the first impeller and the inlet of the first diffuser, and the first variable diffuser reciprocates axially under the drive of the first drive mechanism to adjust the axial width of the first flow channel.

[0006] The second variable diffuser and the second drive mechanism are provided in the second flow channel between the outlet of the second impeller and the inlet of the second diffuser. The second variable diffuser is driven by the second drive mechanism to reciprocate axially to adjust the axial width of the second flow channel.

[0007] Furthermore, the first driving mechanism is a mechanical driving structure or a pneumatic driving structure, and the second driving mechanism is a mechanical driving structure or a pneumatic driving structure.

[0008] Furthermore, the first impeller and the second impeller are located on the same side of the drive motor, and the second drive mechanism is a pneumatic drive structure.

[0009] Furthermore, the second drive mechanism includes an intake pipe, a cylinder, and an outlet pipe arranged in sequence. A first regulating valve is provided on the intake pipe, and a second regulating valve is provided on the outlet pipe. The cylinder is used to drive the second variable diffuser to move axially.

[0010] Furthermore, both the air inlet pipe and the air outlet pipe are connected to an external air source; or

[0011] The air inlet pipe is connected to the air outlet of the centrifugal compressor, and the air outlet pipe is connected to the air inlet of the centrifugal compressor.

[0012] Furthermore, the ratio of the radius at the outlet of the first variable diffuser to the radius at the outlet of the first impeller is 1.15-1.25; the ratio of the radius at the outlet of the second variable diffuser to the radius at the outlet of the second impeller is 1.15-1.25.

[0013] Secondly, embodiments of this application also provide a control method for a centrifugal compressor, used to control the centrifugal compressor provided in the first aspect of embodiments of this application, the control method comprising:

[0014] When the centrifugal compressor is operating within the first range, the first flow channel and the second flow channel are kept at their maximum axial width, and the speed of the drive motor is adjusted to control the flow rate.

[0015] When the centrifugal compressor operates in the second range, at least one of the first variable diffuser and the second variable diffuser is driven to adjust the axial width of at least one of the first flow channel and the second flow channel, wherein the first range is higher than the second range.

[0016] Furthermore, when the centrifugal compressor operates within the range of 100%-80%, the first flow channel and the second flow channel are kept at their maximum axial width, and the speed of the drive motor is adjusted for flow control.

[0017] When the centrifugal compressor operates at a range of less than 80%, at least one of the first variable diffuser and the second variable diffuser is driven to adjust the axial width of at least one of the first flow channel and the second flow channel.

[0018] Furthermore, when the centrifugal compressor operates within the range of 80% to 50%, the first flow channel is kept at its maximum axial width, and the second variable diffuser is driven to adjust the axial width of the second flow channel; when the centrifugal compressor operates within the range of 50%, the first variable diffuser and the second variable diffuser are adjusted in conjunction, and the axial widths of both the first and second flow channels are adjusted.

[0019] Furthermore, the process of coordinated adjustment between the first variable diffuser and the second variable diffuser includes:

[0020] When the centrifugal compressor experiences surge under a certain operating condition, the second variable diffuser is first adjusted to gradually reduce the axial width of the second flow channel until the surge is eliminated.

[0021] When the axial width of the second flow channel is adjusted to the minimum, the centrifugal compressor still surges. Further adjustment of the first variable diffuser gradually reduces the axial width of the first flow channel until the surge is eliminated.

[0022] Furthermore, the axial width of the first impeller outlet is b1, the axial width of the second impeller outlet is b2, the adjustment range of the axial width of the first flow channel is 0.5b1 to 0.95b1, and the adjustment range of the axial width of the second flow channel is 0.5b2 to 0.95b2.

[0023] This application has the following beneficial effects: It proposes a centrifugal compressor with a multi-stage adjustable diffuser. The axial width of the first flow channel is adjusted by the first variable diffuser, and the axial width of the second flow channel is adjusted by the second variable diffuser. The airflow can be reasonably regulated, which can effectively improve the performance of the centrifugal compressor under low load conditions, and at the same time broaden the operating range of the centrifugal compressor. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application. In the drawings:

[0025] Figure 1 A cross-sectional view of a centrifugal compressor provided in an embodiment of this application is schematically shown;

[0026] Figure 2 A schematic diagram illustrating the airflow structure principle in the centrifugal compressor provided in the embodiments of this application is given;

[0027] Figure 3 It is given schematically. Figure 2 Airflow direction in the airflow structure;

[0028] Figure 4 It is given schematically. Figure 2 Key parameters of the airflow mechanism;

[0029] Figure 5 A schematic top view of the adjustable diffuser in the centrifugal compressor provided in the embodiments of this application is given;

[0030] Figure 6A schematic cross-sectional view of the adjustable diffuser and its adjacent structure in a centrifugal compressor provided in an embodiment of this application is given;

[0031] Figure 7 A cross-sectional view of another centrifugal compressor provided in an embodiment of this application is schematically shown;

[0032] Figure 8 It is given schematically. Figure 7 The diagram shows the working principle of the first variable diffuser in the centrifugal compressor; and

[0033] Figure 9 It is given schematically. Figure 7 The diagram shows the working principle of the second variable diffuser in the centrifugal compressor.

[0034] In the picture:

[0035] 1. Housing; 2. Drive motor; 3. First impeller; 4. Second impeller; 5. First diffuser; 6. Second diffuser; 7. Return valve; 8. First variable diffuser; 9. Second variable diffuser; 10. First flow channel; 11. Second flow channel; 12. Volute; 13. Shaft; 14. Drive rod; 15. Inlet pipe; 16. Cylinder; 17. Outlet pipe; 18. First regulating valve; 19. Second regulating valve; 20. Piston; 21. First drive mechanism; 22. Second drive mechanism; 23. Planar section; 24. Inclined section. Detailed Implementation

[0036] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0037] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification, claims and accompanying drawings of this application are intended to cover non-exclusive inclusion. For example, a system, product or device that includes a series of units is not necessarily limited to those units that are explicitly listed, but may include units that are not explicitly listed or that are inherent to such products or devices.

[0038] In this application, the terms "upper," "lower," "inner," "middle," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0039] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0040] Furthermore, the terms "set up," "connect," and "fix" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0041] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0042] refer to Figure 1-3 As shown, the main structure of the centrifugal compressor provided in this application embodiment includes a housing 1, a drive motor 2, a first impeller 3, a second impeller 4, a first diffuser 5, a second diffuser 6, a return flow device 7, a first variable diffuser 8, a first drive mechanism 21, a second variable diffuser 9, and a second drive mechanism 22. The drive motor 2, the first impeller 3, the second impeller 4, the first diffuser 5, the second diffuser 6, the return flow device 7, the first variable diffuser 8, and the second variable diffuser 9 are all disposed inside the housing 1. The first impeller 3 and the second impeller 4 are both sleeved on the rotating shaft 13. The drive motor 2 drives the rotating shaft 13 to rotate around its axis, thereby driving the rotation of the first impeller 3 and the second impeller 4. The return flow device 7 is connected to the outlet of the first diffuser 5 and the inlet of the second impeller 4 respectively. The first variable diffuser 8 is disposed in the first flow channel 10 between the outlet of the first impeller 3 and the inlet of the first diffuser 5. The first variable diffuser 8 moves axially reciprocally under the drive of the first drive mechanism 21 to adjust the axial width of the first flow channel 10. The second variable diffuser 9 is disposed in the second flow channel 11 between the outlet of the second impeller 4 and the inlet of the second diffuser 6. The second variable diffuser 9 moves axially reciprocally under the drive of the second drive mechanism 22 to adjust the axial width of the second flow channel 11.

[0043] In the example shown, the inlets of both the first impeller 3 and the second impeller 4 are arranged axially, and the outlets of both the first impeller 3 and the second impeller 4 are arranged radially. Figure 3 As shown, the working medium enters the first impeller 3 axially and is compressed by the rotating first impeller 3 before being discharged. The compressed working medium is then sent to the inlet of the second impeller 4 via the first variable diffuser 8, the first diffuser 5, and the return flow device 7, where it is further compressed by the rotating second impeller 4. After being discharged from the second impeller 4, the further compressed working medium passes through the second variable diffuser 9 and the second diffuser 6 before entering the next stage impeller or the volute 12. It should be noted that the centrifugal compressor shown in the accompanying drawings is a two-stage compressor, but the embodiments of this application can also be used in compressors with more stages. When the centrifugal compressor is a two-stage compressor, it includes only two impellers. In this case, the working medium is discharged from the second impeller 4 and passes through the second variable diffuser 9 and the second diffuser 6 before entering the volute 12. When the centrifugal compressor is a multi-stage compressor, and the second impeller 4 is not the last stage impeller, the working medium is discharged from the second impeller 4 and passes through the second variable diffuser 9 and the second diffuser 6 before entering the next stage impeller. In the embodiments and accompanying drawings of this application, a centrifugal compressor as a two-stage compressor is used as an example to illustrate this application.

[0044] In this embodiment, the drive motor 2 adjusts the rotor speed according to the speed control command provided by the controller, thereby adjusting the rotational speed of the first impeller 3 and the second impeller 4. The drive motor 2 is preferably an asynchronous variable frequency motor. The output speed is adjusted by using a frequency converter as the controller. Variable frequency speed control not only achieves stepless speed regulation, but also, by appropriately adjusting the relationship between voltage and frequency according to different load characteristics, ensures that the drive motor 2 always operates in the high-efficiency range and maintains good dynamic performance.

[0045] In the centrifugal compressor provided in the above embodiment, a first variable diffuser 8 is disposed in a first flow channel 10 between the outlet of the first impeller 3 and the inlet of the first diffuser 5. The first variable diffuser 8 reciprocates axially under the drive of the first drive mechanism 21 to adjust the axial width of the first flow channel 10. A second variable diffuser 9 is disposed in a second flow channel 11 between the outlet of the second impeller 4 and the inlet of the second diffuser 6. The second variable diffuser 9 reciprocates axially under the drive of the second drive mechanism 22 to adjust the axial width of the second flow channel 11, thereby realizing the adjustment of the flow area of ​​the first flow channel 10 and the flow area of ​​the second flow channel 11. When the centrifugal compressor is under high load, its load operation can be achieved by adjusting the speed of the drive motor 2. Under low load, the axial width of the first flow channel 10 and the second flow channel 11 can be changed by adjusting the first and second variable diffusers, thereby increasing the flow velocity of the working medium and preventing surge. This allows the centrifugal compressor to operate normally under lower loads, expanding its operating range. Furthermore, when the centrifugal compressor is operating under low load, adjusting the first and second variable diffusers changes the axial width of the first flow channel 10 and the second flow channel 11. Increasing or decreasing the axial width and cross-sectional area of ​​the 11 will cause the radial velocity of the working medium to decrease or increase. Since the working medium also has a tangential velocity after flowing out from the first impeller 3 and the second impeller 4, the resultant velocity of the working medium includes a radial velocity and a tangential velocity in the circumferential direction. According to the principle of the right triangle of resultant velocity, when the radial velocity decreases or increases, the direction of the resultant velocity of the working medium will inevitably change, which will lead to an increase or decrease in the angle between the resultant velocity direction and the radial surface, thereby achieving the purpose of adjusting the airflow angle. This can reduce the airflow loss under this working condition and improve the performance of the centrifugal compressor.

[0046] As an optional implementation, the first variable diffuser 8 and the second variable diffuser 9 are structured as follows: Figure 5 and 6As shown, the first variable diffuser 8 and the second variable diffuser 9 have annular cross-sectional shapes. The first impeller 3 is located inside the inner ring of the first variable diffuser 8, and the first diffuser 5 is located outside the outer ring of the first variable diffuser 8. The second impeller 4 is located inside the inner ring of the second variable diffuser 9, and the second diffuser 6 is located outside the outer ring of the second variable diffuser 9. A drive rod 14 is provided on the side of the first variable diffuser 8 away from the first flow channel 10 and on the side of the second variable diffuser 9 away from the second flow channel 11. The first variable diffuser 8 moves axially when the drive rod 14 is pushed by the first drive mechanism 21, and the second variable diffuser 9 moves axially when the drive rod 14 is pushed by the second drive mechanism 22. Preferably, multiple drive rods 14 are provided on the first variable diffuser 8 or the second variable diffuser 9, and the multiple drive rods 14 are evenly distributed circumferentially, which can uniformly provide multiple force application points and improve the stability of the axial movement of the first variable diffuser 8 or the second variable diffuser 9. For example, in the accompanying drawings of this application, three drive rods 14 are provided on the first variable diffuser 8 or the second variable diffuser 9, and the three drive rods 14 are evenly distributed along the circumference.

[0047] In some embodiments, the first drive mechanism 21 and the second drive mechanism 22 may be selected as mechanical drive structures. These mechanical drive mechanisms include, but are not limited to, cam assemblies, rack and pinion assemblies, linear motor assemblies, and crank-slider assemblies. For example, the mechanical drive mechanism may be selected as a cam assembly, which includes a cam, a reset member, and a motor as a power source. The motor drives the cam to rotate, and the edge of the cam abuts against the drive rod 14 to achieve synchronous control. When the load on the centrifugal compressor decreases, the motor causes the cam to rotate continuously in one direction. The cam pushes the guide rod to move axially, realizing the translation of the first or second variable diffuser from left to right, reducing the width of the first flow channel 10 or the second flow channel 11, making it convergent, and reducing turbulence losses. When the motor causes the cam to rotate continuously in the opposite direction, the reset member pushes the guide rod to move axially, realizing the translation of the first or second variable diffuser from right to left, increasing the axial width of the first or second flow channel 10 to meet high flow rate requirements. The reset member is preferably a spring.

[0048] In some embodiments, the first drive mechanism 21 and the second drive mechanism 22 may be pneumatic drive structures. The pneumatic drive structure mainly introduces a high-pressure air source into the air supply chamber of the cylinder 16 to generate pressure, which causes the drive rod 14 to drive the first variable diffuser or the second variable diffuser to move axially.

[0049] It should be noted that the first drive mechanism 21 and the second drive mechanism 22 can both be selected as mechanical drive mechanisms, or both can be selected as pneumatic drive mechanisms. Alternatively, one of the first drive mechanism 21 and the second drive mechanism 22 can be selected as a mechanical drive mechanism and the other as a pneumatic drive mechanism. Those skilled in the art can make reasonable selections according to design requirements.

[0050] In production practice, centrifugal compressors are selected in many scenarios as follows: Figure 1 The single-cantilever centrifugal compressor shown has a multi-stage pneumatic impeller structure mainly distributed on the same side of the drive motor 2. Specifically, in this embodiment, the first impeller 3 and the second impeller 4 are both located on the same side of the drive motor 2. Because the single-cantilever multi-stage centrifugal compressor requires a more compact structure, an excessively long cantilever would severely affect the structure and operational stability of the centrifugal compressor, increasing the difficulty of adjusting the operating range of the two-stage impellers. The second drive mechanism 22 is located between the first impeller 3 and the second impeller 4. Since mechanical drive mechanisms occupy a large amount of space, choosing a mechanical drive mechanism for the second drive mechanism 22 would inevitably significantly increase the length of the single cantilever. Therefore, in this embodiment, the second drive mechanism 22 is preferably a pneumatic drive structure that occupies less space, such as... Figure 7-9 As shown, a centrifugal compressor is provided, wherein the first drive mechanism 21 is selected as a mechanical drive structure, and the working principle of the first variable diffuser 8 is as follows. Figure 8 As shown, the second drive mechanism is a pneumatic drive structure, and the working principle of the second variable diffuser 9 is as follows: Figure 9 As shown.

[0051] As an optional implementation of the second drive mechanism 22, such as Figure 7 and 9As shown, the second drive mechanism 22 includes an inlet pipe 15, a cylinder 16, and an outlet pipe 17 arranged sequentially. A first regulating valve 18 is provided on the inlet pipe 15, and a second regulating valve 19 is provided on the outlet pipe 17. The cylinder 16 drives the second variable diffuser 9 to move axially. The cylinder 16 has a cavity, and a piston 20 is disposed within the cavity. The piston 20 is slidably disposed within the cavity and is connected to the second variable diffuser 9 via a drive rod 14. By changing the pressure of the medium within the cavity, the piston 20 is driven to slide, thereby causing the second variable diffuser 9 to move axially. The first regulating valve 18 is located on the inlet pipe 15 and is used to control the flow of high-pressure gas. The second regulating valve 19 is located on the outlet pipe 17 and is used to control the flow of high-pressure gas. During the process of adjusting the pressure of the medium in the cavity, the inflow and outflow of high-pressure gas can be flexibly controlled by adjusting the opening of the first regulating valve 18 and the second regulating valve 19, thereby flexibly controlling the pressure in the cavity and, consequently, flexibly controlling the axial displacement of the second variable diffuser 9. The second variable diffuser involved in this embodiment is driven by a cylinder 16. This driving method has a small structural size, is easy to install, and can be designed as a unit module for convenient independent use. It can be applied to other established models without affecting other structures, and is especially suitable for centrifugal compressors with a single cantilever structure. Both the first regulating valve 18 and the second regulating valve 19 are preferably electronic regulating valves suitable for automatic control.

[0052] In some embodiments, the high-pressure air source used in the second drive mechanism 22 is derived from an external air source, in which case both the inlet pipe 15 and the outlet pipe 17 are connected to the external air source; in other embodiments, the high-pressure air source can be a medium compressed by the centrifugal compressor itself, such as... Figure 9 As shown, the inlet pipe 15 is connected to the volute 12 or the outlet of the centrifugal compressor, and the outlet pipe 17 is connected to the inlet of the centrifugal compressor. The second variable diffuser involved in this application introduces high-pressure gas through the outlet of the volute 12 via the inlet pipe 15. The inlet gas pressure is automatically adjusted by an electronic regulating valve, and the outlet gas pressure is also automatically adjusted by an electronic regulating valve. Finally, the gas flows into the inlet of the centrifugal compressor. During operation, it can automatically adjust according to different pressure ratios, flow rates, and inlet / outlet pressures.

[0053] Technicians have found in practice that, for example Figure 4 As shown, the relative sizes of the radius R2 at the outlet of the first variable diffuser 8 and the radius R1 at the outlet of the first impeller 3, and the relative sizes of the radius R4 at the outlet of the second variable diffuser 9 and the radius R3 at the outlet of the second impeller 4, affect the operating range of the centrifugal compressor.

[0054] The value of R4 / R3 is controlled to be 1.25. The axial width of the first flow channel 10 is 0.5 times the axial width b1 of the outlet of the first impeller 3, and the axial width of the second flow channel 11 is 0.5 times the axial width b2 of the outlet of the second impeller 4. The centrifugal compressor is operated by adjusting the value of R2 / R1. The operating conditions of the centrifugal compressor are adjusted, and the minimum operating range achievable under different values ​​of R2 / R1 is tested and recorded in Table 1. It should be noted that the wall of the flow channel formed by the first variable diffuser includes an interconnected planar section 23 and an inclined section 24. The planar section 23 is far away from the inclined section 24 relative to the inclined section 24. The planar section 23 is perpendicular to the axial direction, and the inclined section 24 is inclined relative to the axial direction. In the direction that gradually approaches the planar section 23, the axial width of the flow channel corresponding to the inclined section 24 gradually decreases, so that the inclined section 24 plays a guiding role, guiding the working medium at the impeller outlet to the flow channel corresponding to the planar section 23. The axial width of the flow channel corresponding to the planar segment 23 region of the first variable diffuser is denoted as the axial width of the first flow, and the axial width of the flow channel corresponding to the planar segment 23 region of the second variable diffuser is denoted as the axial width of the second flow channel.

[0055] Table 1

[0056] R2 / R1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.40 Minimum operating range 33％ 31％ 30.5％ 30.2％ 30％ 29.8％ 30.5％ 31.8％

[0057] As can be seen from Table 1, when the ratio of the radius R2 at the outlet of the first variable diffuser 8 to the radius R1 at the outlet of the first impeller 3 is between 1.15 and 1.35, the minimum operating range that can be achieved is 29.8%-30.5%, which means that the centrifugal compressor has a relatively large operating range. Within this ratio range, the uniform mixing of the airflow at the outlet of the first impeller of the centrifugal compressor can be effectively guaranteed. When the ratio is greater than 1.3, the minimum operating range of the centrifugal compressor will increase, which is not conducive to the convergence characteristics of the diffuser and will instead reduce the adjustable operating range. However, when the ratio of the radius R2 at the outlet of the first variable diffuser 8 to the radius R1 at the outlet of the first impeller 3 exceeds 1.25, the diameter of the first impeller 3 is usually not arbitrarily changed to ensure the centrifugal compression effect. This would result in an excessively large outer diameter of the first variable diffuser 8, which would have adverse effects on the structural layout and compatibility with other structures of the centrifugal compressor. Therefore, the ratio of the radius R2 at the outlet of the first variable diffuser 8 to the radius R1 at the outlet of the first impeller 3 is preferably 1.15-1.25. Furthermore, when the values ​​of R4 / R3, the ratio of the axial width of the first flow channel 10 to the axial width of the outlet of the first impeller 3, and the ratio of the axial width of the second flow channel 11 to the axial width of the outlet of the second impeller 4 are adjusted to other specific parameters, repeating the above testing process yields the same conclusion: when the ratio of the radius R2 at the outlet of the first variable diffuser 8 to the radius R1 at the outlet of the first impeller 3 is between 1.15 and 1.35, the minimum operating range achievable by the centrifugal compressor is relatively low.

[0058] The value of R2 / R1 is controlled to be 1.25. The axial width of the first flow channel 10 is 0.5 times the axial width of the outlet of the first impeller 3, and the axial width of the second flow channel 11 is 0.5 times the axial width of the outlet of the second impeller 4. The centrifugal compressor is operated by adjusting the value of R4 / R3. The operating conditions of the centrifugal compressor are adjusted, and the minimum operating range that can be achieved under different values ​​of R4 / R3 is tested and recorded in Table 2.

[0059] Table 2

[0060] R2 / R1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.40 Minimum operating range 33.3％ 31.4％ 30.6％ 30.3％ 30.1％ 29.7％ 30.4％ 31.6％

[0061] As can be seen from Table 2, when the ratio of the radius R4 at the outlet of the second variable diffuser 9 to the radius R3 at the outlet of the second impeller 4 is between 1.15 and 1.35, the minimum operating range that can be achieved is 29.7%-30.6%, which means that the centrifugal compressor has a relatively large operating range. Within this ratio range, the uniform mixing of the airflow at the outlet of the second impeller 4 of the centrifugal compressor can be effectively guaranteed. When the ratio is greater than 1.3, the minimum operating range of the centrifugal compressor will increase, which is not conducive to the convergence characteristics of the diffuser and will instead reduce the adjustable operating range. However, when the ratio of the radius R4 at the outlet of the second variable diffuser 9 to the radius R3 at the outlet of the second impeller 4 exceeds 1.25, the diameter of the second impeller 4 cannot be arbitrarily changed to ensure the centrifugal compression effect. This would result in an excessively large outer diameter of the second variable diffuser 9, which would adversely affect the structural layout and compatibility with other structures of the centrifugal compressor. Therefore, the preferred ratio of the radius R4 at the outlet of the second variable diffuser 9 to the radius R3 at the outlet of the second impeller 4 is 1.15-1.25. Furthermore, when the values ​​of R2 / R1, the ratio of the axial width of the first flow channel 10 to the axial width of the outlet of the first impeller 3, and the ratio of the axial width of the second flow channel 11 to the axial width of the outlet of the second impeller 4 are adjusted to other specific parameters, repeating the above testing process yields the same conclusion: when the ratio of the radius R4 at the outlet of the second variable diffuser 9 to the radius R3 at the outlet of the second impeller 4 is between 1.15 and 1.35, the minimum operating range achievable by the centrifugal compressor is relatively low.

[0062] Technicians have also discovered in practice that, for example Figure 4 As shown, the ratio of the axial width of the first flow channel 10 to the axial width b1 of the outlet of the first impeller 3, and the ratio of the axial width of the second flow channel 11 to the axial width b2 of the outlet of the second impeller 4, will affect the operating range of the centrifugal compressor.

[0063] The values ​​of R4 / R3 and R2 / R1 are both controlled to be 1.25. The axial width of the second flow channel 11 is controlled to be 0.5 times the axial width b2 of the outlet of the second impeller 4. The axial width of the first flow channel 10 is adjusted. The centrifugal compressor is run and its operating conditions are adjusted. The minimum operating range that the centrifugal compressor can achieve under different axial widths of the first flow channel 10 is tested and recorded in Table 3.

[0064] As shown in Table 3, the adjustment range of the first variable diffuser satisfies the condition that when the axial width of the first flow channel is 0.3b1 to 0.95b1, the minimum operating range achievable by the centrifugal compressor is 30%-45%, indicating a relatively large achievable operating range. However, when the axial width of the first flow channel is less than 0.5b1, the flow area of ​​the airflow channel is too small, leading to blockage and a significant reduction in centrifugal performance. Therefore, the axial width of the first flow channel should be 0.5b1 to 0.95b1. Furthermore, by adjusting the values ​​of R4 / R3, R2 / R1, and the ratio of the axial width of the second flow channel 11 to the axial width of the outlet of the second impeller 4 to other specific parameters, repeating the above testing process yields the same conclusion: when the axial width of the first flow channel is 0.5b1 to 0.95b1, the minimum achievable operating range of the centrifugal compressor is lower, and excessively low compressor performance can be avoided.

[0065] Table 3

[0066] First flow channel axial width Minimum operating range 0.3b1 45％ 0.35b1 43.1％ 0.4b1 42％ 0.45b1 38.4％ 0.5b1 30％ 0.55b1 31.70％ 0.6b1 33.20％ 0.65b1 34％ 0.7b1 35％ 0.75b1 38.3％ 0.8b1 42％ 0.85b1 43.7％ 0.9b1 44％ 0.95b1 45％ b1 48％

[0067] The values ​​of R4 / R3 and R2 / R1 are both controlled to be 1.25. The axial width of the first flow channel 10 is controlled to be 0.5 times the axial width b1 of the outlet of the first impeller 3. The axial width of the second flow channel 11 is adjusted. The centrifugal compressor is run and its operating conditions are adjusted. The minimum operating range that the centrifugal compressor can achieve under different axial widths of the second flow channel 11 is tested and recorded in Table 4.

[0068] Table 4

[0069]

[0070]

[0071] As shown in Table 4, the adjustment range of the second variable diffuser satisfies the condition that when the axial width of the second flow channel is 0.35b² to 0.95b², the minimum operating range achievable by the centrifugal compressor is 29.3% to 44.7%, indicating a relatively large achievable operating range. However, when the axial width of the second flow channel is less than 0.5b², the flow area of ​​the airflow channel is too small, leading to blockage and a significant reduction in centrifugal compressor performance. Therefore, the axial width of the second flow channel should be 0.5b² to 0.95b². Furthermore, by adjusting the values ​​of R4 / R3, R2 / R1, and the ratio of the axial width of the first flow channel 10 to the axial width of the outlet of the first impeller 3 to other specific parameters, repeating the above testing process yields the same conclusion: when the axial width of the second flow channel is 0.5b² to 0.95b², the minimum achievable operating range of the centrifugal compressor is lower, and excessively low compressor performance can be avoided.

[0072] This application also provides a control method for a centrifugal compressor, used to control the centrifugal compressor disclosed in the foregoing embodiments of this application. The control method for the centrifugal compressor includes the following steps.

[0073] When the centrifugal compressor is operating in the first range, the first flow channel 10 and the second flow channel 11 are kept at their maximum axial width, and the speed of the drive motor 2 is adjusted to control the flow rate.

[0074] When the centrifugal compressor operates in the second range, at least one of the first variable diffuser and the second variable diffuser is driven to adjust the axial width of at least one of the first flow channel 10 and the second flow channel 11, wherein the first range is higher than the second range.

[0075] In the control method described above, the first range is higher than the second range. Its main function is to allow for high-load operation by adjusting the speed of the drive motor. Under low-load conditions, the axial width of the first and second flow channels can be adjusted by regulating the first and second variable diffusers to prevent surge. This allows the centrifugal compressor to operate normally under lower loads, thus expanding the operating range of the centrifuge. Furthermore, when the centrifugal compressor is under low-load conditions, adjusting the first and second variable diffusers according to the flow rate can regulate the airflow angle, thereby reducing friction and separation losses in the first and second flow channels, reducing airflow losses under these conditions, and ultimately improving the performance of the centrifugal compressor.

[0076] In some embodiments, the first range is 100%-80%, and the second range is below 80%. That is, when the centrifugal compressor operates within the 100%-80% range, the first flow channel 10 and the second flow channel 11 are kept at their maximum axial width, and the speed of the drive motor 2 is adjusted for flow control. When the centrifugal compressor operates below 80%, at least one of the first and second variable diffusers is driven to adjust the axial width of at least one of the first and second flow channels 10 and 11. Within the 80%-100% operating range, the load operation can be fully achieved by adjusting the speed of the drive motor without adjusting the first and second variable diffusers, ensuring that the first and second flow channels remain at their maximum opening and guaranteeing compressor performance. When the operating range is less than 80%, the centrifugal compressor is under low load. At this time, the adjustable diffuser can prevent surge, allowing the centrifugal compressor to operate normally under lower loads, thus widening the centrifuge's operating range. Furthermore, by adjusting the airflow angle, the centrifuge's performance is improved.

[0077] In some embodiments, when the centrifugal compressor operates within the range of 80% to 50%, the first flow channel 10 is kept at its maximum axial width, and the second variable diffuser is driven to adjust the axial width of the second flow channel 11. When the centrifugal compressor operates below 50%, the first and second variable diffusers are adjusted in conjunction, and the axial widths of both the first and second flow channels 10 and 11 are adjusted. Technicians have found that surge in centrifugal compressors typically occurs first in the high-compression stage and propagates from there to the low-compression stages. Therefore, prioritizing the adjustment of the housing transformer in the high-compression stage when surge occurs is more targeted. Furthermore, the lower the flow rate, the greater the likelihood of surge. Therefore, for operating ranges less than 80%, within the relatively high 80% to 50% operating range, there is no need to adjust the first variable diffuser; only the second variable diffuser needs adjustment to eliminate surge. At this time, the first flow channel at the first variable diffuser is fully open, and the compressor's first-stage compression efficiency is near its optimal point. High-efficiency operation results in a lower gas temperature at the inlet of the second impeller, reducing the power consumption of the second-stage compression. The second variable diffuser then activates, narrowing the second flow channel and reducing the unit load. This process ensures efficient and stable operation of the unit within the operating range. For relatively low operating ranges less than 50%, if the second variable diffuser's activation is insufficient to accommodate the reduced load, the first variable diffuser will also activate. The first flow channel after the first impeller narrows to accommodate the reduced load, reducing the turbulence intensity of the gas in the first variable diffuser and its flow channel. This coordinated adjustment of the first and second variable diffusers eliminates surge.

[0078] Preferably, in the above embodiment, the process of linkage adjustment between the first variable diffuser and the second variable diffuser may include: when the centrifugal compressor experiences surge under a certain operating condition, firstly, the second variable diffuser is adjusted to gradually reduce the axial width of the second flow channel 11 until the surge is eliminated; when the axial width of the second flow channel 11 is adjusted to its minimum, and the centrifugal compressor still experiences surge, the first variable diffuser is further adjusted to gradually reduce the axial width of the first flow channel 10 until the surge is eliminated. In the above process, the surge phenomenon of centrifugal compressors usually occurs first in the high compression stage and is transmitted from the high compression stage to the low compression stage, making the operation of the first and second variable diffusers more operable and quickly eliminating the surge phenomenon. Based on the relevant descriptions of the foregoing embodiments, the adjustment range of the axial width of the first flow channel 10 is 0.5b1 to 0.95b1, and the adjustment range of the axial width of the second flow channel 11 is 0.5b2 to 0.95b2.

[0079] Some embodiments in this specification are described in a progressive or parallel manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0080] The above are merely specific embodiments of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A centrifugal compressor, characterized in that, The centrifugal compressor includes a housing, within which are disposed a drive motor, a first impeller, a second impeller, a first diffuser, a second diffuser, and a return flow device. The return flow device is connected to the outlet of the first diffuser and the inlet of the second impeller. The centrifugal compressor further includes: A first variable diffuser and a first drive mechanism, wherein the first variable diffuser is disposed in a first flow channel between the outlet of the first impeller and the inlet of the first diffuser, and the first variable diffuser reciprocates axially under the drive of the first drive mechanism to adjust the axial width of the first flow channel. The second variable diffuser and the second drive mechanism are provided in the second flow channel between the outlet of the second impeller and the inlet of the second diffuser. The second variable diffuser is driven by the second drive mechanism to reciprocate axially to adjust the axial width of the second flow channel. The first and second variable diffusers have annular cross-sectional shapes. The first impeller is located inside the inner ring of the first variable diffuser, and the second impeller is located inside the inner ring of the second variable diffuser. Both the first and second impellers are mounted on a rotating shaft driven by a drive motor. The ratio of the radius at the outlet of the first variable diffuser to the radius at the outlet of the first impeller is 1.15-1.35; the ratio of the radius at the outlet of the second variable diffuser to the radius at the outlet of the second impeller is also 1.15-1.

35.

2. The centrifugal compressor according to claim 1, characterized in that, The first driving mechanism is a mechanical driving structure or a pneumatic driving structure, and the second driving mechanism is a mechanical driving structure or a pneumatic driving structure.

3. The centrifugal compressor according to claim 1, characterized in that, The first impeller and the second impeller are located on the same side of the drive motor, and the second drive mechanism is a pneumatic drive structure.

4. The centrifugal compressor according to claim 1, characterized in that, The second drive mechanism includes an intake pipe, a cylinder, and an outlet pipe arranged in sequence. A first regulating valve is provided on the intake pipe, and a second regulating valve is provided on the outlet pipe. The cylinder is used to drive the second variable diffuser to move axially.

5. The centrifugal compressor according to claim 4, characterized in that, Both the air inlet pipe and the air outlet pipe are connected to an external air source; or The air inlet pipe is connected to the air outlet of the centrifugal compressor, and the air outlet pipe is connected to the air inlet of the centrifugal compressor.

6. A control method for a centrifugal compressor, used to control the centrifugal compressor as described in any one of claims 1-5, characterized in that, The control method includes: When the centrifugal compressor is operating within the first range, the first flow channel and the second flow channel are kept at their maximum axial width, and the speed of the drive motor is adjusted to control the flow rate. When the centrifugal compressor operates in the second range, at least one of the first variable diffuser and the second variable diffuser is driven to adjust the axial width of at least one of the first flow channel and the second flow channel, wherein the first range is higher than the second range.

7. The control method for a centrifugal compressor according to claim 6, characterized in that, When the centrifugal compressor operates within the range of 100%-80%, the first and second flow channels are kept at their maximum axial width, and the speed of the drive motor is adjusted to control the flow rate. When the centrifugal compressor operates at less than 80% of its capacity, at least one of the first variable diffuser and the second variable diffuser is driven to adjust the axial width of at least one of the first flow channel and the second flow channel.

8. The control method for a centrifugal compressor according to claim 7, characterized in that, When the centrifugal compressor operates within the range of 80% to 50%, the first flow channel is kept at its maximum axial width, and the second variable diffuser is driven to adjust the axial width of the second flow channel. When the operating range of the centrifugal compressor is less than 50%, the first variable diffuser and the second variable diffuser are adjusted in conjunction, and the axial width of the first flow channel and the second flow channel are both adjusted.

9. The control method for a centrifugal compressor according to claim 8, characterized in that, The process of coordinated adjustment between the first variable diffuser and the second variable diffuser includes: When the centrifugal compressor experiences surge under a certain operating condition, the second variable diffuser is first adjusted to gradually reduce the axial width of the second flow channel until the surge is eliminated. When the axial width of the second flow channel is adjusted to the minimum, the centrifugal compressor still surges. Further adjustment of the first variable diffuser gradually reduces the axial width of the first flow channel until the surge is eliminated.

10. The control method for a centrifugal compressor according to any one of claims 6-9, characterized in that, The axial width of the first impeller outlet is b1, the axial width of the second impeller outlet is b2, the adjustment range of the axial width of the first flow channel is 0.5b1~0.95b1, and the adjustment range of the axial width of the second flow channel is 0.5b2~0.95b2.

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