Supercritical carbon dioxide centrifugal compressor

Abstract

The application belongs to the field of compressors and discloses a supercritical carbon dioxide centrifugal compressor, which comprises an impeller, a radial diffuser and a volute, the impeller comprises a hub, a plurality of long blades and a plurality of short blades, the plurality of long blades are uniformly and spacedly arranged on one side of the hub along the circumferential direction of the hub, one short blade is arranged between every two adjacent long blades, one end of the long blade away from the center of the hub and one end of the short blade away from the center of the hub are located on the same circle, and the length of the short blade along the radial direction of the hub is smaller than the length of the long blade along the radial direction of the hub. The length of the short blade along the radial direction of the hub is smaller than the length of the long blade along the radial direction of the hub, the short blade can effectively control the boundary layer flow on the surface of the blade, inhibit the flow separation of the blade head, weaken the vortex and backflow, improve the flow field and improve the stability of the compressor, so that the choked flow and the stable working range are increased, and the surge margin of the compressor is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of compressors, in particular to a supercritical carbon dioxide centrifugal compressor. BACKGROUND

[0002] Supercritical carbon dioxide Brayton cycle power generation technology is a rapidly developing frontier technology in recent years. The technology is a closed cycle turbine power generation technology using supercritical carbon dioxide as the working medium. The main features of the technology are as follows: the cycle working medium is carbon dioxide, the thermodynamic state of which is maintained near and above the critical point, and the technology has the advantages of high cycle efficiency, high power density, and wide applicability of heat sources.

[0003] The main function of the supercritical carbon dioxide compressor is to increase the pressure of the working medium in the system, and it is a core component in the supercritical carbon dioxide power generation system. The supercritical carbon dioxide compressor has the characteristics of high speed and complex operating conditions.

[0004] Compressor surge is a low-frequency, high-amplitude airflow oscillation phenomenon that occurs along the flow direction of the compressor. From the characteristic curve of the compressor, the compressor has a certain flow stable working range. When the working medium flow is small to a certain extent, surge will occur, causing the working medium flow to fluctuate, the pressure to be high and low, and even causing the working medium to flow backward, accompanied by strong mechanical vibration, affecting the safety of the entire power generation system.

[0005] The supercritical carbon dioxide compressor is more prone to changes in flow due to the sharp changes in density and other properties near the critical point, which can lead to surge. Therefore, the surge phenomenon of the supercritical carbon dioxide compressor should be paid more attention to.

[0006] The surge of the compressor can be measured by the surge margin M. The larger the surge margin, the wider the range of stable operation of the compressor. The calculation formula of the surge margin M is as follows:

[0007]

[0008] wherein, is the total pressure ratio at the surge point; is the total pressure ratio at the design point; m d is the mass flow rate at the design point, with the unit of kg / s; m s is the mass flow rate at the surge point, with the unit of kg / s. The surge margin of a general conventional compressor is 20% to 30%.

[0009] In 2010, Sandia National Laboratories built a supercritical carbon dioxide compressor test platform, and carried out experimental research on the supercritical carbon dioxide compressor designed by it. The results prove the feasibility of supercritical carbon dioxide compression near the critical point. Domestic research on supercritical carbon dioxide compressors started late. In recent years, research on supercritical carbon dioxide centrifugal compressors has gradually increased, but research on improving the surge margin of supercritical carbon dioxide compressors is still relatively small. At present, no institution has solved or disclosed a wide surge margin centrifugal compressor using supercritical carbon dioxide as the working medium. SUMMARY

[0010] The purpose of the present application is to provide a supercritical carbon dioxide centrifugal compressor, which can improve the surge margin of the compressor.

[0011] The technical solutions provided by the present application are as follows:

[0012] A supercritical carbon dioxide centrifugal compressor, comprising an impeller, a radial diffuser and a volute, the impeller comprising a hub, a plurality of long blades and a plurality of short blades, the plurality of long blades being uniformly spaced along the circumferential direction of the hub and arranged on one side of the hub, one short blade being arranged between every two adjacent long blades, the end of the long blade away from the center of the hub and the end of the short blade away from the center of the hub being located on the same circle, and the length of the short blade along the radial direction of the hub being smaller than the length of the long blade along the radial direction of the hub.

[0013] In some embodiments, the length of the short blade along the radial direction of the hub is 50% to 70% of the length of the long blade along the radial direction of the hub.

[0014] In some embodiments, the shape of the short blade is the same as that of the long blade.

[0015] In some embodiments, the short blade is arranged at the center of the two adjacent long blades.

[0016] In some embodiments, a hub cover is further arranged on the impeller, and the ratio of the radius of the hub to the radius of the hub cover is 0.3 to 0.5.

[0017] In some embodiments, the tip clearance of the impeller is less than or equal to 0.3 mm.

[0018] In some embodiments, the radial diffuser is composed of two parallel wall surfaces, forming a working fluid flow channel.

[0019] In some embodiments, the radial diffuser is a vaneless diffuser.

[0020] In some embodiments, the inlet width and the outlet width of the radial diffuser are the same as the outlet width of the impeller, respectively.

[0021] In some embodiments, the ratio of the outlet radius of the radial diffuser to the inlet radius of the radial diffuser is 1.5-1.7.

[0022] The technical effect of the present application is that:

[0023] (1) The length of the short blade along the hub radius is less than the length of the long blade along the hub radius, and the short blade can effectively control the boundary layer flow on the blade surface, suppress the flow separation at the blade head, weaken the vortex and backflow, improve the flow field and increase the stability of the compressor, thereby increasing the choked flow and the stable working range, and further improving the surge margin of the compressor.

[0024] (2) The tip clearance t of the supercritical carbon dioxide centrifugal impeller is ≤0.3mm, so as to reduce the tip clearance leakage flow loss and improve the surge margin.

[0025] (3) The radial diffuser is a bladeless diffuser, and the diffuser degree is small, which can reduce the risk of flow separation and avoid the phenomenon that the blade surface in the flow passage of the blade diffuser is prone to flow separation, leading to flow stall and even compressor surge, so that the surge margin of the supercritical carbon dioxide compressor can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0026] The present application will be further described in detail below in combination with the drawings and specific embodiments:

[0027] Figure 1 is a cross-sectional schematic view of a supercritical carbon dioxide centrifugal compressor provided by an embodiment of the present application;

[0028] Figure 2 is a schematic view of an impeller provided by an embodiment of the present application;

[0029] Figure 3 is a schematic view of an impeller inlet provided by an embodiment of the present application;

[0030] Figure 4 is a schematic view of a blade tip clearance provided by an embodiment of the present application;

[0031] Figure 5 is a schematic view of an impeller and a radial diffuser provided by an embodiment of the present application.

[0032] BRIEF DESCRIPTION OF DRAWINGS

[0033] 10, impeller; 11, hub; 12, long blade; 121, first long blade; 122, second long blade; 13, short blade; 14, impeller cover; 20, radial diffuser; 21, hub wall; 22, shroud wall; 30, volute. DETAILED DESCRIPTION

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] In order to make the drawing simple, only the parts related to the present application are shown in the drawings, which do not represent the actual structure of the product. In addition, in order to make the drawing simple and easy to understand, in some drawings, only one of the parts with the same structure or function is shown schematically, or only one of them is marked. In this document, "one" not only means "only one", but also means "more than one" situation.

[0036] It should be further understood that the term "and / or" used in the present application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0037] In this document, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0038] In addition, in the description of the present application, the terms "first", "second" and the like are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0039] In one embodiment of the present application, as shown in Figure 1 A supercritical carbon dioxide centrifugal compressor, comprising an impeller 10, a radial diffuser 20 and a volute 30, the impeller 10 communicates with the radial diffuser 20, the radial diffuser 20 communicates with the volute 30, when the impeller 10 rotates, the working medium is sucked into and compressed by the impeller 10, forced to enter the radial diffuser 20, and then enter the volute 30, so as to be delivered to an intake manifold of an engine at an elevated pressure.

[0040] The impeller 10 functions to work on the carbon dioxide working medium to increase the working medium pressure, and the radial diffuser 20 functions to convert the dynamic pressure energy of the high-pressure high-speed working medium at the outlet of the impeller 10 into static pressure energy, so as to further increase the working medium pressure and reduce the working medium flow rate, so as to reduce the flow loss along the downstream pipeline.

[0041] As shown in Figure 2 The impeller 10 includes a hub 11, a plurality of long blades 12 and a plurality of short blades 13. The plurality of long blades 12 are uniformly and spacedly arranged on one side of the hub 11 along the circumferential direction of the hub 11, and one short blade 13 is arranged between every two adjacent long blades 12. The end of the long blade 12 away from the center of the hub 11 and the end of the short blade 13 away from the center of the hub 11 are located on the same circle, and preferably, the end of the long blade 12 away from the center of the hub 11 and the end of the short blade 13 away from the center of the hub 11 can be located on the outer circle of the hub 11. The radial length of the short blade 13 along the hub 11 is less than the radial length of the long blade 12 along the hub 11.

[0042] The long blade 12 is the main blade of the impeller 10, and the short blade 13 can also be referred to as a splitter blade. The radial length of the short blade 13 along the hub 11 is less than the radial length of the long blade 12 along the hub 11. The short blade 13 can effectively control the boundary layer flow on the blade surface, suppress the flow separation at the blade head, weaken the vortex and backflow, improve the flow field and improve the stability of the compressor, thereby increasing the choked flow and the stable working range, and further improving the surge margin of the compressor.

[0043] The supercritical carbon dioxide centrifugal compressor can obviously reduce the airflow separation and secondary loss in the compressor and improve the surge margin of the supercritical carbon dioxide compressor. The supercritical carbon dioxide centrifugal compressor has a surge margin of ≥50%, which can meet the safe and stable operation requirements of the supercritical carbon dioxide unit.

[0044] Preferably, the radial length of the short blade 13 along the hub 11 is 50% to 70% of the radial length of the long blade 12 along the hub 11. The shape of the short blade 13 is the same as that of the long blade 12. When the shape of the short blade 13 is the same as that of the long blade 12 and the length of the short blade 13 is 50% to 70% of the length of the long blade 12, the short blade 13 has a better effect of weakening the vortex and backflow, and has a better effect of improving the surge margin of the compressor.

[0045] In some embodiments, a short blade 13 is arranged at the center of two adjacent long blades 12. The short blade 13 has the best effect of blade head flow separation when arranged at the center of two adjacent long blades 12. For example, two adjacent long blades 12 are a first long blade 121 and a second long blade 122 in sequence along the rotation direction of the impeller 10, the short blade 13 is arranged between the first long blade 121 and the second long blade 122, assuming that the impeller 10 rotates counterclockwise, the first long blade 121 is below the short blade 13, the second long blade 122 is above the short blade 13, and the distance from any point on the short blade 13 to the second long blade 122 is equal to the distance from the same point on the short blade 13 to the first long blade 121.

[0046] As shown in Figure 3 , the impeller 10 is further provided with an impeller cover 14, and the ratio of the radius R1 of the hub 11 to the radius R2 of the impeller cover 14 is 0.3-0.5. Under the condition of satisfying the rigidity of the shaft, reducing the radius of the hub 11 can reduce the flow velocity of the inlet gas flow, so as to reduce the flow loss of the impeller 10.

[0047] Further, the tip clearance t of the impeller 10 is less than or equal to 0.3mm, so as to reduce the tip clearance leakage flow loss and improve the surge margin. As shown in Figure 4 , the tip clearance t of the impeller 10 is the gap between the impeller 10 and the wall surface of the radial diffuser 20, the smaller the tip clearance, the smaller the leakage flow loss, so as to effectively improve the surge margin.

[0048] Further, the radial diffuser 20 of the present embodiment is a vaneless diffuser, which is composed of two smooth wall surfaces, as shown in Figure 5 , for example, which is defined by a hub wall 21 and a shroud wall 22, so as to form a flow channel for the working medium leaving the impeller 10, the hub wall 21 can be a part of a bearing housing or a back plate of a compressor housing, and the shroud wall 22 is a part of a compressor housing.

[0049] The radial diffuser 20 is adjacent to the impeller 10 and has an inlet at the top end of the impeller 10, and has an outlet at the end away from the inlet of the radial diffuser 20, the working medium from the impeller 10 enters the radial diffuser 20 from the inlet of the radial diffuser 20, and is discharged from the outlet of the radial diffuser 20 and then enters the volute 30.

[0050] The inlet width B2 and the outlet width B3 of the radial diffuser 20 are the same as the outlet width B1 of the impeller 10, and the ratio of the outlet radius R4 of the radial diffuser 20 to the inlet radius R3 is 1.5-1.7, so as to reduce the diffusing degree of the radial diffuser 20, wherein the outlet radius of the radial diffuser 20 refers to the distance from the outlet of the radial diffuser 20 to the central axis of the impeller 10, and the inlet radius of the radial diffuser 20 refers to the distance from the inlet of the radial diffuser 20 to the central axis of the impeller 10. The working medium enters the radial diffuser 20 in a spiral shape under the action of the impeller 10, and has a rotational speed, so that the working medium still flows along a logarithmic spiral path in the flow passage of the radial diffuser 20. Since the diffusing degree of the radial diffuser 20 is small, the risk of flow separation can be reduced, and the phenomenon that flow separation easily occurs on the surface of the blade in the flow passage of the blade diffuser, which leads to flow stall or even compressor surge, can be avoided, so that the surge margin of the supercritical carbon dioxide compressor can be improved.

[0051] The above only describes the preferred embodiments of the present application, and it should be pointed out that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A centrifugal compressor for supercritical carbon dioxide comprising an impeller, a radial diffuser and a volute, characterised in that, The impeller comprises a hub, a plurality of long blades and a plurality of short blades, the plurality of long blades are evenly spaced on one side of the hub along the circumferential direction of the hub, one short blade is arranged between every two adjacent long blades, the end of the long blade away from the center of the hub is on the same circle with the end of the short blade away from the center of the hub, and the length of the short blade along the radial direction of the hub is less than the length of the long blade along the radial direction of the hub; The length of the short blade along the radial direction of the hub is 50% to 70% of the length of the long blade along the radial direction of the hub; The short blade is arranged at the center of the two adjacent long blades; The impeller further comprises a cover, the cover is arranged on the impeller, and the ratio of the radius of the hub to the radius of the cover is 0.3 to 0.5; The tip clearance of the impeller is less than or equal to 0.3 mm; The radial diffuser is composed of two parallel wall surfaces, forming a working medium flow channel; The ratio of the outlet radius of the radial diffuser to the inlet radius of the radial diffuser is 1.5 to 1.

7.

2. A supercritical carbon dioxide centrifugal compressor according to claim 1, wherein The shape of the short blade is the same as that of the long blade.

3. A supercritical carbon dioxide centrifugal compressor according to claim 1, wherein The radial diffuser is a bladeless diffuser.

4. A supercritical carbon dioxide centrifugal compressor according to claim 1, wherein The inlet width and the outlet width of the radial diffuser are the same as the outlet width of the impeller, respectively.

5. A supercritical carbon dioxide centrifugal compressor according to claim 1, wherein The end of the long blade away from the center of the hub and the end of the short blade away from the center of the hub are both on the outer circle of the hub.

6. A supercritical carbon dioxide centrifugal compressor according to claim 1, wherein The tip clearance of the impeller is the clearance between the impeller and the wall surface of the radial diffuser.

7. A supercritical carbon dioxide centrifugal compressor according to claim 1, wherein The outlet radius of the radial diffuser refers to the distance between the outlet of the radial diffuser and the center axis of the impeller, and the inlet radius of the radial diffuser refers to the distance between the inlet of the radial diffuser and the center axis of the impeller.

Images