Supercritical carbon dioxide centrifugal compressor and its aerodynamic design method

Abstract

This invention relates to the field of centrifugal compressor technology, specifically disclosing a supercritical carbon dioxide centrifugal compressor and its aerodynamic design method. The centrifugal compressor includes a centrifugal impeller; on the circumferential direction of the impeller disk, multiple main blades and multiple branch blades are arranged in an alternating structure, and the inlet portion of each branch blade is recessed and offset from the inlet portion of each main blade along the axial direction of the impeller disk. This invention, through optimized design of the centrifugal impeller, effectively avoids condensation at the inlet of the centrifugal compressor under near-critical conditions for S-CO2, which is beneficial for improving compressor efficiency, widening the operating range, and allowing for the selection of inlet parameters that are closer to the critical point. This, in turn, effectively improves the cycle efficiency of the S-CO2 power generation system, possessing significant engineering importance and broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of centrifugal compressor technology, specifically a supercritical carbon dioxide centrifugal compressor and its aerodynamic design method. Background Technology

[0002] Supercritical carbon dioxide (S-CO2) Brayton power cycle systems effectively balance efficiency and safety, demonstrating significant application value not only in fossil fuel power generation but also promising prospects in nuclear, geothermal, and solar power generation. As a core component of the S-CO2 Brayton power cycle system, a thorough understanding and optimized design of the centrifugal compressor's aerodynamic performance can effectively improve its operational efficiency and safety.

[0003] S-CO2 possesses unique physical properties, combining the density, heat transfer, and heat carrying capacity of a liquid with the flow properties of a gas, making it an ideal circulating working fluid. Centrifugal compressors using S-CO2 are characterized by smaller size and lower power consumption. Furthermore, the properties of S-CO2 change as it flows through different locations within the centrifugal compressor, resulting in varying performance characteristics of the compressor.

[0004] Theoretical research and practical experience have shown that the closer the parameters at the inlet of the centrifugal compressor are to the supercritical point of CO2 (pressure 7.38 MPa, temperature 31.1℃), the higher the circulation efficiency of the entire system. However, due to the property distortion of CO2 near the critical point, the closer to the critical point, the more drastic the property fluctuations become. This can easily lead to localized condensation at the inlet of the centrifugal compressor, which directly affects the operating efficiency and even the operational safety of the centrifugal compressor, greatly increasing the design difficulty of the centrifugal compressor.

[0005] Therefore, optimizing the design of centrifugal compressors to effectively avoid condensation of S-CO2 at the compressor inlet under near-critical conditions, thereby improving compressor operating efficiency and expanding its operating range, has significant technical and economic implications. Summary of the Invention

[0006] The technical objective of this invention is to provide a supercritical carbon dioxide centrifugal compressor that can effectively avoid condensation of S-CO2 at the inlet of the centrifugal compressor under near-critical conditions, thereby improving the operating efficiency and expanding the operating range of the centrifugal compressor, and to address the special characteristics of the aforementioned S-CO2 Brayton power cycle system and the properties of S-CO2 in the centrifugal compressor.

[0007] The technical objective of this invention is achieved through the following technical solution: a supercritical carbon dioxide centrifugal compressor, comprising a centrifugal impeller; The centrifugal impeller has multiple main blades and multiple diverter blades arranged alternately in the circumferential direction of the impeller disk, and the inlet portion of each diverter blade is recessed and offset from the inlet portion of each main blade along the axial direction of the impeller disk.

[0008] Furthermore, the thickness of the second inlet portion of the diverter blade is less than the thickness of the first inlet portion of the main blade.

[0009] Furthermore, the second outlet portion of the diverter blade is aligned with the first outlet portion of the main blade along the axial direction of the disc.

[0010] Furthermore, the axial profile of the diverter blade, except for the inlet portion, is consistent with the axial profile of the main blade.

[0011] A pneumatic design method for a supercritical carbon dioxide centrifugal compressor, wherein the pneumatic design method is based on the supercritical carbon dioxide centrifugal compressor described above, and optimizes the aerodynamic performance to avoid condensation at the inlet of the centrifugal compressor under near-critical conditions. The aerodynamic design method includes the following specific processes: The axial width of the splitter blade along the axis of the impeller is set to a; The axial width of the main blade along the wheel axis is set to b; The axial width coefficient x of the splitter blade is set to satisfy the following relationship: x = a / b and x < 1.

[0012] Furthermore, the axial width coefficient x of the diverter blade ranges from 0.62 to 0.73.

[0013] Furthermore, the aerodynamic design method also includes the following specific processes: The angle between the splitter blade and the adjacent pressure-side main blade is set to c; The angle between the diverter blade and the adjacent suction side main blade is set to d; The circumferential angle coefficient y of the splitter blades is set to satisfy the following relationship: y = c / (c+d) and y < 1.

[0014] Furthermore, the circumferential angle coefficient y of the diverter blade ranges from 0.50 to 0.62.

[0015] Furthermore, the aerodynamic design method also includes the following specific processes: Three-dimensional simulation was used for modeling and analysis verification. The actual physical properties of CO2 were introduced into the numerical simulation process, and the physical properties near the critical point were locally refined to achieve rapid iterative design of supercritical carbon dioxide compressors near the critical point.

[0016] Furthermore, the encryption range of the local encryption is 6.5MPa to 8.5MPa pressure and 300K to 315K temperature.

[0017] The beneficial technical effects of the present invention are as follows: The above-mentioned technical measures, addressing the specific characteristics of the S-CO2 Brayton power cycle system and the properties of S-CO2 within the centrifugal compressor, involve adding a flow-diverting blade to the circumferential direction of the centrifugal impeller. Based on the addition of the flow-diverting blade, the inlet portion of the flow-diverting blade differs from the inlet portion of the main blade in the axial direction of the impeller. This difference is determined by the relative positions constrained by the axial width coefficient and the circumferential angle coefficient, thereby adjusting the variation law of the channel area, reducing the peak Mach number in the blade inlet region, and preventing condensation when the working fluid pressure and temperature suddenly drop and the system leaves the supercritical region.

[0018] Thus, the above-mentioned technical measures, through optimized design of the centrifugal impeller of the centrifugal compressor and verified by three-dimensional simulation analysis, can effectively avoid the condensation phenomenon at the inlet of the centrifugal compressor under near-critical conditions of S-CO2. This is beneficial to improving compressor efficiency and expanding the operating range. It also enables the selection of inlet parameters of the centrifugal compressor to be closer to the critical point, thereby effectively improving the cycle efficiency of the S-CO2 power generation system. This has important engineering significance and broad application prospects. Attached Figure Description

[0019] Figure 1 This is a three-dimensional model schematic diagram (stereoscopic view) of the centrifugal impeller of the present invention.

[0020] Figure 2 This is a schematic diagram of another three-dimensional model of the centrifugal impeller of the present invention (planar view).

[0021] Figure 3 This is a partial meridional plane schematic diagram of the centrifugal impeller of the present invention.

[0022] The symbols in the diagram mean: 1—centrifugal impeller; 11—disc; 12—main blade; 12-1—pressure side main blade; 12-2—suction side main blade; 13—diverter blade; 14—inlet section one; 15—inlet section two; 16—outlet section one; 17—outlet section two. Detailed Implementation

[0023] This invention relates to the field of centrifugal compressor technology, specifically a supercritical carbon dioxide (i.e., S-CO2) centrifugal compressor, and the aerodynamic design method of this centrifugal compressor. The following description is in conjunction with the accompanying drawings. Figure 1 , Figure 2 and Figure 3 The technical solution of this invention will be clearly and thoroughly explained.

[0024] It should be noted that the accompanying drawings of this invention are schematic, and unnecessary details have been simplified to clarify the technical objectives of this invention, so as to avoid obscuring the technical solutions contributed by this invention to the prior art. Furthermore, the terms "approximately" or "basically" used below to refer to quantities or fit relationships mean that reasonable assembly and processing errors are allowed in the industry, and do not literally describe absolute quantities or fit relationships.

[0025] See Figure 1 , Figure 2 and Figure 3 As shown, the present invention is a supercritical carbon dioxide (i.e., S-CO2) centrifugal compressor, which includes a centrifugal impeller 1. The centrifugal impeller 1 is mainly composed of a disc 11 and multiple blades arranged circumferentially around the outer periphery of the disc 11. The profile of each blade is a three-dimensional twisted structure in the axial, circumferential and radial directions (the specific blade profile is not the technical contribution of the present invention). Except as specifically emphasized below, the profiles of each blade are consistent.

[0026] To eliminate localized condensation at the compressor inlet and improve compressor operating efficiency and safety, the blades arranged on the outer periphery of the aforementioned impeller 11 are divided into multiple main blades 12 and multiple branch blades 13 based on the difference in the position of the inlet part in the axial direction of the impeller 11. The number of main blades 12 and branch blades 13 is the same, and each main blade 12 and each branch blade 13 is arranged in an alternating structure in the circumferential direction of the impeller 11.

[0027] More specifically, each main blade 12 and each branch blade 13 are aligned with the impeller outlet root as the alignment reference. The outlet portion 17 of the branch blade 13 is aligned with the outlet portion 16 of the main blade 12 along the axis of the impeller 11. However, the inlet portion 15 of the branch blade 13 is recessed and offset from the inlet portion 14 of the main blade 12 along the axis of the impeller 11. This makes the axial width of the branch blade 13 along the impeller 11 smaller than the axial width of the main blade 12 along the impeller 11. Thus, the branch blade 13 with a smaller axial width and the main blade 12 with a larger axial width are arranged alternately on the outer periphery of the impeller 11. Except for the difference in the inlet portion, the axial profile of the branch blade 13 is basically consistent with the axial profile of the main blade 12.

[0028] In addition to the axial position, the differences in the inlet portion also include the difference in blade thickness. Under the condition of meeting the structural strength technical requirements, the thickness of the inlet portion of the splitter blade 13 should be reduced as much as possible. That is, the thickness of the second inlet portion 15 of the splitter blade 13 should be less than the thickness of the first inlet portion 14 of the main blade 12.

[0029] The above is the basic structure of the centrifugal impeller 1 of the centrifugal compressor of the present invention. In order to obtain the best aerodynamic performance and avoid the condensation phenomenon of S-CO2 at the inlet of the centrifugal compressor under near-critical conditions, the above centrifugal impeller 1 structure is optimized by the following aerodynamic design method.

[0030] The aerodynamic design method of the present invention includes the following specific processes: The axial width of the flow divider blade 13 along the axis of the impeller 11 is set as a (that is, the axial distance between the middle diameter of the inlet portion 15 of the flow divider blade 13 and the root of the impeller outlet). The axial width of the main blade 12 along the axis of the impeller 11 is set to b (that is, the axial distance between the inlet portion 14 of the main blade 12 and the root of the impeller outlet). The axial width coefficient x of the splitter blade 13 is set to satisfy the following relationship: x = a / b and x < 1; The angle between the flow divider blade 13 and the adjacent pressure-side main blade 12-1 is set to c; The angle between the diversion blade 13 and the adjacent suction side main blade 12-2 is set as d; Set the circumferential angle coefficient y of the splitter blade 13 to satisfy the following relationship: y = c / (c + d) and y < 1.

[0031] As a preferred option after repeated verification, the axial width coefficient x of the above-mentioned flow divider blade 13 is in the range of 0.62 to 0.73; the circumferential angle coefficient y of the above-mentioned flow divider blade 13 is in the range of 0.50 to 0.62.

[0032] The aforementioned aerodynamic design method also includes subsequent three-dimensional simulation (i.e., CFD technology) analysis and verification, specifically including: Based on the design parameters of the centrifugal compressor, the basic aerodynamic scheme of the centrifugal impeller is designed, and the starting position of the splitting blades is selected according to the above-mentioned optimization coefficients. Three-dimensional simulation was used for corresponding modeling and analysis verification. The actual physical properties of CO2 are introduced into the numerical simulation process to locally refine the physical properties near the critical point. The preferred refinement range is 6.5MPa~8.5MPa and 300K~315K. To achieve rapid iterative design of a near-critical supercritical carbon dioxide compressor, it is possible to accurately analyze whether condensation occurs in the centrifugal impeller.

[0033] The aforementioned design for the S-CO2 centrifugal compressor involves adding diverter blades circumferentially to the centrifugal impeller. The total number of blades can be determined reasonably according to the design parameters of the centrifugal compressor. The addition of diverter blades differentiates the inlet locations of the diverter blades from those of the main blades along the impeller's axial direction. This differentiation is not random but determined by the combined constraints of the relative positions under the axial width coefficient and the circumferential angle coefficient. More preferably, this differentiation is determined by the combined constraints of the relative positions under the axial width coefficient, the circumferential angle coefficient, and the blade thickness. The blade thickness, which is involved in the constraint determination, can only be determined based on the qualitative principles of satisfying the centrifugal compressor design parameters and cannot be absolute. Thus, through optimized design, condensation at the inlet of the centrifugal compressor under near-critical conditions can be effectively avoided, improving compressor efficiency, expanding the operating range, and allowing for the selection of compressor inlet parameters that are conducive to approaching the critical point. This effectively improves the cycle efficiency of the S-CO2 power generation system, possessing significant engineering importance and broad application prospects.

[0034] The above specific technical solutions are only used to illustrate the present invention, and are not intended to limit it.

[0035] Although the present invention has been described in detail with reference to the specific technical solutions described above, those skilled in the art should understand that modifications can still be made to the specific technical solutions described above, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the present invention.

Claims

1. A supercritical carbon dioxide centrifugal compressor, comprising a centrifugal impeller (1); Its features are: The centrifugal impeller (1) has multiple main blades (12) and multiple diversion blades (13) arranged in an alternating structure on the circumferential direction of the impeller (11), and the inlet portion (15) of each diversion blade (13) is recessed and offset from the inlet portion (14) of each main blade (12) along the axial direction of the impeller (11).

2. The supercritical carbon dioxide centrifugal compressor according to claim 1, characterized in that: The thickness of the second inlet portion (15) of the diverter blade (13) is less than the thickness of the first inlet portion (14) of the main blade (12).

3. The supercritical carbon dioxide centrifugal compressor according to claim 1, characterized in that: The second outlet portion (17) of the splitter blade (13) is aligned with the first outlet portion (16) of the main blade (12) along the axial direction of the wheel (11).

4. The supercritical carbon dioxide centrifugal compressor according to any one of claims 1 to 3, characterized in that: The axial profile of the splitter blade (13), except for the inlet portion, is consistent with the axial profile of the main blade (12).

5. A pneumatic design method for a supercritical carbon dioxide centrifugal compressor, characterized in that: The aerodynamic design method is based on the supercritical carbon dioxide centrifugal compressor of any one of claims 1 to 4, and optimizes the aerodynamic performance to avoid condensation at the inlet of the centrifugal compressor under near-critical conditions. The aerodynamic design method includes the following specific processes: The axial width of the splitter blade (13) along the axis of the wheel disk (11) is set to a; The axial width of the main blade (12) along the axis of the disk (11) is set to b; The axial width coefficient x of the splitter blade (13) is set to satisfy the following relationship: x = a / b and x < 1.

6. The aerodynamic design method for a supercritical carbon dioxide centrifugal compressor according to claim 5, characterized in that: The axial width coefficient x of the splitter blade (13) ranges from 0.62 to 0.

73.

7. The aerodynamic design method for a supercritical carbon dioxide centrifugal compressor according to claim 5, characterized in that: The aerodynamic design method also includes the following specific processes: The angle between the splitter blade (13) and the adjacent pressure side main blade (12-1) is set to c; The angle between the diversion blade (13) and the adjacent suction side main blade (12-2) is set as d; The circumferential angle coefficient y of the splitter blade (13) is set to satisfy the following relationship: y = c / (c+d) and y < 1.

8. The aerodynamic design method for a supercritical carbon dioxide centrifugal compressor according to claim 7, characterized in that: The circumferential angle coefficient y of the splitter blade (13) ranges from 0.50 to 0.

62.

9. The aerodynamic design method for a supercritical carbon dioxide centrifugal compressor according to any one of claims 5 to 8, characterized in that: The aerodynamic design method also includes the following specific processes: Three-dimensional simulation was used for modeling and analysis verification. The actual physical properties of CO2 were introduced into the numerical simulation process, and the physical properties near the critical point were locally refined to achieve rapid iterative design of supercritical carbon dioxide centrifugal compressors near the critical point.

10. The aerodynamic design method for a supercritical carbon dioxide centrifugal compressor according to claim 9, characterized in that: The local encryption range is a pressure of 6.5MPa to 8.5MPa and a temperature of 300K to 315K.

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