Axial force balance structure of axial flow-centrifugal combined compressor and application of axial force balance structure

Abstract

The invention discloses an axial force balance structure of an axial flow-centrifugal combined compressor and application of the axial force balance structure, and the structure comprises a combined rotor, an axial flow-centrifugal combined compressor and a centrifugal pump, the radial bearing and the thrust bearing are used for supporting the rotor and bearing axial force; the axial flow blade row and the centrifugal impeller are fixedly connected to the front and rear sections of the rotor respectively; the plurality of groups of vent hole structures are arranged on the rotor reducing part and are communicated with the intermediate shaft cavity; the multiple sets of sealing ring structures form a plurality of sealing cavities used for controlling the pressure in the cavities. By selectively forming the second vent hole and / or the third vent hole, high-pressure gas in the fourth sealing cavity or the fifth sealing cavity is introduced into the first sealing cavity, the pressure of the first sealing cavity is increased, backward axial thrust is generated, forward axial thrust generated when the rotor operates is counteracted, and balance of axial force is achieved. The compressor is compact in structure, free of external air entraining, capable of effectively balancing axial force and improving the stability and efficiency of the compressor, and suitable for a high-power compressed air energy storage system.

Description

Technical Field

[0001] The present invention relates to an axial force balance structure for an axial - centrifugal combined compressor, and particularly to a pneumatic axial force balance structure for an axial - centrifugal combined compressor applied to compressed air energy storage, belonging to the technical field of compressed air energy storage compressors. Background Art

[0002] With the development of compressed air energy storage systems towards high - power, higher requirements are put forward for parameters such as the flow rate and pressure ratio of compressors. The axial - centrifugal combined compressor solution has the advantages of large flow rate and high pressure ratio and is very suitable for high - power compressed air energy storage systems, but it poses higher requirements for the axial force balance device of this combined compressor.

[0003] For a conventional rotor system with small flow rate and low pressure ratio, the axial force generated by the impeller and the rotating shaft can directly act on the thrust bearing. However, for the rotor of this large - flow - rate and high - pressure - ratio compressor, the pneumatic axial force may exceed the bearing's load - bearing range. If not properly handled, it is extremely likely to cause serious consequences such as bearing overload, axial displacement, and even instability of the whole machine. To solve this problem, an axial force balance disk is generally set in the prior art, and external pipeline air is introduced to form a sufficient differential pressure on both sides of the balance disk to reduce the overall axial force of the rotor. However, this solution has the following obvious disadvantages. First, the balance disk structure increases the rotor complexity and bearing span, deteriorating the dynamic characteristics of the rotor. Second, the external air - intake pipeline system is complex, which not only increases the manufacturing cost but also reduces the system reliability. Finally, the balance disk and the air - intake system will generate additional energy losses, reducing the overall efficiency of the compressor. In addition, the adjustment flexibility of the traditional balance structure is poor and it is difficult to cope with the change of axial force under different working conditions.

[0004] In the prior art, taking the balance disk structure for adjusting the axial force of a high - pressure rotor system of an engine disclosed in Chinese Patent CN111255522A as an example, it adjusts the axial force by changing the differential pressure on both sides of the balance disk. However, this solution usually relies on external air intake, the system is relatively complex, and the selection of the size and position of the balance disk has a great influence on the dynamic characteristics of the rotor. In addition, Patent CN118881602A discloses a self - adjusting structure for the axial force of a compressor, which realizes axial force balance through the coordinated action of a high - pressure chamber, a low - pressure chamber, and a pressure - relief chamber. However, it needs to be equipped with a complex sealing honeycomb structure and multi - stage air - intake channels, resulting in an increase in the number of sealing interfaces, an increased risk of leakage, and a demanding processing accuracy requirement for the honeycomb structure.

[0005] As described above, the axial force balance device of the existing axial-flow centrifugal combined compressor will lead to a complex rotor structure and an increased bearing span. In addition, in the existing design, to ensure sufficient pressure difference on both sides of the balance disk, a special gas path structure needs to be designed on both sides of the balance disk, resulting in a more complex compressor system. Therefore, how to achieve efficient balance and dynamic adjustment of the axial force through innovative structural design while ensuring the aerodynamic performance, and at the same time avoid the increase in span and complexity brought by the traditional thrust disk has become an urgent technical problem to be solved in the technical field of compressed air energy storage compressors. Summary of the Invention

[0006] (1) Objectives of the Invention

[0007] To solve the above-mentioned technical problems such as the complex structure of the existing axial force balance device, the objective of the present invention is to provide an axial force balance structure for an axial-flow centrifugal combined compressor and an axial-flow centrifugal combined compressor adopting this structure. By arranging ventilation holes inside the rotor and constructing a connected shaft cavity to guide the airflow between different sealed cavities inside the compressor, it can meet the requirements of balancing the axial force, and the axial force can be reduced by adjusting the structure without affecting the compressor efficiency. The present invention does not adopt the traditional thrust disk structure, does not additionally increase the bearing span, and is easy to implement.

[0008] (2) Technical Solutions

[0009] To achieve the objective of the invention and solve its technical problems, the present invention adopts the following technical solutions:

[0010] The first objective of the present invention is to provide an axial force balance structure for an axial-flow centrifugal combined compressor, which is used for balancing the axial force of a large-flow high-pressure ratio axial-flow centrifugal combined compressor in a high-power compressed air energy storage system, and includes:

[0011] A combined rotor, including a front shaft section and a rear shaft section, which are tightly connected into one body, and a semi-hollow cavity with a closed front end and an open rear end is provided at the center of the front shaft section. A front-end groove recessed towards the rear end side is provided at the center of the front end of the rear shaft section. After the end faces of the semi-hollow cavity and the front-end groove are butted, a closed and axially extending intermediate shaft cavity is formed.

[0012] Multiple sets of vent hole structures, at least including a plurality of first vent holes arranged circumferentially on the reduced-diameter part of the front shaft section, a plurality of second vent holes and / or third vent holes arranged circumferentially on the reduced-diameter part of the rear shaft section, and each of the first vent holes, second vent holes, and third vent holes communicates with the intermediate shaft cavity. And among them, the reduced-diameter part of the front shaft section is formed between its front shaft shoulder and the main body part, the reduced-diameter part of the rear shaft section is formed on the shaft section between its main body part and the front connecting flange, and the second vent holes are arranged axially near the position of its front connecting flange, and the third vent holes are arranged near the position of its main body part;

[0013] Multiple sets of seal ring structures, including a plurality of seal rings arranged in sequence along the axial direction, including: a first seal ring and a second seal ring arranged on both sides of the first vent hole before and after, and form a first seal cavity between the reduced-diameter part of the front shaft section and the air seal body, and the second seal ring and the outer wall front-end groove of the front shaft section main body part and the air seal body cooperate to form a second seal cavity; a third seal ring and a fourth seal ring arranged on both sides of the second vent hole before and after, the third seal ring and the outer wall rear-end groove of the front shaft section main body part and the partition cooperate to form a third seal cavity, the third seal ring and the fourth seal ring form a fourth seal cavity with the reduced-diameter part of the rear shaft section and the partition, and the fourth seal ring and the back area of the centrifugal impeller disc form a fifth seal cavity;

[0014] Among them, the second vent hole is used to introduce the high-pressure gas in the fourth seal cavity into the first seal cavity, the third vent hole is used to introduce the high-pressure gas in the fifth seal cavity into the first seal cavity, and the air extraction path between different pressure sources is realized by selectively opening the second vent hole and / or the third vent hole, so as to increase the pressure of the first seal cavity and generate an axial thrust backward, offset the forward axial thrust generated by the axial flow blade row and other components during the operation of the rotor, and realize the balance of the axial force.

[0015] The second invention object of the present invention is to provide an axial-flow - centrifugal combined compressor provided with the above-mentioned axial force balance structure of the axial-flow - centrifugal combined compressor of the present invention.

[0016] (3) Technical effects

[0017] Compared with the prior art, the axial force balance structure of the axial-flow - centrifugal combined compressor of the present invention and its application have the following beneficial and remarkable technical effects:

[0018] (1) By setting a plurality of vent holes and seal cavities, the present invention realizes internal air extraction by using the pressure difference between different seal cavities, so that without increasing the bearing span and system complexity, the axial force of the axial-flow - centrifugal combined compressor can be effectively reduced and adjusted;

[0019] (2) The rotating shaft of the present invention adopts a hollow shaft design, which saves raw materials and reduces costs. At the same time, it improves the bearing force condition and the rotor dynamic performance. Moreover, the present invention does not adopt the traditional thrust disc structure, reducing the component processing cost and providing the safety of the system. At the same time, the overall axial force is adjusted by bleeding air and changing the shaft diameter at the sealing ring, and there are various ways to adjust the axial force. And this internal air bleeding method avoids the additional energy loss brought by the traditional balance disc structure, improving the overall efficiency of the compressor.

[0020] (3) By selectively opening different ventilation holes, the compressor of the present invention can adjust the balance of the axial force according to different working conditions, meet a wider range of usage requirements, improve the flexibility and adaptability of the system, and has significant technical advantages in improving the operation efficiency, stability and reducing the maintenance cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which:

[0022] Figure 1 is a schematic diagram of the axial force balance structure of the axial-flow and centrifugal combined compressor of the present invention;

[0023] Figure 2 is a schematic diagram of the axial force balance principle of the compressor;

[0024] Figure 3 is a schematic diagram of the axial-flow and centrifugal combined compressor structure of the present invention;

[0025] Description of the reference numerals: front shaft section 10, semi-hollow cavity 11, front end shaft shoulder 12 of the front shaft section, main body part 13 of the front shaft section, variable diameter part 14 of the front shaft section, front end groove 15 on the outer wall of the main body part of the front shaft section, rear end groove 16 on the outer wall of the main body part of the front shaft section, rear shaft section 20, front end groove 21, rear end shaft shoulder 22 of the rear shaft section, main body part 23 of the rear shaft section, variable diameter part 24 of the rear shaft section, intermediate shaft cavity 30, first ventilation hole 31, second ventilation hole 32, third ventilation hole 33, sealing ring structure 40, first sealing ring 41, second sealing ring 42, third sealing ring 43, fourth sealing ring 44, sealing cavity 50, first sealing cavity 51, second sealing cavity 52, third sealing cavity 53, fourth sealing cavity 54, fifth sealing cavity 55, sixth sealing cavity 56, radial and axial support structure 60, first radial bearing 61, second radial bearing 62, thrust bearing 63, front bearing housing 64, rear bearing housing 65, axial flow blade row 70, axial flow inlet cylinder 71, stator vane carrier 72, axial flow exhaust cylinder 73, centrifugal impeller 80, centrifugal volute 81, centrifugal inlet cylinder 82, shroud seal 83, centrifugal impeller shroud 84, hydraulic bolt 90. Detailed implementation manners

[0026] To make the purposes, technical solutions and advantages of the implementation of the present invention clearer, the technical solutions in the embodiments of the present invention will be described in more detail below with reference to the accompanying drawings in the embodiments of the present invention. The described embodiments are part of the embodiments of the present invention, rather than all the embodiments, and the described embodiments are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0027] Embodiment 1: Axial force balance structure

[0028] As a specific embodiment, as Figure 1 , Figure 2 shown, the axial force balance structure of the axial-flow / centrifugal combined compressor provided by the embodiment of the present invention includes an axial-flow blade row 70, a combined rotor, a centrifugal impeller 80, a sealing ring structure 40, a radial and axial support structure 60, etc., and is used to achieve the axial force balance of the large-flow high-pressure-ratio axial-flow / centrifugal combined compressor in a high-power compressed air energy storage system.

[0029] In the embodiment of the present invention, the combined rotor is composed of a front shaft section 10 and a rear shaft section 20, and is tightly connected into a whole by a hydraulic bolt 90. Among them, the front shaft section 10 is a semi-hollow shaft, specifically, a semi-hollow cavity 11 with a closed front end and an open rear end is provided at its center. A front-end groove 21 recessed toward the rear-end side is provided at the center of the front end of the rear shaft section 20. After the end faces of the semi-hollow cavity 11 and the front-end groove 21 are butted, a closed and axially extending intermediate shaft cavity 30 is formed. And a front-shaft-section diameter-changing part 14 is formed between the front-shaft shoulder 12 and the main body part 13 of the front shaft section 10. The shaft section between the main body part 23 of the rear shaft section 20 and the front-end connection flange forms a rear-shaft-section diameter-changing part 24. A first vent hole 31 is arranged circumferentially along the front-shaft-section diameter-changing shaft part 14, and a second vent hole 32 and / or a third vent hole 33 are arranged circumferentially at the rear-shaft-section diameter-changing shaft part 24. The second vent hole 32 is arranged axially at a position close to the front-end connection flange of the rear shaft section 20, and the third vent hole 33 is arranged at a position close to the main body part 23 of the rear shaft section 20. A plurality of each vent hole are provided and are evenly distributed circumferentially, and the first vent hole 31, the second vent hole 32, and the third vent hole 33 are all communicated with the intermediate shaft cavity 30. Therefore, the combined rotor forms a connected shaft cavity, and due to the pressure difference at both ends of the vent hole, an air flow channel is formed in the shaft cavity.

[0030] Preferably, the number, diameter, and circumferential distribution positions of the first vent hole 31, the second vent hole 32, and the third vent hole 33 can be optimized according to the balance requirements. Among them, the number of the first vent holes 31 is preferably 12 - 24, evenly distributed circumferentially on the variable-diameter part 14 of the front shaft section, and the diameter of each vent hole is 10 - 30 mm; the number of the second vent holes 32 and the third vent holes 33 is preferably 12 - 24 respectively, evenly distributed circumferentially on the variable-diameter part 24 of the rear shaft section, and the diameter of each vent hole is 10 - 20 mm.

[0031] Further, in the axial force balance structure of the compressor of the present invention, there is a radial and axial support structure 60, including a first radial bearing 61, a second radial bearing 62, and a thrust bearing 63. The first radial bearing 61 is arranged at the front shaft shoulder 12 of the front shaft section 10, and the second radial bearing 62 and the thrust bearing 63 are arranged at the rear shaft shoulder 22 of the rear shaft section 20. The radial bearings 61 and 62 play a role in supporting the rotor, and the thrust bearing 63 is used to bear the overall axial force of the rotor.

[0032] Further, in the axial force balance structure of the compressor of the present invention, the axial flow blade row 70 is fixedly connected to the outer wall of the main body part 13 of the front shaft section through a tenon joint structure. The tenon joint structure adopts one of a dovetail tenon, a fir tree tenon, a T-shaped tenon, or a fork-shaped tenon, etc. And the inlet and outlet angles, twist degrees, chord lengths, and blade profile parameters of each stage of the axial flow blades are optimized according to the aerodynamic requirements to minimize the axial force generated while ensuring the efficiency. The centrifugal impeller 80 is installed on the outer wall of the main body part 23 of the rear shaft section by a hot sleeve method.

[0033] In the axial force balance structure of the compressor of the present invention, a first seal ring 41 and a second seal ring 42 are respectively arranged on the front and rear sides of the first vent hole 31 of the front shaft section 10, and a first sealing cavity 51 is formed between the variable-diameter part 14 of the front shaft section and the air seal body. The second seal ring 42 cooperates with the front-end groove 15 of the outer wall of the main body part 13 of the front shaft section and the air seal body to form a second sealing cavity 52. A third seal ring 43 and a fourth seal ring 44 are arranged on the front and rear sides of the second vent hole 32. The third seal ring 43 cooperates with the rear-end groove 16 of the outer wall of the main body part 13 of the front shaft section and the partition to form a third sealing cavity 53. The third seal ring 43 cooperates with the fourth seal ring 44 behind the centrifugal impeller disk and the partition to form a fourth sealing cavity 54. The fourth seal ring 44 behind the centrifugal impeller disk and the back area of the centrifugal impeller disk form a fifth sealing cavity 55. A sixth sealing cavity is formed between the impeller shroud 84 of the centrifugal impeller and the shroud seal 83.

[0034] Preferably, each sealing ring is one or a combination of a labyrinth sealing ring, a brush sealing ring or a dry gas seal, which is used to form an efficient seal between the rotating component and the stationary component. Among them, the sealing ring located in the high-pressure area adopts a multi-stage labyrinth structure or a dry gas seal structure to improve the sealing effect and reduce leakage loss. The sealing ring located in the low-pressure area adopts a labyrinth structure or a brush structure to reduce the manufacturing cost and friction loss. Moreover, the material of each sealing ring is selected as an alloy material with wear resistance, high temperature resistance and corrosion resistance to ensure good sealing performance and service life under high-speed and high-temperature conditions.

[0035] On the compressor rotating shaft, the pneumatic axial force is as follows: (1) The axial forces generated forward are the axial flow blade row 70, the third sealing cavity 53, the fourth sealing cavity 54, and the sixth sealing cavity 56; (2) The axial forces generated backward are the first sealing cavity 51, the second sealing cavity 52, and the fifth sealing cavity 55; (3) The intermediate shaft cavity 30 is an inner cavity that does not generate axial thrust. By controlling the pressure distribution and the corresponding effective acting area in each sealing cavity, the generated backward axial force and forward axial force reach a balanced state, and the pressure in each sealing cavity changes with the operating conditions of the compressor. The pressure in the first sealing cavity 51 is adjusted in real time through the internal air intake channel to ensure the axial force balance effect under different operating conditions. And under normal operating conditions, the axial thrust generated by the blade row is very large. Therefore, after comprehensively considering the axial forces of the blade row and each sealing cavity, the rotating shaft as a whole receives an axial thrust forward.

[0036] In the embodiment of the present invention, the second vent hole 32 and the third vent hole 33 are combined and set according to the operating conditions of the compressor and the requirements of axial force balance, including the following three operating modes: Mode 1, only the second vent hole 32 is opened, and the third vent hole 33 is not opened, which is applicable to the condition of small axial force; Mode 2, only the third vent hole 33 is opened, and the second vent hole 32 is not opened, which is applicable to the condition of large axial force; Mode 3, both the second vent hole 32 and the third vent hole 33 are opened. By adjusting the quantity, diameter and distribution position of the two groups of vent holes, fine adjustment of the axial force is achieved, which is applicable to the condition of large axial force change or precise control required; the difference in the axial force balance effect under different modes is mainly determined by the introduced gas pressure and flow rate.

[0037] Specifically, in the conventional design, only the first vent hole 31 and the second vent hole 32 are provided. If there is no vent hole, the chamber pressure in the first sealing cavity 51 is close to the ambient pressure, so the backward axial thrust generated there is small. However, in the structure proposed by the present invention, a high-pressure gas (the chamber pressure here is lower than the exhaust pressure of the centrifugal impeller) is introduced from the fourth sealing cavity 54 to the first sealing cavity 51 through the second vent hole 32. Therefore, the axial thrust generated by the first sealing cavity 51 is significantly increased, and the air intake described in this structure uses the axial hole as the channel, without increasing the complexity of the structural system and the bearing span.

[0038] Optional design solution: only the first vent hole 31 and the third vent hole 33 are provided. A high-pressure gas (the chamber pressure here is equivalent to the exhaust pressure of the centrifugal impeller) is introduced from the fifth sealing chamber 55 to the first sealing chamber 51 through the third vent hole 33. Therefore, a greater axial thrust will be generated in the first sealing chamber 51 for a greater axial force balance requirement. In addition to adjusting the pressure of the chamber, increasing the force-bearing area is also an important means to adjust the axial thrust. For the structure proposed in the present invention, the axial thrust backward can be increased by increasing the hub diameters at the front shaft connection and the back of the centrifugal impeller disk and decreasing the diameter at the rear shaft connection, so as to effectively reduce the total axial thrust of the rotating shaft. For example, the diameter of the front shaft section variable diameter part 14 can be set to be larger than the diameter of the rear shaft section variable diameter part 24 to increase the effective acting areas of the first sealing chamber 51 and the second sealing chamber 52, thereby generating a greater axial force backward under the same pressure condition; at the same time, the diameter of the front shaft shoulder 12 at the front end of the front shaft section 10 is larger than the diameter of the rear shaft shoulder 22 at the rear end of the rear shaft section 20 to optimize the distribution of the axial force, so that the axial force balance effect is more significant on the premise of ensuring the mechanical strength.

[0039] Through the technical solution of Embodiment 1, the present invention provides an efficient and simple axial force balance structure. Through the combined design of the combined rotor structure, multiple groups of vent holes and the seal ring, the efficient balance and precise adjustment of the axial force are realized. This structure not only avoids the increase in span and complexity brought by the traditional balance disk, but also can flexibly adjust the air intake path and pressure distribution according to different working conditions requirements, so as to ensure that the compressor can maintain a stable and reliable working state under various operating conditions.

[0040] Embodiment 2: Axial-flow - centrifugal combined compressor

[0041] Based on the above Embodiment 1, this Embodiment 2 further provides an axial-flow - centrifugal combined compressor including the above axial force balance structure, as Figure 3 shown. This compressor mainly consists of an axial-flow part and a centrifugal part. The axial-flow part includes an axial-flow inlet cylinder 71, a stator blade carrier cylinder 72, an axial-flow blade row 70 and an axial-flow exhaust cylinder 73, which are used to realize the preliminary compression and acceleration of the air flow; the centrifugal part includes a centrifugal inlet cylinder 82, a centrifugal impeller 80, a centrifugal volute 81, a shroud seal 83 and a centrifugal impeller shroud 84, which are used to realize the further compression and supercharging of the air flow.

[0042] The combined rotor is formed by connecting the front shaft section 10 and the rear shaft section 20 through a hydraulic bolt 90, and is supported by a radial and axial support structure 60. Among them, the first radial bearing 61 is located in the front bearing housing 64, and the second radial bearing 62 and the thrust bearing 63 are located in the rear bearing housing 65 to ensure the stable operation of the rotor. The axial flow blade row 70 is fixedly connected to the front shaft section 10, and the centrifugal impeller 80 is fixedly connected to the rear shaft section 20 to achieve continuous compression of the air flow. Through the first vent hole 31 on the front shaft section 10 and the second vent hole 32 or the third vent hole 33 on the rear shaft section 20, and each sealing cavity 50 (including the first to sixth sealing cavities 51 to 56) formed by the seal ring structure 40 (including the first to fourth seal rings 41 to 44), the balance and adjustment of the axial force are realized, thereby improving the compressor efficiency and operation stability.

[0043] Through the above embodiments, the object of the present invention is completely and effectively achieved. Those skilled in the art can understand that the present invention includes but is not limited to the content described in the drawings and the above specific embodiments. Although the present invention has been described with respect to the currently considered most practical and preferred embodiments, it should be understood that the present invention is not limited to the disclosed embodiments, and any modification that does not deviate from the functional and structural principles of the present invention will be included in the scope of the claims.

Claims

1. An axial force balance structure for an axial-flow and centrifugal combined compressor, characterized in that Comprising: A combined rotor, including a front shaft section and a rear shaft section, which are tightly connected into one body, and a semi-hollow cavity with a closed front end and an open rear end is provided at the center of the front shaft section. A front-end groove recessed towards the rear end side is provided at the center of the front end of the rear shaft section. After the end faces of the semi-hollow cavity and the front-end groove are butted, a closed and axially extending intermediate shaft cavity is formed. Multiple groups of vent hole structures, at least including a plurality of first vent holes arranged circumferentially on the diameter-changing part of the front shaft section, a plurality of second vent holes and / or third vent holes arranged circumferentially on the diameter-changing part of the rear shaft section, and each vent hole communicates with the intermediate shaft cavity. Among them, the diameter-changing part of the front shaft section is formed between its front shaft shoulder and the main body part, and the diameter-changing part of the rear shaft section is formed on the shaft section between its main body part and the front connecting flange. The second vent holes are arranged axially near its front connecting flange, and the third vent holes are arranged near its main body part. Multiple groups of seal ring structures, including a plurality of seal rings arranged axially in sequence, including: a first seal ring and a second seal ring arranged on both sides of the first vent hole before and after, and a first sealing cavity is formed between the first seal ring and the second seal ring and the diameter-changing part of the front shaft section and the air seal body. The second seal ring and the outer wall front-end groove of the main body part of the front shaft section and the air seal body cooperate to form a second sealing cavity; a third seal ring and a fourth seal ring are arranged on both sides of the second vent hole before and after. The third seal ring and the outer wall rear-end groove of the main body part of the front shaft section and the partition board cooperate to form a third sealing cavity. The third seal ring and the fourth seal ring and the diameter-changing part of the rear shaft section and the partition board form a fourth sealing cavity. The fourth seal ring and the back area of the centrifugal impeller disk form a fifth sealing cavity. Among them, the second vent hole is used to introduce the high-pressure gas in the fourth sealing cavity into the first sealing cavity, and the third vent hole is used to introduce the high-pressure gas in the fifth sealing cavity into the first sealing cavity. By selectively opening the second vent hole and / or the third vent hole, the air intake path between different pressure sources is realized.

2. The axial force balance structure of the axial-flow and centrifugal combined compressor according to claim 1, wherein The front shaft section and the rear shaft section are tightly connected by a plurality of hydraulic bolts. The plurality of hydraulic bolts are evenly distributed circumferentially between the flange connection surfaces of the front shaft section and the rear shaft section, and a sealing structure is provided between the flange connection surfaces of the front shaft section and the rear shaft section.

3. The axial force balance structure of the axial-flow and centrifugal combined compressor according to claim 1, wherein, The first sealing cavity, the second sealing cavity and the fifth sealing cavity generate an axial force backward, and the axial flow blade row and the third sealing cavity and the fourth sealing cavity generate an axial force forward. By controlling the pressure distribution in each sealing cavity and its corresponding effective action area, the generated backward axial force and forward axial force reach a balanced state.

4. The axial force balance structure of the axial-centrifugal combined compressor according to claim 1 or 3, characterized in that, It also includes a centrifugal impeller cover. The centrifugal impeller cover and the stator partition form a closed cavity, and a sixth sealing cavity is formed by setting a seal between the centrifugal impeller cover and the cover. The pressure in the sixth sealing cavity generates an axial force forward.

5. The axial force balance structure of the axial-flow and centrifugal combined compressor according to claim 1, wherein The diameters of the diameter-changing parts and the shaft shoulders of the front and rear shaft sections are optimized and adjusted according to the actual axial force results to obtain reasonable diameters of the diameter-changing parts and the shaft shoulders of the front and rear shaft sections, so as to increase the effective action areas of the first sealing cavity and the second sealing cavity and optimize the distribution of the axial force.

6. The axial force balance structure of the axial-flow and centrifugal combined compressor according to claim 1, wherein The number, diameter, and circumferential distribution positions of each ventilation hole are optimized according to the balance requirements. Among them, the first ventilation holes are evenly distributed circumferentially on the stepped part of the front shaft section, and the second and third ventilation holes are evenly distributed circumferentially on the stepped part of the rear shaft section.

7. The axial force balancing structure of the axial-centrifugal combined compressor according to claim 1, characterized in that: Each sealing ring is one or a combination of a labyrinth sealing ring, a brush sealing ring, or a dry gas seal. Among them, the sealing rings located in the high-pressure area adopt a multi-stage labyrinth structure or a dry gas seal structure, and the sealing rings located in the low-pressure area adopt a labyrinth structure or a brush structure. Moreover, the materials of each sealing ring are selected from wear-resistant, high-temperature-resistant, and corrosion-resistant alloy materials.

8. The axial force balance structure of the axial - centrifugal combined compressor according to claim 1, characterized in that, A radial and axial support structure is also provided, including a first radial bearing, a second radial bearing, and a thrust bearing. The first radial bearing is assembled on the front shoulder of the front shaft section, and the second radial bearing and the thrust bearing are assembled on the rear shoulder of the rear shaft section. Each radial bearing is used to support the rotor, and the thrust bearing is used to bear the overall axial force of the rotor.

9. The axial force balance structure of the axial-flow and centrifugal combined compressor according to claim 1, characterized in that, An axial flow blade row and a centrifugal impeller are also provided. The axial flow blade row is fixedly connected to the outer wall of the main body part of the front shaft section through a tenon joint structure. The tenon joint structure is one of a dovetail tenon, a fir tree tenon, a T-shaped tenon, or a fork-shaped tenon, etc. Moreover, the inlet and outlet angles, twist degrees, chord lengths, and blade profile parameters of each stage of the axial flow blades are optimized according to the aerodynamic requirements to minimize the axial force generated while ensuring efficiency. The centrifugal impeller is fixedly connected to the outer wall of the main body part of the rear shaft section by a hot sleeve method.

10. The axial force balance structure of the axial-flow and centrifugal combined compressor according to claim 1, characterized in that, The second and third ventilation holes are combined and set according to the operating conditions of the compressor and the axial force balance requirements, including the following three operating modes: Mode 1, only the second ventilation hole is opened, and the third ventilation hole is not opened, which is applicable to the condition of a small axial force; Mode 2, only the third ventilation hole is opened, and the second ventilation hole is not opened, which is applicable to the condition of a large axial force; Mode 3, both the second and third ventilation holes are opened. By adjusting the number, diameter, and distribution positions of the two groups of ventilation holes, fine adjustment of the axial force is achieved, which is applicable to the condition of a large change in axial force or the need for precise control.

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