CN112983849A

CN112983849A - Centrifugal compressor structure with axial force capable of being automatically balanced

Info

Publication number: CN112983849A
Application number: CN202110186719.9A
Authority: CN
Inventors: 侯予; 初阳; 杨潇翎; 赖天伟; 王喆峰; 陈双涛; 张泽
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2021-02-10
Filing date: 2021-02-10
Publication date: 2021-06-18
Anticipated expiration: 2041-02-10
Also published as: CN112983849B

Abstract

The invention belongs to the field of fluid machinery, and relates to a centrifugal compressor structure capable of automatically balancing axial force, which comprises: the primary volute and the secondary volute are respectively arranged at two ends of the motor shell, a primary impeller and a secondary impeller are respectively arranged at two ends of the main shaft back to back, and the primary impeller and the secondary impeller are respectively positioned in the primary volute and the secondary volute; a first-stage shaft seal is arranged between the motor shell and the first-stage volute, and a second-stage shaft seal is arranged between the motor shell and the second-stage volute. The invention controls the wheel back pressure of the primary impeller and the secondary impeller by adjusting the air inlet pressure of the primary shaft seal and the secondary shaft seal, and the wheel back pressure is respectively balanced with the axial force generated by the front-back pressure difference of the primary impeller and the axial force generated by the front-back pressure difference of the secondary impeller, thereby avoiding the abrasion and the failure of the centrifugal compressor caused by the unbalance of the axial force, improving the performance of the compressor and prolonging the service life of the compressor. Meanwhile, the wheel back can be used as a thrust disc, a thrust bearing is omitted, and the positioning precision of the impeller and the compactness of the whole machine are improved.

Description

Centrifugal compressor structure with axial force capable of being automatically balanced

Technical Field

The invention belongs to the field of fluid machinery, and relates to a centrifugal compressor structure capable of automatically balancing axial force.

Background

The centrifugal compressor is used as one of fluid machines, is widely applied to the industrial fields of metallurgy, petrochemical industry, natural gas transportation, refrigeration, power and the like, and plays an important role in promoting economic development.

The pressure of gas in the centrifugal compressor is increased because when the gas flows through the impeller, the impeller rotates at high speed to do work on the gas to raise the pressure of the gas, and meanwhile, the gas obtains high speed, when the gas passes through the diffuser and the volute expansion channel, the flowing speed of the gas is gradually reduced, and kinetic energy is converted into pressure to further increase the pressure.

The traditional centrifugal compressor operates stably under the design working condition, but some defects and defects often exist under the non-design working condition, for example, axial force imbalance causes shafting drunkenness when the compressor operates, axial load is increased, bearing abrasion is serious, and the performance and the service life of the compressor are influenced. In addition, the conventional centrifugal compressor is easy to cause the problem of unbalanced axial force when the pressure difference between the impeller and the back side of the impeller is too large under the working condition of high pressure.

Disclosure of Invention

In view of the above, the main object of the present invention is to provide a centrifugal compressor structure with an axial force capable of being automatically balanced, so as to overcome the above-mentioned drawbacks of the prior art.

The technical scheme for solving the problems is as follows: a centrifugal compressor structure capable of automatically balancing axial force is characterized by comprising:

the device comprises a motor shell, a main shaft, a motor, a primary volute and a secondary volute; the motor is positioned in the motor shell and drives the main shaft to rotate;

the primary volute and the secondary volute are respectively arranged at two ends of the motor shell, a primary impeller and a secondary impeller are respectively arranged at two ends of the main shaft back to back, and the primary impeller and the secondary impeller are respectively positioned in the primary volute and the secondary volute;

a primary shaft seal is arranged between the motor shell and the primary volute, and a secondary shaft seal is arranged between the motor shell and the secondary volute;

the first-stage shaft seal separates a chamber of the first-stage volute from a chamber in the motor shell, and the second-stage shaft seal separates a chamber of the second-stage volute from a chamber in the motor shell, so that the first-stage impeller and the second-stage impeller in the compressor are relatively independent and do not influence each other when in operation on the basis of reducing the leakage amount of gas at the outlet of the impeller to the back of the impeller. The motor shell is provided with an upper through hole and a lower through hole at positions close to the inner side of the primary shaft seal and the secondary shaft seal respectively, and the inlet of the upper through hole is connected with a filter.

Furthermore, a first vent hole and a third vent hole are respectively formed in the motor shell at positions corresponding to the primary shaft seal and the secondary shaft seal; the first-stage shaft seal and the second-stage shaft seal are provided with a second vent hole and a fourth vent hole, and outlet axes of the second vent hole and the fourth vent hole are parallel to the main shaft and point to the backs of the first-stage impeller and the second-stage impeller; the first vent hole and the third vent hole are respectively communicated with the second vent hole and the fourth vent hole.

The pressure of the back of the first-stage impeller and the second-stage impeller is adjusted by adjusting the pressure introduced into the vent holes, so that the axial force of the first-stage impeller and the second-stage impeller is balanced, and the problems of deformation and overlarge vibration caused by overlarge axial force of a single impeller are solved. In addition, the air supply to the impeller wheel back can reduce the leakage of the impeller outlet, and the purpose of effective sealing is achieved.

Furthermore, the number of the second vent holes and the fourth vent holes is multiple, and the second vent holes and the fourth vent holes are uniformly distributed in the circumferential direction, so that the wheel backs of the first-stage impeller and the second-stage impeller have uniform pressure.

Further, a first dynamic pressure radial gas bearing is arranged on the main shaft and abuts against the inner side of the primary shaft seal; and a second dynamic pressure radial gas bearing is arranged on the inner side of the secondary shaft seal in a propping manner, the first dynamic pressure radial gas bearing and the second dynamic pressure radial gas bearing jointly support the main shaft and bear the radial load of the main shaft, and the axial load of the main shaft is borne under the joint action of the two stages of impeller backs. The back of the two-stage impeller wheel is directly used as a thrust surface, so that the structure of the compressor is more compact, the positioning precision of the impeller can be improved, the impeller can be ensured to run safely and stably under the condition of small gap, and the efficiency of the impeller is further improved.

Furthermore, a primary inlet and a primary outlet are arranged on the primary volute, the primary inlet is arranged at the center of the primary volute, and the primary outlet is arranged on the circumference of the primary volute; the second-stage volute is provided with a second-stage inlet and a second-stage outlet, the second-stage inlet is arranged at the center of the second-stage volute, and the second-stage outlet is arranged on the circumference of the second-stage volute. The primary outlet is communicated with the secondary inlet.

Further, the first-stage volute and the first-stage shaft seal are assembled to form a first-stage impeller diffuser, and the outlet of the first-stage impeller is over against the inlet of the first-stage impeller diffuser; the second-stage volute and the second-stage shaft seal are assembled to form a second-stage impeller diffuser, and the outlet of the second-stage impeller is opposite to the inlet of the second-stage impeller diffuser.

Further, the motor comprises a motor rotor and a motor stator, the motor stator is fixed in the motor shell, and the motor rotor drives the spindle to rotate.

Furthermore, the first vent hole and the third vent hole on the motor shell are respectively provided with a joint communicated with external equipment.

The invention has the advantages that:

1) when the invention works, the pressure difference between the front and the back of the first-stage impeller can generate an axial force, and the pressure difference between the front and the back of the second-stage impeller can also generate an axial force. The wheel back pressure of the first-stage impeller and the wheel back pressure of the second-stage impeller are controlled by adjusting the air inlet pressure of the first-stage shaft seal and the air inlet pressure of the second-stage shaft seal, the axial force generated by the front-back pressure difference of the first-stage impeller and the axial force generated by the front-back pressure difference of the second-stage impeller can be balanced respectively, the abrasion and the failure of the centrifugal compressor caused by the unbalanced axial force are avoided, and the performance and the service life of the compressor are improved.

2) Compact and efficient. The invention directly uses the two-stage impeller wheel back as the thrust surface without a thrust bearing, improves the compactness of the compressor, ensures the accurate positioning of the impeller, reduces the vibration and the deformation of the impeller, and reduces the clearance of the impeller, thereby improving the efficiency of the impeller. Meanwhile, air supply to the wheel back improves the pressure of the wheel back, and leakage of an impeller outlet can be reduced.

3. Clean, long life and high reliability. The invention adopts the gas bearing, which has no abrasion, low maintenance cost and good cleanness. In addition, the axial loads of the impellers on the two sides can be actively balanced, the running state of the rotor is stable, the reliability of the bearing is high, and the service life is long.

Drawings

Fig. 1 is a schematic structural diagram of a centrifugal compressor capable of automatically balancing axial force according to an embodiment of the present invention;

FIG. 2 is a schematic view of a configuration of a primary shaft seal in the centrifugal compressor shown in FIG. 1;

FIG. 3 is a schematic view of the construction of the secondary shaft seal in the centrifugal compressor of FIG. 1;

fig. 4 is a schematic view of the operation of the centrifugal compressor shown in fig. 1.

Wherein: 1. a motor housing, 2, a first dynamic pressure radial bearing, 3, a motor, 5, a second dynamic pressure radial bearing, 6, a first-stage impeller diffuser, 7, a second-stage impeller diffuser, 12, a first-stage volute, 13, a second-stage volute, 14, a main shaft, 15, a motor rotor, 16, a motor stator, 17, an upper joint, 18, a lower joint, 21, a first-stage shaft seal, 22, a second-stage shaft seal, 27, a first-stage impeller, 30, a second-stage impeller, 31, a first vent hole, 32, a second vent hole, 33, a third vent hole, 34, a fourth vent hole, 35, an upper through hole, 36, a lower through hole, 37, a first joint, 38, a second joint, 41, a first-stage inlet, 42, a first-stage outlet, 43, a second-stage inlet, 44, a second-stage outlet, 48, a chamber, 100, a centrifugal compressor, 101, a second-stage compressor, 102, a, Economizer 105, first throttle valve 106, second throttle valve 107, dual stage compression cycle evaporator 108, reservoir 109, third throttle valve 110, fourth throttle valve.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings of the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention.

A centrifugal compressor structure with automatically balanced axial force is shown in figure 1 and comprises a motor housing 1, a spindle 14 positioned in the motor housing 1 and a motor 3 installed in the motor housing 1. At the left end of the motor housing 1, a primary volute 12 and a primary shaft seal 21 are mounted. At the right end of the motor housing, a secondary volute 13 and a secondary shaft seal 22 are mounted. At the left end of the main shaft 14, a primary impeller 27 is mounted. At the right end of the main shaft 14, a secondary impeller 30 is mounted.

A primary inlet 41 and a primary outlet 42 are arranged on the primary volute 12, the primary inlet 41 is arranged at the center of the primary volute 12, and the primary outlet 42 is arranged on the circumference of the primary volute 12; the secondary volute 13 is provided with a secondary inlet 43 and a secondary outlet 44, the secondary inlet 43 is arranged at the center of the secondary volute 13, and the secondary outlet 44 is arranged on the circumference of the secondary volute 13.

The first-stage impeller 27 is positioned in the first-stage volute 12, the first-stage volute 12 and the first-stage shaft seal 21 are assembled to form a first-stage impeller diffuser 6, and the outlet of the first-stage impeller 27 is opposite to the inlet of the first-stage impeller diffuser 6. The second-stage impeller 30 is positioned in the second-stage volute 13, the second-stage volute 13 and the second-stage shaft seal 22 are assembled to form a second-stage impeller diffuser 7, and the outlet of the second-stage impeller 30 is opposite to the inlet of the second-stage impeller diffuser 7.

The first-stage shaft seal 21 separates the first-stage volute chamber 12 from the chamber where the motor 3 is located, the second-stage shaft seal 22 separates the second-stage volute 13 from the chamber of the motor housing 1, and the first-stage impeller 27 and the second-stage impeller 30 in the compressor are relatively independent and do not affect each other when in operation. At the left end of the motor housing 1 in the state shown in fig. 1, an upper through hole 35 is provided, and an inlet of the upper through hole 35 is connected with the filter and then the upper joint 17 (not shown) is installed; a lower through hole 36 is formed in the motor housing 1 at a position close to the inner side of the secondary shaft seal 22, and a lower coupling 18 (not shown) for communicating with an external device is mounted outside the lower through hole 36. The medium such as coolant can be supplied into the motor housing 1 through the upper joint 17 and the filter, and the medium such as coolant in the motor housing 1 can be discharged through the lower joint 18 and the lower through hole 36, so that the motor 3 can be cooled, and the operation failure caused by overheating of the motor 3 can be prevented. As a preferred embodiment of the present invention, a first vent hole 31 is opened at a position where the primary shaft seal 21 is installed at an end of the motor housing 1, for example, at a left end of the motor housing 1 in the state shown in fig. 1, and a first joint 37 (not shown) for communicating with an external device is installed outside the first vent hole 31; the first-stage shaft seal 21 is provided with a second vent hole 32, the inlet axis of the second vent hole 32 is vertical to the main shaft 14, and the outlet axis of the second vent hole 32 is parallel to the main shaft 14 and points to the first-stage impeller 27; the first vent hole 31 at the end of the motor housing 1 communicates with the second vent hole 32 on the primary shaft seal 21.

A third air vent hole 33 is opened at a position where the secondary shaft seal 22 is mounted at an end of the motor housing 1, for example, at a right end of the motor housing 1 in the state shown in fig. 1, and a second joint 38 (not shown) communicating with an external device is mounted outside the third air vent hole 33; the second-stage shaft seal 22 is provided with a fourth air vent 34, the inlet axis of the fourth air vent 34 is vertical to the main shaft 14, and the outlet axis of the fourth air vent 34 is parallel to the main shaft 14 and points to the first-stage impeller 30; the third air vent hole 33 at the end of the motor housing 1 is communicated with the fourth air vent hole 34 on the secondary shaft seal 22.

As shown in fig. 2 and 3, the second vent 32 and the fourth vent 34 may comprise a plurality of vents to provide uniform pressure at the backs of the first-stage impeller 27 and the second-stage impeller 30.

As a preferred embodiment of the present invention, a first hydrodynamic radial gas bearing 2 is provided on the main shaft 14 against the inside of the primary shaft seal 21, for example, at the left side of the main shaft in the state shown in fig. 1; and a second dynamic pressure radial gas bearing 5 is arranged on the inner side of the secondary shaft seal. The two dynamic pressure radial gas bearings jointly support the main shaft and bear the radial load of the main shaft, the back of the two-stage impeller wheel is directly used as a thrust surface, and the combined action of the two-stage impeller wheel is utilized to bear the axial load of the main shaft.

In the working process of the centrifugal compressor, a cooling medium can enter a cavity 48 where the motor is located, and dynamic pressure radial gas friction pairs are formed among the first dynamic pressure radial gas bearing 2, the second dynamic pressure radial gas bearing 5 and the main shaft 14; the medium enters the wheel backs of the impellers of all stages through the first vent holes 31 and the third vent holes 33 at the two ends of the motor shell, and when the impellers of all stages rotate at high speed, an air film is generated between the shaft seal of each stage and the wheel backs of the impellers to provide axial load and balance the axial force of the impellers. When the main shaft 14 rotates, the medium entering the chamber 48 in which the motor is located will flow through the gaps between the first hydrodynamic radial gas bearing 2, the second hydrodynamic radial gas bearing 5 and the main shaft 14. The relative motion of the first dynamic pressure radial gas bearing 2, the second dynamic pressure radial gas bearing 5 and the main shaft 14 can generate a dynamic pressure effect, so that a gas film has high pressure and good bearing capacity, and the dynamic pressure radial gas bearing can achieve a self-lubricating effect. Compare with traditional lubricating oil lubrication, can not only prevent that the each other of medium and lubricating oil from leading to the worsening of lubricated state, can also prevent the adverse effect that lubricating oil runs off and bring and reduce the heat transfer effect of medium in heat exchange equipment.

After the motor 3 is powered on, an alternating magnetic field is generated between the motor rotor 15 and the motor stator 16, the alternating magnetic field acts on the motor rotor 15, the motor rotor 15 drives the main shaft 14 to rotate, the main shaft 14 further drives the first-stage impeller 27 and the second-stage impeller 30 to rotate, working media are sucked from the first-stage inlet 41 and the second-stage inlet 43 respectively and do work on the working media, the pressure of the working media is improved, and the pressurized working media have larger kinetic energy after flowing out of the impellers. After passing through the first-stage impeller diffuser 6 and the second-stage impeller diffuser 7, most of the kinetic energy is converted into pressure energy to further increase the pressure of the working medium, and finally the working medium is discharged through a first-stage outlet 42 positioned on the circumference of the first-stage volute 12 and a second-stage outlet 44 positioned on the circumference of the second-stage volute 13.

In the above process, since the working medium entering the first-stage volute 12 and the second-stage volute 13 is pressurized by the first-stage impeller 27 and the second-stage impeller 30, pressure difference exists between the front side and the back side of the first-stage impeller 27 and the back side of the second-stage impeller 30. In fig. 1, the left side of the primary impeller 27 is the front side of the wheel, and the right side of the wheel is the back side of the wheel, because the pressurizing process occurs in front of the wheel, the average pressure in front of the wheel is lower than the pressurized pressure, and the back side of the wheel has the pressurized pressure. The pressure difference between the wheel back pressure and the wheel front pressure generates an axial force on the main shaft 14, and the direction of the axial force is changed by factors such as the sectional area of the primary impeller 27, the sectional area of the main shaft 14, the operation condition and the like. Similarly, in fig. 1, the pressure difference between the back pressure and the front pressure of the secondary impeller 30 also generates an axial force on the main shaft 14, and the direction of the axial force is also changed by the sectional area of the secondary impeller, the sectional area of the main shaft 14, the operation condition, and the like. In the design process, the axial force generated by the backpressure difference of the front wheel of the first-stage impeller 27 and the axial force generated by the backpressure difference of the front wheel of the second-stage impeller 30 are balanced to each other as much as possible, so that the faults and losses caused by the unbalance of the axial forces are avoided.

In order to illustrate the working principle of the centrifugal compressor structure with the automatic balance of the axial force, the principle of the centrifugal compressor structure is illustrated by taking an economizer-containing one-stage throttling two-stage compression cycle as an example. Embodiments of the present invention are not limited to this cycle and may be applied to a variety of other types of two-stage compression cycles. Referring to fig. 4, the centrifugal compressor according to the embodiment of the present invention operates according to the following principle:

the centrifugal compressor 100 provided by the embodiment of the invention is powered on, and the working medium firstly flows through the first-stage inlet 41 at the central position of the first-stage volute 12 of the first-stage compressor 102 and enters the inner cavity of the first-stage volute 12. The primary impeller 27 of the primary compressor 102 works on the sucked gas working medium to increase the pressure of the gas working medium. The pressurized gas working medium flows out of the primary compressor 102 through the outlet 42 in the circumferential direction of the primary volute 12 and enters the secondary compressor 101 from the secondary inlet 43 in the center of the secondary volute 13. The secondary impeller 30 of the secondary compressor 101 applies work to the gas working medium and then flows out of the secondary compressor from the secondary outlet 44 in the circumferential direction of the secondary volute 13. During the operation of the primary compressor 102, along with the gradual increase of the rotation speed of the main shaft 14, the first hydrodynamic radial gas bearing 2 and the second hydrodynamic radial gas bearing 5 respectively form gas films with the main shaft 14, and the lubrication mode is changed into gas lubrication.

The high-temperature and high-pressure gaseous refrigerant pressurized by the secondary compressor 101 flows through the two-stage compression cycle condenser 103 to be cooled to a liquid state, and then enters the liquid storage tank 108, and the refrigerant flowing out is divided into two paths to enter the economizer 104. One path of refrigerant flows through the first throttling valve 105 and enters the economizer 104 to absorb heat to reduce the temperature of the other path of refrigerant in the economizer, then the refrigerant is purified by a filter after passing through an upper connector 17 on the centrifugal compressor 100 and enters the motor housing 1, and the refrigerant flows out through a lower connector 18 after cooling the motor 3 in the motor housing 1. Then mixed with the gas at the outlet of the first-stage compressor 102 and enters the second-stage inlet 43 at the central position of the second-stage compressor 101 for second-stage compression. The other refrigerant flows through the economizer 104 to be cooled (after being absorbed with the previous refrigerant), then flows through the second throttle valve 106, then flows into the two-stage compression cycle evaporator 107 to be evaporated and absorb heat to generate cooling capacity, and then is sucked by the one-stage compressor 102 to perform the next cycle.

The high-temperature and high-pressure gas flowing out of the secondary outlet 44 of the secondary compressor 101 is divided into two paths of refrigerants except that most of the high-temperature and high-pressure gas flows into the condenser to participate in the main circulation. One path of refrigerant flows through the third throttle valve 109, then flows through the first vent hole 31 and the second vent hole 32 through the joint 37, reaches the wheel back of the first-stage impeller 27, adjusts the pressure difference between the front of the first-stage impeller 27 and the wheel back, then part of refrigerant is discharged along with the first-stage compression, and part of refrigerant flows through the first-stage shaft seal and enters the motor shell for second-stage compression. The other path of refrigerant flows through the fourth throttle valve 110, then flows through the third vent hole 33 and the fourth vent hole 34 through the joint 38, and reaches the wheel back of the secondary impeller 30, the pressure difference between the front wheel and the wheel back of the secondary impeller 30 is adjusted, then part of refrigerant is discharged along with the secondary compression, and part of refrigerant flows through the secondary shaft seal 22, enters the motor housing 1 and then enters the secondary compression.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all equivalent structures or equivalent flow transformations made by using the contents of the specification and the drawings, or applied directly or indirectly to other related systems, are included in the scope of the present invention.

Claims

1. A centrifugal compressor structure with an automatically balanced axial force is characterized in that:

comprises a motor shell (1), a main shaft (14), a motor (3), a first-stage volute (12) and a second-stage volute (13); the motor (3) is positioned in the motor shell (1), and the motor (3) drives the spindle (14) to rotate;

the primary volute (12) and the secondary volute (13) are respectively installed at two ends of the motor shell (1), the two ends of the main shaft (14) are back-to-back respectively provided with a primary impeller (27) and a secondary impeller (30), and the primary impeller (27) and the secondary impeller (30) are respectively located in the primary volute (12) and the secondary volute (13);

a primary shaft seal (21) is arranged between the motor shell (1) and the primary volute (12), and a secondary shaft seal (22) is arranged between the motor shell (1) and the secondary volute (13);

the primary shaft seal (21) separates a chamber of the primary volute (12) from a chamber in the motor shell (1), and the secondary shaft seal (22) separates a chamber of the secondary volute (13) from a chamber in the motor shell (1); an upper through hole (35) and a lower through hole (36) are respectively formed in the position, close to the inner side of the primary shaft seal (21) and the position, close to the secondary shaft seal (22), of the motor shell (1), and the inlet of the upper through hole (35) is connected with a filter.

2. A centrifugal compressor structure with self-balancing axial force, as claimed in claim 1, wherein:

a first vent hole (31) and a third vent hole (33) are respectively formed in the positions, corresponding to the primary shaft seal (21) and the secondary shaft seal (22), on the motor shell (1); the primary shaft seal (21) and the secondary shaft seal (22) are provided with a second vent hole (32) and a fourth vent hole (34), and outlet axes of the second vent hole (32) and the fourth vent hole (34) are parallel to the main shaft (14) and point to wheel backs of the primary impeller (27) and the secondary impeller (30); the first vent hole (31) and the third vent hole (33) are respectively communicated with the second vent hole (32) and the fourth vent hole (34).

3. A centrifugal compressor structure capable of automatically balancing axial force according to claim 2, wherein:

the number of the second vent holes (32) and the fourth vent holes (34) is multiple, and the second vent holes and the fourth vent holes are uniformly distributed in the circumferential direction.

4. A centrifugal compressor structure with self-balancing axial force, as claimed in claim 3, wherein:

a first dynamic pressure radial gas bearing (2) is arranged on the main shaft (14) and abuts against the inner side of the primary shaft seal (21); and a second dynamic pressure radial gas bearing (5) is arranged on the inner side of the secondary shaft seal (22) in a propping manner, and the main shaft (14) is supported by the first dynamic pressure radial gas bearing (2) and the second dynamic pressure radial gas bearing (5) together.

5. A centrifugal compressor structure with self-balancing axial force, as claimed in claim 4, wherein:

a primary inlet (41) and a primary outlet (42) are arranged on the primary volute (12), the primary inlet (41) is arranged at the central position of the primary volute (12), and the primary outlet (42) is arranged on the circumference of the primary volute (12); the two-stage volute (13) is provided with a two-stage inlet (43) and a two-stage outlet (44), the two-stage inlet (43) is arranged at the center of the two-stage volute (13), the two-stage outlet (44) is arranged on the circumference of the two-stage volute (13), and the one-stage outlet (42) is communicated with the two-stage inlet (43).

6. A centrifugal compressor structure capable of automatically balancing axial force according to claim 5, wherein:

the first-stage volute (12) and the first-stage shaft seal (21) are assembled to form a first-stage impeller diffuser (6), and the outlet of the first-stage impeller (27) is opposite to the inlet of the first-stage impeller (27) diffuser (6); the two-stage volute (13) and the two-stage shaft seal (22) are assembled to form a two-stage impeller diffuser (7), and the outlet of the two-stage impeller (30) is over against the inlet of the two-stage impeller diffuser (7).

7. A centrifugal compressor structure with self-balancing axial force, as claimed in claim 6, wherein:

the motor (3) comprises a motor (3) rotor and a motor (3) stator, the motor (3) stator is fixed in the motor shell (1), and the motor (3) rotor drives the spindle (14) to rotate.

8. A centrifugal compressor structure with self-balancing axial force, as claimed in claim 7, wherein:

and joints communicated with external equipment are respectively arranged on the first vent hole (31) and the third vent hole (33) on the motor shell (1).