A self-cooling system and method for a closed two-stage centrifugal water vapor compressor directly driven by a high-speed permanent magnet motor

Abstract

The present invention discloses a self-cooling system for a closed two-stage centrifugal water vapor compressor directly driven by a high-speed permanent magnet motor. The motor is arranged in a closed housing, and the motor housing is respectively connected to the rear cover plates of the two-stage compressor by bolts to form a closed system. After the high-temperature and high-pressure water vapor at the outlet of the secondary compressor is cooled, it enters the closed system by using the pressure difference, and cools the motor and bearings in turn through the cooling channel to ensure that they operate within a safe temperature range. The water vapor after passing through the cooling channel is decompressed to the first-stage inlet pressure and then returns to the first-stage compressor inlet for compression. The present invention completely utilizes compressed medium for cooling, and the cooling medium can be recycled, without the need for additional cooling equipment, thereby solving the cooling problem of high-speed permanent magnet motors and magnetic suspension bearings in a closed system, making the structure simpler and the cost lower. The sealed leaked gas can return to the first-stage compressor inlet through the cooling circuit for re-compression, thereby improving the working efficiency of the compressor as a whole.

Description

Technical Field

[0001] The invention relates to a cooling technology for a high-speed permanent magnet motor and a high-speed magnetic suspension bearing, and in particular to a self-cooling system and method for a closed two-stage centrifugal water vapor compressor directly driven by a high-speed permanent magnet motor. Background Art

[0002] The centrifugal compressor directly driven by a high-speed permanent magnet motor eliminates the intermediate transmission links such as the speed increaser, has low mechanical loss, high working efficiency, and broad application prospects in the future. The high-speed permanent magnet motor must be guaranteed to operate within a safe temperature range, so its heat dissipation design is extremely important. The traditional heat dissipation method is oil immersion cooling of the motor stator or surface circulating water cooling, and the motor rotor is cooled by compressed air. This method requires the configuration of a corresponding oil station, water pump, circulating heat dissipation system, and a large amount of compressed cooling air. The structure is complex and is not suitable for closed centrifugal compressor systems. Therefore, the heat dissipation and cooling of the closed high-speed motor directly driven water vapor centrifugal compressor system has become an important issue in the design.

[0003] At present, there is also a way to directly use compressed medium for cooling. Patent 201710091125 discloses a cooling method and cooling system for a high-speed permanent magnet motor directly driven centrifuge rotor:

[0004] like Figure 1 In the device shown, the screw of the fixed impeller at the second-stage air inlet end of the two-stage compression centrifuge, the axis center and the radial are connected through drilling holes to form a coolant passage. At the same time, several holes connected to the atmosphere are opened on the motor housing 36. In this way, when the centrifuge is working normally, the air pressure at the secondary air inlet end is above 1.5 bar, and the air pressure inside the motor is relatively low. The pressure difference causes the room temperature gas at the air inlet end of the centrifuge to take away most of the heat inside the shaft 42 through the axis center blind hole and the radial holes connected to the blind hole. At the same time, through the rotation of the shaft, the shaft surface and the gas undergo secondary heat exchange to achieve cooling, and finally flow out from the holes on the motor housing into the atmosphere.

[0005] This patent opens a hole in the motor housing to communicate with the atmosphere, reduces the internal air pressure of the motor to atmospheric pressure, and realizes the pressure difference required for the circulation of cooling gas. Since the hole is connected to the atmosphere, it is only applicable to compression systems with air as the medium. The present invention draws out cooling gas from the outlet of the secondary compressor, directly utilizes the pressure difference between the outlet of the secondary compressor and the inlet of the primary compressor to overcome the flow channel resistance, and allows the cooling gas to flow smoothly without opening a hole. For this reason, the present invention is applicable to closed systems of air and other media. The present invention uses water vapor for cooling. Compared with cooling with compressed air, the demand for cooling gas can be reduced by 77%, and the size of the cooling channel is more compact. Summary of the invention

[0006] The purpose of the present invention is to provide a self-cooling system for a closed two-stage centrifugal water vapor compressor directly driven by a high-speed permanent magnet motor, so as to solve the problem that the traditional cooling method is not suitable for a closed system.

[0007] The present invention is achieved through the following technical solutions:

[0008] A self-cooling system for a closed two-stage centrifugal water vapor compressor directly driven by a high-speed permanent magnet motor, wherein the first-stage impeller and the second-stage impeller are fixed on the rotating shaft by a pull rod, the first-stage seal is arranged in the first-stage rear cover plate, and the first-stage rear cover plate is connected to the first-stage volute and the motor housing by bolts. The second-stage seal is arranged in the second-stage rear cover plate, and the second-stage rear cover plate is connected to the second-stage volute and the motor housing by bolts. The radial support of the rotor is achieved by supporting magnetic suspension bearings, and the axial positioning of the rotor is achieved by thrust magnetic suspension bearings.

[0009] The air gap between the motor stator and the motor rotor forms the inner cooling channel of the motor stator winding. The air gap between the motor stator and the motor housing forms the outer cooling channel of the motor stator winding. The air gap between the primary side support magnetic suspension bearing and the rotating shaft forms the primary side support magnetic suspension bearing cooling channel, the air gap between the secondary side support magnetic suspension bearing rotating shaft forms the secondary side support magnetic suspension bearing cooling channel, and the air gap between the thrust plate and the balance magnet of the thrust magnetic suspension bearing and the air gap between the bearing and the rotating shaft form the thrust magnetic suspension bearing cooling channel.

[0010] The motor and bearings are cooled completely by using the system's compressed medium, water vapor. The water vapor cooling circuit is as follows: the water vapor enters the first-stage impeller, passes through the first-stage volute for inter-stage cooling, then enters the second-stage impeller, passes through the second-stage volute for cooling, and then enters the closed system from the steam inlet, passes through the second-stage side support magnetic bearing cooling channel, the thrust magnetic bearing cooling channel, the motor stator winding internal and external cooling channels, the first-stage side support magnetic bearing cooling channel, and finally flows out from the steam outlet, passes through the pressure regulating valve to reduce the pressure to the first-stage impeller inlet pressure, and returns to the first-stage impeller inlet after cooling to enter the cycle again.

[0011] Water vapor leaking from the primary and secondary seals can enter the cooling circuit and participate in the circulation.

[0012] The advantages and beneficial effects of the present invention are:

[0013] The present invention draws out the cooling gas from the outlet of the secondary compressor and directly utilizes the pressure difference between the outlet of the secondary compressor and the inlet of the primary compressor to overcome the flow resistance, so that the cooling gas can flow smoothly without opening holes. For this reason, the present invention is applicable to closed systems of air and other media.

[0014] The present invention completely utilizes compressed medium for cooling and the cooling medium can be recycled. Compared with the traditional heat dissipation method, it does not need to configure the corresponding oil station, water pump and circulating heat dissipation system and a large amount of compressed cooling air and other additional cooling equipment. Compared with cooling with compressed air, the required cooling gas volume can be reduced by 77% by using water vapor for cooling. The size of the cooling flow channel is more compact, which solves the cooling problem of high-speed permanent magnet motors and magnetic suspension bearings in closed systems, making the structure more compact and simple, and the cost is lower. The power for the circulation of cooling gas in the present invention comes from the pressure difference between the outlet of the secondary compressor and the inlet of the primary compressor of the system itself, which is suitable for closed systems and different media, and broadens the scope of application. The sealed leakage gas returns to the inlet of the primary compressor through the cooling circuit for re-compression, and the efficiency of the whole machine can be increased by 0.98%, improving and enhancing the working efficiency of the compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A patent has been applied for the cooling method and cooling system for the high-speed permanent magnet motor direct-driven centrifuge rotor.

[0016] Figure 2 This is a schematic structural diagram of a closed two-stage centrifugal water vapor compressor cooling system directly driven by a high-speed permanent magnet motor in Example 1 of the present invention.

[0017] Figure 3 for Figure 2 The enlarged view of the part marked with I.

[0018] Figure 4 and Figure 2 A partial enlarged view of the part marked with K.

[0019] In the figure: 1 is a primary volute, 2 is a primary impeller, 3 is a steam outlet, 4 is a primary rear cover, 5 is a primary seal, 6 is a rotating shaft, 7 is a supporting magnetic bearing, 8 is a motor housing, 9 is a motor stator, 10 is a motor rotor, 11 is a thrust magnetic bearing, 12 is a secondary seal, 13 is a secondary rear cover, 14 is a steam inlet, 15 is a secondary impeller, 16 is a secondary volute, and 17 is a pressure regulating valve. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0021] See also Figure 2The present invention provides a self-cooling system for a closed two-stage centrifugal water vapor compressor directly driven by a high-speed permanent magnet motor. The first-stage impeller 2 and the second-stage impeller 15 are fixed on the rotating shaft 6 by a pull rod, and the first-stage seal 5 is arranged in the first-stage rear cover plate 4, and the first-stage rear cover plate is connected to the first-stage volute 1 and the motor housing 8 by bolts. The second-stage seal 12 is arranged in the second-stage rear cover plate 13, and the second-stage rear cover plate is connected to the second-stage volute 16 and the motor housing 8 by bolts. The radial support of the rotor is achieved by the support magnetic suspension bearing 7, and the axial positioning of the rotor is achieved by the thrust magnetic suspension bearing 11.

[0022] The air gap between the motor stator 9 and the motor rotor 10 forms an inner cooling channel for the motor stator winding. The air gap between the motor stator 9 and the motor housing 8 forms an outer cooling channel for the motor stator winding. The air gap between the primary side support magnetic suspension bearing 7 and the rotating shaft 6 forms a primary side support magnetic suspension bearing cooling channel, the air gap between the secondary side support magnetic suspension bearing 7 and the rotating shaft 6 forms a secondary side support magnetic suspension bearing cooling channel, and the air gap between the thrust plate and the balance magnet of the thrust magnetic suspension bearing 11 and the air gap between the bearing and the rotating shaft 6 form a thrust magnetic suspension bearing cooling channel.

[0023] The motor and bearings are cooled by using water vapor as a compressed medium of the system. The water vapor cooling circuit is as follows: the water vapor enters the first-stage impeller 2, passes through the first-stage volute 1 for inter-stage cooling, then enters the second-stage impeller 15, passes through the second-stage volute 16 for cooling, and then enters the closed system from the steam inlet 14, passes through the second-stage side support magnetic suspension bearing cooling channel, the thrust magnetic suspension bearing cooling channel, the motor stator winding inner and outer cooling channels, the first-stage side support magnetic suspension bearing cooling channel in turn, and then flows out from the steam outlet 3, passes through the pressure regulating valve 17 to reduce the pressure to the first-stage impeller inlet pressure, and returns to the first-stage impeller inlet after cooling to enter the cycle again.

[0024] See also Figure 3 , Figure 4 The water vapor leaking from the primary seal 5 and the secondary seal 12 can enter the cooling circuit and participate in the circulation.

[0025] The working principle of the present invention is:

[0026] In the closed two-stage centrifugal compressor system, the pressure difference between the outlet of the secondary compressor and the inlet of the primary compressor is utilized. The high-temperature and high-pressure water vapor at the outlet of the secondary compressor is cooled and then enters the closed system from the steam inlet 14. Most of the internal heat is taken away through the cooling channels of the motor and bearings to ensure that it operates within a safe temperature range. The cooled water vapor returns from 3 to the inlet of the primary compressor to re-participate in the circulation, thereby realizing self-cooling of the closed system.

[0027] Embodiment 1:

[0028] See also Figure 2 , Figure 2 It is a closed two-stage centrifugal water vapor compressor directly driven by a high-speed permanent magnet motor with a speed greater than 18600r / min and a power greater than 30kW. The first-stage impeller 2 and the second-stage impeller 15 are fixed on the rotating shaft 6 by a pull rod. The first-stage seal 5 is arranged in the first-stage rear cover plate 4, and the first-stage rear cover plate is connected to the first-stage volute 1 and the motor housing 8 by bolts. The second-stage seal 12 is arranged in the second-stage rear cover plate 13, and the second-stage rear cover plate is connected to the second-stage volute 16 and the motor housing 8 by bolts. The radial support of the rotor is achieved by the support magnetic suspension bearing 7, and the axial positioning of the rotor is achieved by the thrust magnetic suspension bearing 11.

[0029] During normal operation, the heat dissipation of the motor is greater than 0.6kW, the heat dissipation of the support magnetic bearing is greater than 0.5kW, and the heat dissipation of the thrust magnetic bearing is greater than 0.2kW. This heat needs to be taken away by the cooling gas. The cooling process is:

[0030] The first-stage centrifugal compressor sucks in 1000Pa, 7℃ saturated water vapor, and produces 2600Pa, 98℃ superheated water vapor after compression. After interstage cooling to eliminate superheat, it enters the second-stage centrifugal compressor, and produces 5630Pa, 114℃ superheated water vapor after secondary compression. The high-temperature and high-pressure water vapor is cooled to eliminate superheat, and the temperature is reduced to the saturation temperature of 35℃ at 5630Pa. It enters the closed system from the steam inlet 14, and passes through the cooling channel of the secondary side support magnetic suspension bearing, the cooling channel of the thrust magnetic suspension bearing, the internal and external cooling channels of the motor stator winding, and the cooling channel of the first-stage side support magnetic suspension bearing in turn, taking away the internal heat of the bearing and the motor to ensure that it operates within a safe temperature range. Then it flows out from the steam outlet 3, and the pressure is reduced to 1000Pa at the inlet pressure of the first-stage impeller through the pressure regulating valve 17. After cooling, it returns to the inlet of the first-stage impeller and enters the cycle again.

[0031] The state parameters of the cooling gas entering the system from the steam inlet 14 are: pressure 5630Pa, temperature 35°C, enthalpy 2322.8kJ / kg;

[0032] The state parameters of the cooling gas flowing out of the system from 3 are: pressure 1050Pa, temperature 80℃, enthalpy 2650.8kJ / kg;

[0033] The total heat dissipation of the motor and bearings that needs to be removed is: 1.8kW

[0034] The required cooling gas flow rate is:

[0035]

[0036] This translates to a volume flow rate of 448.

[0037] Under the same working conditions, if compressed air is used for cooling, the required compressed air volume is 2026. Under the premise of achieving the same cooling effect, the present invention reduces the required cooling air volume by 77%, and the cooling flow channel size is more compact.

[0038] In this embodiment, the leakage of the primary side seal 5 is 2.38 kg / h, and the leakage of the secondary side seal 12 is 2.40 kg / h. This part of the leaked gas can be returned to the primary inlet through the cooling circuit for compression again, and the overall efficiency can be improved by 0.98%. The above is an exemplary description of the present invention. It should be noted that any simple deformation, modification or equivalent replacement that can be made by other technicians in this field without spending creative labor falls within the protection scope of the present invention without departing from the core of the present invention.

Claims

1. A self-cooling system for a closed two-stage centrifugal water vapor compressor directly driven by a high-speed permanent magnet motor, characterized in that: The invention comprises a first-stage impeller (2) and a second-stage impeller (15), wherein the first-stage impeller (2) and the second-stage impeller (15) are fixed on a rotating shaft (6) by a pull rod, a first-stage seal (5) is arranged in a first-stage rear cover plate (4), and the first-stage rear cover plate is connected to a first-stage volute (1) and a motor housing (8) by bolts; a second-stage seal (12) is arranged in a second-stage rear cover plate (13), and the second-stage rear cover plate is connected to a second-stage volute (16) and a motor housing (8) by bolts; radial support of the rotor is achieved by a supporting magnetic suspension bearing (7), and axial positioning of the rotor is achieved by a thrust magnetic suspension bearing (11); The air gap between the motor stator (9) and the motor rotor (10) forms an inner cooling channel of the motor stator winding, the air gap between the motor stator (9) and the motor housing (8) forms an outer cooling channel of the motor stator winding, the air gap between the primary side support magnetic suspension bearing (7) and the rotating shaft (6) forms a primary side support magnetic suspension bearing cooling channel, the air gap between the secondary side support magnetic suspension bearing (7) and the rotating shaft (6) forms a secondary side support magnetic suspension bearing cooling channel, and the air gap between the thrust plate and the balance magnet of the thrust magnetic suspension bearing (11) and the air gap between the bearing and the rotating shaft (6) form a thrust magnetic suspension bearing cooling channel; After being cooled, the water vapor at the outlet of the second-stage compressor of the two-stage centrifugal water vapor compressor enters the closed system from the steam inlet (14) by utilizing the pressure difference between the outlet of the second-stage compressor and the inlet of the first-stage compressor, and passes through the internal and external cooling channels of the stator winding and the cooling channels of the magnetic bearing to remove the heat inside the bearing and the motor. The cooled water vapor returns to the inlet of the first-stage compressor to participate in compression and is circulated; The water vapor cooling circuit is as follows: the water vapor enters the first-stage impeller (2), passes through the first-stage volute (1) for inter-stage cooling, then enters the second-stage impeller (15), passes through the second-stage volute (16) for cooling, then enters the closed system from the steam inlet (14), passes through the second-stage side support magnetic suspension bearing cooling channel, the thrust magnetic suspension bearing cooling channel, the motor stator winding inner and outer cooling channels, the first-stage side support magnetic suspension bearing cooling channel in sequence, then flows out from the steam outlet (3), passes through the pressure regulating valve (17) to reduce the pressure to the first-stage impeller inlet pressure, and after cooling, returns to the first-stage impeller inlet and enters the cycle again.

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