CN1108501C - Centrifugal compressor unit for 5 or 8KW refrigeration system - Google Patents

Abstract

A 5 or 8 kW refrigeration system includes a two-stage centrifugal compressor unit with a condenser, an evaporator, and an electric motor equipped with a cooling system. The condenser inlet is connected to the compressor unit outlet, which is then connected to the evaporator inlet and the cooling system via piping through first and second throttling devices. The evaporator outlet communicates with the compressor unit inlet, and the cooling system outlet is connected to the compressor unit second-stage inlet. The system also features a cooling skirt, the cavity of which is located between the stator and the motor housing. The system also includes a separator vessel, a recuperator heat exchanger, and a heat regulating valve. The valve is controlled by the coolant pressure and temperature at the cooling skirt outlet and is installed in series with the piping connecting the condenser outlet to the evaporator. The separator vessel is connected to the coolant inlet in the vapor phase. The recuperator heat exchanger is connected to the piping connecting the condenser outlet and the evaporator inlet via the evaporator coolant. The second throttling device is a heat regulating valve controlled by the coolant temperature and pressure in the cooling skirt coolant discharge pipe.

Description

Centrifugal compressor unit for 5 or 8KW refrigeration system

technical field

The invention belongs to the field of heat and power engineering, and can also be used in refrigeration technology.

current technology

A known refrigeration system comprises a condenser, an evaporator and a two-stage centrifugal compressor unit with an electric motor built in between the stages. The electric motor is equipped with a cooling system provided with coolant inlet and outlet pipes communicating with the interior cavity of the casing. In addition, the inlet of the condenser is connected with the outlet of the compressor unit, and the outlet of the condenser is connected with the evaporator through the first throttling device through the pipeline, and connected with the motor cooling system through the second throttling device through the second pipeline. The evaporator outlet is in communication with the compressor train inlet, and the gas coolant discharge pipe is connected with the outlet of the second stage 1 of the compressor train.

Disadvantages of this known cooling system are low efficiency and reliability due to wet vapor entering the discharge pipe of the first stage of the compressor, the presence of oil in the system, a narrow range of controllability and the impossibility of using ecologically safe of refrigerant.

A known centrifugal compressor unit for a refrigeration system comprises a two-stage centrifugal compressor with rotors, a diffuser, a plenum, inlet and outlet lines for the second stage and compression in the first and second stages. Built-in electric motor between units. The rotor of the electric motor is located on the same bearing-mounted shaft as the rotor of the centrifugal stage, while the stator is fixed in its housing, forming a cooling skirt between them. In addition, the motor casing is provided with a gas coolant inlet pipe and a discharge pipe connected to the outlet pipe 1 of the second-stage compressor unit.

The disadvantage of this known centrifugal compressor unit for cooling systems is the low reliability due to the unsatisfactory design of the cooling system of the electric motor, the incomplete cancellation of the axial forces on the shaft of the unit, the large volume of the electric motor and the Its basic design cannot be applied to small units, such as units with a cooling capacity of 5 and 8kW.

Contents of the invention

For refrigeration systems, the invention seeks to increase efficiency and reliability while ensuring eco-safety through the use of environmentally safe refrigerants; it also expands the range of cooling capacity and control.

For the centrifugal compressor unit of the above system, the present invention seeks to improve the reliability, reduce the size and expand the scope of use.

The composition of the refrigeration system of 5 or 8kW in the present invention includes a condenser, an evaporator and a two-stage centrifugal compressor unit with a built-in motor between compressor stages. The electric motor is equipped with a cooling system provided with coolant inlet and outlet pipes communicating with the inner cavity of the electric motor. In addition, the inlet of the condenser is connected with the outlet of the compressor unit, and the outlet of the condenser is connected with the inlet of the evaporator through the first throttling device through the pipeline, and connected with the motor cooling system through the second throttling device through the second pipeline. The evaporator outlet communicates with the compressor train inlet, and the coolant discharge pipe connects with the outlet of the second stage of the compressor train. We plan to equip the system with an additional throttling device, a separator vessel, and a recuperative heat exchanger, and set up the cooling system for the motor with a cooling skirt that is in contact with the inner cavity of the motor housing insulation. The cooling skirt cavity is located between the stator and the motor casing and is connected to the second coolant inlet and outlet pipes. In addition, the additional throttling device is a thermal regulating valve controlled by the coolant pressure and temperature at its inlet, and the separator vessel is installed in series on the line connecting the condenser outlet to the evaporator, before the first throttling device . The separator vessel is connected in the gas phase to the coolant input pipe while the recuperator heat exchanger is connected in the coolant to the line connecting the evaporator outlet to the condenser inlet and to the pipe connecting the condenser outlet to the evaporator inlet , after the separator container. In addition, the second pipeline drawn from the condenser is connected to the second coolant inlet pipe, the second coolant discharge pipe is connected to the separator container, and the additional throttling device on the second pipeline is provided by the second A thermoregulator valve that controls the temperature and pressure of the coolant in the coolant discharge pipe.

In addition, the first throttling device installed on the pipeline from the condenser to the evaporator is a thermal regulating valve controlled by the pressure and temperature of the coolant at the outlet of the evaporator.

This refrigeration system is equipped with a device for controlling the speed of the motor according to the temperature of the air leaving the evaporator.

The 5 or 8kW centrifugal compressor unit used in the above refrigeration system in the present invention includes a double-stage centrifuge with rotors, a diffusion valve, a collection chamber and inlet and outlet pipelines. The first-level outlet pipeline is connected with the second-level inlet pipeline by a conveying pipe. There is a built-in electric motor between the stages; its rotor and the rotor of the compressor stage are located on a shaft mounted with pneumatic bearings, and its stator is fixed inside the motor casing, forming a cooling skirt between them. In addition, a coolant inlet pipe and a discharge pipe are arranged inside the motor casing, which are connected with the outlet pipe of the second stage of the compressor unit. For this unit, we plan to form a cooling skirt with longitudinal grooves on the surface of the stator in contact with the casing, the ends of which are connected to annular grooves on the inner surface of the motor. In addition, each annular groove is connected to a second coolant inlet pipe or outlet pipe, and the inlet pipe and outlet pipe are connected to the inner cavity of the motor housing from different sides of the stator.

In addition, longitudinal grooves are provided on the surface of the stator in contact with the rotor.

The rotating shaft of the centrifugal compressor unit is installed on radial pneumatic bearings.

Centrifugal compressor units are equipped with bi-directional axial aerodynamic bearings mounted on the shaft in the cavity of the motor casing by means of gimbals, between the stator and one of the coolant inlet or discharge pipes.

Brief introduction to the drawings

The drawings illustrate the invention.

Figure 1 shows a schematic diagram of a refrigeration system.

Figure 2 is a cross-sectional view of a centrifugal compressor unit used in the system described above.

The refrigeration system (see Figure 1) consists of a condenser 1, an evaporator 2 and a two-stage centrifugal compressor unit with 5 stages 3 and 4 built-in motors 6 of the compressor unit. The motor is provided with a cooling system provided with coolant inlet and outlet pipes 7 and 8 connected to the interior 9 of the motor 6 . In addition, the inlet 11 of the condenser 1 is connected to the outlet 12 of the compressor unit 5, and the outlet 13 of the condenser is connected to the inlet 16 of the evaporator 2 through the first throttling device 15 through the pipeline 14, and through the second pipeline 17 through the first Two throttling devices 18 are connected with the motor 6 cooling system.

The outlet 19 of the evaporator 2 communicates with the inlet 21 of the compressor unit 5 via a line 20 , and the gaseous coolant discharge pipe 8 is connected with the inlet 22 of the second stage 4 of the compressor unit 5 . In addition, this system is also equipped with an additional throttling device 23, a separator container 24 and a recuperative heat exchanger 25, and adopts a cooling skirt 26 to provide a cooling system for the motor 6, and the cooling skirt 26 is connected to the motor 6. 6 The inner chamber 9 of the casing 10 is insulated. The cooling skirt cavity 27 is located between the stator 28 and the motor housing 10 and is connected to the second coolant supply and discharge lines 29 and 30 . In addition, an additional throttling device 23 is a thermal regulating valve controlled by the pressure and temperature of the coolant at its outlet, and a separator vessel 24 is installed in series on the line 14 connecting the outlet 13 of the condenser 1 to the evaporator 2, Before the first throttling device 15 . The separator vessel 24 is connected in the gas phase to the coolant inlet pipe 7, while the recuperator heat exchanger 25 is connected in the coolant to the line 20 connecting the condenser outlet 19 and the inlet 21 of the compressor unit 5, and to the connection Line 14 to outlet 13 of condenser 1 , outlet 16 of evaporator 2 after separator vessel 24 . In addition, the second pipeline 17 drawn from the condenser 1 is connected to the second coolant inlet pipe 29 of the cooling skirt 26, and the second coolant discharge pipe 30 is connected to the separator container 24 and is located in the second pipeline 17. The additional throttling device 18 is a thermal regulating valve controlled by the temperature and pressure of the coolant in the second coolant discharge pipe 30 .

The first throttling device 15 installed on the pipeline from the condenser 1 to the evaporator 2 is a thermal regulating valve controlled by the pressure and temperature of the coolant at the outlet 19 of the evaporator 2 .

This refrigerating system is equipped with a device 31 for controlling the rotational speed of the motor 6 according to the temperature of the air leaving the evaporator 2 [by means of a signal from a temperature sensor 32].

The composition of the centrifugal compressor unit of the above-mentioned refrigeration system (see Figure 2) includes double centrifuge stages 3, 4 with rotors 33 and 34, diffuser pipes 35 and 36, collection chambers 37 and 38 and inlet and outlet pipes 39 and 40 . In addition, the outlet pipe 40 of the first stage 3 and the inlet pipe 39 of the second stage 4 are connected by a delivery pipe 41 . Between the stages 3 and 4 of the compressor unit 5 there is a built-in electric motor 6; the motor rotor 42 and the compressor stage 3 and 4 rotors 33 and 34 are located on a rotating shaft 43 mounted using pneumatic bearings 44, while the stator 28 of the motor 6 It is fixed inside its housing 10, forming a cooling skirt 26 therebetween. In addition, the casing 10 of the motor 6 is provided with a coolant inlet pipe 7 and a discharge pipe 8 , which are connected to the outlet pipe 39 of the second stage 4 of the compressor unit 5 . The cooling skirt 26 is formed on the surface 45 of the stator 28 in contact with the casing 10 by a longitudinal groove 46 whose ends are connected with annular grooves 47 and 48 on the inner surface 49 of the casing 10 of the motor 6 . In addition, each annular groove 47 and 48 is connected to a second coolant inlet or outlet pipe 29 and 30, and the inlet pipe 29 and the outlet pipe 30 are connected to the inner chamber 9 of the motor 6 casing 10 from different sides of the stator 28 .

In the surface 50 of the stator 28 longitudinal slots 51 are provided in contact with the rotor 42 . The rotating shaft 43 of the centrifugal compressor unit is mounted on radial pneumatic bearings or roller bearings. The centrifugal compressor unit is equipped with a two-way axial pneumatic bearing 52, which is installed on the rotating shaft in the inner cavity 9 of the casing 10 of the motor 6 by means of a universal suspension bracket 53, and is located on the stator 28 and the coolant inlet pipe 7 or discharge pipe 8 one of.

Best Embodiment of the Invention

The working process of this cooling system and centrifugal compressor unit is as follows. Switching on the motor 6 starts the centrifugal compressor 5 . Coolant vapor is withdrawn from the evaporator 2 and is heated as it passes through the recuperator heat exchanger 25 . In the first stage 3 of the centrifugal compressor 5, the coolant vapor is compressed and passed through the inlet 22 to the second stage 4, where it communicates with the coolant discharge pipe 8 from the inner cavity 9 of the casing 10 of the electric motor 6. Coolant vapor mixing.

The coolant vapor enters the interior 9 from the separator container 24 through the coolant supply line 7 . The rotor 42 and the stator 28 of the electric motor 6 are cooled as the coolant vapor passes through the gap between the stator 28 and the rotor 42 and passes through the coolant discharge pipe 8 along the longitudinal grooves 51 on the surface of the stator 28 . After mixing, the coolant vapor is compressed in the second stage 4 of the centrifugal compressor 5 and thereafter sent by its outlet 12 to the inlet 11 of the condenser 1 . In the condenser 1, the coolant vapor condenses as its heat is carried away by the cooling air.

Most of the liquid coolant is sent from the condenser 1 along the pipeline 14 to the separator vessel 24 via the first throttling device 23, which is a thermal regulating valve that works on the principle of supercooled liquid coolant . In addition, the liquid coolant is throttled down to an intermediate pressure in the separator vessel 24 where the vapor-liquid coolant mixture is hydrodynamically separated into vapor and liquid.

A small part of the liquid coolant in the condenser 1 is sent to the second coolant inlet pipe 29 through the second throttling device 18 along the second pipeline 17, and is sent into the cavity of the skirt cover 26 as it is sent into the motor 6 27 , in which part of the liquid coolant evaporates due to the heat absorbed by the stator 28 . Coolant vapor is sent from the cooling skirt cavity 26 to the separator vessel 24 along the second coolant drain 30 .

From the separator vessel 24 the liquid coolant passes through the recuperator heat exchanger 25 and is subcooled by the coolant vapor which is sent from the evaporator along the line 20 to the first stage of the compressor unit 5 Entrance 21 from 3. After passing through the recuperative heat exchanger 25 , the liquid coolant is throttled in the first throttling device 15 and enters the inlet 16 of the evaporator 2 . The coolant thus circulates through the refrigeration system.

The refrigeration capacity of the refrigeration system can be smoothly controlled by changing the rotation speed of the rotor 42 , and the rotation speed is controlled by means of the device 31 according to the signal of the temperature sensor 32 .

The means 31 for controlling the speed of the rotor 42 of the electric motor 6 can gradually accelerate the rotor 42 to the speed at which the shaft 43 of the motor rotor 42 and the compressor rotor 33 disengage from the surface of the radial aerodynamic bearing 44 . industrial application

In the proposed compressor unit, effective cooling of the stator 28 of the motor 6 by means of the cooling skirt 26 is achieved by longitudinal grooves 46 on the surface 45 of the stator 28 (this ensures a large area for cooling the stator) and This is achieved by utilizing the annular grooves 47 and 48 on the inner surface 49 of the housing 10 of the motor 6 to form the inner cavity 27 of the cooling skirt. One of the annular grooves serves to distribute the coolant vapor sent from the second coolant inlet pipe 29 along the longitudinal groove 46 , while the other serves to collect the coolant and send it to the second coolant outlet pipe 30 .

Because the two-way axial aerodynamic thrust bearing 52 that adopts the universal suspension bracket 53 is installed on the rotating shaft 43 in the motor 6 casing 10 between the stator 28 and the coolant inlet pipe or one of the discharge pipes 7 and 8, it Cooled by the coolant passing through it.

Due to the layout characteristics of this refrigeration system and the design of its centrifugal compressor unit, it can work with high molecular weight refrigerants that are harmless to ozone, such as RC318, R218 and their mixtures.

Claims (4)

1. A 5 or 8kW centrifugal compressor unit for refrigeration systems, which consists of double centrifuge stages with rotors, diffusion pipes, collection chambers and inlet and outlet pipelines, wherein the first stage outlet pipeline is connected to the second The secondary inlet pipeline is connected by a delivery pipe; there is a built-in motor between the stages, and its rotor and the rotor of the compressor stage are located on a rotating shaft installed with an aerodynamic bearing, while its stator is fixed inside the motor casing, forming a gap between them. Cooling the skirt, while the motor housing is provided with coolant inlet pipes and discharge pipes, which are connected to the outlet pipes of the second stage of the compressor unit; it is characterized in that the stator is formed by longitudinal grooves on the surface of the stator that is in contact with the housing The end of the longitudinal groove is connected with the annular groove on the inner surface of the motor; in addition, each annular groove is connected with the second coolant inlet pipe or outlet pipe, and the inlet pipe and outlet pipe are connected from different sides of the stator. Connected to the inner surface of the motor housing. 2. The centrifugal compressor unit as claimed in claim 1, characterized in that longitudinal grooves are provided on the surface of the stator to contact the rotor. 3. Centrifugal compressor unit as claimed in claim 1, characterized in that the shaft of the centrifugal compressor unit is mounted on radial aerodynamic bearings in the form of three self-aligning segments. 4. The centrifugal compressor unit as claimed in claim 1, characterized in that the centrifugal compressor unit is equipped with double-sided axial pneumatic bearings, and the bearings are installed on the rotating shaft in the inner cavity of the motor casing by means of a universal suspension bracket , between the stator and one of the coolant inlet or outlet pipes.

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