JPH06235555A - Refrigerating plant using oil-free type screw compressor - Google Patents

Abstract

PURPOSE:To obtain a refrigerating plant which uses a refrigerant in which oil is insoluble, and can be operated without any difficulty even in the case the viscosity of oil becomes high as the evaporation temperature of a refrigerating cycle is low. CONSTITUTION:NH3 refrigerant gas compressed by a screw compressor 1 is liquefied at a condenser 2 and then a portion of refrigerant liquid is sprayed into the compressor 1 at a position after gas is closed inside. The remaining refrigerant is depressurized by an expansion valve 5 and flows into an evaporator 3. The refrigerant liquid in a liquid reservoir pot 7 is repeatedly circulated by a liquid pump 6 and flash-evaporated in the evaporator 3 through a refrigerant spray pipe 10. At this time, a thin film evaporation takes place on the heat exchange surface of a load side heat exchanger 17. Lubricating oil is supplied into a timing gear housing of the screw pump 1 by the use of an oil pump 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refrigerating apparatus using an oil-free screw compressor, which is suitable when a refrigerant in which oil does not dissolve is used and the temperature of the evaporator is low and the viscosity of the oil is high.

[0002]

2. Description of the Related Art Conventionally, in a refrigerating apparatus using a screw compressor, even when Freon is used as a refrigerant.
Even when NH ₃ was used, an oil injection type screw compressor was used, and an oil free type screw compressor was not used.

When Freon is used as the refrigerant, the oil dissolves in Freon, so there are few problems. However, when NH ₃ is used, the oil does not dissolve and separates from NH _3, and enters the evaporator. Oil does not come back with gas. In addition, when the operation of the refrigerator becomes lower than about -20 ° C in the evaporator temperature, for example, the viscosity of the oil becomes high, and it is difficult to remove the oil stored in the evaporator. Therefore, it has been necessary to stop the operation of the refrigerator once, raise the temperature of the oil, lower the viscosity of the oil, and drain the oil.

FIG. 3 shows an example of a refrigeration cycle using a conventional oil-injection type screw compressor, in which an insoluble oil is used with an NH ₃ refrigerant or the like, and a Freon refrigerant and a soluble oil are used. It is used in all cases.

The refrigerant gas compressed from the screw compressor 35 flows through the oil separator 36, the discharge pipe 37 and the condenser 38,
The high-pressure refrigerant liquid cooled and condensed by the heat exchanger 39 is decompressed from the liquid pipe 40 through the expansion valve 41, flows into the evaporator 42, and is evaporated. Then, the load side heat exchanger 43 is cooled. On the other hand, the oil separated from the bottom of the oil separator 36 is the oil pump 44,
It is injected into the casing from the oil injection port 46 of the rotor of the screw compressor 35 after the gas is closed through the oil cooler 45. Also, the oil reservoir pot 47 at the bottom of the evaporator 42 communicates with an oil reservoir 49 via a solenoid valve or a temperature type automatic expansion valve 48, and a purge pipe 50 from the top of the oil reservoir 49 via the solenoid valve 48. It communicates with the low voltage section.

In the embodiment of FIG. 3, the mixed discharge gas of oil and refrigerant gas from the screw compressor is separated in the oil separator 36, and the oil is discharged from the oil injection port as described above.
It is injected from 46 and recirculation is performed. The oil that has not been separated by the oil separator 36 flows into the evaporator 42 through the condenser 38 together with the refrigerant liquid.

When the refrigerant dissolves oil by Freon or the like, an oil removing device from the evaporator 42 is unnecessary,
The heat transfer is not good as the oil circulates in the refrigeration cycle. Further, when the refrigerant does not dissolve the oil in NH ₃ or the like, the viscosity of the oil becomes high in proportion to the low temperature at a low temperature, for example, −20 ° C. or lower, and it becomes difficult to take out the oil accumulated at the bottom of the evaporator 42. . Therefore, a device for removing the oil as shown by the dotted line in FIG. 3 is provided, and the accumulated oil is injected from the introduction pipe 51 to the position after the rotor of the screw compressor is closed and recirculated. However, as the temperature becomes lower, this oil removal becomes more difficult.

FIG. 4 is an example of a refrigerating cycle in which a conventional oil injection type screw compressor is used and NH ₃ is used as a refrigerant. It is a component that has the same structure and performs the same function. The refrigerant liquid decompressed by the expansion valve 41 flows into the low pressure liquid receiver 54, and the liquid level is adjusted by the level controller 55. A large amount of the refrigerant liquid stored in the low-pressure receiver 54, together with the invading oil, is evaporated by the liquid pump 56 via the distribution valve 58.
After flowing into 57 and cooling the load side heat exchanger 59, it returns to the low pressure liquid receiver 54 again, and this circulation is repeated.

As the temperature of the evaporator gradually decreases,
The viscosity of oil gradually increases. Therefore, the liquid pump 56 must force the refrigerant liquid and oil in the low-pressure receiver 54 to constantly circulate in the evaporator 57 to prevent the oil from separating and stagnating in the low-pressure receiver 54. Further, the oil that is separated into two layers in the low pressure liquid receiver 54 is guided from an oil drain valve 60 to an oil drain reservoir (not shown), and an oil drain operation is required.

Moreover, the structure of the prior art shown in FIGS. 3 and 4 is complicated.

[0011]

As described above, the conventional technique has various problems.

In order to eliminate these problems, the present invention adopts an oil-free type screw compressor and uses a timing gear to prevent oil from being mixed in the evaporator (low pressure side). It is intended to obtain a simple oil-free type screw compressor refrigerating apparatus.

[0013]

In order to achieve the above-mentioned object, the refrigerating apparatus of the present invention uses a refrigerant that does not dissolve oil and the evaporator temperature of the refrigerating cycle is low and the viscosity of the oil is high. In this case, the screw compressor is an oil-free type, and has a liquid injection port for injecting a part of the high-pressure refrigerant liquid from the condenser to the position of the rotor of the screw compressor after the gas is closed.

Further, in order to achieve the above-mentioned object, the refrigerating apparatus of the present invention uses NH ₃ as a refrigerant, and further returns the refrigerant liquid in the liquid reservoir pot attached to the evaporator to the evaporator and injects it. A recirculation pipe for performing thin film evaporation on the heat exchange surface of the load side heat exchanger is attached to the evaporator, and a liquid pump is provided in the recirculation pipe.

In order to achieve the above object, the refrigerating apparatus of the present invention is provided with an inverter or a pole number converting motor for controlling the rotation speed of the screw compressor.

[0016]

Since the screw compressor is an oil-free type, no oil flows into the evaporator side, and one of the high-pressure refrigerant liquids from the condenser injected at the position after the gas is closed in the rotor of the screw compressor. The section removes heat of compression to improve compressor efficiency.

Further, thin film evaporation is carried out in the evaporator by a recirculation pipe having a liquid pump attached to the evaporator, and a small amount of refrigerant produces a highly efficient cooling effect. Furthermore, the rotation speed of the screw compressor is controlled by an inverter system or a pole number conversion motor to cope with fluctuations in the load of the refrigeration system.

[0018]

Embodiments of the present invention will be described with reference to the drawings.

In FIG. 1, 1 is an oil-free type screw compressor, 2 is a condenser, 3 is an evaporator, 4 is a liquid amount adjusting valve, 5 is an expansion valve, 6 is a liquid pump, 7 is a liquid storage pot, 8 is an oil pump, 9 is an oil cooler, 10 is a refrigerant liquid injection pipe, and 11 is a recirculation pipe.

NH ₃ compressed by the screw compressor 1
Of the refrigerant gas reaches the condenser 2 via the discharge pipe 12, where it is cooled and liquefied by the cooling water heat exchanger 14, and the refrigerant liquid flows out to the liquid pipe 13. The liquid pipe 13 is provided with a branch pipe 15 in the middle thereof, so that the amount of the refrigerant liquid adjusted by the liquid amount adjusting valve 4 is discharged from the liquid injection port 16 at a position after the gas of the rotor of the screw compressor 1 is closed by the screw. It is injected into the casing of the compressor 1. The injected refrigerant liquid evaporates and exhibits a cooling effect similar to isothermal compression, and also has a sealing effect to improve the efficiency of the compressor.

The refrigerant liquid in the liquid pipe 13 is decompressed by the expansion valve 5 and introduced into the evaporator 3. A load side heat exchanger is provided in the evaporator 3.
17 is provided and is cooled by the refrigerant that evaporates in the evaporator 3. The low-pressure liquid receiver is not provided, and the refrigerant liquid in the evaporator 3 is provided with the liquid reservoir pot 7, from which the liquid pump 6 is reintroduced to the upper portion of the evaporator 3 through the recirculation pipe 11, and the refrigerant liquid injection pipe 10 is provided. From the
The refrigerant liquid repeats its circulation as it flash-evaporates.

Since the screw compressor 1 is an oil-free type, no oil is mixed in the refrigerant gas discharged from the compressor to the discharge pipe 12, and therefore no oil flows into the evaporator 3. Therefore, unlike the prior art, it is not necessary to introduce a large amount of refrigerant liquid into the evaporator 3, and the liquid pump 6 can be used to inject and flush the surface of the load side heat exchanger 17 to perform thin film evaporation. Not only can the amount of the generated refrigerant be reduced, but the heat transfer coefficient between the refrigerant and the load-side fluid can be improved.

FIG. 2 shows an embodiment of the oil-free type screw compressor 1 used in the embodiment shown in FIG. 1, in which two meshing male rotors 22 and female rotors 23 are housed in a rotor casing 26, and their respective shafts are accommodated. The timing gears 24 and 25 are assembled on top of each other so that the two rotors do not come into metal contact with each other by synchronizing the gears having the ratio of the number of teeth of the rotors.

The refrigerant gas is sucked from the suction port 20 and compressed without being mixed with oil, and is discharged from the discharge port 21 to the discharge pipe 12.
(Fig. 1). The gear box 27 is flushed with oil, that is, lubricating oil. The rotating shafts of the male rotor 22 and the female rotor 23 are supported by bearings 30, and an oil seal 31 provided at the end of each bearing 30 prevents lubricating oil from entering the rotor casing 19. A mechanical seal 32 is provided at the outer end of the bearing 30 of the drive shaft 28 to provide a gas and oil seal with the outside air. The oil pump 8 (FIG. 1) supplies the lubricating oil to the inside of the gear box 27, the oil seal 31, and the mechanical seal 32. Also, in the case of a hermetic compressor using a hermetic motor or a canned motor, no seal is provided and the mechanical seal 32 is eliminated.

The capability control by changing the rotation speed of the screw compressor, which is performed according to the change of the load, is performed by an inverter system that changes the power supply frequency or by providing a pole number conversion motor. The control is 2-pole (3000 rpm 3
600r. p. m) The number of rotations equal to or higher than the above is performed. Increasing this speed will increase the efficiency of the oil-free compressor. This eliminates the need for a speed increasing gear device.

[0026]

EFFECTS OF THE INVENTION Since the oil-free type screw compressor does not allow oil to enter the evaporator side, the evaporator is not affected by oil contamination and heat transfer is very good. There is no problem even in the operation of the refrigerating device in the case of a low temperature that raises the temperature.

Further, the refrigerant liquid can be injected to the position of the intermediate pressure of the screw rotor of the compressor to be evaporated, whereby the compression heat can be removed and the compressor efficiency can be improved.

Further, the load fluctuation of the refrigeration system can be controlled by controlling the rotation speed of the screw compressor by means of an inverter or a pole number conversion motor, and an unloader mechanism in the compressor is not required.

Further, since the oil does not flow into the evaporator, it is possible to adopt the liquid pump system, and the recirculation pipe having the liquid pump allows the refrigerant to be thin-film evaporated in the evaporator. It can be a wet evaporator, and thus a high efficiency cooling effect can be obtained with a small amount of refrigerant.

Moreover, since no oil enters the evaporator at all, there is no need to worry about oil draining, and continuous operation can be carried out even in a refrigerating machine at a low temperature such as -30 ° C. Further, a high-pressure oil separator and a low-pressure oil removing device are unnecessary, which simplifies the device and makes it economical.

[Brief description of drawings]

FIG. 1 is a flow sheet diagram of an embodiment of a refrigerating apparatus of the present invention.

FIG. 2 is an explanatory diagram of a screw compressor with a timing gear used in the above embodiment.

FIG. 3 is a prior art flowsheet diagram.

FIG. 4 is a different prior art flowsheet diagram.

[Explanation of symbols]

 1 Screw compressor 2 Condenser 3 Evaporator 6 Liquid pump 7 Liquid storage pot 11 Recirculation pipe 16 Liquid injection port 17 Load side heat exchanger

Claims (4)

[Claims] 1. A screw compressor is an oil-free type, which has a liquid injection port for injecting a part of high-pressure refrigerant liquid from a condenser to a position after gas closing of a rotor of the screw compressor to dissolve oil. A refrigerating apparatus using an oil-free screw compressor, which is used when the evaporator temperature of the refrigeration cycle is low and the viscosity of the oil is high using a non-refrigerant. 2. A refrigeration system using an oil-free screw compressor according to claim 1, wherein the refrigerant is NH ₃ . 3. A recirculation pipe is attached to the evaporator so as to return the refrigerant liquid in a liquid reservoir pot attached to the evaporator to the evaporator and inject it to perform thin film evaporation on the heat exchange surface of the load side heat exchanger of the evaporator. A refrigeration system using an oil-free screw compressor according to claim 1, wherein a liquid pump is provided in the recirculation pipe. 4. The refrigeration system using an oil-free screw compressor according to claim 1, further comprising an inverter or a pole number conversion motor for controlling the rotation speed of the screw compressor.