JP4236163B2 - Ammonia refrigeration system using working fluid composition composed of lubricating oil and ammonia refrigerant - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ammonia refrigeration apparatus using a working fluid composition composed of lubricating oil and ammonia refrigerant .
[0002]
[Prior art]
Conventionally, chlorofluorocarbon has been widely used as a refrigerant in the vapor compression refrigeration system, but it is clear that chlorofluorocarbon released into the atmosphere causes environmental problems that destroy the ozone layer over a long period of time and affect the global warming. In recent years, ammonia that has been used for a long time as a refrigerant that does not cause such environmental problems has been reviewed again. Fluorocarbons are generally compatible with paraffinic and naphthenic mineral oils that are generally used as lubricating oils for refrigerators, but ammonia is very incompatible with these lubricating oils, so ammonia refrigerators Then, an oil separator is provided at the compressor outlet to separate the ammonia gas discharged from the compressor from the lubricating oil. However, even if an oil separator is provided, the misted lubricating oil cannot be completely separated, and the discharge side of the compressor is heated to a high temperature, so that the lubricating oil is mixed in the ammonia as a mist. Then, the oil entering the refrigeration cycle is accompanied by the ammonia, and the lubricating oil entering the cycle is insoluble in ammonia and heavy in specific gravity, so it easily collects in the piping path of the cycle and accumulates in various places in the cycle path. In addition, it is necessary to provide an oil drainage part, collect these lubricating oils, and return them to the compressor again, which inevitably complicates the configuration.
[0003]
As a solution, an ammonia refrigeration apparatus using a working fluid composition composed of ammonia-compatible lubricating oil and ammonia refrigerant is disclosed (for example, Patent Document 1). As described in Patent Document 1, it is preferable to reduce the amount of lubricating oil as much as possible as long as the lubricating performance can be maintained. According to the type and application of the machine, the ratio of the lubricating oil is set to 3 to 30 wt% in order to maintain the lubricating performance of the compressor. On the compressor side, the ratio of the lubricating oil is increased, and an oil separator is provided at the exit from the compressor to separate the lubricating oil, and thereafter the ratio of the lubricating oil is reduced in the path to the compressor inlet. Sometimes. Then, the separated lubricating oil is returned to the compressor again (see FIG. 3 of Patent Document 1).
[0004]
The two-layer separation region of the compatible oil is determined by the temperature of the working fluid composition and the ratio of the lubricating oil. Patent Document 1 discloses a compatible oil that does not separate into two layers even at −50 ° C. or lower. However, two layers are separated even at high temperatures. FIG. 2 generally shows the two-layer separation characteristics of PAG (polyalkylene glycol), which is one of the compatible oils. The two-layer separation region is on the low temperature side and the high temperature side. Therefore, when the proportion of the lubricating oil is high to some extent, there is a lubricating oil separated into two layers in the gaseous working fluid composition having a high temperature inside the compressor and in the oil separator after leaving the compressor. is doing.
[0005]
In the case of a configuration using an oil separator, the wall of the oil separator is cooled by outside air while the operation of the refrigerator is stopped, and the refrigerant condenses on the inner wall surface of the oil separator, and the condensate becomes the oil separator. The oil is excessively dissolved in the lubricating oil separated into two layers, and the viscosity of the lubricating oil is lowered. The lubricating oil having the reduced viscosity is accumulated at the bottom of the oil separator. At the next start-up, the reduced viscosity lubricating oil is sent to the compressor, which may result in insufficient lubrication of the compressor rotor, bearings, seals, etc., which may cause damage.
[0006]
[Patent Document 1]
Japanese Patent No. 3241694 specification
[Problems to be solved by the invention]
Conventionally, in order to avoid this phenomenon, measures have been taken such as covering the oil separator with a heat insulating material and heating it with a heater or the like during stoppage. However, this method has a drawback in that the cost of covering with a heat insulating material and the electricity cost for heating with a heater are excessive.
[0008]
The present invention was made to eliminate such drawbacks, and it is not necessary to cover the oil separator with a heat insulating material so that the oil separator does not cool after stopping the operation of the refrigerator, and to heat with a heater or the like during the stop, An object of the present invention is to provide an ammonia refrigerating apparatus using a working fluid composition composed of lubricating oil and ammonia refrigerant .
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a refrigeration system comprising a compressor, a condenser, an expander and an evaporator using a working fluid composition composed of a lubricating oil compatible with an ammonia refrigerant and an ammonia refrigerant. And an oil separator on the outlet side of the compressor in the refrigeration cycle path, and check valves on the refrigeration cycle path on the compressor inlet side and the oil separator outlet side, respectively. An ammonia refrigeration system ,
Wherein upstream of the compressor inlet side check valve from the oil separator via an on-off valve with pressure relief path is connected in the path connecting the compressor inlet and the evaporator, in the oil separator Pressure detecting means for detecting pressure is provided, and the pressure in the oil separator is set based on a predetermined reference ambient temperature, measured ambient temperature, or oil separator surface temperature when the refrigeration apparatus is stopped. The present invention proposes an ammonia refrigerating apparatus , characterized in that a control device is provided for performing on-off control of the on-off valve so as to be equal to or lower than a saturated vapor pressure of the refrigerant .
[0010]
During operation of the refrigeration system, the oil separator is always supplied with a working fluid composition composed of high-pressure and high-temperature refrigerant gas compressed by the compressor and lubricating oil compatible with the refrigerant. The inner wall surface has a temperature close to that of the working fluid composition. The working fluid composition contains two layers of lubricating oil. On the other hand, when the operation of the refrigeration system is stopped, the supply of the high-pressure and high-temperature working fluid composition to the oil separator is stopped, so the oil separator is cooled by the ambient temperature and the inner wall surface temperature of the oil separator is lowered. When the inner wall surface temperature becomes lower than the saturation temperature of the refrigerant vapor at the pressure, the refrigerant condenses on the inner wall surface. The condensate of the refrigerant dissolves in the lubricating oil in the oil separator and causes a decrease in the viscosity of the lubricating oil. However, when the amount of dissolution becomes excessive, the viscosity of the lubricating oil also greatly decreases.
[0011]
The lubricating oil having the reduced viscosity is accumulated at the bottom of the oil separator, and is then sent to the compressor as lubricating oil when the refrigeration apparatus is started. Therefore, the rotor, bearings, seals, etc. of the compressor that has been supplied with the lubricating oil whose viscosity has been lowered and the lubricity has been lowered may be damaged due to insufficient lubrication.
[0012]
By the way, the saturation temperature of the refrigerant vapor is lower as the pressure is lower. Therefore, by lowering the pressure in the oil separator during the operation stop of the refrigerating apparatus, the saturation temperature of the refrigerant vapor, i.e. the temperature at which the refrigerant is condensed drops. If residual values decrease condensation temperature, it is possible to prevent a reduction viscosity of the lubricating oil due to excessive penetration of the refrigerant liquid oil separator is condensed on the inner wall surface is cooled from the periphery at the time of shutdown. Therefore, based on the previously determined standard ambient temperature or measured ambient temperature or the oil separator surface temperature the pressure in the oil separator during shutdown, if the refrigerant in the oil separator inner wall is reduced to a pressure which does not condense, Even when the temperature of the working fluid composition in the oil separator decreases during the operation stop, the ammonia refrigerant does not condense on the inner wall of the oil separator. The pressure equal to or lower than the saturated vapor pressure of the refrigerant in claim 1 refers to such a pressure. When the operation is stopped, the pressure in the oil separator is reduced by connecting the oil separator to the path from the evaporator to the compressor inlet check valve by a pressure relief path, and providing an open / close valve in the pressure relief path. By controlling the on-off valve so that the pressure in the oil separator becomes a predetermined pressure or less.
[0013]
The saturated vapor pressure of the refrigerant may be the saturated vapor pressure of the refrigerant at the predetermined reference ambient temperature, measured ambient temperature, or oil separator surface temperature. Since the ambient temperature varies depending on the season or the environment, the saturation vapor pressure of the refrigerant may be a saturated vapor pressure of at the coolant to the temperature set in advance a reference ambient temperature, or measuring the ambient temperature or the oil separator the surface temperature may be the saturated vapor pressure of at the refrigerant. Saturated vapor pressure of the refrigerant temperature detected from the advance based on the input is reference temperature may be calculated by the control device, or ambient temperature detector or the oil separator surface temperature detector to the control device It may be calculated by the control device based on the above. Further, it is preferable that a stop signal notifying the stop of the refrigeration apparatus is sent to the control device, and the pressure control operation is performed by the stop signal. For example, the stop signal may be generated by detecting the rotation of the compressor and issuing a stop signal, or by detecting a change in the situation of a part whose situation changes due to operation stop.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. However, the dimensions, materials, shapes, relative positions, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention unless otherwise specified.
[0015]
FIG. 1 is a diagram showing a schematic configuration of a refrigeration apparatus provided with the refrigerant excessive penetration preventing apparatus of the present invention. In the figure, 1 is a compressor, 2 is an oil separator, 3 is a condenser, 4 is an evaporator, and 5 is an expansion valve. The working fluid composition composed of the ammonia refrigerant compressed by the compressor 1 and the compatible oil is separated from the lubricating oil separated into two layers by the oil separator 2, and the ammonia refrigerant containing the compatible lubricating oil is condensed by the condenser 3. Then, the gas-liquid mixed state in which the pressure is reduced by being throttled by the expansion valve 5 is sent to the evaporator 4, evaporated by the evaporator, and sent to the inlet of the compressor 1. Lubricating oil accumulated at the bottom of the oil separator 2 is sent to the compressor 1 via the regulating valve 13, the lubricating oil cooler 11, and the pump 12 to lubricate the compressor rotor, bearings, seals and the like. The adjusting valve 13 adjusts the flow rate of the lubricating oil cooler 11 to adjust the temperature of the lubricating oil supplied to the compressor 1. Reference numeral 14 is a check valve disposed upstream of the compressor, and 15 is a check valve disposed downstream of the oil separator. Reference numeral 16 denotes a flow of a cooling medium for cooling the condenser 3, and 17 denotes a flow of a medium that receives cold heat in the evaporator 4. The above is the same configuration as the conventional refrigeration apparatus.
[0016]
6 is a pressure relief path for connecting the oil separator 2 to the upstream side of the compressor in a path connecting the evaporator 4 and the inlet of the compressor 1, and 7 is an on-off valve interposed in the pressure relief path 6. 8 is a pressure detector for detecting the pressure in the oil separator 2, 81 is an ambient temperature detector, and 82 is an oil separator surface temperature detector. Controller 9 calculates the detection calculates the saturated vapor pressure of at the coolant temperature, or the saturated vapor pressure of at the refrigerant in advance input criteria ambient temperature. When the operation of the refrigeration system is stopped, a signal notifying the control device 9 is sent (signal transmitter is not shown), and the control device 9 that has received the stop signal opens the on-off valve 7 and oils. The pressure in the separator 2 is released through the pressure relief path 6 to the path between the evaporator 4 and the compressor 1 on the low pressure side, the pressure in the oil separator 2 is lowered, and the oil detected by the pressure detector 8 When the pressure in the separator 2 decreases to the calculated saturated vapor pressure (predetermined pressure) or a pressure lower than that, the on-off valve is controlled to close the on-off valve 7. As a result, the pressure in the oil separator 2 is maintained at a predetermined pressure or a lower pressure while the refrigerator is stopped.
[0017]
Ambient temperature season, because it depends on the surrounding environment, leave input a reference ambient temperature according to the season and the ambient environment in advance the control device, the saturated vapor pressure of at the coolant temperature as a predetermined pressure seek it may be, or the measurement ambient temperature or the oil separator surface temperature control device may be a predetermined pressure seek input to the saturated vapor pressure of at the coolant to the temperature. Since the temperature in the oil separator does not become lower than the ambient temperature or the oil separator surface temperature, the predetermined pressure is obtained as described above, and the pressure in the oil separator is calculated as the calculated saturated vapor pressure (predetermined pressure). if below, the refrigerant in the oil separator does not condense.
[0018]
【The invention's effect】
The present invention is implemented in the form described above, and has the effects described below. That is, by decreasing to below a predetermined pressure the pressure in the oil separator when stopping the operation of the refrigerator to escape to the low pressure side, the refrigerant to condense in the oil separator wall by cooling during stop When the refrigerant condenses on the inner wall surface, it is possible to prevent the condensed refrigerant liquid from being excessively dissolved in the lubricating oil in the oil separator and reducing the viscosity of the lubricating oil. Thereby, when restarting a refrigerator, generation | occurrence | production of damage to a compressor rotor, a bearing, a seal | sticker, etc. by the lubricity falling by viscosity reduction can be prevented.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a refrigeration apparatus provided with an apparatus for preventing excessive refrigerant penetration into refrigeration oil according to an embodiment of the present invention.
FIG. 2 is a graph generally showing two-layer separation characteristics of a lubricating oil compatible with an ammonia refrigerant .
[Explanation of sign]
DESCRIPTION OF SYMBOLS 1 Compressor 2 Oil separator 3 Condenser 4 Evaporator 5 Expansion valve 6 Pressure relief path 7 On-off valve 8 Pressure detector 9 Control device 11 Lubricating oil cooler 12 Pump 13 Adjustment valve 14, 15 Check valve 81 Ambient temperature detection 82 Oil separator surface temperature detector

Claims (3)

A refrigeration cycle comprising a compressor, a condenser, an expander, and an evaporator is formed using a working fluid composition composed of an ammonia refrigerant, a compatible lubricating oil, and an ammonia refrigerant, and the refrigeration cycle path is compressed. An ammonia refrigeration apparatus provided with an oil separator on the outlet side of the machine, and provided with a check valve on each of the compressor inlet side and the refrigeration cycle path on the oil separator outlet side ,
A pressure relief path is connected to the upstream side of the check valve on the compressor inlet side of the path connecting the evaporator and the compressor inlet via an on-off valve from the oil separator, and in the oil separator Pressure detecting means for detecting pressure is provided, and the pressure in the oil separator is set based on a predetermined reference ambient temperature, measured ambient temperature, or oil separator surface temperature when the refrigeration apparatus is stopped. An ammonia refrigerating apparatus , comprising: a control device that performs opening / closing control of the on-off valve so that the pressure becomes equal to or lower than a saturated vapor pressure of the refrigerant . Disposed ambient temperature sensor or the oil separator surface temperature sensor to send the detected temperature to the controller, the saturated vapor pressure of at coolant to the temperature detected by the control device is characterized in that it is calculated The ammonia refrigeration apparatus according to claim 1. A refrigeration device stop signal is sent to the control device, and the control device controls opening and closing of the on- off valve based on the stop signal to control the oil separator internal pressure to be equal to or lower than the saturated vapor pressure of the refrigerant. The ammonia refrigerating apparatus according to claim 1, characterized in that:

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