JP4294351B2 - CO2 refrigeration cycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a CO<SB>2</SB>refrigerating cycle of a cascade two-stage compression type using CO<SB>2</SB>as refrigerant for cooling and heating operation at the same time, allowing efficient utilization of energy by using lubricating oil for a compressor separately to be non-compatible and compatible. <P>SOLUTION: The cascade two-stage compression CO<SB>2</SB>refrigerating cycle according to the first invention comprises a low-stage CO<SB>2</SB>refrigerating cycle 18 consisting of a low-stage evaporator 10, a low-stage compressor 11, a cascade condenser 12, and a (low-stage) expansion valve 13, to be operated by CO<SB>2</SB>refrigerant in a region including a low temperature saturated region, and a high-stage compressor 14, a gas cooler 15, a (high-stage) expansion valve 16 and a high-stage evaporator 17. <P>COPYRIGHT: (C)2005,JPO&amp;NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a CO ₂ refrigeration cycle, and in particular, a CO ₂ refrigeration cycle having both a cold heat source and a high temperature heat source, a single-stage expansion method using a single lubricating oil, a two-stage expansion method two-stage compression CO ₂ refrigeration cycle, The present invention relates to a cascade type two-stage compression CO ₂ refrigeration cycle using different types of lubricating oils.
[0002]
[Prior art]
In recent years, due to regulations on fluorocarbon refrigerants for protecting the global environment, the emergence of an efficient CO ₂ refrigeration cycle using CO ₂ (carbon dioxide) that is peculiar to ozone layer destruction, global warming, and the like is expected.
In addition, from the standpoint of efficient use of energy, the emergence of a versatile heat supply system that can simultaneously supply cold and hot heat is expected.
[0003]
Conventionally, as a means for performing cooling at a low temperature of minus several tens of degrees, a dual refrigeration cycle in which a high-stage high-stage cycle and a low-temperature-side low stage cycle are combined via a cascade capacitor has been used.
The cascade type two-stage compression refrigeration cycle forming the binary refrigeration cycle includes, for example, a high-stage ammonia refrigeration circuit using ammonia refrigerant and a low-stage CO ₂ refrigeration circuit using CO ₂ as a refrigerant. The cascade type two-stage compression refrigeration cycle is provided in a store such as a convenience store or a supermarket, and a condensing unit comprising the ammonia refrigeration circuit, a CO ₂ refrigeration circuit excluding an evaporator, and a cascade condenser is provided outside the store. The evaporator of the CO ₂ refrigeration circuit is installed in a showcase in the store.
[0004]
There is a proposal related to a cooling device that combines the high-stage ammonia refrigeration circuit and the low-stage CO ₂ refrigeration circuit. (For example, refer to Patent Document 1.)
The proposal has the following configuration as shown in FIG.
That is, as shown in the figure, the cascade type two-stage compression refrigeration cycle according to the present proposal includes an ammonia refrigeration circuit 51 and a CO ₂ refrigeration circuit 53, which are combined via a cascade capacitor 54.
In the ammonia refrigeration circuit 51, a high-stage compressor 55, a condenser 56, an ammonia receiver 57, an expansion valve 58, and a cascade capacitor 54 are formed in this order.
The CO ₂ refrigeration circuit 53 includes a cascade capacitor 54, a CO ₂ receiver 60, and an evaporator 61 in this order.
The two-stage compression refrigeration cycle is provided in a store such as a convenience store or a supermarket. A condensing unit C including the ammonia refrigeration circuit 51, a CO ₂ refrigeration circuit 53 excluding the evaporator 61, and a cascade capacitor 54 is provided. The evaporator 61 of the CO ₂ refrigeration circuit 53 is disposed outside the store, and is configured to be installed in a showcase S in the store.
[0005]
In the cascade type two-stage compression refrigeration cycle, the ammonia refrigerant is circulated by the high-stage compressor 55 provided in the high-stage ammonia refrigeration circuit 51, and the low-stage CO ₂ refrigeration circuit is circulated by the cascade condenser 54. The CO ₂ gas flowing through 53 is liquefied by deprivation heat, and the liquefied CO ₂ liquid refrigerant flows into the evaporator 61 in the showcase S to be vaporized, and the natural circulation and evaporator of the CO ₂ refrigerant are liquefied and vaporized. 61 is configured to release cold heat.
[0006]
When an excessive pressure rise in the low-stage CO ₂ refrigeration circuit 53 is caused by an accident in the high-stage ammonia refrigeration circuit 51 of the cascade type two-stage compression refrigeration cycle, the excessive pressure is discharged from the relief valve 62, It is intended for safe driving.
[0007]
On the other hand as one of CFC measures of refrigerants used in conventional vapor compression refrigeration cycle, the refrigeration cycle using CO ₂ is proposed, in order to use the low CO ₂ of the critical point as a refrigerant, the refrigeration cycle is critical The cycle includes a supercritical region exceeding the point, and generally includes the following problems.
That is, there is a problem that the liquid-phase refrigerant is sucked into the compressor and causes the compressor to be damaged, and a problem that the efficiency of the cycle is lowered.
The former problem is that in the case of a normal CO ₂ cycle using CO ₂ , the pressure on the gas cooler outlet side is determined by the opening of the pressure reducing valve based on the CO ₂ temperature on the gas cooler outlet side that cools the supercritical high-temperature high-pressure CO ₂ gas. Due to the adjustment, the degree of superheat on the outlet side of the evaporator becomes insufficient, and the liquid refrigerant is sucked into the compressor.
[0008]
This proposal has been made in view of the above problems. As an embodiment of the proposal, a two-stage expansion two-stage compression refrigeration cycle is formed, the work capacity of the high-stage compressor is reduced, the refrigeration capacity of the CO ₂ cycle is increased, and the coefficient of performance is improved. .
That is, as shown in FIG. 5A, the high stage compressor 71b, the gas cooler 72, the high stage side pressure reducing valve 73, the intermediate cooler 74, the low stage side pressure reducing valve 75, the low stage side evaporator 76, the low stage side evaporator It comprises the stage side compressor 71a.
The opening degree of the high-stage pressure reducing valve 73 is adjusted by the control device 73c based on the detected values of the temperature sensor 73a and the pressure sensor 73b provided on the outlet side of the gas cooler 72, and the opening degree of the low-stage pressure reducing valve 75 is adjusted. Is configured to be adjusted via a temperature sensing cylinder 75a.
That is, in the case of the present embodiment, during the equilibrium operation, the total amount of the high-side CO ₂ gas at the outlet of the gas cooler is reduced to the intermediate pressure by the intermediate cooler 74 via the high-stage pressure reducing valve 73, and then the intermediate cooler The intermediate-pressure liquid refrigerant at the bottom of 74 is decompressed by the low-stage pressure reducing valve 75 and flows into the low-stage evaporator 76.
[0009]
The operating state of the refrigeration cycle is shown in the ph diagram of FIG.
That is, at the point A, the intermediate pressure CO ₂ gas from the intermediate cooler 74 flowing into the high stage side compressor 71b and the cooling gas of the discharge gas at the point A ′ of the low stage side compressor 71a merge and are sucked. At point B, the supercritical high-pressure high-temperature CO ₂ gas flows into the gas cooler 72, and at point C, the low-temperature supercritical high-pressure CO ₂ gas cooled by the outside air in the gas cooler flows into the high-stage pressure reducing valve 73 to reduce the pressure to the intermediate pressure. To do. Next, the CO ₂ in the gas-liquid two-phase state formed by the pressure reduction at the point D forms an intermediate pressure superheated gas phase CO ₂ and flows into the high-stage compressor 71b at the point A, and at the point E, the liquid refrigerant. And the pressure of the formed liquid refrigerant is reduced to the point F by the low pressure reducing valve 75 through the temperature sensing cylinder 75a. Next, superheated steam is formed at point G via the low-stage evaporator 76 and flows into the low-stage compressor 71a.
[0010]
With the above configuration, since the liquid phase CO ₂ having a specific enthalpy equal to or lower than that of the saturated liquid flows into the low stage side pressure reducing valve 75, the specific enthalpy difference at the inlet / outlet of the low stage side evaporator 76 can be increased. In addition, the vapor phase CO ₂ separated by the intercooler 74 is introduced into the high stage compressor 71b to improve the refrigeration efficiency of the CO ₂ cycle.
In the above proposal, cold heat of about 0 ° C. is obtained by the low-stage evaporator 76.
[0011]
In the CO ₂ refrigeration cycle for the CO ₂ refrigerant, the refrigerant CO ₂ is placed in a state containing a supercritical region, in the compressor has likely problems discharge temperature rises, the lubricant for the compressor to be used There is a problem of oil deterioration due to an increase in discharge temperature.
CO ₂ dissolves in a certain temperature range with compressor lubricants such as naphthenic and paraffinic mineral oils, alkylbenzene oils, ether oils, ester oils, polyoxyalkylene glycol oils, carbonate oils, etc. There is a problem (oil return to the compressor) that does not completely dissolve even in a wide temperature range that obtains a lower temperature than the start.
[0012]
Various proposals for solving the above problems have been made. Among them, ethane, which is a hydrocarbon structurally close to compressor lubricating oil and highly azeotropic with CO ₂ , is used in a small amount range. There is also a proposal for an oil return of compressor oil that coexists with a reduction in compressor discharge temperature using a low temperature working body to be mixed.
With regard to the oil return, there have been proposals relating to a lubricating oil for a compressor in the supercritical CO ₂ refrigeration cycle. (For example, refer to Patent Document 3.)
[0013]
The above proposal is based on a supercritical CO ₂ refrigeration cycle including a compressor 81, a gas cooler 82, a pressure reducing valve 83, and an evaporator 84 as shown in FIG. 6A, and CO ₂ flowing from the evaporator 84 and an excess liquid phase. The accumulator 85 is configured to store the lubricating oil that lubricates the CO ₂ and the compressor 81. When the pressure of the refrigeration cycle is higher than the critical pressure, the lubricating oil has a compatibility lower than the critical pressure. Those having higher values are used, and since the compatibility is low on the low pressure side on the evaporator 84 side, liquid phase lubricating oil and liquid phase CO ₂ in a separated state exist separately. Therefore, as shown in FIG. 6B, in the tank 86, the liquid phase lubricating oil having a large specific gravity is accumulated in the lower portion, and the liquid phase CO ₂ is accumulated thereon. The compressor 81 is provided with a U-shaped suction pipe 87 introduced into the accumulator 85, and liquid phase lubrication in the separated and stored state from a suction hole 87 a provided at the lower curved portion of the U-shaped suction pipe 87. The oil and liquid phase CO ₂ can be inhaled.
[0014]
With the above configuration, on the side where the pressure of the refrigeration cycle is lower than the critical pressure, the liquid phase CO ₂ is not fed into the compressor, and only the lubricating oil is introduced into the compressor 81, resulting in deterioration of the coefficient of performance and the compressor. 81 can be prevented from being damaged.
Also, on the supercritical pressure side such as a gas cooler that is higher than the critical pressure, the compatibility of the lubricating oil becomes high, and the lubricating oil circulates in the gas cooler together with CO ₂ , so that the lubricating oil is prevented from staying in the gas cooler and has a refrigerating capacity. I try to improve.
[0015]
[Patent Document 1]
JP-A-2002-243290 [Patent Document 2]
JP-A-10-115470 [Patent Document 3]
JP-A-11-94380 [0016]
Looking at the above prior art, Document 1 relates to a cascade type two-stage compression refrigeration cycle in which an ammonia refrigeration circuit provided on the high stage side and a CO ₂ refrigeration circuit provided on the low stage side are combined via a cascade capacitor. , Which relates to safety measures for the low-stage CO ₂ refrigeration circuit for coping with the occurrence of an accident in the high-stage ammonia refrigeration circuit, the description relating to the compressor oil used on the high-stage side and the low-stage side in the cascade refrigeration cycle No.
Reference 2 relates to the circuit configuration of the CO ₂ refrigeration cycle exceeding the critical pressure. As one example, the circuit configuration and operating conditions of the two-stage expansion two-stage compression refrigeration cycle using CO ₂ as a refrigerant are described. However, there is no description of the lubricating oil used on the high and low stages. In this case, the refrigeration cycle is intended for car air conditioners, and the cold heat source generated by the low-stage evaporator is intended for about 0 ° C.
Reference 3 describes the handling of lubricating oil that changes its compatibility between the critical pressure of the lubricating oil and the critical pressure in the CO ₂ refrigeration cycle using CO ₂ as a refrigerant. On the high pressure side of the gas cooler, Due to the nature of the used lubricating oil, which becomes highly compatible, the lubricating oil moves together with the refrigerant to prevent stagnation in the gas cooler, and on the low pressure side of the evaporator outlet, the properties that make the lubricating oil less compatible and the use of a special actuator The separated lubricating oil is taken out separately to prevent the liquid refrigerant from being sucked into the compressor, and the separated lubricating oil is taken out and supplied.
[0017]
[Problems to be solved by the invention]
By the way, as mentioned above,
In recent years, refrigeration cycles using CO ₂ (carbon dioxide), which is one of natural refrigerants and has an ozone depletion coefficient of zero and a global warming coefficient of 1, have been used due to the regulation of fluorocarbon refrigerants for protecting the global environment. Therefore, there is a strong demand for improvement in efficiency. In addition, from the standpoint of efficient use of energy, the emergence of a versatile heat supply system that can simultaneously supply cold and hot heat is expected.
[0018]
However, as described above, in the prior art, rather than the advantage of using CO ₂ having a low critical point as a refrigerant, the CO ₂ cycle received by the refrigeration cycle due to its use is increased in pressure, reduced in refrigeration efficiency, and lubricated. There are many things that have been solved all the time to solve individual problems with oil.
The present invention makes it possible to make efficient use of energy by appropriately using a lubricating oil for a compressor having incompatible or compatible properties by utilizing the advantages brought about by using CO ₂ as a refrigerant. The purpose is to provide a CO ₂ refrigeration cycle capable of simultaneously supplying cold and hot heat.
[0019]
[Means for Solving the Problems]
Therefore, the first related to CO ₂ refrigeration cycle of the present invention is directed, and a low-stage CO ₂ refrigeration cycle that operates in a region including a high-stage CO ₂ refrigeration cycle and the low temperature saturation zone to operate in a region including the supercritical region In a cascaded two-stage compression CO ₂ refrigeration cycle combined through a cascade condenser,
The high-stage CO ₂ is circulated CO ₂ refrigerant by the compressor provided in the refrigerating cycle, is liquefied by Datsunetsu CO ₂ gas flowing through the low-stage CO ₂ refrigeration cycle by the high-stage-side evaporator cascade condenser The liquefied CO ₂ liquid refrigerant flows into the low-stage evaporator and is vaporized to form a cold heat source to obtain a heat of about 75 to 85 ° C. from the gas cooler of the high-stage CO ₂ refrigeration cycle, said to obtain a cold heat of -50 to-75 ° C. than cold heat source of the low-stage CO ₂ refrigeration cycle, the circulation of the hot CO ₂ refrigerant of the high-stage CO ₂ refrigeration cycle lubricating compressor incompatible A different type of lubricating oil for the compressor is used via the cascade condenser so that the oil becomes a compatible lubricating oil for the compressor in the circulation of the low-temperature CO ₂ refrigerant in the low-stage CO ₂ refrigeration cycle ; Octopus The features.
[0020]
In the first aspect of the present invention, two sets of CO ₂ refrigeration cycles each using CO ₂ as a refrigerant are prepared and combined through a cascade capacitor, and one of the CO ₂ refrigeration cycles includes a supercritical region. in the high-stage CO ₂ refrigeration cycle that operates by forming causes the other to form a low-stage CO ₂ refrigeration cycle operates in a region including a cold saturated zone,
Circulating the CO ₂ refrigerant by the compressor provided in the high-stage CO ₂ refrigeration cycle, the CO ₂ gas flowing through the low-stage CO ₂ refrigeration cycle by the evaporator of the high-stage cascade condenser is liquefied by Datsunetsu, The liquefied CO ₂ liquid refrigerant flows into the low-stage evaporator and is vaporized to form a cold heat source to obtain a heat of about 75 to 85 ° C. from the gas cooler of the high-stage supercritical CO ₂ refrigeration cycle. , -50 to -75 ° C cold is obtained from the cold source.
Then, using a compressor lubricating oil incompatible for circulation of hot CO ₂ refrigerant of the high-stage CO ₂ refrigeration cycle, the circulation of the low-temperature CO ₂ refrigerant in the low-stage CO ₂ refrigeration cycle compatibility using the compressor lubricating oil, via the cascade condenser allows the use of a compressor lubricating oil of the incompatible compatible heterogeneous safe driving, high efficiency, to form a cold heat heat source frozen A cycle is obtained.
[0021]
The second invention related to the CO ₂ refrigeration cycle of the present invention compresses the CO ₂ refrigerant gas evaporated by the evaporator with a low stage compressor and discharges the low stage compressor with an intermediate cooler. In a two-stage compression CO ₂ refrigeration cycle in which a high-stage compressor is compressed after cooling and a gas cooler is provided on the discharge side of the high-stage compressor ,
A heat exchanger for heating the low-temperature intake gas of the low-stage compressor using a part of the sensible heat of the CO ₂ gas on the discharge side of the gas cooler is provided, and the intermediate cooler is cooled by the gas cooler and the heat exchange A part of the CO ₂ gas that has passed through the vessel is bypassed, and the decompression flow is made to flow to an intermediate pressure by the expansion valve for intermediate cooling, so that incompatible lubricating oil can be used in the two-stage compression CO ₂ refrigeration cycle. Features.
[0022]
The second invention of the present invention uses CO ₂ as a refrigerant and uses a lubricating oil that is incompatible with CO ₂ according to the above-described configuration , and performs two-stage compression by two-stage compression CO ₂ refrigeration cycle. The compression efficiency is improved and the high-stage compression temperature is lowered.
[0023]
[0024]
[0025]
The lubricating oil used in the two-stage compressed CO ₂ refrigeration cycle of the present invention uses an oil that is incompatible with CO ₂ used as a refrigerant, and is separated from a high-pressure high-temperature gas in an oil separator on the high stage side, The separated incompatible oil is collected and recirculated to the suction side of the high-stage compressor. On the low-stage side, the downstream-side evaporated gas from the low-stage evaporator is removed by the sensible heat of the high-side high-temperature gas on the high-stage side. It is configured to improve the flowability of the incompatible oil by heating to improve the reflux from the oil separator to the lower stage compressor.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the form of the Example of this invention is demonstrated with the example of illustration. However, unless otherwise specified, the dimensions, shapes, relative positions, and the like of the components described in this embodiment are merely illustrative examples, and are not intended to limit the scope of the present invention. Absent. The details of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of a cascade type two-stage compression CO ₂ refrigeration cycle of the first invention of the present invention, and FIG. 2 is a ph diagram of FIG.
FIG. 3 is a diagram showing a schematic configuration of a one-stage expansion two-stage compression CO ₂ refrigeration cycle according to the second invention of the present invention.
[0027]
As shown in FIG. 1, the cascade type two-stage compression CO ₂ refrigeration cycle which is the first invention of the present invention is
A low stage side CO ₂ refrigeration cycle 18 comprising a low stage side evaporator 10, a low stage side compressor 11, a cascade condenser 12 and an expansion valve 13, and operating in a region including a low temperature saturation region;
The high stage side compressor 14, the gas cooler 15, the expansion valve 16, and the high stage side evaporator 17, and a high stage side CO ₂ refrigeration cycle 19 that operates in a region including the supercritical region,
The cascade condenser 12 forming the low-stage side condenser is provided with a high-stage side evaporator 17 so that the CO ₂ gas flowing through the low-stage side refrigeration cycle is liquefied by deprived heat and the liquefied CO ₂ liquid refrigerant is reduced. A high temperature stage that operates in a region including the supercritical CO ₂ region, while flowing into the stage-side evaporator 10 and vaporizing it to form a cold heat source to obtain cold heat of −50 to −75 ° C. from the cold heat source. A refrigeration cycle is configured in which a temperature of about 75 to 85 ° C. is obtained from the gas cooler 15 of the side CO ₂ refrigeration cycle 19 and cold and heat can be supplied simultaneously.
[0028]
An incompatible compressor lubricating oil is used for circulation of the high temperature CO ₂ refrigerant in the high stage CO ₂ refrigeration cycle 19, and compatibility is used for circulation of the low temperature CO ₂ refrigerant in the low stage CO ₂ refrigeration cycle 18. This compressor lubricant oil can be used, and the incompatible and compatible compressor lubricant oils can be used via the cascade capacitor 12, and safe operation and high efficiency can be performed simultaneously with a cold source and a hot source. A refrigeration cycle that can be supplied is obtained.
[0029]
FIG. 2 shows a ph diagram of the cascaded two-stage compression type CO ₂ refrigeration cycle of FIG. 1, and as shown in the figure, the high stage side compression provided in the high stage CO ₂ refrigeration cycle 19 is shown. The pressure of the CO ₂ refrigerant is increased from (5) to (6) by the machine 14 to form a high-pressure and high-temperature supercritical CO ₂ gas, which is then cooled by the gas cooler 15 from (6) to (7) and at a high temperature due to sensible heat. A heat source is formed, and then, from (7) to (8), liquefied CO ₂ is formed by pressure reduction by the expansion valve 16. Next, heat removal in the evaporation process by the high-stage evaporator 17 built in the cascade condenser 12 from (8) to (5) is performed, and the low-stage CO ₂ refrigeration cycle 18 passing through the cascade condenser 12 is performed. From (2) to (3) above, the CO ₂ gas is cooled with a temperature difference of about 10 ° C., and then from (3) to (4), the expansion valve 13 is used to reduce the pressure to two-phase. ₂ is vaporized by the flow into the lower stage evaporator 10 to form a cold heat source.
[0030]
FIG. 3 is a diagram showing a schematic configuration of a one-stage expansion two-stage compression CO ₂ refrigeration cycle according to the second invention of the present invention.
As shown in FIG. 3, the single-stage expansion two-stage compression CO ₂ refrigeration cycle of the second invention includes a low-stage compressor 21, an oil separator 21 a, an intermediate cooler 22, a heat exchanger 24, and an intermediate cooling expansion valve 25. The gas cooler 26, the oil separator 27a, the high stage compressor 27, the low stage expansion valve 28, and the low stage evaporator 29. The refrigerant is CO ₂ and the incompatible oil is used as the lubricating oil. The two compressors of the high-stage compressor 27 and the low-stage compressor 21 are divided into two parts and compressed, and the compression ratio is reduced by one to prevent a reduction in compression efficiency. Further, the discharge gas after being compressed by the low-stage compressor 21 is cooled by the intermediate cooler 22 and then compressed again by the high-stage compressor 27, thereby reducing the discharge temperature after the high-stage compression.
[0031]
That is, the refrigerant evaporation in the low stage evaporator 29 becomes superheated refrigerant vapor compressed to an intermediate pressure by the low stage compressor 21, and is introduced into the intermediate cooler 22 via the oil separator 21a.
In the intermediate cooler 22, a part of the high-side CO ₂ gas that is cooled by the gas cooler 26 and passes through the heat exchanger 24 is bypassed, and is decompressed to the intermediate pressure by the intermediate cooling expansion valve 25.
Then, by the above-mentioned reduced pressure cooling, the superheated steam from the low stage compressor 21 is returned to the saturated state and sucked into the high stage compressor 27, the high side CO ₂ gas from the gas cooler 26 is supercooled, and the evaporator 29 The refrigeration effect is improved.
In addition, it is possible to supply a high-temperature heat source from the gas cooler 26 and a cold-heat source from the low-stage evaporator 29 simultaneously.
[0032]
As described above, the working fluid on the high side from the gas cooler 26 is introduced into the heat exchanger 24 to form superheated steam, which is adapted to use incompatible oil.
[0033]
【The invention's effect】
The present invention has the following effects by the above configuration.
By using a CO ₂ refrigerant, a two-stage compression CO ₂ refrigeration cycle using a single-stage expansion system or a two-stage expansion system using a single lubricant, or a cascade-type two-stage compression CO ₂ refrigeration cycle using a different type of lubricant In addition, it is possible to provide a CO ₂ refrigeration cycle that enables simultaneous supply of a cold / hot heat source and a high-temperature heat source.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a cascade type two-stage compression CO ₂ refrigeration cycle according to a first invention of the present invention.
FIG. 2 is a ph diagram of FIG.
FIG. 3 is a diagram showing a schematic configuration of a one-stage expansion two-stage compression CO ₂ refrigeration cycle according to the second invention of the present invention.
FIG. 4 is a diagram showing a schematic configuration of an example of a conventional cascade type two-stage compression refrigeration cycle.
5A is a diagram showing a schematic configuration of an example of a conventional one-stage expansion two-stage compression CO ₂ refrigeration cycle, and FIG. 5B is a ph diagram of FIG. 5A.
6A is a circuit diagram provided with a return oil device in a conventional CO ₂ refrigeration cycle, and FIG. 6B is a diagram showing a schematic configuration of the return oil device of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Low stage side evaporator 11 Low stage side compressor 12 Cascade condenser 13, 16 Expansion valve 14 High stage side compressor 15 Gas cooler 17 High stage side evaporator 21 Low stage compressor 21a, 27a Oil separator 22 Intermediate cooler 24 Heat exchanger 25 Intermediate cooling expansion valve 26 Gas cooler 27 High stage compressor 28 Low stage expansion valve 29 Low stage evaporator

Claims (2)

In the high-stage CO ₂ refrigeration cycle and the low temperature saturated region cascaded two-stage compression CO ₂ refrigeration cycle in combination through a cascade condenser and a low-stage CO ₂ refrigeration cycle that operates in a region including operating in a region including the supercritical region ,
The high-stage CO ₂ is circulated CO ₂ refrigerant by the compressor provided in the refrigerating cycle, is liquefied by Datsunetsu CO ₂ gas flowing through the low-stage CO ₂ refrigeration cycle by the high-stage-side evaporator cascade condenser The liquefied CO ₂ liquid refrigerant flows into the low-stage evaporator and is vaporized to form a cold heat source to obtain a heat of about 75 to 85 ° C. from the gas cooler of the high-stage CO ₂ refrigeration cycle, said to obtain a cold heat of -50 to-75 ° C. than cold heat source of the low-stage CO ₂ refrigeration cycle, the circulation of the hot CO ₂ refrigerant of the high-stage CO ₂ refrigeration cycle lubricating compressor incompatible A different type of lubricating oil for the compressor is used via the cascade condenser so that the oil becomes a compatible lubricating oil for the compressor in the circulation of the low-temperature CO ₂ refrigerant in the low-stage CO ₂ refrigeration cycle ; Octopus CO ₂ refrigeration cycle, wherein. The CO ₂ refrigerant gas evaporated by the evaporator is compressed by a low-stage compressor, and the discharge gas of the low-stage compressor is cooled by an intermediate cooler and then compressed by a high-stage compressor, and the high-stage compressor In a two-stage compression CO ₂ refrigeration cycle in which a gas cooler is provided on the discharge side of
A heat exchanger for heating the low-temperature intake gas of the low-stage compressor using a part of the sensible heat of the CO ₂ gas on the discharge side of the gas cooler is provided, and the intermediate cooler is cooled by the gas cooler and the heat exchange A part of the CO ₂ gas that has passed through the vessel is bypassed, and the decompression flow is made to flow to an intermediate pressure by the expansion valve for intermediate cooling, so that incompatible lubricating oil can be used in the two-stage compression CO ₂ refrigeration cycle. Characteristic CO ₂ refrigeration cycle.

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