WO2022249565A1

WO2022249565A1 - Multi-stage compression refrigeration apparatus

Info

Publication number: WO2022249565A1
Application number: PCT/JP2022/004822
Authority: WO
Inventors: 直樹黒田; 篤塩谷; 実希山田; 寿幸石田; 有二岡田; 有悟笹谷; 航平松本; 崚平在本; 真悟佐藤
Original assignee: 三菱重工サーマルシステムズ株式会社
Priority date: 2021-05-27
Filing date: 2022-02-08
Publication date: 2022-12-01
Also published as: JP2022181836A; EP4350255A1

Abstract

Provided is a refrigeration apparatus capable of stably operating while improving the efficiency of a refrigeration cycle.　The refrigeration apparatus is provided with a compression section including three or more stages of compression mechanisms, a first heat exchanger, a pressure reduction section, a second heat exchanger, a plurality of intermediate-pressure injection flow paths that are provided between a high-pressure pressure reduction mechanism and a low-pressure pressure reduction mechanism and supply a refrigerant at an intermediate pressure, which is between a high pressure and a low pressure, between the compression mechanisms, a gas-liquid separator that supplies a gas-phase refrigerant to a high-pressure intermediate-pressure injection flow path on a relatively high-pressure side among the plurality of intermediate-pressure injection flow paths, and an internal heat exchanger that supplies a refrigerant that has absorbed heat from a liquid refrigerant, which is a liquid-phase refrigerant supplied from the gas-liquid separator, by heat exchange between the liquid refrigerant and a two-phase refrigerant obtained by reducing pressure of a part of the liquid refrigerant to the intermediate-pressure injection flow path on a low-pressure side relative to the high-pressure intermediate-pressure injection flow path.

Description

Multi-stage compression refrigeration equipment

The present disclosure relates to a refrigeration system that compresses refrigerant in multiple stages.

Patent Document 1 discloses a refrigeration system with a two-stage compression mechanism. Such a refrigeration system includes an electric compressor having a low-stage compression mechanism and a high-stage compression mechanism in a closed housing, a radiator, a high-pressure expansion valve, a gas-liquid separator, a low-pressure expansion valve, an evaporator, It is equipped with gas injection piping. Gas refrigerant introduced into the housing of the electric compressor from the gas-liquid separator through the gas injection pipe is sucked into the high-stage compression mechanism together with refrigerant discharged into the housing from the low-stage compression mechanism.

JP 2017-44420 A

A refrigerant with a low GWP is adopted for the purpose of reducing the global warming potential (GWP) and improving the energy consumption efficiency (COP; Coefficient of Performance). Development and commercialization are underway.
When a refrigerant containing _CO2 is used as the refrigerant, in order to keep the high refrigerant discharge temperature within the permissible limit due to high-pressure operation, the high pressure set for the radiator and the low pressure set for the evaporator must be maintained. It is effective to introduce intermediate-pressure refrigerant from the gas-liquid separator between the low-stage compression mechanism and the high-stage compression mechanism (intermediate-pressure injection). According to such a configuration, it is possible to suppress the discharge temperature by injecting refrigerant having a temperature lower than that of the refrigerant discharged from the low-stage compression mechanism. In addition, since the liquid refrigerant is supplied from the gas-liquid separator to the low-pressure expansion valve, the enthalpy obtained by the evaporator is expanded compared to the case of single-stage compression, so the refrigeration capacity is increased and the COP is improved. be able to.

In a refrigerating device that employs a refrigerant with a low GWP, it is desired to realize a refrigerating device that increases the COP while suppressing the discharge temperature from the compressor by further increasing the number of stages of the compression mechanism. . However, according to test research by the inventor of the present disclosure, it was found that the liquid level of each of the plurality of gas-liquid separators is not fixed when the number of stages is increased to 3 or more. Generally, in order to avoid flashing (generation of air bubbles in the refrigerant), the liquid refrigerant is stored in the gas-liquid separator, and the refrigerant is supercooled by the supercooling heat exchanger.
For example, when the number of stages of the compression mechanism/expansion valve is increased to, for example, "4", in a refrigeration system operated by a four-stage compression and four-expansion cycle, due to local fluctuations in refrigerant pressure, etc., three gas The liquid level of the liquid refrigerant stored in each of the liquid separators is uneven. Due to the uneven distribution of the liquid refrigerant, if the liquid cannot be secured in the gas-liquid separator on the low-pressure side that flows the refrigerant into the evaporator, and the refrigerant flows into the low-pressure decompression mechanism and the evaporator in a two-phase state, the efficiency will deteriorate. In addition, the operation of the refrigeration system may become unstable. In order to avoid this, it is conceivable to detect the liquid level in each of the three gas-liquid separators and control the operation of the compressor based on the liquid level, but such control is difficult.

In view of the above, an object of the present disclosure is to provide a refrigeration system that can stably operate while improving the efficiency of the refrigeration cycle.

The present disclosure is a refrigerating device that circulates a refrigerant by a refrigerating cycle, and includes a compression section that includes three or more stages of compression mechanisms that are connected in series and each compresses the refrigerant, and the refrigerant discharged from the compression section is discharged to the outside air. A first heat exchanger that dissipates heat, a high-pressure pressure reducing mechanism on the relatively high pressure side, and a low pressure pressure reducing mechanism on the relatively low pressure side. A high-pressure decompression unit that is reduced by a mechanism, a second heat exchanger that causes the refrigerant that has passed through the decompression unit to absorb heat from a heat load, and a high pressure that is provided between the high-pressure decompression mechanism and the low-pressure decompression mechanism and set in the first heat exchanger and a plurality of intermediate pressure injection passages for supplying intermediate pressure refrigerant between the compression mechanism and the low pressure set in the second heat exchanger, and among the plurality of intermediate pressure injection passages A gas-liquid separator that supplies gas-phase refrigerant to the high-pressure intermediate pressure injection passage on the relatively high-pressure side, a liquid refrigerant that is a liquid-phase refrigerant supplied from the gas-liquid separator, and a part of the liquid refrigerant an internal heat exchanger that supplies the refrigerant absorbed heat from the liquid refrigerant by exchanging heat with the pressure-reduced two-phase refrigerant to the intermediate-pressure injection passage on the low-pressure side with respect to the high-pressure intermediate-pressure injection passage; Prepare.

In the present disclosure, by combining one or more gas-liquid separators and one or more internal heat exchangers as two types of intermediate pressure injection means, intermediate pressure injection corresponding to the number of compression stages N (3 or more) and the gas-liquid separator is arranged on the high-pressure side of the internal heat exchanger. As a result, the number of gas-liquid separators is smaller than when a gas-liquid separator is arranged at each stage of the intermediate pressure injection, so it is possible to suppress the decrease in efficiency and the instability of the operating state due to the uneven distribution of the liquid refrigerant. can.
In addition, since the gas-liquid separator is arranged on the high-pressure side of the internal heat exchanger, saturated liquid can flow from the gas-liquid separator into the internal heat exchanger to supercool the refrigerant. Stable and efficient operation is possible by supercooling, and there is no need to install a supercooling heat exchanger for inflowing the refrigerant that has passed through the internal heat exchanger, which contributes to cost reduction, miniaturization and weight reduction of the device. can do.

1 is a diagram showing a circuit configuration of a refrigeration system according to an embodiment of the present disclosure; FIG. 2 is a Moliere diagram of the refrigeration system shown in FIG. 1. FIG. It is a Moliere diagram of a refrigeration system according to a comparative example. FIG. 10 is a diagram showing a circuit configuration of a refrigeration system according to a modified example of the present disclosure; 5 is a Moliere diagram of the refrigeration system shown in FIG. 4; FIG.

An embodiment of the present disclosure will be described below with reference to the accompanying drawings.
[Basic elements of the refrigeration cycle]
The multi-stage compression refrigerating apparatus 1 shown in FIG. 1 circulates a refrigerant in a refrigerating cycle to cool an appropriate heat load (for example, the air in the apparatus housing and stored items) using outside air as a heat source.
The refrigerating apparatus 1 includes, as basic elements forming a refrigerating cycle, a compression section 10 for compressing the refrigerant, a radiator E1 (first heat exchanger) for releasing heat from the refrigerant to the outside air, and a decompression section 20 for reducing the pressure of the refrigerant. and a heat absorber E2 (second heat exchanger) that absorbs heat from the heat load to the refrigerant. The refrigerant compressed by compression section 10 flows through radiator E<b>1 , decompression section 20 , and heat absorber E<b>2 in this order, and is sucked into compression section 10 .

The refrigerant circuit of the refrigeration apparatus 1 of the present embodiment is arbitrarily selected from, for example, HFC (Hydro Fluoro Carbon) refrigerant, HFO (Hydro Fluoro Olefin) refrigerant, carbon dioxide (CO ₂ ) refrigerant, hydrocarbon refrigerant, and the like. A single refrigerant or mixed refrigerant is enclosed. From the viewpoint of GWP reduction, this embodiment employs a refrigerant containing at least a portion of carbon dioxide (CO ₂ ).

[Multi-stage compression mechanism/decompression mechanism]
The compression section 10 includes multiple stages of compression mechanisms 11 to 14 connected in series. The first-stage compression mechanism 11, the second-stage compression mechanism 12, the third-stage compression mechanism 13, and the fourth-stage compression mechanism 14 sequentially compress the refrigerant from the low-pressure side L to the high-pressure side H over a plurality of steps. The number of stages N of the compression unit 10 is 3 or more, and as an example, the number of stages N is "4". The first to fourth stages are indicated by the symbols n1, n2, n3 and n4.

FIG. 2 is a Moliere diagram showing the relationship between the pressure of the refrigerant in the refrigeration system 1 and the specific enthalpy. The symbols r1, r2, etc. shown in FIG. 2 correspond to the same symbols shown in FIG.
As shown in FIG. 2, the refrigeration system 1 is operated in a four-stage compression, two-stage expansion refrigeration cycle.

The refrigeration system 1 of this embodiment includes two

electric compressors

101 and 102, a control device 15 capable of controlling the operation of the electric motors and expansion valves of the

electric compressors

101 and 102, and the

electric compressors

101 and 102. and an intermediate cooling heat exchanger 16 provided between.
The first electric compressor 101 rotates the first stage compression mechanism 11 and the second stage compression mechanism 12 that are connected in series, a housing 101A that houses the

compression mechanisms

11 and 12, and the

compression mechanisms

11 and 12. and an electric motor 101B.
The second electric compressor 102 rotates the third stage compression mechanism 13 and the fourth stage compression mechanism 14 that are connected in series, a housing 102A that houses the

compression mechanisms

13 and 14, and the

compression mechanisms

13 and 14. and an electric motor 102B.

The intermediate cooling heat exchanger 16 cools the refrigerant discharged from the second-stage compression mechanism 12 by radiating heat to the outside air, and supplies the refrigerant to the suction portion of the third-stage compression mechanism 13 (operating points r4 to r5 in FIG. 2). What).

The first stage compression mechanism 11 corresponds to, for example, a rotary compression mechanism including a piston rotor and a cylinder. The third stage compression mechanism 13 is also the same. The second stage compression mechanism 12 corresponds to, for example, a scroll compression mechanism including a pair of scroll members. The same applies to the fourth stage compression mechanism 14 .

The decompression unit 20 includes a low pressure decompression mechanism 21 on the relatively low pressure side L and a high pressure decompression mechanism 22 on the relatively high pressure side H. As shown in FIG. Each of the

decompression mechanisms

21 and 22 may be an expansion valve, a capillary tube, or the like. In particular, it is preferable that the expansion valve is capable of adjusting the degree of opening of the throttle.
The high-pressure pressure reducing mechanism 22 and the low-pressure pressure reducing mechanism 21 sequentially reduce the pressure of the refrigerant that has passed through the radiator E1 in this order.

As shown in FIG. 2, the pressure of the refrigerant increases stepwise as the refrigerant is compressed by the multi-stage compression mechanisms 11-14 of n1, n2, n3, and n4. Along with this, the discharge temperature of the refrigerant rises.
Lowering the temperature of the refrigerant (from r4 to r5) by the action of the intermediate cooling heat exchanger 16 that releases heat from the refrigerant to the outside air can contribute to suppressing the discharge temperature of the compression section 10 as a whole.

The pressure between the suction pressure to the first stage n1 of compression and the discharge pressure from the second stage n2 is called the first intermediate pressure _P1 . Similarly, the pressure between the suction pressure to the second stage n2 and the discharge pressure from the third stage n3 is called a second intermediate pressure _P2 , and the pressure from the suction pressure to the third stage n3 and the pressure from the fourth stage n4 is The pressure between it and the discharge pressure is called a third intermediate pressure _P3 . A relationship of P ₁ <P ₂ <P ₃ holds.
The critical temperature of _CO2 is lower than that of other refrigerants such as HFCs (Hydro Fluoro Carbon). Therefore, in steady operation of the refrigeration system 1, the _CO2 refrigerant is compressed to a pressure exceeding the critical pressure _PC by the compression section 10 that compresses the refrigerant in multiple stages. However, the pressure (r12, r13, r14) of the refrigerant that has passed through the radiator E1 and the high-pressure pressure reducing mechanism 22, that is, the third intermediate pressure _P3 remains below the critical pressure _PC .

(intermediate pressure injection)
The refrigeration system 1 supplies intermediate-pressure refrigerant obtained by gas-liquid separation of the refrigerant between the low-pressure pressure reducing mechanism 21 and the high-pressure pressure reducing mechanism 22 between the first to fourth stage compression mechanisms 11 to 14, respectively. Intermediate pressure injection is performed. Therefore, the refrigerating apparatus 1 corresponds to N-1 intermediate pressure injection means (31 to 33) provided between the low pressure pressure reducing mechanism 21 and the high pressure pressure reducing mechanism 22 and the intermediate pressure injection means (31 to 33), respectively. It has N−1 intermediate pressure injection flow paths 41 to 43 .

Refrigerant at intermediate pressures P ₁ , P ₂ , and P ₃ is supplied between the serially connected compression mechanisms 11 to 14 through the intermediate pressure injection passages 41 to 43, respectively, thereby performing second to fourth stage compression. The discharge temperature of each of the mechanisms 12-14 can be reduced.
A valve can be provided in each of the intermediate pressure injection flow paths 41 to 43 as required. The valve may be switched open or closed depending on operating conditions.

The intermediate pressure injection means (31-33) consist of a single gas-liquid separator 33 (liquid receiver) and

internal heat exchangers

32, 31, as shown in FIG. The gas-liquid separator 33 is arranged on the high pressure side H with respect to the

internal heat exchangers

32 and 31 . The high pressure internal heat exchanger 32 is arranged on the high pressure side H with respect to the low pressure internal heat exchanger 31 .
These gas-liquid separator 33, internal heat exchanger 32, and internal heat exchanger 31 pass the intermediate-pressure refrigerant through corresponding intermediate-pressure injection passages 41-43 to the second to fourth-stage compression mechanisms 12-4, respectively. 14.

The refrigerant discharged from the fourth stage compression mechanism 14 is decompressed by the high pressure decompression mechanism 22 and flows into the gas-liquid separator 33 . The refrigerant that has flowed into the gas-liquid separator 33 is separated into a gas phase and a liquid phase based on the density difference inside the storage tank 33A. This corresponds to the state change from r12 to r13 and r14 as shown in FIG. A third intermediate pressure injection channel 43 is connected to the gas phase region 33B above the liquid surface in the storage tank 33A.

The gas-phase refrigerant at the third intermediate pressure _P3 separated from the liquid phase in the gas-liquid separator 33 is supplied to the intermediate-pressure injection on the high-pressure side H through the third intermediate-pressure injection passage 43 (from r13 to r8 ).
The temperature of the refrigerant at the third intermediate pressure _P3 supplied to the fourth stage compression mechanism 14 through the third intermediate pressure injection passage 43 is lower than the temperature of the refrigerant discharged from the third stage compression mechanism 13 . Therefore, the temperature of the refrigerant to be sucked into the fourth stage compression mechanism 14 is lowered (r7 to r8). As a result, the temperature of the refrigerant discharged from the fourth stage compression mechanism 14 also drops, so the intermediate pressure gas injection contributes to the reduction of the discharge temperature.

On the other hand, the liquid-phase refrigerant (liquid refrigerant) stored in the storage tank 33A is supplied to the high-pressure internal heat exchanger 32 and the low-pressure internal heat exchanger 31, and the high-pressure internal heat exchanger 32 and the low-pressure internal heat exchanger 31 While subcooling is provided by each, a part thereof passes through the second intermediate pressure injection passage 42 and the first intermediate pressure injection passage 41, respectively, to the third intermediate pressure injection. It is subjected to intermediate pressure injection. The flow rate of the refrigerant gradually decreases as the injection of the intermediate pressures P ₁ , P ₂ and P ₃ is performed. Therefore, the capacity of the high-pressure internal heat exchanger 32 upstream of the refrigerant flow from the high-pressure pressure reducing mechanism 22 to the low-pressure pressure reducing mechanism 21 is greater than the capacity of the low-pressure internal heat exchanger 31 downstream. Under the rated conditions of the refrigeration system 1 , the capacity of the high-pressure internal heat exchanger 32 is, for example, about 2.5 times as large as the capacity of the low-pressure internal heat exchanger 31 .

Both the high-pressure internal heat exchanger 32 and the low-pressure internal heat exchanger 31 depressurize the liquid refrigerant supplied from the gas-liquid separator 33 and part of the liquid refrigerant supplied from the gas-liquid separator 33 through the decompression mechanism (321, 311) to exchange heat with a two-phase refrigerant that is depressurized.
The high-pressure internal heat exchanger 32 includes a main flow path 320 into which the liquid refrigerant supplied from inside the gas-liquid separator 33 in a saturated state flows, a decompression mechanism 321, and the liquid refrigerant supplied from the gas-liquid separator 33. A two-phase refrigerant that has undergone a branch flow path 322 that partially flows into the decompression mechanism 321 and the decompression from the third intermediate pressure _P3 to the second intermediate pressure _P2 by the decompression mechanism 321 (from r14 to r15 in FIG. 2) and a heat absorption channel 323 into which the heat is introduced.

The refrigerant flowing through the heat absorption passage 323 is gasified (from r15 to r16) by absorbing heat from the refrigerant flowing through the main passage 320 , and is sucked into the third stage compression mechanism 13 through the second intermediate pressure injection passage 42 .
On the other hand, the refrigerant flowing through the main flow path 320 is subcooled (from r14 to r17) by dissipating heat to the refrigerant flowing through the heat absorption flow path 323, and flows into the low-pressure internal heat exchanger 31.

When the second intermediate pressure injection flow path 42 supplies the refrigerant at the second intermediate pressure _P2 to the suction portion of the third stage compression mechanism 13 (from r16 to r6), it flows out of the intermediate cooling heat exchanger 16 and flows into the third stage. The temperature of the refrigerant sucked into the three-stage compression mechanism 13 decreases (from r5 to r6). Between the second-stage compression mechanism 12 and the third-stage compression mechanism 13, in addition to the injection action of the intermediate pressure _P2 , the third-stage compression mechanism is also affected by the action of the intermediate cooling heat exchanger 16 (from r4 to r5). Since the intake temperature to 13 is lowered, the discharge temperature can be further suppressed.

The low-pressure internal heat exchanger 31 includes a main flow path 310 into which the supercooled liquid refrigerant (supercooled liquid) flowing out from the high-pressure internal heat exchanger 32 flows, a pressure reducing mechanism 311, and a pressure reducing mechanism for part of the supercooled liquid. 311, and an endothermic flow path 313 into which the two-phase refrigerant that has undergone decompression (from r17 to r18) from the second intermediate pressure _P2 to the first intermediate pressure _P1 by the decompression mechanism 311 flows. It has The refrigerant flowing through the heat absorption passage 313 absorbs heat from the refrigerant flowing through the main passage 310 to be gasified (from r18 to r19), and is sucked into the second stage compression mechanism 12 through the first intermediate pressure injection passage 41 ( r19 to r3). As a result, the temperature of the refrigerant sucked into the second stage compression mechanism 12 is lowered (from r2 to r3).

On the other hand, the refrigerant flowing through the main flow path 310 increases the degree of subcooling (from r17 to r20) by dissipating heat to the refrigerant flowing through the heat absorption flow path 313, and flows into the low-pressure pressure reducing mechanism 21.
Since the liquid refrigerant at the first intermediate pressure _P1 flowing out from the low-pressure internal heat exchanger 31 is sufficiently supercooled, it directly flows to the low-pressure pressure reducing mechanism 21 without passing through the heat exchanger for supercooling. It flows in and is decompressed by the low pressure decompression mechanism 21 (from r20 to r21). After passing through the low-pressure pressure reducing mechanism 21, the refrigerant absorbs heat from the heat load by the heat absorber E2, evaporates, and is sucked into the first stage compression mechanism 11 (from r21 to r22).

Liquid refrigerant flowing from the gas-liquid separator 33 to the internal heat exchanger 32, liquid refrigerant flowing from the high-pressure internal heat exchanger 32 to the low-pressure internal heat exchanger 31, and low-pressure pressure reducing mechanism 21 from the low-pressure internal heat exchanger 31 correspond to the third intermediate pressure _P3 (r14, r17 and r20). Therefore, the expansion process in the refrigeration cycle is aggregated into two stages: decompression from the high pressure _PH to the third intermediate pressure P3 by the high pressure decompression mechanism 22, and decompression from the third intermediate pressure _P3 to the low pressure _PL _. . That is, the refrigeration system 1 is operated in a state where the number of stages of expansion is smaller than the number of stages N of compression, that is, in a four-stage compression and two-stage expansion cycle.

[Main actions and effects]
In order to improve the COP while using a refrigerant with a low GWP, it is effective to increase the number of stages N, such as from single-stage compression to two-stage compression, three-stage compression, and four-stage compression.
The operation and effect of the refrigeration system 1 of this embodiment will be described below with reference to comparative examples.
When adopting multi-stage compression of three or more stages, based on the example of two-stage compression (for example, the above-mentioned Patent Document 1), the refrigeration system is provided with the same number of pressure reduction mechanisms as the number of compression stages N and N-1 gas-liquid It is conceivable to provide a separator. For example, in the case of a four-stage refrigeration system, a decompression mechanism, a gas-liquid separator, a decompression mechanism, a gas-liquid separator, a decompression mechanism, a gas-liquid separator, and a decompression mechanism are arranged from the high pressure side H to the low pressure side L. Arranged in this order, intermediate-pressure gas-phase refrigerant is supplied from each gas-liquid separator to the suction portion of the compression mechanism through the intermediate-pressure injection passage.
Such a comparative refrigeration system operates in a cycle of N-stage compression and N-stage expansion, as indicated by the solid line in FIG. N is, for example, "4".
The refrigerating apparatus of the comparative example may include a subcooling heat exchanger that exchanges heat between the liquid refrigerant flowing out of the gas-liquid separator on the lowest pressure side L and the outside air. In that case, the refrigerant is supercooled, as indicated by the dashed-dotted arrows in FIG.

The refrigeration system of the comparative example has N-1 gas-liquid separators, so if the number of stages N is 3 or more, it has 2 or more gas-liquid separators. In that case, it is difficult to secure liquid refrigerant in a predetermined gas-liquid separator among the plurality of gas-liquid separators. Even if the subcooling heat exchanger is provided on the lowest pressure side L, in order to prevent the refrigerant from flowing into the low pressure pressure reducing mechanism 21 and the heat absorber E2 in a two-phase state, at least it is located on the lowest pressure side L It is desirable to secure liquid refrigerant in the gas-liquid separator and supply the liquid refrigerant from the gas-liquid separator to the low-pressure pressure reducing mechanism 21 . For this purpose, it is necessary to control the rotation speeds of the compression mechanisms 11 to 14 based on the liquid levels of the N−1 gas-liquid separators. At least two level sensors are required to keep track of the level of each of the N-1 gas-liquid separators.

Unlike the comparative example, the refrigerating apparatus 1 of the present embodiment does not include a number of decompression mechanisms and gas-liquid separators corresponding to the number of stages N when increasing the number of stages N, or a number of internal separators corresponding to the number of stages N A single gas-liquid separator 33 is provided on the high pressure side H and

internal heat exchangers

32 and 31 are provided on the low pressure side L without providing a heat exchanger. In other words, the refrigeration system 1 of the present embodiment does not have the same number of gas-liquid separators as the required number of intermediate pressure injection stages (N-1), and the number of gas-liquid separators is less than the required intermediate pressure injection stage number (N-1). of gas-liquid separator 33.
The number of gas-liquid separators 33 provided in the refrigerating apparatus 1 is small with respect to the required number of stages (N−1) for intermediate pressure injection, so gas-liquid separation that can occur when a plurality of gas-liquid separators are provided. The degree of uneven distribution of the refrigerant between the vessels is reduced. As a result, the effect of improving efficiency by increasing the number of compression stages N is ensured while suppressing the decrease in efficiency and the instability of the operating state due to the uneven distribution of the liquid refrigerant, and the operating state of the refrigeration system 1 is stabilized. be able to.

In particular, since the refrigerating apparatus 1 of the present embodiment includes only the single gas-liquid separator 33 as a gas-liquid separator, the liquid amount in some of the plurality of gas-liquid separators is It is possible to ensure that the liquid refrigerant is stored in the specific gas-liquid separator 33 without falling into a state of exhaustion. Then, control based on the liquid level of the gas-liquid separator becomes unnecessary, and the liquid level sensor becomes unnecessary. Even if liquid level sensors are installed, the number can be reduced.

As described above, according to the refrigerating apparatus 1 of the present embodiment, the following effects can be obtained.
(1) Since only a single gas-liquid separator 33 is provided as a gas-liquid separator, unlike the case where a plurality of gas-liquid separators are provided, the liquid refrigerant moves between the gas-liquid separators Without doing so, it is possible to ensure that the liquid refrigerant is stored in a specific gas-liquid separator 33 . Therefore, there is no need to perform control based on the liquid level in the gas-liquid separator. The simplification of control can reduce the cost of the refrigeration system 1 .

(2) Since the gas-liquid separator 33 is arranged on the high pressure side H with respect to the

internal heat exchangers

32 and 31 , the saturated liquid flows from the gas-liquid separator 33 into the

internal heat exchangers

32 and 31 . Therefore, supercooling can be applied to the refrigerant. As a result, the COP can be improved, the occurrence of flash can be suppressed, and the refrigeration system 1 can be operated stably and efficiently. does not need to flow into the subcooling heat exchanger. In other words, the refrigerant that has passed through the

internal heat exchangers

32 and 31 should be allowed to flow directly into the low-pressure pressure reducing mechanism 21 .
Then, the subcooling heat exchanger is not required as compared with the comparative example, and the refrigerant circuit configuration can be simplified, which can contribute to cost reduction, size reduction, and weight reduction of the device.
In the present embodiment, a sufficient degree of supercooling can be obtained by sequentially flowing the liquid refrigerant from the gas-liquid separator 33 into the two

internal heat exchangers

32 and 31 . Therefore, in addition to being highly effective in improving efficiency and stabilizing operation, there is no need to add a supercooling heat exchanger with a large capacity in order to increase the degree of supercooling, which reduces costs and reduces the size and weight of the device. The effect of conversion is also great.

(3) If the high-pressure internal heat exchanger 32 and/or the low-pressure internal heat exchanger 31 is provided with an expansion valve as a decompression mechanism, by adjusting the degree of opening of the expansion valve, as shown in FIG. It is possible to perform intermediate pressure injection with a phase refrigerant. For example, when the high-pressure internal heat exchanger 32 is provided with an expansion valve as the decompression mechanism 321, the second intermediate pressure _P2 by the two-phase refrigerant is passed through the second intermediate pressure injection passage 42 by adjusting the opening degree of the expansion valve. injection (from r16 to r6) to the third stage compression mechanism 13 becomes possible.
Alternatively, if the low-pressure internal heat exchanger 31 is provided with an expansion valve as the decompression mechanism 311, the injection of the first intermediate pressure _P1 (from r19 to r3) by the two-phase refrigerant is controlled by adjusting the opening of the expansion valve. It becomes possible to perform this for the two-stage compression mechanism 12 .
By injecting the two-phase refrigerant, the refrigerant suction temperature into the compression mechanism is lowered, so the discharge temperature can be suppressed to the allowable limit.

(4) In general, a gas-liquid separator is provided with a heat insulating material to keep the refrigerant at a low temperature. By arranging the gas-liquid separator 33 on the high pressure side H with respect to the

internal heat exchangers

31 and 32, the pressure in the gas-liquid separator is Since the saturation temperature is high, the temperature difference between the gas-liquid separator 33 and the outside air temperature is small. Therefore, the thickness of the heat insulating material provided in the gas-liquid separator 33 can be reduced, which contributes to cost reduction, miniaturization and weight reduction of the device.

For example, under rated conditions _of the refrigeration _system 1, as shown in FIG _. When two corresponding

internal heat exchangers

32 and 31 are provided, the temperature at the liquid outlet of the gas-liquid separator 33 is 20°, which is the smallest temperature difference from the outside air temperature. The liquid outlet temperature is according to cycle calculations. The same applies to the following.
Although not shown, it has a single gas-liquid separator corresponding to the second intermediate pressure _P2 , and two internal heat exchangers corresponding to the third intermediate pressure _P3 and the first intermediate pressure _P1 respectively. In the case the temperature at the liquid outlet of the gas-liquid separator is 2°.
Furthermore, if we have a single gas-liquid separator corresponding to the first intermediate pressure _P1 and two internal heat exchangers corresponding to the third intermediate pressure _P3 and the second intermediate pressure _P2 respectively, The temperature at the liquid outlet of the gas-liquid separator is -12°.

The higher the pressure saturation temperature of the gas-liquid separator is, the smaller the temperature difference between the gas-liquid separator and the outside air can be explained by the Moliere diagram of FIG. . As can be seen from FIG. 3, the pressure saturation temperature of the high-pressure gas-liquid separator (r12) is T1, the pressure saturation temperature of the medium-pressure gas-liquid separator (r15) is T2, and the low-pressure gas-liquid separator (r18) ) is T3, it is clear that T1>T2>T3. The higher the pressure saturation temperature, the smaller the temperature difference between the gas-liquid separator and the outside air.

As described above, according to the refrigeration system 1 of the present embodiment, one or more gas-liquid separators 33 and one or more

internal heat exchangers

31 and 32 as two types of intermediate pressure injection means are combined. to satisfy the required number of intermediate pressure injection stages (N-1) corresponding to the number of compression stages N (3 or more), and the gas-liquid separator 33 is arranged on the high pressure side H of the

internal heat exchangers

31 and 32. As a result, the COP can be improved while using a low GWP refrigerant such as CO ₂ , and the refrigeration system 1 can be stably operated while maintaining the discharge temperature below the allowable limit.

[Modification]
The refrigerating apparatus 1 does not necessarily have the high-pressure internal heat exchanger 32 and the low-pressure internal heat exchanger 31, and may have only a single internal heat exchanger, or may have three or more internal heat exchangers, depending on the number of stages N. of internal heat exchangers. Even in such a case, it is possible to obtain the same effects as those obtained by the above-described embodiment.

The refrigerating apparatus 1-2 shown in FIG. 4 includes N-stage (four-stage) compression mechanisms 11 to 14, and two gas-

liquid separators

33 and 32 as N−1 (three) intermediate pressure injection means. -2 and a single internal heat exchanger 31. FIG. 5 is a Moliere diagram of the refrigerator 1-2.
The refrigerator 1-2 has three decompression mechanisms 21 to 23 forming a decompression unit 20, including a decompression mechanism 22 positioned between two gas-liquid separators 33 and 32-2. Therefore, it is operated by a cycle of 4-stage compression and 3-stage expansion.

Like the refrigerating device 1 of the above embodiment, the refrigerating device 1-2 also includes two gas-liquid separators 33 and 32-2, which are smaller than the required number of stages (N-1) for intermediate pressure injection. As a result, the degree of uneven distribution of the liquid refrigerant between the gas-liquid separators 33, 32-2 is reduced. As a result, it is possible to secure the effect of improving the efficiency by increasing the number of compression stages N while suppressing the deterioration of the cycle efficiency and the instability of the operating state, and contribute to the stabilization of the operating state of the refrigerating apparatus 1-2. can be done.

In addition, since the gas-liquid separators 33 and 32-2 are arranged on the high pressure side H of the internal heat exchanger 31, the saturated liquid flows into the internal heat exchanger 31 from the gas-liquid separator 32-2. Therefore, the refrigerant can be subcooled (from r17 to r20 in FIG. 5). It is possible to operate stably and efficiently by supercooling, and there is no need to add a supercooling heat exchanger to obtain supercooling. can.

In addition, by adjusting the degree of opening of the expansion valve provided as the decompression mechanism 311 in the internal heat exchanger 31, it is possible to inject the two-phase refrigerant at the first intermediate pressure _P1 (from r19 to r3). As a result, the temperature of the refrigerant sucked into the second-stage compression mechanism 12 is lowered, so that the temperature of the refrigerant discharged from the compression section 10 can be suppressed to the allowable limit.
Furthermore, by arranging the gas-liquid separators 33, 32-2 on the high pressure side H of the internal heat exchanger 31, the gas-liquid separators 33, 32-2 on the low pressure side L of the internal heat exchanger 31, Compared to the case where 32-2 is arranged, the thickness of the heat insulating material can be reduced, which contributes to the miniaturization and weight reduction of the device.

In addition to the above, it is possible to select the configurations mentioned in the above embodiments or change them to other configurations as appropriate.

(Appendix)
The refrigeration system described above is understood as follows.
[1] The refrigerating devices 1 and 1-2 that circulate the refrigerant by a refrigerating cycle include a compression section 10 that includes three or more stages of compression mechanisms 11 to 14 that are connected in series and each compresses the refrigerant, and discharge from the compression section 10 A first heat exchanger (E1) for releasing the heat of the discharged refrigerant to the outside air, a relatively high pressure side high pressure pressure reducing mechanism 22, and a relatively low pressure side low pressure pressure reducing mechanism 21, the first heat exchanger A decompression unit 20 that reduces the pressure of the refrigerant that has passed through E1 by a high-pressure decompression mechanism 22 and a low-pressure decompression mechanism 21, a second heat exchanger (E2) that causes the refrigerant that has passed through the decompression unit 20 to absorb heat from a heat load, and a high-pressure decompression mechanism 22. and the low-pressure pressure reducing mechanism 21, and the intermediate pressure between the high pressure _PH set in the first heat exchanger (E1) and the low pressure _PL set in the second heat exchanger (E2) A plurality of intermediate pressure injection passages 41 to 43 for supplying the refrigerants P ₁ , P ₂ and P ₃ between the compression mechanisms, and a relatively high pressure among the plurality of intermediate pressure injection passages 41 to 43 A gas-liquid separator 33 (or 33, 32-2) that supplies gas-phase refrigerant to the high-pressure intermediate-pressure injection flow path (43 or 43, 42) on the side H, and the liquid supplied from the gas-liquid separator 33 A liquid refrigerant, which is a phase refrigerant, and a two-phase refrigerant, which is a part of the liquid refrigerant whose pressure is reduced, are heat-exchanged to absorb heat from the liquid refrigerant. 42) are provided with internal heat exchangers 32, 31 (or 31) that supply to the intermediate pressure injection passages 42, 41 (or 41) on the low pressure side L.
[2] Only one gas-liquid separator 33 is provided in the refrigeration system 1, and one or more

internal heat exchangers

32 and 31 are provided between the gas-liquid separator 33 and the low-pressure pressure reducing mechanism 21. be done.
[3] The refrigerating apparatus 1 is provided with a highest pressure gas-liquid separator (33), which is the gas-liquid separator 33 located on the highest pressure side H and to which the refrigerant is directly supplied from the high-pressure decompression mechanism 22.
[4] The refrigerating apparatus 1, 1-2 includes the lowest pressure internal heat exchanger (31), which is the internal heat exchanger 31 located on the lowest pressure side L and causes the refrigerant to flow directly into the low pressure decompression mechanism 21. Prepare.
[5] The

internal heat exchangers

31, 32 include expansion valves (311, 321) that reduce the pressure of a portion of the liquid refrigerant to expand it.
[6] The refrigerating apparatus 1 includes two or more

internal heat exchangers

31 and 32, and the capacity of the internal heat exchanger 32 located on the relatively high pressure side H is determined by the capacity of the internal heat exchanger 32 located on the relatively low pressure side. greater than the capacity of the exchanger 31.
[7] The refrigerant contains at least a portion of carbon dioxide.

1, 1-2 Refrigerating device 10 compression unit 11 first-stage compression mechanism 12 two-stage compression mechanism 13 three-stage compression mechanism 14 four-stage compression mechanism 15 controller 16 intermediate cooling heat exchanger 20 decompression unit 21 low-pressure decompression mechanism 22 high-pressure decompression mechanism 21 to 23 decompression mechanism 31 low pressure internal heat exchanger (minimum pressure internal heat exchanger)
32 high-pressure internal heat exchanger 32-2 gas-liquid separator 33 gas-liquid separator (highest pressure gas-liquid separator)
33A storage tank 33B gas phase region 41 first intermediate pressure injection channel 42 second intermediate pressure injection channel 43 third intermediate pressure injection channel (high pressure intermediate pressure injection channel)
101 First electric compressor 101A Housing 101B Electric motor 102 Second electric compressor 102A Housing 102B Electric motor 310 Main channel 311 Pressure reducing mechanism 312 Branch channel 313 Heat absorption channel 320 Main channel 321 Pressure reducing mechanism 322 Branch channel 323 Heat absorption channel E1 Heat dissipation vessel (first heat exchanger)
E2 heat absorber (second heat exchanger)
H High pressure side L Low pressure side N Number of stages P ₁ , P ₂ , P ₃ Intermediate pressure P _C Critical pressure PH High pressure _{P L} _Low pressure n1, n2, n3, n4 Stages

Claims

A refrigeration device that circulates a refrigerant by a refrigeration cycle,
a compression unit including three or more stages of compression mechanisms that are connected in series and each compresses the refrigerant;
a first heat exchanger that releases the heat of the refrigerant discharged from the compression unit to the outside air;
A pressure reducing mechanism including a high pressure pressure reducing mechanism on a relatively high pressure side and a low pressure pressure reducing mechanism on a relatively low pressure side, wherein the pressure of the refrigerant that has passed through the first heat exchanger is reduced by the high pressure pressure reducing mechanism and the low pressure pressure reducing mechanism. Department and
a second heat exchanger that causes the refrigerant that has passed through the decompression unit to absorb heat from a heat load;
The refrigerant at an intermediate pressure between the high pressure set in the first heat exchanger and the low pressure set in the second heat exchanger is provided between the high pressure pressure reduction mechanism and the low pressure pressure reduction mechanism. a plurality of intermediate pressure injection flow paths supplied between the compression mechanism and the compression mechanism;
a gas-liquid separator that supplies the gas-phase refrigerant to a relatively high-pressure-side high-pressure intermediate-pressure injection channel among the plurality of intermediate-pressure injection channels;
The refrigerant absorbed heat from the liquid refrigerant by exchanging heat between the liquid refrigerant, which is the liquid-phase refrigerant supplied from the gas-liquid separator, and the two-phase refrigerant obtained by decompressing a part of the liquid refrigerant. to the intermediate pressure injection channel on the low pressure side with respect to the high pressure intermediate pressure injection channel.
Only one gas-liquid separator is provided,
One or more internal heat exchangers are provided between the gas-liquid separator and the low-pressure pressure reducing mechanism,
Refrigeration equipment according to claim 1 .
The gas-liquid separator located on the highest pressure side, comprising the highest pressure gas-liquid separator to which the refrigerant is directly supplied from the high pressure decompression mechanism,
3. The refrigeration system according to claim 1 or 2.
The internal heat exchanger located on the lowest pressure side, comprising the lowest pressure internal heat exchanger that allows the refrigerant to flow directly into the low pressure decompression mechanism,
3. The refrigeration system according to claim 1 or 2.
The internal heat exchanger is
including an expansion valve that reduces the pressure of a portion of the liquid refrigerant to expand it,
A refrigeration system according to any one of claims 1 to 4.
comprising two or more of the internal heat exchangers;
The capacity of the internal heat exchanger located on the relatively high pressure side is greater than the capacity of the internal heat exchanger located on the relatively low pressure side.
A refrigeration system according to any one of claims 1 to 5.
The refrigerant contains at least a portion of carbon dioxide,
A refrigeration apparatus according to any one of claims 1 to 6.