HK1107395B - Refrigeration circuit and method for operating a refrigeration circuit - Google Patents

Description

Refrigeration circuit and method for operating a refrigeration circuit

Technical Field

The invention relates to a refrigeration circuit in which a single-component or multi-component refrigerant circulates, comprising, in the direction of flow, a liquefier, a collecting vessel, a pressure reduction device connected upstream of the evaporator, an evaporator and a single-stage compressor unit.

The invention also relates to a method for operating a refrigeration circuit.

Background

The term "liquefier" is to be understood to mean both a liquefier and a gas cooler.

Refrigeration cycles of this type are well known. They are implemented, for example, in refrigeration systems, such as so-called hybrid refrigeration systems used in supermarkets. Composite refrigeration units are commonly used therein to provide cooling to a plurality of cold users, such as refrigerator cabinets, freezers, and deep-freezer cabinets. For this purpose, a single-component or multi-component refrigerant or refrigerant mixture is circulated within them.

A refrigeration cycle circuit of the prior art or a refrigeration plant in which a cycle circuit of the type described can be implemented will now be described in detail with the aid of the embodiment shown in fig. 1.

The single-component or multi-component refrigerant circulating in the high refrigeration cycle is condensed in a liquefier or gas cooler a, hereinafter simply referred to as liquefier a, by heat exchange, preferably by heat exchange with the outside air, which liquefier is usually arranged outside the supermarket, for example on the roof thereof.

The liquid refrigerant is delivered by the liquefier a via a line B to a (refrigerant) receiver C. There must always be a large amount of refrigerant in the refrigeration cycle so that all cold user evaporators can be filled at maximum refrigeration demand. However, since the individual evaporator is only partially charged or even completely emptied at low refrigeration demands, excess refrigerant must be collected in the collector C provided for this purpose during this time.

The refrigerant reaches the cold user of the so-called standard refrigeration cycle from the receiver C through the liquid conduit D. Here, the users F and F' shown in fig. 1 represent any number of standard refrigeration cycle users. In front of each of the above-mentioned cold consumers is connected an expansion valve E or E' in which the refrigerant flowing in the cold consumer or in one or more evaporators of the cold consumer is decompressed. The refrigerant thus depressurized evaporates in the evaporators of the cold users F and F' and thus cools the corresponding refrigerated cabinets or compartments.

The refrigerant evaporated in the cold consumers F and F' of the standard refrigeration cycle is then fed through the suction line G to the compressor unit H and compressed therein to the desired pressure of between 10 and 25 bar. In the usual case, the compressor unit is constructed only as a single stage and has a plurality of compressors connected in parallel.

The refrigerant compressed in the compressor unit H is then fed again to the liquefier a via the pressure line I.

The refrigerant is conveyed by the collector C through a second liquid conduit D 'to the condenser K and is evaporated therein by heat exchange with the refrigerant of the cryogenic cycle circuit, to be explained later, before it is fed to the compressor unit H through the conduit G'.

The refrigerant of the cryogenic cycle that is liquefied in the condenser K is fed to the accumulator M of the cryogenic cycle through a pipe L. The refrigerant is sent by the accumulator through the pipe N to the user P, representing any number of users, in front of which the pressure reducing device O is connected, and is evaporated in said user. The evaporated refrigerant is supplied via a suction line Q to a single-stage or multi-stage compressor unit R, compressed in the latter to a pressure of between 25 and 40 bar and then supplied via a pressure line S to the condenser K already mentioned.

For example, R404A is used as the refrigerant of the standard refrigeration cycle, and carbon dioxide is used for the cryogenic cycle.

The compressor units H and R, the collectors C and M and the condenser K shown in fig. 1 are generally provided in separate machine rooms. And 80 to 90% of the entire network of pipes is located in the shop of a supermarket, in the storage room or other space accessible to staff and customers. This is acceptable to the supermarket operator both from a psychological point of view and for cost reasons, as long as the pipeline network is operated at a pressure of not more than 35 to 40 bar.

Currently there is a switch to using CO in the standard refrigeration cycle described above₂The refrigerant operates.

To date, natural CO₂The meaningful use of refrigerants in commercial refrigeration has failed on the one hand due to the insufficient energy efficiency of simple single-stage cycles at high (ambient) air temperatures. On the other hand due to CO₂The high operating pressures required for the material properties of (a), up to 100 bar or more, make the manufacture of the respective refrigeration circuit or refrigeration device extremely difficult for economic reasons. Thus CO₂The refrigerant has hitherto only been used in cryogenic cascade systems, as explained by way of example in fig. 1, since the working pressure achieved there does not exceed the usual maximum pressure level of 40 bar.

Based on the aforementioned higher pressure or pressure state, the pipe network of the refrigeration cycle circuit must be designed to this pressure or pressure level. The materials required for this purpose are considerably more expensive than those which can be used at the pressure levels achieved hitherto. Such relatively high pressure levels are furthermore difficult for the plant operator to obtain.

Using CO₂Another problem with refrigerants is that supercritical operation of the refrigeration circuit is required at correspondingly high ambient temperatures. Height ofCauses a relatively high pressure reducing vapor fraction at the evaporator inlet. The effective refrigeration capacity per volume of the circulating refrigerant is thereby reduced, but the suction line and the liquid line as well as the evaporator must be correspondingly increased in size in order to keep the pressure losses as low as possible.

Disclosure of Invention

The object of the present invention is to provide a refrigeration circuit of the type mentioned and a method for operating a refrigeration circuit, which avoid the above-mentioned disadvantages.

In order to solve this problem, a refrigeration circuit is proposed, which is characterized in that an intermediate pressure reduction device is arranged between the liquefier and the collecting vessel.

In terms of method, the proposed solution to the problem is to depressurize the refrigerant to an (intermediate) pressure of 5 to 40 bar in an intermediate depressurization device arranged between the liquefier and the collecting vessel.

In particular, the invention proposes a refrigeration cycle in which a single-component or multi-component refrigerant circulates, which refrigeration cycle is capable of supercritical operation and has, in the direction of flow, a liquefier/gas cooler, a collecting vessel, a pressure reduction device connected upstream of the evaporator, an evaporator and a first compressor unit of single-stage compression, characterized in that: an intermediate pressure reduction device is disposed between the liquefier/gas cooler and the collection vessel; the gas chamber of the collecting container is connected with the input end of the first compressor unit; and a pressure reducing valve is arranged in the connecting pipe between the gas chamber of the collecting container and the input end of the compressor unit.

Preferably, a heat exchanger is connected in front of the collecting vessel between the liquefier/gas cooler and the intermediate pressure reduction device.

Preferably, the conduit from the liquefier/gas cooler is divided into a first conduit portion and a second conduit portion, the second conduit portion being provided with a pressure reducing valve, the refrigerant from the second conduit portion being evaporated in the heat exchanger by cooling of the refrigerant from the first conduit portion.

Preferably, the pressure conduit connecting the first compressor unit and the liquefier/gas cooler is connected to a conduit connecting the liquefier/gas cooler and the collecting vessel.

Preferably, the conduit with the valve therein connects the first conduit portion after the heat exchanger with the pressure conduit after the first compressor unit.

Preferably, the pressure conduit connecting the first compressor unit and the liquefier/gas cooler is connected to the collection vessel.

Preferably, a pressure relief valve is provided in the conduit connecting the pressure conduit with the collection container.

Preferably, a first heat exchanger/superheater is provided which is connected by a conduit to the collecting vessel and by a conduit to the first compressor unit, wherein the flash gas drawn off from the collecting vessel is superheated by the compressed refrigerant from the first compressor unit.

Preferably, a second heat exchanger/subcooler is arranged between the collecting vessel and the pressure reduction device connected upstream of the evaporator.

Preferably, the second heat exchanger/subcooler is connected on the input side to the gas chamber of the collecting vessel.

Preferably, the liquid refrigerant from the collection vessel is subcooled in a second heat exchanger/subcooler by flashed gas from the collection vessel and depressurized in a pressure reducing valve.

Preferably, the refrigerant drawn off by the accumulator is supplied to one or more cryogenic users via a pipe, a pressure reducing valve is connected in front of the cryogenic users, a second compressor unit is provided which is supplied via a suction pipe with the refrigerant evaporated in the cryogenic users, and the refrigerant compressed in the second compressor unit is supplied via a suction pipe to the first compressor unit.

In another aspect, the present invention provides a method for supercritical operation of the above-described refrigeration cycle in which a single-component or multi-component refrigerant is circulated, wherein: in an intermediate pressure reduction device arranged between the liquefier/gas cooler and the collecting vessel, the refrigerant is reduced in pressure to an intermediate pressure of 5 to 40 bar, which is kept constant by means of a pressure reduction valve arranged in the connecting line between the gas chamber of the collecting vessel and the inlet of the first compressor unit.

Preferably, the refrigerant is cooled before the intermediate pressure reduction device.

Preferably, the cooling of the refrigerant is achieved by one tap of the refrigerant.

Preferably, the refrigerant drawn from the collection vessel is subcooled.

Preferably, this subcooling of the refrigerant withdrawn from the collection vessel is achieved by flash gas withdrawn from the collection vessel.

Preferably, at least one partial stream of the flash gas withdrawn from the collecting vessel is at least temporarily superheated by the compressed refrigerant.

Preferably, the intermediate pressure is regulated by means of at least one valve to a constant value and/or to a constant difference with respect to the suction pressure.

Drawings

FIG. 1 shows a prior art refrigeration cycle circuit;

fig. 2 shows a combined refrigeration plant in which a possible configuration of the refrigeration cycle circuit according to the invention is implemented;

fig. 3 shows an embodiment of the refrigeration cycle according to the invention or of the method according to the invention for operating a refrigeration cycle;

fig. 4 and 5 show two further alternative embodiments of the refrigeration circuit according to the invention or of the method according to the invention for operating a refrigeration circuit.

Detailed Description

The refrigeration circuit according to the invention and the method according to the invention for operating a refrigeration circuit and further configurations thereof are described in detail below with reference to the exemplary embodiments shown in fig. 2 to 5.

Fig. 2 shows a combined refrigerating device in which a possible configuration of the refrigerating circuit according to the invention is realized. A process is described below in which HFKW(s), FKW(s) or CO can be used₂As a refrigerant.

The refrigerant compressed in the first compressor unit 6 to a pressure of between 10 and 120 bar is conveyed via a pressure line 7 to the liquefier or gas cooler 1 and is condensed or cooled therein against the ambient air to a saturation temperature. The refrigerant is conveyed through the pipes 2, 2' and 2 "to the refrigerant collector 3, but now according to the invention the refrigerant is decompressed in the intermediate decompression device a to an intermediate pressure of 5 to 40 bar. This intermediate pressure reduction offers the advantage that the subsequently connected pipe network and the collector 3 must now be designed at a lower pressure level.

The pressure to which the refrigerant is depressurized in the intermediate depressurization device a is preferably selected here such that it is still below the desired minimum liquefaction pressure.

According to an advantageous embodiment of the refrigeration circuit according to the invention, the pressure line 7 is connected or connectable to the collecting container 3, preferably to the gas chamber thereof. The connection between the pressure line 7 and the collecting container 3 can be realized, for example, by a connecting line 17, in which a pressure relief valve h is arranged.

According to an advantageous embodiment of the refrigeration circuit according to the invention, the pressure line 7 is connected or connectable to a line or line section 2 or 2', 2 ″ which connects the liquefier 1 to the collecting vessel 3. The connection between the pressure line 7 and the line 2 or 2', 2 ″ can be realized, for example, by a connecting line 18, shown by a dashed line, in which a valve j is arranged.

According to an advantageous embodiment of the refrigeration circuit according to the invention, the collecting container 3, preferably the gas chamber thereof, is connected or connectable to the input of the first compressor element 6.

This connection between the collecting container 3 and the inlet of the first compressor element 6 is effected via a connecting line 12, which opens into a suction line 11 as shown in fig. 2.

The selected intermediate pressure can now be kept constant for all operating conditions by means of a pressure reduction valve e arranged in the line 12 and a pressure reduction valve h arranged in the line 17 or a valve j arranged in the line 18. But may also be adjusted so as to have a constant difference with respect to the suction pressure. This makes it possible to achieve: the reduced-pressure vapor component on the evaporator is relatively small, as a result of which the dimensions of the liquid line and the suction line can be correspondingly small. This also applies to the condensate line, since no gaseous components have to flow back into the liquefier 1 through it now. Thus, by the invention it is also possible to achieve: the required refrigerant charge can be reduced by about 30%.

Refrigerant is drawn off from the accumulator 3 through the suction conduit 4 and delivered to the refrigerant user or to its heat exchangers E2 and E3. A pressure reducing valve b or c is connected upstream of each of the heat exchangers, and the refrigerant flowing into the cold consumers is reduced in pressure in the pressure reducing valves. The refrigerant evaporated in the cold consumers E2 and E3 is then fed back to the first compressor unit 6 via the suction line 5 or is drawn off from the evaporators E2 and E3 via the first compressor unit.

A portion of the refrigerant drawn off by the accumulator 3 through the line 4 is sent to one or more cryogenic users through the line 8, represented by the heat exchanger E4, before which a pressure reducing valve d is also connected. This refrigerant partial stream, after evaporation in heat exchanger or cold consumer E4, is fed via suction line 9 to second compressor unit 10 and compressed therein to the input pressure of first compressor unit 6. The refrigerant partial stream thus compressed is then supplied via line 11 to the input side of the first compressor unit 6.

In order to extend the invention, it is proposed that: as shown in fig. 2, a heat exchanger E1 can be connected in front of the collecting container 3.

The heat exchanger E1 is preferably connected or connectable on the input side to the output of the liquefier 1.

As shown in fig. 2, the partial flow of liquefied or cooled refrigerant to saturation temperature can now be drawn off from the liquefier or gas cooler 1 or from the line 2 via the line 13 in which the pressure reducing valve f is arranged and evaporated in the heat exchanger E1 by the refrigerant to be cooled to saturation temperature which is fed to the heat exchanger E1 via the line 2'. The vaporized refrigerant partial stream is then fed via a line 14 to a compressor 6 'which is assigned to the first compressor unit 6 described above and which preferably draws at a higher pressure level, the vaporized refrigerant partial stream being compressed in this compressor 6' to the desired final pressure of the first compressor unit 6.

As an alternative to the (additional) compressor 6' described above, it is also possible to supply the sucked-off partial pressure steam to one or more cylinders of each compressor at a higher pressure level when using multi-cylinder compressors.

The refrigerant flow to be depressurized in the intermediate depressurization device a is preferably cooled by means of the heat exchanger E1 to such an extent that the depressurization vapor fraction of the depressurized refrigerant is minimized.

Alternatively or additionally, the partial pressure-reducing steam present in the collector 3 can also be drawn off at a higher pressure level by means of the compressor 6' via the line 12 and the line 15 indicated by a dashed line.

Fig. 3 shows an exemplary embodiment of a refrigeration circuit according to the invention or of a method according to the invention for operating a refrigeration circuit, in which the refrigerant drawn off from the collecting vessel 3 via the line 4 is subcooled in a heat exchanger/subcooler E5.

Here, according to an advantageous configuration of the invention, the re-cooling is achieved by heat exchange with the flash gas drawn from the collecting vessel 3 through the conduit 12.

Liquid conduits having a temperature level below ambient temperature, such as the conduits 4 shown in fig. 2 and 3, are subjected to thermal radiation. This leads to partial evaporation of the refrigerant flowing in the liquid line, thus leading to the formation of an undesirable vapor component. To avoid this, the refrigerant is recooled up to now either by expansion and subsequent evaporation of the refrigerant partial flow or by internal heat transfer with the suction gas flow, which is superheated here.

In the refrigeration circuit according to the invention or the method according to the invention, the temperature spacing between the suction line and the liquid line or the refrigerant circulating therein may be too small to achieve its internal heat transfer for the necessary recooling of the refrigerant flowing in the liquid line.

Therefore, in order to improve the present invention, as described above, it is proposed: refrigerant drawn from collection vessel 3 through line 4 is subcooled in heat exchanger or subcooler E5 by flash gas passing from collection vessel 3 through line 12 and depressurized in valve E. After passing through heat exchanger or subcooler E5, the refrigerant, depressurized and superheated in heat exchanger/subcooler E5, is fed to the input of the first compressor unit 6 through line sections 12' and 11. Sufficient subcooling of the refrigerant flowing therein is achieved in liquid line 4 by superheating of the flash gas stream withdrawn from collection vessel 3 through line 12; this subcooling of the refrigerant improves the regulating operation of the pressure-reducing or injection valves b, c and d, which are connected in front of the evaporators E2, E3 and E4.

Droplets exiting collection vessel 3 through conduit 12, which are not precipitated due to their too small size and/or overfilling of collection vessel 3 and are entrained by the flash gas, evaporate at the latest in heat exchanger/subcooler E5. The method therefore also has the advantage that the operational reliability of the compressor or compressor unit is increased due to the reliable superheating of the flash gas stream.

Fig. 4 and 5 show two further alternative embodiments of the refrigeration circuit according to the invention or of the method according to the invention for operating a refrigeration circuit. For the sake of clarity, only parts of the refrigeration circuit according to the invention shown in fig. 2 and 3 are shown in fig. 4 and 5.

In order to develop the method according to the invention for operating a refrigeration circuit, it is proposed that at least one partial flow of the flash gas drawn off from the collecting vessel is superheated at least temporarily by at least one partial flow of the compressed refrigerant.

Fig. 4 shows a possible configuration of the method according to the invention, in which a partial stream of the flash gas drawn off from the collecting vessel 3 via the line 12 is at least temporarily fed via the line 16 to a heat exchanger/superheater E6 and superheated in this heat exchanger by the refrigerant compressed in the first compressor unit 6.

In the method shown in fig. 4, the flash gas stream to be superheated is superheated in a heat exchanger/superheater E6 by the total refrigerant stream compressed in the first compressor unit 6, which refrigerant stream is fed via a conduit 7 to a liquefier or cooler, not shown in fig. 4.

After passing through heat exchanger/heater E6, the flash gas stream is fed via line 16 'to the input of compressor 6' of first compressor unit 6.

In fig. 5 a method is shown wherein the flash gas stream withdrawn from collection vessel 3 via line 12, open valve g and line 16 is superheated in heat exchanger E7 by the compressed refrigerant stream in line 7. This flash gas stream can be fed to the first compressor unit 6 after passing through heat exchanger E7 in such a way that: one or more cylinders of a multi-cylinder compressor pump the flash gas at a higher pressure level. Instead of the valve g, valves x, y and z may be provided.

The methods shown in fig. 4 and 5 ensure that: the liquid components contained in the flash gas are reliably evaporated, thereby resulting in a higher reliability of the compressor or first compressor unit 6.

Claims (19)

1. Refrigeration circuit in which a single-component or multi-component refrigerant circulates, which refrigeration circuit is capable of supercritical operation and which has, in the direction of flow, a liquefier/gas cooler (1), a collecting container (3), a pressure reduction device (b, c) connected upstream of the evaporator (E2, E3), an evaporator (E2, E3) and a first compressor unit (6) of single-stage compression, characterized in that: an intermediate pressure reduction device (a) is arranged between the liquefier/gas cooler (1) and the collecting vessel (3); the gas chamber of the collecting container (3) is connected to the input of the first compressor unit (6); and a pressure relief valve (e) is arranged in the connecting line (11, 12) between the gas chamber of the collecting container (3) and the inlet of the compressor unit (6).

2. The refrigeration cycle circuit according to claim 1, wherein: a heat exchanger (E1) is connected upstream of the collecting container (3) between the liquefier/gas cooler (1) and the intermediate decompression device (a).

3. The refrigeration cycle circuit according to claim 2, wherein: the conduit (2) from the liquefier/gas cooler (1) is divided into a first conduit portion (2 ') and a second conduit portion (13), the second conduit portion (13) being provided with a pressure reducing valve, and refrigerant from the second conduit portion (13) is evaporated in a heat exchanger (E1) by cooling of refrigerant from the first conduit portion (2').

4. A refrigeration cycle circuit according to claim 3, wherein: the pressure line (7) connecting the first compressor unit (6) and the liquefier/gas cooler (1) is connected to a line (2, 2') connecting the liquefier/gas cooler (1) and the collecting vessel (3).

5. The refrigeration cycle circuit according to claim 4, wherein: wherein a conduit (18) with a valve (j) connects the first conduit portion (2') after the heat exchanger (E1) with the pressure conduit (7) after the first compressor unit (6).

6. The refrigeration cycle circuit according to claim 1, wherein: a pressure line (7) connecting the first compressor unit (6) and the liquefier/gas cooler (1) is connected to the collecting vessel (3).

7. The refrigeration cycle circuit according to claim 6, wherein: a pressure reducing valve (h) is arranged in a pipe (17) connecting the pressure pipe (7) and the collecting container (3).

8. The refrigeration cycle circuit according to claim 1, wherein: a first heat exchanger/superheater (E6) connected to the collection vessel (3) by a conduit (16) and to the first compressor unit (6) by a conduit (16') is provided, wherein the flash gas withdrawn from the collection vessel (3) is superheated by the compressed refrigerant from the first compressor unit (6).

9. The refrigeration cycle circuit according to claim 1, wherein: a second heat exchanger/subcooler (E5) is arranged between the collecting vessel (3) and the pressure reduction device (c, b, d) connected upstream of the evaporator.

10. The refrigeration cycle circuit according to claim 9, wherein: the second heat exchanger/subcooler (E5) is connected (12) on the input side to the gas chamber of the collecting container (3).

11. The refrigeration cycle circuit according to claim 10, wherein: the liquid refrigerant from the collection vessel (3) is subcooled in a second heat exchanger/subcooler (E5) by flash gas from the collection vessel (3) and depressurized in a depressurization valve (E).

12. The refrigeration cycle circuit according to claim 1, wherein: the refrigerant drawn off by the accumulator (3) is fed to one or more cryogenic consumers (E4) via a line (8), a pressure reducing valve (d) is connected upstream of the cryogenic consumers (E4), a second compressor unit (10) is provided, the second compressor unit (10) is fed via a suction line (9) with the refrigerant evaporated in the cryogenic consumers (E4), and the refrigerant compressed in the second compressor unit (10) is fed via a suction line (11) to the first compressor unit (6).

13. Method for the supercritical operation of a refrigeration cycle according to claim 1, in which a single-component or multi-component refrigerant is circulated, wherein: the refrigerant is depressurized in an intermediate depressurization device (a) arranged between the liquefier/gas cooler (1) and the collecting vessel (3) to an intermediate pressure of 5 to 40 bar, which is kept constant by means of a depressurization valve (e) in a connecting line (11, 12) arranged between the gas chamber of the collecting vessel (3) and the input of the first compressor unit (6).

14. The method of claim 13, wherein: the refrigerant (2) is cooled (E1) before the intermediate decompression device (a).

15. The method of claim 14, wherein: the cooling (E1) of the refrigerant (2) is effected by a partial flow (13) of the refrigerant.

16. Method according to one of the preceding claims 13 to 14, characterized in that: the refrigerant (4) drawn from the collecting container (3) is recooled (E5).

17. The method of claim 16, wherein: this subcooling (E5) of the refrigerant (4) withdrawn from the collection vessel (3) is achieved by means of flash gas (12) withdrawn from the collection vessel (3).

18. Method according to one of the preceding claims 13 to 14, characterized in that: at least one partial stream of the flash gas (12) withdrawn from the collecting vessel (3) is superheated (E6, E7) at least temporarily by the compressed refrigerant (7).

19. Method according to one of the preceding claims 13 to 14, characterized in that: the intermediate pressure is regulated by means of at least one valve (e, h, j) to a constant value and/or to a constant difference with respect to the suction pressure.