EP2264385B1 - Refrigeration cycle and method of operating a refrigerating cycle - Google Patents

Abstract

Refrigerant is circulated in a predetermined flow direction comprised of a heat-rejecting heat exchanger (4), intermediate throttle valve (6), receiver (8), evaporator throttle valves (10), evaporator (14), compressor (20) and flash gas tapping line (26). The flash gas tapping line is connected to the receiver and to the compressor. An independent claim is also included for a refrigeration circuit operating method.

Description

The invention relates to a refrigeration cycle in which a one- or multi-component refrigerant circulates, comprising in the flow direction a condenser, a collecting container, an expansion device upstream of an evaporator, an evaporator and a compressor unit.

Furthermore, the invention relates to a method for operating a refrigeration cycle.

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

Generic refrigeration cycles are well known. They are for example in refrigeration systems, so-called composite refrigeration systems, such as those used in supermarkets, implemented. Composite refrigerators generally supply a large number of refrigeration consumers, such as refrigerators, refrigerators and freezers. For this purpose circulates in them a one- or multi-component refrigerant or refrigerant mixture.

A counting of the prior art refrigeration cycle or a refrigeration system in which such a refrigeration cycle is realized, is based on the in the FIG. 1 illustrated embodiment explained in more detail.

The circulating in the refrigeration cycle one- or multi-component refrigerant is in a condenser or gas cooler A - hereinafter referred to only as a condenser - which is usually outside the supermarket, for example, on the roof, arranged by heat exchange, preferably against outside air, condensed.

The liquid refrigerant from the condenser A is fed via line B to a (refrigerant) collector C. Within a refrigeration cycle always so much refrigerant must be present that even with maximum cooling demand, the evaporator of all refrigeration consumers can be filled. However, with lower cooling requirements individual evaporators are only partially filled or even completely empty, the excess refrigerant must be collected during these times in the designated collector C.

From the collector C, the refrigerant passes through the liquid line D to the cold consumers of the so-called normal cooling circuit. Here are the in the FIG. 1 represented consumers F and F 'for any number of consumers of the normal refrigeration cycle. Each of the aforementioned refrigeration consumers is preceded by an expansion valve E or E ', in which the refrigerant flowing into the refrigeration appliance or the evaporator or the evaporator of the refrigeration consumer is expanded. The so-relaxed refrigerant is evaporated in the evaporators of the refrigerant consumers F and F 'and thus cools the corresponding refrigeration cabinets and rooms.

The refrigerant evaporated in the refrigeration consumers F and F 'of the normal refrigeration cycle is then fed via the suction line G to the compressor unit H and compressed therein to the desired pressure between 10 and 25 bar. As a rule, the compressor unit H is designed to be single-stage and has several compressors connected in parallel.

The compressed in the compressor unit H refrigerant is then fed via the pressure line I in turn to the aforementioned condenser A.

Via a second liquid line D 'is the condenser C refrigerant supplied to the condenser K and evaporated in this heat exchange with the refrigerant of the still to be explained Tiefkühlkreislaufes before it is fed via the line G' of the compressor unit H.

The liquefied in the condenser K refrigerant of the freezing circuit is supplied via line L to the collector M of the freezing circuit. For this, via the line N, the refrigerant to the consumer P - this is for any number of consumers -, which is preceded by a relaxation device O, supplied and evaporated in this. Via the suction line Q, the vaporized refrigerant is fed to the single or multi-stage compressor unit R, compressed in this to a pressure between 25 and 40 bar and then fed via the pressure line S to the aforementioned capacitor K.

As a refrigerant of the normal refrigeration cycle, for example, R 404A is used, while for the freezing cycle carbon dioxide is used.

The in the FIG. 1 shown compressor units H and R, the collector C and M and the capacitor K are usually arranged in a separate machine room. However, about 80 to 90% of the entire pipeline network is located in the sales rooms, the storage areas or other areas of a supermarket accessible to employees and customers. As long as this line network operates at pressures of no more than 35 to 40 bar, this is acceptable to the supermarket operators both from a psychological point of view and for cost reasons.

Currently, it is going to operate even the above-described normal cooling circuit with the refrigerant CO ₂ .

The sensible use of the natural refrigerant CO ₂ in commercial refrigeration fails on the one hand due to the insufficient energetic efficiency of the simple, single-stage cycle at high (outside) air temperatures. On the other hand, owing to the material properties of CO _2, high working pressures - up to 100 bar and above - are required, which make it extremely difficult to manufacture corresponding refrigeration circuits or refrigeration plants for economic reasons. Commercially, the refrigerant CO _{2 is} therefore so far only used in cascade systems in the freezing - as exemplified by the FIG. 1 is explained - since the working pressures realized there do not exceed the usual maximum pressure of 40 bar.

Due to the above-mentioned higher pressures or pressure, the pipe network of the refrigeration cycle must be designed for these pressures or pressure. However, the materials required for this are far more expensive than those that can be used in the previously implemented printing layers. In addition, however, such relatively high pressure levels are also very difficult to convey to plant operators.

Another problem is especially when using CO ₂ as a refrigerant in that at high ambient temperatures, a supercritical operation of the refrigeration cycle is required. High outside air temperatures have the consequence that at the evaporator inlet comparatively high throttle vapor components occur. This reduces the effective volumetric cooling capacity of the circulating refrigerant, however, both suction and liquid lines and the evaporators must be sized accordingly larger to keep the pressure losses as low as possible.

Object of the present invention is to provide a generic refrigeration cycle and a method for operating a refrigeration cycle, which avoids the disadvantages mentioned.

To solve this problem, a refrigeration cycle is proposed, which is characterized in that between the condenser and the collecting container, an intermediate-expansion device is arranged.

The method, the object is achieved in that in the intermediate between the condenser and the collecting intermediate relaxation device, a relaxation of the refrigerant to an (intermediate) pressure of 5 to 40 bar.

From the DE 195 22 884 A1 is a method for operating a compression refrigeration system with the working fluid carbon dioxide (CO2) with a two-stage throttling and division of the circulating mass flow of working fluid known. In this case, the working medium mass flow is passed after the first throttle stage in a subcritical working medium pressure separator, which is the lower in the lower part of the medium pressure separating large liquid Arbeitsmittelmassestromanteil the evaporator is supplied to the upper part of the Mitteleldruckabscheidesammlers separating smaller vapor Arbeitsmittelmassestromanteil is about a second throttle level to close relaxes the evaporation pressure and serves in an internal heat exchanger by evaporation and overheating to subcool the supercritical high pressure gas. After evaporation and overheating, the smaller mass fraction of the working fluid is mixed with the evaporator strands in a collecting tube integrated in the evaporator. In the DE 195 22 884 A1 disclosed refrigerant circuit and method correspond to the preambles of claims 1 and 14. From the JP 2000 154941 A For example, a refrigerator / refrigerator is known, comprising a compressor, a condenser, a throttle device and an evaporator, which are annularly connected to each other by lines, and with a gas-liquid separator, which is provided on a downstream side of the throttle unit. The refrigerator / refrigerator includes a liquid line for conducting liquid refrigerant separated by the gas-liquid separator to the evaporator; and a gas conduit for conducting gaseous refrigerant separated from the gas-liquid separator to an inlet side of the compressor, the gas conduit being in heat exchange with a conduit section between the outlet side of the compressor and an inlet of the condenser. A refrigeration cycle, and a method for operating a refrigeration cycle and other embodiments thereof are the same below with reference to in the Figures 2 and 3 shown embodiments explained in more detail, wherein the FIG. 4 shows a refrigeration cycle according to the invention.

This shows the FIG. 2 a composite refrigeration system in which a possible embodiment of a refrigeration cycle is realized. In the following, a procedure is described in which as a refrigerant HFC (s), HFC (s) or CO ₂ can be used.

The compressed in the compressor unit 6 to a pressure between 10 and 120 bar refrigerant is supplied via the pressure line 7 to the condenser or gas cooler 1 and condensed in this against outside air or deprived. The refrigerant is supplied to the refrigerant collector 3 via the lines 2, 2 'and 2 ", but according to the invention it is expanded in the intermediate expansion device a to an intermediate pressure of 5 to 40 bar and the collector 3 need only be designed for a lower pressure position The pressure to which the refrigerant in the mentioned intermediate expansion device a is relieved is preferably selected so that it is still below the lowest expected condensing pressure.

According to an advantageous embodiment of a refrigeration cycle, the pressure line 7 with the collecting container 3, preferably with the gas space, connected or connectable. This connection between the pressure line 7 and the collecting container 3 can take place, for example, via a connecting line 17, in which an expansion valve h is arranged.

According to an advantageous embodiment of a refrigeration cycle, the pressure line 7 is connected or connectable to the line or line sections 2 or 2 ', 2 "connecting the condenser 1 and the collecting container 3. This connection between the pressure line 7 and the line 2 or 2 ', 2 "can be done, for example, via the connecting line 18 shown in dashed lines, in which a valve j is arranged.

According to an advantageous embodiment of a refrigeration cycle of the collecting container 3, preferably the gas space, connected to the input of the compressor unit 6 or connectable.

This connection between the collecting container 3 and the input of the compressor unit 6 can, for example, via a connecting line 12, as in the FIG. 2 shown, in the suction line 11 opens, done.

By way of the expansion valve e provided in the line 12 and the expansion valve h provided in the line 17 or the valve j provided in the line 18, the selected intermediate pressure can now be kept constant for all operating conditions. However, a regulation is also possible in such a way that there is a constant difference value to the suction pressure. This ensures that the throttle steam fraction at the evaporators is comparatively small, with the result that the liquid and suction lines can be dimensioned correspondingly smaller. This also applies to the condensate line, since now no gaseous components have to flow through them back into the condenser 1. By means of the invention is thus also achieved that can be reduced by up to about 30%, the required refrigerant charge.

Via the suction line 4 refrigerant is withdrawn from the collector 3 and the refrigerant consumers or their heat exchangers E2 and E3 supplied. This is preceded by a respective expansion valve b and c, in which the refrigerant flowing into the refrigeration consumer is expanded. The refrigerant evaporated in the refrigeration consumers E2 and E3 is then fed back to the compressor unit 6 via the suction line 5 or sucked out of the evaporators E2 and E3 by the latter.

A portion of the withdrawn from the collector 3 via line 4 refrigerant is fed via line 8 to one or more frozen consumers - represented by the heat exchanger E4 -, which is also preceded by an expansion valve d supplied. After the evaporation in the heat exchanger or cold consumer E4, this partial refrigerant flow is fed via the suction line 9 to the compressor unit 10 and compressed therein to the inlet pressure of the compressor unit 6. The thus compressed refrigerant partial stream is then fed via line 11 to the input side of the compressor unit 6. Further training suggests that - as in the FIG. 2 represented - the collecting container 3, a heat exchanger E1 can be connected upstream.

Here, the heat exchanger E1 is preferably connected on the input side to the output of the condenser 1 or connectable.

Like in the FIG. 2 a partial flow of the liquefied or desiccant refrigerant can now be withdrawn from the condenser or gas cooler 1 or line 2 via line 13, in which an expansion valve f is provided, and in the heat exchanger E1 against the heat exchanger E1 to be heated via line 2 'supplied refrigerant to be evaporated. The vaporized refrigerant partial stream is then fed via line 14 to a compressor 6 ', which is associated with the above-described compressor unit 6 and which preferably sucks at a higher pressure level, and in this compressed to the desired final pressure of the compressor unit 6.

By means of the heat exchanger E1, the refrigerant stream to be expanded in the intermediate expansion device a is preferably cooled to such an extent that the throttled vapor portion of the expanded refrigerant is minimized.

Alternatively or additionally, the resulting in the collector 3 throttle steam fractions can be sucked off via the line 12 and the dashed line 15 by means of the compressor 6 'at a higher pressure level.

In the FIG. 3 1 shows an embodiment of a refrigeration cycle or a method for operating a refrigeration cycle, in which the refrigerant drawn off from the collecting container 3 via the line 4 is subjected to supercooling in the heat exchanger E5. In this case, the subcooling takes place - in accordance with an advantageous embodiment - in heat exchange with the flash gas withdrawn from the collecting container 3 via line 12.

Liquid lines, such as those in the Figures 2 and 3 shown line 4, with a temperature level below the ambient temperature exposed to heat radiation. This has the consequence that the refrigerant flowing inside the liquid line partially evaporates, thus resulting in the formation of undesirable vapor contents. In order to prevent this, refrigerants are previously undercooled either by an expansion of a partial flow of the refrigerant and subsequent evaporation or by an internal heat transfer to a suction gas stream, which is thereby overheated. The temperature difference between the suction and liquid line or the circulating refrigerant therein may be too low to realize an internal heat transfer for the required supercooling of the refrigerant flowing in the liquid line. Further education is therefore - as already mentioned - proposed to subcool the withdrawn from the sump 3 via line 4 refrigerant in the heat exchanger or subcooler E5 against the expanded from the sump 3 via line 12 and in the valve e flash gas. After passing through the heat exchanger or subcooler E5, the expanded refrigerant which has been overheated in the heat exchanger E5 is fed via the line sections 12 'and 11 to the inlet of the compressor unit 6. Due to the overheating of the withdrawn from the reservoir 3 via line 12 Flashgasstromes a sufficient subcooling of the refrigerant flowing in it is achieved in the liquid line 4; This supercooling of the refrigerant improves the regular operation of the expansion or injection valves b, c and d, which are upstream of the evaporators E2, E3 and E4.

Liquid droplets which are not separated from the collecting container 3 via line 12 due to a too small dimensioning and / or overfilling of the collecting container 3 and carried along with the flash gas, are evaporated at the latest in the heat exchanger / subcooler E5. The procedure described thus has the additional advantage that the reliability of the compressor or compressor unit 6 is increased due to a safe overheating of the flash gas stream.

The FIG. 4 shows an embodiment of the refrigeration cycle according to the invention or the method according to the invention for operating a refrigeration cycle. For the sake of clarity is in the FIG. 4 only a part of the in the FIG. 2 and 3 shown refrigerant circuit shown.

The method according to the invention for operating a refrigeration cycle further develops that at least a partial flow of the flash gas withdrawn from the collecting container is at least temporarily overheated against at least a partial flow of the compressed refrigerant.

The FIG. 4 shows a possible embodiment of the method according to the invention, in which at least temporarily a partial flow of the withdrawn from the reservoir 3 via line 12 flash gas via line 16 to a heat exchanger E6 and superheated in this against the compressed in the compressor unit 6 refrigerant.

When in the FIG. 4 As shown, the Flashgasstrom to be overheated in the heat exchanger E6 against the entire, compressed in the compressor unit 6 refrigerant flow via line 7 in the FIG. 4 not shown condenser or desuperheater is supplied, superheated.

After passing through the heat exchanger / superheater E6, the flash gas stream is supplied via line 16 'to the inlet of the compressor 6' of the compressor unit 6.

The in the FIG. 4 The procedure described makes it possible to ensure that liquid components contained in the flash gas are unambiguously vaporized, resulting in increased safety for the compressor or compressor unit 6.

Claims (14)

1. A refrigeration circuit in which a single-component or multi-component refrigerant, in particular CO₂, circulates, said refrigeration circuit enabling transcritical operation and comprising, in the direction of flow, a condenser/gas cooler (1), an intermediate relief device (a), a collecting container (3), a relief device (b, c) disposed upstream of an evaporator (E2, E3), an evaporator (E2, E3), and a compressor unit (6) connected to the evaporator (E2, E3) by a suction line (5), the compressor unit (6) being connected to the condenser/gas cooler (1) by means of a pressure line (7), and the gas space of the collecting container (3) being connected or connectable to an input of the compressor unit (6) via a line (12, 16), characterized in that a heat exchanger (E6) is provided, to which a partial flow of the flash gas that is drawn out of the collecting container (3) via the line (12, 16) is fed, at least intermittently, and in which this partial flow is superheated in relation to the compressed refrigerant in the pressure line (7).
2. The refrigeration circuit according to Claim 1, wherein, after passing through the heat exchanger/superheater (E6), the flash gas is fed via a line (16') to the input of the compressor (6') of the compressor unit (6).
3. The refrigeration circuit according to Claim 1 or 2, wherein a heat transfer means (E1) is connected upstream of the collecting container (3).
4. The refrigeration circuit according to Claim 3, wherein the heat transfer means (E1) is connected or connectable (2, 13) on an input side to the output of the condenser/gas cooler (1).
5. The refrigeration circuit according to Claim 3 or 4, wherein the line (2) from the condenser/gas cooler (1) is divided into a first line section (2') and a second line section (13), wherein a relief valve (f) is located in the second line section (13), and wherein the refrigerant in the second line section (13) is evaporated in the heat transfer means (E1) against the refrigerant in the first line section (2').
6. The refrigeration circuit according to Claim 5, wherein the second line section (13, 14) downstream of the heat transfer means (E1) is connected or connectable to the input of the compressor (6') of the compressor unit (6).
7. The refrigeration circuit according to Claim 5 or 6, wherein the pressure line (7) is connected or connectable to the line (2, 2', 2") that connects the condenser/gas cooler (1) to the collecting container (3).
8. The refrigeration circuit according to any of Claims 5 to 7, wherein the line (18) with a valve (j) disposed therein connects the first line section (2') downstream of the heat transfer unit (E1) to the pressure line (7) downstream of the compressor unit (6).
9. The refrigeration circuit according to any of the preceding claims, wherein the pressure line (7) is connected or connectable to the collecting container (3), preferably to the gas space thereof.
10. The refrigeration circuit according to Claim 9, wherein a relief valve (h) is provided in the line (17) that connects the pressure line (7) to the collecting container (3).
11. The refrigeration circuit according to any of the preceding claims, wherein the refrigerant drawn from the collecting container (3) is fed via a line (8) to one or more deep-freeze consumers (E4) having a relief valve (d) connected upstream thereof.
12. The refrigeration circuit according to Claim 11, wherein a compressor unit (10) is provided which is supplied via a suction line (9) with refrigerant evaporated in the deep-freeze consumer (E4), and wherein the refrigerant compressed in the compressor unit (10) is fed via a suction line (11) to the compressor unit (6).
13. A method for operating a refrigeration circuit, in which a single-component or multi-component refrigerant, in particular CO₂, circulates in the direction of flow through a condenser/gas cooler (1), an intermediate relief device (a), a collecting container (3), a relief device (b, c) connected upstream of an evaporator (E2, E3), an evaporator (E2, E3), and a compressor unit (6) connected to the evaporator (E2, E3) via a suction line (5), in which flash gas from the gas space of the collecting container (3) is fed via a line (12, 16) to the input of the compressor unit (6), characterized in that, in the intermediate relief device (a) disposed between the condenser/gas cooler (1) and the collecting container (3), a pressure release of the refrigerant to an intermediate pressure of 5 to 40 bar is effected, and a partial flow of the flash gas (12, 16) drawn from the collecting container (3) is superheated (E6), at least intermittently, in relation to the compressed refrigerant (7) in the pressure line (7) that connects the compressor unit (6) to the condenser/gas cooler (1).
14. The method according to Claim 13, wherein the refrigerant (2) is cooled before its intermediate relief (a).

Images