EP1789732B1 - Refrigeration circuit and method for operating a refrigeration circuit - 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 single-stage compressing 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 condensed 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, 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 evaporated refrigerant is fed to the single or multi-stage compressor unit R, in this to a pressure compressed 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.

Out P. Ostertag: cooling processes represented using the Entropietafel, Berlin, published by Julius Springer, 1933, XP-001169097, pages 39 to 43 , a refrigeration cycle with a two-stage throttling is known. In this case, two regulating valves are connected in series, between which a separator sits. In the first valve is throttled to an intermediate pressure and the resulting vapor excreted, the second valve receives only the liquid remained part of the refrigerant flowing to the evaporator and thence to the compressor. Its cylinder is provided in the manner of the DC steam engine with slots, which are located in the middle of the shell and which are connected to the separator. If the piston frees these slots after passing through its useful stroke, the accumulated in the separator steam can fall into the cylinder.

From the DE 195 22 884 A1 a method for operating a compression refrigeration system with the working fluid carbon dioxide with a two-stage throttling and division of the circulating working fluid flow is known. In this case, the working medium mass flow is passed after the first throttle stage in a subcritical working medium pressure collector, which in the lower part of the medium pressure separator collecting, larger liquid Arbeitsmittelmassestromanteil supplied to the evaporator, the separating in the upper part of the medium pressure separating, smaller vapor Arbeitsmittelmassestromanteil a second throttle level close to the Evaporating pressure relaxes. In an internal heat exchanger, the smaller vapor mass of the working medium mass used by evaporation and overheating serves to subcool the supercritical high-pressure gas. After evaporation and overheating, the smaller working medium mass fraction is mixed in a collecting tube integrated in the evaporator with the outlet of the evaporator strands.

From the US 933 682 a refrigeration cycle is known, comprising a compressor, which comprises a Hochdrucksaugeingang and a Niedrigdrucksaugeingang with a condenser, with a collecting container, the liquid refrigerant in its lower part and gaseous refrigerant in its upper part, with a line which the liquid refrigerant of the Capacitor to the Sump leads, with a pressure reducing valve in this line, with a high-pressure cooler, with a line leading from the lower part of the sump to the radiator, with a line leading from the radiator to the upper part of the sump, with a line, which leads from the upper part of the collecting container to the high-pressure inlet of the compressor, with a low-pressure radiator, with a line leading from the lower part of the collecting container to the low-pressure radiator, with a pressure reducing valve in this line and with a line coming from the low-pressure radiator the low pressure suction inlet of the compressor leads.

The EP 0 180 904 B1 discloses a cooling device with a multi-cylinder piston compressor, which also includes a subcooler for the refrigerant liquid in the line between the condenser and expansion element.

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.

Verfahrensseitg the task is achieved in that takes place in the intermediate between the condenser and the collecting intermediate Entspanriungsvorrichtung a relaxation of the refrigerant to an (intermediate) pressure of 5 to 40 bar.

The inventive refrigeration cycle, the inventive method for operating a refrigeration cycle and other embodiments thereof are described below with reference to in the FIGS. 2 to 5 shown embodiments explained in more detail.

This shows the FIG. 2 a composite refrigeration system in which a possible embodiment of the refrigeration cycle according to the invention 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. About the lines 2, 2 'and 2 ", the refrigerant is supplied to the refrigerant collector 3, but now it is relaxed according to the invention in the intermediate expansion device a to an intermediate pressure of 5 to 40. This intermediate relaxation offers the advantage that the downstream line network and the collector 3 only to a lower Pressure must be designed.

The pressure to which the refrigerant is expanded in the mentioned intermediate relaxation device a, is hereby preferably selected so that it is still below the lowest expected condensing pressure.

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

According to an advantageous embodiment of the refrigeration cycle according to the invention 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, it is also possible a scheme such that a constant difference value to the suction pressure exists. 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 fed to the Kältemittelverbrauchem or their heat exchanger E2 and E3. 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.

The invention further, it is proposed 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.

As an alternative to the above-mentioned (additional) compressor 6 'can be carried out at a higher pressure level to one or more cylinders of each compressor when using mehrylindrischerer compressor also a supply of the sucked throttled vapor portion.

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 the refrigeration cycle according to the invention or of the method according to the invention 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.

Here, the supercooling - according to an advantageous embodiment of the invention - in heat exchange with the withdrawn from the reservoir 3 via line 12 flash gas.

Liquid lines, such as those in the Figures 2 and 3 shown line 4, with a temperature level below the ambient temperature are 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. To prevent this, refrigerant so far either by an expansion of a partial flow of the refrigerant and subsequent evaporation or by an internal heat transfer against a suction gas stream, which is thereby overheated, subcooled.

In the refrigeration cycle according to the invention or the procedure according to the invention, the temperature interval 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.

The invention further developing is therefore-as already mentioned - proposed to cool the withdrawn from the sump 3 via line 4 refrigerant in the heat exchanger or subcooler E5 against the relaxed 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 entrained with the flash gas, are vaporized latest in the heat exchanger / subcooler E5 The above described method 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 a further, embodiment of the refrigeration cycle according to the invention or the inventive method for operating a refrigeration cycle. For the sake of clarity is in the FIG. 4 only a section of the in the FIG. 2 and 3 illustrated refrigeration circuit according to the invention 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 fed 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 (19)

1. Refrigeration circuit having a mono- or multi-component refrigerant, especially CO₂, circulating therein, said refrigeration circuit enabling an overcritical operation, said refrigeration circuit comprising, in the direction of flow, a condenser/gascooler (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) with single-stage compression, wherein the gas space of the collecting container (3) is connected or connectible to the input of the compressor unit (6), and wherein a relief valve (e) is provided in the connection line (11, 12) between the gas space of the collecting container (3) and the input of the compressor unit (6),
   characterized in that
   between the collecting container (3) and the expansion device (b, c) connected upstream of an evaporator (E2, E3) there is arranged a heat exchanger/subcooler (E5) and that in the heat exchanger/subcooler (E5) the refrigerant drawn off the collecting container (3) is subcooled with respect to the flash gas being drawn off the collecting container (3) via the connection line (11, 12) and being expanded by the expansion valve (e).
2. Refrigeration circuit according to claim 1, wherein a heat transfer means (E1) is connected upstream of the collecting container (3).
3. Refrigeration circuit according to claim 2, wherein the heat transfer means (E1) is connected or connectible (2, 13) on the input side to the output of the condenser/gascooler (1).
4. Refrigeration circuit according to claim 2 or 3, wherein the line (2) from the condenser/gascooler (1) divides into a first line portion (2') and into a second line portion (13), wherein a relief device (f) is arranged in the second line portion (13), and wherein the refrigerant in the second line portion (13) is evaporated in the heat exchanger (E1) with respect to the refrigerant in the first line portion (2').
5. Refrigeration circuit according to claim 4, wherein the second line portion (13, 14) after the heat exchanger (E1) is connected or connectible to the input of the compressor (6') of the compressor unit (6).
6. Refrigeration circuit according to claim 4 or 5, wherein a pressure line (7) is provided for feeding compressed refrigerant from the compressor unit (6) to the compressor/gascooler (1), and wherein the pressure line (7) is connected or connectible to the line (2, 2', 2") that connects the condenser/gascooler (1) and the collecting container (3).
7. Refrigeration circuit according to any of the claims 4 to 6, wherein a pressure line (7) is provided for feeding compressed refrigerant from the compressor unit (6) to the condenser/gascooler (1), and wherein the line (18) having a valve (j) arranged therein connects the first line portion (2') after the heat exchanger (E1) to the pressure line (7) after the compressor unit (6).
8. Refrigeration circuit according to any of the preceding claims, wherein the gas space of the collecting container (3) is connected or connectible to the input of a compressor (6') of the compressor unit (6).
9. Refrigeration circuit according to any of the preceding claims, wherein a pressure line (7) is provided for feeding compressed refrigerant from the compressor unit (6) to the condenser/gascooler (1), and wherein the pressure line (7) is connected or connectible to the collecting container (3), preferably with the gas space thereof.
10. 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. Refrigeration circuit according to any of the preceding claims, wherein a pressure line (7) is provided for feeding compressed refrigerant from the compressor unit (6) to the condenser/gascooler (1) and wherein a heat exchanger (E6) is provided in which the flash gas drawn off the collecting container is superheated against compressed refrigerant in the pressure line (7).
12. Refrigeration circuit according to claim 11, wherein the flash gas after passage through the heat exchanger/superheater (E6) is fed via a line (16') to the input of the compressor (6') of the compressor unit (6).
13. Refrigeration circuit according to any of the preceding claims, wherein the refrigerant drawn off the collecting container (3) is fed via a line (8) to one or more freezing cold consumers (E4) having an expansion valve (d) connected upstream thereof.
14. Refrigeration circuit according to claim 13, wherein a compressor unit (10) is provided that is supplied via a suction line (9) with refrigerant evaporated in the freezing cold consumer (E4), and wherein the refrigerant compressed in the compressor unit (10) is fed to the compressor unit (6) via a suction line (11).
15. Method for overcritical operation of a refrigeration circuit according to any of the preceding claims, in which a mono- or multi-component refrigerant, especially CO₂, circulates, wherein pressure relief of the refrigerant to an intermediate pressure of 5 to 40 bar is effected in the intermediate relief device (a) arranged between the condenser/gascooler (1) and the collecting container (3),
    characterized in that
    the intermediate pressure is kept constant by means of the relief valve (e) in the connection line (11, 12) between the gas space of the collecting container (3) and the input of the compressor unit (6) and that the refrigerant drawn off the collecting container (3) is subcooled in a heat exchanger/subcooler (E5) with respect to the flash gas being drawn off the collecting container (3) via the connection line (11, 12) and being expanded in the relief valve (e).
16. Method according to claim 15, wherein the refrigerant (2) is subjected to cooling (E1) prior to intermediate pressure-relief (a) of the same.
17. Method according to claim 16, wherein the cooling (E1) of the refrigerant (2) is effected with respect to a partial flow of the refrigerant (13).
18. Method according to any of claims 15 to 17, wherein at least a partial flow of the flash gas (12) withdrawn from the collecting container (3) is superheated (E6, E7) at least temporarily with respect to the compressed refrigerant (7).
19. Method according to any of claims 15 to 18, wherein the intermediate pressure is regulated to a constant value and/or to a constant difference from the suction pressure by means of at least one valve (e, h, j).

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