EP2667116B1 - Method and device for cooling - Google Patents

Description

The invention relates to a method and a device for cooling a medium or a plurality of media.

In particular, in the temperature range between minus 56 ° C and minus 79 ° C are systems for cooling a medium, for example a gas stream, are used, which operate on the principle of indirect cooling by means of a heterogeneous mixture, the heterogeneous mixture, for example, from carbon dioxide and a in consists of this temperature range in the liquid state carrier medium. Such a plant is about from the DE 30 04 114 A1 known. The refrigeration system described therein operates with a heat transfer medium consisting of a suspension of solid carbon dioxide particles in terpene as a liquid carrier medium. To produce the suspension, pressurized liquid carbon dioxide (carbonic anhydride) is converted to solid carbon dioxide particles and carbon dioxide gas by expansion. The carbon dioxide particles are then fed to the carrier medium to form the suspension and cool it. By varying the final pressure of the expansion of this object, the temperature of the resulting carbon dioxide - and thus the suspension - between minus 56 ° C (at pressures just below the triple point) and minus 79 ° C (with relaxation to 1 bar final pressure) can be set. The suspension is then pumped through a sublimator (heat exchanger) in which the particles of coal dioxide sublimate in heat exchange with the medium to be cooled, for example a gas stream, at least partially. The cooled gas stream can then be used, for example, for freezing and storing food. The remaining mixture, containing terpene, carbon dioxide vapor and optionally remaining in the terpene carbon dioxide particles, is separated; the thereby separated gaseous carbon dioxide is sucked off and can then be liquefied in a compressor and used in a renewed cooling cycle.

In order to improve the homogeneity of the suspension is in the EP 0 948 727 B1 proposed to continuously circulate the transport fluid containing the carbon dioxide particles in the mixing container. This is done according to the teaching of this document, characterized in that the suspension produced in the mixing container is partially returned by means of a pump in the liquid phase of the mixing container, so that it is constantly kept in motion. The transport liquid used in this article instead of terpene limonene.

In the JP 2004 170007 A describes a cooling system for the range of -56 ° C or below, in which a cooling mixture of solid carbon dioxide particles and a brine liquid for cooling a medium in a heat exchanger is used. When exchanging heat with the medium, the carbon dioxide partially evaporates. The gaseous carbon dioxide formed during the expansion or cooling is separated from the cooling mixture and liquefied. Subsequently, the liquid carbon dioxide is expanded to produce carbon dioxide particles and carbon dioxide gas and mixed upstream of the heat exchanger to the cooling mixture.

A similar item is from the EP 0 948 727 A1 known. There, too, a mixture of solid carbon dioxide particles and a brine liquid is used as the cooling medium. Again, during the heat exchange with a medium in a heat exchanger evaporating carbon dioxide is separated from the cooling mixture, liquefied and then relaxed. While used in the relaxation of carbon dioxide particles together with the cooling mixture for cooling the medium, the resulting during the expansion of carbon dioxide gas is separated before being fed to the heat exchanger from the cooling mixture.

Another object in which a mixture of carbon dioxide and a transport liquid (methanol or ethanol) is used as a cold medium, is in the JP 2003 014333 A described.

A disadvantage of the objects described above, however, is the risk that the carbon dioxide particles in the suspension coagulate and thereby blocks the cooling system completely or partially. As before occurring inhomogeneities of the suspension also lead to irregular cooling performance and thus to difficulties in the control of the system.

The object of the present invention is therefore to provide a cooling method and a cooling device which is or is particularly suitable for the generation of temperatures in the range between -56 ° C and -79 ° C and at the or the risk of disturbance due coagulation of solid carbon dioxide particles is minimized.

This object is achieved by a method for cooling a medium, in which a liquid carrier medium is mixed with liquid carbon dioxide under a pressure at which the mixture is in the liquid state, then the mixture of carrier medium and liquid carbon dioxide is expanded while being cooled to a pressure in which at least a portion of the carbon dioxide evaporates, then the expanded mixture is fed to a separator in which vaporized carbon dioxide is separated from the carrier medium, the separated carrier medium is again pressurized and recirculated for mixing with liquid carbon dioxide, the mixture after the relaxation and / or the carrier medium from the separator passes through a heat exchanger in which it is brought into thermal contact with a medium to be cooled and the pressurized carrier medium before it is fed to the liquid carbon dioxide to a temperature above the melt point of carbon dioxide is brought at each pressure.

In contrast to the mentioned methods according to the prior art, the mixing of the carrier medium with the carbon dioxide takes place according to the invention at a pressure at which the forming mixture is present in the liquid state. The two liquids mix thoroughly. Only then is the mixture expanded, with part of the carbon dioxide in gaseous form, while the remaining part of the carbon dioxide forms a suspension with the carrier medium or can go completely or partially into solution. The forming suspension or solution is characterized by a high degree of homogeneity, whereby a risk of transport problems due to dry ice coagulation hardly exists. Unlike the prior art, the support medium in the process according to the invention - as well as the carbon dioxide - two different pressure levels, it is crucial that the mixture of carrier medium and carbon dioxide at and immediately after mixing has a pressure at which it is a mixture of Liquids and not for example as a suspension. As a rule, this pressure value should have a value above the triple point of carbon dioxide (5.18 bar), it may differ depending on the solubility of carbon dioxide and carrier medium into each other. The mixture present at this high pressure, and thus the carrier medium contained therein, is relaxed to a value which is between 0 and a value at which part of the carbon dioxide present in the mixture evaporates. In the event that no or only a negligible solution of carbon dioxide in the carrier medium takes place, this lower pressure value is a maximum of 5.18 bar. Due to the relaxation is a strong cooling, for example, to a temperature of up to minus 79 ° C with relaxation to 1 bar, with relaxation to a lower pressure value than 1 bar even lower, to, for example, minus 85 ° C. From its relaxation, the mixture is thus available as a refrigerant for the heat exchange with a medium or with several media, the heat exchange can take place downstream of the place of relaxation and / or downstream of the separation of the gaseous carbon dioxide. Likewise, the cold of the separated gaseous carbon dioxide can be used for heat exchange with a medium. The heat exchange can take place indirectly or directly, whereby in the latter case care should be taken that the medium to be cooled can be completely separated again from the mixture or the carbon dioxide after thorough mixing.

Preferably, the mass flow of the liquid carbon dioxide and / or the mass flow of the pressurized carrier medium is / are regulated in dependence on a predetermined or measured cooling capacity or the temperature of a medium to be cooled.

The invention provides that the pressurized carrier medium is brought to a temperature above the melting point of carbon dioxide at the respective pressure before it is fed to the liquid carbon dioxide. This ensures that the liquid carbon dioxide does not freeze out during its mixing with the liquid carrier medium. The temperature increase of the carrier medium can be done for example by a correspondingly controlled heater, and / or the carrier medium is brought by heat exchange with a medium to be cooled to the appropriate temperature.

A further expedient development of the invention provides that a carrier medium is used, in which the carbon dioxide is at least partially soluble. The at least partial dissolution of the carbon dioxide in the carrier medium or the carrier medium in the carbon dioxide not only improves the fluidity of the suspension, but also determines the thermodynamic properties of the mixture, thus providing a further degree of freedom for adapting the method of the invention to the respective cooling task , In particular, in this way, by choosing a suitable carbon dioxide-releasing carrier medium, the temperature in the preparation of the mixture and the temperature can be influenced after its relaxation.

Ethanol is used as a particularly advantageous, inexpensive and environmentally friendly carrier medium. However, in the context of the invention, in principle all carrier media can be used which, at the mentioned temperature and pressure ratios in the liquid state, for example other alcohols or terpenes.

An advantageous development of the invention provides that the separated evaporated carbon dioxide is pressure-liquefied and recycled in the circuit for mixing with the carrier medium. In this case, therefore, both the carrier medium and the carbon dioxide is recycled, whereby a particularly efficient process management is made possible.

In order to further increase the efficiency of the method according to the invention, a further advantageous embodiment provides that the gaseous carbon dioxide separated off in the separator is likewise used in a heat exchanger for cooling a medium. The medium to be cooled can be the same medium or the same media which is also cooled by the carrier medium or the mixture, or else by another medium. The cold content of the gaseous carbon dioxide can also be used, in particular, to pre-cool the liquid carbon dioxide intended for mixing with the carrier medium.

• eine Mischeinrichtung, in die eine Zuleitung für flüssiges Kohlendioxid und eine Zuleitung für unter Druck stehendes flüssiges Trägermedium einmündet, und die in eine Ausleitung für ein Gemisch aus flüssigem Kohlendioxid und Trägermedium ausmündet,
• ein stromab zur Mischeinrichtung in der Ausleitung für das Gemisch angeordneten Entspannungsorgan zum Entspannen des Gemisches,
• ein Separator zum Abtrennen von bei der Entspannung verdampftem Kohlendioxid vom flüssigen Trägermedium, in den die Ausleitung für das Gemisch ausmündet und der eine Ausleitung für das flüssige Trägermedium und eine Ausleitung für verdampftes Kohlendioxid aufweist, wobei die Ausleitung für das flüssige Trägermedium mit einer Einrichtung zur Druckerhöhung ausgerüstet und mit der Zuleitung für das Trägermedium an die Mischeinrichtung strömungsverbunden ist,
• wenigstens ein mit einer Zuleitung und einer Ableitung für ein zu kühlendes Medium ausgerüsteter Wärmetauscher, der/die in der Ausleitung für das flüssige Trägermedium, stromab zum Separator angeordnet ist/sind.

The object of the invention is also achieved with a device for cooling a medium, which has the following features:

• a mixing device into which a supply of liquid carbon dioxide and a supply line for pressurized liquid carrier medium opens, and which opens into a discharge for a mixture of liquid carbon dioxide and carrier medium,
• a relaxation device arranged downstream of the mixing device in the outlet for the mixture for releasing the mixture,
• a separator for separating carbon dioxide vaporized during the expansion from the liquid carrier medium into which the discharge for the mixture discharges and which has a discharge for the liquid carrier medium and a vaporized carbon dioxide discharge, the discharge for the liquid carrier medium being provided with a device for Equipped pressure increase and is flow-connected to the supply line for the carrier medium to the mixing device,
• at least one equipped with a supply line and a discharge for a medium to be cooled heat exchanger / which is arranged in the outlet for the liquid carrier medium, downstream of the separator / are.

In the device according to the invention thus takes place at a pressure-resistant mixing device, such as a pressure vessel or a pressure-resistant fitting in which substantially the pressure of the supply lines is maintained, merging liquid carbon dioxide and carrier medium at a pressure at which the forming mixture as pure Liquid mixture is present. When merging at the mixing device or in an optionally adjoining the mixing device mixing section / takes place an intimate mixing of the two liquids. If a suitable carrier medium is selected, partial or complete dissolution of the carbon dioxide in the carrier medium can also take place. As a result of the expansion of the mixture or of the solution on the expansion element, the carrier medium cools down and is then available as a heat exchange medium for cooling another medium. For this purpose, the expansion element can also be arranged directly on or in a heat exchanger, which serves to cool a medium; the expansion device can also be arranged directly at the mouth of the discharge for the mixture in the separator. In the separator, the gaseous carbon dioxide formed during the expansion at least largely separates from the carrier medium and is withdrawn via the outlet for the gaseous carbon dioxide, while the carrier medium accumulates in a lower region of the separator. The separator acts in this way at the same time as a storage container for the carrier medium, which is withdrawn from there and fed after pressure increase again the liquid carbon dioxide for mixing with this.

Preferably, in the discharge for the vaporized carbon dioxide, a compressor and a cooler are provided to liquefy the carbon dioxide. The diversion for the gaseous carbon dioxide is also fluidly connected to the opening into the mixing device inlet for liquid carbon dioxide. This makes it possible to completely or partially recycle the carbon dioxide. Compressor and cooler can be provided in a common arrangement or be present as separate facilities. The cooling required for re-liquefaction of the carbon dioxide can also be at least partially accomplished in that the carbon dioxide gas removed from the separator is used to pre-cool the carbon dioxide to be supplied to the mixing device and thereby cools down.

Advantageously, located in the outlet for the vaporized carbon dioxide, a heat exchanger, by means of which a medium can be cooled. In this way, the cooling power contained in the gaseous carbon dioxide is also utilized profitably.

A yet further advantageous embodiment of the device according to the invention is characterized by a control device which controls the flow rate of the liquid carbon dioxide and / or the flow rate of the liquid carrier medium as a function of the cooling capacity of the heat exchanger and / or the temperature of a medium to be cooled.

A preferred use of the method and the device according to the invention consists in the cooling of one or more media in the temperature range between minus 56 ° C and minus 85 ° C, the temperature range between minus 79 ° C and minus 85 ° C and below, in particular by relaxation of the mixture to a pressure value of less than 1 bar. can be.

• Fig. 1: Eine erfindungsgemäße Vorrichtung zum Kühlen eines Mediums in einer ersten Ausführungsform und
• Fig. 2: Eine erfindungsgemäße Vorrichtung zum Kühlen eines Mediums in einer zweiten Ausführungsform.

Reference to the drawings, an exemplary embodiments of the invention will be explained in more detail below. In a schematic view show:

• Fig. 1 A device according to the invention for cooling a medium in a first embodiment and
• Fig. 2 A device according to the invention for cooling a medium in a second embodiment.

Fig. 1 shows an inventive device 1 for cooling a medium with the aid of a mixture of carbon dioxide and a carrier medium. The carrier medium is a substance which is in the liquid state in the entire temperature and pressure range in which the cooling process described below takes place, ie, for example, in the temperature range between minus 56 ° C. and minus 79 ° C. and at pressures between 1 bar and a pressure above the triple point pressure of carbon dioxide (5.18 bar), z. B. 20 bar. For example, the carrier medium is ethanol. The apparatus 1 comprises a mixing device 2, for example a mixing nozzle, at which liquid carbon dioxide, which is introduced via a carbon dioxide line 3, is mixed with the carrier medium, which is introduced under pressure via a feed line 4. The mixing device 2 opens into a discharge 6, in which after a mixing section 7 an expansion valve 8 is arranged. Downstream to the expansion valve 8, the outlet 6 passes through a heat exchanger 9, in which the mixture guided in the outlet 6 enters into indirect heat exchange with a medium to be cooled, which is introduced in a liquid or gaseous medium flow (indicated by arrows). The outlet 6 opens into a separator 10 a. The separator 10 is essentially a vessel equipped with thermally insulated walls, in whose geodesically lower section a liquid phase 12 consisting predominantly of carrier medium is present and in the upper area of which a gas phase 11 consisting predominantly of gaseous carbon dioxide is present. The liquid phase 12 is fluidly connected to a discharge 14, in which a device 15 is arranged to increase the pressure, which is driven in the embodiment with a motor 16. Downstream to the device 15, the outlet 14 passes through a second heat exchanger 17, in which the guided through the discharge 14 carrier medium is brought in the embodiment shown here in heat exchange with the same medium as the guided through the outlet 6 mixture in the heat exchanger 9. The discharge 14th finally leads into the supply line 4 or goes into this. In the Drawing not shown, but nevertheless present, is a, for example, in the separator 10 opening filling line, can be drained from the circuit via the carrier medium or supplied to this. The separator 10 further comprises a gas discharge 19, which is fluidly connected to the gas phase in the separator 10. The gas discharge 19 passes through a heat exchanger 20 in which the gaseous carbon dioxide guided through the gas discharge enters into indirect heat exchange with the carbon dioxide introduced through the carbon dioxide line 3.

In use of the device 1, a mixture of liquid carbon dioxide and carrier medium is generated in the mixing device 2, which intimately mixes in the subsequent mixing section 7 as a mixture of liquids. Depending on the choice of the carrier medium, partial or complete dissolution of the carbon dioxide in the carrier medium or of the carrier medium in the carbon dioxide may also occur. The mixture has in the mixing section 7, for example, a pressure of 10 to 20 bar and a temperature of minus 56 ° C. At the expansion nozzle 8, the mixture is expanded under strong cooling and fed to the heat exchanger 9, wherein the carbon dioxide partially passes into gaseous form. In the heat exchanger 9, a heat exchange with the medium to be cooled takes place, wherein the guided through the outlet 6, relaxed mixture heat is supplied. The mixture then passes into the separator 10, in which a separation takes place into gaseous carbon dioxide and carrier medium, carbon dioxide possibly being dissolved in the carrier medium or being present as a suspension. In the separator 10, the carrier medium has a temperature of, for example, minus 78 ° C. and a pressure of, for example, 1 bar. The carrier medium is then brought by means of the device 15 to the outlet pressure, ie the pressure of the carrier medium at the mixing device 2 (for example 10 to 20 bar) and returned to the mixing device 2. In this case, before reaching the mixing device 2, the carrier medium passes through the heat exchanger 17, in which it is heated by heat exchange with the medium to be cooled and preferably brought to a temperature above the solidification temperature of liquid carbon dioxide at the mixing device at the mixing of both liquids Pressure is.

According to the invention, the carrier medium is thus recycled, wherein it passes through two pressure stages in succession. Due to the mixing of carrier medium and carbon dioxide taking place at the mixing device 2 or in the mixing section 7 as two substances present in liquid form at a pressure preferably above the triple point of carbon dioxide, a particularly thorough mixing takes place, whereby a suspension forming during the expansion becomes a very has high homogeneity. The risk of clogging of the lines by coagulating Trockeneisteilchen is therefore low.

The gaseous carbon dioxide separated from the carrier medium in the separator 10 is in the gas phase 11 at the same temperature and pressure as the carrier medium in the liquid phase 12 (for example, minus 78 ° C and 1 bar). The gaseous carbon dioxide is discharged via the gas outlet 19 and supplied, for example, to another utilization or released into the atmosphere. The coldness of the gaseous carbon dioxide is used in the heat exchanger 20 to pre-cool the liquid carbon dioxide in the carbon dioxide line 3, but - not shown here - can alternatively or additionally be used to cool another medium.

To control the cooling capacity in the heat exchangers 9, 17 and / or the temperature to which the medium is cooled, serves in the embodiment according to Fig. 1 a regulation of the carrier medium flow. The temperature of the mixture downstream of the heat exchanger 9 is measured by a sensor 21 and used as a control variable for the control of the power of the motor 16. At the same flow rate of the supplied liquid carbon dioxide, the cooling capacity is regulated in this way via the flow rate of the carrier medium.

In the Fig. 2 shown device 1 'differs from the device 1 Fig. 1 only by the type of regulation, which is why the same or identically acting components in both devices are indicated by the same reference numerals. In contrast to the embodiment according to Fig. 1 In this variant, the regulation of the cooling capacity of the heat exchangers 9, 17 takes place via a variation of the mass flow of the supplied liquid carbon dioxide. The power of the motor 16 and thus the flow rate of the carrier medium remains constant during an operating phase of the device 1 '. The sensor 21 is operatively connected to a quantity control valve 22 in the carbon dioxide line 3, which regulates the mass flow of the supplied carbon dioxide in dependence on the values measured at the sensor 21, wherein, of course, care must be taken that no such strong pressure reduction takes place at the volume control valve 22 that already 3 dry ice particles are formed immediately behind the flow control valve 22 in the supply line.

In a variant of a device according to the invention which is not shown here, the gas discharge line 19 is flow-connected to the carbon dioxide feed line 3 via a compressor and, if appropriate, a cooling device, thus allowing a circulation of the carbon dioxide. Within the scope of the invention, it is also conceivable to dispense with one of the heat exchangers 9, 17 and to allow the cooling of the medium to take place only via the respectively remaining heat exchanger. If the heat exchanger 9 is omitted, the expansion nozzle 8 can also be arranged directly at the junction of the outlet 6 in the separator. In the context of the invention, it is possible to accommodate the two heat exchangers 9, 17 in a common housing or in different housings. Likewise, the heat exchangers 9, 17 can be used for cooling different media. Furthermore, it is possible to lower the pressure in the separator 10 and in the outlet 6, downstream of the expansion valve 8, to values below 1 bar by, for example, arranging a corresponding pressure reduction device in the gas outlet 19, likewise not shown here. In this case, depending on the pressure on the relaxed, also temperatures below -79 ° C can be achieved.

The device according to the invention and the method according to the invention are particularly suitable for cooling tasks in the temperature range between minus 56 ° C. and minus 79 ° C. and below, in particular for applications in the field of the food processing industry, pharmacy or the chemical industry; the invention is of course not limited thereto.

LIST OF REFERENCE NUMBERS

1,1 '

contraption

2

mixing device

3

carbon dioxide line

4

Supply line (for carrier medium)

5

-

6

Recovery

7

mixing section

8th

expansion valve

9

heat exchangers

10

separator

11

gas phase

12

liquid phase

13

-

14

Recovery

15

Device for increasing the pressure

16

engine

17

heat exchangers

18

-

19

gas discharge

20

heat exchangers

21

sensor

22

Flow Control Valve

Claims (12)

1. Method for cooling a medium, in which a liquid carrier medium is mixed with liquid carbon dioxide at a pressure at which the mixture is in the liquid state, and the mixture of carrier medium and liquid carbon dioxide is then expanded, under cooling, to a pressure at which at least part of the carbon dioxide evaporates, and then the expanded mixture is conveyed to a separator (10) in which evaporated carbon dioxide is separated from the carrier medium, the separated carrier medium is again pressurized and fed back, in the circuit, to be mixed with liquid carbon dioxide, wherein the mixture after expansion and/or the carrier medium from the separator (10) pass(es) through a heat exchanger (9, 17) in which it is brought into thermal contact with a medium which is to be cooled,
   characterized in that the pressurized carrier medium, prior to being supplied to the liquid carbon dioxide, is brought to a temperature above the melting point of carbon dioxide at the respective pressure.
2. Method according to Claim 1, characterized in that the mass flow rate of liquid carbon dioxide and/or the mass flow rate of the pressurized carrier medium are/is controlled in dependence on a predefined or measured cooling power.
3. Method according to either of the preceding claims,
   characterized in that use is made of a carrier medium in which the carbon dioxide is at least partially soluble.
4. Method according to one of the preceding claims,
   characterized in that ethanol is used as carrier medium.
5. Method according to one of the preceding claims,
   characterized in that the separated and evaporated carbon dioxide is pressure-liquefied and is fed back, in the circuit, to be mixed with the carrier medium.
6. Method according to one of the preceding claims,
   characterized in that the separated and evaporated carbon dioxide is used in a heat exchanger (20) to cool a medium.
7. Device for cooling a medium,

   - having a mixing device (2) into which opens an inlet (3) for liquid carbon dioxide and an inlet (4) for pressurized liquid carrier medium, and which discharges into an outlet (6) for a mixture of liquid carbon dioxide and carrier medium,

   - having a separator (10) for separating, from the liquid carrier medium, carbon dioxide evaporated during expansion, into which separator the outlet (6) for the mixture discharges, the separator being equipped with an outlet (14) for the liquid carrier medium and with an outlet (19) for evaporated carbon dioxide, wherein the outlet (14) for the liquid carrier medium is equipped with a pressure-increasing device (15) and is fluidically connected to the inlet (4) for the carrier medium to the mixing device (2),

   characterized by

   - an expansion member (8), arranged downstream of the mixing device (2) in the outlet (6) for the mixture, for expanding the mixture,

   - at least one heat exchanger (17) which is equipped with an inlet and an outlet for a medium which is to be cooled, and/or a heating device, which are/is arranged in the outlet (14) for the liquid carrier medium, downstream of the separator (10).
8. Device according to Claim 7, characterized by at least one heat exchanger (9) which is equipped with an inlet and an outlet for a medium that is to be cooled, and which is arranged in the outlet (6) for the mixture, downstream of the expansion member (8).
9. Device according to Claim 7 or 8, characterized in that a compressor and a cooler are provided in the outlet (19) for the evaporated carbon dioxide, and the outlet (19) is fluidically connected to the inlet (3), discharging into the mixing device, for liquid carbon,dioxide.
10. Device according to one of Claims 7 to 9,
    characterized in that a heat exchanger (20) for cooling a medium is provided in the outlet (19) for the evaporated carbon dioxide.
11. Device according to one of Claims 7 to 10,
    characterized by a control device (21, 22) for controlling the mass flow rate of the liquid carbon dioxide and/or the mass flow rate of the liquid carrier medium in dependence on the cooling power of the heat exchanger(s) (9, 17) and/or the temperature of a medium that is to be cooled.
12. Use of a method according to one of Claims 1 to 6 and of a device according to one of Claims 7 to 11 for cooling one or more media in the temperature range between -85°C and -56°C.

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