DEVICE AND METHOD FOR PRODUCEING A TEMPERATE, COLD GAS STREAM

Description

[0001] The invention relates to a device for generating a temperature-controlled, cold gas stream, comprising a storage tank for storing cryogenically liquefied gas and a withdrawal line connected to the storage tank for withdrawing liquefied gas from the storage tank, and an evaporator unit integrated in the withdrawal line, which is equipped with a heat exchanger surface for indirect thermal contact of the liquefied gas with a heat transfer fluid. The invention further relates to a corresponding method. Document US 3,091,096 A discloses a device for generating a temperature-controlled, cold gas stream.

[0002] Cryogenic media such as nitrogen, oxygen, or carbon dioxide are often stored in liquid form in thermally insulated tanks. Since consumers typically require the stored medium in gaseous form, after liquid withdrawal, the stored medium is converted into the gas phase. This is usually done using air-heated evaporators (hereinafter also referred to as "air evaporators"). However, air-heated evaporators have the disadvantage that ice can form, particularly under unfavorable weather conditions and / or heavy loads, which can significantly impair the evaporator's functionality.

[0003] Instead of air-heated evaporators, heat exchangers can also be used in which the liquid medium comes into indirect thermal contact with a heat transfer fluid and evaporates, while the heat transfer fluid cools down. Such heat exchangers are designed, for example, as tubular heat exchangers or as cooling coils.

[0004] In heat exchangers, a process fluid can be used as the heat transfer fluid. This fluid is generated as a warm medium during an industrial process and must be cooled to a lower operating temperature before further use. The present invention relates to such heat transfer fluids. For example, this could be a hot product stream or a cooling medium, particularly cooling water, which is circulated in a cooling circuit using a refrigeration system. The refrigeration system is thus at least partially relieved of the load by the evaporation of the cryogenic medium. The use of such heat transfer fluids for evaporating cryogenic media has proven effective. It saves the user at least some of the separate cooling of the heat transfer fluid to its operating temperature and / or the aforementioned problems associated with using an air-heated evaporator.

[0005] A problem with using heat transfer fluid-controlled heat exchangers is that the heat transfer fluid often does not have a constant heat content, or the flow rate of the heat transfer fluid is irregular. Consequently, the temperature of the evaporated cryogenic medium also fluctuates in a way that is difficult to control. However, there are applications where the use of a cold gas stream with a stable temperature is required. For example, in the carbonation of beverages, the degree of carbonation—that is, the amount of carbon dioxide that can dissolve in the beverage or in the water used to produce the beverage—depends sensitively on the temperature of the supplied carbon dioxide gas. The carbon dioxide used for this purpose is usually stored in a cold, liquefied state in low-pressure or medium-pressure tanks and evaporated before being added to the beverage or water.In such cases, the use of a heat transfer fluid with a highly fluctuating heat content for the evaporation of carbon dioxide has been avoided until now. Furthermore, a complex additional system for temperature control of the carbon dioxide gas is required.

[0006] The invention is therefore based on the objective of providing a way to supply a cold, precisely temperature-controlled gas stream from the evaporation of a cryogenically liquefied gas, in which evaporation-related temperature fluctuations are compensated.

[0007] This problem is solved by a device having the features of claim 1 and by a method having the features of claim 5.

[0008] A device according to the invention of the type and purpose mentioned above is therefore characterized in that a liquid line branches off from the extraction line, downstream to the storage tank and upstream to the evaporator unit, which opens into the extraction line downstream to the evaporator unit at an injection device, wherein the injection device is equipped with a measuring device for detecting the temperature in the extraction line downstream to the evaporator unit and with a control valve operatively connected to the measuring device for controlling the injection of liquefied gas into the extraction line.

[0009] The temperature measurement at the measuring device can be performed upstream or downstream of the injection device. Particularly when a fluid with an irregular and / or difficult-to-predict heat input is used as the heat transfer fluid in the evaporator unit, the device according to the invention enables the provision of a cold gas stream with high temperature stability.

[0010] The heat transfer fluid is, for example, a cooling medium from a cooling circuit, such as cooling water. In this circuit, the heat transfer fluid flows from a process cooler to a cooling unit, which preferably includes a refrigeration unit in addition to the evaporator unit of the device according to the invention. In the refrigeration unit, some of the heat transferred from the process cooler to the heat transfer fluid is dissipated. The evaporator unit thus relieves the refrigeration unit or can even replace it, for example, in the event of a temporary refrigeration unit failure or if the heat input from the cooling medium does not result in an undesirably high temperature increase of the gas beyond that required for the evaporation of the liquefied gas.

[0011] To achieve rapid mixing after the introduction of the liquefied gas into the vaporized gas, it is particularly advantageous for the injection device to include an end section of the liquid line, equipped with a spray nozzle or a sintered body, which projects into the interior of the extraction line. The liquefied gas flows from the liquid line into the spray nozzle or sintered body and is finely dispersed and sprayed into the gas flowing through the extraction line. There, it spreads throughout the gas stream and rapidly vaporizes. A fine-pored sintered body, made of metal or ceramic and mounted on the end section of the liquid line, is particularly suitable for this fine dispersal. The liquefied gas is introduced into the surrounding gas stream through the openings of this sintered body.

[0012] To further improve the efficiency of the injection process, the end section of the liquid line is preferably oriented within the extraction line such that the liquefied gas flows counter-currently to the vaporized gas in the extraction line. The end section of the liquid line is therefore, for example, arranged concentrically inside the extraction line, with its outlet opening, where the spray nozzle or sintered body is located, facing the gas flow in the extraction line.

[0013] A particularly preferred embodiment of the invention provides that the evaporator unit comprises a heat exchanger for thermally contacting the liquefied gas with the heat transfer fluid, an air evaporator arranged parallel to the heat exchanger, and a switching arrangement for the controlled activation and deactivation of the heat exchanger and / or air evaporator. The air evaporator is used particularly when the heat input via the heat transfer fluid is insufficient to completely evaporate the liquefied gas passing through the evaporator unit.This can be ensured, for example, by a suitable control loop that measures the temperature of the vaporized gas in the supply line downstream of the vaporizer unit (but upstream of the liquefied gas feed unit) and, if a predetermined temperature value is undershot, activates the air vaporizer so that at least a portion of the liquefied gas flows through the air vaporizer. The temperature of the vaporized gas, which should not be undershot, is higher than the temperature that the vaporized gas should have in a consumer connected to the supply line (hereinafter referred to as the "target temperature"), so that the target temperature can be precisely set by the subsequent supply of the liquefied gas at the feed unit.

[0014] Preferably, the cryogenically liquefied gas stored in the storage tank is a liquefied atmospheric gas, such as liquid nitrogen, liquid oxygen or liquid argon, or liquid carbon dioxide.

[0015] A method for generating a tempered, cold gas stream, in which cryogenically liquefied gas is taken from a storage tank, evaporated in an evaporator unit by indirect heat exchange with a heat transfer fluid to form a stream of evaporated gas, and the stream of evaporated gas is supplied to a consumer, is characterized according to the invention in that liquefied gas from the storage tank is supplied to the stream of evaporated gas at an inlet device downstream of the evaporator unit, wherein the amount of liquefied gas supplied is controlled as a function of the temperature of the evaporated gas.

[0016] The amount of liquefied gas supplied to the injection device is expediently regulated depending on the target temperature at which the gas should be present at the consumer.

[0017] In the method according to the invention, the gas already vaporized in the evaporator unit is tempered by a temperature-controlled supply of liquefied gas from the storage tank and supplied to a consumer, for example a beverage carbonation system, at a precisely defined temperature. In this way, precise temperature control of the vaporized gas supplied to the consumer is possible, particularly when there is an irregular or difficult-to-predict heat input from the heat transfer fluid to the vaporized gas in the evaporator unit.

[0018] The preferred use of the device or method according to the invention lies in the generation of a tempered, cold gas stream in a process within the food industry, particularly for use in a device for carbonating beverages and / or for inerting products, packaging, or containers. This device or devices are connected downstream of the device according to the invention as consumers and are connected to the extraction line, downstream of the feed device for the liquefied gas. Nitrogen or carbon dioxide is preferably used as the gas stream to be tempered.

[0019] The drawings will be used to explain an embodiment of the invention in more detail. The schematic views show: Fig. 1 : The circuit diagram of a device according to the invention, Fig. 2 : A liquefied gas injection system of the device according to the invention made of Fig. 1in longitudinal section

[0020] The in Fig. 1 The device shown 1 serves to generate a temperature-controlled cold gas stream, as is used particularly in the food industry, for example in the carbonation of beverages or the inerting of food products. In a beverage carbonation system, the vaporized carbon dioxide is added to a beverage and at least partially dissolved in it. The desired or achievable degree of carbonation depends, among other things, on the temperature of the supplied gas and therefore requires uniform temperature control of the supplied gas stream during production.

[0021] The device 1 comprises a thermally well-insulated storage tank 2 for a cryogenically liquefied gas, for example, liquid nitrogen or liquid carbon dioxide. Liquefied gas is drawn from the storage tank 2 via a withdrawal line 3 and fed to a vaporization unit 4.

[0022] The evaporator unit 4 comprises a heat exchanger 5 in which the liquefied gas comes into indirect thermal contact with a heat transfer fluid and thereby evaporates. The heat transfer fluid is preferably cooling water or another medium that must be cooled anyway during an industrial process and whose excess heat can advantageously be used to evaporate the liquefied gas. In the embodiment shown here, the heat transfer fluid is a cooling medium that is circulated in a cooling circuit 6. The cooling medium passes successively through a process cooler 7, a chiller 8, and the heat exchanger 5.In the embodiment shown here, the heat exchanger 5 therefore serves primarily to support the chiller 8, which otherwise takes over the majority of the cooling of the heat transfer fluid heated in the process cooler 7; however, within the scope of the invention it is not excluded that the heat exchanger regularly or in the event of a failure of the chiller 6 completely takes over its role in the cooling circuit 6.

[0023] In the heat exchanger 5, the heat transfer fluid of the cooling circuit 6 comes into indirect thermal contact with the liquefied gas from the storage tank 2, which is supplied via the upstream part of the extraction line 3 to the heat exchanger 5, at a heat exchanger surface 9. The liquefied gas then evaporates and flows as vaporized gas through the downstream part of the extraction line 3 to the heat exchanger 5.

[0024] In the event that the heat input from the heat transfer fluid into the liquefied gas in the heat exchanger 5 is insufficient to completely vaporize the liquefied gas, the evaporator unit 4 in the embodiment shown here includes an air evaporator 10 arranged parallel to the heat exchanger 5. A control valve 11 regulates the flow of the liquefied gas into the heat exchanger 5 and / or the air evaporator 10 depending on a parameter measured at a sensor 12 in a section of the supply line 3 downstream of the heat exchanger 5, and which is in particular the temperature or consistency of the gas in this section of the supply line 3. If, for example, the temperature of the gas at the sensor 12 falls below a predetermined value, the flow of the liquefied gas is directed wholly or partially through the air evaporator 10 to ensure complete vaporization of the gas.

[0025] A liquid line 13 branches off from the extraction line 3, running downstream to the storage tank 2 but upstream to the evaporator unit 4. This liquid line 13 rejoins the extraction line 3 downstream of the evaporator unit 4 at an injection device 15, which is described in more detail below. The liquid line 13 is equipped with a control valve 16. Depending on a parameter measured at a measuring device 17 downstream of the injection device 15 in the extraction line 3, in particular the temperature of the evaporated gas, the valve regulates the flow of liquefied gas into the evaporated gas flowing through the extraction line 3. The measuring device 17 can also be located upstream of the injection device 15 in the extraction line, but downstream of the evaporator unit 4.

[0026] During operation of the device 1, liquefied gas is drawn from the storage tank 2, vaporized in the vaporizer unit 4, and supplied to its intended use in a consumer 14 connected downstream of the intake line to the feed device 15. For example, the consumer 14 is a device for carbonating beverages. In this case, it is necessary that the gas reaches the consumer 14 at a precisely defined temperature (target temperature).

[0027] The amount of heat transferred to the vaporized gas via the heat exchanger 5 and / or the air evaporator 10 is not always sufficiently constant and can fluctuate over time. The amount of heat transferred via the air evaporator 10 depends particularly on atmospheric factors such as ambient temperature, ambient pressure, and humidity, which make precise temperature control of the vaporized gas in the discharge line difficult or even impossible. Therefore, the temperature of the vaporized gas in the discharge line 3, upstream of the feed device 15, depends on either the ambient temperature or the temperature of the cooling medium, depending on whether the gas flow at the control valve 11 is routed through the air evaporator 10 or the heat exchanger 5. However, it should always be above the target temperature of the gas.To compensate for temperature fluctuations, liquefied gas is introduced directly into the vaporized gas in the extraction line 3 at the inlet device 15, preferably cooling it to the target temperature. This is achieved with high precision by the temperature control of the control valve 16; the device 1 thus enables very accurate temperature control of the vaporized gas in the extraction line 3 before it is supplied to the consumer 14. At the same time, further, separate heating or cooling of the vaporized gas before supplying it to the consumer 14 is unnecessary.

[0028] In Fig. 2A particularly advantageous injection system 15 of the device 1 according to the invention is shown. The injection system 15 is arranged in the extraction line 3, downstream of the evaporator unit 4. It comprises an L-shaped bent end section 18 of the liquid line 13, one leg of which is arranged inside, preferably concentrically, the extraction line 3 and has an outlet opening 20 directed against the flow direction of the evaporated gas in the extraction line 3, as indicated by arrow 19. A spreading element, for example a spray nozzle or a sintered body 21 made of metal or ceramic, is mounted at the outlet opening 20, which leads to a very fine distribution of the liquefied gas in the stream of evaporated gas.Due to the fine distribution of the liquefied gas in the stream of the vaporized gas, a thorough mixing occurs and the liquefied gas evaporates rapidly, so that a gas with a largely homogeneous temperature is already present at the measuring device 17. Reference symbol list :

[0029] 1 Device 2 Tank 3 Extraction line 4 Evaporator unit 5 Heat exchanger 6 Cooling circuit 7 Process cooler 8 Refrigeration unit 9 Heat exchanger surface 10 Air evaporator 11 Control valve 12 Sensor 13 Liquid line 14 Consumer 15 Feed device 16 Control valve 17 Measuring device 18 End section (of liquid line 13) 19 Arrow 20 Outlet 21 Sintered body

Claims

1. Apparatus for generating a temperature-controlled, cold gas stream, comprising a storage tank (2) for storing cryogenically liquefied gas and a withdrawal line (3), connected to the storage tank (2), for withdrawing liquefied gas from the storage tank (2) and comprising an evaporator unit (4) integrated in the withdrawal line (3), wherein branching off of the withdrawal line (3), downstream of the storage tank (2) and upstream of the evaporator unit (4), is a liquid feed line (13) which leads into the withdrawal line (3) downstream of the evaporator unit (4) at an introduction device (15), wherein the introduction device (15) is equipped with a measuring device (17) for recording the temperature in the withdrawal line (3) downstream of the evaporator unit (4) and with a control valve (16), operatively connected to the measuring device (17), for controlling the introduction of liquefied gas into the withdrawal line (3), characterized in that the evaporator unit (4) comprises a heat exchanger (5) with a heat-exchanger surface (9) for causing the liquefied gas to come into indirect thermal contact with a heat transfer fluid, an air evaporator (10) arranged parallel to the heat exchanger (5), and a switching arrangement (11, 12) for the controlled switching on and off of the heat exchanger (5) and / or air evaporator (10).

2. Apparatus according to Claim 1, characterized in that the introduction device (15) comprises an end portion (18) of the liquid feed line (13), this end portion being equipped with a spray nozzle or a sintering body (21) and protruding into the inside of the withdrawal line (3).

3. Apparatus according to Claim 2, characterized in that the end portion (18) of the liquid feed line (13) is oriented inside the withdrawal line (3) such that the liquefied gas inside it flows in in a counterflow arrangement with respect to the evaporated gas in the withdrawal line (3) surrounding the end portion (18).

4. Apparatus according to one of the preceding claims, characterized in that the cryogenically liquefied gas used in the storage tank (2) is an atmospheric gas, such as nitrogen, oxygen or argon, or carbon dioxide.

5. Method for generating a temperature-controlled, cold gas stream in an apparatus according to Claims 1-4, in which cryogenic liquefied gas is withdrawn from a storage tank (2), evaporated in an evaporator unit (4) by indirect heat exchange with a heat transfer fluid to afford a stream of evaporated gas, and the stream of evaporated gas is fed to a consumer (14), characterized in that liquefied gas from the storage tank (2) is fed into the stream of the evaporated gas at an introduction device (15) downstream of the evaporator unit (4), wherein the amount of liquefied gas fed in is controlled on the basis of a temperature of the evaporated gas.

6. Method according to Claim 5, characterized in that the amount of liquefied gas fed in at the introduction device (15) is controlled on the basis of a determination temperature to be reached in the consumer (14).

7. Use of an apparatus according to Claims 1 to 4 or of a method according to Claim 5 or 6 to generate a temperature-controlled, cold gas stream in a process in the foodstuff industry.