DEVICE FOR DOSING CARBON DIOXIDE SNOW

Description

[0001] The invention relates to a device for dosing carbon dioxide snow, with a snow horn which comprises a relaxation chamber which is closed at the top and opens out at the bottom at an opening of the snow horn and a relaxation nozzle which opens out inside the relaxation chamber and is connected to a supply line for liquid carbon dioxide.

[0002] To ensure high product quality, it is often necessary to cool temperature-sensitive products, particularly food, pharmaceutical products, biological, or medical samples, very quickly to storage temperature after production. This challenge, particularly with small-volume products such as tissue samples or small, chunky food items, is to ensure adequate cooling while also not overcooling the product with an excessive amount of coolant. In other cases, it is necessary to harden the surface of a product by encrusting. By applying a cryogenic medium such as liquid nitrogen or carbon dioxide snow, the product surface is quickly frozen and thus solidified, making it possible to stabilize the shape or external dimensions of the product for further processing.

[0003] For this purpose, it is known to subject the surface of a product, in particular a food product, to a stream of carbon dioxide particles generated in a snow horn of the type mentioned above. A snow horn comprises an expansion nozzle that opens into a downwardly open, usually cylindrical or conically widening expansion chamber in the geodesic sense. Liquid carbon dioxide is supplied under pressure and expanded at the expansion nozzle. During expansion, a mixture of gaseous carbon dioxide and carbon dioxide snow is created, which falls under the effect of gravity onto a product arranged below the outlet opening of the expansion chamber. Such systems are described, for example, in US Pat. No. 4,652,287 A or DE 198 52 185 A1.However, they have the disadvantage that the gas evolution during the expansion of the liquid carbon dioxide creates a strong, turbulent gas flow that immediately blows away at least some of the carbon dioxide snow applied to the product surface. This significantly reduces the efficiency and reliability of the process. Various approaches have already been pursued to mitigate the problem of turbulent gas flow. For example, WO 2007 / 012636 A1 describes a snow horn whose lower section is made of a gas-permeable material through which the carbon dioxide gas, but not the snow, can escape. EP 2 363 377 A1 proposes hurling the snow-gas mixture produced against a conveyor screw arranged in the expansion chamber, where it separates.The gas is then discharged via an exhaust line, while the snow is transported to its destination by the conveyor screw. However, with these devices, there is a risk that the functionality of the device may be impaired by carbon dioxide snow sticking to parts of the device or by moisture penetrating the device, which can lead to the formation of water ice. Furthermore, they are only partially suitable for dosing small amounts of carbon dioxide snow. In the system described in EP 2 363 377 A1, the additional operation of a motor-driven conveyor screw reduces the overall efficiency of the system.

[0004] US Pat. No. 4,415,346 A and EP 1 076 798 A1 disclose arrangements for generating carbon dioxide snow. These arrangements comprise a snow horn arranged within an outer tube connected to an extraction device for removing the carbon dioxide gas. However, a disadvantage is that a significant portion of the resulting carbon dioxide snow is extracted along with the gas and lost for the cooling task. Further arrangements for generating carbon dioxide snow are known from EP 1 577 262 A1 and US Pat. No. 3 492 829 A.

[0005] The object of the invention is therefore to create a device for dosing carbon dioxide snow that can deliver a precise and consistent amount of carbon dioxide snow, is simple in construction and handling, and can be flexibly adapted to different requirements.

[0006] This object is achieved by a device having the features of patent claim 1. Advantageous embodiments of the invention are specified in the subclaims.

[0007] A device according to the invention of the type and purpose mentioned at the outset is thus characterized in that the snow horn is accommodated within a casing tube which is closed at the top and projects downwards relative to the mouth opening of the snow horn and has a mouth funnel which tapers towards an outlet opening on the underside of the casing tube.

[0008] A device according to the invention for dosing carbon dioxide snow thus comprises a vertically arranged snow horn, which has a—geodetically speaking—expansion chamber that is closed at the top and opens at the bottom into an opening of the snow horn. The expansion chamber can have a circular or angular, in particular rectangular, cross-section and can be cylindrical, bell-shaped, or conical in its longitudinal extension. An expansion nozzle connected to a supply line for liquid carbon dioxide is arranged inside the expansion chamber, preferably on the closed upper side of the expansion chamber.

[0009] Furthermore, the snow horn is arranged within a vertically arranged casing tube, which is also closed at its top and has a downwardly opening. The casing tube, which can have a round or square cross-section, protrudes longitudinally from the bottom of the snow horn's outlet opening, so that a vertical gap exists between the snow horn's outlet opening and the casing tube's outlet opening. In this area, the casing tube is also equipped with a conical outlet funnel that tapers towards the outlet opening.

[0010] The snow horn is mounted in the casing tube in such a way that there is a horizontal gap on all sides between the inner wall of the casing tube and the outer wall of the snow horn's expansion chamber, so that the snow horn is housed in a cavity that is fluidly connected to the snow horn's outlet. For example, the snow horn and casing tube have a circular cross-section, and the snow horn is mounted coaxially within the casing tube, with an annular gap at the level of the snow horn's outlet.

[0011] According to the invention, the jacket tube arranged around the snow horn fulfills three functions. Firstly, the hollow space (jacket space) between the inner wall of the jacket tube and the outer wall of the expansion chamber of the snow horn serves as a buffer volume, which temporarily absorbs at least a portion of the carbon dioxide gas produced during the expansion of liquid carbon dioxide at the expansion nozzle and thus reduces the gas flow emerging through the outlet funnel of the jacket tube. The carbon dioxide snow produced thus falls evenly under the effect of gravity onto a product arranged below the outlet opening of the jacket tube and is not, or only to a small extent, entrained by the flow of carbon dioxide gas. Since the jacket space is closed at the top, any snow particles that may have entered the jacket space are not lost, but after a short period of turbulence in the jacket space also fall onto the product surface.

[0012] Secondly, the casing tube serves to thermally insulate the Schneehorn, as the cold carbon dioxide gas briefly penetrating the casing reliably shields the ambient heat from the wall of the expansion chamber. This allows even small amounts of carbon dioxide snow to be generated in the Schneehorn without the risk of the carbon dioxide snow sublimating on its way to the casing tube's outlet.

[0013] Thirdly, the outlet funnel of the casing tube, which projects downwards relative to the outlet opening of the snow horn, prevents the penetration of ambient moisture during operation of the device according to the invention.

[0014] To ensure that the shell space can effectively fulfill its function as a buffer volume, the volume of the shell space, minus the volume filled by the snow horn in the shell space, should be at least twice, preferably at least three times, the volume of the snow horn's expansion chamber. For example, if the shell tube and snow horn are cylindrical, the shell tube arranged coaxially to the snow horn should have an inner diameter that corresponds to 1.4 to three times the inner diameter of the snow horn's expansion chamber.

[0015] Preferably, the cross-section of the casing pipe's outlet opening at the lower end of the discharge funnel is equal to or smaller than the cross-section of the snow horn's outlet opening. This reliably prevents ambient moisture from penetrating the casing pipe during operation.

[0016] To enable accurate measurement of the amount of snow produced and, during consecutive use, a reliably consistent discharge rate, it is advantageous to install a phase separator upstream of the expansion nozzle. In the phase separator, any gas phase contained in the liquid carbon dioxide is at least largely separated.

[0017] In a practical embodiment, the device according to the invention comprises a carbon dioxide gas extraction device, which is preferably arranged below the outlet opening of the casing tube. For example, the extraction device is arranged below a transport device by means of which products to be cooled or containers to be filled are guided past the outlet opening and are charged or filled with carbon dioxide snow. The extraction device extracts the carbon dioxide gas escaping from the outlet opening of the casing tube. The carbon dioxide gas thus flows around the products or containers on its way to the extraction device, thus providing an additional cooling effect. Furthermore, the extracted carbon dioxide gas can be used, for example, to pre-cool the products to be cooled or to pre-cool the liquid carbon dioxide supplied to the snow horn.However, in the case of devices in which only small amounts of snow are to be produced during operation and thus only a small amount of carbon dioxide gas is produced, an extraction device can also be omitted, provided that this is justifiable from a safety perspective.

[0018] The device according to the invention enables, in particular, the precise dosing and placement of even small amounts of CO2 snow, for example, between 0.5 g and 10 g, on product surfaces or in containers. Accordingly, it is also possible to use small expansion nozzles to expand the liquid carbon dioxide, which, for example, have nozzle openings with a diameter of less than 5 mm, for example, 0.4 mm to 4.5 mm. Furthermore, the invention enables a reliably consistent amount of carbon dioxide snow to be dispensed in rapid succession onto product surfaces or into containers.

[0019] A preferred use of the device according to the invention is the freezing of products and / or the freezing of product surfaces (crusting), for example of food products, pharmaceutical products or medical or biological samples.

[0020] An embodiment of the invention will be explained in more detail with reference to the drawing. The only drawing ( Fig. 1 ) shows schematically a device according to the invention in longitudinal section.

[0021] The Fig. 1The device 1 shown comprises a snow horn 2 arranged within a casing tube 3. In the exemplary embodiment shown here, the snow horn 2 and the casing tube 3 are radially symmetrical about a longitudinal axis 4 of the device 1, with the snow horn 2 being arranged coaxially within the casing tube 3. However, other cross-sections, for example rectangular or square cross-sections, are also possible for the snow horn 2 and / or the casing tube 3 within the scope of the invention.

[0022] The snow horn 2 comprises, in a manner known per se, a substantially cylindrical expansion chamber 5 arranged vertically in the geodetic sense, at the upper end face 6 of which an expansion nozzle 7 opens. The expansion nozzle 7 is connected to a pressure-resistant carbon dioxide supply line 8, which in turn is connected to a source of liquid carbon dioxide (not shown here), for example a tank. While the expansion chamber 5 is gas-tightly sealed at its upper end face 6 and merely has a similarly gas-tight passage for the expansion nozzle 7, it has an opening 9 at its lower end face, which extends over the entire cross-sectional area of ​​the expansion chamber 5.

[0023] The jacket tube 3, which is arranged radially spaced from the snow horn 2, forming a jacket space 10, is also sealed gas-tight at its upper end face 11 and merely has a gas-tight passage for the snow horn 2. In the exemplary embodiment shown here, the upper end faces 6, 11 of the snow horn 2 and the jacket tube 3 are flush with one another; however, it is also conceivable for the upper end face 11 of the jacket tube 3 to be arranged vertically spaced above the upper end face 6 of the snow horn 2; in this case, the gas-tight passage is limited to a passage for the expansion nozzle 7 or for the carbon dioxide supply line 8.

[0024] The casing tube 3, cylindrical in its upper section 12, merges into a conical, downwardly tapered outlet funnel 13 approximately at the level of the outlet opening 9 of the snow horn 2, leaving an annular gap 14 open between the outlet funnel 13 and the expansion chamber 5. An outlet mask 15 is detachably attached to the lower end of the outlet funnel 13. The outlet mask 15, which is also conical and downwardly tapered in the embodiment shown here, opens on the underside to an outlet opening 16 of the casing tube 3. With the exception of the outlet opening 16, the casing tube 3 is closed and can be equipped with thermal insulation on the outside.

[0025] Depending on the size and surface properties of the products to be cooled, the outlet mask 15 can be exchanged and replaced with one adapted to a different product or product series. In particular, outlet masks with different areas or cross-sections of the outlet opening 16 can be used on the same device 1.

[0026] Below the outlet opening 16 of the casing tube 3 is the working area in which a product or a plurality of products to be cooled are to be exposed to carbon dioxide snow. In the embodiment shown here, a transport device 17, for example a conveyor belt, is provided below the outlet opening 16, by means of which the products 18a, 18b, 18c to be cooled are transported one after the other below the outlet opening 16. An extraction device 19 for extracting the carbon dioxide gas produced during the production of the carbon dioxide snow is arranged below the transport device 17.

[0027] A phase separator 21 is arranged in the carbon dioxide supply line 8, which serves to separate any gas components present in the supplied liquid carbon dioxide. The phase separator 21 is equipped with a pressure-maintaining valve 22, which ensures the operation of the device 1 under predetermined pressure conditions. In particular, it serves to maintain the pressure in the carbon dioxide supply line 8 at a working pressure above the triple point pressure of 5.18 bar. Furthermore, a solenoid valve 23 is arranged in the carbon dioxide supply line 8, which can be controlled by means of an electronic controller 24. To avoid dead space in which carbon dioxide snow can accumulate during operational breaks and thus impair the functionality of the device 1, the solenoid valve 23 is arranged directly upstream of the expansion nozzle 7.If the goal is to produce very small amounts of snow, the opening of the expansion nozzle 7 should also have a small diameter to avoid the formation of snow inside the expansion nozzle 7.

[0028] During operation of the device 1, the products 18a, 18b, 18c to be cooled are guided one after the other in the direction of arrow 25 below the outlet opening 16 by means of the transport device 17. Liquid carbon dioxide is present in the carbon dioxide supply line 8 at a working pressure of over 5.18 bar, for example, at a pressure of 7 bar to 20 bar. In accordance with a control signal issued by the controller 24, the solenoid valve 23 is opened for a short period of time, for example, 1 to 2 seconds. After passing through the phase separator 21, the liquid carbon dioxide flows to the expansion nozzle 7, where it expands to form a mixture of carbon dioxide snow and carbon dioxide gas. Part of the resulting carbon dioxide gas flows through the annular gap 14 into the jacket space 10, thereby reducing the gas flow toward the outlet opening 16. At the same time, it thermally shields the snow horn 2 from ambient heat.The carbon dioxide snow produced during the expansion falls evenly onto a product 18a, 18b, 18c to be cooled and can be dosed very precisely.

[0029] For example, the duration of the solenoid valve opening is 2 seconds. During this time, a quantity of, for example, 10g of carbon dioxide snow has formed in the snow horn 2, which falls onto the surface of the product 18a, forming a layer of snow 26 there. The product 18a covered with the layer of snow 26 is then transported out of the work area and replaced by a subsequent product 18b to be cooled. The carbon dioxide gas produced during the expansion is extracted by the extraction device 19 and discharged to the outside or used for another purpose.

[0030] The device 1 enables highly efficient dispensing of even small amounts of carbon dioxide snow. A large number of products 18a, 18b, 18c can be rapidly and successively charged with a precisely measured and consistently constant amount of carbon dioxide snow, or containers can be filled with it. Impairment of the functionality of the device 1 due to sticky carbon dioxide snow is reliably prevented due to the design according to the invention. List of reference symbols

[0031] 1Device 2Snow horn 3Jacket tube 4Longitudinal axis 5Expansion chamber 6Upper end face (snow horn) 7Expansion nozzle 8Carbon dioxide supply line 9Mouth opening 10Jacket chamber 11Upper end face (jacket tube) 12Upper section 13Mouth funnel 14Annular gap 15Exit mask 16Exit opening 17Transport device 18a, 18b, 18cProduct 19Suction device 20- 21Phase separator 22Pressure valve 23Solenoid valve 24Control .25Arrow 26Snow layer

Claims

1. Device for metering carbon dioxide snow, comprising a snow horn (2), which comprises a relaxation chamber (5), for relaxing liquid carbon dioxide while producing a mixture of carbon dioxide snow and carbon dioxide gas, which is closed towards the top and opens out on the lower side at a mouth opening (9) of the snow horn (2), and a relaxation nozzle (7) which opens out in the interior of the relaxation chamber (5) and is connected to a supply line (8) for liquid carbon dioxide, wherein the snow horn (2) is received within a casing tube (3) which is closed towards the top and projects downwards from the mouth opening (9) of the snow horn (2), characterized in that the casing tube (3) has a mouth funnel (13) which tapers towards a lower-side outlet opening (16) of the casing tube (3).

2. Device according to Claim 1, characterized in that the internal volume of the casing tube (3), minus the volume absorbed by the snow horn (2), is at least twice, preferably at least three times, the volume of the relaxation chamber (5) of the snow horn (2).

3. Device according to Claim 1 or 2, characterized in that the opening cross section of the outlet opening (16) of the casing tube (3) is equal to or smaller than the opening cross section of the mouth opening (9) of the snow horn (2).

4. Device according to one of the preceding claims, characterized in that a replaceable outlet mask (14) is releasably attached to the mouth funnel (13) of the casing tube (3).

5. Device according to one of the preceding claims, characterized in that a phase separator (21) is disposed upstream of the relaxation nozzle (7).