DEVICE FOR COOLING LIQUIDS

Description

[0001] The invention relates to a device for cooling liquids by thermal contact with a cryogenic medium, comprising a container for receiving a liquid bath of a liquid to be cooled, with a heat exchanger arranged in the liquid bath for cooling the liquid by heat exchange with a liquefied cryogenic cooling medium, which heat exchanger is equipped with an inlet and an outlet for the cooling medium and with a heat exchanger surface for indirect heat exchange between the liquid and the cooling medium.

[0002] In many technical fields there is a need to keep liquids of various types at a specified maximum temperature or to cool them to a specified temperature for further processing.

[0003] For example, the temperature of fresh concrete is increasingly being limited in many countries due to legal recommendations, regulations, and guidelines, as well as project-specific specifications, to prevent thermal stress cracking, which can reduce the compressive strength of the concrete and the longevity of the structure. One option for controlling the temperature of fresh concrete is to cool the mixing water used in the production of the fresh concrete, bringing it to a temperature of, for example, just above 0°C. Cooling systems based on electricity or liquid nitrogen are currently used for this purpose.

[0004] When cooling using a cryogenic cooling medium, such as liquid nitrogen, this is either introduced directly into the liquid, for example using lances, or indirect cooling takes place on a heat exchanger surface of a heat exchanger, whereby the liquid to be cooled is constantly moved by means of pumps, stirrers or other agitators in order to ensure the most uniform cooling of the liquid and to prevent icing of the heat exchanger surface.

[0005] WO 2012 / 010705 A1 describes a process in which a cold-liquefied gas is introduced via a nozzle directly into the process water used to cool fresh concrete, whereby at least part of the added water freezes to ice.

[0006] From DE 3 828 136 A1 it is known to cool a liquid by introducing a liquefied gas via a nozzle directly into the bottom area of ​​the container in which the liquid is stored.

[0007] EP 2 142 862 B1 discloses a method for cooling water, in which a cold-liquefied gas is injected dropwise into the water so that a suspension of unfrozen and frozen water is formed, which is used as process water in concrete production.

[0008] However, the disadvantage of these systems, in which liquefied gas is fed directly into the process water, is that there is a risk of icing at the point where the liquefied gas is introduced, which can impair the functionality of the equipment as a whole.

[0009] US 5 140 822 A discloses a device according to the preamble of claim 1.

[0010] DE 10 2005 039 570 A1 discloses a method for cooling aggregates in concrete production, particularly the mixing water used in the process. Liquid nitrogen is used as the cooling medium; it evaporates and is then added to the mixing water as a cold gas. The vaporization enthalpy of the nitrogen is also used to cool the mixing water. The liquid nitrogen first passes through a heat exchanger surrounded by the mixing water and evaporates in the process. The prior evaporation of the liquid nitrogen at least reduces the risk of icing at the point of gas entry.

[0011] However, the conventional heat exchangers mentioned in DE 10 2005 039 570 A1 for the technical implementation of the process described therein are only poorly suited for energy transport between liquid nitrogen and water. Due to the low temperatures of nitrogen, ice can form on the heat exchanger tubes carrying the cooling medium and, if the distance between these tubes is only small, the entire heat exchanger can freeze over, resulting in a significant loss of performance. To prevent this type of icing, a considerable flow velocity must be generated in the liquid. However, it has been shown that the flow velocity generated by agitators or pumps is usually too low to effectively prevent icing of the heat exchanger tubes during heat transfer from water to liquid nitrogen.The use of agitators with sufficient power is in many cases not economically viable.

[0012] The invention is therefore based on the object of creating a device for cooling liquids, in particular a device for cooling added water in the production of fresh concrete, in which the risk of icing is further reduced compared to the objects according to the prior art.

[0013] This object is achieved by a device having the features of patent claim 1.

[0014] Advantageous embodiments of the invention are specified in the subclaims.

[0015] A device according to the invention of the type and intended purpose mentioned at the outset is thus characterized in that the outlet for the cooling medium is fluidly connected to an inlet device opening into the liquid bath below the heat exchanger surface for introducing evaporated cooling medium into the liquid.

[0016] According to the invention, the cold of the cryogenic cooling medium is used twice, and at the same time, the flow created when the gaseous refrigerant is introduced into the liquid bath is used to prevent icing on the heat exchanger surface. Firstly, the liquid cooling medium flowing in the heat exchanger absorbs heat from the surrounding liquid bath, at least partially evaporating. Secondly, the evaporated cooling medium, which is then still at a comparatively low temperature, is at least partially fed into the liquid itself at the introduction device. The introduction device is arranged geodetically below the heat exchanger surface and is equipped with at least one outlet opening from which the evaporated cooling medium emerges and subsequently rises in the form of gas bubbles in the liquid.The rising gas bubbles create an upward flow in the liquid bath, resulting in homogeneous mixing of the liquid and a uniform temperature distribution. At the same time, the rising gas bubbles flow around the heat exchanger surface, preventing or reducing the formation of an ice layer on the surface. This eliminates the need for equipment such as agitators or similar devices to mix the liquid, or for extended downtimes to defrost the heat exchanger surface.

[0017] The heat exchanger surface is preferably a tube heat exchanger in which heat transfer takes place on one tube or on several tubes with thermally highly conductive walls (heat exchanger tubes) through which the cooling medium flows and around which the liquid to be cooled flows. For example, the heat exchanger surface comprises a coiled tube with one or more turns and / or a plurality of heat exchanger tubes arranged parallel to one another. To improve heat transfer, the tube(s) or individual sections thereof can be designed as finned tubes. To enable effective flow around the heat exchanger surface by the rising gas bubbles of the introduced gaseous cooling medium in the liquid bath, the tubes or tube sections or turns are arranged at a distance from one another.

[0018] In a particularly preferred embodiment of the invention, the heat exchanger surface comprises a pipe coil arranged in the liquid bath, which has one or more turns that run spirally or helically around a vertically or obliquely upwardly arranged axis. The individual turns can each have the same cross-section, so that the pipe coil as a whole has a - possibly oblique - cylindrical shape. Alternatively, the turns can each have different cross-sectional areas; in particular, the cross-sectional areas of the turns can continuously increase or decrease from bottom to top, so that the pipe coil as a whole has a - possibly oblique - conical or pyramidal shape, with an opening angle of, for example, between 20° and 45°, preferably between 25° and 60°. The cross-sections of the individual turns can be circular or of a different geometry, for example oval or square.

[0019] The individual turns of the coil, which is preferably constructed from a finned tube, are spaced apart from one another. For example, the vertical distance between the turns is between 0.2 tube diameters and one tube diameter. For example, if the tube diameter of a device used to cool make-up water, for example, is between 20 mm and 50 mm, the distance between the turns in a cylindrical coil should also be at least 5 mm to 50 mm. Smaller distances are particularly suitable for flat, conical or pyramid-shaped coils, as the upward flow in the liquid bath induced by the rising gas bubbles of the introduced cooling medium can directly surround all the turns.

[0020] Preferably, means are provided in the container for directing a flow induced by the introduction of the cooling medium in the liquid bath towards the turns of the coiled tube. This is preferably a passive flow element. For example, it is a body arranged within the coiled tube in the shape of a cone with its tip pointing downwards. By such a cone, the flow rising within the coiled tube is deflected in the radial direction, i.e., towards the circumferential tube of the coiled tube. Such a configuration is particularly advantageous for embodiments of the invention which have a cylindrical coiled tube arranged vertically in the liquid bath as the heat exchanger surface.

[0021] The feed device is, for example, a tubular or flat element equipped with one or more outlet openings for generating gas bubbles rising in the liquid. The outlet opening(s) is / are preferably arranged in the feed device such that as large a portion of the heat exchanger surface as possible is surrounded by the rising gas bubbles. For example, the outlet opening(s) is / are each a simple bore in the casing of the feed device, which is otherwise designed as a hollow body. The outlet opening(s) can also be part of a nozzle directed, for example, towards the heat exchanger surface. The feed device can also be equipped with flow-promoting elements, for example with a Venturi nozzle arranged in the container upstream of the outlet opening or nozzle.

[0022] In another advantageous embodiment, the feed device is a sintered body made of metal, ceramic or plastic, the pore openings of which represent the outlet openings.

[0023] A connecting line is expediently provided as a flow connection between the heat exchanger outlet and the inlet device, which runs in sections above a liquid bath in the tank. The at least partially evaporated cooling medium is thus guided in sections geodetically above a liquid fill level in the tank intended for use by the device. This ensures that no liquid can penetrate into the heat exchanger during device downtimes, which could cause freezing there after resumption of operation.

[0024] Alternatively or additionally, means for preventing backflow of liquid from the liquid bath can also be provided in the connecting line and / or the feed device, for example, flaps or check valves arranged in the connecting line or the feed device to prevent liquid from penetrating during a break in operation or during a low supply of cooling medium. Likewise, the outlet opening(s) of the feed device can preferably each be equipped with a self-closing valve, a flap, or a liquid-tight but gas-permeable sintered body.

[0025] The container can be an open container, such as a basin or pond. However, a closed container with a gas outlet is preferred, as this allows the escaping gas flow to be discharged in a controlled manner.

[0026] In order to be able to control the temperature of the liquid, an advantageous embodiment of the invention provides that the device is equipped with a control device. The control device comprises one or more controllable valves by means of which the flow of the cooling medium through the heat exchanger and / or the proportion of evaporated cooling medium supplied to the inlet system can be adjusted, a measuring device for measuring at least one operating parameter, such as the temperature of the liquid or the occurrence of icing or the thickness of any ice layer, and a control unit by means of which the valve(s) can be controlled depending on the measured operating parameter(s).

[0027] The liquid to be cooled is preferably water or an aqueous medium, especially mixing water for the production of fresh concrete. The cryogenic cooling medium is preferably liquid nitrogen or another medium in a cryogenically liquefied state.

[0028] The device according to the invention is preferably used for cooling mixing water in the production of fresh concrete.

[0029] Embodiments of the invention will be explained in more detail with reference to the drawings. Schematic views show: Fig. 1 : A device according to the invention in a longitudinal section along the section line I - I in Fig. 2 , Fig. 2 : The device according to the invention from Fig. 1 in a top view with the container open, Fig. 3 : The heat exchanger surface of a device according to the invention in another embodiment in longitudinal section.

[0030] The device 1 according to the invention shown in the drawings comprises a container 2 for holding a liquid to be cooled, for example, mixing water for the production of fresh concrete, and a heat exchanger 3 arranged within the container 2. The container 2 is equipped with a supply line 4 for supplying the liquid to be cooled and with an outlet line 5 for discharging the cooled liquid. A valve 6, 7 is provided in each of the supply line 4 and the outlet line 5 to control the flow of the liquid.

[0031] The heat exchanger 3 comprises a heat exchanger surface 8 in the form of a pipe coil, which is connected to a supply line 9 for a liquid cooling medium, in the exemplary embodiment a cryogenic cooling medium such as liquid nitrogen. A valve 10 for controlling the flow of cooling medium is arranged in the supply line 9. The pipe coil of the heat exchanger surface 8, which preferably consists of a finned tube, comprises a plurality of windings 11a, 11b, 11c, 11d arranged one above the other, which are vertically spaced from one another and are therefore completely surrounded by surrounding liquid. The cross-sectional areas of the windings 11a, 11b, 11c, 11d become increasingly larger from the mouth of the supply line 9 downwards and thus form, in the example shown here, a pyramid-shaped spiral with a rectangular pyramid base and a vertical axis.Furthermore, within the scope of the invention, it is equally conceivable for the windings to form a cylindrical spiral, a conical spiral opening upwards, or one arranged obliquely within the container 2. Furthermore, the heat exchanger surface 8 may also comprise more or fewer windings than the four windings 11a, 11b, 11c, 11d shown here.

[0032] The geodetically lowest coil 11d opens into a gas return line 12, through which the cooling medium evaporated in the heat exchanger 3 is discharged. Outside the vessel 2, a gas line 13 branches off from the gas return line 12, by means of which at least a portion of the evaporated cooling medium can be directed to an inlet device 14, which is arranged geodetically below the heat exchanger surface 8 in the vessel 2. The proportions of gas branched off to the inlet device 14 or discharged can be controlled manually or automatically according to a program using valves 15a, 15b, for example, depending on a measured parameter.

[0033] The feed device 14 is a tubular or other hollow body with an additional geometry, equipped with outlet openings for the vaporized cooling medium. For example, the feed device 14 is a tube equipped with one or more bores 16. It can also be a gas-permeable sintered body or an arrangement with at least one self-closing nozzle.

[0034] During operation of the device 1, the container 2 is filled with the cooling liquid, for example, additive water, to a level at which the heat exchanger surface 8 is completely within a liquid bath 17. The liquid cooling medium, for example, liquid nitrogen, is then introduced via the supply line 9. The liquid nitrogen evaporates at least partially upon thermal contact with the additive water on the heat exchanger surface 8, cooling the liquid bath 17. The evaporated nitrogen then flows at least partially to the feed device 14, where it is introduced into the liquid bath 17 in gaseous form. The resulting gas bubbles rise in the liquid bath 17, leading to an upward flow and intensive mixing of the liquid bath 17.The pyramidal arrangement of the windings 11a, 11b, 11c, 11d ensures that all windings 11a, 11b, 11c, 11d are directly impacted by the ascending flow in the liquid bath 17 and are surrounded by it. This at least largely prevents the formation of an ice layer on the outer walls of the windings 11a, 11b, 11c, 11d. To prevent liquid from the liquid bath 17 from penetrating the windings 11a, 11b, 11c, 11d of the heat exchanger surface during an operational break, the gas line 13 runs at least partially above the level of the liquid bath 17.

[0035] The vaporized nitrogen accumulates above the liquid bath 17 in a gas phase 18 in an upper region of the container 2. It flows out via an exhaust line 19, where it is combined with the portion of the vaporized nitrogen from the gas return line 12 that is not fed to the feed device 14. The nitrogen can then be released into the environment or used for another purpose. A valve 20 with a safety valve 21 controls the amount of gas flowing out.

[0036] The temperature in the liquid bath 17 is continuously monitored by a temperature gauge 22. As soon as a predetermined temperature of, for example, between 1°C and 6°C is reached, the added water can be removed via the outlet 5 and fed to its intended use.

[0037] The temperature of the liquid bath 17 can be controlled by a control unit 23, which is operatively connected to the temperature sensor 20 and the valves 10, 15a, 15b. For this purpose, the total flow rate of the cooling medium conveyed through line 9 and / or the proportion of the evaporated cooling medium conveyed via the branch line 13 to the feed device 14 is regulated according to a predefined program depending on the measured temperature.

[0038] In Fig. 31 shows a heat exchanger of a device according to the invention in another embodiment. The device 25 shown therein comprises a heat exchanger 26 equipped with a heat exchanger surface 27 in the form of a vertically arranged, cylindrical pipe coil. The heat exchanger surface 27 comprises a plurality of windings 28a, 28b, 28c, 28d arranged vertically one above the other and spaced from one another, which are arranged in a liquid bath 29 consisting, for example, of added water. During operation of the device 25, liquid nitrogen or another liquefied gas is passed through the windings 28a, 28b, 28c, 28d and evaporated in thermal contact with the surrounding liquid bath 29 before being introduced in gaseous form into the liquid bath 29 at an introduction device 30 arranged below the heat exchanger 26. The introduction of the gas leads to an upward flow in the liquid bath 29, according to the direction of arrow 31.

[0039] To direct the upward flow toward the windings 28a, 28b, 28c, 28d, a flow body 32 is arranged axially inside the heat exchanger 26. In the embodiment shown here, the flow body 32 has the shape of a cone standing on its tip and serves to direct the flow induced by the gas introduced into the liquid bath 29 toward the windings 28a, 28b, 28c, 28d radially surrounding the flow body 32. The continuous flow of liquid around the windings 28a, 28b, 28c, 28d prevents the formation of ice layers on the outer surface of the windings 28a, 28b, 28c, 28b. In this way, ice formation can be effectively prevented even if the windings 28a, 28b, 28c, 28d completely or partially overlap in vertical projection.

[0040] The flow body 32 does not necessarily have to have the shape of an inverted cone; rather, any shape is suitable that is capable of directing an upward flow in the liquid bath 29 in the direction of the turns 28a, 28b, 28c, 28d.

[0041] In order to prevent water from the liquid bath 29 from penetrating into the windings 28a, 28b, 28c, 28d during breaks in operation and leading to ice formation there after resumption of operation, the flow connection between the heat exchanger 26 and the input device 30 is established via a line 33 which runs above the liquid bath 29 at least in a section 34.

[0042] The invention is not limited to the embodiment shown here; in particular, a device according to the invention can also be used for cooling liquids other than additive water and / or can be operated with cooling media other than liquid nitrogen. List of reference symbols

[0043] 1 device 17 liquid bath 2 container 18 Gas phase 3 heat exchanger 19 exhaust pipe 4 supply line 20 valve 5 Excretion 21 safety valve 6 valve 22 Temperature gauge 7 valve 23 Control unit 8 Heat exchanger surface 24 - 9 Supply line (for liquid cooling medium) 25 device 26 heat exchanger 10 valve 27 Heat exchanger surface 11a, 11b, 11c, 11d winding 28a, 28b, 28c, 28d winding 12 Gas return line 29 liquid bath 13 Line 30 Entry setup 14 Feed device (for evaporated cooling medium) 31 Arrow 32 Flow body 15a, 15b valve 33 Line 16 drilling 34 Section

Claims

1. Device for cooling liquids by heat contact with a cryogenic medium, having a container (2) for receiving a liquid bath (17, 29) of a liquid to be cooled, having a heat exchanger (3, 26) disposed in the liquid bath (17, 29) for cooling the liquid by exchanging heat with a liquefied cryogenic cooling medium, which heat exchanger (3, 26) is equipped with an inlet line (9) and an outlet line (12) for the cooling medium and with a heat exchanger surface (8, 27) for the indirect heat exchange between the liquid and the cooling medium, characterized in that the outlet line (12) for the cooling medium is fluidically connected via a connecting line (13, 33) to an introduction device (14, 30) which, below the heat exchanger surface, opens into the liquid bath (17, 29) for the introduction of evaporated cooling medium into the liquid.

2. Device according to Claim 1, characterized in that the heat exchanger surface (8, 27) comprises a pipe coil of which the coils (11a, 11b, 11c, 11d; 28a, 28b, 28c, 28b) are disposed about an axis extending vertically or obliquely upwards.

3. Device according to Claim 2, characterized in that the coils (11a, 11b, 11c, 11d; 28a, 28b, 28c, 28d) of the pipe coil are formed in such a manner that the cross-sectional areas of the coils (11a, 11b, 11c, 11d; 28a, 28b, 28c, 28b) decrease or increase in size from bottom to top.

4. Device according to Claim 2 or 3, characterized in that provided in the container (2) are means to direct a flow emanating from the introduction device (14, 30) in the direction of the coils (11a, 11b, 11c, 11d; 28a, 28b, 28c, 28b).

5. Device according to one of the preceding claims, characterized in that the connecting line (13, 33) at least in portions extends above a liquid bath (17, 29) in the container (2).

6. Device according to any one of the preceding claims, characterized in that the connecting line (13, 33) or the introduction device (14, 30) is equipped with means for preventing the inflow of liquid from the liquid bath (17, 29).

7. Device according to one of the preceding claims, characterized in that the introduction device (14, 30) has at least one exit opening (16) which is equipped with a self-closing valve or a liquid-tight but gas-permeable sintered body.

8. Device according to one of the preceding claims, characterized in that the container (2) is formed as a closed container which is equipped with an exhaust gas line (19) which leads out of an upper region of the container (2).

9. Device according to one of the preceding claims, characterized by a feedback-control device (21) for feedback-controlling the temperature of the liquid in the container (2).

10. Device according to one of the preceding claims, characterized in that the cryogenic cooling medium is liquid nitrogen.

11. Use of a device (1, 25) according to one of Claims 1 to 10 for the cooling of mixing water in concrete production.