Dry expansion evaporator for ammonia refrigeration equipment

Abstract

The invention relates to a dry expansion evaporator (1) for an ammonia refrigeration plant, having a collection tube (2) and an outlet tube (3) for a refrigerant gas, characterized in that the collection tube (2) and the outlet tube (3) are connected to each other via a siphon (5), the open ends of the collection tube (2) and the outlet tube (3) being arranged adjacent to each other, and the lowest position of the refrigerant evaporator tube (6) is integrated into the collecting tube (2).

Description

[0001] The present invention relates to a dry expansion evaporator for an ammonia refrigeration device.

[0002] Typical dry expansion evaporators are used in refrigeration and cooling equipment in, for example, warehouses and cold stores and in air conditioning.

[0003] In addition, ammonia refrigeration equipment is increasingly used in the industrial, trade and commercial sectors. Ammonia as a refrigerant is called R717, is a natural refrigerant, and has no direct greenhouse effect (GWP) and no ozone depletion potential (ODP). Therefore, in order to replace the climate-harmful CFC refrigerants, various efforts are being made to reuse ammonia as a refrigerant to a greater extent.

[0004] However, in order to ensure efficient operation of ammonia refrigeration plants, so-called flooded evaporators are used in ammonia refrigeration plants. Flooded operation of the evaporator results in a large refrigerant charge and, moreover, a high space requirement for the liquid separator downstream of the evaporator.

[0005] Due to the toxicity of ammonia and the technical requirements mentioned, efforts are being made to reduce the filling volume of the equipment. This is possible, for example, if the ammonia refrigeration equipment is operated in the so-called dry expansion mode.

[0006] In the dry expansion mode of operation, a two-phase mixture of refrigerant continuously flows through the evaporator of the ammonia refrigeration equipment. The refrigerant is completely evaporated in the evaporator of the refrigeration equipment. Subsequently, the gaseous dry refrigerant is sucked into the compressor and further circulated after compression.

[0007] In ammonia refrigeration equipment, refrigerating machine oil is added to the refrigerant in order to lubricate the moving machine parts of the compressor and to achieve sealing of the pressure build-up area within the compressor. In addition, the heat generated in the lubrication gap is dissipated by the refrigerating machine oil. In order to ensure low-friction operation of the compressor, refrigerating machine oil must be continuously supplied to the compressor in an appropriate dosage and kept circulating.

[0008] Furthermore, in order to defrost an iced evaporator in an ammonia refrigeration plant, in a refrigerant-air refrigeration plant, hot gas defrost is applied to the evaporator to heat and melt ice by reversing the operation of the refrigeration plant. This makes it more difficult for the refrigerant to condense in the evaporator and for liquid condensate to accumulate in the evaporator.

[0009] However, as mentioned above, a known disadvantage, in particular in the application of so-called hot gas defrosting in the prior art, is the generation of condensate in the evaporator, which accumulates in the lower part of the evaporator and remains there. This is due in particular to the design of the collector of the evaporator with a high suction opening due to the construction of the evaporator, with the result that in some cases an iced evaporator can only be defrosted inadequately.

[0010] Another disadvantage is that the refrigerant ammonia mixes relatively poorly with refrigeration oil.

[0011] In the dry expansion operation of an ammonia refrigeration unit, a nearly miscible oil is added to the refrigerant ammonia. When the ammonia is in the gas phase, the oil settles at the corresponding lowest point in the components of the refrigeration unit.

[0012] In ammonia refrigeration equipment, this effect therefore leads to the risk of accumulation of refrigeration oil at the outlet of the evaporator in the lowest tube row. Due to the risk of liquid shock, the accumulation of refrigeration oil in certain areas of the equipment should be reduced and the affected parts should be deoiled. If this aspect is ignored, a surge-like suction of the liquid mixture by the compressor occurs when refrigeration oil accumulates in the evaporator. As a result, there is a risk of flooding the compressor chamber with oil, which can lead to the compressor being destroyed by liquid shock.

[0013] It is known from EP 3 705 813 A1 to avoid such liquid impacts of the lubricant located in the refrigerant circuit by adopting an inclined suction opening which, given the different oil accumulations and the different filling levels of the ends of the collecting pipes designed for oil separation, has only a slight influence on the flow behavior in the refrigerant circuit. However, the configuration disclosed therein is not suitable for continuous tolerance of highly varying liquid quantities, such as may occur, for example, in reverse operation for defrosting the evaporator.

[0014] The object of the present invention is to design an evaporator for an ammonia refrigeration plant in dry expansion operation such that the risk of liquid shock to the compressor is reduced.

[0015] This object is achieved by the subject matter having the features according to claim 1. Further developments are indicated in the dependent patent claims.

[0016] The object of the invention is achieved in particular by a dry expansion evaporator for an ammonia refrigeration plant, which, in addition to the standard components of the evaporator, is equipped with at least one collecting pipe and an outlet pipe for the refrigerant gas. According to the invention, the collecting pipe and the outlet pipe are connected to each other by a siphon and are arranged adjacent to each other. As a result, the desired flow direction is formed in the siphon. The siphon is preferably arranged on the bottom of the evaporator at the lowest position of the dry expansion evaporator.

[0017] A syphon is generally an odour-proof or gas-tight but liquid-permeable closure for pipe systems and containers. The operating principle is based on an S-shaped tube, the lower bend of which always remains filled with liquid, thereby preventing the passage of gases (e.g. channel gases). However, the syphon in the refrigeration device can also be used in the normally gas-permeable operating mode if the syphon is only not completely filled with liquid. According to the invention, the syphon used in this operating mode can be used as a buffer container for the liquid volumes occurring in different operating modes. According to the invention, the syphon is designed such that it comprises a collecting container which can be constructed independently of the flow cross section of the connected pipeline.

[0018] The syphon is preferably formed as a flat upright cylindrical container with a flat closed syphon bottom as a lower boundary. The side surface is formed by a cylindrical syphon sleeve. A syphon cover closes the syphon at the top. In the syphon cover, holes for a vertical collecting pipe and holes for a vertical insertion end of an outlet pipe are arranged, penetrating the syphon cover from above.

[0019] Advantageously, the outlet pipe consists essentially of three zones, respectively in the direction opposite to the flow direction: a horizontal section connected to the suction port of the compressor, a manifold connected to the horizontal section and a vertical section. The vertical section has an insertion end at its end, which is implemented as a bevel. With the insertion end, the outlet pipe is advantageously inserted into the syphon up to the syphon bottom. The syphon bottom thus acts as a stop during assembly when the outlet pipe is inserted. At the same time, it is ensured that even in the case of a low liquid level in the syphon, the beveled end of the outlet pipe extends into the liquid and optimally guides the liquid into the flow circuit, which is important for the continuous lubrication of the moving parts.

[0020] Preferably, the insertion end of the outlet pipe in the syphon is formed as a baffle, in that the longest part of the beveled end of the outlet pipe is arranged on the side facing away from the collecting pipe. The refrigerant evaporator pipe is incorporated into the collecting pipe above the syphon, so that the syphon forms the lowest point of the evaporator. If the manifold is located directly above the insertion end of the outlet pipe, an evaporator with a low construction height can be achieved. In this case, the invention is particularly preferred as a design of a flat evaporator.

[0021] If the base area of ​​the siphon is significantly larger than the cross section of the outlet pipe, stable flow conditions can be achieved in the siphon which are only influenced to a small extent by the amount of liquid present in the siphon. The immersion depth of the beveled end of the outlet pipe will vary only slightly. The desired flow direction will always be established between the collecting pipe and the outlet pipe. It has been shown that, in particular in the case of larger evaporators with a power of more than 50 kW, it is advantageous if the area of ​​the siphon base is at least four times the cross section of the outlet pipe. The invention is accordingly suitable for evaporators with a power of more than 50 kW.

[0022] The concept of the present invention can be summarized as follows:

[0023] The accumulated refrigerant is sucked in and de-oiled via a siphon at the lowest point of the evaporator of the refrigeration unit, so that no further accumulation of condensate and refrigeration oil occurs. Compared with conventional separators in flooded evaporators, the siphon is realized in a very small space and in a very space-saving manner. The siphon is arranged at the lower end of the refrigerant collector below the last tube row and thus represents the lowest point of the evaporator where refrigerant and refrigeration oil accumulate. According to this configuration, the liquid in the evaporator runs to this point driven by gravity.

[0024] The suction opening is designed to be beveled and is inserted vertically from above into the syphon and all the way to the syphon bottom. The open side of the insertion is designed to be beveled so that a supporting effect is achieved on the suction of refrigerant and refrigeration oil due to the surface tension between the tube and the oil. The inserted tube also acts as a baffle with proper alignment, allowing the suction of gaseous refrigerant from the evaporator with low pressure losses.

[0025] The advantages of the invention are manifold. Complete extraction of refrigerant and refrigeration oil from the evaporator can be achieved via the syphon. As a result, the defrosting time of an iced evaporator is greatly shortened, since the evaporator is completely emptied of liquid and hot gas defrosting can be immediately effective in a timely manner. Furthermore, temporary oil accumulation in the evaporator is avoided and, instead, continuous oil suction and thus continuous oil supply to the compressor is ensured. Thus, protection of the compressor is achieved, preventing surge oil inflow and flooding of the compressor chamber.

[0026] Further details, features and advantages of the design of the present invention will become apparent from the following description of exemplary embodiments with reference to the associated drawings, in which:

[0027] Figure 1 : A side view showing a partial area of ​​a dry expansion evaporator,

[0028] Figure 2 : shows a perspective view of a syphon with a collecting pipe and an outlet pipe, and

[0029] Figure 3 : Shows a side view of the siphon.

[0030] Figure 1 A cross section of a dry expansion evaporator 1 of an ammonia refrigeration plant in the region of the evaporator bottom 4 is shown. The dry expansion evaporator 1 is characterized in that a collecting pipe 2 for leaking refrigerant gas and an outlet pipe 3 for connection to the suction port of the compressor of the refrigeration plant are fluidly connected to each other via a siphon 5. The refrigerant gas flows from the collecting pipe 2 into the outlet pipe 3 via the siphon 5 and is subsequently drawn in by the compressor of the refrigeration plant. The liquid refrigerant or condensate in the collecting pipe 2 and the liquid refrigeration oil flow downward into the siphon 5 under the action of gravity and are continuously entrained by the gas flow.

[0031] The syphon 5 is arranged at the lowest point of the dry expansion evaporator 1 so that the settled refrigerant oil and liquid refrigerant can be continuously drawn out of the evaporator during operation, thereby ensuring that no liquid accumulation is formed in the dry expansion evaporator 1 .

[0032] Figure 2 A perspective view of a syphon 5 is shown as a component of a dry expansion evaporator 1. The collecting pipe 2 is arranged vertically and ends in the syphon 5, so that any condensate of the refrigerant and refrigerant oil that may form accumulate in the syphon 5. An outlet pipe 3 for the refrigerant vapor is arranged upwardly outside the syphon 5, via which outlet pipe 3 the refrigerant-oil mixture leaves the dry expansion evaporator 1 towards the suction port of the compressor of the refrigeration device.

[0033] By way of example, refrigerant evaporator tubes 6 are shown which are arranged vertically and lead to the collecting tube 2. The lowest refrigerant evaporator tube 6 is arranged above the inlet of the collecting tube 2 into the siphon 5.

[0034] In the perspective view, the syphon 5 is shown as a flat cylindrical container, the diameter of which is the sum of the diameter of the collecting pipe 2 and the diameter of the outlet pipe 3 .

[0035] Figure 3 A detail of the syphon 5 is shown, enlarged in a side view. The syphon 5 consists of a cylindrical syphon jacket 10, a flat syphon bottom 9 and a perforated syphon cover 11. The vertical section of the outlet pipe 3 is inserted into the syphon 5 from above, the bottom of which is beveled and faces the syphon bottom 9. The lowest refrigerant evaporator tube 6 joins the collecting pipe 2 above the syphon 5 so that the entire refrigerant volume flow passes through the syphon 5. The refrigerant volume flow undergoes a deflection of 180° from the inlet into the syphon 5 through the collecting pipe 2 to the outlet from the syphon 5 through the insertion end 7 of the outlet pipe 3. The refrigerant flow undergoes a further deflection of 90° in the region of the manifold 8 and leaves the outlet pipe 3 in the horizontal direction to the compressor, not shown.

[0036] Reference Mark List

[0037] 1. Dry expansion evaporator

[0038] 2. Collection tube

[0039] 3. Exit pipe

[0040] 4. Evaporator bottom

[0041] 5. Siphon

[0042] 6. Refrigerant evaporator tube

[0043] 7. Insert the outlet pipe into the end

[0044] 8. Manifold

[0045] 9. Siphon bottom

[0046] 10. Syphon set

[0047] 11. Syphon cover.

Claims

1. A dry expansion evaporator (1) for an ammonia refrigeration device, the dry expansion evaporator (1) having a collecting pipe (2) and an outlet pipe (3) for refrigerant gas, characterized in that: The collecting pipe (2) and the outlet pipe (3) are connected to each other via a siphon (5), wherein the open end of the collecting pipe (2) and the open end of the outlet pipe (3) are arranged adjacent to each other, and the lowest position of the refrigerant evaporator tube (6) is incorporated into the collecting pipe (2).

2. The dry expansion evaporator (1) according to claim 1, characterized in that: The siphon (5) is arranged on the evaporator bottom (4) at the lowest position of the dry expansion evaporator (1).

3. The dry expansion evaporator (1) according to claim 1 or 2, characterized in that: The syphon (5) is formed as a flat upright cylindrical container having a closed syphon bottom (9) at the bottom and an inlet for a vertical collecting pipe (2) and a vertical insertion end (7) of the outlet pipe (3) at the top.

4. The dry expansion evaporator (1) according to any one of claims 1 to 3, characterized in that: The outlet pipe (3) is formed by a horizontal section, a manifold (8) and a vertical section, wherein the vertical section is implemented as an insertion end (7) of the outlet pipe (3) having a bevel.

5. The dry expansion evaporator (1) according to claim 4, characterized in that: The beveled end of the outlet pipe (3) is inserted into the syphon (5) up to the syphon bottom (9).

6. The dry expansion evaporator (1) according to any one of claims 1 to 5, characterized in that: The inserted end (7) of the outlet pipe (3) forms an impact plate region in the siphon (5), since the longest part of the beveled end of the outlet pipe (3) is arranged on the side facing away from the collecting pipe (2).

7. The dry expansion evaporator (1) according to any one of claims 1 to 6, characterized in that: A refrigerant evaporator tube (6) is incorporated into the collecting tube (2) above the siphon (5).

8. The dry expansion evaporator (1) according to any one of claims 1 to 7, characterized in that: The dry expansion evaporator (1) is embodied as a flat evaporator.

9. The dry expansion evaporator (1) according to any one of claims 1 to 8, characterized in that: The area of ​​the siphon bottom (9) is at least four times the cross-section of the outlet pipe (3).

10. The dry expansion evaporator (1) according to any one of claims 1 to 9, characterized in that: The dry expansion evaporator (1) is designed to have a power of more than 50 kW.

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