Arrangement for separating a lubricant-refrigerant solution

Abstract

Arrangement (14) for separating a lubricant-refrigerant solution, in particular an oil-refrigerant solution, into at least one first liquid phase and a second liquid phase different from the first liquid phase, wherein the arrangement (14) comprises: a temperature adjustment device (16) configured to bring the lubricant-refrigerant solution to a predetermined temperature at which the at least one first liquid phase and the second liquid phase different from the first liquid phase are formed, and a separation device (22) for separating the at least two different liquid phases, as well as an arrangement (12) for compressing refrigerant and refrigeration circuit (10).

Description

The present invention relates to an arrangement for separating a lubricant-refrigerant solution according to claim 1, an arrangement for compressing refrigerant according to claim 5, and a refrigeration circuit according to claim 9. Nowadays, compressors are used in large numbers not only in long-established fields of application, such as the generation of compressed air (especially in industry and trade) or the generation of cold, for example for air conditioning purposes in the commercial and private sectors or for cooling or freezing goods in the trade and transport sector, but also increasingly in applications such as heat pumps. With few exceptions, the so-called "dry-running" compressors, modern applications generally utilize compressors lubricated with a lubricant, usually oil. Besides the reduced wear, which is either unattainable or only achievable with significant technical effort in dry-running compressors, the lubricant also serves as a seal, for example in screw compressors. When compressors are used in refrigeration technology or heat pumps (both of which are part of a refrigeration cycle), they typically compress a refrigerant, which, after compression, is brought into a liquid state in a condenser. The liquid refrigerant is then expanded in an expansion vessel before evaporating in its expanded state and subsequently being returned to the compressor. Particularly within the compressor itself, the refrigerant comes into contact with the lubricant. In oil-flooded screw compressors, this contact is very intensive. Oil separators are used to separate the lubricant and refrigerant, separating the (liquid) lubricant from the (gaseous) refrigerant. The oil separator, which can be designed, for example, as a demister or droplet separator, is usually located on the high-pressure side of the compressor and separates the lubricant from the refrigerant after the compression process. An example of a screw compressor with an oil separator is known from DE 10 2013 020 532 A1, which originates from the applicant. It is generally overlooked that refrigerants can dissolve in lubricants upon contact. For example, in a refrigeration system using oil as a lubricant and ammonia as a refrigerant, an ammonia gas stream circulates within the compressor along with sealing and lubricating oil. After compression, the oil (in liquid form, although an aerosol state is considered liquid in this application) is separated from the ammonia gas mass stream. Depending on the type and composition of the oil, its temperature, and pressure, up to approximately 8% or even more ammonia remains in solution within the oil. This solution is filtered and then supplied to the bearings and the compression chamber. Analysis shows that the lubricating properties of the oil decrease with increasing ammonia content. Based on the prior art described above, the object of the present invention is to provide an arrangement for separating a lubricant-refrigerant solution, in particular an oil-refrigerant solution, and a corresponding arrangement for compressing refrigerant, which can reduce the amount of dissolved refrigerant, at least in part, of the lubricant. Furthermore, it is an object of the present invention to provide a corresponding refrigeration cycle. The aspect of the problem which is directed to specify an arrangement for separating a lubricant-refrigerant solution, in particular an oil-refrigerant solution, is solved by an arrangement for separating a lubricant-refrigerant solution, in particular an oil-refrigerant solution, having the features of claim 1. Accordingly, this aspect of the problem of the present invention is achieved by an arrangement for separating a lubricant-refrigerant solution, in particular an oil-refrigerant solution, into at least one first liquid phase and a second liquid phase that differs from the first liquid phase (in its composition), wherein the arrangement comprises: - a temperature adjustment device configured to bring the lubricant-refrigerant solution to a predetermined temperature at which at least one first liquid phase and a second liquid phase that differs from the first liquid phase are formed, and - a separation device for separating the at least two different liquid phases. This process involves the separation of the oil-refrigerant solution into two distinct liquid phases with differing compositions. In other words, the lubricant-refrigerant solution separates into two liquids of different compositions. Depending on the oil and refrigerant used, and the target temperature, either liquid refrigerant and liquid lubricant will exist separately, or a refrigerant-poor and lubricant-rich phase, or a refrigerant-rich and lubricant-poor phase, will occur. In particular, the first liquid phase can be low in refrigerant and rich in lubricant, and the second liquid phase can be rich in refrigerant and low in lubricant. Especially in oil-sealed compressors, such as oil-flooded screw compressors, the lubricant-rich phase can then be used to lubricate bearings, etc., while the refrigerant-rich phase can be fed into a refrigeration cycle or, after evaporation, into the compression process. This results in an energy-efficient compression process. The temperature adjustment device can be a primary heat exchanger. This allows the lubricant-refrigerant solution to be easily brought to the desired temperature, usually by heating it, but depending on the solution, it may also be achieved by cooling. Alternatively, direct heating / cooling is possible instead of a heat exchanger. The arrangement optionally includes a liquid-liquid decanter, a centrifuge, or a scraper plate. These elements, used to separate the two phases, can reliably separate them based on their differing densities. A scraper plate ensures purely mechanical separation without requiring any energy for the separation process. Alternative designs also utilize other elements for separation, exploiting the different densities or other properties of the two phases. For example, differing magnetic properties of the two phases could be used. The aspect of the problem that concerns an arrangement for compressing refrigerant is solved by an arrangement for compressing refrigerant according to claim 5. The solution to the problem concerning the arrangement for compressing refrigerant is therefore an arrangement for compressing refrigerant, comprising a compressor for compressing the refrigerant and an arrangement for separating a lubricant-refrigerant solution, as described above. The arrangement for separating the lubricant-refrigerant solution can be located on the high-pressure side of the compressor, or in alternative embodiments, integrated into the compressor. It serves to reliably separate the lubricant-refrigerant solution into two phases: liquid refrigerant and liquid lubricant, or a refrigerant-poor and lubricant-rich phase, and a refrigerant-rich and lubricant-poor phase. In possible embodiments, the lubricant-refrigerant solution flows in one direction, and the arrangement further comprises a liquid separator, in particular a lubricant separator, and more specifically an oil separator, which is in fluid communication with the arrangement for separating the lubricant-refrigerant solution and which is arranged upstream of the arrangement for separating the lubricant-refrigerant solution. In other words, the arrangement optionally comprises a liquid separator in which a mixture of the (liquid) lubricant-refrigerant solution (which may, for example, be carried in droplet form in the refrigerant or be present as an aerosol) and gaseous refrigerant is separated.Depending on where the liquid separator is located (high-pressure side of the compressor or low-pressure side; preferably the liquid separator is located on the high-pressure side of the compressor), the separated gaseous refrigerant can, for example, be fed into a refrigeration circuit, while the separated (liquid) lubricant-refrigerant solution can be fed to the arrangement for separating the lubricant-refrigerant solution (liquid-liquid separation). The separating device optionally has a first outlet for discharging the first phase, wherein the compressor has a suction side and / or a lubricant supply, and wherein the first outlet of the separating device is in fluid communication with the compressor, in particular the suction side and / or the lubricant supply of the compressor. As explained above, this allows the lubricant-refrigerant solution, separated into two phases, to be used in the most optimal way possible. A refrigerant-rich phase, or a phase consisting solely of refrigerant, can be fed into a refrigeration circuit, while a lubricant-rich phase, or a phase consisting solely of lubricant, can be fed into a lubrication circuit, particularly a compressor lubrication circuit. However, especially in the case of an arrangement where the compressor is an oil-flooded compressor, the lubricant-rich phase, or a phase consisting solely of lubricant, can also be fed to a suction side of the compressor (possibly after depressurization). The compressor can optionally be an oil-flooded screw compressor or a reciprocating compressor. Lubrication plays a crucial role, especially with these two compressor types, making a lubricant with the best possible lubricating properties (i.e., without dissolved refrigerant or with a low proportion of dissolved refrigerant) desirable. The low-lubricant phase can be introduced, particularly in an oil-flooded screw compressor, shortly before the end of the compression process, especially via a refrigerant injection port. The aspect of the task that concerns a refrigeration cycle is solved by a refrigeration cycle with an arrangement for compressing refrigerant, as described above. The liquid separator can have a liquid separator inlet and a liquid separator gas outlet. Furthermore, the refrigeration circuit can have a second heat exchanger, in particular a condenser, with a second heat exchanger inlet and a second heat exchanger outlet, an expansion device, in particular an expansion valve, with an expansion device inlet and an expansion device outlet, and a third heat exchanger, in particular an evaporator, with a third heat exchanger inlet and a third heat exchanger outlet. The compressor can also have a compressor outlet for discharging compressed refrigerant, and the compressor outlet can be in fluid communication with the liquid separator inlet, while the liquid separator gas outlet can be in fluid communication with the second heat exchanger inlet.The second heat exchanger outlet can be in fluid communication with the expansion element inlet, while the expansion element outlet can be in fluid communication with the third heat exchanger inlet, and the third heat exchanger outlet can be in fluid communication with a compressor inlet. The liquid separator may further have a liquid separator liquid outlet which is in fluid communication with the arrangement for separating the lubricant-refrigerant solution, in particular the temperature adjustment device thereof. The arrangement for separating the lubricant-refrigerant solution, in particular the separating device, may further have a second outlet for discharging the second phase, wherein the second outlet of the device for separating the lubricant-refrigerant solution is in fluid communication with the expansion organ inlet. The aforementioned design details result in a refrigeration cycle that can be operated energy-efficiently. Back-expansion can be reduced, particularly when using the refrigerant injection port to supply the lubricant-poor, i.e., refrigerant-rich, phase. Optionally, the refrigerant used can be a natural refrigerant, in particular ammonia or CO2, or propane or pentane. Natural refrigerants are available in large quantities and have a significantly lower global warming potential than synthetic refrigerants. The described features can be implemented individually or in any combination. The invention is described below by way of example with reference to the accompanying drawing and one embodiment. Further optional features of the invention are also specified in the following figure description. In the drawings, Fig. 1 shows an embodiment of a refrigeration circuit according to the invention, which includes an embodiment of an arrangement according to the invention for compressing refrigerant, wherein the refrigeration circuit or the arrangement for compressing refrigerant includes an embodiment of an arrangement according to the invention for separating a lubricant-refrigerant solution. Fig. 1 shows, as already explained above, an embodiment of a refrigeration circuit 10 according to the invention, which includes an embodiment of an arrangement 12 according to the invention for compressing refrigerant, wherein the refrigeration circuit 10 or the arrangement 12 for compressing refrigerant includes an embodiment of an arrangement 14 according to the invention for separating a lubricant-refrigerant solution. The arrangement 14 for separating the lubricant-refrigerant solution, in the embodiment described here, is an arrangement for separating an oil-refrigerant solution; that is, in the embodiment described here, oil is used as the lubricant. Furthermore, ammonia is used as the refrigerant in the present embodiment. The oil-refrigerant solution being separated is in a liquid state. The separation occurs into a first liquid phase and a second liquid phase that differs from the first liquid phase in its composition (and also density). When ammonia is used as a refrigerant and oil as a lubricant, the oil-refrigerant solution separates into a first liquid phase, which is low in refrigerant and rich in lubricant, and a second liquid phase, which is rich in refrigerant and low in lubricant. A complete separation of the two components, oil and ammonia, is not possible, but a near-complete separation into the aforementioned low-refrigerant, high-lubricant first phase and the high-refrigerant, low-lubricant second phase is. In alternative embodiments where other refrigerants and / or lubricants are used, a complete separation of the lubricant-refrigerant solution is also conceivable. The arrangement 14 for separating the oil-refrigerant solution includes a temperature adjustment device in the form of a first heat exchanger 16. The first heat exchanger 16, which has a first heat exchanger inlet 18 for supplying the oil-refrigerant solution and a first heat exchanger outlet 20 for discharging the oil-refrigerant solution, is designed to bring the oil-refrigerant solution (oil-ammonia solution) to a predetermined or desired temperature at which the first liquid phase and the second liquid phase, which differs from the first liquid phase, coexist or exist in coexistence. It should be explicitly emphasized once again that the first phase and the second phase into which the solution is separated are both liquid phases, as is the initial phase, i.e. the oil-refrigerant solution (generally the lubricant-refrigerant solution). The arrangement 14 further comprises a separating device 22 for separating the at least two different liquid phases, i.e., the arrangement 14 comprises a liquid-liquid separating device. In the embodiment described and shown in Fig. 1, the separating device 22 comprises a liquid-liquid decanter 24. The separating device 22 further comprises a separating device inlet 26 for supplying the oil-ammonia solution, as well as a first separating device outlet 28 for discharging the first phase (refrigerant-poor and lubricant-rich phase, i.e., ammonia-poor and oil-rich phase) and a second separating device outlet 30 for discharging the second phase (refrigerant-rich and lubricant-poor phase, i.e., ammonia-rich and oil-poor phase). In alternative embodiments, the separating device 18 may include a different centrifuging device or a scraper plate for separating the first phase from the second phase. Phase separation, i.e., the separation of the first phase from the second phase, is usually achieved by exploiting the different densities of the first and second phases. In alternative embodiments, water can be used as a lubricant, for example. In alternative embodiments, all refrigerants known for the respective application, as well as those developed in the future, are conceivable. These can be broadly categorized into natural and synthetic refrigerants. Examples of synthetic refrigerants include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons and hydrofluorocarbons (HFCs and HFCs). Examples of natural refrigerants include ammonia (NH3), propane, butane, and carbon dioxide (CO2). It should be noted that the above list is not exhaustive and makes no claim to completeness. When ammonia is used as a refrigerant and oil as a lubricant, the oil-refrigerant solution separates into a first liquid phase, which is low in refrigerant and rich in lubricant, and a second liquid phase, which is rich in refrigerant and low in lubricant. A complete separation of the two components, oil and ammonia, is not possible, but a near-complete separation into the aforementioned low-refrigerant, high-lubricant first phase and the high-refrigerant, low-lubricant second phase is. In alternative embodiments where other refrigerants and / or lubricants are used, a complete separation of the lubricant-refrigerant solution is also conceivable, i.e., a separation of the lubricant-refrigerant solution into a phase that consists exclusively of refrigerant or exclusively of refrigerant with low “lubricant impurities”, and a phase that consists exclusively of lubricant or exclusively of lubricant with low “refrigerant impurities”. The refrigeration circuit 10 further comprises a compressor in the form of an oil-flooded screw compressor 32 for compressing the refrigerant, which has a compressor inlet 34 for supplying the refrigerant to be compressed (also referred to as the suction side) and a compressor outlet 36 for discharging the compressed refrigerant (also referred to as the high-pressure side or pressure side). The screw compressor 32, together with the arrangement 14 for separating the lubricant-refrigerant solution, i.e., the oil-ammonia solution, is part of the arrangement 12. In alternative embodiments, the use of other compressors, in particular for example reciprocating compressors or scroll compressors, is possible. The arrangement 12 and thus the refrigeration circuit 10 further includes a liquid separator, in the form of an oil separator 38, which has a liquid separator inlet in the form of an oil separator inlet 40, a liquid separator gas outlet in the form of an oil separator gas outlet 42 and a liquid separator liquid outlet in the form of an oil separator liquid outlet 44. The refrigeration circuit 10 further comprises a second heat exchanger 46 in the form of a condenser with a second heat exchanger inlet 48 (condenser inlet) and a second heat exchanger outlet 50, an expansion element 52 in the form of an expansion valve, with an expansion element inlet 54 and an expansion element outlet 56, and a third heat exchanger 58 in the form of an evaporator, with a third heat exchanger inlet 60 and a third heat exchanger outlet 62. In the refrigeration circuit 10, the compressor outlet 36 and the oil separator inlet 40 are in fluid communication; that is, refrigerant compressed in the oil-flooded screw compressor 32 is fed to the oil separator 38 via the compressor outlet 36 and the oil separator inlet 40. The compressed refrigerant fed to the oil separator 38 contains lubricant, i.e., oil, which is used to lubricate the compressor and to seal it during the compression process. The oil can be carried along in droplet form or often forms an aerosol. In the oil separator, the liquid oil or the oil separated as an aerosol is separated from the compressed refrigerant (ammonia), which is present in gaseous form under high pressure. The oil-free refrigerant is fed via the oil separator gas outlet 42 and the second heat exchanger inlet 48, which are in fluid communication with each other, to the second heat exchanger 46, which functions as a condenser. In the second heat exchanger 46, the gas is condensed, i.e., converted into a liquid state, with heat being removed. After the refrigerant condenses, it is fed to the expansion element 52 via the second heat exchanger outlet 50 and the expansion element inlet 54, which are in fluid communication with each other, where it is expanded and thereby cooled while simultaneously reducing the pressure. After expansion, the refrigerant passes through the expansion organ outlet 56 and the third heat exchanger inlet 60, which are in fluid communication with each other, into the third heat exchanger 58, where it is evaporated while absorbing energy. In its evaporated state, the refrigerant is then fed to the screw compressor 32 for recompression via the third heat exchanger outlet 62 and the compressor inlet 34, which are in fluid communication with each other. The liquid separated in the oil separator 38 consists of oil and refrigerant dissolved therein, in the described embodiment therefore an oil-ammonia solution. The oil-ammonia solution is fed to the first heat exchanger 16 via the oil separator liquid outlet 44 and the first heat exchanger inlet 18. In the first heat exchanger, the oil-ammonia solution is brought to a predetermined temperature, which depends on the components of the solution (i.e., oil and ammonia), at which the oil-ammonia solution (generally the lubricant-refrigerant solution) separates into two phases of different composition, namely the first phase and the second phase already explained above. The temperature selection can also take into account the concentrations of the components in solution and, if applicable, a desired composition of the first phase and the second phase. The liquid, separated into two phases, is then fed (in its separated state, i.e., in a state of coexistence of the first and second phases) via the first heat exchanger outlet 20 and the separation device inlet 26 to the separation device 22, where the first phase is separated from the second phase. The liquid-liquid decanter 24 serves this purpose. The first phase (low-refrigerant, high-lubricant phase) is then fed to the screw compressor 32 via the first separating device outlet 28, where the supplied high-lubricant phase is used for lubrication purposes, i.e., fed into a lubrication circuit of the screw compressor 32. Alternatively, the first phase could also be fed to the compressor inlet 34 and then serve for sealing during the compression process. The second phase (refrigerant-rich, lubricant-poor phase, i.e., ammonia-rich and oil-poor phase) is fed via the second separating device outlet 30 for the discharge of the second phase and the expansion element inlet 54 to the expansion element 52, where the ammonia-rich and oil-poor fluid is expanded and then, like the remaining refrigerant, is fed to the third heat exchanger, etc. In alternative embodiments, the second phase can also be fed to the third heat exchanger. If the screw compressor has an economizer, the second phase can also be fed to the compressor's economizer (indirectly via an evaporator) or directly, provided that evaporation is ensured in the supply lines or in a collection volume, etc. Preferably, however, the second phase is fed to the refrigerant injection port. Finally, it should be noted that, although the invention is described with reference to an embodiment with fixed combinations of features, it also includes other conceivable advantageous combinations, as specified in particular, but not exhaustively, by the dependent claims. All features disclosed in the application documents are claimed as essential to the invention insofar as they are novel, individually or in combination, compared to the prior art. Reference symbol list: 10 Refrigeration circuit 12 Refrigerant compression arrangement 14 Lubricant-refrigerant solution separation arrangement 16 First heat exchanger 18 First heat exchanger inlet 20 First heat exchanger outlet 22 Separation device 24 Liquid-liquid decanter 26 Separation device inlet 28 First Separation device outlet 30 Second Separation device outlet 32 ​​Screw compressor 34 Compressor inlet 36 Compressor outlet 38 Oil separator 40 Oil separator inlet 42 Oil separator gas outlet 44 Oil separator liquid outlet 46 Second heat exchanger 48 Second heat exchanger inlet 50 Second heat exchanger outlet 52 Expansion device 54 Expansion device inlet 56 Expansion device outlet 58 Third heat exchanger 60 Third heat exchanger inlet 62 Third heat exchanger outlet QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature DE 10 2013 020 532 A1

[0005]

Claims

Arrangement (14) for separating a lubricant-refrigerant solution, in particular an oil-refrigerant solution, into at least one first liquid phase and a second liquid phase different from the first liquid phase, wherein the arrangement (14) comprises: - a temperature adjustment device (16) configured to bring the lubricant-refrigerant solution to a predetermined temperature at which the at least one first liquid phase and the second liquid phase different from the first liquid phase are formed, and - a separation device (22) for separating the at least two different liquid phases. Arrangement (14) according to one of the preceding claims, wherein the first liquid phase is a refrigerant-poor and lubricant-rich phase and wherein the second liquid phase is a refrigerant-rich and lubricant-poor phase. Arrangement (14) according to one of the preceding claims, wherein the temperature adjustment device (16) is a first heat exchanger (16). Arrangement (14) according to one of the preceding claims, wherein the arrangement (14) comprises a liquid-liquid decanter (24), a centrifuge or a scraper plate. Arrangement (12) for compressing refrigerant, wherein the arrangement (12) comprises: a compressor for compressing the refrigerant and an arrangement (14) for separating a lubricant-refrigerant solution according to any of the preceding claims. Arrangement (12) according to claim 5, wherein the lubricant-refrigerant solution flows in a flow direction and the arrangement (12) further comprises a liquid separator (38), in particular a lubricant separator, and further in particular an oil separator (38), which is in fluid communication with the arrangement (14) for separating the lubricant-refrigerant solution and which is arranged upstream of the arrangement (14) for separating the lubricant-refrigerant solution. Arrangement (12) according to claim 5 or 6, wherein the separating device (22) has a first outlet (28) for discharging the first phase, wherein the compressor (32) has a suction side and / or a lubricant supply, and wherein the first outlet (28) of the separating device (22) is in fluid communication with the compressor, in particular the suction side and / or the lubricant supply of the compressor. Arrangement according to one of claims 5 to 7, wherein the compressor is an oil-flooded screw compressor (32) or a reciprocating compressor. Refrigeration circuit (10) comprising an arrangement (12) according to one of claims 5 to 8. Refrigeration circuit (10) according to claim 9, wherein the arrangement (12) is an arrangement (12) according to any one of claims 6 to 8, wherein the liquid separator (38) has a liquid separator inlet (40) and a liquid separator gas outlet (42), wherein the refrigeration circuit (10) further comprises a second heat exchanger (46), in particular a condenser, with a second heat exchanger inlet (48) and a second heat exchanger outlet (50), an expansion element (52), in particular an expansion valve, with an expansion element inlet (54) and an expansion element outlet (56), and a third heat exchanger (58), in particular an evaporator, with a third heat exchanger inlet (60) and a third heat exchanger outlet (62), the compressor (32) further comprising a compressor outlet (36) for discharging compressed refrigerant, - the compressor outlet (36) of the compressor with the Liquid separator inlet (40) is in fluid communication,The liquid separator outlet (42) is in fluid communication with the second heat exchanger inlet (48), the second heat exchanger outlet (50) is in fluid communication with the expansion element inlet (54), the expansion element outlet (56) is in fluid communication with the third heat exchanger inlet (60), and the third heat exchanger outlet (62) is in fluid communication with a compressor inlet (34). Refrigeration circuit (10) according to claim 9 or 10, wherein the arrangement (12) is an arrangement (12) according to one of claims 6 to 8 and wherein the liquid separator (38) has a liquid separator liquid outlet (44) which is in fluid communication with the arrangement (14) for separating the lubricant-refrigerant solution, in particular the temperature adjustment device (16) thereof. Refrigeration circuit (10) according to claim 9 or 10, wherein the separating device (22) has a second outlet (30) for discharging the second phase, wherein the second outlet (30) of the separating device (22) is in fluid communication with the expansion organ inlet (54). Refrigeration circuit (10) according to one of claims 9 to 12, wherein the refrigerant is a natural refrigerant, in particular ammonia or CO2 or propane or pentane.

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