Coolant circuit and method for operating a cooling system

Abstract

The present invention relates to a coolant circuit that comprises at least one evaporator and compressor. More specifically, the present invention relates to a cooling circuit (10) in which a coolant is conducted from a gas cooler (12) via a first injection valve (18) to a first evaporator (20), and the coolant is furthermore conducted from the gas cooler (12) to a second injection valve (22) and via the second injection valve (22) to a second evaporator (24), wherein a higher pressure prevails at the second evaporator (24) than at the first evaporator (20), and the coolant is conducted from the first evaporator (20) via a discharge line to a first compressor (34), and wherein the coolant is conducted from the second evaporator (24) via a second compressor (30) to the first compressor (34), characterized in that the second compressor (30) is connected to an oil separator (32), and oil that has been separated off in the oil separator (32) is used for lubricating the first compressor (34). The invention also relates to a corresponding method.

Description

[0001] COOLANT CIRCUIT AND METHOD FOR OPERATING A COOLING SYSTEM

[0002] Field of the invention

[0003] The present invention relates to a coolant circuit comprising at least one evaporator and compressor. The coolant comprises a lubricant that can be separated using an oil separator. The invention also relates to a corresponding method.

[0004] Background of the invention

[0005] WO 2023 / 073020 A1 discloses a separation device, a compressor with a separation device, and a refrigeration system with a separation device. This publication relates to the separation of a lubricating medium from a refrigerant. A separation device with a cyclone chamber is used for this purpose.

[0006] The present invention also concerns the separation of a lubricant from a refrigerant. It is not concerned with the specific physical structure of a separation device, but rather with the arrangement of such a device in a refrigeration circuit.

[0007] The present invention therefore aims to improve problems of the prior art, including those that have so far been addressed primarily with regard to the constructive optimization of a separation device.

[0008] The present invention aims to provide an efficient and reliable cooling circuit in a simple, economical manner. This object is achieved by a cooling circuit according to claim 1.

[0009] Advantageous further developments are specified in the subclaims.

[0010] Further description

[0011] The present invention generally relates to a cooling circuit, i.e., a circuit that carries a coolant and to which the coolant is exposed to various pressures and / or temperatures. The coolant circuit should comprise at least a first injection valve and a first evaporator. The coolant circuit should further comprise at least two compressors.

[0012] The precise design of the injection valve(s) is not relevant to the present invention; they can generally be valves or flow components. The precise design of the compressors is also not relevant to the present invention; they can generally be valves or flow components that compress the coolant and therefore have a low-pressure side and a high-pressure side.

[0013] As a general rule, the coolant circuit will also include a gas cooler. Alternatively to or in addition to a gas cooler, another component can be used that works effectively with an evaporator and can generally influence the temperature or pressure of the coolant in a suitable manner.

[0014] Typically, a suitable cooling circuit can be constructed as follows:

[0015] The coolant is fed from a gas cooler (directly or indirectly, possibly from the medium-pressure tank) via a first injection valve to a first evaporator. Suitable lines are provided for this purpose. The coolant is then fed from the gas cooler to a second injection valve. The injection valves can be arranged in parallel on a line downstream of the gas cooler. Alternatively, the two injection valves could also be connected to the gas cooler via separate lines.

[0016] The coolant can be supplied to the injectors via a phase separator. This component separates a liquid and a gaseous coolant phase. A medium-pressure tank with appropriate outlets is suitable for this purpose.

[0017] From the first injector, the coolant is directed to a first evaporator, and from the second injector, the coolant is directed to a second evaporator. The second evaporator should be at a higher pressure than the first evaporator.

[0018] A typical refrigeration circuit consists of a first circuit for cooling a row of refrigerated counters and a second circuit for cooling a row of freezer counters. The second circuit is therefore also called a deep-freeze circuit. To achieve deep cooling, the second circuit operates at a higher pressure.

[0019] It is advisable to have a pressure of between 10 and 40 bar, typically 30 bar, between the first injection valve and the first evaporator.

[0020] The pressure between the second injector and the second compressor is typically between 60 and 90 bar, often 80 bar. (The unit bar is used throughout; it can be converted to the current SI unit Pascal; 1 bar is equal to 10,000 Pascals.)

[0021] The refrigerant is fed from the second evaporator via a second compressor to the first compressor. This has the advantage of allowing pressure adjustment between the circuits, meaning the pressure can be increased before the refrigerant is fed to the low-pressure side of the first compressor.

[0022] According to the present invention, however, the coolant is not fed directly from the second compressor to the low-pressure side of the first compressor, but is first fed to an oil separator. The oil separator is capable of separating lubricating oil residues, which are typically carried in the coolant, from the coolant. This has the advantage that the first compressor compresses purer coolant. This, in turn, will generally increase the reliability and service life of the compressor. Here, lubricating oil is generally referred to, but lubricating oil should refer to any lubricant and, in general, to substances carried in the coolant.

[0023] The present invention provides that the oil is not only separated but also collected in the oil separator. The oil separator thus also functions as an oil collector. The collected oil is used to lubricate at least one compressor. According to the invention, it should be used at least to lubricate the second compressor. It is expedient if the oil can also be used to lubricate the first compressor.

[0024] The invention also relates to a method, namely a method for operating a cooling system, which has a gas cooler (12), a first injection valve (18), a first evaporator (20), a second injection valve (22), a second evaporator (24), a first compressor (34), a second compressor (30), and an oil separator (32), and in which a coolant is guided from a gas cooler (12) via a first injection valve (18) to a first evaporator (20), and the coolant is guided from the gas cooler (12) further to a second injection valve (22) and via the second injection valve (22) to a second evaporator (24), wherein a higher pressure is present at the second evaporator (24) than at the first evaporator (20), and the coolant is guided from the first evaporator (20) via a discharge line to a first compressor (34), and wherein the coolant is guided from the second evaporator (24) via a second compressor (30) is led to the first compressor (34),characterized in that the second compressor (30) is connected to an oil separator (32) and oil separated in the oil separator (32) is used to lubricate the first compressor (34).

[0025] Further features and advantages of the invention will become apparent from the following drawings and the associated description.

[0026] In the figures and the accompanying descriptions, features of the invention are described in combination. However, these features can also be encompassed by an inventive subject matter in other combinations. Each disclosed feature is therefore also to be considered as disclosed in technically reasonable combinations with other features. Some of the figures are slightly simplified and schematic.

[0027] Fig. 1 shows a schematic representation of the coolant circuit according to the invention;

[0028] Fig. 2 shows a coolant circuit according to the prior art;

[0029] Fig. 3 shows a schematic representation of the geometric

[0030] Arrangement of oil separator and first compressor

[0031] Fig. 1 schematically illustrates the coolant circuit 10. The gas cooler 12 can be considered the starting point of the coolant circuit. The coolant is fed to the high-pressure valve 14. From there, the pressure is reduced and it is fed into the medium-pressure tank 16. The medium-pressure tank 16 can separate the liquid and gaseous coolants.

[0032] The coolant (in predominantly liquid form) is then fed to the first injection valve 18. From there, it is fed to the first evaporator 20. The injection valve 18 and the evaporator 20 form the normal cooling section of the circuit.

[0033] From the medium-pressure tank 16, coolant is also supplied to the injection valve 22 and from there to the second compressor 24. The injection valve 22 and the compressor 24 form the low-temperature section of the cooling circuit.

[0034] Additional coolant is fed from the medium-pressure vessel 16 via the valve 26 to a return line 28. This is typically a gaseous coolant portion. The medium-pressure vessel is therefore preferably capable of separating gaseous and liquid coolant. Liquid coolant, in particular, should be fed to the injection valves 18 and 22. In the low-temperature section, the coolant is fed from the second evaporator 24 to the compressor 30 (low-temperature compressor). From there, the coolant is fed further to the oil separator 32. The oil separator 32 also receives coolant from the normal-temperature section. Coolant is fed from the oil separator 32 to the compressor 34. From the compressor 34, the coolant is fed to the second oil separator 36. There, the circuit is closed and the coolant is fed back to the gas cooler 12.

[0035] From the second oil separator 36, separated oil is also returned to the oil separator 32 via the valve 38.

[0036] Coolant, in particular gaseous coolant, is led via the return line 28 to the compressor 34, compressed there, and led back to the gas cooler 12 via the oil separator 36.

[0037] The oil collected in the oil separator 32 is used to lubricate the compressors. For this purpose, the discharge line 40 is provided, which lubricates the compressor 30 via the supply line 42 and the valve 44. Furthermore, the supply line 46 is arranged downstream of the line 40 and lubricates the compressor 34 via the valve 48.

[0038] In this context, the pressure conditions must be considered. Different pressures prevail at different points in the cooling circuit; for simplicity, these are referred to as high pressure, intermediate pressure, elevated intermediate pressure, and low pressure.

[0039] The exact pressure conditions are less relevant to the functioning of the cooling circuit and lubrication than the specific pressure differences. However, the principle is most easily understood using exemplary pressure data. Downstream of the injection valve 22, i.e. on the high-pressure side of the low-temperature refrigeration evaporator 24, a pressure of typically 80 bar prevails. Downstream of the evaporator, this pressure is greatly reduced to approximately 12 bar, so that approximately 12 bar is present on the low-pressure side of the compressor 30. The compressor 30 raises this pressure to a medium-pressure range of approximately 30 bar. This approximately 30 bar then prevails in the area of ​​the oil separator 30. This approximately 30 bar is then also present on the low-pressure side of the compressor or medium-temperature refrigeration compressor 34. The compressor itself increases the pressure again to a high-pressure range, often to approximately 80 bar.Oil separated in the second oil separator 36 can be discharged to the oil separator 32 via the valve 38 at reduced pressure, typically again 30 bar.

[0040] The pressure conditions are important for lubrication capabilities. Oil at a pressure of approximately 30 bar is supplied to compressor 30 via supply line 42 and valve 44. Supplying the oil to this compressor is straightforward, as it is sufficient for the supplied oil pressure to be higher than the pressure on the low-pressure side of the compressor, which is approximately 12 bar.

[0041] The pressure conditions related to the lubrication of compressor 34 are more challenging. Compressor 34 has a pressure of 30 bar on its low-pressure side, which is the same pressure as the pressure level in oil separator 32. However, a higher pressure is required for efficient lubrication of the compressor. This pressure must ensure the supply of oil. (Supplying oil via pumps would be theoretically conceivable, but has proven technically disadvantageous.)

[0042] For effective lubrication, a pressure increase is therefore desirable. A slight pressure increase is sufficient, and the aim is to achieve a higher mean pressure. The present invention has shown that a slight pressure increase is possible through the clever geometric arrangement of the oil separator 32 relative to the compressor 34. The oil separator 32 should be positioned above the compressor 34, and in particular above its pressure supply line. Due to atmospheric pressure, a higher positioning corresponds to a higher pressure, with a height difference of 10 meters corresponding to a pressure difference of approximately 1 bar. It has proven sufficient to choose a height difference of approximately 1 meter, i.e. a pressure difference of 0.1 bar. In this way, the medium-temperature refrigeration compressor 34 can also be lubricated using the oil separator (and oil collector) 32.

[0043] Fig. 2 shows a schematic representation of a known cooling circuit from the prior art. The cooling circuit shown is similar to that in Fig. 1 in some respects; in particular, there is a normal cooling circuit and a low-temperature cooling circuit. Analogous components have been designated analogously in the figure.

[0044] The gas cooler 12 can therefore again be considered the starting point of the cooling circuit. From there, coolant is fed to the high-pressure valve 14. The coolant is then collected at reduced pressure in the medium-pressure tank 16. Portions of the coolant, particularly a gaseous portion, are fed via the medium-pressure valve 26 to the return line 28. The remaining coolant, especially the liquid phase, is fed to the first injection valve and the second injection valve 22. From the first injection valve 18, the coolant is fed further to the first evaporator 20. The injection valve 18 and the evaporator 20 form the essential elements of the normal cooling circuit.

[0045] From the second injection valve 22, the coolant is fed to the second evaporator 24. The injection valve 22 and the evaporator 24 form the essential components of the deep-freeze circuit. The compressor 30 is located downstream of the second evaporator 24 as the compressor in the deep-freeze circuit. From there, the coolant is fed to the first compressor 34. The coolant is thus further compressed in the compressor 34 at a pressure that is higher than the outlet pressure of the second evaporator 24.

[0046] An oil separator 36 is located downstream of the first compressor 34. This oil separator serves to separate any remaining lubricant or oil from the coolant. The separated oil is fed via valve 38 to the oil collector 50. The oil collector 50 supplies the compressors 30 and 34 with lubricating oil. For this purpose, oil is fed via valve 44 to compressor 30 and via valve 48 to compressor 34.

[0047] In contrast to the situation according to the invention shown in Fig. 1, oil is separated exclusively in the oil separator 36. However, this means that a lubricant-oil mixture is fed from the second compressor 30 to the first compressor 34. The first compressor must therefore compress not only coolant, but also coolant significantly enriched with lubricant. This reduces its service life and operational reliability.

[0048] The present invention allows for an improved operating mode for the first compressor 34. However, this requires a novel coolant routing and collection.

[0049] Fig. 3 shows a schematic view of the arrangement of the oil separator 32, particularly relative to the first compressor 34. The oil separator is physically arranged at a greater height. A suitable height difference is in the range of 1 to 2 meters. From the oil separator 32, the oil is guided via lines 40 and 46 and via the valve 48 to the first compressor 34. It is crucial that the compressor is arranged lower in the direction of gravity than the oil compressor 32, and in particular its outlet. This can be achieved in practice by placing the oil compressor 32 on supports. Overall, it can be seen how an advantageous cooling circuit can be designed that enables more reliable and maintenance-free cooling than previous cooling circuits.

[0050]

[0051] 10 Cooling circuit

[0052] 12 gas coolers

[0053] 14 High pressure valve

[0054] 16 medium-pressure vessels

[0055] 18 Injector

[0056] 20 evaporators

[0057] 22 Injector

[0058] 24 evaporators

[0059] 26 Medium pressure valve

[0060] 28 Return line

[0061] 30 compressors

[0062] 32 oil separators

[0063] 34 compressors

[0064] 36 oil separators

[0065] 38 Valve

[0066] 40 Lubricant drainage

[0067] 42 Lubricant supply line

[0068] 44 Valve

[0069] 46 Lubricant supply line

[0070] 48 Valve

[0071] 50 oil collectors

[0072] 52 Line

Claims

1. A cooling circuit (10) in which a coolant is led from a gas cooler (12) via a first injection valve (18) to a first evaporator (20), and the coolant is further led from the gas cooler (12) to a second injection valve (22) and via the second injection valve (22) to a second evaporator (24), wherein a higher pressure is present at the second evaporator (24) than at the first evaporator (20), and the coolant is led from the first evaporator (20) via a discharge line to a first compressor (34), and wherein the coolant is led from the second evaporator (24) via a second compressor (30) to the first compressor (34), characterized in that the second compressor (30) is connected to an oil separator (32), and oil separated in the oil separator (32) is used to lubricate the first compressor (34).

2. Cooling circuit (10) according to the preceding claim, wherein oil separated in the oil separator (32) is used to lubricate the second compressor (30).

3. Cooling circuit (10) according to one of the preceding claims, in which the coolant is led from a gas cooler (12) via a phase separator (16) to the first injection valve (18).

4. Cooling circuit (10) according to one of the preceding claims, in which a pressure of more than 40 bar is present between the second injection valve (22) and the second compressor (24).

5. Cooling circuit (10) according to one of the preceding claims, in which a pressure of between 10 and 40 bar is present between the first evaporator (18) and the first compressor (20).

6. Cooling circuit (10) according to one of the preceding claims, wherein the pressure in the oil separator (32) is higher by a first pressure difference than the pressure applied to the low-pressure side of the first compressor (34).

7. Cooling circuit (10) according to the preceding claim, wherein the first pressure difference is between 0.02 bar and 1.0 bar.

8. Cooling circuit (10) according to the preceding claim, wherein the oil separator (32) is provided at a greater height than the first compressor (34).

9. Cooling circuit (10) according to the preceding claim, wherein the height difference between the oil separator (32) and the first compressor (34) is 0.5 to 2 meters.

10. Cooling circuit (10) according to one of the preceding claims, in which a second oil separator (36) is provided on the high-pressure side of the first compressor (34). 11.A method for operating a cooling system comprising a gas cooler (12), a first injection valve (18), a first evaporator (20), a second injection valve (22), a second evaporator (24), a first compressor (34), a second compressor (30), and an oil separator (32), wherein a coolant is guided from a gas cooler (12) via a first injection valve (18) to a first evaporator (20), and the coolant is guided from the gas cooler (12) further to a second injection valve (22) and via the second injection valve (22) to a second evaporator (24), wherein a higher pressure is present at the second evaporator (24) than at the first evaporator (20), and the coolant is guided from the first evaporator (20) via a discharge line to a first compressor (34), and wherein the coolant is guided from the second evaporator (24) via a second compressor (30) to the first compressor (34). is guided, characterized in that the second compressor (30) is provided with a. Oil separator (32) is connected and oil separated in the oil separator (32) is used to lubricate the first compressor (34).

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