A low-temperature centrifuge unit with ejector return oil concentration and preheating device and control method

Abstract

This invention discloses a low-temperature centrifugal chiller unit with an ejector-driven oil return, concentration, and preheating device and its control method, relating to the field of refrigeration equipment. It aims to solve the problem of direct return of low-temperature oil affecting the oil temperature of the external oil tank. The device includes a centrifugal chiller unit with a primary / secondary compressor, a condenser, and an economizer. The concentration and preheating device connects to a gas-liquid separator via a first ejector to eject oil-rich liquid refrigerant. Internal heat exchange tubes introduce high-temperature liquid refrigerant into the condenser. The bottom output pipe connects to a third ejector and ultimately to the external oil tank. A second ejector can also be installed to recover oil collected from the lower-stage compressor. The control method is divided into modes based on the evaporation temperature: when the temperature is below a first threshold, the first ejector and the second equalizing pipe are opened first for concentration and preheating, then the third ejector is opened for oil return; when the temperature is above the threshold, the third ejector is opened directly. This device can preheat the returned oil, stabilize the oil temperature in the tank, and ensure the unit's operation.

Description

Technical Field

[0001] This solution relates to the field of refrigeration equipment, specifically to a low-temperature centrifugal unit ejector return oil concentration preheating device and control method. Background Technology

[0002] When a centrifugal refrigeration unit or cryogenic unit is running, the shaft systems of the compressor require oil lubrication. The lubricating oil in the oil tank, driven by an oil pump, lubricates rotating parts such as bearings and gears, and also cools these parts, carrying away heat generated by the shaft systems and preventing failure. However, the oil circuit and refrigerant flow path of a centrifugal unit are not completely isolated. During operation, oil leaks into the refrigerant system through seals. This oil, circulating with the refrigerant, eventually accumulates in the gas-liquid separator of the siphon heat exchanger or at the bottom of the evaporator, forming an oil-rich zone. If this oil is not recovered, the oil level in the tank will continuously drop, causing the oil pump to cavitate and triggering a low oil pressure alarm and shutdown. Therefore, it is necessary to recover the mixture of oil and refrigerant from the oil-rich zone of the evaporator back to the oil tank.

[0003] Existing cryogenic units capable of operating below -20℃ are primarily open-type screw chiller units. These units have large-capacity oil separators, and the ejected oil returns to the separator without affecting the oil temperature within this large capacity. However, with technological advancements, centrifugal chiller units capable of operating below -20℃ have been developed. Compared to screw chiller units, centrifugal chiller units lack oil separators, requiring the recovered oil to be transported to an external oil tank. However, the external oil tanks for centrifugal chiller units are compact and small in volume. Directly introducing the cryogenic oil ejected from the oil-rich zone of the evaporator into the external tank would affect the overall oil temperature within the tank, thus impacting the overall operational stability of the unit. Summary of the Invention

[0004] The technical problem to be solved by this invention is to avoid the low-temperature oil drawn back from the oil-rich area of ​​the evaporator from affecting the overall oil temperature of the external oil tank of the centrifuge unit.

[0005] The specific technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] A low-temperature centrifugal unit ejector return oil concentration and preheating device, wherein the centrifugal unit includes a primary compressor, a secondary compressor, a condenser, an economizer, an evaporator, a gas-liquid separator, and an external oil tank;

[0007] The external oil tank is used to supply lubricating oil to all shafts in the system;

[0008] The concentration and preheating device is connected to the gas-liquid separator via the ejector end of the first ejector, and is used to eject the oil-rich liquid refrigerant in the gas-liquid separator.

[0009] The concentration preheating device is equipped with a heat exchange tube, the inlet end of which is connected to the condenser for introducing liquid refrigerant with a high temperature into the condenser.

[0010] The concentration preheating device is provided with an output pipe at the bottom, which is connected to the ejector end of the third ejector. The driving gas end of the third ejector is connected to the economizer, and the output end of the third ejector is connected to the external oil tank.

[0011] Furthermore, the external oil tank is connected to the suction port of the low-stage compressor via the first pressure equalization pipe; the concentration preheating device is connected to the gas-liquid separator via the second pressure equalization pipe.

[0012] Furthermore, the outlet end of the heat exchange tube is connected to the economizer.

[0013] Furthermore, the driving gas end of the first ejector is connected to the economizer.

[0014] Furthermore, it also includes a second ejector, the driving gas end of the second ejector being connected to the economizer, the ejector end of the second ejector being connected to the oil collection point of the low-stage compressor, and the output end of the second ejector being connected to the concentration and preheating device, for ejecting the oil collected at the oil collection point of the low-stage compressor to the concentration and preheating device.

[0015] Furthermore, a demister is provided at the connection between the concentration preheating device and the second equalizing pipe.

[0016] Furthermore, the demister is a wire mesh.

[0017] Furthermore, the first ejector, the second ejector, the third ejector, and the second equalizing tube can all be controlled to switch on / off.

[0018] Furthermore, the method of using the above-mentioned low-temperature centrifuge unit's ejector return oil concentration and preheating device is as follows:

[0019] Ensure that the liquid refrigerant in the condenser continuously flows through the heat exchange tubes of the concentration and preheating device.

[0020] S1. Obtain the system evaporation temperature

[0021] S2. Determine if the evaporation temperature is below the first threshold. If it is, turn on the first ejector and the second equalizing tube, and turn off the third ejector; otherwise, proceed to step S5.

[0022] S3. When the timer reaches the set duration T1, close the second equalizing tube and open the third ejector.

[0023] S4. When the timer reaches the set duration T2, return to step S1;

[0024] S5. Close the second equalizing tube, open the third ejector, and return to step S1.

[0025] Compared with existing technologies, this solution has the following advantages:

[0026] 1. The low-temperature centrifugal chiller unit's ejector return oil concentration preheating device can preheat the ejected low-temperature liquid refrigerant. Compared with direct ejection to the external oil tank, the overall oil temperature of the external oil tank does not fluctuate, and the oil temperature of the entire system will not drop rapidly.

[0027] 2. The ejector control method for oil concentration and preheating based on temperature allows for continuous injection and recovery of oil to the external oil tank when the evaporation temperature is above the first temperature threshold. When the evaporation temperature is below the first temperature threshold, the system operates in concentration and preheating mode to preheat the recovered oil for a longer period. Under the premise that the liquid level in the external oil tank does not affect the system operation, this method can ensure effective oil recovery without affecting the overall oil temperature in the external oil tank. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a low-temperature centrifuge unit that includes a concentration and preheating device;

[0029] Figure 2 This is a schematic diagram of the concentration preheating device of the present invention in the ambient temperature ejector working state.

[0030] Figure 3 This is a schematic diagram of the oil return concentration and preheating state of the concentration and preheating device of the present invention;

[0031] Figure 4 This is a schematic diagram of the low-temperature ejection state of the concentration preheating device of the present invention;

[0032] Figure 5 This is a flowchart illustrating the usage method of the low-temperature centrifuge unit ejector return oil concentration and preheating device of the present invention.

[0033] The following is a list of component names represented by the reference numerals in the attached diagram:

[0034] 1. Primary compressor; 2. Secondary compressor; 3. Condenser; 4. Economizer; 5. Evaporator; 6. Gas-liquid separator; 7. External oil tank; 8. First ejector; 9. Second ejector; 10. Third ejector; 11. First equalizing pipe; 12. Second equalizing pipe; 13. Concentration preheating device; 14. Heat exchanger tube; 15. Demister. Detailed Implementation

[0035] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0036] Example 1:

[0037] refer to Figure 1 The diagram shows a low-temperature centrifuge unit including a concentration and preheating device. The centrifuge unit includes a primary compressor 1, a secondary compressor 2, a condenser 3, an economizer 4, an evaporator 5, a gas-liquid separator 6, and an external oil tank 7.

[0038] The external oil tank 7 is used to supply lubricating oil to all shafts in the system; the external oil tank 7 is connected to the suction port of the low-stage compressor through the first pressure equalization pipe 11;

[0039] The concentration preheating device 13 is connected to the gas-liquid separator 6 via the second equalizing pipe 12. It is connected to the gas-liquid separator 6 through the ejector end of the first ejector 8. The driving gas end of the first ejector 8 is connected to the economizer 4 to eject the oil-rich liquid refrigerant in the gas-liquid separator 6.

[0040] It also includes a second ejector 9, the driving gas end of the second ejector 9 is connected to the economizer 4, the ejector end of the second ejector 9 is connected to the oil collection point of the low-stage compressor, and the output end of the second ejector 9 is connected to the concentration and preheating device 13, so as to eject the oil collected at the oil collection point of the low-stage compressor to the concentration and preheating device 13.

[0041] The concentration preheating device 13 has an output pipe at its bottom, which is connected to the ejector end of the third ejector 10. The driving gas end of the third ejector 10 is connected to the economizer 4, and the output end of the third ejector 10 is connected to the external oil tank 7. A demister 15, which is a wire mesh, is provided at the connection position between the concentration preheating device 13 and the second equalizing pipe 12.

[0042] The concentration preheating device 13 is equipped with a heat exchange tube 14. The inlet end of the heat exchange tube 14 is connected to the condenser 3, and the outlet end of the heat exchange tube 14 is connected to the economizer 4, so as to introduce liquid refrigerant with a higher temperature in the condenser.

[0043] The first ejector 8, the second ejector 9, the third ejector 10, and the second equalizing tube 12 can all control the switching state.

[0044] In this case, the driving gas ends of the first ejector 8, the second ejector 9, and the third ejector 10 are all connected to the economizer 4. This is to ensure that the pressure difference between the driving gas source end and the output end of the ejector is within the optimal operating pressure difference range of the ejector. If this pressure difference is too large or too small, it will affect the ejection effect. The ejectors used in this case are ejectors originally designed for the pressure ratio of a single compressor (to avoid the high cost caused by customization). Relying on the pressure difference between the condenser 3 and the evaporator 5, the oil-rich liquid in the evaporator 5 is ejected to the oil tank. The pressure difference between the condenser 3 and the evaporator 5 is usually below 900 kPa. The cryogenic unit in this embodiment is a dual-compressor series unit. Experimental observation shows that when the pressure difference between the condenser 3 and the evaporator 5 exceeds 1300 kPa, the ejector function disappears. At this time, it is still far from the rated operating point of the unit. Therefore, directly using the pressure difference between the condenser 3 and the evaporator 5 of this unit will not meet the normal ejection and oil return requirements of the unit. Therefore, in this scheme, the driving gas of the ejector needs to be drawn from the economizer 4 so that the ejector can work within its normal ejection pressure difference range.

[0045] Example 2: Method of using the low-temperature centrifuge unit ejector oil return concentration and preheating device as described in Example 1:

[0046] Ensure that the liquid refrigerant at a relatively high temperature (approximately 37°C) inside the condenser 3 continuously flows through the tube side of the heat exchange tube 14 of the concentration and preheating device 13;

[0047] Please refer to Figure 5 As shown,

[0048] S1. Obtain the system evaporation temperature

[0049] S2. Determine if the evaporation temperature is below -7℃. If it is, proceed to the concentration preheating mode; otherwise, skip to step S5. (Reference) Figure 3 As shown, the concentration and preheating mode is as follows: the first ejector 8 is turned on, the second equalizing pipe 12 is turned on, and the third ejector 10 is turned off. The liquid refrigerant injected into the concentration and preheating device 13 from the gas-liquid separator 6 is heated and undergoes a boiling phase change. The gaseous refrigerant returns to the gas-liquid separator 6 through the equalizing port. A demister 15 made of wire mesh is installed at the equalizing port to separate the oil droplets carried by the gaseous refrigerant and return the oil droplets to the concentration and preheating device 13. The connection of the second equalizing pipe 12 also ensures the pressure difference between the driving gas end and the output end of the first ejector 8, ensuring the ejection effect.

[0050] S3. Record the duration of the system's operation in the concentration preheating mode until the set duration T1 (e.g., 4 hours) is reached, then enter the ejector return oil mode. (Refer to...) Figure 4As shown, the ejector oil return mode is to close the second equalizing pipe 12 and open the third ejector 10, so that the mixture of oil and liquid refrigerant at a certain level accumulated at the bottom of the concentration preheating device 13 is ejected and sucked into the external oil tank 7 through the third ejector 10, and the oil temperature of the external oil tank 7 does not fluctuate.

[0051] S4. Record the operating time of the system in ejector return mode until the set time T2 (e.g., 0.5 hours) is reached, then return to step S1;

[0052] Since the first ejector 8 and the second ejector 9 recover leaked oil, the amount cannot be too large. Therefore, after a long preheating period, the accumulated oil can be introduced into the external oil tank 7 through the third ejector 10 in a short time.

[0053] S5, Reference Figure 2 As shown, the second equalizing pipe 12 is closed and the third ejector 10 is opened. The liquid refrigerant injected from the gas-liquid separator 6 into the concentration and preheating device 13 exchanges heat with the liquid refrigerant in the tube. After the temperature rises, it is directly injected into the external oil tank 7. The oil temperature in the oil tank does not fluctuate. Since the temperature of the oil injected back at this time is not too low, it is sufficient to raise it to an appropriate temperature during the process of flowing through the concentration and preheating device 13, so as not to affect the oil temperature in the external oil tank 7. Then, return to step S1.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-temperature centrifugal compressor unit ejection oil concentration preheating device, the centrifugal compressor unit comprising a primary compressor, a secondary compressor, a condenser, an economizer, an evaporator, a gas-liquid separator and an external oil tank; the external oil tank is used to provide lubricating oil to the shafting in the system; characterized in that the concentration preheating device is connected to the gas-liquid separator through the ejection end of the first ejector for ejecting the oil-rich liquid refrigerant in the gas-liquid separator; the concentration preheating device is provided with a heat exchange pipe, the inlet end of the heat exchange pipe is connected to the condenser for introducing the liquid refrigerant in the condenser; the concentration preheating device is provided with an output pipe at the bottom, the output pipe is connected to the ejection end of the third ejector, the drive gas end of the third ejector is connected to the economizer, and the output end of the third ejector is connected to the external oil tank; the concentration preheating device is connected to the gas-liquid separator through the second equalizing pipe, the outlet end of the heat exchange pipe is connected to the economizer, and the drive gas end of the first ejector is connected to the economizer.

2. The cryogenic centrifuge pack ejector oil return concentration pre-heat apparatus of claim 1, wherein, The external oil tank is connected to the low-stage compressor suction port through the first equalizing pipe.

3. A cryogenic centrifuge set ejection oil concentration preheating device according to claim 1 or 2, characterized in that, Further comprising a second ejector, the drive gas end of the second ejector is connected to the economizer, the ejection end of the second ejector is connected to the oil collection place of the low-stage compressor, and the output end of the second ejector is connected to the concentration preheating device for ejecting the oil collected at the oil collection place of the low-stage compressor to the concentration preheating device.

4. The cryogenic centrifuge set ejection oil concentration preheating device according to claim 2, characterized in that, The concentration preheating device is provided with a demister at the connection with the second equalizing pipe.

5. The cryogenic centrifuge set ejection oil concentration preheating device according to claim 4, characterized in that, The demister is a steel wire mesh.

6. The cryogenic centrifuge set ejection oil concentration preheating device according to claim 3, characterized in that, The first ejector, the second ejector, the third ejector and the second equalizing pipe can be controlled in an on-off state.

7. A method of using a low temperature centrifuge set ejector oil return concentration preheating device according to any one of claims 1 to 6: characterized in that, Ensure that the liquid refrigerant in the condenser continuously flows through the heat exchange pipe of the concentration preheating device: S1, acquire the system evaporation temperature; S2, determine whether the evaporation temperature is lower than the first threshold value, if lower than the first temperature threshold value, turn on the first ejector and the second equalizing pipe, and turn off the third ejector; otherwise, jump to step S5; S3, time until reaching the set time T1, turn off the second equalizing pipe and turn on the third ejector; S4, time until reaching the set time T2, return to step S1; S5, turn off the second equalizing pipe, turn on the third ejector, and return to step S1.

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