Oil return pipeline and oil return control method of compressor and single-machine two-stage screw compressor

Abstract

The invention discloses an oil return pipeline of a compressor, an oil return control method and a single-machine two-stage screw compressor. The oil return pipeline of the compressor comprises an oil separator and an oil return header pipe, one end of the oil return header pipe is connected with the oil separator, the other end of the oil return header pipe is divided into a first oil return branch pipe and a second oil return branch pipe, the first oil return branch pipe is connected with an oil return opening of a first-stage rotor of the compressor, and the second oil return branch pipe is connected with an oil return opening of a second-stage rotor of the compressor. The oil return header pipe, the first oil return branch pipe and the second oil return branch pipe are respectively provided with a pressure sensor, and the first oil return branch pipe and the second oil return branch pipe are respectively provided with a first electromagnetic valve and a second electromagnetic valve. The pressure difference between the oil pressure P1 of the oil return main pipe and the pressure PL of the air inlet side of the compressor is used as a parameter for judging the amount of oil needed by the compressor, and the pressure difference is compared with the preset pressure difference, so that the real-time oil supply amount of the compressor needing effective lubrication and cooling is accurately reflected, and it is guaranteed that oil supply to the compressor is safely, timely and accurately adjusted.

Description

Technical Field

[0001] The present invention relates to the technical field of refrigeration compressors, and in particular to an oil return pipeline of a compressor, an oil return control method of the compressor, and a single-machine two-stage screw compressor. Background Art

[0002] During the operation of the compressor, the internal components will generate heat due to friction, so it is necessary to lubricate and cool down the compressor by inputting lubricating oil to ensure the normal operation of the compressor. When the refrigeration compressor is working normally, the lubricating oil will be sucked in and flow with the refrigerant. During this period, the oil vapor mixed with the gaseous refrigerant will be separated and recovered through the oil separator and the return oil pipeline. That is, the return oil pipeline can collect the lubricating oil vapor discharged from the compressor in the oil separator, and then send it back to the compressor through the return oil pipeline, so that the lubricating oil can be circulated in the refrigeration system. The delivery of lubricating oil through the return oil pipeline can keep the compressor with sufficient lubricating oil, maintain the oil balance of the system, and avoid the wear and damage of the compressor caused by insufficient oil and reduce the refrigeration efficiency. Therefore, the return oil pipeline of the refrigeration compressor is an important part of the refrigeration system, and its design and optimization are directly related to the operating reliability and service life of the compressor.

[0003] The single-unit two-stage screw compressor unit has the characteristics of wide theoretical exhaust volume span, low evaporation temperature, and wide temperature coverage. It is widely used in ultra-low temperature quick freezing warehouses, quick freezing tunnels and other places with special requirements for refrigeration systems. The single-unit two-stage screw compressor realizes the two-stage compression of the single compressor, and has the advantage of high compression efficiency compared with the conventional single-stage screw compressor. However, the compressor has an additional set of rotors. In order to achieve smooth operation of the compressor, the oil return volume of the compressor needs to be increased.

[0004] However, the amount of oil return from the compressor affects the performance of the compressor. When the amount of oil return is low, the compressor may overheat and wear due to lack of oil, thereby reducing its service life. When the amount of oil return is high, too much oil will lead to reduced energy efficiency. Therefore, the amount of oil return from the two-stage compressor unit needs to be controlled within an appropriate range. The current oil return method for a single-machine two-stage screw compressor is to select one of the two oil return ports in the compressor to connect to the oil return port (i.e., choose one of two) based on the needs of the whole machine, and the oil return volume is calculated at the beginning of the design of the refrigeration unit, and the diameter of the oil return pipe is calculated based on the oil return volume. Once the diameter of the oil return pipe is determined, the oil return volume of the compressor is fixed, so during operation, it is impossible to adjust the oil return volume in real time according to the needs of the compressor, and it is difficult to meet the requirements of changes in the compressor's work.

[0005] Therefore, how to overcome the defect that the return oil volume of the existing two-stage compressor is constant during operation and cannot be adjusted in real time according to the needs of the compressor is a technical problem that needs to be solved in this field. Summary of the invention

[0006] In order to solve the technical problem that the return oil volume of the existing two-stage compressor cannot be adjusted in real time according to the needs of the compressor during operation, the present invention proposes an oil return pipeline and an oil return control method with adjustable return oil volume during the operation of the compressor, and a single two-stage screw compressor with the oil return pipeline. The control method proposed by the present invention can timely and accurately adjust the return oil volume of the compressor by real-time monitoring of the system load and making real-time judgments based on the pressure difference.

[0007] The present invention provides a two-stage compressor oil return pipeline, including an oil separator, characterized in that it also includes an oil return main pipe with one end connected to the oil outlet of the oil separator, the other end of the oil return main pipe is divided into a first oil return branch pipe and a second oil return branch pipe, the first oil return branch pipe is connected to the oil return port of the first-stage rotor of the compressor, and the second oil return branch pipe is connected to the oil return port of the second-stage rotor of the compressor, the oil return main pipe and the first and second oil return branches are each provided with a pressure sensor, and the first and second oil return branches are respectively provided with a first solenoid valve and a second solenoid valve. The controller can control the opening and closing of the first and second solenoid valves arranged on the first and second oil return branches according to the pressure difference between the oil pressure of the oil return main pipe and the pressure on the intake side of the compressor, thereby accurately controlling in real time whether the respective oil return branches provide oil supply to the first and second rotors of the two-stage compressor.

[0008] Preferably, the oil return main pipe is provided with a start stop valve, and the first and second oil return branch pipes are provided with a first end stop valve and a second end stop valve, respectively. The oil circuit is shut off through the start and end stop valves in the oil return pipeline, i.e., through the start stop valve, the first end stop valve, and the second end stop valve, so as to overhaul or replace the components in the oil return pipeline.

[0009] Preferably, an oil filter is provided on the oil return main pipe, which can be used to filter impurities in the liquid in the oil return pipeline to prevent the compressor rotor from being worn or even damaged due to the entry of impurities.

[0010] Preferably, the oil return main pipe is also provided with an oil flow switch, which can be used to determine whether oil flows in the oil return pipeline.

[0011] Preferably, the start stop valve, the first end stop valve, the second end stop valve, the oil flow switch, the first solenoid valve, the second solenoid valve, the oil return main pipe, and the first and second oil return branch pipes are each provided with a pressure sensor and are all connected to the controller by telecommunication. In addition to being used to control the start and end stop valves in the oil return pipeline, that is, to shut off the oil circuit through the start stop valve, the first end stop valve, and the second end stop valve, so as to overhaul or replace components in the oil return pipeline, the controller can also be used to monitor the system load in real time, and compare and judge the pressure difference of the compressor unit with the preset pressure difference value, so as to intelligently adjust the oil return volume of the two-stage compressor through different shut-off combinations of the first solenoid valve and the second solenoid valve.

[0012] Preferably, the internal flow passages of the oil return port of the first stage rotor and the oil return port of the second stage rotor of the two-stage compressor are interconnected, that is, it can be ensured that when any oil return branch pipe is opened for oil supply, oil can be supplied for lubrication and cooling of the first and second rotors of the two-stage compressor.

[0013] Preferably, the diameters of the first and second oil return branches are one large and one small, and the diameter ratio of the two oil return branches is 1.25: 1. By supplying oil through different oil return pipe diameters, the oil supply amount can be accurately adjusted according to the real-time oil supply status of the compressor to ensure that the oil supply amount is neither too much nor too little.

[0014] Preferably, the terminal stop valve, pressure sensor and solenoid valve on the first and second oil return branches are connected to their respective oil return pipelines in sequence starting from the rotor oil return port of the compressor. Such installation is convenient for controlling the oil supply of the oil return branch, convenient for observing the oil pressure of the oil return branch, and can also meet the customary installation. According to different requirements, the front and back order of each component can also be changed.

[0015] Preferably, the start stop valve, oil filter, oil flow switch and pressure sensor on the oil return main pipe are connected to the oil return main pipe in sequence from the oil outlet of the oil separator. Such installation is convenient for controlling the oil supply amount of the oil return main line, convenient for observing the oil supply status and oil pressure of the oil return main line, and can also meet the customary installation. According to different requirements, the front and back order of each component can also be changed.

[0016] The present invention provides a single-unit two-stage screw compressor, which comprises the oil return pipeline of the two-stage compressor.

[0017] The oil return control method of the two-stage compressor provided by the present invention comprises the following steps:

[0018] When P1-PL<ΔP, the oil return main pipe, the first oil return branch pipe and the second oil return branch pipe are all open circuits;

[0019] When ΔP+X<P1-PL, the oil return main pipe is open, the large diameter oil return branch pipe of the first and second oil return branch pipes is closed, and the small diameter oil return branch pipe is open;

[0020] When ΔP≤P1-PL≤ΔP+X, the oil return branch pipe with a larger diameter among the first and second oil return branch pipes is an open circuit, and the oil return branch pipe with a smaller diameter is a closed circuit;

[0021] Among them, ΔP is the preset pressure difference; X is the preset pressure difference coefficient; P1 is the oil pressure of the oil return main pipe; PL is the suction side pressure of the two-stage compressor.

[0022] During the operation of the compressor unit, when P1-PL approaches the preset pressure difference value ΔP, it means that the return oil volume at this time is the return oil volume under the optimal operating condition of the compressor. When the compressor return oil volume is greater than the return oil volume under the optimal operating state and is within a certain range, the heat exchange of the compressor is not significantly affected. At this time, the pressure difference fluctuation range of P1-PL is ΔP+X (generally X is 100KPa). When the unit is running, the pressure difference P1-PL is used as a parameter to judge how much oil the compressor needs to supply in real time, and the oil pressure P1 of the return oil main pipe is kept changing with the change of the intake side pressure PL. Always maintain the oil pressure P1 of the return oil main pipe greater than the pressure difference of the intake side pressure PL within a reasonable range, so as to accurately reflect the real-time oil supply required by the compressor for effective lubrication and cooling, and ensure safe, timely and accurate adjustment of the oil supply to the compressor.

[0023] Preferably, the oil return control method further comprises the following steps:

[0024] When ΔP+X<P1-PL, the oil return main pipe is open, the first oil return branch pipe is closed, and the second oil return branch pipe is open;

[0025] When ΔP≤P1-PL≤ΔP+X, the oil return main pipe is open, the first oil return branch pipe is open, and the second oil return branch pipe is closed;

[0026] Wherein, the diameter of the first oil return branch pipe is larger than the diameter of the second oil return branch pipe.

[0027] The present invention connects the oil separator with the corresponding oil return ports of the first and second stage rotors of the two-stage compressor through the oil return main pipe and the first and second oil return branches. In addition, pressure sensors are respectively arranged on the oil return main pipe and the first and second oil return branches, and the first and second solenoid valves are correspondingly arranged on the first and second oil return branches. The pressure difference (P1-PL) between the oil pressure P1 of the oil return main pipe and the pressure PL on the intake side of the two-stage compressor is used as a parameter for judging how much oil the compressor needs to supply in real time, and the oil pressure P1 of the oil return main pipe is kept changing with the change of the intake side pressure PL. That is, when it is judged that P1-PL<ΔP (preset pressure difference), the oil return volume of the compressor is small, and the oil return main pipe and the first and second solenoid valves are opened at the same time to increase the oil return volume; when ΔP+X (X is the preset pressure difference coefficient)<P1-PL, the oil return volume of the compressor is too much, the large diameter oil return branch is closed, and the oil supply of the small diameter oil return branch is opened to reduce the oil return volume; when ΔP≤P1-PL≤ΔP+X, the oil supply of the large diameter oil return branch can meet the demand, that is, the large diameter oil return branch maintains the open state, and the oil supply of the small diameter oil return branch is shut off. In this way, the oil pressure P1 of the oil return main pipe is always maintained greater than the pressure difference of the intake side pressure PL within a reasonable range. In order to accurately reflect the real-time oil supply required for effective lubrication and cooling of the compressor, and ensure safe, timely and accurate adjustment of the oil supply to the compressor. Through the optimization design of the oil return pipeline structure, through real-time monitoring of the system load, and based on the comparison and judgment of the pressure difference, the intelligent adjustment of the compressor return oil volume is realized. To achieve efficient oil return of a single two-stage compressor unit, increase the stability and service life of the compressor, and improve the overall performance and reliability of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the appearance of a single-unit two-stage screw compressor;

[0029] Figure 2 It is a cross-sectional schematic diagram of a single two-stage screw compressor;

[0030] Figure 3 A schematic diagram of the oil return pipeline structure of a single-unit two-stage screw compressor provided by the present invention;

[0031] Figure 4 for Figure 3 The schematic diagram of the first solenoid valve and the second solenoid valve in the oil return line being opened simultaneously to supply oil is shown;

[0032] Figure 5 for Figure 3 The schematic diagram of the first solenoid valve in the oil return line being closed and the second solenoid valve being opened to supply oil;

[0033] Figure 6 for Figure 3 The schematic diagram of the second solenoid valve in the oil return line shown is closed and the first solenoid valve is opened to supply oil;

[0034] Figure 7 It is a flow chart of the oil return quantity control method of the two-stage compressor.

[0035] in:

[0036] 1-Oil separator;

[0037] 2-Starting stop valve;

[0038] 3-First end stop valve;

[0039] 4-Second end stop valve;

[0040] 5-Oil filter;

[0041] 6-Oil flow switch;

[0042] 7- first solenoid valve;

[0043] 8- second solenoid valve;

[0044] 9- Single-unit two-stage screw compressor;

[0045] 91-The first stage (low pressure stage) rotor of a single two-stage screw compressor;

[0046] 92-Oil return port of the first stage of a single-unit two-stage screw compressor;

[0047] 93-The second stage (high pressure stage) rotor of a single two-stage screw compressor;

[0048] 94-Oil return port of the second stage of a single-unit two-stage screw compressor;

[0049] 95-compressor housing;

[0050] P1-Oil pressure of the oil return main;

[0051] P2-Oil pressure of the first oil return branch;

[0052] P3-Oil pressure of the second oil return branch;

[0053] PL - pressure on the intake side of the two-stage compressor;

[0054] PH - Pressure on the discharge side of a two-stage compressor. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention is described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the following specific embodiments are only used to explain the present invention and do not constitute a limitation to the present invention.

[0056] like Figure 1 , 2As shown, the basic structure of a single double-stage screw compressor 9 provided by the present invention. The compressor includes a housing 95, a motor arranged in the housing in sequence, a first-stage (low-pressure stage) rotor 91 and a second-stage (high-pressure stage) rotor 93. The gaseous refrigerant enters the first-stage rotor 91 through the right-end air intake of the compressor 9 for the first compression, and then passes through the second-stage rotor 93 for the second compression. The double compression is achieved by a single compressor, which has the advantage of high compression efficiency compared with conventional single-stage screw compressors. However, the single-stage two-stage compressor has an additional set of rotors, which will increase friction, wear and heat generation. In order to achieve smooth operation of the compressor, the amount of return oil used for compressor lubrication and cooling needs to be increased. However, the level of the compressor return oil volume affects the performance of the compressor. When the return oil volume is low, the compressor may overheat and wear due to lack of oil, thereby reducing its service life. When the return oil volume is high, too much oil will lead to reduced energy efficiency. Therefore, the return oil volume of the two-stage compressor unit needs to be controlled within an appropriate range.

[0057] In order to keep the oil return volume of a single two-stage screw compressor at a constant level during operation, Figure 1 , 2 3 shows the first embodiment of the oil return pipeline of a single-machine two-stage screw compressor provided by the present invention. The basic structure of this embodiment includes an oil separator 1, and also includes an oil return main pipe whose left end is connected to the oil outlet of the oil separator 1, and the right end of the oil return main pipe is divided into a first oil return branch pipe and a second oil return branch pipe. The first oil return branch pipe is connected to the oil return port 92 of the first-stage rotor 91 of the compressor 9, and the second oil return branch pipe is connected to the oil return port 94 of the second-stage rotor 93 of the compressor. The oil return main pipe is provided with a pressure sensor to read the oil pressure P1 of the oil return main pipe, the first oil return branch pipe is provided with a pressure sensor to read the oil pressure P2 of the first oil return branch, and the second oil return branch pipe is provided with a pressure sensor to read the oil pressure P3 of the second oil return branch. The pressure on the intake side of the compressor is PL, and the pressure on the exhaust side of the compressor is PH. The first oil return branch pipe is provided with a first solenoid valve 7, and the second oil return branch pipe is provided with a second solenoid valve 8. The first and second solenoid valves can be used to control whether oil is supplied to each oil return branch pipe. In this embodiment, the diameters of the first and second oil return branches are one large and one small, that is, the diameter of the first oil return branch is larger than the diameter of the second oil return branch, and the diameter ratio of the oil return branch is 1.25: 1. By supplying oil through different oil return pipe diameters, the oil supply amount can be accurately adjusted according to the real-time oil supply status of the compressor to ensure that the oil supply amount is neither too much nor too little.

[0058] In order to ensure that the single-machine two-stage screw compressor 9 can run efficiently and smoothly, a start stop valve 2 is provided on the return oil main pipe, a first end stop valve 3 is provided on the first return oil branch pipe, and a second end stop valve 4 is provided on the second return oil branch pipe. The oil circuit is shut off by the start and end stop valves in the return oil pipeline, that is, by the start stop valve 2, the first end stop valve 3, and the second end stop valve 4, so as to overhaul or replace the components in the return oil pipeline. An oil filter 5 and an oil flow switch 6 are provided on the return oil main pipe. The oil filter 5 can be used to filter impurities in the liquid of the return oil pipeline to prevent the compressor rotor from being worn or even damaged due to the entry of impurities. The oil flow switch 6 can be used to determine whether there is oil flowing in the return oil pipeline. Obviously, it also includes a controller that maintains telecommunication connection with the start stop valve 2, the first end stop valve 3, the second end stop valve 4, the oil flow switch 6, the first solenoid valve 7, the second solenoid valve 8, and the pressure sensors provided on the return oil main pipe and the first and second return oil branches. In addition to being used to control the start and end stop valves in the return oil pipeline, that is, to shut off the oil circuit through the end stop valve 2, the first end stop valve 3, and the second end stop valve 4 to facilitate maintenance or replacement of components in the return oil pipeline, the controller can also intelligently adjust the return oil volume of the two-stage compressor through real-time monitoring of the system load and comparison and judgment based on the pressure difference of the compressor unit and the preset pressure difference value through different shut-off combinations of the first solenoid valve 7 and the second solenoid valve 8.

[0059] In addition, the internal flow channels of the oil return port of the first stage rotor and the oil return port of the second stage rotor of the double compressor are interconnected. That is, it can be ensured that when any oil return branch is opened for oil supply, the first and second rotors of the two-stage compressor can be supplied with oil for lubrication and cooling. The end stop valves 3, 4, pressure sensors and the first and second solenoid valves 7, 8 on the first and second oil return branches are connected to their respective oil return pipelines in sequence starting from the rotor oil return port of the compressor. Such installation is convenient for controlling the oil supply of the oil return branch, convenient for observing the oil pressure of the oil return branch, and can also meet the customary installation. According to different requirements, the front and back order of each component can also be changed. The start stop valve 2, oil filter 5, oil flow switch 6 and pressure sensor on the oil return main pipe are connected to the oil return main pipe in sequence starting from the oil outlet of the oil separator 1. Such installation is convenient for controlling the oil supply of the oil return main circuit, convenient for observing the oil supply status and oil pressure of the oil return main circuit, and can also meet the customary installation. According to different requirements, the front and back order of each component can also be changed.

[0060] like Figure 4-Figure 7 As shown, the oil return control method of a single-unit two-stage screw compressor provided by the present invention comprises the following steps:

[0061] In this embodiment, the diameter of the first oil return branch pipe is larger than the diameter of the second oil return branch pipe, and the diameter ratio of the two oil return branch pipes is 1.25:1.

[0062] When P1-PL<ΔP, the oil return main pipe and the first and second oil return branches are all in an open circuit state, that is, the first and second oil return branches are both supplying oil to the rotor chamber of the compressor, increasing the oil return amount, such as Figure 4 shown.

[0063] When ΔP+X<P1-PL, the compressor returns too much oil, and the return oil main pipe is open, the first return oil branch pipe with a large diameter is closed, and the second return oil branch pipe with a small diameter is open, reducing the return oil volume. Figure 5 shown.

[0064] When ΔP≤P1-PL≤ΔP+X, the oil supply flow of the large diameter oil return branch pipe meets the demand, that is, the first oil return branch pipe with large diameter is open circuit, and the second oil return branch pipe with small diameter is closed circuit. Figure 6 shown.

[0065] Among them, ΔP is the preset pressure difference; X is the preset pressure difference coefficient, for example, X is 100KPa. According to different situations, different ΔP and X can be preset; P1 is the oil pressure of the oil return main pipe; PL is the suction side pressure of the compressor.

[0066] During the operation of a single two-stage screw compressor unit, when P1-PL approaches the preset pressure difference ΔP, the oil return volume at this time is the oil return volume under the optimal operating condition of the compressor. When the compressor oil return volume is greater than the oil return volume under the optimal operating condition and is within a certain range, the compressor heat exchange is not significantly affected, and the pressure difference value range of P1-PL at this time is ΔP+X. Maintaining the oil supply within this pressure difference range ΔP+X can enable the compressor to operate normally.

[0067] Usually, the fluid flow rate is linearly related to the pressure, that is, when the suction volume increases, the suction pressure (PL) will increase accordingly. Then, when the oil supply flow rate of the oil return main pipe increases, the oil pressure (P1) of the oil return main pipe will increase accordingly. According to the relationship between oil pressure and flow rate, the present invention uses the change of pressure to reflect the change of flow rate.

[0068] When the diameter of the oil return pipe is determined, the fluid flow rate increases per unit time, and the flow rate increases accordingly. In the single-machine two-stage screw compressor system described in the present invention: the increase in the suction volume (pressure PL on the intake side) increases the gas flow rate flowing through the compressor. If the return oil volume (oil pressure P1 of the oil return main pipe) remains unchanged at this time, the lubricating oil that enters the compressor through the oil return port for rotor lubrication and cooling will quickly be discharged from the compressor along with the compressed gas, which will affect the lubrication and cooling of the compressor. Therefore, it is necessary to increase the oil supply entering the compressor (i.e., P1 increases) to maintain effective lubrication and cooling of the compressor.

[0069] After theoretical analysis and experimental verification, the present invention selects the pressure difference (P1-PL) between the oil pressure P1 of the oil return main and the intake side pressure PL as a parameter for judging how much oil is supplied to the compressor, and keeps the oil pressure P1 of the oil return main changing with the change of the intake side pressure PL, and always maintains the oil pressure P1 of the oil return main greater than the pressure difference of the intake side pressure PL within a reasonable range, so as to accurately reflect the real-time oil supply required by the compressor for effective lubrication and cooling. This can ensure safe, timely and accurate supply of lubricating oil to the compressor. The study also found that the exhaust pressure PH of the compressor is mainly related to the compression ratio of the compressor, and cannot be used as a parameter to judge the amount of return oil given to the compressor.

[0070] Please refer to Figure 1-Figure 7The second embodiment of the oil return pipeline of a single-machine two-stage screw compressor provided by the present invention has a basic structure comprising an oil separator 1, and also comprising an oil return main pipe whose left end is connected to the oil outlet of the oil separator 1, and the right end of the oil return main pipe is divided into a first oil return branch pipe and a second oil return branch pipe, the first oil return branch pipe is connected to the oil return port 92 of the first-stage rotor 91 of the compressor 9, and the second oil return branch pipe is connected to the oil return port 94 of the second-stage rotor 93 of the compressor. The oil return main pipe is provided with a start stop valve 2, a first end stop valve 3 is provided on the first oil return branch pipe, and a second end stop valve 4 is provided on the second oil return branch pipe. The oil return pipeline is cut off through the start and end stop valves, that is, through the start stop valve 2, the first end stop valve 3, and the second end stop valve 4, so as to overhaul or replace the components in the oil return pipeline. The oil return main pipe is provided with an oil filter 5 and an oil flow switch 6. The oil filter 5 can be used to filter impurities in the liquid of the oil return pipeline to prevent the compressor rotor from being worn or even damaged due to the entry of impurities. The oil flow switch 6 can be used to determine whether there is oil flowing in the oil return pipeline. The return oil main pipe is provided with a pressure sensor to read the oil pressure P1 of the return oil main pipe, the first return oil branch pipe is provided with a pressure sensor to read the oil pressure P2 of the first return oil branch, and the second return oil branch pipe is provided with a pressure sensor to read the oil pressure P3 of the second return oil branch. The pressure on the intake side of the compressor is PL, and the pressure on the exhaust side of the compressor is PH. The first return oil branch pipe is provided with a first solenoid valve 7, and the second return oil branch pipe is provided with a second solenoid valve 8. The first and second solenoid valves can be used to control whether oil is supplied in each return oil branch pipe. It also includes a controller that maintains telecommunication connection with the starting stop valve 2, the first end stop valve 3, the second end stop valve 4, the oil flow switch 6, the first solenoid valve 7, the second solenoid valve 8, and the pressure sensors provided on the return oil main pipe and the first and second return oil branches. In addition to being used to control the start and end stop valves in the return oil pipeline, that is, to shut off the oil circuit through the end stop valve 2, the first end stop valve 3, and the second end stop valve 4 to facilitate maintenance or replacement of components in the return oil pipeline, the controller can also intelligently adjust the return oil volume of the two-stage compressor through real-time monitoring of the system load and comparison and judgment based on the pressure difference of the compressor unit with the preset value through different shut-off combinations of the first solenoid valve 7 and the second solenoid valve 8.

[0071] In addition, the internal flow passages of the oil return port of the first stage rotor and the oil return port of the second stage rotor of the double-stage compressor are interconnected, that is, it can be ensured that when any oil return branch pipe is opened for oil supply, the first and second rotors of the double-stage compressor can be supplied with oil for lubrication and cooling.

[0072] The diameters of the first and second oil return branches in this embodiment are also one large and one small, which is different from the structure of the oil return pipeline in the first embodiment in that the diameter of the second oil return branch is set larger than the diameter of the first oil return branch, and the diameter ratio of the two oil return branches is 1.25: 1. By supplying oil through different oil return pipe diameters, the oil supply amount can be accurately adjusted according to the real-time oil supply status of the compressor to ensure that the oil supply amount is neither too much nor too little.

[0073] The two-stage compressor oil return control method of this embodiment includes the following steps:

[0074] In this embodiment, the diameter of the second oil return branch pipe is larger than the diameter of the first oil return branch pipe.

[0075] When P1-PL<ΔP, the oil return main pipe and the first and second oil return branches are all in an open circuit state, that is, the first and second oil return branches both supply oil to the rotor cavity of the compressor, increasing the return oil volume.

[0076] When ΔP+X<P1-PL, the compressor returns too much oil, the main oil return pipe is open, the second oil return branch pipe with a large diameter is closed, and the first oil return branch pipe with a small diameter is open, reducing the return oil volume.

[0077] When ΔP≤P1-PL≤ΔP+X, the oil supply flow of the large-diameter oil return branch pipe meets the demand, that is, the large-diameter second oil return branch pipe is an open circuit, and the small-diameter first oil return branch pipe is a closed circuit.

[0078] Among them, ΔP is the preset pressure difference; X is the preset pressure difference coefficient, for example, X is 100KPa. Different ΔP and X can be selected according to different situations; P1 is the oil pressure of the oil return main pipe; PL is the suction side pressure of the two-stage compressor. Since the internal oil return lines of the compressor are connected, the diameter of the first branch pipe and the diameter of the second branch pipe can be selected as needed, and the size ratio of the two oil return branch pipes can be kept at 1.25:1.

[0079] The present invention connects the oil separator with the corresponding oil return ports of the first and second stage rotors of the two-stage compressor through the oil return main pipe and the first and second oil return branches. In addition, pressure sensors are respectively arranged on the oil return main pipe, the first and second oil return branches, and the first and second solenoid valves are correspondingly arranged on the first and second oil return branches. The pressure difference (P1-PL) between the oil pressure P1 of the oil return main pipe of the oil separator and the pressure PL on the intake side of the two-stage compressor is used as a parameter for judging how much oil the compressor needs to be supplied in real time, and the oil pressure P1 of the oil return main pipe is kept changing with the change of the intake side pressure PL, so that the oil pressure P1 of the oil return main pipe is always maintained greater than the intake side pressure PL, so that the pressure difference between the two is within a reasonable range. In order to accurately reflect the real-time oil supply required by the compressor for effective lubrication and cooling, and ensure safe, timely and accurate adjustment of the oil supply to the compressor. The present invention optimizes the design of the oil return pipeline structure, monitors the system load in real time, and realizes intelligent adjustment of the compressor return oil volume based on comparative judgment of the pressure difference, so as to achieve efficient oil return of a single-machine two-stage compressor unit, increase the stability and service life of the compressor, and improve the overall performance and reliability of the unit.

[0080] It should be noted that the terms used in this specification are only for describing specific embodiments and are not intended to limit the present invention. Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the technical features and steps described in these embodiments do not limit the scope of protection of the present invention. For the technology, methods and equipment known to ordinary technicians in the relevant field, this specification is not discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as part of this specification. Any specific value in this specification should be interpreted as being merely exemplary and not constituting a limitation of the present invention.

[0081] For the convenience of description, the terms describing the position used in the specification, such as "above...", "to the left of...", "in front of...", etc., are only used to describe the spatial position relationship between a certain component and other components of the embodiment shown in the figure. When the position of the component is different, the relative position will change. Therefore, the position relationship of the embodiment of the drawing should not constitute a limitation to the present invention.

[0082] In addition, it should be noted that the words "first", "second" and the like used in the specification are only used to distinguish similar components, and there is no order of precedence, so they cannot be understood as limiting the scope of protection of the present invention. The above description is only a specific implementation of the present invention. It should be pointed out that any modification, equivalent substitution and change made within the spirit and framework of the present invention should be included in the scope of protection of the present invention.

Claims

1. An oil return pipeline of a two-stage compressor, comprising an oil separator, characterized in that: It also includes an oil return main pipe with one end connected to the oil separator, and the other end of the oil return main pipe is divided into a first oil return branch pipe and a second oil return branch pipe. The first oil return branch pipe is connected to the oil return port of the first-stage rotor of the compressor, and the second oil return branch pipe is connected to the oil return port of the second-stage rotor of the compressor. The oil return main pipe and the first and second oil return branches are respectively provided with a pressure sensor, the first oil branch pipe is provided with a first solenoid valve, and the second oil return branch pipe is provided with a second solenoid valve.

2. The oil return pipeline of the two-stage compressor according to claim 1, characterized in that: The main oil return pipe is provided with a start-end stop valve, the first oil return branch pipe is provided with a first end stop valve, and the second oil return branch pipe is provided with a second end stop valve.

3. The oil return pipeline of the two-stage compressor according to claim 1, characterized in that: An oil filter is arranged on the oil return main pipe.

4. The oil return pipeline of the two-stage compressor according to claim 1, characterized in that: An oil flow switch is also provided on the oil return main pipe.

5. The oil return pipeline of the two-stage compressor according to claim 2, characterized in that: The pressure sensors respectively provided on the starting stop valve, the first end stop valve, the second end stop valve, the oil flow switch, the first solenoid valve, the second solenoid valve, the return oil main pipe and the first and second return oil branch pipes are all connected to the controller by telecommunication.

6. The oil return pipeline of the two-stage compressor according to claim 1, characterized in that: The internal flow passages of the oil return port of the first-stage rotor and the oil return port of the second-stage rotor of the compressor are in an interconnected state.

7. The oil return pipeline of the two-stage compressor according to claim 1, characterized in that: The diameters of the first oil return branch pipe and the second oil return branch pipe are one large and one small, and the diameter ratio of the two oil return branch pipes is 1.25:

1.

8. The oil return pipeline of the two-stage compressor according to claim 1, characterized in that: The terminal stop valves, pressure sensors and solenoid valves on the first oil return branch pipe and the second oil return branch pipe are sequentially connected to their respective oil return pipelines starting from the rotor oil return port of the compressor.

9. The oil return pipeline of the two-stage compressor according to claim 1, characterized in that: The start stop valve, oil filter, oil flow switch and pressure sensor on the oil return main pipe are connected to the oil return main pipe in sequence starting from the oil outlet of the oil separator.

10. A single-unit two-stage screw compressor, characterized in that: An oil return pipeline comprising a two-stage compressor as claimed in any one of claims 1 to 9.

11. A method for controlling oil return of an oil return pipeline of a two-stage compressor according to any one of claims 1 to 9, comprising the following steps: When P1-PL<ΔP, the oil return main pipe and the first and second oil return branch pipes are open circuits; When ΔP+X<P1-PL, the oil return main pipe is open, the large diameter oil return branch pipe of the first and second oil return branch pipes is closed, and the small diameter oil return branch pipe is open; When ΔP≤P1-PL≤ΔP+X, the oil return branch pipe with a larger diameter among the first and second oil return branch pipes is an open circuit, and the oil return branch pipe with a smaller diameter is a closed circuit; in, ΔP is the preset pressure difference; X is the preset pressure difference coefficient; P1 is the oil pressure of the oil return main pipe; PL is the suction side pressure of the two-stage compressor.

12. The oil return control method according to claim 11, characterized in that: The steps include: When ΔP+X<P1-PL, the oil return main pipe is open, the first oil return branch pipe is closed, and the second oil return branch pipe is open; When ΔP≤P1-PL≤ΔP+X, the oil return main pipe is open, the first oil return branch pipe is open, and the second oil return branch pipe is closed; Wherein, the diameter of the first oil return branch pipe is larger than the diameter of the second oil return branch pipe.

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