Cascade heat pump system for oil-water separation of oil field and control method thereof

Abstract

The present application relates to the technical field of cascade heat pump, and particularly provides a cascade heat pump system for oil-water separation of oil field and a control method thereof, aiming to solve the problem of low operation energy efficiency of the existing cascade heat pump system for oil-water separation of oil field. To this end, the cascade heat pump system comprises a high-pressure refrigerant circulation loop, a low-pressure refrigerant circulation loop, an oil heat preservation water circulation loop and a first water tank, the oil heat preservation water circulation loop comprises a first water circulation branch and a second water circulation branch both connected with the first water tank and heat-exchanged through the first water tank, and the first water circulation branch and the second water circulation branch are heat-exchanged with the high-pressure refrigerant circulation loop and the low-pressure refrigerant circulation loop through a first intermediate heat exchanger and a second intermediate heat exchanger respectively. Based on this, by arranging the oil heat preservation water circulation loop between the high-pressure refrigerant circulation loop and the low-pressure refrigerant circulation loop, the oil in the heat preservation oil tank can be heat preserved, and the operation energy efficiency of the cascade heat pump system can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of cascade heat pump technology, specifically providing a cascade heat pump system and its control method for oil-water separation in oil fields. Background Technology

[0002] Cascade heat pump systems typically consist of a high-pressure refrigerant circulation loop and a low-pressure refrigerant circulation loop. These two loops exchange heat through a shared intermediate heat exchanger to provide high-temperature hot water. However, existing cascade heat pump systems, especially those used for oil-water separation in oil fields, still require cascade operation outside of their rated operating conditions, such as when the outdoor ambient temperature is high. This means that even under conditions where the temperature difference between evaporation and condensation is small, two-stage compression is still employed, resulting in significant energy losses and consequently, low energy efficiency and energy waste.

[0003] Accordingly, there is a need in the field for a new cascade heat pump system for oil-water separation in oilfields and its control method to solve the above-mentioned technical problems. Summary of the Invention

[0004] The present invention aims to solve the above-mentioned technical problems, namely, to solve the problem of low operating energy efficiency of existing cascade heat pump systems used for oil-water separation in oil fields.

[0005] In a first aspect, the present invention provides a cascade heat pump system for oil-water separation in oilfields, the cascade heat pump system comprising a high-pressure refrigerant circulation loop, a low-pressure refrigerant circulation loop, an oil-insulated water circulation loop, and a first water tank.

[0006] The high-pressure refrigerant circulation loop is equipped with a first compressor, a first heat exchanger, a first throttling component, and a first intermediate heat exchanger; the low-pressure refrigerant circulation loop is equipped with a second compressor, a second intermediate heat exchanger, a refrigerant pump, a second throttling component, and a second heat exchanger.

[0007] The oil-insulated water circulation loop includes a first water circulation branch and a second water circulation branch. Both ends of the first and second water circulation branches are connected to the first water tank. A portion of the first water circulation branch is disposed in the first intermediate heat exchanger to exchange heat with the high-pressure refrigerant circulation loop. A portion of the second water circulation branch is disposed in the second intermediate heat exchanger to exchange heat with the low-pressure refrigerant circulation loop. An insulated oil tank is also disposed on the second water circulation branch. The water in the first water circulation branch exchanges heat with the water in the second water circulation branch through the first water tank to insulate the oil in the insulated oil tank.

[0008] In the preferred embodiment of the above-mentioned cascade heat pump system, a second water tank and a separation oil tank are provided on the oil-water separation circulation loop, and a part of the oil-water separation circulation loop is provided in the first heat exchanger to exchange heat with the high-pressure refrigerant circulation loop.

[0009] In the preferred embodiment of the above-mentioned cascade heat pump system, the cascade heat pump system further includes a first refrigerant circulation branch.

[0010] The first end of the first refrigerant circulation branch is connected between the second intermediate heat exchanger and the refrigerant pump, and the second end of the first refrigerant circulation branch is connected between the refrigerant pump and the second throttling component. A first control valve is provided on the first refrigerant circulation branch.

[0011] In the preferred embodiment of the above-mentioned cascade heat pump system, the cascade heat pump system further includes a second refrigerant circulation branch.

[0012] The first end of the second refrigerant circulation branch is connected between the second heat exchanger and the second compressor, and the second end of the second refrigerant circulation branch is connected between the second compressor and the second intermediate heat exchanger. A second control valve is provided on the second refrigerant circulation branch.

[0013] In the preferred embodiment of the above-mentioned cascade heat pump system, the first control valve is a one-way valve; and / or

[0014] The second control valve is a check valve.

[0015] In the preferred embodiment of the above-mentioned cascade heat pump system, the first intermediate heat exchanger is a plate heat exchanger; and / or

[0016] The second intermediate heat exchanger is a plate heat exchanger.

[0017] In the preferred embodiment of the above-mentioned cascade heat pump system, a first gas separator is further provided on the high-pressure refrigerant circulation loop, and the first gas separator is located at the air inlet of the first compressor; and / or,

[0018] A second gas separator is also provided on the low-pressure refrigerant circulation loop, and the second gas separator is located at the air inlet of the second compressor.

[0019] On the other hand, the present invention also provides a control method for a cascade heat pump system for oil-water separation in oil fields. The cascade heat pump system includes a high-pressure refrigerant circulation loop, a low-pressure refrigerant circulation loop, an oil-insulated water circulation loop, a first water tank, a first refrigerant circulation branch, and a second refrigerant circulation branch.

[0020] The high-pressure refrigerant circulation loop is equipped with a first compressor, a first heat exchanger, a first throttling component, and a first intermediate heat exchanger; the low-pressure refrigerant circulation loop is equipped with a second compressor, a second intermediate heat exchanger, a refrigerant pump, a second throttling component, and a second heat exchanger.

[0021] The oil-insulated water circulation loop includes a first water circulation branch and a second water circulation branch. Both ends of the first and second water circulation branches are connected to the first water tank. A portion of the first water circulation branch is disposed in the first intermediate heat exchanger to exchange heat with the high-pressure refrigerant circulation loop, and a portion of the second water circulation branch is disposed in the second intermediate heat exchanger to exchange heat with the low-pressure refrigerant circulation loop. An insulated oil tank is also disposed on the second water circulation branch. Water in the first water circulation branch exchanges heat with water in the second water circulation branch through the first water tank to insulate the oil in the insulated oil tank.

[0022] The first end of the first refrigerant circulation branch is connected between the second intermediate heat exchanger and the refrigerant pump, and the second end of the first refrigerant circulation branch is connected between the refrigerant pump and the second throttling component. A first control valve is provided on the first refrigerant circulation branch.

[0023] The first end of the second refrigerant circulation branch is connected between the second heat exchanger and the second compressor, and the second end of the second refrigerant circulation branch is connected between the second compressor and the second intermediate heat exchanger. A second control valve is provided on the second refrigerant circulation branch.

[0024] When the high-pressure refrigerant circulation loop is operating, the control method includes:

[0025] Obtain the outdoor ambient temperature;

[0026] Based on the outdoor ambient temperature and the preset ambient temperature, the connection status of the first refrigerant circulation branch and the second refrigerant circulation branch, as well as the operating status of the refrigerant pump and the second compressor, are controlled.

[0027] In the preferred embodiment of the above control method, the step of "controlling the connection status of the first refrigerant circulation branch and the second refrigerant circulation branch, as well as the operating status of the refrigerant pump and the second compressor, according to the outdoor ambient temperature and the preset ambient temperature" includes:

[0028] If the outdoor ambient temperature is greater than or equal to the preset ambient temperature, then the first refrigerant circulation branch is disconnected, the second refrigerant circulation branch is connected, the refrigerant pump is running, and the second compressor is not running.

[0029] In the preferred embodiment of the above control method, the step of "controlling the connection status of the first refrigerant circulation branch and the second refrigerant circulation branch and the operating status of the refrigerant pump and the second compressor according to the outdoor ambient temperature and the preset ambient temperature" further includes:

[0030] If the outdoor ambient temperature is lower than the preset ambient temperature, then the first refrigerant circulation branch is connected, the second refrigerant circulation branch is disconnected, the refrigerant pump is not running, and the second compressor is running.

[0031] When the above technical solution is adopted, the cascade heat pump system of the present invention sets up an oil-insulated water circulation loop and a first water tank between the high-pressure refrigerant circulation loop and the low-pressure refrigerant circulation loop to exchange heat with the water in the oil-insulated water circulation loop, thereby keeping the oil in the insulated oil tank on the oil-insulated water circulation loop warm, effectively improving the operating energy efficiency of the cascade heat pump system. Attached Figure Description

[0032] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0033] Figure 1 This is a schematic diagram of the cascade heat pump system of the present invention;

[0034] Figure 2 This is a flowchart of the main steps of the control method of the present invention;

[0035] Figure 3 This is a flowchart illustrating the specific steps of a preferred embodiment of the control method of the present invention;

[0036] Figure label:

[0037] 1. High-pressure refrigerant circulation loop; 11. First compressor; 12. First heat exchanger; 13. First throttling component; 14. First intermediate heat exchanger; 15. First gas separator;

[0038] 2. Low-pressure refrigerant circulation loop; 21. Second compressor; 22. Second intermediate heat exchanger; 23. Refrigerant pump; 24. Second throttling component; 25. Second heat exchanger; 26. Second gas separator;

[0039] 3. First water tank;

[0040] 4. First water circulation branch;

[0041] 5. Second water circulation branch; 51. Insulated oil tank;

[0042] 6. Oil-water separation circulation loop; 61. Second water tank; 62. Oil separation tank;

[0043] 7. First refrigerant circulation branch; 71. First control valve;

[0044] 8. Second refrigerant circulation branch; 81. Second control valve. Detailed Implementation

[0045] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios. It will be understood by those skilled in the art that such changes regarding application scenarios do not depart from the basic principles of the present invention and fall within the scope of protection of the present invention.

[0046] It should be noted that, in the description of this preferred embodiment, unless otherwise explicitly specified and limited, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, the terms "connected" and "linked" should be interpreted broadly; for example, they can refer to mechanical connections or electrical connections, direct connections or indirect connections via an intermediate medium, or connections within two components. Therefore, they should not be construed as limiting the invention. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0047] Furthermore, it should be noted that although the various steps of the control method of the present invention are described in a specific order in the description of the present invention, these orders are not restrictive. Without departing from the basic principles of the present invention, those skilled in the art can perform the steps in different orders.

[0048] First refer to Figure 1 , Figure 1 This is a schematic diagram of the cascade heat pump system of the present invention. Figure 1 As shown, the cascade heat pump system of the present invention includes a high-pressure refrigerant circulation loop 1, a low-pressure refrigerant circulation loop 2, an oil-insulated water circulation loop, and a first water tank 3. The high-pressure refrigerant circulation loop 1 is equipped with a first compressor 11, a first heat exchanger 12, a first throttling component 13, and a first intermediate heat exchanger 14. The low-pressure refrigerant circulation loop 2 is equipped with a second compressor 21, a second intermediate heat exchanger 22, a refrigerant pump 23, a second throttling component 24, and a second heat exchanger 25.

[0049] It should be noted that the present invention does not impose any restrictions on the specific structure and model of the first compressor 11, the second compressor 21, the first throttling component 13, the second throttling component 24, the first heat exchanger 12, and the second heat exchanger 25; the first compressor 11 and the second compressor 21 can be variable frequency compressors or fixed frequency compressors; the first throttling component 13 and the second throttling component 24 can be electronic expansion valves, capillary tubes, or thermostatic expansion valves; the first heat exchanger 12 and the second heat exchanger 25 can be plate heat exchangers or shell and tube heat exchangers, which are not limiting, and those skilled in the art can set them according to the actual situation.

[0050] In addition, the oil-insulating water circulation loop includes a first water circulation branch 4 and a second water circulation branch 5. Both ends of the first water circulation branch 4 and the second water circulation branch 5 are connected to the first water tank 3. A part of the first water circulation branch 4 is set in the first intermediate heat exchanger 14 to exchange heat with the high-pressure refrigerant circulation loop 1. A part of the second water circulation branch 5 is set in the second intermediate heat exchanger 22 to exchange heat with the low-pressure refrigerant circulation loop 2. An insulated oil tank 51 is also set on the second water circulation branch 5. The water in the first water circulation branch 4 exchanges heat with the water in the second water circulation branch 5 through the first water tank 3 to keep the oil in the insulated oil tank 51 warm.

[0051] It should be noted that the present invention does not impose any restrictions on the specific structure of the first intermediate heat exchanger 14, the second intermediate heat exchanger 22, the first water tank 3, and the insulated oil tank 51. Those skilled in the art can set them according to the actual situation. Preferably, the first intermediate heat exchanger 14 and the second intermediate heat exchanger 22 are plate heat exchangers to effectively improve the heat exchange efficiency of the cascade heat pump system. Specifically, both the first intermediate heat exchanger 14 and the second intermediate heat exchanger 22 include a first heat exchange channel and a second heat exchange channel. The refrigerant in the high-pressure refrigerant circulation loop 1 and the refrigerant in the low-pressure refrigerant circulation loop 2 flows through the first heat exchange channel, and the water in the first water circulation branch 4 and the second water circulation branch 5 flows through the second heat exchange channel. The first heat exchange channel and the second heat exchange channel are staggered to achieve the purpose of heat exchange between the refrigerant in the high-pressure refrigerant circulation loop 1 and the low-pressure refrigerant circulation loop 2 and the water in the first water circulation branch 4 and the second water circulation branch 5.

[0052] Furthermore, it should be noted that this invention does not impose any restrictions on the specific types of refrigerants flowing in the high-pressure refrigerant circulation loop 1 and the low-pressure refrigerant circulation loop 2, nor on the heat exchange sources of the first heat exchanger 12 and the second heat exchanger 25. Those skilled in the art can set these restrictions according to actual conditions. As a specific embodiment, the refrigerant in the high-pressure refrigerant circulation loop 1 is refrigerant R134a, and the refrigerant in the low-pressure refrigerant circulation loop 2 is refrigerant R410A. The heat exchange source of the second heat exchanger 25 is an oilfield heating circuit. Of course, this invention does not impose any restrictions on the specific structure of the oilfield heating circuit; those skilled in the art can set these restrictions according to actual conditions.

[0053] Preferably, the cascade heat pump system further includes an oil-water separation circulation loop 6, in which water serves as the heat source for the refrigerant in the first heat exchanger 12; specifically, the oil-water separation circulation loop 6 is provided with a second water tank 61 and an oil separation tank 62, and a portion of the oil-water separation circulation loop 6 is disposed in the first heat exchanger 12 to exchange heat with the high-pressure refrigerant circulation loop 1.

[0054] It should be noted that the present invention does not impose any restrictions on the specific structure of the second water tank 61 and the oil separation tank 62, and those skilled in the art can set them according to the actual situation. Furthermore, it should be noted that the present invention does not impose any restrictions on other structures provided on the oil-insulating water circulation loop and the oil-separating water circulation loop 6, and those skilled in the art can set other structures on the oil-insulating water circulation loop and the oil-separating water circulation loop 6 according to the actual situation.

[0055] Furthermore, in this specific embodiment, the cascade heat pump system further includes a first refrigerant circulation branch 7. The first end of the first refrigerant circulation branch 7 is connected between the second intermediate heat exchanger 22 and the refrigerant pump 23, and the second end of the first refrigerant circulation branch 7 is connected between the refrigerant pump 23 and the second throttling component 24. A first control valve 71 is provided on the first refrigerant circulation branch 7. The first refrigerant circulation branch 7 and the first control valve 71 on it can selectively connect the refrigerant pump 23 to the low-pressure refrigerant circulation loop 2. That is, the operating state of the refrigerant pump 23 can be selectively controlled according to the actual operating conditions of the cascade heat pump system, thereby further improving the operating efficiency of the cascade heat pump system.

[0056] Preferably, the cascade heat pump system further includes a second refrigerant circulation branch 8. The first end of the second refrigerant circulation branch 8 is connected between the second heat exchanger 25 and the second compressor 21, and the second end of the second refrigerant circulation branch 8 is connected between the second compressor 21 and the second intermediate heat exchanger 22. A second control valve 81 is provided on the second refrigerant circulation branch 8. The second refrigerant circulation branch 8 and the second control valve 81 on it can selectively connect the second compressor 21 to the low-pressure refrigerant circulation loop 2. That is, the operating state of the second compressor 21 can be selectively controlled according to the actual operating conditions of the cascade heat pump system, thereby further improving the operating efficiency of the cascade heat pump system.

[0057] It should be noted that the present invention does not impose any restrictions on the specific structure and type of the first control valve 71 and the second control valve 81. They can be electromagnetic control valves or hydraulic control valves, one-way control valves or multi-way control valves, none of which are limiting. Preferably, in this specific embodiment, the first control valve 71 is a first one-way valve, the second control valve 81 is a second one-way valve, and the first one-way valve is configured to allow refrigerant to flow only from one side of the second intermediate heat exchanger 22 to one side of the second throttling member 24, and the second one-way valve is configured to allow refrigerant to flow only from one side of the second heat exchanger 25 to one side of the second intermediate heat exchanger 22, so as to further effectively ensure that the refrigerant does not flow back.

[0058] More preferably, a first gas separator 15 is further provided on the high-pressure refrigerant circulation loop 1, and the first gas separator 15 is located at the air inlet of the first compressor 11. A second gas separator 26 is further provided on the low-pressure refrigerant circulation loop 2, and the second gas separator 26 is located at the air inlet of the second compressor 21. The provision of the first gas separator 15 and the second gas separator 26 can effectively prevent liquid slugging in the first compressor 11 and the second compressor 21, and effectively ensure the service life of the first compressor 11 and the second compressor 21. It should be noted that the present invention does not impose any limitations on the specific structure of the first gas separator 15 and the second gas separator 26, and those skilled in the art can set them according to the actual situation.

[0059] Furthermore, the cascade heat pump system also includes a temperature sensor and a controller (not shown in the figure). The temperature sensor can acquire the ambient temperature near the cascade heat pump system, and the controller can acquire the ambient temperature detected by the temperature sensor. The controller can also control the operating status of the first control valve 71, the second control valve 81, the refrigerant pump 23, and the second compressor 21, etc., which are not limiting. It should be noted that the present invention does not impose any restrictions on the specific number or location of the temperature sensors, as long as they can acquire the ambient temperature. Those skilled in the art can set them according to actual conditions. In addition, those skilled in the art will understand that the present invention does not impose any restrictions on the specific structure and model of the controller, and the controller can be either the original controller of the cascade heat pump system or a controller separately set up to execute the control method of the present invention. Those skilled in the art can set the structure and model of the controller according to actual usage requirements.

[0060] See next Figure 2 , Figure 2 This is a flowchart of the main steps of the control method of the present invention. Figure 2 As shown, based on the cascade heat pump system described in the above embodiments, the control method of the present invention mainly includes the following steps:

[0061] S1: Obtain the outdoor ambient temperature;

[0062] S2: Based on the outdoor ambient temperature and the preset ambient temperature, control the connection status of the first refrigerant circulation branch and the second refrigerant circulation branch, as well as the operating status of the refrigerant pump and the second compressor.

[0063] First, in step S1, while the high-pressure refrigerant circulation loop 1 is operating, the controller acquires the outdoor ambient temperature near the cascade heat pump system. Of course, this invention does not impose any restrictions on the specific timing or method of acquiring the outdoor ambient temperature; the controller can acquire it in real time or at certain intervals, which are not limiting. Those skilled in the art can set these parameters according to actual conditions. Preferably, the controller acquires the outdoor ambient temperature in real time so that the operating status of the cascade heat pump system can be adjusted promptly and effectively, thereby effectively improving the operating energy efficiency of the cascade heat pump system.

[0064] Next, in step S2, the controller controls the connection status of the first refrigerant circulation branch 7 and the second refrigerant circulation branch 8, as well as the operating status of the refrigerant pump 23 and the second compressor 21, based on the outdoor ambient temperature and the preset ambient temperature.

[0065] It should be noted that the present invention does not impose any restrictions on the specific setting value of the preset ambient temperature. Those skilled in the art can set it according to the actual operation of the cascade heat pump system, or obtain it according to the actual usage needs of the user. These are not limiting.

[0066] Furthermore, it should be noted that the present invention does not impose any restrictions on the specific control methods of the controller for the connection state of the first refrigerant circulation branch 7 and the second refrigerant circulation branch 8, as well as the operating state of the refrigerant pump 23 and the second compressor 21. It can compare or make a comparison between the outdoor ambient temperature and the preset ambient temperature, and then control the connection state of the first refrigerant circulation branch 7 and the second refrigerant circulation branch 8, as well as the operating state of the refrigerant pump 23 and the second compressor 21, based on the comparison or comparison results. These are not restrictive, and those skilled in the art can set them according to the actual situation.

[0067] See next Figure 3 , Figure 3 This is a flowchart illustrating the specific steps of a preferred embodiment of the control method of the present invention. Figure 3 As shown, based on the cascade heat pump system described in the above embodiments, the control method of the preferred embodiment of the present invention includes the following steps:

[0068] S101: Obtain outdoor ambient temperature;

[0069] S102: If the outdoor ambient temperature is greater than or equal to the preset ambient temperature, then the first refrigerant circulation branch is disconnected, the second refrigerant circulation branch is connected, the refrigerant pump is running, and the second compressor is not running.

[0070] S103: If the outdoor ambient temperature is lower than the preset ambient temperature, the first refrigerant circulation branch is connected, the second refrigerant circulation branch is disconnected, the refrigerant pump is not running, and the second compressor is running.

[0071] First, in step S101, when the high-pressure refrigerant circulation loop 1 is operating, the controller acquires the outdoor ambient temperature near the cascade heat pump system. Of course, this invention does not impose any restrictions on the specific timing or method of acquiring the outdoor ambient temperature. The controller can acquire it in real time or at certain intervals; these are not limiting, and those skilled in the art can set them according to actual conditions. Preferably, the controller acquires the outdoor ambient temperature in real time so that the operating status of the cascade heat pump system can be adjusted promptly and effectively, thereby effectively improving the operating energy efficiency of the cascade heat pump system.

[0072] Next, the controller controls the connection status of the first refrigerant circulation branch 7 and the second refrigerant circulation branch 8, as well as the operating status of the refrigerant pump 23 and the second compressor 21, based on the outdoor ambient temperature and the preset ambient temperature. It should be noted that the present invention does not impose any restrictions on the specific setting value of the preset ambient temperature. Those skilled in the art can set it according to the actual operating conditions of the cascade heat pump system, or according to the actual usage needs of the user; these are not limiting factors.

[0073] Specifically, in step S102, if the outdoor ambient temperature is greater than or equal to the preset ambient temperature, the controller controls the first refrigerant circulation branch 7 to be disconnected, the second refrigerant circulation branch 8 to be connected, the refrigerant pump 23 to run, and the second compressor 21 to be disconnected. At this time, the first control valve 71 is closed, the second control valve 81 is opened, and the refrigerant in the low-pressure refrigerant circulation loop 2 is discharged from the outlet of the refrigerant pump 23 and flows through the second throttling component 24, the second heat exchanger 25, the second gas separator 26, the second control valve 81, and the second intermediate heat exchanger 22 before returning to the refrigerant pump 23 from the inlet, completing one cycle.

[0074] Further, in step S103, if the outdoor ambient temperature is lower than the preset ambient temperature, the controller controls the first refrigerant circulation branch 7 to be connected, the second refrigerant circulation branch 8 to be disconnected, the refrigerant pump 23 to be deactivated, and the second compressor 21 to be activated. At this time, the first control valve 71 is opened, the second control valve 81 is closed, and the refrigerant in the low-pressure refrigerant circulation loop 2 is discharged from the exhaust port of the second compressor 21 and flows through the second intermediate heat exchanger 22, the first control valve 71, the second throttling component 24, the second heat exchanger 25, and the second gas separator 26 before returning to the second compressor 21 from the intake port, completing one cycle.

[0075] Based on the above control logic, frequent start-up and shutdown of the cascade heat pump system can be effectively avoided, thereby effectively preventing the cascade heat pump system from being in an unstable operating state for a long time. The cascade heat pump system of the present invention controls the second compressor 21 and the refrigerant pump 23 to operate selectively based on the outdoor ambient temperature and the preset ambient temperature, extending the system start-up and shutdown cycle and effectively ensuring the operating energy efficiency of the cascade heat pump system.

[0076] It should be noted that the operating mode of the cascade heat pump system of the present invention is not limited to the two situations mentioned above. Those skilled in the art can set the operating mode of the cascade heat pump system according to the actual situation. Those skilled in the art can understand that the change of the specific operating mode of the cascade heat pump system does not deviate from the basic principle of the present invention and still falls within the protection scope of the present invention.

[0077] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A cascade heat pump system for oil-water separation in oilfields, characterized in that, The cascade heat pump system includes a high-pressure refrigerant circulation loop, a low-pressure refrigerant circulation loop, an oil-insulated water circulation loop, and a first water tank. The high-pressure refrigerant circulation loop is equipped with a first compressor, a first heat exchanger, a first throttling component, and a first intermediate heat exchanger; the low-pressure refrigerant circulation loop is equipped with a second compressor, a second intermediate heat exchanger, a refrigerant pump, a second throttling component, and a second heat exchanger. The oil-insulated water circulation loop includes a first water circulation branch and a second water circulation branch. Both ends of the first and second water circulation branches are connected to the first water tank. A portion of the first water circulation branch is disposed in the first intermediate heat exchanger to exchange heat with the high-pressure refrigerant circulation loop. A portion of the second water circulation branch is disposed in the second intermediate heat exchanger to exchange heat with the low-pressure refrigerant circulation loop. An insulated oil tank is also disposed on the second water circulation branch. The water in the first water circulation branch exchanges heat with the water in the second water circulation branch through the first water tank to insulate the oil in the insulated oil tank.

2. The cascade heat pump system according to claim 1, characterized in that, The cascade heat pump system also includes an oil-water separation circulation loop. The oil-water separation circulation loop is equipped with a second water tank and a separation oil tank, and a portion of the oil-water separation circulation loop is located in the first heat exchanger to exchange heat with the high-pressure refrigerant circulation loop.

3. The cascade heat pump system according to claim 1, characterized in that, The cascade heat pump system also includes a first refrigerant circulation branch. The first end of the first refrigerant circulation branch is connected between the second intermediate heat exchanger and the refrigerant pump, and the second end of the first refrigerant circulation branch is connected between the refrigerant pump and the second throttling component. A first control valve is provided on the first refrigerant circulation branch.

4. The cascade heat pump system according to claim 3, characterized in that, The cascade heat pump system also includes a second refrigerant circulation branch. The first end of the second refrigerant circulation branch is connected between the second heat exchanger and the second compressor, and the second end of the second refrigerant circulation branch is connected between the second compressor and the second intermediate heat exchanger. A second control valve is provided on the second refrigerant circulation branch.

5. The cascade heat pump system according to claim 4, characterized in that, The first control valve is a check valve; and / or The second control valve is a check valve.

6. The cascade heat pump system according to any one of claims 1 to 5, characterized in that, The first intermediate heat exchanger is a plate heat exchanger; and / or The second intermediate heat exchanger is a plate heat exchanger.

7. The cascade heat pump system according to any one of claims 1 to 5, characterized in that, The high-pressure refrigerant circulation loop is further equipped with a first gas separator, which is located at the air inlet of the first compressor; and / or, A second gas separator is also provided on the low-pressure refrigerant circulation loop, and the second gas separator is located at the air inlet of the second compressor.

8. A control method for a cascade heat pump system used for oil-water separation in oilfields, characterized in that, The cascade heat pump system includes a high-pressure refrigerant circulation loop, a low-pressure refrigerant circulation loop, an oil-insulated water circulation loop, a first water tank, a first refrigerant circulation branch, and a second refrigerant circulation branch. The high-pressure refrigerant circulation loop is equipped with a first compressor, a first heat exchanger, a first throttling component, and a first intermediate heat exchanger; the low-pressure refrigerant circulation loop is equipped with a second compressor, a second intermediate heat exchanger, a refrigerant pump, a second throttling component, and a second heat exchanger. The oil-insulated water circulation loop includes a first water circulation branch and a second water circulation branch. Both ends of the first and second water circulation branches are connected to the first water tank. A portion of the first water circulation branch is disposed in the first intermediate heat exchanger to exchange heat with the high-pressure refrigerant circulation loop, and a portion of the second water circulation branch is disposed in the second intermediate heat exchanger to exchange heat with the low-pressure refrigerant circulation loop. An insulated oil tank is also disposed on the second water circulation branch. Water in the first water circulation branch exchanges heat with water in the second water circulation branch through the first water tank to insulate the oil in the insulated oil tank. The first end of the first refrigerant circulation branch is connected between the second intermediate heat exchanger and the refrigerant pump, and the second end of the first refrigerant circulation branch is connected between the refrigerant pump and the second throttling component. A first control valve is provided on the first refrigerant circulation branch. The first end of the second refrigerant circulation branch is connected between the second heat exchanger and the second compressor, and the second end of the second refrigerant circulation branch is connected between the second compressor and the second intermediate heat exchanger. A second control valve is provided on the second refrigerant circulation branch. When the high-pressure refrigerant circulation loop is operating, the control method includes: Obtain the outdoor ambient temperature; Based on the outdoor ambient temperature and the preset ambient temperature, the connection status of the first refrigerant circulation branch and the second refrigerant circulation branch, as well as the operating status of the refrigerant pump and the second compressor, are controlled.

9. The control method according to claim 8, characterized in that, The steps of "controlling the connection status of the first refrigerant circulation branch and the second refrigerant circulation branch, as well as the operating status of the refrigerant pump and the second compressor, based on the outdoor ambient temperature and the preset ambient temperature" include: If the outdoor ambient temperature is greater than or equal to the preset ambient temperature, then the first refrigerant circulation branch is disconnected, the second refrigerant circulation branch is connected, the refrigerant pump is running, and the second compressor is not running.

10. The control method according to claim 8, characterized in that, The step of "controlling the connection status of the first refrigerant circulation branch and the second refrigerant circulation branch, as well as the operating status of the refrigerant pump and the second compressor, based on the outdoor ambient temperature and the preset ambient temperature" further includes: If the outdoor ambient temperature is lower than the preset ambient temperature, then the first refrigerant circulation branch is connected, the second refrigerant circulation branch is disconnected, the refrigerant pump is not running, and the second compressor is running.

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