Multi-stage membrane separation system and separation method

Abstract

The application provides a multi-section membrane separation system and a separation method. The multi-section membrane separation system comprises an energy recovery device (1) and at least two sections of membrane separation devices connected in series, wherein the membrane separation devices comprise a first-section membrane separation device (21) and a last-section membrane separation device (22), one end of the energy recovery device (1) is communicated with the first-section membrane separation device (21), the other end is communicated with the last-section membrane separation device (22), a piston group (12) is arranged in the energy recovery device (1), and the piston group (12) can conduct the liquid pressure in the last-section membrane separation device (22) to the first-section membrane separation device (21). The multi-section membrane separation system and the separation method can solve the problem that the existing multi-section membrane separation system has a large energy loss in the energy recovery process, thereby reducing the energy recovery rate.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and more specifically, to a multi-stage membrane separation system and separation method. Background Technology

[0002] Membrane separation technology, as a highly efficient and environmentally friendly separation method, has been widely used in water treatment, food industry, biomedicine, and chemical industry. Its core advantage lies in its ability to achieve precise separation of target substances through physical filtration, making it particularly suitable for treating solutions containing tiny particles or molecules. However, traditional membrane separation processes often involve high energy consumption, especially in multi-stage series high-pressure systems. To ensure sufficient permeability and recovery rates, pumps are continuously used to increase fluid pressure, which not only increases operating costs but also places an additional burden on the environment. To reduce pump usage, improve energy utilization efficiency, and lower operating costs, energy recovery devices have emerged. These devices aim to recover and reuse excess pressure generated during membrane separation, reducing the number and power of required pumps, retaining only necessary inter-stage booster pumps, thereby reducing overall energy consumption.

[0003] Currently, existing multi-stage membrane separation systems mainly employ two types of energy recovery devices: pressure exchange type and centrifugal type. However, pressure exchange type energy recovery devices typically require pressure reducing valves to lower the pressure to match the feed requirements of the first-stage membrane unit. This pressure reduction process leads to significant energy loss, thus reducing the energy recovery rate. Centrifugal energy recovery devices utilize a "pressure energy - shaft work - pressure energy" energy transfer mechanism. Due to the energy transformation, energy loss is inevitable during this process, further reducing the energy recovery rate. Summary of the Invention

[0004] The main objective of this invention is to provide a multi-stage membrane separation system and separation method that can solve the problem of large energy loss and low energy recovery rate in existing multi-stage membrane separation systems during the energy recovery process.

[0005] To achieve the above objectives, according to one aspect of the present invention, a multi-stage membrane separation system is provided, including an energy recovery device and at least two membrane separation devices connected in series. The membrane separation devices include a first-stage membrane separation device and a last-stage membrane separation device. One end of the energy recovery device is connected to the first-stage membrane separation device, and the other end is connected to the last-stage membrane separation device. A piston assembly is provided inside the energy recovery device, which can transmit the liquid pressure in the last-stage membrane separation device to the first-stage membrane separation device.

[0006] Furthermore, the membrane separation device includes an inlet end and a concentrate end, and the energy recovery device includes a hydraulic cylinder. One end of the hydraulic cylinder is connected to the inlet end of the first-stage membrane separation device, and the other end of the hydraulic cylinder is connected to the concentrate end of the last-stage membrane separation device. A piston assembly is disposed inside the hydraulic cylinder, and the piston assembly can move inside the hydraulic cylinder to transmit the pressure of the concentrate end of the last-stage membrane separation device to the inlet end of the first-stage membrane separation device.

[0007] Furthermore, the hydraulic cylinder includes a first cylinder body and a second cylinder body, the first cylinder body and the second cylinder body are connected, a first piston is disposed in the first cylinder body, a second piston is disposed in the second cylinder body, and the first piston and the second piston are fixedly connected by a connecting rod to form a piston assembly.

[0008] Furthermore, the diameter of the first piston is larger than that of the second piston, the inner diameter of the first cylinder matches the diameter of the first piston, the inner diameter of the second cylinder matches the diameter of the second piston, the first cylinder is connected to the water inlet of the first-stage membrane separation device, and the second cylinder is connected to the concentrate end of the last-stage membrane separation device.

[0009] Furthermore, the chamber located on the side of the first piston away from the second piston within the first cylinder is the driven fluid chamber, which can contain the driven fluid. A first inlet pipe and a first outlet pipe are provided on the side of the driven fluid chamber away from the second cylinder. The driven fluid can enter the driven fluid chamber through the first inlet pipe, and the driven fluid in the driven fluid chamber can be transported to the inlet end of the first membrane separation device through the first outlet pipe.

[0010] Furthermore, the chamber located on the side of the second piston away from the first piston within the second cylinder is the driving fluid chamber, which can contain the driving fluid. A second inlet pipe and a second outlet pipe are provided on the side of the driving fluid chamber away from the second cylinder. The driving fluid can enter the driving fluid chamber from the concentrate end of the final membrane separation device through the second inlet pipe, and the driving fluid in the driving fluid chamber can be discharged through the second outlet pipe.

[0011] Furthermore, an inter-stage booster pump is installed between two adjacent membrane separation units. The inter-stage booster pump connects the concentrate end of the front membrane separation unit with the inlet end of the rear membrane separation unit. The inter-stage booster pump can increase the inlet pressure of the inlet end of the rear membrane separation unit.

[0012] Furthermore, a first check valve is installed on the first inlet pipe, which unidirectionally flows into the driven fluid chamber; a second check valve is installed on the first outlet pipe, which unidirectionally flows from the driven fluid chamber to the inlet end of the first membrane separation device; an inlet valve is installed on the second inlet pipe; and a drain valve is installed on the second outlet pipe.

[0013] According to another aspect of the present invention, a separation method is also provided, based on the above-described multi-stage membrane separation system, the separation method comprising: controlling the movement of a piston assembly within an energy recovery device to recover energy from the final stage membrane separation device; and controlling the piston assembly within the energy recovery device to reset.

[0014] Furthermore, the steps of controlling the movement of the piston assembly within the energy recovery device to recover energy from the final membrane separator include: opening the inlet valve; closing the drain valve; and completing the recovery of energy from the concentrate end of the final membrane separator when the first outlet pipe stops discharging water, or when the piston assembly moves to a preset position in the direction of the driven fluid chamber, or when the piston assembly moves a preset stroke in the direction of the driven fluid chamber.

[0015] Furthermore, the steps for controlling the piston assembly reset within the energy recovery device include: closing the inlet valve; opening the drain valve; and completing the piston assembly reset within the energy recovery device when the second outlet pipe stops discharging water, or when the piston assembly moves towards the driving fluid chamber to a preset position, or when the piston assembly moves towards the driving fluid chamber for a preset distance.

[0016] The core function of the energy recovery device, applying the technical solution of this invention, is to recover and reuse the high-pressure energy generated during membrane separation, particularly the concentrate pressure in the final membrane separation unit, thus achieving internal energy recycling. The piston assembly is the actuator in the energy recovery process. By adjusting the area ratio between the pistons, the high-pressure energy on the concentrate side of the final membrane separation unit is transferred to the low-pressure fluid on the feed side of the first membrane separation unit. This design eliminates the need for an additional pressure-reducing valve and eliminates the need for an additional energy conversion process, making the recovery of pressure energy more direct and efficient. The first membrane separation unit is the initial stage of the entire membrane separation system. After filtration, the liquid is separated into clean liquid and concentrate. The clean liquid is transported to subsequent processes for recycling, while the concentrate is transported to the next membrane separation unit for further filtration. The final membrane separation unit is responsible for processing the high-concentration fluid separated by the previous membrane separation unit. One end of the energy recovery device is connected to the first membrane separation unit, and the other end is connected to the final membrane separation unit. This configuration allows the energy recovery device to directly utilize the high-pressure concentrate generated by the final membrane separation unit, converting its energy into pressurization for the feed to the first membrane separation unit. The energy recovery device is equipped with a piston assembly that can directly transmit the liquid pressure in the terminal membrane separation unit to the primary membrane separation unit. Compared with the pressure exchange and centrifugal energy recovery devices in the prior art, there is no need to install a pressure reducing valve or convert the pressure, which greatly reduces energy loss and significantly improves the energy recovery rate. Attached Figure Description

[0017] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0018] Figure 1 A schematic diagram of the piping of the multi-stage membrane separation system of the present invention is shown;

[0019] Figure 2 A cross-sectional view of the pressure recovery device of the multi-stage membrane separation system of the present invention is shown;

[0020] Figure 3 A schematic diagram of the separation method of the present invention is shown;

[0021] Figure 4 A schematic diagram illustrating the steps of controlling the movement of a piston assembly within an energy recovery device in the separation method of the present invention to recover energy from the final membrane separation device is shown.

[0022] Figure 5 A schematic diagram illustrating the steps of resetting the piston assembly within the energy recovery device of the separation method of the present invention is shown.

[0023] The above figures include the following reference numerals:

[0024] 1. Energy recovery device; 11. Hydraulic cylinder; 111. First cylinder body; 112. Second cylinder body; 113. Driven fluid chamber; 114. Driven fluid chamber; 12. Piston assembly; 121. First piston; 122. Second piston; 123. Connecting rod; 13. First inlet pipe; 14. First outlet pipe; 15. Second inlet pipe; 16. Second outlet pipe; 171. First check valve; 172. Second check valve; 18. Inlet valve; 19. Drain valve; 21. First-stage membrane separation device; 22. Last-stage membrane separation device; 23. Inlet end; 24. Concentrate end; 3. Inter-stage booster pump; 4. Pressure pump. Detailed Implementation

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] See also Figures 1 to 5As shown, the present invention provides a multi-stage membrane separation system, which includes an energy recovery device 1 and at least two membrane separation devices connected in series. The membrane separation devices include a first-stage membrane separation device 21 and a last-stage membrane separation device 22. One end of the energy recovery device 1 is connected to the first-stage membrane separation device 21, and the other end is connected to the last-stage membrane separation device 22. A piston assembly 12 is provided inside the energy recovery device 1, which can transmit the liquid pressure in the last-stage membrane separation device 22 to the first-stage membrane separation device 21.

[0027] In the above technical solution, the core function of the energy recovery device 1 is to recover and reuse the high-pressure energy generated during the membrane separation process, especially the concentrate pressure in the final membrane separation device 22, thereby achieving internal energy recycling. The piston assembly is the actuator in the energy recovery process. By adjusting the area ratio between the pistons, the high-pressure energy on the concentrate side of the final membrane separation device 22 is transferred to the low-pressure fluid on the inlet side of the first membrane separation device 21. This design eliminates the need for an additional pressure reducing valve and eliminates the need for an additional energy conversion process, making the recovery of pressure energy more direct and efficient. The first membrane separation device 21 is the initial stage of the entire membrane separation system. After filtration in the first membrane separation device 21, clean liquid and concentrate are separated. The clean liquid is transported to subsequent processes for recovery, while the concentrate is transported to the next membrane separation device for further filtration. The final membrane separation device 22 is responsible for processing the high-concentration fluid after filtration and separation by the first membrane separation device. One end of the energy recovery device is connected to the first-stage membrane separation device, and the other end is connected to the last-stage membrane separation device. This configuration allows the energy recovery device to directly utilize the high-pressure concentrate generated by the last-stage membrane separation device and convert its energy into pressurization for the feed to the first-stage membrane separation device.

[0028] The energy recovery device 1 is equipped with a piston assembly 12, which can directly transmit the liquid pressure in the final membrane separation device 22 to the first membrane separation device 21. Compared with the pressure exchange type and centrifugal type energy recovery devices in the prior art, there is no need to set up a pressure reducing valve or convert the pressure, which greatly reduces energy loss and significantly improves the energy recovery rate.

[0029] In one embodiment of the present invention, the membrane separation device includes an inlet end 23 and a concentrate end 24, and the energy recovery device 1 includes a hydraulic cylinder 11. One end of the hydraulic cylinder 11 is connected to the inlet end 23 of the first-stage membrane separation device 21, and the other end of the hydraulic cylinder 11 is connected to the concentrate end 24 of the final-stage membrane separation device 22. A piston assembly 12 is disposed inside the hydraulic cylinder 11, and the piston assembly 12 can move inside the hydraulic cylinder 11 to transmit the pressure of the concentrate end 24 of the final-stage membrane separation device 22 to the inlet end 23 of the first-stage membrane separation device 21.

[0030] In the above technical solution, the liquid to be filtered enters the membrane separation device through the inlet 23. Under the filtration action of the membrane separation, the filtered pure water is discharged from the outlet of the membrane separation device, while the high-concentration fluid remaining in the device is discharged from the concentrate 24. One end of the hydraulic cylinder is connected to the inlet of the first membrane and the other end is connected to the concentrate of the last membrane. The hydraulic cylinder can accommodate the liquid to be filtered and the concentrate as an energy transfer medium, and guide and limit the movement of the piston assembly inside the hydraulic cylinder. The piston assembly reciprocates within the hydraulic cylinder, ensuring that the high-pressure energy at the concentrate 24 of the last membrane separation device 22 can be directly transferred to the inlet 23 of the first membrane separation device 21. The design of the hydraulic cylinder and piston assembly allows for direct and efficient recovery of pressure energy within the system, avoiding energy loss in traditional pressure reducing valves or centrifugal pumps, and significantly improving energy recovery efficiency and overall system energy efficiency.

[0031] In one embodiment of the present invention, the hydraulic cylinder 11 includes a first cylinder body 111 and a second cylinder body 112. The first cylinder body 111 and the second cylinder body 112 are connected. A first piston 121 is disposed in the first cylinder body 111 and a second piston 122 is disposed in the second cylinder body 112. The first piston 121 and the second piston 122 are fixedly connected by a connecting rod 123 to form a piston assembly 12.

[0032] In the above technical solution, the two cylinders respectively house the first piston and the second piston, and their internal interconnection design allows the pistons to reciprocate between the two cylinders to transmit pressure. The first piston 121 and the second piston 122, as the core components of the piston assembly, move within their respective cylinders and are fixedly connected by a connecting rod. This ensures that pressure can be directly transmitted between the first piston 121 and the second piston 122, avoiding energy loss caused by other forms of pressure conversion. Simultaneously, the connecting rod connects the first piston 121 and the second piston 122 into a single unit, preventing pressure imbalance and energy waste due to asynchronous piston movement, thus ensuring synchronous movement and efficient pressure transmission.

[0033] In one embodiment of the present invention, the diameter of the first piston 121 is larger than the diameter of the second piston 122, the inner diameter of the first cylinder 111 matches the diameter of the first piston 121, the inner diameter of the second cylinder 112 matches the diameter of the second piston 122, the first cylinder 111 is connected to the water inlet 23 of the first-stage membrane separation device 21, and the second cylinder 112 is connected to the concentrate end 24 of the final-stage membrane separation device 22.

[0034] In the above technical solution, the pressure-bearing area of ​​the first piston 121 is greater than that of the second piston 122. The high-pressure concentrate discharged from the concentrate end 24 of the final membrane separation device 22 drives the second piston 122 with a smaller pressure-bearing area to move toward the first cylinder 111, thereby driving the first piston 121 with a larger pressure-bearing area to transport the liquid to be filtered in the first cylinder 111 to the inlet end 23 of the first membrane separation device 21. Due to the difference in the pressure-bearing areas of the first piston 121 and the second piston 122, the high pressure at the concentrate end 24 is reduced to the pressure level that the inlet end 23 of the first membrane separator 21 can withstand after being conducted by the piston assembly. For example, if the cross-sectional area of ​​the first piston 121 is nA (n>1) and the cross-sectional area of ​​the second piston 122 is A, when the driving pressure of the concentrate end 24 on the second piston 122 is nP, according to the pressure-area formula, the driven pressure of the first piston 121 on the inlet end 23 of the first membrane separator 21 is P, so that the pressure during the energy transfer process naturally drops to the level that the inlet end of the first membrane device can withstand, without the need for an additional pressure reducing valve, thereby avoiding energy loss.

[0035] Since the pressure-bearing areas of the first piston 121 and the second piston 122 are different, but their strokes are the same, the flow rate of the driven fluid is n times the flow rate of the driving fluid. The area ratio of the first piston 121 and the second piston 122 can be determined based on the inlet water pressure of the first membrane separation device and the concentrate pressure of the last membrane separation device in the multi-stage membrane separation system.

[0036] In one embodiment of the present invention, the chamber located on the side of the first piston 121 away from the second piston 122 within the first cylinder 111 is a driven fluid chamber 113. The driven fluid chamber 113 can contain the driven fluid. A first inlet pipe 13 and a first outlet pipe 14 are provided on the side of the driven fluid chamber 113 away from the second cylinder 112. The driven fluid can enter the driven fluid chamber 113 through the first inlet pipe 13, and the driven fluid in the driven fluid chamber 113 can be transported to the inlet end 23 of the first membrane separation device 21 through the first outlet pipe 14.

[0037] In the above technical solution, the driven fluid chamber 113 is used to contain the driven fluid, which is usually the liquid to be filtered. The first inlet pipe is responsible for introducing the fluid to be treated into the driven fluid chamber, while the first outlet pipe transports the driven fluid pushed by the first piston 121 from the driven fluid chamber 113 to the inlet 23 of the first membrane separation device 21 to realize the transmission of pressure.

[0038] In one embodiment of the present invention, the chamber located on the side of the second piston 122 away from the first piston 121 within the second cylinder 112 is a driving fluid chamber 114. The driving fluid chamber 114 can contain driving fluid. A second inlet pipe 15 and a second outlet pipe 16 are provided on the side of the driving fluid chamber 114 away from the second cylinder 112. The driving fluid can enter the driving fluid chamber 114 from the concentrate end 24 of the final membrane separator 22 through the second inlet pipe 15. The driving fluid in the driving fluid chamber 114 can be discharged through the second outlet pipe 16.

[0039] In the above technical solution, the driving fluid chamber 114 is used to contain high-pressure concentrate from the final membrane separator. The high pressure of the concentrate drives the second piston to move. The second inlet pipe 15 connects the driving fluid chamber 114 and the concentrate end 24 of the final membrane separator 22, ensuring that the concentrate can flow from the final membrane separator 22 into the driving fluid chamber 114. When the piston assembly moves back to the second cylinder 112, the driving fluid in the driving fluid chamber 114 can be discharged through the second outlet pipe 16.

[0040] In one embodiment of the present invention, an inter-stage booster pump 3 is provided between two adjacent membrane separation devices. The inter-stage booster pump 3 connects the concentrate end 24 of the front membrane separation device with the water inlet end 23 of the rear membrane separation device. The inter-stage booster pump 3 can increase the water inlet pressure of the water inlet end 23 of the rear membrane separation device.

[0041] In the above technical solution, the function of the inter-stage booster pump 3 is to pressurize the fluid discharged from the concentrate end 24 of the front membrane unit and send it to the inlet end 23 of the rear membrane unit, to compensate for the pressure loss caused during the membrane separation process, and to ensure that the fluid can enter the rear membrane unit at the required pressure level, thereby improving the recovery rate of the multi-stage membrane separation system.

[0042] In one embodiment of the present invention, a first check valve 171 is provided on the first inlet pipe 13, which is unidirectionally openable to the driven fluid chamber 113; a second check valve 172 is provided on the first outlet pipe 14, which is unidirectionally openable from the driven fluid chamber 113 to the inlet end 23 of the first membrane separation device 21; an inlet valve 18 is provided on the second inlet pipe 15; and a drain valve 19 is provided on the second outlet pipe 16.

[0043] In the above technical solution, the check valve is mainly used to prevent the fluid from flowing backward. Specifically, the first check valve 171 on the first inlet pipe 13 ensures that the driven fluid can enter the driven fluid chamber 113 unidirectionally from the first inlet pipe 13, and the second check valve 172 on the first outlet pipe 14 ensures that the driven fluid can be unidirectionally transported through the first outlet pipe 14 to the inlet end 23 of the first-stage membrane separation device 21. When the piston assembly moves towards the driven fluid chamber 113, the driven fluid can only flow out through the first outlet pipe 14 to the inlet end 23 of the first-stage membrane separation device 21, and will not flow out through the first outlet pipe 14. When the piston assembly moves back to its original position towards the driven fluid chamber 114, the driven fluid can enter the driven fluid chamber 113 from the first inlet pipe 13, preparing for the next pressure transmission. By setting the first check valve 171 and the second check valve 172, the normal operation of the differential pressure energy recovery device in this embodiment of the invention is ensured, thereby significantly improving the stability, reliability, and energy efficiency of the entire membrane separation system.

[0044] In one embodiment of the present invention, the energy recovery device is connected in parallel with the first-stage membrane separation device 21. A booster pump 4 is installed on the branch where the first-stage membrane separation device 21 is located. The booster pump 4 is located at the front end of the water inlet 23 of the first-stage membrane separation device 21. The high-pressure concentrate from the last-stage membrane separation device in the multi-stage membrane separation system is used as the driving force to realize the pressure transmission of the feed to the first-stage membrane separation device in the energy recovery device. At the same time, the driven fluid in the energy recovery device is transported to the water inlet 23 of the first-stage membrane separation device 21 under the pressure of the high-pressure concentrate from the last-stage membrane separation device. There is no need to pressurize through the booster pump 4, which reduces the amount of feed from the booster pump 4 to the first-stage membrane separation device 21, thereby achieving the effect of reducing energy consumption.

[0045] In one embodiment of the present invention, the pressure exchange process of the differential pressure energy recovery device is carried out in a hydraulic cylinder. Each differential pressure energy recovery device consists of two or more hydraulic cylinders connected in series or in parallel to ensure that the pressure exchange process can be carried out continuously.

[0046] In one embodiment of the present invention, the operating pressure range of the differential pressure energy recovery device is 2MPa~10MPa.

[0047] In one embodiment of the present invention, the membrane system is a two-stage membrane system. The feed rate of the first-stage membrane unit is 100 m³ / h, the feed pressure is 4 MPa, and the recovery rate is 40%, meaning the concentrate flow rate entering the second-stage membrane unit is 60 m³ / h. An inter-stage booster pump with a head of 200 m is installed between the first and second-stage membrane units. Considering the flow resistance loss of the first-stage membrane unit and connecting pipelines is 0.1 MPa, the feed pressure of the second-stage membrane unit is 6.9 MPa, and the recovery rate is 40%. The final concentrate side pressure of the second-stage membrane unit is 6.8 MPa, and the flow rate is 3... If the flow rate is 6 m³ / h, then this fluid is the driving fluid for the differential pressure energy recovery device; the driving fluid flow rate of the differential pressure energy recovery device is 36 m³ / h, and the pressure is 6.8 MPa; the pressure that the driven fluid needs to reach is 4 MPa, so the cross-sectional area ratio of the first piston to the second piston is 1.7:1, and the flow rate of the driven fluid is 61.2 m³ / h; therefore, in this two-stage membrane system, the parameters of the booster pump are a flow rate of 38.8 m³ / h and a head of 400 m; the parameters of the inter-stage booster pump are a flow rate of 60 m³ / h and a head of 200 m.

[0048] In one embodiment of the present invention, the membrane system is a three-stage membrane system. The feed rate of the first-stage membrane unit is 100 m³ / h, the feed pressure is 4 MPa, and the recovery rate is 40%, meaning the concentrate flow rate entering the second stage is 60 m³ / h. A booster pump with a head of 200 m is installed between the first and second-stage membrane units. Considering the flow resistance loss of the first-stage membrane unit and connecting pipeline is 0.1 MPa, the feed pressure of the second stage is 6.9 MPa, and the recovery rate is 40%, meaning the concentrate flow rate entering the third-stage membrane unit is 36 m³ / h. A booster pump with a head of 150 m is installed between the second and third-stage membrane units. Considering the flow resistance loss of the second-stage membrane unit and connecting pipeline is 0.1 MPa, the feed pressure of the second stage is 8.3 MPa, and the recovery rate is 30%. The final concentrate side pressure of the three-stage membrane unit is 8.2 MPa, and the flow rate is 25.2 m³ / h. Therefore, this fluid is the driving fluid of the differential pressure energy recovery device. The driving fluid of the differential pressure energy recovery device has a flow rate of 25.2 m³ / h and a pressure of 8.2 MPa. The pressure that the driven fluid needs to reach is 4 MPa, so the cross-sectional area ratio of the first piston to the second piston is 2.1:1, and the flow rate of the driven fluid is 52.92 m³ / h. Therefore, in this two-stage membrane system, the parameters of the booster pump are a flow rate of 47.08 m³ / h and a head of 400 m; the parameters of the interstage booster pump in the second stage are a flow rate of 60 m³ / h and a head of 200 m; and the parameters of the interstage booster pump in the third stage are a flow rate of 36 m³ / h and a head of 150 m.

[0049] See also Figures 1 to 5 As shown, the present invention also provides a separation method based on the multi-stage membrane separation system of the above embodiments. The separation method includes: controlling the movement of the piston group in the energy recovery device to recover energy from the final membrane separation device; and controlling the piston group in the energy recovery device to reset.

[0050] In the above technical solution, the piston assembly within the energy recovery device reciprocates within a hydraulic cylinder, directly transferring the high-pressure energy carried in the concentrate from the final membrane separator to the inlet of the first membrane separator. Compared to existing pressure-exchange and centrifugal energy recovery devices, this eliminates the need for pressure-reducing valves or other pressure conversion methods, significantly reducing energy losses during recovery and substantially improving the energy recovery rate. Subsequently, the piston assembly within the energy recovery device is reset, ensuring that the differential pressure energy recovery device of this invention is ready for the next energy reception and transfer cycle, guaranteeing continuous and efficient operation of the energy recovery device.

[0051] In one embodiment of the present invention, the step of controlling the movement of the piston assembly in the energy recovery device to recover energy from the final membrane separator includes: opening the inlet valve; closing the drain valve; and completing the recovery of energy from the concentrate end of the final membrane separator when the first outlet pipe stops discharging water, or the piston assembly moves to a preset position in the direction of the driven fluid chamber, or the piston assembly moves a preset stroke in the direction of the driven fluid chamber.

[0052] In the above technical solution, opening the inlet valve allows high-pressure concentrate to enter the drive fluid chamber from the concentrate end of the final membrane separator as the driving fluid. Closing the drain valve prevents the fluid in the drive fluid chamber from being discharged prematurely during energy recovery, ensuring sufficient pressure is built up in the chamber to drive the piston assembly. After opening the inlet valve and closing the drain valve, high-pressure concentrate enters the drive fluid chamber, pushing the piston assembly towards the first chamber, thereby discharging the liquid to be filtered from the driven fluid chamber to the inlet end of the first membrane separator, achieving concentrate end pressure recovery. When the first outlet pipe stops discharging water, it indicates that all the liquid in the driven fluid chamber has been discharged, thus completing the energy recovery at the concentrate end of the final membrane separator. Furthermore, the completion of energy recovery at the concentrate end of the final membrane separator can be determined based on the piston assembly's position or stroke. When the piston assembly moves to a preset position or travels a preset stroke towards the driven fluid chamber, the energy recovery at the concentrate end of the final membrane separator is complete.

[0053] In one embodiment of the present invention, the step of controlling the piston assembly reset in the energy recovery device includes: closing the water inlet valve; opening the drain valve; and completing the piston assembly reset in the energy recovery device when the second water outlet pipe stops discharging water, or the piston assembly moves to a preset position in the direction of the driving fluid chamber, or the piston assembly moves a preset distance in the direction of the driving fluid chamber.

[0054] In the above technical solution, since the concentrate pressure at the concentrate end of the final membrane separator is higher than the pressure of the liquid to be filtered injected into the driven fluid chamber through the first inlet pipe, when resetting the piston assembly, the inlet valve needs to be closed first to prevent the second piston from being pushed by the concentrate pressure. Then, the drain valve is opened, and the piston assembly moves towards the driving fluid chamber under the pressure of the liquid to be filtered in the driven fluid chamber, discharging the concentrate in the driving fluid chamber through the second outlet pipe into the hydraulic cylinder, thus resetting the piston assembly. When the second outlet pipe stops discharging water, all the concentrate in the driving fluid chamber has been discharged, indicating that the piston assembly has now reset to its limit position towards the driving fluid chamber, thereby completing the piston assembly reset within the energy recovery device. Furthermore, it can determine whether the piston group has been reset based on the movement position or stroke of the piston group. When the piston group moves to a preset position in the direction of the driving fluid chamber, or when the piston group moves a preset stroke in the direction of the driving fluid chamber, the energy recovery at the concentrate end of the final membrane separation device is completed, ensuring that the differential pressure energy recovery device of the present invention can be prepared for the next cycle of receiving and transmitting energy, thereby realizing the continuous and efficient operation of the energy recovery device.

[0055] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: The core function of the energy recovery device 1 is to recover and reuse the high-pressure energy generated during the membrane separation process, especially the concentrate pressure in the final membrane separation device 22, thereby realizing the internal recycling of energy. The piston assembly is the actuator in the energy recovery process. By adjusting the area ratio between the pistons, the high-pressure energy on the concentrate side of the final membrane separation device 22 is transferred to the low-pressure fluid on the inlet side of the first membrane separation device 21. This design eliminates the need for an additional pressure reducing valve and eliminates the need for an additional energy conversion process, making the recovery of pressure energy more direct and efficient. The first membrane separation device 21 is the initial stage of the entire membrane separation system. After the liquid is filtered by the first membrane separation device 21, clean liquid and concentrate are separated. The clean liquid is sent to the subsequent process for recovery, while the concentrate is sent to the next membrane separation device for further filtration. The final membrane separation device 22 is responsible for processing the high-concentration fluid after filtration and separation by the first membrane separation device. One end of the energy recovery device is connected to the first-stage membrane separation device, and the other end is connected to the last-stage membrane separation device. This configuration allows the energy recovery device to directly utilize the high-pressure concentrate generated by the last-stage membrane separation device and convert its energy into pressurization for the feed to the first-stage membrane separation device.

[0056] The energy recovery device 1 is equipped with a piston assembly 12, which can directly transmit the liquid pressure in the final membrane separation device 22 to the first membrane separation device 21. Compared with the pressure exchange type and centrifugal type energy recovery devices in the prior art, there is no need to set up a pressure reducing valve or convert the pressure, which greatly reduces energy loss and significantly improves the energy recovery rate.

[0057] Obviously, the embodiments described above are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0058] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-stage membrane separation system, characterized in that, The device includes an energy recovery device (1) and at least two membrane separation devices connected in series. The membrane separation devices include a first membrane separation device (21) and a last membrane separation device (22). One end of the energy recovery device (1) is connected to the first membrane separation device (21), and the other end is connected to the last membrane separation device (22). A piston assembly (12) is provided inside the energy recovery device (1). The piston assembly (12) can transmit the liquid pressure in the last membrane separation device (22) to the first membrane separation device (21).

2. The multi-stage membrane separation system according to claim 1, characterized in that, The membrane separation device includes an inlet end (23) and a concentrate end (24). The energy recovery device (1) includes a hydraulic cylinder (11). One end of the hydraulic cylinder (11) is connected to the inlet end (23) of the first-stage membrane separation device (21), and the other end of the hydraulic cylinder (11) is connected to the concentrate end (24) of the last-stage membrane separation device (22). The piston assembly (12) is disposed in the hydraulic cylinder (11). The piston assembly (12) can move in the hydraulic cylinder (11) to transmit the pressure of the concentrate end (24) of the last-stage membrane separation device (22) to the inlet end (23) of the first-stage membrane separation device (21).

3. The multi-stage membrane separation system according to claim 2, characterized in that, The hydraulic cylinder (11) includes a first cylinder body (111) and a second cylinder body (112). The first cylinder body (111) and the second cylinder body (112) are connected. A first piston (121) is provided in the first cylinder body (111), and a second piston (122) is provided in the second cylinder body (112). The first piston (121) and the second piston (122) are fixedly connected by a connecting rod (123) to form a piston assembly (12).

4. The multi-stage membrane separation system according to claim 3, characterized in that, The diameter of the first piston (121) is larger than the diameter of the second piston (122). The inner diameter of the first cylinder (111) matches the diameter of the first piston (121). The inner diameter of the second cylinder (112) matches the diameter of the second piston (122). The first cylinder (111) is connected to the water inlet (23) of the first-stage membrane separation device (21). The second cylinder (112) is connected to the concentrate end (24) of the last-stage membrane separation device (22).

5. The multi-stage membrane separation system according to claim 4, characterized in that, The chamber located on the side of the first piston (121) away from the second piston (122) within the first cylinder (111) is the driven fluid chamber (113). The driven fluid chamber (113) can contain the driven fluid. A first inlet pipe (13) and a first outlet pipe (14) are provided on the side of the driven fluid chamber (113) away from the second cylinder (112). The driven fluid can enter the driven fluid chamber (113) through the first inlet pipe (13). The driven fluid in the driven fluid chamber (113) can be transported to the inlet end (23) of the first membrane separation device (21) through the first outlet pipe (14).

6. The multi-stage membrane separation system according to claim 5, characterized in that, The chamber located on the side of the second piston (122) away from the first piston (121) within the second cylinder (112) is the driving fluid chamber (114). The driving fluid chamber (114) can contain driving fluid. A second inlet pipe (15) and a second outlet pipe (16) are provided on the side of the driving fluid chamber (114) away from the second cylinder (112). The driving fluid can enter the driving fluid chamber (114) through the second inlet pipe (15) from the concentrate end (24) of the final membrane separator (22). The driving fluid in the driving fluid chamber (114) can be discharged through the second outlet pipe (16).

7. The multi-stage membrane separation system according to claim 2, characterized in that, An inter-segment booster pump (3) is provided between two adjacent membrane separation devices. The inter-segment booster pump (3) connects the concentrate end (24) of the front membrane separation device with the water inlet end (23) of the rear membrane separation device. The inter-segment booster pump (3) can increase the water inlet pressure of the water inlet end (23) of the rear membrane separation device.

8. The multi-stage membrane separation system according to claim 6, characterized in that, A first check valve (171) is provided on the first inlet pipe (13), and the first check valve (171) is unidirectionally connected to the driven fluid chamber (113). A second check valve (172) is provided on the first outlet pipe (14), and the second check valve (172) is unidirectionally connected from the driven fluid chamber (113) to the inlet end (23) of the first membrane separation device (21). An inlet valve (18) is provided on the second inlet pipe (15), and a drain valve (19) is provided on the second outlet pipe (16).

9. A separation method, characterized in that, Based on the multi-stage membrane separation system as described in any one of claims 1 to 8, the separation method includes: Control the movement of the piston assembly within the energy recovery device to recover energy from the final membrane separation unit; Reset the piston assembly within the energy recovery device.

10. The separation method according to claim 9, characterized in that, The steps for controlling the movement of the piston assembly within the energy recovery device to recover energy from the final membrane separation unit include: Open the water inlet valve; Close the drain valve; When the first outlet pipe stops discharging water, or when the piston assembly moves to a preset position towards the driven fluid chamber, or when the piston assembly moves a preset stroke towards the driven fluid chamber, the energy recovery at the concentrate end of the final membrane separation device is completed.

11. The separation method according to claim 9, characterized in that, The steps for resetting the piston assembly within the energy recovery device include: Close the inlet valve; Open the drain valve; When the second water outlet pipe stops discharging water, or when the piston assembly moves to a preset position in the direction of the driving fluid chamber, or when the piston assembly moves a preset distance in the direction of the driving fluid chamber, the piston assembly in the energy recovery device is reset.

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