An apparatus and method for automatically adjusting the pressure of a membrane to remove N2 from SF6 gas.

Abstract

This invention discloses an automatic pressure-regulating membrane separator for removing N2 from SF6 gas. The device includes an inlet, a proportional valve, a compressor, a main flow controller, a first pressure sensor, a membrane separation assembly, an SF6 purity detection unit, a second pressure sensor, a third solenoid valve, and a filling port connected in series. On the other side of the membrane separation assembly, the first solenoid valve, a tail gas flow controller, a trace SF6 detection assembly, and an outlet are connected in series. An additional gas path connects the SF6 purity detection unit and the second pressure sensor, connecting in series to the return flow controller and the second solenoid valve, forming a loop at the inlet after the proportional valve and before the compressor. The recovered N2 and SF6 are detected by the trace SF6 detection assembly and the SF6 purity detection unit, thereby adjusting the opening of the proportional valve and the set value of the flow controller to improve the membrane separation effect and the purity of the recovered SF6 gas.

Description

Technical Field

[0001] This invention relates to the field of insulating gas separation, recovery and purification technology for GIS equipment, specifically an automatic pressure-regulating membrane separation device and method for removing N2 from SF6 gas. Background Technology

[0002] The power grid company has decided to promote the application of SF6 / N2 mixed gas GIS equipment. If the filling gas is substandard or if the SF6 / N2 mixed insulating gas electrical equipment malfunctions during operation, the SF6 / N2 mixed insulating gas will need to be separated, recovered, and purified.

[0003] Currently, the separation of SF6 / N2 mixed gases is often achieved by using polymer membranes, which utilize the different permeability of different types of gases through polymer membranes.

[0004] However, in order to achieve the best separation effect during the operation of the above process, the pressure at both ends is usually kept constant, i.e., the speed is constant. But at different stages, the gas concentration is different, and maintaining the same pressure will reduce the separation efficiency.

[0005] Existing technologies, such as the sulfur hexafluoride and nitrogen mixed gas recovery and separation device disclosed in CN214437798U, involve a mixed gas inlet pipeline connected to high-voltage electrical equipment. A first compressor extracts the sulfur hexafluoride and nitrogen mixed gas from the high-voltage electrical equipment. A PLC control device maintains the inlet pressure of the membrane separator at a stable 0.7 MPa by controlling the opening of a first electromagnetic proportional regulating valve. The sulfur hexafluoride and nitrogen mixed gas is separated by a primary separation membrane, with nitrogen entering the nitrogen discharge pipeline. The separated sulfur hexafluoride mixed gas then enters... The secondary separation membrane separates a high-concentration nitrogen-mixed gas, which is then returned to the primary compressor via a pipeline. An online sulfur hexafluoride (SF6) concentration monitoring instrument monitors the purity of the separated high-purity SF6 gas. When the purity is below 95%, the gas separated by the secondary separation membrane is returned to the primary compressor via the non-conforming gas return pipeline and reflux pipeline, where it undergoes further separation and purification by the primary and secondary separation membranes. When the purity is above 95%, the device closes the second solenoid valve and opens the second electromagnetic proportional regulating valve, allowing the SF6 gas to enter the SF6 storage tank. When the pressure in the SF6 storage tank is >0.3 MPa, the second compressor starts, filling the cylinder with SF6 gas; when the pressure in the SF6 storage tank is <0.08 MPa, the second compressor stops. A PLC controller controls the opening of the second electromagnetic proportional valve to maintain a stable outlet pressure for the membrane separation device, thus ensuring that the concentration of SF6 gas at the outlet is above 95%. In this scheme, the pressure difference between the front and back ends remains consistent throughout the separation and recovery process. However, the gas flow rate or pressure is not considered in stages during the entire membrane separation process, which fails to maximize the separation effect and results in low purity of the SF6 gas that is ultimately separated and recovered. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to improve the membrane separation effect and increase the purity of the recovered SF6 gas.

[0007] The present invention solves the above-mentioned technical problems through the following technical means:

[0008] The first aspect of this invention provides an automatic pressure-regulating membrane separation device for removing N2 from SF6 gas, comprising an inlet, a proportional valve, a compressor, a main flow controller, a first pressure sensor, a membrane separation assembly, an SF6 purity detection unit, a second pressure sensor, a third solenoid valve, and a filling port connected in series. On the other side of the membrane separation assembly, the first solenoid valve, a tail gas flow controller, a trace SF6 detection assembly, and an outlet are connected in series. An additional gas path connects the SF6 purity detection unit and the second pressure sensor, connecting in series to the return flow controller and the second solenoid valve, forming a loop at the inlet after the proportional valve and before the compressor. The recovered N2 and SF6 are detected by the trace SF6 detection assembly and the SF6 purity detection unit, thereby adjusting the opening of the proportional valve and the set value of the flow controller to improve the membrane separation effect and the purity of the recovered SF6 gas.

[0009] Beneficial effects: The automatic pressure-regulating membrane separation device of the present invention removes N2 from SF6 gas. The SF6 / N2 mixed gas enters the device and undergoes multiple stages and multiple cycles, as well as gas flow or pressure control to achieve separation, and the purity of SF6 gas is higher than or equal to 99%.

[0010] The proportional valve of this invention controls the N2 content in the mixed gas; increasing the opening of the proportional valve increases the N2 content and thus the pressure in the device. The flow controller controls the gas flow rate and pressure. The SF6 purity detection unit determines whether the separated gas needs to be returned for membrane separation again by detecting the purity of the recovered SF6. The trace SF6 detection component compares the detected SF6 content in the recovered N2 with the set value to adjust the flow controller's set value and control the separation efficiency of the membrane separation component.

[0011] Preferably, the separation process for the SF6 / N2 mixed gas entering the device is divided into three stages: initial separation, intermediate separation, and final separation.

[0012] The second aspect of the present invention provides a method for removing N2 from SF6 gas by automatic pressure regulating membrane separation. The method is divided into three separation stages: initial separation, intermediate separation, and final separation. The recovered N2 and SF6 are detected by a trace SF6 detection component and an SF6 purity detection unit, and the opening degree of the proportional valve and the set value of the flow controller are adjusted.

[0013] Preferably, when the SF6 purity detection unit detects that the purity of the recovered SF6 is less than 95%, the SF6 / N2 mixed gas enters the intermediate separation stage from the initial separation stage.

[0014] Preferably, when the SF6 purity detection unit detects that the purity of the recovered SF6 is close to 99%, the SF6 / N2 mixed gas enters the final separation stage from the intermediate separation stage.

[0015] Preferably, if the content of SF6 gas in the recovered N2 detected by the trace SF6 detection component is higher than a set value, the set flow rate of the reflux section flow controller is increased; if the content of SF6 gas is lower than the set value, the set flow rate of the reflux section flow controller is decreased.

[0016] Preferably, the SF6 purity detection unit detects the purity of the recovered SF6 gas. If the purity reaches 99% or higher, the third solenoid valve is opened to fill the separated gas that meets the standard. If the purity does not reach 99%, the gas is returned to the compressor inlet for membrane separation again.

[0017] Preferably, when the SF6 / N2 mixed gas enters the device for the initial separation stage, the opening of the proportional valve is reduced. At this time, the set flow rate of the tail gas section flow controller is greater than the set flow rate of the main flow controller and the set flow rate of the return flow controller.

[0018] The device measures the SF6 gas content in N2 after membrane separation using a trace SF6 detection component. If the SF6 gas content is higher than the set value, the proportional valve opening and the set flow rate of the main flow controller are further reduced, while the set flow rate of the return flow controller is increased. If the SF6 gas content is lower than the set value, the proportional valve opening and the set flow rate of the main flow controller are further increased, while the set flow rate of the return flow controller is decreased.

[0019] Then, the SF6 gas after membrane separation is tested by the SF6 purity detection unit. If the purity is lower than 99%, the gas that does not meet the standard is returned to the compressor inlet for membrane separation again. If it is lower than 95%, the set flow rate of the tail gas section flow controller is set to be greater than the set flow rate of the main flow controller and equal to the set flow rate of the return flow controller. The gas that does not meet the standard enters the staged return device, and then enters the intermediate separation stage.

[0020] Preferably, during the intermediate separation stage, the proportional valve opening is increased, at which point the device controls the tail gas section flow controller set flow value > the main flow controller set flow value = the return flow section flow controller set flow value.

[0021] The device measures the SF6 gas content in N2 after membrane separation using a trace SF6 detection component. If the SF6 gas content is higher than the set value, the set flow rate of the reflux section flow controller is increased; if the SF6 gas content is lower than the set value, the set flow rate of the reflux section flow controller is decreased.

[0022] Then, the SF6 gas after membrane separation is tested by the SF6 purity detection unit. If the purity is lower than 99% but higher than 95%, the setting device controls the main flow controller to set the flow rate value = the return flow controller to set the flow rate value = the tail gas flow controller to set the flow rate value. The gas that does not meet the standard is returned to the compressor inlet for membrane separation again.

[0023] Preferably, after multiple intermediate separation stages, the SF6 / N2 mixed gas enters the final separation stage. At this time, the set flow rate of the main flow controller is greater than the set flow rate of the return flow controller, which is twice the set flow rate of the tail gas flow controller.

[0024] The device measures the SF6 gas content in the N2 after membrane separation using a trace SF6 detection component. If the SF6 gas content is higher than the set value, the set flow rate of the tail gas section flow controller is lowered and the set flow rate of the reflux section flow controller is increased. If the SF6 gas content is lower than the set value, the set flow rate of the tail gas section flow controller is increased and the set flow rate of the reflux section flow controller is lowered.

[0025] The device uses an SF6 purity detection unit to detect the gas after membrane separation. If the purity is higher than 99%, the second solenoid valve is closed and the third solenoid valve is opened to fill the gas that meets the separation standard. If the purity is still lower than 99%, the device sets the main flow controller to the set flow value, the return flow controller to the set flow value, and the exhaust gas controller to the set flow value. The gas that does not meet the standard is returned to the compressor inlet for membrane separation again.

[0026] Beneficial effects: The automatic pressure-regulating membrane separation method for removing N2 from SF6 gas of the present invention solves the problem of low membrane separation efficiency caused by constant pressure (which cannot be dynamically adjusted with changes in gas concentration) when separating SF6 / N2 mixed gas; and improves the purity of recovered SF6 gas.

[0027] The advantages of this invention are:

[0028] The present invention relates to an automatic pressure-regulating membrane separation device for removing N2 from SF6 gas. The SF6 / N2 mixed gas enters the device and undergoes multiple stages and multiple cycles, as well as gas flow or pressure control to achieve separation, and the purity of the SF6 gas is higher than or equal to 99%.

[0029] The proportional valve of this invention controls the N2 content in the mixed gas; increasing the opening of the proportional valve increases the N2 content and thus the pressure in the device. The flow controller controls the gas flow rate and pressure. The SF6 purity detection unit determines whether the separated gas needs to be returned for membrane separation again by detecting the purity of the recovered SF6. The trace SF6 detection component compares the detected SF6 content in the recovered N2 with the set value to adjust the flow controller's set value and control the separation efficiency of the membrane separation component.

[0030] The automatic pressure-regulating membrane separation method for removing N2 from SF6 gas of the present invention solves the problem of low membrane separation efficiency caused by constant pressure (which cannot be dynamically adjusted according to changes in gas concentration) when separating SF6 / N2 mixed gas; and improves the purity of recovered SF6 gas. Attached Figure Description

[0031] Figure 1 This is the automatic pressure-regulating membrane separation device for removing N2 from SF6 gas as described in Example 1;

[0032] 1. Inlet, 2. Proportional valve, 3. Compressor, 4. Main flow controller, 5. First pressure sensor, 6. Membrane separation assembly, 7. First solenoid valve, 8. Exhaust gas flow controller, 9. Trace SF6 detection assembly, 10. Emission port, 11. SF6 purity detection unit, 12. Recirculation flow controller, 13. Second solenoid valve, 14. Second pressure sensor, 15. Third solenoid valve, 16. Filling port. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] like Figure 1As shown, an automatic pressure-regulating membrane separator for removing N2 from SF6 gas comprises an inlet 1, a proportional valve 2, a compressor 3, a main flow controller 4, a first pressure sensor 5, a membrane separation assembly 6, an SF6 purity detection unit 11, a second pressure sensor 14, a third solenoid valve 15, and a filling port 16 connected in series. On the other side of the membrane separation assembly 6, a first solenoid valve 7, a tail gas flow controller 8, a trace SF6 detection assembly 9, and an outlet 10 are connected in series. An additional gas path connects the SF6 purity detection unit 11 and the second pressure sensor 14, connecting in series to a return flow controller 12 and a second solenoid valve 13, forming a loop at the inlet after the proportional valve 2 and before the compressor 3. The recovered N2 and SF6 are detected by the trace SF6 detection assembly 9 and the SF6 purity detection unit 11, thereby adjusting the opening of the proportional valve 2 and the set value of the flow controller to improve the membrane separation effect and the purity of the recovered SF6 gas.

[0036] Example 2

[0037] Currently, the purity control of SF6 gas after separation and recovery of SF6 / N2 mixed gas in the power industry is as follows: the purity of SF6 recovered and stored after separation is not less than 99%. However, due to the varying degrees of separation for different gas volumes during membrane separation, and the potential for insufficient performance with a single membrane separation cycle, multiple cycles are necessary. Therefore, various separation scenarios and stages require separate consideration. Based on a comprehensive analysis of different separation and recovery scenarios, the separation process is divided into three stages: initial separation, intermediate separation, and final separation. The initial separation stage occurs during the initial recovery of the SF6 / N2 mixture. At this point, separation has not yet begun, the SF6 / N2 mixture ratio is approximately 30:70, and the N2 concentration is high, requiring rapid and efficient N2 separation. The intermediate separation stage occurs after one or two initial separations. At this stage, most of the N2 in the mixture has been separated, but some remains, and the SF6 purity is below 99%. Therefore, it is necessary to accelerate the circulation efficiency and perform multiple membrane separations to quickly remove the residual SF6. The final separation stage occurs after multiple intermediate separations. At this point, the SF6 purity should be around 99%. If it does not meet the standard, pressurization is applied to separate the residual N2. If it does meet the standard, rapid filling and collection completes the separation task.

[0038] A method for removing N2 from SF6 gas using an automatic pressure-regulating membrane separation system comprises the following three separation stages:

[0039] (1) Initial separation stage (at which time the N2 concentration is high)

[0040] When the SF6 / N2 mixed gas enters the device, the opening of the proportional valve 2 is reduced, and the gas enters the membrane separation module 6 for separation. At this time, the flow rate set by the tail gas flow controller 8 is greater than the flow rate set by the main flow controller 4, which is greater than the flow rate set by the return flow controller 12. Since the N2 content in the gas path is relatively high at this time, the tail gas flow rate needs to be adjusted to the maximum so that the N2 separated by the membrane can be quickly discharged. However, the pressure difference between the inside and outside of the membrane separation module 6 cannot be too large. If it is too large, the SF6 gas will be separated out along with the N2, resulting in the N2 emission not meeting the requirements. Therefore, it is necessary to limit the inlet gas flow rate or pressure at the front end of the membrane separation module 6 and limit the outlet gas flow rate or pressure at the rear end of the membrane separation module 6 to keep the gas in the membrane separation module 6 in a smooth flow state to achieve the maximum efficiency of membrane separation.

[0041] The device measures the SF6 gas content in N2 after membrane separation using the micro SF6 detection component 9. If the SF6 gas content is higher than the set value, the opening of the proportional valve 2 and the set flow value of the main flow controller 4 are further reduced, while the set flow value of the return flow controller 12 is increased. If the SF6 gas content is lower than the set value, the opening of the proportional valve 2 and the set flow value of the main flow controller 4 are further increased, while the set flow value of the return flow controller 12 is decreased.

[0042] Then, the SF6 gas after membrane separation is detected by the SF6 purity detection unit 11. If the purity is lower than 99%, the gas that does not meet the standard is returned to the air inlet of the compressor 3 for membrane separation again. If it is lower than 95%, the setting device controls the flow rate of the tail gas section flow controller 8 to be greater than the flow rate of the main flow controller 4 and equal to the flow rate of the return flow controller 12. The gas that does not meet the standard is returned to the air inlet of the compressor 3 for membrane separation again. At this time, the intermediate separation stage is entered.

[0043] (2) Intermediate separation stage (at this time, N2 is low, but SF6 gas purity does not meet the standard)

[0044] When the SF6 / N2 mixed gas enters the device, it enters the intermediate separation stage. The N2 concentration in the gas path is relatively low, while the SF6 concentration is relatively high. The total gas volume in the gas path is less than that in the initial separation stage. The opening of the proportional valve 2 is increased. At this time, the set flow value of the tail gas section flow controller 8 is greater than the set flow value of the main flow controller 4, which equals the set flow value of the return flow controller 12. Although the N2 content in the gas path is low at this time, the purity has not reached the separation requirements. Therefore, it is still necessary to set the tail gas section gas flow to the maximum so that the N2 separated by the membrane can be quickly discharged. Since the gas volume inside the device is significantly less than that in the initial separation stage, the set flow value of the main flow controller 4 needs to be slightly higher than that in the previous stage. The gas flow or pressure at the front input and rear output of the membrane separation component 6 is kept in an open state. The gas flow rate is fast, but the pressure difference between the front and rear ends is small, which speeds up the number of times the gas exchanges with the membrane separation component 6 per unit time.

[0045] The device measures the SF6 gas content in N2 after membrane separation using the micro SF6 detection component 9. If the SF6 gas content is higher than the set value, the set flow rate of the reflux section flow controller 12 is increased; if the SF6 gas content is lower than the set value, the set flow rate of the reflux section flow controller 12 is decreased.

[0046] Then, the SF6 gas after membrane separation is detected by the SF6 purity detection unit 11. If the purity is lower than 99% but higher than 95%, the setting device controls the main flow controller 4 to set the flow rate value = the return flow controller 12 to set the flow rate value = the tail gas flow controller 8 to set the flow rate value. The gas that does not meet the standard is returned to the air inlet of the compressor 3 for membrane separation again.

[0047] (3) End of separation stage (at this time, N2 is extremely low and SF6 gas purity can reach 99%)

[0048] After multiple intermediate separations, the N2 concentration in the gas path is relatively low, while the SF6 concentration is relatively high. At this point, the set flow rate of the main flow controller 4 is greater than the set flow rate of the return flow controller 12, which is twice the set flow rate of the tail gas flow controller 8. Since the N2 content in the gas path is low at this time, the amount of gas separated by the membrane is also small. Therefore, the set flow rate of the tail gas flow controller 8 is reduced, the set flow rate of the main flow controller 4 is increased, and the set flow rate of the return flow controller 12 is reduced. This keeps the membrane separation assembly 6 under a high pressure differential and restricts the gas flow at the tail gas end, thereby further increasing the membrane separation intensity.

[0049] The device measures the SF6 gas content in N2 after membrane separation using the micro SF6 detection component 9. If the SF6 gas content is higher than the set value, the set flow rate of the tail gas section flow control 8 is reduced, and the set flow rate of the return flow controller 12 is increased. If the SF6 gas content is lower than the set value, the set flow rate of the tail gas section flow control 8 is increased, and the set flow rate of the return flow controller 12 is reduced.

[0050] Then, the SF6 gas after membrane separation is tested by the SF6 purity detection unit 11. If the purity is higher than 99%, the second solenoid valve 13 is closed and the third solenoid valve 15 is opened to fill the separated gas that meets the standard. If the purity is still lower than 99%, the setting device controls the main flow controller 4 to set the flow rate value = the return flow controller 12 to set the flow rate value = the tail gas flow controller 8 to set the flow rate value. The gas that does not meet the standard is returned to the air inlet of the compressor 3 for membrane separation again.

[0051] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An automatic pressure-regulating membrane separator for removing N2 from SF6 gas, characterized in that, The system includes an air inlet (1), a proportional valve (2), a compressor (3), a main flow controller (4), a first pressure sensor (5), a membrane separation assembly (6), an SF6 purity detection unit (11), a second pressure sensor (14), a third solenoid valve (15), and a filling port (16) connected in series. On the other side of the membrane separation assembly (6), the first solenoid valve (7), the tail gas section flow controller (8), the trace SF6 detection assembly (9), and the discharge port (10) are connected in series. The SF6 purity detection unit (11) and the second pressure sensor (14) are connected to a separate gas path, which is connected in series to the return flow controller (12), the second solenoid valve (13) and the air inlet after the proportional valve (2) and before the compressor (3) to form a loop. The recovered N2 and SF6 are detected by the trace SF6 detection assembly (9) and the SF6 purity detection unit (11), thereby adjusting the opening of the proportional valve (2) and the set value of the flow controller to improve the membrane separation effect and the purity of the recovered SF6 gas. When the SF6 / N2 mixed gas enters the device for separation, it is divided into three separation stages: initial separation, intermediate separation and final separation. The recovered N2 and SF6 are detected by the trace SF6 detection component (9) and the SF6 purity detection unit (11), and the opening size of the proportional valve (2) and the set value of the flow controller are adjusted.

2. A method for removing N2 from SF6 gas using an automatic pressure-regulating membrane separator with the apparatus described in claim 1, characterized in that, When the SF6 purity detection unit (11) detects that the purity of the recovered SF6 is less than 95%, the SF6 / N2 mixed gas enters the intermediate separation stage from the initial separation stage; when the SF6 purity detection unit (11) detects that the purity of the recovered SF6 is close to 99%, the SF6 / N2 mixed gas enters the final separation stage from the intermediate separation stage.

3. The method according to claim 2, characterized in that, If the content of SF6 gas in the recovered N2 detected by the trace SF6 detection component (9) is higher than the set value, the set flow value of the return flow controller (12) will be increased; if the content of SF6 gas is lower than the set value, the set flow value of the return flow controller (12) will be decreased.

4. The method according to claim 2, characterized in that, The SF6 purity detection unit (11) detects the purity of the recovered SF6 gas. If the purity reaches 99% or above, the third solenoid valve (15) is opened to fill the separated qualified gas. If the purity does not reach 99%, the gas is returned to the air inlet of the compressor (3) for membrane separation again.

5. The method according to claim 2, characterized in that, When the SF6 / N2 mixed gas enters the device for the initial separation stage, the opening of the proportional valve (2) is reduced. At this time, the set flow value of the tail gas section flow controller (8) is greater than the set flow value of the main flow controller (4) and the set flow value of the return flow controller (12). The device measures the SF6 gas content in N2 after membrane separation using a micro SF6 detection component (9). If the SF6 gas content is higher than the set value, the opening of the proportional valve (2) and the set flow value of the main flow controller (4) are further reduced, and the set flow value of the return flow controller (12) is increased. If the SF6 gas content is lower than the set value, the opening of the proportional valve (2) and the set flow value of the main flow controller (4) are further increased, and the set flow value of the return flow controller (12) is decreased. Then, the SF6 gas after membrane separation is detected by the SF6 purity detection unit (11). If the purity is lower than 99%, the gas that does not meet the standard is returned to the air inlet of the compressor (3) for membrane separation again. If it is below 95%, the set flow value of the tail gas section flow controller (8) is greater than the set flow value of the main flow controller (4) and the set flow value of the return flow controller (12). The gas that does not meet the standard is returned to the inlet of the compressor (3) for membrane separation again. At this time, it enters the intermediate separation stage.

6. The method according to claim 3, characterized in that, During the intermediate separation stage, the opening of the proportional valve (2) is increased. At this time, the set flow value of the tail gas section flow controller (8) is greater than the set flow value of the main flow controller (4) and the set flow value of the return flow controller (12). The device measures the content of SF6 gas in N2 after membrane separation by a micro SF6 detection component (9). If the SF6 gas content is higher than the set value, the flow rate of the reflux section flow controller (12) is increased; if the SF6 gas content is lower than the set value, the flow rate of the reflux section flow controller (12) is decreased. Then, the SF6 gas after membrane separation is detected by the SF6 purity detection unit (11). If the purity is lower than 99% but higher than 95%, the setting device controls the main flow controller (4) to set the flow value = the return flow controller (12) to set the flow value = the tail gas flow controller (8) to set the flow value. The gas that does not meet the standard is returned to the air inlet of the compressor (3) for membrane separation again.

7. The method according to claim 6, characterized in that, After multiple intermediate separation stages, the SF6 / N2 mixed gas enters the final separation stage. At this time, the flow rate set by the main flow controller (4) is greater than the flow rate set by the return flow controller (12) and twice the flow rate set by the tail gas flow controller (8). The device measures the SF6 gas content in N2 after membrane separation using a micro SF6 detection component (9). If the SF6 gas content is higher than the set value, the set flow rate of the tail gas section flow controller (8) is lowered and the set flow rate of the return flow controller (12) is increased. If the SF6 gas content is lower than the set value, the set flow rate of the tail gas section flow controller (8) is increased and the set flow rate of the return flow controller (12) is lowered. The device detects the gas after membrane separation through the SF6 purity detection unit (11). If the purity is higher than 99%, the second solenoid valve (13) is closed and the third solenoid valve (15) is opened to fill the separated gas that meets the standard. If the purity is still lower than 99%, the device controls the main flow controller (4) to set the flow value = the return flow controller (12) to set the flow value = the tail gas flow controller (8) to set the flow value. The gas that does not meet the standard is returned to the air inlet of the compressor (3) for membrane separation again.

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