SF6 / N2 mixed gas membrane separation method and device with membrane inlet gas temperature and pressure self-adjusting function

Abstract

The invention provides an SF6 / N2 mixed gas membrane separation method and device with a membrane inlet gas temperature and pressure self-adjusting function, the device comprises a plurality of purification devices, each purification device comprises a compressor, a heater and a polymeric membrane which are arranged in sequence, at least two purification devices are arranged on a purification pipeline of the device, and the compressor is connected with the heater. A permeation opening of the polymeric membrane of each purification device is connected to a gas inlet of the first purification device on the purification pipeline through the purification device on the permeation pipeline, and an SF6 purity detection module is arranged on a pipeline of a gas outlet of the purification device on the purification pipeline; a gas outlet of each purification device on the permeation pipeline is provided with a discharged tail gas detection module, and the temperature and pressure of membrane inlet gas of a polymeric membrane of each purification device are adjusted according to detection and judgment of the SF6 purity detection module and the discharged tail gas detection module; therefore, the finished gas at the gas outlet of the purification pipeline and the tail gas discharged from the gas outlet of the permeation pipeline meet preset requirements.

Description

Technical Field

[0001] The present invention relates to the field of gas separation, in particular to the separation of mixed gases of SF6 and N2. Background Art

[0002] In order to achieve further environmental protection, the existing electrical equipment is promoting the use of SF6 / N2 (volume ratio 30%:70%) mixed gas to replace the strong greenhouse gas SF6 gas as an insulating medium. The SF6 / N2 mixed gas needs to be recovered when the electrical equipment is retired and repaired, and the recovered gas needs to be separated before it can be put into use again. Different from the traditional pure SF6 gas separation process, the SF6 / N2 mixed gas contains a high proportion of N2. Membrane separation technology is often used to extract N2 from the sulfur hexafluoride mixed insulating gas. After treatment, the residual SF6 meets environmental protection requirements and is discharged. After separation, the SF6 is recovered to a cylinder or tank for storage, and then deeply purified and recycled to improve work efficiency.

[0003] The separation effect of polymer membrane is closely related to the temperature and pressure of the gas entering the membrane. Generally speaking, the temperature and pressure of the gas entering the membrane are positively correlated with the separation effect, but as the temperature and pressure increase, the effect of increasing the temperature and pressure on the optimization of polymer membrane separation will gradually decrease, and too high temperature and pressure will promote the aging of the membrane group. Therefore, in order to take into account both the separation effect and the life of the membrane group, in the actual application of polymer membranes, the gas entering the membrane will be adjusted to the preset optimal working temperature and pressure through the temperature and pressure control modules.

[0004] However, as the polymer membrane ages during use, its optimal operating temperature and pressure will also change. If it continues to work at the preset optimal operating temperature and pressure, the separation effect will be poor, the purity of SF6 in the output gas will decrease, and the exhaust gas will contain a high concentration of SF6, which will not meet environmental protection requirements. In addition, the polymer membrane is generally composed of multiple polymer membranes in series and parallel. The degree of aging may vary between different polymer membranes, and the mismatch between their working conditions will increase, which will further reduce the separation effect. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to improve the separation effect of SF6 / N2 mixed gas.

[0006] The present invention solves the above-mentioned technical problems through the following technical means: a SF6 / N2 mixed gas membrane separation method with self-regulation of membrane inlet gas temperature and pressure, including several sets of purification devices, each set of purification devices including a compressor, a heater and a polymer membrane arranged in sequence, at least two sets of purification devices are arranged on the purification pipeline of the device, the permeation port of the polymer membrane of each set of purification devices is connected to the air inlet of the first set of purification devices on the purification pipeline through the purification device arranged on the permeation pipeline, an SF6 purity detection module is arranged on the pipeline of the purification device outlet on the purification pipeline, and an exhaust gas detection module is arranged at the outlet of the purification device on the permeation pipeline, and the membrane inlet gas temperature and pressure of the polymer membrane of each purification device are adjusted according to the detection and judgment of the SF6 purity detection module and the exhaust gas detection module, so that the finished gas at the outlet of the purification pipeline and the exhaust gas at the outlet of the permeation pipeline meet the preset requirements.

[0007] As a further optimized technical solution, the temperature and pressure of the gas entering the polymer membrane of each purification device are adjusted according to the detection judgment of the SF6 purity detection module and the exhaust gas detection module, so that the finished gas at the outlet of the purification pipeline and the exhaust gas at the outlet of the permeation pipeline meet the preset requirements, including:

[0008] The gas to be separated enters the membrane separation system from the air inlet, and the pressure and temperature of each purification device are controlled at the set working conditions. The finished gas flowing out after separation by the last set of purification devices on the purification pipeline enters the SF6 purity detection module (11) to determine whether its SF6 purity meets ≥95%. The waste gas flowing out after separation by the last set of purification devices on the permeation pipeline enters the exhaust gas detection module (12) for SF6 concentration detection to determine whether it is ≤500ppm.

[0009] There are four results from the above judgment:

[0010] ① The purity of SF6 in the finished gas is ≥95%, and the concentration of SF6 in the exhaust gas is ≤500ppm;

[0011] ② The purity of SF6 in the finished gas is less than 95%, and the concentration of SF6 in the exhaust gas is ≤500ppm;

[0012] ③ The purity of SF6 in the finished gas is ≥95%, and the concentration of SF6 in the exhaust gas is >500ppm;

[0013] ④ The purity of SF6 in the finished gas is less than 95%, and the concentration of SF6 in the exhaust gas is greater than 500ppm;

[0014] 1) If the judgment result is ①, there is no need to change the gas inlet temperature and pressure of each set of polymer membrane of the purification device;

[0015] 2) If the judgment result is ②, it means that the working result of the purification device on the permeation pipeline meets the requirements, and the inlet gas temperature and pressure of the polymer membrane of the purification device on the purification pipeline need to be adjusted:

[0016] 3) If the judgment result is ③, it means that the working performance of the polymer membrane of the purification device on the permeation pipeline has declined and needs to be adjusted;

[0017] 4) If the judgment result is ④, there are 3 situations:

[0018] A. The performance of the polymer membrane in the first half of the purification pipeline and the permeation pipeline is degraded;

[0019] B. The performance of the polymer membrane in the second half of the purification pipeline and the permeation pipeline is degraded;

[0020] C. The performance of the polymer membrane on the purification pipeline and the polymer membrane on the permeation pipeline are both degraded;

[0021] Adjust them separately.

[0022] As a further optimized technical solution, taking the case where a first purification device and a second purification device are sequentially arranged on the purification pipeline and a third purification device is arranged on the permeation pipeline as an example, the temperature and pressure of the gas entering the polymer membrane of each purification device are adjusted specifically including the following steps:

[0023] 1) If the judgment result is ①, there is no need to change the inlet gas temperature and pressure of the polymer membranes of the three purification devices.

[0024] 2) If the judgment result is ②, it means that the working result of the third polymer membrane (10) of the third purification device meets the requirements, and the inlet gas temperature and pressure of the first polymer membrane (4) and the second polymer membrane (7) of the first purification device and the second purification device need to be adjusted:

[0025] First, the temperature and pressure of the gas entering the first polymer membrane (4) are adjusted, and the pressure and temperature of the gas entering the membrane are respectively increased by ΔP and ΔT through the first compressor (2) and the first heater (3) of the first purification device, and the indication value of the SF6 purity detection module (11) is observed to be ≥95%; if so, the regulation is stopped, and the optimal working condition of the first polymer membrane (4) is updated to (P 1,1 、T 1,1 );

[0026] On the contrary, after the temperature and pressure of the first polymer membrane (4) are adjusted, the purity increase value △Z of the SF6 gas in the finished gas is determined: if △Z ≥ 2%, it means that the adjustment of its temperature and pressure has a good effect, and the temperature and pressure are continued to be increased by △P and △T; if 1% ≤ △Z < 2%, it means that the effect of the adjustment of its temperature and pressure is general, and the gas entering the membrane is maintained at the temperature and pressure, and the optimal working condition of the first polymer membrane (4) is updated to (P 1,1 、T 1,1 ), continue to adjust the temperature and pressure of the second polymer film (7); if △Z≤1%, it means that the effect of adjusting the temperature and pressure is poor, and the temperature and pressure are returned to (P 1,0 、T 1,0 ), continue to adjust the temperature and pressure of the second polymer membrane (7);

[0027] The temperature and pressure adjustment method of the second polymer membrane (7) is the same as above. If the purity of SF6 in the finished gas after adjustment is ≥95%, the adjustment is stopped and the optimal working condition of the first polymer membrane (4) is updated to (P 2,1 、T 2,1 );

[0028] On the contrary, the purity increase value △Z of SF6 gas in the finished gas is further determined: if △Z≥2%, the temperature and pressure are further increased by △P and △T; if 1%≤△Z<2%, the gas entering the membrane is kept at the temperature and pressure, and the optimal working condition of the second polymer membrane (7) is updated to (P 2,1 、T 2,1 ), and in turn, the temperature and pressure of the first polymer film (4) are adjusted again; if △Z≤1%, the temperature and pressure are returned to (P 1,0 、T 1,0 ), which indicates that the working performance of the first polymer film (4) and the second polymer film (7) has seriously deteriorated and both need to be replaced;

[0029] 3) If the judgment result is ③, it means that the working performance of the third polymer membrane (10) of the third purification device has declined and needs to be adjusted. The pressure and temperature of the gas entering the membrane are respectively increased by △P and △T through the third compressor (8) and the third heater (9) of the third purification device. If the SF6 gas concentration in the exhaust gas is less than 500ppm, the adjustment is stopped and the optimal working condition of the third polymer membrane (10) is updated to (P 3,1 、T 3,1 ), on the contrary, determine the decrease value △C of the SF6 gas concentration in the exhaust gas: if △C≥2%, it means that the adjustment of its temperature and pressure has a good effect, and continue to increase its temperature and pressure by △P and △T; if △C<2%, it means that the effect of adjusting its temperature and pressure is poor, and the working performance of the third polymer membrane (10) is seriously degraded and needs to be replaced;

[0030] 4) If the judgment result is ④, there are 3 situations:

[0031] A. the performance of the first polymer membrane (4) of the first purification device and the third polymer membrane (10) of the third purification device are degraded;

[0032] B. the performance of the second polymer membrane (7) of the second purification device and the third polymer membrane (10) of the third purification device is degraded;

[0033] C. The performance of the first polymer membrane (4), the second polymer membrane (7) of the first purification device and the third polymer membrane (10) of the third purification device are all degraded;

[0034] First, the temperature and pressure of the gas entering the first polymer membrane (4) and the third polymer membrane (10) are adjusted;

[0035] If the purity of SF6 gas in the finished gas is ≥95% and the concentration of SF6 gas in the exhaust gas is <500ppm, the optimal working conditions for stopping adjustment and updating the first polymer membrane (4) and the third polymer membrane (10) are (P 1,1 , T 1,1 ) and (P 3,1 , T 3,1 );

[0036] If the purity of SF6 gas in the finished gas is ≥95% and the concentration of SF6 gas in the exhaust gas is ≥500ppm, stop adjusting the working conditions of the gas entering the first polymer membrane (4). At this time, determine the decrease value △C of the SF6 gas concentration in the exhaust gas: if △C is ≥2%, continue to increase its temperature and pressure by △P and △T; if △C is less than 2%, it means that the effect of adjusting its temperature and pressure is poor, and the working performance of the third polymer membrane (10) is seriously degraded and needs to be replaced;

[0037] If the purity of SF6 gas in the finished gas is less than 95% and the concentration of SF6 gas in the exhaust gas is less than 500ppm, stop adjusting the working conditions of the gas inlet to the third polymer membrane (4), and refer to step 2);

[0038] If the purity of SF6 gas in the finished gas is less than 95% and the concentration of SF6 gas in the exhaust gas is ≥500ppm, the temperature and pressure of the gas entering the first polymer membrane (4), the second polymer membrane (7) and the third polymer membrane are regulated at the same time. If they meet the requirements after regulation, update (P 1,1 , T 1,1 )、(P 2,1 , T 2,1 ) and (P 3,1 , T 3,1 ); if the purity of SF6 gas is less than 95% after adjustment, update (P 3,1 , T3,1 ), refer to step 2) to adjust the temperature and pressure of the gas entering the first polymer membrane (4) and the second polymer membrane (7); after adjustment, the SF6 gas concentration in the exhaust gas is less than 500ppm, and the (P 1,1 , T 1,1 ) and (P 2,1 , T 2,1 ), refer to step 3) to adjust the temperature and pressure of the gas entering the third polymer membrane (10).

[0039] The present invention also provides a device for separating SF6 / N2 mixed gases by membranes with a method for self-regulating the temperature and pressure of the gas entering the membrane as described in any one of the above items, comprising an air inlet (1), a first compressor (2), a first heater (3), a first polymer membrane (4), a second compressor (5), a second heater (6) and a second polymer membrane (7) connected in sequence, the air outlet of the second polymer membrane (7) serving as a finished gas outlet 13 of the device, an SF6 purity detection module (11) being arranged on the pipeline of the air outlet of the second polymer membrane (7), the air outlets of the first polymer membrane (4) and the second polymer membrane (7) being simultaneously connected to a third compressor (8), the third compressor (8) being connected in sequence to a third heater (9) and a third polymer membrane (10), the air outlet of the third polymer membrane (10) serving as an exhaust gas discharge outlet, an exhaust gas detection module (12) being arranged on the air outlet pipeline of the third polymer membrane (10), and the air outlet of the third polymer membrane (10) being connected to the inlet of the first compressor (2).

[0040] As a further optimized technical solution, the present invention also provides another temperature and pressure regulation method, which adopts fuzzy PID control technology to adjust the inlet gas temperature and pressure of the polymer membrane of each purification device according to the detection and judgment of the SF6 purity detection module and the exhaust gas detection module. Each set of purification device is respectively provided with a corresponding fuzzy PID module, and each fuzzy PID module is a cascade structure. Therefore, the main loop in the cascade structure is a pressure fuzzy PID controller, and the sub-loop is a temperature fuzzy PID controller. The inputs of each fuzzy PID controller are pressure, temperature, and the corresponding SF6 gas proportion at the polymer membrane outlet. The object of each fuzzy PID controller is the compressor or heater at the corresponding polymer membrane inlet, thereby controlling the SF6 gas proportion at the corresponding polymer membrane outlet.

[0041] As a further optimized technical solution, the temperature and pressure of the gas entering the polymer membrane of each purification device are adjusted according to the detection judgment of the SF6 purity detection module and the exhaust gas detection module, so that the finished gas at the outlet of the purification pipeline and the exhaust gas at the outlet of the permeation pipeline meet the preset requirements, including:

[0042] The gas to be separated enters the membrane separation system from the air inlet, and the pressure and temperature of each purification device are controlled at the set working conditions. The finished gas flowing out after separation by the last set of purification devices on the purification pipeline enters the SF6 purity detection module (11) to determine whether its SF6 purity meets ≥95%. The waste gas flowing out after separation by the last set of purification devices on the permeation pipeline enters the exhaust gas detection module (12) for SF6 concentration detection to determine whether it is ≤500ppm.

[0043] There are four results from the above judgment:

[0044] ① The purity of SF6 in the finished gas is ≥95%, and the concentration of SF6 in the exhaust gas is ≤500ppm;

[0045] ② The purity of SF6 in the finished gas is less than 95%, and the concentration of SF6 in the exhaust gas is ≤500ppm;

[0046] ③ The purity of SF6 in the finished gas is ≥95%, and the concentration of SF6 in the exhaust gas is >500ppm;

[0047] ④ The purity of SF6 in the finished gas is less than 95%, and the concentration of SF6 in the exhaust gas is greater than 500ppm;

[0048] 1) If the judgment result is ①, there is no need to change the temperature and pressure of the gas entering the polymer membrane.

[0049] 2) If the judgment result is ②, it means that the working result of the third polymer membrane (10) of the third purification device meets the requirements, and the inlet gas temperature and pressure of the first polymer membrane (4) and the second polymer membrane (7) of the first purification device and the second purification device need to be adjusted;

[0050] 3) If the judgment result is ③, it means that the working performance of the third polymer membrane (10) of the third purification device has declined and needs to be adjusted. The control module object is the SF6 gas concentration at the outlet of the purification device, and the SF6 gas concentration in the exhaust gas is also controlled to be less than 500ppm.

[0051] 4) If the judgment result is ④, there are 3 situations:

[0052] A. The performance of the polymer membrane in the first half of the purification pipeline and the permeation pipeline is degraded;

[0053] B. The performance of the polymer membrane in the second half of the purification pipeline and the permeation pipeline is degraded;

[0054] C. The performance of the polymer membrane on the purification pipeline and the polymer membrane on the permeation pipeline are both degraded;

[0055] Adjust them separately.

[0056] As a further optimized technical solution, the adjustment in 2) if the judgment result is ② includes:

[0057] The main and sub-loops of each fuzzy PID module adopt the first-order inertia hysteresis model, so the cascade system transfer function is:

[0058]

[0059] Where G(s) is the transfer function; K is the system gain; T1 and T2 are the inertia time constants of the inner and outer loops respectively; τ is the system lag time constant;

[0060] By analyzing the unit step response curve generated during the control process, the response characteristics of the three fuzzy PID modules are determined, and the system transfer function is:

[0061]

[0062] The fuzzy control rules of each fuzzy PID controller are the same.

[0063] As a further optimized technical solution, taking the case where the first purification device and the second purification device are sequentially arranged on the purification pipeline and the third purification device is arranged on the permeation pipeline, if the judgment result of 2) is ②, the specific steps include:

[0064] The main and sub-loops of each fuzzy PID module adopt the first-order inertia hysteresis model, so the cascade system transfer function is:

[0065]

[0066] Where G(s) is the transfer function; K is the system gain; T1 and T2 are the inertia time constants of the inner and outer loops respectively; τ is the system lag time constant;

[0067] By analyzing the unit step response curve generated during the control process, the response characteristics of the three fuzzy PID modules are determined, and the system transfer function is:

[0068]

[0069] The fuzzy control rules of each fuzzy PID controller are the same;

[0070] A first mass flow controller (15) and a second mass flow controller (16) are respectively arranged between the gas outlet of the first polymer membrane (4) and the gas outlet of the second polymer membrane (7) and the SF6 purity detection module (11). The output flow rate of the first mass flow controller (15) is controlled to be 150 ml / min, and the output flow rate Q of the second MFC16 changes at a uniform speed. The SF6 purity detection result is set to C, and the SF6 purity C1 and C2 in the output gas of the first polymer membrane (4) and the second polymer membrane (7) are calculated by the following formula:

[0071]

[0072] When C1 or C2 deviates from the normal value within a certain range, it is considered that the polymer membrane needs to be optimized, and the compressor output pressure and heater temperature are adjusted through the corresponding PID control module to make C1 or C2 within the normal range.

[0073] Corresponding to the above method, the present invention also provides an SF6 / N2 mixed gas membrane separation device with self-regulation of the temperature and pressure of the membrane inlet gas, comprising an air inlet (1), a first compressor (2), a first heater (3), a first polymer membrane (4), a second compressor (5), a second heater (6) and a second polymer membrane (7) connected in sequence, the air outlet of the second polymer membrane (7) serving as the finished gas outlet 13 of the device, an SF6 purity detection module (11) being arranged on the pipelines of the air outlets of the first polymer membrane (4) and the second polymer membrane (7), and a first mass flow controller (MFC) 15 and a second mass flow controller (MFC) 16 being arranged between the air outlet of the first polymer membrane (4) and the air outlet of the second polymer membrane (7) and the SF6 purity detection module (11), respectively, and the output end of the SF6 purity detection module (11) being connected to the inlet of the first compressor (2). The air outlets of the first polymer membrane (4) and the second polymer membrane (7) are simultaneously connected to a third compressor (8), and the third compressor (8) is connected in sequence to a third heater (9) and a third polymer membrane (10). The air outlet of the third polymer membrane (10) serves as an exhaust gas discharge port. An exhaust gas detection module (12) is arranged on the air outlet pipeline of the third polymer membrane (10), and the air outlet of the third polymer membrane (10) is connected to the inlet of the first compressor (2).

[0074] The invention has the advantages of automatically adjusting the inlet temperature and pressure of the polymer membrane according to the SF6 purity and tail gas detection results, so as to ensure that the purity of the separated and purified SF6 gas and the SF6 concentration in the exhaust gas meet the requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 It is a principle block diagram of a SF6 / N2 mixed gas membrane separation device with self-regulation of the temperature and pressure of the membrane inlet gas in an embodiment of the present invention.

[0076] Figure 2 This is a temperature self-regulation principle block diagram of the SF6 / N2 mixed gas membrane separation device with self-regulation of the temperature and pressure of the membrane inlet gas in the second embodiment of the present invention.

[0077] Figure 3 It is a connection structure diagram of the PID control module in the second embodiment of the present invention. DETAILED DESCRIPTION

[0078] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0079] It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. The illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention. The illustrations only show components related to the present invention and are not drawn according to the number, shape and size of components in actual implementation. The type, quantity and proportion of each component in actual implementation can be changed arbitrarily, and the component layout type may also be more complicated.

[0080] The ordinal numbers used in the specification and claims, such as "first", "second", "third", etc., to modify the corresponding elements, do not themselves mean that the elements have any ordinal numbers, nor do they represent the order of one element and another element, or the order in the manufacturing method. The use of these ordinal numbers is only used to clearly distinguish a component with a certain name from another component with the same name.

[0081] Embodiment 1

[0082] In the present invention, the Figure 1The SF6 / N2 mixed gas separation device with a membrane inlet gas temperature and pressure self-regulation process is shown in the figure. It is used for SF6 / N2 mixed gas and retrograde separation. The device includes an air inlet 1, a first compressor 2, a first heater 3, a first polymer membrane 4, a second compressor 5, a second heater 6 and a second polymer membrane 7 which are connected in sequence. The air outlet of the second polymer membrane 7 serves as a finished gas outlet 13 of the device. An SF6 purity detection module 11 is arranged on the air outlet pipeline of the second polymer membrane 7. The air outlets of the first polymer membrane 4 and the second polymer membrane 7 are simultaneously connected to a third compressor 8. The third compressor 8 is connected to a third heater 9 and a third polymer membrane 10 in sequence. The air outlet of the third polymer membrane 10 serves as an exhaust gas discharge port. An exhaust gas detection module 12 is arranged on the air outlet pipeline of the third polymer membrane 10. The air outlet of the third polymer membrane 10 is connected to the inlet of the first compressor 2.

[0083] The working process of the SF6 / N2 mixed gas separation device with the membrane gas temperature and pressure self-regulation process includes:

[0084] (1) Separation process

[0085] The gas to be separated enters the membrane separation system from the gas inlet 1, and the pressure and temperature are controlled by the first compressor 2 and the first heater 3 to a set first working condition (P 1,0 , T 1,0 ). Since the permeability of N2 in the polymer membrane is faster than that of SF6, when passing through the first polymer membrane 4, N2 flows out from the permeation port on the side of the first polymer membrane 4, and SF6 flows out from the gas outlet of the first polymer membrane 4. The purity of the SF6 gas separated by the first polymer membrane 4 is relatively low, which does not meet the requirement that the purity of SF6 gas is above 95%, and needs to enter the second polymer membrane 7 for further separation; in addition, the purity of the SF6 gas flowing out of the permeation port is relatively high, which does not meet the environmental protection requirement that the concentration of SF6 gas in the exhaust gas is not higher than 500ppm, and also needs to enter the third polymer membrane 10 for further separation.

[0086] The SF6 gas flowing out of the first polymer membrane 4 is controlled in pressure and temperature to a set second working condition (P 2,0 , T 2,0 ), after separation through the second polymer membrane 7, the SF6 purity of the finished gas flowing out of the outlet of the second polymer membrane 7 is relatively high, and enters the SF6 purity detection module 11 to determine whether its SF6 purity meets ≥95%. The gas flowing out of the permeation port on the side of the second polymer membrane 7 and the gas flowing out of the permeation port of the first polymer membrane 4 are merged through the gas path and then enter the third polymer membrane 10 through the third compressor 8 and the third heater 9 for further separation. The third compressor 8 and the third heater 9 control the pressure and temperature of the gas entering the membrane to set the third working condition (P 3,0 , T 3,0), the SF6 purity in the gas separated by the third polymer membrane 10 is relatively high, the gas flowing out of the gas outlet of the third polymer membrane 10 flows into the exhaust gas detection module 12 for SF6 concentration detection to determine whether it is ≤500ppm, and the gas flowing out of the permeation port of the third polymer membrane 10 returns to the front end of the first compressor 2 through the gas path for separation again.

[0087] (2) Temperature and pressure self-regulation process

[0088] According to the detection and judgment of the SF6 purity detection module 11 and the exhaust gas detection module 12 in step (1), four results may appear:

[0089] ① The purity of SF6 in the finished gas is ≥95%, and the concentration of SF6 in the exhaust gas is ≤500ppm;

[0090] ② The purity of SF6 in the finished gas is less than 95%, and the concentration of SF6 in the exhaust gas is ≤500ppm;

[0091] ③ The purity of SF6 in the finished gas is ≥95%, and the concentration of SF6 in the exhaust gas is >500ppm;

[0092] ④ The purity of SF6 in the finished gas is less than 95%, and the concentration of SF6 in the exhaust gas is greater than 500ppm.

[0093] 1) If the judgment result is ①, there is no need to change the inlet gas temperature and pressure of the three polymer membranes.

[0094] 2) If the judgment result is ②, it means that the working result of the third polymer membrane 10 meets the requirements, and the temperature and pressure of the gas entering the first polymer membrane 4 and the second polymer membrane 7 need to be adjusted:

[0095] First, adjust the temperature and pressure of the gas entering the first polymer membrane 4. Use the first compressor 2 and the first heater 3 to increase the gas pressure and temperature by △P (generally 0.1MPa) and △T (generally 5°C), respectively, and observe whether the value indicated by the SF6 purity detection module 11 is ≥95%; if so, stop adjusting and update the optimal working condition of the first polymer membrane 4 to (P 1,1 , T 1,1 ).

[0096] On the contrary, after adjusting the temperature and pressure of the first polymer membrane 4, the purity increase value of SF6 gas in the finished gas is determined as follows: if △Z ≥ 2%, it means that the adjustment of its temperature and pressure has a good effect, and the temperature and pressure are continued to be increased by △P and △T; if 1% ≤ △Z < 2%, it means that the effect of adjusting its temperature and pressure is general, and the gas entering the membrane is maintained at the temperature and pressure, and the optimal working condition of the first polymer membrane 4 is updated to (P 1,1 , T 1,1), continue to adjust the temperature and pressure of the second polymer film 7; if △Z≤1%, it means that the effect of adjusting the temperature and pressure is poor, and it is already in the best working condition. In order to increase its service life, the temperature and pressure are returned to (P 1,0 、T 1,0 ), continue to adjust the temperature and pressure of the second polymer film 7.

[0097] The temperature and pressure adjustment method of the second polymer membrane 7 is the same as above. If the purity of SF6 in the finished gas after adjustment is ≥95%, stop the adjustment and update the optimal working condition of the first polymer membrane 4 to (P 2,1 、T 2,1 ).

[0098] On the contrary, the purity growth value of SF6 gas in the finished gas is further determined. If △Z ≥ 2%, the temperature and pressure are further increased by △P and △T. If 1% ≤ △Z < 2%, the gas entering the membrane is kept at the temperature and pressure, and the optimal working condition of the second polymer membrane 7 is updated to (P 2,1 、T 2,1 ), in turn, the temperature and pressure of the first polymer film 4 are adjusted again; if △Z≤1%, the temperature and pressure are returned to (P 1,0 、T 1,0 ), which indicates that the working performance of the first polymer film 4 and the second polymer film 7 has been seriously degraded and both need to be replaced.

[0099] 3) If the judgment result is ③, it means that the working performance of the third polymer membrane 10 has decreased and needs to be adjusted. The pressure and temperature of the gas entering the membrane are respectively increased by △P (generally 0.1MPa) and

[0100] △T (generally 5℃), if the SF6 gas concentration in the exhaust gas is less than 500ppm, stop adjusting and update the third polymer film 10. The best working condition is (P 3,1 、T 3,1 ). On the contrary, the SF6 gas concentration drop value △C in the exhaust gas is determined: if △C ≥ 2%, it means that the adjustment of its temperature and pressure has a good effect, and the temperature and pressure continue to be increased by △P and △T; if △C < 2%, it means that the effect of the temperature and pressure adjustment is poor, and the working performance of the third polymer membrane 10 is seriously degraded and needs to be replaced.

[0101] 4) If the judgment result is ④, there are 3 situations:

[0102] A. The performance of the first polymer film 4 and the third polymer film 10 is degraded;

[0103] B. The performance of the second polymer film 7 and the third polymer film 10 is degraded;

[0104] C. The performance of the first polymer film 4, the second polymer film 7 and the third polymer film 10 are all degraded.

[0105] First, the temperature and pressure of the gas entering the first polymer film 4 and the third polymer film 10 are adjusted.

[0106] If the purity of SF6 gas in the finished gas is ≥95%, and the concentration of SF6 gas in the exhaust gas is <500ppm, the optimal working condition for stopping adjustment and updating the first polymer film 4 and the third polymer film 10 is (P 1,1 , T 1,1 ) and (P 3,1 , T 3,1 ).

[0107] If the purity of SF6 gas in the finished gas is ≥95%, and the concentration of SF6 gas in the exhaust gas is ≥500ppm, stop adjusting the working conditions of the gas entering the first polymer membrane 4, and then determine the decrease value of SF6 gas concentration in the exhaust gas △C: if △C ≥2%, continue to increase its temperature and pressure by △P and △T; if △C <2%, it means that the effect of adjusting its temperature and pressure is poor, and the working performance of the third polymer membrane 10 is seriously degraded, and it needs to be replaced.

[0108] If the purity of SF6 gas in the finished gas is less than 95% and the concentration of SF6 gas in the exhaust gas is less than 500ppm, stop adjusting the working conditions of the gas inlet to the third polymer membrane 4, and refer to the relevant contents from the third section of step 2) to the end of step 2).

[0109] If the purity of SF6 gas in the finished gas is less than 95%, the concentration of SF6 gas in the exhaust gas is ≥500ppm. The temperature and pressure of the gas entering the first polymer membrane 4, the second polymer membrane 7 and the third polymer membrane are regulated at the same time. If they meet the requirements after regulation, update (P 1,1 , T 1,1 )、(P 2,1 , T 2,1 ) and (P 3,1 , T 3,1 ); if the purity of SF6 gas is less than 95% after adjustment, update (P 3,1 , T 3,1 ), refer to step 2) to adjust the temperature and pressure of the gas entering the first polymer membrane 4 and the second polymer membrane 7; after adjusting, the concentration of SF6 gas in the exhaust gas is less than 500ppm, and update (P 1,1 , T 1,1 ) and (P 2,1 , T 2,1 ), refer to step 3) to adjust the temperature and pressure of the gas entering the third polymer membrane 10.

[0110] As a person skilled in the art can understand, the number of the above-mentioned polymer membranes is only an example, and the number of polymer membranes in the purification pipeline where the gas outlet is located or the permeation pipeline where the gas permeation port is located can be one or more.

[0111] Embodiment 2

[0112] In the present invention, the Figure 2 The SF6 / N2 mixed gas separation device shown in the figure has a self-regulating process for the temperature and pressure of the membrane inlet gas, and is used for the retrograde separation of the SF6 / N2 mixed gas. The device includes an air inlet 1, a first compressor 2, a first heater 3, a first polymer membrane 4, a second compressor 5, a second heater 6 and a second polymer membrane 7 connected in sequence. The air outlet of the second polymer membrane 7 serves as a finished gas outlet 13 of the device. An SF6 purity detection module 11 is arranged on the pipelines of the air outlets of the first polymer membrane 4 and the second polymer membrane 7, and a first mass flow controller (MFC) 15 and a second mass flow controller (MFC) 16 are respectively arranged between the air outlet of the first polymer membrane 4 and the air outlet of the second polymer membrane 7 and the SF6 purity detection module 11. The output end of the SF6 purity detection module 11 is connected to the inlet of the first compressor 2. The air outlets of the first polymer membrane 4 and the second polymer membrane 7 are simultaneously connected to the third compressor 8, and the third compressor 8 is sequentially connected to the third heater 9 and the third polymer membrane 10, the air outlet of the third polymer membrane 10 is used as an exhaust gas discharge port, and an exhaust gas detection module 12 is arranged on the air outlet pipeline of the third polymer membrane 10, and the air outlet of the third polymer membrane 10 is connected to the inlet of the first compressor 2.

[0113] The working process of the SF6 / N2 mixed gas separation device with the membrane gas temperature and pressure self-regulation process includes:

[0114] (1) Separation process

[0115] The gas to be separated enters the membrane separation system from the gas inlet 1, and the pressure and temperature are controlled by the first compressor 2 and the first heater 3 to a set first working condition (P 1,0 、T 1,0 ). Since the permeability of N2 in the polymer membrane is faster than that of SF6, when passing through the first polymer membrane 4, N2 flows out from the permeation port on the side of the first polymer membrane 4, and SF6 flows out from the gas outlet of the first polymer membrane 4. The purity of the SF6 gas separated by the first polymer membrane 4 is relatively low, which does not meet the requirement that the purity of SF6 gas is above 95%, and needs to enter the second polymer membrane 7 for further separation; in addition, the purity of the SF6 gas flowing out of the permeation port is relatively high, which does not meet the environmental protection requirement that the concentration of SF6 gas in the exhaust gas is not higher than 500ppm, and also needs to enter the third polymer membrane 10 for further separation.

[0116] The SF6 gas flowing out of the first polymer membrane 4 is controlled in pressure and temperature to a set second working condition (P 2,0 , T 2,0 ), after separation through the second polymer membrane 7, the SF6 purity of the finished gas flowing out of the outlet of the second polymer membrane 7 is relatively high, and enters the SF6 purity detection module 11 to determine whether its SF6 purity meets ≥95%. The gas flowing out of the permeation port on the side of the second polymer membrane 7 and the gas flowing out of the permeation port of the first polymer membrane 4 are merged through the gas path and then enter the third polymer membrane 10 through the third compressor 8 and the third heater 9 for further separation. The third compressor 8 and the third heater 9 control the pressure and temperature of the gas entering the membrane to set the third working condition (P 3,0 , T 3,0 ), the SF6 purity in the gas separated by the third polymer membrane 10 is relatively high, the gas flowing out of the gas outlet of the third polymer membrane 10 flows into the exhaust gas detection module 12 for SF6 concentration detection to determine whether it is ≤500ppm, and the gas flowing out of the permeation port of the third polymer membrane 10 returns to the front end of the first compressor 2 through the gas path for separation again.

[0117] (2) Temperature and pressure self-regulation process

[0118] According to the detection and judgment of the SF6 purity detection module 11 and the exhaust gas detection module 12 in step (1), four results may appear:

[0119] ① The purity of SF6 in the finished gas is ≥95%, and the concentration of SF6 in the exhaust gas is ≤500ppm;

[0120] ② The purity of SF6 in the finished gas is less than 95%, and the concentration of SF6 in the exhaust gas is ≤500ppm;

[0121] ③ The purity of SF6 in the finished gas is ≥95%, and the concentration of SF6 in the exhaust gas is >500ppm;

[0122] ④ The purity of SF6 in the finished gas is less than 95%, and the concentration of SF6 in the exhaust gas is greater than 500ppm.

[0123] 1) If the judgment result is ①, there is no need to change the inlet gas temperature and pressure of the three polymer membranes.

[0124] 2) If the judgment result is ②, it means that the working result of the third polymer membrane 10 meets the requirements, and the temperature and pressure of the gas entering the first polymer membrane 4 and the second polymer membrane 7 need to be adjusted:

[0125] The fuzzy PID control technology is used to adjust the film entry temperature and pressure. The present invention sets three fuzzy PID modules: a first fuzzy PID module 100, a second fuzzy PID module 200, and a third fuzzy PID module 300, which respectively control the film entry temperature and pressure of three polymer films: the first polymer film 4, the second polymer film 7, and the third polymer film 10. Figure 3 As shown in the figure, each fuzzy PID module is a cascade structure. Since changing the membrane inlet gas pressure has a more obvious effect on the separation effect, the main loop in the cascade structure is a pressure fuzzy PID controller, and the sub-loop is a temperature fuzzy PID controller. The inputs of each fuzzy PID controller are pressure, temperature, and the proportion of SF6 gas at the corresponding polymer membrane outlet. The object of each fuzzy PID controller is the compressor or heater at the corresponding polymer membrane inlet, thereby controlling the proportion of SF6 gas at the corresponding polymer membrane outlet.

[0126] The main and sub-loops of each fuzzy PID module adopt the first-order inertia hysteresis model, so the cascade system transfer function is:

[0127]

[0128] Where G(s) is the transfer function; K is the system gain; T1 and T2 are the inertia time constants of the inner and outer loops respectively; τ is the system lag time constant.

[0129] By analyzing the unit step response curve generated during the control process, the response characteristics of the three fuzzy PID modules are determined, and the system transfer function is:

[0130]

[0131] The fuzzy control rules of each fuzzy PID controller are the same, see Table 1, which is the prior art and will not be described in detail.

[0132] Table 1ΔK p , ΔK i , ΔK d Fuzzy control rules

[0133]

[0134] The fuzzy domain ranges of the parameters of each fuzzy PID controller are the same, as shown in Table 2, which is the prior art and will not be described in detail.

[0135] Table 2 Fuzzy domain range of each parameter in fuzzy PID control

[0136]

[0137] The SF6 purity detection module 11 requires the detection flow rate to be generally between 250ml / min and 350ml / min, and controls the output flow rate of the first mass flow controller (MFC) 15 to be 150ml / min, and the output flow rate Q of the second MFC 16 to change uniformly between 100ml / min and 200ml / min. Let the SF6 purity detection result be C, then the SF6 purity C1 and C2 in the output gas of the first polymer membrane 4 and the second polymer membrane 7 can be calculated by the following formula:

[0138]

[0139] When C1 or C2 deviates from the normal value within a certain range, it is considered that the polymer membrane needs to be optimized, and the compressor (variable frequency) output pressure and heater temperature are adjusted through the corresponding PID control module to make C1 or C2 within the normal range.

[0140] 3) If the judgment result is ③, it means that the working performance of the third polymer film 10 has decreased and needs to be adjusted. The control module object is the SF6 gas concentration at the module outlet based on the pressure, temperature, and SF6 gas concentration at the module outlet. Similarly, the SF6 gas concentration in the exhaust gas is controlled to be less than 500ppm.

[0141] 4) If the judgment result is ④, it is necessary to adjust the first polymer film or the second polymer film, and the third polymer film, the method is the same as 2) + 3).

[0142] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A SF6 / N2 mixed gas membrane separation method with self-regulation of membrane inlet gas temperature and pressure, characterized in that: The invention comprises several sets of purification devices, each set of purification devices comprises a compressor, a heater and a polymer membrane which are arranged in sequence, at least two sets of purification devices are arranged on the purification pipeline of the device, the permeation port of the polymer membrane of each set of purification devices is connected to the air inlet of the first set of purification devices on the purification pipeline through the purification device arranged on the permeation pipeline, an SF6 purity detection module is arranged on the pipeline of the air outlet of the purification device on the purification pipeline, and an exhaust gas detection module is arranged at the air outlet of the purification device on the permeation pipeline, and the air inlet of the purification device on the permeation pipeline is adjusted according to the detection and judgment of the SF6 purity detection module and the exhaust gas detection module, so that the finished gas at the air outlet of the purification pipeline and the exhaust gas at the air outlet of the permeation pipeline meet the preset requirements.

2. A SF6 / N2 mixed gas membrane separation method with self-regulation of inlet gas temperature and pressure as claimed in claim 1, characterized in that: The temperature and pressure of the gas entering the polymer membrane of each purification device are adjusted according to the detection judgment of the SF6 purity detection module and the exhaust gas detection module, so that the finished gas at the outlet of the purification pipeline and the exhaust gas at the outlet of the permeation pipeline meet the preset requirements, including: The gas to be separated enters the membrane separation system from the air inlet, and the pressure and temperature of each purification device are controlled at the set working conditions. The finished gas flowing out after separation by the last set of purification devices on the purification pipeline enters the SF6 purity detection module (11) to determine whether its SF6 purity meets ≥95%. The waste gas flowing out after separation by the last set of purification devices on the permeation pipeline enters the exhaust gas detection module (12) for SF6 concentration detection to determine whether it is ≤500ppm. There are four results from the above judgment: ① The purity of SF6 in the finished gas is ≥95%, and the concentration of SF6 in the exhaust gas is ≤500ppm; ② The purity of SF6 in the finished gas is less than 95%, and the concentration of SF6 in the exhaust gas is ≤500ppm; ③ The purity of SF6 in the finished gas is ≥95%, and the concentration of SF6 in the exhaust gas is >500ppm; ④ The purity of SF6 in the finished gas is less than 95%, and the concentration of SF6 in the exhaust gas is greater than 500ppm; 1) If the judgment result is ①, there is no need to change the gas inlet temperature and pressure of each set of polymer membrane of the purification device; 2) If the judgment result is ②, it means that the working result of the purification device on the permeation pipeline meets the requirements, and the inlet gas temperature and pressure of the polymer membrane of the purification device on the purification pipeline need to be adjusted: 3) If the judgment result is ③, it means that the working performance of the polymer membrane of the purification device on the permeation pipeline has declined and needs to be adjusted; 4) If the judgment result is ④, there are 3 situations: A. The performance of the polymer membrane in the first half of the purification pipeline and the permeation pipeline is degraded; B. The performance of the polymer membrane in the second half of the purification pipeline and the permeation pipeline is degraded; C. The performance of the polymer membrane on the purification pipeline and the polymer membrane on the permeation pipeline are both degraded; Adjust them separately.

3. A SF6 / N2 mixed gas membrane separation method with self-regulation of inlet gas temperature and pressure as claimed in claim 2, characterized in that: Taking the example of sequentially arranging a first purification device and a second purification device on the purification pipeline and arranging a third purification device on the permeation pipeline, the step of adjusting the inlet gas temperature and pressure of the polymer membrane of each purification device specifically includes the following steps: 1) If the judgment result is ①, there is no need to change the inlet gas temperature and pressure of the polymer membranes of the three purification devices. 2) If the judgment result is ②, it means that the working result of the third polymer membrane (10) of the third purification device meets the requirements, and the inlet gas temperature and pressure of the first polymer membrane (4) and the second polymer membrane (7) of the first purification device and the second purification device need to be adjusted: First, the temperature and pressure of the gas entering the first polymer membrane (4) are adjusted, and the pressure and temperature of the gas entering the membrane are respectively increased by ΔP and ΔT through the first compressor (2) and the first heater (3) of the first purification device, and the indication value of the SF6 purity detection module (11) is observed to be ≥95%; if so, the regulation is stopped, and the optimal working condition of the first polymer membrane (4) is updated to (P 1,1 , T 1,1 ); On the contrary, after the temperature and pressure of the first polymer membrane (4) are adjusted, the purity increase value △Z of the SF6 gas in the finished gas is determined: if △Z ≥ 2%, it means that the adjustment of its temperature and pressure has a good effect, and the temperature and pressure are continued to be increased by △P and △T; if 1% ≤ △Z < 2%, it means that the effect of the adjustment of its temperature and pressure is general, and the gas entering the membrane is maintained at the temperature and pressure, and the optimal working condition of the first polymer membrane (4) is updated to (P 1,1 , T 1,1 ), continue to adjust the temperature and pressure of the second polymer film (7); if △Z≤1%, it means that the effect of adjusting the temperature and pressure is poor, and the temperature and pressure are returned to (P 1,0 , T 1,0 ), continue to adjust the temperature and pressure of the second polymer membrane (7); The temperature and pressure adjustment method of the second polymer membrane (7) is the same as above. If the purity of SF6 in the finished gas after adjustment is ≥95%, the adjustment is stopped and the optimal working condition of the first polymer membrane (4) is updated to (P 2,1 , T 2,1 ); On the contrary, the purity increase value △Z of SF6 gas in the finished gas is further determined: if △Z≥2%, the temperature and pressure are further increased by △P and △T; if 1%≤△Z<2%, the gas entering the membrane is kept at the temperature and pressure, and the optimal working condition of the second polymer membrane (7) is updated to (P 2,1 , T 2,1 ), and in turn, the temperature and pressure of the first polymer film (4) are adjusted again; if △Z≤1%, the temperature and pressure are returned to (P 1,0 , T 1,0 ), which indicates that the working performance of the first polymer film (4) and the second polymer film (7) has seriously deteriorated and both need to be replaced; 3) If the judgment result is ③, it means that the working performance of the third polymer membrane (10) of the third purification device has declined and needs to be adjusted. The pressure and temperature of the gas entering the membrane are respectively increased by △P and △T through the third compressor (8) and the third heater (9) of the third purification device. If the SF6 gas concentration in the exhaust gas is less than 500ppm, the adjustment is stopped and the optimal working condition of the third polymer membrane (10) is updated to (P 3,1 , T 3,1 ), on the contrary, determine the decrease value △C of the SF6 gas concentration in the exhaust gas: if △C≥2%, it means that the adjustment of its temperature and pressure has a good effect, and continue to increase its temperature and pressure by △P and △T; if △C<2%, it means that the effect of adjusting its temperature and pressure is poor, and the working performance of the third polymer membrane (10) is seriously degraded and needs to be replaced; 4) If the judgment result is ④, there are 3 situations: A. the performance of the first polymer membrane (4) of the first purification device and the third polymer membrane (10) of the third purification device are degraded; B. the performance of the second polymer membrane (7) of the second purification device and the third polymer membrane (10) of the third purification device is degraded; C. The performance of the first polymer membrane (4), the second polymer membrane (7) of the first purification device and the third polymer membrane (10) of the third purification device are all degraded; First, the temperature and pressure of the gas entering the first polymer membrane (4) and the third polymer membrane (10) are adjusted; If the purity of SF6 gas in the finished gas is ≥95% and the concentration of SF6 gas in the exhaust gas is <500ppm, the optimal working conditions for stopping adjustment and updating the first polymer membrane (4) and the third polymer membrane (10) are (P 1,1 , T 1,1 ) and (P 3,1 , T 3,1 ); If the purity of SF6 gas in the finished gas is ≥95% and the concentration of SF6 gas in the exhaust gas is ≥500ppm, stop adjusting the working conditions of the gas entering the first polymer membrane (4). At this time, determine the decrease value △C of the SF6 gas concentration in the exhaust gas: if △C is ≥2%, continue to increase its temperature and pressure by △P and △T; if △C is less than 2%, it means that the effect of adjusting its temperature and pressure is poor, and the working performance of the third polymer membrane (10) is seriously degraded and needs to be replaced; If the purity of SF6 gas in the finished gas is less than 95% and the concentration of SF6 gas in the exhaust gas is less than 500ppm, stop adjusting the working conditions of the gas inlet to the third polymer membrane (4), and refer to step 2); If the purity of SF6 gas in the finished gas is less than 95% and the concentration of SF6 gas in the exhaust gas is ≥500ppm, the temperature and pressure of the gas entering the first polymer membrane (4), the second polymer membrane (7) and the third polymer membrane are regulated at the same time. If they meet the requirements after regulation, update (P 1,1 , T 1,1 )、(P 2,1 , T 2,1 ) and (P 3,1 , T 3,1 ); if the purity of SF6 gas is less than 95% after adjustment, update (P 3,1 , T 3,1 ), refer to step 2) to adjust the temperature and pressure of the gas entering the first polymer membrane (4) and the second polymer membrane (7); after adjustment, the SF6 gas concentration in the exhaust gas is less than 500ppm, and the (P 1,1 , T 1,1 ) and (P 2,1 , T 2,1 ), refer to step 3) to adjust the temperature and pressure of the gas entering the third polymer membrane (10).

4. A SF6 / N2 mixed gas membrane separation method with self-regulation of inlet gas temperature and pressure as claimed in claim 3, characterized in that: △P is 0.1MPa and △T is 5℃.

5. The SF6 / N2 mixed gas membrane separation method with self-regulation of the temperature and pressure of the membrane inlet gas according to claim 1, characterized in that: The fuzzy PID control technology is used to adjust the inlet gas temperature and pressure of the polymer membrane of each purification device according to the detection and judgment of the SF6 purity detection module and the exhaust gas detection module. Each set of purification device is respectively provided with a corresponding fuzzy PID module, and each fuzzy PID module is a cascade structure. Therefore, the main loop in the cascade structure is a pressure fuzzy PID controller, and the secondary loop is a temperature fuzzy PID controller. The inputs of each fuzzy PID controller are pressure, temperature, and the proportion of SF6 gas at the corresponding polymer membrane outlet. The object of each fuzzy PID controller is the compressor or heater at the corresponding polymer membrane inlet, thereby controlling the proportion of SF6 gas at the corresponding polymer membrane outlet.

6. A SF6 / N2 mixed gas membrane separation method with self-regulation of inlet gas temperature and pressure as claimed in claim 5, characterized in that: The temperature and pressure of the gas entering the polymer membrane of each purification device are adjusted according to the detection judgment of the SF6 purity detection module and the exhaust gas detection module, so that the finished gas at the outlet of the purification pipeline and the exhaust gas at the outlet of the permeation pipeline meet the preset requirements, including: The gas to be separated enters the membrane separation system from the air inlet, and the pressure and temperature of each purification device are controlled at the set working conditions. The finished gas flowing out after separation by the last set of purification devices on the purification pipeline enters the SF6 purity detection module (11) to determine whether its SF6 purity meets ≥95%. The waste gas flowing out after separation by the last set of purification devices on the permeation pipeline enters the exhaust gas detection module (12) for SF6 concentration detection to determine whether it is ≤500ppm. There are four results from the above judgment: ① The purity of SF6 in the finished gas is ≥95%, and the concentration of SF6 in the exhaust gas is ≤500ppm; ② The purity of SF6 in the finished gas is less than 95%, and the concentration of SF6 in the exhaust gas is ≤500ppm; ③ The purity of SF6 in the finished gas is ≥95%, and the concentration of SF6 in the exhaust gas is >500ppm; ④ The purity of SF6 in the finished gas is less than 95%, and the concentration of SF6 in the exhaust gas is greater than 500ppm; 1) If the judgment result is ①, there is no need to change the temperature and pressure of the gas entering the polymer membrane. 2) If the judgment result is ②, it means that the working result of the third polymer membrane (10) of the third purification device meets the requirements, and the inlet gas temperature and pressure of the first polymer membrane (4) and the second polymer membrane (7) of the first purification device and the second purification device need to be adjusted; 3) If the judgment result is ③, it means that the working performance of the third polymer membrane (10) of the third purification device has declined and needs to be adjusted. The control module object is the SF6 gas concentration at the outlet of the purification device, and the SF6 gas concentration in the exhaust gas is also controlled to be less than 500ppm. 4) If the judgment result is ④, there are 3 situations: A. The performance of the polymer membrane in the first half of the purification pipeline and the permeation pipeline is degraded; B. The performance of the polymer membrane in the second half of the purification pipeline and the permeation pipeline is degraded; C. The performance of the polymer membrane on the purification pipeline and the polymer membrane on the permeation pipeline are both degraded; Adjust them separately.

7. A SF6 / N2 mixed gas membrane separation method with self-regulation of inlet gas temperature and pressure as claimed in claim 6, characterized in that: The adjustment in 2) if the judgment result is ② includes: The main and sub-loops of each fuzzy PID module adopt the first-order inertia hysteresis model, so the cascade system transfer function is: Where G(s) is the transfer function; K is the system gain; T1 and T2 are the inertia time constants of the inner and outer loops respectively; τ is the system lag time constant; By analyzing the unit step response curve generated during the control process, the response characteristics of the three fuzzy PID modules are determined, and the system transfer function is: The fuzzy control rules of each fuzzy PID controller are the same.

8. A SF6 / N2 mixed gas membrane separation method with self-regulation of inlet gas temperature and pressure as claimed in claim 6, characterized in that: Taking the case where the first purification device and the second purification device are sequentially arranged on the purification pipeline, and the third purification device is arranged on the permeation pipeline as an example, if the judgment result of 2) is ②, the method specifically includes: The main and sub-loops of each fuzzy PID module adopt the first-order inertia hysteresis model, so the cascade system transfer function is: Where G(s) is the transfer function; K is the system gain; T1 and T2 are the inertia time constants of the inner and outer loops respectively; τ is the system lag time constant; By analyzing the unit step response curve generated during the control process, the response characteristics of the three fuzzy PID modules are determined, and the system transfer function is: The fuzzy control rules of each fuzzy PID controller are the same; A first mass flow controller (15) and a second mass flow controller (16) are respectively arranged between the gas outlet of the first polymer membrane (4) and the gas outlet of the second polymer membrane (7) and the SF6 purity detection module (11). The output flow rate of the first mass flow controller (15) is controlled to be 150 ml / min, and the output flow rate Q of the second mass flow controller (16) changes at a uniform speed. If the SF6 purity detection result is C, the SF6 purity C1 and C2 in the output gas of the first polymer membrane (4) and the second polymer membrane (7) are calculated by the following formula: When C1 or C2 deviates from the normal value within a certain range, it is considered that the polymer membrane needs to be optimized, and the compressor output pressure and heater temperature are adjusted through the corresponding PID control module to make C1 or C2 within the normal range.

9. A device for separation of SF6 / N2 mixed gas membranes with self-regulation of inlet gas temperature and pressure according to any one of claims 1 to 4, characterized in that: The device comprises an air inlet (1), a first compressor (2), a first heater (3), a first polymer membrane (4), a second compressor (5), a second heater (6) and a second polymer membrane (7) which are connected in sequence; the air outlet of the second polymer membrane (7) serves as a finished gas outlet 13 of the device; an SF6 purity detection module (11) is arranged on the pipeline of the air outlet of the second polymer membrane (7); the air outlets of the first polymer membrane (4) and the second polymer membrane (7) are simultaneously connected to a third compressor (8); the third compressor (8) is connected in sequence to a third heater (9) and a third polymer membrane (10); the air outlet of the third polymer membrane (10) serves as an exhaust gas discharge outlet; an exhaust gas detection module (12) is arranged on the air outlet pipeline of the third polymer membrane (10); and the air outlet of the third polymer membrane (10) is connected to the inlet of the first compressor (2).

10. A device for separation of SF6 / N2 mixed gas membranes with self-regulation of inlet gas temperature and pressure according to any one of claims 5 to 8, characterized in that: The invention comprises an air inlet (1), a first compressor (2), a first heater (3), a first polymer membrane (4), a second compressor (5), a second heater (6) and a second polymer membrane (7) which are connected in sequence, wherein the air outlet of the second polymer membrane (7) serves as a finished gas outlet 13 of the device, an SF6 purity detection module (11) is arranged on the pipelines of the air outlets of the first polymer membrane (4) and the second polymer membrane (7), and a first mass flow controller (MFC) 15 and a second mass flow controller (MFC) 16 are arranged between the air outlet of the first polymer membrane (4) and the air outlet of the second polymer membrane (7) and the SF6 purity detection module (11), respectively, and the output end of the SF6 purity detection module (11) is connected to the inlet of the first compressor (2). The air outlets of the first polymer membrane (4) and the second polymer membrane (7) are simultaneously connected to a third compressor (8), and the third compressor (8) is connected in sequence to a third heater (9) and a third polymer membrane (10). The air outlet of the third polymer membrane (10) serves as an exhaust gas discharge port. An exhaust gas detection module (12) is arranged on the air outlet pipeline of the third polymer membrane (10), and the air outlet of the third polymer membrane (10) is connected to the inlet of the first compressor (2).

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