Hydrogenation energy station for purifying hydrogen-doped natural gas by using multi-stage membrane separation method

Abstract

The application discloses a hydrogen-doped natural gas purifying hydrogen energy station by using a multistage membrane separation method, and belongs to the technical field of hydrogen purification. The hydrogen-doped natural gas purifying hydrogen energy station solves the problem that it is difficult to purify hydrogen-doped natural gas to obtain standard hydrogen gas required by a hydrogen fuel cell in the prior art. The multistage membrane separation method purifying system is connected with a town hydrogen-doped natural gas pipe network. The permeation side of the multistage membrane separation method purifying system is sequentially connected with a hydrogen gas compression unit, a hydrogen gas storage unit and a hydrogenation area. An intelligent control system comprises a controller and a visual screen. The controller is used for controlling the multistage membrane separation method purifying system, and the visual screen is used for displaying the operation condition of the hydrogen energy station. The hydrogen energy station can be applied to different pressure levels of hydrogen-doped natural gas pipes to extract hydrogen gas for gas supply and energy supply.

Description

Technical Field

[0001] This invention relates to a hydrogen refueling station for purifying hydrogen-blended natural gas, and more particularly to a hydrogen refueling station for purifying hydrogen-blended natural gas using a multi-stage membrane separation method, belonging to the field of hydrogen purification technology. Background Technology

[0002] Currently, hydrogen transportation mainly relies on tube trailers. However, with the increasing number of hydrogen refueling stations, the low efficiency and poor economics of tube trailer transportation have become apparent, making it difficult to guarantee hydrogen supply. Therefore, utilizing existing natural gas pipelines to blend natural gas with a certain proportion of hydrogen will eliminate the cost and technical problems of hydrogen infrastructure construction in a short period of time, significantly improving the scale and efficiency of hydrogen energy distribution. The application of hydrogen-blended natural gas in the transportation sector is still in the research and development stage. For example, if hydrogen-blended natural gas with a blending ratio of 4%-20% is directly used in compressed natural gas (CNG) vehicles at CNG refueling stations, there is a risk of explosion in hot summer weather. Furthermore, in hydrogen refueling stations, hydrogen fuel cells require high hydrogen purity, with a purity standard greater than 99.97%. In conclusion, purifying hydrogen-blended natural gas at energy stations to obtain hydrogen of the required purity standard for hydrogen fuel cells reduces the risks of directly using hydrogen-blended natural gas in CNG vehicles while meeting the hydrogen supply demand at the refueling stage, thus promoting the development of new energy stations.

[0003] The most mature hydrogen purification method currently is pressure swing adsorption (PSA). However, it is suitable for large-scale gas purification, requires large-scale equipment, and has good purification effect when the hydrogen content is greater than 50%. On the one hand, the hydrogen blending ratio in the hydrogen-blended natural gas demonstration projects carried out at home and abroad is generally between 4% and 20%. If PSA is used, it means that a large amount of gas needs to be adsorbed but only a small amount of hydrogen can be recovered. On the other hand, the daily hydrogen refueling capacity of conventional hydrogen refueling stations is around 300 Nm³. 3 The gas demand is relatively small for a given hourly rate. Therefore, pressure swing adsorption (PSA) is not suitable for purifying gas at hydrogen refueling stations. To meet hydrogen supply demands, an energy station is needed that can purify hydrogen-blended natural gas to obtain the hydrogen purity required for fuel cells. Summary of the Invention

[0004] A brief overview of the invention is given below to provide a basic understanding of certain aspects of it. It should be understood that this overview is not an exhaustive summary of the invention. It is not intended to identify key or essential parts of the invention, nor is it intended to limit the scope of the invention. Its purpose is merely to present certain concepts in a simplified form as a prelude to the more detailed description that follows.

[0005] In view of this, in order to solve the problem that it is difficult to purify hydrogen-blended natural gas to obtain the standard purity hydrogen required for hydrogen fuel cells in the existing technology, the present invention provides a hydrogen refueling station that uses a multi-stage membrane separation method to purify hydrogen-blended natural gas.

[0006] The technical solution is as follows: A hydrogen refueling energy station that uses a multi-stage membrane separation method to purify hydrogen-blended natural gas includes a multi-stage membrane separation purification system, a photovoltaic power generation system, an energy storage area, a hydrogen compression unit, a hydrogen storage unit, a natural gas compressor, a hydrogen refueling area, a gas refueling area, a charging area, and an intelligent control system;

[0007] The multi-stage membrane separation purification system is connected to the urban hydrogen-blended natural gas pipeline network.

[0008] The permeate side of the multi-stage membrane separation purification system is sequentially connected to the hydrogen compression unit, the hydrogen storage unit, and the hydrogenation zone.

[0009] The permeate side of the multi-stage membrane separation purification system is sequentially connected to the natural gas compressor and the gas filling area.

[0010] The photovoltaic power generation system, the energy storage area, and the charging area are connected in sequence. The energy storage area provides power to the multi-stage membrane separation purification system, the hydrogen compression unit, and the natural gas compressor.

[0011] The intelligent control system includes a controller and a visualization screen. The intelligent control system is connected to the multi-stage membrane separation purification system, the photovoltaic power generation system, the energy storage area, the hydrogen compression unit, the hydrogen storage unit, the natural gas compressor, the hydrogen refueling area, the gas refueling area, and the charging area. The controller is used to control the multi-stage membrane separation purification system, and the visualization screen is used to display the operation status of the hydrogen refueling station.

[0012] Furthermore, the urban hydrogen-blended natural gas pipeline network includes high-pressure urban hydrogen-blended natural gas pipelines, medium-pressure urban hydrogen-blended natural gas pipelines, and low-pressure urban hydrogen-blended natural gas pipelines;

[0013] The multi-stage membrane separation purification system includes a high-pressure membrane separation system and a medium-pressure membrane separation system, both of which are connected to a hydrogen compression unit.

[0014] The high-pressure urban hydrogen-blended natural gas pipeline is connected to the high-pressure membrane separation system, the medium-pressure urban hydrogen-blended natural gas pipeline is connected to the medium-pressure membrane separation system, and the low-pressure urban hydrogen-blended natural gas pipeline is connected to the permeate side of both the high-pressure and medium-pressure membrane separation systems.

[0015] Furthermore, the high-pressure membrane separation system includes a high-pressure regulating valve, a high-pressure membrane separation system heating heat exchanger, a high-pressure membrane separation system primary membrane separator, a high-pressure membrane separation system secondary membrane separator, and a high-pressure membrane separation system cooling heat exchanger;

[0016] The high-pressure urban hydrogen-blended natural gas pipeline is connected to the inlet of the high-pressure regulating valve, and the outlet of the high-pressure regulating valve is connected to the inlet of the high-pressure membrane separation system's heating heat exchanger. The primary membrane separator of the high-pressure membrane separation system is equipped with a feed side, a permeate side, and a permeate side. The outlet of the high-pressure membrane separation system's heating heat exchanger is connected to the feed side of the primary membrane separator. The secondary membrane separator of the high-pressure membrane separation system is equipped with a feed side, a permeate side, and a permeate side. The permeate side of the primary membrane separator is connected to the feed side of the secondary membrane separator. The permeate side of the primary membrane separator and the permeate side of the secondary membrane separator are connected to the low-pressure urban hydrogen-blended natural gas pipeline through the high-pressure membrane separation system's cooling heat exchanger. The permeate side of the secondary membrane separator is connected to the hydrogen compression unit.

[0017] Furthermore, the medium-pressure membrane separation system includes a medium-pressure regulating valve, a medium-pressure membrane separation system heating heat exchanger, a medium-pressure membrane separation system primary membrane separator, a primary separation vacuum pump, a compressor, a secondary separation vacuum pump, a medium-pressure membrane separation system secondary membrane separator, and a medium-pressure membrane separation system cooling heat exchanger;

[0018] The medium-pressure town hydrogen-blended natural gas pipeline is connected to the inlet of the medium-pressure regulating valve. The outlet of the medium-pressure regulating valve is connected to the inlet of the heating heat exchanger of the medium-pressure membrane separation system. The primary membrane separator of the medium-pressure membrane separation system is equipped with a feed side, a residual side, and a permeate side. The outlet of the heating heat exchanger is connected to the feed side of the primary membrane separator. The secondary membrane separator of the medium-pressure membrane separation system is equipped with a secondary membrane separator. The feed side of the medium-pressure membrane separation system, the permeate side of the secondary membrane separator, and the residual side of the secondary membrane separator are connected to the feed side of the medium-pressure membrane separation system. The permeate side of the primary membrane separator is connected to the primary separation vacuum pump, compressor, and feed side of the secondary membrane separator. The residual side of the primary membrane separator and the residual side of the secondary membrane separator are connected to the low-pressure hydrogen-blended natural gas pipeline through the cooling heat exchanger of the medium-pressure membrane separation system. The permeate side of the secondary membrane separator is connected to the hydrogen compression unit through the secondary separation vacuum pump.

[0019] Furthermore, the control method for the high-pressure membrane separation system is as follows:

[0020] The controller controls the high-pressure regulating valve and the high-pressure membrane separation system's heating heat exchanger, and stores the generated data. The data is then displayed in real-time on a visual screen. Specifically:

[0021] The feed gas from the high-pressure urban hydrogen-blended natural gas pipeline enters the high-pressure membrane separation system, and the output permeate component hydrogen has a mole fraction x in the feed gas. 氢1 Then, the pressure is adjusted via the high-pressure regulating valve to determine whether the driving pressure difference of the first-stage membrane separator in the high-pressure membrane separation system meets the requirements. If not, the pressure is further adjusted via the high-pressure regulating valve until the driving pressure difference meets the requirements. If it does, the feed-side pressure p of the first-stage membrane separator in the high-pressure membrane separation system is output. x1 The system then heats the gas through the high-pressure membrane separation system's heating heat exchanger to determine if the operating temperature of the first-stage membrane separator meets the requirements. If not, heat exchange continues through the high-pressure membrane separation system's heating heat exchanger until the operating temperature meets the requirements. If so, the operating temperature T1 of the first-stage membrane separator is output. Then, the high-pressure membrane separation system performs first-stage membrane separation, further determining if the hydrogen purity on the permeate side of the first-stage membrane separator is greater than 90%. If not, the pressure is adjusted through the high-pressure regulating valve, and the above operation is repeated until the hydrogen purity is greater than 90%. If so, the hydrogen purity and the volumetric flow rate V of the gas on the permeate side of the first-stage membrane separator are output. P1 High-pressure membrane separation system, first-stage membrane separator, permeate side pressure p y1 The mole fraction y of hydrogen gas, a permeate component, in the permeate side of the first-stage membrane separator of a high-pressure membrane separation system. 氢1 Subsequently, secondary membrane separation is performed in the high-pressure membrane separation system. The purity of hydrogen on the permeate side of the secondary membrane separator is determined to be greater than 99.97%. If not, the process continues, starting with the feed gas from the high-pressure town hydrogen-blended natural gas pipeline entering the high-pressure membrane separation system, repeating the above operation until the hydrogen purity exceeds 99.97%. If it does, the output data includes the hydrogen purity and the volumetric flow rate V of the gas on the permeate side of the secondary membrane separation system. P2 High-pressure membrane separation system, secondary membrane separator, feed side pressure p x2 High-pressure membrane separation system, secondary membrane separator, permeate side pressure p y2 Operating temperature T2 and mole fraction y of hydrogen on the permeate side of the secondary membrane separator in a high-pressure membrane separation system. 氢2 The system determines whether the hydrogen permeation flux J meets the hydrogen supply requirements of the hydrogen refueling station. If not, it continues to feed gas from the high-pressure town hydrogen-blended natural gas pipeline into the high-pressure membrane separation system until the requirements are met. If so, the high-pressure membrane separation system ends its operation.

[0022] Furthermore, the control method for the medium-pressure membrane separation system is as follows:

[0023] The controller manages the medium-pressure regulating valve, the medium-pressure membrane separation system's heating heat exchanger, and the compressor, and stores the generated data. The data is then displayed in real-time on a visual screen. Specifically:

[0024] Medium-pressure urban hydrogen-blended natural gas feedstock enters a high-pressure membrane separation system, outputting the permeate component hydrogen at a mole fraction x in the feedstock. 氢1 Then, the pressure is adjusted through the medium-pressure regulating valve to determine whether the driving pressure difference of the primary membrane separator in the medium-pressure membrane separation system meets the requirements. If not, the pressure is further adjusted through the medium-pressure regulating valve until the driving pressure difference meets the requirements. If so, the feed side pressure p of the primary membrane separator in the medium-pressure membrane separation system is output. x1 The system then heats the gas through the medium-pressure membrane separation system's heating heat exchanger to determine if the operating temperature of the first-stage membrane separator meets the requirements. If not, heat exchange continues through the heating heat exchanger until the operating temperature meets the requirements. If so, the operating temperature T1' of the first-stage membrane separator is output. Next, the system performs first-stage membrane separation and determines if the hydrogen purity on the permeate side of the first-stage membrane separator is greater than 90%. If not, the pressure is adjusted through the medium-pressure regulating valve until the hydrogen purity is greater than 90%. If so, the hydrogen purity and the volumetric flow rate V of the gas on the permeate side of the first-stage membrane separator are output. P1 'The osmotic side pressure p of the primary membrane separator in the medium-pressure membrane separation system' y1 'and the mole fraction y of hydrogen gas, a permeate component, in the permeate side of the primary membrane separator of a medium-pressure membrane separation system 氢1 The compressor then compresses the material, and it is determined whether the driving pressure difference of the secondary membrane separator in the medium-pressure membrane separation system meets the requirements. If not, the pressure is further adjusted by the compressor until the driving pressure difference meets the requirements. If it does, the feed side pressure p of the secondary membrane separator in the medium-pressure membrane separation system is output. x2 Then, the secondary membrane separation of the medium-pressure membrane separation system is performed. It is determined whether the hydrogen purity on the permeate side of the secondary membrane separator is greater than 99.97%. If not, the process continues from the compressor compression stage, repeating the above steps until the hydrogen purity is greater than 99.97%. If it is, the hydrogen purity and the volumetric flow rate V of the gas on the permeate side of the secondary membrane separation system are output. P2 'The feed side pressure p of the secondary membrane separator in the medium-pressure membrane separation system' x2 ', Medium-pressure membrane separation system, secondary membrane separator, permeate side pressure p y2 'Operating temperature T2 of the secondary membrane separator in the medium-pressure membrane separation system' and 'molar fraction y of hydrogen in the permeate component on the permeate side of the medium-pressure membrane separation system' 氢2Then, it is determined whether the hydrogen permeation flux J' meets the hydrogen supply demand of the hydrogen refueling station. If not, the process continues from the feed gas from the medium-pressure town hydrogen-blended natural gas pipeline into the high-pressure membrane separation system, repeating the above process until the demand is met. If so, the medium-pressure membrane separation system ends its operation.

[0025] Furthermore, the mole fraction y of the permeate component hydrogen on the permeate side of the first-stage membrane separator in the high-pressure membrane separation system. 氢1 Equal to the molar composition x of the permeate component hydrogen on the feed side of the secondary membrane separator in a high-pressure membrane separation system. 氢2 .

[0026] Furthermore, the mole fraction y of the permeate component hydrogen on the permeate side of the primary membrane separator in the medium-pressure membrane separation system. 氢1 'equals the molar composition of the permeate component hydrogen on the feed side of the secondary membrane separator in a medium-pressure membrane separation system x' 氢2 '.

[0027] The beneficial effects of this invention are as follows: This invention utilizes a multi-stage membrane separation method to purify hydrogen-blended natural gas. The urban hydrogen-blended natural gas pipeline network is sequentially connected to the multi-stage membrane separation purification system, hydrogen compression unit, hydrogen storage unit, and hydrogen refueling area. This achieves an effective supply of hydrogen of the purity required for hydrogen fuel cells. Furthermore, the residual gas after the multi-stage membrane separation purification system can be used to compensate the urban hydrogen-blended natural gas pipeline network or directly transported to natural gas users. Alternatively, the residual gas from the multi-stage membrane separation purification system can be transported to the natural gas compressor to supply gas to the newly added refueling area, avoiding resource waste. The intelligent scheduling system of this invention includes a controller and a visualization screen. The controller can control the heat exchanger in the multi-stage membrane separation purification system to heat it until the required operating temperature is reached during hydrogen purification. It can also adjust the pressure required during hydrogen purification by controlling the opening of the pressure regulating valve. The visualization screen can display the data of the hydrogen purification process in real time. The invention also includes a photovoltaic power generation system and an energy storage area, which can generate and store clean energy to provide power to the multi-stage membrane separation purification system and the hydrogen compression unit. At the same time, it can provide power to the added charging area, making the hydrogen refueling station's services more diversified, improving economic efficiency while saving land resources. Attached Figure Description

[0028] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0029] Figure 1 This is a schematic diagram of a hydrogen refueling station that uses a multi-stage membrane separation method to purify hydrogen-blended natural gas.

[0030] Figure 2This is a schematic diagram of an embodiment of a hydrogen refueling station that uses a multi-stage membrane separation method to purify hydrogen-blended natural gas;

[0031] Figure 3 This is a schematic diagram of a high-pressure membrane separation system.

[0032] Figure 4 This is a schematic diagram of a medium-pressure membrane separation system.

[0033] Figure 5 This is a schematic diagram of the control method for a high-pressure membrane separation system.

[0034] Figure 6 This is a schematic diagram of the control method for a medium-pressure membrane separation system;

[0035] Figure 7 This is a schematic diagram of a membrane separator.

[0036] Figure reference numerals: 1. High-pressure urban hydrogen-blended natural gas pipeline; 2. High-pressure regulating valve; 3. High-pressure membrane separation system heating heat exchanger; 4. Feed side of the primary membrane separator in the high-pressure membrane separation system; 5. Residual side of the primary membrane separator in the high-pressure membrane separation system; 6. Permeate side of the primary membrane separator in the high-pressure membrane separation system; 7. Feed side of the secondary membrane separator in the high-pressure membrane separation system; 8. Permeate side of the secondary membrane separator in the high-pressure membrane separation system; 9. Residual side of the secondary membrane separator in the high-pressure membrane separation system; 10. High-pressure membrane separation system cooling heat exchanger; 11. Low-pressure hydrogen-blended natural gas pipeline; 12. Medium-pressure urban hydrogen-blended natural gas pipeline; 13. Medium-pressure regulating valve; 14. Medium-pressure membrane separation system heating heat exchanger; 15. 16. Feed side of primary membrane separator in medium-pressure membrane separation system; 17. Permeate side of primary membrane separator in medium-pressure membrane separation system; 18. Vacuum pump for primary separation in medium-pressure membrane separation system; 19. Compressor; 20. Feed side of secondary membrane separator in medium-pressure membrane separation system; 21. Vacuum pump for secondary separation in medium-pressure membrane separation system; 22. Permeate side of secondary membrane separator in medium-pressure membrane separation system; 23. Permeate side of secondary membrane separator in medium-pressure membrane separation system; 24. Cooling heat exchanger in medium-pressure membrane separation system; A. Primary membrane separator in high-pressure membrane separation system; B. Secondary membrane separator in high-pressure membrane separation system; C. Primary membrane separator in medium-pressure membrane separation system; D. Secondary membrane separator in medium-pressure membrane separation system. Detailed Implementation

[0037] To make the technical solutions and advantages of the embodiments of the present invention clearer, the exemplary embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not an exhaustive list of all embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0038] refer to Figures 1-7This embodiment describes a hydrogen refueling station that uses a multi-stage membrane separation method to purify hydrogen-blended natural gas. The station includes a multi-stage membrane separation purification system, a photovoltaic power generation system, an energy storage area, a hydrogen compression unit, a hydrogen storage unit, a natural gas compressor, a hydrogen refueling area, a gas refueling area, a charging area, and an intelligent control system.

[0039] The multi-stage membrane separation purification system is connected to the urban hydrogen-blended natural gas pipeline network.

[0040] The permeate side of the multi-stage membrane separation purification system is sequentially connected to the hydrogen compression unit, the hydrogen storage unit, and the hydrogenation zone.

[0041] The permeate side of the multi-stage membrane separation purification system is sequentially connected to the natural gas compressor and the gas filling area.

[0042] The photovoltaic power generation system, the energy storage area, and the charging area are connected in sequence. The energy storage area provides power to the multi-stage membrane separation purification system, the hydrogen compression unit, and the natural gas compressor.

[0043] The intelligent control system includes a controller and a visualization screen. The intelligent control system is connected to the multi-stage membrane separation purification system, the photovoltaic power generation system, the energy storage area, the hydrogen compression unit, the hydrogen storage unit, the natural gas compressor, the hydrogen refueling area, the gas refueling area, and the charging area. The controller is used to control the multi-stage membrane separation purification system, and the visualization screen is used to display the operation status of the hydrogen refueling station.

[0044] Furthermore, the urban hydrogen-blended natural gas pipeline network includes a high-pressure urban hydrogen-blended natural gas pipeline 1, a medium-pressure urban hydrogen-blended natural gas pipeline 12, and a low-pressure urban hydrogen-blended natural gas pipeline 11;

[0045] The multi-stage membrane separation purification system includes a high-pressure membrane separation system and a medium-pressure membrane separation system, both of which are connected to a hydrogen compression unit.

[0046] The high-pressure urban hydrogen-blended natural gas pipeline 1 is connected to the high-pressure membrane separation system, the medium-pressure urban hydrogen-blended natural gas pipeline 12 is connected to the medium-pressure membrane separation system, and the low-pressure urban hydrogen-blended natural gas pipeline 11 is connected to the permeate side of both the high-pressure and medium-pressure membrane separation systems.

[0047] Furthermore, the high-pressure membrane separation system includes a high-pressure regulating valve 2, a high-pressure membrane separation system heating heat exchanger 3, a high-pressure membrane separation system primary membrane separator A, a high-pressure membrane separation system secondary membrane separator B, and a high-pressure membrane separation system cooling heat exchanger 10;

[0048] The high-pressure town hydrogen-blended natural gas pipeline 1 is connected to the inlet of the high-pressure regulating valve 2, and the outlet of the high-pressure regulating valve 2 is connected to the inlet of the high-pressure membrane separation system heat exchanger 3. The first-stage membrane separator A of the high-pressure membrane separation system is equipped with a feed side 4, a residual side 5, and a permeate side 6. The outlet of the high-pressure membrane separation system heat exchanger 3 is connected to the feed side 4 of the first-stage membrane separator. The second-stage membrane separator B of the high-pressure membrane separation system is equipped with an inlet... The feed side 7, the permeate side 8 of the secondary membrane separator of the high-pressure membrane separation system, and the residual side 9 of the secondary membrane separator of the high-pressure membrane separation system are connected; the permeate side 6 of the primary membrane separator of the high-pressure membrane separation system is connected to the feed side 7 of the secondary membrane separator of the high-pressure membrane separation system; the residual side 5 of the primary membrane separator of the high-pressure membrane separation system and the residual side 9 of the secondary membrane separator of the high-pressure membrane separation system are connected through the inlet of the cooling heat exchanger 10 of the high-pressure membrane separation system; the outlet of the cooling heat exchanger 10 of the high-pressure membrane separation system is connected to the low-pressure urban hydrogen-blended natural gas pipeline 11; and the permeate side 8 of the secondary membrane separator of the high-pressure membrane separation system is connected to the hydrogen compression unit.

[0049] Furthermore, the medium-pressure membrane separation system includes a medium-pressure regulating valve 13, a medium-pressure membrane separation system heating heat exchanger 14, a medium-pressure membrane separation system primary membrane separator C, a primary separation vacuum pump 18, a compressor 19, a secondary separation vacuum pump 21, a medium-pressure membrane separation system secondary membrane separator D, and a medium-pressure membrane separation system cooling heat exchanger 24;

[0050] The medium-pressure urban hydrogen-blended natural gas pipeline 12 is connected to the inlet of the medium-pressure regulating valve 13. The outlet of the medium-pressure regulating valve 13 is connected to the inlet of the heating heat exchanger 14 of the medium-pressure membrane separation system. The primary membrane separator C of the medium-pressure membrane separation system is equipped with a feed side 15, a residual side 16, and a permeate side 17. The outlet of the heating heat exchanger 14 is connected to the feed side 15 of the primary membrane separator. The secondary membrane separator D of the medium-pressure membrane separation system is equipped with a feed... Side 20, the permeate side 22 and the residual side 23 of the secondary membrane separator of the medium-pressure membrane separation system, the permeate side 17 of the primary membrane separator of the medium-pressure membrane separation system is connected to the primary separation vacuum pump 18, the compressor 19 and the feed side 20 of the secondary membrane separator of the medium-pressure membrane separation system, the residual side 16 of the primary membrane separator of the medium-pressure membrane separation system and the residual side 23 of the secondary membrane separator of the medium-pressure membrane separation system are connected to the low-pressure hydrogen-blended natural gas pipeline 11 through the cooling heat exchanger 24 of the medium-pressure membrane separation system, and the permeate side 22 of the secondary membrane separator of the medium-pressure membrane separation system is connected to the hydrogen compression unit through the secondary separation vacuum pump 21;

[0051] Specifically, when constructing a hydrogen refueling station, a nearby urban hydrogen-blended natural gas pipeline can be selected as both the feed gas supply and recovery end. A multi-stage membrane separation and purification system with the same pressure rating can be matched to the pipeline. In this embodiment, the pressure range of high-pressure urban hydrogen-blended natural gas pipeline 1 is 0.4-4 MPa, the pressure range of medium-pressure urban hydrogen-blended natural gas pipeline 12 is 0.01-0.4 MPa, and the pressure of low-pressure urban hydrogen-blended natural gas pipeline 11 is less than 0.01 MPa. The hydrogen blending ratio of the blended natural gas ranges from 4% to 20%. All urban hydrogen-blended natural gas pipelines are operated at ambient temperature. This is to meet the requirement of a daily hydrogen refueling capacity of 300 Nm³ for the hydrogen refueling station. 3 / h-3000Nm 3 To meet the demand of [number] hours, the hydrogen compression unit is equipped with a primary compressor and a secondary compressor. The hydrogen storage unit is equipped with a hydrogen storage tank with an internal pressure of 35 MPa and a hydrogen storage tank with an internal pressure of 70 MPa. The energy storage area is connected to the primary and secondary compressors respectively. The permeate side of the high-pressure membrane separation system and the medium-pressure membrane separation system is connected to the primary compressor. The primary compressor, the 35 MPa hydrogen storage tank, and the hydrogen refueling area are connected in sequence. The primary compressor, the secondary compressor, the 70 MPa hydrogen storage tank, and the hydrogen refueling area are connected in sequence. The permeate side of the high-pressure membrane separation system and the medium-pressure membrane separation system is connected to the natural gas user. The electrical energy generated by the photovoltaic power generation system is stored in the energy storage area and can be controlled [to generate electricity]. The device powers the primary compressor, secondary compressor, and electrical equipment in the multi-stage membrane separation purification system, as well as the charging area in the hydrogen refueling station. The primary membrane separator in the multi-stage membrane separation purification system uses hollow fiber carbon molecular sieve membranes with a carbonization temperature range of 500℃-600℃. The secondary membrane separator uses hollow fiber metal hybrid matrix membranes. The intelligent control system employs a DCS control system with remote monitoring, alarm display, control, and storage functions. During operation, the controller can be pre-set with the pressure limit value adjusted by the pressure regulating valve according to the operating conditions. When the limit value is exceeded, the visual screen displays the pressure data and triggers an alarm.

[0052] Furthermore, the control method for the high-pressure membrane separation system is as follows:

[0053] The controller controls the high-pressure regulating valve and the high-pressure membrane separation system's heating heat exchanger, and stores the generated data. The data is then displayed in real-time on a visual screen. Specifically:

[0054] The feed gas from the high-pressure town hydrogen-blended natural gas pipeline 1 enters the high-pressure membrane separation system, and the output permeate component hydrogen has a mole fraction x in the feed gas. 氢1Then, the pressure is adjusted via high-pressure regulating valve 2 to determine whether the driving pressure difference of the primary membrane separator A in the high-pressure membrane separation system meets the requirements. If not, the pressure is further adjusted via high-pressure regulating valve 2 until the driving pressure difference meets the requirements. If so, the pressure p on the feed side 4 of the primary membrane separator in the high-pressure membrane separation system is output. x1 The system then heats the gas through the high-pressure membrane separation system's heating heat exchanger 3 to determine if the operating temperature of the first-stage membrane separator A meets the requirements. If not, heat exchange continues through the high-pressure membrane separation system's heating heat exchanger 3 until the operating temperature meets the requirements. If so, the operating temperature T1 of the first-stage membrane separator A is output. Then, the high-pressure membrane separation system performs first-stage membrane separation, further determining if the hydrogen purity on the permeate side 6 of the first-stage membrane separator is greater than 90%. If not, the pressure is adjusted through the high-pressure regulating valve 2, and the above operation is repeated until the hydrogen purity is greater than 90%. If so, the hydrogen purity and the volumetric flow rate V of the gas on the permeate side 6 of the first-stage membrane separator are output. P1 High-pressure membrane separation system, first-stage membrane separator, permeate side, 6 p pressure y1 The mole fraction y of hydrogen gas in the permeate component of the first-stage membrane separator of the high-pressure membrane separation system on the permeate side. 氢1 Subsequently, secondary membrane separation is performed in the high-pressure membrane separation system. It is determined whether the hydrogen purity on the permeate side 8 of the secondary membrane separator is greater than 99.97%. If not, the process continues, starting with the feed gas from the high-pressure town hydrogen-blended natural gas pipeline 1 entering the high-pressure membrane separation system, repeating the above operation until the hydrogen purity is greater than 99.97%. If it is, the hydrogen purity and the volumetric flow rate V of the gas on the permeate side 8 of the secondary membrane separator are output. P2 High-pressure membrane separation system, secondary membrane separator, feed side pressure 7p x2 High-pressure membrane separation system, secondary membrane separator, permeate side pressure 8 p y2 The operating temperature T2 of the secondary membrane separator B in the high-pressure membrane separation system and the mole fraction y of hydrogen on the permeate side of the secondary membrane separator in the high-pressure membrane separation system. 氢2 Determine whether the hydrogen permeation flux J meets the hydrogen supply demand of the hydrogen refueling station. If not, continue to feed gas from the high-pressure town hydrogen-blended natural gas pipeline 1 into the high-pressure membrane separation system until the demand is met. If yes, the high-pressure membrane separation system will stop working.

[0055] Furthermore, the control method for the medium-pressure membrane separation system is as follows:

[0056] The controller manages the medium-pressure regulating valve, the medium-pressure membrane separation system's heating heat exchanger, and the compressor, and stores the generated data. The data is then displayed in real-time on a visual screen. Specifically:

[0057] The feed gas from the medium-pressure urban hydrogen-blended natural gas pipeline 12 enters the high-pressure membrane separation system, and the output permeate component hydrogen has a mole fraction x in the feed gas. 氢1 Then, the pressure is adjusted through the medium-pressure regulating valve 13 to determine whether the driving pressure difference of the primary membrane separator C in the medium-pressure membrane separation system meets the requirements. If not, the pressure is further adjusted through the medium-pressure regulating valve 13 until the driving pressure difference meets the requirements. If so, the pressure p on the feed side 15 of the primary membrane separator in the medium-pressure membrane separation system is output. x1 The system then heats the gas through the medium-pressure membrane separation system's heating heat exchanger 14 to determine if the operating temperature of the first-stage membrane separator C meets the requirements. If not, heat exchange continues through the medium-pressure membrane separation system's heating heat exchanger 14 until the operating temperature meets the requirements. If so, the operating temperature T1' of the first-stage membrane separator C is output. Then, the system performs first-stage membrane separation and determines if the hydrogen purity on the permeate side 17 of the first-stage membrane separator is greater than 90%. If not, the pressure is adjusted through the medium-pressure regulating valve 13 until the hydrogen purity is greater than 90%. If so, the hydrogen purity and the volumetric flow rate V of the gas on the permeate side 17 of the first-stage membrane separator are output. P1 ', Medium-pressure membrane separation system, primary membrane separator, permeate side 17 pressure p y1 'and the mole fraction y of hydrogen gas in the permeate component of the first-stage membrane separator of the medium-pressure membrane separation system on the permeate side 17'. 氢1 Then, the compressor 19 compresses the material, and it is determined whether the driving pressure difference of the secondary membrane separator D in the medium-pressure membrane separation system meets the requirements. If not, the pressure is adjusted by the compressor 19 until the driving pressure difference meets the requirements. If it does, the pressure p on the feed side 20 of the secondary membrane separator in the medium-pressure membrane separation system is output. x2 Then, the secondary membrane separation of the medium-pressure membrane separation system is performed. It is determined whether the hydrogen purity on the permeate side 22 of the secondary membrane separator is greater than 99.97%. If not, the process continues from compressor 19, repeating the above steps until the hydrogen purity is greater than 99.97%. If it is, the hydrogen purity and the volumetric flow rate V of the gas on the permeate side of the secondary membrane separation system are output. P2 ', Medium-pressure membrane separation system, secondary membrane separator, feed side pressure 20 p x2 ', Medium-pressure membrane separation system, secondary membrane separator, permeate side 22 pressure p y2 'The operating temperature T2 of the secondary membrane separator D in the medium-pressure membrane separation system' and the mole fraction y of hydrogen in the permeate component 22 of the secondary membrane separator in the medium-pressure membrane separation system. 氢2Then, it is determined whether the hydrogen permeation flux J' meets the hydrogen supply demand of the hydrogen refueling station. If not, the process continues from the raw material gas from the medium-pressure urban hydrogen-blended natural gas pipeline 12 into the high-pressure membrane separation system, and the above process is repeated until the demand is met. If so, the medium-pressure membrane separation system ends its operation.

[0058] Specifically, the permeation flux of hydrogen, the permeating component of the membrane, is expressed as:

[0059]

[0060] Where J is the permeation flux of hydrogen gas, the permeate component of the membrane, in GPUs, and 10 -9 mol / m 2 ·s·Pa = 3 GPU; V P x represents the volumetric flow rate of the permeate gas, expressed in ml / s. i y represents the mole fraction of osmotic component i upstream; i A is the mole fraction of permeate component i downstream; A is the membrane area in cm². 2 T represents the operating temperature, in Kelvin (K); p x Upstream pressure, in cmHg; p y Downstream pressure, in cmHg; φ xi The fugacity coefficient of permeable component i upstream is much less than 1; φ yi Let i be the fugacity coefficient of the permeate component i downstream, approximately 1. After the advanced membrane separation system finishes operation, the hydrogen flow from the permeate side 8 of the secondary membrane separator in the high-pressure membrane separation system is directed to the primary compressor and then, after passing through a hydrogen storage tank with an internal pressure of 35 MPa, is supplied to the hydrogen refueling area. After the intermediate membrane separation system finishes operation, the hydrogen flow from the permeate side 22 of the secondary membrane separator in the medium-pressure membrane separation system is directed to the primary compressor and then, after passing through the secondary compressor, enters a hydrogen storage tank with an internal pressure of 70 MPa to supply hydrogen to the hydrogen refueling area. The natural gas from the residual permeate side 9 of the secondary membrane separator in the high-pressure membrane separation system and the residual permeate side 16 of the secondary membrane separator in the medium-pressure membrane separation system can be dispatched back to the urban hydrogen-blended natural gas pipeline network or directly transported to natural gas users through the controller, or it can be processed by a natural gas compressor and supplied to the gas refueling area.

[0061] Furthermore, the mole fraction y of the permeate component hydrogen in the permeate side 6 of the first-stage membrane separator of the high-pressure membrane separation system... 氢1 Equal to the molar composition x of the permeate component hydrogen on the feed side of the secondary membrane separator in the high-pressure membrane separation system. 氢2 .

[0062] Furthermore, the mole fraction y of the permeate component hydrogen in the permeate side 17 of the first-stage membrane separator of the medium-pressure membrane separation system is... 氢1 'Equals the molar composition x of the permeate component hydrogen on the feed side of the secondary membrane separator in a medium-pressure membrane separation system.'氢2 '.

[0063] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

Claims

1. A hydrogen refueling station that purifies hydrogen-blended natural gas using a multi-stage membrane separation method, characterized in that, It includes a multi-stage membrane separation purification system, a photovoltaic power generation system, an energy storage area, a hydrogen compression unit, a hydrogen storage unit, a natural gas compressor, a hydrogen refueling area, a gas refueling area, a charging area, and an intelligent control system; The multi-stage membrane separation purification system is connected to the urban hydrogen-blended natural gas pipeline network. The permeate side of the multi-stage membrane separation purification system is sequentially connected to the hydrogen compression unit, the hydrogen storage unit, and the hydrogenation zone. The permeate side of the multi-stage membrane separation purification system is sequentially connected to the natural gas compressor and the gas filling area. The photovoltaic power generation system, the energy storage area, and the charging area are connected in sequence. The energy storage area provides power to the multi-stage membrane separation purification system, the hydrogen compression unit, and the natural gas compressor. The intelligent control system includes a controller and a visualization screen. The intelligent control system is connected to a multi-stage membrane separation purification system, a photovoltaic power generation system, an energy storage area, a hydrogen compression unit, a hydrogen storage unit, a natural gas compressor, a hydrogen refueling area, a gas refueling area, and a charging area. The controller is used to control the multi-stage membrane separation purification system, and the visualization screen is used to display the operating status of the hydrogen refueling energy station. The urban hydrogen-blended natural gas pipeline network includes a high-pressure urban hydrogen-blended natural gas pipeline (1), a medium-pressure urban hydrogen-blended natural gas pipeline (12), and a low-pressure urban hydrogen-blended natural gas pipeline (11). The multi-stage membrane separation purification system includes a high-pressure membrane separation system and a medium-pressure membrane separation system, both of which are connected to a hydrogen compression unit. The high-pressure urban hydrogen-blended natural gas pipeline (1) is connected to the high-pressure membrane separation system, the medium-pressure urban hydrogen-blended natural gas pipeline (12) is connected to the medium-pressure membrane separation system, and the low-pressure urban hydrogen-blended natural gas pipeline (11) is connected to the permeate side of both the high-pressure and medium-pressure membrane separation systems. The high-pressure membrane separation system includes a high-pressure regulating valve (2), a high-pressure membrane separation system heating heat exchanger (3), a high-pressure membrane separation system primary membrane separator (A), a high-pressure membrane separation system secondary membrane separator (B), and a high-pressure membrane separation system cooling heat exchanger (10). The medium-pressure membrane separation system includes a medium-pressure regulating valve (13), a medium-pressure membrane separation system heating heat exchanger (14), a medium-pressure membrane separation system primary membrane separator (C), a primary separation vacuum pump (18), a compressor (19), a secondary separation vacuum pump (21), a medium-pressure membrane separation system secondary membrane separator (D), and a medium-pressure membrane separation system cooling heat exchanger (24). The membrane material of the first-stage membrane separator in the multi-stage membrane separation purification system is hollow fiber carbon molecular sieve membrane, and the membrane material of the second-stage membrane separator in the multi-stage membrane separation purification system is hollow fiber metal hybrid matrix membrane.

2. A hydrogen refueling station for purifying hydrogen-blended natural gas using a multi-stage membrane separation method according to claim 1, characterized in that, The high-pressure town hydrogen-blended natural gas pipeline (1) is connected to the inlet of the high-pressure regulating valve (2), and the outlet of the high-pressure regulating valve (2) is connected to the inlet of the high-pressure membrane separation system heating heat exchanger (3). The high-pressure membrane separation system primary membrane separator (A) is equipped with a feed side (4), a permeate side (5), and a permeate side (6). The outlet of the high-pressure membrane separation system heating heat exchanger (3) is connected to the feed side (4). The high-pressure membrane separation system secondary membrane separator (B) is equipped with a high-pressure... The feed side (7) of the secondary membrane separator of the membrane separation system, the permeate side (8) of the secondary membrane separator of the high-pressure membrane separation system, and the residual side (9) of the secondary membrane separator of the high-pressure membrane separation system; the permeate side (6) of the primary membrane separator of the high-pressure membrane separation system is connected to the feed side (7) of the secondary membrane separator of the high-pressure membrane separation system; the residual side (5) of the primary membrane separator of the high-pressure membrane separation system and the residual side (9) of the secondary membrane separator of the high-pressure membrane separation system are connected to the low-pressure urban hydrogen-blended natural gas pipeline (11) through the cooling heat exchanger (10) of the high-pressure membrane separation system, and the permeate side (8) of the secondary membrane separator of the high-pressure membrane separation system is connected to the hydrogen compression unit.

3. A hydrogen refueling station for purifying hydrogen-doped natural gas using a multi-stage membrane separation method according to claim 2, characterized in that, The medium-pressure urban hydrogen-blended natural gas pipeline (12) is connected to the inlet of the medium-pressure regulating valve (13), and the outlet of the medium-pressure regulating valve (13) is connected to the inlet of the heating heat exchanger (14) of the medium-pressure membrane separation system. The primary membrane separator (C) of the medium-pressure membrane separation system is equipped with a feed side (15), a residual side (16), and a permeate side (17). The outlet of the heating heat exchanger (14) of the medium-pressure membrane separation system is connected to the feed side (15). The secondary membrane separator (D) of the medium-pressure membrane separation system is equipped with a feed side (15). 20) The permeate side (22) and the residual side (23) of the secondary membrane separator of the medium-pressure membrane separation system are connected. The permeate side (17) of the primary membrane separator of the medium-pressure membrane separation system is connected to the primary separation vacuum pump (18), the compressor (19) and the feed side (20) of the secondary membrane separator of the medium-pressure membrane separation system. The residual side (16) of the primary membrane separator of the medium-pressure membrane separation system and the residual side (23) of the secondary membrane separator of the medium-pressure membrane separation system are connected to the low-pressure hydrogen-blended natural gas pipeline (11) through the cooling heat exchanger (24) of the medium-pressure membrane separation system. The permeate side (22) of the secondary membrane separator of the medium-pressure membrane separation system is connected to the hydrogen compression unit through the secondary separation vacuum pump (21).

4. A hydrogen refueling station for purifying hydrogen-doped natural gas using a multi-stage membrane separation method according to claim 3, characterized in that, The control method for the high-pressure membrane separation system is as follows: The controller controls the high-pressure regulating valve and the high-pressure membrane separation system heating heat exchanger in the high-pressure membrane separation system and stores the generated data. The data generated in the high-pressure membrane separation system is displayed in real time through a visualization screen. The feed gas from the high-pressure urban hydrogen-blended natural gas pipeline enters the high-pressure membrane separation system, and the output permeate component hydrogen molar fraction is... Then, the pressure is adjusted via the high-pressure regulating valve to determine whether the driving pressure difference of the primary membrane separator in the high-pressure membrane separation system meets the requirements. If not, the pressure is further adjusted via the high-pressure regulating valve until the driving pressure difference meets the requirements. If it does, the feed side pressure of the primary membrane separator in the high-pressure membrane separation system is output. The system then heats the membrane separator through the high-pressure membrane separation system's heating heat exchanger to determine if the operating temperature of the first-stage membrane separator meets the requirements. If not, heat exchange continues through the high-pressure membrane separation system's heating heat exchanger until the operating temperature meets the requirements. If it does, the operating temperature of the first-stage membrane separator is output. Subsequently, the high-pressure membrane separation system performs primary membrane separation. It then determines whether the hydrogen purity on the permeate side of the primary membrane separator is greater than 90%. If not, the pressure is adjusted via the high-pressure regulating valve, and the above operation is repeated until the hydrogen purity exceeds 90%. If it does, the hydrogen purity and the volumetric flow rate of the gas on the permeate side of the primary membrane separator are output. High-pressure membrane separation system, first-stage membrane separator, permeate side pressure The mole fraction of hydrogen gas in the permeate component of the first-stage membrane separator of a high-pressure membrane separation system. Subsequently, secondary membrane separation is performed in the high-pressure membrane separation system. The purity of hydrogen on the permeate side of the secondary membrane separator is determined to be greater than 99.97%. If not, the process continues, starting with the feed gas from the high-pressure town hydrogen-blended natural gas pipeline entering the high-pressure membrane separation system, repeating the above operation until the hydrogen purity exceeds 99.97%. If it does, the hydrogen purity and the volumetric flow rate of the gas on the permeate side of the secondary membrane separator are output. High-pressure membrane separation system, secondary membrane separator feed side pressure High-pressure membrane separation system, secondary membrane separator, osmosis side pressure Operating temperature of the secondary membrane separator in the high-pressure membrane separation system The mole fraction of hydrogen permeate in the permeate side of the secondary membrane separator of a high-pressure membrane separation system. Determine the hydrogen permeation flux If the hydrogen supply demand of the hydrogen refueling station is not met, the process continues until the demand is met. If it is met, the high-pressure membrane separation system will stop operating.

5. A hydrogen refueling station for purifying hydrogen-doped natural gas using a multi-stage membrane separation method according to claim 4, characterized in that, The control method for the medium-pressure membrane separation system is as follows: The controller manages the medium-pressure regulating valve, the medium-pressure membrane separation system's heating heat exchanger, and the compressor, and stores the generated data. The data is then displayed in real-time on a visual screen. Specifically: The feed gas from the medium-pressure urban hydrogen-blended natural gas pipeline enters the high-pressure membrane separation system, and the output permeate component hydrogen mole fraction is determined by the following parameters: Then, the pressure is adjusted via the medium-pressure regulating valve to determine whether the driving pressure difference of the primary membrane separator in the medium-pressure membrane separation system meets the requirements. If not, the pressure is further adjusted via the medium-pressure regulating valve until the driving pressure difference meets the requirements. If it does, the feed side pressure of the primary membrane separator in the medium-pressure membrane separation system is output. The system then heats the membrane separator through the medium-pressure membrane separation system's heating heat exchanger to determine if the operating temperature of the primary membrane separator meets the requirements. If not, heat exchange continues through the medium-pressure membrane separation system's heating heat exchanger until the operating temperature meets the requirements. If it does, the operating temperature of the primary membrane separator is output. Subsequently, the first-stage membrane separation of the medium-pressure membrane separation system is performed. The system then determines whether the hydrogen purity on the permeate side of the first-stage membrane separator is greater than 90%. If not, the pressure is continuously adjusted via the medium-pressure regulating valve until the hydrogen purity exceeds 90%. If it does, the system outputs the hydrogen purity and the volumetric flow rate of the gas on the permeate side of the first-stage membrane separator. Medium-pressure membrane separation system, first-stage membrane separator, permeate side pressure The mole fraction of hydrogen gas as a permeate component in the permeate side of the primary membrane separator of a medium-pressure membrane separation system. The compressor then compresses the material, and it is determined whether the driving pressure difference of the secondary membrane separator in the medium-pressure membrane separation system meets the requirements. If not, the pressure is further adjusted by the compressor until the driving pressure difference meets the requirements. If it does, the feed-side pressure of the secondary membrane separator in the medium-pressure membrane separation system is output. Then, the secondary membrane separation of the medium-pressure membrane separation system is performed. It is determined whether the hydrogen purity on the permeate side of the secondary membrane separator in the medium-pressure membrane separation system is greater than 99.97%. If not, the process continues from the compressor compression stage, repeating the above steps until the hydrogen purity is greater than 99.97%. If it is, the hydrogen purity and the volumetric flow rate of the gas on the permeate side of the secondary membrane separation in the medium-pressure membrane separation system are output. Medium-pressure membrane separation system, secondary membrane separator feed side pressure Medium-pressure membrane separation system, secondary membrane separator, osmosis side pressure 'Operating temperature of the secondary membrane separator in the medium-pressure membrane separation system' 'and the mole fraction of hydrogen in the permeate component of the secondary membrane separator in a medium-pressure membrane separation system This allows for the determination of hydrogen permeation flux. If the hydrogen supply demand of the hydrogen refueling station is not met, the process continues from the feed gas from the medium-pressure town hydrogen-blended natural gas pipeline into the high-pressure membrane separation system, repeating the above process until the demand is met. If it is met, the medium-pressure membrane separation system will stop working.

6. A hydrogen refueling station for purifying hydrogen-doped natural gas using a multi-stage membrane separation method according to claim 5, characterized in that, Mole fraction of hydrogen in the permeate component of a high-pressure membrane separation system on the permeate side of the primary membrane separator. Equal to the molar composition of the permeate component hydrogen on the feed side of the secondary membrane separator in a high-pressure membrane separation system. .

7. A hydrogen refueling station for purifying hydrogen-doped natural gas using a multi-stage membrane separation method according to claim 6, characterized in that, Mole fraction of hydrogen in the permeate component of a medium-pressure membrane separation system on the permeate side of the primary membrane separator. Equal to the molar composition of the permeate component hydrogen on the feed side of the secondary membrane separator in a medium-pressure membrane separation system. .

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