Multi-stage natural gas helium extraction device and process

Abstract

The invention belongs to the technical field of helium extraction, and particularly discloses a multi-stage natural gas helium extraction device and method.The device comprises a pretreatment unit communicated with a natural gas pipe network and a multi-stage membrane separation unit connected with the pretreatment unit, and the multi-stage membrane separation unit comprises a first-stage membrane separation set to an Nth-stage membrane separation set; in the multi-stage membrane separation unit, in the second-stage membrane separation group to the N-stage membrane separation group, a first pressure swing adsorption unit is arranged at an impermeable gas outlet of each stage of membrane separation group, and desorption gas pipelines of the plurality of first pressure swing adsorption units are sequentially communicated with a decarburization compressor, a pretreatment unit and a pipe network; a product gas pipeline of the first pressure swing adsorption unit and a permeation gas outlet of each stage of membrane separation group from the second stage of membrane separation group to the Nth stage of membrane separation group are connected with a dehydrogenation tower, and the dehydrogenation tower is connected with a temperature swing adsorption refining unit through a pressure swing adsorption gas inlet compressor and a crude helium pressure swing adsorption unit in sequence.

Description

Technical Field

[0001] This invention relates to the field of natural gas helium extraction technology, and more particularly to multi-stage natural gas helium extraction equipment and processes. Background Technology

[0002] Helium, a non-renewable rare gas, plays a crucial role in fourth-generation nuclear energy systems, scientific research, semiconductors, medicine, petrochemicals, aerospace, and maritime industries. Its demand is increasing year by year, but currently, China relies on imports for approximately 85% of its helium, posing a significant challenge to supply chain security. Helium primarily originates from natural gas, coalbed methane, and associated natural gas. However, the helium content in my country's natural gas is relatively low (300ppm~2000ppm). Therefore, conventional helium extraction membrane separation processes typically employ two-stage or three-stage membrane separation. This involves multi-stage enrichment, catalytic oxidation dehydrogenation, crude helium pressure swing adsorption, and temperature swing adsorption purification of the low-helium-content feedstock natural gas to ultimately obtain high-purity helium. However, in conventional helium extraction processes, the non-permeate gas from the two-stage or three-stage membrane separation group needs to be returned to the previous stage for recycling. This results in a large equipment throughput and high pressure requirements for the interstage compressor outlet, leading to a large number of membrane separation groups and high compressor pressure ratios, significantly increasing investment and operating costs. Project construction experience shows that the investment cost of the membrane separation unit and interstage compressor in conventional helium extraction membrane separation processes accounts for about 35% of the total project investment, and the operating cost of the interstage compressor accounts for about 50% of the total operating cost of the unit. Therefore, the key competitiveness of natural gas helium extraction membrane separation technology lies in whether it can reduce the processing load of the membrane separation unit and interstage compressor, and reduce the pressure ratio of the interstage compressor.

[0003] Invention patent CN120204889A discloses an integrated device and method for helium extraction using membrane separation technology. However, this method employs a two-stage membrane separation process, which results in the return of the second-stage membrane exhaust gas to the front-end recirculation stage. Furthermore, because the return of this exhaust gas to the first-stage membrane inlet requires a relatively high pressure, the outlet pressure of the first-stage membrane interstage compressor is also high, leading to problems such as high cost and energy consumption for both the first-stage membrane separation unit and the interstage compressor. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-stage natural gas helium extraction device and method, which, by adding pressure swing adsorption and other methods, eliminates the need for non-permeable gases from subsequent non-primary membrane separations, such as the non-permeable gases from the second to Nth stage membrane separation groups, to return to the inlet of the previous stage membrane to form a cycle, thereby reducing investment costs and operating energy consumption.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions.

[0006] On one hand, a multi-stage natural gas helium extraction device includes a pretreatment unit connected to a natural gas pipeline network and a multi-stage membrane separation unit connected to the pretreatment unit. The multi-stage membrane separation unit includes a first-stage membrane separation group to an Nth-stage membrane separation group, where N is a natural number greater than or equal to 2. In the multi-stage membrane separation unit, the permeate outlet of each stage membrane separation group is connected to the inlet of the next stage membrane separation group. In the second to Nth stage membrane separation groups, a first pressure swing adsorption unit is provided at the non-permeate outlet of each stage membrane separation group. Several first pressure swing adsorption units are sequentially connected to a decarbonization compressor, the pretreatment unit, and the natural gas pipeline network through desorption gas pipelines. The product gas pipeline of the first pressure swing adsorption unit, and the permeate gas outlet of each membrane separation group from the second to the Nth stage membrane separation group, are all connected to the dehydrogenation tower. The dehydrogenation tower is connected in sequence through the pressure swing adsorption inlet compressor, the crude helium pressure swing adsorption unit, and the temperature swing adsorption purification unit.

[0007] Furthermore, between the first-stage membrane separation group and the Nth-stage membrane separation group, and between adjacent membrane separation groups, an interstage compressor and a second pressure swing adsorption unit are sequentially arranged, with the interstage compressor located close to the previous-stage membrane separation group.

[0008] Furthermore, the product gas outlet and desorption gas outlet of the second pressure swing adsorption unit are respectively connected to the next stage membrane separation unit and the decarbonization compressor.

[0009] Furthermore, the second pressure swing adsorption unit is filled with an adsorbent material, and the pressure swing adsorption temperature of the adsorbent material is 50-60℃.

[0010] Furthermore, it also includes a heat-saving device located between the pretreatment unit and the first-stage membrane separation group. After passing through the heat-saving device, the non-permeable gas of the first-stage membrane separation group is connected to the pretreatment unit as regeneration gas in one path and to the outlet of the decarbonization compressor in the other path.

[0011] Furthermore, the regenerated gas at the outlet of the energy-saving device is divided into a cold blowing pipeline and a hot blowing pipeline connected to the pretreatment unit, and the hot blowing pipeline is connected to the cold blowing pipeline through the dehydrated regenerated gas heat exchanger and the regenerated gas heater.

[0012] Furthermore, the desorbed gas from the crude helium pressure swing adsorption unit is connected to the inlet of at least one of the membrane separation groups from the second-stage membrane separation group to the Nth-stage membrane separation group via a crude helium desorbed gas compressor to form a circulating helium recovery pipeline.

[0013] Furthermore, the pretreatment unit includes at least a dehydration unit, and the outlet of the decarbonization compressor is connected to the inlet of the pretreatment unit and the natural gas pipeline via a bypass pipe.

[0014] Furthermore, the decarbonization compressor is connected to the pretreatment unit and the natural gas pipeline network after passing through the dehydration regeneration gas heat exchanger and the water cooler.

[0015] On the other hand, a multi-stage natural gas helium extraction method includes the following steps. Pre-treatment and preheating of natural gas from the pipeline network; The pretreated and preheated natural gas is subjected to helium extraction through multi-stage membrane separation. In the multi-stage membrane separation, from the second separation to the last separation, the non-permeable gas obtained from each separation is subjected to pressure swing adsorption, decarbonized and compressed, and then returned to the pretreatment or pipeline. The permeate gas separated by multi-stage membrane separation and the adsorption product gas after pressure swing adsorption are sequentially purified by dehydrogenation, pressure swing adsorption inlet gas compression, crude helium pressure swing adsorption, and temperature swing adsorption to obtain helium products.

[0016] Furthermore, in the multi-stage membrane separation, the permeate gas between adjacent stages enters the next stage of membrane separation after interstage compression and re-pressure swing adsorption, and the temperature difference before and after the re-pressure swing adsorption is 5-10℃.

[0017] Furthermore, in the preheating step, the preheating temperature is not lower than 55°C.

[0018] Furthermore, the heat generated after the non-permeable gas pressure swing adsorption is decarbonized and compressed to obtain hot gas, which is then exchanged with dehydrated regeneration gas to form the dehydration heat in the pretreatment.

[0019] The beneficial effects of this invention are as follows: In existing technologies, multi-stage natural gas helium extraction processes typically employ two-stage or N-stage membrane separation groups to improve helium recovery rates. Each of these groups, from the second to the Nth stage, is divided into two sections. In the first section, permeate enters the next stage membrane separation group, while non-permeate enters the second stage. Both the non-permeate and permeate produced in the second stage need to be returned to the previous stage for recirculation and pressurization, thus increasing the processing load on the membrane separation groups and interstage compressors, resulting in higher energy consumption and costs.

[0020] This invention improves the traditional process flow by returning the non-permeate gas and permeate gas from the second to Nth stage membrane separation units to the previous stage for recirculation and pressurization. Instead, the gas passes through a first pressure swing adsorption (PSA) unit to remove methane and nitrogen, then directly returns to the decarbonization compressor and finally to the natural gas pipeline. This process improvement significantly reduces the processing load of the previous stage membrane separation unit and lowers the process requirements for the return gas pressure. Furthermore, by incorporating a low-cost first PSA unit to remove methane and nitrogen and recover helium, it replaces the separation function of the second to Nth stage membrane separation units in the prior art, thus reducing the number of membrane separation units required for each stage.

[0021] The helium extraction method in this invention can significantly reduce the investment cost of membrane separation units and interstage compressors, as well as the energy consumption of compressor operation, thus exhibiting strong technical and economic advantages. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the multi-stage natural gas helium extraction device provided by the present invention; In the picture: 1. Pretreatment unit; 2. Heat saver; 3. Raw material heater; 4. First-stage membrane separation unit; 5. Interstage compressor; 6. Second pressure swing adsorption unit; 7. Decarbonization compressor; 8. Dehydration regeneration gas heat exchanger; 9. Water cooler; 10. Regeneration gas heater; 11. Second-stage membrane separation unit; 12. First pressure swing adsorption unit; 13. Dehydrogenation tower; 14. Pressure swing adsorption inlet compressor; 15. Crude helium pressure swing adsorption unit; 16. Crude helium desorption gas compressor; 17. Temperature swing adsorption purification unit; 18. Non-permeable gas cooler. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. Equivalent changes or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0024] See attached document Figure 1 As shown, the multi-stage natural gas helium extraction device in this embodiment includes a pretreatment unit 1 connected to a natural gas pipeline network, and a multi-stage membrane separation unit connected to the pretreatment unit 1. Specifically, the multi-stage membrane separation unit includes a first-stage membrane separation group 4 to an Nth-stage membrane separation group, where N is a natural number greater than or equal to 2, meaning that at least two stages of membrane separation units are provided in this embodiment. In use, in the multi-stage membrane separation unit, the permeate outlet of each stage of the membrane separation group is connected to the inlet of the next stage of the membrane separation group, that is, the permeate from the previous stage forms the inlet of the next stage. Unlike the prior art, in this embodiment, in the second-stage membrane separation group 11 to the Nth-stage membrane separation group, a first pressure swing adsorption unit 12 is provided at the non-permeate outlet of each stage of the membrane separation group. In order to recover and reuse the desorbed gas, the desorbed gas in the first pressure swing adsorption unit 12 will pass through the desorbed gas pipeline, through the decarbonization compressor 7, and then return to either the pretreatment unit 1 or the natural gas pipeline network for reuse.

[0025] Specifically, the product gas in the first pressure swing adsorption (PSA) unit 12 enters the dehydrogenation tower 13 via a product gas pipeline. Of course, the permeate gas from the membrane separators in the second stage and subsequent Nth stages is also connected to the dehydrogenation tower 13. Finally, it is refined sequentially through the PSA inlet compressor 14, the crude helium PSA unit 15, the crude helium desorption compressor 16, and the temperature swing adsorption purification unit 17 to obtain the final helium product. In this embodiment, during the crude helium purification process, the dehydrogenated crude helium enters the crude helium PSA unit 15, and the desorbed gas is pressurized by the crude helium desorption compressor 16 and returned to the second-stage membrane separation group and the first PSA unit 12 for helium recycling. This effectively improves helium extraction efficiency and reduces losses.

[0026] In this embodiment, the non-permeable gas from the second to Nth stage membrane separation groups is directly returned to the decarbonization compressor 7 after being demethane and nitrogen removed by the first pressure swing adsorption unit 12, and finally returned to the natural gas pipeline. After the above-mentioned process improvement, the processing load of the previous stage membrane separation group is significantly reduced, and the process requirements for the return gas pressure are reduced. At the same time, by setting up the first pressure swing adsorption unit 12 with low investment cost to remove methane and nitrogen and recover helium, it partially replaces the separation function of the second to Nth stage membrane separation groups. Therefore, the number of membrane separation groups in the corresponding stages can be reduced, which can significantly reduce the investment cost of the membrane separation groups and the interstage compressor 5, as well as the compressor operating energy consumption.

[0027] As a further improvement, in this embodiment, between the first-stage membrane separation group and the Nth-stage membrane separation group, an interstage compressor 5 and a second pressure swing adsorption unit 6 are sequentially arranged between adjacent membrane separation groups. The interstage compressor 5 is located close to the membrane separation group of the previous stage. For example, when there are 3-stage membrane separation groups, an interstage compressor 5 and a second pressure swing adsorption unit 6 are arranged between the first and second stages, and then an interstage compressor 5 and a second pressure swing adsorption unit 6 are arranged between the second-stage membrane separation group and the third membrane separation group. At this time, combined with the first pressure swing adsorption unit, the two work together to reduce the pressure of the second-stage membrane separation group, subsequent other separation membrane groups, and the pressure swing adsorption decarbonization system. The outlet pressure of the interstage compressor is reduced. Since the membrane separation group cannot effectively separate carbon dioxide and other substances in natural gas, and each stage of membrane separation will also cause carbon dioxide enrichment and concentration, the first pressure swing adsorption unit 12 can directly remove most of the methane, nitrogen, and other substances from the tail gas of the second-stage membrane separation group and recover helium.

[0028] In this embodiment, the desorbed gas from the second-stage membrane separation group 11 and subsequent membrane separation groups can be directly returned to the inlet of the decarbonization compressor 7, pressurized, and then returned to the natural gas pipeline, effectively reducing cycle energy consumption. At this time, the crude helium, after removing methane and nitrogen impurities, is depressurized by a pressure reducing valve and mixed with the permeate gas from the second-stage membrane before entering the dehydrogenation unit, improving the helium recovery rate. Of course, only a portion of the desorbed gas from the membrane separation groups can be pressurized and reused, or all stages of the second-stage and subsequent membrane separation groups can be reused.

[0029] In this embodiment, the second pressure swing adsorption (PSA) unit 6 is filled with adsorbent material, and the PSA temperature of the adsorbent material is 50-60°C. This PSA temperature reduces the cooling water consumption of the interstage compressor 5 and avoids the need for an additional electric heater between the second PSA unit 6 and the second-stage membrane separation group 11, resulting in savings in both investment and operating costs. In the prior art, the optimal operating temperature for general PSA technology is below 40°C, and the optimal operating temperature for the membrane separation group is generally around 60°C. In conventional technology, the outlet temperature of the interstage compressor is controlled at 40°C before entering the second PSA (decarbonization) unit. The product gas from the second PSA (decarbonization) unit then needs to be heated to 60°C by an electric heater before being sent to the second-stage membrane separation group, resulting in higher overall costs.

[0030] The adsorbent in this embodiment is from Hangzhou Dong'an Technology Co., Ltd., and its product name is "Special Adsorbent," specifically designed for CO2 capture. This adsorbent has the following characteristics: First, it has a large CO2 adsorption capacity. Second, it has strong CO2 adsorption force, making it highly suitable for the removal and concentration of low-partial-pressure CO2. Third, the adsorbent operates at temperatures between 55℃ and 75℃, solving the problem of conventional adsorbents having low operating temperatures and requiring cooling before use. Fourth, this adsorbent has a high separation coefficient between CO2 and other components, resulting in a high recovery rate of effective components. Due to the high separation coefficient, the CH4 recovery rate is high, reducing the power consumption of the exhaust gas compressor.

[0031] In existing technologies, the operating temperature of adsorbents is generally 40℃, while the operating temperature of this adsorbent, 50-60℃, is more suitable. On the one hand, this can save on the cooling water consumption at the outlet of the interstage compressor 5. On the other hand, since the optimal operating temperature of the membrane separation unit is generally 60℃, it avoids the need to add an additional electric heater to heat the product gas of the second pressure swing adsorption unit 6 to 60℃ before sending it into the second-stage membrane separation unit 11. In summary, both investment costs and operating expenses are reduced to a certain extent, achieving energy-saving effects.

[0032] In this embodiment, a heat-saving device 2 is added to utilize the non-permeable gas in the first-stage membrane separation group 4. After passing through the heat-saving device 2, the non-permeable gas from the first-stage membrane separation group 4 is divided into two paths: one path serves as cold-blown regeneration gas connected to the pretreatment unit 1, and the other path serves as hot-blown regeneration gas connected to the dehydration regeneration gas heat exchanger 8. In practical use, the regeneration gas at the outlet of the heat-saving device 2 is divided into a cold-blown regeneration gas pipeline connected to the pretreatment unit 1 and a hot-blown regeneration gas pipeline. The hot-blown regeneration gas pipeline is connected to the cold-blown regeneration gas pipeline via the dehydration regeneration gas heat exchanger 8 and the regeneration gas heater 10.

[0033] In this embodiment, the pretreatment unit 1 (specifically the dehydration unit) has three operating states: dehydration, regeneration, and cold blowing. After cold blowing is completed, it re-enters the dehydration state, continuously cycling through these states. The operating temperature for the dehydration state is room temperature; the operating temperature for the regeneration state is 150°C; and the operating temperature for the cold blowing state is reduced from 150°C to room temperature. Therefore, different regeneration gas pipelines are used for different operating states.

[0034] In this embodiment, preheating by the heat-saving device 2 reduces the power of the downstream feedstock heater, thereby lowering operating energy consumption. After preheating by the heat-saving device 2, the temperature of the entire feedstock gas is 60°C. After pretreatment by the pretreatment unit 1, the temperature of the feedstock natural gas is generally around 20°C. Compared to direct heating, preheating by the heat-saving device 2 before heating consumes only 1 / 8 of the energy.

[0035] Specifically, the crude helium pressure swing adsorption (PSA) unit 15 is connected to the inlet of at least one of the membrane separation groups (from the second-stage membrane separation group to the Nth-stage membrane separation group) via a crude helium desorption compressor 16, forming a helium recycling pipeline. At this time, the dehydrogenated crude helium enters the crude helium PSA unit 15, and the desorbed gas, after being pressurized by the crude helium desorption compressor 16, returns to the second-stage membrane separation group 11 and the first PSA unit 12 for the tail gas of the second-stage membrane, thus recycling helium. This effectively improves helium extraction efficiency and reduces losses.

[0036] In this embodiment, the pretreatment unit can be a dehydration unit. The outlet of the decarbonization compressor 7 is connected to the inlet of the dehydration unit in the pretreatment unit 1 and the natural gas pipeline via a bypass pipe. In this case, the heat from the outlet of the decarbonization compressor 7 can be used to preheat the regenerated gas in the natural gas dehydration unit, which can effectively reduce the power consumption of the regenerated gas heater 10 and the cooling water consumption of the decarbonization compressor 7.

[0037] In this embodiment, to ensure the incoming gas, a dehydration regeneration gas heat exchanger 8 and a water cooler 9 can be added after the decarbonization compressor 7. The dehydration regeneration gas heat exchanger 8 is added because the approximately 120°C hot gas, after pressure swing adsorption of the regeneration gas and the non-permeable gas, is compressed by the decarbonization compressor 7 and then heats the gas through the dehydration regeneration gas heat exchanger 8, forming the dehydration heat in the pretreatment unit. Adding the water cooler 9 facilitates the adjustment of the temperature returned to the natural gas pipeline network.

[0038] Meanwhile, conventional helium enrichment processes typically employ a two-stage membrane separator to separate and recover helium from the tail gas of the second or third stage membrane separation group in order to improve helium recovery. Both the tail gas and permeate from the second-stage membrane separator need to be returned to the front end for recirculation, resulting in high energy consumption and cost. This process incorporates a first pressure swing adsorption (PSA) unit 12 in the tail gas of the second stage membrane separation group 11. Since the tail gas of the second stage membrane separation group 11 does not need to return to the inlet of the first stage membrane separation group 4, it passes through the first PSA unit 12, removing most of the methane, nitrogen, etc., to recover helium. The crude helium product gas from the first PSA unit 12 is depressurized by a pressure reducing valve and mixed with the permeate from the second stage membrane separation group 11 before entering the dehydrogenation tower 13. The desorbed gas is directly returned to the inlet of the decarbonization desorbed gas compressor (i.e., the decarbonization compressor 7), pressurized, and then returned to the pipeline network, effectively reducing recirculation energy consumption. Through this process, the outlet pressure of the interstage compressor 5 is reduced, thus lowering the pressure of both the second stage membrane separation group 11 and the second PSA unit 6. Specifically, the inlet gas of the first pressure swing adsorption unit 12 is the cooled non-permeable gas from the second-stage membrane separation group 11, with a pressure of 3.05 MPa. The pressure drop of this unit is approximately 0.1 MPa, meaning the product gas pressure before the pressure reducing valve is 2.95 MPa; the desorption gas pressure can be controlled at 20 kPag, thus ensuring that the inlet pressure of the decarbonization compressor does not exceed the limit. At this time, the first pressure swing adsorption unit 12 can effectively adsorb gases such as methane and nitrogen (desorption gas) to obtain gases such as helium and hydrogen (product gas).

[0039] In actual production, the product gas from the first pressure swing adsorption unit 12 is combined with the permeate gas through a pressure reducing valve and enters the dehydrogenation tower 13, and an air / oxygen inlet is provided between the permeate gas and the dehydrogenation tower 13.

[0040] This invention also discloses a multi-stage natural gas helium extraction method, comprising the following steps: Pre-treatment and preheating of natural gas from the pipeline network; During preheating, the preheating temperature is not lower than 55℃. Preheating here can reduce the power of the downstream raw material heater, thereby reducing operating energy consumption.

[0041] The pretreated and preheated natural gas is subjected to helium extraction through a multi-stage membrane separation unit. In the multi-stage membrane separation unit, from the second stage to the last stage, the non-permeable gas obtained from each stage is adsorbed by the first pressure swing adsorption unit, compressed by the decarbonization compressor, and then returned to the pretreatment or pipeline. The permeate gas from the multi-stage membrane separation unit and the product gas adsorbed by the first pressure swing adsorption unit are sequentially processed through dehydrogenation, pressure swing adsorption inlet compressor compression, crude helium pressure swing adsorption, and temperature swing adsorption purification to obtain helium product.

[0042] Specifically, in the multi-stage membrane separation, the permeate gas between adjacent stages enters the next stage of membrane separation after interstage compression and re-pressure swing adsorption, and the temperature difference before and after the re-pressure swing adsorption is 5-10℃.

[0043] In order to make full use of thermal energy, a portion of the regenerated gas and the non-permeable gas pressure swing adsorption, after being compressed by the decarbonization compressor to about 120°C, can be used as the heat generated by the heat exchange of the regenerated gas after dehydration through the dehydration regeneration gas heat exchange equipment, and then used as the dehydration heat in the pretreatment.

[0044] The helium extraction method in this embodiment can be integrated with the apparatus described in the embodiment, taking two-stage separation as an example, as follows: Natural gas from the pipeline is pretreated by pretreatment unit 1, preheated by heat exchanger 2, and then heated by raw material heater 3 before entering the first-stage membrane separation group 4 for separation. At this point, the non-permeable gas returns to heat exchanger 2 for heat recovery, while the permeable gas enters the interstage compressor 5 and the second pressure swing adsorption unit 6 for processing. The resulting product gas enters the subsequent second-stage membrane separation group 11. The non-permeable gas from this membrane separation group is cooled by non-permeable gas cooler 18 before entering the first pressure swing adsorption unit 12. The desorbed gas from this unit passes through decarbonization compressor 7 and finally returns to the natural gas pipeline. The outlet gas from decarbonization compressor 7 then returns to the natural gas pipeline through dehydration regeneration gas heat exchanger 8 and water cooler 9. The hot-blown regeneration gas in heat exchanger 2 returns to pretreatment unit 1 after passing through dehydration regeneration gas heat exchanger 8 and regeneration gas heater 10 for recycling.

[0045] The permeate gas in the second-stage membrane separation unit 11 and the non-permeate gas in the second-stage membrane separation unit 11 (which passes through a pressure reducing valve) processed by the first pressure swing adsorption unit 12 are sequentially passed through the dehydrogenation tower 13, the pressure swing adsorption inlet compressor 14, the crude helium pressure swing adsorption unit 15, and the temperature swing adsorption purification unit 17 to obtain a high-purity helium product.

[0046] In this embodiment, the desorbed gas from the crude helium pressure swing adsorption unit 15 will return to the second-stage membrane separation group 11 via the crude helium desorbed gas compressor 16, and merge with the product gas in the second pressure swing adsorption unit 6.

[0047] The process flow in this embodiment is as follows: Low-helium natural gas from the natural gas pipeline contains methane, nitrogen, carbon dioxide, helium, hydrogen and other components, of which the helium content is 300ppm-2000ppm. The content is too low, so it is extracted using existing technology, and the helium recovery rate is about 80%-90%.

[0048] However, the existing extraction technology has relatively high investment costs and operating expenses. Therefore, the specific details of this invention are as follows: First, the product enters the dehydration unit for the drying tower to remove moisture. The dehydration adopts molecular sieve adsorption technology. The dehydrated product gas is preheated to 55°C by the heat saver 2. The preheating by the heat saver can reduce the power of the downstream raw material heater, thereby reducing the operating energy consumption.

[0049] Secondly, the natural gas, preheated to 55°C, is then heated to 60°C by the raw material heater 3. After pretreatment by the pretreatment unit, the temperature of the raw material natural gas is generally around 20°C. Compared to direct heating, the method of preheating by the energy-saving device 2 in this embodiment consumes only 1 / 8 of the energy.

[0050] Natural gas, heated by feedstock heater 3, undergoes multi-stage membrane separation. In this embodiment, a two-stage membrane separation group is used as an example. It first enters the first-stage membrane separation group 4 (i.e., the membrane separator), where helium in the natural gas is concentrated on the permeate side. After being pressurized by interstage compressor 5, the permeate pressure becomes 3.3 MPa. It then enters the second pressure swing adsorption (PSA) unit 6, which removes carbon dioxide from the gas. During this process, the inlet pressure of the decarbonization compressor is 20 kPag, and the outlet pressure is 3.1 MPa. At this point, since the incoming gas pressure from the natural gas pipeline is 3.3 MPa, most of it returns to the natural gas pipeline after passing through the pretreatment unit 1, the heat saver 2, the raw material heater 3, and the non-permeable gas end of the first-stage membrane separation group 4. The total pressure drop of the equipment is 0.3 MPa, that is, the return pressure is 3.0 MPa. Therefore, the desorbed gas from the second pressure swing adsorption unit 6 needs to be pressurized to 3.1 MPa by the decarbonization compressor 7 before it can return to the natural gas pipeline. At this time, the decarbonized desorbed gas passes through the decarbonization compressor 7, and the pressure is increased from 20 kPag to 3.1 MPa. The high-temperature gas at the outlet exchanges heat with the non-permeable gas of the membrane separator in the dehydration regeneration gas heat exchanger 8 to recover heat. After being cooled by the water cooler 9, it returns to the pipeline. After the non-permeable gas from the first-stage membrane separation group 4 exchanges heat with the product gas from the dehydration unit in the heat saver 2, it is split into two paths through a three-way valve. One path mixes with the decarbonization desorption gas and returns to the pipeline network, while the other path serves as regeneration gas for the dehydration system. This regeneration gas is further divided into two paths: one path exchanges heat with the hot gas from the outlet of the decarbonization compressor before entering the dehydration unit through the regeneration gas heater 10 for thermal regeneration, reducing the energy consumption of the regeneration gas heater and recovering heat from the compressor. The other path of regeneration gas serves as cold blowing gas to purge and cool the drying tower after thermal regeneration.

[0051] The outlet gas from the interstage compressor, after being controlled at a temperature of 50-85℃, preferably 60℃, and at 3.3 MPa, enters the second pressure swing adsorption (PSA) unit 6. At this point, the temperature of the decarbonized product gas is 55-90℃, preferably 65℃, and at 3.2 MPa. It then enters the second-stage membrane separation group 11. The permeate gas in the second-stage membrane separation group 11 enters the dehydrogenation tower 13, where the temperature is 63-65℃ and the pressure is 0.4 MPa. The temperature inside the dehydrogenation tower 13 is generally 60-63℃, and the pressure is 0.4 MPa. The non-permeate gas in the second-stage membrane separation group 11, after being cooled by the non-permeate gas cooler 18, enters the first PSA unit 12, which is composed of a PSA demethanization unit. This removes impurities such as methane and nitrogen, and recovers helium from the non-permeate gas. This improves helium recovery rate, facilitates operation, reduces membrane equipment, and lowers costs. In the second-stage membrane separation unit 11, the non-permeable gas has a temperature of 63~65℃ and a pressure of 3.1MPag before being cooled by the cooler. After cooling, the temperature becomes 40℃ and the pressure becomes 3.05MPag.

[0052] After the pressure swing adsorption (PSA) product gas is reduced in temperature by a pressure reducing valve, its temperature is 42℃ and its pressure is 0.4 MPa. It then mixes with the permeate gas from the second-stage membrane separation unit 11 (at this point, the permeate gas temperature is 63-65℃ and its pressure is 0.4 MPa) and enters the dehydrogenation tower 13. In the dehydrogenation tower 13, a catalytic oxidation reaction is carried out to obtain the dehydrogenation product gas, which has a temperature of 60℃ and a pressure of 0.1 MPa. The desorbed gas from the first PSA unit 12 (temperature 40℃, pressure 20 kPag) enters the decarbonization desorbed gas compressor (i.e., the decarbonization compressor 7). The product gas from the outlet of dehydrogenation tower 13 (temperature 60℃, pressure 0.1MPag) is pressurized by pressure swing adsorption (PSA) inlet compressor 14 to a temperature of 40℃ and a pressure of 2.5MPag. It then enters the crude helium PSA unit 15. The desorbed gas obtained after crude helium PSA unit 15 has a temperature of 40℃ and a pressure of 20kPag. It is then pressurized by crude helium desorbed gas compressor 16 and returned to the inlet of the second-stage membrane separation group 11 for helium recycling. The gas after being pressurized by crude helium desorbed gas compressor 16 has a temperature of 60℃ and a pressure of 3.25MPag.

[0053] The desorbed gas from the temperature swing adsorption purification unit 17 is returned to the inlet of the pressure swing adsorption compressor 14 for helium recycling, thereby improving the helium yield. After temperature swing adsorption purification, the crude helium gas yields high-purity helium product gas for filling or liquefaction.

[0054] In this embodiment, helium-containing natural gas enters the dehydration unit. The preferred dehydration process is molecular sieve adsorption. After dehydration, the dried gas passes through the heat exchanger 2 and fully exchanges heat with the tail gas from the first-stage membrane separation group 4. It is then heated to the required temperature by the raw material heater 3 and enters the first-stage membrane separation group 4. Helium is concentrated on the permeate side of the first-stage membrane separation group 4. The permeate is pressurized by the interstage compressor 5 and then enters the second pressure swing adsorption unit 6 to remove carbon dioxide from the gas. The decarbonized desorbed gas is pressurized by the decarbonization compressor 7. The high-temperature outlet gas exchanges heat with the non-permeate gas from the first-stage membrane separation group 4 in the dehydration regeneration gas heat exchanger 8 to recover heat. After being cooled by the water cooler 9, it returns to the pipeline network. After the non-permeable gas and dehydrated product gas in the first-stage membrane separation group 4 exchange heat in the heat saver 2, they are split into two paths through a three-way valve. One path mixes with the decarbonization desorption gas and returns to the pipeline network, while the other path serves as regeneration gas for the dehydration system. This regeneration gas is further divided into two paths: one path exchanges heat with the hot gas exiting the decarbonization compressor and then enters the dehydration unit through the regeneration gas heater 10 for thermal regeneration, reducing the energy consumption of the regeneration gas heater and recovering heat from the compressor. The other path of regeneration gas serves as cold blowing gas to purge and cool the drying tower after thermal regeneration.

[0055] The outlet gas from interstage compressor 5 enters the second pressure swing adsorption (PSA) unit 6 after being controlled at a temperature of 50-85℃. The decarbonization product gas (55-90℃) enters the second-stage membrane separation group 11, and the permeate gas from membrane separator #2 enters the dehydrogenation tower 13. The non-permeate gas from the second-stage membrane separation group 11 is cooled by cooler 17 and then enters the first PSA unit 12 to remove impurities such as methane and nitrogen, and recover helium from the non-permeate side tail gas, which can improve the helium recovery rate, facilitate operation, reduce membrane equipment, and lower costs. The PSA product gas is reduced in pressure by a pressure reducing valve and then mixed with the permeate gas from the second-stage membrane separation group before entering the dehydrogenation tower 13. In the dehydrogenation tower, a catalytic oxidation reaction is carried out to cool and dehydrate the gas, obtaining the dehydrogenation product gas. The PSA desorbed gas enters the inlet of the decarbonization compressor 7. The product gas from the outlet of the dehydrogenation tower 13 is pressurized by the pressure swing adsorption inlet compressor 14 and enters the crude helium pressure swing adsorption unit 15. The desorbed gas from the crude helium pressure swing adsorption unit is pressurized by the crude helium desorbed gas compressor and returned to the inlet of the second-stage membrane separation group 11 for helium recycling.

[0056] The optimal operating temperature for pressure swing adsorption (PSA) technology is generally below 40℃, while the optimal operating temperature for membrane separation units is generally around 60℃. In conventional technology, the outlet temperature of the interstage compressor is controlled at 40℃ before entering the second PSA (decarbonization) unit. The product gas from the second PSA (decarbonization) unit needs to be heated to 60℃ by an electric heater before being sent to the second-stage membrane separation unit.

[0057] The second pressure swing adsorption unit of this technology uses a new type of adsorbent with an optimal operating temperature of 60°C. This reduces the cooling water consumption of the interstage compressor 5 and avoids the need to add an electric heater between the second pressure swing adsorption unit 6 and the second-stage membrane separation group, resulting in savings in investment costs and operating expenses.

[0058] The desorbed gas from the temperature swing adsorption purification unit 17 is returned to the inlet of the pressure swing adsorption compressor 14 for helium recycling, thereby improving the helium yield. After temperature swing adsorption purification, the crude helium gas yields high-purity helium product gas for filling or liquefaction.

[0059] Taking a membrane separation helium extraction device for pipeline natural gas (0.2% He content) with a daily processing capacity of 1 million cubic meters as an example, the helium produced by this invention is approximately 1600 cubic meters per day, with a helium extraction rate of 80%~85%, which is basically close to that of existing technologies. However, the investment and operating costs are significantly reduced. It is estimated that, compared with existing technologies, the reduction in the throughput and pressure of the interstage compressor can reduce investment costs by 20-35% and operating costs by 30-40%; replacing the second-stage membrane separation unit with the first pressure swing adsorption unit can reduce investment costs by 35-45%; furthermore, compared with existing technologies, the energy consumption of the raw natural gas is reduced by more than 80% by preheating it in a heat saver before it enters the heater for heating, compared with direct heating by the heater; using the decarbonization adsorbent of the second pressure swing adsorption unit with an optimal operating temperature of 60℃ can reduce the cooling water consumption at the outlet of the interstage compressor by 20%-25%, and at the same time, the electric heater between the second pressure swing adsorption (decarbonization) unit and the second-stage membrane separation unit can be eliminated, resulting in a reduction in investment costs of about 3% and operating costs of about 5%; by setting up a dehydrated regenerated gas heat exchanger to utilize the heat from the outlet of the decarbonized compressor, the operating costs can be reduced by about 2% compared with direct heating by the regenerated gas heater.

[0060] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

[0061] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0062] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A multi-stage natural gas helium extraction unit, characterized in that, The system includes a pretreatment unit (1) connected to a natural gas pipeline network, and a multi-stage membrane separation unit connected to the pretreatment unit (1). The multi-stage membrane separation unit includes a first-stage membrane separation group (4) to an Nth-stage membrane separation group, where N is a natural number greater than or equal to 2. In the multi-stage membrane separation unit, the permeate outlet of each stage membrane separation group is connected to the inlet of the next stage membrane separation group. In the second-stage membrane separation group (11) to the Nth-stage membrane separation group, a first pressure swing adsorption unit (12) is provided at the non-permeate outlet of each stage membrane separation group. Several first pressure swing adsorption units (12) are connected to the decarbonization compressor (7), the pretreatment unit (1), and the natural gas pipeline network in sequence through desorption gas pipelines. The product gas pipeline of the first pressure swing adsorption unit (12), and the permeate gas outlet of each membrane separation group from the second-stage membrane separation group (11) to the Nth-stage membrane separation group are all connected to the dehydrogenation tower (13), which is connected to the temperature swing adsorption purification unit (17) in sequence through the pressure swing adsorption inlet compressor (14), the crude helium pressure swing adsorption unit (15).

2. The multi-stage natural gas helium extraction device according to claim 1, characterized in that, Between the first-stage membrane separation group (4) and the Nth-stage membrane separation group, an interstage compressor (5) and a second pressure swing adsorption unit (6) are sequentially arranged between adjacent membrane separation groups, and the interstage compressor (5) is arranged close to the membrane separation group of the previous stage.

3. The multi-stage natural gas helium extraction device according to claim 2, characterized in that, The product gas outlet and desorption gas outlet of the second pressure swing adsorption unit (6) are respectively connected to the next stage membrane separation group and the decarbonization compressor (7).

4. The multi-stage natural gas helium extraction device according to claim 2, characterized in that, The second pressure swing adsorption unit is filled with an adsorbent material, and the pressure swing adsorption temperature of the adsorbent material is 50-60℃.

5. The multi-stage natural gas helium extraction device according to claim 1, characterized in that, It also includes a heat-saving device (2) located between the pretreatment unit (1) and the first-stage membrane separation group (4). After the non-permeable gas of the first-stage membrane separation group (4) passes through the heat-saving device (2), one path is connected to the pretreatment unit (1) as regeneration gas, and the other path is connected to the outlet of the decarbonization compressor (7).

6. The multi-stage natural gas helium extraction device according to claim 5, characterized in that, The regenerated gas at the outlet of the heat saver (2) is divided into a cold blowing pipeline and a hot blowing pipeline connected to the pretreatment unit (1), and the hot blowing pipeline is connected to the cold blowing pipeline through the dehydrated regenerated gas heat exchanger (8) and the regenerated gas heater (10).

7. The multi-stage natural gas helium extraction device according to claim 1, characterized in that, The desorbed gas from the crude helium pressure swing adsorption unit (15) is connected to the inlet of at least one of the membrane separation groups from the second-stage membrane separation group (11) to the Nth-stage membrane separation group via the crude helium desorbed gas compressor (16), forming a circulating helium recovery pipeline.

8. The multi-stage natural gas helium extraction device according to claim 1, characterized in that, The pretreatment unit (1) includes at least a dehydration unit, and the outlet of the decarbonization compressor (7) is connected to the inlet of the pretreatment unit (11) and the natural gas pipeline via a bypass pipe.

9. The multi-stage natural gas helium extraction device according to claim 1, characterized in that, The decarbonization compressor (7) is connected to the pretreatment unit (1) and the natural gas pipeline after passing through the dehydration regeneration gas heat exchanger (8) and the water cooler (9).

10. A multi-stage natural gas helium extraction method, characterized in that, Includes the following steps, Pre-treatment and preheating of natural gas from the pipeline network; The pretreated and preheated natural gas is subjected to helium extraction through multi-stage membrane separation. In the multi-stage membrane separation, from the second separation to the last separation, the non-permeable gas obtained from each separation is subjected to pressure swing adsorption, decarbonized and compressed, and then returned to the pretreatment or pipeline. The permeate gas separated by multi-stage membrane separation and the adsorption product gas after pressure swing adsorption are sequentially purified by dehydrogenation, pressure swing adsorption inlet gas compression, crude helium pressure swing adsorption, and temperature swing adsorption to obtain helium products.

11. A multi-stage natural gas helium extraction method according to claim 10, characterized in that, In the multi-stage membrane separation, the permeate gas between adjacent stages enters the next stage of membrane separation after interstage compression and re-pressure swing adsorption, and the temperature difference before and after the re-pressure swing adsorption is 5-10℃.

12. The multi-stage natural gas helium extraction method according to claim 10, characterized in that, During the preheating process, the preheating temperature shall not be lower than 55°C.

13. A multi-stage natural gas helium extraction method according to claim 10, characterized in that, The heat generated by the non-permeable gas pressure swing adsorption is compressed after decarbonization to obtain hot gas. The hot gas is then exchanged with dehydrated regeneration gas to form the dehydration heat in the pretreatment.

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