An apparatus and process for purifying helium from lean helium natural gas

Abstract

The present application relates to a kind of equipment and process for purifying helium from helium-lean natural gas, equipment for purifying helium from helium-lean helium-lean natural gas includes pre-purification system, membrane separation system, desulfurization unit, hydrogen removal unit, low-temperature impurity removal unit.The present application is mainly used according to the present situation of resources to solve the helium purification in helium-lean, helium-lean natural gas, by pre-purification, remove all CO2, water, heavy hydrocarbon, part of organic sulfur and inorganic sulfur in raw gas, greatly reduce the fast gas component of membrane separator, it is conducive to the concentration of helium, adopt multistage membrane separator to carry out helium concentration, it is applicable to process helium-lean, helium-lean natural gas, and in the process, catalytic hydrogenation process+dry desulfurization is used to remove sulfide completely, which plays a very key role for helium purification;The present application solves the problems of decarburization, desulfurization, dehydrogenation, drying, trace impurities, especially neon removal in natural gas, thereby improving the purity of helium.

Description

Technical Field

[0001] This invention relates to the field of helium production technology, specifically to an apparatus and process for purifying helium from lean helium natural gas. Background Technology

[0002] Helium is an indispensable strategic material for military and aerospace industries. However, my country is a helium-poor country with outdated helium extraction technology, and more than 95% of its helium must be imported, with imports increasing year by year. Currently, the mainstream helium extraction technology internationally is the cryogenic method, which is used in China's prevalent helium-poor and even ultra-poor helium fields. This method involves huge investment and energy consumption and has no industrialization value.

[0003] Chinese patents CN214087729U ("A System for Extracting and Purifying Helium from Natural Gas at Room Temperature") and CN215113528U ("A Device for Extracting Helium from Natural Gas to Produce Liquid Helium") disclose technologies for extracting helium from natural gas. CN214087729U uses pressure swing adsorption (PSA) as the final means of decarbonization and helium purification, resulting in incomplete impurity removal. Impurities tend to accumulate during the process, leading to substandard helium purity. Furthermore, it does not consider drying and dehydration, making it difficult to guarantee the product dew point. CN215113528U uses MDEA for decarbonization, failing to consider the impact of amine volatilization or entrainment on the tolerance and performance of subsequent separation membranes. Additionally, the membrane separator experiences high back pressure downstream, resulting in a small pressure differential during membrane separation operation, leading to poor separation performance and a significant increase in membrane equipment investment, making it uneconomical.

[0004] The existing technologies for extracting helium from natural gas generally suffer from the following problems:

[0005] 1) Natural gas from domestic gas fields contains trace amounts of sulfur. The national standard requires that the total sulfur content of natural gas not exceed 100 mg / cm³. 3 The existing publicly available technologies do not consider the removal of organic and inorganic sulfur. Neither PSA nor MDEA can completely remove organic sulfur to meet the catalyst requirements for subsequent catalytic dehydrogenation, which can easily cause catalyst poisoning. At the same time, hydrogen impurities cannot be separated from helium, ultimately resulting in unqualified helium purity.

[0006] 2) Existing technologies do not take into account the rational organization of heat exchange in the process, resulting in "cold and hot diseases". For example, the heat generated by the compressor is cooled for decarbonization, the dehydrogenation reaction requires heating, and subsequent processes require cooling. If dehydrogenation is carried out at room temperature, it is difficult to guarantee the H2 removal rate, which directly affects the purity of helium.

[0007] 3) The existing technology is applicable to natural gas with a He content of about 0.1%, while the current situation of domestic gas fields is that the natural gas is helium-poor or even extremely helium-poor, which makes it impossible to obtain effective separation and purification.

[0008] Therefore, the technology for extracting helium from domestic low- and very low-helium natural gas resources needs further improvement. Summary of the Invention

[0009] The first technical problem to be solved by the present invention is to provide a method for purifying helium from helium-poor and extra-poor helium natural gas that can be directly extracted from natural gas pretreated from helium-poor and extra-poor helium gas fields (0.03-0.1% He) and purified into high-purity helium (99.999%).

[0010] The second technical problem to be solved by the present invention is to provide a device for purifying helium from lean and extra-lean helium natural gas, which can solve the problems of natural gas decarbonization, desulfurization, dehydrogenation, drying, and removal of trace impurities, especially neon, thereby improving the purity of the product.

[0011] The third technical problem to be solved by the present invention is to provide a process for purifying helium from lean helium and extra-lean helium natural gas, in view of the current state of the prior art. This process solves the problems of incomplete CO2 removal, adverse effects on subsequent membrane separation, and corrosion of downstream systems by setting a purification process at the front end of the process. The existing "cold and hot disease" problem is solved by optimizing the process heat exchange.

[0012] The technical solution adopted by the present invention to solve at least one of the above-mentioned technical problems is as follows:

[0013] An apparatus for purifying helium from lean helium and extra-lean helium natural gas includes:

[0014] The pre-purification system has an inlet for the input of lean helium natural gas, used to remove CO2, water, heavy hydrocarbons and some sulfides from the intake gas;

[0015] A membrane separation system, located downstream of the pre-purification system, includes at least two sets of membrane separators connected in series or parallel, used to perform permeation separation on the material to obtain non-permeable gas to be supplied to the natural gas pipeline and permeable gas after helium enrichment;

[0016] A desulfurization unit, connected to the membrane separation system, is used to remove sulfides from the process gas;

[0017] A dehydrogenation unit, connected to the membrane separation system and located downstream of the desulfurization unit, is used to remove residual hydrogen from the process gas; and

[0018] A low-temperature impurity removal unit is located downstream of the membrane separation system and the dehydrogenation unit, and is used to remove at least one of CH4, N2, Ar, O2 and Ne contained in the process gas.

[0019] The aforementioned desulfurization, dehydrogenation, and impurity removal facilities can be further modified, implemented in a distributed and hierarchical manner, or integrated and coupled with each other.

[0020] Preferably, the desulfurization unit is connected in series between two adjacent membrane separators, including an upstream hydrogenation reactor and a downstream desulfurization tower. The hydrogenation reactor is used to react hydrogen and organic sulfides in natural gas to convert organic sulfur into inorganic sulfur sulfides, and the desulfurization tower is used to remove inorganic sulfur sulfides.

[0021] Preferably, a second compressor is provided between two adjacent membrane separators. The primary inlet of the second compressor is connected to the permeate gas side of the membrane separator upstream of it, and the final outlet is connected to the top inlet of the desulfurization tower. The middle outlet of the second compressor is connected to the top inlet of the hydrogenation reactor, and the bottom outlet of the hydrogenation reactor is connected to the final inlet of the second compressor.

[0022] Preferably, the dehydrogenation unit is connected in series between two adjacent membrane separators, including an upstream catalytic dehydrogenation reactor and a downstream dehydrogenation cooler. The catalytic dehydrogenation reactor is used to remove residual hydrogen from the process gas, and the dehydrogenation cooler is used to cool the process gas after the residual hydrogen has been removed, in preparation for it to enter the downstream membrane separator.

[0023] Preferably, the low-temperature impurity removal unit includes a crude helium precooler and a low-temperature adsorber connected in series downstream of the membrane separation system. The crude helium precooler is used to lower the water dew point, and the low-temperature adsorber is used to remove at least one of CH4, N2, Ar, O2, and Ne contained in the process gas.

[0024] Preferably, the membrane separation system includes membrane separators #1, #2, #3, and #4 connected in series. A compressor #1 for pressurizing the process gas is installed between membrane separators #1 and #2. A compressor #2 for pressurizing the process gas is installed between membrane separators #2 and #3. A compressor #3 for pressurizing the process gas is installed between membrane separators #3 and #4. A compressor #4 for pressurizing the process gas is installed between membrane separator #4 and the low-temperature impurity removal unit.

[0025] Preferably, the dehydrogenation and desulfurization units can be positioned according to the H2 content in the feed gas. When the H2 content in the feed gas is high, the desulfurization unit is located between membrane separator #2 and membrane separator #3 and is connected to compressor #2, while the dehydrogenation unit is located between membrane separator #3 and membrane separator #4. When the H2 content in the feed gas is low (preferably the hydrogen concentration entering the dehydrogenation reactor does not exceed 2%), the dehydrogenation unit is located downstream of membrane separator #4, while the desulfurization unit is located between membrane separator #3 and membrane separator #4 and is connected to compressor #3.

[0026] Preferably, the top of membrane separator #1 is connected to a first pipe that connects its non-permeable gas side to the natural gas pipeline network; the top of membrane separator #2 is connected to a second pipe that connects its non-permeable gas side to the first pipe; the second pipe is equipped with a natural gas buffer tank and a natural gas booster connected in series along the gas flow direction; the top of membrane separator #3 is connected to a third pipe that connects its non-permeable gas side to the second pipe upstream of the natural gas buffer tank; and the top of membrane separator #4 is connected to a fourth pipe that connects its non-permeable gas side to the pipeline downstream of the desulfurization unit and upstream of membrane separator #3.

[0027] Preferably, the pre-purification system is a TSA purification system, which is a temperature-switching adsorption system, including an adsorption unit and a regeneration unit. The adsorption unit is filled with an adsorbent for adsorbing CO2, water, heavy hydrocarbons, and some sulfides. The regeneration unit includes a fifth pipe, a regeneration gas heater, a sixth pipe, and a regeneration gas cooler. The fifth pipe is connected near the inlet of the first pipe to the bottom inlet of the TSA purification system. The regeneration gas heater is located on the fifth pipe and is used to heat part of the non-permeable gas in the first pipe before it is introduced into the TSA purification system to purge impurities adsorbed in the adsorbent. The sixth pipe is connected between the top outlet of the TSA purification system and the first pipe, and the connection point with the first pipe is located after the fifth pipe and before the natural gas booster. The regeneration gas cooler is located on the sixth pipe and is used to cool the heated non-permeable gas.

[0028] Preferably, the number of membrane separation stages and the membrane separation operating pressure difference in this invention need to be determined comprehensively based on the helium content of the feed gas, the project scale, and the techno-economic feasibility, and no specific restrictions are imposed.

[0029] In this invention, the desulfurization tower employs a dry desulfurization process, which uses an active desulfurizing agent (such as ZnO) to completely remove inorganic sulfur. The crude helium precooler operates on the principle of compression refrigeration drying, but can also be replaced by a molecular sieve adsorption drying structure or a triethylene glycol dehydration principle. The permeate pressure (back pressure) of the membrane separator is automatically controlled by the compressor at its outlet; for safety reasons, negative pressure is not generated.

[0030] The TSA purification system of the present invention can be replaced by MEA (referring to the amino acid method) + water washing system. This is to effectively eliminate amino acid entrainment and fundamentally avoid the impact of volatile solvents on membrane separation.

[0031] A process for purifying helium from helium-poor and extra-helium-poor natural gas includes the following steps:

[0032] The lean helium-containing sulfur-containing natural gas from the gas field processing plant first enters the TSA purification unit to remove all CO2, water, heavy hydrocarbons and some sulfides, and then enters the No. 1 membrane separator.

[0033] After permeation treatment by membrane separator #1, non-permeate gas without helium and permeate gas containing helium are obtained. The non-permeate gas is sent directly to the natural gas pipeline network with almost no pressure reduction. The permeate gas is unpressurized, and the helium in the permeate gas is enriched. After being pressurized by compressor #1, it is sent to membrane separator #2.

[0034] After permeation treatment by membrane separator #2, the helium concentration in the permeate gas is increased. It is then pressurized and heated by compressor #2 before entering the hydrogenation reactor.

[0035] In the hydrogenation reactor, a catalyst (such as cobalt-molybdenum) is used to react hydrogen and organic sulfides in natural gas. The organic sulfides are converted into inorganic sulfides, which are then re-enter the final stage of compressor #2 for pressurization and cooling before entering the desulfurization tower.

[0036] In the desulfurization tower, inorganic sulfides are removed to below 0.1 ppm and then enter the No. 3 membrane separator;

[0037] After permeation treatment by membrane separator #3, the helium concentration in the permeate gas is further increased. After being pressurized and heated by compressor #3, it is sent to the catalytic dehydrogenation reactor and dehydrogenation cooler in sequence. After passing through the catalytic dehydrogenation reactor and dehydrogenation cooler, the residual hydrogen in the process gas is completely removed and cooled before entering membrane separator #4.

[0038] After permeation treatment by membrane separator #4, crude helium that meets the requirements for low-temperature adsorption is obtained at the outlet. After being compressed by compressor #4, it enters the crude helium precooler to lower the water dew point. Then, it passes through the low-temperature adsorber to almost completely remove residual CH4, N2, Ar, O2, and Ne impurities, resulting in helium with a purity of not less than 99.999%.

[0039] The non-permeable gas from membrane separators #2 and #3 first enters the natural gas buffer tank, then is pressurized by the natural gas booster before being connected to the pipeline network. The non-permeable gas from membrane separator #4, which contains a large amount of helium, is returned to the inlet of membrane separator #3 for recovery. During the regeneration step of the pre-purification system, the non-permeable gas from membrane separator #1 is heated by the regeneration gas heater and then cooled to room temperature by the regeneration gas cooler after the impurities adsorbed in the adsorbent are blown out from the bottom of the pre-purification system adsorption tower and connected to the natural gas pipeline network.

[0040] Compared with existing technologies, the advantages of this invention are as follows: Based on the current domestic resource situation, this invention is mainly used to solve the problem of helium purification in lean and extra-lean helium natural gas. Through pre-purification, all CO2, water, heavy hydrocarbons, and some organic and inorganic sulfur in the raw gas are removed, which greatly reduces the fast gas components in the membrane separator and is conducive to helium enrichment. The multi-stage membrane separator is used for helium enrichment and is suitable for processing lean and extra-lean helium natural gas. In addition, in this process, catalytic hydrogenation process + dry desulfurization is used to thoroughly remove sulfides, which also plays a very important role in helium purification.

[0041] Specifically, this invention incorporates pre-purification at the process front end, resolving the issues of incomplete CO2 removal, which negatively impacts subsequent membrane separation performance and causes corrosion to downstream systems. The use of compression heat for hydrogenation and dehydrogenation reactions optimizes system heat exchange, addressing the existing "cold-heat syndrome" problem. The invention employs low-temperature adsorption below the liquid nitrogen temperature range for residual purification, significantly improving selectivity and efficiency, and thoroughly removing impurities such as neon and argon that are difficult to adsorb at room temperature, effectively ensuring product purity. A helium pre-cooling unit is installed before purification for cooling and dehydration, along with a molecular sieve dehydration process, effectively meeting product dew point requirements. A TSA purification system removes CO2 to below 20 ppm, and the regeneration medium uses non-permeable gas, eliminating the need for nitrogen and preventing excess impurities from entering the process gas. A compressor at the membrane separator outlet controls the pressure, ensuring membrane operation under reasonable pressure differential and low back pressure, effectively guaranteeing the concentration and recovery rate of the membrane separator with reasonable investment.

[0042] This invention is applicable to the purification of helium in natural gas processing plants of various gas fields, with a helium content of 0.03% to 0.1% and a processing scale of ≥2 million cubic meters per day. Attached Figure Description

[0043] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention;

[0044] Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0045] Figure 3 This is another structural schematic diagram of Embodiment 2 of the present invention. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0047] Example 1:

[0048] like Figure 1 As shown, the apparatus for purifying helium from lean helium natural gas in this embodiment includes:

[0049] The pre-purification system 1 has an inlet for the input of lean helium natural gas, which is used to remove CO2, water, heavy hydrocarbons and some sulfides from the intake gas;

[0050] Membrane separation system A, located downstream of pre-purification system 1, includes at least two sets of membrane separators connected in series, used to perform permeation separation on materials to obtain non-permeable gas to be sent to the natural gas pipeline and permeable gas after helium enrichment;

[0051] Desulfurization unit B is connected to membrane separation system A and is used to remove sulfides from process gas;

[0052] Dehydrogenation unit C, connected to membrane separation system A and located downstream of desulfurization unit B, is used to remove residual hydrogen from the process gas; and

[0053] The low-temperature impurity removal unit D is located downstream of the membrane separation system A and the dehydrogenation unit C, and is used to remove CH4, N2, Ar, O2, Ne and other impurities contained in the process gas.

[0054] Specifically, membrane separation system A is a multi-stage series membrane separator group, which can be configured as needed. In this embodiment, membrane separation system A includes membrane separator 2 (1#), membrane separator 4 (2#), membrane separator 8 (3#), and membrane separator 12 (4#) connected in series. A compressor 3 (1#) for pressurizing the process gas is installed between membrane separator 2 (1#) and membrane separator 4 (2#). A compressor 5 (2#) for pressurizing the process gas is installed between membrane separator 4 (2#) and membrane separator 8 (3#). A compressor 9 (3#) for pressurizing the process gas is installed between membrane separator 8 (3#) and membrane separator 12 (4#). A compressor 13 (4#) for pressurizing the process gas is installed between membrane separator 12 (4#) and the low-temperature impurity removal unit D.

[0055] The dehydrogenation and desulfurization positions can be set according to the H2 content in the feed gas. When the H2 content in the feed gas is high, the desulfurization unit B is located between membrane separator 4 (2#) and membrane separator 8 (3#) and connected to compressor 5 (2#). The dehydrogenation unit C is located between membrane separator 8 (3#) and membrane separator 12 (4#). When the H2 content in the feed gas is low (the hydrogen concentration entering the dehydrogenation reactor should preferably not exceed 2%), the dehydrogenation unit C is located downstream of membrane separator 4 (4#). The desulfurization unit B is located between membrane separator 8 (3#) and membrane separator 12 (4#) and connected to compressor 9 (3#).

[0056] In this embodiment, desulfurization unit B includes an upstream hydrogenation reactor 6 and a downstream desulfurization tower 7. The hydrogenation reactor 6 reacts hydrogen and organic sulfides in natural gas to convert organic sulfur into inorganic sulfur sulfides. The desulfurization tower 7 removes the inorganic sulfur sulfides. The primary inlet of compressor #2 5 is connected to the permeate side of membrane separator #2 4 upstream of it, and its final outlet is connected to the top inlet of desulfurization tower 7. The middle outlet of compressor #2 5 is connected to the top inlet of hydrogenation reactor 6, and the bottom outlet of hydrogenation reactor 6 is connected to the final inlet of compressor #2 5.

[0057] The dehydrogenation unit C in this embodiment includes an upstream catalytic dehydrogenation reactor 10 and a downstream dehydrogenation cooler 11. The catalytic dehydrogenation reactor 10 is used to remove residual hydrogen from the process gas, and the dehydrogenation cooler 11 is used to cool the process gas after the residual hydrogen is removed, in preparation for it to enter the downstream No. 4 membrane separator 12.

[0058] The low-temperature impurity removal unit D in this embodiment includes a crude helium precooler 14 and a low-temperature adsorber 15 connected in series downstream of the membrane separation system A. The crude helium precooler 14 is used to lower the water dew point, and the low-temperature adsorber 15 is used to remove CH4, N2, Ar, O2, Ne and other impurities contained in the process gas.

[0059] In this embodiment, the top of membrane separator 2 is connected to a first pipe 01 that connects its non-permeable gas side to the natural gas pipeline network. The top of membrane separator 4 is connected to a second pipe 02 that connects its non-permeable gas side to the first pipe 01. A natural gas buffer tank 18 and a natural gas booster 19 are installed on the second pipe 02 in series along the gas flow direction. The top of membrane separator 8 is connected to a third pipe 03 that connects its non-permeable gas side to the second pipe 02 upstream of the natural gas buffer tank 18. The top of membrane separator 12 is connected to a fourth pipe 04 that connects its non-permeable gas side to the pipeline downstream of desulfurization unit B and upstream of membrane separator 8.

[0060] The pre-purification system 1 in this embodiment is a TSA purification system. The TSA purification system is a temperature-switching adsorption system, which includes an adsorption unit and a regeneration unit. The adsorption unit is filled with an adsorbent for adsorbing CO2, water, heavy hydrocarbons and some sulfides. The regeneration unit includes a fifth pipe 05, a regeneration gas heater 16, a sixth pipe 06 and a regeneration gas cooler 17. The fifth pipe 05 is connected between the inlet of the first pipe 01 and the bottom inlet of the TSA purification system. The regeneration gas heater 16 is installed on the fifth pipe 05 and is used to heat some of the non-permeable gas in the first pipe 01 before it is fed into the TSA purification system to blow away impurities adsorbed in the adsorbent. The sixth pipe 06 is connected between the top outlet of the TSA purification system and the first pipe 01, and the connection point with the first pipe 01 is located after the fifth pipe 05 and before the natural gas booster 19. The regeneration gas cooler 17 is installed on the sixth pipe 06 and is used to cool the heated non-permeable gas.

[0061] In this embodiment, the desulfurization tower 7 employs a dry desulfurization process, which uses an active desulfurizing agent (such as ZnO) to completely remove inorganic sulfur. The crude helium precooler 14 includes a compression refrigeration and molecular sieve drying structure. The membrane separator's permeate pressure (back pressure) is automatically controlled by the compressor at its outlet, preferably between 0 and 10 kPa. For safety reasons, negative pressure is avoided. The TSA purification system in this embodiment can also be replaced with an MEA (amylamine method) + water washing system. This is to effectively eliminate amylamine entrainment and fundamentally avoid the impact of volatile solvents on membrane separation.

[0062] This embodiment describes a process for purifying helium from helium-poor and extra-helium-poor natural gas, comprising the following steps:

[0063] The sulfur-containing, low-helium natural gas from the gas field processing plant, with a pressure of approximately 3.5 MPa and a helium concentration of 0.05%, first enters the TSA purification unit to remove all CO2, water, heavy hydrocarbons, and some sulfides, and then enters membrane separator #1.

[0064] After permeation treatment by membrane separator 2 (No. 1), non-permeate gas without helium and permeate gas containing helium are obtained. The non-permeate gas is sent directly to the natural gas pipeline network with almost no pressure reduction. The permeate gas is unpressurized, and the volume concentration of helium in the permeate gas is 0.35% to 0.4%. It is pressurized to 2.0 MPa by compressor 3 (No. 1) and sent to membrane separator 4 (No. 2).

[0065] After permeation treatment by membrane separator 4, the helium concentration in the permeate becomes 1.58% to 1.8%. It is then pressurized to 1.0 MPa and heated to 180°C by compressor 5 before entering hydrogenation reactor 6.

[0066] In the hydrogenation reactor 6, a catalyst (such as cobalt-molybdenum) is used to react hydrogen and organic sulfides in natural gas. The organic sulfides are converted into inorganic sulfides and then re-enter the final stage of compressor 5 to be pressurized to 2.0 MPa and cooled to 40°C before entering the desulfurization tower 7.

[0067] In desulfurization tower 7, inorganic sulfides are completely removed to below 0.1 ppm and then enter membrane separator 8 (No. 3).

[0068] After permeation treatment by membrane separator 8 (No. 3), the helium concentration in the permeate gas is increased to 9.0%–10.3%. After being pressurized to 2.0 MPa and heated to 180°C by compressor 9 (No. 3), the gas is sequentially fed into catalytic dehydrogenation reactor 10 and dehydrogenation cooler 11. After passing through catalytic dehydrogenation reactor 10 and dehydrogenation cooler 11, the residual hydrogen in the process gas is completely removed and cooled before entering membrane separator 12 (No. 4).

[0069] After permeation treatment by membrane separator 12, crude helium with a concentration of 53.9% to 61.2% is obtained at the outlet. After being compressed to 2.0 MPa by compressor 13, it enters crude helium precooler 14 to lower the water dew point to 2 to 5°C. Then, it passes through low temperature adsorber 15 to remove the remaining CH4, N2, Ar, O2, and Ne impurities, and helium with a purity of not less than 99.999% is obtained.

[0070] In the above process, the non-permeable gas from membrane separators 4 (2#) and 8 (3#) first enters the natural gas buffer tank 18, then is pressurized to 3.5 MPa by the natural gas booster 19 and connected to the pipeline network. The non-permeable gas from membrane separator 12 (4#) contains a large amount of helium and is returned to the inlet of membrane separator 8 (3#) for recovery. The TSA purification system adopts a temperature-switching adsorption process, including two adsorbers filled with molecular sieves. One adsorbs and the other regenerates, operating sequentially and continuously. During the regeneration step, the non-permeable gas from membrane separator 2 (1#) is heated to 190°C by the regeneration gas heater 16 and then blown out impurities adsorbed in the adsorbent from the bottom of the TSA purification system adsorption tower. After being cooled to room temperature by the regeneration gas cooler 17, it is connected to the natural gas pipeline network. The helium recovery rate of the entire process is over 93%.

[0071] Example 2:

[0072] like Figures 2-3 As shown, the equipment for purifying helium from lean helium natural gas in this embodiment can also adopt such structural modifications. Of course, its operating principle and basic process steps are consistent with those in Embodiment 1.

Claims

1. An apparatus for purifying helium from lean helium natural gas, characterized in that... include: The pre-purification system has an inlet for the input of lean helium natural gas, used to remove CO2, water, heavy hydrocarbons and some sulfides from the intake gas; A membrane separation system, located downstream of the pre-purification system, includes at least two sets of membrane separators connected in series, used to perform permeation separation on the material to obtain non-permeable gas to be supplied to the natural gas pipeline and permeable gas enriched with helium. A desulfurization unit, connected to the membrane separation system, is used to remove sulfides from the process gas; A dehydrogenation unit, connected to the membrane separation system and located downstream of the desulfurization unit, is used to remove residual hydrogen from the process gas. as well as A low-temperature impurity removal unit is located downstream of the membrane separation system and the dehydrogenation unit, and is used to remove at least one of CH4, N2, Ar, O2 and Ne contained in the process gas.

2. The apparatus for purifying helium from lean helium natural gas according to claim 1, characterized in that: The desulfurization unit is connected in series between two adjacent membrane separators and includes an upstream hydrogenation reactor and a downstream desulfurization tower. The hydrogenation reactor is used to react H2 and organic sulfides in natural gas to convert organic sulfides into inorganic sulfides, and the desulfurization tower is used to remove inorganic sulfides.

3. The apparatus for purifying helium from lean helium natural gas according to claim 2, characterized in that: A No. 2 compressor is installed between two adjacent membrane separators. The primary inlet of the No. 2 compressor is connected to the permeate gas side of the membrane separator upstream of it, and the final outlet is connected to the top inlet of the desulfurization tower. The middle outlet of the No. 2 compressor is connected to the top inlet of the hydrogenation reactor, and the bottom outlet of the hydrogenation reactor is connected to the final inlet of the No. 2 compressor.

4. The apparatus for purifying helium from lean helium natural gas according to claim 1, 2, or 3, characterized in that: The dehydrogenation unit is connected in series between two adjacent membrane separators and includes an upstream catalytic dehydrogenation reactor and a downstream dehydrogenation cooler. The catalytic dehydrogenation reactor is used to remove residual hydrogen from the process gas, and the dehydrogenation cooler is used to cool the process gas after the residual hydrogen has been removed, in preparation for it to enter the downstream membrane separator.

5. The apparatus for purifying helium from lean helium natural gas according to claim 1, 2, or 3, characterized in that: The low-temperature impurity removal unit includes a crude helium precooler and a low-temperature adsorber connected in series downstream of the membrane separation system. The crude helium precooler is used to lower the water dew point, and the low-temperature adsorber is used to remove at least one of CH4, N2, Ar, O2 and Ne contained in the process gas.

6. The apparatus for purifying helium from lean helium natural gas according to claim 1, 2, or 3, characterized in that: The membrane separation system includes membrane separators #1, #2, #3, and #4 connected in series. A compressor #1 for pressurizing the process gas is installed between membrane separators #1 and #2. A compressor #2 for pressurizing the process gas is installed between membrane separators #2 and #3. A compressor #3 for pressurizing the process gas is installed between membrane separators #3 and #4. A compressor #4 for pressurizing the process gas is installed between membrane separator #4 and the low-temperature impurity removal unit.

7. The apparatus for purifying helium from lean helium natural gas according to claim 6, characterized in that: The desulfurization unit is located between membrane separator #2 and membrane separator #3 and is connected to compressor #2. The dehydrogenation unit is located between membrane separator #3 and membrane separator #4. When the H2 content in the feed gas is low, the dehydrogenation unit is located downstream of membrane separator #4, and the desulfurization unit is located between membrane separator #3 and membrane separator #4 and is connected to compressor #3.

8. The apparatus for purifying helium from lean helium natural gas according to claim 6, characterized in that: The top of membrane separator #1 is connected to a first pipe that connects its non-permeable gas side to the natural gas pipeline network. The top of membrane separator #2 is connected to a second pipe that connects its non-permeable gas side to the first pipe. A natural gas buffer tank and a natural gas booster are installed on the second pipe in series along the gas flow direction. The top of membrane separator #3 is connected to a third pipe that connects its non-permeable gas side to the second pipe upstream of the natural gas buffer tank. The top of membrane separator #4 is connected to a fourth pipe that connects its non-permeable gas side to the pipeline downstream of the desulfurization unit and upstream of membrane separator #3.

9. The apparatus for purifying helium from lean helium natural gas according to claim 8, characterized in that: The pre-purification system is a TSA purification system, which includes an adsorption unit and a regeneration unit. The adsorption unit is filled with an adsorbent for adsorbing CO2, water, heavy hydrocarbons, and some sulfides. The regeneration unit includes a fifth pipe, a regeneration gas heater, a sixth pipe, and a regeneration gas cooler. The fifth pipe is connected near the inlet of the first pipe to the bottom inlet of the TSA purification system. The regeneration gas heater is located on the fifth pipe and is used to heat part of the non-permeable gas in the first pipe before it is fed into the TSA purification system to purge impurities adsorbed in the adsorbent. The sixth pipe is connected between the top outlet of the TSA purification system and the first pipe, and the connection point with the first pipe is located after the fifth pipe and before the natural gas booster. The regeneration gas cooler is located on the sixth pipe and is used to cool the heated non-permeable gas.

10. A process for purifying helium from lean helium natural gas, characterized in that... Includes the following steps: The lean helium-containing sulfur-containing natural gas from the gas field processing plant first enters the TSA purification unit to remove all CO2, water, heavy hydrocarbons and some sulfides, and then enters the No. 1 membrane separator. After permeation treatment by membrane separator #1, non-permeate gas without helium and permeate gas containing helium are obtained. The non-permeate gas is sent directly to the natural gas pipeline network with almost no pressure reduction. The permeate gas is unpressurized, and the volume concentration of helium in the permeate gas is 0.35% to 0.4%. It is pressurized by compressor #1 and then sent to membrane separator #2. After permeation treatment by membrane separator #2, the helium concentration in the resulting permeate gas becomes 1.58% to 1.8%. It is then pressurized and heated by compressor #2 before entering the hydrogenation reactor. In the hydrogenation reactor, a cobalt-molybdenum catalyst is used to react hydrogen and organic sulfides in natural gas. The organic sulfides are converted into inorganic sulfides, which are then re-enter the final stage of compressor #2 for pressurization and cooling before entering the desulfurization tower. In the desulfurization tower, inorganic sulfides are completely removed to below 0.1 ppm and then enter the No. 3 membrane separator; After permeation treatment by membrane separator #3, the helium concentration in the permeate gas is increased to 9.0%–10.3%. After being pressurized and heated by compressor #3, it is sequentially sent to the catalytic dehydrogenation reactor and dehydrogenation cooler. After passing through the catalytic dehydrogenation reactor and dehydrogenation cooler, the residual hydrogen in the process gas is completely removed and cooled before entering membrane separator #4. After permeation treatment by membrane separator #4, crude helium with a concentration of 53.9% to 61.2% is obtained at the outlet. After being compressed by compressor #4, it enters crude helium precooler to lower the water dew point to 2 to 5°C. Then, it passes through low temperature adsorber to remove the remaining CH4, N2, Ar, O2, and Ne impurities, and obtains helium with a purity of not less than 99.999%. In this process, the non-permeable gas from membrane separators #2 and #3 first enters the natural gas buffer tank, then is pressurized by the natural gas booster before being connected to the pipeline network. The non-permeable gas from membrane separator #4, which contains a large amount of helium, is returned to the inlet of membrane separator #3 for recovery. During the regeneration step of the pre-purification system, the non-permeable gas from membrane separator #1 is heated by the regeneration gas heater and then blown out of the top of the pre-purification system adsorption tower to remove impurities adsorbed in the adsorbent. After being cooled to room temperature by the regeneration gas cooler, it is connected to the natural gas pipeline network.

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