A device and method for BOG cryogenic separation, alloy adsorption and combined helium extraction

Abstract

The invention discloses a device and method for BOG deep cold separation alloy adsorption combined helium extraction, and belongs to the field of deep cold equipment. After deep cold denitrification, BOG gas is obtained to obtain a high-concentration hydrogen-helium mixed gas, which contains a large amount of N2 and a small amount of CH4 impurities, and then a high-concentration hydrogen-helium mixed gas greater than 92%vol is obtained through a membrane separation hydrogen-helium extraction unit; and then further purified through a PSA refining hydrogen-helium unit to obtain an ultra-high concentration hydrogen-helium mixed gas of 99.999%vol. The ultra-high concentration hydrogen-helium mixed gas is then subjected to primary and deep dehydrogenation treatments through an alloy dehydrogenation unit to obtain a pure helium product with an H2 content of less than 1ppmv. Finally, in order to ensure that the impurities in the pure helium product meet the requirements of the high-purity helium standard and avoid the influence of the uncertainty of the Ne content, a high-purity helium product gas that meets the standard is obtained after passing through a TSA purification unit. Finally, the high-purity helium product gas is directly filled into a gas cylinder, a container or a tube bundle vehicle through a high-purity helium filling unit. The high-purity helium product gas obtained by the device can meet the relevant standards.

Description

Technical Field

[0001] The invention belongs to the field of cryogenic equipment, and in particular relates to a device and a method for BOG cryogenic separation alloy adsorption combined helium extraction. Background Art

[0002] LNG equipment is used to produce liquefied natural gas (LNG). Liquefied natural gas (LNG) is a cryogenic liquid mixture made by pre-treating natural gas raw materials, removing impurities, and then cooling them at -162°C. During the low-temperature storage process, the natural gas in the LNG storage tank will inevitably evaporate naturally to produce flash gas BOG (Boil-Off Gas). These BOG gases mainly contain methane, nitrogen and other hydrocarbon gases.

[0003] The generation of BOG is a problem that LNG receiving stations and storage facilities must deal with because it affects the pressure stability of storage tanks, and untreated BOG emissions may cause energy waste and environmental problems. In the prior art, LNG plants usually use a series of methods to treat BOG, such as recondensation, pressurized external transmission, compression to CNG (compressed natural gas) or flare combustion. Therefore, it is urgent to develop a method for extracting helium from BOG gas using cryogenic separation and alloy adsorption. Summary of the invention

[0004] The object of the present invention is to solve the deficiencies in the prior art and to provide a device and method for BOG cryogenic separation and alloy adsorption combined helium extraction.

[0005] The specific technical solutions adopted by the present invention are as follows:

[0006] In a first aspect, the present invention provides a BOG cryogenic separation alloy adsorption combined helium extraction device, comprising a denitrification tower cold box, a membrane separation hydrogen helium extraction unit, a PSA refined hydrogen helium unit, an alloy dehydrogenation unit, a TSA purification unit and a high-purity helium filling unit;

[0007] The inlet of the denitrification tower cold box receives low-temperature BOG gas from the LNG storage tank, and the denitrification tower cold box is connected to the BOG compressor through a pipeline; the low-temperature BOG gas is denitrified after heat exchange and reheating with the pressurized BOG gas from the BOG compressor in the denitrification tower cold box to obtain a hydrogen-helium mixed gas; the outlet of the denitrification tower cold box is connected to the inlet of the membrane separation hydrogen-helium extraction unit through a pipeline, and the hydrogen-helium mixed gas is purified in the membrane separation hydrogen-helium extraction unit to obtain a high-concentration hydrogen-helium mixed gas;

[0008] The outlet of the membrane separation hydrogen and helium extraction unit is connected to the PSA refined hydrogen and helium unit through a post-membrane booster, and the high-concentration hydrogen and helium mixed gas is further purified in the PSA refined hydrogen and helium unit to obtain an ultra-high concentration hydrogen and helium mixed gas and a PSA desorption regeneration gas; the PSA refined hydrogen and helium unit is provided with a PSA desorption regeneration gas outlet and an ultra-high concentration hydrogen and helium mixed gas outlet; the PSA desorption regeneration gas outlet of the PSA refined hydrogen and helium unit is connected to a BOG compressor through a pipeline for recycling;

[0009] The ultra-high concentration hydrogen-helium mixed gas outlet of the PSA refined hydrogen-helium unit is connected to the alloy dehydrogenation unit through a pipeline, and the ultra-high concentration hydrogen-helium mixed gas is separated in the alloy dehydrogenation unit to obtain by-product hydrogen and pure helium product gas with a hydrogen content of less than 1ppmv; the alloy dehydrogenation unit is provided with a hydrogen outlet and a pure helium product gas outlet; the hydrogen outlet of the alloy dehydrogenation unit is connected to an external fuel gas system through a pipeline;

[0010] The pure helium product gas outlet of the alloy dehydrogenation unit is connected to the TSA purification unit through a pipeline, and the helium in the product gas is purified in the TSA purification unit to obtain high-purity helium and TSA desorption regeneration gas; the TSA purification unit is provided with a helium outlet and a TSA desorption regeneration gas outlet, and the TSA desorption regeneration gas outlet of the TSA purification unit is connected to the BOG compressor through a pipeline for recycling; the helium outlet of the TSA purification unit is connected to the high-purity helium filling unit through a pipeline.

[0011] Preferably, the high-concentration hydrogen-helium mixed gas obtained by the membrane separation hydrogen-helium extraction unit has a gas volume percentage greater than 92% vol and a pressure of 0.4 MPa.

[0012] Preferably, the gas volume percentage of the ultra-high concentration hydrogen-helium mixed gas obtained through the PSA refining hydrogen-helium unit reaches 99.999% vol.

[0013] Preferably, the BOG compressor pressurizes the BOG gas to 1.8-2.2 MPa; and the post-membrane booster pressurizes the high-concentration hydrogen-helium mixed gas to 2.0 MPa.

[0014] Preferably, the membrane separation hydrogen and helium extraction unit comprises a primary membrane separation process and a secondary membrane separation process; an inter-membrane booster for increasing the primary membrane permeate gas pressure is provided between the primary membrane separation process and the secondary membrane separation process; and a helium recovery cold box for concentrating and recovering helium in the primary membrane non-permeate gas is provided after the primary membrane separation process.

[0015] Furthermore, the inter-membrane booster pressurizes the primary membrane permeate gas to 2.2 MPa.

[0016] Preferably, a pure helium booster is provided on the pipeline between the alloy dehydrogenation unit and the TSA purification unit.

[0017] Preferably, the alloy dehydrogenation unit consists of a two-stage separation system, each of which includes three groups of beds; one group is responsible for adsorbing hydrogen, another group is regenerated to release hydrogen after adsorption saturation, and the third group is in standby mode; the regeneration process of the adsorption saturated bed is completed through a vacuum process, and the adsorption capacity is restored after desorption.

[0018] Preferably, the TSA purification unit adopts a two-tower low-temperature adsorption process, one low-temperature adsorber performs adsorption purification work, and the other low-temperature adsorber performs desorption and regeneration, and the two low-temperature adsorbers alternately adsorb and regenerate to achieve continuous purification of helium.

[0019] In a second aspect, the present invention provides a method for BOG cryogenic separation and alloy adsorption combined helium extraction using the device described in the first aspect, which is as follows:

[0020] S1: Low-temperature BOG from the LNG storage tank enters the denitrification tower cold box and exchanges heat with the pressurized BOG for reheating; the BOG gas that meets the denitrification requirements is denitrified in the denitrification tower cold box to obtain a high-concentration hydrogen-helium mixed gas containing a large amount of nitrogen impurities and a small amount of methane impurities, as well as LNG; the high-concentration hydrogen-helium mixed gas is separated by a membrane through a pipeline to the hydrogen-helium extraction unit, and the LNG is sent to the LNG storage tank through a pipeline;

[0021] S2: the hydrogen-helium mixed gas obtained in step S1 enters the membrane separation hydrogen-helium extraction unit through a pipeline; the membrane separation hydrogen-helium extraction unit includes a primary membrane separation process and a secondary membrane separation process; the hydrogen-helium mixed gas passes through the primary membrane separation process to obtain primary membrane permeate gas and primary membrane non-permeate gas, wherein the primary membrane permeate gas is pressurized by an inter-membrane booster and then enters the secondary membrane separation process for further separation to obtain a high-concentration hydrogen-helium mixed gas and a secondary membrane non-permeate gas; wherein the gas volume percentage of the high-concentration hydrogen-helium mixed gas is greater than 92% vol;

[0022] The non-permeate gas from the primary membrane enters the helium recovery cold box, which recovers the rich nitrogen gas with high helium concentration that has recovery value. The rich nitrogen gas is refluxed to the BOG compressor for recycling; the non-permeate gas from the secondary membrane is refluxed to the entrance of the primary membrane separation process for recycling;

[0023] S3: The high-concentration hydrogen-helium mixed gas obtained in step S2 is pressurized to 2.0 MPa by a post-membrane booster, and then enters a PSA refined hydrogen-helium unit for purification to obtain an ultra-high-concentration hydrogen-helium mixed gas and a PSA desorption regeneration gas; wherein the gas volume percentage of the ultra-high-concentration hydrogen-helium mixed gas reaches 99.999% vol; and the PSA desorption regeneration gas is refluxed to the BOG compressor for recycling;

[0024] S4: The ultra-high concentration hydrogen-helium mixed gas obtained in step S3 enters the alloy dehydrogenation unit through a pipeline for separation to obtain by-product hydrogen and pure helium product gas with a hydrogen content of less than 1 ppmv; hydrogen is used as a clean energy source and connected to an external fuel gas system through a pipeline;

[0025] S5: The product gas obtained in step S4 is pressurized by a pure helium booster and enters a TSA purification unit; the TSA purification unit uses a two-tower low-temperature adsorption process to deeply remove N in the product gas. 2 , Ar, CH 4 , H 2 , Ne impurities to obtain high-purity helium and TSA desorption regeneration gas; TSA desorption regeneration gas is refluxed to the BOG compressor for recycling, and is intermittently vented to avoid the circulation and accumulation of impurities; high-purity helium is directly filled into gas cylinders, containers or tube bundle trucks through the high-purity helium filling unit.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The device provided by the present invention adopts a combined process of crude denitrification by cryogenic separation and fine denitrification by membrane separation to effectively remove nitrogen and a small amount of methane from BOG gas, thereby increasing the concentration of helium and hydrogen. This innovative combination not only improves the operational flexibility of the device, but also enhances the stability of the entire system.

[0028] (2) The alloy dehydrogenation unit used in the device provided by the present invention can adapt to various proportions of hydrogen / helium mixed gases, effectively separate hydrogen and helium, and does not require combustion throughout the process, which greatly improves the safety of operation. In addition, since no external gas is introduced into the entire process, even changes or fluctuations in the upstream gas components will not affect the stable operation of the process. The product gas of the alloy dehydrogenation unit is widely used ultra-pure hydrogen, which not only saves energy but also reduces production costs.

[0029] (3) The device provided by the present invention is provided with a helium recovery cold box to effectively recover the non-permeable gas of the primary membrane in the membrane separation hydrogen and helium extraction unit, so that the amount of helium recovered in this process accounts for 3.6% of the total amount of product helium. In addition, the desorption regeneration gas in the PSA refining hydrogen and helium unit and the TSA purification unit is also sent back to the compressor of the BOG denitrification process for recovery, further improving the helium recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A flow chart of the device for BOG cryogenic separation and alloy adsorption combined with helium extraction provided in this embodiment;

[0031] In the figure: denitrification tower cold box 1, membrane separation hydrogen and helium extraction unit 2, PSA refined hydrogen and helium unit 3, alloy dehydrogenation unit 4, TSA purification unit 5, high-purity helium filling unit 6, BOG compressor 7, inter-membrane booster 8, post-membrane booster 9, pure helium booster 10, helium recovery cold box 11. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation mode of the present invention is described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0033] During the low-temperature storage process, the natural gas in the LNG tank will inevitably evaporate naturally to produce flash gas BOG (Boil-Off Gas). These BOG gases mainly contain methane, nitrogen, hydrogen and other impurity gases.

[0034] like Figure 1 As shown, in a preferred embodiment of the present invention, a device for BOG deep cold separation alloy adsorption combined helium extraction is provided, including a denitrification tower cold box 1, a membrane separation hydrogen helium extraction unit 2, a PSA hydrogen and helium refining unit 3, an alloy dehydrogenation unit 4, a TSA purification unit 5 and a high-purity helium filling unit 6.

[0035] In the device provided by the present invention, the inlet of the denitrification tower cold box 1 receives low-temperature BOG gas from the LNG storage tank. The denitrification tower cold box 1 is connected to the BOG compressor 7 through a pipeline; the low-temperature BOG gas is heat-exchanged and reheated with the pressurized BOG gas from the BOG compressor 7 in the denitrification tower cold box 1, and the reheated BOG gas is discharged from the denitrification tower cold box 1 to the BOG compressor 7 to be pressurized to 1.8-2.2MPa, and then returns to the denitrification tower cold box 1, and denitrifies after heat exchange with the low-temperature BOG gas to obtain a higher concentration of hydrogen-helium mixed gas and LNG. The higher concentration hydrogen-helium mixed gas is separated by a membrane and sent to the hydrogen-helium extraction unit 2, and the LNG is sent to the LNG storage tank through a pipeline.

[0036] In the device provided by the present invention, the outlet of the denitrification tower cold box 1 is connected to the inlet of the membrane separation hydrogen and helium extraction unit 2 through a pipeline. The high-concentration hydrogen and helium mixed gas is purified in the membrane separation hydrogen and helium extraction unit 2.

[0037] In this embodiment, the membrane separation hydrogen-helium extraction unit 2 includes a primary membrane separation process and a secondary membrane separation process. The high-concentration hydrogen-helium mixed gas obtained after denitrification is filtered out of a large amount of methane and nitrogen in the BOG gas through the primary membrane separation process and the secondary membrane separation process, and the hydrogen-helium mixed gas is concentrated by about 20 times to obtain a high-concentration hydrogen-helium mixed gas with a gas volume percentage greater than 92% vol and a pressure of 0.4 MPa, which is used as the feed gas for the next-stage PSA refining hydrogen-helium unit 3.

[0038] Due to the working principle of membrane separation, the pressure of the membrane permeate gas is generally lower than 0.5MPa. In order to ensure the separation effect of the secondary membrane, in this embodiment, an inter-membrane booster 8 is provided between the primary membrane separation process and the secondary membrane separation process to increase the pressure of the primary membrane permeate gas, and the primary membrane permeate gas is pressurized to 2.2MPa.

[0039] In the membrane separation hydrogen and helium extraction unit 2, in order to improve the recovery rate of helium, a helium recovery cold box 11 for concentrating and recovering helium in the primary membrane non-permeate gas is provided after the primary membrane separation process. The helium recovery cold box 11 recovers the rich nitrogen gas containing a high concentration of helium with recovery value, and the rich nitrogen gas is refluxed to the BOG compressor 7 for recycling. In this embodiment, the helium recovery cold box 11 recovers the primary membrane non-permeate gas with a helium content of up to 1600ppmv. Those skilled in the art can recover the required helium according to the actual working conditions.

[0040] In the membrane separation hydrogen and helium extraction unit 2, the secondary membrane non-permeate gas obtained in the secondary membrane separation process is refluxed to the inlet of the primary membrane separation process through a pipeline for recovery, which greatly improves the helium recovery rate of the entire device. In this embodiment, the secondary membrane non-permeate gas with a helium volume percentage of up to 20% vol is refluxed to the inlet of the primary membrane separation process. Those skilled in the art can recover the required helium according to actual working conditions.

[0041] In the device provided by the present invention, the outlet of the membrane separation hydrogen and helium extraction unit 2 is connected to the PSA refining hydrogen and helium unit 3 through a pipeline, and the high-concentration hydrogen and helium mixed gas with a gas volume percentage greater than 92% vol is further purified in the PSA refining hydrogen and helium unit 3 to obtain an ultra-high concentration hydrogen and helium mixed gas and PSA desorption regeneration gas. Among them, the gas volume percentage of the ultra-high concentration hydrogen and helium mixed gas reaches 99.999% vol.

[0042] It should be noted that the PSA pressure swing adsorption refining hydrogen and helium unit is a device for purifying hydrogen and helium, which uses pressure swing adsorption technology to separate and purify gases. Different gases are separated because of differences in adsorption capacity. In this unit, a high-concentration hydrogen and helium mixture passes through an adsorbent bed. Under the sequential selective adsorption of a variety of adsorbents, impurities such as nitrogen and methane are adsorbed. Hydrogen and helium, due to their smaller molecular size and lower adsorption affinity, usually pass through the adsorbent bed without being adsorbed, thereby achieving separation from impurities nitrogen and methane. This process usually includes multiple steps, such as adsorption, equalizing pressure reduction, inversion, equalizing pressure increase and pressurization. Through the cyclic operation of these steps, high-purity hydrogen and helium can be continuously extracted from the mixed gas. Those skilled in the art can make specific settings for the PSA refining hydrogen and helium unit according to actual needs.

[0043] Due to the principle of the membrane separation system, the permeate gas pressure of the high-concentration hydrogen-helium mixture is generally lower than 0.5 MPa. In order to ensure the normal, stable and efficient operation of the PSA refined hydrogen-helium unit 3, in this embodiment, a post-membrane booster 9 is provided between the membrane separation hydrogen-helium extraction unit 2 and the PSA refined hydrogen-helium unit 3 to pressurize the high-concentration hydrogen-helium mixture to 2 MPa.

[0044] In the device provided by the present invention, the PSA refined hydrogen and helium unit 3 is provided with a PSA desorption regeneration gas outlet and an ultra-high concentration hydrogen and helium mixed gas outlet; the PSA desorption regeneration gas outlet of the PSA refined hydrogen and helium unit 3 is connected to the BOG compressor 7 through a pipeline for recycling; the ultra-high concentration hydrogen and helium mixed gas outlet of the PSA refined hydrogen and helium unit 3 is connected to the alloy dehydrogenation unit 4 through a pipeline, and the ultra-high concentration hydrogen and helium mixed gas is separated in the alloy dehydrogenation unit 4 to obtain by-product hydrogen and pure helium product gas with a hydrogen content of less than 1ppmv.

[0045] In this embodiment, the alloy dehydrogenation unit 4 is composed of a two-stage separation system, and each stage of the separation system includes three groups of beds; one group is responsible for adsorbing hydrogen, another group is regenerated and releases hydrogen after adsorption saturation, and the third group is in a standby state; the regeneration process of the adsorption saturated bed is completed by a vacuum pumping process, and the adsorption capacity is restored after desorption.

[0046] In the device provided by the present invention, the alloy dehydrogenation unit 4 is provided with a hydrogen outlet and a product gas outlet; the hydrogen outlet of the alloy dehydrogenation unit 4 is connected to the external fuel gas system through a pipeline. The product gas outlet of the alloy dehydrogenation unit 4 is connected to the TSA purification unit 5 through a pipeline. A pure helium booster 10 is provided on the pipeline between the alloy dehydrogenation unit 4 and the TSA purification unit 5. The helium in the product gas is purified in the TSA purification unit 5 to obtain high-purity helium and TSA desorption regeneration gas.

[0047] It should be noted that the TSA temperature swing adsorption purification unit is a gas purification technology that uses the property that the adsorption capacity of the adsorbent for different gas components changes with temperature to achieve gas separation and purification. Those skilled in the art can make specific settings for the TSA purification unit according to actual needs.

[0048] In this embodiment, the TSA purification unit 5 adopts a two-tower low-temperature adsorption process, one low-temperature adsorber performs adsorption purification work, and the other low-temperature adsorber performs desorption regeneration. The two low-temperature adsorbers alternately adsorb and regenerate to deeply remove N in the gas. 2 , Ar, CH 4 , H 2 , Ne and other impurities to achieve continuous purification of helium.

[0049] In the device provided by the present invention, the TSA purification unit 5 is provided with a helium outlet and a TSA desorption regeneration gas outlet. The TSA desorption regeneration gas generated in the TSA purification unit 5 contains high-concentration helium. In order to improve the recovery rate of helium, the TSA desorption regeneration gas outlet of the TSA purification unit 5 is connected to the BOG compressor 7 through a pipeline for recycling; the helium outlet of the TSA purification unit 5 is connected to the high-purity helium filling unit 6 through a pipeline. The high-purity helium that meets the standards obtained by the TSA purification unit 5 is close to room temperature, and the high-purity helium is directly filled into gas cylinders, containers or tube bundle trucks through the high-purity helium filling unit 6 for subsequent applications.

[0050] The method for carrying out BOG cryogenic separation and alloy adsorption combined helium extraction using the device provided in this embodiment is as follows:

[0051] S1: Low-temperature BOG from the LNG storage tank enters the denitrification tower cold box 1 and exchanges heat with the pressurized BOG for reheating; the BOG gas that meets the denitrification requirements is denitrified in the denitrification tower cold box 1 to obtain a large amount of impurities N 2 And a small amount of impurities CH 4 A high-concentration hydrogen-helium mixed gas, and LNG; wherein the high-concentration hydrogen-helium mixed gas is sent to the membrane separation hydrogen-helium extraction unit 2 through a pipeline, and the LNG is sent to the LNG storage tank through a pipeline;

[0052] S2: the hydrogen-helium mixed gas obtained in step S1 enters the membrane separation hydrogen-helium extraction unit 2 through a pipeline; the membrane separation hydrogen-helium extraction unit 2 includes a primary membrane separation process and a secondary membrane separation process; the hydrogen-helium mixed gas passes through the primary membrane separation process to obtain primary membrane permeate gas and primary membrane non-permeate gas, wherein the primary membrane permeate gas is pressurized by the inter-membrane booster 8 and then enters the secondary membrane separation process for further separation to obtain a high-concentration hydrogen-helium mixed gas and a secondary membrane non-permeate gas; wherein the gas volume percentage of the high-concentration hydrogen-helium mixed gas is greater than 92% vol;

[0053] The non-permeated gas from the primary membrane enters the helium recovery cold box 11, which recovers the rich nitrogen gas with high helium concentration and has recovery value. The rich nitrogen gas is refluxed to the BOG compressor 7 for recycling; the non-permeated gas from the secondary membrane is refluxed to the inlet of the primary membrane separation process for recycling;

[0054] S3: The high-concentration hydrogen-helium mixed gas obtained in step S2 is pressurized to 2.0 MPa by the post-membrane booster 9, and then enters the PSA refined hydrogen-helium unit 3 for purification to obtain an ultra-high-concentration hydrogen-helium mixed gas and a PSA desorption regeneration gas; wherein the gas volume percentage of the ultra-high-concentration hydrogen-helium mixed gas reaches 99.999% vol; the PSA desorption regeneration gas is refluxed to the BOG compressor 7 for recycling;

[0055] S4: The ultra-high concentration hydrogen-helium mixed gas obtained in step S3 enters the alloy dehydrogenation unit 4 through a pipeline for separation to obtain by-product hydrogen gas and pure helium product gas with a hydrogen content of less than 1 ppmv; hydrogen is used as a clean energy source and connected to an external fuel gas system through a pipeline;

[0056] S5: The product gas obtained in step S4 is pressurized by the pure helium booster 10 and enters the TSA purification unit 5; the TSA purification unit 5 uses a two-tower low-temperature adsorption process to deeply remove N in the product gas. 2 , Ar, CH 4 , H 2 , Ne impurities, and high-purity helium and TSA desorption regeneration gas are obtained; the TSA desorption regeneration gas is refluxed to the BOG compressor 7 for recycling, and is intermittently vented to avoid the circulation and accumulation of impurities; the high-purity helium is directly filled into gas cylinders, containers or tube bundle trucks through the high-purity helium filling unit 6.

[0057] The impurity content in the high-purity helium finally obtained meets the requirements for high-purity helium in the national standard "Pure Helium, High-Purity Helium and Ultra-Pure Helium" GB / T4844-2011, as follows:

[0058]

[0059] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A device for BOG cryogenic separation and alloy adsorption combined with helium extraction, characterized in that: It comprises a denitrification tower cold box (1), a membrane separation hydrogen and helium extraction unit (2), a PSA hydrogen and helium refining unit (3), an alloy dehydrogenation unit (4), a TSA purification unit (5) and a high-purity helium filling unit (6); The inlet of the denitrification tower cold box (1) receives low-temperature BOG gas from the LNG storage tank, and the denitrification tower cold box (1) is connected to the BOG compressor (7) via a pipeline; the low-temperature BOG gas is denitrified after heat exchange and temperature recovery with the pressurized BOG gas from the BOG compressor (7) in the denitrification tower cold box (1), thereby obtaining a hydrogen-helium mixed gas; the outlet of the denitrification tower cold box (1) is connected to the inlet of a membrane separation hydrogen-helium extraction unit (2) via a pipeline, and the hydrogen-helium mixed gas is purified in the membrane separation hydrogen-helium extraction unit (2), thereby obtaining a high-concentration hydrogen-helium mixed gas; The outlet of the membrane separation hydrogen and helium extraction unit (2) is connected to the PSA hydrogen and helium refining unit (3) via a post-membrane booster (9); the high-concentration hydrogen and helium mixed gas is further purified in the PSA hydrogen and helium refining unit (3) to obtain an ultra-high-concentration hydrogen and helium mixed gas and a PSA desorption regeneration gas; the PSA hydrogen and helium refining unit (3) is provided with a PSA desorption regeneration gas outlet and an ultra-high-concentration hydrogen and helium mixed gas outlet; the PSA desorption regeneration gas outlet of the PSA hydrogen and helium refining unit (3) is connected to a BOG compressor (7) via a pipeline for recycling; The ultra-high concentration hydrogen-helium mixed gas outlet of the PSA refined hydrogen-helium unit (3) is connected to the alloy dehydrogenation unit (4) through a pipeline, and the ultra-high concentration hydrogen-helium mixed gas is separated in the alloy dehydrogenation unit (4) to obtain by-product hydrogen and pure helium product gas with a hydrogen content of less than 1 ppmv; the alloy dehydrogenation unit (4) is provided with a hydrogen outlet and a pure helium product gas outlet; the hydrogen outlet of the alloy dehydrogenation unit (4) is connected to an external fuel gas system through a pipeline; the alloy dehydrogenation unit (4) is composed of a two-stage separation system, each stage of the separation system includes three groups of beds; one group is responsible for adsorbing hydrogen, another group is regenerated to release hydrogen after adsorption saturation, and the third group is in a standby state; the regeneration process of the adsorption saturated bed is completed by a vacuum pumping process, and the adsorption capacity is restored after desorption; The pure helium product gas outlet of the alloy dehydrogenation unit (4) is connected to the TSA purification unit (5) via a pipeline, and the helium in the product gas is purified in the TSA purification unit (5) to obtain high-purity helium and TSA desorption regeneration gas; the TSA purification unit (5) is provided with a helium outlet and a TSA desorption regeneration gas outlet, and the TSA desorption regeneration gas outlet of the TSA purification unit (5) is connected to the BOG compressor (7) via a pipeline for recycling; the helium outlet of the TSA purification unit (5) is connected to the high-purity helium filling unit (6) via a pipeline.

2. The device for BOG cryogenic separation and alloy adsorption combined with helium extraction according to claim 1, characterized in that: The high-concentration hydrogen-helium mixed gas obtained by the membrane separation hydrogen-helium extraction unit (2) has a gas volume percentage greater than 92% vol and a pressure of 0.4 MPa.

3. The device for BOG cryogenic separation and alloy adsorption combined with helium extraction according to claim 1, characterized in that: The gas volume percentage of the ultra-high concentration hydrogen-helium mixed gas obtained by the PSA refining hydrogen-helium unit (3) reaches 99.999% vol.

4. The device for BOG cryogenic separation and alloy adsorption combined with helium extraction according to claim 1, characterized in that: The BOG compressor (7) pressurizes the BOG gas to 1.8-2.2 MPa; and the post-membrane booster (9) pressurizes the high-concentration hydrogen-helium mixed gas to 2.0 MPa.

5. The device for BOG cryogenic separation and alloy adsorption combined with helium extraction according to claim 1, characterized in that: The membrane separation hydrogen and helium extraction unit (2) comprises a primary membrane separation process and a secondary membrane separation process; an inter-membrane booster (8) for increasing the pressure of the primary membrane permeate gas is provided between the primary membrane separation process and the secondary membrane separation process; and a helium recovery cold box (11) for concentrating and recovering helium in the primary membrane non-permeate gas is provided after the primary membrane separation process.

6. The device for BOG cryogenic separation and alloy adsorption combined helium extraction according to claim 5, characterized in that: The inter-membrane booster (8) boosts the pressure of the primary membrane permeate gas to 2.2 MPa.

7. The device for BOG cryogenic separation and alloy adsorption combined with helium extraction according to claim 1, characterized in that: A pure helium booster (10) is provided on the pipeline between the alloy dehydrogenation unit (4) and the TSA purification unit (5).

8. The device for BOG cryogenic separation and alloy adsorption combined with helium extraction according to claim 1, characterized in that: The TSA purification unit (5) adopts a two-tower low-temperature adsorption process, wherein one low-temperature adsorber performs adsorption purification work and the other low-temperature adsorber performs desorption regeneration. The two low-temperature adsorbers alternately adsorb and regenerate to achieve continuous purification of helium.

9. A method for BOG cryogenic separation and alloy adsorption combined helium extraction using the device described in any one of claims 1 to 8, characterized in that: The details are as follows: S1: Low-temperature BOG from the LNG storage tank enters the denitrification tower cold box (1) and is heat-exchanged with the pressurized BOG to restore temperature; the BOG gas that meets the denitrification requirements is denitrified in the denitrification tower cold box (1) to obtain a high-concentration hydrogen-helium mixed gas containing a large amount of nitrogen impurities and a small amount of methane impurities, as well as LNG; the high-concentration hydrogen-helium mixed gas is separated by a membrane through a pipeline to a hydrogen-helium extraction unit (2), and the LNG is sent to the LNG storage tank through a pipeline; S2: the hydrogen-helium mixed gas obtained in step S1 enters the membrane separation hydrogen-helium extraction unit (2) through a pipeline; the membrane separation hydrogen-helium extraction unit (2) comprises a primary membrane separation process and a secondary membrane separation process; the hydrogen-helium mixed gas passes through the primary membrane separation process to obtain primary membrane permeate gas and primary membrane non-permeate gas, wherein the primary membrane permeate gas is pressurized by an inter-membrane booster (8) and then enters the secondary membrane separation process for further separation to obtain a high-concentration hydrogen-helium mixed gas and a secondary membrane non-permeate gas; wherein the gas volume percentage of the high-concentration hydrogen-helium mixed gas is greater than 92%vol; The non-permeate gas of the primary membrane enters the helium recovery cold box (11), and the helium recovery cold box (11) recovers the rich nitrogen gas containing a relatively high concentration of helium with recovery value, and the rich nitrogen gas is refluxed to the BOG compressor (7) for recycling; the non-permeate gas of the secondary membrane is refluxed to the inlet of the primary membrane separation process for recycling; S3: The high-concentration hydrogen-helium mixed gas obtained in step S2 is pressurized to 2.0 MPa by a post-membrane booster (9), and then enters a PSA refining hydrogen-helium unit (3) for purification to obtain an ultra-high-concentration hydrogen-helium mixed gas and a PSA desorption regeneration gas; wherein the gas volume percentage of the ultra-high-concentration hydrogen-helium mixed gas reaches 99.999%vol; the PSA desorption regeneration gas is refluxed to the BOG compressor (7) for recycling; S4: The ultra-high concentration hydrogen-helium mixed gas obtained in step S3 enters the alloy dehydrogenation unit (4) through a pipeline for separation to obtain by-product hydrogen gas and pure helium product gas with a hydrogen content of less than 1 ppmv; the hydrogen is used as a clean energy source and connected to an external fuel gas system through a pipeline; S5: The product gas obtained in step S4 is pressurized by a pure helium booster (10) and then enters a TSA purification unit (5); the TSA purification unit (5) uses a two-tower low-temperature adsorption process to deeply remove N2, Ar, CH4, H2, and Ne impurities in the product gas to obtain high-purity helium and TSA desorption regeneration gas; the TSA desorption regeneration gas is refluxed to the BOG compressor (7) for recycling and is intermittently vented to avoid the circulation and accumulation of impurities; the high-purity helium is directly filled into a gas cylinder, a container or a tube bundle truck through a high-purity helium filling unit (6).

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