A BOG helium extraction system and helium extraction method

Abstract

The present invention discloses a BOG helium extraction system and a helium extraction method. The BOG helium extraction system comprises a cryogenic distillation unit and a palladium membrane separation and dehydrogenation unit. The cryogenic distillation unit is used to separate a first-stage crude helium gas including a small amount of nitrogen, hydrogen and a small amount of oxygen from BOG by a cryogenic method. The palladium membrane separation and dehydrogenation unit is used to remove the hydrogen in the first-stage crude helium gas by a palladium membrane separation method to obtain a second-stage crude helium gas. The present invention separates and removes hydrogen from BOG by a palladium membrane separation and dehydrogenation unit, simplifies the dehydrogenation process, reduces the control requirements in the dehydrogenation process, eliminates safety hazards, and can recycle and reuse hydrogen to avoid waste of resources.

Description

Technical Field

[0001] The invention relates to a BOG helium extraction system and a helium extraction method, belonging to the technical field of chemical industry. Background Art

[0002] At present, there are many feasible solutions for extracting helium from BOG at home and abroad, but when dealing with the separation of helium and hydrogen, the liquefaction method and multi-stage catalytic oxidation method are mainly used. Although the liquefaction method can achieve better separation of helium and hydrogen, since the liquefaction points of helium and hydrogen are very close, it is nothing more than a complete separation of helium and hydrogen, and the energy consumption is very high. At present, the most common method for treating hydrogen in helium is to add excess oxygen, oxidize hydrogen into water through a multi-stage catalytic oxidation method, and then remove water and excess oxygen respectively, and finally purify hydrogen from helium. However, the above scheme has a complicated process and high control requirements. Once the temperature is not well controlled, there will be safety hazards. Moreover, the catalytic combustion of hydrogen causes a great waste of hydrogen resources. Summary of the invention

[0003] The purpose of the present invention is to provide a BOG helium extraction system and a helium extraction method, which separates and removes hydrogen in BOG through a palladium membrane separation and dehydrogenation unit, simplifies the dehydrogenation process, reduces the control requirements in the dehydrogenation process, eliminates safety hazards, and can recycle and reuse hydrogen to avoid waste of resources.

[0004] The BOG helium extraction system provided by the present invention comprises a cryogenic distillation unit and a palladium membrane separation and dehydrogenation unit;

[0005] The cryogenic distillation unit is used to separate the first-stage crude helium from BOG by cryogenic method, wherein the first-stage crude helium contains a small amount of nitrogen, hydrogen and a small amount of oxygen;

[0006] The palladium membrane separation and dehydrogenation unit is used to remove hydrogen from the first-stage crude helium gas by palladium membrane separation to obtain the second-stage crude helium gas;

[0007] The palladium membrane separation and dehydrogenation unit comprises a palladium membrane separator and a palladium membrane separation air inlet pipeline and a palladium membrane separation exhaust pipeline connected thereto;

[0008] The palladium membrane separation air intake pipeline includes a nitrogen / crude helium air intake pipeline;

[0009] The palladium membrane separation exhaust pipeline includes a nitrogen exhaust pipeline, a hydrogen exhaust pipeline and a second-stage crude helium exhaust pipeline.

[0010] In the above-mentioned BOG helium extraction system, the nitrogen / crude helium inlet pipeline is provided with a flow control valve, a flow meter, a heat exchanger I and an explosion-proof heater in sequence;

[0011] The nitrogen exhaust pipeline is provided with a heat exchanger II and a back pressure valve;

[0012] The hydrogen exhaust pipeline is provided with a heat exchanger III, a hydrogen buffer tank and a vacuum compressor.

[0013] In the above-mentioned BOG helium extraction system, the cryogenic distillation unit includes a cryogenic distillation heat exchanger, a cryogenic distillation separation tank and a distillation tower;

[0014] The BOG gas flows through the cryogenic distillation heat exchanger and then enters the cryogenic distillation separation tank. The first-stage crude helium is obtained at the top of the cryogenic distillation separation tank. The first-stage crude helium flows through the cryogenic distillation heat exchanger and then enters the first-stage crude helium exhaust pipeline. The first-stage crude helium exhaust pipeline is connected to the nitrogen / crude helium inlet pipeline. The bottom of the cryogenic distillation separation tank is connected to the distillation tower. Nitrogen and methane are obtained at the top and bottom of the distillation tower respectively. The gases flow through the cryogenic distillation heat exchanger and then enter the cryogenic distillation nitrogen exhaust pipeline and the methane exhaust pipeline respectively.

[0015] In the above-mentioned BOG helium extraction system, the BOG helium extraction system further comprises a low-temperature crude extraction unit and a low-temperature adsorption fine extraction unit;

[0016] The low-temperature crude extraction unit is used to remove nitrogen and oxygen from the second-stage crude helium gas by cryogenic method to obtain the third-stage crude helium gas;

[0017] The low-temperature adsorption and stripping unit is used to remove nitrogen and oxygen from the third-stage crude helium by a low-temperature adsorption method to obtain stripped helium.

[0018] In the above-mentioned BOG helium extraction system, the low-temperature crude extraction unit includes a low-temperature crude extraction heat exchanger and a low-temperature crude extraction separation tank;

[0019] The second stage crude helium flows through the cryogenic crude stripping heat exchanger and then enters the cryogenic crude stripping separation tank. The third stage crude helium and nitrogen are obtained at the tank top and tank bottom of the cryogenic crude stripping separation tank, and are discharged and enter the cryogenic adsorption fine stripping unit respectively after flowing through the cryogenic crude stripping heat exchanger.

[0020] In the above-mentioned BOG helium extraction system, the low-temperature adsorption extraction unit includes a first adsorber, a second adsorber, a low-temperature adsorption extraction air inlet pipeline and a low-temperature adsorption extraction air exhaust pipeline;

[0021] The low-temperature adsorption refined extraction air intake pipeline includes a low-temperature adsorption crude helium air intake pipeline and a low-temperature adsorption nitrogen air intake pipeline;

[0022] The low-temperature adsorption crude helium gas inlet pipeline is used to introduce the third-stage crude helium gas;

[0023] The low-temperature adsorption exhaust pipeline includes a refined helium exhaust pipeline and a low-temperature adsorption nitrogen exhaust pipeline;

[0024] An external electric heating furnace is arranged on the low-temperature adsorbed nitrogen inlet pipeline.

[0025] In the above-mentioned BOG helium extraction system, the BOG helium extraction system further comprises a dryer, the inlet of the dryer is connected to the second-stage crude helium exhaust pipeline, and the outlet of the dryer is connected to the low-temperature crude extraction unit.

[0026] Based on the BOG helium extraction system, the present invention further provides a BOG helium extraction method.

[0027] The BOG helium extraction method comprises low-temperature distillation performed by the low-temperature distillation unit and palladium membrane separation and dehydrogenation performed by the palladium membrane separation and dehydrogenation unit;

[0028] Obtaining first-stage crude helium through the cryogenic distillation step;

[0029] The second-stage crude helium gas is obtained by the step of removing hydrogen through the palladium membrane separation.

[0030] Specifically, the steps of separating and removing hydrogen with palladium membrane are as follows:

[0031] 1) introducing nitrogen into the palladium membrane separation and dehydrogenation unit through the nitrogen / crude helium inlet pipeline, and adjusting the system pressure of the palladium membrane separation and dehydrogenation unit to a predetermined pressure value;

[0032] 2) heating the palladium membrane separation and dehydrogenation unit to a predetermined system temperature;

[0033] 3) introducing the first-stage crude helium into the palladium membrane separation and dehydrogenation unit through the nitrogen / crude helium inlet pipeline, and obtaining the second-stage crude helium and hydrogen through the palladium membrane separation and dehydrogenation unit.

[0034] Specifically, the BOG helium extraction method further includes low-temperature crude extraction using the low-temperature crude extraction unit and low-temperature adsorption fine extraction using the low-temperature adsorption fine extraction unit;

[0035] The third stage crude helium is obtained by the step of low temperature crude extraction;

[0036] The refined helium is obtained through the step of low-temperature adsorption and refined extraction.

[0037] Specifically, after the step of separating and removing hydrogen through the palladium membrane and before the step of crude extraction at low temperature, a step of drying the second-stage crude helium is also included.

[0038] The BOG helium extraction system and helium extraction method provided by the present invention separate and remove hydrogen in BOG through a palladium membrane separation and dehydrogenation unit, simplify the dehydrogenation process, reduce the control requirements in the dehydrogenation process, eliminate safety hazards, and can recycle and reuse hydrogen to avoid waste of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the structure of the palladium membrane separation and dehydrogenation unit in the BOG helium extraction system of the present invention.

[0040] Figure 2 It is a schematic diagram of the structure of the cryogenic distillation unit in the BOG helium extraction system of the present invention.

[0041] Figure 3 It is a schematic structural diagram of a low-temperature crude extraction unit and a low-temperature adsorption fine extraction unit in the BOG helium extraction system of the present invention.

[0042] Figure 4 It is a structural schematic diagram of the BOG helium extraction system of the present invention.

[0043] Figure 5 The process diagram of the BOG helium extraction method of the present invention is shown in FIG. Figure 1 .

[0044] Figure 6 The process diagram of the BOG helium extraction method of the present invention is shown in FIG. Figure 2 .

[0045] The marks in the figure are as follows:

[0046] 1 flow control valve, 2 flow meter, 3 heat exchanger, 4 explosion-proof heater, 5 palladium membrane separator, 6 back pressure valve, 7 vacuum unit, 8 cryogenic distillation heat exchanger, 9 cryogenic distillation separation tank, 10 distillation tower, 11 cryogenic crude extraction heat exchanger, 12 cryogenic crude extraction separation tank, 13 first adsorber, 14 second adsorber, 15 external electric heating furnace, 16 dryer. DETAILED DESCRIPTION

[0047] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0048] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0049] Helium is a colorless, odorless, monatomic rare gas with an extremely low boiling point (-268.85°C) and strong diffusivity. It is insoluble in water and has good thermal conductivity. It plays an irreplaceable and important role in the fields of national defense, biomedicine, nuclear industry, electrical industry, semiconductor manufacturing, and cryogenic industry. It is an important resource related to national security and the development of high-tech enterprises. Helium is mainly distributed in the mantle, rocks, air, and natural gas. However, the concentration of helium in the air is extremely low, making it difficult to achieve resource utilization. Therefore, extracting helium from natural gas, especially extracting helium from non-condensable tail gas (BOG) during the natural gas liquefaction process, is an important way to utilize helium resources.

[0050] At present, there are multiple feasible solutions for extracting helium from BOG at home and abroad, some of which have been industrialized, such as: cryogenic method, liquefaction method, pressure swing adsorption (PSA), membrane separation method, and a combination of two or more of the above methods. Although these existing methods for extracting helium have certain value, they also have some limitations. Although the membrane separation method has great advantages in its modularity and energy saving, it can only obtain helium with a concentration of 99% (no more than 99.9%); the PSA method is very mature, but there is a problem of low yield for the purification of low-concentration helium. Cryogenic method is the main method for extracting helium from natural gas. The basic principle is that the boiling points of different components in natural gas are different. Helium is difficult to liquefy under low temperature conditions. CH4, N2 and other alkanes can be liquefied and separated by low-temperature distillation. Although the above methods have been industrialized, the liquefaction method and multi-stage catalytic oxidation method are mainly used to separate helium and hydrogen. Although the liquefaction method can achieve a good separation of helium and hydrogen, since the liquefaction points of helium and hydrogen are very close, it is nothing more than a complete separation of helium and hydrogen, and the energy consumption is very high. At present, the most common method for treating hydrogen in helium is to add excess oxygen, oxidize the hydrogen into water through a multi-stage catalytic oxidation method, and then remove the water and excess oxygen separately, and finally purify the hydrogen from the helium. However, the above scheme has a complicated process and high control requirements. If the temperature is not well controlled, there will be safety hazards. In addition, the catalytic combustion of hydrogen causes a great waste of hydrogen resources.

[0051] The present invention adopts the processes of low-temperature distillation, palladium membrane separation and dehydrogenation, low-temperature crude extraction and low-temperature adsorption and refined extraction. Low-temperature distillation can improve the recovery efficiency of helium and separate most of the methane to obtain high-concentration methane gas. Palladium membrane separation and dehydrogenation can obtain high-concentration hydrogen. Low-temperature adsorption can obtain high-purity helium.

[0052] The technical solution of the present invention and how the technical solution of the present invention solves the above-mentioned technical problems are described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present invention will be described below in conjunction with the accompanying drawings.

[0053] The present invention provides a BOG helium extraction system, which comprises: a cryogenic distillation unit, which is used to separate a first-stage crude helium gas including a small amount of nitrogen, hydrogen and a small amount of oxygen from BOG by a cryogenic method; and a palladium membrane separation and dehydrogenation unit, which is used to remove hydrogen from the first-stage crude helium gas by a palladium membrane separation method to obtain a second-stage crude helium gas. The structure of the palladium membrane separation and dehydrogenation unit is as follows: Figure 1 and Figure 4 As shown, it includes a palladium membrane separator, a palladium membrane separation inlet pipeline and a palladium membrane separation exhaust pipeline; wherein the palladium membrane separation inlet pipeline includes a nitrogen / crude helium inlet pipeline; the palladium membrane separation exhaust pipeline includes a nitrogen exhaust pipeline, a hydrogen exhaust pipeline and a second-stage crude helium exhaust pipeline; the nitrogen / crude helium inlet pipeline is provided with a flow control valve 1, a flow meter 2, a heat exchanger 3 and an explosion-proof heater 4 in sequence, the nitrogen exhaust pipeline is provided with a heat exchanger 3 and a back pressure valve 6 in sequence, and the hydrogen exhaust pipeline is provided with a heat exchanger 3, a hydrogen buffer tank and a vacuum compressor 7 in sequence; wherein the flow control valve 1, the flow meter 2 and the back pressure valve 6 are used to adjust the system pressure of the palladium membrane separation dehydrogenation unit.

[0054] The metal palladium membrane of the palladium membrane separator 5 has a selective permeability to H2, and hydrogen permeates the palladium membrane following the "dissolution-diffusion" model. The specific mechanism is that the H2 molecule is first chemically adsorbed on the Pd surface, dissociated into two H atoms by two adjacent Pd atoms, and then dissolved in the Pd bulk phase. If the pressure of H2 on both sides of the membrane is different, there will be an H / Pd concentration gradient on both sides of the membrane. The chemical potential gradient caused by the concentration gradient causes the hydrogen atoms to diffuse from the high chemical potential to the low chemical potential side, and then the two H atoms are coupled to H2 molecules. In the process of extracting helium from BOG, the palladium membrane separation and dehydrogenation unit is used to separate and remove hydrogen from BOG, simplifying the dehydrogenation process, reducing the control requirements in the dehydrogenation process, eliminating safety hazards, and being able to recycle and reuse hydrogen to avoid waste of resources.

[0055] In a specific embodiment of the present invention, the structure of the cryogenic distillation unit is as follows: Figure 2 as well as Figure 4 As shown, it includes: a cryogenic distillation heat exchanger 8, a cryogenic distillation separation tank 9, a distillation tower 10, a cryogenic distillation air inlet pipeline and a cryogenic distillation exhaust pipeline. The cryogenic distillation exhaust pipeline includes: a cryogenic distillation nitrogen exhaust pipeline, a methane exhaust pipeline and a first-stage crude helium exhaust pipeline; wherein the first-stage crude helium exhaust pipeline is connected to the nitrogen / crude helium inlet pipeline.

[0056] During the helium extraction process, BOG gas enters the cryogenic stripping heat exchanger and is cooled to a cryogenic temperature by the refluxed liquid nitrogen. After being cooled and liquefied in the cryogenic stripping heat exchanger 8, the BOG gas enters the cryogenic distillation separation tank 9. Methane and nitrogen are obtained at the bottom of the cryogenic distillation separation tank, and the first stage crude helium is obtained at the top of the cryogenic distillation separation tank 9. The components are a small amount of nitrogen, hydrogen, and helium. After reheating, it is transported to the palladium membrane separation crude helium inlet pipeline. The tank bottom liquid of the cryogenic distillation separation tank 9 enters the distillation tower 10 to separate and purify methane and nitrogen. A 95% concentration of methane gas can be obtained, which can be used as a raw gas for LNG or a boiler fuel gas for a factory to improve resource utilization. Before the crude helium is passed through the palladium membrane separation and dehydrogenation unit, nitrogen is first passed through. After adjusting the system temperature and system pressure of the palladium membrane separation and dehydrogenation unit to a suitable predetermined value, the first stage crude helium is passed through for the palladium membrane separation and dehydrogenation process.

[0057] In addition, by pre-heating the palladium membrane separation and dehydrogenation unit to a predetermined temperature through nitrogen and purging the oxygen therein, oxidation of hydrogen can be avoided and potential safety hazards can be eliminated; by adjusting the system pressure to a predetermined value using a flow control valve, a flow meter and a back pressure valve, the efficiency of extracting hydrogen from crude helium can be improved.

[0058] In a specific embodiment of the present invention, the BOG helium extraction system of the present invention also includes a low-temperature crude extraction unit, which is used to further remove nitrogen and oxygen in the second-stage crude helium gas by a cryogenic method to obtain a third-stage crude helium gas, and a low-temperature adsorption fine extraction unit, which is used to adsorb and remove remaining impurities in the third-stage crude helium gas by a low-temperature adsorption method to obtain finely extracted helium gas.

[0059] In a specific embodiment of the present invention, the structure of the low temperature crude extraction unit is as follows: Figure 3 as well as Figure 4 As shown, it includes a cryogenic crude extraction heat exchanger 11, a cryogenic crude extraction separation tank 12, a cryogenic crude extraction air intake pipeline and a cryogenic crude extraction exhaust pipeline; the cryogenic crude extraction exhaust pipeline includes a cryogenic crude extraction nitrogen exhaust pipeline and a third-stage crude helium exhaust pipeline, and the cryogenic crude extraction air intake pipeline is connected to the second-stage crude helium exhaust pipeline.

[0060] The second-stage crude helium enters the cryogenic crude heat exchanger 11, is cooled to a cryogenic temperature by the refluxed liquid nitrogen, and enters the cryogenic crude separation tank 12 after liquefaction. Nitrogen and residual oxygen are obtained at the bottom of the cryogenic crude separation tank 12, and the third-stage crude helium is obtained at the top of the cryogenic crude separation tank 12. The components are nitrogen, oxygen, and helium, and are transported to the cryogenic adsorption fine extraction unit after reheating. The cryogenic crude extraction unit can perform a cryogenic crude extraction on the second-stage crude helium again, thereby further reducing the nitrogen and oxygen in the crude helium.

[0061] In a specific embodiment of the present invention, the structure of the low temperature adsorption extraction unit is as follows: Figure 3 and Figure 4 As shown, it includes: a first adsorber 13, a second adsorber 14, a low-temperature adsorption and finishing air inlet pipeline and a low-temperature adsorption and finishing air exhaust pipeline; the low-temperature adsorption and finishing air inlet pipeline includes a low-temperature adsorption crude helium air inlet pipeline and a low-temperature adsorption nitrogen air inlet pipeline, and the low-temperature adsorption crude helium air inlet pipeline is connected to the third-stage crude helium air exhaust pipeline; the low-temperature adsorption exhaust pipeline includes a finishing helium air exhaust pipeline and a low-temperature adsorption nitrogen air exhaust pipeline; an external electric heating furnace 15 is arranged on the low-temperature adsorption nitrogen air inlet pipeline.

[0062] In the third stage, the crude helium enters the low-temperature purification unit. The purification unit contains two adsorbers, which are equipped with molecular sieves and activated carbon. The two adsorbers are switched. When the first adsorber 13 is adsorbing, the second adsorber 14 is regenerated; when the first adsorber 13 is saturated with adsorption, the second adsorber 14 is also regenerated; the two adsorbers are automatically switched, and the cycle repeats. The regeneration gas of the adsorber uses nitrogen, which is heated by an external electric heating furnace 15 and passed into the adsorber for regeneration. The remaining trace impurities such as oxygen and nitrogen in the crude helium are adsorbed in the low-temperature adsorber, and the purity of the helium reaches more than 99.999% at the outlet.

[0063] In a specific embodiment of the present invention, the BOG helium extraction system of the present invention further includes: Figure 4 The dryer 16 shown is connected to the second-stage crude helium exhaust pipeline at one end and to the low-temperature crude extraction air intake pipeline at the other end, and is used for drying the second-stage crude helium.

[0064] A small amount of water vapor produced during the palladium membrane separation and dehydrogenation process may remain in the crude helium in the second stage. Drying the water vapor can facilitate the subsequent low-temperature crude extraction process and low-temperature adsorption extraction process to improve the purity of the final helium product.

[0065] Figure 5 A flow chart showing a specific embodiment of the method for extracting helium from BOG according to the present invention.

[0066] exist Figure 5 In the specific embodiment shown, the BOG helium extraction method of the present invention includes a low-temperature distillation process S501 using the above-mentioned BOG helium extraction system to separate a first-stage crude helium gas including a small amount of nitrogen, hydrogen and a small amount of oxygen from BOG by a deep cooling method; and a palladium membrane separation and dehydrogenation process S502 to remove hydrogen from the first-stage crude helium gas by a palladium membrane separation method to obtain a second-stage crude helium gas.

[0067] In a specific embodiment of the present invention, the above-mentioned palladium membrane separation and dehydrogenation process S502 specifically includes: introducing nitrogen into the palladium membrane separation and dehydrogenation unit through a nitrogen / crude helium inlet pipeline, and adjusting the system pressure of the palladium membrane separation and dehydrogenation unit to a predetermined pressure value by using a flow control valve, a flow meter and a back pressure valve; heating the nitrogen in the palladium membrane separation and dehydrogenation unit to a predetermined system temperature by using a heat exchanger and an explosion-proof electric heater; introducing the first-stage crude helium into the palladium membrane separation and dehydrogenation unit through a nitrogen / crude helium inlet pipeline, and separating the hydrogen in the first-stage crude helium by using a palladium membrane separator; and recycling the separated hydrogen through a hydrogen exhaust pipeline, and obtaining the second-stage crude helium through a second-stage crude helium exhaust pipeline.

[0068] Using a palladium membrane separation and dehydrogenation unit to separate and remove hydrogen from BOG can simplify the dehydrogenation process, reduce control requirements during the dehydrogenation process, eliminate safety hazards, and recycle and reuse hydrogen to avoid waste of resources.

[0069] In a specific embodiment of the present invention, the BOG helium extraction method of the present invention is as follows Figure 6 As shown, it also includes process S603, a low-temperature crude extraction process, in which nitrogen and oxygen in the second-stage crude helium are further removed by a deep cooling method to obtain a third-stage crude helium; and process S604, a low-temperature adsorption fine extraction process, in which the remaining nitrogen and oxygen in the third-stage crude helium are adsorbed and removed by a low-temperature adsorption method to obtain finely extracted helium, which can be beneficial to further remove impurities in the crude helium to obtain high-purity helium.

[0070] In addition, by pre-introducing nitrogen to displace the air in the palladium membrane separation and dehydrogenation unit, and using a flow control valve, flow meter, and back pressure valve to adjust the system pressure to a predetermined value, hydrogen oxidation can be avoided and safety hazards can be eliminated.

[0071] In a specific embodiment of the present invention, the BOG helium extraction method of the present invention further comprises: drying the second-stage crude helium gas after the palladium membrane separation and dehydrogenation process and before the low-temperature crude extraction process, such as Figure 6 As shown in S603. A small amount of water vapor generated in the palladium membrane separation and dehydrogenation process may remain in the crude helium in the second stage. Drying the water vapor can facilitate the subsequent low-temperature crude extraction process and low-temperature adsorption fine extraction process to improve the purity of the final helium product.

[0072] Combine the following Figure 4 and Figure 6The BOG helium extraction method of the present invention is described as follows: BOG gas enters the cryogenic stripping heat exchanger 8 and is cooled to a cryogenic temperature by the refluxed liquid nitrogen. After being cooled and liquefied in the cryogenic stripping heat exchanger 8, the BOG gas enters the cryogenic distillation separation tank 9. Methane and nitrogen are obtained at the bottom of the cryogenic distillation separation tank 9, and the first-stage crude helium is obtained at the top of the cryogenic distillation separation tank 9, which is composed of a small amount of nitrogen, hydrogen, and helium. After reheating, it is transported to the palladium membrane separation crude helium inlet pipeline. The liquid at the bottom of the cryogenic distillation separation tank 9 enters the distillation tower 10, and the methane and nitrogen are separated and purified to obtain a methane gas with a concentration of 95%, which can be used as a raw gas for LNG or a boiler fuel gas for a factory. Before the crude helium is passed through the palladium membrane separation and dehydrogenation unit, nitrogen is first used. The gas is regulated by a flow control valve and flows through a flow meter and injected into the system. After passing through the heat exchanger 3 and the explosion-proof electric heater 4, it enters the palladium membrane separator 5. The high-purity nitrogen flowing out of the palladium membrane separator 5 is heat exchanged by the heat exchanger, and then adjusted to the system set pressure by the flow control valve, flow meter and back pressure valve, and then enters the tail gas vent pipeline for emptying, and then the system heating program is started. When the inlet temperature of the raw gas reaches 400°C, the nitrogen is stopped and switched to the raw gas. The gas is also regulated by the flow control valve, flows through the flow meter and is injected into the system. After passing through the heat exchanger 3 and the explosion-proof electric heater 4, it then enters the palladium membrane separator 5. Under the action of the pressure difference, the hydrogen penetrates the palladium membrane in the form of dissolution and diffusion. After entering the inside of the palladium membrane tube, the gas enters the hydrogen buffer tank after heat exchange by the heat exchanger and metering by the flow meter, and then enters the pipeline network after being pressurized by the hydrogen compressor 7. The obtained second-stage crude helium is transported to the dryer after passing through the heat exchanger and precision filter. The second-stage crude helium that has been dried enters the low-temperature crude extraction heat exchanger 11, is cooled to the cryogenic temperature by the refluxed liquid nitrogen, and enters the low-temperature crude extraction separation tank 12 after liquefaction. Nitrogen and residual oxygen are obtained at the bottom of the low-temperature crude separation tank 12, and the third-stage crude helium is obtained at the top of the low-temperature crude separation tank 12. The components are: nitrogen, oxygen, and helium. After reheating, it is transported to the low-temperature adsorption and extraction unit; the low-temperature extraction unit includes two adsorbers, which are equipped with molecular sieves and activated carbon. The two adsorbers are switched, and when the first adsorber 13 is adsorbing, the second adsorber 14 is regenerated; when the first adsorber 13 is saturated with adsorption, the second adsorber 14 is also regenerated; the two adsorbers are automatically switched, and the cycle is repeated. The regeneration gas of the adsorber uses nitrogen, which is heated by an external electric heating furnace 15 and passed into the adsorber for regeneration. The remaining trace impurities such as oxygen and nitrogen in the crude helium are adsorbed in the low-temperature adsorber, and the purity of the helium reaches more than 99.999% at the outlet.

[0073] In the several embodiments provided by the present invention, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0074] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0075] The above are only embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A BOG helium extraction system, comprising a cryogenic distillation unit and a palladium membrane separation and dehydrogenation unit; The cryogenic distillation unit is used to separate the first-stage crude helium from BOG by cryogenic method, wherein the first-stage crude helium contains a small amount of nitrogen, hydrogen and a small amount of oxygen; The palladium membrane separation and dehydrogenation unit is used to remove hydrogen from the first-stage crude helium gas by a palladium membrane separation method to obtain the second-stage crude helium gas; The palladium membrane separation and dehydrogenation unit comprises a palladium membrane separator and a palladium membrane separation air inlet pipeline and a palladium membrane separation exhaust pipeline connected thereto; The palladium membrane separation air intake pipeline includes a nitrogen / crude helium air intake pipeline; The palladium membrane separation exhaust pipeline includes a nitrogen exhaust pipeline, a hydrogen exhaust pipeline and a second-stage crude helium exhaust pipeline.

2. The BOG helium extraction system according to claim 1, characterized in that: The nitrogen / crude helium inlet pipeline is provided with a flow control valve, a flow meter, a heat exchanger I and an explosion-proof heater in sequence; The nitrogen exhaust pipeline is provided with a heat exchanger II and a back pressure valve; The hydrogen exhaust pipeline is provided with a heat exchanger III, a hydrogen buffer tank and a vacuum compressor.

3. The BOG helium extraction system according to claim 1 or 2, characterized in that: The cryogenic distillation unit comprises a cryogenic distillation heat exchanger, a cryogenic distillation separation tank and a distillation tower; The BOG gas flows through the cryogenic distillation heat exchanger and then enters the cryogenic distillation separation tank. The first-stage crude helium is obtained at the top of the cryogenic distillation separation tank. The first-stage crude helium flows through the cryogenic distillation heat exchanger and then enters the first-stage crude helium exhaust pipeline. The first-stage crude helium exhaust pipeline is connected to the nitrogen / crude helium inlet pipeline. The bottom of the cryogenic distillation separation tank is connected to the distillation tower. Nitrogen and methane are obtained at the top and bottom of the distillation tower respectively. The gases flow through the cryogenic distillation heat exchanger and then enter the cryogenic distillation nitrogen exhaust pipeline and the methane exhaust pipeline respectively.

4. The BOG helium extraction system according to claim 3, characterized in that: The BOG helium extraction system also includes a low-temperature crude extraction unit and a low-temperature adsorption fine extraction unit; The low-temperature crude extraction unit is used to remove nitrogen and oxygen from the second-stage crude helium gas by cryogenic method to obtain the third-stage crude helium gas; The low-temperature adsorption and stripping unit is used to remove nitrogen and oxygen from the third-stage crude helium by a low-temperature adsorption method to obtain stripped helium.

5. The BOG helium extraction system according to claim 4, characterized in that: The low temperature crude extraction unit comprises a low temperature crude extraction heat exchanger and a low temperature crude extraction separation tank; The second stage crude helium flows through the cryogenic crude stripping heat exchanger and then enters the cryogenic crude stripping separation tank. The third stage crude helium and nitrogen are obtained at the tank top and tank bottom of the cryogenic crude stripping separation tank, and are discharged and enter the cryogenic adsorption fine stripping unit respectively after flowing through the cryogenic crude stripping heat exchanger.

6. The BOG helium extraction system according to claim 5, characterized in that: The low-temperature adsorption and refining unit comprises a first adsorber, a second adsorber, a low-temperature adsorption and refining air inlet pipeline and a low-temperature adsorption and refining air outlet pipeline; The low-temperature adsorption refined extraction air intake pipeline includes a low-temperature adsorption crude helium air intake pipeline and a low-temperature adsorption nitrogen air intake pipeline; The low-temperature adsorption crude helium gas inlet pipeline is used to introduce the third-stage crude helium gas; The low-temperature adsorption extraction exhaust pipeline includes an extraction helium exhaust pipeline and a low-temperature adsorption nitrogen exhaust pipeline; An external electric heating furnace is arranged on the low-temperature adsorbed nitrogen inlet pipeline.

7. The BOG helium extraction system according to claim 6, characterized in that: The BOG helium extraction system further includes a dryer, the inlet of the dryer is connected to the second-stage crude helium exhaust pipeline, and the outlet of the dryer is connected to the low-temperature crude extraction unit.

8. A method for extracting helium from BOG, comprising the step of extracting helium using the BOG helium extraction system according to any one of claims 1 to 7; The BOG helium extraction method comprises low-temperature distillation performed by the low-temperature distillation unit and palladium membrane separation and dehydrogenation performed by the palladium membrane separation and dehydrogenation unit; Obtaining first-stage crude helium through the cryogenic distillation step; The second-stage crude helium gas is obtained by the step of removing hydrogen through the palladium membrane separation.

9. The method for extracting helium from BOG according to claim 8, characterized in that: The steps of separating and removing hydrogen with palladium membrane are as follows: 1) introducing nitrogen into the palladium membrane separation and dehydrogenation unit through the nitrogen / crude helium inlet pipeline, and adjusting the system pressure of the palladium membrane separation and dehydrogenation unit to a predetermined pressure value; 2) heating the palladium membrane separation and dehydrogenation unit to a predetermined system temperature; 3) introducing the first-stage crude helium into the palladium membrane separation and dehydrogenation unit through the nitrogen / crude helium inlet pipeline, and obtaining the second-stage crude helium and hydrogen through the palladium membrane separation and dehydrogenation unit.

10. The method for extracting helium from BOG according to claim 8 or 9, characterized in that: The BOG helium extraction method also includes low-temperature crude extraction using a low-temperature crude extraction unit and low-temperature adsorption fine extraction using a low-temperature adsorption fine extraction unit; The third stage crude helium is obtained by the step of low temperature crude extraction; The refined helium is obtained by the step of low temperature adsorption and refined extraction; After the step of separating and removing hydrogen through the palladium membrane and before the step of crude extraction at low temperature, the step of drying the second-stage crude helium is also included.

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