System and method for extracting helium from BOG (Boil Off Gas) by normal-temperature method

Abstract

The invention discloses a system and a method for extracting helium from BOG (Boil Off Gas) gas by a normal-temperature method, and provides a BOG helium extraction system based on metal dehydrogenation aiming at the problems of potential safety hazards, high cost investment and the like in the prior art of helium extraction by adopting a conventional oxygen-adding catalytic oxidation method for dehydrogenation. The purity of a helium product is improved, the operation cost of a helium extraction system is reduced, and the operation stability of the system is guaranteed; on the other hand, secondary membrane separation retentate gas and pressure swing adsorption desorbed gas are effectively recovered, so that the purity of the helium product is ensured, the yield of the helium product of the system is effectively improved, and the loss of the helium product with high additional value is reduced; the problem that the product yield is low when the product purity is high in traditional pressure swing adsorption purification of helium is solved.

Description

Technical Field

[0001] The present invention relates to a helium extraction technology, and in particular to a BOG gas room temperature helium extraction system and method. Background Art

[0002] The helium content in my country's natural gas is very low, and its helium content is usually less than 0.05% (V / V). Extracting helium from helium-poor natural gas requires large investment and high production costs. The development of the liquefied natural gas (LNG) industry has created conditions for the extraction of helium from natural gas. When natural gas is liquefied, most of the methane is liquefied; the remaining gas that is not liquefied is called flash gas (BOG), including methane with a boiling point lower than CH 4 N of gas 2 , H 2 and He have not been liquefied. However, since the boiling point of hydrogen is close to that of helium, it is difficult to remove it by cryogenic distillation or membrane separation. To extract helium from BOG gas, methane and nitrogen can be separated by cryogenic distillation or membrane separation, and then hydrogen can be removed from BOG gas.

[0003] There are many feasible solutions for extracting helium from BOG at home and abroad, and some of them have been industrially implemented, such as: cryogenic method, liquefaction method, pressure swing adsorption (PSA) method, membrane separation, and a combination of two or more of the above methods. When extracting helium from BOG, after the methane and nitrogen in BOG are separated, the hydrogen in the remaining helium tail gas is usually dehydrogenated by oxygen catalytic oxidation. The hydrogen-oxygen catalytic oxidation reaction is an exothermic reaction. The use of catalytic oxidation for dehydrogenation will result in a high temperature in the catalytic oxidation unit, which brings safety risks. On the other hand, in order to remove hydrogen impurities to a lower content in the conventional BOG gas room temperature method for extracting helium, the addition of excess oxygen during the dehydrogenation process also introduces new impurities into the system; moreover, the reaction of hydrogen and oxygen will generate water, and molecular sieve dehydration is generally required after dehydrogenation, which is complicated and requires a large investment.

[0004] In view of this, this application is hereby filed. Summary of the invention

[0005] In view of the safety risks and high cost of dehydrogenation using conventional oxygen-added catalytic oxidation in the prior art of helium extraction, the present invention provides a BOG helium extraction system based on metal dehydrogenation, which can improve the yield and purity of the helium product while also greatly ensuring the stable operation of the system.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a BOG gas room temperature helium extraction system, the system comprises a BOG compression device, a control device, a metal hydrogen absorption and dehydrogenation device, a membrane separation helium concentration device, a crude helium compressor, and a room temperature pressure swing adsorption device; the BOG compression device, the control device, the metal hydrogen absorption and dehydrogenation device, the membrane separation helium concentration device, the crude helium compressor, and the room temperature pressure swing adsorption device are connected in sequence through pipelines; wherein,

[0008] The metal hydrogen absorption and dehydrogenation device is provided with a metal hydrogen absorption material bed. The reversible principle of the reaction between metal material and hydrogen is utilized. In the forward reaction, hydrogen is absorbed and heat is released; in the reverse reaction, hydrogen is released and heat is absorbed. The temperature and pressure are changed by the control device so that the reaction is repeated in the forward and reverse directions, thereby realizing the hydrogen absorption and release function of the material. The dehydrogenated BOG gas enters the membrane separation and helium concentration device downstream of the system.

[0009] The metal material in the metal hydrogen absorption and dehydrogenation device is one or more of Mg, Ti, Nb, V, Zr or rare earth metals.

[0010] The BOG compression device is a diaphragm compressor.

[0011] Optionally, the membrane separation and helium concentration device is a primary membrane separation system, and the dehydrogenated BOG gas is separated and concentrated into primary crude helium (permeate gas) through a membrane module, and the primary permeate gas is returned to the inlet of the BOG compression device for recovery for circulation or external transmission; the permeate gas passes through the crude helium compressor and enters the normal temperature pressure swing adsorption device for purification.

[0012] Optionally, the membrane separation and helium concentration device is a two-stage membrane separation system, which includes a primary membrane separation and helium concentration device and a secondary membrane separation and helium concentration device, with a buffer tank and an inter-membrane compression device provided between the two.

[0013] The inter-membrane compression device compresses the primary crude helium (permeate gas) of the primary membrane separation and helium concentration device to a certain pressure and then enters the secondary membrane separation and helium concentration device. The secondary crude helium (permeate gas) obtained by the membrane separation enters the crude helium compressor, and the secondary raffinate gas returns to the inlet of the BOG compression device for recovery; the secondary crude helium is compressed to a certain pressure and enters the normal temperature pressure swing adsorption device for purification.

[0014] Optionally, there are two metal hydrogen absorption and dehydrogenation devices connected in parallel, one absorbs hydrogen at the working pressure and temperature, and the other reduces the pressure and releases hydrogen by heating; the temperature and pressure are regulated by the control device; the two sets of material beds are alternated every 2-3 hours.

[0015] Optionally, the control device monitors and controls the pressure and temperature of the metal hydrogen absorption and dehydrogenation device through a pressure sensor and a temperature sensor.

[0016] To achieve the above object, the present invention also provides the following technical solutions:

[0017] A method for extracting helium from BOG gas at room temperature, the method being applied to the above-mentioned helium extraction system, comprising the following steps:

[0018] 1) The feed gas and the retentate gas from the secondary membrane separation device are input into the BOG compression system for pressurization treatment;

[0019] 2) The pressurized raw gas is cooled by circulating water or air cooler and then enters the metal hydrogen absorption and dehydrogenation device to remove the hydrogen content through the reaction of hydrogen impurities with metals;

[0020] 3) The dehydrogenated feed gas is fed into a primary membrane separation system to concentrate the helium component therein, and the slightly positive pressure permeate gas is the primary crude helium, which then enters the inter-membrane compression system step 4) or the crude helium compression system step 6); the high-pressure retentate gas is returned to the inlet of the BOG compression device for recycling or external transmission;

[0021] 4) Inputting the primary crude helium into the inter-membrane compression device for compression treatment;

[0022] 5) The compressed primary crude helium is input into the secondary membrane separation system for concentration treatment, and the permeate gas is the secondary crude helium, which then enters the crude helium compression device; the retentate gas generated in this stage is returned to the inlet of the BOG compression device for circulation;

[0023] 6) pressurizing the primary or secondary crude helium through a crude helium compression device;

[0024] 7) The pressurized primary or secondary crude helium is input into the normal temperature pressure swing adsorption device to obtain helium and desorbed gas, the helium is recovered, and the desorbed gas is returned to the inlet of the BOG compression device or input into the membrane compressor for circulation.

[0025] Furthermore, in step 1) of the above method, the pressure of the raw gas is 1.3-2.0 MPa, and the helium content is <0.5%.

[0026] Furthermore, the pressure of the metal hydrogen absorption and dehydrogenation device in step 2) of the above method is controlled at 1.3-2.0 MPa, the working temperature for absorbing hydrogen is controlled at 0-30 degrees Celsius, and the working temperature for releasing hydrogen is controlled at 80-120 degrees Celsius.

[0027] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0028] The present invention provides a BOG gas room temperature helium extraction system and method. The hydrogen content in BOG is generally 200-1000ppm, which is relatively low, which makes it possible to use metal hydrogen absorption method to dehydrogenate. The present invention uses metal hydrogen absorption + two-stage membrane separation + pressure swing adsorption process to extract helium from BOG. ​​The purity of the helium product is ≥99.999%, the yield is ≥90%, the operation energy consumption is low, the process is simple, and the system stability is strong. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 A schematic flow chart of a BOG helium extraction system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0032] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is apparent to one of ordinary skill in the art that these specific details are not necessarily employed to practice the present invention. In other embodiments, in order to avoid obscuring the present invention, well-known structures, circuits, materials, or methods are not specifically described.

[0033] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment," "an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. In addition, it will be appreciated by those of ordinary skill in the art that the figures provided herein are for illustrative purposes and that the figures are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0034] In the description of the present invention, the directions or positional relationships indicated by terms such as “front”, “rear”, “left”, “right”, “up”, “down”, “vertical”, “horizontal”, “high”, “low”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the scope of protection of the present invention.

[0035] Example 1

[0036] The purpose of the present invention is to provide a BOG gas helium extraction system and method, so as to improve the yield and purity of helium, improve the stability of system operation, and reduce the cost of system operation. The gas content of the BOG mixed gas is: helium 0.5%, hydrogen 0.05%, nitrogen 6%, methane 92.4499%, oxygen 1%, water 0.0001%.

[0037] like Figure 1 As shown, the system includes a buffer tank, a BOG compressor, a control device, a metal hydrogen absorber, a primary membrane separation helium extraction device, a buffer tank, an inter-membrane compression system, a secondary membrane separation helium extraction device, a crude helium compressor, and a pressure swing adsorption system, which are sequentially connected through pipelines.

[0038] The BOG compressor uses a diaphragm compressor to compress the feed gas with a pressure of about 0.01 MPa and a helium content of 0.5% and the retentate gas with a pressure of 1.3 MPa from the secondary membrane separation system from a slightly positive pressure to 2.5 MPa to meet the subsequent process intake conditions.

[0039] The metal hydrogen absorption and dehydrogenation system: utilizes the reversible principle of the reaction between metal and hydrogen, and the forward reaction absorbs hydrogen and releases heat; the reverse reaction releases hydrogen and absorbs heat. By changing the temperature and pressure conditions by the controller, the reaction can be repeated in the forward and reverse directions to realize the hydrogen absorption and release function of the material; in the specific implementation of the present invention, two sets of hydrogen absorption material beds are used, and the pressurized raw gas and permeate gas enter the metal hydrogen absorption and dehydrogenation system after being cooled by circulating water or air cooler. Through one of the hydrogen absorption material beds of the metal hydrogen absorption and dehydrogenation system, hydrogen is absorbed under the condition of 0-30 degrees Celsius, and helium and other impurities pass through the bed body. When the bed body is saturated with hydrogen, the pressure is reduced to 0.01MPa, and the pressure is detected by the pressure sensor of the control unit, and it is heated to 80-120 degrees Celsius, and the temperature is detected by the control unit to release the absorbed hydrogen; at the same time, the other set of material beds performs hydrogen absorption work; the two sets of hydrogen-helium separation beds are alternated every 2 hours to realize continuous operation of the system.

[0040] The specific implementation of the present invention uses Mg and Ti as metal hydrogen storage materials for two sets of hydrogen absorber material beds to remove hydrogen impurities in BOG to below 1 ppm, and the dehydrogenated BOG enters the membrane separation system downstream of the system.

[0041] The membrane separation in the specific implementation manner is a two-stage membrane separation system:

[0042] The first-stage membrane separation helium extraction system: the dehydrogenated raw gas is separated and concentrated into primary crude helium (permeate gas) through a membrane module, and the helium component concentration is concentrated to about 10-14%. The residual gas enters the LNG device fuel gas system or is exported. This stage of membrane separation is mainly responsible for recovering as much helium as possible in the raw gas to improve the yield, and the membrane module area is relatively large;

[0043] Inter-membrane compression system: compresses the primary crude helium of the primary membrane separation and helium concentration system to a pressure of 1.3MPa to meet the subsequent process intake conditions;

[0044] Secondary membrane separation helium extraction system: The pressurized primary crude helium is separated and concentrated several times through membrane components to obtain secondary crude helium. The permeate gas is the secondary crude helium with a pressure of about 10kPa and a helium component concentration of about 65%. The permeate gas obtained by this stage of membrane separation directly enters the crude helium compression system, and the residual gas is returned to the inlet of the BOG compression system for recovery. The main function of this stage of membrane separation is to increase the helium content to the purity required for subsequent pressure swing adsorption.

[0045] The crude helium compression system compresses the concentrated secondary crude helium to 1.5 MPa to meet the air intake conditions of subsequent processes.

[0046] The pressure swing adsorption system is used to further purify the secondary crude helium to obtain a pure helium product with a helium content of 99.999%. The desorbed gas is returned to the inlet of the membrane compressor to recover the adsorbed helium, further improving the helium yield.

[0047] The specific data of Example 1 can be seen in the material balance table of Table 1; from the data in the table, it can be seen that the metal hydrogen absorption device of Example 1 can well remove hydrogen from BOG, and at the same time, high-purity helium of 99.999% can be obtained through the system.

[0048] Table 1 Material balance

[0049]

[0050]

[0051] Example 2

[0052] The purpose of the present invention is to provide a BOG gas helium extraction system and method, so as to improve the yield and purity of helium, improve the stability of system operation, and reduce the cost of system operation. The gas content of the BOG mixed gas is: helium 1.568%, hydrogen 0.1%, nitrogen 15.3649%, methane 82.712899%, oxygen 0.2542%, water 0.0001%.

[0053] like Figure 1 As shown, the system includes a buffer tank, a BOG compressor, a control device, a metal hydrogen absorber, a primary membrane separation helium extraction device, a buffer tank, an inter-membrane compression system, a secondary membrane separation helium extraction device, a crude helium compressor, and a pressure swing adsorption system, which are sequentially connected through pipelines.

[0054] The BOG compressor uses a diaphragm compressor to compress the feed gas with a pressure of about 0.01 MPa and a helium content of 1.568% and the retentate gas with a pressure of 1.3 MPa from the secondary membrane separation system from a slightly positive pressure to 2.1 MPa to meet the subsequent process intake conditions.

[0055] The metal hydrogen absorption and dehydrogenation system: utilizes the reversible principle of the reaction between metal and hydrogen, and the forward reaction absorbs hydrogen and releases heat; the reverse reaction releases hydrogen and absorbs heat. By changing the temperature and pressure conditions by the controller, the reaction can be repeated in the forward and reverse directions to realize the hydrogen absorption and release function of the material; in the specific implementation of the present invention, two sets of hydrogen absorption material beds are used, and the pressurized raw gas and permeate gas enter the metal hydrogen absorption and dehydrogenation system after being cooled by circulating water or air cooler. Through one of the hydrogen absorption material beds of the metal hydrogen absorption and dehydrogenation system, hydrogen is absorbed under the condition of 0-30 degrees Celsius, and helium and other impurities pass through the bed body. When the bed body is saturated with hydrogen, the pressure is reduced to 0.01MPa, and the pressure is detected by the pressure sensor of the control unit, and it is heated to 80-120 degrees Celsius, and the temperature is detected by the control unit to release the absorbed hydrogen; at the same time, the other set of material beds performs hydrogen absorption work; the two sets of hydrogen-helium separation beds are alternated every 2 hours to realize continuous operation of the system.

[0056] The specific implementation of the present invention uses Mg and Ti as metal hydrogen storage materials for two sets of hydrogen absorber material beds to remove hydrogen impurities in BOG to below 1 ppm, and the dehydrogenated BOG enters the membrane separation system downstream of the system.

[0057] The membrane separation in the specific implementation manner is a two-stage membrane separation system:

[0058] The first-stage membrane separation helium extraction system: the dehydrogenated raw gas is separated and concentrated into primary crude helium (permeate gas) through the membrane module, and the helium component concentration is concentrated to about 10%. The permeate gas enters the LNG device fuel gas system or is exported. This stage of membrane separation is mainly responsible for recovering as much helium as possible in the raw gas to improve the yield, and the membrane module area is relatively large;

[0059] Inter-membrane compression system: compresses the primary crude helium of the primary membrane separation and helium concentration system to a pressure of 1.3MPa to meet the subsequent process intake conditions;

[0060] Secondary membrane separation helium extraction system: The pressurized primary crude helium is concentrated several times through membrane assembly permeation separation to obtain secondary crude helium. The permeate gas is the secondary crude helium with a pressure of about 10kPa and a helium component concentration of about 55%. The permeate gas obtained by this stage of membrane separation directly enters the crude helium compression system, and the residual gas is returned to the inlet of the BOG compression system for recovery. The main function of this stage of membrane separation is to increase the helium content to the purity required for subsequent pressure swing adsorption.

[0061] The crude helium compression system compresses the concentrated secondary crude helium to 1.5 MPa to meet the air intake conditions of subsequent processes.

[0062] The pressure swing adsorption system is used to further purify the secondary crude helium to obtain a pure helium product with a helium content of 99.999%. The desorbed gas is returned to the inlet of the membrane compressor to recover the adsorbed helium, further improving the helium yield.

[0063] The specific data of Example 2 is shown in the material balance table of Table 2; from the data in the table, it can be seen that the metal hydrogen absorption device of Example 2 can well remove hydrogen from BOG, and at the same time, high-purity helium of 99.999% can be obtained through the system.

[0064] Table 2 Material balance

[0065]

[0066]

[0067] In summary, the present invention improves the purity of helium products, reduces the operating cost of the helium extraction system, and ensures the stability of system operation through the application of the metal hydrogen absorption system on the one hand; on the other hand, the secondary membrane separation retentate gas and the desorbed gas of the pressure swing adsorption are effectively recovered, which effectively improves the yield of the system helium product while ensuring the purity of the helium product and reduces the loss of high value-added helium products; and solves the problem of low product yield when the product purity is high in the traditional pressure swing adsorption helium purification.

[0068] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A BOG gas room temperature helium extraction system, characterized in that: The system comprises a BOG compression device, a control device, a metal hydrogen absorption and dehydrogenation device, a membrane separation and helium concentration device, a crude helium compressor, and a normal temperature pressure swing adsorption device; the BOG compression device, the control device, the metal hydrogen absorption and dehydrogenation device, the membrane separation and helium concentration device, the crude helium compressor, and the normal temperature pressure swing adsorption device are connected in sequence through pipelines; wherein a metal hydrogen absorption material bed is arranged in the metal hydrogen absorption and dehydrogenation device, and the reversible principle of the reaction between metal material and hydrogen is utilized, and the forward reaction absorbs hydrogen and releases heat; the reverse reaction releases hydrogen and absorbs heat; the temperature and pressure are changed by the control device so that the reaction is repeatedly carried out in the forward and reverse directions, so as to realize the hydrogen absorption and release function of the material, and the dehydrogenated BOG gas enters the membrane separation and helium concentration device downstream of the system.

2. The BOG gas room temperature helium extraction system according to claim 1, characterized in that: The metal material in the metal hydrogen absorption and dehydrogenation device is one or more of Mg, Ti, Nb, V, Zr or rare earth metals.

3. The BOG gas room temperature helium extraction system according to claim 1, characterized in that: The BOG compression device is a diaphragm compressor.

4. The BOG gas room temperature helium extraction system according to claim 1, characterized in that: The membrane separation and helium concentration device is a primary membrane separation system, which separates and concentrates the dehydrogenated BOG into primary crude helium (permeate gas) through membrane modules, and the primary permeate gas is returned to the inlet of the BOG compression device for recycling or external transmission; the permeate gas passes through the crude helium compressor and enters the normal temperature pressure swing adsorption device for purification.

5. The BOG gas room temperature helium extraction system according to claim 4, characterized in that: The membrane separation and helium concentration device is a two-stage membrane separation system, which includes a primary membrane separation and helium concentration device and a secondary membrane separation and helium concentration device, with a buffer tank and an inter-membrane compression device disposed between the two. The inter-membrane compression device compresses the primary crude helium (permeate gas) of the primary membrane separation and helium concentration device to a certain pressure and then enters the secondary membrane separation and helium concentration device. The secondary crude helium (permeate gas) obtained by the membrane separation enters the crude helium compressor, and the secondary retentate gas returns to the inlet of the BOG compression device for recycling. The secondary crude helium is compressed to a certain pressure and enters the normal temperature pressure swing adsorption device for purification.

6. The BOG gas room temperature helium extraction system according to claim 1, characterized in that: The metal hydrogen absorption and dehydrogenation devices are two in parallel, one absorbs hydrogen at the working pressure and temperature, and the other reduces the pressure and releases hydrogen by heating; the temperature and pressure are regulated by the control device; the two sets of material beds are alternated every 2-3 hours.

7. The BOG gas room temperature helium extraction system according to claim 6, characterized in that: The control device monitors and controls the pressure and temperature of the metal hydrogen absorption and dehydrogenation device through a pressure sensor and a temperature sensor.

8. A method for extracting helium from BOG gas at room temperature, characterized in that: The steps include: 1) The feed gas and the retentate gas from the secondary membrane separation device are input into the BOG compression system for pressurization treatment; 2) The pressurized raw gas is cooled by circulating water or air cooler and then enters the metal hydrogen absorption and dehydrogenation device to remove the hydrogen content through the reaction between hydrogen impurities and metals; 3) The dehydrogenated feed gas is fed into a primary membrane separation system to concentrate the helium component therein, and the slightly positive pressure permeate gas is the primary crude helium, which then enters the inter-membrane compression system step 4) or the crude helium compression system step 6); the high-pressure retentate gas is returned to the inlet of the BOG compression device for recycling or external transmission; 4) Inputting the primary crude helium into the inter-membrane compression device for compression treatment; 5) The compressed primary crude helium is input into the secondary membrane separation system for concentration treatment, and the permeate gas is the secondary crude helium, which then enters the crude helium compression device; the retentate gas generated in this stage is returned to the inlet of the BOG compression device for circulation; 6) pressurizing the primary or secondary crude helium through a crude helium compression device; 7) The pressurized primary or secondary crude helium is input into the normal temperature pressure swing adsorption device to obtain helium and desorbed gas, the helium is recovered, and the desorbed gas is returned to the inlet of the BOG compression device or input into the membrane compressor for circulation.

9. The method for extracting helium from BOG gas at room temperature according to claim 8, characterized in that: The pressure of the raw gas in step 1) is 1.3-2.0 MPa.

10. The method for extracting helium from BOG gas at room temperature according to claim 8, characterized in that: The pressure of the metal hydrogen absorption and dehydrogenation device in step 2) is controlled at 1.3-2.0 MPa, the working temperature of absorbing hydrogen is controlled at 0-30 degrees Celsius, and the working temperature of releasing hydrogen is controlled at 80-120 degrees Celsius.

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