Dehydrogenation method based on BOG gas helium extraction

Abstract

The invention belongs to the technical field of helium extraction, and particularly relates to a dehydrogenation method based on BOG (boil-off gas) helium extraction, which comprises the following steps: mixing dehydrogenation raw material gas with oxygen to obtain mixed gas, preheating the mixed gas, respectively reacting hydrogen and methane in the mixed gas with oxygen to generate water and carbon dioxide, cooling the reacted gas, drying and adsorbing to obtain the BOG helium extraction. Water and carbon dioxide are removed to obtain crude helium, the crude helium is divided into low-temperature extraction raw material gas and recycle gas, the low-temperature extraction raw material gas is pressurized and then enters a subsequent process, after the recycle gas is pressurized, one part of the recycle raw material gas is mixed with helium-rich gas to obtain dehydrogenation raw material gas, and the other part of the recycle gas serves as internal recycle gas to be mixed with the recycle gas; and adjusting the amount of the circulating feed gas according to the amount of the helium-rich gas. The temperature in the reactor can be balanced, explosion generated in the methane catalytic oxidation process due to the fact that the temperature in the reactor is too high is prevented, the content of hydrogen in the mixed gas can be reduced by adding the circulating raw material gas, and hydrogen explosion is prevented.

Description

Technical Field

[0001] The invention belongs to the technical field of helium extraction, and in particular relates to a dehydrogenation method based on BOG gas helium extraction. Background Art

[0002] Helium is a rare gas that is abundant in the universe but rare on Earth. It mainly exists in the atmosphere, rocks and natural gas. Helium is usually a colorless and odorless gas. It is the only substance that cannot solidify under standard atmospheric pressure. Its special physical properties determine the special uses of helium. As a scarce strategic resource for the development of national defense and high-tech industries, helium is widely used in military industry, scientific research, petrochemicals, refrigeration, medical treatment, semiconductors, pipeline leak detection, superconducting experiments, metal manufacturing, deep-sea diving, high-precision welding, optoelectronic product production and other fields, which is of great significance to scientific research.

[0003] There are many feasible solutions for extracting helium from BOG at home and abroad. Because hydrogen and helium coexist and have similar molecular weights and are not easy to separate, the existing helium purification methods are mostly catalytic oxidation to remove hydrogen from BOG gas. Specifically, oxygen-added hydrogen removal and methane removal systems are used for dehydrogenation. Since the explosion limit of hydrogen in the air is 4%-7.2%, part of the gas obtained by the oxygen-added hydrogen removal and methane removal system is usually used as circulating gas to enter the inlet of the oxygen-added hydrogen removal and methane removal system to dilute the hydrogen content of the feed gas of the oxygen-added hydrogen removal and methane removal system to prevent hydrogen explosion.

[0004] However, in normal production, the BOG gas volume in the BOG helium extraction system will change due to load fluctuations in the LNG plant. Since catalytic oxidation is an exothermic reaction, the heat released by the reaction in the reactor of the oxygen addition, dehydrogenation and demethane removal system will decrease, causing the temperature in the reactor to be unstable. Especially when the BOG gas volume is small, the temperature in the reactor will drop, which will cause the catalytic oxidation reaction to fail to proceed normally. Summary of the invention

[0005] The purpose of the present invention is to provide a method for extracting high-purity helium from BOG, so as to solve the technical problems existing in the existing methods for extracting high-purity helium.

[0006] In order to achieve the above technical purpose, the technical solution of the present invention is: A dehydrogenation method based on helium extraction from BOG gas comprises the following steps: dehydrogenation raw gas is first mixed with oxygen to obtain a mixed gas, after the mixed gas is preheated, hydrogen and methane in the mixed gas react with oxygen respectively to generate water and carbon dioxide, the reacted gas is cooled and then dried and adsorbed to remove water and carbon dioxide to obtain crude helium, the crude helium is divided into two parts, namely low-temperature extraction raw gas and circulating gas, the low-temperature extraction raw gas is pressurized and enters a subsequent process, the circulating gas is pressurized and divided into two parts, one part is circulating raw gas mixed with helium-rich gas to obtain dehydrogenation raw gas, the other part is used as inner circulating gas to mix with circulating gas and continue to participate in the pressurization process of circulating gas, before the helium-rich gas is mixed with circulating gas, the gas volume of the helium-rich gas is detected, and the volume of the circulating raw gas is adjusted according to the volume of the helium-rich gas.

[0007] As a further improvement, a circulating gas compressor is used for circulating gas pressurization, and the outlet of the circulating gas compressor is connected to two pipelines, namely a circulating raw gas pipeline and a bypass pipeline. The circulating raw gas is mixed with the helium-rich gas through the circulating raw gas pipeline, and the internal circulating gas enters the bypass pipeline.

[0008] As a further improvement, the outlet of the bypass pipeline is connected to the inlet of the circulating air compressor, a bypass valve is arranged on the bypass pipeline, and the internal circulating gas continues to be pressurized after being mixed with the circulating gas at the inlet of the circulating air compressor through the bypass pipeline.

[0009] As a further improvement, if it is detected that the amount of helium-rich gas is reduced, the bypass valve is adjusted to reduce the amount of the circulating raw gas entering the circulating raw gas pipeline, increase the amount of the internal circulating gas entering the bypass pipeline, and ensure that the hydrogen content in the mixed gas is less than 2%, while reducing the amount of oxygen mixed with the dehydrogenated raw gas.

[0010] As a further improvement, if an increase in the amount of helium-rich gas is detected, the bypass valve is adjusted to increase the amount of the circulating raw gas entering the circulating raw gas pipeline, reduce the amount of the internal circulating gas entering the bypass pipeline, and ensure that the hydrogen content in the mixed gas is less than 2%, while increasing the amount of oxygen mixed with the dehydrogenated raw gas.

[0011] As a further improvement, the bypass pipeline includes a first bypass pipeline and a second bypass pipeline, the first bypass pipeline and the second bypass pipeline are connected in parallel, a manual bypass valve is arranged on the first bypass pipeline, and a pneumatic bypass valve is arranged on the second bypass pipeline.

[0012] Due to the adoption of the above technical solution, the beneficial effects of the present invention are: The dehydrogenation method based on helium extraction from BOG gas provided by the present invention uses a part of the circulating gas as circulating raw gas and mixes it with helium-rich gas to form dehydrogenation raw gas, which is mixed with oxygen and then enters the reactor for catalytic oxidation dehydrogenation. The temperature in the reactor can be balanced to prevent the temperature in the reactor from being too high, which may cause an explosion during the catalytic oxidation of methane. In addition, the addition of the circulating raw gas can also reduce the hydrogen content in the mixed gas to prevent hydrogen explosion.

[0013] The circulating gas is divided into circulating raw gas and internal circulating gas. The amount of internal circulating gas and circulating raw gas is adjusted according to the amount of helium-rich gas to balance the temperature in the reactor and prevent the temperature imbalance in the reactor caused by the change in the amount of helium-rich gas. This can ensure the normal progress of catalytic oxidation in the reactor without causing the risk of explosion.

[0014] Since the catalytic oxidation reaction in the reactor is an exothermic reaction, when the amount of helium-rich gas decreases, if the amount of circulating raw gas is not changed, the temperature in the reactor will drop and the catalytic oxidation cannot proceed normally. The opening of the bypass valve is adjusted to reduce the circulating raw gas and increase the internal circulating gas, thereby balancing the temperature in the reactor. When the amount of helium-rich gas increases, if the amount of circulating raw gas is not changed, the temperature in the reactor will rise, which may easily lead to the risk of explosion. The opening of the bypass valve is adjusted to increase the circulating raw gas and reduce the internal circulating gas, thereby balancing the temperature in the reactor.

[0015] The internal circulating gas enters the circulating gas inlet pipe from the bypass pipe, mixes with the circulating gas from the buffer tank and then enters the circulating gas compressor again, which reduces the inlet and outlet pressure difference of the circulating gas compressor and can extend the service life of the circulating gas compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the process flow chart of this embodiment; Figure 2 is a flow chart of the equipment of this embodiment; Among them, 1-mixer, 2-preheater, 3-reactor, 4-cooler, 5-drying adsorber, 6-compressor, 7-buffer tank, 8-circulating air compressor, 9-circulating raw gas pipeline, 10-first bypass pipeline, 11-second bypass pipeline, 12-manual regulating valve, 13-pneumatic regulating valve, 14-dehydrogenation raw gas inlet pipeline, 15-oxygen pipeline, 16-circulating gas inlet pipeline. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] like Figure 1-2As shown, a dehydrogenation method based on helium extraction from BOG gas comprises the following steps: a dehydrogenation raw gas is first mixed with oxygen to obtain a mixed gas, after the mixed gas is preheated, hydrogen and methane in the mixed gas react with oxygen respectively to generate water and carbon dioxide, the reacted gas is cooled and then dried and adsorbed to remove water and carbon dioxide to obtain crude helium, the crude helium is divided into two parts, namely, low-temperature extraction raw gas and circulating gas, the low-temperature extraction raw gas is pressurized and enters a subsequent process, the circulating gas is pressurized and divided into two parts, one part is the circulating raw gas mixed with helium-rich gas to obtain the dehydrogenation raw gas, the other part is mixed with the circulating gas as the inner circulating gas, and continues to participate in the pressurization process of the circulating gas, before the helium-rich gas is mixed with the circulating gas, the amount of the helium-rich gas is detected, and the amount of the circulating raw gas is adjusted according to the amount of the helium-rich gas.

[0019] When it is detected that the amount of helium-rich gas is reduced, the amount of circulating raw gas mixed with the helium-rich gas is reduced, the amount of internal circulating gas is increased, and the hydrogen content in the mixed gas is ensured to be less than 2%, while the amount of oxygen mixed with the dehydrogenated raw gas is reduced.

[0020] When it is detected that the amount of helium-rich gas increases, the amount of circulating raw gas mixed with the helium-rich gas is increased, the amount of internal circulating gas is reduced, and the hydrogen content in the mixed gas is ensured to be less than 2%. At the same time, the amount of oxygen mixed with the dehydrogenated raw gas is increased.

[0021] In this embodiment, the dehydrogenation raw gas is mixed with oxygen in the mixer 1 to obtain a mixed gas, the mixed gas enters the preheater 2 for preheating and then enters the reactor 3, a catalytic oxidation reaction is carried out in the reactor 3, and after the reaction is completed, it enters the cooler 4 for cooling, and the cooled gas enters the dry adsorber 5, which is filled with activated carbon and molecular sieves for adsorbing water and carbon dioxide. A part of the crude helium obtained at the outlet of the dry adsorber 5 is used as the low-temperature extraction raw gas and is pressurized by the compressor 6 before entering the subsequent low-temperature extraction system, and the other part is used as the circulating gas.

[0022] The mixer 1 is provided with two inlets, which are respectively connected to the dehydrogenation raw gas inlet pipeline 14 and the oxygen pipeline 15; the outlet of the drying adsorber 5 is connected to the compressor 6 and the buffer tank 7; and the outlet of the buffer tank 7 is connected to the circulating gas compressor 8 through the circulating gas inlet pipeline 16.

[0023] After the circulating gas enters the circulating gas compressor 8 for pressurization, a part of it is mixed with the helium-rich gas as the circulating raw gas to form the dehydrogenation raw gas, and the other part is returned to the inlet of the circulating gas compressor 8 as the internal circulating gas, mixed with the circulating gas entering the circulating gas compressor 8, and continues to enter the pressurization process.

[0024] The outlet of the circulating gas compressor 8 is connected to two pipelines, namely the circulating raw gas pipeline 9 and the bypass pipeline. The outlet of the bypass pipeline is connected to the circulating gas inlet pipeline 16. A bypass valve is arranged on the bypass pipeline. The circulating raw gas pipeline 9 is connected to the dehydrogenation raw gas inlet pipeline 14. The circulating raw gas enters the dehydrogenation raw gas inlet pipeline 14 from the circulating raw gas pipeline 9 and mixes with the helium-rich gas to form the dehydrogenation raw gas. The inner circulating gas enters the bypass pipeline, returns to the circulating gas inlet pipeline 16, mixes with the circulating gas from the buffer tank 7, and re-enters the circulating gas compressor 8.

[0025] The bypass pipeline includes a first bypass pipeline 10 and a second bypass pipeline 11. The first bypass pipeline 10 and the second bypass pipeline 11 are connected in parallel. A manual bypass valve is arranged on the first bypass pipeline 10, and a pneumatic bypass valve is arranged on the second bypass pipeline 11. By arranging a manual regulating valve 12, it is prevented that the pneumatic regulating valve 13 fails or is overhauled and affects the normal production.

[0026] A helium-rich gas flowmeter is provided on the dehydrogenation raw gas inlet pipeline 14 for detecting the amount of helium-rich gas entering the dehydrogenation raw gas inlet pipeline 14 . The helium-rich gas flowmeter is provided at an end away from the mixer 1 .

[0027] An oxygen regulating valve is provided on the oxygen pipeline 15 for adjusting the amount of oxygen entering the mixer 1 .

[0028] A circulating gas inlet regulating valve is provided on the circulating gas inlet pipeline 16, and a circulating raw gas regulating valve is provided on the circulating raw gas pipeline 9.

[0029] In the actual production process, the heating power of the preheater is constant. When the helium-rich gas flowmeter detects a decrease in the amount of helium-rich gas, the heat generated by the catalytic oxidation reaction decreases due to the decrease in the content of hydrogen and methane entering the reactor, which will cause the temperature in the reactor to drop and affect the occurrence of catalytic oxidation. At this time, the bypass valve needs to be adjusted to reduce the amount of circulating raw gas entering the circulating raw gas pipeline, increase the amount of internal circulating gas entering the bypass pipeline, and ensure that the hydrogen content in the mixed gas is less than 2%, maintain the temperature balance in the reactor, prevent the temperature in the reactor from being too low to affect the smooth progress of the catalytic oxidation reaction, and prevent hydrogen from exploding.

[0030] When the helium-rich gas flowmeter detects an increase in helium-rich gas, the temperature inside the reactor will rise, and methane will be prone to explosion during catalytic oxidation. Therefore, the bypass valve needs to be adjusted to increase the amount of circulating raw gas entering the circulating raw gas pipeline, reduce the amount of internal circulating gas entering the bypass pipeline, and ensure that the hydrogen content in the mixed gas is less than 2% to maintain the temperature balance in the reactor.

[0031] The internal circulating gas enters the circulating gas inlet pipe from the bypass pipe, mixes with the circulating gas from the buffer tank and then enters the circulating gas compressor again, which reduces the inlet and outlet pressure difference of the circulating gas compressor and can extend the service life of the circulating gas compressor.

[0032] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A dehydrogenation method based on helium extraction from BOG gas, characterized in that: The following steps are involved: The dehydrogenation raw gas is first mixed with oxygen to obtain a mixed gas. After the mixed gas is preheated, the hydrogen and methane in the mixed gas react with oxygen to generate water and carbon dioxide respectively. The reacted gas is cooled and then dried and adsorbed to remove water and carbon dioxide to obtain crude helium. The crude helium is divided into two parts, namely, low-temperature extraction raw gas and circulating gas. The low-temperature extraction raw gas enters the subsequent process after pressurization. The circulating gas is divided into two parts after pressurization. One part is the circulating raw gas mixed with the helium-rich gas to obtain the dehydrogenation raw gas, and the other part is mixed with the circulating gas as the inner circulating gas and continues to participate in the pressurization process of the circulating gas. Before the helium-rich gas is mixed with the circulating gas, the amount of the helium-rich gas is detected, and the amount of the circulating raw gas is adjusted according to the amount of the helium-rich gas.

2. The dehydrogenation method based on helium extraction from BOG gas according to claim 1, characterized in that: The circulating gas is pressurized by a circulating gas compressor, and the outlet of the circulating gas compressor is connected to two pipelines, namely the circulating raw gas pipeline and the bypass pipeline. The circulating raw gas is mixed with the helium-rich gas through the circulating raw gas pipeline, and the internal circulating gas enters the bypass pipeline.

3. The dehydrogenation method based on helium extraction from BOG gas according to claim 2, characterized in that: The outlet of the bypass pipeline is connected to the inlet of the circulating air compressor. A bypass valve is arranged on the bypass pipeline. The internal circulating gas passes through the bypass pipeline and is continuously pressurized after being mixed with the circulating gas at the inlet of the circulating air compressor.

4. The dehydrogenation method based on helium extraction from BOG gas according to claim 3, characterized in that: If it is detected that the amount of helium-rich gas is reduced, the bypass valve is adjusted to reduce the amount of the circulating raw gas entering the circulating raw gas pipeline, increase the amount of the internal circulating gas entering the bypass pipeline, and ensure that the hydrogen content in the mixed gas is less than 2%, while reducing the amount of oxygen mixed with the dehydrogenation raw gas.

5. The dehydrogenation method based on helium extraction from BOG gas according to claim 3, characterized in that: If an increase in the amount of helium-rich gas is detected, the bypass valve is adjusted to increase the amount of the circulating raw gas entering the circulating raw gas pipeline, reduce the amount of the internal circulating gas entering the bypass pipeline, and ensure that the hydrogen content in the mixed gas is less than 2%, while increasing the amount of oxygen mixed with the dehydrogenation raw gas.

6. The dehydrogenation method based on helium extraction from BOG gas according to claim 2, characterized in that: The bypass pipeline comprises a first bypass pipeline and a second bypass pipeline, the first bypass pipeline and the second bypass pipeline are connected in parallel, a manual bypass valve is arranged on the first bypass pipeline, and a pneumatic bypass valve is arranged on the second bypass pipeline.

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