阅读说明：本技术 从液化天然气的闪蒸汽中提纯氦气并液化的系统和方法 (System and method for purifying helium from flash steam of liquefied natural gas and liquefying helium ) 是由 张孔明 王华琛 于 2020-11-20 设计创作，主要内容包括：本发明的从液化天然气的闪蒸汽中提纯氦气并液化的系统及方法,系统设于原液化天然气出冷箱的节流阀后的手阀旁通管道上,包括闪蒸汽压力和流量控制装置、逐级分离装置、深度冷却分离纯化装置、液化装置和循环装置,闪蒸汽压力和流量控制装置用于控制进入后续装置的闪蒸汽的压力和流量,并保证氦气的回收率；逐级分离装置连通于闪蒸汽压力和流量控制装置,充分利用闪蒸汽的冷量而使闪蒸汽逐级深冷分离形成粗氦；深度冷却分离纯化装置连通于逐级分离装置,用于形成纯氦；液化装置连通于深度冷却分离纯化装置,用于形成液态氦和制冷氦气；循环装置在上述装置间循环冷却介质,向逐级分离装置、深度冷却分离纯化装置和液化装置提供冷量。(The system is arranged on a hand valve bypass pipeline behind a throttling valve of a raw liquefied natural gas outlet cold box and comprises a flash steam pressure and flow control device, a step-by-step separation device, a deep cooling separation and purification device, a liquefaction device and a circulation device, wherein the flash steam pressure and flow control device is used for controlling the pressure and flow of flash steam entering a subsequent device and ensuring the recovery rate of helium; the step-by-step separation device is communicated with the flash steam pressure and flow control device, and the cold energy of the flash steam is fully utilized to perform step-by-step cryogenic separation on the flash steam to form crude helium; the deep cooling separation and purification device is communicated with the step-by-step separation device and is used for forming pure helium; the liquefying device is communicated with the deep cooling separation and purification device and is used for forming liquid helium and refrigeration helium; the circulating device circulates cooling medium among the devices to provide cold for the step-by-step separation device, the deep cooling separation and purification device and the liquefaction device.)

1. A system for purifying helium and liquefying from flash steam of liquefied natural gas is characterized in that the system is arranged on a hand valve bypass pipeline behind a throttling valve of a raw liquefied natural gas outlet cold box, and the system comprises:

the flash steam pressure and flow control device is used for controlling the pressure and flow of flash steam entering the subsequent device and ensuring the recovery rate of helium;

the step-by-step separation device is communicated with the flash steam pressure and flow control device and can fully utilize the cold energy of the flash steam to perform step-by-step cryogenic separation on the flash steam so as to form crude helium;

the deep cooling separation and purification device is communicated with the step-by-step separation device and is used for purifying the crude helium to form pure helium;

the liquefying device is communicated with the deep cooling separation and purification device and is used for liquefying the pure helium by adopting pure helium circulating expansion, pure helium liquefying expansion and pure helium throttling liquefaction processes to form liquid helium and refrigeration helium; and

a circulating device for circulating a cooling medium among the stepwise separation device, the deep cooling separation and purification device, and the liquefaction device, and capable of supplying cold to the stepwise separation device, the deep cooling separation and purification device, and the liquefaction device;

wherein the cooling medium comprises the refrigerated helium gas.

2. The system for purifying and liquefying helium from flash vapor of liquefied natural gas as claimed in claim 1, wherein the flash vapor pressure and flow control device comprises a gas-liquid separation device, a flow control valve, a pressure control valve and a pressure controller, an inlet of the flow control valve is communicated with a gas phase outlet of the gas-liquid separation device, and an outlet of the flow control valve is communicated with the progressive separation device;

the pressure control valve and the pressure controller are disposed at an inlet of the gas-liquid separation device.

3. The system for purifying and liquefying helium from flash vapor of liquefied natural gas as claimed in claim 1, wherein the stepwise separation means comprises a plurality of temperature intervals arranged in sequence from bottom to top, the plurality of temperature intervals having gradually lower temperatures from bottom to top;

flash steam can loop through from bottom to top between a plurality of temperature intervals, make between a plurality of temperature intervals can be right flash steam carries out cryrogenic step by step.

4. The system for purifying and liquefying helium from flash vapor of liquefied natural gas according to claim 3, wherein the stepwise separation means comprises four temperature intervals, namely a first temperature interval, a second temperature interval, a third temperature interval and a fourth temperature interval from bottom to top;

the cooling medium in the circulating device passes through the fourth temperature interval from top to bottom to provide cooling capacity for the fourth temperature interval and passes through the upper space of the third temperature interval to provide cooling capacity for the upper space of the third temperature interval;

separating a first liquid substance after the flash steam passes through the fourth temperature interval, wherein the first liquid substance passes through the third temperature interval from top to bottom so as to provide cold energy for the third temperature interval;

separating a second liquid substance from the flash steam after the flash steam passes through the third temperature interval, wherein the second liquid substance can provide cold energy for the second temperature interval;

the step-by-step separation device comprises a tank body, a first partition plate and a second partition plate, wherein the first partition plate and the second partition plate are arranged in the tank body from bottom to top at intervals;

the space between the first partition plate and the bottom wall of the tank body is the first temperature interval;

the space above the second partition board is the fourth temperature interval; a liquid collecting tank is arranged on the second partition plate, and flash steam can enter the fourth temperature interval through the liquid collecting tank;

a plurality of tube bundles are arranged on the upper surface of the first clapboard; in the vertical direction, the second liquid substance submerges each tube bundle, and the space submerged by the second liquid substance is the second temperature interval;

the space between the first partition plate and the second partition plate except the second temperature zone is the third temperature zone;

each tube bundle is respectively communicated with the first temperature interval and the third temperature interval, so that the flash steam can enter the third temperature interval from the first temperature interval through the tube bundles, and a third liquid substance is separated after the flash steam passes through the second temperature interval;

the system further comprises a liquid level control device for controlling the level of the second liquid substance so that the second liquid substance floods each tube bundle;

the temperature of the first temperature interval is between-165 ℃ and-140 ℃; the temperature of the second temperature interval is between-181 ℃ and-165 ℃; the temperature of the third temperature interval is between-205 ℃ and-185 ℃; the temperature of the fourth temperature interval is between-230 ℃ and-210 ℃.

5. The system for purifying and liquefying helium from flash vapor of liquefied natural gas as claimed in claim 4, wherein the system further comprises an external cold source, and the external cold source is capable of providing cold energy to the third temperature interval.

6. The system for purifying and liquefying helium from flash vapor of liquefied natural gas as claimed in claim 5, wherein the system further comprises a total cooling tank, the total cooling tank is communicated with the stage-by-stage separation device; the total cold box provides heat exchange places for the crude helium, the cooling medium, the pure helium, the refrigerated helium and the external cold source.

7. The system for purifying and liquefying helium from flash vapor of liquefied natural gas according to claim 6, wherein the deep cooling separation purification apparatus comprises a purification cold box, a first purification and separation tank and a second purification and separation tank; the purification cold box can provide cold energy for the crude helium;

the inlet of the first purification separation tank is communicated with the total cooling box and is used for preliminarily purifying the crude helium precooled by the total cooling box; the liquid phase outlet of the first purification and separation tank is communicated with the inlet of a pressure regulating valve, and the outlet of the pressure regulating valve is communicated with a gathering port in front of a large tank of the original liquefied natural gas;

the purification cold box is communicated with a gas phase outlet of the first purification and separation tank;

the inlet of the second purification and separation tank is communicated with the purification cold box and is used for purifying the crude helium which is subjected to deep cooling by the purification cold box;

the gas phase outlet of the second purification and separation tank is used for discharging pure helium; and a liquid phase outlet of the second purification and separation tank can be communicated with a gathering port in front of the original liquefied natural gas large tank, so that impurities generated in the second purification and separation tank can be discharged into the original liquefied natural gas large tank.

8. The system for purifying and liquefying helium from flash vapor of liquefied natural gas according to claim 7, wherein the liquefying device comprises a liquefaction cold tank, a liquefaction throttling valve, a helium liquid separation tank, a circulating expansion machine, a liquefaction expansion machine and a circulating helium flow control valve;

the inlet of the circulating helium flow control valve is communicated with the gas phase outlet of the second purification and separation tank, and the outlet of the circulating helium flow control valve is communicated with the inlet of the circulating expansion machine;

the outlet of the circulating expansion machine is communicated with the liquefaction cold box;

the outlet of the liquefaction expansion machine is communicated with the liquefaction cold box;

the inlet of the liquefaction throttling valve is communicated with the liquefaction cold box, and the outlet of the liquefaction throttling valve is communicated with the inlet of the helium liquid separation tank;

an outlet at the bottom of the helium liquid separation tank is used for discharging liquid helium, and a gas phase outlet of the helium liquid separation tank is communicated with the liquefaction cold box;

the helium acted by the circulating expansion machine and the helium discharged from a gas phase outlet of the helium liquid separation tank respectively pass through the liquefaction cold box and are mixed, and the mixture flows into the purification cold box;

wherein the liquefaction cold box provides cold for the pure helium.

9. A method for purifying helium from flash steam of liquefied natural gas and liquefying the helium is characterized by comprising the following steps:

controlling the pressure and flow of the flash steam to ensure the pressure and flow of the flash steam and helium recovery rate of a subsequent path;

the cold energy of the flash steam is fully utilized to carry out gradual cryogenic separation treatment on the flash steam to form crude helium;

carrying out deep cooling separation and purification treatment on the crude helium to form pure helium;

carrying out liquefaction treatment on the pure helium by adopting processes of pure helium circulating expansion, pure helium liquefaction expansion and pure helium throttling liquefaction to form liquid helium and refrigeration helium; and

providing a circulating cooling medium to provide cold energy in the processes of carrying out the step-by-step cryogenic separation treatment, the deep cooling separation purification treatment and the liquefaction treatment; wherein said cooling medium comprises said refrigerated helium gas.

10. The method for purifying helium gas from flash steam of liquefied natural gas and liquefying according to claim 9, wherein the flash steam is subjected to a stepwise cryogenic separation treatment comprising:

the flash steam sequentially passes through a first temperature interval, a second temperature interval, a third temperature interval and a fourth temperature interval with gradually-reduced temperatures and is subjected to gradual deep cooling; wherein the temperature of the first temperature interval is between-165 ℃ and-140 ℃; the temperature of the second temperature interval is between-181 ℃ and-165 ℃; the temperature of the third temperature interval is between-205 ℃ and-185 ℃; the temperature of the fourth temperature interval is between-230 ℃ and-210 ℃;

utilizing the cold energy of the cooling medium to provide cold energy for the upper spaces of the fourth temperature interval and the third temperature interval;

separating a first liquid substance after the flash steam passes through the fourth temperature interval, and providing cold energy for the third temperature interval by utilizing the first liquid substance to pass through the third temperature interval;

separating a second liquid substance after the flash steam passes through the third temperature interval, and providing cold energy for the second temperature interval by using the second liquid substance;

the method further comprises the following steps: and providing an external cold source to provide cold energy for the third temperature interval.

Technical Field

The invention relates to the technical field of helium purification and liquefaction in general, and particularly relates to a system and a method for purifying helium from flash steam of liquefied natural gas and liquefying the helium.

Background

Helium is an important strategic material, and has very important application and high strategic position in the fields of chip manufacturing, aerospace, national defense, low-temperature superconduction, semiconductor production, optical fiber, nuclear magnetic resonance, special metal smelting, gas leakage detection and the like.

Helium can provide an ultra-clean environment for chip manufacturing and solve the rocket fuel manufacturing challenges. In 23 days 7 and 7 in 2020, the Changyang fifth-carrier rocket successfully launches the first Mars detection task 'Tianwenyi' detector in China to lift off and send into a preset track, wherein helium is used as fuel of a pumping rocket; in addition, helium gas can achieve rapid cooling of parts in the semiconductor chip, thereby improving productivity, and also can control a heat transfer rate to improve production efficiency and reduce defects.

From the standpoint of helium distribution, helium is extremely rare and non-renewable on earth and is known as "gaseous rare earth", the united states is the world's largest helium resource country, and the global helium resource amounts to about 520 billion cubic meters, with 206 billion united states, 100 billion kata, 82 billion arabia and liya, and 70 billion russia, accounting for about 90% of reserves, with over one third of the world's helium reserves in the united states, and with only 11 billion cubic meters of helium reserves in china, belonging to "poor helium countries".

From the helium production perspective, the current mainstream technology is natural gas stripping of helium, and the united states has the largest helium-rich natural gas field worldwide and the largest helium producing country worldwide. In 2018, the global helium yield is 1.6 billion cubic meters, the local yield in the United states accounts for 56.25 percent of the world, and the market can be called as a super helium market.

However, not only is the helium storage capacity small in China, but also helium-rich natural gas fields are few, the cost for directly extracting helium is high, and industrialization is difficult to realize. In 2018, the total helium demand of China is about 2200 million cubic meters (about 4000 tons), 95 percent of helium comes from import, and China currently needs about 4300 tons of helium per year.

In recent years, with the rapid development of high technology in aerospace, defense industry and the like in China, the demand of helium is more and more large, and in 2016-2018, the demand of helium in China maintains approximately 20% of acceleration rate, so that helium is more and more expensive in recent years. The average price of helium imported in China in 2019 is $ 57/kg, and is greatly increased by 18% compared with $ 48/kg in the same period in 2018.

In summary, helium resources are the "rare earths" in gases for china. Helium gas has risen to the height of national benefits and national safety, and therefore, the self-production of high-purity helium is a requirement of national safety and a requirement of industrial development in China.

As the process equipment for extracting helium is more, the technical route is long, the cost is high, and the market competitiveness is lacked. The technology for purifying and liquefying helium is relatively complex, the technology is mainly mastered in America and strictly blocks China all the time, helium resources in China can be almost obtained from natural gas only, and the content is generally low, so that the technology is used for simultaneously developing and co-producing high-purity helium in the existing mature natural gas liquefaction industry, is a necessary way for extracting the high-purity helium, and has important significance for improving the economy of the whole device. However, most of the prior art techniques for purifying helium and liquefying consume much energy, resulting in excessive costs.

Disclosure of Invention

Embodiments of the present invention provide a system and a method for purifying helium from flash vapor of liquefied natural gas and liquefying the same, which can purify helium and liquefy the same with less energy consumption.

The system for purifying and liquefying helium from flash steam of liquefied natural gas in the embodiment of the invention is arranged on a hand valve bypass pipeline behind a throttling valve of a raw liquefied natural gas outlet cold box, and comprises:

the flash steam pressure and flow control device is used for controlling the pressure and flow of flash steam entering the subsequent device and ensuring the recovery rate of helium;

the step-by-step separation device is communicated with the flash steam pressure and flow control device and can fully utilize the cold energy of the flash steam to perform step-by-step cryogenic separation on the flash steam so as to form crude helium;

the deep cooling separation and purification device is communicated with the step-by-step separation device and is used for purifying the crude helium to form pure helium;

the liquefying device is communicated with the deep cooling separation and purification device and is used for liquefying the pure helium by adopting pure helium circulating expansion, pure helium liquefying expansion and pure helium throttling liquefaction processes to form liquid helium and refrigeration helium; and

a circulating device for circulating a cooling medium among the stepwise separation device, the deep cooling separation and purification device, and the liquefaction device, and capable of supplying cold to the stepwise separation device, the deep cooling separation and purification device, and the liquefaction device;

wherein the cooling medium comprises the refrigerated helium gas.

According to some embodiments of the present invention, the flash steam pressure and flow control device comprises a gas-liquid separation device, a flow control valve, a pressure control valve and a pressure controller, wherein an inlet of the flow control valve is communicated with a gas phase outlet of the gas-liquid separation device, and an outlet of the flow control valve is communicated with the step-by-step separation device;

the pressure control valve and the pressure controller are disposed at an inlet of the gas-liquid separation device.

According to some embodiments of the present invention, the step-by-step separation device includes a plurality of temperature intervals arranged in sequence from bottom to top, the plurality of temperature intervals having gradually lower temperatures from bottom to top;

flash steam can loop through from bottom to top between a plurality of temperature intervals, make between a plurality of temperature intervals can be right flash steam carries out cryrogenic step by step.

According to some embodiments of the invention, the stepwise separation means comprises four temperature intervals, a first temperature interval, a second temperature interval, a third temperature interval and a fourth temperature interval from bottom to top;

the cooling medium in the circulating device passes through the fourth temperature interval from top to bottom to provide cooling capacity for the fourth temperature interval and passes through the upper space of the third temperature interval to provide cooling capacity for the upper space of the third temperature interval;

separating a first liquid substance after the flash steam passes through the fourth temperature interval, wherein the first liquid substance passes through the third temperature interval from top to bottom so as to provide cold energy for the third temperature interval;

separating a second liquid substance from the flash steam after the flash steam passes through the third temperature interval, wherein the second liquid substance can provide cold energy for the second temperature interval;

the step-by-step separation device comprises a tank body, a first partition plate and a second partition plate, wherein the first partition plate and the second partition plate are arranged in the tank body from bottom to top at intervals;

the space between the first partition plate and the bottom wall of the tank body is the first temperature interval;

the space above the second partition board is the fourth temperature interval; a liquid collecting tank is arranged on the second partition plate, and flash steam can enter the fourth temperature interval through the liquid collecting tank;

a plurality of tube bundles are arranged on the upper surface of the first clapboard; in the vertical direction, the second liquid substance submerges each tube bundle, and the space submerged by the second liquid substance is the second temperature interval;

the space between the first partition plate and the second partition plate except the second temperature zone is the third temperature zone;

each tube bundle is respectively communicated with the first temperature interval and the third temperature interval, so that the flash steam can enter the third temperature interval from the first temperature interval through the tube bundles, and a third liquid substance is separated after the flash steam passes through the second temperature interval;

the system further comprises a liquid level control device for controlling the level of the second liquid substance so that the second liquid substance floods each tube bundle;

the temperature of the first temperature interval is between-165 ℃ and-140 ℃; the temperature of the second temperature interval is between-181 ℃ and-165 ℃; the temperature of the third temperature interval is between-205 ℃ and-185 ℃; the temperature of the fourth temperature interval is between-230 ℃ and-210 ℃.

According to some embodiments of the present invention, the system further comprises an external cold source, and the external cold source can provide cold for the third temperature interval.

According to some embodiments of the invention, the system further comprises a total cold box, the total cold box being in communication with the progressive separation device; the total cold box provides heat exchange places for the crude helium, the cooling medium, the pure helium, the refrigerated helium and the external cold source.

According to some embodiments of the invention, the deep cooling separation purification apparatus comprises a purification cold box, a first purification and separation tank, and a second purification and separation tank; the purification cold box can provide cold energy for the crude helium;

the inlet of the first purification separation tank is communicated with the total cooling box and is used for preliminarily purifying the crude helium precooled by the total cooling box; the liquid phase outlet of the first purification and separation tank is communicated with the inlet of a pressure regulating valve, and the outlet of the pressure regulating valve is communicated with a gathering port in front of a large tank of the original liquefied natural gas;

the purification cold box is communicated with a gas phase outlet of the first purification and separation tank;

the inlet of the second purification and separation tank is communicated with the purification cold box and is used for purifying the crude helium which is subjected to deep cooling by the purification cold box;

the gas phase outlet of the second purification and separation tank is used for discharging pure helium; and a liquid phase outlet of the second purification and separation tank can be communicated with a gathering port in front of the original liquefied natural gas large tank, so that impurities generated in the second purification and separation tank can be discharged into the original liquefied natural gas large tank.

According to some embodiments of the invention, the liquefaction plant comprises a liquefaction cold tank, a liquefaction throttle valve, a helium gas liquid separation tank, a recycle expander, a liquefaction expander and a recycle helium gas flow control valve;

the inlet of the circulating helium flow control valve is communicated with the gas phase outlet of the second purification and separation tank, and the outlet of the circulating helium flow control valve is communicated with the inlet of the circulating expansion machine;

the outlet of the circulating expansion machine is communicated with the liquefaction cold box;

the outlet of the liquefaction expansion machine is communicated with the liquefaction cold box;

the inlet of the liquefaction throttling valve is communicated with the liquefaction cold box, and the outlet of the liquefaction throttling valve is communicated with the inlet of the helium liquid separation tank;

an outlet at the bottom of the helium liquid separation tank is used for discharging liquid helium, and a gas phase outlet of the helium liquid separation tank is communicated with the liquefaction cold box;

the helium acted by the circulating expansion machine and the helium discharged from a gas phase outlet of the helium liquid separation tank respectively pass through the liquefaction cold box and are mixed, and the mixture flows into the purification cold box;

wherein the liquefaction cold box provides cold for the pure helium.

The method for purifying helium from flash steam of liquefied natural gas and liquefying the helium comprises the following steps of:

controlling the pressure and flow of the flash steam to ensure the pressure and flow of the flash steam and helium recovery rate of a subsequent path;

the cold energy of the flash steam is fully utilized to carry out gradual cryogenic separation treatment on the flash steam to form crude helium;

carrying out deep cooling separation and purification treatment on the crude helium to form pure helium;

carrying out liquefaction treatment on the pure helium by adopting processes of pure helium circulating expansion, pure helium liquefaction expansion and pure helium throttling liquefaction to form liquid helium and refrigeration helium; and

providing a circulating cooling medium to provide cold energy in the processes of carrying out the step-by-step cryogenic separation treatment, the deep cooling separation purification treatment and the liquefaction treatment; wherein said cooling medium comprises said refrigerated helium gas.

According to some embodiments of the invention, the step-by-step cryogenic separation treatment of the flash steam comprises:

the flash steam sequentially passes through a first temperature interval, a second temperature interval, a third temperature interval and a fourth temperature interval with gradually-reduced temperatures and is subjected to gradual deep cooling; wherein the temperature of the first temperature interval is between-165 ℃ and-140 ℃; the temperature of the second temperature interval is between-181 ℃ and-165 ℃; the temperature of the third temperature interval is between-205 ℃ and-185 ℃; the temperature of the fourth temperature interval is between-230 ℃ and-210 ℃;

utilizing the cold energy of the cooling medium to provide cold energy for the upper spaces of the fourth temperature interval and the third temperature interval;

separating a first liquid substance after the flash steam passes through the fourth temperature interval, and providing cold energy for the third temperature interval by utilizing the first liquid substance to pass through the third temperature interval;

separating a second liquid substance after the flash steam passes through the third temperature interval, and providing cold energy for the second temperature interval by using the second liquid substance;

the method further comprises the following steps: and providing an external cold source to provide cold energy for the third temperature interval.

One embodiment in the above application has the following advantages or benefits:

the system and the method for purifying helium from flash steam of liquefied natural gas and liquefying break through the conventional technical means of firstly carrying out rewarming and pressurizing on the flash steam in the prior art or related technologies, but continuously carry out step-by-step deep cooling and step-by-step separation operation on the flash steam by utilizing the cold energy of the flash steam, and remove most of hydrocarbons and nitrogen in the flash steam based on the different boiling points of all components in the flash steam. Therefore, the amount of crude helium for removing most of methane and nitrogen is greatly less than that of flash steam, the recovery rate of helium is not influenced too much, the energy consumption of a subsequent purification device and liquefaction is greatly reduced, and the problem of high energy consumption in the prior art or the related technology is effectively solved.

The embodiment of the invention fully utilizes the cold energy of flash steam generated by liquefied natural gas to remove most of hydrocarbons and most of nitrogen; after dehydrogenation and denitrification, the residual small amount of oxygen, carbon dioxide and the extremely small amount of crude helium of hydrocarbons pass through a cryogenic purification separation tank to complete purification and subsequent liquefaction under the working conditions of high pressure and low temperature.

The embodiment of the invention has the advantages of low energy consumption, low investment, high pure helium recovery rate, small equipment size, easy skid-mounting and good economic and social benefits.

Drawings

The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings.

Fig. 1 is a process flow diagram of a system for purifying and liquefying helium from flash vapor of liquefied natural gas according to an embodiment of the present invention.

Fig. 2 is a schematic structural diagram of a progressive separation apparatus according to an embodiment of the present invention.

Fig. 3 shows a schematic structural diagram of a dehydrogenation unit according to an embodiment of the present invention.

Detailed Description

Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and thus their detailed description will be omitted.

The integral idea of the invention is to firstly control the flow and pressure of flash steam, then fully utilize the cold energy of the flash steam to continue deep cooling, firstly separate and remove most of hydrocarbons and nitrogen, then remove hydrogen and most of the rest nitrogen in a step-by-step separation device by utilizing the different boiling points of all components in the flash steam, only leave a very small amount of nitrogen, methane, oxygen and the like in the rest crude helium, then purify the crude helium at high pressure and low temperature to reach the purity requirement of the commercial helium, then continue deep cooling through the cyclic expansion and liquefaction expansion of the helium, reach and exceed the liquefaction critical condition of the helium, and complete the liquefaction of the helium through throttling.

The system and the method for purifying helium from flash steam of liquefied natural gas and liquefying break through the conventional technical means of firstly carrying out rewarming and pressurizing on the flash steam in the prior art or related technologies, but continuously carry out step-by-step deep cooling and step-by-step separation operation on the flash steam by utilizing the cold energy of the flash steam, and remove most of hydrocarbons and nitrogen in the flash steam based on the different boiling points of all components in the flash steam. Therefore, the amount of crude helium for removing most of methane and nitrogen is greatly less than that of flash steam, the recovery rate of helium is not influenced too much, the energy consumption of a subsequent purification device and liquefaction is greatly reduced, and the problem of high energy consumption in the prior art or the related technology is effectively solved.

The connection relationship and the operation principle between the components of the system for purifying helium from flash vapor of liquefied natural gas and liquefying according to the embodiment of the present invention are described in detail below with reference to the accompanying drawings.

Referring to fig. 1, fig. 1 is a process flow diagram of a system for purifying and liquefying helium from flash vapor of liquefied natural gas according to an embodiment of the present invention. The system of the embodiment of the invention comprises: flash steam pressure and flow control device, multifunctional low-temperature separation device, low-temperature high-pressure deep cooling separation and purification device, liquefaction device and circulation device.

The multi-functional cryogenic separation plant 10 is used for progressively cryogenic separation of flash steam to form crude helium. The low-temperature high-pressure deep cooling separation and purification device is connected to the multifunctional low-temperature separation device 10, and the liquefaction device is connected to the low-temperature high-pressure deep cooling separation and purification device. The cryogenic high-pressure deep cooling separation purification apparatus may include a dehydrogenation unit for removing hydrogen from the crude helium, a denitrification unit for removing nitrogen from the crude helium, and a purification separation tank for purifying the crude helium to form pure helium, a first purification separation tank 811, and a second purification separation tank 805. The liquefying device is used for liquefying pure helium by adopting pure helium circulating expansion, pure helium liquefying expansion and pure helium throttling liquefaction processes to form liquid helium and refrigeration helium. The circulating device is used for circulating cooling media among the step-by-step separation device, the low-temperature high-pressure deep cooling separation and purification device and the purification device, and can provide cold energy for the step-by-step separation device, the low-temperature high-pressure deep cooling separation and purification device and the purification device.

With continued reference to fig. 1, the system of the embodiment of the present invention further includes a main cooling box 20 and a circulation pipeline, wherein the main cooling box 20 is communicated with the multi-functional step-by-step separation device 10. The total cold box 10 provides a heat exchange place for crude helium, a cooling medium, pure helium, refrigerated helium gas and an external cold source. Outlet 112 of multi-functional cryogenic separation device 10 is connected to inlet 205 of main cold box 20 so that crude helium can enter main cold box 20 from multi-functional cryogenic separation device 10.

The deep cooling separation purification apparatus includes a purification cold box 80, a first purification and separation tank 811, and a second purification and separation tank 805. The purification cold box can provide cold for the crude helium. An inlet of the first purification and separation tank 811 is communicated with the total cooling box 10 and is used for purifying helium gas pre-cooled by the total cooling box 10; the liquid phase outlet of the first purification and separation tank 811 is communicated with the inlet of a pressure regulating valve 813, and the outlet of the pressure regulating valve 813 is communicated with a large tank of the raw liquefied natural gas; the purification cold box 80 is communicated with a gas phase outlet of the first purification and separation tank 811; the inlet of the second purification and separation tank 805 is connected to the purification cold box and is used for purifying the helium gas cryogenically cooled by the purification cold box 80.

The liquefaction device comprises a liquefaction cold box 90, a liquefaction throttle valve 906, a helium liquid separation tank 907, a circulating expansion machine 902, a liquefaction expansion machine 903 and a circulating helium flow control valve 901; the inlet of the circulating helium flow control valve 901 is communicated with the gas phase outlet of the second purification and separation tank 805, and the outlet of the circulating helium flow control valve 901 is communicated with the inlet of the circulating expansion machine 902; the outlet of the circulation expansion machine 902 is communicated with the liquefaction cold box 90; the outlet of the liquefaction expansion machine 903 is communicated with the liquefaction cold box 90; the inlet of the liquefaction throttle valve 906 is communicated with the liquefaction cold box 90, and the outlet of the liquefaction throttle valve 906 is communicated with the inlet of the helium liquid separation tank 907; the bottom outlet of the helium gas-liquid separation tank 907 is used for discharging liquid helium, and the gas phase outlet of the helium gas-liquid separation tank 907 is communicated with the liquefied cold box 90; the helium acted by the circulating expansion machine 902 and the helium discharged from the gas phase outlet of the helium liquid separation tank 907 pass through the liquefaction cold box 90 respectively and are mixed, and flow into the purification cold box 80; wherein the liquefaction cold box 90 provides cold for pure helium.

Generally, flash steam of liquefied natural gas contains about 60 to 80% of methane,About 20% of nitrogen, about 2-10% of helium, a small amount of ethane, oxygen, hydrogen, carbon dioxide and the like, wherein flash steam enters from the lower inlet of the multifunctional low-temperature separation device 10, so that the cold energy of the flash steam is fully utilized, and under the cooling condition of external cold energy, the internal flash steam is gradually deep-cooled from the bottom to the top and is gradually separated. The crude helium (He% > 60%, CH) then exits the top of the multi-functional cryogenic separation device 10₄％＜ 0.5％，N₂％＜30％，H₂% of 3 to 8%, O₂、CO₂Etc. are all in ppm order).

After the flash steam passes through the multifunctional low-temperature separation device 10, most of the crude helium after the hydrocarbon and the nitrogen are removed is removed, and the flow rate of the crude helium is greatly reduced compared with the original flash steam, so that the load of subsequent devices (such as a dehydrogenation unit, a denitrification unit, a purification separation tank, a liquefaction device and the like) is greatly reduced, and the energy consumption is reduced. Therefore, the system of the embodiment of the invention has advantages over the traditional helium extraction scheme for reheating and pressurizing flash steam.

The crude helium is preheated by a total cooling box 20 from the multifunctional low-temperature separation device 10, and then is subjected to multi-stage medium-pressure dehydrogenation treatment by pressurization and heating, so that almost all hydrogen is removed; and continuously pressurizing and compressing the crude helium after the hydrogen is removed, and then removing most of nitrogen.

Thus, the crude helium after the hydrogen and most of nitrogen are removed also contains a small amount of oxygen, carbon dioxide, water, nitrogen, methane and the like, and the crude helium enters a cryogenic low-temperature high-pressure deep cooling separation and purification device. Specifically, after pre-cooling of crude helium is realized through the total cold box 20, preliminary purification is realized through the first purification and separation tank 811, deep cooling is realized through the purification and cold box 80, and further purification is realized through the second purification and separation tank 805, purification is completed in the purification and separation tank under the working condition of high pressure and low temperature, high-purity commodity helium is discharged from the top of the purification and separation tank, and impurities are discharged from the bottom of the purification and separation tank or mixed with the liquefied natural gas to enter the crude liquefied natural gas big tank.

After the high-purity helium separated from the purification separation tank is mixed with the refrigeration helium, one part of the high-purity helium enters the circulating expansion machine 902 after the helium circulation flow is controlled by the flow control valve 901, the other part of the high-purity helium enters the liquefaction critical condition of the helium after passing through the liquefaction expansion machine 903 and then is subjected to high cryogenic cooling to reach and exceed the liquefaction critical condition of the helium, and the high-purity helium enters the helium gas-liquid separation tank 907 after passing through the throttle valve 906. The bottom of the helium gas-liquid separation tank 907 is liquid helium, the top gas phase part and the helium circulating part after the helium is circularly expanded provide high cryogenic cooling capacity for the liquefied part of helium, then the residual cooling capacity provides cooling capacity for the precooled purified crude helium and the circulated precooled helium, the residual cooling capacity continues to provide matched temperature gradient cooling capacity from top to bottom in the multifunctional cryogenic separation device 10 and from bottom to top flash steam entering the multifunctional cryogenic separation device 10, and then the residual cooling capacity enters a helium circulating compressor after being preheated by the total cold box 20 to complete circulation.

The multifunctional low-temperature separation device 10 of the embodiment of the invention comprises a plurality of temperature intervals which are sequentially arranged from bottom to top, and the temperatures of the temperature intervals become lower gradually from bottom to top. The flash steam can sequentially pass through the plurality of temperature intervals from bottom to top, so that the flash steam can be deeply cooled step by step in the plurality of temperature intervals.

In this embodiment, the temperature intervals are four, and are a first temperature interval 2100, a second temperature interval 2200, a third temperature interval 2300, and a fourth temperature interval 2400 from bottom to top. Specifically, the bottom-up flash steam first passes through the first temperature zone 2100, the second temperature zone 2200, and the third temperature zone 2300 to remove most of the hydrocarbons, and then enters the fourth temperature zone 2400. The cold is exchanged with the lower temperature refrigerant in the fourth temperature interval 2400 to remove most of the nitrogen (> 80%). Thus, crude helium comes out of the top of the separation tank.

In one embodiment, the first temperature interval 2100 ranges from-165 ℃ to-140 ℃; the temperature of the second temperature interval 2200 is between-181 ℃ and-165 ℃; the temperature of the third temperature interval 2300 is between-205 ℃ and-185 ℃; the temperature of the fourth temperature interval 2400 is between-230 ℃ and-210 ℃.

The multifunctional low-temperature separation device 10 makes full use of the cold energy of flash steam and the cold energy from outside, the flash steam is cooled by exchanging with refrigerant media in different temperature ranges from bottom to top, the internal flash steam is gradually cooled from bottom to top, and is gradually separated, most of hydrocarbons (methane in the crude helium is less than 0.5%) and most of nitrogen (more than 80%) are removed, and the crude helium (more than 60%) comes out from the top.

Referring to fig. 2, fig. 2 is a schematic diagram of a multi-functional cryogenic separation device 10 according to an embodiment of the present invention. The multi-functional cryogenic separation device 10 of an embodiment of the present invention comprises a tank, a first partition 125 and a second partition 121.

The tank body is sequentially provided with a third liquid substance outlet 129, a lower flash steam inlet 101, a liquid level control outlet 127, an external cold source liquid nitrogen gasification outlet 110, an external cold source liquid nitrogen inlet 103, a second liquid substance outlet 111, a cryogenic refrigerant outlet 109, a cryogenic refrigerant inlet 108 and a crude helium outlet 112 at the top from bottom to top.

The first and second partitions 125 and 121 are provided in the tank body at intervals from bottom to top. The space between the first partition 125 and the bottom wall of the can is a first temperature range 2100. The inlet 101 for flash steam into the knock-out drum is located above the first temperature interval 2100. The second barrier 121 is disposed spaced apart from the first barrier 125 in a vertical direction. The space between the first and second separators 125 and 121 excluding the second temperature zone 2200 is a third temperature zone 2300.

The space above the first partition 125 is a second temperature zone 2200, and the upper surface of the first partition 125 is provided with a plurality of tube bundles 126. A plurality of tube bundles 126 may be welded to the first baffle 125. Each tube bundle 126 is respectively communicated with the first temperature interval 2100 and the third temperature interval 2300, and the flash steam enters the first temperature interval 2100, passes through the plurality of tube bundles 126 from bottom to top and enters the third temperature interval 2300.

The second partition plate 121 is provided with a liquid collection tank 113, and the liquid collection tank 113 is a passage through which flash steam after most of methane is removed enters the upper part of the second partition plate 121.

The tank body is internally provided with a coil 104, a coil 105, a coil 106 and a coil 107. The coil pipes 106 are wound from top to bottom, and a part of the coil pipes 106 are disposed in the fourth temperature zone 2400, and another part of the coil pipes 106 are disposed in the third temperature zone 2300 through the second barrier 121.

The tank is provided with an inlet 108 and an outlet 109, and one end of the coil 106 is connected to the inlet 108 and the other end is connected to the outlet 109. The cooling medium is in communication with the coil 106 through an inlet 108 and an outlet 109. The cooling medium can enter the coil 106 and provide cooling to the fourth temperature interval 2400 and a portion of the third temperature interval 2300.

After the flash steam enters the fourth temperature interval 2400 from bottom to top, the flash steam and the cold energy of the coil pipe 106 realize heat exchange, and the first liquid substance is separated from the flash steam. The first liquid substance is liquid nitrogen and liquefied natural gas separated from flash steam. Wherein the flash steam in the fourth temperature interval 2400 has stripped off most of the methane and most of the nitrogen.

The first liquid substance is able to pass through the second baffle 121 and flow towards the outlet 111 through the coil 105 disposed between the first baffle 125 and the second baffle 121. After exiting from outlet 111, the first liquid substance can flow into inlet 203 of total cold box 20 and exit from outlet 204, thereby effecting heat exchange. After the first liquid mass heat exchange is complete and exits the outlet 204, it may be returned to the large tank of raw liquefied natural gas.

The cooling capacity remained after the cooling medium exchanges cold with the flash steam in the fourth temperature interval 2400 can exchange cold with the flash steam in the third temperature interval 2300 through the coil pipe 106. Wherein the flash steam in the third temperature interval 2300 has stripped most of the methane. The flash steam after the cold exchange in the third temperature interval 2300 can separate liquefied natural gas, and the liquefied natural gas falls on the first partition 125 and forms a liquid level in the second temperature interval 2200.

Meanwhile, the cold energy of the first liquid substance in the coil 105 can be exchanged with the flash steam from which most of the methane is removed in the third temperature interval 2300, so that the generated liquefied natural gas can fall on the first partition 125 and form a liquid level in the second temperature interval 2200.

Of course, it is understood that an external cold source, such as liquid nitrogen, may be provided to prevent insufficient cold in the third temperature interval 2300 or when the system is powered on. An external cold source is communicated with the coil 104 through the inlet 103 and flows out of the outlet 110, so that cold can be provided for the third temperature interval 2300. After passing through the third temperature zone 2300, the external cold source may be communicated with the inlet 201 of the total cold box 20 and flow out of the outlet 202, thereby implementing heat exchange. After the flash vapor from which most of the methane is removed is cooled by the coil 104, the resulting lng also falls on the first partition 125 and forms a liquid level in the second temperature interval 2200. Meanwhile, the external cold source can supplement cold when the operation fluctuation cold is insufficient, or supplement cold when the system is just started.

That is, the second liquid substance separated after the flash vapor passes through the third temperature section 2300 (the cold energy in the third temperature section 2300 may be from the coil 104, the coil 105 and a part of the coil 106) includes the lng generated by the flash vapor and the coil 104, the coil 105 and a part of the coil 106.

The upper surface of the first partition 125 should have a certain level formed by the second liquid substance. That is, in the vertical direction, the second liquid substance is required to flood at least part of each tube bundle 126, and the space flooded by the second liquid substance is the second temperature interval 2200.

Of course, it is understood that the coil 106 may not pass through the second partition 121 into the third temperature zone 2300, but rather may first pass through the multi-functional cryogenic separation device 10, enter the space below the second partition 121, exchange the cold with the coil 107, and then pass into the outlet 109.

It will be appreciated that the coils 104, 105, 106 and 107 described above may be intertwined to provide maximum cold exchange area to provide maximum cold exchange capacity.

Each tube bundle 126 is respectively communicated with the first temperature interval 2100 and the third temperature interval 2300, so that the flash steam can enter the third temperature interval 2300 from the first temperature interval 2100 through the tube bundle 126, and can exchange cold with the second liquid substance when passing through the second temperature interval 2200 to generate the third liquid substance. The third liquid substance may comprise lng from which flash vapor falls after cryogenic cooling in the second temperature interval 2200. The lng drops to the bottom of the tank (i.e., first temperature interval 2100) and may be returned to the raw lng tank through outlet 129 and controlled by valve 114. The third liquid substance can be discharged by means of the head of the bottom outlet 129.

In one embodiment, the surface of the housing of the multi-functional cryogenic separation device 10 can be subjected to deep cold-holding treatment.

The level control device is used to control the level of the second liquid substance so that the second liquid substance can flood each tube bundle 126. The fluid level control device may include a fluid level display 102 and a fluid level control valve 115. When the level of the second liquid substance is too high, the level control valve 115 may be controlled to open to allow the second liquid substance to flow out of the outlet 127.

The inlet 206 of the crude helium dehydrogenation compressor 30 is connected with the total cooling box 20, and a crude helium return pipeline is connected between the crude helium dehydrogenation compressor 30 and the total cooling box 20 and is controlled by a valve 120, so that unqualified crude helium can be returned to the raw liquefied natural gas large tank.

Crude helium coming out of the top of the multifunctional low-temperature separation device 10 is reheated by a total cooling box 20, then is pressurized to medium pressure by a crude helium dehydrogenation compressor 30 and enters dehydrogenation equipment for medium-pressure dehydrogenation, and almost all hydrogen is removed; if the crude helium is unqualified, the flash steam can also be returned to the liquefied natural gas large tank through a flash steam return line.

It is understood that lng, vaporized liquid nitrogen, and rejected crude helium, purified impurities, etc. generated during the helium stripping separation process may be connected to the lng export inlet via the return manifold port 122.

The helium dehydrogenation compressor 30 is connected to the crude helium dehydrogenation heater 301, and the heated crude helium enters the dehydrogenation equipment 40.

The dehydrogenation unit 40 may be a palladium tube dehydrogenation or a palladium catalytic dehydrogenation.

As shown in fig. 3, fig. 3 is a schematic structural diagram of a dehydrogenation unit according to an embodiment of the present invention. Crude helium enters the dehydrogenation unit 40 through an inlet 401, high-purity hydrogen flows out through an outlet 402 under the action of a palladium pipe 404, and hydrogen-free gas flows out through an outlet 403.

Specifically, metal palladium (Pd) has high selectivity and permeability to hydrogen, hydrogen is introduced into a palladium tube, hydrogen molecules are decomposed into hydrogen atoms on the surface of a palladium alloy membrane under the catalytic action of palladium, and the hydrogen atoms are further ionized into hydrogen ions, namely

H₂-----→2H

H-----→H⁺+e

And with H⁺Permeates through the palladium alloy membrane, and has a hydrogen ion radius of 1.5X 10 due to the lattice constant of 0.338nm of palladium^-6nm, then combine with electrons to form hydrogen atoms, which recombine to form hydrogen molecules, i.e.

H⁺+e-----→H

H+H-----→H₂

The palladium alloy membrane allows only hydrogen to pass through, while other gas molecules hardly pass through. This is because the catalytic action of metallic palladium and the high permeability of palladium to hydrogen, oxygen impurities remain on one side of the palladium tube with the hydrogenation of water under the catalytic action of the palladium alloy.

If the palladium catalytic dehydrogenation is adopted, the method comprises a reaction bed, a reaction gas inlet, an oxygen inlet, a proportional mixer, a combustor, a cooler and the like, wherein excess high-purity oxygen, hydrogen and a very small amount of methane are introduced to perform combustion reaction on the reaction bed to generate water and carbon dioxide (or carbon monoxide), and the rest excess oxygen, helium, nitrogen, water and carbon dioxide.

H₂+O₂-----→H₂O

CH₄+O₂-----→CO₂+H₂O

The catalytic combustion can realize complete combustion oxidation of hydrogen, methane and the like at low temperature (200-400 ℃) by means of the action of a palladium catalyst, and has the advantages of low energy consumption, convenient and safe operation and high purification efficiency.

The crude helium after hydrogen removal by the palladium tube contains helium, a very small amount of methane, oxygen and a small amount of nitrogen; the crude helium after hydrogen removal by the palladium catalytic reaction contains helium and a small amount of nitrogen, oxygen, carbon dioxide and water.

The crude helium after hydrogen removal is subjected to high-pressure denitrification by a crude helium denitrification compressor and a high-pressure denitrification device, most of nitrogen is removed, and the device can be used for regeneration operation, one denitrification and the other regeneration.

Referring to fig. 1, the dehydrogenation unit 40 is connected to a pre-air cooler 501, and a crude helium denitrification compressor 50 is disposed between the post-air cooler 502 and the pre-air cooler 501.

The after-air cooler 502 is connected to the inlet 601 of the denitrification unit, the outlet 602 of which is connected to the inlet 209 of the main cooling box 20.

The denitrification device 60 is composed of denitrification molecular sieves 604A and 604B, the inlet and outlet of the denitrification molecular sieve 604A are respectively controlled by valves 603A and 603C, and the inlet and outlet of the denitrification molecular sieve 604B are respectively controlled by valves 603B and 603D.

In the present embodiment, the outlet 2010 of the total cold box 20 is connected to the inlet of the first purification and separation tank 811, and the gas phase outlet of the first purification and separation tank 811 is connected to the inlet 801 of the purification cold box 80. A liquid phase outlet 812 at the bottom of the first purification and separation tank 811 is pressure-regulated by a pressure regulating valve 813, mixed with the generated liquefied natural gas via a pipe 814, and introduced into the LNG bomb through the collection port 122. It can be understood that the crude helium after the removal of hydrogen, most of methane and nitrogen after pressurization contains helium and a very small amount of nitrogen, oxygen, methane, carbon dioxide, water and the like, and enters a cryogenic purification system after being precooled by the total cooling box 20, under the working conditions of high pressure and low temperature, the purification is completed by the first and second purification separation tanks, the gas discharged from the top of the second purification separation tank 805 is high-purity commodity helium, the gas discharged from the bottom is impurities, and the impurities are discharged out of the device.

The purification cold box 80 is connected to the inlet 804 of the second purification and separation tank 805. The gas phase outlet 809 of the second purification and separation tank 805 is connected with the outlet of the circulating helium check valve 807 for mixing, one part of the mixed gas enters the circulating helium flow control valve 901 and the helium circulating expansion machine 902, and the other part of the mixed gas enters the helium liquefying expansion machine 903. The bottom of the second purification and separation tank 805 is provided with a liquid phase outlet 8010 for discharging purified impurities.

On one hand, the purification of the crude helium must ensure enough cold quantity, and some trace impurities such as methane, nitrogen, oxygen, carbon dioxide, water and the like are completely removed under the working condition of low temperature and high pressure to meet the requirement of commercial helium; on the other hand, in the foregoing process, as much impurities as possible should be removed, so that the concentration of impurities in the purified helium gas is as low as possible, and the crude helium tube bundle in the purification cold box 80 cannot be frozen and blocked, therefore, a helium gas circulation process is required, and the amount of the circulated helium gas and other process parameters are comprehensively considered by controlling.

Referring to fig. 1, lng, liquid nitrogen, unqualified crude helium, purified impurities, etc. generated during the helium extraction separation process may be connected to the inlet 3 of the large tank through the return header 122.

The helium flow control valve 901 is connected to a helium recycle expander 902, the outlet 905 of which is connected to the liquefaction cold box 90.

The embodiment of the invention fully utilizes the characteristics of helium and adopts the processes of high-pressure helium circulating expansion, high-pressure helium liquefying expansion and medium-pressure helium throttling liquefaction.

An outlet 904 of the helium liquefaction expansion machine is connected with the liquefaction cold box 90, an outlet 9012 of the liquefaction cold box 90 is connected with a helium liquefaction throttling valve 906, and the other end of the helium liquefaction throttling valve 906 is connected with a helium liquid separation tank 907.

The outlet at the bottom of the helium liquid separation tank 907 is a liquid helium outlet 908, the top gas phase outlet 9013 is connected with the inlet 909 of the gas helium liquefaction cold box 90, the outlet 9010 of the gas helium liquefaction cold box 90 is mixed with the outlet 9011 of the circulating helium liquefaction cold box 90, the mixing port 9014 of the two is connected with the inlet 806 of the circulating helium purification cold box 80, and the outlet 808 of the circulating helium purification cold box 80 is connected with the inlet 108 of the multifunctional cryogenic separation device 10.

After the high-purity helium separated by the purification and separation tank 805 is mixed with circulating helium gas, one part of the high-purity helium enters a pure helium circulating expansion machine 902, the other part of the high-purity helium passes through a pure helium liquefying expansion machine 903 and then is deeply deep-cooled to reach and exceed the liquefying critical condition of the helium gas, and the high-purity helium enters a helium gas-liquid separation tank 907 after passing through a throttle valve 906; the bottom of the helium gas-liquid separation tank 907 is liquid helium, the top gas phase part and the helium gas after cyclic expansion are combined together to provide high cryogenic cooling capacity for part of the helium gas to be liquefied, then the residual cooling capacity provides cooling capacity for the pre-cooled crude helium to be purified and the cyclic pre-cooled helium gas, the residual cooling capacity provides matched temperature gradient cooling capacity for flash steam entering a fourth temperature interval 2400 and a third temperature interval 2300 inside the multifunctional low-temperature separation device 10, and the flash steam enters a helium gas circulating compressor through a total cooling box 20 for reheating to complete circulation.

The outlet 109 of the multi-functional cryogenic separation device 10 is connected to the helium recycle preheat inlet 207 of the main cold box 20.

The helium recycle preheat outlet 208 of the total cold box 20 is connected to the inlet 703 of the pre-buffer tank 701 of the helium recycle compressor 70.

The gas phase outlet 704 of the pre-buffer tank 701 of the helium gas circulation compressor 70 is connected with the helium gas circulation compressor 70, the helium gas circulation compressor 70 is connected with the after-air cooler 702, and the after-air cooler 702 is connected with the helium gas circulation pre-cooling inlet 2011 of the total cooling box 20.

A helium circulating pre-cooling outlet 2012 of the total cooling box 20 is connected with a circulating helium cryogenic inlet 802 of the crude helium purification cooling box 80, a circulating helium cryogenic outlet 803 of the purification cooling box 80 is connected with one end of a circulating helium check valve 807, and the other end of the check valve 807 is respectively connected with an inlet of a helium liquefaction expansion machine 903, an inlet of a circulating helium flow control valve 901 and a gas phase outlet 809 of the purification separation tank.

As can be seen from the above description of the main cold box 20, the purification cold box 80, and the liquefaction cold box 90, the main cold box 20 provides a place for heat exchange between crude helium, circulating pure helium, helium gas for refrigeration, and cryogenic nitrogen, the purification cold box 80 can provide cold for crude helium, and the liquefaction cold box 90 can provide cold for pure helium.

As an example, all equipment, connecting pipes, valves, containers, meters, etc. requiring low temperature are subjected to deep cold insulation treatment.

The system for purifying and liquefying helium from flash steam of liquefied natural gas can be arranged in front of an original large liquefied natural gas tank and is arranged on a hand valve bypass pipeline behind a throttling J-T valve of a raw liquefied natural gas outlet cold box, so that the system provided by the embodiment of the invention cannot influence the production operation of a raw liquefied natural gas plant, and liquefied natural gas and unqualified crude helium from different device nodes can be recovered.

Specifically, the liquefied natural gas from the cold box of the original liquefied natural gas factory enters the system of the embodiment of the invention from the outlet 1 and crosses the hand valve 5 behind the original J-T valve 2, namely the system of the embodiment of the invention is installed on the bypass pipeline of the hand valve 5 behind the J-T valve 2 of the original liquefied natural gas entering the large tank and enters the system through the inlet hand valve 123 of the system; liquefied natural gas and unqualified helium from the system return to the gathering port 122 through the outlet hand valve 124 of the system and then enter the original liquefied natural gas large tank through the hand valve 4 and the inlet 3.

The flash steam pressure and flow control device of the embodiment of the invention comprises a gas-liquid separation tank 116, a flow control valve 117, a liquid level control valve 118, a flow controller 119, a pressure control valve 130 and a pressure controller 131. An inlet of the flow control valve 117 is communicated with a gas phase outlet of the gas-liquid separation device 116, and an outlet of the flow control valve 117 is communicated with the progressive separation device 10. A pressure control valve 130 and a pressure controller 131 are provided at the inlet of the gas-liquid separation device 113.

Liquefied natural gas which comes from the outside of the system and is in a quasi-saturated state after being throttled by the J-T valve enters the gas-liquid separation device 116 at the inlet of the system, and a flash steam flow control valve 117 is arranged at a gas phase outlet of the gas-liquid separation device 116 to control the flash steam flow of a subsequent device so as to ensure the flow requirement and the cold requirement of a helium extraction device and ensure the recovery rate of helium. A flow controller 119 is installed on the gas phase outlet pipe to confirm the amount of flash steam.

Of course, it is understood that the system of the embodiment of the invention can also be installed at the flash steam outlet at the top of the raw liquefied natural gas tank.

The gas-liquid separation device 116 is used for performing gas-liquid separation on the liquefied natural gas, flash steam coming out of the top of the gas-liquid separation device 116 enters from the bottom of the multifunctional low-temperature separation device 10, and the liquefied natural gas coming out of the bottom of the gas-liquid separation device 116 enters a liquefied natural gas large tank of a raw liquefaction plant after being controlled by a liquid level control valve 118.

In one embodiment, the gas-liquid separation device 116 may be a horizontal separator to evaporate the maximum amount of helium over as large an area as possible.

The gas phase outlet conduit 128 of the gas-liquid separation device 116 is connected to the lower inlet connection 101 of the multi-functional cryogenic separation device 10.

The height of the gas-liquid separation device 116 is lower than that of the multifunctional cryogenic separation device 10, so that the liquefied natural gas generated at the bottom of the multifunctional cryogenic separation device 10 can be collected into the bottom outlet of the gas-liquid separation device through the outlet valve by the height difference of the outlet valve and the multifunctional cryogenic separation device.

The embodiment of the invention also provides a method for purifying helium from flash steam of liquefied natural gas and liquefying the helium, which comprises the following steps:

controlling the pressure and flow of the flash steam to ensure the pressure and flow of the flash steam and helium recovery rate of a subsequent path;

the cold energy of the flash steam is fully utilized to carry out gradual cryogenic separation treatment on the flash steam to form crude helium;

carrying out deep cooling separation and purification treatment on the crude helium to form pure helium;

carrying out liquefaction treatment on the pure helium by adopting processes of pure helium circulating expansion, pure helium liquefaction expansion and pure helium throttling liquefaction to form liquid helium and refrigeration helium; and

providing a circulating cooling medium to provide cold energy in the processes of carrying out the step-by-step cryogenic separation treatment, the deep cooling separation purification treatment and the liquefaction treatment; wherein said cooling medium comprises said refrigerated helium gas.

In one embodiment, the flash steam is subjected to a step-by-step cryogenic separation treatment, which includes:

the flash steam sequentially passes through a first temperature interval, a second temperature interval, a third temperature interval and a fourth temperature interval with gradually-reduced temperatures and is subjected to gradual deep cooling;

wherein the temperature of the first temperature interval is between-165 ℃ and-140 ℃; the temperature of the second temperature interval is between-181 ℃ and-165 ℃; the temperature of the third temperature interval is between-205 ℃ and-185 ℃; the temperature of the fourth temperature interval is between-230 ℃ and-210 ℃;

utilizing the cold energy of the cooling medium to provide cold energy for the upper spaces of the fourth temperature interval and the third temperature interval;

separating a first liquid substance after the flash steam passes through the fourth temperature interval, and providing cold energy for the third temperature interval by utilizing the first liquid substance to pass through the third temperature interval;

separating a second liquid substance after the flash steam passes through the third temperature interval, and providing cold energy for the second temperature interval by using the second liquid substance;

the method further comprises the following steps: and providing an external cold source to provide cold energy for the third temperature interval.

The method of the embodiment of the invention fully utilizes the technical means of flash steam pressure flow control, flash steam cold energy low-temperature low-pressure gradual removal of most of hydrocarbons and nitrogen, crude helium (high-temperature) medium-pressure dehydrogenation, crude helium (normal-temperature) high-pressure denitrification, crude helium low-temperature high-pressure purification, pure helium low-temperature high-pressure expansion and throttling liquefaction, pure helium low-temperature high-pressure expansion cycle and normal-temperature pressurization cycle.

In summary, the system and the method for purifying helium from flash steam of liquefied natural gas and liquefying the helium according to the embodiment of the invention have the advantages and beneficial effects that:

(1) the system implemented by the invention is arranged in front of the large tank of the original liquefied natural gas and on the by-pass pipeline of the hand valve behind the throttling J-T valve of the liquefied natural gas outlet cold box, does not influence the production operation of the original liquefied natural gas factory, and can recover the liquefied natural gas and unqualified crude helium from different device nodes.

(2) According to the embodiment of the invention, the characteristics of the flash steam of the liquefied natural gas are fully utilized, the pressure and flow control valve of the flash steam is arranged at the inlet of the device, the pressure and flow requirements and the cold requirement of the subsequent device can be met by adjusting the pressure and flow of the flash steam, and the helium recovery rate is improved to the greatest extent.

(3) The embodiment of the invention breaks through the conventional technical means of firstly carrying out rewarming pressurization on the flash steam in the prior art or the related technology, but fully utilizes the cold energy of the flash steam under certain flash steam pressure, and continuously carries out step-by-step deep cooling and step-by-step separation operation on the flash steam by utilizing different temperature intervals to remove most of hydrocarbons and nitrogen. Therefore, the amount of crude helium for removing most of methane and nitrogen is greatly less than that of flash steam, the recovery rate of helium is not greatly influenced, and the energy consumption of purification and liquefaction of a subsequent device is greatly reduced.

(4) The embodiment of the invention fully utilizes the temperature gradients at different nodes of the subsequent path to provide cold energy for flash steam and crude helium at different nodes, thereby greatly saving energy consumption.

(5) In order to produce liquid helium, crude helium must be purified first, and then sufficient cold energy is provided for high-purity helium.

(6) The embodiment of the invention fully utilizes the characteristics of helium, adopts the processes of high-pressure helium circulating expansion, high-pressure helium liquefying expansion and medium-pressure helium throttling liquefaction, improves the working conditions of the expansion machine, and greatly reduces the design and processing requirements on the expansion machine.

In the embodiments of the invention, the terms "first", "second", and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance; the term "plurality" means two or more unless expressly limited otherwise. The terms "mounted," "connected," "fixed," and the like are to be construed broadly, and for example, "connected" may be a fixed connection, a removable connection, or an integral connection; "coupled" may be direct or indirect through an intermediary. Specific meanings of the above terms in the embodiments of the invention may be understood by those of ordinary skill in the art according to specific situations.

In the description of the embodiments of the present invention, it should be understood that the terms "upper", "lower", "left", "right", "front", "rear", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the embodiments of the present invention and simplifying the description, but do not indicate or imply that the referred device or unit must have a specific direction, be configured and operated in a specific orientation, and thus, should not be construed as limiting the embodiments of the present invention.

In the description herein, reference to the term "one embodiment," "some embodiments," "a specific embodiment," or the like, means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of an embodiment of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The above embodiments are merely preferred embodiments of the present invention, and are not intended to limit the present invention, and various modifications and changes may be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the embodiments of the invention should be included in the protection scope of the embodiments of the invention.