Process for co-production of LNG and helium by cryogenic-membrane separation of natural gas

Abstract

The present application relates to a kind of co-production LNG natural gas cryogenic-membrane separation helium extraction process.The present application includes crude helium extraction unit, membrane separation unit, heat exchange unit, mixed refrigerant refrigeration system, nitrogen expansion cycle refrigeration system.Crude helium extraction unit includes first-stage helium extraction column and second-stage helium extraction column;Membrane separation unit includes first-stage membrane separator and second-stage membrane separator;Heat exchange unit includes heat exchanger;Mixed refrigerant refrigeration system includes compressor, cooler, gas-liquid separator, throttle valve;Nitrogen expansion cycle refrigeration system includes compressor, cooler and throttle valve.The production process uses the technical scheme of mixed refrigerant refrigeration+nitrogen expansion cycle refrigeration+double-tower cryogenic rectification crude helium extraction+membrane separation fine helium extraction.The process is under the same condition with other processes, helium recovery rate is high, energy consumption is low, device operating temperature is low, LNG production and recovery rate are high, equipment investment is less and helium purity is high, can produce LNG and fine helium two products simultaneously.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical separation technology, and relates to helium extraction from natural gas, in particular to a cogeneration LNG natural gas cryogenic-membrane separation helium extraction process. BACKGROUND

[0002] As a kind of rare gas, helium has good heat conduction performance and strong diffusivity, and is widely used in many fields such as medicine and new energy development. With the need of economic development, the demand for helium is increasing. Helium is mainly derived from natural gas containing helium, and domestic helium resources are relatively scarce. If the helium in the natural gas containing helium is not purified and directly processed into finished natural gas, it will cause waste of helium resources. Therefore, it is of great significance to recover and purify helium in natural gas containing helium.

[0003] The basic situation of helium resources in China is that the reserves are small and the concentration is low. The refrigeration process for the purpose of helium extraction alone has the disadvantages of high equipment investment, high energy consumption and low liquefied natural gas (LNG) yield. In recent years, the impact of imported helium on the market makes the original process not competitive, so the study of helium concentration process is increasingly important.

[0004] In view of the low helium concentration of natural gas in China, and to obtain higher yield, cogeneration of liquefied natural gas and helium is a better choice for helium extraction industry. The original helium extraction process is aimed at helium extraction, and the by-product is liquefied natural gas, which has a low liquefaction rate. However, using the liquefied natural gas process, the by-product is helium, and if the helium recovery rate can reach more than 90%, the economic benefit will be significantly higher than that of the original process.

[0005] Because the natural gas liquefaction process is combined with the helium extraction process, the helium produced has a low concentration and needs to be treated again in subsequent applications. Therefore, after using the natural gas to extract crude helium and cogenerate LNG process, membrane separation method is added to extract fine helium at one time, so that the concentration of helium reaches 99.99%. Membrane separation has the advantages of simple on-site operation and energy saving, and has high selectivity and permeation capacity for helium / methane. The cogeneration process has high helium recovery rate, can improve the liquefaction rate of the liquefaction process, and has the advantages of low energy consumption, high product yield and high helium concentration. Therefore, it is necessary to establish a cogeneration LNG natural gas cryogenic-membrane separation helium extraction process.

[0006] In summary, natural gas helium extraction faces the problems of high energy consumption and cost. In order to solve these problems, a cogeneration LNG natural gas cryogenic-membrane separation helium extraction process is proposed, which can share the pretreatment and utility facilities for the joint production of two products, reduce investment and operating costs, and make the natural gas extraction fine helium and cogeneration LNG process economically competitive. SUMMARY

[0007] In view of the problems of large investment, high operation cost, low product purity and high energy consumption in the existing natural gas helium extraction technology, the purpose of the present application is to provide a cogeneration LNG natural gas cryogenic-membrane separation helium extraction process, which adopts a technical scheme of mixed refrigerant refrigeration, nitrogen expansion cycle refrigeration, double-tower low-temperature rectification extraction of crude helium and membrane separation extraction of refined helium, and can produce LNG and refined helium at the same time, and the process has high helium recovery rate, low energy consumption, low operation temperature, high LNG yield and recovery rate, low equipment investment and high helium purity compared with other processes, and can extract high-purity helium at one time.

[0008] In order to achieve the above-mentioned purpose, the present application provides a cogeneration LNG natural gas cryogenic-membrane separation helium extraction process, which comprises a crude helium extraction unit, a membrane separation refined helium extraction unit, a heat exchange unit, a mixed refrigerant refrigeration system and a nitrogen expansion cycle refrigeration system.

[0009] The crude helium extraction unit comprises a first helium extraction tower T-100, a tower top cooler H-100 and a tower bottom reboiler H-101, a second helium extraction tower T-101, a tower top cooler H-102 and a tower bottom reboiler H-103; the membrane separation refined helium extraction unit comprises a compressor K-103, a cooler E-103, a first membrane separator OP-100, a compressor K-102, a cooler E-102, a second membrane separator OP-101; the heat exchange unit comprises a heat exchanger LNG-100, a heat exchanger LNG-101, a heat exchanger LNG-102 and a heat exchanger LNG-103; the mixed refrigerant refrigeration system comprises a gas-liquid separator V-100, a gas-liquid separator V-101, a throttle valve VLV-100, a cooler E-104, a compressor K-101, a cooler E-101, a compressor K-100 and a cooler E-100; and the nitrogen expansion cycle refrigeration system comprises a compressor K-104, a cooler E-105, a throttle valve VLV-101 and a cooler E-106.

[0010] The crude helium extraction unit is connected with the heat exchanger LNG-100 through a raw material gas inlet pipeline, and the heat exchanger LNG-100, the heat exchanger LNG-101, the heat exchanger LNG-102, the first helium extraction tower T-100 and the tower top cooler H-100 are sequentially communicated; the first helium extraction tower T-100, the tower top cooler H-100, the heat exchanger LNG-103, the second helium extraction tower T-101 and the tower top cooler H-102 are sequentially communicated; the first helium extraction tower T-100, the tower bottom reboiler H-101, the heat exchanger LNG-103 and the gas-liquid separator V-102 are sequentially communicated; the second helium extraction tower T-101, the tower top cooler H-102, the heat exchanger LNG-102, the heat exchanger LNG-101 and the heat exchanger LNG-100 are sequentially communicated; and the second helium extraction tower T-101 produces liquid nitrogen through the tower bottom reboiler H-103.

[0011] The membrane separation helium extraction unit extracts helium from the crude helium extraction unit into the compressor K-103; the compressor K-103, the cooler E-103, the first-stage membrane separator OP-100, the compressor K-102, the cooler E-102, and the second-stage membrane separator OP-101 are sequentially connected, and the refined helium is produced after two-stage membrane separation;

[0012] The mixed refrigerant refrigeration system, the outlet of the compressor K-101, the cooler E-101, the compressor K-100, the cooler E-100, and the gas-liquid separator V-100 are sequentially connected; the top of the gas-liquid separator V-100 is sequentially connected with the heat exchanger LNG-100 and the gas-liquid separator V-101; the bottom of the gas-liquid separator V-100 is connected with the heat exchanger LNG-100 and then connected with the pipeline to the inlet of the compressor K-101; the bottom of the gas-liquid separator V-101 is connected with the heat exchanger LNG-101 and then connected with the pipeline to the inlet of the compressor K-101; the top of the gas-liquid separator V-101 is sequentially connected with the heat exchanger LNG-101, the heat exchanger LNG-102, the throttle valve VLV-100, the cooler E-104, the heat exchanger LNG-102, the heat exchanger LNG-101, the heat exchanger LNG-100, and the inlet of the compressor K-101, and the cycle is repeated;

[0013] The nitrogen expansion cycle refrigeration system, the outlet of the compressor K-104, the cooler E-105, the heat exchanger LNG-103, the throttle valve VLV-101, the cooler E-106, the heat exchanger LNG-103, and the inlet of the compressor K-104 are sequentially connected.

[0014] The above-mentioned co-production of LNG natural gas cryogenic-membrane separation helium extraction process, the raw gas can be at room temperature, any pressure containing helium natural gas, the applicable raw gas condition range is wide.

[0015] The above-mentioned co-production of LNG natural gas cryogenic-membrane separation helium extraction process, the heat exchanger includes the heat exchanger LNG-100, the heat exchanger LNG-101, the heat exchanger LNG-102, and the heat exchanger LNG-103, which mainly functions to realize heat exchange and transfer in the production of the device and is a conventional device in the field. In the present application, the heat exchanger LNG-100 is provided with a first heat exchange channel, a second heat exchange channel, a third heat exchange channel, a fourth heat exchange channel, and a fifth heat exchange channel;

[0016] The raw material gas inlet pipeline is connected with the first end of the third heat exchange channel, and the last end of the third heat exchange channel is connected with the heat exchanger LNG-101 through a pipeline; the first end of the first heat exchange channel is connected with the top of the gas-liquid separator V-100 through a pipeline, and the last end of the first heat exchange channel is connected with the gas-liquid separator V-101 through a pipeline; the first end of the second heat exchange channel is connected with the bottom of the gas-liquid separator V-100 through a pipeline, and the last end of the second heat exchange channel is connected with the inlet pipeline of the compressor K-101 through a pipeline; the first end of the fourth heat exchange channel is connected with the inlet of the compressor K-101 through a pipeline, and the last end of the fourth heat exchange channel is connected with the heat exchanger LNG-101 through a pipeline; the first end of the fifth heat exchange channel is connected with the inlet of the compressor K-103 through a pipeline, and the last end of the fifth heat exchange channel is connected with the heat exchanger LNG-102 through a pipeline.

[0017] In the present application, the heat exchanger LNG-101 is provided with a sixth heat exchange channel, a seventh heat exchange channel, an eighth heat exchange channel and a ninth heat exchange channel.

[0018] The first end of the sixth heat exchange channel is connected with the top of the gas-liquid separator V-101 through a pipeline, and the last end of the sixth heat exchange channel is connected with the heat exchanger LNG-102 through a pipeline; the first end of the seventh heat exchange channel is connected with the bottom of the gas-liquid separator V-101 through a pipeline, and the last end of the seventh heat exchange channel is connected with the inlet pipeline of the compressor K-101 through a pipeline; the first end of the eighth heat exchange channel is connected with the last end of the third heat exchange channel of the heat exchanger LNG-100 through a pipeline, and the last end of the eighth heat exchange channel is connected with the heat exchanger LNG-102 through a pipeline; the first end of the ninth heat exchange channel is connected with the last end of the fourth heat exchange channel of the heat exchanger LNG-100 through a pipeline, and the last end of the ninth heat exchange channel is connected with the heat exchanger LNG-102 through a pipeline.

[0019] In the present application, the heat exchanger LNG-102 is provided with a tenth heat exchange channel, an eleventh heat exchange channel, a twelfth heat exchange channel and a thirteenth heat exchange channel.

[0020] The first end of the tenth heat exchange channel is connected with the last end of the sixth heat exchange channel of the heat exchanger LNG-101 through a pipeline, and the last end of the tenth heat exchange channel is connected with the throttle valve VLV-100 through a pipeline; the first end of the eleventh heat exchange channel is connected with the last end of the eighth heat exchange channel of the heat exchanger LNG-101 through a pipeline, and the last end of the eleventh heat exchange channel is connected with the first-stage helium extraction tower T-100 through a pipeline; the first end of the twelfth heat exchange channel is connected with the last end of the ninth heat exchange channel of the heat exchanger LNG-101 through a pipeline, and the last end of the twelfth heat exchange channel is connected with the cooler E-104 through a pipeline; the first end of the thirteenth heat exchange channel is connected with the last end of the fifth heat exchange channel of the heat exchanger LNG-100 through a pipeline, and the last end of the thirteenth heat exchange channel is connected with the second-stage helium extraction tower T-101 and the tower top cooler H-102 through a pipeline.

[0021] In the present application, the heat exchanger LNG-103 is provided with a fourteenth heat exchange channel, a fifteenth heat exchange channel, a sixteenth heat exchange channel and a seventeenth heat exchange channel.

[0022] The first end of the fourteenth heat exchange channel is connected with the inlet of the compressor K-104 through a pipeline, and the last end of the fourteenth heat exchange channel is connected with the outlet of the cooler E-106 through a pipeline; the first end of the fifteenth heat exchange channel is connected with the first-stage helium extraction column T-100 and the tower bottom reboiler H-101 through a pipeline, and the last end of the fifteenth heat exchange channel is connected with the gas-liquid separator V-102 through a pipeline; the first end of the sixteenth heat exchange channel is connected with the outlet of the cooler E-105 through a pipeline, and the last end of the sixteenth heat exchange channel is connected with the throttle valve VLV-101 through a pipeline; the first end of the seventeenth heat exchange channel is connected with the first-stage helium extraction column T-100 and the tower top cooler H-100 through a pipeline, and the last end of the seventeenth heat exchange channel is connected with the second-stage helium extraction column T-101 through a pipeline.

[0023] The above-mentioned co-production of LNG natural gas cryogenic-membrane separation helium extraction process is composed of the third heat exchange channel of the heat exchanger LNG-100, the eighth heat exchange channel of the heat exchanger LNG-101, the eleventh heat exchange channel of the heat exchanger LNG-102, the first-stage helium extraction column T-100, the tower top cooler H-100, the seventeenth heat exchange channel of the heat exchanger LNG-103, the second-stage helium extraction column T-101, the tower top cooler H-102, the thirteenth heat exchange channel of the heat exchanger LNG-102, the fifth heat exchange channel of the heat exchanger LNG-100 and the connecting pipelines between the adjacent components, and together constitutes a crude helium production circuit; the compressor K-103, the cooler E-103, the first-stage membrane separator OP-100, the compressor K-102, the cooler E-102, the second-stage membrane separator OP-101 and the connecting pipelines between the adjacent components together constitute a refined helium production circuit; the first-stage helium extraction column T-100, the tower bottom reboiler H-101, the fifteenth heat exchange channel of the heat exchanger LNG-103, the gas-liquid separator V-102 and the connecting pipelines between the adjacent components together constitute an LNG production circuit.

[0024] The above-mentioned co-production of LNG natural gas cryogenic-membrane separation helium extraction process, the mixed refrigerant refrigeration system usually adopts a mixed refrigerant composed of nitrogen, methane, ethane, propane, butane and pentane as a circulating refrigerant, and through the different condensation temperatures of different components, the corresponding components in the natural gas are condensed by means of throttling and gasification in sequence, so as to achieve the purpose of refrigeration.

[0025] The above-mentioned co-production of LNG natural gas cryogenic-membrane separation helium extraction process, the nitrogen expansion cycle refrigeration system provides cold energy for the heat exchanger LNG-103, and adopts nitrogen as a circulating refrigerant.

[0026] Compared with the prior art, the technical scheme provided by the present application has the following beneficial effects:

[0027] (1) The application provides a LNG natural gas cryogenic-membrane separation helium extraction process suitable for co-production, helium in raw material natural gas is concentrated through a heat exchanger, a first helium extraction tower and a second helium extraction tower, so that the concentration of helium in the gas phase material is increased, and a crude helium product is obtained. The crude helium product is gradually separated through a first membrane separator and a second membrane separator, so that the concentration of helium is further increased, and finally a refined helium product is obtained. The application integrates the traditional natural gas liquefaction process and the natural gas helium extraction process, and adds the membrane separation process in the natural gas helium extraction process. The integration of the three processes reduces the equipment investment and the recycling of cold energy, reduces the waste of resources. And the concentration of extracted helium is greatly increased, which is conducive to reducing the subsequent separation energy consumption of extracted refined helium and reducing the overall cold energy loss of the device.

[0028] (2) The application provides a LNG natural gas cryogenic-membrane separation helium extraction process suitable for co-production, the crude helium extraction unit adopts a mixed refrigerant refrigeration and nitrogen circulation refrigeration process, the produced crude helium product has high concentration, high helium recovery rate, low comprehensive energy consumption of the device, low minimum operating temperature of the device, high LNG liquefaction rate and less equipment investment.

[0029] (3) The application provides a LNG natural gas cryogenic-membrane separation helium extraction process suitable for co-production, the membrane separation process is adopted, so that the concentration of helium is increased, and the required concentration of helium can be produced at any time, which reduces the subsequent equipment investment caused by the change of required concentration.

[0030] (4) The application provides a LNG natural gas cryogenic-membrane separation helium extraction process suitable for co-production, which improves the economy of natural gas helium extraction, makes the LNG natural gas cryogenic-membrane separation helium extraction process have economic competitiveness, is of great significance, helps to further promote the development of helium-containing natural gas helium extraction technology, drives the research and development and improvement of related industry equipment, materials and the like, thereby supporting the development of domestic high-tech industry, and can effectively guarantee the helium demand of national defense and military industry such as aerospace, navigation and nuclear industry. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a process flow chart of the LNG natural gas cryogenic-membrane separation helium extraction process of the application;

[0032] Explanation of reference numerals in the attached diagram: K-101 - Compressor; E-101 - Cooler; K-100 - Compressor; E-100 - Cooler; V-100 - Gas-liquid separator; LNG-100 - Heat exchanger; V-101 - Gas-liquid separator; LNG-101 - Heat exchanger; LNG-102 - Heat exchanger; VLV-100 - Throttling valve; E-104 - Cooler; T-100 - First-stage helium stripping tower; H-100 - Cooler; H-101 - Reboiler; L NG-103 - Heat exchanger; K-104 - Compressor; E-105 - Cooler; VLV-101 - Throttling valve; E-106 - Cooler; V-102 - Gas-liquid separator; T-101 - Secondary helium stripper; H-102 - Cooler; H-103 - Reboiler; K-103 - Compressor; E-103 - Cooler; OP-100 - Primary membrane separator; K-102 - Compressor; E-102 - Cooler; OP-101 - Secondary membrane separator. Detailed Implementation

[0033] The following will be combined with the appendix Figure 1 The present invention provides a clear and complete description of the cryogenic membrane separation helium extraction process for co-producing LNG. Obviously, the described embodiments are only a part of the embodiments of the present invention.

[0034] This embodiment provides a cryogenic-membrane separation helium extraction process for co-producing LNG, such as... Figure 1 As shown, it includes a crude helium extraction unit, a membrane separation and helium refining unit, a heat exchange unit, a mixed refrigerant refrigeration system, and a nitrogen expansion cycle refrigeration system, all connected by pipelines.

[0035] The crude helium extraction unit includes a primary helium extraction tower T-100, a top cooler H-100, and a bottom reboiler H-101; a secondary helium extraction tower T-101, a top cooler H-102, and a bottom reboiler H-103.

[0036] The membrane separation and helium extraction unit includes compressor K-103, cooler E-103, primary membrane separator OP-100, compressor K-102, cooler E-102, and secondary membrane separator OP-101.

[0037] The heat exchange unit comprises a heat exchanger LNG-100, a heat exchanger LNG-101, a heat exchanger LNG-102, and a heat exchanger LNG-103. The heat exchanger LNG-100 is provided with a first heat exchange channel, a second heat exchange channel, a third heat exchange channel, a fourth heat exchange channel, and a fifth heat exchange channel. The heat exchanger LNG-101 is provided with a sixth heat exchange channel, a seventh heat exchange channel, an eighth heat exchange channel, and a ninth heat exchange channel. The heat exchanger LNG-102 is provided with a tenth heat exchange channel, an eleventh heat exchange channel, a twelfth heat exchange channel, and a thirteenth heat exchange channel. The heat exchanger LNG-103 is provided with a fourteenth heat exchange channel, a fifteenth heat exchange channel, a sixteenth heat exchange channel, and a seventeenth heat exchange channel.

[0038] The mixed refrigerant refrigeration system comprises a gas-liquid separator V-100, a gas-liquid separator V-101, a throttling valve VLV-100, a cooler E-104, a compressor K-101, a cooler E-101, a compressor K-100, and a cooler E-100.

[0039] The nitrogen expansion cycle refrigeration system comprises a compressor K-104, a cooler E-105, a throttling valve VLV-101, and a cooler E-106.

[0040] The raw gas inlet pipeline is connected to the first end of the third heat exchange channel, and the last end of the third heat exchange channel is connected to the heat exchanger LNG-101 through a pipeline. The first end of the first heat exchange channel is connected to the top of the gas-liquid separator V-100 through a pipeline, and the last end of the first heat exchange channel is connected to the gas-liquid separator V-101 through a pipeline. The first end of the second heat exchange channel is connected to the bottom of the gas-liquid separator V-100 through a pipeline, and the last end of the second heat exchange channel is connected to the inlet pipeline of the compressor K-101 through a pipeline. The first end of the fourth heat exchange channel is connected to the inlet of the compressor K-101 through a pipeline, and the last end of the fourth heat exchange channel is connected to the heat exchanger LNG-101 through a pipeline. The first end of the fifth heat exchange channel is connected to the inlet of the compressor K-103 through a pipeline, and the last end of the fifth heat exchange channel is connected to the heat exchanger LNG-102 through a pipeline.

[0041] The first end of the sixth heat exchange channel is connected to the top of the gas-liquid separator V-101 through a pipeline, and the last end of the sixth heat exchange channel is connected to the heat exchanger LNG-102 through a pipeline. The first end of the seventh heat exchange channel is connected to the bottom of the gas-liquid separator V-101 through a pipeline, and the last end of the seventh heat exchange channel is connected to the inlet pipeline of the compressor K-101 through a pipeline. The first end of the eighth heat exchange channel is connected to the last end of the third heat exchange channel of the heat exchanger LNG-100 through a pipeline, and the last end of the eighth heat exchange channel is connected to the heat exchanger LNG-102 through a pipeline. The first end of the ninth heat exchange channel is connected to the last end of the fourth heat exchange channel of the heat exchanger LNG-100 through a pipeline, and the last end of the ninth heat exchange channel is connected to the heat exchanger LNG-102 through a pipeline.

[0042] The first end of the tenth heat exchange passage is connected with the sixth heat exchange passage of the heat exchanger LNG-101 through a pipeline, and the last end of the tenth heat exchange passage is connected with the throttle valve VLV-100 through a pipeline; the first end of the eleventh heat exchange passage is connected with the eighth heat exchange passage of the heat exchanger LNG-101 through a pipeline, and the last end of the eleventh heat exchange passage is connected with the first-stage helium extraction tower T-100 through a pipeline; the first end of the twelfth heat exchange passage is connected with the ninth heat exchange passage of the heat exchanger LNG-101 through a pipeline, and the last end of the twelfth heat exchange passage is connected with the cooler E-104 through a pipeline; the first end of the thirteenth heat exchange passage is connected with the fifth heat exchange passage of the heat exchanger LNG-100 through a pipeline, and the last end of the thirteenth heat exchange passage is connected with the second-stage helium extraction tower T-101 and the overhead cooler H-102 through a pipeline.

[0043] The first end of the fourteenth heat exchange passage is connected with the inlet of the compressor K-104 through a pipeline, and the last end of the fourteenth heat exchange passage is connected with the outlet of the cooler E-106 through a pipeline; the first end of the fifteenth heat exchange passage is connected with the first-stage helium extraction tower T-100 and the bottom reboiler H-101 through a pipeline, and the last end of the fifteenth heat exchange passage is connected with the gas-liquid separator V-102 through a pipeline; the first end of the sixteenth heat exchange passage is connected with the outlet of the cooler E-105 through a pipeline, and the last end of the sixteenth heat exchange passage is connected with the throttle valve VLV-101 through a pipeline; the first end of the seventeenth heat exchange passage is connected with the first-stage helium extraction tower T-100 and the overhead cooler H-100 through a pipeline, and the last end of the seventeenth heat exchange passage is connected with the second-stage helium extraction tower T-101 through a pipeline.

[0044] The third heat exchange passage of the heat exchanger LNG-100, the eighth heat exchange passage of the heat exchanger LNG-101, the eleventh heat exchange passage of the heat exchanger LNG-102, the first-stage helium extraction tower T-100, the overhead cooler H-100, the seventeenth heat exchange passage of the heat exchanger LNG-103, the second-stage helium extraction tower T-101, the overhead cooler H-102, the thirteenth heat exchange passage of the heat exchanger LNG-102, the fifth heat exchange passage of the heat exchanger LNG-100, and the connecting pipelines between adjacent components jointly constitute a crude helium production loop; the compressor K-103, the cooler E-103, the first-stage membrane separator OP-100, the compressor K-102, the cooler E-102, the second-stage membrane separator OP-101, and the connecting pipelines between adjacent components jointly constitute a refined helium production loop; the first-stage helium extraction tower T-100, the bottom reboiler H-101, the fifteenth heat exchange passage of the heat exchanger LNG-103, the gas-liquid separator V-102, and the connecting pipelines between adjacent components jointly constitute an LNG production loop.

[0045] The mixed refrigerant refrigeration system generally uses a mixed refrigerant containing nitrogen, methane, ethane, propane, butane and pentane as the circulating refrigerant, and sequentially throttles and vaporizes different components by virtue of different condensing temperatures of the different components to condense corresponding components in the natural gas, so as to achieve the refrigeration purpose.

[0046] The nitrogen expansion cycle refrigeration system provides cold energy for the heat exchanger LNG-103, and uses nitrogen as the circulating refrigerant.

[0047] The process for co-production of LNG and helium separation by low-temperature membrane separation provided by the application can use natural gas containing helium at any temperature and pressure as raw material gas, and is suitable for a wide range of raw material gas conditions. The process for co-production of LNG and helium separation by low-temperature membrane separation provided by the application is described in detail below using natural gas containing helium as raw material gas. The pressure of the raw material gas is 2.3 MPa, the temperature is 35 DEG C, the processing scale is 3.7 x 105 m3 / d, and the main components of the raw material gas are methane 91.57%, ethane 0.08%, propane 0.01%, nitrogen 8.14% and helium 0.20%. 3

[0048] The raw material gas is cooled to -115 DEG C by the third heat exchange channel of the heat exchanger LNG-100, the eighth heat exchange channel of the heat exchanger LNG-101 and the eleventh heat exchange channel of the heat exchanger LNG-102, and then enters the first helium separation column T-100. The liquid phase from the first helium separation column T-100 and the bottom reboiler H-101 is cooled and throttled by the heat exchanger LNG-103, and the temperature is -162 DEG C and the pressure is 0.2 MPa, and the LNG is exported to an LNG storage tank, and the LNG liquefaction rate is 92.4%. The gas phase from the first helium separation column T-100 and the overhead cooler H-100, at which time the helium concentration is 4.28%, is cooled by the heat exchanger LNG-103, and the temperature is -151 DEG C, and then enters the second helium separation column T-101, and helium and nitrogen are separated. The helium concentration of the helium gas discharged from the second helium separation column T-101 and the overhead cooler H-102 is 60.52%, and then the helium is heated by the heat exchanger LNG-102 and the heat exchanger LNG-100, and becomes crude helium which enters the membrane separation unit for refined helium extraction.

[0049] The crude helium from the crude helium extraction unit is compressed by the compressor K-103 and the cooler E-103, and then enters the first membrane separator OP-100. After being separated by the first membrane separator OP-100, the helium concentration is 92.67%. Then the helium is compressed by the compressor K-102 and the cooler E-102, and then enters the second membrane separator OP-101. After being separated by the second membrane separator OP-101, refined helium with a helium concentration of 99.99% is obtained, and the helium recovery rate is 99.99%.

[0050] ​The mixed refrigerant refrigeration system has a mixed refrigerant component of 3% nitrogen, 26% methane, 28% ethane, 32% propane, 8% butane and 3% pentane. The mixed refrigerant from the first end of the fourth heat exchange channel of the heat exchanger LNG-100 has a temperature of 30°C and a pressure of 0.14 MPa. The mixed refrigerant then sequentially passes through the compressor K-101, the cooler E-101, the compressor K-100 and the cooler E-100, and has a temperature of 31°C and a pressure of 2.93 MPa. The mixed refrigerant then enters the gas-liquid separator V-100. The gas phase discharged from the top of the gas-liquid separator V-100 exchanges heat in the first heat exchange channel of the heat exchanger LNG-100, and has a temperature of -51°C. The liquid phase discharged from the bottom of the gas-liquid separator V-100 exchanges heat in the second heat exchange channel of the heat exchanger LNG-100, and is communicated to the inlet pipeline of the compressor K-101. The liquid phase discharged from the bottom of the gas-liquid separator V-101 exchanges heat in the seventh heat exchange channel of the heat exchanger LNG-101, and is communicated to the inlet pipeline of the compressor K-101. The gas phase discharged from the top of the gas-liquid separator V-101 exchanges heat in the sixth heat exchange channel of the heat exchanger LNG-101 and the tenth heat exchange channel of the heat exchanger LNG-102, and has a temperature of -120°C and a pressure of 2.9 MPa. The gas phase then throttles through the throttling valve VLV-100, cools in the cooler E-104, and has a temperature of -153.7°C and a pressure of 0.23 MPa. The gas phase then sequentially passes through the twelfth heat exchange channel of the heat exchanger LNG-102, the ninth heat exchange channel of the heat exchanger LNG-101, the fourth heat exchange channel of the heat exchanger LNG-100 and the compressor K-101, and the cycle is repeated.

[0051] The nitrogen expansion cycle refrigeration system provides cold energy for the heat exchanger LNG-103, and uses nitrogen as the circulating refrigerant. The nitrogen from the first end of the fourteenth heat exchange channel of the heat exchanger LNG-103 has a temperature of 30°C and a pressure of 0.22 MPa. The nitrogen then sequentially passes through the compressor K-104 and the cooler E-105, and has a temperature of 30°C and a pressure of 4 MPa. The nitrogen then exchanges heat in the sixteenth heat exchange channel of the heat exchanger LNG-103, throttles through the throttling valve VLV-101, cools in the cooler E-106, and has a temperature of -190°C and a pressure of 0.23 MPa. The nitrogen then enters the fourteenth heat exchange channel of the heat exchanger LNG-103, and the cycle is repeated.

[0052] The above-described embodiments are intended to help the reader understand the principles of the present application, and the protection scope of the present application is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make several combinations and improvements without departing from the principles of the present application, and these combinations and improvements are also within the protection scope of the present application.

Claims

1. A process for the co-production of LNG and cryogenic membrane separation of helium from natural gas, characterized in that: The crude helium extraction unit, the membrane separation helium extraction unit, the heat exchange unit, the mixed refrigerant refrigeration system, and the nitrogen expansion cycle refrigeration system. The crude helium extraction unit includes a first helium extraction tower T-100, a tower top cooler H-100, and a tower bottom reboiler H-101, a second helium extraction tower T-101, a tower top cooler H-102, and a tower bottom reboiler H-103; the membrane separation helium extraction unit includes a compressor K-103, a cooler E-103, a first membrane separator OP-100, a compressor K-102, a cooler E-102, and a second membrane separator OP-101; the heat exchange unit includes heat exchangers LNG-100, LNG-101, LNG-102, and LNG-103; the mixed refrigerant refrigeration system includes gas-liquid separators V-100 and V-101, a throttle valve VLV-100, a cooler E-104, a compressor K-101, a cooler E-101, a compressor K-100, and a cooler E-100; and the nitrogen expansion cycle refrigeration system includes a compressor K-104, a cooler E-105, a throttle valve VLV-101, and a cooler E-106. The crude helium extraction unit is connected with the heat exchanger LNG-100 through a raw material gas inlet pipeline, and the heat exchanger LNG-100, the heat exchanger LNG-101, the heat exchanger LNG-102, the first helium extraction tower T-100, and the tower top cooler H-100 are sequentially connected; the first helium extraction tower T-100, the tower top cooler H-100, the heat exchanger LNG-103, the second helium extraction tower T-101, and the tower top cooler H-102 are sequentially connected; the first helium extraction tower T-100, the tower bottom reboiler H-101, the heat exchanger LNG-103, and the gas-liquid separator V-102 are sequentially connected; the second helium extraction tower T-101, the tower top cooler H-102, the heat exchanger LNG-102, the heat exchanger LNG-101, and the heat exchanger LNG-100 are sequentially connected; and the second helium extraction tower T-101 and the tower bottom reboiler H-103 produce liquid nitrogen. The membrane separation helium extraction unit is connected with the crude helium extraction unit through the crude helium extraction unit, and the crude helium extraction unit is connected with the compressor K-103; the compressor K-103, the cooler E-103, the first membrane separator OP-100, the compressor K-102, the cooler E-102, and the second membrane separator OP-101 are sequentially connected, and the two-stage membrane separation produces refined helium. The mixed refrigerant refrigeration system, the outlet of the compressor K-101, the cooler E-101, the compressor K-100, the cooler E-100, and the gas-liquid separator V-100 are sequentially communicated; the top of the gas-liquid separator V-100 is sequentially communicated with the heat exchanger LNG-100 and the gas-liquid separator V-101; the bottom of the gas-liquid separator V-100 is communicated with the heat exchanger LNG-100 and then connected with the pipeline to the inlet of the compressor K-101; the bottom of the gas-liquid separator V-101 is communicated with the heat exchanger LNG-101 and then connected with the pipeline to the inlet of the compressor K-101; the top of the gas-liquid separator V-101 is sequentially communicated with the heat exchanger LNG-101, the heat exchanger LNG-102, the throttle valve VLV-100, the cooler E-104, the heat exchanger LNG-102, the heat exchanger LNG-101, the heat exchanger LNG-100, and the inlet of the compressor K-101, and the cycle is repeated; The nitrogen expansion cycle refrigeration system, the outlet of the compressor K-104, the cooler E-105, the heat exchanger LNG-103, the throttle valve VLV-101, the cooler E-106, the heat exchanger LNG-103, and the inlet of the compressor K-104 are sequentially communicated.

2. The process for co-production of LNG and cryogenic membrane separation of helium from natural gas according to claim 1, characterized in that: The heat exchanger LNG-100 is provided with a first heat exchange channel, a second heat exchange channel, a third heat exchange channel, a fourth heat exchange channel, and a fifth heat exchange channel; The raw gas inlet pipeline is connected with the first end of the third heat exchange channel, the last end of the third heat exchange channel is connected with the heat exchanger LNG-101 through a pipeline; the first end of the first heat exchange channel is connected with the top of the gas-liquid separator V-100 through a pipeline, and the last end of the first heat exchange channel is connected with the gas-liquid separator V-101 through a pipeline; the first end of the second heat exchange channel is connected with the bottom of the gas-liquid separator V-100 through a pipeline, and the last end of the second heat exchange channel is connected with the pipeline to the inlet of the compressor K-101 through a pipeline; the first end of the fourth heat exchange channel is connected with the inlet of the compressor K-101 through a pipeline, and the last end of the fourth heat exchange channel is connected with the heat exchanger LNG-101 through a pipeline; the first end of the fifth heat exchange channel is connected with the inlet of the compressor K-103 through a pipeline, and the last end of the fifth heat exchange channel is connected with the heat exchanger LNG-102 through a pipeline.

3. The process for co-production of LNG and cryogenic membrane separation of helium from natural gas according to claim 2, characterized in that: The heat exchanger LNG-101 is provided with a sixth heat exchange channel, a seventh heat exchange channel, an eighth heat exchange channel, and a ninth heat exchange channel; The first end of the sixth heat exchange channel is connected with the top of the gas-liquid separator V-101 through a pipeline, and the last end of the sixth heat exchange channel is connected with the heat exchanger LNG-102 through a pipeline; the first end of the seventh heat exchange channel is connected with the bottom of the gas-liquid separator V-101 through a pipeline, and the last end of the seventh heat exchange channel is connected with the pipeline to the inlet of the compressor K-101 through a pipeline; the first end of the eighth heat exchange channel is connected with the last end of the third heat exchange channel of the heat exchanger LNG-100 through a pipeline, and the last end of the eighth heat exchange channel is connected with the heat exchanger LNG-102 through a pipeline; the first end of the ninth heat exchange channel is connected with the last end of the fourth heat exchange channel of the heat exchanger LNG-100 through a pipeline, and the last end of the ninth heat exchange channel is connected with the heat exchanger LNG-102 through a pipeline.

4. The process for co-production of LNG and cryogenic membrane separation of helium from natural gas according to claim 3, characterized in that: The heat exchanger LNG-102 is internally provided with a tenth heat exchange channel, an eleventh heat exchange channel, a twelfth heat exchange channel and a thirteenth heat exchange channel. The first end of the tenth heat exchange channel is connected with the sixth heat exchange channel of the heat exchanger LNG-101 through a pipeline, and the last end of the tenth heat exchange channel is connected with the throttle valve VLV-100 through a pipeline; the first end of the eleventh heat exchange channel is connected with the eighth heat exchange channel of the heat exchanger LNG-101 through a pipeline, and the last end of the eleventh heat exchange channel is connected with the first-stage helium extraction tower T-100 through a pipeline; the first end of the twelfth heat exchange channel is connected with the ninth heat exchange channel of the heat exchanger LNG-101 through a pipeline, and the last end of the twelfth heat exchange channel is connected with the cooler E-104 through a pipeline; the first end of the thirteenth heat exchange channel is connected with the fifth heat exchange channel of the heat exchanger LNG-100 through a pipeline, and the last end of the thirteenth heat exchange channel is connected with the second-stage helium extraction tower T-101 and the overhead cooler H-102 through a pipeline.

5. The process for co-production of LNG and cryogenic membrane separation of helium from natural gas according to claim 4, characterized by that: The heat exchanger LNG-103 is internally provided with a fourteenth heat exchange channel, a fifteenth heat exchange channel, a sixteenth heat exchange channel and a seventeenth heat exchange channel. The first end of the fourteenth heat exchange channel is connected with the inlet of the compressor K-104 through a pipeline, and the last end of the fourteenth heat exchange channel is connected with the outlet of the cooler E-106 through a pipeline; the first end of the fifteenth heat exchange channel is connected with the first-stage helium extraction tower T-100 and the bottom reboiler H-101 through a pipeline, and the last end of the fifteenth heat exchange channel is connected with the gas-liquid separator V-102 through a pipeline; the first end of the sixteenth heat exchange channel is connected with the outlet of the cooler E-105 through a pipeline, and the last end of the sixteenth heat exchange channel is connected with the throttle valve VLV-101 through a pipeline; the first end of the seventeenth heat exchange channel is connected with the first-stage helium extraction tower T-100 and the overhead cooler H-100 through a pipeline, and the last end of the seventeenth heat exchange channel is connected with the second-stage helium extraction tower T-101 through a pipeline.

6. The process for co-production of LNG and cryogenic membrane separation of helium according to any one of claims 1 to 5, characterized in that: The mixed refrigerant refrigeration system provides cold energy for the heat exchanger LNG-100, the heat exchanger LNG-101 and the heat exchanger LNG-102, adopts a mixed refrigerant composed of nitrogen, methane, ethane, propane, butane and pentane as the circulating refrigerant; the nitrogen expansion refrigeration system provides cold energy for the heat exchanger LNG-103, and adopts nitrogen as the circulating refrigerant.

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