A natural gas helium extraction device and method of low-temperature rectification coupled with membrane separation

Abstract

The present application relates to a kind of low-temperature rectification coupling membrane separation's natural gas helium extraction equipment and method.The present application combines low-temperature rectification process with membrane separation technology, first, crude helium gas with higher helium content is prepared from helium-containing natural gas by low-temperature rectification process, then, crude helium gas is preliminarily purified by membrane separation process, finally, high-purity helium gas is prepared by pressure swing adsorption technology, the purpose of extracting helium from natural gas with He content less than 0.1% is achieved;Not only the drawbacks that helium can be separated from natural gas only by cooling to below-200℃ in traditional method are solved, but also the requirements and dependence on membrane separation technology are reduced, the demand for cold energy is reduced, and the risk of future technology substitution is effectively reduced, the process flow is simplified, and the economic benefit is improved;The present application improves the reliability of process and reduces the risk in operation process, which is beneficial to improve the economic benefit of enterprise and maintain long-period stable operation of device.

Description

Technical Field

[0001] This invention relates to the field of helium production technology, specifically to a cryogenic distillation coupled membrane separation equipment and method for helium extraction from natural gas. Background Technology

[0002] Helium (He) is a colorless, odorless, monatomic rare gas with an extremely low boiling point (-268.85℃), excellent diffusivity, poor solubility in water, and good thermal conductivity. It plays an irreplaceable role in defense, biomedicine, nuclear facilities, electrical industry, semiconductor manufacturing, and cryogenic industries, and is a vital resource for national security and the development of high-tech industries. He is mainly distributed in the mantle, rocks, air, and natural gas. The concentration of He in the air is low, making it difficult to achieve resource utilization. Extracting He from natural gas, especially from non-condensable tail gas during natural gas liquefaction, is currently the only way to utilize He as a resource.

[0003] Currently, there are two main processes for extracting helium from natural gas: cryogenic condensation and membrane separation. These two processes also have the following problems:

[0004] 1. Natural gas has a low helium content. Extracting helium from natural gas using the cryogenic condensation method requires multiple cryogenic separations of the natural gas. Helium has a low boiling point, and to obtain high-purity helium, the mixed gas needs to be cooled to below -200°C. This not only increases the number of equipment, the processing capacity of the equipment, and the process length, but the extremely low operating temperature also places extremely high demands on cooling capacity, equipment, and materials, resulting in a significant increase in investment, a larger footprint, higher production costs, and a worse economic effect.

[0005] 2. When using membrane separation to extract helium from natural gas, the following challenges exist:

[0006] ① Membrane separation technology is still in the early stages of development, with high production costs and limited application in the field of natural gas helium extraction. Using membrane separation technology throughout the entire process will lead to increased production risks, significantly increased investment costs, and poor economic benefits.

[0007] ② The pressure drop of natural gas after passing through the membrane is large, so it needs to be compressed before entering the next stage of membrane separation. Multi-stage membrane separation + compression will result in a large energy loss, which is uneconomical from the perspective of energy saving.

[0008] ③ Currently, there are no mature large-scale membrane separation industrial plants for natural gas helium extraction in China. When the processing volume is large, the application effect of membrane separation method still needs to be verified.

[0009] ④ The future development direction of membrane separation technology is still unknown, and the production lines built by enterprises with a large investment may be subject to technological substitution.

[0010] 3. Currently, the natural gas helium extraction processes used in industry are mostly used to process natural gas with a high helium content, which is generally greater than 0.4%. However, the helium content of natural gas varies greatly depending on the location of the natural gas mine. Using cryogenic condensation and membrane separation methods to process low-helium natural gas will not only lead to further increases in investment, but the purity of the extracted helium may not meet the application requirements. Summary of the Invention

[0011] The first technical problem to be solved by the present invention is to provide a natural gas helium extraction device that can effectively reduce the device's demand for cooling capacity, thereby reducing the device's operating risks and energy consumption, and can extract helium from natural gas with a He content of less than 0.1% by using a cryogenic distillation coupled membrane separation method.

[0012] The second technical problem to be solved by the present invention is to provide a method for helium extraction from natural gas by cryogenic distillation coupled membrane separation, in light of the current state of the prior art.

[0013] The technical solution adopted by the present invention to solve at least one of the above-mentioned technical problems is as follows:

[0014] A cryogenic distillation coupled membrane separation helium extraction device for natural gas includes:

[0015] The drying unit has an inlet for the input of lean helium natural gas and is used to remove water from the natural gas;

[0016] The first purification unit is connected downstream of the drying unit and is used to desulfurize and deacidify the natural gas.

[0017] A cryogenic distillation column is connected downstream of the first purification unit and is used to perform cryogenic separation on the natural gas after it has been processed by the drying unit and the first purification unit. The bottom of the cryogenic distillation column is provided with a first output port for liquid phase output and the top is provided with a second output port for crude helium gas obtained from the separation.

[0018] A hydrogenation reactor and a dehydrogenation reactor are connected downstream of the cryogenic distillation column. The hydrogenation reactor and the dehydrogenation reactor are connected in series along the gas flow direction to remove H2 contained in the crude helium gas obtained from the cryogenic distillation column.

[0019] A membrane separation unit, connected downstream of the dehydrogenation reactor, is used to perform membrane separation on crude helium to obtain crude helium with a purity of 30% to 60%.

[0020] The second purification unit is connected downstream of the membrane separation unit and is used to remove other impurities from the crude helium gas after it has been processed by the membrane separation unit to obtain helium gas.

[0021] Preferably, the membrane separation unit is provided with a first output pipe for outputting the separated tail gas, and the outlet of the first output pipe is connected to the inlet of the cryogenic distillation column.

[0022] Preferably, the second purification unit is provided with a second output pipe for outputting the obtained desorbed gas, and the outlet of the second output pipe is connected to the inlet of the membrane separation unit.

[0023] Preferably, a first heat exchanger for cooling the natural gas entering the cryogenic distillation column is provided between the first purification unit and the cryogenic distillation column; a second heat exchanger for heating the crude helium gas is provided at the inlet of the hydrogenation reactor.

[0024] Preferably, a first compressor for pressurizing the crude helium gas supplied to the first heat exchanger is provided at the outlet of the membrane separation unit. Preferably, a second compressor for pressurizing the desorbed gas supplied to the membrane separation unit via the second output pipe is provided downstream of the second purification unit.

[0025] Preferably, the first purification unit is a PSA purification unit that can reduce the concentrations of H2O, CO2, and sulfides in natural gas to trace levels through desulfurization and decarbonization.

[0026] Preferably, the second purification unit is a PSA purification unit capable of removing N2 and CH4 from crude helium gas through pressure swing adsorption.

[0027] A method for helium extraction from natural gas via cryogenic distillation coupled with membrane separation includes the following steps:

[0028] (1) The helium-containing natural gas is dehydrated in the drying unit and then desulfurized and deacidified in the first purification unit to avoid blockage or corrosion of pipelines and equipment caused by H2O, CO2 and sulfides in the natural gas at low temperature. The dehydration treatment is completed in the drying unit. The process can be triethylene glycol dehydration or other processes that can achieve similar effects. This invention does not limit the process used in the drying unit. The desulfurization and deacidification treatment is completed in the PSA unit. The separation effect is achieved by utilizing the difference in adsorption performance of different media in the mixed gas on the adsorbent under different pressures. After desulfurization and decarbonization in the first purification unit, the concentration of H2O, CO2 and sulfides in the natural gas is reduced to trace levels.

[0029] (2) After being dehydrated, desulfurized and deacidified, the natural gas is cooled and then enters a cryogenic distillation tower for cryogenic separation. The liquid collected at the bottom of the tower is sold as a by-product LNG. The top of the tower separates crude helium gas with a high helium content. The crude helium gas composition includes at least He, H2, N2 and O2. The recovery rate of He in the crude helium gas is not less than 99.5% and the recovery rate of CH4 is not higher than 2%.

[0030] (3) After heating the crude helium to 40-100℃, it enters the hydrogenation reactor for catalytic hydrogenation reaction, and then enters the dehydrogenation reactor to remove the small amount of H2 contained in the crude helium. After the reaction, the H2 concentration drops to below 20ppb.

[0031] (4) The crude helium gas after catalytic hydrogenation reaction also contains N2 and CH4 impurities. The crude helium gas containing impurities is sent to the membrane separation unit. The crude helium gas is separated by a polycarbonate membrane or a polyimide He separation membrane with high He selectivity. Because the pressure drop is large after the gas permeates the membrane, the crude helium gas is pressurized by a compressor after membrane separation. The helium product obtained after the treatment has a helium purity of 30% to 60%. The tail gas separated after membrane separation also contains helium. Its components include He, CH4 and N2. The tail gas is pressurized and mixed with fresh natural gas and then enters low temperature distillation treatment.

[0032] (5) The crude helium gas after membrane separation also contains a small amount of N2 and CH4 impurities. The crude helium gas containing impurities is sent to the second purification unit and He is purified by pressure swing adsorption technology. The helium product obtained after treatment has a helium purity of more than 99.99%. The desorbed gas separated by the second purification unit also contains helium, and its components include He, CH4 and N2. The desorbed gas is pressurized and sent to the membrane separation unit to be mixed with the crude helium gas for purification.

[0033] In this invention, the raw material natural gas contains He, H2, N2, CO2, CH4, C2H6, C3H8, and C4H. 10 C5H 12 The components include H2S, COS, CH3SH, CS2, H2O, and O2, with CH4 having the highest content and He content ranging from 0.03% to 0.1% (volume fraction).

[0034] Compared with existing technologies, the advantages of this invention are as follows: This invention combines cryogenic distillation with membrane separation technology. First, a high-helium-content crude helium gas is obtained from helium-containing natural gas through cryogenic distillation. Then, the crude helium gas is preliminarily purified through membrane separation. Finally, high-purity helium gas is obtained through pressure swing adsorption (PSA), achieving the goal of extracting helium from natural gas with a He content of less than 0.1%. This not only solves the drawback of traditional methods that require cooling natural gas to below -200°C to separate helium, but also reduces the requirements and dependence on membrane separation technology, decreases the demand for cooling energy, effectively reduces the risk of future technology replacement, simplifies the process flow, reduces the size of some key equipment and unnecessary energy consumption, and improves economic efficiency. It is also applicable to low-helium natural gas with a helium content far below the average level. From an industrial perspective, this invention improves process reliability and reduces operational risks, which is beneficial for improving the economic benefits of enterprises and ensuring the long-term stable operation of the equipment. Attached Figure Description

[0035] Figure 1 The above are process flow diagrams for embodiments 1 and 2 of the present invention. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0037] Example 1:

[0038] like Figure 1 As shown, the cryogenic distillation coupled membrane separation natural gas helium extraction equipment of this embodiment includes:

[0039] Drying unit 1 has an inlet for inputting lean helium natural gas and is used to remove water from the natural gas;

[0040] The first purification unit 2 is connected downstream of the drying unit and is used to desulfurize and deacidify the natural gas.

[0041] The cryogenic distillation column 4 is connected downstream of the first purification unit 2 and is used to perform cryogenic separation on the natural gas after it has been processed by the drying unit 1 and the first purification unit 2. The bottom of the cryogenic distillation column 4 is provided with a first output port for liquid phase output and the top is provided with a second output port for crude helium gas obtained from separation.

[0042] Hydrogenation reactor 6 and dehydrogenation reactor 7 are connected downstream of the cryogenic distillation column 4. Hydrogenation reactor 6 and dehydrogenation reactor 7 are connected in series along the gas flow direction to remove H2 contained in the crude helium gas obtained from the cryogenic distillation column 4.

[0043] Membrane separation unit 8 is connected downstream of the dehydrogenation reactor 7 and is used to perform membrane separation on crude helium to obtain crude helium with a purity of 30% to 60%.

[0044] The second purification unit 9 is connected downstream of the membrane separation unit 8 and is used to remove other impurities from the crude helium gas after it has been processed by the membrane separation unit 8 to obtain helium gas.

[0045] The membrane separation unit 8 is provided with a first output pipe for outputting the separated tail gas, and the outlet of the first output pipe is connected to the inlet of the low-temperature distillation column 4. The second purification unit 9 is provided with a second output pipe for outputting the obtained desorbed gas, and the outlet of the second output pipe is connected to the inlet of the membrane separation unit 8.

[0046] A first heat exchanger 3 is provided between the first purification unit 2 and the low-temperature distillation column 4 to cool the natural gas entering the low-temperature distillation column 4; a second heat exchanger 5 is provided at the inlet of the hydrogenation reactor 6 to heat the crude helium gas.

[0047] A second compressor 11 is installed downstream of the second purification unit 9 to pressurize the desorbed gas supplied to the membrane separation unit 8 via the second output pipe. A first compressor 10 is installed at the outlet of the membrane separation unit 8 to pressurize the crude helium gas supplied to the first heater 3.

[0048] The first purification unit 2 is a PSA purification unit that reduces the concentrations of H2O, CO2, and sulfides in natural gas to trace levels through desulfurization and decarbonization. The second purification unit 9 is a PSA purification unit that removes N2 and CH4 from crude helium gas through pressure swing adsorption.

[0049] The method for helium extraction from natural gas using cryogenic distillation coupled membrane separation in this embodiment includes the following steps:

[0050] (1) The helium-containing natural gas undergoes dehydration treatment in drying unit 1, followed by desulfurization and deacidification treatment in the first purification unit 2 to prevent H2O, CO2, and sulfides in the natural gas from causing blockage or corrosion inside pipelines and equipment at low temperatures; the above-mentioned raw material natural gas contains He, H2, N2, CO2, CH4, C2H6, C3H8, and C4H 10 C5H 12 The natural gas contains H2S, COS, CH3SH, CS2, H2O, and O2, with CH4 being the most abundant. He content ranges from 0.03% to 0.1% (volume fraction), and the contents of other components vary depending on the natural gas's origin. Dehydration is completed in the drying unit, using either triethylene glycol dehydration or other processes that achieve similar results. This invention does not limit the process used in the drying unit. Desulfurization and deacidification are completed in the PSA unit, utilizing the differences in adsorption performance of different media in the mixed gas under different pressures to achieve separation. After desulfurization and decarbonization in the first purification unit, the concentrations of H2O, CO2, and sulfides in the natural gas are reduced to trace levels.

[0051] (2) After being dehydrated, desulfurized and deacidified, the natural gas is cooled and enters the cryogenic distillation tower 4 for cryogenic separation. The liquid collected at the bottom of the tower is sold as a by-product LNG. The top of the tower separates crude helium gas with a high helium content. The crude helium gas composition includes at least He, H2, N2 and O2. The recovery rate of He in the crude helium gas is not less than 99.5% and the recovery rate of CH4 is not higher than 2%.

[0052] (3) After heating the crude helium to 40-100℃, it enters the hydrogenation reactor 6 for catalytic hydrogenation reaction, and then enters the dehydrogenation reactor 7 to remove the small amount of H2 contained in the crude helium. After the reaction, the H2 concentration drops to below 20ppb.

[0053] (4) The crude helium gas after catalytic hydrogenation reaction also contains N2 and CH4 impurities. The crude helium gas containing impurities is sent to membrane separation unit 8. A polycarbonate membrane or a polyimide He separation membrane with high He selectivity is used to separate the crude helium gas. Because the pressure drop is large after the gas passes through the membrane, the crude helium gas is pressurized by a compressor after membrane separation. The helium product obtained after treatment has a helium purity of 30% to 60%. The tail gas separated after membrane separation also contains helium. Its components include He, CH4 and N2. The tail gas is pressurized and mixed with fresh natural gas before entering low temperature distillation treatment.

[0054] (5) The crude helium gas after membrane separation also contains a small amount of N2 and CH4 impurities. The crude helium gas containing impurities is sent to the second purification unit 9 and He is purified by pressure swing adsorption technology. The helium product obtained after treatment has a helium purity of more than 99.99%. The desorbed gas separated by the second purification unit 9 also contains helium, and its components include He, CH4 and N2. The desorbed gas is pressurized and sent to the membrane separation unit to be mixed with the crude helium gas for purification.

[0055] Using ambient temperature, 3.5 MPaG low-helium-content natural gas from a natural gas well as the raw material, the specific helium extraction method is further explained as follows: The ambient temperature, 3.5 MPaG low-helium-content natural gas from the natural gas well is sent to the drying unit, where a triethylene glycol dehydration process is used to remove moisture from the natural gas. The dehydrated natural gas is sent to the first purification unit to remove acidic gases such as CO2, H2S, COS, and CS2. After being cooled in a cold box, the natural gas enters a cryogenic distillation column. The pressure at the top of the distillation column is approximately 3.3 MPaG, and the effluent is crude helium gas, whose main components are He, H2, N2, and CH4, with a helium content of approximately 6.5%. The bottom product of the cryogenic distillation column is liquefied natural gas (LNG), which can be exported as an LNG product. The crude helium gas is sent to the catalytic hydrogenation unit, where, under the action of a catalyst, oxygen and hydrogen react to generate water, which is then removed, thus achieving the purpose of hydrogen removal. The dehydrogenated crude helium is sent to a membrane separation unit, where a membrane with high He selectivity is used for separation. The purity of the separated crude helium is approximately 46%, but the pressure is low, requiring a compressor for pressurization. The tail gas separated after membrane separation still contains a significant amount of helium. After pressurization, it is mixed with fresh natural gas and returned to cryogenic distillation. The crude helium leaving the membrane separation unit enters a second purification unit, where He is purified using pressure swing adsorption (PSA). The resulting helium product has a helium purity higher than 99.99%. The desorbed gas separated in the second purification unit still contains a significant amount of helium, and its components should include He, CH4, N2, etc. After pressurization, it is sent to the membrane separation unit to be mixed with the crude helium for further purification. The corresponding logistics data is as follows:

[0056]

[0057] Example 2:

[0058] Low-helium natural gas (3.5 MPaG) at ambient temperature from the natural gas pipeline is sent to the first purification unit to remove CO2. After CO2 removal, the natural gas passes through a TSA unit to remove trace amounts of CO2, H2S, COS, and other acidic gases. It is then cooled in a cold box before entering a cryogenic distillation column. The pressure at the top of the distillation column is approximately 3.3 MPaG. The effluent is crude helium, primarily composed of He, H2, N2, and CH4, with a helium content of approximately 6.5%. The bottom product of the cryogenic distillation column is liquefied natural gas (LNG), which can be exported as LNG. The crude helium is then sent to a catalytic hydrogenation unit, where, under the action of a catalyst, oxygen and hydrogen react to generate and remove water, thus removing hydrogen. The dehydrogenated crude helium is then sent to a membrane separation unit, where a membrane with high He selectivity is used for membrane separation. The purity of the separated crude helium is approximately 46%, but the pressure is low, requiring a compressor for pressurization. The tail gas separated after membrane separation still contains a significant amount of helium. After pressurization, it is mixed with fresh natural gas and returned to cryogenic distillation. The crude helium gas leaving the membrane separation unit enters the second purification unit, where He is purified using pressure swing adsorption (PSA). The resulting helium product has a helium purity higher than 99.99%. The desorbed gas separated from the second purification unit still contains a significant amount of helium, and its components should include He, CH4, N2, etc. After pressurization, it is sent to the membrane separation unit to mix with the crude helium gas for further purification. The corresponding logistics data is as follows:

[0059]

Claims

1. A cryogenic distillation coupled membrane separation device for helium extraction from natural gas, characterized in that... include: The drying unit has an inlet for the input of lean helium natural gas and is used to remove water from the natural gas; The first purification unit is connected downstream of the drying unit and is used to desulfurize and deacidify the natural gas. A cryogenic distillation column is connected downstream of the first purification unit and is used to perform cryogenic separation on the natural gas after it has been processed by the drying unit and the first purification unit. The bottom of the cryogenic distillation column is provided with a first output port for liquid phase output and the top is provided with a second output port for crude helium gas obtained from the separation. A hydrogenation reactor and a dehydrogenation reactor are connected downstream of the cryogenic distillation column. The hydrogenation reactor and the dehydrogenation reactor are connected in series along the gas flow direction to remove H2 contained in the crude helium gas obtained from the cryogenic distillation column. A membrane separation unit, connected downstream of the dehydrogenation reactor, is used to perform membrane separation on crude helium to obtain crude helium with a purity of 30% to 60%. The second purification unit is connected downstream of the membrane separation unit and is used to remove other impurities from the crude helium gas after it has been processed by the membrane separation unit to obtain helium gas. The outlet of the membrane separation unit is equipped with a second compressor for pressurizing the crude helium gas supplied to the first heater. A first heat exchanger for cooling the natural gas entering the low-temperature distillation column is provided between the first purification unit and the low-temperature distillation column; a second heat exchanger for heating the crude helium gas is provided at the inlet of the hydrogenation reactor.

2. The cryogenic distillation coupled membrane separation natural gas helium extraction equipment according to claim 1, characterized in that: The membrane separation unit is provided with a first output pipe for outputting the separated tail gas, and the outlet of the first output pipe is connected to the inlet of the cryogenic distillation column.

3. The natural gas helium extraction equipment using cryogenic distillation coupled membrane separation according to claim 1, characterized in that: The second purification unit is provided with a second output pipe for outputting the obtained desorbed gas, and the outlet of the second output pipe is connected to the inlet of the membrane separation unit.

4. The natural gas helium extraction equipment using cryogenic distillation coupled membrane separation according to claim 3, characterized in that: A second compressor is provided downstream of the second purification unit for pressurizing the desorption gas that is sent to the membrane separation unit via the second output pipe.

5. The natural gas helium extraction equipment using cryogenic distillation coupled membrane separation according to any one of claims 1 to 4, characterized in that: The first purification unit is a PSA purification unit that can reduce the concentration of H2O, CO2, and sulfides in natural gas to trace levels through desulfurization and decarbonization.

6. The natural gas helium extraction equipment using cryogenic distillation coupled membrane separation according to any one of claims 1 to 4, characterized in that: The second purification unit is a PSA purification unit that can remove N2 and CH4 from crude helium gas through pressure swing adsorption.

7. A method for helium extraction from natural gas via cryogenic distillation coupled with membrane separation, characterized in that, The natural gas helium extraction equipment using the cryogenic distillation coupled membrane separation method described in any one of claims 1 to 6 Includes the following steps: (1) Helium-containing natural gas is dehydrated in the drying unit and then desulfurized and deacidified in the first purification unit to avoid blockage or corrosion of pipelines and equipment caused by H2O, CO2 and sulfides in natural gas at low temperature; after desulfurization and decarbonization in the first purification unit, the concentration of H2O, CO2 and sulfides in natural gas is reduced to trace amounts. (2) After being dehydrated, desulfurized and deacidified, the natural gas is cooled and then enters a cryogenic distillation column for cryogenic separation. The liquid collected at the bottom of the column is sold as a by-product, and crude helium gas with a high helium content is separated at the top of the column. The crude helium gas contains at least He, H2, N2 and O2. The recovery rate of He in the crude helium gas is not less than 99.5% and the recovery rate of CH4 is not higher than 2%. (3) After heating the crude helium to 40~100℃, it enters the hydrogenation reactor for catalytic hydrogenation reaction, and then enters the dehydrogenation reactor to remove the small amount of H2 contained in the crude helium. After the reaction, the H2 concentration drops to below 20ppb. (4) The crude helium gas after catalytic hydrogenation reaction also contains N2 and CH4 impurities. The crude helium gas containing impurities is sent to the membrane separation unit and the crude helium gas is separated by the separation membrane. Because the pressure drop is large after the gas passes through the membrane, the crude helium gas is pressurized by the compressor after membrane separation. The helium product obtained after treatment has a helium purity of 30% to 60%. The tail gas separated after membrane separation also contains helium. Its components include He, CH4 and N2. The tail gas is pressurized and mixed with fresh natural gas before entering the low temperature distillation treatment. (5) The crude helium gas after membrane separation also contains a small amount of N2 and CH4 impurities. The crude helium gas containing impurities is sent to the second purification unit and He is purified by pressure swing adsorption technology. The helium product obtained after treatment has a helium purity of more than 99.99%. The desorbed gas separated by the second purification unit also contains helium, and its components include He, CH4 and N2. The desorbed gas is pressurized and sent to the membrane separation unit to be mixed with the crude helium gas for purification.

8. The method for helium extraction from natural gas via cryogenic distillation coupled membrane separation according to claim 7, characterized in that: The raw material natural gas contains He, H2, N2, CO2, CH4, C2H6, C3H8, and C4H. 10 C5H 12 H2S, COS, CH3SH, CS2, H2O, O2, where CH The content of 4 was the highest, while the content of He ranged from 0.03% to 0.1%.

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