CN114106897A - Coupling system and method for preparing methane from carbon dioxide and preparing LNG from natural gas - Google Patents
Coupling system and method for preparing methane from carbon dioxide and preparing LNG from natural gas Download PDFInfo
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- CN114106897A CN114106897A CN202111407955.5A CN202111407955A CN114106897A CN 114106897 A CN114106897 A CN 114106897A CN 202111407955 A CN202111407955 A CN 202111407955A CN 114106897 A CN114106897 A CN 114106897A
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- C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
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- C07C1/12—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon from carbon dioxide with hydrogen
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Abstract
The invention discloses a coupling system and a coupling system for preparing methane from carbon dioxide and preparing LNG from natural gas. The method uses green electrolysis to produce hydrogen or the green hydrogen supplied from the outside reacts with carbon dioxide to generate methane, and the methane is coupled with natural gas liquefaction, so that the heat generated by methanation is used for natural gas liquefaction, the consumption of natural gas liquefied fuel natural gas is saved, and the yield of LNG is increased.
Description
Technical Field
The invention belongs to the field of LNG (liquefied natural gas) preparation by natural gas liquefaction, and particularly relates to a coupling system and method for preparing methane from carbon dioxide and LNG from natural gas.
Background
At present, in the process of preparing LNG by natural gas liquefaction, a certain amount of carbon dioxide is contained in natural gas, the carbon dioxide needs to be removed, the MDEA decarburization process is mostly adopted for carbon dioxide removal, heat needs to be consumed in the MDEA decarburization process, and the heat needed by the MDEA decarburization process and other heat needs of a liquefaction plant are provided by burning liquefied flash steam and part of raw material methane gas in natural gas liquefaction. The carbon dioxide removed from the MDEA and the carbon dioxide generated by fuel combustion are not recovered, and simultaneously, the natural gas also contains a small amount of sulfur which is also discharged to the atmosphere from the MDEA decarburization gas, thereby polluting the environment.
Disclosure of Invention
In view of the above, the main objective of the present invention is to provide a coupling system and method for preparing methane from carbon dioxide and LNG from natural gas.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
the embodiment of the invention provides a coupling system for preparing methane from carbon dioxide and preparing LNG from natural gas, which comprises a raw material natural gas compressor, a natural gas decarburization absorption tower, a natural gas drying and liquefying device, a natural gas decarburization regeneration tower, a carbon dioxide compressor, a carbon dioxide purification device and a methanation device, wherein the raw material natural gas compressor, the natural gas decarburization absorption tower and the natural gas drying and liquefying device are sequentially connected, one path of the natural gas drying and liquefying device outputs flash evaporation gas, the other path of the natural gas drying and liquefying device outputs liquefied natural gas LNG, the natural gas decarburization regeneration tower and the natural gas decarburization absorption tower are used for absorbing carbon dioxide, the inlet end of the carbon dioxide compressor, the natural gas decarburization regeneration tower and the outlet end of the carbon dioxide compressor are sequentially connected with the carbon dioxide purification device, a hydrogen pipeline and the methanation device, and the outlet end of the methanation device is connected with the raw material natural gas compressor, the natural gas decarburization regeneration tower and the methanation device, The natural gas decarbonization absorption tower is used for providing methane prepared by recovered carbon dioxide.
In the above scheme, the methanation device comprises an ejector, a first methanation reactor, a first steam generator, a second steam generator, a first heat recoverer, a second methanation reactor, a second heat recoverer, a second methanation water cooler, a first methanation gas heat exchanger, a third methanation water cooler and a methanation water generation flash tank, wherein the ejector, the first methanation reactor, the first steam generator, the second steam generator, the first heat recoverer, the second methanation reactor, the second heat recoverer, the second methanation water cooler, the third methanation gas heat exchanger, the third methanation water cooler and the methanation water generation flash tank are sequentially connected, the first steam generator and the second steam generator are connected with the ejector, the outlet end of the third methanation water cooler is connected with a raw material natural gas compressor, the first steam generator and the second steam generator, and the outlet end of the third methanation water cooler is connected with the raw material natural gas compressor, The water outlets of the first heat recoverer, the third methanation water cooler and the second methanation water cooler are connected with a methanation water generation flash tank, and the gas outlet end of the methanation water generation flash tank is connected between the natural gas decarburization regeneration tower and a carbon dioxide compressor; and the third methanation reactor is connected with a third methanation gas heat exchanger.
In the scheme, the system further comprises a hydrogen electrolysis device, wherein the hydrogen electrolysis device is arranged between the methanation water generation flash tank of the methanation device and the ejector; the device comprises a recovered water purification device, a water electrolysis hydrogen production device and a hydrogen compressor, wherein the recovered water purification device, the water electrolysis hydrogen production device and the hydrogen compressor are sequentially connected between the methanation water generation flash tank and the ejector.
In the above scheme, this system still includes tail gas processing apparatus, tail gas processing apparatus is connected with natural gas drying and liquefying plant, and the device prepares steamer, flue gas decarbonization absorption tower, flue gas decarbonization regenerator including the burning of flash distillation gas, the flash distillation gas output end of natural gas drying and liquefying plant connects gradually the burning of flash distillation gas and prepares steamer, flue gas decarbonization absorption tower, flue gas decarbonization absorber output flue gas, the flue gas decarbonization regenerator is connected with flue gas decarbonization absorption tower to connect and be used for providing the carbon dioxide of retrieving between natural gas decarbonization regenerator, carbon dioxide compressor.
In the scheme, the system further comprises a flash gas extraction device, the flash gas extraction device is connected with the natural gas drying and liquefying device, the device comprises a flash gas pressure swing adsorption methane extraction unit, and the flash gas pressure swing adsorption methane extraction unit is connected with the natural gas drying and liquefying device and used for exhausting tail gas and providing recovered methane for the natural gas drying and liquefying device.
In the scheme, the system also comprises a flash evaporation gas extraction device which is connected with the natural gas drying and liquefying device, the device comprises a natural gas liquefaction flash gas stripping helium methanation unit, a flash gas stripping helium pressure swing adsorption methane extraction unit, a flash gas stripping helium oxidative dehydrogenation unit and a flash gas stripping helium pressure swing adsorption helium extraction unit, the outlet end of the natural gas drying and liquefying device is sequentially connected with a natural gas liquefaction flash gas stripping helium methanation unit, a flash gas stripping helium pressure swing adsorption methane extraction unit, a flash gas stripping helium oxidative dehydrogenation unit and a flash gas stripping helium pressure swing adsorption helium extraction unit, the flash gas stripping helium pressure swing adsorption methane extraction unit is connected with a raw material natural gas compressor, the system is used for providing recovered methane, and one path of output tail gas at the outlet end of the flash gas stripping helium pressure swing adsorption helium extracting unit and one path of output recovered high-purity helium.
The embodiment of the invention also provides a coupling process for preparing methane from carbon dioxide and preparing LNG from natural gas, which comprises the following steps: compressing raw natural gas by a raw natural gas compressor, mixing the raw natural gas with methanated methane gas, then feeding the mixture into a natural gas decarburization absorption tower, absorbing carbon dioxide in the natural gas by regenerated MEDA solution, feeding the MEDA solution absorbing the carbon dioxide into a natural gas decarburization regeneration tower, feeding the regenerated carbon dioxide into a carbon dioxide compressor, and feeding the regenerated MEDA solution into an absorption tower for circular absorption; the natural gas from which the carbon dioxide is removed enters a natural gas drying and liquefying device to prepare an LNG product; the natural gas decarburization regeneration tower and the flash evaporation gas are mixed and then enter a carbon dioxide compressor for compression, the compressed gas enters a carbon dioxide purification device to remove sulfides in carbon dioxide to be below 0.05ppm, and then the gas passes through a methanation device to generate methane gas and is sent into a natural gas decarburization absorption tower.
In the above scheme, the method specifically comprises: mixing purified carbon dioxide and compressed hydrogen, then feeding the mixture into an ejector, injecting methanation reaction gas to return to the ejector for mixing, feeding the mixture into a first methanation reactor for methanation reaction, then feeding the mixture into a first steam generator for cooling and generating steam, feeding one part of the mixture back to the ejector, feeding the rest of the mixture into a second steam generator for cooling again and generating steam, then feeding the mixture into a first heat recoverer for cooling, wherein the first heat recoverer is used as a reboiler of a natural gas decarburization regeneration tower, condensed water discharged from the first heat recoverer is fed into a methanation water flash tank, gas discharged from the first heat recoverer is fed into a second methanation reactor, the gas firstly enters one side of the second methanation reactor for heat exchange, is heated by the other side of the second methanation reactor with catalyst, and then enters the other side of the second methanation reactor with catalyst for methanation reaction, the gas out of the second methanation water cooler enters a second heat recoverer for cooling, then enters a second methanation water cooler for cooling, the second heat recoverer is used as a reboiler of a natural gas decarburization regeneration tower, condensed water out of the second methanation water cooler is sent to a methanation water flash tank, the gas out of the second methanation water cooler enters a third methanation gas heat exchanger to be heated by outlet gas of the third methanation reactor, then enters a third methanation reactor for methanation reaction, the reaction gas out of the third methanation reactor sequentially enters a third methanation gas heat exchanger and a third methanation water cooler for cooling, the condensed water out of the third methanation water cooler is sent to a methanation water flash tank, the methane-containing gas out of the third methanation water cooler is sent to a natural gas decarburization absorption tower, flash gas generated by methanation of the methanation water flash tank is sent to a carbon dioxide compressor for compression, and feeding the water after flash evaporation into an electrolytic hydrogen device.
In the above scheme, the method specifically comprises: the recovered water purification device purifies the water after flash evaporation, the purified water enters the water electrolysis hydrogen production device to produce hydrogen through electrolysis, and the water outlet electrolysis hydrogen production device is compressed by a hydrogen compressor and is sent to the ejector.
In the above scheme, the method further comprises: and (2) introducing the flash gas into the natural gas liquefaction flash gas stripping helium methanation unit, simultaneously adding carbon dioxide for methanation reaction, reducing the hydrogen concentration to be below 1%, introducing the flash gas stripping helium pressure swing adsorption methane extraction unit, extracting methane, returning the extracted methane to a raw material natural gas compressor for recovery, introducing helium-containing gas after methane extraction into the flash gas stripping helium oxidative dehydrogenation unit, adding oxygen from a hydrogen electrolysis device byproduct and residual hydrogen in helium to react to generate water, introducing the water into the flash gas stripping helium pressure swing adsorption helium extraction unit to extract a high-purity helium product, and exhausting tail gas after helium extraction.
Compared with the prior art, the method uses green electrolysis to produce hydrogen or the green hydrogen supplied from the outside reacts with carbon dioxide to generate methane, is coupled with natural gas liquefaction, uses the heat generated by methanation for natural gas liquefaction, saves the consumption of natural gas liquefied fuel natural gas, increases the yield of LNG, can also provide the carbon dioxide and oxygen required by helium extraction from helium-containing natural gas, and reduces the emission of sulfides.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:
fig. 1 is a schematic connection diagram of a coupling system for producing methane from carbon dioxide and LNG from natural gas according to an embodiment of the present invention;
fig. 2 is a schematic connection diagram of a coupling system for producing methane from carbon dioxide and LNG from natural gas according to embodiment 1 of the present invention;
fig. 3 is a schematic connection diagram of a coupling system for producing methane from carbon dioxide and LNG from natural gas according to embodiment 2 of the present invention;
fig. 4 is a schematic connection diagram of a coupling system for producing methane from carbon dioxide and LNG from natural gas according to embodiment 3 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The same or similar reference numerals in the drawings of the present embodiment correspond to the same or similar components; in the description of the present invention, it is to be understood that the terms "upper", "lower", "left", "right", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, the terms describing the positional relationships in the drawings are only for illustrative purposes and are not to be construed as limitations of the present patent, and specific meanings of the terms may be understood by those skilled in the art according to specific situations.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, article, or apparatus that comprises the element.
The embodiment of the invention provides a coupling system for preparing methane from carbon dioxide and preparing LNG from natural gas, which comprises a raw material natural gas compressor 1, a natural gas decarburization absorption tower 2, a natural gas drying and liquefying device 3, a natural gas decarburization regeneration tower 4, a carbon dioxide compressor 5, a carbon dioxide purification device 6 and a methanation device 7, wherein the raw material natural gas compressor 1, the natural gas decarburization absorption tower 2 and the natural gas drying and liquefying device 3 are sequentially connected, one path of the natural gas drying and liquefying device 3 outputs flash gas, the other path of the natural gas drying and liquefying device outputs liquefied natural gas LNG, the natural gas decarburization regeneration tower 4 and the natural gas decarburization absorption tower 2 are used for absorbing carbon dioxide, the inlet end of the carbon dioxide compressor 5 is connected with the natural gas decarburization regeneration tower 4, and the outlet end of the carbon dioxide purification device 6, a hydrogen pipeline and the methanation device 7 are sequentially connected, the outlet end of the methanation device 7 is connected between the raw material natural gas compressor 1 and the natural gas decarburization absorption tower 2 and is used for providing methane prepared from recovered carbon dioxide.
The methanation device 7 comprises an ejector 71, a first methanation reactor 72, a first steam generator 73, a second steam generator 74, a first heat recoverer 75, a second methanation reactor 76, a second heat recoverer 77, a second methanation water cooler 78, a third methanation gas heat exchanger 79, a third methanation water cooler 710 and a methanation water flash tank 711, wherein the ejector 71, the first methanation reactor 72, the first steam generator 73, the second steam generator 74, the first heat recoverer 75, the second methanation reactor 76, the second heat recoverer 77, the second methanation water cooler 78, the third methanation gas heat exchanger 79, the third methanation water cooler 710 and the methanation water flash tank 711 are sequentially connected, the first steam generator 73 and the second steam generator 74 are connected with the ejector 71, the outlet end of the third methanation water cooler 710 is connected with the raw natural gas compressor 1, the first steam generator 73 and the second steam generator 74, and the outlet end of the third methanation water cooler 710 is connected with the raw natural gas compressor 1, the first heat recoverer 75, the second methanation water cooler 78, the third methanation water cooler 710 and the methanation water flash tank 711 are sequentially connected with the first methanation gas heat recoverer, Water outlets of the first heat recoverer 75, the third methanation water cooler 710 and the second methanation water cooler 78 are connected with a methanation water generation flash tank 711 among the natural gas decarburization absorption towers 2, and an air outlet end of the methanation water generation flash tank 711 is connected between the natural gas decarburization regeneration tower 4 and the carbon dioxide compressor 5; the third alkylation reactor 712 is coupled to a third alkylation gas heat exchanger 79.
Further, the system also comprises an electrolytic hydrogen device 8, wherein the electrolytic hydrogen device 8 is arranged between the methanation water generation flash tank 711 of the methanation device 7 and the ejector 71; the device comprises a recovery water purification device 81, a water electrolysis hydrogen production device 82 and a hydrogen compressor 83, wherein the recovery water purification device 81, the water electrolysis hydrogen production device 82 and the hydrogen compressor 83 are sequentially connected between a methanation generation water flash tank 711 and an ejector 71.
The gas compressed by the last stage of the hydrogen compressor 83 is not cooled and is sent to the subsequent methanation device 7, the source of the hydrogen is not limited to electrolytic hydrogen, the flow of the electrolytic hydrogen or the externally supplied hydrogen is determined according to the flow of the recovered carbon dioxide, the ratio of the flow of the hydrogen to the flow of the carbon dioxide (hydrogen-carbon ratio) is smaller than the theoretical ratio of the hydrogen to the carbon dioxide to react to generate methane, and the hydrogen-carbon ratio is controlled to be 3.6-4.
Further, the system further comprises a tail gas treatment device 9, the tail gas treatment device 9 is connected with the natural gas drying and liquefying device 3, the device comprises a flash gas combustion preparation steamer 91, a flue gas decarburization absorption tower 92 and a flue gas decarburization regeneration tower 93, the flash gas output end of the natural gas drying and liquefying device 3 is sequentially connected with the flash gas combustion preparation steamer 91 and the flue gas decarburization absorption tower 92, the flue gas decarburization absorption tower 92 outputs flue gas, and the flue gas decarburization regeneration tower 93 is connected with the flue gas decarburization absorption tower 92 and is connected between the natural gas decarburization regeneration tower 4 and the carbon dioxide compressor 5 for providing recovered carbon dioxide.
Further, the system also comprises a flash gas extraction device 10, wherein the flash gas extraction device 10 is connected with the natural gas drying and liquefying device 3, the device comprises a flash gas pressure swing adsorption methane extraction unit 1001, and the flash gas pressure swing adsorption methane extraction unit 1001 is connected with the natural gas drying and liquefying device 3 and is used for exhausting tail gas and providing recovered methane for the natural gas drying and liquefying device 3.
Further, the system also comprises a flash evaporation gas extraction device 10, the flash evaporation gas extraction device 10 is connected with the natural gas drying and liquefying device 3, the device comprises a natural gas liquefaction flash stripping helium methanation unit 1002, a flash stripping helium pressure swing adsorption methane extraction unit 1003, a flash stripping helium oxidation dehydrogenation unit 1004 and a flash stripping helium pressure swing adsorption helium extraction unit 1005, the outlet end of the natural gas drying and liquefying device 3 is sequentially connected with a natural gas liquefaction flash gas stripping helium methanation unit 1002, a flash gas stripping helium pressure swing adsorption methane extraction unit 1003, a flash gas stripping helium oxidation dehydrogenation unit 1004 and a flash gas stripping helium pressure swing adsorption helium extraction unit 1005, the flash evaporation gas stripping helium pressure swing adsorption methane extraction unit 1003 is connected with a raw material natural gas compressor 1, the outlet end of the flash gas stripping helium pressure swing adsorption helium extraction unit 1005 outputs one path of tail gas and one path of high-purity helium gas which are recovered.
Further, the system also comprises a flash gas extraction device 10, wherein the flash gas extraction device 10 is connected with the natural gas drying and liquefying device 3, the device comprises a flash gas pressure swing adsorption methane extraction unit 1006, the flash gas pressure swing adsorption methane extraction unit 1006 extracts methane in the flash gas and returns the methane to the natural gas drying and liquefying device 3 for recycling, and tail gas is discharged after the methane is extracted.
The embodiment of the invention also provides a coupling process for preparing methane from carbon dioxide and preparing LNG from natural gas, which comprises the following steps: compressing raw natural gas by a raw natural gas compressor 1, mixing the raw natural gas with methanated methane gas, then feeding the mixture into a natural gas decarburization absorption tower 2, absorbing carbon dioxide in the natural gas by regenerated MEDA solution, feeding the MEDA solution absorbing the carbon dioxide into a natural gas decarburization regeneration tower 4, feeding the regenerated carbon dioxide into a carbon dioxide compressor 5, and feeding the regenerated MEDA solution into the absorption tower 2 for cyclic absorption; the natural gas from which the carbon dioxide is removed enters a natural gas drying and liquefying device 3 to prepare an LNG product; the natural gas decarburization regeneration tower 4 and the flash evaporation gas are mixed and then enter a carbon dioxide compressor 5 for compression, the compressed gas enters a carbon dioxide purification device 6 for removing sulfide in carbon dioxide to be below 0.05ppm, and then the gas passes through a methanation device 7 for generating methane-containing gas and is sent into a natural gas decarburization absorption tower 2.
The method specifically comprises the following steps: mixing the purified carbon dioxide and the compressed hydrogen, then feeding the mixture into an ejector 71, injecting the methanation reaction gas back into the ejector 71 for mixing, feeding the mixture into a first methanation reactor 72 for methanation reaction, then feeding the mixture into a first steam generator 73 for cooling and generating steam, feeding a part of the mixture back into the ejector 71, feeding the rest of the mixture into a second steam generator 74 for cooling again and generating steam, then feeding the mixture into a first heat recoverer 75 for cooling, wherein the first heat recoverer 75 is used as a reboiler of a natural gas decarburization regeneration tower 4, feeding condensed water out of the first heat recoverer 75 into a methanation water flash tank 711, feeding the gas out of the first heat recoverer 75 into a second methanation reactor 76, feeding the gas into one side of the second methanation reactor 76 for heat exchange, heating the gas by the other side of the second methanation reactor 76, which is provided with a catalyst, and feeding the gas into the other side of the second methanation reactor 72, which is provided with the catalyst, for methanation reaction, the gas out of the second methanation water cooler 72 enters a second heat recoverer 77 for cooling, then enters a second methanation water cooler 78 for cooling, the second heat recoverer 77 is used as a reboiler of the natural gas decarburization regeneration tower 4, condensed water out of the second methanation water cooler 78 is demethanized to generate a water flash tank 711, the gas out of the second methanation water cooler 78 enters a third methanation gas heat exchanger 79 to be heated by outlet gas of the third methanation reactor 712, then enters a third methanation reactor 712 for methanation reaction, the reaction gas out of the third methanation reactor 712 sequentially enters a third methanation gas heat exchanger 79 and a third methanation water cooler 710 for cooling, the condensed water out of the third methanation water cooler 710 is demethanized to generate a water flash tank, the gas out of the third methanation water cooler 711 contains 96.6% of methane and enters a natural gas decarburization absorption tower 2, the flash steam generated by methanation in the water flash tank 711 is compressed by the carbon dioxide compressor 5, and the water after flash evaporation is sent to the hydrogen electrolysis device 8.
The method specifically comprises the following steps: the recovered water purification device 81 purifies the water after flash evaporation, the purified water enters the water electrolysis hydrogen production device 82 for electrolysis hydrogen production, and the water outlet electrolysis hydrogen production device 82 is compressed by the hydrogen compressor 83 and is sent to the ejector 71.
The method further comprises the following steps: the flash gas enters the natural gas liquefaction flash gas stripping helium methanation unit 1002, carbon dioxide is added for methanation reaction, the concentration of hydrogen is reduced to be below 1%, the flash gas stripping helium pressure swing adsorption methane extraction unit 1003 is then entered, methane is extracted and returned to the raw material natural gas compressor 1 for recovery, helium-containing gas after methane extraction enters the flash gas stripping helium oxidation dehydrogenation unit 1004, oxygen from the by-product of the hydrogen electrolysis device 82 is added to react with the residual hydrogen in the helium to generate water, then the flash gas stripping helium pressure swing adsorption helium extractor 1005 is entered to extract a high-purity helium product, and the tail gas is emptied after the helium is extracted.
When the helium content in the flash gas is high and helium products in the flash gas need to be recovered, a process of recovering the helium adopts methanation and an oxygen dehydrogenation process, according to the total amount of hydrogen in the flash gas, part of carbon dioxide separated from the purified carbon dioxide according to a hydrogen-carbon ratio of about 2 (hydrogen to carbon dioxide) is mixed with the flash gas, methanation reaction is carried out, most of hydrogen in the flash gas is reacted to generate methane, and then the helium, a small amount of hydrogen and other components are separated through PSA pressure swing adsorption. Other components mainly comprise methane, nitrogen and unreacted carbon dioxide, the methane, the carbon dioxide and the nitrogen are separated through PSA pressure swing adsorption, the nitrogen is discharged, and the methane and the carbon dioxide return to natural gas for decarburization and recovery; separating a certain amount of oxygen from the electrolytic hydrogen byproduct oxygen, mixing the oxygen with a small amount of hydrogen and helium separated by PSA pressure swing adsorption, performing oxidation reaction, completely generating water from the hydrogen in the helium, and purifying the helium by PSA pressure swing adsorption to obtain a high-purity helium product.
Example 1:
the process flow of coupling the preparation of methane from carbon dioxide and the preparation of LNG from natural gas in the embodiment is as follows:
as shown in FIG. 1, in this example, LNG is prepared by liquefying natural gas at 100 ten thousand squares daily, the natural gas pressure is about 0.4MPa (G), and the flow rate is 41700Nm3H, the composition is as follows: 90.36% of methane, 1.08% of ethane, 0.2% of other alkanes, 3.22% of carbon dioxide and 5.14% of nitrogen, wherein the raw natural gas is compressed to 3.6Mpa (G) by a raw natural gas compressor 1, the raw natural gas is mixed with methanated methane gas and then enters a natural gas decarburization absorption tower 2, the carbon dioxide in the natural gas is absorbed by a regenerated MEDA solution, the MEDA solution absorbing the carbon dioxide enters a natural gas decarburization regeneration tower 4, and the regenerated carbon dioxide is about 1424Nm3The regenerated MEDA solution is sent to an absorption tower 2 for cyclic absorption; the natural gas after the carbon dioxide removal enters a natural gas drying and liquefying device 3 to prepare about 41493Nm3H LNG product. Flash gas of about 304Nm in the natural gas drying and liquefying plant 33H is of33% of methane enters a flash gas combustion steam preparation device 91, flash gas combustion flue gas enters a flue gas decarburization absorption tower 92 to absorb carbon dioxide by using regenerated amine solution, the absorbed flue gas is discharged, the amine solution absorbing the carbon dioxide enters a flue gas decarburization regeneration tower 93, and the regenerated carbon dioxide is about 100Nm3The/h is compressed by a carbon dioxide compressor 6, and the regenerated amine solution is circularly absorbed by an absorption tower 92.
The carbon dioxide regenerated from the natural gas decarburization regeneration tower 4 and the flue gas decarburization regeneration tower 93 and the flash evaporation gas of the methanation water flash evaporation tank 711 are mixed and then enter the carbon dioxide compressor 6 to be compressed to 4.1Mpa (G), the final stage of the compressor 6 is not cooled, the temperature of the outlet carbon dioxide is about 123 ℃, and the mixture enters the carbon dioxide purification device 6 to remove the sulfides in the carbon dioxide to below 0.05 ppm. The purified water enters a water electrolysis hydrogen production device 82 to produce hydrogen by electrolysis, the pressure of hydrogen from the water electrolysis hydrogen production device 82 is about 2.0Mpa (G), the hydrogen is compressed to 4.1Mpa (G) by a hydrogen compressor 83, the compressed outlet is not cooled, the temperature of the outlet hydrogen is about 102 ℃, and the flow rate is 5799Nm3/h。
Mixing the purified carbon dioxide with the compressed hydrogen, introducing into an injector 71, and adjusting the temperature to 330 deg.C and 21997Nm3The methanation reaction gas is injected to return to the ejector to be mixed, the mixed temperature is about 282 ℃, the mixed reaction gas enters the first methanation reactor 72 to be subjected to methanation reaction, the outlet temperature of the first methanation reactor 72 is about 483 ℃, the mixed reaction gas enters the first steam generator 73 to be cooled to 330 ℃ and generate steam, the reaction gas out of the first steam generator 73 is divided into two parts, one part returns to the ejector 71, the other part enters the second steam generator 74 to be cooled to 200 ℃ and generate steam, then the reaction gas enters the first heat recoverer 75 to be cooled to 120 ℃, the first heat recoverer 75 serves as a reboiler of the natural gas decarburization regeneration tower 4 to provide regeneration heat for the regeneration tower 4, the condensation water out of the first heat recoverer 75 is subjected to demethanization to generate a water flash tank 711, and the gas out of the first heat recoverer 75 enters the second methanation reactor 76. The gas out of the first heat recoverer 75 enters a second methanation reactor 76, the second methanation reactor 76 is a reactor with a heat exchange device, the gas firstly enters one side of the second methanation reactor 76 for heat exchange, and the second methanation reactor 76 is provided with a catalystHeating the other side of the catalyst to about 290 ℃, then introducing the heated other side of the catalyst into a second methanation reactor 76 for methanation reaction, introducing the obtained reaction gas out of the second methanation reactor 76 with a temperature of about 354 ℃, introducing the obtained reaction gas into a second heat recoverer 77 for cooling to 120 ℃, introducing the obtained reaction gas into the second heat recoverer 77 as a reboiler of a natural gas decarburization regeneration tower 4 for providing regeneration heat for the regeneration tower 4, introducing the obtained gas out of the second heat recoverer 77 into a first methanation water cooler 78 for cooling to 40 ℃, introducing the obtained gas out of the first methanation water cooler 78 for demethanization to generate a water flash tank 711, introducing the obtained gas out of the first methanation water cooler 78 into a first methanation gas heat exchanger 79, heating the obtained gas to about 290 ℃ by the outlet gas of a third methanation reactor 712, introducing the obtained gas out of the third methanation reactor 712 with a temperature of about 317 ℃, sequentially introducing the obtained gas into the first methanation gas heat exchanger 79 and the third methanation water cooler 710 for cooling to 40 ℃, the condensed water from the third alkylation water cooler 710 is subjected to demethanization to generate a water flash tank 711, and the gas from the third alkylation water cooler 710 contains 96.6 percent of methane and about 1534Nm3And h, removing the natural gas decarburization absorption tower 2. About 2340kg/h of water generated by methanation enters a methanation water generation flash tank 711, and the flash steam is about 30Nm3And h, the carbon dioxide is removed, the water is compressed by the compressor 6, about 2330kg/h of water after flash evaporation is purified by the recovered water purification device 81, and then the water is sent to the water electrolysis hydrogen production device 82 to produce hydrogen through electrolysis.
The invention adopts green electricity to electrolyze and produce hydrogen, then prepares methane from the hydrogen and the recovered carbon dioxide, and couples the heat of methanation with the liquefaction of natural gas, compared with the liquefaction of natural gas without recovering carbon dioxide, reduces the fuel natural gas by about 300Nm3Increased LNG production 1760Nm3/h, emission reduction of carbon dioxide 1760Nm3And h, the annual emission reduction of carbon dioxide is 2.8 million tons, the annual emission reduction of sulfides is about 27 tons, the near zero emission of the carbon dioxide of the LNG product prepared from natural gas is realized, and the byproduct saturated steam is 5.5 t/h.
Example 2:
the process flow of coupling the preparation of methane from carbon dioxide and the preparation of LNG from natural gas in the embodiment is as follows:
as shown in fig. 2. In this embodiment, the LNG is prepared by liquefying natural gas at 150 ten thousand squares every day, and the pressure of the natural gas is about0.2MPa (G) and a flow rate of 62500Nm3H, the composition is as follows: 92% of methane, 1% of ethane, 4% of carbon dioxide and 3% of nitrogen, wherein the raw material natural gas is compressed to 4.0Mpa (G) by a raw material natural gas compressor 1, mixed with methanated methane gas and then enters a natural gas decarburization absorption tower 2, the carbon dioxide in the natural gas is absorbed by regenerated MEDA solution, the MEDA solution absorbing the carbon dioxide enters a natural gas decarburization regeneration tower 4, and the regenerated carbon dioxide is about 2690Nm3The regenerated MEDA solution is sent to an absorption tower 2 for cyclic absorption; the natural gas from which the carbon dioxide is removed enters a natural gas drying and liquefying device 3 to prepare about 66485Nm3H LNG product. Flash gas of about 269Nm in the natural gas drying and liquefying plant 33And h, the methane containing 44% enters a flash evaporation gas pressure swing adsorption methane extractor 1001, the methane is extracted and returned to the natural gas drying and liquefying device 3 for recovery, and the tail gas after methane extraction is discharged.
Mixing the natural gas decarbonization regeneration tower 4 and flash steam of the methanation water generation flash tank 711, compressing the mixture in a carbon dioxide compressor 6 to 4.5Mpa (G), not cooling the final stage of the compressor 6, and enabling the outlet carbon dioxide to have the temperature of about 125 ℃, and then mixing the outlet carbon dioxide with externally added carbon dioxide and 4483Nm3And the mixture is mixed and then enters a carbon dioxide purification device 6 to remove the sulfide in the carbon dioxide to below 0.05 ppm. The purified water enters a water electrolysis hydrogen production device 82 to produce hydrogen by electrolysis, the pressure of hydrogen from the hydrogen production device 82 is about 2.5Mpa (G), the hydrogen is compressed to 4.5Mpa (G) by a hydrogen compressor 83, the compressed outlet is not cooled, the temperature of the outlet hydrogen is about 113 ℃, and the flow rate is 27960Nm3/h。
Mixing the purified carbon dioxide and compressed hydrogen, introducing into injector 71, and heating to 330 deg.C and 105436Nm3Injecting the methanation reaction gas to return to the ejector for mixing, enabling the mixed gas to have a temperature of about 280 ℃, entering the first methanation reactor 72 for methanation reaction, enabling the mixed gas to have an outlet temperature of about 486 ℃ from the first methanation reactor 72, entering the first steam generator 73 for cooling to 330 ℃ and generating steam, enabling the reaction gas exiting the first steam generator 73 to be divided into two parts, enabling one part to return to the ejector 71, enabling the other part to enter the second steam generator 74 for cooling to 160 ℃ and generating steam, and then entering the first heatThe temperature of the recoverer 75 is reduced to 120 ℃, the first heat recoverer 75 is used as a reboiler of the natural gas decarburization regeneration tower 4 to provide regeneration heat for the regeneration tower 4, condensed water is removed from the first heat recoverer 75 for dealkylation to generate a water flash tank 711, and gas discharged from the first heat recoverer 75 enters the second methanation reactor 76. The gas discharged from the first heat recoverer 75 enters a second methanation reactor 76, the second methanation reactor 76 is a reactor with a heat exchange device, the gas firstly enters one side of the second methanation reactor 76 for heat exchange, is heated to about 290 ℃ by the other side of the second methanation reactor 76 filled with a catalyst, then enters the other side of the second methanation reactor 76 filled with the catalyst for methanation reaction, the temperature of the gas discharged from the second methanation reactor 76 is about 355 ℃, the gas enters a second heat recoverer 77 for cooling to 120 ℃, the second heat recoverer 77 serves as a reboiler of a natural gas decarburization regeneration tower 4 for providing regeneration heat for the regeneration tower 4, the second heat is discharged, enters a first methanation water cooler 78 for cooling to 40 ℃, the condensed water of the first methanation water cooler 78 for demethanization is discharged to generate a water flash tank 711, the gas discharged from the first methanation water cooler 78 enters a first methanation gas heat exchanger 79, is heated to about 290 ℃ by the outlet gas of the third methanation reactor 712, then the gas enters a third methanation reactor 712 for methanation reaction, the temperature of the reaction gas discharged from the third methanation reactor 712 is about 323 ℃, the reaction gas sequentially enters a first methanation gas heat exchanger 79 and a third methanation water cooler 710 for cooling to 40 ℃, condensed water discharged from the third methanation water cooler 710 is subjected to demethanization to generate a water flash tank 711, the gas discharged from the third methanation water cooler 710 contains 96.7 percent of methane, and the flow rate is 7209Nm3And h, removing the natural gas decarburization absorption tower 2. The water generated by methanation enters a flash tank 711 for generating water by methanation at a rate of 11247kg/h, and the flash gas is about 155Nm3And h, the carbon dioxide-removing compressor 6 compresses the water, 11233kg/h of the water after flash evaporation is purified by the recovered water purification device 81, and then the water is sent to the water electrolysis hydrogen production device 82 to produce hydrogen through electrolysis.
The method adopts green electricity to electrolyze and produce hydrogen, then prepares methane from the hydrogen, the recovered carbon dioxide and the externally supplied carbon dioxide, couples the methanation heat with the natural gas liquefaction, and reduces the fuel natural gas by about 450Nm compared with the natural gas liquefaction without recovering the carbon dioxide3H, increaseLNG production 8780Nm3Per hour, carbon dioxide reduction 8780Nm3And h, the annual emission reduction of carbon dioxide is 14.8 million tons, the annual emission reduction of sulfides is about 40 tons, the negative emission of carbon dioxide of LNG products prepared from natural gas is realized, and the byproduct of saturated steam is 25 t/h.
Example 3:
the process flow of coupling the preparation of methane from carbon dioxide and the preparation of LNG from natural gas in the embodiment is as follows:
the flow is shown in fig. 3. In this embodiment, LNG is liquefied from 200 ten thousand squares of natural gas per day, and the natural gas pressure is about 0.2MPa (G) and the flow rate is 83300Nm3H, the composition is as follows: 91% of methane, 1% of ethane, 4% of carbon dioxide, 3.99% of nitrogen, 0.07% of helium and 0.03% of hydrogen, compressing raw natural gas to 4.0Mpa (G) by a raw natural gas compressor 1, mixing the raw natural gas with methanated methane, feeding the mixture into a natural gas decarburization absorption tower 2, absorbing carbon dioxide in the natural gas by regenerated MEDA solution, feeding the MEDA solution absorbing the carbon dioxide into a natural gas decarburization regeneration tower 4, wherein the regenerated carbon dioxide is about 3657Nm3The regenerated MEDA solution is sent to an absorption tower 2 for cyclic absorption; the natural gas after the carbon dioxide removal enters a natural gas drying and liquefying device 3 to prepare about 83131Nm3H LNG product. Flash gas of about 243Nm in the natural gas drying and liquefying plant 33The methane containing 23 percent of methane, 36 percent of nitrogen, 24 percent of helium and 17 percent of hydrogen enters a natural gas liquefaction flash stripping helium methanator 1002, and simultaneously 40Nm of carbon dioxide is added3Performing methanation reaction, reducing the hydrogen concentration to be below 0.7 percent, then entering a flash stripping helium pressure swing adsorption methane extractor 1003, extracting methane, returning the extracted methane to a raw material natural gas compressor 1 for recycling, entering a flash stripping helium oxidation dehydrogenation device 1004 after extracting methane, adding 2Nm3The oxygen reacts with the residual hydrogen in the helium to generate water, and then the water enters a flash evaporation helium stripping pressure swing adsorption helium extractor 1005 to extract 55Nm3H, exhausting tail gas after extracting helium from a high-purity helium product.
The natural gas decarbonization regeneration tower 4 and flash evaporation gas of the methanation water generation flash evaporation tank 711 are mixed and then enter a carbon dioxide compressor 6 to be compressed to 4.5Mpa (G), the final stage of the compressor 6 is not cooled,the temperature of outlet carbon dioxide is about 125 ℃, then the carbon dioxide enters a carbon dioxide purification device 6 to remove sulfide in the carbon dioxide to be below 0.05ppm, and then the carbon dioxide is separated to be 40Nm3The/h goes to the natural gas liquefaction flash gas stripping helium methanator 1002, and the rest goes to the ejector 71. The purified water enters a water electrolysis hydrogen production device 82 to produce hydrogen by electrolysis, the pressure of hydrogen from the hydrogen production device 82 is about 2.5Mpa (G), the hydrogen is compressed to 4.5Mpa (G) by a hydrogen compressor 83, the compressed outlet is not cooled, the temperature of the outlet hydrogen is about 113 ℃, and the flow rate is 13000Nm3/h。
Mixing the purified carbon dioxide and compressed hydrogen, introducing into injector 71, and heating to 330 deg.C and 50187Nm3Injecting the methanation reaction gas to return to the ejector for mixing, wherein the mixed temperature is about 284 ℃, the mixed reaction gas enters the first methanation reactor 72 for methanation reaction, the outlet temperature of the first methanation reactor 72 is about 488 ℃, the mixed reaction gas enters the first steam generator 73 for cooling to 330 ℃ and generating steam, the reaction gas discharged from the first steam generator 73 is divided into two parts, one part returns to the ejector 71, the other part enters the second steam generator 74 for cooling to 220 ℃ and generating steam, then the reaction gas enters the first heat recoverer 75 for cooling to 120 ℃, the first heat recoverer 75 serves as a reboiler of the natural gas decarburization regeneration tower 4 for providing regeneration heat for the regeneration tower 4, the condensed water discharged from the first heat recoverer 75 is subjected to demethanization to generate a water flash tank 711, and the gas discharged from the first heat recoverer 75 enters the second methanation reactor 76. The gas discharged from the first heat recoverer 75 enters a second methanation reactor 76, the second methanation reactor 76 is a reactor with a heat exchange device, the gas firstly enters one side of the second methanation reactor 76 for heat exchange, is heated to about 290 ℃ by the other side of the second methanation reactor 76 filled with a catalyst, then enters the other side of the second methanation reactor 76 filled with the catalyst for methanation reaction, the temperature of the gas discharged from the second methanation reactor 76 is about 358 ℃, the gas enters a second heat recoverer 77 for cooling to 120 ℃, the second heat recoverer 77 serves as a reboiler of a natural gas decarburization regeneration tower 4 for providing regeneration heat for the regeneration tower 4, the second heat recoverer 77 enters a first methanation water cooler 78 for cooling to 40 ℃, condensed water discharged from the first methanation water cooler 78 for demethanization to generate a water flash tank 711, and the first methanation water-cooling water is dischargedThe gas in the device 78 enters a first methanation gas heat exchanger 79 and is heated to about 290 ℃ by the outlet gas of a third methanation reactor 712, then enters the third methanation reactor 712 for methanation reaction, the temperature of the reaction gas out of the third methanation reactor 712 is about 323 ℃, the gas sequentially enters the first methanation gas heat exchanger 79 and a third methanation water cooler 710 for cooling to 40 ℃, the condensed water in the third methanation water cooler 710 is discharged for demethanization to generate water flash tank 711, the gas out of the third methanation water cooler 710 contains 96.6 percent of methane and about 3430Nm3And h, removing the natural gas decarburization absorption tower 2. About 6670kg/h of water generated by methanation enters a methanation water generation flash tank 711, and the flash gas is about 73Nm3And h, the carbon dioxide is removed, the water is compressed by the compressor 6, about 6610kg/h of water after flash evaporation is purified by the recovered water purification device 81, and then the water is sent to the water electrolysis hydrogen production device 82 to produce hydrogen through electrolysis.
The method adopts green electricity to electrolyze to produce hydrogen, then prepares methane from hydrogen and recycled carbon dioxide, couples the methanation heat with natural gas liquefaction, simultaneously uses partial carbon dioxide and byproduct oxygen of hydrogen electrolysis for extracting helium from flash evaporation gas, and reduces fuel natural gas by about 600 Nm compared with natural gas liquefaction without recycling carbon dioxide3Increased LNG production 3880Nm3H, reduction of carbon dioxide 3880Nm3And h, 6.1 million tons of carbon dioxide are discharged in year, about 54 tons of sulfide are discharged in year, the near zero emission of the carbon dioxide of the LNG product prepared from natural gas is realized, meanwhile, 8.4t/h of saturated steam is byproduct, and 55Nm of helium is byproduct3/h。
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention.
Claims (10)
1. The coupling system for preparing methane from carbon dioxide and preparing LNG from natural gas is characterized by comprising a raw material natural gas compressor, a natural gas decarburization absorption tower, a natural gas drying and liquefying device, a natural gas decarburization regeneration tower, a carbon dioxide compressor, a carbon dioxide purification device and a methanation device, wherein the raw material natural gas compressor, the natural gas decarburization absorption tower and the natural gas drying and liquefying device are sequentially connected, one path of flash gas is output from the natural gas drying and liquefying device, the other path of liquefied natural gas LNG is output from the natural gas decarburization regeneration tower and the natural gas decarburization absorption tower, the inlet end of the carbon dioxide compressor is connected with the natural gas decarburization regeneration tower, the outlet end of the carbon dioxide compressor is sequentially connected with the carbon dioxide purification device, a hydrogen pipeline and the methanation device, and the outlet end of the methanation device is connected with the raw material natural gas compressor, the natural gas decarburization regeneration tower and the natural gas decarburization absorption tower, The natural gas decarbonization absorption tower is used for providing methane prepared by recovered carbon dioxide.
2. The coupling system for coupling carbon dioxide to methane and natural gas to LNG as claimed in claim 1, wherein the methanation device comprises an ejector, a first methanation reactor, a first steam generator, a second steam generator, a first heat recoverer, a second methanation reactor, a second heat recoverer, a second methanation water cooler, a first methanation gas heat exchanger, a third methanation water cooler, and a methanation water flash tank, the ejector, the first methanation reactor, the first steam generator, the second steam generator, the first heat recoverer, the second methanation reactor, the second heat recoverer, the second methanation water cooler, the third methanation gas heat exchanger, the third methanation water cooler, and the methanation water flash tank are sequentially connected, the first steam generator and the second steam generator are connected with the ejector, the outlet end of the third methanation water cooler is connected between the raw material natural gas compressor and the natural gas decarburization absorption tower, the water outlets of the first heat recoverer, the third methanation water cooler and the second methanation water cooler are all connected with a methanation water flash tank, and the gas outlet end of the methanation water flash tank is connected between the natural gas decarburization regeneration tower and the carbon dioxide compressor; and the third methanation reactor is connected with a third methanation gas heat exchanger.
3. The coupling system for producing methane from carbon dioxide and LNG from natural gas according to claim 1 or 2, further comprising an electrolytic hydrogen device disposed between the methanation water generation flash tank of the methanation device and the ejector; the device comprises a recovered water purification device, a water electrolysis hydrogen production device and a hydrogen compressor, wherein the recovered water purification device, the water electrolysis hydrogen production device and the hydrogen compressor are sequentially connected between the methanation water generation flash tank and the ejector.
4. The coupling system for preparing methane from carbon dioxide and LNG from natural gas according to claim 3, further comprising a tail gas treatment device, wherein the tail gas treatment device is connected to the natural gas drying and liquefying device, the device comprises a flash gas combustion preparation steamer, a flue gas decarburization absorption tower, and a flue gas decarburization regeneration tower, the flash gas output end of the natural gas drying and liquefying device is sequentially connected to the flash gas combustion preparation steamer and the flue gas decarburization absorption tower, the flue gas decarburization absorption tower outputs flue gas, and the flue gas decarburization regeneration tower is connected to the flue gas decarburization absorption tower and connected between the natural gas decarburization regeneration tower and the carbon dioxide compressor for providing recovered carbon dioxide.
5. The coupled system for preparing methane from carbon dioxide and LNG from natural gas according to claim 4, further comprising a flash gas extraction device connected to the natural gas drying and liquefying device, wherein the device comprises a flash gas pressure swing adsorption methane extraction unit connected to the natural gas drying and liquefying device for exhausting tail gas and providing recovered methane to the natural gas drying and liquefying device.
6. The coupled system for producing methane from carbon dioxide and LNG from natural gas according to claim 4, it is characterized in that the system also comprises a flash evaporation gas extraction device which is connected with the natural gas drying and liquefying device, the device comprises a natural gas liquefaction flash gas stripping helium methanation unit, a flash gas stripping helium pressure swing adsorption methane extraction unit, a flash gas stripping helium oxidative dehydrogenation unit and a flash gas stripping helium pressure swing adsorption helium extraction unit, the outlet end of the natural gas drying and liquefying device is sequentially connected with a natural gas liquefaction flash gas stripping helium methanation unit, a flash gas stripping helium pressure swing adsorption methane extraction unit, a flash gas stripping helium oxidative dehydrogenation unit and a flash gas stripping helium pressure swing adsorption helium extraction unit, the flash gas stripping helium pressure swing adsorption methane extraction unit is connected with a raw material natural gas compressor, the system is used for providing recovered methane, and one path of output tail gas at the outlet end of the flash gas stripping helium pressure swing adsorption helium extracting unit and one path of output recovered high-purity helium.
7. A coupling process for preparing methane from carbon dioxide and preparing LNG from natural gas is characterized by comprising the following steps: compressing raw natural gas by a raw natural gas compressor, mixing the raw natural gas with methanated methane gas, then feeding the mixture into a natural gas decarburization absorption tower, absorbing carbon dioxide in the natural gas by regenerated MEDA solution, feeding the MEDA solution absorbing the carbon dioxide into a natural gas decarburization regeneration tower, feeding the regenerated carbon dioxide into a carbon dioxide compressor, and feeding the regenerated MEDA solution into an absorption tower for circular absorption; the natural gas from which the carbon dioxide is removed enters a natural gas drying and liquefying device to prepare an LNG product; the natural gas decarburization regeneration tower and the flash evaporation gas are mixed and then enter a carbon dioxide compressor for compression, the compressed gas enters a carbon dioxide purification device to remove sulfides in carbon dioxide to be below 0.05ppm, and then the gas passes through a methanation device to generate methane gas and is sent into a natural gas decarburization absorption tower.
8. The coupling process for preparing methane from carbon dioxide and preparing LNG from natural gas according to claim 7, wherein the method specifically comprises: mixing purified carbon dioxide and compressed hydrogen, then feeding the mixture into an ejector, injecting methanation reaction gas to return to the ejector for mixing, feeding the mixture into a first methanation reactor for methanation reaction, then feeding the mixture into a first steam generator for cooling and generating steam, feeding one part of the mixture back to the ejector, feeding the rest of the mixture into a second steam generator for cooling again and generating steam, then feeding the mixture into a first heat recoverer for cooling, wherein the first heat recoverer is used as a reboiler of a natural gas decarburization regeneration tower, condensed water discharged from the first heat recoverer is fed into a methanation water flash tank, gas discharged from the first heat recoverer is fed into a second methanation reactor, the gas firstly enters one side of the second methanation reactor for heat exchange, is heated by the other side of the second methanation reactor with catalyst, and then enters the other side of the second methanation reactor with catalyst for methanation reaction, the gas out of the second methanation water cooler enters a second heat recoverer for cooling, then enters a second methanation water cooler for cooling, the second heat recoverer is used as a reboiler of a natural gas decarburization regeneration tower, condensed water out of the second methanation water cooler is sent to a methanation water flash tank, the gas out of the second methanation water cooler enters a third methanation gas heat exchanger to be heated by outlet gas of the third methanation reactor, then enters a third methanation reactor for methanation reaction, the reaction gas out of the third methanation reactor sequentially enters a third methanation gas heat exchanger and a third methanation water cooler for cooling, the condensed water out of the third methanation water cooler is sent to a methanation water flash tank, the methane-containing gas out of the third methanation water cooler is sent to a natural gas decarburization absorption tower, flash gas generated by methanation of the methanation water flash tank is sent to a carbon dioxide compressor for compression, and feeding the water after flash evaporation into an electrolytic hydrogen device.
9. The coupling process for preparing methane from carbon dioxide and preparing LNG from natural gas according to claim 8, wherein the method specifically comprises: the recovered water purification device purifies the water after flash evaporation, the purified water enters the water electrolysis hydrogen production device to produce hydrogen through electrolysis, and the water outlet electrolysis hydrogen production device is compressed by a hydrogen compressor and is sent to the ejector.
10. The coupled process of carbon dioxide to methane and natural gas to LNG of claim 8 or 9, wherein the method further comprises: and (2) introducing the flash gas into the natural gas liquefaction flash gas stripping helium methanation unit, simultaneously adding carbon dioxide for methanation reaction, reducing the hydrogen concentration to be below 1%, introducing the flash gas stripping helium pressure swing adsorption methane extraction unit, extracting methane, returning the extracted methane to a raw material natural gas compressor for recovery, introducing helium-containing gas after methane extraction into the flash gas stripping helium oxidative dehydrogenation unit, adding oxygen from a hydrogen electrolysis device byproduct and residual hydrogen in helium to react to generate water, introducing the water into the flash gas stripping helium pressure swing adsorption helium extraction unit to extract a high-purity helium product, and exhausting tail gas after helium extraction.
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| CN109609220A (en) * | 2018-11-29 | 2019-04-12 | 山西易高煤层气有限公司 | A kind of method of coal bed gas LNG natural gas |
| CN110295071A (en) * | 2019-06-21 | 2019-10-01 | 浙江臻泰能源科技有限公司 | The bio-natural gas preparation facilities and method of joint Methane decarbonization purification technique and hydrogenation of carbon dioxide methanation |
| CN110358594A (en) * | 2019-06-21 | 2019-10-22 | 清华四川能源互联网研究院 | Water electrolysis hydrogen production and CO2The device and method of methanation synthetic natural gas |
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