CN103980930A - Device for recovery of light hydrocarbons and co-production of LNG from tail gas of Fischer-Tropsch synthesis and method thereof - Google Patents
Device for recovery of light hydrocarbons and co-production of LNG from tail gas of Fischer-Tropsch synthesis and method thereof Download PDFInfo
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- 229930195733 hydrocarbon Natural products 0.000 title claims abstract description 37
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 8
- 238000011084 recovery Methods 0.000 title claims abstract description 5
- 239000007789 gas Substances 0.000 claims abstract description 177
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 37
- 239000004215 Carbon black (E152) Substances 0.000 claims abstract description 28
- 239000007788 liquid Substances 0.000 claims abstract description 24
- 239000001257 hydrogen Substances 0.000 claims abstract description 14
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 14
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- 238000003860 storage Methods 0.000 claims abstract description 7
- 239000002737 fuel gas Substances 0.000 claims abstract description 5
- 238000000926 separation method Methods 0.000 claims description 62
- 239000003507 refrigerant Substances 0.000 claims description 60
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 41
- 239000012528 membrane Substances 0.000 claims description 39
- 239000003949 liquefied natural gas Substances 0.000 claims description 35
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 21
- 239000001569 carbon dioxide Substances 0.000 claims description 20
- 230000008569 process Effects 0.000 claims description 20
- 238000005057 refrigeration Methods 0.000 claims description 18
- 238000010521 absorption reaction Methods 0.000 claims description 16
- 150000001412 amines Chemical class 0.000 claims description 15
- 230000018044 dehydration Effects 0.000 claims description 15
- 238000006297 dehydration reaction Methods 0.000 claims description 15
- 238000001816 cooling Methods 0.000 claims description 14
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 11
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 11
- 239000002808 molecular sieve Substances 0.000 claims description 10
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 claims description 10
- 238000005262 decarbonization Methods 0.000 claims description 8
- 229910052757 nitrogen Inorganic materials 0.000 claims description 7
- 230000008929 regeneration Effects 0.000 claims description 6
- 238000011069 regeneration method Methods 0.000 claims description 6
- 230000020335 dealkylation Effects 0.000 claims description 4
- 238000006900 dealkylation reaction Methods 0.000 claims description 4
- 238000003303 reheating Methods 0.000 claims description 3
- 238000003795 desorption Methods 0.000 claims description 2
- 230000008901 benefit Effects 0.000 abstract description 4
- 238000011143 downstream manufacturing Methods 0.000 abstract description 4
- 239000000047 product Substances 0.000 abstract description 4
- 238000005261 decarburization Methods 0.000 abstract description 2
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- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 6
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- LCGLNKUTAGEVQW-UHFFFAOYSA-N Dimethyl ether Chemical compound COC LCGLNKUTAGEVQW-UHFFFAOYSA-N 0.000 description 2
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 2
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
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- 239000000463 material Substances 0.000 description 2
- CRVGTESFCCXCTH-UHFFFAOYSA-N methyl diethanolamine Chemical class OCCN(C)CCO CRVGTESFCCXCTH-UHFFFAOYSA-N 0.000 description 2
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- -1 Benfield) Chemical compound 0.000 description 1
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 description 1
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- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 1
- 241000695274 Processa Species 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 238000007036 catalytic synthesis reaction Methods 0.000 description 1
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- 238000001704 evaporation Methods 0.000 description 1
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- 238000002309 gasification Methods 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- VUZPPFZMUPKLLV-UHFFFAOYSA-N methane;hydrate Chemical compound C.O VUZPPFZMUPKLLV-UHFFFAOYSA-N 0.000 description 1
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- 229940072033 potash Drugs 0.000 description 1
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Substances [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 description 1
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- 239000001294 propane Substances 0.000 description 1
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 1
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- 230000002194 synthesizing effect Effects 0.000 description 1
- YTWOHSWDLJUCRK-UHFFFAOYSA-N thiolane 1,1-dioxide Chemical compound O=S1(=O)CCCC1.O=S1(=O)CCCC1 YTWOHSWDLJUCRK-UHFFFAOYSA-N 0.000 description 1
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- Separation Using Semi-Permeable Membranes (AREA)
- Separation By Low-Temperature Treatments (AREA)
Abstract
The invention discloses a method for recovery of light hydrocarbons and co-production of LNG from tail gas of Fischer-Tropsch synthesis. The method comprises the following steps: tail gas from a Fischer-Tropsch synthesis unit passes through a supercharging decarburization unit to remove a CO2 component and then remove H2O therein; the purified tail gas is cooled and then enters a dethanizer; light hydrocarbons are removed from the tail gas in the dethanizer, cooled at the bottom of the dethanizer and then enters a downstream process unit; the tail gas at the top of the dethanizer enters a demethanizer; liquid methane flows out of the demethanizer and cryogenic treatment is continuously carried out to obtain LNG which enters an LNG storage tank; after the tail gas at the top of the demethanizer is reheated, H2, CO and N2 therein are separated; a separated permeate gas with an appropriate H2/CO ratio returns the Fischer-Tropsch synthesis unit or a PSA hydrogen production device; and the N2-containing tail gas is emptied or used as a fuel gas. By the use of the method for recovering light hydrocarbons from the tail gas, operating cost of the device can be reduced effectively, yield of hydrocarbon products is raised, and LNG is coproduced. Then, good economic benefit can be obtained.
Description
Technical Field
The invention relates to a method for recovering light hydrocarbon and co-producing LNG from tail gas of Fischer-Tropsch synthesis.
Background
Fischer-Tropsch synthesis is a synthesis gas (CO + H) discovered in the twenties of the twentieth century2) The reaction for the catalytic synthesis of hydrocarbon liquid fuels over a catalyst is found by Fischer and Tropsch chemists in germany, also known for short as Fischer-Tropsch synthesis or F-T synthesis. Fischer-Tropsch synthesis, as a method for synthesizing hydrocarbon liquid fuel from synthesis gas, has been industrialized in China. The synthesis gas can be obtained by gasifying coal or biomass, the biomass resource of Chinese coal is rich, but the petroleum resource is relatively insufficient, the demand of liquid fuel is continuously increased along with the development of the economic society, and the conversion of the coal or the biomass into the liquid fuel by using Fischer-Tropsch synthesis plays an important role in relieving the insufficient supply of the liquid fuel in China and promoting the sustainable and stable development of the economic society.
A large amount of Fischer-Tropsch synthesis tail gas is generated in the Fischer-Tropsch synthesis reaction process, and the Fischer-Tropsch synthesis tail gas mainly contains H2CO, light hydrocarbon, methane and CO2、N2And the like. Fischer-Tropsch synthesis tail gas is generally recycled to the inlet of the Fischer-Tropsch synthesis reactor to increase the overall hydrocarbon conversion and yield, and the remainder is usually burned as fuel and also recycled to the gasification unit.
The effective components of the Fischer-Tropsch synthesis are CO and H2The existence of hydrocarbons in the Fischer-Tropsch synthesis tail gas reduces the partial pressure of effective components, increases the load of a Fischer-Tropsch synthesis reactor system, and causes higher equipment investment and operation cost.
Disclosure of Invention
The invention aims to provide a method for recovering light hydrocarbon from tail gas of Fischer-Tropsch synthesis and coproducing LNG (liquefied natural gas). the method for recovering hydrocarbons in the tail gas can effectively reduce the operation cost of a device, not only can improve the yield of hydrocarbon products, but also can coproduce liquefied methane (LNG for short), thereby obtaining better economic benefit.
The invention relates to a device for recovering light hydrocarbon and coproducing LNG (liquefied natural gas) from tail gas of Fischer-Tropsch synthesis, which comprises a pressurization decarbonization unit, a dehydration unit, a cryogenic separation unit, a membrane separation unit and a refrigeration unit; the pressurizing and decarbonizing unit consists of a tail gas compressor, a carbon dioxide absorption tower, an amine-rich liquid flash tank, a lean and rich amine heat exchanger, a carbon dioxide desorption tower, a lean amine cooler, a lean amine filter and a lean amine booster pump; the pressure boosting and decarbonizing unit is used for boosting the synthetic tail gas to 4.0-6.0 MPa; the dehydration unit consists of a molecular sieve tower, a regenerated gas heater, a regenerated gas cooler and a regenerated gas separator; the dehydration unit is used for dehydrating the synthetic tail gas and controlling the water content of the synthetic tail gas to be not more than 50 ppm; the membrane separation unit consists of a tail gas heater and a membrane separation component; the refrigerating unit consists of a refrigerant compressor, a refrigerant compressor interstage cooler, a refrigerant compressor interstage separator, a refrigerant compressor outlet cooler, a refrigerant compressor outlet separator, a refrigerant compressor interstage booster pump and a cold box; the refrigerant compressor is a centrifugal compressor; the cryogenic separation unit consists of a deethanizer, a deethanizer bottom reboiler, a deethanizer top cooler, a demethanizer bottom reboiler and a demethanizer top cooler, wherein the deethanizer top cooler and the demethanizer cooler adopt plate-fin heat exchangers; the cryogenic separation unit is used for removing C in tail gas3 +And (4) components.
The invention relates to a method for recovering light hydrocarbon and coproducing LNG (liquefied natural gas) from tail gas of Fischer-Tropsch synthesis, which comprises the following steps:
step one, a tail gas compressor is utilized to pressurize Fischer-Tropsch synthesis tail gas from a Fischer-Tropsch synthesis unit to 4.0 MPa-6.0 MPa, and the Fischer-Tropsch synthesis tail gas is cooled to 40-50 ℃;
step two, the pressurized Fischer-Tropsch synthesis tail gas enters a carbon dioxide absorption tower, and the carbon dioxide in the Fischer-Tropsch synthesis tail gas is absorbed and removed by the carbon dioxide absorption tower;
step three, the decarbonized tail gas from which the carbon dioxide is removed enters a downstream molecular sieve tower, the molecular sieve tower absorbs and removes water in the decarbonized tail gas, and the water content of the dehydrated purified gas is not more than 50 ppm;
step four, the dehydrated purified gas enters a cold box and is cooled to the temperature of minus 40 ℃ to minus 60 ℃;
step five, the cooled dehydrated and purified gas enters a deethanizer for separation, gas-phase components flow out from the tower top of the deethanizer, and light hydrocarbon flows out from the tower bottom of the deethanizer and is conveyed to a downstream device;
step six, after the gas-phase component flowing out of the top of the deethanizer enters a demethanizer, wherein: the hydrocarbon-removing tail gas flows out from the top of the demethanizer, and the liquid methane flows out from the bottom of the demethanizer;
seventhly, continuously carrying out deep cooling on the liquid methane to obtain liquefied natural gas, and then conveying the liquefied natural gas to an LNG storage tank; the hydrocarbon-removed tail gas enters a cold box to be reheated to 0-20 ℃, then the temperature of the tail gas is raised to 40-50 ℃ by a tail gas heater, the tail gas enters a membrane separation assembly, hydrogen-rich gas generated by the membrane separation assembly is conveyed to a Fischer-Tropsch synthesis device or a PSA hydrogen production device, and the nitrogen-rich gas is discharged;
step eight, the low-pressure refrigerant is pressurized and cooled by the refrigerant compressor to become a high-pressure refrigerant, the high-pressure refrigerant is throttled and depressurized in the cold box, the low-pressure refrigerant is reheated after cold energy is provided for the cryogenic separation unit, and then the low-pressure refrigerant is pressurized and recycled by the refrigerant compressor.
In the seventh step, the CO/H in the hydrogen-rich gas can be adjusted by controlling the amount of the de-hydrocarbon tail gas entering the membrane separation assembly2The ratio of (a) to (b).
Compared with the prior art, the invention has the beneficial effects that:
the method of the invention is a combined process of decarburization, dehydration, cryogenic separation, membrane separation and refrigeration. Firstly removing carbon dioxide and water from tail gas from a Fischer-Tropsch synthesis device, cooling the tail gas, then feeding the cooled tail gas into a cryogenic deethanizer, removing light hydrocarbon from the tail gas in the deethanizer, flowing out of the deethanizer from the bottom of the tower, cooling the cooled tail gas, then feeding the cooled tail gas into a downstream process unit, removing the tail gas from the top of the deethanizer into a demethanizer, and removing the tail gas from the bottom of theThe main component of the bottom material flow of the methane tower is liquid methane, the liquid methane is continuously subjected to cryogenic cooling to be LNG after flowing out of the bottom material flow, the LNG is sent to an LNG storage tank, tail gas at the top of the demethanizer is reheated and then enters a membrane separation unit, and H in the tail gas is subjected to H separation2CO and N2Separation is carried out. Separation of appropriate H2The permeation gas with the ratio of/CO returns to a Fischer-Tropsch synthesis device or a PSA hydrogen production device and contains N2The tail gas is discharged or used as fuel gas. The invention can improve the yield of hydrocarbon products and coproduce LNG, thereby obtaining better economic benefit.
Drawings
FIG. 1 is a process diagram of an embodiment 1 of the present invention for recovering light hydrocarbons and co-producing LNG from Fischer-Tropsch synthesis tail gas;
FIG. 2 is a process diagram of example 2 of the present invention for the recovery of light hydrocarbons and the co-production of LNG from the tail gas of Fischer-Tropsch synthesis;
FIG. 3 is a process flow diagram for the recovery of light hydrocarbons and the co-production of LNG from the tail gas of the Fischer-Tropsch synthesis according to the present invention.
In the figure: 101-Fischer-Tropsch synthesis tail gas; 102-decarbonizing the tail gas; 103-dehydrating and purifying the gas; 104-high pressure refrigerant; 105-a low pressure refrigerant; 106-light hydrocarbon; 107-liquid methane; 108-hydrocarbon removal tail gas; 109-hydrogen rich gas; 110-nitrogen rich gas.
Detailed Description
The technical solution of the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.
As shown in FIG. 3, the device for recovering light hydrocarbon and co-producing LNG from tail gas of Fischer-Tropsch synthesis comprises a pressurized decarbonization unit 10, a dehydration unit 20, a cryogenic separation unit 30, a membrane separation unit 50 and a refrigeration unit 40.
The pressurizing and decarbonizing unit 10 is composed of a tail gas compressor 1, a carbon dioxide absorption tower 2, an amine-rich liquid flash tank 3, a lean and rich amine heat exchanger 4, a carbon dioxide analysis tower 5, a lean amine cooler 6, a lean amine filter 7 and a lean amine booster pump 8; the pressure boost decarbonization unit 10 is used for boosting the synthetic tail gas to 4.0-6.0 MPa. The pressure-enhanced decarbonization unit 10 can be selected from a chemical absorption method, a physical absorption method or a physical-chemical absorption method. Typical chemical absorption methods are: monoethanolamine (MEA), Diethanolamine (DEA), activated N-Methyldiethanolamine (MDEA), hot potash (e.g., Benfield), etc.; typical physical absorption methods are: the propylene carbonate method (Fluor), the low-temperature methanol washing method (Rectisol), the dimethyl ether with polyethylene glycol method (Selexol/NHD), the N-methylpyrrolidone NMP method (Purisol), and the like, and typical physical-chemical absorption methods include: normal temperature methanol washing (Amisol), Sulfolane (Sulfolane) and Hiperl (Hi-Pure).
The dehydration unit 20 is composed of a molecular sieve tower 11, a regeneration gas heater 12, a regeneration gas cooler 13 and a regeneration gas separator 14; the dehydration unit 20 is used for dehydrating the synthesis tail gas and controlling the water content of the synthesis tail gas to be not more than 50 ppm. The dehydration unit 20 may select a cooling dehydration method, a solvent absorption method, a solid adsorption method, a chemical reaction method, and a membrane separation method. Typical solid sorption dehydration methods are: activated alumina adsorption, silica gel adsorption and molecular sieve adsorption and their combined dewatering process.
The refrigeration unit 40 is composed of a refrigerant compressor 31, a refrigerant compressor interstage cooler 32, a refrigerant compressor interstage separator 33, a refrigerant compressor outlet cooler 35, a refrigerant compressor outlet separator 36, a refrigerant compressor interstage booster pump 34 and a cold box 37; the refrigerant compressor is a centrifugal compressor; the refrigeration unit 40 mainly provides refrigeration capacity for the whole device, and the refrigeration unit 40 can select a cascade liquefaction process, a mixed refrigerant liquefaction process and a liquefaction process with an expander. The mixed refrigerant liquefaction process can be as follows: closed Mixed Refrigerant refrigeration liquefaction process (Closed Mixed Refrigerant Cycle), Propane pre-cooled Mixed Refrigerant liquefaction process (C3/MRC), CII liquefaction process (Integrated Incorporated cassette), and dual Mixed Refrigerant refrigeration liquefaction processA Double Cycle mixed refrigerant liquefaction process (DMR). The refrigerant adopted by the mixed refrigerant liquefaction process is C1～C5And N2. The core equipment cold box 37 of the refrigeration unit 40 may be a plate fin type cold box or a coiled tube type cold box.
The cryogenic separation unit 30 is composed of a deethanizer 21, a deethanizer bottom reboiler 22, a deethanizer top cooler 23, a demethanizer 24, a demethanizer bottom reboiler 25 and a demethanizer top cooler 26, wherein the deethanizer top cooler 23 and the demethanizer top cooler 26 adopt plate-fin heat exchangers; the cryogenic separation unit 30 is used for removing C in the tail gas3 +And (4) components. The main function of the deethanizer 21 is to cryogenically remove C in Fischer-Tropsch synthesis tail gas3 +Component (containing C)3Component), the number of theoretical plates of the deethanizer is 5-40, preferably 30, the temperature at the top of the deethanizer is-120-20 ℃, the preferred temperature at the top of the deethanizer is-100-50 ℃, the temperature at the bottom of the deethanizer is 20-140 ℃, the preferred temperature at the bottom of the deethanizer is 100-120 ℃, the operating pressure is 1.0-6.0 MPa, and the preferred operating pressure is 3.1-4.0 MPa; the overhead gas of the deethanizer is the stripping C3 +Component (containing C)3Component) of dry gas, the main components of which are CO and H2、N2And CH4(ii) a The tower bottom component of the deethanizer is C3 +The components flow out from the bottom of the deethanizer, are cooled and conveyed to a downstream process unit, and are further separated into LPG and light hydrocarbon. And cooling the tower top dry gas of the deethanizer and then feeding the cooled tower top dry gas into the demethanizer. The main function of the demethanizer is to remove CH in dry gas by deep cooling4The number of theoretical plates of the demethanizer is 5-40, the preferable number is 30, the temperature of the top of the demethanizer is-120-170 ℃, the temperature of the top of the demethanizer is-100-160 ℃, the temperature of the bottom of the demethanizer is-88-130 ℃, the temperature of the bottom of the demethanizer is-60-130 ℃, the operating pressure is 1.0-6.0 MPa, the preferable operating pressure is 3.1-4.0 MPa, the gas at the top of the demethanizer is the tail gas after hydrocarbon removal, and the main components of the gas are CO and H2And N2(ii) a The bottom component of the demethanizer is CH4From the bottom of the demethanizer to a subsequent effluentAnd then is transported to an LNG storage tank after cryogenic cooling.
The membrane separation unit 50 is composed of a tail gas heater 41 and a membrane separation assembly 42; the separation membrane selected by the membrane separation unit 50 includes an asymmetric membrane or a thin-layer composite membrane. The membrane separation unit 50 can adjust the amount of the purified tail gas entering the membrane separation unit according to the requirement, and control the degree of membrane separation, so that any H can be produced after part of the non-permeate gas obtained by the membrane separation unit 50 is mixed with the purified tail gas which does not enter the membrane separation unit2The gas with the/CO ratio returns to the Fischer-Tropsch synthesis unit. The membrane separation unit 50 may recover only hydrogen, CO and N therein2As fuel gas or as blow-down.
The invention relates to a method for recovering light hydrocarbon and coproducing LNG from tail gas of Fischer-Tropsch synthesis, which mainly comprises the following processes: the tail gas from the Fischer-Tropsch synthesis unit is first passed through a pressurised decarbonisation unit 10 to remove CO therefrom2The components are then passed through a dehydration unit 20 to remove H therefrom2Cooling the purified tail gas, feeding the cooled tail gas into a deethanizer of a cryogenic separation unit 30, removing light hydrocarbon from the tail gas in the deethanizer, cooling the tail gas from the bottom of the deethanizer, feeding the cooled tail gas to a downstream process unit, feeding the tail gas from the top of the deethanizer into a demethanizer, continuously cooling the liquid methane from the bottom of the demethanizer to LNG, feeding the LNG to an LNG storage tank, reheating the tail gas from the top of the demethanizer, feeding the reheated tail gas into a membrane separation unit, and separating H from the liquid methane2CO and N2Separation is carried out. Separation of appropriate H2The permeation gas with the ratio of/CO is returned to the Fischer-Tropsch synthesis reactor and contains N2And (5) exhausting tail gas. As shown in fig. 1, the method specifically comprises the following steps:
step one, a tail gas compressor 1 is utilized to pressurize Fischer-Tropsch synthesis tail gas 101 from a Fischer-Tropsch synthesis unit to 4.0 MPa-6.0 MPa, and the Fischer-Tropsch synthesis tail gas is cooled to 40-50 ℃;
step two, the pressurized Fischer-Tropsch synthesis tail gas 101 enters a carbon dioxide absorption tower 2, and the carbon dioxide in the Fischer-Tropsch synthesis tail gas is absorbed and removed by the carbon dioxide absorption tower 2;
step three, the decarbonized tail gas 102 from which the carbon dioxide is removed enters a downstream molecular sieve tower 11, the molecular sieve tower 11 absorbs and removes water in the decarbonized tail gas 102, and the water content of the dehydrated purified gas 103 is not more than 50 ppm;
step four, the dehydrated purified gas 103 is cooled to minus 40 ℃ to minus 60 ℃ after entering a cold box 37;
step five, the cooled dehydrated and purified gas 103 enters a deethanizer 21 for separation, gas-phase components flow out from the tower top of the deethanizer 21, and light hydrocarbon 106 flows out from the tower bottom of the deethanizer 21 and then is conveyed to a downstream device;
step six, after the gas phase component flowing out from the top of the deethanizer enters the demethanizer 24, wherein: the hydrocarbon-removed tail gas 108 flows out of the top of the demethanizer 24, and the liquid methane 107 flows out of the bottom of the demethanizer 24;
seventhly, continuously carrying out deep cooling on the liquid methane 107 to obtain liquefied natural gas, and then conveying the liquefied natural gas to an LNG storage tank; the dealkylation tail gas 108 enters the cold box 37 to be reheated to 0-20 ℃, then is heated to 40-50 ℃ by the tail gas heater 41 and enters the membrane separation component 42, and meanwhile, the CO/H in the hydrogen-rich gas 109 can be adjusted by controlling the amount of the dealkylation tail gas 108 entering the membrane separation component 422The hydrogen-rich gas 109 produced by the membrane separation module 42 is sent to a downstream device, and the nitrogen-rich gas 110 is emptied or used as fuel gas;
and step eight, the low-pressure refrigerant 104 is pressurized and cooled by the refrigerant compressor 31 to become a high-pressure refrigerant 105, the high-pressure refrigerant 105 is throttled and depressurized in the cold box 37, cold energy is provided for the cryogenic separation unit 30, then the low-pressure refrigerant 104 is reheated, and the refrigerant compressor 31 is used in a pressurization cycle.
As shown in FIG. 1, Fischer-Tropsch synthesis tail gas 101 from a Fischer-Tropsch synthesis unit is pressurized and subjected to carbon dioxide removal in a pressurized decarbonization unit 10. The decarbonized tail gas 102 after decarbonization is removed water in the tail gas by the dehydration unit 20, the dehydrated purified gas 103 enters the cryogenic separation unit 30, the gas is cooled to a certain temperature by a cold box in the cryogenic separation unit 30 and then enters the deethanizer 21, and the tower bottom liquid of the deethanizer 21, namely light hydrocarbon 106, is cooledThen the tail gas is transmitted to a downstream device, the tail gas at the top of the deethanizer enters a demethanizer 24 after being continuously cooled by a cold box, the liquid at the bottom of the demethanizer 24 is continuously subjected to deep cooling by the cold box to form liquid methane 107, and the tail gas 108 from the demethanizer 24 after being reheated enters a membrane separation unit 50. The refrigeration capacity of the cryogenic separation unit 30 is provided by the refrigeration unit 40, the refrigeration unit 40 releases the refrigeration capacity through the physical processes of temperature reduction, flash evaporation, reheating and the like in the cold box by the high-pressure refrigerant 104, then the refrigeration capacity is changed into the low-pressure refrigerant 105, the low-pressure refrigerant is returned to the refrigeration unit 40, the low-pressure refrigerant is pressurized by the refrigerant compressor and then returned to the cryogenic separation unit 30, and the circulation of a refrigerant system is realized. The dehydrocarbon tail gas 108 is separated into hydrogen-rich gas 109 and nitrogen-rich gas 110 in the membrane separation unit 50 by using the selective permeability of the membrane module, and at the same time, as shown in fig. 2, the amount of the purified tail gas entering the membrane separation unit can be adjusted according to the need, and the degree of membrane separation can be controlled, so that any H can be produced after the part of the non-permeable gas obtained by the membrane separation unit 50 is mixed with the purified tail gas which does not enter the membrane separation unit2The gas with the/CO ratio returns to the Fischer-Tropsch synthesis unit. Data of various streams (including Fischer-Tropsch synthesis tail gas 101, decarbonization tail gas 102, dehydrated purified gas 103, high-pressure refrigerant 104, low-pressure refrigerant 105, light hydrocarbon 106, liquid methane 107, dealkylation tail gas 108, hydrogen-rich gas 109 and nitrogen-rich gas 110) formed in the process are shown in Table 1:
in summary, the examples and the data in Table 1 show that the method of the present invention can be used to treat Fischer-Tropsch synthesis tail gas to obtain suitable CO/H2Compared with the hydrogen-rich gas, light hydrocarbon and methane in the Fischer-Tropsch synthesis tail gas are recovered to the maximum extent and become final products, and the economic benefit is remarkable. Meanwhile, the number of process equipment is small, and the operation is simple.
While the present invention has been described with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are illustrative only and not restrictive, and various modifications which do not depart from the spirit of the present invention and which are intended to be covered by the claims of the present invention may be made by those skilled in the art.
Claims (3)
1. A device for recovering light hydrocarbon and co-producing LNG from tail gas of Fischer-Tropsch synthesis comprises a pressurization decarbonization unit (10), a dehydration unit (20), a cryogenic separation unit (30), a membrane separation unit (50) and a refrigeration unit (40); wherein,
the pressurizing and decarbonizing unit (10) is composed of a tail gas compressor (1), a carbon dioxide absorption tower (2), an amine-rich liquid flash tank (3), a lean and rich amine heat exchanger (4), a carbon dioxide desorption tower (5), a lean amine cooler (6), a lean amine filter (7) and a lean amine booster pump (8); the pressure boosting and decarbonizing unit (10) is used for boosting the synthetic tail gas to 4.0-6.0 MPa;
the dehydration unit (20) is composed of a molecular sieve tower (11), a regeneration gas heater (12), a regeneration gas cooler (13) and a regeneration gas separator (14); the dehydration unit (20) is used for dehydrating the synthetic tail gas and controlling the water content of the synthetic tail gas to be not more than 50 ppm;
the membrane separation unit (50) is composed of a tail gas heater (41) and a membrane separation assembly (42);
the refrigeration unit (40) is composed of a refrigerant compressor (31), a refrigerant compressor interstage cooler (32), a refrigerant compressor interstage separator (33), a refrigerant compressor outlet cooler (35), a refrigerant compressor outlet separator (36), a refrigerant compressor interstage booster pump (34) and a cold box (37); the refrigerant compressor is a centrifugal compressor;
the method is characterized in that:
the cryogenic separation unit (30) is composed of a deethanizer (21), a deethanizer bottom reboiler (22), a deethanizer top cooler (23), a demethanizer (24), a demethanizer bottom reboiler (25) and a demethanizer top cooler (26), wherein the deethanizer top cooler (23) and the demethanizer bottom cooler (26) adopt plate-fin heat exchangers; the cryogenic separation unit (30) is used for removing C in the tail gas3 +And (4) components.
2. A process for the recovery of light hydrocarbons and the co-production of LNG from the tail gas of a fischer-tropsch synthesis, using the plant of claim 1, and comprising the following steps:
step one, a tail gas compressor (1) is utilized to pressurize Fischer-Tropsch synthesis tail gas (101) from a Fischer-Tropsch synthesis unit to 4.0 MPa-6.0 MPa, and the Fischer-Tropsch synthesis tail gas is cooled to 40-50 ℃;
step two, the pressurized Fischer-Tropsch synthesis tail gas (101) enters a carbon dioxide absorption tower (2), and the carbon dioxide in the Fischer-Tropsch synthesis tail gas is absorbed and removed by the carbon dioxide absorption tower (2);
step three, the decarbonized tail gas (102) from which the carbon dioxide is removed enters a downstream molecular sieve tower (11), the molecular sieve tower (11) absorbs and removes water in the decarbonized tail gas (102), and the water content of the dehydrated purified gas (103) is not more than 50 ppm;
step four, the dehydrated purified gas (103) enters a cold box (37) and is cooled to minus 40 ℃ to minus 60 ℃;
step five, the cooled dehydrated and purified gas (103) enters a deethanizer (21) for separation, gas-phase components flow out from the top of the deethanizer (21), and light hydrocarbon (106) flows out from the bottom of the deethanizer (21) and then is conveyed to a downstream device;
step six, after the gas-phase component flowing out of the top of the deethanizer enters a demethanizer (24), wherein: the hydrocarbon-removing tail gas (108) flows out from the top of the demethanizer (24), and the liquid methane (107) flows out from the bottom of the demethanizer (24);
seventhly, continuously carrying out cryogenic cooling on the liquid methane (107) to obtain liquefied natural gas, and then conveying the liquefied natural gas to an LNG storage tank; the dealkylation tail gas (108) enters a cold box (37) to be reheated to 0-20 ℃, then is heated to 40-50 ℃ by a tail gas heater (41) and enters a membrane separation assembly (42), a hydrogen-rich gas (109) generated by the membrane separation assembly (42) is conveyed to a downstream device, and a nitrogen-rich gas (110) is discharged or used as fuel gas;
and step eight, the low-pressure refrigerant (104) is supercharged and cooled by the refrigerant compressor (31) to become a high-pressure refrigerant (105), the high-pressure refrigerant (105) is throttled and depressurized in the cold box (37), the low-pressure refrigerant (104) is formed by reheating after cold energy is provided for the cryogenic separation unit (30), and then the low-pressure refrigerant is supercharged and recycled by the refrigerant compressor (31).
3. The method for recovering light hydrocarbons and CO-producing LNG from Fischer-Tropsch synthesis tail gas as claimed in claim 2, wherein in step seven, the CO/H content of the hydrogen-rich gas (109) is adjusted by controlling the amount of the de-hydrocarbon tail gas (108) entering the membrane separation assembly (42)2The ratio of (a) to (b).
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| CN105838465A (en) * | 2016-05-20 | 2016-08-10 | 北京中科瑞奥能源科技股份有限公司 | Process and system for preparing liquefied natural gas by utilizing Fischer-Tropsch synthesis tail gas |
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| GB2617450B (en) * | 2022-03-15 | 2024-05-08 | Johnson Matthey Davy Technologies Ltd | Apparatus and methods for gas-liquid separation |
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| CN115253612B (en) * | 2022-08-25 | 2024-02-02 | 国家能源集团宁夏煤业有限责任公司 | Fischer-Tropsch synthesis tail gas separation and recovery system and method |
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