CN113368663B - Treatment method of Fischer-Tropsch synthesis decarbonized tail gas and equipment system for implementing method - Google Patents

Treatment method of Fischer-Tropsch synthesis decarbonized tail gas and equipment system for implementing method Download PDF

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CN113368663B
CN113368663B CN202110538334.4A CN202110538334A CN113368663B CN 113368663 B CN113368663 B CN 113368663B CN 202110538334 A CN202110538334 A CN 202110538334A CN 113368663 B CN113368663 B CN 113368663B
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methanol
tower
gas
outlet
washing
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CN113368663A (en
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贺树民
高军虎
李向阳
张宇
郝栩
董根全
杨勇
李永旺
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Zhongke Synthetic Oil Technology Co Ltd
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Abstract

The invention relates to a method for treating Fischer-Tropsch synthesis decarbonized tail gas and a device system for implementing the method. The process of the invention is carried out by CO 2 Absorption, extraction separation, solution regeneration and tail gas washing etc. process and handle ft synthesis decarbonization tail gas, can the carbon dioxide in the ft synthesis decarbonization tail gas of degree of depth desorption to produce purified gas, light hydrocarbon, crude naphtha and fuel gas, the by-product waste water simultaneously as the product. Compared with the traditional acid gas removal process, the invention has the advantages of simple process and capability of achieving fine CO removal 2 The method has the characteristics of cost saving, less hydrocarbon loss, less cold loss and the like.

Description

Treatment method of Fischer-Tropsch synthesis decarbonized tail gas and equipment system for implementing method
Technical Field
The invention relates to a treatment method of Fischer-Tropsch synthesis decarbonized tail gas, in particular to a method for deeply removing carbon dioxide in Fischer-Tropsch synthesis decarbonized tail gas and a corresponding equipment system.
Background
The Fischer-Tropsch synthesis reaction of indirect coal liquefaction refers to CO and H 2 Hydrogenation under the action of catalystThe reaction produces hydrocarbons with different chain lengths and oxygen-containing compounds. The reaction was first discovered in 1913 by two scientists of franz and hans, tropisch, germany, and only large-scale industrial application is currently performed in south africa and china worldwide. The Shanxi institute of coal chemistry, Chinese academy of sciences, and the Chinese synthetic oil technology Limited company have undergone nearly 30 years of autonomous research and development to obtain a Fischer-Tropsch synthesis high-temperature slurry bed process technology, which has been successfully applied to megaton-level projects: the national energy group Ningxia coal industry group Limited company 400 ten thousand tons per year indirect coal liquefaction project, the Shanxi Lu' an group 100 ten thousand tons per year coal oil production project and the inner Mongolia Yutai 120 ten thousand tons per year fine chemical project.
The Fischer-Tropsch synthesis decarbonization tail gas mainly comprises H 2 、CO、CH 4 、N 2 Light hydrocarbon (C) 2～10 Hydrocarbons) and small amounts of CO 2 Of equal composition to H therein 2 、CO、CH 4 Light hydrocarbon (C) 2～10 The hydrocarbon) is recycled, and has high recycling value. At present, various methods such as absorption, separation, methanation, membrane separation and the like are mainly adopted to realize H 2 、CO、CH 4 Light hydrocarbon (C) 2～10 Hydrocarbons) from the process.
Chinese patent ZL201110034922.0 discloses a Fischer-Tropsch synthesis tail gas treatment method, which comprises the steps of decarburization, membrane separation, low-temperature oil washing, tail gas conversion, Pressure Swing Adsorption (PSA) and the like, wherein CO in the tail gas is removed by a decarburization unit 2 And the low-temperature oil washing unit recovers liquefied gas components in the tail gas, and the PAS unit recovers hydrogen.
Chinese patent ZL201410455603.0 discloses a decarbonization method of Fischer-Tropsch synthesis tail gas through coal-based indirect liquefaction, which adopts low-temperature methanol as an absorption medium to selectively absorb various components in the Fischer-Tropsch synthesis tail gas, and realizes CO in the Fischer-Tropsch synthesis tail gas through the steps of cooling, washing, extracting, regenerating, stripping and the like 2 Removal of and CO, H 2 And recycling of low carbon hydrocarbons.
The Chinese patent application CN201910952440.X discloses a Fischer-Tropsch synthesis tail gas recycling system process, which comprises the steps of purifying Fischer-Tropsch synthesis tail gas, then enabling the Fischer-Tropsch synthesis tail gas to enter a cryogenic separation system, cooling and liquefying the purified Fischer-Tropsch synthesis tail gas, and recycling carbon two, carbon three and heavier components; condensing and liquefying methane in the tail gas to prepare an LNG product; purifying hydrogen and carbon monoxide by a PSA unit; this patent application is concerned with the recovery of light hydrocarbons and LNG from fischer-tropsch tail gas.
The inventor finds that in the actual production process, after the Fischer-Tropsch synthesis tail gas is subjected to decarburization treatment, the obtained decarburization tail gas still contains a small amount (less than or equal to 2%) of CO 2 If the decarbonized tail gas from Fischer-Tropsch synthesis is directly discharged or combusted, the atmosphere is seriously polluted, and energy waste is caused, so that the method is not suitable for the high-efficiency clean utilization of the current energy.
Therefore, the inventor finds that the deep decarburization treatment of the Fischer-Tropsch synthesis decarbonized tail gas is necessary as an effective method for environmental protection and reasonable utilization of energy, however, the tail gas treatment method disclosed in the prior art is a fresh treatment method related to the Fischer-Tropsch synthesis decarbonized tail gas.
Disclosure of Invention
In view of the above problems, the present invention aims to provide a method for treating a Fischer-Tropsch synthesis decarbonized tail gas, which comprises CO 2 The method is developed aiming at the characteristics of the Fischer-Tropsch synthesis decarbonization tail gas, and can be used for separating and producing purified gas, light hydrocarbon, crude naphtha, fuel gas and waste water.
Specifically, the above object of the present invention is achieved by:
in one aspect, the invention provides a method for treating Fischer-Tropsch synthesis decarbonized tail gas, wherein the method comprises the following steps:
(1) pretreatment: cooling Fischer-Tropsch synthesis decarburization tail gas serving as feed gas by a cooler, sending the cooled Fischer-Tropsch synthesis decarburization tail gas into a flash tank for separation and dehydration, mixing the cooled Fischer-Tropsch synthesis decarburization tail gas with a predetermined amount of methanol, then exchanging heat by a heat exchanger, and continuously cooling the cooled Fischer-Tropsch synthesis decarburization tail gas by a quencher to obtain cooled feed gas;
(2) pre-washing section treatment of the absorption tower: feeding the cooled raw material gas into an absorption tower, and washing out naphtha through a semi-lean methanol I in a prewashing section at the lower part of the absorption tower to obtain the product containingOil methanol and de-oiled feed gas; extracting the oil-containing methanol from the bottom of the prewashing section, and carrying out flash evaporation to obtain a flash vapor phase G 1 And a liquid phase L after flash evaporation 1 ；
(3) Treatment of a main washing section of the absorption tower: the deoiling raw material gas enters a main washing section at the middle part of the absorption tower and is in countercurrent contact with semi-lean methanol II to wash out CO in the deoiling raw material gas 2 And light hydrocarbon to obtain and absorb CO 2 And a light hydrocarbon rich methanol and light hydrocarbon depleted feed gas; pumping out the rich methanol from the bottom of the main washing section, circulating the rich methanol to the heat exchanger in the step (1) to exchange heat with feed gas, and then carrying out flash evaporation to obtain a flash vapor phase G 2 And a liquid phase L after flash evaporation 2 ；
(4) Fine washing section treatment of an absorption tower: feeding the light hydrocarbon-removed raw gas into the upper fine washing section of the absorption tower, and further washing off CO in the light hydrocarbon-removed raw gas by countercurrent contact with lean methanol 2 Obtaining semi-poor methanol III and purified gas; sending a part of the semi-lean methanol III to a prewashing section and a main washing section of the absorption tower to be respectively used as semi-lean methanol I and semi-lean methanol II for recycling; reheating and flashing another part of the semi-lean methanol III to obtain a flash vapor phase G 3 And a liquid phase L after flash evaporation 3 (ii) a (5) Treating by a regeneration tower and a tail gas washing tower: subjecting said flashed liquid phase L 3 Further decompressing, entering the top of the regeneration tower, and flowing from top to bottom to enable the liquid phase L 3 CO in 2 Gradually desorbing to obtain desorbed methanol and desorbed gas phase; leading out the desorbed methanol from the bottom of the regeneration tower, and recycling the desorbed methanol to the upper section of the absorption tower in the step (4) for use as lean methanol; leading out the desorption gas phase from the top of the regeneration tower, and obtaining a flash vapor phase G through cooling and flash evaporation 4 And a liquid phase L after flash evaporation 4 (ii) a Bringing the flash vapor phase G 1 、G 3 And/or G 4 Entering a tail gas washing tower for dealcoholization to obtain tail gas as fuel gas;
(6) and (3) treatment by an extractor: subjecting said flashed liquid phase L 1 And/or L 4 Entering the lower part of an extractor, and contacting with process water flowing from top to bottom in the extractor to realize liquid-liquid extraction separation to obtainA raw naphtha product and a methanol/water mixture;
(7) light dydrocarbon removing tower and light dydrocarbon washing tower treatment: withdrawing the methanol/water mixture from the lower part of the extractor, optionally with the flashed liquid phase L 2 Sent to a light hydrocarbon removing tower together, and treated to obtain a gas phase G at the top of the light hydrocarbon removing tower 5 And a liquid phase L for removing light hydrocarbon at the bottom of the tower 5 (ii) a Subjecting the overhead gas phase G 5 And/or the flash vapor phase G 2 Entering a light hydrocarbon washing tower for dealcoholization to obtain light hydrocarbon and a liquid phase at the bottom of the light hydrocarbon washing tower; recycling the liquid phase at the bottom of the light hydrocarbon scrubber to the tail gas scrubber of step (5) for the flash vapor phase G 1 、G 3 And G 4 Dealcoholizing;
(8) and (3) treating by using a methanol/water separation tower: making the light dydrocarbon-removed liquid phase L 5 And (3) entering a methanol/water separation tower to regenerate methanol and a circulating water phase, discharging the circulating water phase from a tower bottom of the methanol/water separation tower, recycling one part of the circulating water phase to the extractor in the step (6) to be used as the process water, and discharging the other part of the circulating water phase to be used as wastewater to be discharged out of a battery limit.
In another aspect, the invention provides an equipment system for implementing the method for processing the decarbonized tail gas in the Fischer-Tropsch synthesis, wherein the equipment system comprises the following units:
the absorption tower comprises a lower pre-washing section, a middle main washing section and an upper fine washing section;
an inlet of the tail gas washing tower is connected to an outlet of the lower pre-washing section of the absorption tower, an outlet of the upper fine-washing section and an outlet of the top of the regeneration tower in a fluid communication manner;
a regenerator column having an inlet fluidly connected to the absorber column upper polishing section outlet and a regenerator column bottom outlet fluidly connected to the absorber column upper polishing section methanol-lean inlet;
an extractor having an inlet connected in fluid communication to the absorber lower prewash section outlet and the regenerator bottom outlet;
an inlet of the light hydrocarbon removing tower is connected to an outlet at the lower part of the extractor and an outlet of a main washing section in the middle of the absorption tower in a fluid communication manner;
an inlet of the light hydrocarbon washing tower is connected to an outlet at the top of the light hydrocarbon removal tower and an outlet at the middle main washing section of the absorption tower in a fluid communication manner;
a methanol/water separation column having an inlet fluidly connected to the light hydrocarbon removal column bottoms outlet and a methanol/water separation column bottoms outlet fluidly connected to the process water inlet of the extractor, a top outlet fluidly connected to the methanol-lean inlet of the upper polishing section of the absorber column;
the tail gas washing tower comprises a tail gas washing tower, wherein a tower top inlet of the tail gas washing tower is connected to a tower bottom outlet of the light hydrocarbon washing tower in a fluid communication mode, and a tower bottom inlet of the tail gas washing tower is connected to a pre-washing section outlet at the lower part of the absorption tower, a fine-washing section outlet at the upper part of the absorption tower and/or a tower bottom outlet of the regeneration tower in a fluid communication mode.
The technical scheme provided by the invention has the following advantages:
1. the flow is simple, 6 rectifying towers and 1 extractor are adopted to finish the CO in the decarbonized tail gas 2 And (4) deeply removing.
2. The fine removal requirement is met, and CO in the gas is purified 2 The content was reduced to 10 ppm.
3. The invention has the advantages of low investment cost, simple operation and easy popularization.
4. The hydrocarbon loss is less, compared with a hot potash process or an MDEA (methyl-dimethyl-ammonium-ethyl-ammonium) process, the hydrocarbon loss of the process is basically not lost, and the process has certain significance for improving the overall energy conversion rate of a system.
5. The loss of cold energy is avoided, and the purified gas which is discharged from the absorption tower directly enters the cryogenic separation, so that the loss of cold energy caused by the reheating of the purified gas is avoided.
Drawings
FIG. 1 is a process diagram for the deep removal of carbon dioxide from a Fischer-Tropsch synthesis decarbonized tail gas in accordance with an exemplary embodiment of the present invention;
in the above drawings, the respective reference numerals denote: 1. 7, 12, 14, 17, 18, 25 coolers; 2. 6, 10, 15, 28 flash tanks; 3. 9, 19, 23, 27 heat exchangers; 4, a quencher; 5 an absorption tower; 8. 16, 21 pressure pumps; 11 a regeneration tower; 13 poor methanol storage tank; 20 an extractor; 22 light hydrocarbon removing tower; a 24 methanol/water separation column; 26 tail gas washing tower; 29 light hydrocarbon washing tower; 101 fischer-tropsch synthesis off-gas (also referred to as "feed gas" or "off-gas") from decarbonation; 102 and 105 cooled feed gases; 103 flash evaporation of the raw gas; 104, the raw gas after heat exchange; 106 purifying the gas; 107 oil-containing methanol (naphtha-rich methanol); 108 liquid phase L after flash evaporation 1 (ii) a 109 liquid phase L after heat exchange 1 (ii) a 110 methanol/water mixture a; 111 pressurized methanol/water mixture; 112 light dydrocarbon removing liquid phase L 5 (ii) a 113 light hydrocarbon removal liquid phase L after heat exchange 5 (ii) a 114 regenerating the methanol; 115. 116, 117, 118, and 119 are lean in methanol; 120 and 147 water; 121 rich in methanol; 122, rich methanol after heat exchange; 123 liquid phase L after flash evaporation 2 (ii) a 124 methanol/water mixed solution b; 125. 126, 127 and 130 are semi-lean in methanol III; 128 semi-lean methanol II; 129 semi-lean methanol I; 131 flash vapor phase G 3 (ii) a 132 liquid phase L after flash evaporation 3 (ii) a 133 methanol after the resolution (recycled methanol); 134 cooled recycle methanol; 135 resolving the gas phase; 136 cooling to resolve the gas phase; 137 flash vapor phase G 4 (ii) a 138 make-up of methanol; 139 flash evaporated liquid phase L 4 (ii) a 140 flash vapor phase G 1 (ii) a 141 and 149 mixed light hydrocarbons; 145 light hydrocarbon removing tower top gas phase G 5 (ii) a 146 washing tower top light hydrocarbon; 148 raw naphtha; 150 flash vapor phase G 2 (ii) a 151 light hydrocarbon washing tower bottom liquid phase; 152 tail gas; 153 waste water; 154 circulating the aqueous phase; 155 cooled circulating aqueous phase.
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are intended for purposes of illustration and explanation only and are not intended to limit the scope of the invention.
In the present invention, the terms "Fischer-Tropsch synthesis decarbonated tail gas", "decarbonated tail gas" and "feed gas" are used interchangeably and are tail gases from a Fischer-Tropsch synthesis decarbonated tail gas unit,mainly composed of H 2 、CO、CH 4 、N 2 Light hydrocarbon (C) 2～10 Hydrocarbons) and small amounts of CO 2 And the like.
In the present invention, the term "semi-lean methanol" refers to CO 2 Methanol with the content less than or equal to 4 percent (volume fraction).
In the present invention, the term "methanol lean" refers to CO 2 Methanol in an amount of < 1ppm (volume fraction).
In the present invention, the term "methanol-rich" refers to CO 2 Methanol in a content of > 4% (volume fraction).
In the present invention, the term "oleaginous methanol" refers to naphtha-containing methanol obtained by washing a portion of naphtha from the decarbonated tail gas by semi-lean methanol.
In the present invention, the term "light hydrocarbon" means C 1～10 And (c) a hydrocarbon mixture of alkanes, alkenes, and/or alkynes.
In one embodiment, the invention relates to a method for treating Fischer-Tropsch synthesis decarbonized tail gas, wherein the method comprises the following steps:
(1) pretreatment: cooling the Fischer-Tropsch synthesis decarbonized tail gas serving as the raw material gas by a cooler, sending the cooled Fischer-Tropsch synthesis decarbonized tail gas into a flash tank for separation and dehydration, mixing the cooled Fischer-Tropsch synthesis decarbonized tail gas with a predetermined amount of methanol, then exchanging heat by a heat exchanger, and continuously cooling by a quencher to obtain the cooled raw material gas;
(2) pre-washing section treatment of the absorption tower: feeding the cooled feed gas into an absorption tower, and washing naphtha in a pre-washing section at the lower part of the absorption tower by using semi-lean methanol I to obtain oil-containing methanol and deoiled feed gas; extracting the oil-containing methanol from the bottom of the prewashing section, and carrying out flash evaporation to obtain a flash vapor phase G 1 And a liquid phase L after flash evaporation 1 ；
(3) Treatment of a main washing section of the absorption tower: the deoiling raw material gas enters a main washing section at the middle part of the absorption tower and is in countercurrent contact with semi-lean methanol II to wash out CO in the deoiling raw material gas 2 And light hydrocarbon to obtain and absorb CO 2 And a light hydrocarbon rich methanol and light hydrocarbon depleted feed gas; the rich methanol is pumped out from the bottom of the main washing section and circulated to the heat exchanger in the step (1) to exchange heat with feed gasThen subjected to flash evaporation to obtain a flash vapor phase G 2 And a liquid phase L after flash evaporation 2 ；
(4) Fine washing section treatment of an absorption tower: feeding the light hydrocarbon-removed raw gas into the upper fine washing section of the absorption tower, and further washing off CO in the light hydrocarbon-removed raw gas by countercurrent contact with lean methanol 2 Obtaining semi-poor methanol III and purified gas; sending a part of the semi-lean methanol III to a prewashing section and a main washing section of the absorption tower to be respectively used as semi-lean methanol I and semi-lean methanol II for recycling; reheating and flashing another part of the semi-lean methanol III to obtain a flash vapor phase G 3 And a liquid phase L after flash evaporation 3
(5) Treating by a regeneration tower and a tail gas washing tower: subjecting said flashed liquid phase L 3 Further decompressing, entering the top of the regeneration tower, and flowing from top to bottom to enable the liquid phase L 3 CO in 2 Gradually desorbing to obtain desorbed methanol and desorbed gas phase; leading out the desorbed methanol from the bottom of the regeneration tower, and circulating the desorbed methanol to the upper section of the absorption tower in the step (4) for use as lean methanol; leading out the desorption gas phase from the top of the regeneration tower, and obtaining a flash vapor phase G through cooling and flash evaporation 4 And a liquid phase L after flash evaporation 4 (ii) a Bringing the flash vapor phase G 1 、G 3 And/or G 4 Entering a tail gas washing tower for dealcoholization to obtain tail gas as fuel gas;
(6) and (3) treatment by an extractor: subjecting said flashed liquid phase L 1 And/or L 4 The naphtha enters the lower part of an extractor and is contacted with process water flowing from top to bottom in the extractor to realize liquid-liquid extraction separation, so that a crude naphtha product and a methanol/water mixture are obtained;
(7) light dydrocarbon removing tower and light dydrocarbon washing tower treatment: withdrawing the methanol/water mixture from the lower part of the extractor, optionally with the flashed liquid phase L 2 Sent to a light hydrocarbon removing tower together, and treated to obtain a gas phase G at the top of the light hydrocarbon removing tower 5 And a liquid phase L for removing light hydrocarbon at the bottom of the tower 5 (ii) a Subjecting the overhead gas phase G 5 And/or the flash vapor phase G 2 Entering a light hydrocarbon washing tower for dealcoholization to obtain light hydrocarbon and a liquid phase at the bottom of the light hydrocarbon washing tower; making the light hydrocarbonThe liquid phase at the bottom of the washing tower is recycled to the tail gas washing tower in the step (5) for the flash vapor phase G 1 、G 3 And G 4 Dealcoholizing;
(8) and (3) treatment of a methanol/water separation tower: making the light dydrocarbon-removed liquid phase L 5 And (3) entering a methanol/water separation tower to regenerate methanol and a circulating water phase, discharging the circulating water phase from a tower bottom of the methanol/water separation tower, recycling one part of the circulating water phase to the extractor in the step (6) to be used as the process water, and discharging the other part of the circulating water phase to be used as wastewater to be discharged out of a battery limit.
In a preferred embodiment, in step (1), the feed gas contains H 2 、CO、CH 4 、N 2 、CO 2 And C 2～10 Light hydrocarbon.
In the invention, the raw material gas is decarbonized tail gas produced by a Fischer-Tropsch synthesis decarbonization unit. In a preferred embodiment, in step (1), the Fischer-Tropsch synthesis decarbonised tail gas has a CH relative to the total volume of the Fischer-Tropsch synthesis decarbonised tail gas 4 The content of the components is 0.1-30% (volume fraction), and CO 2 The content of the components is 1-5% (volume fraction), and the content of the other components is 20-89.5% (volume fraction).
In a preferred embodiment, in the step (1), before being fed into the flash tank, the Fischer-Tropsch synthesis decarbonized tail gas is cooled to-20 to 10 ℃ through the cooler.
In the invention, in the step (1), the Fischer-Tropsch synthesis decarbonization tail gas is separated and dehydrated in the flash tank, the obtained water phase is led out from the bottom of the flash tank, and the obtained gas phase is mixed with a predetermined amount of methanol.
In a preferred embodiment, in step (1), the predetermined amount of methanol is used in an amount of 100 to 5000kg/h, such as 100 to 500kg/h or 500 to 5000 kg/h.
In a preferred embodiment, in step (1), the temperature of the cooled feed gas is in the range of-60 to-20 ℃, for example-60 to-40 ℃ or-40 to-20 ℃.
In a preferred embodiment, in steps (2) to (4), the absorption column (also referred to as CO) 2 Absorber column) operating pressure of 0The pressure is 8MPa, the temperature of the tower bottom is-60-50 ℃, and the temperature of the outlet of the tower top is-60-0 ℃.
In a preferred embodiment, in step (4), the purified gas is passed to a molecular sieve desorption unit to adsorb trace amounts of water and CO 2 Then the product H is obtained by further entering a cryogenic separation unit for separation 2 、CO/N 2 Mixed gas and LNG.
In a preferred embodiment, in the step (5), the regeneration tower (also called solvent regeneration tower) has an operating pressure of 0 to 6MPa and a temperature of 0 to 150 ℃.
In a preferred embodiment, in the step (5), the operation pressure of the tail gas washing tower is 0 to 2MPa, and the temperature is-10 to 200 ℃. In the invention, the tail gas washing tower is used for washing methanol carried in the discharged tail gas.
In a preferred embodiment, in step (5), a portion of the desorbed methanol is recycled to step (1) for use as the predetermined amount of methanol.
In a preferred embodiment, in the step (6), the operating pressure of the extractor (also called an extraction separator) is 0-4 MPa, the temperature is-20-50 ℃, and the extracting agent is water.
In a preferred embodiment, in the step (7), the operating pressure of the light dydrocarbon removing tower is 0 to 1MPa, and the temperature is 0 to 120 ℃.
In a preferred embodiment, in the step (7), the operating pressure of the light hydrocarbon washing tower is 0 to 1MPa, and the temperature is-10 to 200 ℃.
In a preferred embodiment, in step (7), the light hydrocarbon obtained from the light hydrocarbon wash column overhead is optionally subjected to CO desorption with the decarbonization unit of the crude naphtha product obtained in step (6) 2 Then the product dry gas, LPG and stable naphtha are obtained by separation in an absorption desorption unit.
In a preferred embodiment, in the step (8), the operating pressure of the methanol/water separation column is 0 to 1.5MPa, and the temperature is 20 to 190 ℃.
In a preferred embodiment, the method comprises the steps of:
(1) pretreatment: cooling the Fischer-Tropsch synthesis decarbonized tail gas serving as the raw material gas to-20-10 ℃ through a cooler, sending the cooled Fischer-Tropsch synthesis decarbonized tail gas into a flash tank for separation and dehydration, mixing a gas phase with a predetermined amount of methanol, then carrying out heat exchange through a heat exchanger, and continuously cooling the gas to-60 to-20 ℃ through a quencher to obtain a cooled raw material gas;
(2) pre-washing section treatment of the absorption tower: feeding the cooled raw material gas into an absorption tower, and washing naphtha from a pre-washing section at the lower part of the absorption tower through semi-lean methanol I pressurized by a pump to obtain oil-containing methanol and deoiled raw material gas; pumping the oil-containing methanol out of the bottom of the prewashing section, and carrying out flash evaporation by a flash tank to obtain a flash vapor phase G 1 And a liquid phase L after flash evaporation 1 ；
(3) Treatment of a main washing section of the absorption tower: the deoiling raw material gas enters a main washing section at the middle part of the absorption tower and is in countercurrent contact with semi-lean methanol II to wash out CO in the deoiling raw material gas 2 And light hydrocarbon to obtain absorbed CO 2 And a light hydrocarbon rich methanol and light hydrocarbon depleted feed gas; pumping the rich methanol out of the bottom of the main washing section, circulating to the heat exchanger in the step to exchange heat with the feed gas, continuously reheating the raw gas by the heat exchanger, and then entering a flash tank to be flashed to obtain a flash vapor phase G 2 And the liquid phase L after flashing 2 ；
(4) Fine washing section treatment of an absorption tower: the light hydrocarbon-removing raw gas enters the fine washing section at the upper part of the absorption tower through a gas lifting plate, and is further washed to remove CO in the light hydrocarbon-removing raw gas through countercurrent contact with lean methanol entering from the top of the tower 2 Obtaining semi-lean methanol III and purified gas; pressurizing a part of the semi-lean methanol III by a pump, and then sending the pressurized part of the semi-lean methanol III to a prewashing section and a main washing section of the absorption tower to be respectively used as semi-lean methanol I and semi-lean methanol II for recycling; reheating the other part of the semi-lean methanol III by a heat exchanger and flashing by a flash tank to obtain a flash vapor phase G 3 And a liquid phase L after flash evaporation 3 ；
(5) Treating by a regeneration tower and a tail gas washing tower: subjecting said flashed liquid phase L 3 Further decompressing, entering the top of the regeneration tower, and flowing from top to bottom to enable the liquid phase L 3 CO in 2 Gradually desorbing to obtain desorbed methanolA gas-suction phase; leading out the desorbed methanol from the bottom of the regeneration tower, cooling the methanol by a cooler, leading out lean methanol by a lean methanol storage tank, pressurizing the lean methanol by a pump, cooling the lean methanol by a first lean methanol cooler and a second lean methanol cooler respectively, and circulating the cooled lean methanol to the fine washing section at the upper part of the absorption tower in the step (4) for use as the lean methanol; leading out the desorption gas phase from the top of the regeneration tower, cooling by a cooler and flashing by a flash tank to obtain a flash vapor phase G 4 And a liquid phase L after flash evaporation 4 (ii) a Bringing the flash vapor phase G 1 、G 3 And/or G 4 Entering a tail gas washing tower for dealcoholization to obtain tail gas; optionally introducing said tail gas as fuel gas to a pipe network;
(6) and (3) treatment by an extractor: subjecting said flashed liquid phase L 1 After heat exchange by a heat exchanger, the liquid phase L is subjected to flash evaporation 4 The naphtha and methanol are fed into the lower part of an extractor together, and are contacted with process water flowing from top to bottom in the extractor to realize liquid-liquid extraction separation, so that a crude naphtha product and a methanol/water mixture are obtained; optionally further separating the crude naphtha product to obtain a stabilized naphtha;
(7) light dydrocarbon removing tower and light dydrocarbon washing tower treatment: withdrawing the methanol/water mixture from the lower part of the extractor, optionally with the flashed liquid phase L 2 Pressurizing the mixture by a pressurizing pump, sending the mixture to a light hydrocarbon removing tower, and treating the mixture to obtain a gas phase G at the top of the light hydrocarbon removing tower 5 And a liquid phase L for removing light hydrocarbon at the bottom of the tower 5 (ii) a Subjecting the overhead gas phase G 5 And/or the flash vapor phase G 2 Entering a light hydrocarbon washing tower for dealcoholization to obtain light hydrocarbon and a liquid phase at the bottom of the light hydrocarbon washing tower; recycling the liquid phase at the bottom of the light hydrocarbon scrubber to the tail gas scrubber of step (5) for the flash vapor phase G 1 、G 3 And G 4 Dealcoholizing;
(8) and (3) treating by using a methanol/water separation tower: making the light dydrocarbon-removed liquid phase L 5 Entering a methanol/water separation tower to regenerate methanol and a circulating water phase, discharging the circulating water phase from a tower kettle of the methanol/water separation tower, cooling one part of the circulating water phase by a cooler, circulating the cooled part of the circulating water phase to the extractor in the step (6) to be used as the process water, and taking the other part of the circulating water phase as the process waterAnd discharging the wastewater out of the boundary area.
In another embodiment, the invention relates to a plant system for implementing the method for treating the Fischer-Tropsch synthesis decarbonized tail gas, wherein the plant system comprises the following units:
the absorption tower comprises a lower pre-washing section, a middle main washing section and an upper fine washing section;
the inlet of the tail gas washing tower is connected to the outlet of the lower pre-washing section of the absorption tower, the outlet of the upper fine-washing section and the outlet of the top of the regeneration tower in a fluid communication manner;
a regenerator column having an inlet fluidly connected to the absorber column upper polishing section outlet and a regenerator column bottom outlet fluidly connected to the absorber column upper polishing section methanol-lean inlet;
an extractor having an inlet connected in fluid communication to the absorber lower prewash section outlet and the regenerator bottom outlet;
an inlet of the light hydrocarbon removing tower is connected to an outlet at the lower part of the extractor and an outlet of a main washing section in the middle of the absorption tower in a fluid communication manner;
an inlet of the light hydrocarbon washing tower is connected to an outlet at the top of the light hydrocarbon removing tower and an outlet of a main washing section in the middle of the absorption tower in a fluid communication manner;
a methanol/water separation column having an inlet fluidly connected to the light hydrocarbon removal column bottoms outlet and a methanol/water separation column bottoms outlet fluidly connected to the process water inlet of the extractor, a top outlet fluidly connected to the methanol-lean inlet of the upper polishing section of the absorber column;
the tail gas washing tower comprises a tail gas washing tower, wherein a tower top inlet of the tail gas washing tower is connected to a tower bottom outlet of the light hydrocarbon washing tower in a fluid communication mode, and a tower bottom inlet of the tail gas washing tower is connected to a pre-washing section outlet at the lower part of the absorption tower, a fine-washing section outlet at the upper part of the absorption tower and/or a tower bottom outlet of the regeneration tower in a fluid communication mode.
In a preferred embodiment, the facility system further comprises a methanol-lean storage tank, an inlet of the methanol-lean storage tank being fluidly connected to the regenerator bottom outlet and the top outlet of the methanol/water separation column, and an outlet of the methanol-lean storage tank being fluidly connected to the methanol-lean inlet of the absorber polishing section.
In a preferred embodiment, the plant system further comprises a plurality of coolers, heat exchangers, booster pumps and flash tanks.
In a preferred embodiment, the plurality of coolers are respectively provided at one or more of the following locations: upstream of the absorber column bottoms inlet; a semi-lean methanol outlet of the fine washing section of the absorption tower is connected with a semi-lean methanol inlet of the main washing section and/or the prewashing section; the outlet of the regeneration tower is arranged between the inlet of the tail gas washing tower and the outlet of the regeneration tower; the outlet at the bottom of the regeneration tower is connected with the inlet of the poor methanol storage tank; an outlet of the poor methanol storage tank is connected with a poor methanol inlet of the fine washing section of the absorption tower; and between the bottom outlet of the methanol/water separation tower and the process water inlet of the extractor.
In a preferred embodiment, the plurality of heat exchangers are respectively disposed at one or more of the following locations: the upper stream of the tower bottom inlet of the absorption tower; a semi-lean methanol outlet of the fine washing section of the absorption tower is connected with an inlet of the tail gas washing tower and/or the regeneration tower; an outlet of the pre-washing section of the absorption tower is connected with an inlet of the extractor; an outlet at the bottom of the light hydrocarbon removal tower and an inlet of the methanol/water separation tower; and between the outlet of the lower prewashing section of the absorption tower and the inlet of the light dydrocarbon removing tower.
In a preferred embodiment, the plurality of pressurizing pumps are respectively provided at one or more of the following positions: a semi-lean methanol outlet of the fine washing section of the absorption tower and a semi-lean methanol inlet of the main washing section and/or the pre-washing section; an outlet of the poor methanol storage tank is connected with a poor methanol inlet of the fine washing section of the absorption tower; an outlet at the lower part of the extractor and an inlet of the light dydrocarbon removing tower; and between the outlet of the lower prewashing section of the absorption tower and the inlet of the light dydrocarbon removing tower.
In a preferred embodiment, the flash tanks are respectively provided at one or more of the following locations: the upper stream of the tower bottom inlet of the absorption tower; an outlet of the lower pre-washing section of the absorption tower is arranged between an inlet of the tail gas washing tower and an outlet of the lower pre-washing section of the absorption tower; the outlet of the upper fine washing section of the absorption tower is connected with the inlet of the regeneration tower; and between the outlet of the middle main washing section of the absorption tower and the inlet of the light hydrocarbon washing tower.
The method of the invention is generally described as follows:
the tail gas (hereinafter referred to as raw material gas) from a Fischer-Tropsch synthesis decarburization tail gas unit is cooled by a cooler, then sent into a flash tank for separation and dehydration, mixed with methanol with the use amount of 100-5000 kg/h, subjected to heat exchange with rich methanol from a main washing section of an absorption tower by a heat exchanger, continuously cooled by a quencher, and then sent into a lower section (a prewashing section) of the absorption tower from a kettle of the absorption tower.
Washing naphtha by a flow of semi-lean methanol I pressurized by a pump in the lower section (pre-washing section) raw gas of the absorption tower to obtain oil-containing methanol and deoiled raw gas; extracting oil-containing methanol from the bottom of the prewashing section of the absorption tower, and performing reduced pressure flash evaporation in a flash tank to obtain a flash vapor phase G 1 And a liquid phase L after flash evaporation 1 (i.e., methanol/naphtha oil phase flash-evaporated by flash tank), flash gas phase G 1 Then removing tail gas and washing the tower to remove alcohol; liquid phase L after flash evaporation 1 After reheating, the mixture enters an extractor at the temperature of-10 to 20 ℃.
In the interruption (main washing section) of the absorption tower, deoiling raw material gas is in countercurrent contact with semi-lean methanol II, and CO in the deoiling raw material gas is washed 2 And light hydrocarbon to obtain absorbed CO 2 And a light hydrocarbon rich methanol and light hydrocarbon depleted feed gas; pumping out the rich methanol from the bottom of the main washing section, reheating the rich methanol with feed gas in a heat exchanger, and then entering a flash tank to obtain a flash vapor phase G 2 And a liquid phase L after flash evaporation 2 。
Passing through the lower section and the middle section of the absorption tower, the raw gas of the light hydrocarbon (i.e. the light hydrocarbon-removing raw gas) which is washed down passes through the gas-lifting plate to the upper section (fine washing section) of the absorption tower, and the lean methanol enters from the top of the towerCO in the light hydrocarbon-removing raw material gas 2 Absorbed by lean methanol when the methanol counter-currently contacts with the lean methanol entering from the top of the tower, and CO is extracted and absorbed from the bottom of a fine washing section of the absorption tower 2 Is referred to as semi-lean methanol (i.e., semi-lean methanol III).
Pressurizing a part of the semi-lean methanol III by a pump, continuously feeding the pressurized part of the semi-lean methanol III into a main washing section and a prewashing section to be respectively used as the semi-lean methanol I and the semi-lean methanol II for recycling, reheating the other part of the semi-lean methanol III by a heat exchanger, decompressing and feeding the reheated part of the semi-lean methanol III into a flash tank, and treating to obtain a flash vapor phase G 3 And a liquid phase L after flash evaporation 3 (ii) a Flash vapor phase G 3 Dealcoholizing in a tail gas-removing washing tower and obtaining a liquid phase L 3 Further reduced pressure is sent to the top of the upper section of the regeneration column. The liquid phase at the top of the regeneration tower automatically flows to the lower part of the tower, and CO in the methanol 2 Gradually desorbing to obtain desorbed methanol and desorbed gas phase; leading out the desorption gas phase from the top of the regeneration tower, and obtaining a flash vapor phase G through cooling and flash evaporation 4 And a liquid phase L after flash evaporation 4 (ii) a The desorbed methanol is then drawn from the bottom of the methanol-lean regeneration column, and is referred to as recycled methanol. After several times of decompression, heat exchange and temperature rise desorption, the residual CO in the circulating methanol 2 Very little (< 1ppm) and the methanol solution can be recycled as a regenerated lean methanol solution. Wherein, poor methanol automatically flows from the tower bottom of the regeneration tower and is stored and buffered in a poor methanol storage tank through a water cooler. The poor methanol is pressurized by a pump, is cooled by a refrigerant in a first poor methanol cooler and then passes through a second poor methanol cooler, and the cooled circulating methanol enters the top of the upper section of the absorption tower to complete circulation.
Liquid phase L after flash evaporation 1 (i.e. methanol/naphtha oil phase flashed by flash tank) and separated liquid phase L from the top condenser of the poor methanol regeneration tower 4 And enters the lower part of the extractor. The process water from the bottom of the methanol/water separation tower is cooled and then enters the extractor. The specific gravity of the water phase is downward flowing by gravity, the specific gravity of the methanol/hydrocarbon phase is small and upward floating, the methanol with stronger affinity with water and the downward moving water form a new methanol water phase due to the reverse flowing mixing, and the hydrocarbon is extracted into an oil phase which moves upward and is separated out, so that liquid-liquid extraction is realized. Under the extractorThe top of the portion overflows the oil phase to obtain a crude naphtha product. The methanol/water mixture is led out from the lower part of the extractor and enters a methanol-rich liquid phase part L of the flash drum for flash evaporation 2 Pressurizing by a pressurizing pump, sending to a light hydrocarbon removing tower, and treating to obtain a gas phase G at the top of the light hydrocarbon removing tower 5 And a liquid phase L for removing light hydrocarbon at the bottom of the tower 5 。
Gas phase G at top of light hydrocarbon removing tower 5 And/or the flash vapor phase G 2 Dealcoholizing in a light hydrocarbon-removing washing column to remove the liquid phase part L of light hydrocarbon 5 The methanol/water separation tower is used for regenerating methanol and a circulating water phase. The methanol/water separation column bottom discharge water is divided into two parts: one stream of water is circulated to the extractor to be used as the process water; the other strand is used as wastewater discharge boundary area. Circulating the tower bottom liquid phase after the light hydrocarbon washing tower washes the methanol to a tail gas washing tower for washing the flash vapor phase G 1 、G 3 And G 4 Dealcoholizing to obtain light hydrocarbon, and using the tail gas as fuel gas to pipe network.
The method of the present invention will be further explained in connection with the description in fig. 1, but it will be understood by those skilled in the art that the scope of the present invention is not limited to the description in fig. 1:
(i) pretreatment: cooling Fischer-Tropsch synthesis decarbonization tail gas (101) serving as raw material gas to-20-10 ℃ through a cooler (1), sending the cooled Fischer-Tropsch synthesis decarbonization tail gas into a flash tank (2) for separation and dehydration, mixing a gas phase with a predetermined amount of methanol (116), then exchanging heat through a heat exchanger (3), and continuously cooling the gas through a quencher (4) to-60-20 ℃ to obtain cooled raw material gas (105);
(ii) pre-washing section treatment of the absorption tower: feeding the cooled feed gas (105) into an absorption tower (5), and washing naphtha in a pre-washing section at the lower part of the absorption tower by semi-lean methanol I (129) pressurized by a pump (8) to obtain oil-containing methanol (107) and deoiled feed gas; pumping the oil-containing methanol (107) out of the bottom of the prewashing section, and carrying out flash evaporation through a flash evaporation tank (6) to obtain a flash vapor phase G 1 (140) And a liquid phase L after flash evaporation 1 (108)；
(iii) Treatment of a main washing section of the absorption tower: feeding the deoiled raw material gas into a main washing section at the middle part of the absorption tower, and washing off CO in the deoiled raw material gas by countercurrent contact with semi-lean methanol II (128) 2 And light hydrocarbon to obtain absorbed CO 2 And a light hydrocarbon rich methanol (121) and a light hydrocarbon depleted feed gas; and (3) extracting the rich methanol (121) from the bottom of the main washing section, circulating the rich methanol to the heat exchanger (3) in the step (i) to exchange heat with the feed gas, continuously reheating the rich methanol by the heat exchanger (27), and then entering a flash tank (28) to be flashed to obtain a flash vapor phase G 2 (150) And a liquid phase L after flash evaporation 2 (123)；
(iv) Fine washing section treatment of an absorption tower: the light hydrocarbon-removed raw gas enters the fine washing section at the upper part of the absorption tower through a gas lifting plate, and is further washed to remove CO in the light hydrocarbon-removed raw gas by countercurrent contact with poor methanol (119) entering from the top of the absorption tower 2 Obtaining semi-lean methanol III (125) and a purified gas (106); pressurizing a part of the semi-lean methanol III by a pump (8) and then sending the pressurized part of the semi-lean methanol III to a prewashing section and a main washing section of the absorption tower to be respectively used as semi-lean methanol I and semi-lean methanol II for recycling; reheating the other part of the semi-lean methanol III by a heat exchanger (9) and flashing by a flash tank (10) to obtain a flash vapor phase G 3 (131) And a liquid phase L after flash evaporation 3 (132)；
(v) Treating by a regeneration tower and a tail gas washing tower: subjecting said flashed liquid phase L 3 Further depressurized and introduced into the top of a regeneration column (11) and flows from top to bottom to allow the liquid phase L to flow 3 CO in 2 Gradually desorbing to obtain desorbed methanol (133) and desorbed gas phase (135); leading out the desorbed methanol (133) from the bottom of the regeneration tower (11), cooling by a cooler (12), leading out lean methanol (115) by a lean methanol storage tank (13), pressurizing the lean methanol (115) by a pump (16), cooling by a first lean methanol cooler (17) and a second lean methanol cooler (18) respectively, and circulating to the upper section of the absorption tower in the step (iv) for use as lean methanol (119); leading out the desorption gas phase (135) from the top of the regeneration tower, cooling by a cooler (14) and flashing by a flash tank (15) to obtain a flash vapor phase G 4 (137) And a liquid phase L after flash evaporation 4 (139) (ii) a Bringing the flash vapor phase G 1 (140)、G 3 (131) And/or G 4 (137) Entering a tail gas washing tower (26) for dealcoholization to obtain tail gas (152); optionally introducing the tail gas (152) as a fuel gas to a pipe network;
(vi) and (3) treatment by an extractor: subjecting said flashed liquid phase L 1 (108) After heat exchange by a heat exchanger (19), the liquid phase L is flash evaporated 4 (139) Entering the lower part of an extractor (20) together, and realizing liquid-liquid extraction separation by contacting with process water (155) flowing from top to bottom in the extractor (20) to obtain a crude naphtha product (148) and a methanol/water mixture (110); optionally further separating the raw naphtha product (148) to obtain a stabilized naphtha;
(vii) light dydrocarbon removing tower and light dydrocarbon washing tower treatment: withdrawing the methanol/water mixture (110) from the lower part of the extractor (20), optionally with the flashed liquid phase L 2 (123) Pressurized by a pressurizing pump (21) and then sent to a light hydrocarbon removing tower (22) to be treated to obtain a gas phase G at the top of the light hydrocarbon removing tower 5 (145) And a liquid phase L for removing light hydrocarbon at the bottom of the tower 5 (112) (ii) a Subjecting the overhead gas phase G 5 (145) And/or the flash vapor phase G 2 (150) Entering a light hydrocarbon washing tower (29) for dealcoholization to obtain light hydrocarbon (146) and a light hydrocarbon washing tower bottom liquid phase (151); (vi) recycling said light hydrocarbon scrubber bottoms liquid phase (151) to said tail gas scrubber (26) of step (v) for scrubbing said flash vapor phase G 1 、G 3 And G 4 Dealcoholizing;
(viii) and (3) treating by using a methanol/water separation tower: making the light dydrocarbon-removed liquid phase L 5 (112) And (2) entering a methanol/water separation tower (24) to regenerate methanol (114) and a circulating water phase (154), discharging the circulating water phase (154) from the tower bottom of the methanol/water separation tower (24), cooling a part of the circulating water phase by a cooler (25), circulating the cooled circulating water phase to the extractor (20) in the step (vi) to be used as the process water (155), and discharging the other part of the circulating water phase as waste water (153) out of a battery limit.
Examples
The present invention will be described in further detail with reference to examples. These examples are merely illustrative and should not be construed as limiting the scope of the invention. All technical solutions and modifications thereof implemented based on the above contents of the present invention fall within the scope of the present invention.
Example 1
Taking a Fischer-Tropsch synthesis plant producing 240 million tons per year as an example, the Fischer-Tropsch synthesis decarbonized tail gas produced by the Fischer-Tropsch synthesis plant is 8487.5kmol/h, and the main composition (v%) is as shown in the following table 1:
table 1:
CO 8.85％
H 2 64.19％
CO 2 2.01％
H 2 O 0.75％
N 2 9.45％
CH 4 8.49％
C 2 H 4 0.24％
C 2 H 6 1.23％
C 3 H 6 1.42％
C 3 H 8 0.77％
C 4 H 8 1.01％
C 4 H 10 0.49％
C 5+ 1.11％
the separation of the Fischer-Tropsch synthesis decarbonated tail gas was carried out in the manner shown in FIG. 1.
The decarbonized tail gas (101) enters a cooler (1) to be cooled to about 10 ℃, after separation and dehydration are carried out in a flash tank (2), the decarbonized tail gas is mixed with methanol with the dosage of 500kg/h, and then the mixture is continuously cooled to-40 ℃ in a quencher (4) after heat exchange with rich methanol (121) from a main washing section of an absorption tower (5) in a heat exchanger (3), and the decarbonized tail gas enters a prewashing section of the absorption tower (5). Washing most of naphtha with a stream of semi-lean methanol (129) pressurized by a pump (7) in a pre-washing section; the other half-lean methanol (128) washes off most of light hydrocarbon and CO 2 . Extracting the oil-containing methanol (107) from the tower bottom of the absorption tower (5), reducing the pressure to 0.5MPa, flashing a vapor phase (140), and then removing a tail gas washing tower (26) for washing and dealcoholizing; the flash liquid phase (108) is sent to a heat exchanger (19) to be reheated to 0 ℃, and then enters an extractor (20) for extraction and separation. The raw material gas of the main washing section of the absorption tower (5) is in countercurrent contact with semi-lean methanol (128), and CO in the raw material gas is washed away 2 And light hydrocarbon, absorb CO 2 And the rich methanol (121) of the light hydrocarbon is pumped out from the bottom of the main washing section, exchanges heat with the feed gas in the heat exchanger (3), is reheated to 10 ℃ in the heat exchanger (27), and then enters the flash tank (28). The decarbonized tail gas of the washed light hydrocarbon passes through the gas lifting plate to the upper section (fine washing section) of the absorption tower (5), the poor methanol (119) enters from the top of the tower, and CO in the raw material gas 2 Is absorbed by lean methanol (119) when the lean methanol is in countercurrent contact with the lean methanol, and CO is extracted and absorbed from the bottom of a fine washing section of the absorption tower (5) 2 Methanol (125)The top of the column is a purified gas (106). One part of the semi-lean methanol (125) is pressurized by a pump (8) and continuously enters a main washing section and a prewashing section, and the other part of the semi-lean methanol is reheated by a heat exchanger (9) and decompressed to enter a flash tank (10). After flash evaporation, the semi-lean methanol is divided into a gas phase (131) and a liquid phase (132), the gas phase (131) is removed from a tail gas washing tower (26) for dealcoholization, and the liquid phase (132) is sent to the top of the upper section of a regeneration tower (11). The methanol (133) resolved by the tower is led out from the bottom of the poor methanol regeneration tower (11), and the poor methanol flows automatically from the tower bottom of the regeneration tower (11) and is stored in a poor methanol storage tank (13) through a water cooler (12). The lean methanol (115) is pressurized by a pump (16), cooled in a cooler (17) and cooled by circulating methanol by a cooler (18) to enter the top of the upper section of the absorption tower (5) to complete circulation. The methanol/naphtha oil phase (108) flashed by the flash tank (6) is separated from the liquid phase (139) from the flash tank (15) at the top of the methanol-poor regeneration tower (15) and enters the lower part of the extractor (20). The process water (154) from the bottom of the methanol/water separation column 24 is also fed into the extractor (20) after cooling. The oil phase overflowed from extractor 20 to obtain a crude naphtha (148) product, with extractor 20 operating at a pressure of 0.2MPa and a temperature of 10 ℃. The methanol/water (110) is led out from the lower part of the extractor (20), and is pressurized by a pressurizing pump (21) together with the methanol-rich liquid phase (123) entering the flash tank for flash evaporation, and then is sent to a light hydrocarbon removing tower (22) (the pressure of the light hydrocarbon removing tower is 0.2MPa, and the temperature is 90 ℃). A gas phase (145) at the top of the light hydrocarbon removing tower (22) is removed from a light hydrocarbon removing washing tower (29) (the pressure of the light hydrocarbon washing tower is 0.12MPa, the temperature is 40 ℃) for removing alcohol, and a liquid phase (112) is removed from a methanol/water separating tower (24) (the pressure of the methanol/water separating tower is 0.15MPa, the temperature is 115 ℃) for regenerating methanol (114) and a circulating water phase. The bottom water of the methanol/water separation tower (24) is discharged, and the discharged water is divided into two parts: a flow of water (154) to the extractor (20); the other stream is discharged as waste water (153) to the battery limits. The liquid (151) after the light hydrocarbon (149) is washed by the light hydrocarbon washing tower (29) and the methanol is continuously washed by the tail gas washing tower (26) (the pressure of the tail gas washing tower is 0.11MPa, the temperature is 40 ℃), and the light hydrocarbon (146) is ejected out of the washing tower (29).
Table 2 shows part of the material flow data of examples
Unit of 101 106 148 146 152 153 147
Temperature of ℃ 65.00 -41.59 4.59 28.20 24.37 12.00 30.00
Pressure of MPa 3.38 3.15 0.15 0.12 0.11 0.15 0.30
Flow rate kmol/hr 8487.50 7620.56 173.33 496.61 160.55 258.09 277.54
CO mol％ 8.85％ 9.64％ 0.00％ 1.22％ 6.17％ 0.00％ 0.00％
H2 mol％ 64.19％ 71.09％ 0.00％ 2.40％ 11.77％ 0.00％ 0.00％
CO2 mol％ 2.01％ 0.00％ 0.64％ 17.31％ 51.59％ 0.00％ 0.00％
H 2 O mol％ 0.75％ 0.00％ 1.31％ 3.24％ 2.58％ 100.00％ 100.00％
N 2 mol％ 9.45％ 10.40％ 0.00％ 0.65％ 3.63％ 0.00％ 0.00％
CH 4 mol％ 8.49％ 8.85％ 0.01％ 3.70％ 17.07％ 0.00％ 0.00％
C 2 H 4 mol％ 0.24％ 0.00％ 0.10％ 3.88％ 0.76％ 0.00％ 0.00％
C 2 H 6 mol％ 1.23％ 0.00％ 1.20％ 20.41％ 0.52％ 0.00％ 0.00％
C 3 H 6 mol％ 1.42％ 0.00％ 6.89％ 21.49％ 0.93％ 0.00％ 0.00％
C 3 H 8 mol％ 0.77％ 0.00％ 4.79％ 11.10％ 1.45％ 0.00％ 0.00％
C 4 H 8 mol％ 1.01％ 0.00％ 25.79％ 7.87％ 0.96％ 0.00％ 0.00％
C 4 H 10 mol％ 0.49％ 0.00％ 12.05％ 4.15％ 0.03％ 0.00％ 0.00％
C 5+ mol％ 1.11％ 0.00％ 47.06％ 2.56％ 0.07％ 0.00％ 0.00％
CH4O mol％ 0.00％ 0.01％ 0.16％ 0.02％ 2.46％ 0.00％ 0.00％
Having described embodiments of the present invention in detail, it will be apparent to those skilled in the art that many modifications and variations can be made without departing from the basic spirit of the invention. All such variations and modifications are intended to be within the scope of the present invention.

Claims (24)

1. A method for processing Fischer-Tropsch synthesis decarbonized tail gas comprises the following steps:
(1) pretreatment: cooling the Fischer-Tropsch synthesis decarbonized tail gas serving as the raw material gas by a cooler, sending the cooled Fischer-Tropsch synthesis decarbonized tail gas into a flash tank for separation and dehydration, mixing the cooled Fischer-Tropsch synthesis decarbonized tail gas with a predetermined amount of methanol, then exchanging heat by a heat exchanger, and continuously cooling by a quencher to obtain the cooled raw material gas;
(2) pre-washing section treatment of the absorption tower: feeding the cooled raw gas into an absorption tower, and passing the cooled raw gas through a semi-lean methanol in a pre-washing section at the lower part of the absorption tower
Figure DEST_PATH_IMAGE002
Washing naphtha to obtain oil-containing methanol and deoiled feed gas; extracting the oil-containing methanol from the bottom of the prewashing section, and carrying out flash evaporation to obtain a flash vapor phase G 1 And the liquid phase L after flashing 1 ；
(3) Treatment of a main washing section of the absorption tower: the deoiling raw material gas enters the main washing section at the middle part of the absorption tower and passes through the main washing section and the semi-lean sectionMethanol
Figure 435925DEST_PATH_IMAGE002
Figure 789283DEST_PATH_IMAGE002
Countercurrent contact washing off CO in the solution 2 And light hydrocarbon to obtain and absorb CO 2 And a light hydrocarbon rich methanol and light hydrocarbon depleted feed gas; pumping out the rich methanol from the bottom of the main washing section, circulating the rich methanol to the heat exchanger in the step (1) to exchange heat with feed gas, and then carrying out flash evaporation to obtain a flash vapor phase G 2 And a liquid phase L after flash evaporation 2 ；
(4) Fine washing section treatment of an absorption tower: feeding the light hydrocarbon-removed raw gas into the upper fine washing section of the absorption tower, and further washing off CO in the light hydrocarbon-removed raw gas by countercurrent contact with lean methanol 2 To obtain semi-poor methanol
Figure 772283DEST_PATH_IMAGE002
Figure 105175DEST_PATH_IMAGE002
Figure 122810DEST_PATH_IMAGE002
And a purge gas; subjecting the semi-lean methanol
Figure 148535DEST_PATH_IMAGE002
Figure 848857DEST_PATH_IMAGE002
Figure 251019DEST_PATH_IMAGE002
A part of the methanol is sent to a prewashing section and a main washing section of the absorption tower and respectively used as the semi-lean methanol
Figure 592002DEST_PATH_IMAGE002
And semi-lean methanol
Figure 224846DEST_PATH_IMAGE002
Figure 385700DEST_PATH_IMAGE002
Recycling; subjecting the semi-lean methanol
Figure 529237DEST_PATH_IMAGE002
Figure 960611DEST_PATH_IMAGE002
Figure 62559DEST_PATH_IMAGE002
Is reheated and flashed to obtain a flash vapor phase G 3 And a liquid phase L after flash evaporation 3 ；
(5) Treating by a regeneration tower and a tail gas washing tower: subjecting said flashed liquid phase L 3 Further decompressing, entering the top of a regeneration tower, and flowing from top to bottom to enable the liquid phase L after flashing 3 CO in 2 Gradually desorbing to obtain desorbed methanol and desorbed gas phase; leading out the desorbed methanol from the bottom of the regeneration tower, and recycling the desorbed methanol to the upper section of the absorption tower in the step (4) for use as lean methanol; leading out the desorption gas phase from the top of the regeneration tower, and obtaining a flash vapor phase G through cooling and flash evaporation 4 And a liquid phase L after flash evaporation 4 (ii) a Bringing the flash vapor phase G 1 、G 3 And/or G 4 Entering a tail gas washing tower for dealcoholization to obtain tail gas as fuel gas;
(6) and (3) treatment by an extractor: subjecting said flashed liquid phase L 1 And/or L 4 The naphtha enters the lower part of an extractor, and is contacted with process water flowing from top to bottom in the extractor to realize liquid-liquid extraction separation, so that a crude naphtha product and a methanol/water mixture are obtained;
(7) light dydrocarbon removing tower and light dydrocarbon washing tower treatment: the methanol/water mixture is led out from the lower part of the extractor and is mixed with the liquid phase L after flash evaporation 2 Sent to a light hydrocarbon removing tower together, and the light hydrocarbon is obtained after treatmentGas phase G at the top of the column 5 And a liquid phase L for removing light hydrocarbon at the bottom of the tower 5 (ii) a Making the light hydrocarbon removing tower top gas phase G 5 And/or the flash vapor phase G 2 Entering a light hydrocarbon washing tower for dealcoholization to obtain light hydrocarbon and a liquid phase at the bottom of the light hydrocarbon washing tower; recycling the liquid phase at the bottom of the light hydrocarbon scrubber to the tail gas scrubber of step (5) for the flash vapor phase G 1 、G 3 And G 4 Dealcoholizing;
(8) and (3) treating by using a methanol/water separation tower: subjecting said delignified hydrocarbon liquid phase L 5 And (4) entering a methanol/water separation tower to regenerate methanol and a circulating water phase, discharging the circulating water phase from a tower kettle of the methanol/water separation tower, circulating one part of the circulating water phase to the extractor in the step (6) to be used as the process water, and discharging the other part of the circulating water phase to be used as wastewater to be discharged from a battery limit.
2. The process of claim 1, wherein in step (1), the feed gas comprises H 2 、CO、CH 4 、N 2 、CO 2 And C 2~10 Light hydrocarbons.
3. The method of claim 1 or 2, wherein the Fischer-Tropsch synthesis decarbonation tail gas comprises 0.1 to 30 percent CH in volume fraction relative to the total volume of the Fischer-Tropsch synthesis decarbonation tail gas 4 And 1-5% of CO 2 。
4. The process of claim 1 or claim 2, wherein in step (1) the Fischer-Tropsch synthesis decarbonised tail gas is cooled to a temperature of from-20 to 10 ℃ by the cooler before being fed to the flash tank.
5. The method according to claim 1 or 2, wherein the predetermined amount of methanol is used in an amount of 100 to 5000kg/h in step (1).
6. The method according to claim 1 or 2, wherein in step (1), the temperature of the cooled feed gas is-60 to-20 ℃.
7. The process according to claim 1 or 2, wherein in the steps (2) to (4), the operating pressure of the absorption column is 0 to 8MPa, the bottom temperature is-60 to 50 ℃, and the top outlet temperature is-60 to 0 ℃.
8. The method of claim 1 or 2, wherein in step (4), the purified gas is passed to a molecular sieve desorption unit to adsorb trace amounts of water and CO 2 Then the product H is obtained by further entering a cryogenic separation unit for separation 2 、CO/N 2 Mixed gas and LNG.
9. The method according to claim 1 or 2, wherein in the step (5), the regeneration tower is operated at a pressure of 0 to 6MPa and a temperature of 0 to 150 ℃.
10. The method according to claim 1 or 2, wherein in the step (5), the operating pressure of the tail gas washing tower is 0 to 2MPa, and the temperature is-10 to 200 ℃.
11. The method according to claim 1 or 2, wherein in step (5), a portion of the desorbed methanol is recycled to step (1) for use as the predetermined amount of methanol.
12. The method according to claim 1 or 2, wherein in the step (6), the extractor is operated at a pressure of 0 to 4MPa and a temperature of-20 to 50 ℃.
13. The method of claim 1 or 2, wherein in step (7), the operating pressure of the light dydrocarbon removing tower is 0-1 MPa, and the temperature is 0-120 ℃.
14. The method of claim 1 or 2, wherein in step (7), the light hydrocarbon scrubber is operated at a pressure of 0 to 1MPa and a temperature of-10 to 200 ℃.
15. As claimed in claimThe method of claim 1 or 2, wherein in step (7), the light hydrocarbon obtained from the top of the light hydrocarbon washing tower and the crude naphtha product obtained in step (6) are decarbonized to desorb CO 2 Then the product dry gas, LPG and stable naphtha are obtained by separation in an absorption desorption unit.
16. The process according to claim 1 or 2, wherein in the step (8), the operating pressure of the methanol/water separation column is 0 to 1.5MPa and the temperature is 20 to 190 ℃.
17. The method according to claim 1 or 2, wherein the method comprises the steps of:
(1) pretreatment: cooling Fischer-Tropsch synthesis decarbonized tail gas serving as feed gas to-20-10 ℃ through a cooler, sending the cooled Fischer-Tropsch synthesis decarbonized tail gas into a flash tank for separation and dehydration, mixing a gas phase with a predetermined amount of methanol, then carrying out heat exchange through a heat exchanger, and continuously cooling the gas to-60 to-20 ℃ through a quencher to obtain cooled feed gas;
(2) and (3) treatment of a prewashing section of the absorption tower: feeding the cooled raw material gas into an absorption tower, and passing the cooled raw material gas through a semi-lean methanol pressurized by a pump at a pre-washing section at the lower part of the absorption tower
Figure 241868DEST_PATH_IMAGE002
Washing naphtha to obtain oil-containing methanol and deoiled feed gas; pumping the oil-containing methanol out of the bottom of the prewashing section, and carrying out flash evaporation by a flash tank to obtain a flash vapor phase G 1 And a liquid phase L after flash evaporation 1 ；
(3) Treatment of a main washing section of the absorption tower: the deoiling raw material gas enters the main washing section at the middle part of the absorption tower and passes through the absorption tower and semi-lean methanol
Figure 985833DEST_PATH_IMAGE002
Figure 596681DEST_PATH_IMAGE002
Countercurrent contact washing off CO in the solution 2 And light hydrocarbon to obtain absorbed CO 2 Methanol-rich and light hydrocarbon-depleted feedstock with light hydrocarbonsGas; pumping the rich methanol out of the bottom of the main washing section, circulating to the heat exchanger in the step (1), exchanging heat with the feed gas, continuously reheating the raw gas by the heat exchanger, and then entering a flash tank to be flashed to obtain a flash vapor phase G 2 And a liquid phase L after flash evaporation 2 ；
(4) Fine washing section treatment of an absorption tower: the light hydrocarbon-removing raw gas enters the fine washing section at the upper part of the absorption tower through a gas lifting plate, and is further washed to remove CO in the light hydrocarbon-removing raw gas through countercurrent contact with lean methanol entering from the top of the tower 2 To obtain semi-poor methanol
Figure 400689DEST_PATH_IMAGE002
Figure 598452DEST_PATH_IMAGE002
Figure 146108DEST_PATH_IMAGE002
And a purge gas; subjecting the semi-lean methanol
Figure 112927DEST_PATH_IMAGE002
Figure 353415DEST_PATH_IMAGE002
Figure 772895DEST_PATH_IMAGE002
Is pressurized by a pump and then is sent to a prewashing section and a main washing section of the absorption tower to be respectively used as the semi-lean methanol
Figure 124242DEST_PATH_IMAGE002
And semi-lean methanol
Figure 441173DEST_PATH_IMAGE002
Figure 852563DEST_PATH_IMAGE002
Recycling; subjecting the semi-lean methanol
Figure 759339DEST_PATH_IMAGE002
Figure 914377DEST_PATH_IMAGE002
Figure 590209DEST_PATH_IMAGE002
The other part of the mixed solution is reheated by a heat exchanger and is flashed by a flash tank to obtain a flash vapor phase G 3 And a liquid phase L after flash evaporation 3 ；
(5) Treating by a regeneration tower and a tail gas washing tower: subjecting said flashed liquid phase L 3 Further decompressing, entering the top of a regeneration tower, and flowing from top to bottom to enable the liquid phase L after flashing 3 CO in 2 Gradually desorbing to obtain desorbed methanol and desorbed gas phase; leading out the desorbed methanol from the bottom of the regeneration tower, cooling the desorbed methanol by a cooler, leading out lean methanol by a lean methanol storage tank, pressurizing the lean methanol by a pump, cooling the lean methanol by a first lean methanol cooler and a second lean methanol cooler respectively, and circulating the cooled lean methanol to the fine washing section at the upper part of the absorption tower in the step (4) for use as the lean methanol; leading out the desorption gas phase from the top of the regeneration tower, cooling by a cooler and flashing by a flash tank to obtain a flash vapor phase G 4 And a liquid phase L after flash evaporation 4 (ii) a Bringing the flash vapor phase G 1 、G 3 And/or G 4 Entering a tail gas washing tower for dealcoholization to obtain tail gas; taking the tail gas as fuel gas and leading the fuel gas to a pipe network;
(6) and (3) treatment by an extractor: subjecting said flashed liquid phase L 1 After heat exchange by a heat exchanger, the liquid phase L is subjected to flash evaporation 4 The naphtha and methanol are fed into the lower part of an extractor together, and are contacted with process water flowing from top to bottom in the extractor to realize liquid-liquid extraction separation, so that a crude naphtha product and a methanol/water mixture are obtained; further separating the crude naphtha product to obtain a stabilized naphtha;
(7) light dydrocarbon removing tower and light dydrocarbon washing tower treatment: the methanol/water mixture is led out from the lower part of the extractor and is mixed with the liquid phase L after flash evaporation 2 Pressurizing the mixture by a pressurizing pump, sending the mixture to a light hydrocarbon removing tower, and treating the mixture to obtain a gas phase G at the top of the light hydrocarbon removing tower 5 And a liquid phase L for removing light hydrocarbon at the bottom of the tower 5 (ii) a Subjecting the overhead gas phase G 5 And/or the flash vapor phase G 2 Entering a light hydrocarbon washing tower for dealcoholization to obtain light hydrocarbon and a liquid phase at the bottom of the light hydrocarbon washing tower; recycling the liquid phase at the bottom of the light hydrocarbon scrubber to the tail gas scrubber of step (5) for the flash vapor phase G 1 、G 3 And G 4 Dealcoholizing;
(8) and (3) treating by using a methanol/water separation tower: making the light dydrocarbon-removed liquid phase L 5 And (3) entering a methanol/water separation tower to regenerate methanol and a circulating water phase, discharging the circulating water phase from a tower kettle of the methanol/water separation tower, cooling one part of the circulating water phase by a cooler, circulating the cooled part of the circulating water phase to the extractor in the step (6) to be used as the process water, and discharging the other part of the circulating water phase to a battery limit as wastewater.
18. An equipment system for carrying out the method of any one of claims 1 to 17, wherein the equipment system comprises the following units:
the absorption tower comprises a lower pre-washing section, a middle main washing section and an upper fine washing section;
an inlet of the tail gas washing tower is connected to an outlet of the lower pre-washing section of the absorption tower, an outlet of the upper fine-washing section and an outlet of the top of the regeneration tower in a fluid communication manner;
a regenerator column having an inlet fluidly connected to the absorber column upper polishing section outlet and a regenerator column bottom outlet fluidly connected to the absorber column upper polishing section methanol-lean inlet;
an extractor having an inlet connected in fluid communication to the absorber lower prewash section outlet and the regenerator bottom outlet;
an inlet of the light hydrocarbon removing tower is connected to an outlet at the lower part of the extractor and an outlet of a main washing section in the middle of the absorption tower in a fluid communication manner;
an inlet of the light hydrocarbon washing tower is connected to an outlet at the top of the light hydrocarbon removal tower and an outlet at the middle main washing section of the absorption tower in a fluid communication manner;
a methanol/water separation column having an inlet fluidly connected to the light hydrocarbon removal column bottoms outlet and a methanol/water separation column bottoms outlet fluidly connected to the process water inlet of the extractor, a top outlet fluidly connected to the methanol-lean inlet of the upper polishing section of the absorber column;
and the top inlet of the tail gas washing tower is connected to the bottom outlet of the light hydrocarbon washing tower in a fluid communication manner, and the bottom inlet of the tail gas washing tower is connected to the outlet of the lower pre-washing section of the absorption tower, the outlet of the upper fine-washing section of the absorption tower and/or the outlet of the bottom of the regeneration tower in a fluid communication manner.
19. The plant system of claim 18 further comprising a methanol-lean storage tank having an inlet fluidly connected to the regenerator bottom outlet and the methanol/water separation column overhead outlet, and an outlet fluidly connected to the methanol-lean inlet of the absorber polishing section.
20. The plant system of claim 18 or 19, wherein the plant system further comprises a plurality of coolers, heat exchangers, booster pumps and flash tanks.
21. The plant system of claim 20, wherein the plurality of coolers are respectively disposed at one or more of: the upper stream of the tower bottom inlet of the absorption tower; a semi-lean methanol outlet of the fine washing section of the absorption tower is connected with a semi-lean methanol inlet of the main washing section and/or the prewashing section; the outlet of the regeneration tower is arranged between the inlet of the tail gas washing tower and the outlet of the regeneration tower; the outlet at the bottom of the regeneration tower is connected with the inlet of the poor methanol storage tank; an outlet of the poor methanol storage tank is connected with a poor methanol inlet of the fine washing section of the absorption tower; and between the bottom outlet of the methanol/water separation tower and the process water inlet of the extractor.
22. The plant system as claimed in claim 18 or 19, wherein the plurality of heat exchangers are respectively provided at one or more of the following positions: the upper stream of the tower bottom inlet of the absorption tower; a semi-lean methanol outlet of the fine washing section of the absorption tower is connected with an inlet of the tail gas washing tower and/or the regeneration tower; an outlet of the pre-washing section of the absorption tower is connected with an inlet of the extractor; an outlet at the bottom of the light hydrocarbon removal tower and an inlet of the methanol/water separation tower; and between the outlet of the lower prewashing section of the absorption tower and the inlet of the light dydrocarbon removing tower.
23. The facility system according to claim 18 or 19, wherein the plurality of pressurizing pumps are respectively provided at one or more of the following locations: a semi-lean methanol outlet of the fine washing section of the absorption tower is connected with a semi-lean methanol inlet of the main washing section and/or the prewashing section; an outlet of the poor methanol storage tank is connected with a poor methanol inlet of the fine washing section of the absorption tower; an outlet at the lower part of the extractor and an inlet of the light dydrocarbon removing tower; and between the outlet of the lower prewashing section of the absorption tower and the inlet of the light dydrocarbon removing tower.
24. The plant system of claim 18 or 19, wherein the flash tank is provided at one or more of the following locations, respectively: the upper stream of the tower bottom inlet of the absorption tower; an outlet of the lower pre-washing section of the absorption tower is arranged between an inlet of the tail gas washing tower and an outlet of the lower pre-washing section of the absorption tower; the outlet of the upper fine washing section of the absorption tower is connected with the inlet of the regeneration tower; and between the outlet of the middle main washing section of the absorption tower and the inlet of the light hydrocarbon washing tower.
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