CN117018819A - Method and system for reducing water content of low-temperature methanol washing system - Google Patents
Method and system for reducing water content of low-temperature methanol washing system Download PDFInfo
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- CN117018819A CN117018819A CN202311088645.0A CN202311088645A CN117018819A CN 117018819 A CN117018819 A CN 117018819A CN 202311088645 A CN202311088645 A CN 202311088645A CN 117018819 A CN117018819 A CN 117018819A
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- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 title claims abstract description 908
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 157
- 238000005406 washing Methods 0.000 title claims abstract description 56
- 238000000034 method Methods 0.000 title claims abstract description 18
- GBMDVOWEEQVZKZ-UHFFFAOYSA-N methanol;hydrate Chemical compound O.OC GBMDVOWEEQVZKZ-UHFFFAOYSA-N 0.000 claims abstract description 140
- 238000000926 separation method Methods 0.000 claims abstract description 120
- 239000002253 acid Substances 0.000 claims abstract description 30
- 238000001704 evaporation Methods 0.000 claims abstract description 13
- 230000008020 evaporation Effects 0.000 claims abstract description 11
- 238000007599 discharging Methods 0.000 claims description 40
- 238000010521 absorption reaction Methods 0.000 claims description 33
- 230000008929 regeneration Effects 0.000 claims description 25
- 238000011069 regeneration method Methods 0.000 claims description 25
- 239000002351 wastewater Substances 0.000 claims description 15
- 238000005201 scrubbing Methods 0.000 claims description 14
- 238000004064 recycling Methods 0.000 claims description 8
- 239000012535 impurity Substances 0.000 claims description 2
- 238000005260 corrosion Methods 0.000 abstract description 4
- 230000007797 corrosion Effects 0.000 abstract description 4
- 239000007789 gas Substances 0.000 description 232
- 229910052717 sulfur Inorganic materials 0.000 description 33
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 30
- 239000011593 sulfur Substances 0.000 description 30
- 238000003795 desorption Methods 0.000 description 15
- 239000002994 raw material Substances 0.000 description 15
- 238000010992 reflux Methods 0.000 description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 229910052757 nitrogen Inorganic materials 0.000 description 6
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 3
- 229910002092 carbon dioxide Inorganic materials 0.000 description 3
- 239000001569 carbon dioxide Substances 0.000 description 3
- 239000012141 concentrate Substances 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 238000011084 recovery Methods 0.000 description 3
- 238000005507 spraying Methods 0.000 description 3
- 239000006096 absorbing agent Substances 0.000 description 2
- 239000003245 coal Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 238000000746 purification Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1456—Removing acid components
- B01D53/1468—Removing hydrogen sulfide
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1418—Recovery of products
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1425—Regeneration of liquid absorbents
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1456—Removing acid components
- B01D53/1475—Removing carbon dioxide
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
- B01D53/1493—Selection of liquid materials for use as absorbents
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2252/00—Absorbents, i.e. solvents and liquid materials for gas absorption
- B01D2252/20—Organic absorbents
- B01D2252/202—Alcohols or their derivatives
- B01D2252/2021—Methanol
Abstract
The application provides a method and a system for reducing the water content of a low-temperature methanol washing system. The method for reducing the water content of the low-temperature methanol washing system comprises the following steps: rectifying the aqueous methanol obtained by low-temperature methanol washing by using a methanol-water separation tower to remove water contained in the aqueous methanol, wherein the feed from the top tray of the methanol-water separation tower is from CO removal 2 And the aqueous methanol in the acid gas methanol washing system is subjected to flash evaporation treatment on the rich methanol by using a first methanol water flash tank to remove dissolved gas, gas is discharged from the top, and the rich methanol discharged from the bottom enters the middle part of the methanol-water separation tower. The method for reducing the water content of the low-temperature methanol washing system can effectively reduce the water content of the circulating methanol, increase the operation stability and reduce the equipment corrosion.
Description
Technical Field
The application relates to the field of gas purification in coal chemical industry, in particular to a method and a system for reducing the water content of a low-temperature methanol washing system.
Background
The raw material gas of the coal chemical plant contains saturated water, the water and the methanol are mutually dissolved, after the methanol is washed, the water in the gas can be dissolved in the methanol, and the purified gas basically contains no water, so the water in the raw material gas is removed by a low-temperature methanol washing method, and the purified synthesis gas which meets the downstream requirement and contains no water is obtained.
After the water is dissolved in the methanol, the water in the methanol is separated out by adopting a method of adding a methanol-water separation tower and is discharged out of the system, so that the water content in the system is maintained at a lower level.
Fig. 1 shows a schematic diagram of a conventional cryogenic methanol scrubbing system. The system comprises:
(1) A heat exchanger for cooling the raw material gas, wherein the raw material gas sprayed with a small amount of methanol, the purified gas from the top of the absorption tower and the CO from the top of the desorption tower are mixed in the heat exchanger 2 Heat exchange is carried out on the product gas, so that the raw material gas is cooled; for the purified gas and CO after heat exchange 2 Collecting product gas, wherein methanol is sprayed to prevent icing;
(2) A feed gas separation tank for separating the methanol-rich gas from the gas, feeding the feed gas cooled by the heat exchanger, discharging the feed gas from the top, and discharging the separated methanol-rich gas from the bottom;
(3) An absorption tower for using methanol to remove water and CO from the raw material gas 2 And H 2 S and other acid gases are absorbed and purified, the raw gas from a raw gas liquid separating tank is fed from the lower part of an absorption tower, lean methanol from the bottom of a thermal regeneration tower is fed from a top column plate of the absorption tower, and the lean methanol contacts with the raw gas in a countercurrent way to absorb moisture and CO in the raw gas 2 And H 2 S and other acid gases, after heat exchange, discharging purified gas to a collecting device through a heat exchanger, discharging sulfur-free rich methanol from the middle part of an absorption tower, and discharging sulfur-containing rich methanol from the bottom of the absorption tower;
(4) A sulfur-free methanol flash tank, wherein sulfur-free rich methanol from the middle part of the absorption tower is fed into the sulfur-free methanol flash tank for flash evaporation treatment, the top exhaust gas is compressed and then enters a heat exchanger together with raw gas for recycling, and the sulfur-free rich methanol is discharged from the bottom;
(5) The sulfur-containing methanol flash tank is used for feeding sulfur-containing rich methanol from the bottom of the absorption tower into the sulfur-containing methanol flash tank for flash evaporation treatment, compressing top exhaust gas, then feeding the compressed top exhaust gas and raw gas into a heat exchanger for recycling, and discharging the sulfur-containing rich methanol from the bottom into the middle part of the concentration tower;
(6) A desorber for receiving sulfur-free methanol from the bottom of the sulfur-free flash tank at the upper part and carrying out CO 2 Desorbing and discharging CO from the top of the desorber 2 Product gas is discharged from the middle part and the bottom of the desorption tower respectively, and is rich in sulfur-free methanol and rich in sulfur-containing methanol;
(7) A concentration column for further desorbing carbon dioxide to relatively concentrate acid gas such as hydrogen sulfide, feeding sulfur-containing rich methanol from the bottom of the desorption column from the lower part of the concentration column, feeding sulfur-containing rich methanol from the bottom of the sulfur-containing methanol flash tank from the middle part of the concentration column, feeding sulfur-free rich methanol discharged from the middle part of the desorption column from the upper part of the concentration column, feeding nitrogen from the lower part of the concentration column, and discharging a small amount of H from the top of the concentration column 2 Acid gas such as S and CO 2 And N 2 The mixed gas of (2) is sent to a tail gas washing tower;
(8) A thermal regeneration tower for removing H 2 S and other acid gases, sulfur-containing rich methanol from the bottom of the concentration tower is fed into the middle part of the thermal regeneration tower, lean methanol steam from the top of the methanol-water separation tower enters the lower part of the thermal regeneration tower after being cooled, and H-containing steam is discharged from the top 2 S and other acid gases enter a Claus recovery system, lean methanol is discharged from the bottom and divided into three parts, one part is used for spraying raw material gas, the other part enters the upper part of an absorption tower, and the other part enters a methanol-water separation tower from a top tower plate for continuously removing water in the system;
(9) A methanol-water separation column for removing water from the aqueous methanol from the heat regeneration column and the rich methanol from the bottom of the feed gas separation tank, feeding the lean methanol from the bottom of the heat regeneration column to the top tray of the methanol-water separation column, feeding the rich methanol from the bottom of the feed gas separation tank to the middle part of the methanol-water separation column, feeding the tail gas washing water from the bottom of the tail gas washing column to the middle part of the methanol-water separation column, discharging the waste water containing a small amount of methanol from the bottom, and discharging the lean methanol vapor from the top; and
(10) The tail gas washing tower is used for removing a small amount of residual methanol in the tail gas, enabling the tail gas to reach the standard and be discharged, feeding desalted water from a feed inlet positioned at a top layer tower plate of the tail gas washing tower, feeding the tail gas from the top of the concentration tower from a feed inlet positioned at a bottom layer tower plate, discharging purified tail gas from the top, and discharging tail gas washing water from the bottom.
The methanol circulating in the system is dehydrated in the methanol-water separation tower, so that the system can stably run. The water content of the methanol in the system is kept at a low level by continuously removing the water in the methanol through the methanol-water separation tower.
However, when the water content in the raw gas is higher, the system moisture removal effect is poor, and the residual moisture in the system is more during the original start-up, so that the methanol water content in the system is higher, the water content in the refluxing methanol from the thermal regeneration tower is higher, the refluxing effect cannot be achieved, the water content in the gas phase at the top of the tower balanced with the refluxing effect is higher, the water is returned to the system, once the water quantity brought back to the system is larger than the water quantity discharged from the system, the water quantity of the system cannot be reduced, a vicious circle is formed, the water content can be continuously increased, normal operation is influenced, and meanwhile, the corrosion of equipment is aggravated.
Disclosure of Invention
In view of the foregoing problems with the prior art, the present application provides a system and method for reducing the water content of a low temperature methanol scrubbing system. The system for reducing the water content of the low-temperature methanol washing system has the advantages of improving the methanol-water separation effect, quickly and efficiently separating out the water content of the system, reducing the water content of the methanol of the system and stabilizing the water content of the methanol in the system at a lower level.
According to a first aspect of the present application there is provided a method of reducing the water content of a cryogenic methanol wash system comprising:
rectifying the aqueous methanol obtained by low-temperature methanol washing by using a methanol-water separation tower to remove water contained in the aqueous methanol, discharging methanol from the top of the methanol-water separation tower, and discharging wastewater from the bottom of the methanol-water separation tower; wherein,
feeding through a feed inlet at the top tray of the methanol-water separation column 2 And an acid gas, preferably via CO removal 2 And the aqueous methanol of the acid gas methanol washing system is methanol from the bottom of the thermal regeneration tower;
flash evaporating the methanol-rich from the bottom of the feed gas separation tank by using a first methanol water flash tank to remove dissolved gas, discharging gas from the top, and introducing the methanol-rich discharged from the bottom into the middle part of a methanol-water separation tower; and
optionally, the tail gas washing water is subjected to flash evaporation treatment by using a second methanol water flash tank to remove dissolved gas in the tail gas washing water, the gas discharged from the top enters a tail gas absorption tower, and the tail gas washing water discharged from the bottom enters the middle part of the methanol-water separation tower.
Before entering the methanol-water separation tower, the methanol-water flash tank is used for carrying out flash evaporation treatment on the methanol-rich and/or tail gas washing water from the feed gas separation tank so as to remove the gas dissolved in the methanol-water separation tower, reduce the gas entering the methanol-water separation tower, reduce the gas phase quantity at the top of the methanol-water separation tower, further reduce the water quantity returned to the system, simultaneously reduce the gas phase load of the methanol-water separation tower and improve the operation stability.
Preferably, anhydrous methanol is introduced into the methanol-water separation column; when introducing anhydrous methanol, feeding the anhydrous methanol into the methanol-water separation tower from a feed port positioned at a top tray of the methanol-water separation tower; through CO removal 2 And the aqueous methanol of the acid gas methanol wash system is fed to the methanol-water separation column from a feed port located at 3 to 8 trays below the top tray.
Preferably, the off-gas wash water is fed from a feed inlet located at 1/3 to 2/3 of the total tray number of the methanol-water separation column.
The water content of the methanol steam at the top of the methanol-water separation tower can be reduced by adding the anhydrous methanol, so that the water content of the methanol which flows back to the absorption tower can be reduced, and the safe operation of the device is effectively ensured.
The feed amount of the anhydrous methanol is determined according to the water content of the discharged lean methanol from the top of the methanol-water separation column, and when the water content of the discharged lean methanol exceeds a predetermined value, the anhydrous methanol is fed or the feed amount of the anhydrous methanol is increased. Control of the introduction of anhydrous methanol by a valve and control of the removal of CO 2 And acid gas, from the top tray or from a tray located 3 to 8 layers below the top tray.
Preferably, when the water content of the methanol vapor discharged from the top of the methanol-water separation column is more than 0.5mol%, anhydrous methanol is fed in an amount corresponding to that of the CO-removed methanol 2 And the weight ratio of the methanol washing system of the acid gas is 1:2-1:1.
Preferably, the methanol washing system is used for purifying raw gas and removing CO 2 And the aqueous methanol in the methanol washing system of the acid gas is purified and CO removed by absorbing impurities in the raw gas 2 And H 2 The aqueous methanol obtained after acid gas such as S preferably has a water content of 1 to 2wt%.
Preferably, the water content of the methanol vapor discharged from the top of the methanol-water separation column is 0.1mol% to 0.5mol%, and the methanol content in the water discharged from the bottom of the methanol-water separation column is 0.01wt% or less.
Preferably, the operating conditions of the methanol-water separation column are: 0.23-0.26 MPaG, 100-140 ℃.
Preferably, the operating conditions of the first methanol water flash tank are: the operating pressure is 0.4-0.8 MPaG, and the temperature is 30-70 ℃.
Preferably, the working conditions of the second methanol water flash tank are: the operating pressure is 0.4-0.8 MPaG, and the temperature is 70-120 ℃.
According to a second aspect of the present application there is provided a system for reducing the water content of a cryogenic methanol wash system comprising:
the methanol-water separation tower is used for separating water and methanol, and is provided with feed inlets at the top-layer tower plate and at the positions of 3 to 8 layers of tower plates below the top-layer tower plate respectively, and is used for feeding anhydrous methanol or water-containing methanol obtained by low-temperature methanol washing; a methanol rich feed inlet for feeding methanol rich from the bottom of the first methanol flash tank; a tail gas washing water feed port for feeding tail gas washing water, the feed port being located at 1/3 to 2/3 of the total tray number of the methanol-water separation column; a methanol vapor outlet for discharging dehydrated methanol vapor, the methanol vapor outlet being located at the top of the methanol-water separation column; and a waste water outlet for discharging waste water, the waste water outlet being located at the bottom of the methanol-water separation column;
a first methanol-water flash tank for removing gas from the methanol-rich gas in the feed gas separation tank and connected to the bottom of the feed gas separation tank by a pipe to feed the methanol-rich gas from the feed gas separation tank, the top of the first methanol-water flash tank being connected to the middle of the concentration column to feed the separated gas to the concentration column, the bottom of the first methanol flash tank being connected to the middle of the methanol-water separation column by a pipe to feed the methanol-rich gas at the bottom of the first methanol flash tank to the methanol-water separation column; and
an optional second methanol water flash tank for removing gas from the off-gas wash water from the off-gas wash column and connected to the bottom of the off-gas wash column by a conduit for feeding off-gas wash water from the off-gas wash column, the top of the second methanol water flash tank being connected to the bottom of the off-gas wash column for recycling the separated gas to the off-gas wash column.
In the application, the first methanol water flash tank and/or the second methanol water flash tank are added to realize the following beneficial effects:
a large amount of CO may be entrained in the methanol rich from the feed gas knock-out pot 2 Through a newly added methanol water flash tank, CO dissolved in the rich methanol can be effectively removed 2 And the gas is prevented from entering the methanol-water separation tower from excessive gas phase. Excessive gas phase enters the methanol-water separation tower, so that the operation load is increased, the top gas phase quantity is increased, the water content of the circulating methanol is increased due to the increase of the gas phase quantity, and the control of the water content of the methanol in the system is not facilitated.
The washing water of the tail gas water washing tower is subjected to flash evaporation by a second methanol water flash tank before entering the methanol water separation tower, and the separated gas phase is mainly CO 2 And water, which is returned to the exhaust gas before the exhaust gas washing. Meanwhile, the gas phase entering the methanol-water separation tower can be reduced, the operation load is reduced, the top gas phase quantity is reduced, and the water quantity entering the front system is controlled.
In the conventional flow, the reflux methanol from the bottom of the thermal regeneration tower enters the top column plate of the methanol-water separation tower, when the water content of the system methanol is higher, the water content of the reflux methanol from the thermal regeneration tower is higher, the reflux effect cannot be achieved, the water content of the gas phase at the top of the tower balanced with the reflux methanol is higher, the water is returned to the system, once the water quantity of the water returned to the system is larger than the water quantity discharged from the system, the water quantity of the system cannot be reduced, a vicious circulation is formed, the water content can be continuously increased, the normal operation is influenced, and meanwhile, the corrosion of equipment is aggravated.
Preferably, when introducing anhydrous methanol, anhydrous methanol is fed from a feed port located at the top tray, and aqueous methanol is fed from a feed port located at the tray of 3 to 8 layers below the top tray; when no anhydrous methanol is introduced, aqueous methanol is fed from a feed port located at the top tray, and a feed port located at the tray 3 to 8 layers below the top tray is closed.
The system for reducing the water content of a cryogenic methanol wash system according to the present application is part of a cryogenic methanol wash system.
According to a third aspect of the present application there is provided a low temperature methanol wash system comprising:
1) A heat exchanger for cooling the raw material gas, wherein the raw material gas sprayed with a small amount of methanol, the purified gas from the top of the absorption tower and the CO from the top of the desorption tower are mixed in the heat exchanger 2 Heat exchange is carried out on the product gas, so that the raw material gas is cooled; for the purified gas and CO after heat exchange 2 Collecting product gas;
2) A feed gas separation tank for separating the methanol-rich gas from the gas, feeding the feed gas cooled by the heat exchanger, discharging the feed gas from the top, and discharging the methanol-rich gas from the bottom;
3) An absorption tower for using methanol to remove water and CO from the raw material gas 2 And H 2 S and other acid gases are absorbed and purified, the raw gas from a raw gas liquid separating tank is fed from the lower part of an absorption tower, and lean methanol from the bottom of a thermal regeneration tower is fed from a top column plate of the absorption tower, so that the lean methanol and the raw gas are in countercurrent contact to absorb moisture and CO in the raw gas 2 And H 2 S and other acid gases, after heat exchange, discharging purified gas to a collecting device through a heat exchanger, discharging sulfur-free rich methanol from the middle part of an absorption tower, and discharging sulfur-containing rich methanol from the bottom of the absorption tower;
(4) A sulfur-free methanol flash tank, wherein sulfur-free rich methanol from the middle part of the absorption tower is fed into the sulfur-free methanol flash tank for flash evaporation treatment, the top exhaust gas is compressed and then enters a heat exchanger together with raw gas for recycling, and the sulfur-free rich methanol is discharged from the bottom;
(5) A sulfur-containing methanol flash tank, wherein the sulfur-containing rich methanol from the bottom of the absorption tower is fed into the sulfur-containing flash tank for flash evaporation treatment, the top exhaust gas is compressed and then enters a heat exchanger together with the raw material gas for recycling, and the bottom exhaust sulfur-containing rich methanol enters the middle part of the concentration tower;
6) A desorption tower which receives the sulfur-free rich methanol from the bottom of the sulfur-free flash tank at the upper part and carries out CO 2 Desorbing C discharged from the top of the desorberO 2 Discharging the sulfur-free rich methanol and the sulfur-containing rich methanol from the middle part and the bottom of the desorption tower respectively after heat exchange by a heat exchanger;
7) A concentration column for further desorbing carbon dioxide to relatively concentrate acid gas such as hydrogen sulfide, feeding sulfur-containing rich methanol from the bottom of the desorption column at the lower part of the concentration column, feeding sulfur-containing rich methanol from the bottom of the sulfur-containing methanol flash tank from the middle part of the concentration column, feeding gas from the top of the first methanol water flash tank from the middle part of the concentration column, and feeding sulfur-free rich methanol discharged from the middle part of the desorption column from the top tray of the concentration column, feeding nitrogen from the bottom tray of the concentration column, and discharging a large amount of CO from the top of the concentration column 2 Small amount of H 2 S and N 2 The mixed gas of (2) is sent to a tail gas washing tower;
8) A thermal regeneration tower for further removing H in methanol 2 S and other acid gases, sulfur-containing rich methanol from the bottom of the concentration tower is fed into the middle part of the thermal regeneration tower, lean methanol steam from the top of the methanol-water separation tower enters the lower part of the thermal regeneration tower after being cooled, and H-containing steam is discharged from the top 2 S and other acid gases enter a Claus recovery system, lean methanol is discharged from the bottom and divided into three parts, one part is used for spraying raw material gas, the other part enters an absorption tower through a feed inlet positioned at a top column plate, and the other part enters a methanol-water separation tower for continuously removing water in the system;
9) A methanol-water separation column for removing water from the aqueous methanol, the feed ports being provided at the top-layer tray and at the trays of 3 to 8 layers below the top-layer tray, respectively, and when the anhydrous methanol is introduced, the anhydrous methanol is fed from the feed port located at the top-layer tray, the aqueous methanol from the bottom of the thermal regeneration column is fed from the feed port located at the tray of 3 to 8 layers below the top-layer tray, and when the anhydrous methanol is not introduced, the aqueous methanol from the thermal regeneration column is fed from the feed port located at the tray of the top-layer tray, and the feed port located at the tray of 3 to 8 layers below the top-layer tray is closed; a methanol-rich feed inlet for feeding methanol-rich from the bottom of the first methanol flash tank, which is provided in the middle of the methanol-water separation column; the middle part of the methanol-water separation tower is provided with a tail gas washing water feed port, and the tail gas washing water from the second methanol water flash tank is received from the feed port; a methanol steam outlet is arranged at the top of the methanol-water separation tower, and dehydrated methanol steam is discharged from the outlet; and a waste water discharge port is provided at the bottom of the methanol-water separation tower to discharge waste water, wherein the content of methanol in the waste water is 0.01wt% or less; wherein, the operation conditions of the methanol-water separation tower are as follows: 0.23-0.26MPaG, 100-140 ℃;
10 A first methanol-water flash tank that receives the methanol-rich gas from the bottom of the feed gas separation tank and performs a flash operation to remove the gas dissolved therein, and feeds the methanol-rich gas subjected to the flash treatment to the middle part of the methanol-water separation column, and the gas discharged from the top to the middle part of the concentration column;
11 A tail gas washing tower for removing methanol from the tail gas, feeding gas from the top of the concentration tower from a feed inlet located at a bottom tray, feeding desalted water from a feed inlet located at a top tray, discharging tail gas washing water from the bottom, discharging tail gas from the top,
12 A second methanol flash tank for flashing off the off-gas wash water from the off-gas wash column to remove dissolved gas therein, which receives off-gas wash water from the off-gas wash column, and after the flash treatment, the off-gas wash water at the bottom of the second methanol flash tank is fed into the methanol-water separation column through an off-gas wash water feed port of the methanol-water separation column, and the gas discharged from the top enters the off-gas wash column together with the gas from the top of the concentration column.
In the application, the vicious circle caused by the excessive water content of the system is prevented by arranging a feed inlet for introducing anhydrous methanol at the top tray of the methanol-water separation tower.
Normally, if the water content of the system is not high, no absolute methanol is required to be introduced.
When the water content of the system is high, anhydrous methanol is introduced, the water content in the gas phase at the top of the methanol-water separation tower and the balanced top of the methanol-water separation tower can be reduced, the water content of the system before the gas phase is brought into the system can be reduced, the water content of lean methanol is reduced, and the safe operation of the device is effectively ensured.
According to the application, the anhydrous methanol is introduced into the top of the methanol-water separation tower, so that the water content of a gas phase at the top of the methanol-water separation tower is reduced, the water quantity returned to the system is reduced, and particularly when the water content of the system is higher, the system water can be effectively discharged; in addition, the two aqueous solutions entering the methanol-water separation tower flash to remove dissolved gas, so that the gas entering the methanol-water separation tower is reduced, the gas phase quantity at the top of the methanol-water separation tower is reduced, the water quantity returned to the system is further reduced, the gas phase load of the methanol-water separation tower is reduced, and the operation stability is improved. The long-period operation of the scheme of the application ensures that the water content in the lean methanol fed into the absorption tower is less than 0.5mol percent, and the water content of partial devices can be less than 0.1mol percent.
Drawings
FIG. 1 is a schematic diagram of a prior art cryogenic methanol scrubbing system;
fig. 2 is a schematic diagram of a cryogenic methanol scrubbing system including a system for reducing the methanol water content of a cryogenic methanol system in accordance with the present application.
Detailed Description
An apparatus and system for reducing the water content in methanol of a cryogenic methanol system according to the present application will be described in detail with reference to the accompanying drawings. It should be noted that the following examples are only for describing the present application and are not intended to limit the scope of the present application.
It should be noted that the structures of the absorption tower, the desorption tower, the concentration tower, the thermal regeneration tower, the methanol-water separation tower and the tail gas washing tower in the low-temperature methanol washing system are well known to those skilled in the art, and are not described herein. In addition, the cryogenic methanol scrubbing system includes conventional heat exchangers, valves, pumps, heaters, etc., the functions and roles of which are well known to those skilled in the art and are not shown in the drawings nor developed in detail for the sake of brevity.
The terms "methanol-rich", "methanol-lean" are used to distinguish between the water content of methanol, "methanol-rich" refers to methanol having a higher water content, and "methanol-lean" refers to methanol having a lower water content.
The term "top of a column" refers to the top of the corresponding column. The term "middle of the column" refers to the intermediate tray position of the plurality of trays in the column. The term "upper portion of the column" refers to a location below the top tray and above the middle tray; the term "lower portion of the column" refers to a location below the intermediate tray and above the bottom tray; the term "bottom of the column" means at the very bottom of the column.
Example 1
The system for reducing the water content of the low-temperature methanol is a part of a low-temperature methanol washing system of raw gas.
The low-temperature methanol washing system of the raw gas comprises:
1) A heat exchanger for cooling the raw gas, wherein the raw gas sprayed with a small amount of methanol, the purified gas from the top of the absorption tower and the CO from the top of the desorption tower are cooled 2 Heat exchange is carried out on the product gas, so that the raw gas is cooled; for the purified gas and CO after heat exchange 2 Collecting product gas, wherein methanol is sprayed to prevent icing;
2) A raw gas separation tank for separating methanol-rich gas from gas, feeding raw gas cooled by a heat exchanger, discharging the raw gas from the top, and discharging the methanol-rich gas from the bottom;
3) An absorption tower for using methanol to remove water and CO from the raw gas 2 And H 2 S and other acid gases are absorbed and purified, raw gas from a feed gas liquid separating tank is fed from the lower part of an absorption tower, lean methanol from the bottom of a thermal regeneration tower is fed from a top column plate of the absorption tower, and the lean methanol is in countercurrent contact with the raw gas to absorb moisture and CO in the raw gas 2 And H 2 S and other acid gases, discharging purified gas after heat exchange to a collecting device through a heat exchanger, discharging sulfur-free rich methanol from the middle part of an absorption tower, and discharging sulfur-containing rich methanol from the bottom of the absorption tower, wherein the raw gas comprises the following components: h 2 ：50.8mol％，CO 2 ：42.31mol％，CO：5.98mol％，N 2 ：0.4mol％，H 2 O：0.22mol％，H 2 S：0.19mol％，Ar：0.07mol％，CH 4 ：0.03mol％。
4) A sulfur-free methanol flash tank, wherein sulfur-free rich methanol from the middle part of the absorption tower is fed into the sulfur-free methanol flash tank for flash evaporation treatment, top exhaust gas is compressed and then enters a heat exchanger together with raw gas for recycling, and the sulfur-free rich methanol is discharged from the bottom;
5) A sulfur-containing methanol flash tank, wherein the sulfur-containing rich methanol from the bottom of the absorption tower is fed into the sulfur-containing flash tank for flash evaporation treatment, the top exhaust gas is compressed and then enters a heat exchanger together with the raw material gas for recycling, and the bottom exhaust sulfur-containing rich methanol enters the middle part of the concentration tower;
6) A desorption tower which receives the sulfur-free rich methanol from the bottom of the sulfur-free flash tank at the upper part and carries out CO 2 Desorbing CO discharged from the top of the desorber 2 Discharging the sulfur-free rich methanol and the sulfur-containing rich methanol from the middle part and the bottom of the desorption tower respectively after heat exchange by a heat exchanger;
7) A concentration column for further desorbing carbon dioxide to relatively concentrate acid gas such as hydrogen sulfide, feeding sulfur-containing rich methanol from the bottom of the desorption column at the lower part of the concentration column, feeding sulfur-containing rich methanol from the bottom of the sulfur-containing methanol flash tank from the middle part of the concentration column, feeding gas from the top of the first methanol water flash tank from the middle part of the concentration column, and feeding sulfur-free rich methanol discharged from the middle part of the desorption column from the top tray of the concentration column, feeding nitrogen from the bottom tray of the concentration column, and discharging a large amount of CO from the top of the concentration column 2 Small amount of H 2 S and N 2 The mixed gas of (2) is sent to a tail gas washing tower;
8) A thermal regeneration tower for further removing H in methanol 2 S and other acid gases, sulfur-containing rich methanol from the bottom of the concentration tower is fed into the middle part of the thermal regeneration tower, lean methanol steam from the top of the methanol-water separation tower enters the lower part of the thermal regeneration tower after being cooled, and H-containing steam is discharged from the top 2 S and other acid gases enter a Claus recovery system, lean methanol is discharged from the bottom and divided into three parts, one part is used for spraying raw material gas, the other part enters an absorption tower through a feed inlet positioned at a top column plate, and the other part enters a methanol-water separation tower for continuously removing water in the system;
9) A methanol-water separation column for removing water from methanol, the methanol-water separation column having 56 stages of trays, feed ports being provided at the 56 th stage and at the 52 th stage, respectively, and when anhydrous methanol is introduced, anhydrous methanol is fed from the feed port located at the 56 th stage, aqueous methanol from the bottom of the thermal regeneration column is fed from the feed port located at the 52 th stage, and when anhydrous methanol is not introduced, aqueous methanol from the bottom of the thermal regeneration column is fed from the feed port located at the 56 th stage, and the feed port located at the 52 th stage is closed; a methanol-rich feed inlet is arranged at a layer 28 column plate of the methanol-water separation tower so as to feed methanol-rich from the bottom of the first methanol flash tank; and an off-gas wash water feed port is provided at the 28 th stage tray from which off-gas wash water from the second methanol water flash tank is fed; a methanol steam outlet is arranged at the top of the methanol-water separation tower, and dehydrated methanol steam is discharged from the outlet; and a waste water discharge port is provided at the bottom of the methanol-water separation tower to discharge waste water, wherein the content of methanol in the waste water is 0.01wt% or less; wherein, the operation conditions of the methanol-water separation tower are as follows: 0.23-0.26MPaG, 100-140 ℃;
10 A first methanol-water flash tank that receives the methanol-rich gas from the bottom of the feed gas separation tank and performs a flash operation to remove the gas dissolved therein, and feeds the methanol-rich gas subjected to the flash treatment to the middle part of the methanol-water separation column, and the gas discharged from the top to the middle part of the concentration column, the operation conditions of the first methanol-water flash tank being: 0.5MPaG,52 ℃;
11 A tail gas washing tower for removing methanol from the tail gas, feeding gas from the top of the concentration tower from a feed inlet located at a bottom tray, feeding desalted water from a feed inlet located at a top tray, discharging tail gas washing water from the bottom, discharging tail gas from the top,
12 A second methanol flash tank for flashing off-gas wash water from the off-gas wash column to remove dissolved gas therein, which receives off-gas wash water from the off-gas wash column, the off-gas wash water at the bottom of the second methanol flash tank being fed to the methanol water separation column through an off-gas wash water feed port of the methanol water separation column after the flash treatment, the gas discharged from the top entering the off-gas wash column together with the gas from the top of the concentration column, the second methanol water flash tank operating conditions being: 0.45MPaG,113 ℃.
A methanol-water separation tower of a low-temperature methanol washing device matched with a device for producing 200 ten thousand tons of methanol in a certain year, wherein the water content in a gas phase at the top of the methanol-water separation tower is 0.815koml/h (the water content is 0.22 mol%) under the condition that anhydrous methanol is not added, and the water content in rich methanol fed into the methanol-water separation tower through a first methanol-water flash tank is 25.19mol%; after 72 hours of operation, the water content in the methanol fed to the absorber was 1.57mol%.
The weight ratio of the anhydrous methanol added amount to the aqueous methanol from the bottom of the thermal regeneration tower is 1:1, a step of; the calculated water carry-over of the overhead gas phase was 0.352koml/h (water content 0.064 mol%) with a water content of 25.13mol% in the methanol-rich water fed to the methanol-water separation column via the first methanol-water flash tank. After 72 hours of operation, the water content in the methanol fed to the absorber was 0.47mol%.
Comparative example 1
The same operation as in example 1 was performed, except that the first methanol water flasher and the second methanol water flasher were not provided, and that anhydrous methanol was not introduced. Wherein the gas phase carrying amount in the methanol-water separation column was 1.368koml/h (water content: 3.72 mol%). The water content is much higher than in example 1. Higher water content affects methanol to CO 2 And H 2 S has the absorption effect, the purification index is not easy to ensure, and the circulation quantity is increased, so that the consumption is increased, and the operation of the device is not facilitated; meanwhile, the corrosion of equipment is aggravated due to high water content, and the service life of the device is influenced. Devices not employing the inventive arrangements require significant replacement of methanol to reduce the water content of the recycled methanol.
Claims (10)
1. A method of reducing the water content of a low temperature methanol wash system comprising:
rectifying the aqueous methanol obtained by low-temperature methanol washing by using a methanol-water separation tower to remove water contained in the aqueous methanol, discharging methanol from the top of the methanol-water separation tower, and discharging wastewater from the bottom of the methanol-water separation tower; wherein,
feeding through a feed inlet at the top tray of the methanol-water separation column 2 And an acid gas, preferably via CO removal 2 And the aqueous methanol of the acid gas methanol washing system is methanol from the bottom of the thermal regeneration tower;
flash evaporating the methanol-rich gas from the bottom of the feed gas separation tank by using a first methanol water flash tank to remove dissolved gas, discharging gas from the top, and introducing the methanol-rich gas discharged from the bottom into the middle part of a methanol-water separation tower; and
optionally, the tail gas washing water is subjected to flash evaporation treatment by using a second methanol water flash tank to remove dissolved gas in the tail gas washing water, the gas discharged from the top enters a tail gas absorption tower, and the tail gas washing water discharged from the bottom enters the middle part of the methanol-water separation tower.
2. The method for reducing the water content of a cryogenic methanol scrubbing system as recited in claim 1, wherein,
introducing anhydrous methanol into the methanol-water separation tower, and feeding the anhydrous methanol into the methanol-water separation tower from a feed port positioned at a top tray of the methanol-water separation tower when the anhydrous methanol is introduced; through CO removal 2 And the aqueous methanol of the acid gas methanol scrubbing system is fed to the methanol-water separation column from a feed port located at 3 to 8 trays below the top tray.
3. A method for reducing the water content of a cryogenic methanol scrubbing system as claimed in claim 1 or 2, wherein,
the off-gas washing water is fed from a feed port located at 1/3 to 2/3 of the total tray number of the methanol-water separation column.
4. A process for reducing the water content of a cryogenic methanol scrubbing system as claimed in any one of claims 1 to 3, wherein,
when the water content of the methanol vapor fed out from the top of the methanol-water separation column exceeds 0.5mol%, anhydrous methanol is introduced in an amount corresponding to that of the methanol vapor subjected to CO removal 2 And acid gasThe weight ratio of the aqueous methanol of the methanol washing system is 1:2-1:1;
preferably, the methanol washing system is used for purifying raw gas and removing CO 2 And the aqueous methanol in the methanol washing system of the acid gas is purified by absorbing impurities in the raw gas, and CO is removed 2 And H 2 The aqueous methanol obtained after acid gas such as S preferably has a water content of 1 to 2wt%.
5. The method for reducing the water content of a cryogenic methanol scrubbing system as claimed in any one of claims 1 to 4, wherein,
the water content of the methanol vapor discharged from the top of the methanol-water separation column is 0.1mol% to 0.5mol%, and the methanol content of the water discharged from the bottom of the methanol-water separation column is 0.01wt% or less.
6. The method for reducing the water content of a cryogenic methanol scrubbing system as claimed in any one of claims 1 to 5, wherein,
the operating conditions of the methanol-water separation tower are as follows: 0.23-0.26 MPaG, 100-140 ℃.
7. The method for reducing the water content of a cryogenic methanol scrubbing system as claimed in any one of claims 1 to 6, wherein,
the working conditions of the first methanol water flash tank are as follows: the operating pressure is 0.4-0.8 MPaG, and the temperature is 30-70 ℃.
8. The method for reducing the water content of a cryogenic methanol scrubbing system as claimed in any one of claims 1 to 7, wherein,
the working conditions of the second methanol water flash tank are as follows: the operating pressure is 0.4-0.8 MPaG, and the temperature is 70-120 ℃.
9. A system for reducing the water content of a cryogenic methanol wash system comprising:
the methanol-water separation tower is used for separating water and methanol, and is provided with feed inlets at the top-layer tower plate and at the positions of 3 to 8 layers of tower plates below the top-layer tower plate respectively, and is used for feeding anhydrous methanol or water-containing methanol obtained by low-temperature methanol washing; a methanol rich feed inlet for feeding methanol rich from the bottom of the first methanol flash tank; a tail gas washing water feed port for feeding tail gas washing water, the feed port being located at 1/3 to 2/3 of the total tray number of the methanol-water separation column; a methanol vapor outlet for discharging dehydrated methanol vapor, the methanol vapor outlet being located at the top of the methanol-water separation column; and a waste water outlet for discharging waste water, the waste water outlet being located at the bottom of the methanol-water separation column;
a first methanol-water flash tank for removing gas from the methanol-rich gas in the feed gas separation tank and connected to the bottom of the feed gas separation tank by a pipe to feed the methanol-rich gas from the feed gas separation tank, the top of the first methanol-water flash tank being connected to the middle of the concentration column to feed the separated gas to the concentration column, the bottom of the first methanol flash tank being connected to the middle of the methanol-water separation column by a pipe to feed the methanol-rich gas at the bottom of the first methanol flash tank to the methanol-water separation column; and
an optional second methanol water flash tank for removing gas from the off-gas wash water from the off-gas wash column and connected to the bottom of the off-gas wash column by a conduit for feeding off-gas wash water from the off-gas wash column, the top of the second methanol water flash tank being connected to the bottom of the off-gas wash column for recycling the separated gas to the off-gas wash column.
10. The system for reducing the water content of a cryogenic methanol scrubbing system of claim 9 wherein,
when introducing the anhydrous methanol, feeding the anhydrous methanol from a feed inlet positioned at the top-layer column plate, and feeding the low-temperature methanol-washed water-containing methanol from a feed inlet positioned at the column plate of 3 to 8 layers below the top-layer column plate; when no anhydrous methanol is introduced, aqueous methanol is fed from a feed port located at the top tray, and a feed port located at the tray 3 to 8 layers below the top tray is closed.
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