CN112933631A - Five-tower four-effect rectification system and recovery method for NMP waste liquid - Google Patents
Five-tower four-effect rectification system and recovery method for NMP waste liquid Download PDFInfo
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- B01D3/007—Energy recuperation; Heat pumps
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- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
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- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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Abstract
The invention relates to the technical field of solvent recovery, in particular to a method for recovering NMP waste liquid, which comprises the following steps: step 1: preheating waste liquid containing NMP and then entering a primary concentration tower; step 2: entering a first-stage concentration tower for first dehydration concentration; and step 3: sending the mixture into a secondary concentration tower for secondary dehydration and concentration; and 4, step 4: carrying out third dehydration concentration in a third-stage concentration tower; and 5: feeding the gas phase into a flash tank, defoaming the gas phase by a wire mesh demister, and feeding the gas phase into a four-stage concentration tower; step 6: and (3) carrying out fourth dehydration concentration on the gas entering the fourth-stage concentration tower in the fourth-stage concentration tower, and carrying out step 7: the tower bottom liquid after dehydration and concentration is sent to the middle part of the rectifying tower for feeding, so that the mixed liquid is separated; and 8: the NMP finished product is pumped into a finished product cooler by a pump, is cooled by circulating water and then is sent into a finished product tank in a tank area, the whole process of the invention is carried out at low temperature, and the NMP is not decomposed basically, so the recovery rate of the NMP finished product is about 99 percent.
Description
Technical Field
The invention relates to the technical field of solvent recovery, in particular to a five-tower four-effect rectification system and a recovery method for NMP waste liquid.
Background
NMP, also known as N-methylpyrrolidone, is a polar solvent with excellent high-grade solvent, strong selectivity and good stability. The method is widely applied to the industries of lithium batteries, medicines, pesticides, pigments, cleaning agents, insulating materials and the like, NMP waste liquid (the content of NMP is about 20-50%) is generated when the method is used, the method for treating the NMP waste liquid by adopting a rectification method is the best choice at present, and a plurality of domestic rectification recovery methods for the NMP waste liquid exist, but two problems generally exist: high energy consumption and high operating temperature.
Chinese patent No. CN108658829A discloses a method for recovering and refining NMP, which is technically a three-tower single-effect rectification recovery method. The operating conditions were as follows: firstly, the operating pressure of a first dehydration and rectification tower is 20-100kPa, the reflux ratio is 0.2-1, the theoretical plate number is 40-60, the temperature at the top of the tower is 60-100 ℃, and the temperature at the bottom of the tower is 135-180 ℃; the operating pressure of the second dehydration and rectification tower is 10-50kPa, the reflux ratio is 1-4, the theoretical plate number is 25-50, the tower top temperature is 135 ℃ plus 100 ℃, and the tower kettle temperature is 170 ℃ plus 140 ℃; the operation pressure of the NMP rectifying tower is 10-50kPa, the reflux ratio is 0.5-3, the theoretical plate number is 40-60, the tower top temperature is 140-170 ℃, and the tower bottom temperature is 145-175 ℃. This method has two problems: firstly, primary steam is only utilized once, and steam cannot be effectively utilized secondarily, so that the overall energy consumption is high, and about 2 tons of steam are estimated to be needed for treating 1 ton of NMP waste liquid; ② the operation temperature is high. The temperature of the tower bottom of the whole system is between 135 ℃ and 180 ℃, and the decomposition and hydrolysis amount of NMP is large. According to the related data, NMP is decomposed and hydrolyzed to generate succinic acid semi-amide at the temperature of 150-160 ℃; meanwhile, 4-methylamino butyric acid is hydrolyzed to generate 4-methylamino butyric acid in the presence of acid or alkali and at the temperature of more than 160 ℃, and the decomposition amount and the hydrolysis amount are increased sharply along with the increase of the temperature. Because the two substances have stronger acidity and corrosivity, the corrosion to equipment is serious, and the use of the equipment is seriously influenced. Therefore, the NMP waste liquid distillation system and the NMP waste liquid recovery method must strictly control the decomposition and hydrolysis of NMP, that is, the lower the operation temperature, the better.
Disclosure of Invention
The invention aims to solve the problems of NMP decomposition, hydrolysis and energy consumption of equipment in the process of recycling NMP waste liquid in the prior art, and provides a five-tower four-effect rectification system and a recycling method of the NMP waste liquid.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for recovering NMP waste liquid comprises the following steps:
step 1: conveying the NMP-containing waste liquid into a feed preheater through a waste liquid pump, preheating the waste liquid by using steam flashed by steam condensate water, and then conveying the waste liquid into a primary concentration tower;
step 2: preheating the waste liquid, and then feeding the waste liquid into a primary concentration tower for primary dehydration concentration, wherein the tower top temperature of the primary concentration tower is 45.5 ℃, and the corresponding tower kettle temperature is 50 ℃;
and step 3: the tower bottom liquid after dehydration and concentration in the first-stage concentration tower is sent to a second-stage concentration tower by a discharge pump for second dehydration and concentration, wherein the tower top temperature of the second-stage concentration tower is 60 ℃, and the corresponding tower bottom temperature is 63 ℃;
and 4, step 4: the tower bottom liquid after dehydration and concentration in the second-stage concentration tower is sent to a third-stage concentration tower by a discharge pump for third dehydration and concentration, wherein the tower top temperature of the third-stage concentration tower is 73 ℃, and the corresponding tower bottom temperature is 77 ℃;
and 5: the tower bottom liquid after dehydration and concentration in the third-stage concentration tower is sent to a flash tank by a discharge pump, then sent to a feeding evaporator by a forced circulation pump, subjected to heat exchange with primary steam, sent to the flash tank for decompression and flash evaporation to separate gas and liquid, and the gas phase is defoamed by a wire mesh demister and then enters a fourth-stage concentration tower;
step 6: the gas of the gas phase entering the four-stage concentration tower is dehydrated and concentrated for the fourth time in the four-stage concentration tower, wherein the tower top temperature of the four-stage concentration tower is 87 ℃, and the corresponding tower kettle temperature is 101 ℃;
and 7: the tower bottom liquid NMP dehydrated and concentrated by the four-stage concentration tower is conveyed to the middle part of the rectification tower by a discharge pump to be fed, the volatile component water in the liquid phase in the rectification tower is transferred to the gas phase, the nonvolatile component NMP in the gas phase is transferred to the liquid phase, the gas phase and the liquid phase are in countercurrent contact in the tower, and the mixed liquid is subjected to partial gasification and partial condensation for multiple times, so that the mixed liquid is separated, pure water with NMP of less than 200ppm is obtained at the tower top, pure NMP with water of less than 100ppm is obtained at the tower bottom, the tower top of the rectification tower is 45.5 ℃, and the corresponding tower bottom temperature is 135 ℃;
and 8: when the water content of the tower bottom liquid of the rectifying tower is less than 100ppm, the NMP finished product is pumped into a finished product cooler and then is sent into a finished product tank in the tank area after being cooled by circulating water.
Preferably, the treatment of water in the material comprises the following steps:
step 1: the water vapor at the top of the primary concentration tower enters a tower top condenser to exchange heat with circulating water to form liquid tower top water, the liquid tower top water enters a tower top liquid tank of the primary concentration tower, one part of the liquid tower top water is sent back to the primary concentration tower by a reflux pump, and the other part of the liquid tower top water is sent to a tower top liquid tank of the secondary concentration tower by a water outlet pump;
step 2: the water vapor at the top of the secondary concentrating tower enters a reboiler of the primary concentrating tower and exchanges heat with the tower bottom liquid of the primary concentrating tower to form liquid tower top water, and then the liquid tower top water enters a liquid tank at the top of the secondary concentrating tower, wherein one part of the liquid tower top water is sent back to the secondary concentrating tower by a reflux pump, and the other part of the liquid tower top water is sent to a liquid tank at the top of the tertiary concentrating tower by an effluent pump;
and step 3: the water vapor at the top of the third-stage concentration tower enters a reboiler of the second-stage concentration tower to exchange heat with the tower bottom liquid of the second-stage concentration tower to form liquid tower top water, and then enters a liquid tank at the top of the third-stage concentration tower, wherein one part of the liquid tower top water is sent back to the third-stage concentration tower by a reflux pump, and the other part of the liquid tower top water is sent to a liquid tank at the top of the fourth;
and 4, step 4: the water vapor at the top of the four-stage concentration tower enters a reboiler of the three-stage concentration tower to exchange heat with the tower bottom liquid of the three-stage concentration tower to form liquid tower top water, and then enters a liquid tank at the top of the four-stage concentration tower, wherein one part of the liquid tower top water is sent back to the four-stage concentration tower by a reflux pump, and the other part of the liquid tower top water is sent to a tank area by an effluent pump and then is returned to a;
and 5: the water vapor at the top of the rectifying tower enters a condenser at the top of the rectifying tower to exchange heat with circulating water to form liquid tower top water, the liquid tower top water enters a liquid tank at the top of the rectifying tower, one part of the liquid tower top water is sent back to the rectifying tower by a reflux pump, and the other part of the liquid tower top water is sent to a gas-water separation tank by a water outlet pump and then sent to a liquid tank at the top of a four-stage concentration tower.
Preferably, the treatment of the high boiling substances and the solid substances in the material comprises the following steps:
step 1: the discharge flow is adjusted by using a discharge adjusting valve of the flash tank, and mixed liquid containing high-boiling-point substances, solid substances, NMP and water in the flash tank is continuously extracted in a micro-scale manner and enters the evaporation kettle, so that the high-boiling-point substances and the solid substances in the flash tank can maintain a balanced low concentration, and the blockage of a heat exchange tube in the feeding evaporator is reduced;
step 2: heating the mixed liquid containing high-boiling-point substances, solid substances, NMP and water in an evaporation kettle by using primary steam, and gasifying the water and the NMP at low temperature by adopting high vacuum to enter a primary concentration tower;
and step 3: after water and NMP are gasified, a mixed liquid containing high-boiling-point substances, solid substances and a small amount of NMP is obtained in the evaporation kettle and is sent to a hazardous waste incineration center for incineration by an evaporation kettle discharge pump bucket.
Preferably, the energy utilization comprises the steps of:
step 1: the energy sources of the four-stage concentration tower reboiler, the feeding evaporator and the rectifying tower reboiler are primary steam heating, and the respective steam flow is regulated by respective steam regulating valves to control the respective temperatures of the three devices;
step 2: a reboiler of the four-stage concentration tower heats tower bottom liquid by adopting primary steam, and water in the tower bottom liquid exchanges heat, is gasified and rises to form tower top steam of the four-stage concentration tower;
and step 3: the feeding evaporator heats the liquid in the flash tank by adopting primary steam, so that NMP and water are gasified and enter the four-stage concentration tower, and the water vapor rises to form tower top water vapor of the four-stage concentration tower;
and 4, step 4: the tower top steam of the fourth-stage concentration tower heats a reboiler of the third-stage concentration tower, and water in tower bottom liquid is gasified and ascended through heat exchange to form tower top steam of the third-stage concentration tower;
and 5: the tower top steam of the third-stage concentration tower heats a reboiler of the second-stage concentration tower, and water in tower bottom liquid is gasified and ascended through heat exchange to form tower top steam of the second-stage concentration tower;
step 6: the tower top steam of the secondary concentration tower heats a reboiler of the primary concentration tower, and water in tower bottom liquid is gasified and ascended through heat exchange to form the tower top steam of the primary concentration tower;
and 7: the tower top water vapor of the primary concentration tower exchanges heat with circulating water to form liquid tower top water which enters a tower top liquid tank of the primary concentration tower;
and 8: the rectifying tower reboiler heats tower bottoms by adopting primary steam, and water in the tower is subjected to heat exchange and gasification to rise through energy transfer to form tower top steam of the rectifying tower;
and step 9: the tower top water vapor of the rectifying tower exchanges heat with circulating water to form liquid tower top water which enters a tower top liquid tank of the rectifying tower.
Preferably, the vacuum utilization comprises the steps of:
step 1: the first-stage concentration tower, the second-stage concentration tower, the third-stage concentration tower, the fourth-stage concentration tower and the rectifying tower are all operated in vacuum, and the respective vacuum degrees of the five towers are controlled by adjusting the air inlet flow through respective vacuum adjusting valves;
step 2: the first-stage concentration tower adopts a water ring vacuum pump for pumping, and the vacuum degree at the top of the tower is as follows: -0.09 MPa;
and step 3: the second-stage concentration tower adopts a water ring vacuum pump for pumping, and the vacuum degree at the top of the tower is as follows: -0.08 MPa;
and 4, step 4: the third-stage concentration tower adopts a water ring vacuum pump for pumping, and the vacuum degree at the top of the tower is as follows: -0.0625 MPa;
and 5: the four-stage concentration tower adopts a water ring vacuum pump for pumping, and the vacuum degree at the top of the tower is as follows: -0.038 MPa;
step 6: the rectifying tower adopts a water ring vacuum pump for suction, and the vacuum degree at the top of the tower is as follows: -0.09 MPa.
Preferably, a five-tower four-effect rectification system for NMP waste liquid comprises: the system comprises a feed preheater, a first-stage concentration tower, a second-stage concentration tower, a third-stage concentration tower, a fourth-stage concentration tower, a rectifying tower, a flash tank, a feed evaporator and a finished product cooler;
the material outlet of the waste liquid tank of the tank area is connected with the material inlet of the feeding preheater through a waste liquid pump, the material outlet of the feeding preheater is connected with the material inlet of the first-stage concentration tower, the material outlet of the first-stage concentration tower is connected with the material inlet of the second-stage concentration tower through a discharge pump, the material outlet of the second-stage concentration tower is connected with the material inlet of the third-stage concentration tower through a discharge pump, the material outlet of the third-stage concentration tower is connected with the liquid-phase material inlet of the flash tank through a forced circulation pump, the material outlet of the feeding evaporator is connected with the gas-phase material inlet of the flash tank, the gas-phase material outlet of the flash tank is connected with the material inlet of the fourth-stage concentration tower, the material outlet of the fourth-stage concentration tower is connected with the material inlet of the rectifying tower through a discharge pump, the material outlet of the rectifying tower is connected with the material inlet of, the material outlet of the finished product cooler is connected with the material inlet of the finished product tank in the tank area.
Preferably, the method further comprises the following steps: the system comprises a tower top condenser, a first-stage concentration tower reboiler, a second-stage concentration tower reboiler, a third-stage concentration tower reboiler, a fourth-stage concentration tower reboiler, a rectification tower top condenser, a first-stage concentration tower top liquid tank, a second-stage concentration tower top liquid tank, a third-stage concentration tower top liquid tank, a fourth-stage concentration tower top liquid tank, a rectification tower top liquid tank and a gas-water separation tank;
the tower top steam outlet of the first-stage concentration tower is connected with the steam inlet of the tower top condenser, the condensed water outlet of the tower top condenser is connected with the condensed water inlet of the tower top liquid tank of the first-stage concentration tower, the water outlet of the tower top liquid tank of the first-stage concentration tower is connected with the tower top reflux port of the first-stage concentration tower through a reflux pump, the water outlet of the tower top liquid tank of the first-stage concentration tower is connected with the water inlet of the tower top liquid tank of the second-stage concentration tower through a water outlet pump, the tower top steam outlet of the tower top liquid tank of the second-stage concentration tower is connected with the steam inlet of the reboiler of the first-stage concentration tower, the condensed water outlet of the tower top liquid tank of the second-stage concentration tower is connected with the tower top reflux port of the second-stage concentration tower through the reflux pump, the water outlet of the tower top liquid tank of the second-stage concentration tower is connected with the, the condensed water outlet of the reboiler of the second-stage concentration tower is connected with the condensed water inlet of the liquid tank at the top of the third-stage concentration tower, the water outlet of the liquid tank at the top of the third-stage concentration tower is connected with the water inlet of the liquid tank at the top of the fourth-stage concentration tower through a water outlet pump, the steam outlet of the top of the fourth-stage concentration tower is connected with the steam inlet of the reboiler of the third-stage concentration tower, the condensed water outlet of the reboiler of the third-stage concentration tower is connected with the condensed water inlet of the liquid tank at the top of the fourth-stage concentration tower, the water outlet of the liquid tank at the top of the fourth-stage concentration tower is connected with the top reflux port of the fourth-stage concentration tower through a reflux pump, the water outlet of the liquid tank at the top of the fourth-stage concentration tower is connected with the water inlet of the water tank at the top of the tank area through a water outlet pump, the steam outlet of the top of the rectifying tower, the water outlet of the rectifying tower top liquid tank is connected with the tower top reflux port of the rectifying tower through a reflux pump, the water outlet of the rectifying tower top liquid tank is connected with the water inlet of the gas-water separation tank through a water outlet pump, and the water outlet of the gas-water separation tank is connected with the water inlet of the four-stage concentration tower top liquid tank through a water outlet pump of the gas-water separation tank.
Preferably, the method further comprises the following steps: a flash evaporation tank, an evaporation kettle and a primary concentration tower;
the slag notch of flash tank links to each other with the feed inlet of evaporating kettle, and the gaseous phase discharge gate of evaporating kettle links to each other with the gaseous phase feed inlet of one-level concentrator, and evaporating kettle's liquid phase discharge gate links to each other with the bucket through evaporating kettle discharge pump, and primary steam links to each other with evaporating kettle's steam inlet, and evaporating kettle's comdenstion water export links to each other with the comdenstion water import of hot-water tank.
Preferably, the method further comprises the following steps: a four-stage concentration tower reboiler, a feeding evaporator, a rectifying tower reboiler, a three-stage concentration tower reboiler, a two-stage concentration tower reboiler, a one-stage concentration tower top liquid tank, a rectifying tower top liquid tank, a tower top condenser and a rectifying tower top condenser;
a first steam, a four-stage concentration tower reboiler and a feeding evaporator, the steam inlet of rectifying column reboiler links to each other, the comdenstion water export of three equipment links to each other with the comdenstion water import of hot water tank, the top of the tower steam outlet of level four rectifying column links to each other with the steam inlet of tertiary rectifying column reboiler, the top of the tower steam outlet of tertiary rectifying column links to each other with the steam inlet of second grade rectifying column reboiler, the top of the tower steam outlet of first grade rectifying column links to each other with the steam inlet of top of the tower condenser, the comdenstion water export of top of the tower condenser links to each other with the comdenstion water import of first grade rectifying column top of the tower fluid reservoir, the top of the tower steam outlet of rectifying column links to each other with the steam inlet of rectifying column top of the tower fluid reservoir, the comdenstion water export of rectifying column top of the tower condenser links to each.
Preferably, the method further comprises the following steps: a water ring vacuum pump of a first-stage concentration tower, a second-stage concentration tower, a third-stage concentration tower, a fourth-stage concentration tower and a rectifying tower;
vacuum ports of the first-stage concentration tower, the second-stage concentration tower, the third-stage concentration tower, the fourth-stage concentration tower and the rectifying tower are connected with air inlets of respective water ring vacuum pumps, and an air outlet of each water ring vacuum pump is connected with an air inlet of the gas-water separation tank.
The invention has the beneficial effects that:
1. the invention has the advantage of solving the problems of NMP decomposition and hydrolysis. The decomposition and hydrolysis of NMP are carried out at high temperature, so that the hydrolysis and decomposition of NMP can be fundamentally inhibited only by adopting low-temperature concentration and low-temperature rectification. The NMP is subjected to primary concentration under the working condition that the temperature of a tower kettle of a primary concentration tower is 50 ℃, secondary concentration under the working condition that the temperature of a tower kettle of a secondary concentration tower is 63 ℃, tertiary concentration under the working condition that the temperature of a tower kettle of a tertiary concentration tower is 77 ℃ and quaternary concentration under the working condition that the temperature of a tower kettle of a quaternary concentration tower is 101 ℃, and the NMP is rectified under the working condition that the temperature of a tower kettle of a rectification tower is 135 ℃, wherein the whole process is carried out at low temperature, and the NMP is not decomposed basically, so that the recovery rate of the NMP finished product is about 99%.
2. The invention has the advantages of solving the problem of energy consumption, and having obvious energy-saving effect because the steam is utilized for four times.
Drawings
FIG. 1 is a process flow diagram of a five-tower four-effect rectification system for NMP waste liquid provided by the invention.
In the figure: 1 first-stage concentration tower top liquid tank, 2 tower top condensers, 3 centrifugal pumps, 4 first-stage concentration towers, 5 second-stage concentration towers, 6 third-stage concentration towers, 7 gas-water separation tanks, 8 fourth-stage concentration towers, 9 rectification tower top liquid tank, 10 rectification towers, 11 preheaters, 12 hot water tanks, 13 second-stage concentration tower top liquid tanks, 14 vacuum pumps, 15 third-stage concentration tower top liquid tanks, 16 fourth-stage concentration tower top liquid tanks, 17 evaporation kettles, 18 flash tanks and 19 rectification tower top condensers.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
A method for recovering NMP waste liquid comprises the following steps:
step 1: conveying the NMP-containing waste liquid into a feed preheater through a waste liquid pump, preheating the waste liquid by using steam flashed by steam condensate water, and then conveying the waste liquid into a primary concentration tower;
step 2: preheating the waste liquid, and then feeding the waste liquid into a primary concentration tower for primary dehydration concentration, wherein the tower top temperature of the primary concentration tower is 45.5 ℃, and the corresponding tower kettle temperature is 50 ℃;
and step 3: the tower bottom liquid after dehydration and concentration in the first-stage concentration tower is sent to a second-stage concentration tower by a discharge pump for second dehydration and concentration, wherein the tower top temperature of the second-stage concentration tower is 60 ℃, and the corresponding tower bottom temperature is 63 ℃;
and 4, step 4: the tower bottom liquid after dehydration and concentration in the second-stage concentration tower is sent to a third-stage concentration tower by a discharge pump for third dehydration and concentration, wherein the tower top temperature of the third-stage concentration tower is 73 ℃, and the corresponding tower bottom temperature is 77 ℃;
and 5: the tower bottom liquid after dehydration and concentration in the third-stage concentration tower is sent to a flash tank by a discharge pump, then sent to a feeding evaporator by a forced circulation pump, subjected to heat exchange with primary steam, sent to the flash tank for decompression and flash evaporation to separate gas and liquid, and the gas phase is defoamed by a wire mesh demister and then enters a fourth-stage concentration tower;
step 6: the gas of the gas phase entering the four-stage concentration tower is dehydrated and concentrated for the fourth time in the four-stage concentration tower, wherein the tower top temperature of the four-stage concentration tower is 87 ℃, and the corresponding tower kettle temperature is 101 ℃;
and 7: the tower bottom liquid NMP dehydrated and concentrated by the four-stage concentration tower is conveyed to the middle part of the rectification tower by a discharge pump to be fed, the volatile component water in the liquid phase in the rectification tower is transferred to the gas phase, the nonvolatile component NMP in the gas phase is transferred to the liquid phase, the gas phase and the liquid phase are in countercurrent contact in the tower, and the mixed liquid is subjected to partial gasification and partial condensation for multiple times, so that the mixed liquid is separated, pure water with NMP of less than 200ppm is obtained at the tower top, pure NMP with water of less than 100ppm is obtained at the tower bottom, the tower top of the rectification tower is 45.5 ℃, and the corresponding tower bottom temperature is 135 ℃;
and 8: when the water content of the tower bottom liquid of the rectifying tower is less than 100ppm, the NMP finished product is pumped into a finished product cooler and then is sent into a finished product tank in the tank area after being cooled by circulating water.
Further, the treatment of water in the material comprises the following steps:
step 1: the water vapor at the top of the primary concentration tower enters a tower top condenser to exchange heat with circulating water to form liquid tower top water, the liquid tower top water enters a tower top liquid tank of the primary concentration tower, one part of the liquid tower top water is sent back to the primary concentration tower by a reflux pump, and the other part of the liquid tower top water is sent to a tower top liquid tank of the secondary concentration tower by a water outlet pump;
step 2: the water vapor at the top of the secondary concentrating tower enters a reboiler of the primary concentrating tower and exchanges heat with the tower bottom liquid of the primary concentrating tower to form liquid tower top water, and then the liquid tower top water enters a liquid tank at the top of the secondary concentrating tower, wherein one part of the liquid tower top water is sent back to the secondary concentrating tower by a reflux pump, and the other part of the liquid tower top water is sent to a liquid tank at the top of the tertiary concentrating tower by an effluent pump;
and step 3: the water vapor at the top of the third-stage concentration tower enters a reboiler of the second-stage concentration tower to exchange heat with the tower bottom liquid of the second-stage concentration tower to form liquid tower top water, and then enters a liquid tank at the top of the third-stage concentration tower, wherein one part of the liquid tower top water is sent back to the third-stage concentration tower by a reflux pump, and the other part of the liquid tower top water is sent to a liquid tank at the top of the fourth;
and 4, step 4: the water vapor at the top of the four-stage concentration tower enters a reboiler of the three-stage concentration tower to exchange heat with the tower bottom liquid of the three-stage concentration tower to form liquid tower top water, and then enters a liquid tank at the top of the four-stage concentration tower, wherein one part of the liquid tower top water is sent back to the four-stage concentration tower by a reflux pump, and the other part of the liquid tower top water is sent to a tank area by an effluent pump and then is returned to a;
and 5: the water vapor at the top of the rectifying tower enters a condenser at the top of the rectifying tower to exchange heat with circulating water to form liquid tower top water, the liquid tower top water enters a liquid tank at the top of the rectifying tower, one part of the liquid tower top water is sent back to the rectifying tower by a reflux pump, and the other part of the liquid tower top water is sent to a gas-water separation tank by a water outlet pump and then sent to a liquid tank at the top of a four-stage concentration tower.
Further, the treatment of high boiling point substance and solid substance in the material comprises the following steps:
step 1: the discharge flow is adjusted by using a discharge adjusting valve of the flash tank, and mixed liquid containing high-boiling-point substances, solid substances, NMP and water in the flash tank is continuously extracted in a micro-scale manner and enters the evaporation kettle, so that the high-boiling-point substances and the solid substances in the flash tank can maintain a balanced low concentration, and the blockage of a heat exchange tube in the feeding evaporator is reduced;
step 2: heating the mixed liquid containing high-boiling-point substances, solid substances, NMP and water in an evaporation kettle by using primary steam, and gasifying the water and the NMP at low temperature by adopting high vacuum to enter a primary concentration tower;
and step 3: after water and NMP are gasified, a mixed liquid containing high-boiling-point substances, solid substances and a small amount of NMP is obtained in the evaporation kettle and is sent to a hazardous waste incineration center for incineration by an evaporation kettle discharge pump bucket.
Further, the energy utilization comprises the following steps:
step 1: the energy sources of the four-stage concentration tower reboiler, the feeding evaporator and the rectifying tower reboiler are primary steam heating, and the respective steam flow is regulated by respective steam regulating valves to control the respective temperatures of the three devices;
step 2: a reboiler of the four-stage concentration tower heats tower bottom liquid by adopting primary steam, and water in the tower bottom liquid exchanges heat, is gasified and rises to form tower top steam of the four-stage concentration tower;
and step 3: the feeding evaporator heats the liquid in the flash tank by adopting primary steam, so that NMP and water are gasified and enter the four-stage concentration tower, and the water vapor rises to form tower top water vapor of the four-stage concentration tower;
and 4, step 4: the tower top steam of the fourth-stage concentration tower heats a reboiler of the third-stage concentration tower, and water in tower bottom liquid is gasified and ascended through heat exchange to form tower top steam of the third-stage concentration tower;
and 5: the tower top steam of the third-stage concentration tower heats a reboiler of the second-stage concentration tower, and water in tower bottom liquid is gasified and ascended through heat exchange to form tower top steam of the second-stage concentration tower;
step 6: the tower top steam of the secondary concentration tower heats a reboiler of the primary concentration tower, and water in tower bottom liquid is gasified and ascended through heat exchange to form the tower top steam of the primary concentration tower;
and 7: the tower top water vapor of the primary concentration tower exchanges heat with circulating water to form liquid tower top water which enters a tower top liquid tank of the primary concentration tower;
and 8: the rectifying tower reboiler heats tower bottoms by adopting primary steam, and water in the tower is subjected to heat exchange and gasification to rise through energy transfer to form tower top steam of the rectifying tower;
and step 9: the tower top water vapor of the rectifying tower exchanges heat with circulating water to form liquid tower top water which enters a tower top liquid tank of the rectifying tower.
Further, the vacuum utilization comprises the following steps:
step 1: the first-stage concentration tower, the second-stage concentration tower, the third-stage concentration tower, the fourth-stage concentration tower and the rectifying tower are all operated in vacuum, and the respective vacuum degrees of the five towers are controlled by adjusting the air inlet flow through respective vacuum adjusting valves;
step 2: the first-stage concentration tower adopts a water ring vacuum pump for pumping, and the vacuum degree at the top of the tower is as follows: -0.09 MPa;
and step 3: the second-stage concentration tower adopts a water ring vacuum pump for pumping, and the vacuum degree at the top of the tower is as follows: -0.08 MPa;
and 4, step 4: the third-stage concentration tower adopts a water ring vacuum pump for pumping, and the vacuum degree at the top of the tower is as follows: -0.0625 MPa;
and 5: the four-stage concentration tower adopts a water ring vacuum pump for pumping, and the vacuum degree at the top of the tower is as follows: -0.038 MPa;
step 6: the rectifying tower adopts a water ring vacuum pump for suction, and the vacuum degree at the top of the tower is as follows: -0.09 MPa.
Referring to fig. 1, a five-tower four-effect rectification system for NMP waste liquid comprises: a feed preheater 11, a first-stage concentration tower 4, a second-stage concentration tower 5, a third-stage concentration tower 6, a fourth-stage concentration tower 8, a rectifying tower 10, a flash tank 18, a feed evaporator and a finished product cooler;
the material outlet of the waste liquid tank of the tank area is connected with the material inlet of the feeding preheater 11 through a waste liquid pump, the material outlet of the feeding preheater 11 is connected with the material inlet of the first-stage concentration tower 4, the material outlet of the first-stage concentration tower 4 is connected with the material inlet of the second-stage concentration tower 5 through a discharge pump (a centrifugal pump 3), the material outlet of the second-stage concentration tower 5 is connected with the material inlet of the third-stage concentration tower 6 through a discharge pump, the material outlet of the third-stage concentration tower 6 is connected with the liquid-phase material inlet of the flash tank 18 through a discharge pump, the liquid-phase material outlet of the flash tank 18 is connected with the material inlet of the feeding evaporator through a forced circulation pump (a centrifugal pump 3), the material outlet of the feeding evaporator is connected with the gas-phase material inlet of the flash tank 18, the gas-phase material outlet of the flash tank 18 is connected with the material inlet of the fourth-, the material outlet of the rectifying tower 10 is connected with the material inlet of the finished product cooler through an NMP finished product pump (centrifugal pump 3), and the material outlet of the finished product cooler is connected with the material inlet of the finished product tank in the tank field.
Further, the method also comprises the following steps: a tower top condenser 2, a first-stage concentration tower 4 reboiler, a second-stage concentration tower 5 reboiler, a third-stage concentration tower 6 reboiler, a fourth-stage concentration tower 8 reboiler, a rectification tower top condenser 19, a first-stage concentration tower top liquid tank 1, a second-stage concentration tower top liquid tank 13, a third-stage concentration tower top liquid tank 15, a fourth-stage concentration tower top liquid tank 16, a rectification tower top liquid tank 9 and a gas-water separation tank 7;
the top steam outlet of the first-stage concentration tower 4 is connected with the steam inlet of the top condenser 2, the condensed water outlet of the top condenser 2 is connected with the condensed water inlet of the top liquid tank 1 of the first-stage concentration tower, the water outlet of the top liquid tank 1 of the first-stage concentration tower is connected with the top reflux port of the first-stage concentration tower 4 through a reflux pump (centrifugal pump 3), the water outlet of the top liquid tank 1 of the first-stage concentration tower is connected with the water inlet of the top liquid tank 13 of the second-stage concentration tower through a water outlet pump (centrifugal pump 3), the top steam outlet of the second-stage concentration tower 5 is connected with the steam inlet of the reboiler of the first-stage concentration tower 4, the condensed water outlet of the reboiler of the first-stage concentration tower 4 is connected with the condensed water inlet of the top liquid tank 13 of the second-stage concentration tower, the water outlet of the top liquid tank 13 of the second-stage concentration tower is connected with the top reflux port of the, the steam outlet of the top of the third-level concentrating tower 6 is connected with the steam inlet of the reboiler of the second-level concentrating tower 5, the condensed water outlet of the reboiler of the second-level concentrating tower 5 is connected with the condensed water inlet of the liquid tank 15 at the top of the third-level concentrating tower, the water outlet of the liquid tank 15 at the top of the third-level concentrating tower is connected with the top reflux port of the liquid tank 16 at the top of the fourth-level concentrating tower through a reflux pump, the top steam outlet of the liquid tank 15 at the top of the fourth-level concentrating tower 8 is connected with the steam inlet of the reboiler of the third-level concentrating tower 6, the condensed water outlet of the liquid tank 16 at the top of the third-level concentrating tower 6 is connected with the condensed water inlet of the liquid tank 16 at the top of the fourth-level concentrating tower through a water outlet pump, the water outlet of the liquid tank 16 at the top of the fourth-level concentrating tower is connected with the top reflux port of, the top steam outlet of the rectifying tower 10 is connected with the steam inlet of the rectifying tower top condenser 19, the condensed water outlet of the rectifying tower top condenser 19 is connected with the condensed water inlet of the rectifying tower top liquid tank 9, the water outlet of the rectifying tower top liquid tank 9 is connected with the top reflux port of the rectifying tower 10 through a reflux pump, the water outlet of the rectifying tower top liquid tank 9 is connected with the water inlet of the gas-water separation tank 7 through a water outlet pump, and the water outlet of the gas-water separation tank 7 is connected with the water inlet of the four-stage concentration tower top liquid tank 16 through a water outlet pump of the gas-water separation tank 7.
Further, the method also comprises the following steps: a flash tank 18, an evaporation kettle 17 and a primary concentration tower 4;
the slag hole of flash tank 18 links to each other with the feed inlet of reation kettle 17, and reation kettle 17's gaseous phase discharge gate links to each other with the gaseous phase feed inlet of one-level enrichment tower 4, and reation kettle 17's liquid phase discharge gate links to each other with the bucket through reation kettle 17 discharge pump, and primary steam links to each other with reation kettle 17's steam inlet, and reation kettle 17's comdenstion water export links to each other with the comdenstion water import of hot-water tank 12.
Further, the method also comprises the following steps: a four-stage concentration tower 8 reboiler, a feeding evaporator, a rectifying tower 10 reboiler, a three-stage concentration tower 6 reboiler, a two-stage concentration tower 5 reboiler, a one-stage concentration tower 4 reboiler, a one-stage concentration tower top liquid tank 1, a rectifying tower top liquid tank 9, a tower top condenser 2 and a rectifying tower top condenser 19;
a first steam, a four-stage concentration tower 8 reboiler and a feeding evaporator, steam inlet of rectifying column 10 reboiler links to each other, the comdenstion water export of three equipment links to each other with the comdenstion water import of hot water tank 12, the top of the tower steam outlet of level four rectifying column 8 links to each other with the steam inlet of tertiary rectifying column 6 reboiler, the top of the tower steam outlet of tertiary rectifying column 6 links to each other with the steam inlet of secondary concentrating column 5 reboiler, the top of the tower steam outlet of secondary concentrating column 5 links to each other with the steam inlet of one-level concentrating column 4 reboiler, the top of the tower steam outlet of one-level concentrating column 4 links to each other with the steam inlet of overhead condenser 2, the comdenstion water export of overhead condenser 2 links to each other with the comdenstion water import of one-level concentrating column overhead liquid tank 1, the top of the tower steam outlet of rectifying column 10 links to each other with the steam inlet of rectifying column overhead condenser 19, the comdenstion.
Further, the method also comprises the following steps: a water ring vacuum pump 14 of a first-stage concentration tower 4, a second-stage concentration tower 5, a third-stage concentration tower 6, a fourth-stage concentration tower 8 and a rectifying tower 10;
vacuum ports of the first-stage concentration tower 4, the second-stage concentration tower 5, the third-stage concentration tower 6, the fourth-stage concentration tower 8 and the rectifying tower 10 are connected with air inlets of respective water ring vacuum pumps 14, and an air outlet of the water ring vacuum pump 14 is connected with an air inlet of the gas-water separation tank 7.
The following table compares the operating conditions of a three column single effect rectification system with the present invention.
The invention has the advantage of solving the problems of NMP decomposition and hydrolysis. The decomposition and hydrolysis of NMP are carried out at high temperature, so that the hydrolysis and decomposition of NMP can be fundamentally inhibited only by adopting low-temperature concentration and low-temperature rectification. The NMP is subjected to primary concentration under the working condition that the temperature of a tower kettle of a primary concentration tower is 50 ℃, secondary concentration under the working condition that the temperature of a tower kettle of a secondary concentration tower is 63 ℃, tertiary concentration under the working condition that the temperature of a tower kettle of a tertiary concentration tower is 77 ℃ and quaternary concentration under the working condition that the temperature of a tower kettle of a quaternary concentration tower is 101 ℃, and the NMP is rectified under the working condition that the temperature of a tower kettle of a rectification tower is 135 ℃, wherein the whole process is carried out at low temperature, and the NMP is not decomposed basically, so that the recovery rate of the NMP finished product is about 99%.
The invention has the advantages of solving the problem of energy consumption, and having obvious energy-saving effect because the steam is utilized for four times.
According to the data, the invention not only solves the hydrolysis and decomposition of NMP, but also reduces energy consumption and creates good economic benefit.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (10)
1. The method for recovering the NMP waste liquid is characterized in that the method for recovering the NMP in the material comprises the following steps:
step 1: conveying the NMP-containing waste liquid into a feed preheater through a waste liquid pump, preheating the waste liquid by using steam flashed by steam condensate water, and then conveying the waste liquid into a primary concentration tower;
step 2: preheating the waste liquid, and then feeding the waste liquid into a primary concentration tower for primary dehydration concentration, wherein the tower top temperature of the primary concentration tower is 45.5 ℃, and the corresponding tower kettle temperature is 50 ℃;
and step 3: the tower bottom liquid after dehydration and concentration in the first-stage concentration tower is sent to a second-stage concentration tower by a discharge pump for second dehydration and concentration, wherein the tower top temperature of the second-stage concentration tower is 60 ℃, and the corresponding tower bottom temperature is 63 ℃;
and 4, step 4: the tower bottom liquid after dehydration and concentration in the second-stage concentration tower is sent to a third-stage concentration tower by a discharge pump for third dehydration and concentration, wherein the tower top temperature of the third-stage concentration tower is 73 ℃, and the corresponding tower bottom temperature is 77 ℃;
and 5: the tower bottom liquid after dehydration and concentration in the third-stage concentration tower is sent to a flash tank by a discharge pump, then sent to a feeding evaporator by a forced circulation pump, subjected to heat exchange with primary steam, sent to the flash tank for decompression and flash evaporation to separate gas and liquid, and the gas phase is defoamed by a wire mesh demister and then enters a fourth-stage concentration tower;
step 6: the gas of the gas phase entering the four-stage concentration tower is dehydrated and concentrated for the fourth time in the four-stage concentration tower, wherein the tower top temperature of the four-stage concentration tower is 87 ℃, and the corresponding tower kettle temperature is 101 ℃;
and 7: the tower bottom liquid NMP dehydrated and concentrated by the four-stage concentration tower is conveyed to the middle part of the rectification tower by a discharge pump to be fed, the volatile component water in the liquid phase in the rectification tower is transferred to the gas phase, the nonvolatile component NMP in the gas phase is transferred to the liquid phase, the gas phase and the liquid phase are in countercurrent contact in the tower, and the mixed liquid is subjected to partial gasification and partial condensation for multiple times, so that the mixed liquid is separated, pure water with NMP of less than 200ppm is obtained at the tower top, pure NMP with water of less than 100ppm is obtained at the tower bottom, the tower top of the rectification tower is 45.5 ℃, and the corresponding tower bottom temperature is 135 ℃;
and 8: when the water content of the tower bottom liquid of the rectifying tower is less than 100ppm, the NMP finished product is pumped into a finished product cooler and then is sent into a finished product tank in the tank area after being cooled by circulating water.
2. The method for recovering NMP waste liquid according to claim 1, wherein the treatment of water in the material comprises the steps of:
step 1: the water vapor at the top of the primary concentration tower enters a tower top condenser to exchange heat with circulating water to form liquid tower top water, the liquid tower top water enters a tower top liquid tank of the primary concentration tower, one part of the liquid tower top water is sent back to the primary concentration tower by a reflux pump, and the other part of the liquid tower top water is sent to a tower top liquid tank of the secondary concentration tower by a water outlet pump;
step 2: the water vapor at the top of the secondary concentrating tower enters a reboiler of the primary concentrating tower and exchanges heat with the tower bottom liquid of the primary concentrating tower to form liquid tower top water, and then the liquid tower top water enters a liquid tank at the top of the secondary concentrating tower, wherein one part of the liquid tower top water is sent back to the secondary concentrating tower by a reflux pump, and the other part of the liquid tower top water is sent to a liquid tank at the top of the tertiary concentrating tower by an effluent pump;
and step 3: the water vapor at the top of the third-stage concentration tower enters a reboiler of the second-stage concentration tower to exchange heat with the tower bottom liquid of the second-stage concentration tower to form liquid tower top water, and then enters a liquid tank at the top of the third-stage concentration tower, wherein one part of the liquid tower top water is sent back to the third-stage concentration tower by a reflux pump, and the other part of the liquid tower top water is sent to a liquid tank at the top of the fourth;
and 4, step 4: the water vapor at the top of the four-stage concentration tower enters a reboiler of the three-stage concentration tower to exchange heat with the tower bottom liquid of the three-stage concentration tower to form liquid tower top water, and then enters a liquid tank at the top of the four-stage concentration tower, wherein one part of the liquid tower top water is sent back to the four-stage concentration tower by a reflux pump, and the other part of the liquid tower top water is sent to a tank area by an effluent pump and then is returned to a;
and 5: the water vapor at the top of the rectifying tower enters a condenser at the top of the rectifying tower to exchange heat with circulating water to form liquid tower top water, the liquid tower top water enters a liquid tank at the top of the rectifying tower, one part of the liquid tower top water is sent back to the rectifying tower by a reflux pump, and the other part of the liquid tower top water is sent to a gas-water separation tank by a water outlet pump and then sent to a liquid tank at the top of a four-stage concentration tower.
3. A method for recovering waste liquid of NMP according to claim 1, wherein the treatment of high boiling substance and solid substance in the material comprises the following steps:
step 1: the discharge flow is adjusted by using a discharge adjusting valve of the flash tank, and mixed liquid containing high-boiling-point substances, solid substances, NMP and water in the flash tank is continuously extracted in a micro-scale manner and enters the evaporation kettle, so that the high-boiling-point substances and the solid substances in the flash tank can maintain a balanced low concentration, and the blockage of a heat exchange tube in the feeding evaporator is reduced;
step 2: heating the mixed liquid containing high-boiling-point substances, solid substances, NMP and water in an evaporation kettle by using primary steam, and gasifying the water and the NMP at low temperature by adopting high vacuum to enter a primary concentration tower;
and step 3: after water and NMP are gasified, a mixed liquid containing high-boiling-point substances, solid substances and a small amount of NMP is obtained in the evaporation kettle and is sent to a hazardous waste incineration center for incineration by an evaporation kettle discharge pump bucket.
4. The method according to claim 1, wherein the energy utilization step comprises the steps of:
step 1: the energy sources of the four-stage concentration tower reboiler, the feeding evaporator and the rectifying tower reboiler are primary steam heating, and the respective steam flow is regulated by respective steam regulating valves to control the respective temperatures of the three devices;
step 2: a reboiler of the four-stage concentration tower heats tower bottom liquid by adopting primary steam, and water in the tower bottom liquid exchanges heat, is gasified and rises to form tower top steam of the four-stage concentration tower;
and step 3: the feeding evaporator heats the liquid in the flash tank by adopting primary steam, so that NMP and water are gasified and enter the four-stage concentration tower, and the water vapor rises to form tower top water vapor of the four-stage concentration tower;
and 4, step 4: the tower top steam of the fourth-stage concentration tower heats a reboiler of the third-stage concentration tower, and water in tower bottom liquid is gasified and ascended through heat exchange to form tower top steam of the third-stage concentration tower;
and 5: the tower top steam of the third-stage concentration tower heats a reboiler of the second-stage concentration tower, and water in tower bottom liquid is gasified and ascended through heat exchange to form tower top steam of the second-stage concentration tower;
step 6: the tower top steam of the secondary concentration tower heats a reboiler of the primary concentration tower, and water in tower bottom liquid is gasified and ascended through heat exchange to form the tower top steam of the primary concentration tower;
and 7: the tower top water vapor of the primary concentration tower exchanges heat with circulating water to form liquid tower top water which enters a tower top liquid tank of the primary concentration tower;
and 8: the rectifying tower reboiler heats tower bottoms by adopting primary steam, and water in the tower is subjected to heat exchange and gasification to rise through energy transfer to form tower top steam of the rectifying tower;
and step 9: the tower top water vapor of the rectifying tower exchanges heat with circulating water to form liquid tower top water which enters a tower top liquid tank of the rectifying tower.
5. The method according to claim 1, wherein the vacuum utilization comprises the steps of:
step 1: the first-stage concentration tower, the second-stage concentration tower, the third-stage concentration tower, the fourth-stage concentration tower and the rectifying tower are all operated in vacuum, and the respective vacuum degrees of the five towers are controlled by adjusting the air inlet flow through respective vacuum adjusting valves;
step 2: the first-stage concentration tower adopts a water ring vacuum pump for pumping, and the vacuum degree at the top of the tower is as follows: -0.09 MPa;
and step 3: the second-stage concentration tower adopts a water ring vacuum pump for pumping, and the vacuum degree at the top of the tower is as follows: -0.08 MPa;
and 4, step 4: the third-stage concentration tower adopts a water ring vacuum pump for pumping, and the vacuum degree at the top of the tower is as follows: -0.0625 MPa;
and 5: the four-stage concentration tower adopts a water ring vacuum pump for pumping, and the vacuum degree at the top of the tower is as follows: -0.038 MPa;
step 6: the rectifying tower adopts a water ring vacuum pump for suction, and the vacuum degree at the top of the tower is as follows: -0.09 MPa.
6. The five-tower four-effect rectification system for the NMP waste liquid according to any one of claims 1-5, comprising: the system comprises a feed preheater, a first-stage concentration tower, a second-stage concentration tower, a third-stage concentration tower, a fourth-stage concentration tower, a rectifying tower, a flash tank, a feed evaporator and a finished product cooler;
the material outlet of the waste liquid tank of the tank area is connected with the material inlet of the feeding preheater through a waste liquid pump, the material outlet of the feeding preheater is connected with the material inlet of the first-stage concentration tower, the material outlet of the first-stage concentration tower is connected with the material inlet of the second-stage concentration tower through a discharge pump, the material outlet of the second-stage concentration tower is connected with the material inlet of the third-stage concentration tower through a discharge pump, the material outlet of the third-stage concentration tower is connected with the liquid-phase material inlet of the flash tank through a forced circulation pump, the material outlet of the feeding evaporator is connected with the gas-phase material inlet of the flash tank, the gas-phase material outlet of the flash tank is connected with the material inlet of the fourth-stage concentration tower, the material outlet of the fourth-stage concentration tower is connected with the material inlet of the rectifying tower through a discharge pump, the material outlet of the rectifying tower is connected with the material inlet of, the material outlet of the finished product cooler is connected with the material inlet of the finished product tank in the tank area.
7. The five-tower four-effect rectification system for NMP waste liquid according to claim 6, further comprising: the system comprises a tower top condenser, a first-stage concentration tower reboiler, a second-stage concentration tower reboiler, a third-stage concentration tower reboiler, a fourth-stage concentration tower reboiler, a rectification tower top condenser, a first-stage concentration tower top liquid tank, a second-stage concentration tower top liquid tank, a third-stage concentration tower top liquid tank, a fourth-stage concentration tower top liquid tank, a rectification tower top liquid tank and a gas-water separation tank;
the tower top steam outlet of the first-stage concentration tower is connected with the steam inlet of the tower top condenser, the condensed water outlet of the tower top condenser is connected with the condensed water inlet of the tower top liquid tank of the first-stage concentration tower, the water outlet of the tower top liquid tank of the first-stage concentration tower is connected with the tower top reflux port of the first-stage concentration tower through a reflux pump, the water outlet of the tower top liquid tank of the first-stage concentration tower is connected with the water inlet of the tower top liquid tank of the second-stage concentration tower through a water outlet pump, the tower top steam outlet of the tower top liquid tank of the second-stage concentration tower is connected with the steam inlet of the reboiler of the first-stage concentration tower, the condensed water outlet of the tower top liquid tank of the second-stage concentration tower is connected with the tower top reflux port of the second-stage concentration tower through the reflux pump, the water outlet of the tower top liquid tank of the second-stage concentration tower is connected with the, the condensed water outlet of the reboiler of the second-stage concentration tower is connected with the condensed water inlet of the liquid tank at the top of the third-stage concentration tower, the water outlet of the liquid tank at the top of the third-stage concentration tower is connected with the water inlet of the liquid tank at the top of the fourth-stage concentration tower through a water outlet pump, the steam outlet of the top of the fourth-stage concentration tower is connected with the steam inlet of the reboiler of the third-stage concentration tower, the condensed water outlet of the reboiler of the third-stage concentration tower is connected with the condensed water inlet of the liquid tank at the top of the fourth-stage concentration tower, the water outlet of the liquid tank at the top of the fourth-stage concentration tower is connected with the top reflux port of the fourth-stage concentration tower through a reflux pump, the water outlet of the liquid tank at the top of the fourth-stage concentration tower is connected with the water inlet of the water tank at the top of the tank area through a water outlet pump, the steam outlet of the top of the rectifying tower, the water outlet of the rectifying tower top liquid tank is connected with the tower top reflux port of the rectifying tower through a reflux pump, the water outlet of the rectifying tower top liquid tank is connected with the water inlet of the gas-water separation tank through a water outlet pump, and the water outlet of the gas-water separation tank is connected with the water inlet of the four-stage concentration tower top liquid tank through a water outlet pump of the gas-water separation tank.
8. The five-tower four-effect rectification system for NMP waste liquid according to claim 6, further comprising: a flash evaporation tank, an evaporation kettle and a primary concentration tower;
the slag notch of flash tank links to each other with the feed inlet of evaporating kettle, and the gaseous phase discharge gate of evaporating kettle links to each other with the gaseous phase feed inlet of one-level concentrator, and evaporating kettle's liquid phase discharge gate links to each other with the bucket through evaporating kettle discharge pump, and primary steam links to each other with evaporating kettle's steam inlet, and evaporating kettle's comdenstion water export links to each other with the comdenstion water import of hot-water tank.
9. The five-tower four-effect rectification system for NMP waste liquid according to claim 6, further comprising: a four-stage concentration tower reboiler, a feeding evaporator, a rectifying tower reboiler, a three-stage concentration tower reboiler, a two-stage concentration tower reboiler, a one-stage concentration tower top liquid tank, a rectifying tower top liquid tank, a tower top condenser and a rectifying tower top condenser;
a first steam, a four-stage concentration tower reboiler and a feeding evaporator, the steam inlet of rectifying column reboiler links to each other, the comdenstion water export of three equipment links to each other with the comdenstion water import of hot water tank, the top of the tower steam outlet of level four rectifying column links to each other with the steam inlet of tertiary rectifying column reboiler, the top of the tower steam outlet of tertiary rectifying column links to each other with the steam inlet of second grade rectifying column reboiler, the top of the tower steam outlet of first grade rectifying column links to each other with the steam inlet of top of the tower condenser, the comdenstion water export of top of the tower condenser links to each other with the comdenstion water import of first grade rectifying column top of the tower fluid reservoir, the top of the tower steam outlet of rectifying column links to each other with the steam inlet of rectifying column top of the tower fluid reservoir, the comdenstion water export of rectifying column top of the tower condenser links to each.
10. The five-tower four-effect rectification system for NMP waste liquid according to claim 6, further comprising: a water ring vacuum pump of a first-stage concentration tower, a second-stage concentration tower, a third-stage concentration tower, a fourth-stage concentration tower and a rectifying tower;
vacuum ports of the first-stage concentration tower, the second-stage concentration tower, the third-stage concentration tower, the fourth-stage concentration tower and the rectifying tower are connected with air inlets of respective water ring vacuum pumps, and an air outlet of each water ring vacuum pump is connected with an air inlet of the gas-water separation tank.
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