NMP wastewater low-temperature recovery system and method thereof

Abstract

The invention discloses an NMP wastewater low-temperature recovery system and a method thereof. The recovery system comprises a raw material barrel, a middle barrel, a concentrated liquid barrel, a product pool, a low-temperature heat pump evaporation unit, a low-temperature scraper evaporation unit and a filtering unit, the low-temperature heat pump evaporation unit is communicated with the raw material barrel and the middle barrel, NMP wastewater enters the low-temperature heat pump evaporation unit from the raw material barrel and then is evaporated and separated, distilled water formed by steam condensation is independently collected, and the NMP wastewater is purified into NMP liquid with the concentration of 80%; the low-temperature scraper evaporation unit is communicated with the middle barrel and the concentrated liquid barrel, NMP liquid with the concentration of 80% enters the low-temperature scraper evaporation unit from the middle barrel and then is evaporated and separated, distilled water formed by steam condensation is independently collected, and the NMP liquid with the concentration of 99.9% is purified and discharged into the concentrated liquid barrel; the filtering unit is communicated with the concentrated liquid barrel and the product pool, NMP liquid with the concentration of 99.9% enters the filtering unit from the concentrated liquid barrel to filter impurities, and finally the NMP liquid is discharged into the product pool; the recovery method is applied to the recovery system.

Description

Technical Field

[0001] The invention belongs to the technical field of NMP wastewater treatment, and in particular relates to a low-temperature recovery system and method for NMP wastewater. Background Art

[0002] N-Methylpyrrolidone (hereinafter referred to as NMP) is a polar solvent with strong selectivity and good stability. In the manufacture of lithium-ion secondary batteries, electrode materials composed of active materials such as lithium compounds, binders such as polyvinylidene fluoride, and NMP as a solvent are coated on a substrate and fired to make electrodes.

[0003] During the electrode production process, the NMP solvent used is constantly volatilized. If the NMP waste gas is directly discharged into the environment without being recovered, it will cause environmental pollution on the one hand and a huge waste of resources on the other hand. Therefore, in the prior art, the volatilized NMP gas is firstly made into NMP wastewater by adsorption method, and then the NMP liquid is recovered by distillation tower purification technology.

[0004] However, the purity of NMP liquid recovered by distillation tower purification technology is not high. In order to obtain high-concentration NMP concentrate, it is usually necessary to set up multiple groups of distillation towers and NMP storage tanks for combined use, which will increase the overall floor space and total energy consumption, resulting in high cost of use. Summary of the invention

[0005] Technical issues solved The invention provides a low-temperature NMP wastewater recovery system and method thereof, which can improve the purity of NMP liquid recovery while reducing the total amount of equipment, thereby reducing the overall floor space and reducing the overall energy consumption.

[0006] Technical Solution To achieve the above object, the present invention provides the following technical solutions: A low-temperature recovery system for NMP wastewater comprises a raw material barrel, an intermediate barrel, a concentrated liquid barrel, a product pool, a low-temperature heat pump evaporation unit, a low-temperature scraper evaporation unit and a filtering unit; the low-temperature heat pump evaporation unit is connected to the raw material barrel and the intermediate barrel, NMP wastewater enters the low-temperature heat pump evaporation unit from the raw material barrel and evaporates and separates, distilled water formed by steam condensation is collected separately, and the NMP wastewater is purified to an NMP liquid with a concentration of 80%; the low-temperature scraper evaporation unit is connected to the intermediate barrel and the concentrated liquid barrel, NMP liquid with a concentration of 80% enters the low-temperature scraper evaporation unit from the intermediate barrel and evaporates and separates, distilled water formed by steam condensation is collected separately, and the concentration of NMP liquid is purified to 99.9% and discharged into the concentrated liquid barrel; the filtering unit is connected to the concentrated liquid barrel and the product pool, NMP liquid with a concentration of 99.9% enters the filtering unit from the concentrated liquid barrel to filter out impurities, and finally discharged into the product pool.

[0007] Preferably, the low-temperature heat pump evaporation unit comprises a vacuum distillation kettle, a compressor, a heat exchange tube, a condenser and an evaporator; the vacuum distillation kettle is respectively connected to the raw material barrel, the intermediate barrel and the evaporator; the evaporator is respectively directly connected to the compressor head end and connected to the condenser tail end through an expansion valve, the heat exchange tube is installed in the vacuum distillation kettle and connects the compressor tail end and the condenser head end; the evaporator is also equipped with a water diversion pipe; wherein, after the compressor adds liquid refrigerant, a high-temperature and high-pressure gaseous refrigerant is generated, and the high-temperature and high-pressure gaseous refrigerant path When passing through the heat exchange tube, heat is exchanged with the NMP wastewater in the vacuum distillation kettle, so that the water in the NMP wastewater evaporates at low temperature and forms secondary steam. The high-temperature and high-pressure gaseous refrigerant passing through the heat exchange tube forms a low-temperature and high-pressure gaseous refrigerant under the action of the condenser and the expansion valve. The low-temperature and high-pressure gaseous refrigerant exchanges heat with the secondary steam entering the evaporator from the vacuum distillation kettle, so that the secondary steam is condensed into distilled water and discharged to the outside through the water inlet pipe, while the low-temperature and high-pressure gaseous refrigerant is condensed into a low-temperature and low-pressure liquid refrigerant and enters the compressor for continued use.

[0008] Preferably, the low-temperature scraper evaporation unit comprises a vacuum reactor, a stirring assembly and a condenser; the vacuum reactor is respectively connected to the intermediate barrel, the concentrated liquid barrel and the condenser, and a heat exchange base is installed on the vacuum reactor; the stirring assembly comprises a spiral scraper and a reducer, the spiral scraper is rotatably installed inside the vacuum reactor, and the reducer is installed outside the vacuum reactor and is drivingly connected to the spiral scraper; cooling water can enter and exit the condenser, and a drain pipe is also installed on the condenser; wherein, when high-temperature steam enters the heat exchange base, it exchanges heat with the NMP liquid in the vacuum reactor, so that the water in the NMP liquid evaporates to form secondary steam, and the secondary steam enters the condenser and condenses to form distilled water, which is discharged through the drain pipe, and the high-temperature steam that loses heat condenses to form a water body and is discharged from the heat exchange base.

[0009] Preferably, it also includes a first suction unit and a second suction unit; the first suction unit includes a first water tank, a first centrifugal pump and a first ejector; the first water tank can take in and out cooling water, and the first water tank is equipped with a first conduit located above the liquid level and a second conduit located below the liquid level, the first conduit is equipped with a first clean water pipe connected to the outside, and the second conduit is equipped with a first ball valve; the first centrifugal pump connects the first conduit and the second conduit, and the first ejector connects the first conduit and the water diversion pipe; the second suction unit includes a second water tank, a second centrifugal pump and a second ejector; the second water tank can take in and out cooling water, and the second water tank is equipped with a third conduit located above the liquid level and a fourth conduit located below the liquid level, the third conduit is equipped with a second clean water pipe connected to the outside, and the fourth conduit is equipped with a second ball valve; the second centrifugal pump connects the third conduit and the fourth conduit, and the second ejector connects the third conduit and the drain pipe.

[0010] Preferably, the low-temperature scraper evaporation unit also includes a filter tank, which is connected to the vacuum reactor and the condenser, and is equipped with a defoamer and a sensing component; the filter tank is used to filter out impurities in the secondary steam, and the defoamer is used to eliminate bubbles in the secondary steam; the sensing component includes a temperature sensor for detecting the temperature of the secondary steam, a pressure sensor for detecting the air pressure of the secondary steam, and a foam sensor for detecting the amount of foam in the secondary steam.

[0011] Preferably, the low-temperature scraper evaporation unit further comprises a drainage tank, which is connected to the heat exchange base for storing and discharging water formed by condensation of steam.

[0012] Preferably, the filtering unit adopts a bag filter or is replaced by the low-temperature scraper evaporation unit.

[0013] A method for recovering NMP wastewater at low temperature is applied to the above-mentioned NMP wastewater at low temperature recovery system, which comprises the following steps: S1: collecting NMP wastewater with a concentration of 25% through the raw material barrel, opening the first ball valve and starting the first centrifugal pump, so that the first ejector generates negative pressure. Since the first ejector, the water diversion pipe, the evaporator and the vacuum distillation kettle are connected to each other, the air in the vacuum distillation kettle can be extracted under the action of negative pressure. After the vacuum distillation kettle is vacuumed, the first ball valve is closed, and the vacuum degree is -0.093 to -0.098 MPa; S2: The NMP wastewater in the raw material barrel is discharged into the vacuum distillation kettle, and liquid refrigerant is added to the compressor. The high-temperature and high-pressure gaseous refrigerant generated by the compressor passes through the heat exchange tube and exchanges heat with the NMP wastewater in the vacuum distillation kettle, so that the water in the NMP wastewater evaporates at a temperature of 30 to 40°C to form secondary steam. The high-temperature and high-pressure gaseous refrigerant at the heat exchange tube passes through the condenser and the expansion valve to form a low-temperature and high-pressure gaseous refrigerant. The low-temperature and high-pressure gaseous refrigerant enters the evaporator and exchanges heat with the secondary steam entering the evaporator. The distilled water formed by the condensation of the secondary steam flows into the first ejector and is discharged from the first water purification pipe. The low-temperature and high-pressure gaseous refrigerant condenses to form a low-temperature and low-pressure gaseous refrigerant that enters the compressor for reuse, and the NMP wastewater retained in the vacuum distillation kettle is purified to an NMP liquid with a concentration of 80%; S3: collecting NMP liquid with a concentration of 80% through the intermediate barrel, opening the second ball valve and starting the second centrifugal pump, so that the second ejector generates negative pressure. Since the second ejector, the drain pipe, the condenser and the vacuum reactor are connected to each other, the air in the vacuum reactor can be extracted under the action of negative pressure. After the vacuum reactor is vacuumed, the second ball valve is closed, and the vacuum degree is -0.093 to -0.098 MPa; S4: draining the NMP liquid in the middle barrel into the vacuum reactor, starting the reducer to drive the spiral scraper to rotate and stir the NMP liquid, and then delivering high-temperature steam to the heat exchange base. The high-temperature steam exchanges heat with the NMP liquid, so that the water in the NMP liquid evaporates at a low temperature of 45-48° C. to form secondary steam, and the secondary steam enters the condenser to condense to form distilled water. The formed distilled water flows into the second ejector and is discharged from the second water purification pipe. The steam in the heat exchange base loses heat and condenses to form water and is discharged, and the NMP liquid remaining in the vacuum reactor is purified to a concentration of 99.9% NMP liquid; S5: collecting NMP liquid with a concentration of 99.9% through the concentrated liquid barrel; S6: Discharge the NMP liquid in the concentrate barrel into the filtration unit to filter out impurities in the NMP liquid, and finally discharge it into the product pool.

[0014] (III) Beneficial effects The present invention provides a low-temperature recovery system and method for NMP wastewater. Compared with the prior art, the present invention can improve the recovery purity of NMP liquid only by using a low-temperature heat pump evaporation unit and a low-temperature scraper evaporation unit, and does not need to set up a plurality of groups of distillation towers for combined use, which can effectively reduce the total amount of equipment and shorten the pipe path between the equipment, thereby reducing the overall floor space and reducing the overall energy consumption; at the same time, since the entire recovery process is carried out at a low temperature, the operation safety can also be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings: Figure 1 The use process of the present invention is shown Figure 1 ; Figure 2 The use process of the present invention is shown Figure 2 ; Figure 3 The schematic diagram of the structure of the low-temperature heat pump evaporation unit of the present invention is shown; Figure 4 Shows a magnification of the 3-part structure Figure 1 ; Figure 5 Shows a magnification of the 3-part structure Figure 2 ; Figure 6 The schematic diagram of the structure of the low-temperature scraper evaporation unit of the present invention is shown; Figure 7 Show Figure 6 Zoom in on some structures Figure 1 ; Figure 8 Figure 6 Zoom in on some structures Figure 2 ; Fig. 9 Figure 6 Zoom in on some structures Figure 3 ; Fig.10 Shows Figure 1-Figure 9 Annotated diagram of each component in the.

[0016] In the figure: 1 low-temperature heat pump evaporation unit, 11 vacuum distillation kettle, 12 compressor, 13 heat exchange tube, 14 condenser, 15 evaporator, 150 water pipe, 16 expansion valve, 2 low-temperature scraper evaporation unit, 21 vacuum reactor, 22 stirring assembly, 221 spiral scraper, 222 reducer, 23 condenser, 230 drain pipe, 24 heat exchange base, 25 filter tank, 251 defoamer, 252 sensing assembly, 2521 temperature sensor, 252 2 pressure sensor, 2523 foam sensor, 26 drainage tank, 3 first suction unit, 31 first water tank, 311 first conduit, 312 second conduit, 3120 first ball valve, 313 first clean water pipe, 32 first centrifugal pump, 33 first ejector, 4 second suction unit, 41 second water tank, 411 third conduit, 412 fourth conduit, 4120 second ball valve, 413 second clean water pipe, 42 second centrifugal pump, 43 second ejector. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] See attached Figure 1 -Attached Fig.10 , a low-temperature recovery system for NMP wastewater, comprising a raw material barrel, an intermediate barrel, a concentrate barrel, a product pool, a low-temperature heat pump evaporation unit 1, a low-temperature scraper evaporation unit 2 and a filtration unit; The low-temperature heat pump evaporation unit 1 is connected to the raw material barrel and the intermediate barrel. The NMP wastewater enters the low-temperature heat pump evaporation unit 1 from the raw material barrel and evaporates and separates. The distilled water formed by the condensation of the steam is collected separately, and the NMP wastewater is purified to an NMP liquid with a concentration of 80%; The low-temperature scraper evaporation unit 2 is connected to the middle barrel and the concentrated liquid barrel. The NMP liquid with a concentration of 80% enters the low-temperature scraper evaporation unit 2 from the middle barrel and is evaporated and separated. The distilled water formed by the condensation of steam is collected separately, and the concentration of the NMP liquid is purified to 99.9% and discharged into the concentrated liquid barrel. The filtration unit connects the concentrate tank and the product pool. NMP liquid with a concentration of 99.9% enters the filtration unit from the concentrate tank to filter out impurities and is finally discharged into the product pool.

[0019] Specifically, compared with the prior art, the present solution can improve the recovery purity of NMP liquid only by using the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2, without the need to set up a multi-stage distillation tower for combined use, which can effectively reduce the total amount of equipment and shorten the pipe path between the equipment, thereby reducing the overall floor space and reducing the overall energy consumption; at the same time, since the entire recovery process is carried out at low temperature, the operational safety can also be effectively improved.

[0020] It should be noted that the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2 can be standard equipment or non-standard equipment. Standard equipment can be directly purchased on the market and is an existing product, but there is currently no relevant technology that combines the two and applies them to NMP liquid purification and recovery; while non-standard equipment adds or reduces some structural parts to make the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2 have other functions; in the present invention, the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2 preferably use non-standard equipment, as follows: See attached Figure 1 -Attached Fig. 9 The low-temperature heat pump evaporation unit 1 includes a vacuum still 11, a compressor 12, a heat exchange tube 13, a condenser 14 and an evaporator 15; the vacuum still 11 is connected to the raw material barrel, the intermediate barrel and the evaporator 15 respectively; the evaporator 15 is directly connected to the head end of the compressor 12 and the tail end of the condenser 14 through the expansion valve 16, and the heat exchange tube 13 is installed in the vacuum still 11 and connected to the tail end of the compressor 12 and the head end of the condenser 14; the evaporator 15 is also installed with a water guide pipe 150; Among them, after the compressor 12 adds liquid refrigerant, it generates high-temperature and high-pressure gaseous refrigerant. When passing through the heat exchange tube 13, the high-temperature and high-pressure gaseous refrigerant exchanges heat with the NMP wastewater in the vacuum distillation kettle 11, so that the water in the NMP wastewater evaporates at low temperature and forms secondary steam. The high-temperature and high-pressure gaseous refrigerant passing through the heat exchange tube 13 forms a low-temperature and high-pressure gaseous refrigerant under the action of the condenser 14 and the expansion valve 16. The low-temperature and high-pressure gaseous refrigerant exchanges heat with the secondary steam entering the evaporator 15 from the vacuum distillation kettle 11, so that the secondary steam is condensed into distilled water and discharged to the outside through the water inlet pipe 150, while the low-temperature and high-pressure gaseous refrigerant is condensed into a low-temperature and low-pressure liquid refrigerant and enters the compressor 12 for continued use.

[0021] Specifically, in the existing distillation tower purification technology, it is necessary to continuously fill the NMP wastewater with fillers to exchange heat. Not only is the heat exchange efficiency low, but the thermal enthalpy required for the entire process is very high, resulting in high overall energy consumption.

[0022] In the present application, since the gaseous refrigerant generated by the compressor 12 is used to exchange heat with the NMP wastewater, the water in the NMP wastewater is evaporated into secondary steam at a low temperature, and the gaseous refrigerant can be returned to the compressor 12 after heat exchange with the secondary steam and used as a liquid refrigerant, thereby realizing the reuse and circulation of heat exchange materials, thereby effectively improving the heat exchange efficiency and reducing energy consumption.

[0023] According to actual tests, if the amount of NMP wastewater delivered by the raw material barrel to the vacuum distillation kettle 11 is 8T / D (tons / day), and the vacuum degree of the vacuum distillation kettle 11 is -0.093~-0.098MPa, and the evaporation temperature is 30~40℃, then the total power of this low-temperature heat pump evaporation unit 1 is 45KW, the energy consumption is 160KW-180KW / m³, and 5.5T / D of water is evaporated. For specific data, please refer to Table 1.

[0024] Table 1 See attached Figure 1 -Attached Fig. 9 The low-temperature scraper evaporation unit 2 includes a vacuum reactor 21, a stirring assembly 22 and a condenser 23; the vacuum reactor 21 is respectively connected to the intermediate barrel, the concentrated liquid barrel and the condenser 23, and a heat exchange base 24 is installed on the vacuum reactor 21; the stirring assembly 22 includes a spiral scraper 221 and a reducer 222, the spiral scraper 221 is rotatably installed inside the vacuum reactor 21, and the reducer 222 is installed outside the vacuum reactor 21 and is drivingly connected to the spiral scraper 221; the condenser 23 can flow in and out of cooling water, and a drain pipe 230 is also installed on the condenser 23; wherein, when the high-temperature steam enters the heat exchange base 24, it exchanges heat with the NMP liquid in the vacuum reactor 21, so that the water in the NMP liquid evaporates to form secondary steam, and the secondary steam enters the condenser 23 and condenses to form distilled water, which is discharged through the drain pipe 230, and the high-temperature steam that loses heat condenses to form a water body and is discharged from the heat exchange base 24. Since the high-temperature steam does not contact the mixed secondary steam, the water body formed by its condensation can be directly recycled.

[0025] Specifically, in the present application, the spiral scraper 221 is used to stir the NMP liquid with a concentration of 80% to make it evenly dispersed, which is beneficial to the heat exchange between the water in the NMP liquid and the steam, thereby improving the heat exchange efficiency; at the same time, the water in the NMP liquid evaporates at a low temperature to form secondary steam during the heat exchange process, and the secondary steam enters the condenser 23 and directly exchanges heat with the cooling water that is continuously circulating in and out, and can be condensed to form distilled water, and the energy consumption required for the whole process is very small.

[0026] According to actual tests, if the amount of NMP liquid delivered by the intermediate barrel to the vacuum reactor 21 is 2.5T / D (tons / day), and the vacuum degree of the vacuum reactor 21 is -0.093~-0.098MPa, and the evaporation temperature is 45~48℃, then the total power of the low-temperature scraper evaporation unit 2 is 4.5KW, and 0.5T / D of water is evaporated. For specific data, please refer to Table 2.

[0027] Table 2 In summary, referring to Table 1 and Table 2, the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2 treat 8T / D of NMP wastewater with a total power of only 49.5KW, which is 39.6RMB / T in total based on the electricity price of 0.8RMB / kW.H; the circulating cooling water requires 30T / H, with a loss rate of 1%, which is 3RMB / T in total based on the water price of 3RMB / T; the total cost is 42.3RMB / T, which has high economic benefits.

[0028] On the other hand, the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2 are complete sets of equipment, which can be directly pulled to the site and connected to the power supply for use, without the need for engineering installation and debugging, which can reduce installation costs; and the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2 have a compact structure, with a maximum height of no more than 3.8 meters, which solves the problem of limited space.

[0029] See attached Figure 1 -Attached Fig. 9, considering that in the prior art, a separate vacuum pumping device is usually required to vacuum the distillation tower, and a separate pump body is required to transport NMP wastewater between the distillation towers for each distillation; resulting in a large footprint and high cost. In order to solve this problem; the present invention also includes a first suction unit 3 and a second suction unit 4; the first suction unit 3 includes a first water tank 31, a first centrifugal pump 32 and a first ejector 33; the first water tank 31 can be fed with cooling water, and the first water tank 31 is equipped with a first conduit 311 located above the liquid surface and a second conduit 312 located below the liquid surface, the first conduit 311 is equipped with a first clean water pipe 313 connected to the outside, and the second conduit 312 is equipped with a first ball valve 3 120; the first centrifugal pump 32 is connected to the first conduit 311 and the second conduit 312, and the first ejector 33 is connected to the first conduit 311 and the water diversion pipe 150; the second suction unit 4 includes a second water tank 41, a second centrifugal pump 42 and a second ejector 43; the second water tank 41 can be supplied with cooling water, and the second water tank 41 is provided with a third conduit 411 located above the liquid surface and a fourth conduit 412 located below the liquid surface, the third conduit 411 is provided with a second clean water pipe 413 connected to the outside, and the fourth conduit 412 is provided with a second ball valve 4120; the second centrifugal pump 42 is connected to the third conduit 411 and the fourth conduit 412, and the second ejector 43 is connected to the third conduit 411 and the drain pipe 230.

[0030] Specifically, when evacuating, open the first ball valve 3120 and start the first centrifugal pump 32, so that the first ejector 33 generates negative pressure. Since the first ejector 33, the water pipe 150, the evaporator 15 and the vacuum distillation kettle 11 are interconnected, the air in the vacuum distillation kettle 11 can be extracted under the action of negative pressure. Since the vacuum distillation kettle 11 is in a negative pressure state at this time, the NMP waste water in the raw material barrel can be actively sucked; when discharging the distilled water in the evaporator 15, close the first ball valve 3120 to cut off the connection between the first centrifugal pump 32 and the first water tank 31, and use the negative pressure generated by the cooperation of the first centrifugal pump 32 and the first ejector 33 to smoothly discharge the distilled water in the evaporator 15 through the water pipe 150.

[0031] Similarly, when evacuating, open the second ball valve 4120 and start the second centrifugal pump 42, so that the second ejector 43 generates negative pressure. Since the second ejector 43, the drain pipe 230, the condenser 23 and the vacuum reactor 21 are interconnected, the air in the vacuum reactor 21 can be extracted under the action of negative pressure. Since the vacuum reactor 21 is in a negative pressure state at this time, the NMP liquid in the middle barrel can be actively sucked. When discharging the distilled water in the condenser 23, close the second ball valve 4120 to cut off the connection between the second centrifugal pump 42 and the second water tank 41. The distilled water in the condenser 23 can be smoothly discharged through the drain pipe 230 by using the negative pressure generated by the cooperation of the second centrifugal pump 42 and the second ejector 43.

[0032] In summary, the first suction unit 3 and the second suction unit 4 are both integrated with the vacuum function and the drainage function, so the overall volume is small, the total amount of equipment used is small, and the floor space can be further reduced; in addition, since the vacuum distillation kettle 11 and the vacuum reaction kettle 21 can rely on negative pressure self-priming to correspondingly suck the NMP waste water in the raw material barrel and the NMP liquid in the intermediate barrel, there is no need to additionally set up a pump body as a conveying power source, which can effectively reduce the overall energy consumption.

[0033] See attached Figure 1 -Attached Fig. 9 In actual operation, the secondary steam discharged from the vacuum reactor 21 may still be mixed with impurities and bubbles. To solve this problem, in the present invention, the low-temperature scraper evaporation unit 2 also includes a filter tank 25, the filter tank 25 is connected to the vacuum reactor 21 and the condenser 23, and a defoamer 251 and a sensing component 252 are installed on the filter tank 25; the sensing component 252 includes a temperature sensor 2521, a pressure sensor 2522 and a foam sensor 2523.

[0034] Specifically, the filter tank 25 is used to filter out impurities in the secondary steam, the defoamer 251 is used to eliminate bubbles in the secondary steam, the temperature sensor 2521 is used to detect the temperature of the secondary steam, the pressure sensor 2522 is used to detect the air pressure of the secondary steam, and the foam sensor 2523 is used to detect the amount of foam in the secondary steam; the above structures are used in combination to improve the purity of the secondary steam entering the condenser 14, thereby improving the quality of the distilled water finally condensed.

[0035] See attached Figure 1 -Attached Fig. 9 The low-temperature scraper evaporation unit 2 further includes a drainage tank 26 , which is connected to the heat exchange base 24 for storing and discharging water formed by condensation of steam.

[0036] See attached Figure 1 -Attached Fig. 9 The filter unit adopts a bag filter or is replaced by a low-temperature scraper evaporation unit 2.

[0037] Specifically, when a bag filter is used as the filtration unit, some special components dissolved in the NMP liquid cannot be effectively filtered out, and the service life of the bag filter is relatively short.

[0038] When the filtration unit adopts the low-temperature scraper evaporation unit 2, the special components in the NMP liquid can be evaporated to the greatest extent, and impurities can be effectively filtered out through multiple evaporations to improve the purity of the NMP liquid. In addition, the service life of the low-temperature scraper evaporation unit 2 is relatively long.

[0039] See attached Figure 1 -Attached Fig. 9 A method for recovering NMP wastewater at low temperature is applied to the above-mentioned NMP wastewater at low temperature recovery system. There are various embodiments according to different situations. For the convenience of understanding the present invention, examples are given as follows: Embodiment 1 Without specifically defining the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2, the low-temperature recovery method for NMP wastewater comprises the following steps: S1: Collect NMP wastewater with a concentration of 25% through a raw material barrel; S2: The NMP wastewater in the raw material barrel is discharged into the low-temperature heat pump evaporation unit 1, and the NMP wastewater is heated at a temperature of 30 to 40° C. under a vacuum degree of -0.093 to -0.098 MPa, so that the water in the NMP wastewater is evaporated and separated to form secondary steam, and the distilled water formed by the condensation of the secondary steam is collected separately, and the retained NMP wastewater is purified to an NMP liquid with a concentration of 80%; S3: collecting NMP liquid with a concentration of 80% through an intermediate barrel; S4: The NMP liquid in the middle barrel is discharged into the low-temperature scraper evaporation unit 2, and the NMP liquid is heated at a temperature of 45 to 48° C. under a vacuum degree of -0.093 to -0.098 MPa, so that the water in the NMP liquid continues to evaporate and separate to form secondary steam, and the distilled water formed by the condensation of the secondary steam is collected separately, and the remaining NMP liquid is purified to a concentration of 99.9% NMP liquid; S5: collecting NMP liquid with a concentration of 99.9% through a concentrated liquid bucket; S6: The NMP liquid in the concentrate barrel is discharged into the filtration unit to filter out impurities in the NMP liquid, and finally discharged into the product pool.

[0040] Specifically, in Example 1, the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2 are not restricted. Under the premise of ensuring the processing conditions, the manufacturer can choose components with corresponding functions to assemble the corresponding low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2; and compared with the prior art, this solution can ensure the recovery purity of the NMP liquid only through the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2, and can effectively reduce the total amount of equipment, reduce the overall floor space and reduce the overall energy consumption.

[0041] Embodiment 2 In the case where the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2 are specifically defined, but the first suction unit 3 and the second suction unit 4 are not defined, the low-temperature recovery method of NMP wastewater includes the following steps: S1: collect NMP wastewater with a concentration of 25% through the raw material barrel, and evacuate the vacuum distillation kettle 11 to a vacuum degree of -0.093 to -0.098 MPa; S2: The NMP wastewater in the raw material barrel is discharged into the vacuum distillation kettle 11, and liquid refrigerant is added to the compressor 12. The high-temperature and high-pressure gaseous refrigerant generated by the compressor 12 passes through the heat exchange tube 13 and exchanges heat with the NMP wastewater in the vacuum distillation kettle 11, so that the water in the NMP wastewater evaporates at a temperature of 30 to 40°C to form secondary steam. The high-temperature and high-pressure gaseous refrigerant at the heat exchange tube 13 passes through the condenser 14 and the expansion valve 16 to form a low-temperature and high-pressure gaseous refrigerant. The low-temperature and high-pressure gaseous refrigerant enters the evaporator 15 and exchanges heat with the secondary steam entering the evaporator 15. The secondary steam condenses to form distilled water and is discharged through the water guide pipe 150. The low-temperature and high-pressure gaseous refrigerant condenses to form a low-temperature and low-pressure gaseous refrigerant that enters the compressor 12 for reuse, and the NMP wastewater retained in the vacuum distillation kettle 11 is purified to an NMP liquid with a concentration of 80%; S3: collecting NMP liquid with a concentration of 80% through the intermediate barrel, and evacuating the vacuum reactor 21 to a vacuum degree of -0.093 to -0.098 MPa; S4: The NMP liquid in the middle barrel is discharged into the vacuum reactor 21, and an appropriate amount of scale inhibitor can be added at the same time. The reducer 222 is started to drive the spiral scraper 221 to rotate and stir the NMP liquid, and then high-temperature steam is transported to the heat exchange base 24. The high-temperature steam exchanges heat with the NMP liquid, so that the water in the NMP liquid evaporates at a temperature of 45 to 48° C. to form secondary steam. The secondary steam enters the condenser 23 and condenses to form distilled water and is discharged through the drain pipe 230. The steam in the heat exchange base 24 loses heat and condenses to form water and is discharged, and the NMP liquid retained in the vacuum reactor 21 is purified to a concentration of 99.9% NMP liquid; S5: collecting NMP liquid with a concentration of 99.9% through a concentrated liquid bucket; S6: The NMP liquid in the concentrate barrel is discharged into the filtration unit to filter out impurities in the NMP liquid, and finally discharged into the product pool.

[0042] Specifically, in Example 2, the specific structural components of the low-temperature heat pump evaporator unit 1 and the low-temperature scraper evaporator unit 2 are defined. Example 2 is essentially one of the optimal solutions of Example 1, so the problems it solves and the effects it has are generally the same as those of Example 1, both of which are aimed at ensuring the purity of the recovered NMP liquid while reducing the total amount of equipment, thereby reducing the overall floor space and reducing the overall energy consumption; in addition, the gaseous refrigerant in Example 2 can be returned to the compressor 12 after heat exchange with the secondary steam and used as a liquid refrigerant, realizing the reuse and circulation of heat exchange materials, thereby further reducing costs.

[0043] Embodiment 3 In the case of specifically defining the low-temperature heat pump evaporation unit 1, the low-temperature scraper evaporation unit 2, the first suction unit 3 and the second suction unit 4, the low-temperature recovery method of NMP wastewater includes the following steps: S1: Collect NMP wastewater with a concentration of 25% through the raw material barrel, open the first ball valve 3120 and start the first centrifugal pump 32, so that the first ejector 33 generates negative pressure. Since the first ejector 33, the water diversion pipe 150, the evaporator 15 and the vacuum distillation kettle 11 are connected to each other, the air in the vacuum distillation kettle 11 can be extracted under the action of negative pressure. After the vacuum distillation kettle 11 is vacuumed, the first ball valve 3120 is closed, and the vacuum degree is -0.093 to -0.098 MPa; S2: The NMP wastewater in the raw material barrel is discharged into the vacuum distillation kettle 11, and liquid refrigerant is added to the compressor 12. The high-temperature and high-pressure gaseous refrigerant generated by the compressor 12 passes through the heat exchange tube 13 and exchanges heat with the NMP wastewater in the vacuum distillation kettle 11, so that the water in the NMP wastewater evaporates at a temperature of 30 to 40°C to form secondary steam. The high-temperature and high-pressure gaseous refrigerant at the heat exchange tube 13 passes through the condenser 14 and the expansion valve 16 to form a low-temperature and high-pressure gaseous refrigerant. The low-temperature and high-pressure gaseous refrigerant enters the evaporator 15 and exchanges heat with the secondary steam entering the evaporator 15. The distilled water formed by the condensation of the secondary steam flows into the first ejector 33 and is discharged from the first clean water pipe 313. The low-temperature and high-pressure gaseous refrigerant condenses to form a low-temperature and low-pressure gaseous refrigerant that enters the compressor 12 for reuse, and the NMP wastewater retained in the vacuum distillation kettle 11 is purified to a NMP liquid with a concentration of 80%; S3: collect NMP liquid with a concentration of 80% through the middle barrel, open the second ball valve 4120 and start the second centrifugal pump 42, so that the second ejector 43 generates negative pressure. Since the second ejector 43, the drain pipe 230, the condenser 23 and the vacuum reactor 21 are connected to each other, the air in the vacuum reactor 21 can be extracted under the action of negative pressure. After the vacuum reactor 21 is vacuumed, the second ball valve 4120 is closed, and the vacuum degree is -0.093 to -0.098 MPa; S4: the liquid NMP in the middle barrel is discharged into the vacuum reactor 21, the reducer 222 is started to drive the spiral scraper 221 to rotate and stir the NMP liquid, and then the high-temperature steam is transported to the heat exchange base 24. The high-temperature steam exchanges heat with the NMP liquid, so that the water in the NMP liquid evaporates at a temperature of 45-48°C to form secondary steam, and the secondary steam enters the condenser 23 to condense into distilled water. The distilled water flows into the second ejector 43 and is discharged from the second clean water pipe 413. The steam in the heat exchange base 24 loses heat and condenses to form water and is discharged, and the NMP liquid remaining in the vacuum reactor 21 is purified to a concentration of 99.9% NMP liquid; S5: collecting NMP liquid with a concentration of 99.9% through a concentrated liquid bucket; S6: The NMP liquid in the concentrate barrel is discharged into the filtration unit to filter out impurities in the NMP liquid, and finally discharged into the product pool.

[0044] Specifically, in the prior art, separate vacuuming equipment is usually equipped to vacuum each level of the distillation tower, which occupies a large area and is costly; in Example 3, a specific first suction unit 3 and a second suction unit 4 are added, and the first suction unit 3 and the second suction unit 4 are both integrated with drainage function and vacuuming function, so the overall volume is small, the total amount of equipment used is small, the occupied space can be reduced, and the overall energy consumption can be reduced; the remaining components are the same as those in Example 2 and will not be repeated here.

[0045] It should be noted that vacuum reactors or vacuum distillation kettles are prone to generate dirt after long-term use. After use, scale inhibitors can be added to the vacuum reactors or vacuum distillation kettles for cleaning.

[0046] It should also be noted that, although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present application.

Claims

1. A low-temperature NMP wastewater recovery system, comprising a raw material barrel, an intermediate barrel, a concentrate barrel and a product pool, characterized in that: Also includes: A low-temperature heat pump evaporation unit, wherein the low-temperature heat pump evaporation unit is connected to the raw material barrel and the intermediate barrel, and the NMP wastewater enters the low-temperature heat pump evaporation unit from the raw material barrel and evaporates and separates, and the distilled water formed by the condensation of the steam is collected separately, and the NMP wastewater is purified to an NMP liquid with a concentration of 80%; A low-temperature scraper evaporation unit, wherein the low-temperature scraper evaporation unit is connected to the intermediate barrel and the concentrated liquid barrel, and the NMP liquid with a concentration of 80% enters the low-temperature scraper evaporation unit from the intermediate barrel and evaporates and separates, and the distilled water formed by the condensation of steam is collected separately, and the concentration of the NMP liquid is purified to 99.9% and discharged into the concentrated liquid barrel; The filtration unit is connected to the concentrate barrel and the product pool. NMP liquid with a concentration of 99.9% enters the filtration unit from the concentrate barrel to filter out impurities and is finally discharged into the product pool.

2. A NMP wastewater low temperature recovery system according to claim 1, characterized in that, The low-temperature heat pump evaporation unit comprises a vacuum distillation kettle, a compressor, a heat exchange tube, a condenser and an evaporator; the vacuum distillation kettle is respectively connected to the raw material barrel, the intermediate barrel and the evaporator; the evaporator is respectively directly connected to the compressor head end and connected to the condenser tail end through an expansion valve, the heat exchange tube is installed in the vacuum distillation kettle and connects the compressor tail end and the condenser head end; the evaporator is also installed with a water diversion pipe; Among them, after the liquid refrigerant is added to the compressor, a high-temperature and high-pressure gaseous refrigerant is generated. When the high-temperature and high-pressure gaseous refrigerant passes through the heat exchange tube, it exchanges heat with the NMP wastewater in the vacuum distillation kettle, so that the water in the NMP wastewater evaporates at a low temperature and forms secondary steam. The high-temperature and high-pressure gaseous refrigerant passing through the heat exchange tube forms a low-temperature and high-pressure gaseous refrigerant under the action of the condenser and the expansion valve. The low-temperature and high-pressure gaseous refrigerant exchanges heat with the secondary steam entering the evaporator from the vacuum distillation kettle, so that the secondary steam is condensed into distilled water and discharged to the outside through the water inlet pipe, while the low-temperature and high-pressure gaseous refrigerant is condensed into a low-temperature and low-pressure liquid refrigerant and enters the compressor for continued use.

3. A NMP wastewater low temperature recovery system according to claim 2, characterized in that, The low-temperature scraper evaporation unit includes a vacuum reactor, a stirring assembly and a condenser; the vacuum reactor is respectively connected to the intermediate barrel, the concentrated liquid barrel and the condenser, and a heat exchange base is installed on the vacuum reactor; the stirring assembly includes a spiral scraper and a reducer, the spiral scraper is rotatably installed inside the vacuum reactor, and the reducer is installed outside the vacuum reactor and is drivingly connected to the spiral scraper; the condenser can inlet and outlet cooling water, and a drain pipe is also installed on the condenser; When the high-temperature steam enters the heat exchange base, it exchanges heat with the NMP liquid in the vacuum reactor, so that the water in the NMP liquid evaporates to form secondary steam, and the secondary steam enters the condenser and condenses to form distilled water, which is discharged through the drain pipe, while the high-temperature steam that loses heat condenses to form water and is discharged from the heat exchange base.

4. A NMP wastewater low temperature recovery system according to claim 3, characterized in that, Also includes a first suction unit and a second suction unit; The first suction unit includes a first water tank, a first centrifugal pump and a first ejector; the first water tank can be used to take in and out cooling water, and the first water tank is equipped with a first conduit located above the liquid surface and a second conduit located below the liquid surface, the first conduit is equipped with a first clean water pipe connected to the outside, and the second conduit is equipped with a first ball valve; the first centrifugal pump is connected to the first conduit and the second conduit, and the first ejector is connected to the first conduit and the water diversion pipe; The second suction unit includes a second water tank, a second centrifugal pump and a second ejector; the second water tank can be used to take in and out cooling water, and the second water tank is equipped with a third conduit located above the liquid surface and a fourth conduit located below the liquid surface, the third conduit is equipped with a second clean water pipe connected to the outside, and the fourth conduit is equipped with a second ball valve; the second centrifugal pump is connected to the third conduit and the fourth conduit, and the second ejector is connected to the third conduit and the drain pipe.

5. A NMP wastewater low temperature recovery system according to claim 3, characterized in that, The low-temperature scraper evaporation unit also includes a filter tank, which is connected to the vacuum reactor and the condenser, and is equipped with a defoamer and a sensing component; the filter tank is used to filter out impurities in the secondary steam, and the defoamer is used to eliminate bubbles in the secondary steam; the sensing component includes a temperature sensor for detecting the air temperature of the secondary steam, a pressure sensor for detecting the air pressure of the secondary steam, and a foam sensor for detecting the amount of foam in the secondary steam.

6. A NMP wastewater low temperature recovery system according to claim 3, characterized in that, The low-temperature scraper evaporation unit further includes a drainage tank connected to the heat exchange base for storing and discharging water formed by condensation of steam.

7. A NMP wastewater low temperature recovery system according to claim 3, characterized in that, The filtering unit adopts a bag filter or is replaced by the low-temperature scraper evaporation unit.

8. A method for recovering NMP wastewater at low temperature, applied to the NMP wastewater at low temperature recovery system according to claim 1, characterized in that: The following steps are involved: S1: collecting NMP wastewater with a concentration of 25% through the raw material barrel; S2: Discharge the NMP wastewater in the raw material barrel into the low-temperature heat pump evaporation unit, heat the NMP wastewater at a temperature of 30 to 40° C. under a vacuum degree of -0.093 to -0.098 MPa, so that the water in the NMP wastewater is evaporated and separated to form secondary steam, and the distilled water formed by the condensation of the secondary steam is collected separately, and the retained NMP wastewater is purified to an NMP liquid with a concentration of 80%; S3: collecting NMP liquid with a concentration of 80% through the intermediate barrel; S4: discharging the NMP liquid in the intermediate barrel into the low-temperature scraper evaporation unit, heating the NMP liquid at a temperature of 45 to 48° C. under a vacuum degree of -0.093 to -0.098 MPa, so that the water in the NMP liquid continues to evaporate and separate to form secondary steam, and the distilled water formed by the condensation of the secondary steam is collected separately, and the remaining NMP liquid is purified to a concentration of 99.9% NMP liquid; S5: collecting NMP liquid with a concentration of 99.9% through the concentrated liquid barrel; S6: Discharge the NMP liquid in the concentrate barrel into the filtration unit to filter out impurities in the NMP liquid, and finally discharge it into the product pool.

9. A method for recovering NMP wastewater at low temperature, applied to the NMP wastewater at low temperature recovery system according to claim 3, characterized in that: The following steps are involved: S1: collecting NMP wastewater with a concentration of 25% through the raw material barrel, and evacuating the vacuum distillation kettle to a vacuum degree of -0.093 to -0.098 MPa; S2: The NMP wastewater in the raw material barrel is discharged into the vacuum distillation kettle, and liquid refrigerant is added to the compressor. The high-temperature and high-pressure gaseous refrigerant generated by the compressor passes through the heat exchange tube and exchanges heat with the NMP wastewater in the vacuum distillation kettle, so that the water in the NMP wastewater evaporates at a low temperature of 30 to 40°C to form secondary steam. The high-temperature and high-pressure gaseous refrigerant at the heat exchange tube passes through the condenser and the expansion valve to form a low-temperature and high-pressure gaseous refrigerant. The low-temperature and high-pressure gaseous refrigerant enters the evaporator and exchanges heat with the secondary steam entering the evaporator. The secondary steam condenses to form distilled water and is discharged through the water diversion pipe. The low-temperature and high-pressure gaseous refrigerant condenses to form a low-temperature and low-pressure gaseous refrigerant that enters the compressor for reuse, and the NMP wastewater retained in the vacuum distillation kettle is purified to an NMP liquid with a concentration of 80%; S3: collecting NMP liquid with a concentration of 80% through the intermediate barrel, and evacuating the vacuum reactor to a vacuum degree of -0.093 to -0.098 MPa; S4: draining the NMP liquid in the intermediate barrel into the vacuum reactor, starting the reducer to drive the spiral scraper to rotate and stir the NMP liquid, and then delivering high-temperature steam to the heat exchange base. The high-temperature steam exchanges heat with the NMP liquid, so that the water in the NMP liquid evaporates at a temperature of 45 to 48° C. to form secondary steam, which enters the condenser and condenses to form distilled water and is discharged through the drain pipe. The steam in the heat exchange base loses heat and condenses to form water and is discharged, while the NMP liquid remaining in the vacuum reactor is purified to a concentration of 99.9% NMP liquid; S5: collecting NMP liquid with a concentration of 99.9% through the concentrated liquid barrel; S6: Discharge the NMP liquid in the concentrate barrel into the filtration unit to filter out impurities in the NMP liquid, and finally discharge it into the product pool.

10. A method for recovering NMP wastewater at low temperature, applied to the NMP wastewater at low temperature recovery system according to claim 4, characterized in that: The following steps are involved: S1: collecting NMP wastewater with a concentration of 25% through the raw material barrel, opening the first ball valve and starting the first centrifugal pump, so that the first ejector generates negative pressure. Since the first ejector, the water diversion pipe, the evaporator and the vacuum distillation kettle are connected to each other, the air in the vacuum distillation kettle can be extracted under the action of negative pressure. After the vacuum distillation kettle is vacuumed, the first ball valve is closed, and the vacuum degree is -0.093 to -0.098 MPa; S2: The NMP wastewater in the raw material barrel is discharged into the vacuum distillation kettle, and liquid refrigerant is added to the compressor. The high-temperature and high-pressure gaseous refrigerant generated by the compressor passes through the heat exchange tube and exchanges heat with the NMP wastewater in the vacuum distillation kettle, so that the water in the NMP wastewater evaporates at a temperature of 30 to 40°C to form secondary steam. The high-temperature and high-pressure gaseous refrigerant at the heat exchange tube passes through the condenser and the expansion valve to form a low-temperature and high-pressure gaseous refrigerant. The low-temperature and high-pressure gaseous refrigerant enters the evaporator and exchanges heat with the secondary steam entering the evaporator. The distilled water formed by the condensation of the secondary steam flows into the first ejector and is discharged from the first water purification pipe. The low-temperature and high-pressure gaseous refrigerant condenses to form a low-temperature and low-pressure gaseous refrigerant that enters the compressor for reuse, and the NMP wastewater retained in the vacuum distillation kettle is purified to an NMP liquid with a concentration of 80%; S3: collecting NMP liquid with a concentration of 80% through the intermediate barrel, opening the second ball valve and starting the second centrifugal pump, so that the second ejector generates negative pressure. Since the second ejector, the drain pipe, the condenser and the vacuum reactor are connected to each other, the air in the vacuum reactor can be extracted under the action of negative pressure. After the vacuum reactor is vacuumed, the second ball valve is closed, and the vacuum degree is -0.093 to -0.098 MPa; S4: draining the NMP liquid in the middle barrel into the vacuum reactor, starting the reducer to drive the spiral scraper to rotate and stir the NMP liquid, and then delivering high-temperature steam to the heat exchange base. The high-temperature steam exchanges heat with the NMP liquid, so that the water in the NMP liquid evaporates at a low temperature of 45-48° C. to form secondary steam, and the secondary steam enters the condenser to condense to form distilled water. The formed distilled water flows into the second ejector and is discharged from the second water purification pipe. The steam in the heat exchange base loses heat and condenses to form water and is discharged, and the NMP liquid remaining in the vacuum reactor is purified to a concentration of 99.9% NMP liquid; S5: collecting NMP liquid with a concentration of 99.9% through the concentrated liquid barrel; S6: Discharge the NMP liquid in the concentrate barrel into the filtration unit to filter out impurities in the NMP liquid, and finally discharge it into the product pool.

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