Nmp wastewater low-temperature recovery system and method thereof

Abstract

A low-temperature recovery system for NMP wastewater and a method thereof, the recovery system comprising 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 filtration unit; the low-temperature heat pump evaporation unit is connected with the raw material barrel and the intermediate barrel, NMP wastewater is evaporated and separated after entering the low-temperature heat pump evaporation unit from the raw material barrel, distilled water formed by condensation of steam is collected separately, and NMP wastewater is purified to NMP liquid with a concentration of 80%; the low-temperature scraper evaporation unit is connected with the intermediate barrel and the concentrated liquid barrel, NMP liquid with a concentration of 80% is evaporated and separated after entering the low-temperature scraper evaporation unit from the intermediate barrel, distilled water formed by condensation of steam is collected separately, and the concentration of NMP liquid is purified to 99.9% and discharged into the concentrated liquid barrel; the filtration unit is connected with the concentrated liquid barrel and the product pool, NMP liquid with a concentration of 99.9% is filtered to remove impurities after entering the filtration unit from the concentrated liquid barrel, and is finally discharged into the product pool; the recovery method is applied to the recovery system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of NMP wastewater treatment, and particularly relates to an NMP wastewater low-temperature recovery system and a method thereof. BACKGROUND

[0002] N-methyl pyrrolidone (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 formed by active substances such as lithium compounds, binders such as polyvinylidene fluoride, and NMP as a solvent are coated on a substrate, and the electrode is manufactured by firing the coated substrate.

[0003] In the electrode production process, the NMP solvent used is constantly volatilized. If the NMP waste gas is directly discharged into the environment without recovery treatment, it will not only cause environmental pollution, but also cause great waste of resources. Therefore, in the prior art, the volatilized NMP gas is first made into NMP wastewater by adsorption method, and then the NMP liquid is recovered by distillation tower purification technology.

[0004] However, the NMP liquid recovered by the distillation tower purification technology has low purity. In order to obtain high-concentration NMP liquid, multiple distillation towers and NMP storage tanks are usually combined for use, which increases the overall land occupation and total energy consumption, resulting in high use cost. SUMMARY

[0005] Technical problems solved

[0006] The application provides an NMP wastewater low-temperature recovery system and a method thereof, which can improve the purity of NMP liquid recovery while reducing the total equipment quantity, thereby reducing the overall land occupation and energy consumption.

[0007] Technical scheme

[0008] To achieve the above object, the application provides the following technical scheme:

[0009] The application discloses a low-temperature recovery system for NMP wastewater, which 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 with the raw material barrel and the intermediate barrel; NMP wastewater is evaporated and separated after entering the low-temperature heat pump evaporation unit from the raw material barrel; distilled water formed by condensation of steam is collected separately, and NMP wastewater is purified to NMP liquid with a concentration of 80%; the low-temperature scraper evaporation unit is connected with the intermediate barrel and the concentrated liquid barrel; NMP liquid with a concentration of 80% is evaporated and separated after entering the low-temperature scraper evaporation unit from the intermediate barrel; distilled water formed by condensation of steam 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 with the concentrated liquid barrel and the product pool; NMP liquid with a concentration of 99.9% is filtered to remove impurities after entering the filtering unit from the concentrated liquid barrel, and is finally discharged into the product pool.

[0010] Preferably, the low-temperature heat pump evaporation unit comprises a vacuum distillation kettle, a compressor, a heat exchange pipe, a condenser and an evaporator; the vacuum distillation kettle is connected with the raw material barrel, the intermediate barrel and the evaporator respectively; the evaporator is directly connected with the front end of the compressor and connected with the tail end of the condenser through an expansion valve; the heat exchange pipe is installed in the vacuum distillation kettle and connected with the tail end of the compressor and the front end of the condenser; a water inlet pipe is further installed on the evaporator; wherein the compressor generates high-temperature and high-pressure gaseous refrigerant after adding liquid refrigerant; the high-temperature and high-pressure gaseous refrigerant exchanges heat with NMP wastewater in the vacuum distillation kettle when passing through the heat exchange pipe, so that water in the NMP wastewater is evaporated at low temperature and forms secondary steam; the high-temperature and high-pressure gaseous refrigerant passing through the heat exchange pipe forms 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, and the low-temperature and high-pressure gaseous refrigerant is condensed into low-temperature and low-pressure liquid refrigerant and enters the compressor for continuous use.

[0011] Preferably, the low-temperature scraped-surface evaporation unit comprises a vacuum reactor, a stirring assembly and a condenser tube; the vacuum reactor is connected to the intermediate barrel, the concentrated liquid barrel and the condenser tube respectively, and a heat exchange base is installed on the vacuum reactor; the stirring assembly comprises a spiral scraper and a speed reducer, the spiral scraper is rotatably installed inside the vacuum reactor, and the speed reducer is installed outside the vacuum reactor and is drivingly connected to the spiral scraper; the condenser tube can be supplied with cooling water, and a drain pipe is also installed on the condenser tube; 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, the secondary steam enters the condenser tube to condense to form distilled water, the distilled water is discharged through the drain pipe, and the high-temperature steam that loses heat is condensed to form water and is discharged from the heat exchange base.

[0012] Preferably, the low-temperature scraped-surface evaporation unit further comprises a first suction unit and a second suction unit; the first suction unit comprises a first water tank, a first centrifugal pump and a first jet; the first water tank can be supplied with cooling water, and a first conduit above the liquid surface and a second conduit below the liquid surface are installed on the first water tank, a first clean water pipe connected to the outside world is installed on the first conduit, and a first ball valve is installed on the second conduit; the first centrifugal pump is connected to the first conduit and the second conduit, and the first jet is connected to the first conduit and the water pipe; the second suction unit comprises a second water tank, a second centrifugal pump and a second jet; the second water tank can be supplied with cooling water, and a third conduit above the liquid surface and a fourth conduit below the liquid surface are installed on the second water tank, a second clean water pipe connected to the outside world is installed on the third conduit, and a second ball valve is installed on the fourth conduit; the second centrifugal pump is connected to the third conduit and the fourth conduit, and the second jet is connected to the third conduit and the drain pipe.

[0013] Preferably, the low-temperature scraped-surface evaporation unit further comprises a filter tank, the filter tank is connected to the vacuum reactor and the condenser tube, and a defoamer and a sensing assembly are installed on the filter tank; the filter tank is used to filter impurities in the secondary steam, the defoamer is used to eliminate bubbles in the secondary steam, and the sensing assembly comprises a temperature sensor for detecting the temperature of the secondary steam, a pressure sensor for detecting the pressure of the secondary steam, and a foam sensor for detecting the amount of foam in the secondary steam.

[0014] Preferably, the low-temperature scraped-surface evaporation unit further comprises a drain tank, the drain tank is connected to the heat exchange base for storing and discharging water formed by condensation of steam.

[0015] Preferably, the filter unit adopts a bag filter or is replaced by the low-temperature scraped-surface evaporation unit.

[0016] A low-temperature recovery method of NMP wastewater, applied to the low-temperature recovery system of NMP wastewater, comprising the following steps:

[0017] 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 jet device generates negative pressure, and due to the mutual connection of the first jet device, the water inlet pipe, the evaporator and the vacuum distillation kettle, the air in the vacuum distillation kettle can be extracted under the action of negative pressure, and the first ball valve is closed after the vacuum inside the vacuum distillation kettle, and the vacuum degree is-0.093 to-0.098 MPa;

[0018] S2: Discharging the NMP wastewater in the raw material barrel into the vacuum distillation kettle, adding liquid refrigerant to the compressor, and the high-temperature and high-pressure gaseous refrigerant generated by the compressor passes through the heat exchange pipe and exchanges heat with the NMP wastewater in the vacuum distillation kettle, so that the water in the NMP wastewater is low-temperature evaporated to form secondary steam at a temperature of 30-40℃, the high-temperature and high-pressure gaseous refrigerant at the heat exchange pipe forms low-temperature and high-pressure gaseous refrigerant after passing through the condenser and the expansion valve, the low-temperature and high-pressure gaseous refrigerant enters the evaporator and exchanges heat with the secondary steam entering the evaporator, the distilled water condensed by the secondary steam flows into the first jet device and is discharged from the first water pipe, and the low-temperature and high-pressure gaseous refrigerant is condensed into low-temperature and low-pressure gaseous refrigerant and enters the compressor for reuse, and the NMP wastewater remaining in the vacuum distillation kettle is purified to NMP liquid with a concentration of 80%;

[0019] 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 jet device generates negative pressure, and due to the mutual connection of the second jet device, the drain pipe, the condensing pipe and the vacuum reaction kettle, the air in the vacuum reaction kettle can be extracted under the action of negative pressure, and the second ball valve is closed after the vacuum inside the vacuum reaction kettle, and the vacuum degree is-0.093 to-0.098 MPa;

[0020] S4: Discharging the NMP liquid in the intermediate barrel into the vacuum reaction kettle, starting the speed reducer to drive the spiral scraper to rotate and stir the NMP liquid, and feeding high-temperature steam to the heat exchange base, and the high-temperature steam exchanges heat with the NMP liquid, so that the water in the NMP liquid is low-temperature evaporated to form secondary steam at a temperature of 45-48℃, the secondary steam enters the condensing pipe and is condensed to form distilled water, the distilled water flows into the second jet device and is discharged from the second water pipe, the steam in the heat exchange base loses heat and is condensed to form water and is discharged, and the NMP liquid remaining in the vacuum reaction kettle is purified to NMP liquid with a concentration of 99.9%;

[0021] S5: Collecting NMP liquid with a concentration of 99.9% through the concentrated liquid barrel;

[0022] S6: Discharging the NMP liquid in the concentrated liquid barrel into the filtering unit to filter out the impurities of the NMP liquid, and finally discharging into the product pool.

[0023] (III) Beneficial effects

[0024] The NMP wastewater low-temperature recovery system and method provided by the application can improve the recovery purity of NMP liquid through only a low-temperature heat pump evaporation unit and a low-temperature scraper evaporation unit, without the need to set multiple groups of distillation towers for combined use, so that the total equipment amount can be effectively reduced, the pipe length between devices can be shortened, the overall land occupation can be reduced, and the overall energy consumption can be reduced; meanwhile, since the whole recovery process is carried out at low temperature, the operation safety can also be effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings are included to provide a further understanding of the application, and constitute a part of the specification, illustrate the application, and are used to explain the application together with the embodiments of the application, and do not constitute a limitation on the application, and in the drawings:

[0026] Figure 1 The use flow of the application is shown Figure 1 ;

[0027] Figure 2 The use flow of the application is shown Figure 2 ;

[0028] Figure 3 The structure schematic diagram of the low-temperature heat pump evaporation unit of the application is shown

[0029] Figure 4 The enlargement of part of the structure is shown Figure 3 ; Figure 1 ;

[0030] Figure 5 The enlargement of part of the structure is shown Figure 3 ; Figure 2

[0031] Figure 6 The structure schematic diagram of the low-temperature scraper evaporation unit of the application is shown

[0032] Figure 7 The enlargement of part of the structure is shown Figure 6 ; Figure 1

[0033] The enlargement of part of the structure is shown Figure 8 ; Figure 6 The enlargement of part of the structure is shown Figure 2 ; ​

[0034] Figure 9 shown Figure 6 enlarged view of a portion of the structure Figure 3 ;

[0035] Figure 10 shown Figures 1-9 annotated view of the components in the figure.

[0036] In the figure: 1 low-temperature heat pump evaporation unit, 11 vacuum distillation kettle, 12 compressor, 13 heat exchange pipe, 14 condenser, 15 evaporator, 150 water pipe, 16 expansion valve, 2 low-temperature scraper evaporation unit, 21 vacuum reaction kettle, 22 stirring assembly, 221 spiral scraper, 222 speed reducer, 23 condensing pipe, 230 drain pipe, 24 heat exchange base, 25 filter tank, 251 defoamer, 252 sensing assembly, 2521 temperature sensor, 2522 pressure sensor, 2523 foam sensor, 26 drain 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 jet device, 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 jet device. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0038] Reference is made to the accompanying Figure 1 - the accompanying Figure 10 , an NMP wastewater low-temperature recovery system, comprising a raw material barrel, an intermediate barrel, a concentrated liquid barrel, a product pool, a low-temperature heat pump evaporation unit 1, a low-temperature scraper evaporation unit 2, and a filtering unit;

[0039] 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 is evaporated and separated. The distilled water formed by condensation of the steam is collected separately, and the NMP wastewater is purified to an NMP liquid with a concentration of 80%;

[0040] The low-temperature scraper evaporation unit 2 is connected to the intermediate barrel and the concentrated liquid barrel. The NMP liquid with a concentration of 80% enters the low-temperature scraper evaporation unit 2 from the intermediate barrel and is evaporated and separated. The distilled water formed by condensation of the steam is collected separately, and the concentration of the NMP liquid is purified to 99.9% and discharged into the concentrated liquid barrel;

[0041] The filtering unit is connected with the concentrated liquid barrel and the product pool, and the NMP liquid with a concentration of 99.9% is filtered to remove impurities in the filtering unit and finally discharged into the product pool.

[0042] Specifically, compared with the prior art, the present scheme can improve the recovery purity of NMP liquid by only 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, so that the total equipment amount can be effectively reduced, the pipe length between devices can be shortened, the overall land occupation can be reduced, and the overall energy consumption can be reduced; at the same time, since the whole recovery process is carried out at low temperature, the operation safety can also be effectively improved.

[0043] It should be noted that the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2 can be standard or non-standard equipment, the standard equipment can be directly purchased on the market and belongs to the existing products, but there is no related technology for combining the two and applying them to NMP liquid purification and recovery; the non-standard equipment increases 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 application, the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2 preferentially use non-standard equipment, and the specific conditions are as follows:

[0044] Referring to the drawings Figure 1 - the drawings Figure 9 The low-temperature heat pump evaporation unit 1 comprises a vacuum distillation kettle 11, a compressor 12, a heat exchange pipe 13, a condenser 14 and an evaporator 15; the vacuum distillation kettle 11 is connected with the raw material barrel, the intermediate barrel and the evaporator 15 respectively; the evaporator 15 is directly connected with the front end of the compressor 12 and connected with the tail end of the condenser 14 through an expansion valve 16 respectively, the heat exchange pipe 13 is installed in the vacuum distillation kettle 11 and connected with the tail end of the compressor 12 and the front end of the condenser 14; and a water inlet pipe 150 is further installed on the evaporator 15;

[0045] The compressor 12 generates high-temperature and high-pressure gaseous refrigerant after adding liquid refrigerant, the high-temperature and high-pressure gaseous refrigerant exchanges heat with the NMP waste water in the vacuum distillation kettle 11 when passing through the heat exchange pipe 13, so that the water in the NMP waste water is evaporated at low temperature and forms secondary steam, the high-temperature and high-pressure gaseous refrigerant passing through the heat exchange pipe 13 forms 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, and the low-temperature and high-pressure gaseous refrigerant is condensed into low-temperature and low-pressure liquid refrigerant and enters the compressor 12 for continuous use.

[0046] Specifically, in the existing rectification tower purification technology, the NMP waste water needs to be continuously filled to exchange heat, not only the heat exchange efficiency is low, but also the heat enthalpy required in the whole process is very high, resulting in high overall energy consumption.

[0047] In the present application, the gaseous refrigerant generated by the compressor 12 is used to exchange heat with the NMP wastewater, so that the moisture in the NMP wastewater is evaporated into secondary steam at low temperature, and the gaseous refrigerant can be returned to the compressor 12 as liquid refrigerant after exchanging heat with the secondary steam, realizing the reuse and circulation of the heat exchange materials, thereby effectively improving the heat exchange efficiency and reducing the energy consumption.

[0048] Through actual test, if the NMP wastewater amount transported by the raw material barrel to the vacuum distillation kettle 11 is 8T / D (ton / 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 the low-temperature heat pump evaporation unit 1 is 45KW, the energy consumption is 160KW-180KW / m³, and 5.5T / D of moisture is evaporated, for specific data, please refer to Table 1.

[0049] Table 1

[0050] Referring to the drawings Figure 1 - the drawings Figure 9 The low-temperature scraped blade evaporation unit 2 includes a vacuum reaction kettle 21, a stirring assembly 22 and a condenser pipe 23; the vacuum reaction kettle 21 is connected to the intermediate barrel, the concentrated liquid barrel and the condenser pipe 23 respectively, and a heat exchange base 24 is installed on the vacuum reaction kettle 21; the stirring assembly 22 includes a spiral scraper 221 and a speed reducer 222, the spiral scraper 221 is rotatably installed inside the vacuum reaction kettle 21, and the speed reducer 222 is installed outside the vacuum reaction kettle 21 and is drivingly connected with the spiral scraper 221; the condenser pipe 23 can enter and exit cooling water, and a drain pipe 230 is also installed on the condenser pipe 23; wherein, when the high-temperature steam enters the heat exchange base 24, it exchanges heat with the NMP liquid in the vacuum reaction kettle 21, so that the moisture in the NMP liquid evaporates to form secondary steam, the secondary steam enters the condenser pipe 23 to condense to form distilled water, and the distilled water is discharged through the drain pipe 230, while the high-temperature steam loses heat and condenses to form water which is discharged from the heat exchange base 24. Since the high-temperature steam does not contact the mixed secondary steam, the water condensed from the high-temperature steam can be directly recycled.

[0051] Specifically, in the present application, the NMP liquid with a concentration of 80% is stirred by the spiral scraper 221, so that it is uniformly dispersed, which is beneficial to the heat exchange between the moisture in the NMP liquid and the steam, and improves the heat exchange efficiency; at the same time, the moisture in the NMP liquid is evaporated to form secondary steam at low temperature in the heat exchange process, and the secondary steam directly exchanges heat with the cooling water which is continuously circulated in and out after entering the condenser pipe 23, so as to condense to form distilled water, and the energy consumption required in the whole process is very small.

[0052] Through actual test, if the NMP liquid amount delivered by the intermediate barrel to the vacuum reaction kettle 21 is 2.5 T / D (ton / day), and the vacuum degree of the vacuum reaction kettle 21 is -0.093 to -0.098 MPa, and the evaporation temperature is 45 to 48℃, then the total power of the low-temperature scraped blade evaporation unit 2 is 4.5 KW, and 0.5 T / D of moisture is evaporated, and the specific data can be referred to Table 2.

[0053] Table 2

[0054] In summary, referring to Table 1 and Table 2, the low-temperature heat pump evaporation unit 1 and the low-temperature scraped blade evaporation unit 2 process 8 T / D of NMP wastewater liquid, and the total power only needs 49.5 KW, and according to the electricity price of 0.8 RMB / kW.H, the total cost is 39.6 RMB / T; the circulating cooling water needs 30 T / H, and the loss rate is 1%, and according to the water price of 3 RMB / T, the total cost is 2.7 RMB / T; the total cost is 42.3 RMB / T, and it has very high economic benefits.

[0055] On the other hand, the low-temperature heat pump evaporation unit 1 and the low-temperature scraped blade evaporation unit 2 are complete sets of devices, and can be directly connected to the site to use electricity, without the need for engineering installation and debugging, so that the installation cost can be reduced; and the low-temperature heat pump evaporation unit 1 and the low-temperature scraped blade evaporation unit 2 are compact in structure, and the maximum height is not more than 3.8 meters, so that the problem of limited land space is solved.

[0056] Referring to the drawings Figure 1 - the drawings Figure 9, considering that in the prior art, a separate vacuumizing device is usually provided to vacuumize the distillation column, and a separate pump body is used to transport NMP wastewater between the distillation columns each time of rectification, which results in large floor area and high cost, in order to solve the problem, the first suction unit 3 and the second suction unit 4 are further included in the application; the first suction unit 3 includes a first water tank 31, a first centrifugal pump 32 and a first jet device 33; the first water tank 31 can be in and out of cooling water, and a first conduit 311 above the liquid level and a second conduit 312 below the liquid level are installed on the first water tank 31, a first clean water pipe 313 connected to the outside world is installed on the first conduit 311, and a first ball valve 3120 is installed on the second conduit 312; the first centrifugal pump 32 is connected to the first conduit 311 and the second conduit 312, and the first jet device 33 is connected to the first conduit 311 and the water inlet pipe 150; the second suction unit 4 includes a second water tank 41, a second centrifugal pump 42 and a second jet device 43; the second water tank 41 can be in and out of cooling water, and a third conduit 411 above the liquid level and a fourth conduit 412 below the liquid level are installed on the second water tank 41, a second clean water pipe 413 connected to the outside world is installed on the third conduit 411, and a second ball valve 4120 is installed on the fourth conduit 412; the second centrifugal pump 42 is connected to the third conduit 411 and the fourth conduit 412, and the second jet device 43 is connected to the third conduit 411 and the drain pipe 230.

[0057] Specifically, when vacuumizing, the first ball valve 3120 is opened and the first centrifugal pump 32 is started, so that the first jet device 33 generates negative pressure, since the first jet device 33, the water inlet 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; when discharging the distilled water in the evaporator 15, the first ball valve 3120 is closed to cut off the connection between the first centrifugal pump 32 and the first water tank 31, and the negative pressure generated by the cooperation of the first centrifugal pump 32 and the first jet device 33 can smoothly discharge the distilled water in the evaporator 15 through the water inlet pipe 150.

[0058] Similarly, when vacuumizing, the second ball valve 4120 is opened and the second centrifugal pump 42 is started, so that the second jet device 43 generates negative pressure, and since the second jet device 43, the drain pipe 230, the condensing pipe 23 and the vacuum reaction kettle 21 are connected with each other, air in the vacuum reaction kettle 21 can be pumped out under the action of negative pressure; when the distilled water in the condensing pipe 23 is discharged, the second ball valve 4120 is closed to cut off the connection between the second centrifugal pump 42 and the second water tank 41, and the negative pressure generated by the cooperation of the second centrifugal pump 42 and the second jet device 43 can smoothly discharge the distilled water in the condensing pipe 23 through the drain pipe 230.

[0059] In summary, the first suction unit 3 and the second suction unit 4 are integrated with vacuumizing function and water discharging function, so the overall volume is small, the total amount of equipment used is less, and the occupied space can be further reduced; in addition, since the vacuum distillation kettle 11 and the vacuum reaction kettle 21 can rely on the negative pressure self-suction mode to correspondingly suck the NMP wastewater in the raw material barrel and the NMP liquid in the intermediate barrel, an additional pump body as a power source is not needed, and the overall energy consumption can be effectively reduced.

[0060] Referring to the accompanying drawings Figure 1 - the accompanying drawings Figure 9 In actual operation, impurities and bubbles may still be mixed in the secondary steam discharged from the vacuum reaction kettle 21, in order to solve this problem, the low-temperature scraper evaporation unit 2 further comprises a filter tank 25, the filter tank 25 is connected with the vacuum reaction kettle 21 and the condensing pipe 23, and a defoaming device 251 and a sensing assembly 252 are installed on the filter tank 25; the sensing assembly 252 comprises a temperature sensor 2521, a pressure sensor 2522 and a foam sensor 2523.

[0061] Specifically, the filter tank 25 is used to filter impurities in the secondary steam, the defoaming device 251 is used to eliminate bubbles in the secondary steam, the temperature sensor 2521 is used to detect the air 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-mentioned structures are used in cooperation, which can improve the purity of the secondary steam entering the condenser 14, so that the quality of the distilled water condensed finally is improved.

[0062] Referring to the accompanying drawings Figure 1 - the accompanying drawings Figure 9 The low-temperature scraper evaporation unit 2 further comprises a drain tank 26, and the drain tank 26 is connected with the heat exchange base 24, so as to store and discharge the water formed by steam condensation.

[0063] Referring to the accompanying drawings Figure 1 - the accompanying drawings Figure 9 The filter unit is a bag filter or is replaced by the low-temperature scraper evaporation unit 2.

[0064] Specifically, when the filter unit adopts a cloth bag filter, some special components dissolved in the NMP liquid cannot be effectively filtered out, and the service life of the cloth bag filter is relatively short.

[0065] When the filter unit adopts the low-temperature scraper evaporation unit 2, the special components in the NMP liquid can be evaporated to the maximum extent, impurities can be effectively filtered out through multiple evaporation, the purity of the NMP liquid is improved, and the service life of the low-temperature scraper evaporation unit 2 is relatively long.

[0066] Referring to the accompanying drawings Figure 1 -Appendix Figure 9 A low-temperature recovery method of NMP wastewater is applied to the above-mentioned low-temperature recovery system of NMP wastewater, has multiple embodiments according to different situations, and is specifically as follows for the convenience of understanding the present application:

[0067] Embodiment one

[0068] Without specifically limiting the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2, the low-temperature recovery method of NMP wastewater includes the following steps:

[0069] S1: Collecting NMP wastewater with a concentration of 25% through a raw material barrel;

[0070] S2: Discharging the NMP wastewater in the raw material barrel into the low-temperature heat pump evaporation unit 1, heating the NMP wastewater at a temperature of 30-40°C under a vacuum degree of -0.093 to -0.098 MPa, evaporating and separating the water in the NMP wastewater to form secondary steam, and collecting the distilled water formed by condensing the secondary steam, while the remaining NMP wastewater is purified to NMP liquid with a concentration of 80%;

[0071] S3: Collecting NMP liquid with a concentration of 80% through an intermediate barrel;

[0072] S4: Discharging the NMP liquid in the intermediate barrel into the low-temperature scraper evaporation unit 2, heating the NMP liquid at a temperature of 45-48°C under a vacuum degree of -0.093 to -0.098 MPa, continuing to evaporate and separate the water in the NMP liquid to form secondary steam, and collecting the distilled water formed by condensing the secondary steam, while the remaining NMP liquid is purified to NMP liquid with a concentration of 99.9%;

[0073] S5: Collecting NMP liquid with a concentration of 99.9% through a concentrated liquid barrel;

[0074] S6: Discharging the NMP liquid in the concentrated liquid barrel into the filter unit to filter out impurities in the NMP liquid, and finally discharging into a product pool.

[0075] Specifically, in the first embodiment, the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2 are not limited, and under the premise of ensuring the processing conditions, the manufacturer can select the corresponding components with the corresponding functions to assemble the corresponding low-temperature heat pump evaporation unit 1 and low-temperature scraper evaporation unit 2; and compared with the prior art, the present scheme 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 equipment quantity, reduce the overall land occupation space and reduce the overall energy consumption.

[0076] The second embodiment

[0077] In the case of specifically limiting the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2, but not limiting the first suction unit 3 and the second suction unit 4, the NMP wastewater low-temperature recovery method comprises the following steps:

[0078] S1: Collecting NMP wastewater with a concentration of 25% through a raw material barrel, and vacuumizing the vacuum distillation kettle 11, the vacuum degree being -0.093 to -0.098 MPa;

[0079] S2: Discharging the NMP wastewater in the raw material barrel into the vacuum distillation kettle 11, adding liquid refrigerant to the compressor 12, the high-temperature and high-pressure gaseous refrigerant generated by the compressor 12 passing through the heat exchange pipe 13 and exchanging heat with the NMP wastewater in the vacuum distillation kettle 11, so that the water in the NMP wastewater is low-temperature evaporated to form secondary steam at a temperature of 30 to 40°C, the high-temperature and high-pressure gaseous refrigerant at the heat exchange pipe 13 forms low-temperature and high-pressure gaseous refrigerant after passing through the condenser 14 and the expansion valve 16, 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 is condensed to form distilled water and is discharged through the water guide pipe 150, the low-temperature and high-pressure gaseous refrigerant is condensed to form low-temperature and low-pressure gaseous refrigerant into the compressor 12 for reuse, and the NMP wastewater remaining in the vacuum distillation kettle 11 is purified to NMP liquid with a concentration of 80%;

[0080] S3: Collecting NMP liquid with a concentration of 80% through an intermediate barrel, and vacuumizing the vacuum reaction kettle 21, the vacuum degree being -0.093 to -0.098 MPa;

[0081] S4: The NMP liquid in the intermediate barrel is discharged into the vacuum reaction kettle 21, and an appropriate amount of scale inhibitor can be added. The reducer 222 is started to drive the spiral scraper 221 to rotate and stir the NMP liquid. High-temperature steam is transported to the heat exchange base 24. The high-temperature steam exchanges heat with the NMP liquid, causing the water in the NMP liquid to evaporate at a low temperature of 45-48°C to form secondary steam. The secondary steam enters the condenser tube 23 and condenses to form distilled water, which is discharged through the drain pipe 230. The steam in the heat exchange base 24 loses heat and condenses to form water, which is discharged. The NMP liquid remaining in the vacuum reaction kettle 21 is purified to an NMP liquid with a concentration of 99.9%;

[0082] S5: The NMP liquid with a concentration of 99.9% is collected in the concentrated liquid barrel;

[0083] S6: The NMP liquid in the concentrated liquid barrel is discharged into the filtration unit to remove impurities in the NMP liquid, and finally discharged into the product pool.

[0084] Specifically, in Example Two, the specific structural components of the low-temperature heat pump evaporation unit 1 and the low-temperature scraper evaporation unit 2 are defined. Example Two is essentially one of the optimal solutions of Example One, so the problems solved and the effects possessed are basically the same as those of Example One, which aims to ensure the purity of the recovered NMP liquid while reducing the total equipment quantity, thereby reducing the overall land occupation and reducing the overall energy consumption. In addition, the gaseous refrigerant in Example Two can be returned to the compressor 12 after heat exchange with the secondary steam for use as liquid refrigerant, realizing the reuse and circulation of heat exchange materials, thereby further reducing costs.

[0085] Example Three

[0086] In the specific definition of 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 NMP wastewater low-temperature recovery method includes the following steps:

[0087] S1: Collect NMP wastewater with a concentration of 25% in the raw material barrel. Open the first ball valve 3120 and start the first centrifugal pump 32. The first jet device 33 generates negative pressure. Since the first jet device 33, the water guide 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 vacuumized, the first ball valve 3120 is closed. The vacuum degree is -0.093 to -0.098 MPa;

[0088] S2: The NMP wastewater in the raw material barrel is discharged into the vacuum distillation kettle 11, 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 pipe 13 and exchanges heat with the NMP wastewater in the vacuum distillation kettle 11, so that the moisture in the NMP wastewater is evaporated at a low temperature to form secondary steam at a temperature of 30-40℃, the high-temperature and high-pressure gaseous refrigerant at the heat exchange pipe 13 forms low-temperature and high-pressure gaseous refrigerant after passing through the condenser 14 and the expansion valve 16, 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 flowing into the first jet device 33 and discharged from the first clean water pipe 313, and the low-temperature and high-pressure gaseous refrigerant condenses to form low-temperature and low-pressure gaseous refrigerant entering the compressor 12 for reuse, and the NMP wastewater remaining in the vacuum distillation kettle 11 is purified to NMP liquid with a concentration of 80%;

[0089] S3: The NMP liquid with a concentration of 80% is collected through the intermediate barrel, the second ball valve 4120 is opened and the second centrifugal pump 42 is started, so that the second jet device 43 generates negative pressure, and since the second jet device 43, the drain pipe 230, the condensing pipe 23 and the vacuum reaction kettle 21 are connected with each other, the air in the vacuum reaction kettle 21 can be extracted under the action of negative pressure, the second ball valve 4120 is closed after the vacuum reaction kettle 21 is vacuumized, and the vacuum degree is-0.093 to-0.098 MPa;

[0090] S4: The NMP liquid in the intermediate barrel is discharged into the vacuum reaction kettle 21, the reducer 222 is started to drive the spiral scraper 221 to rotate and stir the NMP liquid, high-temperature steam is supplied to the heat exchange base 24, the high-temperature steam exchanges heat with the NMP liquid, so that the moisture in the NMP liquid is evaporated at a low temperature to form secondary steam at a temperature of 45-48℃, the secondary steam enters the condensing pipe 23 to condense to form distilled water, the distilled water flows into the second jet device 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 reaction kettle 21 is purified to NMP liquid with a concentration of 99.9%;

[0091] S5: The NMP liquid with a concentration of 99.9% is collected through the concentrated liquid barrel;

[0092] S6: The NMP liquid in the concentrated liquid barrel is discharged into the filtration unit to filter out impurities in the NMP liquid, and finally discharged into the product pool.

[0093] Specifically, in the prior art, a separate vacuum pumping device is usually provided to pump the vacuum for each stage of the distillation column, which occupies a large floor space and is high in cost; in the third embodiment, the first and second pumping units 3 and 4 are added, and the first and second pumping units 3 and 4 are integrated with the drainage function and the vacuum pumping function, so the overall volume is small, the total amount of equipment used is small, the floor space can be reduced, and the overall energy consumption can be reduced; the remaining components are the same as those in the second embodiment, which will not be repeated here.

[0094] It should be noted that the vacuum reaction kettle or the vacuum distillation kettle is prone to fouling after long-term use, and a scale inhibitor can be added to the vacuum reaction kettle or the vacuum distillation kettle for cleaning after use.

[0095] It should be noted that although the embodiments of the present application have been shown and described, those skilled in the art can understand that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and spirits of the present application.

Claims

1. A low-temperature NMP wastewater recovery system, comprising a raw material tank, an intermediate tank, a concentrate tank, and a product tank, characterized in that, Also includes: The low-temperature heat pump evaporation unit connects the raw material tank and the intermediate tank. After NMP wastewater enters the low-temperature heat pump evaporation unit from the raw material tank, it is evaporated and separated. The distilled water formed by steam condensation is collected separately, while the NMP wastewater is purified to NMP liquid with a concentration of 80%. The low-temperature scraped evaporation unit connects the intermediate tank and the concentrate tank. NMP liquid with a concentration of 80% enters the low-temperature scraped evaporation unit from the intermediate tank and is evaporated and separated. The distilled water formed by the condensation of the steam is collected separately, while the concentration of the NMP liquid is purified to 99.9% and discharged into the concentrate tank. A filtration unit is connected to the concentrate tank and the product tank. NMP liquid with a concentration of 99.9% enters the filtration unit from the concentrate tank to remove impurities and is finally discharged into the product tank. The low-temperature heat pump evaporation unit includes a vacuum distillation kettle, a compressor, heat exchange tubes, a condenser, and an evaporator. The vacuum distillation kettle is connected to the raw material tank, the intermediate tank, and the evaporator. The evaporator is directly connected to the beginning of the compressor and connected to the end of the condenser via an expansion valve. The heat exchange tubes are installed inside the vacuum distillation kettle and connect the end of the compressor and the beginning of the condenser. A water inlet pipe is also installed on the evaporator. The low-temperature scraper evaporation unit includes a vacuum reactor, a stirring assembly, and a condenser tube. The vacuum reactor is connected to the intermediate tank, the concentrate tank, and the condenser tube, 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 driven by the spiral scraper. Cooling water can enter and exit the condenser tube, and a drain pipe is also installed on the condenser tube. The compressor generates high-temperature, high-pressure gaseous refrigerant after adding liquid refrigerant. This high-temperature, high-pressure gaseous refrigerant exchanges heat with NMP wastewater in the vacuum distillation vessel as it passes through the heat exchange tube, causing the water in the NMP wastewater to evaporate at low temperature and form secondary steam. The high-temperature, high-pressure gaseous refrigerant passing through the heat exchange tube forms low-temperature, high-pressure gaseous refrigerant under the action of the condenser and the expansion valve. This low-temperature, high-pressure gaseous refrigerant exchanges heat with the secondary steam entering the evaporator from the vacuum distillation vessel, causing the secondary steam to condense into distilled water and be discharged to the outside via the water inlet pipe. The low-temperature, high-pressure gaseous refrigerant then condenses into low-temperature, low-pressure liquid refrigerant and enters the compressor for continued use. When the high-temperature steam enters the heat exchange base, it exchanges heat with the NMP liquid in the vacuum reactor, causing the water in the NMP liquid to evaporate and form secondary steam. This secondary steam enters the condenser tube and condenses into distilled water, which is discharged via the drain pipe. The high-temperature steam, having lost heat, condenses into water and is discharged from the heat exchange base.

2. The NMP wastewater low-temperature recovery system according to claim 1, characterized in that, 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 receive and discharge cooling water, and a first conduit located above the liquid surface and a second conduit located below the liquid surface are installed on the first water tank. A first clean water pipe connected to the outside is installed on the first conduit, and a first ball valve is installed on the second conduit; the first centrifugal pump connects the first conduit and the second conduit, and the first ejector connects the first conduit and the water inlet pipe; The second suction unit includes a second water tank, a second centrifugal pump, and a second ejector; the second water tank can receive and discharge cooling water, and a third conduit located above the liquid surface and a fourth conduit located below the liquid surface are installed on the second water tank. A second clean water pipe connected to the outside is installed on the third conduit, and a second ball valve is installed on the fourth conduit; the second centrifugal pump connects to the third conduit and the fourth conduit, and the second ejector connects to the third conduit and the drain pipe.

3. The NMP wastewater low-temperature recovery system according to claim 1, characterized in that, The low-temperature scraped evaporation unit also includes a filter tank, which is connected to the vacuum reactor and the condenser tube. The filter tank 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 pressure of the secondary steam, and a foam sensor for detecting the amount of foam in the secondary steam.

4. The NMP wastewater low-temperature recovery system according to claim 1, characterized in that, The low-temperature scraper evaporation unit also includes a drain tank, which is connected to the heat exchange base for storing and discharging water formed by steam condensation.

5. The NMP wastewater low-temperature recovery system according to claim 1, characterized in that, The filtration unit can be a bag filter or replaced with the low-temperature scraper evaporation unit.

6. A method for low-temperature recovery of NMP wastewater, applied to the low-temperature recovery system for NMP wastewater as described in claim 1, characterized in that, Includes the following steps: S1: Collect NMP wastewater with a concentration of 25% through the raw material tank, and evacuate the vacuum distillation kettle to a vacuum degree of -0.093 to -0.098 MPa; S2: The NMP wastewater in the raw material tank is discharged into the vacuum distillation kettle. 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 30-40°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 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 inlet pipe. The low-temperature and high-pressure gaseous refrigerant condenses to form low-temperature and low-pressure gaseous refrigerant and enters the compressor for reuse. The NMP wastewater remaining in the vacuum distillation kettle is purified to NMP liquid with a concentration of 80%. S3: Collect 80% NMP liquid through the intermediate tank, and evacuate the vacuum reactor to a vacuum degree of -0.093 to -0.098 MPa; S4: The NMP liquid in the intermediate tank is discharged into the vacuum reactor. The reducer is started to drive the spiral scraper to rotate and stir the NMP liquid. High-temperature steam is then supplied to the heat exchange base. The high-temperature steam exchanges heat with the NMP liquid, causing the water in the NMP liquid to evaporate at a low temperature of 45-48°C to form secondary steam. The secondary steam enters the condenser tube and condenses to form distilled water, which is then discharged through the drain pipe. The steam in the heat exchange base loses heat and condenses to form water, which is then discharged. The NMP liquid remaining in the vacuum reactor is purified to a concentration of 99.9% NMP liquid. S5: Collect NMP liquid with a concentration of 99.9% through the concentrate tank; S6: The NMP liquid in the concentrate tank is discharged into the filtration unit to filter out NMP liquid impurities, and finally discharged into the product pool.

7. A method for low-temperature recovery of NMP wastewater, applied to the low-temperature recovery system for NMP wastewater as described in claim 2, characterized in that, Includes the following steps: S1: Collect 25% NMP wastewater through the raw material tank, open the first ball valve and start the first centrifugal pump to generate negative pressure in the first ejector. Since the first ejector, the water inlet pipe, the evaporator and the vacuum distillation kettle are interconnected, the air in the vacuum distillation kettle can be extracted under the action of negative pressure. After the vacuum distillation kettle is evacuated, close the first ball valve. The vacuum degree is -0.093 to -0.098 MPa. S2: The NMP wastewater in the raw material tank is discharged into the vacuum distillation kettle. 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 30-40°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 clean water pipe. The low-temperature and high-pressure gaseous refrigerant condenses to form a low-temperature and low-pressure gaseous refrigerant, which enters the compressor for reuse. The NMP wastewater remaining in the vacuum distillation kettle is purified to NMP liquid with a concentration of 80%. S3: Collect 80% NMP liquid through the intermediate tank, open the second ball valve and start the second centrifugal pump to generate negative pressure in the second ejector. Since the second ejector, the drain pipe, the condenser and the vacuum reactor are interconnected, the air in the vacuum reactor can be extracted under the action of negative pressure. After the vacuum reactor is evacuated, close the second ball valve. The vacuum degree is -0.093 to -0.098 MPa. S4: The NMP liquid in the intermediate tank is discharged into the vacuum reactor. The reducer is started to drive the spiral scraper to rotate and stir the NMP liquid. High-temperature steam is then supplied to the heat exchange base. The high-temperature steam exchanges heat with the NMP liquid, causing the water in the NMP liquid to evaporate at a low temperature of 45-48°C to form secondary steam. The secondary steam enters the condenser and condenses to form distilled water. The formed distilled water flows into the second ejector and is discharged from the second clean water pipe. The steam in the heat exchange base loses heat and condenses to form water and is discharged. The NMP liquid remaining in the vacuum reactor is purified to a concentration of 99.9% NMP liquid. S5: Collect NMP liquid with a concentration of 99.9% through the concentrate tank; S6: The NMP liquid in the concentrate tank is discharged into the filtration unit to filter out NMP liquid impurities, and finally discharged into the product pool.

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