CN212025229U - DMAc thermal coupling refining and recycling system - Google Patents
DMAc thermal coupling refining and recycling system Download PDFInfo
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- CN212025229U CN212025229U CN202020419640.7U CN202020419640U CN212025229U CN 212025229 U CN212025229 U CN 212025229U CN 202020419640 U CN202020419640 U CN 202020419640U CN 212025229 U CN212025229 U CN 212025229U
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Abstract
The utility model discloses a refined recovery system of DMAc thermal coupling, including dehydration tower and refined tower, dehydration tower bottom of the tower adopt the export with the import intercommunication at refined tower middle part, the gaseous phase in refined top of the tower adopts the export and sets up in a heat transfer passageway intercommunication of the thermal coupling heat exchanger in dehydration tower bottom, another heat transfer passageway and the circulation intercommunication of dehydration tower bottom of thermal coupling heat exchanger. The utility model discloses a system can make the material that can regard as the DMAc product that the refining tower top was extracted and the circulation liquid at the bottom of the dehydration tower carry out the thermal coupling, has guaranteed product purity and rate of recovery to effectively reduce the energy consumption.
Description
Technical Field
The invention relates to a DMAc waste liquid refining and recycling process system and a DMAc waste liquid refining and recycling method, and belongs to the field of chemical solvent recycling.
Background
N, N-dimethylacetamide (DMAc) is an aprotic highly polar solvent, has a slight ammonia odor, is strong in dissolving power, has a wide range of soluble substances, can be freely mixed and dissolved with water, aromatic compounds, esters, ketones, alcohols, ethers, benzene, chloroform and the like, and can activate compound molecules, so that the N, N-dimethylacetamide is widely used as a solvent and a catalyst.
The solvent is used as a solvent with high boiling point, high flash point, high thermal stability and stable chemical property, and can be used for spinning solvents of polyacrylonitrile, synthetic resins and natural resins, copolymers such as vinyl formate and vinylpyridine and solvents of aromatic carboxylic acid; the catalyst can be used for the processes of preparing cyanuric acid by heating urea, preparing nitrile by reacting alkyl halide with metal cyanide, preparing alkyl alkyne by reacting sodium acetylene with alkyl halide, preparing isocyanate by reacting organic halide with cyanate and the like. N, N-dimethylacetamide can also be used as an electrolytic solvent and a solvent for a photographic color former, a paint remover, an organic synthetic material, a pesticide and a medicinal material.
The DMAc waste liquid usually contains impurities such as water, amines, acetic acid and the like, and the DMAc can be industrially recycled by adopting a double-tower rectification process, namely, the DMAc waste liquid firstly enters a dehydrating tower, the amines and wastewater are extracted from the top of the dehydrating tower, and materials at the bottom of the dehydrating tower are sent to a refining tower; and (3) returning the crude DMAc product extracted from the top of the refining tower to the dehydrating tower, extracting the DMAc product from the side line of the refining tower, and sending the acetic acid-containing waste liquid at the bottom of the refining tower to a waste liquid treatment process. However, the conventional double-tower rectification process is adopted, so that the energy consumption is high, and generally 1.2 tons of DMAc product steam is consumed.
Patent CN 105418447A discloses a scheme of using gas phase at the top of a dehydrating tower as a heating medium of a thermal coupling heat exchanger, which reduces the heat load of a reboiler at the bottom of a refining tower and can save about 10-20% of steam consumption. However, the operating pressure of the dehydration tower is up to 0.2MPa, the temperature of the tower bottom is up to 150 ℃, the DMAc can have a more remarkable hydrolysis reaction under the working condition of the process, and the generated acetic acid can accelerate the DMAc hydrolysis rate, so that the DMAc yield is reduced. In addition, in order to realize thermal coupling, the process needs to ensure that the DMAc material (namely the material at the bottom of the dehydrating tower) entering the thermal coupling heat exchanger has about 50 percent of water content so as to meet the requirement of the thermal coupling process on heat exchange temperature difference, thereby greatly increasing the water content in the raw materials and increasing the whole load of the system. The DMAc yield obtained by adopting the process is only 95.9 percent through calculation, and the steam consumption of the DMAc product is about 0.9 ton.
Patent CN 104478752B discloses a technical scheme of adding an intermediate reboiler at a proper position in the middle of a dehydration tower, using a DMAc gas phase at the top of a refining tower as a heating medium of the intermediate reboiler, reducing the heat load of the reboiler at the bottom of the dehydration tower, and saving about 25-40% of steam consumption. However, in the process, an intermediate tower plate is required to be arranged at a proper position in the middle of a dehydration tower, the material extracted from the intermediate tower plate exchanges heat with the gas phase at the top of a refining tower, the requirement of heat exchange temperature difference is required to be met, the temperature fluctuation of the liquid phase material extracted from the adjacent theoretical stages of the stripping section of the dehydration tower is large, the temperature fluctuation is calculated to be 70 ℃, 77 ℃, 87 ℃, 98 ℃, 104 ℃, 105 ℃, 106 ℃ and 108 ℃, the process adopts 83 ℃ gas phase DMAC as a heat source to heat and vaporize the 70 ℃ liquid in the dehydration tower, and the position of the 70 ℃ material needs to be accurately found to ensure the effective heat exchange temperature difference, but in the actual industrial production, the dehydration tower is a packed tower, only a liquid collecting plate can be arranged in the space between two adjacent sections of packing to extract the liquid phase material, the material composition and the operation pressure of the uncertain position of the liquid collecting plate have uncertainty, and therefore, the temperature of, namely, a middle reboiler is arranged at a certain position in the dehydration tower, so that the risk of realizing effective heat exchange is difficult. On the other hand, the temperature of gas phase materials at the top of the deacidification tower (83 ℃) is subjected to heat exchange with materials extracted by the dehydration tower (70 ℃), the utilization rate of latent heat of vaporization of the gas phase at the top of the refining tower is only 60%, the materials extracted by the dehydration tower are heated and partially vaporized, the temperature of the materials is increased to about 77 ℃ according to the calculation of a rectification principle and vapor-liquid balance data, the average logarithmic temperature difference of heat exchange is only 9.3 ℃, the requirement of the logarithmic temperature difference is met, a middle reboiler needs large area and equipment investment, and the heat transfer load is 2000KW, and the heat transfer coefficient is 350W/m2At the temperature of 60 ℃, the heat exchange area of the equipment of the process is about 631m2The equipment investment is about 157.8 ten thousand.
Disclosure of Invention
The invention aims to provide a DMAc recovery process system and a DMAc recovery method which are more energy-saving and environment-friendly on the premise of ensuring the purity and recovery rate of DMAc products, and the DMAc recovery process system and the DMAc recovery method are high in purity and recovery rate and energy consumption is reduced by more than 40% compared with that of a conventional process.
The invention firstly provides a DMAc thermal coupling refining recovery system, which comprises a dehydrating tower and a refining tower, wherein a bottom extraction outlet of the dehydrating tower is communicated with an inlet in the middle of the refining tower, a gas-phase extraction outlet at the top of the refining tower is communicated with one heat exchange channel of a thermal coupling heat exchanger arranged at the bottom of the dehydrating tower, and the other heat exchange channel of the thermal coupling heat exchanger is circularly communicated with the bottom of the dehydrating tower.
Wherein, the middle part of the dehydration tower is provided with a DMAc raw material inlet. The waste gas extraction and outlet is arranged at the top of the dehydration tower and is communicated with a reflux tank of the dehydration tower through a condenser of the dehydration tower, the outlet of the reflux tank of the dehydration tower is divided into two paths through a reflux pump of the dehydration tower, one path is communicated with the top reflux of the dehydration tower, and the other path is used as a waste water extraction channel. The bottom of the dehydration tower is also circularly communicated with at least one dehydration tower reboiler.
And the bottom production outlet of the dehydration tower is communicated with the inlet in the middle of the refining tower through a dehydration tower liquid pump. And a heat exchange channel communicated with the thermal coupling heat exchanger at the top of the refining tower is divided into two paths through a refining tower reflux tank and a refining tower reflux pump, one path is communicated with the refining tower top reflux, and the other path is used as a DMAc product extraction channel. The bottom of the refining tower is circularly communicated with at least one refining tower reboiler. And a rectification raffinate extraction channel is arranged at the bottom of the refining tower, and a refining tower liquid pump is arranged on the rectification raffinate extraction channel.
The invention also provides a DMAc thermal coupling refining recovery method, which comprises the process of thermally coupling the material which is extracted from the top of the refining tower and can be used as the DMAc product with the circulating liquid (reboiling liquid) at the bottom of the dehydrating tower. According to the invention, through the thermal coupling process, all heat of the gas phase extracted from the top of the refining tower can be preferentially used for reboiling heat at the bottom of the dehydrating tower, so that the utilization of heat in the system can be realized to the maximum extent, the DMAc recovery energy consumption and equipment investment are reduced, meanwhile, because the operation control pressure and temperature at the bottom of the dehydrating tower and the top of the refining tower can be conveniently and stably controlled (the temperature fluctuation control can be realized to be not more than +/-1 ℃), the two materials in the thermal coupling process are stable in composition, the heat exchange state and the heat exchange energy efficiency can also be stably maintained, stable energy conservation can be realized, and the unstable condition of the system caused by temperature fluctuation and.
Wherein the DMAc raw material enters from the middle part of the dehydration tower. And waste gas is extracted from the top of the dehydration tower, the waste gas is condensed and then divided into two strands, one strand is used as reflux liquid to flow back into the dehydration tower, and the other strand is used as waste water to be extracted.
And after the refining tower stably runs, the circulating liquid at the bottom of the dehydrating tower is thermally coupled with the gas phase extracted from the top of the refining tower.
And the produced liquid at the bottom of the dehydrating tower enters the refining tower from the middle part. The gas phase at the top of the refining tower is divided into two parts after heat exchange (thermal coupling) with the circulating liquid at the bottom of the dehydrating tower, one part is used as reflux liquid to flow back into the refining tower, and the other part is used as a product to be extracted. The circulating liquid at the bottom of the refining tower can exchange heat through other heat sources. And a rectification residual liquid is produced at the bottom of the refining tower.
Wherein the average logarithmic temperature difference between the gas phase at the top of the refining tower and the circulating liquid at the bottom of the dehydrating tower is not lower than 15 ℃. The average logarithmic temperature difference of the system can exceed 15 ℃, the area and equipment investment of the thermal coupling heat exchanger can be effectively reduced, and the equipment investment of the method can be as low as 77.3 ten thousand yuan (Table 2).
The DMAc raw material comprises, by mass, water with the mass fraction of less than 20%, DMAc with the mass fraction of 75-98% and impurities with the mass fraction of 0.1-1%, and the lower water content of the raw material can reduce the overall load of a system and is beneficial to reducing the energy consumption of the system.
Wherein the operation pressure of the dehydration tower is 5-15 KPaA, and the pressure drop of the whole tower is not more than 4 Kpa; the operating pressure of the refining tower is 15-25 KPaA, and the pressure drop of the whole tower is not more than 5 Kpa; the operation pressure difference between the refining tower and the dehydrating tower is not less than 15 Kpa. Because the temperature and the pressure in the system have the correspondence, the temperature of the bottom of the dehydrating tower is 85-105 ℃, the temperature of the top of the refining tower is 105-120 ℃, and the temperature difference between the top of the refining tower and the bottom of the dehydrating tower is not less than 17 ℃ within the operating pressure range of the two towers. The process can realize the operating conditions, can effectively reduce the material temperature in the rectification process (not more than 125 ℃) while ensuring that the average logarithmic temperature difference of the heat exchange of the two towers is not less than 15 ℃, and effectively reduces the DMAc decomposition rate, so that the DMAc recovery rate can reach more than 99 percent (Table 1).
The reflux ratio of the dehydration tower is 2-6, the reflux ratio of the refining tower is 40-70, and the reflux ratio can be adaptively adjusted according to the operation conditions under different working conditions.
The system can realize the process recovery method, can effectively improve the product recovery rate (above 99%) under the condition of ensuring the product purity (above 99.9%), reduce the equipment investment (as low as 77.3 ten thousand yuan), and save the system energy consumption (saving the steam consumption by above 40% and reducing the steam consumption of a ton of DMAc product to below 0.6 ton).
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a schematic diagram of the system architecture of the present invention.
The system comprises a dehydration tower 1, a dehydration tower 2, a dehydration tower condenser 3, a dehydration tower reflux tank 4, a dehydration tower reflux pump 5, a dehydration tower reboiler 6, a dehydration tower liquid pump 7, a refining tower 8, a thermal coupling heat exchanger 9, a refining tower reflux tank 10, a refining tower reboiler 11 and a refining tower liquid pump 12.
Detailed Description
For a better understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings.
The structure of the system of the present invention is shown in fig. 1. The device comprises a dehydration tower 1 and a refining tower 7, wherein a bottom extraction outlet of the dehydration tower 1 is communicated with an inlet in the middle of the refining tower 7, a gas phase extraction outlet at the top of the refining tower 7 is communicated with one heat exchange channel of a thermal coupling heat exchanger 8 arranged at the bottom of the dehydration tower 1, and the other heat exchange channel of the thermal coupling heat exchanger 8 is circularly communicated with the bottom of the dehydration tower 1. The middle part of the dehydration tower 1 is provided with a DMAc raw material inlet. The top of the dehydration tower 1 is provided with a waste gas extraction outlet, the waste gas extraction outlet is communicated with a dehydration tower reflux tank 3 through a dehydration tower condenser 2, the outlet of the dehydration tower reflux tank 3 is divided into two paths through a dehydration tower reflux pump 4, and the two paths are communicated with the top reflux of the dehydration tower 1 and are taken as a waste water extraction channel. The bottom of the dehydration tower 1 is also circularly communicated with at least one dehydration tower reboiler 5. The bottom extraction outlet of the dehydration tower 1 is communicated with the inlet at the middle part of the refining tower 7 through a dehydration tower liquid pump 6. And a heat exchange channel communicated with the thermal coupling heat exchanger 8 at the top of the refining tower 7 is divided into two paths through a refining tower reflux tank 9 and a refining tower reflux pump 10, wherein one path is communicated with the top of the refining tower 7 in a reflux manner, and the other path is used as a DMAc product extraction channel. The bottom of the refining tower 7 is circularly communicated with at least one refining tower reboiler 11. And a rectification raffinate extraction channel is arranged at the bottom of the rectification tower 7, and a rectification tower liquid pump 12 is arranged on the rectification raffinate extraction channel.
The method and effects of the present invention are further illustrated below using two application examples.
Example 1
DMAc raw material is sent to the middle part of the dehydrating tower 1, the mass fraction of water in the raw material is 7.8%, the mass fraction of DMAc is 90.9%, the mass fraction of heavy impurities is 1.3%, and the feeding amount is 25500 Kg/h.
The operation pressure of the dehydration tower 1 is 12KPaA, the pressure drop of the whole tower is 4KPa, the temperature of the bottom of the tower is 103 +/-1 ℃, the reflux ratio is 3, the gas phase extracted from the top of the tower is condensed by a condenser 2 of the dehydration tower, the liquid phase enters a reflux tank 3 of the dehydration tower, one part of the liquid phase is used as reflux liquid to return to the top of the dehydration tower through a reflux pump 4 of the dehydration tower, and the other part of the liquid phase is used as the top of the tower to. The material at the bottom of the dehydrating tower 1 is sent to a refining tower 7 through a dehydrating tower liquid pump 6.
The operation pressure of the refining tower 7 is 25KPaA, the pressure drop of the whole tower is 5KPa, the temperature of the tower top is 120 +/-1 ℃, the reflux ratio is 55, the gas phase extracted from the tower top passes through a thermal coupling heat exchanger 8 to exchange heat with the materials at the tower bottom of the dehydrating tower for condensation, the condensed liquid phase materials enter a refining tower reflux tank 9, one part of the condensed liquid phase materials is returned to the tower top of the refining tower 7 as reflux liquid through a refining tower reflux pump 10, and the other part of the condensed liquid phase materials is extracted from the tower top and sent to a. The material at the bottom of the product refining tower 7 is sent to the waste liquid treatment process by a product refining tower liquid pump 12.
By adopting the above example, the purity of the DMAc product is 99.9%, the recovery rate of the DMAc is about 99.0%, and the steam consumption of the DMAc product is about 0.6 ton; the steam consumption of the DMAc product per ton of the conventional process is 1.18 tons, i.e., 49% energy savings per ton of DMAc product.
Example 2
DMAc raw material is sent to the middle part of the dehydrating tower 1, the mass fraction of water in the raw material is 5%, the mass fraction of DMAc is 94.5%, the mass fraction of heavy impurities is 0.5%, and the feeding amount is 10000 Kg/h.
The operation pressure of the dehydrating tower 1 is 11KPaA, the pressure drop of the whole tower is 3KPa, the temperature of the tower bottom is 101 +/-1 ℃, the reflux ratio is 3.5, the gas phase extracted from the tower top is condensed by a dehydrating tower condenser 2, the liquid phase enters a dehydrating tower reflux tank 3, one part of the liquid phase is used as reflux liquid to return to the tower top of the dehydrating tower through a dehydrating tower reflux pump 4, and the other part of the liquid phase is used as the extracted liquid from the tower top and sent to a wastewater treatment process. The material at the bottom of the dehydrating tower is sent to a refining tower 7 through a dehydrating tower liquid pump 6.
The operation pressure of the refining tower 7 is 24KPaA, the pressure drop of the whole tower is 4KPa, the temperature of the tower top is 118 +/-1 ℃, the reflux ratio is 50, the gas phase extracted from the tower top passes through a thermal coupling heat exchanger 8 to exchange heat with the materials at the tower bottom of the dehydrating tower for condensation, the condensed liquid phase materials enter a refining tower reflux tank 9, one part of the condensed liquid phase materials is returned to the tower top of the refining tower 7 as reflux liquid through a refining tower reflux pump 10, and the other part of the condensed liquid phase materials is extracted from the tower top and sent to a. The material at the bottom of the refining tower 7 is sent to the waste liquid treatment process by a refining tower liquid pump 12.
By adopting the above example, the purity of the DMAc product is 99.9 percent, the recovery rate of the DMAc is about 99.1 percent, and the steam consumption of the DMAc product is about 0.54 ton; the typical process steam consumption for a ton of DMAc product was 1.02 tons. Namely, the energy saving of the DMAc product per ton is 47 percent.
Example 3
In order to further evaluate the influence of the operating pressure and the operating temperature of the two towers on the recovery rate of the DMAc product, the invention further adjusts the operating pressure at the bottom of the dehydrating tower in different ranges, the temperature at the bottom of the dehydrating tower is correspondingly adjusted at the same time, and the obtained recovery rate of the DMAc is shown in Table 1. As can be seen from Table 1, the present invention limits the operating pressure at the bottom of the dehydration column to below 15KPaA, which is beneficial to increasing the DMAc product recovery rate.
TABLE 1 operating temperature at the bottom of the dehydration column and DMAc recovery
| Serial number | Operating pressure | Operating | DMAc recovery | |
| 1 | 15KPaA | 110℃ | 99.8％ | |
| 2 | 20KPaA | 118℃ | 99.5％ | |
| 3 | 25KPaA | 124℃ | 99.1％ | |
| 4 | 50KPaA | 145℃ | 97.6％ |
Example 4
In order to further evaluate the influence of the average logarithmic temperature difference in the thermal coupling heat exchanger 8 on the system economy, the invention further adjusts the temperature of two heat exchange materials in the thermal coupling heat exchanger 8,the thermal coupling heat exchanger 8 adopts a universal heat exchange load of 2000KW and a heat transfer coefficient of 350W/m2The temperature of the reaction mixture is shown in Table 2, and the heat exchange area and the equipment investment of the obtained equipment are shown in the example. As can be seen from Table 2, the present invention limits the average logarithmic temperature difference to more than 15 ℃ and can effectively reduce the equipment heat exchange area and equipment investment.
TABLE 2 area and equipment investment of thermally coupled heat exchanger under different mean logarithmic temperature differences
| Serial number | Temperature of heat source | Temperature of material to be heated | Mean logarithmic temperature difference | Area of heat exchange | Investment in |
| 1 | 106℃ | 89℃ | 17.4 | 346m2 | 86.5 ten thousand |
| 2 | 114℃ | 96℃ | 18.2 | 327m2 | 81.8 ten thousand |
| 3 | 120℃ | 103℃ | 18.9 | 309m2 | 77.3 ten thousand |
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (8)
1. The DMAc thermal coupling refining recovery system comprises a dehydrating tower (1) and a refining tower (7), wherein a bottom extraction outlet of the dehydrating tower (1) is communicated with an inlet in the middle of the refining tower (7), a gas-phase extraction outlet at the top of the refining tower (7) is communicated with one heat exchange channel of a thermal coupling heat exchanger (8) arranged at the bottom of the dehydrating tower (1), and the other heat exchange channel of the thermal coupling heat exchanger (8) is circularly communicated with the bottom of the dehydrating tower (1).
2. The DMAc thermally coupled refinery recovery system of claim 1, wherein the dehydrating column (1) has a DMAc feed inlet at the middle.
3. The DMAc thermally coupled refined recovery system of claim 1, wherein an exhaust gas extraction outlet is arranged at the top of the dehydration tower (1), the exhaust gas extraction outlet is communicated with the dehydration tower reflux tank (3) through a dehydration tower condenser (2), an outlet of the dehydration tower reflux tank (3) is divided into two paths through a dehydration tower reflux pump (4), one path is communicated with the top reflux of the dehydration tower (1), and the other path is used as a wastewater extraction path.
4. The DMAc thermally coupled refinery recovery system of claim 1, wherein the bottom of the dehydration column (1) is further in circulating communication with at least one dehydration column reboiler (5).
5. The DMAc thermally coupled refinery recovery system of claim 1, wherein the dehydration column (1) bottoms outlet is in communication with the middle inlet of the refinery column (7) via a dehydration column liquid pump (6).
6. The DMAc thermally coupled refined recovery system of claim 1, wherein a heat exchange channel communicating the top of the refining tower (7) with the thermally coupled heat exchanger (8) is divided into two paths by a refining tower reflux tank (9) and a refining tower reflux pump (10), one path is in reflux communication with the top of the refining tower (7), and the other path is used as a DMAc product extraction channel.
7. The DMAc thermally coupled refinery recovery system of claim 1, wherein the refinery column (7) bottoms is in circulating communication with at least one refinery column reboiler (11).
8. The DMAc thermally coupled refined recovery system of claim 1 wherein the bottoms of the refining column (7) is provided with a raffinate withdrawal passage, which is provided with a refining column liquid pump (12).
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