DMF (Dimethyl Formamide) waste liquid treatment method based on vapor compression technology

Abstract

The invention discloses a DMF (Dimethyl Formamide) waste liquid treatment method based on a steam compression technology, which comprises the following steps: step 1, rectification treatment: DMF waste liquid enters a rectification module for rectification treatment, a first dehydration tower of the rectification module is supplied with heat by a steam compressor, a heat source of a second dehydration tower is supplied by a third dehydration tower, a heat source of the third dehydrating tower is provided by the rectifying tower and the refining tower; dehydrating for the second time; dehydrating for the third time; performing rectification; performing refining; step 2, liquid treatment: conveying tower top water generated in the treatment process of the rectification module into a deamination unit for deamination treatment; performing steam stripping; biochemical treatment; and step 3, gas treatment. According to the DMF waste liquid treatment method based on the vapor compression technology, recycling of resources is achieved, the utilization rate of energy is further increased, and pollution to the environment is reduced.

Description

[0001] This application is a divisional application of the invention patent application with the application date of December 2, 2024, application number 2024117480264, and invention title "DMF Waste Liquid Treatment System and Treatment Method". Technical Field

[0002] The present invention belongs to the technical field of waste treatment, and particularly relates to a DMF waste liquid treatment method based on steam compression technology to realize the reuse of DMF and related by-products. Background Art

[0003] During the production processes of industries such as artificial leather, automotive interiors, and textile post-finishing, DMF waste liquid is generated, usually with a concentration of 15% - 30%. Directly discharging it into the sewage tank results in too high a concentration and too high treatment costs. Therefore, it is necessary to separate and purify the DMF waste liquid through rectification to obtain DMF with improved purity, achieving resource reuse and cost reduction and efficiency improvement for enterprises.

[0004] Currently, the mainstream processes for DMF waste liquid treatment are four-column double-effect or five-column triple-effect, which have problems such as relatively high energy consumption, ammonia nitrogen exceeding the standard in the top water of the dimethylamine tower after deamination in the sewage tank, and strong odors in the sewage tank exhaust gas.

[0005] For example, the patent with the application number CN201220566985.0 and title "A DMF Rectification Recovery Circulation System" and the patent with the application number CN201510175184.X and title "A Six-Column Four-Effect Rectification System for DMAC or DMF Waste Liquid and Its Recovery Method" both utilize steam heat sources and make the energy efficiency be utilized multiple times through pressure reduction. However, their energy utilization rate is not high, the energy consumption is relatively large, and the by-products in the process are not effectively recovered and utilized.

[0006] Another example is the patent with the application number CN202310807616.9 and title "An Exhaust Gas and Waste Liquid Residue Treatment Process for a DMF Recovery Device". It does not detail the recovery rectification process of DMF, and the sewage in the main by-products is not treated, nor is the exhaust gas generated during the sewage treatment reused.

[0007] The disclosure of the above background art content is only used to assist in understanding the inventive concept and technical solution of the present invention, and it does not necessarily belong to the prior art of this patent application. Without clear evidence indicating that the above content was publicly available before the application date of this patent application, the above background art should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0008] In view of this, in order to overcome the deficiencies of the prior art, the object of the present invention is to provide an improved DMF waste liquid treatment system, which can achieve the reuse of resources and energy, further improve the energy utilization rate, and reduce energy consumption and costs.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A DMF waste liquid treatment system includes a rectification module, a liquid treatment module, and a gas treatment module. The overhead water generated by the rectification module enters the liquid treatment module for treatment, and the gas phase generated by the rectification module enters the gas treatment module for treatment. The liquid treatment module includes a deamination unit, a stripping unit, and a sewage treatment unit. The deamination unit includes a deamination tower. The stripping unit is connected to the top of the deamination tower, and the sewage treatment unit is connected to the bottom of the deamination tower. The gas phases generated by the stripping unit and the sewage treatment unit enter the gas treatment module. The wastewater after stripping by the stripping unit is mixed with the overhead water generated by the rectification module and then enters the deamination tower for deamination treatment again. The gas treatment module includes an incinerator and a waste heat boiler. The incinerator is used to incinerate the gas phase, and the waste heat boiler is used to collect the energy generated by the incineration and provide energy to the rectification module, the deamination unit, and the stripping unit.

[0011] The rectification module includes a first dehydration unit, and the first dehydration unit includes a first dehydration tower, a steam compressor, and a first reboiler. The steam compressor connects the top of the first dehydration tower and the first reboiler. The steam compressor is used to compress the overhead steam of the first dehydration tower.

[0012] The rectification module includes a rectification unit and a refining unit. The rectification unit includes a rectification tower, and the refining unit includes a refining tower. The refining tower is fed with gas phase. A return liquid pump is arranged between the bottom of the refining tower and the bottom of the rectification tower. The return liquid pump is used to transport the bottom material of the refining tower to the rectification tower. The liquid refluxing in the refining tower will accumulate in the tower kettle and is transported to the tower kettle of the rectification tower for reheating again by the power provided by the return liquid pump.

[0013] According to some preferred embodiments of the present invention, the first reboiler is connected to the bottom of the first dehydration tower and the middle position of the first dehydration tower, and the first reboiler is connected to the deamination tower. The first dehydration unit uses a steam compressor to recompress the overhead steam of the first dehydration tower to increase the pressure and temperature, further enhancing its dehydration ability to reduce the subsequent steam usage and treatment costs.

[0014] According to some preferred implementation aspects of the present invention, the rectification module includes a second dehydration unit, and the second dehydration unit includes a second dehydration tower, a first cooler, and a second reboiler. The bottom of the first dehydration tower is connected to the second dehydration tower. The first cooler is arranged at the top of the second dehydration tower. The second reboiler is connected to the bottom of the second dehydration tower and an intermediate position of the second dehydration tower, and the second reboiler is connected to the deamination tower.

[0015] According to some preferred implementation aspects of the present invention, the rectification module includes a third dehydration unit, and the third dehydration unit includes a third dehydration tower, a third reboiler, and a fourth reboiler. The third reboiler and the fourth reboiler are arranged in parallel and are connected between the bottom of the third dehydration tower and an intermediate position of the third dehydration tower. The fourth reboiler is connected to the deamination tower, and the second reboiler is connected to the top of the third dehydration tower, that is, energy is provided to the second dehydration tower through the top steam of the third dehydration tower and the second reboiler.

[0016] According to some preferred implementation aspects of the present invention, the rectification unit includes a fifth reboiler. The fifth reboiler is connected to the bottom of the rectification tower and an intermediate position of the rectification tower. The waste heat boiler is used to provide heat to the fifth reboiler. The fourth reboiler is connected to the top of the rectification tower, that is, energy is provided to the third dehydration tower through the top steam of the rectification tower and the fourth reboiler.

[0017] According to some preferred implementation aspects of the present invention, a heater is arranged between the bottom of the third dehydration tower and the rectification tower. The heater is connected to a recovery boiler, and the recovery boiler is connected to an intermediate position of the third dehydration tower and the bottom of the rectification tower. The waste heat boiler is used to provide heat to the recovery boiler.

[0018] According to some preferred implementation aspects of the present invention, the intermediate position of the refining tower is connected to the intermediate position of the rectification tower. The third reboiler is connected to the top of the refining tower, that is, energy is provided to the third dehydration tower through the top water of the refining tower and the third reboiler.

[0019] In the present invention, the first dehydration tower of the rectification module is heated by a steam compressor. The heat source of the second dehydration tower is provided by the third dehydration tower, and the heat source of the third dehydration tower is provided by the rectification tower and the refining tower. The present invention uses negative pressure gradient control to ensure that the temperature difference between towers enables the reuse of steam 3 times or more. Combined with the heating of the first dehydration tower by a steam compressor, the steam energy consumption of the overall equipment is reduced by more than half compared to traditional equipment.

[0020] According to some preferred implementation aspects of the present invention, the deamination unit includes a second cooler arranged at the top of the deamination tower, and a sixth reboiler arranged at the bottom and an intermediate position of the deamination tower. The waste heat boiler is used to provide heat to the sixth reboiler.

[0021] According to some preferred implementation aspects of the present invention, the sewage treatment unit includes a sewage tank for biochemically treating the bottom material of the deammoniation tower, and the sewage tank is connected to the incinerator for conveying the gas phase generated during the biochemical treatment process to the incinerator for incineration.

[0022] According to some preferred implementation aspects of the present invention, the stripping unit includes a stripping tower, a third cooler and a gas-liquid separator arranged at the top of the stripping tower, and a seventh reboiler arranged at the bottom and the middle position of the stripping tower. The waste heat boiler is used to provide heat to the seventh reboiler, and the incinerator is connected to the gas-liquid separator; the bottom of the stripping tower is connected to the deamination tower. The concentration of the wastewater (the main gas after stripping is dimethylamine) is relatively reduced after being stripped by the stripping tower, and it is mixed with the top water of the dehydration tower and the rectification tower and enters the deamination tower for deamination concentration again.

[0023] The present invention also provides a method for treating DMF waste liquid by the above-mentioned DMF waste liquid treatment system, including the following steps:

[0024] Convey the DMF waste liquid to the rectification module for treatment, and convey the gas phase generated during the treatment process to the incinerator for incineration. The heat generated by the incineration heats the water into steam in the waste heat boiler, and the heat is transmitted to the rectification module, the deamination unit and the stripping unit through the steam;

[0025] The top water generated during the treatment process of the rectification module is conveyed to the deamination unit for deamination treatment, and the generated liquid enters the sewage treatment unit for biochemical treatment. The gas generated during the biochemical treatment process is conveyed to the incinerator, and the liquid after biochemical treatment meets the standards for discharge or is used for the absorption of DMF and forms DMF waste liquid again;

[0026] The gas phase generated during the deamination treatment enters the stripping unit, and the gas after gas-liquid separation enters the incinerator, and the liquid flows back to the stripping unit.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: The DMF waste liquid treatment method based on steam compression technology of the present invention generates dimethylamine top water during the rectification process. The dimethylamine and water are separated by the stripping tower, and the wastewater enters the sewage tank. At the same time, the dimethylamine gas, the biogas in the sewage tank and the vacuum tail gas of the rectification enter the incinerator to burn together. The high-temperature flue gas generates a certain amount of steam through the waste heat boiler and returns to the front end to provide energy for relevant components, realizing the recycling of resources, further improving the energy utilization rate, and reducing environmental pollution; through the cooperation of the deammoniation unit, the sewage treatment unit and the stripping unit, the extraction of dimethylamine is more sufficient, the energy density of combustion is higher, and the energy recycling is more sufficient; and the sewage treatment cost is lower, and the effluent quality is better, and it can be directly recycled or discharged. Brief Description of the Drawings

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0029] Figure 1 It is a schematic structural diagram of the DMF waste liquid treatment system in the embodiments of the present invention;

[0030] Figure 2 It is a schematic flow diagram of the DMF waste liquid treatment method in the embodiments of the present invention;

[0031] In the drawings, the reference numerals are: the first dehydration tower - 1, the steam compressor - 2, the first reboiler - 3, the first transfer pump - 4, the first discharge pump - 5, the second dehydration tower - 6, the first cooler - 7, the second reboiler - 8, the second transfer pump - 9, the third transfer pump - 10, the second discharge pump - 11, the third dehydration tower - 12, the third reboiler - 13, the fourth transfer pump - 14, the fourth reboiler - 15, the fifth transfer pump - 16, the third discharge pump - 17, the heater - 18, the rectification tower - 19, the fifth reboiler - 20, the return liquid pump - 21, the refining tower - 22, the recovery boiler - 23, the deamination tower - 24, the fourth discharge pump - 25, the sixth reboiler - 26, the sixth transfer pump - 27, the stripping tower - 28, the fifth discharge pump - 29, the seventh reboiler - 30, the third cooler - 31, the gas - liquid separator - 32, the reflux pump - 33, the incinerator - 34, the waste heat boiler - 35, the sewage tank - 36, the second cooler - 37. Detailed Embodiments

[0032] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] Embodiment 1 DMF Waste Liquid Treatment System

[0034] As Figure 1 and Figure 2As shown in the figure, the DMF waste liquid treatment system of this embodiment includes a rectification module, a liquid treatment module, and a gas treatment module. The overhead water generated by the rectification module enters the liquid treatment module for treatment, and the gas phase (vacuum tail gas) generated by the rectification module enters the gas treatment module for treatment. The arrows in the figure represent the flow direction of substances.

[0035] The composition and structure of each module are introduced in detail as follows:

[0036] (1) Rectification module

[0037] The rectification module in this embodiment successively includes a first dehydration unit, a second dehydration unit, a third dehydration unit, a rectification unit, and a refining unit, which respectively include a first dehydration tower 1, a second dehydration tower 6, a third dehydration tower 12, a rectification tower 19, and a refining tower 22. After being treated by the rectification unit, the DMF waste liquid is concentrated to more than 99.5%. The refining unit further concentrates on the basis of the rectification unit and has two functions: 1. Further remove moisture, and the moisture is discharged from the top of the tower as a light component. 2. Reduce the acid value, and the formic acid complex salt is enriched at the bottom of the tower and is transported back to the rectification tower through a return liquid pump and then to the recovery boiler.

[0038] Specifically, the first dehydration unit includes a first dehydration tower 1, a steam compressor 2, and a first reboiler 3. The steam compressor 2 is connected to the top of the first dehydration tower 1 and the first reboiler 3. The first reboiler 3 is connected to the bottom of the first dehydration tower 1 and the middle position of the first dehydration tower 1. The first reboiler 3 is connected to the top of the first dehydration tower 1 and the deamination tower 24 through a first transfer pump 4. The bottom of the first dehydration tower 1 is connected to the first reboiler 3 and the second dehydration tower 6 through a first discharge pump 5. The first discharge pump 5 serves as the circulation pump for the first reboiler 3, and the flow rate of the first discharge pump 5 during operation is all used for circulation of the first reboiler 3. Only when the liquid level of the second dehydration tower 6 is lower than the set value, a small part of the flow rate (such as 3%-10%) of the first discharge pump 5 is transported to the second dehydration tower 6 as a supplement.

[0039] The second dehydration unit includes a second dehydration tower 6, a first cooler 7, and a second reboiler 8. The first cooler 7 is arranged at the top of the second dehydration tower 6 and is connected to the side of the top of the second dehydration tower 6 and the deamination tower 24 through a second transfer pump 9. The second reboiler 8 is connected to the bottom of the second dehydration tower 6 and the middle position of the second dehydration tower 6, and the second reboiler 8 is connected to the deamination tower 24. The energy is provided to the second dehydration tower 6 by the overhead steam of the third dehydration tower 12 and the second reboiler 8. The second reboiler 8 is connected to the top of the third dehydration tower 12 and the deamination tower 24 through a third transfer pump 10. The bottom of the second dehydration tower 6 is connected to the third dehydration tower 12 through a second discharge pump 11.

[0040] The third dehydration unit includes a third dehydration tower 12, a third reboiler 13 and a fourth reboiler 15. The third reboiler 13 and the fourth reboiler 15 are arranged in parallel and are connected between the bottom of the third dehydration tower 12 and the middle position of the third dehydration tower 12. The third reboiler 13 and the fourth reboiler 15 are respectively connected to the top of the purification tower 22 and the top of the rectification tower 19, that is, the energy is provided to the third dehydration tower 12 through the top steam of the purification tower 22 and the third reboiler 13, and the top steam of the rectification tower 19 and the fourth reboiler 15 together. The third reboiler 13 is connected to the top of the rectification tower 19 and the top of the purification tower 22 through a fourth transfer pump 14; the fourth reboiler 15 is connected to the top of the deamination tower 24 and the top of the rectification tower 19 through a fifth transfer pump 16. The proportion of the bottom material of the third dehydration tower 12 entering the third reboiler 13 and the fourth reboiler 15 is distributed according to the top steam flow rates of the corresponding purification tower 22 and the rectification tower 19 to maximize the energy utilization.

[0041] The rectification unit includes a rectification tower 19 and a fifth reboiler 20. The fifth reboiler 20 is connected between the bottom of the rectification tower 19 and the middle position of the rectification tower 19. A heater 18 is arranged between the bottom of the third dehydration tower 12 and the bottom of the rectification tower 19. The heater 18 is connected to a recovery boiler 23. The recovery boiler 23 is connected between the middle position of the third dehydration tower 12 and the bottom of the rectification tower 19. A waste heat boiler 35 is used to provide heat to the fifth reboiler 20 and the recovery boiler 23.

[0042] Preferably, the third dehydration tower 12 is connected to the rectification tower 19 through a third discharge pump 17. The heater 18 is arranged on the pipeline where the third discharge pump 17 is located. The third reboiler 13 and the fourth reboiler 15 are also connected to the connecting pipeline.

[0043] The purification unit includes a purification tower 22. The purification tower 22 is connected to the rectification tower 19. A return liquid pump 21 is arranged between the bottom of the purification tower 22 and the bottom of the rectification tower 19. The material discharged from the middle position of the purification tower 22 is the DMF product. The purification tower 22 is fed with gas from the rectification tower 19. The heat of the purification tower 22 is provided by the rectification unit. The purification tower 22 has no additional heat source. There is no temperature difference between the purification unit and the rectification unit. Therefore, the purification unit cannot realize the reheating function for the rectification unit. Therefore, a third reboiler 13 corresponding to the top of the purification tower 22 and a fourth reboiler 15 corresponding to the top of the rectification tower 19 are arranged in the third dehydration tower 12 to fully collect and utilize the heat of the purification tower 22 and the rectification tower 19.

[0044] In this embodiment, the first dehydration unit uses a steam compressor 2 to recompress the overhead steam of the first dehydration tower 1, increasing the pressure and temperature, further enhancing its dehydration capacity, and reducing the subsequent steam usage and treatment costs. The heat source of the second dehydration tower 6 is provided by the overhead steam of the third dehydration tower 12, and the heat source of the third dehydration tower 12 is provided by the distillation tower 19 and the refining tower 22. This embodiment uses negative pressure gradient control to ensure a tower - to - tower temperature difference for steam reuse three or more times; combined with the first dehydration tower 1 being heated by the steam compressor 2, the steam energy consumption of the overall equipment is more than half lower than that of traditional equipment.

[0045] (2) Liquid treatment module

[0046] The liquid treatment module includes a deamination unit, a stripping unit, and a sewage treatment unit.

[0047] The deamination unit includes a deamination tower 24, a second cooler 37 arranged at the top of the deamination tower 24, and a sixth reboiler 26 arranged at the bottom and the middle position of the deamination tower 24. The stripping unit is connected to the top of the deamination tower 24, and the sewage treatment unit is connected to the bottom of the deamination tower 24 through a fourth discharge pump 25. The gas phases generated by the stripping unit and the sewage treatment unit enter the gas treatment module for treatment.

[0048] The stripping unit includes a stripping tower 28, a third cooler 31 and a gas - liquid separator 32 arranged at the top of the stripping tower 28, and a seventh reboiler 30 arranged between the bottom and the middle position of the stripping tower 28. The incinerator 34 is connected to the gas - liquid separator 32; the bottom of the stripping tower 28 is connected to the top of the deamination tower 24 through a fifth discharge pump 29. A reflux pump 33 is arranged between the gas - liquid separator 32 and the stripping tower 28 to return the liquid after gas - liquid separation to the stripping tower 28.

[0049] The sewage treatment unit includes a sewage tank 36. The sewage tank 36 is used for biochemical treatment of the bottom material of the deamination tower 24, and the sewage tank 36 is connected to the incinerator 34 to convey the gas phase generated during the biochemical treatment process to the incinerator 34 for incineration.

[0050] (3) Gas treatment module

[0051] The gas treatment module includes an incinerator 34 and a waste heat boiler 35. The waste heat boiler 35 is used to collect the energy generated by incineration and provide energy to the distillation module, the deamination unit, and the stripping unit. In this embodiment, the waste heat boiler 35 is used to heat the fifth reboiler 20, the sixth reboiler 26, the seventh reboiler 30, and the recovery boiler 23.

[0052] The working process of the DMF waste liquid treatment system in this embodiment is briefly described as follows:

[0053] DMF waste liquid with a concentration of 15 - 30% enters the first dehydration tower 1, and heat source is supplemented through the first reboiler 3 to evaporate the water with a lower boiling point at the bottom of the first dehydration tower 1. The evaporated water rises to the top of the tower. The gas phase (top steam) enters the steam compressor 2, where electrical energy is converted into the internal energy of the steam (the temperature and pressure increase), and the temperature of the saturated steam at the top of the tower increases by 10 - 25°C. The steam then enters the first reboiler 3 to provide heat for heating and evaporating the liquid waste at the bottom of the tower. At the same time, the top steam after being cooled is condensed into liquid water (top water). Part of it is refluxed to the first dehydration tower 1 through the first transfer pump 4, and the remaining part enters the deamination tower 24. The flow rate of the reflux to the first dehydration tower 1 or the flow rate entering the deamination tower 24 is regulated according to the concentration of the top water. Generally, it is required that the COD in the top water is less than 1000 ppm. When the value is higher, the flow rate of the reflux to the top of the first dehydration tower 1 is increased to reduce the concentration; when the value is lower, the flow rate of the reflux to the top of the first dehydration tower 1 is decreased to save energy consumption.

[0054] The concentration of the waste liquid at the bottom of the first dehydration tower 1 after concentration is increased to 40 - 45%, and it enters the second dehydration tower 6 through the first discharge pump 5. The second reboiler 8 heats and evaporates the waste liquid at the bottom of the second dehydration tower 6. A first cooler 7 is provided at the top of the second dehydration tower 6 to condense the gas phase top steam into a liquid phase, and part of it is refluxed to the second dehydration tower 6, and part enters the deamination tower 24.

[0055] The concentration of the bottom liquid after concentration in the second dehydration tower 6 is 50 - 55%, and it is transported to the third dehydration tower 12 through the second tower discharge pump. The third dehydration tower 12 is provided with two reboilers, namely the third reboiler 13 and the fourth reboiler 15. The waste liquid at the bottom of the third dehydration tower 12 is heated and evaporated through the heating of the two reboilers. The top steam provides heat for the second reboiler 8 while being condensed into a liquid (top water) itself. Part of it is refluxed to the third dehydration tower 12 through the third transfer pump 10, and part enters the deamination tower 24.

[0056] The concentration of the bottom liquid after concentration in the third dehydration tower 12 is 75 - 85%, and it is transported to the heater 18 through the third discharge pump 17. The liquid is completely evaporated into gas using steam. Some solid components and high-boiling impurities enter the recovery boiler 23 to further evaporate DMF and enter the third dehydration tower 12. The remaining distillation residues, impurities, and high-boiling substances are disposed of externally.

[0057] The gas phase coming out of the heater 18 enters the distillation tower 19. The gas phase at the top of the distillation tower 19 enters the fourth reboiler 15 and is condensed, and part of it is refluxed to the distillation tower 19, and part enters the deamination tower 24. DMF is concentrated at the bottom of the distillation tower 19 with a concentration of 98% or above, and further water is removed by evaporation through the fifth reboiler 20.

[0058] High-purity DMF gas is discharged from the middle side line of the rectification column 19 and enters the refining column 22. The light components rise from the top of the refining column 22 to the third reboiler 13 and are condensed from gas phase to liquid phase. Most of the liquid is refluxed, and a small part of the liquid with high water content is refluxed to the bottom of the rectification column 19. The DMF product is discharged from the side line of the refining column 22 in liquid phase, and the concentration can reach 99.5% or above.

[0059] The main component of the overhead water generated by the above device is a mixed liquid of water, DMF and dimethylamine. This liquid enters the deamination column 24 and is heated by the sixth reboiler 26. The low-boiling components and dimethylamine waste gas are condensed from the top of the column to a high-concentration liquid by the second cooler 37 and then enter the dimethylamine stripping column 28 for stripping.

[0060] The bottom of the stripping column 28 is heated to about 95 °C by the seventh reboiler 30 to fully vaporize dimethylamine, which then enters the third cooler 31 from the top of the column for cooling. The cooled liquid and non-condensable gas are separated by the gas-liquid separator 32. The liquid re-enters the stripping column 28 for evaporation through the reflux pump 33, and the high-concentration dimethylamine gas enters the waste gas incinerator 34 for incineration treatment. The low-concentration bottom liquid after stripping is mixed with the overhead water of the rectification module through the fifth discharge pump 29 and enters the deamination column 24 for re-deamination. The bottom liquid after deamination enters the sewage tank 36 through the fourth discharge pump 25 for biochemical treatment. Biogas and other gases generated during the treatment process are sent to the incinerator 34, and the heat after the waste gas is burned heats the waste heat boiler 35 to generate high-temperature steam, which provides heat for the rectification module. The gas treated by the incinerator 34 meets the emission standards and is directly discharged.

[0061] Example 2 DMF waste liquid treatment method

[0062] As Figure 1 and Figure 2 shown, based on the DMF waste liquid treatment system in Example 1, this example provides a DMF waste liquid treatment method, including the following steps:

[0063] Step 1. Rectification treatment

[0064] (1) First dehydration

[0065] The DMF waste liquid enters the first dehydration tower 1 for the first dehydration. The overhead steam passes through the steam compressor 2 and then enters the first reboiler 3 to heat the material transported from the first dehydration tower 1 to the first reboiler 3 by the first discharge pump 5. The heated material re-enters the first dehydration tower 1. The overhead steam is condensed by the first reboiler 3 to form overhead water, and part of it is transported to the deamination column 24 through the first transfer pump 4, and part of it is refluxed to the first dehydration tower 1.

[0066] The bottom material of the first dehydration tower 1 after concentration is transported to the second dehydration tower 6 through the first discharge pump 5 for the second dehydration.

[0067] (2) Second dehydration

[0068] The overhead steam of the second dehydration tower 6 is cooled by the first cooler 7, and the overhead water formed after cooling is partially transported to the deamination tower 24 by the second transfer pump 9 and partially refluxed to the second dehydration tower 6.

[0069] The overhead steam entering the second reboiler 8 from the top of the third dehydration tower 12 heats the material entering the second reboiler 8 from the bottom of the second dehydration tower 6 through the second discharge pump 11. After heating, the material re-enters the second dehydration tower 6. The overhead steam forms overhead water after condensation in the second reboiler 8 and is partially transported to the deamination tower 24 by the third transfer pump 10 and partially refluxed to the third dehydration tower 12.

[0070] The concentrated bottom material of the second dehydration tower 6 is transported to the third dehydration tower 12 by the second discharge pump 11 for the third dehydration.

[0071] (3) Third dehydration

[0072] The overhead steam entering the third reboiler 13 from the top of the refining tower 22 heats the material entering the third reboiler 13 from the bottom of the third dehydration tower 12 through the third discharge pump 17; the overhead steam entering the fourth reboiler 15 from the top of the distillation tower 19 heats the material entering the fourth reboiler 15 from the bottom of the third dehydration tower 12 through the third discharge pump 17; after heating, the material re-enters the third dehydration tower 12. The overhead steam of the distillation tower 19 forms overhead water after condensation in the fourth reboiler 15 and is partially transported to the deamination tower 24 by the fifth transfer pump 16 and partially refluxed to the distillation tower 19. The overhead steam of the refining tower 22 is condensed in the third reboiler 13 and is partially transported to the distillation tower 19 by the fourth transfer pump 14 and partially returned to the refining tower 22.

[0073] The concentrated bottom material of the third dehydration tower 12 is transported to the heater 18 by the third discharge pump 17, heated to steam and then transported to the distillation tower 19 for distillation. The heated solid components and high-boiling impurities enter the recovery boiler 23 to further evaporate DMF and enter the third dehydration tower 12. The waste residues such as the remaining rectification residues, impurities and high-boiling substances in the recovery boiler 23 are disposed of externally. The energy of the recovery boiler 23 is provided by the high-temperature steam generated by the waste heat boiler 35 to heat water.

[0074] (4) Rectification

[0075] The bottom material of the rectification column 19 can also enter the recovery boiler 23 and be heated again. The high-temperature steam generated by heating water by the waste heat boiler 35 of the gas treatment module enters the fifth reboiler 20, and heats the material entering the fifth reboiler 20 from the bottom of the rectification column 19; the heated material re-enters the rectification column 19. The water is removed by evaporation through the fifth reboiler 20 of the rectification column 19, so that DMF is enriched at the bottom of the rectification column 19 with a concentration of 98% or above.

[0076] (5) Refining

[0077] The material in the rectification column 19 enters the refining column 22 from the middle position of the column body for refining, and is condensed and discharged from the middle position of the refining column 22. The light components in the refining column 22 rise from the top of the refining column 22 to the third reboiler 13 and are condensed from gas phase to liquid phase. Most of the liquid is refluxed to the refining column 22 through the fourth delivery pump 14, and a small part of the liquid with high moisture content is refluxed to the rectification column 19.

[0078] A return liquid pump 21 is arranged between the bottom of the refining column 22 and the bottom of the rectification column 19, and the bottom material of the refining column 22 re-enters the rectification column 19 through the return liquid pump 21 for rectification.

[0079] The overhead tail gas generated during the rectification process in the dehydration tower, rectification column 19 and refining column 22 directly enters the incinerator 34 for incineration.

[0080] Step 2: Liquid treatment

[0081] The overhead water (a mixed liquid mainly composed of water, DMF and dimethylamine) generated during the treatment process of the rectification module is transported to the deamination unit for deamination treatment. Specifically as follows:

[0082] (1) Deamination

[0083] The top steam of the deamination tower 24 is cooled to a high-concentration liquid by the second cooler 37, and a part of it is transported to the stripping tower 28 by the sixth delivery pump 27, and the other part returns to the deamination tower 24 again.

[0084] The high-temperature steam generated by heating water by the waste heat boiler 35 of the gas treatment module enters the sixth reboiler 26, and heats the material entering the sixth reboiler 26 from the bottom of the deamination tower 24; the heated material re-enters the deamination tower 24.

[0085] (2) Stripping

[0086] The top steam of the stripping tower 28 enters the third cooler 31, and the cooled liquid and non-condensable gas enter the gas-liquid separator 32. After gas-liquid separation by the gas-liquid separator 32, the high-concentration dimethylamine gas enters the incinerator 34 for incineration, and the liquid returns to the stripping tower 28 through the reflux pump 33 for evaporation.

[0087] The high-temperature steam generated by heating water with the waste heat boiler 35 of the gas treatment module enters the seventh reboiler 30 to heat the material transported from the bottom of the stripping column 28 to the seventh reboiler 30, and the heated material re-enters the stripping column 28.

[0088] The bottom material of the stripping column 28 is mixed with the overhead water of the rectification module by the fifth discharge pump 29 and enters the deamination column 24 for re-deamination.

[0089] (3) Biological treatment

[0090] The low-concentration bottom material of the deamination column 24 after stripping is transported to the sewage treatment unit by the fourth discharge pump 25 for biological treatment. The sewage treatment unit includes a sewage tank 36. The gas generated during the biological treatment process is transported to the incinerator 34, and the liquid after biological treatment meets the standards for discharge or is used for the absorption of DMF and forms DMF waste liquid again, forming a recycling loop.

[0091] Step Three: Gas treatment

[0092] The gas mainly consists of three parts: the overhead vacuum tail gas in the rectification module, the gas after cooling and gas-liquid separation of the overhead steam of the stripping column 28, and the gas generated during the biological treatment process. These three parts of gas enter the incinerator 34 for incineration, and the gas after incineration treatment meets the standards for discharge. The energy during the incineration process is used to heat water through the waste heat boiler 35 to generate high-temperature steam, and this high-temperature steam returns to the front end to heat relevant components. In this embodiment, it is used to heat the fifth reboiler 20, the sixth reboiler 26, the seventh reboiler 30, and the recovery boiler 23.

[0093] For the convenience of description and understanding, the above steps are numbered and described separately, but they do not have a limiting meaning. In actual situations, at least some of the above steps can be carried out simultaneously or without a sequential order.

[0094] The concentration of the DMF waste liquid generated during the production process is generally 15% - 30%. Directly entering the sewage tank has too high a concentration and too high a treatment cost. In the present invention, the DMF aqueous solution enters the rectification module, and after purification, the finished DMF has a purity of over 99.5% and is recycled for production to achieve resource reuse, reducing costs and increasing efficiency for the enterprise; during the rectification process, a small amount of DMF is hydrolyzed to produce dimethylamine overhead water. The dimethylamine and water are separated through the deamination column and the stripping column, and the wastewater enters the sewage tank. The dimethylamine gas enters the incinerator and burns together with the biogas in the sewage tank and the rectification vacuum tail gas. The high-temperature flue gas generates a certain amount of steam through the waste heat boiler and returns to the front end to supply heat to the rectification module. Moreover, the first dehydration tower in the present invention adopts steam recompression technology, and the overall energy consumption can be saved by more than 50%. Through the DMF waste liquid treatment system of the present invention, the separation and utilization efficiency of substances is effectively improved.

[0095] The above embodiments are only used to illustrate the technical concept and features of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It is not intended to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for treating DMF waste liquid based on steam compression technology, characterized in that, It includes the following steps: Step 1: Rectification treatment The DMF waste liquid enters the rectification module for rectification treatment. The first dehydration tower of the rectification module is heated by a steam compressor, the heat source of the second dehydration tower is provided by the third dehydration tower, and the heat source of the third dehydration tower is provided by the rectification tower and the purification tower: First dehydration: The DMF waste liquid enters the first dehydration tower for the first dehydration. The overhead steam passes through the steam compressor and then enters the first reboiler to heat the material at the bottom of the first dehydration tower transported by the first discharge pump into the material in the first reboiler, and the heated material re-enters the first dehydration tower; the steam compressor is used to recompress the overhead steam of the first dehydration tower to increase the pressure and temperature of the steam; Second dehydration: The concentrated bottom material of the first dehydration tower is transported by the first discharge pump to the second dehydration tower for the second dehydration; Third dehydration: The concentrated bottom material of the second dehydration tower is transported by the second discharge pump to the third dehydration tower for the third dehydration; Rectification: The concentrated bottom material of the third dehydration tower is transported by the third discharge pump to the heater, heated into steam and then transported to the rectification tower for rectification; Purification: The material in the rectification tower enters the purification tower from the middle position of the tower body for purification, and then is condensed and discharged from the middle position of the purification tower; Step 2: Liquid treatment The overhead water generated during the treatment process of the rectification module is transported to the deamination unit for deamination treatment: Deamination: The overhead steam of the deamination tower is cooled to a high-concentration liquid by the second cooler and then part of it is transported to the stripping tower by the sixth transfer pump, and the other part returns to the deamination tower; Stripping: The overhead steam of the stripping tower enters the third cooler, and the cooled liquid and non-condensable gas enter the gas-liquid separator. After gas-liquid separation by the gas-liquid separator, the high-concentration dimethylamine gas enters the incinerator for incineration, and the liquid returns to the stripping tower for evaporation through the reflux pump; Biochemical treatment: The low-concentration bottom material of the deamination tower after stripping is transported by the fourth discharge pump to the sewage treatment unit for biochemical treatment. The gas generated during the biochemical treatment process is transported to the incinerator, and the liquid after biochemical treatment meets the standards for discharge or is used for the absorption of DMF and forms DMF waste liquid again to form a recycling; Step 3: Gas treatment The gas phase generated by the rectification module enters the gas treatment module for treatment: The gas enters the incinerator for incineration, and the gas after incineration treatment meets the standards for discharge; the energy during the incineration process heats water through the waste heat boiler to generate high-temperature steam, and this high-temperature steam returns to the front end for heating the fifth reboiler, the sixth reboiler, the seventh reboiler and the recovery boiler.

2. The DMF waste liquid treatment method according to claim 1, characterized in that The overhead steam of the first dehydration tower forms overhead water after condensation in the first reboiler and is transported by the first transfer pump, part of it is transported to the deamination tower, and the other part is refluxed to the first dehydration tower.

3. The DMF waste liquid treatment method according to claim 2, characterized in that, The flow rate of the reflux to the first dehydration tower or entering the deamination tower is regulated according to the concentration of the overhead water of the first dehydration tower. When the concentration is higher than the set value, the flow rate of the reflux to the top of the first dehydration tower is increased to reduce the concentration; when the concentration is lower than the set value, the flow rate of the reflux to the top of the first dehydration tower is decreased to save energy consumption.

4. The DMF waste liquid treatment method according to claim 1, wherein, The overhead steam of the second dehydration tower is cooled by the first cooler, and the overhead water formed after cooling is pumped to the deamination tower by the second transfer pump for part, and part is refluxed to the second dehydration tower.

5. The DMF waste liquid treatment method according to claim 1, wherein The overhead steam of the third dehydration tower entering the second reboiler heats the material entering the second reboiler from the bottom of the second dehydration tower by the second discharge pump. After heating, the material re-enters the second dehydration tower. The overhead steam forms overhead water after condensation in the second reboiler and is pumped to the deamination tower by the third transfer pump for part, and part is refluxed to the third dehydration tower.

6. The DMF waste liquid treatment method according to claim 1, characterized in that, The overhead steam of the refining tower entering the third reboiler heats the material entering the third reboiler from the bottom of the third dehydration tower by the third discharge pump. After heating, the material re-enters the third dehydration tower. The overhead steam of the rectification tower forms overhead water after condensation in the fourth reboiler and is pumped to the deamination tower by the fifth transfer pump for part, and part is refluxed to the rectification tower. The overhead steam of the rectification tower entering the fourth reboiler heats the material entering the fourth reboiler from the bottom of the third dehydration tower by the third discharge pump. After heating, the material re-enters the third dehydration tower. The overhead steam of the refining tower forms overhead water after condensation in the third reboiler and is pumped to the rectification tower by the fourth transfer pump for part, and part returns to the refining tower.

7. The DMF waste liquid treatment method according to claim 1, characterized in that The solid content and high-boiling impurities after being heated by the heater enter the recovery boiler to further evaporate DMF and enter the third dehydration tower. The rectification residue, impurities and high-boiling waste residues remaining in the recovery boiler are disposed of externally. The energy of the recovery boiler is provided by the high-temperature steam generated by the waste heat boiler heating water.

8. The DMF waste liquid treatment method according to claim 1, characterized in that, The bottom material of the rectification tower enters the recovery boiler and is heated again. The high-temperature steam generated by the waste heat boiler of the gas treatment module heating water enters the fifth reboiler to heat the material entering the fifth reboiler from the bottom of the rectification tower. After heating, the material re-enters the rectification tower.

9. The DMF waste liquid treatment method according to claim 1, characterized in that The light components in the refining tower rise from the top of the refining tower to the third reboiler and condense from gas phase to liquid phase. Part of the liquid is refluxed to the refining tower by the fourth transfer pump, and part of the liquid with high water content is refluxed to the rectification tower.

10. The DMF waste liquid treatment method according to claim 1, characterized in that, The refining tower is fed with rectification tower gas phase. A return liquid pump is arranged between the bottom of the refining tower and the rectification tower. The bottom material of the refining tower re-enters the rectification tower through the return liquid pump for reheating and rectification.

11. The DMF waste liquid treatment method according to claim 1, wherein The high-temperature steam generated by the waste heat boiler of the gas treatment module heating water enters the sixth reboiler to heat the material entering the sixth reboiler from the bottom of the deamination tower. After heating, the material re-enters the deamination tower. The high-temperature steam generated by the waste heat boiler of the gas treatment module heating water enters the seventh reboiler to heat the material transported from the bottom of the stripping tower to the seventh reboiler. After heating, the material re-enters the stripping tower.

12. The DMF waste liquid treatment method according to claim 1, characterized in that, The bottom material of the stripping tower is mixed with the overhead water of the rectification module by the fifth discharge pump and enters the deamination tower for re-deamination.

13. The DMF waste liquid treatment method according to claim 1, wherein, The proportion of the bottom material of the third dehydration tower entering the third reboiler and the fourth reboiler is allocated according to the overhead steam flow rates of the corresponding refining tower and rectification tower.

14. The DMF waste liquid treatment method according to claim 1, characterized in that, The first discharge pump is the circulation pump of the first reboiler; when the liquid level of the second dehydration tower is lower than the set value, a part of the flow rate in the first discharge pump is transported to the second dehydration tower as a supplement.

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