A distillation system and method for DMF aqueous solution

Abstract

The present invention belongs to the technical field of wastewater recovery and treatment, and specifically relates to a distillation system and method for a DMF aqueous solution. The distillation system for the DMF aqueous solution comprises a raw material preheater (24), an MVR dehydration tower (1), a dehydration tower (5), a flash tank (11), a distillation tower (13), a deacidification tower (15) and an MVR deamine tower (17). The distillation system and method are used to recover DMF, have the characteristics of good economy, good stability and high recovery rate, and have good promotion and application value.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater recovery and treatment, and in particular relates to a distillation system and method for a DMF aqueous solution. Background Art

[0002] DMF is also known as dimethylformamide. DMF itself is not only a widely used chemical raw material, but also an excellent solvent. Apart from halogenated hydrocarbons, DMF can also be mixed with many organic substances, including water. It is precisely because of DMF's good fusion ability that it has excellent solubility in various organic substances.

[0003] DMF is mainly used in polyurethane synthetic leather, acrylic fiber and spandex, medicine, petrochemical industry, and can also be used as a gas absorbent to purify gas. The above industries will produce a large amount of aqueous solution containing DMF during the application process. From the perspective of environmental protection and economy, it is required to recover DMF from the DMF aqueous solution. Due to the large difference in boiling point between DMF and water, it is usually recovered by distillation. Water is discharged from the top of the distillation tower as a light component, and DMF is discharged from the bottom of the distillation tower as a heavy component. Due to the high heat of evaporation of water, this process is an extremely energy-intensive process. For example, the synthetic leather industry usually produces DMF wastewater with a mass fraction of 20%. For 1 ton of this wastewater, a single distillation tower is used for dehydration. Under the condition of a reflux ratio of 1, 2*0.8=1.6 tons of steam are required to remove 0.8 tons of water; if a double distillation tower (double effect) is used for dehydration, under the condition of a reflux ratio of 1, 2*0.8 / 2=0.8 tons of steam are required to remove 0.8 tons of water; if three distillation towers (three effects) are used for dehydration, under the condition of a reflux ratio of 1, 2*0.8 / 3=0.533 tons of steam are required to remove 0.8 tons of water; if four distillation towers (three effects) are used for dehydration, under the condition of a reflux ratio of 1, 2*0.8 / 4=0.4 tons of steam are required to remove 0.8 tons of water. It can be seen that with the increase in the number of distillation towers (increase in the number of effects), the energy consumption of treating a unit of DMF aqueous solution decreases, but the marginal benefit decreases. In addition, there needs to be a temperature difference between the effects. As the number of effects increases, the maximum temperature of the effect increases, and the temperature increase will accelerate the hydrolysis of DMF into dimethylamine and formic acid during the distillation process, reduce the yield, and increase the cost of wastewater and waste gas treatment. Taking all factors into consideration, most of the three-effect distillation systems are currently used to recover DMF from DMF aqueous solution.

[0004] In recent years, with the advancement of technology, mechanical vapor recompression (MVR) technology has been applied to the distillation recovery of DMF wastewater. MVR is an energy-saving technology that reuses the energy of secondary steam generated by itself, thereby reducing the demand for external energy. As early as the 1960s, Germany and France have successfully applied this technology to the fields of chemical industry, food, papermaking, medicine, seawater desalination and sewage treatment. The working process of the evaporator is to compress the low-temperature steam through the compressor, increase the temperature and pressure, increase the thermal enthalpy, and then enter the heat exchanger for condensation to make full use of the latent heat of the steam. Except for the start-up, no steam is required during the entire evaporation process. Using this technology combined with traditional three-effect distillation, the DMF wastewater recovery technology of MVR+three-effect distillation has been developed, which reflects good economic benefits.

[0005] After comparative calculation and analysis, MVR+triple-effect distillation, MVR+double-effect distillation and MVR+single-effect distillation technologies are used to recover DMF from DMF wastewater with a mass fraction of about 20% in the synthetic leather industry. It is found that MVR+double-effect distillation is the best choice. From the perspective of energy consumption, MVR+single-effect distillation is better than MVR+double-effect distillation and better than MVR+triple-effect distillation. The main reason is that the amount of water that can be added by MVR is MVR+single-effect distillation is greater than MVR+double-effect distillation is greater than MVR+triple-effect distillation. The more water added by MVR, the more electricity is used, and the better the economy. Usually, 100kWh of electricity can replace 1 ton of steam, and the price of one ton of steam is much higher than 100kWh of electricity; in addition, as the number of effects decreases, the complexity of the method decreases, reducing equipment costs and operating difficulties. However, MVR+single-effect distillation has problems such as unstable method, difficult control of MVR dehydration ratio, and poor stability of large compressors. Therefore, the present invention adopts the basic method of MVR+double-effect distillation for the recovery of DMF in DMF wastewater. Summary of the invention

[0006] The purpose of the present invention is to provide a distillation system and method for a DMF aqueous solution; the recovery system is used to recover DMF, has the characteristics of good economy, good stability and high recovery rate, and has good promotion and application value.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A distillation system for a DMF aqueous solution, comprising a raw material preheater (24), an MVR dehydration tower (1), a dehydration tower (5), a flash tank (11), a distillation tower (13), a deacidification tower (15), and an MVR deamine tower (17);

[0009] The feed inlet of the MVR dehydration tower (1) is connected to the tube outlet of the raw material preheater (24), and the tube inlet of the raw material preheater (24) is the inlet of the raw material DMF aqueous solution; one of the bottom liquid outlet pipelines of the MVR dehydration tower (1) is connected to the feed inlet of the dehydration tower (5), and the other is connected to the liquid phase reflux port of the MVR dehydration tower (1) through the tube of the MVR dehydration tower reboiler (3); one of the bottom liquid outlet pipelines of the dehydration tower (5) is connected to the flash tank (11). The gas outlet of the flash tank (11) is connected to the feed inlet of the distillation tower (13); one of the bottom liquid outlet pipelines of the distillation tower (13) is connected to the feed inlet of the deacidification tower (15); the other of the bottom liquid outlet pipelines of the distillation tower (13) is connected to the feed inlet of the deacidification tower (15); the other of the bottom liquid outlet pipelines of the distillation tower (13) is connected to the liquid reflux port of the distillation tower (13) through the pipe side of the distillation tower reboiler (14); the top gas outlet of the deacidification tower (15) is connected to the DMF product extraction pipeline;

[0010] The top gas outlet of the MVR dehydration tower (1) is communicated with the inlet of the MVR dehydration tower compressor (2), the outlet of the MVR dehydration tower compressor (2) is communicated with the shell side inlet of the MVR dehydration tower reboiler (3), the shell side outlet of the MVR dehydration tower reboiler (3) is communicated with the inlet of the MVR dehydration tower reflux tank (4), and the bottom liquid outlet of the MVR dehydration tower reflux tank (4) is communicated with the feed inlet of the MVR deamine removal tower (17);

[0011] The top gas outlet of the dehydration tower (5) is connected to the tube-side inlet of the dehydration tower condenser (6), the tube-side outlet of the dehydration tower condenser (6) is connected to the inlet of the dehydration tower reflux tank (7), and the bottom liquid outlet of the dehydration tower reflux tank (7) is respectively connected to the feed inlet of the MVR deamine tower (17) and the gas phase reflux port of the dehydration tower (5);

[0012] The top gas outlet of the distillation tower (13) is connected to the shell side inlet of the dehydration tower reboiler (8), the shell side outlet of the dehydration tower reboiler (8) is connected to the inlet of the distillation tower reflux tank (9), and the bottom liquid outlet of the distillation tower reflux tank (9) is connected to the feed inlet of the MVR deamine tower (17).

[0013] Furthermore, it also includes a tail gas treatment unit; the tail gas treatment unit includes a tail gas condenser (21), a gas-liquid separator (22) and a tail gas washing tower (23); the top gas outlet of the MVR dehydration tower reflux tank (4), the top gas outlet of the dehydration tower reflux tank (7), and the top gas outlet of the distillation tower reflux tank (9) are all connected to the tube side inlet of the tail gas condenser (21), the tube side outlet of the tail gas condenser (21) is connected to the inlet of the gas-liquid separator (22), the top gas outlet of the gas-liquid separator (22) is connected to the gas inlet of the tail gas washing tower (23), and the bottom liquid outlet of the gas-liquid separator (22) is connected to the dimethylamine waste liquid pipeline; the bottom liquid outlet of the tail gas washing tower (23) is connected to the feed inlet of the MVR deamine tower (17).

[0014] Furthermore, the top gas outlet of the MVR deamine tower (17) is communicated with the inlet of the MVR deamine tower compressor (18), the outlet of the MVR deamine tower compressor (18) is communicated with the shell side inlet of the MVR deamine tower reboiler (19), the shell side outlet of the MVR deamine tower reboiler (19) is communicated with the inlet of the MVR deamine tower reflux tank (20), the top gas outlet of the MVR deamine tower reflux tank (20) is communicated with the tube side inlet of the tail gas condenser (21), the bottom liquid outlet of the MVR deamine tower reflux tank (20) is communicated with the top gas phase reflux port of the MVR deamine tower (17), the bottom liquid outlet of the MVR deamine tower (17) is connected to the liquid phase reflux port of the MVR deamine tower (17) through the tube side of the MVR deamine tower reboiler (19), and is communicated with the shell side inlet of the raw material preheater (24).

[0015] Furthermore, the flash tank (11) is provided with an inlet A and an inlet B; a flash heater (10) is provided on the pipeline of the inlet A, a heat recovery device (12) is provided on the pipeline of the inlet B, and the flash heater (10) and the heat recovery device (12) are connected to each other; the bottom liquid outlet of the dehydration tower (5) is connected to the inlet A through the flash heater (10), and the top gas outlet of the deacidification tower (15) is connected to the DMF product extraction pipeline through the heat recovery device (12).

[0016] Furthermore, the MVR dehydration tower (1), the dehydration tower (5), the deacidification tower (15) and the MVR deamine tower (17) are all distillation towers; and / or, the MVR dehydration tower compressor (2) and the MVR deamine tower compressor (18) are all centrifugal compressors; and / or, the MVR dehydration tower reboiler (3), the dehydration tower condenser (6), the dehydration tower reboiler (8), the flash heater (10), the heat recovery device (12), the MVR deamine tower reboiler (19), the tail gas condenser (21) and the raw material preheater (24) are all shell and tube heat exchangers; and / or, the tail gas scrubbing tower (23) is a packed spray tower.

[0017] In addition, the present invention also provides a distillation method for a DMF aqueous solution, which adopts the above-mentioned distillation system and comprises the following steps:

[0018] S1, the raw material DMF aqueous solution is preheated by the raw material preheater (24), and then passed into the MVR dehydration tower (1) for primary distillation separation. The gas phase light component is extracted from the top of the tower, compressed by the MVR dehydration tower compressor (2), heat exchanged by the MVR dehydration tower reboiler (3), condensed by the MVR dehydration tower reflux tank (4) and separated into gas and liquid, to obtain non-condensable gas and tower top water; the tower top water is divided into two streams, the first stream enters the gas phase reflux port at the top of the MVR dehydration tower (1) as reflux liquid, and the second stream is sent to the MVR deamine tower (17) for distillation; the liquid phase heavy component is discharged from the bottom of the MVR dehydration tower (1) and is divided into two streams, the first stream is refluxed to the MVR dehydration tower (1) after heat exchange, and the second stream enters the dehydration tower (5) for secondary distillation;

[0019] S2, after secondary distillation separation in the dehydration tower (5), the gas phase light component is extracted from the top of the tower, condensed in the dehydration tower condenser (6), and separated into gas and liquid in the dehydration tower reflux tank (7), to obtain non-condensable gas and tower top water; the tower top water is divided into two streams, the first stream is refluxed to the dehydration tower (5) through the gas phase reflux port of the dehydration tower (5), and the second stream is sent to the MVR deamine tower (17) for distillation; the liquid phase heavy component is discharged from the bottom of the dehydration tower (5) and divided into two streams, the first stream is refluxed to the dehydration tower (5) after heat exchange in the dehydration tower reboiler (8), and the second stream enters the flash tank (11) for flash evaporation;

[0020] S3, after flash evaporation in the flash tank (11), the gas phase and the liquid phase are separated; the liquid phase is divided into three streams, the first stream enters the flash heater (10), the second stream is discharged as the kettle residue, and the third stream is heated by the heat recovery device (12) to form a gas-liquid mixture and enter the flash heater (10);

[0021] S4, the gas phase after flash evaporation is introduced into the feed port of the distillation tower (13) for three-stage distillation separation, the gas phase light component is extracted from the top of the tower, and after heat exchange in the tube side of the dehydration tower reboiler (8), condensation in the distillation tower reflux tank (9) and gas-liquid separation, non-condensable gas and tower top water are obtained; the tower top water is divided into two streams, the first stream is refluxed to the distillation tower (13) through the gas phase reflux port of the distillation tower (13), and the second stream is sent to the MVR deamine tower (17) for distillation; the liquid phase heavy component is discharged from the bottom of the distillation tower (13) and divided into two streams, the first stream is refluxed to the distillation tower (13) after heat exchange in the distillation tower reboiler (14), and the second stream enters the deacidification tower (15) for distillation;

[0022] S5. After distillation and separation in the deacidification tower (15), the light gaseous component is extracted from the top of the tower and enters the heat recovery device (12) to be condensed into liquid. The liquid is divided into two streams. The first stream is refluxed to the gaseous reflux port of the deacidification tower (15), and the second stream is the DMF product extracted. The heavy liquid component is discharged from the bottom of the deacidification tower (15) and is divided into two streams. The first stream is refluxed to the deacidification tower (15) after heat exchange, and the second stream is the formic acid waste liquid.

[0023] Furthermore, the gaseous light components after distillation in the MVR deamine tower (17) are compressed by the MVR deamine tower compressor (18), heat exchanged by the MVR deamine tower reboiler (19), condensed by the MVR deamine tower reflux tank (20), and separated into gas and liquid to obtain non-condensable gas and reflux water; the reflux water is refluxed into the MVR deamine tower (17) through the gas phase reflux port of the MVR deamine tower (17); the liquid phase heavy components are discharged from the bottom of the MVR deamine tower (17) and divided into two streams, the first stream is refluxed to the MVR deamine tower (17) after heat exchange, and the second stream is condensed by the raw material preheater (24) and then divided into two streams, the first stream enters the top of the tail gas washing tower (23), and the second stream is extracted as the top water of the MVR deamine tower.

[0024] Furthermore, in step S1, the top water produced in the MVR dehydration tower reflux tank (4) is divided into two streams, and the mass ratio of the first stream to the second stream is (3-5):5. After the liquid phase heavy component is discharged from the bottom of the MVR dehydration tower (1), it is divided into two streams, and the mass ratio of the first stream to the second stream is (20-30):1.

[0025] And / or, in step S2, the top water produced in the dehydration tower reflux tank (7) is separated into two streams, and the mass ratio of the first stream to the second stream is (3-4):5; after the liquid phase heavy component is discharged from the bottom of the dehydration tower (5), it is separated into two streams, and the mass ratio of the first stream to the second stream is (20-30):1;

[0026] and / or, in step S3, the liquid phase is divided into three streams, and the mass ratio of the first stream, the second stream and the third stream is: (40-50):1:(40-50);

[0027] And / or, in step S4, the top water produced in the reflux tank (9) of the distillation tower is separated into two streams, the mass ratio of the first stream to the second stream is (3-5):1, and the liquid phase heavy component is separated into two streams after being discharged from the bottom of the distillation tower (13), the mass ratio of the first stream to the second stream is (20-30):1;

[0028] And / or, in step S5, the liquid generated by the heat recovery device (12) is divided into two streams, and the mass ratio of the first stream to the second stream is (1-3):1; after the liquid phase heavy component is discharged from the bottom of the deacidification tower (15), it is divided into two streams, and the mass ratio of the first stream to the second stream is (20-40):1.

[0029] Furthermore, the MVR dehydration tower (1) has a top pressure of 60-80 kPa, a top temperature of 80-90° C., a bottom pressure of 61 kPa, and a bottom temperature of 83-93° C.;

[0030] And / or, the dehydration tower (5) has a top pressure of 10-15 kPa, a top temperature of 46-50° C., a bottom pressure of 11-16 kPa, and a bottom temperature of 52-57° C.;

[0031] And / or, the top pressure of the distillation tower (13) is 30-35 kPa, the top temperature is 67-70°C, the bottom pressure is 31-36 kPa, and the bottom temperature is 108-111°C;

[0032] And / or, the deacidification tower (15) has a top pressure of 30-35 kPa, a top temperature of 111-117° C., a bottom pressure of 31-36 kPa, and a bottom temperature of 118-125° C.

[0033] Furthermore, the top pressure of the MVR deamine tower (17) is 60-70 kPa, the top temperature is 86-95°C, the bottom pressure is 61-71 kPa, and the bottom temperature is 87-97°C; and / or, after the liquid phase heavy component is discharged from the bottom of the MVR deamine tower (17), it is divided into two streams, the mass ratio of the first stream to the second stream is (30-50):1, and the second stream is condensed in a raw material preheater and then divided into two streams, the mass ratio of the first stream to the second stream is 1:(10-20).

[0034] Compared with the closest prior art, the technical solution provided by the present invention has the following excellent effects:

[0035] First, the distillation system of the DMF aqueous solution of the present invention is used to recover DMF, has the characteristics of good economy, good stability and high recovery rate, and has good promotion and application value; specifically, the treatment cost of unit DMF wastewater is lower than that of the existing MVR+three-effect distillation method, the complexity of the method is reduced, and the MVR dehydration ratio is high; and the stability is good, which is more stable than MVR+single-effect distillation. Specifically, the concentration of the DMF concentrated liquid entering the distillation tower is controllable, the compressor load is small, and the compressor stability is good; second, in the distillation method of the DMF aqueous solution of the present invention, the non-condensable gas is washed with tower top water, so as to reduce the dimethylamine concentration in the dimethylamine waste gas; and the steam condensate is evaporated under reduced pressure and reused for a second time, so as to reduce energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them:

[0037] Figure 1 It is a schematic diagram of the distillation system of the DMF aqueous solution of the present invention.

[0038] In the figure: 1-MVR dehydration tower, 2-MVR dehydration tower compressor, 3-MVR dehydration tower reboiler, 4-MVR dehydration tower reflux tank, 5-dehydration tower, 6-dehydration tower condenser, 7-dehydration tower reflux tank, 8-dehydration tower reboiler, 9-distillation tower reflux tank, 10-flash heater, 11-flash tank, 12-heat recovery device, 13-distillation tower, 14-distillation tower reboiler, 15-deacidification tower, 16-deacidification tower reboiler, 17-MVR deamine tower, 18-MVR deamine tower compressor, 19-MVR deamine tower reboiler, 20-MVR deamine tower reflux tank , 21- tail gas condenser, 22- gas-liquid separator, 23- tail gas washing tower, 24- raw material preheater, 101- first tee, 102- second tee, 103- third tee, 104- fourth tee, 105- fifth tee, 106- sixth tee, 107- seventh tee, 108- eighth tee, 109- ninth tee, 110- thirteenth tee, 111- eleventh tee, 112- twelfth tee, 113- thirteenth tee, 114- fourteenth tee, 115- fifteenth tee, 116- sixteenth tee, 1001- first fourteenth. DETAILED DESCRIPTION

[0039] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0040] In the description of the present invention, the terms "longitudinal", "lateral", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on the present invention. The terms "connected" and "connected" used in the present invention should be understood in a broad sense. For example, they can be fixed connections or detachable connections; they can be directly connected or indirectly connected through intermediate components. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0041] Example 1

[0042] A DMF aqueous solution distillation system comprises an MVR dehydration tower 1, an MVR dehydration tower compressor 2, an MVR dehydration tower reboiler 3, an MVR dehydration tower reflux tank 4, a dehydration tower 5, a dehydration tower condenser 6, a dehydration tower reflux tank 7, a dehydration tower reboiler 8, a distillation tower reflux tank 9, a flash heater 10, a flash tank 11, a heat recovery device 12, a distillation tower 13, a distillation tower reboiler 14, a deacidification tower 15, a deacidification tower reboiler 16, an MVR deamine tower 17, an MVR deamine tower compressor 18, an MVR deamine tower reboiler 19, an MVR deamine tower reflux tank 20, a tail gas condenser 21, a gas-liquid separator 22, a tail gas scrubber 23 and a raw material preheater 24;

[0043] The MVR dehydration tower 1, dehydration tower 5, distillation tower 13 and deacidification tower 15 are all distillation towers, and are all provided with a feed inlet, a tower top gas outlet, a tower top reflux inlet, a tower bottom liquid outlet, and a tower bottom reflux inlet;

[0044] The MVR deamine tower 17 is a distillation tower, which is provided with a feed inlet A, a feed inlet B, a tower top gas outlet, a tower top reflux inlet, a tower bottom liquid outlet, and a tower bottom reflux inlet;

[0045] The MVR dehydration tower compressor 2 and the MVR deamine tower compressor 18 are both centrifugal compressors, provided with an inlet and an outlet;

[0046] The MVR dehydration tower reboiler 3, dehydration tower condenser 6, dehydration tower reboiler 8, flash heater 10, heat recovery device 12, distillation tower reboiler 14, deacidification tower reboiler 16, MVR deamine tower reboiler 19, tail gas condenser 21 and raw material preheater 24 are all shell and tube heat exchangers, and are provided with tube side inlet, tube side outlet, shell side inlet and shell side outlet;

[0047] The MVR dehydration tower reflux tank 4, the dehydration tower reflux tank 7, the distillation tower reflux tank 9, the MVR deamine tower reflux tank 20 and the gas-liquid separator 22 are all tanks, with an inlet in the middle, a gas outlet at the top and a liquid outlet at the bottom;

[0048] The flash tank 11 is a tank, with an inlet A and an inlet B in the middle, a gas outlet at the top, and a liquid outlet at the bottom;

[0049] The tail gas washing tower 23 is a packed spray tower, and a water inlet and a gas outlet are arranged at the top of the packed spray tower, and a water outlet and a gas inlet are arranged at the bottom;

[0050] The feed inlet of the MVR dehydration tower 1 is connected to the tube outlet of the raw material preheater 24, and the tube inlet of the raw material preheater 24 is the inlet of the raw material DMF solution; the top gas outlet of the MVR dehydration tower 1 is connected to the inlet of the MVR dehydration tower compressor 2, the outlet of the MVR dehydration tower compressor 2 is connected to the shell inlet of the MVR dehydration tower reboiler 3, and the shell outlet of the MVR dehydration tower reboiler 3 is connected to the inlet of the MVR dehydration tower reflux tank 4; the bottom liquid outlet of the MVR dehydration tower 1 is connected to the first tee 101 and then divided into the first and second pipelines. The first pipeline is connected to the tube-side inlet of the MVR dehydration tower reboiler 3, the tube-side outlet of the MVR dehydration tower reboiler 3 is connected to the tower kettle reflux port, and the second pipeline is connected to the feed port of the dehydration tower 5; the liquid outlet of the MVR dehydration tower reflux tank 4 is connected to the second tee 102 and then divided into the first and second pipelines, the first pipeline is connected to the tower top reflux port of the MVR dehydration tower 1; the second pipeline of the second tee 102 is connected to the first port of the third tee 103; the gas outlet of the MVR dehydration tower reflux tank 4 is connected to the first port of the fourth tee 104;

[0051] The top gas outlet of the dehydration tower 5 is connected to the tube-side inlet of the dehydration tower condenser 6, and the tube-side outlet of the dehydration tower condenser 6 is connected to the inlet of the dehydration tower reflux tank 7. The shell-side inlet and shell-side outlet of the dehydration tower condenser 6 are the inlet and outlet of the cooling water respectively; the gas outlet of the dehydration tower reflux tank 7 is connected to the second port of the fourth three-way 104; the liquid outlet of the dehydration tower reflux tank 7 is connected to the fifth three-way 105 and is divided into the first and second pipelines, and the first pipeline is connected to the dehydration tower 5 The first pipeline is connected to the top reflux port of the dehydration tower 5, the second pipeline is connected to the second port of the third tee 103; the third port of the third tee 103 is connected to the first port of the thirteenth tee 110; the bottom liquid outlet of the dehydration tower 5 is connected to the sixth tee 106 and then divided into the first and second pipelines, the first pipeline is connected to the tube side inlet of the dehydration tower reboiler 8, the tube side outlet of the dehydration tower reboiler 8 is connected to the bottom reflux port of the dehydration tower 5, and the second pipeline is connected to the first port of the seventh tee 107;

[0052] The second port of the seventh three-way valve 107 is connected to the tube-side inlet of the flash heater 10, and the third port is connected to the first port of the first four-way valve 1001; the second port of the first four-way valve 1001 is connected to the liquid outlet of the flash tank 11, the third port is connected to the tube-side inlet of the heat recovery device 12, and the fourth port is the kettle residue discharge outlet; the tube-side outlet of the flash heater 10 is connected to the inlet A of the flash tank 11; the shell-side inlet and outlet of the flash heater 10 are respectively the steam inlet and the condensed water outlet; the tube-side outlet of the heat recovery device 12 is connected to the inlet B of the flash tank 11; the gas outlet of the flash tank 11 is connected to the feed port of the distillation tower 13;

[0053] The top gas outlet of the distillation tower 13 is connected to the shell side inlet of the dehydration tower reboiler 8, and the shell side outlet of the dehydration tower reboiler 8 is connected to the inlet of the distillation tower reflux tank 9; the gas outlet of the distillation tower reflux tank 9 is connected to the eighth tee 108 and is divided into a first and a second pipeline, the first pipeline is connected to the third port of the fourth tee 104, and the second pipeline is connected to the first port of the sixteenth tee 116; the liquid outlet of the distillation tower reflux tank 9 is connected to the ninth tee 109 and is divided into a first and a second pipeline, the first pipeline is connected to the top reflux port of the distillation tower 13, The second pipeline is connected to the second port of the thirteenth passage 110; the second port of the thirteenth passage 110 is connected to the feed port A of the MVR deamine tower 17; the bottom liquid outlet of the distillation tower 13 is connected to the eleventh passage 111 and is divided into the first and second pipelines, the first pipeline is connected to the pipe side inlet of the distillation tower reboiler 14, the pipe side outlet of the distillation tower reboiler 14 is connected to the bottom reflux port of the distillation tower 13, and the second pipeline is connected to the feed port of the deacidification tower 15; the shell side inlet and outlet of the distillation tower reboiler 14 are respectively the steam inlet and the condensed water outlet;

[0054] The top gas outlet of the deacidification tower 15 is connected to the shell side inlet of the heat recovery device 12; the shell side outlet of the heat recovery device 12 is connected to the twelfth tee 112 and is divided into the first and second pipelines, the first pipeline is connected to the top reflux port of the deacidification tower 15, and the second pipeline is the DMF product outlet; the bottom liquid outlet of the deacidification tower 15 is connected to the thirteenth tee 113 and is divided into the first and second pipelines, the first pipeline is connected to the tube side inlet of the deacidification tower reboiler 16, the tube side outlet of the deacidification tower reboiler 16 is connected to the bottom reflux port of the deacidification tower 15, and the second pipeline is the formic acid waste liquid outlet; the shell side inlet and outlet of the deacidification tower reboiler 16 are respectively the steam inlet and the condensed water outlet;

[0055] The top gas outlet of the MVR deamine tower 17 is communicated with the inlet of the MVR deamine tower compressor 18, the outlet of the MVR deamine tower compressor 18 is communicated with the shell side inlet of the MVR deamine tower reboiler 19, the shell side outlet of the MVR deamine tower reboiler 19 is communicated with the inlet of the MVR deamine tower reflux tank 20; the gas outlet of the MVR deamine tower reflux tank 20 is communicated with the second port of the sixteenth tee 116; the third port of the sixteenth tee 116 is communicated with the tube side inlet of the tail gas condenser 21, the tube side outlet of the tail gas condenser 21 is communicated with the inlet of the gas-liquid separator 22; the shell side outlet of the tail gas condenser 21 is communicated with the inlet of the gas-liquid separator 22; The inlet and outlet of the MVR deamine tower reflux tank 20 are respectively a cooling water inlet and a cooling water outlet; the liquid outlet of the MVR deamine tower reflux tank 20 is connected to the top reflux port of the MVR deamine tower 17; the bottom liquid outlet of the MVR deamine tower 17 is connected to the fourteenth three-way 114 and is divided into a first and a second pipeline, the first pipeline is connected to the tube side inlet of the MVR deamine tower reboiler 19, and the tube side outlet of the MVR deamine tower reboiler 19 is connected to the bottom reflux port of the MVR deamine tower 17; the shell side inlet and outlet of the MVR deamine tower reboiler 19 are respectively a steam inlet and a condensed water outlet, and the second pipeline is connected to the shell side inlet of the raw material preheater 24;

[0056] The shell side outlet of the raw material preheater 24 is connected to the fifteenth tee 115 and is divided into the first and second pipelines, the first pipeline is connected to the water inlet of the tail gas washing tower 23, and the second pipeline is the water outlet of the top of the MVR deamine tower; the gas outlet of the gas-liquid separator 22 is connected to the gas inlet of the tail gas washing tower 23, and the liquid outlet is the dimethylamine waste liquid outlet; the liquid outlet of the tail gas washing tower 23 is connected to the feed port B of the MVR deamine tower 17, and the gas outlet is the dimethylamine waste gas outlet.

[0057] Compared with the MVR+triple-effect distillation, the MVR+two-effect distillation of the present invention has one less distillation tower for dehydration between the dehydration tower and the flash tank. Although such a setting reduces the number of effects of the secondary steam utilization of the distillation, the dehydration ratio of the MVR dehydration tower can be increased (the reason is that the MVR+three-effect distillation is subject to the problem of easy blockage of the heat exchanger, and the DMF concentration entering the distillation tower cannot exceed 70%, so the dehydration ratio of the MVR tower needs to be strictly controlled at 50% of the total feed amount). The dehydration ratio of the MVR tower using the MVR+two-effect distillation process of the present invention can be increased to 60%. According to simulation calculations, the MVR tower can reduce the system consumption of 1 ton of steam for every 100 kWh of electricity used. The price of electricity does not exceed 1 yuan / kWh, while the price of steam is usually 200 yuan / ton, thereby improving the economy of the system. In addition, compared with the traditional MVR+three-effect distillation process, the present invention is provided with a tail gas washing tower for washing tail gas, which can reduce the malodorous dimethylamine waste gas in the tail gas and reduce the risk of pipeline explosion.

[0058] The process of working of utilizing the system of the present embodiment to reclaim the DMF aqueous solution is as follows:

[0059] The DMF solution is a 10% aqueous solution by mass. The DMF solution at room temperature is preheated to 60°C by a raw material preheater 24 and then enters an MVR dehydration tower 1 for distillation to obtain a tower top gas phase and a tower bottom liquid phase. The MVR dehydration tower 1 has a tower top pressure of 60 kPa (absolute pressure, the same below) and a tower bottom pressure of 80°C, and a tower bottom pressure of 61 kPa and a tower bottom temperature of 83°C. The tower top gas phase is increased in pressure to 105 kPa and a temperature to 101°C by an MVR dehydration tower compressor 2, and then condensed into a 95°C steam-water mixture by shell heat exchange in an MVR dehydration tower reboiler 3; the steam-water mixture enters an MVR dehydration tower reflux tank 4 for separation into non-condensable gas and tower top water, and the non-condensable gas is separated into non-condensable gas and tower top water by a fourth tee 104, an eighth tee 108 and a first tee 109. The sixteenth tee 116 enters the tube side of the tail gas condenser 21 for condensation; the tower top water is divided into the first and second streams after passing through the second tee 102, and the mass ratio of the first stream to the second stream is 3:5. The first stream of tower top water enters the top of the MVR dehydration tower 1 as reflux liquid, and the second stream enters the MVR deamine tower 17 as part of the tower feed after passing through the third tee 103 and the thirteenth tee 110; the tower bottom liquid phase of the MVR dehydration tower 1 enters the first tee 101 and is divided into the first and second streams, and the mass ratio of the first stream to the second stream is 20:1. The first stream is heated by the tube side of the MVR dehydration tower reboiler 3 to form a 90°C steam-water mixture and enters the bottom of the MVR dehydration tower reboiler 3, and the second stream enters the dehydration tower 5 as the tower feed;

[0060] The dehydration tower 5 is rectified to obtain a tower top gas phase and a tower bottom liquid phase, the tower top pressure of the dehydration tower 5 is 10kPa, the temperature is 46°C, the tower bottom pressure is 11kPa, the temperature is 52°C; the tower top gas phase of the dehydration tower 5 enters the dehydration tower condenser 6 to condense into a gas-liquid mixture, and then enters the dehydration tower reflux tank 7 to separate into non-condensable gas and tower top water, the non-condensable gas enters the pipe side of the tail gas condenser 21 through the fourth tee 104, the eighth tee 108 and the sixteenth tee 116 to condense, and the tower top water enters the fifth tee 10 5 is divided into a first stream and a second stream, the mass ratio of the first stream to the second stream is 3:5, the first stream enters the top of the dehydration tower 5 as reflux liquid, and the second stream enters the MVR deamine tower 17 as part of the feed of the tower after passing through the third tee 103 and the thirteenth tee 110; the bottom liquid phase of the dehydration tower 5 enters the sixth tee 106 and is divided into a first stream and a second stream, the mass ratio of the first stream to the second stream is 20:1, and the first stream enters the bottom of the dehydration tower 5 through the tube side of the dehydration tower reboiler 8;

[0061] The second stream of the sixth tee 106 passes through the seventh tee 107 and enters the flash heater 10 to be heated to 107°C to form a gas-liquid mixture. The pressure of the tube side of the flash heater 10 is 31 kPa. The gas-liquid mixture enters the flash tank 11 to be separated into a gas phase and a concentrated liquid. The concentrated liquid enters the first tee 1001 to be separated into a first stream, a second stream and a third stream. The mass ratio of the first stream to the second stream to the third stream is 40:1:40. The first stream enters the flash heater 10 through the seventh tee 107, the second stream is discharged as residual liquid, and the third stream is heated to 108°C through the shell side of the heat recovery device 12 to form a gas-liquid mixture and enter the flash heater 10.

[0062] The gas phase of the flash heater 10 enters the distillation tower 13 for distillation to form a top gas phase and a bottom liquid phase. The top pressure of the distillation tower 13 is 30 kPa and the temperature is 67° C. The bottom pressure is 31 kPa, the temperature is 108°C, the top gas phase is condensed into a liquid-gas-liquid mixture through the shell side of the dehydration tower reboiler 8, and the gas-liquid mixture enters the reflux tank 9 of the distillation tower to be separated into non-condensable gas and top water, and the non-condensable gas enters the tube side of the tail gas condenser 21 through the eighth tee 108 and the sixteenth tee 116 for condensation; the top water of the distillation tower reflux tank 9 is divided into a first strand and a second strand through the ninth tee 109, and the mass ratio of the first strand to the second strand is 3:5, the first strand enters the top of the distillation tower 13 as reflux liquid, and the second strand enters the MVR deamine tower 17 as part of the feed of the tower after passing through the thirteenth tee 110; the bottom liquid phase of the distillation tower 13 enters the eleventh tee 111 and is divided into a first strand and a second strand, and the mass flow ratio of the first strand and the second strand is 20:1, the first strand is heated into a gas-liquid mixture through the tube side of the distillation tower reboiler 14 and enters the bottom of the distillation tower 13, and the second strand enters the deacidification tower 15 as the raw material of the tower;

[0063] The deacidification tower 15 is rectified to form a tower top gas phase and a tower bottom liquid phase. The tower top pressure of the deacidification tower 15 is 30 kPa and the temperature is 111°C, and the tower bottom pressure is 31 kPa and the temperature is 118°C. The tower top gas phase enters the shell side of the heat recovery device 12 and is condensed into liquid. The liquid enters the twelfth tee 112 and is divided into a first strand and a second strand. The mass flow ratio between the first strand and the second strand is 1-3:1. The first strand enters the tower top of the deacidification tower 15 as reflux liquid, and the second strand is a DMF product with a mass purity of 98; the tower bottom liquid phase of the deacidification tower 15 enters the thirteenth tee 113 and is divided into a first strand and a second strand. The mass flow ratio between the first strand and the second strand is 20:1. The first strand enters the tube side of the deacidification tower reboiler 16 and is heated into a gas-liquid mixture and then enters the tower bottom of the deacidification tower 15. The second strand is formic acid waste liquid with a formic acid content of 30%;

[0064] The tower top water and the washing water from the bottom of the tail gas washing tower 23 are used as raw materials to enter the MVR deamine tower 17 for distillation to obtain a tower top gas phase and a tower bottom liquid phase. The tower top pressure of the MVR deamine tower 17 is 60kPa and the temperature is 86°C, and the tower bottom pressure is 61kPa and the temperature is 87°C. The tower top gas phase passes through the MVR dehydration tower compressor (2) and the pressure is increased to 105kPa and the temperature is increased to 130°C. Then, it is partially condensed into a gas-liquid mixture through the shell side of the MVR deamine tower reboiler 19. The gas-liquid mixture enters the MVR deamine tower reflux tank 20 and is separated into non-condensable gas and reflux water. The non-condensable gas enters the tube side of the tail gas condenser 21 through the sixteenth tee 116 for condensation. The tail gas condenser 21 tube side outlet obtains a gas-liquid mixed liquid, which enters the gas-liquid separator 22 and is separated into non-condensable gas and condensate. The non-condensable gas enters the tail gas washing tower The bottom of the tower 23 is washed and discharged as dimethylamine waste gas, and the condensate is dimethylamine waste liquid; the bottom liquid phase of the MVR deamine tower 17 enters the fourteenth tee 114 and is divided into a first stream and a second stream, and the mass flow ratio between the first stream and the second stream is 30:1. The first stream is heated to a gas-liquid mixture through the tube side of the MVR deamine tower reboiler 19 and enters the bottom of the MVR deamine tower 17; the second stream of the fourteenth tee 114 is condensed to 30°C through the shell side of the raw material preheater 24 and enters the fifteenth tee 115 and is divided into a first stream and a second stream, and the mass flow ratio between the first stream and the second stream is 1:10. The first stream enters the top of the tail gas washing tower 23 and is discharged from the bottom to the MVR deamine tower 17 as washing water, and the second stream is the top water of the MVR deamine tower, and the mass content of DMF in the top water of the MVR deamine tower is 50 ppm.

[0065] The proportion of the tower top water in the present invention is equal to the reflux ratio of the distillation process. The larger the reflux ratio, the better the distillation separation effect, but the higher the energy consumption. The distribution of the tower top water is set on the basis of comprehensive consideration of the separation effect and energy consumption. Such a proportion can ensure that the content of DMF in the tower top water is less than 200ppm; the proportion of the tower bottom liquid is distributed in consideration of the flow rate requirements in the reboiler tube. The larger the flow rate in the tube, the larger the total heat transfer coefficient, which is beneficial to improving the heat transfer efficiency, but increases the energy consumption. The present invention proposes the above proportion on the basis of comprehensive consideration of the heat transfer effect and energy consumption, thereby ensuring the heat exchange performance of the tower bottom reboiler.

[0066] The main parameters of the present invention, MVR+triple-effect distillation and MVR+single-effect distillation are compared as shown in Table 1 below:

[0067] Table 1

[0068]

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A distillation system for DMF aqueous solution, characterized in that, It includes a raw material preheater (24), an MVR dehydration tower (1), a dehydration tower (5), a flash tank (11), a distillation tower (13), a deacidification tower (15) and an MVR deamine tower (17); The feed inlet of the MVR dehydration tower (1) is connected to the tube outlet of the raw material preheater (24), and the tube inlet of the raw material preheater (24) is the inlet of the raw material DMF aqueous solution; one of the bottom liquid outlet pipelines of the MVR dehydration tower (1) is connected to the feed inlet of the dehydration tower (5), and the other is connected to the liquid phase reflux port of the MVR dehydration tower (1) through the tube of the MVR dehydration tower reboiler (3); one of the bottom liquid outlet pipelines of the dehydration tower (5) is connected to the flash tank (11). The gas outlet of the flash tank (11) is connected to the feed inlet of the distillation tower (13); one of the bottom liquid outlet pipelines of the distillation tower (13) is connected to the feed inlet of the deacidification tower (15); the other of the bottom liquid outlet pipelines of the distillation tower (13) is connected to the feed inlet of the deacidification tower (15); the other of the bottom liquid outlet pipelines of the distillation tower (13) is connected to the liquid reflux port of the distillation tower (13) through the pipe side of the distillation tower reboiler (14); the top gas outlet of the deacidification tower (15) is connected to the DMF product extraction pipeline; The top gas outlet of the MVR dehydration tower (1) is communicated with the inlet of the MVR dehydration tower compressor (2), the outlet of the MVR dehydration tower compressor (2) is communicated with the shell side inlet of the MVR dehydration tower reboiler (3), the shell side outlet of the MVR dehydration tower reboiler (3) is communicated with the inlet of the MVR dehydration tower reflux tank (4), and the bottom liquid outlet of the MVR dehydration tower reflux tank (4) is communicated with the feed inlet of the MVR deamine removal tower (17); The top gas outlet of the dehydration tower (5) is connected to the tube-side inlet of the dehydration tower condenser (6), the tube-side outlet of the dehydration tower condenser (6) is connected to the inlet of the dehydration tower reflux tank (7), and the bottom liquid outlet of the dehydration tower reflux tank (7) is respectively connected to the feed inlet of the MVR deamine tower (17) and the gas phase reflux port of the dehydration tower (5); The top gas outlet of the distillation tower (13) is connected to the shell side inlet of the dehydration tower reboiler (8), the shell side outlet of the dehydration tower reboiler (8) is connected to the inlet of the distillation tower reflux tank (9), and the bottom liquid outlet of the distillation tower reflux tank (9) is connected to the feed inlet of the MVR deamine tower (17); The invention also comprises a tail gas treatment unit; the tail gas treatment unit comprises a tail gas condenser (21), a gas-liquid separator (22) and a tail gas washing tower (23); the top gas outlet of the MVR dehydration tower reflux tank (4), the top gas outlet of the dehydration tower reflux tank (7) and the top gas outlet of the distillation tower reflux tank (9) are all connected to the tube side inlet of the tail gas condenser (21); the tube side outlet of the tail gas condenser (21) is connected to the inlet of the gas-liquid separator (22); the top gas outlet of the gas-liquid separator (22) is connected to the gas inlet of the tail gas washing tower (23); the bottom liquid outlet of the gas-liquid separator (22) is connected to the dimethylamine waste liquid pipeline; the bottom liquid outlet of the tail gas washing tower (23) is connected to the feed inlet of the MVR deamine tower (17).

2. The distillation system according to claim 1, characterized in that: The top gas outlet of the MVR deamine tower (17) is communicated with the inlet of the MVR deamine tower compressor (18), the outlet of the MVR deamine tower compressor (18) is communicated with the shell side inlet of the MVR deamine tower reboiler (19), the shell side outlet of the MVR deamine tower reboiler (19) is communicated with the inlet of the MVR deamine tower reflux tank (20), the top gas outlet of the MVR deamine tower reflux tank (20) is communicated with the tube side inlet of the tail gas condenser (21), the bottom liquid outlet of the MVR deamine tower reflux tank (20) is communicated with the top gas phase reflux port of the MVR deamine tower (17), the bottom liquid outlet of the MVR deamine tower (17) is connected to the liquid phase reflux port of the MVR deamine tower (17) through the tube side of the MVR deamine tower reboiler (19), and is communicated with the shell side inlet of the raw material preheater (24).

3. The distillation system according to claim 2, characterized in that: The flash tank (11) is provided with an inlet A and an inlet B; a flash heater (10) is provided on the pipeline of the inlet A, a heat recovery device (12) is provided on the pipeline of the inlet B, and the flash heater (10) and the heat recovery device (12) are connected to each other; the bottom liquid outlet of the dehydration tower (5) is connected to the inlet A through the flash heater (10), and the top gas outlet of the deacidification tower (15) is connected to the DMF product extraction pipeline through the heat recovery device (12).

4. The distillation system according to claim 3, characterized in that: The MVR dehydration tower (1), the dehydration tower (5), the deacidification tower (15) and the MVR deamine tower (17) are all distillation towers; and / or, the MVR dehydration tower compressor (2) and the MVR deamine tower compressor (18) are all centrifugal compressors; and / or, the MVR dehydration tower reboiler (3), the dehydration tower condenser (6), the dehydration tower reboiler (8), the flash heater (10), the heat recovery device (12), the MVR deamine tower reboiler (19), the tail gas condenser (21) and the raw material preheater (24) are all shell and tube heat exchangers; and / or, the tail gas scrubbing tower (23) is a packed spray tower.

5. A rectification method for a DMF aqueous solution, characterized in that, The distillation system according to any one of claims 1 to 4 is used, comprising the following steps: S1, the raw material DMF aqueous solution is preheated by the raw material preheater (24), and then passed into the MVR dehydration tower (1) for primary distillation separation. The gas phase light component is extracted from the top of the tower, compressed by the MVR dehydration tower compressor (2), heat exchanged by the MVR dehydration tower reboiler (3), condensed by the MVR dehydration tower reflux tank (4) and separated into gas and liquid, to obtain non-condensable gas and tower top water; the tower top water is divided into two streams, the first stream enters the gas phase reflux port at the top of the MVR dehydration tower (1) as reflux liquid, and the second stream is sent to the MVR deamine tower (17) for distillation; the liquid phase heavy component is discharged from the bottom of the MVR dehydration tower (1) and is divided into two streams, the first stream is refluxed to the MVR dehydration tower (1) after heat exchange, and the second stream enters the dehydration tower (5) for secondary distillation; S2, after secondary distillation separation in the dehydration tower (5), the gas phase light component is extracted from the top of the tower, condensed in the dehydration tower condenser (6), and separated into gas and liquid in the dehydration tower reflux tank (7), to obtain non-condensable gas and tower top water; the tower top water is divided into two streams, the first stream is refluxed to the dehydration tower (5) through the gas phase reflux port of the dehydration tower (5), and the second stream is sent to the MVR deamine tower (17) for distillation; the liquid phase heavy component is discharged from the bottom of the dehydration tower (5) and divided into two streams, the first stream is refluxed to the dehydration tower (5) after heat exchange in the dehydration tower reboiler (8), and the second stream enters the flash tank (11) for flash evaporation; S3, after flash evaporation in the flash tank (11), the gas phase and the liquid phase are separated; the liquid phase is divided into three streams, the first stream enters the flash heater (10), the second stream is discharged as the kettle residue, and the third stream is heated by the heat recovery device (12) to form a gas-liquid mixture and enter the flash heater (10); S4, the gas phase after flash evaporation is introduced into the feed port of the distillation tower (13) for three-stage distillation separation, the gas phase light component is extracted from the top of the tower, and after heat exchange in the tube side of the dehydration tower reboiler (8), condensation in the distillation tower reflux tank (9) and gas-liquid separation, non-condensable gas and tower top water are obtained; the tower top water is divided into two streams, the first stream is refluxed to the distillation tower (13) through the gas phase reflux port of the distillation tower (13), and the second stream is sent to the MVR deamine tower (17) for distillation; the liquid phase heavy component is discharged from the bottom of the distillation tower (13) and divided into two streams, the first stream is refluxed to the distillation tower (13) after heat exchange in the distillation tower reboiler (14), and the second stream enters the deacidification tower (15) for distillation; S5. After distillation and separation in the deacidification tower (15), the light gaseous component is extracted from the top of the tower and enters the heat recovery device (12) to be condensed into liquid. The liquid is divided into two streams. The first stream is refluxed to the gaseous reflux port of the deacidification tower (15), and the second stream is the DMF product extracted. The heavy liquid component is discharged from the bottom of the deacidification tower (15) and is divided into two streams. The first stream is refluxed to the deacidification tower (15) after heat exchange, and the second stream is the formic acid waste liquid.

6. The distillation method according to claim 5, characterized in that: After the gaseous light components are distilled in the MVR deamine tower (17), they are compressed by the MVR deamine tower compressor (18), heat exchanged by the MVR deamine tower reboiler (19), condensed by the MVR deamine tower reflux tank (20), and separated into gas and liquid, to obtain non-condensable gas and reflux water; the reflux water is refluxed into the MVR deamine tower (17) through the gas phase reflux port of the MVR deamine tower (17); the liquid heavy components are discharged from the bottom of the MVR deamine tower (17) and divided into two streams, the first stream is refluxed to the MVR deamine tower (17) after heat exchange, and the second stream is condensed by the raw material preheater (24) and then divided into two streams, the first stream enters the top of the tail gas washing tower (23), and the second stream is extracted as the top water of the MVR deamine tower.

7. The distillation method according to claim 5, characterized in that: In step S1, the top water produced in the reflux tank (4) of the MVR dehydration tower is separated into two streams, and the mass ratio of the first stream to the second stream is (3-5):

5. After the liquid phase heavy component is discharged from the bottom of the MVR dehydration tower (1), it is separated into two streams, and the mass ratio of the first stream to the second stream is (20-30):

1. And / or, in step S2, the top water produced by the dehydration tower reflux tank (7) is divided into two streams, and the mass ratio of the first stream to the second stream is (3-4):5; After the liquid phase heavy component is discharged from the bottom of the dehydration tower (5), it is divided into two streams, and the mass ratio of the first stream to the second stream is (20-30):1; and / or, in step S3, the liquid phase is divided into three streams, and the mass ratio of the first stream, the second stream and the third stream is: (40-50):1:(40-50); And / or, in step S4, the top water produced in the reflux tank (9) of the distillation tower is separated into two streams, the mass ratio of the first stream to the second stream is (3-5):1, and the liquid phase heavy component is separated into two streams after being discharged from the bottom of the distillation tower (13), the mass ratio of the first stream to the second stream is (20-30):1; And / or, in step S5, the liquid generated by the heat recovery device (12) is divided into two streams, and the mass ratio of the first stream to the second stream is (1-3):1; after the liquid phase heavy component is discharged from the bottom of the deacidification tower (15), it is divided into two streams, and the mass ratio of the first stream to the second stream is (20-40):

1.

8. The distillation method according to claim 5, characterized in that: The MVR dehydration tower (1) has a top pressure of 60-80 kPa, a top temperature of 80-90° C., a bottom pressure of 61 kPa, and a bottom temperature of 83-93° C.; And / or, the dehydration tower (5) has a top pressure of 10-15 kPa, a top temperature of 46-50° C., a bottom pressure of 11-16 kPa, and a bottom temperature of 52-57° C.; And / or, the top pressure of the distillation tower (13) is 30-35 kPa, the top temperature is 67-70°C, the bottom pressure is 31-36 kPa, and the bottom temperature is 108-111°C; And / or, the deacidification tower (15) has a top pressure of 30-35 kPa, a top temperature of 111-117° C., a bottom pressure of 31-36 kPa, and a bottom temperature of 118-125° C.

9. The distillation method according to claim 6, characterized in that: The top pressure of the MVR deamine tower (17) is 60-70 kPa, the top temperature is 86-95°C, the bottom pressure is 61-71 kPa, and the bottom temperature is 87-97°C; and / or, after the liquid phase heavy component is discharged from the bottom of the MVR deamine tower (17), it is divided into two streams, the mass ratio of the first stream to the second stream is (30-50):1, and the second stream is condensed in a raw material preheater and then divided into two streams, the mass ratio of the first stream to the second stream is 1:(10-20).

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