An evaporation system and an evaporation method and use based on the system

Abstract

In order to solve the problems in the prior art, the application discloses an evaporation system, an evaporation method based on the system and application, the evaporation system comprises a steam compression unit and a DTB crystallizer, and the evaporation method comprises the following steps: performing a neutralization reaction or an evaporation crystallization treatment in the DTB crystallizer; meanwhile, clear liquid in a clear liquid cavity of the DTB crystallizer is pumped out and sent to a cold side of a heat exchanger; secondary steam generated in the DTB crystallizer is sent to the steam compression unit to be compressed step by step to increase temperature and pressure; the compressed steam is sent to a hot side of the heat exchanger to exchange heat with the clear liquid in the cold side; the clear liquid in the heat exchanger is sent back to the DTB crystallizer after heat exchange to continue to participate in the reaction or the crystallization process after the temperature of the clear liquid is increased to a preset temperature; and the steam after heat exchange is condensed into condensed water and discharged. The application effectively realizes the organic combination of the DTB crystallizer and the steam circulation device.

Description

Technical Field

[0001] This invention relates to the field of evaporation technology, and in particular to an evaporation system, an evaporation method based on the system, and its applications. Background Technology

[0002] DTB crystallizers are typical internal circulation crystallizers. By incorporating a flow guiding mechanism within the crystallizer to create circulation channels, they ensure excellent mixing conditions for the crystal slurry. Good internal circulation can be achieved with only a low pressure head, and high flow velocities can be maintained at all flow cross-sections within the crystallizer, resulting in a crystal slurry density of 30%-40 wt%. In evaporation crystallization, DTB crystallizers can rapidly eliminate supersaturation at the boiling interface, keeping the solution supersaturation at a low level. This results in the production of larger crystals that are less prone to scaling, making them one of the main types of continuous crystallizers. DTB crystallizers are commonly used in evaporation and reaction crystallization operations and are widely applied in the crystallization production of products such as potassium chloride, ammonium sulfate, and ammonium chloride.

[0003] Mechanical vapor recompression (MVR) technology is one of the most advanced energy-saving technologies in the field of evaporation crystallization. Its principle is to use a steam compressor to compress the secondary steam generated by evaporation, converting electrical energy into heat energy and increasing the enthalpy of the secondary steam. The secondary steam with increased heat energy is then returned to the evaporator or crystallizer as a heating source, realizing the recycling of the latent heat of the secondary steam. MVR technology can make the economic efficiency of live steam equivalent to 30 effects of multi-effect evaporation, and can achieve "zero" steam consumption during normal operation.

[0004] In existing technologies combining DTB crystallization and MVR, there are reports of using secondary steam generated in the flash chamber of the DTB crystallizer, compressed and heated by an MVR steam compressor, to heat the material inside the evaporator. However, existing technologies generally suffer from the following shortcomings: Firstly, existing technologies generally only use single-stage steam compressors. The pressure ratio and temperature rise capacity of single-stage compressors are limited, and the temperature rise is usually only 10-15℃, which is difficult to meet the requirements of crystallization processes that require high-boiling-point materials or large heat transfer temperature differences.

[0005] Secondly, existing technologies do not involve the coupling design of clear liquid circulation and steam heating in DTB crystallizers, making it impossible to achieve precise control of the temperature field inside the crystallizer.

[0006] Third, for multi-stage series crystallization processes, existing technologies lack a system solution for the coupling and reuse of secondary steam between different crystallizers. Each crystallizer operates independently, resulting in low energy utilization efficiency.

[0007] Fourth, although there are reports of existing technologies using MVR evaporation separation devices with two-stage compressors in series, their application scenarios are for the graded crystallization of low-boiling salts and high-boiling salts in wastewater treatment, and do not involve the clear liquid circulation heating and multi-mode steam reuse of DTB crystallizers. Summary of the Invention

[0008] To address at least one of the drawbacks of the prior art, the present invention provides the following technical solution: An evaporation system includes: at least one DTB crystallizer, and a heating unit and a vapor compression unit connected to the DTB crystallizer.

[0009] The DTB crystallizer includes: a hollow circulation chamber connected to the feed pipeline, with a flow guiding mechanism located near the bottom; a clear liquid chamber outside the flow guiding mechanism; a crystal slurry outlet at the bottom of the circulation chamber and a steam outlet at the top.

[0010] The heating unit includes a heat exchanger. The refrigerant inlet of the heat exchanger is connected to the upper part of the clear liquid chamber of the DTB crystallizer through a first pipeline, and the refrigerant outlet is connected to the bottom of the flow guiding mechanism of the DTB crystallizer through a second pipeline. The heat medium inlet of the heat exchanger is connected to the steam outlet of the DTB crystallizer through a third pipeline, and the heat medium outlet is connected to the collection mechanism through a fourth pipeline.

[0011] The steam compression unit is installed on the third pipeline and pressurizes and heats the steam outlet of the DTB crystallizer before delivering it to the heat medium inlet of the heat exchanger; the steam compression unit includes at least two MVR fan units connected in series through interstage steam pipelines.

[0012] The first pipeline is equipped with a circulation pump for extracting the clear liquid in the clear liquid chamber and transporting it to the refrigerant inlet of the heat exchanger.

[0013] The third pipeline includes a live steam replenishment pipeline in the section between the steam compression unit and the DTB crystallizer.

[0014] Furthermore, the circulating chamber of the DTB crystallizer is equipped with a defoaming device at the steam outlet.

[0015] Furthermore, the present invention also provides an evaporation method based on the above-described evaporation system, comprising the following steps: Step 1: Neutralize or evaporate crystallize the DTB crystallizer; at the same time, extract the clear liquid from the clear liquid chamber of the DTB crystallizer and send it to the cold side of the heat exchanger.

[0016] Step 2: The secondary steam generated in the DTB crystallizer in Step 1 is sent to the steam compression unit and compressed and heated in stages by the MVR blower unit.

[0017] Step 3: The steam compressed by the multi-stage MVR fan is sent to the hot side of the heat exchanger to exchange heat with the clear liquid on the cold side.

[0018] Step 4: After the temperature of the clear liquid after heat exchange in the heat exchanger rises to the preset temperature, it is sent back to the DTB crystallizer to continue to participate in the reaction or crystallization process; the steam after heat exchange is condensed into condensate and then discharged.

[0019] Furthermore, the step-by-step compression and temperature / pressure increase method described in step 2 is as follows: independently control the compression ratio of each MVR fan to be 1.2-2.0, and independently control the temperature rise after compression of each MVR fan to be 10-15℃.

[0020] Furthermore, when the system contains only one DTB crystallizer, the secondary steam from the DTB crystallizer is compressed by a multi-stage MVR fan and then reused in the heat exchanger of the original DTB crystallizer.

[0021] Furthermore, when the system contains two or more DTB crystallizers, the secondary steam from the first DTB crystallizer is compressed by a multi-stage MVR fan and then reused in the heat exchanger of the second DTB crystallizer. The secondary steam from the second DTB crystallizer is compressed by a multi-stage MVR fan and then reused in the heat exchanger of the third DTB crystallizer, and so on.

[0022] Furthermore, the system pressure inside the first DTB crystallizer is controlled to be lower than the system pressure inside the second DTB crystallizer, and the system temperature inside the first DTB crystallizer is higher than the system temperature inside the second DTB crystallizer; the system pressure inside the second DTB crystallizer is controlled to be lower than the system pressure inside the third DTB crystallizer, and the system temperature inside the second DTB crystallizer is higher than the system temperature inside the third DTB crystallizer, and so on.

[0023] Furthermore, when the system includes a DTB crystallizer for neutralization reaction and a DTB crystallizer for evaporation crystallization, the secondary steam from the DTB crystallizer for neutralization reaction is recycled to the heat exchanger of the DTB crystallizer for evaporation crystallization after being compressed by a multi-stage MVR.

[0024] Furthermore, a portion of the secondary steam from the DTB crystallizer used for evaporation crystallization is compressed through a multi-stage MVR system and then reused in the heat exchanger of the DTB crystallizer used for evaporation crystallization.

[0025] Furthermore, when the system is started, live steam is introduced into the system through the live steam replenishment pipeline. After the DTB crystallizer stably generates sufficient secondary steam, the live steam replenishment valve is gradually closed, and the system enters normal circulation operation.

[0026] In a third aspect, the present invention provides a method for producing methionine hydroxy analogues, the method comprising the reaction process of methionine hydroxy analogues and the crystallization process of the byproduct ammonium sulfate during the production of methionine hydroxy analogues based on the above-described evaporation method.

[0027] Furthermore, the evaporation system includes at least a reaction DTB crystallizer and an evaporation crystallizer, wherein the reaction DTB crystallizer is used for the reaction process of methionine hydroxy analogues, and the evaporation crystallizer is used for the crystallization process of the byproduct ammonium sulfate.

[0028] In a fourth aspect, the present invention provides a method for producing caprolactam, wherein the method is based on the above-described evaporation method for crystallizing ammonium sulfate, a byproduct of caprolactam production.

[0029] The beneficial effects of this invention are as follows: 1. This invention effectively combines the DTB crystallizer and the MVR steam circulation device, and achieves precise control of the temperature field inside the crystallizer through the coupling design of the two.

[0030] 2. This invention overcomes the shortcomings of existing single-stage MVR steam circulation systems for DTB crystallizers, such as limited compression temperature rise and a single energy recovery path.

[0031] 3. This invention can perform stepped temperature and pressure increases on the steam discharged from the DTB crystallizer and combine it with clear liquid circulation heating to achieve efficient heat energy recovery and reuse. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the process flow for the single DTB crystallizer reuse mode of the present invention. Figure 2 This is a schematic diagram of the process flow for the multi-DTB crystallizer series-connected reuse mode of the present invention. Figure 3 This is a schematic diagram of the process flow of the neutralization reaction-evaporation crystallization coupled reuse mode in this invention.

[0033] In the diagram: 1. DTB crystallizer; 2. Flow guiding mechanism; 3. Feed pipeline; 4. First pipeline; 5. Circulating pump; 6. Heat exchanger; 7. Second pipeline; 8. Defogging device; 9. Third pipeline; 10. Steam compression unit; 11. Live steam replenishment pipeline; 12. Live steam replenishment valve; 13. Fourth pipeline; 14. Collection mechanism; 15. First DTB crystallizer; 16. Second DTB crystallizer; 17. DTB crystallizer for neutralization reaction; 18. DTB crystallizer for evaporation crystallization; 19. Feed pipeline 1; 20. Feed pipeline 2; 21. Product collection pipeline; 22. Product collection pump; 23. Product feed pipeline; 24. Steam regulating valve to steam compression unit; 25. Steam regulating valve to steam condenser; 26. Steam condenser; 27. Collection mechanism. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0035] Example 1 An evaporation system, such as Figure 1 As shown, it includes: a DTB crystallizer 1, a heating unit and a vapor compression unit connected to the DTB crystallizer 1.

[0036] The DTB crystallizer 1 includes: a hollow circulation chamber connected to the feed pipe 3, and a flow guiding mechanism 2 located near the bottom of the circulation chamber. A clear liquid chamber is located outside the flow guiding mechanism 2 within the circulation chamber; a crystal slurry outlet is located at the bottom of the circulation chamber, and a steam outlet is located at the top. A defoaming device 8 is located at the steam outlet.

[0037] The heating unit includes a heat exchanger 6. The refrigerant inlet of the heat exchanger 6 is connected to the upper part of the clear liquid chamber of the DTB crystallizer 1 through a first pipe 4, and the refrigerant outlet is connected to the bottom of the flow guiding mechanism 2 of the DTB crystallizer 1 through a second pipe 7. The heat medium inlet of the heat exchanger 6 is connected to the steam outlet of the DTB crystallizer 1 through a third pipe 9, and the heat medium outlet is connected to the collection mechanism 14 through a fourth pipe 13.

[0038] The vapor compression unit 10 is installed on the third pipeline 9 and pressurizes and heats the steam outlet of the DTB crystallizer 1 before delivering it to the heat medium inlet of the heat exchanger 6. The vapor compression unit 10 includes 2-10 MVR fan units connected in series via interstage steam pipelines. The inlet of the first MVR fan is connected to the third pipeline 9 at the top of the DTB crystallizer 1, and a demister 8 is installed before the third pipeline 9. The outlet of the last MVR fan is connected to the heat medium inlet of the heat exchanger 6. Adjacent MVR fans are connected via interstage steam pipelines.

[0039] The first pipeline 4 is equipped with a circulation pump 5 for extracting the clear liquid in the clear liquid chamber and transporting it to the refrigerant inlet end of the heat exchanger.

[0040] The third pipeline 9 has a live steam replenishment pipeline 13 in the pipeline section between the steam compression unit 10 and the DTB crystallizer 1.

[0041] Taking ammonium sulfate feedstock solution as an example, based on the above system, the evaporation method includes the following steps: (1) Ammonium sulfate feedstock solution is continuously fed into DTB crystallizer 1, where it undergoes negative pressure evaporation and crystallization. The absolute pressure of DTB crystallizer 1 is controlled at 12-16 kPaA, and the material temperature is 50-60℃. A large amount of secondary steam is generated during the crystallization process, with a secondary steam temperature of 45-55℃. At the same time, circulating pump 5 extracts the clear liquid (temperature of about 50-55℃) from the clear liquid chamber of DTB crystallizer 1 and sends it to the refrigerant inlet of heat exchanger 6.

[0042] (2) The secondary steam generated in step (1) is sent to four MVR blowers connected in series to remove entrained droplets and solid particles by the demister 8, and then compressed and heated in stages. The compression ratio of each MVR blower is independently controlled at 1.4-1.8, and the temperature rise of each compression stage is 10-15℃.

[0043] After four stages of compression, the steam pressure increases from approximately 12 kPaA at the inlet to approximately 55-70 kPaA at the outlet, and the steam temperature increases from approximately 50°C at the inlet to approximately 95-115°C at the outlet, with a total temperature rise of approximately 40-60°C.

[0044] (3) The steam compressed by the fourth MVR fan 14 is sent to the heat medium inlet end of the heat exchanger 6 and exchanged heat with the clear liquid on the cold side in a countercurrent manner. After the clear liquid is heated to 70-90°C, it is sent back to the bottom of the guide mechanism 2 of the DTB crystallizer 1 through the second pipeline 7. After entering the guide mechanism, it mixes with the crystal slurry and continues to participate in the crystallization process.

[0045] (4) The steam after heat exchange is condensed into condensate, which is discharged through the fourth pipeline 13. Part of it is collected to the collection mechanism 14 and can be used as a preheating heat source for other sections of the system.

[0046] When the system is started, live steam is introduced into the system through the live steam replenishment pipeline 11. After the DTB crystallizer 1 stably generates sufficient secondary steam, the live steam replenishment valve 12 is gradually closed, and the system enters normal circulation operation.

[0047] Example 2 An evaporation system, such as Figure 2 As shown, compared with the system described in Embodiment 1, the difference is that the system in this embodiment includes two DTB crystallizers 1, namely a first DTB crystallizer 15 and a second DTB crystallizer 16. The two DTB crystallizers are arranged in parallel, and each DTB crystallizer is equipped with an independent heating unit and is connected by a steam compression unit 10 composed of four MVR fans connected in series.

[0048] Taking the ammonium sulfate feedstock solution generated during caprolactam production as an example, based on the above system, the evaporation method includes the following steps: (1) The ammonium sulfate feedstock solution generated during caprolactam production is continuously fed into the first DTB crystallizer 15 and the second DTB crystallizer 16, which are arranged in parallel, and negative pressure evaporation crystallization occurs simultaneously in both crystallizers. The absolute pressure of the first DTB crystallizer 15 is controlled at 20-25 kPaA, and the material temperature is 60-70°C; the absolute pressure of the second DTB crystallizer 16 is controlled at 12-16 kPaA, and the material temperature is 50-60°C. During the crystallization process, each crystallizer generates a large amount of secondary steam.

[0049] (2) The secondary steam (temperature 60-70℃) generated by the first DTB crystallizer 15 is sent to the steam compression unit 10 for staged compression to increase temperature and pressure after the demister 8 removes entrained droplets and solid particles. The compression ratio of each stage of the MVR blower is independently controlled at 1.4-1.8, and the temperature rise of each stage of compression is 10-15℃. After 4 stages of compression, the steam temperature rises from about 65℃ to about 110-120℃, with a total temperature rise of about 45-55℃.

[0050] (3) The high-temperature steam compressed by the MVR fan unit 10 is sent to the heat medium inlet end of the heat exchanger 6 of the second DTB crystallizer 16 to exchange heat with the clear liquid on the cold side of the second DTB crystallizer 16 in a countercurrent manner. After the clear liquid of the second DTB crystallizer 16 is heated to 80-90°C, it is sent back to the bottom of the guide mechanism of the second DTB crystallizer 16 through the second pipeline. After entering the guide mechanism, it mixes with the crystal slurry and continues to participate in the crystallization process.

[0051] (4) The steam after heat exchange in each heat exchanger is condensed into condensate, which is discharged through the corresponding fourth pipeline. Part of it is collected by the collection mechanism and can be used as a preheating heat source for other sections of the system.

[0052] When the system starts up, live steam is introduced into the hot side inlet of the two heat exchangers through the live steam replenishment pipeline 11. After both DTB crystallizers have stably generated sufficient secondary steam, the live steam replenishment valves 12 are gradually closed, and the system enters normal circulation operation.

[0053] This embodiment achieves cascaded energy utilization by reusing different devices in series, further improving the overall energy utilization rate.

[0054] Example 3 An evaporation system, such as Figure 3 As shown, the system differs from Example 1 in that it includes: a DTB crystallizer 17 for neutralization reaction and a DTB crystallizer 18 for evaporation crystallization.

[0055] The DTB crystallizer 17 for the neutralization reaction is used in the neutralization reaction process. It is equipped with a feed line 19 for reactant 1 and a feed line 20 for reactant 2. During the reaction, a large amount of heat is released, and the generated secondary steam has a high temperature (about 60-70℃) and a large flow rate. The secondary steam generated by the DTB crystallizer 17 for the neutralization reaction is heated and pressurized by its multi-stage steam compression unit (4 MVR fans in series) and then reused in the heat exchanger of the DTB crystallizer 18 for evaporation crystallization as a heating source for the DTB crystallizer 18 for evaporation crystallization. At the same time, by adjusting the steam regulating valve 24 for the MVR fan unit and the steam regulating valve 25 for the steam condenser, part of the steam in the DTB crystallizer 18 for evaporation crystallization can be reused, further improving energy utilization efficiency. After reactant 1 and reactant 2 fully react in the DTB crystallizer 17 for the neutralization reaction, the product is transported to the product feed line 23 of the DTB crystallizer 18 for evaporation crystallization via the product collection line 21 and the product collection pump 22, where it crystallizes into the final product.

[0056] Taking the production of methionine hydroxy analogues as an example, based on the above system, the evaporation method includes the following steps: (1) In the production process of methionine hydroxy analogs, sulfuric acid-containing methionine hydroxy analogs are continuously fed into the DTB crystallizer 17 for neutralization reaction via reactant A feed line 19. At the same time, ammonia gas is introduced into the flow guiding mechanism of the DTB crystallizer 17 for neutralization reaction via reactant B feed line 20. The two reactants undergo a neutralization reaction in the DTB crystallizer 17 to produce ammonium sulfate and an aqueous solution of methionine hydroxy analogs. A large amount of heat of reaction is released during the neutralization reaction, which promotes the evaporation of water in the system to generate secondary steam. The absolute pressure of the DTB crystallizer 17 for neutralization reaction is controlled at 20-30 kPaA, and the material temperature is controlled at 60-70℃.

[0057] (2) The secondary steam (temperature 60-70℃) generated by the DTB crystallizer 17 for the neutralization reaction is sent to the steam compression unit 10, which consists of four MVR blowers connected in series, after removing entrained droplets by a demister. The steam is then compressed and heated in stages. The compression ratio of each MVR blower is independently controlled at 1.4-1.8, and the temperature rise of each compression stage is 10-15℃. After four stages of compression, the steam temperature rises from about 65℃ to about 110-120℃, with a total temperature rise of about 45-55℃.

[0058] (3) The high-temperature steam compressed by the steam compression unit 10 is sent to the heat medium end inlet of the heat exchanger of the DTB crystallizer 18 for evaporation crystallization, and exchanges heat with the clear liquid on the cold side of the DTB crystallizer 18 for evaporation crystallization in a countercurrent manner. After the clear liquid of the DTB crystallizer 18 for evaporation crystallization is heated to 80-90°C, it is sent back to the bottom of its guiding mechanism through the second pipeline. After entering the guiding mechanism, it mixes with the crystal slurry to maintain the evaporation crystallization temperature.

[0059] Meanwhile, the ammonium sulfate and methionine hydroxy analogue mixed solution generated in the DTB crystallizer 17 for neutralization reaction is continuously transported by the product collection pump 22 through the product collection pipeline 21 to the product feed pipeline 23 of the DTB crystallizer 18 for evaporation crystallization, and enters the DTB crystallizer 18 for evaporation crystallization. The ammonium sulfate solution undergoes negative pressure evaporation crystallization in the DTB crystallizer 18, with the operating absolute pressure of the DTB crystallizer 18 controlled at 12-16 kPaA and the material temperature at 50-60°C. Ammonium sulfate continues to crystallize and precipitate, and the crystalline product is collected by centrifuge.

[0060] (4) After the DTB crystallizer 18 for evaporation crystallization is operating stably, a large amount of secondary steam (temperature 50-60℃) is generated at its top. This third pipeline is divided into two control paths: one path goes to the steam regulating valve 24 of the MVR blower unit and enters the steam compression unit 10 for compression, temperature increase and pressure increase. The compressed steam (temperature about 100-110℃) is reused to the heat medium end inlet of the heat exchanger of the DTB crystallizer 18 for evaporation crystallization as a supplementary heating heat source; the other path goes to the steam regulating valve 25 of the steam condenser and enters the steam condenser 26 to condense the excess steam into condensate for recycling. By adjusting the opening of the steam regulating valve 24 and the steam regulating valve 25, the steam reuse ratio of the DTB crystallizer 18 for evaporation crystallization can be flexibly controlled, and the excess steam can be recovered in the form of condensate while meeting its own heat demand.

[0061] The steam after heat exchange in each heat exchanger condenses into condensate, which is discharged through the fourth pipeline. A portion of the condensate is collected by the collection mechanism and can be used as a preheating heat source for other sections of the system.

[0062] When the system starts up, live steam is introduced into the heat exchanger of the DTB crystallizer 18 for evaporation and crystallization through the live steam supply pipeline for preheating. After the DTB crystallizer 17 for neutralization reaction stably generates sufficient secondary steam, the live steam supply valve is gradually closed and the system enters normal circulation operation.

[0063] This embodiment realizes energy coupling between the neutralization reaction unit and the evaporation crystallization unit. Specifically, the excess reaction heat released during the neutralization reaction is recovered in the form of secondary steam and used to drive the evaporation crystallization process, realizing cross-unit energy utilization and significantly reducing the external steam consumption of the entire process.

[0064] According to one embodiment of the present invention, the MVR blower is one of a Roots steam compressor, a centrifugal steam compressor, or a single-screw steam compressor.

[0065] The contents not described in detail in this specification are prior art known to those skilled in the art. Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An evaporation system, characterized in that, include: At least one DTB crystallizer, and a heating unit and a vapor compression unit connected to the DTB crystallizer; The DTB crystallizer includes a hollow circulation chamber that is connected to the feed pipeline and has a flow guiding mechanism located near the bottom. The circulation chamber has a clear liquid chamber outside the flow guiding mechanism; the bottom of the circulation chamber has a crystal slurry outlet and the top has a steam outlet; The heating unit includes a heat exchanger. The refrigerant inlet of the heat exchanger is connected to the upper part of the clear liquid chamber of the DTB crystallizer through a first pipeline, and the refrigerant outlet is connected to the bottom of the flow guiding mechanism of the DTB crystallizer through a second pipeline. The heat medium inlet of the heat exchanger is connected to the steam outlet of the DTB crystallizer through a third pipeline, and the heat medium outlet is connected to the collection mechanism through a fourth pipeline. The steam compression unit is installed on the third pipeline and pressurizes and heats the steam outlet of the DTB crystallizer before delivering it to the heat medium inlet of the heat exchanger; the steam compression unit includes at least two MVR fan units connected in series through interstage steam pipelines. The first pipeline is equipped with a circulation pump for extracting the clear liquid in the clear liquid chamber and transporting it to the refrigerant inlet end of the heat exchanger; The third pipeline includes a live steam replenishment pipeline in the section between the steam compression unit and the DTB crystallizer.

2. The evaporation system according to claim 1, characterized in that, The DTB crystallizer has a defoaming device installed at the steam outlet in the circulation chamber.

3. An evaporation method, characterized in that, Based on the evaporation system according to any one of claims 1-2, the following steps are included: Step 1: Neutralize or evaporate crystallize the DTB crystallizer; at the same time, extract the clear liquid from the clear liquid chamber of the DTB crystallizer and send it to the cold side of the heat exchanger. Step 2: The secondary steam generated in the DTB crystallizer in Step 1 is sent to the steam compression unit and compressed and heated in stages by the MVR blower unit. Step 3: The steam compressed by the multi-stage MVR fan is sent to the hot side of the heat exchanger to exchange heat with the clear liquid on the cold side; Step 4: After the temperature of the clear liquid after heat exchange in the heat exchanger rises to the preset temperature, it is sent back to the DTB crystallizer to continue to participate in the reaction or crystallization process; the steam after heat exchange is condensed into condensate and then discharged.

4. The evaporation method according to claim 3, characterized in that, The step-by-step compression and temperature / pressure increase method described in step 2 is as follows: independently control the compression ratio of each MVR fan to 1.2-2.0, and independently control the temperature rise after compression of each MVR fan to 10-15℃.

5. The evaporation method according to claim 3, characterized in that, When the system contains only one DTB crystallizer, the secondary steam from the DTB crystallizer is compressed by a multi-stage MVR blower and then reused in the heat exchanger of the original DTB crystallizer.

6. The evaporation method according to claim 3, characterized in that, When the system contains two or more DTB crystallizers, the secondary steam from the first DTB crystallizer is compressed by a multi-stage MVR fan and then reused in the heat exchanger of the second DTB crystallizer. The secondary steam from the second DTB crystallizer is compressed by a multi-stage MVR fan and then reused in the heat exchanger of the third DTB crystallizer, and so on.

7. The evaporation method according to claim 6, characterized in that, The system pressure inside the first DTB crystallizer is controlled to be lower than that inside the second DTB crystallizer, and the system temperature inside the first DTB crystallizer is higher than that inside the second DTB crystallizer; the system pressure inside the second DTB crystallizer is controlled to be lower than that inside the third DTB crystallizer, and the system temperature inside the second DTB crystallizer is higher than that inside the third DTB crystallizer, and so on.

8. The evaporation method according to claim 3, characterized in that, When the system includes a DTB crystallizer for neutralization reaction and a DTB crystallizer for evaporation crystallization, the secondary steam from the DTB crystallizer for neutralization reaction is recycled to the heat exchanger of the DTB crystallizer for evaporation crystallization after being compressed by a multi-stage MVR.

9. The evaporation method according to claim 8, characterized in that, Part of the secondary steam from the DTB crystallizer used for evaporation crystallization is compressed by a multi-stage MVR and then reused in the heat exchanger of the DTB crystallizer used for evaporation crystallization.

10. The evaporation method according to claim 3, characterized in that, When the system is started, live steam is introduced into the system through the live steam replenishment pipeline. After the DTB crystallizer stably produces a sufficient amount of secondary steam, the live steam replenishment valve is gradually closed, and the system enters normal circulation operation.

11. A method for producing a methionine hydroxy analogue, characterized in that, The evaporation method described in any one of claims 3-10 is used to carry out the reaction process of methionine hydroxy analog and the crystallization process of the byproduct ammonium sulfate in the production of methionine hydroxy analog.

12. The method for producing methionine hydroxy analogues according to claim 11, characterized in that, The evaporation system includes at least a reaction DTB crystallizer and an evaporation crystallizer, wherein the reaction DTB crystallizer is used for the reaction process of methionine hydroxy analogues, and the evaporation crystallizer is used for the crystallization process of the byproduct ammonium sulfate.

13. A method for producing caprolactam, characterized in that, The crystallization process of ammonium sulfate, a byproduct, during the production of caprolactam is carried out using the evaporation method described in any one of claims 3-10.

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