Succinic acid multistage continuous crystallization system and method and application

Abstract

The invention discloses a succinic acid multistage continuous crystallization system and method and application. The succinic acid multi-stage continuous crystallization system comprises a first-stage crystallization kettle, a second-stage crystallization kettle and a last-stage crystallization kettle which are connected in sequence, a first crystal mush outlet of the first-stage crystallization kettle is connected with a second crystal mush inlet of the second-stage crystallization kettle through a pipeline, and a second crystal mush outlet of the second-stage crystallization kettle is connected with a last-stage crystal mush inlet of the last-stage crystallization kettle through a pipeline, and a final-stage crystal mush outlet of the final-stage crystallization kettle is respectively connected with a crystal mush inlet of the crystallization external cooler and a solid-liquid separation section through pipelines. According to the invention, multi-stage step-by-step cooling crystallization is adopted, the crystallization quality is high, in addition, a mode of combining multi-stage vacuum flash evaporation crystallization and first-stage external cooling crystallization is adopted, the succinic acid crystallization time is shortened, and the crystallization efficiency is improved; meanwhile, the crystallization final temperature is reduced, the content of residual succinic acid in the mother liquor is reduced, and the succinic acid productivity is improved.

Description

Technical Field

[0001] The invention relates to the technical field of succinic acid preparation, and in particular to a succinic acid multi-stage continuous crystallization system, method and application. Background Art

[0002] In the past two years, with the sudden expansion of the biodegradable plastics market, polybutylene succinate (PBS) has attracted great attention due to its excellent processing and mechanical properties and its completely biodegradable characteristics. As the direct upstream raw material of PBS, succinic acid will usher in explosive growth in the future market size.

[0003] At present, the industrial continuous crystallization process of succinic acid mainly adopts three-stage vacuum cooling crystallization, but due to the influence of vacuum degree, the temperature of crystal slurry can only drop to 30℃ after crystallization, and a lot of succinic acid cannot be precipitated. At the same time, most of the processes use crystal slurry internal circulation crystallizers, and a guide tube is set inside the crystallizer to make the crystal slurry circulate inside the crystallizer, but the crystal slurry stays in the crystallizer for a long time, resulting in low production capacity of the crystallization device, which is not suitable for the growing demand for succinic acid production capacity.

[0004] Therefore, there is an urgent need for a device and method for succinic acid crystallization with higher efficiency and higher production capacity. Summary of the invention

[0005] In order to solve the problem that the succinic acid crystallization process in the prior art has low production efficiency and is not suitable for mass production, the present invention provides a succinic acid multi-stage continuous crystallization system, method and application.

[0006] One of the purposes of the present invention is to provide a succinic acid multi-stage continuous crystallization system, comprising a primary crystallization kettle, a secondary crystallization kettle and a final crystallization kettle connected in sequence, wherein a first slurry outlet of the primary crystallization kettle is connected to a second slurry inlet of the secondary crystallization kettle by a pipeline, and the second slurry outlet of the secondary crystallization kettle is connected to a final slurry inlet of the final crystallization kettle by a pipeline, wherein the final slurry outlet of the final crystallization kettle is respectively connected to a slurry inlet of a crystallization external cooler and a solid-liquid separation section through pipelines.

[0007] The solid-liquid separation section includes a conventional solid-liquid separation device in the prior art, and the operating conditions of the solid-liquid separation are also conventional operating conditions in the prior art. Those skilled in the art can perform solid-liquid separation operations according to actual conditions.

[0008] In a preferred embodiment of the present invention,

[0009] The primary crystallization kettle is provided with a succinic acid solution inlet and a first gas outlet; preferably, a primary condenser is further provided after the first gas outlet; and / or,

[0010] The secondary crystallization kettle is provided with a second gas outlet; preferably, a secondary condenser is further provided after the second gas outlet; and / or,

[0011] The primary condenser and the secondary condenser are connected to a vacuum pump via a pipeline; and / or,

[0012] The final crystallization kettle is provided with an externally cooled crystal slurry circulation inlet; preferably, the crystal slurry outlet of the crystallization external cooler is connected to the externally cooled crystal slurry circulation inlet through a pipeline.

[0013] In a preferred embodiment of the present invention,

[0014] A first-stage slurry delivery pump is arranged on the pipeline connecting the first slurry outlet to the second-stage crystallization kettle; and / or,

[0015] A secondary slurry delivery pump is provided on the pipeline connecting the second slurry outlet to the final crystallization kettle; and / or,

[0016] A final-stage slurry delivery pump is provided on the pipeline connecting the final-stage slurry outlet to the solid-liquid separation section; and / or,

[0017] A slurry external circulation pump is provided on the pipeline connecting the final slurry outlet to the crystallization external cooler; preferably,

[0018] The first-stage slurry delivery pump, the second-stage slurry delivery pump, the final-stage slurry delivery pump, and the slurry external circulation pump are each independently an axial flow pump, a Tesla pump, a centrifugal pump, or a vortex pump.

[0019] In a preferred embodiment of the present invention,

[0020] The secondary crystallization kettle comprises more than one crystallization kettle. Preferably, when the secondary crystallization kettle comprises more than two crystallization kettles, the more than two crystallization kettles are connected in series; and / or,

[0021] The final crystallization kettle comprises more than one crystallization kettle. Preferably, when the final crystallization kettle comprises more than two crystallization kettles, the more than two crystallization kettles are connected in series; and each crystallization kettle is connected to a crystallization external cooler.

[0022] In a preferred embodiment of the present invention,

[0023] The first-stage crystallization kettle, the second-stage crystallization kettle and the final-stage crystallization kettle are each optionally provided with a cooling water jacket; and / or,

[0024] The first-stage crystallization kettle, the second-stage crystallization kettle and the final-stage crystallization kettle are each optionally provided with a stirring paddle. Preferably, the stirring paddle is one of a multi-layer turbine paddle, a frame-type stirring paddle, an anchor-type stirring paddle or a combined blade-type stirring paddle.

[0025] In a preferred embodiment of the present invention,

[0026] The crystallization external cooler includes more than one slurry external cooler, preferably includes at least two parallel slurry external coolers, the final slurry outlet of the final crystallization kettle is connected to the slurry inlet of each slurry external cooler by a pipeline, and the slurry outlet of each slurry external cooler is connected to the external cooling slurry circulation inlet of the final crystallization kettle by a pipeline.

[0027] In a preferred embodiment of the present invention,

[0028] A switch valve is provided on the connecting pipeline between the final slurry outlet of the final crystallization kettle and the slurry inlet of each slurry external cooler; preferably, a cleaning liquid inlet is provided on the connecting pipeline between the switch valve on the connecting pipeline between the final slurry outlet and the slurry inlet of each slurry external cooler and the slurry inlet of each slurry external cooler; and / or,

[0029] A switching valve is provided on the connecting pipeline between the slurry outlet of each slurry external cooler and the externally cooled slurry circulation inlet of the final crystallization kettle; preferably, a cleaning liquid outlet is provided on the connecting pipeline between the switching valve on the connecting pipeline between the slurry outlet of each slurry external cooler and the externally cooled slurry circulation inlet of the final crystallization kettle and the slurry outlet of each slurry external cooler.

[0030] In a preferred embodiment of the present invention,

[0031] Each slurry external cooler is provided with a cooling medium inlet and a cooling medium outlet; preferably,

[0032] A cooling medium reflux port is optionally provided at the bottom of each slurry external cooler; further preferably,

[0033] The system is also provided with a cooling medium tank, and the cooling medium tank is connected to the cooling medium return port through a pipeline.

[0034] The cooling medium tank is preferably a low-temperature water tank.

[0035] In a preferred embodiment of the present invention,

[0036] The slurry external cooler includes a slurry external cooler shell, a slurry conveying pipeline for conveying slurry arranged in the slurry external cooler shell, and a cooling medium cavity between the slurry conveying pipeline and the shell; preferably, the cooling medium inlet and the cooling medium outlet are respectively arranged at the upper and lower ends of the cooling medium cavity.

[0037] The succinic acid multi-stage continuous crystallization system of the present invention can adopt the following specific technical scheme:

[0038] The succinic acid multi-stage continuous crystallization system comprises a primary crystallization kettle, a secondary crystallization kettle and a final crystallization kettle, wherein at least one secondary crystallization kettle is provided, the primary crystallization kettle and the secondary crystallization kettle are connected via a primary slurry delivery pump, adjacent secondary crystallization kettles are connected via a secondary slurry delivery pump, the secondary crystallization kettle and the final crystallization kettle are connected via a secondary slurry delivery pump, the final crystallization kettle and the crystallization external cooler are connected via a slurry external circulation pump, the top of the crystallization external cooler is connected to the top of the final crystallization kettle, the top of the primary crystallization kettle is connected to a primary condenser, the top of each secondary crystallization kettle is connected to a secondary condenser, the primary condenser and the secondary condenser are both connected to a vacuum pump, and a cooling water jacket is provided in the final crystallization kettle.

[0039] The second object of the present invention is to provide a multi-stage continuous crystallization method of succinic acid using the system of one of the objects of the present invention, including the steps of subjecting the succinic acid solution to two-stage vacuum flash cooling crystallization, and then subjecting the succinic acid solution to one-stage cooling crystallization, wherein part of the obtained slurry is discharged to the solid-liquid separation section, and part of it is sent to a crystallization external cooler for cooling and then circulated back to the final crystallization kettle.

[0040] In a preferred embodiment of the present invention,

[0041] The method comprises:

[0042] A. Discharging the primary succinic acid slurry obtained by vacuum flash cooling and crystallization of the succinic acid solution in a primary crystallization kettle;

[0043] B. discharging the secondary succinic acid slurry obtained by vacuum flash cooling and crystallization of the primary succinic acid slurry in the secondary crystallization kettle;

[0044] C. Cooling and crystallizing the secondary succinic acid slurry in a final crystallization kettle to obtain a final succinic acid slurry;

[0045] D. Part of the final stage succinic acid slurry is discharged to the solid-liquid separation section, and part of it is sent to the crystallization external cooler for cooling to obtain the externally cooled succinic acid slurry which is then recycled back to the final stage crystallization kettle.

[0046] In the final crystallization kettle, the present invention utilizes the low-temperature water in the jacket to cool down and crystallize the succinic acid slurry in the crystallization kettle on the one hand, and utilizes the low-temperature succinic acid slurry circulated back from the crystallization external cooler to mix with the newly entered secondary succinic acid slurry on the other hand, so that the newly entered secondary succinic acid slurry is cooled and crystallized; the crystal slurry after crystallization is partially discharged to the solid-liquid separation section, and partially sent to the crystallization external cooler for circulation.

[0047] In a preferred embodiment of the present invention,

[0048] In step A, the succinic acid solution is a succinic acid solution obtained by any conventional succinic acid preparation method in the prior art, and the temperature of the succinic acid solution is preferably 70-90° C., more preferably 75-85° C.; and / or, the concentration of the succinic acid solution is preferably 24-30%, more preferably 25-28%; and / or, the negative pressure in the primary crystallization kettle is -0.07 to -0.09 Mpag; and / or, the temperature of the primary succinic acid slurry obtained in the primary crystallization kettle is 50-57° C., preferably 50-55° C.; and / or, the solid content of the primary succinic acid slurry obtained in the primary crystallization kettle is 6-12%, preferably 9-12%; and / or,

[0049] In step B, the negative pressure in the secondary crystallization kettle is -0.085 to -0.098 MPag; and / or, the temperature of the secondary succinic acid slurry obtained in the secondary crystallization kettle is 35 to 50° C., preferably 40 to 45° C.; and / or, the solid content of the secondary succinic acid slurry obtained in the secondary crystallization kettle is 15 to 19%, preferably 16 to 19%; and / or,

[0050] In step C, the temperature of the final succinic acid slurry is 18-23° C., preferably 18-21° C.; and / or the solid content of the final succinic acid slurry is 20-28%, preferably 24-27%; and / or,

[0051] In step D, the portion of the final succinic acid slurry sent to the crystallization external cooler is 60-95% of the total mass of the final succinic acid slurry, preferably 80-90%; and / or, the final succinic acid slurry sent to the crystallization external cooler for cooling is cooled to 15-18°C, preferably 15-17°C in the crystal slurry external cooler to obtain the externally cooled succinic acid slurry and returned to the final crystallization kettle; and / or, the externally cooled succinic acid slurry circulated back to the final crystallization kettle from the crystallization external cooler is mixed with the newly entered secondary succinic acid slurry and continues to be cooled and crystallized in the final crystallization kettle.

[0052] In the present invention, when the succinic acid slurry is cooled to 35-50° C., preferably 40-45° C., by vacuum flash evaporation, the subsequent crystallization kettle can be replaced by a non-vacuum crystallization kettle with an external cooler, thereby reducing the succinic acid crystallization time and improving the crystallization efficiency; at the same time, the crystallization endpoint temperature is reduced and the residual succinic acid content in the mother liquor is reduced.

[0053] In a preferred embodiment of the present invention,

[0054] When the crystallization external cooler comprises at least two parallel slurry external coolers, the final succinic acid slurry fed into the crystallization external cooler is alternately cooled in at least two parallel slurry external coolers and then circulated back to the final crystallization kettle, and at the same time, the slurry external coolers from which the slurry is discharged from the at least two parallel slurry external coolers are alternately cleaned; preferably,

[0055] When the crystallization external cooler includes two parallel slurry external coolers, the cooling and cleaning steps of the final succinic acid slurry fed into the crystallization external cooler in the two parallel slurry external coolers include:

[0056] 1) the final stage succinic acid slurry sent to the crystallization external cooler is cooled in the first slurry external cooler and then returned to the final stage crystallization kettle;

[0057] 2) cleaning the first slurry external cooler; during this period, the final succinic acid slurry discharged from the final crystallization kettle is cooled in the second slurry external cooler and then returned to the final crystallization kettle;

[0058] 3) Cleaning the second slurry external cooler;

[0059] 4) Optionally, steps 1) to 3) are repeated; when the repeated operation is performed, step 1) is performed while step 3) is performed.

[0060] In a preferred embodiment of the present invention,

[0061] The first slurry external cooler adopts cooling medium 1 for cooling operation, the second slurry external cooler adopts cooling medium 2 for cooling operation, the jacket of the final crystallization kettle is introduced with cooling medium 3, cooling medium 1, cooling medium 2 and cooling medium 3 are the same or different, and are preferably at least one of water and sodium chloride aqueous solution; and / or, the temperature of cooling medium 1, cooling medium 2 and cooling medium 3 when entering each device is preferably 7-15°C; and / or,

[0062] In step 2), the first slurry external cooler is cleaned with cleaning liquid 1; and / or, the cleaning time of the first slurry external cooler with cleaning liquid 1 is 10 to 60 minutes, preferably 30 to 60 minutes; and / or, in step 3), the second slurry external cooler is cleaned with cleaning liquid 2; and / or, the cleaning time of the second slurry external cooler with cleaning liquid 2 is 10 to 60 minutes, preferably 30 to 60 minutes; and / or, the cleaning liquid 1 and the cleaning liquid 2 are the same or different, and are independently preferably at least one of water and unsaturated filtered mother liquor of succinic acid slurry; preferably, the cleaning liquid 1 and the cleaning liquid 2 are the same, which will make the system simpler. The cleaned water or unsaturated filtered mother liquor of succinic acid slurry can be recycled and reused.

[0063] The multi-stage continuous crystallization method of succinic acid of the present invention can adopt the following specific technical scheme:

[0064] Step A: The high-temperature succinic acid solution enters the primary crystallization kettle through the succinic acid solution inlet on the primary crystallization kettle, the succinic acid solution is subjected to vacuum flash evaporation and cooling crystallization in the primary crystallization kettle, the vacuum pump evacuates the primary condenser and the primary crystallization kettle, and the primary condenser condenses the steam in the primary crystallization kettle and recycles it for reuse; in step A, a cooling water jacket is provided in the primary crystallization kettle, when the flash evaporation in the primary crystallization kettle does not reach a predetermined temperature, a cooling medium is introduced into the cooling water jacket in the primary crystallization kettle for cooling crystallization;

[0065] Step B: the primary succinic acid slurry crystallized from the primary crystallization kettle is transported to the secondary crystallization kettle from the first slurry outlet on the primary crystallization kettle via the primary slurry delivery pump, the primary succinic acid slurry is subjected to vacuum flash cooling crystallization in the secondary crystallization kettle, the vacuum pump evacuates the secondary condenser and the secondary crystallization kettle, the secondary condenser condenses the steam in the secondary crystallization kettle and recycles it; when the secondary crystallization kettle includes more than two crystallization kettles, the slurry is transported between adjacent crystallization kettles by the secondary slurry delivery pump; in step B, a cooling water jacket is provided in the secondary crystallization kettle, when the flash evaporation in the secondary crystallization kettle does not reach a predetermined temperature, a cooling medium is introduced into the cooling water jacket in the secondary crystallization kettle for cooling crystallization;

[0066] Step C: The secondary succinic acid slurry crystallized from the secondary crystallization kettle is transported to the final crystallization kettle from the second slurry outlet on the secondary crystallization kettle via the secondary slurry delivery pump, and a cooling medium is provided in the cooling water jacket of the final crystallization kettle, and the secondary succinic acid slurry is cooled and crystallized in the final crystallization kettle; in step C, the cooling medium in the cooling water jacket of the final crystallization kettle is low-temperature water, the temperature of the low-temperature water is 7-15° C., and the pressure is 0.2-0.7 MPa, preferably 0.2-0.5 MPa;

[0067] Step D: Part of the final succinic acid slurry crystallized by the final crystallization kettle is discharged to the solid-liquid separation section, and part of it is transported to the crystallization external cooler by the slurry external circulation pump for further cooling and then returned to the final crystallization kettle; the final succinic acid slurry discharged to the solid-liquid separation section in step D is transported to the subsequent solid-liquid separation section by the final slurry transport pump connected to the final crystallization kettle; preferably, when the crystallization external cooler includes two parallel slurry external coolers, the final succinic acid slurry can be externally cooled once in the first slurry external cooler and returned to the final crystallization kettle, and then the next external cooling is carried out in the second slurry external cooler, and then the next external cooling is carried out in the first slurry external cooler, and so on alternately in the two parallel The external cooling operation can be performed in the crystal slurry external cooler and the crystal slurry external coolers for discharging the crystal slurry in the two parallel crystal slurry external coolers can be cleaned alternately at the same time; the final succinic acid slurry can also be continuously externally cooled in the first crystal slurry external cooler, and when the first crystal slurry external cooler works continuously for 2 to 18 hours, the second crystal slurry external cooler can be switched to make the final succinic acid slurry continuously externally cooled in the second crystal slurry external cooler, and when the second crystal slurry external cooler works continuously for 2 to 18 hours, the first crystal slurry external cooler can be switched to work again, and the external cooling operation can be performed alternately in the two parallel crystal slurry external coolers and the crystal slurry external coolers for discharging the crystal slurry that are not working in the two parallel crystal slurry external coolers can be cleaned alternately at the same time.

[0068] The succinic acid slurry is alternately cooled in the first slurry external cooler and the second slurry external cooler and the other slurry external cooler is cleaned at the same time, so the continuity and stability of crystallization are ensured. The online cleaning is performed during the cooling process to ensure the reliability of the crystallization process. The method is suitable for mass production processes and has high production efficiency.

[0069] The third object of the present invention is to provide an application of the system of one of the objects of the present invention or the method of the second object of the present invention in the field of succinic acid crystallization.

[0070] Through the above technical scheme, the beneficial effects of the present invention are as follows: when the succinic acid multi-stage continuous crystallization system of the present invention is used, the succinic acid solution is first subjected to vacuum flash cooling crystallization in a first-stage crystallization kettle, and then the crystal slurry enters one or more second-stage crystallization kettles for vacuum flash cooling crystallization, and then the crystal slurry enters a final-stage crystallization kettle for cooling and crystallization, and then is sent to a crystallization external cooler, and the succinic acid crystal slurry is further cooled and returned to the final-stage crystallization kettle, and multi-stage step-by-step cooling crystallization is adopted, and the crystal quality is high. In addition, a combination of multi-stage vacuum flash crystallization and first-stage external cooling crystallization is adopted, which reduces the succinic acid crystallization time and improves the crystallization efficiency; at the same time, the crystallization terminal temperature is reduced, the residual succinic acid content in the mother liquor is reduced, and the succinic acid production capacity is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 It is a simplified process flow diagram of the present invention.

[0072] Figure 2 The figure is a simplified process flow diagram of the final crystallization kettle and the two crystal slurry external coolers when the crystallization external cooler includes two parallel crystal slurry external coolers. Figure 2 In the figure, the first slurry external cooler 41 and the second slurry external cooler 42 are two parallel external coolers with the same structure. Therefore, the slurry inlet 401, the slurry outlet 402, the slurry external cooler shell 43, the slurry delivery pipeline 44, the cooling medium cavity 45, the cooling medium (low-temperature water) outlet 46 and the cooling medium (low-temperature water) inlet 47, the cooling medium (low-temperature water) reflux port 48, the cleaning liquid inlet 5 connected to the slurry inlet of the slurry external cooler, the cleaning liquid outlet 6 connected to the slurry outlet of the slurry external cooler, and the vent port 7 connected to the cooling medium (low-temperature water) outlet of the slurry external cooler are only marked on the second slurry external cooler 42, and are not repeated on the first slurry external cooler 41. DETAILED DESCRIPTION

[0073] The present invention is described in detail below in conjunction with specific embodiments and drawings. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention still fall within the scope of protection of the present invention.

[0074] Example 1

[0075] Reference Figure 1, take a succinic acid multi-stage continuous crystallization system including a secondary crystallization kettle and a slurry external cooler as an example to illustrate: the succinic acid multi-stage continuous crystallization system includes a primary crystallization kettle 10, a secondary crystallization kettle 20 and a final crystallization kettle 30, the primary crystallization kettle 10 is connected to the secondary crystallization kettle 20 by a primary slurry delivery pump 11, the secondary crystallization kettle 20 is connected to the final crystallization kettle 30 by a secondary slurry delivery pump 21, the final crystallization kettle 30 is connected to the slurry inlet 401 at the bottom of the crystallization external cooler 40 by a slurry external circulation pump 31, the slurry outlet 402 at the top of the crystallization external cooler 40 is connected to the external cooling slurry circulation inlet 303 at the top of the final crystallization kettle 30, the final crystallization kettle 30 is also connected to the final slurry delivery pump 32, the final slurry delivery pump 32 is connected to the subsequent solid-liquid separation section, the primary crystallization kettle 10 is connected to the primary condenser 12, the secondary crystallization kettle 20 is connected to the final crystallization kettle 30 by a secondary slurry delivery pump 21, the final crystallization kettle 30 is connected to the slurry inlet 401 at the bottom of the crystallization external cooler 40 by a slurry external circulation pump 31, the slurry outlet 402 at the top of the crystallization external cooler 40 is connected to the external cooling slurry circulation inlet 303 at the top of the final crystallization kettle 30, the final crystallization kettle 30 is also connected to the final slurry delivery pump 32, the final slurry delivery pump 32 is connected to the subsequent solid-liqui The first-stage crystallization kettle 20 is connected to the second-stage condenser 22, and the first-stage condenser 12 and the second-stage condenser 22 are both connected to the vacuum pump 50. The first-stage crystallization kettle 10 is provided with a succinic acid solution inlet 102, and the first-stage crystallization kettle 10 is provided with a first slurry outlet 103 connected to the first-stage slurry delivery pump 11 at the bottom, and a first gas outlet 104 connected to the first-stage condenser 12 at the top. The second-stage crystallization kettle 20 is provided with a second slurry inlet 202 at the top, and a second gas outlet 203 connected to the second-stage condenser 22 is also provided at the top, and a second slurry outlet 204 connected to the second slurry delivery pump 21 is provided at the bottom. The final-stage crystallization kettle 30 is provided with a final-stage slurry inlet 302 at the top, and a final-stage slurry outlet 304 connected to the final-stage slurry delivery pump 32 and the slurry external circulation pump 31 at the bottom. A cooling water jacket is provided in the final-stage crystallization kettle 30, which is a third cooling water jacket 301. The third cooling water jacket 301 is used to pass a cooling medium to cool and crystallize the slurry in the final-stage crystallization kettle 30.

[0076] In this embodiment, cooling water jackets are provided in the primary crystallization kettle 10 and the secondary crystallization kettle 20, which are respectively the first cooling water jacket 101 and the second cooling water jacket 201. The first cooling water jacket 101 and the second cooling water jacket 201 are standby options. When the flash evaporation in the primary crystallization kettle 10 and the secondary crystallization kettle 20 does not reach the predetermined temperature, a cooling medium (low-temperature water with a temperature of 7°C) is introduced into the cooling water jackets of the primary crystallization kettle 10 and the secondary crystallization kettle 20 for cooling crystallization.

[0077] In this embodiment, agitators are provided in the first-stage crystallization kettle 10, the second-stage crystallization kettle 20 and the final-stage crystallization kettle 30, and the stirring form is a multi-layer turbine propeller; the slurry delivery pump and the slurry external circulation pump are centrifugal pumps.

[0078] The succinic acid multi-stage continuous crystallization method using the above-mentioned succinic acid multi-stage continuous crystallization system comprises the following steps:

[0079] Step A: A succinic acid solution having a temperature of 80° C. and a concentration of 26.5% enters the primary crystallization kettle 10 through the succinic acid solution inlet 102 on the primary crystallization kettle 10, and the succinic acid solution is subjected to vacuum flash evaporation and cooling and crystallization to 55° C. in the primary crystallization kettle 10 to obtain primary succinic acid slurry, and a vacuum pump 50 evacuates the primary condenser 12 and the primary crystallization kettle 10, and the negative pressure in the primary crystallization kettle 10 reaches -0.088 Mpag; the primary condenser 12 condenses the steam in the primary crystallization kettle 10 and recycles it for reuse;

[0080] Step B: The primary succinic acid slurry with a solid content of 9.8% crystallized from the primary crystallization kettle 10 is transported to the secondary crystallization kettle 20 through the first slurry outlet 103 on the primary crystallization kettle 10 via the primary slurry transport pump 11. The primary succinic acid slurry is vacuum flashed and cooled to 45° C. in the secondary crystallization kettle 20 to obtain the secondary succinic acid slurry. The vacuum pump 50 evacuates the secondary condenser 22 and the secondary crystallization kettle 20, and the negative pressure in the secondary crystallization kettle 20 reaches -0.092 MPag; the secondary condenser 22 condenses the steam in the secondary crystallization kettle 20 and recycles it for reuse;

[0081] Step C: The secondary succinic acid slurry with a solid content of 17% crystallized from the secondary crystallization kettle 20 is transported to the final crystallization kettle 30 through the second slurry outlet 204 on the secondary crystallization kettle 20 via the secondary slurry delivery pump 21. A cooling medium is provided in the cooling water jacket 301 of the final crystallization kettle 30. The cooling medium in the cooling water jacket 301 of the final crystallization kettle 30 is low-temperature water. The temperature of the low-temperature water is 7° C. and the pressure is 0.6 MPaG. The secondary succinic acid slurry is cooled and crystallized to 20° C. in the final crystallization kettle to obtain a final succinic acid slurry with a solid content of 24.5%;

[0082] Step D: 10% of the final succinic acid slurry obtained by crystallization in the final crystallization kettle 30 is transported to the subsequent solid-liquid separation section by the final slurry delivery pump 32 connected to the final crystallization kettle 30, and 90% of the final succinic acid slurry is transported to the crystallization external cooler 40 by the slurry external circulation pump 31. The final succinic acid slurry is further cooled to 17°C to obtain externally cooled succinic acid slurry and then returned to the final crystallization kettle 30. The temperature of the low-temperature water introduced into the crystallization external cooler 40 is 7°C. The particle size of the succinic acid obtained by crystallization is 0.5-2.0 mm, of which the succinic acid with a particle size of 0.6-1.25 mm accounts for about 82%.

[0083] In this embodiment, the time for vacuum flash cooling crystallization in the first crystallization kettle, vacuum flash cooling crystallization in the second crystallization kettle and cooling crystallization in the final crystallization kettle is 40 minutes.

[0084] The externally cooled succinic acid slurry circulating back to the final crystallization kettle is mixed with the newly entered secondary succinic acid slurry to continue the next round of cooling crystallization in the final crystallization kettle.

[0085] Example 2

[0086] Reference Figure 1 and Figure 2 , take a succinic acid multi-stage continuous crystallization system including a secondary crystallization kettle and two parallel slurry external coolers as an example to illustrate: the succinic acid multi-stage continuous crystallization system includes a primary crystallization kettle 10, a secondary crystallization kettle 20 and a final crystallization kettle 30, the primary crystallization kettle 10 and the secondary crystallization kettle 20 are connected by a primary slurry delivery pump 11, the secondary crystallization kettle 20 and the final crystallization kettle 30 are connected by a secondary slurry delivery pump 21, the final crystallization kettle 30 and the slurry inlet 401 at the bottom of the first slurry external cooler 41 and the second slurry external cooler 42 of the crystallization external cooler 40 are respectively connected by a slurry external circulation pump 31, the slurry outlet 402 at the top of the first slurry external cooler 41 and the second slurry external cooler 42 of the crystallization external cooler 40 are respectively connected to the external cooling slurry circulation inlet 303 at the top of the final crystallization kettle 30, the final crystallization kettle 30 is also connected to the final slurry delivery pump 32, and the final slurry delivery pump 32 is connected to the subsequent solid-liquid In the separation section, the first-stage crystallization kettle 10 is connected to the first-stage condenser 12, and the second-stage crystallization kettle 20 is connected to the second-stage condenser 22. Both the first-stage condenser 12 and the second-stage condenser 22 are connected to the vacuum pump 50. The first-stage crystallization kettle 10 is provided with a succinic acid solution inlet 102, and the first-stage crystallization kettle 10 is provided with a first slurry outlet 103 connected to the first-stage slurry delivery pump 11 at the bottom, and a first gas outlet 104 connected to the first-stage condenser 12 at the top. The second-stage crystallization kettle 20 is provided with a second slurry inlet 202 at the top, and a second gas outlet 203 connected to the second-stage condenser 22 is also provided at the top, and a second slurry outlet 204 connected to the second slurry delivery pump 21 is provided at the bottom. The final-stage crystallization kettle 30 is provided with a final-stage slurry inlet 302 at the top, and a final-stage slurry outlet 304 connected to the final-stage slurry delivery pump 32 and the slurry external circulation pump 31 at the bottom. A cooling water jacket is provided in the final-stage crystallization kettle 30, which is the third cooling water jacket 301. The third cooling water jacket 301 is used to pass cooling medium to cool and crystallize the slurry in the final crystallization kettle 30 .

[0087] The slurry inlet 401 of the first slurry external cooler 41 and the second slurry external cooler 42 are respectively connected to the slurry external circulation pump 31, and the slurry outlet 402 of the first slurry external cooler 41 and the second slurry external cooler 42 are respectively connected to the external cooling slurry circulation inlet 303 on the top of the final crystallization kettle 30. The first slurry external cooler 41 and the second slurry external cooler 42 both include a slurry external cooler shell 43, a slurry conveying pipeline 44 for conveying slurry arranged in the slurry external cooler shell, and a cooling medium cavity 45 between the slurry conveying pipeline and the shell. The upper and lower ends of the cooling medium cavity 45 are respectively provided with a cooling medium (low temperature water) outlet 46 and a cooling medium (low temperature water) inlet 47, and the bottom of the cooling medium cavity 45 is also provided with a cooling medium (low temperature water) reflux port 48 connected to a low temperature water tank, and the low temperature water tank 9 is arranged below the crystal external cooler 40; the slurry outlet 402 and the slurry inlet 401 of the crystal slurry external cooler are respectively arranged at the upper and lower ends of the crystal slurry external cooler shell 43, and the slurry inlet 401 is respectively connected to a cleaning liquid inlet 5, and the slurry outlet 402 is respectively connected to a cleaning liquid outlet 6. The cooling medium (low temperature water) outlet 46 is respectively connected to a vent 7. The vent 7 of the first crystal slurry external cooler 41 and the second crystal slurry external cooler 42 is respectively controlled to open by the first crystal slurry external cooler vent valve 71 and the second crystal slurry external cooler vent valve 72. When it is necessary to discharge the cooling medium (low temperature water) in the cooling medium cavity 45, the vent 7 can be opened to facilitate the drainage. The final crystallization kettle 30 is provided with a first slurry reflux port 306 and a second slurry reflux port 305 connected to the slurry inlet 401 of the first slurry external cooler 41 and the second slurry external cooler 42, respectively. The first slurry reflux port 306 and the second slurry reflux port 305 are respectively controlled to open by the first slurry reflux port valve 35 and the second slurry reflux port valve 34, and the first slurry reflux port 306 is convenient for recycling the slurry in the first slurry external cooler 41 into the final crystallization kettle 30 for recycling and crystallization. The second slurry reflux port 305 is convenient for recycling the slurry in the second slurry external cooler 42 into the final crystallization kettle 30 for recycling and crystallization.

[0088] In this embodiment, cooling water jackets are provided in the primary crystallization kettle 10 and the secondary crystallization kettle 20, which are respectively the first cooling water jacket 101 and the second cooling water jacket 201. The first cooling water jacket 101 and the second cooling water jacket 201 are standby options. When the flash evaporation in the primary crystallization kettle 10 and the secondary crystallization kettle 20 does not reach the predetermined temperature, a cooling medium (low-temperature water with a temperature of 7°C) is introduced into the cooling water jackets of the primary crystallization kettle 10 and the secondary crystallization kettle 20 for cooling crystallization.

[0089] In this embodiment, agitators are provided in the first-stage crystallization kettle 10, the second-stage crystallization kettle 20 and the final-stage crystallization kettle 30, and the stirring form is a multi-layer turbine propeller; the slurry delivery pump and the slurry external circulation pump are centrifugal pumps.

[0090] The succinic acid multi-stage continuous crystallization method using the above-mentioned succinic acid multi-stage continuous crystallization system comprises the following steps:

[0091] Step A: A succinic acid solution having a temperature of 80° C. and a concentration of 26.5% enters the primary crystallization kettle 10 through the succinic acid solution inlet 102 on the primary crystallization kettle 10, and the succinic acid solution is subjected to vacuum flash evaporation and cooling and crystallization to 50° C. in the primary crystallization kettle 10 to obtain primary succinic acid slurry, and a vacuum pump 50 evacuates the primary condenser 12 and the primary crystallization kettle 10, and the negative pressure in the primary crystallization kettle 10 reaches -0.09 Mpag; the primary condenser 12 condenses the steam in the primary crystallization kettle 10 and recycles it for reuse;

[0092] Step B: The primary succinic acid slurry with a solid content of 11% crystallized from the primary crystallization kettle 10 is transported to the secondary crystallization kettle 20 through the first slurry outlet 103 on the primary crystallization kettle 10 via the primary slurry transport pump 11. The primary succinic acid slurry is vacuum flashed and cooled to 40° C. in the secondary crystallization kettle 20 to obtain the secondary succinic acid slurry. The vacuum pump 50 evacuates the secondary condenser 22 and the secondary crystallization kettle 20, and the negative pressure in the secondary crystallization kettle 20 reaches -0.094 MPag; the secondary condenser 22 condenses the steam in the secondary crystallization kettle 20 and recycles it for reuse;

[0093] Step C: The secondary succinic acid slurry with a solid content of 18% crystallized from the secondary crystallization kettle 20 is transported to the final crystallization kettle 30 through the second slurry outlet 204 on the secondary crystallization kettle 20 via the secondary slurry delivery pump 21. A cooling medium is provided in the cooling water jacket 301 of the final crystallization kettle 30. The cooling medium in the cooling water jacket 301 of the final crystallization kettle 30 is low-temperature water. The temperature of the low-temperature water is 7° C. and the pressure is 0.6 MPaG. The secondary succinic acid slurry is cooled and crystallized to 18° C. in the final crystallization kettle to obtain a final succinic acid slurry with a solid content of 27%;

[0094] Step D: 10% of the total mass of the final succinic acid slurry obtained by crystallization in the final crystallization kettle 30 is transported to the subsequent solid-liquid separation section by the final crystal slurry delivery pump 32 connected to the final crystallization kettle 30, and 90% of the total mass of the final succinic acid slurry obtained is transported to the crystallization external cooler 40 by the crystal slurry external circulation pump 31. The final succinic acid slurry is further cooled to 15°C to obtain externally cooled succinic acid slurry and then returned to the final crystallization kettle 30. The particle size of the succinic acid obtained by crystallization is 0.5-1.8 mm, of which the succinic acid with a particle size of 0.6-1.25 mm accounts for about 85%.

[0095] In this embodiment, the time for vacuum flash cooling crystallization in the first crystallization kettle, vacuum flash cooling crystallization in the second crystallization kettle and cooling crystallization in the final crystallization kettle is 45 minutes.

[0096] The externally cooled succinic acid slurry circulating back to the final crystallization kettle is mixed with the newly entered secondary succinic acid slurry to continue the next round of cooling crystallization in the final crystallization kettle.

[0097] In this embodiment, the cooling operation of the final stage succinic acid slurry in the crystallization external cooler 40 is specifically as follows:

[0098] Step 1): Open the first valve 411 between the slurry external circulation pump 31 and the slurry inlet 401 of the first slurry external cooler 41, and the second valve 421 between the slurry outlet 402 of the first slurry external cooler 41 and the externally cooled slurry circulation inlet 303, close the third valve 412 between the slurry external circulation pump 31 and the slurry inlet 401 of the second slurry external cooler 42, and the fourth valve 422 between the slurry outlet 402 of the second slurry external cooler 42 and the externally cooled slurry circulation inlet 303, close the second low-temperature water inlet valve 471 and the second low-temperature water outlet valve 461 of the second slurry external cooler 42, and open the first low-temperature water inlet valve 472 and the first low-temperature water outlet valve 462 of the first slurry external cooler 41 , close the first low-temperature water reflux valve 481 of the first slurry external cooler 41. At this time, 90% of the total mass of the final succinic acid slurry obtained by crystallization in the final crystallization kettle 30 is discharged into the first slurry external cooler 41 for cooling operation to obtain 15°C externally cooled succinic acid slurry, which then flows into the final crystallization kettle 30 and mixes with the newly entered secondary succinic acid slurry to continue to carry out the next round of cooling crystallization in the final crystallization kettle 30; the temperature of the low-temperature water introduced into the first slurry external cooler 41 is 7°C; in step 1), after the slurry flows out from the slurry outlet of the first slurry external cooler 41 into the final crystallization kettle 30, the slurry remaining in the first slurry external cooler 41 is recovered to the final crystallization kettle 30 through the first slurry reflux port 306 for further recovery and crystallization;

[0099] Step 2): When the first slurry external cooler 41 works continuously for 12 hours and the externally cooled succinic acid slurry flows into the final crystallization kettle 30, the second slurry external cooler 42 is switched to work, and the first slurry external cooler 41 is cleaned. The specific operations are as follows: close the first valve 411 between the slurry external circulation pump 31 and the slurry inlet 401 of the first slurry external cooler 41, and the second valve 421 between the slurry outlet 402 of the first slurry external cooler 41 and the externally cooled slurry circulation inlet 303, open the third valve 412 between the slurry external circulation pump 31 and the slurry inlet 401 of the second slurry external cooler 42, and the fourth valve 422 between the slurry outlet 402 of the second slurry external cooler 42 and the externally cooled slurry circulation inlet 303, close the first low-temperature water inlet valve 472 of the first slurry external cooler 41 and The first low-temperature water outlet valve 462 opens the second low-temperature water inlet valve 471 and the second low-temperature water outlet valve 461 of the second crystal slurry external cooler 42, and the first low-temperature water return port valve 481 of the low-temperature water return port of the first crystal slurry external cooler 41 is opened. At this time, 90% of the total mass of the final succinic acid slurry obtained by crystallization in the final crystallization kettle 30 is discharged from the final crystallization kettle 30 to the second crystal slurry external cooler 42 for cooling, and after cooling to 15°C, it is discharged and returned to the final crystallization kettle 30 to mix with the newly entered secondary succinic acid slurry and continue to be cooled and crystallized in the final crystallization kettle 30 for the next round; and the low-temperature water in the cooling medium cavity 45 of the first crystal slurry external cooler 41 flows into the low-temperature water tank 9 through the low-temperature water return port 48; the low-temperature water tank 9 is connected to the low-temperature water pump 8 for discharging the low-temperature water in the low-temperature water tank 9. The temperature of the low-temperature water introduced into the second crystal slurry external cooler 42 is 7°C. In step 2), after the slurry flows out from the slurry outlet 402 of the second slurry external cooler 42 into the final crystallization kettle 30, the slurry remaining in the second slurry external cooler 42 is recovered into the final crystallization kettle 30 through the second slurry reflux port 305 for further crystallization.

[0100] In this embodiment, the low-temperature water outlet 46 of the first slurry external cooler 41 and the low-temperature water outlet 46 of the second slurry external cooler 42 are respectively connected with a vent 7. In step 1), when the low-temperature water in the cooling medium cavity of the first slurry external cooler needs to be discharged, the vent connected to the low-temperature water outlet of the first slurry external cooler is opened for drainage; in step 2), when the low-temperature water in the cooling medium cavity of the second slurry external cooler needs to be discharged, the vent connected to the low-temperature water outlet of the second slurry external cooler is opened for drainage.

[0101] When the succinic acid slurry begins to cool down in the second slurry external cooler 42, the first cleaning liquid inlet valve 51 and the first cleaning liquid outlet valve 61 of the first slurry external cooler 41 are opened, and the second cleaning liquid inlet valve 52 and the second cleaning liquid outlet valve 62 of the second slurry external cooler 42 are kept closed, and the cleaning liquid preheated to 40°C is sent to the first slurry external cooler 41 for cleaning; in this embodiment, the cleaning liquid is the unsaturated filtered mother liquor of the succinic acid slurry, and the filtered mother liquor after cleaning is recycled and reused, so that no waste liquid is generated to pollute the environment. After the first slurry external cooler 41 is cleaned for 30 minutes, the crystals bonded to the slurry conveying pipeline are fully dissolved, and then the first cleaning liquid inlet valve 51 and the first cleaning liquid outlet valve 61 of the first slurry external cooler 41 are closed.

[0102] Step 3): After the second crystal slurry external cooler 42 has been working continuously for 12 hours, the first crystal slurry external cooler 41 is switched to work. At the same time, the second crystal slurry external cooler 42 is cleaned. The cleaning operation conditions of the second crystal slurry external cooler 42 are the same as those of step 2), and the crystal slurry external cooling and cooling operation of the first crystal slurry external cooler 41 is the same as that of step 1). In this way, the crystallization external cooler 40 does not need to be stopped for cleaning, ensuring that at least one crystal slurry external cooler in the crystallization external cooler 40 can cool the incoming final succinic acid crystal slurry at any time.

[0103] Comparative Example

[0104] The process of continuous crystallization of succinic acid in the prior art is adopted, and three-stage vacuum cooling crystallization is adopted. However, due to the influence of vacuum degree, the temperature of the slurry can only be reduced to 30°C after crystallization, and a large amount of succinic acid cannot be precipitated. At the same time, the process adopts a crystal slurry internal circulation crystallizer, and a guide tube is set inside the crystallizer to make the slurry circulate inside the crystallizer, but the slurry stays in the crystallizer for a long time, resulting in a low production capacity of the crystallization device, which is not suitable for the growing demand for succinic acid production capacity.

[0105] The succinic acid multi-stage continuous crystallization system of the present invention is used. The succinic acid solution is first subjected to vacuum flash cooling crystallization in a first-stage crystallization kettle, and then the slurry enters more than one second-stage crystallization kettle for vacuum flash cooling crystallization, and then the slurry enters the final crystallization kettle for cooling crystallization, and then is sent to the crystallization external cooler. The succinic acid slurry is further cooled and returned to the final crystallization kettle, and multi-stage step-by-step cooling crystallization is adopted. The temperature difference between each stage of crystallization is small, and crystal explosion is prevented, so that the crystallization in the crystallization kettle is relatively uniform, and the particle size distribution of the crystal particles is narrowed. At the same time, multi-stage crystallization can increase the granularity of the succinic acid product, and improve the quality of the succinic acid product. In addition, the mode of combining multi-stage vacuum flash crystallization and first-stage external cooling crystallization is adopted to reduce the succinic acid crystallization time and improve the crystallization efficiency; at the same time, the crystallization terminal temperature is reduced, the residual succinic acid content in the mother liquor is reduced, the succinic acid production capacity is improved, and the stability of the subsequent unit operation is also greatly beneficial. Large-scale and continuous production of succinic acid crystallization process is realized.

[0106] Although the specific embodiments of the present invention are described in detail in conjunction with the accompanying drawings, it should not be understood as limiting the scope of protection of the present invention. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still belong to the scope of protection of the present invention.

Claims

1. A succinic acid multi-stage continuous crystallization system, comprising a first-stage crystallization kettle, a second-stage crystallization kettle and a final-stage crystallization kettle connected in sequence, wherein the first slurry outlet of the first-stage crystallization kettle is connected to the second slurry inlet of the second-stage crystallization kettle by a pipeline, and the second slurry outlet of the second-stage crystallization kettle is connected to the final slurry inlet of the final-stage crystallization kettle by a pipeline, wherein: The final crystal slurry outlet of the final crystallization kettle is connected to the crystal slurry inlet of the crystallization external cooler and the solid-liquid separation section through pipelines.

2. The system according to claim 1, characterized in that: The primary crystallization kettle is provided with a succinic acid solution inlet and a first gas outlet; preferably, a primary condenser is further provided after the first gas outlet; and / or, The secondary crystallization kettle is provided with a second gas outlet; preferably, a secondary condenser is further provided after the second gas outlet; and / or, The primary condenser and the secondary condenser are connected to a vacuum pump via a pipeline; and / or, The final crystallization kettle is provided with an externally cooled crystal slurry circulation inlet; preferably, the crystal slurry outlet of the crystallization external cooler is connected to the externally cooled crystal slurry circulation inlet through a pipeline.

3. The system according to claim 1, characterized in that: A first-stage slurry delivery pump is arranged on the pipeline connecting the first slurry outlet to the second-stage crystallization kettle; and / or, A secondary slurry delivery pump is provided on the pipeline connecting the second slurry outlet to the final crystallization kettle; and / or, A final-stage slurry delivery pump is provided on the pipeline connecting the final-stage slurry outlet to the solid-liquid separation section; and / or, A slurry external circulation pump is provided on the pipeline connecting the final slurry outlet to the crystallization external cooler; preferably, The first-stage slurry delivery pump, the second-stage slurry delivery pump, the final-stage slurry delivery pump, and the slurry external circulation pump are each independently an axial flow pump, a Tesla pump, a centrifugal pump, or a vortex pump.

4. The system according to claim 1, characterized in that: The secondary crystallization kettle comprises more than one crystallization kettle. Preferably, when the secondary crystallization kettle comprises more than two crystallization kettles, the more than two crystallization kettles are connected in series; and / or, The final crystallization kettle comprises more than one crystallization kettle. Preferably, when the final crystallization kettle comprises more than two crystallization kettles, the more than two crystallization kettles are connected in series; and each crystallization kettle is connected to a crystallization external cooler.

5. The system according to claim 1, characterized in that: The first-stage crystallization kettle, the second-stage crystallization kettle and the final-stage crystallization kettle are each optionally provided with a cooling water jacket; and / or, The first-stage crystallization kettle, the second-stage crystallization kettle and the final-stage crystallization kettle are each optionally provided with a stirring paddle. Preferably, the stirring paddle is one of a multi-layer turbine paddle, a frame-type stirring paddle, an anchor-type stirring paddle or a combined blade-type stirring paddle.

6. A system according to any one of claims 1 to 5, characterized in that: The crystallization external cooler includes more than one slurry external cooler, preferably includes at least two parallel slurry external coolers, the final slurry outlet of the final crystallization kettle is connected to the slurry inlet of each slurry external cooler by a pipeline, and the slurry outlet of each slurry external cooler is connected to the external cooling slurry circulation inlet of the final crystallization kettle by a pipeline.

7. The system according to claim 6, characterized in that: A switch valve is provided on the connecting pipeline between the final slurry outlet of the final crystallization kettle and the slurry inlet of each slurry external cooler; preferably, a cleaning liquid inlet is provided on the connecting pipeline between the switch valve on the connecting pipeline between the final slurry outlet and the slurry inlet of each slurry external cooler and the slurry inlet of each slurry external cooler; and / or, A switching valve is provided on the connecting pipeline between the slurry outlet of each slurry external cooler and the externally cooled slurry circulation inlet of the final crystallization kettle; preferably, a cleaning liquid outlet is provided on the connecting pipeline between the switching valve on the connecting pipeline between the slurry outlet of each slurry external cooler and the externally cooled slurry circulation inlet of the final crystallization kettle and the slurry outlet of each slurry external cooler.

8. The system according to claim 6, characterized in that: Each slurry external cooler is provided with a cooling medium inlet and a cooling medium outlet; preferably, A cooling medium reflux port is optionally provided at the bottom of each slurry external cooler; further preferably, The system is also provided with a cooling medium tank, and the cooling medium tank is connected to the cooling medium return port through a pipeline.

9. The system according to claim 8, characterized in that: The slurry external cooler comprises a slurry external cooler shell, a slurry conveying pipeline for conveying slurry arranged in the slurry external cooler shell, and a cooling medium cavity between the slurry conveying pipeline and the shell; preferably, The cooling medium inlet and the cooling medium outlet are respectively arranged at the upper and lower ends of the cooling medium cavity.

10. A multi-stage continuous crystallization method for succinic acid using the system according to any one of claims 1 to 9, comprising the steps of subjecting a succinic acid solution to two-stage vacuum flash cooling crystallization, and then subjecting the succinic acid solution to one-stage cooling crystallization, wherein part of the obtained slurry is discharged to a solid-liquid separation section, and part of the obtained slurry is sent to a crystallization external cooler for cooling and then circulated back to a final crystallization kettle.

11. The method according to claim 10, characterized in that The method comprises: A. Discharging the primary succinic acid slurry obtained by vacuum flash cooling and crystallization of the succinic acid solution in a primary crystallization kettle; B. discharging the secondary succinic acid slurry obtained by vacuum flash cooling and crystallization of the primary succinic acid slurry in the secondary crystallization kettle; C. Cooling and crystallizing the secondary succinic acid slurry in a final crystallization kettle to obtain a final succinic acid slurry; D. Part of the final stage succinic acid slurry is discharged to the solid-liquid separation section, and part of it is sent to the crystallization external cooler for cooling to obtain the externally cooled succinic acid slurry which is then recycled back to the final stage crystallization kettle.

12. The method according to claim 11, characterized in that: In step A, the temperature of the succinic acid solution is 70 to 90° C., preferably 75 to 85° C.; and / or, the concentration of the succinic acid solution is 24 to 30%, preferably 25 to 28%; and / or, the negative pressure in the primary crystallization kettle is -0.07 to -0.09 Mpag; and / or, the temperature of the primary succinic acid slurry obtained in the primary crystallization kettle is 50 to 57° C., preferably 50 to 55° C.; and / or, the solid content of the primary succinic acid slurry obtained in the primary crystallization kettle is 6 to 12%, preferably 9 to 12%; and / or, In step B, the negative pressure in the secondary crystallization kettle is -0.085 to -0.098 MPag; and / or, the temperature of the secondary succinic acid slurry obtained in the secondary crystallization kettle is 35 to 50° C., preferably 40 to 45° C.; and / or, the solid content of the secondary succinic acid slurry obtained in the secondary crystallization kettle is 15 to 19%, preferably 16 to 19%; and / or, In step C, the temperature of the final succinic acid slurry is 18-23° C., preferably 18-21° C.; and / or the solid content of the final succinic acid slurry is 20-28%, preferably 24-27%; and / or, In step D, the portion of the final succinic acid slurry sent to the crystallization external cooler is 60-95% of the total mass of the final succinic acid slurry, preferably 80-90%; and / or, the final succinic acid slurry sent to the crystallization external cooler for cooling is cooled to 15-18°C, preferably 15-17°C in the crystal slurry external cooler to obtain the externally cooled succinic acid slurry and returned to the final crystallization kettle; and / or, the externally cooled succinic acid slurry circulated back to the final crystallization kettle from the crystallization external cooler is mixed with the newly entered secondary succinic acid slurry and continues to be cooled and crystallized in the final crystallization kettle.

13. The method according to claim 11, characterized in that: When the crystallization external cooler comprises at least two parallel slurry external coolers, the final succinic acid slurry fed into the crystallization external cooler is alternately cooled in at least two parallel slurry external coolers and then circulated back to the final crystallization kettle, and at the same time, the slurry external coolers from which the slurry is discharged from the at least two parallel slurry external coolers are alternately cleaned; preferably, When the crystallization external cooler includes two parallel slurry external coolers, the cooling and cleaning steps of the final succinic acid slurry fed into the crystallization external cooler in the two parallel slurry external coolers include: 1) the final stage succinic acid slurry sent to the crystallization external cooler is cooled in the first slurry external cooler and then returned to the final stage crystallization kettle; 2) cleaning the first slurry external cooler; during this period, the final succinic acid slurry discharged from the final crystallization kettle is cooled in the second slurry external cooler and then returned to the final crystallization kettle; 3) Cleaning the second slurry external cooler; 4) Optionally, repeat steps 1) to 3).

14. The method according to claim 13, characterized in that: The first slurry external cooler adopts cooling medium 1 for cooling operation, the second slurry external cooler adopts cooling medium 2 for cooling operation, the jacket of the final crystallization kettle is introduced with cooling medium 3, cooling medium 1, cooling medium 2 and cooling medium 3 are the same or different, and are preferably at least one of water and sodium chloride aqueous solution; and / or, the temperature of cooling medium 1, cooling medium 2 and cooling medium 3 when entering each device is preferably 7-15°C; and / or, In step 2), the first slurry external cooler is cleaned with cleaning liquid 1; and / or, the first slurry external cooler is cleaned with cleaning liquid 1 for 10 to 60 minutes, preferably 30 to 60 minutes; and / or, in step 3), the second slurry external cooler is cleaned with cleaning liquid 2; and / or, the second slurry external cooler is cleaned with cleaning liquid 2 for 10 to 60 minutes, preferably 30 to 60 minutes; and / or, the cleaning liquid 1 and the cleaning liquid 2 are the same or different, and are independently preferably at least one of water and unsaturated filtered mother liquor of succinic acid slurry; preferably, the cleaning liquid 1 and the cleaning liquid 2 are the same.

15. Use of the system according to any one of claims 1 to 9 or the method according to any one of claims 10 to 14 in the field of succinic acid crystallization.

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