A method and apparatus for graded drying of polyacrylonitrile

Abstract

This invention provides a method and apparatus for graded drying of polyacrylonitrile (PAC), belonging to the field of PAC drying. The graded drying apparatus for PAC of this invention includes: a primary paddle dryer, a feeder, a secondary flash dryer, a closed-loop nitrogen circulation system, a cyclone dust collector, a bag filter, and a control module. This invention also provides a method for graded drying of PAC, comprising the following steps: pre-drying preparation, primary paddle drying, secondary flash drying, graded storage, nitrogen purification, and continuous drying. The graded drying method and apparatus for PAC of this invention effectively avoid problems such as adhesion, deposition, and agglomeration of the wet copolymerized PAC during the drying process, eliminate the risk of combustion and explosion during the drying process, and effectively reduce nitrogen consumption and heat energy consumption while improving drying effect and efficiency, thus reducing production costs.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polyacrylonitrile drying, and particularly relates to a grading drying method and device for polyacrylonitrile. BACKGROUND

[0002] The two-step method for producing polyacrylonitrile-based carbon fiber refers to a process that first obtains a copolymer slurry through a copolymerization reaction, then filters the slurry to obtain a copolylyonitrile filter cake with a high water content, and then dries the copolylyonitrile filter cake through a drying system to obtain polyacrylonitrile powder, and finally prepares a spinning solution, and then spins, carbonizes and obtains carbon fiber. The raw material copolylyonitrile is an important precursor for the production of carbon fiber, and the drying process of the copolylyonitrile is particularly important for the quality of the carbon fiber.

[0003] At present, the drying methods mainly used by domestic carbon fiber and acrylic enterprises for copolylyonitrile include fluidized bed drying, paddle drying, flash drying and chain plate drying, and enterprises using chain plate drying systems are the most common. However, the existing fluidized bed drying process for polyacrylonitrile is prone to wet material agglomeration during the drying process due to the material characteristics of the copolylyonitrile. As the amount of copolylyonitrile material increases, the fluidization effect gradually decreases, and a dead bed phenomenon may occur. Due to this drawback, the fluidized bed drying process has been gradually replaced by other drying processes. The chain plate drying process is an open cycle, and the polyacrylonitrile powder is a flammable and explosive material. Open drying can easily cause serious safety hazards, and the chain plate drying system generally does not have a crushing or scattering device, so the obtained product has large particles and needs to be crushed separately.

[0004] The inventors found that in the drying process of copolylyonitrile using the paddle drying process, the material advances smoothly and does not agglomerate. However, the paddle shaft and paddle root are prone to wet material adhesion, and the adhesion and deposition of wet material seriously affect the drying effect and efficiency, increase the equipment maintenance frequency and cost, and the polyacrylonitrile after paddle drying is difficult to meet the requirement of water content ≤1%, and cannot meet the subsequent application requirements. The inventors further found that the flash drying process has a relatively ideal drying effect on copolylyonitrile, and the water content of the polyacrylonitrile after drying basically meets the requirement of ≤1%, and there is no obvious wall adhesion of the material during the flash drying process. However, in order to achieve an ideal drying effect, a higher temperature is required for flash drying, usually a high temperature of 150℃ or above, and the drying energy consumption is high. Moreover, the drying temperature exceeds the glass transition temperature of polyacrylonitrile, and the polyacrylonitrile is prone to quality change due to high temperature during the drying process.

[0005] In summary, the existing drying technology for copolylyonitrile has many defects in terms of drying effect, drying energy consumption and drying process, and needs to be improved. SUMMARY

[0006] To solve the technical problems in the prior art, the application provides a grading drying method and device for polyacrylonitrile, which effectively avoids the problems of wall sticking, deposition and agglomeration of the wet copolymerized polyacrylonitrile material in the drying process, eliminates the hidden danger of combustion and explosion in the drying process of the copolymerized polyacrylonitrile, and effectively reduces the nitrogen consumption and heat energy consumption while improving the drying effect and drying efficiency, thereby reducing the production cost.

[0007] To solve the above technical problems, the technical solutions adopted by the application are as follows:

[0008] A grading drying device for polyacrylonitrile comprises a primary paddle dryer, a feeder, a secondary flash drying machine, a nitrogen closed-loop circulation device, a cyclone dust collector, a bag dust collector and a control module.

[0009] The nitrogen closed-loop circulation device is used for heating, supplying and supplementing the nitrogen in the grading drying device for polyacrylonitrile.

[0010] The primary paddle dryer comprises a drying cavity, and the drying cavity inlet is communicated with a wet material supply pipeline, which is used for primary paddle drying of the wet material.

[0011] A hollow rotating shaft is arranged at the horizontal central axis of the drying cavity, and the gas inlet end of the hollow rotating shaft is communicated with the hot nitrogen gas supply pipeline of the nitrogen closed-loop circulation device.

[0012] A plurality of hollow paddles are arranged on the hollow rotating shaft, and the cavity of the hollow rotating shaft is communicated with the cavities of the hollow paddles, so that the hot nitrogen gas flows in the hollow rotating shaft and the hollow paddles while the hollow rotating shaft drives the hollow paddles to rotate.

[0013] The hollow paddles are uniformly provided with through spray holes, so that the hot nitrogen gas in the hollow paddles is sprayed into the drying cavity through the spray holes.

[0014] Preferably, the hot nitrogen gas is used, and the temperature of the outer surface of the hollow rotating shaft and the hollow paddle in contact with the wet material is adjusted to 88-90 DEG C.

[0015] The diameter of the spray hole is 1.8-2.3 mm.

[0016] Further, a self-control adjusting valve is arranged on the gas inlet pipeline of the hollow rotating shaft, and the control module is electrically connected with the self-control adjusting valve; the control module can control the opening degree of the self-control adjusting valve, and adjust the spray flow and time of the hot nitrogen gas at the spray hole.

[0017] Preferably, the control module is provided with a high-flow spray point and a low-flow spray point at the spray hole.

[0018] The high-flow injection point controls the valve opening of the automatic control regulating valve to be 85-90%;

[0019] The low-flow injection point controls the valve opening of the automatic control regulating valve to be 45-50%;

[0020] The staggered time of the high-flow injection point and the low-flow injection point is 8-12s.

[0021] Further, the feeding port of the feeder is in communication with the dry cavity discharge port of the primary paddle dryer; and the discharge port of the feeder is in communication with the feeding port of the secondary flash drying machine.

[0022] The feeding port of the secondary flash drying machine is in communication with the discharge port of the feeder; and the gas inlet of the secondary flash drying machine is in communication with the hot nitrogen gas supply pipeline of the nitrogen closed circulation device, for receiving the hot nitrogen gas from the nitrogen closed circulation device.

[0023] Further, the feeding port of the cyclone separator is in communication with the discharge port of the secondary flash drying machine; and the top discharge port of the cyclone separator is in communication with the feeding port of the bag-type dust collector, for cyclone classification of the discharge of the secondary flash drying machine.

[0024] In the cyclone classification process, the polyacrylonitrile powder with a particle size of ≥50μm is discharged from the bottom discharge port of the cyclone dust collector to the large-particle-size product storage bin; and the polyacrylonitrile powder with a particle size of <50μm is discharged from the top discharge port of the cyclone separator to the bag-type dust collector for collection, and then discharged to the small-particle-size product storage bin.

[0025] A method for grading drying of polyacrylonitrile, characterized by comprising the following steps: drying preparation, primary paddle drying, secondary flash drying, grading storage, nitrogen impurity removal, and continuous drying.

[0026] The drying preparation adopts nitrogen to replace air completely, and heats the nitrogen to 90-92℃ to obtain hot nitrogen gas; and the hot nitrogen gas is circulated to preheat the primary paddle dryer and the secondary flash drying machine.

[0027] The primary paddle drying is performed as follows: the wet material with a water content of 45-55wt% is fed into the dry cavity of the primary paddle dryer; and the hot nitrogen gas at 90-92℃ is continuously introduced into the jacket and the hollow shaft of the primary paddle dryer, to obtain primary dried material.

[0028] The hollow shaft is provided with a plurality of hollow paddles, and the hollow paddles are uniformly provided with through injection holes; the cavity of the hollow shaft is in communication with the cavities of the hollow paddles, and the hot nitrogen gas flows in the hollow shaft and the hollow paddles, and is injected into the dry cavity through the injection holes.

[0029] The secondary flash drying, the first-stage dried material is fed into the secondary flash drying machine; the first-stage dried material is subjected to secondary flash drying under the condition of hot nitrogen circulation and stirring to obtain secondary dried material.

[0030] Preferably, in the first-stage paddle drying, the feeding rate of the wet material is 3000-3300 kg / h; the rotating speed of the hollow paddle is 4-10 rpm, and the residence time of the wet material in the first-stage paddle drying machine is 20-25 min.

[0031] In the secondary flash drying, the feeding rate of the first-stage dried material is 3000-3300 kg / h; the residence time of the material is 8-12 s.

[0032] Preferably, in the first-stage paddle drying, the hot nitrogen is sprayed at high flow rate and low flow rate at the spraying hole.

[0033] The staggered time of high flow rate spraying and low flow rate spraying is 8-12 s.

[0034] Further, the hierarchical storage, the secondary dried material is subjected to cyclone classification, the polyacrylonitrile powder with a particle size of ≥50 μm is collected and stored, and the polyacrylonitrile powder with a particle size of <50 μm is collected by a bag-type dust collector after cyclone separation and stored.

[0035] In the nitrogen impurity removal, during the first-stage paddle drying and the secondary flash drying, the nitrogen is introduced into the spray tower through the bag-type dust collector, the impurities in the nitrogen are removed through countercurrent spraying of desalted water, and the hot nitrogen is obtained again after water removal and heating to be recycled.

[0036] The continuous drying, the first-stage paddle drying, the secondary flash drying, the hierarchical storage and the nitrogen impurity removal are repeatedly performed.

[0037] Compared with the prior art, the present application has the following beneficial effects:

[0038] (1) The hierarchical drying method and device for polyacrylonitrile can effectively avoid the problems of wall sticking, deposition and agglomeration of the copolymerized polyacrylonitrile wet material during drying, eliminate the safety hazard of combustion and explosion during the drying process of the copolymerized polyacrylonitrile, effectively reduce the nitrogen consumption and heat consumption, and reduce the production cost while improving the drying effect and drying efficiency.

[0039] (2) In the first-stage paddle drying process of the hierarchical drying method and device for polyacrylonitrile, the problems of wall sticking, deposition and agglomeration of the copolymerized polyacrylonitrile wet material can make the polyacrylonitrile wet material be fully dispersed and dried, and effectively improve the smoothness in the subsequent powder conveying process.

[0040] (3) The graded drying method and apparatus for polyacrylonitrile of the present invention, compared with the traditional process of using paddle drying or flash drying alone, can effectively avoid the polymer from undergoing quality change due to high temperature, and can achieve effective and rapid drying of polyacrylonitrile under lower temperature conditions; at the same time, the reduction of drying temperature effectively reduces heat energy consumption and effectively achieves energy saving and consumption reduction; in addition, the improvement of drying efficiency and drying effect makes the powder conveying smoother, which can greatly reduce the failure rate of the equipment.

[0041] (4) The graded drying method and apparatus for polyacrylonitrile of the present invention has extremely low nitrogen consumption during the drying process and the drying process is completely sealed, which effectively improves the safety of polyacrylonitrile during the drying process.

[0042] (5) The graded drying method and apparatus for polyacrylonitrile of the present invention can dry polyacrylonitrile with a moisture content of ≤1wt% within 20-25 minutes, which effectively improves the drying effect and drying efficiency. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of a nitrogen closed-loop drying method for polyacrylonitrile.

[0044] In the diagram, 1-steam heater, 2-first-stage paddle dryer, 3-screw feeder, 4-second-stage flash dryer, 5-cyclone dust collector, 6-bag filter dust collector, 7-washing tower, 8-demister, 9-circulating fan, 10-nitrogen generator, 11-oxygen content detector, 12-automatic control valve.

[0045] Figure 2 This is a schematic diagram of the hollow blades inside a primary blade dryer.

[0046] In the diagram, 21-hollow shaft, 22-hollow blade, 23-jet nozzle. Detailed Implementation

[0047] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0048] Example 1

[0049] like Figure 1 As shown, this embodiment provides a staged drying device for polyacrylonitrile, including: a nitrogen closed-loop circulation device, a primary paddle dryer 2, a screw feeder 3, a secondary flash dryer 4, a cyclone dust collector 5, a bag filter dust collector 6, and a control module.

[0050] The primary paddle dryer 2 comprises a drying cavity, the drying cavity inlet communicates with the wet material supply pipeline, and the drying cavity outlet communicates with the feeding inlet of the screw feeder 3, which is used for outputting the wet material after primary paddle drying to the screw feeder 3.

[0051] The hollow rotating shaft 21 is provided at the horizontal central axis of the drying cavity, and a plurality of hollow paddles 22 are further provided on the hollow rotating shaft 21; the cavity of the hollow rotating shaft 21 communicates with the cavities of the hollow paddles 22, and the hollow rotating shaft 21 and the hollow paddles 22 are internally gas flowable. The gas inlet end of the hollow rotating shaft 21 communicates with the hot nitrogen gas supply pipeline of the nitrogen closed circulation device, which is used for receiving the hot nitrogen gas from the nitrogen closed circulation device and supplying the hot nitrogen gas to each hollow paddle 22 in communication therewith, so as to control the temperature of the outer surface of the hollow rotating shaft 21 and the hollow paddles 22 in contact with the wet material to be 88-90℃; the hollow rotating shaft 21 drives the hollow paddles 22 to rotate, so as to paddle dry the wet material and obtain primary dried material.

[0052] As shown in Figure 2 The hollow paddles 22 of the primary paddle dryer 2 are further uniformly provided with through blowing holes 23, the hot nitrogen gas in the hollow paddles 22 can be blown into the drying cavity through the blowing holes 23 to contact and dry the wet material in the drying cavity, and to blow the material in the drying cavity to prevent the wet material from sticking to the wall and depositing; at the same time, the hot nitrogen gas blowing maintains a slightly positive pressure environment in the drying cavity, which is beneficial to the conveying of the material.

[0053] Preferably, the diameter of the blowing hole 23 is 1.8-2.3mm.

[0054] The gas inlet pipeline of the hollow rotating shaft 21 is further provided with an automatic control adjusting valve 12, and the control module is electrically connected with the automatic control adjusting valve 12; the control module is pre-set with a pulse blowing program, and the opening degree of the automatic control adjusting valve 12 is controlled to realize the periodic change of the blowing flow and time of the hot nitrogen gas.

[0055] Preferably, the control module is pre-set with a high-flow blowing point (valve opening degree 85-90%) and a low-flow blowing point (valve opening degree 45-50%), and the staggered time of the high-flow blowing point and the low-flow blowing point is 8-12s; the hot nitrogen gas with different flow rates is maintained by staggered blowing to realize pulse blowing of the wet material in the drying cavity.

[0056] The feeding inlet of the screw feeder 3 communicates with the drying cavity outlet of the primary paddle dryer 2; the outlet of the screw feeder 3 communicates with the feeding inlet of the secondary flash drying machine 4; which is used for screw extruding the primary dried material into the secondary flash drying machine 4.

[0057] The feed inlet of the secondary flash drying machine 4 is communicated with the discharge outlet of the screw feeder 3; meanwhile, the gas inlet of the secondary flash drying machine 4 is communicated with the hot nitrogen gas supply pipeline of the nitrogen closed circulation device, for receiving the hot nitrogen gas from the nitrogen closed circulation device to perform secondary flash drying on the primary dried material in the secondary flash drying machine 4, so as to obtain the secondary dried material.

[0058] The lower part of the secondary flash drying machine 4 is provided with a mechanical stirring paddle, for stirring to form a vortex type rotating gas flow, further crushing and drying the primary flash dried material, and controlling the moisture content of the secondary flash dried material to be less than 1wt%.

[0059] The feed inlet of the cyclone separator is communicated with the discharge outlet of the secondary flash drying machine, the top discharge outlet of the cyclone separator is communicated with the feed inlet of the bag-type dust collector 6, for receiving the secondary dried material and performing cyclone classification; during the cyclone classification process, the polyacrylonitrile powder with large particle size (50μm and above, about 95wt% of the secondary dried material) is separated from the cyclone nitrogen gas flow and trapped on the wall, and collected at the bottom of the cyclone dust collector 5 under the action of gravity, and discharged from the bottom discharge outlet to the product storage bin for storage; the polyacrylonitrile powder with small particle size (about 5wt% of the secondary dried material) will be driven by the cyclone nitrogen gas flow, enter the bag-type dust collector 6 through the top discharge outlet of the cyclone separator, and be collected and discharged to the product storage bin for storage.

[0060] The nitrogen closed circulation device includes a nitrogen generating device 10, a steam heater 1, a spray tower 7, a demister 8, a circulating fan 9, and an oxygen content detector 11, for maintaining the continuous circulation of nitrogen in the classification drying device.

[0061] The nitrogen generating device 10 is communicated with the nitrogen pipeline of the nitrogen closed circulation device, for supplying and supplementing the nitrogen of the nitrogen closed circulation device;

[0062] The oxygen content detector 11 is arranged on the nitrogen pipeline of the nitrogen closed circulation device downstream of the circulating fan 9, and is electrically connected with the nitrogen generating device 10 through a control module; for real-time detection and remote transmission of the oxygen content in the nitrogen to the control module, and when the oxygen content in the nitrogen is higher than 3.5%, the control module controls the nitrogen generating device 10 to start and supplement the nitrogen in the nitrogen closed circulation device.

[0063] One end of the steam heater 1 is communicated with the nitrogen pipeline of the nitrogen closed circulation device, and the other end is respectively connected in parallel with the primary paddle dryer 2 and the secondary flash drying machine 4; for heating the nitrogen passing through the steam heater 1 to 90-92℃, and supplying the hot nitrogen to the primary paddle dryer 2 and the secondary flash drying machine 4 respectively.

[0064] The steam heater 1 comprises a condensate heat exchange module and a steam heat exchange module; the condensate heat exchange module uses 75-80℃ steam condensate water to preheat nitrogen, the working pressure is 0.2-0.3MPa, and the heat exchange area is 792m 2 ; the steam heat exchange module uses 165-171℃ water vapor to heat the nitrogen preheated by the condensate heat exchange module, the working pressure is 0.6-0.7MPa, and the heat exchange area is 1584m 2 .

[0065] The lower air inlet of the elution tower 7 is communicated with the air outlet of the bag-type dust collector 6, which is used to collect the nitrogen flowing out of the bag-type dust collector 6, and the desalted water is sprayed to clean and collect a small amount of residual polyacrylonitrile powder in the nitrogen.

[0066] The air inlet of the demister 8 is communicated with the upper air outlet of the elution tower 7, and the nitrogen in the elution tower 7 after being washed by the desalted water enters the demister 8 to remove water mist in the nitrogen circulation process.

[0067] The air inlet of the circulating fan 9 is communicated with the air outlet of the demister 8, which is used to drive the flow of nitrogen in the nitrogen closed circulation device.

[0068] The control module is a PLC controller or a DCS controller.

[0069] Further, on the basis of the foregoing embodiment, in the grading drying device for polyacrylonitrile provided by the embodiment, a first solid moisture on-line detector and a first automatic cumulative weighing instrument are sequentially arranged on the wet material supply pipeline at the front end of the first paddle dryer 2, and a second solid moisture on-line detector and a second automatic cumulative weighing instrument are sequentially arranged at the discharge port of the screw feeder 3.

[0070] The first solid moisture on-line detector is used to detect the moisture content of the wet material before entering the first paddle dryer 2 and remotely transmit the detection result to the control module. The first automatic cumulative weighing instrument is used to automatically weigh and accumulate the total weight of the wet material entering the first paddle dryer and remotely transmit the total weight to the control module.

[0071] The second solid moisture on-line detector is used to detect the moisture content of the first dried material and remotely transmit the detection result to the control module. The second automatic cumulative weighing instrument is used to automatically weigh and accumulate the total weight of the first dried material and remotely transmit the total weight to the control module.

[0072] The control module receives the aforementioned detection data, calculates the absolute dry material weight of the wet material entering the first-stage paddle dryer 2 and the absolute dry material weight of the first-stage dried material, and calculates the absolute dry material weight attenuation value; if the absolute dry material weight attenuation value < 2wt%, the high-flow injection point position, the low-flow injection point position, and the staggered time remain unchanged. If the absolute dry material weight attenuation value ≥ 2wt%, the valve opening of the high-flow injection point position is increased by 4-5%, the valve opening of the low-flow injection point position is reduced by 4-5%, and the staggered time of the high-flow injection point position and the low-flow injection point position is shortened by 2-4s.

[0073] The calculation method of the absolute dry material weight attenuation value is: [(absolute dry material weight of the wet material - absolute dry material weight of the first-stage dried material) / absolute dry material weight of the wet material] * 100%.

[0074] Further, the control module also has an algorithm model based on machine learning technology pre-established. The algorithm model based on machine learning technology is established by training a plurality of sets of training data, and the plurality of sets of training data at least include: real-time data of the first-stage paddle dryer 2 drying the first batch of wet material; real-time data of the first-stage paddle dryer 2 drying the second batch of wet material; real-time data of the first-stage paddle dryer 2 drying the third batch of wet material;...; real-time data of the first-stage paddle dryer 2 drying the nth batch of wet material.

[0075] The real-time data in the plurality of sets of training data at least include: the nitrogen gas temperature entering the first-stage paddle dryer 2, the nitrogen gas flow entering the first-stage paddle dryer 2, the valve opening of the high-flow injection point position, the nitrogen gas flow rate in the hollow shaft 21 at the high-flow injection point position, the valve opening of the low-flow injection point position, the nitrogen gas flow rate in the hollow shaft 21 at the low-flow injection point position, and the absolute dry material weight attenuation value.

[0076] And the aforementioned algorithm model based on machine learning technology can be continuously learned and optimized, so that the algorithm model is more perfect, and by adjusting the flow and frequency of high-flow injection and low-flow injection, the paddle drying process of the first-stage paddle dryer 2 is further optimized, the drying effect and drying efficiency are improved, the nitrogen gas consumption and heat energy consumption are reduced, and the problems of wall sticking, deposition, and agglomeration of the material in the first-stage paddle dryer 2 during the drying process are avoided.

[0077] Meanwhile, the control module also has a storage calculation unit built-in, which is used to obtain historical running data, historical output data, and historical control process data sent by the control module, and train the algorithm model according to the historical running data, the historical output data, and the historical control process data; and send the trained algorithm model to the control module.

[0078] Example 2

[0079] The embodiment also provides a staged drying method for polyacrylonitrile, in particular to the following:

[0080] (1) Preparation before drying

[0081] Before the wet material of polyacrylonitrile is transported, the nitrogen making device 10, the circulating fan 9 and the oxygen content detector 11 of the nitrogen closed circulation device are started, the nitrogen supplement amount of the nitrogen making device is controlled to be 150-300 m 3 / h, the air in the device is replaced, when the oxygen content detected by the oxygen content detector 11 is lower than 1%, the nitrogen making device 10 is stopped, and the nitrogen supplement into the nitrogen closed circulation device is stopped; at the same time, the steam heater 1 is started, the temperature of the nitrogen is heated to 90-92℃, and the nitrogen is preheated through the nitrogen circulation and the first-stage paddle dryer 2 and the second-stage flash dryer 4.

[0082] The steam heater 1 comprises a condensate heat exchange module and a steam heat exchange module.

[0083] The condensate heat exchange module preheats the nitrogen by using 75-80℃ steam condensate water, and the working pressure is 0.2-0.3 MPa.

[0084] The steam heat exchange module heats the nitrogen preheated by the condensate heat exchange module by using 165-171℃ water vapor, and the working pressure is 0.6-0.7 MPa.

[0085] (2) First-stage paddle drying

[0086] The wet material (i.e. polyacrylonitrile filter cake) with a water content of 45-55 wt% is transported into the drying cavity of the first-stage paddle dryer 2 through the wet material supply pipeline at a feeding rate of 3000-3300 kg / h, the hot nitrogen with a temperature of 90-92℃ is continuously introduced into the jacket and the hollow shaft 21 of the first-stage paddle dryer 2, the hollow shaft 21 is rotated to drive the hollow paddle 22 to rotate, the paddle rotating speed is controlled to be 4-10 rpm, and the wet material is subjected to the first-stage paddle drying; the residence time of the wet material in the first-stage paddle dryer 2 is controlled to be 20-25 min, the first-stage paddle drying is completed, and the first-stage dried material (with a water content of 25-28 wt%) is obtained.

[0087] During the first-stage paddle drying, the hot nitrogen is sprayed on the wet material in the drying cavity through the blowing holes 23 of the hollow paddle 22 in the hollow shaft 21. At the same time, the opening degree of the self-control adjusting valve 12 located on the air inlet pipeline of the hollow shaft 21 is controlled by the control system, so that the flow rate and time of the hot nitrogen spraying are periodically changed.

[0088] In this embodiment, the hot nitrogen gas is sprayed at high flow rate and low flow rate through the spraying hole 23; specifically, the valve opening degree of the automatic control valve 12 is controlled to be 90-100% for 8-12s, and then the valve opening degree of the automatic control valve 12 is controlled to be 40-50% for 8-12s, and the above steps are repeated to realize pulse spraying of the wet material in the drying cavity.

[0089] Further, for the algorithm model based on machine learning technology constructed in the control module, the following processing is further included: pre-establishing the algorithm model, obtaining real-time data, calculating output data according to the running data by using the algorithm model, so as to adjust the flow rate and frequency of high flow rate spraying and low flow rate spraying according to the output data, thereby reducing the nitrogen consumption and heat consumption while improving the drying effect and drying efficiency, and avoiding the problems of wall sticking, deposition and agglomeration of the material in the primary paddle dryer 2 during the drying process.

[0090] In the obtaining of real-time data, the real-time data at least includes: the temperature of the nitrogen gas entering the primary paddle dryer 2, the flow rate of the nitrogen gas entering the primary paddle dryer 2, the valve opening degree of the high flow rate spraying point, the flow rate of the nitrogen gas in the hollow shaft 21 at the high flow rate spraying point, the valve opening degree of the low flow rate spraying point, the flow rate of the nitrogen gas in the hollow shaft 21 at the low flow rate spraying point, and the absolute dry material weight decay value.

[0091] (3) Secondary flash drying

[0092] The primary dried material is fed into the secondary flash dryer 4 through the screw feeder 3 at a feeding rate of 3000-3300 kg / h; at the same time, the primary dried material in the secondary flash dryer 4 is subjected to secondary flash drying under the condition of hot nitrogen gas circulation, the material residence time is controlled to be 8-12s, and the secondary dried material (moisture content ≤1wt%) is obtained, which is discharged to the cyclone dust collector 5 at a discharge rate of 1600-1800 kg / h under the pushing of the nitrogen gas flow.

[0093] During the secondary drying process, the mechanical stirring paddle arranged at the lower part of the secondary flash dryer 4 is controlled to rotate at a speed of 15-20 rpm, and a vortex rotating air flow is formed by stirring to further crush and dry the primary flash dried material.

[0094] (4) Graded storage

[0095] The secondary dried material is fed into a cyclone separator, and cyclone classification is performed under the action of centrifugal force. During the cyclone classification process, the polyacrylonitrile powder with a large particle size (50 μm and above) (about 95 wt% of the secondary dried material) is separated from the cyclone nitrogen gas flow and captured on the wall, and then collected at the bottom of the cyclone dust collector 5 under the action of gravity, and discharged from the bottom discharge port to the large particle size product storage bin for storage; the polyacrylonitrile powder with a small particle size (about 5 wt% of the secondary dried material) is pushed into the bag dust collector 6 by the cyclone nitrogen gas flow and collected, and discharged to the small particle size product storage bin for storage.

[0096] (5) Nitrogen impurity removal

[0097] During the primary paddle drying and secondary flash drying processes, the circulating fan 9 is used to maintain the continuous circulation of hot nitrogen gas. The nitrogen gas carrying water vapor, volatile medium and a small amount of fine polyacrylonitrile particles enters the bottom of the spray tower 7 from the bottom of the bag dust collector 6 outlet, and the desalted water is used to spray in a countercurrent manner to remove the volatile medium and a small amount of fine polyacrylonitrile particles in the nitrogen gas. After the nitrogen gas enters the demister 8 to remove water vapor, it is again introduced into the steam heater 1 by the circulating fan 9 to be heated to 90-92°C to obtain hot nitrogen gas.

[0098] (6) Continuous drying

[0099] The foregoing steps (2) to (5) are repeated to achieve continuous classification drying of polyacrylonitrile under closed nitrogen circulation.

[0100] Finally, it should be noted that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for the fractional drying of polyacrylonitrile, characterized in that, Comprising the following steps: Step 1, dry preparation, before the polyacrylonitrile wet material delivery, start nitrogen closed cycle device nitrogen device (10), circulating fan (9), oxygen content detector (11), control the nitrogen supplement amount is 150-300 m 3 / h, replace the air in the device, when the oxygen content detected by the oxygen content detector (11) is less than 1%, control the nitrogen device (10) to stop working and stop supplementing nitrogen into the nitrogen closed cycle device; at the same time, start the steam heater (1) to heat the nitrogen temperature to 90-92℃; Preheat the first-stage paddle dryer (2) and the second-stage flash dryer (4) by circulating nitrogen; Step 2, first-stage paddle drying: the polyacrylonitrile wet material with a moisture content of 45-55wt% is transported into the drying chamber of the first-stage paddle dryer (2) through the wet material supply pipeline at a feeding rate of 3000-3300kg / h, hot nitrogen gas with a temperature of 90-92℃ is continuously introduced into the jacket and the hollow shaft (21) of the first-stage paddle dryer (2), the hollow shaft (21) is rotated to drive the hollow paddle (22) to rotate, the paddle rotation speed is controlled at 4-10rpm, and the wet material is subjected to first-stage paddle drying; the residence time of the wet material in the first-stage paddle dryer (2) is controlled at 20-25min, the first-stage paddle drying is completed, and first-stage dried material with a moisture content of 25-28wt% is obtained; The hollow shaft (21) is provided with a plurality of hollow paddles (22), and the hollow paddles (22) are uniformly provided with through blowing holes (23); the cavity of the hollow shaft (21) is in communication with the cavities of the hollow paddles (22), hot nitrogen gas flows in the hollow shaft (21) and the hollow paddles (22), and is blown into the drying chamber through the blowing holes (23); a self-control adjusting valve (12) is arranged on the gas inlet pipeline of the hollow shaft (21), and a control module is electrically connected with the self-control adjusting valve (12); the control module can control the opening degree of the self-control adjusting valve (12), so as to adjust the blowing flow and time of hot nitrogen gas at the blowing holes (23); In the first-stage paddle drying, the hot nitrogen gas is blown at high flow and low flow at the blowing holes (23); at the high-flow blowing point, the valve opening degree of the self-control adjusting valve (12) is controlled at 85-90%; at the low-flow blowing point, the valve opening degree of the self-control adjusting valve (12) is controlled at 45-50%; the staggered time of high-flow blowing and low-flow blowing is 8-12s; The first solid moisture on-line detector, the first automatic cumulative weighing instrument, the second solid moisture on-line detector and the second automatic cumulative weighing instrument are sequentially arranged on the wet material supply pipeline at the front end of the primary paddle dryer (2); the first solid moisture on-line detector is used for detecting the moisture content of the wet material before entering the primary paddle dryer (2) and transmitting the detection data to the control module; the first automatic cumulative weighing instrument is used for automatically weighing and cumulatively detecting the total weight of the wet material entering the primary paddle dryer and transmitting the detection data to the control module; the second solid moisture on-line detector is used for detecting the moisture content of the primary dried material and transmitting the detection data to the control module; the second automatic cumulative weighing instrument is used for automatically weighing and cumulatively detecting the total weight of the primary dried material and transmitting the detection data to the control module; the control module receives the detection data, calculates the absolute dry material weight of the wet material before entering the primary paddle dryer (2) and the absolute dry material weight of the primary dried material, and calculates the absolute dry material weight attenuation value; if the absolute dry material weight attenuation value is less than 2wt%, the high-flow injection point, the low-flow injection point and the staggered time are kept unchanged; if the absolute dry material weight attenuation value is greater than or equal to 2wt%, the valve opening degree of the high-flow injection point is increased by 4-5%, the valve opening degree of the low-flow injection point is reduced by 4-5%, and the staggered time of the high-flow injection point and the low-flow injection point is shortened by 2-4s; the calculation method of the absolute dry material weight attenuation value is: [(wet material absolute dry material weight-primary dried material absolute dry material weight) / wet material absolute dry material weight]×100%; Step 3, secondary flash drying, the primary dried material is fed into the secondary flash dryer (4) at a feeding rate of 3000-3300kg / h through the screw feeder (3); at the same time, the primary dried material in the secondary flash dryer (4) is subjected to secondary flash drying under the condition of hot nitrogen circulation, the material residence time is controlled to be 8-12s, and the secondary dried material with a moisture content of less than or equal to 1wt% is obtained; the secondary dried material is discharged into the cyclone dust collector (5) at a discharge rate of 1600-1800kg / h under the pushing of the nitrogen gas flow; Step 4, graded storage, the secondary dried material is subjected to graded storage; Step 5, nitrogen impurity removal, during the primary paddle drying and the secondary flash drying, the circulating fan (9) is used to keep the continuous circulation of the hot nitrogen gas; the nitrogen gas carrying the easily volatile medium and the fine polyacrylonitrile particles enters into the leaching tower (7) through the bag dust collector (6); after being removed by the desalted water countercurrent spraying, the nitrogen gas enters into the demister (8) to remove water, and then enters into the steam heater (1) again through the circulating fan (9) to be heated to 90-92℃, so as to obtain the hot nitrogen gas; Step 6, continuous drying, steps 2 to 5 are repeated to realize the continuous graded drying of the polyacrylonitrile under the closed circulation of the nitrogen gas.

2. The fractional drying process for polyacrylonitrile according to claim 1, characterized in that, The secondary dried material is subjected to cyclone grading, and the polyacrylonitrile powder with a particle size of more than or equal to 50μm is collected and stored; The polyacrylonitrile powder with particle size less than 50 μm is collected by a bag dust collector (6) after cyclone separation and stored.

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