Drying method and system for EVOH resin

Abstract

The invention provides a drying method for EVOH resin and a matched drying system, which are used for drying EVOH resin particles in an alcoholysis process, a two-stage drying system is adopted, first-stage drying is performed firstly, an initial drying stage and a constant-speed drying stage are completed in sequence by adopting a double-shaft vacuum paddle dryer, and the drying process is completed by adopting a double-shaft vacuum paddle dryer. The moisture content of EVOH resin particles subjected to first-stage drying is 10-20%, then second-stage drying is carried out, and a drying tower is adopted to complete the deceleration drying stage. Volatile components in the EVOH resin particles can be more thoroughly removed, the purity of the EVOH resin particles is improved, the drying rate is increased, and the drying time is shortened.

Description

Technical Field

[0001] The invention relates to the technical field of EVOH resin production, and more specifically to a drying method and system for EVOH resin. Background Art

[0002] EVOH (ethylene-vinyl alcohol copolymer) is a crystalline polymer with a chain molecular structure. It is obtained by the polymerization reaction of ethylene and vinyl acetate to obtain EVA (ethylene-vinyl acetate copolymer), and then by alcoholysis of EVA.

[0003] The production process of EVOH may contain some impurities, such as unreacted raw materials, oligomers, water, alcohol, aldehyde and acid. Since EVOH itself has good gas barrier properties and close molecular arrangement, when the temperature rises too quickly during high-temperature processing, these impurities can easily form a layer of crystals on the surface of EVOH particles, wrapping the particles, making it impossible to remove the volatile components inside the particles, affecting product performance. During high-temperature melting treatment, hydroxyl dehydration is likely to occur, and conjugated double bonds are generated in the molecular structure, causing the product to turn yellow and affecting the thermal stability of the EVOH material. This places high demands on the drying system in the EVOH production process.

[0004] The function of the EVOH production drying system is to remove the volatile components in the EVOH resin particles to ensure the stability of subsequent processing and the quality of the product. The common drying technologies are as follows:

[0005] Hot air flow drying is a method of drying granular solid materials by dispersing and suspending them in a high-speed hot air flow under pneumatic conveying. Its advantages are simple operation and fast drying speed, but its disadvantages are high power consumption, excessive ventilation volume, high energy consumption, easy particle wear, and large equipment size.

[0006] Vacuum paddle drying uses high-speed rotating paddles to bring the material to be dried into contact with a heat medium, evaporating its moisture and discharging it from the equipment. At the same time, the dried material will quickly lose moisture under a vacuum state, thereby achieving the purpose of drying. The disadvantage is that dead corners are easily formed locally during the drying process, causing the EVOH resin to aggregate and not flow for a long time, and it is always in a dried state, resulting in yellowing.

[0007] Patent CN114427786A discloses an ethylene-vinyl alcohol copolymer drying device, including a drying box, an air jet, a curved slide, etc., which can effectively solve the problem of EVOH movement difficulties leading to channel blockage. The drying process is mainly divided into an initial stage, a constant speed drying stage, and a deceleration drying stage. The initial stage is a heating stage, the purpose of which is to heat the object to the starting temperature of water evaporation, usually called the critical temperature. At this stage, heat needs to be transferred to the object, usually through hot air or other heat transfer media in contact with the surface of the object to evaporate the moisture in the object. When the moisture content in the object is reduced to a certain level, it enters a constant speed drying stage, and all the heat transferred by the air to the material is used to evaporate the moisture. The heat transfer between the air and the material is equal to the vaporization rate of the moisture on the surface of the material, so the temperature of the surface of the material remains constant. When the drying process enters the deceleration drying stage, the main function is to control the color development period and the shrinkage setting period. The main restrictive factors at this stage are the control of temperature and humidity.

[0008] As mentioned above, the current drying process has the problems of slow drying speed and low drying efficiency, poor treatment effect on heat-sensitive materials, excessive energy consumption, and improper temperature control during the drying process will also cause yellowing of EVOH products. Summary of the invention

[0009] In order to solve the above technical problems, the present invention proposes a drying method for EVOH resin, and proposes a drying system for EVOH resin for implementing the method, which is used for drying EVOH resin particles in the alcoholysis process, can more thoroughly remove the volatile components inside the EVOH resin particles, improve the purity of the EVOH resin particles, increase the drying rate and shorten the drying time.

[0010] To achieve the above object, the present invention adopts the following technical solution:

[0011] A drying method for EVOH resin, used for drying EVOH resin particles in an alcoholysis process, adopting a two-stage drying system, firstly performing a first-stage drying, using a double-shaft vacuum paddle dryer to sequentially complete an initial drying stage and a constant-speed drying stage, and then performing a second-stage drying, using a drying tower to complete a deceleration drying stage;

[0012] First-stage drying: before the formal feeding, the temperature of the double-shaft vacuum paddle dryer is raised and maintained at 60-80°C. This process takes at least 16-48 hours. The wet EVOH resin particles conveyed by pneumatic conveying are received by the first-stage bag filter. After gas-solid separation, the wet EVOH resin particles are output to the first-stage buffer tank for buffering, and then sent to the double-shaft vacuum paddle dryer through the first-stage feeding screw conveyor. Under the stirring of the two paddle shafts, the surface of the wet EVOH resin particles is constantly in contact with the hollow paddle wall, the outer peripheral wall of the two hollow shafts, and the jacket wall. The volatile components inside the EVOH resin particles are heated and evaporated by conduction heating. The initial drying stage and the constant speed drying stage are successively experienced to heat and evaporate the volatile components until the moisture content of the EVOH resin particles is 10-20%. The first-stage drying is completed. The EVOH resin particles are transported in a spiral trajectory toward the discharge port of the double-shaft vacuum paddle dryer as the two paddle shafts rotate, and are discharged from the discharge port into the first-stage discharge screw conveyor.

[0013] In the second-stage drying, the deceleration drying stage uses a second-stage bag filter to receive the EVOH resin particles output from the first-stage discharge screw conveyor and pneumatically conveyed. After gas-solid separation, the EVOH resin particles are output to the second-stage buffer tank for buffering, and then sent to the drying tower through the second-stage feeding screw conveyor. The drying tower adopts hot air drying, feeding from the top and discharging from the bottom. The feed port and the discharge port are connected by a drying slideway that spirals downward along the vertical spiral. The EVOH resin particles entering the drying tower fall on the drying slideway and spiral down along the drying slideway, dividing the space in the tower vertically into at least three sections, and a 110-130℃ heated airflow is introduced horizontally into each section, and part of the heated airflow is discharged horizontally along the direction of introduction. The introduction directions of the adjacent two sections of heated airflow are opposite, and the heated airflow circulates from bottom to top through the hot air system outside the tower section by section, and the heated airflow continuously exchanges heat with the EVOH resin particles to make the volatiles inside the EVOH resin particles The volatile components are further evaporated by heat, and the EVOH resin particles stay in the drying tower for 8-10 hours to complete the second-stage drying. After being discharged from the discharge port, they are pneumatically conveyed to the EVOH silo. During the first-stage drying, the moisture content of the EVOH resin particles is high and they are in a constant-speed drying state, that is, the moisture reduction rate is approximately a fixed value. During the second-stage drying, they are in a deceleration drying state, and the moisture content of the EVOH resin particles is already very low. The moisture reduction rate will gradually decrease instead of the previous fixed value. The moisture inside the EVOH resin particles will diffuse along the micropores, and the micropores of the wet resin will gradually disappear as they dry. During the deceleration drying stage, the EVOH resin particles on the drying slide exchange heat with the heated airflow blown up from the bottom of the drying slide, and the volatile components such as methanol and water inside the particles are evaporated, and part of the heated airflow is extracted by the induced draft fan. The purpose of extracting part of the heated airflow for reheating is to maintain the drying temperature in the tower and to compensate for the heat absorbed by the gasification of the volatile components in the EVOH resin particles.

[0014] In the first stage drying process, hot air drying is used as an auxiliary. On the discharge side, heated gas with a temperature of 110-130°C is sprayed from the bottom of the EVOH resin particles into the biaxial vacuum paddle dryer. The spraying interval is 0.1-0.3s and the spraying flow rate is 8000-12000Nm 3 / h, the heated gas keeps circulating and contacts with the surface of the EVOH resin particles stirred by the two blade shafts, which is used to accelerate the drying of the EVOH resin particles; and nitrogen is sprayed into the drying dead corners in the double-axis vacuum blade dryer, with a spray temperature of 80-100°C, a spray interval of 0.1-0.3s, and a spray flow rate of 8000-12000Nm 3 / h to eliminate drying dead corners; the injection interval and injection flow rate of heating gas and nitrogen are controlled by matching solenoid valves respectively.

[0015] Features of this drying method for EVOH resin also include:

[0016] In order to prevent the micropores of EVOH resin particles from being closed prematurely due to high temperature drying, so that they cannot be further dried, the steam entering the double-shaft vacuum paddle dryer must be at a low temperature. The steam pressure entering the two paddle shafts and the jacket of the double-shaft vacuum paddle dryer is 1.0-2.0kgf / cm 2 (G), the temperature is 110-130℃, and it is cooled by the desuperheater before entering. The cooling water of the desuperheater is provided by the desuperheater pump, which comes from the condensate collection tank. The steam entering the two blade shafts enters through the rotary joint connected to the blade shaft, and the steam condensate is also discharged from the rotary joint and enters the hot shaft condensate tank. The gas phase of the hot shaft condensate pipe is connected to the steam inlet entering the blade shaft to ensure pressure balance.

[0017] The jacket of the double-shaft vacuum paddle dryer is divided into three sections along the paddle shaft from the feed side to the discharge side, which are composed of the front section jacket, the middle section jacket, and the rear section jacket. The temperatures of the three sections are 80±2℃, 95±2℃, and 110±2℃ respectively. The condensed water generated after the steam heat exchange in each section of the jacket enters the jacket condensation tank, and the gas phase of the jacket condensation tank is connected to the steam inlet of the jacket to ensure pressure balance.

[0018] The front section jacket, the middle section jacket, and the rear section jacket are all honeycomb structures. The three section jackets are independent of each other, and the rigidity of the equipment is enhanced by using the honeycomb structure jacket. The upper cover of the double-axis vacuum paddle dryer is insulated with steam accompanying pipes to avoid condensation.

[0019] The space inside the drying tower is divided into 4-8 sections vertically. The hot air system outside the tower equipped with each section can discharge the heated air inside the tower horizontally by using an induced draft fan, and the heated air flow to be introduced into the tower is heated to 110-130° C. by using a heated air flow preheater.

[0020] The discharge rate of the drying tower is 600-900 kg / h.

[0021] The volatile components inside the EVOH resin particles include methanol and water, which evaporate as they dry and are heated.

[0022] The present invention also proposes a drying system for EVOH resin, which is used to implement the above-mentioned drying method for EVOH resin, including a first-stage drying system and a second-stage drying system;

[0023] The first-stage drying system includes a first-stage bag filter, a first-stage buffer tank, a first-stage feeding screw conveyor, a double-axis vacuum paddle dryer, and a first-stage discharging screw conveyor connected in sequence along the conveying direction of the EVOH resin particles; the first-stage bag filter performs gas-solid separation on the fed EVOH resin particle wet material, and the separated EVOH resin particle wet material falls into the first-stage buffer tank below through the solid outlet, the first-stage buffer tank is fed from the top of the tank and discharged from the bottom of the tank, and the EVOH resin particle wet material is input into the first-stage feeding screw conveyor through the discharge pipeline at the bottom of the tank, and is fed to the double-axis vacuum paddle dryer through the first-stage feeding screw conveyor; the double-axis vacuum paddle dryer is conductive and horizontal, with top feeding and bottom discharging, and the inlet and outlet are along the axis of the paddle shaft. On both sides of the distribution, at each drying dead corner, a blowing head with a blowing direction toward the drying dead corner is arranged, each blowing head is connected to an external nitrogen gas circuit, and gas is supplied by an external nitrogen gas source through the external nitrogen gas circuit; the double-axis vacuum paddle dryer is also provided with a hot air drying system, the hot air drying system is provided with a heating gas circulation pipeline, a heating gas preheater, and a vacuum pump, which is pumped by a vacuum pump and heated by a heating gas preheater, and the heated heating gas is sent into the dryer from the discharge port through the heating gas circulation pipeline, and after heat exchange with the EVOH resin particle wet material, it flows back to the heating gas preheater and circulates; the EVOH resin particles dried by the double-axis vacuum paddle dryer are fed to the second-stage bag filter of the second-stage drying system through a first-stage discharge screw conveyor;

[0024] The second-stage drying system includes a second-stage bag filter, a second-stage buffer tank, a second-stage feeding screw conveyor, and a drying tower which are connected in sequence along the conveying direction of the EVOH resin particles; the discharge of the first-stage discharging screw conveyor is pneumatically conveyed into the second-stage bag filter for gas-solid separation, and the separated EVOH resin particles fall into the second-stage buffer tank below through the solid outlet, and the second-stage buffer tank is discharged from the bottom of the feeding tank at the top of the tank, and the EVOH resin particles are input into the second-stage feeding screw conveyor through the discharge pipeline at the bottom of the tank, and are fed into the drying tower through the second-stage feeding screw conveyor. The fed EVOH resin particles fall evenly onto the drying slide in the tower through the distributor in the drying tower, and the drying tower is fed from the top of the tower and discharged from the bottom. The drying slide spirals downward along the vertical direction and is connected between the inlet and outlet ports. The space in the tower is vertically divided into at least three sections, and each section is equipped with a set of hot air outside the tower. The system is characterized in that the external hot air system heats the gas through a heated air flow preheater, and a heated air flow of 110-130°C is introduced into the tower in the section area in a horizontal direction, and the heated air flow can be extracted by an induced draft fan in a horizontal direction along the direction of the introduction, and the external hot air systems of each section of the tower are sequentially connected from bottom to top, and the heated air flow extracted by the induced draft fan of the lower section is sent to the heated air flow preheater of the external hot air system of the upper section of the tower, and circulates in sequence, and is introduced into the condenser through the heated air flow preheater of the external hot air system of the upper section of the tower, and heat is exchanged with the refrigerant circulating water, so that most of the water and methanol gas are condensed, and part of the non-condensable tail gas enters the heated air flow preheater after being treated, and enters the drying tower again after being heated to 110-130°C to exchange heat with the EVOH resin particles; the bottom discharge port of the drying tower is connected to the air delivery pipeline, and the dried EVOH resin particles are output to the EVOH silo.

[0025] Each inlet and outlet is equipped with a valve with adjustable opening, which is used for opening and closing the inlet and outlet and for adjusting the inlet and outlet speed, either manually or electrically, and is configured according to process requirements.

[0026] The distributor can be a tension distributor, a speed differential distributor or an electronically controlled distributor.

[0027] The external nitrogen gas circuit is formed with multiple nitrogen branches, which are connected to each spray head one by one through multiple nitrogen branches. The spray head can be configured in the area where the particles are not easy to flow in the dryer, and the drying dead corners can be eliminated by fluidization to ensure the quality of EVOH resin particles. Before the double-axis vacuum paddle dryer is officially put into drying, nitrogen replacement is also required until the oxygen content in the drying environment is qualified. The purpose of nitrogen replacement is to prevent accidents caused by equipment friction and ignition.

[0028] In the first-stage drying system, the heating gas is compressed air or nitrogen from which moisture has been removed, and the heating gas preheater is heated by direct steam; in the second-stage drying system, the heating gas flow is compressed air from which moisture has been removed and part of the supplementary nitrogen.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] The present invention comprises two-stage drying steps, wherein a first-stage drying system including a double-axis vacuum paddle dryer is used to sequentially complete an initial drying stage and a constant-speed drying stage by using a paddle-type vacuum suspension drying technology, and a second-stage drying system including a drying tower is used to complete a deceleration drying stage by using a filling tower drying method, thereby significantly improving the drying rate of EVOH resin particles and shortening the drying time, solving the prior art problem that EVOH resin particles are difficult to move and are prone to clogging pipelines, and through two-stage drying, volatile components in EVOH resin particles are removed more thoroughly, thereby improving the purity of EVOH resin particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a process flow chart of the first-stage drying system in the present invention;

[0032] Figure 2 It is a process flow chart of the second-stage drying system in the present invention.

[0033] In the figure:

[0034] 11 first-stage bag filter; 12 first-stage buffer tank; 13 first-stage feeding screw conveyor; 14 double-shaft vacuum paddle dryer; 15 first-stage discharging screw conveyor; 16 external nitrogen gas circuit; 17 heating gas circulation pipeline; 18 heating gas preheater; 19 jacketed condensate tank; 110 hot shaft condensate tank;

[0035] 21 second-stage bag filter; 22 second-stage buffer tank; 23 second-stage feeding screw conveyor; 24 drying tower; 241 drying slide; 25 first-stage induced draft fan; 26 first-stage heating air flow preheater; 27 second-stage induced draft fan; 28 second-stage heating air flow preheater; 29 third-stage induced draft fan; 210 third-stage heating air flow preheater; 211 fourth-stage induced draft fan; 212 fourth-stage heating air flow preheater; 213 condenser. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Example 1

[0038] Figure 1 A first-order drying system is shown.

[0039] Before the material is officially added, the double-shaft vacuum paddle dryer 14 needs to be slowly heated to 60-80°C and then kept warm. This process takes at least 16 hours.

[0040] The wet EVOH resin particles are separated from the solid by the first-stage bag filter 11, and fall into the first-stage buffer tank 12 from the solid outlet. The material falling speed is controlled by the manual valve at the solid outlet, and then enter the double-axis vacuum paddle dryer 14 through the discharge screw of the first-stage buffer tank 12. Several nitrogen branches are arranged on the outside of the dryer to supply nitrogen to the blowing heads of the dead corners in the dryer. After the wet EVOH resin particles enter the dryer, they are stirred by the two paddle shafts and continuously obtain heat from the hollow paddle wall, the outer peripheral walls of the two hollow shafts, and the jacket wall, so that the volatile substances such as methanol and water inside are evaporated by heat. After completing the first-stage drying, the moisture content of the EVOH resin particles discharged from the double-axis vacuum paddle dryer 14 is 16%.

[0041] The steam pressure entering the double-shaft vacuum paddle dryer 14 is 1.5 kgf / cm 2 (G), temperature is 120℃.

[0042] On the discharge side, heating gas with a temperature of 120°C is sprayed from the bottom of the EVOH resin pellets into the biaxial vacuum paddle dryer 14, and the spraying interval and flow rate are controlled by a solenoid valve, and accelerated drying is achieved by auxiliary hot air drying. The heating gas is pumped by a vacuum pump, including reflux gas and supplementary nitrogen, and the reflux gas is compressed air to remove moisture.

[0043] The EVOH resin particles that have completed the first-stage drying are further transported to the second-stage drying system.

[0044] Figure 2 A second-stage drying system is shown.

[0045] The EVOH resin particles from the first-stage drying system are blown into the second-stage bag filter 21 for gas-solid separation, fall into the second-stage buffer tank 22 through the solid outlet, and are then sent to the drying tower 24 through the second-stage feeding screw conveyor 23.

[0046] After entering the drying tower 24, the EVOH resin particles are evenly distributed on the drying slide 241 through the distributor inside the tower.

[0047] The EVOH resin particles on the drying slide 241 exchange heat with the heated air flow blown up from the bottom of the tower, so that volatile components such as methanol and water inside the particles are evaporated. The heated air flow is drawn out by the lowest induced draft fan and enters the adjacent upper condenser 213 to exchange heat with the refrigerant circulating water. Most of the water and methanol gases are condensed, and part of the non-condensable exhaust gas enters the lowest heated air flow preheater after treatment, and enters the drying tower 24 again after being heated to 110°C.

[0048] At the height of the Nth tower plate counting upward from the bottom of the drying tower 24, part of the heated air flow is drawn out from the tower side through the first-stage induced draft fan 25, and enters the second-stage heated air flow preheater 28. The drawn heated air flow is heated to 110°C by steam, and then enters the drying tower 24, where it is blown upward from the bottom of the drying chute 241 to exchange heat with the EVOH resin particles.

[0049] The drying tower 24 is equipped with a total of 4 sections of external hot air systems to complete the sequential circulation of the heated air flow, namely, a first-stage induced draft fan 25 and a first-stage heated air flow preheater 26, a second-stage induced draft fan 27 and a second-stage heated air flow preheater 28, a third-stage induced draft fan 29 and a third-stage heated air flow preheater 210, and a fourth-stage induced draft fan 211 and a fourth-stage heated air flow preheater 212.

[0050] The drying tower 24 discharges materials from the bottom of the tower, and the discharge rate is controlled at 700kg / h, and is blown into the EVOH silo by air.

[0051] Example 2

[0052] The drying system for EVOH resin of Example 1 is used to treat EVOH resin particles, specifically:

[0053] 100 g of EVOH resin particles containing 50% volatile components were weighed and subjected to primary drying and secondary drying in sequence.

[0054] The EVOH resin particles treated in Example 2 were weighed, and the volatile component removal rate was calculated according to the formula [(m1-m2) / m3]×100%, where m1 is the mass before treatment, in g, m2 is the mass after treatment, in g, and m3 is the mass of volatile components in the original particles, which is 50 g. The results are shown in Table 1.

[0055] Embodiment 3-6

[0056] Except that the number of induced draft fans and heated air flow preheaters is different from that in Example 2 (as shown in Table 1), other parameters and steps of Examples 3-6 are the same as those in Example 2.

[0057] The EVOH resin particles treated in Examples 3-6 were weighed, and the volatile component removal rate was calculated according to the formula [(m1-m2) / m3]×100%, where m1 is the mass before treatment, in g, m2 is the mass after treatment, in g, and m3 is the mass of volatile components in the original particles, which is 50 g. The results are shown in Table 1.

[0058] Table 1:

[0059]

[0060] As can be seen from Table 1, the removal rate of volatile components in EVOH resin particles in Examples 2-6 reaches 55.0%-97.6%, and the more the number of hot air systems outside the tower in the second-stage drying tower 24 is, the higher the removal rate is. It can be seen that the drying method and system for EVOH resin in the embodiment of the present invention can effectively remove volatile components in EVOH resin particles, help reduce the yellowing rate of the resin, and improve the drying efficiency in production.

[0061] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A drying method for EVOH resin, characterized in that: The EVOH resin particles are dried in the alcoholysis process using a two-stage drying system, firstly performing a first-stage drying process using a double-shaft vacuum paddle dryer (14) to sequentially complete an initial drying stage and a constant-speed drying stage, and then performing a second-stage drying process using a drying tower (24) to complete a deceleration drying stage; First-stage drying: before the material is formally added, the temperature of the double-shaft vacuum paddle dryer (14) is raised and maintained at 60-80°C. This process takes at least 16-48 hours. The wet EVOH resin particles conveyed by pneumatic conveying are received by the first-stage bag filter (11). After gas-solid separation, the wet EVOH resin particles are output to the first-stage buffer tank (12) for buffering, and then sent to the double-shaft vacuum paddle dryer (14) through the first-stage feeding screw conveyor (13). Under the stirring of the two paddle shafts, the surface of the wet EVOH resin particles is contacted with the air. The wall surface of the core blade, the outer peripheral walls of the two hollow shafts, and the wall surface of the jacket are in continuous contact, and the volatile components inside the EVOH resin particles are evaporated by heat through conduction heating, and the initial drying stage and the constant speed drying stage are sequentially experienced, so that the volatile components are evaporated by heat until the moisture content of the EVOH resin particles reaches 10-20%, completing the first-stage drying. The EVOH resin particles are conveyed in a spiral trajectory toward the discharge port of the double-axis vacuum blade dryer (14) along with the rotation of the two blade shafts, and are discharged from the discharge port into the first-stage discharge screw conveyor (15); In the second-stage drying, the deceleration drying stage uses a second-stage bag filter (21) to receive the EVOH resin particles output from the first-stage discharge screw conveyor (15) and pneumatically conveyed, and after gas-solid separation, the EVOH resin particles are output to the second-stage buffer tank (22) for buffering, and then sent to the drying tower (24) through the second-stage feeding screw conveyor (23). The drying tower (24) adopts hot air drying, feeds from the top and discharges from the bottom. The feed port and the discharge port are connected by a drying slide (241) running downward along the vertical spiral. The EVOH resin particles entering the drying tower (24) fall onto the drying slide (241) and are dried along the drying tower (24). The drying slide (241) spirals down and down, and the space inside the tower is divided into at least three sections vertically. A 110-130° C. heated airflow is introduced into each section horizontally, and part of the heated airflow is discharged horizontally along the direction of introduction. The introduction directions of the heated airflows in two adjacent sections are opposite. The heated airflow circulates from bottom to top through the hot air system outside the tower, and the heated airflow continuously exchanges heat with the EVOH resin particles, so that the volatile components inside the EVOH resin particles are further evaporated by heat. The EVOH resin particles stay in the drying tower (24) for 8-10 hours to complete the second stage drying. After being discharged from the discharge port, they are pneumatically conveyed to the EVOH silo. In the first-stage drying process, hot air drying is used as an auxiliary. On the discharge side, heated gas at a temperature of 110-130° C. is blown from below the EVOH resin particles into a biaxial vacuum paddle dryer (14) at a blowing interval of 0.1-0.3 s and a blowing flow rate of 8000-12000 Nm 3 / h, the heated gas is kept circulating and in contact with the surface of the EVOH resin particles stirred by the two blade shafts, so as to accelerate the drying of the EVOH resin particles; and nitrogen is sprayed into the drying dead corners in the double-axis vacuum blade dryer (14), with the spraying temperature being 80-100°C, the spraying interval being 0.1-0.3s, and the spraying flow rate being 8000-12000Nm 3 / h to eliminate drying dead corners.

2. The drying method for EVOH resin according to claim 1, characterized in that: The steam pressure in the two blade shafts and the jacket of the double-shaft vacuum paddle dryer (14) is 1.0-2.0 kgf / cm 2 (G), the temperature is 110-130℃, and it is cooled by a temperature reducer before entering.

3. The drying method for EVOH resin according to claim 1 or 2, characterized in that: The jacket of the double-shaft vacuum paddle dryer (14) is divided into three sections along the axial direction of the paddle shaft from the feeding side to the discharging side, and is composed of a front section jacket, a middle section jacket, and a rear section jacket, and the temperatures of the three sections are 80±2°C, 95±2°C, and 110±2°C, respectively.

4. The drying method for EVOH resin according to claim 3, characterized in that: The front section jacket, the middle section jacket and the rear section jacket are all honeycomb structures.

5. The drying method for EVOH resin according to claim 1, characterized in that: The space inside the drying tower (24) is divided into 4-8 sections vertically. The hot air system outside the tower matched with each section can discharge the heated air inside the tower horizontally by using an induced draft fan, and the heated air preheater is used to heat the heated air to be introduced into the tower to 110-130°C.

6. The drying method for EVOH resin according to claim 1, characterized in that: The discharge rate of the drying tower (24) is 600-900 kg / h.

7. The drying method for EVOH resin according to claim 1, characterized in that: The volatile components inside the EVOH resin particles include methanol and water.

8. A drying system for EVOH resin, characterized in that: A drying method for EVOH resin for implementing any one of claims 1 to 7, comprising a first-stage drying system and a second-stage drying system; The first-stage drying system includes a first-stage bag filter (11), a first-stage buffer tank (12), a first-stage feeding screw conveyor (13), a double-axis vacuum paddle dryer (14), and a first-stage discharging screw conveyor (15) which are connected in sequence along the conveying direction of the EVOH resin particles; the first-stage bag filter (11) performs gas-solid separation on the EVOH resin particle wet material fed in, and the separated EVOH resin particle wet material falls into the first-stage buffer tank (12) below through the solid outlet; the first-stage buffer tank (12) feeds from the top of the tank and discharges from the bottom of the tank; the EVOH resin particle wet material is input into the first-stage feeding screw conveyor (13) through the discharge pipeline at the bottom of the tank, and is fed into the double-axis vacuum paddle dryer (14) through the first-stage feeding screw conveyor (13); the double-axis vacuum paddle dryer (14) is conductive and horizontal, with top feeding and bottom discharging, and the inlet and outlet are arranged along the paddle shaft. The axial direction is divided into two sides, and a blowing head with a blowing direction toward the drying dead corner is arranged at each drying dead corner, and each blowing head is connected to an external nitrogen gas path (16), and gas is supplied by an external nitrogen gas source through the external nitrogen gas path (16); the double-axis vacuum paddle dryer (14) is also provided with a hot air drying system, and the hot air drying system is provided with a heating gas circulation pipeline (17), a heating gas preheater (18), and a vacuum pump. The heating gas is pumped by the vacuum pump and heated by the heating gas preheater (18). The heated heating gas is sent into the dryer from the discharge port through the heating gas circulation pipeline (17), and after heat exchange with the EVOH resin particle wet material, it flows back to the heating gas preheater (18) and circulates; the EVOH resin particles dried by the double-axis vacuum paddle dryer (14) are fed to the second-stage bag filter (21) of the second-stage drying system through the first-stage discharge screw conveyor (15); The second-stage drying system includes a second-stage bag filter (21), a second-stage buffer tank (22), a second-stage feeding screw conveyor (23), and a drying tower (24) which are connected in sequence along the conveying direction of the EVOH resin particles; the discharge of the first-stage discharge screw conveyor (15) is pneumatically conveyed into the second-stage bag filter (21) for gas-solid separation, and the separated EVOH resin particles fall into the second-stage buffer tank (22) below through the solid outlet; the second-stage buffer tank (22) is discharged from the bottom of the feeding tank through the top of the tank, and the EVOH resin particles are input into the second-stage feeding screw conveyor (23) through the discharge pipeline at the bottom of the tank, and the second-stage feeding screw conveyor (23) is used to feed the drying tower (24), and the fed EVOH resin particles are evenly dropped through the distributor in the drying tower (24). To the drying slide (241) in the tower, the drying tower (24) is fed at the top and discharged at the bottom, the drying slide (241) spirals downward vertically and is connected between the inlet and outlet, the space in the tower is vertically divided into at least three sections, each section is equipped with a set of external hot air system, the external hot air system heats the gas through a heated air flow preheater, and a 110-130°C heated air flow is introduced into the tower in the section area in the horizontal direction, and the heated air flow can be extracted horizontally through an induced draft fan along the direction of introduction, the external hot air systems of each section are connected in sequence from bottom to top, and the heated air flow extracted by the induced draft fan of the lower section is sent to the heated air flow preheater of the external hot air system of the upper section, and the bottom outlet of the drying tower (24) is connected to an air delivery pipeline to output the dried EVOH resin particles to the EVOH silo. Each inlet and outlet is equipped with a valve with adjustable opening, which is used for opening and closing the inlet and outlet and for adjusting the inlet and outlet speed.

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