CN221147123U

CN221147123U - Crystallization drying device and system for PLA (polylactic acid) slices

Info

Publication number: CN221147123U
Application number: CN202322536442.5U
Authority: CN
Inventors: 韩国政; 孙伟光; 张全生
Original assignee: Zhengzhou Zhongyuan Drying Engineering Co ltd
Current assignee: Zhengzhou Zhongyuan Drying Engineering Co ltd
Priority date: 2023-09-15
Filing date: 2023-09-15
Publication date: 2024-06-14
Anticipated expiration: 2033-09-15

Abstract

The utility model belongs to the field of crystallization and drying of low-melting-point PLA slices, and particularly relates to a crystallization and drying device and system for PLA slices. The novel cooling and cooling device comprises a double-air-duct crystallization bed and a drying tower which are sequentially communicated through a material pipeline, wherein a cooling fluidized bed is arranged between the double-air-duct crystallization bed and the drying tower, and PLA slices after preliminary crystallization in a pre-crystallization tank and crystallization in the double-air-duct crystallization bed are subjected to cooling treatment, and the PLA slices are cooled to below the glass transition temperature, so that the PLA slices entering the drying tower are prevented from deforming and adhering.

Description

Crystallization drying device and system for PLA (polylactic acid) slices

Technical Field

The utility model belongs to the field of crystallization and drying of low-melting-point PLA slices, and particularly relates to a crystallization and drying device and system for PLA slices.

Background

The polymerized PLA melt is cut into particles similar to ellipsoids in an underwater rotary-cut granulator, and the PLA particles are a semi-finished product with high temperature (about 70 ℃ to 80 ℃) which can be packaged and used after a crystallization drying process.

Disclosure of utility model

The utility model aims to solve the problems in the prior art and provide a crystallization drying device and system for PLA slices.

The technical scheme of the utility model is as follows:

The utility model provides a PLA sliced crystallization drying device, includes crystallization bed, the drying tower that communicates in proper order through the material pipeline, two crystallization beds with the material pipeline between the drying tower still is provided with the cooling fluidized bed.

Because of the low glass transition temperature (60-65 ℃) of PLA, the temperature of the PLA slice after preliminary crystallization in a pre-crystallization tank and crystallization in a double-air-duct crystallization bed is far higher than the glass transition temperature of the PLA slice, and the PLA slice at the moment is in an amorphous state like soft sweets, is easy to deform and adhere to the scene due to self gravity and mutual extrusion, and seriously forms a large block shape, so that the crystallized PLA slice is required to be subjected to cooling treatment, and the PLA slice is cooled to be below the glass transition temperature through the cooling fluidized bed and the cooling circulation system to harden, so that the PLA slice entering the drying tower is ensured not to deform and adhere.

Here, since PLA chips are crystalline polymer materials, the heat distortion temperature of the material is mainly affected by the crystallization region, and when the crystallinity is within a certain range, the heat distortion temperature of the material is close to the melting temperature, and the melting temperature of PLA chips is about 170 ℃, i.e., the PLA chips after crystallization are heated again to about 170 ℃, the adhesion phenomenon occurs. In the crystallization bed, initial PLA slices are heated and crystallized at 90-100 ℃ to gradually increase the crystallinity, the crystallization bed has higher crystallinity, then the temperature is quickly reduced to not more than 40 ℃ by a cooling fluidized bed to quickly harden the surface of the crystallized PLA slices, and crystallization is stopped, so that when the cooled PLA slices enter a drying tower again, the PLA slices are accumulated or heated at 70-80 ℃ to be difficult to generate adhesion and agglomerate, wherein the cooling temperature of the PLA slices in the cooling fluidized bed is preferably not more than 40 ℃, but not limited to not more than 40 ℃, and the further cooling temperature is not more than the glass transition temperature (60-65 ℃) of the PLA slices.

Further, the crystallization bed comprises a double-air-channel crystallization bed, a heating crystallization circulation system consisting of a first cyclone separator, a first centrifugal fan, a second centrifugal fan, a first electric heater and a second electric heater is sequentially arranged on a pipeline from an air outlet to an air inlet of the double-air-channel crystallization bed, and the control temperature of the first electric heater and the second electric heater communicated with the double-air-channel crystallization bed is 90-100 ℃.

Further, a cooling circulation system consisting of a second cyclone separator, a third centrifugal fan and a cooler is arranged on the cooling fluidized bed, and preferably, the control temperature of the cooler communicated with the cooling fluidized bed is not more than 40 ℃.

After the cooling of the cooling fluidized bed, the surface of the PLA slice is rapidly hardened to form a glass state, the thermal deformation temperature of the PLA slice after the PLA slice is in a stripped state is increased, and the thermal deformation temperature of the PLA slice is close to the melting temperature, so that the PLA slice can be effectively prevented from softening and adhering in a drying tower.

Further, a drying system consisting of a fan, a condenser, a dehumidifier and a third electric heater is arranged at a drying air inlet at the lower part of the drying tower, and the control temperature of the third electric heater communicated with the drying tower is 70-80 ℃.

Further, a first rotary valve is arranged on a material pipeline between the pre-crystallization tank and the double-air-duct crystallization bed, and a second rotary valve is arranged on a material pipeline between the cooling fluidized bed and the double-air-duct crystallization bed.

The utility model also provides a crystallization drying system of the PLA slice, which comprises any one of the crystallization drying devices of the PLA slice.

In the present PLA sheet crystallization drying system, the control temperature of the twin tunnel crystallizer is 90 ℃ -100 ℃ (the crystallization temperature of the PLA sheet is generally considered to be between 90 ℃ -110 ℃, in which range the higher the temperature is, the faster the crystallization speed, in this embodiment, 90 ℃ -100 ℃ is the preferred temperature under the condition of ensuring no deformation adhesion of the PLA sheet), the cooling of the PLA sheet in the cooling fluidized bed, and the drying temperature in the drying tower is 70 ℃ -80 ℃.

The PLA sheet belongs to a crystalline polymer material, the heat distortion temperature of the material is mainly affected by the crystallization area, when the crystallinity is within a certain range (for example, when the crystallinity is 30-40%), the heat distortion temperature of the material is close to the melting temperature, and the melting temperature of the PLA sheet is about 170 ℃, namely, the adhesion phenomenon can occur when the crystallized PLA sheet is heated again to about 170 ℃. In the crystallization bed, initial PLA slices are heated and crystallized at 90-100 ℃ to gradually improve the crystallinity, the crystallization bed has higher crystallinity, and then the cooling fluidized bed is cooled to 40 ℃ preferably, so that the surface of the PLA slices is rapidly hardened to form a glassy state, and the thermal deformation temperature of the PLA slices forming the glassy state is close to the melting temperature, therefore, when the cooled PLA slices after crystallization enter a drying tower again, the phenomenon of caking and agglomeration is not easy to occur when the cooled PLA slices are piled up or heated at 70-80 ℃.

That is, ① in the pre-crystallization tank, yu Wengao at the glass transition temperature of the PLA sheet, so the crystallinity of the PLA sheet will increase; ② The heating temperature in the double-air-channel crystallization bed is 90-100 ℃ which is higher than the crystallization temperature of PLA slices, so that the crystallinity is continuously increased; ③ When the crystallinity of the PLA slice is increased to a certain range, such as 30-40%, the temperature of the PLA slice is reduced to below 40 ℃ by a cooling fluidized bed, so that the surface of the PLA slice is rapidly hardened to form a glassy state, and the thermal deformation temperature of the PLA slice is close to the melting temperature (150-170 ℃); ④ The cooled PLA slice enters a drying tower for drying, and at the moment, the temperature of the drying tower is 70-80 ℃, but the thermal deformation temperature of the PLA slice is far higher than the temperature of the drying tower, so that the phenomenon of softening adhesion between the slices can not occur.

In fact, there is a tendency that the heat distortion temperature of the PLA sheet increases and decreases with the increase of crystallinity, and when the PLA sheet has a crystallinity of 30% to 40%, the heat distortion temperature reaches an extreme value, so that it is preferable that the crystallinity of the PLA sheet is controlled to 30% to 40% in the present application. The crystallinity can be adjusted by controlling the heating time in a dual tunnel crystallization bed, in which case it is preferred that the PLA sheet is heated for 40-45 minutes. In this case, the cooling temperature of the PLA chips in the cooling fluidized bed is preferably not more than 40℃but not limited to not more than 40℃and the cooling temperature may be set to be not more than the glass transition temperature (60 to 65 ℃) of the PLA chips, so that the crystallized chips are rapidly cooled to form a glassy state and then further dried.

Compared with the prior art, the device and the system have the positive effects that: due to the characteristic of low glass transition temperature (60-65 ℃) of the PLA slice, the PLA slice is subjected to preliminary crystallization by a pre-crystallization tank and cooling treatment after crystallization by a double-air-duct crystallization bed, and the PLA slice is cooled to below the glass transition temperature, so that the PLA slice entering a drying tower is ensured to be not deformed and not adhered. And not only can the high-melting-point PLA be processed, but also the low-melting-point PLA which appears in the last two years can be processed, and the productivity of a polymerization section is perfectly matched.

Drawings

FIG. 1 is a schematic diagram of the connection relationship of the present utility model.

In the figure:

A pre-crystallization tank 1001, a first rotary valve 1002, a double-air-channel crystallization bed 1003, a first cyclone 1004, a first centrifugal fan 1005A, a second centrifugal fan 1005B, a first electric heater 1006A, a second electric heater 1006B;

A second rotary valve 2001 for cooling the fluidized bed 2002, a second cyclone 2003, a third centrifugal fan 2004, and a cooler 2005;

A drying tower 3001, a filter screen 3002, a fan 3003, a condenser 3004, a dehumidifier 3005, and a third electric heater 3006.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present utility model more apparent, the technical solutions of the embodiments of the present utility model will be further described in detail below with reference to the accompanying drawings, and it is apparent that the described embodiments are some embodiments of the present utility model, but not all embodiments. In the interest of clarity and conciseness, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals.

It is also to be noted herein that elements and features described in one drawing or embodiment of the utility model may be combined with elements and features shown in one or more other drawings or embodiments, and that only device structures closely related to the solution according to the utility model are described in the drawings and description in order to avoid obscuring the utility model in unnecessary detail.

Embodiment one: as shown in fig. 1, a crystallization and drying device for PLA slices comprises a pre-crystallization tank 1001, a double-air-channel crystallization bed 1003, a cooling fluidized bed 2002 and a drying tower 3001 which are sequentially communicated through material pipelines, wherein a first rotary valve 1002 is arranged on the material pipeline between the pre-crystallization tank 1001 and the double-air-channel crystallization bed 1003, and a second rotary valve 2001 is arranged on the material pipeline between the cooling fluidized bed 2002 and the double-air-channel crystallization bed 1003.

The double-air-duct crystallization bed 1003 is communicated with a heating crystallization circulation system consisting of a first cyclone separator 1004, a first centrifugal fan 1005A, a second centrifugal fan 1005B, a first electric heater 1006A and a second electric heater 1006B.

The cooling fluidized bed 2002 is sequentially communicated with a second cyclone 2003, a third centrifugal fan 2004 and a cooler 2005 through a gas pipeline, and the gas outlet of the cooler 2005 is communicated with the gas inlet of the cooling fluidized bed 2002, so that a cooling circulation system is formed, wherein an emptying port is arranged on the gas pipeline between the second cyclone 2003 and the third centrifugal fan 2004. The drying air inlet at the lower part of the drying tower 3001 is communicated with a drying system consisting of a filter screen 3002, a fan 3003, a condenser 3004, a dehumidifier 3005 and a third electric heater 3005.

In this embodiment, the crystallization drying system of the PLA sheet controls the operation of the crystallization drying device of the PLA sheet by a PLC controller not shown in the drawing. The control temperatures of the first electric heater 1006A and the second electric heater 1006B communicated with the double-air-duct crystallization bed 1003 are 90-100 ℃, and in the embodiment, the control temperatures of the first electric heater 1006A and the second electric heater 1006B are 90 ℃ and 100 ℃ respectively; the temperature of the first electric heater 1006A is lower because the slices without crystallization at all fall first to the first zone and the second zone, and the raw slices are relatively more and the temperature is too high to be easily adhered. The first and second areas are mainly used for improving the softening point of the slice, the temperature of the third and fourth areas can be improved to the highest crystallization rate temperature of the slice, and the slice at the moment can not be adhered any more, so that the aim of completely crystallizing the slice in a specified time is fulfilled. The cooler 2005 in communication with the cooled fluidized bed 2002 controls the temperature to be no greater than 40 ℃, in this embodiment, the cooler 2005 controls the temperature to be 40 ℃; the third electric heater in communication with the drying tower 3001 controls the temperature to be 70 ℃ to 80 ℃, in this embodiment, 70 ℃.

In order to more clearly demonstrate the present utility model, a specific operation and description will now be made of the crystallization and drying apparatus and system for PLA chips of the present utility model, and with reference to fig. 1, PLA chips from a dicing system enter a pre-crystallization tank 1001, where the PLA chips stay in the pre-crystallization tank 1001 for about 20 to 25 minutes by means of their own waste heat, and during this process, the PLA chips undergo a crystallization reaction, and the color becomes slightly blurred from transparent.

The damping cone (see CN217248846U for details) provided in the pre-crystallization tank 1001 can avoid too fast flow of PLA slices in the middle of the pre-crystallization tank, making the middle flow consistent with the periphery, ensuring first-in first-out and uniform residence time of PLA slices, which makes PLA slices entering the dual-air-channel crystallization bed 1003 via the first rotary valve 1002 have almost the same crystallinity.

Here, the capacity of the pre-crystallization tank 1001 determines the residence time of the PLA chips in the pre-crystallization tank 1001, and the temperature at which the PLA chips from the upstream pelletizing system enter the pre-crystallization tank 1001 is higher than the glass transition temperature of the PLA chips, so that the PLA chips in the pre-crystallization tank 1001 cannot stay too much for about 20 to 25 minutes in the pre-crystallization tank 1001, otherwise the residence time is too long and deformation and blocking occur. During this process, PLA chips undergo crystallization reactions due to stacking and preheating, and the color becomes slightly hazy from transparent.

Five partitions are arranged in the double-air-duct crystallization bed 1003, as shown in fig. 1, the first, second, third, fourth and fifth regions from left to right are arranged at intervals through weir plates, and because the PLA crystallization speed is relatively slow and the crystallization time is relatively long, the double-air-duct corresponds to the four regions, namely each air duct corresponds to two regions, and is used for setting the crystallization temperatures of different regions to different temperatures, the temperature setting of the first and second regions of feeding needs to be lower, and the temperature setting of the third and fourth regions and the adjacent discharge holes is higher than the temperature setting of the feeding region, so that the crystallization of PLA is facilitated, and the agglomeration of slices is prevented.

Here, the temperature settings of the first and second zones of the feed are required to be low because the slices completely free of crystallization first fall into the first and second zones, and the raw slices are relatively large and the temperature is too high to be easily adhered. The first and second areas are mainly used for improving the softening point of the slice, the temperature of the third and fourth areas can be improved to the highest crystallization rate temperature of the slice, and the slice at the moment can not be adhered any more, so that the aim of completely crystallizing the slice in a specified time is fulfilled.

The four areas of the double-air-channel crystallization bed share two air inlet channels, the first area and the second area close to the feed inlet are connected with the first air inlet, the second air inlet close to the third area and the fourth area of the discharge outlet are connected, and the areas of the two areas at the discharge end are smaller, because the sections are partially crystallized after reaching the third area and the fourth area, the area of the first area and the second area is large, and the mixing proportion of raw clinker is required to be achieved, for example, the mixing proportion of the raw clinker is 1:9.

The fifth zone is connected with the discharge port of the double air channel crystallization bed 1003. The provision of the weirs increases the residence time of the slices in the double tunnel crystallization bed 2003 and enables a more uniform mixing of the raw clinker. Butterfly valves are respectively arranged on two air duct inlets of the double-air duct crystallization bed, and are used for controlling the wind speed and the wind quantity of the air duct inlets.

The hot air temperature of the two air channels is set through a corresponding first electric heater 1006A and a corresponding second electric heater 1006B respectively, hot air and PLA slices are subjected to heat exchange in the double-air-channel crystallization bed 1003, so that the PLA slices are heated to 90-100 ℃ for crystallization reaction, the hot air losing heat is subjected to dust removal through a first cyclone separator 1004, pressurized through a corresponding first centrifugal fan 1005A and a corresponding second centrifugal fan 1005B, then flows through a corresponding first electric heater 1006A and a corresponding second electric heater 1006B again for heating, and the PLA slices are sequentially and circularly heated. In this embodiment, the air inlet passage formed by the first centrifugal fan 1005A and the first electric heater 1006A is communicated with the air inlets of the first and second regions in the dual-air-channel crystallization bed 1003, the air inlet passage formed by the second centrifugal fan 1005B and the second electric heater 1006B is communicated with the air inlets of the third and fourth regions in the dual-air-channel crystallization bed 1003, and in this embodiment, the air inlet temperature of the first and second regions in the dual-air-channel crystallization bed 1003 is lower than the air inlet temperature of the third and fourth regions, for example, the first and second regions are rapidly heated to 90 ℃, the third and fourth regions are heated to 100 ℃, and the wind speed of the first and second regions are higher than the wind speed and the wind speed of the third and fourth regions, mainly because PLA slices in the first and second regions must be blown up by wind, such as a jump state, i.e. a fluidized state, and flow to the discharge port in sequence, so as to prevent the occurrence of stop caking. The residence time of the PLA pellets in the double air duct crystallization bed 1003 is controlled to be 40-45 minutes at the temperature of 90-100 ℃, so that the crystallinity of the PLA pellets can be controlled to be 30% -40%.

The PLA slices in the double-air-duct crystallization bed 1003 are in a leap state of 'randomly jumping' under the action of hot air, and along with the continuous entering of the feeding quantity, the leap PLA slices skip the weir plate to enter the two areas from the first area of the double-air-duct crystallization bed 1003, then enter the three and four areas from the second area, enter the blanking pipeline after passing through the last weir plate in the four areas, and then enter the cooling fluidized bed 2002 through the second rotary valve 2001.

PLA slices entering the cooling fluidized bed 2002 are in a fluctuation state on the bed surface, and cold air with the temperature of below 40 ℃ regulated and controlled by a cooler 2006 is in direct contact with hot PLA slices in the cooling fluidized bed 2002, so that the PLA slices are cooled to the temperature of 50-55 ℃ and then enter a drying tower 3001 for drying.

Because the temperature of the PLA slices after preliminary crystallization in the pre-crystallization tank 1001 and crystallization in the double-air-duct crystallization bed 1003 is far higher than the glass transition temperature of the PLA slices, the slices are in an amorphous state like soft sweets, and directly enter the drying tower to be dried at a high temperature for a long time, so that deformation and adhesion sites are easily caused by self gravity and mutual extrusion, and the PLA slices are seriously formed into large blocks, the PLA slices after crystallization are subjected to cooling treatment in the embodiment, and the PLA slices are cooled to a temperature ranging from 50 ℃ to 55 ℃ below the glass transition temperature due to the characteristic that the PLA slices have low glass transition temperature (60-65 ℃) so as to harden the PLA slices, so that the PLA slices entering the drying tower 3001 can be ensured not to deform and adhere.

The hot air subjected to heat exchange with PLA chips in the cooling fluidized bed 2002 is subjected to dust removal by the second cyclone 2003, is boosted by the third centrifugal fan 2004, enters the cooler 2005 again for cooling, and enters the cooling fluidized bed 2002 after the air temperature is reduced to below 40 ℃, and is circulated in sequence.

The PLA slices entering the drying tower 3001 flow downward in a plug flow, and the plug flow benefits from the air inlet distributor of the drying tower 3001 (see the damping cone and the air inlet distributor disclosed in patent document CN217248846U for details), so that the incoming hot air can be uniformly distributed on the whole cross section, meanwhile, the special cone design of the PLA slices also blocks the flow of the material in the center of the drying tower, which is the key for enabling the PLA material in the center of the drying tower 3001 and the PLA material in the periphery to form stable plug flow, and the PLA material is ensured to have the same residence time in the drying tower 3001. The hot air entering the drying tower 3001 is the drying air which is pressurized by the Roots blower 3003 after being filtered by the filter 3002, is primarily dehumidified by the pre-condenser 3004 and is heated by the third electric heater 3006 after being dehumidified by the dehumidifier 3005, the dew point of the air exiting the dehumidifier 3005 can reach the dew point of-75 degrees, the dehumidifier 3005 used in the method is an atmospheric pressure energy-saving dehumidifier, and the energy is saved by about 30% -35% compared with the high-pressure dehumidifier when the same air quantity is processed. The dry air with the temperature of 70-80 ℃ entering the drying tower 3001 and PLA slices form reverse flow, and finally enter a cooling circulation system with a cooling fluidized bed 2002 through a feed inlet pipeline arranged at the upper part of the drying tower 3001 and are discharged into the atmosphere through a discharge port of the cooling circulation system.

The foregoing description is only illustrative of the preferred embodiment of the present utility model, and is not to be construed as limiting the utility model, but is to be construed as limiting the utility model to any and all simple modifications, equivalent variations and adaptations of the embodiments described above, which are within the scope of the utility model, may be made by those skilled in the art without departing from the scope of the utility model.

Claims

1. The crystallization drying device for PLA slices is characterized by comprising a crystallization bed and a drying tower which are sequentially communicated through a material pipeline, wherein a cooling fluidized bed is further arranged on the material pipeline between the crystallization bed and the drying tower.

2. The crystallization and drying device for PLA sheet according to claim 1, wherein: the crystallization bed is a double-air-channel crystallization bed, and a heating crystallization circulation system consisting of a first cyclone separator, a first centrifugal fan, a second centrifugal fan, a first electric heater and a second electric heater is arranged on the double-air-channel crystallization bed.

3. The crystallization and drying device for PLA sheet according to claim 1, wherein: and the cooling fluidized bed is provided with a cooling circulation system consisting of a second cyclone separator, a third centrifugal fan and a cooler.

4. The crystallization and drying device for PLA sheet according to claim 1, wherein: the drying air inlet at the lower part of the drying tower is provided with a drying system consisting of a fan, a condenser, a dehumidifier and a third electric heater.

5. The crystallization and drying device for PLA sheet according to claim 1, wherein: the crystallization bed is characterized in that a first rotary valve is arranged on a feed inlet pipeline of the crystallization bed, and a second rotary valve is arranged on a material pipeline between the cooling fluidized bed and the crystallization bed.

6. A crystallization drying system for PLA chips, comprising a crystallization drying device for PLA chips according to any one of claims 1-5.