Drying method and system for full-biodegradable polyester chip

Abstract

The invention belongs to the field of polyester chip drying, and particularly relates to a drying method and system for full-biodegradable polyester chips. Specifically, the drying system comprises a buffer storage bin, a dryer connected with a discharge port of the buffer storage bin, a first gas supply device used for continuously introducing gas into the buffer storage bin, and a second gas supply device used for continuously introducing gas into the dryer, the dew point testing equipment is arranged at an air outlet of the buffer stock bin, the dew point testing equipment is arranged at an air outlet of the dryer, and the dryer is provided with a dynamic assembly which enables the polyester chips to keep dynamic.

Description

Technical Field

[0001] The invention belongs to the field of polyester chip drying, and in particular relates to a drying method and system for fully biodegradable polyester chips. Background Art

[0002] Fully biodegradable polyester is an aliphatic polyester with a simple and regular repeating ester bond structure. The presence of ester bonds in the molecular chain makes the fully biodegradable material contain carboxyl and hydroxyl groups, which are particularly sensitive to water and heat. Under high temperature and humid environment, the moisture in the fully biodegradable slices will cause the fully biodegradable polyester to undergo hydrolysis reaction, resulting in the depolymerization of the molecular chain and the generation of molecular chain segments with terminal carboxyl and terminal hydroxyl groups. When the fully biodegradable polyester is close to the glass transition temperature, the molecular weight decreases significantly with the increase of hydrolysis time. If the fully biodegradable polyester slices are directly packaged without drying, the moisture in the polyester slices will directly affect the shelf life of the product and thus affect the stability of downstream processing. Therefore, for the packaging of the slices and for the downstream melt processing, it is necessary to fully dry them first, strictly control the moisture content in the system, and prevent excessive moisture from causing hydrolysis during the processing, resulting in molecular chain breakage and molecular weight reduction, thereby affecting the physical properties of the processed and formed products.

[0003] In the industrial production of fully biodegradable polyester, after the polymerization of fully biodegradable polyester is completed, air-cooled strands and underwater pelletizing are generally used for slicing. Air-cooled strands absorb moisture from the cooling air during the cooling process, and the moisture content of air-cooled stranded fully biodegradable polyester slices is generally around 0.06%; while centrifugal dehydration is generally used after underwater pelletizing, and the moisture content of fully biodegradable polyester slices is around 0.2%. Regardless of the slicing method used, if the fully biodegradable polyester slices are directly bagged and packaged, the moisture in the slices in the package is likely to cause hydrolysis.

[0004] Among the existing drying methods, traditional hot air drying takes a long time. Although it can reduce the moisture content of the output material to a predetermined value, there is a hydrolysis reaction during the drying process, and when the moisture content in the slices is reduced to a certain level in the later stage of drying, local condensation reactions are prone to occur. Therefore, it is urgent to provide a new drying method to improve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a drying method and system for fully biodegradable polyester chips.

[0006] According to a first aspect of the present invention, a polyester chip drying system is provided, the drying system comprising a buffer silo, a dryer connected to the outlet of the buffer silo, a first air supply device for continuously introducing gas into the buffer silo, a second air supply device for continuously introducing gas into the dryer, and a dew point testing device arranged at the outlet of the buffer silo and a dew point testing device arranged at the outlet of the dryer, wherein the dryer is provided with a dynamic component for keeping the polyester chips dynamic.

[0007] In one or more embodiments, the first air supply device includes a first heater, the first heater is connected to the air inlet of the buffer silo, and a first stirring component is disposed in the buffer silo;

[0008] The second air supply device includes a second heater, and the second heater is connected to the air inlet of the dryer.

[0009] In one or more embodiments, the dynamic component includes a hollow screw conveying shaft and a transmission device connected to the hollow screw conveying shaft, the dryer is a single-shaft spiral stirring dryer, which includes a shell, at least one hollow screw conveying shaft arranged in the shell, and at least one transmission device arranged outside the shell, one transmission device is connected to one hollow screw conveying shaft, two adjacent hollow screw conveying shafts are separated by a partition, and the conveying directions of the two adjacent hollow screw conveying shafts are opposite, and a gas material channel is left between the partition and the shell;

[0010] The shaft body of the last-stage hollow screw conveyor shaft is hollow inside and has air holes on its surface. One end of the shaft body is connected to a rotary joint provided with an air inlet, and the other end is connected to the transmission device. The discharge port of the dryer is arranged below one end of the last-stage hollow screw conveyor shaft close to the air inlet.

[0011] In one or more embodiments, the drying system further comprises a first gas purification circulation device for purifying and recycling the gas flowing out of the buffer silo;

[0012] The first gas purification circulation device includes a filter, and a first cooler, a first dehumidifier and a first fan connected to the filter in sequence, the air outlet of the cache silo is connected to the filter, an exhaust port is provided on the pipeline connecting the filter and the first cooler, and the air outlet of the first fan is connected to the first air supply device.

[0013] In one or more embodiments, the drying system further comprises a second gas purification circulation device for purifying and recycling the gas flowing out of the dryer;

[0014] The second gas purification circulation device includes a cyclone separator, and a catalytic oxidizer, a second cooler, a second dehumidifier and a second fan connected to the cyclone separator in sequence, the air outlet of the dryer is connected to the cyclone separator, and the air outlet of the second fan is connected to the second air supply device.

[0015] In one or more embodiments, the drying system further comprises a cooling silo connected to the discharge port of the dryer, wherein a spiral coil is arranged in the cooling silo, and a plurality of through holes are arranged on the coil, one end of the coil is an air inlet end, and an air outlet is arranged at the upper part of the cooling silo;

[0016] The air outlet of the second fan is connected to the air inlet end of the coil, and the air outlet of the cooling silo is connected to the second air supply device.

[0017] The second aspect of the present invention provides a method for drying polyester chips using the drying system according to the first aspect of the present invention, the method comprising the steps of:

[0018] (1) In a buffer silo, a first hot air flow is used to pre-dehumidify the polyester chip raw material to obtain a pre-dehumidified polyester chip;

[0019] (2) in a dryer, using a second hot air flow to dry the pre-dehumidified polyester chips to obtain dried polyester chips, wherein the drying temperature in the dryer is greater than the buffer temperature in the buffer silo;

[0020] The gas dew point temperature of the first hot gas flow at the gas outlet of the buffer silo is ≤-10°C;

[0021] The gas dew point temperature of the second hot gas flow at the gas outlet of the dryer is ≤-10°C.

[0022] In one or more embodiments, the buffer temperature in the buffer silo is 90-130°C.

[0023] In one or more embodiments, the buffering time in the buffer silo is 0.1 to 2 hours.

[0024] In one or more embodiments, the gas dew point temperature of the first hot gas flow at the gas outlet of the buffer silo is -40°C to -10°C.

[0025] In one or more embodiments, the gas dew point temperature of the first hot gas flow at the gas inlet of the buffer silo is ≤ -40°C.

[0026] In one or more embodiments, the drying temperature in the dryer is 100°C to 200°C.

[0027] In one or more embodiments, the drying time in the dryer is 0.5 to 5 hours.

[0028] In one or more embodiments, the gas dew point temperature of the second hot gas flow at the gas outlet of the dryer is -40°C to -10°C.

[0029] In one or more embodiments, the gas dew point temperature of the second hot gas stream at the gas inlet of the dryer is ≤ -40°C.

[0030] In one or more embodiments, the particle size of the polyester chip raw material is ≥1.5 mm.

[0031] In one or more embodiments, the moisture content of the polyester chip raw material is 0.03 to 0.3 wt %.

[0032] In one or more embodiments, the polyester chip raw material has a melt index of 10 to 80 g / 10 min (230° C., 2.16 kg).

[0033] In one or more embodiments, the residual monomer content of the polyester chip raw material is 1 to 5 wt %.

[0034] In one or more embodiments, the moisture content of the dried polyester chips is < 0.008 wt%.

[0035] In one or more embodiments, the melt index of the dried polyester chips is 3 to 50 g / 10 min (230° C., 2.16 kg).

[0036] In one or more embodiments, the residual monomer content of the dried polyester chips is < 1 wt%. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of a drying system in one or more embodiments of the present invention; wherein 1-buffer silo, 11-first stirring assembly, 2-dryer, 3-cooling silo, 31-coil, 41-first cyclone separator, 42-second cyclone separator, 5-catalytic oxidizer, 61-first cooler, 62-second cooler, 71-first dehumidifier, 72-second dehumidifier, 81-first fan, 82-second fan, 91-first heater, 92-second heater, b-rotary valve, c-filter.

[0038] Figure 2 It is a schematic diagram of a primary single-axis spiral stirring dryer in one or more embodiments of the present invention; wherein 21 is a feed port, 22 is a discharge port, 23 is an air inlet, 24 is an air outlet, 25 is a rotary joint, 26 is a vent, and 27 is a transmission device.

[0039] Figure 3 It is a schematic diagram of a two-stage single-axis spiral stirring dryer in one or more embodiments of the present invention; wherein 21'-feed port, 22'-discharge port, 23'-air inlet, 24'-air outlet, 25'-rotating joint, 26'-air vent, 27'-transmission device, 28'-partition, 29'-air-feed channel. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0041] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0042] Herein, “comprising”, “including”, “containing” and similar terms encompass the meanings of “consisting essentially of” and “consisting of”. For example, when “A comprises B and C” is disclosed herein, “A consists essentially of B and C” and “A consists of B and C” should be deemed to be disclosed herein.

[0043] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0044] In this document, unless otherwise specified, percentage refers to mass percentage and ratio refers to mass ratio.

[0045] Herein, when describing embodiments or examples, it should be understood that they are not used to limit the present invention to these embodiments or examples. On the contrary, all substitutes, improvements and equivalents of the methods and materials described in the present invention can be included in the scope limited by the claims.

[0046] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0047] In this article, the gas-to-material ratio refers to the ratio of gas and material entering the buffer silo or dryer. The gas-to-material ratio entering the buffer silo is the ratio of the volume of the first hot air flow entering the buffer silo to the mass of the polyester chip raw material. The gas-to-material ratio entering the dryer is the ratio of the volume of the second hot air flow entering the dryer to the mass of the pre-dehumidified polyester chips. For example, 1: (50-150) L / g means that 1 L of gas is passed for every 50-150 g of material. The gas-to-material ratio entering the buffer silo or dryer can be adjusted according to the gas dew point temperature at the outlet of each device. The larger the gas-to-material ratio, the less water content in the gas at the outlet and the lower the gas dew point temperature; on the contrary, the smaller the gas-to-material ratio, the more water content in the gas at the outlet and the higher the gas dew point temperature. The gas dew point temperature at the outlet can be measured by a dew point meter. For example, the gas-to-material ratio entering the buffer silo can be 1: (50-150) L / g, such as 1: 50 L / g, 1: 110 L / g, 1: 150 L / g, or a range between any two values. For another example, the gas-to-material ratio entering the dryer can be 1: (10-100) L / g, such as 1: 20 L / g, 1: 60 L / g, 1: 80 L / g, or a range between any two values.

[0048] The invention provides a drying method, comprising: pre-dehumidifying fully biodegradable polyester chips in a buffer silo and then entering a dryer for deep drying; wherein the polyester chips are dried by hot air convection in both the buffer silo and the dryer, the buffer temperature in the buffer silo is 90-130°C, the buffer time is 0.1-2h, and the gas dew point temperature at the gas outlet of the buffer silo is not higher than -10°C; the drying temperature in the dryer is 100-200°C, the drying temperature in the dryer is greater than the buffer temperature in the buffer silo, the drying time is 0.5-5h, the gas dew point temperature at the gas outlet of the dryer is not higher than -10°C, and the dryer is provided with a dynamic component for keeping the polyester chips dynamic; further, the material after drying enters a cooling silo for cooling.

[0049] At higher temperatures, moisture in the environment (including some moisture that escapes from the polyester chips) and moisture in the polyester chips are prone to cause hydrolysis of the polyester. In the present invention, the polyester chips enter and exit the buffer silo from top to bottom, and the gas enters and exits from bottom to top in the buffer silo. The temperature in the buffer silo is relatively low, and the hot air convection in the buffer silo can take away some of the moisture that escapes from the polyester chips. At the same time, the present invention also needs to control the gas dew point temperature at the gas outlet of the buffer silo. The gas dew point temperature at the gas outlet can reflect the moisture content in the environment in the buffer silo. By keeping the gas dew point temperature at the gas outlet below -10°C, the environment in the buffer silo is always kept at a low dew point temperature state, which can prevent the moisture content in the buffer silo from being too high and reduce the occurrence of polyester hydrolysis.

[0050] The polyester chips pre-dehumidified in the buffer silo are sent to the dryer for deep drying. The drying temperature in the dryer is higher than the buffer temperature in the buffer silo. Low dew point gas is continuously introduced into the dryer. The hot air convection can continuously take away the unreacted monomers and oligomers in the polyester chips and the moisture released from the polyester chips. The polyester chips remain dynamic under the action of the dynamic components during the drying process to avoid adhesion. Similarly, it is also necessary to control the gas dew point temperature at the dryer outlet. The gas dew point temperature at the outlet can reflect the moisture content in the dryer environment. By keeping the gas dew point temperature at the outlet below -10°C, the moisture content in the dryer can be prevented from being too high, reducing the occurrence of polyester hydrolysis reaction.

[0051] Polyester chips drying system

[0052] like Figure 1 As shown, the present invention provides a drying system for polyester chips, comprising a buffer silo 1, a dryer 2 connected to the outlet of the buffer silo 1, a first air supply device for continuously introducing gas into the buffer silo 1, a second air supply device for continuously introducing gas into the dryer 2, and a dew point testing device arranged at the outlet of the buffer silo 1 and a dew point testing device arranged at the outlet of the dryer 2, wherein the dryer 2 is provided with a dynamic component for keeping the polyester chips dynamic.

[0053] The buffer silo 1 is provided with a feed port, a discharge port, an air inlet and an air outlet, and the dryer 2 is provided with a feed port, a discharge port, an air inlet and an air outlet. As a further preferred solution, a dew point test device is provided at the air inlet of the buffer silo 1 and at the air inlet of the dryer 2. Exemplarily, the dew point test device is an online dew point meter.

[0054] As a further preferred solution, a first stirring component 11 for dynamically pre-dehumidifying the material is provided in the buffer silo 1. The first stirring component 11 can be a stirring component commonly used in the art, and the material is turned upward when the first stirring component 11 rotates. For example, the first stirring component 11 can be a paddle stirring component.

[0055] The first gas supply device includes a first heater 91, and the first heater 91 is connected to the air inlet of the buffer silo 1. The second gas supply device includes a second heater 92, and the second heater 92 is connected to the air inlet of the dryer 2. Specifically, the first heater 91 is used to heat the gas entering the buffer silo 1; the second heater 92 is used to heat the gas entering the dryer 2. In a preferred embodiment, a gas volume control valve is provided on the pipeline connecting the first heater 91 and the buffer silo 1, and / or on the pipeline connecting the second heater 92 and the dryer 2, and the gas flow entering the buffer silo 1 and / or the dryer 2 is controlled by providing the gas volume control valve.

[0056] In some embodiments, an inner wall of the shell of the dryer 2 is provided with an interlayer, heat transfer oil is introduced into the interlayer, a heat transfer oil outlet and a heat transfer oil inlet are provided on the shell, and a heat insulation material is further wrapped on the outer surface of the shell of the dryer 2. The temperature of the heat transfer oil may be the same as the temperature of the gas introduced into the dryer 2, or higher than the temperature of the gas, preferably the same as the temperature of the gas introduced into the dryer 2.

[0057] In some embodiments, the drying system of the present invention further comprises a cooling silo 3 connected to the discharge port of the dryer 2. The cooling silo 3 is provided with a feed port and a discharge port, the discharge port of the dryer 2 is connected to the feed port of the cooling silo 3, the discharge port of the cooling silo 3 is the outlet of the dried material, and the material dried by the dryer 2 first enters the cooling silo 3, and is packaged after being cooled.

[0058] Furthermore, a spiral coil 31 is provided in the cooling silo 3 , and a plurality of through holes are provided on the coil 31 , one end of the coil 31 is an air inlet end, and the other end of the coil 31 can be closed or open, and an air outlet is provided at the upper part of the cooling silo 3 .

[0059] The low-temperature, dry gas enters the coil 31 through the air inlet of the cooling silo 3 (i.e., the air inlet end of the coil 31), and then flows out of the coil 31 through the through hole to exchange heat and further exchange moisture with the material in the cooling silo 3, and then flows out through the air outlet at the top of the cooling silo 3. The gas flowing out of the cooling silo 3 has a very low water content, and can also be mixed with the gas entering the buffer silo 1 from the gas inlet in the pipeline leading to the first heater 91, and then enter the first heater 91 to achieve the recycling of the gas; and / or, mixed with the gas entering the dryer 2 from the gas inlet in the pipeline leading to the second heater 92, and then enter the second heater 92 to achieve the recycling of the gas.

[0060] When the drying system of the present invention dries the raw materials, the first airflow is heated to a set temperature in the first heater 91 and then enters the buffer silo 1, the second airflow is heated to a set temperature in the second heater 92 and then enters the dryer 2, the material enters the buffer silo 1 from the feed port of the buffer silo 1, is pre-dehumidified by the thermal convection of the first airflow with a certain temperature, and then is discharged from the discharge port of the buffer silo 1 into the dryer 2, and is further dried by the thermal convection of the second airflow with a certain temperature in the dryer 2 and then discharged from the discharge port of the dryer 2. Preferably, the material discharged from the discharge port of the dryer 2 enters the cooling silo 3, is cooled and further dried in the cooling silo 3, and then is discharged from the discharge port of the cooling silo 3.

[0061] Furthermore, a first cyclone separator 41 is provided between the material raw material inlet for the polyester chips to enter the drying system of the present invention and the buffer silo 1 .

[0062] Furthermore, a rotary valve b is provided on the pipeline connecting the first cyclone separator 41 and the feed port of the cache silo 1, the pipeline connecting the discharge port of the cache silo 1 and the feed port of the dryer 2, the pipeline connecting the discharge port of the dryer 2 and the feed port of the cooling silo 3, and the pipeline connecting the discharge port of the cooling silo 3 and the dried material outlet. The rotary valve b can be used to adjust the flow direction and flow rate of the material.

[0063] Furthermore, the drying system of the present invention also includes a first gas purification circulation device for purifying and recycling the gas flowing out of the buffer silo 1. The first gas purification circulation device includes a filter c, and a first cooler 61, a first dehumidifier 71 and a first fan 81 connected to the filter c in sequence. The air outlet of the buffer silo 1 is connected to the filter c, and the air outlet of the first fan 81 is connected to the first heater 91. An exhaust port is also provided on the pipeline connecting the filter c and the first cooler 61, which is used to discharge part of the moisture out of the drying system.

[0064] In actual application, the gas discharged from the gas outlet of the buffer silo 1 enters the filter c, a small part of the wet gas is separated after filtration and discharged directly from the drying system, and then enters the first cooler 61, is cooled in the first cooler 61, and then enters the first dehumidifier 71, is dehumidified in the first dehumidifier 71, and then enters the first fan 81. The gas flows out of the first fan 81 and enters the first heater 91. After being heated to a specific temperature by the first heater 91, it enters the buffer silo 1 through the air inlet of the buffer silo 1. The gas inlet of the fresh low dew point gas entering the buffer silo 1 can be set on the pipeline connecting the first dehumidifier 71 and the first fan 81, and can also be set on the pipeline connecting the first fan 81 and the first heater 91.

[0065] Furthermore, the drying system of the present invention also includes a second gas purification circulation device for purifying and recycling the gas flowing out of the dryer 2. The second gas purification circulation device includes a second cyclone separator 42, and a catalytic oxidizer 5, a second cooler 62, a second dehumidifier 72 and a second fan 82 connected to the second cyclone separator 42 in sequence, the air outlet of the dryer 2 is connected to the second cyclone separator 42, and the air outlet of the second fan 82 is connected to the second heater 92. As a further preferred solution, the air outlet of the second fan 82 is connected to the air inlet end of the coil 31 in the cooling silo 3, and the air outlet at the upper end of the cooling silo 3 is connected to the second heater 92.

[0066] In practical applications, the gas discharged from the air outlet of the dryer 2 enters the second cyclone separator 42, is separated from the entrained solid and liquid impurities in the second cyclone separator 42 (dust removal), then enters the catalytic oxidizer 5, removes organic small molecule impurities in the catalytic oxidizer 5, then enters the second cooler 62, cools down in the second cooler 62, then enters the second dehumidifier 72, dehumidifies in the second dehumidifier 72, then enters the second fan 82, and after the gas flows out of the second fan 82, enters the cooling silo 3, exchanges heat and moisture with the material in the cooling silo 3, then enters the second heater 92, is heated to a specific temperature by the second heater 92, and then enters the dryer 2 through the air inlet of the dryer 2. The gas inlet of the fresh low dew point gas entering the dryer 2 is set on the pipeline connecting the air outlet of the cooling silo 3 and the second heater 92.

[0067] The first dehumidifier 71 and the second dehumidifier 72 may be dehumidifiers commonly used in the art. For example, the first dehumidifier 71 and the second dehumidifier 72 may dehumidify the gas through the molecular sieves contained therein.

[0068] In some embodiments, the cooling temperature in the first cooler 61 is ≤60°C, for example, 30-60°C or 40-50°C; the cooling temperature in the second cooler 62 is ≤60°C, for example, 30-60°C, 40-50°C. The cooling temperature in the first cooler 61 and the cooling temperature in the second cooler 62 may be the same or different.

[0069] In the above embodiment, the dynamic component of the dryer 2 may be a spiral conveying component, a stirring component, a vibration component, or a drum component, etc. Specifically, the dryer 2 may be a vertical dryer or a horizontal dryer. The vertical dryer includes but is not limited to a vibrating countercurrent dryer, a tower dryer with a stirring component, and a fluidized bed dryer with a stirring component. By adopting a vibrating countercurrent dryer, the material is not prone to "bridging" or agglomeration in a spiral vibration environment. By setting a stirring component in a tower dryer or a fluidized bed dryer, the material can be kept dynamically dry during the drying process to prevent the material from sticking. The horizontal dryer includes but is not limited to a single-axis spiral stirring dryer, a double-axis spiral stirring dryer, a multi-axis spiral stirring dryer, and a drum dryer.

[0070] In the dryer 2, the flow direction of the gas is opposite to the flow direction of the material. For example, in a vertical dryer, the low dew point hot gas enters from the air inlet at the bottom of the dryer, passes through the material layer and flows in the opposite direction to the material for drying, and the material can produce "reciprocating motion" in the drying equipment; in a horizontal dryer, the material flows in the horizontal dryer in a plug flow, and the main flow direction of the gas is opposite to the material conveying direction.

[0071] In some embodiments, the dynamic component includes a hollow screw conveying shaft and a transmission device connected to the hollow screw conveying shaft. The dryer 2 is a single-axis spiral stirring dryer, which includes a shell, at least one hollow screw conveying shaft arranged in the shell, and at least one transmission device arranged outside the shell. A transmission device is connected to a hollow screw conveying shaft. Two adjacent hollow screw conveying shafts are separated by a partition, and the conveying directions of the two adjacent hollow screw conveying shafts are opposite. An air-material channel is left between the partition and the shell; the shaft body of the last-stage hollow screw conveying shaft is hollow inside and has air holes on the surface. One end of the shaft is connected to a rotary joint provided with an air inlet, and the other end is connected to the transmission device. The discharge port of the dryer is arranged below one end of the last-stage hollow screw conveying shaft close to the air inlet.

[0072] The hollow spiral conveyor shaft includes a central shaft and conveying blades spirally wrapped around the central shaft. The transmission device drives the conveying blades to rotate by connecting with the central shaft, thereby promoting material transportation.

[0073] The gas enters the last stage of the hollow screw conveyor shaft from the air inlet arranged on the rotary joint, and flows out from the air vent of the last stage of the hollow screw conveyor shaft into the shell to dry the material, and finally flows out from the air outlet of the single-axis spiral stirring dryer. The conveying direction of the material at the same stage in the shell is opposite to the mainstream flow direction of the gas.

[0074] Specifically, the single-shaft spiral stirring dryer can be a one-stage, two-stage or more single-shaft spiral stirring dryer. The number of hollow spiral conveying shafts and the number of transmission devices contained in the one-stage, two-stage or more single-shaft spiral stirring dryer are the same as its level, and one transmission device is connected to one hollow spiral conveying shaft.

[0075] The structure of the first-stage single-axis spiral stirring dryer is as follows: Figure 2 The housing of the single-axis spiral stirring dryer is provided with a feed port 21, a discharge port 22 and an air outlet 24. The feed port 21 and the air outlet 24 are arranged above the end of the hollow spiral conveying shaft away from the air inlet 23, and the discharge port 22 is arranged below the end of the hollow spiral conveying shaft close to the air inlet 23. The center axis of the hollow spiral conveying shaft is hollow inside and a plurality of air vents 26 are arranged on the surface.

[0076] The material (such as polyester chips, fully biodegradable polyester chips) enters from the feed port 21 and exits from the discharge port 22 of the single-axis spiral stirring dryer. The low dew point gas enters from the air inlet 23 of the rotary joint 25 and is discharged from the vent 26 on the hollow spiral conveying shaft. It passes through the material layer in the spiral to exchange water and heat with the material and is finally discharged from the outlet 24. The material conveying direction is opposite to the main flow direction of the gas. The hollow spiral conveying shaft rotates under the drive of the transmission device 27, thereby promoting the material conveying. The material undergoes interface renewal under the action of the hollow spiral conveying shaft, and the material moves in a plug flow to prevent adhesion.

[0077] The structure of the two-stage or more single-shaft spiral stirring dryer is similar, such as Figure 3 As shown, taking a two-stage single-axis spiral stirring dryer as an example, each stage includes a hollow spiral conveying shaft and a transmission device 27', the two-stage hollow spiral conveying shafts are stacked up and down and separated by a partition 28', the conveying directions of the upper and lower hollow spiral conveying shafts are opposite, the starting end of the lower hollow spiral conveying shaft is located below the end of the upper hollow spiral conveying shaft, so that the upper and lower materials are conveyed in opposite directions; the channel formed between the partition 28' and the shell is an air channel 29', which is the discharge port of the upper single-axis spiral stirring dryer and the feed port of the next single-axis spiral stirring dryer, and also the air outlet of the next single-axis spiral stirring dryer and the air inlet of the upper single-axis spiral stirring dryer.

[0078] The air inlet 23' of the entire single-axis spiral stirring dryer is arranged on a rotary joint 25' connected to one end of the next-stage hollow spiral conveying shaft, and the discharge port 22' is arranged below the end of the next-stage hollow spiral conveying shaft close to the air inlet 23', that is, the discharge port 22' and the air inlet 23' are located on the same side of the single-axis spiral stirring dryer; the feed port 21' and the air outlet 24' are arranged above the previous-stage hollow spiral conveying shaft and on the same side as the discharge port 22' and the air inlet 23' (when the single-axis spiral stirring dryer is a 2N-stage single-axis spiral stirring dryer). Only the central axis of the next-stage hollow screw conveying shaft is hollow inside and has an air vent 26' on its surface. The gas in the next-stage hollow screw conveying shaft is discharged from the air vent 26' into the shell, passes through the material layer in the next-stage screw to perform hydrothermal exchange with the material, and the exchanged gas enters the material layer in the previous-stage screw through the gas-material channel 29' to perform hydrothermal exchange with the material, and is finally discharged from the gas outlet 24'. The material conveying direction of each stage is opposite to the mainstream flow direction of the gas.

[0079] Preferably, the diameter of the vent holes 26, 26' is 0.1-1 mm, preferably 0.4-0.6 mm or 0.2-0.8 mm.

[0080] Preferably, the gap between the portion of the hollow spiral conveying shaft closest to the shell and the shell is less than 1 mm.

[0081] Preferably, the spiral pitch of the hollow spiral conveying shaft is 100-500 mm, preferably 250-350 mm, for example 320 mm.

[0082] Drying method

[0083] The present invention provides a method for drying polyester chips, wherein the polyester chips are dried using the above drying system, and the method comprises the steps of:

[0084] (1) In a buffer silo, a first hot air flow is used to pre-dehumidify the polyester chip raw material to obtain a pre-dehumidified polyester chip;

[0085] (2) in a dryer, using a second hot air flow to dry the pre-dehumidified polyester chips to obtain dried polyester chips, wherein the drying temperature in the dryer is greater than the buffer temperature in the buffer silo;

[0086] The gas dew point temperature of the first hot gas flow at the gas outlet of the buffer silo is ≤-10°C;

[0087] The gas dew point temperature of the second hot gas flow at the gas outlet of the dryer is ≤-10°C.

[0088] Preferably, in step (1), the gas dew point temperature of the first hot gas flow at the gas outlet of the buffer silo is controlled to be -40°C to -10°C, for example, -40°C, -35°C, -30°C, or within a range consisting of any two values.

[0089] Further, the gas dew point temperature of the first hot gas flow at the air inlet of the buffer silo is ≤-40°C, such as -40°C, -45°C, -50°C, or within a range consisting of any two values.

[0090] In the present invention, the buffer temperature refers to the set temperature in the buffer silo, and the buffer time refers to the residence time of the material in the buffer silo. In some embodiments, the first hot air flow pre-dehumidifies the polyester chip raw material by convection. In some embodiments, the buffer temperature in the buffer silo is 90-130°C, preferably 90-120°C, 100-115°C, for example 105°C. The buffer time in the buffer silo is 0.1-2h, preferably 0.5-1h.

[0091] In some embodiments, a first stirring component is provided in the buffer silo, and the stirring mode of the first stirring component is to turn the material upward when rotating, for example, the first stirring component is a paddle stirring component. The stirring speed of the first stirring component is 5 to 50 rpm, preferably 10 to 25 rpm, 20 to 30 rpm or 15 to 40 rpm.

[0092] In step (2), the gas dew point temperature of the second hot gas flow at the gas outlet of the dryer is -40°C to -10°C, for example, -40°C, -20°C, -10°C, or within a range consisting of any two values.

[0093] Further, the gas dew point temperature of the second hot gas flow at the air inlet of the dryer is ≤ -40°C, such as -40°C, -45°C, -50°C, or within a range consisting of any two values.

[0094] In step (2), the pre-dehumidified polyester chips are dried by convection drying using a second hot air flow. In the dryer, the drying temperature can be 100 to 200° C., such as 120° C., 150° C., 180° C., or a range between any two values. The drying time in the dryer can be 0.5 to 5 hours, such as 1 hour, 3 hours, 5 hours, or a range between any two values.

[0095] In a preferred embodiment, the dryer is the above-mentioned single-shaft spiral stirring dryer. Preferably, the rotation speed of the single-shaft spiral stirring dryer is 2 to 50 rpm, preferably 5 to 30 rpm, for example 6 rpm. The material filling rate in the single-shaft spiral stirring dryer is 5 to 95%, preferably 40 to 85%, for example 60%.

[0096] The first hot gas flow and the second hot gas flow are each independently selected from one or more of air, nitrogen and an inert gas. Preferably, the first hot gas flow and the second hot gas flow are the same gas.

[0097] In some embodiments, the polyester chips are polyglycolic acid chips; preferably, the polyester chips are fully biodegradable polyglycolic acid chips. Polyglycolic acid chips are copolymers containing repeating units of glycolic acid.

[0098] In a preferred embodiment, the dried polyester chips are sent to a cooling silo for cooling. The temperature of the cooling silo can be ≤60°C, for example, 20°C, 40°C, 50°C, or between any two numerical values; preferably 30-60°C. Preferably, the temperature of the cooling silo is the same as the cooling temperature of the cooler 62.

[0099] In another preferred embodiment, the method comprises conveying the pelletized polyester chips to a buffer silo in a low dew point environment. The gas dew point temperature of the low dew point environment is ≤ -30°C, such as -30°C, -40°C, -45°C, or in a range between any two values.

[0100] The particle size of the polyester chip raw material may be ≥1.5 mm; preferably 1.5-6 mm or 2-6 mm. Further, the moisture content of the polyester chip raw material may be 0.03-0.3 wt%. Further, the melt index of the polyester chip raw material may be 10-80 g / 10 min (230° C., 2.16 kg). Further, the residual monomer content of the polyester chip raw material may be 1-5 wt%.

[0101] The moisture content of the dried polyester chips may be less than 0.008 wt %. Further, the melt index of the dried polyester chips may be 3 to 50 g / 10 min (230° C., 2.16 kg). Further, the residual monomer content of the dried polyester chips may be less than 1 wt %.

[0102] The embodiments of the present invention have the following beneficial effects:

[0103] 1. Pre-dehumidify the polyester chip raw materials in the buffer silo and control the gas dew point temperature at the outlet of the buffer silo to solve the problem of material hydrolysis caused by storing polyester chips in the buffer silo before drying in industrial production.

[0104] 2. Further add a stirring component in the buffer silo to prevent materials from sticking and bridging in the buffer silo.

[0105] 3. During the drying process, the polyester chips are dynamically dried to prevent adhesion. At the same time, the gas dew point temperature at the dryer outlet is controlled to prevent the chips from hydrolyzing during the drying process.

[0106] 4. The single-axis spiral stirring dryer is used. The material moves in a plug flow in the dryer, which can be produced continuously without mixed flow that causes uneven drying of slices. The contact surface between the material and the gas can be quickly updated, which is conducive to the removal of moisture. However, the existing hot air drying usually only adjusts the relevant process parameters based on whether the moisture content of the output material meets the standard. The drying time is too long, and the adverse effects of moisture in the environment on polyester materials during the drying process are ignored.

[0107] 5. Equipped with gas purification and circulation device. The high-temperature gas discharged from the buffer silo is mainly water. After filtering, part of it is discharged, and the other part is cooled and dehydrated. The purified gas can be reused. The high-temperature gas discharged from the dryer contains a small amount of monomers and oligomers. After passing through the catalytic oxidizer, the monomers and oligomers in the gas are completely removed, and then the gas is cooled and dehydrated. The purified gas can be reused; further, the purified gas first passes through the cooling silo to cool the material, which can increase the gas temperature. When the gas is circulated again, energy consumption is further saved.

[0108] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples without specifying specific conditions are usually based on conventional conditions or the conditions recommended by the manufacturer. Unless otherwise stated, percentages and parts are calculated by weight.

[0109] Test method:

[0110] 1. Moisture test

[0111] Refer to GB / T37191-2018 Determination of moisture content of raw rubber, Karl Fischer method.

[0112] 2. Melt index test

[0113] (1) Set the test temperature of the test instrument to 230°C and preheat the instrument; (2) Load 6-8 g of dry polymer into a barrel through a funnel and compact the material with a piston; (3) After heating for 4 min, cut a section every 10 s under a weight of 2.16 kg, and obtain a total of ten sections; (4) Weigh the mass of each sample and calculate its MFR.

[0114] MFR = 600 W / t (g / 10 min), where W is the average mass of each sample segment and t is the cutting time interval of each segment.

[0115] 3. Particle size test

[0116] Place the particles in a 4-10 mesh sieve and use mechanical vibration or manual method to make the particles pass through the sieve until the desired particles are obtained.

[0117] 4. Residual monomer test

[0118] Take about 0.5g of the sample and place it in a sealed container. Accurately add 15ml of hexafluoroisopropanol to dissolve it. After the dissolution is complete, transfer the test solution to a 100ml round-bottom (flat-bottom) flask, add 15ml of hexafluoroisopropanol in a sealed container and brush it clean. Transfer it to the flask, accurately add 10ml of acetone, shake to precipitate the polymer, shake to dissolve, filter, and take the filtrate; take 1μL of the above-mentioned reference solution and test solution respectively, inject them into the gas chromatograph, record the chromatogram, and calculate the content of residual small molecules.

[0119] The raw materials of the following specific examples are: the particle size of the polyglycolic acid chips before entering the drying system is 2.8 mm, the moisture content is 0.2%, the melt index is 80 g / 10 min (230°C, 2.16 kg), the residual monomer is 3%, and the material density of the polyglycolic acid chips is 1.5 g / cm 3 , bulk density 1g / cm 3 .

[0120] In the embodiment, the tower dryer and the first-stage single-axis spiral stirring dryer are both non-standard customized, and the dew point testing equipment is a LY60SP intelligent dew point meter.

[0121] Example 1

[0122] use Figure 1 The drying system shown dries polyglycolic acid slices, wherein a paddle stirring assembly is provided in the buffer silo 1, and the dryer 2 is specifically a first-stage single-axis spiral stirring dryer, the diameter of the vent hole of the hollow spiral conveying shaft is 0.5 mm, the spiral pitch of the hollow spiral conveying shaft is 320 mm, and the gap between the hollow spiral conveying shaft and the shell is 0.5 mm.

[0123] The gas entering the buffer silo is air, the gas dew point temperature at the gas inlet of the buffer silo is -50°C, the buffer silo temperature is 120°C, the stirring speed is 12 rpm, the buffer time is 0.5h, the temperature of the cooler 61 is 40°C, and the gas dew point temperature at the gas outlet of the buffer silo is -25°C;

[0124] The gas entering the dryer is air, the gas dew point temperature at the dryer air inlet is -50°C, the temperature of the single-shaft spiral agitator dryer is 190°C, the material filling rate in the dryer is 60%, the stirring rate is 6 rpm, the dryer jacket temperature is 190°C, the gas dew point temperature at the dryer gas outlet is -35°C, the drying time is 5h, the temperature of the cooler 62 is 40°C, and the temperature in the cooling silo is 60°C;

[0125] The moisture content of the polyester chips after drying was measured to be 0.0028 wt %, the melt index was 24 g / 10 min, and the residual monomer content was 0.3 wt %.

[0126] Example 2

[0127] The polyglycolic acid slices were dried using the same drying system as in Example 1.

[0128] The gas entering the buffer silo is air, the gas dew point temperature at the buffer silo air inlet is -50°C, the buffer silo temperature is 130°C, the stirring speed is 6 rpm, the buffer time is 0.1h, the temperature of the cooler 61 is 40°C, and the gas dew point temperature at the buffer silo gas outlet is -20°C;

[0129] The gas entering the dryer is air, the gas dew point temperature at the dryer air inlet is -50°C, the temperature of the single-axis spiral stirring dryer is 180°C, the material filling rate in the dryer is 85%, the stirring rate is 10 rpm, the jacket temperature is 180°C, the gas dew point temperature at the dryer gas outlet is -20°C, the drying time is 4h, the temperature of the cooler 62 is 60°C, and the temperature in the cooling silo is 60°C;

[0130] The moisture content of the polyester chips after drying was measured to be 0.0035 wt %, the melt index was 31 g / 10 min, and the residual monomer content was 0.6 wt %.

[0131] Example 3

[0132] The polyglycolic acid slices were dried using the same drying system as in Example 1.

[0133] The gas entering the buffer silo is air, the gas dew point temperature at the buffer silo air inlet is -50°C, the buffer silo temperature is 90°C, the stirring speed is 20 rpm, the buffer time is 1h, the temperature of the cooler 61 is 40°C, and the gas dew point temperature at the buffer silo gas outlet is -10°C;

[0134] The gas entering the dryer is air, the gas dew point temperature at the dryer inlet is -50°C, the temperature of the single-axis spiral stirring dryer is 190°C, the material filling rate in the dryer is 70%, the stirring rate is 14 rpm, the jacket temperature is 190°C, the gas dew point temperature at the dryer gas outlet is -10°C, the drying time is 3h, the temperature of the cooler 62 is 50°C, and the temperature in the cooling silo is 50°C;

[0135] The moisture content of the polyester chips after drying was measured to be 0.0041 wt%, the melt index was 38 g / 10 min, and the residual monomer content was 0.5 wt%.

[0136] Example 4

[0137] The polyglycolic acid slices were dried using the same drying system as in Example 1.

[0138] The gas entering the buffer silo is air, the gas dew point temperature at the buffer silo air inlet is -50°C, the buffer silo temperature is 100°C, the stirring speed is 20 rpm, the buffer time is 2h, the temperature of the cooler 61 is 50°C, and the gas dew point temperature at the buffer silo gas outlet is -20°C;

[0139] The gas entering the dryer is air, the gas dew point temperature at the dryer air inlet is -50°C, the temperature of the single-axis spiral stirring dryer is 200°C, the material filling rate in the dryer is 40%, the stirring rate is 28 rpm, the jacket temperature is 200°C, the gas dew point temperature at the dryer gas outlet is -35°C, the drying time is 0.5h, the temperature of the cooler 62 is 60°C, and the temperature in the cooling silo is 60°C;

[0140] The moisture content of the polyester chips after drying was measured to be 0.0046 wt %, the melt index was 47 g / 10 min, and the residual monomer content was 0.9 wt %.

[0141] Example 5

[0142] use Figure 1 The drying system shown is used to dry polyglycolic acid chips, wherein the dryer 2 is specifically a tower dryer with a stirring component.

[0143] The gas entering the buffer silo is air, the gas dew point temperature at the buffer silo air inlet is -50°C, the buffer silo temperature is 120°C, the stirring speed is 10 rpm, the buffer time is 0.5h, the cooler 61 temperature is 50°C, and the gas dew point temperature at the buffer silo gas outlet is -20°C;

[0144] The gas entering the dryer is air, the gas dew point temperature at the dryer inlet is -50°C, the vertical drying tower temperature is 150°C, the material filling rate is 29%, the stirring rate is 20 rpm, the jacket temperature is 150°C, the dryer gas outlet dew point is -30°C, the drying time is 3h, the temperature of the cooler 62 is 60°C, and the temperature in the cooling silo is 60°C;

[0145] The moisture content of the polyester chips after drying was measured to be 0.0029 wt %, the melt index was 28 g / 10 min, and the residual monomer content was 0.4 wt %.

[0146] Example 6

[0147] The polyglycolic acid slices were dried using the same drying system as in Example 5.

[0148] The gas entering the buffer silo is air, the gas dew point temperature at the buffer silo air inlet is -50°C, the buffer silo temperature is 120°C, the stirring speed is 15 rpm, the buffer time is 0.2h, the temperature of the cooler 61 is 50°C, and the gas dew point temperature at the buffer silo gas outlet is -10°C;

[0149] The gas entering the dryer is air, the gas dew point temperature at the dryer inlet is -50°C, the vertical drying tower temperature is 140°C, the material filling rate is 48%, the stirring rate is 20 rpm, the jacket temperature is 140°C, the dryer gas outlet dew point is -30°C, the drying time is 5h, the temperature of the cooler 62 is 60°C, and the temperature in the cooling silo is 60°C;

[0150] The moisture content of the polyester chips after drying was measured to be 0.0038 wt %, the melt index was 41 g / 10 min, and the residual monomer content was 0.7 wt %.

[0151] Comparative Example 1

[0152] The same drying system as in Example 1 is used to dry the polyglycolic acid slices. The difference between this comparative example and Example 1 is that the gas-to-material ratio entering the buffer silo and the gas-to-material ratio entering the dryer are reduced, and the gas dew point temperature at the gas outlet of the buffer silo and the gas dew point temperature at the gas outlet of the dryer are controlled at 0°C.

[0153] The moisture content of the polyester chips after drying was measured to be 0.0048wt%, the melt index was 60g / 10min, and the residual monomer content was 1.3wt%. Although the moisture content of the polyester chips after drying was below 0.005wt%, the residual monomer test results and the melt index test results were significantly higher than the test results of Example 1.

[0154] Comparative Example 2

[0155] The polyglycolic acid slices were dried using the same drying system as in Example 1.

[0156] The buffer silo is only used for the intermediate buffering of incoming polyglycolic acid chips. No low dew point heating gas is passed through it. The stirring speed is 12 rpm and the buffering time is 0.5h.

[0157] The gas entering the dryer is air, the gas dew point temperature at the dryer air inlet is -50°C, the temperature of the single-shaft spiral agitator dryer is 190°C, the material filling rate in the dryer is 60%, the stirring rate is 6 rpm, the dryer jacket temperature is 190°C, the gas dew point temperature at the dryer gas outlet is -35°C, the drying time is 5h, the temperature of the cooler 62 is 60°C, and the temperature in the cooling silo is 60°C;

[0158] The moisture content of the polyester chips after drying was measured to be 0.005 wt %, the melt index was 73 g / 10 min, and the residual monomer content was 1.43 wt %.

[0159] The difference between this comparative example and Example 1 is that the polyester chips are temporarily stored in a buffer silo, the buffer silo is not passed through with low dew point heating gas for pre-dehydration, and the chips are directly dried in a dryer. Although the moisture content of the polyester chips can be reduced to 0.005wt%, the residual monomer test results and the melt index test results are significantly higher than the test results of Example 1.

Claims

1. A polyester chip drying system, characterized in that: The drying system includes a buffer silo, a dryer connected to the outlet of the buffer silo, a first air supply device for continuously introducing gas into the buffer silo, a second air supply device for continuously introducing gas into the dryer, and a dew point testing device arranged at the outlet of the buffer silo and a dew point testing device arranged at the outlet of the dryer. The dryer is provided with a dynamic component for keeping the polyester chips dynamic.

2. The drying system according to claim 1, characterized in that: The first air supply device includes a first heater, the first heater is connected to the air inlet of the buffer silo, and a first stirring component is arranged in the buffer silo; The second air supply device includes a second heater, and the second heater is connected to the air inlet of the dryer.

3. The drying system according to claim 1, characterized in that: The dynamic component includes a hollow screw conveying shaft and a transmission device connected to the hollow screw conveying shaft. The dryer is a single-shaft spiral stirring dryer, which includes a shell, at least one hollow screw conveying shaft arranged in the shell, and at least one transmission device arranged outside the shell, one transmission device is connected to one hollow screw conveying shaft, two adjacent hollow screw conveying shafts are separated by a partition, and the conveying directions of the two adjacent hollow screw conveying shafts are opposite, and a gas material channel is left between the partition and the shell; The shaft body of the last-stage hollow screw conveyor shaft is hollow inside and has air holes on its surface. One end of the shaft body is connected to a rotary joint provided with an air inlet, and the other end is connected to the transmission device. The discharge port of the dryer is arranged below one end of the last-stage hollow screw conveyor shaft close to the air inlet.

4. The drying system according to claims 1 to 3, characterized in that: The drying system further comprises a first gas purification circulation device for purifying and recycling the gas flowing out of the buffer silo; The first gas purification circulation device includes a filter, and a first cooler, a first dehumidifier and a first fan connected to the filter in sequence, the air outlet of the cache silo is connected to the filter, an exhaust port is provided on the pipeline connecting the filter and the first cooler, and the air outlet of the first fan is connected to the first air supply device.

5. The drying system according to any one of claims 1 to 3, characterized in that: The drying system further comprises a second gas purification circulation device for purifying and recycling the gas flowing out of the dryer; The second gas purification circulation device includes a cyclone separator, and a catalytic oxidizer, a second cooler, a second dehumidifier and a second fan connected to the cyclone separator in sequence, the air outlet of the dryer is connected to the cyclone separator, and the air outlet of the second fan is connected to the second air supply device.

6. The drying system according to claim 5, characterized in that: The drying system further comprises a cooling silo connected to the discharge port of the dryer, wherein a spiral coil is arranged in the cooling silo, and a plurality of through holes are arranged on the coil, one end of the coil is an air inlet end, and an air outlet is arranged at the upper part of the cooling silo; The air outlet of the second fan is connected to the air inlet end of the coil, and the air outlet of the cooling silo is connected to the second air supply device.

7. A method for drying polyester chips by a drying system as claimed in any one of claims 1 to 6, characterized in that: The method comprises the steps of: (1) In a buffer silo, a first hot air flow is used to pre-dehumidify the polyester chip raw material to obtain a pre-dehumidified polyester chip; (2) in a dryer, using a second hot air flow to dry the pre-dehumidified polyester chips to obtain dried polyester chips, wherein the drying temperature in the dryer is greater than the buffer temperature in the buffer silo; The gas dew point temperature of the first hot gas flow at the gas outlet of the buffer silo is ≤-10°C; The gas dew point temperature of the second hot gas flow at the gas outlet of the dryer is ≤-10°C.

8. The drying method according to claim 7, characterized in that Step (1) has one or more of the following characteristics: The cache temperature in the cache silo is 90-130°C; The cache time in the cache silo is 0.1 to 2 hours; The gas dew point temperature of the first hot gas flow at the gas outlet of the buffer silo is -40°C to -10°C; The gas dew point temperature of the first hot air flow at the air inlet of the buffer silo is ≤-40°C.

9. The drying method according to claim 7, characterized in that: Step (2) has one or more of the following characteristics: The drying temperature in the dryer is 100°C to 200°C; The drying time in the dryer is 0.5 to 5 hours; The gas dew point temperature of the second hot gas flow at the gas outlet of the dryer is -40°C to -10°C; The gas dew point temperature of the second hot gas flow at the air inlet of the dryer is ≤-40°C.

10. The drying method according to any one of claims 7 to 9, characterized in that: The polyester chip raw material has the following characteristics: The particle size of the polyester chip raw material is ≥1.5mm; The moisture content of the polyester chip raw material is 0.03-0.3wt%; The melt index of the polyester chip raw material is 10 to 80 g / 10 min (230° C., 2.16 kg); The residual monomer content of the polyester chip raw material is 1 to 5 wt%; And the dried polyester chips have the following characteristics: The moisture content of the dried polyester chips is less than 0.008wt%; The melt index of the dried polyester chips is 3 to 50 g / 10 min (230°C, 2.16 kg); The residual monomer content of the dried polyester chips is less than 1 wt%.

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