Closed-circulation polycarbonate flake deep drying and devolatilization device and process

Abstract

The present invention provides a closed-loop polycarbonate flake deep drying and devolatilization device and process, comprising: a primary fluidized bed dryer, a secondary fluidized bed dryer, a ridge-type drying tower, and a barrel-type drying tower. The primary fluidized bed dryer is used to dry wet PC material with a moisture content of 25% to 40% to obtain a primary fluidized bed dryer intermediate product with a moisture content of 10% to 20%; the secondary fluidized bed dryer is connected to the primary fluidized bed dryer to dry the primary fluidized bed dryer intermediate product to obtain a secondary fluidized bed dryer intermediate product with a moisture content of 1% to 8%; the ridge-type drying tower is connected to the secondary fluidized bed dryer to reduce the speed of drying the secondary fluidized bed dryer intermediate product to obtain a ridge-type drying tower intermediate product with a moisture content of ≤1000ppmw; and the barrel-type drying tower is connected to the ridge-type drying tower to deeply dry the ridge-type drying tower intermediate product to obtain a final product with a moisture content of less than 300ppm and a dichloromethane content of less than 100ppm.

Description

Technical Field

[0001] The invention relates to the technical field of polycarbonate production drying and energy saving, and in particular to a nitrogen closed-circulation polycarbonate flake deep drying and devolatilization process and equipment. Background Art

[0002] Polycarbonate (PC) is a high-molecular polymer material with a carbonate base as its basic unit. Due to its unique structure, it has become the fastest-growing general-purpose engineering plastic among the five major engineering plastics. In the domestic production process of polycarbonate (PC), the drying process, as one of the processing steps, is a key process affecting its product quality. On the one hand, the main purpose of the drying process is to control the moisture content and residual volatile methylene chloride in the finished polycarbonate (PC) product, ensuring that the product's moisture content is below 1 / 10,000 and the residual methylene chloride is below 1 / 100,000,000,000, making the product odorless. On the other hand, the high temperature of the material during the drying process prevents contact with oxygen, requiring nitrogen as a drying heat source. Direct nitrogen discharge results in high nitrogen consumption and high costs. Therefore, adopting appropriate drying processes and drying equipment to address these issues has become a key issue in polycarbonate production. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a closed-circulation polycarbonate flake deep drying and devolatilization device, which is characterized by comprising:

[0004] The first-stage fluidized bed dryer dries the wet PC material with a moisture content of 25% to 40% to obtain a first-stage fluidized bed dryer intermediate product with a moisture content of 10% to 20%;

[0005] a secondary fluidized bed dryer connected to the primary fluidized bed dryer for drying the intermediate product of the primary fluidized bed dryer to obtain a secondary fluidized bed dryer intermediate product having a moisture content of 1% to 8%;

[0006] A ridge drying tower is connected to the secondary fluidized bed dryer to reduce the speed of the intermediate product of the secondary fluidized bed dryer to obtain a ridge drying tower intermediate product with a moisture content of ≤1000ppmw;

[0007] The barrel-type drying tower is connected to the ridge-type drying tower to deeply dry the intermediate product of the ridge-type drying tower to obtain a final product with a water content of less than 300 ppm and a dichloromethane content of less than 100 ppm.

[0008] In one embodiment, the primary fluidized bed dryer, the secondary fluidized bed dryer, the ridge-type drying tower, and the barrel-type drying tower are all provided with a material inlet, a drying carrier gas inlet, a gas outlet, and a solid outlet, wherein the primary fluidized bed dryer and the secondary fluidized bed dryer each have multiple drying chambers, and the material inlet, drying carrier gas inlet, gas outlet, and solid outlet of the primary fluidized bed dryer are all connected to the drying chambers thereof, and the material inlet, drying carrier gas inlet, gas outlet, and solid outlet of the secondary fluidized bed dryer are all connected to the drying chambers thereof.

[0009] In one embodiment, a dry carrier gas pipeline system is further provided for providing dry carrier gas, and the dry carrier gas system is respectively connected to the dry carrier gas inlets of the primary fluidized bed dryer, the secondary fluidized bed dryer, the ridge-type drying tower and the barrel-type drying tower.

[0010] In one embodiment, the dry carrier gas pipeline system includes an input pipeline, an output pipeline and a dry carrier gas dehumidification tower, the outlet of the dry carrier gas dehumidification tower is connected to the input pipeline, and the inlet of the dry carrier gas dehumidification tower is connected to the output pipeline. The input pipeline is connected to the dry carrier gas inlets of each of the primary fluidized bed dryer, the secondary fluidized bed dryer, the ridge drying tower and the barrel trough drying tower, and the output pipeline is connected to the gas outlets of each of the primary fluidized bed dryer, the secondary fluidized bed dryer, the ridge drying tower and the barrel trough drying tower. The dry carrier gas dehumidification tower dries the dry carrier gas containing water vapor discharged from the primary fluidized bed dryer, the secondary fluidized bed dryer, the ridge drying tower and the barrel trough drying tower and transported through the output pipeline. The dry carrier gas dehumidification tower dries the dry carrier gas containing water vapor and then transports it to the input pipe for recycling.

[0011] In one embodiment, a first dry carrier gas input device, a second dry carrier gas input device, and a third dry carrier gas input device are further provided, wherein one end of the first dry carrier gas input device is connected to the dry carrier gas inlet of the primary fluidized bed dryer, and the other end is connected to the input pipeline of the dry carrier gas pipeline system;

[0012] One end of the second dry carrier gas input device is connected to the dry carrier gas inlet of the secondary fluidized bed dryer, and the other end is connected to the input pipeline of the dry carrier gas pipeline system;

[0013] One end of the third dry carrier gas input device is connected to the dry carrier gas inlet of the roof-type drying tower, and the other end is connected to the input pipeline of the dry carrier gas pipeline system.

[0014] In one embodiment, the first dry carrier gas input device includes a primary blower and a primary heater, and the dry carrier gas inlet of the primary fluidized bed dryer is connected to the primary blower and the primary heater. The dry carrier gas is pressurized by the primary blower and heated by the primary heater and then delivered to the drying chamber of the primary fluidized bed dryer.

[0015] The second dry carrier gas input device includes a secondary blower and a secondary heater. The dry carrier gas inlet of the secondary fluidized bed dryer is connected to the secondary blower and the secondary heater. The dry carrier gas is pressurized by the secondary blower and heated by the secondary heater and then delivered to the drying chamber of the secondary fluidized bed dryer.

[0016] The third dry carrier gas input device includes a three-stage blower and a three-stage heater. The dry carrier gas inlet of the ridge-type drying tower is connected to the three-stage blower and the three-stage heater. The dry carrier gas is pressurized by the three-stage blower and heated by the three-stage heater and then sent to the ridge-type drying tower.

[0017] In one embodiment, a first solid discharge air conveying system is connected between the solid outlet of the primary fluidized bed dryer and the material inlet of the secondary fluidized bed dryer to transport the intermediate product of the primary fluidized bed dryer to the secondary fluidized bed dryer, and a second solid discharge air conveying system is connected between the discharge port of the ridge-type drying tower and the material inlet of the barrel-type drying tower. The first solid discharge air conveying system is connected to the drying carrier gas pipeline system, and the second solid discharge air conveying system is connected to the drying carrier gas pipeline system.

[0018] In one embodiment, the gas outlet of the primary fluidized bed dryer is connected to a primary gas-solid separation device, and the primary gas-solid separation device is connected to an output pipeline of a dry carrier gas pipeline system and a dry carrier gas dehumidification tower;

[0019] The gas outlet of the secondary fluidized bed dryer is connected to a secondary gas-solid separation device, and the secondary gas-solid separation device is connected to the output pipeline of the dry carrier gas pipeline system and the gas outlet of the secondary fluidized bed dryer.

[0020] In one embodiment, the first solid discharging air conveying system includes a first conveying fan and a first conveying and separation bin, and the second solid discharging air conveying system includes a second conveying fan and a second conveying and separation bin. The first conveying fan and the first conveying and separation bin are connected to the input pipeline of the drying carrier gas pipeline system, wherein the first conveying fan is directly connected to the input pipeline, and the outlet of the first conveying and separation bin is connected to the material inlet of the secondary fluidized bed dryer; the second conveying fan and the second conveying and separation bin are connected to the input pipeline of the drying carrier gas pipeline system, wherein the second conveying fan is directly connected to the input pipeline, the second conveying and separation bin is connected to the inlet of the barrel-type drying tower, and the outlet of the second conveying and separation bin is connected to the output pipeline.

[0021] In one embodiment, the material inlet and gas outlet of the ridge type drying tower are located at the top of the ridge type drying tower, and the dry carrier gas inlet and solid outlet of the ridge type drying tower are located at the bottom of the ridge type drying tower. The material inlet of the ridge type drying tower is connected to the solid outlet of the secondary fluidized bed dryer. The intermediate product of the secondary fluidized bed dryer enters the interior of the ridge type drying tower from the top of the ridge type drying tower, and the dry carrier gas enters the ridge type drying tower from the bottom of the ridge type drying tower.

[0022] In one embodiment, the ridge-type drying tower has six drying sections, which are sequentially arranged from top to bottom with a first drying section, a second drying section, a third drying section, a fourth drying section, a fifth drying section, and a sixth drying section which are mutually closed. Adjacent drying sections are connected to a circulation pipeline, and an inter-section blower and an inter-section heater are provided on the circulation pipeline. The sixth drying section is connected to a three-stage blower and a three-stage heater. Part of the dry carrier gas from the dehumidification tower is pressurized by a three-stage blower and heated by a three-stage heater, and then enters the ridge-type drying tower from the sixth drying section at the bottom of the ridge-type drying tower. The dry carrier gas of the next stage is pressurized by an inter-section blower and heated by an inter-section heater, and then enters the previous drying section. The gas outlet is arranged in the first drying section, and the gas outlet is connected to the first-stage blower of the first-stage fluidized bed dryer.

[0023] In one embodiment, a supplementary pipeline for supplementing dry carrier gas is provided on the side of the barrel-type drying tower, and the supplementary pipeline is provided with a heater. A circulation pipeline and a material inlet are provided on the top of the barrel-type drying tower. The material inlet and the circulation pipeline are connected to the side of the barrel-type drying tower. The circulation pipeline is provided with a heater, a third conveying fan and a bag dust collector. The circulation pipeline is connected to the input pipeline of the dry carrier gas pipeline system.

[0024] In one embodiment, the top of the drying carrier gas dehumidification tower is connected to the input pipeline, and the bottom of the drying carrier gas dehumidification tower is connected to the output pipeline. A first cold water circulation pipeline for spraying cooling water is provided at the top of the drying carrier gas dehumidification tower, and both ends of the first cold water circulation pipeline are connected to the drying carrier gas dehumidification tower. The first cold water circulation pipeline is provided with a primary cooler and a primary circulation pump. A second cold water circulation pipeline for cooling the hot water at the bottom of the dehumidification tower is provided at the bottom of the drying carrier gas dehumidification tower, and both ends of the second cold water circulation pipeline are connected to the drying carrier gas dehumidification tower. The second cold water circulation pipeline is provided with a secondary cooler and a secondary circulation pump. The secondary cooler cools the bottom hot water and inputs it into the drying carrier gas dehumidification tower for reuse through the secondary circulation pump. The second cold water circulation pipeline is connected to a sewage discharge pipeline.

[0025] The present invention also provides a closed-cycle polycarbonate flake deep drying and devolatilization process, which is characterized by:

[0026] Step S1, feeding wet PC material with a moisture content of 25% to 40% into a primary fluidized bed dryer for drying to obtain a primary fluidized bed dryer intermediate product with a moisture content of 10% to 20%;

[0027] Step S2, feeding the intermediate product of the primary fluidized bed dryer into a secondary fluidized bed dryer for drying to obtain a secondary fluidized bed dryer intermediate product having a moisture content of 1% to 8%;

[0028] Step S3, feeding the intermediate product of the secondary fluidized bed dryer into a ridge-type drying tower for speed reduction drying to obtain an intermediate product of the ridge-type drying tower with a moisture content of ≤1000 ppmw;

[0029] In step S4, the intermediate product of the ridge drying tower is sent to a barrel drying tower for deep drying to obtain a final product with a water content of less than 300 ppm and a dichloromethane content of less than 100 ppm.

[0030] In one embodiment, in step S1, wet PC material with a water content of 25% to 35% is pressurized by a first-stage blower and heated by a first-stage heater (16) and then sent to a drying chamber of a first-stage fluidized bed dryer for drying.

[0031] In one embodiment, in step S1, the dry carrier gas is further included in the drying chamber of the first-stage fluidized bed dryer after passing through the first-stage blower and the first-stage heater in sequence, and the dry carrier gas exchanges heat and mass with the wet PC material with a water content of 25% to 35%.

[0032] In one embodiment, step S1 further includes converting the dry carrier gas into a first-level mixed wet carrier gas containing moisture and a small amount of PC particles through heat and mass transfer with the wet PC material, separating the entrained PC particles from the first-level mixed wet carrier gas through a first-level cyclone separator to obtain a first-level wet carrier gas, and recycling part of the first-level wet carrier gas to the inlet of the first-level blower as a dry carrier gas, and sending the other part of the first-level wet carrier gas to a dehumidification tower for drying through a dehumidification induced draft fan.

[0033] In one embodiment, in step S2, the intermediate product of the primary fluidized bed dryer obtained after step S1 is first subjected to gas-solid separation to obtain solid material and gaseous material. The solid material enters the drying chamber 02 of the secondary fluidized bed dryer, and the gaseous material enters the secondary dust collector 31 and is then mixed with the exhaust gas from the secondary fluidized bed dryer 02; the solid material enters the drying chamber 02 of the secondary fluidized bed dryer.

[0034] In one embodiment, in step S2, the dry carrier gas is further pressurized by a secondary blower and heated by a secondary heater and then sent to the drying chamber of the secondary fluidized bed dryer 02, and heat and mass are exchanged with the intermediate product of the primary fluidized bed dryer entering the drying chamber of the secondary fluidized bed dryer. When the moisture content of the intermediate product of the primary fluidized bed dryer is reduced to 1% to 8%, it is discharged from the secondary fluidized bed dryer.

[0035] In one embodiment, in step S2, the dry carrier gas is converted into a secondary mixed wet carrier gas containing a small amount of PC particles and moisture through heat and mass transfer with the wet PC material, and the secondary mixed wet carrier gas is separated from the entrained PC particles by a secondary cyclone separator to obtain a secondary wet carrier gas, and part of the secondary wet carrier gas is recycled to the inlet of the first blower as the dry carrier gas of the first fluidized bed drying chamber 01, and the other part of the secondary wet carrier gas is sent to the inlet of the second blower, mixed with part of the dehumidified carrier gas from the dehumidification tower, and used as the dry carrier gas of the drying chamber 02 of the secondary fluidized bed dryer.

[0036] In one embodiment, in step S3, the secondary fluidized bed dryer intermediate product from the secondary fluidized bed dryer 02 enters from the top of the ridge-type drying tower 03, and part of the dehumidified carrier gas from the dehumidification tower 05 is pressurized by the three-stage blower 09 and heated by the three-stage heater 18 and then enters the drying tower from the bottom of the ridge-type drying tower 03.

[0037] In one embodiment, step S3 further includes each drying section being equipped with an inter-section blower (10-14) and an inter-section heater (19-23). ​​Dry carrier gas enters the ridge-type drying tower from bottom to top. The inter-section blower extracts dry carrier gas from the previous drying section of the ridge-type drying tower 03, and after being heated to 100 to 140° C. by the inter-section heater, the dry carrier gas enters the next drying section of the ridge-type drying tower 03, where it comes into contact with and dries the solid material entering the ridge-type drying tower from top to bottom.

[0038] In one embodiment, in step S3, the ridge-type drying tower 03 is further included as having six drying sections, namely, the first drying section, the second drying section, the third drying section, the fourth drying section, the fifth drying section, and the sixth drying section from top to bottom. The wet carrier gas discharged from the sixth drying section is pressurized by the inter-section blower 15 and heated by the inter-section heater 23 and then enters the fifth drying section of the drying tower. The wet carrier gas discharged from the fifth drying section enters the fourth to the first drying sections in sequence and contacts and dries with the intermediate product of the secondary fluidized bed dryer. The intermediate product of the secondary fluidized bed dryer is dried in the six drying sections of the ridge-type drying tower 03 to obtain a ridge-type drying tower intermediate product with a water content of 500 to 1000 ppm.

[0039] In one embodiment, step S4 further includes separating the intermediate product of the ridge drying tower through a separation silo to obtain a solid material, and then sending the solid material to the barrel drying tower 04 for drying. In the barrel drying tower 04, the solid material is contacted with the dry carrier gas entering the barrel drying tower 04 to remove moisture to obtain a final product with a water content of less than 300 ppm and a dichloromethane content of less than 100 ppm.

[0040] In one embodiment, in step S4, the dry carrier gas entering the barrel-type drying tower 04 is heated to 100° C. by a heater and then enters from the bottom side of the barrel-type drying tower. The hot dry carrier gas entering the barrel-type drying tower 04 contacts the solid material, and the dry carrier gas absorbs the moisture of the solid material to become a wet hot carrier gas. The wet hot carrier gas is discharged through a pressure control valve arranged at the top of the barrel-type drying tower. The wet hot carrier gas is then dusted by a bag dust collector 33, and then pressurized by a circulating fan 15 and heated by a circulating heater 26 before returning to the barrel-type drying tower 04.

[0041] In one embodiment, in step S1, the first-level wet carrier gas is also sent into the dehumidification tower 05 under the action of the dehumidification induced draft fan 37, and is directly contacted with the cooling water sprayed from the top of the tower to complete cooling and dehumidification to obtain dehumidified carrier gas. The dehumidified carrier gas is discharged from the top of the dehumidification tower and is divided into four streams, which are respectively sent to the inlet of the secondary blower 07, the first-level conveying fan 08, the third-level blower 09 and the secondary conveying fan 36 for recycling as dry carrier gas.

[0042] The primary and secondary fluidized bed dryers used in the present invention are pulsed fluidized bed dryers, suitable for drying heat-sensitive bulk materials. The bulk material is placed on a perforated plate, and gas is transported from its lower portion, causing the material particles to move on the gas distribution plate and become suspended in the airflow. A pulsed rotary airflow distributor then periodically supplies air. By adjusting the pulse frequency and pulsed airflow conductivity of the airflow, the gas flow rate or fluidized zone through the perforated plate undergoes periodic changes, drying the material. This effectively overcomes drawbacks such as channeling, dead zones, and local overheating, and offers advantages such as an enhanced heat transfer coefficient and a shortened residence time. This equipment consists of a fluidizing section, an airflow distributor, a top settling section, an air supply cone, a rotary airflow distributor, and other major components. The gas distribution plate is the core of the equipment and is key to the proper operation of the system.

[0043] The ridge-type drying tower used in this invention is composed of multiple layers of staggered, roof-shaped pipes, forming a vertical, closed box structure. This drying tower features multiple units that can be used in series, a long residence time, a compact structure, and a long service life. It is particularly suitable for drying flaky materials and achieves a high drying depth.

[0044] The barrel-type drying tower employed in this invention operates on the principle that material is continuously fed into the drying tower from the top of the dryer, where it descends in a moving bed fashion under its own weight. Hot nitrogen enters the barrel-type drying tower through a hot nitrogen distribution plate at the bottom. To maintain a steady flow of material, the barrel-type drying tower is equipped with an inner tube and a distribution plate. The inner tube is mounted within the barrel of the barrel-type drying tower. The special structure of the distribution plate and inner tube ensures uniform contact between the material and the hot nitrogen, resulting in a uniform product. It is primarily used for deep devolatilization and drying of particulate materials. Its key characteristic is that the drying process requires very little heat but a very long drying time. The material has already been dried to a very low moisture content by the pre-drying system. At this point, the material has already spent a certain amount of time in the deceleration drying stage and has been heated to or above the required evaporation temperature by the pre-drying system. At this temperature, the moisture in the material slowly evaporates, lowering the material temperature. The hot nitrogen permeates the entire barrel (drying tower), enveloping the material, flowing slowly from bottom to top at an extremely low flow rate. The evaporated moisture in the material slowly diffuses into the nitrogen and is carried out of the silo by the nitrogen. The hot nitrogen in the barrel (drying tower) only needs to provide a small amount of heat required for the evaporation of water to ensure that the material stays at this temperature for a long time, ensuring that the material evaporates to the required drying requirements.

[0045] The present invention has the following advantages: adopting a nitrogen countercurrent circulation drying process improves the thermal efficiency of nitrogen, reduces the nitrogen consumption in the drying process, and reduces the operating cost; selecting high-efficiency dryers such as ridge-type drying towers and barrel-type drying towers meets the requirements of deep drying and devolatilization of materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0047] Figure 1 It is a schematic diagram of the process flow of the present invention.

[0048] Figure 2 Schematic diagram of the pulse fluidized bed dryer structure.

[0049] Figure 3 Schematic diagram of the ridge-type drying tower structure.

[0050] Figure 4 Schematic diagram of a barrel drying tower.

[0051] Reference numerals: 01—first stage fluidized bed dryer;

[0052] 010 gas outlet, 011 gas distribution plate, 012 drying carrier gas inlet, 013 solid outlet, 014 air flow distributor; 015 material inlet; 016 partition plate, 017 branch air inlet pipe, 018 inverted conical groove, 019 drying chamber;

[0053] 02—Secondary fluidized bed dryer;

[0054] 03—Ridge type drying tower

[0055] 030 first drying section; 031 second drying section; 032 third drying section; 033 fourth drying section; 034 fifth drying section; 035 sixth drying section; 035 air inlet, 037 air outlet, 038 solid outlet, 039 material inlet;

[0056] 04—Barrel trough drying tower

[0057] 040, material inlet; 041 cylinder; 0410 inner tube; 042 gas distribution plate; 043 box; 044 hot air inlet; 045 hot air outlet; 046 pore; 047 solid outlet;

[0058] 05 Drying carrier gas dehumidification tower; 06-First stage blower; 07-Second stage blower; 08-First conveying fan; 09-Third stage blower; 10-Intersection blower; 11-Intersection blower; 12-Intersection blower; 13-Intersection blower; 14-Intersection blower; 15-Circulating fan; 16-First stage heater; 17-Second stage heater; 18-Third stage heater; 19-Intersection heater; 20-Intersection heater; 21-Intersection heater Heater; 22 - Inter-stage heater; 23 - Inter-stage heater; 24 - Preheater; 25 - Nitrogen heater; 26 - Circulation heater; 27 - Secondary cooler; 28 - Primary cooler; 29 - Primary cyclone dust collector; 30 - First conveying and separation bin; 31 - Secondary dust collector; 32 - Second conveying and separation bin; 33 - Bag dust collector; 34 - Secondary circulation pump; 35 - Primary circulation pump; 36 - Secondary conveying fan; 37 - Dehumidification induced draft fan;

[0059] 100-Dry carrier gas pipeline system;

[0060] 1001 input pipeline;

[0061] 1002 output pipeline. DETAILED DESCRIPTION

[0062] The detailed description and technical contents of the present invention are described as follows with reference to the accompanying drawings:

[0063] The closed-loop polycarbonate flake deep drying and devolatilization device provided by the present invention is characterized in that it includes: a primary fluidized bed dryer 01, a secondary fluidized bed dryer 02, a ridge-type drying tower, and a barrel-type drying tower 04. The primary fluidized bed dryer 01 is used to dry wet PC materials with a moisture content of 25% to 40% to obtain the primary fluidized bed dryer 01 intermediate product with a moisture content of 10% to 20%; the secondary fluidized bed dryer 02 is connected to the primary fluidized bed dryer 01 to dry the primary fluidized bed dryer 01 intermediate product. Drying is performed to obtain an intermediate product of the secondary fluidized bed dryer 02 with a moisture content of 1% to 8%; a ridge-type drying tower 03 is connected to the secondary fluidized bed dryer 02 to perform speed reduction drying on the intermediate product of the secondary fluidized bed dryer 02 to obtain an intermediate product of the ridge-type drying tower 03 with a moisture content of ≤1000ppmw; a barrel-type drying tower 04 is connected to the ridge-type drying tower 03 to perform deep drying on the intermediate product of the ridge-type drying tower 03 to obtain a final product with a moisture content of less than 300ppm and a dichloromethane content of less than 100ppm.

[0064] The first-stage fluidized bed dryer 01, the second-stage fluidized bed dryer 02, the ridge-type drying tower 03, and the barrel-type drying tower 04 are all provided with a material inlet, a drying carrier gas inlet, a gas outlet, and a solid outlet. The first-stage fluidized bed dryer 01 and the second-stage fluidized bed dryer 02 both have a plurality of drying chambers 019. The material inlet, drying carrier gas inlet, gas outlet, and solid outlet of the first-stage fluidized bed dryer 01 are all connected to the drying chambers thereof, and the material inlet, drying carrier gas inlet, gas outlet, and solid outlet of the second-stage fluidized bed dryer 02 are all connected to the drying chambers thereof.

[0065] See also Figure 2 , Figure 2 The structure diagram of the fluidized bed dryer is shown in FIG. 1 . The present application adopts a first-stage fluidized bed dryer 01 and a second-stage fluidized bed dryer 02. Both have the same structure. The first-stage fluidized bed dryer 01 is used as an example. The fluidized bed dryer includes a gas outlet 010, a gas distribution plate 011, a dry carrier gas inlet 012, a solid outlet 013, an air flow distributor 014, and a material inlet 015. The wet PC material with a water content of 25% to 35% enters from the material inlet 015. The wet PC material with a water content of 25% to 35% is a bulk material. The bulk material is placed on the gas distribution plate 011. The gas distribution plate is a perforated plate with partitions 016 spaced apart on the perforated plate. An inverted conical groove 018 is provided below the gas distribution plate. The air flow distributor is provided with a circular tube. Channel 020 and multiple branch air inlet pipes 017, the multiple branch air inlet pipes 017 are connected to the circular pipe 020 along the circumference of the circular pipe 020, one end of each branch air inlet pipe 017 is connected to the circular pipe and the other end extends into the inverted conical groove 018, the circular pipe 020 is connected to the dry carrier gas inlet of the first-stage fluidized bed dryer 01, the dry carrier gas enters the circular pipe 020 from the dry carrier gas inlet and then enters the inverted conical groove 018 through multiple branch air inlet pipes 017. For example, the dry carrier gas of the present application is blown from bottom to top toward the gas distribution plate, the bulk material passes over the partition 016 and gathers toward the solid outlet, and is discharged through the solid outlet, and the dried wet dry carrier gas and other particulate matter are discharged from the gas outlet 010.

[0066] The drying and devolatilization device has a drying carrier gas pipeline system 100 for providing a drying carrier gas, and the drying carrier gas system is respectively connected to the drying carrier gas inlets of the first-stage fluidized bed dryer 01, the second-stage fluidized bed dryer 02, the first-stage fluidized bed dryer and the barrel-type drying tower 04. During the drying process, dry nitrogen at a certain temperature is used as a drying medium, and the nitrogen is recycled to ensure good economic performance of the system. The drying carrier gas pipeline system includes an input pipeline 1001, an output pipeline 1002 and a drying carrier gas dehumidification tower 05, the outlet of the drying carrier gas dehumidification tower 05 is connected to the input pipeline, the inlet of the drying carrier gas dehumidification tower is connected to the output pipeline, the input pipeline is connected to the drying carrier gas inlets of each of the first-stage fluidized bed dryer 01, the second-stage fluidized bed dryer 02, the ridge-type drying tower 03 and the barrel-type drying tower 04, and the output pipeline is connected to each of the first-stage fluidized bed dryer 01, the second-stage fluidized bed dryer 02, the ridge-type drying tower 03 and the barrel-type drying tower 04. The gas outlets of the fluidized bed dryer 01, the secondary fluidized bed dryer 02, the ridge type drying tower 03 and the barrel type drying tower 04 are connected. The dry carrier gas dehumidification tower dries the dry carrier gas containing water vapor discharged from the primary fluidized bed dryer 01, the secondary fluidized bed dryer 02, the ridge type drying tower 03 and the barrel type drying tower 04 through the output pipeline. The dry carrier gas dehumidification tower dries the dry carrier gas containing water vapor and then transports it to the input pipe for recycling.

[0067] The drying and devolatilization device is also provided with a first drying carrier gas input device, a second drying carrier gas input device and a third drying carrier gas input device. One end of the first drying carrier gas input device is connected to the drying carrier gas inlet of the first-level fluidized bed dryer 01, and the other end is connected to the input pipeline of the drying carrier gas pipeline system; one end of the second drying carrier gas input device is connected to the drying carrier gas inlet of the second-level fluidized bed dryer 02, and the other end is connected to the input pipeline of the drying carrier gas pipeline system; one end of the third drying carrier gas input device is connected to the drying carrier gas inlet of the roof-type drying tower 03, and the other end is connected to the input pipeline of the drying carrier gas pipeline system. The first dry carrier gas input device includes a primary blower 06 and a primary heater 16. The dry carrier gas inlet of the primary fluidized bed dryer 01 is connected to the primary blower 06 and the primary heater 16. The dry carrier gas is pressurized by the primary blower 06 and heated by the primary heater 16 and then sent to the drying chamber of the primary fluidized bed dryer 01. The second dry carrier gas input device includes a secondary blower 07 and a secondary heater 17. The dry carrier gas inlet of the secondary fluidized bed dryer 02 is connected to the secondary blower 06 and the primary heater 16. The dry carrier gas is pressurized by the secondary blower 07 and heated by the secondary heater 17 and then sent to the drying chamber of the secondary fluidized bed dryer 02; the third dry carrier gas input device includes a third blower 09 and a third heater 18, and the dry carrier gas inlet of the ridge-type drying tower 03 is connected to the third blower 09 and the third heater 18, and the dry carrier gas is pressurized by the third blower 09 and heated by the third heater 18 and then sent to the roof-type drying tower 03.

[0068] A first solid discharging air conveying system is connected between the solid outlet of the first-level fluidized bed dryer 01 and the material inlet of the second-level fluidized bed dryer 02 to transport the intermediate product of the first-level fluidized bed dryer 01 to the second-level fluidized bed dryer 02. A second solid discharging air conveying system is connected between the discharge port of the ridge-type drying tower 03 and the material inlet of the barrel-type drying tower 04. The first solid discharging air conveying system is connected to the drying carrier gas pipeline system, and the second solid discharging air conveying system is connected to the drying carrier gas pipeline system.

[0069] The gas outlet of the first-level fluidized bed dryer 01 is connected to the first-level gas-solid separation device, and the first-level gas-solid separation device is connected to the output pipeline of the dry carrier gas pipeline system and the dry carrier gas dehumidification tower; the gas outlet of the second-level fluidized bed dryer 02 is connected to the second-level gas-solid separation device, and the second-level gas-solid separation device is connected to the output pipeline of the dry carrier gas pipeline system and the gas outlet of the second-level fluidized bed dryer 02.

[0070] The first solid discharging air conveying system includes a first conveying fan 08 and a first conveying and separation bin 30, and the second solid discharging air conveying system includes a second conveying fan 36 and a second conveying and separation bin 32. The first conveying fan 08 and the first conveying and separation bin 30 are connected to the input pipeline of the drying carrier gas pipeline system, wherein the first conveying fan 08 is directly connected to the input pipeline, and the outlet of the first conveying and separation bin 30 is connected to the material inlet of the secondary fluidized bed dryer 02; the second conveying fan 36 and the second conveying and separation bin 32 are connected to the input pipeline of the drying carrier gas pipeline system, wherein the second conveying fan 36 is directly connected to the input pipeline, the second conveying and separation bin 32 is connected to the inlet of the barrel-type drying tower 04, and the outlet of the second conveying and separation bin 32 is connected to the output pipeline.

[0071] The material inlet and gas outlet of the ridge-type drying tower 03 are located at the top of the ridge-type drying tower 03, and the dry carrier gas inlet and solid outlet of the ridge-type drying tower 03 are located at the bottom of the ridge-type drying tower 03. The material inlet of the ridge-type drying tower 03 is connected to the solid outlet of the secondary fluidized bed dryer 02. The intermediate product of the secondary fluidized bed dryer 02 enters the interior of the ridge-type drying tower 03 from the top of the ridge-type drying tower 03, and the dry carrier gas enters the ridge-type drying tower 03 from the bottom of the ridge-type drying tower 03 upward.

[0072] See also Figure 3 , Figure 3 Schematic diagram of the ridge-type drying tower structure. The ridge-type drying tower 03 is composed of multiple layers of pipes similar to the shape of a ridge arranged in a staggered manner, forming a vertical closed box structure.

[0073] The characteristics of this drying tower are that multiple drying sections can be used in series, the residence time is long, the material is not easy to be pulverized and broken, the structure is compact, and the service life is long. It is very suitable for drying flaky materials and has a high drying depth. The ridge-type drying tower 03 has six drying sections, which are sequentially provided from bottom to top with the first drying section 030, the second drying section 031, the third drying section 032, the fourth drying section 033, the fifth drying section 034, and the sixth drying section 035, which are mutually closed. Circulation pipelines are connected between adjacent drying sections. In this embodiment, the first drying section 030 is provided with an air inlet 036, the second drying section is provided with an air outlet 037, the third drying section 032 is provided with an air inlet, the fourth drying section is provided with an air outlet, the fifth drying section is provided with an air inlet, and the sixth drying section is provided with an air outlet. The circulation pipeline is provided with inter-section blowers (10-14) and inter-section heaters (19-23). The sixth drying section is connected to the three-stage blower 09 and the three-stage heater 18. Part of the dry carrier gas from the dehumidification tower 05 is pressurized by the three-stage blower 09 and heated by the three-stage heater 18, and then enters the ridge-type drying tower 03 from the sixth drying section at the bottom of the ridge-type drying tower 03. The dry carrier gas of the next stage enters the previous drying section after being pressurized by the inter-stage blower and heated by the inter-stage heater. The gas outlet is set in the first drying section 030, and the gas outlet is connected to the first blower 06 of the first fluidized bed dryer 01. A feed pipe with a material inlet 039 is connected above the sixth drying section, and a conical tube with a solid outlet 038 is connected below the first drying section 030.

[0074] See also Figure 4 , Figure 4 This is a schematic diagram of the structure of a barrel-type drying tower. A supplementary pipeline for supplementing dry carrier gas is provided on the side of the barrel-type drying tower 04. The supplementary pipeline is provided with a heater. A circulation pipeline is provided on the top of the barrel-type drying tower 04. The circulation pipeline is connected to the side of the barrel-type drying tower 04. A heater, a third conveying fan and a bag dust collector 33 are provided on the circulation pipeline. The circulation pipeline is connected to the input pipeline of the dry carrier gas pipeline system.

[0075] The barrel-type drying tower 04 comprises a cylinder, an inner tube, a gas distribution plate, and a housing. The inner tube is located within the cylinder, with its ends forming a cone and a cylindrical middle section. The lower conical surface of the inner tube is interspersed with apertures 046, through which solid material enters the housing. The gas distribution plate is a cone, the top of which snaps into the housing. The gas distribution plate within the housing is equipped with ventilation holes. The housing has three layers, with the inner layers interconnected. Each layer has a hot air inlet 044. The material inlet is a feed pipe located at the top of the barrel-type drying tower 04. A hot air outlet 45 is also located at the top of the barrel-type drying tower 04. The feed pipe extends into the cylinder, with its outlet facing the inner tube. The bottom of the housing serves as the solids outlet.

[0076] Material is continuously fed into the barrel-type drying tower 04 through the top material inlet of the dryer. It descends in a moving bed pattern under its own weight, while a hot drying carrier gas, such as nitrogen, enters the trough through a gas distribution plate at the bottom. To maintain a steady flow of material, an inner tube is installed within the dryer cylinder. The special structure of the distribution plate and inner tube ensures uniform contact between the material and the hot nitrogen, resulting in a uniform product. This method is primarily used for deep devolatilization and drying of particulate materials. Its key characteristics are low heat requirements but long drying times. The material has already been dried to a very low moisture content by the pre-drying system. At this point, the material has already spent a certain amount of time in the deceleration drying section, having been heated to or above the required evaporation temperature by the pre-drying system. At this temperature, the moisture in the material slowly evaporates, lowering the material temperature. The hot nitrogen permeates the entire barrel-type drying tower 04, enveloping the material and flowing slowly from bottom to top at an extremely low flow rate. The evaporated moisture in the material slowly diffuses into the nitrogen and is carried out of the barrel-type drying tower 04 by the nitrogen. The hot nitrogen in the barrel drying tower 04 only needs to provide a small amount of heat required for the evaporation of water to ensure that the material stays at this temperature for a long time, ensuring that the material evaporates to the required drying requirements.

[0077] The top of the drying carrier gas dehumidification tower 05 is connected to the input pipeline, and the bottom of the drying carrier gas dehumidification tower 05 is connected to the output pipeline. The top of the drying carrier gas dehumidification tower 05 is provided with a first cold water circulation pipeline for spraying cooling water. The two ends of the first cold water circulation pipeline are connected to the drying carrier gas dehumidification tower 05. The first cold water circulation pipeline is provided with a primary cooler 28 and a primary circulation pump 35. A second cold water circulation pipeline for cooling the hot water at the bottom of the dehumidification tower is provided at the bottom of the drying carrier gas dehumidification tower 05. The two ends of the second cold water circulation pipeline are connected to the drying carrier gas dehumidification tower 05. The second cold water circulation pipeline is provided with a secondary cooler 27 and a secondary circulation pump 34. The secondary cooler 27 cools the bottom hot water and inputs it into the drying carrier gas dehumidification tower 05 for reuse through the secondary circulation pump. The second cold water circulation pipeline is connected to a sewage discharge pipeline.

[0078] The first and second stage fluidized bed dryers 02 used in the present invention are pulsed fluidized bed dryers. The first and second stage fluidized bed dryers 02 are suitable for drying heat-sensitive bulk materials. The basic structure is as follows: Figure 1As shown, the pulse fluidized bed dryer is provided with a gas distribution plate, the solid outlet is arranged on the upper side of the gas distribution plate, a plurality of spaced partitions are provided on the gas distribution plate, a plurality of inverted conical grooves arranged side by side are provided below the gas distribution plate, and an air flow distributor is provided below the inverted conical grooves, which is connected to the dry carrier gas inlet, and the air flow distributor is provided with a circular pipe and a plurality of branch air inlet pipes 017, and the plurality of branch air inlet pipes 017 are arranged in a circumferential rotation along the circular pipe. The air flow distributor is a rotating air flow distributor, and the branch air inlet pipes 017 extend into the inverted conical grooves, and the dry carrier gas is input into the inverted conical grooves from the branch air inlet pipes 017. The dry carrier gas moves from bottom to top and impacts the gas distribution plate, causing the material particles to move on the gas distribution plate and be suspended in the air flow. The material particles pass through the partitions step by step and are discharged from the solid outlet. The pulse rotary air flow distributor supplies air periodically and adjusts the pulse frequency and pulse air flow conductivity of the air flow to make the gas flow or fluidized area through the orifice plate change periodically, thereby drying the material. It can effectively overcome the disadvantages of channel flow, dead zone and local overheating, and has the advantages of enhanced heat transfer coefficient and shortened residence time.

[0079] The invention provides a closed-cycle deep drying and devolatilization process for polycarbonate flakes, characterized in that:

[0080] Step S1, feeding the wet PC material with a moisture content of 25% to 35% into the primary fluidized bed dryer 01 for drying to obtain the primary fluidized bed dryer 01 intermediate product with a moisture content of 10% to 20%;

[0081] Step S2, feeding the intermediate product of the primary fluidized bed dryer 01 into the secondary fluidized bed dryer 02 for drying to obtain the intermediate product of the secondary fluidized bed dryer 02 with a moisture content of 1% to 8%;

[0082] Step S3: feeding the intermediate product of the secondary fluidized bed dryer 02 into a ridge-type drying tower for speed reduction drying to obtain a ridge-type drying tower intermediate product with a moisture content of ≤1000 ppmw;

[0083] In step S4, the intermediate product of the ridge drying tower is sent to the barrel drying tower 04 for deep drying to obtain a final product with a water content of less than 300 ppm and a dichloromethane content of less than 100 ppm.

[0084] In step S1 , wet PC material with a water content of 25% to 35% is pressurized by the primary blower 06 and heated by the primary heater 16 and then sent to the drying chamber of the primary fluidized bed dryer 01 for drying.

[0085] In step S1, the dry carrier gas passes through the first-level blower 06 and the first-level heater in sequence and enters the drying chamber of the first-level fluidized bed dryer 01 as the dry carrier gas, and the dry carrier gas exchanges heat and mass with the wet PC material containing 25% to 35% water.

[0086] In step S1, the dry carrier gas is converted into a first-level mixed wet carrier gas containing moisture and a small amount of PC particles through heat and mass transfer with the wet PC material. The first-level mixed wet carrier gas is separated from the entrained PC particles by a first-level cyclone separator to obtain a first-level wet carrier gas, and part of the first-level wet carrier gas is recycled to the inlet of the first-level blower 06 as a dry carrier gas, and the other part of the first-level wet carrier gas is sent to the dehumidification tower for drying through the dehumidification induced draft fan.

[0087] In step S2, the intermediate product of the primary fluidized bed dryer 01 obtained after step S1 is first subjected to gas-solid separation to obtain solid material and gaseous material. The solid material enters the drying chamber 02 of the secondary fluidized bed dryer 02, and the gaseous material enters the secondary dust collector 31 and is then mixed with the exhaust gas from the secondary fluidized bed dryer 0202; the solid material enters the drying chamber 02 of the secondary fluidized bed dryer 02.

[0088] In step S2, the dry carrier gas is pressurized by the secondary blower 07 and heated by the secondary heater 17 and then sent to the drying chamber of the secondary fluidized bed dryer 0202, and heat and mass transfer is carried out with the intermediate product of the primary fluidized bed dryer 01 entering the drying chamber of the secondary fluidized bed dryer 02. When the moisture content of the intermediate product of the primary fluidized bed dryer 01 drops to 1% to 8%, it is discharged from the secondary fluidized bed dryer 02.

[0089] In step S2, the dry carrier gas is converted into a secondary mixed wet carrier gas containing a small amount of PC particles and moisture through heat and mass transfer with the wet PC material. The secondary mixed wet carrier gas is separated from the entrained PC particles by a secondary cyclone separator to obtain a secondary wet carrier gas, and part of the secondary wet carrier gas is recycled to the inlet of the first blower 06 as the dry carrier gas of the first fluidized bed drying chamber 01, and the other part of the secondary wet carrier gas is sent to the inlet of the second blower 07, mixed with part of the dehumidified carrier gas from the dehumidification tower, and used as the dry carrier gas of the drying chamber of the second fluidized bed dryer 02.

[0090] In step S3, the secondary fluidized bed dryer intermediate product from the secondary fluidized bed dryer 02 enters from the top of the ridge-type drying tower 03, and part of the dehumidified carrier gas from the dehumidification tower 05 is pressurized by the third-stage blower 09 and heated by the third-stage heater 18 before entering the drying tower from the bottom of the ridge-type drying tower 03.

[0091] In step S3, each drying section is equipped with inter-section blowers 10-14 and inter-section heaters 19-23. Dry carrier gas enters the ridge drying tower from bottom to top. The inter-section blowers draw dry carrier gas from the previous drying section of the ridge drying tower 03, heat it to 100 to 140°C through the inter-section heaters, and then enter the next drying section of the ridge drying tower 03 to come into contact with and dry the solid material entering the ridge drying tower from top to bottom.

[0092] In step S3, it also includes that the ridge-type drying tower 03 has six drying sections, which are, from top to bottom, the first drying section 030, the second drying section 031, the third drying section 032, the fourth drying section, the fifth drying section, and the sixth drying section. The wet carrier gas discharged from the sixth drying section is pressurized by the inter-section blower 15 and heated by the inter-section heater 23 and then enters the fifth drying section of the drying tower. The wet carrier gas discharged from the fifth drying section enters the fourth to first drying sections 030 in sequence and contacts and dries with the intermediate product of the secondary fluidized bed dryer. The intermediate product of the secondary fluidized bed dryer 02 is dried in the six drying sections of the ridge-type drying tower 03 to obtain a ridge-type drying tower intermediate product with a water content of 500 to 1000 ppm.

[0093] In detail, the intermediate product of the secondary fluidized bed dryer 02 is sent to the ridge drying tower and enters from the top of the ridge drying tower 03. The ridge drying tower 03 adopts a six-stage drying method. Part of the nitrogen from the dehumidification tower 05 is pressurized by the three-stage blower 09 and heated by the three-stage heater 18, and then enters the drying tower from the sixth drying stage at the bottom of the ridge drying tower 03. The ridge drying tower 03 is divided into six sections from top to bottom. Each section is equipped with an inter-section blower 10 to 14 and an inter-section heater 19 to 23. The inter-section blower is blown from the roof. Dry carrier gas is drawn from the first section of the ridge drying tower 03, heated to 140°C by an inter-section heater, and then enters the next section of the roof drying tower 03, where it comes into contact with and dries the solid material flowing downward. The wet dry carrier gas discharged from the sixth drying section is pressurized by the inter-section blower 15 and heated by the inter-section heater 23 before entering the fifth drying section of the drying tower. The discharged wet dry carrier gas then enters the fourth, second, and first drying sections, where it comes into contact with and dries the material. The wet carrier gas is finally discharged from the top of the drying tower and delivered to the inlet of the first-stage blower 06 for recycling as carrier gas for the first-stage fluidized bed dryer 01. The dried material, with a moisture content of approximately 0.1%, is discharged from the solids outlet at the bottom of the drying tower and conveyed to the barrel drying tower 04 by the second conveying blower 36 of the second solids discharge air conveying system and the second separation silo.

[0094] In step S4, the intermediate product of the ridge drying tower is first separated in a separation silo to obtain a solid material, and the solid material is sent to the barrel drying tower 04 for drying. In the barrel drying tower 04, the solid material is contacted with the dry carrier gas entering the barrel drying tower 04 to remove moisture to obtain a final product with a water content of less than 300 ppm and a dichloromethane content of less than 100 ppm.

[0095] In step S4, the dry carrier gas entering the barrel-type drying tower 04 is heated to 100° C. by a heater and then enters from the bottom side of the barrel-type drying tower 04. The hot dry carrier gas entering the barrel-type drying tower 04 contacts the solid material, and the dry carrier gas absorbs the moisture of the solid material to become a moist hot carrier gas. The moist hot carrier gas is discharged from a pressure control valve arranged at the top of the barrel-type drying tower 04. The moist hot carrier gas is then dusted by a bag dust collector 33, and then pressurized by a circulating fan 15 and heated by a circulating heater 26 before returning to the barrel-type drying tower 04.

[0096] In step S1, the first-level wet carrier gas is also sent into the dehumidification tower 05 under the action of the dehumidification induced draft fan 37, and is directly contacted with the cooling water sprayed from the top of the tower to complete cooling and dehumidification to obtain dehumidified carrier gas. The dehumidified carrier gas is discharged from the top of the dehumidification tower and is divided into four streams, which are respectively sent to the inlet of the secondary blower 07, the first-level conveying fan 08, the third-level blower 09 and the secondary conveying fan 36 for recycling as dry carrier gas.

[0097] A wet PC flake material containing approximately 30% water (mass fraction, the same below) enters the drying chamber of the first-stage fluidized bed dryer 01, where it is fluidized and dried by contact with a carrier gas that has been pressurized by the first-stage blower 06 and heated by the first-stage heater 16 and then delivered to the drying chamber of the first-stage fluidized bed dryer 01. When the moisture content of the material drops to 15%, it is discharged from the fluidized bed. The dry carrier gas from the first-stage fluidized bed dryer 01 is delivered by the first-stage blower 06 to the first-stage heater 16, heated to 140°C, and then enters the drying chamber of the first-stage fluidized bed dryer 01 as a dry carrier gas. The dry carrier gas increases its moisture content through heat and mass transfer with the wet PC material, while carrying away a small amount of PC particles. The entrained PC particles are then separated by the first-stage cyclone separator 29. A portion of the carrier gas that passes through the first-stage cyclone separator 29 is recycled to the inlet of the first-stage blower 06 as a dry carrier gas, and the other portion is delivered to the nitrogen dehumidification tower 05 via the dehumidification induced draft fan 37 for cooling and dehydration.

[0098] The material coming out of the primary fluidized bed dryer 01 is sent to the conveying separation bin 30 through the air conveying system for gas-solid separation. The solid material enters the secondary fluidized bed dryer 02, and the gas phase is sent to the secondary dust collector 31 to mix with the tail gas from the secondary fluidized bed dryer 02; the solid material enters the secondary fluidized bed dryer 02, and is contacted with the carrier gas in the drying chamber of the secondary fluidized bed 02 after being pressurized by the secondary blower 07 and heated by the secondary heater 17, and is fluidized and dried. When the moisture content of the material drops to 6%, it is discharged from the fluidized bed; the dry carrier gas of the secondary fluidized bed dryer 02 is sent to the secondary heater by the secondary blower 07. 17 is heated to 130 to 150°C and then enters the drying chamber of the secondary fluidized bed dryer 02 as a dry carrier gas; the dry carrier gas increases its moisture content through heat and mass transfer with the wet PC material, and at the same time takes away a small amount of PC particles, and then passes through the secondary cyclone separator 31 to separate the entrained PC particles; part of the carrier gas passing through the secondary cyclone separator 31 is recycled to the inlet of the first blower 06 as the dry carrier gas of the first fluidized bed dryer 01, and the other part is sent to the inlet of the second blower 07 and mixed with part of the dehumidified carrier gas from the nitrogen dehumidification tower 05 to be used as the dry carrier gas of the secondary fluidized bed dryer 02.

[0099] The solids discharge air conveying system for the primary fluidized bed dryer 01 consists of a conveying fan 08, a conveying and separation bin 30, and a conveying pipeline. The carrier gas for the air conveying comes from dehumidified nitrogen in the nitrogen dehumidification tower 05. After delivering the solids to the conveying and separation bin 30, it is mixed with the exhaust gas from the secondary fluidized bed dryer in the secondary cyclone separator 31 before entering the system's carrier gas system.

[0100] The three-stage air delivery system includes key equipment such as the two-stage conveying fan 36 and the separation silo 32. The air delivery system delivers the air from the ridge-type drying tower 03 to the four-stage barrel-type drying system.

[0101] The control scheme adopts pressure balance control and key position temperature setting, mainly controlling the fluidized bed outlet pressure stability to ensure system stability; controlling the temperature of the drying material in each section to ensure product quality.

[0102] The dried material from the bottom of the ridge-type drying tower 03 is sent to the separation silo 04 by the air conveying system. After the solid material is separated by the separation silo, it enters the barrel-type drying tower 04 for drying. In the barrel-type drying tower 04, the material comes into contact with hot nitrogen to remove the final moisture to below 300ppm, and is discharged to the subsequent product collection system.

[0103] Dry nitrogen from the utility is heated to 100°C by the nitrogen heater 25 and then enters from the bottom side of the barrel-type drying tower 04. It is discharged at the top under the control of the pressure control valve. Part of the nitrogen extracted from the top of the barrel-type drying tower 04 is dust-removed by the bag dust collector 33 and then pressurized by the circulating fan 15. It is then heated to 90 to 110°C by the circulating heater 26 and returned to the barrel-type drying tower 04 for drying.

[0104] The wet carrier gas from the fluidized bed drying unit is fed into the nitrogen dehumidification tower 05 by dehumidification induced draft fan 37. It comes into direct contact with cooling water at approximately 25°C sprayed into the tower's top, achieving cooling and dehumidification. The dehumidified nitrogen is discharged from the top of the tower and divided into four streams, which are respectively fed to the inlets of the secondary blower 07, the primary conveying blower 08, the tertiary blower 09, and the secondary conveying blower 36 for recycling as carrier gas. Hot water at the bottom of the tower, below 65°C, is cooled in two stages, the primary cooler 27 and the secondary cooler 28, to approximately 25°C before being recirculated into the tower from the top. The liquid level at the bottom of the dehumidification tower is controlled by an automatic valve to remove water introduced into the system by the wet PC material. The cooling media in the primary cooler 27 and the secondary cooler 28 are circulating water and chilled water, respectively.

[0105] The primary and secondary fluidized bed dryers used in the present invention are pulsed fluidized bed dryers, and their basic structure is as follows: Figure 1 As shown, the fluidized bed dryer is suitable for drying heat-sensitive bulk materials. The bulk material is placed on a perforated plate, and gas is delivered from its lower portion, causing the material particles to move on the gas distribution plate and become suspended in the airflow. A pulsed rotary air distributor then periodically supplies air. By adjusting the pulse frequency and pulsed airflow conductivity, the gas flow rate through the perforated plate or the fluidized zone undergoes periodic changes, drying the material. This effectively overcomes drawbacks such as channeling, dead zones, and localized overheating, and offers advantages such as enhanced heat transfer coefficient and shortened residence time. This equipment consists of a fluidizing section, air distributor, top settling section, air supply cone, and rotary air distributor. The gas distribution plate is the core of the equipment and crucial to the system's proper operation.

[0106] The ridge-type drying tower used in this invention is composed of multiple layers of staggered, roof-shaped pipes, forming a vertical, closed box structure. This drying tower features multiple units that can be used in series, a long residence time, a compact structure, and a long service life. It is particularly suitable for drying flaky materials and achieves a high drying depth.

[0107] The barrel-type drying tower employed in this invention operates on the principle that material is continuously fed into the drying tower from the top of the dryer, where it descends in a moving bed fashion under its own weight. Hot nitrogen enters the barrel-type drying tower through a hot nitrogen distribution plate at the bottom. To maintain a steady flow of material, the barrel-type drying tower is equipped with an inner tube and a distribution plate. The inner tube is mounted within the barrel of the barrel-type drying tower. The special structure of the distribution plate and inner tube ensures uniform contact between the material and the hot nitrogen, resulting in a uniform product. It is primarily used for deep devolatilization and drying of particulate materials. Its key characteristic is that the drying process requires very little heat but a very long drying time. The material has already been dried to a very low moisture content by the pre-drying system. At this point, the material has already spent a certain amount of time in the deceleration drying stage and has been heated to or above the required evaporation temperature by the pre-drying system. At this temperature, the moisture in the material slowly evaporates, lowering the material temperature. The hot nitrogen permeates the entire barrel (drying tower), enveloping the material, flowing slowly from bottom to top at an extremely low flow rate. The evaporated moisture in the material slowly diffuses into the nitrogen and is carried out of the silo by the nitrogen. The hot nitrogen in the barrel (drying tower) only needs to provide a small amount of heat required for the evaporation of water to ensure that the material stays at this temperature for a long time, ensuring that the material evaporates to the required drying requirements.

[0108] The present invention has the following advantages: adopting a nitrogen countercurrent circulation drying process improves the thermal efficiency of nitrogen, reduces the nitrogen consumption in the drying process, and reduces the operating cost; selecting high-efficiency dryers such as ridge-type drying towers and barrel-type drying towers meets the requirements of deep drying and devolatilization of materials.

Claims

1. A closed-circulation polycarbonate flake deep drying and devolatilization device, characterized in that: include: In the first-stage fluidized bed dryer, the dry carrier gas passes through the first-stage blower and the first-stage heater in sequence and enters the drying chamber of the first-stage fluidized bed dryer as the dry carrier gas. The wet PC material with a moisture content of 25% to 40% is put into the first-stage fluidized bed dryer for drying to obtain the first-stage fluidized bed dryer intermediate product with a moisture content of 10% to 20%. The dry carrier gas is converted into a first-stage mixed wet carrier gas containing moisture and a small amount of PC particles through heat and mass transfer with the wet PC material. The first-stage mixed wet carrier gas is separated from the entrained PC particles by the first-stage cyclone separator to obtain a The first-stage wet carrier gas is recycled to the inlet of the first-stage blower as a dry carrier gas, and the other part of the first-stage wet carrier gas is sent to the dehumidification tower under the action of the dehumidification induced draft fan, and is directly contacted with the cooling water sprayed from the top of the tower to complete the cooling and dehumidification to obtain the dehumidified carrier gas. The dehumidified carrier gas is discharged from the top of the dehumidification tower and is divided into four streams, which are respectively sent to the inlet of the second-stage blower, the first-stage conveying blower, the third-stage blower and the second-stage conveying blower as the dry carrier gas for recycling in the second-stage fluidized bed dryer, the ridge-type drying tower and the barrel-type drying tower; a secondary fluidized bed dryer connected to the primary fluidized bed dryer to dry the intermediate product of the primary fluidized bed dryer to obtain a secondary fluidized bed dryer intermediate product having a moisture content of 1% to 8%; A ridge drying tower is connected to the secondary fluidized bed dryer to reduce the speed of the intermediate product of the secondary fluidized bed dryer to obtain a ridge drying tower intermediate product with a moisture content of ≤1000ppmw; The barrel-type drying tower is connected to the ridge-type drying tower, and the intermediate product of the ridge-type drying tower is deeply dried to obtain a final product with a water content of less than 300ppm and a dichloromethane content of less than 100ppm. The side of the barrel-type drying tower is provided with a supplementary pipeline for supplementing dry carrier gas, and the supplementary pipeline is provided with a heater. The top of the barrel-type drying tower is provided with a circulation pipeline and a material inlet. The material inlet is connected to the side of the barrel-type drying tower with the circulation pipeline. The circulation pipeline is provided with a heater, a third conveying fan and a bag dust collector. The circulation pipeline is connected to the input pipeline of the dry carrier gas pipeline system. The drying tower also includes a cylinder, an inner tube, a gas distribution plate, and a box. The cylinder is provided with an inner tube, the two ends of the inner tube are cones, and the middle section is cylindrical. The lower cone surface of the inner tube is spaced apart with holes, and solid materials enter the box through the holes. The gas distribution plate is cone-shaped, and the top of the cone is stuck in the box. The gas distribution plate located in the box is provided with ventilation holes. The box has three layers, and the inner layers are interconnected. Each layer of the box is provided with a hot air inlet. The material inlet is a feed pipe, which is located at the top of the barrel trough drying tower. The hot air outlet is located at the top of the barrel trough drying tower. The feed pipe extends into the cylinder, and the outlet of the feed pipe faces the inner tube. The bottom of the box is a solid outlet; and A dry carrier gas pipeline system is used to provide dry carrier gas. The dry carrier gas system is respectively connected to the dry carrier gas inlet of the primary fluidized bed dryer, the secondary fluidized bed dryer, the ridge type drying tower and the barrel type drying tower. The dry carrier gas pipeline system includes an input pipeline, an output pipeline and a dry carrier gas dehumidification tower. The outlet of the dry carrier gas dehumidification tower is connected to the input pipeline, the inlet of the dry carrier gas dehumidification tower is connected to the output pipeline, and the input pipeline is connected to each of the primary fluidized bed dryer, the secondary fluidized bed dryer, the ridge type drying tower and the barrel type drying tower. The dry carrier gas dehumidification tower is connected to the dry carrier gas inlet of the first-stage fluidized bed dryer, the second-stage fluidized bed dryer, the ridge-type drying tower and the barrel-type drying tower, and the output pipeline is connected to the gas outlet of each of the first-stage fluidized bed dryer, the second-stage fluidized bed dryer, the ridge-type drying tower and the barrel-type drying tower. The dry carrier gas dehumidification tower dries the dry carrier gas containing water vapor discharged from the first-stage fluidized bed dryer, the second-stage fluidized bed dryer, the ridge-type drying tower and the barrel-type drying tower through the output pipeline. The dry carrier gas dehumidification tower dries the dry carrier gas containing water vapor and then transports it to the input pipeline for recycling; The primary fluidized bed dryer, the secondary fluidized bed dryer, the ridge-type drying tower, and the barrel-type drying tower are all provided with a material inlet, a drying carrier gas inlet, a gas outlet, and a solid outlet. The primary fluidized bed dryer and the secondary fluidized bed dryer each have multiple drying chambers. The material inlet, drying carrier gas inlet, gas outlet, and solid outlet of the primary fluidized bed dryer are all in communication with the drying chambers thereof. The material inlet, drying carrier gas inlet, gas outlet, and solid outlet of the secondary fluidized bed dryer are all in communication with the drying chambers thereof. The first-stage fluidized bed dryer and the second-stage fluidized bed dryer are pulse fluidized bed dryers. The pulse fluidized bed dryer is provided with a gas distribution plate. The solid outlet is provided on the upper side of the gas distribution plate. A plurality of spaced partitions are provided on the gas distribution plate. A plurality of inverted conical grooves are provided side by side below the gas distribution plate. An air flow distributor is provided below the inverted conical grooves. The air flow distributor is connected to the dry carrier gas inlet. The air flow distributor is provided with an annular pipe and a plurality of branch air inlet pipes. The plurality of branch air inlet pipes are arranged in a circumferential rotation along the annular pipe. The air flow distributor is a rotating air flow distributor. The branch air inlet pipes extend into the inverted conical grooves. The dry carrier gas is input into the inverted conical grooves from the branch air inlet pipes. The dry carrier gas moves from bottom to top to impact the gas distribution plate. The rotating air flow distributor supplies air periodically. By adjusting the pulse frequency of the air flow and the pulse air flow conductivity, the gas flow or fluidization area passing through the gas distribution plate changes periodically, thereby drying the material.

2. The closed-circulation polycarbonate flake deep drying and devolatilization device according to claim 1, characterized in that: A first dry carrier gas input device, a second dry carrier gas input device and a third dry carrier gas input device are also provided, one end of the first dry carrier gas input device is connected to the dry carrier gas inlet of the primary fluidized bed dryer, and the other end is connected to the input pipeline of the dry carrier gas pipeline system; One end of the second dry carrier gas input device is connected to the dry carrier gas inlet of the secondary fluidized bed dryer, and the other end is connected to the input pipeline of the dry carrier gas pipeline system; One end of the third dry carrier gas input device is connected to the dry carrier gas inlet of the roof-type drying tower, and the other end is connected to the input pipeline of the dry carrier gas pipeline system.

3. The closed-circulation polycarbonate flake deep drying and devolatilization device according to claim 2, characterized in that: The first dry carrier gas input device includes a primary blower and a primary heater. The dry carrier gas inlet of the primary fluidized bed dryer is connected to the primary blower and the primary heater. The dry carrier gas is pressurized by the primary blower and heated by the primary heater and then delivered to the drying chamber of the primary fluidized bed dryer. The second dry carrier gas input device includes a secondary blower and a secondary heater. The dry carrier gas inlet of the secondary fluidized bed dryer is connected to the secondary blower and the secondary heater. The dry carrier gas is pressurized by the secondary blower and heated by the secondary heater and then delivered to the drying chamber of the secondary fluidized bed dryer. The third dry carrier gas input device includes a three-stage blower and a three-stage heater. The dry carrier gas inlet of the ridge-type drying tower is connected to the three-stage blower and the three-stage heater. The dry carrier gas is pressurized by the three-stage blower and heated by the three-stage heater and then sent to the ridge-type drying tower.

4. The closed-circulation polycarbonate flake deep drying and devolatilization device according to claim 1, characterized in that: A first solid discharging air conveying system is connected between the solid outlet of the first-level fluidized bed dryer and the material inlet of the second-level fluidized bed dryer to transport the intermediate product of the first-level fluidized bed dryer to the second-level fluidized bed dryer. A second solid discharging air conveying system is connected between the discharge port of the ridge-type drying tower and the material inlet of the barrel-type drying tower. The first solid discharging air conveying system is connected to the drying carrier gas pipeline system, and the second solid discharging air conveying system is connected to the drying carrier gas pipeline system.

5. The closed-circulation polycarbonate flake deep drying and devolatilization device according to claim 3, characterized in that: The gas outlet of the primary fluidized bed dryer is connected to a primary gas-solid separation device, and the primary gas-solid separation device is connected to the output pipeline of the dry carrier gas pipeline system and the dry carrier gas dehumidification tower; The gas outlet of the secondary fluidized bed dryer is connected to a secondary gas-solid separation device, and the secondary gas-solid separation device is connected to the output pipeline of the dry carrier gas pipeline system and the gas outlet of the secondary fluidized bed dryer.

6. The closed-circulation polycarbonate flake deep drying and devolatilization device according to claim 4, characterized in that: The first solid discharging air conveying system includes a first conveying fan and a first conveying and separation bin, and the second solid discharging air conveying system includes a second conveying fan and a second conveying and separation bin. The first conveying fan and the first conveying and separation bin are connected to the input pipeline of the drying carrier gas pipeline system, wherein the first conveying fan is directly connected to the input pipeline, and the outlet of the first conveying and separation bin is connected to the material inlet of the secondary fluidized bed dryer; the second conveying fan and the second conveying and separation bin are connected to the input pipeline of the drying carrier gas pipeline system, wherein the second conveying fan is directly connected to the input pipeline, the second conveying and separation bin is connected to the inlet of the barrel-type drying tower, and the outlet of the second conveying and separation bin is connected to the output pipeline.

7. The closed-circulation polycarbonate flake deep drying and devolatilization device according to claim 1, characterized in that: The material inlet and gas outlet of the ridge type drying tower are located at the top of the ridge type drying tower, and the dry carrier gas inlet and solid outlet of the ridge type drying tower are located at the bottom of the ridge type drying tower. The material inlet of the ridge type drying tower is connected to the solid outlet of the secondary fluidized bed dryer. The intermediate product of the secondary fluidized bed dryer enters the interior of the ridge type drying tower from the top of the ridge type drying tower, and the dry carrier gas enters the ridge type drying tower from the bottom of the ridge type drying tower.

8. The closed-circulation polycarbonate flake deep drying and devolatilization device according to claim 5, characterized in that: The ridge-type drying tower has six drying sections, which are sequentially arranged from top to bottom with the first drying section, the second drying section, the third drying section, the fourth drying section, the fifth drying section and the sixth drying section which are closed to each other. Adjacent drying sections are connected with a circulation pipeline, and the circulation pipeline is provided with an inter-section blower and an inter-section heater. The sixth drying section is connected with a three-stage blower and a three-stage heater. Part of the dry carrier gas from the dry carrier gas dehumidification tower is pressurized by the three-stage blower and heated by the three-stage heater, and then enters the ridge-type drying tower from the sixth drying section at the bottom of the ridge-type drying tower. The dry carrier gas of the next stage is pressurized by the inter-section blower and heated by the inter-section heater, and then enters the previous drying section. The gas outlet is arranged in the first drying section, and the gas outlet is connected to the first-stage blower of the first-stage fluidized bed dryer.

9. The closed-circulation polycarbonate flake deep drying and devolatilization device according to claim 1, characterized in that: The top of the drying carrier gas dehumidification tower is connected to the input pipeline, and the bottom of the drying carrier gas dehumidification tower is connected to the output pipeline. A first cold water circulation pipeline for spraying cooling water is provided on the top of the drying carrier gas dehumidification tower. Both ends of the first cold water circulation pipeline are connected to the drying carrier gas dehumidification tower. The first cold water circulation pipeline is provided with a primary cooler and a primary circulation pump. A second cold water circulation pipeline for cooling the hot water at the bottom of the dehumidification tower is provided at the bottom of the drying carrier gas dehumidification tower. Both ends of the second cold water circulation pipeline are connected to the drying carrier gas dehumidification tower. The second cold water circulation pipeline is provided with a secondary cooler and a secondary circulation pump. The secondary cooler cools the bottom hot water and inputs it into the drying carrier gas dehumidification tower for reuse through the secondary circulation pump. The second cold water circulation pipeline is connected to a sewage discharge pipeline.

10. A closed-loop polycarbonate flake deep drying and devolatilization process, characterized in that: The closed-circulation polycarbonate flake deep drying and devolatilization device according to any one of claims 1 to 9 is used, and the closed-circulation polycarbonate flake deep drying and devolatilization process comprises the following steps: Step S1, the dry carrier gas passes through the first-level blower and the first-level heater in sequence and enters the drying chamber of the first-level fluidized bed dryer as the dry carrier gas, and the wet PC material with a moisture content of 25% to 35% is put into the first-level fluidized bed dryer for drying to obtain the first-level fluidized bed dryer intermediate product with a moisture content of 10% to 20%. The dry carrier gas is converted into a first-level mixed wet carrier gas containing moisture and a small amount of PC particles through heat and mass transfer with the wet PC material. The first-level mixed wet carrier gas is separated by the first-level cyclone separator to obtain the entrained PC particles. To the first-level wet carrier gas, part of the first-level wet carrier gas is recycled to the inlet of the first-level blower as a dry carrier gas, and the other part of the first-level wet carrier gas is sent to the dehumidification tower under the action of the dehumidification induced draft fan, and is directly contacted with the cooling water sprayed from the top of the tower to complete the cooling and dehumidification to obtain the dehumidified carrier gas. The dehumidified carrier gas is discharged from the top of the dehumidification tower and is divided into four streams, which are respectively sent to the inlet of the second-level blower, the first-level conveying blower, the third-level blower and the second-level conveying blower as the dry carrier gas for the second-level fluidized bed dryer, the ridge-type drying tower and the barrel-type drying tower. In step S2, the dry carrier gas is pressurized by the secondary blower and heated by the secondary heater before being sent to the drying chamber of the secondary fluidized bed dryer. The intermediate product of the primary fluidized bed dryer is placed in the secondary fluidized bed dryer for drying. The dry carrier gas exchanges heat and mass with the intermediate product of the primary fluidized bed dryer entering the drying chamber of the secondary fluidized bed dryer. When the moisture content of the intermediate product of the primary fluidized bed dryer is reduced to 1% to 8%, the intermediate product of the secondary fluidized bed dryer is discharged from the secondary fluidized bed dryer, thereby obtaining an intermediate product of the secondary fluidized bed dryer having a moisture content of 1% to 8%. In step S3, the intermediate product of the secondary fluidized bed dryer enters the ridge drying tower from the top of the ridge drying tower. Part of the dehumidified carrier gas from the dehumidification tower is pressurized by a three-stage blower and heated by a three-stage heater before entering the drying tower from the bottom of the ridge drying tower. Each drying section of the ridge drying tower is equipped with an inter-section blower and an inter-section heater. The dry carrier gas enters the ridge drying tower from the bottom to the top. The inter-section blower draws dry carrier gas from the previous drying section of the ridge drying tower, heats it to 100 to 140° C. by the inter-section heater, and then enters the next drying section of the ridge drying tower to contact and dry with the solid material entering the ridge drying tower from the top to the bottom, thereby obtaining a ridge drying tower intermediate product with a moisture content of ≤1000 ppmw. In step S4, the intermediate product of the ridge drying tower is sent to a barrel drying tower for deep drying to obtain a final product with a moisture content of less than 300 ppm and a dichloromethane content of less than 100 ppm. Among them, the first-level fluidized bed dryer and the second-level fluidized bed dryer are pulse fluidized bed dryers. The pulse fluidized bed dryer is provided with a gas distribution plate, the solid outlet is provided on the upper side of the gas distribution plate, a plurality of spaced partitions are provided on the gas distribution plate, a plurality of inverted conical grooves arranged side by side are provided below the gas distribution plate, and an air flow distributor is provided below the inverted conical grooves. The air flow distributor is connected to the dry carrier gas inlet, the air flow distributor is provided with a circular pipe and a plurality of branch air inlet pipes, and the plurality of branch air inlet pipes are arranged in a circumferential rotation along the circular pipe. The air flow distributor is a rotating air flow distributor, the branch air inlet pipes extend into the inverted conical grooves, and the dry carrier gas is input into the inverted conical grooves from the branch air inlet pipes. The dry carrier gas moves from bottom to top to impact the gas distribution plate. The rotating air flow distributor periodically supplies air, and by adjusting the pulse frequency of the air flow and the pulse air flow conductivity, the gas flow or fluidization area passing through the gas distribution plate changes periodically to dry the material.

11. The closed-cycle polycarbonate flake deep drying and devolatilization process according to claim 10, characterized in that: In step S1, wet PC material with a moisture content of 25% to 40% is pressurized by a primary blower and heated by a primary heater, and then sent to the drying chamber of a primary fluidized bed dryer for drying.

12. The closed-cycle polycarbonate flake deep drying and devolatilization process according to claim 10, characterized in that: In step S1 , the dry carrier gas exchanges heat and mass with the wet PC material containing 25% to 35% water.

13. The closed-cycle polycarbonate flake deep drying and devolatilization process according to claim 10, characterized in that: In step S2, the intermediate product of the primary fluidized bed dryer obtained after step S1 is first subjected to gas-solid separation to obtain solid material and gaseous material. The solid material enters the drying chamber of the secondary fluidized bed dryer, and the gaseous material enters the secondary dust collector and is then mixed with the exhaust gas from the secondary fluidized bed dryer. The solid material enters the drying chamber of the secondary fluidized bed dryer.

14. The closed-cycle polycarbonate flake deep drying and devolatilization process according to claim 10, characterized in that: In step S2, the dry carrier gas is converted into a secondary mixed wet carrier gas containing a small amount of PC particles and moisture through heat and mass transfer with the wet PC material, and the secondary mixed wet carrier gas is separated from the entrained PC particles by a secondary cyclone separator to obtain a secondary wet carrier gas, and part of the secondary wet carrier gas is recycled to the inlet of the first blower as the dry carrier gas of the first fluidized bed drying chamber, and the other part of the secondary wet carrier gas is sent to the inlet of the second blower, mixed with part of the dehumidified carrier gas from the dehumidification tower, and used as the dry carrier gas of the drying chamber of the secondary fluidized bed dryer.

15. The closed-cycle polycarbonate flake deep drying and devolatilization process according to claim 10, characterized in that: In step S3, it also includes that the ridge-type drying tower has six drying sections, which are the first drying section, the second drying section, the third drying section, the fourth drying section, the fifth drying section, and the sixth drying section from top to bottom. The wet carrier gas discharged from the sixth drying section enters the fifth drying section of the drying tower after being pressurized by the inter-section blower and heated by the inter-section heater. The wet carrier gas discharged from the fifth drying section enters the fourth drying section to the first drying section in turn and contacts with the intermediate product of the secondary fluidized bed dryer for drying. The intermediate product of the secondary fluidized bed dryer is dried in the six drying sections of the ridge-type drying tower to obtain a ridge-type drying tower intermediate product with a water content of 500~1000ppm.

16. The closed-cycle polycarbonate flake deep drying and devolatilization process according to claim 10, characterized in that: In step S4, the intermediate product of the ridge drying tower is first separated in a separation silo to obtain a solid material, and the solid material is sent to a barrel drying tower for drying. In the barrel drying tower, the solid material is contacted with a dry carrier gas entering the barrel drying tower to remove moisture to obtain a final product with a water content of less than 300 ppm and a dichloromethane content of less than 100 ppm.

17. The closed-cycle polycarbonate flake deep drying and devolatilization process according to claim 16, characterized in that: In step S4, the dry carrier gas entering the barrel-type drying tower is heated to 100° C. by a heater and then enters from the bottom side of the barrel-type drying tower. The hot dry carrier gas entering the barrel-type drying tower contacts the solid material, and the dry carrier gas absorbs moisture from the solid material to become a wet hot carrier gas. The wet hot carrier gas is discharged through a pressure control valve provided at the top of the barrel-type drying tower under the control of a pressure control valve. The wet hot carrier gas is then dusted by a bag dust collector, pressurized by a circulating fan, and heated by a circulating heater before returning to the barrel-type drying tower.

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