Low-temperature closed-loop circulating fluidized drying system

Abstract

The invention discloses a low-temperature closed-loop circulating fluidized drying system, relates to drying of dimethyl azodiisobutyrate, and aims to solve the problems that in the prior art, the dimethyl azodiisobutyrate is extremely easy to form a molten state at a relatively high drying temperature, the drying efficiency is low due to the fact that the crystal form is damaged, and the drying quality cannot be ensured. A vertical boiling fluidization device in the system is used for drying materials, a dust removal device efficiently intercepts solid particles in nitrogen, a low-temperature cooling recovery device sprays low-temperature water and absorbs an organic solvent in the nitrogen, a micro-heat adsorption device removes moisture in the nitrogen, and low-temperature dry nitrogen is obtained and then circulated to the vertical boiling fluidization device. According to the whole drying system, the drying temperature of the dimethyl azobisisobutyrate wet product is controlled to be 15 DEG C or below, the drying efficiency of the dimethyl azobisisobutyrate wet product is greatly improved through the drying system, and the quality of the obtained dimethyl azobisisobutyrate wet product is also greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of chemical product manufacturing technology, and relates to the drying of dimethyl azobisisobutyrate, and particularly to a low-temperature closed-loop vertical fluidized bed drying system for drying dimethyl azobisisobutyrate. Background Technology

[0002] Dimethyl azobisisobutyrate (DIBY) is an important free radical initiator, mainly used in the polymerization of olefins, acrylic acid, and their esters. In the polymerization of styrene, it yields polymers containing ester-terminated groups and can be hydrolyzed to generate products containing carboxyl-terminated groups. DIBY is a thermosensitive material, easily decomposed at high temperatures, and has a low melting point, reported in the literature as 22-28℃.

[0003] The invention patent application number 201811386205.2 also discloses a method for preparing dimethyl azobisisobutyrate. In a reactor equipped with a stirrer and reflux device, 2,2'-azobisisobutyronitrile, methanol, and dichloroethane are first added; stirring is started, and thionyl chloride is slowly added dropwise under cooling, while the temperature is controlled and maintained for the reaction; after the reaction, cold water is added dropwise for hydrolysis; after the hydrolysis reaction, the mixture is allowed to stand for the first phase separation; the organic phase obtained after the first phase separation is washed with water and then subjected to a second phase separation; the organic phase after the second phase separation is subjected to vacuum distillation until all dichloroethane is recovered, yielding liquid dimethyl azobisisobutyrate; the liquid dimethyl azobisisobutyrate is then cooled at low temperature to obtain a white solid dimethyl azobisisobutyrate product. The white solid dimethyl azobisisobutyrate product has a purity (HPLC) of over 98% and a yield of 85-95%. This method uses cheaper thionyl chloride instead of hydrogen chloride gas. Thionyl chloride is liquid at room temperature, making it easier to control the rate and amount during addition, and shortening the reaction time to 6 hours.

[0004] As mentioned above, existing literature reports focus on improving the synthesis method of dimethyl azobisisobutyrate. For example, invention patent application number 201610526787.4 discloses a synthesis method of dimethyl azobisisobutyrate, which includes: (1) condensation: adding azobisisobutyronitrile, methanol, and isophorone into a reaction vessel, adding phosphorus trichloride solution to react, and centrifuging to obtain azoimine methyl ether hydrochloride solid material; (2) hydrolysis: adding pure water into a hydrolysis vessel, adding azoimine methyl ether hydrochloride solid material into the hydrolysis vessel for hydrolysis; (3) phase separation: placing the hydrolyzed liquid into a phase separation vessel, and using the phase transfer agent hexadecyltrimethylammonium chloride for phase separation; (4) recrystallization; (5) drying. The invention lies in its synthesis method. Through the optimization design of the process route and raw materials, the raw materials are environmentally friendly and non-toxic, and the reaction is stable and easy to control, which greatly improves the safety of the reaction. Regarding its drying process, it is simply described as placing the wet product of dimethyl azobisisobutyrate in a drying room for 24 hours at a drying temperature of ≤25℃.

[0005] In existing technologies, the drying of dimethyl azobisisobutyrate (DIBOB) is mostly carried out in drying chambers. However, this method involves long drying times, and the selected drying temperature reaches the melting point of DIBOB, causing the product to easily melt, resulting in the destruction of its crystalline structure. Solvents introduced into the wet product become trapped within the melt and are difficult to remove, leading to low drying efficiency and inconsistent drying quality. Furthermore, drying in a drying chamber typically requires manual or mechanical handling of the wet solid material in and out of the chamber. The handling process is poorly sealed, allowing organic solvents in the wet product to evaporate and form fugitive emissions, polluting the environment. This method also involves high labor intensity, poor operating conditions, and limited equipment processing capacity. Summary of the Invention

[0006] The purpose of this invention is to provide a low-temperature closed-loop circulating fluidized bed drying system to address the problems in the prior art where the high drying temperature of dimethyl azobisisobutyrate easily leads to a molten state, damages the crystal morphology, resulting in low final drying efficiency and difficulty in guaranteeing drying quality.

[0007] To achieve the above objectives, the present invention specifically adopts the following technical solution: A low-temperature closed-loop circulating fluidized bed drying system includes a vertical boiling fluidized bed device, a dust removal device, a low-temperature cooling and recovery device, and a micro-heat adsorption device arranged sequentially to form a closed loop. A vertical fluidized bed apparatus includes a fluidized bed body with a feed inlet on one side of its upper surface. A material distribution and dispersion mechanism is located within the fluidized bed body. This mechanism includes a connecting rod within the fluidized bed body, with several material distribution plates evenly distributed on the outer side of the connecting rod. Gaps are provided between the material distribution plates. The connecting rod is inclined at both ends and equipped with a vibration device. A blowing mechanism is located within the fluidized bed body, below the material distribution and dispersion mechanism. This blowing mechanism includes several inclined scrapers evenly distributed on opposite front and rear sides of the fluidized bed body. A shaft is rotatably mounted on opposite front and rear sides of the fluidized bed body between the scrapers. A perforated roller is positioned between opposite shafts. A motor is located on one side of the fluidized bed body, corresponding to one of the shaft positions. The motor is fixedly connected to one end of the shaft extending out of the fluidized bed body. Each end of the shaft extending out of the fluidized bed body is fitted with meshing gears. Each end of the shaft extending out of the fluidized bed body has a through hole, which is connected to the drum. A connecting pipe is inserted into the through hole, and a spiral air outlet pipe is provided at one end of the connecting pipe extending into the drum. Air outlet holes are evenly distributed on the outer side of the air outlet pipe. Several steam outlet holes are evenly distributed on the outer side of the fluidized bed body, located between the material distribution mechanism and the blowing mechanism. Each steam outlet hole is connected to a pipe, and the pipe is connected to a cyclone separator through a pipe connector. A discharge pipe is provided inside the fluidized bed body and below the blowing mechanism. The discharge end of the cyclone separator is connected to the discharge pipe for discharge. Several vibrating motors are evenly distributed on the outer side of the fluidized bed body. Support feet are provided under the fluidized bed body, and noise reduction and vibration damping mechanisms are provided under the support feet.

[0008] The dust collection device includes an inlet duct, a housing, internal partitions, a filtration system, a cleaning system, a top cover, and an exhaust duct. The internal partitions divide the interior space into two or more independent compartments. Each compartment has an ash hopper and an ash discharge valve at the bottom, an air inlet at the bottom connected to the inlet duct, a filtration system and a cleaning system at the top, and a top cover and an exhaust port at the top. The dust collection device filters nitrogen gas, removing solid particles. The filtered nitrogen then enters a cryogenic cooling and recovery unit. The cryogenic cooling and recovery device sprays an absorbent into the nitrogen gas. The absorbent absorbs the organic solvent in the nitrogen gas, and the nitrogen gas after the organic solvent is removed enters the micro-thermal adsorption device. The micro-thermal adsorption device includes an input subsystem, an output subsystem, and two identical heating and filtering devices. The input end of the input subsystem is connected to the output end of an air compressor, and the output ends of the input subsystem are connected to the two heating and filtering devices respectively. The output ends of the two heating and filtering devices are connected to the input end of the output subsystem, and the output end of the output subsystem outputs to the gas-using equipment. The two heating and filtering devices operate alternately. The micro-thermal adsorption device dries nitrogen at low temperature to obtain low-temperature circulating nitrogen, which is then circulated to a vertical boiling fluidized bed for reuse.

[0009] Furthermore, the temperature of the low-temperature circulating nitrogen gas blown into the vertical fluidized bed is no more than 15°C, and the material to be dried in the vertical fluidized bed is a crystalline material at 0~5°C.

[0010] Furthermore, the absorbent sprayed inside the low-temperature cooling and recovery device is 5°C low-temperature water; after the absorbent absorbs the organic solvent, nitrogen gas is formed into water-saturated nitrogen gas, and the temperature of the water-saturated nitrogen gas is 5-8°C.

[0011] Furthermore, after the nitrogen gas is dried by the micro-thermal adsorption device, a low-temperature circulating nitrogen gas with a dew point below -40°C is obtained. The low-temperature circulating nitrogen gas is then circulated to the vertical boiling fluidization device after being adjusted to 15°C.

[0012] Furthermore, it also includes an exhaust fan, which is located in a closed loop consisting of a vertical fluidized bed, a dust removal device, a low-temperature cooling and recovery device, and a micro-heat adsorption device. The exhaust fan of the exhaust fan drives the nitrogen to circulate in the closed loop.

[0013] The beneficial effects of this invention are as follows: 1. In this invention, the system adopts a closed, circulating system consisting of a vertical fluidized bed device, a dust removal device, a low-temperature cooling and recovery device, and a micro-thermal adsorption device. The vertical fluidized bed device uses a fluidized bed structure to dry the material; the dust removal device uses a bag filter to efficiently intercept solid particles in the nitrogen gas; the low-temperature cooling and recovery device uses a spray tower to spray low-temperature water from top to bottom and absorb organic solvents in the nitrogen gas; and the micro-thermal adsorption device finally removes moisture from the nitrogen gas and obtains low-temperature dried nitrogen gas, which is then circulated back to the vertical fluidized bed device. The entire drying system controls the drying temperature of the wet azodiisobutyrate product at 15°C or below, effectively solving the problem that the high drying temperature of azodiisobutyrate easily leads to a molten state, damages the crystal morphology, and results in low final drying efficiency and difficulty in guaranteeing the drying quality. This drying system greatly improves the drying efficiency of the wet azodiisobutyrate product and also greatly improves the quality of the obtained wet azodiisobutyrate product.

[0014] 2. In this invention, the entire system is in a sealed state, there is no environmental pollution, nitrogen is recycled, the problem of organic solvents being prone to explosion is solved, and it is suitable for continuous and large-scale industrial production.

[0015] 3. In this invention, the vertical fluidized bed device is equipped with multiple spiral air outlet pipes and air outlet holes, which are evenly distributed within the fluidized bed body. A hot air blower connected to the external pipe blows hot air out of the air outlet holes, providing a large amount of evenly distributed hot air within the fluidized bed body. The motor drives the gears to mesh with each other, which drives the rotation of the drum. The material falling onto the drum is rolled up and dried. At the same time, the scraper can scrape the material on the drum to the upper surface of the drum for drying, ensuring that no material is missed, greatly improving the drying efficiency and drying effect.

[0016] 4. In this invention, the dust removal device integrates two or more independently operating dust removal systems in the same housing. Each dust removal system is equipped with an independent dust-laden gas inlet pipe and a clean gas outlet pipe, and each pipe is equipped with an independent gas control valve. Compared with installing multiple dust removal devices in parallel, this greatly saves space.

[0017] 5. In this invention, the micro-thermal adsorption device can continuously and stably purify and dry the gas, thereby obtaining dry and clean gas. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the drying process of the present invention; Figure 2 This is a schematic diagram of the main structure of the vertical boiling fluidization device of the present invention; Figure 3 This is a schematic diagram of the external structure of the vertical boiling fluidization device of the present invention. Figure 4 This is a schematic diagram of the dust removal device of the present invention; Figure 5 This is a schematic diagram of the microthermal adsorption device of the present invention.

[0019] The attached figures are labeled as follows: 2-1, fluidized bed body; 2-2, feed inlet; 2-3, connecting rod; 2-4, material distribution plate; 2-5, scraper; 2-6, shaft; 2-7, gear; 2-8, motor; 2-9, through hole; 2-10, connecting pipe; 2-11, air outlet pipe; 2-12, air outlet hole; 2-13, air outlet hole; 2-14, pipe; 2-15, cyclone separator; 2-16, discharge pipe; 2-17, vibrating motor; 2-18, support. 2-19. Foot; 2-20. Fixing block; 2-21. Receiving groove; 2-22. Elastic block; 2-23. Buffer layer; 2-24. Support block; 3-1. Box body; 3-2. Fiber insulation layer; 3-3. Filter plate; 3-4. Ceramic filter sheet; 3-5. Fixing hook; 3-6. High-temperature resistant sealing ring; 3-7. Sealing material; 3-8. Top cover; 3-9. Exhaust pipe; 3-10. Exhaust control valve; 3-11. Backflush gas pipe; 3-12. Backflush control valve 3-13. Control valve; 3-14. Fastening bolts; 3-15. Air inlet pipe; 3-16. Ash discharge valve; 4-1. Pre-filter; 4-2. Precision filter; 4-3. Air inlet valve; 4-4. First air inlet ball valve; 4-5. Second air inlet ball valve; 4-6. Pressure equalizing ball valve; 4-7. Second exhaust ball valve; 4-8. First exhaust ball valve; 4-9. Silencer; 4-10. Heating and filtering device; 4-11. Safety valve; 4-12. External heater; 4-13. Needle valve, 4-14, Second pressure reducing gauge, 4-15, Second pressure reducing valve, 4-16, First pressure reducing gauge, 4-17, First pressure reducing valve, 4-18, Pressure maintaining valve, 4-19, Post-filter, 4-20, Drain valve, 4-21, Second pressure gauge, 4-22, Fourth check valve, 4-23, Exhaust shut-off valve, 4-24, First check valve, 4-25, First pressure gauge, 4-26, Second check valve, 4-27, Third check valve. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0021] Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] This embodiment provides a low-temperature closed-loop circulating fluidized bed drying system, which is mainly used to process wet azobisisobutyrate dimethyl product obtained by crystallization with water or organic solvent, that is, to dry low-melting-point azobisisobutyrate dimethyl ester under low-temperature conditions.

[0023] The system includes a vertical boiling fluidization device, a dust removal device, a low-temperature cooling and recovery device, and a micro-thermal adsorption device, which are arranged in sequence to form a closed loop.

[0024] The vertical fluidized bed device includes a fluidized bed body 2-1. An inlet 2-2 is located on one side of the upper surface of the fluidized bed body 2-1. A material distribution and dispersion mechanism is located inside the fluidized bed body 2-1. This mechanism includes a connecting rod 2-3 located within the fluidized bed body 2-1. Several distribution plates 2-4 are evenly distributed on the outer surface of the connecting rod 2-3, with gaps between the distribution plates 2-4. The connecting rod 2-3 is inclined downwards from one end near the inlet 2-2 to the other end, and is located inside the fluidized bed body 2-1 and below the material distribution and dispersion mechanism. The fluidized bed body 2-1 is equipped with a blowing mechanism, which includes several inclined scrapers 2-5 evenly distributed on opposite front and rear sides. Shafts 2-6 are rotatably mounted on opposite front and rear sides of the fluidized bed body 2-1 between the scrapers 2-5. A perforated roller is positioned between opposite shafts 2-6. A motor 2-8 is located on one side of the fluidized bed body 2-1, corresponding to one of the shafts 2-6. The motor 2-8 is fixedly connected to one end of the shaft 2-6 extending out of the fluidized bed body 2-1. The other end of each fluidized bed body 2-1 is fitted with meshing gears 2-7. Each shaft 2-6 extending from the other end of the fluidized bed body 2-1 has a through hole 2-9, which communicates with the drum. A connecting pipe 2-10 is inserted into the through hole 2-9. One end of the connecting pipe 2-10 extending into the drum has a spiral air outlet pipe 2-11. Air outlet holes 2-12 are evenly distributed on the outer surface of the air outlet pipe 2-11. Several steam outlet holes are evenly distributed on the outer surface of the fluidized bed body 2-1, located between the material distribution mechanism and the blowing mechanism. 2-13, steam outlet 2-13 is connected to pipe 2-14, pipe 2-14 is connected to cyclone separator 2-15 through pipe connector, discharge pipe 2-16 is provided inside the fluidized bed body 2-1 and below the blowing mechanism, cyclone separator 2-15 discharges material through discharge pipe 2-16, several vibrating motors 2-17 are evenly distributed on the outer side of fluidized bed body 2-1, support feet 2-18 are provided below fluidized bed body 2-1, and noise reduction and vibration damping mechanism is provided below support feet 2-18. The noise reduction and vibration damping mechanism includes a fixing block 2-19 below support feet 2-18, a receiving groove 2-20 on the fixing block 2-19, elastic blocks 2-21 evenly distributed on the inner side of receiving groove 2-20, a buffer layer 2-22 woven from several elastic strips inside receiving groove 2-20, and support blocks 2-23 at the four corners below fixing block 2-19.In a vertical fluidized bed reactor, a vacuum feeding system is used to input the crystalline material (i.e., wet dimethyl azobisisobutyrate) into the reactor. Multiple spiral-shaped air outlet pipes 2-11 and air outlets 2-12 are installed, evenly distributing the material within the fluidized bed body 2-1. A hot air blower connected to the connecting pipe 2-10 blows hot air out through the air outlets 2-12, providing a relatively large and evenly distributed amount of hot air within the fluidized bed body 2-1. Meanwhile, a motor 2-8 drives gears 2-7, which mesh to rotate the drum. The material falling onto the drum is then... The material is dried by being blown up by a rolling airflow. Simultaneously, scrapers 2-5 scrape the material on the drum to its upper surface, where it is blown up by hot air inside the drum for drying. This ensures no material is missed, significantly improving drying efficiency and effect. Boiling material containing water vapor is drawn in by a cyclone separator 2-15 for material-gas separation. The separated water vapor is discharged, and the material exits through the discharge pipe 2-16. The material dried by the perforated drum falls onto the inclined bottom surface of the fluidized bed body 2-1, facilitating the discharge of the dried material. A buffer layer 2-22, woven from several elastic strips, is combined with elastic blocks 2-21, ensuring that the fluidized bed body 2-1 only contacts the buffer layer 2-22 and elastic blocks 2-21. Due to the elastic deformation capacity, the resulting vibrations are canceled out by the buffer layer 2-22 and elastic blocks 2-21, greatly reducing the vibration of the fluidized bed body 2-1 caused by the vibration motor 2-17, thus improving noise reduction and vibration damping effects. In the dust removal device, the dust removal device (which can be a bag filter) uses a bag filter to remove dust and a high-efficiency filter to filter nitrogen gas, intercepting and filtering out solid particles in the nitrogen gas. The filtered nitrogen gas then enters a low-temperature cooling and recovery device, and the filtered solid particles are collected and removed.

[0025] The dust removal device mainly includes a housing 3-1, a fiber insulation layer 3-2, a filter plate 3-3, a ceramic filter sheet 3-4, a fixing hook 3-5, a high-temperature resistant sealing ring 3-6, sealing material 3-7, a top cover 3-8, an exhaust pipe 3-9, an exhaust control valve 3-10, a backflush gas pipe 3-11, a backflush control valve 3-12, fastening bolts 3-13, an inlet pipe 3-14, a dust hopper and a dust discharge valve 3-15, an inlet control valve, fastening screws, backflush nozzles, a backflush baffle, and an internal partition 20. The internal partition 20 divides the interior of the housing 3-1 into compartment A and compartment B, which are sealed and not connected. Dust hoppers and dust discharge valves 3-15 are respectively installed at the bottom of compartment A and compartment B. An air inlet is provided at the bottom of the compartment and connected to the inlet pipe 3-14. The filtration system and dust removal system are installed at the top. Each compartment has a separate top cover 3-8 and an exhaust port.

[0026] A cryogenic cooling and recovery device sprays an absorbent into nitrogen gas. The absorbent absorbs the organic solvents in the nitrogen gas, and the nitrogen gas, after the organic solvents are removed, enters a microthermal adsorption device. This cryogenic cooling and recovery device uses 5°C cryogenic water as the absorbent to absorb the organic solvents in the nitrogen gas. The absorption occurs within the device (which can be a spray tower). The device has tiered nozzles that spray cryogenic water from top to bottom, forming highly dispersed mist-like droplets. The organic solvents in the nitrogen gas are fully absorbed through contact with the mist-like water and collected from the bottom of the device in a collection tank. The absorbent sprayed within the device is 5°C cryogenic water; after the absorbent absorbs the organic solvents, the nitrogen gas becomes water-saturated nitrogen gas with a temperature of 5-8°C.

[0027] The micro-thermal adsorption device includes a pre-filter 4-1, a precision filter 4-2, an inlet valve 4-3, a first inlet ball valve 4-4, a second inlet ball valve 4-5, a first exhaust ball valve 4-8, a second exhaust ball valve 4-7, a pressure equalizing ball valve 4-6, and a silencer 4-9. The input end of the pre-filter serves as the input end of the entire input subsystem. The output end of the pre-filter is connected to the input end of the precision filter. The output end of the precision filter is connected to the inlet end of the inlet valve. The outlet end of the inlet valve is connected to the inlet end of one of the heating and filtering devices via the first inlet ball valve. The outlet end of the inlet valve is connected to the inlet end of the other heating and filtering device via the second inlet ball valve. The two ends of the pressure equalizing ball valve are respectively connected to the inlet ends of the two heating and filtering devices. The inlet ends of the two heating and filtering devices are respectively connected to the silencer via the first exhaust ball valve and the second exhaust ball valve. This structure allows for primary filtration of the incoming air, ensuring the cleanliness of the final output air. The air in the input subsystem can be supplied using an existing air pump, and the silencer effectively reduces noise. The output subsystem includes an external heater 4-12, a first pressure gauge 4-25, a second pressure gauge 4-21, a first pressure reducing gauge 4-16, a second pressure reducing gauge 4-14, a first check valve 4-24, a second check valve 4-26, a third check valve 4-27, a fourth check valve 4-22, a needle valve 4-13, a safety valve 4-19, an exhaust shut-off valve 4-23, a post-filter 4-19, a pressure maintaining valve 4-18, a first pressure reducing valve 4-17, and a second pressure reducing valve 4-15. The outlet of one of the heating and filtering devices is connected to the inlet of a first one-way valve. The outlet of the first one-way valve is connected to the inlet of a subsequent filter via an exhaust shut-off valve. The inlet of the first one-way valve is also connected to the outlet of a second one-way valve, which is connected to the outlet of an external heater. The inlet of a third one-way valve is connected to the outlet of the external heater, and its outlet is connected to the inlet of a fourth one-way valve. The outlet of the fourth one-way valve is connected to the inlet of a subsequent filter via an exhaust shut-off valve. The inlet of the fourth one-way valve is also connected to the outlet of another heating and filtering device. The outlet of the subsequent filter is connected to a pressure maintaining valve. The outlet of the first pressure reducing valve is connected to the inlet of the second pressure reducing valve, and the outlet of the second pressure reducing valve is connected to the inlet of the external heater via a safety valve and a needle valve. The outlet of the second pressure reducing valve also serves as the air source output port for the actuator. The first and second pressure gauges are respectively installed at the outlets of the two heating and filtering devices. The first pressure reducing gauge is installed on the pipeline between the first and second pressure reducing valves, and the second pressure reducing gauge is installed at the output end of the second pressure reducing valve. This structure allows for further filtration and heating of the output air, ensuring that the output air reaches the required cleanliness and temperature.The pre-filter, precision filter, and post-filter mentioned above all use existing air filter structures, which will not be elaborated here. Additionally, drain valves are installed at the drain ports of the pre-filter, precision filter, and post-filter. The micro-thermal adsorption device includes an input subsystem, an output subsystem, and two identical heating and filtering devices. The input end of the input subsystem is connected to the output end of the air compressor, meaning the air compressor uses ammonia from the low-temperature cooling recovery device as a gas source to supply gas to the entire system. The output end of the input subsystem is connected to the two heating and filtering devices 4-18, and the output ends of the two heating and filtering devices 4-18 are connected to the input end of the output subsystem. The output end of the output subsystem outputs gas to the gas-using equipment. The two heating and filtering devices 4-18 operate alternately. Through this structure, the compressed ammonia provided by the compressor can be continuously and stably purified and dried, thereby providing gas for the circulation system. After drying the nitrogen, the micro-thermal adsorption device obtains low-temperature circulating nitrogen with a dew point below -40℃. This low-temperature circulating nitrogen is then heated to 15℃ and circulated to a vertical boiling fluidized bed for further drying.

[0028] In addition, to better drive and enhance the flow of nitrogen in the closed loop, the drying system is also equipped with an induced draft fan. This fan is located within the closed loop consisting of a vertical fluidized bed, a dust removal unit, a low-temperature cooling and recovery unit, and a micro-thermal adsorption unit. The induced draft fan drives the nitrogen to circulate within the closed loop. This induced draft fan can drive the nitrogen to circulate throughout the entire system.

[0029] Furthermore, in vertical fluidized bed drying apparatuses, the material to be dried is organic crystalline particles at 0-5℃. Conventional airflow drying with dry air carries the risk of forming explosive dust mixtures. Therefore, inert gases such as nitrogen and helium are preferred, and from an economic perspective, nitrogen is undoubtedly the best choice. Contrary to existing literature, experiments in this embodiment show that the nitrogen temperature should not exceed 15℃. This effectively prevents the crystals from melting during the drying process while still achieving rapid drying. Because airflow drying involves large gas volumes, the existing process of removing dust from the drying exhaust gas in fluidized bed drying is unsuitable for this apparatus. Such emissions would prevent gas recycling, and direct recycling would continuously increase the gas moisture content, making stable operation impossible. Therefore, the dried nitrogen must undergo dust removal, impurity removal, and dehydration to meet the requirements for recycling.

[0030] In this embodiment, after being fed by a vacuum feeding system, the wet material is fluidized in a vertical fluidized bed by a stream of dry nitrogen. In this state, the crystalline material is highly dispersed in the nitrogen. The nitrogen comes into contact with the surface of the wet material, accelerating the vaporization of water and solvent, thereby achieving the purpose of rapid drying. The vaporized water and solvent are discharged from the upper part of the fluidized bed with the nitrogen. Solid impurities are removed by a dust collector, methanol is removed by low-temperature water absorption, and the dried nitrogen is obtained by dehydration by a micro-thermal adsorption device and recycled for use in the drying system.

Claims

1. A low-temperature closed-loop circulating fluidized bed drying system, characterized in that: It includes a vertical boiling fluidization device, a dust removal device, a low-temperature cooling and recovery device, and a micro-heat adsorption device, which are arranged in sequence to form a closed loop; The vertical fluidized bed device includes a fluidized bed body, with a feed inlet on one side of the upper side of the fluidized bed body. A material distribution and dispersing mechanism is provided inside the fluidized bed body. The material distribution and dispersing mechanism includes a connecting rod provided inside the fluidized bed body. Several material distribution plates are evenly distributed on the outer side of the connecting rod. There are gaps between the material distribution plates. The connecting rod is inclined to connect the two ends and is equipped with a vibration device. A blowing mechanism is provided inside the fluidized bed body and below the material distribution and dispersing mechanism. The dust removal device includes a housing, internal partitions that divide the housing into two or more compartments, ash hoppers and ash discharge valves placed at the bottom of the compartments, a filtration system and a dust removal system placed inside the compartments, and a top cover placed on the top of the compartments. Each compartment is equipped with an air inlet pipe and an exhaust pipe. The cryogenic cooling and recovery device sprays an absorbent into the nitrogen gas. The absorbent absorbs the organic solvent in the nitrogen gas, and the nitrogen gas after the organic solvent is removed enters the micro-thermal adsorption device. The micro-thermal adsorption device includes an input subsystem, an output subsystem, and two identical heating and filtering devices. The input end of the input subsystem is connected to the output end of the air compressor, and the output end of the input subsystem is connected to the two heating and filtering devices respectively. The output ends of the two heating and filtering devices are connected to the input end of the output subsystem, and the output end of the output subsystem outputs to the air-consuming equipment. The two heating and filtering devices work alternately.

2. The low-temperature closed-loop circulating fluidized bed drying system as described in claim 1, characterized in that: The blowing mechanism includes several inclined scrapers evenly distributed on opposite front and rear sides of the fluidized bed body. Shafts rotatably connect to opposite front and rear sides of the fluidized bed body, located between the scrapers. Perforated rollers are positioned between opposite shafts. A motor is located on one side of the fluidized bed body, corresponding to one of the shafts. The motor is fixedly connected to one end of the shaft extending beyond the fluidized bed body. Meshing gears are fitted onto the other end of the shaft extending beyond the fluidized bed body. Each other end of the shaft has a through hole that mates with the roller. A connecting pipe is inserted into the through hole for connection. One end of the tube extending into the drum is provided with a spiral air outlet pipe, and air outlet holes are evenly distributed on the outer side of the air outlet pipe. Several steam outlet holes are evenly distributed on the outer side of the fluidized bed body and located between the material distribution and blowing mechanism. Each steam outlet hole is connected to a pipe, and the pipe is connected to a cyclone separator through a pipe connector. A discharge pipe is provided inside the fluidized bed body and below the blowing mechanism. The discharge end of the cyclone separator cooperates with the discharge pipe to discharge material. Several vibrating motors are evenly distributed on the outer side of the fluidized bed body. Support feet are provided under the fluidized bed body, and noise reduction and vibration damping mechanisms are provided under the support feet.

3. The low-temperature closed-loop circulating fluidized bed drying system as described in claim 1, characterized in that: The temperature of the low-temperature circulating nitrogen gas blown into the vertical fluidized bed is no more than 15°C, and the material to be dried in the vertical fluidized bed is a crystalline material at 0~5°C.

4. The low-temperature closed-loop circulating fluidized bed drying system as described in claim 1, characterized in that: The absorbent sprayed inside the low-temperature cooling and recovery device is 5°C low-temperature water; after the absorbent absorbs the organic solvent, nitrogen gas is formed into water-saturated nitrogen gas, and the temperature of water-saturated nitrogen gas is 5-8°C.

5. The low-temperature closed-loop circulating fluidized bed drying system as described in claim 1, characterized in that: After the nitrogen gas is dried by the micro-thermal adsorption device, a low-temperature circulating nitrogen gas with a dew point below -40°C is obtained. The low-temperature circulating nitrogen gas is then circulated to the vertical boiling fluidization device after being adjusted to 15°C.

6. The low-temperature closed-loop circulating fluidized bed drying system as described in claim 1, characterized in that: It also includes an exhaust fan, which is located in a closed loop consisting of a vertical boiling vibration fluidization device, a dust removal device, a low-temperature cooling and recovery device, and a micro-heat adsorption device. The exhaust fan of the exhaust fan drives the nitrogen to circulate in the closed loop.

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