Continuously producing nitrogen closed-loop acetic acid recovery flash drying system

Abstract

The present invention relates to a nitrogen closed-loop acetic acid recovery and flash drying system capable of continuous production. The system comprises a nitrogen source, a heater, an explosion-proof blower, a flash dryer, a screw feeder, a cyclone separator, a heat exchanger, a condenser cooler, a solvent recovery tank, and a first cryogenic crystallizer and a second cryogenic crystallizer arranged in parallel. Fins are provided in the first cryogenic crystallizer and the second cryogenic crystallizer, and a cold source medium for condensation and a hot source medium for liquefaction can be introduced into the fins. The first cryogenic crystallizer and the second cryogenic crystallizer can be alternately in a condensation and crystallization state and a heating and melting state, thereby realizing continuous recovery of acetic acid.

Description

Technical Field

[0001] The present invention relates to the technical field of drying equipment, in particular to a nitrogen closed-circuit acetic acid recovery flash drying system and a working method thereof. Background Art

[0002] Solid-state fermentation is a traditional vinegar production process in my country, producing vinegar with excellent flavor. However, its drawbacks include long production cycles, high labor intensity, and low vinegar yields. This is due to the low recovery rate of acetic acid in the raw materials during production and the lack of suitable acetic acid recovery equipment.

[0003] Chinese patent document CN101776372A discloses a nitrogen closed-circuit drying and solvent recovery system, which consists of a fluidized bed dryer, a condensing device, a solid-gas separator, a circulating fan, a nitrogen heater, a solvent recovery tank, etc. Hot N2 is used to dry the fluidized bed desiccant. The discharged nitrogen is recovered through the condenser to recover the solvent, and is reheated by the circulating fan and then enters the fluidized bed for drying again. This cycle is closed and has no tail gas emissions. It can achieve continuous production, recover the solvent, and no wastewater discharge.

[0004] Chinese patent document CN201281534Y discloses a closed-loop boiling drying unit that can also achieve solvent recovery; and inert gas can be filled into the system to achieve closed-loop circulation. However, the production process is intermittent, and each batch of production requires reloading and unloading, resulting in low production efficiency and high labor intensity. The air in the system needs to be replaced with nitrogen for each batch, and the drying time is long.

[0005] To achieve continuous production, Chinese patent document CN102022895A discloses a closed-loop fluidized bed dryer main unit. The hopper is made into a flip-type perforated plate. Through mechanical transmission, the hopper is flipped regularly to achieve intermittent continuous production without disrupting the nitrogen circulation of the system. However, the operation of the entire system is unstable. Each time the solvent is loaded, the recovery decreases from a large amount to a small amount. The circulation temperature fluctuates due to the change in evaporation amount. This is inevitable. In addition, the sealing of the flip plate is also a problem. Once material sticks to the plate surface, air leakage and material leakage will occur, affecting the drying effect.

[0006] The above systems all have obvious defects, such as low heat exchange efficiency resulting in high energy consumption, inability to produce continuously resulting in low efficiency, or low solvent recovery rate, which affects the drying effect. In summary, designing a nitrogen closed-loop circulation system suitable for automated continuous production and high reliability for recovering acetic acid with a low flash point, high volatility, and a pungent odor is a technical problem that technicians in this field urgently need to solve. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a nitrogen closed-circuit acetic acid recovery flash drying system with a simple structure and continuous production.

[0008] In order to solve the above technical problems, the present invention provides a nitrogen closed-loop acetic acid recovery flash drying system, comprising: a nitrogen source, a heater, an explosion-proof blower, a flash dryer, a spiral feeder, a cyclone separator, a heat exchanger, a condenser cooler, a solvent recovery tank, a first cryogenic crystallizer and a second cryogenic crystallizer arranged in parallel, wherein the nitrogen source, the heater, the explosion-proof blower, the flash dryer and the cyclone separator are sequentially connected by a pipeline seal, the gas discharged from the cyclone separator outlet mixed with gaseous acetic acid is cooled by the heat exchanger and then enters the condenser cooler, and the condenser cooler cools the mixed gas. The gas of gaseous acetic acid is condensed, and the condenser cooler is connected to the solvent recovery tank, so that the gaseous acetic acid enters the solvent recovery tank after being cooled; fins are set in the first cryogenic crystallizer and the second cryogenic crystallizer, and the cold source medium for condensation and the heat source medium for liquefaction can be introduced into the fins. The air inlets of the first cryogenic crystallizer and the second cryogenic crystallizer are respectively connected to the air outlet of the condenser cooler, and a first valve is set between the first cryogenic crystallizer and the condenser cooler, and a second valve is set between the second cryogenic crystallizer and the condenser cooler. When the first valve is opened, When the second valve is closed, the gas mixed with gaseous acetic acid flowing out of the condenser cooler enters the first cryogenic crystallizer, a cold source medium is introduced into the fins of the first cryogenic crystallizer, the gaseous acetic acid condenses on the fins of the first cryogenic crystallizer, a heat source medium is introduced into the fins of the second cryogenic crystallizer, and the solid acetic acid on the fins of the second cryogenic crystallizer is heated and liquefied; when the first valve is closed and the second valve is opened, the gas mixed with gaseous acetic acid flowing out of the condenser cooler enters the second cryogenic crystallizer, a cold source medium is introduced into the fins of the second cryogenic crystallizer, and the gaseous acetic acid condenses on the fins of the second cryogenic crystallizer On the top, a heat source medium is introduced into the fins of the first cryogenic crystallizer, and the solid acetic acid on the fins of the first cryogenic crystallizer is heated and liquefied; so that the first cryogenic crystallizer and the second cryogenic crystallizer can alternately condense and liquefy, the first cryogenic crystallizer and the second cryogenic crystallizer are connected to the solvent recovery tank, and the gaseous acetic acid can enter the solvent recovery tank after being condensed and liquefied; the gas outlets of the first cryogenic crystallizer and the second cryogenic crystallizer are connected to the heat exchanger, and the gas cooled by the first cryogenic crystallizer and the second cryogenic crystallizer enters the heat exchanger, is preheated by the heat exchanger, and then enters the heater to realize a closed-loop circulation.

[0009] Furthermore, the nitrogen closed-loop acetic acid recovery flash drying system also includes a bag dust collector, which is arranged between the cyclone separator and the heat exchanger. An ultrafine filter bag with a filtration accuracy of no more than 1um is provided in the bag dust collector to ensure the filtration effect and prevent dust materials from continuing to circulate in the system; the ultrafine filter bag is a PTFE peritoneal filter bag.

[0010] Furthermore, a volute-shaped dual-channel air inlet is provided at the bottom of the flash dryer to ensure uniform air intake. A figure-eight stirring blade is provided inside the flash dryer, which is driven to rotate by a magnetic sealing mechanism. This frictionless blade has a good sealing effect and is leak-free. The sealing performance meets the requirements of GMP (Good Manufacturing Practice) and FDA (Food and Drug Administration) regulations. A rotating classifying ring is provided in the air outlet duct of the flash dryer to control the mesh fineness and final moisture content of the material, and to control the residence time of large particles in the flash dryer. Particles that do not meet the particle size or moisture requirements do not pass through the rotating classifying ring and return to the bottom for further crushing and drying.

[0011] Furthermore, the screw feeder includes a coarse crusher for crushing materials and a shaftless screw conveyor for conveying materials. The feed port of the shaftless screw conveyor is connected to the discharge port of the coarse crusher, and the discharge port of the shaftless screw conveyor is connected to the feed port of the flash dryer. Under the shaftless screw conveyor, the flash dryer is fed with materials at regular intervals and in fixed quantities. The materials are not squeezed during the feeding process, and no secondary agglomeration will occur, which is conducive to the dispersion of the materials.

[0012] Furthermore, the heat exchanger is an air-to-air plate heat exchanger, which performs heat exchange between the low-temperature gas from the cryogenic crystallizer and the high-temperature gas from the bag dust collector, so that the temperature of the low-temperature gas from the cryogenic crystallizer can be preheated from 0°C to 20°C, and the temperature of the high-temperature gas from the bag dust collector can be reduced from 80°C to 60°C. By using a heat exchanger for heat exchange, energy consumption can be reduced by more than 15%, energy utilization can be improved, and the power consumption of the heater can be appropriately reduced, thereby achieving scientific and reasonable energy conservation.

[0013] Furthermore, a first-level water-cooled liquefaction zone and a second-level chilled water liquefaction zone are sequentially arranged in the condenser cooler. The cooling medium of the first-level water-cooled liquefaction zone is room temperature water, and the cooling medium of the second-level chilled water liquefaction zone is -5°C chilled brine, so that the gas mixed with gaseous acetic acid is cooled, and the gaseous acetic acid therein is converted into liquid acetic acid, which is collected into a solvent recovery tank; a water retainer is provided at the air outlet of the condenser cooler to minimize the entrainment of acetic acid mist in the circulating gas as much as possible, which can effectively reduce the acetic acid content entering the cryogenic crystallizer; under normal circumstances, the solvent recovery rate through the first-level water cooling and the second-level chilled water cooling is about 85%, and the remaining small amount of gaseous acetic acid enters the cryogenic crystallizer with the circulating gas for three-level condensation, which can greatly reduce the solvent content in the circulating gas.

[0014] Furthermore, the cold source medium introduced into the first cryogenic crystallizer and the second cryogenic crystallizer is -18°C frozen brine, and the heat source medium introduced into the first cryogenic crystallizer and the second cryogenic crystallizer is hot nitrogen at not less than 120°C to ensure the liquefaction effect. When the cold source medium is introduced into the fins of the first cryogenic crystallizer and the second cryogenic crystallizer, the fins are in a condensed state, and the gas mixed with a small amount of gaseous acetic acid passes through the fins, and the gaseous acetic acid condenses and crystallizes into solid acetic acid attached to the surface of the fins; when the heat source medium is introduced into the first cryogenic crystallizer and the second cryogenic crystallizer, the fins are in a melted state, and the solid acetic acid attached to the surface of the fins is heated and melted, and the obtained liquid acetic acid enters the solvent recovery tank.

[0015] Furthermore, the nitrogen closed-loop acetic acid recovery flash drying system also includes a frozen brine recovery tank. The frozen brine in the fins of the first cryogenic crystallizer and the second cryogenic crystallizer can enter the frozen brine recovery tank to ensure that the frozen brine can be discharged cleanly before hot nitrogen is introduced into the fins of the first cryogenic crystallizer or the second cryogenic crystallizer.

[0016] The working method of the above-mentioned nitrogen closed-loop acetic acid recovery flash drying system includes the following steps:

[0017] A. The materials to be recycled enter the coarse crusher, where they are crushed and sent to the flash dryer via a shaftless screw conveyor, where they are broken up and chopped by an eight-shaped stirring blade.

[0018] B. The nitrogen in the nitrogen source is heated to a temperature of not less than 120°C by a heater and enters a flash dryer. The material in the flash dryer is flash dried to achieve solid-gas separation, obtaining gaseous acetic acid and particulate material. The gaseous acetic acid is mixed with the nitrogen to form a gas mixed with gaseous acetic acid. The particulate material that meets the particle size and humidity requirements enters the cyclone separator and the bag dust collector in sequence along with the gas mixed with gaseous acetic acid. The cyclone separator performs a primary recovery of the particulate material, and the bag dust collector performs a secondary recovery of particulate material with a smaller particle size to ensure the solid-gas separation effect. The temperature of the gas mixed with gaseous acetic acid drops to about 110°C when it is discharged from the flash dryer and enters the cyclone separator, and drops to about 100°C when it is discharged from the cyclone separator and enters the bag dust collector.

[0019] C. The gas mixed with gaseous acetic acid drops to about 90°C when discharged from the bag filter, enters the air-to-air plate heat exchanger for heat exchange, and drops to about 70°C. It then enters the condenser cooler and passes through the primary water-cooled liquefaction zone and the secondary chilled water liquefaction zone of the condenser cooler for cooling. The room temperature water in the primary water-cooled liquefaction zone and the -5°C frozen brine in the secondary chilled water liquefaction zone are used for condensation and cooling, respectively. The obtained liquid acetic acid enters the solvent recovery tank. The gas mixed with a small amount of gaseous acetic acid drops to about 13°C when discharged from the condenser cooler.

[0020] D. The first valve is opened and the second valve is closed. At the same time, -18°C frozen brine is introduced into the fins of the first cryogenic crystallizer. At this time, the first cryogenic crystallizer is in a condensation and crystallization state. The gas discharged from the condensation cooler enters the first cryogenic crystallizer. A small amount of gaseous acetic acid in the gas condenses and crystallizes and adheres to the surface of the fins. The gas temperature drops to about 0°C. After being discharged from the first cryogenic crystallizer, it enters the heat exchanger for heat exchange. The gas after heat exchange enters the heater and flash dryer for recycling.

[0021] E. After the first cryogenic crystallizer is in a condensation and crystallization state for a preset time, the first valve is closed and the second valve is opened. At the same time, -18°C frozen brine is introduced into the fins of the second cryogenic crystallizer. At this time, the second cryogenic crystallizer is in a condensation and crystallization state, and the gas discharged from the condenser cooler enters the second cryogenic crystallizer. A small amount of gaseous acetic acid in the gas condenses and crystallizes and adheres to the surface of the fin. The gas temperature drops to about 0°C. After being discharged from the second cryogenic crystallizer, it also enters the heat exchanger for heat exchange. The gas after heat exchange enters the heater and flash dryer for recycling. Hot nitrogen with a temperature of not less than 120°C is introduced into the fins of the first cryogenic crystallizer. The first cryogenic crystallizer is in a heated and melted state, and the solid acetic acid attached to the surface of the fin is heated and melted. The obtained liquid acetic acid enters the solvent recovery tank.

[0022] F. The first cryogenic crystallizer and the second cryogenic crystallizer are alternately in the condensation crystallization state and the heating melting state, which can realize the continuous recovery of acetic acid.

[0023] Technical effects of the invention: (1) Compared with the prior art, the nitrogen closed-loop acetic acid recovery flash drying system of the present invention is provided with a first cryogenic crystallizer and a second cryogenic crystallizer which can alternately be in a condensation crystallization state and a heating and melting state. When the first cryogenic crystallizer is in the condensation crystallization state, the second cryogenic crystallizer is in a heating and melting state. When the second cryogenic crystallizer is in the condensation crystallization state, the first cryogenic crystallizer is in a heating and melting state, thereby realizing a continuous condensation and solidification-heating liquefaction process of acetic acid and realizing continuous recovery of acetic acid; (2) adopting two-stage cooling of water cooling and frozen brine cooling in the condenser cooler can reduce the content of gaseous acetic acid in the gas to less than 15%, and combining with the frozen brine condensation of the cryogenic crystallizer, adopting three-stage cooling recovery can reduce the content of acetic acid in the gas to less than 0.1%; (3) The gas discharged from the cryogenic crystallizer enters the heat exchanger as low-temperature gas for preheating, which can reduce energy consumption by more than 15% and improve energy utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described in detail below with reference to the accompanying drawings:

[0025] Figure 1 Schematic diagram of the structure of the nitrogen closed-loop acetic acid recovery flash drying system of the present invention;

[0026] Figure 2 It is a structural schematic diagram of the flash dryer and the spiral feeder in the present invention.

[0027] In the figure: explosion-proof blower 10, nitrogen air inlet 11, heater 12, cyclone separator 13, bag dust collector 14, heat exchanger 15, second blower 16, nitrogen gas storage tank 17, nitrogen exhaust port 18, flash dryer 2, figure eight stirring blade 21, magnetic sealing mechanism 22, flash machine air inlet 23, flash machine exhaust port 24, screw feeder 3, coarse crusher 31, shaftless screw conveyor 32, first cryogenic crystallizer 41, second cryogenic crystallizer 42, solvent recovery tank 43, frozen brine recovery tank 44, condenser cooler 5. Implementation Method

[0028] Example 1 Figures 1 to 2 As shown, the nitrogen closed-loop acetic acid recovery flash drying system of this embodiment includes a nitrogen source, an explosion-proof blower 10, a heater 12, a flash dryer 2, a screw feeder 3, a cyclone separator 13, a bag dust collector 14, a heat exchanger 15, a condenser cooler 5, a solvent recovery tank 43, a first cryogenic crystallizer 41 and a second cryogenic crystallizer 42 arranged in parallel, the nitrogen source, the explosion-proof blower 10, the heater 12, the flash dryer 2, the cyclone separator 13, and the bag dust collector 14 are sealed and connected in sequence through a pipeline, the nitrogen in the nitrogen source enters the pipeline and the heater 12 through the nitrogen inlet 11, and is introduced into the flash machine inlet 23 of the flash dryer 2 by the explosion-proof blower 10, and the material to be recovered enters the flash dryer 2 through the screw feeder 3 for heating and drying.

[0029] A volute-shaped double-channel air inlet is provided at the bottom of the flash dryer 2 to ensure uniform air intake; an eight-shaped stirring blade 21 is provided inside the flash dryer 2, and the eight-shaped stirring blade 21 is driven to rotate by a magnetic sealing mechanism 22, which is frictionless, has a good sealing effect, and does not leak. The sealing performance meets the requirements of GMP (Good Manufacture Practice, Pharmaceutical Production Quality Management Specification) and FDA (Food and Drug Administration). Administration (FDA) specifications; a rotating classifying ring is provided in the air outlet duct of the flash dryer 2 to control the mesh fineness and final moisture content of the material, and to control the residence time of large particles in the flash dryer. Particles that do not meet the required particle size or moisture content fail to pass through the rotating classifying ring and are returned to the lower portion for further crushing and drying. The specific structure of the dual-channel air inlet in the flash dryer 2 can be found in the description of Chinese Patent Authorization Publication No. CN201548024U, Rotary Flash Dryer; the specific structure of the magnetic sealing mechanism can be found in the description of Chinese Patent Authorization Publication No. CN202836139U, Medicinal Flash Dryer, and will not be described in detail here.

[0030] The screw feeder 3 includes a coarse crusher 31 for crushing materials and a shaftless screw conveyor 32 for conveying materials. The feed port of the shaftless screw conveyor 32 is connected to the discharge port of the coarse crusher 31, and the discharge port of the shaftless screw conveyor 32 is connected to the feed port of the flash dryer 2. Under the shaftless screw conveyor, the flash dryer 2 is fed with materials at regular intervals and in a fixed quantity. In the process of feeding materials, the materials are not squeezed and secondary agglomeration will not occur, which is conducive to the dispersion of the materials.

[0031] The material obtained after drying by the flash dryer 2 and the gas mixed with gaseous acetic acid enter the cyclone separator 13 through the flash machine exhaust port 24, and the cyclone separator 13 recovers the particulate material. The cyclone separator 13 includes a cylindrical cylinder and a conical cylinder. An air outlet pipe is provided at the top axis of the cylindrical cylinder. The bottom end of the cylindrical cyclone cylinder and the top end of the conical cylinder are fixedly connected. An air inlet with a rectangular cross section is provided at the top of the side wall of the cylindrical cyclone cylinder. The air inlet enters the cyclone along the side wall of the cyclone cylinder. Inside the cylinder, the gas entering from the air inlet can spiral downward on the inner wall of the cyclone cylinder. A discharge port is set at the bottom end of the conical cylinder. The width b of the air inlet is 0.21 times the diameter D of the cyclone cylinder, and the height h of the air inlet is 0.42 times the diameter D of the cyclone cylinder, so that the gas entering the cyclone cylinder has an optimized separation efficiency. The specific structure of the cyclone separator refers to the applicant's prior application with patent application number CN2017215471247, which will not be described in detail here.

[0032] The gas mixed with gaseous acetic acid and a small amount of particulate matter discharged from the air outlet of the cyclone separator 13 enters the bag dust collector 14. The bag dust collector 14 is equipped with an ultrafine filter bag with a filtration accuracy of no more than 1 μm. The ultrafine filter bag is a PTFE peritoneal filter bag. The ultrafine filter bag performs secondary filtration to ensure the filtration effect and prevent dust materials from continuing to circulate in the system. The gas mixed with acetic acid discharged from bag filter 14 is cooled by heat exchanger 15 and then enters condenser cooler 5, where it condenses the gas mixed with acetic acid. Condenser cooler 5 is sequentially provided with a primary water-cooled liquefaction zone and a secondary chilled water liquefaction zone. The cooling medium in the primary water-cooled liquefaction zone is room temperature water, while the cooling medium in the secondary chilled water liquefaction zone is -5°C chilled brine. This cools the gas mixed with acetic acid, converting the gaseous acetic acid into liquid acetic acid. Condenser cooler 5 is connected to solvent recovery tank 43 via a pipeline, allowing the gaseous acetic acid to be cooled and converted into liquid acetic acid before entering solvent recovery tank 43. A water retainer is provided at the air outlet of condenser cooler 5 to minimize the entrainment of acetic acid mist in the circulating gas, effectively reducing the acetic acid content entering the cryogenic crystallizer. Under normal circumstances, the solvent recovery rate through the primary water-cooled and secondary chilled water-cooled processes is approximately 85%. The remaining small amount of gaseous acetic acid enters the cryogenic crystallizer with the circulating gas for tertiary condensation.

[0033] Fins are provided in the first cryogenic crystallizer 41 and the second cryogenic crystallizer 42, and a cold source medium for condensation and a heat source medium for liquefaction can be introduced into the fins. When the cold source medium is introduced into the fins of the first cryogenic crystallizer 41 and the second cryogenic crystallizer 42, the fins are in a condensing state, and a gas mixed with a small amount of gaseous acetic acid passes through the fins, and the gaseous acetic acid condenses and crystallizes into solid acetic acid attached to the surface of the fins; when the heat source medium is introduced into the first cryogenic crystallizer 41 and the second cryogenic crystallizer 42, the fins are in a melting state, and the solid acetic acid attached to the surface of the fins is heated and melted, and the obtained liquid acetic acid enters the solvent recovery tank.

[0034] The cold source medium introduced into the first cryogenic crystallizer 41 and the second cryogenic crystallizer 42 is -18°C frozen brine, and the heat source medium introduced into the first cryogenic crystallizer 41 and the second cryogenic crystallizer 42 is hot nitrogen at not less than 120°C to ensure the liquefaction effect. The air inlets of the first cryogenic crystallizer 41 and the second cryogenic crystallizer 42 are respectively connected to the air outlet of the condenser cooler 5. A first valve is set between the first cryogenic crystallizer 41 and the condenser cooler 5, and a second valve is set between the second cryogenic crystallizer 42 and the condenser cooler 5. When the first valve is opened and the second valve is closed, the condenser cooler The gas mixed with gaseous acetic acid flowing out of the condenser cooler enters the first cryogenic crystallizer 41, a cooling medium is introduced into the fins of the first cryogenic crystallizer 41, and the gaseous acetic acid condenses on the fins of the first cryogenic crystallizer 41. A heat source medium is introduced into the fins of the second cryogenic crystallizer 42, and the solid acetic acid on the fins of the second cryogenic crystallizer 42 is heated and liquefied. When the first valve is closed and the second valve is opened, the gas mixed with gaseous acetic acid flowing out of the condenser cooler enters the second cryogenic crystallizer 42, a cooling medium is introduced into the fins of the second cryogenic crystallizer 42, and the gaseous acetic acid condenses on the fins of the second cryogenic crystallizer 42. The heat source medium is introduced into the fins of the cryogenic crystallizer 41, and the solid acetic acid on the fins of the first cryogenic crystallizer 41 is heated and liquefied; so that the first cryogenic crystallizer 41 and the second cryogenic crystallizer 42 can be alternately condensed and liquefied, and the first cryogenic crystallizer 41 and the second cryogenic crystallizer 42 are connected to the solvent recovery tank 43 through a pipeline, and the gaseous acetic acid can enter the solvent recovery tank 43 after being condensed and liquefied; the gas outlets of the first cryogenic crystallizer 41 and the second cryogenic crystallizer 42 are connected to the heat exchanger through a pipeline, and the gas cooled by the first cryogenic crystallizer 41 and the second cryogenic crystallizer 42 enters the heat exchanger 15, and the heat exchange The device 15 is an air-to-air plate heat exchanger, which performs heat exchange between the low-temperature gas from the cryogenic crystallizer and the high-temperature gas from the bag dust collector 14, so that the temperature of the low-temperature gas from the cryogenic crystallizer can be preheated from 0°C to 20°C, and the temperature of the high-temperature gas from the bag dust collector 14 can be reduced from 80°C to 60°C. By adopting the heat exchanger 15 for heat exchange, the gas preheated by the heat exchanger 15 enters the heater 12, realizing a closed-loop circulation, which can reduce energy consumption by more than 15%, improve energy utilization, and appropriately reduce the power consumption of the heater 12, thereby scientifically and rationally saving energy.

[0035] Preferably, the nitrogen closed-loop acetic acid recovery flash drying system also includes a frozen brine recovery tank 44 connected to the first cryogenic crystallizer 41, the second cryogenic crystallizer 42, and the condenser cooler 5. The frozen brine in the fins of the first cryogenic crystallizer 41, the second cryogenic crystallizer 42, and the condenser cooler 5 can enter the frozen brine recovery tank 43 to ensure that the frozen brine can be discharged cleanly before hot nitrogen is introduced into the fins of the first cryogenic crystallizer 41 or the second cryogenic crystallizer 42.

[0036] Preferably, the nitrogen closed-loop acetic acid recovery flash drying system further includes a nitrogen storage tank 17 and a second blower 16. The nitrogen storage tank 17 is used to store nitrogen to ensure pressure balance in the system; the second blower 16 is placed between the heat exchanger 15 and the condenser cooler 5 to ensure gas delivery pressure; the nitrogen closed-loop acetic acid recovery flash drying system is also provided with a nitrogen exhaust port 18 for discharging gas in the system in an emergency.

[0037] Preferably, the flash dryer 2, the spiral feeder 3, the cyclone separator 13, the bag dust collector 14, the heat exchanger 15, the condenser cooler 5, the solvent recovery tank 43, the first cryogenic crystallizer 41, and the second cryogenic crystallizer 42 that are in direct contact with acetic acid are made of 316Ti stainless steel, which can improve their resistance to intergranular corrosion and increase their service life. Example

[0038] The working method of the above-mentioned nitrogen closed-loop acetic acid recovery flash drying system includes the following steps:

[0039] A. The material to be recycled enters the coarse crusher 31, is crushed by the coarse crusher 31 and is sent to the flash dryer 2 through the shaftless screw conveyor 32, where the material is broken up and chopped by the figure-eight stirring blade 21.

[0040] B. The nitrogen in the nitrogen source is heated to a temperature of not less than 120° C. by the heater 12 and enters the flash dryer 2. The material in the flash dryer 2 is flash dried to achieve solid-gas separation, and gaseous acetic acid and particulate material are obtained. The gaseous acetic acid is mixed with the nitrogen to form a gas mixed with gaseous acetic acid. The particulate material that meets the particle size and humidity requirements enters the cyclone separator 13 and the bag dust collector 14 in sequence along with the gas mixed with gaseous acetic acid. The cyclone separator 13 performs a primary recovery of the particulate material, and the bag dust collector 14 performs a secondary recovery of particulate material with a smaller particle size, thereby ensuring the solid-gas separation effect. The temperature of the gas mixed with gaseous acetic acid drops to about 110° C. when it is discharged from the flash dryer 2 and enters the cyclone separator 13. The temperature drops to about 100° C. when it is discharged from the cyclone separator 13 and enters the bag dust collector 14.

[0041] C. The gas mixed with gaseous acetic acid drops to about 90°C when discharged from the bag filter 14, enters the air-to-air plate heat exchanger 15 for heat exchange, and then drops to about 70°C. It then enters the condenser cooler 5, and sequentially passes through the primary water-cooled liquefaction zone and the secondary chilled water liquefaction zone of the condenser cooler 5 for cooling. The room temperature water in the primary water-cooled liquefaction zone and the -5°C chilled brine in the secondary chilled water liquefaction zone are used for condensation and cooling, respectively. The obtained liquid acetic acid enters the solvent recovery tank 43. The gas mixed with a small amount of gaseous acetic acid drops to about 13°C when discharged from the condenser cooler 5.

[0042] D. The first valve is opened and the second valve is closed. At the same time, -18°C chilled brine is introduced into the fins of the first cryogenic crystallizer 41. At this time, the first cryogenic crystallizer 41 is in a condensation and crystallization state. The gas discharged from the condenser cooler 5 enters the first cryogenic crystallizer 41. A small amount of gaseous acetic acid in the gas condenses and crystallizes and adheres to the surface of the fins. The gas temperature drops to about 0°C. After being discharged from the first cryogenic crystallizer 41, the gas enters the heat exchanger 15 for heat exchange. The gas after heat exchange enters the heater 12 and the flash dryer 2 for recycling.

[0043] E. After the first cryogenic crystallizer 41 is in the condensation and crystallization state for a preset time, the first valve is closed and the second valve is opened. At the same time, -18°C frozen brine is introduced into the fins of the second cryogenic crystallizer 42. At this time, the second cryogenic crystallizer 42 is in the condensation and crystallization state, and the gas discharged from the condenser cooler 5 enters the second cryogenic crystallizer 42. A small amount of gaseous acetic acid in the gas condenses and crystallizes and adheres to the surface of the fin. The gas temperature drops to about 0°C. After being discharged from the second cryogenic crystallizer 42, it also enters the heat exchanger 15 for heat exchange. The gas after heat exchange enters the heater 12 and the flash dryer 2 for recycling. Hot nitrogen with a temperature of not less than 120°C is introduced into the fins of the first cryogenic crystallizer 41. The first cryogenic crystallizer 41 is in a heated and melted state. The solid acetic acid attached to the surface of the fin is heated and melted, and the obtained liquid acetic acid enters the solvent recovery tank 43.

[0044] F. The first cryogenic crystallizer 41 and the second cryogenic crystallizer 42 are alternately in a condensation crystallization state and a heating and melting state, thereby realizing continuous recovery of acetic acid.

[0045] Obviously, the above embodiments are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all embodiments here. However, such obvious variations or modifications arising from the spirit of the present invention remain within the scope of protection of the present invention.

Claims

1. A method for operating a nitrogen closed-circuit acetic acid recovery flash drying system, characterized in that: The system includes: a nitrogen source, an explosion-proof blower, a heater, a flash dryer, a spiral feeder, a cyclone separator, a heat exchanger, a condenser cooler, a solvent recovery tank, a first cryogenic crystallizer and a second cryogenic crystallizer arranged in parallel, wherein the nitrogen source, the explosion-proof blower, the heater, the flash dryer and the cyclone separator are sequentially connected by a pipeline seal, the gas mixed with gaseous acetic acid discharged from the cyclone separator outlet passes through a bag dust collector and then is cooled by the heat exchanger before entering the condenser cooler, and the gas mixed with gaseous acetic acid is cooled by the condenser cooler. The gas is condensed, and the condenser cooler is connected to the solvent recovery tank, so that the gaseous acetic acid enters the solvent recovery tank after being cooled; fins are provided in the first cryogenic crystallizer and the second cryogenic crystallizer, and a cold source medium for condensation and a heat source medium for liquefaction can be introduced into the fins, and the air inlets of the first cryogenic crystallizer and the second cryogenic crystallizer are respectively connected to the air outlet of the condenser cooler, a first valve is provided between the first cryogenic crystallizer and the condenser cooler, and a second valve is provided between the second cryogenic crystallizer and the condenser cooler; The screw feeder includes a coarse crusher for crushing materials and a shaftless screw conveyor for conveying materials, the feed port of the shaftless screw conveyor is connected to the discharge port of the coarse crusher, and the discharge port of the shaftless screw conveyor is connected to the feed port of the flash dryer; The condenser cooler is provided with a primary water-cooled liquefaction zone and a secondary chilled water liquefaction zone in sequence. The cooling medium of the primary water-cooled liquefaction zone is room temperature water, and the cooling medium of the secondary chilled water liquefaction zone is -5°C chilled brine. A water retainer is provided at the air outlet of the condenser cooler. The cold source medium introduced into the first cryogenic crystallizer and the second cryogenic crystallizer is -18°C frozen brine, and the heat source medium introduced into the first cryogenic crystallizer and the second cryogenic crystallizer is hot nitrogen gas at not less than 120°C; The nitrogen closed-circuit acetic acid recovery flash drying system further includes a frozen brine recovery tank, and the frozen brine in the fins of the first cryogenic crystallizer and the second cryogenic crystallizer can enter the frozen brine recovery tank; The working method comprises the following steps: A. The material to be recycled enters the coarse crusher, where it is crushed and then sent to the flash dryer via a shaftless screw conveyor, where it is broken up and chopped by an eight-shaped stirring blade; B. The nitrogen in the nitrogen source is heated to a temperature of not less than 120°C by a heater and enters a flash dryer. The material in the flash dryer is flash dried to achieve solid-gas separation, obtaining gaseous acetic acid and particulate material. The gaseous acetic acid is mixed with the nitrogen to form a gas mixed with gaseous acetic acid. The particulate material that meets the particle size and humidity requirements enters the cyclone separator and the bag dust collector in sequence along with the gas mixed with gaseous acetic acid. The cyclone separator performs a primary recovery of the particulate material, and the bag dust collector performs a secondary recovery of particulate material with a smaller particle size to ensure the solid-gas separation effect. The temperature of the gas mixed with gaseous acetic acid drops to 110°C when it is discharged from the flash dryer and enters the cyclone separator, and drops to 100°C when it is discharged from the cyclone separator and enters the bag dust collector. C. The gas mixed with gaseous acetic acid drops to 90°C when discharged from the bag filter, enters the air-to-air plate heat exchanger for heat exchange, and then drops to 70°C. It then enters the condenser cooler and passes through the primary water-cooled liquefaction zone and the secondary chilled water liquefaction zone of the condenser cooler for cooling. The room temperature water in the primary water-cooled liquefaction zone and the -5°C chilled brine in the secondary chilled water liquefaction zone are used for condensation and cooling, respectively. The obtained liquid acetic acid enters the solvent recovery tank. The gas mixed with a small amount of gaseous acetic acid drops to 13°C when discharged from the condenser cooler. D. The first valve is opened and the second valve is closed. At the same time, -18°C frozen brine is introduced into the fins of the first cryogenic crystallizer. At this time, the first cryogenic crystallizer is in a condensation and crystallization state. The gas discharged from the condenser cooler enters the first cryogenic crystallizer. A small amount of gaseous acetic acid in the gas condenses and crystallizes and adheres to the surface of the fins. The gas temperature drops to 0°C. After being discharged from the first cryogenic crystallizer, it enters the heat exchanger for heat exchange. The gas after heat exchange enters the heater and flash dryer for recycling. E. After the first cryogenic crystallizer is in a condensation and crystallization state for a preset time, the first valve is closed and the second valve is opened. At the same time, -18°C frozen brine is introduced into the fins of the second cryogenic crystallizer. At this time, the second cryogenic crystallizer is in a condensation and crystallization state, and the gas discharged from the condenser cooler enters the second cryogenic crystallizer. A small amount of gaseous acetic acid in the gas condenses and crystallizes and adheres to the surface of the fin. The gas temperature drops to 0°C. After being discharged from the second cryogenic crystallizer, it also enters the heat exchanger for heat exchange. The gas after heat exchange enters the heater and flash dryer for recycling; hot nitrogen with a temperature of not less than 120°C is introduced into the fins of the first cryogenic crystallizer. The first cryogenic crystallizer is in a heating and melting state, and the solid acetic acid attached to the surface of the fin is heated and melted. The obtained liquid acetic acid enters the solvent recovery tank; F. The first cryogenic crystallizer and the second cryogenic crystallizer are alternately in the condensation crystallization state and the heating and melting state, which can realize the continuous recovery of acetic acid; The heat exchanger is an air-air plate heat exchanger, which performs heat exchange between the low-temperature gas from the cryogenic crystallizer and the high-temperature gas from the bag dust collector, so that the temperature of the low-temperature gas from the cryogenic crystallizer can be preheated from 0°C to 20°C, and the temperature of the high-temperature gas from the bag dust collector can be reduced from 80°C to 60°C.

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