Urea scrub column off-gas separation system

Abstract

The utility model belongs to tail gas gas-liquid separation device technical field, concretely relates to a kind of urea scrubbing tower tail gas separation system.The urea scrubbing tower tail gas separation system, including urea scrubbing tower, cold gas demister, tail gas separator and neutralization reactor, the urea scrubbing tower is connected with cyclone separator by side wall pipeline, cyclone separator is connected with cold gas demister, and cold gas demister top process gas conveying pipeline is provided with three branches, respectively with tail gas separator, carrier gas compressor and crystallizer connection, tail gas separator top gas outlet is connected with neutralization reactor.The urea scrubbing tower tail gas separation system of the utility model, through the cold gas demister and tail gas separator of series connection between urea scrubbing tower and neutralization reactor design, through to the multistage separation structure optimization inside tail gas separator, the problem that current device tail gas impurity removal is not thorough, easy to carry liquid solid is solved, it is favorable to realize tail gas deep purification and stable neutralization reaction.

Description

Technical Field

[0001] This utility model belongs to the technical field of tail gas gas-liquid separation devices, specifically relating to a urea scrubbing tower tail gas separation system. Background Technology

[0002] Low-pressure gas-phase catalytic oxidation is one of the mainstream industrial production processes for melamine. This process uses molten urea as raw material, which is fed into a reactor and undergoes a high-temperature pyrolysis reaction under the action of a catalyst to produce melamine. The process gas produced at the reactor outlet has a complex composition, including gaseous melamine, incompletely converted molten urea, isocyanate, ammonia, carbon dioxide, and inert carrier gas, while also carrying melamine solid particles and molten urea droplets.

[0003] The industry's standard process flow is as follows: The reactor process gas is first fed into a melamine trap to complete the initial gas-solid separation of melamine crystals; the process gas discharged from the trap enters a urea scrubbing tower, where high-temperature molten urea is used for co-current scrubbing to wash and recover residual urea, isocyanate, and trace amounts of melamine particles from the gas phase; the purified process gas is then split into three streams: one is sent to the crystallizer as low-temperature quenching gas, another is returned to the reactor as fluidizing carrier gas, and the remaining tail gas is discharged. This discharged tail gas contains a large amount of ammonia, which has high resource recovery value; however, it still contains fine molten urea droplets, ultrafine melamine dust, and methylammonium salt impurities. If directly used in downstream production, these impurities will continue to accumulate, causing scaling and blockage of the equipment, deterioration of by-product quality, and a series of other problems.

[0004] CN223454019U discloses an apparatus for producing ammonium nitrate solution from melamine tail gas. The main body consists of a transverse tubular neutralization reactor and a neutralization flash tank tangentially connected. This apparatus utilizes the ammonia and nitric acid in the melamine tail gas for complete neutralization, relies on tangential feeding to improve flash separation efficiency, and is equipped with a circulating mixing, mist recovery, and anti-vortex structure to realize the resource utilization of tail gas, producing an ammonium nitrate solution with a concentration of 75%~80%, and producing recoverable process steam as a byproduct. However, this patent does not perform in-depth removal of molten urea droplets, melamine solid particles, and methylammonium salt impurities present in the tail gas. The simple mist recovery structure built into the melamine system can only intercept a small amount of large-diameter liquid droplets and cannot remove fine droplets and ultrafine solid dust.

[0005] Currently, the gas-liquid separation devices used for process gas purification in industry are mainly cyclone separators, such as the cyclone separator with built-in corrugated plate structure disclosed in patent CN209076241U. The main body consists of a cylinder, a cone, process gas inlet and outlet pipelines, and a drain pipeline with a control valve. The core improvement is that corrugated plates are uniformly welded to the outer circumference of the process gas outlet pipeline arranged vertically on the upper part of the cylinder to form a conical cap-type gas-liquid separation internal component. The process gas is first initially separated into droplets by cyclone centrifugation, and then repeatedly deflected by the corrugated plates to capture the molten urea droplets entrained in the gas, completely solving the problem of liquid carryover at the outlet of traditional devices. The corrugated plate structure is simple and does not increase system resistance, which can simplify the melamine production line and improve the separation effect, product quality, and overall operational stability of the device. However, this device has limited ability to separate fine molten urea droplets and melamine solid dust, and is only suitable for coarse separation scenarios. Moreover, it is very easy for gas phase liquid and solid carryover problems to occur when the load fluctuates, affecting the subsequent ammonium nitrate production.

[0006] In general, in the existing low-pressure gas-phase catalytic process for melamine, the recycled tail gas discharged from the urea scrubbing tower still lacks a stable and effective solid-liquid separation system. Conventional simple mist recovery devices and cyclone-corrugated plate composite separators are difficult to efficiently remove fine molten urea droplets, ultrafine melamine dust, and methylammonium salt impurities from the tail gas. Therefore, it is necessary to develop a urea scrubbing tower tail gas separation system to achieve deep removal of fine droplets and solid dust from the tail gas, so as to ensure the stable and continuous operation of the subsequent neutralization and preparation of ammonium nitrate solution. Utility Model Content

[0007] The purpose of this invention is to provide a tail gas separation system for a urea scrubbing tower. By designing a cold gas demister and a tail gas separator connected in series between the urea scrubbing tower and the neutralization reactor, and by optimizing the multi-stage separation structure inside the tail gas separator, the problem of incomplete removal of tail gas impurities and easy liquid and solid carryover in existing devices is solved, which is conducive to achieving deep purification of tail gas and stable neutralization reaction.

[0008] To achieve the above objectives, the technical solution of this utility model is as follows: A urea scrubbing tower tail gas separation system includes a urea scrubbing tower, a cold gas demister, a tail gas separator, and a neutralization reactor. The urea scrubbing tower is connected to a cyclone separator via a side wall pipe. The cyclone separator is connected to the cold gas demister. The process gas delivery pipeline at the top of the cold gas demister has three branches, which are respectively connected to the tail gas separator, a carrier gas compressor, and a crystallizer. The top outlet of the tail gas separator is connected to the neutralization reactor.

[0009] The exhaust gas separator is divided into an upper filtration zone, a middle cyclone separation zone, and a lower liquid storage zone. An annular air inlet cavity is formed between the inner wall of the middle cyclone separation zone and its internal components. An air inlet is provided on the side wall of the middle cyclone separation zone, and this inlet is connected to the annular air inlet cavity. A spiral baffle is installed inside the annular air inlet cavity, arranged spirally along the cylinder wall to guide the process gas entering the annular air inlet cavity to flow spirally downwards along the cylinder wall. A filter is installed in the upper filtration zone. The filter element; the internal components of the central cyclone separation zone, from bottom to top, are a liquid collection tray, a wire mesh demister, a conical separation plate, and a baffle plate; the center of the conical separation plate is connected to a downcomer b, which passes through the center of the conical separation plate, the wire mesh demister, and the liquid collection tray in sequence; downcomers a are respectively provided on both sides of the liquid collection tray; downcomers a and b are fixedly connected by a support frame; the cavity below the liquid collection tray forms the lower liquid storage area; a drain port is provided at the bottom of the exhaust gas separator, and the drain port is connected to a drain pipe.

[0010] Preferably, the lower ends of both downcomer a and downcomer b are inserted below the liquid surface of the lower storage area to form a liquid seal, preventing the gas phase from flowing upwards along the downcomer and short-circuiting.

[0011] Preferably, the exhaust gas separator has cleaning ports on its lower and upper side walls that are connected to cleaning water pipes, and manholes are also provided on its upper and lower side walls.

[0012] Preferably, the exhaust gas separator is equipped with a level gauge and a thermometer at the bottom, a pressure gauge at the top, and a drain valve on the drain pipe, with the level gauge and the drain valve forming a control loop.

[0013] Preferably, the carrier gas compressor is connected to the carrier gas separator, the top of the carrier gas separator is provided with two branches, one connected to the buffer tank and the other connected to the melamine reactor, and the bottom of the carrier gas separator is provided with a sewage discharge pipe.

[0014] Preferably, the top of the buffer tank is provided with a backflush gas pipeline, which merges with the venting pipeline and shares the venting port at the top of the exhaust gas separator; the backflush mode and the venting mode are independently controlled by corresponding control valves, and the two modes do not interfere with each other.

[0015] Preferably, the crystallizer is connected to the melamine trap, the melamine trap is connected to the cooling fan, the cooling fan is connected to the upper part of the urea washing tower, and the bottom of the urea washing tower is provided with a liquid urine inlet connected to the liquid urine delivery pipeline.

[0016] The urea scrubbing tower serves as the primary scrubbing unit for the tail gas, introducing liquid urea as the scrubbing medium to scrub and absorb ammonia and melamine components in the tail gas. The tail gas first passes through a cyclone separator to achieve primary gas-solid-liquid centrifugal separation, removing large droplets and crystalline particles, and then enters a cold gas demister for further condensation and demisting. The liquid phase at the bottom of the two-stage unit is directly returned to the tower bottom, realizing material recovery and recycling, and reducing material loss. A portion of the urea material enriched in the tower bottom is sent to the melamine reactor as a production raw material, shortening the material transfer process and avoiding crystallization blockage problems caused by intermediate material storage.

[0017] The crystallizer can crystallize and separate melamine from the reaction product gas. The cooling gas required for melamine crystallization comes from the urea scrubbing tower. After being defoamed by a cold gas demister, it is injected into the crystallizer from the cold gas nozzle at the bottom. Inside the crystallizer, the reaction product gas flowing downwards comes into contact with the upward-flowing cold gas and mixes thoroughly, exchanging heat. Melamine crystals in the reaction product gas precipitate and flow downwards with the gas to the crystallizer outlet. The process mixed gas containing melamine powder coming out of the crystallizer outlet enters the upper part of the melamine trap tangentially through the outlet pipe. Under the action of centrifugal force, the melamine powder is thrown against the wall and flows down the wall, collecting at the bottom of the melamine trap and being sent to the packaging station via the conveying system. The process gas in the melamine trap is then transported back to the urea scrubbing tower by a cold gas fan, flowing down in parallel with the liquid urea in the tower. The gas and liquid are thoroughly mixed, completing heat and mass transfer. Unreacted urea, isocyanate, and melamine not captured by the trap are washed off by molten urea and mixed into the urea for recycling.

[0018] Preferably, both the cyclone separator and the cold gas demister are provided with a pipeline at the bottom that returns to the bottom of the urea washing tower. The bottom of the urea washing tower is provided with a urea output pipeline with two branches, one of which is connected to the melamine reactor and the other returns to the upper part of the urea washing tower.

[0019] Preferably, control valves and flow meters are installed on all three branches of the process gas delivery pipeline at the top of the cold gas demister; the process gas delivery pipeline adopts a multi-branch parallel distribution structure, and the gas volume of each branch is independently adjusted by the control valves and flow meters. The process gas can be flexibly distributed according to different working conditions such as start-up, normal production, and crystallization recovery. A portion of the gas is sent to the tail gas deep purification unit, a portion is pressurized and used as the system carrier gas for the reaction, and a portion is sent to the crystallization unit to recover melamine products. One gas source can supply multiple process units at the same time.

[0020] Preferably, the conical separation plate is an inverted conical ventilated structure with several vent holes on its surface; the baffle plate includes a central sleeve and circumferentially distributed inclined blades; the wire mesh demister is a baffle-type wire mesh demister; furthermore, during system operation, the conical separation plate has an inclined guiding function, and the falling droplets and solid impurities are pre-removed by inertial collision, which reduces the load on the wire mesh, extends the life of the wire mesh, and prevents all impurities from falling directly and accumulating, thus blocking the wire mesh pores.

[0021] Preferably, the liquid collection tray is a horizontal disc-shaped structure, with a central through hole for the downcomer b to pass through, and side through holes for assembling the downcomer a on both sides of the liquid collection tray; the liquid collection tray is provided with a gas lifting structure, which includes multiple gas lifting grooves, the upper part of the gas lifting grooves is closed, and the upper part of the side wall of the gas lifting grooves is provided with gas lifting holes.

[0022] The exhaust gas separator is equipped with upper and lower partitioned cleaning ports and pipelines for online flushing of filter elements to dissolve urea and melamine crystals and extend the continuous operation cycle; the upper and lower manholes facilitate the segmented maintenance and replacement of filter elements and internal parts; furthermore, considering that the exhaust gas from the urea scrubbing tower contains molten urea, ammonium methyl ester, and trace amounts of melamine aerosol, which have high critical crystallization temperatures, crystallize upon cooling, and are prone to wall adhesion and pore blockage when cold, the exhaust gas separator of this system is also equipped with a steam jacket for heating.

[0023] The working principle of the system described in this utility model is as follows: The process gas used in this system is essentially the gas generated by the low-pressure gas-phase catalytic reaction of melamine, which originates from the high-temperature cracking and polymerization reaction of urea in the melamine reactor. Inside the urea scrubbing tower, most of the molten urea is pumped from the tower to two nozzles at the top of the tower via a liquid urea pump. It flows down alongside the process gas to scrub the process gas before being recycled back into the tower. A small portion is sent to the melamine reactor to produce melamine. The high-temperature process gas discharged from the melamine reactor first enters a hot gas cooler for cooling and conditioning. The cooled process gas then passes through a primary separator and a hot gas filter for multi-stage solid and impurity removal. The primary separator uses centrifugation to remove large particles of byproducts and dust. The hot gas filter uses a high-precision filter medium to intercept fine deammoniation products and ultrafine catalyst powder. Impurities form a filter cake on the outer wall of the filter tube. To avoid filter cake accumulation causing increased resistance and reduced gas flow, the filter components are continuously pulsed backflushed during operation. The detached filter residue and slag are collected at the bottom of the cone of the unit, ultimately yielding clean reaction process gas with solid impurities and high-boiling-point impurities removed. The clean process gas after dust removal enters the crystallizer from top to bottom, completing the crystallization of melamine and the separation of the product. The low-temperature quenching gas required for crystallization is taken from the low-temperature process gas purified by the urea scrubbing tower. After the mist is completely removed by the cold gas demister, the cold gas is injected upward from the nozzle at the bottom of the crystallizer, where it fully exchanges heat with the downward high-temperature process gas in a countercurrent manner and cools down rapidly. As the temperature decreases, the gaseous melamine reaches a supersaturated state, precipitating out melamine solid powder, which falls downward with the process gas. The gas containing the powder enters the melamine trap tangentially, where centrifugal force throws the melamine powder to the wall of the trap and causes it to slide down and accumulate. The melamine powder collected at the bottom is sent to the packaging station through the conveying system to achieve product recovery. The process tail gas after the solid product is separated is discharged from the top of the melamine trap, pressurized by the cold gas fan, and sent to the urea scrubbing tower to enter the circulating scrubbing and purification process. The urea scrubbing tower serves as the primary scrubbing and purification unit for the circulating process gas and the material recycling function. The molten urea stored in the tower bottom is pumped to multiple spray nozzles inside the tower via a liquid urea pump, and sprayed evenly from top to bottom. It forms a parallel flow with the upward process tail gas for heat and mass transfer, capturing unreacted urea, isocyanate, and trace amounts of unseparated melamine particles in the tail gas, enriching the impurities and integrating them into the molten urea. The scrubbed molten urea falls back into the tower bottom for recycling, and a portion of the molten urea is pressurized and sent back to the reactor as a reaction feedstock, realizing a closed-loop circulation of raw materials, greatly reducing material loss, and avoiding crystallization blockage problems caused by intermediate material storage and transportation.

[0024] The process gas, initially purified by the urea scrubbing tower, still contains fine molten urea droplets, melamine ultrafine dust, and trace impurities of methylammonium salt. It first enters a matching cyclone separator for primary centrifugal coarse separation, removing large-diameter droplets and particles. Then, it enters a cold gas demister for condensation and demisting, where spiral baffles further remove gaseous mist. All liquid phase at the bottom of the cyclone separator and cold gas demister is returned to the bottom of the urea scrubbing tower, achieving complete material recovery. The clean process gas from the cold gas demister outlet is distributed through multiple pipelines equipped with independent control valves and flow meters, and is divided into three streams to supply each process unit according to different operating conditions: one stream serves as the quenching gas source for the crystallizer, one stream is pressurized and used as the fluidizing carrier gas for the reactor, and the other stream is sent to the tail gas separator for deep purification, used in subsequent ammonium nitrate production.

[0025] The process gas entering the exhaust gas separator for deep purification enters the annular intake cavity through the air inlet on the middle side wall. Within the annular intake cavity, the process gas is guided by the spiral baffles and moves in a spiral downward swirling motion along the cylinder wall. Under the action of centrifugal force, large droplets and crystalline impurities carried by the gas are thrown towards the inner wall of the cylinder, slide down along the cylinder wall, and directly settle into the lower liquid storage area, completing the pre-separation of the intake stage.

[0026] The process gas spirals downwards along the annular air inlet cavity and then turns upwards as a whole after reaching the lower space of the device. The upward airflow first passes through the air riser hole of the liquid collection plate riser groove, and then flows from bottom to top through the wire mesh demister, the conical separation plate, and the baffle flow equalization plate, removing the remaining liquid droplets and solid particles carried in the rising airflow step by step, and then enters the upper filter element.

[0027] The wire mesh demister captures fine droplets in the rising airflow. The liquid phase flows downwards and collects in the collection tray, where it is then guided into the lower storage area by downcomers a on both sides of the collection tray. During operation and backflushing, droplets and particulate impurities that fall off the filter element and baffle plate fall downwards onto the upper surface of the conical separation plate. They then collect along the conical surface into the central downcomer b, passing directly through the wire mesh demister and collection tray to the storage area. Impurities do not fall onto the surface of the wire mesh demister, thus avoiding the risk of the wire mesh being blocked by solid particles.

[0028] The lower ends of downcomer a and downcomer b are both submerged below the liquid surface in the storage area to form a liquid seal, preventing gas from flowing out and short-circuiting; all liquid phases are collected in the lower storage area and discharged through the bottom drain port and drain pipe; the level gauge collects the liquid level signal in the storage area in real time, and forms a control loop with the drain valve to realize automatic drainage.

[0029] The process gas, after passing through the baffle plate from bottom to top, flows through the filter array in the upper filtration zone from the outside to the inside. Ultrafine dust and trace crystalline impurities are trapped on the surface of the filter elements, completing the fine filtration of the exhaust gas. The vertical filter elements facilitate the detachment of the filter cake and liquid membrane by gravity, and with pulse regeneration, the filter elements can be reused online. The deeply purified exhaust gas is transported from the top outlet of the exhaust gas separator to the neutralization reactor to carry out subsequent reactions to produce ammonium nitrate.

[0030] In addition, the exhaust gas separator is equipped with upper and lower cleaning ports, each with its own cleaning water pipeline, allowing for cleaning during shutdown and maintenance. During system operation, backflushing can be performed using a backflushing air pipeline led from the buffer tank. Utilizing the system's own process air source, the filter element is periodically pulsed backflushed and regenerated to remove ultrafine dust and trace amounts of crystalline filter cake accumulated on the outer surface of the filter element, restoring its filtration throughput and enabling online reuse. Under normal production conditions, the backflushing control valve is closed, and the buffer tank stores backflushing air at a certain pressure. When the pressure gauge shows an abnormal pressure, the periodic backflushing process is initiated, closing the top outlet valve and inlet pipeline from the exhaust gas separator to the neutralization reactor, cutting off the external supply of purified exhaust gas. The gas supply line is opened; the vent line control valve remains closed; the backflush gas line control valve is opened, and the high-pressure backflush gas from the buffer tank enters the upper filtration zone of the tail gas separator through the top vent; the backflush gas passes through the filter element from the inside to the outside in reverse, peeling off the filter cake and crystal particles attached to the outer surface of the filter element; the detached solid filter cake and liquid film fall downwards by gravity and fall to the middle cyclone separation zone; after being intercepted by the conical separation plate, it is introduced into the downcomer b along the conical surface, and part of it falls into the collection tray and is guided down by the downcomer a, and finally enters the lower liquid storage zone; after a single backflush is completed, the backflush gas line control valve is closed, the normal process flow of the tail gas separator is restored, the outlet valve to the neutralization reactor is opened, and the deep purification operation of the tail gas is restarted.

[0031] Compared with the prior art, the beneficial effects of this utility model are as follows: This utility model discloses a urea scrubbing tower tail gas separation system, which employs a multi-stage series purification process involving a cyclone separator, a cold gas demister, and a tail gas separator. The tail gas separator incorporates a composite separation structure with a built-in cyclone separator, wire mesh, conical guide plate, and filter element. This effectively removes fine urea droplets, melamine dust, and methylammonium salt impurities from the tail gas of the urea scrubbing tower, reducing scaling and clogging in the downstream neutralization reactor and ensuring stable operation of the ammonium nitrate preparation process. The conical separation plate and double downcomer structure reduce solid particle clogging of the wire mesh demister, and the downcomer liquid seal prevents gas short circuits, improving the operational reliability of the separation device.

[0032] The urea scrubbing tower tail gas separation system of this utility model has a cold gas demister with multiple adjustable gas distribution branches, so that the same process gas can be supplied to the crystallization, carrier gas and tail gas purification units respectively; the cyclone separator and the cold gas demister liquid phase return to the urea scrubbing tower bottom realize material recovery. At the same time, the filter element in the tail gas separator can be regenerated online with the backflush pipeline, reducing material loss and the frequency of unit shutdown and maintenance. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the tail gas separation system of the urea scrubbing tower in this utility model; Figure 2 This is a schematic diagram of the exhaust gas separator in this utility model; Figure 3 This is a schematic diagram of the structure of the liquid collection tray in this utility model; Figure 4 This is a schematic diagram of the flow distribution plate in this utility model.

[0034] In the diagram: 1. Urea scrubbing tower; 101. Cyclone separator; 102. Urea output pipeline; 2. Cold air demister; 3. Tail gas separator; 301. Air inlet; 302. Cleaning port; 303. Air outlet; 304. Manhole; 305. Wire mesh demister; 306. Filter element; 307. Conical separation plate; 308. Baffle plate; 309. Drain; 310. Downcomer a; 311. Downcomer b; 312. Collection tray; 313. Support frame; 314. 1. Vent outlet; 315. Gas lifting structure; 316. Gas lifting tank; 4. Neutralization reactor; 5. Crystallizer; 6. Triamine trap; 7. Cooling fan; 8. Carrier gas compressor; 9. Carrier gas separator; 10. Melamine reactor; 11. Buffer tank; 12. Liquid and urine delivery pipeline; 13. Control valve; 14. Flow meter; 15. Backflush gas pipeline; 16. Drainage pipeline; 17. Level gauge; 18. Thermometer; 19. Drain valve; 20. Pressure gauge; 21. Cleaning water pipeline. Detailed Implementation

[0035] The technical solution of this utility model will be further described below with reference to the accompanying drawings.

[0036] like Figures 1-4 As shown, a urea scrubbing tower tail gas separation system includes a urea scrubbing tower 1, a cold gas demister 2, a tail gas separator 3, and a neutralization reactor 4. The urea scrubbing tower 1 is connected to the cold gas demister 2 via a cyclone separator 101 connected to the side wall pipe. The process gas delivery pipeline at the top of the cold gas demister 2 is provided with three branches, which are respectively connected to the tail gas separator 3, the carrier gas compressor 8, and the crystallizer 5. The top outlet 303 of the tail gas separator 3 is connected to the neutralization reactor 4. The exhaust gas separator 3 is divided into an upper filtration zone, a middle cyclone separation zone, and a lower liquid storage zone. An annular air intake cavity is formed between the inner wall of the cylinder and the internal components of the middle cyclone separation zone. An air inlet 301 is provided on the side wall of the middle cyclone separation zone, and the air inlet 301 is connected to the annular air intake cavity. A spiral baffle plate arranged spirally along the cylinder wall is installed in the annular air intake cavity. A filter element 306 is provided in the upper filtration zone. In the internal components of the middle cyclone separation zone, from bottom to top, a liquid collection tray 312, a wire mesh demister 305, a conical separation plate 307, and a baffle plate 308 are arranged sequentially. The lower cavity of the liquid collection tray 312 is the lower liquid storage zone. A drain port 309 is provided at the bottom of the exhaust gas separator 3 and is connected to the drain pipe 16.

[0037] The center of the conical separation plate 307 is connected to the downcomer b311, which passes through the center of the conical separation plate 307, the wire mesh demister 305, and the collection tray 312 in sequence. Downcomers a310 are respectively provided on both sides of the collection tray 312, and downcomers a310 and b311 are fixedly connected by a support frame 313. The lower ends of downcomers a310 and b311 are inserted below the liquid surface of the lower liquid storage area to form a liquid seal.

[0038] The exhaust gas separator 3 is provided with cleaning ports 302 on the lower and upper side walls, which are connected to the cleaning water pipeline 21. The upper and lower side walls are also provided with manholes 304. The bottom of the exhaust gas separator 3 is provided with a level gauge 17 and a thermometer 18, and the top is provided with a pressure gauge 20. The drain pipeline 16 is provided with a drain valve 19. The level gauge 17 and the drain valve 19 form a control loop.

[0039] The carrier gas compressor 8 is connected to the carrier gas separator 9. The top of the carrier gas separator 9 is provided with two branches, one of which is connected to the buffer tank 11 and the other of which is connected to the melamine reactor 10. The bottom of the carrier gas separator 9 is provided with a sewage discharge pipe.

[0040] The buffer tank 11 is provided with a backflush gas pipeline 15 at the top. The backflush gas pipeline 15 and the vent pipeline share the top vent port 314 of the exhaust gas separator 3 after they merge.

[0041] The crystallizer 5 is connected to the triamine trap 6, the triamine trap 6 is connected to the cooling fan 7, the cooling fan 7 is connected to the upper part of the urea washing tower 1, and the bottom of the urea washing tower 1 is provided with a liquid urine inlet connected to the liquid urine conveying pipeline 12.

[0042] Both the cyclone separator 101 and the cold gas demister 2 are equipped with pipelines that return to the bottom of the urea washing tower 1. The bottom of the urea washing tower 1 is equipped with a urea output pipeline 102. The urea output pipeline 102 is equipped with two branches, one of which is connected to the melamine reactor 10, and the other returns to the upper part of the urea washing tower 1.

[0043] Control valves 13 and flow meters 14 are installed on the three branches of the process gas delivery pipeline at the top of the cold gas demister 2.

[0044] The conical separation plate 307 has an inverted conical air-permeable structure with several air holes on its surface; the baffle plate 308 includes a central sleeve and circumferentially distributed inclined blades; the wire mesh demister 305 is a baffle-type wire mesh demister.

[0045] The liquid collection tray 312 is a horizontal disc-shaped structure. The center of the liquid collection tray 312 is provided with a central through hole for the downcomer b311 to pass through. The sides of the liquid collection tray 312 are respectively provided with side through holes for assembling downcomer a310. The liquid collection tray 312 is provided with a gas lifting structure 315. The gas lifting structure 315 includes a plurality of gas lifting grooves 316. The gas lifting grooves 316 are closed at the top. The upper part of the side wall of the gas lifting groove 316 is provided with a gas lifting hole.

[0046] Example 1 The operation process of the urea scrubbing tower tail gas separation system is as follows: In the initial stage of system operation, molten urea is fed into the bottom of urea scrubbing tower 1 through liquid urea conveying pipeline 12. The spray structure inside the tower evenly sprays the molten urea, which comes into contact with the circulating process tail gas in parallel flow for washing, capturing unreacted urea, isocyanate, and trace amounts of melamine particles in the tail gas, thus achieving primary purification of the tail gas. The molten urea enriched in the bottom of urea scrubbing tower 1 is divided into two paths through urea output pipeline 102. One path is sent to melamine reactor 10 as production raw material, and the other path flows back to the upper part of urea scrubbing tower 1 to form a closed loop. The process tail gas after preliminary washing enters cyclone separator 101 through the side wall pipeline of urea scrubbing tower 1, where centrifugal force removes large droplets and solid impurities, completing the primary coarse separation.

[0047] The process gas, pretreated by cyclone separator 101, is sent to cold gas demister 2 for further condensation and removal of gaseous mist and large-particle impurities. The liquid material at the bottom of both cyclone separator 101 and cold gas demister 2 is returned to the bottom of urea washing tower 1, achieving material recovery. The process gas at the top of cold gas demister 2 is precisely distributed through three branches equipped with control valve 13 and flow meter 14. The three process gas branches correspond to different operating conditions: the first branch enters crystallizer 5 as quenching cold gas, exchanging heat with the high-temperature process gas to cause melamine crystallization. The gas containing powder is collected by centrifugation in melamine collector 6, and then the process gas is sent back to urea washing tower 1 for circulation by cold gas fan 7; the second branch is pressurized by carrier gas compressor 8 and sent to carrier gas separator 9. Part of the separated gas is sent to melamine reactor 10 as fluidizing carrier gas, and part is stored in buffer tank 11 for pressure stabilization and standby; the third branch process gas is sent to tail gas separator 3 for deep purification.

[0048] The process gas to be purified enters the annular inlet cavity through the inlet 301 of the tail gas separator 3, spirals downward along the spiral baffle plate on the cylinder wall, and pre-separates large particulate impurities by centrifugal force. Then the airflow turns back upward and passes sequentially through the gas lifting structure of the liquid collection plate 312, the wire mesh demister 305, the conical separation plate 307, and the baffle flow equalization plate 308, removing fine droplets and dust step by step. Finally, it completes the ultra-fine impurity filtration through the upper filter element 306. The separated liquid phase and solid impurities are respectively collected into the lower liquid storage area through the downcomer a310 on both sides of the liquid collection plate 312 and the downcomer b311 in the center of the conical separation plate 307. The liquid seal at the lower end of the two downcomer pipes can prevent gas phase cross-flow and short circuit. The liquid level gauge 17 at the bottom of the device is linked to the drain valve 19, and the liquid can be drained through the drain pipe 16 according to the liquid level.

[0049] During system operation, the buffer tank 11 can be supplied with high-pressure gas through the backflush gas pipeline 15 and the top vent 314 of the tail gas separator 3 to perform pulse backflush on the filter element 306, removing crystalline dust and filter cake from the surface of the filter element. The detached impurities fall by gravity and flow into the liquid storage area, realizing online regeneration of the filter element and ensuring continuous and stable operation of the device. The clean tail gas after multi-stage deep purification by the tail gas separator 3 is finally transported to the neutralization reactor 4 through the top outlet 303. Ammonium nitrate solution is prepared through the neutralization reaction, completing the resource utilization of the tail gas. At the same time, the cleaning port 302 and manhole 304 of the tail gas separator 3 can meet the daily inspection, cleaning and maintenance needs of the device.

Claims

1. A urea scrubbing tower tail gas separation system, characterized in that, The system includes a urea scrubbing tower (1), a cold gas demister (2), a tail gas separator (3), and a neutralization reactor (4). The urea scrubbing tower (1) is connected to the cold gas demister (2) via a cyclone separator (101) connected to the side wall pipe. The cold gas demister (2) has three branches on its top process gas delivery pipeline, which are respectively connected to the tail gas separator (3), the carrier gas compressor (8), and the crystallizer (5). The tail gas separator (3) has a top outlet (303) connected to the neutralization reactor (4). The exhaust gas separator (3) is divided into an upper filtration zone, a middle cyclone separation zone and a lower liquid storage zone. An annular air intake cavity is formed between the inner wall of the cylinder and the internal components of the middle cyclone separation zone. An air inlet (301) is provided on the side wall of the middle cyclone separation zone. The air inlet (301) is connected to the annular air intake cavity. A spiral baffle plate arranged spirally along the cylinder wall is installed in the annular air intake cavity. A filter element (306) is provided in the upper filtration zone. In the internal components of the middle cyclone separation zone, a liquid collection plate (312), a wire mesh demister (305), a conical separation plate (307), and a baffle plate (308) are arranged from bottom to top. The lower cavity of the liquid collection plate (312) is the lower liquid storage zone. A drain port (309) is provided at the bottom of the exhaust gas separator (3) and connected to the drain pipe (16).

2. The urea scrubbing tower tail gas separation system according to claim 1, characterized in that, The center of the conical separation plate (307) is connected to the downcomer b (311), and the downcomer b (311) passes through the center of the conical separation plate (307), the wire mesh demister (305) and the collection tray (312) in sequence; downcomers a (310) are respectively provided on both sides of the collection tray (312), and downcomers a (310) and downcomers b (311) are fixedly connected by a support frame (313); the lower ends of downcomers a (310) and downcomers b (311) are inserted below the liquid surface of the lower liquid storage area to form a liquid seal.

3. The urea scrubbing tower tail gas separation system according to claim 1, characterized in that, The exhaust gas separator (3) is provided with a cleaning port (302) on the lower and upper side walls, which is connected to the cleaning water pipeline (21). The upper and lower side walls are also provided with a manhole (304). The exhaust gas separator (3) is provided with a level gauge (17) and a thermometer (18) at the bottom, and a pressure gauge (20) at the top. A drain valve (19) is provided on the drain pipeline (16). The level gauge (17) and the drain valve (19) form a control loop.

4. The urea scrubbing tower tail gas separation system according to claim 1, characterized in that, The carrier gas compressor (8) is connected to the carrier gas separator (9). The top of the carrier gas separator (9) is provided with two branches, one of which is connected to the buffer tank (11) and the other of which is connected to the melamine reactor (10). The bottom of the carrier gas separator (9) is provided with a sewage discharge pipe.

5. The urea scrubbing tower tail gas separation system according to claim 4, characterized in that, The buffer tank (11) is provided with a backflush gas pipeline (15) at the top. The backflush gas pipeline (15) and the vent pipeline share the vent port (314) at the top of the tail gas separator (3) after they merge.

6. The urea scrubbing tower tail gas separation system according to claim 1, characterized in that, The crystallizer (5) is connected to the triamine trap (6), the triamine trap (6) is connected to the air cooler (7), the air cooler (7) is connected to the upper part of the urea scrubbing tower (1), and the bottom of the urea scrubbing tower (1) is provided with a liquid urine inlet connected to the liquid urine delivery pipeline (12).

7. The urea scrubbing tower tail gas separation system according to claim 1, characterized in that, The bottom of the cyclone separator (101) and the cold gas demister (2) are both provided with pipelines that return to the bottom of the urea washing tower (1). The bottom of the bottom of the urea washing tower (1) is provided with a urea output pipeline (102). The urea output pipeline (102) is provided with two branches, one of which is connected to the melamine reactor (10) and the other is returned to the upper part of the urea washing tower (1).

8. The urea scrubbing tower tail gas separation system according to claim 1, characterized in that, Control valves (13) and flow meters (14) are installed on the three branches of the process gas delivery pipeline at the top of the cold gas demister (2).

9. The urea scrubbing tower tail gas separation system according to claim 1, characterized in that, The conical separation plate (307) has an inverted conical air-permeable structure with several air-permeable holes on its surface; the baffle plate (308) includes a central sleeve and circumferentially distributed inclined blades; the wire mesh demister (305) is a baffle-type wire mesh demister.

10. The urea scrubbing tower tail gas separation system according to claim 1, characterized in that, The liquid collection plate (312) is a horizontal disc-shaped structure. The center of the liquid collection plate (312) is provided with a central through hole for the downcomer b (311) to pass through. The sides of the liquid collection plate (312) are respectively provided with side through holes for assembling downcomer a (310). The liquid collection plate (312) is provided with a gas lifting structure (315). The gas lifting structure (315) includes multiple gas lifting grooves (316). The gas lifting grooves (316) are closed at the top. The upper part of the side wall of the gas lifting groove (316) is provided with a gas lifting hole.

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