Wet dust removal and ammonia recovery device for urea granulation tail gas

Abstract

The utility model discloses a wet dust removal and ammonia recovery device for urea granulation tail gas. A primary circulating liquid forward kinetic energy spray washing system, a secondary circulating liquid reverse efficient spray washing system and a tertiary desorption liquid forward kinetic energy spray washing system are sequentially arranged in a tower top recovery device of a granulation tower from bottom to top; a desorption liquid pump, a circulating liquid tank and a washing liquid circulating pump are arranged at the bottom of the recovery device; a horizontal flow efficient blade demister is arranged at the upper end of the third-stage desorption liquid forward kinetic energy spray washing system, and the horizontal flow efficient blade demister is a hexahedral blade box defined by blades. Ammonia gas in the granulation tail gas is in full contact with the three-stage spray washing system, more ammonia gas is dissolved in washing liquid through the gas-liquid mass transfer process, the ammonia gas in the granulation tail gas is efficiently recycled, the ammonia content in the tail gas is reduced, the environmental pollution is reduced, and the production cost is reduced.

Description

Technical Field

[0001] The utility model belongs to the field of chemical granulation tail gas recovery, and particularly relates to a wet dust removal and ammonia recovery device for urea granulation tail gas. Background Art

[0002] In the process of urea production, the tail gas of the urea granulation tower contains or generates urea dust containing free ammonia, with a particle size in the range of about 0.1 - 20 μm. The urea dust is discharged into the atmosphere with the flowing air, and the particulate matter content exceeds the standard. A large amount of dust forms an aerosol with water vapor, and the urea particulate matter content exceeds the standard, resulting in serious tail gas trailing and not meeting the environmental protection emission requirements; the dust ammonia content in the granulation tower exceeds the standard, and the dust with excessive ammonia content is discharged into the atmosphere, polluting the atmospheric environment, easily harming the human respiratory system of the surrounding villagers, and causing trouble to life; the granulation tail gas contains atomized urea droplets, resulting in secondary pollution and corrosion of surrounding buildings and steel in open-air yards.

[0003] Currently, the country's requirements for the emission concentrations of ammonia and particulate matter in urea vent tail gas are getting higher and higher. Therefore, it is necessary to treat the granulation tower dust, and it is necessary to continuously optimize and transform the emission facilities of the device to achieve the purpose of energy conservation and emission reduction and reduce environmental pollution. Summary of the Invention

[0004] In order to reduce environmental pollution and production costs, the utility model discloses a wet dust removal and ammonia recovery device for urea granulation tail gas. The ammonia in the granulation tail gas is fully contacted with a three-stage spray washing system, and through the gas-liquid mass transfer process, more ammonia is dissolved into the washing liquid, efficiently recovering the ammonia in the granulation tail gas and reducing the ammonia content in the tail gas.

[0005] The technical solution of the utility model is a wet dust removal and ammonia recovery device for urea granulation tail gas, including the top of the granulation tower. It is characterized in that a first-stage circulating liquid forward kinetic energy spray washing system, a second-stage circulating liquid reverse high-efficiency spray washing system, and a third-stage desorbing liquid forward kinetic energy spray washing system are successively arranged from bottom to top in the recovery device at the top of the granulation tower; a desorbing liquid pump, a circulating liquid tank, and a washing liquid circulating pump are arranged at the bottom of the granulation tower recovery device; a horizontal flow high-efficiency vane demister is arranged at the upper end of the third-stage desorbing liquid forward kinetic energy spray washing system, and the horizontal flow high-efficiency vane demister is a hexahedral vane box surrounded by vanes.

[0006] Further, the spraying directions of the washing liquid of the first-stage circulating liquid forward kinetic energy spray washing system and the third-stage desorbing liquid forward kinetic energy spray washing system are the same as the direction of the granulation tail gas flow; the spraying direction of the washing liquid of the second-stage circulating liquid countercurrent high-efficiency spray system is opposite to the direction of the granulation tail gas flow.

[0007] Furthermore, a first-level desorption liquid backwashing system for the blades is arranged on the inner side of the horizontal flow high-efficiency blade demister; a second-level steam backwashing system is arranged on the upper end of the horizontal flow high-efficiency blade demister to steam backwash the blades; a third-level desorption liquid backwashing system is arranged on the upper end of the horizontal flow high-efficiency blade demister to backwash the blades in multiple directions to reduce scaling.

[0008] Furthermore, the outlet of the desorption liquid pump is divided into three routes: the main route 1 of the desorption liquid pump outlet is connected to the three-stage desorption liquid forward kinetic energy spray washing system to perform three-stage washing of the urea granulation tail gas; the desorption liquid pump outlet bypass is connected to the first-stage desorption liquid backwashing system of the blades and the third-stage desorption liquid backwashing system of the blades to perform two-stage desorption liquid backwashing on the blades; the main route 2 of the desorption liquid pump outlet is connected to the top of the circulating liquid tank to replenish the circulating liquid in the circulating liquid tank.

[0009] Furthermore, the bottom outlet of the circulating liquid tank is connected to the washing liquid circulating pump, and the outlet of the washing liquid circulating pump is divided into three routes: the main route of the pump outlet is connected to the primary circulating liquid forward kinetic energy spray washing system to perform primary washing of the urea granulation tail gas; the main route of the pump outlet is connected to the secondary circulating liquid reverse high-efficiency spray washing system to perform secondary washing of the urea granulation tail gas; the pump outlet bypass circulating washing liquid is sent to the off-site urea device.

[0010] The utility model has the following beneficial effects:

[0011] 1. When the total pressure of the fan is ≤350Pa, the solid (urea granules) aerosol in the system is removed by three-stage spray washing, and ammonia in the urea granulation tail gas can be absorbed at the same time. The three-stage spray washing system has high operational flexibility while ensuring the washing and dust removal effect. The liquid is dispersed into tiny mist particles using special atomization technology, which can better cover the surface of dust particles and improve the washing effect. This liquid-solid mass transfer process transfers urea granules into urea droplets; water has a good absorption capacity for ammonia, and the ammonia in the granulation tail gas is fully in contact with the three-stage spray washing liquid. This gas-liquid mass transfer process dissolves more ammonia into the washing liquid. This washing process can recover the ammonia in the granulation tail gas and reduce the ammonia content in the tail gas.

[0012] 2. Remove liquid (urea solution) aerosol through horizontal flow high-efficiency blade demister 2. The horizontal flow high-efficiency blade demister 2 adopts a hexahedral structure, and the urea granulation tail gas enters the hexahedral blade box from the horizontal direction. The blade demister can remove droplets ≥ 8μm with an efficiency of 100%, ensuring that the total liquid entrainment content in every 1 million cubic meters of outlet gas does not exceed 12.4 liters, ensuring that the maximum area is effectively intercepted. The mist droplets entrained in the airflow have a good demisting effect.

[0013] 3. Add a blade desorption liquid backwashing system to prevent clogging of the high-efficiency blade demister. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic process flow diagram of the device of the present utility model;

[0015] Figure 2 is Figure 1 a partially enlarged top view schematic diagram of the horizontal flow high-efficiency vane demister 2 in

[0016] Explanation of reference numerals: 1. Granulation tower top recovery device; 2. Horizontal flow high-efficiency vane demister; 3. Vane primary desorbing liquid backwashing system; 4. Vane secondary steam backwashing system; 5. Vane tertiary desorbing liquid backwashing system; 6. Tertiary desorbing liquid forward kinetic energy spray washing system; 7. Secondary circulating liquid reverse high-efficiency spray washing system; 8. Primary circulating liquid forward kinetic energy spray washing system; 9. Urea granulation tail gas; 10. Desorbing liquid pump; 11. Circulating liquid tank; 12. Washing liquid circulating pump; 13. Second main path at the outlet of the desorbing liquid pump; 14. First main path at the outlet of the desorbing liquid pump; 15. Bypass at the outlet of the desorbing liquid pump; 16. First main path at the outlet of the washing liquid circulating pump; 17. Second main path at the outlet of the washing liquid circulating pump; 18. Bypass at the outlet of the washing liquid circulating pump. Detailed implementation manners

[0017] As Figure 1 shown, a wet dust removal and ammonia recovery device for urea granulation tail gas includes a granulation tower top recovery device 1, a horizontal flow high-efficiency vane demister 2, a vane primary desorbing liquid backwashing system 3, a vane secondary steam backwashing system 4, a vane tertiary desorbing liquid backwashing system 5, a tertiary desorbing liquid forward kinetic energy spray washing system 6, a secondary circulating liquid reverse high-efficiency spray washing system 7, a primary circulating liquid forward kinetic energy spray washing system 8, urea granulation tail gas 9, a desorbing liquid pump 10, a circulating liquid tank 11, and a washing liquid circulating pump 12.

[0018] The urea granulation tail gas 9 enters the granulation tower top recovery device 1, and the rising urea granulation tail gas flow sequentially contacts with the primary circulating liquid forward kinetic energy spray washing system 8, the secondary circulating liquid reverse high-efficiency spray washing system 7, and the tertiary desorbing liquid forward kinetic energy spray washing system 6, wetting and capturing dust particles. The dust particles collide, diffuse, and adhere to each other. This liquid-solid mass transfer process transfers urea particles into urea droplets, and finally settles under the action of gravity; water has good absorption capacity for ammonia, and the ammonia in the granulation tail gas is in full contact with the tertiary spray washing system. This gas-liquid mass transfer process dissolves more ammonia into the washing liquid. This washing process can recover ammonia in the urea granulation tail gas and reduce the ammonia content in the tail gas.

[0019] Among them, the urea granulation tail gas 9 first enters the primary circulating liquid forward kinetic energy spray washing system 8. The washing liquid is in the same direction as the gas flow. The washing liquid mist flow is injected into the dust-containing urea granulation tail gas 9 flow, covering its space completely. When the sprayed mist flow contacts and collides with the forward gas flow, the dispersion degree is very good, achieving the purpose of dust removal and dust washing.

[0020] Then it enters the secondary loop liquid reverse high-efficiency spray system 7. The washing liquid flows in the opposite direction to the air flow. The dust-containing urea granulation tail gas 9 rising with the air flow in the tower comes into full reverse contact with the washing liquid mist flow. The droplets descending after atomization are captured due to inertial collision, interception and aggregation. The washing liquid comes into full reverse contact with the urea granulation tail gas 9, and at the same time, ammonia in the urea granulation tail gas can be recovered, reducing the ammonia content in the tail gas.

[0021] The urea granulation tail gas 8 finally enters the tertiary desorption liquid forward kinetic energy spray washing system 6. The urea content in the desorption liquid is very low. The wetted dust particles collide, diffuse and bond with each other, and finally settle under the action of gravity. The desorption liquid performs the third fine washing on the dust, and the washing effect is better. The liquid-solid mass transfer process between urea and the desorption liquid transfers urea particles into urea droplets. The gas-liquid mass transfer process between ammonia and the desorption liquid recovers ammonia in the tail gas, reducing the ammonia content in the tail gas.

[0022] The two-stage forward kinetic energy spray washing system can not only provide kinetic energy for the dust-containing gas, but also reduce the fluid mass transfer resistance, thereby improving the washing efficiency of absorbing and dissolving urea dust particles.

[0023] The liquid entrained by the urea granulation tail gas 9 during the upward process after being sprayed and washed by the tertiary desorption liquid forward kinetic energy spray washing system 6 enters the horizontal flow high-efficiency vane demister 2. As Figure 2 shown, the horizontal flow high-efficiency vane demister 2 adopts a hexahedron structure. The urea granulation tail gas enters from the inside and exits from the outside of the hexahedron vane box in the horizontal direction, effectively intercepting the mist-like droplets entrained in the air flow with the largest area, and meeting the requirements of demisting efficiency and low pressure drop, ensuring that the total liquid entrainment content in every 1 million cubic meters of outlet gas does not exceed 12.4 liters. The purified gas after removing the mist is discharged into the atmosphere. The efficiency of removing droplets ≥8μm by the vane demister can reach 100%.

[0024] After removing the mist, the purified gas is discharged into the atmosphere, ensuring that the dust content in the granulation tower exhaust gas ≤20mg / m 3 and the ammonia concentration ≤30mg / m 3 , eliminating the trailing phenomenon and meeting the environmental protection requirements.

[0025] During the process of the gas passing through each area of the vane, the gas will be forced by the vane to undergo multiple rapid flow direction changes. Under the action of centrifugal force, the droplets will collide with the vane multiple times in terms of kinetic energy. After the droplets adhere to the vane surface, a liquid film is formed through the coalescence effect between the droplets. The liquid film adhering to the vane surface is pushed into the vane sandwich under the combined action of its own gravity, liquid surface tension and gas kinetic energy, converges into a stream in the sandwich, and flows into the circulating liquid tank 11 below the vane under the action of gravity for collection.

[0026] A blade primary desorbing liquid backwashing system 3 is added inside the horizontal-flow high-efficiency blade demister 2. The desorbing liquid has a low urea content and performs full-coverage backwashing to reduce scaling.

[0027] A secondary steam backwashing system 4 is added at the upper end of the horizontal-flow high-efficiency blade demister 2. Low-pressure steam from outside the plant is sent to the secondary steam backwashing system 4 of the blade to perform steam backwashing on the blade, reducing the deposition and scaling of urea and biuret on the blade.

[0028] A tertiary desorbing liquid backwashing system 5 is added at the upper end of the horizontal-flow high-efficiency blade demister 2 to perform multi-directional backwashing and reduce scaling.

[0029] The outlet of the desorbing liquid pump 10 is divided into three paths: the main path 1 of the desorbing liquid pump outlet is connected to the tertiary desorbing liquid forward kinetic energy spray washing system 6 to perform tertiary spray washing on the urea granulation tail gas 9; the bypass of the desorbing liquid pump outlet is connected to the blade primary desorbing liquid backwashing system 3 and the blade tertiary desorbing liquid backwashing system 5 to perform secondary desorbing liquid backwashing on the blade; the main path 2 of the desorbing liquid pump outlet is connected to the top of the circulating liquid tank 11 to replenish the circulating liquid in the circulating liquid tank.

[0030] The bottom outlet of the circulating liquid tank 11 is connected to the washing liquid circulation pump 12. The outlet of the washing liquid circulation pump 12 is divided into three paths: the main path 1 of the pump outlet is connected to the primary circulating liquid forward kinetic energy spray washing system 8 to perform primary spray washing on the urea granulation tail gas 9; the main path 2 of the pump outlet is connected to the secondary circulating liquid reverse high-efficiency spray washing system 7 to perform secondary spray washing on the urea granulation tail gas 9; the bypass of the pump outlet circulates the washing liquid and sends it to the urea plant outside the plant.

Claims

1. A wet dust removal and ammonia recovery device for urea granulation tail gas, including a recovery device (1) at the top of the granulation tower, characterized in that In the granulation tower top recovery device (1), from bottom to top, there are successively arranged a primary circulating liquid forward kinetic energy spray washing system (8), a secondary circulating liquid reverse high-efficiency spray washing system (7), and a tertiary desorbing liquid forward kinetic energy spray washing system (6); at the bottom of the granulation tower top recovery device (1), there are arranged a desorbing liquid pump (10), a circulating liquid tank (11), and a washing liquid circulating pump (12); at the upper end of the tertiary desorbing liquid forward kinetic energy spray washing system (6), there is arranged a horizontal flow high-efficiency vane demister (2), and the horizontal flow high-efficiency vane demister is a hexahedral vane box surrounded by vanes.

2. The wet dust removal and ammonia recovery device for urea granulation tail gas according to claim 1, characterized in that, The washing liquid spraying directions of the primary circulating liquid forward kinetic energy spray washing system (8) and the tertiary desorbing liquid forward kinetic energy spray washing system (6) are the same as the direction of the granulation tail gas flow; the washing liquid spraying direction of the secondary circulating liquid reverse high-efficiency spray washing system (7) is opposite to the direction of the granulation tail gas flow.

3. The wet dust removal and ammonia recovery device for urea granulation tail gas according to claim 1, characterized in that, Inside the horizontal flow high-efficiency vane demister (2), a primary desorbing liquid reverse cleaning system for vanes (3) is arranged; at the upper end of the horizontal flow high-efficiency vane demister (2), a secondary steam backwashing system (4) is arranged to perform steam backwashing on the vanes; at the upper end of the horizontal flow high-efficiency vane demister (2), a tertiary desorbing liquid reverse cleaning system for vanes (5) is arranged to perform multi-directional reverse washing on the vanes to reduce fouling.

4. The wet dust removal and ammonia recovery device for urea granulation tail gas according to claim 1, characterized in that the solution The outlet of the desorbing liquid pump (10) is divided into three paths: the main path one (14) of the desorbing liquid pump outlet is connected to the tertiary desorbing liquid forward kinetic energy spray washing system (6) to perform tertiary washing on the urea granulation tail gas (9); the bypass (15) of the desorbing liquid pump outlet is connected to the primary desorbing liquid reverse cleaning system for vanes (3) and the tertiary desorbing liquid reverse cleaning system for vanes (5) to perform secondary desorbing liquid reverse cleaning on the vanes; the main path two (13) of the desorbing liquid pump outlet is connected to the top of the circulating liquid tank (11) to supply the circulating liquid in the circulating liquid tank.

5. The wet dust removal and ammonia recovery device for urea granulation tail gas according to claim 1, characterized in that, The bottom outlet of the circulating liquid tank (11) is connected to the washing liquid circulating pump (12), and the outlet of the washing liquid circulating pump (12) is divided into three paths: the main path one (16) of the pump outlet is connected to the primary circulating liquid forward kinetic energy spray washing system (8) to perform primary washing on the urea granulation tail gas (9); the main path two (17) of the pump outlet is connected to the secondary circulating liquid reverse high-efficiency spray washing system (7) to perform secondary washing on the urea granulation tail gas (9); The bypass circulating washing liquid (18) of the pump outlet is sent to the off-site urea plant.

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