Safety-based urea multi-strand ammonia gas treatment and recovery system and method

Abstract

The invention discloses a urea multi-strand ammonia gas treatment and recovery system and method based on safety. According to the method, low-pressure absorption tower emptying tail gas and exhaust funnel emptying tail gas are combined for treatment, and methods of online monitoring, multi-stage absorption demisting, fire retardance, carbon dioxide absorption, ammonia recovery, multi-stage cooling and the like are adopted, so that the explosion risk is reduced, the enterprise safety is ensured, ammonia in the low-pressure absorption tower emptying tail gas and the exhaust funnel emptying tail gas is reduced to 20mg / Nm < 3 >, and the energy consumption is reduced. The numerical value is far lower than 30mg / Nm < 3 > required by the environmental protection laws, the excellent performance of the method in the aspect of reducing ammonia emission is embodied, meanwhile, ammonia products are recycled, and recycling of ammonia resources is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of ammonia treatment and recovery, and in particular relates to a safe urea-based multi-stream ammonia treatment and recovery system and method. Background Art

[0002] At present, most of the domestic urea production equipment adopts the carbon dioxide stripping urea production process. The exhaust gas of this process has a high ammonia component during operation. At present, the exhaust gas sources include: atmospheric pressure absorption tower venting, ammonia tank gas phase, urine tank gas phase, and analytical tower venting. The ammonia content in the exhaust gas discharged from the exhaust is generally 3×10 4 ~5×10 4 mg / Nm 3 The ammonia content in the tail gas of the low-pressure absorption tower is generally 1×10 4 ~3×10 4 mg / Nm 3 This is far beyond my country's air pollutant emission standard of 30mg / Nm 3 In addition to exceeding pollution standards, there is also a waste of ammonia resources, with about 1,000 tons of ammonia resources wasted each year.

[0003] The main components of the gas sources in the exhaust pipe and the tail gas of the low-pressure absorption tower include: ammonia, hydrogen, oxygen and other flammable and explosive gases; currently, the proportion of these components in most companies is within the explosion risk area, which poses an explosion risk and a major safety hazard.

[0004] The current method for treating urea exhaust gas is as follows: Figure 1 , the exhaust gas in the exhaust pipe 101 is introduced into the exhaust air washing tower 102. The exhaust air washing tower is divided into an upper and a lower section. The top uses cooled steam condensate to circulate and wash the gas washed in the lower section. The washed gas is directly discharged, and the dilute ammonia water formed after washing is added to the lower section of the exhaust air washing tower to circulate and wash the exhaust gas at the outlet of the exhaust main pipe; in order to further improve the absorption effect, carbon dioxide gas is added to the lower part of the exhaust air washing tower to reduce the ammonia content in the exhaust gas of the exhaust main pipe to less than 0.1%. A part of the effluent of the exhaust air washing tower with a lower concentration is introduced into the top of the atmospheric absorption tower as a washing liquid, and a part is introduced into the top of the low-pressure absorption tower as a washing liquid, which can greatly reduce the amount of desalted water used in the system.

[0005] The existing processing methods have the following problems:

[0006] 1. No explosion-proof treatment has been carried out, and the exhaust gas contains flammable and explosive gases such as hydrogen and ammonia, which poses a risk of explosion.

[0007] 2. Under normal pressure and temperature, the solubility of carbon dioxide in water is very low, and the solubility of carbon dioxide in water is 0.9 kg / m 3Under this working condition, the actual absorption effect of carbon dioxide is very small; there is a strong ammonia smell near the vent cylinder, and the ammonia removal effect is not achieved.

[0008] 3. Washing water is used as washing water for the atmospheric absorption tower. Ammonia accumulates in the system, and the system is at risk of corrosion and blockage. In addition, ammonia resources are not effectively recovered, resulting in a waste of ammonia resources. Summary of the invention

[0009] The present invention provides a safe urea multi-stream ammonia treatment and recovery system and method. The tail gas discharged from the low-pressure absorption tower and the tail gas discharged from the exhaust pipe are combined for treatment, and online monitoring, multi-stage absorption and demisting, fire prevention, carbon dioxide absorption, ammonia recovery, multi-stage cooling and other methods are adopted to reduce the risk of explosion, ensure the safety of the enterprise, and reduce the ammonia in the tail gas discharged from the low-pressure absorption tower and the tail gas discharged from the exhaust pipe to 20mg / Nm 3 , while recovering the ammonia product.

[0010] The technical scheme of the present invention is: a safe urea multi-stream ammonia treatment and recovery system, including an exhaust pipe, characterized in that it also includes an online gas detection system, an ammonia absorption and washing tower, a carbon dioxide high-efficiency absorption device, an ammonia evaporation tower, a partial condenser, a flame arrester, a washing liquid pump, a dilute ammonia water pump, and a purified water pump; the exhaust gas discharged from the low-pressure absorption tower and the exhaust pipe exhaust gas cut off by a pneumatic cut-off valve arranged in the exhaust pipe are sent to a gas ejector through a pipeline, and the two gases with different pressures are combined and processed by the ejector, and an online gas detection system is arranged on the combined gas pipeline;

[0011] The exhaust gas after combined treatment by the gas ejector is sent to the ammonia absorption scrubber through a pipeline. The ammonia absorption scrubber adopts a packed tower, which is divided into an upper section and a lower section. The ammonia absorption scrubber is filled with a first layer of packing and a second layer of packing. A wire mesh demister is installed at the gas outlet of the ammonia absorption scrubber.

[0012] One end of the dilute ammonia water pump is connected to the outlet pipeline at the bottom of the ammonia absorption washing tower, and the other end, a part of which is connected to the circulating washing liquid cooler pipeline and then passed into the top of the first layer of packing in the middle section of the ammonia absorption washing tower; the other part is connected to the purified water primary cooler pipeline and then passed into the upper part of the ammonia distillation tower;

[0013] A gas distributor and a CO2 refiner are arranged in the carbon dioxide efficient absorption device, and a carbon dioxide inlet, a carbon dioxide outlet, a purified water inlet, a washing liquid outlet and a baffle are arranged on the shell of the carbon dioxide efficient absorption device;

[0014] The carbon dioxide gas from outside the boundary is connected to the gas distributor pipeline of the lower section of the carbon dioxide high-efficiency absorption device after passing through the regulating valve, and the carbon dioxide gas outlet is connected to the middle and upper pipelines of the ammonia absorption washing tower at the same time;

[0015] One end of the purified water pump is connected to the lower section pipeline of the ammonia distillation tower, and the other end is connected to the primary cooler pipeline. The primary cooler is connected to the secondary cooler pipeline and then connected to the purified water inlet pipeline of the upper section of the carbon dioxide high-efficiency absorption device;

[0016] One end of the washing liquid pump is connected to the middle washing liquid outlet of the carbon dioxide high-efficiency absorption device, and the other end is connected to the washing liquid cooler pipeline and then introduced into the top of the first layer of filler in the ammonia absorption washing tower;

[0017] A stream of steam is introduced from the outside and passed into the bottom of the ammonia distillation tower, in which a fractionator is arranged; the gas phase is connected to the ammonia condenser pipeline through the top of the fractionator, the ammonia condenser is connected to the fractionator pipeline, the bottom of the fractionator is connected to the external pipeline, and the top is connected to the external pipeline; the purified water at the bottom of the ammonia distillation tower is sent to the purified water pump through the pipeline.

[0018] Furthermore, the online gas detection system includes: an online hydrogen analyzer is arranged on the merged gas pipeline, which is interlocked with a second pneumatic regulating valve on the exhaust gas discharged from the low-pressure absorption tower; a first online ammonia analyzer is arranged on the merged gas pipeline, which is interlocked with a first pneumatic regulating valve on the exhaust gas discharged from the exhaust pipe; and at the same time, it is interlocked with a pneumatic shut-off valve.

[0019] Furthermore, the outlet height of the washing liquid is set in the middle of the carbon dioxide high-efficiency absorption device; a baffle is set at the top of the gas distributor, and the baffle is set at an angle of 43 to 56 degrees.

[0020] Furthermore, the CO2 gas outside the boundary is connected to the carbon dioxide inlet pipeline at the bottom of the carbon dioxide pressure absorption device.

[0021] Furthermore, one end of the flame arrester is connected to the top pipeline of the ammonia absorption washing tower, and the other end is connected to the exhaust pipe pipeline. The flame arrester uses a corrugated filter element.

[0022] Furthermore, a stream of desalted water is introduced from the outside and sent to the top of the first layer of filler in the ammonia absorption washing tower.

[0023] A safe urea multi-stream ammonia treatment and recovery method, characterized in that the exhaust gas discharged from the exhaust pipe and the exhaust gas discharged from the low-pressure absorption tower are combined through an ejector and enter from the lower section of the ammonia absorption washing tower; the exhaust gas is fully contacted with the washing liquid cooled by the circulating washing liquid cooler in the second layer of filler for cooling, and the heat is removed. The exhaust gas after the cooling treatment rises and passes through the first layer of filler and is fully absorbed by the washing liquid cooled by the washing liquid cooler in the first layer of filler. The washed exhaust gas is removed from the entrained liquid foam by the wire mesh demister, and then passes through the flame arrester and is led to the exhaust pipe, and is discharged smoothly by utilizing the residual pressure of the gas in the ammonia absorption washing tower;

[0024] The purified water from the ammonia evaporation tower kettle is sent to the purified water pump; the purified water from the ammonia evaporation tower kettle is heat exchanged with the dilute ammonia water at the bottom of the ammonia washing absorption tower and then sent to the carbon dioxide absorption device for recycling as washing liquid; at the same time, the purified water sent to the carbon dioxide high-efficiency absorption device is subjected to secondary cooling. The purified water from the bottom of the ammonia evaporation tower passes through the primary purified water cooler and the secondary purified water cooler and is cooled to 18-24°C, thereby increasing the solubility of CO2;

[0025] The combined tail gas contacts the washing liquid treated by the carbon dioxide absorption device, and the solute containing ammonia is efficiently absorbed; a stream of steam is introduced from the outside and passed into the bottom of the ammonia distillation tower, and the dilute ammonia water containing solute sent by the dilute ammonia water pump is condensed and concentrated in the gas phase by the fractionator, and then condensed by the ammonia condenser and sent to the fractionator to make ammonia water, which is then sent to the ammonia water recovery system;

[0026] The carbon dioxide gas from outside enters the lower gas distributor of the carbon dioxide efficient absorption device after passing through the regulating valve; the unabsorbed CO2 is discharged through the carbon dioxide gas outlet at the upper part of the carbon dioxide efficient absorption device and then sent to the middle and upper parts of the ammonia absorption washing tower through the pipeline;

[0027] Undissolved CO2 gas is introduced into the upper part of the ammonia absorption scrubber for explosion-proof treatment, and the ammonia content in the exhaust gas is further reduced to ensure that the NH3 content in the exhaust gas is less than 20mg / Nm 3 .

[0028] Furthermore, explosion-proof treatment is achieved through two-level online monitoring and control: the first level is to respectively set an online hydrogen analyzer and a first online ammonia analyzer on the combined gas pipeline; wherein the online hydrogen analyzer is interlocked with the second pneumatic control valve; the first online ammonia analyzer is interlocked with the first pneumatic control valve; the valve opening is controlled simultaneously; the ratio of H2 / H2+NH3 is controlled outside the range of 4.6 to 75%, and when the ratio of H2 / H2+NH3 is greater than 4.6, the opening of the first pneumatic control valve is increased while the opening of the second pneumatic control valve is decreased. When the ratio of H2 / H2+NH3 is less than 75, the opening of the second pneumatic regulating valve is increased while the opening of the first pneumatic regulating valve is decreased to increase the exhaust gas discharged from the low-pressure absorption tower with high H2 content, which is conducive to the ratio of H2 / H2+NH3 shifting to the safe area; when the ratio of H2 / H2+NH3 is within the range of 4.6% to 75%, and the interlocking regulating valve cannot shift to the safe area, the pneumatic shut-off valve is opened for emergency venting;

[0029] The second stage is to set a second online ammonia analyzer on the treated exhaust pipeline, which is interlocked with the third pneumatic control valve. When the NH3 content in the treated exhaust gas deviates, the valve opening of the CO2 pipeline control valve is interlocked to adjust the partial pressure of NH3 in the exhaust gas. While increasing the explosion-proof safety, it also improves the absorption effect of NH3. At the same time, the H2 / H2+NH3 ratio is monitored and adjusted to be greater than 75%.

[0030] The innovative points of the present invention are as follows:

[0031] 1. Low-pressure tail gas ejects normal-pressure tail gas: The tail gas discharged from the low-pressure absorption tower enters the gas ejector 207. The pressure of the tail gas from the low-pressure absorption tower is 0.2-0.3MPa. A high-speed gas volume is formed in the ejector to form a negative pressure zone. The tail gas discharged at normal pressure is introduced into the exhaust pipe 201 and combined through the gas ejector 207 for treatment, so that gases of different pressures can be treated at the same time without the need for additional power sources. This saves energy while improving the safety of the system. At the same time, the combined tail gas pressure is greater than 0.05MPa, providing sufficient pressure to overcome the pressure loss of the tail gas treatment system, so that the treated gas can be discharged smoothly. Common gas pressurization mostly uses fans, compressors, etc., which are equipped with motors. Sparks or high-temperature hot surfaces may be generated due to electrical contact, mechanical friction, etc. In an explosive environment, these sparks or high-temperature hot surfaces are sufficient to ignite combustible gases, vapors or dust in the air, thereby causing an explosion.

[0032] 2. Carbon dioxide efficient absorption device 218 ( Figure 3): The solubility of carbon dioxide in water increases with increasing pressure and increases with decreasing temperature; this system introduces 0.2-0.3MPa CO2 gas from the CO2 compression section, and enters the carbon dioxide efficient absorption device 218 from the carbon dioxide inlet 21801. A gas distributor 21805 is set in the device, and a baffle 21807 is set at the top of the distributor. The baffle is set at an angle of 43-56°. The baffle can effectively disperse the fluid to a wider area to avoid the formation of an uneven flow pattern around the distributor. The appropriate angle, number and position of the baffle can accurately control the flow direction and flow rate of the fluid to achieve a more uniform fluid distribution. The appropriate baffle angle can avoid eddies and dead zones and promote the overall flow of the fluid. The selection of the baffle angle is closely related to the density and pressure of the medium. A carbon dioxide refiner 21804 is set to refine CO2 into tiny bubbles. The refined CO2 is evenly released into the target environment, which is conducive to the absorption of CO2. At the same time, the purified water introduced into the carbon dioxide efficient absorption device 218 is subjected to secondary cooling. The purified water from the bottom of the ammonia distillation tower 223 passes through the primary purified water cooler 221 and the secondary purified water cooler 220 and is cooled to 18-24°C, thereby increasing the solubility of CO2. When the purified water is at 20°C, the solubility is 5.8kg / m 3 After adding the internals, the solubility increased to 6.5 kg / m 3 Appropriate temperature and pressure are conducive to the dissolution of CO2 in water. CO2 dissolves in the desorption liquid to generate HCO3 - and CO3 2- The density of the liquid in which CO2 is dissolved is less than that of the desorption liquid. The washing liquid outlet 21806 is set at the middle of the absorption device, and the high-concentration carbonic acid solution is sent to the ammonia absorption washing tower for absorption. The undissolved CO2 is discharged from the top carbon dioxide outlet 21802 of the carbon dioxide efficient absorption device and sent to the middle and upper parts of the ammonia absorption washing tower 209. The addition of carbon dioxide changes the proportion of components in the exhaust air and adjusts the equilibrium partial pressure of the gas. This makes H2 / H2+NH3 deviate from the explosion hazard area by 4.6-75%, improving the safety of the system.

[0033] 3. Two-level online monitoring and control to improve explosion-proof safety factor: the first level is to set up an online hydrogen analyzer 205 and a first online ammonia analyzer 203 on the combined gas pipeline. The online hydrogen analyzer 205 is interlocked with the second pneumatic regulating valve 206; the first online ammonia analyzer 203 is interlocked with the first pneumatic regulating valve 204; the valve opening is controlled at the same time; the ratio of H2 / H2+NH3 is controlled outside the range of 4.6-75%. When the ratio of H2 / H2+NH3 is greater than 4.6, the opening of the first pneumatic regulating valve 204 is increased while the opening of the second pneumatic regulating valve 206 is decreased, so as to increase the exhaust gas with high ammonia content, which is conducive to the shift of the ratio of H2 / H2+NH3 to the safe area; when the ratio of H2 / H2+NH3 is less than 75, the opening of the second pneumatic regulating valve 206 is increased while the opening of the first pneumatic regulating valve 204 is decreased, so as to increase the exhaust gas with high H2 content from the low-pressure absorption tower, which is conducive to the shift of the ratio of H2 / H2+NH3 to the safe area; when the ratio of H2 / H2+NH3 is within the range of 4.6-75%, and the interlocking regulating valve cannot shift to the safe area, the pneumatic shut-off valve 202 is opened for emergency venting. The second stage is to set a second online ammonia analyzer 213 on the treated exhaust pipeline, which is interlocked with the third pneumatic control valve 214. When the NH3 content in the treated exhaust gas deviates, the valve opening of the CO2 pipeline control valve is interlocked to adjust the partial pressure of NH3 in the exhaust gas, increase the explosion-proof safety and improve the absorption effect of NH3. At the same time, the H2 / H2+NH3 ratio is monitored and adjusted to be greater than 75%.

[0034] 4. A flame arrester 215 is introduced on the treated exhaust gas pipeline: The corrugated filter element selected in the present invention generally has better flame arresting ability and smaller flow resistance. In flammable and explosive places, a detonation flame arrester is set. The flame arrester generally consists of a shell and a filter element. The shell has sufficient strength to withstand the impact pressure generated by the explosion. The filter element is the main component to prevent the spread of flames. The flame arrester can also effectively filter harmful substances in the flue gas, reduce pollutant emissions, and contribute to environmental protection. The flame arrester can also prevent backfire. The filter element is the core component of the flame arrester, and its structure (such as metal mesh type, corrugated type, etc.) and channel size will directly affect the fire-blocking effect. The corrugated filter element selected in the present invention generally has better flame arresting ability and smaller flow resistance.

[0035] 5. Segmented washing design of ammonia absorption washing tower 209: Through the washing design of the upper and lower sections, the washing liquid cooling cycle of the circulating washing liquid cooler 208 is first adopted to realize the pre-cooling and pre-washing of the tail gas, and the temperature is reduced to 22-24 degrees Celsius, and the harmful substances such as ammonia in the tail gas are efficiently removed, while reducing the energy consumption and cost in the treatment process, with the advantages of simple operation and convenient maintenance; and then the washing liquid cooler 219 is used to fully absorb and wash the washing liquid cooled to 20-22 degrees Celsius, thereby improving the washing and absorption efficiency. At the same time, the tail gas absorption washing tower is provided with a micro-positive pressure multi-stage filler, which can realize the efficient purification of the tail gas and the standard emission.

[0036] 6. An ammonia recovery system is set up: a 0.05-0.08MPa ammonia evaporation tower 223 is used to concentrate the diluted ammonia water with a concentration of 1.5-2.0% after washing, and the treated purified water (ammonia is less than 50ppm) is sent to the washing system for washing, and the treated ammonia is sent to the ammonia recovery system, and the ammonia concentration is between 13% and 16%. The present invention does not have an extra wastewater treatment burden.

[0037] The present invention has the following beneficial effects

[0038] 1. Significantly reduce ammonia emission content: Through the treatment method of the present invention, the ammonia content in the urea exhaust gas is successfully controlled at an extremely low level, that is, less than 20 mg / Nm 3 This value is far lower than the 30mg / Nm required by the Environmental Protection Law. 3 , which reflects the excellent performance of the present invention in reducing ammonia emissions.

[0039] 2. Reduce the risk of explosion: The present invention greatly reduces the concentration of ammonia in the tail gas by efficiently absorbing and recovering ammonia. At the same time, the inert gas carbon dioxide is introduced to adjust the gas partial pressure ratio so that H2 / H2+NH3 shifts to the safe area, thereby effectively eliminating the risk of explosion and providing a strong guarantee for the safe production of the enterprise.

[0040] 3. Achieve recycling of ammonia resources: In addition to reducing emissions, the present invention also focuses on recycling ammonia resources. The amount of ammonia resources recycled by this method reaches about 1,000 tons per year, which not only solves environmental problems but also creates considerable economic benefits for enterprises. At the same time, the recycled ammonia can be further processed and utilized, realizing the recycling of resources and avoiding the accumulation of ammonia in the system.

[0041] 4. Solve the problem of ammonia-containing wastewater treatment and realize the reuse of water resources.

[0042] 5. Small footprint and strong adaptability: Due to the simple and compact structure of the equipment, the treatment device of the present invention occupies a small area and is particularly suitable for application in the transformation system with tight land resources. At the same time, the method also has strong adaptability and can meet the needs of urea production enterprises of different scales and different working conditions.

[0043] 6. Ability to operate stably for a long period of time: Through optimized design and material selection, the present invention can maintain long-term stable operation in harsh working environments, which not only reduces the failure rate and downtime of equipment, but also improves the production efficiency and economic benefits of the enterprise. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of a urea exhaust gas treatment system in the prior art;

[0045] Figure 2 It is a schematic diagram of the system of the present invention;

[0046] Figure 3 is a schematic diagram of a carbon dioxide efficient absorption device 218 of the system of the present invention;

[0047] Description of the accompanying drawings: 201-exhaust pipe, 202-pneumatic shut-off valve, first pneumatic regulating valve-204, second pneumatic regulating valve 206, third pneumatic regulating valve 214, first online ammonia analyzer-203, second online ammonia analyzer 213, 205-online hydrogen analyzer, 207-gas ejector, 208-circulating washing liquid cooler, 209-ammonia absorption washing tower, 210-first layer of packing, 211-second layer of packing, 212-wire mesh, 215-flame arrester, 216-washing liquid pump, 217-dilute ammonia water Pump, 218-carbon dioxide high-efficiency absorption device, 219-washing liquid cooler, 220-purified water secondary cooler, 221-purified water primary cooler, 222-purified water pump, 223-ammonia evaporation tower, 224-contractor, 225-ammonia condenser, 226-condenser; 21801-carbon dioxide inlet, 21802-carbon dioxide outlet, purified water inlet-21803, 21804-CO2 refiner, 21805-gas distributor, 21806-washing liquid outlet, 21807-baffle. DETAILED DESCRIPTION

[0048] like Figure 2 As shown, a safe urea-based multi-stream ammonia treatment and recovery system includes an exhaust pipe 201, an online gas detection system, an ammonia absorption and washing tower 209, a carbon dioxide high-efficiency absorption device 218, an ammonia evaporation tower 223, a partial condenser 226, a flame arrester 215, a washing liquid pump 216, a dilute ammonia water pump 217, a purified water pump 222, etc.

[0049] The tail gas discharged from the low-pressure absorption tower and the tail gas discharged from the exhaust pipe cut off by the pneumatic shut-off valve 202 provided in the exhaust pipe 201 are sent to the gas ejector 207 together, and are sent to the ammonia absorption washing tower 209 after being combined and processed by the gas ejector. The two gases with different pressures are combined and processed by the ejector 207. The hydrogen line monitoring device 205 and the second pneumatic shut-off valve 206 on the tail gas discharged from the low-pressure absorption tower are interlocked and controlled on the gas pipeline after the combination; and the first ammonia line monitoring device 203 and the first pneumatic shut-off valve 204 on the tail gas discharged from the exhaust pipe are interlocked and controlled on the gas pipeline after the combination; and the pneumatic shut-off valve 202 is interlocked and controlled at the same time.

[0050] The ammonia absorption washing tower 209 is a packed tower, which is divided into two sections, each section has different functions. The lower section performs pre-washing and cooling, and the upper section uses cooling absorption washing. A wire mesh demister 212 is installed at the gas outlet of the tail gas absorption washing tower 209 to effectively remove the mist entrained in the tail gas, making the discharged tail gas purer and achieving effective ammonia removal. The first layer of packing 210 and the second layer of packing 211 are filled in the tail gas absorption washing tower 209.

[0051] A stream of desalted water is introduced from the outside and sent to the top of the first layer of filler 211 of the ammonia absorption washing tower 209.

[0052] One end of the washing liquid cooler 219 is connected to the washing liquid pump 216, and the other end is passed through a pipeline to the top of the first layer of filler 211 in the upper section of the ammonia absorption washing tower 209. The other end of the washing liquid pump 216 is connected to the middle washing liquid outlet 21806 of the carbon dioxide high-efficiency absorption device 218.

[0053] One end of the dilute ammonia water pump 217 is connected to the bottom outlet of the ammonia absorption washing tower 209, and at the other end, a part of it is passed through the pipeline through the circulating washing liquid cooler 208 to the top of the first layer of filler 210 in the middle section of the ammonia absorption washing tower; the other part is sent to the upper part of the ammonia evaporation tower 223 after heat exchange in the purified water primary cooler 221.

[0054] The carbon dioxide pressure absorption device 218 is provided with a CO2 refiner 21804 and a gas distributor 21805, each of which has different functions. The gas distributor distributes the gas uniformly, and the CO2 refiner refines, bubbles, and diffuses the gas to dissolve the CO2 gas more efficiently.

[0055] The shell of the carbon dioxide efficient absorption device 218 is provided with a carbon dioxide inlet 21801, a carbon dioxide outlet 21802, a purified water inlet 21803, a washing liquid outlet 21806 and a baffle 21807.

[0056] The CO2 gas outside the boundary is connected to the carbon dioxide inlet 21801 at the bottom of the carbon dioxide pressure absorption device 218 through a pipeline.

[0057] The carbon dioxide gas from outside the boundary enters below the lower gas distributor 21805 of the carbon dioxide efficient absorption device 218 after passing through the third pneumatic regulating valve 214. The unabsorbed carbon dioxide is discharged through the carbon dioxide gas outlet pipeline 2108 at the upper part of the carbon dioxide efficient absorption device 218 and then sent to the middle and upper parts of the ammonia absorption washing tower 209 through the pipeline.

[0058] One end of the purified water pump 222 is connected to the lower section of the ammonia evaporation tower 223, and the other end is cooled by the purified water primary cooler 221, and then cooled again by the purified water secondary cooler 220 before being sent to the purified water inlet 21803 of the upper section of the carbon dioxide high-efficiency absorption device 218.

[0059] The carbon dioxide pressurized absorption device 218 passes the undissolved CO2 gas into the middle and upper parts of the ammonia absorption washing tower 209 through a pipeline.

[0060] The tail gas after ammonia absorption and washing at the top of the ammonia absorption and washing tower 209 passes through the flame arrester 215 and is sent to the exhaust pipe for venting. One end of the flame arrester 215 is connected to the top of the ammonia absorption and washing tower, and the other end is connected to the exhaust pipe 201.

[0061] A pneumatic shut-off valve is added in the exhaust pipe 201 to isolate 202.

[0062] An online hydrogen analyzer 205 is provided to monitor the hydrogen content in the combined vented air online. By monitoring the hydrogen content and controlling the second pneumatic regulating valve 206, the proportion of H2 content in the system can be realized, thereby effectively ensuring safety.

[0063] A first online ammonia analyzer 203 is provided to monitor online the hydrogen content in the combined vented air. By monitoring the hydrogen content and controlling the first pneumatic regulating valve 204, the H2 content in the system can be controlled, thereby effectively ensuring safety.

[0064] At the same time, a second online ammonia analyzer 213 is set to monitor the ammonia content in the treated tail gas online and control the third pneumatic regulating valve 214 in the CO2 gas to ensure that the NH 3 The content is less than 20mg / Nm 3 .

[0065] An ammonia evaporation tower 223 is provided, and a stream of steam is introduced from the outside and passed into the bottom of the ammonia evaporation tower 223 to strip the dilute ammonia water delivered by the dilute ammonia water pump.

[0066] A portion of the diluted ammonia water after washing is sent to the top of the ammonia evaporation tower 223 through the diluted ammonia water pump 217, and the steam gas is passed into the lower part of the ammonia evaporation tower to make the concentration of the purified water less than 50ppm. After heat exchange with the diluted ammonia water in the bottom of the ammonia washing absorption tower 209 through the purified water pump 222, it is sent to the washing system for reuse. The evaporated ammonia gas passes through the fractionator 226, and then condensed by the ammonia condenser 225 and sent to the ammonia condensation tank. The condensed diluted ammonia water is sent to the ammonia water reuse system. The purified water at the bottom of the tower is sent to the purified water pump 222.

[0067] The process is as follows:

[0068] The tail gas discharged from the exhaust pipe and the tail gas discharged from the low-pressure absorption tower are combined through the ejector 207 and enter from the lower section of the ammonia absorption washing tower 209; while being fully contacted and cooled with the washing liquid cooled by the circulating washing liquid cooler 208 in the second layer of filler 210, a primary pre-washing is performed to remove the heat, and the tail gas after the cooling treatment rises through the first layer of filler 211 and is fully absorbed by the washing liquid cooled by the washing liquid cooler 2219 in the first layer of filler 211. After washing, the tail gas passes through the wire mesh demister 212 to remove the entrained liquid foam, and then passes through the flame arrester 215 and is led to the exhaust pipe 201, and is smoothly discharged by utilizing the residual pressure of the gas in the ammonia absorption washing tower 209.

[0069] The combined tail gas contacts the washing liquid treated by the carbon dioxide absorption device 218, and the solute containing ammonia is efficiently absorbed. The dilute ammonia water containing the solute is sent to the ammonia evaporation tower 223 for ammonia concentration. The concentrated ammonia water is sent to the ammonia recovery system after passing through the decompressor 224, the ammonia condenser 225, and the decompressor 226. The purified water in the bottom of the ammonia evaporation tower 223 is heat exchanged with the dilute ammonia water at the bottom of the ammonia washing absorption tower and then sent to the carbon dioxide absorption device 218 for recycling as a washing liquid.

[0070] Undissolved CO2 gas is introduced into the upper part of the tail gas absorption scrubber for explosion-proof treatment, and the ammonia content in the exhaust gas is further reduced to ensure that the NH3 content in the tail gas is less than 20mg / Nm 3 .

[0071] The urea multi-stream ammonia treatment method proposed in the present invention shows significant advantages and inventive effects in solving ammonia emission problems, ensuring safe production, resource recycling and utilization, and technical and economic efficiency.

Claims

1. A safe urea multi-stream ammonia treatment and recovery system, comprising an exhaust pipe (201), characterized in that The invention also includes an online gas detection system, an ammonia absorption and washing tower (209), a carbon dioxide high-efficiency absorption device (218), an ammonia evaporation tower (223), a partial condenser (226), a flame arrester (215), a washing liquid pump (216), a dilute ammonia water pump (217), and a purified water pump (222); the exhaust gas discharged from the low-pressure absorption tower and the exhaust pipe exhaust gas cut off by the pneumatic shut-off valve (202) provided in the exhaust pipe (201) are sent to the gas ejector (207) through a pipeline, and the two gases with different pressures are combined and processed by the ejector (207), and an online gas detection system is provided on the combined gas pipeline; The exhaust gas after the gas ejector combined treatment is sent to the ammonia absorption washing tower (209) through a pipeline. The ammonia absorption washing tower (209) adopts a packed tower, which is divided into an upper section and a lower section. The ammonia absorption washing tower is filled with a first layer of packing (210) and a second layer of packing (211). A wire mesh demister (212) is installed at the gas outlet of the ammonia absorption washing tower. One end of the dilute ammonia water pump (217) is connected to the outlet pipeline at the bottom of the ammonia absorption washing tower (209), and the other end, a part of which is connected to the pipeline of the circulating washing liquid cooler (208) and then passed to the top of the first layer of packing (210) in the middle section of the ammonia absorption washing tower; the other part is connected to the pipeline of the purified water primary cooler (221) and then passed to the upper part of the ammonia evaporation tower (223); A gas distributor (21805) and a CO2 refiner (21804) are provided in the carbon dioxide efficient absorption device (218); a carbon dioxide inlet (21801), a carbon dioxide outlet (21802), a purified water inlet (21803), a washing liquid outlet (21806), and a baffle (21807) are provided on the shell of the carbon dioxide efficient absorption device (218); The carbon dioxide gas from outside the boundary is connected to the gas distributor (21805) pipeline of the lower section of the carbon dioxide efficient absorption device (218) after passing through the regulating valve (214), and the carbon dioxide gas outlet (21802) is connected to the middle and upper pipelines of the ammonia absorption washing tower (209) at the same time; One end of the purified water pump (222) is connected to the lower section pipeline of the ammonia evaporation tower (223), and the other end is connected to the pipeline of the primary cooler (221). The primary cooler (221) is connected to the pipeline of the secondary cooler (220) and then connected to the purified water inlet (21803) pipeline of the upper section of the carbon dioxide high-efficiency absorption device (218); One end of the washing liquid pump (216) is connected to the middle washing liquid outlet (21806) of the carbon dioxide high-efficiency absorption device (218), and the other end is connected to the washing liquid cooler (219) pipeline and then introduced into the upper part of the first layer of filler (211) in the ammonia absorption washing tower (209); A stream of steam is introduced from the outside and passed into the bottom of the ammonia evaporation tower (223). A fractionator (224) is provided in the ammonia evaporation tower (223). The gas phase is connected to the pipeline of the ammonia condenser (225) through the top of the fractionator (224). The ammonia condenser (225) is connected to the pipeline of the fractionator (226). The bottom of the fractionator (226) is connected to the external pipeline, and the top is connected to the external pipeline. The purified water at the bottom of the ammonia evaporation tower (223) is sent to the purified water pump (222) through the pipeline.

2. The safe urea multi-stream ammonia treatment and recovery system according to claim 1 is characterized in that: The online gas detection system comprises: an online hydrogen analyzer (205) is arranged on the combined gas pipeline and interlocked with a second pneumatic regulating valve (206) on the exhaust gas discharged from the low-pressure absorption tower; a first online ammonia analyzer (203) is arranged on the combined gas pipeline and interlocked with a first pneumatic regulating valve (204) on the exhaust gas discharged from the exhaust pipe; and at the same time, it is interlocked with a pneumatic shut-off valve (202).

3. The safe urea multi-stream ammonia treatment and recovery system according to claim 1 is characterized in that: The washing liquid outlet (21806) is arranged at a height in the middle of the carbon dioxide efficient absorption device (218); a baffle (21807) is arranged at the top of the gas distributor (21805), and the baffle is arranged at an angle of 43 to 56 degrees.

4. The safe urea multi-stream ammonia treatment and recovery system according to claim 1 is characterized in that: The CO2 gas outside the boundary is connected to the carbon dioxide inlet (21801) pipeline at the bottom of the carbon dioxide pressure absorption device (218).

5. The safe urea multi-stream ammonia treatment and recovery system according to claim 1 is characterized in that: One end of the flame arrester (215) is connected to the top pipeline of the ammonia absorption washing tower, and the other end is connected to the pipeline of the exhaust pipe (201). The flame arrester (215) uses a corrugated filter element.

6. The safe urea multi-stream ammonia treatment and recovery system according to claim 1 is characterized in that: A stream of desalted water is introduced from the outside and sent to the top of the first layer of filler (211) of the ammonia absorption washing tower (209).

7. A safe urea multi-stream ammonia treatment and recovery method, characterized in that: The exhaust gas discharged from the exhaust pipe and the exhaust gas discharged from the low-pressure absorption tower are combined through the ejector (207) and enter the lower section of the ammonia absorption washing tower (209); the exhaust gas is fully contacted with the washing liquid cooled by the circulating washing liquid cooler (208) in the second layer of filler (210) for cooling, and a primary pre-washing is performed to remove heat. The exhaust gas after cooling rises and passes through the first layer of filler (211) and is fully absorbed by the washing liquid cooled by the washing liquid cooler (219) in the first layer of filler (21). The washed exhaust gas is removed from the entrained liquid foam by the wire mesh demister (212) and then passes through the flame arrester (215) and is introduced to the exhaust pipe (201), and is smoothly discharged by utilizing the residual pressure of the gas in the ammonia absorption washing tower (209); The purified water from the bottom of the ammonia evaporation tower (223) is sent to the purified water pump (222); the purified water from the bottom of the ammonia evaporation tower (223) is heat exchanged with the dilute ammonia water at the bottom of the ammonia washing absorption tower and then sent to the carbon dioxide absorption device (218) for recycling as a washing liquid; at the same time, the purified water sent to the carbon dioxide high-efficiency absorption device (218) is subjected to secondary cooling, and the purified water from the bottom of the ammonia evaporation tower (223) passes through the primary purified water cooler (221) and the secondary purified water cooler (220) and is cooled to 18-24° C., thereby increasing the solubility of CO2; The combined tail gas is contacted with the washing liquid treated by the carbon dioxide absorption device (218), and the solute containing ammonia is efficiently absorbed; a stream of steam is introduced from the outside and passed into the bottom of the ammonia evaporation tower (223), and the dilute ammonia water containing solute sent by the dilute ammonia water pump (217) is condensed and concentrated in the gas phase by the fractionator (224), and then condensed by the ammonia condenser (225) and sent to the fractionator (226) to make ammonia water, which is then sent to the ammonia water recovery system; The carbon dioxide gas from outside enters below the lower gas distributor (21805) of the carbon dioxide efficient absorption device (218) after passing through the regulating valve (214); the unabsorbed CO2 is discharged through the carbon dioxide gas outlet (21802) at the upper part of the carbon dioxide efficient absorption device (218) and then sent to the middle and upper parts of the ammonia absorption washing tower (209) through a pipeline; Undissolved CO2 gas is introduced into the upper part of the ammonia absorption scrubber (208) for explosion-proof treatment, and the ammonia content in the exhaust gas is further reduced to ensure that the NH3 content in the exhaust gas is less than 20 mg / Nm 3 .

8. The safe urea multi-stream ammonia treatment and recovery method according to claim 7 is characterized in that: The explosion-proof treatment is realized by two-level online monitoring control: the first level is to respectively set an online hydrogen analyzer (205) and a first online ammonia analyzer (203) on the combined gas pipeline; wherein the online hydrogen analyzer (205) is interlocked with the second pneumatic regulating valve (206); the first online ammonia analyzer (203) is interlocked with the first pneumatic regulating valve (204); the opening of the valve is controlled at the same time; the ratio of H2 / H2+NH3 is controlled outside the range of 4.6 to 75%, and when the ratio of H2 / H2+NH3 is greater than 4.6, the opening of the first pneumatic regulating valve (204) is increased while the opening of the second pneumatic regulating valve is decreased. The opening of the regulating valve (206) increases the exhaust gas with high ammonia content, which is conducive to the ratio of H2 / H2+NH3 shifting to the safe area; when the ratio of H2 / H2+NH3 is less than 75, the opening of the second pneumatic regulating valve (206) is increased and the opening of the first pneumatic regulating valve (204) is decreased, so that the exhaust gas with high H2 content from the low-pressure absorption tower is increased, which is conducive to the ratio of H2 / H2+NH3 shifting to the safe area; when the ratio of H2 / H2+NH3 is within the range of 4.6% to 75%, and the interlocking regulating valve cannot shift to the safe area, the interlocking pneumatic shut-off valve (202) is opened for emergency venting; The second stage is to set a second online ammonia analyzer (213) on the treated tail gas pipeline, which is interlocked with the third pneumatic control valve (214). When the NH3 content in the treated tail gas deviates, the valve opening of the CO2 pipeline control valve is interlocked to adjust the partial pressure of NH3 in the tail gas. The increase of CO2 gas adjusts the explosion-proof safety and improves the absorption effect of NH3. At the same time, the ratio of H2 / H2+NH3 is monitored and adjusted to be greater than 75%.

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