Emptying tail gas treatment device for methylamine production device

Abstract

The utility model relates to an emptying tail gas treatment device for a methylamine production device. The emptying tail gas treatment device comprises a tail gas absorption unit, a tail gas washing unit and a three-stage emission protection unit, the tail gas absorption unit comprises a tail gas absorption tower, a methanol feeding cooler communicated with the tail gas absorption tower, a tail gas absorption tower bottom circulating pump and a tail gas absorption tower circulating cooler; the tail gas washing unit comprises a tail gas washing tower, a desalted water feeding cooler communicated with the tail gas washing tower, a tail gas washing tower bottom circulating pump and a tail gas washing tower circulating cooler; the device is novel in structure and solves the problem of excessive emission of tail gas. Under the normal technological process, activated carbon is used for adsorption treatment of vented tail gas, the activated carbon adsorption tank is temporarily switched to an incinerator or a torch for treatment only when an agent needs to be replaced or a tail gas emission system is in an abnormal state, and unstable combustion, non-combustion and even tempering explosion caused by the fact that the incinerator or the torch is used for treating the vented tail gas for a long time are avoided.

Description

Technical Field

[0001] This utility model relates to a treatment device, specifically a treatment device for vent gas from a methylamine production unit. Background Technology

[0002] Methylamine (CH3NH2) is an important organic intermediate and a crucial raw material for industries such as pesticides, pharmaceuticals, defense chemicals, rubber, leather, synthetic dyes, chemical fibers, surfactants, and photography.

[0003] Industrially, methylamine is produced using the methanol gas-phase catalytic ammoniation method. Methanol and ammonia are reacted at high temperatures in a converter equipped with an activated alumina catalyst to synthesize methylamine. However, the methylation reaction does not stop at the monomethylamine stage; therefore, the product includes a mixture of monomethylamine, dimethylamine, and trimethylamine. Controlling the ratio of methanol to ammonia, with an excess of ammonia, and adding water and recycling trimethylamine, promotes the formation of monomethylamine and dimethylamine. When the amount of ammonia is 2.5 times that of methanol, the reaction temperature is 425℃, and the reaction pressure is 2.45 MPa, a mixed amine of 10-12% monomethylamine, 8-9% dimethylamine, and 11-13% trimethylamine can be obtained. This method uses abundant and inexpensive raw materials, allows for large-scale continuous production, has low requirements for equipment and materials, and the process conditions are easy to meet. The product ratios of the three methylamines can be flexibly adjusted according to market demand. This process is currently the most widely used industrial production method in the methylamine industry, and all existing methylamine plants in my country use this process.

[0004] Methylamine is produced by the methanol gas-phase catalytic ammoniation method, employing a five-tower distillation process. During operation, the distillation towers generate vent gas, whose main components are hydrogen, carbon monoxide, methanol, organic amines, and VOCs. Therefore, a vent gas treatment device is needed. Early methylamine production plants typically treated the vent gas in a methanol absorption tower before direct emission into the atmosphere. Although methanol absorption removes most of the organic matter in the vent gas, a small amount remains. In later methylamine plants, the vent gas is typically sent to an incinerator or flare for further treatment after methanol absorption to meet emission standards. An existing utility model patent (patent number ZL202420444645.3) discloses a "deep cryogenic + adsorption" methylamine vent gas treatment device, but it does not consider how to treat the methylamine vent gas when the adsorbent is replaced or fails, nor does it include backup treatment measures.

[0005] Because the concentration of combustibles in the vented exhaust gas is low and the emissions are indirect, the combustion in the flare or incinerator may be unstable or even fail to ignite, and there is even a risk of backfire and explosion. This means that the vented exhaust gas from the methylamine unit cannot be treated by flare or incinerator for extended periods. Utility Model Content

[0006] In view of the above situation and to overcome the defects of the prior art, this utility model provides a venting tail gas treatment device for a methylamine production unit, which effectively solves the problems mentioned in the background art.

[0007] To achieve the above objectives, this utility model provides the following technical solution: This utility model includes:

[0008] Exhaust gas absorption unit, exhaust gas washing unit, and three-stage emission protection unit;

[0009] The tail gas absorption unit includes a tail gas absorption tower, a methanol feed cooler connected to the tail gas absorption tower, a bottom circulation pump of the tail gas absorption tower, and a tail gas absorption tower circulation cooler.

[0010] The tail gas washing unit includes a tail gas washing tower, a demineralized water feed cooler connected to the tail gas washing tower, a tail gas washing tower bottom circulation pump, and a tail gas washing tower circulation cooler.

[0011] The three-level emission protection unit includes:

[0012] Main processing pathway: Activated carbon adsorption tank A and activated carbon adsorption tank B connected in sequence;

[0013] Backup treatment path: connected in sequence to the exhaust gas fan and incinerator;

[0014] Emergency response route: connected to the flare system;

[0015] The inlet ends of the three passages are connected to the top gas phase outlet of the tail gas scrubbing tower via valve groups.

[0016] Preferably, the bottom of the tail gas absorption tower is connected to the venting tail gas inlet of the methylamine device, and the top is connected to the bottom of the tail gas washing tower through the top condenser of the tail gas absorption tower.

[0017] The top gas phase outlet of the tail gas washing tower is connected to three passages of the three-stage emission protection unit through a valve group.

[0018] Preferably, the valve assembly includes:

[0019] The first check valve and the first shut-off valve on the main processing path;

[0020] The second check valve, the second shut-off valve, and the third flame arrester are on the backup processing circuit;

[0021] The emergency response route includes a third check valve, a third shut-off valve, and a first flame arrester.

[0022] Preferably, the activated carbon adsorption tank A and the activated carbon adsorption tank B are connected in series, wherein:

[0023] Activated carbon adsorption tank A is used to remove methanol;

[0024] Activated carbon adsorption tank B is used to remove organic amines;

[0025] Differential pressure gauges and shut-off valves are installed on the inlet and outlet pipelines of both adsorption tanks.

[0026] Preferably, the inlet of the exhaust gas fan is equipped with a nitrogen replenishment regulating valve and a second pressure transmitter, and the outlet is equipped with an exhaust gas fan frequency converter, a third pressure transmitter and an exhaust gas flow meter.

[0027] The nitrogen supplementation regulating valve and the second pressure transmitter form a closed-loop control of the fan inlet pressure.

[0028] The frequency converter of the exhaust gas fan and the third pressure transmitter constitute a closed-loop control of the fan outlet pressure.

[0029] Preferably, an online gas analyzer is installed on the top gas phase outlet pipeline of the tail gas washing tower to monitor the tail gas composition in real time and control the switching of the valve group.

[0030] Preferably, the emergency handling path is equipped with a first pressure transmitter, which together with the third shut-off valve forms an overpressure relief control loop.

[0031] Preferably, the bottoms of the tail gas absorption tower and the tail gas washing tower are connected to a flow meter and a flow control valve respectively through an external pipeline to form a closed-loop control of the liquid level.

[0032] Beneficial effects: Enhanced absorption: Fresh methanol and demineralized water feeds are first cooled by cold water before entering the tail gas absorption tower and tail gas scrubbing tower respectively to absorb the vented tail gas, enhancing the absorption effect of methanol and demineralized water on soluble substances in the vented tail gas. Simultaneously, the vented tail gas enters from the bottom of the tail gas absorption tower and tail gas scrubbing tower respectively, while methanol and demineralized water enter from the top of the tail gas absorption tower and tail gas scrubbing tower respectively. The circulating liquid in the tail gas absorption tower circulation pump and the tail gas scrubbing tower circulation pump is cooled by circulating water and then returned to the tower from the middle of the tail gas absorption tower and tail gas scrubbing tower respectively. This counter-current gas-liquid contact, combined with double spraying, further enhances the absorption effect.

[0033] Precise control of the bottom liquid level: The bottom liquid of the tail gas absorption tower and the tail gas washing tower are respectively connected to the external regulating valve and the flow meter to form a control loop, so as to precisely control the bottom liquid level.

[0034] To address the issue of excessive exhaust gas emissions: A three-layer emission protection system is implemented for the vented exhaust gas after passing through the exhaust gas absorption tower and the exhaust gas washing tower, completely resolving the problem of excessive emissions. Under normal process conditions, the vented exhaust gas is treated with activated carbon adsorption. Only when the activated carbon adsorption tank needs replacement or is temporarily unusable due to maintenance or repair needs is the system temporarily switched to an incinerator or flare for treatment. This avoids the problems of unstable combustion, non-combustion, or even backfire and explosion caused by prolonged use of incinerators or flares for vented exhaust gas treatment.

[0035] To prevent material cross-contamination and backfire: The three-way process of the exhaust gas venting tower at the top is equipped with shut-off valves, check valves and flame arresters to prevent the risk of material cross-contamination and backfire.

[0036] To ensure stable inlet air pressure for the exhaust fan: The nitrogen supplementation regulating valve and the pressure before the exhaust fan form a control loop to ensure stable inlet air pressure for the exhaust fan. The exhaust fan frequency converter and the exhaust fan outlet pressure form a control loop to ensure stable outlet air pressure for the exhaust fan.

[0037] To ensure stable system pressure: The flare shut-off valve and the system pressure form a control loop. When the system is over-pressured, the shut-off valve will automatically open to relieve pressure and ensure stable system pressure.

[0038] Accurately determining adsorbent replacement time: Activated carbon adsorption tanks are connected in series. The first adsorption tank primarily removes methanol from the vented exhaust gas, while the second adsorption tank primarily removes organic amines and other organic compounds. Shut-off valves are installed before and after each adsorption tank to completely disconnect it from the system. Differential pressure gauges are installed on the inlet and outlet pipelines of the activated carbon adsorption tanks. The pressure difference can be used to qualitatively determine the adsorbent's adsorption saturation. Simultaneously, samples can be periodically taken from the exhaust port for analysis. The analysis results can be used to quantitatively determine the adsorbent's adsorption saturation, thereby deciding the replacement time.

[0039] Timely reminders to switch treatment pathways: An online gas analyzer is installed on the vent gas pipeline at the top of the tail gas washing tower. When the composition of the vent gas exceeds the activated carbon adsorption limit, the control system issues an alarm, reminding the operator to manually disconnect the vent gas from the activated carbon adsorption system and manually switch the vent gas into the incinerator or flare for treatment. Attached Figure Description

[0040] The accompanying drawings are provided to further illustrate the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention, but do not constitute a limitation thereof. In the drawings:

[0041] Figure 1 This is a schematic diagram of the overall structure of this utility model;

[0042] Labels in the diagram: 1. Methanol feed cooler; 2. Tail gas absorption tower; 3. Tail gas absorption tower bottom circulation pump; 4. Tail gas absorption tower circulating cooler; 5. Tail gas absorption tower top cooler; 6. First flow control valve; 7. First flow meter; 8. Tail gas absorption tower level gauge; 9. Demineralized water feed cooler; 10. Tail gas scrubbing tower; 11. Tail gas scrubbing tower bottom circulation pump; 12. Tail gas scrubbing tower circulating cooler; 13. Second flow control valve; 14. Second flow meter; 15. Tail gas scrubbing tower level gauge; 16. First flame arrester; 17. First shut-off valve; 18. First... 19. Check valve; 20. First pressure transmitter; 21. Online gas analyzer; 22. Second check valve; 23. Second shut-off valve; 24. Activated carbon adsorption tank A; 25. Activated carbon adsorption tank B; 26. Third shut-off valve; 27. Second flame arrester; 28. Differential pressure gauge; 29. ​​Third check valve; 30. Fourth shut-off valve; 31. Second pressure transmitter; 32. Third flame arrester; 33. Nitrogen regulating valve; 34. Exhaust gas fan; 35. Exhaust gas fan frequency converter; 36. Third pressure transmitter; 37. Exhaust gas flow meter; 38. Fourth flame arrester; 39. Fifth shut-off valve. Detailed Implementation

[0043] The following is in conjunction with the appendix Figure 1 The specific embodiments of this utility model will be described in further detail.

[0044] Example 1, by Figure 1 This utility model provides a vent gas treatment device for a methylamine production unit, comprising:

[0045] Exhaust gas absorption unit, exhaust gas washing unit, and three-stage emission protection unit;

[0046] The tail gas absorption unit includes a tail gas absorption tower 2, a methanol feed cooler 1 connected to the tail gas absorption tower, a tail gas absorption tower bottom circulation pump 3, and a tail gas absorption tower circulation cooler 4.

[0047] The tail gas washing unit includes a tail gas washing tower 10, a demineralized water feed cooler 9 connected to the tail gas washing tower, a tail gas washing tower bottom circulation pump 11, and a tail gas washing tower circulation cooler 12.

[0048] The three-level emission protection unit includes:

[0049] Main processing pathway: Activated carbon adsorption tank A23 and activated carbon adsorption tank B24 connected in sequence;

[0050] Backup treatment path: exhaust gas fan 33 and incinerator connected in sequence;

[0051] Emergency response route: connected to the flare system;

[0052] The inlet ends of the three passages are connected to the top gas phase outlet of the tail gas scrubbing tower 10 via valve groups.

[0053] The tail gas absorption unit includes a tail gas absorption tower 2, a methanol feed cooler 1 connected to the tail gas absorption tower, a tail gas absorption tower bottom circulation pump 3, and a tail gas absorption tower circulation cooler 4. The bottom of the tail gas absorption tower 2 is connected to the vent gas inlet of the methylamine unit, and the top is connected to the bottom of the tail gas washing tower 10 via a tail gas absorption tower top condenser 5. Fresh methanol enters the tail gas absorption tower 2 from the top after being cooled by the methanol feed cooler 1 (using 7°C cold water as the cooling medium), while the vent gas from the methylamine unit enters the tail gas absorption tower 2 from the bottom. The cooled methanol and the vent gas come into counter-current contact within the tail gas absorption tower 2. The methanol absorbs some soluble substances from the vent gas and then enters the bottom of the tail gas absorption tower 2. Through the tail gas absorption tower bottom circulation pump 3, part of the methanol is circulated back to the tail gas absorption tower 2 via the tail gas absorption tower circulation cooler 4 (circulating water cooling) to continue being used as an absorption medium, while the rest is directly sent to the methylamine unit as methanol feedstock. The vented tail gas, after being absorbed by methanol, enters the top condenser 5 of the tail gas absorption tower (with 7°C cold water as the cooling medium) from the top of the tower. The condensed liquid phase returns to the tail gas absorption tower 2, while the gas phase enters the tail gas water washing tower 10 from the bottom.

[0054] The tail gas washing unit includes a tail gas washing tower 10, a demineralized water feed cooler 9 connected to the tail gas washing tower, a tail gas washing tower bottom circulation pump 11, and a tail gas washing tower circulation cooler 12. Fresh demineralized water enters the tail gas washing tower 10 from the top after being cooled by the tail gas washing tower feed cooler 9 (using 7°C cold water as the cooling medium) from the boundary area. The cooled demineralized water and the tail gas absorbed by methanol come into counter-current contact within the tail gas washing tower 10 to further remove organic matter. After absorbing some soluble substances in the vented tail gas, the demineralized water enters the bottom of the tail gas washing tower 10. Through the tail gas washing tower bottom circulation pump 11, part of it is circulated back to the tail gas washing tower 10 via the tail gas washing tower circulation cooler 12 (cooled by circulating water) to continue being used as an absorption medium, while part is directly sent to the wastewater treatment plant for treatment.

[0055] The three-stage emission protection unit includes a main treatment path, a backup treatment path, and an emergency treatment path. The main treatment path consists of activated carbon adsorption tanks A23 and B24 connected in sequence; the backup treatment path consists of exhaust gas fan 33 and incinerator connected in sequence; and the emergency treatment path is connected to the flare system. The inlet ends of the three paths are connected to the top gas phase outlet of the tail gas scrubbing tower 10 through valve groups.

[0056] The top gas phase outlet of the tail gas scrubbing tower 10 is connected to three passages of the three-stage emission protection unit via valve assemblies. The valve assemblies include: a first check valve 21 and a first shut-off valve 22 on the main treatment passage; a second check valve 28, a second shut-off valve 29, and a third flame arrester 31 on the backup treatment passage; and a third check valve 18, a third shut-off valve 17, and a first flame arrester 16 on the emergency treatment passage.

[0057] Activated carbon adsorption tanks A23 and B24 are connected in series. Activated carbon adsorption tank A23 is used to remove methanol, and activated carbon adsorption tank B24 is used to remove organic amines. Differential pressure gauges 27 and shut-off valves 22 and 25 are installed on the inlet and outlet pipelines of both adsorption tanks.

[0058] The exhaust gas fan 33 is equipped with a nitrogen replenishment regulating valve 32 and a second pressure transmitter 30 at its inlet, and an exhaust gas fan frequency converter 34, a third pressure transmitter 35, and an exhaust gas flow meter 36 at its outlet. The nitrogen replenishment regulating valve 32 and the second pressure transmitter 30 form a closed-loop control of the fan inlet pressure, and the exhaust gas fan frequency converter 34 and the third pressure transmitter 35 form a closed-loop control of the fan outlet pressure.

[0059] An online gas analyzer 20 is installed on the top gas phase outlet pipeline of the tail gas scrubbing tower 10 to monitor the tail gas composition in real time and control the switching of the valve group. A first pressure transmitter 19 is installed on the emergency treatment path, which, together with the third shut-off valve 17, forms an overpressure relief control loop.

[0060] The bottoms of the tail gas absorption tower 2 and the tail gas washing tower 10 are connected to flow meters 7 and 14 and flow control valves 6 and 13 respectively through external pipelines to form a closed-loop control of liquid level.

[0061] Working Principle: Methanol Cooling and Absorption Process: Fresh methanol is introduced from the boundary area and first passes through methanol feed cooler 1, where it is cooled using 7°C cold water as the cooling medium. It then enters the tail gas absorption tower 2 from the top. Simultaneously, the vented tail gas from the methylamine unit enters from the bottom of tail gas absorption tower 2, where it comes into counter-current contact with the cooled methanol. Because methanol has a good absorption capacity for some soluble substances in the tail gas, such as methanol itself and some organic amines, during the counter-current gas-liquid contact process, the methanol absorbs these soluble substances and flows downwards, eventually entering the bottom of tail gas absorption tower 2.

[0062] Methanol recycling and external delivery: The methanol solution at the bottom of the tower is treated in two parts: one part is extracted by the bottom circulation pump 3 of the tail gas absorption tower, cooled by circulating water in the tail gas absorption tower circulation cooler 4, and then sent back to the middle of the tail gas absorption tower 2 to continue to be used as an absorption medium, so as to improve the utilization rate and absorption effect of methanol; the other part is sent directly to the methylamine unit as the methanol raw material required for production, realizing the recycling of materials.

[0063] Preliminary treatment and transportation of exhaust gas: The vented exhaust gas after methanol absorption is discharged from the top of the exhaust gas absorption tower 2 and enters the top condenser 5 of the exhaust gas absorption tower, where it is condensed using 7°C cold water as the cooling medium. The condensed liquid methanol is returned to the exhaust gas absorption tower 2, while the uncondensed gaseous exhaust gas is discharged from the bottom of the condenser and enters the next step of the exhaust gas water washing unit.

[0064] Demineralized water cooling and washing process: Fresh demineralized water is introduced from the boundary area and cooled with 7°C cold water in the demineralized water feed cooler 9, then enters the tail gas washing tower 10 from the top. Gas-phase tail gas from the tail gas absorption tower 2 enters from the bottom of the tail gas washing tower 10 and comes into counter-current contact with the cooled demineralized water inside the tower. The demineralized water can further absorb residual organic matter in the tail gas, such as organic amines and VOCs that were not completely absorbed by methanol, thus purifying the tail gas at a deeper level.

[0065] Demineralized water circulation and treatment: After the demineralized water that has absorbed pollutants enters the bottom of the tail gas scrubbing tower 10, it is also divided into two parts: one part is drawn out by the tail gas scrubbing tower bottom circulation pump 11, cooled by circulating water in the tail gas scrubbing tower circulation cooler 12, and then sent back to the middle of the tail gas scrubbing tower 10 to continue to participate in the water washing process; the other part is sent directly to the sewage treatment device for treatment to avoid the accumulation of pollutants.

[0066] Exhaust gas output after water washing: The exhaust gas after water washing is discharged from the top gas phase outlet of the exhaust gas water washing tower 10. At this time, most of the organic matter in the exhaust gas has been removed, but it may still contain a small amount of residual pollutants, which need to be finally treated by the three-stage emission protection unit.

[0067] Normal operating conditions of the main treatment path: When the composition of the tail gas at the top of the tail gas scrubbing tower 10 meets the activated carbon adsorption conditions, the tail gas enters the main treatment path: first, it passes through the second check valve 21 and the second shut-off valve 22, and then sequentially enters the activated carbon adsorption tanks A23 and B24, which are connected in series. Activated carbon adsorption tank A23 is mainly used to adsorb and remove methanol from the tail gas, while activated carbon adsorption tank B24 is mainly used to adsorb and remove organic amines and other organic compounds. After deep adsorption treatment by activated carbon, the concentration of pollutants in the tail gas is further reduced to meet emission standards, and finally, it is discharged into the atmosphere through the third shut-off valve 25 and the second flame arrester 26.

[0068] Backup treatment path activated carbon maintenance condition: When activated carbon adsorption tanks A23 or B24 need to be replaced or are under maintenance, the main treatment path is closed and the exhaust gas is switched to the backup treatment path: At this time, the third check valve 28 and the fourth shut-off valve 29 are opened, and the exhaust gas enters the exhaust gas fan 33 after passing through the third flame arrester 31. The exhaust gas fan 33 transports the exhaust gas to the incinerator for high-temperature incineration treatment to ensure that the pollutants in the exhaust gas are completely decomposed and meet the emission standards.

[0069] Abnormal operating conditions of the emergency treatment pathway system: When the activated carbon adsorption tank needs to be replaced or repaired, and at the same time the exhaust fan 33 malfunctions or the incinerator is under maintenance, the exhaust gas enters the emergency treatment pathway: the first check valve 18 and the first shut-off valve 17 are opened, and the exhaust gas is discharged to the flare system after passing through the first flame arrester 16. The pollutants in the exhaust gas are destroyed by combustion in the flare, which serves as a last safety measure to prevent the exhaust gas from exceeding the emission standard.

[0070] Pressure Control: Exhaust Gas Fan Inlet Pressure Control: A nitrogen supplementation regulating valve 32 and a second pressure transmitter 30 are installed at the inlet of the exhaust gas fan 33, forming a closed-loop control circuit. When the inlet pressure of the exhaust gas fan changes, the second pressure transmitter 30 feeds a signal back to the control system. The control system automatically adjusts the opening of the nitrogen supplementation regulating valve 32 to maintain a stable inlet pressure by supplementing nitrogen, ensuring the normal operation of the exhaust gas fan 33.

[0071] Exhaust gas fan outlet pressure control: The outlet of the exhaust gas fan 33 is equipped with an exhaust gas fan frequency converter 34, a third pressure transmitter 35, and an exhaust gas flow meter 36. The third pressure transmitter 35 monitors the outlet pressure in real time and transmits the signal to the control system. The control system adjusts the frequency of the exhaust gas fan frequency converter 34 to change the fan speed, thereby controlling the outlet pressure of the fan and keeping it within a stable range.

[0072] Overpressure relief control: A first pressure transmitter 19 is installed in the emergency handling path, which, together with the first shut-off valve 17, forms an overpressure relief control loop. When the system pressure exceeds the set value, the first pressure transmitter 19 sends a signal, and the control system automatically opens the first shut-off valve 17 to discharge some of the exhaust gas to the flare system, thus relieving pressure and ensuring system pressure stability to prevent safety accidents caused by overpressure.

[0073] Adsorbent Status Monitoring and Switching Control: Differential pressure gauges 27 are installed on the inlet and outlet pipelines of activated carbon adsorption tanks A23 and B24. The adsorption saturation of the adsorbent is qualitatively determined by monitoring the pressure difference between the inlet and outlet of the adsorption tank. When the pressure difference increases to a certain level, it indicates that the adsorbent may be approaching saturation. Simultaneously, exhaust gas components are periodically sampled and analyzed at the outlet, and the adsorption saturation of the adsorbent is quantitatively determined based on the analysis results. When the adsorbent reaches saturation, the operator can switch to another activated carbon adsorption tank and perform adsorbent replacement as needed. Furthermore, an online gas analyzer 20 is installed on the gas phase outlet pipeline at the top of the exhaust gas washing tower 10 to monitor the exhaust gas composition in real time. When the exhaust gas composition exceeds the activated carbon adsorption limit, the online gas analyzer 20 issues an alarm signal, reminding the operator to manually disconnect the vented exhaust gas from the activated carbon adsorption system and switch to a backup or emergency treatment path to ensure the exhaust gas treatment effect and system safety.

[0074] Beneficial effects: Enhanced absorption: Fresh methanol and demineralized water feeds are first cooled by cold water before entering the tail gas absorption tower and tail gas scrubbing tower respectively to absorb the vented tail gas, enhancing the absorption effect of methanol and demineralized water on soluble substances in the vented tail gas. Simultaneously, the vented tail gas enters from the bottom of the tail gas absorption tower and tail gas scrubbing tower respectively, while methanol and demineralized water enter from the top of the tail gas absorption tower and tail gas scrubbing tower respectively. The circulating liquid in the tail gas absorption tower circulation pump and the tail gas scrubbing tower circulation pump is cooled by circulating water and then returned to the tower from the middle of the tail gas absorption tower and tail gas scrubbing tower respectively. This counter-current gas-liquid contact, combined with double spraying, further enhances the absorption effect.

[0075] Precise control of the bottom liquid level: The bottom liquid of the tail gas absorption tower and the tail gas washing tower are respectively connected to the external regulating valve and the flow meter to form a control loop, so as to precisely control the bottom liquid level.

[0076] To address the issue of excessive exhaust gas emissions: A three-layer emission protection system is implemented for the vented exhaust gas after passing through the exhaust gas absorption tower and the exhaust gas washing tower, completely resolving the problem of excessive emissions. Under normal process conditions, the vented exhaust gas is treated with activated carbon adsorption. Only when the activated carbon adsorption tank needs replacement or is temporarily unusable due to maintenance or repair needs is the system temporarily switched to an incinerator or flare for treatment. This avoids the problems of unstable combustion, non-combustion, or even backfire and explosion caused by prolonged use of incinerators or flares for vented exhaust gas treatment.

[0077] To prevent material cross-contamination and backfire: The three-way process of the exhaust gas venting tower at the top is equipped with shut-off valves, check valves and flame arresters to prevent the risk of material cross-contamination and backfire.

[0078] To ensure stable inlet air pressure for the exhaust fan: The nitrogen supplementation regulating valve and the pressure before the exhaust fan form a control loop to ensure stable inlet air pressure for the exhaust fan. The exhaust fan frequency converter and the exhaust fan outlet pressure form a control loop to ensure stable outlet air pressure for the exhaust fan.

[0079] To ensure stable system pressure: The flare shut-off valve and the system pressure form a control loop. When the system is over-pressured, the shut-off valve will automatically open to relieve pressure and ensure stable system pressure.

[0080] Accurately determining adsorbent replacement time: Activated carbon adsorption tanks are connected in series. The first adsorption tank primarily removes methanol from the vented exhaust gas, while the second adsorption tank primarily removes organic amines and other organic compounds. Shut-off valves are installed before and after each adsorption tank to completely disconnect it from the system. Differential pressure gauges are installed on the inlet and outlet pipelines of the activated carbon adsorption tanks. The pressure difference can be used to qualitatively determine the adsorbent's adsorption saturation. Simultaneously, samples can be periodically taken from the exhaust port for analysis. The analysis results can be used to quantitatively determine the adsorbent's adsorption saturation, thereby deciding the replacement time.

[0081] Timely reminders to switch treatment pathways: An online gas analyzer is installed on the vent gas pipeline at the top of the tail gas washing tower. When the composition of the vent gas exceeds the activated carbon adsorption limit, the control system issues an alarm, reminding the operator to manually disconnect the vent gas from the activated carbon adsorption system and manually switch the vent gas into the incinerator or flare for treatment.

[0082] Finally, it should be noted that the above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A vent gas treatment device for a methylamine production unit, characterized in that: include: Exhaust gas absorption unit, exhaust gas washing unit, and three-stage emission protection unit; The tail gas absorption unit includes a tail gas absorption tower (2), a methanol feed cooler (1) connected to the tail gas absorption tower, a tail gas absorption tower bottom circulation pump (3), and a tail gas absorption tower circulation cooler (4). The tail gas washing unit includes a tail gas washing tower (10), a demineralized water feed cooler (9) connected to the tail gas washing tower, a tail gas washing tower bottom circulation pump (11), and a tail gas washing tower circulation cooler (12). The three-level emission protection unit includes: Main processing pathway: Activated carbon adsorption tank A (23) and activated carbon adsorption tank B (24) connected in sequence; Alternate treatment pathway: exhaust gas fan (33) and incinerator connected in sequence; Emergency response route: connected to the flare system; The inlet ends of the three passages are connected to the top gas phase outlet of the tail gas scrubbing tower (10) via valve groups.

2. The vent gas treatment device for a methylamine production unit according to claim 1, characterized in that: The bottom of the tail gas absorption tower (2) is connected to the venting tail gas inlet of the methylamine device, and the top is connected to the bottom of the tail gas water washing tower (10) through the tail gas absorption tower top condenser (5). The top gas phase outlet of the tail gas washing tower (10) is connected to three passages of the three-stage emission protection unit through a valve group.

3. The vent gas treatment device for a methylamine production unit according to claim 2, characterized in that: The valve assembly includes: The first check valve (21) and the first shut-off valve (22) on the main processing path; The backup processing circuit includes a second check valve (28), a second shut-off valve (29), and a third flame arrester (31); The emergency response path includes a third check valve (18), a third shut-off valve (17), and a first flame arrester (16).

4. The vent gas treatment device for a methylamine production unit according to claim 3, characterized in that: The activated carbon adsorption tank A (23) and activated carbon adsorption tank B (24) are connected in series, wherein: Activated carbon adsorption tank A(23) is used to remove methanol; Activated carbon adsorption tank B(24) is used to remove organic amines; Differential pressure gauges (27) and shut-off valves (22, 25) are installed on the inlet and outlet pipelines of both adsorption tanks.

5. The vent gas treatment device for a methylamine production unit according to claim 4, characterized in that: The exhaust gas fan (33) is equipped with a nitrogen replenishment regulating valve (32) and a second pressure transmitter (30) at its inlet, and an exhaust gas fan frequency converter (34), a third pressure transmitter (35) and an exhaust gas flow meter (36) at its outlet. The nitrogen supplementation regulating valve (32) and the second pressure transmitter (30) constitute a closed-loop control of the fan inlet pressure; The exhaust gas fan frequency converter (34) and the third pressure transmitter (35) constitute a closed-loop control of the fan outlet pressure.

6. The vent gas treatment device for a methylamine production unit according to claim 5, characterized in that: An online gas analyzer (20) is installed on the top gas phase outlet pipeline of the tail gas washing tower (10) to monitor the tail gas composition in real time and control the switching of the valve group.

7. The vent gas treatment device for a methylamine production unit according to claim 6, characterized in that: The emergency response path is equipped with a first pressure transmitter (19), which together with the third shut-off valve (17) forms an overpressure relief control loop.

8. The vent gas treatment device for a methylamine production unit according to claim 7, characterized in that: The bottoms of the tail gas absorption tower (2) and the tail gas washing tower (10) are connected to flow meters (7,14) and flow control valves (6,13) respectively through external pipelines to form a closed-loop control of liquid level.

Images