A VOCs exhaust gas treatment system

Abstract

This utility model discloses a VOCs waste gas treatment system, comprising a gas buffer tank, an alkaline absorption tower, a primary reaction absorption tower, a secondary reaction absorption tower, a clean water scrubbing tower, a waste gas exhaust fan, a venting stack, a waste gas discharge pipe, and a waste gas return pipe. One exhaust fan is connected to the bottom of the venting stack via the waste gas discharge pipe, and the other is connected to the waste gas discharge pipe at the inlet end of the alkaline absorption tower via the waste gas return pipe. Compared with existing technologies, this utility model designs the treatment system specifically for the purification process of pharmaceutical-grade amino acids, solving the problem of excessive VOCs content in waste gas. The process innovatively employs wet chemical advanced oxidation, enabling the removal of organic gas components from the gas phase and allowing for the recycling of the activated carbon reaction bed. Furthermore, through automated control technology, it ensures that the system's exhaust gas always meets emission standards.

Description

Technical Field

[0001] This utility model relates to the field of waste gas treatment, and in particular to a VOCs waste gas treatment system. Background Technology

[0002] Currently, in the production process of purifying crude amino acids to raw material-grade refined amino acids, especially to pharmaceutical-grade refined amino acids, a large amount of organic solvents must be used for dissolution and separation. Because most organic solvents have low flash points and easily vaporize into gases, they become harmful VOCs in the waste gas. The waste gas must be treated to meet standards before being discharged. To ensure that the waste gas emissions meet standards, networked online monitoring systems are installed at the emission points to detect whether emissions exceed the standards. However, in the production process of pharmaceutical-grade refined amino acids, the waste gas generated lacks specific analytical data, making it difficult to determine the exact VOC content. Therefore, only qualitative treatment can be performed during production. Our company's current treatment process involves spraying the waste gas, then treating it through a two-stage Fenton + UV light oxidation process, followed by alkaline spraying before discharge through an exhaust stack. However, the treatment effect is still unsatisfactory; even with monitoring by the networked online monitoring system on the exhaust stack, excessive emissions are still observed. The main reason is that the required residence time for waste gas oxidation is insufficient, resulting in unsatisfactory oxidation treatment. The spraying effect is also poor, with a small contact area between the sprayed oxidant and the waste gas, leading to the inability of the discharged waste gas to consistently and stably meet emission standards. Therefore, a treatment process and equipment that can solve the above problems is urgently needed.

[0003] Existing VOCs treatment methods are limited in form and difficult to apply directly to amino acid purification production, with limited treatment effects. The main methods for treating waste gas include combustion, spraying + UV photolysis, and activated adsorption. Combustion, a special form of oxidation, is the best way to eliminate all organic matter, completely oxidizing it into carbon dioxide and water (incomplete combustion produces carbon monoxide and water, and in the presence of chlorine, it produces dioxins, a class of carcinogens). Catalytic combustion, also known as low-temperature combustion, oxidizes organic waste gas into carbon dioxide and water at lower temperatures in the presence of a catalyst. Combustion requires high temperatures, and due to the presence of open flames, regulations require sufficient fire safety distances from adjacent buildings. Furthermore, both combustion and catalytic combustion consume large amounts of energy (gas or electricity) to provide the high temperatures. Although catalytic combustion operates at lower temperatures, its applicability is limited by the susceptibility to catalyst poisoning, and its effects are generally unsatisfactory. Its spraying + UV photolysis process has a certain effect on oxidizing and decomposing VOCs in waste gas, but the treatment effect is poor and its practicality in actual production is not strong. Its activated adsorption method uses an adsorption system such as activated carbon to greatly reduce the VOC concentration and achieve the emission standard of waste gas. It is suitable for quantitative waste gas treatment. The adsorption capacity of activated carbon is about 2 days. After its surface is full, it can no longer adsorb VOCs waste gas. It is necessary to remove the activated carbon and regenerate it for reuse. It cannot achieve continuous production of enterprises. Moreover, the residence time of VOCs waste gas on the surface of activated carbon is very short. The waste gas can pass through the activated carbon adsorption bed in a few seconds. It is difficult to control its adsorption time. Often, the waste gas is emitted before it is fully adsorbed, resulting in the waste gas emission exceeding the standard. Furthermore, due to the large fluctuation of VOCs content in waste gas during the production process, we cannot know the adsorption status of activated carbon, and the replacement cycle of activated carbon is also difficult to control. Utility Model Content

[0004] The purpose of this invention is to provide a VOCs waste gas treatment system that solves the above-mentioned problems.

[0005] To achieve the above objectives, the technical solution adopted by this utility model is: a VOCs waste gas treatment system, comprising a waste gas treatment system including a gas buffer tank, an alkaline absorption tower, a primary reaction absorption tower, a secondary reaction absorption tower, a clean water scrubbing tower, a waste gas exhaust fan, a venting exhaust stack, a waste gas discharge pipe, and a waste gas return pipe. The gas buffer tank, alkaline absorption tower, primary reaction absorption tower, secondary reaction absorption tower, clean water scrubbing tower, and waste gas exhaust fan are sequentially connected through the waste gas discharge pipe. The outlet of the waste gas exhaust fan is equipped with a three-way control regulating valve. The waste gas exhaust fan is divided into two paths through the three-way control regulating valve: one path is connected to the bottom of the venting exhaust stack through the waste gas discharge pipe, and the other path is connected to the waste gas discharge pipe at the inlet end of the alkaline absorption tower through the waste gas return pipe.

[0006] The alkaline absorption tower is equipped with a secondary packing support plate. The packing support plate of the alkaline absorption tower is covered with packing and filter media. A spray device is provided above the filter media. Both the primary and secondary reaction absorption towers are equipped with secondary packing support plates. The packing support plates of the primary and secondary reaction absorption towers are covered with packing and activated carbon. A spray device is provided above the activated carbon. The upper part of the clear water washing tower is equipped with a UV ultraviolet light irradiation catalytic conversion bed. The lower part of the clear water washing tower is equipped with a packing support plate. The packing support plate of the clear water washing tower is covered with packing and filter media. A spray device is provided above the filter media.

[0007] Preferably, the spraying device adopts a mesh-type spray pipe, which is disc-shaped and consists of a main water inlet pipe, spray branch pipes, and an outer ring pipe. Both ends of the main water inlet pipe are water inlets. There are several spray branch pipes, each of which is perpendicular to the main water inlet pipe and welded between the main water inlet pipe and the outer ring pipe. The spray branch pipes are internally connected to the main water inlet pipe. Spray nozzles are evenly spaced at the bottom of the main water inlet pipe and the spray branch pipes.

[0008] Preferably, the gas buffer tank is connected to the lower part of the alkali absorption tower via an exhaust gas discharge pipe, the top of the alkali absorption tower is connected to the lower part of the primary reaction absorption tower via an exhaust gas discharge pipe, the top of the primary reaction absorption tower is connected to the lower part of the secondary reaction absorption tower via an exhaust gas discharge pipe, the top of the secondary reaction absorption tower is connected to the top of the clean water scrubbing tower via an exhaust gas discharge pipe, and the lower part of the clean water scrubbing tower is connected to the exhaust gas induced draft fan outlet via an exhaust gas discharge pipe.

[0009] Preferably, each of the alkali absorption towers is equipped with an alkali spray pump at its bottom, which is connected to a spray device inside the alkali absorption tower. The bottom of the alkali absorption tower is connected to a sewage tank via a sewage drain pipe. Both the primary and secondary reaction absorption towers are equipped with reaction spray pumps at their bottoms, which are connected to corresponding spray devices inside the primary and secondary reaction absorption towers. The reaction spray pumps are connected to the bottom of the primary and secondary reaction absorption towers via sewage drain pipes to the sewage tank. The clean water washing tower is equipped with a washing spray pump at its bottom, which is connected to a spray device inside the clean water washing tower. The bottom of the clean water washing tower is connected to a sewage tank via a sewage drain pipe.

[0010] Preferably, the gas buffer tank is connected to the waste gas collection pipeline of the amino acid purification production line, and an emergency pressure relief valve is provided on the top of the gas buffer tank.

[0011] Preferably, the top of the water washing tower is equipped with an oxygen inlet pipe.

[0012] Preferably, both the primary and secondary reaction absorption towers employ two-stage spherical activated carbon adsorption, wherein the spherical activated carbon has a particle diameter of 10 mm and a thickness of 1500 mm, and the spray liquid sprayed by the reaction spray pump is a solution containing an oxidant.

[0013] Compared with the prior art, the advantages of this utility model are:

[0014] (1) This utility model analyzes 17 organic gas components in the VOCs in the waste gas during the purification of pharmaceutical-grade amino acids and designs a targeted treatment system. A gas buffer tank is used to reduce the concentration and compositional differences in the waste gas, mitigating the impact on subsequent waste gas treatment systems and homogenizing the waste gas. An alkaline absorption tower is used to wash the waste gas with hot alkali to remove ethanol, acetic acid, methanol, tetrahydrofuran, pyridine, acetone, ethyl formate, ethyl acetate, tert-butyl ester, dichloroethane, and chloroacetyl. A primary and secondary reaction absorption tower are used to treat petroleum ether, 1,4-dioxane, N,N-dimethylformamide, dichloromethane, and toluene using wet advanced oxidation. A water washing tower is used to eliminate any remaining trace organic gas molecules in the waste gas, thus solving the problem of excessive VOCs content in the waste gas during the purification of pharmaceutical-grade amino acids.

[0015] (2) The process of this utility model innovatively adopts wet chemical advanced oxidation to convert organic matter into carbon dioxide and water. In order to ensure the reaction time of this chemical reaction, the structure of the reaction absorption tower is designed. The waste gas is in contact with the activated carbon reaction bed through a spray device, so that the waste gas is in contact with the activated carbon for a long time, and the organic gas is adsorbed on the surface of the activated carbon. The VOCs gas adsorbed on the surface of the activated carbon and the chemical oxidant deposited on the surface of the activated carbon undergo gas-liquid contact reaction, oxidizing the organic gas molecules into water-soluble dehydrogenated and oxygenated oxidized molecules or fully oxidized carbon dioxide and water molecules. In this way, the organic gas components are eliminated from the gas phase and enter the water to become COD or carbon dioxide and water in the water.

[0016] (3) By designing the structure of the spray device, multiple sprays are carried out to achieve gas-liquid contact and increase the time for waste gas to pass through the reaction bed, thereby improving the reaction effect. Since the adsorption capacity of activated carbon can reach about two days, which is greater than the reaction time of VOCs gas and oxidant, the activated carbon reaction bed can be recycled through the continuous adsorption of activated carbon, the continuous oxidation and decomposition of VOCs gas, and the continuous spraying and rinsing effect of the spray device.

[0017] (4) This utility model adopts automatic control technology. Based on the changes in VOCs content in the exhaust gas monitored by the online monitoring system, the three-way control regulating valve is switched on and off to realize the pipeline conversion between the exhaust gas return pipe and the exhaust gas discharge pipe on the closed venting exhaust stack. This allows the system to adjust the exhaust gas discharge volume according to the actual production conditions. When the VOCs content gradually increases, the external discharge volume is gradually closed. Before reaching the standard emission level, the external discharge is closed in advance to ensure that the exhaust gas discharged by the system is always in compliance with the emission standards. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the system structure of this utility model;

[0019] Figure 2 This is a schematic diagram of the principle structure of the spraying device of this utility model;

[0020] Figure 3 This is a schematic diagram of the spray surface of the spray head of the spray device of this utility model.

[0021] In the diagram: 1. Gas buffer tank; 2. Alkali absorption tower; 3. Primary reaction absorption tower; 4. Secondary reaction absorption tower; 5. Clean water scrubbing tower; 6. Exhaust gas exhaust fan; 7. Vent stack; 8. Three-way control valve; 9. Exhaust gas discharge pipe; 10. Exhaust gas return pipe; 11. Oxygen inlet pipe; 12. Spray device; 121. Main water inlet pipe; 122. Spray branch pipe; 123. Outer ring pipe; 124. Spray head; 13. Filter media; 14. Activated carbon; 15. UV irradiated catalytic conversion bed; 16. Alkali spray pump; 17. Reaction spray pump; 18. Scrubbing spray pump. Detailed Implementation

[0022] The present invention will be further described below. Through testing of the harmful gas components in the waste gas during the amino acid purification process, the approximate organic components of VOCs in the waste gas are: 1. Ethanol; 2. Acetic acid; 3. Methanol; 4. Ethyl formate; 5. Ethyl acetate; 6. Tert-butyl ester; 7. Triethylamine; 8. Petroleum ether; 9. 1,4-Dioxane; 10. N,N-Dimethylformamide; 11. Tetrahydrofuran; 12. Dichloromethane; 13. Dichloroethane; 14. Chloroacetyl; 15. Pyridine; 16. Acetone; 17. Toluene. These are 17 organic gas components. Among them, 6 organic gas components are readily soluble in water: ethanol, acetic acid, methanol, tetrahydrofuran, pyridine, and acetone. Tetrahydrofuran has the lowest solubility in water, with a saturated solubility of 15 g / 100 mL at 25°C. Five other organic gaseous components readily undergo hydrolysis with water: ethyl formate, ethyl acetate, tert-butyl formate, dichloroethane, and chloroacetyl. Heating accelerates their hydrolysis, and the hydrolysis products generate corresponding acids that react with sodium hydroxide to form their sodium salts, further accelerating the hydrolysis. One more organic gaseous component dissolves in dilute sulfuric acid and reacts with it to form organic salts: triethylamine. This triethylamine reacts with sulfuric acid to form triethanolamine sulfate and triethanolamine hydrogen sulfate, both of which are soluble in water, and the resulting solution is acidic. Finally, the remaining five organic gaseous components are relatively inert and difficult to remove from the gas phase through simple water washing or hydrolysis: petroleum ether; 1,4-dioxane; N,N-dimethylformamide; dichloromethane; and toluene. These components share the characteristic that unsaturated hydrocarbons and cycloalkanes can be oxidized by strong oxidants and removed from the gas phase.

[0023] Due to the company's product manufacturing process, organic waste gas originates from multiple exhaust points across three workshops. To minimize the impact of differences in waste gas concentration and composition on the subsequent waste gas treatment system, the waste gas should be homogenized and buffered. Based on the different properties of the waste gas components and adhering to the principles of ease of control and economic rationality, a process design proceeding from easy to difficult removal is adopted, as detailed below:

[0024] A VOCs exhaust gas treatment system, see Figure 1The invention includes a waste gas treatment system comprising a gas buffer tank 1, an alkaline absorption tower 2, a primary reaction absorption tower 3, a secondary reaction absorption tower 4, a clean water scrubbing tower 5, a waste gas exhaust fan 6, a venting exhaust stack 7, a waste gas discharge pipe 9, and a waste gas return pipe 10. The gas buffer tank 1, alkaline absorption tower 2, primary reaction absorption tower 3, secondary reaction absorption tower 4, clean water scrubbing tower 5, and waste gas exhaust fan 6 are sequentially connected via the waste gas discharge pipe 9. The exhaust fan 6 has a three-way control valve 8 at its outlet, which divides the exhaust fan 6 into two paths: one path connects to the bottom of the venting exhaust stack via the waste gas discharge pipe 9, and the other path connects to the inlet of the alkaline absorption tower 2 and the exhaust gas discharge pipe 9 via the waste gas return pipe 10. This invention reduces the concentration and compositional differences of waste gas through the gas buffer tank 1, thereby mitigating the impact on the subsequent waste gas treatment system and homogenizing and buffering the waste gas. The waste gas contains 11 organic gas components, including ethanol, acetic acid, methanol, tetrahydrofuran, pyridine, acetone, ethyl formate, ethyl acetate, tert-butyl ester, dichloroethane, and chloroacetyl, which are washed by hot alkali in alkaline absorption tower 2. The waste gas is treated with wet advanced oxidation using primary reaction absorption tower 3 and secondary reaction absorption tower 4 to remove five organic gas components: petroleum ether, 1,4-dioxane, N,N-dimethylformamide, dichloromethane, and toluene, as well as triethanolamine. A water scrubbing tower 5 removes any remaining trace organic gas molecules. The waste gas emission rate and the waste gas return pipe 10 are controlled via a three-way control valve 8, based on changes in the organic gas content in the venting stack 7 monitored by an online monitoring system. Before the VOCs content in the waste gas exceeds the standard, the waste gas return pipe 10 is opened, and the system enters self-circulation mode, stopping external emissions. Once the standard is met, the waste gas return pipe 10 is closed, ensuring that emissions do not exceed the standard.

[0025] To ensure sufficient reaction time for VOC-containing waste gas within the alkaline absorption tower 2, primary reaction absorption tower 3, secondary reaction absorption tower 4, and clean water scrubbing tower 5, structural designs were implemented for these components. The alkaline absorption tower 2 is equipped with a secondary packing support plate, facilitating the construction of two layers of filter media reaction beds for two alkaline reactions, thus improving VOC gas recovery. The packing support plate is covered with packing material and filter media 13. The packing material facilitates the installation of the filter media 13 and prevents leakage. A spray device 1 is installed above the filter media 13. 2. When the waste gas enters from the alkaline absorption tower 2, it enters the filter media reaction bed from the bottom of the packing. The gaps between the filter media 13 and the alkaline solution between the gaps can reduce the flow time of the waste gas and increase the reaction time of hydrolysis and dissolution in dilute sodium hydroxide solution. The pores on the surface of the filter media 13 facilitate the adhesion of gas and sodium hydroxide solution, improving the hydrolysis and dissolution effect of ethanol, acetic acid, methanol, tetrahydrofuran, pyridine, acetone, ethyl formate, ethyl acetate, tert-butyl ester, dichloroethane, and chloroacetyl. The waste gas exiting the filter media 13 will also have gas-liquid contact with the alkaline solution sprayed by the spraying device 12. The recovered VOCs fall back into the filter media reaction bed with the sprayed alkaline solution.

[0026] Both the primary reaction absorption tower 3 and the secondary reaction absorption tower 4 are equipped with secondary packing support plates, forming a four-layer activated carbon reaction bed. This increases the adsorption time and number of times the activated carbon 14 adsorbs. The packing support plates are covered with packing material and activated carbon 14. The packing material prevents the activated carbon 14 from leaking out of the packing support plates. The activated carbon 14 can adsorb petroleum ether, 1,4-dioxane, N,N-dimethylformamide, dichloromethane, and toluene in the waste gas onto its surface. Since the oxidation reaction of the above-mentioned VOCs gases requires a long time, the contact time between the VOCs gases and the oxidant is extended by the adsorption properties of the activated carbon 14, which adsorbs the VOCs gases onto its surface. A spray device 12 is installed above the activated carbon 14. When the spray device 12 is turned on, the oxidant spray liquid is sprayed. During spraying, the spray liquid is simply applied to wet the activated carbon reaction bed. The spray liquid is applied from above the activated carbon, slowly flowing through the bed from top to bottom, and finally dripping from the bottom, creating a slow-flowing process. This process carries away the decomposed VOCs from the activated carbon reaction bed. Simultaneously, the wetted activated carbon reaction bed has reduced porosity, extending the time it takes for VOCs to pass through. When VOCs are adsorbed onto the surface of activated carbon 14, they undergo an oxidation reaction with the oxidant-containing spray, decomposing into COD or carbon dioxide and water, and then detaching from the surface of activated carbon 14. At this point, the surface of activated carbon 14 can begin adsorbing new VOCs. Since the adsorption capacity of activated carbon 14 can reach approximately two days, exceeding the reaction time between VOCs and the oxidant, the activated carbon reaction bed can be recycled through continuous adsorption by activated carbon 14, continuous oxidation and decomposition of VOCs, and the spraying flow of the spray device 12.

[0027] The upper part of the water scrubbing tower 5 is equipped with a UV irradiation catalytic conversion bed 15 layers. The UV irradiation catalytic conversion bed consists of four packing layers and three UV lamps, with a 200mm gap between each packing layer. The three UV lamps are located in the gaps between the packing layers, forming the UV irradiation catalytic conversion bed 15 layers. The waste gas, together with the oxygen introduced by the oxygen inlet pipe 11, is converted into active organic ions and oxygen atoms under the action of ultraviolet light. The lower part of the water scrubbing tower 5 is equipped with a packing support plate, on which packing and filter media 13 are laid. A spray device 12 is provided above the filter media 13. The filter media 13 bed and the UV irradiation catalytic conversion bed 15 layers in the water scrubbing tower 5 further absorb VOCs in the exhaust gas, further reducing the VOCs content in the waste gas.

[0028] To further improve the spraying effect and ensure that the exhaust gas is fully sprayed, multiple spraying devices 12 were designed within the system, and the structural design of the spraying devices 12 was carried out. (See attached document.) Figure 2The spraying device 12 adopts a mesh-type spray pipe, which is disc-shaped and consists of a main water inlet pipe 121, spray branch pipes 122, and an outer ring pipe 123. The diameter of the outer ring pipe 123 is the same as the diameter of the tower body and can be fixed to the inner wall of the tower body. Both ends of the main water inlet pipe 121 are water inlets, and water enters from both ends simultaneously, so that the water pressure at both ends of the spraying device 12 is balanced, making the spray from each nozzle 124 more uniform. Water entering from one end can easily cause the spray to be far from the water inlet end. In cases where the water pressure at head 124 is insufficient and the spray surface is uneven, several spray branch pipes 122 are provided. Each spray branch pipe 122 is perpendicular to the main water inlet pipe 121 and welded between the main water inlet pipe 121 and the outer annular pipe 123. The spray branch pipes 122 are internally connected to the main water inlet pipe 121. Spray nozzles 124 are evenly spaced at the bottom of the main water inlet pipe 121 and the spray branch pipes 122. When the spray nozzles 124 spray, the spray pattern below the spray device 12 is mesh-like. (See [reference]). Figure 3 The spraying device 12 achieves uniform spraying over a large area, and there are no gaps between the spraying ranges of each spray head, which can effectively improve the spraying effect.

[0029] The gas buffer tank 1 is connected to the lower part of the alkaline absorption tower 2 through the exhaust pipe 9. The top of the alkaline absorption tower 2 is connected to the lower part of the primary reaction absorption tower 3 through the exhaust pipe 9. The top of the primary reaction absorption tower 3 is connected to the lower part of the secondary reaction absorption tower 4 through the exhaust pipe 9. The alkaline absorption tower 2, the primary reaction absorption tower 3, and the secondary reaction absorption tower 4 adopt a bottom-inlet method, with exhaust gas entering from the bottom of the tower and exiting from the top. Since the cleaning and washing tower needs to be oxygenated for UV photolysis, it adopts a top-inlet and bottom-outlet method. The top of the secondary reaction absorption tower 4 is connected to the top of the clean water washing tower 5 through the exhaust pipe 9. The lower part of the clean water washing tower 5 is connected to the exhaust port of the exhaust fan 6 through the exhaust pipe 9.

[0030] Each of the alkaline absorption towers 2 is equipped with an alkaline spray pump 16 at its bottom. The alkaline spray pump 16 is connected to the spray device 12 inside the alkaline absorption tower 2. The alkaline spray pump 16 pumps spray water containing added alkaline solution into the spray device 12 of the alkaline absorption tower 2. The bottom of the alkaline absorption tower 2 is connected to a sewage tank through a sewage drain pipe. Each of the primary reaction absorption tower 3 and the secondary reaction absorption tower 4 is equipped with a reaction spray pump 17 at its bottom. The reaction spray pump 17 is connected to the corresponding spray device 12 inside the primary reaction absorption tower 3 and the secondary reaction absorption tower 4. The reaction spray pump 17 pumps spray water containing added oxidant. The spray water is pumped into the spray device 12 of the primary reaction absorption tower 3 and the secondary reaction absorption tower 4. The reaction spray pump 17 is connected to the bottom of the primary reaction absorption tower 3 and the secondary reaction absorption tower 4 through a sewage drain pipe and is connected to the sewage tank. The bottom of the clean water washing tower 5 is equipped with a washing spray pump 18, which is connected to the spray device 12 in the clean water washing tower 5. The washing spray pump 18 pumps the spray water into the spray device 12 of the clean water washing tower 5. The bottom of the clean water washing tower 5 is connected to the sewage tank through a sewage drain pipe. The sewage at the bottom of each tower is discharged into the sewage tank through the sewage drain pipe for sewage treatment.

[0031] The gas buffer tank 1 is connected to the waste gas collection pipeline of the amino acid purification production line. The top of the gas buffer tank 1 is equipped with an emergency pressure relief valve for safe pressure relief. The top of the water washing tower 5 is equipped with an oxygen inlet pipe 11 to supplement the oxygen required during the UV photolysis process.

[0032] A VOCs waste gas treatment process, the process is as follows:

[0033] a. During the preparation stage of the exhaust gas treatment system, the inlet of the gas buffer tank 1 is closed, the exhaust gas treatment system is started, the exhaust of the venting exhaust stack 7 is closed through the three-way control regulating valve 8, and the exhaust gas return pipe 10 is opened to carry out internal self-circulation of the system through the exhaust gas return pipe 10.

[0034] b. In the alkaline absorption stage, after the waste gas treatment system meets the waste gas treatment conditions, the waste gas collection pipe is opened, the exhaust of the venting exhaust stack 7 is opened, and the waste gas return pipe 10 is closed. The waste gas enters the alkaline absorption tower 2 from the gas buffer tank 1. For the 6 kinds of organic waste gas components that are easily soluble in water and the 5 kinds of organic gas components that are easily hydrolyzed and whose hydrolysis products are soluble in dilute sodium hydroxide solution, dilute sodium hydroxide alkaline solution is used for washing. In order to accelerate the hydrolysis and washing dissolution rate, the alkaline solution is heated. The 11 kinds of organic gas components in the waste gas, namely ethanol, acetic acid, methanol, tetrahydrofuran, pyridine, acetone, ethyl formate, ethyl acetate, tert-butyl ester, dichloroethane, and chloroacetyl, are absorbed by the hot sodium hydroxide alkaline solution. The above organic gas components enter the liquid phase from the gas phase and become the COD components in the wastewater, while most of the organic gases are removed from the gas phase.

[0035] After removing easily water-soluble and hydrolyzable organic gas components, there is still one organic waste gas component called triethanolamine. Based on its chemical properties, it belongs to the organic amine category and is a standard alkaline organic compound. It readily reacts with inorganic acid salts, nitric acid, and sulfuric acid to form water-soluble organic ammonium salts, which are easily removed by water. Simultaneously, the inorganic acid salts of organic amines readily hydrolyze to form organic bases and corresponding acids. However, considering that triethanolamine accounts for only one-seventeenth of the total, and taking into account factors such as investment and operating costs, a dilute sulfuric acid washing and absorption process is omitted. Instead, triethanolamine, along with the last five organic gas components—petroleum ether, 1,4-dioxane, N,N-dimethylformamide, dichloromethane, and toluene—are directly fed into a wet advanced oxidation removal process for oxidation treatment.

[0036] c. In the wet chemical advanced oxidation stage, the waste gas after alkaline washing sequentially enters the primary reaction absorption tower 3 and the secondary reaction absorption tower 4. Activated carbon is used to adsorb organic gases on the surface of the activated carbon. With the help of the reaction spray pump 17 and the spray device 12, the organic gases stay on the surface of the activated carbon for a long time. The gas adsorbed on the surface of the activated carbon undergoes a gas-liquid contact reaction with the chemical oxidant deposited on the surface of the activated carbon. The organic gas molecules are oxidized into water-soluble dehydrogenated and oxygenated oxidized molecules or completely oxidized carbon dioxide and water molecules. The organic gases are then eliminated from the gas phase and enter the water as COD or carbon dioxide and water in the water.

[0037] This process innovatively employs wet chemical advanced oxidation. While there are very few successful cases of wet oxidation in the field of waste gas treatment, it is relatively common in wastewater treatment, as it can oxidize COD in wastewater into carbon dioxide and water. According to the mechanism of organic oxidation-reduction, dehydrogenation and oxygenation are both oxidation reactions, while deoxygenation and hydrogenation are both reduction reactions. The complete conversion of organic matter into carbon dioxide and water is considered complete oxidation. Except for combustion, the time required for complete oxidation of organic matter is usually quite long, often lasting several hours or even one or two days. Therefore, the time required for incomplete oxidation is greatly shortened, ranging from a few minutes to several hours. In order to ensure the reaction time of this chemical reaction, this invention designs the structure inside the reaction absorption tower. By using a spray device 12 in conjunction with an activated carbon reaction bed, the time for organic gas to pass through the activated carbon reaction bed can be increased. The organic gas has sufficient time to be adsorbed on the surface of the activated carbon for oxidation. The VOCs gas adsorbed on the surface of the activated carbon undergoes a gas-liquid contact reaction with the chemical oxidant deposited on the surface of the activated carbon, oxidizing the organic gas molecules into water-soluble dehydrogenated and oxygenated oxidized molecules or completely oxidized carbon dioxide and water molecules. In this way, the organic gas components are eliminated from the gas phase and enter the water as COD or carbon dioxide and water in the water.

[0038] In step c, both the primary reaction absorption tower 3 and the secondary reaction absorption tower 4 employ two-stage spherical activated carbon 14 for adsorption. The spherical activated carbon 14 has a large contact area, making it easy to adsorb. The spherical activated carbon 14 has a particle diameter of 10 mm and a thickness of 1500 mm, which can effectively absorb VOCs gas. The spray liquid sprayed by the reaction spray pump 17 is a solution containing an oxidant. During the liquid supply process of the alkaline spray pump 16, the reaction spray pump 17, and the washing spray pump 18, a catalyst that promotes the reaction can also be added. The catalyst can be adsorbed on the filter material 13 and the activated carbon 14 to accelerate the reaction.

[0039] d. In the water washing stage, after the organic waste gas VOCs in the exhaust gas are dissolved in water, hydrolyzed and wet chemical advanced oxidation, there may still be a very small amount of organic gas molecules that have not been eliminated. The exhaust gas after reaction absorption enters the upper part of the water washing tower 5 and enters the catalytic conversion bed irradiated by ultraviolet light together with oxygen. Under the action of ultraviolet light, it is transformed into active organic ions and oxygen atoms, and then undergoes an oxidation reaction with the filter material 13 with catalyst in the lower part of the water washing tower 5 to generate water-soluble oxidized organic molecules or carbon dioxide and water, which are further removed.

[0040] e. In the quantitative emission control stage, monitoring data from the online monitoring system is collected. Based on the changes in VOCs content in the emitted exhaust gas, the three-way control valve 8 is controlled automatically to switch between the exhaust gas return pipe 10 and the exhaust gas discharge pipe 9 on the closed venting stack 7. Finally, the organic gas component content in the exhaust gas is tested and, if it meets the VOCs emission requirements, it is discharged in compliance with standards. The three-way control valve 8 is the connecting control valve between the exhaust gas return pipe 10 and the exhaust gas discharge pipe between the exhaust gas fan 6 and the venting stack 7. When the exhaust gas return pipe 10 is fully open, the exhaust gas discharge pipe is fully closed; conversely, when the exhaust gas discharge pipe is fully open, the exhaust gas return pipe 10 is fully closed. Its control principle is as follows: Before the exhaust gas induced draft fan 6 starts, the exhaust gas return pipe 10 is in a fully open state, and the exhaust gas exhaust pipe at the front end of the venting exhaust stack 7 is in a fully closed state. After the exhaust gas induced draft fan 6 starts, the exhaust gas return pipe 10 gradually closes at a uniform speed. When the time after the induced draft fan starts reaches 5 minutes, the exhaust gas return pipe 10 reaches a fully closed state. At this time, the exhaust gas exhaust pipe at the front end of the exhaust stack is in a fully open state. The exhaust pipe being in a fully open state is a necessary condition for the centrifuge, filter press, and vacuum pump motor in the production workshop to start receiving power. After receiving power at the production workshop, the control of the three-way control regulating valve 8 begins to be controlled by the signal from the gas online detector in the venting exhaust stack 7.

[0041] The specific control method is as follows: A specified value is set based on the national exhaust emission standards. For example, the specified value is set to 50%-95% of the VOCs content in the national exhaust emission standards. When the online detection signal at the top of the venting stack 7 does not reach the specified value of 50%, the exhaust pipe at the front end of the stack is fully open. When the online detection signal at the top of the venting stack 7 reaches the specified value of 50%, and is gradually increasing, the exhaust pipe at the front end of the venting stack 7 begins to gradually close, and the exhaust return pipe 10 gradually opens. Before the detection data reaches the specified value of 95%, the exhaust pipe at the front end of the venting stack 7 goes from closed to fully closed, and the return pipe opens to fully open. Before the VOCs content in the exhaust gas exceeds the standard, external emissions are stopped, thus ensuring that emissions do not exceed the standard. Interlocking control can also be used to cut off the power supply to the centrifuge, filter press, and vacuum pump to prevent continuous exhaust gas generation. The system is restarted only after the VOCs content in the system decreases to meet the requirements. If the detection signal is within the range of 50% to 95%, the three-way control regulating valve 8 gradually closes the exhaust pipe at the front end of the vent exhaust stack 7 and opens the exhaust return pipe 10 by the same amount as the specified value increases; as the detected specified value decreases, the exhaust return pipe 10 gradually closes and the return pipe gradually closes, while the exhaust pipe at the front end of the vent exhaust stack 7 is opened by the same amount. In this way, the exhaust emission can be adjusted according to the actual production conditions.

[0042] The above provides a detailed description of the VOCs waste gas treatment system provided by this utility model. Specific examples have been used to illustrate the principle and implementation of this utility model. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​this utility model. At the same time, for those skilled in the art, based on the idea of ​​this utility model, there will be changes in the specific implementation and application scope. Changes and improvements to this utility model are possible without exceeding the concept and scope specified in the appended claims. Therefore, the content of this specification should not be construed as a limitation of this utility model.

Claims

1. A VOCs waste gas treatment system, comprising a waste gas treatment system, characterized in that: The waste gas treatment system includes a gas buffer tank, an alkaline absorption tower, a primary reaction absorption tower, a secondary reaction absorption tower, a clean water scrubbing tower, a waste gas exhaust fan, a venting stack, a waste gas discharge pipe, and a waste gas return pipe. The gas buffer tank, alkaline absorption tower, primary reaction absorption tower, secondary reaction absorption tower, clean water scrubbing tower, and waste gas exhaust fan are sequentially connected via the waste gas discharge pipe. The exhaust fan's outlet is equipped with a three-way control valve, which divides the exhaust fan into two paths: one path connects to the bottom of the venting stack via the waste gas discharge pipe, and the other path connects to the waste gas discharge pipe at the inlet end of the alkaline absorption tower via the waste gas return pipe. The alkaline absorption tower is equipped with a secondary packing support plate. The packing support plate of the alkaline absorption tower is covered with packing and filter media. A spray device is provided above the filter media. Both the primary and secondary reaction absorption towers are equipped with secondary packing support plates. The packing support plates of the primary and secondary reaction absorption towers are covered with packing and activated carbon. A spray device is provided above the activated carbon. The upper part of the clear water washing tower is equipped with a UV ultraviolet light irradiation catalytic conversion bed. The lower part of the clear water washing tower is equipped with a packing support plate. The packing support plate of the clear water washing tower is covered with packing and filter media. A spray device is provided above the filter media.

2. The VOCs waste gas treatment system according to claim 1, characterized in that: The spraying device uses a mesh-type spray pipe, which is disc-shaped and consists of a main water inlet pipe, spray branch pipes, and an outer ring pipe. Both ends of the main water inlet pipe are water inlets. There are several spray branch pipes, all of which are perpendicular to the main water inlet pipe and welded between the main water inlet pipe and the outer ring pipe. The spray branch pipes are internally connected to the main water inlet pipe. Spray nozzles are evenly spaced at the bottom of the main water inlet pipe and the spray branch pipes.

3. The VOCs waste gas treatment system according to claim 2, characterized in that: The gas buffer tank is connected to the lower part of the alkali absorption tower via an exhaust gas discharge pipe. The top of the alkali absorption tower is connected to the lower part of the primary reaction absorption tower via an exhaust gas discharge pipe. The top of the primary reaction absorption tower is connected to the lower part of the secondary reaction absorption tower via an exhaust gas discharge pipe. The top of the secondary reaction absorption tower is connected to the top of the clean water scrubbing tower via an exhaust gas discharge pipe. The lower part of the clean water scrubbing tower is connected to the exhaust gas induced draft fan outlet via an exhaust gas discharge pipe.

4. The VOCs waste gas treatment system according to claim 1, characterized in that: Each of the alkaline absorption towers is equipped with an alkaline spray pump at its bottom, which is connected to the spraying device inside the alkaline absorption tower. The bottom of the alkaline absorption tower is connected to a sewage tank via a sewage drain pipe. Both the primary and secondary reaction absorption towers are equipped with reaction spray pumps at their bottoms, which are connected to the corresponding spraying devices inside the primary and secondary reaction absorption towers. The reaction spray pumps are connected to the bottom of the primary and secondary reaction absorption towers via sewage drain pipes to the sewage tank. The clean water washing tower is equipped with a washing spray pump at its bottom, which is connected to the spraying device inside the clean water washing tower. The bottom of the clean water washing tower is connected to a sewage tank via a sewage drain pipe.

5. A VOCs waste gas treatment system according to claim 1, characterized in that: The gas buffer tank is connected to the exhaust gas collection pipe of the amino acid purification production line. The exhaust gas discharge pipe includes a centrifuge exhaust gas collection pipe, a vacuum pump exhaust gas collection pipe and a filter press exhaust gas collection pipe. An emergency pressure relief valve is provided on the top of the gas buffer tank.

6. The VOCs waste gas treatment system according to claim 1, characterized in that: The top of the water washing tower is equipped with an oxygen inlet pipe.

7. A VOCs waste gas treatment system according to claim 4, characterized in that: Both the primary and secondary reaction absorption towers employ two-stage spherical activated carbon adsorption. The spherical activated carbon has a particle diameter of 10 mm and a thickness of 1500 mm. The spray liquid used by the reaction spray pump is a solution containing an oxidant.

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