A system and method for comprehensive utilization of VOC waste gas from anoxic pool of coking wastewater

Abstract

The present invention provides a system and method for comprehensive utilization of VOC waste gas in an anoxic pool of coking wastewater, belonging to the technical field of sewage treatment. The system includes a closed anoxic pool, an absorption tower, a gas-liquid separator, a blower, a buffer tank, a closed aerobic pool and a gas stripping device; the method is to utilize the gas generated in the anoxic pool to separate carbon dioxide and water vapor in sequence, and the obtained oxygen-free gas is partially refluxed into the anoxic pool for anaerobic aeration and stirring; the remaining oxygen-free gas enters the aerobic pool as a gas stripping power source; in the process of separating carbon dioxide, sodium hydroxide is used to react with carbon dioxide to generate sodium carbonate, and an absorption liquid containing sodium carbonate and sodium hydroxide is generated, which is added to the aerobic pool to supplement the alkali source. The present invention recycles carbon dioxide, reduces carbon emissions, saves the cost of adding alkali to the aerobic pool, reduces the dissolved oxygen in the reflux nitrification liquid by the gas stripping method, improves the denitrification efficiency of the anoxic pool, and saves equipment maintenance costs.

Description

Technical Field

[0001] The invention relates to a waste gas recovery and utilization process, and in particular to a system and method for comprehensive utilization of VOC waste gas from a coking wastewater anoxic tank. Background Art

[0002] Coking phenol-cyanide wastewater is high in ammonia nitrogen and total nitrogen. The treatment process is generally AO or secondary AO or other modified processes containing AO. The function of pool A (anoxic pool) is denitrification, reducing nitrate nitrogen to nitrogen gas, and the dissolved oxygen is required to be controlled at <0.5mg / L; pool O (aerobic pool) converts ammonia nitrogen into nitrate nitrogen, and controls dissolved oxygen>2mg / L. In current sewage treatment projects, both anoxic pools and aerobic pools need to be equipped with VOC treatment facilities. The general VOC device process is to cover each treatment pool, and use a fan to form a negative pressure to suck the gas in the VOC cover. After being treated by acid washing, alkali washing, biological filter and other devices, it is discharged into the atmosphere through a discharge tube. This treatment method has a large gas volume and is relatively simple, and does not take into account the value of energy saving and waste gas recycling. Summary of the invention

[0003] In view of the above problems, the present invention provides a system and method for comprehensive utilization of VOC waste gas from anoxic tanks of coking wastewater.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is:

[0005] A VOC waste gas comprehensive utilization system for anoxic pools of coking wastewater, the system comprising a closed anoxic pool, an absorption tower, a gas-liquid separator, a blower, a buffer tank, a closed aerobic pool and a gas stripping device;

[0006] A perforated aeration device is provided in the anoxic tank; the inside of the closed anoxic tank is connected to the bottom of the absorption tower through a gas recovery pipeline, and the outlet at the top of the absorption tower is connected to the inlet of the buffer tank through a pipeline in sequence through a gas-liquid separator and a blower;

[0007] The buffer tank is provided with two outlets, the first outlet being connected to the perforated aeration device in the anoxic tank;

[0008] An air stripping device is arranged in the aerobic tank; the second outlet of the buffer tank is connected to the air stripping device at the end of the aerobic tank; the air stripping device is also connected to the anoxic tank;

[0009] The anoxic pool is also provided with a connecting pipe leading to the aerobic pool; the aerobic pool is also connected to the VOC system.

[0010] Further, the system also includes an absorption liquid storage tank;

[0011] The middle and lower part of the absorption tower is provided with an external liquid alkali pipeline and a spray device, and the side wall of the absorption tower near the bottom is also provided with an absorption liquid outlet, and the absorption liquid outlet is connected to a circulation pipeline, which is also connected to the absorption liquid storage tank and the spray device of the absorption tower respectively;

[0012] The absorption liquid storage tank is connected to the aerobic tank.

[0013] Furthermore, a tee is provided on the circulation pipeline near the bottom of the absorption tower, and the circulation pipeline is connected to the absorption liquid storage tank and the spray device of the absorption tower through the tee respectively; a circulation pump is provided on the circulation pipeline between the tee and the spray device of the absorption tower;

[0014] An alkali adding pump is arranged on the pipeline connecting the absorption liquid storage tank and the aerobic tank.

[0015] Furthermore, a packing layer is provided in the absorption tower;

[0016] A steam heating device or an electric heating device is installed on the absorption tower, and a temperature controller is provided. The temperature controller automatically controls the absorption tower for use in special working conditions such as low temperatures in winter. The absorption liquid is directly heated to prevent the precipitation of sodium carbonate due to supersaturation caused by the absorption liquid being too low in temperature.

[0017] Furthermore, the gas stripping device is a conventional gas stripping device, which is arranged in the aerobic tank and includes an air inlet pipe, a liquid inlet pipe, a lifting pipe and a discharge pipe, and the lifting pipe is connected to the air inlet pipe, the liquid inlet pipe and the discharge pipe respectively;

[0018] The air inlet pipe and liquid inlet pipe of the air stripping device are both located below the liquid surface of the aerobic tank;

[0019] The air inlet pipe of the air stripping device is connected to the second outlet of the buffer tank through the air stripping pipeline, and a pressure reducing valve is provided on the air stripping pipeline between the buffer tank and the air inlet pipe;

[0020] The discharge pipe of the gas stripping device serves as a nitrification liquid reflux pipe and is connected to the anoxic tank.

[0021] Furthermore, the discharge pipe of the gas lift device is inclined downward from the aerobic tank to the anoxic tank, and the inclination slope is 0.5~1%. The diameter of the discharge pipe must be selected to ensure that the pipeline is not full at the maximum design reflux water volume and that the gas can pass through to form an oxygen-free gas circulation path.

[0022] Furthermore, a concrete top cover is added above the closed anoxic pool, and a flange manhole is provided to ensure the sealing effect;

[0023] The enclosed aerobic pool is sealed by a VOC cover, and the aerobic pool is connected to the VOC system through a pipeline above the VOC cover of the aerobic pool;

[0024] A one-way breathing valve is installed on the connecting pipe between the closed anoxic pool and the VOC cover of the aerobic pool; the gas generated in the anoxic pool accumulates continuously. When the air pressure difference between the anoxic pool and the aerobic pool exceeds 2000Pa, the one-way breathing valve opens, and the excess gas in the anoxic pool is led to the space inside the VOC cover of the aerobic pool, and after mixing with the VOC gas generated by the aerobic pool, it is discharged to the VOC system for treatment to ensure the air pressure balance of the system.

[0025] A method for comprehensive utilization of VOC waste gas from an anoxic pool of coking wastewater, the method comprising utilizing the above system to sequentially separate carbon dioxide and water vapor from the gas generated in the anoxic pool, and then returning the resulting oxygen-free gas to the anoxic pool for anaerobic aeration and stirring; the remaining oxygen-free gas enters the aerobic pool as a gas lift power source, and gas lifts the nitrified liquid in the aerobic pool back to the anoxic pool;

[0026] When there is too much gas in the anoxic pool, it is led to the aerobic pool, mixed with the gas produced in the aerobic pool, and then discharged;

[0027] At the same time, in the process of separating carbon dioxide, sodium hydroxide is used to react with carbon dioxide to generate sodium carbonate, forming an absorption liquid containing sodium carbonate and sodium hydroxide. The absorption liquid is added to the aerobic tank to supplement the alkali source.

[0028] Furthermore, the method comprises the following specific steps:

[0029] Gas circulation: The gas generated in the anoxic pool is sucked by the blower and enters the absorption tower. The sodium hydroxide in the circulating sprayed absorption liquid reacts with carbon dioxide to separate carbon dioxide. The gas after carbon dioxide separation enters the gas-liquid separator to separate water vapor, and then enters the blower for pressurization. The pressurized oxygen-free gas enters the buffer tank to buffer the pressure of the entire system.

[0030] Part of the oxygen-free gas in the buffer tank flows back to the anoxic tank through the first outlet for anaerobic aeration and stirring;

[0031] The remaining oxygen-free gas in the buffer tank enters the gas stripping device at the end of the aerobic tank through the second outlet, and acts as a gas stripping power source to strip the nitrified liquid in the aerobic tank and return it to the anoxic tank. At the same time, the oxygen-free gas, which acts as a gas stripping power source, also flows back to the anoxic tank through the discharge pipe of the gas stripping device to continue circulating.

[0032] When there is too much gas in the anoxic pool, it is led to the aerobic pool, mixed with the VOC gas produced in the aerobic pool, and then discharged into the VOC system for treatment;

[0033] Liquid circulation: Add absorption stock solution containing sodium hydroxide into the absorption tower, and the circulation pump controls the continuous circulation spraying from top to bottom in the absorption tower to absorb carbon dioxide and form alkaline absorption liquid; during the spraying process, the absorption liquid / absorption stock solution forms a liquid film on the filler, and the gas entering the absorption tower passes from bottom to top. The sodium hydroxide on the liquid film reacts chemically with the carbon dioxide in the gas to form sodium carbonate, which is dissolved in the absorption liquid falling from the spray. The absorption liquid contains sodium carbonate and sodium hydroxide;

[0034] Part of the absorption liquid will also be discharged regularly or discharged into the absorption liquid storage tank according to the alkali addition demand of the aerobic pool. The absorption liquid in the absorption liquid storage tank is then transported to the aerobic pool through the alkali addition pump to replenish the alkali source in the aerobic pool.

[0035] Furthermore, during the gas circulation process, the gas residence time in the entire absorption tower is 0.6~1s;

[0036] The air pressure in the anoxic pool is controlled to be 1000~2000Pa higher than that in the aerobic pool; when the gas generated in the anoxic pool continues to accumulate and the pressure difference between the anoxic pool and the aerobic pool exceeds 2000Pa, the one-way breathing valve on the connecting pipe between the anoxic pool and the aerobic pool is opened, and the excess gas in the anoxic pool is led to the space inside the VOC shed cover of the aerobic pool, and after mixing with the VOC gas generated in the aerobic pool, it is discharged into the VOC system through the pipeline for treatment, thereby ensuring the air pressure balance of the VOC waste gas comprehensive utilization system of the anoxic pool of coking wastewater;

[0037] The absorption stock solution is made of liquid caustic soda or flake caustic soda, and the concentration of sodium hydroxide in the absorption stock solution is 10~15%;

[0038] According to different operating conditions such as air temperature, the sodium carbonate concentration in the absorption liquid is controlled at 10-15% and discharged into the absorption liquid storage tank to ensure that the sodium carbonate does not precipitate and scale.

[0039] Under special operating conditions such as low temperatures in winter, the steam heating device or electric heating device on the absorption tower can also be turned on to maintain the temperature of the absorption liquid and prevent the supersaturation and precipitation of sodium carbonate.

[0040] The beneficial effects of the VOC waste gas comprehensive utilization system and method of the coking wastewater anoxic tank of the present invention are:

[0041] Since biochemical aerobic denitrification utilizes the nitrification of nitrifying bacteria to convert ammonia nitrogen into nitrate nitrogen, hydrogen ions are released during the reaction to reduce the pH, and alkali needs to be added to supplement the alkalinity. There are two methods for adding alkali: liquid alkali (sodium hydroxide) and soda ash (sodium carbonate). Liquid alkali is relatively cheap, but has strong alkalinity. A slight excess can easily cause a sudden pH jump, resulting in rapid pH fluctuations, which has an adverse effect on microorganisms and requires high operation control. Soda ash is expensive, but its weak alkaline buffering properties will not cause rapid pH fluctuations even if it is excessive, which is beneficial to the stability of pH in the aerobic tank. Therefore, most sewage treatment plants currently choose to add soda ash, but this method will lead to a significant increase in treatment costs. The present invention uses a blower to suck the gas in the anoxic tank, and the sodium hydroxide solution in the absorption tower absorbs most of the carbon dioxide and then converts it into an absorption liquid containing sodium carbonate and sodium hydroxide. The absorption liquid containing sodium carbonate and sodium hydroxide is then added to the aerobic tank, which improves the stability of alkali addition in the aerobic tank, saves a lot of costs compared to directly adding commercial sodium carbonate, and also reduces greenhouse gas emissions.

[0042] The gas in the anoxic pool after the absorption tower mainly contains nitrogen and a small amount of carbon dioxide. After being pressurized by the blower, part of this oxygen-free gas is returned to the anoxic pool for anaerobic aeration and stirring, which avoids the increase of dissolved oxygen caused by the use of fresh air for stirring in the anoxic pool, and also reduces the large amount of energy consumption and high equipment maintenance frequency of mechanical stirring. By arranging a corrosion-resistant perforated aeration device in the anoxic pool and using separated oxygen-free gas for aeration and stirring, energy consumption can be saved, and the equipment maintenance cost is almost zero;

[0043] At the same time, since the reflux mode of the nitrification liquid in the aerobic pool is generally water pump reflux and gas lift reflux, gas lift reflux is more energy-efficient than water pump reflux, but it will increase the dissolved oxygen content in the reflux liquid (i.e., nitrification liquid). After the reflux liquid enters the anoxic pool, the dissolved oxygen concentration in the anoxic pool will increase, reducing the denitrification efficiency of the anoxic pool, and also limiting the reflux multiple of the gas lift reflux to be too high; the present invention adopts another part of the oxygen-free gas compressed by the blower, and after the pressure is reduced by the pressure reducing valve, it is introduced into the gas lift device at the end of the aerobic pool as the gas source of the gas lift device, and adopts the oxygen-free gas for gas lift reflux, which can avoid the increase of the dissolved oxygen concentration in the anoxic pool caused by the increase of the oxygen content in the reflux liquid; at the same time, the oxygen-free gas also returns to the anoxic pool through the discharge pipe of the gas lift device to continue to circulate;

[0044] The present invention optimizes the VOC gas collection and treatment method of the anoxic tank, recovers carbon dioxide, reduces carbon emissions, saves alkali addition costs in the aerobic tank, reduces dissolved oxygen in the reflux nitrification liquid under the gas lift method, improves the denitrification efficiency of the anoxic tank, and saves the anoxic tank equipment maintenance costs;

[0045] The system and method of the present invention are applicable to the treatment of all sewage with high ammonia nitrogen content and using the AO process as the main treatment process. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of the structure of a VOC waste gas comprehensive utilization system of a coking wastewater anoxic tank in an embodiment of the present invention;

[0047] Figure 2 This is a gas circulation process flow chart of a method for comprehensive utilization of VOC waste gas from anoxic tanks of coking wastewater in an embodiment of the present invention;

[0048] Figure 3 This is a liquid circulation process flow chart of a method for comprehensive utilization of VOC waste gas from anoxic tanks of coking wastewater in an embodiment of the present invention;

[0049] Among them, 1. anoxic tank; 11. perforated aeration device; 12. gas recovery pipe; 13. one-way breathing valve; 2. absorption tower; 21. circulation pump; 22. heating device; 3. gas-liquid separator; 4. blower; 5. buffer tank; 51. aeration pipeline; 52. pipeline for air lift; 53. pressure reducing valve; 6. aerobic tank; 61. air lift device; 611. air inlet pipe; 612. discharge pipe; 7. absorption liquid storage tank; 71. alkali pump. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present invention are described clearly and completely below. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0051] Embodiment A system and method for comprehensive utilization of VOC waste gas from anoxic tank of coking wastewater

[0052] 1. A comprehensive utilization system of VOC waste gas from anoxic pool of coking wastewater

[0053] like Figure 1 As shown, this embodiment is a VOC waste gas comprehensive utilization system of anoxic pool of coking wastewater, comprising a closed anoxic pool 1, an absorption tower 2, a gas-liquid separator 3, a blower 4, a buffer tank 5, a closed aerobic pool 6, a gas stripping device 61 and an absorption liquid storage tank 7;

[0054] A concrete top cover is added above the anoxic pool 1, and a flange manhole is provided to ensure a sealing effect; a perforated aeration device 11 is provided near the bottom of the anoxic pool 1;

[0055] The inside of the closed anoxic pool 1 is connected to the bottom of the absorption tower 2 through a gas recovery pipe 12, and the outlet at the top of the absorption tower 2 is connected to the inlet of the middle and lower part of the buffer tank 5 through a pipeline in sequence through the gas-liquid separator 3 and the blower 4; the gas generated by the anoxic pool 1 passes through the absorption tower 2 to absorb carbon dioxide, the gas-liquid separator 3 separates water vapor, and the blower 4 pressurizes, and then enters the buffer tank 5 as oxygen-free gas; the air volume of the blower 4 is the air intake of the absorption tower 2, which is much larger than the original gas generated by the biochemical reaction of the anoxic pool 1, so the gas generated by the anoxic pool 1 is circulated into the absorption tower 2 for multiple times, which can effectively improve the carbon dioxide absorption rate. A drain valve is set at the bottom / or the middle and lower part of the gas-liquid separator 3.

[0056] The buffer tank 5 is provided with two outlets, the first outlet at the top is connected to the perforated aeration device 11 at the bottom of the anoxic tank 1 through the aeration pipe 51, and the perforated aeration device 11 is a corrosion-resistant perforated aeration device 11; the oxygen-free gas in the buffer tank 5 is anaerobically aerated and stirred through the perforated aeration device 11 at the bottom of the anoxic tank 1 to form an oxygen-free gas circulation passage; a drain valve is also provided at the bottom of the buffer tank 5 to regularly discharge the accumulated water that may be generated during the use of the buffer tank 5.

[0057] The aerobic tank 6 is provided with an air stripping device 61; the second outlet at the upper middle portion of the buffer tank 5 is connected to the air inlet pipe 611 of the air stripping device 61 at the end of the aerobic tank 6 through the air stripping pipeline 52; a pressure reducing valve 53 is provided on the air stripping pipeline 52; the oxygen-free gas flowing out of the second outlet enters the air stripping device 61 at the end of the aerobic tank 6 as an air stripping power source after being decompressed;

[0058] The stripping device 61 is a conventional stripping device 61, which is arranged in the aerobic tank 6, and includes an air inlet pipe 611, a liquid inlet pipe, a lifting pipe and a discharge pipe 612, and the lifting pipe is connected with the air inlet pipe 611, the liquid inlet pipe and the discharge pipe 612 respectively; the air inlet pipe 611 and the liquid inlet pipe of the stripping device 61 are both located below the liquid surface of the liquid in the aerobic tank 6, and the air inlet pipe 611 of the stripping device 61 is connected with the second outlet at the bottom of the buffer tank 5 through the air stripping pipeline 52; the discharge pipe 612 of the stripping device 61 is used as a nitrification liquid reflux pipe, which is connected with the anoxic tank 1, and the discharge pipe 612 is inclined downward from the aerobic tank 6 to the anoxic tank 1, and the inclination slope is 0.5-1%. The diameter of the discharge pipe needs to be selected to ensure that the pipe is not full under the maximum design reflux water volume, and the gas can pass through to form a second oxygen-free gas circulation path.

[0059] The enclosed aerobic pool 6 is sealed by a VOC cover, and the top of the VOC cover of the aerobic pool 6 is connected to the VOC system through a pipeline;

[0060] A connecting pipe leading to the VOC cover of the aerobic pool is provided in the closed anoxic pool 1, and a one-way breathing valve 13 is provided on the connecting pipe; the gas generated in the anoxic pool 1 is continuously accumulated, and when the pressure difference between the anoxic pool 1 and the aerobic pool 6 exceeds 2000Pa, the one-way breathing valve 13 is opened, and the excess gas in the anoxic pool 1 is led to the space inside the VOC cover of the aerobic pool 6, and after mixing with the VOC gas generated by the aerobic pool 6, it is discharged to the VOC system for treatment to ensure the system pressure balance.

[0061] Based on the structure of a conventional chemical absorption tower 2, the absorption tower 2 is provided with a steam heating device 22 or an electric heating device 22 near the bottom of the absorption tower 2 (below the liquid level of the absorption liquid), and is equipped with a temperature controller, which is automatically controlled by the temperature controller and is used in special working conditions such as low temperatures in winter. In order to prevent the absorption liquid from being oversaturated and precipitated due to excessively low temperature, the absorption liquid is directly heated.

[0062] An external liquid alkali pipeline is provided in the middle and lower part of the absorption tower 2, and a spray device is provided on the top. An absorption liquid outlet is also provided on the side wall of the absorption tower 2 near the bottom, and a circulation pipeline is connected to the absorption liquid outlet. A tee is provided on the circulation pipeline near the bottom of the absorption tower 2, and the circulation pipeline is connected to the absorption liquid storage tank 7 and the spray device on the top of the absorption tower 2 through the tee respectively; a circulation pump 21 is provided on the circulation pipeline between the tee and the spray device on the top of the absorption tower 2; the circulation pipeline is passed into the absorption tower 2 at one end of the top of the absorption tower 2 and is connected to the spray device on the top of the absorption tower 2; a packing layer (the packing layer is generally a PP step ring) is also provided in the absorption tower 2; the absorption liquid / absorption stock solution in the absorption tower 2 is continuously circulated by the circulation pump 21 to the spray device on the top of the absorption tower 2, sprayed from top to bottom, and a liquid film is formed on the packing layer, and the gas passes from bottom to top, and a chemical absorption reaction of sodium hydroxide and carbon dioxide occurs on the liquid film to generate sodium carbonate.

[0063] The absorption liquid storage tank 7 is also connected to the aerobic pool 6 through a pipeline via an alkali pump 71. The absorption liquid in the absorption tower 2 is discharged regularly or discharged into the absorption liquid storage tank 7 according to the alkali addition demand of the aerobic pool 6, and the absorption liquid in the absorption liquid storage tank 7 is transported to the aerobic pool 6 via the alkali pump 71.

[0064] 2. A comprehensive utilization method of VOC waste gas from anoxic pool of coking wastewater

[0065] This embodiment is a method for comprehensive utilization of VOC waste gas from anoxic pool of coking wastewater. The above-mentioned VOC waste gas comprehensive utilization system of anoxic pool of coking wastewater is used for treatment. In the biochemical process of AO or containing AO, the denitrifying bacteria in the anoxic pool 1 will use the sewage carbon source or the external carbon source to denitrify the nitrate. Taking the volatile phenol, the main carbon source in the coking wastewater, as an example, there is the following theoretical biochemical reaction: 28NO3 - +5C6H6O—→30CO2+14N2+H2O+28OH -. From the reaction equation, we can see that the denitrification reaction will generate 14 mol of nitrogen and 30 mol of carbon dioxide. For example, the total nitrogen in the coking phenol-cyanide wastewater is generally 300~400 mg / L. Based on the total nitrogen removal rate of 80% in the first-level A pool, the phenol-cyanide wastewater of a coking plant with an annual output of 1 million tons is 35m³ / h. The denitrification unit will release about 28~38 kg / h of carbon dioxide. During normal operation, carbon dioxide and nitrogen are both produced by the biochemical reaction in the anoxic pool 1, and the concentration is relatively high. Therefore, the separation and recycling of carbon dioxide and the reuse of oxygen-free gas can be considered. The specific process is as follows:

[0066] Gas circulation: Figure 2 As shown, the gas generated in the anoxic pool 1 is sucked by the blower 4 and enters the absorption tower 2 to react with the carbon dioxide in the gas generated in the anoxic pool 1 by the sodium hydroxide in the circulating sprayed absorption liquid to separate the carbon dioxide. The gas after the separation of carbon dioxide enters the gas-liquid separator 3 to separate the water vapor, and then enters the blower 4 for pressurization. The pressurized oxygen-free gas enters the buffer tank 5 to buffer the pressure of the entire system; the gas residence time of the entire absorption tower 2 is 0.6~1s. The water vapor separated in the gas-liquid separator 3 is regularly discharged through the drain valve. The accumulated water generated at the bottom of the buffer tank 5 is regularly discharged through the drain valve.

[0067] Since the air volume of the blower 4 is the air intake of the absorption tower 2, which is much larger than the original gas generated by the biochemical reaction in the anoxic pool 1, the gas generated in the anoxic pool 1 is circulated into the absorption tower 2 for many times, thereby improving the carbon dioxide absorption rate. The air volume of the blower 4 is selected according to the sum of the aeration intensity of the anoxic pool 1, 5-7 Nm³ / ㎡ / h, and the air volume required for gas lift.

[0068] Part of the oxygen-free gas in the buffer tank 5 flows back to the anoxic tank 1 through the first outlet for anaerobic aeration and stirring;

[0069] The remaining oxygen-free gas in the buffer tank 5 enters the gas stripping device 61 at the end of the aerobic tank 6 through the second outlet, and acts as a gas stripping power source to strip the nitrified liquid in the aerobic tank 6 and return it to the anoxic tank 1; at the same time, the oxygen-free gas, which acts as a gas stripping power source, also flows back to the anoxic tank 1 through the discharge pipe 612 of the gas stripping device 61 to continue circulating;

[0070] At the same time, the air pressure in the anoxic pool 1 is controlled to be 1000-2000Pa higher than the air pressure in the aerobic pool 6; when the gas generated in the anoxic pool 1 continues to accumulate and the pressure difference between the anoxic pool 1 and the aerobic pool 6 exceeds 2000Pa, the one-way breathing valve 13 on the connecting pipe between the anoxic pool 1 and the aerobic pool 6 is opened, and the excess gas in the anoxic pool 1 is led to the space inside the VOC cover of the aerobic pool 6, and after mixing with the VOC gas generated in the aerobic pool 6, it is discharged into the VOC system through the pipeline for treatment, thereby ensuring the air pressure balance of the entire coking wastewater anoxic pool VOC waste gas comprehensive utilization system.

[0071] Liquid circulation: Figure 3 As shown, an absorption stock solution with a sodium hydroxide concentration of 10-15% made of liquid caustic soda or flake caustic soda is added into the absorption tower 2, and the circulation pump 21 controls the continuous circulation spraying from top to bottom in the absorption tower 2 to absorb the carbon dioxide in the gas generated in the anoxic pool 1 to form an absorption liquid. During the spraying process, the absorption liquid / absorption stock solution forms a liquid film on the filler, and the gas entering the absorption tower 2 passes from bottom to top. The sodium hydroxide on the liquid film reacts chemically with the carbon dioxide in the gas to generate sodium carbonate, which is dissolved in the absorption liquid falling from the spray. The absorption liquid contains sodium carbonate and sodium hydroxide.

[0072] According to different operating conditions such as temperature, the sodium carbonate concentration in the absorption liquid is controlled to be 10-15% to ensure that sodium carbonate does not precipitate and scale, and then discharged into the absorption liquid storage tank 7. In special operating conditions such as low temperature in winter, the steam heating device 22 or the electric heating device 22 on the absorption tower 2 can also be turned on to maintain the temperature of the absorption liquid to prevent the supersaturation precipitation of sodium carbonate.

[0073] Part of the absorption liquid will also be discharged regularly or discharged into the absorption liquid storage tank 7 according to the alkali addition demand of the aerobic tank 6. The absorption liquid in the absorption liquid storage tank 7 is then transported to the aerobic tank 6 through the alkali addition pump 71 to supplement the alkali source in the aerobic tank 6.

[0074] Since the method of the present invention is a continuous dynamic process, the water quality of coking wastewater and various process parameters are dynamically changing parameters. Therefore, during the treatment process, it is only necessary to control the various process parameters within the parameter range specified in the above embodiment, and there is no need to list the parameter point values ​​at a specific moment.

[0075] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A VOC waste gas comprehensive utilization system for coking wastewater anoxic tank, characterized in that: The system comprises a closed anoxic tank, an absorption tower, a gas-liquid separator, a blower, a buffer tank, a closed aerobic tank and a gas stripping device; A perforated aeration device is provided in the anoxic tank; the inside of the closed anoxic tank is connected to the bottom of the absorption tower through a gas recovery pipeline, and the outlet at the top of the absorption tower is connected to the inlet of the buffer tank through a pipeline in sequence through a gas-liquid separator and a blower; The buffer tank is provided with two outlets, the first outlet being connected to the perforated aeration device in the anoxic tank; An air stripping device is arranged in the aerobic tank; the second outlet of the buffer tank is connected to the air stripping device at the end of the aerobic tank; the air stripping device is also connected to the anoxic tank; A connecting pipe leading to the aerobic pool is also provided in the anoxic pool; the aerobic pool is also connected to the VOC system; the system also includes an absorption liquid storage tank; The middle and lower part of the absorption tower is provided with an external liquid alkali pipeline and a spray device. The absorption liquid outlet is provided on the side wall of the absorption tower near the bottom. The absorption liquid outlet is connected to a circulation pipeline, which is also connected to the absorption liquid storage tank and the spray device of the absorption tower respectively. The absorption liquid storage tank is connected to the aerobic tank.

2. The VOC waste gas comprehensive utilization system of coking wastewater anoxic tank according to claim 1 is characterized in that: A tee is provided on the circulation pipeline near the bottom of the absorption tower, and the circulation pipeline is connected to the absorption liquid storage tank and the spray device of the absorption tower through the tee respectively; a circulation pump is provided on the circulation pipeline between the tee and the spray device of the absorption tower; An alkali adding pump is arranged on the pipeline connecting the absorption liquid storage tank and the aerobic tank.

3. The VOC waste gas comprehensive utilization system of the coking wastewater anoxic tank according to claim 1 or 2 is characterized in that: A packing layer is also provided in the absorption tower; A steam heating device or an electric heating device is installed on the absorption tower, and a temperature controller is provided as well.

4. The VOC waste gas comprehensive utilization system of the coking wastewater anoxic tank according to claim 1 or 2, characterized in that: The gas stripping device is arranged in the aerobic tank, and comprises an air inlet pipe, a liquid inlet pipe, a lifting pipe and a discharge pipe, wherein the lifting pipe is respectively connected with the air inlet pipe, the liquid inlet pipe and the discharge pipe; The air inlet pipe and liquid inlet pipe of the air stripping device are both located below the liquid surface of the aerobic tank; The air inlet pipe of the air stripping device is connected to the second outlet of the buffer tank through the air stripping pipeline, and a pressure reducing valve is provided on the air stripping pipeline between the buffer tank and the air inlet pipe; The discharge pipe of the gas stripping device is connected to the anoxic tank.

5. The VOC waste gas comprehensive utilization system of coking wastewater anoxic tank according to claim 4 is characterized in that: The discharge pipe is inclined downward from the aerobic tank to the anoxic tank.

6. The VOC waste gas comprehensive utilization system of the coking wastewater anoxic tank according to claim 1, 2 or 5, characterized in that: A concrete cover is added above the closed anoxic pool; The enclosed aerobic pool is sealed by a VOC cover, and the aerobic pool is connected to the VOC system through a pipeline above the VOC cover of the aerobic pool; A one-way breathing valve is provided on the connecting pipe between the closed anoxic pool and the VOC cover of the aerobic pool.

7. A method for comprehensive utilization of VOC waste gas from anoxic pool of coking wastewater, characterized in that: The method comprises the following specific steps: Gas circulation: The gas generated in the anoxic pool is sucked by the blower and enters the absorption tower. The sodium hydroxide in the circulating sprayed absorption liquid reacts with carbon dioxide to separate carbon dioxide. The gas after carbon dioxide separation enters the gas-liquid separator to separate water vapor, and then enters the blower for pressurization. The pressurized oxygen-free gas enters the buffer tank; Part of the oxygen-free gas in the buffer tank flows back to the anoxic tank through the first outlet for anaerobic aeration and stirring; The remaining oxygen-free gas in the buffer tank enters the gas stripping device at the end of the aerobic tank through the second outlet, and serves as a gas stripping power source to strip the nitrified liquid in the aerobic tank and return it to the anoxic tank; When there is too much gas in the anoxic pool, it is led to the aerobic pool, mixed with the VOC gas produced in the aerobic pool, and then discharged into the VOC system for treatment; Meanwhile, in the process of separating carbon dioxide, sodium hydroxide is used to react with carbon dioxide to generate sodium carbonate, thereby forming an absorption liquid containing sodium carbonate and sodium hydroxide; Liquid circulation: Add the absorption stock solution containing sodium hydroxide into the absorption tower, and the circulation pump controls the continuous circulation and spraying from top to bottom in the absorption tower to absorb carbon dioxide and form absorption liquid; Part of the absorption liquid is discharged regularly or discharged into the absorption liquid storage tank according to the alkali addition demand of the aerobic tank. The absorption liquid in the absorption liquid storage tank is then transported to the aerobic tank through the alkali addition pump to supplement the alkali source in the aerobic tank.

8. The method for comprehensive utilization of VOC waste gas from anoxic tanks of coking wastewater according to claim 7, characterized in that: During the gas circulation process, the gas residence time in the entire absorption tower is 0.6~1s; The air pressure in the anoxic pool is controlled to be 1000~2000Pa higher than that in the aerobic pool; when the gas generated in the anoxic pool continues to accumulate and the pressure difference between the anoxic pool and the aerobic pool exceeds 2000Pa, the one-way breathing valve on the connecting pipe between the anoxic pool and the aerobic pool is opened, and the excess gas in the anoxic pool is led to the space inside the VOC shed cover of the aerobic pool, and after mixing with the VOC gas generated in the aerobic pool, it is discharged into the VOC system through the pipeline for treatment; The absorption stock solution is made of liquid caustic soda or flake caustic soda, and the concentration of sodium hydroxide in the absorption stock solution is 10~15%; When the concentration of sodium carbonate in the absorption liquid is 10-15%, it is discharged into the absorption liquid storage tank; When the temperature is low in winter, turn on the steam heating device or electric heating device on the absorption tower to maintain the temperature of the absorption liquid.

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