A coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system and method

Abstract

The application discloses a coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system and method, which comprises an aeration tank, an inclined tube sedimentation tank, a dosing device, a buffer water tank, a quartz sand filter, an intermediate water tank, a mixer, a liquid alkali storage tank, a deamination tower kettle, an external discharge pH adjusting tank, a sulfuric acid storage tank, an ammonium sulfate circulating tank, an aeration fan, a stripping fan, a gas buffer bag, an ammonium sulfate circulating pump and a sulfuric acid pump; ammonia nitrogen-containing wastewater pipelines are sequentially connected with the aeration tank and the inclined tube sedimentation tank, the overflow port of the inclined tube sedimentation tank is connected with the water inlet of the buffer water tank, and the water outlet of the buffer water tank is sequentially connected with the quartz sand filter, the intermediate water tank, the mixer and the deamination tower kettle; the aeration fan is connected with the gas inlet of the aeration tank, the dosing device is connected with the dosing port of the inclined tube sedimentation tank, and the liquid alkali storage tank is connected with the alkali inlet of the mixer. After being treated by the system and method, the ammonia nitrogen in the effluent is stable and up to the standard, the pH value is stable, and the wastewater discharge meets the first-level standard of the national wastewater comprehensive discharge standard.

Description

Technical Field

[0001] This invention relates to a wastewater treatment system and method, and more particularly to an ammonia nitrogen treatment system and method for wastewater from a coke oven gas direct reduction plant. Background Technology

[0002] Direct reduction ironmaking technology is a cutting-edge technology in the steel industry. Its final products are iron and water, reducing CO2 emissions. It is an important direction for reducing energy consumption, improving the structure of steel products, and enhancing the quality of steel products, and it is also an important aspect of innovation leadership. Internationally, the conventional method of producing reducing process gases from natural gas is widely used. For traditional industrial enterprises, renewable energy hydrogen production is an important approach. Therefore, direct reduction technology using coke oven gas as the reducing gas source in gas-based vertical shaft furnace hydrogen metallurgy has broad prospects.

[0003] However, unlike the traditional hydrogen metallurgical process using natural gas as the reducing gas, which produces low ammonia nitrogen content and whose cooling water wastewater can be directly discharged, the hydrogen metallurgical process using coke oven gas as the reducing gas has an N2 content of approximately 5%–6%. During the hydrogen metallurgical process gas circulation, N2 enrichment reaches over 15%. In the low-temperature zone of the vertical shaft furnace, nitrogen and hydrogen synthesize ammonia under suitable conditions of high temperature, high pressure, and a catalyst (such as an iron catalyst). The chemical equation is 3H2 + N2 → 2NH3. After forming NH3, due to its easy solubility in water, a large amount of ammonia nitrogen will remain in the circulating cooling water system after the process gas is directly cooled in contact with the circulating cooling water. However, my country's environmental protection requirements stipulate that the ammonia nitrogen content in wastewater discharge must be less than 15 mg / L. How to efficiently remove ammonia nitrogen from wastewater while saving costs and investment is a current problem facing ammonia nitrogen treatment in coke oven gas direct reduction plants.

[0004] In direct reduction coke oven gas plants, the reducing gases from the vertical shaft furnaces are recycled during production. The top gas discharged from the furnace after participating in the reduction reaction undergoes multiple washing and purification processes. This purification process uses a large amount of water, which also needs to be recycled. After multiple cycles, the conductivity, turbidity, total iron, total hardness, chloride ions, and ammonia nitrogen levels in the cooling water system will exceed standards. Long-term accumulation of these levels will negatively impact water quality, affecting heat transfer efficiency and equipment performance, and causing corrosion of equipment and pipelines. Therefore, the circulating water system needs to periodically discharge substandard water and replenish it with a certain amount of fresh water. However, at this point, the ammonia nitrogen level in the system is usually above 100 mg / L. Direct discharge of this water will cause eutrophication, disrupting the balance of the aquatic ecosystem and consequently affecting human living environment and health. Furthermore, the large amount of ammonia nitrogen in the wastewater cannot be recovered and reused, resulting in significant resource waste.

[0005] Currently, most ammonia removal systems in my country are designed for wastewater with high concentrations of ammonia nitrogen. For example, the ammonia nitrogen concentration in fertilizer wastewater is 400–700 mg / L, the ammonia nitrogen concentration in wastewater generated during monosodium glutamate production is as high as 5000–6000 mg / L, the concentration in coking wastewater is 200–700 mg / L, the ammonia nitrogen concentration in landfill leachate is as high as 2000 mg / L, the ammonia nitrogen concentration in coal gas wastewater is 200–250 mg / L, and the ammonia nitrogen concentration in livestock wastewater is 800–2200 mg / L.

[0006] Production practice has revealed that the ammonia nitrogen concentration in the washing and cooling wastewater of coke oven gas direct reduction plants is typically 40–150 mg / L, which is relatively low. Therefore, it is necessary to design an ammonia nitrogen treatment system for wastewater from coke oven gas direct reduction plants that meets national safety and environmental protection standards while operating economically, and allows for the recycling of byproducts, thus achieving optimal economic efficiency and environmental protection. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a highly efficient and energy-saving ammonia nitrogen treatment system for wastewater from a coke oven gas direct reduction plant; the present invention also provides a method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant with good treatment effect.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the system of the present invention is as follows: it includes an aeration tank, an inclined tube sedimentation tank, a dosing device, a buffer tank, a quartz sand filter, an intermediate water tank, a mixer, a liquid alkali storage tank, a deammoniation tower, an external discharge pH adjustment tank, a sulfuric acid storage tank, an ammonium sulfate circulation tank, an aeration blower, a stripping blower, a gas buffer tank, an ammonium sulfate circulation pump, and a sulfuric acid pump; the ammonia nitrogen-containing wastewater pipeline is sequentially connected to the aeration tank and the inclined tube sedimentation tank, the overflow outlet of the inclined tube sedimentation tank is connected to the inlet of the buffer tank, and the outlet of the buffer tank is sequentially connected to the quartz sand filter, the intermediate water tank, and the intermediate water tank. The system includes a water tank, a mixer, and a deammoniation tower. The aeration blower is connected to the air inlet of the aeration box, the dosing device is connected to the dosing port of the inclined tube sedimentation tank, and the liquid alkali storage tank is connected to the alkali inlet of the mixer. The stripping blower and the gas buffer are connected between the circulating process gas outlet and the circulating process gas inlet of the deammoniation tower. The ammonium sulfate circulating tank and the ammonium sulfate circulating pump are connected between the ammonium sulfate outlet and the ammonium sulfate inlet of the deammoniation tower. The outlet of the deammoniation tower is connected to the external discharge pH adjustment tank. The sulfuric acid storage tank is connected to both the ammonium sulfate circulating tank and the external discharge pH adjustment tank via a sulfuric acid pump.

[0009] Furthermore, it also includes an ammonium sulfate evaporator, an ammonium sulfate concentration tank, an ammonium sulfate finished product tank, an ammonium sulfate concentration pump, and an ejector; the inlet of the ammonium sulfate concentration tank is connected to the outlet of the ammonium sulfate circulation pump, and valves are provided between the outlet of the ammonium sulfate circulation pump and both the deammonium removal tower and the ammonium sulfate concentration tank; the outlet of the ammonium sulfate concentration tank is connected to the inlet of the ammonium sulfate evaporator through the ammonium sulfate concentration pump, and the outlet of the ammonium sulfate evaporator is connected to the inlet of the ammonium sulfate concentration tank through the ejector.

[0010] Furthermore, the aeration box, inclined tube sedimentation tank, buffer tank, and intermediate tank are all connected to an odor collection pipe, which is connected to the air inlet of the jet injector.

[0011] Furthermore, the steam inlet of the ammonium sulfate evaporator is connected to the process steam pipeline, and the steam outlet of the ammonium sulfate evaporator is connected to the inlet of the stripping blower.

[0012] Furthermore, it also includes a No. 1 plate heat exchanger; the cold water pipeline of the No. 1 plate heat exchanger is connected to the pipeline between the outlet of the mixer and the inlet of the deammoniation tower; the hot water pipeline of the No. 1 plate heat exchanger is connected to the pipeline between the outlet of the deammoniation tower and the external pH adjustment tank.

[0013] To solve the above-mentioned technical problems, the method of the present invention adopts the above-mentioned treatment system, and the technical solution adopted includes the following steps: 1) The ammonia nitrogen-containing wastewater enters the aeration tank for aeration;

[0014] 2) The aerated wastewater enters the inclined tube sedimentation tank to mix, react, and settle with the reagents;

[0015] 3) The clear liquid at the top of the inclined tube sedimentation tank enters the buffer tank and then enters the quartz sand filter for filtration;

[0016] 4) The filtered wastewater enters the mixer through the intermediate water tank and mixes with liquid alkali to form a mixed waste liquid;

[0017] 5) The mixed waste liquid enters the deammoniation tower and is circulated with ammonium sulfate solution while sulfuric acid is added for gas stripping deammoniation;

[0018] 6) The wastewater discharged from the deammoniation tower is adjusted to pH with sulfuric acid before being discharged.

[0019] Furthermore, in step 5), after the ammonium sulfate solution reaches the set concentration, it is concentrated by cyclic evaporation to obtain the finished ammonium sulfate solution.

[0020] Furthermore, during the cyclic evaporation and concentration process of the ammonium sulfate solution, the odor generated by the treatment system is carried into the ammonium sulfate concentration tank for absorption by the negative pressure generated during the jetting process by the jet ejector.

[0021] Furthermore, during the circulating evaporation and concentration process of the ammonium sulfate solution, the steam discharged from the ammonium sulfate evaporator is mixed with the mixed waste liquid and enters the deammoniation tower.

[0022] Furthermore, the mixed waste liquid exchanges heat with the wastewater discharged from the deammoniation tower before entering the deammoniation tower.

[0023] The beneficial effects of adopting the above technical solution are as follows: 1. The wastewater ammonia nitrogen treatment system of the present invention for coke oven gas direct reduction plant is a new type of sewage treatment system designed for coke oven gas hydrogen metallurgical wastewater in my country, rather than simply applying the traditional general industrial sewage treatment system.

[0024] 2. Before treatment using the system and method of this invention, the ammonia nitrogen content of the wastewater containing ammonia nitrogen was 40-150 mg / L. After treatment by this system and method, the ammonia nitrogen content of the effluent was stably up to standard, reduced to <15 mg / L, and the pH value was stable at 7-9, which met the national wastewater discharge standards.

[0025] 3. Compared with other wastewater treatment systems, the steam supply is significantly reduced because the raw water has already been heated by heat exchange with the waste heat of the water discharged from the deammoniation tower before entering the tower. This preheating of the raw water will greatly reduce heat energy consumption and improve heat energy utilization, which means that steam consumption will be greatly reduced.

[0026] 4. By designing and using an ejector, the negative pressure generated when ammonium sulfate is concentrated carries the odor generated by the system into the ammonium sulfate concentration tank for absorption, thus preventing the odor from escaping and protecting the environment and the health of on-site operators.

[0027] 5. The system and method of this invention include a primary sedimentation and sludge removal system and a chemical dosing device. The primary sedimentation and sludge removal system performs preliminary filtration of coke oven gas and hydrogen metallurgical wastewater, reducing the burden on downstream treatment processes (such as filtration and ammonia removal), thereby reducing energy and material consumption. The secondary filtration system further filters impurities that are not easily settled, improving the overall filtration efficiency of the system, reducing pipe and valve blockage, and concentrating the settled sludge in the clarifier, facilitating subsequent sludge recycling and disposal, preventing direct sludge discharge, protecting the environment, extending equipment lifespan, and ensuring stable system operation.

[0028] 6. The system and method of this invention are designed to neutralize the qualified ammonia nitrogen wastewater by adding acid and adjust the pH value. At the same time, a stirrer is provided to ensure the neutralization effect of the discharged wastewater and to treat the wastewater thoroughly.

[0029] 7. In this invention, the process gas inside the deammoniation tower is recycled through a stripping blower. The water vapor from ammonium sulfate concentration is also piped to the inlet of the stripping blower for secondary reuse of waste heat, further reducing steam consumption, eliminating the environmental impact of exhaust gas, and saving energy. Simultaneously, targeted improvements have been made to address the shortcomings of traditional deammoniation methods. A gas buffer pack has been added between the outlet of the stripping blower and the outlet of the deammoniation tower, balancing the pressure inside and outside the tower. This ensures a stable and uniform pressure when the gas enters the tower, guaranteeing a stable and continuous flow of gas. In case of emergencies, this provides a buffer time, allowing the system sufficient adjustment time. This stable airflow helps improve deammoniation efficiency.

[0030] 8. The system and method of the present invention are equipped with a buffer tank and an intermediate tank, which can serve as two-stage buffer zones to balance the impact caused by water volume fluctuations, avoid the decline in treatment effect caused by unstable flow, and reduce the impact and damage to downstream equipment.

[0031] 9. The system and method of this invention include a wastewater aeration stage, and aeration adjustment can effectively regulate the water quality entering the ammonia removal system. Through the aeration process, the oxygen concentration in the water is increased, which facilitates oxidation-reduction reactions, degrading organic pollutants (including ammonia-containing substances) in the water into inorganic substances, thereby purifying the water quality.

[0032] 10. The system and method of the present invention recycle and reuse the steam condensate generated by the ammonium sulfate evaporator, and after separating the sludge from the sludge generated by the inclined tube sedimentation tank, the sludge and the clear liquid are also designed to be recycled and reused, which can reduce the system's operating consumption and reduce production costs.

[0033] 11. The ammonia nitrogen removed by the system and method of this invention produces ammonium sulfate, a byproduct that can be used in other processes, such as fertilizer production, thus realizing resource recycling, reducing secondary pollution, and benefiting environmental protection.

[0034] 12. The wastewater ammonia nitrogen treatment system proposed in this invention can operate automatically, is simple to operate, and is easy to use. Operators can be put to work after simple training without complicated operations, which can reduce labor costs. Attached Figure Description

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0036] Figure 1 This is a schematic diagram of the structure of the present invention.

[0037] In the diagram: 1. Aeration box; 2. Inclined tube sedimentation tank; 3. Dosing device; 4. Buffer tank; 5. Quartz sand filter; 6. Intermediate water tank; 7. Mixer; 8. Liquid alkali storage tank; 9. Deammoniation tower; 10. Plate heat exchanger No. 1; 11. Plate heat exchanger No. 2; 12. External discharge pH adjustment tank; 13. Sulfuric acid storage tank; 14. Ammonium sulfate circulation tank; 15. Ammonium sulfate evaporator; 16. Ammonium sulfate concentration tank; 17. Ammonium sulfate finished product tank; 18. Aeration blower; 19. Dosing pump; 20. 21. Sludge discharge pump; 22. Sludge filter press; 23. Filter inlet pump; 24. Tower inlet pump; 25. Liquid alkali pump; 26. Stripping blower; 27. Gas buffer tank; 28. Wastewater discharge pump; 29. ​​Ammonium sulfate circulation pump; 30. Ammonium sulfate concentration pump; 31. Ammonium sulfate discharge pump; 32. Electric valve No. 1; 33. Electric valve No. 2; 34. Sedimentation tank inlet pump; 35. Sulfuric acid pump; 36. Tower bottom outlet pump; 37. Electric valve No. 4; 38. Ejector. Detailed Implementation

[0038] Figure 1As shown, the ammonia nitrogen treatment system for wastewater from this coke oven gas direct reduction plant includes an aeration tank 1, an inclined tube sedimentation tank 2, a dosing device 3, a buffer tank 4, a quartz sand filter 5, an intermediate water tank 6, a mixer 7, a liquid alkali storage tank 8, a deammoniation tower 9, a No. 1 plate heat exchanger 10, a No. 2 plate heat exchanger 11, an external discharge pH adjustment tank 12, a sulfuric acid storage tank 13, an ammonium sulfate circulation tank 14, an ammonium sulfate evaporator 15, an ammonium sulfate concentration tank 16, an ammonium sulfate finished product tank 17, and an aeration blower. 18. Dosing pump; 19. Sludge discharge pump; 20. Sludge filter press; 21. Filter inlet pump; 22. Tower inlet pump; 23. Liquid alkali pump; 24. Stripping blower; 25. Gas buffer pack; 26. Wastewater discharge pump; 27. Ammonium sulfate circulation pump; 28. Ammonium sulfate concentration pump; 29. ​​Ammonium sulfate discharge pump; 30. Electric valve No. 1; 31. Electric valve No. 2; 32. Sedimentation tank inlet pump; 33. Sulfuric acid pump; 34. Tower bottom outlet pump; 35. Electric valve No. 3; 36. Electric valve No. 4; 37. and ejector; 38. The inlet of the aeration tank 1 is connected to the ammonia-nitrogen wastewater pipeline, and the outlet is connected to the inlet of the inclined tube sedimentation tank 2 via the sedimentation tank inlet pump 33. The air inlet at the bottom of the aeration tank 1 is connected to the outlet of the aeration blower 18. The aeration tank 1 is equipped with a level gauge, which is interlocked with the sedimentation tank inlet pump 33. When the liquid level in the aeration tank 1 is high, the sedimentation tank inlet pump 33 starts; when the liquid level in the aeration tank 1 is low, the sedimentation tank inlet pump 33 stops. The bottom of the inclined tube sedimentation tank 2 is equipped with a sludge discharge port, which is connected to the sludge filter press 21 via the sludge discharge pump 20. The dosing device 3 is connected to the dosing port of the inclined tube sedimentation tank 2 via the dosing pump 19. The inlet of the dosing device 3 is connected to the demineralized water pipeline, allowing for manual dosing followed by opening the demineralized water pipeline for reagent addition and dilution. The dosing device 3 is equipped with a stirring device to ensure uniform mixing of the reagents. The overflow outlet of the inclined tube sedimentation tank 2 is connected to the inlet of the buffer water tank 4. The outlet of the buffer water tank 4 is connected to the inlet of the quartz sand filter 5 via the filter inlet pump 22. The outlet of the quartz sand filter 5 is connected to the inlet of the intermediate water tank 6. The outlet of the intermediate water tank 6 is connected to the inlet of the mixer 7 via the tower pump 23. The buffer water tank 4 is equipped with a level gauge and is interlocked with the filter inlet pump 22. When the level in the buffer water tank 4 is high, the filter inlet pump 22 starts; when the level in the buffer water tank 4 is low, the filter inlet pump 22 stops. The intermediate water tank 6 is equipped with a level gauge and is interlocked with the tower pump 23. When the level in the intermediate water tank 6 is high, the tower pump 23 starts; when the level in the intermediate water tank 6 is low, the tower pump 23 stops. The outlet of the liquid alkali storage tank 8 is connected to the inlet of the mixer 7 via the liquid alkali pump 24. The inlet of the liquid alkali storage tank 8 is connected to a tanker truck for transporting alkali via a pipeline. The liquid alkali storage tank 8 is equipped with a level gauge and is interlocked with the liquid alkali pump 24. When the liquid level in the liquid alkali storage tank 8 is high, the liquid alkali pump 24 can start and inject liquid alkali according to the pH value detected in the mixer 7. When the liquid level in the liquid alkali storage tank 8 is low, the liquid alkali pump 24 stops running. After the liquid alkali pump 24 stops running, the entire system is shut down by interlock.

[0039] Figure 1 As shown, in the ammonia nitrogen treatment system for wastewater from this coke oven gas direct reduction plant, the outlet of the mixer 7 is connected to the inlet of the deammoniation tower bottom 9 via the cold water pipeline of the No. 1 plate heat exchanger 10. The outlet of the deammoniation tower bottom 9 is connected to the inlet of the discharge pH adjustment tank 12 via the bottom water pump 35 and the hot water pipeline of the No. 1 plate heat exchanger 10. The outlet of the discharge pH adjustment tank 12 is connected to the qualified discharge wastewater pipeline via the wastewater discharge pump 27 and the hot water pipeline of the No. 2 plate heat exchanger 11. The inlet and outlet of the cold water pipeline of the No. 2 plate heat exchanger 11 are connected to the cold medium water pipeline of the clean circulating water pool of the coke oven gas direct reduction plant. The circulating process gas outlet at the top of the deammoniation tower 9 is connected to the inlet of the stripping blower 25, the outlet of the stripping blower 25 is connected to the inlet of the gas buffer pack 26, and the outlet of the gas buffer pack 26 is connected to the circulating process gas inlet in the middle of the deammoniation tower 9. In this way, the circulating process gas in the deammoniation tower 9 flows from bottom to top, and the circulating process gas is connected to the inlet of the stripping blower 25 through the pipeline from the top outlet of the deammoniation tower 9, and the cycle continues.

[0040] Figure 1 As shown, in this coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system, the ammonium sulfate outlet of the deammoniation tower 9 is connected to the inlet of the ammonium sulfate circulation tank 14. The outlet of the ammonium sulfate circulation tank 14 is connected to the ammonium sulfate inlet of the deammoniation tower 9 and the inlet of the ammonium sulfate concentration tank 16 via an ammonium sulfate circulation pump 28. A first electric valve 31 is installed in the pipeline between the ammonium sulfate circulation pump 28 and the ammonium sulfate inlet of the deammoniation tower 9, and a second electric valve 32 is installed in the pipeline between the ammonium sulfate circulation pump 28 and the inlet of the ammonium sulfate concentration tank 16. The acid outlet of the sulfuric acid storage tank 13 is connected to the acid inlet of the ammonium sulfate circulation tank 14 and the acid inlet of the discharge pH adjustment tank 12 via a sulfuric acid pump 34. The acid inlet of the sulfuric acid storage tank 13 is connected to an acid truck via a pipeline. The steam inlet of the deammoniation tower 9 is connected to the process steam pipeline. The ammonium sulfate circulation tank 14 is equipped with a level gauge and is interlocked with the ammonium sulfate circulation pump 28. When the level in the ammonium sulfate circulation tank 14 is high, the ammonium sulfate circulation pump 28 starts and stops when the level in the ammonium sulfate circulation tank 14 is low. The discharge pH adjustment tank 12 is equipped with a level gauge and is interlocked with the wastewater discharge pump 27. When the level in the discharge pH adjustment tank 12 is high, the wastewater discharge pump 27 starts and stops when the level in the pH adjustment tank 12 is low. At the same time, the discharge pH adjustment tank 12 is equipped with a stirring device at the top to ensure that the mixed waste liquid in the tank is fully mixed with the sulfuric acid used to adjust the pH value, so that the pH value of the mixed waste liquid reaches the standard of 7-9. The sulfuric acid storage tank 13 is equipped with a level gauge and an interlocking system with the sulfuric acid pump 34. When the sulfuric acid level in the storage tank 13 is high, the sulfuric acid pump 34 can be started to inject sulfuric acid according to the level or pH value of the ammonium sulfate circulation tank 14. When the sulfuric acid level in the storage tank 13 is low, the sulfuric acid pump 34 stops running. After the sulfuric acid pump 34 stops running, the entire system is shut down by interlocking.

[0041] Figure 1 As shown, in the ammonia nitrogen treatment system for wastewater from the coke oven gas direct reduction plant, the outlet of the ammonium sulfate concentration tank 16 is connected to the inlet of the ammonium sulfate evaporator 15 via an ammonium sulfate concentration pump 29. The outlet of the ammonium sulfate evaporator 15 is connected to the inlet of the ammonium sulfate concentration tank 16 via an ejector 38. A third electric valve 36 is installed in the pipeline between the outlet of the ammonium sulfate evaporator 15 and the ejector 38. The outlet of the ammonium sulfate evaporator 15 is also connected to the inlet of the ammonium sulfate finished product tank 17. A fourth electric valve 37 is installed in the pipeline between the outlet of the ammonium sulfate evaporator 15 and the inlet of the ammonium sulfate finished product tank 17. The outlet of the ammonium sulfate finished product tank 17 is connected to a tank truck via an ammonium sulfate exhaust pump 30. The steam inlet of the ammonium sulfate evaporator 15 is connected to the process steam pipeline, and the steam outlet of the ammonium sulfate evaporator 15 is connected to the inlet of the stripping blower 25. The ammonium sulfate concentration tank 16 is equipped with a level gauge and is interlocked with the tank. When the level in the ammonium sulfate concentration tank 16 is high, the tank starts operating; when the level is low, the tank stops operating. The ammonium sulfate evaporator 15 has a condensate outlet for condensate recovery. The ammonium sulfate finished product tank 17 is equipped with a level gauge. When the level in the finished product tank 17 exceeds the warning level, the system automatically alarms, contacts a tank truck to arrive, and then manually starts the ammonium sulfate discharge pump to drain the finished ammonium sulfate solution.

[0042] Figure 1 As shown, in the ammonia nitrogen treatment system for wastewater from this coke oven gas direct reduction plant, the first electric valve 31 and the second electric valve 32 are interlocked. When the first electric valve 31 is open, the second electric valve 32 is closed, and when the first electric valve 31 is closed, the second electric valve 32 is opened. The third electric valve 36 and the fourth electric valve 37 are interlocked. When the third electric valve 36 is open, the fourth electric valve 37 is closed, and when the third electric valve 36 is closed, the fourth electric valve 37 is opened.

[0043] Figure 1 As shown, the ammonia nitrogen treatment system for wastewater from this coke oven gas direct reduction plant is configured with two pumps for each of the following pumps: dosing pump 19, sludge discharge pump 20, filter inlet pump 22, tower inlet pump 23, liquid alkali pump 24, stripping blower 25, gas buffer tank 26, wastewater discharge pump 27, ammonium sulfate circulation pump 28, ammonium sulfate concentration pump 29, ammonium sulfate discharge pump 30, sedimentation tank inlet pump 33, sulfuric acid pump 34, and tower bottom outlet pump 35. These pumps share inlet and outlet pipelines and operate on a standby basis. If one pump fails and stops, the system will issue an alarm, and the standby pump will automatically start to ensure the overall normal operation of the system. All pump outlet pipelines are equipped with check valves to prevent backflow of related materials.

[0044] Figure 1As shown, in this coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system, the aeration blower and the stripping blower are both centrifugal compressors. The stripping blower is equipped with a matching frequency converter for adjustment, and the speed and air volume can be adjusted by observing the stripping situation in the ammonia removal tower 9.

[0045] The technical principle behind the ammonia nitrogen treatment method for wastewater from this coke oven gas direct reduction plant is as follows: Ammonia nitrogen refers to free ammonia (NH3) and ammonium ions (NH4) in water. + Nitrogen exists in the form of NH4+. The reaction principle of this treatment method is that ammonium salt and sodium hydroxide react under heating conditions to produce ammonia gas. The ionic equation for the reaction is: NH4+ + +OH - NH3↑+H2O NH3·H2O, H2SO4 + 2NH3·H2O = (NH4)2SO4 + 2H2O. Upon addition of sodium hydroxide, a large amount of OH- is produced upon dissolution. - This will promote the equilibrium to shift to the right, and the dissolution of sodium hydroxide will release a large amount of heat. At the same time, it will reduce the solubility of ammonia, which will facilitate the volatilization of ammonia and its overflow from the ammonia-nitrogen-containing wastewater. The volatilized ammonia will react with sulfuric acid to form ammonium sulfate.

[0046] Figure 1 As shown, the method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant includes the following steps:

[0047] 1) The ammonia nitrogen-containing wastewater enters the aeration tank 1, where it is aerated by compressed air blown out by the aeration blower 18; the ammonia nitrogen concentration in the ammonia nitrogen-containing wastewater is 40-150 mg / L.

[0048] 2) The aerated wastewater is pumped from the outlet of aeration box 1 by sedimentation tank inlet pump 33 and transported to inclined tube sedimentation tank 2. The dosing pump 19 adds the chemicals from dosing device 3. The wastewater and chemicals are mixed and reacted, and then sedimentation occurs. The chemicals are coagulants and flocculants.

[0049] 3) The clear liquid in the upper layer of the inclined tube sedimentation tank 2 overflows into the buffer water tank 4, and is then transported to the quartz sand filter 5 by the filter inlet pump 22 for further filtration to remove impurities from the water;

[0050] 4) The filtered wastewater enters the intermediate water tank 6, and is then sent to the mixer 7 by the tower pump 23; the liquid alkali pump 24 sends 30-35 wt% liquid alkali from the liquid alkali storage tank 8 into the mixer 7; the wastewater and liquid alkali are mixed to form a mixed waste liquid, and the pH value rises to 11-13 after mixing; the liquid alkali is NaOH solution.

[0051] 5) The mixed waste liquid enters the cold water pipeline of the No. 1 plate heat exchanger 10 for heat exchange and temperature rise, and then enters the interior of the deammoniation tower 9 from the water inlet of the deammoniation tower 9 for ammonia nitrogen removal.

[0052] The ammonia nitrogen removal process is as follows: High-pH ammonia nitrogen-containing wastewater enters from the top of the deammoniation tower 9 and gradually flows downward along the multi-stage tower plates. The gas blown out by the stripping blower 25 passes through the gas buffer pack 7 and is blown into the circulating process gas inlet of the deammoniation tower 9, flowing upward through the multi-stage tower plates. Process steam enters the interior of the deammoniation tower 9 from the steam inlet and flows upward to heat the deammoniation tower 9. Under the combined action of process steam heating and strong counter-current airflow stripping, the ammonia nitrogen in the high-pH ammonia nitrogen-containing wastewater is converted into ammonia gas, which overflows from the wastewater and is carried upward by the airflow to the upper absorption section of the deammoniation tower 9. At this time, the overflowing ammonia gas reacts with sulfuric acid or unsaturated ammonium sulfate solution with a concentration of 25% to 30% (vol) from the ammonium sulfate circulation tank 14, which is introduced by the ammonium sulfate circulation pump 28 through the ammonium sulfate inlet at the top of the deammoniation tower 9 and sprayed through the nozzle to generate ammonium sulfate solution.

[0053] 6) The sulfuric acid solution in the ammonium sulfate circulation tank 14 is added by drawing sulfuric acid from the acid outlet of the sulfuric acid storage tank 13 through the sulfuric acid pump 34. When the pH of the ammonium sulfate solution in the ammonium sulfate circulation tank 14 reaches the set value, the first electric valve 31 is closed and the second electric valve 32 is opened, so that the ammonium sulfate solution is transported to the ammonium sulfate concentration tank 16 for storage.

[0054] 7) The ammonium sulfate solution in the ammonium sulfate concentration tank 16 is sent from the outlet to the inlet of the ammonium sulfate evaporator 15 through the ammonium sulfate concentration pump 34. The ammonium sulfate solution is evaporated and concentrated in the ammonium sulfate evaporator 15 by indirect heat exchange with process steam. When the ammonium sulfate concentration does not reach the set concentration, the No. 3 electric valve 36 is opened, and the solution is continuously circulated and concentrated between the evaporator 15 and the ammonium sulfate concentration tank 16 through the ejector 38 until the ammonium sulfate concentrate reaches a qualified concentration of 25% to 30%. Then, the No. 4 electric valve 37 is opened to transport the solution to the ammonium sulfate finished product tank 17. After that, the tanker truck is notified to arrive, and the ammonium sulfate discharge pump 30 is manually opened to transport the qualified ammonium sulfate solution in the ammonium sulfate finished product tank 17 to other processes for use.

[0055] 8) After ammonia nitrogen removal, the wastewater flows from the outlet of the ammonia removal tower 9 through the hot water pipeline of the No. 1 plate heat exchanger 10 to the discharge pH adjustment tank 12. According to the pH value detection in the discharge pH adjustment tank 12, a certain amount of sulfuric acid solution is automatically added. After being fully stirred and mixed by the agitator in the tank, the wastewater from the outlet of the discharge pH adjustment tank 12 is cooled again through the hot water pipeline of the No. 2 plate heat exchanger 11 via the wastewater discharge pump 27, and then becomes qualified discharge wastewater.

[0056] 9) The water vapor evaporated from the ammonium sulfate solution in the ammonium sulfate evaporator 15 is connected to the inlet of the stripping blower 25 through a pipeline from the water vapor outlet at the top of the ammonium sulfate evaporator 15. After mixing with the circulating process gas blown out by the stripping blower 25, it enters the deammoniation tower 9 for recycling. The steam pipeline of the ammonium sulfate evaporator 15 is equipped with a condensate outlet. The condensate is recovered through the pipeline to the turbid circulating water system of the coke oven gas direct reduction plant, realizing the recycling of condensate, increasing water recycling and saving water resources.

[0057] 10) The cold water pipeline of the No. 2 plate heat exchanger 11 is connected to the cold medium water in the clean circulation water pool of the coke oven gas direct reduction plant, and provides heat exchange and cooling for qualified wastewater discharged from the outlet of the pH adjustment tank 12 through the hot water pipeline of the No. 2 plate heat exchanger 11.

[0058] 11) The sludge settled at the bottom of the inclined tube sedimentation tank 2 is pumped out from the sludge discharge port of the inclined tube sedimentation tank 2 by the sludge discharge pump 20 at regular intervals and transported to the sludge filter press 21. The sludge filter press 21 can further dewater and separate the sludge, and the clear liquid and sludge are recycled separately. The clear liquid is recycled into the turbid circulating water system of the coke oven gas direct reduction plant to realize water recycling. Since the sludge contains iron, it can be recycled and used in the sintering or pelletizing process.

[0059] 12) Odor collection pipes are installed above aeration box 1, inclined tube sedimentation tank 2, buffer tank 4, and intermediate tank 6. When ammonium sulfate flows out of ammonium sulfate evaporator 15 through electric valve 36 and passes through ejector 38, a negative pressure is formed in ejector 38. This negative pressure can draw the odor generated in aeration box 1, inclined tube sedimentation tank 2, buffer tank 4, and intermediate tank 6 back to ammonium sulfate concentration tank 16, thereby reducing odor emissions and protecting the environment.

[0060] 13) In this treatment method, the system steam working pressure is 0.3MPa~0.7MPa, the working temperature of the deammoniation tower is 86~98℃, the sulfuric acid concentration is 25%~30vol%, the liquid alkali concentration is 30~35wt%, and the ammonia nitrogen content in the ammonia nitrogen-containing wastewater entering the system is 40~150mg / L.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system, characterized in that: It includes an aeration tank (1), an inclined tube sedimentation tank (2), a dosing device (3), a buffer tank (4), a quartz sand filter (5), an intermediate water tank (6), a mixer (7), a liquid alkali storage tank (8), a deammoniation tower (9), an external discharge pH adjustment tank (12), a sulfuric acid storage tank (13), an ammonium sulfate circulation tank (14), an aeration blower (18), a stripping blower (25), a gas buffer pack (26), an ammonium sulfate circulation pump (28), and a sulfuric acid pump (34); the ammonia nitrogen-containing wastewater pipeline is connected in sequence to the aeration tank (1) and the inclined tube sedimentation tank (2), the overflow outlet of the inclined tube sedimentation tank (2) is connected to the inlet of the buffer tank (4), and the outlet of the buffer tank (4) is connected in sequence to the quartz sand filter (5), the intermediate water tank (6), the mixer (7), the liquid alkali storage tank (8), the deammoniation tower (9), the external discharge pH adjustment tank (12), the sulfuric acid storage tank (13), the ammonium sulfate circulation tank (14), the aeration blower (18), the stripping blower (25), the gas buffer pack (26), the ammonium sulfate circulation pump (28), and the sulfuric acid pump (34); the ammonia nitrogen-containing wastewater pipeline is connected in sequence to the aeration tank (1) and the inclined tube sedimentation tank (2), the overflow outlet of the inclined tube sedimentation tank (2) is connected to the inlet of the buffer tank (4), and the outlet of the buffer tank (4) is connected in sequence to the quartz sand filter (5), the intermediate water tank (6), the mixer (9), the liquid alkali storage tank (12), the deammoniation tower (23), the liquid alkali storage tank (24), the liquid alkali storage tank (25), the gas buffer pack (26), the ammonium sulfate circulation pump (28), and the sulfuric acid pump (34); the ammonia 7) and the deammoniation tower (9); the aeration blower (18) is connected to the air inlet of the aeration box (1), the dosing device (3) is connected to the dosing port of the inclined tube sedimentation tank (2), and the liquid alkali storage tank (8) is connected to the alkali inlet of the mixer (7); the stripping blower (25) and the gas buffer pack (26) are connected between the circulating process gas outlet and the circulating process gas inlet of the deammoniation tower (9); the ammonium sulfate circulation tank (14) and the ammonium sulfate circulation pump (28) are connected between the ammonium sulfate outlet and the ammonium sulfate inlet of the deammoniation tower (9); the outlet of the deammoniation tower (9) is connected to the discharge pH adjustment tank (12); the sulfuric acid storage tank (13) is connected to the ammonium sulfate circulation tank (14) and the discharge pH adjustment tank (12) respectively through the sulfuric acid pump (34); It also includes an ammonium sulfate evaporator (15), an ammonium sulfate concentration tank (16), an ammonium sulfate finished product tank (17), an ammonium sulfate concentration pump (29), and an ejector (38); the inlet of the ammonium sulfate concentration tank (16) is connected to the outlet of the ammonium sulfate circulation pump (28), and valves are provided between the outlet of the ammonium sulfate circulation pump (28) and the deammonium sulfate desulfurization tower (9) and the ammonium sulfate concentration tank (16); the outlet of the ammonium sulfate concentration tank (16) is connected to the inlet of the ammonium sulfate evaporator (15) through the ammonium sulfate concentration pump (29), and the outlet of the ammonium sulfate evaporator (15) is connected to the inlet of the ammonium sulfate concentration tank (16) through the ejector (38); The aeration box (1), inclined tube sedimentation tank (2), buffer tank (4), and intermediate tank (6) are all connected to an odor collection pipe, which is connected to the air inlet of the jet injector (38). It also includes the No. 1 plate heat exchanger (10).

2. The ammonia nitrogen treatment system for wastewater from a coke oven gas direct reduction plant according to claim 1, characterized in that: The steam inlet of the ammonium sulfate evaporator (15) is connected to the process steam pipeline, and the steam outlet of the ammonium sulfate evaporator (15) is connected to the inlet of the blower (25).

3. A coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system according to claim 1 or 2, characterized in that: The cold water pipeline of the No. 1 plate heat exchanger (10) is connected to the pipeline between the outlet of the mixer (7) and the inlet of the deammoniation tower (9); the hot water pipeline of the No. 1 plate heat exchanger (10) is connected to the pipeline between the outlet of the deammoniation tower (9) and the external discharge pH adjustment tank (12).

4. A method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant, employing the treatment system described in any one of claims 1-3, characterized in that, The process includes the following steps: 1) The ammonia-nitrogen-containing wastewater enters the aeration tank (1) for aeration; 2) The aerated wastewater enters the inclined tube sedimentation tank (2) to be mixed, reacted and precipitated with the reagent; 3) The clear liquid in the upper layer of the inclined tube sedimentation tank (2) enters the buffer tank (4) and then enters the quartz sand filter (5) for filtration; 4) The filtered wastewater enters the mixer (7) through the intermediate water tank (6) and mixes with the liquid alkali to form a mixed waste liquid; 5) The mixed waste liquid enters the deammoniation tower (9) and is deammonised by gas stripping through the circulation of ammonium sulfate solution and the addition of sulfuric acid; 6) The wastewater discharged from the deammoniation tower (9) is added with sulfuric acid to adjust the pH before being discharged.

5. The method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant according to claim 4, characterized in that: In step 5), after the ammonium sulfate solution reaches the set concentration, it is concentrated by cyclic evaporation to obtain the finished ammonium sulfate solution.

6. The method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant according to claim 5, characterized in that: During the circulating evaporation and concentration process of the ammonium sulfate solution, the odor generated by the treatment system is carried into the ammonium sulfate concentration tank for absorption by the negative pressure generated by the ejector during the jetting process.

7. The method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant according to claim 5, characterized in that: During the circulating evaporation and concentration process of the ammonium sulfate solution, the steam discharged from the ammonium sulfate evaporator (15) is mixed with the mixed waste liquid and enters the deammonium removal tower (9).

8. A method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant according to any one of claims 4-7, characterized in that: The mixed waste liquid exchanges heat with the wastewater discharged from the deammoniation tower (9) before entering the deammoniation tower (9).

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