Ammonia nitrogen treatment system and method for coke oven gas direct reduction factory wastewater

Abstract

The invention discloses an ammonia nitrogen treatment system and method for coke oven gas direct reduction factory wastewater. Comprising an aeration tank, an inclined tube sedimentation tank, a dosing device, a buffer water tank, a quartz sand filter, a middle water tank, a mixer, a liquid caustic soda storage tank, a deamination tower kettle, a discharged pH regulating tank, a sulfuric acid storage tank, an ammonium sulfate circulating tank, an aeration fan, an air stripping fan, a gas buffer bag, an ammonium sulfate circulating pump and a sulfuric acid pump, an ammonia-nitrogen-containing wastewater pipeline is sequentially communicated with an aeration tank and an inclined tube sedimentation tank, an overflow port of the inclined tube sedimentation tank is communicated with a water inlet of a buffer water tank, and a water outlet of the buffer water tank is sequentially communicated with a quartz sand filter, a middle water tank, a mixer and a deamination tower kettle; the aeration fan is communicated with an air inlet of the aeration box, the dosing device is communicated with a dosing port of the inclined tube sedimentation tank, and the liquid caustic soda storage tank is communicated with a caustic soda inlet of the mixer. After the system and the method are adopted for treatment, the ammonia nitrogen of the effluent stably reaches the standard, the pH value is stable, and the effluent meets the first-level wastewater discharge standard of the national Integrated Wastewater Discharge Standard.

Description

Technical Field

[0001] The invention relates to a wastewater treatment system and method, in particular to a system and method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant. Background Art

[0002] Direct reduction ironmaking technology is a cutting-edge technology for the development of the steel industry. Its final products are iron and water, which reduces CO2 emissions. It is an important direction for reducing energy consumption, improving the structure of steel products, and improving the quality of steel products. It is also an important part of innovation leadership. The conventional method of preparing reduction process gas using natural gas is widely used internationally. For traditional industrial enterprises, renewable energy hydrogen production is an important way. Therefore, the direct reduction technology using coke oven gas as the reduction gas source has broad prospects for gas-based vertical furnace hydrogen metallurgical processes.

[0003] However, unlike the low ammonia nitrogen content produced in the traditional hydrogen metallurgical process using natural gas as the reducing gas, the cooling water wastewater can be directly discharged. In the hydrogen metallurgical process using coke oven gas as the reducing gas, the N2 content in the coke oven gas is about 5% to 6%. In the hydrogen metallurgical process gas cycle, the N2 enrichment reaches more than 15%. In the low temperature zone of the shaft furnace, nitrogen and hydrogen will synthesize ammonia under the appropriate conditions of high temperature, high pressure and catalyst (such as iron catalyst). The chemical equation principle is 3H2+N2→2NH3. After NH3 is formed, due to its soluble nature in water, the process gas will be directly contacted and cooled by the circulating cooling water, and a large amount of ammonia nitrogen will exist in the circulating cooling water system. However, my country's environmental protection requires that the ammonia nitrogen content of the discharged wastewater must be less than 15mg / L. How to efficiently remove ammonia nitrogen from the wastewater and save costs and investment is a problem currently faced by the ammonia nitrogen treatment of wastewater in coke oven gas direct reduction plants.

[0004] The reducing gas from the shaft furnace of the direct reduction plant of coke oven gas is recycled during the production process. The top gas discharged from the top of the shaft furnace after participating in the reduction reaction needs to be washed and purified many times. The water consumption for gas purification is large, and the water also needs to be recycled. After the washing cooling water in the cooling water system is recycled many times, the conductivity, turbidity, total iron, total hardness, chloride ion, ammonia nitrogen and other indicators of the circulating water will exceed the standard. Long-term accumulation will have a negative impact on the water quality, affect the heat transfer efficiency and equipment performance, and cause corrosion of equipment and pipelines. Therefore, the circulating water system needs to regularly discharge the unqualified water in the system and add a certain amount of new water into the system. However, the ammonia nitrogen in the water in the system usually reaches more than 100 mg / L at this time. Direct discharge will cause eutrophication of the water body, destroy the balance of the water ecosystem, and then affect the human living environment and health. In addition, a large amount of ammonia nitrogen in the wastewater cannot be recycled, which also causes a huge waste of resources.

[0005] At present, most of my country's deammonification systems are aimed at high-concentration ammonia nitrogen wastewater. For example, the ammonia nitrogen concentration of fertilizer wastewater is 400-700 mg / L, the ammonia nitrogen concentration of wastewater generated during the production of monosodium glutamate is as high as 5000-6000 mg / L, the concentration of 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 aquaculture wastewater is 800-2200 mg / L.

[0006] Through production practice, it is found that the ammonia nitrogen concentration in the washing cooling water wastewater of the coke oven gas direct reduction plant is usually 40-150 mg / L, which is at a relatively low level. Therefore, it is necessary to design a wastewater ammonia nitrogen treatment system suitable for the coke oven gas direct reduction plant, so that the ammonia nitrogen content of the wastewater can reach the national safety and environmental protection standards while operating economically, and the by-products produced can be recycled to achieve the best economic 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 system for treating ammonia nitrogen in 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] In order to solve the above technical problems, the technical scheme adopted by the system of the present invention is: it includes an aeration box, 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 deammonification tower kettle, an external pH adjustment tank, a sulfuric acid storage tank, an ammonium sulfate circulation tank, an aeration fan, a blow-off fan, a gas buffer bag, an ammonium sulfate circulation pump and a sulfuric acid pump; the ammonia nitrogen-containing wastewater pipeline is connected to the aeration box and the inclined tube sedimentation tank in sequence, the overflow port of the inclined tube sedimentation tank is connected to the water inlet of the buffer water tank, and the water outlet of the buffer water tank is connected to the quartz sand filter, the intermediate water tank, the mixer, the liquid alkali storage tank, the deammonification tower kettle, the external pH adjustment tank, the sulfuric acid storage tank, the ammonium sulfate circulation tank, the aeration fan, the blow-off fan, the gas buffer bag, the ammonium sulfate circulation pump and the sulfuric acid pump in sequence. water tank, mixer and deamination tower kettle; the aeration fan 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 fan and the gas buffer bag are connected between the circulating process gas outlet and the circulating process gas inlet of the deamination tower kettle; the ammonium sulfate circulation tank and the ammonium sulfate circulation pump are connected between the ammonium sulfate outlet and the ammonium sulfate inlet of the deamination tower kettle; the water outlet of the deamination tower kettle is connected to the external pH adjustment tank; the sulfuric acid storage tank is respectively connected to the ammonium sulfate circulation tank and the external pH adjustment tank through the 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 liquid 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 the deammonification tower kettle and the ammonium sulfate concentration tank; the discharge port of the ammonium sulfate concentration tank is connected to the feed port of the ammonium sulfate evaporator through the ammonium sulfate concentration pump, and the discharge port of the ammonium sulfate evaporator is connected to the feed port of the ammonium sulfate concentration tank through the ejector.

[0010] Furthermore, the aeration tank, the inclined tube sedimentation tank, the buffer water tank, and the intermediate water tank are all connected to the odor collection pipe, and the odor collection pipe is connected to the air inlet of the ejector.

[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 fan.

[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 water outlet of the mixer and the water inlet of the deamination tower kettle; the hot water pipeline of the No. 1 plate heat exchanger is connected to the pipeline between the water outlet of the deamination tower kettle and the external pH adjustment tank.

[0013] In order to solve the above technical problems, the method of the present invention adopts the above treatment system, and the technical solution adopted includes the following steps: 1) the ammonia nitrogen-containing wastewater enters an aeration box for aeration; 2) The aerated wastewater enters the inclined tube sedimentation tank to mix, react and precipitate with the reagents; 3) The supernatant liquid of the inclined tube sedimentation tank enters the buffer water tank and then enters the quartz sand filter for filtration; 4) The filtered wastewater enters the mixer through the intermediate water tank and is mixed with liquid alkali to form mixed waste liquid; 5) The mixed waste liquid enters the deamination tower kettle, circulates the ammonium sulfate solution and adds sulfuric acid to perform gas stripping deamination; 6) The wastewater discharged from the deamination tower kettle is discharged after adding sulfuric acid to adjust the pH.

[0014] Furthermore, in step 5), after the ammonium sulfate solution reaches a set concentration, it is concentrated by cyclic evaporation to obtain an ammonium sulfate finished solution.

[0015] Furthermore, during the circulating evaporation and concentration process of the ammonium sulfate solution, the negative pressure generated by the ejector during the ejection process brings the odor generated by the treatment system into the ammonium sulfate concentration tank for absorption.

[0016] 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 deamination tower kettle.

[0017] Furthermore, the mixed waste liquid is heat exchanged with the waste water discharged from the deamination tower kettle before entering the deamination tower kettle.

[0018] The beneficial effects of adopting the above technical solution are: 1. The wastewater ammonia nitrogen treatment system for coke oven gas direct reduction plant of the present invention 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.

[0019] 2. Before treatment with the system and method of the present invention, the ammonia nitrogen content of the wastewater containing ammonia nitrogen was 40-150 mg / L. After treatment with the system and method, the ammonia nitrogen content in the effluent was stable and met the standards, the ammonia nitrogen content dropped to <15 mg / L, and the pH value was stabilized at 7-9, which met the national wastewater discharge standards.

[0020] 3. Compared with other sewage treatment systems, the steam supply is higher because the raw water has been heated by the waste heat discharged from the deamination tower kettle before entering the deamination tower kettle. Therefore, the preheated raw water will greatly reduce the consumption of thermal energy and improve the utilization rate of thermal energy, which means that the consumption of steam will be greatly reduced.

[0021] 4. By designing and using an ejector, the negative pressure generated by the ejector when ammonium sulfate is concentrated is used to bring the odor generated by the system into the ammonium sulfate concentration tank for absorption, thereby avoiding the escape of odor and protecting the environment and the health of on-site operators.

[0022] 5. The system and method of the present invention are provided with a primary sedimentation and mud removal system and a dosing device. The primary sedimentation and mud removal system performs preliminary filtration on the coke oven gas hydrogen metallurgical wastewater, which can reduce the burden of downstream treatment processes (such as filtration, deammoniation, etc.), thereby reducing energy consumption and material consumption. The secondary filtration system further filters impurities that are not easy to precipitate, improves the overall filtration efficiency of the system, reduces the blockage of pipelines and valves, and the precipitated sludge is concentrated in the clarifier, which is convenient for subsequent sludge recovery and disposal, avoids direct sludge discharge, protects the environment, extends the service life of the equipment, and ensures stable operation of the system.

[0023] 6. The system and method of the present invention is designed to neutralize the wastewater that has passed the ammonia nitrogen treatment by adding acid to the external discharge system, and adjust the pH value. At the same time, a stirrer is provided to ensure the neutralization effect of the external discharge wastewater, and to treat the wastewater comprehensively and thoroughly.

[0024] 7. The process gas in the deamination tower kettle of the present invention is recycled through a stripping blower, and the water vapor after the ammonium sulfate is concentrated is also connected to the air inlet of the stripping blower through a pipeline to obtain secondary reuse of the waste heat of steam, thereby further reducing steam consumption, eliminating the impact of exhaust gas on the environment, and saving energy. At the same time, targeted improvements have been made based on the shortcomings of traditional deamination methods. A gas buffer bag is added between the outlet of the stripping blower and the entry into the deamination tower kettle, which can balance the pressure inside and outside the deamination tower, ensure that the gas can maintain a stable and uniform pressure when entering the deamination tower, ensure that the amount of gas entering the deamination tower is stable and continuous, and can provide a certain buffer time in an emergency state, so that the system has enough time to adjust. This stable airflow helps to improve the deamination efficiency.

[0025] 8. The system and method of the present invention respectively set up a cache water tank and an intermediate water tank which can serve as two-level buffer areas, which can balance the impact caused by water volume fluctuations, avoid the decline in treatment effect due to unstable flow, and reduce the impact and damage to downstream equipment.

[0026] 9. The system and method of the present invention are provided with a wastewater aeration link, and aeration regulation can effectively regulate the water quality entering the deammonification system. Through the aeration process, the oxygen concentration in the water is increased, which is conducive to the redox reaction and degrades the organic pollutants (including ammonia-containing substances) in the water into inorganic substances, thereby purifying the water quality.

[0027] 10. The system and method of the present invention recycle the steam condensate produced by the ammonium sulfate evaporator, and after the sludge produced by the inclined tube sedimentation tank is separated from the sludge and water, the sludge and the clear liquid are also designed to be recycled, which can reduce the operating consumption of the system and also reduce the production cost.

[0028] 11. The byproduct ammonium sulfate produced by the ammonia nitrogen removed by the system and method of the present invention can be used in other processes, such as producing fertilizers, etc., thus realizing resource recycling, reducing secondary pollution, and being beneficial to environmental protection.

[0029] 12. The wastewater ammonia nitrogen treatment system proposed by the present invention can be automatically operated, is simple to operate, and is easy to use. Operators can take up their posts after simple training, and do not require complicated operations, while reducing labor costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0031] Figure 1 It is a structural schematic diagram of the present invention.

[0032] In the figure: 1. Aeration tank; 2. Inclined tube sedimentation tank; 3. Dosing device; 4. Buffer water tank; 5. Quartz sand filter; 6. Intermediate water tank; 7. Mixer; 8. Liquid alkali storage tank; 9. Deammoniation tower kettle; 10. Plate heat exchanger No. 1; 11. Plate heat exchanger No. 2; 12. External 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 fan; 19. Dosing pump; 20 , sludge discharge pump; 21. Sludge filter press; 22. Filter water inlet pump; 23. Tower inlet pump; 24. Liquid alkali pump; 25. Blow-off fan; 26. Gas buffer bag; 27. Wastewater effluent pump; 28. Ammonium sulfate circulation pump; 29. ​​Ammonium sulfate concentration pump; 30. Ammonium sulfate effluent pump; 31. No. 1 electric valve; 32. No. 2 electric valve; 33. Sedimentation tank inlet pump; 34. Sulfuric acid pump; 35. Tower kettle outlet pump; 36. No. 3 electric valve; 37. No. 4 electric valve; 38. Ejector. DETAILED DESCRIPTION

[0033] Figure 1As shown, the wastewater ammonia nitrogen treatment system of the coke oven gas direct reduction plant includes an aeration tank 1, an inclined tube sedimentation tank 2, a dosing device 3, a buffer water tank 4, a quartz sand filter 5, an intermediate water tank 6, a mixer 7, a liquid alkali storage tank 8, a deammonification tower kettle 9, a No. 1 plate heat exchanger 10, a No. 2 plate heat exchanger 11, an external 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 fan 18, dosing pump 19, sludge discharge pump 20, sludge filter press 21, filter water inlet pump 22, tower inlet pump 23, liquid alkali pump 24, stripping fan 25, gas buffer bag 26, wastewater efflux pump 27, ammonium sulfate circulation pump 28, ammonium sulfate concentration pump 29, ammonium sulfate efflux pump 30, No. 1 electric valve 31, No. 2 electric valve 32, sedimentation tank inlet pump 33, sulfuric acid pump 34, tower bottom outlet pump 35, No. 3 electric valve 36, No. 4 electric valve 37 and ejector 38. The water inlet of the aeration box 1 is connected to the ammonia nitrogen-containing wastewater pipeline, and the water outlet is connected to the water inlet of the inclined tube sedimentation tank 2 through the sedimentation tank water inlet pump 33. The air inlet at the bottom of the aeration box 1 is connected to the outlet of the aeration fan 18; the aeration box 1 is provided with a liquid level gauge and is interlocked with the sedimentation tank water inlet pump 33. When the liquid level of the aeration box 1 is high, the sedimentation tank water inlet pump 33 starts, and when the liquid level of the aeration box 1 is low, the sedimentation tank water inlet pump 33 stops running. The bottom of the inclined tube sedimentation tank 2 is provided with a mud discharge port, which is connected to the mud filter press 21 through the mud discharge pump 20; the dosing device 3 is connected to the dosing port of the inclined tube sedimentation tank 2 through the dosing pump 19; the inlet of the dosing device 3 is connected to the desalted water pipeline, and the desalted water pipeline can be opened after manual dosing to add the agent and add water. A stirring device is provided inside the dosing device 3 to stir the agent evenly. The overflow port of the inclined tube sedimentation tank 2 is connected to the water inlet of the buffer water tank 4, and the water outlet of the buffer water tank 4 is connected to the water inlet of the quartz sand filter 5 through the filter inlet pump 22. The water outlet of the quartz sand filter 5 is connected to the water inlet of the intermediate water tank 6, and the water outlet of the intermediate water tank 6 is connected to the water inlet of the mixer 7 through the tower pump 23. The buffer water tank 4 is provided with a liquid level meter and the filter inlet pump 22 are interlocked. When the liquid level of the buffer water tank 4 is high, the filter inlet pump 22 starts, and when the liquid level of the buffer water tank 4 is low, the filter inlet pump 22 stops running. The intermediate water tank 6 is provided with a liquid level meter and the tower pump 23 are interlocked. When the liquid level of the intermediate water tank 6 is high, the tower pump 23 starts, and when the liquid level of the intermediate water tank 6 is low, the tower pump 23 stops running. The alkali outlet of the liquid alkali storage tank 8 is connected to the alkali inlet of the mixer 7 through the liquid alkali pump 24, and the alkali inlet of the liquid alkali storage tank 8 is connected to the alkali tank truck through a pipeline. The liquid alkali storage tank 8 is provided with a liquid level meter and is interlocked with the liquid alkali pump 24. When the liquid level of the liquid alkali storage tank 8 is high, the liquid alkali pump 24 can be started to inject liquid alkali according to the pH value detected in the mixer 7. When the liquid level of 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 in an interlocked manner.

[0034] Figure 1 As shown, in the wastewater ammonia nitrogen treatment system of the coke oven gas direct reduction plant, the liquid outlet of the mixer 7 is connected to the water inlet of the deamination tower kettle 9 through the cold water pipeline of the No. 1 plate heat exchanger 10, and the water outlet of the deamination tower kettle 9 is connected to the water inlet of the external pH adjustment tank 12 through the tower kettle outlet pump 35 through the hot water pipeline of the No. 1 plate heat exchanger 10, and the water outlet of the external pH adjustment tank 12 is connected to the qualified external wastewater pipeline through the wastewater external pump 27 through 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 refrigerant water pipeline of the clean water pool of the coke oven gas direct reduction plant. The circulating process gas outlet at the top of the deamination tower kettle 9 is connected to the inlet of the blow-off fan 25, the outlet of the blow-off fan 25 is connected to the inlet of the gas buffer bag 26, and the outlet of the gas buffer bag 26 is connected to the circulating process gas inlet in the middle of the deamination tower kettle 9; in this way, the circulating process gas in the deamination tower kettle 9 flows from bottom to top, and the circulating process gas is connected to the inlet of the blow-off fan 25 from the top outlet of the deamination tower kettle 9 through a pipeline, and the cycle is repeated.

[0035] Figure 1 As shown, in the present coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system, the ammonium sulfate outlet of the deamination tower kettle 9 is connected to the liquid inlet of the ammonium sulfate circulation tank 14, and the liquid outlet of the ammonium sulfate circulation tank 14 is respectively connected to the ammonium sulfate inlet of the deamination tower kettle 9 and the liquid inlet of the ammonium sulfate concentration tank 16 through the ammonium sulfate circulation pump 28; the pipeline between the ammonium sulfate circulation pump 28 and the ammonium sulfate inlet of the deamination tower kettle 9 is provided with a No. 1 electric valve 31, and the pipeline between the ammonium sulfate circulation pump 28 and the liquid inlet of the ammonium sulfate concentration tank 16 is provided with a No. 2 electric valve 32; the acid outlet of the sulfuric acid storage tank 13 is respectively connected to the acid inlet of the ammonium sulfate circulation tank 14 and the acid inlet of the external pH adjustment tank 12 through the sulfuric acid pump 34, and the acid inlet of the sulfuric acid storage tank 13 is connected to the acid tank truck through a pipeline. The steam inlet of the deamination tower kettle 9 is connected to the process steam pipeline. The ammonium sulfate circulation tank 14 is provided with a level meter and is interlocked with the ammonium sulfate circulation pump 28. When the liquid level of the ammonium sulfate circulation tank 14 is high, the ammonium sulfate circulation pump 28 starts, and when the liquid level of the ammonium sulfate circulation tank 14 is low, the ammonium sulfate circulation pump 28 stops running. The external pH adjustment tank 12 is provided with a level meter and is interlocked with the wastewater external discharge pump 27. When the liquid level of the external pH adjustment tank 12 is high, the wastewater external discharge pump 27 starts, and when the liquid level of the pH adjustment tank 12 is low, the wastewater external discharge pump 27 stops running; at the same time, a stirring device is provided on the top of the external pH adjustment tank 12 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 to 9. The sulfuric acid storage tank 13 is provided with a liquid level meter and is interlocked with the sulfuric acid pump 34. When the liquid level of the sulfuric acid storage tank 13 is high, the sulfuric acid pump 34 can be started, and sulfuric acid is injected according to the liquid level in the ammonium sulfate circulation tank 14 or the pH value detection situation. When the liquid level of the sulfuric acid 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 in an interlocked manner.

[0036] Figure 1 As shown, in the present coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system, the discharge port of the ammonium sulfate concentration tank 16 is connected to the feed port of the ammonium sulfate evaporator 15 through the ammonium sulfate concentration pump 29, and the discharge port of the ammonium sulfate evaporator 15 is connected to the feed port of the ammonium sulfate concentration tank 16 through the ejector 38, and the pipeline between the discharge port of the ammonium sulfate evaporator 15 and the ejector 38 is provided with a No. 3 electric valve 36. The discharge port of the ammonium sulfate evaporator 15 is also connected to the inlet of the ammonium sulfate finished product tank 17, and the pipeline between the discharge port of the ammonium sulfate evaporator 15 and the inlet of the ammonium sulfate finished product tank 17 is provided with a No. 4 electric valve 37. The outlet of the ammonium sulfate finished product tank 17 is connected to the tank truck through the ammonium sulfate effluent 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 fan 25. The ammonium sulfate concentration tank 16 is provided with a liquid level meter and is interlocked with the ammonium sulfate concentration tank 16. When the liquid level of the ammonium sulfate concentration tank 16 is high, the ammonium sulfate concentration tank 16 starts, and when the liquid level of the ammonium sulfate concentration tank 16 is low, the ammonium sulfate concentration tank 16 stops running. The ammonium sulfate evaporator 15 is provided with a condensed water outlet for condensed water recovery. The ammonium sulfate finished product tank 17 is provided with a liquid level meter. When the liquid level of the ammonium sulfate finished product tank 17 exceeds the warning liquid level, the system automatically alarms, and after the tank truck is in place, the ammonium sulfate effluent pump is manually opened to discharge the ammonium sulfate finished product liquid.

[0037] Figure 1 As shown, in the present coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system, the No. 1 electric valve 31 and the No. 2 electric valve 32 are interlocked with each other, when the No. 1 electric valve 31 is opened, the No. 2 electric valve 32 is closed, and when the No. 1 electric valve 31 is closed, the No. 2 electric valve 32 is opened. The No. 3 electric valve 36 and the No. 4 electric valve 37 are interlocked with each other, when the No. 3 electric valve 36 is opened, the No. 4 electric valve 37 is closed, and when the No. 3 electric valve 36 is closed, the No. 4 electric valve 37 is opened.

[0038] Figure 1 As shown, in the wastewater ammonia nitrogen treatment system of the coke oven gas direct reduction plant, the dosing pump 19, sludge discharge pump 20, filter water inlet pump 22, tower inlet pump 23, liquid alkali pump 24, blow-off fan 25, gas buffer bag 26, wastewater efflux pump 27, ammonium sulfate circulation pump 28, ammonium sulfate concentration pump 29, ammonium sulfate efflux pump 30, sedimentation tank water inlet pump 33, sulfuric acid pump 34, tower bottom water outlet pump 35 are all equipped with two sets, sharing the inlet and outlet water pipelines, one for backup and one for use during operation. After a pump is damaged and shut down, the system issues an alarm, and the standby pump automatically starts to ensure the normal operation of the system as a whole. The outlet pipelines of all pumps are equipped with check valves to prevent the backflow of related materials.

[0039] Figure 1As shown, in the present coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system, the aeration fan and the blow-off fan are both centrifugal compressors, wherein the blow-off fan is equipped with a matching frequency converter for adjustment, and the speed and air volume can be adjusted by observing the blow-off situation in the deamination tower kettle 9.

[0040] The technical principle adopted by the method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant is: Ammonia nitrogen refers to the free ammonia (NH3) and ammonium ions (NH4 + ) in the form of nitrogen. The reaction principle of this treatment method is that ammonium salt and sodium hydroxide react under heating conditions to generate ammonia gas. The ionic equation of the reaction is: NH4 + +OH - NH3↑+H2O NH3·H2O, H2SO4+2NH3·H2O=(NH4)2SO4+2H2O, after adding sodium hydroxide, it dissolves and produces a large amount of OH - , which will promote the equilibrium to move 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 is conducive to the volatilization of ammonia and overflow from the ammonia nitrogen-containing wastewater. The volatilized ammonia reacts with sulfuric acid to form ammonium sulfate.

[0041] Figure 1 As shown, the method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant comprises the following steps: 1) The ammonia nitrogen-containing wastewater enters the aeration box 1 and is aerated by compressed air blown by the aeration fan 18 in the aeration box 1; the ammonia nitrogen concentration in the ammonia nitrogen-containing wastewater is 40-150 mg / L; 2) The aerated wastewater is pumped out from the outlet of the aeration tank 1 by the sedimentation tank inlet pump 33 and transported to the inclined tube sedimentation tank 2. The dosing pump 19 adds the reagent in the dosing device 3, and the wastewater and the reagent are mixed and reacted, and then precipitated; the types of the reagents are coagulants and flocculants; 3) The supernatant in the inclined tube sedimentation tank 2 overflows into the buffer water tank 4, and is then transported to the quartz sand filter 5 through the filter inlet pump 22 to further filter and remove impurities in the water; 4) The filtered wastewater enters the intermediate water tank 6, and then is sent to the mixer 7 through the tower inlet pump 23; the liquid alkali pump 24 sends the 30-35wt% liquid alkali in the liquid alkali storage tank 8 into the mixer 7; the wastewater and the liquid alkali are mixed to form a mixed waste liquid, and the pH value is increased to 11-13 after mixing; the liquid alkali is a NaOH solution; 5) The mixed waste liquid enters the cold water pipeline of the first plate heat exchanger 10 for heat exchange and temperature rise, and then enters the deamination tower kettle 9 from the water inlet to the interior of the deamination tower kettle 9 for ammonia nitrogen removal.

[0042] The ammonia nitrogen removal process is as follows: high pH ammonia nitrogen-containing wastewater enters from the upper part of the deamination tower kettle 9 and gradually flows downward along the multi-stage tower plate; the gas blown out by the stripping fan 25 passes through the gas buffer bag 7 and then blown into the circulating process gas inlet of the deamination tower kettle 9 and flows upward through the multi-stage tower plate; the process steam enters from the steam inlet of the deamination tower kettle 9 into the interior of the deamination tower kettle 9 and flows upward to heat the deamination tower kettle 9; under the combined action of process steam heating and strong reverse airflow stripping, the ammonia nitrogen substance in the high pH ammonia nitrogen-containing wastewater is converted into ammonia gas and overflows from the wastewater and is carried upward with the airflow to the upper absorption section of the deamination tower kettle 9; at this time, the overflowing ammonia gas reacts with 25% to 30% (vol) sulfuric acid or unsaturated ammonium sulfate solution in the ammonium sulfate circulation tank 14 through the ammonium sulfate inlet at the upper part of the deamination tower kettle 9 via the ammonium sulfate circulation pump 28 and then enters through the nozzle for spraying to generate ammonium sulfate solution.

[0043] 6) The sulfuric acid solution in the ammonium sulfate circulation tank 14 is added by extracting 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 No. 1 electric valve 31 is closed and the No. 2 electric valve 32 is opened, and the ammonium sulfate solution is transported to the ammonium sulfate concentration tank 16 for storage.

[0044] 7) The ammonium sulfate solution in the ammonium sulfate concentration tank 16 is fed from the discharge port to the feed port 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 contact with the process steam for heat exchange and temperature rise. When the ammonium sulfate concentration does not reach the set concentration, the No. 3 electric valve 36 is opened, and the ammonium sulfate 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 product with a concentration of 25% to 30%. The No. 4 electric valve 37 is opened to transport it to the ammonium sulfate finished product tank 17, and then the tank truck is notified to arrive, and the ammonium sulfate effluent 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.

[0045] 8) The wastewater after the removal of ammonia nitrogen flows from the outlet of the deammonification tower kettle 9 through the hot water pipeline of the No. 1 plate heat exchanger 10 to the external discharge pH adjustment tank 12 after heat exchange and cooling. According to the pH value detection in the external discharge pH adjustment tank 12, a certain amount of sulfuric acid solution is automatically added. After being fully stirred and mixed by the mixer in the tank, the outlet of the external discharge pH adjustment tank 12 passes through the wastewater external discharge pump 27 and the hot water pipeline of the No. 2 plate heat exchanger 11 to cool down again to become a qualified external discharge wastewater discharge system.

[0046] 9) The water vapor evaporated from the ammonium sulfate solution in the ammonium sulfate evaporator 15 is connected to the inlet of the blow-off fan 25 through a pipeline from the water vapor outlet at the upper part of the ammonium sulfate evaporator 15, and is mixed with the circulating process gas blown out by the blow-off fan 25 and then enters the deamination tower kettle 9 for recycling. The steam pipeline of the ammonium sulfate evaporator 15 is provided with a condensed water outlet, and the condensed water is recovered to the turbid circulating water system of the coke oven gas direct reduction plant through the pipeline, so as to realize the recycling of condensed water, increase the recycling of water, and save water resources.

[0047] 10) The cold water pipeline of the No. 2 plate heat exchanger 11 is connected to the clean circulating water pool refrigerant water of the coke oven gas direct reduction plant, providing heat exchange and cooling for the qualified external wastewater discharged from the outlet of the external pH adjustment tank 12 through the hot water pipeline of the No. 2 plate heat exchanger 11.

[0048] 11) The sludge precipitated in the lower part of the inclined tube sedimentation tank 2 is pumped out from the sludge discharge port of the inclined tube sedimentation tank 2 and transported to the sludge filter press 21 by the sludge discharge pump 20 started at a fixed time. The sludge filter press 21 can further dehydrate and separate the sludge, and the clear liquid and the sludge are recovered separately. The clear liquid is recovered to the turbid circulating water system of the coke oven gas direct reduction plant to achieve water recycling. Since the sludge contains iron, it can be recycled and used in the sintering or pelletizing process.

[0049] 12) Through the odor collecting pipes arranged above the aeration tank 1, the inclined tube sedimentation tank 2, the buffer water tank 4, and the intermediate water tank 6, when the ammonium sulfate flows out from the ammonium sulfate evaporator 15 through the No. 3 electric valve 36 and passes through the ejector 38, a negative pressure will be formed in the ejector 38, and the odor generated in the aeration tank 1, the inclined tube sedimentation tank 2, the buffer water tank 4 and the intermediate water tank 6 can be pumped back into the ammonium sulfate concentration tank 16, thereby reducing the emission of odor and protecting the environment.

[0050] 13) In this treatment method, the system steam working pressure is 0.3MPa~0.7MPa, the deamination tower kettle working temperature 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 wastewater entering the system is 40~150mg / L.

[0051] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system, characterized by: The invention comprises an aeration tank (1), an inclined tube sedimentation tank (2), a dosing device (3), a buffer water tank (4), a quartz sand filter (5), an intermediate water tank (6), a mixer (7), a liquid alkali storage tank (8), a deammoniation tower kettle (9), an external pH adjustment tank (12), a sulfuric acid storage tank (13), an ammonium sulfate circulation tank (14), an aeration fan (18), a blow-off fan (25), a gas buffer bag (26), an ammonium sulfate circulation pump (28) and a sulfuric acid pump (34); a pipeline for wastewater containing ammonia nitrogen is connected to the aeration tank (1) and the inclined tube sedimentation tank (2) in sequence, an overflow port of the inclined tube sedimentation tank (2) is connected to a water inlet of the buffer water tank (4), and a water outlet of the buffer water tank (4) is connected to the quartz sand filter (5), the intermediate water tank (6), the mixer ( 7) and the deamination tower kettle (9); the aeration fan (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 fan (25) and the gas buffer bag (26) are connected between the circulating process gas outlet and the circulating process gas inlet of the deamination tower kettle (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 deamination tower kettle (9); the water outlet of the deamination tower kettle (9) is connected to the external pH adjustment tank (12); the sulfuric acid storage tank (13) is respectively connected to the ammonium sulfate circulation tank (14) and the external pH adjustment tank (12) through the sulfuric acid pump (34).

2. A coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system according to claim 1, characterized in that: The invention also comprises 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 liquid 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), the deammonification tower kettle (9), and the ammonium sulfate concentration tank (16); the discharge port of the ammonium sulfate concentration tank (16) is connected to the feed port of the ammonium sulfate evaporator (15) through the ammonium sulfate concentration pump (29), and the discharge port of the ammonium sulfate evaporator (15) is connected to the feed port of the ammonium sulfate concentration tank (16) through the ejector (38).

3. A coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system according to claim 2, characterized in that: The aeration tank (1), the inclined tube sedimentation tank (2), the buffer water tank (4), and the intermediate water tank (6) are all connected to an odor collection pipe at their tops, and the odor collection pipe is connected to an air inlet of the ejector (38).

4. A coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system according to claim 2, 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 stripping fan (25).

5. A coke oven gas direct reduction plant wastewater ammonia nitrogen treatment system according to any one of claims 1 to 4, characterized in that: It also includes a No. 1 plate heat exchanger (10); the cold water pipeline of the No. 1 plate heat exchanger (10) is connected to the pipeline between the water outlet of the mixer (7) and the water inlet of the deamination tower kettle (9); the hot water pipeline of the No. 1 plate heat exchanger (10) is connected to the pipeline between the water outlet of the deamination tower kettle (9) and the external pH adjustment tank (12).

6. A method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant, using the treatment system according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: 1) the ammonia nitrogen-containing wastewater enters an aeration box (1) for aeration; 2) The aerated wastewater enters the inclined tube sedimentation tank (2) to mix, react and precipitate with the reagents; 3) The upper clear liquid of the inclined tube sedimentation tank (2) enters the buffer water 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 is mixed with liquid alkali to form a mixed waste liquid; 5) The mixed waste liquid enters the deamination tower kettle (9) and is circulated with ammonium sulfate solution and sulfuric acid is added to perform gas stripping deamination; 6) The wastewater discharged from the deamination tower kettle (9) is discharged after adding sulfuric acid to adjust the pH.

7. The method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant according to claim 6, characterized in that: In the step 5), after the ammonium sulfate solution reaches a set concentration, it is concentrated by cyclic evaporation to obtain an ammonium sulfate finished solution.

8. The method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant according to claim 7, characterized in that: During the circulating evaporation and concentration process of the ammonium sulfate solution, the odor generated by the treatment system is brought into the ammonium sulfate concentration tank for absorption through the negative pressure generated by the ejector during the ejection process.

9. The method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant according to claim 7, 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 deammoniation tower kettle (9).

10. A method for treating ammonia nitrogen in wastewater from a coke oven gas direct reduction plant according to any one of claims 6 to 9, characterized in that: Before the mixed waste liquid enters the deamination tower kettle (9), heat is exchanged with waste water discharged from the deamination tower kettle (9).

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