Apparatus and method for recovering ammonia from wastewater

Abstract

This invention discloses an apparatus for recovering ammonia from wastewater, comprising: a stripping tower, a steam stripping tower, a first preheater, a second preheater, an air separator, a booster pump, a first condenser, a second condenser, a gas-liquid separator, an ammonia compressor, a liquid ammonia storage tank, and an ammonia water storage tank. This invention also discloses a method for recovering ammonia from wastewater, comprising: ammonia wastewater, after preheating, entering the stripping tower from the top; compressed gas being introduced from the bottom of the stripping tower; the gas phase entering the air separator from the top of the stripping tower, and the liquid phase being liquid ammonia; the gas phase being pressurized and returning to the stripping tower; the liquid phase at the bottom of the stripping tower then entering the steam stripping tower from the top; the gas phase at the top of the steam stripping tower being condensed and entering the gas-liquid separator; the gas phase in the lower part of the steam stripping tower being condensed, with the condensate flowing to the ammonia water storage tank, and the gas phase entering the gas-liquid separator; the gas phase separated by the gas-liquid separator being compressed to obtain liquid ammonia, and the liquid phase separated by the gas-liquid separator being pumped into the ammonia water storage tank. This invention reduces steam energy consumption and saves ammonia recovery costs.

Description

Technical Field

[0001] This invention belongs to the field of ammonia recovery and relates to an apparatus and method for recovering ammonia from wastewater. Background Technology

[0002] In the production process of paraquat, 1-methylpyridine chloride is used as a raw material, cyanide as a catalyst, and liquid ammonia as a solvent for polymerization. The reaction product, after ammonia recovery, water washing, and pressure filtration, enters the oxidation section. The wastewater from the pressure filtration contains a large amount of impurities such as free ammonia and cyanide, with a free ammonia concentration exceeding 250,000 mg / L. If the wastewater is directly acidified, neutralized, or oxidized, on the one hand, a large amount of additional acid is required, increasing treatment costs and wastewater volume; on the other hand, the free ammonia is converted into ammonium salts, increasing the production of waste salts. If a heating and distillation method is used, more than 80% of the free ammonia can be recovered. The free ammonia can then be compressed and reused as a solvent in the polymerization section.

[0003] Patent CN215711819U discloses an ammonia recovery and utilization device for wastewater. Steam is introduced into an ammonia stripping tower, and the wastewater is uniformly heated through a steam distribution pipe, stripping ammonia and some water vapor from the wastewater. The ammonia is condensed in a condenser at the top of the tower, and the condensed ammonia solution is sent to the ammonia treatment process. Wastewater from the bottom of the tower is pumped into a feed preheater to heat the incoming wastewater before being sent to the wastewater treatment process. This patent directly uses steam heating and distillation to recover ammonia from wastewater, resulting in high energy consumption and a low ammonia recovery rate. Furthermore, the ammonia solution recovered from the wastewater needs to be further distilled to obtain liquid ammonia, increasing distillation costs.

[0004] Patent application CN115385360A discloses a low-temperature, low-pressure ammonia recovery process. This process uses negative pressure and ambient temperature evaporation to treat high-concentration ammonia-containing wastewater, reducing the ammonia concentration in the wastewater to 15 mg / L. The recovered ammonia water can be reused in production. The entire process is simple to operate and does not generate secondary pollution. However, during the negative pressure extraction of ammonia-containing wastewater using a vacuum pump, a large amount of ammonia is pumped away, resulting in ammonia loss. Summary of the Invention

[0005] The purpose of this invention is to address the problems of high energy consumption, large losses, and low efficiency in recovering ammonia from ammonia-containing wastewater, and to propose a device for recovering ammonia from wastewater. Based on this device, ammonia recovery can effectively reduce energy consumption, save production costs, and is suitable for industrial applications.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] An apparatus for recovering ammonia from wastewater includes: a stripping tower 3, a stripping tower 7, a first preheater 1, a second preheater 6, an air separator 4, a booster pump 5, a first condenser 8, a second condenser 9, a gas-liquid separator 10, an ammonia compressor 12, a liquid ammonia storage tank 13, and an ammonia water storage tank 11.

[0008] The stripping tower 3 has a liquid inlet at its upper part, which is connected to the first preheater 1. High-concentration ammonia wastewater is preheated by the first preheater 1 before entering the stripping tower 3. The stripping tower 3 has an air inlet at its lower part, through which compressed gas is introduced to strip the ammonia wastewater within the tower. The stripping tower 3 has an air outlet at its top, which is connected to the air inlet of an air separator 4. The air outlet of the air separator 4 is connected to the air inlet of the stripping tower 3 via a booster pump 5. The liquid outlet of the air separator 4 is connected to a liquid ammonia storage tank 13. The stripping tower 3 has a liquid outlet at its bottom, which is connected to the feed inlet at the top of the stripping tower 7 via a second preheater 6. The stripping tower 7 has air outlets at its top and lower middle parts, and a gas phase sampling point. The outlet of the stripping tower 7 is connected to the inlet of the first condenser 8, the outlet of the first condenser 8 is connected to the inlet of the gas-liquid separator 10, and the outlet of the first condenser 8 is connected to the stripping tower 7 so that the liquid phase of the first condenser 8 flows back into the stripping tower 7; the gas phase outlet of the stripping tower 7 is connected to the inlet of the second condenser 9, the outlet of the second condenser 9 is connected to the inlet of the gas-liquid separator 10, and the outlet of the second condenser 9 is connected to the ammonia storage tank 11; the bottom outlet of the stripping tower 7 is connected to the wastewater storage tank via the second preheater 6 and the first preheater 1 in sequence; the outlet of the gas-liquid separator 10 is connected to the liquid ammonia storage tank 13 via the ammonia compressor 12, and the outlet of the gas-liquid separator 10 is connected to the ammonia storage tank 11.

[0009] The inlet of the stripping tower 3 is connected to a spraying device, which sprays high-concentration ammonia wastewater downward inside the stripping tower 3; the inlet of the stripping tower 7 is connected to a spraying device, which sprays liquid downward inside the stripping tower 7.

[0010] Both the stripping tower 3 and the stripping tower 7 are packed towers. The packing material is selected from one or a combination of Raschig rings, polypropylene Pall rings, and polypropylene hollow spheres.

[0011] In the stripping tower 3, the height of the packing layer is 1 / 10 to 1 / 2 of the tower height, preferably 1 / 7 to 1 / 4 of the tower height.

[0012] In the stripping tower 7, the height of the packing layer is 1 / 10 to 1 / 2 of the tower height, preferably 1 / 7 to 1 / 4 of the tower height.

[0013] Demisters are installed at the top of both the stripping tower 3 and the stripping tower 7.

[0014] The air inlet pipe of the stripping tower 3 is equipped with a three-way valve 2. The two air inlets of the three-way valve 2 are respectively connected to the fresh compressed gas feed pipe and the outlet of the booster pump 5; the air outlet of the three-way valve 2 is connected to the air inlet of the stripping tower 3.

[0015] The air separator 4 is equipped with a level gauge and a regulating valve is installed at the outlet of the air separator 4. The level gauge and the regulating valve are interlocked. When the liquid level of the air separator 4 is lower than 10-20% of the volume of the air separator, the regulating valve is closed to prevent the liquid ammonia in the liquid ammonia storage tank 13 from being vaporized and back-suctioned into the booster pump when the liquid level of the air separator is too low or there is no liquid.

[0016] The gas phase outlet is "umbrella-shaped". Specifically, "umbrella-shaped" means that the gas phase outlet opening faces downward and is surrounded by a cover plate. The gas phase outlet is connected to the air inlet of the second condenser 9 through a pipeline. Gas enters the pipeline from the gas phase outlet. The "umbrella-shaped" gas phase outlet can prevent the wastewater sprayed from the top of the stripping tower from contaminating the extracted gas phase.

[0017] The first condenser 8 uses hot water chiller for cooling, and the second condenser 9 uses circulating water for cooling. At the same time, the liquid ammonia in the first condenser 8 and the second condenser 9 are depressurized and the gas phase is extracted. The condensers will cool the material due to the heat absorption of liquid ammonia vaporization.

[0018] The pressure of the booster pump 5 is interlocked with the pressure of the compressed gas. When the outlet pressure of the booster pump 5 is greater than or equal to the inlet pressure of the compressed gas, the booster pump stops working; when the outlet pressure of the booster pump 5 is less than the inlet pressure of the compressed gas, the booster pump starts.

[0019] The gas-liquid separator 10 is a gas-liquid cyclone separator, and the feed inlet of the gas-liquid separator 10 is located in the lower middle part.

[0020] Another object of the present invention is to provide a method for recovering ammonia from wastewater, comprising: high-concentration ammonia wastewater being preheated by a first preheater 1 and then entering a stripping tower 3 from the top; simultaneously, compressed gas is introduced from the bottom of the stripping tower 3 to strip the high-concentration ammonia wastewater; the gas phase enters an air separator 4 from the top of the stripping tower 3; the liquid phase separated by the air separator 4 is liquid ammonia, which enters a liquid ammonia storage tank 13; the separated gas phase is pressurized by a booster pump 5 and returned to the stripping tower 3 for circulating stripping; the liquid phase at the bottom of the stripping tower 3 is preheated by a second preheater 6 and then enters a stripping tower 7 from the top for stripping; stripping... The gas phase at the top of tower 7 is condensed by the first condenser 8, and the condensate is returned to stripping tower 7. The gas phase then enters the gas-liquid separator 10 for separation. The gas phase in the lower part of stripping tower 7 enters the second condenser 9 through the gas phase outlet for condensation. The condensate flows to the ammonia storage tank 11, and the gas phase then enters the gas-liquid separator 10 for separation. The gas phase separated by the gas-liquid separator 10 is compressed by the ammonia compressor 12 to obtain liquid ammonia, which then enters the liquid ammonia storage tank 13. The liquid phase separated by the gas-liquid separator 10 is pumped into the ammonia storage tank 11. The liquid phase at the bottom of stripping tower 7 enters the second preheater 6 and the first preheater 1 in sequence for waste heat recovery and utilization, and then is discharged to the wastewater storage tank.

[0021] The concentration of free ammonia in the high-concentration ammonia wastewater is 250,000 to 400,000 mg / L.

[0022] The high-concentration ammonia wastewater is preheated to 30-60°C, preferably to 30-50°C, by the first preheater 1 before entering the stripping tower 3.

[0023] The compressed gas entering the stripping tower is one of the non-condensable gases such as air, nitrogen, and inert gas, preferably nitrogen; the pressure of the compressed gas is 0.5 to 0.8 MPa, and the gas phase separated by the air separator is pressurized to the same pressure as the fresh compressed gas and returned to the stripping tower for stripping.

[0024] In stripping tower 3, the gas-liquid ratio is 100:1 to 3000:1, preferably 500:1 to 1000:1. The pressure (gauge pressure) inside stripping tower 3 is a slightly positive pressure of about 40 kPa.

[0025] The temperature inside the stripping tower 3 is 10–50°C, preferably 20–40°C. Steam and / or condensate are used to insulate the stripping tower.

[0026] The residence time of the high-concentration ammonia wastewater in the stripping tower 3 is 1 to 6 hours, preferably 2 to 3 hours.

[0027] The liquid phase at the bottom of the stripping tower 3 is preheated to 50-80°C, preferably to 60-70°C, by the second preheater 6 before entering the stripping tower 7.

[0028] The bottom temperature of the stripping tower 7 is 100-120℃, preferably 105-115℃; the top temperature of the stripping tower 7 is 20-60℃, preferably 30-40℃.

[0029] After the liquid phase at the bottom of stripping tower 3 enters stripping tower 7, the residence time in stripping tower 7 is 1 to 6 hours, preferably 2 to 3 hours.

[0030] The beneficial effects of this invention are:

[0031] (1) The present invention uses a stripping tower and a steam stripping tower in combination to recover ammonia from high-concentration ammonia-containing wastewater, to obtain liquid ammonia and a portion of ammonia water, thereby reducing steam energy consumption and saving ammonia recovery costs.

[0032] (2) The gas at the top of the stripping tower is not discharged, but is directly pressurized and reused in the stripping tower to avoid venting waste gas and polluting the atmosphere.

[0033] (3) The liquid discharged from the bottom of the stripping tower is preheated by the second preheater and the first preheater respectively, so as to make full use of the waste heat of the material.

[0034] (4) The first condenser is cooled by hot water ice machine, the second condenser is cooled by circulating water, and liquid ammonia vaporization is used to assist in cooling the material in the condenser.

[0035] (5) Use a gas-liquid separator to remove the water entrained in liquid ammonia and improve the purity of liquid ammonia;

[0036] (6) A first condenser is installed at the top of the stripping tower. The gas phase at the top of the tower enters the first condenser and is condensed. The condensate is returned to the stripping tower to purify and cool the gas phase at the top of the tower, thereby improving the purity of the gas phase at the top of the stripping tower. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a device for recovering ammonia from wastewater.

[0038] Figure 1 In the middle, 1-first preheater, 2-three-way valve, 3-stripping tower, 4-air separator, 5-booster pump, 6-second preheater, 7-stripping tower, 8-first condenser, 9-second condenser, 10-gas-liquid separator, 11-ammonia water storage tank, 12-ammonia compressor, 13-liquid ammonia storage tank. Detailed Implementation

[0039] Example 1

[0040] like Figure 1As shown, an apparatus for recovering ammonia from wastewater includes: a stripping tower 3, a stripping tower 7, a first preheater 1, a second preheater 6, a three-way valve 2, an air separator 4, a booster pump 5, a first condenser 8, a second condenser 9, a gas-liquid separator 10, an ammonia compressor 12, a liquid ammonia storage tank 13, and an ammonia water storage tank 11.

[0041] The stripping tower 3 has a liquid inlet at its upper part, which is connected to the first preheater 1. High-concentration ammonia wastewater is preheated by the first preheater 1 and then enters the stripping tower 3. The liquid inlet of the stripping tower 3 is connected to a spray device, which sprays the high-concentration ammonia wastewater downwards inside the stripping tower. The stripping tower 3 has an air inlet at its lower part, which is connected to the air outlet of a three-way valve 3. The two air inlets of the three-way valve 3 are respectively connected to a fresh compressed gas feed pipeline and the outlet of a booster pump 5. Compressed gas is introduced into the stripping tower 3 through the air inlet, and the ammonia wastewater is treated within the stripping tower 3. The stripping tower 3 is equipped with an outlet at its top, which is connected to the inlet of an air separator 4. The outlet of the air separator 4 is connected to the inlet of the stripping tower 3 via a booster pump 5. The gas phase separated by the air separator is pressurized by the booster pump 5 to the same pressure as the fresh compressed gas and returned to the stripping tower for stripping. The liquid outlet of the air separator 4 is connected to a liquid ammonia storage tank 13. The bottom of the stripping tower 3 is equipped with a liquid outlet, which is connected to the feed inlet at the top of the stripping tower 7 via a second preheater 6. The inlet of stripper 7 is connected to a spraying device to spray liquid downwards inside the stripping tower. The stripping tower 7 has an outlet at its top, a lower middle section, and an "umbrella-shaped" gas phase collection outlet. The outlet of stripping tower 7 is connected to the inlet of the first condenser 8, the outlet of the first condenser 8 is connected to the inlet of the lower middle section of the gas-liquid separator 10, the outlet of the first condenser 8 is connected to stripping tower 7 to allow the liquid phase from the first condenser 8 to flow back into the stripping tower, and the gas phase collection outlet of stripping tower 7 is connected to the inlet of the second condenser 9. The outlet of the gas separator 10 is connected to the feed inlet at the lower part of the gas-liquid separator 10, and the outlet of the second condenser 9 is connected to the ammonia storage tank 11; the bottom outlet of the stripping tower 7 is connected to the heating medium inlet of the second preheater 6, the heating medium outlet of the second preheater 6 is connected to the heating medium inlet of the first preheater 1, and the heating medium outlet of the first preheater 1 is connected to the wastewater storage tank; the outlet of the gas-liquid separator 10 is connected to the liquid ammonia storage tank 13 via the ammonia compressor 12, and the outlet of the gas-liquid separator 10 is connected to the ammonia storage tank 11.

[0042] Both the stripping tower 3 and the stripping tower 7 are packed towers, and the packing material is Raschig rings.

[0043] In the stripping tower 3, the height of the packing layer is 1 / 6 of the tower height. In the stripping tower 7, the height of the packing layer is 1 / 6 of the tower height.

[0044] Demisters are installed at the top of both the stripping tower 3 and the stripping tower 7.

[0045] The air separator 4 is equipped with a level gauge and a regulating valve is installed at the outlet of the air separator 4. The level gauge and the regulating valve are interlocked. When the liquid level of the air separator 4 is lower than 15%, the regulating valve is closed.

[0046] The stripping tower 7 is provided with an "umbrella-shaped" gas phase extraction outlet in the middle and lower part to prevent wastewater from contaminating the extracted gas phase.

[0047] The first condenser 8 uses hot water chiller for cooling, and the second condenser 9 uses circulating water for cooling. At the same time, the liquid ammonia in the first condenser 8 and the second condenser 9 are depressurized and the gas phase is extracted. The condenser will assist in cooling the material inside the condenser due to the heat absorption of liquid ammonia vaporization.

[0048] The pressure of the booster pump 5 is interlocked with the pressure of the compressed gas. When the outlet pressure of the booster pump 5 is greater than or equal to the inlet pressure of the compressed gas, the booster pump stops working; when the outlet pressure of the booster pump 5 is lower than the inlet pressure of the compressed gas, the booster pump starts.

[0049] The gas-liquid separator 10 is a gas-liquid cyclone separator.

[0050] Based on the ammonia recovery device from wastewater described in this embodiment, the method for recovering ammonia from the wastewater of the paraquat synthesis filter press section is as follows:

[0051] Wastewater from the paraquat synthesis and filter press process (free ammonia concentration 284,000 mg / L) is preheated to 30°C in the first preheater 1 and then discharged at a flow rate of 3 m / s. 3 / h is pumped into stripping tower 3 from the top, while nitrogen gas is compressed (flow rate 1500m³ / h). 3 The high-concentration ammonia wastewater enters the stripping tower from the bottom at a pressure of 0.5 MPa per hour. Compressed nitrogen gas is used to strip the wastewater. The temperature inside the stripping tower is 20-30°C, and the pressure (gauge pressure) is a slightly positive pressure of about 40 kPa. The residence time of the wastewater in the stripping tower is 2 hours. The gas phase enters the air separator 4 from the top of the stripping tower. The separated liquid phase enters the liquid ammonia storage tank 13. The separated gas phase is pressurized to 0.5 MPa by the booster pump 4 and returned to the stripping tower for recycling.

[0052] Wastewater discharged from the bottom of stripping tower 3 is heated to 60°C by the second preheater 6 and then enters the stripping tower 7 from the top for stripping. The temperature at the bottom of the stripping tower is 110°C, and the temperature at the top of the stripping tower is 35°C. The wastewater stays in the stripping tower for 2 hours. The gas phase at the top of the stripping tower is condensed to 10-15°C by the first condenser 8. The liquid phase in the first condenser 8 is refluxed into the stripping tower, and the gas phase enters the gas-liquid cyclone separator 10 for gas-liquid separation. The gas phase in the lower part of the stripping tower enters the second condenser through the gas phase outlet. The liquid phase is stored in ammonia storage tank 11, and the gas phase enters a gas-liquid cyclone separator for gas-liquid separation. The gas phase separated by the gas-liquid cyclone separator is compressed by ammonia compressor 12 and enters liquid ammonia storage tank 13. The separated liquid phase is pumped into ammonia storage tank 11. The wastewater at the bottom of the stripping tower enters the second preheater 6 and the first preheater 5 in sequence for waste heat recovery and utilization. The liquid to be entered into stripping tower 7 and the wastewater to be entered into stripping tower 3 are preheated respectively, and then discharged to wastewater storage tank.

[0053] A sample was taken from the wastewater outlet pipe of the first preheater 1, and the free ammonia concentration in the wastewater (i.e., the wastewater from the bottom of the stripping tower 7 after waste heat recovery) was found to be 53,000 mg / L. The wastewater further enters the dripping acid-concentration process to convert the free ammonia into ammonium salts; the hourly liquid ammonia production is 0.652 tons; the hourly ammonia water production with a free ammonia concentration of 280,000 mg / L is 0.30 m³. 3 The steam consumption for stripping is 0.61 tons / ton of wastewater from the filter press section.

[0054] Example 2

[0055] Wastewater from the paraquat synthesis and filter press process (free ammonia concentration 284,000 mg / L) is preheated to 30°C in the first preheater 1 and then discharged at a flow rate of 3 m / s. 3 / h is pumped into the stripping tower from the top, while simultaneously compressing nitrogen (flow rate 2000m³ / h). 3 The wastewater enters the stripping tower from the bottom at a pressure of 0.5 MPa per hour. The temperature inside the stripping tower is 20–30°C, and the pressure (gauge pressure) is a slightly positive pressure of about 40 kPa. The residence time of the wastewater in the stripping tower is 2 hours. The gas phase enters the air separator from the top of the stripping tower. The separated liquid phase enters the liquid ammonia storage tank. The separated gas phase is pressurized to 0.5 MPa by a booster pump and returned to the stripping tower for recycling.

[0056] Wastewater discharged from the bottom of the stripping tower is heated to 60°C by the second preheater 6 and then enters the stripping tower for stripping. The temperature at the bottom of the stripping tower is 110°C, and the temperature at the top of the stripping tower is 35°C. The residence time of the wastewater in the stripping tower is 2 hours. The gas phase at the top of the stripping tower is condensed to 10-15°C by the first condenser. The liquid phase in the first condenser flows back from the top of the stripping tower into the stripping tower, and the gas phase enters the cyclone separator for gas-liquid separation. The gas phase in the lower part of the stripping tower is separated into gas phase and liquid phase. The product enters the second condenser at the outlet, where it is condensed to 30-40°C. The liquid phase is stored in the ammonia storage tank, while the gas phase enters the gas-liquid cyclone separator for gas-liquid separation. The gas phase separated by the gas-liquid cyclone separator is compressed by the ammonia compressor and then enters the liquid ammonia storage tank. The liquid phase separated by the gas-liquid separator is pumped into the ammonia storage tank. The wastewater from the bottom of the stripping tower enters the second preheater and the first preheater in sequence to preheat the liquid to be entered into the stripping tower and the wastewater to be entered into the stripping tower, respectively, before being discharged into the wastewater storage tank.

[0057] Samples were taken from the wastewater outlet pipe of the first preheater, and the free ammonia concentration in the wastewater was found to be 42,000 mg / L; the hourly liquid ammonia production was 0.678 tons, and the hourly ammonia water production was 0.28 m³ / h with a free ammonia concentration of 280,000 mg / L. 3 The steam consumption for stripping is 0.57 tons / ton of wastewater from the filter press section.

[0058] Example 3

[0059] Wastewater from the paraquat synthesis and filter press process (free ammonia concentration 284,000 mg / L) is preheated to 30°C in the first preheater 1 and then discharged at a flow rate of 3 m / s. 3 / h is pumped into the stripping tower from the top, while simultaneously compressing nitrogen gas (flow rate 3000m³ / h). 3 The wastewater enters the stripping tower from the bottom at a pressure of 0.5 MPa per hour. The temperature inside the stripping tower is 20–30°C, and the pressure (gauge pressure) is a slightly positive pressure of about 40 kPa. The residence time of the wastewater in the stripping tower is 2 hours. The gas phase enters the air separator from the top of the stripping tower. The separated liquid phase enters the liquid ammonia storage tank. The separated gas phase is pressurized to 0.5 MPa by a booster pump and returned to the stripping tower for recycling.

[0060] Wastewater discharged from the bottom of the stripping tower is heated to 60°C by the second preheater 6 and then enters the stripping tower from the top for stripping. The temperature at the bottom of the stripping tower is 110°C, and the temperature at the top of the stripping tower is 35°C. The residence time of the wastewater in the stripping tower is 2 hours. The gas phase at the top of the stripping tower is condensed to 10-15°C by the first condenser. The liquid phase in the first condenser flows back from the top of the stripping tower into the stripping tower, and the gas phase enters the cyclone separator for gas-liquid separation. The gas phase in the lower part of the stripping tower is then... The gas phase enters the second condenser at the outlet, where it is condensed to 30-40°C. The liquid phase is stored in the ammonia storage tank. The gas phase then enters the gas-liquid cyclone separator for separation. The gas phase separated by the gas-liquid cyclone separator is compressed by the ammonia compressor and enters the liquid ammonia storage tank. The liquid phase separated by the gas-liquid separator is pumped into the ammonia storage tank. The wastewater from the bottom of the stripping tower enters the second preheater and the first preheater in sequence to preheat the liquid to be entered into the stripping tower and the wastewater to be entered into the stripping tower, respectively, and is then discharged into the wastewater storage tank.

[0061] Samples were taken from the wastewater outlet pipe of the first preheater, and the free ammonia concentration in the wastewater was found to be 24,000 mg / L; the hourly liquid ammonia production was 0.723 tons, and the hourly ammonia water production was 0.24 m³ / h with a free ammonia concentration of 280,000 mg / L. 3 The steam consumption for stripping is 0.49 tons / ton of wastewater from the filter press section.

[0062] Example 4

[0063] Wastewater from the paraquat synthesis and filter press process (free ammonia concentration 284,000 mg / L) is preheated to 30°C in the first preheater 1 and then discharged at a flow rate of 3 m / s. 3 / h is pumped into the stripping tower from the top, while nitrogen gas is compressed (flow rate 4000m³ / h). 3 The wastewater enters the stripping tower from the bottom at a pressure of 0.5 MPa per hour. The temperature inside the stripping tower is 20–30°C, and the pressure (gauge pressure) is a slightly positive pressure of about 40 kPa. The residence time of the wastewater in the stripping tower is 2 hours. The gas phase enters the air separator from the top of the stripping tower. The separated liquid phase enters the liquid ammonia storage tank. The separated gas phase is pressurized to 0.5 MPa by a booster pump and returned to the stripping tower for recycling.

[0064] Wastewater discharged from the bottom of the stripping tower is heated to 60°C by the second preheater 6 and then enters the stripping tower from the top for stripping. The temperature at the bottom of the stripping tower is 110°C, and the temperature at the top of the stripping tower is 35°C. The residence time of the wastewater in the stripping tower is 2 hours. The gas phase at the top of the stripping tower is condensed to 10-15°C by the first condenser. The liquid phase in the first condenser flows back from the top of the stripping tower into the stripping tower, and the gas phase enters the cyclone separator for gas-liquid separation. The gas phase in the lower part of the stripping tower is separated into gas phase and liquid phase. The product enters the second condenser at the outlet, where it is condensed to 30-40°C. The liquid phase is stored in the ammonia storage tank, while the gas phase enters the gas-liquid cyclone separator for gas-liquid separation. The gas phase separated by the gas-liquid cyclone separator is compressed by the ammonia compressor and then enters the liquid ammonia storage tank. The liquid phase separated by the gas-liquid separator is pumped into the ammonia storage tank. The wastewater from the bottom of the stripping tower enters the second preheater and the first preheater in sequence to preheat the liquid to be entered into the stripping tower and the wastewater to be entered into the stripping tower, respectively, before being discharged into the wastewater storage tank.

[0065] Samples were taken from the wastewater outlet pipe of the first preheater, and the free ammonia concentration in the wastewater was found to be 25,000 mg / L; the hourly liquid ammonia production was 0.721 tons, and the hourly ammonia water production with a free ammonia concentration of 280,000 mg / L was 0.24 m³. 3 The steam consumption for stripping is 0.50 tons / ton of wastewater from the filter press section.

[0066] Example 5

[0067] Wastewater from the paraquat synthesis and filter press process (free ammonia concentration 284,000 mg / L) is preheated to 30°C in the first preheater 1 and then discharged at a flow rate of 3 m / s. 3 / h is pumped into the stripping tower from the top, while simultaneously compressing nitrogen gas (flow rate 3000m³ / h). 3 The wastewater enters the stripping tower from the bottom at a pressure of 0.5 MPa per hour. The temperature inside the stripping tower is 30-40°C, and the pressure (gauge pressure) is a slightly positive pressure of about 40 kPa. The residence time of the wastewater in the stripping tower is 2 hours. The gas phase enters the air separator from the top of the stripping tower. The separated liquid phase enters the liquid ammonia storage tank. The separated gas phase is pressurized to 0.5 MPa by a booster pump and returned to the stripping tower for recycling.

[0068] Wastewater discharged from the bottom of the stripping tower is heated to 60°C by the second preheater 6 and then enters the stripping tower from the top for stripping. The temperature at the bottom of the stripping tower is 110°C, and the temperature at the top of the stripping tower is 35°C. After the wastewater stays for 2 hours, the gas phase at the top of the stripping tower is condensed to 10-15°C by the first condenser. The liquid phase in the first condenser flows back from the top of the stripping tower into the stripping tower, and the gas phase enters the cyclone separator for gas-liquid separation. The gas phase in the lower part of the stripping tower enters through the gas phase outlet. The liquid phase enters the second condenser and is condensed to 30-40°C. The liquid phase is stored in the ammonia water storage tank, and the gas phase enters the gas-liquid cyclone separator for gas-liquid separation. The gas phase separated by the gas-liquid cyclone separator is compressed by the ammonia compressor and enters the liquid ammonia storage tank. The liquid phase separated by the gas-liquid separator is pumped into the ammonia water storage tank. The wastewater at the bottom of the stripping tower enters the second preheater and the first preheater in sequence to preheat the liquid to be entered into the stripping tower and the wastewater to be entered into the stripping tower, respectively, and is discharged to the wastewater storage tank.

[0069] Samples were taken from the wastewater outlet pipe of the first preheater, and the free ammonia concentration in the wastewater was found to be 21,000 mg / L; the hourly liquid ammonia production was 0.732 tons, and the hourly ammonia water production was 0.23 m³ / h with a free ammonia concentration of 280,000 mg / L. 3 The steam consumption for stripping is 0.48 tons / ton of wastewater from the filter press section.

Claims

1. An apparatus for recovering ammonia from wastewater, wherein the concentration of free ammonia in high-concentration ammonia wastewater is 250,000 to 400,000 mg / L, characterized in that: include: Stripping tower, stripping tower, first preheater, second preheater, air separator, booster pump, first condenser, second condenser, gas-liquid separator, ammonia compressor, liquid ammonia storage tank, ammonia water storage tank; The stripping tower has a liquid inlet at its upper part, which is connected to a first preheater. High-concentration ammonia wastewater is preheated by the first preheater before entering the stripping tower. The stripping tower also has an air inlet at its lower part, through which compressed gas is introduced to strip the ammonia wastewater within the tower. An air outlet is located at the top of the stripping tower, connected to the air inlet of an air separator. The air outlet of the air separator is connected to the air inlet of the stripping tower via a booster pump. The liquid outlet of the air separator is connected to a liquid ammonia storage tank. A liquid outlet is located at the bottom of the stripping tower, connected to the feed inlet at the top of the stripping tower via a second preheater. The stripping tower also has outlets at its top and lower middle sections. The stripping tower has a gas inlet and a gas phase outlet. The gas outlet of the stripping tower is connected to the feed inlet of the first condenser, the gas outlet of the first condenser is connected to the feed inlet of the gas-liquid separator, and the liquid outlet of the first condenser is connected to the stripping tower so that the liquid phase from the first condenser flows back into the stripping tower. The gas phase outlet of the stripping tower is connected to the gas inlet of the second condenser, the gas outlet of the second condenser is connected to the feed inlet of the gas-liquid separator, and the liquid outlet of the second condenser is connected to the ammonia storage tank. The bottom liquid outlet of the stripping tower is connected to the wastewater storage tank sequentially via the second preheater and the first preheater. The gas outlet of the gas-liquid separator is connected to the liquid ammonia storage tank via an ammonia compressor, and the liquid outlet of the gas-liquid separator is connected to the ammonia storage tank. Both the stripping tower and the steam stripping tower are packed towers; the packing material is selected from one or a combination of Raschig rings, polypropylene Pall rings, and polypropylene hollow spheres. In the stripping tower, the height of the packing layer is 1 / 10 to 1 / 2 of the tower height; in the stripping tower, the height of the packing layer is 1 / 10 to 1 / 2 of the tower height. Demisters are installed at the top of both the stripping tower and the steam stripping tower. The air separator is equipped with a level gauge and a regulating valve is installed at the liquid outlet of the air separator. The level gauge and the regulating valve are interlocked. When the liquid level of the air separator is lower than 10-20%, the regulating valve is closed. The pressure of the booster pump is interlocked with the pressure of the compressed gas; when the outlet pressure of the booster pump is greater than or equal to the inlet pressure of the compressed gas, the booster pump stops working, and when the outlet pressure of the booster pump is less than the inlet pressure of the compressed gas, the booster pump starts.

2. The apparatus for recovering ammonia from wastewater according to claim 1, characterized in that: The inlet of the stripping tower is connected to a spraying device, which sprays high-concentration ammonia wastewater downward inside the stripping tower; the inlet of the stripping tower is connected to a spraying device, which sprays liquid downward inside the stripping tower. In the stripping tower, the height of the packing layer is 1 / 7 to 1 / 4 of the tower height; in the stripping tower, the height of the packing layer is 1 / 7 to 1 / 4 of the tower height.

3. The apparatus for recovering ammonia from wastewater according to claim 1, characterized in that: The air inlet pipeline of the stripping tower is equipped with a three-way valve. The two air inlets of the three-way valve are connected to the fresh compressed gas feed pipeline and the booster pump outlet, respectively; the air outlet of the three-way valve is connected to the air inlet of the stripping tower.

4. The apparatus for recovering ammonia from wastewater according to claim 1, characterized in that: The gas phase extraction outlet is shaped like an umbrella.

5. The apparatus for recovering ammonia from wastewater according to claim 1, characterized in that: The gas-liquid separator is a gas-liquid cyclone separator.

6. A method for recovering ammonia from wastewater based on the apparatus of claim 1, characterized in that: include: High-concentration ammonia wastewater, after being preheated in the first preheater, enters the stripping tower from the top. Simultaneously, compressed gas is introduced from the bottom of the stripping tower to strip the high-concentration ammonia wastewater. The gas phase enters the air separator from the top of the stripping tower. The liquid ammonia separated by the air separator enters the liquid ammonia storage tank. The separated gas phase is pressurized by a booster pump and returned to the stripping tower for circulating stripping. The liquid phase at the bottom of the stripping tower, after being preheated in the second preheater, enters the stripping tower from the top for stripping. The gas phase at the top of the stripping tower is cooled by the first cooler... The condenser condenses the liquid, which is then returned to the stripping tower. The gas phase enters the gas-liquid separator for further separation. The gas phase in the lower part of the stripping tower enters the second condenser through the gas phase outlet for condensation. The condensate flows to the ammonia storage tank, and the gas phase enters the gas-liquid separator for further separation. The gas phase separated by the gas-liquid separator is compressed by the ammonia compressor to obtain liquid ammonia, which then enters the liquid ammonia storage tank. The liquid phase separated by the gas-liquid separator is pumped into the ammonia storage tank. The liquid phase at the bottom of the stripping tower sequentially enters the second preheater and the first preheater for waste heat recovery and utilization, and is then discharged to the wastewater storage tank. The concentration of free ammonia in the high-concentration ammonia wastewater is 250,000 to 400,000 mg / L. The high-concentration ammonia wastewater is preheated to 30-50°C by the first preheater; The compressed gas is one of air, nitrogen, or an inert gas, and the pressure of the compressed gas is 0.5–0.8 MPa; In the stripping tower, the gas-liquid ratio is 100:1 to 3000:1; The pressure inside the stripping tower is a slightly positive pressure of 40 kPa; The temperature inside the stripping tower is 10–50°C; The residence time of high-concentration ammonia wastewater in the stripping tower is 1 to 6 hours; The liquid phase at the bottom of the stripping tower is preheated to 50-80°C by a second preheater; The bottom temperature of the stripping tower is 100-120℃; the top temperature of the stripping tower is 20-60℃. The liquid phase at the bottom of the stripping tower enters the stripping tower and remains there for 1 to 6 hours.

7. The method for recovering ammonia from wastewater according to claim 6, characterized in that: The compressed gas is nitrogen; In the stripping tower, the gas-liquid ratio is 500:1 to 1000:1; The temperature inside the stripping tower is 20–40°C; The residence time of high-concentration ammonia wastewater in the stripping tower is 2 to 3 hours.

8. The method for recovering ammonia from wastewater according to claim 6, characterized in that: The liquid phase at the bottom of the stripping tower is preheated to 60-70°C by a second preheater; The bottom temperature of the stripping tower is 105-115℃; the top temperature of the stripping tower is 30-40℃. The liquid phase at the bottom of the stripping tower enters the stripping tower and remains there for 2 to 3 hours.

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