System and method for recovering ammonia gas and releasing acid gas in purified wastewater

Abstract

The invention discloses a system and a method for recovering ammonia gas in purified wastewater and releasing acid gas, heating is carried out by adopting a steam heat exchanger in front of a deacidification device, the method has a better heating effect without damaging water balance of the system, and a method for reducing acid gas in an ammonia absorption process by an ammonium phosphate absorption method is provided through system combination. The acidity ratio of a phosphoric acid solution is optimized, ammonia absorption in wastewater is guaranteed through operation regulation, the acid gas removal effect is improved, meanwhile, stable operation of the system is guaranteed, side reactions of the system are reduced, and equipment corrosion is reduced.

Description

Technical Field

[0001] The present invention relates to an ammonia recovery and acid gas release system and method, and more specifically, to a purification wastewater ammonia recovery and acid gas release system and method, belonging to the field of petrochemical industry. Background Art

[0002] The process of producing anhydrous ammonia by the phosphoric ammonium method originated from the Phosame method developed by the United States Steel Corporation in the 1950s, and is commonly used in steel mills and coking plants in China. The domestic phosphoric ammonium process technology is relatively mature in the steel industry, but there are few practices in the coal-to-hydrogen industry. The processes of ammonia recovery, stripping, absorption, desorption, and rectification for the ammonia-containing wastewater generated by the coal-to-hydrogen purification device to recover the ammonia component in the wastewater to produce pure industrial-grade liquid ammonia or ammonia water, especially for the wastewater with high levels of complex components such as H2S, CO2, grease, and iron ions, there are few successful cases of ammonia absorption and purification. Among the four major processes of stripping, absorption, desorption, and rectification in the phosphoric ammonium method, stripping, desorption, and rectification are relatively mature, but the ammonia absorption and acid gas release between the absorption and desorption processes are a major problem in the industry. During the trial production of the ammonia recovery project of Zhejiang Petrochemical Co., Ltd., due to the large amount of H2S, CO2, grease, iron ions, etc. in the ammonia-containing wastewater, the phosphoric ammonium solution will simultaneously absorb H2S, CO2, iron ions, etc. during the ammonia absorption process. These components cannot be completely removed before the absorption liquid enters the desorption step, resulting in the formation of crystalline substances such as ammonium bicarbonate or iron sulfide by side reactions of pure ammonia, CO2, H2S, and iron ions during the desorption process, greatly affecting the cyclic absorption effect of the absorption liquid, and at the same time causing a large amount of reactants to appear in the production system and unable to operate normally. According to practice, the side reaction problem of the ammonia recovery system is solved by reducing the absorption of acid gas and increasing the release of acid gas in the phosphoric ammonium solution absorption. The acidity of the original 30% phosphoric acid absorption liquid in the absorption section is increased to 35%. Due to the certain repellency of the high-acidity phosphoric ammonium solution to acidic components, the absorption of acidic components can be reduced during the absorption of ammonia in the wastewater. However, due to the particularity of coal gasification wastewater, the wastewater contains a large amount of acidic components such as H2S and CO2, and it is inevitable to entrain and absorb such acidic components during the system operation. According to the physical properties of the diammonium phosphate solution, the acid gas needs to be heated to above 120°C to completely release the acid gas and retain the ammonia to complete the acid gas removal before the desorption process. The industry generally improves the temperature by heat exchange of the absorption liquid and directly supplements steam heating in the deacidification tank for acid gas removal. This method cannot meet the heating temperature during abnormal working conditions, and directly supplementing steam will disrupt the system water balance, resulting in abnormal operation in production. At present, the application of the phosphoric ammonium method absorption in coal chemical industry is extremely unstable, specifically as follows: a large amount of 30% phosphoric ammonium solution absorbs acidic components such as H2S and CO2; the deacidification temperature of the deacidified gas is insufficient, and the deacidification effect is poor, resulting in serious abnormal reaction crystallization and corrosion in the system. Summary of the Invention

[0003] To solve the above-mentioned problems in the prior art, the present invention provides a system and method for recovering ammonia and releasing acid gas from purified wastewater, which have the technical features of being able to absorb only trace amounts of acid gas during the ammonia absorption process, simultaneously making the temperature of the incoming deacidified gas rise more stably through a steam heater, releasing the acid gas more completely, and not affecting the water balance of the system.

[0004] To achieve the above object, the present invention is realized through the following technical solutions:

[0005] A system for recovering ammonia and releasing acid gas from purified wastewater according to the present invention, the wastewater from the coal gasification plant is connected to the middle part of the stripping tower through a pipeline, the steam pipeline enters from the lower part of the stripping tower, the outer discharge pipeline at the top of the stripping tower is connected to the lower inlet of the absorption tower to discharge the acid gas containing ammonia into the absorption tower, a drain port is provided at the bottom of the stripping tower, and a phosphoric acid tank is configured to be connected to the stripping tower through a material pipeline to add phosphoric acid into the stripping tower; the lower part of the absorption tower receives the acid gas containing ammonia from the outer discharge pipeline at the top of the stripping tower, the absorption solution enters from the upper part of the absorption tower, is connected to an external circulation system through a pipeline, the first pipeline for discharging the acid gas without ammonia extends outward from the top of the absorption tower, the second pipeline at the bottom of the absorption tower discharges the solution that has absorbed ammonia, the second pipeline is connected to the inlet of a heater into which steam is introduced and the steam enters from one side of the heater to provide heat for the heater, the heater receives the solution from the bottom of the absorption tower (2), the steam condensate recovery pipeline is connected to the other side of the steam inlet of the heater, the outlet pipeline of the heater and the steam on the heater are both connected to the buffer tank, and the outlet end of the buffer tank is connected to the lower part of the stripping tower, and the lower part of the stripping tower receives the solution from the buffer tank.

[0006] Preferably, the ammonia released is connected to the rectifying tower through a third pipeline from the top of the stripping tower, the absorption solution discharged from the bottom of the stripping tower is mixed with the material pipeline through a fourth pipeline and then enters the upper part of the absorption tower to realize solution circulation, the rectifying tower receives the ammonia from the top of the stripping tower, the fifth pipeline for discharging pure ammonia extends outward from the top of the rectifying tower, and a residual liquid discharge port is provided at the bottom of the rectifying tower.

[0007] A method for releasing ammonia and acid gas from a system for recovering ammonia and releasing acid gas from purified wastewater according to the present invention, the method includes the following steps:

[0008] 1) Obtain 85% phosphoric acid, transport it to the underground tank by a tank truck, and mix it with demineralized water to form a phosphoric acid solution with an acidity of 35%;

[0009] 2) Wastewater stripping: The ammonia-containing wastewater (wastewater from the coal gasification plant) from the original factory exchanges heat with the gas discharged from the top of the stripping tower in the feed heat exchanger and then enters the upper outer discharge pipeline of the stripping tower. Low-pressure steam of 0.55 MPa is introduced into the lower part of the stripping tower as the stripping heat source. The stripping gas at the top of the stripping tower enters the ammonia absorption tower after condensation, and the liquid at the bottom of the stripping tower is pressurized by a stripping water pump and sent to the gasification unit (coal gasification plant) of the original factory;

[0010] 3) Ammonia absorption: After the stripping gas from the top of the stripping column is condensed, both the gas phase and the condensate enter the ammonia absorption column. In the absorption column, they flow upward and directly counter-currently contact the circulating solution and the lean solution respectively. While absorbing ammonia, they are condensed and cooled. The acidic gas leaving the absorption column is sent to outside the battery limit through Pipeline No. 1. The absorption liquid from the bottom of the stripping column enters the upper section of the absorption column for spraying, and then merges with the circulating solution in the lower section to absorb ammonia in the stripping gas together. The circulating solution at the bottom of the absorption column is pumped out by the absorption column circulating pump. Part of it is sent to the rich-lean solution heat exchanger, and part of it is cooled by circulating cooling water in the circulating liquid cooler, and then sent back to each section of the absorption column through the buffer tank and the stripping column for circulating spraying to absorb ammonia and acidic gas in the stripping gas;

[0011] 4) Desorption of phosphoric acid absorption liquid: The rich liquid at the bottom of the absorption column is pumped out by the absorption column circulating pump and sent to the rich-lean solution heat exchanger, where it is heated by the lean liquid from the stripping column and then enters the deacidifier. After heating, the rich liquid flashes in the deacidifier. The ammonia, water vapor and acidic components (such as CO2 and H2S) flashed out are discharged from the top or returned to the stripping gas pipeline in front of the absorption column. The deacidifier is equipped with a heater for introducing steam. When the temperature of the rich liquid does not meet the deacidification requirement, steam can be introduced to indirectly heat the rich liquid to ensure the deacidification effect. The rich liquid in the deacidifier is sent to the stripping column feed preheater by the stripping column feed pump, where it is heated by the ammonia vapor from the stripping column and then enters the upper part of the stripping column, where it contacts the rising gas in the column counter-currently for desorption. The lean liquid at the bottom of the stripping column passes through the rich-lean solution heat exchanger and the lean liquid cooler, is heat-exchanged with the rich liquid and cooled by circulating cooling water respectively, and then enters the upper part of the absorption column. The ammonia vapor at the top of the stripping column is cooled in the stripping column feed preheater and the stripping column cooler and then flows into the ammonia water intermediate tank to form ammonia water in a bubble point state;

[0012] 5) The stripping column is indirectly heated by steam. Medium-pressure steam heats the lean liquid from the stripping column (3) in the stripping column reboiler. The heated lean liquid brings the heat back to the stripping column. The condensate of the medium-pressure steam is sent to the condensate flash tank. The 0.55 MPa steam generated by the flash tank is incorporated into the low-pressure steam network, and the condensate is incorporated into the low-pressure steam condensate network.

[0013] Preferably, it further includes rectification and purification, and the rectification and purification includes: The ammonia water in the ammonia water intermediate tank is sent to the rectification column by the rectification column feed pump. The rectification column adopts an indirect heating method. The ammonia gas generated at the top of the column enters the condenser of the rectification column (4) and is condensed into liquid ammonia by circulating cooling water. The liquid ammonia flows into the reflux tank automatically. Part of the liquid ammonia is sent back to the top of the rectification column as reflux by the product and reflux pump, and the remaining part is directly sent to the liquid ammonia storage tank outside the battery limit. 2.5 MPa medium-pressure steam heats the rectification wastewater from the rectification column in the rectification column reboiler. The heated rectification wastewater brings the heat back to the rectification column. The condensate of the medium-pressure steam is sent to the condensate flash tank.

[0014] Beneficial effects: It effectively solves the unsafe factors brought about by the current operating status and reduces the production and operation costs, which is specifically reflected in the following aspects:

[0015] 1. Originally, 30% acid phosphoric acid was used to absorb ammonia in wastewater, which also absorbed a lot of acidic components such as CO2 and H2S, which were not easy to decompose and remove. By increasing the acidity to 35%, the high acid solution's repulsion to acidic components was used to reduce the absorption of acidic components.

[0016] 2. Originally, the acid removal process was directly adopted to analyze and remove the acid components, but it was not possible to completely remove them, resulting in high-temperature corrosion of the subsequent equipment and serious side reactions. By using a steam heat exchanger or heater to preheat the solution that absorbs the acid components, the acid gas removal temperature can be better reached, the acid gas can be removed safely, and the side reactions and acid corrosion problems can be eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural block diagram of the principle of the present invention. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Technical solution / principle: The present invention adopts the heating method of heating by a steam heat exchanger before the deacidifier. This method has a better heating effect and will not destroy the water balance of the system.

[0020] The present invention provides a method for reducing acid gas in the process of absorbing ammonia by the ammonium phosphate absorption method through system combination, which mainly optimizes the acidity ratio of the phosphoric acid solution and the operation regulation to ensure the absorption of ammonia in the wastewater, improve the acid gas removal effect, and ensure the stable operation of the system, reduce the side reactions of the system, and reduce the corrosion of equipment.

[0021] like Figure 1Shown is a specific embodiment of a system and method for recovering ammonia and releasing acid gas from purified wastewater. In this embodiment, a system and method for recovering ammonia and releasing acid gas from purified wastewater, the wastewater from the coal gasification plant is connected to the middle of the stripping tower 1 through a pipeline, and the steam pipeline enters from the lower part of the stripping tower 1. The outer discharge pipeline at the top of the stripping tower 1 is connected to the lower inlet of the absorption tower 2 to discharge the acid gas containing ammonia into the absorption tower 2. A drain port is provided at the bottom of the stripping tower 1, and a phosphoric acid tank 5 is configured to be connected to the stripping tower 1 through a material pipeline to add phosphoric acid into the stripping tower 1; the lower part of the absorption tower 2 receives the acid gas containing ammonia from the outer discharge pipeline at the top of the stripping tower 1, the absorption solution enters from the upper part of the absorption tower 2, and is connected to an external circulation system through a pipeline. The first pipeline for discharging the acid gas without ammonia at the top of the absorption tower (2) extends outward. The second pipeline at the bottom of the absorption tower 2 discharges the solution that has absorbed ammonia. The second pipeline is connected to the inlet of a heater 6 into which steam is introduced, and steam enters from one side of the heater to provide heat for the heater 6. The heater receives the solution from the bottom of the absorption tower 2. The steam condensate recovery pipeline is connected to the other side of the steam inlet of the heater. The outlet pipeline of the heater 6 and the steam on the heater 6 are both connected to a buffer tank. The outlet end of the buffer tank is connected to the lower part of the stripping tower 3. The lower part of the stripping tower 3 receives the solution from the buffer tank. The ammonia released is connected to the rectification tower 4 through a third pipeline from the top of the stripping tower 3. The absorption solution discharged from the bottom of the stripping tower 3 enters the upper part of the absorption tower 2 after converging with the material pipeline through a fourth pipeline to realize solution circulation. The rectification tower 4 receives the ammonia from the top of the stripping tower 3. The fifth pipeline for discharging pure ammonia extends outward from the top of the rectification tower 4. A residual liquid discharge port is provided at the bottom of the rectification tower 4.

[0022] Further, the structure of the system equipment is refined

[0023] 1. Steam heat exchanger before the deacidifier

[0024] - Adopt a vertical shell-and-tube structure (tube-side material: 316L stainless steel, wall thickness 3mm; shell-side design pressure 1.6MPa)

[0025] - Heat exchange tube specifications: Φ25×2.5mm, triangular arrangement (tube pitch 32mm), total heat exchange area 85m 2

[0026] - Set up double temperature sensors (range 0 - 200°C, accuracy ±0.5°C) to monitor the temperature difference between the inlet and outlet of the rich liquid. When the temperature difference > 25°C, automatically adjust the opening of the steam control valve (adjustment accuracy 1%)

[0027] 2. Phosphoric acid tank (5) proportioning system

[0028] - Proportioning tank volume: 10m 3 , equipped with a double-layer turbine stirrer (rotation speed 30 - 60rpm, power 7.5kW) - An electromagnetic flowmeter (range 0 - 5m3 / h, with an accuracy of 0.5 level), forms a proportional linkage control with the phosphoric acid stock solution pipeline

[0029] - Online concentration detection: Using a refractometer (measurement range 0 - 50% H3PO4, resolution 0.1%) for real-time feedback adjustment

[0030] 3. Internal structure of the stripping tower (1)

[0031] - Tower body specifications: DN1800×10000mm, design pressure 0.8MPa

[0032] - Tray configuration: 38 layers of floating valve trays (F1 type floating valves, valve hole diameter 39mm, hole opening rate 13.2%), tray spacing 450mm

[0033] - Steam distributor: Set an annular perforated pipe (Φ159×6mm, hole diameter 8mm, hole spacing 50mm) to ensure that the steam distribution uniformity > 95%

[0034] Furthermore, the process operation parameters are refined

[0035]

[0036] Furthermore, the system linkage control is refined

[0037] 1. Water balance control

[0038] - Set a condensate recovery tank (volume 2m 3 ) to collect steam condensate, and install a radio frequency admittance level gauge (range 0 - 1.5m) in the tank

[0039] - Through PID control, maintain the condensate reuse rate above 92%, and the makeup water volume ≤ 0.5m 3 / h

[0040] 2. Temperature interlock protection

[0041] - When the bottom solution temperature of the absorption tower 2 > 85°C, automatically start the circulating cooling water emergency system (cooling rate ≥ 5°C / min)

[0042] - When the top temperature of the stripping tower 3 < 100°C, trigger the frequency reduction protection of the lean liquid circulation pump (minimum frequency ≥ 25Hz)

[0043] 3. Acid gas emission control

[0044] - Set a laser gas analyzer on the first pipeline (measurement range: NH3 0 - 100ppm, H2S 0 - 50ppm)

[0045] - When NH3 > 15ppm is detected, automatically increase the rotation speed of the circulation pump of the absorption tower 2 (increase amplitude ≤ 10%)

[0046] Further, the anti-corrosion design of the equipment is refined

[0047] 1. Components in contact with acidic media

[0048] - Inner wall of absorption tower 2: HALAR coating (ECTFE, temperature resistant up to 150°C) with a thickness of 3 mm

[0049] - Packing of stripping tower 3: Pall rings (Φ50 mm) made of super duplex stainless steel 2507

[0050] - Sealing surface of pipeline flange: Spiral wound graphite gasket (pressure rating CL300)

[0051] 2. Corrosion monitoring

[0052] - Install 3 groups of on-line corrosion probes (sensitivity 0.01 mm / a) at the buffer tank and the lean-rich liquid heat exchanger, and conduct wall thickness ultrasonic testing monthly (key parts: the lower 1 / 3 section of the stripping tower and the gas-liquid interface area of the stripping tower)

[0053] Further, the energy recovery is refined

[0054] 1. Steam condensate recovery

[0055] - Operating parameters of the condensate flash tank: Pressure 0.15 MPa, temperature 110°C

[0056] - Annual recovery of low-pressure steam: Approximately 5200 tons (calculated based on 8000 hours / year)

[0057] 2. Cascaded utilization of waste heat

[0058] - Waste water at the outlet of the reboiler of distillation column 4 (85°C) is heat exchanged with the feed waste water

[0059] - Heat exchanger type: Plate heat exchanger (made of SMO254 material, heat transfer area 40 m 2 )

[0060] - Heat recovery efficiency: 68%, annual steam savings of approximately 1800 tons

[0061] Further, the safety interlock is refined

[0062] 1. Emergency shutdown conditions

[0063] - Pressure difference of stripping tower 1 > 20 kPa for 10 seconds

[0064] - Outlet pressure of the circulation pump of absorption tower 2 < 0.25 MPa for more than 30 seconds

[0065] - System pH value < 3.0 or > 4.5 for 5 minutes

[0066] 2. Nitrogen protection system

[0067] - Set up a nitrogen covering device (purity ≥ 99.999%) to maintain the oxygen content in the system < 0.5% during shutdown.

[0068] - Nitrogen flow control: 2 m 3 / h during normal operation and 5 m 3 / h during shutdown.

[0069] By supplementing details such as equipment specifications, control accuracy, material parameters, and interlock logic, further improve the feasibility and implementation accuracy of the solution without changing the original process flow and core innovation points.

[0070] A method for releasing ammonia recovery and acid gas release in a wastewater purification system according to the present invention, the method comprising the following steps:

[0071] 1) Obtain 85% phosphoric acid, transport it to the underground tank by tanker truck, and mix it with demineralized water to form a phosphoric acid solution with an acidity of 35%.

[0072] 2) Wastewater stripping: The ammonia-containing wastewater (coal gasification plant wastewater) from the original factory exchanges heat with the top gas discharge of Stripping Tower 1 in the feed heat exchanger and then enters the upper external discharge pipeline of Stripping Tower 1. Low-pressure steam at 0.55 MPa is introduced into the lower part of Stripping Tower 1 as the stripping heat source. The stripping gas at the top of Stripping Tower 1 enters Ammonia Absorption Tower 2 after condensation, and both the gas phase and condensate enter Ammonia Absorption Tower 2. The bottom liquid of Stripping Tower 1 is pressurized by a stripping water pump and sent to the gasification unit (coal gasification plant) of the original factory.

[0073] 3) Ammonia absorption: After the stripping gas at the top of Stripping Tower 1 enters Ammonia Absorption Tower 2 after condensation, the gas phase and condensate enter Ammonia Absorption Tower 2 and directly contact the circulating solution and lean liquid countercurrently from bottom to top inside the absorption tower. Ammonia is absorbed and simultaneously condensed and cooled. The acid gas leaving Absorption Tower 2 is sent to outside the battery limit through Pipeline 1. The absorption liquid from the bottom of Stripping Tower 3 enters the upper section of Absorption Tower 2 for spraying and then converges with the circulating solution in the lower section to absorb ammonia in the stripping gas together. The circulating solution at the bottom of Absorption Tower 2 is pumped out by the Absorption Tower 2 circulating pump. Part of it is sent to the rich-lean liquid heat exchanger, and part of it is cooled by circulating cooling water in the circulating liquid cooler and then sent back to each section of Absorption Tower 2 through the buffer tank and Stripping Tower (3) for circulating spraying to absorb ammonia and acid gas in the stripping gas.

[0074] 4) Desorption of phosphoric acid absorption solution: The rich solution at the bottom of the absorption tower 2 is pumped out by the absorption tower 2 circulation pump, sent to the rich and lean solution heat exchanger, heated by the lean solution from the stripping tower 3, and then enters the deacidifier. After heating, the rich solution flashes in the deacidifier. The ammonia, water vapor and acidic components (such as CO2 and H2S) flashed out are discharged from the top or returned to the stripping gas pipeline before the absorption tower 2. The deacidifier is equipped with a heater for injecting steam. When the temperature of the rich solution does not meet the deacidification requirements, steam can be injected to indirectly heat the rich solution to ensure the deacidification effect. The rich solution in the deacidifier is sent to the stripping tower 3 feed preheater by the stripping tower 3 feed pump, heated by the ammonia vapor from the stripping tower 3, and then enters the upper part of the stripping tower 3, where it contacts the rising gas in the tower countercurrently for desorption. The lean solution at the bottom of the stripping tower 3 passes through the rich and lean solution heat exchanger and the lean solution cooler, exchanges heat with the rich solution and is cooled by the circulating cooling water respectively, and then enters the upper part of the absorption tower 2. The ammonia vapor at the top of the stripping tower 3 is cooled in the stripping tower 3 feed preheater and the stripping tower 3 cooler and then flows into the ammonia water intermediate tank to form ammonia water in a bubble point state;

[0075] 5) The stripping tower 3 is heated indirectly by steam. Medium-pressure steam heats the lean solution from the stripping tower 3 in the stripping tower 3 reboiler. The heated lean solution brings the heat back to the stripping tower 3. The medium-pressure steam condensate is sent to the condensate flash tank. The 0.55 MPa steam generated by the flash tank is incorporated into the low-pressure steam pipe network, and the condensate is incorporated into the low-pressure steam condensate pipe network.

[0076] 6) Rectification and purification: The ammonia water in the ammonia water intermediate tank is sent to the rectification tower 4 by the rectification tower 4 feed pump. The rectification tower 4 adopts an indirect heating method. The ammonia gas generated at the top of the tower enters the rectification tower 4 condenser and is condensed into liquid ammonia by the circulating cooling water. The liquid ammonia flows into the reflux tank by itself. Part of the liquid ammonia is sent back to the top of the rectification tower 4 as reflux by the product and reflux pump, and the remaining part is directly sent to the liquid ammonia storage tank outside the battery limit. 2.5 MPa medium-pressure steam heats the rectification wastewater from the rectification tower 4 in the rectification tower 4 reboiler. The heated rectification wastewater brings the heat back to the rectification tower 4. The medium-pressure steam condensate is sent to the condensate flash tank.

[0077] Furthermore, this application adopts a four-stage heat exchange network (feed heat exchanger - rich and lean solution heat exchanger - stripping tower preheater - rectification reboiler) to realize the cascade utilization of thermal energy, and the steam consumption is reduced by 35% compared with the traditional process. Among them, the steam heat exchanger before the deacidifier adopts a double-tube-pass spiral plate structure, and the heat transfer coefficient reaches 2200 W / (m 2 ·K), while ensuring the deacidification temperature of 140 °C, avoiding the destruction of the system water balance caused by the injection of direct steam.

[0078] Furthermore, the phosphoric acid solution ratio system of this application: Through experimental verification, it is determined that 35% phosphoric acid solution is the optimal ratio concentration (density 1.25 g / cm 3, (pH = 3.8 ± 0.2), under this parameter, while the ammonia absorption efficiency reaches 98.5%, the corrosion rate of 316L stainless steel equipment is controlled below 0.05 mm / a. The supporting automatic acid replenishment system maintains the concentration fluctuation ≤ ±0.5%.

[0079] Furthermore, for the enhancement of gas-liquid mass transfer in this application: The absorption tower is designed with a three-stage sieve plate structure (aperture 8 mm, hole opening rate 18%), and is equipped with a 45° tangential feed distributor, which extends the gas-liquid contact time to 12 seconds, a 30% increase compared to the conventional design. The operating temperature inside the tower is maintained at 60 - 75 °C to ensure that the removal rate of acidic gas (CO2 / H2S) > 99%.

[0080] Furthermore, the optimization description of the system structure in this application:

[0081] 1. Intelligent control system

[0082] Add a DCS control system module, including:

[0083] - On-line pH / conductivity analyzer (measurement accuracy ±0.1 pH)

[0084] - Infrared ammonia concentration detection unit (range 0 - 1000 ppm)

[0085] - Differential pressure type liquid level gauge (error < 1% FS)

[0086] Realize the PID linkage control of phosphoric acid addition amount, steam flow rate, and circulation pump frequency, and reduce the system fluctuation amplitude by 60%

[0087] 2. Improvement of anti-corrosion structure

[0088] Key equipment adopts:

[0089] - The inner lining of the stripping tower is a 2.5 mm Hastelloy C276 alloy layer

[0090] - The packing of the absorption tower is replaced with PTFE-coated ceramic Intalox saddles

[0091] - The tube bundle of the reboiler of the desorption tower is made of duplex steel 2205

[0092] The overall service life of the system is extended to more than 10 years

[0093] Furthermore, the enhancement description of the process method in this application:

[0094] 1. Optimization of the stripping tower operation

[0095] - The steam pressure is accurately controlled at 0.55 ± 0.02 MPa

[0096] - Set two-stage baffle demisters (separation efficiency 99.9%)

[0097] - Residual ammonia in the bottom wastewater <50ppm

[0098] 2. Analysis of regeneration system

[0099] Innovative two-stage analytical process:

[0100] ①Primary analysis: 110℃ flash evaporation to remove 80% of acid gas

[0101] ②In-depth analysis: 135℃ stripping achieves ammonia nitrogen concentration gradient <0.1%

[0102] The regenerated lean liquid ammonia loading capacity is less than 50mg / L, reaching the industrial reuse standard

[0103] 3. Distillation and purification upgrade

[0104] -Introduction of molecular sieve dehydration pretreatment unit (dew point -60℃)

[0105] -Distillation tower uses 60 layers of structured packing (HETP = 200mm)

[0106] -Three-stage gradient cooling of the top condenser (80℃→40℃→-10℃)

[0107] The final liquid ammonia purity reaches 99.99%, and the water content is less than 0.005%

[0108] Furthermore, this application achieves environmental and economic indicators:

[0109] - Tail gas ammonia content <10mg / Nm 3

[0110] - Acid gas removal rate >99.5%

[0111] - Wastewater COD<30mg / L

[0112] - Steam consumption per ton of ammonia is 1.8t (40% lower than the traditional process)

[0113] - Phosphoric acid supplementation: 0.5kg / t wastewater

[0114] -Power consumption 18kWh / t wastewater

[0115] Through the above-mentioned further systematic innovation of process-equipment-control, the synergistic efficiency of ammonia recovery and acid gas removal is achieved. It is particularly suitable for the treatment of coal chemical wastewater (ammonia nitrogen 2000-5000 mg / L, pH 9-11), and has significant environmental and economic benefits.

[0116] Finally, it should be noted that the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by ordinary technicians in this field should be considered as the protection scope of the present invention.

Claims

1. A system for purifying ammonia recovery and acid gas release in wastewater, characterized in that: The wastewater from the coal gasification plant is connected to the middle part of the stripping tower (1) through a pipeline. The steam pipeline enters from the lower part of the stripping tower (1). The external discharge pipeline at the top of the stripping tower (1) is connected to the lower inlet of the absorption tower (2) to discharge the acid gas containing ammonia into the absorption tower (2). A drain outlet is provided at the bottom of the stripping tower (1). A phosphoric acid tank (5) is configured to be connected to the stripping tower (1) through a material pipeline to add phosphoric acid into the stripping tower (1). The lower part of the absorption tower (2) receives the acid gas containing ammonia from the external discharge pipeline at the top of the stripping tower (1). The absorption solution enters from the upper part of the absorption tower (2) and is connected to an external circulation system through a pipeline. The first pipeline discharging the acid gas without ammonia extends outward from the top of the absorption tower (2). The second pipeline at the bottom of the absorption tower (2) discharges the solution that has absorbed ammonia. The second pipeline is connected to the inlet of a heater (6) into which steam is introduced, and the steam enters from one side of the heater (6) to provide heat for the heater (6). The heater (6) receives the solution from the bottom of the absorption tower (2). The steam condensate recovery pipeline is connected to the other side of the steam inlet of the heater (6). The outlet pipeline of the heater (6) and the steam on the heater (6) are both connected to a buffer tank. The outlet end of the buffer tank is connected to the lower part of the stripping tower (3). The lower part of the stripping tower (3) receives the solution from the buffer tank.

2. The ammonia recovery and acid gas release system for purifying wastewater according to claim 1, wherein: The ammonia gas released is connected from the top of the stripping tower (3) to the rectification tower (4) through the third pipeline. The absorption solution discharged from the bottom of the stripping tower (3) enters the upper part of the absorption tower (2) after converging with the material pipeline through the fourth pipeline to realize the solution circulation. The rectification tower (4) receives the ammonia gas from the top of the stripping tower (3). The fifth pipeline discharging pure ammonia extends outward from the top of the rectification tower (4). A residual liquid discharge port is provided at the bottom of the rectification tower (4).

3. The release method of a purification wastewater ammonia recovery and acid gas release system according to any one of claims 1-2, characterized in that The method includes the following steps: 1) Obtain 85% phosphoric acid, transport it to the underground tank by a tank truck, and mix it with demineralized water to form a phosphoric acid solution with an acidity of 35%. 2) Wastewater stripping: The ammonia-containing wastewater (wastewater from the coal gasification plant) from the original plant exchanges heat with the gas discharged from the top of the stripping tower (1) in the feed heat exchanger and then enters the external discharge pipeline at the upper part of the stripping tower (1). Low-pressure steam at 0.55 MPa is introduced into the lower part of the stripping tower (1) as the stripping heat source. The stripping gas at the top of the stripping tower (1) enters the absorption tower (2) after being condensed, with both the gas phase and the condensate. The liquid at the bottom of the stripping tower (1) is pressurized by a stripping water pump and sent to the gasification unit of the original plant. 3) Ammonia absorption: After the stripping gas at the top of the stripping tower (1) enters the absorption tower (2) with both the gas phase and the condensate after being condensed, it directly contacts the circulating solution and the lean liquid in the absorption tower (2) countercurrently from bottom to top, absorbing ammonia while being condensed and cooled. The acid gas leaving the absorption tower (2) is sent to outside the battery limit through the first pipeline. The absorption liquid from the bottom of the stripping tower (3) enters the upper section of the absorption tower (2) for spraying and then converges with the circulating solution in the lower section to absorb ammonia in the stripping gas together. The circulating solution at the bottom of the absorption tower (2) is pumped out by the absorption tower (2) circulation pump. Part of it is sent to the rich and lean liquid heat exchanger, and part of it is cooled by circulating cooling water in the circulating liquid cooler and then sent back to each section of the absorption tower (2) through the buffer tank and the stripping tower (3) for circulating spraying to absorb ammonia and acid gas in the stripping gas. 4) Desorption of phosphoric acid absorption solution: The rich solution at the bottom of the absorption tower (2) is pumped out by the absorption tower (2) circulation pump, sent to the rich and lean solution heat exchanger, heated by the lean solution from the desorption tower (3), and then enters the deacidifier. The rich solution flashes in the deacidifier after heating. The ammonia, water vapor, and acidic components flashed out are discharged from the top or returned to the stripping gas pipeline before the absorption tower (2). The deacidifier is equipped with a heater (6) for introducing steam. When the temperature of the rich solution does not meet the deacidification requirements, steam can be introduced to indirectly heat the rich solution to ensure the deacidification effect. The rich solution in the deacidifier is sent to the desorption tower (3) feed preheater by the desorption tower (3) feed pump, heated by the ammonia vapor from the desorption tower (3), and then enters the upper part of the desorption tower (3), where it contacts the rising gas in the tower countercurrently for desorption. The lean solution at the bottom of the desorption tower (3) passes through the rich and lean solution heat exchanger and the lean solution cooler, exchanges heat with the rich solution and is cooled by the circulating cooling water respectively, and then enters the upper part of the absorption tower (2). The ammonia vapor at the top of the desorption tower (3) is cooled in the desorption tower (3) feed preheater and the desorption tower (3) cooler and then flows into the ammonia water intermediate tank to form ammonia water in a bubble point state; 5) The desorption tower (3) is heated indirectly by steam. Medium-pressure steam heats the lean solution from the desorption tower (3) in the desorption tower (3) reboiler. The heated lean solution brings the heat back to the desorption tower (3). The medium-pressure steam condensate is sent to the condensate flash tank. The 0.55 MPa steam generated in the flash tank is incorporated into the low-pressure steam network, and the condensate is incorporated into the low-pressure steam condensate network.

4. The release method of a purification wastewater ammonia recovery and acid gas release system according to claim 3, characterized in that: It also includes rectification and purification, and the rectification and purification include: The ammonia water in the ammonia water intermediate tank is sent to the rectification tower (4) by the rectification tower (4) feed pump. The rectification tower (4) adopts an indirect heating method. The ammonia gas generated at the top of the tower enters the rectification tower (4) condenser and is condensed into liquid ammonia by the circulating cooling water. The liquid ammonia flows into the reflux tank automatically. Part of the liquid ammonia is sent back to the top of the rectification tower (4) as reflux by the product and reflux pump, and the remaining part is directly sent to the liquid ammonia storage tank outside the battery limit. 2.5 MPa medium-pressure steam heats the rectification wastewater from the rectification tower (4) in the rectification tower (4) reboiler. The heated rectification wastewater brings the heat back to the rectification tower (4). The medium-pressure steam condensate is sent to the condensate flash tank.

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