Nitrogen oxide separation and absorption system for nitric acid production

Abstract

The utility model belongs to nitric acid production technical field, concretely relates to a kind of nitrogen oxide separation absorption system for nitric acid production.The nitrogen oxide separation absorption system for nitric acid production, including ammonia oxidation furnace-waste heat boiler integrated furnace, ammonia oxidation furnace-waste heat boiler integrated furnace is connected by cooler with nitrogen oxide separator, nitrogen oxide separator top is connected with the bottom air inlet of absorption tower by compressor;The bottom of absorption tower is provided with delivery pump and bleaching tower connection, the upper portion of absorption tower is connected with absorption water pipeline, and the bottom of bleaching tower is provided with finished product nitric acid delivery pipeline.The nitrogen oxide separation absorption system for nitric acid production of the utility model, secondary air subsection enters absorption tower, reduces the loss, effectively improves nitrogen oxide overall oxidation absorption efficiency, reduces unreacted nitrogen oxide with tail gas discharge;Absorption tower uses single overflow double S type tray of staggered arrangement, prolongs gas-liquid contact time, improves nitrogen oxide absorption conversion rate.

Description

Technical Field

[0001] This utility model belongs to the field of nitric acid production technology, and specifically relates to a nitrogen oxide separation and absorption system for nitric acid production. Background Technology

[0002] Nitric acid is an indispensable basic chemical raw material in the fields of fertilizer, metallurgy, dyes, explosives, and electronics manufacturing. The mainstream industrial production route is the ammonia oxidation process, which includes three core stages: ammonia oxidation, nitrogen oxide condensation and separation, and NOx absorption. Ammonia is catalytically oxidized by a platinum mesh to produce NO. The high-temperature reaction gas is cooled and condensed to separate crude nitric acid from nitrogen oxides, and then sent to an absorption tower to react countercurrently with the absorbent liquid to produce the finished dilute nitric acid. Currently, the industry generally adopts a dual-pressurization process, but existing complete systems and single-tower equipment suffer from multiple pain points, including insufficient NOx conversion rate, limited finished acid concentration, and high environmental costs.

[0003] CN121869080A discloses a pressurized nitrogen oxide absorption system and process. The system consists of four parts: a gas compression device, an independent oxidation reaction device, a dilute nitric acid absorption tower, and a water absorption tower, with a supporting circulation pipeline for absorbent reuse. The process involves mixing NOx tail gas with air / oxygen and oxidizing it under the action of a catalyst. The oxidized mixture first enters the acid absorption tower, where it is absorbed by counter-current spraying with dilute nitric acid. Tail gas that does not meet standards is sent to a subsequent water absorption tower for deep treatment. The dilute acid produced from the water absorption is returned to the acid tower as a supplementary feedstock. The entire system has bottom collection and top spraying circulation structures in both tower stages, eliminating the need for additional alkali washing and allowing SCR to control NOx in the tail gas to below 200 ppm, thus addressing the pain points of low absorption efficiency at atmospheric pressure and the need for secondary treatment of tail gas. However, its dual-tower split structure results in high equipment investment, complex piping, and high energy consumption. Furthermore, as the main absorbent, under high-pressure absorption conditions, a large amount of NOx gas physically dissolves in the dilute nitric acid, affecting system stability and weakening absorption efficiency.

[0004] CN216223763U discloses an absorption tower for nitric acid production. Addressing the issues of insufficient gas-liquid contact and direct emission of tail gas pollution in traditional absorption towers, the internal structure of the tower has been optimized. The absorption tower features a nitric acid product outlet at the bottom and a NOx inlet at the lower part. Above the inlet, a main liquid inlet pipe and multiple branch liquid spray pipes are installed. A flow-limiting plate with uniformly spaced flow-limiting orifices is added between the spray pipes and the inlet to extend the gas residence time, disperse the airflow, increase the gas-liquid reverse contact area, and enhance the reaction conversion rate of NO2 and water. Furthermore, a purification component is installed above the spray area inside the tower to intercept acid mist and adsorb residual nitrogen oxides. In summary, this absorption tower can complete absorption and simple tail gas purification with only a single tower, without multi-stage series connection or external reaction equipment, resulting in a simple structure and low cost. However, while the perforated flow-limiting plate between the inlet and the spray pipes can extend the gas residence time, it comes at the cost of significantly increasing system pressure drop and blower energy consumption. Moreover, the flow-limiting orifices are prone to blockage by acid mist condensate during long-term operation, affecting operational stability.

[0005] CN221580177U discloses a nitric acid absorption tower for improving gas-liquid separation. The tower contains multiple layers of atomizing discs, swirl plates, and multi-stage baffle demisters arranged from bottom to top. The atomizing discs employ a coaxial annular water distribution pipe with a multi-nozzle structure, ensuring thorough atomization of the absorbent liquid and significantly increasing the gas-liquid contact area. The bottom swirl plates utilize centrifugal force to separate large-diameter acid droplets, while the upper multi-stage baffle demisters capture tiny droplets step by step, reducing nitric acid loss with the exhaust gas and minimizing raw material loss. The raw material gas flows counter-currently from the bottom of the tower upwards, while the absorbent liquid flows downwards, generating nitric acid which is discharged from the bottom of the tower. The exhaust gas is discharged after multi-layer separation. This absorption tower reduces nitric acid entrainment loss by optimizing the mass transfer and droplet separation components within the tower. However, the atomization of the absorbent liquid relies on nozzles, making cleaning and maintenance difficult after long-term operation.

[0006] In summary, the existing separation and absorption systems used in the preparation of nitric acid each have their own improvements, but none of them can balance absorption efficiency and product quality. In order to improve the absorption effect, they are often equipped with complicated equipment, resulting in high energy consumption and maintenance costs. Utility Model Content

[0007] To overcome the aforementioned deficiencies in the existing technology, this utility model provides a nitrogen oxide separation and absorption system for nitric acid production. Secondary air enters the absorption tower in stages, reducing losses while effectively improving the overall oxidation and absorption efficiency of nitrogen oxides and reducing the discharge of unreacted nitrogen oxides with the tail gas. The absorption tower adopts a staggered arrangement of single overflow double S-shaped tower plates, which prolongs the gas-liquid contact time and improves the nitrogen oxide absorption and conversion rate.

[0008] To achieve the above objectives, the technical solution of this utility model is as follows: A nitrogen oxide separation and absorption system for nitric acid production includes an integrated ammonia oxidizer-waste heat boiler, a nitrogen oxide separator, and an absorption tower. The integrated ammonia oxidizer-waste heat boiler has a feed inlet at its top connected to a preheater, which is connected to a mixer. The inlet of the mixer is connected to both an ammonia gas delivery pipeline and an air delivery pipeline. The integrated ammonia oxidizer-waste heat boiler is connected to the nitrogen oxide separator via a cooler. The top of the nitrogen oxide separator has a pipeline connected to a compressor, which is connected to the air inlet at the bottom of the absorption tower. A delivery pump at the bottom of the absorption tower is connected to a bleaching tower, and the upper part of the absorption tower is connected to an absorption water pipeline. A finished nitric acid delivery pipeline is located at the bottom of the bleaching tower. A secondary air pipeline at the top of the bleaching tower is connected to both the nitrogen oxide separator and the absorption tower. The air delivery pipeline also has a branch line connected to the bleaching tower.

[0009] Preferably, the top of the integrated ammonia oxidizer-waste heat boiler is connected to a hydrogen delivery pipeline. The upper part of the furnace body is the ammonia oxidizer, and the lower part is the waste heat boiler. The ammonia oxidizer has two layers of perforated distribution plates and a catalytic mesh layer arranged from top to bottom. The hydrogen delivery pipeline is a T-shaped inner extension pipe, and the outlet of the hydrogen delivery pipeline is located above the catalytic mesh layer. An ignition device is installed on the side wall of the ammonia oxidizer. A coil is installed inside the waste heat boiler.

[0010] The integrated ammonia oxidizer-waste heat boiler consists of an ammonia oxidizer at the top for completing the ammonia catalytic oxidation reaction and a circulating tubular waste heat boiler at the bottom for waste heat recovery. The two sections are directly connected, eliminating the need for high-temperature flue gas transmission pipelines, which reduces heat loss and avoids raw material loss caused by high-temperature decomposition of nitric oxide. At the same time, water-cooled wall tubes are also installed inside the furnace to protect the shell. Ammonia and air enter the upper ammonia oxidation furnace space through a mixer. The gas first passes through two layers of inclined perforated distribution plates to achieve uniform distribution. After the airflow is evenly distributed, it flows downwards through the entire catalytic wire mesh assembly. From top to bottom, this assembly consists of 6 layers of metal wire mesh, 7 layers of platinum-rhodium catalytic mesh, 3 layers of protective mesh, and 2 layers of platinum recovery mesh. The entire mesh is stacked and supported on a ceramic Raschig ring base. The 7-layer platinum-rhodium alloy mesh serves as the core catalytic layer, catalyzing the reaction of ammonia and oxygen at a high temperature of 850-920℃ to generate nitric oxide, which is required for nitric acid production. The high-temperature flue gas generated at approximately 900℃ passes through the Raschig ring gaps and directly enters the waste heat boiler below. The feedwater inside the tubes and the high-temperature flue gas outside the tubes form an efficient counter-current heat exchange, rapidly absorbing the large amount of reaction heat released during ammonia oxidation, producing medium-pressure steam as a byproduct. Simultaneously, it rapidly cools the high-temperature flue gas to below 350℃, effectively inhibiting the high-temperature decomposition of nitric oxide and improving the overall yield of nitric acid.

[0011] Preferably, the bottom of the nitrogen oxide separator is provided with a pipeline connected to the circulating liquid inlet at the bottom of the absorption tower, which is used to return the nitric acid obtained by the nitrogen oxide separator to the absorption tower for further absorption to obtain crude nitric acid.

[0012] Preferably, the bottom of the absorption tower is equipped with an internal circulation pipeline with a circulation pump, and the output end of the circulation pipeline is connected to the circulation liquid inlet at the bottom of the absorption tower to realize internal circulation in the absorption tower.

[0013] Preferably, the absorption tower is provided with a wire mesh demister and multiple layers of trays from top to bottom. Each tray is divided into a liquid receiving zone, a flow zone, and a liquid descending zone. The liquid receiving zone and liquid descending zone of the odd-numbered and even-numbered trays are arranged in opposite directions and staggered.

[0014] Preferably, the tray surface in the flow zone is provided with sieve holes, and an overflow weir is installed at the top of the flow zone. The overflow weirs are arranged in an alternating pattern to form a double S-shaped gas-liquid flow channel. The downcomer zone is provided with downcomers, and there are no openings on the tray surfaces in the downcomer zone and the receiving zone. Furthermore, there are two downcomers in total, located symmetrically, and the line connecting the center points of the two downcomers is arranged horizontally with the overflow weir. A T-shaped stiffener is installed on one side of the overflow weir, and the T-shaped stiffener is welded to the inner wall of the absorption tower.

[0015] Preferably, the bottom pump of the absorption tower is also provided with a branch line connected to the dilute nitric acid temporary storage tank, and the dilute nitric acid temporary storage tank is provided with a return pipeline connected to the middle of the absorption tower.

[0016] Preferably, the top of the absorption tower is provided with a pipeline connected to the gas-liquid separator, the bottom of the gas-liquid separator is provided with a pipeline returning to the upper part of the absorption tower, and the top of the gas-liquid separator is provided with a tail gas pipeline connected to the tail gas treatment system.

[0017] The absorption tower adopts a sieve plate tower with unequal plate spacing. The shell and tower plates are made of 00Cr19Ni10 stainless steel. The tower plates adopt a single overflow double S-shaped liquid flow method to prolong the gas-liquid contact time. The tower is equipped with cooling coils, which are bent from seamless 00Cr19Ni10 stainless steel pipes. The tower plates inside the absorption tower are divided into two parts. The lower section of the tower has a high NOx concentration and a large amount of heat released during absorption. Therefore, it is cooled by circulating water from outside the boundary, which is pressurized by a relay pump. The upper section of the tower has a low NOx concentration and a small amount of heat released. It reuses the low-temperature circulating water from the ammonia evaporator to recover low-temperature cold energy and save energy. The segmented temperature control ensures that the temperature of each tower plate is uniform, stabilizes the NOx dissolution balance, and avoids the decomposition of nitric acid and the decrease in absorption rate caused by high temperature. In addition, secondary air is continuously introduced into the tower during the absorption process. As nitrogen oxides continuously dissolve into the nitric acid liquid phase, they will continuously consume oxygen in the gas phase. Insufficient oxygen content will cause incomplete oxidation of low-valence nitrogen oxides. The introduced secondary air can replenish the oxygen required for the oxidation reaction, promote the full conversion of nitrogen oxides into nitrogen dioxide, and improve the NOx absorption and utilization rate.

[0018] The bleaching tower is a vertical pressure stripping tower, with the shell and internal components made of 00Cr19Ni10 stainless steel. The tower is filled with packing material and equipped with a top-mounted wire mesh demister. Crude nitric acid flows counter-currently from top to bottom, while bleaching air flows counter-currently from bottom to top, extending the gas-liquid mass transfer contact time. The bleaching tower is divided into an upper feed distribution zone, a middle stripping mass transfer zone, and a bottom finished acid collection zone. The middle section is the core stripping section, where process air is introduced to strip dissolved nitrogen oxides from the crude nitric acid. The top-mounted wire mesh demister intercepts entrained acid mist, reducing material loss. The process air introduced at the bottom of the tower continuously reduces the partial pressure of NOx in the gas phase, disrupting the nitrogen oxide dissolution balance in the crude nitric acid and desorbing low-valence nitrogen oxides such as NO and N2O4 from the liquid phase into the gas phase. The nitrogen oxide-containing air at the top of the tower is used as secondary air, with 80% sent to a nitrogen oxide separator and 20% to an absorption tower for reuse, improving the overall utilization rate of nitrogen oxides, reducing tail gas pollutant emissions, and lowering raw material loss and tail gas treatment operating costs.

[0019] The working principle of this utility model is as follows: After the trial run and inspection are completed, before the raw material gas is transported, the air supply pipeline is controlled to supply air to the integrated ammonia oxidation furnace-waste heat boiler to complete the start-up and ignition. During ignition, the process air fan is started, and the air flow rate of the mixed gas path is controlled to 20%-30% of the rated load. The air is continuously blown through the furnace body for no less than 15 minutes to remove all residual combustible gases and impurities in the furnace. A slight positive pressure is maintained in the furnace. Then, the furnace side wall ignition device is started to generate a high-temperature electric arc, and the high-purity hydrogen supply pipeline is opened. The hydrogen is ignited above the catalytic mesh, and the hydrogen flame is used to preheat the platinum-rhodium catalytic mesh to an activation temperature of over 700°C. After the catalytic grid reaches the required temperature, ammonia gas is fed into the mixer along with process air via the ammonia gas delivery pipeline to achieve uniform mixing. The ammonia concentration in the mixed gas is 9.5%. The mixed gas is then transported to the preheater and preheated to 220-260℃. It is then fed into the ammonia oxidation furnace chamber at the top of the integrated ammonia oxidation furnace-waste heat boiler through the top feed hole. The mixed gas undergoes a self-sustaining ammonia oxidation reaction on the high-temperature catalytic grid. After the furnace temperature is stabilized at 870℃, the hydrogen pipeline is gradually closed to complete ignition. The system then enters normal production mode. An ammonia oxidation reaction occurs inside the furnace at a reaction temperature of 870℃ and a pressure of 0.43MPa, generating NOx gas. High-temperature flue gas passes through the gaps in the ceramic Raschig ring base and directly enters the integrated circulating waste heat boiler at the bottom of the furnace. The feedwater inside the tubes exchanges heat with the high-temperature flue gas outside the tubes in a countercurrent manner, quickly recovering the waste heat of the reaction and producing medium-pressure steam. The NOx-containing flue gas, after being cooled by the waste heat boiler, is passed into a cooler for further cooling, and then sent to a nitrogen oxide separator. A small amount of condensed dilute nitric acid in the flue gas is separated and precipitated in the separator. The separated dilute nitric acid is returned to the circulating liquid inlet at the bottom of the absorber through a pipeline to participate in the absorption reaction again, improving the raw material utilization rate. After the liquid nitric acid is removed, the gaseous NOx is mixed with the secondary air entering the nitrogen oxide separator. The mixture is then sent to the compressor for pressurization through the top pipeline of the nitrogen oxide separator. The pressurized NOx process gas enters the absorption tower from the bottom inlet and mixes with the absorption water. The pressure of the absorption tower is controlled at 1.0 MPa for countercurrent absorption. The absorber tower is equipped with wire mesh demisters and multiple staggered trays arranged sequentially from top to bottom. The liquid receiving and descending zones of the odd-numbered and even-numbered trays are staggered, creating a single overflow channel for the absorbent liquid. The tray flow areas are perforated and fitted with staggered overflow weirs, forming a double S-shaped gas-liquid flow channel on the horizontal tray plane. This effectively prolongs the residence time of the gas and liquid phases, enhancing the mass transfer and absorption of nitrogen oxides and absorbent water. Simultaneously, two independent cooling circuits are installed for segmented temperature control. The lower part of the tower is a high-NOx concentration absorption zone with a large heat release during the absorption reaction. Pressurized circulating water is used in this zone to exchange heat through cooling coils, stabilizing the tower temperature at 40-50℃. The upper part of the tower has a lower NOx concentration and less heat release, utilizing a low-temperature circulating water cooling system from an ammonia evaporator to control the temperature at 25-40℃. During the absorption process, as the oxidation reaction proceeds, oxygen is gradually consumed. The system continuously introduces secondary air into the middle of the absorption tower through a secondary air pipeline to promptly and fully oxidize low-valence nitrogen oxides such as nitric oxide and dinitrogen trioxide generated during the absorption process into more water-soluble nitrogen dioxide. This prevents incomplete oxidation due to insufficient oxygen content in the tower, significantly improving the overall absorption and utilization rate of nitrogen oxides. At the top of the tower, room-temperature demineralized water is continuously introduced as an absorbent, where nitrogen dioxide reacts fully with water to generate dilute nitric acid. A circulation pump is installed at the bottom of the absorption tower to build an internal circulation pipeline, continuously transporting the crude nitric acid enriched at the bottom of the tower back to the circulating liquid inlet at the bottom of the tower, further improving the degree of gas-liquid contact and increasing the NOx dissolution and conversion rate. The crude nitric acid generated at the bottom of the tower is pressurized by a transfer pump and sent to the bleaching tower for refining. Air is introduced into the lower part of the bleaching tower and the airflow passes upward through the crude nitric acid liquid phase, stripping away the free nitrogen oxides dissolved inside the crude nitric acid, thus completing the nitric acid bleaching and purification. The qualified finished nitric acid after removing impurity gases is transported to the outside and stored through the finished nitric acid conveying pipeline at the bottom of the bleaching tower. The gas at the top of the tower is returned as secondary air to the nitrogen oxide separator and absorption tower for reuse. After absorption at the top of the absorption tower, the exhaust gas first passes through a wire mesh demister at the top of the tower to initially capture entrained nitric acid droplets. Then, it is sent along the pipeline to a gas-liquid separator for deep gas-liquid separation. The nitric acid liquid collected at the bottom of the gas-liquid separator is sent back to the top of the absorption tower through a return pipeline to participate in absorption again, recovering most of the entrained acid and reducing material loss. The clean exhaust gas after acid mist removal is transported from the exhaust gas pipeline at the top of the gas-liquid separator to the exhaust gas treatment system for treatment, and the air in it is recovered for use as secondary air.

[0020] In addition, the bottom pump of the absorption tower is equipped with a branch line connected to the dilute nitric acid temporary storage tank. Its working process is as follows: When the system stops after the absorption process, the nitrogen oxide inlet is first cut off, and the absorption water is continuously introduced into the tower for 5 minutes to flush out the residual absorption liquid on the tower plate to prevent corrosion of the tower plate components. At this stage, the concentration of nitric acid produced is low and does not meet the process requirements for refining in the bleaching tower. Therefore, the low-concentration dilute nitric acid is sent to the dilute nitric acid temporary storage tank for storage through the transfer pump branch line. When the unit is restarted, the initial absorption water delivery capacity is limited due to the height of the absorption tower. In order to prevent the nitrogen oxide inlet speed from being too fast and causing incomplete absorption, the dilute nitric acid stored in the temporary storage tank is transported back to the middle of the absorption tower through the matching return pipeline. It partially replaces the fresh absorption water to participate in the absorption reaction, realizes the recycling of low-concentration dilute nitric acid, reduces the consumption of demineralized water, and improves the material utilization rate.

[0021] Compared with the prior art, the beneficial effects of this utility model are as follows: (1) This utility model adopts an integrated structure of ammonia oxidation furnace and waste heat boiler, which eliminates the need for high-temperature flue gas transmission pipeline, reduces heat loss, and quickly recovers the by-product steam from the reaction waste heat. At the same time, it rapidly cools the flue gas to inhibit the decomposition of nitric oxide and improve the yield of raw materials. The multi-layer distribution plate and gradient catalytic mesh inside the furnace can distribute gas evenly. Combined with a dedicated hydrogen ignition pipeline, it ensures stable and safe start-up and ignition.

[0022] (2) By supplementing the absorption tower and the nitrogen oxide separator with secondary air, this utility model can effectively improve the overall oxidation absorption efficiency of nitrogen oxides, reduce the discharge of unreacted nitrogen oxides with the tail gas, and reduce the concentration of pollutants in the tail gas. At the same time, the absorption tower adopts a staggered arrangement of single overflow double S-shaped tower plates, which prolongs the gas-liquid contact time and improves the nitrogen oxide absorption conversion rate.

[0023] (3) This utility model is equipped with a multi-channel liquid return pipeline, which can recycle and reuse low-concentration dilute nitric acid, reducing material loss and fresh water consumption. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the nitrogen oxide separation and absorption system for nitric acid production in this utility model; Figure 2 This is a schematic diagram of the perforated plate at the integrated ammonia oxidation furnace-waste heat boiler in this utility model; Figure 3 This is a schematic diagram of the odd-numbered trays of the absorption tower in this utility model; Figure 4 This is a schematic diagram of the even-numbered trays of the absorption tower in this utility model.

[0025] In the diagram: 1. Ammonia oxidation furnace-waste heat boiler integrated furnace; 101. Perforated distribution plate; 102. Ignition device; 103. Catalytic mesh layer; 104. Coil; 2. Nitrogen oxide separator; 3. Absorption tower; 301. Tower tray; 302. Wire mesh demister; 303. Overflow weir; 304. Downcomer; 305. Flow zone; 306. Sieve holes; 307. T-shaped rib; 308. Receiving zone; 309. Downcomer; 4. Bleaching tower; 5. Ammonia gas transmission pipeline; 6. Air transmission pipeline; 7. Hydrogen gas transmission pipeline; 8. Mixer; 9. Preheater; 10. Compressor; 11. Secondary air pipeline; 12. Cooler; 13. Gas-liquid separator; 14. Dilute nitric acid temporary storage tank; 15. Absorption water pipeline; 16. Tail gas treatment system; 17. Finished nitric acid transmission pipeline. Detailed Implementation

[0026] The technical solution of this utility model will be further described below with reference to the accompanying drawings.

[0027] like Figures 1-4 As shown, a nitrogen oxide separation and absorption system for nitric acid production includes an integrated ammonia oxidizer-waste heat boiler 1, a nitrogen oxide separator 2, an absorption tower 3, and a secondary air pipeline 11. The integrated ammonia oxidizer-waste heat boiler 1 has a feed inlet at the top connected to a preheater 9, which is connected to a mixer 8. The inlet of the mixer 8 is connected to an ammonia gas delivery pipeline 5 and an air delivery pipeline 6, respectively. The integrated ammonia oxidizer-waste heat boiler 1 is connected to the nitrogen oxide separator 2 via a cooler 12. The top of the nitrogen oxide separator 2 has a pipeline connected to a compressor 10, which is connected to the air inlet at the bottom of the absorption tower 3. The bottom of the absorption tower 3 has a delivery pump connected to a bleaching tower 4, and the upper part of the absorption tower 3 is connected to an absorption water pipeline 15. The bottom of the bleaching tower 4 has a finished nitric acid delivery pipeline 17. The top of the bleaching tower 4 has a secondary air pipeline 11 connected to both the nitrogen oxide separator 2 and the absorption tower 3. The air delivery pipeline 6 also has a branch connected to the bleaching tower 4.

[0028] The top of the integrated ammonia oxidizer-waste heat boiler 1 is connected to the hydrogen transmission pipeline 7. The upper part of the furnace body is the ammonia oxidizer, and the lower part is the waste heat boiler.

[0029] The ammonia oxidizer has two layers of perforated distribution plates 101 and a catalytic mesh layer 103 arranged from top to bottom inside. The hydrogen delivery pipeline 7 is a T-shaped inner extension pipe. The outlet of the hydrogen delivery pipeline 7 is located above the catalytic mesh layer 103. An ignition device 102 is installed on the side wall of the ammonia oxidizer. A coil 104 is installed inside the waste heat boiler.

[0030] The bottom of the nitrogen oxide separator 2 is provided with a pipeline connected to the lower circulating liquid inlet of the absorption tower 3; the bottom of the absorption tower 3 is provided with an internal circulation pipeline with a circulation pump, and the output end of the circulation pipeline is connected to the lower circulating liquid inlet of the absorption tower 3.

[0031] The absorption tower 3 is equipped with a wire mesh demister 302 and a multi-layer tower plate 301 arranged from top to bottom. Each tower plate 301 is divided into a liquid receiving area 308, a flow area 305 and a liquid descending area 309. The liquid receiving area 308 and the liquid descending area 309 of the odd-numbered and even-numbered layers are arranged in opposite staggered positions.

[0032] The surface of the flow area 305 of the tray 301 is provided with sieve holes 306. An overflow weir 303 is installed on the upper part of the flow area 305. The overflow weirs 303 are arranged in an alternating manner to form a double S-shaped gas-liquid flow channel. The downcomer 309 is provided with a downcomer pipe 304. There are no openings on the surface of the trays in the downcomer 309 and the receiving area 308. A T-shaped stiffener 307 is installed on one side of the overflow weir 303. The T-shaped stiffener 307 is welded to the inner wall of the absorption tower 3 cylinder.

[0033] The bottom pump of the absorption tower 3 is also equipped with a branch line connected to the dilute nitric acid temporary storage tank 14, and the dilute nitric acid temporary storage tank 14 is equipped with a return pipeline connected to the middle of the absorption tower 3.

[0034] The top of the absorption tower 3 is provided with a pipeline connected to the gas-liquid separator 13, the bottom of the gas-liquid separator 13 is provided with a pipeline for reflux to the upper part of the absorption tower 3, and the top of the gas-liquid separator 13 is provided with a tail gas pipeline connected to the tail gas treatment system 16.

[0035] The nitrogen oxide separation and absorption system for nitric acid production, when in operation, includes the following steps: Before system startup, air is first introduced into the integrated ammonia oxidizer-waste heat boiler 1 through air supply pipeline 6 to purge the furnace body and maintain a slight positive pressure inside the furnace. Then, a high-temperature electric arc is generated by ignition device 102 to ignite hydrogen through hydrogen supply pipeline 7, preheating the catalytic mesh layer 103 to the activation temperature. Subsequently, ammonia gas is transported through ammonia supply pipeline 5, and preheated process air is transported through air supply pipeline 6 to mixer 8 for uniform mixing, producing a mixed gas with an ammonia concentration of 9.5%. The mixed gas is then preheated to 220-260℃ by preheater 9 before being sent into the integrated ammonia oxidizer-waste heat boiler 1. In the furnace 1, gas is evenly distributed through the perforated distribution plate 101, and an ammonia oxidation reaction occurs on the catalytic mesh layer 103, stabilizing the furnace temperature at 870℃ and the pressure at 0.43MPa. The high-temperature flue gas generated by the reaction enters the lower part of the furnace body, and recovers waste heat and by-product medium-pressure steam through the heat exchanger 104. The cooled flue gas is further cooled by the cooler 12 and then sent to the nitrogen oxide separator 2. The separated dilute nitric acid is returned to the absorption tower 3 for recycling. The NOx gas after liquid removal is mixed with the air supplied by the secondary air pipeline 11, and after being pressurized by the compressor 10, it is sent to the absorption tower 3. Pressurized NOx process gas enters the absorption tower 3 from the bottom and comes into countercurrent contact with the demineralized water supplied by the absorption water pipeline 15, and the absorption reaction takes place under a pressure of 1.0 MPa. The multi-layer tower plate 301 in the absorption tower 3 adopts an odd-even layer staggered structure, and the absorption is completed by relying on the double S-shaped gas-liquid channel formed by the liquid receiving area 308, the liquid falling area 309, the flow area 305 with sieve holes 306 and the staggered overflow weir 303. During the production process, air is continuously supplied into the tower to fully oxidize the low-valent nitrogen oxides into nitrogen dioxide. The nitric acid conversion effect is improved by the circulation pipeline in the tower. The crude nitric acid generated by the reaction is transported to the bleaching tower 4 by the transfer pump. Preheated air is introduced into the bottom of the bleaching tower 4 to remove the nitrogen oxides dissolved in the crude nitric acid. The purified qualified finished nitric acid is sent for storage, and the gas at the top of the tower is reused as secondary air. The unabsorbed tail gas at the top of the absorption tower 3 is first collected by the wire mesh demister 302 to capture acid droplets, and then sent to the gas-liquid separator 13 to complete deep gas-liquid separation. The separated nitric acid liquid is returned to the absorption tower 3 for reuse, and the tail gas is sent to the tail gas treatment system 16 to recover air. When the system is shut down, the air inlet is cut off and the absorption tower 3 is continuously flushed with water. The low-concentration dilute nitric acid produced is sent to the dilute nitric acid temporary storage tank 14 for storage. When the unit is restarted, the dilute nitric acid in the dilute nitric acid temporary storage tank 14 is returned to the middle of the absorption tower 3 to replace part of the fresh absorption water, so as to realize the recycling of waste liquid.

Claims

1. A nitrogen oxide separation and absorption system for nitric acid production, characterized in that, The system includes an integrated ammonia oxidizer-waste heat boiler (1), a nitrogen oxide separator (2), and an absorption tower (3). The integrated ammonia oxidizer-waste heat boiler (1) has a feed hole at the top connected to a preheater (9), which is connected to a mixer (8). The inlet of the mixer (8) is connected to an ammonia gas pipeline (5) and an air pipeline (6). The integrated ammonia oxidizer-waste heat boiler (1) is connected to the nitrogen oxide separator (2) via a cooler (12). The separator (2) is equipped with a pipeline connected to the compressor (10) at the top, and the compressor (10) is connected to the air inlet at the bottom of the absorption tower (3); the absorption tower (3) is equipped with a delivery pump at the bottom connected to the bleaching tower (4), and the upper part of the absorption tower (3) is connected to the absorption water pipeline (15); the bleaching tower (4) is equipped with a finished nitric acid delivery pipeline (17) at the bottom; the bleaching tower (4) is equipped with a secondary air pipeline (11) at the top, which is connected to the nitrogen oxide separator (2) and the absorption tower (3) respectively.

2. The nitrogen oxide separation and absorption system for nitric acid production according to claim 1, characterized in that, The top of the ammonia oxidizer-waste heat boiler integrated furnace (1) is connected to the hydrogen transmission pipeline (7). The upper part of the furnace body is the ammonia oxidizer and the lower part is the waste heat boiler.

3. The nitrogen oxide separation and absorption system for nitric acid production according to claim 2, characterized in that, The ammonia oxidizer has two layers of perforated distribution plates (101) and a catalytic mesh layer (103) arranged from top to bottom inside. The hydrogen delivery pipeline (7) is a T-shaped inner extension pipe. The outlet of the hydrogen delivery pipeline (7) is located above the catalytic mesh layer (103). An ignition device (102) is installed on the side wall of the ammonia oxidizer. A coil (104) is installed inside the waste heat boiler.

4. The nitrogen oxide separation and absorption system for nitric acid production according to claim 1, characterized in that, The bottom of the nitrogen oxide separator (2) is provided with a pipeline that connects to the lower circulating liquid inlet of the absorption tower (3).

5. The nitrogen oxide separation and absorption system for nitric acid production according to claim 4, characterized in that, The bottom of the absorption tower (3) is equipped with an internal circulation pipeline with a circulation pump, and the output end of the circulation pipeline is connected to the lower circulation liquid inlet of the absorption tower (3).

6. The nitrogen oxide separation and absorption system for nitric acid production according to claim 1, characterized in that, The absorption tower (3) is equipped with a wire mesh demister (302) and a multi-layer tray (301) from top to bottom. Each tray (301) is divided into a liquid receiving area (308), a flow area (305) and a liquid falling area (309). The liquid receiving area (308) and liquid falling area (309) of the odd-numbered and even-numbered layers are arranged in opposite directions.

7. The nitrogen oxide separation and absorption system for nitric acid production according to claim 6, characterized in that, The tray (301) has a sieve hole (306) on the surface of the flow area (305). An overflow weir (303) is installed on the upper part of the flow area (305). The overflow weirs (303) are arranged in an alternating manner to form a double S-shaped gas-liquid flow channel. The downcomer (309) is provided with a downcomer pipe (304). There are no openings on the tray surface of the downcomer (309) and the liquid receiving area (308). A T-shaped stiffener (307) is installed on one side of the overflow weir (303). The T-shaped stiffener (307) is welded to the inner wall of the absorption tower (3).

8. The nitrogen oxide separation and absorption system for nitric acid production according to claim 1, characterized in that, The bottom pump of the absorption tower (3) is also equipped with a branch line connected to the dilute nitric acid storage tank (14), and the dilute nitric acid storage tank (14) is equipped with a return pipeline connected to the middle of the absorption tower (3).

9. The nitrogen oxide separation and absorption system for nitric acid production according to claim 1, characterized in that, The top of the absorption tower (3) is provided with a pipeline connected to the gas-liquid separator (13), the bottom of the gas-liquid separator (13) is provided with a pipeline for return to the upper part of the absorption tower (3), and the top of the gas-liquid separator (13) is provided with a tail gas pipeline connected to the tail gas treatment system (16).

10. The nitrogen oxide separation and absorption system for nitric acid production according to claim 1, characterized in that, The air delivery pipeline (6) is provided with a branch that connects to the bleaching tower (4).

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