Process for producing dilute nitric acid by tail gas oxygenation circulation method

Abstract

This invention discloses a process for producing dilute nitric acid using a tail gas oxygenation cycle, belonging to the field of nitric acid preparation. First, the nitrogen-oxygen ratio is controlled to heat the nitrogen-oxygen mixture before it enters an ammonia mixer. The mixture undergoes ammonia oxidation in an oxidation furnace to produce NO. After recovering heat through a waste heat boiler, economizer, and demineralized water preheater, the mixture is cooled by a rapid cooler and then enters a dilute acid separator. The condensed dilute acid from the bottom of the separator is transported to an oxidation absorption tower. At the bottom of the oxidation absorption tower, NO is further oxidized to NO2 in the mixed gas. The remaining NO at the bottom of the oxidation absorption tower... x The mixed gas enters the upper part of the oxidation absorption tower through a baffle plate, where oxidation and absorption occur simultaneously. In the lower part of the absorption section, 55-60% dilute nitric acid is formed and flows to the upper part of the bleaching tower. After treatment in the bleaching tower, the finished acid flows out. The tail gas from the top of the oxidation absorption tower is pressurized by a booster and then enters an oxygen mixer for recycling. This invention solves the problem of tail gas pollution in nitric acid production, with low investment costs, high finished acid concentration, and low energy consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to a process for producing dilute nitric acid by tail gas oxygenation circulation method, belonging to the field of nitric acid production. BACKGROUND

[0002] At present, according to the different pressures of ammonia oxidation and nitrogen oxide absorption, the industrial production processes of dilute nitric acid are divided into normal pressure method, comprehensive method, medium pressure method, high pressure method and double pressurization method. The normal pressure method and the comprehensive method have been eliminated due to low product acid concentration and non-compliance of tail gas emission. The high pressure method has the disadvantages of low ammonia oxidation rate and high ammonia consumption, and is only used in some devices in a few countries such as the United States where ammonia price is low. The medium pressure method and the double pressurization method are the two mainstream production processes at present due to their advantages of high product acid concentration, low ammonia consumption and low platinum consumption, etc. After the tail gas is treated by selective catalytic reduction technology (SCR), the NOx content is less than 100 mg / m³, which is much lower than the national emission limit of 200 mg / m³. At present, although the NOx content in the tail gas of the nitric acid process has been far lower than the national requirement index, due to the large number of nitric acid production enterprises, the total amount of tail gas emission is huge, and the NOx in the tail gas pollutes the environment to a certain extent. x x x

[0003] Under the background of global response to climate change and carbon neutralization, the energy transformation of major countries in the world is accelerating, and green hydrogen is the most sustainable and truly carbon-free, so it is also becoming the focus of global new energy development. In recent years, with the increasing support of the Chinese government for the green hydrogen industry, China has become the largest country in global green hydrogen production capacity. Green hydrogen is produced by using renewable energy (such as solar energy, wind energy, nuclear energy, etc.) to generate electricity, and then converting the electricity into green hydrogen through water electrolysis hydrogen production equipment, while producing green oxygen as a byproduct. Therefore, while vigorously developing the green hydrogen industry, efficient utilization of green oxygen is a problem that needs to be considered. SUMMARY

[0004] The present application aims to provide a process for producing dilute nitric acid by tail gas oxygenation circulation method, which effectively solves the problem of environmental pollution of tail gas in nitric acid production.

[0005] The process for producing dilute nitric acid by tail gas oxygenation circulation method provided by the present application can utilize the byproduct green oxygen in green hydrogen production, avoid environmental pollution, has low investment cost, high finished acid concentration, low energy consumption, and good economic and environmental benefits.

[0006] The present application provides a process for producing dilute nitric acid by tail gas oxygenation circulation method, which includes the following contents:

[0007] ​​​(1) Establish a nitrogen circulation system: oxygen mixer connected to the nitrogen input pipeline, to the system input 0.45~0.5MPa normal temperature N2establish circulation system, the system circulation after stopping input N2;

[0008] (2) 0.5~0.55MPa, 80-120℃ O2through the bleaching tower into the oxygen mixer and N2mixing, N2:O2molar ratio control in the range of 3.2~3.5, the nitrogen oxygen mixture in the oxygen mixer is heated to 130~160℃ by the heater into the ammonia mixer;

[0009] (3) ammonia mixer connected to the ammonia input pipeline, 0.55~0.6MPa of gaseous ammonia is preheated to 90~120℃ by the ammonia preheater into the ammonia mixer, and the nitrogen oxygen mixture is mixed in the ammonia mixer, and the oxygen ammonia molar ratio is controlled in the range of 1.8~2;

[0010] (4) the mixed gas discharged from the ammonia mixer enters the oxidation furnace, and the ammonia oxidation is generated at 850~920℃. The mixed gas is cooled to about 40℃ by the waste heat boiler, the economizer and the desalted water preheater after recovering heat, and then enters the dilute acid separator;

[0011] (5) the condensed dilute acid from the lower part of the dilute acid separator is transported to the corresponding acid concentration tray in the middle part of the oxidation absorption tower by the dilute acid pump, and the NO x gas from the upper part of the dilute acid separator enters the bottom of the oxidation absorption tower. At the same time, the secondary oxygen from the bleaching tower also enters the bottom of the oxidation absorption tower to increase the oxygen content of the NO x mixed gas, and the flow of the secondary oxygen is 15~17% (volume percent) of the primary oxygen; the NO in the mixed gas at the bottom of the oxidation absorption tower is further oxidized into NO2, and the temperature of the mixed gas is maintained at about 40℃ under the cooling effect of the circulating water, and the condensed concentrated acid is formed, which is circulated at the bottom of the oxidation absorption tower by the concentrated acid pump, and the excess condensed concentrated acid is sent to the middle part of the oxidation absorption tower; the remaining NO x mixed gas passes through the riser cap of the partition plate into the upper part of the oxidation absorption tower for oxidation and absorption; the desalted water as the absorption liquid enters from the upper part of the oxidation absorption tower, and the 55~60% dilute nitric acid formed in the lower part of the absorption section flows to the upper part of the bleaching tower;

[0012] (6) the NO x gas in the crude acid is removed by O2in the bleaching tower, and the finished acid flows out at the bottom of the bleaching tower;

[0013] (7) the tail gas (0.37-0.42MPa) from the top of the oxidation absorption tower is pressurized to 0.45~0.5MPa by the booster, and then recycled for use, mixed with O2in the oxygen mixer, and then the next production cycle is carried out.

[0014] The application provides a device for producing dilute nitric acid by tail gas oxygenation circulation method, comprising an oxidation furnace, a waste heat boiler arranged at the bottom of the oxidation furnace, an ammonia mixer connected with the inlet of the oxidation furnace, a economizer, a platinum recovery device, a desalted water preheater, a fast cooler and a dilute acid separator connected with the outlet of the oxidation furnace, the dilute acid separator being connected with an oxidation absorption tower and a dilute acid pump respectively, the dilute acid pump being connected with the middle part of the oxidation absorption tower, and liquid being sent to the middle part of the oxidation absorption tower through the dilute acid pump; the bottom outlet of the oxidation absorption tower is connected with a concentrated acid pump and the middle part of the oxidation absorption tower to form a circulation; the middle outlet of the oxidation absorption tower is connected with a bleaching tower, and the outlet is a crude acid outlet; the top outlet of the bleaching tower is connected with the bottom of the oxidation absorption tower and an oxygen mixer respectively; the tail gas outlet of the top of the oxidation absorption tower is connected with a booster, the tail gas is pressurized by the booster and then enters the oxygen mixer, and the oxygen mixer is connected with the ammonia mixer through a tail gas preheater.

[0015] The structure of the oxidation absorption tower is as follows: the upper section of the oxidation absorption tower is an absorption section, and the main function is absorption; the lower section is an oxidation section, and the main function is oxidation; the upper and lower sections are isolated by a partition plate, the partition plate is provided with a gas lifting cap, the mixed gas in the oxidation section enters the absorption section through the gas lifting cap, and the liquid in the absorption section cannot flow into the oxidation section; the inside of the oxidation section is provided with a jet tray, the concentrated acid formed in the oxidation section is circulated on the tray by a pump to strengthen the oxidation of NO in the mixed gas, and the excess concentrated acid is sent to the absorption section; the inside of the absorption section is provided with a jet tray, the crude acid, the dilute acid and the desalted water enter the tower from the lower part, the middle part and the upper part of the absorption section respectively to absorb and oxidize, and finally the nitric acid with the required concentration is obtained and flows out from the outlet on the tower wall at the bottom of the absorption section.

[0016] The innovation points of the application are as follows:

[0017] (1) The oxygen-containing and nitrogen-containing oxide gas in the tail gas is fully circulated, and there is no need to equip an expensive SCR system, which saves investment and reduces operating costs, and there is no tail gas emission in the production process; the application makes the by-product green oxygen in the green hydrogen production process be resourceized, which is beneficial to the healthy development of the green hydrogen industry;

[0018] (2) The temperature of the mixed gas at the inlet of the oxidation furnace is low, the ammonia-air ratio is increased, and the production efficiency is improved;

[0019] (3) The oxidation of the mixed gas is carried out by using concentrated acid, which further improves the oxidation degree and the concentration of the finished product acid;

[0020] (4) The oxidation absorption tower adopts a jet tray structure, which improves the oxidation rate and the absorption rate, reduces the pressure loss, reduces the height of the oxidation absorption tower, and saves investment;

[0021] (5) The tail gas directly uses a booster to increase the pressure, which greatly reduces the power consumption; in the traditional process, air is compressed from normal pressure to 0.45-0.5 MPa, and in the present process, the tail gas is compressed from 0.37-0.42 MPa to 0.45-0.5 MPa.

[0022] (6) The gas contains no particulate impurities, which improves the service life and consumption of the platinum catalyst; the exhaust gas is fully recycled without the need for an exhaust gas turbine, saving investment.

[0023] The beneficial effects of this invention are:

[0024] This invention provides a process for producing dilute nitric acid by oxygenation and recycling of tail gas. It makes resource-efficient use of green oxygen, a byproduct of green hydrogen production, effectively solving the environmental pollution problem of tail gas in nitric acid production. It has low investment costs, high acid concentration in the finished product, and low energy consumption, resulting in good economic and environmental benefits. Attached Figure Description

[0025] Figure 1 This is a flow chart of the production process of dilute nitric acid according to the present invention.

[0026] Figure 2 This is a schematic diagram of the dilute nitric acid production apparatus of the present invention.

[0027] In the diagram: 1 is the oxidizer, 2 is the waste heat boiler, 3 is the ammonia mixer, 4 is the economizer, 5 is the platinum recovery unit, 6 is the demineralized water preheater, 7 is the rapid cooler, 8 is the dilute acid separator, 9 is the oxidation absorption tower, 10 is the dilute acid pump, 11 is the concentrated acid pump, 12 is the bleaching tower, 13 is the oxygen mixer, 14 is the booster compressor, 15 is the tail gas preheater, 16 is the gas ammonia preheater, and 17 is the gas lift cap; A is nitrogen, B is gas ammonia, C is oxygen, D is condensed concentrated acid, E is demineralized water, F is finished acid, G is circulating water, H is chilled water, J is deoxygenated water, and K is boiler feedwater. Detailed Implementation

[0028] The present invention will be further illustrated by the following embodiments, but is not limited to the following embodiments.

[0029] This invention provides an apparatus for producing dilute nitric acid using a tail gas oxygenation recycling method, such as... Figure 2 As shown, the system includes an oxidizer 1, a waste heat boiler 2 at the bottom of the oxidizer 1, an ammonia mixer 3 connected to the oxidizer inlet, and an economizer 4, a platinum recovery unit 5, a demineralized water preheater 6, a rapid cooler 7, and a dilute acid separator 8 connected to the oxidizer absorption tower 9 and a dilute acid pump 10. The dilute acid pump 10 is connected to the middle of the oxidizer absorption tower 9, and the condensed dilute acid is sent to the upper part of the oxidizer absorption tower through the dilute acid pump 10. The bottom outlet of the oxidizer absorption tower is connected to a concentrated acid pump 11, which forms a circulation with the middle of the oxidizer absorption tower. The middle outlet of the oxidizer absorption tower is connected to a bleaching tower 12, which is the crude acid outlet. The top outlet of the bleaching tower 12 is connected to the bottom of the oxidizer absorption tower and an oxygen mixer 13. The tail gas outlet at the top of the oxidizer absorption tower is connected to a booster compressor 14. After being pressurized by the booster compressor 14, the tail gas is sent to the oxygen mixer 13. The oxygen mixer is connected to the ammonia mixer 3 through a tail gas preheater 15.

[0030] The structure of the oxidation absorption tower 9 is as follows: the upper section of the oxidation absorption tower is an absorption section, and the main function is absorption; the lower section is an oxidation section, and the main function is oxidation; the upper and lower sections are separated by a baffle, and the baffle is provided with a gas lifting cap, the mixed gas in the oxidation section enters the absorption section through the gas lifting cap, and the liquid in the absorption section cannot flow into the oxidation section; the inside of the oxidation section is provided with a jet tray, and the condensed concentrated acid formed in the oxidation section is circulated on the tray by a pump to strengthen the oxidation of NO in the mixed gas, and the excess concentrated acid is sent to the absorption section; the inside of the absorption section is provided with a jet tray, and the crude acid, the dilute acid and the desalted water enter the tower from the lower part, the middle part and the upper part of the absorption section respectively to absorb and oxidize, and finally the required concentration of nitric acid is obtained from the outlet at the bottom of the tower wall of the absorption section.

[0031] The application provides a process for producing dilute nitric acid by tail gas oxygen circulation method, which comprises the following contents:

[0032] (1) Establish a nitrogen circulation system: the oxygen mixer 13 is connected with the nitrogen A input pipeline, 0.45-0.5 MPa normal temperature N2 is input into the system to establish a circulation system, and the input of N2 is stopped after the system is circulated;

[0033] (2) 0.5-0.55 MPa, 80-120 DEG C oxygen C enters the oxygen mixer 13 after passing through the bleaching tower 12 and is mixed with N2, the N2:O2 molar ratio is controlled in the range of 3.2-3.5, the nitrogen-oxygen mixed gas in the oxygen mixer 13 is heated to 130-160 DEG C by the tail gas preheater 15 and then enters the ammonia mixer 3;

[0034] (3) The ammonia mixer 3 is connected with the gaseous ammonia B input pipeline, the gaseous ammonia B with a pressure of 0.55-0.6 MPa is preheated to 90-120 DEG C by the gaseous ammonia preheater 16 and then enters the ammonia mixer 3, and the oxygen-ammonia molar ratio is controlled in the range of 1.8-2;

[0035] (4) The mixed gas discharged from the ammonia mixer 3 enters the oxidation furnace 1, ammonia oxidation is carried out at 850-920 DEG C to generate NO, the mixed gas is cooled to about 40 DEG C by the waste heat boiler 2, the economizer 4 and the desalted water preheater 6 after recovering heat, and then enters the dilute acid separator 8;

[0036] (5) The condensed dilute acid from the lower part of the dilute acid separator 8 is transported to the corresponding acid concentration tray in the middle part of the oxidation absorption tower 9 by the dilute acid pump 10, and the NO x gas from the upper part of the dilute acid separator 8 enters the bottom of the oxidation absorption tower. At the same time, the secondary oxygen from the bleaching tower 12 also enters the bottom of the oxidation absorption tower to increase the concentration of NO xThe oxygen content of the mixed gas is 15-17% (volume percent) of the primary oxygen gas (referring to the oxygen gas from the oxygen mixer), and the flow rate of the secondary oxygen gas is 15-17% of the primary oxygen gas (referring to the oxygen gas from the oxygen mixer) ; the NO in the mixed gas at the bottom of the oxidation absorption tower 9 is further oxidized into NO2, and the mixed gas temperature is maintained at about 40°C under the cooling action of the circulating water, while the condensed concentrated acid is formed, the condensed concentrated acid D is circulated at the bottom of the oxidation absorption tower by the concentrated acid pump 11, and the excess condensed concentrated acid is sent to the middle part of the oxidation absorption tower; the residual NO in the oxidation absorption tower bottom is absorbed by the circulating water, and the residual NO2 is reduced into NO by the reducing agent in the circulating water x The mixed gas enters the upper part of the oxidation absorption tower through the riser cap 17 of the partition plate and is oxidized and absorbed at the same time; the desalted water E as the absorption liquid enters from the upper part of the oxidation absorption tower, and the 55-60% dilute nitric acid formed at the lower part of the absorption section flows to the upper part of the bleaching tower;

[0037] (6) The NO in the crude acid is blown off by O2 in the bleaching tower 12 x The gas is then discharged from the bottom of the bleaching tower as the finished product acid F;

[0038] (7) The tail gas (0.37-0.42 MPa) from the top of the oxidation absorption tower is pressurized to 0.45-0.5 MPa by the booster and then recycled, mixed with O2 in the oxygen mixer, and then used in the next production cycle.

[0039] The implementation of the present application will be further illustrated by specific examples as follows: Example 1

[0040] After establishing a circulation system by introducing 0.45 MPa of ambient temperature N2 before the oxygen mixer, the N2 supply is stopped. Primary oxygen at 0.5 MPa and 80°C is introduced into the bleaching tower, controlled at a molar ratio of N2:O2 = 3.5:1. The primary oxygen and N2 are mixed in the oxygen mixer and then heated to 160°C in the tail gas preheater before entering the ammonia mixer. Gaseous ammonia at 0.65 MPa is preheated to 100°C in the ammonia preheater and enters the ammonia mixer, where it is mixed with the nitrogen-oxygen mixture, maintaining an oxygen-ammonia molar ratio of 2:1. The gas exiting the ammonia mixer enters the oxidation furnace for ammonia oxidation, with the furnace temperature at 860°C. The mixed gas exiting the oxidation furnace passes through a waste heat boiler, economizer, platinum recovery unit, and demineralized water preheater for heat and platinum recovery before entering the rapid cooler. In the rapid cooler, the mixed gas is rapidly cooled to 40°C, condensing dilute nitric acid. The condensed dilute nitric acid and gas then enter a separator for separation. The separated condensed dilute acid flows out from the bottom of the separator and is pumped to the middle of the oxidation absorption tower as a makeup absorbent. The separated gas exits from the top of the separator and enters the oxidation section at the bottom of the oxidation absorption tower. Simultaneously, secondary oxygen is introduced into the oxidation section to increase the oxygen concentration in the mixed gas and improve the oxidation rate of NO. The amount of secondary oxygen added is 17% of the amount of primary oxygen. The gas temperature in the oxidation section is controlled at 40℃, where NO is further oxidized to NO2. Nitric acid condenses and flows out from the bottom of the tower, then is pumped to the top of the oxidation section for circulation. Excess condensed concentrated acid is sent to the corresponding acid concentration position in the upper absorption section of the oxidation absorption tower. The mixed gas in the oxidation section enters the absorption section through the riser in the middle of the tower. In the absorption section, the mixed gas continues the oxidation absorption reaction. The crude nitric acid exiting the lower part of the absorption section enters the top of the bleaching tower, where NO is counter-blown away by O2 entering from the bottom. x The gas flows out from the bottom, and the finished product has an acid concentration of 55% and a temperature of 50℃.

[0041] Demineralized water at 30°C is added as the absorbent from the top of the oxidation absorption tower, and the heat generated by the absorption is removed by cooling water. The exhaust gas exiting from the top of the tower has a temperature of 30°C and a pressure of 0.37 MPa, which is increased to 0.45 MPa by a booster pump for continued recycling.

[0042] In this embodiment, the ammonia consumption is 282 kg / t acid, the electricity consumption is 38 kWh / t acid, and the platinum consumption is 0.07 g / t acid. Example 2

[0043] After the circulation system is established by passing 0.5 MPa normal temperature N2, stop passing N2, pass 0.55 MPa, 100℃ primary oxygen into the bleaching tower, control according to the molar ratio N2:O2=3.2:1; the primary oxygen and N2 are mixed after passing through the oxygen mixer, enter the tail gas preheater to heat to 130℃, then enter the ammonia mixer. The 0.6 MPa gaseous ammonia is heated to 90℃ by the ammonia preheater, enters the ammonia mixer, and is mixed with the nitrogen oxygen mixed gas in the ammonia mixer, control the oxygen ammonia molar ratio to be 1.8. The gas out of the ammonia mixer enters the oxidation furnace to carry out the ammonia oxidation reaction, the temperature in the oxidation furnace is 920℃. The mixed gas out of the oxidation furnace passes through the waste heat boiler, the coal economizer, the platinum recovery device, the desalted water preheater to recover heat and platinum, then enters the rapid cooler. The mixed gas is rapidly cooled to 40℃ in the rapid cooler and condenses dilute nitric acid, then the condensed dilute acid and the gas enter the separator to separate. The condensed dilute acid separated out flows out from the lower part of the separator, is sent to the middle part of the oxidation absorption tower by the dilute acid pump as the supplementary absorption liquid; the separated gas out from the upper part of the separator enters the oxidation section in the lower part of the oxidation absorption tower, at the same time, secondary oxygen is passed into the oxidation section to increase the oxygen concentration in the mixed gas and improve the oxidation rate of NO, the addition amount of the secondary oxygen is 15% of the amount of the primary oxygen. The temperature of the gas in the oxidation section is controlled to be 40℃, NO is further oxidized into NO2, at the same time, nitric acid is condensed and flows out from the bottom of the tower, and is sent to the top of the oxidation section by the concentrated acid pump to circulate, the excess condensed concentrated acid is sent to the corresponding acid concentration position in the upper part of the oxidation absorption tower. The mixed gas in the oxidation section enters the absorption section through the gas lifting cap in the middle part of the tower, the mixed gas continues to carry out the oxidation absorption reaction in the absorption section, the crude nitric acid out of the lower part of the absorption section enters the top of the bleaching tower, and the O2 passed into the bleaching tower from the lower part is used to remove NO in the liquid, then the product acid with a concentration of 60% and a temperature of 52℃ flows out from the bottom. x

[0044] The desalted water at 20℃ is used as the absorption liquid and is added from the top of the oxidation absorption tower, the heat generated by the absorption is removed by the cooling water. The tail gas out of the top of the tower has a temperature of 20℃ and a pressure of 0.42 MPa, and is lifted to a pressure of 0.5 MPa by the lifting machine to continue to be used in the circulation.

[0045] In the embodiment, the ammonia consumption is 282 kg / t acid, the power consumption is 34 Kw.h / t acid, and the platinum consumption is 0.075 g / t acid.

[0046] Table 1 Comparison between the embodiment of the application and the traditional medium pressure process

[0047]

[0048] ​Part of data of traditional medium-pressure process in Table 1 is quoted from the following document: Tang Wenqiong, Zhang Yousen. Analysis of production status and development proposal of nitric acid industry in China, Chemical Fertilizer Industry, 2013 (2). By comparison, compared with the traditional technology, the process of the present application effectively solves the problem of environmental pollution of tail gas in the production of nitric acid, the concentration of finished acid is high, the investment cost is low, and the energy consumption is low.

[0049] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A process for the production of dilute nitric acid by tail gas oxygenation cycle characterized in that It comprises the following steps: (1) Establish a nitrogen circulation system: the oxygen mixer is connected to the nitrogen input pipeline, and 0.45-0.5 MPa normal temperature N2 is input into the system to establish a circulation system, and the system is circulated after stopping the input of N2; (2) 0.5-0.55 MPa, 80-120℃ O2 passes through the bleaching tower and enters the oxygen mixer to be mixed with N2, and the N2:O2 molar ratio is controlled at 3.2-3.5, and the nitrogen-oxygen mixed gas in the oxygen mixer is heated to 130-160℃ by the tail gas preheater and then enters the ammonia mixer; (3) The ammonia mixer is connected to the gaseous ammonia input pipeline, and the gaseous ammonia with a pressure of 0.55-0.65 MPa is preheated to 90-120℃ by the gaseous ammonia preheater and then enters the ammonia mixer to be mixed with the nitrogen-oxygen mixed gas, and the oxygen-ammonia molar ratio is controlled at 1.8-2; (4) The mixed gas discharged from the ammonia mixer enters the oxidation furnace to generate NO by ammonia oxidation at 850-920℃, and the mixed gas is cooled to 40℃ by the waste heat boiler, the economizer and the desalted water preheater after recovering heat, and then enters the dilute acid separator; (5) The condensed dilute acid from the lower part of the dilute acid separator is transported to the corresponding acid concentration tray in the middle part of the oxidation absorption tower by the dilute acid pump. The NO x The gas enters the bottom of the oxidation absorption tower; at the same time, the secondary oxygen from the bleaching tower also enters the bottom of the oxidation absorption tower to increase the NO x The oxygen content of the mixed gas, the NO in the mixed gas at the bottom of the oxidation absorption tower is further oxidized to NO2, and the temperature of the mixed gas is maintained at 40°C under the cooling action of circulating water, while forming condensed concentrated acid. The condensed concentrated acid is circulated at the bottom of the oxidation absorption tower by the concentrated acid pump, and the excess condensed concentrated acid is sent to the middle part of the oxidation absorption tower. The remaining NO x The mixed gas enters the upper part of the oxidation absorption tower through the riser cap of the partition, and is oxidized and absorbed at the same time; the desalted water as the absorption liquid enters from the upper part of the oxidation absorption tower, and forms 55-60% dilute nitric acid at the lower part of the absorption section to flow to the upper part of the bleaching tower. In the oxidation absorption tower, the oxidation section is internally provided with a jet tray, the concentrated acid formed in the oxidation section is circulated on the tray by a pump to strengthen the oxidation of NO in the mixed gas, and the excess concentrated acid is sent to the absorption section; the absorption section is internally provided with a jet tray, and the crude acid, the dilute acid and the desalted water enter the tower from the lower part, the middle part and the upper part of the absorption section respectively to absorb and oxidize, thereby improving the oxidation rate and the absorption rate; (6) Removal of NO from the crude acid by O2 blowing in the bleaching tower x and the product acid flows out at the bottom of the bleaching tower; (7) The tail gas from the top of the oxidation absorption tower is pressurized to 0.45-0.5 MPa by the booster and then recycled, enters the oxygen mixer to be mixed with O2, and then the next production cycle is carried out.

2. The process for the production of dilute nitric acid by tail gas oxygenated cycle according to claim 1, characterized in that: The primary oxygen from the bleaching tower is connected to the oxygen mixer, and the secondary oxygen of the bleaching tower enters the bottom of the oxidation absorption tower, and the volume flow of the secondary oxygen is 15-17% of that of the primary oxygen.

3. A device for the production of dilute nitric acid by the oxygen-added tail gas cycle process according to claim 1 or 2, characterized in that: The oxidation furnace is provided with a waste heat boiler at the bottom, and the inlet of the oxidation furnace is connected to the ammonia mixer, and the outlet of the oxidation furnace is connected to the economizer, the platinum recovery device, the desalted water preheater, the quick cooler, the dilute acid separator, the dilute acid separator is connected to the oxidation absorption tower and the dilute acid pump respectively, the dilute acid pump is connected to the middle part of the oxidation absorption tower, and the liquid is sent to the middle part of the oxidation absorption tower by the dilute acid pump; the bottom outlet of the oxidation absorption tower is connected to the concentrated acid pump and the middle part of the oxidation absorption tower to form a circulation; the middle outlet of the oxidation absorption tower is connected to the bleaching tower, and the outlet of the bleaching tower at the top is connected to the bottom of the oxidation absorption tower and the oxygen mixer respectively; the tail gas outlet at the top of the oxidation absorption tower is connected to the booster, and the tail gas is pressurized by the booster and then connected to the oxygen mixer, and the oxygen mixer is connected to the ammonia mixer through the tail gas preheater.

4. The apparatus for producing dilute nitric acid by tail gas oxidation cycle according to claim 3, characterized in that: The upper section of the oxidation absorption tower is an absorption section, and the lower section is an oxidation section. A baffle is arranged between the upper and lower sections. The baffle is provided with a gas lifting cap. The mixed gas in the oxidation section enters the absorption section through the gas lifting cap, and the liquid in the absorption section cannot flow into the oxidation section. The oxidation section is internally provided with a spray tray. The condensed concentrated acid formed in the oxidation section is circulated on the tray by a pump to strengthen the oxidation of NO in the mixed gas. The excess condensed concentrated acid is sent to the absorption section. The absorption section is internally provided with a spray tray. The condensed concentrated acid, the condensed dilute acid and the desalted water enter the tower from the lower part, the middle part and the upper part of the absorption section respectively to absorb and oxidize. Finally, the required concentration of nitric acid is obtained and flows out from the outlet of the tower wall at the bottom of the absorption section.

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