CN-121972125-A - Nitric acid absorption tower and absorption process thereof

CN121972125ACN 121972125 ACN121972125 ACN 121972125ACN-121972125-A

Abstract

The invention discloses a nitric acid absorption tower and an absorption process thereof, and belongs to the technical field of nitric acid production. The nitric acid absorption tower comprises an absorption unit, a washing unit and a recovery unit, wherein a plurality of absorption structures are linearly arranged in an absorption box of the absorption unit and are used for spraying and absorbing nitrogen oxides to form nitric acid, the washing unit is arranged above the absorption unit, a plurality of linearly-arranged gas mixing structures are arranged in the washing box and are used for mixing air and nitric acid to wash the nitric acid, the recovery unit is arranged between the washing unit and the absorption unit, the washing unit is connected with the recovery unit through an exhaust pipe arranged at the upper part of the washing unit, the recovery unit is connected with the absorption box through an air return pipe, and the recovered gas is sent into the absorption box. The nitric acid absorption tower and the absorption process thereof can solve the problems of low nitrogen oxide conversion rate and low nitric acid concentration of the existing absorption tower.

Inventors

ZHANG FENG
SUN LIHUI
CHEN YI
LIU YAN
CHEN JINGNAN

Assignees

山东华阳迪尔化工股份有限公司

Dates

Publication Date: 20260505
Application Date: 20260205

Claims (10)

1. A nitric acid absorption tower is characterized by comprising, The absorption unit comprises an absorption box, wherein the top of the absorption box is provided with an exhaust port, the bottom of the absorption box is provided with a liquid outlet, and the lower part of the absorption box is provided with an air inlet for enabling nitrogen oxides to enter the absorption box; The washing unit is positioned above the absorption unit, the absorption box is connected with the washing unit through a liquid outlet, the washing unit comprises a washing box, the lower part of the washing box is provided with a liquid outlet, the inside of the washing box is provided with a plurality of gas mixing structures distributed in a linear array, and the mixing structures are used for mixing air and nitric acid and washing the nitric acid; The recovery unit is arranged between the washing unit and the absorption unit, the washing unit is connected with the recovery unit through an exhaust pipe arranged at the upper part of the washing unit, the recovery unit is connected with the absorption box through an air return pipe, and the gas after recovery treatment is sent into the absorption box.
2. The nitric acid absorption tower according to claim 1, wherein the absorption structure comprises absorption frames, adjacent absorption frames are fixedly connected in a sealing mode, a plurality of first through holes for enabling nitrogen oxide gas and absorption liquid to pass through are uniformly formed in the bottoms of the absorption frames, a supporting plate is arranged in the absorption frames, second through holes are formed in the supporting plate, fillers are filled in the absorption frames and located above the supporting plate, and a flow equalizing assembly is arranged between the absorption frames and the absorption box.
3. The nitric acid absorption tower according to claim 2, wherein the flow equalizing assembly comprises a partition plate, the absorption frame is fixedly connected with the absorption box in a sealing way through an annular partition plate, the partition plate is positioned at the lower part of the absorption frame, a plurality of liquid inlet holes and overflow holes are uniformly formed in the side wall of the absorption frame, the liquid inlet holes are formed in the upper part of the partition plate, the overflow holes are formed in the lower part of the partition plate, absorption liquid on the partition plate enters the absorption frame through the liquid inlet holes, and absorption liquid in the absorption frame enters the downstream partition plate through the overflow holes.
4. A nitric acid absorption tower according to claim 3, wherein the bottom of the absorption tank is connected with the top of the absorption tank through a liquid inlet pipe, a first circulating pump is arranged on the liquid inlet pipe and used for conveying absorption liquid at the bottom of the absorption tank to the top of the absorption tank, a plurality of spraying pipes are arranged at the bottom of the absorption tank and communicated with the liquid inlet pipe, and the spraying pipes are located right above the absorption frame.
5. The nitric acid absorption tower according to claim 4, wherein the gas mixing structure comprises a flow equalizing plate, a plurality of flow equalizing holes are uniformly formed in the flow equalizing plate, a rotating shaft is arranged in a sealing rotation mode in the center of the flow equalizing plate, the rotating shaft is in sealing rotation connection with the washing box, a plurality of gas outlet plates are arranged on the rotating shaft in a circumferential array mode, the gas outlet plates are located above the flow equalizing plate, the inner cavities of the gas outlet plates are communicated with the inner cavities of the rotating shaft, the end heads of the rotating shaft are connected with the air pump through rotary joints, air sent out by the gas outlet plates is mixed with nitric acid on the flow equalizing plate to wash the nitric acid, a driving wheel connected with a motor is arranged on the rotating shaft, and the motor drives the rotating shaft to rotate through the driving wheel.
6. The nitric acid absorption tower as set forth in claim 5, wherein the gas outlet plate is an arc plate, a plurality of flow-through holes are uniformly arranged on the gas outlet plate, a plurality of gas outlet holes communicated with the cavity inside the gas outlet plate are uniformly arranged in the flow-through holes, and the gas holes in the gas outlet plate are uniformly mixed with the nitric acid on the flow-equalizing plate through the gas outlet holes.
7. A nitric acid absorption tower according to claim 6, wherein the recovery unit comprises a recovery box, one end of the recovery box is provided with a ground air inlet end which is communicated with a washing box through an exhaust pipe, the other end of the recovery box is provided with a ground air outlet end which is communicated with the middle of the absorption box through an air return pipe, a second circulating pump is arranged on the air return pipe, two fixing plates are arranged in the recovery box and divide the recovery box into an independent and closed uniform cavity, an oxidation cavity and a condensation cavity, the exhaust pipe is arranged on the uniform cavity, a secondary air inlet is arranged on the side wall of the uniform cavity, a uniform structure for uniformly mixing the recovered gas and the air is arranged in the uniform cavity, a plurality of connecting pipes are uniformly arranged in the oxidation cavity, the gas in the uniform cavity enters the condensation cavity through the connecting pipes, the oxidation cavity is connected with an external refrigerator through a cooling water inlet and an outlet which are arranged on the side wall of the oxidation cavity, the condensation cavity is provided with a condensation pipe for condensing and drying the recovered gas, and the air return pipe is arranged in the condensation cavity.
8. The nitric acid absorption tower according to claim 7, wherein the uniform structure comprises a first uniform plate and a second uniform plate which are connected in a sealing way, a plurality of first grooves are uniformly formed in one side, close to the second uniform plate, of the first uniform plate, a plurality of first uniform holes penetrating through the first uniform plate are uniformly formed in the first grooves, a plurality of second grooves perpendicular to the first grooves are uniformly formed in the second uniform plate, a plurality of second uniform holes penetrating through the second uniform plate are uniformly formed in the second grooves, the first uniform holes and the second uniform holes are arranged in a staggered mode, the pore diameter of the second uniform holes is smaller than that of the first uniform holes, and the number of the second uniform holes is larger than that of the first uniform holes.
9. An absorption process in a nitric acid absorption tower according to claim 8, comprising the steps of: S1, nitrogen oxide gas enters the absorption box from the bottom of the absorption box through an air inlet, desalted water absorption liquid enters the upper part of the absorption frame from a water inlet at the top of the absorption tower, absorption liquid is sprayed into a filler, the nitrogen oxide gas and the absorption liquid are subjected to contact mixing reaction in the filler to generate nitric acid, one part of the absorption liquid in the absorption frame enters the lower absorption frame through a first through hole, the other part of the absorption liquid enters the upper part of the partition plate through an overflow hole, and the absorption liquid above the partition plate enters the lower absorption frame through a liquid inlet; s2, after the collection height of the nitric acid solution at the bottom of the absorption box exceeds the liquid inlet end of the liquid inlet pipe, closing desalted water, opening a first circulating pump, and sending the nitric acid solution at the bottom of the absorption box into a spray pipe at the top of the absorption box through the liquid inlet pipe by the first circulating pump, wherein nitric acid is used as absorption liquid to react with nitrogen oxides; S3, opening a valve at a liquid outlet, enabling nitric acid in the absorption box to enter the washing box through the liquid outlet, starting the air pump and the motor, enabling the motor to drive the rotating shaft to rotate, enabling air in the rotating shaft to enter the inside of the rotating shaft through the rotary joint, enabling the air in the rotating shaft to enter the washing box through an air outlet hole formed in the air outlet plate, enabling the air to contact with the nitric acid on the flow equalizing plate, washing the nitric acid, collecting the washed nitric acid at the bottom of the washing box, and discharging the nitric acid through the liquid outlet hole; S4, the recovered gas enters a recovery tank through an exhaust pipe, the recovered gas and secondary air are uniformly mixed in a uniform cavity through a first uniform plate and a second uniform plate, the uniformly mixed gas enters a connecting pipe, oxidation is carried out in an oxidation cavity, the oxidized recovered gas enters a condensation cavity for condensation and drying, the dried recovered gas is sent into the middle of an absorption tank through an air return pipe, and nitric acid absorption liquid absorbs the recovered gas.
10. The process for absorbing nitric acid by using a nitric acid absorption tower according to claim 9, wherein in S2, the oxidation degree of nitrogen oxides entering an absorption tank is not lower than 90%, the mass percentage of oxygen is 3% -5%, the pressure in the absorption tank is 0.45MPa-0.6MPa, the upper temperature of the absorption tank is 20-30 ℃, the lower temperature of the absorption tank is 40-50 ℃, the spraying density is 8m 3 /m 2 ·h-15m 3 /m 2 h, the gas speed is 0.5m/-0.8m/S, and the residence time of gas in the absorption tower is 5S-8S; In the step S3, the pressure in the washing tank is 0.45-0.6 MPa, the temperature is 30-45 ℃, 8m 3 -12m 3 of air is introduced into each ton of crude nitric acid, and the spraying density is 6m 3 /m 2 ·h-10m 3 /m 2 h; In the step S4, the pressure of the recovered gas in the oxidation cavity of the recovery box is 0.45-0.58 MPa, the temperature is 25-35 ℃, the mass percentage of oxygen in the recovered gas in the uniform cavity is 5-6%, the residence time of the recovered gas in the oxidation cavity is 8S-12S, the oxidation degree of the recovered gas in the return pipe is not lower than 85%, the water vapor content is not higher than 5g/m 3 , and the air inflow of the recovered gas in the absorption box is 10-15% of the total air inflow.

Description

Nitric acid absorption tower and absorption process thereof Technical Field The invention relates to the technical field of nitric acid production, in particular to a nitric acid absorption tower and an absorption process thereof. Background Nitric acid is used as an important basic chemical raw material, is widely applied to a plurality of industrial fields of chemical fertilizers, explosives, dyes, metallurgy and the like, and the high efficiency, high purity and environmental protection of the production process are all the core directions of industrial research. The medium-pressure method for preparing dilute nitric acid is one of the current mainstream production processes because of moderate equipment investment and reasonable energy consumption, and the core of the method realizes nitric acid generation through the reaction of nitrogen oxides (NO x) in an absorption tower and absorption liquid. However, the existing nitric acid absorption tower and absorption process still have a plurality of technical pain points in practical application, which restrict the yield, concentration and production environmental protection of nitric acid: The nitrogen oxide absorption efficiency is insufficient, the gas-liquid contact form in the traditional absorption tower is single, most of the nitrogen oxide and the absorption liquid are in simple spraying or single-layer filler contact, the mixing uniformity of the nitrogen oxide and the absorption liquid is poor, the mass transfer resistance is high, and the NO 2 conversion rate is low. The concentration of nitric acid is difficult to increase, the prior art usually adopts pure water as an initial absorption liquid, a large amount of water brought by the pure water can dilute generated nitric acid, and the rapid increase of the concentration of nitric acid in the initial absorption stage is easy to inhibit the forward progress of reversible reaction, so that the concentration of nitric acid in a finished product is low. In addition, the NO x dissolved in the crude nitric acid cannot be removed efficiently, so that not only is the nitric acid yellow/brown color tone displayed, but also the purity of the product can be influenced due to the exceeding of the nitrous acid content. The tail gas is not fully recycled, namely, the tail gas containing NO x generated in the absorption and washing process is directly discharged or is discharged after simple treatment in the traditional process, so that not only is the waste of nitrogen oxide resources caused, but also the problem of environmental pollution is caused. In order to solve the technical problems, development of a nitric acid absorption tower and an absorption process with optimized structure and cooperative process is needed to improve the conversion rate of nitrogen oxides and the concentration of nitric acid, reduce the emission of pollutants and meet the high-efficiency and environment-friendly requirements of industrial production. Disclosure of Invention The invention aims to provide a nitric acid absorption tower and an absorption process thereof, which solve the problems of low nitrogen oxide conversion rate and low nitric acid concentration of the existing absorption tower. In order to achieve the above object, the present invention provides a nitric acid absorption tower comprising, The absorption unit comprises an absorption box, wherein the top of the absorption box is provided with an exhaust port, the bottom of the absorption box is provided with a liquid outlet, and the lower part of the absorption box is provided with an air inlet for enabling nitrogen oxides to enter the absorption box; The washing unit is positioned above the absorption unit, the absorption box is connected with the washing unit through a liquid outlet, the washing unit comprises a washing box, the lower part of the washing box is provided with a liquid outlet, the inside of the washing box is provided with a plurality of gas mixing structures distributed in a linear array, and the mixing structures are used for mixing air and nitric acid and washing the nitric acid; The recovery unit is arranged between the washing unit and the absorption unit, the washing unit is connected with the recovery unit through an exhaust pipe arranged at the upper part of the washing unit, the recovery unit is connected with the absorption box through an air return pipe, and the gas after recovery treatment is sent into the absorption box. Preferably, the absorption structure comprises absorption frames, the adjacent absorption frames are fixedly connected in a sealing mode, a plurality of first through holes for enabling nitrogen oxide gas and absorption liquid to pass through are uniformly formed in the bottoms of the absorption frames, a supporting plate is arranged in the absorption frames, second through holes are formed in the supporting plate, fillers are filled in the absorption frames and located above the supporting plate, and a flow equalizi