CN1864812A - A nitric oxides (NOX) waste pollution control in industrial process and resource reclaiming method - Google Patents
A nitric oxides (NOX) waste pollution control in industrial process and resource reclaiming method Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 53
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 11
- 239000002699 waste material Substances 0.000 title description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims abstract description 76
- 229910017604 nitric acid Inorganic materials 0.000 claims abstract description 76
- 239000007789 gas Substances 0.000 claims abstract description 48
- 230000008719 thickening Effects 0.000 claims abstract description 45
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 claims abstract description 37
- 239000002912 waste gas Substances 0.000 claims abstract description 30
- 230000008569 process Effects 0.000 claims abstract description 21
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 16
- 239000002253 acid Substances 0.000 claims abstract description 13
- 238000002156 mixing Methods 0.000 claims abstract description 7
- 238000010521 absorption reaction Methods 0.000 claims description 94
- 239000007788 liquid Substances 0.000 claims description 34
- 238000012856 packing Methods 0.000 claims description 16
- 238000004064 recycling Methods 0.000 claims description 14
- 238000006243 chemical reaction Methods 0.000 claims description 10
- 239000000945 filler Substances 0.000 claims description 10
- GQPLMRYTRLFLPF-UHFFFAOYSA-N nitrous oxide Inorganic materials [O-][N+]#N GQPLMRYTRLFLPF-UHFFFAOYSA-N 0.000 claims description 7
- 238000010992 reflux Methods 0.000 claims description 6
- 239000002250 absorbent Substances 0.000 claims description 5
- 230000002745 absorbent Effects 0.000 claims description 5
- 238000012546 transfer Methods 0.000 claims description 5
- 230000006837 decompression Effects 0.000 claims description 3
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- 239000000203 mixture Substances 0.000 claims description 3
- 230000009467 reduction Effects 0.000 claims description 3
- 238000005507 spraying Methods 0.000 claims description 3
- 239000004063 acid-resistant material Substances 0.000 claims description 2
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- 229910052799 carbon Inorganic materials 0.000 claims description 2
- 239000002184 metal Substances 0.000 claims description 2
- 229910052751 metal Inorganic materials 0.000 claims description 2
- 239000007769 metal material Substances 0.000 claims description 2
- 229910052755 nonmetal Inorganic materials 0.000 claims description 2
- 230000000630 rising effect Effects 0.000 claims 1
- 238000004061 bleaching Methods 0.000 abstract description 4
- 230000000694 effects Effects 0.000 abstract description 4
- 238000007599 discharging Methods 0.000 abstract 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 abstract 1
- 229910002651 NO3 Inorganic materials 0.000 abstract 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 abstract 1
- 239000003463 adsorbent Substances 0.000 abstract 1
- 239000007800 oxidant agent Substances 0.000 description 8
- 230000001590 oxidative effect Effects 0.000 description 7
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 6
- 230000007613 environmental effect Effects 0.000 description 5
- 239000010410 layer Substances 0.000 description 5
- 229910001220 stainless steel Inorganic materials 0.000 description 5
- 239000010935 stainless steel Substances 0.000 description 5
- 125000004122 cyclic group Chemical group 0.000 description 4
- ODUCDPQEXGNKDN-UHFFFAOYSA-N Nitrogen oxide(NO) Natural products O=N ODUCDPQEXGNKDN-UHFFFAOYSA-N 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 230000018109 developmental process Effects 0.000 description 3
- 150000007524 organic acids Chemical class 0.000 description 3
- 241000282414 Homo sapiens Species 0.000 description 2
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 239000003054 catalyst Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 description 2
- 239000000779 smoke Substances 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
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- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 description 1
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- RJIWZDNTCBHXAL-UHFFFAOYSA-N nitroxoline Chemical compound C1=CN=C2C(O)=CC=C([N+]([O-])=O)C2=C1 RJIWZDNTCBHXAL-UHFFFAOYSA-N 0.000 description 1
- 235000005985 organic acids Nutrition 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- -1 polytetrafluoroethylene Polymers 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
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- 230000036632 reaction speed Effects 0.000 description 1
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- 229910001961 silver nitrate Inorganic materials 0.000 description 1
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- Gas Separation By Absorption (AREA)
Abstract
The invention relates to a method for treating and reusing waste gas containing nitrogen oxide generated in industrial process. It comprises following steps: mixing waste gas containing nitrogen oxide with air according to a certain proportion, plural serial adsorbing it in tower by introducing it from bottom of head tower, discharging it from top of tail tower, discharging generated hydrogene nitrate of low concentration from bottom of head tower, proceeding decompressing and thickening process in thickening tower, which includes bleaching and dewatering; hydrogen nitrate of low concentration is introduced from top of thickening tower, hydrogen nitrate of high concentration being 45-65% is discharged from bottom; supercharging nitrogen oxide extracted from thickening tower top with vacuum system, then introducing it into adsorbing process again; the water or diluted acid from thickening tower is used as adsorbent and is added from top of tail tower in adsorbing process and counter current contacts with gas in tower for mass transferring. The waste gas treatment effect is good, and the discharging concentration of nitrogen oxide in exhaust gas is less than 50 ppm; all the nitrogen oxide in exhaust gas is recycled to generate aqua fortis with mass concentration being more than 55%.
Description
Technical Field
The present invention belongs to NOXThe technical fields of waste gas environment-friendly emission, regeneration and recycling and circular economy.
Background
Nitric acid is commonly used in industrial processes as an oxidant for the production of methanol catalysts, organic acids, and numerous fine chemicals. Nitric acid is reduced to form nitrogen oxides (mainly NO and NO)2Collectively called NOX) Yellow or brown smoke, commonly known as 'yellow dragon', is one of the important pollution sources causing atmospheric pollution. NOXThe waste gas not only causes acid rain and acid mist, but also can destroy the ozone layer, and brings serious harm to the natural environment, the production and the life of human beings. Thus, NOXThe absorption and resource utilization of the method are important components in environmental governance and various nitric acid industrial production, which not only meet the requirements of economic sustainable development in China, but also meet the requirements of human health. With the rapid development of petrochemical industry in recent years, the application range and the dosage of nitric acid are remarkably increased, and NO is generatedXThe source of the waste gas is increased, the scale is enlarged, and the environmental protection problem is very urgent. At present, many provinces and cities in China have developed an industrial policy that the standard emission of tail gas containing nitrogen oxides is required to be taken as the primary condition for the operation of nitric acid industry.
Currently for containing NOXThe waste gas treatment method mainly comprises a dry method and a wet method, wherein the dry method can not effectively recover nitrogen oxide resources, so that the method is mainly used for treating the tail gas of the automobile and is rarely used for treating the tail gas of the nitric acid industry. The wet method is generally to absorb NO by water, or dilute acid, alkali solutionX. The absorption with alkali liquor has the advantages of high absorption rate, easy standard of tail gas emission, and normal pressure operation, thus saving investment and lowering operation cost. However, the produced salt products have low value, and the added lye system is usually corrosive, so that the storage and transportation cost is high, and the operation is careless and the secondary pollution is easy to cause.
The reaction formula of the process for absorbing nitrogen oxides by using water or dilute acid is as follows:
one patent for nitric acid manufacture, recycle or recovery was proposed by the Deringer-Kard company, USA (CN 96199789.3): first nitric acid is used to react NOXOxidation of NO in the source to nitrogen oxides of valence 3 (e.g. N)2O3) Then oxygen and water are introduced for reaction to generate nitric acid. This indicates NOXOther reversible and irreversible reactions also exist during the conversion to nitric acid. Since part of the reaction is recycled (e.g. NO is oxidised to NO)2And NO2And reacts with water to generate NO), practice proves that the method of normal-pressure single-tower or multi-tower series absorption of water or dilute nitric acid is adopted, the tail gas emission hardly reaches the national emission standard, and some are even 'yellow dragon'. Patent CN02138494.0 proposes an absorption towerThe absorption equipment, the jet pump is the auxiliary absorption equipment, the method of single-stage circulation absorption of nitrogen oxide in tail gas by dilute nitric acid under normal pressure. The actual effect is to be examined.
Theoretically, the pressurization is beneficial to the forward progress of the reaction, and the reaction speed can be greatly improved. The selection of the operating pressure is very critical: the selected pressure is low, so that the absorption process is long, the investment is large, the operation requirement is high, and the tail gas emission is difficult to reach the standard; however, too high a pressure, in addition to placing higher demands on the plant, also increases the operating costs linearly with increasing pressure. Determining an optimum operating pressure is therefore a key issue that needs to be addressed first.
Another key point that is easily overlooked is the control of the temperature of the absorption process and the amount of circulationof the absorption liquid in each section. NOXThe absorption process is a strongly exothermic reaction, and if heat transfer is carried out in time in each absorption stage, the operating temperature will rise, which will be detrimental to NOXThe exhaust emission is easy to exceed the standard. The circulation amount of the absorption liquid in each absorption section is also an important operation parameter, the spraying amount is small, and the contact area of gas and the absorption liquidDecrease and decrease the absorption effect. With NO in the exhaust gasXThe reduction of concentration and flow rate, the reaction scale and the generated heat of each absorption section are gradually reduced, and the liquid circulation amount and the heat exchange amount are correspondingly reduced.
When the exhaust emission concentration reaches the standard, the concentration of nitric acid in absorption liquid discharged from an absorption system is generally 20-45%, the solubility of nitrous gas in nitric acid is rapidly increased along with the increase of the concentration of nitric acid, the liquid is easy to appear yellow green and disperse brown smoke, and the quality is poor. International patent CN99126938.1 introduces nitric acid/nitrous gas stream after absorption system into bleaching zone, and adds oxygen into stream to further oxidize and remove nitrous gas in absorption liquid, and raise yield and concentration of nitric acid. The acid liquor after bleaching can be sent to a dehydration thickening section for concentration. Patent CN02213457.3 proposes a nitric acid thickening tower, which mainly adopts ceramic structured packing and a liquid distributor of polytetrafluoroethylene. The concentration of the concentrated nitric acid can reach 49 percent at present, and the product is white high-quality nitric acid at the moment. In general, more than 55% concentrated nitric acid is used as an oxidizing agent in industry, so that the obtained acidsolution needs to be mixed with 98% high-concentration nitric acid to obtain more than 55% nitric acid. The high-concentration nitric acid with the concentration of 98% is high in price, the nitric acid is not economical when being mixed into the nitric acid with the concentration of 55-60% for use, in addition, the high-concentration nitric acid has high storage and transportation requirements, the mixing process is a strong heat release process, nitrous gas is easy to generate, and the operation risk is high. The limit concentration of the nitric acid concentration can reach 65%, if the process conditions and the separation performance of the concentration increasing process can be improved, the concentration of the concentrated nitric acid can reach 55%, so that the nitric acid can be recycled, and the trouble of introducing a high-concentration nitric acid system is avoided.
Disclosure of Invention
The present invention provides an industrial process Nitrogen Oxide (NO)X) Waste gas treatment and resource utilization method, not only ensuring NO contentXThe environmental protection emission of the waste gas can also be used for NO in the waste gasXAnd recycling is carried out completely, and 55-65% of high-concentration nitric acid is generated for industrial recycling. Meanwhile, secondary pollution sources such as waste water and waste gas are not generated in the whole process.
The technical scheme of the invention is as follows:
industrial process Nitrogen Oxide (NO)X) The waste gas treating and resource utilizing process consists of pressurized absorption section and decompression concentration section, and the pressurized absorption section adopts single tower or multiple towers to absorb in series: will contain NOXAfter the waste gas and the air are mixed in proportion, the mixture enters from the bottom of a first tower at the absolute pressure of 2.5-5 atm for multistage series absorption, the absorption process is carried out at the temperature of 5-30 ℃, the purified gas is discharged from the top of a tail tower, and the low-concentration nitric acid generated after absorption and reaction is discharged from the bottom of the first tower and enters a pressure reduction and concentration section; the reduced pressure thickening section adopts a thickening tower to bleach and dewater, low-concentration nitric acid enters from the top of the thickening tower, high-concentration nitric acid with the concentration of 45-65% is discharged from the bottom of the thickening tower, the pressure at the top of the thickening tower is 50-100mmHg, the temperature is controlled to be 40-55 ℃, the pressure at the bottom of the thickening tower is not higher than 150mmHg, the temperature is controlled to be not higher than 80 ℃, and NO-containing nitric acid extracted by a vacuum system at the top of the thickening towerXThe gas enters the absorption section again after being pressurized, the water or dilute acid distilled from the thickening tower is taken as an absorbent, added from the top end of the tail tower of the absorption section, and is in countercurrent contact with the gas entering the tower and carries out mass transfer.
NO as defined aboveXMethod for treating waste gas and recycling, containing NOXThe method for determining the mixing ratio of the exhaust gas and the air comprises the following steps: 1 volume of NO consumes 0.75 volume of O2(ii) a 1 volume of NO2Consuming 0.25 volume O2(ii) a 1 volume of air contains 0.2 volume of O2. According to NO and NO in the exhaust gas2The content, the proportion and the flow of the air are calculated to obtain the flow V of the theoretical airTActual mixed air flow VAAnd VTThe ratio of (A) to (B) is 1.5-2: 1.
NO as defined aboveXThe waste gas treatment and resource method adopts 3-7 stages of serial absorption in the absorption section, and the absorption operation pressure is 2.5-5 atm (absolute pressure): when the operation pressure is less than or equal to 3atm, adopting 6-7 stages of absorption, adopting double towers or 3 towers in series connection, wherein each tower consists of 2-3 stages; when the operation pressure is less than 4atm and less than 3atm, 4-5-stage absorption is adopted, double towers are connected in series, and each tower consists of 2-3 stages; when the operating pressure is more than or equal to 4atm, 3 toAnd 4-stage absorption, wherein single tower or double towers are connected in series, and each tower consists of 2-3 stages.
NO as defined aboveXThe waste gas treating and resource utilizing method includes one packing stage, one fixing device, one liquid distributor over the packing stage and one liquid collecting tank below the packing stage. The height of the packing is 3-6 m, and random packing or regular packing made of various acid-resistant materials can be adopted.
NO as defined aboveXIn the waste gas treatment and recycling method, each absorption stage is provided with an external circulating heat exchange structure, so that the operating temperature of an absorption working section is ensured to be between 5 and 30 ℃. Liquid flowing out of the packing layer is collected by the liquid collecting tank, pumped into an external heat exchanger by the circulating pump, and enters the liquid distributor at the top of the stage for forced circulation after heat exchange. The circulating volumes of all levels of liquid are equal or gradually reduced in sequence, and the spraying density is 30-100 m3/m2h is between.
NO as defined aboveXMethod for treating and recycling waste gas, NO in tail gas discharged from top of tail tower in absorption sectionXThe discharge concentration is less than 50ppm, and the speed is less than 0.25 kg/h; nitric acid with the mass concentration of 35-55% is obtained from the bottom of the first tower of the absorption working section, and the flow of the absorption liquid at the top of the tail tower can be flexibly adjusted by controlling the flow of the absorption liquid as required. When the concentration of nitric acid obtained in the absorption section is higher than 40%In time, it becomes yellowish green due to dissolved nitrous gases and darkens with increasing concentration.
NO as defined aboveXThe waste gas treating and resource utilizing process includes the absorption section tail tower to obtain nitric acid, and the decompression concentration tower to decolorize and concentrate the nitric acid. According to the concentration of the final nitric acid, one-stage or multi-stage concentration can be adopted, the pressure of the tops of all concentration towers is 50-100mmHg, the temperature is controlled to be 40-55 ℃, the pressure of the bottom of the concentration tower is not higher than 150mmHg, the temperature is controlled to be not higher than 80 ℃, the concentration of the concentrated nitric acid is 45-65%, and the concentrated nitric acid is colorless or slightly white.
NO as defined aboveXThe waste gas treating and resource utilizing process includes concentration towers with theoretical plates in 5-12, reflux ratio controlled in 2-5, rectification section and stripping section in the ratio of 2-4 to 1. The mass transfer element can be composed of single-stage or multi-stage random packing layers or regular packing layers, and the height of each stage of packing is 2-6 m; it is also possible to use a tray composition of not more than 20 stages. The filler, the tower plate and the tower internals are made of nitric acid resistant metal and/or non-metal materials.
NO as defined aboveXA process for treating waste gas and reclaiming it includes such steps as heating the nitrous gas dissolved in nitric acid solution in thickening tower, allowing it to escape from liquid phase, gradually reacting with water while raising it to obtain water-insoluble NO, pumping it out by vacuum system on top of tower, pressurizing, mixing it with waste gas containing air, and absorbing again. And (3) water or dilute acid (the mass concentration of nitric acid is 0-0.5%) evaporated from the top of the tower is partially refluxed after condensation, and extracted part returns to the absorption section and enters the top of the tail tower to be used as absorption liquid.
The invention has the following advantages:
1. good waste gas treatment effect and NO in tail gasXThe discharge concentration is less than 50ppm, the speed is less than 0.25kg/h and is far lower than the current domestic and foreign discharge standards;
2. NO in tail gasXAll the nitric acid is recycled and regenerated into resources, and concentrated nitric acid with the mass concentration of more than 55 percent and capable of being directly used as an oxidant is generated and recycled;
3. the bleaching and thickening units are integrated, the process is simple, and the space and the investment are saved;
4. secondary waste acid and waste water are not generated in the treatment process, so that the method is green and environment-friendly;
5. the invention has high output/investment ratio, and is especially suitable for large-flow NOXHigh concentration and high environmental protection emission requirement. The method conformsto the current national development trend of environmental protection and circular economy.
Drawings
FIG. 1 is a flow chart of the method of the present invention in example 3, wherein: 1 is NOXThe mixed gas of (3); 2 is water or dilute nitric acid absorption liquid; 3 and 4 are inter-column liquid phase streams; 5 is acid liquor discharged by an absorption system; 6 and 7 are gas phase streams between columns; 8 is qualified exhaust gas; 9 coming out of thickening towerWater or dilute nitric acid; 10 is nitric acid at a concentration of about 60%; 11 is a first-stage absorption tower; 12 is a second stage absorption tower; 13 is a third stage absorption tower; and 14, a thickening tower.
Detailed Description
Example 1: production of organic acid products with 56% nitric acid as oxidant to produce NOXExhaust gas, flow 4.6m3/h，NOXIn a volume concentration of 75%, wherein NO and NO2About 2: 1. Mixing waste gas and air according to the volume ratio of 1: 4, and then entering an absorption section, wherein the operation pressure of the absorption section is 2.6atm, 6-stage absorption is adopted, three towers are connected in series, and each tower has 2 stages, as shown in figure 1. Each stage is provided with a liquid distributor, a stainless steel filler 3m, a liquid collecting box and other accessories. The 6-stage liquid circulation volume is 5m3H is used as the reference value. The tower diameter of the absorption tower is 0.4 m. NO in vented tail gasXThe discharge concentration was 22ppm and the rate was 0.12 kg/h. Nitric acid (in yellow green) with mass concentration of 48% flows out from the absorption section, enters a thickening tower, the diameter of the tower is 0.6m, 12 layers of sieve plate towers are arranged, and 9 plates (counted from top to bottom) are fed above the tower. The operation pressure is 100mmHg, the overhead temperature is 55 ℃, the kettle temperature is 78 ℃, the reflux ratio is 3, and all internal parts are made of acid-resistant stainless steel materials. Concentrated nitric acid (colorless) with the mass concentration of 56% is extracted from the tower bottom and directly used as an oxidant of organic acid. And gas pumped out by the tower top vacuum system is pressurized and then returns to the absorption section for cyclic absorption, and dilute nitric acid with the mass concentration of 0.5% is evaporated from the tower top and enters from the last cyclic stage of the absorption section as an absorbent.
Example 2: methanol catalyst produced by using 62% concentrated nitric acid as oxidant to produce NO and NO2Gas, ratio about 1: 1, flow 10.2m3H is used as the reference value. Mixing waste gas and air according to the volume ratio of 1: 3.5, and then entering an absorption working section, wherein the operation pressure of the absorption working section is 4atm, 4-stage absorption is adopted, double towers are connected in series, and each tower has 2 stages. Each stage is provided with a liquid distributor, a stainless steel filler 4m, a liquid collecting box and other accessories, and the circulation volume of the liquid of 4 stages is respectively 80, 55 and 55m3H is used as the reference value. The tower diameters of the absorption tower are 0.6m and 0.4m respectively. NO in vented tail gasXEmission concentration 45ppm, rate 02 kg/h. Nitric acid (yellowish green in color, with a dissolved part of NO) with a mass concentration of 45% flowing out of the absorption sectionX) And entering a thickening working section, wherein the thickening working section adopts double towers (stages) connected in series, the tower diameters of the thickening towers are 0.8m, the single layer of acid-resistant stainless steel filler is 3m, the operation pressure is 100mmHg, the first-stage thickening tower is fed in from the tower bottom, the reflux ratio is 2, the tower top temperature is 55 ℃, and the tower bottom temperature is 75 ℃. The gas extracted from the top of the first-stage thickening tower is pressurized and then returned to the absorption section for cyclic absorption, 0.5% of dilute nitric acid extracted from the top of the tail tower of the absorption tower enters the last cyclic stage of the absorption section, and 52% of nitric acid extracted from the tower kettle enters the second-stage thickening tower. The second thickening tower has the operation pressure of 50mmHg, the rectifying section of 4m, the stripping section of 2m, the reflux ratio of 3, the top temperature of the thickening tower of 42 ℃, the bottom temperature of the thickening tower of 79 ℃, and concentrated nitric acid (colorless) with the mass concentration of 62 percent extracted from the bottom of the thickening tower, and is directly used as an oxidant. The top of the concentration tower is evaporated to pure water (nitric acid is less than 10ppm), which can be used as absorbent to enter from the last circulating stage of the absorption section, and can also be used for other purposes.
Example 3: silver nitrate is produced by using 98% concentrated nitric acid as oxidant to produce NO2Gas flow rate 32.50m 3/h.Waste gas and air are mixed according to the volume ratio of 1: 2.5 and then enter an absorption section, the operation pressure of the absorption section is 5atm, and an absorbent is clean water. The single tower is adopted for 3-stage absorption, and the tower diameter is 0.8 m. Each stage is provided with a liquid distributor, a stainless steel filler 5m, a liquid collecting box and other accessories, and the circulation volume of the 3-stage liquid is 150m 3/h. NO invented tail gasXThe discharge concentration was 32ppm and the rate was 0.18 kg/h. The nitric acid (colorless) with the mass concentration of 38 percent flows out from the absorption section and enters the factory to produce 98 percent concentrated nitric acid for processing.
Claims (8)
1. A method for treating and recycling nitrogen oxide waste gas in an industrial process is characterized by comprising the following steps: the method comprises a pressurization absorption working section and a decompression concentration-increasing working section, wherein the pressurization absorption working section adopts single tower or multiple towers to carry out series absorption: will contain NOXThe waste gas and the air are mixed in proportion, and enter from the bottom of a first tower at an absolute pressure of 2.5-5 atm for multi-stage series absorption, the absorption process is carried out at 5-30 ℃, and the purified gasGas is discharged from the top of the tail tower, and the low-concentration nitric acid generated after absorption and reaction is discharged from the bottom of the first tower and enters a pressure reduction and concentration section; the reduced pressure thickening working section adopts a thickening tower to bleach and dewater, low-concentration nitric acid enters from the top of the thickening tower or the middle of the tower, high-concentration nitric acid with the concentration of 45-65% is discharged from the bottom of the thickening tower, the pressure at the top of the thickening tower is 50-100mmHg, the temperature is controlled to be 40-55 ℃, the pressure at the bottom of the thickening tower is not higher than 150mmHg, the temperature is controlled to be not higher than 80 ℃, and NO-containing nitric acid extracted by a vacuum system at the top of the thickening towerXThe gas enters the absorption section again after being pressurized, the water or dilute acid distilled from the thickening tower is taken as an absorbent, added from the top end of the tail tower of the absorption section, and is in countercurrent contact with the gas entering the tower and carries out mass transfer.
2. The method for treating and recycling exhaust gas as claimed in claim 1, wherein: containing NOXThe method for determining the mixing ratio of the exhaust gas and the air comprises the following steps: 1 volume of NO consumes 0.75 volume of O2(ii) a 1 volume of NO2Consuming 0.25 volume O2(ii) a 1 volume of air contains 0.2 volume of O2According to NO, NO in the exhaust gas2The content, proportion and flow of the theoretical air are calculatedTActual mixed air flow VAAnd VTThe ratio of (A) to (B) is 1.5: 1-2: 1.
3. The method for treating and recycling exhaust gas as claimed in claim 1, wherein: the absorption working section adopts 3-7 stages of series absorption, and the absolute pressure of absorption operation is 2.5-5 atm: when the operation pressure is less than or equal to 3atm, adopting 6-7 stages of absorption, adopting double towers or 3 towers in series connection, wherein each tower consists of 2-3 stages; when the operation pressure is less than 4atm and less than 3atm, 4-5-stage absorption is adopted, double towers are connected in series, and each tower consists of 2-3 stages; when the operating pressure is more than or equal to 4atm, 3-4 stages of absorption are adopted, single tower or double towers are adopted to be connected in series, and each tower is composed of 2-3 stages.
4. The method for treating and recycling exhaust gas as claimed in claim 3, wherein: each stage of absorption specific device comprises a filler and a fixing device thereof, a liquid distributor above the filler and a liquid collecting tank below the filler, the liquid collecting tank can be omitted in the absorption stage at the lowest part of the tower, the height of the filler is 3-6 m, and random packing or regular packing made of various acid-resistant materials is adopted.
5. The method for treating and recycling exhaust gas as claimed in claim 3, wherein: each absorption stage is provided with an external circulation heat exchange structure, the operation temperature of the absorption working section is ensured to be 5-30 ℃, liquid flowing out of the packing layer is collected by the liquid collecting tank, pumped into the external heat exchanger by the circulating pump, enters the liquid distributor at the top of the stage after heat exchange for forced circulation, the liquid circulation volume of each stage is equal or gradually reduced in sequence, and the spraying density is 30-100 m3/m2h is between.
6. The method for treating and recycling exhaust gas as claimed in claim 1, wherein: and (3) allowing nitric acid obtained at the bottom of a tail tower of an absorption working section to enter a reduced-pressure thickening tower for decoloring and thickening, adopting one-stage or multi-stage concentration according to the concentration of the final nitric acid, wherein the pressure at the tops of all thickening towers is 50-100mmHg, the temperature is controlled to be 40-55 ℃, the pressure at the bottom of the thickening tower is not higher than 150mmHg, the temperature is controlled to be not higher than 80 ℃, and the concentration of the concentrated nitric acid is 45-65%.
7. The method for treating and recycling exhaust gasas claimed in claim 6, wherein: the number of theoretical plates of each thickening tower is 5-12, the reflux ratio is controlled to be 2-5, the thickening tower is provided with a rectifying section and a stripping section, the ratio of the number of the theoretical plates of the rectifying section to the number of the theoretical plates of the stripping section is 2-4: 1, a mass transfer element is composed of a single-stage or multi-stage random packing layer, and the height of each stage of packing is 2-6 m; or the tower plate with no more than 20 layers is adopted, and the filler, the tower plate and the tower internals are made of nitric acid resistant metal and/or non-metal materials.
8. The method for treating and recycling exhaust gas as claimed in claim 1, wherein: nitrous gas dissolved in nitric acid solution entering a thickening tower escapes from a liquid phase after being heated, and continuously reacts with water step by step in the rising process to finally become water-insoluble NO, the water-insoluble NO is extracted by a tower top vacuum system, the water-insoluble NO is mixed with waste gas containing a certain proportion of air after being pressurized, the mixture enters an absorption section again for treatment, water or dilute acid evaporated from the tower top partially refluxes after being condensed, and part of the extracted water returns to an absorption section and enters the top of a tail tower to be used as absorption liquid.
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| GB2056420A (en) * | 1979-04-12 | 1981-03-18 | Humphreys & Glasgow Ltd | Removal of nitrogen oxides |
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