CN115814571A - Process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas - Google Patents
Process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas Download PDFInfo
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- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 title claims abstract description 358
- 238000010521 absorption reaction Methods 0.000 title claims abstract description 236
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 title claims abstract description 100
- 229910017604 nitric acid Inorganic materials 0.000 title claims abstract description 100
- 125000004122 cyclic group Chemical group 0.000 title claims abstract description 41
- 230000003647 oxidation Effects 0.000 title claims abstract description 39
- 238000007254 oxidation reaction Methods 0.000 title claims abstract description 39
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 34
- 239000002912 waste gas Substances 0.000 title claims abstract description 34
- 239000007789 gas Substances 0.000 claims abstract description 112
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 45
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 45
- 239000001301 oxygen Substances 0.000 claims abstract description 45
- 238000000034 method Methods 0.000 claims abstract description 27
- 230000008569 process Effects 0.000 claims abstract description 20
- 238000001816 cooling Methods 0.000 claims abstract description 13
- 238000007906 compression Methods 0.000 claims abstract description 7
- 230000006835 compression Effects 0.000 claims abstract description 6
- 238000002156 mixing Methods 0.000 claims abstract description 5
- 239000007788 liquid Substances 0.000 claims description 56
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 33
- MGWGWNFMUOTEHG-UHFFFAOYSA-N 4-(3,5-dimethylphenyl)-1,3-thiazol-2-amine Chemical compound CC1=CC(C)=CC(C=2N=C(N)SC=2)=C1 MGWGWNFMUOTEHG-UHFFFAOYSA-N 0.000 claims description 16
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 claims description 16
- 238000012856 packing Methods 0.000 claims description 15
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 14
- 239000000203 mixture Substances 0.000 claims description 13
- 239000002994 raw material Substances 0.000 claims description 9
- 229910052757 nitrogen Inorganic materials 0.000 claims description 8
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 5
- 238000006243 chemical reaction Methods 0.000 claims description 5
- 239000011261 inert gas Substances 0.000 claims description 3
- 239000007791 liquid phase Substances 0.000 claims description 3
- 230000000630 rising effect Effects 0.000 claims description 3
- 238000005265 energy consumption Methods 0.000 abstract description 5
- 239000002440 industrial waste Substances 0.000 abstract description 2
- 239000006227 byproduct Substances 0.000 abstract 1
- 239000000047 product Substances 0.000 description 16
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- 239000003054 catalyst Substances 0.000 description 4
- 230000008901 benefit Effects 0.000 description 3
- 239000003344 environmental pollutant Substances 0.000 description 3
- 230000014759 maintenance of location Effects 0.000 description 3
- 231100000719 pollutant Toxicity 0.000 description 3
- 239000002250 absorbent Substances 0.000 description 2
- 230000002745 absorbent Effects 0.000 description 2
- 229910001882 dioxygen Inorganic materials 0.000 description 2
- 239000002360 explosive Substances 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 239000000618 nitrogen fertilizer Substances 0.000 description 2
- 239000003507 refrigerant Substances 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000003463 adsorbent Substances 0.000 description 1
- 239000000809 air pollutant Substances 0.000 description 1
- 231100001243 air pollutant Toxicity 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000012847 fine chemical Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000000678 plasma activation Methods 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 238000004886 process control Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- 239000002351 wastewater Substances 0.000 description 1
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Abstract
The invention belongs to the technical field of industrial waste gas treatment, and particularly relates to a process for preparing dilute nitric acid by cyclic oxidation and absorption of high-concentration nitrogen oxides in waste gas. The method comprises the following steps: 1) Mixing waste gas containing nitrogen oxides, fresh oxygen and circulating gas, and entering a first-stage absorption tower after compression or compression cooling; 2) Multi-stage absorption reaction in the first-stage absorption tower; 3) A small part of the gas containing nitrogen oxide in the first-stage absorption tower enters the second-stage absorption tower to carry out multi-stage absorption reaction and the like. After the treatment of the cyclic oxidation absorption process, the concentration of nitrogen oxides in the waste gas can be reduced to 100mg/Nm 3 The absorption rate of the nitrogen oxide is as high as 99.99%, the byproduct dilute nitric acid can be reused by a production device, the investment is low, no secondary pollution is caused, and the problems of low nitrogen oxide removal rate, high investment and high energy consumption in the existing high-concentration nitrogen oxide waste gas treatment process can be effectively solved.
Description
Technical Field
The invention belongs to the technical field of industrial waste gas treatment, and particularly relates to a process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas.
Background
Nitrogen Oxides (NO) x ) Mainly comprising N 2 O、NO、NO 2 、N 2 O 3 、N 2 O 4 、N 2 O 5 The wastewater is mainly discharged from nitric acid application enterprises such as nitric acid plants, nitrogen fertilizer plants, fuel plants, explosive plants, sulfuric acid plants, catalyst plants and the like, and forms photochemical smog and nitric acid typeAcid rain, one of the major atmospheric pollutants that destroys the ozone layer. Therefore, very strict nitrogen oxide emission standards are set up at home and abroad. The maximum allowable emission concentration of nitrogen oxides of a chimney with the length of 60 meters specified in GB16297-1996 Integrated emission Standard for air pollutants is not more than 240mg/m 3 The emission limit of nitrogen oxides is specified in GB31573-2015 discharge Standard for pollutants for inorganic chemical industry to be 100mg/m 3 。
The industrial methods for producing nitrogen oxide waste gas include reduction, biological, adsorption, liquid absorption, and plasma activation. In the liquid absorption method, if water/dilute nitric acid is used as an absorbent, the emission index of nitrogen oxide in tail gas is ensured, and the removed NO is removed x The dilute nitric acid is recovered, which is beneficial to realizing the whole process control and clean production.
Currently, wet removal of exhaust gas NO by water/dilute nitric acid x The device mostly adopts multi-stage series absorption, because the nitrogen oxide waste gas contains NO, and water absorbs NO 2 NO is generated again thereafter, and therefore the problem of NO oxidation has an influence on the absorption efficiency. Although the oxidation degree of nitrogen oxide can be greatly improved under high pressure, thereby improving the absorption rate of nitrogen oxide, the higher pressure brings energy consumption problem, the operation cost is greatly increased, and when NO is used x Removing to 300mg/Nm 3 Lower NO when x The concentration index is difficult to achieve.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas. The invention supplements fresh oxygen, nitrogen oxide reacts with oxygen to generate nitrogen dioxide under the action of an efficient mass transfer internal part, and the nitrogen dioxide reacts with the absorbent dilute nitric acid in a countercurrent contact manner to generate nitric acid and nitric oxide; the absorption liquid at the bottom of each section in the tower is pumped out, cooled and heat-removed, and then returns to the tower, and the unreacted nitric oxide-containing circulating gas at the top of the absorption tower returns to the raw material gas inlet, so that the circulating oxidation absorption of nitric oxide in the system is realized. The concentration of nitrogen oxide in the purified gas can be as low as 100mg/Nm by adopting the process 3 Low investment, low energy consumption, nearly zero discharge of waste and pollutants,can effectively solve the problem of the prior wet method for removing the NO in the waste gas by using water/dilute nitric acid x High investment, high energy consumption and high removal precision.
In order to achieve the above purpose, the specific technical scheme of the invention is as follows:
a process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas is characterized by comprising the following steps:
1) The nitrogen oxide-containing gas, fresh oxygen and returned recycle gas are mixed, compressed (cooled as required) and then enter the primary absorption tower.
2) The first-stage absorption tower adopts multi-section absorption reaction, wherein in each absorption reaction section, nitric oxide in the rising gas reacts with oxygen to generate nitrogen dioxide; the nitrogen dioxide and the descending dilute nitric acid are in countercurrent contact reaction to generate nitric acid and nitric oxide; most of the dilute nitric acid at the bottom of each absorption reaction section is collected by a liquid collecting tank, and is pumped out by a circulating liquid pump and cooled and then returns to the top of the section for cyclic absorption; a small portion of the nitric acid overflows down to the top of the upper absorption reaction section. And (3) sending the dilute nitric acid accumulated in the tower kettle of the first-stage absorption tower to a dilute nitric acid storage tank as a product, mixing most of the nitrogen oxide-containing gas at the tower top as a circulating gas with the nitrogen oxide-containing gas and fresh oxygen, and entering next cycle of cyclic oxidation absorption.
3) A small part of gas containing nitrogen oxide in the first-stage absorption tower enters a second-stage absorption tower, the second-stage absorption tower also adopts multi-section absorption reaction, wherein absorption liquid at the tail section of the absorption reaction section adopts desalted water, and liquid phase at the bottom of the tail section does not circulate and flows downwards to the top of the last absorption reaction section. Most of the dilute nitric acid at the bottom of the rest absorption reaction sections of the secondary absorption tower is collected by a liquid collecting tank, and is pumped out by a circulating liquid pump to be cooled and then returns to the top of the section for cyclic absorption; a small portion of the nitric acid overflows down to the top of the upper absorption reaction section. And (4) sending the dilute nitric acid accumulated in the tower kettle of the secondary absorption tower to the top of the primary absorption tower as absorption liquid. The pressure control is adopted at the tower top, and the concentration of nitrogen oxides is as low as 100mg/Nm 3 The overhead gas can be directly discharged to the atmosphere.
According to the invention, the process for preparing the dilute nitric acid by the cyclic oxidation absorption of the high-concentration nitrogen oxides in the waste gas comprises the following specific embodimentThe gas containing nitrogen oxide is NO x (N 2 O、NO、NO 2 、N 2 O 3 、N 2 O 4 、N 2 O 5 ) The nitrogen oxide-containing gas treated by the method comprises high-concentration nitrogen oxide gas discharged by nitric acid plants, nitrogen fertilizer plants, fuel plants, explosive plants, sulfuric acid plants, catalyst plants and the like, wherein the molar content of the nitrogen oxide is not less than 50%.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the fresh oxygen is pure oxygen with a molar composition of more than 99.6% or oxygen-enriched oxygen with a molar composition of more than 90%, and the rest components are inert gases such as nitrogen and the like. Flow determination principle of fresh oxygen: the ratio of the molar flow of the available oxygen in the oxygen gas to the molar flow of the converted nitric oxide (containing nitrogen dioxide to be absorbed and regenerated into nitric oxide) in the raw material gas is not less than 0.6.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the pressure after compression is 0.01-1.0 MPaG, and the temperature after cooling is 10-40 ℃. When the temperature rise of the compressed gas is not higher than 60 ℃, the cooling step can be omitted.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the absorption reaction section can be a packing section, a tower plate section and a high-efficiency internal part mass transfer section, and can also be a free combination of the packing section, the tower plate section and the high-efficiency internal part mass transfer section.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the retention time of the treated nitrogen oxide gas in each absorption reaction section is not less than 5 seconds.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the number of absorption reaction sections of a first-stage absorption tower is 2-5 stages, and the number of absorption reaction sections of a second-stage absorption tower is 2-5 stages; the specific number of the absorption reaction sections in the first-stage absorption tower and the second-stage absorption tower is determined according to the required concentration of the dilute nitric acid product and the index requirement of the concentration of the nitrogen oxide in the treated gas.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the liquid collecting tank can be a tower internal part type with a riser and a liquid collecting disc, and can also be a liquid collecting buffer tank outside the tower.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the temperature of the pumped circulating liquid after cooling is 10-40 ℃.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the operation temperature of each absorption reaction section of the primary absorption tower and the secondary absorption tower is 10-40 ℃.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in exhaust gas, the total heat release of nitric oxide oxidation and nitrogen dioxide absorption is calculated according to the content of nitrogen oxides in raw material gas, so that the flow of the circulating liquid pump is determined on the basis of ensuring the operating temperature of each absorption reaction section of the primary absorption tower and the secondary absorption tower.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the mass concentration of the dilute nitric acid product at the tower bottom of the primary absorption tower is 10-40%.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the ratio of the molar flow of the circulating gas of the primary absorption tower to the total molar flow of the top gas of the primary absorption tower is 0.01-0.99.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the temperature of the desalted water is 10-40 ℃.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the cooling refrigerant in the process is circulating cooling water or chilled water with the temperature of 5 ℃ or above or other refrigerants capable of providing the cold energy of 10-40 ℃.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, the flow rate of desalted water fed to the top of the secondary absorption tower is determined as follows: when the dilute nitric acid of the tower kettle product of the primary absorption tower does not meet the required mass concentration, the desalted water is not supplemented or is supplemented to the top of the secondary absorption tower less; when the dilute nitric acid of the product at the tower bottom of the primary absorption tower meets the required mass concentration, according to the content of nitrogen oxides in the raw material gas, the desalted water is continuously supplemented to the tower top of the secondary absorption tower, the tower bottom of the primary absorption tower accumulates the dilute nitric acid, and the dilute nitric acid product is sent to a dilute nitric acid storage tank through the liquid level control of the tower bottom; and when the mass concentration of the dilute nitric acid at the tower bottom of the primary absorption tower is higher than 30%, increasing the flow of the desalted water to be supplemented into the tower top of the secondary absorption tower.
According to a specific embodiment of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas, when the pressure of the tower top of the secondary absorption tower does not exceed a set value, tower top gas enters a circulating gas main pipe; when the overhead pressure exceeds a set value, the nitrogen oxide concentration is as low as 100mg/Nm 3 The tower top gas can be directly discharged to the atmosphere.
Compared with the prior art, the invention has the positive effects that:
the method has the advantages of simple process flow, small equipment quantity and low investment.
The process method provided by the invention is operated at low temperature and low pressure, and has no consumption of catalysts, adsorbents, chemicals and the like, and low overall energy consumption.
Thirdly, the invention can remove the nitrogen oxide to 100mg/Nm 3 Meets the most harsh discharge limit value in China and has high removal precision.
(IV) reacting NO by the process of the invention x The reaction is recycled into the product dilute nitric acid, the cyclic production in the whole process is realized, and the energy-saving and emission-reducing benefits are obvious.
Drawings
Fig. 1 is a schematic flow chart of a process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in exhaust gas according to embodiment 1 of the present invention.
Fig. 2 is a schematic process flow diagram of a process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in exhaust gas according to embodiment 2 of the present invention.
FIG. 3 is a schematic view of a process flow for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in exhaust gas.
Wherein, the names corresponding to the reference numbers are:
t1-first-stage absorption tower, T2-second-stage absorption tower, C1-compressor (complete set), P1-P5-circulating liquid pump 1-5, E1-5-circulating liquid cooler, E6-desalted water cooler and E7-tail gas cooler.
Detailed Description
A process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas comprises the following steps:
step 1):
the nitrogen oxide-containing gas, the fresh oxygen and the returned circulating gas are mixed, compressed and cooled and then enter a first-stage absorption tower.
The temperature of the nitrogen oxide gas is normal temperature to 100 ℃, the pressure is 0.1kPaG to 20kPaG, and the molar composition of the nitrogen oxide is as follows: 50% -100%, water 0% -50%, oxygen: 0% -30%, nitrogen: 3 to 5 percent.
Specifically, the temperature of the fresh oxygen is normal temperature, the pressure is 0.1-1.0 MPaG, the molar composition of the fresh oxygen is pure oxygen with the content of more than 99.6 percent or oxygen with the content of more than 90 percent, and the rest components are inert gases such as nitrogen and the like. Flow determination principle of fresh oxygen: the ratio of the molar flow of the available oxygen in the oxygen gas to the molar flow of the converted nitric oxide (containing nitrogen dioxide to be absorbed and regenerated into nitric oxide) in the raw material gas is not less than 0.6.
Preferably, the fresh oxygen has a molar composition of more than 99.6%.
Furthermore, the nitrogen oxide-containing gas, fresh oxygen and the returned recycle gas are mixed and compressed to 0.01 to 1.0MPaG.
Preferably, the post-compression outlet pressure is 0.01 to 0.1MPaG.
Preferably, the cooling step can be omitted when the gas temperature rise after compression is not higher than 60 ℃.
Step 2):
the first-stage absorption tower adopts multi-section absorption reaction, wherein in each absorption reaction section, nitric oxide in the rising gas reacts with oxygen to generate nitrogen dioxide; the nitrogen dioxide and the descending dilute nitric acid are in countercurrent contact reaction to generate nitric acid and nitric oxide; most of the dilute nitric acid at the bottom of each absorption reaction section is collected by a liquid collecting tank, and is pumped out by a circulating liquid pump and cooled and then returns to the top of the section for cyclic absorption; a small portion of the nitric acid overflows down to the top of the upper absorption reaction section. And (3) sending the dilute nitric acid accumulated in the tower kettle of the first-stage absorption tower to a dilute nitric acid storage tank as a product, mixing most of the nitrogen oxide-containing gas at the tower top as a circulating gas with the nitrogen oxide-containing gas and fresh oxygen, and entering next cycle of cyclic oxidation absorption.
Specifically, the absorption reaction section can be a packing section, a tower plate section and a high-efficiency internal part mass transfer section, and can also be a free combination of the packing section, the tower plate section and the high-efficiency internal part mass transfer section.
Specifically, the residence time of the treated nitrogen oxide gas in each of the absorption reaction sections is not less than 5 seconds.
Specifically, the number of absorption reaction sections of the first-stage absorption tower is 2-5 stages, and the number of absorption reaction sections of the second-stage absorption tower is 2-5 stages; the specific number of the absorption reaction sections in the first-stage absorption tower and the second-stage absorption tower is determined according to the required concentration of the dilute nitric acid product and the index requirement of the concentration of the nitrogen oxide in the treated gas.
Preferably, when the system pressure is not more than 0.1MPaG, the absorption temperature is not higher than 20 ℃, and the quality concentration requirement of the product dilute nitric acid is not lower than 20%, the first-stage absorption tower is provided with 3 sections, and the second-stage absorption tower is provided with 3 sections.
Specifically, the liquid collecting tank can be a tower internal part type with a gas lift pipe liquid collecting disc and the like, and can also be a liquid collecting buffer tank outside the tower. The temperature of the circulating liquid pumped out of the liquid collecting box after cooling is 10-40 ℃.
Preferably, the temperature of the circulating liquid pumped out from the header tank after cooling is 12 ℃.
Specifically, the total heat release of nitric oxide oxidation and nitrogen dioxide absorption is calculated according to the content of nitrogen oxides in the raw material gas, so as to ensure that the operating temperature of each absorption reaction section of the primary absorption tower and the secondary absorption tower is 12-40 ℃.
Preferably, the operation temperature of each absorption reaction section of the first-stage absorption tower and the second-stage absorption tower is ensured to be 12-20 ℃.
Specifically, in order to ensure the circulating absorption effect, the mass concentration of the dilute nitric acid product in the tower kettle of the primary absorption tower is 10-40%.
Specifically, the ratio of the molar flow of the circulating gas of the primary absorption tower to the total molar flow of the overhead gas of the primary absorption tower is 0.01-0.99.
Preferably, the ratio of the molar flow of the circulating gas of the first-stage absorption tower to the total molar flow of the overhead gas of the absorption tower is 0.7-0.95, and the concentration index of the gaseous nitrogen oxide at the top of the second-stage absorption tower is better ensured to be as low as possible while the treatment gas amount is properly increased.
And step 3):
a small part of gas containing nitrogen oxide in the first-stage absorption tower enters a second-stage absorption tower, the second-stage absorption tower also adopts multi-section absorption reaction, wherein absorption liquid at the tail section of the absorption reaction section adopts desalted water, and liquid phase at the bottom of the tail section does not circulate and flows downwards to the top of the last absorption reaction section. Most of the dilute nitric acid at the bottom of the rest absorption reaction sections of the secondary absorption tower is collected by a liquid collecting tank, and is pumped out by a circulating liquid pump to be cooled and then returns to the top of the section for cyclic absorption; a small portion of the nitric acid overflows down to the top of the upper absorption reaction section. And (4) sending the dilute nitric acid accumulated in the tower kettle of the secondary absorption tower to the top of the primary absorption tower as absorption liquid. The pressure control is adopted at the tower top, and the concentration of nitrogen oxides is as low as 100mg/Nm 3 The overhead gas can be directly discharged to the atmosphere.
Specifically, the temperature of the desalted water is 10-40 ℃.
Preferably, the temperature of the desalinated water is 12 ℃.
Specifically, the flow rate of the desalted water fed to the top of the secondary absorption tower is determined in the following manner: when the dilute nitric acid of the tower kettle product of the primary absorption tower does not meet the required mass concentration, the desalted water is not supplemented or is supplemented to the top of the secondary absorption tower less; when the dilute nitric acid of the product at the tower bottom of the primary absorption tower meets the required mass concentration, according to the content of nitrogen oxides in the raw material gas, the desalted water is continuously supplemented to the top of the secondary absorption tower, the dilute nitric acid is accumulated at the tower bottom of the primary absorption tower, and the dilute nitric acid product is sent to a dilute nitric acid storage tank through the liquid level control of the tower bottom; and when the mass concentration of the dilute nitric acid at the tower bottom of the primary absorption tower is higher than 30%, increasing the flow of the desalted water to be supplemented into the tower top of the secondary absorption tower.
Specifically, when the tower top pressure of the secondary absorption tower does not exceed a set value, tower top gas enters a circulating gas main pipe; when the overhead pressure exceeds a set value, the nitrogen oxide concentration is as low as 100mg/Nm 3 The overhead gas can be directly discharged to the atmosphere.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas is specifically described below by combining specific process procedures and principles.
Example 1:
the flow of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas is shown in figure 1.
The nitrogen oxide-containing gas of a certain fine chemical company has a temperature of 50 ℃, a pressure of 1kPaG and a flow rate of 113.27Nm 3 The molar composition is nitrogen dioxide: 65.66%, nitric oxide 19.78%, nitric acid: 0.09%, oxygen: 2.47%, water: 7.75 percent. The fresh oxygen temperature is normal temperature, the pressure is 0.5MPaG, and the flow rate is 35Nm 3 The molar composition is oxygen: 99.6%, nitrogen: 0.4 percent. The ratio of the molar flow of available oxygen in the oxygen to the molar flow of the converted nitric oxide in the feed gas (including the nitrogen dioxide absorbed to regenerate nitric oxide) was calculated to be about 0.64.
Nitrogen oxide-containing gas, fresh oxygen and recycled gas (pressure 8kPaG, temperature 14 ℃ C., flow 7)0Nm 3 H), after mixing, the mixture enters a primary absorption tower T1 after being pressurized to 10kPaG by a fan C1.
The diameter of the first-stage absorption tower T1 is DN600, three sections of regular packing are adopted, the height of each section of packing is 2 meters, and the retention time of gas in each absorption reaction section is about 9.6 seconds.
The flow rate of the circulating liquid at the bottom of each section of the first-stage absorption tower T1 is 15T/h, the temperature is 14-20 ℃, the circulating liquid is pressurized to 0.3MPaG by a circulating liquid pump P1/P2/P3, and then the circulating liquid is cooled to 12 ℃ by a circulating gas cooler E1/E2/E3 and then returns to the first-stage absorption tower T1 for circulating absorption.
The flow rate of dilute nitric acid of a tower bottom product of the first-stage absorption tower T1 is 889.2kg/h, and the mass concentration is about 28.9%; the pressure of the top gas of the first-stage absorption tower T1 is 8kPaG, the temperature is 14 ℃, and the flow rate is 89Nm 3 /h，NO x At a concentration of about 1923mg/Nm 3 (ii) a About 70Nm in the overhead gas 3 The/h is returned to the inlet of the fan C1 as a circulating gas, 19Nm 3 And/h enters a secondary absorption tower T2.
The diameter of the T2 tower of the secondary absorption tower is DN400, three sections are adopted, bubble cap tower plates are selected at the upper part of the tower, and the number of the tower plates is 10; the middle part and the lower part of the tower adopt regular packing, and the height of each section of packing is 2 meters. The residence time of the gas in each absorption reaction zone was about 47.6 seconds.
The flow rate of fresh desalted water is 650kg/h, and the fresh desalted water is cooled to 12 ℃ by a desalted water cooler E6 and then enters a bubble cap tower plate section of a secondary absorption tower T2. The flow rate of the circulating liquid at the bottom of each packing section is 15T/h, the temperature is 12 ℃, the pressure is increased to 0.3MPaG by a circulating liquid pump P4/P5, and the circulating liquid is cooled to 12 ℃ by a circulating liquid cooler E4/E5 and then returns to a secondary absorption tower T2 for circulating absorption.
The flow of the dilute nitric acid accumulated at the tower bottom of the second-stage absorption tower T2 is about 650kg/h, and the dilute nitric acid is cooled and then is sent to the top of the first-stage absorption tower T1; the overhead gas pressure of the second-stage absorption tower T2 is 6kPaG, the temperature is 12 ℃, and the flow rate is 18Nm 3 /h，NO x The concentration is not more than 100mg/Nm 3 (ii) a About 10Nm in the overhead gas 3 The/h is taken as the circulating gas to return to the inlet of a fan C1, and the accumulated 8Nm of the system 3 The purified gas is directly discharged into the atmosphere through a pressure regulating valve.
Example 2:
the flow of the process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas is shown in figure 2.
The nitrogen oxide-containing gas generated by a metal-making apparatus of a catalyst production company has a temperature of 90 ℃, a pressure of 0.1kPaG, and a flow rate of 210Nm 3 The molar composition is 67.72 percent of nitric oxide, oxygen: 0.06%, nitrogen: 0.23%, water: 31.99 percent. The fresh oxygen temperature is normal temperature, the pressure is 0.8MPaG, and the flow rate is 115Nm 3 The molar composition is oxygen: 99.6%, nitrogen: 0.4 percent. The ratio of the molar flow of available oxygen in the oxygen to the molar flow of the converted nitric oxide in the feed gas (containing nitrogen dioxide absorbed to regenerate nitric oxide) was calculated to be about 0.6.
Nitrogen oxide-containing gas, fresh oxygen and recycle gas returned (pressure 0.13MPaG, temperature 12 ℃, flow 230Nm 3 H), cooling the mixture to 40 ℃ in a tail gas cooler E7, pressurizing the mixture to 0.1MPaG by a liquid ring compressor C1, and then entering a primary absorption tower T1.
The diameter of the first-stage absorption tower T1 is DN800, two sections of structured packing are adopted, the height of each section of packing is 2 meters, and the retention time of gas in each absorption reaction section is about 9.28 seconds.
The flow rate of the circulating liquid at the bottom of each section of the primary absorption tower T1 is 60T/h, the temperature is 12-19 ℃, the circulating liquid is pressurized to 0.35MPaG by a circulating liquid pump P1/P2, and then the circulating liquid is cooled to 12 ℃ by a circulating gas cooler E1/E2 and then returns to the primary absorption tower T1 for circulating absorption.
The flow rate of dilute nitric acid of a tower bottom product of the first-stage absorption tower T1 is 1296kg/h, and the mass concentration is about 30 percent; the pressure of the top gas of the first-stage absorption tower T1 is 98kPaG, the temperature is 12 ℃, and the flow rate is 239Nm 3 /h，NO x At a concentration of about 1000mg/Nm 3 (ii) a About 230Nm in the overhead gas 3 The/h is returned to the inlet of the fan C1 as a recycle gas, 29Nm 3 And/h enters a secondary absorption tower T2.
The diameter of a T2 tower of the secondary absorption tower is DN400, two sections are adopted, bubble cap tower plates are selected at the upper part of the tower, and the number of the tower plates is 10; the lower part of the tower adopts regular packing, and the height of the packing is 2 meters. The residence time of the gas in each absorption reaction zone was about 56.5 seconds.
The flow rate of fresh desalted water is 900kg/h, and the fresh desalted water is cooled to 12 ℃ by a desalted water cooler E6 and then enters a bubble cap tower plate section of a secondary absorption tower T2. The flow rate of the circulating liquid at the bottom of the filling section is 60T/h, the temperature is 12 ℃, the pressure is increased to 0.35MPaG by a circulating liquid pump P4, and the circulating liquid is cooled to 12 ℃ by a circulating liquid cooler E4 and then returns to a secondary absorption tower T2 for circulating absorption.
The flow rate of dilute nitric acid accumulated in the tower kettle of the secondary absorption tower T2 is about 900kg/h, and the dilute nitric acid is cooled and then sent to the top of the primary absorption tower T1; the pressure of the overhead gas of the second-stage absorption tower T2 is 96kPaG, the temperature is 12 ℃, and the flow rate is 29Nm 3 /h，NO x The concentration is not more than 100mg/Nm 3 (ii) a About 20Nm in the overhead gas 3 The pressure/h is taken as the circulating gas to return to the inlet of a fan C1, and 9Nm accumulated in the system 3 The h purified gas is directly discharged into the atmosphere via a pressure regulating valve.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. A process for preparing dilute nitric acid by cyclic oxidation absorption of high-concentration nitrogen oxides in waste gas is characterized by comprising the following steps:
1) Mixing waste gas containing nitrogen oxides, fresh oxygen and circulating gas, and entering a first-stage absorption tower after compression or compression cooling;
2) The first-stage absorption tower adopts multi-stage absorption reaction, wherein in each absorption reaction stage, nitric oxide in the rising gas reacts with oxygen to generate nitrogen dioxide; the nitrogen dioxide and the descending dilute nitric acid are in countercurrent contact reaction to generate nitric acid and nitric oxide; most of the dilute nitric acid at the bottom of each absorption reaction section is collected by a liquid collecting tank, and is pumped out by a circulating liquid pump and cooled and then returns to the top of the section for cyclic absorption; a small part of nitric acid overflows downwards to the top of the upper absorption reaction section; dilute nitric acid accumulated in the tower kettle of the first-stage absorption tower is taken as a product and sent to a dilute nitric acid storage tank, most of nitrogen oxide-containing gas at the tower top is taken as circulating gas, mixed with nitrogen oxide-containing gas and fresh oxygen, and enters next cycle of cyclic oxidation absorption;
3) A small part of gas containing nitrogen oxide in the first-stage absorption tower enters a second-stage absorption tower which also adopts multi-stage absorption reaction, wherein, the absorption liquid at the end of the absorption reaction section adopts desalted water, and the bottom of the end section adopts desalted waterThe liquid phase does not circulate and flows downwards to the top of the upper absorption reaction section; most of the dilute nitric acid at the bottom of the rest absorption reaction sections of the secondary absorption tower is collected by a liquid collecting tank, and is pumped out by a circulating liquid pump to be cooled and then returns to the top of the section for cyclic absorption; a small part of nitric acid overflows downwards to the top of the upper absorption reaction section; dilute nitric acid accumulated in the tower kettle of the secondary absorption tower is sent to the tower top of the primary absorption tower to be used as absorption liquid; the pressure control is adopted at the tower top, and the concentration of nitrogen oxides is as low as 100mg/Nm 3 The overhead gas below can be directly discharged to the atmosphere.
2. The process of claim 1 wherein the nitrogen oxide-containing exhaust gas is NO-containing x After the gas containing the nitrogen oxides, the waste gas containing the nitrogen oxides, the fresh oxygen and the circulating gas are mixed, the molar content of the nitrogen oxides is not less than 50 percent.
3. The process according to claim 1, wherein the fresh oxygen is pure oxygen having a molar composition of 99.6% or more or oxygen-enriched oxygen having an oxygen content of 90% or more, and the remaining components are inert gases such as nitrogen.
4. A process according to claim 1 or 3, wherein the flow rate of fresh oxygen determines the principle: the ratio of the molar flow of the effective oxygen in the oxygen to the molar flow of the converted nitric oxide in the raw material gas is not less than 0.6, and the ratio of the molar flow of the circulating gas of the first-stage absorption tower to the total molar flow of the top gas of the first-stage absorption tower is 0.01-0.99; converting nitrogen dioxide contained in the nitric oxide into nitric oxide by absorption.
5. The process according to claim 1, wherein in the step 1), the pressure of the compressed mixed gas is 0.01 to 1.0MPaG, and the temperature of the absorption liquid and the gas after cooling is 10 to 30 ℃; when the temperature rise of the compressed gas is not higher than 60 ℃, the cooling step is omitted.
6. The process of claim 1, wherein the reaction receiving sections of the multistage absorption reaction in step 2) and step 3) are a packing section, a tray section and a high-efficiency internals mass transfer section, or a free combination of the packing section, the tray section and the high-efficiency internals mass transfer section; the residence time of the treated nitrogen oxide gas in each absorption reaction section is not less than 5 seconds
7. The process according to claim 6, wherein the number of the absorption reaction sections of the first-stage absorption tower is 2 to 5 stages, and the number of the absorption reaction sections of the second-stage absorption tower is 2 to 5 stages; the mass concentration of the dilute nitric acid product in the tower kettle of the primary absorption tower is 10-40%.
8. The process of claim 7, wherein in step 2) and step 3), the header tank is of the type of tower internals with riser trays or is a tower external header buffer tank; the temperature of the pumped circulation liquid after cooling is 10-40 ℃; the operation temperature of each absorption reaction section of the first-stage absorption tower and the second-stage absorption tower is 10-40 ℃.
9. The process according to claim 1, wherein the flow rate of the desalted water fed to the top of the secondary absorption tower is determined as follows: when the dilute nitric acid of the tower kettle product of the primary absorption tower does not meet the required mass concentration, the desalted water is not supplemented or is supplemented to the top of the secondary absorption tower less; when the dilute nitric acid of the product at the tower bottom of the primary absorption tower meets the required mass concentration, according to the content of nitrogen oxides in the raw material gas, the desalted water is continuously supplemented to the tower top of the secondary absorption tower, the tower bottom of the primary absorption tower accumulates the dilute nitric acid, and the dilute nitric acid product is sent to a dilute nitric acid storage tank through the liquid level control of the tower bottom; and when the mass concentration of the dilute nitric acid at the tower bottom of the primary absorption tower is higher than 30%, increasing the flow of the desalted water to be supplemented into the tower top of the secondary absorption tower.
10. The process of claim 1, wherein in step 3), when the pressure of the top of the secondary absorption tower does not exceed a set value, the top gas enters a circulating gas main pipe; when the overhead pressure exceeds a set value, the nitrogen oxide concentration is as low as 100mg/Nm 3 The overhead gas can be directly discharged to the atmosphere.
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| CN114130163A (en) * | 2021-11-01 | 2022-03-04 | 新疆兴发化工有限公司 | Environment-friendly treatment process and device for acid preparation through absorption of oxidation tail gas |
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| US5017348A (en) * | 1989-01-26 | 1991-05-21 | Beco Engineering Company | Treatment of nitrogen oxides |
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