CN111228991A - Denitration system for flue gas denitration by using chlorine dioxide and packed tower - Google Patents
Denitration system for flue gas denitration by using chlorine dioxide and packed tower Download PDFInfo
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- CN111228991A CN111228991A CN202010165257.8A CN202010165257A CN111228991A CN 111228991 A CN111228991 A CN 111228991A CN 202010165257 A CN202010165257 A CN 202010165257A CN 111228991 A CN111228991 A CN 111228991A
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- chlorine dioxide
- flue gas
- nitric acid
- packed tower
- denitration
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- OSVXSBDYLRYLIG-UHFFFAOYSA-N dioxidochlorine(.) Chemical compound O=Cl=O OSVXSBDYLRYLIG-UHFFFAOYSA-N 0.000 title claims abstract description 232
- 235000019398 chlorine dioxide Nutrition 0.000 title claims abstract description 117
- 239000004155 Chlorine dioxide Substances 0.000 title claims abstract description 113
- 239000003546 flue gas Substances 0.000 title claims abstract description 95
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 title claims abstract description 94
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims abstract description 109
- 229910017604 nitric acid Inorganic materials 0.000 claims abstract description 109
- 238000012856 packing Methods 0.000 claims abstract description 59
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 30
- 230000003647 oxidation Effects 0.000 claims abstract description 29
- 239000002253 acid Substances 0.000 claims abstract description 25
- 239000000460 chlorine Substances 0.000 claims abstract description 10
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229910052801 chlorine Inorganic materials 0.000 claims abstract description 7
- 239000007788 liquid Substances 0.000 claims description 44
- 238000001816 cooling Methods 0.000 claims description 3
- 238000005507 spraying Methods 0.000 claims description 3
- 238000005516 engineering process Methods 0.000 abstract description 10
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 142
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 description 42
- 238000010521 absorption reaction Methods 0.000 description 30
- 238000000034 method Methods 0.000 description 25
- 239000000945 filler Substances 0.000 description 22
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 21
- 229910001868 water Inorganic materials 0.000 description 17
- 239000002250 absorbent Substances 0.000 description 13
- 230000002745 absorbent Effects 0.000 description 13
- 239000007789 gas Substances 0.000 description 13
- 230000001590 oxidative effect Effects 0.000 description 13
- 239000000047 product Substances 0.000 description 13
- 239000000243 solution Substances 0.000 description 13
- 238000006243 chemical reaction Methods 0.000 description 12
- 239000002994 raw material Substances 0.000 description 12
- 230000000694 effects Effects 0.000 description 11
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 11
- 239000007800 oxidant agent Substances 0.000 description 10
- UKLNMMHNWFDKNT-UHFFFAOYSA-M sodium chlorite Chemical compound [Na+].[O-]Cl=O UKLNMMHNWFDKNT-UHFFFAOYSA-M 0.000 description 10
- 229960002218 sodium chlorite Drugs 0.000 description 10
- BZSXEZOLBIJVQK-UHFFFAOYSA-N 2-methylsulfonylbenzoic acid Chemical compound CS(=O)(=O)C1=CC=CC=C1C(O)=O BZSXEZOLBIJVQK-UHFFFAOYSA-N 0.000 description 9
- 239000000203 mixture Substances 0.000 description 7
- HEMHJVSKTPXQMS-UHFFFAOYSA-M sodium hydroxide Inorganic materials [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 7
- QBWCMBCROVPCKQ-UHFFFAOYSA-N chlorous acid Chemical compound OCl=O QBWCMBCROVPCKQ-UHFFFAOYSA-N 0.000 description 6
- 238000002360 preparation method Methods 0.000 description 6
- 230000001105 regulatory effect Effects 0.000 description 6
- 239000003513 alkali Substances 0.000 description 5
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 4
- 239000007921 spray Substances 0.000 description 4
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 3
- 239000012670 alkaline solution Substances 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 3
- 238000002474 experimental method Methods 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 239000000779 smoke Substances 0.000 description 3
- 239000010959 steel Substances 0.000 description 3
- 230000001360 synchronised effect Effects 0.000 description 3
- 238000012546 transfer Methods 0.000 description 3
- 238000005406 washing Methods 0.000 description 3
- 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 description 2
- KZBUYRJDOAKODT-UHFFFAOYSA-N Chlorine Chemical compound ClCl KZBUYRJDOAKODT-UHFFFAOYSA-N 0.000 description 2
- 238000010531 catalytic reduction reaction Methods 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- 239000007795 chemical reaction product Substances 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 230000001788 irregular Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 239000011780 sodium chloride Substances 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000010964 304L stainless steel Substances 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 229910002651 NO3 Inorganic materials 0.000 description 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 1
- IOVCWXUNBOPUCH-UHFFFAOYSA-M Nitrite anion Chemical compound [O-]N=O IOVCWXUNBOPUCH-UHFFFAOYSA-M 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- 239000004743 Polypropylene Substances 0.000 description 1
- 241000736911 Turritella communis Species 0.000 description 1
- 231100000987 absorbed dose Toxicity 0.000 description 1
- 239000012190 activator Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 238000012824 chemical production Methods 0.000 description 1
- TVWHTOUAJSGEKT-UHFFFAOYSA-N chlorine trioxide Chemical compound [O]Cl(=O)=O TVWHTOUAJSGEKT-UHFFFAOYSA-N 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000006477 desulfuration reaction Methods 0.000 description 1
- 230000023556 desulfurization Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000003651 drinking water Substances 0.000 description 1
- 235000020188 drinking water Nutrition 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- 238000006386 neutralization reaction Methods 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 239000004800 polyvinyl chloride Substances 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 238000006479 redox reaction Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000010865 sewage Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 230000001954 sterilising effect Effects 0.000 description 1
- 238000006276 transfer reaction Methods 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/75—Multi-step processes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/54—Nitrogen compounds
- B01D53/56—Nitrogen oxides
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/76—Gas phase processes, e.g. by using aerosols
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/77—Liquid phase processes
- B01D53/78—Liquid phase processes with gas-liquid contact
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2251/00—Reactants
- B01D2251/10—Oxidants
- B01D2251/108—Halogens or halogen compounds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2258/00—Sources of waste gases
- B01D2258/02—Other waste gases
- B01D2258/0283—Flue gases
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Health & Medical Sciences (AREA)
- Biomedical Technology (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Dispersion Chemistry (AREA)
- Treating Waste Gases (AREA)
Abstract
The invention discloses a denitration system for denitration of flue gas by using chlorine dioxide and a packed tower, which comprises the packed tower, a chlorine dioxide supply system and a nitric acid supply system, wherein a packing layer is arranged in the packed tower, a flue gas inlet of the packed tower is arranged above the packing layer, a flue gas outlet of the packed tower is arranged below the packing layer, the chlorine dioxide supply system conveys the chlorine dioxide to the upper part of the packing layer of the packed tower through a chlorine inlet pipe, the nitric acid supply system also conveys the nitric acid to the upper part of the packing layer through an acid inlet pipe, and the chlorine dioxide oxidizes NO in the flue gas and the nitric acid absorbs oxidation products at the same time. The invention can solve the problem of low denitration efficiency in the prior oxidation technology, and combines the packed tower with chlorine dioxide and nitric acid for denitration, thereby having good economic and social benefits.
Description
Technical Field
The invention relates to the technical field of flue gas denitration, in particular to a denitration system for flue gas denitration by using chlorine dioxide and a packed tower.
Background
Coal-fired power generation, steel mill steelmaking and other processes taking coal and petroleum as heat sources are one of the main sources of nitrogen oxide increase in the environment. In order to reduce the influence on the environment, various manufacturers adopt various methods to reduce the emission of nitrogen oxides in the combustion tail gas (the flue gas), namely, the flue gas is subjected to denitration treatment. In general flue gas, NO usually accounts for about 90% of the total content of nitrogen oxides, but NO is difficult to dissolve in water, so that the NO is difficult to remove by a water washing or nitric acid neutralization mode, which is also the difficulty of the current flue gas denitration. The existing flue gas denitration technology mainly comprises two main types, namely a catalytic reduction method and an oxidation method. Compared with a catalytic reduction method, the oxidation method theoretically has the advantages of simple process, low cost and the like, so that the method becomes the research and research direction in the field of flue gas denitration at present. ClO2 is a green oxidant with strong oxidizability and low cost, so that the application of ClO2 in an oxidation absorption method for denitration is a better choice. Publication No. CN109718653A entitled "a flue gas desulfurization and denitration apparatus and method" discloses a technology for denitration by using chlorine dioxide, and also discloses patents such as publication nos. CN110624385A, CN106975337A, CN105771577A, and CN105169913A, and also discloses technologies for denitration by using chlorine dioxide, respectively. In the mentioned patent technology, the technical idea of denitration adopts the technical route of "oxidizing NO in flue gas into high-valence nitrogen oxide which is easy to react with nitric acid by chlorine dioxide, and then washing and absorbing by alkaline solution". However, in actual production, the denitration effect of the technical route is not very good. Analyzing the reason, the technical route has an oxidation space and an absorption space in the process, but the existing process does not pay attention to the connection between the two spaces, so that the removal effect of nitrogen oxides in the flue gas is poor.
Disclosure of Invention
In order to solve the technical problems, the invention provides a denitration system for flue gas denitration by using chlorine dioxide and a packed tower, which can solve the technical problems of poor denitration effect and high cost of the chlorine dioxide in the prior art. The content is as follows:
a denitration system for denitration of flue gas by using chlorine dioxide and a packed tower is characterized in that the denitration system comprises the packed tower, a chlorine dioxide supply system and a nitric acid supply system, a packing layer is arranged in the packed tower, a flue gas inlet of the packed tower is arranged above the packing layer, a flue gas outlet is arranged below the packing layer, the chlorine dioxide supply system conveys the chlorine dioxide into the packed tower through a chlorine inlet pipe, the nitric acid supply system conveys the nitric acid into the packed tower through an acid inlet pipe, a distributor of the chlorine dioxide in the tower is arranged above the packing layer, a distributor of the nitric acid in the tower is also arranged above the packing layer, the flue gas enters the packing layer from the upper part of the packing layer, the chlorine dioxide and the nitric acid also enter the packing layer from the upper part of the packing layer, the chlorine dioxide oxidizes NO in the flue gas in gaps among the packing, the nitric acid absorbs oxidation products at the same time, and the flue gas, the liquid flows to an acid liquid tank at the bottom of the tower after flowing out of the packing layer.
Preferably wherein the chlorine dioxide distributor is located below the nitric acid distributor.
Preferably wherein the chlorine dioxide enters the packing layer co-currently with the flue gas.
Preferably wherein the nitric acid is sprayed into the layer of packing.
Preferably, a nitric acid cooling device is arranged on the pipeline of the acid inlet pipe of the nitric acid supply system.
Preferably, wherein the liquid recycle in the acid tank is applied in the nitric acid feed system.
The content of the invention is specifically described as follows:
theoretical basis of the invention
1. The existing oxidation denitration technology has the poor denitration effect because:
(1) the applicant believes that in the gaseous state, NO is in the direction of NO2There is an equilibrium relationship upon transformation:
2NO2↔ O2+ 2NO ①
at higher temperatures, lower pressures and lower concentrations of NO, NO is not readily converted to NO2Or NO after conversion2This immediately turns to NO, even if the NO in the flue gas can be oxidized by an oxidant such as chlorine dioxide, since the NO concentration in the flue gas is very low, equation ① proceeds to the right, and a large proportion of NO will eventually be present even if the NO in the flue gas is oxidized.
2ClO2+4NO →4NO2+Cl 2②
2NO2→ O2+ 2NO ③
According to the equilibrium relationship (equation ①), if the concentration of NO in the flue gas is low (the actual NO in the flue gas generally does not exceed 300 mg/m)3) Even if NO is oxidized to higher valence NO2(equation ②) but in accordance with equation ③ above2And back to NO, a large proportion of NO will also be present in the final flue gas. This is also the reason why the denitration effect of the oxidant (including chlorine dioxide) is not high in the existing oxidation denitration technology. Of course, the prior art can improve the denitration effect by increasing the input amount of the oxidant, which inevitably increases the cost greatly.
(2) In the prior art, the link of NO oxidation in the flue gas is separated from the high-valence nitrogen oxide absorption environment.
As mentioned above, the prior art adopts the technical route of "oxidizing NO in the flue gas into high-valence nitrogen oxide which is easy to react with alkali liquor by chlorine dioxide, and then washing and absorbing with alkaline solution". Based on the analysis, in the technical route, due to the separation of oxidation and absorption, although NO in the flue gas undergoes oxidation, because NO and NO2 have an equilibrium conversion relationship, a large proportion of NO still exists when the flue gas contacts the absorption liquid, and the absorption liquid cannot adsorb the NO, and the final result is poor denitration effect of the flue gas.
2. The difference between the present invention and the prior art lies in:
(1) the absorbent of the oxidation products in the system is changed from alkaline solution to nitric acid.
The main product after NO oxidation in the flue gas is NO2, and the absorption of the oxidation product is mainly the absorption of NO 2. The technical route of absorption in the prior art is that NO2 reacts with soluble alkali liquor to generate nitrate and/or nitrite, so that NO2 is removed from flue gas.
Prior theory revealed that NO2 is soluble in water:
3NO2+ H2O = 2HNO3+ NO ④
water may thus act as an absorbent for NO 2. However, pure water absorption has disadvantages of absorption speed and efficiency. The prior theory and experiment show that: the absorption capacity of nitric acid for NO2 was significantly higher than that of water, as noted in "study on absorption of NO2 by water and dilute nitric acid" by gunn et al, it was found that the absorption efficiency of NO2 was significantly improved with the increase of the absorbed dose when 15% nitric acid was used as the absorbent. This is because NO2 is more soluble in nitric acid than water. Furthermore, it is reported in the literature that when the nitric acid concentration is higher than 12%, the solubility of NO in nitric acid is remarkably increased, and meanwhile, the oxidizability of the nitric acid solution is gradually enhanced along with the increase of the nitric acid concentration, and both of the nitric acid solution and the nitric acid solution are beneficial to oxidizing NO into NO2 and then react with water, so that the absorption capacity is remarkably improved. However, it was experimentally verified that the nitrogen oxides detected at the end of the flue gas increase when the mass concentration of nitric acid exceeds 50%, in particular 60%, indicating that a high concentration of nitric acid is not advantageous for use as the absorbent of the present invention. Experiments show that the optimal concentration of the nitric acid is 10-30%.
In the application, the nitric acid can be used as an absorbent of NO2 by combining the oxidation effect of chlorine dioxide, and can also be used for synergistically absorbing NO, so that the use of an oxidant can be saved, and the economic efficiency is higher.
4NO+2ClO2＝Cl2+4NO 2②
3NO2+H2O＝2HNO3+NO ④
Cl2+ NO + H2O = NO2+2HCl ⑤
2NO+ClO2+H2O＝NO2+HNO3+ HCl ⑥
2HNO3+ 3NO = 2HNO2+ N2O4⑦
2ClO2+ 4HNO2= 4HNO3+ Cl 2⑧
2ClO2+ 2N2O4+ H2O = 4HNO3+ Cl2⑨
The reason why nitric acid is not used as an absorbent in the prior art in the field is that, firstly, the technology of absorbing NO2 by nitric acid is generally used under the condition of high NO2 content, such as NO2 absorption technology in the nitric acid preparation process; secondly, as mentioned above, in the field, NO2 is converted back to NO during the absorption of the smoke, and the content of NO2 in the smoke is not high.
(2) In the invention, the NO oxidation link in the flue gas and the absorption link of the high-valence nitrogen oxide are almost synchronous, namely the NO is absorbed immediately after being oxidized.
The oxidant (chlorine dioxide), the flue gas and the absorbent (nitric acid) enter the filler layer at the same time and descend in irregular gaps among the fillers, the chlorine dioxide oxidizes NO in the flue gas while descending, an oxidation product is directly contacted with the absorbent (nitric acid), and the oxidation product is immediately absorbed, because the oxidation and the absorption are synchronous in a nitric acid environment, each reactant can be carried out according to the formulas ② and ④ - ⑨, and the formula ③ has NO chance, so that the technical means of immediately absorbing the NO in the flue gas after oxidation is a key for solving the technical problem of low denitration efficiency in the flue gas, and is also a technical means different from the prior art.
(3) Compared with the prior art, the residual chlorine dioxide in the absorption liquid can be reused.
In the invention, the absorption liquid is nitric acid, the reaction product is mainly nitric acid, and chlorine dioxide can stably exist in the nitric acid. When the chlorine dioxide and NO in the flue gas are remained after reaction, the chlorine dioxide is remained in the nitric acid and can be contacted with the flue gas again through the circulating system to oxidize the NO in the flue gas. In the prior art, the absorption liquid is soluble alkali liquid, and patents such as CN109718653A, CN110624385A, CN106975337A, CN105771577A, CN105169913A and the like all adopt alkali liquid as an absorbent.
The disadvantages of using soluble lye as absorbent are: after oxidation, the unreacted chlorine dioxide is neutralized and consumed, and a corresponding portion of the lye is also consumed.
ClO2+ OH-= ClO3 -+ H2O
Thus, the present invention has significant cost advantages over the prior art. In addition, sodium chlorite and nitric acid can be used as raw materials for preparing chlorine dioxide, and the denitration product can be directly used as the nitric acid, so that the cost of the method is lower.
(II) packed tower
The packed tower in the prior art is one of important devices for gas-liquid mass transfer in chemical production. The tower body is often a vertical cylinder, a packing support plate is arranged at the lower part in the tower, packing is used as a contact component between gas and liquid, or is placed on the support plate in a random or whole-building mode, a packing press plate is arranged above the packing to press the packing, and then a liquid distributor is arranged above the packing. The working principle of the packed tower is as follows: the liquid is sprayed onto the filler from the upper part through the liquid distributor and flows down along the surface of each filler; the gas is fed from the bottom of the tower, is in a countercurrent state with the liquid, contacts with the liquid in the gap of the packing and has mass transfer.
The packed tower of the invention has basically the same structure as the packed tower and also comprises a tower shell, a packing support plate, packing, a liquid distributor and the like, but the working principle of the packed tower of the invention is different from the prior art, in the invention, flue gas and nitric acid pass through the packing in a gas-liquid cocurrent flow mode, and in addition, chlorine dioxide also flows along with the nitric acid. The working principle of the packed tower of the invention is as follows: the flue gas enters from the upper part of the packed tower, passes through gaps among the packing and exits from the packed tower from a flue gas outlet; chlorine dioxide enters the packing layer from the upper part of the packing layer; nitric acid enters the packing layer from the upper part of the packing layer, passes through gaps among the packing, finally flows to the bottom of the packed tower, and the bottom of the packed tower is used as an acid liquid tank for collecting and storing acid liquid after reaction. The flue gas, the chlorine dioxide and the nitric acid are contacted and collided in the irregular gap channel of the filler, and the reaction and the absorption are completed.
The first reason for adopting flue gas and nitric acid downstream flow is that the media involved in the packed tower are as follows: the flue gas, the chlorine dioxide and the nitric acid are different from the traditional packed tower which only relates to two media of a gas and a liquid, and the reaction related to the packing is also different from the simple mass transfer reaction between the traditional packing. As mentioned above, the reactions between the substances mainly include the oxidation reaction of chlorine dioxide to NO in flue gas and the absorption reaction of nitric acid to high-valence nitrogen oxides. Concurrent flow can ensure the reaction time of each reaction.
The second reason of adopting gas-liquid cocurrent flow is that the tail gas smoke volume of chemical plants, power plants, steel plants and the like is large, the components are complex, and equipment with high mass transfer effect is difficult to adapt to the occasion. However, the flue gas and the liquid adopt a downstream route, so that the process requirements can be met, the air resistance can be reduced, the cost is saved, and the traditional packed tower can be applied to flue gas treatment occasions.
The filler in the invention can adopt the fillers related in the prior art, such as Raschig ring filler, pall ring filler, stepped ring filler, saddle-shaped filler, rectangular saddle-shaped filler and the like in bulk filler, and even can adopt spherical filler; grid packing, corrugated packing and the like in the regular packing. Considering the process environment, the material of the filler is preferably oxidation-resistant, acid-base-resistant, such as ceramic, stainless steel, PE, PP, PVC and other plastics, stainless steel and the like.
The liquid distributor corresponds to the nitric acid distributor in the invention, and the function is the same as that of the traditional packed tower. The distributor can be in the form of tube, double-layer calandria, slot, disk, impact, nozzle, tower, shower nozzle, etc. The nitric acid in the present invention may be used in any of the above forms depending on the diameter of the packed column; considering that the gas and the liquid are in a downstream state, the component can be omitted, and the liquid is directly injected into the packing layer through the acid inlet pipe.
(III) chlorine dioxide and chlorine dioxide supply system
1. Preparation of chlorine dioxide
The chlorine dioxide can be a chlorine dioxide-containing aqueous solution, a chlorine dioxide-containing gas, or a mixture of a chlorine dioxide-containing aqueous solution and a chlorine dioxide gas.
The preparation of chlorine dioxide is a matter of prior art. As disclosed in patent publication No. CN 209362207U: the chlorine dioxide generator for sterilizing drinking water and sewage is mainly a chlorine dioxide preparation device using sodium chlorate and hydrochloric acid as raw materials, when the equipment is operated, the sodium chlorate solution and hydrochloric acid solution are fed into the chlorine dioxide generator according to a certain proportion, and chemical reaction is produced in the equipment to produce reaction products of chlorine dioxide, chlorine, sodium chloride and water, etc. The raw materials for producing chlorine dioxide are sodium chlorate and hydrochloric acid; publication No. CN110624385A also discloses a production method of chlorine dioxide denitration: a low-temperature denitration method for a sodium chlorite solution is characterized in that a 25% sodium chlorite aqueous solution is adopted as an oxidant, an acid solution is adopted as an activator, the acid solution is continuously added into the sodium chlorite solution when the denitration device is used, the sodium chlorite is conveyed to a flue gas inlet pipe through a conveying pump, the oxidant is sprayed into flue gas through an atomizing spray gun, chlorine dioxide is generated by the sodium chlorite through reaction with the acid solution, the nitrogen monoxide is oxidized into nitrogen dioxide by the chlorine dioxide generated after the heat of the flue gas is evaporated, and the oxidized nitrogen dioxide is absorbed by sodium hydroxide sprayed by an alkaline tower. The raw materials are sodium chlorite and acid; publication No. CN105771577A discloses an improved process for the preparation of chlorine dioxide: the method comprises the following steps: (1) taking a sodium chlorate solution with the mass concentration of 15-18% and industrial hydrochloric acid with the mass concentration of 31% as raw materials, preheating the raw materials to 55-70 ℃, and then adopting a metering pump to mix the raw materials according to the volume ratio of the industrial hydrochloric acid: the sodium chlorate solution =1 (1-1.2) is prepared by respectively feeding the sodium chlorate solution and industrial hydrochloric acid into two V-shaped pipes with an included angle of 55-65 degrees of a three-way pipeline, and carrying out mixing reaction in a third pipeline; (2) the method comprises the steps of obtaining a mixture containing strong oxidant ClO2 after mixing reaction in a pipeline, uniformly distributing the mixture through a distribution spraying device at the outlet end of the pipeline, dispersing the gas-liquid mixture into fine mist, directly extending a spray head of the distribution spraying device into a flue gas pipeline, uniformly mixing the mixture with flue gas, carrying out redox reaction on low-valence Nitrogen Oxides (NO) in the flue gas and ClO2, oxidizing the low-valence Nitrogen Oxides (NO) into high-valence nitrogen oxides (NO 2), and absorbing the oxidized product by alkali liquor. Sodium chlorate and hydrochloric acid are also used as raw materials.
The large-scale preparation of chlorine dioxide is generally carried out by electrolyzing saline water to obtain sodium chlorate and then reacting the sodium chlorate with hydrochloric acid (or sulfuric acid) under specific conditions.
In summary, all the technical means for preparing chlorine dioxide in the prior art can be applied to the present invention as one of the technical features of the present invention.
When the invention is applied, a chlorine dioxide generator and corresponding raw materials can be directly purchased from the market, so as to obtain chlorine dioxide.
In the present invention, chlorine dioxide can be prepared from sodium chlorite and dilute nitric acid, which generally refers to nitric acid having a mass concentration of less than 65%. Compared with the prior art, dilute nitric acid is used for replacing sulfuric acid or hydrochloric acid, and the denitration product can be applied to denitration raw materials, so that the process can be optimized, and the cost can be saved. However, experiments prove that when the mass concentration of the nitric acid exceeds 30%, the yield of the chlorine dioxide is obviously reduced, so that in each scheme of the invention, the mass concentration of the nitric acid is generally less than 30%.
According to the formula ②④⑤⑥, 1 mole of chlorine dioxide can oxidize 5 moles of NO, so that theoretically, the ratio of the input amount of chlorine dioxide in unit time to the amount of NO in unit time of the flue gas is 3: 5, according to the formula ⑦, nitric acid can play a role in assisting the oxidation, and the input amount of chlorine dioxide can be smaller, such as 1: 2, 1: 3, or even smaller, which has cost advantage compared with the prior art.
2. Chlorine dioxide supply system
The chlorine dioxide supply system comprises a chlorine dioxide generator, a booster pump, a valve, a chlorine inlet pipe, a chlorine dioxide distributor and the like. The function is to supply chlorine dioxide to the turbulent ball tower and distribute the chlorine dioxide in the flue gas.
The chlorine dioxide distributor is a device for uniformly distributing chlorine dioxide generated by a chlorine dioxide generator in flue gas flowing through a packed tower. When chlorine dioxide is supplied in the system as a liquid or a mixture of gas and liquid, various liquid spray heads, liquid atomizer spray heads, and specialized liquid distributors disclosed in the foregoing patents, etc. may be used. When chlorine dioxide is supplied in the form of a gas, gas distributors, gas nozzles, etc. as disclosed in the prior art may be used.
(IV) nitric acid and nitric acid supply system
The nitric acid refers to an aqueous solution of HNO 3. Nitric acid is used as an absorbent for NO2, and the absorption effect is better when the concentration is higher, but when the concentration in nitric acid exceeds a certain value, such as 50-70% by mass, the nitric acid becomes extremely volatile and forms a new pollution source. Thus, the nitric acid used in the present invention is required to have a concentration of not more than 60%, preferably 10 to 30%.
The amount of nitric acid used in the present invention will depend on the particular process parameters and, in general, the nitric acid used is preferably such that the NO2 oxidized in the process is sufficiently absorbed.
In the invention, nitric acid can be used as an absorbent of nitrogen oxide and also can be used as a raw material for preparing chlorine dioxide, so that the chlorine dioxide is prepared from sodium chlorite and nitric acid, and the invention is beneficial to environmental protection (the use of chloride ions in the process is reduced). In addition, in the invention, nitric acid is further selected from acid liquor containing absorption products, and the scheme can save cost (the absorption products are also used for preparing the oxidizing agent).
The nitric acid supply system comprises a nitric acid tank, a pressure pump, a valve, an acid inlet pipe, a nitric acid distributor and the like. The function is to transport nitric acid to the packing layer. After nitric acid absorbs oxidation products, the concentration of the nitric acid is increased, and the absorption capacity is stronger, so that in a preferable scheme, the nitric acid in the acid liquid tank is reused, the process is simplified, and the cost is saved; considering that the volatility of the nitric acid is increased when the temperature of the nitric acid is increased, and the nitric acid with higher concentration can leak along with the flue gas, in a preferred scheme, a cooling device of the nitric acid is arranged on a circulating pipeline of the nitric acid, and the purpose is to cool the nitric acid.
The invention has the beneficial effects that:
1. the nitric acid is used as an absorbent, can be recycled, and saves the cost.
2. The method provides guarantee for the oxidation and absorption of NO in nitric acid, the oxidation and absorption are almost synchronous, and the denitration efficiency is improved.
3. The chlorine dioxide is combined with the packed tower and the nitric acid to carry out flue gas denitration, so that an unexpected effect is achieved, and the denitration efficiency is improved.
Drawings
FIG. 1: a schematic diagram of a denitration system of a best mode.
Best mode for carrying out the invention
The invention is described with reference to the accompanying figure 1:
the packed column was a cylinder of diameter 0.8m, height 5m, wall thickness 8mm, and made of 304L stainless steel. The flue gas inlet 1 is arranged at the top of the packed tower, a 90-degree conical solid nozzle 2 is arranged at the upper part in the tower, the nozzle 2 is a nitric acid distributor, and the nozzle 2 is connected with an acid inlet pipe 3 of nitric acid; a chlorine dioxide distributor 4 is arranged at a position 0.5 meter below the nozzle 2, the chlorine dioxide distributor 4 is a 120-degree solid conical atomizing nozzle, and the distance from the chlorine dioxide distributor to the filler layer 6 is 0.5 m. The chlorine dioxide distributor 4 is connected with a chlorine dioxide inlet pipe 5, the chlorine inlet pipe 5 is connected with a chlorine dioxide generator 10, and a gas booster pump 11 and a flow regulating valve 12 are further arranged on the pipeline. The lower part of the chlorine dioxide distributor 4 is provided with a filler layer 6, the filler is a ceramic raschig ring, the layer height of the filler layer 6 is 2m, and the filler is supported by a filler support plate 7. The flue gas outlet 8 is arranged at the position 0.8m below the packing support plate 7 and 0.6m away from the bottom of the tower, the bottom of the packed tower is used as an acid liquid tank 9, and nitric acid with the mass concentration of 20% is added before the tower starts to operate. The pipeline of the nitric acid inlet pipe 3 is provided with a booster pump 13 and a flow regulating valve 14, and the other end of the pipeline is connected to an acid liquid tank 9 at the bottom of the packing tower.
The flue gas is the sintering flue gas of a sintering workshop of a certain steel mill. The initial flue gas parameters are: the temperature of the flue gas is 137 ℃, the humidity of the flue gas is 0.01-0.03%, and the NO content is 181mg/m3Flue gas flow of 900m3/h。
The chlorine dioxide generator 10 is QKJ-2000 type chlorine dioxide generator from Jinan Qili environmental protection science and technology Limited, the raw materials are sodium chlorite and hydrochloric acid (30%), the output is a gas-liquid mixture, and the unit yield of chlorine dioxide is 2000 g/h.
The flue gas enters the packed tower through a flue gas inlet 1 and flows downwards from the top of the tower; opening a nitric acid regulating valve 14 and a booster pump 13, conveying the nitric acid in an acid liquid tank 9 to a nozzle 2 through an acid inlet pipe 3, and regulating the flow of the nitric acid through the regulating valve 14 to ensure that the input quantity per hour is not less than 20 kg; the chlorine dioxide generator 10 is started, the flow regulating valve 11 and the booster pump 12 are opened, and the chlorine dioxide generated by the chlorine dioxide generator 10 is conveyed to the chlorine dioxide distributor 4 through the chlorine inlet pipe 5. The flow of chlorine dioxide is adjusted by the adjusting valve 11, so that the input amount of pure chlorine dioxide is not less than 600 g/h. Flue gas, nitric acid and chlorine dioxide enter the packing layer 6 from above at the same time and flow down along the gaps of the packing. In the gaps between the fillers, NO in the flue gas is oxidized by chlorine dioxide, and nitric acid simultaneously absorbs the oxidation products. After the flue gas flows out of the packing layer 6, the flue gas flows out of the packed tower from a flue gas outlet 8, and the liquid flows into an acid liquid tank 9 at the bottom of the tower.
Measured at the flue gas outlet 8 of the packed tower, the NO content is 32, 35, 38, 41 and the like, and the range is 30-45mg/m3。
Claims (6)
1. A denitration system for denitration of flue gas by using chlorine dioxide and a packed tower is characterized in that the denitration system comprises the packed tower, a chlorine dioxide supply system and a nitric acid supply system, a packing layer is arranged in the packed tower, a flue gas inlet of the packed tower is arranged above the packing layer, a flue gas outlet is arranged below the packing layer, the chlorine dioxide supply system conveys the chlorine dioxide into the packed tower through a chlorine inlet pipe, the nitric acid supply system conveys the nitric acid into the packed tower through an acid inlet pipe, a distributor of the chlorine dioxide in the tower is arranged above the packing layer, a distributor of the nitric acid in the tower is also arranged above the packing layer, the flue gas enters the packing layer from the upper part of the packing layer, the chlorine dioxide and the nitric acid also enter the packing layer from the upper part of the packing layer, the chlorine dioxide oxidizes NO in the flue gas in gaps among the packing, the nitric acid absorbs oxidation products at the same time, and the flue gas, the liquid flows to an acid liquid tank at the bottom of the tower after flowing out of the packing layer.
2. The denitrification system for flue gas denitrification with chlorine dioxide and packed tower of claim 1, wherein the chlorine dioxide distributor is located below the nitric acid distributor.
3. The denitrification system for flue gas denitrification utilizing chlorine dioxide and a packed tower of claim 1, wherein the chlorine dioxide enters the packing layer in the same direction as the flue gas.
4. The denitrification system for flue gas denitrification with chlorine dioxide and packed tower of claim 1, wherein the nitric acid enters the packing layer in a spraying manner.
5. The denitration system for flue gas denitration by using chlorine dioxide and a packed tower as claimed in claim 1, wherein a nitric acid cooling device is provided on an acid inlet pipe of the nitric acid supply system.
6. The denitration system for flue gas denitration using chlorine dioxide and a packed tower according to claims 1 to 5, wherein liquid recycle in the acid liquid tank is applied to the nitric acid supply system.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111888908A (en) * | 2020-08-26 | 2020-11-06 | 安德里茨（中国）有限公司 | Flue gas denitration device and method |
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