阅读说明：本技术 同时去除废气中含有的硫氧化物和氮氧化物的方法及装置 (Method and device for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas ) 是由 柳海润 赵相济 尹大盛 石东圭 林泰贤 韩修旼 于 2020-04-08 设计创作，主要内容包括：本发明涉及一种同时去除废气中含有的硫氧化物和氮氧化物的方法及装置,更详细地,涉及一种在与脱硫工艺相同的运行条件下通过湿法工艺来进行废气的脱氮工艺,从而可以在一个湿法工艺设备中能够同时进行废气的脱氮工艺和脱硫工艺的同时去除废气中含有的硫氧化物和氮氧化物的方法及装置。(The present invention relates to a method and apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, and more particularly, to a method and apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, which can simultaneously perform a denitrification process and a desulfurization process of exhaust gas in one wet process equipment by performing a denitrification process of exhaust gas through a wet process under the same operation conditions as the desulfurization process.)

1. A method for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, comprising:

a step (a) of oxidizing nitrogen oxides contained in the exhaust gas by reacting the exhaust gas with ozone;

a step (b) of obtaining an absorbent by mixing an organic acid or an organic acid salt in an alkaline earth metal compound in an aqueous solution state or a slurry state; and

a step (c) of performing denitrification and desulfurization of the exhaust gas by contacting the exhaust gas oxidized by the reaction with ozone in the step (a) with the absorbent in the step (b).

2. The method for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to claim 1,

the alkaline earth metal compound of step (b) is selected from the group consisting of calcium carbonate, calcium hydroxide and mixtures thereof.

3. The method for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to claim 1,

the organic acid of step (b) is selected from the group consisting of RCOOH, dicarboxylic acids having a carbon number of 1 to 20, and mixtures thereof; wherein R in RCOOH is H or alkyl with 1-18 carbon atoms.

4. The method for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to claim 1,

the content of the organic acid or organic acid salt in the step (b) is 1ppm to 3000ppm with respect to the solid content in the absorbent.

5. The method for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to claim 1,

the step (a) includes: and a step of oxidizing nitrogen monoxide contained in the exhaust gas to nitrogen dioxide by reacting the exhaust gas with ozone.

6. The method for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to claim 5,

the desulfurization in the step (c) is a desulfurization reaction carried out by a reaction of sulfur oxides in the exhaust gas and alkaline earth metal compounds in the absorbent,

the denitrification in the step (c) is a denitrification reaction performed by a reaction between an alkaline earth metal sulfite produced by a desulfurization reaction between a sulfur oxide in the exhaust gas and an alkaline earth metal compound in the absorbent and nitrogen dioxide obtained by reacting nitrogen monoxide contained in the exhaust gas with ozone.

7. An apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, comprising:

a gas phase reaction unit for oxidizing nitrogen oxides contained in the exhaust gas by reacting the exhaust gas with ozone;

an absorbent storage unit that stores an absorbent obtained by mixing an organic acid or an organic acid salt with an alkaline earth metal compound in an aqueous solution state or a slurry state; and

and a wet reaction part for denitrifying and desulfurizing the exhaust gas containing sulfur oxides and nitrogen oxides by contacting the absorbent in the absorbent storage part with the exhaust gas oxidized in the gas phase reaction part.

8. The apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to claim 7,

the gas phase reaction part is an air duct or a reactor for conveying waste gas.

9. The apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to claim 7,

the alkaline earth metal compound is selected from the group consisting of calcium carbonate, calcium hydroxide and mixtures thereof.

10. The apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to claim 7,

the organic acid is selected from the group consisting of RCOOH, dicarboxylic acids having 1 to 20 carbon atoms, and mixtures thereof; wherein R in RCOOH is H or alkyl with 1-18 carbon atoms.

11. The apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to claim 7,

the gas phase reaction section oxidizes nitrogen monoxide contained in the exhaust gas into nitrogen dioxide by reacting the exhaust gas with ozone.

12. The apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to claim 11,

the desulfurization in the wet reaction section is a desulfurization reaction that proceeds by the reaction of sulfur oxides of the exhaust gas and alkaline earth metal compounds in the absorbent,

the denitrification in the wet reaction section is a denitrification reaction performed by a reaction between an alkaline earth metal sulfite, which is generated by a desulfurization reaction between a sulfur oxide in the exhaust gas and an alkaline earth metal compound in the absorbent, and nitrogen dioxide obtained by reacting nitrogen monoxide contained in the exhaust gas with ozone.

13. The apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to claim 7,

the gas phase reaction part comprises a grid nozzle for injecting ozone for fully mixing the exhaust gas and the ozone, and the nozzle is arranged in the step before the wet reaction part.

14. The apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to claim 7,

the wet reaction section is an absorption tower used in a flue gas desulfurization device in a thermal power plant, and an absorbent supplied from the absorbent storage section (20) is injected into the absorption tower, and the injected absorbent contacts the exhaust gas oxidized in the gas phase reaction section, thereby denitrifying and desulfurizing the exhaust gas containing sulfur oxides and nitrogen oxides.

Technical Field

The present invention relates to a method and an apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, and more particularly, to a method and an apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas and simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas by a wet process.

Background

When fossil fuel is burned, sulfur in the fuel is oxidized to generate sulfur dioxide as sulfur oxide, and nitrogen components in the fuel are oxidized or combustion air is decomposed at high temperature to inevitably generate Nitrogen Oxide (NO)_x). Sulfur Oxides (SO)_x) And Nitrogen Oxides (NO)_x) When discharged into the atmosphere, the particles are combined with water vapor, inorganic substances, and the like in the air to form fine particles having a PM of 2.5 or less, and become a major air pollutant that reduces the visible distance and induces cardiopulmonary disease (korean atmospheric environmental society, vol. 3, No. 2, year 2015, month 4, pages 143 to 156).

For removing Sulfur Oxides (SO) in an atmospheric pollution discharge facility using fossil fuels_x) Although a limestone wet desulfurization apparatus is generally used, the desulfurization rate is 80% to 90%, and therefore a part of the amount of generated gas is discharged into the atmosphere.

In addition, for removing Nitrogen Oxides (NO)_X) The most common and most effective denitrification method of (1) is Selective Catalytic Reduction (SCR), but the denitrification rate is only 70% to 90%, so that it is inevitable to discharge 10% to 30% of the produced amount into the atmosphere. Therefore, in order to improve the quality of the atmospheric environment, the development of further emission reduction technology is required.

Generally, an air pollution control apparatus using fossil fuel is arranged in the order of selective catalytic reduction, electric dust collector, and Flue Gas Desulfurization (FGD). Selective catalytic reduction is a process for reducing nitrogen oxides to nitrogen (N) by injecting gaseous ammonia or urea₂) Removing nitrogen oxides. The flue gas desulfurization device sprays limestone slurry to make sulfur dioxide (SO)₂) The gas is absorbed by the limestone slurry, oxidized and converted to solid gypsum to remove sulfur dioxide. However, if the amount of the denitrifier and the desulfurizing agent to be injected is increased to increase the removal rate, the increased unreacted substances cause the trouble of the apparatus.

Residual Nitrogen Oxides (NO) that are not removed even by treatment with selective catalytic reduction_x) Most of the nitrogen monoxide (NO) is hardly soluble, and therefore, it is not removed in the absorption tower of the flue gas desulfurization apparatus, and is inevitably discharged to the atmosphere. For more complete removal, it is necessary to develop a wet denitrification technique for removing nitrogen oxides by an absorption method in an absorption tower of a flue gas desulfurization apparatus.

As a related prior art, there is disclosed a method of preparing an oxynitride by a plasma method and reacting it with Na₂S、Na₂SO₃Method for conducting reaction to remove nitrogen oxides (Korean patent publication No. 10-1800517 (published: 2017.11.23), Moo beer Chang, How Ming Lee, Feeling Wu)&Chi Ren Lai, journal of the air and waste management Association, 54: 941-949), and further discloses that SO is added to_x、NO_xAdsorbed in alcohol or glycol as organic solvent toRemoval of SO_x、NO_x(korean granted patent No. 10-1871197 (publication date: 2018.06.27)), but these prior arts have the following problems: in order to simultaneously treat desulfurization and denitrification, further use of expensive Na is required₂S、Na₂SO₃And additionally, a desulfurization and denitrification solution, which is a complex solution containing polyhydric alcohol and/or polyethylene glycol, needs to be prepared for use, and also the temperature of flue gas needs to be adjusted before desulfurization and denitrification is performed, and there are problems in the treatment of desulfurization waste water, and the like. And thus there is a limitation in practical use.

Further, Korean granted patent No. 10-1724358 (publication date: 2017.04.10) discloses the following: a method for adsorbing a flue gas by liquid droplets produced from hydrogen peroxide in an adsorption tower after oxidizing the flue gas with ozone. Korean laid-open patent No. 10-2017-0021713 (published: 2017.02.28) discloses an electrolysis apparatus for trapping nitrides of exhaust gas by causing redox reaction of Fe-EDTA by supplying electric energy. These prior arts have problems that a new process needs to be constructed, etc.

Therefore, there is a need to develop a more efficient desulfurization and denitrification method capable of solving the safety problems and environmental problems associated with the existing desulfurization process, while increasing the SO content without increasing the equipment_xAnd NO_xWhile removing the rate.

Disclosure of Invention

Problems to be solved by the invention

The main object of the present invention is to provide a method and apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, which can simultaneously perform a denitrification process and a desulfurization process of exhaust gas by one wet process, and can economically simultaneously treat sulfur oxides and nitrogen oxides without changing equipment for denitrification or adding expensive additives for denitrification in the existing wet desulfurization process.

Means for solving the problems

In order to achieve the above object, one embodiment of the present invention provides a method for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, including: (a) a step of oxidizing nitrogen oxides contained in the exhaust gas by reacting the exhaust gas with ozone; (b) a step of obtaining an absorbent by mixing an organic acid or an organic acid salt in an alkaline earth metal compound in an aqueous solution state or a slurry state; and (c) a step of performing denitrification and desulfurization of the exhaust gas by contacting the exhaust gas oxidized by the reaction with ozone in the step (a) with the absorbent in the step (b).

In a preferred embodiment of the present invention, the alkaline earth metal compound of the step (b) is selected from the group consisting of calcium carbonate, calcium hydroxide and a mixture thereof.

In a preferred embodiment of the present invention, the organic acid in the step (b) is selected from the group consisting of RCOOH (R ═ H or an alkyl group having 1 to 18 carbon atoms), a dicarboxylic acid having 1 to 20 carbon atoms, and a mixture thereof.

In a preferred embodiment of the present invention, the content of the organic acid or organic acid salt in the step (b) is 1 to 3000ppm based on the solid content in the absorbent.

In a preferred embodiment of the present invention, the step (a) includes: oxidation of Nitric Oxide (NO) contained in the exhaust gas to nitrogen dioxide (NO) by reaction of the exhaust gas with ozone₂) The step (2).

In a preferred embodiment of the present invention, the desulfurization in the step (c) is a desulfurization reaction carried out by a reaction between sulfur oxides in the exhaust gas and alkaline earth metal compounds in the absorbent. The denitrification in the step (c) is nitrogen dioxide (NO) obtained by reacting an alkaline earth metal sulfite produced by a desulfurization reaction between sulfur oxide in the exhaust gas and an alkaline earth metal compound in the absorbent with nitrogen monoxide (NO) contained in the exhaust gas and ozone₂) The denitrification reaction is carried out.

In another embodiment of the present invention, there is provided an apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, including: a gas phase reaction unit for oxidizing nitrogen oxides contained in the exhaust gas by reacting the exhaust gas with ozone; an absorbent storage unit for storing an absorbent by mixing an organic acid or an organic acid salt with an alkaline earth metal compound in an aqueous solution state or a slurry state; and a wet reaction section for performing denitrification and desulfurization of the exhaust gas containing sulfur oxides and nitrogen oxides by bringing the absorbent in the absorbent storage section into contact with the exhaust gas oxidized in the gas phase reaction section.

In another preferred embodiment of the present invention, the gas phase reaction section is a pipe or a reactor for transporting an exhaust gas.

In a preferred embodiment of the present invention, the alkaline earth metal compound is selected from the group consisting of calcium carbonate, calcium hydroxide and a mixture thereof.

In another preferred embodiment of the present invention, the organic acid is selected from the group consisting of RCOOH (R ═ H or an alkyl group having 1 to 18 carbon atoms), a dicarboxylic acid having 1 to 20 carbon atoms, and a mixture thereof.

In another preferred embodiment of the present invention, the gas phase reaction section includes: oxidation of Nitric Oxide (NO) contained in the exhaust gas to nitrogen dioxide (NO) by reaction of the exhaust gas with ozone₂)。

In another preferred embodiment of the present invention, the desulfurization in the wet reaction section is a desulfurization reaction that proceeds by a reaction between sulfur oxides in the exhaust gas and alkaline earth metal compounds in the absorbent. The nitrogen removal in the wet reaction section is nitrogen dioxide (NO) obtained by reacting an alkaline earth metal sulfite produced by a desulfurization reaction between sulfur oxide in the exhaust gas and an alkaline earth metal compound in the absorbent with nitrogen monoxide (NO) and ozone contained in the exhaust gas in the gas phase reaction section₂) The denitrification reaction is carried out.

In another preferred embodiment of the present invention, the gas phase reaction part includes a grid nozzle for injecting ozone so as to sufficiently mix the exhaust gas and the ozone.

In another preferred embodiment of the present invention, the wet reaction section is an absorption tower used in a flue gas desulfurization apparatus in a thermal power plant, the absorption tower is injected with an absorbent supplied from the absorbent storage section, and the injected absorbent contacts the oxidized exhaust gas in the gas phase reaction section to denitrify and desulfurize the exhaust gas containing sulfur oxides and nitrogen oxides.

Effects of the invention

According to the present invention, the denitrification process of the exhaust gas is performed by the wet process under the same operation condition as the desulfurization process, and not only the denitrification process and the desulfurization process of the exhaust gas can be simultaneously performed on one wet process apparatus (wet flue gas desulfurization apparatus), but also the denitrification and the desulfurization can be performed without changing or adding an apparatus for denitrification in the existing operating wet process, thereby being economical, and having an effect of reducing the inefficiency and the side effect which occur when different operation conditions are respectively applied to the denitrification process and the desulfurization process.

In addition, according to the present invention, nitrogen monoxide (NO) of exhaust gas having low reactivity is converted into nitrogen dioxide (NO) having high reactivity by ozone₂) And the reaction rate of sulfur oxide and absorbent in the exhaust gas is increased by the input of organic acid or organic acid salt, and the intermediate product of sulfur oxide produced at this time is used as a denitrifier, thereby eliminating the need to add expensive denitrifier (Na) as an additive₂S、Na₂SO₃) Therefore, it has an effect of being able to realize higher efficiency of denitrification and desulfurization of exhaust gas.

Drawings

Fig. 1 is a schematic diagram of the simultaneous removal of sulfur oxides and nitrogen oxides from exhaust gas according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of simultaneous removal of sulfur oxides and nitrogen oxides from an exhaust gas according to another embodiment of the present invention.

Fig. 3 is a structural diagram of simultaneously removing sulfur oxides and nitrogen oxides in exhaust gas according to an embodiment of the present invention.

Description of reference numerals:

10: a gas phase reaction section; 11: a mass flow meter; 15: an air duct; 20: an absorbent storage section;

21. 33: a pipeline; 22: a storage tank; 23. 32: a stirring unit;

30: a wet reaction section; 31: a wet reactor; 35: an absorption tower.

Detailed Description

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Generally, the nomenclature used in this specification is those well known and commonly employed in the art.

In the present specification, the term "includes" or "including" a certain component means that other components may be included without excluding other components unless otherwise specified.

The present invention relates to a method for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, which comprises: (a) a step of oxidizing nitrogen oxides contained in the exhaust gas by reacting the exhaust gas with ozone; (b) a step of obtaining an absorbent by mixing an organic acid or an organic acid salt in an alkaline earth metal compound in an aqueous solution state or a slurry state; and (c) a step of performing denitrification and desulfurization of the exhaust gas by contacting the exhaust gas oxidized by the reaction with ozone in the step (a) with the absorbent in the step (b).

In addition, the present invention relates to an apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, comprising: a gas phase reaction unit for oxidizing nitrogen oxides contained in the exhaust gas by reacting the exhaust gas with ozone; an absorbent storage unit for storing an absorbent by mixing an organic acid or an organic acid salt with an alkaline earth metal compound in an aqueous solution state or a slurry state; and a wet reaction section for denitrifying and desulfurizing the exhaust gas containing sulfur oxides and nitrogen oxides by bringing the absorbent in the absorbent storage section into contact with the exhaust gas oxidized in the gas phase reaction section.

More particularly, the present invention relates to a method and apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, which can simultaneously perform a nitrogen removal process and a sulfur removal process of exhaust gas through one wet treatment process, and can economically simultaneously treat sulfur oxides and nitrogen oxides without changing equipment for nitrogen removal or inputting expensive additives for nitrogen removal in the existing wet desulfurization process, by using a wet desulfurization process for removing sulfur oxides and nitrogen oxides contained in exhaust gas.

Hereinafter, a method and apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to the present invention will be described in detail in terms of steps with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of the simultaneous removal of sulfur oxides and nitrogen oxides from an exhaust gas according to an embodiment of the present invention; FIG. 2 is a schematic diagram of the simultaneous removal of sulfur oxides and nitrogen oxides from an exhaust gas according to another embodiment of the present invention; fig. 3 is a structural diagram of simultaneously removing sulfur oxides and nitrogen oxides in exhaust gas according to an embodiment of the present invention.

According to the invention, Sulfur Oxides (SO) contained in the exhaust gas are removed simultaneously_x) And Nitrogen Oxides (NO)_x) The device comprises: a gas phase reaction part 10, an absorbent storage part 20 and a wet reaction part 30.

The gas phase reaction part 10 is disposed between an exhaust gas generation source (not shown) and the wet reaction part 30. The exhaust gas discharged from the exhaust gas generating source is supplied to the gas phase reaction unit 10, and then supplied to the wet process reaction unit 30 through the gas phase reaction unit 10.

The gas phase reaction section 10 reacts the exhaust gas with ozone to react with Nitrogen Oxides (NO) contained in the exhaust gas_x) Oxidation is carried out [ step (a) ].

Nitrogen Oxides (NO) contained in the exhaust gas_x) Most consist of Nitric Oxide (NO) which is less reactive and soluble and more difficult to wet process. In the present invention, nitrogen monoxide (NO) in such nitrogen oxides is converted into highly reactive and soluble and wet-processable nitrogen dioxide (NO) by selective oxidation reaction with ozone₂) Accordingly, the denitrification process in the wet reaction section 30, which will be described later, can be performed, and thus the effect of the present invention can be improved.

For example, through the above step (a), Nitric Oxide (NO) contained in the exhaust gas may be generated according to the following reaction formula 1Conversion to nitrogen dioxide (NO)₂)。

[ reaction scheme 1 ]

NO(g)+O₃→NO₂(g)+O₂

At this time, the exhaust gas and ozone may be injected into the gas phase reaction portion 10 by adjusting the flow rate using the mass flow meter 11 or the like. The gas phase reaction section 10 may use an exhaust gas duct (duct)15, a teflon tube reactor 12, or the like, but is not limited thereto. The gas residence time in the reactor may be changed by changing the length of the reactor using the above-described tube, the gas residence time in the gas phase reaction portion may be changed, and the gas residence time in the gas phase reaction portion is proportional to the volume of the reactor, and thus may be preferably 2 seconds to 10 seconds, but is not limited thereto.

In the present invention, the gas phase reaction part 10 includes a grid nozzle (not shown) for injecting ozone in order to sufficiently mix the exhaust gas and the ozone, and as shown in fig. 1, the nozzle is provided in a step before the wet reaction part.

The reaction conditions in the gas phase reaction section 10 are 160 ℃ or lower, and preferably 130 ℃ or lower. Since the molar ratio of ozone to nitrogen oxide reacts equivalently with nitrogen oxide, ozone may be injected in an equivalent amount to remove nitrogen oxide. If ozone is used in an excessive amount, ozone is discharged into the atmosphere to cause pollution, and therefore, the equivalent ratio of ozone to nitrogen oxides is preferably 1 or less.

On the one hand, the absorbent storage section 20 stores an absorbent obtained by mixing an organic acid or an organic acid salt in an alkaline earth metal compound in an aqueous solution state or a slurry state, and supplies the stored absorbent to the wet reaction section 30 where denitrification and desulfurization are performed [ step b ].

The absorbent storage part 20 may be connected to the wet reaction part through a connection pipe 21. The above-mentioned connection pipe 21 is connected at one side to the absorbent storage part 20 and at the other side to the wet reaction part 30, so that the absorbent stored in the absorbent storage part 20 can be supplied to the wet reaction part 30 through the connection pipe, and may further include a pump, a valve, etc. used therein.

The absorbent can be prepared by mixing an organic acid or an organic acid salt with an alkaline earth metal compound in an aqueous solution state or a slurry state in which the alkaline earth metal compound is dispersed in water. At this time, the above mixing can be easily performed by a method used in the art.

The alkaline earth metal compound may be one or more selected from the group consisting of calcium carbonate and calcium hydroxide, and calcium carbonate is preferable in terms of treatment cost and practicality.

In one aspect, the organic acid is selected from the group consisting of RCOOH (R ═ H or an alkyl group having 1 to 18 carbon atoms), a dicarboxylic acid having 1 to 20 carbon atoms, and a mixture thereof, and preferably formic acid, and the organic acid salt is preferably an alkaline earth metal salt of formic acid.

The absorbent of the present invention as described above is prepared by mixing an organic acid or an organic acid salt with an alkaline earth metal compound, and the surface of the alkaline earth metal compound is continuously consumed by an ion exchange reaction with the organic acid on the surface of the alkaline earth metal compound, so that the particle size of the absorbent can be made smaller.

This principle is very similar to CMP of semiconductor processes and the etching rate of the calcium carbonate surface depends on the acid content and the degree of movement of the particles. Although the particle size is smaller as the acid content is higher or the movement of particles is larger, the degree thereof is determined in terms of COD of wastewater and cost limit.

In addition, in general, alkaline earth metal compounds have very low solubility in water, and therefore have a problem of very low reactivity with sulfur oxides and nitrogen oxides caused in an aqueous phase. This problem can be solved by adding an organic acid, because an alkali metal salt such as a calcium salt which improves water solubility can be formed by the reaction of the alkaline earth metal compound with the organic acid. That is, since sulfur oxides can only react with calcium in the aqueous phase, the higher the concentration of calcium salt that can dissolve in water in the wet process, the more calcium ions come into contact with sulfur oxides, and sulfur oxides can be effectively removed.

In particular, when formic acid is used as the above-mentioned organic acid, sufficient effects can be obtained with a smaller amount of the organic acid due to the lower molecular weight of formic acid, and corrosion and/or erosion in the apparatus can be prevented while minimizing the increase in COD.

Generally, in order to promote the removal of sulfur oxides from exhaust gas, it is necessary to continuously add a considerable amount of dibasic acid (dibasic acid) or the like to maintain a sufficient concentration in the liquid phase, but it is known that such an excessive amount of dibasic acid or the like can promote corrosion and/or erosion in the apparatus for a long period of time, and in addition, COD problems occur. That is, when COD is increased, there is a disadvantage that it is removed by performing the wastewater process again.

However, formic acid has a carbon number half that of a dibasic acid and has excellent physicochemical properties such as water solubility, compared with a dibasic acid, and therefore, when formic acid is used in combination with an absorbent, the particle size of the absorbent can be significantly reduced. Further, by producing an alkali metal salt having improved solubility, it is possible to not only improve the desulfurization and denitrification efficiency but also solve the safety problem and the environmental problem in the conventional desulfurization and denitrification process using a dibasic acid as an organic acid.

Specifically, in the present invention, as the absorbent for desulfurization and denitrification, a dibasic acid having a carbon number (e.g., HOOC-CH) is preferably contained₂-CH₂-COOH) as an additive, not only can an alkali metal salt having excellent water solubility be produced as compared with a dibasic acid, but also the particle size of the absorbent becomes smaller as the surface of the absorbent is consumed by an ion exchange reaction with the surface of the alkaline earth metal compound, so that the reactivity and the absorption rate of sulfur oxide and nitrogen oxide in the exhaust gas can be further improved.

In the present invention, the organic acid or organic acid salt contained in the absorbent is 1ppm to 3000ppm, preferably 10ppm to 2000ppm, based on the solid content of the absorbent.

If the organic acid or organic acid salt is mixed in an amount of less than 1ppm based on the solid content, the effect of mixing the organic acid or organic acid salt cannot be obtained, and if it exceeds 3000ppm, the cost may be increased and problems such as COD and corrosion may occur.

In addition, in the present invention, in order to promote dissolution of calcium in the absorbent, and further, in order to promote desulfurization and denitrification, the absorbent containing the above organic acid may include an additional organic acid in addition to formic acid, and the above additional organic acid includes an organic acid containing only a carboxyl group (e.g., acetic acid, propionic acid, butyl carboxylic acid, amyl carboxylic acid, adipic acid, succinic acid, maleic acid, malic acid, etc.) or an organic acid containing both a carboxyl group and a hydroxyl group (e.g., 3-hydroxypropionic acid, glycolic acid, etc.). The organic acid containing both the carboxyl group and the hydroxyl group may be a polymer or a monomolecular.

The absorbent storage part 20 may include a storage tank 22 and a stirring unit 23. The storage tank 22 for storing the absorbent may store the absorbent in an aqueous solution state or a slurry state. The storage tank 22 may be connected to the wet reaction part 30 through a connection pipe 21.

The stirring unit 23 provided in the storage tank 22 can promote the reaction between the organic acid or the organic acid salt and the alkaline earth metal compound by stirring and homogenizing the absorbent stored in the storage tank 22.

As described above, the absorbent in the absorbent storage section 20 and the exhaust gas oxidized in the gas phase reaction section 10 are supplied to the wet reaction section 30, and the exhaust gas supplied to the above-mentioned wet reaction section 30 and the absorbent are contacted in the wet reaction section, thereby performing denitrification and desulfurization of the exhaust gas [ step (c) ].

In the wet reaction section 30, desulfurization is performed by a reaction between sulfur oxides in the exhaust gas and alkaline earth metal compounds in the absorbent; by means of alkaline earth metal Sulfites (SO)₃ ^2-) And nitrogen removal by reaction with nitrogen dioxide generated by oxidation and absorption of nitrogen monoxide in the exhaust gas, wherein the alkaline earth metal sulfite is an intermediate product generated by desulfurization reaction of sulfur oxide in the exhaust gas and alkaline earth metal compound in the absorbent.

In one example, the desulfurization in the wet reaction part 30 is performed by: in the process of passing the sulfur oxides in the exhaust gas through the inside of the liquid phase reactor or the absorption tower of the flue gas desulfurization apparatus in a thermal power plant or the like, the sulfur oxides are absorbed in the sprayed limestone slurry.

On the one hand, in the case where the absorbent containing calcium carbonate is supplied from the above-described absorbent storage part to the wet reaction part, desulfurization and denitrification reactions may be performed according to the following reaction formulae 2 to 7.

[ reaction scheme 2 ]

(parallel reaction, reaction Slow)

[ reaction scheme 3 ]

CaCO₃(s)+2H⁺→Ca²⁺+H₂O+CO₂(g) (Slow)

[ reaction scheme 4 ]

CaCO₃(s)+2RCOOH(l)→Ca(RCOO)₂(l)+H₂O+CO₂(Kuai)

[ equation 5 ]

Ca(RCOO)₂(l)+2H⁺→Ca²⁺+2RCOOH (l) (quick)

[ equation 6 ]

Ca²⁺+SO₃ ^2-(l)→CaSO₃(S) (quick)

[ reaction scheme 7 ]

CaSO₃(s)+1/2NO₂→CaSO₄(s)+1/4N₂(Kuai)

As shown in the above reaction formulas 2 to 7, sulfur dioxide (SO) in the exhaust gas supplied from the gas phase reaction section 10₂) Reacts with water in the absorbent to generate hydrogen ions and sulfite ions, and the generated hydrogen ions (protons) react with calcium carbonate of the absorbent to generate calcium ions. However, calcium ions generated therein have a slow reaction rate, and thus the completeness of desulfurization and decarburization reactions is limited.

Thus, according to the invention, when addingIn the case of adding an organic acid or an organic acid salt, calcium ions can be rapidly generated according to reaction formulas 4 and 5. The calcium ions generated in this way react with previously generated sulfite ions according to reaction formula 6 to generate calcium sulfite (CaSO)₃). The calcium sulfite produced at this time reacts with nitrogen dioxide produced in the gas phase reaction section, and the calcium sulfite is changed into calcium sulfate, and nitrogen dioxide is converted into nitrogen to perform denitrification.

In one aspect, the desulfurization reaction is carried out by passing sulfur dioxide contained in the flue gas over sulfite ions (SO)₃ ^2-) Finally to calcium sulfate (calcium salt) and thus removed from the exhaust gas.

That is, as shown in reaction formula 7, calcium sulfite (CaSO) is generated by desulfurization of the sulfur dioxide₃) As a reducing agent for nitrogen oxides, and by means of the above-mentioned calcium sulphite (CaSO)₃) Reaction with nitrogen dioxide to produce nitrogen (N)₂) And calcium sulfate (CaSO)₄). Therefore, the method of the present invention is technically characterized in that, in the case where organic acids are contained in calcium carbonate, such calcium sulfite, which can be produced through a desulfurization reaction, can be more rapidly reacted and used for denitrification, and thus, nitrogen dioxide in exhaust gas is converted into nitrogen (N)₂) Is removed from the exhaust gas.

As a result, the organic acid or organic acid salt mixed in the absorbent not only absorbs sulfur oxides but also improves the absorption of nitrogen oxides, and at the same time, the reaction speed of the slow reaction of equations 2 and 3 can be increased by the catalytic action of equations 4 to 5, and as a result, the above-mentioned organic acid or organic acid salt can play a decisive role in producing more calcium sulfite.

In this case, in order to improve the denitrification efficiency of the exhaust gas, it is necessary to increase the concentration of calcium sulfite as a reducing agent. For this reason, it is necessary to increase the desulfurization rate, and thus, the expensive denitrification additive (Na) applicable to the conventional denitrification reaction of exhaust gas is not used in the present invention₂S、Na₂SO₃Etc.), but denitrification of exhaust gas and the like can be performed by using an absorbent mixed with an organic acid or an organic acid saltThe desulfurization efficiency is maximized.

The wet reaction part 30 according to the present invention may include a wet reactor 31 and a stirring unit 32. As described above, the sulfur oxide and the nitrogen oxide are absorbed by the limestone slurry sprayed in the process of passing through the absorption tower 35 of the flue gas desulfurization apparatus at the thermal power plant or the like, so that the desulfurization and the denitrification can be simultaneously performed.

The above-mentioned details can be explained by referring to fig. 2, and fig. 2 shows a specific example in which the desulfurization and denitrification reactions according to the present invention can be performed in a flue gas desulfurization apparatus in a conventional thermal power plant. As a device corresponding to the gas phase reaction section in the present invention, an exhaust gas transport duct for transporting exhaust gas is used. Ozone and Nitrogen Oxide (NO) in exhaust gas generated from the ozone generating part in the air duct_x) In particular Nitric Oxide (NO), to nitrogen dioxide (NO)₂) And a product of oxidation reaction of nitrogen oxide by the ozone (including nitrogen dioxide (NO)₂) The mixed gas) is passed through an absorption tower 35 in the existing flue gas desulfurization apparatus. Further, the slurry supplied from the absorbent storage unit 20 in the absorption tower is sprayed in a direction from above to below, and as a result, the sprayed liquid falls downward due to gravity, wherein the absorbent storage unit 20 contains limestone slurry used for a conventional desulfurization reaction. At this time, the injected slurry and a product (including nitrogen dioxide (NO)) of the oxidation reaction of nitrogen oxide by the ozone are reacted₂) The mixed gas of (b) and thus an apparatus for simultaneously performing a desulfurization reaction and a denitrification reaction is shown in fig. 2.

That is, the wet reaction section in the present invention corresponds to an absorption tower used in a flue gas desulfurization apparatus in a thermal power plant, and the desulfurization and denitrification apparatus may be configured by injecting the absorbent supplied from the absorbent storage section in the present invention into the absorption tower so that the injected absorbent contacts the exhaust gas oxidized from the gas phase reaction section in accordance with the present invention, thereby denitrifying and desulfurizing the exhaust gas containing sulfur oxides and nitrogen oxides.

Therefore, the present invention uses the slurry spraying device and the exhaust gas transportation duct used in the conventional art as they are, and further uses the exhaust gas transportation duct as a gas phase reaction part for the oxidation reaction with ozone. In addition, by merely adding the alkaline earth metal compound and the organic acid or the organic acid salt mixed in the aqueous solution or slurry state in the absorbent storage section and using them as the absorbent, it is possible to achieve an excellent effect of further performing the denitrification reaction in addition to the desulfurization reaction alone in the conventional absorption tower.

On the one hand, in the case where the above-described wet reactor according to the present invention includes the wet reactor 31 and the stirring unit 32 instead of the absorption tower system at the thermal power station or the like of the related art, it is possible to form: inflow ports (not shown) through which the absorbent and the exhaust gas can flow, respectively; a reaction section (not shown) in which denitrification and desulfurization of the absorbent and the exhaust gas can be performed; and an exhaust port for discharging the denitrified and desulfurized product. In addition, the stirring unit 32 is provided to the wet reactor 31, and thus promotes denitrification and desulfurization of the exhaust gas by stirring the absorbent and the exhaust gas supplied to the wet reaction part. In this case, the stirring means 32 can be applied without limitation as long as it is a member for improving the gas-liquid contact efficiency between the absorbent and the exhaust gas; the stirring unit 32 may be a stirrer, a bubble generator (bubble generator), or the like.

Thereafter, the above exhaust gas, after being subjected to removal of nitrogen oxides and sulfur oxides by desulfurization and denitrification processes in the wet reaction section, may be discharged to the outside through the connecting duct 33. At this time, the alkali metal salt generated in the wet reaction section remains in the wet reaction section in an aqueous solution state or a slurry state, and can be recovered and utilized by obtaining or discharging calcium sulfate (gypsum) to a treatment facility (not shown) later.

According to the method and apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas of the present invention, nitrogen monoxide having a low reactivity is converted into nitrogen dioxide having a high reactivity by a reaction with ozone, and then a denitrification process is performed in parallel under the same conditions as a desulfurization process by supplying an absorbent having an aqueous solution state or a slurry state containing an organic acid or an organic acid salt, so that inefficacy and side effects occurring when different operation conditions are applied to the denitrification process and the desulfurization process, respectively, can be reduced, and residual nitrogen oxides, which cannot be removed in a selective catalytic reduction device, can be effectively removed while improving desulfurization performance by originally applying existing wet desulfurization equipment without adding an expensive denitrification additive.

The present invention will be described in more detail with reference to examples of the present invention. However, the following embodiment is merely an example of the present invention, and the scope of the present invention is not limited to the following embodiment.

< examples 1 to 2>

Exhaust gases of korean coal thermal power plant a (example 1) and B (example 2) were sampled, 14ppm ozone was injected in an amount equivalent to that of exhaust gas sampling line having a length of 10m, and nitrogen monoxide (NO) was converted into nitrogen dioxide (NO) by measuring nitrogen monoxide (NO)₂) And is shown in table 1.

TABLE 1

Partitioning	NO(ppm)	NO2(ppm)	Conversion (%)
				Example 1	14	14	100
Example 2	25	25	100

As shown in table 1, it was confirmed that the oxidation reaction of nitric oxide by ozone completely converted nitric oxide into nitrogen dioxide.

< examples 3 to 7>

The nitrogen and sulfur oxides-containing exhaust gas is denitrified and desulfurized using the apparatus shown in fig. 2.

First, a mixture containing 13ppm of Nitric Oxide (NO) and 425ppm of sulfur dioxide (SO) was measured by a mass flow meter₂) With 4.5g/m of exhaust gas³Ozone of 4.8m³The reaction mixture was injected into the gas phase reaction section 10 in a manner of/hr. The molar ratio of ozone to nitric oxide is an equivalence ratio.

The exhaust gas and ozone were retained in the gas phase reaction section for 6.2 seconds, and the exhaust gas was oxidized by the reaction with ozone at normal temperature and pressure. The oxidized exhaust gas was measured at 4.8m³The same was supplied to the wet reaction part 30 in an/hr manner, reacted with the absorbent and the removal rate of nitrogen oxides and sulfur oxides was measured using a combustible gas detector (testo350) and is shown in table 2.

At this time, the absorbent was prepared by adding the organic acid and the content shown in table 2 to the calcium carbonate slurry of 20% solid content, and the absorbent prepared above was supplied to the wet reaction part (100L) in a volume of 50L. In this case, 90% of the absorbent capable of passing 325 mesh was used.

< comparative examples 1 to 3>

The nitrogen oxides and sulfur oxides contained in the exhaust gas were removed in the same manner as in example 1 and were removed under the conditions shown in table 2, and the removal rates of the nitrogen oxides and sulfur oxides were measured by a combustible gas detector and are shown in table 2.

TABLE 2

As shown in table 2, it was confirmed that the removal rates of nitrogen oxide and sulfur oxide were much higher in examples 3 to 7 than in comparative examples 1 and 2, and particularly in the case of mixing 1000ppm or more of formic acid in the organic acid, the removal rate of nitrogen oxide was 90% or more. In addition, as shown in comparative example 1, the removal rate of nitrogen oxide was 50% or more even when the organic acid was not mixed, but when the organic acid was used appropriately, the removal rates of nitrogen oxide and sulfur oxide were higher. In the case of comparative example 3, although the removal rate of nitrogen oxides and sulfur oxides was high, there was generated a side effect of increasing the treatment cost and COD of the desulfurization waste water.

While certain features of the invention have been described in detail above, it will be apparent to those skilled in the art that the invention is not limited to the details shown in the drawings, and that the invention is not limited to the details shown. Accordingly, the actual scope of the invention should be determined only by the attached claims and their equivalents.