KR20200119617A - Method and Apparatus for Simultaneous Removal of SOx and NOx in the Flue Gas - Google Patents

Abstract

The present invention relates to a method and apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas and, more specifically, 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 the exhaust gas in one wet process facility by performing the denitrification process of the exhaust gas as a wet process under the same operating conditions as the desulfurization process.

Description

Method and Apparatus for Simultaneous Removal of SOx and NOx in the Flue Gas}

The present invention relates to a method and a removal device for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, and more particularly, to exhaust gas capable of simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas by a wet method. It relates to a method and a device for removing contained sulfur oxides and nitrogen oxides simultaneously.

When fossil fuels are burned, sulfur components in the fuel are oxidized to generate sulfur dioxide, which is a sulfur oxide, and nitrogen oxides (NO _x ) are inevitably generated due to oxidation of nitrogen components or pyrolysis of combustion air at high temperatures. When sulfur oxides (SO _x ) and nitrogen oxides (NO _x ) are discharged to the atmosphere, they combine with water vapor and inorganic matters present in the air to form ultra-fine dust less than PM2.5, reducing the visible distance and causing cardiopulmonary disease. It is acting as a substance (Non-Patent Document 0001).

Although the wet limestone desulfurization system is generally used to remove sulfur oxides (SO _x ) in fossil fuel air pollution emission facilities, the desulfurization rate is 80% to 90%, so part of the generated amount is discharged to the atmosphere.

In addition, selective catalytic reduction (SCR) is adopted as the most common and effective denitrification method for removing nitrogen oxides (NO _x ), but the denitrification rate is only 70% to 90%, so 10% to 30% of the generated amount is inevitable. Since it is discharged to the atmosphere, further reduction technology development is required to improve the air quality.

In general, air pollution prevention facilities using fossil fuels are arranged in the order of selective catalytic reduction, electric precipitators, and flue gas desulfurization (FGD). In the selective catalytic reduction method, ammonia or urea is injected in the gaseous state to reduce and remove nitrogen oxides to nitrogen (N ₂ ) gas, and the flue gas desulfurization device sprays limestone slurry to absorb sulfurous acid (SO ₂ ) gas into the limestone slurry liquid. It is oxidized and removed by converting it to a solid gypsum (CaSO ₄ ). However, if the amount of denitrifying agent and desulfurizing agent is increased to increase the removal rate, the increased unreacted material causes equipment failure.

The residual nitrogen oxides (NO _x ) that are not removed even after treatment in the selective catalytic reduction method are mostly insoluble nitrogen monoxide (NO), so they are not removed from the absorber of the flue gas desulfurization apparatus and are discharged to the atmosphere. For more complete removal, it is necessary to develop a wet flue gas denitration technology that removes nitrogen oxides by an absorption method in the absorption tower of the flue gas desulfurization system.

As a prior art related to this, a method of removing nitrogen oxides by reacting with Na ₂ S and Na ₂ SO ₃ and removing them by plasma method has been disclosed (Patent Document 0001, Non-Patent Document 0002), and an alcohol or diol compound as an organic solvent A method of removing SO _x and NO _x by adsorption has also been disclosed (Patent Document 0002), but these prior technologies require additional use of expensive Na ₂ S and Na ₂ SO ₃ to simultaneously treat desulfurization and denitrification, and polyols A desulfurization and denitrification solution, which is a composite solution containing a polyglycol-based and/or polyglycol-based solution, must be separately prepared and used, and at the same time, the flue gas temperature must be adjusted before desulfurization and denitrification. there was.

In addition, Korean Patent Registration No. 10-1724358 discloses a method of oxidizing flue gas to ozone and then making a hydrogen peroxide solution into droplets in an adsorption tower to be adsorbed, and Korean Patent No. 10-1724358 discloses iron-ethylenediamine tetraacetic acid ( Fe-EDTA) and a method of removing electrochemically by using the reaction of NO have been disclosed, but these prior arts have problems such as having to construct a new process.

Accordingly, there is a need to develop a technology for a more efficient desulfurization and denitrification method that can solve the stability problems and environmental problems associated with the conventional desulfurization process and increase the simultaneous removal rate of SO _x and NO _x without the addition of facilities.

Korean Patent Registration No. 10-1800517 (Publication date: 2017.07.11) Korean Patent Registration No. 10-1871197 (Publication date: 2017.02.08) Republic of Korea Patent Registration No. 10-1724358 (Publication date: 2017.03.09)

Journal of Korean Society for Atmospheric Environment Vol. 31, No. 2, April 2015, pp. 143~156 Moo Been Chang, How Ming Lee, Feeling Wu & Chi Ren Lai, J. Air & Waste Manage. Assoc., 54:941~949

The main object of the present invention is that it is possible to simultaneously perform the denitrification process and the desulfurization process of exhaust gas with one wet treatment process, change the facilities for denitrification in the previously operated wet desulfurization process, or introduce expensive denitrification additives It is to provide a method and apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas that can economically treat sulfur oxides and nitrogen oxides at the same time.

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

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

In a preferred embodiment of the present invention, the organic acid in 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. It can be characterized.

In a preferred embodiment of the present invention, the content of the organic acid or salt of the organic acid in step (b) may be characterized in that 1 ppm to 3,000 ppm relative to the solid content in the absorbent.

In a preferred embodiment of the present invention, step (a) may include oxidizing nitrogen monoxide (NO) contained in the exhaust gas to nitrogen dioxide (NO ₂ ) by reacting the exhaust gas with ozone. .

In a preferred embodiment of the present invention, the desulfurization of step (c) is performed by a reaction of sulfur oxides of exhaust gas and alkaline earth metal compounds in the absorbent, and the denitration of step (c) is Alkaline earth metal sulfite produced by the desulfurization reaction of sulfur oxide and alkaline earth metal compound in the absorbent, and nitrogen dioxide (NO ₂ ) obtained by reacting nitrogen monoxide (NO) contained in the exhaust gas in step (a) with ozone and It may be characterized in that the denitrification reaction is performed by the reaction of.

Another embodiment of the present invention is an apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, comprising: a gas phase reaction unit that reacts exhaust gas with ozone to oxidize nitrogen oxides contained in exhaust gas; An absorbent storage unit for storing the absorbent by mixing an organic acid or a salt of an organic acid with an alkaline earth metal compound in an aqueous solution or slurry state; And a wet reaction unit for performing denitrification and desulfurization of exhaust gas containing sulfur oxides and nitrogen oxides by contacting the absorbent in the absorbent storage unit with the exhaust gas oxidized in the gas phase reaction unit. And a device for simultaneously removing nitrogen oxides.

In another preferred embodiment of the present invention, the gas phase reaction unit may be a duct or a reactor for transferring exhaust gas.

In another preferred embodiment of the present invention, the alkaline earth metal compound may be selected from the group consisting of calcium carbonate, calcium hydroxide, and mixtures thereof.

In another preferred embodiment of the present invention, the organic acid may be characterized in that it is selected from the group consisting of RCOOH (R = H or an alkyl group having 1 to 18 carbon atoms), dicarboxylic acid having 1 to 20 carbon atoms, and mixtures thereof. have.

In another preferred embodiment of the present invention, the gas phase reaction unit may include reacting the exhaust gas with ozone to oxidize nitrogen monoxide (NO) contained in the exhaust gas to nitrogen dioxide (NO ₂ ).

In another preferred embodiment of the present invention, the desulfurization in the wet reaction unit is performed by a reaction between the sulfur oxide of the exhaust gas and an alkaline earth metal compound in the absorbent, and the denitrification in the wet reaction unit is performed by the exhaust gas. Alkaline earth metal sulfite produced by the desulfurization reaction of sulfur oxide and alkaline earth metal compound in the absorbent, and nitrogen dioxide (NO ₂ ) obtained by reacting nitrogen monoxide (NO) contained in exhaust gas in the gas phase reaction section with ozone It may be characterized in that a denitrification reaction is performed by the reaction.

In another preferred embodiment of the present invention, the gas phase reaction unit may include a grating nozzle for injecting ozone to sufficiently mix exhaust gas and ozone, and the nozzle may be installed before the wet reaction unit.

In another preferred embodiment of the present invention, the wet reaction unit is an absorption tower used in a flue gas desulfurization apparatus in a thermal power plant, and the absorbent supplied from the absorbent storage unit is sprayed into the absorption tower, so that the sprayed absorbent and the gas phase The exhaust gas oxidized in the reaction unit may be brought into contact with each other to perform denitrification and desulfurization of the exhaust gas containing sulfur oxide and nitrogen oxide.

According to the present invention, by performing the exhaust gas denitrification process as a wet process under the same operating conditions as the desulfurization process, it is possible to simultaneously perform the exhaust gas denitrification process and the desulfurization process in one wet process facility (wet flue gas desulfurization apparatus). In addition, in the previously operated wet desulfurization process, both denitrification and desulfurization can be performed without changing or adding equipment for denitrification, so it is economical and the ratio that appears when different operating conditions are applied to each of the denitrification and desulfurization processes. There is an effect that can reduce efficiency and side effects.

In addition, according to the present invention, nitrogen monoxide (NO) of exhaust gas having low reactivity with ozone is converted to highly reactive nitrogen dioxide (NO ₂ ), and reaction rate of sulfur oxide and absorbent in exhaust gas by the introduction of organic acid or salt of organic acid At the same time, at the same time, the intermediate product of the generated sulfur oxide is used as a denitrifying agent, so that high exhaust gas denitrification and desulfurization efficiency can be realized without the addition of expensive denitrification additives (Na ₂ S, Na ₂ SO ₃ ). There is.

1 is a schematic diagram of an apparatus for simultaneously removing sulfur oxides and nitrogen oxides in exhaust gas according to an embodiment of the present invention.
2 is a schematic diagram of an apparatus for simultaneously removing sulfur oxides and nitrogen oxides in exhaust gas according to another embodiment of the present invention.
3 is a block diagram of an apparatus for simultaneously removing sulfur oxide and nitrogen oxide applied to an embodiment of the present invention.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by an expert skilled in the art to which the present invention belongs. In general, the nomenclature used in this specification is well known and commonly used in the art.

Throughout the specification of the present application, when a certain part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

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

The present invention also provides an apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, comprising: a gas phase reaction unit for reacting exhaust gas with ozone to oxidize nitrogen oxides contained in exhaust gas; An absorbent storage unit for storing the absorbent by mixing an organic acid or a salt of an organic acid with an alkaline earth metal compound in an aqueous solution or slurry state; And a wet reaction unit for performing denitrification and desulfurization of exhaust gas containing sulfur oxides and nitrogen oxides by contacting the absorbent in the absorbent storage unit with the exhaust gas oxidized in the gas phase reaction unit. And an apparatus for simultaneously removing nitrogen oxides.

Specifically, the method and removal apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to the present invention include not only desulfurization of sulfur oxides but also nitrogen oxides using a wet desulfurization process for removing sulfur oxides contained in exhaust gas. It relates to a method and apparatus for achieving this denitrification, and it is possible to simultaneously perform the denitrification process and the desulfurization process of exhaust gas with one wet treatment process, and the change of facilities for denitrification in the previously operated wet desulfurization process, or expensive It is possible to economically treat sulfur oxides and nitrogen oxides at the same time without introducing additives for denitrification.

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 for each step with reference to the drawings.

1 is a schematic diagram of a device for simultaneously removing sulfur oxide and nitrogen oxide in exhaust gas according to an embodiment of the present invention, and FIG. 2 is a device for simultaneously removing sulfur oxide and nitrogen oxide in exhaust gas according to another embodiment of the present invention. Fig. 3 is a schematic diagram of an apparatus for simultaneously removing sulfur oxide and nitrogen oxide applied to an embodiment of the present invention.

The apparatus for simultaneously removing sulfur oxides (SO _x ) and nitrogen oxides (NO _x ) contained in exhaust gas according to the present invention includes a gas phase reaction unit 10, an absorbent storage unit 20, and a wet reaction unit 30. .

The gas phase reaction unit 10 is installed to be located between the exhaust gas generating source (not shown) and the wet reaction unit 30. The exhaust gas discharged from the exhaust gas generating source is supplied to the vapor phase reaction unit 10 and then to the wet reaction unit 30 through the vapor phase reaction unit 10.

The gas phase reaction unit 10 oxidizes nitrogen oxides (NO _x ) contained in the exhaust gas by reacting the exhaust gas with ozone [Step (a)].

Nitrogen oxide (NO _x ) contained in the exhaust gas is mostly composed of nitrogen monoxide (NO), which is difficult to wet treatment due to its low reactivity and solubility, and in the present invention, nitrogen monoxide (NO) in the nitrogen oxide is converted into ozone (O ₃ ). By converting to nitrogen dioxide (NO ₂ ) capable of wet treatment due to high reactivity and solubility through a selective oxidation reaction with and, the denitrification treatment for the denitrification process in the wet reaction unit 30 described below is possible, thereby enhancing the effect of the present invention. I can.

For example, through the step (a), nitrogen monoxide (NO) included in the exhaust gas may be converted to nitrogen dioxide (NO ₂ ) according to Reaction Formula 1 below.

[Scheme 1]

NO(g) + O ₃ → NO ₂ (g) + O ₂

At this time, the exhaust gas and ozone may be injected into the gas phase reaction unit 10 by adjusting the flow rate using a mass flow meter 11, etc., and the gas phase reaction unit 10 is a duct 15 for transferring the exhaust gas. Alternatively, a Teflon tube reactor 12 or the like may be used, but is not limited thereto. The gas residence time in the reactor can be changed by changing the length of the reactor using the tube, and the gas residence time in the gas phase reaction unit can change the gas residence time in the reactor, and the gas residence time in the gas phase reaction unit Since is proportional to the volume of the reactor, it may be preferably 2 seconds to 10 seconds, but is not limited thereto.

In addition, in the present invention, the gas phase reaction unit 10 includes a grid-type nozzle (not shown) for injecting ozone to sufficiently mix exhaust gas and ozone, and the nozzle is a wet reaction as shown in FIG. It can be seen that it is installed at the previous stage.

Here, the reaction in the gas phase reaction unit 10 reacts the exhaust gas and ozone under conditions of 160° C. or less, preferably 130° C. or less, and the molar ratio of ozone to nitrogen oxide is equivalent to reacting with nitrogen oxide. Therefore, it is safe to inject ozone as much as the equivalent to remove nitrogen oxides, and if excessive ozone is used, ozone may be released into the atmosphere and become contaminated.Therefore, it is preferable that the equivalent ratio of ozone to nitrogen oxides is 1 or less. Do.

On the other hand, the absorbent storage unit 20 stores an absorbent obtained by mixing an alkaline earth metal compound in an aqueous solution or slurry state with an organic acid or a salt of an organic acid, and the stored absorbent is stored in the wet reaction unit 30 where denitrification and desulfurization are performed. Supply [Step (b)].

The absorbent storage unit 20 may be connected to the wet reaction unit through a connection pipe 21. The connection pipe 21 has one side connected to the absorbent storage unit 20 and the other side connected to the wet reaction unit 30 to transfer the absorbent stored in the absorbent storage unit 20 through a connection pipe. It can be supplied to, and a pump, valve, etc. for this may be additionally provided.

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

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

Meanwhile, the organic acid may be selected from the group consisting of RCOOH (R = H or an alkyl group having 1 to 18 carbon atoms), or a dicarboxylic acid having 1 to 20 carbon atoms and a mixture thereof, and may be preferably formic acid, and an organic acid The salt of may preferably be an alkaline earth metal salt of formic acid.

The absorbent according to the present invention is prepared by mixing an alkaline earth metal compound with an organic acid or a salt of an organic acid, thereby continuously consuming the surface of the alkaline earth metal compound while conducting an ion exchange reaction with the organic acid on the surface of the alkaline earth metal compound. Can be made even smaller.

This principle is very similar to the CMP of the semiconductor process, and the etching rate of the calcium carbonate surface varies depending on the acid content and the degree of movement of the particles. The higher the acid content or the larger the particle movement, the smaller the particle size, but the degree can be determined from the COD and cost limit of the wastewater.

In addition, in general, alkaline earth metal compounds have a problem that their solubility in water is very low and reactivity with sulfur oxides and nitrogen oxides occurring in the aqueous phase is very low. This problem can be solved by the addition of an organic acid, because an alkaline earth metal compound reacts with an organic acid to produce an alkali salt such as a calcium salt having improved water solubility. That is, since sulfur oxide can only react with calcium in the aqueous phase, the higher the concentration of calcium salt soluble in water in the wet process, the greater the number of calcium ions in contact with the sulfur oxide, and the more efficiently the sulfur oxide can be removed. I can.

In particular, when formic acid is used as the organic acid, due to the low molecular weight of formic acid, a sufficient effect can be obtained even with a small amount of organic acid, and at the same time, corrosion and/or erosion in the device can be prevented while minimizing an increase in COD.

In general, in order to promote the removal of sulfur oxides from exhaust gas, a significant amount of dibasic acid, etc., must be continuously added to maintain a sufficient concentration in the liquid phase.However, such an excessive amount of dibasic acid, etc., will cause corrosion and/or corrosion in the device over a long period of time. It can promote erosion and is known to cause COD problems. In other words, if COD increases, there is a disadvantage that a wastewater process to remove it is required again.

However, formic acid has half carbon number than dibasic acid and has excellent physicochemical properties in water solubility. By mixing it with an absorbent, the particle size of the absorbent can be drastically reduced, and an alkali salt with improved solubility is produced. By doing so, it is possible not only to improve the desulfurization and denitrification efficiency, but also to solve stability problems and environmental problems in a conventional desulfurization and denitrification process in which a dibasic acid is applied as an organic acid.

Specifically, in the present invention, as an absorbent for desulfurization and denitrification, by containing formic acid (HCOOH) having half carbon atoms than dibasic acid (for example, HOOC-CH ₂ -CH ₂ -COOH) as an additive, it has excellent solubility in water compared to dibasic acid. In addition to being able to generate alkali salts, as the surface of the absorbent is consumed by the ion exchange reaction on the surface of the alkaline earth metal compound, the particle size of the absorbent is made smaller and the reactivity with sulfur oxides and nitrogen oxides in the exhaust gas and The absorption rate can be further improved.

In the present invention, the organic acid or salt of the organic acid contained in the absorbent may be 1 ppm to 3,000 ppm, preferably 10 ppm to 2,000 ppm, relative to the solid content in the absorbent.

If an organic acid or salt of an organic acid is mixed with less than 1 ppm of the solid content of the absorbent, the effect of mixing the organic acid or salt of an organic acid cannot be exhibited. If it exceeds 3,000 ppm, problems such as COD and corrosion along with an increase in cost May occur.

In addition, in the present invention, the organic acid-containing absorbent promotes the solubilization of calcium from the absorbent and furthermore, in addition to formic acid, to promote desulfurization and denitrification, acetic acid, propionic acid, butylcarboxylic acid, pentyl carboxylic acid, adipic acid, succinic acid , Maleic acid, malic acid, or the like, or an organic acid including a carboxyl group and a hydroxy group at the same time, such as 3-hydroxy-propionic acid or hydroxy-acetic acid. Here, the organic acid including the carboxyl group and the hydroxy group at the same time may be a polymer or a single molecule.

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

In addition, the stirring unit 23 is installed in the storage tank 22, and by stirring and homogenizing the absorbent stored in the storage tank 22, the reaction between an organic acid or a salt of an organic acid and an alkaline earth metal compound can be accelerated. have.

The absorbent in the absorbent storage unit 20 and the exhaust gas oxidized in the gas phase reaction unit 10 are supplied to the wet reaction unit 30, and the exhaust gas and the absorbent supplied to the wet reaction unit 30 are wet reaction. Denitrification and desulfurization of the exhaust gas are performed by contacting the unit [Step (c)].

Desulfurization in the wet reaction unit 30 is achieved by reaction of sulfur oxides of exhaust gas and alkaline earth metal compounds in the absorbent, and denitrification is generated by desulfurization reactions of sulfur oxides of exhaust gas and alkaline earth metal compounds in the absorbent. It is formed by the reaction of alkaline earth metal sulfite (Sulfite, SO ₃ ), which is an intermediate product, and nitrogen dioxide absorbed by oxidizing nitrogen monoxide in exhaust gas.

For example, the desulfurization in the wet reaction unit 30 passes sulfur oxides of exhaust gas into a liquid reactor, or sulfuric acid in a limestone slurry solution sprayed in the process of passing through an absorption tower of a flue gas desulfurization apparatus in a thermal power plant, etc. The cargo is absorbed and desulfurization can occur.

Meanwhile, when an absorbent containing calcium carbonate (CaCO ₃ ) is supplied from the absorbent storage unit to the wet reaction unit, desulfurization and denitrification reactions may be performed according to Reaction Formulas 2 to 7.

[Scheme 2]

SO ₂ (g) + H ₂ O ↔ SO ₃ ^2- (l) + 2H ⁺ (equilibrium reaction, slow)

[Scheme 3]

CaCO ₃ (s) + 2H ⁺ → Ca ^{2 +} + H ₂ O + CO ₂ (g) (slow)

[Scheme 4]

CaCO ₃ (s) + 2RCOOH(l) → Ca(RCOO) ₂ (l) + H ₂ O + CO ₂ (fast)

[Scheme 5]

Ca(RCOO) ₂ (l) + 2H ⁺ → Ca ^{2 +} + 2RCOOH(l) (fast)

[Scheme 6]

Ca ^{2 +} + SO ₃ ^2- (l) → CaSO ₃ (S) (fast)

[Scheme 7]

CaSO ₃ (s) + 1/2NO ₂ → CaSO ₄ (s) + 1/4N ₂ (fast)

As shown in Schemes 2 to 7, sulfur dioxide (SO2) in the exhaust gas supplied from the gas phase reaction unit 10 reacts with water in the absorbent to generate hydrogen ions and sulfite ions, and the generated hydrogen ions (protons) are It reacts with calcium carbonate in the absorbent to produce calcium ions. However, since the reaction rate of calcium ions generated here is slow, there is a limit to the degree of completion of the desulfurization and denitrification reactions.

Accordingly, as in the present invention, when an organic acid or a salt of an organic acid is added, calcium ions can be rapidly generated according to Schemes 4 and 5, and the calcium ions generated by this method are sulfite ions previously generated according to Scheme 6. Calcium sulfite (CaSO ₃ ) is produced by the reaction with, and the calcium sulfite produced at this time reacts with nitrogen dioxide generated in the gas phase reaction section to change to calcium sulfate, and the nitrogen dioxide is converted to nitrogen to perform a denitrification reaction.

On the other hand, sulfur dioxide contained in the exhaust gas is finally converted to calcium sulfate (calcium salt) through sulfite ions (SO ₃ ^2- ) to undergo a desulfurization reaction, thereby being removed from the exhaust gas.

That is, calcium sulfite (CaSO ₃ ) produced by the desulfurization of sulfur dioxide is used as a reducing agent for nitrogen oxides as shown in Scheme 7, and it is converted into nitrogen (N ₂ ) and calcium sulfate (CaSO ₄ ) by reaction with nitrogen dioxide. Is created. Therefore, by making the calcium sulfite that can be generated by the desulfurization reaction include the organic acid in the calcium carbonate, the reaction can proceed more quickly, and the method used for denitrification corresponds to the technical feature of the present invention. The nitrogen dioxide in the gas is converted to nitrogen (N ₂ ) and removed from the exhaust gas.

In the end, the organic acid or salt of the organic acid mixed with the absorbent improves the absorption of the nitrogen oxide as well as the absorption of sulfur oxide, and at the same time, the slow reaction of Schemes 2 and 3 is catalyzed to accelerate the reaction rate as shown in Schemes 4 to 5. As a result, it can play a decisive role in producing a large amount of calcium sulfite (CaSO ₃ ).

At this time, in order to improve the denitration efficiency of the exhaust gas, the concentration of calcium sulfite, which is a reducing agent, must be increased, and the desulfurization rate must be increased for this purpose. In the present invention, Na ₂ S and Na ₂ are conventionally applied to the exhaust gas denitration reaction. The denitrification and desulfurization efficiency of exhaust gas can be maximized by using an absorbent mixed with an organic acid or salt of an organic acid without the use of expensive denitrification additives such as SO ₃ .

The wet reaction unit 30 according to the present invention may include a wet reactor 31 and a stirring unit 32, and as described above, in the process of passing through the absorption tower 35 of the flue gas desulfurization apparatus in a thermal power plant, etc. Sulfur oxides and nitrogen oxides are absorbed in the limestone slurry liquid to be sprayed, so that desulfurization and denitrification are simultaneously performed.

This can be explained in detail from FIG. 2, and FIG. 2 shows a specific example in which the desulfurization and denitrification reaction 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 unit, an exhaust gas transfer duct that transfers exhaust gas is used, and the ozone generated by the ozone generating unit and nitrogen oxide (NO _x ) in the exhaust gas, especially nitrogen monoxide (NO), are used in the duct. It is converted into nitrogen dioxide (NO ₂ ) by oxidation reaction, and the product (mixed gas including nitrogen dioxide (NO ₂ )) by the oxidation reaction of nitrogen oxide by ozone passes through the absorption tower 35 in the existing flue gas desulfurization device, In addition, the slurry liquid supplied from the absorbent storage unit 20 including the limestone slurry liquid used for the existing desulfurization reaction is sprayed upward or downward in the absorption tower, so that the spray liquid eventually falls downward according to gravity. In this case, the sprayed slurry liquid reacts with a product (mixed gas containing nitrogen dioxide (NO ₂ )) according to the oxidation reaction of nitrogen oxides by ozone, thereby showing a device in which a desulfurization reaction and a denitrification reaction are simultaneously performed.

That is, the wet reaction unit in the present invention corresponds to an absorption tower used in a flue gas desulfurization apparatus in a thermal power plant, and the absorbent supplied from the absorbent storage unit according to the present invention is sprayed into the absorption tower, so that the sprayed absorbent and The desulfurization and denitrification apparatus may be configured so that the exhaust gas oxidized in the gas phase reaction unit according to the present invention is brought into contact with each other to perform denitrification and desulfurization of the exhaust gas containing sulfur oxide and nitrogen oxide.

Accordingly, the present invention uses the slurry spray device and the exhaust gas transfer duct in the absorption tower used in the prior art as it is, and additionally uses the exhaust gas transfer duct as a gas phase reaction unit for oxidation reaction with ozone, In addition, by adding only the method of using as an absorbent by mixing an alkaline earth metal compound in an aqueous solution or slurry state with an organic acid or salt of an organic acid in the absorbent storage unit, only the desulfurization reaction in the existing absorption tower is performed, and furthermore, the denitrification reaction is performed. It can show an excellent effect that can be done.

On the other hand, when the wet reactor according to the present invention includes a wet reactor 31 and a stirring unit 32, not an absorption tower method in a thermal power plant according to the prior art, respectively, an absorbent and exhaust gas can be introduced. Each inlet (not shown); A reaction unit (not shown) for performing denitrification and desulfurization of the absorbent and exhaust gas; And an outlet (not shown) through which the products of the denitrification and desulfurization are discharged; may be formed, and the stirring unit 32 is installed in the wet reactor 31, and the absorbent and exhaust gas supplied to the wet reactor By stirring, it is possible to promote the denitrification and desulfurization of the exhaust gas. At this time, the stirring unit 32 may be applied without limitation as long as it is a member capable of increasing the gas-liquid contact efficiency between the absorbent and the exhaust gas, and may be a stirrer, a bubble generator, or the like.

Thereafter, the exhaust gas may be discharged to the outside through the connection duct 33 after nitrogen oxides and sulfur oxides are removed by a desulfurization and denitrification process in the wet reaction unit, and at this time, the alkali salt generated in the wet reaction unit is an aqueous solution. It remains in the wet reaction unit in a state or a slurry state, and can be recycled by obtaining calcium sulfate (gypsum) or being discharged to a treatment facility (not shown).

The method and apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas according to the present invention convert low-reactivity nitrogen monoxide into highly reactive nitrogen dioxide by reaction with ozone, and then contain organic acids or salts of organic acids. By supplying an absorbent in the form of an aqueous solution or slurry and performing the denitrification process in parallel under the same conditions as the desulfurization process, inefficiency and side effects that appear when different operating conditions are applied for each of the denitrification process and the desulfurization process can be reduced, It is possible to effectively remove residual nitrogen oxides that have not been removed in the selective catalytic reduction device while improving the desulfurization performance by applying the existing wet desulfurization equipment as it is without adding expensive denitrification additives.

Hereinafter, the present invention will be described in more detail through examples in the present invention. However, the following examples are only an example of the present invention, and the claims of the present invention are not limited thereto.

< Example 1 to 2>

By sampling the exhaust gas of domestic coal-fired power plants A (Example 1) and B (Example 2), 14 ppm of ozone was injected into an exhaust gas sampling line of 10 m in length, and nitrogen monoxide (NO) to nitrogen dioxide (NO ₂ ). ) Was measured and shown in Table 1.

division NO (ppm) NO ₂ (ppm) Conversion rate (%) Example 1 14 14 100 Example 2 25 25 100

As shown in Table 1, it was confirmed that the entire amount of nitrogen monoxide was converted into nitrogen dioxide by the oxidation reaction of nitrogen monoxide by ozone.

< Example 3 to 7>

Denitrification and desulfurization of exhaust gas containing nitrogen oxides and sulfur oxides were performed using the apparatus shown in FIG. 2.

First, 13 ppm of nitrogen monoxide (NO) and 425 ppm of sulfur dioxide (SO ₂ ) of exhaust gas and 4.5 g/m ³ of ozone were injected into the gas phase reaction unit 10 at 4.8 m ³ /hr using a mass flow meter. The molar ratio of ozone to nitrogen monoxide is an equivalent ratio.

The exhaust gas and ozone stayed in the gas phase reaction unit for 6.2 seconds, and the exhaust gas and ozone were reacted at room temperature and pressure to oxidize. The oxidized exhaust gas was supplied to the wet reaction unit 30 at 4.8 m ³ /hr, reacted with an absorbent, and the removal rates of nitrogen oxides and sulfur oxides were measured with a combustion gas measuring instrument (testo350), and are shown in Table 2.

At this time, the absorbent was prepared by adding the organic acid and content of Table 2 compared to the 20% solid calcium carbonate slurry, and the prepared absorbent was supplied to the wet reaction unit (100 ℓ) in 50 ℓ. At this time, the absorbent was used as an absorbent passing through 325 mesh at 90%.

< Comparative example 1 to 3>

The nitrogen oxides and sulfur oxides contained in the exhaust gas were removed in the same manner as in Example 1, but the nitrogen oxides and sulfur oxides of the exhaust gas were removed under the conditions of Table 2, and the removal rate of the nitrogen oxides and sulfur oxides was measured with a combustion gas meter ( testo350) and shown in Table 2.

division Organic acid Measurement result Kinds Content (ppm) NOx removal rate (%) SOx removal rate (%) Example 3 Formic acid 500 86 100 Example 4 Formic acid 1,000 91.5 100 Example 5 Formic acid 2,000 93.8 100 Example 6 Acetic acid 1,000 85 100 Example 7 dibasic acid 1,000 81 100 Comparative Example 1 - - 56 97 Comparative Example 2 Formic acid 0.01 56 97 Comparative Example 3 Formic acid 4,000 96 100

As shown in Table 2, it was confirmed that the removal rates of nitrogen oxides and sulfur oxides were significantly higher in Examples 3 to 7 than in Comparative Examples 1 and 2. In particular, when mixing 1,000 ppm or more of formic acid among organic acids, 90 It was found to show more than% nitrogen oxide removal rate. In addition, even when the organic acid was not mixed as in Comparative Example 1, a nitrogen oxide removal rate of 50% or more was shown, but it was confirmed that the removal rate of nitrogen oxides and sulfur oxides was higher as the organic acid was properly used, and in the case of Comparative Example 3, nitrogen oxides And the removal rate of sulfur oxides was high, but there was a side effect of increasing treatment cost and COD of desulfurization wastewater.

Specific parts of the present invention have been described in detail above, and the present invention is not limited to those illustrated in the drawings. For those of ordinary skill in the art, these specific descriptions are only preferred embodiments, whereby the It will be clear that the scope is not limited. Accordingly, it will be said that the substantial scope of the present invention is defined by the appended claims and their equivalents.

10: vapor phase reaction unit
11: mass flow meter
15: duct
20: absorbent storage unit
21, 33: piping
22: storage tank
23, 32: stirring unit
30: wet reaction part
31: wet reactor
35: absorption tower

Claims (14)

In the method for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas,
(a) reacting the exhaust gas with ozone to oxidize nitrogen oxides contained in the exhaust gas;
(b) mixing an alkaline earth metal compound in an aqueous solution or slurry state with an organic acid or salt of an organic acid to obtain an absorbent; And
(c) sulfuric acid contained in exhaust gas comprising the 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 step (b). Simultaneous removal method of cargo and nitrogen oxides.
The method of claim 1,
The alkaline earth metal compound of the step (b) is selected from the group consisting of calcium carbonate, calcium hydroxide, and mixtures thereof. A method for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas.
The method of claim 1,
The organic acid in step (b) is contained in exhaust gas, characterized in that it is selected from the group consisting of RCOOH (R = H or an alkyl group having 1 to 18 carbon atoms), dicarboxylic acid having 1 to 20 carbon atoms, and mixtures thereof. Simultaneous removal method of sulfur oxide and nitrogen oxide.
The method of claim 1,
The method for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, wherein the content of the organic acid or salt of the organic acid in the step (b) is 1 ppm to 3,000 ppm based on the solid content in the absorbent.
The method of claim 1,
The step (a) comprises reacting the exhaust gas with ozone to oxidize nitrogen monoxide (NO) contained in the exhaust gas to nitrogen dioxide (NO ₂ ). Simultaneous removal method.
The method of claim 5,
In the desulfurization of step (c), a desulfurization reaction is performed by reaction of the sulfur oxide of the exhaust gas and the alkaline earth metal compound in the absorbent,
In the denitration of step (c), the alkaline earth metal sulfite produced by the desulfurization reaction of the sulfur oxide of the exhaust gas and the alkaline earth metal compound in the absorbent, and nitrogen monoxide (NO) contained in the exhaust gas in the step (a) are ozone. A method for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, characterized in that a denitrification reaction is performed by reaction with nitrogen dioxide (NO ₂ ) obtained by reacting with
In an apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas,
A gas phase reaction unit reacting the exhaust gas with ozone to oxidize nitrogen oxides contained in the exhaust gas;
An absorbent storage unit for storing an absorbent obtained by mixing an organic acid or a salt of an organic acid with an alkaline earth metal compound in an aqueous solution or slurry state; And
Sulfur oxide contained in the exhaust gas including; a wet reaction unit for performing denitrification and desulfurization of the exhaust gas containing sulfur oxide and nitrogen oxide by contacting the absorbent in the absorbent storage unit with the exhaust gas oxidized in the gas phase reaction unit, and Simultaneous nitrogen oxide removal device.
The method of claim 7,
The gaseous reaction unit is a duct or a reactor for transporting exhaust gas. Simultaneous removal of sulfur oxides and nitrogen oxides.
The method of claim 7,
The alkaline earth metal compound is an apparatus for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, characterized in that selected from the group consisting of calcium carbonate, calcium hydroxide, and mixtures thereof.
The method of claim 7,
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 of these sulfur oxides and nitrogen oxides contained in exhaust gas. Simultaneous removal device.
The method of claim 7,
The gas phase reaction unit reacts the exhaust gas with ozone to oxidize nitrogen monoxide (NO) contained in the exhaust gas to nitrogen dioxide (NO ₂ ). Simultaneous removal of sulfur oxides and nitrogen oxides contained in exhaust gas Device.
The method of claim 11,
Desulfurization in the wet reaction unit is performed by a reaction between sulfur oxides of exhaust gas and alkaline earth metal compounds in the absorbent,
The denitration in the wet reaction unit is performed by using the alkaline earth metal sulfite produced by the desulfurization reaction between the sulfur oxide of the exhaust gas and the alkaline earth metal compound in the absorbent, and nitrogen monoxide (NO) contained in the exhaust gas in the gas phase reaction unit with ozone. A device for simultaneously removing sulfur oxides and nitrogen oxides contained in exhaust gas, characterized in that a denitrification reaction is performed by reaction with nitrogen dioxide (NO ₂ ) obtained by the reaction.
The method of claim 7,
The gas phase reaction unit includes a lattice-type nozzle for injecting ozone to sufficiently mix the exhaust gas and ozone, and the nozzle is installed before the wet reaction unit. Removal device.
The method of claim 7,
The wet reaction unit is an absorption tower used in a flue gas desulfurization device in a thermal power plant, and by spraying the absorbent supplied from the absorbent storage unit 20 in the absorption tower, the sprayed absorbent and the oxidized exhaust from the gas phase reaction unit A device for simultaneously removing sulfur oxide and nitrogen oxide, characterized in that the gas is brought into contact with each other to perform denitrification and desulfurization of exhaust gas containing sulfur oxide and nitrogen oxide.

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