WO2007142496A1

WO2007142496A1 - Cleaning method of nitrogen dioxide from stationary sources and the apparatus for the same

Info

Publication number: WO2007142496A1
Application number: PCT/KR2007/002805
Authority: WO
Inventors: Han Jae Jo; Jin Young Kim; Don Sub Ra; Myoung Jin Kha; Jihn Koo Lee; Won Chui Chang; Jung Ho Kim; Jin S. Yoo; Du Soung Kim; Jang Ha Kim; Guang Gyoo Kim
Original assignee: Kocat Inc.; Korea South Power Co., Ltd.
Priority date: 2006-06-10
Filing date: 2007-06-11
Publication date: 2007-12-13

Abstract

Provided is a method for removing nitrogen dioxide from exhaust gas of a stationary source. The method comprises spraying a reactant to a flow path of the nitrogen dioxide- containing exhaust gas from one or more spray points, wherein the reactant is selected from the group consisting of oxygenated hydrocarbon containing three or more carbon atoms and at least one of hydroxyl (OH), ether, aldehyde and ketone groups, oxygenated hydrocarbon containing two or more carbon atoms and at least two of hydroxyl (OH), ether, aldehyde and ketone groups, a carbohydrate, and any combination thereof. The present invention enables effective removal of nitrogen dioxide at a low operation cost, by increasing a removal rate of nitrogen dioxide versus an injection amount of a reactant or reducing a production amount of by-products in a broad temperature range.

Description

[DESCRIPTION] [Invention Title]

CLEANING METHOD OF NITROGEN DIOXIDE FROM STATIONARY SOURCES AND THE APPARATUS FOR THE SAME

[Technical Field]

The present invention relates to a method for removing nitrogen dioxide from exhaust gas of a stationary source. More specifically, the present invention relates to a method and apparatus for removing nitrogen dioxide, comprising converting of nitrogen dioxide in exhaust gas of a stationary source into nitrogen monoxide and nitrogen, which is capable of effectively removing nitrogen dioxide at a low operation cost by increasing a removal rate of nitrogen dioxide versus an injection amount of a reactant or reducing a production amount of by-products in a broad temperature range of particularly 200 to

700 ^°C .

[Background Art]

Nitrogen oxides (NO_x) contained in exhaust gas generally refer to a term encompassing nitrogen monoxide, nitrogen dioxide, nitrous oxide and the like, and are one of the primary causes for environmental pollution, including carbon oxides and sulfur oxides. Recently, strict regulations of environmental standards for emission of exhaust gas have led to increased constructions of power plants using natural gas known as clean fuel. Such an attempt achieves some reduction in the severity of environmental pollution caused by sulfur oxides, but still suffers from problems associated with generation of NO_x from oxidation of nitrogen in the atmosphere at high temperatures. With modifications and changes of operation conditions, nitrogen oxides in exhaust gas are discharged to the atmosphere at a level that meets the Permissible Air Discharge Standards. However, when a concentration of nitrogen dioxide (NO₂) in the exhaust gas is higher than about 12 ppm, this may result in a problem of yellow plume. In particular, NO₂, which is produced largely upon low-load operations, causes a severe problem of yellow plume in downtown areas. Occurrence of yellow plume appears with an increasing concentration of nitrogen dioxide largely having a reddish brown color and is indirectly affected by various factors such as a diameter of a stack, a flow rate and temperature of exhaust gas, a retention time of stack internal gas and the like. For example, in a case of a combined power plant, yellow plume created at a low output of power gives rise to severely psychological and visible pollution among residents around or adjacent to the power plant. For an operation plan for a supply of electricity, it is necessary to draw up a scheme for operation and shutdown of the power plant in the daytime. However, when the operation and shutdown of the gas turbine requiring a low-power operation is conducted in the daytime, yellow plume is observed by neighbors, which causes psychological pollution. For these reasons, the operation and shutdown of the power plant should be made so as not to coincide with the daytime, which creates from a problem of economic loss as compared to normal operation and shutdown of the power plant.

As an attempt to reduce nitrogen oxides including nitrogen dioxide, various techniques have been developed for control of combustion and treatment of exhaust gas. Among them, techniques for reduction of nitrogen oxides via treatment of exhaust gas are broadly divided into two methods with or without the use of catalysts. Korean Patent Application Publication No. 1999-0069935 Al discloses a method for reducing yellow plume using a reducing catalyst. The use of such a catalyst can achieve an effective removal of nitrogen dioxide, but suffers from problems associated with a burden of catalyst installation costs and a dissipation of pressure. Particularly, an amount of the catalyst required in the selective catalytic reduction is determined by a space velocity which is defined by manufacturers or engineering companies. A commercial NH₃-SCR process typically involves a space velocity of 3,000 to 7,00Oh^'1. Accordingly, taking into consideration that a flow rate of exhaust gas from a stationary source is typically in a range of 500,000 to l,000,000Nm³/h even though it may vary depending upon the power generation capacity, 70 to 200 m³ of the catalyst is necessary, which requires enormous expense.

Further, in the stationary sources of exhaust gas using gas as a fuel at the above- specified space velocity, installation of a catalytic reactor in the existing system may lead to occurrence of differential pressure which then interferes with a flow of gas, thereby adversely affecting the combustion reaction at the front end of the apparatus. As a result, additional facility is needed for installation of the catalytic reactor, so a heavy investment is disadvantageously required to remove a small amount of nitrogen dioxide yellow plume. In addition, installation of the catalyst in the existing facility brings about an increase in an installation area, which makes it difficult to secure a building site necessary for an additional facility.

Meanwhile, Selective Non-Catalytic Reduction (SNCR) is a technique for reduction of nitrogen oxides, involving conversion of NO_x into nitrogen and water vapor by direct spraying of ammonia at a high temperature or by direct spraying of an aqueous urea solution. According to this technique, a 60 to 80% level OfNO_x removal was achieved by conversion of NO_x into N₂ and H₂O in a narrow temperature range of 930 to 980 "C . SNCR has reduction efficiency lower than Selective Catalytic Reduction (SCR), but is more effective for reduction of NO_x produced in combustion facilities that are currently commercially operating because it requires low installation costs and a short installation period, and needs substantially no further facility. However, since the optimum temperature range necessary for effectiveness of this method is narrow, injection of ammonia or the urea solution in an equivalent ratio leads to lowering of the reduction efficiency, whereas excessive injection may cause problems such as production of NO_x due to side reactions and formation of ammonium compounds due to ammonia slip.

Particularly, in power plants suffering from public grievance due to yellow plume of nitrogen dioxide, a gas temperature in exhaust gas-inflow pipe upon starting and stopping of the facility is in a range of 200 to 700 ^°C, which does not reach a temperature of 900 to 1,200 ^°C, corresponding to a temperature range at which Selective Non-Catalytic Reduction is applied. Therefore, application of such Selective Non-Catalytic Reduction is difficult without an additional step of temperature elevation. For these reasons, in stationary sources of exhaust gas such as power plants, there have been increased demands for a technique which is capable of removing NO₂ from exhaust gas in the moderate temperature range of 200 to 700 "C .

Further, Korean Patent Application Publication No. 2004-0092497 Al discloses a technique of removing yellow plume using ethanol. However, this technique has room for improvements because a width of an applicable temperature range is not so broad.

[Disclosure] [Technical Problem] Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for removing nitrogen dioxide from exhaust gas of a stationary source, which is capable of effectively removing nitrogen dioxide at a low operation cost, by increasing a removal rate of nitrogen dioxide versus an injection amount of a reactant or reducing a production amount of byproducts in a broad temperature range of particularly 200 to 700 ^"C .

It is another object of the present invention to provide an apparatus to which the aforementioned method can be applied.

[Technical Solution]

In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a method for removing nitrogen dioxide from nitrogen dioxide-containing exhaust gas produced during a combustion process of a stationary source, comprising spraying a reactant to a flow path of the nitrogen dioxide- containing exhaust gas from one or more spray points to thereby remove nitrogen dioxide from exhaust gas of the stationary source, wherein the reactant is selected from the group consisting of oxygenated hydrocarbon containing three or more carbon atoms and at least one of hydroxyl (OH), ether, aldehyde and ketone groups, oxygenated hydrocarbon containing two or more carbon atoms and at least two of hydroxyl (OH), ether, aldehyde and ketone groups, a carbohydrate, and any combination thereof.

In one embodiment of the present invention, the reactant may be sprayed in admixture with ethanol, or otherwise ethanol may be further sprayed from a separate spraying point. In another embodiment of the present invention, the oxygenated hydrocarbon may be iso-propyl alcohol, iso-butyl alcohol or glycerin.

In another embodiment of the present invention, the carbohydrate may be monosaccharide, disaccharide, trisaccharide, tetrasaccharide, or polysaccharide. In another embodiment of the present invention, the monosaccharide may be glucose or fructose.

In another embodiment of the present invention, the disaccharide may be sucrose.

In another embodiment of the present invention, the polysaccharide may be starch.

In another embodiment of the present invention, the carbohydrate may be sugar, wheat flour or starch.

In another embodiment of the present invention, the reactant may be sprayed by a dispersion-assisting fluid. In another embodiment of the present invention, one or more stages are installed inside a pipe arrangement with a single stage being a pipe to which one or more injection units are connected, and the reactant is injected through the stage into exhaust gas.

In accordance with another aspect of the present invention, there is provided an exhaust gas treatment apparatus for removing nitrogen dioxide from nitrogen dioxide- containing exhaust gas produced during a combustion process of a stationary source, comprising a pipe arrangement for providing a flow path of exhaust gas, at least one injection unit connected to the pipe arrangement and supplying a reactant to the exhaust gas passing through the pipe arrangement, and a storage tank connected to the injection unit and storing the reactant. In one embodiment of the present invention, the exhaust gas treatment apparatus may further include an injection pump which is positioned between the storage tank and the injection unit to thereby supply the reactant from the storage tank to the injection unit. In another embodiment of the present invention, the apparatus may further include a fluid feeder connected to the injection unit and supplying a dispersion-assisting fluid to the injection unit.

In another embodiment of the present invention, the injection unit and the fluid feeder may be connected via an ejector, and one end of the ejector may be connected to a flow path of the reactant discharged from the storage tank.

In another embodiment of the present invention, one or more stages are installed inside a pipe arrangement with a single stage being a pipe to which one or more injection units are connected, and the dispersion-assisting fluid and the reactant are injected through the stage into exhaust gas. In another embodiment of the present invention, the apparatus may further may further include a valve positioned at one side of the pipe and controlling a flow of fluids passing through each pipe, one or more temperature sensors installed at the pipe arrangement providing a flow path of the exhaust gas and measuring the temperature of exhaust gas passing through the pipe arrangement, and a control unit connected to the temperature sensor and valve and opening/closing the valve, based on the temperature data input from the temperature sensor.

[Best Mode]

Hereinafter, the present invention will be described in more detail. The present invention is directed to a method for removing nitrogen dioxide from nitrogen dioxide-containing exhaust gas produced during a combustion process of a stationary source, comprising spraying a reactant to a flow path of the nitrogen dioxide- containing exhaust gas from one or more spray points to thereby convert nitrogen dioxide in exhaust gas of a stationary source into nitrogen monoxide and nitrogen at a low operation cost, by increasing a removal rate of nitrogen dioxide versus an injection amount of a reactant or reducing a production amount of by-products in a broad temperature range, wherein the reactant is selected from the group consisting of oxygenated hydrocarbon containing three or more carbon atoms and at least one of hydroxyl (OH), ether, aldehyde and ketone groups, oxygenated hydrocarbon containing two or more carbon atoms and at least two of hydroxyl (OH), ether, aldehyde and ketone groups, a carbohydrate, and any combination thereof.

In the present invention, nitrogen dioxide can be converted into nitrogen monoxide, nitrogen and the like, by using the aforementioned reactant having a reducing ability. Even though there are various kinds of the reactants having a reducing ability, the present invention is characterized by using any one reactant selected from the group consisting of oxygenated hydrocarbon having an oxygen-containing group such as hydroxyl, ether, aldehyde and ketone groups, a carbohydrate, and any combination thereof.

The method of removing nitrogen dioxide to which the reducing agent of the present invention is applied is intended primarily for a temperature range of 200 to 700 ^°C , and the case in which a total concentration of nitrogen oxides is low, but a discharge amount of nitrogen dioxide is high.

Even though a mechanism of thermochemical reactions is complex and it is difficult to predict it, the use of a nitrogen-containing reactant may probably increase production of nitrogen oxides, in addition to molecular nitrogen. The nitrogen-containing reactant reduces nitrogen oxides as a final product of the reaction into nitrogen in a high temperature range (900 to 1100^°C). However, at a moderate temperature range (200 to 700 "C) where the present invention is primarily applied, the reactant may react with oxygen in the atmosphere to probably increase production of nitrogen oxides. At a high temperature, the nitrogen-containing reactant such as ammonia provides nitrogen atoms to a reaction of reducing nitrogen oxides into nitrogen by a radical reaction at a high temperature to replace the nitrogen oxides in exhaust gas with nitrogen molecules in a stable form. On the other hand, at a moderate temperature, it is considered that insufficient production of radicals leads to a decreased production of nitrogen molecules, and production of unstable nitrogen oxides will probably increase. It can be considered that this is because achievement of more thermodynamically stable phase requires getting over a high energy barrier, but an energy enough to overcome the energy barrier cannot be obtained in the moderate temperature range. Therefore, the present invention employs oxygenated hydrocarbon or carbohydrate, free of such a risk, as a reactant for removing nitrogen dioxide.

In order to remove nitrogen dioxide from exhaust gas of a stationary source, the present invention may use oxygenated hydrocarbon or carbohydrate which has a greater number of a reducing functional group such as hydroxyl, ether, aldehyde and ketone groups, as compared to ethanol, or has a greater number of carbon atoms even with the same number of reducing functional group.

It is considered that ethanol contains only one hydroxyl group, whereas the reactant used in the present invention contains a plurality of reducible groups such as hydroxyl, ether, aldehyde and ketone groups, so an equivalent of the reactant consumed to remove nitrogen dioxide is decreased. In addition, when the reactant having a higher number of carbon atoms than ethanol is used even though it does not contain a plurality of reducible functional groups, the reactant has an increased molecular weight and therefore reacts with nitrogen dioxide under milder conditions. Consequently, production of byproducts decreases, and the reducing ability of the reactant is further used to reduce nitrogen dioxide. As a result, the reactant of the present invention exhibits increased conversion thereof into carbon dioxide, thereby decreasing production of by-products, as compared to the use of ethanol, and conversion of nitrogen dioxide is also increased as much as the reactant converts into carbon dioxide. Therefore, it is considered that the use of the reactant of the present invention leads to decreased production of by-products and increased conversion of nitrogen monoxide into nitrogen dioxide versus an equivalent of the reactant.

There is no particular limit to a material that can be used as the reactant, as long as it is at least one reactant selected from the group consisting of oxygenated hydrocarbon containing three or more carbon atoms and at least one of hydroxyl (OH), ether, aldehyde and ketone groups, oxygenated hydrocarbon containing two or more carbon atoms and at least two of hydroxyl (OH), ether, aldehyde and ketone groups, a carbohydrate, and any combination thereof. For example, mention may be made of iso-butyl alcohol, iso-propyl alcohol, glycerin, allyl alcohol, tert-butanol, n-propyl alcohol, ethylene glycol, methoxy propanol, n-butyl alcohol, n-octyl alcohol, iso-octanol, 2-ethyl hexanol, acetyl acetonate, maleic acid, fumaric acid, glyoxal, glyoxalic acid, methoxypropanol, cyclohexanol, cyclohexanone, 1,3-propanediol, 1,2-propanediol, propanal, 1,4-bulanediol, iso- butylaldehyde, n-butylaldehyde, pentanediols, 1,5-hexanediols, glutaraldehyde, dioxane, trioxane, furan, tetrahydrofuran, tartaric acid, citric acid, diethyl acetaldehyde, propargyl alcohol, tert-butylether, glycerincarbonate, glyceraldehyde, glyceric acid, tetralol, tetralone, benzaldehyde, terephthaldehyde, 1,4-cyclohexanedialcohol, xylenol and isomers thereof, oleic acid, stearic acid, palmitic acid, linoleic acid, salicylic acid, vinylcyclohexene, and the like.

Examples of carbohydrates that can be used in the present invention include, but are not limited to, sugar, wheat flour, starch, monosaccharides such as glucose, dextrose and fructose, disaccharides such as sucrose, maltose and lactose, trisaccharide, tetrasaccharide, and polysaccharide such as starch, cellulose, glycogen, pectin, agar, carrageenan, naturally-occurring rubbers and any combination thereof.

The oxygenated hydrocarbon or carbohydrate may include all of compounds that contain the aforementioned components as a main ingredient, regardless of synthetic products and natural products.

Sugar is also known as sucrose. Sucrose is largely used as a chemical name, whereas sugar may collectively refer to artificial or natural products that are called as sugar by usage, such as cane sugar, beet sugar, noncentrifugal sugar, centrifugal sugar, raw sugar, purified sugar, plantation white sugar, white superior soft sugar, white medium soft sugar, soft brown sugar, powdered sugar, block sugar, invert sugar, brown sugar, and the like.

Starch, a polysaccharide produced by condensation of di-glucose, is a mixture of amylose and amylopectin, and is one of a reserve material present in plants having chlorophyll. Starch may generally encompass artificial and natural materials, such as potato starch, sweet potato starch, and the like.

Wheat flour is a powder of a wheat endosperm, and may contain carbohydrates and proteins such as gluten. Carbohydrate contained in the wheat flour is a starch consisting largely of polysaccharide, may account for 70% of the total weight of the wheat flour, and may contain monosaccharide and disaccharide. The reactant may be sprayed in admixture with ethanol, or otherwise ethanol may be further sprayed from a separate spraying point.

As compared to a single spray of ethanol alone, combined spray of the reactant with ethanol may lead to an increased conversion rate of nitrogen dioxide versus a reactant/nitrogen dioxide equivalent, due to the action of the reactant, even though there may be no significant difference in production of by-products therebetween. Conversely, it can be said that production of by-products can be reduced while maintaining the conversion rate of nitrogen dioxide, even when the reactant/nitrogen dioxide equivalent is lowered. That is, as compared to a supply of ethanol alone in a conventional process, it is possible to increase a removal rate of nitrogen dioxide even at the same equivalent ratio, which results in a decrease of ethanol to be used and consequently decreased production of by-products.

According to the present invention, contacting and mixing of exhaust gas with the reactant can be increased by establishing an injection point of the reactant to be one or more points, thereby increasing a region for treating exhaust gas. As a result, removal efficiency of nitrogen dioxide in the exhaust gas can be increased. Further, a decreasing effect of by-product production can be anticipated by allowing the reactant to sufficiently take part in the reaction.

In order to inject the reactant into the exhaust gas of the stationary source, a dispersion-assisting fluid may be used. The dispersion-assisting fluid is used for broad spray of the reactant into the exhaust gas. For use of the aforementioned reactant, non- reactive inert gas or liquid, or a material which is need to be sprayed in the form of a liquid phase, such as sugar, dispersible and harmless fluids, such as solvents having a high solubility of the reactant, may be used. However, in terms of costs and availability, it is also possible to use some of exhaust gas from the front end of a stack or air. In order to remove nitrogen dioxide from exhaust gas of the stationary source, the present invention may be configured such that one or more stages are installed inside a pipe arrangement with a single stage being a pipe to which one or more injection units are connected, and the reactant is injected through the stage into exhaust gas. Spraying of the reactant through multiple stages may ensure that the reaction takes place over a broader reaction region. Further, production of by-product can be decreased by allowing the reactant to sufficiently take part in the reaction.

The method for removing nitrogen dioxide from a stationary source of exhaust gas in accordance with the present invention can be applied to the exhaust gas treatment apparatus as shown in FIG. 1, or the inside of a boiler, front and rear ends of an air preheater, exhaust gas flow ducts, and the like. Since conventional Selective Non- Catalytic Reduction (SNCR) using ammonia can be used only in a high temperature range (900 to l,100^°C), it is necessary to adjust temperature conditions by warming the apparatus when it is desired to use the exhaust gas treatment apparatus. When a separate exhaust gas treatment apparatus is not employed, such a method could be applied only to limited regions meeting high temperature conditions, such as a rear end of a combustion chamber, a secondary combustion chamber, and the like. Further, the removal method of nitrogen dioxide using ethanol can be applied to a limited range of moderate temperatures, so it might be difficult to cope with various operation conditions upon removing nitrogen dioxide. However, the present invention can extend the range of operation conditions that can be applied.

The apparatus for removing nitrogen dioxide from nitrogen dioxide-containing exhaust gas produced during a combustion process of a stationary source may include a pipe arrangement for providing a flow path of exhaust gas, at least one injection unit connected to the pipe arrangement and supplying the reactant to the exhaust gas passing through the pipe arrangement, and a storage tank connected to the injection unit and storing the reactant.

The apparatus may further include an injection pump which is positioned between the storage tank and the injection unit to thereby supply the reactant from the storage tank to the injection unit.

The apparatus may further include a fluid feeder connected to the injection unit and supplying a dispersion-assisting fluid to the injection unit.

The dispersion-assisting fluid is used for broad spray of the reactant into the exhaust gas. For use of the aforementioned reactant, non-reactive inert gas or liquid, or a material which is need to be sprayed in the form of a liquid phase, such as sugar, dispersible and harmless fluids, such as solvents having a high solubility of the reactant, may be used. However, taking into consideration costs and availability, it may also be possible to use some of exhaust gas from the front end of a stack or air.

Particularly, even though the reactant of the present invention may be sprayed into the exhaust gas without being mixed with the dispersion-assisting fluid such as air, steam, water, or the like, single injection of the reactant into the injection unit without being mixed with such a dispersion-assisting fluid may cause the problem that the reactant is not uniformly mixed throughout the exhaust gas. Therefore, in such a case, the present invention preferably provides a separate mixing device at a flow path of the exhaust gas to achieve easy mixing of the exhaust gas with the reactant.

The mixing device is provided for easy mixing of the exhaust gas with the reactant provided at the flow path of the exhaust gas. Therefore, any device may be employed as long as it achieves such a purpose. For example, mention may be made of a blade, swirler, and the like. Meanwhile, the injection unit in accordance with the present invention is intended for single spray of the reactant to the exhaust gas, or for combined spray of the reactant with the dispersion-assisting fluid such as air, steam, water, or the like, to the exhaust gas. There is no particular limit to the injection unit, as long as it can supply the reactant and/or the dispersion-assisting fluid to the flow path through which the exhaust gas flows. For example, there may be used a nozzle or a reactant injection grid (RIG), or the like.

Further, the exhaust gas treatment apparatus in accordance with the present invention performs treatment of pollutants by supplying the reactant to the flow path of the exhaust gas containing nitrogen dioxide, followed by contacting of the reactant with the exhaust gas. Alternatively, pollutants may also be treated by supplying the reactant alone to the flow path of the exhaust gas and then providing a mixing device at the rear of a region to which the reactant is supplied, such that the reactant is mixed the exhaust gas.

Accordingly, the exhaust gas treatment apparatus in accordance with the present invention has an advantage in that the dispersion-assisting fluid is not necessary for extensive spray of the reactant discharged from the injection unit into the exhaust gas.

Further, in the apparatus of the present invention, the injection unit and the fluid feeder may be connected via an ejector, and one end of the ejector may be connected to a flow path of the reactant discharged from the storage tank. This configuration is to achieve uniform spray of the reactant by taking advantage of a venturi principle.

Further, the apparatus of the present invention may be configured such that one or more stages are installed inside a pipe arrangement with a single stage being a pipe to which one or more injection units are connected, and the spray-assisting fluid and the reactant are injected through the stage into exhaust gas. Uniform injection of the reactant into the exhaust gas can be achieved by installation of one or more stages inside the pipe arrangement.

Further, the apparatus may further include a valve positioned at one side of the pipe and controlling a flow of fluids passing through each pipe, one or more temperature sensors installed at the pipe arrangement providing a flow path of the exhaust gas and measuring the temperature of exhaust gas passing through the pipe arrangement, and a control unit connected to the temperature sensor and valve and opening/closing the valve, based on the temperature data input from the temperature sensor. Effective removal of nitrogen dioxide from the exhaust gas can be achieved using the reactant, by opening the valve which is under a temperature range (200 to 700 "C) suitable for reaction of the reactant, based on the temperature data input from the temperature sensor.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings and the following embodiments. These drawings and embodiments are provided only for illustrating the present invention and should not be construed as limiting the scope and spirit of the present invention.

FIG. 1 is a schematic view showing an embodiment of an exhaust gas treatment apparatus in accordance with the present invention, FIG. 2 is a schematic view showing another embodiment of an exhaust gas treatment apparatus in accordance with the present invention, FIG. 3 is a schematic view showing an embodiment of an exhaust gas treatment apparatus in accordance with the present invention, FIG. 4 is a schematic view showing an embodiment of an exhaust gas treatment apparatus in accordance with the present invention, FIG. 5 is a schematic view showing an embodiment of an exhaust gas treatment apparatus in accordance with the present invention, and FIG. 6 is a schematic view showing an embodiment of an exhaust gas treatment apparatus in accordance with the present invention.

Referring to FIG. 1, the exhaust gas treatment apparatus in accordance with the present invention is configured such that the reactant can be supplied to a flow path of the exhaust gas. More specifically, the exhaust gas treatment apparatus may include a pipe arrangement 2 for providing a flow path of exhaust gas, at least one injection unit 4 connected to the pipe arrangement 2 and supplying a reactant to the exhaust gas passing through the pipe arrangement 2, and a storage tank 6 connected to the injection unit 4 and storing the reactant provided to the injection unit 4. In order to accomplish the purpose of providing the reactant to the flow path of exhaust gas, the exhaust gas treatment apparatus in accordance with the present invention can be configured in various forms. If necessary, the apparatus can also be configured such that easy mixing of the reactant with the exhaust gas is made by a co-supply of a dispersion-assisting fluid, consisting of a fluid such as air, steam or water, to the reactant provided to the flow path of exhaust gas. The dispersion- assisting fluid in conjunction with the reactant can be provided to the flow path of exhaust gas, via a fluid feeder 10 connected to one end of the injection unit 4. Further, the exhaust gas treatment apparatus in accordance with the present invention may further include an injection pump 8 between the storage tank 6 and the injection unit 4 to thereby easily supply the reactant 6 from the storage tank 6 to the injection unit 4. One end of the pipe arrangement 2 in accordance with the present invention can be connected to the stationary source, such that a nitrogen dioxide-containing exhaust gas, produced during a combustion process of the stationary source using gas as a fuel, is introduced into the pipe arrangement 2. The other end of the pipe arrangement 2 can be connected to a stack 12 through which the nitrogen dioxide-containing exhaust gas can be discharged to the outside, after the exhaust gas passing through the pipe arrangement 2 is treated. The injection unit 4 in accordance with the present invention is installed inside the pipe arrangement 2 for single spray of the reactant to the nitrogen dioxide-containing exhaust gas, or for combined spray of the reactant with the dispersion-assisting fluid such as air, steam, water, or the like, to the exhaust gas. There is no particular limit to the injection unit 4, as long as it can supply the reactant and/or the dispersion-assisting fluid to the flow path through which the exhaust gas flows. For example, there may be used a nozzle, or a reactant injection grid (RIG) 26 as shown in FIG. 2. Particularly, the injection unit 4 in accordance with the present invention may be installed in any form, as long as it can supply the reactant and/or the dispersion-assisting fluid to the flow path through which the exhaust gas flows. The injection unit 4 may be installed at one side of the pipe arrangement 2 in a form of a single stage or a multistage, and is allowed to easily spray the reactant to the nitrogen dioxide-containing exhaust gas which is introduced along the pipe arrangement 2. Alternatively, the reactant can be supplied to the exhaust gas using RIG as the injection unit 4. As used herein, the term "single stage" refers to a structure where multiple holes are made in one pipe 14 and injection units 4 are connected to the holes, and the term "multistage" refers to a configuration including at least two single stages.

Referring to FIG. 3, the exhaust gas treatment apparatus in accordance with the present invention may include a connection of the mixing device 28 to the rear of the injection unit 4 for supplying the reactant to the exhaust gas to achieve easy mixing of the exhaust gas introduced into the pipe arrangement 2 with the reactant provided to the exhaust gas. If necessary, a fluid feeder may be additionally connected to the exhaust gas treatment apparatus having the mixing device 28.

Referring to FIG. 4, the exhaust gas treatment apparatus in accordance with the present invention may further include a connection of a reactant flow path to the one end of an ejector 22 (using a venturi principle) in the flow path of the dispersion-assisting fluid discharged from the fluid feeder 10 and introduced into the injection unit 4.

Referring to FIG. 5, the dispersion-assisting fluid discharged from the fluid feeder 10 may employ air, steam or water from an external source, or otherwise the exhaust gas may be employed as the dispersion-assisting fluid by connecting a return pipe 24, provided at one side of the pipe arrangement 2, to the fluid feeder 10, returning the exhaust gas flowing along the pipe arrangement 2 to the fluid feeder 10 and then supplying the exhaust gas to the injection unit 4.

Referring to FIG. 6, the exhaust gas treatment apparatus in accordance with the present invention may further include, if desired, a valve positioned at one side of the pipe 14 and controlling a flow of fluids passing through each pipe, at least one temperature sensor 20 installed inside the pipe arrangement 2 and measuring the temperature of exhaust gas passing through the pipe arrangement 2, and a control unit 16 connected to the temperature sensor 20 and the valve 18 and opening/closing the valve 18, based on the temperature data input from the temperature sensor 20. Herein, the temperature sensor 20 may be installed at any position inside the pipe arrangement 2, as long as it is possible to easily measure the temperature of the exhaust gas flowing through the pipe arrangement 2.

If desired, the exhaust gas treatment apparatus in accordance with the present invention can prevent combustion of the reactant due to the exhaust gas discharging at a temperature of 200 to 700 ^°C, by treatment of an insulating material on the injection unit 4 and the outer circumference of the pipe 14 to which the injection unit 4 is connected.

Further, in order to more effectively protect the reactant flowing inside the injection unit 4 and the pipe 14 against high heat, it is possible to prevent combustion of the reactant due to high-temperature exhaust gas by providing a flow path (not shown), through which the dispersion-assisting fluid can pass, inside the pipe 14 and/or the injection unit 4, and transferring external cold air to a flow path through which the dispersion-assisting fluid can pass.

The aforementioned injection unit 4 is intended for combined spray of the dispersion-assisting fluid and the reactant. One end of the injection unit 4 is connected to the fluid feeder 10 which receives the exhaust gas coming from an external source or flowing along the pipe arrangement 2 and supplies the exhaust gas to the injection unit 4.

Then, the injection pump 8 adapted to receive the reactant and/or the storage tank 6 storing the reactant are sequentially connected such that the reactant can be easily transferred to the injection unit 4. At this time, the injection pump 8 is adapted for easy transfer of the reactant from the storage tank 6 to the injection unit 4.

On the other hand, the fluid feeder 10 transfers a gas or liquid (such as compressed air, steam, water, etc.) in conjunction with the reactant to the injection unit 4 to thereby spray the reactant, such that the nitrogen dioxide-containing exhaust gas and the reactant can be easily mixed with each other.

If necessary, the exhaust gas treatment apparatus, configured to supply the dispersion-assisting fluid in conjunction with the reactant to the exhaust gas, may be constructed such that the flow path of the reactant discharged from the storage tank 6 can be combined with the flow path of the dispersion-assisting fluid discharged from the fluid feeder 10. For this purpose, flows of two fluids can be combined by installing an ejector 22 (using a venturi principle) at one end of the path of the pipe 14 connected from the fluid feeder 10 to the injection unit 4 and then connecting the reactant flow path to the one end of the ejector 22. Hereinafter, operation and effects of the exhaust gas treatment apparatus in accordance with the present invention having the aforementioned construction will be described.

For easy and convenient illustration of the exhaust gas treatment apparatus in accordance with the present invention, operation and function of the apparatus will be described with reference to the apparatus shown in FIGS. 1 and 6 as a basic construction.

First, when a nitrogen dioxide-containing exhaust gas is produced in a combustion process of the stationary source using gas as a fuel, the exhaust gas is transferred to the pipe arrangement 2 provided with the injection unit 4. Then, the reactant contained in the storage tank 6 is transferred to the injection unit 4 using the injection pump 8. Herein, the reactant may be moved in conjunction with the dispersion-assisting fluid to the injection unit 4 using the fluid feeder 10.

As the dispersion-assisting fluid, air from the outside may be used after compression thereof, or otherwise there may be used steam or water which has collected heat generated during the combustion process, or some of the recycled exhaust gas moving along the pipe arrangement 2.

Next, the dispersion-assisting fluid and reactant, transferred to the injection unit

4 provided inside the pipe arrangement 2, are supplied to the nitrogen dioxide-containing exhaust gas passing through the pipe arrangement 2 to remove nitrogen dioxide via conversion thereof, and the exhaust gas is passed through the stack 12 connected to the end part of the pipe arrangement 2 and discharged to the outside.

The dispersion-assisting fluid, provided from the fluid feeder 10, is transferred in conjunction with the reactant to the injection unit 4 to thereby spray the reactant, such that the nitrogen dioxide-containing exhaust gas and the reactant can be easily mixed with each other. The exhaust gas treatment apparatus in accordance with the present invention may be constructed and used without provision of the fluid feeder 10. In this case, the exhaust gas and the reactant are easily mixed with each other by passing the reactant, discharged via the injection unit 4 to the exhaust gas, through the mixing device 28, and such a mixing device 28 may be installed and used in conjunction with the fluid feeder 10.

Meanwhile, the exhaust gas treatment apparatus in accordance with the present invention can more effectively treat the exhaust gas, using a control unit 16 positioned at one side of the apparatus and adapted to open/close the valve 18, based on the temperature data input from the temperature sensor 20.

First, the apparatus is constructed to have such a structure that the inside of the pipe arrangement 2 is provided with at least one pipe 14 having a plurality of injection units 4, the pipe 14 is connected to the injection pump 8 and the fluid feeder 10, and the inside of the pipe arrangement 2 is provided with at least one temperature sensor 20. One side of each pipe 14 is provided with the valve 18, and the valve 18 and temperature sensor 20 are connected to the control unit 16.

First, when a nitrogen dioxide-containing exhaust gas is produced in a combustion process of the stationary source using gas as a fuel, the exhaust gas is transferred to the pipe arrangement 2 provided with the pipe 14 having a plurality of injection units 4. At this time, the temperature sensor 20 provided in the pipe arrangement 2 measures the temperature of the exhaust gas flowing into the pipe arrangement 2 and then transmits the data to the control unit 16.

Then, the control unit 16 opens the valve 18 of the pipe 14 having the injection unit 4 which is under a temperature range (e.g. 200 to 700 "C) suitable for reaction of the reactant, based on the temperature data input from the temperature sensor 20, and closes the valves 18 of the remaining pipes 14.

Next, the reactant contained in the storage tank 6 is transferred via the injection pump 8 to the pipe 14 where the valve 18 was open, and at the same time, air from the outside is transferred via the fluid feeder 10 to the pipe 14 where the valve 18 was open.

Next, the air and reactant, transferred to the pipe 14 which was provided inside the pipe arrangement 2 and where the valve 18 was open, are sprayed to the nitrogen dioxide-containing exhaust gas flowing in the pipe arrangement 2 through the injection units 4 provided in the pipe 14 to thereby remove nitrogen dioxide via reduction of nitrogen dioxide into nitrogen monoxide or reaction of nitrogen dioxide with nitrogen, and the exhaust gas is then passed through the stack 12 connected to the end part of the pipe arrangement 2 and discharged to the outside.

The compressed air, provided from the fluid feeder 10, is transferred in conjunction with the reactant to the injection unit 4 to thereby spray the reactant, such that the nitrogen dioxide-containing exhaust gas and the reactant can be easily mixed with each other.

[Description of Drawings]

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view showing an embodiment of an exhaust gas treatment apparatus in accordance with the present invention; FIG. 2 is a schematic view showing another embodiment of an exhaust gas treatment apparatus in accordance with the present invention;

FIG. 3 is a schematic view showing an embodiment of an exhaust gas treatment apparatus in accordance with the present invention; FIG. 4 is a schematic view showing an embodiment of an exhaust gas treatment apparatus in accordance with the present invention;

FIG. 5 is a schematic view showing an embodiment of an exhaust gas treatment apparatus in accordance with the present invention;

FIG. 6 is a schematic view showing an embodiment of an exhaust gas treatment apparatus in accordance with the present invention;

FIG. 7 is a graph showing conversion (%) of nitrogen dioxide using a reactant in accordance with the present invention;

FIG. 8 is a graph showing conversion (%) of nitrogen dioxide depending upon a mole ratio of a reactant in accordance with the present invention/nitrogen dioxide; FIG. 9 is a graph showing conversion (%) of nitrogen dioxide depending upon a mole ratio of a reactant in accordance with the present invention/nitrogen dioxide;

FIG. 10 is a graph showing conversion (%) of nitrogen dioxide depending upon single-stage injection and multistage injection of a reactant in accordance with the present invention; FIG. 11 is a graph showing measurement results of a Nθ₂-removing activity versus time, in Comparative Example 2, Example 12 and Example 13;

FIG. 12 is a graph showing measurement results of a NO₂-removing activity versus time, in Comparative Example 2, Example 14 and Example 15; and

FIG. 13 is a graph showing measurement results of a NO₂-removing activity versus an injection amount of starch, in Example 16 and Example 17. [Mode for Invention] EXAMPLES

Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only for illustrating the present invention and should not be construed as limiting the scope and spirit of the present invention.

Example 1 As shown in FIG. 1, a pipe arrangement of a cylindrical tube (15 cm high x 15 cm wide x 100 cm long) was manufactured using SUS 304, and 4 pipes having a plurality of nozzles (TN050-SRW, Total Nozzle Co., Korea) were installed inside the pipe arrangement at an interval of 20 cm. Then, isobutyl alcohol (Duksan Pharmaceutical Industry Co., Ltd., Korea) as a reactant was charged to a storage tank. The storage tank was connected to an injection pump (M930, Younglin Co., Korea) which was connected to the pipe provided with the nozzles (TN050-SRW, Total Nozzle Co., Korea). Next, the pipe having the nozzles (TN050-SRW, Total Nozzle Co., Korea) was connected to a fluid feeder supplying air from the outside (HP2.5, Air Bank Compressor, Korea). Thereafter, an inflow gas, which has a composition similar to that of exhaust gas produced during a combustion process using LPG and LNG as a fuel, was injected into the aforesaid pipe arrangement. The composition of the inflow gas is set forth in Table 1 below.

Table 1

Meanwhile, using the fluid feeder (HP2.5, Air Bank Compressor, Korea) and the injection pump (M930, Younglin Co., Korea), air from the outside and isobutyl alcohol filled in the storage tank were transferred to the nozzle (TN050-SRW, Total Nozzle Co., Korea) and were sprayed into the pipe arrangement, simultaneously when the inflow gas passed through the pipe arrangement. At this time, the internal temperature of the pipe arrangement was maintained in a range of 250 to 650 ^°C using an electric furnace (Kibo Steel Co., Korea), and the temperature was measured using a K-type thermocouple. A mole ratio of isobutyl alcohol/nitrogen dioxide was adjusted to 3, and the injection unit employed a single stage of the injection pipe at the foremost stage on the exhaust gas inlet side. A contact time between isobutyl alcohol (Duksan Pharmaceutical Co., Ltd., Korea) sprayed from the nozzle (TN050-SRW, Total Nozzle Co., Korea) and the exhaust gas passing through the pipe arrangement was set to 0.731 sec.

In addition, the composition of the exhaust gas before and after the reaction was analyzed using a portable NOx analyzer (MK II , Eurotron, Italy), and the conversion (%) of nitrogen dioxide was calculated according to the following equation 1.

NO₂ conversion (%) = (NO₂ concentration before reaction - NO₂ concentration after reaction)/ NO₂ concentration before reaction x 100 (Equation 1 )

The results thus obtained are shown in FIG. 7.

Example 2 Experiment was carried out in the same manner as in Example 1, except that isopropyl alcohol (Duksan Pharmaceutical Industry Co., Ltd., Korea) was used instead of isobutyl alcohol as a reactant, and a mole ratio of isopropyl alcohol/nitrogen dioxide was set to 3. The results thus obtained are shown in FIG. 7.

Example 3

Experiment was carried out in the same manner as in Example 1, except that glycerin (Doosan Co., Korea) was used instead of isobutyl alcohol as a reactant, and a mole ratio of glycerin/nitrogen dioxide was set to 3. The results thus obtained are shown in FIG. 7.

Example 4

Experiment was carried out in the same manner as in Example 1, except that sugar (Samyang Corporation, Korea) was used instead of isobutyl alcohol as a reactant, and a mole ratio of sugar/nitrogen dioxide was set to 3. The results thus obtained are shown in FIG. 7.

Example 5

Experiment was carried out in the same manner as in Example 1, except that a mole ratio of isobutyl alcohol/nitrogen dioxide was set to 1. The results thus obtained are shown in FIG. 8.

Example 6 Experiment was carried out in the same manner as in Example 1 , except that a mole ratio of isobutyl alcohol/nitrogen dioxide was set to 2. The results thus obtained are shown in FIG. 8.

Example 7

Experiment was carried out in the same manner as in Example 1, except that sugar was used instead of isobutyl alcohol as a reactant, and a removing activity of nitrogen dioxide was measured at a mole ratio of sugar/nitrogen dioxide of 1. The results thus obtained are shown in FIG. 9.

Example 8

Experiment was carried out in the same manner as in Example 1, except that sugar was used instead of isobutyl alcohol as a reactant, and a removing activity of nitrogen dioxide was measured at a mole ratio of sugar/nitrogen dioxide of 2. The results thus obtained are shown in FIG. 9.

A conventional method for removal of nitrogen dioxide from a stationary source using ethanol exhibited NO₂ conversion of 30% at a mole ratio of ethanol/NO₂ of 1 and a temperature of 400 to 600 ^°C , and NO₂ conversion of 45% at a mole ratio of ethanol/NO₂ of

2 and a temperature of 350 to 550 ^°C, respectively. From the results of FIGS. 7 to 9, isobutyl alcohol exhibited NO₂ conversion of more than 45% with a maximum of more than 80%, at a mole ratio of reactant/NO₂ of 3 and a temperature of 300 to 600 ^°C . Further, it can be seen that isopropyl alcohol also exhibited similar profiles, except that a maximum conversion OfNO₂ is more than 70%. From FIG. 8 showing the results with a varying mole ratio of isobutyl alcohol, it can be seen that an increasing mole ratio of isobutyl alcohol leads to an increasing conversion of NO₂, and a mole ratio of isobutyl alcohol of 2 provides a higher conversion of NO₂ and a broader application temperature range, as compared to a mole ratio of ethanol/NO₂ of 2 according to a conventional art.

As shown in FIG. 7, it can be seen that, upon injection of glycerin and sugar, a temperature range showing a maximum NO₂ conversion shifts to a low temperature range, and the maximum NO₂ conversion also increases. It is considered that sugar contains sucrose as a main ingredient, has a very high molecular weight, and is hydrolyzed into glucose having an aldehyde group in an aqueous solution, thereby exhibiting a reducing ability and great NO₂ conversion.

As shown in FIG. 9, it can be seen that an increasing mole ratio of sugar/NO₂ leads to an increase in NO₂ conversion, but the degree of increase is not significant. It is believed that this is because effects with an increasing mole ratio of sugar/NO₂ are not significant, as the NO₂ conversion is high even when a mole ratio of sugar/NO₂ is 1.

Taken altogether, ethanol has only one hydroxyl group, whereas the reactant used in the present invention exhibits a higher removal rate of nitrogen dioxide at the same equivalent ratio as ethanol, when it has a plurality of reducing functional groups such as hydroxyl (OH), ether, aldehyde and ketone groups. Further, it can be considered that the use of the reactant having a greater number of carbon atoms and a higher molecular weight than ethanol allows the reaction of the reactant with nitrogen dioxide under mild conditions, so the reducing ability of the reactant can be completely used for reduction of nitrogen dioxide, thereby increasing conversion of nitrogen dioxide. As a result, it is thought that the reactant converts into carbon dioxide as much as the conversion of nitrogen dioxide increases, and production of by-products, such as formaldehyde, acetaldehyde and the like, decreases.

Comparative Example 1 Experiment was carried out in the same manner as in Example 1, except that ethanol was used instead of isobutyl alcohol as a reactant, and an internal temperature of the pipe arrangement was maintained in a range of 350 to 400 ^°C . At this time, a mole ratio of ethanol/NO₂ and production of by-products were measured at a NO₂ removal activity of 60%. Measurements were made using EPA Method TO-I l. The results thus obtained are shown in Table 2 below.

Example 9

Experiment was carried out in the same manner as in Example 1, except that sugar was used instead of isobutyl alcohol as a reactant, and an internal temperature of the pipe arrangement was maintained in a range of 350 to 400 ^°C . At this time, a mole ratio of sugar/NO₂ and production of by-products were measured at a NO₂ removal activity of 60%. Measurements were made using EPA Method TO-I l. The results thus obtained are shown in Table 2 below.

Table 2

As shown in Table 2, it can be seen that Example 9 exhibited a low mole ratio of reactant/NO₂ and less production of by-products at the same NO₂ removal rate of 60%, as compared to Comparative Example 1. That is, injection of sugar as the reactant exhibited decreases in the mole ratio of reactant/NCh and production of by-products while showing the same NO₂ removal rate as in injection of ethanol.

Further, it can be considered that the use of sugar as the reactant having a higher molecular weight and a greater number of reducing groups than ethanol leads to the reaction of the reactant with nitrogen dioxide under milder conditions, so the reducing ability of the reactant can be completely used for reduction of nitrogen dioxide, and as a result, a mole ratio of the reactant necessary for removal of nitrogen dioxide is lowered as compared to the use of ethanol, and production of by-products such as formaldehyde is decreased. In addition, it is believed that an applicable temperature range is broad, as compared to use of ethanol.

Example 10

Experiment was carried out in the same manner as in Example 1 , except that sugar was used instead of isobutyl alcohol as a reactant, and a mole ratio of sugar/nitrogen dioxide was 0.5. The results thus obtained are shown in FIG. 10.

Example 11

Experiment was carried out in the same manner as in Example 1, except that sugar was used instead of isobutyl alcohol as a reactant, a mole ratio of sugar/nitrogen dioxide was 0.5, and the injection unit employed all of four pipes provided inside the pipe arrangement at an interval of 20 cm. The results thus obtained are shown in FIG. 10. Differences in NO₂ reduction (%) and an application temperature between single-stage spray and multistage spray of the reactant can be seen from FIG. 10. It can be seen that the multistage spray exhibited a higher reduction (%) of NO₂ throughout the entire temperature region under the same mole ratio condition of sugar/NO₂, as compared to single-stage spray. In conclusion, it is considered that the reaction of the reactant with nitrogen dioxide is increased due to spray of the same amount of the reactant over a broad region via multistage spray.

Comparative Example 2

Experiment was carried out in the same manner as in Example 1, except that ethanol was used instead of isobutyl alcohol as a reactant, a mole ratio of ethanol/NO₂ was 1 and an internal temperature of the pipe arrangement was maintained at 420 ^°C . Measurements of by-products were made using EPA Method TO-11.

The composition of the inflow gas is set forth in Table 3 below.

Table 3

Measurement results of by-products are given in Table 4, and measurement results of a removal activity are shown in FIG. 11.

Example 12 Experiment was carried out in the same manner as in Example 1, except that ethanol and wheat flour (CJ Co., Korea) were used instead of isobutyl alcohol as a reactant, a mole ratio of ethanol/NCh was 1 and the wheat flour was injected at a flow rate of 2.5 g/min. The reactant in the form of a powder was injected separately from ethanol, in a manner that a given amount of the reactant is introduced and sprayed by compressed air. An internal temperature of the pipe arrangement was maintained at 420 ^°C . Measurements of by-products were made using EPA Method TO-11. Measurement results of by-products are given in Table 4, and measurement results of a removal activity are shown in FIG. 11.

Example 13

Experiment was carried out in the same manner as in Example 1, except that ethanol and starch (Neulpureun Corp., Korea) were used instead of isobutyl alcohol as a reactant, a mole ratio of ethanol/NO₂ was 1 and starch was injected at a flow rate of 2.5 g/min. The reactant in the form of a powder was injected separately from ethanol, in a manner that a given amount of the reactant is introduced and sprayed by compressed air. An internal temperature of the pipe arrangement was maintained at 420 "C . Measurements of by-products were made using EPA Method TO-I l. Measurement results of by-products are given in Table 4, and measurement results of a removal activity are shown in FIG. 11.

Example 14

Experiment was carried out in the same manner as in Example 1, except that ethanol and wheat flour (CJ Co., Korea) were used instead of isobutyl alcohol as a reactant, a mole ratio of ethanol/NO₂ was 1 and the wheat flour was injected at a flow rate of 5.0 g/min. The reactant in the form of a powder was injected separately from ethanol, in a manner that a given amount of the reactant is introduced and sprayed by compressed air. An internal temperature of the pipe arrangement was maintained at 420 ^°C . Measurements of by-products were made using EPA Method TO-11. Measurement results of by-products are given in Table 4, and measurement results of a removal activity are shown in FIG. 12.

Example 15

Experiment was carried out in the same manner as in Example 1, except that ethanol and starch (Neulpureun Corp., Korea) were used instead of isobutyl alcohol as a reactant, a mole ratio of ethanol/NO₂ was 1 and starch was injected at a flow rate of 5.0 g/min. The reactant in the form of a powder was injected separately from ethanol, in a manner that a given amount of the reactant is introduced and sprayed by compressed air. An internal temperature of the pipe arrangement was maintained at 420 ^°C. Measurements of by-products were made using EPA Method TO-11. Measurement results of by-products are given in Table 4, and measurement results of a removal activity are shown in FIG. 12.

Table 4

As can be seen from Table 4, even though co-spray of starch or wheat flour in conjunction with ethanol exhibited a similar level of by-product production as compared to a single spray of ethanol, FIGS. 11 and 12 showed that a single spray of ethanol (Comparative Example 2) exhibited a conversion of 30%, whereas Examples 12 to 15 exhibited a conversion of 50%, 70%, more than 50%, and more than 70%, respectively. That is, it can be seen that co-spray of starch or wheat flour in conjunction with ethanol leads to a significant increase in NO₂ conversion (%) while maintaining a similar level of by-product production, as compared to a single spray of ethanol. It is considered that conversion of nitrogen dioxide into nitrogen monoxide is mediated by a reducing ability of glucose, a monomer of amylose and amylopectin which are main ingredients of starch. Further, a mixture of ethanol with starch exhibited a higher increase in conversion of nitrogen dioxide into nitrogen monoxide, as compared to a mixture of ethanol with wheat flour. It is considered that this is because wheat flour also contains other ingredients in addition to carbohydrate as a main ingredient, which results in a lower conversion of nitrogen dioxide.

Example 16

Experiment was carried out in the same manner as in Comparative Example 2, except that ethanol and wheat flour (CJ Co., Korea) were used as a reactant, a mole ratio of ethanol/N0₂ was 1 and wheat flour was introduced at varying flow rates of 1.25, 2.5, 5.0, and 7.5 g, respectively.

Example 17 Experiment was carried out in the same manner as in Comparative Example 2, except that ethanol and starch (Neulpureun Corp., Korea) were used as a reactant, a mole ratio of ethanol/NO₂ was 1 and starch was introduced at varying flow rates of 1.25, 2.5, 5.0, and 7.5 g, respectively. FIG. 13 shows measurement results of a NO₂-removing activity in Examples 16 and 17.

Referring to FIG. 13, when an injection amount of starch is higher than 5 g/min, there is no significant change in the NO₂-removing activity while showing an increase in production of dust. It was observed that an injection amount of starch in the range of 0 g to 2.5 g/min exhibits a significant increase in a removal activity, but the range of 2.5 g to 5 g/min does not exhibit a significant increase in a removal activity.

[Industrial Applicability]

As apparent from the above description, the present invention enables removal of nitrogen dioxide from exhaust gas of a stationary source at a low operation cost, by increasing a removal rate of nitrogen dioxide versus an injection amount of a reactant or reducing a production amount of by-products in a broad temperature range.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[CLAIMS]

[Claim 1] A method for removing nitrogen dioxide from nitrogen dioxide- containing exhaust gas produced during a combustion process of a stationary source, comprising spraying a reactant to a flow path of the nitrogen dioxide-containing exhaust gas from one or more spray points to thereby remove nitrogen dioxide from exhaust gas of the stationary source, wherein the reactant is selected from the group consisting of oxygenated hydrocarbon containing three or more carbon atoms and at least one of hydroxyl (OH), ether, aldehyde and ketone groups, oxygenated hydrocarbon containing two or more carbon atoms and at least two of hydroxyl (OH), ether, aldehyde and ketone groups, a carbohydrate, and any combination thereof.

[Claim 2] The method according to claim 1, wherein the reactant is sprayed in admixture with ethanol, or ethanol is further sprayed from a separate spraying point.

[Claim 3] The method according to claim 1, wherein the oxygenated hydrocarbon is iso-propyl alcohol, iso-butyl alcohol or glycerin.

[Claim 4] The method according to claim 1, wherein the carbohydrate is monosaccharide, disaccharide, trisaccharide, tetrasaccharide, or polysaccharide.

[Claim 5] The method according to claim 4, wherein the monosaccharide is glucose or fructose.

[Claim 6] The method according to claim 4, wherein the disaccharide is sucrose.

[Claim 7] The method according to claim 4, wherein the polysaccharide is starch.

[Claim 8] The method according to claim 1, wherein the carbohydrate is sugar, wheat flour or starch.

[Claim 9] The method according to claim 1, wherein the reactant is sprayed by a dispersion-assisting fluid.

[Claim 10] The method according to claim 1, wherein one or more stages are installed inside a pipe arrangement with a single stage being a pipe to which one or more injection units are connected, and the reactant is injected through the stage into exhaust gas.

[Claim 11 ] An exhaust gas treatment apparatus for removing nitrogen dioxide from nitrogen dioxide-containing exhaust gas produced during a combustion process of a stationary source, comprising a pipe arrangement for providing a flow path of exhaust gas, at least one injection unit connected to the pipe arrangement and supplying the reactant of claim 1 to the exhaust gas passing through the pipe arrangement, and a storage tank connected to the injection unit and storing the reactant.

[Claim 12] The apparatus according to claim 11, further comprising an injection pump which is positioned between the storage tank and the injection unit to supply the reactant from the storage tank to the injection unit.

[Claim 13] The apparatus according to claim 11, further comprising a fluid feeder connected to the injection unit and supplying a dispersion-assisting fluid to the injection unit.

[Claim 14] The apparatus according to claim 11, wherein the injection unit and the fluid feeder are connected via an ejector and one end of the ejector is connected to a flow path of the reactant discharged from the storage tank.

[Claim 15] The apparatus according to claim 11, wherein one or more stages are installed inside a pipe arrangement with a single stage being a pipe to which one or more injection units are connected, and the dispersion-assisting fluid and the reactant are injected through the stage into exhaust gas.

[Claim 16] The apparatus according to claim 11, further comprising a valve positioned at one side of the pipe and controlling a flow of fluids passing through each pipe, one or more temperature sensors installed at the pipe arrangement providing a flow path of the exhaust gas and measuring the temperature of exhaust gas passing through the pipe arrangement, and a control unit connected to the temperature sensor and valve and opening/closing the valve, based on the temperature data input from the temperature sensor.