KR102320147B1 - Mixing device for reducing agent and selective catalyst reduction system having the same - Google Patents

Abstract

The reducing agent mixing device is installed in the rear of the reducing agent injection module for injecting the reducing agent to the exhaust gas of the engine discharged through the exhaust pipe, and a carrier through which the exhaust gas and the reducing agent pass, and the carrier is installed inside the carrier and passes through the carrier and a heating unit for heating and vaporizing the reducing agent.

Description

Reductant mixing device and selective catalytic reduction system having the same

The present invention relates to a reducing agent mixing device and a selective catalytic reduction system having the same. More specifically, it relates to a mixing device for heating the reducing agent injected from the reducing agent injection module and a selective catalytic reduction system having the same.

The exhaust gas treatment system of an internal combustion engine, for example, a diesel engine, includes a diesel oxidation catalyst (DOC) device and a selective catalyst reduction (SCR) device to reduce pollutants contained in exhaust gas. The same exhaust gas after-treatment devices may be provided.

In the case of the selective reduction catalyst device, nitrogen oxides can be reduced to nitrogen gas and water by injecting urea water or the like from the reducing agent injection module to _{catalytically react with nitrogen oxides (NO x ).}

However, when the temperature of the exhaust gas is lowered or the flow rate is reduced, the urea water injected from the reducing agent injection module may be attached to the inner wall of the exhaust pipe and crystallized. The crystallized urea water may degrade the performance of the selective reduction catalyst and adversely affect the engine output, _{and react with sulfur oxides (SO 3} ) in the exhaust gas to cause corrosion of the exhaust pipe, ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) can be formed.

An object of the present invention is to provide a reducing agent mixing device for preventing crystallization of urea water in an exhaust pipe.

Another object of the present invention is to provide a selective catalytic reduction system having the above-described reducing agent mixing device.

In order to achieve the above-described object of the present invention, the reducing agent mixing device according to exemplary embodiments of the present invention is installed at the rear of the reducing agent injection module for injecting the reducing agent to the exhaust gas of the engine discharged through the exhaust pipe and a carrier through which the exhaust gas and the reducing agent pass, and a heating unit installed inside the carrier to heat and vaporize the reducing agent passing through the carrier.

In exemplary embodiments, the carrier may have a honeycomb shape.

In exemplary embodiments, the carrier may include cordierite, silicon carbide and pekaloy.

In exemplary embodiments, the reducing agent mixing device may further include a support for protecting the carrier.

In exemplary embodiments, the heating unit may be spirally disposed inside the carrier when viewed from the front.

In example embodiments, the heating unit may be arranged in a plurality of polygonal shapes having different sizes inside the carrier when viewed from the front.

In exemplary embodiments, the reducing agent mixing device may further include a power supply for supplying a current to the heating unit.

The selective catalytic reduction system for achieving another object of the present invention described above is a reducing agent injection module installed in an exhaust pipe through which exhaust gas is discharged from an engine and injecting a reducing agent into the exhaust pipe, the reducing agent injection in the exhaust pipe A selective reduction catalyst device installed at the rear of the module for catalytically reacting the exhaust gas and the reducing agent to reduce nitrogen oxides in the exhaust gas, and installed between the reducing agent injection module and the selective reduction catalyst device in the exhaust pipe and a reducing agent mixing device for vaporizing the reducing agent and mixing it with the exhaust gas.

In exemplary embodiments, the reducing agent mixing device includes a honeycomb-shaped carrier through which the exhaust gas and the reducing agent pass, and a heating unit installed inside the carrier to heat and vaporize the reducing agent passing through the carrier can do.

In exemplary embodiments, the reducing agent injection module may be installed to be spaced apart from the selective reduction catalyst device in the exhaust pipe forward at least 10 times the diameter of the exhaust pipe.

In exemplary embodiments, the selective catalytic reduction system may further include an ammonia slip catalyst device installed behind the selective reduction catalyst device in the exhaust pipe and for removing ammonia in the exhaust pipe.

In exemplary embodiments, the selective catalytic reduction system is a temperature sensor for measuring the temperature of the exhaust gas inside the exhaust pipe and for measuring the concentration of nitrogen oxides contained in the exhaust gas inside the exhaust pipe It may further include a nitrogen oxide concentration sensor.

In exemplary embodiments, the selective catalytic reduction system receives the temperature of the exhaust gas and the nitrogen oxide concentration information in the exhaust gas from the temperature sensor and the nitrogen oxide concentration sensor, respectively, and the reducing agent injection module and the reducing agent It may further include a control unit for controlling the operation of the mixing device.

In exemplary embodiments, the control unit may operate the reducing agent mixing device when the reducing agent injection amount injected from the reducing agent injection module is greater than or equal to a preset injection amount.

In exemplary embodiments, the control unit may operate the reducing agent mixing device when the temperature of the exhaust gas is 350 ℃ or less.

In exemplary embodiments, the reducing agent mixing device may heat the reducing agent injected into the exhaust pipe from the reducing agent injection module. The heated reducing agent can be vaporized and mixed more uniformly with the exhaust gas. Accordingly, the selective reduction catalyst system can more effectively remove nitrogen oxides contained in the exhaust gas.

However, the effects of the present invention are not limited to the above-mentioned effects, and may be variously expanded without departing from the spirit and scope of the present invention.

1 is a view showing a selective catalytic reduction system according to exemplary embodiments.
2 is a view showing a selective catalytic reduction system according to exemplary embodiments.
Figure 3 is a perspective view showing the reducing agent mixing device of Figure 1;
4 is a cross-sectional view taken along line IV-IV of the reducing agent mixing device of FIG. 3 .
5 and 6 are front views showing various structures of the reducing agent mixing apparatus of FIG.
7 is a flowchart illustrating a method for reducing nitrogen oxides using the selective catalytic reduction system of FIG. 1 .

With respect to the embodiments of the present invention disclosed in the text, specific structural or functional descriptions are only exemplified for the purpose of describing the embodiments of the present invention, and the embodiments of the present invention may be embodied in various forms. It should not be construed as being limited to the embodiments described in .

Since the present invention can have various changes and can have various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

Terms such as first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The above terms may be used for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

When a component is referred to as being “connected” or “connected” to another component, it is understood that the other component may be directly connected or connected to the other component, but other components may exist in between. it should be On the other hand, when it is mentioned that a certain element is "directly connected" or "directly connected" to another element, it should be understood that the other element does not exist in the middle. Other expressions describing the relationship between elements, such as "between" and "immediately between" or "neighboring to" and "directly adjacent to", etc., should be interpreted similarly.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that the described feature, number, step, operation, component, part, or combination thereof exists, and includes one or more other features or numbers. , it is to be understood that it does not preclude the possibility of the presence or addition of steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as meanings consistent with the context of the related art, and unless explicitly defined in the present application, they are not to be interpreted in an ideal or excessively formal meaning. .

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. The same reference numerals are used for the same components in the drawings, and repeated descriptions of the same components are omitted.

1 is a view showing a selective catalytic reduction system according to exemplary embodiments. 2 is a view showing a selective catalytic reduction system according to exemplary embodiments. Figure 3 is a perspective view showing the reducing agent mixing device of Figure 1; 4 is a cross-sectional view taken along line IV-IV of the reducing agent mixing device of FIG. 3 . 5 and 6 are front views showing various structures of the reducing agent mixing apparatus of FIG.

1 to 6, the selective catalytic reduction system is a reducing agent injection module 32, a reducing agent mixing device 34 and Selective catalyst reduction (SCR) device 30 may be included. In addition, a diesel oxidation catalyst (DOC) device 20 may be provided in front of the selective reduction catalyst device 30 . In this case, being located in the 'front' indicates relatively closer to the engine based on the flow of exhaust gas discharged from the engine.

In example embodiments, the engine may be a driving source for driving construction machines such as excavators, commercial vehicles such as buses and trucks, and industrial vehicles such as forklifts. The engine generates power by burning fuel, and exhaust gas generated in the combustion process may be discharged to the outside through the exhaust pipe 10 . The exhaust gas may contain environmental pollutants such as various hydrocarbons and nitrogen oxides. The environmental pollutants may be removed through the diesel oxidation catalyst device 20 and the selective reduction catalyst device 30 .

In exemplary embodiments, the diesel oxidation catalyst device 20 may include a honeycomb-shaped first carrier (not shown) installed in the exhaust pipe 10 and an oxidation catalyst coated on the surface of the first carrier. can For example, the first carrier may include a ceramic member such as cordierite, silicon carbide, and pekaloy, and the oxidation catalyst may include Pt, Pd, Rh, Ir, Ag, Sn, Ru, or the like. have. The oxidation catalyst may oxidize carbon monoxide and hydrocarbons in exhaust gas to carbon dioxide and water.

The reducing agent injection module 32 is installed in the exhaust pipe 10 behind the diesel oxidation catalyst device 20, and a reducing agent such as urea water for reducing nitrogen oxides in the exhaust gas can be injected into the exhaust pipe 10. have.

The reducing agent injection module 32 may be connected to the urea water supply module 42 through the pipe 33 to inject the urea water into the exhaust pipe 10 . In addition, the urea water supply module 42 may be connected to the urea water storage tank 40 through the supply line 44 and the recovery line 46 . The urea water storage tank 90 may store an aqueous urea solution called AdBlue or Diesel Exhaust Fluid (DEF) for ammonia production.

1 , in exemplary embodiments, the reducing agent injection module 32 may be installed on a curved portion of the exhaust pipe 10 .

In general, the exhaust pipe 10 may be installed under the vehicle. However, since the size of the vehicle is limited, the length of the exhaust pipe 10 is also limited. Therefore, in some cases, the exhaust pipe 10 may have a curved shape, and the reducing agent injection module 32 may be installed on the curved curved portion of the exhaust pipe 10 .

Alternatively, as shown in FIG. 2 , the reducing agent injection module 32 may be installed in a straight portion of the exhaust pipe 10 . In this case, in order to ensure that the reducing agent injected from the reducing agent injection module 32 is uniformly sprayed on the front surface of the reducing agent mixing device 34 , the reducing agent mixing device 34 is constant with respect to the inner wall of the exhaust pipe 10 . It may be installed obliquely to have an angle (θ).

The selective reduction catalyst device 30 is installed behind the reducing agent injection module 32 inside the exhaust pipe 10, and _{reduces nitrogen oxides (NO x} ) by the following Reaction Formulas 1 to 3 to reduce nitrogen oxides (NO x ) harmless to the human body ( N ₂ ) can be converted to

[Scheme 1]

[Scheme 2]

[Scheme 3]

Urea ((NH ₂ ) ₂ CO) can produce ammonia (NH _{3 ) by hydrolysis.} The ammonia thus generated _{reduces NO and NO 2} , and can be converted into _{nitrogen (N 2} ) harmless to the human body.

The reducing agent mixing device 34 is installed between the reducing agent injection module 32 and the selective reduction catalyst device 30 in the exhaust pipe 10, and uniformly mixes the reducing agent injected from the reducing agent injection module 32 with the exhaust gas It is possible to increase the nitrogen oxide reduction efficiency of the selective reduction catalyst device (30).

3 and 4, the reducing agent mixing device 34 is installed inside the honeycomb-shaped second carrier 110, the second carrier 110 installed in the exhaust pipe 10 to heat the reducing agent It may include a heating unit 120 for heating, and a power supply unit 130 for supplying current to the heating unit 120 . For example, the second carrier may include a ceramic member such as cordierite, silicon carbide, and pekaloy, and the heating unit may include a heating wire for receiving electrical energy and converting it into thermal energy.

The reducing agent injected from the reducing agent injection module 32 and the exhaust gas discharged from the engine may be mixed in the process of passing through the second carrier 110 of the reducing agent mixing device 34 . Specifically, the second carrier 110 may include a plurality of passages 112 arranged in a honeycomb shape, and the reducing agent and the exhaust gas may be mixed with each other in the process of passing through the passages 112 . In addition, although not shown, the reducing agent mixing device 34 may include at least one vane (not shown), and the vane forms turbulence to more uniformly mix the reducing agent and the exhaust gas. .

In general, since the temperature of the exhaust gas discharged from the engine is a high temperature reaching several hundred ℃, the reducing agent injected into the exhaust pipe 10 from the reducing agent injection module 32 can be vaporized immediately. The vaporized reducing agent may be mixed with the exhaust gas, and the reducing agent and the nitrogen oxide may be catalytically reacted using the selective reduction catalyst device 30 to reduce the nitrogen oxide to nitrogen gas and water.

However, when the temperature of the exhaust gas is lowered due to incomplete combustion in the engine or the flow rate of the exhaust gas is small, the reducing agent injected from the reducing agent injection module 32 is not completely vaporized and is attached to the inner wall of the exhaust pipe 10 , etc. It can be crystallized (Crystallization). For example, when the temperature of the exhaust gas is 300 ℃ or less, some of the injected reducing agent may be crystallized, and the crystallized reducing agent may be decomposed again when the temperature rises to 350 ℃ or more. The crystallized reducing agent continues to grow, and the grown reducing agent crystals may degrade the performance of the selective catalytic reduction system.

The heating unit 120 may heat the reducing agent passing through the second carrier 110 inside the reducing agent mixing device 34 by dissipating thermal energy to the surroundings. The heated reducing agent may be vaporized and may be more uniformly mixed with the exhaust gas passing through the passage 112 of the second carrier 110 in this process. In addition, the heating unit 120 may decompose the reducing agent already crystallized and attached to the inner wall of the exhaust pipe 10 or the reducing agent mixing device 34 .

In exemplary embodiments, the heating unit 120 may be disposed to have various shapes inside the second carrier 110 . For example, as shown in FIG. 5 , the heating unit 120 may be spirally disposed inside the second carrier 120 when the reducing agent mixing device 34 is viewed from the front. Alternatively, as shown in FIG. 6, the heating unit 122 may be arranged in a plurality of polygonal shapes having different sizes inside the second carrier 110 when the reducing agent mixing device 34 is viewed from the front. . In addition, although not shown, the heating unit 120 is arranged in a plurality of concentric circles having different sizes inside the second carrier 120 when the reducing agent mixing device 34 is viewed from the front, and various shapes as needed. can be placed as

The power supply unit 130 may receive power from the outside and supply current to the heating unit 120 . For example, the power supply unit 130 may receive power from a vehicle battery. In this case, the power supply unit 130 may be controlled by the control unit 50 to be described later.

In exemplary embodiments, the reducing agent mixing device 34 may further include a support 100 for enclosing and protecting the second carrier 110 . The second carrier 110 may be made of a ceramic material and may be easily broken by an external impact. Therefore, in order to protect the second carrier 110 from external impact, the support 100 may be installed outside the second carrier 110 . Alternatively, the support 100 may be integrally formed with the exhaust pipe 10 .

Referring back to FIG. 1 , the reducing agent injected from the reducing agent injection module 32 is vaporized in the reducing agent mixing device 34 , and the vaporized reducing agent is mixed with the exhaust gas and supplied to the selective catalytic reduction device 30 . In this case, the nitrogen oxide reduction efficiency in the selective catalytic reduction device 30 can be further increased as the reducing agent is uniformly mixed with the exhaust gas. Therefore, in order to secure the mixing time of the reducing agent and the exhaust gas, the reducing agent injection module 32 may be installed to be spaced apart from the selective catalytic reduction device 30 by a certain distance. For example, the reducing agent injection module 32 may be installed to be spaced apart by a distance s of 10 times or more of the diameter d of the exhaust pipe 10 forward from the front end surface of the selective reduction catalyst device 30 .

In exemplary embodiments, the selective catalytic reduction system is at least one temperature sensor 38 and a nitrogen oxide concentration sensor 39 installed in the exhaust pipe 10 , and a reducing agent injection module 32 and a reducing agent mixing device It may further include a control unit 50 for controlling the (34).

The temperature sensor 38 may measure the temperature of the exhaust gas inside the exhaust pipe 10 , and the nitrogen oxide concentration sensor 39 may measure the concentration of nitrogen oxides included in the exhaust gas. For example, the temperature sensor and the nitrogen oxide concentration sensor may be installed in front of the selective reduction catalyst device.

The control unit 50 receives information on the temperature of the exhaust gas and the concentration of nitrogen oxide in the exhaust gas from the temperature sensor 38 and the nitrogen oxide concentration sensor 39, and based on this, the reducing agent injection module 32 and the reducing agent mixing The device 34 may be controlled. For example, the control unit may be included in an engine control unit (ECU) or a reducing agent injection control unit (DCU).

In exemplary embodiments, the selective catalytic reduction system may further include an ammonia slip catalyst device 36 installed behind the selective reduction catalyst device 30 to remove ammonia.

The ammonia generated by the urea injected from the reducing agent injection module 32 may reduce nitrogen oxides in the exhaust gas. At this time, in order to maximize the conversion efficiency of the nitrogen oxides, a greater amount of ammonia than a stoichiometric amount may be supplied. For this reason, the ammonia is not completely consumed through the catalytic reaction, but is released into the atmosphere and may cause air pollution, which is referred to as an ammonia slip phenomenon. The ammonia slip catalyst device 36 can prevent the ammonia slip phenomenon by removing the ammonia not consumed in the selective reduction catalyst device 30 .

As described above, the selective catalytic reduction system according to exemplary embodiments may be vaporized by heating the reducing agent injected into the exhaust pipe 10 . The vaporized reducing agent may be uniformly mixed with the exhaust gas in the process of passing through the second carrier 110 of the reducing agent mixing device 34 . The selective reduction catalyst device 30 may catalytically react the reducing agent with nitrogen oxides in the exhaust gas to reduce the nitrogen oxides to nitrogen gas and water.

Hereinafter, a method for controlling the reducing agent mixing device in the selective catalytic reduction system will be described.

7 is a flowchart illustrating a method for reducing nitrogen oxides using the selective catalytic reduction system of FIG. 1 .

7, the reducing agent injection module 32 injects the reducing agent into the exhaust pipe 10 (S100).

For example, the control unit 50 receives information on whether the engine is operating from the sensors 38 and 39 installed inside the exhaust pipe 10, and operates the reducing agent injection module 32 when the engine is operated. to inject a reducing agent such as urea water into the exhaust pipe 10 .

Next, the necessity of heating the reducing agent is determined (S200).

In exemplary embodiments, the step of determining the need for heating the reducing agent may include the step (S210) of determining whether the injection amount of the reducing agent is greater than or equal to a preset amount.

The reducing agent mixing device 34 may be vaporized by heating the reducing agent sprayed from the reducing agent injection module 32 . Therefore, in order to prevent the heating unit 120 of the reducing agent mixing device 34 from operating when the reducing agent is not actually injected, the control unit 50 heats the reducing agent only when the reducing agent injection amount is greater than or equal to a preset amount. (34) can be controlled. In this case, the injection amount of the reducing agent may be calculated through the amount of nitrogen oxide measured by the nitrogen oxide concentration sensor (39).

In exemplary embodiments, determining the necessity of heating the reducing agent may include determining whether the exhaust gas flow rate is within a preset range (S220). In this case, the flow rate of the exhaust gas may be calculated through the flow rate of air sucked into the engine and the amount of fuel consumed.

For example, if the exhaust gas flow rate inside the exhaust pipe 10 is less than a preset range, it may be determined that the vehicle is not started. In addition, when the intake air flow rate sensor (not shown) fails, the flow rate of the exhaust gas may be measured abnormally high. In order to compensate for this, even when the exhaust gas flow rate exceeds a preset range, it is possible to control so as not to operate the heating unit 120 of the reducing agent mixing device 34.

In exemplary embodiments, the step of determining the need for heating the reducing agent may include a step (S230) of determining whether the temperature of the front end of the selective catalytic reduction device 30 is less than or equal to a preset temperature.

For example, urea may crystallize at temperatures below 300°C and decompose again when the temperature rises above 350°C. Therefore, the control unit 50 receives information on the current temperature of the exhaust gas through the temperature sensor 38 installed in the exhaust pipe 10, and the reducing agent mixing device 34 to heat the reducing agent only when the temperature is 350° C. or less. ) can be controlled

When it is determined that the reducing agent heating is necessary, the reducing agent is heated using the reducing agent mixing device 34 (S300).

For example, the control unit 50 may supply current to the heating unit 120 by controlling the power supply unit 130 of the reducing agent mixing device 34 . The heating unit 120 may heat and vaporize the surrounding reducing agent. At this time, the reducing agent crystallized around the reducing agent mixing device 34 may also be decomposed.

The vaporized reducing agent may be uniformly mixed with the exhaust gas while passing through the second carrier 110 of the reducing agent mixing device 34 . The mixed reducing agent and exhaust gas may be supplied to the selective reduction catalyst device 30, and nitrogen oxides may be reduced to nitrogen and water through a catalytic reaction.

As described above, in the nitrogen oxide reduction method according to exemplary embodiments, a reducing agent such as urea water is injected into the exhaust gas discharged from the engine, and the reducing agent is heated and vaporized to vaporize the degree of mixing with the exhaust gas. ) can be increased. The uniformly mixed reducing agent and exhaust gas may be supplied to the selective reduction catalyst device 30, and nitrogen oxides in the exhaust gas may be reduced to nitrogen harmless to the human body.

Although the above has been described with reference to the embodiments of the present invention, those skilled in the art can variously modify and change the present invention within the scope without departing from the spirit and scope of the present invention described in the claims below. You will understand that you can.

10: exhaust pipe 20: diesel oxidation catalyst device
30: selective reduction catalyst device 32: reducing agent injection module
33: pipe 34, 35: reducing agent mixing device
36: ammonia slip catalyst device 38: temperature sensor
39: nitrogen oxide concentration sensor 40: urea water storage tank
42: urea water supply module 44: supply line
46: recovery line 50: control unit
100: support 110: second carrier
112: passage 120, 122: heating unit
130: power supply

Claims (14)

a carrier installed at the rear of the reducing agent injection module for injecting a reducing agent into the exhaust gas of the engine discharged through the exhaust pipe, and through which the exhaust gas and the reducing agent pass; and
It is installed inside the carrier and includes a heating unit for heating and vaporizing the reducing agent passing through the carrier,
The heating unit is spirally arranged inside the carrier when viewed from the front, characterized in that the reducing agent mixing device to radiate the thermal energy to the surroundings. The reducing agent mixing apparatus according to claim 1, wherein the carrier has a honeycomb shape. The reducing agent mixing apparatus according to claim 1, wherein the carrier comprises at least one selected from the group consisting of cordierite, silicon carbide, and pekaloy. delete The reducing agent mixing apparatus according to claim 1, wherein the heating unit is arranged in a plurality of polygonal shapes having different sizes inside the carrier when viewed from the front. The reducing agent mixing apparatus according to claim 1, further comprising a power supply for supplying an electric current to the heating unit. a reducing agent injection module installed in an exhaust pipe through which exhaust gas is discharged from the engine, and injecting a reducing agent into the exhaust pipe;
a selective reduction catalyst device installed in the rear of the reducing agent injection module in the exhaust pipe to reduce nitrogen oxides in the exhaust gas by catalytically reacting the exhaust gas and the reducing agent; and
It is installed between the reducing agent injection module and the selective reduction catalyst device in the exhaust pipe, and includes a reducing agent mixing device for vaporizing the reducing agent and mixing it with the exhaust gas,
The reducing agent mixing device,
a carrier through which the exhaust gas and the reducing agent pass; and
Selective catalytic reduction system, characterized in that it is spirally installed inside the support when viewed from the front, and comprising a heating unit for heating and vaporizing the reducing agent passing through the support. According to claim 7, wherein the carrier,
A selective catalytic reduction system, characterized in that it is a honeycomb-shaped carrier. The selective catalytic reduction system according to claim 7, wherein the reducing agent injection module is spaced apart from the selective reduction catalyst device in the exhaust pipe by at least 10 times the diameter of the exhaust pipe in front. 8. The selective catalytic reduction system according to claim 7, further comprising an ammonia slip catalyst device installed behind the selective reduction catalyst device in the exhaust pipe to remove ammonia in the exhaust pipe. 8. The method of claim 7,
a temperature sensor for measuring a temperature of the exhaust gas inside the exhaust pipe; and
Selective catalytic reduction system, characterized in that it further comprises a nitrogen oxide concentration sensor for measuring the concentration of nitrogen oxide contained in the exhaust gas inside the exhaust pipe. 12. The method of claim 11, wherein the temperature of the exhaust gas and the concentration information of the nitrogen oxide in the exhaust gas are received from the temperature sensor and the nitrogen oxide concentration sensor, respectively, to control the operation of the reducing agent injection module and the reducing agent mixing device Selective catalytic reduction system, characterized in that it further comprises a control unit for. The selective catalytic reduction system according to claim 12, wherein the control unit operates the reducing agent mixing device when the reducing agent injection amount injected from the reducing agent injection module is greater than or equal to a preset injection amount. The selective catalytic reduction system according to claim 12, wherein the control unit operates the reducing agent mixing device when the temperature of the exhaust gas is 350° C. or less.

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