KR102434014B1 - Method for treating exhaust gas using exhaust gas treatment apparatus - Google Patents

Abstract

The present invention relates to an exhaust gas treatment method using an exhaust gas treatment device. In one embodiment, the exhaust gas treatment method includes: introducing the exhaust gas into an SCR (selective reduction catalyst) unit equipped with a selective reduction catalyst layer through an inlet line; generating a first processing gas from which nitrogen oxides are removed by treating the introduced exhaust gas with a reducing agent containing ammonia (NH ₃ ); and discharging the first processing gas through a discharge line connected to the rear end of the SCR unit.

Description

Exhaust gas treatment method using exhaust gas treatment device {METHOD FOR TREATING EXHAUST GAS USING EXHAUST GAS TREATMENT APPARATUS}

The present invention relates to an exhaust gas treatment method using an exhaust gas treatment device.

Among the technologies for reducing nitrogen oxides emitted from power plants, Selective Catalytic Reduction (SCR) using ammonia NH ₃ ) as a reducing agent is a technology that can remove more than 90% by weight of nitrogen oxides. It is the oldest catalyst technology.

On the other hand, the SCR reaction using ammonia as a reducing agent proceeds in the presence of oxygen at a temperature of 300 ~ 400 ℃ as shown in Chemical Formula 1 below.

[Formula 1]

4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O

In general, NO _x contained in combustion exhaust gas contains more than 90% by weight of NO, so the stoichiometric ratio of NH ₃ and NO is a 1:1 reaction based on a molar ratio, but for further reduction of nitrogen oxide, a precursor of fine dust, Excess ammonia is injected into the denitrification facility to increase the reaction efficiency, and as a result, ammonia not participating in the reaction is discharged from the rear end of the denitration facility, which is called ammonia slip. When ammonia is injected at a molar ratio of 1.2 when 100 ppm of nitrogen oxide is generated based on a 500 MW coal-fired power plant, it can be calculated that 23 kg of ammonia per hour slips at the rear end of the denitrification facility.

On the other hand, in the case of domestic thermal power plants, the emission proportions of sulfur oxides (SOx) and nitrogen oxides (NOx), which are secondary products of fine dust (or secondary generated fine dust), were 34% by weight and 34% by weight, respectively, than the direct emission of fine dust. 7% by weight, which is a high level as a single emission source. As such, when unreacted ammonia is discharged together from the rear end of the denitrification facility, secondary fine dust is generated in the atmosphere as shown in Chemical Formulas 2 and 3 below.

[Formula 2]

NOx + H ₂ O → HNO ₃ + NH ₃ → NH ₄ NO ₃

[Formula 3]

SOx + H ₂ O → H ₂ SO ₄ + NH ₃ → (NH ₄ ) ₂ SO ₄

On the other hand, the catalyst stage in the denitration facility of the power plant is composed of a two-stage catalyst for reducing nitrogen oxides, but there is no process capable of treating ammonia, so unreacted ammonia is discharged as it is. In particular, in the case of combined cycle power plants, only denitrification facilities are installed among the environmental facilities, so when the amount of ammonia injected into the denitrification facility increases, there is a risk of being directly discharged into the atmosphere through the chimney of the power plant. In addition, unreacted ammonia (ammonia slip) generates salt in the flue gas treatment system, causing clogging and corrosion in the piping, which affects the operation of power generation facilities.

As the environmental regulation policy for power plant exhaust gas becomes more stringent, ammonia slip may continue to cause problems as the amount of ammonia injection will be further increased in the future to increase the NOx removal rate. Ammonia is classified as a toxic substance under the Occupational Safety and Health Act and requires minimum emission. There is a need for a process capable of reducing not only oxides but also unreacted ammonia.

On the other hand, the conventionally developed ammonia slip suppression device is a device for minimizing ammonia slip by installing an ammonia oxidation catalyst in a denitration facility SCR reactor or by coating a catalyst material on a discharge line at the rear end of the reactor. However, in the case of adding a catalyst stage in the reactor, it requires a separate installation space in the facility, so it cannot be applied to a facility with a narrow space. There was a problem that post-treatment of the emitted nitrogen oxides was impossible due to the increase in the amount of nitrogen oxide.

Background art related to the present invention is disclosed in Korean Patent Publication No. 2020-0032903 (published on March 27, 2020, title of the invention: selective catalytic reduction system and control method thereof).

One object of the present invention is to provide an exhaust gas treatment device that is excellent in the effect of simultaneously reducing nitrogen oxides and slip ammonia in exhaust gas, and is excellent in preventing the generation of secondary fine dust.

Another object of the present invention is to provide an exhaust gas treatment apparatus that has excellent reducing agent reaction efficiency and can minimize the amount of unreacted reducing agent emission.

Another object of the present invention is to provide an exhaust gas treatment apparatus having excellent facility stability, energy efficiency and economic feasibility during operation of the treatment apparatus.

Another object of the present invention is to provide an exhaust gas treatment apparatus capable of compacting and downsizing the treatment apparatus.

Another object of the present invention is to provide an exhaust gas treatment method using the exhaust gas treatment apparatus.

One aspect of the present invention relates to an exhaust gas treatment system. In one embodiment, the exhaust gas treatment device includes an inlet line through which the exhaust gas is introduced; A first treatment in which the exhaust gas is introduced by being connected to the inlet line, a selective reduction catalyst layer is provided therein, and a reducing agent containing ammonia (NH ₃ ) is injected to treat the introduced exhaust gas to remove nitrogen oxides SCR (Selective Reduction Catalyst) unit for generating gas; a discharge line connected to the rear end of the SCR unit and through which the first processing gas is discharged; and a circulation line connected to the discharge line and the inlet line, wherein the circulation line includes: a first section connected to the discharge line and formed with a first catalyst layer including a transition metal oxide on an inner wall; a second zone in which a second catalyst layer comprising a noble metal is formed on the inner wall; and a third zone connected to the inlet line and formed with a third catalyst layer including a transition metal on an inner wall; at least a portion of the first processing gas is introduced into the circulation line to the first zone; A second process gas is generated by treating slip ammonia (slip NH ₃ ) of the process gas through the second zone and the third zone, and the second process gas is introduced into the inlet line.

In one embodiment, the first catalyst layer includes an active material including copper oxide (CuO) and an alumina-based support supporting the same, and the second catalyst layer includes an active material including platinum (Pt) and rhodium (Rh) and An alumina-based support supporting the same, and the third catalyst layer may include an active material including copper (Cu) and manganese (Mn) and a zeolite-based support supporting the same.

In one embodiment, the second catalyst layer includes 0.1 to 1% by weight of platinum (Pt) and 0.1 to 1% by weight of rhodium (Rh), and the third catalyst layer includes 0.1 to 5% by weight of copper (Cu) and manganese (Mn) 0.1 to 5% by weight.

In one embodiment, the first zone, the second zone, and the third zone may be formed in an area ratio of 1:0.1-5:0.1-5.

In one embodiment, the second processing gas may include nitrogen (N ₂ ) and nitrogen dioxide (NO ₂ ).

In one embodiment, the first processing gas may have a temperature of 200 to 350°C, and the second processing gas may have a temperature of 150 to 350°C.

In one embodiment, one or more circulation fans may be further provided inside the circulation line.

Another aspect of the present invention relates to an exhaust gas treatment method using the exhaust gas treatment apparatus. In one embodiment, the exhaust gas treatment method includes: introducing the exhaust gas into an SCR (selective reduction catalyst) unit equipped with a selective reduction catalyst layer through an inlet line; generating a first processing gas from which nitrogen oxides are removed by treating the introduced exhaust gas with a reducing agent containing ammonia (NH ₃ ); and discharging the first treatment gas through an exhaust line connected to the rear end of the SCR unit, wherein the exhaust gas treatment apparatus is connected to the discharge line and the inlet line a first zone including a circulation line which becomes a second zone in which a second catalyst layer comprising a noble metal is formed on the inner wall; and a third zone connected to the inlet line and formed with a third catalyst layer including a transition metal on an inner wall; at least a portion of the first processing gas is introduced into the circulation line to the first zone; A second process gas is generated by treating slip ammonia (slip NH ₃ ) of the process gas through the second zone and the third zone, and the second process gas is introduced into the inlet line.

In one embodiment, the first catalyst layer includes an active material including copper oxide (CuO) and an alumina-based support supporting the same, and the second catalyst layer includes an active material including platinum (Pt) and rhodium (Rh) and An alumina-based support supporting the same, and the third catalyst layer may include an active material including copper (Cu) and manganese (Mn) and a zeolite-based support supporting the same.

In one embodiment, the second catalyst layer includes 0.1 to 1% by weight of platinum (Pt) and 0.1 to 1% by weight of rhodium (Rh), and the third catalyst layer includes 0.1 to 5% by weight of copper (Cu) and manganese (Mn) 0.1 to 5% by weight.

In one embodiment, the first zone, the second zone, and the third zone may be formed in an area ratio of 1:0.1-5:0.1-5.

In one embodiment, the second processing gas may include nitrogen (N ₂ ) and nitrogen dioxide (NO ₂ ).

When treating exhaust gas using the exhaust gas treatment apparatus according to the present invention, the effect of simultaneously reducing nitrogen oxides and slip ammonia of the exhaust gas is excellent, the effect of preventing the generation of secondary generated fine dust is excellent, and the treated exhaust gas is introduced into the SCR unit, the reaction efficiency of the reducing agent is excellent through induction of the fast SCR reaction, so it is possible to maximize the denitrification efficiency and minimize the amount of unreacted reducing agent. By preventing clogging, facility stability, energy efficiency, and economy are excellent, and compactness and downsizing of the treatment device may be possible.

1 shows an exhaust gas treatment apparatus according to an embodiment of the present invention.

In describing the present invention, if it is determined that a detailed description of a related known technology or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

And the terms described below are terms defined in consideration of functions in the present invention, which may vary depending on the intention or custom of the user or operator, so the definition should be made based on the content throughout this specification describing the present invention.

exhaust gas treatment device

One aspect of the present invention relates to an exhaust gas treatment system. 1 shows an exhaust gas treatment apparatus according to an embodiment of the present invention.

Referring to FIG. 1, the exhaust gas treatment apparatus 1000 includes an inlet line 10 through which exhaust gas is introduced; It is connected to the inlet line 10 to introduce the exhaust gas, a selective reduction catalyst layer is provided therein, and a reducing agent containing ammonia (NH ₃ ) is injected to treat the introduced exhaust gas to remove nitrogen oxides. 1 SCR (selective reduction catalyst) unit 100 for generating a process gas; a discharge line 20 connected to the rear end of the SCR unit 100 through which the first processing gas is discharged; and a circulation line 30 connected to the discharge line 20 and the inlet line 10 .

The exhaust gas may be generated and discharged during power generation using fossil fuels in thermal power plants, combined thermal power plants, and various boiler facilities.

The SCR unit 100 is provided with a selective reduction catalyst layer therein. As the selective reduction catalyst layer, those commonly used in the art may be used without limitation. For example, two or more selective reduction catalyst layers may be stacked. A reducing agent containing ammonia is injected into one side of the SCR unit 100 through a reducing agent inlet (not shown).

The exhaust gas flowing into the SCR unit 100 through the inlet line 10 is in contact with the ammonia-based reducing agent in the presence of oxygen (O ₂ ) on the selective reduction catalyst layer, and nitrogen oxides (NO _X ) in the exhaust gas The first process gas may be generated by reducing and removing nitrogen (N ₂ ) and water (H ₂ O).

In one embodiment, the internal temperature of the SCR unit 100 may be 300 ~ 400 ℃. The reactivity is excellent under the above conditions, so that the first processing gas can be easily generated.

On the other hand, in the process of generating the first processing gas, the reducing agent that does not react with the exhaust gas and is discharged directly to the exhaust line is referred to as slip ammonia (slip NH ₃ ). When the slip ammonia is discharged to the atmosphere, secondary fine dust is generated and adversely affects the human body and the environment. and sequentially reacts to convert the slip ammonia into nitrogen (N ₂ ), and some of the slip ammonia is converted to nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) and transferred to the inlet line, and introduced into the SCR unit It induces a fast SCR response.

In one embodiment, the circulation line 30 is connected to the discharge line, the first zone 31 is formed with a first catalyst layer 32 containing a transition metal oxide on the inner wall; a second zone 33 connected to the first zone 31 and having a second catalyst layer 34 including a noble metal formed on an inner wall thereof; and a third zone 36 connected to the second zone 33 and connected to the inlet line 10, in which a third catalyst layer 35 including a transition metal is formed on an inner wall; are sequentially formed.

At least a portion of the first process gas is introduced into the circulation line, passes through the first zone, the second zone, and the third zone to process slip ammonia (slip NH ₃ ) of the process gas to generate the second process gas and the second process gas is introduced into the inlet line.

As described above, when the first catalyst layer, the second catalyst layer, and the third catalyst layer are formed in the circulation line, a separate installation space is not required, so that the treatment apparatus can be reduced in size and compact. In addition, by installing different catalysts for each zone in the circulation line, the emission of nitrogen oxides can be minimized, thereby reducing nitrogen oxides and slip ammonia in the first process gas at the same time.

In one embodiment, a reaction comprising the following formula (4) may occur in the first zone:

[Formula 4]

4NH ₃ + 5O ₂ → 4NO + 6H ₂ O

Slip ammonia among the first processing gas introduced into the first zone may be converted into nitrogen monoxide (NO) by reacting with the first catalyst layer formed in the first zone.

In one embodiment, the first catalyst layer may include an active material including copper oxide (CuO) and an alumina (Al ₂ O ₃ )-based support supporting the same. When the first catalyst layer is included, the nitrogen monoxide conversion efficiency of the slip ammonia may be excellent.

For example, the first catalyst layer may include 3 to 50% by weight of copper oxide and 50 to 97% by weight of an alumina-based support. When included in the above content range, the durability of the first catalyst layer and the nitrogen monoxide conversion efficiency of the slip ammonia may be excellent.

In one embodiment, in the second zone, a reaction comprising the following formula (5) may occur:

[Formula 5]

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O

As shown in Chemical Formula 5, various metal catalysts can be used for the reaction in which nitrogen monoxide and slip ammonia act as reactants to convert nitrogen, but the present invention uses a noble metal catalyst having excellent oxidation reactivity, and among them, increasing mechanical strength For this purpose, the reaction selectivity of nitrogen may be increased by using a second catalyst layer containing platinum and rhodium.

In one embodiment, the second catalyst layer may include an active material including platinum (Pt) and rhodium (Rh) and an alumina-based support supporting the same. When the second catalyst layer is included, the mechanical strength of the second catalyst layer may be excellent, and nitrogen monoxide (NO) and slip ammonia and nitrogen conversion efficiency in the first process gas may be excellent.

In one embodiment, the second catalyst layer may include 0.1 to 1 wt% of platinum (Pt), 0.1 to 1 wt% of rhodium (Rh), and 98 to 99.5 wt% of an alumina-based support. When included under the above conditions, nitrogen conversion efficiency may be excellent. For example, the second catalyst layer may include an active material including 0.5 to 1.0% by weight of platinum and 0.1 to 0.3% by weight of rhodium, and 98.7 to 99.5% by weight of an alumina-based support.

For another example, the platinum may be included in a higher content than the rhodium. When included under the above conditions, nitrogen conversion efficiency may be excellent.

In one embodiment, in the third zone, a second process gas including nitrogen dioxide (NO ₂ ) may be generated by oxidizing slip ammonia in the first process gas.

In the third zone, a third catalyst layer may be formed to further reduce slip ammonia and nitrogen oxides in the first process gas.

In one embodiment, the third catalyst layer may include an active material including copper (Cu) and manganese (Mn) and a zeolite-based support supporting the same. When the third catalyst layer is applied, nitrogen dioxide is easily converted from slip ammonia, thereby preventing ammonia generation and improving the exhaust gas treatment efficiency of the SCR unit.

The third catalyst layer may include a zeolite support obtained by ion-exchanging copper-manganese having excellent selectivity to nitrogen dioxide (NO ₂ ) rather than nitrogen.

In one embodiment, the third catalyst layer may include an active material including 0.1 to 5 wt% of copper (Cu), 0.1 to 5 wt% of manganese (Mn), and 90 to 99.8 wt% of a zeolite-based support. When included in the above content, the durability of the third catalyst layer may be excellent, and the conversion efficiency of nitrogen dioxide from slip ammonia may be excellent. For example, 1 to 3% by weight of copper, 1 to 3% by weight of manganese, and 94 to 99% by weight of the zeolite-based support may be included.

For example, the third catalyst layer may be formed by ion-exchanging copper and manganese on a zeolite support. When the third catalyst layer is applied, the conversion efficiency to nitrogen dioxide (NO ₂ ) may be superior to that of nitrogen.

In one embodiment, the second processing gas may include nitrogen (N ₂ ) and nitrogen dioxide (NO ₂ ).

The second process gas is introduced into the SCR unit through the inlet line. When the second process gas is introduced, a fast SCR reaction including the following Chemical Formula 6 may occur inside the SCR unit:

[Formula 6]

4NH ₃ + 2NO + 2NO ₂ → 4N ₂ + 6H ₂ O

On the other hand, the reaction in which nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) participate in a stoichiometric ratio of 1:1 is called a fast SCR reaction because it proceeds very quickly compared to a typical selective reduction catalytic reaction.

In general, nitrogen monoxide accounts for 90% by weight or more of nitrogen oxides, so the reaction is difficult to proceed in a general SCR process, but in the present invention, by installing an ammonia oxidation catalyst and a circulation line, slip ammonia is reduced as well as addition of nitrogen oxides reduction is possible.

In one embodiment, the first zone, the second zone, and the third zone may be formed in an area ratio of 1:0.1-5:0.1-5. When formed in the above area ratio, the reaction efficiency is excellent, the slip ammonia reduction effect is excellent, and the second processing gas containing nitrogen dioxide (NO ₂ ) is easily generated, and the fast SCR reactivity of the SCR unit is excellent to improve the denitration efficiency. can be maximized. For example, it may be formed in an area ratio of 1:0.5 to 3:0.5 to 3.

In one embodiment, the temperature of the first processing gas may be 200 to 350°C, and the temperature of the second processing gas may be 150 to 350°C. Reaction efficiency may be excellent under the above conditions.

In one embodiment, one or more circulation fans 40 may be further provided inside the circulation line. Reaction efficiency may be excellent under the above conditions. For example, a circulation fan 40 may be provided inside the second zone 33 .

Exhaust gas treatment method using an exhaust gas treatment device

Another aspect of the present invention relates to an exhaust gas treatment method using the exhaust gas treatment apparatus.

In one embodiment, the exhaust gas treatment method includes: introducing the exhaust gas into an SCR (selective reduction catalyst) unit equipped with a selective reduction catalyst layer through an inlet line; generating a first processing gas from which nitrogen oxides are removed by treating the introduced exhaust gas with a reducing agent containing ammonia (NH ₃ ); and discharging the first treatment gas through an exhaust line connected to the rear end of the SCR unit, wherein the exhaust gas treatment apparatus is connected to the discharge line and the inlet line a first zone including a circulation line which becomes a second zone in which a second catalyst layer comprising a noble metal is formed on the inner wall; and a third zone connected to the inlet line and formed with a third catalyst layer including a transition metal on an inner wall; at least a portion of the first processing gas is introduced into the circulation line to the first zone; A second process gas is generated by treating slip ammonia (slip NH ₃ ) of the process gas through the second zone and the third zone, and the second process gas is introduced into the inlet line.

In one embodiment, the first zone, the second zone, and the third zone may be formed in an area ratio of 1:0.1-5:0.1-5. When formed in the above area ratio, the reaction efficiency is excellent, the slip ammonia reduction effect is excellent, and the second processing gas containing nitrogen dioxide (NO ₂ ) is easily generated, and the fast SCR reactivity of the SCR unit is excellent to improve the denitration efficiency. can be maximized. For example, it may be formed in an area ratio of 1:0.5 to 3:0.5 to 3.

In one embodiment, the second processing gas may include nitrogen (N ₂ ) and nitrogen dioxide (NO ₂ ).

The present invention relates to a process for converting slip ammonia generated when an excessive amount of ammonia used as a reducing agent in a power plant is injected into harmless nitrogen. It is possible to further reduce nitrogen oxides.

In addition, in the present invention, a catalytic reaction is possible without requiring a separate space in the SCR facility. In addition, while the conventional exhaust gas treatment apparatus cannot cope with the reactions oxidized to nitrogen oxides in the ammonia oxidation catalyst reaction, the present invention can minimize ammonia and nitrogen oxide emissions by installing a circulation line to compensate for this. .

Therefore, the exhaust gas treated through the process of the present invention can minimize the amount of ammonia generated at the rear end of the SCR unit, regardless of the amount of ammonia reducing agent injected, thereby improving facility stability and suppressing the generation of secondary fine dust.

In addition, since the present invention can be applied to all denitration facilities to which the selective catalytic reduction method is applied, it can be applied not only to a stationary source such as a power plant but also to a mobile source.

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, these are presented as preferred examples of the present invention and cannot be construed as limiting the present invention in any sense. Content not described here will be omitted because it can be technically inferred sufficiently by those skilled in the art.

Examples and Comparative Examples

Example

An exhaust gas treatment apparatus as shown in FIG. 1 was prepared. Specifically, the inlet line 10 through which the exhaust gas is introduced; It is connected to the inlet line 10 to introduce the exhaust gas, two selective reduction catalyst layers are stacked therein, and a reducing agent containing ammonia (NH ₃ ) is injected to treat the introduced exhaust gas to nitrogen oxides. an SCR (selective reduction catalyst) unit 100 for generating the removed first process gas; a discharge line 20 connected to the rear end of the SCR unit 100 through which the first processing gas is discharged; and a circulation line 30 connected to the discharge line 20 and the inlet line 10; an exhaust gas treatment apparatus 1000 including a was prepared.

The circulation line ₃₀ is connected to the discharge line 20 and the _first zone ( 31); A second catalyst layer 34 comprising an active material containing 0.5% by weight of platinum (Pt) and 0.25% by weight of rhodium (Rh) and an alumina (Al ₂ O ₃ )-based support supporting the same is formed on the inner wall 34 by weight second zone (33); and a third catalyst layer 36 in which 2.5 wt% of copper (Cu) and 2.5 wt% of manganese (Mn) are ion-exchanged to 95 wt% of a zeolite support (ZSM5) on the inner wall of the third catalyst layer (36) connected to the inlet line (10) Zone 35; was sequentially formed (first catalyst layer: second catalyst layer: third catalyst layer = 1: 1: 1 area ratio), and a circulation fan 40 was installed inside the second zone 33 .

Comparative Example 1

An exhaust gas treatment apparatus was prepared in the same manner as in the above embodiment except that the circulation line was not provided.

Comparative Example 2

An exhaust gas treatment apparatus was prepared in the same manner as in the above embodiment, except that the first catalyst layer was formed in the first zone of the circulation line and the catalyst layer was not formed in the second zone and the third zone.

Comparative Example 3

An exhaust gas treatment apparatus was prepared in the same manner as in the above embodiment, except that the first catalyst layer was formed in the first section of the circulation line, the second catalyst layer was formed in the second section, and the catalyst layer was not formed in the third section. .

Experimental Example: Exhaust gas was treated using the exhaust gas treatment apparatuses of Examples and Comparative Examples 1 to 3 above. Specifically, exhaust gas was introduced into an SCR (selective reduction catalyst) unit equipped with a selective reduction catalyst layer through an inlet line, and a reducing agent including ammonia (NH ₃ ) was injected from the reducing agent inlet into the SCR unit, and 300 to 400 ° C. A first process gas from which nitrogen oxides have been removed was generated by treating the introduced exhaust gas under a temperature condition of , and discharged through a discharge line connected to the rear end of the SCR unit.

The first treatment gas of Comparative Example 1 was discharged to the atmosphere as it is, and the first treatment gas discharged through the discharge lines of Examples and Comparative Examples 2 to 3 was introduced into the circulation line, and the first zone and the second zone and the third zone sequentially to generate a second process gas, transport it to the inlet line, and introduce it into the SCR unit.

Then, by collecting the gas finally processed through the Examples and Comparative Examples, the concentration of nitrogen oxide (NO _x ) in the gas (ppm) and the concentration of slip ammonia (NH ₃ ) (ppm) were measured, and the initial The nitrogen oxide removal rate and ammonia unreacted rate were calculated by comparing the concentration of nitrogen oxide in the exhaust gas (ppm) and the value of the initial ammonia concentration (ppm) of the reducing agent input from the reducing agent inlet, and the results are shown in Table 1 below. .

Referring to the results of Table 1, in the case of Examples to which the exhaust gas treatment device of the present invention is applied, Comparative Example 1 to which the circulation line is not applied and Comparative Examples 2 to which the second catalyst layer or the third catalyst layer of the present invention is not applied 3, it was found that both the nitrogen oxide removal rate and the slip ammonia removal rate of the final treated gas were excellent.

Specifically, as compared with Comparative Example 1, it was confirmed that the nitrogen oxide removal rate was increased by 8.0% and the ammonia unreacted rate was lowered by 8.6%, and in Comparative Example 2, the nitrogen monoxide (NO) production amount in the first zone increased due to the increase Since the nitrogen oxide (NOx) concentration was rather increased, the nitrogen oxide removal rate was decreased by 13% compared to the Example, and the effect was lowered than that of Comparative Example 1, and the ammonia unreacted rate was also increased compared to the Example. In Comparative Example 3 to which the third catalyst layer was not applied, it was confirmed that the nitrogen oxide removal rate was reduced by 5% compared to the Example, and the ammonia unreacted rate was 0.9% vapor.

Up to now, the present invention has been mainly examined in the examples. Those of ordinary skill in the art to which the present invention pertains will understand that the present invention can be implemented in modified forms without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments are to be considered in an illustrative rather than a restrictive sense. The scope of the present invention is indicated in the claims rather than the foregoing description, and all differences within the scope equivalent thereto should be construed as being included in the present invention.

10: inlet line 20: outlet line
30: circulation line 31: first zone
32: first catalyst bed 33: second zone
34: second catalyst bed 35: third zone
36: third catalyst layer 40: circulation fan

Claims (1)

introducing the exhaust gas into an SCR (selective reduction catalyst) unit equipped with a selective reduction catalyst layer through an inlet line;
generating a first processing gas from which nitrogen oxides are removed by treating the introduced exhaust gas with a reducing agent containing ammonia (NH ₃ ); and
Discharging the first processing gas through an exhaust line connected to the rear end of the SCR unit;
The exhaust gas treatment device includes a circulation line connected to the discharge line and the inlet line,
The circulation line may include: a first zone connected to the discharge line and formed with a first catalyst layer including a transition metal oxide on an inner wall; a second zone in which a second catalyst layer comprising a noble metal is formed on the inner wall; and a third zone connected to the inlet line and formed with a third catalyst layer including a transition metal on an inner wall; is formed sequentially,
At least a portion of the first processing gas is introduced into the circulation line and passes through the first zone, the second zone, and the third zone to process slip ammonia (slip NH ₃ ) in the processing gas to generate a second processing gas and
The second processing gas is introduced into the inlet line,
The first zone, the second zone and the third zone are formed in an area ratio of 1:0.1-5:0.1-5,
The exhaust gas treatment method, characterized in that the internal temperature of the SCR unit is 300 ~ 400 ℃.

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