JP7171164B2 - Combustion exhaust gas treatment method, combustion exhaust gas treatment device and maintenance method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a combustion exhaust gas treatment method, a combustion exhaust gas treatment apparatus, and a maintenance method thereof. More specifically, the present invention efficiently uses a catalyst, such as a regenerated catalyst, having activity slightly lower than that of a new catalyst or a specific surface area slightly lower than that of a new catalyst, while maintaining the exhaust gas treatment capacity for a long period of time to reduce combustion exhaust gas. The present invention relates to a combustion exhaust gas treatment method, a combustion exhaust gas treatment apparatus, and a maintenance method thereof, which can reduce the cost required for the treatment of.

Hazardous substances such as nitrogen oxides, carbon monoxide, mercury, organic halogen compounds (such as dioxins), ammonia, and VOCs in gases discharged from furnaces such as boilers can be decomposed and removed in the presence of a catalyst. It is done. Catalysts lose activity over long periods of use. Catalysts whose activity has fallen below a predetermined level (used catalysts) are replaced with new catalysts or regenerated catalysts. A regenerated catalyst can be produced from a used catalyst by the methods described in Patent Documents 3, 4, 5, and the like. In general, regenerated catalysts are cheaper than new catalysts, so the demand is increasing. However, the regenerated catalyst has a slightly lower initial activity than the new catalyst, and its activity declines more quickly over time. As a method of using a regenerated catalyst with such characteristics, for example, Patent Document 1 describes denitrification in which nitrogen oxides in exhaust gas are decomposed by the action of a catalyst, and the catalyst is installed in a multiple-stage reactor. Disclosed is a maintenance method for a denitrification apparatus, characterized in that the catalyst in the reactor of the second and subsequent stages of the apparatus is replaced with a regenerated catalyst.

In addition, in order to effectively use a partially deteriorated honeycomb catalyst, for example, Patent Document 2 discloses a honeycomb catalyst that has a gas flow passage through which a gas to be treated passes and performs treatment on the side wall of the gas flow passage. A method for recovering the performance of an exhaust gas treatment device installed in a channel, wherein a predetermined range from the upstream side of the honeycomb catalyst in the flow direction of the gas to be treated is defined as a deteriorated portion, and the deteriorated portion is separated from the inlet side of the exhaust gas channel. Thus, a method for recovering the performance of an exhaust gas treatment device is disclosed, which is characterized by rearranging the honeycomb catalyst.

Furthermore, Patent Document 6 discloses that an adsorbent obtained by impregnating a used catalyst with an aluminum sulfate solution and then drying is installed in the middle of an exhaust gas flow path to remove catalyst poisons. However, the denitration performance cannot be expected from the adsorbent that has not been regenerated.

JP-A-2002-143646 WO2005/056165A JP-A-2000-475 JP 2011-161373 A JP 2017-18919 A JP 2014-97439 A JP-A-1-127029 JP-A-2002-39524

The object of the present invention is to maintain the exhaust gas treatment capacity for a long period of time while using a catalyst such as a regenerated catalyst that has a slightly lower activity than a new catalyst or a slightly lower specific surface area than a new catalyst, thereby reducing the cost of treating combustion exhaust gas. To provide a combustion exhaust gas treatment method, a combustion exhaust gas treatment apparatus, and a maintenance method thereof, which can reduce the

As a result of studies to solve the above problems, the present invention including the following aspects was completed.

[1] A fixed catalyst having a frontmost catalyst layer on which catalyst A is placed and a catalyst layer on which catalyst B having a higher specific surface area or higher activity than catalyst A is placed and which is located after the frontmost catalyst layer in close proximity. A flue gas treatment method comprising passing the flue gas through a bed from the foremost stage to subsequent stages to remove harmful substances in the flue gas.
[2] The combustion exhaust gas treatment method according to [1], wherein the catalyst A is a regenerated catalyst.
[3] The method for treating flue gas according to [1] or [2], wherein at least two fixed catalyst beds are arranged in series with an interval therebetween.

[4] A fixed catalyst having a frontmost catalyst layer on which catalyst A is installed and a catalyst layer on which catalyst B having a higher specific surface area or higher activity than catalyst A is installed and which is located after the frontmost catalyst layer in close proximity. A flue gas treatment apparatus having a bed, a duct for introducing flue gas to the frontmost stage of the fixed catalyst bed, and a duct for discharging flue gas that has passed through the fixed catalyst bed.
[5] The combustion exhaust gas treatment device according to [4], wherein the catalyst A is a regenerated catalyst.
[6] The combustion exhaust gas treatment device according to [4] or [5], wherein at least two fixed catalyst beds are arranged in series with a space therebetween.

[7] A fixed catalyst bed having a frontmost catalyst layer on which a catalyst is placed and a subsequent catalyst layer on which a catalyst is placed in close proximity, and a combustion exhaust gas is introduced into the frontmost stage of the fixed catalyst bed. and a duct for discharging flue gas that has passed through the fixed catalyst bed,
Combustion exhaust gas, including replacing the catalyst installed in the frontmost catalyst layer with a catalyst A having higher activity than the catalyst and lower activity than the catalyst installed in the rearmost catalyst layer. A maintenance method for processing equipment.
[8] further including replacing the catalyst installed in the catalyst layer of at least one stage after the foremost stage with a catalyst B having a higher activity than the catalyst and a higher activity than the catalyst A; [7] 3. The maintenance method for the combustion exhaust gas treatment device according to 1.
[9] The maintenance method according to [8], wherein catalyst B is an unused catalyst or a catalyst that has been used in another stage.
[10] The maintenance method according to [7], [8] or [9], wherein the catalyst A is a regenerated catalyst.

[11] A fixed catalyst bed having a frontmost catalyst layer on which a catalyst is placed and a subsequent catalyst layer on which a catalyst is placed in close proximity, and a combustion exhaust gas is introduced into the frontmost stage of the fixed catalyst bed. and a duct for discharging flue gas that has passed through the fixed catalyst bed,
replacing the catalyst installed in the foremost catalyst layer with a catalyst A having a higher specific surface area than the catalyst and a lower specific surface area than the catalyst installed in the catalyst layer after the foremost stage; A maintenance method for a combustion exhaust gas treatment device.
[12] further comprising replacing the catalyst installed in the catalyst layer of at least one stage after the foremost stage with a catalyst B having a higher specific surface area than the catalyst and a higher specific surface area than the catalyst A, [ 11] maintenance method.
[13] The maintenance method according to [12], wherein the catalyst B is an unused catalyst or a catalyst that has been used in another stage.
[14] The maintenance method according to [11], [12] or [13], wherein the catalyst A is a regenerated catalyst.

According to the present invention, while using a catalyst such as a regenerated catalyst that has a slightly lower activity than a new catalyst or a slightly lower specific surface area than a new catalyst, the exhaust gas treatment capacity is maintained for a long time, and the cost of treating the combustion exhaust gas is can be reduced.
When a honeycomb-shaped catalyst or a plate-shaped catalyst is used for the frontmost catalyst layer, the exhaust gas is rectified in the frontmost catalyst layer, so that the catalysts installed in the rearmost catalyst layers are not poisoned. adhesion is suppressed. Since the removal amount of harmful substances in the catalyst layers in the stages after the frontmost stage is maintained high, the removal rate of harmful substances in the combustion exhaust gas treatment apparatus as a whole can be maintained high.
INDUSTRIAL APPLICABILITY The present invention can be preferably used for denitrification of combustion exhaust gas.

BRIEF DESCRIPTION OF THE DRAWINGS It is a conceptual diagram which shows an example of the flue gas processing apparatus of this invention. FIG. 2 is a conceptual perspective view showing _a catalyst module Fa; FIG. 2 is a conceptual perspective view showing a catalyst module B _a ; _FIG . 2 is a conceptual perspective view showing a catalyst module Fb; _FIG . 2 is a conceptual perspective view showing a catalyst module Fc; 3 is a conceptual perspective view showing a catalyst unit 7; FIG. 3 is a conceptual perspective view showing a catalyst unit 3; FIG. 2 is a conceptual perspective view showing a plate-like catalyst 2; FIG. FIG. 4 is a conceptual diagram showing another example of the combustion exhaust gas treatment apparatus of the present invention;

The combustion exhaust gas treatment method of the present invention comprises a catalyst layer in the foremost stage where catalyst A is installed and a catalyst layer in the stage after the foremost stage where catalyst B having a higher specific surface area or higher activity than catalyst A is installed. It includes removing harmful substances in the flue gas by passing the flue gas through the adjacent fixed catalyst bed from the first stage to the subsequent stages in order.
In addition, in the combustion exhaust gas treatment apparatus of the present invention, the catalyst layer in the foremost stage where the catalyst A is installed and the catalyst layer in the stage after the foremost stage where the catalyst B having a higher specific surface area or higher activity than the catalyst A is installed. , a duct for introducing flue gas to the frontmost stage of the fixed catalyst bed, and a duct for discharging flue gas that has passed through the fixed catalyst bed.

An embodiment of the present invention will be specifically described based on the drawings. In addition, the scope of the present invention is not limited by the following embodiments.

(First embodiment)
FIG. 1 is a conceptual diagram showing an example of a combustion exhaust gas treatment apparatus according to the present invention.
The flue gas treatment apparatus shown in FIG. 5.

The inlet duct 1, the reactor duct 6 and the outlet duct 5 can have a rectangular, trapezoidal, circular, elliptical, or the like cross-sectional shape of the channel viewed from the direction of gas flow. Of these, a rectangular shape is preferable from the viewpoint of ease of processing. A plurality of straightening vanes (not shown) may be provided at the inlet of the vertical channel of the reactor duct 6 over the cross section of the channel (see Patent Documents 7 and 8, etc.). Flue gas G flows through inlet duct 1 , reactor duct 6 and outlet duct 5 in that order.

In the flue gas treatment apparatus shown in FIG. 1, fixed catalyst beds 4a, 4b and 4c are spaced apart and arranged in series.

The fixed catalyst bed 4a has a plurality of catalyst modules Fa provided on the exhaust gas inlet side and _{a plurality of catalyst modules B a provided} on the exhaust gas outlet side in close proximity.

The catalyst module F _a is the frontmost catalyst layer in the fixed catalyst bed 4a. As shown in FIG. 2, the catalyst module F _a is formed by arranging eight catalyst units 7 in a 2×4 arrangement. As shown in FIG. 6, the catalyst unit 7 is formed by stacking a plurality of plate-shaped catalysts 8 (catalyst A: for example, a regenerated catalyst) so that the corrugated spacers 10 face the flat plate portion 9 and accommodated in a rectangular frame. is. A plurality of catalyst modules F _a can be arranged over the flow cross-section of the reactor duct such that substantially all of the exhaust gas G passes through the catalyst modules F _a .

The catalyst module B _a is a catalyst layer after the frontmost stage in the fixed catalyst bed 4a. As shown in FIG. 3, the catalyst module B _a is formed by arranging 16 catalyst units 3 in a 2×2×4 matrix. As shown in FIG. 7, the catalyst unit 3 is formed by stacking a plurality of plate-like catalysts 2 (catalyst B) so that the corrugated spacers face the flat plate portion and housed in a rectangular frame. The plate-like catalyst 2 has the same shape as the plate-like catalyst 8 shown in FIG. The plate-like catalyst 2 has a higher activity or a higher specific surface area than the plate-like catalyst 8 . The plate-shaped catalyst 2 may be a virgin catalyst or a reusable catalyst that has been used in another stage. The plate-like catalyst housed in the upper catalyst unit 3 of the catalyst module B _a is housed in the plate-like catalyst housed in the lower catalyst unit 3 of the catalyst module B _a and the catalyst unit 7 of the catalyst module _Fa . The pressure loss can be reduced by arranging so as to be perpendicular to the plate-like catalyst, which is preferable. A plurality of catalyst modules B _a can be arranged over the flow cross-section of the reactor duct such that substantially all of the exhaust gas G passes through the catalyst modules B _a .

In the space in front of the fixed catalyst bed 4a, the exhaust gas normally flows in a turbulent state. Since most of the turbulent exhaust gas flows into the catalyst module Fa in _a direction other than the direction parallel to the main surface of the plate-like catalyst that constitutes the catalyst module _Fa , the catalyst poison contained in the exhaust gas etc. tend to collide with the plate-shaped catalyst. Catalyst A, which is used as a plate-shaped catalyst constituting catalyst module Fa, has _a slightly lower specific surface area than catalyst B, and therefore adheres to catalyst poisons that collide with catalyst A slightly lower than catalyst B. As a result, the activity of the plate-shaped catalysts constituting the catalyst module F _a is relatively gradual over time.
The exhaust gas that has flowed into the catalyst module _Fa is rectified by the plate-like catalyst. Most of the rectified exhaust gas flowing out of the catalyst module F _a flows into the catalyst module B _a in a direction parallel to the main surface of the plate-like catalyst constituting the catalyst module B _a , so the exhaust gas contains It is difficult for catalyst poisons and the like to collide with the plate-like catalyst. The plate-like catalyst (catalyst B) that constitutes the catalyst module B _a is maintained in a highly active state.
That is, in the present invention, the activity of the catalyst module B _a is maintained at a high level even if the activity of the catalyst module F _a is slightly lowered due to the adhesion of the catalyst poison. Furthermore, a catalyst A having a slightly lower activity or a slightly lower specific surface area than the catalyst B (for example, a regenerated catalyst, a used catalyst with remaining activity performance, a new catalyst with a low specific surface area, etc.) is used in the catalyst module F _a , On the premise that the catalyst B having a higher activity or a higher specific surface area than the catalyst A is used in the catalyst module B _a , the degree of contribution to the removal of harmful substances in the catalyst module B _a is equal to the contribution to the removal of harmful substances in the catalyst module F _a . The superficial velocity of the exhaust gas, etc. can be set to be greater than or equal to the contribution. Thereby, the harmful substance removal rate of the entire fixed catalyst bed 4a can be maintained at a higher value.

The fixed catalyst bed 4b has a plurality of catalyst modules _Fb provided on the exhaust gas inlet side and _a plurality of catalyst modules Ba provided on the exhaust gas outlet side in close proximity.

The catalyst module _Fb is the frontmost catalyst layer in the fixed catalyst bed 4b. As shown in _FIG . 4, the catalyst module Fb is composed of 16 catalyst units 7 arranged in a 2×2×4 arrangement. A plurality of catalyst modules _Fb can be arranged over the flow cross-section of the reactor duct such that substantially all of the exhaust gas G passes through the catalyst modules _Fb . Pressure loss is reduced when the plate-like catalyst housed in the upper catalyst unit 7 of the catalyst module _Fb is arranged perpendicular to the plate-like catalyst housed in the lower catalyst unit 7 of the catalyst module _Fb . It is preferable because it can be
Catalyst module B _a is as already described. The plate-like catalyst housed in the upper catalyst unit 3 of the catalyst module B _a is housed in the plate-like catalyst housed in the lower catalyst unit 3 of the catalyst module B _a and the lower catalyst unit 7 of the catalyst module F _b . The pressure loss can be reduced by arranging so as to be perpendicular to the plate-like catalyst, which is preferable.

In the fixed catalyst bed 4b, as in the fixed catalyst bed 4a, even if the activity of the catalyst module _Fb slightly decreases due to the adhesion of the catalyst poison, the activity of the catalyst module _Ba is maintained high. The overall pollutant removal rate is maintained at a high value.

The catalyst fixed bed 4c has a plurality of catalyst modules _Fc . As shown in FIG. 5, in the catalyst module F _c , eight catalyst units 7 are arranged in a 2×4 arrangement on the exhaust gas inlet side (upper stage), and the catalyst modules 7 are arranged on the exhaust gas outlet side (lower stage) in close proximity to the catalyst units 7 . Then, eight catalyst units 3 are arranged in 2×4. The eight catalyst units 7 arranged in 2×4 form the frontmost catalyst layer in the fixed catalyst bed 4c. Pressure loss is reduced when the plate-like catalyst housed in the upper catalyst unit 7 of the catalyst module _Fc is arranged perpendicular to the plate-like catalyst housed in the lower catalyst unit 3 of the catalyst module _Fc . It is preferable because it can be A plurality of catalyst modules Fc can be arranged over the flow cross-section of the reactor _duct such that substantially all of the exhaust gas G _passes through the catalyst modules Fc.

In the fixed catalyst bed 4c, as in the fixed catalyst bed 4a, even if the activity of the catalyst unit 7 slightly decreases due to the adhesion of catalyst poison, the activity of the catalyst unit 3 is maintained high. Hazardous substance removal rate of is maintained at a high value.

(Second embodiment)
FIG. 9 is a conceptual diagram showing another example of the flue gas treatment apparatus of the present invention.
The flue gas treatment apparatus shown in FIG. 9 comprises an inlet duct 1 with horizontal channels, a reactor duct 6 with vertical channels provided with fixed catalyst beds 4a and 4d, and an outlet duct 5 with horizontal channels. equip. The catalyst fixed bed 4a is as already described in the description of the first embodiment.
The fixed catalyst bed 4d has a plurality of catalyst modules _Fc provided on the upstream side of the exhaust gas flow and a plurality of catalyst modules B _a provided on the downstream side of the exhaust gas flow in close proximity. Catalyst module _Fc and catalyst module _Ba are as already described in the description of the first embodiment. In the fixed catalyst bed 4d as well, it is preferable to dispose the plate-shaped catalyst in the lower stage perpendicular to the plate-shaped catalyst in the upper stage in the same manner as described above, because the pressure loss can be reduced.

In the fixed catalyst bed 4d, as in the fixed catalyst bed 4a, even if the activity of the catalyst module _Fc slightly decreases due to the adhesion of the catalyst poison, the activity of the catalyst module _Ba is maintained high. The overall pollutant removal rate is maintained at a high value.

(Other embodiments)
The fixed catalyst bed can be any number, any combination, any arrangement order, etc. as long as it conforms to the gist of the present invention. Not limited to order. Also, the types and number of catalyst modules constituting the fixed catalyst bed are not limited to those employed in the first embodiment and the second embodiment as long as they conform to the gist of the present invention. Furthermore, in the present invention, as long as it conforms to the gist of the present invention, it is also possible to have a fixed catalyst bed consisting of a catalyst module comprising only catalyst units 3 from the frontmost catalyst layer to the last catalyst layer. Alternatively, it may have a catalyst fixed bed consisting of a catalyst module consisting of only catalyst units 7 from the frontmost catalyst layer to the last catalyst layer.

The maintenance method of the present invention includes a fixed catalyst bed having a frontmost catalyst layer on which a catalyst is installed and a rearmost catalyst layer on which a catalyst is installed in close proximity to each other, and a combustion exhaust gas is placed at the topmost part of the fixed catalyst bed. In a flue gas treatment apparatus having a duct for introduction to the preceding stage and a duct for discharging flue gas that has passed through the catalyst fixed bed, the catalyst installed in the foremost catalyst layer is more active or active than the catalyst. This includes replacing the catalyst with a catalyst A having a higher specific surface area and a lower activity or specific surface area than the catalyst installed in the catalyst layer in the stage after the frontmost stage.
In the maintenance method of the present invention, the catalyst installed in the catalyst layer of at least one stage after the foremost stage has a higher activity or specific surface area than the catalyst and a catalyst B having a higher activity or specific surface area than the catalyst A. Preferably, it further comprises replacing with The replaced catalyst B may be unused catalyst, such as new catalyst, or catalyst that has been used in another stage. Catalyst A to be replaced may be a regenerated catalyst, a catalyst used in another stage, an unused catalyst, etc., as long as the specific surface area or high activity satisfies the relationship defined by the present invention. good too. Incidentally, the regenerated catalyst can be produced from the used catalyst by the methods described in Patent Documents 3, 4, 5 and the like. Furthermore, the maintenance method of the present invention is not limited by the number of times of maintenance.

EXAMPLES Next, the present invention will be described more specifically by showing Examples.

(Example 1)
A plate-shaped denitration catalyst element of 150 mm×550 mm as shown in FIG. 8, which had been used for a long period of time in a denitration device for a coal-fired boiler, was removed from the denitration device. The removed denitration catalyst element was immersed in an aqueous oxalic acid solution of 5 mass % at 60°C. The denitration catalyst element was washed by shaking it for 1 hour while being immersed in an aqueous oxalic acid solution. After that, it was impregnated with an aqueous solution containing 5% by mass of a compound represented by the demonstrative formula (NH ₄ ) ₃ Mo ₂ V ₃ O ₁₅ and activated by drying and heat treatment to obtain a regenerated catalyst element.
A regenerated catalyst element was superimposed and housed in a rectangular cylindrical frame with internal dimensions of 151 mm×151 mm×551 mm to obtain a catalyst unit A as shown in FIG.
Separately, a new denitrification catalyst element of 150 mm×550 mm having the same shape as that shown in FIG. 8 is superimposed and housed in a rectangular cylindrical frame with inner dimensions of 151 mm×151 mm×551 mm to obtain a catalyst unit B as shown in FIG. Obtained. A new denitration catalyst element has higher activity and specific surface area than a regenerated catalyst element.

Catalyst unit A and catalyst unit B were stacked in a denitrification device of a coal-fired boiler so that exhaust gas first flowed into catalyst unit A (front stage) and then flowed into catalyst unit B (back stage). When the accumulated operating hours reached 4000 hours, 8000 hours and 16000 hours, part of the catalyst elements were extracted from the catalyst units A and B, respectively, and 20 mm×100 mm test pieces were cut out from the extracted catalyst elements.
The cut test piece was tested under the conditions shown in Table 1 to measure the denitrification rate. Also, the amount of attached As was measured by analyzing the test piece. The denitration rate of the entire denitration apparatus was measured when the cumulative operating hours reached 4000 hours, 8000 hours and 16000 hours. Those results are shown in Table 2.

(Example 2)
A plate-shaped denitration catalyst element of 150 mm×550 mm as shown in FIG. 8, which had been used for a long period of time in a denitration device for a coal-fired boiler, was removed from the denitration device. The removed denitration catalyst element was immersed in an aqueous oxalic acid solution of 5 mass % at 60°C. The surface of the denitration catalyst element immersed in the aqueous oxalic acid solution was rubbed 20 times with a brush (bristles: made of resin, diameter 200 μm/bristles, bristles length 10 mm). After that, it was impregnated with an aqueous solution containing 5% by mass of a compound represented by the demonstrative formula (NH ₄ ) ₃ Mo ₂ V ₃ O ₁₅ and activated by drying and heat treatment to obtain a regenerated catalyst element. A new denitration catalyst element has higher activity and specific surface area than a regenerated catalyst element.
The denitration rate and the amount of As were measured in the same manner as in Example 1, except that this regenerated catalyst element was used. Those results are shown in Table 3.

(Comparative example 1)
Catalyst units A and B were obtained in the same manner as in Example 1. A new denitration catalyst element has higher activity and specific surface area than a regenerated catalyst element. Catalyst unit B and catalyst unit A were stacked in a denitration apparatus of a coal-fired boiler so that exhaust gas first flowed into catalyst unit B (front stage) and then flowed into catalyst unit A (back stage). When the cumulative operating hours reached 4000 hours, 8000 hours and 16000 hours, part of the catalyst elements were extracted from each of the catalyst units A and B, and test pieces of 20 mm×100 mm were cut out from the extracted catalyst elements.
The cut test piece was tested under the conditions shown in Table 1 to measure the denitrification rate. Also, the amount of attached As was measured by analyzing the test piece. Those results are shown in Table 4.

These results show the following. The rectification by the pre-catalyst can reduce the amount of catalyst poison attached to the post-catalyst. The amount of catalyst poison attached to the front-stage catalyst is larger than the amount of catalyst poison attached to the rear-stage catalyst. A new catalyst has a wider range of pore diameters than a regenerated catalyst and has a relatively high specific surface area, so catalyst poisons tend to adhere to the new catalyst. A regenerated catalyst having a relatively low specific surface area, which causes sintering or the like, has a lower activity and a lower adhesion of catalyst poisons than a new catalyst.
As in Comparative Example 1, when the front-stage catalyst is replaced with a new catalyst and the rear-stage catalyst is replaced with a regenerated catalyst, the activity of the new front-stage catalyst, which had been highly active, rapidly decreases due to the adhesion of catalyst poisons. Since the regenerated catalyst is originally lower in activity than the new catalyst, it cannot compensate for the rapid decrease in activity of the new catalyst, and the denitration rate of the denitrification apparatus as a whole falls below 70% after 16000 hours.
On the other hand, when the front-stage catalyst is replaced with a regenerated catalyst and the rear-stage catalyst is replaced with a new catalyst according to the present invention, the regenerated catalyst has lower adhesion of catalyst poisons than the new catalyst, so the decline in activity is gradual. . Even if the activity of the regenerated catalyst of the front-stage catalyst decreases due to the adhesion of the catalyst poison, the activity of the new catalyst of the rear-stage catalyst is maintained at a high level. As a result, the denitration rate of the entire denitration apparatus can be maintained at 70% or more even after 16,000 hours.

1: inlet duct 2: plate catalyst (catalyst B: for example, new catalyst)
3: Catalyst unit containing catalyst B 4a, 4b, 4c, 4d: Catalyst fixed bed 5: Exit duct 6: Reactor duct 7: Catalyst unit containing catalyst A 8: Plate-like catalyst (catalyst A: for example , regenerated catalyst)
9: flat plate portion 10: spacer portion F _a , F _b , F _c , B _a : catalyst module

Claims (14)

A catalyst layer at the foremost stage on which a catalyst A having a relatively lower specific surface area or lower activity than catalyst B and having relatively lower adhesion of catalyst poison than catalyst B is provided by sintering or the like ;
Catalyst B, which has a wider range of pore diameters than catalyst A, has a relatively higher specific surface area or higher activity than catalyst A, and has relatively higher adhesion of catalyst poisons than catalyst A, is installed at the maximum. In a fixed catalyst bed having a catalyst layer in a later stage in close proximity to a catalyst layer in the previous stage,
To remove harmful substances in the combustion exhaust gas while passing the combustion exhaust gas from the foremost stage to the subsequent stages in succession, so that the catalyst layer in the foremost stage rectifies the combustion exhaust gas and suppresses the adhesion of the catalyst poison to the catalyst B. Combustion exhaust gas treatment method. 2. The method according to claim 1, wherein the degree of contribution to removing harmful substances in the catalyst layers in the stages subsequent to the frontmost stage is set to be greater than or equal to the degree of contribution to removing harmful substances in the frontmost catalyst layer. The flue gas treatment method described. 3. A flue gas treatment method according to claim 1 or 2, wherein at least two of said fixed catalyst beds are spaced apart and installed in series. A catalyst layer at the foremost stage on which a catalyst A having a relatively lower specific surface area or lower activity than catalyst B and having relatively lower adhesion of catalyst poison than catalyst B is provided by sintering or the like ;
Catalyst B, which has a wider range of pore diameters than catalyst A, has a relatively higher specific surface area or higher activity than catalyst A, and has relatively higher adhesion of catalyst poisons than catalyst A, is installed at the maximum. a catalyst fixed bed having a catalyst layer in a later stage in close proximity to that in the previous stage;
Having a duct for introducing flue gas to the front stage of the fixed catalyst bed and a duct for discharging flue gas that has passed through the fixed catalyst bed,
A combustion exhaust gas treatment device in which the catalyst layer at the foremost stage straightens the combustion exhaust gas and suppresses adhesion of catalyst poisons to the catalyst B while removing harmful substances in the combustion exhaust gas. 5. The method according to claim 4, comprising setting the degree of contribution to removing harmful substances in the catalyst layers in the stages after the frontmost stage to be greater than or equal to the degree of contribution to removing harmful substances in the frontmost catalyst layer. A flue gas treatment device as described. 6. A flue gas treatment apparatus according to claim 4 or 5, wherein at least two of said fixed catalyst beds are spaced apart and installed in series. A fixed catalyst bed having a frontmost catalyst layer on which a catalyst is installed and a rear catalyst layer on which a catalyst is installed in close proximity, and a duct for introducing combustion exhaust gas to the frontmost stage of the fixed catalyst bed. , and a duct for discharging flue gas that has passed through the catalyst fixed bed, the frontmost catalyst layer rectifies the flue gas, and the catalyst poison is supplied to the catalyst installed in the catalyst layer after the front. In a combustion exhaust gas treatment device that removes harmful substances in the combustion exhaust gas while suppressing the adhesion of
A catalyst that is formed in a wider range of pore diameters than the catalyst, has a relatively higher activity than the catalyst, and is placed in a catalyst layer after the foremost catalyst layer. Combustion exhaust gas treatment, including replacing with a catalyst A that has relatively lower activity due to sintering or the like than the catalyst layer and relatively lower adhesion of catalyst poison than the catalyst installed in the catalyst layer in the stage after the foremost stage Equipment maintenance method. The catalyst installed in the catalyst layer of at least one stage after the frontmost stage is formed to have a wider range of pore diameters than the catalyst, has a relatively higher activity than the catalyst, and has a relatively higher activity than the catalyst A. 8. The method of maintaining a flue gas treatment system according to claim 7, further comprising replacing the catalyst B with a relatively expensive catalyst. 9. The maintenance method according to claim 8, wherein catalyst B is a virgin catalyst or a catalyst that has been used in another stage. Claim 7, including setting the degree of contribution to removing harmful substances in the catalyst layers in the stages subsequent to the frontmost stage to be greater than or equal to the degree of contribution to removing harmful substances in the frontmost catalyst layer. 9. The maintenance method according to 8 or 9. A fixed catalyst bed having a frontmost catalyst layer on which a catalyst is installed and a rear catalyst layer on which a catalyst is installed in close proximity, and a duct for introducing combustion exhaust gas to the frontmost stage of the fixed catalyst bed. , and a duct for discharging flue gas that has passed through the catalyst fixed bed, the frontmost catalyst layer rectifies the flue gas, and the catalyst poison is supplied to the catalyst installed in the catalyst layer after the front. In a combustion exhaust gas treatment device that removes harmful substances in the combustion exhaust gas while suppressing the adhesion of
The catalyst that has been placed in the frontmost catalyst layer is placed in a catalyst layer that has a wider range of pore diameters than the catalyst, a relatively higher specific surface area than the catalyst, and is located after the frontmost catalyst layer. Combustion, including replacing the catalyst with a catalyst A that has a relatively lower specific surface area than the catalyst by sintering or the like and has relatively lower adhesion of catalyst poison than the catalyst installed in the catalyst layer after the front stage. A maintenance method for an exhaust gas treatment device. The catalyst installed in the catalyst layer of at least one stage after the foremost stage is formed to have a wider range of pore diameters than the catalyst, has a relatively higher specific surface area than the catalyst, and has a specific surface area greater than that of the catalyst A. 12. The method of maintenance of claim 11, further comprising replacing catalyst B with a relatively high . 13. The maintenance method according to claim 12, wherein catalyst B is a virgin catalyst or a catalyst that has been used in another stage. Claim 11, comprising setting the degree of contribution to removing harmful substances in the catalyst layers in the stages after the frontmost stage to be greater than or equal to the degree of contribution to removing harmful substances in the frontmost catalyst layer. 14. The maintenance method according to 12 or 13.

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