JPH11290699A - Honeycomb catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a boundary film diffusion resistance in gas flow paths and enhance a catalytic performance without changing a catalyst manufacturing process by providing a cut part traversing plural parallel gas flow paths. SOLUTION: Cut parts 3 reaching the half of the depth of a honeycomb cross section perpendicularly with gas flow paths 2 are alternately provided from two oppositely positioned side faces. In addition, the cut parts 3 are alternately formed at a specified interval on the same side face to reduce a boundary film diffusion resistance and thereby enhance a catalytic performance. The flow paths 2 are cut off through the entire cell of the honeycomb 1, together with the cut parts 3 from the opposite direction. Therefore, it is expected that the activity of the entire cross section of the parallel gas flow paths 2 can be uniformly enhanced. Further, the cut parts 3 need not be provided perpendicularly with the gas flow paths 2 but can have a specified angle with the gas flow paths 2. Thus, it is possible to enhance the catalytic efficiency by preventing the boundary film diffusion resistance from increasing in the gas flow paths 2 almost without changing a manufacturing process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a honeycomb catalyst, and more particularly to a honeycomb catalyst for flue gas denitration used for removing nitrogen oxides in exhaust gas discharged from a large power boiler, a combustion furnace or the like. And the film diffusion resistance is small,
The present invention relates to a honeycomb catalyst capable of improving catalyst performance.

[0002]

2. Description of the Related Art As a method for removing nitrogen oxides from exhaust gas discharged from thermal power plants and various factories, the nitrogen oxides are made harmless by reacting them with a reducing agent such as ammonia in the presence of a denitration catalyst. And an ammonia catalytic reduction denitration method. When applying ammonia catalytic reduction denitration method, for example, the exhaust gas discharge facilities large thermal power plants, etc., since several hundred m ³ or more catalytic amount is required, compact whole apparatus to reduce the possible catalytic amount It is devised to do so.

In order to reduce the amount of the catalyst while maintaining the exhaust gas purifying performance of the honeycomb catalyst, the activity is improved by improving the catalyst components, or the purifying performance of the catalyst is proportional to the geometric specific surface area of the catalyst body. Therefore, make the cell as small as possible to increase the surface area per unit volume, or because the diffusion resistance due to the membrane in the gas flow path greatly affects the catalyst performance, the gas flow is disturbed and the membrane diffusion resistance is It is conceivable to devise the shape of the catalyst so as to make the particle size as small as possible.

[0004] Among these methods, there is a problem that the degree of freedom for improvement is reduced when the type of exhaust gas is determined. That is, when the gas to be treated is coal combustion exhaust gas containing a large amount of dust, it is necessary to prevent clogging, so that the cell size cannot be reduced so much. Further, in order to suppress wear due to dust and oxidation of SO ₂ in exhaust gas, there is naturally a limit in activating the catalyst.

[0005] The method for this is a method which can be applied sufficiently depending on the device. That is, a catalyst integrally molded by an extrusion method such as a honeycomb catalyst has a constant cross-sectional shape, and it is extremely difficult to form a shape that disturbs a gas flow. 08-19
742), and the wall surface of the catalyst is made wavy (Japanese Patent Application Laid-Open No. 58-1983).
No. 43238), for example, a technique for promoting gas diffusion has been proposed.

However, when these methods are employed, a special extrusion die is required, and a large number of holes are required to be formed in the molded body, which leads to an increase in the number of steps required for producing the catalyst. Problems arise. In addition, in the honeycomb catalyst of integral molding, the length of the catalyst is shortened to such an extent that the velocity boundary layer due to the gas flow is not sufficiently developed to reduce the film diffusion resistance, and by combining a plurality of the catalysts,
There is a method for improving the catalyst performance over an integrally molded catalyst of the same length.

However, even if this method is adopted, the length of the flow path in which the velocity boundary layer develops is unknown. It is unclear whether the catalyst improves its catalytic performance without being affected by the gas flow in the preceding stage. Even if this becomes clear, there is a possibility that the combination of a large number of catalysts having a short length may increase the number of steps or increase the capacity of the catalyst.

As a prior art which defines the length of the catalyst, there is, for example, Japanese Utility Model Laid-Open Publication No. Sho 62-199122, which describes a denitration catalyst arranged in a plurality of stages in a denitration apparatus. Is shorter than that on the downstream side, and the deterioration of the catalyst due to the poisonous substances in the gas to be treated is greater on the upstream side than on the downstream side. It is intended to be.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and to reduce the film diffusion resistance in the gas flow path without changing the catalyst production process. An object of the present invention is to provide a honeycomb catalyst capable of improving catalyst performance.

[0010]

Means for Solving the Problems To achieve the above object, the invention claimed in the present application is as follows. (1) A honeycomb catalyst having a plurality of parallel gas passages, wherein a cut portion is provided so as to cross the gas passages. (2) The honeycomb catalyst according to the above (1), wherein a plurality of the cut portions are provided, and an interval between the cut portions is set to 300 mm or less. (3) The honeycomb catalyst according to the above (1) or (2), wherein a width of the cut portion in a gas flow direction is at least 1/3 of a hydraulic diameter of the gas flow path.

(4) The projected area of the cut portion on a plane perpendicular to the gas flow path is not more than の of the cross-sectional area of the catalyst orthogonal to the gas flow path. )
The honeycomb catalyst according to any one of (1) to (3). (5) The honeycomb catalyst according to any one of (1) to (4), wherein the honeycomb catalyst is an exhaust gas denitration honeycomb catalyst.

In the present invention, a honeycomb catalyst (hereinafter, referred to as a honeycomb catalyst) is used.
A notch is provided across the gas flow path of the honeycomb structure. As a result, the film diffusion resistance decreases, the mass transfer coefficient representing the film diffusion amount increases, and the catalyst efficiency improves. 1 and 2 are explanatory views showing the principle of the present invention. FIG.
That is, a processing temperature of 300 to 400 ° C. and a gas flow rate of 2-1.
FIG. 4 is an explanatory diagram showing a relationship between a catalyst length of a honeycomb-shaped denitration catalyst at 0 m / s and a mass transfer coefficient representing a film diffusion amount. In the figure, (A) shows a honeycomb catalyst having a cell pitch of 3.5 mm and a cell thickness (rib thickness) of 0.5 mm, and (B)
Is cell pitch 4.1 mm, cell thickness (rib thickness) 0.6
In the case of a honeycomb catalyst having a cell pitch of 7 mm.
This shows the case of a honeycomb catalyst having a thickness of 0 mm and a cell thickness (rib thickness) of 1.0 mm. Here, the cell pitch refers to the interval between the ribs forming the honeycomb structure, and the cell thickness refers to the thickness of the rib. FIG. 1B shows the relationship between the cell pitch and the cell thickness.

In FIG. 1, although there is a slight difference depending on the cell size, the mass transfer coefficient gradually decreases (diffusion resistance increases) as the catalyst becomes longer, and becomes almost constant when the catalyst length is 300 mm or more. I have. Therefore, in the case of a gas channel having a length of 300 mm or less, that is, a catalyst having a catalyst length of 300 mm or more, an interval between cut portions is 300 m.
It can be seen that, by providing the cut portion so as to be not more than m, a decrease in the mass transfer coefficient is prevented and the catalytic activity is improved.

FIG. 2 shows the relationship between the distance T between catalysts (expressed as a multiple of the hydraulic diameter H) and the mass transfer coefficient when two honeycomb catalysts are combined so that their gas flow paths communicate with each other. It is shown. In FIG. 2, if the catalyst interval is set to be equal to or larger than the hydraulic diameter of the gas channel, separation of the boundary layer occurs, and a high mass transfer coefficient is maintained. It can be seen that is improved.

Therefore, in the present invention, the cut portion is provided so as to cross the gas flow path of the honeycomb catalyst, and the interval between the cut portions is set to 300 mm or less. Further, the width of the cut portion in the gas flow direction is at least 1/3 of the hydraulic diameter of the gas flow path. Hydraulic diameter, when defining the friction loss of a pipe having a cross-sectional shape other than circular, is introduced as an amount corresponding to the diameter of a circular pipe,
In the present invention, when the cross section of the gas flow path is square, it is preferable that the width of the cut portion is at least 1/3 of the width of the opening of the gas flow path (the length obtained by subtracting the rib thickness from the cell pitch).

In the present invention, the honeycomb catalyst has a cross section of 150 mm from the viewpoint of easy production and handling.
It is preferable that the catalyst has a length of about 500 to 700 mm or more. This is because arranging the individual catalysts using a shorter product having a length smaller than this greatly increases the man-hours required for cutting, unitizing, and blocking, and the merit of performance improvement may be lost.

The effect of improving the catalyst performance in the present invention is more pronounced in a honeycomb catalyst having a relatively large cell size applied to a dirty gas discharged from a coal-fired boiler, for example, and the rate of increase of the mass transfer coefficient is large. Become. In such a catalyst for dirty gas, since there are various means and there are few means for improving the performance, it is more effective to apply the present invention.

In the present invention, the strength of the honeycomb structure is reduced to some extent by providing the cut portions. However, if the direction and depth of the cut portions are determined in consideration of the arrangement of the catalyst and the method of applying a load, sufficient strength can be obtained. Can be secured. Therefore, in the present invention, it is preferable that the projected area of the cut portion on a plane perpendicular to the gas flow path is 以下 or less of the catalyst cross-sectional area orthogonal to the gas flow path.

Even if a large load is applied and a crack is generated from the cut portion, the function of the catalyst is not reduced because the gas flow path is separated.

[0020]

3 to 7 are explanatory views showing one embodiment of a honeycomb catalyst body according to the present invention. The honeycomb catalyst body 1 shown in FIG. 3 is a denitration catalyst in which cut portions 3 are provided alternately from two opposing side surfaces perpendicularly to the gas flow channel 2 to a depth of about の of the honeycomb cross section. The distance between the cuts on the same side is 300m
m or less, for example, 250 mm.

In the present embodiment, the interval between the cut portions is 3
By setting the thickness to be equal to or less than 00 mm, the diffusion resistance of the film becomes small, and the catalytic performance is improved. In addition, the depth of the cut portion is set to の of the honeycomb cross section, and the cut portion from the opposite direction (１ ／ of the honeycomb cross section) is combined with the cut-off portion to cut off the flow path in all the cells of the honeycomb. The same activity improvement can be expected in all cross sections of the parallel gas flow path.

In the present embodiment, the cut portion 3 may be provided by any method at any stage of the catalyst manufacturing process. For example, when the paste immediately after molding is still in a soft state, a method of cutting with a wire is used. After drying or firing, a method using a band saw or a water jet can be employed. FIG. 4 is an explanatory view of a honeycomb catalyst body showing another embodiment of the present invention. This honeycomb catalyst body,
A predetermined cut 3 is made in each corner portion of a cross section orthogonal to the gas flow path 2 to partially increase the denitration activity.

FIG. 5 shows a case where a number of cuts 3 corresponding to １ ／ of the catalyst cross section are provided from two opposing corners of a cross section orthogonal to the gas flow path 2. Are set to 300 mm or less. FIG. 6 shows that the cut portions 3 corresponding to 触媒 of the catalyst cross section are provided at predetermined intervals, that is, at intervals of 300 mm or less from four side surfaces of the honeycomb catalyst body.

According to each of the above embodiments, the cut-off portions 3 crossing the gas flow path 2 are provided at predetermined intervals, so that the film diffusion resistance in the gas flow path is reduced, and the catalyst performance is improved. In the present embodiment, the cut portion 3 is
It is not necessary to be perpendicular to the gas passage 2, and the cut portion 3 may have a predetermined angle with respect to the gas flow path 2 as shown in FIG. FIG. 7 shows the honeycomb catalyst body 1 of FIG. 1 in which the cut portions 3 are provided at a predetermined angle with respect to the gas flow path 2. In the present embodiment, the notch 3
The projected area on a plane perpendicular to the gas flow path 2 is
Is preferably equal to or less than の of the cross section of the catalyst orthogonal to. This ensures the required mechanical strength.

According to each of the embodiments of the present invention, a highly efficient exhaust gas purifying catalyst can be obtained by an extremely simple method without changing the conventional production process. Further, since the same catalyst unit and block as those in the related art can be used, the amount of catalyst can be relatively reduced, and the apparatus can be made more compact.

[0026]

Next, specific embodiments of the present invention will be described. Embodiment 1 FIG. 8 is a sectional view showing a specific embodiment of the present invention.
This honeycomb structure was prepared by applying a denitration catalyst paste having a composition of Ti / W / V to an outer shape of 150 mm square and a cell pitch of 7.
The honeycomb structure was extruded to a width of 1.0 mm and a cell thickness of 1.0 mm, dried, cut into a width of 500 mm, and then placed on one side (upper surface in the drawing) of this honeycomb structure at positions 100 mm and 300 mm from one end. Are provided with cuts 3 each having a depth of about 1/2 of the width of the honeycomb and having a depth of 6 mm, and a similar side face (lower face in the figure) is provided at positions 100 mm and 300 mm from the other end of the honeycomb structure. The cut portion 3 was formed, and then fired at 550 ° C. for 2 hours.

Embodiment 2 FIG. 9 is an explanatory view showing another specific embodiment of the present invention. In the figure, this honeycomb structure has cut notches formed on both upper and lower surfaces in the figure by 55 mm, 165 mm, 275 mm, 385 mm from the end face of the honeycomb structure, respectively.
It was prepared in the same manner as in Example 1 except that the position was mm.

Example 3 A honeycomb catalyst structure was obtained in the same manner as in Example 2 except that the width of the cut portion was 3 mm. Comparative Example 1 A honeycomb catalyst structure was obtained in the same manner as in Example 1 except that the cut portions were not provided.

The denitration activities of the honeycomb structures of Examples 1 to 3 and Comparative Example 1 were measured under the conditions of a gas amount of 240 m ³ N / h and 350 ° C., and the result was set to 1 in Comparative Example 1. The reaction rate constant at that time was shown.

[0030]

[Table 1] * Reference value for denitration rate In Table 1, it can be seen that the reaction rate constant of Example 1 was 17%, that of Example 2 was 26%, and that of Example 3 was 15%. Thereby, Examples 1 to
According to No. 3, the catalyst amount was 17%, 26% and 15% respectively in comparison with Comparative Example 1 in the same activity-based exhaust gas purification apparatus.
It can be reduced.

[0031]

According to the first aspect of the present invention, the notch is provided so as to cross the gas flow path.
The catalyst efficiency can be improved by preventing an increase in the film diffusion resistance in the gas flow path. According to the invention as set forth in claim 2 of the present application, by providing a plurality of the cut portions and setting the interval between the cut portions to 300 mm or less, in addition to the effect of the above invention, the film diffusion resistance in the gas flow path is reduced. It can be less than or equal to a predetermined value.

According to the third aspect of the present invention, the width of the cut portion in the gas flow direction is at least 1/3 of the hydraulic diameter of the gas flow path, so that the mass transfer coefficient in the gas flow path is reduced. Increase. According to the invention as set forth in claim 4 of the present application, the projected area of the cut portion on a plane perpendicular to the gas flow path is one of the catalyst cross-sectional area orthogonal to the gas flow path.
By setting the ratio to / 2 or less, the mechanical strength of the catalyst can be ensured in addition to the effects of the above invention.

According to the fifth aspect of the present invention, since the honeycomb catalyst is a honeycomb catalyst for exhaust gas denitration, the denitration activity of the catalyst can be improved in addition to the effects of the above invention.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing the principle of the present invention.

FIG. 2 is an explanatory diagram showing the principle of the present invention.

FIG. 3 is an explanatory view showing an embodiment of the present invention.

FIG. 4 is an explanatory view showing an embodiment of the present invention.

FIG. 5 is an explanatory view showing an embodiment of the present invention.

FIG. 6 is an explanatory view showing an embodiment of the present invention.

FIG. 7 is an explanatory view showing an embodiment of the present invention.

FIG. 8 is an explanatory view showing a specific embodiment of the present invention.

FIG. 9 is an explanatory view showing another specific embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Honeycomb catalyst body, 2 ... Gas flow path, 3 ... Cut part.

Claims (5)

[Claims] 1. A honeycomb catalyst having a plurality of parallel gas flow paths, wherein a cut portion is provided so as to cross the gas flow paths. 2. The honeycomb catalyst according to claim 1, wherein a plurality of the cut portions are provided, and an interval between the cut portions is 300 mm or less. 3. The width of the cut portion in the gas flow direction is:
The honeycomb catalyst according to claim 1 or 2, wherein the honeycomb catalyst has at least 1/3 of a hydraulic diameter of the gas passage. 4. The projection area of the cut portion on a plane perpendicular to the gas flow path is not more than の of a catalyst cross-sectional area orthogonal to the gas flow path. 4. The honeycomb catalyst according to any one of the above items 3. 5. The honeycomb catalyst according to claim 1, wherein the honeycomb catalyst is an exhaust gas denitration honeycomb catalyst.