JP2002191986A - Catalyst structure for cleaning exhaust gas and metal lath plate used in formation thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst structure for cleaning exhaust gas using a metal lath plate as reticulated matter, preventing the deformation of gas flow channels caused by the curving of the metal lath plate to keep high catalytic contact efficiency. SOLUTION: In the catalyst structure obtained by alternately laminating a large number of catalyst bodies, each of which is molded into a staircase shape, a corrugated shape or a shape having a U-shaped cross section by alternately bending a flat plate-shaped catalyst in opposite directions, and flat plate- shaped metal laths 2 to house them in a unit frame, both ends on the side of the contact parts of the flat plateshaped laths 2 with the unit frame are bent by the same length as a catalyst pitch 9 to form lap widths 6 and the end parts of the lap widths 6 are arranged so as to respectively come into contact with the adjacent flat plate-shaped metal laths 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst structure for purifying exhaust gas and a metal lath plate used for forming the same, and more particularly to a method for efficiently reducing nitrogen oxides (hereinafter referred to as NOx) in exhaust gas with ammonia (NH ₃ ). The present invention relates to an exhaust gas purifying catalyst structure using a plate-like catalyst and a metal lath plate used for forming the same.

[0002]

2. Description of the Related Art NO in smoke exhausted from power plants and the like
x is a causative substance such as acid rain, and as an effective treatment method there is known a flue gas denitration method of performing selective catalytic reduction using NH ₃ as a reducing agent, and is widely used mainly in thermal power plants. Have been. The denitration catalyst is usually formed into a honeycomb shape, a plate shape or the like, and various production methods have been proposed. Among them, expanded metal or woven or non-woven fabric made of ceramic fiber, which has been subjected to aluminum spraying after metal lath processing of a thin metal plate, is used as a substrate, and a catalyst component is applied thereto.
A plate-shaped catalyst obtained by pressing is processed into, for example, a corrugated element, and a plurality of sheets are laminated to form a catalyst structure, which has excellent ventilation loss and is less likely to be blocked by dust and coal combustion ash. It is widely used in denitration equipment for thermal power generation boiler exhaust gas. Japanese Patent Application Laid-Open Nos. 54-79188 and 59-73053, for example, relate to such prior art.

Further, a catalyst structure in which a catalyst body formed in a stepped or corrugated shape and a mesh material such as a flat woven fabric or a metal plate having a large number of holes penetrating the front and back surfaces is alternately laminated,
By disturbing the gas flow through the mesh openings, the contact between the processing gas and the catalyst is promoted, the reaction rate is dramatically improved, and high catalyst performance is obtained. There is an advantage that it can be simplified. Regarding such prior art, for example, International Publication No. WO99
/ 24165.

[0004] In recent years, efforts have been made in many fields to reduce the material cost and the ventilation loss by reducing the thickness of the catalyst in order to improve the efficiency of the exhaust gas denitration apparatus. In the field of denitrification of flue gas from coal-fired boilers, which used a catalyst with a large distance between catalyst bodies (hereinafter referred to as catalyst pitch) at a low gas flow rate, the gas pitch was increased and the catalyst pitch was reduced. The demand for compact denitration equipment is increasing.

FIGS. 5A and 5B are explanatory views showing such a catalyst structure having a narrow catalyst pitch. In the figure, the catalyst structure 3 is obtained by alternately stacking the catalyst bodies 1 and the meshes 2 and matches the recent trend described above. The U.S. denitration catalyst market is 199
It is considered that the demand for HRSG catalysts will increase year by year on the contrary, and the demand for denitration catalysts will increase by about 40% in 2004.
There is a prospect that it will account for. On the other hand, worldwide
As a catalyst for RSG, a honeycomb catalyst having a 2.7 mm pitch has been put into practical use from around 1997, and a 2.3 mm honeycomb has recently appeared in recent years.

[0006]

However, in the above-mentioned prior art, when a metal lath plate is used as a mesh,
There were the following problems. That is, due to an error in the step width in the course of lath processing, the metal lath plate is
However, there is a problem that the bending in the direction indicated by reference numeral 7 remains.
When a large number of catalyst bodies are stacked via a metal lath plate to form a catalyst structure, the bending direction of the metal lath plate is usually
It is arranged so as to coincide with the gas flow direction of the catalyst structure. For this reason, in a catalyst structure using a metal lath plate as a mesh, the curvature of the metal lath plate remains in the gas flow direction as shown in FIG. The flow path shape is easily deformed.
When a shearing force is applied in a direction 8 perpendicular to the bending direction 7, the metal lath is easily cut.

When the catalyst pitch is large, the curvature of the metal lath plate has almost no effect on the catalytic activity.
When the pitch of the catalyst body becomes narrower and the structure becomes a 2-3 mm pitch structure, slight deformation of the metal lath plate causes the gas flow path shape to become non-uniform, causing gas blow-through and reducing catalyst activity. Become. When metal is used for both the catalyst substrate and the mesh, the weight of the lower portion of the catalyst structure increases due to the increase in the number of stacked layers due to the narrower pitch, and the pitch on the lower side decreases while the pitch on the upper side decreases. The pitch is widened, which causes a non-uniform gas flow, which causes a problem that catalyst activity is reduced. As described above, when the pitch of the catalyst laminate is reduced, a new problem arises in that the catalyst performance is reduced due to gas blow-through that has not occurred when the catalyst pitch is wide.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to prevent a gas flow path from being deformed due to the curvature of the metal lath plate in a catalyst structure using a metal lath plate as a mesh, thereby providing a high catalyst. An object of the present invention is to provide an exhaust gas purifying catalyst structure capable of maintaining contact efficiency and a metal lath plate used for forming the same.

[0009]

Means for Solving the Problems To solve the above-mentioned problems, the present inventor has proposed a method of forming a gas in a catalyst structure having a narrow catalyst pitch by alternately stacking a large number of catalyst bodies and reticulated objects and housing the unit frame. As a result of intensive studies on the relationship between the deformation of the flow path shape and the curvature of the metal lath plate as a mesh, both ends of the metal lath plate on the contact side with the unit frame are the same as the width of the distance between the catalyst bodies (catalyst pitch). By bending by the length to form an overlap margin, and laminating so that the end of the overlap margin is in contact with the adjacent metal lath plate, the curvature of the metal lath plate is corrected, and the gas flow path is not deformed. It was found that the gas blow-through disappeared and the catalyst contact efficiency as a whole catalyst structure improved.
The present invention has been reached.

That is, the invention claimed in the present application is as follows. (1) a catalyst body obtained by alternately bending a plate-like catalyst in the opposite direction to form a step-like, corrugated, or U-shaped cross section;
In a catalyst structure in which a large number of flat metal laths are alternately stacked and accommodated in a unit frame, both ends of the flat metal lath on the contact portion side with the unit frame are the same length as the distance between the catalyst bodies. A catalyst structure for purifying exhaust gas, characterized in that it is bent to form an overlap margin, and the ends of the overlap margin are arranged so as to be in contact with adjacent flat metal laths. (2) The exhaust gas purifying catalyst structure according to (1), wherein a catalyst component comprising at least one oxide of titanium, vanadium, molybdenum, and tungsten is carried on the surface of the flat metal lath. body.

(3) A large number of catalyst bodies formed by alternately bending plate-shaped catalysts in the opposite direction to form a step-like, corrugated or U-shaped cross section are stacked, and housed in a unit frame to form a catalyst structure. When forming, it is a flat metal lath disposed between the catalyst bodies, both ends of the contact portion side with the unit frame are bent by the same length as the interval between the catalyst bodies, the tip ends respectively The metal lath plate used for forming the exhaust gas purifying catalyst structure according to the above (1) or (2), wherein an overlap margin is provided so as to contact an adjacent flat metal lath.

[0012]

1A to 1D are explanatory views schematically showing a cross section of an embodiment of the present invention. FIG. 1 shows a catalyst structure in which a large number of catalyst bodies 1 having a step portion and a flat plate portion are laminated via a flat metal lath (metal lath plate) 2, and a unit frame of the metal lath plate 2 in this catalyst structure is shown. (Not shown), an overlap portion 6 formed by bending the catalyst pitch (interval between the catalyst bodies 1) 9 by the same length as the length of the catalyst pitch (interval between the catalyst bodies 1) 9 is provided. The ends are arranged so as to be in contact with the adjacent metal lath plates 2 respectively.

According to this embodiment, the bending of the metal lath in the gas flow direction is corrected by bending both ends of the metal lath plate 2 on the contact portion side with the catalyst unit frame to provide the overlap margin 6 having a predetermined height. Is done. Further, the length of the overlap margin 6 is set to be the same as the catalyst pitch 9, and the end of the overlap margin 6 is arranged so as to be in contact with the adjacent metal lath plate 2, thereby increasing the rigidity of the entire catalyst structure. In addition, the catalyst pitch does not become uneven at the upper and lower portions of the catalyst structure. That is, the cross section of the gas flow path is not deformed,
Prevention of gas drift improves catalyst reaction efficiency.

In the present invention, for example, a catalyst component is applied to a metal substrate having a large number of through-holes penetrating on the front and back sides so as to fill the through-holes (hereinafter, also referred to as a mesh), and is pressed, for example, square or rectangular. Are bent at predetermined intervals in a direction parallel to the pair of sides, for example, in a stepped shape, a corrugated shape, or a U-shape. FIGS. 6A to 6E show examples of the cross-sectional shape of the catalyst body applied to the present invention. As the catalyst component, for example, one containing titanium oxide as a main component and an active component such as vanadium (V), molybdenum (Mo), or tungsten (W) is used. In addition, well-known means such as addition of a binder may be used in combination to obtain a catalyst.

In the present invention, as the metal lath plate,
For example, a steel plate subjected to metal lath processing is used. It is preferable that the surface of the metal lath plate is supported and covered with, for example, a catalyst having the same component as the catalyst component used in the catalyst body so as not to block the through holes of the network. The catalyst component can be rolled or applied by rolling or pressing. The bending direction at the time of forming the overlap margin by bending both ends of the metal lath plate on the contact portion side with the unit frame may be the same direction at both ends or may be opposite to each other. FIG. 2 (a), (b)
FIG. 3 is a view showing a cross section of a metal lath plate used for forming the catalyst structure of the present invention, which is perpendicular to the exhaust gas flow direction. In the figure, a metal lath plate 2 (a) having both ends bent in the same direction to provide an overlapping margin 6 and a metal lath plate 2 having both ends bent in opposite directions to provide an overlapping margin 6 (b) are shown. I have.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described. Example 1 Specific surface area 270m^Two/ g titanium oxide 1.2kg molybdenum
Ammonium ((NH _Four)₆・ Mo₇O_{twenty four}・ 4H_TwoO)
0.25 kg, ammonium metavanadate 0.23 kg,
And 0.3 kg of oxalic acid and water, and kneaded.
And a kaolin-based inorganic fiber (brand name
Wool) 15% by weight, and further kneaded to obtain a water 3
A paste of 0.5% was obtained.

The above paste is applied to the openings of a metal lath base material having a thickness of 0.64 mm and a porosity of 74.0% and the surface of the base material prepared using a pair of rolling rollers. After being molded into the cross-sectional shape of FIG.
It was calcined at 00 ° C. for 2 hours to obtain a catalyst having a width of 498 mm, a length of 500 mm, and a plate thickness of 0.66 mm. On the other hand, the specific surface area is about 270
Ammonium molybdate in 1.2 kg of m ² / g titanium oxide
_{((NH 4) 6 · Mo} 7 O 24 · 4H 2 O) and 0.25 kg, ammonium metavanadate 0.23 kg, and oxalic 0.
After adding water to 3 kg and kneading to make a clay-like material, it was formed into a 3φ column by an extrusion granulator, and the formed body was dried.
The mixture was calcined at 550 ° C. for 2 hours and pulverized with a fine pulverizer to obtain a catalyst powder having a particle size of 1 μm or less having 60% or more. Water was added to the obtained powder to prepare a catalyst slurry having a solid content of 52%.

On the other hand, a steel plate having a thickness of 0.2 mm was processed to obtain a degreased metal lath plate having a width of 506 mm, a length of 500 mm and a thickness of 0.24 mm. This metal lath plate is immersed in the above catalyst slurry, and air is applied to completely open the openings, and 350 ° C.
After baking for 2 hours, the sheet was bent by 3 mm from both ends in the width direction to form an overlap margin as shown in FIG.
A 44 mm metal lath plate was obtained. The obtained catalyst bodies and metal lath plates were alternately laminated so that the outer surface of the overlapping portion of the metal lath plates was in contact with the catalyst unit frame, to obtain a catalyst structure having the structure shown in FIG.

Comparative Example 1 A catalyst structure was formed in the same manner as in Example 1 except that the width of the catalyst body was 500 mm and the metal lath plate was a flat plate having a width of 500 mm without overlapping. )reference). The catalyst structures of Example 1 and Comparative Example 1 were subjected to a denitration performance test under the conditions shown in Table 1, and the results are shown in Table 2. In the table,
The activity ratio is the ratio of the volume-based overall reaction rate constant, and the value of Example 1 was set to 1.

[0020]

[Table 1]

[0021]

[Table 2] In Table 2, it can be seen that Comparative Example 1 has lower catalytic activity than Example 1. This is presumably because the metal lath plate of Comparative Example 1 was not provided with an overlap margin at the end of the metal lath plate in contact with the unit frame, and gas was blown through due to the curvature of the metal lath plate. On the other hand, in the first embodiment,
It is considered that the metal lath plate was provided with overlapping margins at both ends to correct the curvature of the metal lath plate, eliminate gas blow-through due to deformation of the gas flow path shape, improve contact efficiency, and show high catalytic activity. Can be

Example 2 A catalyst was obtained in the same manner as in Example 1 except that the cross-sectional shape was changed to the shape shown in FIG. 5 (a).
A metal lath plate was prepared in the same manner as in Example 1 except that the directions were different at both ends as shown in (d), and the obtained catalyst body and the metal lath plate were replaced with the catalyst lath. The catalyst structure having the structure shown in FIG. In this embodiment, the same effect as in the first embodiment was obtained.

[0023]

According to the invention described in claim 1 of the present application,
Since the gas blow-through caused by the curvature unique to the metal lath, particularly the curvature in the gas flow direction, can be prevented, and the catalyst pitch and the gas flow path cross-sectional shape of the entire catalyst structure can be kept uniform, the rigidity of the catalyst structure is reduced. As a result, the contact efficiency between the gas and the catalyst is improved, and high catalytic activity can be exhibited.

According to the invention as set forth in claim 2 of the present application, in addition to the effects of the above-described invention, a higher catalytic activity can be exhibited as the whole catalyst structure. According to the invention as set forth in claim 3 of the present application, a metal lath plate used when forming a catalyst structure by laminating a large number of catalyst bodies, which does not curve in the gas flow direction and deforms the gas flow path cross section. The result is a metal lath plate that does not have any problem.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross section of an embodiment of an exhaust gas purifying catalyst structure according to the present invention.

FIG. 2 is a diagram showing a cross section of the metal lath plate of the present invention.

FIG. 3 is an explanatory diagram showing a problem of the related art.

FIG. 4 is a diagram showing a metal lath plate after lath processing.

FIG. 5 is an explanatory view showing an example of lamination of a catalyst body and a mesh.

FIG. 6 is an explanatory diagram showing a cross-sectional shape of a catalyst body applied to a catalyst structure.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Catalyst body, 2 ... Net (metal lath plate), 3 ... Catalyst structure, 5 ... Arrow indicating gas flow direction, 6 ... Overlap, 7 ...
Arrows indicating the direction of bending of the lath, 8... Arrows indicating a direction perpendicular to the direction of reference numeral 7, 9...

Continuing on the front page (72) Inventor Koichi Yokoyama 3-36 Takara-cho, Kure-shi, Hiroshima F-term inside Babcock Hitachi Kure Laboratory (reference) 3G091 AA06 BA14 GA03 GB01W GB01X GB10W 4D048 AA06 BA07X BA07Y BA23X BA23Y BA26X BA26Y BA27Y BA39X BA39Y BA41X BA41Y BB04 BB07 CA06 4G069 AA01 AA03 AA11 BA17 BB02A BB02B BB04A BB04B BC54A BC54B BC59A BC59B BC60B CA02 CA03 CA13 DA05 EA12 EA25 EA27 EE06

Claims (3)

[Claims] A unit frame formed by alternately stacking a large number of plate-shaped metal laths and a catalyst body formed by alternately bending a plate-shaped catalyst in the opposite direction to form a stepped, corrugated or U-shaped cross section. In the catalyst structure accommodated in, both ends of the plate-shaped metal lath on the side of the contact portion with the unit frame are bent by the same length as the interval between the catalyst bodies to form an overlap margin,
An exhaust gas purifying catalyst structure, wherein an end of the overlap margin is arranged to be in contact with an adjacent flat metal lath. 2. The exhaust gas purifying catalyst structure according to claim 1, wherein a catalyst component comprising at least one oxide of titanium, vanadium, molybdenum and tungsten is carried on the surface of the flat metal lath. body. 3. A catalyst structure is formed by stacking a large number of catalyst bodies which are formed by bending a plate-like catalyst alternately in the opposite direction to form a step-like, corrugated, or U-shaped cross section, and housed in a unit frame. When doing so, a flat metal lath disposed between the catalyst bodies, both ends of the contact portion side with the unit frame are bent by the same length as the interval between the catalyst bodies, and the tip ends are adjacent to each other. 3. An overlapping margin is provided so as to come into contact with a flat metal lath to be formed.
7. A metal lath plate used for forming the exhaust gas purifying catalyst structure according to the above item.