JP2010253366A - Catalytic structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalytic structure which has a small draft loss, is made compact, has high performance and can be prevented from being clogged with dust. <P>SOLUTION: The catalytic structure is obtained by layering a plurality of plate-like catalysts, on the surface of each of which a component having catalytic activity is deposited, on one another, has a flow path between the adjacent plate-like catalysts and is characterized in that the catalytic structure is divided into two or more stages with respect to the flow direction of gas and the plate-like catalyst-layered directions of the adjacent divided stages are rotated alternately by 90°. It is better in order to exhibit the maximum performance of the catalytic structure when used for cleaning exhaust gas that the ratio L/d of the length L of the plate-like catalyst to the pitch width d of the layered plate-like catalysts is <100 and the ratio s/d of the space s between the adjacent ones of the layered plate-like catalysts to the pitch width d is <5. As a result, the catalytic structure can exhibit such an effect that the catalytic structure has the small draft loss, is made compact, has high performance and can be prevented from being clogged with dust. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a catalyst structure in which plate-like catalysts used in a denitration apparatus for removing nitrogen oxides in boiler exhaust gas are laminated.

Nitrogen oxides (NOx) in smoke emitted from power plants, various factories, automobiles, etc. are the causative substances of photochemical smog and acid rain. As an effective removal method, ammonia (NH ₃ ) is reduced. The flue gas denitration method using selective catalytic reduction as an agent is widely used mainly in thermal power plants. In consideration of activity and durability, a titanium oxide (TiO ₂ ) -based catalyst containing vanadium (V), molybdenum (Mo) or tungsten (W) as an active component is mainly used as the catalyst.

  The denitration catalyst is usually formed into a honeycomb shape or a plate shape, and various manufacturing methods have been invented and devised. In particular, a metal thin plate as shown in FIG. 1 is subjected to metal lath processing, and the catalyst component is pasted. Then, the protrusion 2 having a plurality of strip-shaped protrusions is formed between the flat portions 3 with the same shape cross section in the gas flow direction. A catalyst unit 4 in which a single plate-like catalyst (hereinafter sometimes referred to as a catalyst element) 1 obtained by molding into shapes having parallel and equal intervals is laminated as shown in FIG. By incorporating and laminating in the unit frame (casing) 6 so that the longitudinal direction of the ridge 2 is along the gas flow direction, the catalyst structure 4 is formed, so that the ventilation pressure loss is small, and dust or coal combustion ash is used. It has excellent features such as being hard to be blocked, and is currently used in many denitration devices for boiler exhaust gas for thermal power generation.

  On the other hand, many inventions and devices have been made in the catalyst filling method, and in particular, the catalyst element 1 shown in FIG. 1 has the protrusions of the catalyst elements 1 and 1 arranged adjacent to each other so that the gas flow in the gas flow path is disturbed. As shown in FIG. 4, a catalyst structure 4 obtained by alternately incorporating the portions 2 and 2 into the unit frame (casing) 6 in a perpendicular direction is formed from one side of the unit frame (casing) 6. In the method of introducing gas from a direction orthogonal to the ridge 2 (Japanese Patent Laid-Open No. 55-152552), the gas flow in the flow path is caused by the ridge 2 of the catalyst element 1 orthogonal to the gas flow. It is an excellent method that can be disturbed to obtain a high denitration rate.

JP-A-55-152552

The catalyst structure shown in FIGS. 3 and 4 has the following two problems in achieving a highly efficient and compact apparatus.
The first problem is that when the catalyst element 1 is elongated, the activity of the catalyst per unit area is reduced. This mechanism is as follows.

  That is, it is known that the overall mass transfer coefficient k, which is the performance of the catalyst, is determined by the catalyst surface reaction rate coefficient kw, which is the true denitration performance on the catalyst surface, and the mass transfer coefficient kf, where the reacting gas moves to the catalyst surface. And is represented by the following equation.

k = 1 / (1 / kf + 1 / kw) (1)
Where k: overall mass transfer coefficient (m / h)
kf: Mass transfer coefficient (m / h)
kw: catalyst surface reaction rate coefficient (m / h)
In the above equation (1), when the length of the catalyst element 1 in the gas flow direction becomes longer, the catalyst surface reaction rate constant kw becomes constant, but a boundary layer is developed by the flow on the catalyst surface, and the boundary becomes smaller as it goes downstream. The layer becomes thicker and becomes a resistor from the surface of mass transfer, and the mass transfer coefficient kf becomes small. Therefore, the local overall mass transfer coefficient k decreases as the denitration reaction rate goes downstream. As a result, the average overall mass transfer coefficient averaged in the flow direction becomes larger when the catalyst is shorter than when it is longer.

  The second problem is that the filling method of FIG. 3 increases the pitch between the catalyst elements 1 and 1 and optimizes the length in the gas flow path direction in the catalyst structure 4 to reduce the ventilation loss and the catalyst performance. While the catalyst structure 4 in FIG. 4 can be set freely, the ventilation loss and the degree of freedom to change the performance are small. That is, in the catalyst structure 4 of FIG. 4 in which the protrusions 2 of the catalyst elements 1 having the same shape are laminated so as to be alternately orthogonal to the protrusions 2 of the adjacent catalyst elements 1, the pitch between the catalyst elements 1 and 1 is set. Even if it is changed, the aperture ratio in the gas flow direction of the catalyst structure 4 does not change, so the ventilation loss does not decrease so much and the length of the catalyst structure 4 is fixed to the same size as the opening of the structure 6 and is free. It may be difficult to change.

  Of course, two types of catalyst elements 1 having different shapes can be prepared and used alternately to change the catalyst length in the gas flow direction, but the manufacturing process becomes complicated and the manufacturing cost increases. . Moreover, although the catalyst structure 4 shown in FIG. 4 exerts a great effect on clean gas containing no dust or the like, if the amount of dust is large, it may cause dust clogging.

  An object of the present invention is to provide a catalyst structure that eliminates the above-mentioned problems of the prior art, has low ventilation loss, is compact and has high performance, and can prevent clogging of dust.

The above object of the present invention is achieved by the following configuration.
That is, the invention according to claim 1 carries a component having catalytic activity on the surface, is parallel to each other to partition the flat portion and the flat portion at an interval, and is disposed on the planes on the opposite sides of the flat portion. Catalyst structure in which a plurality of identically shaped plate-like catalysts arranged alternately with strips of strip-like protrusions are stacked at intervals to form a gas flow path between adjacent plate-like catalysts A catalyst structure in which a single unit is formed, and a plurality of stages of the catalyst structure of one unit with respect to the gas flow direction are arranged by alternately rotating the stacking direction of the plate-like catalyst of each stage of the catalyst structure by 90 ° It is.

  According to a second aspect of the present invention, the plate-like catalyst is flat between a plurality of ridges provided at equal intervals parallel to each other and formed of strip-like protrusions formed along the gas flow direction. The catalyst structure according to claim 1, comprising a portion.

  In the invention according to claim 3, the length L in the gas flow direction of the plate-shaped catalyst of one unit of the catalyst structure is L / d <100 with respect to the stacking pitch width d of the plate-shaped catalyst, and each catalyst The catalyst structure according to claim 2, wherein the gap s between the steps in the gas flow direction of the structure is s / d <5 with respect to the stacking pitch width d of the plate-like catalyst.

  The gas flow path formed between the catalyst elements, which is the basic structure of the catalyst structure of the present invention, has the same cross-sectional shape in the direction perpendicular to the gas flow at any position. For example, as shown in FIG. 1, a desired gas flow path can be formed by forming a flat portion 3 and strip-shaped protrusions 2 at equal intervals in the gas flow direction of the plate-like catalyst element.

Furthermore, in order to maximize the function of the present invention, the length L in the gas flow direction of the plate catalyst is L / d <100 with respect to the stacking pitch width d.
And the gap s between the plate-like catalyst structures at each stage is s / d <5
If it is.
According to these inventions, it is possible to exhibit an effect that the ventilation loss is small, compact and high performance, and can prevent clogging of dust.

  According to the present invention, it is possible to provide a compact and high-performance catalyst structure that can prevent clogging of dust while maintaining a small ventilation loss.

It is a perspective view of the catalyst element which provided the protrusion part and flat part of this invention. It is a perspective view which shows the example which has arrange | positioned the catalyst structure of this invention 4 steps | paragraphs in the gas flow direction. It is a figure which shows a general catalyst structure. It is a figure which shows the catalyst structure which incorporated the protrusion part of the catalyst element which is a prior art in the mutually orthogonal direction. It is a figure which shows the relationship between a catalyst activity ratio and catalyst element length.

  Embodiments of the present invention will be described with reference to the drawings.

67 kg of metatitanate slurry (TiO ₂ content: 30 wt%, SO ₄ content: 8 wt%) and 2.4 kg of ammonium paramolybdate (NH ₄ ) ₆ .Mo ₇ O ₂₄ .4H ₂ O), ammonium metavanadate ( 1.28 kg of NH ₄ VO ₃ ) was added and kneaded while evaporating water using a heating kneader to obtain a paste having a water content of about 36%. This was extruded into 3 ¢ columnar shapes, granulated, dried in a fluidized bed dryer, and then calcined in the atmosphere at 250 ° C for 24 hours. The obtained granule was pulverized with a hammer mill to a particle size of 5 μm in average particle size, and used as the first component. The composition at this time is V / Mo / Ti = 4/5/91 (atomic ratio).

20 kg of the powder obtained by the above method, ₃ kg of Al ₂ O ₃ · SiO ₂ inorganic fiber and 10 kg of water were kneaded for 1 hour using a kneader to form a clay. The catalyst paste is applied to the surface of the lath and the surface of the lath by applying aluminum spray to a SUS304 metal lath substrate having a width of 500 mm and a thickness of 0.2 mm using a roller, and a thickness of about 1.0 mm. A flat catalyst having a length of 500 mm was obtained. By press-molding this catalyst, a plurality of ridges 2 having a corrugated cross section are formed at predetermined intervals on both sides of a flat catalyst as shown in FIG. 1 to obtain a catalyst element 1 composed of the ridges 2 and flat portions 3. It was. The catalyst element 1 was obtained by air drying between the flat portions 3 and then firing in the atmosphere at 550 ° C. for 2 hours.

Further, instead of ammonium paramolybdate, a predetermined amount of ammonium paratungstate (NH ₄ ) ₁₀ H ₁₀ W ₁₂ O ₇ O ₄₆ · 6H ₂ O) may be used. In addition, it cut | disconnected so that the length of the gas flow direction of each catalyst element 1 might be set to 200 mm.
The obtained catalyst elements 1 were alternately reversed and 81 sheets were laminated to form a catalyst unit 4, which was bundled by a laminated band 5 to obtain a catalyst laminated element (plate-shaped catalyst structure) 7.

  Further, the catalyst laminated element 7 was arranged in four stages in the gas flow path direction in the unit frame 6. When filling the catalyst stacking element 7 into the unit frame 6, the stacking direction of the catalyst stacking element 7 at each stage was alternately rotated by 90 ° and fixed as shown in FIG. 2. The catalyst laminated element 7 in the unit frame 6 is air-dried and then fired, and the catalyst element 1 in each catalyst laminated element 7 has a lamination pitch d = 5.7 mm and a length L = 200 mm. Four stages were arranged in the flow direction with a gap s = 0 mm.

(Comparative Example 1)
A catalyst element 1 having the same catalyst composition as in Example 1 and a length L = 800 mm in the gas flow direction obtained by the same manufacturing method is laminated at a lamination pitch d = 5.7 mm to obtain an integrated catalyst structure. Obtained.

The catalyst bodies of Example 1 and Comparative Example were made to have a cross section of 150 mm square in the direction perpendicular to the gas flow, the denitration performance was evaluated under the conditions shown in Table 1, and the results obtained are shown in Table 2.

表２から明らかなように、触媒構造体８００ｍｍを流れ方向に４分割することにより、通風圧損はほぼ同等で、反応速度で約４０％向上させることができた。

As is clear from Table 2, by dividing the 800 mm catalyst structure into four parts in the flow direction, the ventilation pressure loss was almost the same, and the reaction rate could be improved by about 40%.

The mechanism of the effect will be described using the embodiment shown in FIGS.
The exhaust gas flows into the catalyst unit 4 and flows along the plurality of catalyst elements 1 constituting the catalyst unit 4. At this time, NOx contained in the exhaust gas is reduced to N ₂ and H ₂ O by NH ₃ gas injected upstream on the catalyst surface. As described above, it is known that the catalyst performance is determined by the catalyst surface reaction rate and the mass transfer rate. In this case, when the length of the catalyst element 1 in the gas flow direction becomes longer, the catalyst surface reaction rate of the catalyst itself does not change, but a boundary layer due to the flow on the catalyst surface develops and becomes thicker toward the downstream side. In terms of mass transfer speed, it becomes a resistor. That is, due to the development of the boundary layer, unreacted NH ₃ and NOx are hardly supplied from the mainstream gas near the catalyst surface, and the activity per unit area is reduced.

As a method for improving the performance of the catalytic reaction, (a) a method of disturbing the flow so as not to develop the boundary layer, (b) a front edge of the catalytic element 1 where the catalyst before the boundary layer develops first contacts the gas A method to utilize is conceivable.
Regarding (a), as described in the prior art, as disclosed in Japanese Patent Application Laid-Open No. 55-152552, the activity per unit area is improved, but the problem of increased ventilation pressure loss is unavoidable. In addition, when applied to a gas containing dust, dust clogging or a region with a high local flow velocity may occur, resulting in powder wear. On the other hand, (b) is achieved by making the flow path length as short as possible.

FIG. 5 shows the effect of length on the overall reaction rate of the catalyst.
The catalyst element 1 of Example 1 (lamination pitch d = 5.7 mm, length L = 200 mm) is compared with the catalyst element 1 in which the length L is changed to 550 mm and 800 mm, respectively. As is apparent from this figure, it is understood that the activity per unit area increases as the length of the catalyst element 1 in the gas flow direction is shorter (this is referred to as shortening). What is important here is the stacking gap of the shortened catalyst elements 1. In general, L / d> 5 is required until the boundary layer developed from the downstream end of the catalytic element 1 is completely rectified. By increasing this gap, the activity per unit area of the catalyst element 1 is improved, but the space that is not filled with the catalyst element 1 is increased, so that the activity per unit volume is reduced, and the catalyst structure. It becomes an obstacle to downsizing.

  Therefore, as a result of various studies in the present invention, it is possible to eliminate the boundary layer without providing a rectifying space by rotating the stacking direction by 90 ° in each stage of the catalyst stacking element 7 provided in four stages in the gas flow direction. I found it. That is, by introducing the short unit in which the velocity distribution and the concentration distribution are generated in the stacking direction of the catalyst element 1 and introducing it into the catalyst stacking element 7 whose stacking direction is rotated by 90 °, the vicinity of the inlet of the catalyst stacking element 7 in each stage It will be rectified in a short time. Thereby, the activity per unit area and the activity per unit volume of the catalyst element 1 can be made compatible.

  The length of the catalyst element 1 in the gas flow direction is desirably as short as possible, and L / d <100 is desirable. On the other hand, if it is too short, it will lead to a decrease in productivity, and an area of 5 <L / d <100 that can ensure productivity is recommended. Further, regarding the gap s between the catalyst laminated elements 7, s / d <5 is allowable in terms of space efficiency and structural strength, but one unit of the catalyst structure 4 in which the catalyst elements 1 are laminated is in contact. Things are most desirable.

  When the catalyst structure of the present invention is used, the catalyst volume and the amount of catalyst can be surely reduced, and there is a possibility of reducing the amount of raw materials used and the product weight.

DESCRIPTION OF SYMBOLS 1 Catalyst element 2 Projection part 3 Flat part 4 Catalyst unit 5 Lamination band 6 Unit frame 7 Catalyst lamination element

Claims (3)

  A protrusion having a strip-like protrusion disposed on a plane parallel to each other and carrying a component having catalytic activity on the surface, parallel to each other and partitioning the flat portion with a space therebetween; A plurality of identically shaped plate-like catalysts arranged alternately are stacked at intervals and a catalyst structure in which a gas flow path is formed between adjacent plate-like catalysts is taken as one unit in the gas flow direction. On the other hand, a catalyst structure characterized in that a plurality of stages of the catalyst structure of one unit are arranged by alternately rotating the stacking direction of the plate-like catalyst of each stage of the catalyst structure by 90 °.   The plate-like catalyst is composed of a plurality of ridges provided at equal intervals parallel to each other and formed of strip-like protrusions formed along the gas flow direction, and a flat part between adjacent ridges. The catalyst structure according to claim 1.   The length L in the gas flow direction of the plate-shaped catalyst of one unit of the catalyst structure is L / d <100 with respect to the stacking pitch width d of the plate-shaped catalyst. The catalyst structure according to claim 2, wherein a gap s between steps is s / d <5 with respect to a stacking pitch width d of the plate-like catalyst.

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