JPS6128377B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> This invention relates to the structure of a plate-shaped catalyst for purifying exhaust gas. <Prior art and its problems> Recently, from the viewpoint of pollution prevention, it has been desired to purify exhaust gas from various combustion equipment. In particular, various measures have been taken to remove nitrogen oxides (hereinafter referred to as NOX) from exhaust gas. One method is to spray a reducing agent such as NH ₃ (ammonia) into the exhaust gas, and then guide the exhaust gas to a denitrification catalyst device that has a built-in catalyst layer to selectively react NOx and NH ₃ to convert N ₂ and H A method has been adopted to make NOx harmless by converting it to ₂ O. In this case, when the exhaust gas contains soot and dust, there is a problem in that the dust accumulates on the catalyst device and deteriorates its function. Therefore, there is a demand for a device with less resistance to the exhaust gas flow, and a denitration device installed parallel to the plate-shaped exhaust gas flow is used. However, the plate-shaped catalyst has a problem in that the adhesion between the catalyst and the substrate is weak, so that the catalyst easily peels off and falls off. This is due to not only the adhesion but also the repeated expansion and contraction of the coated catalyst layer and substrate due to changes in exhaust gas temperature, which causes cracks in the catalyst layer and further promotes peeling off. Also, measures have been taken to use wire mesh as the substrate, but there are problems such as insufficient rigidity, processing of the mounting frame, and troublesome installation of the wire mesh. <Objective of the Invention> The purpose of the present invention is to solve such problems and to propose a structure of a plate-shaped catalyst for purifying exhaust gas, which has a strong adhesion of the catalyst and is easy to manufacture. <Summary of Means> In short, the present invention provides a plate-shaped catalyst for exhaust gas purification in which a catalyst is attached to a substrate, in which a catalyst kneaded with a heat-resistant fibrous material is applied to both surfaces of the metal substrate having a large number of communicating holes. It is characterized by a plate-shaped catalyst that is deposited on the entire surface. <Specific Example> This invention will be explained below with reference to the drawings. Figure 1 is
A cross section in which a plurality of unit catalysts 2 are arranged in rows 3 across a duct 1 through which exhaust gas containing NOx flows, and these rows are provided in multiple stages in a duct 1 forming a denitrification device along the flow of the exhaust gas. It is a front view. The unit catalyst 2 is composed of a plurality of plate-shaped catalysts 2a arranged side by side, and this plate-shaped catalyst 2a (shown in FIG. 2) is attached to a substrate 4.
The catalyst 5 is entirely adhered to both sides of the plate. In this way, there is less resistance to gas flow,
Moreover, there is little chance of dust accumulation, and the catalyst has a chance to fully demonstrate its function. However, in the invention, the thickness of the catalyst layer is made as thin as possible, and the adhesion to the substrate is strong. This is because the effect of promoting the reaction of the catalyst on exhaust gas is limited to the surface area of the catalyst and also because the weight of the unit catalyst is to be made as light as possible. On the other hand, as a catalyst, ore powder, vanadium, titanium, etc.
Powder particles of iron alloy are used, but they do not have adhesive strength on their own, and when they are kneaded with a binder and applied thinly to a substrate, or immersed in a kneaded solution, their retention is mainly mechanical. Since it is based on force, the adhesion force is weak if it is simply attached to a smooth metal surface. In addition, the exhaust gas temperature is 300 to 350°C, and there is repeated thermal expansion and contraction due to load fluctuations and startup/stopping of boilers, etc., resulting in cracks and peeling. The shape of the substrate 4 of the plate-shaped catalyst in this invention is not limited to the flat plate shown in FIG.
It includes a bent plate as shown in the figure, and also includes a case where a flat plate is rolled and welded to form a cylindrical shape to form a multi-tube structure. It goes without saying that wire mesh having appropriate rigidity can also be used as the substrate. In addition, in order to form a catalyst layer with good adhesion to a substrate having a large number of communication holes, this invention uses a catalyst and a heat-resistant fibrous material such as inorganic fiber, rock wool, chestnut burr-like microscopic bodies, and ultrafine metal wire. It is proposed to use a mixture of cut pieces and the like. As a result, the fibrous material can be made fine and uniformly dispersed in the catalyst, and the tensile strength can be improved. Furthermore, by attaching the catalyst to a substrate that has a large number of communicating holes, the difference in elongation between the elongation of the catalyst material due to heat and the elongation of the catalyst becomes smaller, and the cracks in the catalyst that occur due to this become smaller cracks depending on the number of communicating holes. It can be distributed. An embodiment of this invention is shown in FIGS. 3, 4, and 7.
An example will be explained in which the expanded metal shown in the figure is used as a substrate. Expanded metal is a mesh-like thin metal plate that is formed by making short cuts in a staggered arrangement on a thin metal plate and applying a tensile force in a direction perpendicular to the cuts. In its plan view, it consists of metal strips 4a forming a mesh and voids 4b, and as shown in FIG. 4, which is a sectional view taken along line A-A, 4a is inclined with respect to the horizontal. When the substrate is made of expanded metal, the combination of the void portion 4b serving as the communication hole and the metal strip portion 4a protruding at an angle provides resistance to the vibration of the plate surface due to the small eddy current caused by the gas flow of the plate-shaped catalyst. Therefore, there is little chance of the catalyst peeling off due to vibration, and the catalyst can be attached to the substrate reliably and stably. In addition, the force that holds the catalyst on the substrate is mainly caused by the mechanical holding state of the substrate surface, so forming a rough surface with minute open cavities by spraying metal on the surface of the substrate is effective for the catalyst. The effect of preventing peeling off and falling off is further increased. Figure 7 shows SUS304 (13Cr) proposed by the inventors.
This is a microscopically enlarged photographic sketch of the cross-section of the surface of expanded metal when SUS304 is thermally sprayed onto (steel). Metal microparticles 8 formed by molten metal droplets of SUS304 adhere to the SUS304 substrate 4a and grow to form a metallicon layer, and furthermore, form an irregular rough surface and minute open cavities 9, and furthermore, form microscopic particles of 10 μ class on the inner surface. It can be seen that extremely small metal particles 10 made up of metal droplets are attached. Therefore, the catalyst and the heat-resistant fiber 11
When mixed and attached to the substrate, the fibers not only get caught on these ultra-fine metal particles 10, but also the fibers 11 and the catalyst become integrated and solidify inside the micro open cavities 9, making them tough and difficult to escape from, and the shape of the cavities changes. Since it is irregular, the retention of the catalyst layer is further strengthened. On the other hand, even if a crack occurs in the catalyst layer due to repeated thermal expansion and contraction, the catalyst is connected by the fibers 11 and will not fall off. There is no problem in using a mixture of fine fibers and slightly long fibers. The fibers may be of any material as long as they are heat resistant and corrosion resistant, but the material may be cut from metal wire with capillary dimensions. However, experimental results show that inorganic fibers are better because they are easier to obtain and use, and when glass fiber cloth cut into 5-10 mm squares (for example, Kao Wool) is kneaded with a catalyst, it breaks down into cellulose. It becomes invisible and can be mixed in the catalyst layer. The amount of Kao wool mixed in is about 0.1 to 10% (by weight) to produce a sufficient effect and almost no peeling. It was also confirmed that the inclusion of this fiber increased the strength of the catalyst layer and also produced an anti-wear effect. Regarding the heat resistance of the fiber, it is sufficient that the fiber can withstand about 500°C since the temperature condition of the exhaust gas is 300 to 350°C, and is chemically resistant to acids.
Also, depending on the temperature conditions, a temperature below 500℃ can be selected. <Test Example> In order to confirm the effects of the present invention, the following tests were conducted. (1) Catalyst used in the test The catalyst was first formed by adding water to a mixture of 200 mesh powder of titanium oxide (TiO ₂ ) and molybdenum oxide (MoO ₃ ) with a weight ratio of Ti/Mo of approximately 9/1. is added and kneaded using a kneader, and then a heat-resistant fibrous material (kao wool) is added and further kneaded to produce a catalyst paste. Next, apply this paste to the molten metal expanded metal substrate (shown in Figures 3, 4, and 7) such as SUS304 material using a pressure roller, and then use a press to form the chevron-shaped ribs shown in Figure 5. Form into a shape.
This is dried and then calcined to form a plate-shaped catalyst. (2) Test for abrasion caused by exhaust gas In order to perform the experiment under the same conditions as in the case of the actual machine, multiple plate-shaped catalysts were formed into a box shape with a pitch of 6 mm as shown in Figure 8, and the unit was surrounded by a mounting frame. A catalyst box 12 was used. This box-shaped unit catalyst box was placed in multiple stages in a duct through which exhaust gas flows under the following conditions, and its progress was observed. Exhaust gas conditions: (a) Type of exhaust gas: Coal combustion exhaust gas (b) Dust concentration: 15-20g/Nm ³ (c) Temperature: 350℃ (d) Gas flow rate: 4m/s, 6m/s, 8m/s (e) Time 2000hr Table 1 shows the wear rate of the coats with and without Kao wool. Here, the wear rate refers to the following. Wear rate (%) = Catalyst weight before test (Kg/ ^m2 ) - Catalyst weight after test (Kg/ ^m2 )/Amount of catalyst component per ^1m2 before test (Kg/ ^m2 ) x 100 From this table It can be seen that the catalyst containing Kaowool has a remarkable effect.

[Table] (3) Mechanical strength test As a peeling rate test to confirm mechanical strength,
When a plate-shaped catalyst was dropped 10 times from a height of 1 m onto a steel plate and measured by the weight loss of the catalyst, the peeling rate of the expanded metal substrate without metal spraying without Kao wool was 45% on average, but with Kao wool mixed in. In other cases, the average decrease was 25%. It was confirmed that when a catalyst was press-bonded to a metal spray-sprayed substrate, the peeling rate was 7% on average without Kao wool mixed in, but the peeling rate decreased to 3% on average with Kao wool mixed in. Furthermore, in the case of a flat metal substrate without communicating holes, most of the catalyst was peeled off even when metal spraying was performed and Kao wool was further mixed. (4) Peeling rate test by repeated heating and cooling The apparatus used for this test is shown in FIG.
A plurality of plate-shaped catalysts 14 are installed inside the catalyst with their surfaces parallel to the direction in which the cooling air flows. Heating is carried out in an electric furnace to raise the temperature to a constant temperature, which is controlled by an electric furnace temperature controller indicated by reference numeral 18.
When a predetermined temperature is reached, the valve 16 of the cooling air supply pipe 19 is opened and the cooling air with pressure is supplied to the container 15.
is supplied to The control is performed by a catalyst temperature sensing cooling air valve controller 17. The temperature conditions and temperature increase/decrease rates are shown in Table 2 below.

[Table] The experimental results are shown in Figure 11, and the peeling rate (weight loss) of the plate-shaped catalyst according to the present invention is extremely small, and there is virtually no weight loss in the plate-shaped catalyst containing Kao wool. It can be said to be a state.
In addition, in the case of a plate-shaped catalyst having a flat metal substrate without communication holes, a large crack appeared in the catalyst during the first heating and cooling, and most of the catalyst fell off during the second heating and cooling. (5) Catalyst activity test (experiment) Regarding the effect of repeated heating and cooling in the above (4) on the catalyst activity, as shown in FIG. 12, there was no effect at all. <Example> An example of the present invention will be described below with reference to the drawings. FIG. 14 is a perspective view of a denitrification apparatus in which catalyst blocks similar to the unit catalyst boxes (catalyst blocks) containing plate-shaped catalysts shown in FIG. 8 are stacked and accommodated. FIG. 13 shows the structure of a power generation boiler plant equipped with this denitrification device. Air supplied from the forced air blower 22 passes through an air preheater 23, burns fuel in a boiler 24, and becomes combustion exhaust gas.
It flows through the high-temperature electrostatic precipitator 26, is denitrated in the denitrification reaction device 21, and then flows through the air preheater 23 and the denitrification device 2.
7 and is discharged from the chimney 28. The boiler used in practical use was a 500MW coal-fired boiler, and its operating conditions and denitrification performance are shown in Table 3. Although the denitrification equipment was operated for a long time after installation, no deterioration in denitrification performance or wear and tear on the catalyst was observed. The plate-shaped catalysts were housed in a block frame shown in FIG. 8 with pitches of 6 mm. The volume of the space occupied by the block (catalyst filling amount) was 110 m ³ .

[Table] In this example, as the gas temperature fluctuates due to the startup and shutdown of the boiler plant, the catalyst components as a whole repeatedly expand and contract, causing cracks in the catalyst layer. Because the catalyst component to be formed is kneaded with a heat-resistant fibrous material, large cracks do not occur locally, and fine cracks are generated relatively uniformly distributed on the surface of the catalyst layer. The fine cracks increase the surface area of the catalyst that functions as a catalyst, contributing to improved catalyst performance. <Effects of the Invention> By carrying out this invention, the function of preventing catalyst peeling of the plate-shaped catalyst is significantly improved, and various effects such as improved wear resistance, increased strength, and extended life are achieved. This brings about an improvement in the performance itself.

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional view of a denitrification device using a plate-shaped catalyst, Figure 2 is a perspective view of a unit catalyst, Figure 3 is a plan view of expanded metal, and Figure 4 is A-A in Figure 3.
A sectional view, FIGS. 5 and 6 are perspective views showing the shape of a bent plate-shaped catalyst substrate, and FIG. 7 shows a specific example of the present invention, in which a catalyst containing inorganic fibers is attached to a metal sprayed substrate. A sketch of a partially enlarged microscopic photograph of the surface of the object, Figure 8 is a perspective view of a unit catalyst box (catalyst block) containing a plate-shaped catalyst, and Figure 9 is an explanatory diagram of the device used for repeated heating and cooling tests. ,
FIG. 10 is an explanatory diagram of the temperature and time of the heating/cooling cycle, FIG. 11 is a diagram showing the relationship between the peeling rate and the number of heating/cooling cycles, and FIG. 12 is a diagram showing the influence of the activity ratio and the number of heating/cooling cycles. FIG. 13 shows an embodiment of the present invention and is a system diagram of a boiler put to practical use, and FIG. 14 is a perspective view of the denitrification device 21 shown in FIG. 13. DESCRIPTION OF SYMBOLS 1... Duct, 2... Unit catalyst, 2a... Plate catalyst, 3... Row of unit catalysts, 4... Substrate, 4a...
...Metal strip of substrate, 4b...Void (communicating hole), 5...Catalyst, 8...Metal microparticles, 9...Minute open cavity, 10...Ultrafine metal particles, 11...Inorganic fiber (fine connecting piece), 12... unit catalyst box,
21...Denitration equipment.

Claims (1)

[Scope of Claims] 1. In a plate-shaped catalyst for exhaust gas purification in which a catalyst is attached to a substrate, a catalyst kneaded with a heat-resistant fibrous material is attached to the entire surface of both surfaces of the metal substrate having a large number of communicating holes. A plate-shaped catalyst characterized in that it has been formed. 2. The plate-shaped catalyst according to claim 1, wherein a rough surface is formed by metal spraying on both surfaces of the substrate. 3. The plate-shaped catalyst according to claim 1 or 2, wherein the substrate is an expanded heat-resistant metal.