JPH0549858A - Method for promoting reaction of porous solid catalyst in catalytic reactor - Google Patents

Abstract

PURPOSE:To reduce the amt. of the required catalyst and to improve the removing rate for harmful matter by continuously changing the position of a porous solid catalyst provided in a running fluid in such a manner that the position is continuously changed along the crossing direction of the fluid so that the fluid interface film formed on the outer surface of the catalyst is forcedly disturbed. CONSTITUTION:In a catalytic reaction device in which a porous solid catalyst 4 is disposed in a running fluid 10, the position of the porous solid catalyst 4 is changed along the crossing direction of the fluid 10 by a vibrator 8 so that the fluid interface film formed on the outer surface of the catalyst is forcedly disturbed. Thereby, the reaction efficiency of the solid catalyst can be increased without increasing the flow resistance of the fluid, and thus, the amt. of the required catalyst can be reduced and the removing rate for harmful matter can be improve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mainly used as a catalytic reaction apparatus for treating exhaust gas in a waste incinerator, a combustion boiler, etc., and uses a porous solid catalyst. The present invention relates to a method for promoting the reaction of a porous catalyst, which can improve the reaction efficiency of the catalyst, reduce the amount of the catalyst, and improve the removal rate of harmful substances.

[0002]

Exhaust gas from waste incinerators, combustion boilers, internal combustion engines, etc. contains many harmful substances such as hydrogen chloride and other acidic gases, sulfur oxides, nitrogen oxides, heavy metals, and dust particles. Various exhaust gas treatment methods have been developed to remove these harmful substances. Among them, a harmful substance removing device (or a catalytic reaction device) using a so-called porous solid catalyst has been widely used as a device for removing nitrogen oxides, hydrocarbons, carbon monoxide and the like in exhaust gas in recent years.

FIG. 12 shows an example of an exhaust gas treating apparatus A provided in a waste incinerator. A neutralizing absorbent (slaked lime powder) C and an auxiliary agent (diatomaceous earth powder) C'are placed in a combustion exhaust gas B.
In addition, the bag filter device D preliminarily removes dust and acid gas in the exhaust gas, and the reducing agent (NH ₃₎ that selectively reacts with NOx in the exhaust gas B ′ exiting the bag filter device D. Or NH ₄ OH) F, and the exhaust gas B is discharged by the nitrogen oxide removing device E equipped with a porous solid catalyst.
It is for reducing and removing the nitrogen oxides in the ‘ (JP-A-62-74440, etc.). Examples of the porous solid catalyst of the nitrogen oxide removing apparatus E include a honeycomb-type porous solid catalyst in which V ₂ O ₅ is supported on TiO ₂ as a carrier, and Ti.
A porous solid catalyst having a structure in which O ₂ or V ₂ O ₅ is supported on a porous ceramic or the like is often used. Further, in the case of the honeycomb-type porous solid catalyst, a honeycomb cross-section having a square shape or a hexagonal shape is often used, and the diameter and wall thickness of the honeycomb are 8 to 15 mm, and 0.1. 5
Each is selected to be about 2.0 mm.

Thus, the above-mentioned conventional nitrogen oxide removing device E
In this case, the flow velocity of the passing gas in the catalytic reaction device is about 3 m.
/ S, and the SV value is designed to be in the range of about 4000 to 7000 h ^-1 . When the velocity of the passing gas is increased, turbulent flow in the honeycomb passage is increased to increase the reaction efficiency of the catalyst, but on the other hand, the exhaust gas resistance is increased to cause troubles such as abrasion of the catalyst surface. The value of is recommended. Also, the reaction efficiency of the catalyst is
_It changes depending on the injection equivalent ratio of ₃ and the temperature of the exhaust gas, but recently, in order to prevent the emission of dioxins from the waste treatment facility, a bag filter is used in the dust removal device to change the exhaust gas temperature to about 200 ° to 220 °. In addition to the above, the equivalent ratio of NH ₃ is suppressed to about 0.7 or less in order to prevent the generation of white smoke due to the leak NH ₃ . As a result, there are certain restrictions in increasing the catalytic reaction efficiency by increasing the exhaust gas temperature and increasing the NH ₃ equivalent ratio. Under the above-mentioned conditions, in order to perform more advanced denitration, it is necessary to design the SV value to be small, and as a result, the catalyst volume becomes large and the equipment cost and the maintenance cost become expensive. There is a situation. Note that, although FIG. 12 described above relates to a catalytic reaction device for removing a trace amount of harmful substances from exhaust gas, these problems are not limited to the case where the fluid is a gas such as exhaust gas, but also a trace amount of harmful substances in the liquid. It also exists in a catalytic reaction device for removing C by a chemical reaction with a catalyst.

On the other hand, in order to improve such a situation, as a new catalyst structure, a ceramic foam type catalyst, a honeycomb type catalyst composed of a ceramic fiber non-woven plate wall, and the like have been tried (Japanese Patent Laid-Open No. 1-258746). Etc.). However, each of these new attempts has many problems that still need improvement in terms of manufacturing method, dust countermeasures, gas resistance, price, etc., and has not yet been put to practical use.

[0006]

DISCLOSURE OF THE INVENTION The present invention has the above-mentioned problem in the conventional catalytic reaction apparatus using a porous solid catalyst, that is, there is a limit in reducing the amount of the catalyst, We are trying to solve problems such as difficulty in practically reducing equipment cost and maintenance cost, and difficulty in commercialization of new catalyst structure such as ceramic fiber nonwoven fabric due to problems in manufacturing technology and price. Therefore, in a catalytic reaction device that uses an existing porous solid catalyst product and improves the reaction efficiency by combining it with a simple mechanism, it is possible to realize downsizing and cost reduction of the catalytic reaction device. The present invention provides a method for promoting the reaction of a porous solid catalyst.

[0007]

[Means for Solving the Problems] When a chemical reaction is caused by a porous solid catalyst in a flowing gas phase or liquid phase, the raw material components and products involved in the reaction are the following seven processes. It is known to move sequentially through. Transfer of reaction components from the flowing phase to the outer surface of solid catalyst particles Transfer of reaction components to the inner surface of catalyst particles by diffusion in pores Adsorption of reaction components to active sites on the substantial surface of catalyst Adsorbed reaction components Desorption of products from the substantial surface of the catalyst Intra-pore diffusion of products to the outer surface of the catalyst particles Transfer of products from the outer surface of the catalyst particles to the flowing phase Of the above seven processes, And and are involved in outdiffusion and / or in-pore diffusion, and the process of mass transfer rate of and and and is an important factor in dealing with the overall reaction rate of the catalytic reaction. .. In particular, in treating a large amount of exhaust gas such as exhaust gas from waste incinerators, boilers, internal combustion engines, etc. In the case of a catalyst structure having a blow-through part,
The external diffusion process controls the overall reaction rate. Also, in the reaction operation in an extremely low concentration range such as the removal of harmful components contained in exhaust gas at low concentration by a catalyst, the reaction operation is generally performed under the condition that the mass transfer rate controls the overall reaction rate. Will be seen.

On the other hand, the movement of the substance between the flow phase and the outer surface of the catalyst particles is carried out by molecular diffusion of the substance in a stationary thin fluid film formed around the catalyst particles. Further, regarding the mass transfer rate at that time, when the other conditions (external surface area of catalyst, reaction phase concentration in the flowing phase and outer surface of catalyst particles, etc.) are constant, the film mass transfer coefficient kf should be increased. Faster. By the way, in order to increase the kf value, it is first necessary to increase the flow velocity of the flow phase. However, in the case of a passage structure such as a honeycomb catalyst, if the flow velocity is unnecessarily increased, back pressure increases and exhaust gas blows through. As a result, the reaction components are not sufficiently converted, and the reaction efficiency cannot be increased.

Thus, in a real nitrogen oxide removing device such as an incinerator, the above-mentioned S is removed under the contradictory conditions as described above.
By appropriately selecting the V value and the LV value, a catalytic reactor using a porous solid catalyst is designed. The inventor of the present invention is keenly aware of the necessity of measuring the increase of the membrane mass transfer coefficient kf without increasing the flow velocity of the flowing phase through the practical design of many catalytic reactors of this kind. By breaking the conventional stereotype that it should be used in a stationary state and continuously moving the position of the porous solid catalyst relative to the flow direction of the flowing phase, the boundary film is moved. The idea was to increase the mass transfer coefficient kf. The inventor of the present invention repeatedly carried out many tests on the relationship between the moving speed and moving range of the catalyst body and the reaction efficiency based on these ideas.

The present invention was created from the above idea and the result of the reaction efficiency test based on the idea. A porous solid catalyst is provided in a flowing fluid, and a trace amount contained in the fluid by a chemical reaction. In a catalytic reactor that performs a reaction operation for removing harmful substances, etc., the position of the porous solid catalyst is continuously displaced in a direction intersecting with the flow direction of the fluid, and a fluid boundary formed on the surface of the catalyst. Disturbing the membrane is the basic constitution of the invention.

[0011]

[Function] The porous solid catalyst placed in the flow phase makes relative motion at a predetermined speed in the direction intersecting with the flow direction of the fluid to form a stationary fluid film on the outer surface of the solid catalyst particles. Disturbance is given. As a result, the film mass transfer coefficient kf of the catalyst is increased without reducing the fluid passage cross-sectional area of the solid catalyst, and the outward diffusion of the reaction components and reaction products on the surface of the catalyst particles is activated, and the catalyst The reaction efficiency is greatly improved.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are a schematic vertical sectional view and a schematic horizontal sectional view showing the main part of a catalytic reaction device (a device for removing nitrogen oxides in combustion exhaust gas) to which the present invention is applied. In the figure, 1 is an exhaust gas introducing duct, 2 is an exhaust gas introducing duct, 3 is a casing, 4 is a honeycomb-type porous solid catalyst, 5 is a catalyst reinforcing frame,
6 is a roller support, 7 is a roller, 8 is a vibrating device, 9 is a gas seal, and 10 is exhaust gas. The honeycomb-type porous solid catalyst 4 is a known solid catalyst formed by supporting V ₅ O ₂ on a porous ceramic, and generally has poor mechanical strength. Therefore, the honeycomb-type porous solid catalyst 4
By providing the catalyst reinforcing frame 5 on the outer side of, the mechanical strength against vibration is reinforced. The honeycomb-type porous solid catalyst 4 is movably mounted on the upper surface of the roller supporting base 6 through a roller 7 for a predetermined distance, and a vibrating device 8 provided outside the casing 3 serves to remove the exhaust gas 10 from the exhaust gas 10. In the direction perpendicular to the flow direction, about 1 of the honeycomb passage width
Amplitude of about / 2 to several tens of μm, and several hundred Hz to several thousand H
It is forced to vibrate continuously at the frequency of z.

Since the catalyst 4 is forcibly vibrated,
The flow of the exhaust gas 10 is as shown in FIG.
On the other hand, the flow direction changes with time, which disturbs the static fluid film formed in the vicinity of the honeycomb wall surface 4a. That is, in FIG. 3, u is the flow velocity of the exhaust gas 10, v is the vibration velocity in the direction perpendicular to the flow of the exhaust gas, and the fluid flow velocity of ω = u + v is the catalyst wall surface 4.
By acting on a, the fluid film will be disturbed. In the present embodiment, the vibration direction of the catalyst 4 is perpendicular to the flow of the exhaust gas 10 as shown by the arrow A in FIG. 3, but instead of this, the catalyst 4 is moved in a direction having an arbitrary angle α. Of course, it may be vibrated.

FIG. 4 is a partially enlarged sectional view schematically showing the vicinity of the catalyst wall surface 4a, and FIG. 5 is a diagram showing the relationship between the sectional position X in FIG. 4 and the reaction component concentration A ₀ . Is. In FIG. 4, H is a flow phase, G is a fluid boundary film, I is the inner surface of the catalyst main body, K is a pore model, L is a reaction component, and M is a reaction product. Further, in FIG. 5, P ₁ is the reaction component concentration on the outer surface of the catalyst particles, P ₂ is the reaction component concentration in the flow phase, and the fluid boundary film G is disturbed by the vibration of the catalyst 4, P ₁ is greatly improved as compared with the case where the fluid film G is stable (stationary).

FIG. 6 and FIG. 7 are a schematic vertical sectional view and a schematic horizontal sectional view showing the main part of another catalytic reactor to which the present invention is applied. In the present embodiment, the porous solid catalyst 4 is formed as a disk-shaped porous solid catalyst, and is formed by fixing a large number of catalyst disks 4a in parallel to the shaft 11. That is, the disk type catalyst 4 is composed of a disk body carrying a catalyst on a metal disk or a wire mesh or a kneading molded disk type catalyst body 4a, and is rotationally driven by an electric motor 12 at an appropriate speed. As a result, the fluid boundary film G on the outer surface of the disk-shaped catalyst 4 is disturbed as in the case of Example 1, and as a result, the reaction efficiency of the catalyst is improved.

FIG. 8 and FIG. 9 are a schematic vertical sectional view and a schematic horizontal sectional view showing the main part of still another catalytic reaction apparatus to which the present invention is applied. In the present embodiment, a double cylinder type porous solid catalyst is used as the porous solid catalyst 4, and a plurality of cylindrical catalysts 4 are vertically arranged in the casing 3.
By rotating this at a predetermined speed by the electric motor 12, the fluid film formed on the outer surface of the catalyst 4 is disturbed.

FIG. 10 and FIG. 11 show the detailed structure of the double-cylindrical porous solid catalyst 4, which is a cylindrical body 1 made of two stainless wire nets (or punching plates) having different outer diameters.
The catalyst layers are formed by arranging 3a and 13b concentrically and filling the space between them with the granular catalyst 4b. The lower end of the internal space of the cylindrical catalyst 4 is open, and the cylindrical catalyst 4 is rotatably suspended and supported in the casing 3. Exhaust gas 1 flowing into the casing 3
0 passes through the granular catalyst layer forming the peripheral wall of the cylindrical catalyst 4 rotating at a constant speed, enters the internal space thereof, and is discharged into the exhaust gas discharge duct 2 through the opening 4c at the lower end.

[0018]

According to the present invention, the position of the porous solid catalyst disposed in the fluid is continuously forcibly displaced in the direction intersecting with the flow direction of the fluid, and the stationary thin fluid boundary formed on the catalyst surface. By disturbing the membrane, the movement of the reaction components from the flowing phase to the outer surface of the solid catalyst particles and the movement of the product from the outer surface of the catalyst particles to the flowing phase are activated. As a result, as compared with the conventional catalytic reaction apparatus, the catalytic efficiency can be enhanced by promoting the catalytic reaction without increasing the passage resistance of the fluid, and the removal rate of trace harmful substances in the fluid is improved. .. In addition, the so-called SV value and AV value can be increased as compared with the conventional catalytic reaction apparatus, the catalyst volume can be reduced, the apparatus can be downsized, and the equipment cost and maintenance cost of the apparatus can be reduced. Can be done. Furthermore, the vibration or rotational movement of the catalyst body causes a self-cleaning action of removing dust deposits on the catalyst, so that the catalyst cleaning device such as soot blow can be eliminated. Moreover, the device for vibrating or rotating the catalyst body is an extremely simple device that is not heavily loaded by the fluid, and does not cause a significant increase in price or require any troublesome maintenance. The present invention has excellent practical utility as described above.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a catalytic reactor to which the present invention is applied.

FIG. 2 is a schematic cross-sectional view taken along the line E-I of FIG.

FIG. 3 is an explanatory diagram showing movement of a honeycomb-type porous solid catalyst.

FIG. 4 is a partially enlarged cross-sectional view for schematically showing the condition near the outer surface of the catalyst.

FIG. 5 is a diagram showing a situation of reaction component concentrations near the outer surface of the catalyst.

FIG. 6 is a schematic vertical sectional view of another catalytic reaction device to which the present invention is applied.

FIG. 7 is a schematic cross-sectional view taken along the line E-I of FIG.

FIG. 8 is a vertical cross-sectional view of still another catalytic reaction device to which the present invention is applied.

9 is a cross-sectional view taken along the line E-I of FIG.

FIG. 10 is a vertical sectional view of a cylindrical porous solid catalyst.

11 is a cross-sectional view taken along line E-I of FIG.

FIG. 12 shows an example of a harmful substance removing device using a conventional porous solid catalyst.

[Explanation of sign]

1 Exhaust gas introduction duct H Distribution phase 2 Exhaust gas discharge duct G Fluid boundary film 3 Casing I Inner surface of catalyst body 4 Honeycomb type porous solid catalyst K Pore model 5 Catalyst reinforcement frame L Reaction component 6 Roller support M Reaction product 7 Roller P ₁ Reaction on the outer surface of catalyst particles 8 Excitation device Component concentration 9 Gas seal P ₂ Reaction component concentration in flowing phase 10 Exhaust gas 11 Shaft 12 Electric motor 13a, 13b Cylindrical wire mesh

Claims (5)

[Claims] 1. A catalytic reaction apparatus in which a porous solid catalyst is disposed in a flowing fluid and a reaction operation such as removal of a trace amount of harmful substances contained in the fluid by a chemical reaction is carried out. The position of the catalyst is continuously displaced in a direction intersecting with the flow direction of the fluid to disturb the fluid boundary film formed on the catalyst surface. How to accelerate the reaction. 2. The catalytic reaction according to claim 1, wherein the porous solid catalyst is a honeycomb-type porous solid catalyst, and the honeycomb-type porous solid catalyst is forcibly vibrated at a predetermined amplitude and frequency. Method for promoting reaction of porous solid catalyst in apparatus. 3. The catalytic reaction device according to claim 1, wherein the porous solid catalyst is a disk-shaped porous solid catalyst, and the disk-shaped porous solid catalyst is rotationally driven at a predetermined speed. Method for accelerating the reaction of a porous solid catalyst in. 4. The porous solid catalyst is a cylindrical porous solid catalyst in which a granular catalyst is filled in a space of a double wall, and the cylindrical porous solid catalyst is rotationally driven at a predetermined speed, The method for accelerating the reaction of the porous solid catalyst in the catalytic reaction apparatus according to claim 1, wherein the fluid that has passed through the catalyst layer and has flowed into the inside is discharged from the lower opening. 5. A fluid is combustion exhaust gas, and a honeycomb-type porous solid catalyst is used as a catalyst for removing nitrogen oxides, and the porous catalyst has an amplitude of about 0.5 of a honeycomb passage width.
The method for accelerating the reaction of the porous solid catalyst in the catalytic reaction device according to claim 2, wherein forced vibration is performed in the horizontal direction at a frequency of several times to several tens of μm and a frequency of several hundreds to several thousands of hertz.