JP2001187320A - Waste gas treating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste gas treating method in which the discharge of dioxins can be effectively prevented by reconstructing at a low cost the existing incineration equipment constituted of an incinerator, an electric dust collector or a cyclone. SOLUTION: The waste gas of the incinerator is subjected to dust removing treatment by an electric dust collector or cyclone, moreover the waste gas is treated by a ceramic filter to sufficiently remove the dust in the waste gas, then the waste gas is brought into contact with the catalyst layer to decompose and remove the dioxins in the waste gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating exhaust gas, and more particularly to a method for treating exhaust gas capable of stably removing harmful substances such as dioxin contained in exhaust gas from an incinerator for a long period of time.

2. Description of the Related Art Many existing incinerators are of a type in which exhaust gas from an incinerator is treated with an electric dust collector or a cyclone to remove dust, and then discharged into the atmosphere. However, harmful substances such as dioxin (referred to as dioxins in the present invention) are contained in the exhaust gas that has just been subjected to the dust removal treatment, which is a serious social problem. Effective methods have been developed for the removal of dioxins, and the construction of incinerators employing these new technologies can substantially solve the problem of dioxins. However, it is economically difficult to immediately demolish existing incinerators and install new incinerators employing new technologies. For this reason, it is desired to be able to solve the problem of dioxins by using existing incineration equipment and without performing significant remodeling work.

SUMMARY OF THE INVENTION According to the present invention, an existing incinerator comprising an incinerator and an electric precipitator or a cyclone is modified at a low cost so that the emission of dioxins can be effectively prevented. And a method for treating exhaust gas.

The following has been found from the studies by the present inventors. By installing a catalyst layer after an electric dust collector or a cyclone, dioxins can be effectively removed. The dust collection efficiency of the electric precipitator or the cyclone is poor, so the dust removal is insufficient. In the catalyst layer, gaseous dioxins can be decomposed, but dioxins and particulate dioxins contained in dust cannot be removed. The dioxins are usually measured together with dust, particles, and gas. Therefore, as a result, a sufficiently high dioxin removal rate cannot be obtained. It is conceivable to install a bag filter instead of an electric dust collector or cyclone, but the conversion work is very costly. The bag filter has a high dust collection efficiency and can remove most of dust and particulate dioxins.However, since the operation temperature of the bag filter is low, the amount of catalyst is required for sufficient decomposition of dioxins in the catalyst layer. Must be increased, resulting in an economic disadvantage. Further, since the operating temperature is low, the exhaust gas contains sulfur oxides, which causes a problem of catalyst deterioration. In addition, it is conceivable that the exhaust gas treated by the bag filter is heated and introduced into the catalyst layer, but heating leads to an increase in cost. A dioxin in the exhaust gas can be effectively removed by introducing a ceramic filter after the electrostatic precipitator or the cyclone to enhance the dust removal efficiency, sufficiently removing the dust in the exhaust gas, and then introducing the dust into the catalyst layer. Also,
The durability of the catalyst layer can be increased. The present invention has been completed based on the above findings. That is, the present invention is a method for treating exhaust gas, wherein the exhaust gas from the incinerator is subjected to dust removal treatment using an electric dust collector or a cyclone, further treated with a ceramic filter, and then brought into contact with a catalyst layer.

FIG. 1 is a system diagram of the method of the present invention. In FIG. 1, 1 is an incinerator, 2 is an electric dust collector (or cyclone), 3 is a ceramic filter, 4 is a catalytic reactor, and 5 is a chimney. After exhaust gas from the incinerator 1 is introduced into the electric precipitator 2 to perform dust removal processing, the exhaust gas is introduced into the ceramic filter 3 to perform further dust removal processing. The exhaust gas from which dust has been sufficiently removed by the dust removal process is introduced into the catalytic reactor 4, where it is brought into contact with the catalyst layer to decompose and remove dioxins in the exhaust gas. As the ceramic filter, a ceramic filter generally used for removing dust can be used. As the material,
Those having a heat resistance of 500 ° C. or more, such as mullite, SiC and cordierite, are suitably used. The shape is not particularly limited, but a honeycomb shape having a large filtration area and a small pressure loss is preferable. Further, since it is installed on the downstream side of the electric precipitator, it is preferable that the precipitating efficiency of fine particles (about 0.1 μm) is 90% or more. Any catalyst can be used as long as it can decompose dioxins, and can be appropriately selected from known dioxin decomposition catalysts. Among them, the following catalysts (1) and (2) proposed earlier by the present applicant are preferably used (see Japanese Patent Application No. 11-180933). The pore size distribution in the catalysts (1) and (2) was measured using a mercury intrusion porosimeter. <Catalyst (1)> At least one selected from (a) titanium oxide, (b) vanadium oxide, and (c) manganese, cobalt, nickel, zinc, zirconium, niobium, molybdenum, tin, tantalum, lanthanum, and cerium. Containing an oxide of the element of 0.01 to 0.05 μm and 0.1 to
A catalyst having a pore size distribution having a peak in the range of 0.8 μm. Above all, the total pore volume is 0.2 to 0.6 cc / g, the pore volume of the pore group in the range of 0.01 to 0.05 μm is 10 to 70% of the total pore volume, 0.1-0.8
The pore volume of the pore group in the range of μm is 10 to 7 of the total pore volume.
A catalyst that is 0% is preferred. A catalyst in which the component (c) is molybdenum has excellent activity and is preferably used. The content of the component (b) is 0.1 to 25% by weight of the component (a).
And the content of the component (c) is 0.1 to 0.1 of the component (a).
25% by weight. Average particle size is 0.001-100μ
m, preferably 0.01 to 100 μm. Also, B
The specific surface area by ET method 30~250m ² / g, preferably from 40 to 200 m ² / g. The catalyst (1) can be prepared according to a method generally used for a catalyst of this type except that components (a) to (c) are contained as a catalytically active component. The catalyst having the above pore size distribution can also be easily prepared by a conventionally known method such as adjusting the amount of a molding aid such as starch or water added during catalyst preparation, or adding a resin that decomposes or volatilizes during calcining the catalyst during kneading. Can be obtained. <Catalyst (2)> (a) titanium oxide, (b) vanadium oxide, (c)
Manganese, cobalt, nickel, zinc, zirconium,
An oxide of at least one element selected from niobium, molybdenum, tin, tantalum, lanthanum and cerium, and (d) a titanium-silicon composite oxide;
A catalyst having a pore size distribution having peaks in the range of 1 to 0.05 μm and 0.8 to 4 μm. Above all, the total pore volume is 0.2 to 0.6 cc / g, and 0.01 to 0.05 cc / g.
The pore volume of the pore group in the range of μm is 20 to 8 of the total pore volume.
The catalyst is preferably 0%, and the pore volume of the pore group in the range of 0.8 to 4 μm is 5 to 70% of the total pore volume. A catalyst in which the component (c) is molybdenum has excellent activity and is preferably used. The content of the component (b) is 0.1 to 25% by weight of the component (a), and the content of the component (c) is 0.1 to 25% by weight of the component (a). The content of d) is 0.01 to 7 times the weight of the component (a). The average particle size is 0.001 to 100 μm, preferably 0.01 to 100 μm. The specific surface area by the BET method is 30 to 250 m ² / g, preferably 40 to 20 m ² / g.
0 m ² / g. The catalyst (2) is prepared according to a method generally used for this type of catalyst, except that the catalyst (2) contains components (a) to (d) as catalytically active components, similarly to the catalyst (1). Can be. Catalyst (1),
The shape of (2) is not particularly limited, and can be appropriately selected from a plate shape, a corrugated plate shape, a net shape, a honeycomb shape, a columnar shape, a cylindrical shape, and the like. Further, it may be used by being supported on a carrier made of alumina, silica, cordierite, titania, stainless steel, or the like, in the form of a plate, corrugated plate, mesh, honeycomb, column, or cylinder. The operating conditions of the electrostatic precipitator 2, the ceramic filter 3, and the catalyst layer 4 are not particularly limited, and can be appropriately determined in consideration of the type and properties of the exhaust gas, required removal performance, and the like. The operating temperature of the ceramic filter and the catalyst is such that the exhaust gas after the dust collection processing by the electric precipitator 2 is usually introduced as it is into the ceramic filter 3 and the catalyst layer 4, so that the operation of the commonly used electric precipitator is performed. The temperature can be appropriately selected within the temperature range, and is preferably 200 ° C. or more and less than 450 ° C. The space velocity of the exhaust gas in the ceramic filter 3 and the catalyst layer 4 is usually 100 to 100,000 h ^-1 (ST
P), preferably 200 to 50,000 h ^-1 (STP)
It is. The dioxins of the present invention are generally referred to as dioxins, and specific examples thereof include polyhalogenated dibenzoparadioxins, polyhalogenated dibenzofurans, and polyhalogenated biphenyls.

The main effects of the present invention are listed below. Dioxins in exhaust gas can be effectively removed only by installing a ceramic filter and a catalyst layer in an existing incinerator equipped with an electric dust collector or a cyclone. Existing incinerators can be modified at low cost. Since the ceramic filter has heat resistance, it can be operated in a high temperature range, and as a result, exhaust gas can be introduced into the catalyst layer at a high temperature, so that the decomposition efficiency of the catalyst is increased and the amount of the catalyst can be reduced. Since the dust removal efficiency is improved, the durability of the catalyst is improved, and the dioxin removal efficiency is also improved, so that both particulate and gaseous dioxins can be efficiently removed. .1ng
It is possible to reduce the concentration to a low concentration of −TEQ / m ³ or less. Dioxins in exhaust gas can be stably removed over a long period of time. Decomposition of dioxins by catalyst at 200 ° C or higher 45
Since it can be performed at a temperature lower than 0 ° C., the catalyst performance is sufficiently exhibited, and the dioxin removal rate is improved. In particular, the use of the catalysts (1) and (2) further improves the dioxin removal rate.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. Catalyst Preparation Example 1 A solution prepared by dissolving 1.29 kg of ammonium metavanadate and 1.68 kg of oxalic acid in 5 liters of water was added to 18 kg of commercially available titanium oxide powder (DT-51 (trade name), manufactured by Millennium). 1.23 kg of ammonium molybdate and 0.43 kg of monoethanolamine
Was dissolved in 3 liters of water, and phenol resin (Bellpearl (trade name), Kanebo Co., Ltd.) was added.
0.9 kg and starch 0.45 k as molding aid
g, kneaded with a kneader, and then extruded with an extruder to an outer diameter of 80 mm square, an aperture of 4.0 mm, and a wall thickness of 1.0 mm.
mm and a length of 500 mm. Next, after drying at 80 ° C., it was calcined at 450 ° C. for 5 hours in an air atmosphere to obtain a catalyst (1). The composition of the catalyst (1) was V ₂ O ₅ : MoO ₃ : TiO ₂ = 5: 5: 90 (% by weight). Further, as a result of measuring the pore diameter distribution of the catalyst (1) using a mercury intrusion porosimeter, the total pore volume was 0.41 cc / g, and the first pore group (0.01 to
The pore volume of the pore group having a peak of the pore diameter distribution in the range of 0.05 μm and the second pore group (0.1 to 0.8 μm)
The pore volume of the pore group having a pore size distribution peak in the range of was 35% and 57% of the total pore volume, respectively. Further, the BET specific surface area was 75 m ² / g. Catalyst Preparation Example 2 Snowtex-20 (silica gel manufactured by Nissan Chemical Industries, Ltd., about 20% by mass) was added to 700 liters of 10% by mass ammonia water.
SiO ₂ containing) 21.3 kg were added, stirred and mixed, as a sulfuric acid solution (TiO ₂ titanyl sulfate 125g
340 liters / liter, sulfuric acid concentration 0.55 g / liter) were added dropwise with stirring. After leaving the obtained gel for 3 hours, it was filtered, washed with water, and then dried at 150 ° C. for 10 hours. This was fired at 500 ° C., further pulverized using a hammer mill, and classified by a classifier to obtain an average particle diameter of 10 μm.
m were obtained. The composition of the obtained powder is TiO ₂ : S
iO ₂ = 8.5: 1.5 (molar ratio), and no distinctive peak of TiO ₂ or SiO ₂ was observed in the X-ray diffraction chart of the powder. It was confirmed that the composite oxide was a composite oxide of titanium and silicon (Ti-Si composite oxide) having a fine structure. 9 kg of the above Ti-Si composite oxide and 9 kg of commercially available titanium oxide powder (DT-51 (trade name), manufactured by Millennium Co.)
A solution of 1.29 kg of ammonium metavanadate and 1.68 kg of oxalic acid dissolved in 5 liters of water and a solution of 1.23 kg of ammonium paramolybdate and 0.43 kg of monoethanolamine in 3 liters of water were added. Further, 0.9 kg of a phenolic resin (Bellpearl (trade name), manufactured by Kanebo Co., Ltd.) and 0.45 kg of starch as a molding aid are added and mixed, kneaded with a kneader, and then extruded with an extruder to an outer diameter of 80 mm. It was formed into a honeycomb shape having corners, openings of 4.0 mm, wall thickness of 1.0 mm, and length of 500 mm. Then, after drying at 80 ° C., 4
It was calcined at 50 ° C. for 5 hours in an air atmosphere to obtain a catalyst (2). The composition of the catalyst (2) is V ₂ O ₅ : MoO ₃ : Ti
O ₂ : Ti—Si composite oxide = 5: 5: 45: 45 (% by weight). The pore size distribution of the catalyst (2) was measured by a mercury intrusion porosimeter. As a result, the total pore volume was 0.38 cc / g, and the first pore group (0.01 to
The pore volume of the pore group having a pore diameter distribution peak in the range of 0.05 μm and the pores of the second pore group (pore group having a pore diameter distribution peak in the range of 0.8 to 4 μm) The volumes were 57% and 21% of the total pore volume, respectively. Further, the BET specific surface area was 85 m ² / g. Example 1 As shown in FIG. 1, a honeycomb-shaped ceramic filter was installed on the outlet side (dioxins concentration: 1 ng-TEQ / m ³ ) of the electrostatic precipitator, and a catalytic reactor was installed on the downstream side to treat exhaust gas. Was done. Initial performance, 2,000 hours,
Table 1 shows the dioxin removal rates and outlet dioxin concentrations after 5,000 hours and 10,000 hours. <Ceramic filter> Type: Cordierite honeycomb type ceramic filter (9 mm mesh, 1 mm thick, 99% dust collection efficiency) Space velocity: 30,000 h ^-1 Temperature: 250 to 350 ° C <Catalyst layer> Catalyst (1) Space velocity: 4,000 h ^-1 Temperature: 250 to 350 ° C. The dioxin removal rate was determined according to the following equation. Dioxin removal rate (%) = [(dioxin concentration at ceramic filter inlet-dioxin concentration at catalyst reactor outlet) / (dioxin concentration at ceramic filter inlet)] × 100 Example 2 In Example 1, the catalyst (1) Exhaust gas treatment was carried out in the same manner as in Example 1 except that the catalyst (2) was used instead. Initial performance, 2,000 hours, 5,000 hours, 1
Table 1 shows the dioxin removal rate and the concentration of dioxins at the outlet after 000 hours. Comparative Example 1 Exhaust gas was treated in the same manner as in Example 1 except that the exhaust gas was directly introduced into the catalytic reactor without providing a ceramic filter, and the temperature of the catalytic reactor was set to 250 ° C. . Table 1 shows the dioxin removal rate and outlet dioxin concentration. The removal rate of dioxins was determined according to the following equation. Dioxin removal rate (%) = [(catalyst reactor inlet dioxin concentration-catalyst reactor outlet dioxin concentration)
/ (Concentration of dioxins at the inlet of the catalyst reactor)] × 100

[Table 1]

[Brief description of the drawings]

FIG. 1 is a system diagram of the method of the present invention.

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Claims (4)

[Claims] 1. A method for treating exhaust gas, wherein the exhaust gas from the incinerator is subjected to dust removal treatment using an electric dust collector or a cyclone, further treated with a ceramic filter, and then brought into contact with a catalyst layer. 2. The catalyst according to claim 1, wherein the catalyst is selected from (a) titanium oxide, (b) vanadium oxide and (c) manganese, cobalt, nickel, zinc, zirconium, niobium, molybdenum, tin, tantalum, lanthanum and cerium. It contains an oxide of one element and has a content of 0.01 to 0.1.
The method according to claim 1, wherein the catalyst has a pore size distribution having peaks in the range of 05 µm and 0.1 to 0.8 µm. 3. The catalyst comprises (a) titanium oxide, (b) vanadium oxide, (c) manganese, cobalt, nickel, zinc, zirconium, niobium, molybdenum, tin,
It contains an oxide of at least one element selected from tantalum, lanthanum and cerium, and (d) a titanium-silicon composite oxide, and has a particle size of 0.01 to 0.05 μm and 0.1 to 0.05 μm.
The method according to claim 1, wherein the catalyst has a pore size distribution having a peak in the range of 8 to 4 µm. 4. The composition of claim 2, wherein component (c) is molybdenum.
Or the method of 3.