JP2001300219A - Ceramic filter for treating exhaust gas and exhaust gas treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably remove dioxins in exhaust gas generated from a melting or preheating furnace of ferrous scrap, a melting furnace of a non-ferrous metal and alloyed iron, a melting furnace of dust, incineration ash, or the like, a general incinerator, or the like. SOLUTION: The exhaust gas from a melting furnace 1 and a preheating furnace 2 is perfectly burnt in a combustion column 3 to be held to a high temperature and subsequently lowered in its temperature in a cooling column 4 to be introduced into a dust collector 5, which uses an exhaust gas treating ceramic filter wherein a catalyst for decomposing dioxins is supported on a porous sintered body, to remove not only dust but also dioxins. The catalyst is supported in a dispersed state or charged in a candle type ceramic filter to be supported or can be supported on the inside of the candle type ceramic filter, on the outside of a tube type ceramic filter or on the clean gas passage side of a cross flow type ceramic filter in a laminar state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a melting furnace and a preheating furnace for ferrous scrap, a melting furnace for non-ferrous metals and alloyed iron,
The present invention relates to an exhaust gas treatment ceramic filter and an exhaust gas treatment method for removing dioxins in exhaust gas generated from a furnace for melting incineration ash or the like or an incinerator for general waste.

[0002]

2. Description of the Related Art In recent years, environmental regulations have become increasingly strict. Scrap melting furnaces and preheating furnaces, melting furnaces for melting and refining non-ferrous metals and alloyed irons, melting furnaces for melting dust and incinerated ash, etc. Alternatively, regarding exhaust gas generated from an incinerator or the like that incinerates general garbage, it is necessary to reduce not only floating dust but also various harmful substances to below a regulation value. In particular, dioxins are the focus of public attention, and the regulatory values themselves are becoming increasingly strict.

Conventionally, as shown in FIG. 4, the reduction of dioxins in the exhaust gas of the melting furnace 1 and the preheating furnace 2 is performed by reducing the combustion tower 3
It is important to keep the temperature at a high temperature for a certain period of time while completely burning the mixture, and then quickly cool it in the cooling tower 4. In this regard, the Ministry of Health and Welfare guidelines for municipal waste incinerators have already been presented. The exhaust gas after cooling is removed by a dust collector 8 using a bag filter, and dioxins adhere to the dust and are removed.

[0004]

[Problem to be solved by the invention]
The temperature of the exhaust gas in the dust collector 8 is controlled at about 170 ° C., and at the time of stable steady operation at this temperature, dioxins in the exhaust gas are sufficiently removed and reduced without resynthesis. However, dioxins may not be sufficiently removed or reduced at the start-up / end of operation, during unsteady times when combustion is unstable, or at small incinerators or old incinerators. There is still room for improvement.

On the other hand, in exhaust gas treatment of a melting furnace such as an electric furnace which uses a large amount of scrap, a cooling tower 4 is used.
When the subsequent temperature was around 170 ° C. as in the case of incineration of municipal garbage, it was found that the resynthesis of dioxins proceeded. As a result of detailed studies by the present inventors, depending on the type of scrap used, if not cooled down to about 80 ° C. or less, dioxins are decomposed and removed in the combustion tower 3 once. It was found that resynthesis occurred between the cooling tower 4 and the dust collector 8 and could not be removed together with the dust. The cause is said to be largely due to the oil content attached to the scrap, but the clear mechanism is expected to be clarified by detailed research in the future.

[0006] In the cupola type melting furnace, the concentration of dioxins is lower than that of an electric furnace equipped with a preheating furnace because of the reducing exhaust gas containing CO. Not. Therefore, similarly to other melting furnaces, it is necessary to rapidly cool the exhaust gas after maintaining the exhaust gas temperature at a high temperature in the combustion tower. Regulation values cannot be satisfied.

By the way, the exhaust gas heated to a high temperature in the combustion tower 3 is usually directly spray-cooled with water to be rapidly cooled in the cooling tower 4. For this reason, the steam pressure in the exhaust gas sharply increases, and the dew point temperature increases. 1 in urban garbage incineration
There is no industrial problem up to about 70 ° C, but if it is lower than this, the temperature will be lower than the acid dew point, and there will be a problem of corrosion of ducts and dust collectors. And the problems such as clogging of the filter of the dust collector occur.

[0008] Instead of extremely lowering the temperature after the cooling tower 4, a catalyst tower 10 as shown in FIG. Can be processed. However, due to the performance of the catalyst so far, it is necessary to reheat the exhaust gas by the heating device 9 to increase the temperature. Cooling the exhaust gas once and then heating it again is not desirable from the viewpoint of energy saving, and the equipment scale is increased and the investment amount is increased. Therefore, the installation of the catalyst tower 10 cannot be said to be the best measure.

On the other hand, a catalyst is supported on a bag filter,
There are methods for removing nitrogen oxides and dioxins, and some effects are obtained depending on the use conditions. However, the filter cloth bag filter has a thickness of 2
There is a limit to the amount of catalyst supported per unit area because of about 3 mm, and the following issues such as filter cloth combustion and burning due to oxidation heat of metallic iron in dust and heat resistance of filter cloth against rise in exhaust gas temperature. There are many.

That is, the dust in the exhaust gas generated from the molten metal of the iron-based scrap melting furnace contains iron. In particular, in a reducing atmosphere in which the concentration of CO.H ₂ in the exhaust gas component is high, the proportion of metallic iron in the dust increases. Meanwhile C
O · H ₂ concentration is low, i.e., CO ₂ · O ₂ concentration of metallic iron with high oxidizing exhaust gas ratio decreases significantly. When this is shown in the operation timing in the actual scrap melting furnace,
The exhaust gas component becomes a reducing gas in the blowing acid, becomes an oxidizing gas in the initial or final stage of the blowing acid, and is substantially close to the air composition in the non-blowing acid or in the standby state. In the case of batch processing like scrap melting in a converter system, a reducing gas and an oxidizing gas alternately flow in this way. Adhered to the dust collector filter during melting
The dust containing a large amount of the deposited metallic iron is exposed to exhaust gas having a substantially air composition after melting. In this case, the extremely active particulate iron metal is rapidly oxidized and generates heat.
It is said that the ordinary heat-resistant temperature of ordinary filter cloth is 160 to 260 ° C, but it is actually used in the range of about 160 to 200 ° C.
Therefore, when dust adhering to such a filter cloth type bag filter generates and burns for each heat, the life of the bag filter is significantly shortened, and the dust collection performance is rapidly deteriorated.

The present invention relates to a furnace for melting and preheating a steel scrap, a melting furnace for preheating, a melting furnace for non-ferrous metals and alloys, a melting furnace for dust and incinerated ash, and an incinerator for general waste. Dioxins in exhaust gas can be removed while removing dioxins together with dust with a filtration type dust collector at a temperature after the cooling tower where there is no problem such as clogging, and it can sufficiently respond to a rise in dust temperature due to a change in exhaust gas composition. The purpose is to reduce to a level that satisfies the regulation value.

[0012]

Means for Solving the Problems The present invention provides the following (1)-
It is as (5).

(1) A ceramic filter for treating exhaust gas, wherein a catalyst for decomposing dioxins is supported on a porous sintered body.

(2) The exhaust gas treatment ceramic filter according to (1), wherein the catalyst is dispersed and supported.

(3) The exhaust gas treatment ceramic filter according to (1), wherein the catalyst is filled and carried inside a candle-type ceramic filter.

(4) The catalyst according to the above (1), wherein the catalyst is supported in a layer on the inside of a candle type ceramic filter, on the outside of a tube type ceramic filter, or on the side of a clean gas passage of a cross flow type ceramic filter. Ceramic filter for exhaust gas treatment.

(5) After the exhaust gas is completely burned in the combustion tower and kept at a high temperature, the temperature of the exhaust gas is lowered by direct spray cooling or a combination of indirect cooling and direct spray cooling, and thereafter any of the above (1) to (4) An exhaust gas treatment method comprising introducing the ceramic filter for exhaust gas treatment into a dust collector using a filter body to remove dioxins simultaneously with dust removal.

[0018]

FIG. 1 shows an example of an apparatus for carrying out the exhaust gas treatment method of the present invention.

Exhaust gas generated in the melting furnace 1 passes through a scrap preheating furnace 2 and is completely burned and maintained at a high temperature in a combustion tower 3.
It is cooled by the cooling tower 4 by direct water spray, is dust-removed by the dust collector 5, and is released from the stack 7 into the atmosphere while being sucked by the suction fan 6. Here, the filter of the dust collector 5 is constituted by a ceramic filter in which a catalyst for decomposing dioxins is supported on a porous sintered body, and the temperature is high due to fluctuations in exhaust gas temperature, oxidation heat generation of dust due to fluctuations in exhaust gas composition, and the like. The dust collection performance does not change. Rather,
Since the catalyst is supported, dioxins are more efficiently decomposed and removed by the catalytic action even when the temperature rises.

There are two types of ceramic filters: those obtained by processing ceramic fibers into a woven fabric or a felt, and those obtained by sintering to form a porous body. However, woven fabrics and felt-like ones have the same drawbacks as the above-mentioned bag filters even if they are used for filters, because the mechanical strength such as tensile strength and bending characteristics rapidly decreases at high temperatures. . Therefore, in the present invention, a ceramic filter in which a catalyst is supported on a porous sintered body which is unlikely to cause such a problem in strength is used for exhaust gas treatment.

FIG. 2 shows a typical example in which a porous sintered ceramic filter is installed in the dust collector 5. FIG.
(A) shows a case where a candle type ceramic filter 11 having one end closed is used. Dust-containing exhaust gas is introduced from an exhaust gas inlet 13, dust is attached to the outer surface of the candle type ceramic filter 11, and clean gas is removed from the inside. It is extracted and discharged from the exhaust gas outlet 14. The dust adhered to the outer surface of the ceramic filter 11 due to the regular back washing falls into the bottom dust accumulation 15 of the dust collector,
It is discharged outside. FIG. 2B shows an example in which a tubular ceramic filter 12 having both ends opened is used. Dust-containing exhaust gas is introduced from an exhaust gas inlet 13, dust adheres to the inner surface of the tubular ceramic filter 12, and clean air is removed from the outside. The gas is extracted and discharged from the exhaust gas outlet 14. The dust adhered to the inner surface of the ceramic filter 12 due to the regular back washing falls into the bottom dust accumulation 15 of the dust collector and is discharged to the outside. Although not shown, in addition to this, a cross-flow type (a layer in which a plurality of exhaust gas passages are arranged in parallel in a porous sintered body, and a passage for clean gas after dust collection in the porous sintered body) There are various types of ceramic filters, such as a ceramic filter, in which a plurality of layers arranged in parallel are alternately adjacently stacked with the direction of each passage changed by 90 °. It is similar to the example and can be represented here.

FIGS. 3A to 3C show an example in which a catalyst is supported on the candle type ceramic filter shown in FIG. 2A. FIG. 3A shows an example in which a catalyst 16 for decomposing dioxins is dispersed and supported inside a porous sintered body of a candle-type ceramic filter 11. The catalyst 16 is kneaded into the raw material of the ceramic filter and then fired. Since the ceramic filter is extremely porous, the fired ceramic filter is immersed in a catalyst-containing solution to make the catalyst 16 fine particles in the voids. It is carried by being dispersed. The exhaust gas comes into contact with the catalyst 16 while passing through the space, and the dioxins are decomposed and removed by the catalytic reaction. The catalyst in the form of fine particles has various shapes such as a spherical shape, a massive shape, and a linear shape, and any size may be used as long as it can be supported in the voids. FIG. 3B shows an example in which the catalyst 17 is filled on the inner surface side of the candle type ceramic filter 11.
After the exhaust gas passes through the body of the ceramic filter 11 and is collected, the exhaust gas comes into contact with the catalyst 17 at the catalyst filling portion, and dioxins are decomposed and removed by a catalytic reaction. FIG. 3C shows catalyst 1 on the inner surface side of candle type ceramic filter 11.
In this example, the exhaust gas passes through the main body of the ceramic filter 11 and is collected, and then contacts and reacts with the catalyst 18 in the catalyst layer, and is discharged to the inner side of the catalyst layer. The catalyst shapes of FIGS. 3B and 3C also have spherical shapes.
There are various forms such as a lump and a line, and a small size is preferable in view of the reactivity of the catalyst. However, it is necessary to take measures to prevent the catalyst from scattering. In addition, the present invention also includes a catalyst supporting system in which these are combined.

FIGS. 3D and 3E show examples in which a catalyst is supported on the tubular ceramic filter 12 shown in FIG. 2B. FIG. 3D shows an example in which the catalyst 16 is dispersed and supported inside the porous sintered body inside the main body of the tubular ceramic filter 12 as in the case of FIG.
The exhaust gas comes into contact with the catalyst 16 while passing through the space, and the dioxins are decomposed and removed by the catalytic reaction. The catalyst in the form of fine particles has various shapes such as a spherical shape, a massive shape, and a linear shape, and any size may be used as long as it can be supported in the voids. FIG. 3E shows an example in which the catalyst 19 is incorporated in a layer on the outer surface side of the tubular ceramic filter 12, and the exhaust gas is from the ceramic filter 12.
After passing through the main body and collecting dust, the catalyst layer contacts and reacts with the catalyst 19, and escapes to the outer surface side of the catalyst layer. There are various shapes of the catalyst, such as spherical, massive, and linear, and a small size is preferable in view of the reactivity of the catalyst. However, it is necessary to take measures to prevent the catalyst from scattering. In addition, the present invention also includes a catalyst supporting system in which these are combined.

Also, as for the cross-flow type ceramic filter, similarly to the above-mentioned two-type type, a catalyst is dispersed and supported inside a porous sintered body, and dioxins are decomposed and removed while collecting exhaust gas. Alternatively, the catalyst can be carried in a layered manner on the clean gas passage side of the ceramic filter, and the exhaust gas collected through the body of the ceramic filter can be contacted with the catalyst to decompose and remove dioxins. .

There have been many proposals for catalyst components supported on ceramic filters. Noble metals such as platinum, palladium and rhodium and metal oxides such as vanadium, tungsten, chromium, copper, tin, cobalt and manganese have been proposed. A catalyst system using titanium oxide, alumina, silica, zirconia, zeolite or the like as a carrier as an active component is well known. In the present invention, the types of these catalysts are not particularly limited, and the types of the catalyst may be selected according to the properties such as the exhaust gas component and the temperature, and may be directly supported on the ceramic filter.

The heat resistance temperature of the ceramic filter of the porous sintered body is up to about 900 ° C., and the dust has sufficient heat resistance even if the dust generates a little oxidative heat, and has little effect on the dust collection performance and life. Rather, the higher the temperature, the more the catalyst generally improves the oxidative decomposition performance of dioxins, so that a stable removal performance at a high temperature, which is impossible with a filter cloth type bag filter supporting the catalyst, is obtained. In addition, the thickness of the filter cloth type bag filter is about 2 to 3 mm, whereas the thickness of the ceramic filter of the porous sintered body is about 10 mm, and the amount of catalyst carried per unit filtration area is several times larger. Therefore, even when the temperature, flow rate, components, etc. of the exhaust gas are the same, the catalyst-supporting ceramic filter of the present invention has a remarkably improved oxidative decomposition removal rate of dioxins as compared with the catalyst-supporting filter cloth type bag filter.

[0027]

According to the present invention, a melting furnace or a preheating furnace using a large amount of iron-based scrap, a melting furnace for melting and refining non-ferrous metals and alloyed irons, a melting furnace for melting dust and incinerated ash, or a general refuse furnace. Dioxins in exhaust gas are regulated by removing dust and dioxins together with dust by using a filter dust collector at a temperature after the cooling tower where there is no problem such as equipment corrosion and filter clogging in incinerators etc. Can be reduced to a level that can be sufficiently cleared. Further, even if the filter temperature in the dust collector rises due to the oxidative heat of the dust due to the change in the temperature and composition of the exhaust gas, there is no problem such as burning, and the dust collecting function can be sufficiently maintained. Furthermore, the equipment investment can be suppressed to a very small scale by using the minimum necessary equipment configuration without installing equipment such as a catalyst tower after the dust collector.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an apparatus for performing an exhaust gas treatment method of the present invention.

FIG. 2 is a view showing an example of installation of a ceramic filter in a dust collector.

FIG. 3 is a diagram showing an example in which a catalyst is supported on a ceramic filter.

FIG. 4 is a diagram showing an exhaust gas treatment apparatus provided with a conventional catalyst tower.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Melting furnace 2 Preheating furnace 3 Combustion tower 4 Cooling tower 5 Dust collector 6 Suction fan 7 Stack 8 Dust collector 9 Heating device 10 Catalyst tower 11 Candle type ceramic filter 12 Tube type ceramic filter 13 Exhaust gas inlet 14 Exhaust gas outlet 15 Bottom dust reservoir 16 Catalyst 17 Catalyst 18 Catalyst 19 Catalyst

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F23J 15/06 F23J 15/00 H F27D 17/00 105 JK F term (Reference) 3K065 AA16 AA18 AA23 AA24 AB01 AB03 AC01 BA05 BA10 HA02 HA03 3K070 DA05 DA07 DA09 DA25 DA32 DA35 DA37 DA56 4D019 AA01 AA10 BA05 BA06 BB06 BC07 CA03 CB09 4D048 AA11 AB03 BB05 CC41 CC51 CD05 4K056 AA01 AA02 AA05 AA19 BA01 BA03 BB01 DB08

Claims (5)

[Claims] 1. A ceramic filter for exhaust gas treatment, wherein a catalyst for decomposing dioxins is supported on a porous sintered body. 2. The exhaust gas treatment ceramic filter according to claim 1, wherein the catalyst is dispersed and supported. 3. The ceramic filter for exhaust gas treatment according to claim 1, wherein said catalyst is filled and carried inside a candle-type ceramic filter. 4. The catalyst according to claim 1, wherein the catalyst is supported in a layer on the inside of a candle type ceramic filter, on the outside of a tube type ceramic filter, or on the side of a clean gas passage of a cross flow type ceramic filter. Ceramic filter for exhaust gas treatment. 5. The exhaust gas according to claim 1, wherein the exhaust gas is completely burned in a combustion tower and kept at a high temperature, and then the exhaust gas temperature is lowered by direct spray cooling or a combination of indirect cooling and direct spray cooling. An exhaust gas treatment method comprising introducing a treatment ceramic filter into a dust collector used for a filter to remove dioxins simultaneously with dust removal.