JP2001054707A - Bag filter and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bag filter hardly causing the falling of the powder such as catalyst even if the filter is backwashed and capable of maintaining the effect of the catalyst, etc., over a long period of time. SOLUTION: In the bag filter, the dispersion solution containing at least one kind powder selected among acidic gas reaction agent, adsorbing agent, nitrogen oxide decomposition catalyst and dioxin decomposition catalyst and polytetr afluoroethylene(PTFE) is impregnated to an air permeable base material, and the powder is integrated into one body with the air permeable base material by heating to the temp. more than melting point of the PTFE. Or the powder is disposed between PTFE porous membrane, and the laminated body joining the porous membrane is further stuck to the air permeable base material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bag filter for treating exhaust gas generated from various incinerators and a method for producing the same. More specifically, the present invention relates to harmful substances (heavy metals, hydrogen chloride, sulfur oxides,
Nitrogen filter, dioxins, etc.).

[0002]

2. Description of the Related Art In recent years, environmental pollution by dioxins such as polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) contained in exhaust gas from incinerators has become a social problem. Due to the high waste incineration rate in Japan, measures to reduce dioxins in waste incineration equipment are urgently needed. In order to avoid dust collection in the synthesis temperature range of dioxins (200 to 500 ° C.), a device for removing dust from exhaust gas can collect dust at the synthesis temperature or lower from an electric dust collector and has excellent dust removal efficiency. There is a transition to a bug filter.

[0003] Exhaust gases from incinerators contain harmful substances other than dioxins. This harmful substance is removed by charging a reactant or an adsorbent or by a decomposition reaction using a catalyst. For example, acidic gases such as hydrogen fluoride, hydrogen chloride, and sulfur oxides (SOx) can be removed by charging a reactant such as slaked lime powder into an exhaust gas flue and collecting it with a bag filter. . In addition, it has been studied that heavy metals are also adsorbed by introducing an adsorbent such as activated carbon and the like and collected by a bag filter. On the other hand, with respect to nitrogen oxides (NOx), a catalyst denitration method using a catalyst tower (denitration tower) provided downstream of a bag filter is often used together with a non-catalytic denitration method in which ammonia, urea, etc. are charged. . Dioxins have been decomposed by contact with oxidizing agents such as ozone and hydrogen peroxide and denitration catalysts.

[0004] In order to ensure exhaust gas treatment capacity, it is necessary to install a large bag filter, and it is not desirable to provide a catalyst tower separately from the bag filter. In addition, if the catalyst tower is separately installed, the burden is increased economically. For this reason, a bag filter has been proposed which has a function of removing harmful substances in addition to dust removal.

For example, JP-A-1-293123 discloses a bag filter produced by immersing a filter cloth in an emulsion of a denitration catalyst. In addition, Japanese Patent Application Laid-Open
No. 66814 discloses a bag in which a filter cloth impregnated with a slurry of a denitration catalyst is held horizontally, and the filter cloth is dried while rotating about the long axis to dry the filter cloth. A filter is disclosed.

[0006]

The so-called "backwashing" of the bag filter, in which dust adheres and the pressure loss increases as the operation time elapses, so that the air is backflowed during operation to remove the dust. Need to do. However, in the above-mentioned conventional bag filter, since the catalyst is simply attached to the filter cloth as a base material, there is a problem that the catalyst gradually falls off due to the backwash.

Accordingly, an object of the present invention is to solve the above-mentioned problems, and to provide a bag filter and a method of manufacturing the bag filter, in which the catalyst and the like are less likely to fall off than before and the effect of the catalyst and the like can be maintained for a long time.

[0008]

In order to achieve the above object, a bag filter according to the present invention is a bag filter for reducing harmful substances in exhaust gas, comprising a gas-permeable base material, an acid gas reactant, and an adsorbent. Agent, a nitrogen oxide decomposition catalyst and at least one powder selected from dioxin decomposition catalysts, wherein the powder is polytetrafluoroethylene (hereinafter, referred to as
(Referred to as "PTFE") to be integrated with the air-permeable base material.

In the bag filter of the present invention, the powder such as the catalyst is not simply dispersed in the base material but is integrated with the base material by PTFE. PTFE has heat resistance that can be used continuously even at a high temperature of about 260 ° C., and is excellent in chemical resistance, and thus is suitable as a material for fixing a catalyst or the like.

A first method for producing a bag filter according to the present invention is a method for producing a bag filter for reducing harmful substances in exhaust gas, comprising an acid gas reactant, an adsorbent, a nitrogen oxide decomposition catalyst and a dioxin decomposition catalyst. Impregnating a gas-permeable base material with a mixed dispersion in which at least one powder selected from PTFE and PTFE are dispersed;
Heating the powder to a temperature equal to or higher than the melting point of the FE, and integrating the powder with the air-permeable base material by the PTFE solidified after melting.

A second method for producing a bag filter according to the present invention is a method for producing a bag filter for reducing harmful substances in exhaust gas, comprising an acid gas reactant, an adsorbent, a nitrogen oxide decomposition catalyst, and a dioxin. A step of arranging at least one kind of powder selected from cracking catalysts between a plurality of PTFE porous membranes and bonding the plurality of PTFE porous membranes to each other to form a laminate of the PTFE porous membranes; Laminating the laminate and the air-permeable supporting material.

According to these production methods, the above powder can be converted into PT
It is possible to efficiently manufacture a bag filter in which the effects of powder such as a catalyst are maintained for a long period of time by integrating with FE.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. In the bag filter of the present invention, the powder of the catalyst or the like is solidified after at least a part thereof is melted.
It is preferable to be integrated with the air-permeable base material by FE. Specifically, it is preferable that the powder is fixed by PTFE fused to the powder of the catalyst or the like. PTFE is
Since the melt viscosity at the melting point is as high as 10 ¹⁰ poise or more, it is difficult to flow even when it is melted. Therefore, the powder can be fixed to the air-permeable base material without substantially reducing the active surface.

In a preferred embodiment of the bag filter of the present invention, a powder such as a catalyst is fixed in the air-permeable base material. In this mode, for example, a powder of a catalyst or the like impregnated in a gas-permeable base material is similarly impregnated in the base material, and is heated to a melting point or higher.
It is integrated with the breathable substrate by FE.

In another preferred embodiment of the bag filter of the present invention, PTFE is used as a porous membrane. In this embodiment, for example, a powder of a catalyst or the like is made of a plurality of sheets of PTFE.
The powder is integrated with the air-permeable base material by being included in the inside of the layered body made of the porous film and being bonded to the air-permeable base material. When the PTFE porous membranes sandwiching the powder of the catalyst and the like are joined to each other, it is preferable to use so-called heat fusion or PTFE, in which the PTFE porous membranes are pressed together while being heated to the melting point of PTFE or more. When heat fusion is performed, at least a part of the powder is melted, and then the powder is fixed in the laminate by the solidified PTFE.

In both of the above embodiments, the powder of the catalyst or the like is fixed to the base material using PTFE once heated to the melting point or higher as an adhesive, or is sandwiched between the porous PTFE membranes. The powder such as the catalyst is unlikely to fall off the bag filter even if the backwash is repeatedly performed. In addition, the activity of the catalyst and the like is easily maintained. In addition, the bag filter of the present invention is provided as long as the powder capable of reducing harmful substances in the exhaust gas is integrally held by PTFE.
It may further include a powder simply dispersed in the base material.

The air-permeable base material constituting the bag filter is preferably a woven or non-woven fabric made of glass fiber, PTFE, aromatic polyamide, polyimide, polyphenylene sulfide, polyolefin or the like. However, the first
When the air-permeable base material is heated to a temperature equal to or higher than the melting point of PTFE as in the production method described above, the material of the air-permeable base material is preferably glass fiber, PTFE, or aromatic polyamide.

The powder for removing harmful substances contains at least one selected from acid gas reactants, adsorbents, nitrogen oxide decomposition catalysts and dioxin decomposition catalysts. Slaked lime, calcium carbonate, sodium carbonate and the like can be used as the acid gas reactant. These alkaline powders neutralize acidic gases such as hydrogen fluoride, hydrogen chloride and sulfur oxides. Activated carbon, activated alumina and the like can be used as the adsorbent. The adsorbent functions to adsorb and remove heavy metals such as mercury.

As the nitrogen oxide decomposition catalyst (deNOx catalyst), a Pt-TiO ₂ catalyst, a V ₂ O ₅ —TiO ₂ catalyst, or the like is used. A denitration catalyst such as a V ₂ O ₅ —TiO ₂ catalyst also functions as a dioxin decomposition catalyst for decomposing dioxins. The dioxin decomposition catalyst is V ₂ O ₅ -T
In addition to the iO ₂ catalyst, a catalyst (titanium oxide / vanadium pentoxide / tungsten trioxide based three-way catalyst) in which V ₂ O ₅ and WO ₃ are supported on a TiO ₂ carrier can be used.

These powders can be used in an appropriate combination, but preferably contain a denitration catalyst or a dioxin decomposition catalyst, and preferably contain at least a dioxin decomposition catalyst. In addition, since sulfur oxides lower the activity of the denitration catalyst and the like, when the powder contains a catalyst, it is preferable to neutralize the sulfur oxides by previously adding slaked lime powder or the like to the exhaust gas. The powder of the catalyst or the like is not limited to the above example and may be another type of powder as long as it has a function of reducing harmful substances in exhaust gas.

The particle size of the powder is not particularly limited.
When it is about 1 μm to 1 mm, it is easy to integrate with the air-permeable supporting material. The amount of the powder may be appropriately adjusted depending on its activity, adsorption ability, etc., and is preferably about 300 g to 600 g per 1 m ^{2 of} bag filter.

As a method of manufacturing the bag filter of the present invention, the following two methods can be exemplified. The first method is a method using a mixed aqueous dispersion containing powder such as a catalyst and PTFE. This dispersion can be prepared, for example, by adding a powder to a commercially available PTFE dispersion. A preferable ratio in the dispersion is a solid content ratio (weight ratio) of PTFE1 to powder of 0.5 to 5%.
0, more preferably 1 to 20. When the above ratio is 0.
If it is less than 5, the removal of harmful substances will be insufficient, and if it exceeds 50, the powder will not be sufficiently fixed.

Next, the dispersion is impregnated into a breathable substrate such as a nonwoven fabric or a woven fabric. The dispersion may be impregnated by immersing the air-permeable substrate in the dispersion, applying the dispersion to the air-permeable substrate, or the like. After the impregnation of the dispersion, the air-permeable substrate is heated to a temperature equal to or higher than the melting point of PTFE, preferably to 330 to 400C. Thus, the powder of the catalyst or the like is fixed inside the air-permeable base material. The thickness of the gas-permeable base material impregnated with the dispersion is preferably 2 mm or more.

In the second method, at least two sheets of PTFE are used.
This is a method using a porous membrane. In this method, a powder of a catalyst or the like is sprayed on a porous PTFE membrane, and the powder is sandwiched between the porous PTFE membranes by joining this PTFE porous membrane and another PTFE porous membrane. The bonding of the PTFE porous membrane is preferably performed by thermal fusion. PTFE
The thermal fusion of the porous film is preferably performed by using a pressing device or a pair of rolls heated to a temperature equal to or higher than the melting point of PTFE, preferably 330 to 400 ° C. When the amount of the catalyst is insufficient with only the laminate composed of a pair of PTFE porous membranes, the number of laminated PTFE porous membranes may be further increased.

Next, the laminate of the porous PTFE membrane and the air-permeable substrate are joined. This bonding may be performed by heat fusion, or may be performed using an adhesive. The joining by heat fusion can be performed by heating a part of the base material by heating it to a temperature equal to or higher than the melting point of the air-permeable base material, and impregnating the melted base material with a PTFE porous membrane. The bonding with the adhesive can be performed by spraying hot melt powder fibers or dispersion on the bonding surface. Note that P
There is no particular limitation on the number of layers and the order of lamination of the laminate of the TFE porous membrane and the air-permeable substrate. The thickness of the PTFE porous membrane is preferably 5 μm to 200 μm, and the average pore diameter is 0.0
The thickness is preferably 1 μm to 50 μm, and the porosity is preferably 40 to 99%.

FIG. 1 shows the flow of exhaust gas in an exhaust gas treatment apparatus using one embodiment of the bag filter of the present invention. Exhaust gas (800-900 ° C.) from the incinerator is cooled to about 200 ° C. in the cooling tower, and slaked lime and ammonia are added. Acid gases such as hydrogen chloride and sulfur oxides are captured by slaked lime, and nitrogen oxides are captured by ammonia. Thereafter, as a powder, dust and heavy metals are removed, and nitrogen oxides and dioxins are decomposed by a bag filter in which a catalyst and activated carbon are integrated. Thus, the gas from which the harmful substances have been removed is discharged from the chimney.

[0027]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

Example 1 Aqueous dispersion having a PTFE weight concentration of 3% (manufactured by Mitsui DuPont Fluorochemical Co., Ltd.)
“30-J”) 20 kg, titanium oxide / vanadium pentoxide / tungsten trioxide system 3 having an average particle size of 0.05 mm
5.5 kg of the original catalyst was added and stirred. The solid content ratio (weight ratio) of the three-way catalyst to PTFE in this mixed dispersion was 9.2. The mixed dispersion has an inner diameter of 15
cm, glass fiber felt 1.2m long (thickness 3m
m) was immersed to impregnate the felt with the dispersion. Next, the felt was dried in a dryer kept at 150 ° C. for 20 minutes, and then put into a hot-air sintering furnace kept at 350 ° C. for 10 minutes to fix the catalyst to the felt by PTFE. On the bag filter thus obtained, 450 g / m ² of the catalyst was fixed, calculated from the weight increase. When the inside of the bag filter was observed with a scanning electron microscope (SEM), it was confirmed that the catalyst and the PTFE were fused.

Comparative Example 1 A bag filter was obtained using the same glass fiber felt as in Example 1 without any impregnation of the felt.

Comparative Example 2 Example 1 except that a dispersion containing only catalyst without PTFE was used.
In the same way as above, a bug filter was obtained.

Example 2 Between two PTFE porous membranes (thickness 15 μm, average pore diameter 3 μm, porosity 90%)
The three-way catalyst used in Example 1 was substantially uniformly dispersed, and 35
The two PTFE porous membranes were pressure-bonded using a press device maintained at 5 ° C. 55 g / m ² of the catalyst was fixed to the composite sheet as calculated from the weight increase. further,
Six such composite sheets were stacked and pressed in the same manner using the above-mentioned press apparatus to obtain a catalyst-containing PTFE laminate. On the other hand, an aqueous dispersion ("30-J", manufactured by Du Pont-Mitsui Fluorochemicals Co., Ltd.) having a PTFE weight concentration of 6% was applied onto a glass fiber felt (thickness: 3 mm) and dried.
The felt had 23 g / m ² of PTFE calculated from the weight gain. The catalyst-containing PTFE laminate was superimposed on the felt surface and pressed with a press device maintained at 380 ° C. to obtain a filter material. The filter material thus obtained was sewn to obtain a cylindrical bag filter having the same shape and dimensions as in Example 1. In this bug filter,
Observation by SEM confirmed fusion between the catalyst and PTFE.

Example 3 The aqueous dispersion used in Example 1 was mixed with a titanium oxide / vanadium pentoxide / tungsten trioxide-based three-way catalyst 5.5 having an average particle diameter of 0.05 mm.
kg, and 3 kg of activated carbon having an average particle size of 0.1 mm.
Stirred. The mixed dispersion was provided with an inner diameter of 15 cm and a length of 1.
A 2 m polyimide felt (manufactured by Toyobo Co., Ltd., “polyimide fiber P84”, thickness 3 mm) was dipped to impregnate the felt with the dispersion. Next, the felt was dried in a dryer maintained at 150 ° C. for 20 minutes, and then dried.
The felt was put into a hot air firing furnace maintained at 50 ° C. for 10 minutes, and the catalyst was fixed to the felt by PTFE. Calculated from the weight increase, the bag filter
90 g / m ² of catalyst and activated carbon were fixed. Also in this bag filter, observation by SEM confirmed fusion between the activated carbon and the catalyst and PTFE.

Comparative Example 3 Example 3 was repeated except that a dispersion containing only catalyst without PTFE was used.
In the same way as above, a bug filter was obtained.

The following performance evaluation was performed on the bag filters obtained in the above Examples and Comparative Examples. Powder falling resistance The filter cloth carrying the powder was backwashed with an air pulse jet (operating time 0.03 seconds) at a pressure of 3 kg / cm ² , and the relationship between the number of backwashing and the weight loss rate of the powder. Was measured. Table 1 shows the results.

(Table 1) Weight loss rate of powder (%) ―――――――――――――――――――――――――――――― Backwash Number (times) 25 50 100 500 1000 2000 ―――――――――――――――――――――――――――――――― Example 1 4.3 5.8 5.9 5.9 5.9 5.9 Example 2 6.5 6.7 6.7 6.7 6.7 6.7 Example 3 4.1 5.7 5.8 5.9 5.9 5.9 ――――――――――――――――――――――――――――――― ― Comparative Example 2 7.3 9.2 14.2 21.3 25.6 35.2 Comparative Example 3 6.9 10.1 13.3 19.8 25.0 35.1 ――――――――――――――――――――――――――――――― ―

Hazardous Component Removal Performance The removal performance of harmful components contained in exhaust gas from an incinerator with an incineration capacity of 160 t / day was measured. Exhaust gas volume 3000
With respect to 0 Nm ³ / hour, 100 kg / hour of slaked lime powder and 4.5 m ³ / hour of ammonia were added. The operation was performed such that the linear velocity of the exhaust gas passing through the bag filter was 0.7 m / min. The backwash conditions were an operation time of 0.03 seconds and a pulse interval of about 5 minutes. Table 2 shows the performance of removing harmful components 80 hours after the start of operation.

(Table 2) Removal performance of harmful components (%) ―――――――――――――――――――――――――――――― HCl SOx NOx Dioxin Mercury ―――――――――――――――――――――――――――――― Example 1 97 91 83 97 63 Comparative Example 1 97 90 83 41 45 Comparative Example 2 97 90 82 89 46 ―――――――――――――――――――――――――――――― Example 2 98 91 81 95 59 ―― ―――――――――――――――――――――――――――――― Example 3 97 90 79 96 98 Comparative Example 3 98 91 82 86 91 ―――― ――――――――――――――――――――――――――――

As shown in Table 1, in the bag filters of Examples 1 to 3, the rate of weight reduction of the powder by the air pulse jet was 10% or less even after 2000 times of backwashing. As shown in Table 2, the bag filters of Examples 1 to 3 also ensured good performance of removing harmful components, and were particularly excellent in the removal of dioxin.

[0039]

As described above, according to the present invention,
It is possible to provide a bag filter in which the powder of the catalyst or the like does not easily fall off and the effect of the catalyst or the like can be maintained for a long time. By using the bag filter of the present invention, harmful components contained in exhaust gas from an incinerator can be efficiently removed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an exhaust gas treatment process in an exhaust gas treatment device using one embodiment of the bag filter of the present invention.

Claims (6)

[Claims] Claims: 1. A bag filter for reducing harmful substances in exhaust gas, comprising at least one powder selected from a gas-permeable base material, an acid gas reactant, an adsorbent, a nitrogen oxide decomposition catalyst and a dioxin decomposition catalyst. Wherein the powder is integrated with the gas permeable substrate by polytetrafluoroethylene. 2. The bag filter according to claim 1, wherein the powder is fused with polytetrafluoroethylene. 3. The powder is present in a laminate composed of a plurality of polytetrafluoroethylene porous membranes, and the laminate is bonded to a gas-permeable base material so that the powder is integrated with the gas-permeable base material. The bag filter according to claim 1 or 2, wherein: 4. The bag filter according to claim 1, wherein the powder contains a dioxin decomposition catalyst. 5. A method for producing a bag filter for reducing harmful substances in exhaust gas, comprising: at least one powder selected from an acid gas reactant, an adsorbent, a nitrogen oxide decomposition catalyst, and a dioxin decomposition catalyst; A step of impregnating a gas-permeable base material with a mixed dispersion liquid in which tetrafluoroethylene is dispersed, and heating the gas-permeable base material to a temperature equal to or higher than the melting point of polytetrafluoroethylene, and solidifying the polytetrafluoroethylene after melting. And a step of integrating the powder with the air-permeable base material. 6. A method for producing a bag filter for reducing harmful substances in exhaust gas, comprising: a method for producing at least one powder selected from an acid gas reactant, an adsorbent, a nitrogen oxide decomposition catalyst, and a dioxin decomposition catalyst. Disposing between a plurality of polytetrafluoroethylene porous membranes, bonding the plurality of polytetrafluoroethylene porous membranes to each other to form a laminate of polytetrafluoroethylene porous membranes, and And a step of adhering the air-permeable support member to the bag filter.