JP2002136812A - Laminate for bag filter and bag filter using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve property of shaking down a dust cake layer on a bag filter using a polytetrafluoroethylene porous membrane together with a gas- permeable support material. SOLUTION: The gas-permeable support material 3 is laminated with the polytetrafluoroethylene porous membrane 2 and besides an outer later 1 consisting of a gas-permeable material having <=30 g/m2 weight is laminated on the surface of the polytetrafluoroethylene porous membrane. A space is formed between a cake layer formed by dust contained in a gas stream 4 and the polytetrafluoroethylene porous membrane 2 by this outer layer 1, so that the property of shaking down the cake layer by a pulse jet, etc., is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bag filter used for a dust collector for filtering fine particles from a gas stream and a laminate used for the bag filter.

[0002]

2. Description of the Related Art In a bag filter type dust collector, dust is collected by forming a cake layer of dust on the surface of the bag filter. In recent years, polytetrafluoroethylene (hereinafter, referred to as “P”) has been required to satisfy the requirements for bag filters such as high collection efficiency, excellent heat and chemical resistance, and low energy cleaning properties.
Increasingly, porous membranes (referred to as “TFE”) are used as bag filters. The PTFE porous membrane is usually used as a laminated body laminated with another air-permeable support material in order to secure the strength required for removing the cake layer and extend the life. The gas flow containing dust permeates from the PTFE porous membrane side of the laminate, and forms a dust cake layer on the surface of the PTFE porous membrane. PTF
If the E porous membrane is arranged on the upstream side of the gas flow, if it is arranged reversely, it will function as a filter instead of the PTFE porous membrane, but as a gas-permeable supporting material, the excellent properties of the PTFE porous membrane Is no longer available. Since the cake layer itself also functions as a filtration layer, using this bag filter reduces the dust concentration on the downstream side to, for example, 10 mg / m ^3.
It can be reduced to the following level. When the pressure loss of the bag filter increases with the growth of the cake layer, vibration,
The cake layer is removed by a pulse jet or the like.

Several improvements have been proposed for bag filters using a PTFE porous membrane. For example,
Japanese Patent Application Laid-Open No. 2000-176226 discloses that a smooth gas-permeable protective layer is interposed between a gas-permeable supporting material (substrate) and a porous PTFE film so that the adhesion between the gas-permeable supporting material and the PTFE porous film is improved. An improved bug filter is disclosed. When the adhesion is improved, even if a pulse jet or the like is applied for removing the cake layer, the air-permeable support material and the PTFE porous membrane are less likely to be separated.

[0004]

SUMMARY OF THE INVENTION A PTFE porous membrane is
It has high dust collection efficiency and good cake layer removal properties, and is itself suitable as a bag filter material.
However, depending on the operating conditions of the dust collector and the type of dust, there is a case where sufficient wiping properties cannot be exhibited.

The inventors of the present invention have studied and found that the following 2
Under these conditions, it was found that the ability to remove the cake layer from the PTFE porous membrane was reduced. When the dust particles are fine and a dense cake layer is formed When the dust particles are positively charged

[0006] An increase in pressure loss due to a decrease in wiping properties causes problems such as an increase in running cost and breakage of a bag filter. Accordingly, an object of the present invention is to improve the property of removing a cake layer of a bag filter using a porous PTFE membrane.

[0007]

As a result of diligent studies to achieve the above object, the present inventor has found that an outer layer is arranged on the surface of a PTFE porous membrane, and that an outer layer is provided between the PTFE porous membrane and the cake layer. It has been found that if the voids are secured, the cake layer removal property can be improved. It is considered that the drop-off property is reduced in the above case due to an increase in the contact area between the cake layer and the PTFE porous membrane. It is considered that the reason why the wiping property is reduced in the above case is due to the negatively charged characteristic of PTFE. Therefore, if an appropriate gap is secured between the porous PTFE membrane and the cake layer, in these cases as well, a decrease in the wiping performance of the bag filter can be suppressed.

[0008] In order to secure an appropriate void, the basis weight of the outer layer is important. For example, if a gas-permeable material having a large basis weight used as a gas-permeable support material is arranged on the upstream side of the gas flow, the porous PTFE membrane does not function sufficiently as a filter as described above. The laminate for a bag filter of the present invention is obtained by laminating a gas-permeable supporting material and a porous PTFE membrane, and has a basis weight of 30 g / surface on the surface of the porous PTFE membrane.
It is characterized in that an outer layer having a size of m ² or less is further laminated. The basis weight of the outer layer is more preferably 20 g / m ² or less.
This laminate is used as a bag filter by arranging the outer layer so as to be on the upstream side of an air flow (gas flow) containing fine particles to be removed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described with reference to FIG. In the bag filter laminate of FIG. 1, an outer layer 1, a PTFE porous membrane 2, and a gas-permeable supporting material 3 are laminated in this order from the upstream side of a gas flow 4 containing fine particles to be removed.

The porous PTFE membrane 2 can be obtained by a conventionally used method. As one example of this method, a mixture of unfired PTFE powder and a liquid lubricant (such as naphtha) is formed into a film by extrusion and / or rolling, and the liquid lubricant is removed from the unfired film. A method of making the film porous by uniaxial stretching or biaxial stretching can be given.

The PTFE porous membrane is not particularly limited, but has a thickness of 5 μm to 200 μm and a pore size of 0.01 μm to
Preferably, the porosity is 50 μm and the porosity is 40 to 99%. The air permeability of the porous PTFE membrane is 7 ml / cm.
It is preferably at least ² seconds. In this specification, the air permeability is indicated by a measured value based on a method specified in JIS L 1096.

As the air-permeable supporting member 3, a woven fabric, a nonwoven fabric, a metal mesh, a plastic net or the like can be used. Examples of the material of the woven or nonwoven fabric include glass fiber, graphitized fiber, polyolefin fiber, polyamide fiber, polyester fiber, polyvinylidene chloride fiber, and fluorine fiber. Basically, the breathable support material
The bag filter is required to have sufficient strength to secure the strength of the bag filter and to have sufficient air permeability so as not to hinder the function of the bag filter. The basis weight of the air-permeable supporting material is not particularly limited, but is usually larger than the outer layer (for example, 35 g /
m ² or higher) is required.

The outer layer 1 has a lower density than the air-permeable supporting material,
For example, the basis weight is preferably about 10 to ²⁰ g / m ² . As the outer layer, a polymer, a metal mesh, or the like may be used, but a nonwoven fabric is generally suitable. As a material of the nonwoven fabric, a single material such as polyolefin, polyamide, polyester, or polyvinylidene chloride, or a composite product thereof can be used.

The air permeability of the outer layer is preferably at least 10 ml / cm ² · second, particularly preferably at least 15 ml / cm ² · second in order to ensure air permeability of the whole bag filter. On the other hand, the thickness of the outer layer is preferably 0.01 mm or more in order to secure a space between the cake layer and the porous PTFE membrane.

For the bonding of the porous PTFE membrane, the air-permeable supporting material and the outer layer, a conventionally applied heat laminating method, adhesive laminating method and the like can be used. In the thermal lamination method, a part of the material to be laminated on the PTFE porous membrane is melted and impregnated into the PTFE porous membrane. One of the preferable joining methods for securing the adhesive strength required for the bag filter is an adhesive laminating method using fluororubber as an adhesive. The bag filter laminate produced by laminating each material is appropriately cut and processed to increase the surface area (for example, pleating, processing into a cylindrical shape, processing into an envelope shape), and a bag filter is formed. Become.
At the time of processing, the laminate is arranged such that a gas flow containing dust permeates from the outer layer side to the air-permeable support material side.

[0016]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples. (Example) The following PTFE porous membrane, air-permeable supporting material, and outer layer were used. -PTFE porous membrane: "NTF1033" manufactured by Nitto Denko Corporation
(Thickness: 15 μm, pore size: 3.0 μm, porosity: 90%, air permeability: 20 ml / cm ² · second)-Air-permeable support material: Conex nonwoven fabric “FX408ZM” (manufactured by Nippon Felt Industry Co., Ltd.) (thickness: 1.6 mm, basis weight: 475)
g / m ² , air permeability: 14 ml / cm ² · second) ・ Outer layer: Polyolefin nonwoven fabric “PO16UL-00S” manufactured by Tonen Tapils Co., Ltd. (0.08 mm thick, unit weight 1)
6 g / m ² , air permeability 17 ml / cm ² · second)

Here, as an adhesive between the porous PTFE membrane and the air-permeable supporting material, a fluoro rubber latex “GC-250CR” manufactured by Daikin was used. First, the latex was spray-coated on the air-permeable support material at a coating amount of 20 g / m ² , the PTFE porous membranes were overlapped, and pressed from the PTFE porous membrane side by a heating roll of a heat laminating machine.
By the curing of the fluoro rubber, the porous PTFE membrane and the air-permeable supporting material were bonded. Laminating temperature is 180 ° C, laminating speed is 2m / min, laminating pressure is 0.2MPa
And Next, the outer layer was overlaid on the PTFE porous membrane, and pressed by a heating roll from the outer layer side. The outer layer was partially melted and adhered by penetrating into the pores of the porous PTFE membrane. Laminating temperature 140 ° C, laminating speed 2m / min, laminating pressure 0.2MP
a. The bag filter thus obtained has an air permeability of 3.7.
ml / cm ² · sec.

(Comparative Example 1) PT without laminating the outer layer
A bag filter was manufactured by laminating only the FE porous membrane and the air-permeable supporting material. Other points such as a laminating method were the same as in the example. The air permeability of the bag filter is 4.1
ml / cm ² · sec.

Comparative Example 2 A bag filter using a nonwoven fabric having a large basis weight as an outer layer was manufactured. This nonwoven fabric is a polyester-polyolefin core-sheath structure nonwoven fabric manufactured by Unitika Ltd. “Elves T0703WDO” (0.25 mm thick,
The basis weight is 70 g / m ² and the air permeability is 40 ml / cm ² · second). Others such as the lamination method were the same as those in the example, but the lamination temperature when laminating the outer layer was 160
° C, lamination speed 2 m / min, lamination pressure 0.
2 MPa. The air permeability of the bag filter is 4.0 ml /
cm ² · sec.

The bag filters obtained in the above Examples and Comparative Examples were evaluated using a bag filter test apparatus. This bag filter test apparatus evaluates characteristics by flowing an air current containing various dusts into a 100 cm ² bag filter. The differential pressure between the upstream side and the downstream side of the bag filter is continuously monitored, and a pulse jet for removing dust is applied to the bag filter every predetermined time. The test conditions are as follows.

Filtration speed: 3 m / min Dust type: JIS 11 class (Kanto Rohm) Dust concentration: 33 g / m ³ Pulse pressure: 3 MPa Pulse interval: 90 seconds

The above-mentioned dust is classified into ultrafine particles even in JIS test powder, and its median diameter is 1.6 to 2.
3 μm. The maximum pressure loss during the test of each bag filter and the amount of dust remaining on the bag filter immediately after being removed (amount of residual dust) were measured. Table 1 shows the results.

(Table 1) ――――――――――――――――――――――――――――――― (Example) Number of pulses 0 3 40 Pressure Loss (Pa) 186 343 353 Residual dust amount (mg / 100cm ² ) 0 21 42 ――――――――――――――――――――――――――――― -(Comparative Example 1) Number of pulses 0 3 10 Pressure loss (Pa) 167 382 470 Amount of residual dust (mg / 100 cm ² ) 0 27 57 ------------------------------------------- ――――――――――――――― (Comparative Example 2) Number of pulses 0 3 10 Pressure loss (Pa) 186 382 500 Amount of residual dust (mg / 100 cm ² ) 0 27 61 ――――― ――――――――――――――――――――――――――――

In Comparative Examples 1 and 2, the pressure loss and the amount of residual dust were higher than those in Examples. In particular, in Comparative Example 2, despite the air permeability of the outer layer being higher than that of the Example, the final pressure loss is larger than that of the Comparative Example 1 as well as the Example. This result indicates that the basis weight of the outer layer is important.

[0025]

As described above, according to the present invention,
The property of removing a cake layer of a bag filter using a PTFE porous membrane together with a gas-permeable supporting material can be improved. Thereby, even if the dust cake layer is repeatedly wiped off, an increase in pressure loss can be suppressed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a bag filter laminate according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Breathable support material 2 PTFE porous membrane 3 Outer layer 4 Gas flow

Claims (7)

[Claims] 1. An air-permeable support material and a polytetrafluoroethylene porous membrane are laminated, and an outer layer made of a gas-permeable material having a basis weight of 30 g / m ² or less is further provided on the surface of the polytetrafluoroethylene porous membrane. A laminate for a bag filter, which is laminated. 2. The bag filter laminate according to claim 1, wherein the basis weight of the outer layer is 20 g / m ² or less. 3. The bag filter laminate according to claim 1, wherein the air permeability of the outer layer is 10 ml / cm ² · second or more. 4. The bag filter laminate according to claim 1, wherein the outer layer is a nonwoven fabric. 5. The bag filter laminate according to claim 1, wherein the basis weight of the air-permeable supporting material is larger than the basis weight of the outer layer. 6. The bag filter laminate according to claim 1, wherein the basis weight of the air-permeable supporting material is 35 g / m ² or more. 7. A bag filter, wherein the laminate according to any one of claims 1 to 6 is arranged such that an outer layer is on an upstream side of an airflow containing fine particles to be removed.