JPS59127657A - Method and apparatus for filtering fluid - Google Patents

Abstract

PURPOSE:To enhance the collection efficiency of a charged filter material, by applying positive or negative single charge to dust flowed into the charged filter material. CONSTITUTION:As a charged filter material, one obtained by bringing a porous sheet such as paper, a nonwoven fabric or foam to an electret state by corona discharge or high voltage treatment or one charged by mechanical friction is used. In order to ionize dust, a method by corona discharge is pref. The charged filter material 4 and the ionizing part 1 provided to a fluid inflow side are formed of a needle like electrode 2 and a metal net electrode 3. Because dust is gradually accumulated in the filter material, a metal earth electrode is provided so as to be contacted with the effluent side of the charged filter material when efficiency is lowered by repulsive force of charge to escape accumulated charge. When dust is preliminarily ionized, collection efficiency with high capacity can be continued for a long time as compared with the dust collection performed merely by using the charged filter material.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention mainly relates to a method for filtering dust-containing air and a filter device directly used therefor.

More specifically, in order to establish a filter system that provides stable performance with low pressure loss and high collection efficiency, the present invention provides a fluid filtration method and a filtration device based on an electrostatic collection mechanism.

BACKGROUND ART Charged furnace materials in which a filtration material has an electrostatic charge have been proposed as high-performance furnace materials.

One type of charged furnace material is so-called electret material, in which electric charges are embedded in the surface or inner surface of the fibers that make up the filter material (such fibers are generally referred to as electret fibers). (Special Publication No. 56-47299).

It is said that the dust particles passing through are efficiently collected regardless of the charged state of the dust. That is, it is said that positively or negatively charged particles are collected by the force in an electrostatic field, and uncharged neutral particles are collected by the induced force from the charges on the fiber surface.

Therefore, this electret furnace material certainly has higher collection efficiency and lower pressure loss than conventional uncharged P#. Therefore, it is a promising material as an energy-saving furnace material. However, according to the tests conducted by Akira Nakagi, it was found that this high performance was only possible in the early stages, and had the drawback of not being stable for a long time.
In particular, when the purpose is to clean the air in general buildings or indoors, the main target dust is cigarette smoke, but if tested with this smoke, the collection efficiency will quickly drop, rendering it impractical. This is because the tar component in the cigarette smoke covers the electret fibers, weakening the static electric field, or furthermore, the tobacco components enter the fibers, relaxing (neutralizing) the static charge.
This is thought to be due to the occurrence of Similar performance degradation occurs under conditions of high humidity, liquid particles, and mist.

In addition, as one of the charged P materials, there is also a filtration material that is charged by friction (Japanese Patent Application Laid-Open Nos. 58-119478 and 1977-156291), but these Since the electrostatic charge is more unstable, it is not satisfactory against cigarette smoke.

For this reason, there are filtration methods that use electrostatic force, such as a method in which dust particles are charged and collected between agglomerating electrode plates placed behind them, and a dielectric filtration method in which an external electric field is applied to the P material to collect them. However, while these offer relatively stable performance with low pressure drop and high efficiency, they have the drawbacks of high equipment costs and troublesome maintenance.

Therefore, as a result of various studies, the inventor of the present invention found that
Surprisingly, by ionizing the dust collected on charged furnace materials such as wood, it is possible to collect dust permanently and with high efficiency, and the initial collection efficiency is also very high. This discovery led to the present invention.

That is, the present invention provides a fluid filtration method characterized by ionizing dust on the fluid inflow side of the charged furnace material in a method of treating dust-containing fluid using a charged furnace material, and a fluid filtration method that can be directly used in this method. The present invention relates to a fluid filtration device characterized by comprising a charging furnace material and an ionization section.

Although charged furnace materials have excellent initial performance as described above, their performance is not permanent. However, the present inventor has discovered that a surprisingly large effect can be achieved by ionizing the dust flowing into the charged P material, that is, by giving the dust a single positive or negative charge.

In other words, it has been found that by ionizing dust, the collection efficiency of the charged P material can be further improved, and that the collection efficiency can be maintained without deterioration, which had been a drawback in the past.

The method of collecting ionized dust particles with P material is well known, but by collecting ionized dust particles with charged P material as in the present invention, it is possible to use conventional uncharged furnace material. It is revolutionary that the performance of the charged furnace material can be dramatically improved compared to the case where only the charged furnace material was used, and the performance of the charged furnace material is made permanent.

The charging furnace material used in the present invention is paper or nonwoven fabric.

It refers to a porous, net-like material such as foam that has been made into an electret by corona discharge or high voltage treatment, or that has been electrically charged by mechanical friction. In particular, nonwoven fabrics that are heat-treated in a direct current high electric field at a temperature above the glass transition point and below the melting point of the polymer and then kept in the high electric field until the temperature drops below the glass transition point to form an electret can be suitably used. Also, the above-mentioned Japanese Patent Publication No. 56-4729
The electret furnace material disclosed in No. 9 is also suitable.

In the present invention, the method of ionizing dust 1 can be carried out by a known method, and is not particularly limited. Practically speaking, however, it is preferable to conduct this by corona discharge, in which a positive or negative DC voltage of 1 to 15 kilovolts (KV) is applied between the so-called linear or needle-shaped counter electrode and the opposite electrode, depending on the distance. The voltage is applied to generate a corona discharge, which ionizes dust passing near the discharge electrode. At this time, since negative electrode discharge generates a large amount of ozone, positive electrode discharge is usually performed.

In this way, in the present invention, ionized, that is, positively or negatively charged dust particles are treated with a charged furnace material, but as the dust is captured by the P material, the same electric charge is transferred to the inside of the furnace material. Depending on the situation, the efficiency may drop slightly due to the /'T force of the charge. At this time, it is advisable to provide a metal ground electrode in contact with the outflow side of the band tF material to release the accumulated charge.

The filtration device of the present invention is as shown in FIG. Charging furnace material (4) and ionization unit (1) installed on the fluid inflow side
It is extremely simple. Ionization part (1)
consists of an electrode (2) in the shape of a needle or the like and an electrode (8) in the shape of a wire mesh or the like. Because the apparatus of the present invention is thus simple, it is inexpensive and economical in terms of equipment.

As described above, when collecting dust using a charged furnace material, the present invention ionizes the dust in advance. Compared to the case of collecting using a filter, high-performance collecting efficiency can be maintained for a long time, and the equipment is also cheap and maintenance is easy.

The description here mainly focused on air filtration, but
The present invention can be used for gases other than air, and even for liquids in some cases.

Next, the present invention will be explained based on examples. Example 1 As a band 'dLfP material, the area weight a o o f/yti',
Pressure loss 12 NIR made of electret with a thickness of 5 mm
A nonwoven fabric furnace material (manufactured by Minnesota Mining Manufacturer, trademark: Filtrete) of Aq (at a wind speed of 50 cm/s) was used. An ionization section was provided on the fluid inflow side of the charging furnace material.

This ionization part consists of a tungsten wire with a diameter of 0.2mm and a wire mesh made of a metal wire with a diameter of Q and 4mm.
It is as shown in the figure. A device consisting of this charging furnace material and an ionization section was installed in an office with a lot of cigarette smoke, and filtration was performed without applying a positive DC voltage of 12 kilopoles (KV) to the tungsten wire. Filtration speed is 50cm/
The dust concentration was measured using a digital dust meter (manufactured by Shibata Kagaku Kikai ■, product name S-684) on the fluid inflow and outflow sides of the charged furnace material, and the collection efficiency was determined. This result is represented by a line connecting the black circles in FIG.

Reference Example 1 Using the same apparatus as in Example 1 except that the inflowing dust was not charged, the collection efficiency was measured. The results are shown by the line connecting the white circles in FIG.

As is clear from Example 1 and Reference Example 1, if the method of the present invention is used, high trapping efficiency can be maintained for a long period of time, but if the conventional method is used, the trapping efficiency decreases over time and the charging furnace material deteriorates. Replacement will be necessary.

Example 2 In order to investigate the initial collection efficiency by the method according to the present invention, the following experiments were conducted.

As the charged P material, the same nonwoven fabric furnace material used in Example 1 was used.

Regarding dust, we made the following three types of charged states: ■ to ■.

■ Spray saline with a concentration of 0.1% using a sprayer (nozzle diameter 0, 5
myx〆, air pressure 1 kq/cyA), and after drying with a silica gel diffusion dryer, a differential electric mobility classifier (Magazine [Chemical Engineering J 1982
A voltage of 800 volts was applied to a device (similar to the one described in the November issue, page 29) to obtain NaCl particles with a diameter of 0.047 microns. This particle is a negatively charged single charged particle.

■ The particles of ■ were neutralized with americium 241. This particle is an equilibrium charged particle.

■ Charged particles were removed by passing the particles of ■■ between high voltage plates (2 kilovolts) spaced at 5 intervals.

This particle is an uncharged particle.

Using these particles from ■ to ■, increase the filtration rate to 10 to 200.
The number concentration before and after the charging furnace material was measured using a condensation nucleus counter (manufactured by Nippon Kagaku Kogyo ■) to determine the collection efficiency. The results are shown in FIG. 3, where the particles marked ``■'' are shown as black circles, the particles ◯ are shown as half-black circles, and the particles ◯ are shown as white circles.

Reference Example 2 Initial collection efficiency was determined under the same conditions and method as in Example 2, except that an uncharged glass fiber furnace material with the same pressure drop of 12 Aq (at a wind speed of 50 CII/s) was used instead of the charged furnace material. was measured. The results are shown in FIG. 3, in which black squares indicate the use of particles ``■'', half-black squares indicate particles ``■'', and white squares indicate particles ``■''.

As is clear from FIG. 3, the collection efficiency decreases as the speed increases in all cases, but the charged P material has a higher initial collection efficiency than the glass fiber furnace material. Furthermore, with glass fiber furnace materials, there is almost no change in the initial collection efficiency even if the charge state of Nac1 particles changes, whereas with charged furnace materials, the initial collection efficiency is in the order of ■uncharged particles, ■balanced charged particles, and ■singly charged particles. The collection efficiency is high, and in particular, in the case of monotonically charged particles, which is the method according to the present invention, the performance is dramatically improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the device according to the present invention, and FIG. 2 is a graph showing changes in collection efficiency over time in Example 1 and Reference Example 1. FIG. 8 is a graph showing the initial collection efficiency in Example 2 and Reference Example 2. Patent applicant Nippon Vilene Co., Ltd.

Claims (2)

[Claims] (1) A fluid filtration method that uses a charging furnace material to filter a dust-containing fluid, the method comprising ionizing dust on the fluid inflow side of the charging furnace material. (2) A fluid filtration device comprising a charging furnace material and an ionization section that ionizes dust on the fluid inflow side of the charging furnace material.