JPS5822253B2 - electrostatic filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrostatic filter that continuously removes dust from dust-containing gas.

More specifically, it is an electrostatic method in which a dielectric material is filled between electrodes, and while a voltage is applied to the electrodes, a dust-containing gas is flowed into the gap in the dielectric material, causing the dust in the dust-containing gas to adhere to the dielectric material and removing the dust. Regarding filters.

Conventionally, so-called electrostatic filters collect dust by passing dust-containing gas between dielectrics to which a voltage is applied, and there are filters that collect dust on the dielectric by electrostatic force, or filters that collect dust by passing dust-containing gas through the dielectric. 2) A method in which dust is charged by corona discharge is widely used.

FIG. 1 shows an example of a conventionally used method, and this will be explained as a representative example of the conventional method.

In the figure, the dust-containing gas flows in the direction of the arrow, and after the dust is charged by the corona discharge formed between the discharge electrode 4 and the ground electrode 5, the dust is charged by the dielectric between the high voltage electrode 1 and the ground electrode 2. While passing through the gap 3, the dust is collected on the dielectric 3 by the Coulomb force caused by the electric field and removed.

In this method, the higher the voltage applied to the high-voltage electrode 1, the stronger the electric field in the gap in the dielectric 3 and the better the dust removal efficiency, but if the voltage is too high, sparks will occur and the dielectric 3 will be altered. However, it still has disadvantages in that it requires combustion, and that the current does not flow stably and is extremely difficult to control.

In addition, when particulate matter is used for the dielectric material 3, the dust collected on the surface of the particulate matter will be scattered again due to the movement of the particulate matter, and will be discharged to the outside of the filter together with the exhaust gas, resulting in a significant decrease in dust collection efficiency. It will come.

The inventors filled the space between electrodes with a granular dielectric and applied a high voltage between the electrodes. Depending on the properties of the dielectric, the electric field in the gap was stronger than that in the dielectric itself, making the dielectric the electrode. We discovered that multipolar discharge occurs in the voids, and that if there is dust, etc. in the voids, the voids are efficiently charged, and that the dust charged in this way is accumulated on the surface of the granular dielectric material. It looks at the development of new devices that can be effectively combined.

The feature of this method is that dust charging and dust collection are performed at the same place, and by using granular so-called electrical insulators for the dielectric, the dielectric becomes an electrode and multipolar discharge occurs, making it efficient. This means that charging is performed.

Furthermore, if this granular dielectric material is moved and used for circulation, the dust collected on the granular dielectric material can be recovered before it becomes a large amount.

At this time, even if the dust collected on the dielectric material is scattered for some reason, it will be immediately charged by the ion shower of the multipolar discharge and will be captured on the dielectric material again.

The most important condition for the device of the present invention is the apparent electrical resistance of the granular dielectric.

The apparent electrical resistance here refers to the resistance of the filled body when particles are filled into a container without any particular pressure applied and a constant current is passed from both ends of the container.

The apparent resistance is determined by the volume resistivity of the filling body, the apparent density when the body is filled, the state of contact between particles, the state of the atmosphere, such as temperature, humidity, gas properties, amount and properties of attached dust, etc. It changes depending on.

The dielectric has a volume resistivity of 101゜Ω-cm at room temperature.
These particles are made of the above-mentioned insulators, such as gravel, porcelain, glass beads, alumina particles, etc., and their shape is not particularly limited, such as spheres, cylinders, irregular shapes, etc.

When filled with such granular dielectric material, the apparent electrical resistance is 5.
×108Ω-cm When a high voltage is applied on the DL, the electric field in the gap becomes stronger than that in the granular dielectric due to the polarization effect, and a multipolar discharge using the granular dielectric as an electrode occurs in the gap in the granular dielectric.The volume of the granular dielectric If the specific resistance is small, current will flow inside the granular dielectric, and even if the specific resistance is large, if the apparent resistance is small, the current will flow on the surface of the particles, so a high voltage cannot be applied. The electric field in the gaps in the granular dielectric cannot become strong, so multipolar discharge cannot occur.

Even if the apparent electrical resistance is small, it is possible to form a multipolar discharge by flowing a large current, but this is not economical.

Therefore, it is a condition of the present invention that the apparent electrical resistance is 5 x 1080-cm or more.

One of the factors governing the apparent electrical resistance is due to the inherent properties of the dielectric material.

In other words, it is the volume resistivity and shape of the dielectric.

The dielectric material used for the purpose of the present invention is a so-called insulator having a volume resistivity of 1010 Ω-m or more, and is particularly preferably in the form of small particles with a diameter of 1 to 10 m.

The volume resistivity of the insulator is glass at room temperature: 〉1013
．． Sulfur: 1016-1017. Feldspar porcelain: 1013-1
014. Steatite: 10”~1012 Titanium oxide:
)io14Ω-cm, and all of these values decrease as the temperature increases.

Among the electrical resistances inherent to materials, there is a surface resistivity when a current flows through the surface of the material, but its value varies greatly depending on the amount of water in the gas and the electrical resistance of attached dust.

Therefore, when removing dust from a gas with a low temperature and high moisture content, steps are taken to raise the temperature of the gas as the moisture adheres to the dielectric surface and reduces the electrical resistance. In this case, dust adheres to the surface of the dielectric material and reduces the electrical resistance, so in order to remove the adhering dust, the speed of circulation through the granular dielectric material is increased to keep the electrical resistance above 5X]08 Ω-cmJJ. It is being

When the electrical resistance of the dielectric is 5 x 108 Ω-cm or more, if a plate-to-plate electrode is used, a voltage that causes a multipolar discharge is applied to generate a multipolar discharge throughout the gap in the dielectric, and a discharge occurs. sparks and a stable discharge cannot be obtained.

One way to generate a stable single-pole multipolar discharge under the above conditions is to block the electrodes with an insulator and apply an alternating current voltage, similar to silent discharge.

Since the space between the electrodes is blocked by an insulator, it is stable without generating sparks.

For the method of blocking the electrode with an insulator, the electrode may be covered with an insulator.

Another method of obtaining a stable multipolar discharge is to provide an electric field concentration area in the electrodes to make the current density flowing through the dielectric and the air gap non-uniform.

In other words, the current density near the electric field concentration area is increased to generate multipolar discharge, and the current density is decreased in areas far from the electric field concentration area to prevent multipolar discharge from occurring and to allow the current to flow in or on the dielectric surface. That's true.

In order to allow current to flow within or on the dielectric surface, sufficient multipolar discharge cannot be generated unless the apparent electrical resistance of the dielectric is less than 2.times.10.sup.11 .OMEGA.-cm.

Dust often has high electrical resistance, and the electrical resistance may fluctuate over time, so the apparent electrical resistance of the dielectric material to which dust is attached must always be kept at 5X108Ω-crn or higher and below 2X1011Ω-cmJJ. It is difficult.

A third method for obtaining stable multipolar discharge is to provide an electric field concentration section in the electrode and apply a voltage including an AC high frequency region.

By doing this, multipolar discharge occurs in the dielectric gap near the electric field concentration area, and multipolar discharge does not occur in a place far from the electric field concentration area.

The dielectric material located far from the electric field concentration area acts as an insulator in silent discharge, resulting in stable multipolar discharge.

In either method, it is important that the electrode has an electric field concentration area, and multipolar discharge occurs in the dielectric gap near the electric field concentration area, and multipolar discharge occurs in a place far from the electric field concentration area. Preventing this from occurring is a condition for the stability of discharge.

The following advantages can be obtained by using a granular dielectric material.

In other words, by forming the particles into particles, the porosity is small and it is possible to discharge with a low applied voltage.The surface area of the dielectric particles that become the dust collecting electrode can be increased to a large extent. It is easy to move and play, etc.

Another advantage of the electrostatic filter of the present invention is that the charging of dust and the adhesion of dust to a dielectric material by Coulomb force are performed by the same mechanism, so unlike the conventional method, the electrodes for the charging reservoir and the electrode for the dust collecting reservoir are separated. There is no need for installation and the structure is simple.

Next, the electrostatic filter according to the present invention will be explained with reference to the drawings.

In FIG. 2, the high voltage electrode 9 is composed of a linear or needle-shaped electrode having an electric field concentration part, and the AC high voltage generator 11
Connect to.

The ground electrode 8 has a breathable structure and has a structure that holds the dielectric 10.

When the dust-containing gas flows in the direction of the arrow, the dust is charged by multipolar discharge from the dielectric 10 near the high voltage electrode 9 and collected on the surface of the dielectric at a distance from the high voltage electrode 9.

A desirable mode for use as an actual device is that the ground electrode 8
There is a method in which the high-voltage electrode 9 is placed in the center of the two ground electrodes 8 by providing them on both sides and filling the space with a dielectric 10.

Such a configuration is not only desirable for preventing danger to workers, but also extremely convenient for moving the dielectric 10.

Furthermore, an example of implementation of the present invention will be explained with reference to the drawings.

In FIG. 3, the precipitator includes a granular dielectric 10 placed in the middle of a flue 12 and supported by permeable ground electrodes 8 and 8' and a line running longitudinally within the granular dielectric 10. It consists of a high voltage electrode 9 held by an insulator 13, 13'.

The high voltage electrode 9 is connected to an AC high voltage generator (not shown), and an AC high voltage including a high frequency range is applied thereto.

The ground electrode is also connected between the opposing high voltage electrodes 9 at VC8 in the figure.
``Install it as shown.

The dielectric particles travel through the precipitator and are discharged through the valve 19, the rate of flow of which can be varied by adjusting the valve 19.

The discharged particles are supplied to the upper part of the apparatus via the conveyor 21 again after removing dust attached to the particles by the vibration node 20.

In the apparatus shown in Fig. 3, gravel with a diameter of 4 to 6 gates and an apparent electrical resistance of 5 x 109 Ω-crn was used as the dielectric material, and when an alternating current voltage of 30 to 45 KV was applied, the difference was 1 to 1 per area of the ground electrode. A current of 2 ohmAJ flowed.

Approximately 1.0? Exhaust gas containing dust of /Nrn' was sent at a cylinder speed of about 40 (:rn/sec), and dust was collected under the above conditions to obtain a dust removal efficiency of 99 factors or higher.

At this time, the particles were circulated at a linear velocity of 50 cm/Hr within the apparatus.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional electrostatic filter mechanism, FIG. 2 is an explanatory diagram of an electrostatic filter mechanism according to the present invention, and FIG. 3 is an illustration of an example of the implementation of the present invention. It is an explanatory diagram. In FIGS. 2 and 3, 8 represents a ground electrode, 9 represents an electrode having an electric field concentration portion, and 10 represents a movable dielectric body.

Claims (1)

[Claims] 1. In an apparatus for removing dust from a dust-containing gas by passing a dust-containing gas through a gap in a dielectric filled between breathable electrodes to which a voltage is applied, a granular insulator is used as the dielectric. , the apparent electrical resistance in the filled state is 5 x 1080-0, and at least one electrode has an electric field concentration part, and an alternating current voltage is applied between the electrodes. An electrostatic filter that generates multipolar discharge in the air gap and performs charging and dust collection in a single area. 2. The device according to claim 1, wherein at least one of the electrodes is coated with an insulator.