JPS6161864B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dust collector, and particularly to a dust collector using an electrostatic treatment filtration method that effectively collects high-resistance dust.

Conventionally, heavy oil has been mainly used as fuel for boilers for thermal power generation, but as is well known, due to the oil situation, power plants that use coal as fuel are being planned. This coal produces several hundred times more dust in its combustion exhaust gas than heavy oil, and requires the installation of high-performance dust collectors to meet emission regulations.

The apparent specific electrical resistance ρ (hereinafter simply referred to as ρ) of dust in the combustion exhaust gas from coal as fuel varies greatly depending on the type of coal, and its value ranges from 10 Ω-cm to ¹⁰ Ω-cm.
Some reach 10 ¹³ Ω-cm. If a general electrostatic precipitator is used to collect dust exceeding 10 ¹² Ω-cm, a reverse ionization phenomenon may occur and the dust collection rate may drop significantly. As a countermeasure to this problem, some methods have been implemented to reduce the ρ of the dust by adding sulfuric anhydride (SO ₃ ), steam, or water to heat it, but this method requires high running costs and requires operational control. It has drawbacks such as being difficult.

As a dust collection method that is completely unaffected by the ρ of dust, there is a filtration and dust collection device using a bag filter. Although this device has high dust collection efficiency, its biggest drawback is that the filter is clogged by the collected dust, increasing ventilation loss. As a method of brushing off the dust collected on the filter, a method of applying vibration to the filter or backwashing with pressurized air is adopted. Since this brushing is frequently performed during operation, it has the disadvantage of shortening the life of the filter.

It is known that in the filtration dust collection method, if the dust introduced into the filter is charged, the dust collection efficiency will be improved and the increase in ventilation loss can be suppressed compared to when there is no charge. According to this electrostatic treatment filtration method, the number of times the filter is removed is reduced, and the life of the filter can be maintained for a long time. The means of applying electric charge to dust is by corona discharge, which has the electrode configuration of a conventional electrostatic precipitator, but when processing high-resistance dust, it causes reverse ionization like the electrostatic precipitator described above. The disadvantage is that the charged dust is neutralized and the dust cannot be sufficiently charged.

An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a dust collection device that provides sufficient charge even to high-resistance dust that causes reverse ionization in a normal corona discharge field, and that collects the charged dust with a filter. be.

That is, the present invention provides a so-called electrostatic coagulation filtration device that has a charged part that charges dust and a filter that collects the charged dust. This is to keep the strength below the spatial electric field strength. The surface electric field strength of the dust layer can be maintained below a predetermined value by directly wiping the surface of the ground electrode with a brush, cloth, elastic body, or the like to remove dust. In particular, if the ground electrode is moved to an area where the gas to be treated is not flowing to remove dust, there will be less dust that has lost its charge and it will be less likely to be scattered again, and the equipment for removing dust will be easier to arrange.

Hereinafter, the principle structure of the dust collector according to the present invention will be explained in detail based on the embodiment system diagram shown in FIG.
Reference numeral 1 denotes a charging section, which is composed of a discharge electrode and a ground electrode.

When a negative DC high voltage is applied to the discharge electrode from the high voltage power supply 4, corona discharge occurs between the discharge electrode and the ground electrode, and the dust flowing in from the inlet duct 5 is negatively charged.
The charged dust is introduced into the baghouse 6 and captured by the filter 7, and the clean gas is discharged from the outlet duct 8.

The material of the filter 7 may be any fibrous material such as glass, heat-resistant nylon, or Teflon, as long as it can withstand the exhaust gas temperature. Filter 7
The geometrical shape may be any shape such as a cylindrical shape or a flat plate shape. The dust collection mechanism for the filter 7 is one in which dust is collected by electrostatic cohesive force in addition to mechanical filtration, and the dust collection efficiency is higher than that of a conventional filter alone. In addition, compared to a conventional filter alone, the effect of suppressing the increase in ventilation loss when collecting charged dust is that the surface potential of the filter 7 increases due to the charged dust, and the introduced charged dust is caused by a jumping effect on the filter surface. It is presumed that this is because the particles aggregate together and form voids in the dust layer.

Now, in FIG. 1, when high resistance dust exceeding, for example, 10 ¹² Ω-cm flows in from the inlet duct 5, the corona discharge inside the charging device 1 is reversed by the dust layer slightly collected on the ground electrode. Ionization occurs, much of the charged dust is neutralized, and the effectiveness of the charging device 1 is drastically reduced. Therefore, if the surface of the ground electrode can be kept clean at all times, charging can be maintained stably even with high resistance dust. FIG. 2 shows a structural diagram of a moving electrode type charging section for this purpose, and FIG. 3 shows a schematic diagram of a rotating electrode type charging section.

Referring to FIG. 2, a mechanism for removing attached dust will be explained. The ground electrode 3 is divided into a plurality of short plates, and is connected to the upper and lower sprockets 9 and 10 and the link chain 11.
This is a method in which the dust attached to the electrode surface is removed while the electrode passes between the rollers 12.
The roller 12 is rotated in a direction opposite to the direction of movement of the ground plate.

In FIG. 3, a brush 13 is placed in contact with the rotary ground electrode 3 to obtain the same effect as described above.

In order to prevent the occurrence of reverse ionization in the charging device 1, the movement or rotation speed of the ground electrode 3 varies depending on the electrical resistance ρ of the dust and the thickness of the dust layer adhering to the ground electrode, and must be kept at an optimal value. It is.

In FIG. 1, the electric field strength on the surface of the dust layer is measured by a sensor 16 that detects the charge rate of the dust, and an insulator 1.
7. Measure by the charge rate detector 13. When the dust charged by the charging device 1 adheres to the charge rate detection sensor 16 due to electrostatic attraction, the charge rate detection sensor 16 changes depending on the amount of charge that the dust has.
The potential of increases. This potential is the charge rate detector 1
3, it is always measured. This charge rate detector 1
The signal indicating the potential from 3 is led to the potential comparator 14, where it is compared with the set potential, and a signal corresponding to the difference in charging potential at that time is sent to a control device that controls the movement or rotation of the ground electrode. 15 is sent to keep the movement or rotation of the ground electrode 3 at an optimal value and prevent the occurrence of back ionization.

The structure of the charge rate detection sensor 16 may be any shape such as a round bar, a square bar, a tube shape, a wire mesh, a porous plate, etc., and is provided in the dust through which the charged dust passes.
The charging rate detector 13 can easily measure the charging potential using a measuring instrument such as an electrostatic electrometer.

Figure 4 shows that the ground electrode of the charging device is a moving electrode type, the inlet gas temperature is 150°C, and the dust ρ is 10 ¹³ Ω-cm.
The experimental results of the relationship between the moving speed of the ground electrode, the applied voltage, the discharge current, and the potential of the electrification rate detector are shown when processing a gas containing high-resistance dust. Ground electrode 3
If it is not moved, so-called reverse ionization occurs, and an abnormally large amount of discharge current flows. At this time, as the ground electrode is moved, the discharge current decreases as shown in the figure, and approaches a nearly constant value above a certain speed. When the charge rate (potential) of the dust is detected under such conditions, it changes almost symmetrically with the change in the discharge current. In other words, the potential is low in the region where reverse ionization occurs, but the potential is high in the normal range. By moving (or rotating) the ground electrode in this way, reverse ionization can be prevented, and
By measuring the electrification rate of dust, we can determine whether the discharge phenomenon is positive or not.
Since abnormalities can be detected, the moving speed of the ground electrode can be controlled using the signal from the charge rate detector.

Next, FIG. 5 is an apparatus system diagram showing another embodiment of the present invention. In this case, as is clear from the explanation of Fig. 4 above, focusing on the close relationship between the dust charge rate and the discharge current, discharge The current is detected by a discharge current detector provided in the high voltage power supply 4A, and the current is detected by the current comparator 14A and the movement control device 15.
The ground electrode 3 is moved (or rotated) via the ground electrode 3 to control the discharge current to a constant value. That is, the discharge current flowing through the charging device is constantly monitored by a discharge current detector provided in the high voltage power supply 4A, and a signal indicating the discharge current from this detector is guided to the current comparator 14A. It is compared with the current set here, and a signal corresponding to the difference in discharge current at that time is sent to the movement control device 15,
A control signal corresponding to the signal is sent to a ground electrode drive section (not shown).

In the case of the above embodiment, similarly to the embodiment of FIG.
By controlling the ground electrode moving speed to an appropriate value, it is possible to prevent reverse ionization of the charging device.

As described above, according to the present invention, high-resistance dust, which has conventionally been considered difficult to charge, can be charged normally with appropriate power, and along with this, the dust collection rate is high,
Moreover, it is possible to provide an excellent filtration and dust collection device that can suppress an increase in ventilation loss.

[Brief explanation of the drawing]

FIG. 1 is an apparatus system diagram showing an embodiment of the present invention, FIG. 2 is the structure of a moving electrode type charging section, FIG. 3 is the structure of a rotating electrode type charging section, and FIG. 4 is an experiment according to the present invention. An explanatory diagram of the results, FIG. 5 is an apparatus system diagram showing another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Charging device, 6... Filter housing, 7...
Filter, 16... Charge rate detection sensor.

Claims (1)

[Claims] 1. An introduction part for a gas to be processed containing dust, a dust charging part connected to the introduction part and having a discharge electrode and a movable ground electrode for charging the dust, and a dust charging part on the leeward side of the dust charging part. In those having a collecting filter and a clean gas discharge part,
A removal means that is in sliding contact with the movable ground electrode and removes dust from the ground electrode surface, and a sensor that detects the charge rate of the dust or that detects the discharge current of the discharge electrode that is arranged between the dust charging section and the filter. It is composed of a sensor, a comparator that compares the detected amount from the sensor with a predetermined set value, and a control device that controls the moving speed of the ground electrode based on the output signal from the comparator. Characteristic dust collection equipment.