JPH0947686A - Electric dust collector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric dust collector which does not require an air discharge fan, and also does not require a special device for preventing soot from being scattered again. SOLUTION: A chimney 5 is erected in such a manner that it is directly connected to a furnace wall 3 by forming a combustion furnace 2 on a building 1. The chimney 5 is of the circular cross section and is surrounded with a steel plate 6. The inner face of the chimney 5 is lined with, castable refractories 1. In addition, a structure 15 which is independent of the chimney 5 is built on the building 1, and a girder 16 is spanned right above the chimney 5, using the structure 15. The girder 16 is electrically insulated by an insulator 17. Further, a discharge electrode 19 is suspended in the chimney 5 from the girder 16. The discharge electrode 19 has a plurality discharge rods 19a of the needle- like protruding shape on almost the lower half. A negative pole of a direct current high voltage power supply 20 is connected to the discharge electrode 19, and a positive pole is connected to the steel plate 6 surrounding the chimney 5 and at the same time is grounded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic precipitator having a refractory lining and also serving as an exhaust pipe.

[0002]

2. Description of the Related Art Metal refining and blast furnaces (converters, cupolas, etc.), metal heating and heat treatment furnaces (annealing furnaces, etc.), ceramic furnaces (cement kilns, etc.), waste incinerators, drying furnaces, combustion chambers for heat engines, etc. A conventional electrostatic precipitator used for collecting dust from exhaust gas emitted from the exhaust gas has a large pressure loss because the exhaust gas passes between a large number of narrow dust collecting electrodes.
Further, in order to prevent the electrostatic precipitator from being exposed to high heat, it is usual to provide a heat exchanger for exhaust heat recovery or a cooling device which also serves as a gas neutralization device immediately before, which also increases the pressure loss. Due to such pressure loss, exhaust gas cannot be sent out only by natural ventilation, and an exhaust fan is indispensable. However, since the exhaust fan is exposed to corrosive gas and heat, it easily breaks down, and it takes a lot of time and labor for maintenance and inspection.

In addition, the conventional electrostatic precipitator has the following problems. (I) Re-scattering occurs due to hammering to remove the dust particles adhering to the dust collecting electrode. (Ii) Hydrodynamic re-entrainment occurs when the gas velocity is high. (Iii) Occurrence of re-scattering due to the reverse ionization phenomenon that occurs when the electric resistance of soot and dust is significantly higher than 10 ¹² Ω · cm. (Iv) Abnormal re-scattering occurs when the electric resistance of soot and dust is as low as 10 ⁴ Ω · cm or less.

Due to the phenomenon of re-scattering of dust particles collected on the dust collecting electrode, the dust collecting rate is lowered. In order to prevent this, in the conventional dust collector, (i) humidity control of exhaust gas (ii) dust collection at high temperature around 360 ° C (iii) wet electric dust collection (iv) adoption of pulse charging method, etc. Troublesome measures were needed.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electric dust collecting and exhausting device which does not require an exhaust fan and does not require a special device for preventing re-scattering of dust particles. To do.

[0006]

In the present invention, the exhaust pipe (including the chimney) for discharging the exhaust gas generated from the combustion chamber such as the combustion furnace to the atmosphere is exposed to the high temperature of the exhaust gas. The outer circumference is made of steel sheet, and the inner surface is lined with refractory. Castable refractories (refractory concrete mainly of S _i O ₂ and Al ₂ O ₃₎ or the like is suitable as a refractory.

Refractory is an insulator at room temperature, and hardly conducts electricity. However, during operation, the refractory has a surface of 80
At around 0 ° C., the temperature becomes 400 to 500 ° C. in the vicinity of the heat-resistant metal anchor for preventing the falling off, and at such a high temperature, the general refractory material loses its electrical insulating property like the general insulating material. FIG. 1 shows an example of temperature dependence of electric resistance of castable refractories.

Corona discharge requires a high voltage,
Since the current flowing is small, the dust collecting electrode does not necessarily need to be completely conductive like metal. It is sufficient if the conductivity required to release the electric charge of the dust trapped in the dust collecting electrode is sufficient.

In this invention, the discharge electrode is suspended at the center of the exhaust pipe, and a high DC voltage is applied between the discharge electrode and the iron plate around the exhaust pipe. (As for the polarity, the steel plate is on the plus side and the discharge electrode is on the minus side, similar to the general electrostatic precipitator.)

In this device, the discharge electrode is located at the center of the exhaust pipe (chimney), and the inner surface of the exhaust pipe serves as a dust collecting electrode, so that the discharge gap becomes considerably long, but such a long gap corona discharge at high temperature. There is no literature that describes in detail. With a small-sized (short discharge gap) experimental device, 5
It was confirmed that, in a high temperature gas of 00 to 700 ° C., a current larger by two digits or more flows at the same applied voltage as compared with the case of normal temperature. FIG. 2 shows an example of the obtained data. Therefore, even when the discharge gap is long as in the device of the present invention, by providing a large number of discharge needles in the longitudinal direction of the discharge electrode, the voltage is not so high for a long discharge gap, which is an ordinary DC high voltage power supply device. Sufficient corona discharge can be generated.

Furthermore, in spark discharge, the spark starting voltage is said to be proportional to the product of the discharge gap and the gas density,
With a long gap such as this device, the spark voltage becomes a considerably high value even at high temperatures, a large difference from the operating voltage can be taken, and safe operation without the risk of short circuit due to spark discharge can be performed.

When a corona discharge occurs, ionization of gas molecules proceeds, a large number of negative ions and positive ions are generated, the positive ions are immediately neutralized by the discharge electrode, and the negative ions and free electrons are directed to the dust collecting electrode. Run. When the combustion gas passes through such an electric field, particles (dust) in the gas are instantaneously charged by collision of ions and electrons.

The charged dust is attracted to the dust collecting electrode by the action of the electric field between the discharge electrode and the dust collecting electrode which is a refractory. In the present invention, since the distance between the discharge electrode and the dust collecting electrode is large, and the high voltage of the high-voltage power supply device is practically limited, it is difficult to obtain a strong electric field, and the charged dust is collected. The power to attract the poles is weak. However, since both electrodes are long in the direction along the exhaust gas flow, the time for the charged dust to pass through the electric field is long, in combination with the low exhaust gas flow velocity due to the large exhaust pipe cross-sectional area. Therefore, a sufficient dust collecting effect can be obtained even in a weak electric field.

The dust trapped by the dust collecting electrode adheres to the inner surface of the exhaust pipe, but when the thickness of the adhering layer becomes large, it is separated by its own weight and falls. In the conventional dry-type electrostatic precipitator, the dust particles adhering to the dust collecting electrode were wiped off by periodically hammering or applying vibration. It is considered that the soot dust strongly adheres to the dust collecting electrode because the soot dust aggregates by interposing the water contained in the soot dust. In the present invention, since the dust is exposed to a high temperature, there is no aggregated water, and a thick layer is not attached to the dust collecting electrode, and the particles coarsened by the electrode aggregation effect before the attached layer becomes thick are self-weighted. To fall naturally.

In the present invention, since the exhaust pipe can have a large cross-sectional area, the flow velocity of the exhaust gas is sufficiently low, and therefore, the hydrodynamic re-scattering of the collected dust can be prevented.

Further, it is of course possible to apply the present invention to a device having a small amount of exhaust gas and therefore a small exhaust pipe cross-sectional area. In this case, since the discharge gap is relatively short and the temperature is high, the operating voltage can be lowered as compared with the conventional electrostatic precipitator, as can be seen from the data shown in FIG. As a result, the power source can be simplified and electric insulation measures can be simplified.

The discharge electrode has a pointed tip (large curvature)
It is well known that a corona discharge can be easily generated by attaching a discharge needle. When the present invention is applied to a device having a long discharge gap, the operating voltage can be lowered by attaching a large number of discharge needles to the discharge electrode. When the present invention is applied to a device having a short discharge gap, the operating voltage can be changed by selecting the number and shape of the discharge needles.

The exhaust pipe may be formed separately from the combustion chamber, but if the exhaust pipe is erected directly above the combustion chamber, dust that has fallen off from the inner surface of the exhaust pipe falls into the combustion chamber, It can be discharged together with the ash on the floor, which saves time. Therefore, there is no need for a hopper for receiving the soot dust that comes off. Since the flow velocity of the exhaust gas in the exhaust pipe is sufficiently low, dust that has fallen off from the inner surface of the exhaust pipe gently falls along the wall surface.

In the conventional dry-type electrostatic precipitator, when the electric resistance of the dust is high, the dust may be reversely ionized and scattered again from the dust collecting electrode. Although the electric resistance of the soot and dust becomes smaller as the temperature becomes higher, the present invention directly collects dust from the hot exhaust gas in the exhaust pipe, so that the electric resistance of the soot and dust is kept sufficiently low, and the problem of re-scattering due to reverse ionization Is unlikely to happen. Further, in this device, since the dust collecting electrode which is a refractory is not a perfect conductor, even if the electric resistance of the dust is low, the neutralization of the charges is slowly performed in the dust collecting electrode over time, The problem of abnormal re-scattering when the electric resistivity of dust is small is unlikely to occur.

[0020]

EXAMPLE An example in which the present invention is applied to an incinerator will be described with reference to FIG. 3. An incinerator 2 as a combustion chamber is formed on a building 1 and is continuously connected to a furnace wall 3 and exhausted. Launch the chimney 5 as a tube. The chimney 5 has a circular cross-section, the periphery of which is made of a steel plate 6, and the castable refractory 7 is lined on the inner surface thereof. In order to prevent the castable refractory 7 from falling off, a large number of heat-resistant metal anchors 6a are planted on the inner surface of the steel plate 6.

The furnace wall 3 has a charging port 9 for charging the incinerated material 8 into the furnace, a combustion air intake port 10, and an auxiliary burner 1.
1. Provide an alkaline solution spray device 12 for gas neutralization,
The hearth 4 is provided with an ash outlet 13.

A structure 15 independent of the chimney 5 is provided on the building 1, and the girder 16 is passed directly above the chimney 5 using this structure. The girder material 16 is electrically insulated by the insulator 17. The discharge electrode 19 is suspended from the girder material 16 at the center of the chimney 5. The discharge electrode 19 has a large number of discharge needles 19a, which are needle-shaped protrusions, in the lower half.

The negative electrode of the DC high voltage power source 20 is connected to the discharge electrode 19, and the positive electrode is connected to the steel plate 6 around the chimney and grounded.

When the incinerator 8 is burned on the hearth 4, hot exhaust gas passes through the chimney 5 and is discharged from the upper part. The inside of the chimney is filled with high-temperature exhaust gas, the castable refractory 7 on the inner surface of the chimney serves as a dust collecting electrode, and corona discharge occurs with the discharge electrode 19. Due to the corona discharge, the dust in the combustion gas is electrified and attracted to the inner surface of the chimney, which is a dust collecting electrode, and is exposed to the exhaust gas to become hot and adhere to the castable refractory 7 that loses its electrical insulation property. Be neutralized. The movement of the charged dust is shown by arrows in FIG. The dust adhering to the inner surface of the chimney eventually peels off by its own weight and falls along the wall surface to the hearth. The exhaust gas from which the soot and dust have been removed in this way is discharged from the exit of the chimney.

In the above-mentioned embodiment, the chimney is integrally raised from the furnace wall directly above the incinerator, but the present invention is not limited to this, and the incinerator and the chimney are separated and independent. Good.

[0026]

As described above, the present invention has the following effects. The electrostatic precipitator according to claim 1 supports the discharge electrode substantially on the center line of the exhaust pipe, and applies a high DC voltage between the discharge electrode and the metal plate around the exhaust pipe. Is filled with high-temperature exhaust gas, and corona discharge occurs at a lower voltage between the discharge electrode and the refractory on the inner surface of the exhaust pipe, causing a corona discharge at a lower voltage and charging the dust and dirt in the exhaust gas. It can be attracted to and caught by the refractory material that becomes conductive due to the high temperature of the surface. Further, the structure is extremely simple, the equipment cost is low, and the exhaust fan and the dust re-scattering prevention device are not particularly required, so the maintenance is easy.

In the electrostatic precipitator according to the second aspect of the present invention, the discharge needle is attached to the periphery of the discharge electrode, and in combination with the easiness of corona discharge in a high temperature state, even if the discharge gap is long, the voltage is too much. It has the effect that it can be operated sufficiently with a normal DC high-voltage power supply device that is not expensive Also, if the discharge gap is not too long, the operating voltage can be changed by selecting the number and shape of the discharge needles, and there are restrictions on the length of the discharge electrode and the dust collection electrode in the direction of exhaust gas flow. It has an effect that it can widely cope with power supply, restriction on electric insulation, temperature of exhaust gas and the like.

In the electrostatic precipitator according to the third aspect of the present invention, the exhaust pipe is integrally provided directly above the combustion chamber from the wall of the combustion chamber, and when the dust trapped by the dust collecting electrode is peeled off. ,
Since it falls directly into the combustion chamber, it does not require a hopper that receives dust, and it is convenient because dust that falls into the combustion chamber can be treated together with ash.

In the electrostatic precipitator of the fourth aspect, the girder material is passed over a structure independent of the exhaust pipe, and the discharge electrode is suspended from the girder material in the exhaust pipe. There is an effect that the discharge electrode can be supported at the center of the exhaust pipe while maintaining electrical insulation.

[Brief description of drawings]

FIG. 1 is a graph showing electric resistance-temperature characteristics of castable refractories.

FIG. 2 is a discharge voltage-current characteristic diagram of a chimney lined with castable refractories.

FIG. 3 is a schematic sectional view of an electrostatic precipitator according to the present invention.

[Explanation of symbols]

 2 Incinerator (combustion chamber) 5 Chimney (exhaust pipe) 6 Steel plate (metal plate) 7 Castable refractory (dust collector) 15 Structure 16 Girder material 19 Discharge electrode 19a Discharge needle 20 DC high voltage power supply

Claims (4)

[Claims] 1. An exhaust pipe (5) for covering the inner surface of a metal plate (6) with a refractory material (7) for discharging high-temperature exhaust gas to the outside, and the exhaust pipe approximately on the center line of the exhaust pipe. An electrostatic precipitator comprising a discharge electrode (19) electrically insulated from a tube and a high voltage power supply (20) for applying a high DC voltage between the discharge electrode and the metal plate. 2. The electrostatic precipitator according to claim 1, wherein the discharge electrode has a discharge needle (19a) on its periphery. 3. The electrostatic precipitator according to claim 1 or 2, wherein the exhaust pipe is integrally provided directly above the combustion chamber (2) from a wall of the combustion chamber. 4. The girder material (16) is passed over the structure (15) independent of the exhaust pipe, straddling the outlet of the exhaust pipe,
The electrostatic precipitator according to claim 1, 2 or 3, wherein the discharge electrode is suspended from the girder member in the exhaust pipe.