JP2009106841A - Wet electrostatic precipitator and method for preventing corrosion of discharge electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wet electrostatic precipitator which can prevent the corrosion of a discharge electrode by a corrosive mist in the treatment of a gas containing the corrosive mist. <P>SOLUTION: The wet electrostatic precipitator with the discharge electrode arranged along the passage of the gas is equipped with a cylindrical discharge electrode 10 with a passage which can send cold air formed, insulating pipes 14a and 14b connecting both ends of the discharge electrode 10, respectively, and a cooling means 20 which is located upstream of the insulating pipe 14a and supplies cold air to the insulating pipe 14a. The discharge electrode 10 is cooled by being supplied with the cold air, moisture contained in the gas is condensed by the temperature difference between the outer surface of the discharge electrode 10 and the gas, and a wet film is formed on the outer surface of the discharge electrode 10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention particularly relates to a wet electrostatic precipitator in which a discharge electrode is disposed along a flow path of a gas to be treated and a method for preventing corrosion of the discharge electrode.

  In the exhaust gas discharged from the boiler of a coal-fired power plant, in addition to carbon dioxide as the main component, sulfur compounds generated from sulfur contained in the fuel and nitrogen are oxidized in the combustion chamber at high temperature and high pressure. Contains harmful substances such as nitrogen oxides. In order to prevent the exhaust gas discharged there from affecting the surrounding environment, the exhaust gas is continuously exhausted to the atmosphere after being collected through denitrification and desulfurization (Patent Document 1). Here, general exhaust gas treatment equipment is arranged in the order of a denitration device, a dry electrostatic precipitator, a wet desulfurization device, and a wet electrostatic precipitator from the boiler side.

By the way, the sulfur compound contained in the exhaust gas is mainly sulfur dioxide (SO ₂ ), but part of it becomes sulfur trioxide (SO ₃ ) by combustion and catalytic oxidation in the boiler, and the sulfur trioxide reacts with water. To become sulfuric acid. This sulfur trioxide is gaseous when the concentration is several tens of ppm, but the temperature is one hundred degrees or more, but the gas temperature is an acid dew point (for example, when the SO ₃ concentration is 1 to 100 ppm, the sulfuric acid dew point is 150 degrees) or less, it will condense and become sulfuric acid mist. Since this sulfuric acid mist is corrosive, the temperature of the exhaust gas is controlled by an air heater at a temperature higher than the acid dew point, for example, about 170 ° C. or more in the previous stage of the wet desulfurization apparatus to suppress the generation of sulfuric acid mist.

  On the other hand, since the wet desulfurization apparatus has the highest desulfurization performance when the exhaust gas temperature is near the dew point of water, a large amount of circulating water is sprayed in the apparatus. Therefore, in the wet desulfurization apparatus, the exhaust gas temperature is rapidly decreased from about 170 degrees to about 50 to 60 degrees, which is the dew point of moisture. At this time, sulfuric acid in the exhaust gas is misted when the temperature in the wet desulfurization apparatus drops. Since the sulfuric acid mist by such rapid cooling has a small particle size, the probability of collision with the spray slurry is low, and it is difficult to remove with a wet desulfurization apparatus. Therefore, sulfuric acid mist is removed by a wet-type electrostatic precipitator at the subsequent stage.

In the wet electrostatic precipitator, mist such as sulfuric acid mist and remaining dust in the exhaust gas sent from the wet desulfurizer are collected by the dust collecting electrode according to the principle of electrostatic precipitator. The collected mist itself forms a wetting film on the surface of the dust collection electrode and falls naturally.If the amount of mist is small and natural flow is difficult to occur, the washing water is constantly or from the top of the dust collection electrode. Flowing intermittently, mist and dust collected in the dust collecting electrode are washed away.
JP 2002-45643 A

  However, when a gas to be treated containing corrosive mist such as sulfuric acid mist is treated by a wet electrostatic precipitator, mist collects at the dust collecting electrode, and the discharge electrode is easily dried. For this reason, when the corrosive mist in the gas to be treated adheres to the discharge electrode, there is a problem that the corrosive mist is concentrated by drying, the discharge electrode is corroded, and the service life of the discharge electrode is shortened.

  In order to improve such a problem, it is possible to spray wash water from the upper part of a discharge electrode by the method similar to a dust collection electrode, and to wash away the corrosive mist adhering to the discharge electrode. However, in such a method, since the sprayed water droplets are caused to flow by the gas flow, the water droplets cannot reach the lower part of the discharge electrode, and it is difficult to evenly wash away the corrosive mist adhering to the discharge electrode.

  In addition, in the case of a large-scale wet electrostatic precipitator, the discharge electrode is long, and similarly to the above, water droplets cannot reach the lower part of the discharge electrode, and the corrosive mist adhering to the discharge electrode is evenly washed off. Is difficult.

  Further, when the particle diameter of the spray water is increased so that the water droplets do not flow due to the gas flow in the casing, most of the water droplets are collected by the dust collecting electrode. For this reason, a sufficient cleaning effect cannot be obtained. Conversely, a new problem of inducing sparks with water droplets having a large particle size occurs.

  Therefore, in order to solve the above-described problems of the prior art, the present invention can evenly wet the discharge electrode even when processing the gas to be treated containing corrosive mist, and can suppress the corrosion of the discharge electrode. It is an object of the present invention to provide a wet electrostatic precipitator and a discharge prevention method for discharge electrodes.

  In order to achieve the above object, a wet electrostatic precipitator according to the present invention is a wet electrostatic precipitator in which discharge electrodes are arranged along a flow path of a gas to be treated, and blows outside air at a temperature lower than that of the gas to be treated. A cylindrical discharge electrode having a possible flow path is provided, and outside air is blown and cooled to the discharge electrode, and is contained in the gas to be processed due to a temperature difference between the outer surface of the discharge electrode and the gas to be processed. Moisture is condensed to form a wet film on the outer surface of the discharge electrode.

  The wet electrostatic precipitator of the present invention is a wet electrostatic precipitator provided with a discharge electrode along the flow path of the gas to be treated, and includes a cylindrical discharge electrode having a flow path capable of blowing cool air. Cooling the discharge electrode to condense moisture contained in the gas to be processed due to a temperature difference between the outer surface of the discharge electrode and the gas to be processed, thereby forming a wet film on the outer surface of the discharge electrode. It is a feature.

  The wet electrostatic precipitator of the present invention is a wet electrostatic precipitator in which a discharge electrode is disposed along the flow path of the gas to be treated. Insulating pipes connected to both ends of the discharge electrode, and a cooling means for supplying cold air to the insulation pipe on the upstream side of the insulation pipe, and blowing and cooling cold air to the discharge electrode, A wet film is formed on the outer surface of the discharge electrode by condensing moisture contained in the gas to be processed by a temperature difference between the outer surface of the discharge electrode and the gas to be processed.

  In this case, the cooling means may be connected to control means for controlling the temperature and flow rate of the cold air based on the temperature of the gas to be processed.

  According to the discharge electrode corrosion prevention method of the present invention, a cylindrical discharge electrode is disposed along the flow path of the gas to be treated of the wet electrostatic precipitator, and the flow path provided inside the discharge electrode is provided with the cover. A wet film is formed on the outer surface of the discharge electrode by blowing outside air at a temperature lower than that of the processing gas and causing moisture contained in the processing gas to dew due to a temperature difference between the outer surface of the discharge electrode and the gas to be processed. It is characterized by letting.

  According to the present invention configured as described above, the entire discharge electrode is cooled by heat transfer and heat conduction by passing cold air through the internal flow path of the cylindrical discharge electrode. When the gas to be processed comes into contact with the outer surface of the discharge electrode, the gas to be processed is also absorbed and cooled.

  When the gas to be processed falls below the dew point temperature, that is, due to the temperature difference between the outer surface of the discharge electrode and the gas to be processed, a part of moisture (water vapor) contained in the gas to be processed is condensed, and the discharge electrode Adhere to the outer surface of As this process occurs sequentially, a wet film of condensed water is formed on the outer surface of the discharge electrode. This wet film functions as a protective film against the corrosive mist, and even when the corrosive mist adheres to the discharge electrode, the corrosive mist is diluted by the wet film. Therefore, the corrosive force by the corrosive mist of the discharge electrode is reduced, and the effect of significantly suppressing the corrosion of the discharge electrode can be obtained.

  Further, the wetting film formed on the discharge electrode flows down along the longitudinal direction of the pipe-like electrode by its own weight when the thickness of the film increases. For this reason, it does not grow to a certain thickness or more, and the formation of the film is repeated by newly adhering condensed water or mist, so that the function as a protective film does not deteriorate.

  Embodiments of the wet electrostatic precipitator and discharge electrode corrosion prevention method of the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a perspective view showing the main part of the wet type electrostatic precipitator of the present invention. As shown in the drawing, a plurality of discharge electrodes 10 and dust collection electrodes 12 are alternately arranged at predetermined intervals in the casing of the wet type electrostatic precipitator. A gas to be treated containing corrosive mist such as sulfuric acid mist flows between the discharge electrodes 10 and the dust collecting electrodes 12 arranged alternately as indicated by arrows A in the figure from the gas inlet of the casing.

  The sulfuric acid mist and remaining dust in the water to be treated are collected by the dust collecting electrode 12 by the principle of electric dust collecting while passing between the discharge electrode 10 and the dust collecting electrode 12. The processing gas from which sulfuric acid mist and dust have been removed by the electric dust collection is discharged out of the casing through the gas outlet of the casing.

  The sulfuric acid mist collected by the dust collecting electrode 12 itself forms a wetting film on the surface of the dust collecting electrode 12 or naturally flows down, or when the mist amount is small and natural flowing is difficult to occur, it is not illustrated. Washing water is constantly or intermittently flowed from above the dust collecting electrode 12 by the cleaning means, and sulfuric acid mist and dust collected on the dust collecting electrode 12 are washed away.

  FIG. 2 is a schematic explanatory view of a discharge electrode of a wet electrostatic precipitator. FIG. 3 is a cross-sectional view of the discharge electrode of the wet electrostatic precipitator. The discharge electrode 10 shown in FIG. 2 shows the discharge electrode 10 on the same plane disposed between the dust collecting electrodes 12. Each discharge electrode 10 is connected to a high voltage power source (not shown) disposed outside the casing, and a high voltage is applied thereto. As shown in FIG. 3, the discharge electrode 10 has a hollow structure such as a pipe (cylindrical tube). Furthermore, the discharge electrode 10 has an insulating pipe 14 that is an insulating pipe connected to openings at both ends. The insulating pipe 14 has an electrical insulation property that avoids electrical connection with a discharge electrode to which a high voltage is applied, and a curable plastic resin or the like can be used as an example.

  The pipe connected to the upper part of the discharge electrode 10 shown in FIG. 3 is the upstream insulating pipe 14a, to which the cooling means 20 is connected. The cooling means 20 includes a fan 22 that generates cool air having a temperature lower than that of the gas to be processed and blows air to the insulating pipe 14. The fan 22 can blow cool air into the discharge electrode 10 through the insulating pipe 14.

  A cold air flow control valve 24 is attached in the middle of the upstream insulating pipe 14 a and downstream of the connection portion of the cooling means 20. The flow control valve 24 is configured to be able to arbitrarily adjust the amount of cold air supplied to the insulating pipe 14a.

  Control means 30 is connected to the cooling means 20. Further, the control means 30 is connected to a temperature sensor 32 that measures the temperature of the gas to be treated flowing into the wet electrostatic precipitator, a flow control valve 24, and an outside air temperature sensor 34 that measures the outside air temperature. The control means 30 controls the temperature and supply amount of the cold air supplied to the discharge electrode 10 based on the measurement value of the temperature sensor 32, that is, the temperature of the gas to be processed and the measurement value of the outside air temperature sensor 34.

  On the other hand, as shown in FIG. 3, the pipe connected to the lower part of the electrode 10 is the downstream insulating pipe 14b. Cold air that has passed through the discharge electrode 10 flows into the downstream insulating pipe 14b. The cold air may be circulated by exhausting it to the outside or returning it to the upstream insulating pipe 14a.

Next, a method for preventing corrosion of the discharge electrode having the above configuration will be described below.
First, the temperature of the gas to be processed flowing into the wet electrostatic precipitator is measured by the temperature sensor 32, and the measured value is sent to the control means 30. The outside temperature measured by the outside temperature sensor 34 is sent to the control means 30.

  The temperature of the gas to be processed flowing into the wet type electrostatic precipitator is usually a saturated gas of about 50 to 60 degrees. Therefore, the control means 30 supplies a set temperature at which the outer surface temperature of the discharge electrode 10 is lower than the gas to be processed, for example, cold air of 15 degrees to 20 degrees.

  In the control means 30, first, when the outside air temperature is the set temperature of 15 degrees to 20 degrees, the cooling means 20 is stopped and the outside air from the fan 22 is supplied to the upstream insulating pipe 14a.

  On the other hand, when the outside air temperature exceeds the set temperature, the cooling means 20 generates cool air at the set temperature. As an example, the cooling means 20 may be cooled by heat exchange between groundwater and outside air (air) to generate cold air.

  The outside air having the set temperature or the generated cold air is supplied into the upstream insulating pipe 14 a by the fan 22. Outside air or cold air in the insulating pipe 14a flows from the upper part of the discharge electrode 10 to be connected, and is discharged to the insulating pipe 14b on the downstream side of the lower part.

  At this time, the outer surface of the discharge electrode 10 is cooled by blowing outside air or cold air into the discharge electrode 10. When outside air or cold air is blown so that the outer surface temperature of the discharge electrode 10 is lower than the gas to be processed, the gas is cooled when the outer surface of the discharge electrode 10 comes into contact with the gas to be processed. When the gas falls below the dew point temperature, a part of moisture (steam) contained in the gas is condensed on the outer surface of the discharge electrode 10. The outer surface of the discharge electrode 10 becomes wet due to the generated condensed water.

  For this reason, dew condensation water is sequentially generated on the outer surface of the discharge electrode 10, and a wet film is formed on the entire surface of the discharge electrode 10. This wetting film functions as a protective film against corrosive mist. That is, even when the corrosive mist adheres to the discharge electrode 10, the corrosive mist is sufficiently diluted by the wet film, the corrosive force is reduced, and the discharge electrode 10 can be significantly prevented from corroding. And when the thickness of the wet film increases, it flows down naturally by its own weight. Therefore, the wet film does not grow beyond a certain thickness, continues to be generated by newly attached condensed water or mist, and the function as a protective film does not deteriorate.

  In addition, when the discharge electrode 10 is cooled, for example, the set temperature of the cool air supplied to the discharge electrode 10 is too low, and condensation occurs excessively, and sparks due to water droplets occur, depending on the spark frequency, It is advisable to adjust the flow rate of the cold air.

  The present invention can uniformly control the upper and lower surfaces of the outer surface by using the discharge electrode 10 having a flow path through which cool air can be blown. Moreover, even if it is a long discharge electrode, the temperature difference of the outer surface in the upper and lower sides is a slight difference. For this reason, a wet film can be uniformly formed on the entire discharge electrode 10. In the present embodiment, the flow of the gas to be processed has been described as the flow in the horizontal direction. However, the flow of the gas to be processed has the same effect of preventing corrosion regardless of the flow direction such as the vertical direction.

FIG. 4 is an explanatory view of a modification of the wet type electrostatic precipitator.
As shown in the drawing, the discharge electrode 10A according to the modification is formed in a frame shape by connecting a plurality of discharge electrodes arranged on the same plane along the plane of the collection electrode between the collection electrodes. The upper and lower portions of the frame-shaped discharge electrode 10A are provided with connecting portions between the upstream insulating pipe 14a and the downstream insulating pipe 14b, respectively. The frame-shaped discharge electrode 10A has a cylindrical shape as in the embodiment of FIG. 1, forms a cold air flow path, and allows external air or cold air to flow through each other. Therefore, outside air or cold air flows into the frame-shaped discharge electrode 10A from the upstream insulating pipe 14a, is evenly supplied from above to below the discharge electrode 10A, and is discharged from the lower insulating pipe 14b. With this configuration, the discharge area of the discharge electrode is widened, and a wetting film is formed on the outer surface of the cylindrical discharge electrode, so that the same corrosion inhibition effect as that of the discharge electrode shown in FIG. 1 can be obtained.

  In addition to this, it is possible to perform a roughing process to roughen the surface of the discharge electrode. As the rough surface processing, it can be formed using file processing, blast processing, dimple processing, grooving processing or the like. When such rough surface processing is performed, the formation and maintenance of the wet film on the discharge electrode becomes good, and the effect of improving the corrosion inhibiting action is obtained.

  The present invention is particularly applicable in the field of exhaust gas treatment including sulfur oxides.

It is a perspective view which shows the principal part of the wet electric dust collector of this invention. It is a schematic explanatory drawing of the discharge electrode of a wet-type electrostatic precipitator. It is sectional drawing of the discharge electrode of a wet electric dust collector. It is explanatory drawing of the modification of a wet electric dust collector.

Explanation of symbols

10 ......... Discharge electrode, 12 ......... Dust collecting electrode, 14 ......... Insulating pipe, 20 ......... Cooling means, 22 ......... Fan, 24 ......... Flow control valve, 30 ......... Control means, 32... Temperature sensor 34.

Claims (5)

In the wet electrostatic precipitator in which the discharge electrode is disposed along the flow path of the gas to be treated,
A cylindrical discharge electrode having a flow path capable of blowing outside air at a temperature lower than that of the gas to be treated is provided.
Air is blown to the discharge electrode and cooled, and moisture contained in the gas to be treated is condensed due to a temperature difference between the outer surface of the discharge electrode and the gas to be processed, and a wet film is formed on the outer surface of the discharge electrode. A wet type electrostatic precipitator characterized by being formed. In the wet electrostatic precipitator in which the discharge electrode is arranged along the flow path of the gas to be treated,
Provided with a cylindrical discharge electrode formed with a flow path capable of blowing cool air,
The discharge electrode is cooled, and moisture contained in the gas to be processed is condensed by a temperature difference between the outer surface of the discharge electrode and the gas to be processed, and a wet film is formed on the outer surface of the discharge electrode. Wet electric dust collector. In the wet electrostatic precipitator in which the discharge electrode is arranged along the flow path of the gas to be treated,
A cylindrical discharge electrode formed with a flow path capable of blowing cool air;
An insulating pipe connected to each end of the discharge electrode;
A cooling means that is upstream of the insulating pipe and supplies cold air to the insulating pipe;
Cold air is blown to the discharge electrode to cool it, and moisture contained in the gas to be processed is condensed due to a temperature difference between the outer surface of the discharge electrode and the gas to be processed, and a wet film is formed on the outer surface of the discharge electrode. A wet type electrostatic precipitator characterized by being formed.   4. The wet electrostatic precipitator according to claim 3, wherein the cooling means is connected to a control means for controlling the temperature and flow rate of the cold air based on the temperature of the gas to be treated. A cylindrical discharge electrode is disposed along the flow path of the gas to be treated of the wet electrostatic precipitator,
To the flow path provided inside the discharge electrode, blows outside air having a temperature lower than that of the gas to be processed,
The moisture contained in the gas to be treated is condensed by a temperature difference between the outer surface of the discharge electrode and the gas to be treated.
A method for preventing corrosion of a discharge electrode, comprising forming a wet film on an outer surface of the discharge electrode.

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