JP2000202322A - Electric precipitator and its control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To catch mist and dust efficiently without being affected by the mist of water, sulfuric acid, and the like, generated in the decreased temperature desulfurization process of a desulfurizer by a method in which, in an electric precipitator installed on the after stage of the desulfurizer, an exhaust gas heating means is installed on the upstream side in the exhaust gas flow direction of its dust collecting electrodes. SOLUTION: In an electric precipitator 10, discharge electrodes 12 and dust collecting electrodes 14 are installed alternately at prescribed intervals, an exhaust gas 26 containing mist of water, sulfuric acid, and the like, is introduced from an inlet 24, a clean gas 30 removed from the mist and dust is discharged from an outlet 28. A heating means 32 is installed upstream the discharge electrodes 12 and the dust collecting electrodes 14 to heat the exhaust gas introduced from the inlet 24. Steam is used as the heating source of the heating means 32, and the flow rate of the steam is controlled by adjusting the opening of a valve 36 by a controller 18. The temperature of the exhaust gas is measured by a temperature measuring means 22, and calorific value of the heating means 32 and the temperature of the exhaust gas is kept by inputting the measured temperature into the controller 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic precipitator and a method of operating the same, and more particularly, to a method for increasing the temperature of exhaust gas at a stage subsequent to a desulfurizing device for reducing the temperature of the exhaust gas by spraying an alkaline agent or water into the exhaust gas. And a method of operating the same.

[0002]

2. Description of the Related Art An exhaust gas treatment system for a boiler using coal, heavy oil, or the like as a fuel, which is used in a power generation device for selling electricity, is provided with a desulfurization device for removing sulfur oxides in the exhaust gas, and a chimney is provided at a subsequent stage. An electric precipitator is provided to prevent purple smoke. In the desulfurization apparatus, Japanese Patent Application Laid-Open No. 60-156563
As disclosed in the publication of the above-mentioned publication, an alkaline agent such as sodium hydroxide or water such as circulating water is sprayed into the exhaust gas to lower the exhaust gas temperature to a saturation temperature to absorb and remove sulfur oxides. For this reason, exhaust gas containing a large amount of mist such as water or sulfuric acid has been introduced into the electrostatic precipitator.

[0003]

However, in the case of an electric precipitator provided downstream of a desulfurizer for reducing temperature by desulfurization by spraying an alkali agent or water into exhaust gas, depending on the operating condition of the former desulfurizer. There is a problem that the dust and mist collection efficiency of the electric dust collector is reduced.

[0004] The present invention has been made in view of such circumstances, and is capable of removing mist and dust with high efficiency without being affected by mist such as water and sulfuric acid generated in the temperature decreasing desulfurization process of a desulfurization device. An object of the present invention is to provide an electrostatic precipitator for collection and an operation method thereof.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a desulfurization apparatus for reducing the temperature of desulfurization by spraying an alkali agent or water into exhaust gas when removing sulfur oxides from the exhaust gas. In the electric precipitator installed at the subsequent stage,
A heating means for heating the exhaust gas is provided on the upstream side in the exhaust gas flow direction with respect to the dust collecting electrode of the electric dust collector.

According to the present invention, since the heating means for heating the exhaust gas is provided on the upstream side in the exhaust gas flow direction with respect to the dust collecting electrode of the electric dust collector, the moisture contained in the mist can be evaporated. It is possible to increase the mist and dust collection efficiency of the electric dust collector.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. First, the theoretical grounds for configuring the electric precipitator of the present invention and the control method thereof will be described.

[0008] When a high voltage is applied between the discharge electrode and the collection electrode formed inside the electric precipitator, dust and mist in the exhaust gas are charged by ions released by the discharge of the discharge electrode, and the dust is collected. Collected in the finest. The collection efficiency at this time is generally higher when the charge amount is larger, and the charge amount is larger when the discharge current is larger. However, when a large amount of mist is contained in the exhaust gas between the discharge electrode and the collection electrode, the discharge current of the collection device is suppressed by the space charge effect caused by the charging of the mist. Would. The suppression amount of the discharge current is related to the total surface area (specific surface area) of the mist in the unit volume, and the suppression amount of the discharge current is larger when the specific surface area is larger.

Mist, such as water or sulfuric acid, is generated in a temperature-reducing desulfurization device that sprays an alkaline agent or water into the exhaust gas to reduce the temperature and desulfurize the mist. As the volume increases, the total surface area of the mist increases. As a result, the discharge current between the discharge electrode and the dust collection electrode decreases, the charge amount decreases, and the dust and mist collection efficiency decreases. As described above, the collection efficiency of the electrostatic precipitator is affected by the amount of mist contained in the exhaust gas.

FIG. 1 shows a mist concentration ρ (g / m^Three) And
Discharge current I (A) flowing through discharge electrode and dust collection electrode of air dust collector
The relationship is shown below. As can be seen from the figure, the mist concentration ρ
Increases, the discharge current I (A) sharply decreases. Electricity collection
Flow into the thermal desulfurization unit provided in front of the dust unit
Gaseous SO contained in exhaust gas at a temperature of about 150 ° C.
_ThreeIs cooled by water spray in the thermal desulfurization unit
And become liquid. SO_ThreeUp to about 100 ppm at 150 ° C.
But at 100 ° C, to about 0.1 ppm
Or cannot be in gaseous form. Therefore SO _ThreeWhen the temperature drops
Become liquid. Gas when exhausted from the thermal desulfurization unit
Temperature is normal exhaust gas temperature and water saturation temperature
When the temperature drops to 55 ° C, H _TwoSO_FourMist at the core
Water condenses on this nucleus. Therefore, the exhaust at 55 ° C.
The mist contained in the gas is H_TwoSO_Four+ H_TwoMixture of O
And this H_TwoO increases the specific surface area of the mist
Suppresses the discharge current of the electric precipitator provided at the subsequent stage.
Mist and dust collection efficiency of the electrostatic precipitator
Was getting worse.

The present invention has been made based on the above findings, and the specific surface area of the mist is reduced by evaporating the mist of water (H ₂ O) among the mist in the exhaust gas discharged from the temperature reducing desulfurization device. At least, the efficiency of collecting mist and dust of H ₂ SO ₄ by the electric dust collector is improved. FIG. 2 is a cross-sectional view showing an embodiment of the electric precipitator according to the present invention, and the case of a temperature-reduction type electric precipitator will be described.

The electric precipitator 10 mainly includes a discharge electrode 12, a precipitator 14, a heating means 32, a controller 18, a high-voltage power supply 2
0, a temperature measuring means 22, and a cleaning water spray nozzle 46 for cleaning the dust collecting electrode. Exhaust gas containing mist such as water or sulfuric acid is introduced into the interior of the electrostatic precipitator 10 from the inlet 24 in the direction of arrow 26, and the clean gas from which mist and dust have been removed is discharged from the outlet 28 in the direction of arrow 30. You. Inside the electrostatic precipitator 10, a discharge electrode 12 and a precipitating electrode 1 are provided.
4 are alternately provided at predetermined intervals.

The heating means 32 includes the discharge electrode 12 and the dust collection electrode 1.
4, and heats exhaust gas introduced from the inlet 24 of the electrostatic precipitator 10. In the example of the present electrostatic precipitator 10, steam 34 is used as a heating source of the heating means 32, and the flow rate of the steam 34 is controlled by adjusting the opening of the valve 36 according to a command from the controller 18. The flow control signal output from the controller 18 is electrically connected to the valve 36 via the drive cable 38. The discharge control signal output from the control device 18 is electrically connected to the high-voltage power supply 20 via the signal cable 40, and outputs the signal of the discharging current value I0 (A) to the high-voltage power supply 20.
To the control device 18.

The temperature value Tm measured by the temperature measuring means 22
(° C.) is transmitted to the control device 18 via the signal cable 42. The mist and dust in the exhaust gas introduced between the discharge electrode 12 and the dust collecting electrode 14 through the heating means 32 and the temperature measuring means 22 are charged by corona discharge from the discharge electrode 12, and are collected by Coulomb force. Collected on pole 14.

A cleaning water solution 44 is intermittently jetted from a spray nozzle 46 to the discharge electrode 12 and the dust collection electrode 14.
The discharge electrode 12 and the dust collection electrode 14 are intermittently cleaned. Next, the operation of the electric precipitator 10 configured as described above will be described. Exhaust gas containing mist is collected by an electric dust collector 10
And a high voltage is applied between the discharge electrode 12 and the dust collection electrode 14. As a result, the discharge current I (A) flows, and the measured discharge current value Im (A) at this time is sent from the high-voltage power supply 20 to the control device 18 via the signal cable 40 as a measured value. The control device 18 stores a set value I0 (A) of the discharge current I (A) in advance. The mist and dust are charged by the discharge current between the discharge electrode 12 and the dust collection electrode 14, and are collected and collected by the dust collection electrode. The mist and dust are collected from the preset discharge current set value I0 (A). When the measured discharge current value Im (A) is small, the temperature of the exhaust gas to be treated is started by operating the heating means 32 because the collection rate of the mist and dust is reduced by the moisture contained in the mist. . Next, the temperature of the exhaust gas containing mist introduced into the electrostatic precipitator 10 is measured by the temperature measuring means 22. The measured temperature value Tm (° C.) is transmitted to the control device 18. The control device 18 previously stores a set value T0 (° C.) of a temperature convenient for dust collection. Control device 1
Reference numeral 8 controls the valve 36 to adjust the amount of heat generated by the heating means 32 so that the preset temperature set value T0 (° C.) is equal to the measured temperature value Tm (° C.). Control device 1
8 compares the previously stored temperature set value T0 (° C.) with the measured temperature value Tm (° C.), and if the measured temperature value Tm (° C.) is smaller than the set temperature value T 0 (° C.), the valve 36 is opened. A signal for increasing the degree is output to the valve 36 via the drive cable 38. When the measured temperature value Tm (° C.) is larger than the set temperature value To, a signal for decreasing the opening degree of the valve 36 is output to the valve 36 via the drive cable 38. When the flow rate of the steam is increased by increasing the opening of the valve 36, the moisture in the mist in the exhaust gas downstream of the heating means 32 evaporates in accordance with the given amount of heat. The specific surface area of the mist is reduced due to the evaporation of the moisture of the mist, so that the discharge current I (A) is increased, and the efficiency of collecting H ₂ SO ₄ and dust is improved.

In the above-described example of the electric precipitator, the discharge electrode 12
When the current I (A) flowing between the electrode and the dust collecting electrode 14 becomes equal to or less than a preset threshold value I0 (A), the temperature value Tm (° C.) measured by the temperature measuring means 22.
, The amount of steam 34 supplied to the heating means 32 is controlled to keep the mist collection efficiency high.
However, the method is not limited to this method, and the amount of steam 34 supplied to the heating means 32 is controlled in accordance with only the temperature value Tm (° C.) measured by the temperature measuring means 22 to collect mist and dust. Efficiency may be maintained high, or only the discharge current I (A) flowing between the discharge electrode 12 and the dust collection electrode 14 is monitored and supplied to the heating means 32 according to the discharge current I (A). The object of the present invention can be achieved even if the efficiency of collecting mist and dust is kept high by controlling the amount of steam 34 to be collected.

Another embodiment of the invention for controlling the amount of steam 34 supplied to the heating means 32 only in accordance with the discharge current I (A) will be described below. Exhaust gas containing mist and dust is introduced into the electrostatic precipitator 10, and a high voltage is applied between the discharge electrode 12 and the precipitating electrode 14. As a result, the discharge current I
(A) flows, and the discharge current Im (A) at this time is transmitted from the high-voltage power supply 20 to the control device 18 via the signal cable 40,
Sent as a measurement. The control device 18 stores a set value I0 (A) of the discharge current I (A) in advance. The mist and dust are charged by the discharge between the discharge electrode 12 and the dust collection electrode 14, and the discharge current I (A) flows by the space charge effect.
This discharge current I (A) is stored in the stored set value I0.
The heating value of the heating means 32 is controlled so as to approach (A). The controller 18 sets a preset value I of the discharge current stored in advance.
0 (A) and the measured value of the discharge current Im from the high voltage power supply 20
(A) and the measured value Im (A) is changed to the set value I0 (A).
If it is smaller, a signal for increasing the opening of the valve 36 is output to the valve 36 via the drive cable 38.

When the opening degree of the valve 36 is increased and the flow rate of the steam is increased, the moisture in the mist in the exhaust gas downstream of the heating means 32 evaporates in accordance with the given amount of heat. This reduces the specific surface area of the mist and thus increases the discharge current. Conversely, when the measured discharge current value Im (A) is larger than the set value I0 (A), a signal for decreasing the opening degree of the valve 36 is transmitted via the drive cable 38 to the valve 36.
Output to

FIG. 3 shows the discharge current I (mA) flowing between the discharge electrode 12 and the dust collection electrode 14 and the mist collection efficiency G.
(%). FIG. 3 shows that the exhaust gas from the temperature reducing desulfurization device is introduced into the electric precipitator 10 according to the present invention, the mist concentration at the inlet 24 and the flow rate of the steam 34 of the heating means 32 are changed, and the discharge current I (mA) is changed. And mist collection efficiency G
(%) Is a result obtained by an experiment. FIG. 3 shows that when the mist in the exhaust gas evaporates by increasing the flow rate of the steam 34, the discharge current I (mA) increases and the collection efficiency G (%) improves.
Also, if the discharge current I (mA) of the electrostatic precipitator 10 is kept large, the trapping efficiency G (%) is almost the same even if the mist concentration at the inlet 24 of the electric precipitator 10 changes. ing. In the above-described embodiment, steam is used as the heating source of the heating means. However, the present invention is not limited to this. For example, even with an electric heater, heated gas can be directly introduced into exhaust gas. Accordingly, the object of the present invention is achieved.

[0020]

As described above, according to the electrostatic precipitator and the method of controlling the same according to the present invention, the discharge current can always be kept high by evaporating the water in the exhaust gas. The mist and dust collection efficiency can be kept high.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a mist concentration ρ and a discharge current I of an electrostatic precipitator.

FIG. 2 is a cross-sectional view showing an embodiment of the electric precipitator according to the present invention.

FIG. 3 is a diagram showing a discharge current I and a mist collection efficiency G.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Electric dust collecting device 12 ... Discharge electrode 14 ... Dust collecting electrode 18 ... Control device 20 ... High voltage power supply 22 ... Temperature measuring means 32 ... Heating means 34 ... Steam 36 ... Valve

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Akio Yuki 537, Kamigongo, Matsudo-shi, Chiba F-term in Hitachi Plant Construction Machinery Engineering Co., Ltd. 4D054 AA02 AA09 BA01 BA11 CA14 CA19 DA06 EA02 EA21 EA24

Claims (3)

[Claims] 1. When removing sulfur oxides in exhaust gas,
In an electric precipitator provided downstream of a desulfurization device for reducing the temperature and desulfurization by spraying an alkali agent or water into the exhaust gas, the electric precipitator includes an electric dust collector, An electrostatic precipitator provided with a heating means for heating exhaust gas. 2. The electrostatic precipitator according to claim 1, wherein said heating means includes at least one of a heating means using steam and an electric heating type heating means. 3. When removing sulfur oxides in exhaust gas,
In a method for controlling an electrostatic precipitator provided on a downstream side of a desulfurizing device for reducing temperature and desulfurizing by spraying an alkali agent or water into exhaust gas, a discharge is generated between a discharge electrode and a dust collecting electrode of the electric precipitator. Detecting the discharge current value to be discharged, and when the discharge current value becomes lower than a predetermined set current value, heating the exhaust gas upstream of the dust collection electrode in the exhaust gas flow direction. Dust control method.