JPH11253837A - Pulse charged electric precipitator - Google Patents

Abstract

(57) [Summary] [Problem] To reduce the problem of spark and prevent a remarkable decrease in dust collection rate. When the spark frequency per fixed time does not affect the dust collection rate, the voltage applied to the discharge electrode is controlled to an optimum DC base voltage by main control. When the spark frequency exceeds the set value, switch to the spark frequent occurrence control,
The pulse voltage is set to the lower limit set value and charging is resumed by adjusting the output voltage of the DC base power supply. The pulse voltage lower limit set value is a minimum value of a voltage at which corona discharge is uniformly generated on the surface of the discharge electrode when a pulse voltage is applied. Even for high electrical resistivity dust that is likely to cause sparks due to pulse charging control that superimposes the DC base voltage and pulse voltage, a uniform corona discharge is secured on the surface of the discharge electrode and the occurrence of sparks is suppressed. Prevent significant reduction in dust collection rate

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse charged electrostatic precipitator, and more particularly, to a pulse charged electric precipitator provided with a pulse power supply for applying a pulse voltage and a DC base voltage in a superimposed manner.

[0002]

2. Description of the Related Art It is known that when a pulse voltage is charged between a discharge electrode and a dust collecting electrode in an electrostatic precipitator, dust having a high electric resistivity can be collected at a high dust collecting rate. It is used as an electric dust collector. The charging voltage has a waveform in which a pulse voltage having a width of about 100 microseconds and a repetition rate per second of tens to hundreds of times is superimposed on the DC base voltage. In the case of high-resistance dust, the DC base voltage is the corona starting voltage when the DC voltage is charged, or the value slightly higher than this is optimal. A method of setting the above value and performing constant voltage control has been proposed (Japanese Patent Publication No. 5-79383). Further, a control method has been proposed in which the value of the pulse voltage superimposed on the DC base voltage and the number of repetitions thereof are maximized in a range in which spark does not occur (Japanese Patent Publication No. 5-77465). As another method, when the output current of the DC power supply is controlled at a constant current, it has been found through experiments that the optimum DC base voltage that maximizes the dust collection rate is almost constant regardless of the properties of the dust. There has been proposed a method of controlling the peak value, pulse width, and repetition rate of the pulse voltage so that the base voltage becomes the optimum value (Japanese Patent Laid-Open No. 8-168701). The optimum DC base voltage at this time is almost the corona start voltage.

[0003]

However, the conventional pulse-charged electric precipitator has a problem that a very high dust having an electric resistivity of about 10 ¹³ ohm-cm or more cannot be applied to the DC base voltage near the corona start. The reverse ionization phenomenon that inhibits the dust collection action even with a small corona discharge current caused by the dust occurs in the dust layer deposited on the collection electrode, and the spot-like positive corona extends in a flare shape toward the dust collection space by the DC base voltage Become like Therefore, there is a disadvantage that the operation immediately shifts to the spark when the pulse voltage is superimposed. The pulse voltage at this time is very low, and may be generated even at several tenths of a kilovolt of normal operation. If the pulse voltage is lowered so that sparks do not occur, not only does the failure to reduce the amount of dust charged occur, but also the uniformity of the corona discharge on the surface of the discharge electrode, which is a feature of pulse charging, is further suppressed, and the reverse ionization phenomenon is further suppressed. The dust collection rate is remarkably reduced. Further, the chargeable range of the pulse voltage is narrowed, and even if an attempt is made to maintain an optimum DC base voltage by controlling the pulse voltage, sparks occur frequently and normal charging cannot be continued.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a pulse-charged electric precipitator which overcomes the disadvantages of the prior art, reduces the problem of sparks, and does not significantly reduce the dust collection rate.

[0004]

In order to achieve the above-mentioned object, the invention according to claim 1 is a method of collecting a pulse charging voltage obtained by superimposing a DC base voltage from a DC base power supply and a pulse voltage from a pulse power supply. In a pulse charged electric dust collector that applies between the discharge electrode and dust collection electrode provided in the dust collector and collects dust, the pulse output from the pulse power supply to the DC output output from the DC base power supply A spark generation detecting device at the time of voltage superimposition, and when it is detected that spark frequently occurs even at a preset lower limit of the pulse voltage, the output voltage of the pulse power supply is set to the lower limit of the pulse voltage; The output voltage is adjusted to suppress the occurrence of spark. A second aspect of the present invention is the configuration according to the first aspect, wherein the adjustment of the output voltage of the DC base power supply is gradually changed at a constant value until the spark frequency is allowed. A third aspect of the present invention is the configuration according to the first aspect of the present invention, wherein the adjustment of the output voltage of the DC base power supply does not generate a spark, or switches the spark frequency to a value within a permissible range.

[0005]

According to the above configuration, when sparks occur frequently, the peak value of the pulse voltage is set to at least a value at which corona discharge is uniformly generated, and the DC base voltage is adjusted to suppress the spark. Control. According to the present invention, even for high electrical resistivity dust that is likely to cause sparks in pulse charging, a uniform corona discharge is secured on the discharge electrode surface, and the occurrence of sparks is suppressed to significantly reduce the dust collection rate. To prevent

[0006]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of a pulse-charged electric precipitator according to the present invention. The main part of the pulse charged electric precipitator is an electric precipitator 10 and a power supply 2 comprising a DC base power supply 12, a pulse power supply 14 and a controller 16.
0. The pulse power supply 14 is provided with a spark generation detecting device 18 for outputting a pulse voltage.

First, the dust collecting operation of the pulse charged electric dust collector will be described. Gas containing dust generated from a boiler (not shown) is sent from the inlet 10E of the electric dust collector 10 to the dust collecting chamber 10A. . In the dust collecting chamber 10A, the power supply 20 is connected between the discharge electrode 10B and the dust collecting electrode 10C provided therein, and a voltage obtained by superimposing a pulse voltage on the DC base voltage is applied to the dust collecting chamber 10A. Dust in the supplied gas is charged by the discharge from the discharge electrode 10B and collected by the dust collection electrode 10C.

[0008] The dust collected by the dust collecting electrode 10C is separated from the dust collecting electrode 10C by a hammering operation and is separated from the hopper portion 1C.
It falls and accumulates at 0D. The dust deposited on the hopper 10D is discharged out of the electrostatic precipitator 10 by a discharge device (not shown) at regular intervals. On the other hand, the clean gas from which dust has been removed is discharged from the exhaust port 10F of the electrostatic precipitator 10.

Next, the operation of the power supply 20 for outputting a voltage applied between the discharge electrode 10B and the dust collection electrode 10C will be described with reference to Japanese Patent Application Laid-open No.
An outline of the control will be described based on the description of control disclosed in Japanese Patent Application Publication No. 168701. FIG. 2 shows an example of a voltage waveform output from the power supply 20. V _B is a DC base voltage which is output from the DC-based power source 12, the pulse voltage V _P output from the pulse power source 14 on the are superimposed. In the figure, T represents a pulse period, and the number of pulses per unit time (pulse frequency) is represented by 1 / T. W represents the width of one pulse.

[0010] The voltage waveform is determined to an optimum value that maximizes the dust collection rate. Although the optimum value varies by the electric resistivity of the dust, almost the same value for various high electric resistivity dust results in more than 10 ¹¹ ohm-centimeters of the dust collecting experiment, with respect to the optimum value of the DC base voltage V _B Met. Also, the optimal value of the corona discharge current tends to decrease slightly as the electrical resistivity of the dust increases,
It can be considered almost constant. Therefore, in order to operate the dust collection rate at the maximum, control is performed so that the DC base voltage and the corona discharge current output from the DC base power supply 12 are maintained at constant values regardless of the value of the electric resistivity of the collected dust. .
That is, the corona discharge current is forcibly set to the optimum value and the DC base voltage is output from the pulse voltage V
_P , the pulse frequency 1 / T, and the pulse width W are controlled and set to optimal values.

However, when the electrical resistivity reaches a high value of 10 ¹³ ohm-cm or more, if a pulse voltage is superimposed on the optimum DC base voltage and the corona discharge current set, dust that immediately generates a spark is generated. Exists. In such a spark generation state, the application of the above-described optimum voltage waveform cannot be maintained. Also when the spark is lowered pulse voltage until no occurs, the pulse voltage V _P is becomes a few kilovolts, the advantages of the pulse charge is lost. In other words, the reverse ionization phenomenon that impedes the dust collection action due to pulse charging can be suppressed only by applying a steep and high-voltage pulse voltage to the discharge electrode, so that corona discharge occurs uniformly on the discharge electrode and the discharge current becomes even. It is said to flow into the dust collection pole. In the case of DC charging, the location of corona generation on the discharge electrode is spot-shaped, so that a location where the current density flowing into the dust collection electrode is high is created. This location serves as a starting point to cause a reverse ionization phenomenon of the flared positive corona. When a pulse voltage is superimposed, the flare extends to reach a spark.
When flared positive corona is too low the pulse voltage V _P so as not to develop the spark discharge superb corona discharge becomes uneven, there is no back corona suppression effect described above, resulting dust rate is greatly reduced .

[0012] The DC base voltage V _B is optimally near the corona starting voltage as before for dust with less spark generation, but the dust collection rate is significantly reduced for dust where sparks are likely to occur. The present invention is superimposed pulse voltage V _P and the DC base voltage V _B relative to the spark prone dust below corona onset voltage, sparks stop flare-shaped positive corona be the same peak voltage V _B + V _P suppressed to ensure a uniform corona discharge by a high pulse voltage V _P, it is intended to prevent a reduction in dust collection rate.

The charging method according to the present invention for dust, which is liable to generate sparks, will be described with reference to the control flows shown in FIGS. In FIG. 3, the main control is defined as a conventional technique, for example,
This is a known voltage waveform control disclosed in Japanese Patent Application Publication No. 168701. When the spark frequency per fixed time does not affect the dust collection rate, the voltage applied to the discharge electrode is controlled by the main control to the optimum DC base voltage _VBO . V _BO is almost constant and does not depend on the electrical resistivity of the dust and is a value near the corona starting voltage, but the optimum pulse voltage V _PO changes depending on the dust.

When a spark occurs when a pulse voltage is superimposed on the DC base voltage, a spark occurrence detecting device 18 detects that a spark has occurred, and sets the lower limit of the pulse voltage output from the pulse power supply 14 after the spark occurrence. Restart charging by value. The lower limit value of the pulse voltage is a minimum value of a voltage at which corona discharge is uniformly generated on the surface of the discharge electrode when a pulse voltage is applied. FIG. 5 shows an example in which the current distribution on the surface of the dust collecting electrode facing the discharge electrode is measured by changing the pulse voltage.

The minimum pulse voltage at which the uniformity of corona discharge can be ensured varies depending on the thickness and shape of the discharge electrode. However, when the DC base voltage is set near the corona start voltage,
It is about 10 to 20 kV, which is set for each type of discharge electrode. Charging is restarted at the pulse voltage lower limit set value, and no spark is generated, or even if a spark is generated, the spark frequency is counted, and if the frequency is less than an allowable set value, charging is maintained by the main control. When the spark frequency is equal to or higher than the allowable set value, the control is switched to the spark frequent occurrence control and charging is performed.

FIG. 4 shows a detailed control flow of the spark frequent occurrence control. When the spark frequent time control is started, DC-based power source is the base voltage output is switched to the constant voltage control, the pulse voltage V _P output by the pulse power supply is set to the pulse voltage lower limit. On the other hand, the DC base voltage is set to the lower voltage limit at which corona discharge does not occur.

In this state, charging is resumed, and the spark occurrence detecting device 18 detects whether or not spark has occurred. If a spark occurs, it is determined whether the spark frequency is equal to or greater than a set value or less than the set value. As a result, if the value is equal to or greater than the set value, the DC base voltage is reduced to detect the occurrence of spark. This control is performed until the occurrence of spark is eliminated or the spark frequency becomes less than the set value. When the spark is eliminated, the DC base voltage is increased to detect the occurrence of the spark. When it is determined that the spark frequency is less than the set value in the case where a spark has occurred, the DC base voltage is held at the lower limit set value. If there is no spark, the DC base voltage is increased and the spark frequency is kept at the maximum value below the allowable set value.

According to the above-described control, a pulse voltage at which corona discharge is uniform and a high DC base voltage which does not affect the dust collection rate even when a spark is generated are superimposed on the discharge electrode. As a result, it is possible to prevent a remarkable decrease in the dust collection rate even for dust that easily causes sparks. The properties of the dust also change due to changes in the operating state of the boiler, fuel, and the like. Therefore, in order to operate the pulse-charged electric precipitator at the highest dust collection rate for each dust, it is necessary to switch the control method as needed.

As a method, as shown in FIG. 3, after the control is shifted from the main control to the spark frequent control, a change in the state of the dust source, for example, a change in the fuel or a change in the combustion amount, is controlled as a return command signal. Issue a return command and return to main control. After returning to the main control, the state of spark generation is detected again, and FIG.
According to the control flow, the control method of continuing the main control or switching back to the spark frequent occurrence control is selected.

If it is not possible to take in a return command signal from the outside, a timer may be provided, and a return command signal may be issued after the timer set time has elapsed since the control is shifted to the spark frequent occurrence control. In the above-described spark frequent control, the output voltage adjustment of the DC base power supply after setting the output voltage of the pulse power supply to the pulse voltage lower limit value is gradually changed at a constant value until the spark frequency is allowed, or
Alternatively, the spark may be switched to a value that does not generate a spark or that causes the spark frequency to fall within an allowable range.

In this embodiment, only the DC base voltage and the pulse voltage superimposed thereon are described. However, in this method, both the base voltage and the pulse voltage tend to be lower than those for dust that does not cause sparks. As a result, the corona discharge current is also reduced. Therefore, after holding the DC base voltage as shown in FIG. 6, the pulse frequency 1 / T is increased from the time of the main control, and it is determined whether the spark frequency is equal to or more than the set value or less than the set value. When the spark frequency is equal to or higher than the set value, the pulse frequency is reduced, and when the spark frequency is lower than the set value, the pulse frequency is held. By controlling the spark frequency in this manner, the decrease in the corona discharge current may be compensated for. When the pulse frequency is increased, sparks are more likely to occur, but are increased within the allowable range of the spark frequency. In this way, by controlling the pulse frequency, the shortage of the corona discharge current can be compensated and the decrease in the dust collection rate can be further reduced.

As another embodiment, when the DC base voltage is lower than the corona starting voltage, the peak voltage V _B + V
_{Even if P} is higher than when the DC base voltage is set near the corona start voltage, the occurrence of sparks is reduced. Focusing on this, after maintaining the DC base voltage at a value at which spark does not frequently occur in the flow of FIG.
The spark frequency is determined by increasing the pulse voltage. If the spark frequency is equal to or higher than the set value, the pulse voltage is reduced, and if the spark frequency is lower than the set value, the pulse voltage is maintained. As described above, the operation may be performed at a value higher than the pulse voltage lower limit set value. And control the DC base voltage V _B and the pulse voltage V _P according to this example, it is possible to reduce the decrease in complement precipitator rate insufficient to prevent sparks frequent corona discharge current.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a pulse-charged electric precipitator according to the present invention.

FIG. 2 is a diagram showing a voltage waveform output from a power supply in FIG.

FIG. 3 is a flowchart showing a procedure for detecting a spark generation state and switching a power supply control method.

FIG. 4 is a flowchart showing a procedure for controlling an output voltage of a power supply for dust that easily causes sparks.

FIG. 5 is a diagram showing a distribution of a pulse voltage and a current flowing through a dust collection electrode.

FIG. 6 is a flowchart showing a control procedure in another embodiment.

FIG. 7 is a flowchart showing a control procedure in another embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Electric dust collector, 12 ... DC base power supply, 14 ... Pulse power supply, 16 ... Controller, 18 ... Spark occurrence detection device,
20 ... Power supply

Claims (3)

[Claims] 1. A pulse charging voltage obtained by superimposing a DC base voltage from a DC base power supply and a pulse voltage from a pulse power supply is applied between a discharge electrode and a dust collection electrode provided in an electrostatic precipitator. A pulse-charged electrostatic precipitator for collecting dust, comprising a spark generation detecting device when a pulse voltage output from the pulse power supply is superimposed on a DC output output from the DC base power supply, wherein the spark is preset When it is detected that frequent occurrence occurs even at the pulse voltage lower limit value, the output voltage of the pulse power supply is set to the pulse voltage lower limit value, and the output voltage of the DC base power supply is adjusted to suppress the occurrence of spark. And a pulse charged electric precipitator. 2. The pulse-charged electric precipitator according to claim 1, wherein the output voltage of the DC base power supply is gradually changed at a constant value until a spark frequency is allowed. . 3. The pulse-charged electric precipitator according to claim 1, wherein the output voltage of the DC base power supply is adjusted so as not to generate a spark or to switch the spark frequency to a value within an allowable range. apparatus.