JPH0475787B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrostatic precipitator, and more particularly to an electrostatic precipitator that is capable of collecting high-resistance dust.

[Conventional technology]

Generally, in electrostatic precipitators, it is known that when the electrical resistance of dust increases, abnormal discharge called a reverse ionization phenomenon occurs, significantly reducing dust collection performance. This is because when the charged dust adhering to the dust collection electrode plate in the dust collection chamber has a high resistance, electrical dielectric breakdown occurs in the dust layer due to poor charge release from the dust layer, and this dielectric breakdown occurs. The ions neutralize the electric charge in the dust collection space.
One of the measures to suppress the occurrence of this reverse ionization phenomenon is a method of intermittently applying a charging voltage between the discharge electrode and the dust collection electrode (hereinafter abbreviated as an intermittent charging method). This is intended to alleviate the deterioration in dust collection performance.

By the way, the electrical equivalent circuit of the electrostatic precipitator is the second one.
As shown in the figure, it is represented by a parallel circuit of a capacitor C and a resistor R. Here, the capacitor C corresponds to the capacitance between the discharge electrode and the dust collection electrode of the dust collection chamber, and the resistance R corresponds to the discharge resistance between the electrodes. In such an equivalent circuit, when a reverse ionization phenomenon occurs, the discharge resistance between the electrodes becomes extremely small due to a large number of ions, and therefore the discharge time constant (C×R) becomes small. Therefore, when a charging voltage is intermittently applied between the discharge electrode and the dust collection electrode, the charging voltage will change to the solid line 40 in FIG. 3 if no reverse ionization phenomenon occurs.
As shown in the figure, a discharge with a large time constant occurs during a charging pause. On the other hand, when a reverse ionization phenomenon occurs, the time constant of the circuit becomes small, so that the voltage drops below the corona starting voltage when charging is stopped, as shown by the broken line 42 in FIG. It is known that as a result, the dust collection performance decreases at a rate approximately commensurate with the time during which no charging voltage is applied, that is, the charging pause time. For this reason, considering that the electrical resistance of dust changes greatly depending on the temperature of the exhaust gas being processed, the amount of moisture in the gas, the components of the dust, etc., we are trying to prevent the occurrence of reverse ionization due to changes in the electrical resistance of dust. It is necessary to detect in real time and select the most suitable charging method for the device, that is, to switch between a continuous charging method in which a charging voltage is continuously applied and an intermittent charging method.

Therefore, conventionally, as shown in the charging voltage waveform shown in FIG. 4, the bottom value of the charging voltage when the reverse ionization phenomenon shown by the solid line 44 does not occur and the bottom value of the charging voltage when the reverse ionization phenomenon shown by the broken line 46 has occurred. It has been proposed to focus on the fact that there is a difference in the bottom value of the charging voltage, determine the presence or absence of reverse ionization from this bottom value, and automatically select the charging method.

However, while the presence or absence of back ionization in a device operating with a continuous charging method can be detected from the bottom value of the charging voltage, it is possible to detect the occurrence of back ionization in a device operating with an intermittent charging method. There is a problem in that the detection accuracy is poor because the bottom value of the charging voltage decreases only by a small amount due to the effect of suppressing reverse ionization due to charging. For this reason, equipment operating in the intermittent charging mode cannot appropriately switch from the intermittent charging mode to the continuous charging mode in order to prevent deterioration of dust collection performance when the occurrence of the reverse ionization phenomenon stops. There is a problem.

The present invention was made in view of the above circumstances, and it is possible to detect the occurrence of reverse ionization phenomenon with high accuracy even during operation using the intermittent charging method, and when the occurrence of the reverse ionization phenomenon has stopped, the intermittent charging method can be switched off. The object of the present invention is to provide an electrostatic precipitator having a function of automatically switching to continuous charging mode operation.

[Means for solving problems]

In order to achieve the above object, the present invention applies a DC high voltage between the discharge electrode and the dust collection electrode provided in the dust collection chamber to generate corona discharge, and the dust collection is performed by the corona discharge. The electrostatic precipitator includes a corona start voltage setting means for setting the start voltage of corona discharge generated between the electrodes, a power supply means for outputting a DC high voltage to be applied between the electrodes, and a voltage between the electrodes. a voltage detecting means for detecting; a comparing means for comparing a set value of the starting voltage of the corona discharge with a detected value of the voltage detecting means; When the detected value indicates that it is higher than the set value of the corona start voltage setting means, the power supply means is controlled so that a DC high voltage is continuously outputted from the power supply means, and the comparison signal is outputted from the voltage detection means. selection means for controlling the power supply means so that the DC high voltage is intermittently outputted from the power supply means when the detected value is lower than the set value of the corona start voltage setting means; It is characterized by the fact that

[Effect]

The present invention detects a DC high voltage from a power supply means applied between a discharge electrode and a dust collection electrode by a voltage detection means, and uses this detected value and a corona starting voltage set in advance in a corona start voltage setting means. The occurrence of reverse ionization is detected by comparing the discharge starting voltage with a set value by a comparison means. The power supply means is controlled by the selection means operated based on the comparison result of the comparison means so that when no reverse ionization occurs, a high DC voltage is continuously applied between the electrodes; on the other hand,
When reverse ionization occurs, a high DC voltage is intermittently applied between the electrodes. In this way, by automatically causing corona discharge continuously or intermittently depending on whether or not reverse ionization occurs, it is possible to prevent the dust collection performance from deteriorating.

〔Example〕

Hereinafter, preferred embodiments of the electrostatic precipitator according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows the basic configuration of an electrostatic precipitator according to the present invention. and a dust collection chamber 14 in which a discharge electrode 10 and a dust collection electrode 12 are provided.

The power supply circuit 4 of the charge control device 8 includes a power control element 16 such as a thyristor that controls the phase of the AC voltage from the AC power supply 2, a transformer 18 that boosts the AC voltage from the power control element 16, and a transformer 18 that boosts the AC voltage from the transformer 18. It is composed of a rectifier 20 that rectifies the voltage into a DC high voltage (charge voltage). A high DC voltage from the rectifier 20 is applied between the discharge electrode 10 and the dust collection electrode 12 of the dust collection chamber 14 .

The power control element 16 is configured to output an AC voltage when an output signal from an intermittent charging signal generator 30 (described later) is input, and not to output an AC voltage when the output signal is not input. Incidentally, the power control element 16 is controlled to start by a drive circuit (not shown).

On the other hand, the control circuit 6 of the charge control device 8
a charging voltage detector 22 that detects a charging voltage applied between the discharge electrode 10 and the dust collecting electrode 12 of No. 4;
A corona start voltage setter 24 that sets the start voltage of corona discharge, a comparator 26 that compares the levels of signals from the charging voltage detector 22 and the corona start voltage setter 24, and the power control element 1 of the power supply circuit 4.
an intermittent charging signal generator 30 that outputs a control signal for turning on and off 6; and an intermittent charging signal generator 3
The charge mode switch 28 controls the supply of the output signal from 0 to the power control element 16.

The charging voltage detector 22 includes two resistors 32 and 34.
As a result, a detection signal indicating the charged voltage divided by the resistors 32 and 34 is input to the comparator 26.

The comparator 26 compares the level of the detection signal from the charging voltage detector 22 and the output signal from the corona start voltage setter 24 set to a signal level corresponding to the start voltage of corona discharge, and inverts the detection signal in the dust collection chamber 14. This is a circuit for checking whether ionization is occurring. If reverse ionization occurs in the dust collection chamber 14 and the detected value of the charging voltage detector 22 is lower than the set value of the corona start voltage setter 24, a signal is not output from the comparator 26 to the charging method switch 28. It's getting old. On the other hand, when the occurrence of back ionization stops in the dust collection chamber 14 and the detection value of the charging voltage detector 22 becomes higher than the setting value of the corona start voltage setting device 24, the charging method switch 28 is transferred from the comparator 26 to the is designed to output a signal.

The charging method switch 28 is a switch SW1 that operates ON and OFF based on the output signal from the comparator 26.
It is composed of etc. The switch SW1 is closed when the output signal from the comparator 26 is not input, so that the output signal from the intermittent charging signal generator 24 is input to the power control element 16, and the output signal from the comparator 26 is input to the power control element 16. When inputted, it becomes an open state and cuts off the output signal from the intermittent charging signal generator 24.

The intermittent charging signal generator 30 outputs, for example, a constant cycle drive signal for operating the power control element 16 intermittently. As a result, a charging voltage is intermittently applied between the discharge electrode 10 and the dust collection electrode 12 in the dust collection chamber 14, thereby suppressing the reverse ionization phenomenon.

Next, the operation of the electrostatic precipitator constructed as described above will be described.

After the device is started, for example, by a continuous charging method, the power control element 16 is controlled to start based on a control signal from a drive circuit (not shown), and accordingly, the power supply voltage from the AC power supply 2 is phase-controlled and transformer 1
The voltage is boosted by 8, rectified by a rectifier 20, and applied between the discharge electrode 10 and the dust collection electrode 12. The charging voltage applied between the electrodes 10 and 12 is always detected by the charging voltage detector 22, and the charging voltage is transmitted from the charging voltage detector 22 to the comparator 2.
0 is supplied with a signal corresponding to the charging voltage. Therefore, when the comparator 22 detects that reverse ionization has occurred based on the level comparison result between the output signal from the charging voltage detector 22 and the output signal from the corona start voltage setting device 24, The charging method switch 28 is controlled to switch the charging method from the continuous charging method to the intermittent charging method. That is, the comparator 26
The output signal from the charging method switch 28 is no longer input to the charging method switch 28, and the switch SW1 changes from the open state to the closed state. When the switch SW1 is closed, a drive signal is supplied from the intermittent charging signal generator 30 to the power control element 16. As a result, a charging voltage is intermittently applied from the power supply circuit 4 between the discharge electrode 10 and the dust collection electrode.

On the other hand, when it is detected that the generation of back ionization has stopped based on the comparison result of the comparator 26, a signal is outputted from the comparator 26 to the charging method switch 28. The switch SW1 is opened by the signal from the comparator 26, and the drive signal from the intermittent charging signal generator 30 is no longer supplied to the power control element. As a result, the device returns from intermittent charging mode to continuous charging mode.

In this way, in the electrostatic precipitator of the present invention, the discharge electrode 1
The charging voltage applied between the electrodes 0 and 12 is compared with the detected corona starting voltage, and as a result of this comparison, if the charging voltage is lower than the corona starting voltage, reverse ionization has occurred. If the charging voltage is higher than the corona start voltage, it is determined that no reverse ionization has occurred, and the system is configured to operate in the continuous charging method to suppress reverse ionization. ing. As a result, when the generation of back ionization stops during operation with the intermittent charging method, the intermittent charging method automatically switches to the continuous charging method, so even if the generation of back ionization has stopped, the intermittent charging method can be operated. As a result, dust collection performance does not deteriorate as a result of continued use.

〔Effect of the invention〕

As explained above, according to the electrostatic precipitator according to the present invention, the detected value of the charging voltage and the set value of the starting voltage of corona discharge are compared, and the discharge electrode and the dust collecting electrode are adjusted according to the comparison result. Since the structure is configured so that high DC voltage is automatically applied intermittently or continuously between the electrodes, the occurrence of back ionization is stopped during operation when high DC voltage is intermittently applied between the electrodes. When this happens, the DC high voltage is automatically switched from an intermittent application method to a continuous application method, which prevents the dust collection performance from deteriorating.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the overall configuration of an electrostatic precipitator according to the present invention, Fig. 2 is an electric circuit diagram showing an electrical equivalent circuit of a basic electrostatic precipitator, and Figs. 3 and 4 are FIG. 3 is an explanatory diagram showing an example of a voltage waveform of a charging voltage. 2... AC power supply, 10... Discharge electrode, 12...
Dust collection electrode, 16... Power control element, 18... Transformer, 20... Rectifier, 22... Charging voltage detector, 24... Corona start voltage setting device, 26... Comparator, 28... Charging method switching 30...Intermittent charge signal generator.

Claims (1)

[Claims] 1. Electrostatic dust collection in which a DC high voltage is applied between a discharge electrode and a dust collection electrode provided in a dust collection chamber to generate a corona discharge, and dust is collected by the corona discharge. In the apparatus, a corona start voltage setting means for setting a starting voltage of corona discharge generated between the electrodes, a power supply means for outputting a DC high voltage applied between the electrodes, and a voltage detection means for detecting the voltage between the electrodes. means, a comparison means for comparing a set value of the starting voltage of the corona discharge and a detection value of the voltage detection means, and a comparison signal that receives a comparison signal from the comparison means and indicates that the detection value of the voltage detection means is corona. When the voltage is higher than the set value of the starting voltage setting means, the power supply means is controlled so that the DC high voltage is continuously output from the power supply means, and the comparison signal indicates that the detected value of the voltage detection means is higher than the set value of the voltage detection means. selection means for controlling the power supply means so that the DC high voltage is intermittently output from the power supply means when the corona start voltage is lower than the set value of the corona start voltage setting means; Characteristic electrostatic precipitator.