JP3636655B2 - Electric dust collecting method and electric dust collecting device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a control device and a control method for an electrostatic precipitator that collects dust in an airflow such as exhaust gas, and more particularly to an electrostatic precipitator that can suppress a decrease in charge voltage due to frequent spark discharge.
[0002]
[Prior art]
In electric dust collection, it is generally said that the dust collection efficiency increases when the charge voltage applied to the dust collection part consisting of the dust collection electrode and the discharge electrode is high. It is only necessary to maintain a high voltage just before the occurrence of a spark discharge, but in practice, the fact that a spark discharge occurs at a certain frequency is one parameter, and as much as possible near the voltage at which the spark discharge occurs. The charging voltage is controlled so that the time for charging the part becomes longer. Then, when a spark discharge occurs, it detects the spark discharge that occurs inside the dust collector by detecting the phenomenon that the charged voltage of the dust collector decreases rapidly or the phenomenon that the charging current increases significantly. When this is done, charging in the next cycle is temporarily stopped, the charging voltage is lowered, and the spark discharge is extinguished.
[0003]
A conventional example will be described in detail with reference to FIG. 6. The electrostatic precipitator includes a commercial AC power source 30, a power control element 31 including a thyristor connected in reverse parallel for phase control of the AC voltage, a step-up transformer , A high-voltage rectifier 33 that rectifies the AC voltage on the secondary side thereof, a dust collecting part 34 composed of a dust collecting electrode and a discharge electrode, a charge voltage detecting means 35, a detection voltage signal, and a reference signal And a charge voltage determination circuit 36 for generating a signal indicating the possibility of occurrence of a spark discharge by reversing the polarity when the detected voltage signal becomes lower than a reference value. The current detection means 37 for detecting the current flowing through the dust collecting unit 34 and the circuit for calculating the current detection signal and the reference signal and outputting an error signal, the current detection signal being lower than the reference value When the output polarity is reversed A current determination circuit 38 for generating a signal indicating the possibility of the occurrence of the spark discharge, composed of the phase control circuit 39. for generating a drive signal for phase control of the power control device 31.
[0004]
Next, an example of a control method when a typical spark discharge occurs will be described while explaining the operation of the electrostatic precipitator having such a configuration. First, when the charge voltage detection signal is higher than the reference value and when the current detection signal is lower than the reference value, the phase control circuit 39 performs normal phase control on the power control element 31 based on these signals. When the charge voltage detection signal becomes lower than the reference value, the output signal of the charge voltage determination circuit 36 is inverted in polarity, and the output signal becomes a signal indicating the possibility of occurrence of spark discharge. When the current detection signal becomes higher than the reference value, the output signal of the current determination circuit 38 is inverted in polarity, and the output signal becomes a signal indicating the possibility of occurrence of spark discharge. When the polarities of the output signals of both the charge voltage determination circuit 36 and the current determination circuit 38 are inverted, the phase control circuit 39 determines that a spark discharge has occurred, and only a predetermined period, typically a half cycle. The output of the drive signal is stopped, whereby the charge is temporarily interrupted for half a cycle. Along with this, the charging voltage decreased, and the spark discharge was extinguished to prevent the transition to arc discharge. Then, after charging is stopped for a half cycle, recharging is performed to increase the charging voltage at a voltage increase rate θ at a soft start time of about 50 to 100 ms, so that the voltage is lower by ΔV than the charging voltage at the time of spark discharge. After that, the charging voltage was gradually increased at the voltage increase rate θ.
[0005]
[Problems to be solved by the invention]
However, the charge control at the time of occurrence of spark discharge so far, regardless of the possibility of the transition from spark discharge to arc discharge, when the occurrence of spark discharge is detected, the charge is interrupted uniformly and the charge voltage is temporarily set. Spark control was performed to lower ΔV. The normal charge control method after detecting the spark discharge is to stop the thyristor from firing in the next half cycle after the spark discharge has occurred, and then the recurrence of the spark discharge and the electrostatic capacity of the dust collecting part. The charge voltage was gradually increased by soft start to prevent inrush current.
[0006]
In particular, in the case of electrostatic dust collection, which is likely to generate spark discharge, such as coal boiler exhaust gas containing high-resistance dust, as described above, every time a spark discharge occurs, soft start is repeated at the time of charge voltage drop and recharge due to charge interruption. When this occurs, there is a problem that the average value of the charging voltage of the dust collector is lowered and the dust collection efficiency is considerably lowered. It is an object of the present invention to solve such problems and to improve the charging efficiency as compared with the prior art by suppressing a decrease in charging voltage.
[0007]
[Means for Solving the Problems]
To attain the above object, the first invention, the current of the delay phase and supplied to the AC voltage from an AC power source, a discharge electrode arranged opposite to the dust collection electrode and the dust collecting electrode a high voltage is applied between the, in electrostatic precipitation method of collecting dust contained in the air flow passing between them, the generation of spark discharge is detected between said discharge electrode and said collector Chirikyoku When the detection signal indicating the occurrence of the spark discharge is generated between the time when the AC voltage of the AC power supply is zero-crossed and immediately before the power control element is turned on, the power control element is temporarily driven. The charging is continued by performing normal control without interruption, and the detection signal indicating the occurrence of the spark discharge is generated between the time when the power control element is turned on and the time when the next zero cross of the AC voltage of the AC power supply is generated. If the power control element is turned on, There is provided an electrostatic precipitation method characterized by reducing the once charged voltage is stopped between regular.
[0008]
In order to solve the above-described problem, in a second invention, in the first invention , when a detection signal indicating the occurrence of spark discharge is generated when the drive signal of the power control element is at L level , When the normal control is performed without interrupting the driving of the power control element to continue charging, and a detection signal indicating the occurrence of spark discharge is generated when the drive signal of the power control element is at the H level. The electric dust collection method is characterized in that driving of the power control element is interrupted for a predetermined period to temporarily reduce the charging voltage.
[0009]
In order to solve the above-described problem, a third invention is an AC power source, a power control element that controls AC power from the AC power source, a current limiting reactor, a step-up transformer, and a step-up transformer. A high-voltage rectifier that rectifies high-voltage AC voltage and converts it to direct current, and includes dust contained in an airflow passing through a dust collecting portion that includes a dust collecting electrode and a discharge electrode disposed opposite to the dust collecting electrode. In the electrostatic precipitator that collects the electric power, a zero-cross detection circuit that detects a zero-cross point of the voltage of the AC power supply, a phase control circuit that generates a drive signal that controls conduction of the power control element, and the dust collection electrode, A spark detection circuit that provides a spark discharge detection signal when a spark discharge occurs between the discharge electrode and the discharge electrode when the occurrence of a spark discharge is detected when the drive signal output by the phase control circuit is at an L level; Of the power control element Once to continue the charge performs normal control without stopping, said drive signal is a predetermined time to interrupt the driving of the power control device in the case where generation of the spark discharge is detected at the H level An electrostatic precipitator comprising a charge control circuit for once reducing a charge voltage is provided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
First, in describing the present invention, the concept leading to the invention will be described. (1) This invention starts from the idea that if there is a spark discharge that does not shift to arc discharge, it is not necessary to perform spark control such as charge stop or subsequent soft start for such spark discharge. ing. (2) Therefore, it was confirmed from various experiments whether or not there was a spark discharge that did not shift to arc discharge even if the generated spark discharge continued to be charged as it was. (3) As a result, there is an arc discharge that does not shift to the arc discharge even if the generated spark discharge continues to be charged, and at least from the vicinity of the zero crossing point of the AC voltage of the AC power supply to the ON of the power control element, That is, it was confirmed that what occurred during the period when the drive signal was not supplied was such a spark discharge that did not shift to arc discharge.
[0012]
When the drive signal is not supplied and the instantaneous value of the AC power supply voltage drops to the zero crossing point or near the zero crossing point, the instantaneous value of the power supply voltage does not change even if a spark discharge occurs in the dust collector on the load side. Since it has decreased to zero, energy cannot be continuously supplied from the power supply side. From this, it can be said that there is no possibility that the spark discharge generated between the zero cross point or the vicinity thereof and the next turn-on timing of the power control element shifts to the arc discharge.
[0013]
Therefore, according to the present invention, when a spark discharge occurs between the dust collection electrode and the discharge electrode, the control is performed so as to reduce the charging voltage by continuing to drive the power control element as it is, according to the spark discharge occurrence time. Or an electric dust collection method in which the driving of the power control element is interrupted for a predetermined period and the charge voltage is once lowered.
[0014]
Specifically, the present invention detects a spark discharge generated in a dust collecting part including a dust collection electrode and a discharge electrode, and the polarity of the AC voltage of the AC power source that is the power source is the occurrence of the spark discharge, that is, Even if a spark discharge occurs in the period when the power control element such as a thyristor connected in reverse parallel from the vicinity of the zero cross point is generated, that is, even when a spark discharge occurs in a period in which the drive signal of the power control element is not supplied, Charging is continued by performing normal control without temporarily interrupting driving of the power control element. And, when the occurrence of the spark discharge occurs from the time when the power control element is turned on until the next zero crossing time of the AC voltage of the AC power supply, that is, when the drive signal is supplied to the power control element. In the same manner as in the prior art, the driving of the power control element is interrupted for a predetermined period, for example, a half cycle to temporarily lower the charging voltage, and then the power control element is turned on again to increase the charging voltage.
[0015]
More specifically, the spark discharge generated during a period in which the drive signal is generated using the drive signal of the power control element is a spark discharge that shifts to arc discharge, and the drive signal is not generated. The spark discharge generated in is a spark discharge that does not shift to arc discharge. And, when the spark detection signal (H level when spark discharge is detected) is H level and the drive signal is H level, normal spark control (charge stop after spark detection, recharge by soft start) I do. When the spark detection signal is at the H level and the drive signal is at the L level, the charge is not interrupted and the normal charge control is continued as it is. Dust collection efficiency can be improved by such an electric dust collection method that performs new charge control.
[0016]
【Example】
An embodiment of the present invention will be described with reference to FIGS. First, in FIG. 1, 1 is a commercial AC power source, 2 is a charge control panel, 3 is a rectifying transformer circuit, and 4 is a dust collecting unit including a dust collecting electrode and a discharge electrode. The charge control panel 2 detects a zero-crossing point of the AC voltage of the AC power supply 1, a synchronous detection transformer 5 that detects the voltage of the AC power supply 1, a power control element 6 that is composed of a thyristor or IGBT connected in reverse parallel. Including a zero-cross detection circuit 7 and a zero-cross detection circuit 7, a phase control circuit 8 for controlling on / off of the power control element 6, a charge control circuit 9, a spark detection circuit 10, and a constant current control circuit, a constant Although a voltage control circuit and the like are provided, illustration of these is omitted.
[0017]
The charge control circuit 9 outputs a signal that lowers the charge voltage by a predetermined voltage value when the occurrence of a spark discharge is detected, and only when a spark discharge that may shift to arc discharge is detected. Charge interruption for soft start control in which charging is temporarily reduced for a predetermined period of time, for example, half a cycle, and the charging voltage is temporarily reduced, and after the charging interruption, the conduction angle of the power control element 6 is gradually increased. The soft start circuit 12, as will be described later, charge-interrupts only the spark discharge detection signal that is likely to shift to arc discharge by ANDing the drive signal in the phase control circuit 8 and the spark discharge detection signal from the spark detection circuit 10. An AND circuit 14 that passes through the soft start circuit 12 is provided.
[0018]
The spark detection circuit 10 compares the first comparator 16 that compares the charged voltage detection signal with the reference voltage of the reference voltage source 15, and the detection signal of the current flowing through the dust collecting unit 4 and the reference value of the reference current source 17. The second comparator 18, and an AND logic circuit 19 that ANDs the output signals of the comparators 16 and 18, the charge voltage detection signal is smaller than the reference voltage, and the current detection signal is larger than the reference value. In this case, a spark discharge detection signal is output.
[0019]
The rectification transformer circuit 3 includes a current limiting reactor 20, a step-up transformer 21 having a primary winding connected to the current limiting reactor 20, a high-voltage rectifier 22 connected to a secondary winding of the step-up transformer 21, a discharge electrode, The voltage dividing resistors 23 and 24 for dividing the voltage between the grounds, and the shunt resistor 25 connected in series between the dust collecting unit 4 and the high voltage rectifier 22 are included. In the circuit of this embodiment, the current limiting reactor 20 is provided in order to suppress the ripple amount of the charging voltage and to suppress the overcurrent at the time of short circuit, and usually 30 to 30 in combination with the short circuit impedance of the step-up transformer 21. It is set to have a% inductance of about 50%. For this reason, as shown in FIG. 2, the charging current waveform of the dust collection unit 4 is delayed from the AC voltage waveform of the AC power supply 1. The present invention uses, as one condition, that the phase of the charging current is delayed with respect to the AC voltage of the AC power supply 1.
[0020]
Next, the operation of the electrostatic precipitator configured as described above will be described. The synchronous detection transformer 5 of the charge control panel 2 detects a voltage synchronized with the AC voltage of the AC power supply 1 and sends it to the phase control circuit 8 including the zero cross detection circuit 7. The zero-cross detection circuit 7 detects the zero-cross point of the AC power source 1 from this voltage and generates a zero-cross detection signal (D), and fires the power control element 6 starting from the zero-cross point according to the control signal from the charge control circuit 8. A signal (C) is transmitted. An AC voltage whose phase is controlled by the power control element 6 is input to the rectifying transformer circuit 3. The AC voltage applied to the rectification transformer circuit 3 is boosted by the step-up transformer 21, is full-wave rectified by the high-voltage rectifier 22, and is supplied to the dust collector 4.
[0021]
The phase control circuit 8 has a circuit configuration as shown in FIG. 3 and operates as follows. The AC voltage from the synchronous detection transformer 5 is rectified by a full-wave rectifier circuit Re, and the rectified voltage is divided by resistors R1 and R2. The divided rectified voltage is compared with the reference voltage of the reference voltage source Pa set to a voltage slightly higher than 0V by the first comparator CM1, and the comparator CM1 is displayed each time the divided voltage becomes zero. A zero-cross detection signal (D) as shown in 3 (D) is generated. On the other hand, the capacitor C1 is charged with a current flowing from the DC power supply Pb through the resistor R5, and the voltage across the both ends increases almost linearly. When the zero cross detection signal (D) appears at the output of the comparator CM1, the transistor Tr1 is forward-biased through the resistors R3 and R4 each time, and the capacitor C1 is discharged to almost zero. Therefore, the sawtooth wave signal (A1) shown in FIG. 3A is input to one input terminal of the second comparator CM2, and the control signal (A2) from the charge control circuit 9 is input to the other input terminal. Is entered. The control signal (A2) is composed of the output signal of the spark control circuit 11, the output signal of the charge interruption / soft start circuit 12, and the output signals of a constant current control circuit and a constant voltage control circuit (not shown), It varies depending on these output signals.
[0022]
The second comparator CM2 compares the sawtooth wave signal (A1) shown in FIG. 3A with the control signal (A2), and the period when the sawtooth wave signal (A1) is larger than the control signal (A2). The H level driving signal (B) is generated. As shown in FIGS. 2 and 4, the drive signal (B) is at the L level from the zero cross point of the power supply voltage waveform (a) to the next ON point of the power control element 6, and is almost the power control element 6. The period from the ON point to the zero cross point of the next power supply voltage waveform (a) is at the H level. In this embodiment, since the power control element 6 is a thyristor, the drive signal (B) is differentiated by the capacitor C2 and the resistors R6 and R7, and is converted into a steep waveform firing signal C through the transistor Tr2 and the resistor R8. Converted. However, when the power control element 6 is an IGBT or a MOSFET, the drive signal (B) is used as it is for on / off drive.
[0023]
Assume that a relatively large spark discharge occurs at time t1 as shown in FIG. Along with the occurrence of the spark discharge, a sudden decrease in the charging voltage and a rapid increase in the charging current are caused, and this change causes the spark detection circuit 10 to output an H level spark discharge detection signal. However, since the drive signal (B) is at the L level at time t1, the output of the AND logic circuit 14 remains at the L level, and a signal for interrupting the charge is not sent to the charge interrupt / soft start circuit 12. Therefore, it is assumed that the spark discharge generated during this period does not shift to the arc discharge, and is continued as it is without interrupting the driving of the power control element 6.
[0024]
Next, as shown in FIG. 2, if a spark discharge occurs at time t2 when the drive signal (B) is at the H level, the drive signal (B) that is one input of the AND logic circuit 14 is at the H level. Since the spark discharge detection signal which is the other input is also at the H level, the output signal of the AND logic circuit 14 is at the H level. In this case, a signal is sent from the AND logic circuit 14 to the charge interruption / soft start circuit 12, and the charge interruption / soft start circuit 12 is supplied with the drive signal (B) for a predetermined period, for example, a half cycle as in the prior art. The phase control circuit 8 is instructed to operate in the soft start mode after the lapse of the predetermined period. Accordingly, the phase control circuit 8 stops supplying the drive signal (B) to the power control element 6 for a half cycle immediately after the spark discharge is detected, and thereafter, from a predetermined small pulse width as in the prior art. A drive signal (B) having a gradually increasing pulse width is supplied to the power control element 6 and recharging is performed.
[0025]
In this embodiment, when a spark discharge occurs, a spark detection signal is sent from the spark detection circuit 10 to the spark control circuit 11 regardless of the presence or absence of the drive signal (B). Is reduced by a predetermined set voltage value, and then a predetermined charging voltage control is performed in which the voltage is increased at a predetermined inclination.
[0026]
Next, in the embodiment shown in FIG. 5, when a spark discharge occurs while the drive signal (B) is at the L level, the spark discharge does not shift to the arc discharge as described above. The spark control function of the circuit 11 is prohibited, and the output of the AND logic circuit 14 is not the output of the AND logic circuit 19 but the input of the spark control circuit 11 in the circuit of FIG. In this circuit configuration, the output of the AND logic circuit 14 becomes L level only when the drive signal (B) is L level and the spark discharge detection signal is H level, and the spark control circuit 11 does not operate only during this period. Does not perform spark control. Therefore, even if a spark discharge occurs, during this period, the spark control circuit 11 does not perform the predetermined charge voltage control for decreasing the charge voltage by a predetermined set voltage value or thereafter increasing the charge voltage with a predetermined slope. In this embodiment, even if a spark discharge that is not likely to shift to the arc discharge occurs, the charged voltage is not lowered by a predetermined set voltage value, so that the dust collection efficiency can be further improved. This is applied in the case where the probability of shifting to arc discharge is low even if the charging voltage is not lowered by a predetermined set voltage value when the discharge occurs.
[0027]
In the above embodiment, the drive signal of the power control element is used as a signal for discriminating as it is, but a signal having a phase opposite to that of the drive signal is formed as a spark discrimination signal, and the period during which the spark discrimination signal is generated In other words, during the period from the zero cross point of the power supply AC voltage until the next drive signal is generated, the probability of transition to arc discharge is sufficiently small even if spark discharge occurs, and the on-drive of the power control element is left as it is. You may continue.
[0028]
【The invention's effect】
As described above, in the present invention, only the spark discharge that may shift to the arc discharge is interrupted as in the conventional case, and the charging is continued for the spark discharge that does not shift to the arc discharge. Since a decrease in charge voltage can be prevented even during frequent discharges, a decrease in dust collection efficiency can be suppressed. In addition, the implementation means can be easily realized by a combination of means already provided in the power supply apparatus, so that the cost is not increased.
[Brief description of the drawings]
FIG. 1 shows an embodiment of a spark control device for an electrostatic precipitator according to the present invention.
FIG. 2 shows signal waveforms related to spark control of the electrostatic precipitator according to the present invention.
FIG. 3 shows an embodiment of a phase control circuit used in the electrostatic precipitator according to the present invention.
FIG. 4 shows signal waveforms related to spark control of the electrostatic precipitator according to the present invention.
FIG. 5 shows another embodiment of the spark control device of the electrostatic precipitator according to the present invention.
FIG. 6 shows an example of a conventional spark detection device for an electrostatic precipitator.
[Explanation of symbols]
1 .... AC power supply 2 .... Charge control panel 3 .... Rectifier transformer circuit 4 .... Dust collector 5 .... Synchronous detection transformer 6 .... Power control element 7 ... Zero cross detection circuit 8 .... Phase control circuit 9 ..Charge control circuit 10..Spark detection circuit 11..Spark control circuit 12..Charge interruption / soft start circuit

Claims (3)

The current lag phase and supplied to the AC voltage from the AC power source applies a high voltage between the arranged the discharge electrode faces the dust collection electrode and the dust collecting electrode, passes between them In the electric dust collection method to collect dust contained in the airflow
When the occurrence of a spark discharge is detected between the dust collecting electrode and the discharge electrode, a detection signal indicating the occurrence of the spark discharge is activated when the power control element is turned on from the zero crossing point of the AC voltage of the AC power supply. If it occurs during the period immediately before, the normal control is performed without interrupting the drive of the power control element, and the charging is continued.
When the detection signal indicating the occurrence of the spark discharge is generated between the time when the power control element is turned on and the next zero cross time of the AC voltage of the AC power supply, the power control element is turned off for a predetermined period. An electric dust collection method characterized in that the charging voltage is once reduced. In claim 1 ,
When the detection signal indicating the occurrence of spark discharge when the driving signal is at L-level of the power control device occurs, the charge to continue performing once normal control without interrupting the drive of the power control element ,
When the detection signal indicating the occurrence of spark discharge when the driving signal is at H level of the power control element is generated, and wherein reducing the once charged voltage by interrupting a predetermined period the driving of the power control element Electric dust collection method. AC power source, power control element for controlling AC power from AC power source, current limiting reactor, step-up transformer, and high-voltage rectifier that rectifies high-voltage AC voltage from step-up transformer and converts it to DC An electrostatic precipitator that collects dust contained in an airflow passing through a dust collecting portion including a dust collecting electrode and a discharge electrode disposed to face the dust collecting electrode ,
A zero cross detection circuit for detecting a zero cross point of the voltage of the AC power supply;
A phase control circuit for generating a drive signal for controlling conduction of the power control element;
A spark detection circuit to provide a spark discharge detection signal when the spark discharge occurs between the discharge electrode and the collector Chirikyoku,
If the occurrence of spark discharge is detected when the drive signal output from the phase control circuit is at L level, normal control is performed without temporarily stopping the power control element, and charging is continued. A charge control circuit for temporarily lowering a charge voltage by interrupting the drive of the power control element for a predetermined period when occurrence of the spark discharge is detected when the drive signal is at an H level ;
An electric dust collector characterized by comprising: "

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