JPH0251677B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a charge control method for an electrostatic precipitator. More specifically, the present invention relates to a charge control method for an electrostatic precipitator. The present invention relates to a charge control method for an electrostatic precipitator in which a voltage with a superimposed voltage applied thereto is applied.

BACKGROUND ART It is believed that the dust collection performance of an electrostatic precipitator improves as a higher voltage is applied. Therefore,
Efforts are being made to apply as high a voltage as possible. However, if the applied voltage is too high, sparks will occur and a large current will flow, causing the voltage to drop.

In addition, especially when collecting dust with high electrical resistivity, a so-called reverse ionization phenomenon occurs. This reverse ionization phenomenon is a phenomenon in which charges are accumulated in the dust layer collected by the dust collecting electrode, causing dielectric breakdown in the dust layer, and producing a corona with a polarity opposite to that of the discharge electrode. When such a reverse ionization phenomenon occurs, only the applied current increases, the applied voltage decreases, and the dust collection efficiency decreases.

In order to suppress such reverse ionization, the DC voltage (referred to as base voltage) applied to the electrostatic precipitator is
A charging method for an electrostatic precipitator that superimposes pulse voltage (pulse charging method) has been proposed.

This pulse charging generally occurs in a dust collector 3 having a dust collection electrode 1 and a discharge electrode 2, as shown in FIG.
This is carried out by connecting a pulse power source 6 via a coupling capacitor 5 to a discharge electrode 2 connected to a DC power source (referred to as a base power source) 4. The base power supply 4 includes a step-up transformer 7 and a thyristor 8 that supplies commercial power AC to the primary side of the step-up transformer.
and rectifier means such as a rectifier diode bridge 9 connected to the secondary side of the step-up transformer to supply a negative high voltage to the discharge electrode 3.

With the above power supply, the base power supply 4 is usually
The dust collector is always charged, and the voltage from the pulse power source 6 is pulse-charged to the dust collector via the coupling capacitor 5.

In such pulse charging, by controlling the pulse frequency, the corona current can be controlled independently of the precipitator average voltage (substantially the same as the base voltage), which eliminates the reverse ionization phenomenon that has been a problem with conventional precipitators. can be prevented. Therefore, this pulse charging method can significantly improve the performance of the dust collector.

However, what kind of pulse frequency is actually optimal depends on the conditions of the dust to be collected, and various studies have been conducted. There have been some reports on research in Europe and America, and Figure 3 shows the results of research by the inventor of the present invention and others. As shown in FIG. 3, when the dust is a low-resistance fly ash, the dust collection performance increases as the pulse frequency increases, and after a certain value is exceeded, it stabilizes at a substantially constant value. On the other hand, when the dust is high-resistance fly-hot, the dust collection performance increases with an increase in pulse frequency, but decreases after a certain value is exceeded.

Problems to be Solved by the Invention As mentioned above, there has been research on pulse frequency, but the timing of emitting pulses has not been reported, either because it has not received attention or because it is kept secret due to know-how. . Therefore,
In conventional pulse charging, pulses are generated at regular intervals. And the interval is the period of half cycle of power AC (1/120 seconds at 60Hz, 1/100 seconds at 50Hz)
seconds) and not necessarily its half-cycle period or an integer multiple thereof. In other words, the phase of the AC power source at which the pulse is generated is not determined and changes each time the pulse is generated. Therefore, depending on the timing at which the pulse is generated (the phase of the AC power source), various problems arise, as will be described later.

(1) Problems with base power source deterioration and noise generation In the pulse charging power source shown in Figure 2, the absolute value of the secondary winding electromotive force of the transformer 7 of the base power source 4 is
It looks like the dotted line in the graph in Figure A. on the other hand,
The dust collector voltage is a negative voltage because the dust collector functions as a capacitor, but its absolute value is as shown by the solid line in FIG. 4a.

Now, when the primary thyristor 8 of the base power supply 4 fires, the absolute value of the secondary winding electromotive force of the transformer 7 exceeds the absolute value of the dust collector voltage, and a forward voltage is applied to the rectifier bridge, as shown in Figure 4b. The output current begins to flow. When the following equation holds true, a voltage in the opposite direction is applied to the rectifier bridge, so no current flows.

Absolute value of dust collector voltage > Absolute value of transformer secondary winding electromotive force
...(1) Now, when the base power supply output current is flowing, if a pulse is applied to the dust collector as shown in Figure 5a, equation (1) is satisfied, so as shown in Figure 5b The base power supply output current is cut off and becomes zero. At this time, an abnormal voltage is generated in the winding of the base power transformer 7. The base power supply circuit is made with high inductance in order to suppress the current generated when sparks occur in the dust collector, and when the output current is cut off, it prevents this and creates an electromotive force that keeps the current flowing. arise. Furthermore, it may create oscillating voltages inherent in the transformer windings. These degrade transformers and rectifier bridges. It also generates noise in the primary power supply line, causing malfunctions in peripheral control equipment. Therefore, conventional electric precipitator power supplies are designed to have high dielectric strength so that they can withstand such abnormal voltages.

(2) Problem of drop in dust collector voltage When a pulse is applied so as to be superimposed on the base power supply voltage, the dust collector voltage changes as shown in Figure 6.
In FIG. 6, time A is the rising edge of the pulse, time B is the peak, and the period between time A and C is the pulse width. The pulse width varies depending on the pulse charging method, but is often 200 μs or less.

However, with such a pulse application time, the ions move only about 1 to 2 cm. Therefore, by applying the pulse, a cloud of highly concentrated negative ions is formed in a space within 2 cm from the surface of the discharge electrode of the precipitator (time point B, time point C).

FIG. 7 shows the charge distribution and electric flux distribution in such a state. As shown in Figure 7a,
At time A in Figure 6, there are no such clouds, and the precipitator voltage creates an electric field between the discharge electrode and the precipitate electrode, and the electric flux representing this electric field starts from the positive charge on the surface of the precipitate electrode. and terminates at the surface of the discharge electrode.

Then, at time B, as shown in FIG. 7b, the electric flux density increases due to the charge supplied from the pulsed power source. As a result, a part of the negative charge on the discharge electrode is released into space as negative ions, forming a cloud of highly concentrated negative ions within 2 cm from the surface of the dust collector discharge electrode, and the electric flux changes from the positive charge on the surface of the dust collector electrode. Starting from , it is quite possible to terminate at a high concentration of negative ions near the discharge electrode.

At time C, the electric flux density returns to a state similar to that at time A, but a significant cloud of negative ions around the discharge electrode remains. If this is left unattended, the cloud of negative ions will move to the dust collection electrode and will be neutralized and annihilated by the positive charge on the dust collection electrode, so as the ions move, the dust collector voltage will drop.

However, current charging control for electrostatic precipitators does not take this issue into account, so pulse charging and firing of the thyristor on the primary side of the step-up transformer of the base power supply are independent, and the timing C immediately after the pulse From then on, the precipitator voltage drops and is recovered by firing the base power supply primary thyristor. Therefore, since the voltage fluctuates greatly, the precipitator voltage cannot be maintained at the most preferable value, for example, a value near the corona starting voltage, and the dust collection performance cannot be made sufficiently high.

Pulse charging is characterized by the ability to operate at extremely low currents to prevent the occurrence of reverse ionization.
The precipitator voltage during the period between pulses should be near the corona onset voltage. However, if the voltage fluctuates greatly, the voltage may significantly exceed the corona starting voltage, and as a result, a large current flows, making it impossible to prevent the reverse ionization phenomenon. Furthermore, the voltage may be significantly lower than the corona starting voltage, and the dust collection effect is reduced during this period.

SUMMARY OF THE INVENTION Accordingly, the present invention aims to provide a charge control method for an electrostatic precipitator that can eliminate the drawbacks of the conventional pulse charging described above and prevent failure of the base power supply, improve control reliability, and improve dust collection performance. It is.

That is, the present invention aims to provide a charging control method for an electrostatic precipitator in which there is no cutting of the base power output current due to pulse charging and there is no reduction in the voltage of the precipitator due to pulse charging.

Means for Solving the Problems The present inventor conducted various studies for the above-mentioned purpose. First, in order to prevent cutting of the output current of the base power supply, the relationship between the pulse output timing and especially the firing timing of the primary side thyristor of the base power supply is extremely important. Even if a pulse is applied when the output current of the base power supply is not flowing, problems such as cutting of the base power supply output current naturally do not occur.

We also discovered that firing the primary thyristor of the base power supply immediately after pulse charging to increase the base voltage is effective in preventing a drop in precipitator voltage immediately after pulse charging. Such a method has no problem with pulse charging of an electrostatic precipitator.

Therefore, in order to prevent cutting of the base power supply output current and to prevent a drop in the precipitator voltage immediately after pulse charging, it is most preferable to apply a pulse immediately before firing of the primary side thyristor of the base power supply.

The present invention was completed based on this knowledge.

That is, according to the present invention, a voltage in which a DC voltage and a pulse are superimposed is applied to the electrostatic precipitator using a base power source and a pulse power source for applying a DC voltage, and the base power source is comprising a step-up transformer, conduction angle control rectifier means for supplying alternating current to the primary side of the step-up transformer, and rectifier means connected to the secondary side of the step-up transformer;
There is provided a charge control method for an electrostatic precipitator, characterized in that the timing of pulse generation by the pulse power source is immediately before conduction of the conduction angle control rectifier means on the primary side of the base power source.

Effect In the charge control method for an electrostatic precipitator as described above, pulse charging is performed immediately before conduction of the conduction angle control rectifier means on the primary side of the base power supply, so when the output current of the base power supply is not flowing at all times. Therefore, the base power supply output current is not cut due to the application of the pulse.

In addition, immediately after pulse charging, the primary side conduction angle control rectifier means of the base power supply is made conductive and the base power supply voltage is applied, so the drop in precipitator voltage immediately after pulse charging is caused by the base voltage being higher than the base voltage applied. can be effectively prevented.

Embodiments Hereinafter, embodiments of the charge control method for an electrostatic precipitator according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram of a charge control device that implements a charge control method for an electrostatic precipitator according to the present invention. Note that parts that are the same as or correspond to those of the basic pulse charging power source shown in FIG. 2 are given the same reference numerals, and descriptions of these parts will be omitted.

The charge control device shown in FIG. 1 has a base power control device 10, and the base power control device includes:
A commercial power supply alternating current is detected via the voltage transformer 12, and its zero cross is detected. Then, the firing angle is determined based on the detected zero cross, and a firing command is output to the gate pulse shaping circuit 14 after a predetermined time delay α. The gate pulse shaping circuit 14 outputs a gate pulse to the gate of the thyristor 8 in response to the firing command.

The charge control device shown in FIG. 1 further includes a pulse frequency control circuit 16, and the pulse frequency control circuit 16 opens and closes an AND gate 18. The above-mentioned ignition command is also sent to the pulse power source 6 through this AND gate 18 to trigger pulse charging.

Next, the operation will be explained.

The base power control device 10, as described above,
Controls the firing angle α of the primary side thyristor of the base power supply. Control of this firing angle is currently implemented by various methods, and may be performed by any of them. For example, it is possible to perform feedback control so that the base voltage is constant, or to perform feedback control on the spark generation frequency so that the spark generation frequency is maintained below a certain value.

The base power supply control device 10 calculates the value of the firing angle α in this manner, and also picks up the commercial power AC through the voltage transformer 12 and picks up the AC power as shown in FIG.
Detect the zero cross of the AC power supply as shown in the figure below, and use the detected zero cross as a reference (α/180°).
When a time period of x (period of a half cycle of power supply AC) has elapsed, an ignition command is issued as shown in FIG. 8b.

The ignition command is sent to the gate pulse shaping circuit 14, and after receiving the ignition command, the gate pulse shaping circuit 14 receives the high voltage pulse (pulse power supply 6).
After further delaying the application period β, a gate pulse is sent to the base power supply primary side thyristor 8 to ensure that it is ignited (FIG. 8c). Thus,
An electromotive force having an absolute value as shown in FIG. 8d is generated on the secondary winding side of the step-up transformer 7.

The reason for waiting for the high-voltage pulse application period β to elapse in this way is that during this period, the reverse voltage is building up in the rectifier bridge of the base power supply, and the output current no longer flows, so the gate pulse is applied to the primary thyristor. This is because the thyristor cannot be fired even if it is sent. Therefore, even if the pulse is output at the same time as or just before the firing of the primary thyristor of the base power supply, the firing of the primary thyristor is suppressed while the pulse is being applied, so the actual firing of the thyristor is only due to the pulse. This is immediately after the application. Even if β is set to about 1 millisecond with some margin in the high-voltage pulse application period, the effect of the invention hardly changes.

On the other hand, the firing command is further sent to an AND gate 18 which is opened and closed by the pulse frequency control circuit 16.
After checking whether a pulse should be generated or not, it is sent to a pulse power source, which causes the pulse power source to generate an output pulse as shown in FIG. 8e. As a result, a pulse is superimposed on the precipitator voltage as shown in FIG. 8f.

In this way, a pulse will be emitted just before firing of the base power supply primary side thyristor. At this time, the base power supply current has not yet started flowing.
Does not cause abnormal voltage or noise problems (Figure 8g).

Now, the purpose of the pulse frequency control circuit will be explained.
In pulse charging, control of the pulse frequency is important, as discussed above in connection with FIG. Third
As shown in the figure, a pulse frequency of 100 times/second is sufficient for low-resistance fly-fishing, and dust collection performance will not improve if the pulse frequency is more than 100 times/second. However, in cases such as high-resistance fly hot sweetfish, the rate of rotation is 200 times/second or more.
It is better to reduce the pulse frequency to 70/sec. on the other hand,
If the above method is used to generate a pulse every time the thyristor on the primary side of the base power supply is fired, the pulse frequency will be 100 times/second (when the power supply AC is 50Hz) or
120 times/second (when the power supply AC is 60Hz). Therefore, in order to operate at a lower pulse frequency depending on the nature of the collected dust, a portion of the ignition command is not sent to the pulse power source.

For example, as shown in Figure 9, the power supply AC is 60Hz.
If one of the three ignition commands is cut off, the pulse frequency will be 80 times/second. Similarly, if two out of three firing commands are cut, the pulse frequency will be 40 times/
seconds. If a pulse is issued only once out of 15 ignition commands and the rest are cut out, the pulse frequency will be 8 times/second. In this way, the pulse frequency is
Below 120 times/second (at 60 Hz), it can be substantially finely and freely adjusted (see FIG. 9), and the circuit that performs such an adjustment function is the pulse frequency control circuit 16.

In the charge control method for an electrostatic precipitator as described above, since the base power source is of the full-wave rectification type, the base voltage waveform shows a peak once every half cycle of the power source alternating current. At 60Hz, 120 peaks appear per second. When the base power supply primary side thyristor is fired, the base voltage rises, so the point immediately before firing becomes a valley in the base voltage waveform. In the present invention, the pulse is generated at the valley of the base voltage. When generated in all valleys, the pulse frequency is 120 times/second, but various pulse frequencies lower than this can be obtained as shown in FIG.

Furthermore, FIG. 9 shows an example in which several consecutive peaks are used as a fundamental period and at which peaks and troughs in the fundamental period a pulse is generated. The length of this basic period is several peaks (one peak is the length of a half cycle of AC power supply), but it is preferable that the number of peaks is an odd number. This is because the number of times that pulses are emitted for each of the three phases of the AC power source becomes equal during a period twice the basic cycle, and the problem of eccentric excitation of the transformer core due to unbalanced phase loads can be prevented.

Effects of the Invention As is clear from the above description, according to the present invention, it is possible to prevent abnormal voltage from occurring in the base power supply, and it is possible to design the device with less withstand voltage margin. In addition, it is possible to prevent the generation of noise and prevent adverse effects on surrounding digital control equipment. Furthermore, since fluctuations in the DC base voltage of the dust collector are reduced, an appropriate DC base voltage is always maintained.
Dust collection performance is improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a charge control device implementing the charge control method for an electrostatic precipitator according to the present invention, and FIG.
The figure is a block diagram showing the basic configuration of a pulse charging power source that performs pulse charging control of an electrostatic precipitator. Figure 4 is a graph showing the relationship between the electrostatic precipitator voltage and the base power transformer output voltage and base power output current of the electrostatic precipitator, and Figure 5 shows the case where a pulse is superimposed on the base voltage from the base power supply of the electrostatic precipitator. Graph showing the electrostatic precipitator voltage and base power supply output current, Figure 6 is a graph showing the pulse waveform in pulse charging, and Figure 7 is the distribution of charge and electric flux of the discharge electrode and collecting electrode of the dust collector due to pulse charging. FIG. 8 is a graph illustrating the method of base voltage charging and pulse charging by the charge control device of FIG. 1, and FIG. 9 is a graph showing an example of pulse frequency control in pulse charging. Main reference numbers, 1... Dust collection electrode, 2... Discharge electrode,
3... Dust collector, 4... Base power supply, 5... Coupling capacitor, 6... Pulse power supply, 7... Step-up transformer, 8... Thyristor, 9... Rectifier diode bridge, 10... Base power supply control device, 12... Instrument transformer, 14...
Gate pulse shaping circuit, 16...Pulse frequency control circuit, 18...AND gate.

Claims (1)

[Scope of Claims] 1. A base power supply for applying a DC voltage and a pulse power supply are used to apply a voltage in which DC and pulses are superimposed to the electrostatic precipitator, and the base power supply is The electrostatic precipitator comprises a step-up transformer, a conduction angle control rectifier means for supplying alternating current to the primary side of the step-up transformer, and a rectifier connected to the secondary side of the step-up transformer. A charge control method for an electrostatic precipitator, characterized in that the timing of pulse generation by the pulse power source is set to 0 to 1 millisecond before conduction of the conduction angle control rectifier means on the primary side of the base power source. 2. The scope of claims characterized in that the pulse frequency is adjusted by not always generating pulses before the conduction angle control rectifier means on the primary side of the base power supply conducts, but by pausing the pulses at a constant rate. The charge control method for an electrostatic precipitator according to item 1. 3. The electrostatic precipitator according to claim 1 or 2, wherein the conduction angle control rectifier means is a thyristor, and the base power source generates a pulse immediately before the thyristor is fired. charge control method.