JPH0470060B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an electrostatic precipitator.

In conventionally known electrostatic precipitators, for example, the first
As shown in the figure circuit diagram, thyristor, reactor,
A control circuit that includes a high-voltage transformer, a rectifier, and a control circuit that manually or automatically transmits a pulse with a phase angle α corresponding to an analog signal of 0 to 100%, or a control circuit that keeps the spark frequency constant as in spark frequency control. A high DC voltage is obtained from a commercial frequency power supply via a reactor, high voltage transformer, and rectifier by controlling a thyristor using a control circuit that emits pulses with a phase angle α, and this is applied to the dust collecting electrode. ing.

However, in principle, the soot and dust that can be collected by such an electrostatic precipitator has a specific resistance ρd of approximately 10 ⁴ ~
limited to the range of 10 ¹¹ Ωcm, so ρd is 10 ¹¹ to 10 ¹³ Ω
The drawback is that the dust collection performance is extremely poor for soot and dust in the cm range.

In addition to the above-mentioned method in which a current is passed continuously, a pulse-type electrostatic precipitator has been proposed in which a pulse voltage is applied at a period of several milliseconds. According to this pulse system, the maximum value of the pulse voltage can be increased compared to the direct current voltage of the continuous charging type, so it is said that the dust collection performance can be improved compared to the continuous charging type. However, even with this pulse method, it was impossible to prevent reverse ionization that occurs when ρd is extremely high. This is because the voltage is normalized by the capacitance between the discharge electrode and the collection electrode and the large corona discharge resistance, so a large amount of current must be supplied in order to increase the peak voltage of the pulse. This is because reverse ionization occurs due to the current.

Furthermore, in order to improve these conventional methods, for example, as described in JP-A-52-156473, a variable DC high voltage is applied to form a main electric field between a dust collection electrode and a discharge electrode. Dust collection is performed by connecting a high-voltage power source and superimposing it in series to apply a variable voltage whose magnitude, waveform width, repetition period, etc., are variable and which periodically fluctuates over time between the two electrodes. A pulse charging type electrostatic precipitator has been proposed, but this device requires two sets of power supplies as described above, and the pulse power supply using a thyristor must be used at the level of the DC high voltage of the main electric field. Therefore, insulation of the pulse power source is a big problem, and insulation of the control input transformer, etc. is also required, making the device large and expensive, and the control section is subject to high voltage, which is likely to be dangerous in operation.

The problems to be solved by the present invention are (1) In intermittent charging using thyristor control, the minimum charging time is 1/2 of one cycle of the power supply frequency (10 msec for 50 Hz and 8.3 m for 60 Hz).
sec) However, depending on the high-resistance dust, reverse ionization may occur within this time, and the effect of intermittent charging may not be sufficiently obtained.

(2) With intermittent charging using thyristor control, when the charging pause time becomes longer, the maximum amount of dust scattered by hammering during this period increases, and as a result, the effect of suppressing reverse ionization (improving dust collection performance) due to intermittent charging is reduced. Resulting in.

This is the problem.

This decrease in the dust collection performance of known electrostatic precipitators is caused by the occurrence of reverse ionization within the precipitator, but as a result of many years of research, the present inventor has found that it takes about 1 second for the reverse ionization phenomenon to occur. I discovered that there is a time constant. Utilizing this characteristic, if you apply a current intermittently instead of the conventional continuous current and cut the current just before the reverse ionization phenomenon occurs, the ρd can be reduced to 10 ¹¹ ~
It is conceivable to obtain an electrostatic precipitator whose dust collection performance does not deteriorate even when dealing with soot and dust in the range of 10 ¹³ Ωcm.

By the way, as mentioned above, if the period during which the charging current flows is limited to a period of about 1 second corresponding to the time constant, it is possible to prevent the reverse ionization phenomenon before it occurs, but until the voltage drops to a certain level. A certain amount of time is required for this, and if the stopping time is short, the previous and subsequent pulses will overlap, resulting in continuous charging. Approximately 0.01 seconds is required for the level to drop to this specific level.

Therefore, the intermittent charging period is at least 0.01 above.
More than a second is required. On the other hand, as mentioned above, the period during which the charging current flows needs to be 1 second or less, but if the stopping period is too large, the dust collection efficiency will decrease, so the upper limit of the charging period is about 1 second. is appropriate.

The specific number of reverse ionization mentioned above is given by the average corona current, Eds is the dielectric breakdown field strength of the dust layer, and ρd is the apparent resistivity of the dust layer. As long as this is maintained, this is the time during which no reverse ionization phenomenon occurs, regardless of whether the current is increased or decreased.

The present invention was proposed in view of the above circumstances, and is capable of collecting dust even in the range of ρd from 10 ¹¹ to ^{10 13} Ωcm without deteriorating performance, and the device is simple and inexpensive. The purpose of the electrostatic precipitator according to the present invention is to provide an electrostatic precipitator that can be operated safely, and the electrostatic precipitator according to the present invention includes: a thyristor whose input side is connected to a commercial power source;
A high voltage transformer whose primary side is connected to the output side of the thyristor, a high voltage rectifier whose input side is connected to the secondary side of the high voltage transformer and whose output side is connected to the discharge electrode of the electrostatic precipitator, and a charging time A thyristor control circuit that intermittently controls charging of the discharge electrode of the electrostatic precipitator with a DC high voltage; and a thyristor control circuit that adjusts the charging time and charging pause time, and at least the charging voltage is one of the base voltages. The present invention is characterized by comprising: manual and microcomputer means for adjusting the method; and a switching device for switching between the two means.

An embodiment of the present invention will be explained with reference to the drawings.
Fig. 2 is a block diagram showing the thyristor control circuit, Fig. 3 is an enlarged circuit diagram of the intermittent control circuit of Fig. 2, Fig. 4 is a characteristic diagram of the inverter shown in Fig. 3, and Fig. 5 is a block diagram showing the thyristor control circuit.
Figures A, B, and C are voltage waveform diagrams at points G, B, and C in Figure 3, respectively. Figure 6 is a voltage-current characteristic diagram showing the relationship between normal ionization and reverse ionization of an electrostatic precipitator.
Figure A is a diagram showing changes over time in the phase angle, current, and voltage in an electrostatic precipitator according to an embodiment of the present invention, and Figure 7B is a diagram showing the phase angle and current in the known electrostatic precipitator shown in Figure 1. , is a diagram showing changes in voltage with respect to each time.

First, in FIGS. 2 and 3, reference numeral 1 denotes an intermittent control circuit for controlling the phase of the thyristor 2, which is connected to either an automatic circuit 4 or a manual circuit 5 by a changeover switch 3. C is a capacitor, D ₁ , D ₂ , D ₃ , D ₄ are each a diode, R ₁ , R ₂ , R ₃ , R ₄ are each a variable resistor,
R ₅ , R ₆ and R ₇ are resistors, TR ₁ is a transistor, and IV ₁ and IV ₂ are CMOSIC inverters each having input/output characteristics as shown in FIG.

In such a _circuit , the voltage V _A at point G is as _shown in FIG _. The charging voltage, that is, the pulse height A ₁ and _the base voltage, that is, the pulse base height A ₂ can be freely set by variable resistors R ₃ and R ₄ , respectively.

When automatic, for example, adjust the variable resistor R ₃ or pulse height A ₁ with the output of the spark frequency control, or
Alternatively, for example, the variable resistors R ₁ to R ₄ can be optimally controlled by a microcomputer. The algorithm at that time may be, for example, maximizing V _P ×V _AV , which will be described later.

The voltage at point E is almost the same as the voltage at point A, transistor _TR1 is inserted as an emitter follower for current amplification and impedance conversion, and the output at point G is the output of the OR gate at points E and F. The larger one is selected and output.

According to the present invention, by controlling the thyristor with such a control circuit, a variable DC high voltage is intermittently applied to the dust collection electrode in a period range of approximately 0.01 to 1 second using a commercial frequency power source. This is used to collect soot and dust.

To briefly explain the basic properties of electrostatic precipitator action, the voltage-current characteristics when soot and dust undergo normal ionization are as shown in the solid line shown in Figure 6, but when reverse ionization is performed, the characteristics change as shown in the broken line. become that way.
The higher the voltage and current, the higher the dust collection efficiency, but when reverse ionization occurs, the current changes along the broken line, so even if the current flows, the voltage does not increase, and this state This will result in unnecessary current flowing.

The level of dust collection efficiency is proportional to the product of the peak voltage V _P and the temporal average voltage V _AV , V _P ×V _AV , and V _P ×
The larger the _VAV , the greater the dust collection effect.

Incidentally, the conventional pulse charging method mentioned above was not originally intended to suppress and prevent reverse ionization, but by applying steep pulses for a short time, the spark flash voltage was increased compared to the conventional DC continuous charging method. V _P
The purpose is only to increase V _P ×V _AV ∝η and therefore to increase V P ×V AV ∝η.

When the current increases and a reverse ionization phenomenon occurs, the voltage-current characteristic changes from a solid line to a broken line, but there is a time delay of about 1 second.

By the way, in Fig. 6, when comparing the value of V _P ×V _AV , it is V ² _b in the conventional dust collector, whereas,
In the present invention, V ² _a ×V _AV , and depending on the selection of T ₁ , T ₂ , A ₁ , and A ₂ , for example, V ^{2 a} _× V _AV for V 2 _b = 100.
Since V ² _b <V _a2 ×V _AV can be satisfied, such as ≒130, the dust collection effect is large.

At this time, in the present invention, the current flows in pulses like a ₁ a ₂ along the solid line in a short time, and the average current value is small, so the current does not flow along the broken line, but compared to the conventional dust collector. So, when the current increases, reverse ionization occurs and the current increases along the broken line, and when it reaches point b, the voltage cannot be increased any further, that is, it does not reach point _a2 on the solid line.

According to actual measurement results, it has been reported that the dust collection effect of the present invention is increased by 10 to 20% compared to the conventional one.

Figures 7A and B compare the characteristics of the device of the present invention and a conventional dust collector, where A is the phase angle of the device of the present invention;
Current and voltage, B indicates that of a conventional dust collector,
The voltage distribution in FIG. 7A occurs along the solid line in FIG.

Comparing the energy between the device of the present invention and a conventional dust collector, energy = VI, so in the conventional dust collector, for example, 30 kV (average voltage) x 1600 mA (average current) = 48 kW, whereas in the present invention, the energy is 21 kV x 400 mA.
A = 8.4kW, and in this invention, the conventional dust collector
It can be seen that the dust collection effect can be achieved with 17.5% of the energy.

The electrostatic precipitator of the present invention includes manual and microcomputer means for adjusting the charging time _T1 and the charging pause time _T2 , as well as adjusting at least one of the charging voltage _A1 or the base voltage _A2 . Since it is equipped with a switching device that switches to either of the two methods, for example, by switching to manual mode, you can make fine adjustments during trial runs or make fine adjustments that appropriately respond to changes in the properties of the processing gas during operation. I can do it.

Further, during inspection, the microcomputer means can be inspected by switching to manual means, and the manual means can be inspected by switching to the microcomputer means, so that work can be carried out safely without stopping operation.

In addition, when an abnormal operation occurs, the charging time T ₁ and the charging pause time
In addition to adjusting T ₂ , at least one of the adjustments for charge voltage A ₁ and base voltage A ₂ is sequentially switched to manual mode to check for abnormalities, thereby allowing the actual machine to be operated without removing the control device. While driving, it is possible to easily discover which microcomputer circuit is at fault. Furthermore, by adjusting the level of the charging voltage A ₁ (for example, if you want to suppress the increase in the electric field strength of the dust layer from the current level and suppress back ionization, lower the charging voltage A ₁ ) to increase the dust collection efficiency. be able to.

Also, by adjusting the level of the base voltage A ₂ (for example, if you want to increase the dust holding power during the charging pause time compared to the current level, increase the base voltage A ₂ ) to reduce the amount of re-scattering due to hammering. I can do it.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a circuit of a known electrostatic precipitator, Fig. 2 is a block diagram of a thyristor control circuit showing an embodiment of the present invention, and Fig. 3 is an enlarged circuit of the intermittent control circuit shown in Fig. 2. Figure 4 is a characteristic diagram of the inverter in Figure 3, Figure 5 A, B, and C are voltage waveform diagrams at points G, B, and C in Figure 3, respectively.
The figure is a voltage-current characteristic diagram showing the relationship between normal ionization and reverse ionization of an electrostatic precipitator, and Figure 7A shows changes over time in phase angle, current, and voltage in an electrostatic precipitator according to an embodiment of the present invention. Figure 7B shows the phase angle, current, and current in the known electrostatic precipitator shown in Figure 1.
FIG. 3 is a diagram showing changes in voltage over time. 1... Intermittent control circuit, 2... Thyristor, 3...
...Selector switch, 4...Automatic circuit, 5...Manual.

Claims (1)

[Claims] 1. A thyristor whose input side is connected to a commercial power source, a high voltage transformer whose primary side is connected to the output side of the thyristor, whose input side is connected to the secondary side of the high voltage transformer, and whose output side is connected to the output side of the high voltage transformer. a high-voltage rectifier connected to the discharge electrode of the electrostatic precipitator; a thyristor control circuit that intermittently controls charging time to control charging of the discharge electrode of the electrostatic precipitator with DC high voltage; An electric collector characterized in that it comprises manual and microcomputer means for adjusting the rest time and at least one of the charging voltage or the base voltage, and a switching device for switching to either of the two means. dust equipment.