JPH0160302B2 - - Google Patents

Description

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

Conventionally known electrostatic precipitators include, for example, a thyristor, a reactor, a high voltage transformer, a rectifier, and a control circuit that manually or automatically oscillates a pulse having a phase angle α corresponding to an analog signal of 0 to 100%. , by controlling a thyristor using a control circuit that oscillates a pulse with a phase angle α that keeps the spark frequency constant, as in spark frequency control, DC high voltage is generated from a commercial frequency power supply via a reactor, high voltage transformer, and rectifier. is obtained and applied to the dust collecting electrode.

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

This reduction in the dust collection performance of known electrostatic precipitators is due to 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. Since we found out that there is a time constant, by using this property,
Conventionally, current was passed continuously, but by passing current intermittently and cutting off the current before the reverse ionization phenomenon occurs, it can be used against soot and dust with a resistivity in the range of 10 ¹¹ to ^{10 13} Ωcm. Considering an electrostatic precipitator that does not reduce dust collection performance, we proposed a dust collector equipped with a control circuit that intermittently controls a thyristor in Japanese Patent Application No. 54-146238 (Japanese Unexamined Patent Publication No. 56-70859). We have proposed an electrostatic precipitator in which the intermittent charging period and/or charging time width of the electrode can be adjusted to about 0.01 to 1 second.
In this proposal, for example, as shown in the circuit diagram of FIG. 1, the thyristor 3 is turned on intermittently by supplying the signal 2 shown in FIG. 2A from the control circuit 1 to the control terminal 4 of the thyristor 3. arc, AC power supply 8
The transformer 5 and the rectifier 6 are configured to intermittently charge the dust collection electrode 7, and the current 9 to the dust collection electrode 7 is
size A, charging time width T ₁ , charging stop time width T ₂
For example, T ₁ and or T are respectively abbreviated as shown in FIG. 2A and B, respectively.
It is controlled to be 0.01 to 1 second.

However, subsequent research has revealed that the dust collection effect may be increased by reducing the charging time width T ₁ to approximately 0.01 seconds or less. In other words, the time constant t of back ionization of dust is expressed as t=8.85×10 ^-14 ×ε×ρ [sec], where ε: relative permittivity of dust, ρ: resistivity of dust [Ω-cm], For example, when ρ = 10 ¹¹ Ωcm, ε = 2 and t = 0.017 seconds, which is a half wave of the commercial frequency of 50Hz.
Since it is close to 0.01 seconds, when ρ is relatively small in the range of 10 ¹¹ to 10 ¹³ Ωcm, in which the effect of intermittent charging can be expected, that is, when it is close to 10 ¹¹ Ωcm, the charging time width T ₁ is It is desirable to make it as short as possible by thyristor control, that is, to make it one peak (half wave).

The present invention was proposed in view of these new findings, and provides an electrostatic precipitator that can collect dust with a specific resistance in the range of 10 ¹¹ to ^{10 13} Ωcm without deteriorating its performance. For the purpose of
The power is set so that the charging time width T ₁ of intermittent charging applied intermittently with a cycle of ~1 second is 0.001T ₁ <0.01 seconds, and the charging stop time width T ₂ is larger than the charging time width T ₁ . It is characterized by comprising a control circuit that controls the control elements.

An embodiment of the present invention will be explained with reference to the drawings.
Figure 3 is a block diagram of the control circuit in one embodiment of the present invention, Figure 4 A, B, C, and D are output waveform diagrams of each part in Figure 3, and Figure 5 is the reverse of normal ionization in an electrostatic precipitator. FIG. 3 is a voltage-current characteristic diagram showing the relationship with ionization.

In the above figure, 11 is a reference pulse generation circuit that generates pulses with a period of 10 milliseconds at 1/2 of the commercial frequency period, that is, 50Hz (see Figure 4A), and 12 counts the pulses of the reference pulse generation circuit 11. As shown in FIG. 4B, a preset counter outputs one pulse every time a preset N number of pulses are input, and 13 is a counter that outputs 1/2 of the power cycle after the pulse is input from the preset counter 12. This is a thyristor control circuit that makes the thyristor 3 conductive only during the period of (see FIG. 4C).

In such a circuit, one peak (half wave) of current flows through the thyristor 3 as shown in FIG. 4D due to the signal shown in FIG. 4C output from the thyristor control circuit 13, and the period of intermittent charging is T= _T1 + _T2
(see Fig. 2) can be adjusted by setting the count number N of the preset counter 12, and the charging time width can be set to, for example, 1/2 of the power cycle, or 1
A peak (half-wave) power supply can be applied, and the charging stop time width can be made larger than the charging time width, so that, for example, the period T can be an integral multiple of 1/2 of the power supply period. Therefore,
The charging time width t ₀ shown in FIG. 4D falls within the range of 0.001t ₀ <0.01 seconds.

Here, to briefly explain the basic properties of electrostatic precipitation, the voltage-current characteristics when normal ionization of soot dust is performed are as shown in the solid line shown in Figure 5, but when reverse ionization is performed, the characteristics change. It looks like a broken line.
The dust collection effect is large in both voltage and current, but when reverse ionization occurs, the current changes along the broken line, so even if current is passed, the voltage does not increase, and in this state it is wasted. A current will flow.

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.

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, when comparing the values of V _P ×V _AV in FIG. 5, in the conventional dust collector in which a reverse ionization phenomenon other than intermittent charging occurs, the value is V ² _b , whereas in the present invention, it is V _a2 ×V _AV . For example, V _a2 × for V ² _b = 100
Since V ² _b <V _a2 ×V _AV can be satisfied, such as V _AV ≒180, the dust collection effect is great.

At this time, in the present invention, the current flows in a pulse-like manner as 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. In the dust collector, when a current is applied, 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 a ₂ of the solid line.

According to actual measurement results, it has been recognized that the dust collection effect according to the present invention is increased by 10 to 20% compared to conventional methods other than intermittent charging.

Furthermore, when comparing the energy of the device of the present invention and a conventional dust collector other than intermittent charging, the energy = VI, so in the conventional dust collector, for example, 30 kV (average voltage) In the present invention, the power is 21 kV x 400 mA = 8.4 kW, which shows that the present invention can achieve the dust collection effect with 17.5% of the energy of the conventional dust collector. Finally, the intermittent charging type dust collector according to the present invention is different from conventionally known pulse charging type dust collectors.

By the way, the difference between the two is as follows.

Device of the present invention (intermittent charging) Pulse charging type electrostatic precipitator Charging cycle: 0.01 to 1.0s 0.001 to 0.01s Charging time width T ₁ : 0.001T ₁ <0.01s 100μs to 1ms Charging device: Current commercial product + electronic control device Comparison of current commercial products + pulse generator price: 100+2≒120 100+200≒300 Energy: Energy saving No In short, according to the present invention, DC high voltage is generated intermittently by controlling power control elements such as thyristors. In an electrostatic precipitator that applies this between the dust collecting electrodes, the charging time width of the intermittent charge applied intermittently between the dust collecting electrodes is approximately 0.001 to 0.01 seconds, and the charging stop time width is set to approximately 0.001 to 0.01 seconds. An energy-saving electric collector that effectively collects soot and dust having a specific resistance in the range of 10 ⁴ to 10 ¹³ by including a control circuit that controls the power control element so that the charging time width is larger than the charging time width. The present invention is industrially very useful because it provides a dust device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a circuit of a known electrostatic precipitator, FIGS. 2A and B are output waveform diagrams of each part of FIG. 1, and FIG. 3 is a block diagram of a control circuit showing an embodiment of the present invention. 4 is an output waveform diagram of each part in FIG. 3, and FIG. 5 is a voltage-current characteristic diagram showing the relationship between normal ionization and reverse ionization of the electrostatic precipitator. DESCRIPTION OF SYMBOLS 1... Control circuit, 2... Signal, 3... Thyristor, 4... Control terminal, 5... Transformer, 6... Rectifier, 7... Dust collection electrode, 8... Commercial AC power supply, 9...
...Current, 11...Basic pulse generation circuit, 12...
Preset counter, 13...thyristor control circuit.

Claims (1)

[Claims] 1. In an electrostatic precipitator that controls a power control element such as a thyristor to intermittently generate a DC high voltage and applies it between the dust collection electrodes, the power control element such as a thyristor is Control to control a power control element so that the charging time width T ₁ of intermittent charging applied intermittently is 0.001T ₁ <0.01 seconds, and the charging stop time width T ₂ is larger than the charging time width T ₁ An electrostatic precipitator characterized by comprising a circuit.