JPH06343898A - Circuit for electrostatic precipitator - Google Patents

Abstract

PURPOSE:To generate pulse wave form suitable for an electrostatic precipitator with regard to a pulse charge type electrostatic precipitator by using a rotary spark gap. CONSTITUTION:A circuit for an electrostatic precipitator is connected between a DC power source and a dust collecting electrode, and has a rotary spark gap RSG including a rotary electrode and a static electrode, nozzles 4, 8 for blowing out gas around the static electrode, the 1st diode D1 connected to the rotary spark gap in series, the 2nd diode D2 which is connected in parallel to the series connection of the rotary spark gap and the 1st diode and is in the opposite direction of the 1st diode, and an inductance L1 connected to the parallel connection in series.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic precipitator, and more particularly to a pulse charging type electrostatic precipitator. The pulse charging method of the electric dust collector has a great effect on downsizing of the dust collector.
However, pulse charging devices are generally expensive. In particular, when the dust collector body is of a medium size or smaller, the cost of the dust collector body is not so high, and the advantage of downsizing the dust collector body is often offset by the disadvantage of the cost increase of the charging device. Therefore, it is desired to reduce the cost of the pulse charging device.

[0002]

2. Description of the Related Art As a pulse power source for an electrostatic precipitator, one using a semiconductor element such as a thyristor as a switch element and one using a rotary spark gap are known.

When a thyristor is combined with an LC oscillating circuit, it is possible to generate a single pulse waveform suitable for electrostatic dust collection. However, this pulsed power supply is expensive.
A pulse power supply using a rotating spark gap is inexpensive, but a pulse waveform suitable for electrostatic precipitator cannot be obtained.

FIG. 8 shows a pulsed power supply using a rotary spark gap according to the prior art. FIG. 8A shows a circuit configuration and FIG. 8B shows its electric characteristics. Figure 8
In (A), a DC power supply DC is formed by a diode bridge and a transformer supplied with an AC current from an AC power supply. The anode of the DC power supply DC is grounded, and the cathode is rotated through the impedance Z to the rotating spark gap RSG.
It is connected to the.

The interconnection point between the impedance Z and the rotary spark gap RSG is connected to one electrode of the storage capacitor C3. The other electrode of the storage capacitor C3 is grounded.

The rotating spark gap RSG forms a spark gap between the stationary electrode and the rotating electrode, and the rotating electrode is rotationally driven by the motor M. The other terminal of the rotary spark gap RSG is connected to one electrode of the dust collecting electrode EP via the inductance L1. The other electrode of the dust collecting electrode EP is grounded.

The negative charges stored in the storage capacitor C3 are applied to the dust collecting electrode EP via the inductance L1 when the rotary spark gap RSG is turned on.
The dust collecting electrode EP forms a capacitance and constitutes an LC resonance circuit together with the inductance L1.

FIG. 8B shows the characteristics of the rotary spark gap type pulse power supply shown in FIG. 8A. In the figure, the horizontal axis represents time t, and the vertical axis represents the negative voltage of the dust collecting electrode EP. When the rotating spark gap RSG conducts, several cycles of oscillation occur at the frequency defined by the LC resonant circuit. In the characteristics shown, the vibration period is several hundred μ
s.

In the circuit of FIG. 8A, when the inductance L1 is not inserted, the waveform of the EP voltage is as shown in FIG.
As shown in (C), the fall (decay) time is several ms
It becomes a triangular waveform of a degree. The falling speed depends on the RC time constant determined by the product of the equivalent resistance of the corona discharge of the dust collector and the electrostatic capacitance of the electrodes of the dust collector.

As described above, the rotary spark gap pulse power supply having the circuit configuration shown in FIG. 8 (A) cannot form a single-shot pulse waveform and has several cycles of oscillation until LC oscillation is almost completely attenuated. Only multiple pulse waveforms can be formed. If the inductance L1 is omitted, a pulse waveform is not generated, but a triangular waveform voltage is generated.

The voltage waveform desired for the dust collecting electrode of the electrostatic precipitator is a high negative voltage having a single-shot pulse shape and a constant negative voltage in other periods, and the voltage waveforms shown in FIGS. However, it cannot be said that it is suitable as a pulse waveform for an electrostatic precipitator.

[0012]

When a rotary spark gap and an LC resonance circuit are used, a pulse voltage can be generated, but several continuous pulses are generated instead of a single pulse. Such a pulse waveform is not suitable as a pulse voltage for an electrostatic precipitator.

An object of the present invention is to provide a circuit for an electrostatic precipitator which uses a rotary spark gap and can generate a pulse waveform suitable for the electrostatic precipitator.

[0014]

A circuit for an electrostatic precipitator of the present invention is a circuit for an electrostatic precipitator which is connected between a DC power source and a dust collecting electrode, and which has a rotating spark gap including a rotating electrode and a stationary electrode. A nozzle for blowing gas around the stationary electrode; a first diode connected in series to the rotating spark gap; and a first diode connected in series to the rotating spark gap and the first diode;
It has a second diode opposite to the diode and an inductance connected in series with the parallel connection.

[0015]

In the parallel circuit, since the first diode and the second diode are connected in anti-parallel, the oscillating current flows through the first diode for half its cycle and the second diode for the other half cycle.

By connecting the rotating spark gap in parallel with the second diode and in series with the first diode,
It is possible to prevent current from flowing in the rotating spark gap during a half cycle in which the current flows through the second diode.

Further, by blowing gas around the stationary electrode of the rotary spark gap, the arc plasma in the gap of the rotary spark gap can be blown away. If there is no arc plasma in the gap, even if voltage is applied to the gap in the next cycle,
It becomes easy to prevent re-ignition.

[0018]

1 is a circuit diagram of an electrostatic precipitator according to an embodiment of the present invention. The dust collecting electrode EP of the electrostatic precipitator is formed of counter electrodes, through which a gas such as air to be dust-free passes. One of the dust collecting electrodes is grounded, and the other is connected to the power feeding line 2.

The power supply line 2 is connected to the cathode of the DC power supply DC2 that supplies the base voltage and is connected to the anode of the DC power supply DC1 that supplies the main voltage via the coupling capacitor C1 and the inductance L1.

DC power supplies DC1 and DC2 are AC
It includes a transformer connected to the power supply and a diode bridge connected to the secondary winding of the transformer. In the DC power supply DC1, the cathode is grounded, and in the DC power supply DC2, the anode is grounded.

A series connection of a diode D1 and a rotary spark gap RSG and a series connection of a diode D2 and an additional inductance L2 are connected in parallel between an interconnection point of the DC power supply DC1 and the inductance L1 and ground.

The rotating spark gap RSG has one stationary electrode 3 and a pair of rotating electrodes 9a and 9b. The middle point of the pair of rotating electrodes 9a and 9b is connected to the rotating shaft of the motor M and is driven to rotate. It is also possible to use a rotating spark gap having two stationary electrodes, as shown in FIG.

When the stationary electrode 3 and the rotating electrode 9 come closest to each other, discharge occurs in the gap between them and the switch is turned on. A nozzle 1 is provided to blow a gas such as air near the gap.

Regarding the inductance L1 and the ground, the diodes D1 and D2 are connected in antiparallel. When the rotating spark gap RSG is turned on, LC
The half-cycle of the current flowing through the resonance circuit flows through the side including the diode D1, and the other half-cycle flows through the side including the diode D2.

FIG. 2 is a diagram for explaining the function of the anti-parallel diode. FIG. 2A shows a circuit configuration similar to that of FIG. However, in FIG. 2A, the additional inductance L2 is omitted. Further, the dust collecting electrode is equivalently indicated by the capacitance C2. The resistances of the line are shown by R1 and R2.

The current flowing through the diode D1 is i1
, And the current flowing through the diode D2 is indicated by i2. DC power supply DC1 of positive polarity and DC power supply DC2 of negative polarity
Causes the coupling capacitor C1 to be charged. When the rotating spark gap RSG is turned on, the coupling capacitor C
The positive charge stored in 1 flows as a current i1 to the ground through the diode D1.

Since the LC resonance circuit is formed, the current flowing through the inductance L1 oscillates. In the half cycle of the oscillation, the current i1 flows through the diode D1,
In the remaining half cycle, the current i2 passes through the diode D2.
Flows.

FIG. 2B shows the rotary spark gap RS.
The waveforms of the gap current flowing through the G gap and the voltage of the capacitor C2, which is the dust collecting electrode, are shown. As is clear from the figure, the gap current i1 flows every half cycle of vibration. On the other hand, the voltage v of the dust collecting electrode (EP) shows vibration during the entire period shown. Note that EP
The voltage v is shown as negative.

Thus, the anti-parallel diodes D1 and D2 are
By using, it becomes possible to suppress the gap current flowing in the rotary spark gap RSG by half the period.

In the first half cycle, the gap current i1
Flows, and the gap current does not flow in the next half cycle, but the gap current flows again in the next half cycle because the arc plasma generated in the gap portion of the rotary spark gap RSG remains, It is considered that the current flows again when the voltage is applied in the first half cycle of the cycle. That is, although the use of the anti-parallel diode is effective in suppressing the current during the half cycle, it is not sufficient to prevent the occurrence of continuous pulses.

In order to prevent the generation of continuous pulses, it is considered effective to remove the arc plasma existing in the gap portion of the rotary spark gap. As a method of removing the arc plasma, it is considered that a gas such as air is blown and the arc plasma is blown off physically.

FIG. 3 shows an example of the structure of a nozzle for blowing off the arc plasma in the gap part of the rotary spark gap. In FIG. 3A, the nozzle jacket 4 is formed so as to surround the stationary electrode 3 and
A nozzle gap 5 is formed between the stationary electrode 3 and the stationary electrode 3. The nozzle clearance 5 is formed in an annular shape as shown on the right side of FIG.

The nozzle jacket 4 forms a semi-closed space around the stationary electrode 3 and has a gas inlet at the bottom thereof. An insulating hose 7 is connected to this gas intake, and air 6 is supplied. The air 6 is taken from the insulating hose 7 into the air inlet at the bottom of the nozzle jacket 4, and the stationary electrode 3
It blows out from the surrounding nozzle clearance 5. The stationary electrode 3 has, for example, a shape in which the tip of a metal round bar having a diameter of about 2 to 6 mm is rounded.

FIG. 3B shows another shape of the nozzle.
A nozzle 8 is arranged in the vicinity of the stationary electrode 3 at a position where it does not interfere with the rotating electrode 9 and blows air to a gap portion around the stationary electrode 3.

In this embodiment, the stationary electrode 3 is connected to the terminal 11, and the bearing 10 of the rotating electrode 9 is connected to the terminal 12. Air is blown from a nozzle 8 separate from the electrode into a gap portion formed when the rotating electrode 9 comes closest to the stationary electrode 3.

According to the experiments conducted by the inventors, FIG.
The nozzle shape of FIG. 3 (A) was more effective in blowing off the arc plasma than the nozzle shape of (B). Figure 4
[Fig. 4] is a conceptual diagram for explaining a function of air blowing by a nozzle. FIG. 4A schematically shows the shape of the arc generated between the stationary electrode 3 and the rotating electrode 9 when the air is not blown.

When the rotating electrode 9 passes near the stationary electrode 3, it is observed that, for example, five arcs SP1 to SP5 are generated. At this time, the arc plasma 15 is generated as indicated by the hatched portion in the figure.

FIG. 4B shows the generation of an arc when air is blown to the gap portion. When the rotating electrode 9 passes near the stationary electrode 3, arcs SP1 and SP2 due to discharge
However, the arc causes the arc to have a bent shape.

For example, when electrodes having a diameter of 2 mm were used as the stationary electrode 3 and the rotating electrode 9, only two arcs were generated. As experimental conditions, the rotation speed of the rotary electrode was 1450 rpm, the speed of the tip of the rotary electrode was 30 m / s = 3 mm / 100 μs, and the inductance was L.
The C vibration period was 200 μs.

When the gap is shortest, it is about 10 m.
m, and the applied voltage is 10 k for the base DC power supply DC2.
V, the DC power supply DC1 as the main power supply was 30 kV.
In addition, the traveling distance of the rotating electrode corresponding to the adjacent arcs is about 0.6 cm, and as shown in FIG.
When the arc of the book is generated, the traveling distance of the rotating electrode during that time is about 3 cm.

If the electrode is formed of a metal rod having a diameter of 2 mm, the electrode may be consumed due to discharge. 6 mm diameter
When the electrode of No. 2 was used, 5 arcs were still generated when the air was not blown, and when the air was blown, usually 2 arcs and rarely 3 arcs were generated.

Thus, blowing a gas such as air near the gap where the discharge is performed is very effective in preventing continuous pulses. However, even if such a means is used, two arcs are generated and it is not a single-shot pulse. In order to realize a single-shot pulse, it is considered effective to increase the traveling speed of the rotating electrode or lengthen the oscillation period.

FIG. 5 is a diagram for explaining the function of the additional inductance connected in series to the antiparallel diode D2. FIG. 5A shows the circuit when the additional inductance L2 does not exist. In this case, the oscillation cycle is L1,
It is defined by Cm, and the length of one cycle is 2π (L1 ・ C
m) ^1/2 . Here, Cm is a series combined capacity of dust collector electrostatic capacity C2, which is an addition to C1, C1 · C2 / (C1 + C
2) is shown. The EP voltage waveform when the rotation spark gap RSG is turned on only once with this cycle being 100 μs is shown on the right side of the figure. That is, the vibration cycle is 100 μs determined by L1 and Cm.

FIG. 5B shows a case where the additional inductance L2 is connected in series to the antiparallel diode D2. In this configuration, the current i1 flowing through the diode D1 is the same as in the case of FIG. 5A, and the oscillation cycle of the LC resonance is also the same as in FIG. 5A.

However, in the half cycle in which the current i2 flows through the antiparallel diode D2, the current flows through the additional inductance L2. Therefore, the total inductance is (L1 + L12), and the oscillation period of LC resonance is 2π {(L1 + L2) Cm} ^1/2 .

By setting the value of the additional inductance L2 to be several times the value of the inductance L1 or more, the half cycle of the current flowing through the antiparallel diode D2 is
It can be extended longer than other half cycles.

If (L1 + L2) = 10L1, then E
As shown on the right side of the figure, the P voltage becomes √10 times in the latter half cycle. If the arc plasma is removed from the gap portion by blowing air during this period, it is possible to prevent the arc from being generated even if the voltage is applied to the gap again.

The characteristics of the circuit of FIG. 1 having the functions shown in FIGS. 2 to 5 are as shown in FIG. In the figure, the current i flowing through the inductance L1 is shown on the upper side and E on the lower side.
P voltage v is shown.

The current i is the current i1 flowing through the diode D1 in the positive half cycle, and the current i2 flowing through the antiparallel diode D2 in the latter half cycle.

Let τ1, τ2 be the time of each half cycle, and (τ1
+ Τ2) is set to about 100 to 400 μs. At this time, the EP voltage has a shape shown on the lower side in the figure, and the rising edge is steep and the falling edge is somewhat gentle.

By blowing off the arc plasma in the vicinity of the gap with air while the current i2 flows through the anti-parallel diode D2, it is possible to prevent re-ignition even if a voltage is applied to the gap again. When the rotating electrodes approach, a spark is generated in the spark gap and a pulse voltage is generated again.

By increasing the structural strength of the rotary spark gap and increasing the speed of the rotary electrode, it is possible to increase the distance of the rotary electrode traveling within one cycle of LC oscillation and omit the additional inductance L2. is there.

FIG. 7 shows an electrostatic precipitator according to another embodiment of the present invention. FIG. 7A shows a circuit configuration, and FIG.
Indicates its characteristics. In FIG. 7A, the cathode of the single DC power supply DC is connected to the negative electrode of the capacitance C3 via the impedance Z and to the dust collecting electrode EP via the diode circuit and the inductance L1. .

The diode circuit is formed by parallel connection of the side including the diode D1 and the rotary spark gap RSG and the side including the anti-parallel diode D2. A nozzle 1 for blowing air is connected to the stationary electrode of the rotating spark gap RSG.

A negative voltage having an absolute value higher than the absolute value of the voltage (negative voltage) of EP is given to C3 by the DC power supply DC.
When the rotating spark gap RSG is turned on, a current flows from the EP electrode toward the negative electrode of the capacitance C3 through the diode D1, and when the polarity is reversed in the latter half cycle of the oscillation, the capacitance C3 passes through the anti-parallel diode D2 and the EP Electric current flows through the electrodes.

The voltage waveform of the dust collecting electrode EP of the circuit shown in FIG. 7A is shown in FIG. 7B. The horizontal axis in the figure indicates time t,
The vertical axis represents the EP voltage as a negative voltage. In this embodiment,
The oscillation period is determined by the capacitance formed by the dust collecting electrode EP, the series combined capacitance value of C3 and the inductance L1. When only one arc is generated and the remaining arcs are suppressed, a single pulse is generated as shown in FIG. 7 (B), and thereafter, a gentle decay according to the RC time constant occurs.

Here, C is the capacitance formed by the dust collecting electrode EP, and R is the equivalent resistance of the corona of the dust collector. Since R becomes infinite below the corona starting voltage, the gradual attenuation in FIG. 7 asymptotically approaches the corona starting voltage.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example,
It will be apparent to those skilled in the art that various changes, improvements, combinations and the like can be made.

[0059]

As described above, according to the present invention,
Using the rotating spark gap, it becomes possible to generate a pulse voltage suitable for an electrostatic precipitator.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an electrostatic precipitator according to an embodiment of the present invention.

FIG. 2 is a circuit diagram and a waveform diagram for explaining a function of an anti-parallel diode.

FIG. 3 is a schematic diagram showing a configuration of a nozzle.

FIG. 4 is a schematic diagram for explaining the function of air blowing.

5A and 5B are a circuit diagram and a waveform diagram for explaining the function of the additional inductance.

FIG. 6 is a waveform diagram showing characteristics of the circuit shown in FIG.

FIG. 7 is a circuit diagram and a waveform diagram showing an electrostatic precipitator according to another embodiment of the present invention.

FIG. 8 is a circuit diagram and a waveform diagram for explaining an electrostatic precipitator according to a conventional technique.

[Explanation of symbols]

 1 Nozzle 2 Power Supply Line 3 Stationary Electrode 4 Nozzle Jacket 5 Nozzle Clearance 6 Air 7 Insulation Hose 8 Nozzle 9 Rotating Electrode 10 Bearing 11, 12 Terminal RSG Rotating Spark Gap D Diode L Inductance C Capacitance DC DC Power Supply EP Dust Collection Electrode

Claims (2)

[Claims] 1. A circuit for an electrostatic precipitator connected between a DC power source and a dust collecting electrode, comprising: a rotating spark gap including a rotating electrode and a stationary electrode; a nozzle for spraying gas around the stationary electrode; A first diode connected in series to the rotating spark gap, a second diode connected in parallel to the rotating spark gap and the first diode connected in series, and a second diode in a direction opposite to the first diode; A circuit for an electrostatic precipitator having an inductance connected in series. 2. The circuit for an electrostatic precipitator according to claim 1, further comprising an additional inductance connected in series with the second diode.