JPH0157622B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a precharging device for an electrostatic precipitator,
In particular, the present invention relates to a precharging device for an electrostatic precipitator that can be applied to general industrial processes that handle high-resistance dust (for example, coal-fired power plants, cement plants, sintering machines, etc.).

In conventional electrostatic precipitators (EP), when the dust resistance becomes high and the specific resistance value exceeds 10 ¹¹ to 10 ¹² Ω-cm, dielectric breakdown occurs within the dust layer deposited on the dust collecting electrode, so-called reverse ionization. When handling high-resistance dust such as EP for coal-fired power plants or sintering machines,
Generally, the EP capacity is increased to compensate for the decrease in collection performance.

For this reason, various attempts have been made to counter high-resistance dust, one of which is the two-stage EP (Two-stage EP), which is widely used in air purifiers.
EP), that is, a method of suppressing reverse ionization by dividing the dust into a charging section that charges the dust and a dust collection section that collects dust with a high electric field, and reducing the current as much as possible in the high electric field section (initiating conditions for reverse ionization). is ρd×idEdc, and even if the dust resistance ρd is high, if the current id flowing through the dust layer is small, it will not exceed the breakdown voltage Edc of the dust layer.) There are attempts to apply this to general industrial use. However, in this case as well, it is difficult to suppress reverse ionization in the charged part of the dust, and various methods are currently being tried.

For example, a method that uses a pipe as an electrode and cools the electrode by flowing water into the pipe to lower the electrical resistance of the dust and suppress reverse ionization, or a method that uses a third electrode between the collecting electrode and the discharge electrode. There is a third electrode method in which reverse ionization is suppressed by absorbing ions of opposite polarity generated during reverse ionization.

In addition, by improving charge control, a particle charging device called a boxer charger that only charges the dust without causing reverse ionization (patent application filed in 1978)
106400) are also being proposed.

However, none of these methods has been put into practical use because it is difficult to implement them on a commercial scale for general industry.

The present invention has been proposed in view of the above circumstances, and its purpose is to provide a pre-charging device for an electrostatic precipitator that can always maximize the amount of charge given to dust according to the conditions of the processing gas. be.

The precharging device for an electrostatic precipitator according to the present invention comprises:
A pre-charging section that applies a direct current high voltage and a pulsed high voltage in a superimposed manner between the discharge electrode having a uniform cross section in the longitudinal direction and the dust collection electrode capable of forming a uniform electric field distribution, and this pre-charging section. and means for controlling the amount of dust charge detected by the means by means of a direct current high voltage and a pulse high voltage of the pre-charging section. In the two-stage EP, the amount of dust charge at the outlet of the precharging section is detected and the pulse high voltage and DC high voltage (base voltage) applied to the discharge electrode of the precharging section are controlled. Feedback control is carried out so as to maximize the amount of charge applied to the dust at each point, thereby solving the above-mentioned drawbacks of the conventional method.

An embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing the overall configuration of an embodiment of the present invention, FIG. 2 is a plan view showing the electrode configuration of the precharging section in FIG. 1, and FIGS. 3 and 4 are the same as in FIG. Figure 5 is a diagram showing the voltage-current characteristics when voltage is applied to the electrode shown in Figure 2. Figure 6 is a diagram showing the waveform of the voltage applied to the electrode shown in Figure 2. FIG. 7 is a diagram showing the power supply configuration of the pre-charging section in FIG. 1. FIG. 8 is a diagram showing the pulse voltage, base voltage, and dust charging at the exit of the pre-charging section in an embodiment of the present invention. FIG. 9 is a diagram showing the relationship between the voltage and the voltage during pulse charging in one embodiment of the present invention.
FIG. 3 is a diagram showing current characteristics.

In Fig. 1, 1 is a pre-charging section (charging section) that mainly charges dust, and 2 is a dust collection section that mainly collects dust.The combination of these charging section 1 and dust collection section 2 creates a two-stage structure. Formula EP is configured, and the charging part 1 includes a discharge electrode that has a uniform cross section in the longitudinal direction and can obtain high electric field strength as described later, and a dust collection electrode that can form a uniform electric field distribution. By combining these two electrodes, a DC high voltage (base voltage) that forms the main electric field and a pulsed high voltage having a pulse width of several tens of microseconds to several hundred microseconds are applied in a superimposed manner, allowing dust to be electrostatically precipitated. It is designed to provide the necessary charge.

The electrode structure shown in Fig. 2 has a high electric field and low current during normal current charging (the applied voltage waveform is shown in Fig. 3), that is, a corner or It is a combination of a discharge electrode 3 having a round bar or an equivalent shape and having a uniform cross section in the longitudinal direction, and a dust collection electrode 4 which can form a high electric field and is made of a pipe or a flat plate. By pulse charging the discharge electrode 3 of this electrode group with a typical configuration of a pulse power source 5, a normal DC power source 6, and a coupling capacitor 7 shown in FIG. 2, an applied voltage as shown in FIG. Gives a waveform. As shown in FIG. 6, the pulse power source 5 instantaneously discharges the electric charge stored in the internal main capacitor 11 by a high voltage generating transformer 8, a diode 9, and a charging resistor 10 by a switching mechanism 12 such as a spark gap or a thyristor + free-wheeling diode. , which generates a pulsed high voltage with a steep rise. Furthermore, the coupling capacitor 7 capacitively couples the pulse high voltage V _p generated by the pulse power source 5 with the normal DC voltage (base voltage) V _B , resulting in a base voltage V _B as shown in FIG.
Obtain an applied voltage waveform in which a pulsed high voltage V _p is superimposed on the

FIG. 7 shows the configuration of the power supply section of the precharging device according to the present invention. In FIG. 7, 13 is an AC power regulator for adjusting the base voltage V _B (equal to the output of the high-voltage transformer rectifier 14); base voltage
V _B is a high-voltage transformer rectifier that supplies the corona current (base current); 15 is a DC reactor for protecting the high-voltage transformer rectifier 14 from the spark discharge generated inside the precharging device and the pulse voltage V _p ; 1
6 is corona current (current feedback signal a)
A current detector for detection; 17 a voltage detector for detecting base voltage V _B (voltage feedback signal b); 1
8 is an AC power adjustment device for adjusting pulse voltage V _p (which has a positive correlation with the output of the high voltage transformer 19);
9 is a high voltage transformer, 20 is a diode for half-wave rectification of the output of the high voltage transformer 19, 21 is a charging resistor for protecting the high voltage transformer 19 from steep surges, and 22 is for generating pulses. 23 is the switching device, 24 is a waveform shaping resistor (discharge resistor) for generating the pulse voltage V _p , and 25 is the high voltage transformer 1.
9 is a current detector for detecting the low voltage side current (current feedback signal c), 26 is the main capacitor charging voltage
A voltage detector for detecting V _c (voltage feedback signal d), 27 a voltage detector for detecting pulse voltage V _p (voltage feedback signal e), and 28 capacitively coupling pulse voltage V _p and base voltage V _B a coupling capacitor 29 for detecting the amount of charge per unit mass (q/M) of the dust at the outlet of the pre-charging device; The q/M calculation unit 31 calculates /M and converts it into a feedback signal g.
Calculate the optimal values of the pulse voltage V _p and base voltage V _B that will optimize the amount of dust charging at the exit of the pre-charging device,
a control unit 32 that outputs a control command according to the control command;
is a pulse voltage V _p adjustment command output section, and 33 is a base voltage V _B adjustment command output section. 34 is an EP outlet dust concentration detection section.

As shown in FIGS. 7a to 7k, the signal-related configuration is such that the feedback signals to the control unit 31 include a corona current signal (base current) a, a base voltage signal b, a pulse voltage generation power supply low voltage side current signal c, and a main Capacitor charging voltage signal d, pulse voltage signal e, and dust charge amount per unit mass (q/M) signal q
give. As a result, the pulse voltage V _p ,
Adjustment commands h, i and j, k of the base voltage V _B are sent to the respective AC power adjustment devices 13 and 18. In addition, the dust concentration detected by the EP outlet dust concentration detection unit 34
The EP outlet dust concentration is determined by the control unit 31 as a signal l.
sent to.

The operation of the above embodiment of the present invention will be explained.

It has been experimentally confirmed that the voltage-current characteristics (base voltage - corona current) when pulse charging is applied to the precharging device using the electrode group shown in Fig. 2 are as shown in Fig. 5. There is. In other words, by adjusting the pulse voltage V _p and base voltage V _B ,
The corona current (base current, a) flowing between the discharge electrode and the pipe electrode in the precharging device can be changed. Figure 5 shows the characteristics of dust with a high electrical resistivity that easily causes the reverse ionization phenomenon, and it has been experimentally confirmed that there is a noticeable bend in the characteristic curve with pulse charging. There is.
From the rapid increase in current after this bend (top right part), this part is considered to be the starting point of reverse ionization. As the base voltage increases, as shown in Figure 8, the amount of charge q/M per unit mass of the dust at the outlet of the pre-charging device gradually increases from the start of back ionization, and the base voltage is determined by conditions such as the dust and the pulse voltage V _p . It reaches a maximum at voltage V _B , after which q/M starts to decrease for high resistance dust.

The electrode group used in the present invention has a structure that can maintain an extremely high electric field as described above.
It has been experimentally confirmed that it is possible to adjust the corona current by pulse charging, and that the pipe electrode has a uniform current density distribution on the electrode surface, making it difficult for reverse ionization to occur.
For these reasons, it is considered to be extremely suitable for a pre-charging device.

However, even with this configuration, as mentioned above,
In the case of dust exhibiting a significantly high electrical resistivity, there is a possibility that the precharging performance will deteriorate due to reverse ionization. To this end, in the present invention, the amount of dust charge (q/M) per unit mass at the outlet of the precharging device, the dust concentration at the EP outlet, the pulse voltage V _p , the base voltage V _B , and the base current I _B are input as feedback signals,
In order to obtain the optimum amount of charge, the pulse voltage V _p and base voltage V _B are controlled.

The specific operation will be described below according to FIG.

<Base Voltage and Current Adjustment> The AC power adjustment device 13 adjusts the AC power of the commercial power supply according to the signal level from the control unit 31→command output unit 33, and the high voltage transformer rectifier 14 generates a DC high voltage. Based on the control described later, the base current low voltage side current signal (base current) a
and DC high voltage signal (base voltage) b are input to the control unit 31 as a feedback signal, and the AC power adjustment command (base voltage V _B adjustment command) i is inputted every moment so that the base voltage V B is adjusted to the determined base voltage V _B. ，
Output k.

<Pulse voltage V _p adjustment> Pulse voltage V _p determined based on the control described later
According to the adjustment commands h and j, the AC power adjustment device 18 adjusts the AC power of the commercial power source, and the high voltage transformer 1
9 generates AC high voltage.

This AC high voltage is half-wave rectified by the diode 20, and a negative charge is charged to the main capacitor 22.
When the electric charge is momentarily discharged by switching the switching section 23, a steep pulse high voltage is generated in the waveform shaping resistor 24. The pulse voltage is adjusted by the low voltage side AC power. This pulse voltage V _p is capacitively coupled to the base voltage V _B by a coupling capacitor 28, and the pulse voltage is superimposed on the base voltage and applied to the discharge electrode of the precharging device.

<Control method> Fig. 8 shows a general relationship (an example) for high resistance dust between the pulse voltage V _p , the base voltage V _B and the outlet q/M. For example, by inputting the q/M signal g, the pulse voltage V _p signal e, and the base voltage V _B signal b,
Keeping V _p constant and gradually increasing V _B , q/M
By finding the maximum condition for q/M, or by lowering V _B and increasing V _p when a spark occurs when V _B is increased, you can find the maximum condition for q/M.
The exit q/M can be controlled to a maximum or arbitrarily.

The peak in the q/M change curve in Figure 8 is due to the internal reverse electrode or the generation of sparks between the electrodes (V _B is limited by this factor), and the precharging performance is affected by the balance between V _p and V _B. This is because it begins to decline.

Furthermore, as described above, since the EP exit dust concentration signal is fed back to the control section 31, the correlation between the amount of dust charge at the pre-charging section exit and the EP exit dust concentration can be investigated. This correlation can be obtained through experiments, but with this configuration, the amount of dust charge at the exit of the pre-charging section can be calculated using the method described above while the charging control of the dust collection chamber after the pre-charging section is kept constant. By controlling it to the maximum or an arbitrary value, the EP outlet dust concentration can be controlled to the minimum or an arbitrary set level.

As described above, the precharging device according to the present invention exhibits excellent effects in the following respects, extremely satisfying the conditions required of the precharging device described above.

In normal DC charging, a high electric field and a low current are produced (an example is shown in Fig. 5).A high electric field is formed by a square or round bar discharge electrode and a pipe-shaped or flat plate as shown in Fig. 2. Because it is constructed with dust collecting electrodes, it is able to maintain a significantly higher electric field than ordinary discharge electrodes with spikes.

By applying pulse charging to the discharge electrode-collection electrode, a necessary corona current can be obtained while maintaining a high electric field.

By controlling the pulse voltage V _p and the base voltage V _B by feedback, the voltage-current characteristics (V _B - I _B characteristics) during pulse charging can be used to detect dust with high electrical resistivity where reverse ionization occurs. In addition, since the starting point of back ionization can be recognized, it is possible to operate under conditions that suppress back ionization as much as possible.

Further, by detecting the dust q/M at the outlet of the pre-charging device and providing feedback, the dust q/M at the outlet can be controlled to a maximum value or to an arbitrary value.

Furthermore, since the dust charge amount at the exit of the pre-charging section and the dust concentration at the EP exit are taken in as feedback signals, the amount of dust charge at the exit of the pre-charging section is fed back to the pre-charging section so that the dust concentration at the EP exit is minimized or at an arbitrary set level. It can be controlled by adjusting the pulse voltage V _p that charges the discharge electrode and the main base voltage V _B.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the overall configuration of an embodiment of the present invention, FIG. 2 is a plan view showing the electrode configuration of the precharging section in FIG. 1, and FIGS. 3 and 4 are the same as in FIG. Figure 5 is a diagram showing the voltage-current characteristics when voltage is applied to the electrode shown in Figure 2. Figure 6 is a diagram showing the waveform of the voltage applied to the electrode shown in Figure 2. FIG. 7 is a diagram showing the power supply configuration of the pre-charging section in FIG. 1. FIG. 8 is a diagram showing the pulse voltage, base voltage, and dust charging at the exit of the pre-charging section in an embodiment of the present invention. FIG. 9 is a diagram showing the relationship between the voltage and the voltage during pulse charging in one embodiment of the present invention.
FIG. 3 is a diagram showing current characteristics. DESCRIPTION OF SYMBOLS 1... Preliminary charge part, 2... Dust collection part, 3... Discharge electrode, 4... Dust collection electrode, 5... Pulse power supply, 6... Normal DC power supply, 29... Q/M detection part, 30 ……
q/M calculation unit, 31...control unit.

Claims (1)

[Claims] 1. A pre-charging section that applies a direct current high voltage and a pulsed high voltage between the discharge electrode having a uniform cross section in the longitudinal direction and the dust collection electrode capable of forming a uniform electric field distribution, and this pre-charging section. The method includes means for detecting the amount of dust charge at the outlet of the charging section, and means for controlling the amount of dust charge detected by this means using the DC high voltage and pulse high voltage of the pre-charging section. Features: Pre-charging device for electrostatic precipitator.