JPS60209273A - Two-stage electrical dust collector - Google Patents

Abstract

PURPOSE:To improve the dust collection efficiency and to reduce the consumption of electric power by using a discharge electrode having a uniform cross section in an electrified part, and impressing a DC high voltage and a pulse high voltage one upon another to said discharge electrode in a two-stage electrical dust collector. CONSTITUTION:An electrified part 6 consists of a discharge electrode, which is constituted of round or angular wire and has a uniform cross section, and a collecting electrode capable of constituting a uniform electric field, and a DC high voltage is impressed between both electrodes by DC high voltage generators 3c and 3f. A pulse high voltage is further impressed and superposed from pulse voltage generators 8a and 8b through coupling capacitors 9a and 9b. High- resistance dust can be highly charged in this way. Then the charged dust is collected at a dust collecting section 7. Since the pulse electric source is utilized only in the electrified part, the collector can be economized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a two-stage electrostatic precipitator comprising a charging section and a dust collecting section.

Conventional electric dust evaporators (hereinafter referred to as EP) have a high dust resistance and a specific resistance value of 1011 to 1010I20.
If it exceeds -, dielectric breakdown within the dust layer deposited on the dust collecting electrode, a so-called reverse ionization phenomenon, occurs, resulting in a drawback that the collection performance is greatly reduced. Therefore, when handling high-resistance dust such as EP for coal-fired power plants or sintering machines, it is generally necessary to increase the EP capacity to compensate for the decrease in collection performance.

For this reason, various attempts have been made to improve measures against high-resistance dust, one of which is two stage EP (Two stage EP), which is widely used in air purifiers.
P), that is, a method in which reverse ionization is suppressed by dividing the dust into a charging part that charges the dust and a dust collecting part that collects dust with a high electric field, and reducing the current as much as possible in the high electric field part (initiating conditions for reverse ionization). (Pd

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 stain electrode by flowing water through the pipe to lower the electrical resistance of dust and suppress reverse ionization, or a method that uses a pipe between the dust collection electrode and the discharge electrode. There is a third electrode method that attempts to suppress reverse ionization by providing three electrodes and absorbing ions of opposite polarity generated during reverse ionization.

In addition, by improving charge control, we have developed a particle charging device called a boxer charger that only charges dust without causing reverse ionization (Patent Application No. 106400 of 1977, etc.).
etc. have also been proposed.

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

On the other hand, in an attempt to improve the performance of the conventional type of EP through charge control, a pulse charging method is used, that is, a high peak voltage is applied by instantaneously applying a pulsed high voltage, and a uniform current is obtained. There are other ways to improve the dust collection efficiency, but in this case as well, there are problems such as the price of the pulse power source and how to reduce power consumption.

By the way, in the conventional EP shown in FIGS. 1 to 5, high voltage is applied from the DC high voltage generators 3a and 3b shown in FIG. 1 to the dust collection electrode 1 and the discharge electrode 2 shown in FIGS. 2 and 3. When applied, as shown in Fig. 4, under normal conditions it exhibits current-voltage characteristics as shown in (a), and therefore, it can be operated under conditions where high current and voltage are applied, resulting in high collection performance. When reverse ionization occurs due to the collection of high-resistance dust, the characteristics shown in (b) occur, the operating voltage is low, and the effective operating current is suppressed by P2 (any more than that is consumed as a reactive current in the reverse ionization section). ), the collection performance decreases.

For this reason, as shown in FIG.
By adding pulse high voltage devices 8C and 8a to b via coupling capacitors 9c and 9d, the charging characteristics are changed as shown by the dotted line (h) in Fig. 4, and the uniform discharge of pulse charging is achieved. It is also possible to consider a method of improving performance by utilizing the characteristics and operating at a higher operating current density.

However, in the case of conventional EP, dust is charged and collected at the same time in each field, so the discharge characteristics are good to some extent, such as (a), (b), and (b) in Figure 5.
Since it is composed of a discharge electrode 2 (d = 1 to 3 to 0) with spikes as shown in (c) or a small radius of curvature as shown in (e) (d = 1 to 3 to 0), even if pulse charging is superimposed, dust will not be generated. Although it is possible to increase the current effective for charging, it is not possible to expect an increase in the electric field effective for collecting dust, and no significant improvement can be expected.

In addition, charging the entire field of the EP with pulse charges increases the cost of the pulse generator, and when energy is consumed as Joule heat by a waveform shaping resistor as a means for generating pulse voltage, power consumption is required. There were many drawbacks, such as an increase in the number of

The present invention has been proposed in view of the above-mentioned drawbacks of the conventional art. The present invention is characterized in that a discharge electrode having a uniform cross section is used, and a direct current high voltage and a pulsed high voltage are applied to the discharge electrode in a superimposed manner.

In other words, the present invention has a discharge electrode with a uniform cross section that has a high corona initiation voltage and is difficult to pass current when a normal high DC voltage is applied, and a discharge electrode that can create a high uniform electric field on the surface of the electrode plate. In the combination of dust collecting electrodes, by superimposing a DC high voltage and a pulsed high voltage having a pulse width of several 101 seconds to several 100/78 seconds between the two electrodes, a high current density can be achieved while maintaining a high electric field strength even in high resistance dust. By focusing on the property of obtaining dust, this part is used mainly as a charged part for dust, and the subsequent charged section to which a high DC electric field is applied is used as a part for collecting dust.The combination of the two enables economical pulse generation as a whole. This provides a compact, high-performance electrostatic precipitator that uses a power source.

The present invention will be specifically explained below based on the embodiments shown in FIGS. 6 to 11.

As shown in FIGS. 6 and 7, the configuration of the EP is as follows:
and ' in the dust collection part 7, and their combination is the ninth
As shown in the figure, examples of combinations such as a charging section and a dust collecting section or a charging section and a charging section and a charging section and a charging section and a charging section and a charging section and a charging section and a collecting section and a dust collecting section and a charging section and a charging section and a charging section and a charging section and a charging section and a charging section and a charging section and a charging section and a charging section and a dust collecting section and a charging section and a charging section and a charging section and a charging section and a charging section and a dust collecting section and a charging section and a charging section and a charging section and a charging section and a dust collecting section and a plurality of charging sections and a plurality of dust collecting sections, respectively.

The charging portion 6 is formed of a round wire of 3 to 10 mm as shown in (a) in FIG. The discharge electrode 4 shown in (c) has a uniform cross section, and the dust collection electrode 4, such as a flat plate or round shape, has few irregularities and can form a uniform electric field on its surface as shown in Fig. 8. 1a, a DC high voltage is applied between both electrodes 4-1a by DC high voltage generators 3c and 3f shown in FIG. 6, and pulse voltage generators sa, Pulse high voltages of several IQns to several 100 μs supplied by sb are applied in a superimposed manner.

Regarding the dust collection section 7, the conventional and widely used combination of a dust collection electrode and a discharge electrode is also effective in combination with the aforementioned charging section 6, but a more effective combination is shown in Fig. 8. Either reduce the pitch of the discharge electrodes 5 in the gas flow direction, or increase the radius of curvature of the discharge electrodes 5 (equivalent radius of curvature if a discharge electrode other than round is used on the discharge electrode). A combination of the discharge electrode 5 and the dust collecting electrode 1b can be considered so as to obtain the highest possible voltage.

Since the electrostatic precipitator of the present invention is constructed as described above, when a normal DC high voltage is applied, it is a high electric field type as shown in FIG. 10 (c) or (d), but the current By superimposing a pulsed high voltage on the charged part 6, which is made up of a combination of a discharge electrode 4 and a dust collection electrode 1a, which exhibit characteristics that do not flow or are extremely difficult to flow, even high-resistance dust (,)
Since the current-voltage characteristics that allow a relatively high current density to be obtained while maintaining a high electric field strength as shown in the figure are obtained, it becomes possible to impart a high charge to the dust.

In this case, the charging section 6 mainly charges the dust, but of course has a dust collection function to some extent, so that the dust can be removed by hammering or the like as required in a normal dust collector.

Next, the charged dust is collected on a dust collection pole in the dust collection section 7 by the force of the electric field. In this case, high dust collection efficiency can be obtained by combining an electrode configuration of the dust collection section 7 with the above-mentioned charging section 6, which has a high electric field strength with almost no current flowing. In other words, in the multiplier section 7, the dust is charged in advance by the charging section 6, so the current supply only needs to be the minimum necessary to prevent re-scattering, and therefore a high electric field strength can be applied without causing reverse ionization. This makes it possible to maintain high dust collection efficiency, making it possible to achieve overall compactness and high efficiency.

Further, as in a general two-stage EP, it is of course possible to configure the discharge electrode side with a flat plate and configure the dust collection section with a parallel flat plate or a high electric field.

In addition, in the present invention, as shown in FIG. 11, a normal DC high voltage and a pulsed high voltage of several IQns to several 100 μs are superimposed and applied to a small charged section having a discharge electrode 4 having a uniform cross section without thorns. A charging section 6 that mainly performs charging in P
(1) The discharge electrode 4, which has a uniform cross-section without thorns, is usually Even if a DC high voltage of However, by superimposing a pulse voltage of several IQns to several hundreds of tones, a current-voltage characteristic like that shown in FIG. (
P3) Without causing reverse ionization at high current density
Since the operation can be performed as shown in (P4), the function of quickly charging the dust can be greatly improved.

In this case, when the conventional discharge electrode 2 shown in FIG. 5 is used,
The current-voltage characteristics are as shown in Figure 10 (f) during normal charging and as shown in Figure 10 (g) even when pulse charging is applied, so even if the current density is secured, the voltage is low, so the dust The saturation charge amount is suppressed to a low level, and therefore sufficient charge cannot be supplied.〇(2) Also, according to conventional knowledge, the first
Even if the current is increased from the reverse ionization starting condition (P4) of the current-voltage characteristics shown in Figure 0, the current consumption and voltage do not increase due to an increase in only ions of opposite polarity, so the dust collection efficiency does not increase.

However, in the present invention, even when operating beyond P4, the amount of charge on the dust increases, so the dust collection efficiency of the charging section alone does not improve, but the dust collection efficiency of the high electric field section in the subsequent stage improves, so the overall Dust collection efficiency can be improved.

This is because in conventional charging methods, when reverse ionization occurs, current flows locally and the current is consumed only in that area, but when pulses are superimposed, current flows uniformly even when reverse ionization occurs. For this reason, although there is an increase in the number of ions of opposite polarity, it is thought that by increasing the current, the absolute amount of ions supplied increases, and the amount of charge on the dust increases, and this has also been confirmed by experiments.

(3) Also, in the present invention, the functions of the EP are distributed in two stages,
A charging part 6 which is a part that mainly charges dust
By superimposing a pulsed high voltage of several 10 nB to several 100 μS only in a small section of , it is possible to use the pulsed power source economically and efficiently.

In addition, in the electrostatic precipitator of the present invention, for example, in the case of particles of 1 micron, the saturated charge amount is 65% in a charging time of 01 seconds in a calculation example under the conditions of a current density of 02 mA/i and an electric field strength of 3 KV/cm. Since a charge amount of 95 cm can be secured in 1 second, if the gas velocity is set to l mis, the length of the charged portion of several tens of cm to 1 m is sufficient for practical purposes. Since the cost and power consumption of the pulse power source are roughly proportional to the capacitance of the capacitor between the discharge electrode and the dust collection electrode, it is extremely economical to use the pulse power source only in the charging section.

``Thus, the present invention can economically utilize a pulsed power source and provide a compact, high-performance two-stage electrostatic precipitator.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional electrostatic precipitator, Figure 2 is its plan view, Figure 3 is an enlarged view of the electrode section, Figure 4 is its current-voltage characteristic diagram, and Figure 5 is its discharge electrode. FIG. Furthermore, Fig. 6 is a configuration diagram of a two-stage electrostatic precipitator showing one embodiment of the present invention, Fig. 7 is a plan view thereof, Fig. 8 is an enlarged view of its electrode section, and Fig. 9 is its charging diagram. A combination layout diagram of the part and dust collection part,
FIG. 10 is a current-voltage characteristic diagram of the charging section, and FIG. 11 is a perspective view of the discharge electrode. la, lb... Dust collection electrode, 4, 5... Discharge electrode, 6.
...Charging part, 7...Dust collection part, 3c, 3f...
DC high voltage generator, 8a, 8b...Pulse voltage generator @10 4th MV (voltage) 50th b'/ qI mouth ■[ 10th [1iF-Current in chamber 5. ,, -l To Naonada High Voltage V Article 110 (A) (B) υ (d) (Written amendment of meritorious procedure (method) 1. Indication of the case 1982 Patent Application No. 65504 2 Title of the invention 2 paragraphs Relationship with the case of the person making the amendment to type electrostatic precipitator 6 Patent applicant address 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Name (
r+2o) Mitsubishi Heavy Industries, Ltd. 4, Agent Address: Mitsubishi Heavy Industries, Ltd., No. 4, 2-5-5, Marunouchi, Chiyoda-ku, Tokyo (Electricity 212-3111) Figure 4, Figure 10V Continuous high voltage V

Claims (1)

[Claims] In a two-stage electrostatic precipitator, which consists of a charging section that mainly charges dust and a dust collection section that mainly collects dust, a discharge electrode with a uniform cross section is used in the charging section, and a high DC current is applied to the discharge electrode. A two-stage electrostatic precipitator characterized by applying voltage and pulsed high voltage in a superimposed manner.