JPS60209274A - Two-stage electrical dust collector - Google Patents

Abstract

PURPOSE:To enhance the charging function of dust by arranging a rod-shaped dust collecting electrode having a uniform cross section in the direction vertical to a gas flow so that the electrodes may constitute a polygon, and positioning a discharge electrode at the center of the polygon. CONSTITUTION:A dust collecting electrode 2a has a round or the equivalent uniform cross section in the direction vertical to a gas flow G, and a discharge electrode 1a is arranged at a position equidistant from the apexes of a polygon formed by the centers of the dust collecting electrodes 2a. A DC high voltage is impressed from a DC high voltage generator 5, and a pulse high voltage is impressed from a pulse voltage generator 7 through a coupling capacitor 6. Since the structure of electrodes is formed as mentioned above, uniform current density can be obtained, and the dust is uniformly charged. High operating electric field intensity can also be given to high-resistance dust, and hence the charging function is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-stage electrostatic precipitator that improves dust collection efficiency by improving the shape and arrangement of electrodes.

In conventional electrostatic multiplication equipment (EP), when the dust resistance becomes high and its specific resistance value exceeds 1011 to 1012 Ω, dielectric breakdown occurs within the dust layer deposited on the dust collecting electrode, so-called reverse ionization. Because of this, there is a significant decrease in collection performance.

When dealing with high-resistance dust such as EP for coal-fired power plants or sintering machines, the EP capacity is generally 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 (TWOstageEP), which is widely used in air purifiers, in which a charging part that charges the dust and a high-resistance A method of suppressing back ionization by dividing the dust collection section into a dust collecting section that collects dust using an electric field and reducing the current as much as possible in the high electric field section (the initial conditions for reverse ionization are pdxid>Edc, dust resistance pd Even if the current id flowing through the dust particles is high, if the current id flowing through the dust particles does not exceed the breakdown voltage Eda of the dust particles, there is an attempt to apply this to general industrial use.

However, in this case as well, it is difficult to suppress reverse ionization of the charged portions, so various methods have been tried.

For example, a method uses a pipe as a dust collection electrode and cools the electrode by flowing water through the pipe, lowering the electrical resistance of the dust and suppressing reverse ionization.

Alternatively, there is a third electrode method in which a third electrode is provided between the multiplication electrode and the discharge electrode, and the reverse ionization is suppressed by absorbing ions of opposite polarity generated during the reverse ionization.

Further, by devising charge control, a particle charging device called a boxer charger (Patent Application No. 106400 of 1972) has been devised, which applies only an electric charge to dust without causing reverse ionization.

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

The present invention relates to a charging unit that applies an electric charge to dust.

Two general type BP consisting of a dust collection part that collects dust
In order to charge the dust as much as possible in the charging part and obtain high dust collection efficiency in combination with the dust collection part in the latter stage, a polygonal shape consisting of round or equivalently shaped dust collection poles is used. The electrical characteristics formed by the combination of a polygonal (usually rectangular) array and a discharge electrode placed at the center of the polygon are different from the conventional flat-shaped dust collection electrode parallel to the gas flow direction. Unlike the combination with a row of discharge electrodes arranged in the center, this method was created by focusing on the superiority of focusing only on the property of imparting charge to dust.

The novel points of the present invention described above will be summarized.

Instead of the parallel plate-shaped dust collection electrodes that were conventionally used as the charging part of the 2 general formula , by placing it at a position equidistant from each vertex within a polygon (usually a quadrilateral), which increases the charging function of the dust,
In the two-stage electrostatic multiplication device, dust collection electrodes having a uniform rod-like cross section are arranged in a direction perpendicular to the gas flow so as to form a polygon, and the polygon formed by the dust collection electrodes is A two-stage electrostatic precipitator characterized in that it has a charging part formed by disposing discharge electrodes at positions approximately equally spaced from each vertex. Also the second
The figure shows an example of a combination of a charging section and a dust collection section.

In FIG. 1(a), the dust collection electrode 2a has a round or equivalent uniform cross section in the direction perpendicular to the gas flow G, and the discharge electrode 1a has a polygonal shape formed by the center of the dust collection electrode 2a. is placed at a point equidistant from each vertex of the polygon.

Although FIG. 1(a) shows an example of a combination of polygons in which the configuration is a regular quadrilateral, and FIG. 1(b) shows an example of an equilateral triangle, these combinations are not necessarily limited to regular quadrilaterals or equilateral triangles. For example, polygons such as rectangles or isosceles triangles may satisfy the condition that there are points equidistant from each vertex, but polygons such as equilateral quadrilaterals and equilateral triangles are preferable. is desirable.

In addition, the example in FIG. 1 shows an example in which the number of polygons in the gas flow direction indicated by G is two per charging part, but of course there are two polygons per charging part.
The structure is not limited to the above, and may be a single structure or a structure of three or more. In addition.

5 in Figure 1 is a DC voltage generator, ? This is a coupling capacitor for applying 8 pulse voltage on the Fi pulse generator.

As an example of the configuration, in the conventional two-type EP, as shown in Fig. 3, the charging part Y and the dust collecting part Z are integrated, and each of them is connected in the gas flow direction G. However, in the present invention, as shown in FIG. 2, [single number of charging section 3 + dust collection section 4] (only one pair combination of 3 and 4 in FIG. 2(a)) or as shown in FIG. As shown in (a), [multiple combinations of charging section 3 + dust collection section 4] or as shown in Fig. 2 (b), single or multiple combinations of [charging section 3 + dust collection section 4 + dust collection section 4] It can also be applied in various combinations.

Next, the operation of the electrostatic precipitator of the present invention having the above electrode structure will be explained.

With the arrangement and combination of electrodes shown in the present invention, the current density distribution characteristics of the dust collecting electrode 2a or 2b are as shown in FIG. Flow-tight dust I/-2 is obtained. These have been confirmed by the applicant as a result of theoretical calculations and experimental measurements.

On the other hand, the electric field strength distribution t at the shortest point (as shown in FIG. In the conventional electrode configurations shown in , (C) and (d), a portion Pb with high electric field strength exists only in the vicinity of the discharge electrode ib, but in the electrode configurations shown in the present invention shown in (a) and (b), In this case, a portion Pa having a high electric field strength can be formed not only near the discharge electrode 1a but also near the dust collecting electrode 2a, and this has also been confirmed from the results of theoretical calculations and experimental measurements.

As mentioned above, with the electrode configuration shown in the present invention, a uniform current density can be obtained near the dust collecting pole, and a region with high electric field strength can be created both near the discharge electrode and near the dust collecting pole. However, the second explanation will be made regarding the improvement in the function of the general formula BP as a charging unit, that is, the function of imparting charge to dust.

First, the dust taken in by BP is mainly charged by electric field charging, that is, unipolar ions created by corona discharge are driven by the electric field and collide with the particle surface. In this case, the amount of charge q of the dust is as follows. Expressed by the formula.

1/7-・・・・・・(1) q=qoo l+τ/l Here, q~ (saturation charge amount) is proportional to the electric field strength E of the charged part, and τ (charging time constant) is the electric field strength E Because it is proportional to and inversely proportional to the current density i.

In order to increase the amount of charge, it is better to increase the electric field strength E as much as possible, and to increase the amount of charge in a further short time, it is necessary to increase the current density.

As shown in Figure 4, in the present invention, the current density is more uniform than that of conventional electrodes, which has the effect of uniformly charging the dust, as well as increasing the operating electric field strength for high-resistance dust. is obtained, and as a result, the charging function is improved.

In other words, in the case of high-resistance dust, the operating voltage is determined by the point at which reverse ionization begins, and the point at which reverse ionization begins is the product of the current flowing through the dust layer, d, and the dust resistance, Pd, where Pd is the breakdown of the dust layer. Although it is determined by the time when the withstand voltage Edc is exceeded, the fact that the current density passing through the surface of the dust collection electrode is uniform has the effect that operation can be maintained without causing reverse ionization even under high current/voltage conditions. As a result, the charging function can be improved.

Furthermore, as shown in Fig. 5, in the present invention, a region where a high electric field strength can be obtained on the dust collection electrode side [the part indicated by Pa in Fig. 5(a)] is created. is limited to the vicinity of the discharge electrode, but the area that gives the dust a high charge has expanded, so most of the dust carried by the gas flow G is concentrated in the area where the electric field is high, that is, the area where the dust is given a high charge. This improves the charging function.

As shown in FIGS. 1(a) and 1(b), even when a DC high voltage is supplied from the DC high voltage generator 5 to the electrode configuration according to the present invention, the effect is greater than that of the conventional electrode configuration. However, tests have confirmed that the effect is even more pronounced when a pulsed high voltage is applied by the pulsed voltage generator 7 coupled via the coupling capacitor 6.

The electrode configuration of the present invention also has a dust collection function, and the dust collection efficiency per surface area of the dust collection electrode is higher than that of conventional electrode configurations, so it is not a two-stage type. Although it can be used as a normal one-stage EP, if the pipe is arranged in a rectangular configuration between the discharge electrode and the dust collection electrode for general industrial use, the collection per capacity is the same as the conventional electrode. To equalize the dust area, increase the pipe diameter.

Alternatively, considerations such as increasing the number of pipes in the gas flow direction are required, which impairs the above-mentioned advantages and is therefore not practical. Therefore, the present invention is particularly effective for charging portions of the two general formula BP.

[Brief explanation of the drawing]

FIG. 1 is an explanatory view of the electrode configuration showing the planar arrangement of the dust collection electrode and discharge electrode of the present invention, where (a) shows a regular square arrangement and (b) shows an equilateral triangular arrangement. FIG. 2 is an explanatory diagram of an example of a combination of a charging section and a dust collection section of the present invention, (a) is an example in which two sets of charging section and dust collection section are alternately combined, and (b) is an example in which a plurality of charging sections and a dust collection section are combined. An example of a combination of dust collection parts is shown below. Figure 3 is an explanatory diagram of the electrode configuration of a conventional two-stage electrostatic precipitator, and Figure 4 is a current density distribution characteristic diagram of the dust collecting electrode.
) is a characteristic diagram of the present invention, (b) is a conventional characteristic diagram, and Fig. 5 is an electric field strength distribution characteristic diagram. The electric field intensity distribution curve is shown, and (C) shows the conventional high electric field intensity region, and (d) shows the electric field intensity distribution curve. la, lb: discharge electrode 1 2 a, 2 b: dust collection electrode. 3: Charging section, 4: Dust collecting section, G: Gas flow direction. () Figure 1 (Q) (a) Figure 2 Blind. Procedural amendment (voluntary) June 26, 1980 Commissioner of the Japan Patent Office Gakudon Shiga 1 Indication of the case 1988 Patent application No. 066286 2 Title of the invention Two-stage electrostatic precipitator 5 Person making the amendment Relationship to the incident Patent applicant address 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Name (
620) Mitsubishi Heavy Industries, Ltd. 4th Representative (1) The last line of page 1 of the middle cylinder of the specification, "Dust layer" is corrected to "Dust layer." (2) Lines 12 to 14 of page 2 of the specification middle cylinder [・
...PdX1d≧Edc, and dust resistance Pd
...If the current jd flowing through the dust layer is small, the dust layer..."
d≧Edc, dust resistance fd... If the current 1d flowing through the dust layer is small, the dust layer...
” he corrected. (3) In the 13th line of page 3 of the specification, the phrase "collection of materials" is corrected to "commercialization." (4) In the middle cylinder of the specification, page 6, line 9, “8” is replaced with “6”
I am corrected. (5th page 6th line of the specification, line 13 “...1a
``Charging part and collection'' is replaced with ``...1 A charging part consisting of a combination of a silk discharge electrode 1b and a dust collection electrode 2b, a discharge plate 1c that applies a high electric field, and a dust collection electrode 2b. "A collection made up of combinations" is corrected. (6) Page 9, line 16 of the specification [product 1d of dust resistance Pd, xpdJ] [product idX of dust resistance 5d]
I am corrected, "Yu d." (7) Figure 2 (bl is corrected as shown in the attached sheet. (8) Figure 3 is corrected as shown in the attached sheet. (7) No. 20 No. 30

Claims (1)

[Claims] In a two-stage electrostatic precipitator consisting of a charging part and a dust collection part, dust collection electrodes having a rod-like uniform cross section are arranged perpendicular to the gas flow so as to form a polygon, and the dust collection part 2, characterized in that it has a charging section formed by disposing discharge electrodes at positions approximately equally spaced from each vertex of a polygon formed by the electrodes.
Staged electrostatic precipitator.