JPH0238263B2 - DENKISHUJINSOCHI - Google Patents

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a dust collecting plate which is formed by arranging several unit dust collecting electrode plates formed by bending both longitudinal ends of the electrode plates into a mountain shape. This invention relates to an electrostatic precipitator which improves dust collection efficiency and reduces manufacturing costs by regularly arranging discharge electrodes with needles in parallel.

(Prior Art) As a conventional electrostatic precipitator (hereinafter referred to as EP), one in which a discharge electrode made of a discharge wire is arranged between dust collecting electrodes made of a flat plate is mainly used. In such an EP, the discharge wire is generally suspended from the upper frame and suspended by a weight within the steady rest frame at the lower part. Various designs have been made for the cross-sectional shape of the discharge wire, such as circular, square, and star-shaped. The characteristics of the discharge wire are that the thinner it is or the sharper its corners, the better the corona discharge is, and the thicker it is, the less the discharge current decreases and the higher the corona voltage.

Furthermore, if the cross section of the discharge wire is made smaller, it becomes more likely to break due to corrosion, sparks, etc., and the weight must also be made lighter. The discharge phenomenon of the discharge line includes a trichel pulse, and is performed by a bright spot that constantly moves up and down. Therefore, the discharge wire is susceptible to vibration, and once vibration occurs, it is often added to the wrapping impact and causes spark flash. During spark flash, the dust collection effect is zero. If spark flash occurs frequently, the discharge wire will wear out and break, and if this causes a shoot between different poles, it is necessary to shut down the equipment, and on the other hand, the voltage must be lowered to prevent spark flash from occurring. If the unit is operated with a low temperature, the dust collection rate will decrease.

In addition, various types of dust collection electrodes have been developed, such as flat plate type, pipe type (rod curtain), and corrugated plate.The flat plate type has various stiffeners and stiffeners to prevent bending and set the position.
Reinforcement with ribs, etc. is required, making it heavier and more expensive. Similarly, there is a problem in that the manufacturing cost of corrugated plates and other products also increases.

In addition, since the discharge electrode is suspended vertically using gravity, if the lower part changes due to the distortion of the building or the sinking of the foundation, the verticality will be lost and the lower part will become misaligned, causing a spark flash. Since it is easy to use, there is a problem that it is necessary to inspect and repair each time.

In order to solve these problems, the present applicant specified the shape of the dust collecting electrode plate as previously disclosed in Publication of Utility Model Publication No. 60-31790, and installed a discharge electrode with a needle between the opposing dust collecting electrodes. The EP used was proposed.

(Problems to be Solved by the Invention) However, although such EP has achieved a certain degree of improvement in dust collection efficiency, two types of discharge electrodes are used, and the dust collection electrode has a complicated shape and requires time and effort to process. It was desired to improve the dust collection efficiency, make the device more compact, and reduce the cost.

(Means for Solving the Problems) Under these current circumstances, the inventor further investigated the structure of the discharge electrode and the dust collection electrode, and determined that the flat plate type dust collection electrode plate of the EP can be used regardless of the gas amount. Considering that it can be supplied at the lowest price, it is possible to use a flat plate type EP to (a) reduce the size of the entire device; and (b) widen the pitch between the discharge electrodes and dust collection electrodes. (c) Since the price of electrical equipment is determined by voltage, it is possible to reduce the price by reducing the number of parts at both poles. (d) Measure the gas flow velocity in the device to equalize the residence time of all gases throughout the device, (e) Control parts. (f) As a result of conducting various studies on how to prevent or reduce the re-entrainment phenomenon due to low resistance of dust in the device or the reverse ionization phenomenon due to high resistance, The present invention has now been achieved.

In the electrostatic precipitator of the present invention, several unit dust collecting electrode plates each formed by bending both longitudinal ends of the electrode plate into a chevron shape are alternately inverted, and the openings of the chevron portions of the end portions are arranged to face each other. This device is characterized in that dust collecting electrodes made of the above are regularly arranged side by side, and a needle-equipped discharge electrode is arranged in the center between the flat parts of opposing unit dust collecting electrode plates.

The invention will now be explained with reference to the drawings.

FIG. 1 is a horizontal cross-sectional view of a part of a dust collecting section of an electrostatic precipitator according to an example of the present invention. The unit dust collection plate 1 is
In the case of a dry type electrostatic precipitator, usually 1.0 to 3.2 mm, preferably 1.2 to 2.3 mm steel plate or corrosion-resistant steel plate, in the case of a wet type electrostatic precipitator, a 2 to 5 mm non-inductive steel plate,
Using an FRP or PVC plate, as shown in Figure 3, both ends of the electrode plate are usually bent four times in a press operation to form a mountain shape, with a flat part 1-1 and a first bent part 1-
2. It is formed as a unit dust collecting plate 1 consisting of the second bent portion 1-3. At this time, the bending angle θ ₁ is 45°, and θ ₂ is
Preferably, the angle is 90°.

As shown in FIG. 1, several such unit dust collecting plates 1 are alternately inverted so that the openings of the chevron-shaped portions at the ends of adjacent electrode plates 1, 1 face each other to form a pocket portion 2. They are arranged and fixed to the upper and lower frames to form dust collection poles. A necessary number of these dust collecting electrodes are regularly arranged side by side at precise intervals (that is, the distance between the flat parts of opposing unit dust collecting electrode plates is hereinafter referred to as pitch) P to form a dust collecting chamber. The pitch P is preferably 300 mm or more.

Next, the dust collection chamber has an opposing unit dust collection electrode plate 1.
At the center between the flat parts 1-1 and 1-1, P=300
~450mm, install the discharge rod 3 diagonally to the flat part.
A discharge electrode with intersecting needles 4 attached to the intersecting needles is suspended and arranged to constitute a dust collecting section. An example of such a discharge electrode with crossed needles is shown in FIGS. 2a and 2b. The discharge rod 3 is usually a steel round bar with a diameter of 17 to 34 mm, and the discharge needle 4 is a steel wire with a diameter of 2 to 5 mm. Nao wet type EP
In this case, it goes without saying that materials should be used with particular consideration given to corrosion resistance. The discharge electrode is made by attaching a discharge needle 4 with a sharp tip to a discharge rod 3 by a method such as welding. One method for this is to sharpen both ends of a thin round wire that forms the needle on the discharge rod 3 and weld it through a hole provided in the discharge rod 3, as shown in Figures 2a and b. , is preferable because it is the simplest and cheapest way to produce a discharge electrode. The mounting angle θ ₃ of the discharge needle 4 shown in FIG. 2a is preferably 45° with respect to the flat part of the unit dust collecting electrode plate.

Next, in the case of a wide pitch of P=450 mm or more, preferably 450 to 1000 mm, a discharge electrode with needles is arranged only in the direction perpendicular to the flat part to form a dust collecting section.

Figure 6 shows the dust collection section of a widely spaced EP.
The needles of the discharge electrode with crossed needles are indicated by broken lines. The difference (l 7 - l 6 ) between the gap l ₆ between the needle tip and the flat surface 1-1 of the dust collection pole and the distance l ₇ between the surface of the discharge rod 3 and the flat surface (l ₇ - _{l 6} ) shown by the broken line in FIG. 6 increases the pitch. As the ratio to _l7 decreases, the difference between the corona voltage and the spark voltage decreases. Therefore, if the needle tip is directed perpendicularly to the flat surface, the distance _l5 between the needle tip and the flat surface 1-1 becomes small, the corona voltage decreases, and the spark voltage remains unchanged. In addition, in the case of wide-spaced pitches, the electric lines of force from the tip of the needle spread out and become wider when they reach the dust collecting pole surface, and the width also becomes wider due to the high charging voltage, which causes the needles to intersect. A sufficient discharge current can be passed by providing one row perpendicularly to a flat surface.

In addition, the flat part 1-1 of the unit dust collection electrode plate 1 shown in FIG.
The length of is l ₁ = 400 to 550 when P = 300 to 450 mm.
It is preferable that mm, l ₂ =500 to 800 mm. Also P
= 450-1000mm, l ₁ = 480-660mm, l ₂ = 630
It is preferable to take ~850 mm, and the length of the needle of the discharge electrode is l ₃ = 100 to 200 mm for both the needle intersecting the flat surface and the needle in the perpendicular direction, the distance between the needles l ₄
may be appropriately selected within the range of 100 to 300 mm.

In the EP of the present invention, pockets 2 are provided between adjacent unit dust collection plates, but (a) carbon black and other low resistance dust (1×10 ⁴ Ωcm (below), the dust that has been given a negative charge by the corona at the tip of the discharge needle and has moved to the surface of the dust collecting electrode loses its negative charge on the positive electrode surface, which is the dust collecting electrode, and becomes positively charged. It travels toward the load, which is the discharge electrode, but encounters negative ions, neutralizes the positive charge, and travels back and forth between the collecting electrode and the discharge electrode. During this time, as shown in FIG. 4, the gas gradually enters the pocket along with the gas flow. When the dust enters the pocket, as shown in FIG. 5, it is not affected by the electric lines of force and loses its charge, accumulates inside the pocket, and falls into the hopper due to hammering impact.

(b) In addition, if high-resistance dust is mixed in the dust in the inflowing gas, the high-resistance dust gains a negative charge by the discharge needle and moves, and even if it reaches the surface of the collecting electrode plate, Due to its high resistance, it is unable to neutralize the negative charges and stops on the dust collecting electrode plate (positively charged surface), but it peels off due to hammer impact and floats nearby. The gas then slides into the pocket along with the gas flow, accumulates, and falls into the hopper due to hammer impact.

(c) If all the dust has a high resistance of 5×10 ¹¹ Ωcm or more, it will undergo reverse ionization and the dust collection rate will be halved, but if the voltage is raised as much as possible and the current is passed, the dust collection rate will improve slightly.

As mentioned above, Pocket collects low-resistance dust and high-resistance dust during EP operation, such as carbon, etc., which are not fully combusted in heavy oil-fired or pulverized coal-fired boilers and are thought to float in the process gas. , to drive high-resistance dust into the pocket and collect it. For this reason, it is preferable to make the first bent part 1-2 of the unit dust collecting electrode plate 1 longer than the second bent part 1-3, P=300 mm.
In an example of EP, the length of the first bent part 1-2 is
70.5mm, and the length of the second bent part is 41.5mm.
Of course, it is not limited to this only.

Next, Figure 5 is a diagram showing the distribution state of the lines of electric force from the discharge needle in the dust collection chamber to the dust collection electrode plate. This is an imaginary diagram shown with dotted lines. In Figure 5, 2 of the octahedron
The area where the edges are removed becomes the gas passage. In addition, to find the dust collection rate of EP, which consists of parallel plate type dust collection electrodes and a simple discharge wire, and longitudinal flow (vertical gas flow) EP, which has a discharge wire placed in the center of a cylinder with the same pitch as the diameter, Correction value MP for the formula for calculating residence time = 3
It is. This means that if the diameter of the cylindrical cylinder is equal to the pitch of the flat plate type, the residence time of the gas to obtain the dust collection efficiency of the parallel plate type EP is three times that of the flat plate type EP. show.

Further, it is thought that the correction value is about twice as large as that of the dust collecting pole which can be assumed to be the octahedral cylinder of the present invention. If the part shown by the two-dot chain line is removed as a gas passage, the correction value is expected to be about 1.5 times.

Furthermore, due to the bending of the R and Q portions at the tip of 1-3 at the dust inlet of the pocket portion, and the edging effect at the corners, it is thought that the dust collection rate will be improved compared to when those portions are closed and made into flat portions. Therefore, the present invention reduces the EP correction value 1/3 of the conventional parallel plate discharge wire to 1/1.5.
However, it is considered to be sufficient. This fact alone shows that the same dust collection rate can be obtained with a parallel plate and a residence time that is half the EP of a simple discharge wire.

(Functions and Effects) Conventionally, it was thought that the entire electrostatic precipitator could be downsized by narrowing the pitch between the same poles, but this was incorrect. That is, the dust collection rate (η) of the electrostatic precipitator is expressed by Deutsch's equation below.

η=1-exp[-ωA/Q] However, Q=Gas amount (m ³ /sec) ω= Apparent moving speed of dust (m/sec) A= Dust collection area (m ² ) In the above equation, Q is Assuming that ω is constant, it is a function of the applied voltage and increases as the voltage increases.
In order to increase η (to bring it closer to 1), if the space of the entire device is constant, A is inversely proportional to the pitch, so if the pitch is increased, A decreases. Instead, if we increase ω, ω×A will not change. Alternatively, it is also possible to increase η. However, this is an EP
This is the case when the voltage is increased to the spark voltage.
As described above, in industrial EP, the overall size cannot be reduced by narrowing the pitch.

Currently, electrostatic precipitators generally use a pitch of about 250 mm between the collecting electrode plates, but recently wide-spaced EPs have been gradually adopted. The pitch of wide-spacing EP is 400~1000mm and the working voltage is 80~
Unless it is 120kV and has a large amount of gas, the power supply will be expensive and cannot be supplied at a low price. Furthermore, when the inlet dust content increases (10 g/Nm ³ or more), the discharge current decreases due to the space charge effect, and in some cases, almost no corona current flows, resulting in a decrease in efficiency. This phenomenon is very effectively eliminated by the cross-needle discharge electrode in the EP of the present invention.

The EP of the present invention uses flat plate type dust collecting electrodes with chevron-shaped bent portions at both ends as unit dust collecting electrodes, and uses crossed discharge electrodes as discharge electrodes, as described above, so that the corona starting voltage can be reduced. (hereinafter referred to as corona voltage) is extremely low, and the spark starting voltage (hereinafter referred to as spark voltage) is extremely high. For example, when P = 300mm, the actual pitch is the distortion of the electrode plate,
Considering that it is about 3mm including the core deviation, it is about 297mm,
The corona voltage is regulated by a gap (distance between the needle and the flat part of the dust collector plate) of approximately 9.9cm, so
29kVDC (hereinafter abbreviated as DC) (When gas is passed through, it increases due to space charge, but for comparison, the gas is air) Also, the spark voltage is determined by the distance 13.15 between the outer surface of the discharge rod and the flat part of the dust collector plate. cm and therefore the spark voltage is 66kV. Since the difference between corona voltage and spark voltage is large, stable and highly efficient operation is possible. In this way, P= of the present invention
In a 300mm EP, the corona voltage is generated at a relatively low voltage of 30kV or less, and if the rectifier's limiting voltage is 60kV, sparks will not occur no matter how high the voltage is. Spark voltage in this case means spark flash voltage. Since the tip of the needle of the discharge electrode is completely ionized by negative charges, no spark discharge occurs even when a high voltage is applied. The streamer may extend beyond the tip of the needle and cause a small spark, but the bridge in the streamer disappears in a few milliseconds, and after a few seconds, the streamer extends again and repeats the bridging, and the voltage between the electrodes is maintained. Therefore, the dust collection effect is not affected.

Further, even if the gap between the tip of the needle and the flat surface of the dust collecting electrode plate becomes narrow due to installation errors or thermal distortion, for example, due to accumulation of dust, spark flash is unlikely to occur. In this way, stable operation can be achieved even if dust coating occurs.

In the EP of the present invention, as described above, a flat type dust collecting electrode having chevron-shaped bent portions at both ends is used as a unit dust collecting electrode, and a discharge electrode with crossed needles is used as a discharge electrode. By making the dust electrodes widely spaced, it is possible to process even gases with a high dust content. Compared to the conventional EP with P = 250mm, the normal loading voltage is lower and the corona current flows slightly more, so in order to obtain the same dust collection rate.
The entire EP can be made smaller by about 30%, and if it can be mass-produced, it can be manufactured at a cost of more than 50%. Because it is bent, the gas resistance in the gas flow direction is smaller than that of simple fins or ribbed electrode plates.
Since there is no eddy current, the pressure loss is small compared to the protrusion size. (d) Even though the shapes of the unit collection electrode and discharge electrode have been specified, compared to the EP of Utility Model Application Publication No. 166849/1983,
It can be manufactured easily and inexpensively, and effects such as improved dust collection efficiency can be obtained.

[Brief explanation of drawings]

Fig. 1 is a horizontal sectional view of the dust collection part of an electrostatic precipitator equipped with a discharge electrode with crossed needles according to the present invention, Fig. 2a is a horizontal sectional view of the electrode with crossed needles, and Fig. 2b is a horizontal sectional view of the discharge electrode with crossed needles. A perspective view of the electrode, Figure 3 is a horizontal sectional view of the unit dust collection electrode plate,
Figure 4 is an explanatory diagram showing the state in which low-resistance dust and high-resistance dust slide into the pocket of the dust collection electrode, and Figure 5 shows the distribution of electric lines of force from the discharge needle in the dust collection electrode chamber to the dust collection electrode surface. FIG. 6 is a horizontal sectional view of one dust collection electrode chamber of the electrostatic precipitator according to the present invention, which is equipped with a needle-equipped discharge electrode perpendicular to the dust collection electrode surface. 1... Unit dust collection electrode plate, 1-1... Flat part, 1-
2...first bent part, 1-3...second bent part,
2...Pocket part, 3...Discharge rod, 4...Discharge needle.

Claims (1)

[Scope of Claims] 1. A number of unit dust collection electrode plates each formed by bending both longitudinal ends of the electrode plate into a chevron shape are arranged in such a way that they are alternately inverted and the openings of the chevrons at the ends face each other. What is claimed is: 1. An electrostatic precipitator characterized in that dust collecting electrodes are regularly arranged side by side, and a discharge electrode with a needle is arranged in the center between the flat parts of opposing unit dust collecting electrode plates. 2 The distance P between the flat parts of the opposing unit dust collection electrode plates is
2. The electrostatic precipitator according to claim 1, wherein the needle-equipped discharge electrode is a cross-needle discharge electrode having a needle diameter of 300 to 450 mm in a needle direction with respect to the flat portion. 3 The distance P between the flat parts of the opposing unit dust collection electrode plates is
2. The electrostatic precipitator according to claim 1, wherein the discharge electrode has a diameter of 450 mm or more and has a needle in a direction perpendicular to the flat portion.