JPH09192445A - Perforated plate type waste gas washer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust the orifice opening area by combining plural slots to form an orifice and making an upper plate movable from a position at which orifices of each plate are placed one upon another by a distance in which the slots intersecting the moving direction of the upper plate are closed. SOLUTION: A perforated plate 2 of each stage is divided in two each of which is divided in a plurality, and each of divided perforated plates 2 has structure in which an upper plate and a lower plate having orifices 7 in the same shape and the same arrangement are placed one upon another. The lower plate of the divided perforated plate 2 is fixed to a tower body 1 by a supporting ring 11 and beams 12, and the upper plate of the divided perforated plate 2 is driven by a driver 14 through a driving bar 13 and moved on the upper surface of the lower plate at the same time. A perforated plate type waste gas treating device for making good treatment corresponding to the generated quantity of waste gas is thus obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a perforated plate type exhaust gas treatment device having an adjustable orifice opening area.

[0002]

2. Description of the Related Art A perforated plate type exhaust gas treatment apparatus has a perforated plate horizontally installed in a tower for facilitating gas-liquid contact between exhaust gas rising in the tower and a cleaning liquid sprayed in the tower. The inflowing cleaning liquid is blown up by the exhaust gas passing through the orifice to form a spray fluidized bed of the cleaning liquid in the upper space of the perforated plate, and the exhaust gas and the cleaning liquid are vigorously brought into contact with each other to perform the cleaning process of the exhaust gas. Therefore, the structure of the device is simpler than that of an exhaust gas treatment device in which the space in the tower is filled with a gas-liquid contact filler, and uneven flow and clogging are less likely to occur.For example, exhaust gas from etching and other manufacturing processes in semiconductor factories. As described above, it is widely used as a cleaning process for exhaust gas containing a large amount of dust such as silica together with harmful gases such as hydrogen chloride.

The orifice of a perforated plate generally has a hole diameter of 3 to 6
A circular hole with a diameter of 5 to 15% is often used.
While sparging one liter before and after the cleaning liquid on the perforated plate relative to the exhaust gas 1 m ^3, performing exhaust gas cleaning by supplying exhaust gas column, among others wind speed 1 to 2 m / sec. As an orifice other than a circular hole, there is a cross-shaped orifice proposed by the applicant in Japanese Examined Patent Publication No. 3-7411, which widens the opening area of the orifice to prevent clogging by dust and reduces the peripheral length relative to the opening area. It is made longer to improve the gas-liquid contact effect.

In order to obtain a good exhaust gas cleaning effect with the above-mentioned perforated plate type exhaust gas cleaning device, it is necessary to maintain the processing air volume in the upper space of the perforated plate in the range where a spray fluidized bed of the cleaning liquid is formed. The amount of treated air in the optimum range is determined by the velocity of exhaust gas passing through the orifice. With the above-mentioned cross-shaped orifice, the optimum air velocity passing through the orifice is 7 to 10 m / sec. If the amount of treated air is too small, the above-mentioned air velocity passing through the orifice cannot be obtained, and if the amount of treated air is too large, the amount of cleaning liquid staying on the perforated plate increases and ventilation resistance increases.

The exhaust gas cleaning device is delivered with a design specification corresponding to the amount of exhaust gas generated at the time of 100% production by customers. However, some consumers start with a production volume of around 30-40%, 50-60% after 1-2 years, and then gradually increase production to 100% after 3-5 years. Therefore, in many cases, the amount of exhaust gas generated at the beginning of delivery does not reach the amount of treated air that gives good treatment results. Generally, a good treatment result is obtained when the treated air volume is about 80% of the designed value, but the treated effect is significantly reduced when the treated air volume is less than that. When the exhaust gas amount is 30 to 40% of the design value,
Since the wind velocity through the orifice that forms the droplet fluidized bed cannot be obtained in the upper space of the perforated plate, air is introduced into the exhaust gas or the treatment gas is introduced again to maintain the treatment air volume within a predetermined range. Therefore, the power consumption of the blower that supplies the exhaust gas is about the same as that at 100% production.

[0006]

Even if the amount of exhaust gas generated remains small, the baffle plate is installed on the perforated plate to reduce the number of orifices, or one of the superposed perforated plates is moved to reduce the number of orifices. By reducing the opening area, the wind velocity of exhaust gas passing through the orifice can be maintained in the optimum range. However, when more than half of the perforated plate is covered with the baffle plate, a non-uniform flow occurs in the exhaust gas and the cleaning liquid is not evenly distributed.

As a means for adjusting the opening area of the orifice, it is known to rotate or translate one of the two superposed porous plates to change the opening area of the overlapping holes (JP-A-48- No. 56569). However, when the upper plate of the perforated plate is rotationally moved with respect to the lower plate, since the moving distance of the upper plate is different near the center and the outer periphery of the perforated plate, in the fan-shaped orifice divided in the radial direction described in the publication. , The opening area of the orifice near the outer circumference changes greatly, whereas the opening area of the orifice near the center changes little,
The orifice opening area cannot be changed uniformly over the entire perforated plate.

On the other hand, when the upper plate of the perforated plate is moved in parallel with the lower plate, the opening area of the orifice can be uniformly changed over the entire perforated plate. However, in the case where the orifice is a circular hole, as the opening area is narrowed, the rate of change of the orifice opening area with respect to the moving distance of the upper plate increases, so that a difference occurs in the opening area of the orifice. In particular, in an exhaust gas treatment apparatus with a tower diameter of 2 to 3 m, since the perforated plates are divided into two to eight and installed in the tower, the upper plates of the divided perforated plates are moved exactly by the same distance. It is difficult, for example, as shown in FIG. 3, even if there is a difference of about 1 mm between the moving distances d and d ′ of the upper plate, a difference of several times occurs in the area of the orifice openings S and S ′. obtain. Therefore, when the opening areas of the orifices are reduced to about 30%, it is difficult to keep the opening areas of all the orifices uniform. If there is a large difference in the opening area of each orifice,
Since the exhaust gas preferentially passes through the orifice having a large opening area, it becomes impossible to form a uniform fluidized bed on the upper surface of the perforated plate.

According to the present invention, when the upper plate of the superposed porous plates is moved in parallel to adjust the orifice opening area, the rate of change of the opening area due to the difference in the upper plate moving distance is near the lower limit of the opening area adjusting range. It is an object of the present invention to provide a perforated plate type exhaust gas treatment apparatus capable of performing excellent treatment depending on the amount of exhaust gas generated by reducing the above.

[0010]

According to a first aspect of the present invention, there is provided a perforated plate type exhaust gas cleaning device, wherein each of the upper and lower orifices of the two perforated perforated plates has a plurality of elongated holes. It is characterized in that it is formed in combination and the upper plate is movable by a distance that closes at least one long hole intersecting the moving direction of the upper plate.

That is, when one of the long holes intersecting the moving direction of the upper plate is closed by the movement of the upper plate, the opening area of the remaining long holes does not largely change due to the difference in the moving distance of the upper plate. In this way, the above problem can be solved.

Such an orifice can be formed by two long holes that are orthogonal to each other as described in claim 2. For example, two elongated holes may be combined into a T shape, an L shape, and a cross shape, and the two elongated holes may be separated from each other.
Then, as described in claim 3, when the upper plate is moved along one elongated hole, the overlapping portion of the orifices of the upper plate and the lower plate has a length of the vertical hole along the moving direction of the upper plate. Decreased,
The width of the lateral hole orthogonal to the moving direction of the upper plate decreases, and the orifice opening area decreases in proportion to the moving distance of the upper plate.
After the upper plate moves by the width of the horizontal hole and the horizontal hole is closed, the opening area of the remaining vertical holes decreases in proportion to only the length of the vertical holes. The rate of area change becomes small. When the horizontal hole is closed, the opening area of the remaining vertical hole is determined by the width and length of each long hole. By setting this area near the lower limit of the opening area adjustment range, the uniformity of the opening area can be maintained even when the orifice opening area is narrowed.

Further, as described in claim 4, the orifice may be formed by two elongated holes intersecting at an arbitrary angle. In this case, if the upper plate is moved along the bisector of the two long holes, the movement of the upper plate reduces both the length and width of the two long holes. Although the relationship with and becomes slightly complicated, the gas-liquid contact effect is enhanced because the perimeter is always kept large with respect to the opening area. If one oblong hole (both holes when the two oblong holes have the same width) is closed by the movement of the upper plate, there will be two openings at the overlapping part of the oblong hole of the upper plate and the oblong hole of the lower plate. After separation, the area of each opening becomes constant regardless of the moving distance of the upper plate. The area of the two openings is determined by the width of each slot.

Therefore, as described in claim 5, when the upper plates of the divided perforated plates to be divided and installed in the tower are simultaneously moved, the upper plates of the divided perforated plates are moved to close one long hole. In this case, by setting the area of the remaining opening to an area close to the adjustment lower limit, the difference in the moving distance of each upper plate does not have a large effect on the opening area. Even if occurs, the opening area of each orifice can be maintained within the optimum range.

Further, since the residence time of the exhaust gas increases in inverse proportion to the treated air volume, as described in claim 6, among the perforated plates installed in a plurality of stages in the tower, at least the lowest perforated plate has an orifice. By applying a two-layer superposition structure in which the opening area of is adjustable, it becomes possible to perform favorable processing, and it becomes possible to perform exhaust gas cleaning processing while suppressing increases in equipment costs and power costs.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a vertical cross section of a perforated plate type exhaust gas cleaning apparatus of the present invention. The tower main body 1 of the exhaust gas cleaning device is cylindrical, and a porous plate 2 whose orifice opening area can be adjusted is provided in two stages inside the tower main body 1. The exhaust gas is introduced into the lower part of the tower by the blower 3 and rises in the tower. The cleaning liquid is sent from the circulation tank 4 to the spray pipe 6 in the upper part of the tower by the pump 5 and is sprayed on the upper surface of the perforated plate 2. When the exhaust gas passes through the orifice 7 of the porous plate 2, the cleaning liquid flowing into the orifice 7 is blown up to form a droplet fluidized bed in the upper space of the porous plate 2, where the exhaust gas and the cleaning liquid violently contact each other. Cleaning is performed. The exhaust gas that has been washed is separated into droplets by the mist catcher 8 and is discharged from the exhaust port 9 into the atmosphere.

As shown in FIG. 2, the perforated plate 2 in each stage is divided into a total of six pieces, three on the left and right, and each divided perforated plate is an upper plate 2a having orifices 7 of the same shape and the same arrangement. It has a superposed structure with the lower plate 2b, and each lower plate 2b of the divided perforated plate is fixed to the tower body 1 by the support ring 11 and the beam 12, and each upper plate 2a of the divided perforated plate is driven. Stick 1
It is driven by a driving device 14 connected via 3 and simultaneously moves on the upper surface of the lower plate 2b. Beam 1
2 prevents each upper plate 2a from being laterally displaced during movement,
The difference in the movement distance of each upper plate 2a can be corrected by finely adjusting the length of the drive rod 13 while confirming the formation state of the droplet fluidized bed from the sight window 15.

As shown in FIG. 4, each orifice 7 is a 100% opening in which a vertical hole 7a and a horizontal hole 7b having the same width and length are formed in a cross shape orthogonal to each other at the center, and the upper and lower orifices are overlapped with each other. The upper plate 2a is moved from the position along the vertical hole 7a of the orifice to adjust the opening area of the overlapping portion of the upper and lower orifices. Until the upper plate 2a moves by the width of the horizontal hole 7b and the horizontal hole 7b is closed, the length of the vertical hole 7a and the width of the horizontal hole 7b decrease, and the opening area of the orifice is proportional to the moving distance of the upper plate 2a. Is reduced. After the horizontal hole 7b is closed, the area of the remaining opening decreases in proportion only to the length of the vertical hole 7a, so that the rate of change in the area of the opening with respect to the moving distance of the upper plate 2a becomes small. At this time, since the vertical hole 7a still has a sufficient length, the difference in the moving distance of the upper plate 2a does not significantly affect the ratio of the opening area of each orifice.

Until the horizontal hole 7b is closed, the cleaning liquid and the exhaust gas preferentially pass through the vertical hole 7a having the full width rather than the narrowed horizontal hole 7b, and the cleaning liquid flowing into the orifice opening is not blown up. Since it is governed by the exhaust gas velocity passing through the vertical hole 7a, the difference in the moving distance of the upper plate 2a does not significantly affect the droplet fluidized bed forming conditions. Further, the lateral hole 7 having a narrow width is easily blocked by dust,
The blockage of b has little influence on the wind velocity of the exhaust gas passing through the orifice, and the dust clogging the lateral holes 7b can be washed away by moving the upper plate 2a while spraying the cleaning liquid.

Therefore, the vertical hole 7 when the horizontal hole 7b is closed
By setting the opening area S of a to an area close to the lower limit area of the orifice opening area adjustment range, it is possible to maintain the orifice opening area within the optimum range even if there is a difference in the moving distance of the upper plate 2a. The opening area S when the lateral hole 7b is closed is determined by the length and width of each long hole. As shown in FIG. 4, when the vertical holes 7a and the horizontal holes 7b both have the same length and width, when the horizontal holes 7b are closed, the opening area S of the remaining vertical holes 7a is reduced to 50% or less. By increasing the width or length of the vertical hole 7a with respect to the horizontal hole 7b, the opening area when the horizontal hole 7b is closed can be 50% or more.

Instead of moving the upper plate 2a along one elongated hole 7a of the orifice as described above, it is moved along the bisector of two intersecting elongated holes as shown in FIG. You can also In this case, since the length and width of the two elongated holes decrease due to the movement of the upper plate, the relationship between the moving distance of the upper plate and the orifice opening area becomes slightly complicated, but the peripheral length of the orifice opening is always constant. Since it can be kept large, a good gas-liquid contact effect can be maintained. When the two intersecting long holes are closed, the opening S where the long holes of the upper plate and the long holes of the lower plate overlap is separated into two places. The area of the opening S is constant regardless of the moving distance of the upper plate 7a. The areas of the two openings are determined by the widths of two intersecting slots.

The orifice may be formed by combining three or more long holes other than the above-mentioned two long holes.

By selecting the width or length of each slot forming the orifice and setting the opening area S when one slot is closed by the movement of the upper plate to an area close to the lower limit of aperture ratio adjustment. The influence of the difference in the moving distance of the upper plate can be reduced. Therefore, when simultaneously moving the upper plates of the divided perforated plates separately installed in the tower to adjust the orifice opening ratio, even if the lower limit of the opening ratio is about 30%, the opening area of each orifice is Good exhaust gas cleaning treatment can be performed by maintaining the optimum range.

When a plurality of perforated plates are installed in the tower, the removal rate is highest at the lowest perforated plate that comes into contact with the exhaust gas first, and is inversely proportional to the treated air volume of the exhaust gas. Since the residence time of the exhaust gas in the upper space of the perforated plate increases, only the lowermost perforated plate can have the orifice opening area adjustable. Just by forming the droplet fluidized bed in the upper space of the lowermost perforated plate, the contact time between the exhaust gas and the cleaning liquid can be taken sufficiently, and as will be described later, it is constant to form the droplet fluidized bed. Since there is a pressure loss of 1, the adjustment of the orifice opening area of only the lowermost perforated plate can suppress the increase in the equipment cost and the operation cost and can perform the favorable processing.

[0025]

[Example] In a cylindrical tower having an inner diameter of 650 mm, two open holes having a width of 10 mm and a length of 30 mm are orthogonal to each other at the center and have an opening area of 50.
^Two perforated plates with 0 mm ² cross-hole orifices and 30% aperture ratio are stacked and installed in two stages with a gap of 250 mm, and the upper plate of each perforated plate can be moved along the vertical hole of the orifice. Into the exhaust gas treatment device, the exhaust gas containing HCl was introduced from the bottom, and 1.2 to 1.3 per 1 m ^{3 of} exhaust gas from the top.
While spraying 1 liter of washing water, the operating rate (treatment air volume) of the apparatus was changed from 100% to 40%, and the pressure loss and the removal rate of HCl were examined. When the horizontal plate is closed by moving the upper plate of the perforated plate by 10 mm from the 100% opening position, the opening area of the orifice becomes 40%.

FIG. 6 shows the exhaust gas velocity in the tower m / sec and the pressure loss mmA.
Graph 1 shows the pressure change in one perforated plate having the above-mentioned orifice, and graph 2 shows pressure when the moving distance of the upper plate is 0 mm in two superposed perforated plates having the same orifice. The change graphs 3 to 7 show the pressure change every 2 mm from the upper plate moving distance of 2 mm to 10 mm.

As shown in each graph, the pressure loss increases in proportion to the exhaust gas velocity in the tower, but beyond the bending point of the graph, the amount of cleaning liquid retained on the perforated plate increases and the rate of increase in pressure loss. Grows larger.

In Graph 2, the gas passage portion of the orifice is lengthened by the thickness of the perforated plate, so that the ventilation resistance is increased as compared with Graph 1.

In graphs 3 to 7, since the gas passage portion is stepped due to the displacement of the perforated plate, the ventilation resistance increases and the bending point of the graph moves upward.

Table 1 shows that in the above exhaust gas treatment tower, the orifice opening area is adjusted so that the orifice passing wind velocity is 8 to 9 m /
The operation rate is maintained at sec and the operation rate is set to 100 to 40%.

As can be seen from Table 1, the removal rate of HCl was 93% or more, and good treatment results were obtained.

[0032]

[Table 1]

Table 2 shows the same apparatus as described above, with the orifice opening area being 100% and the operating rate being 100 to 40%. As can be seen from Table 2, a good treatment result is obtained up to an operating rate of 80%, but the removal efficiency is reduced at an operating rate of 60% or less.

[0034]

[Table 2]

The operating rates in Table 2 are 100%, 80%, 60%,
The pressure loss at 40% is point A in graph 1 of FIG.
Corresponds to B, C and D. Below the inflection point of each graph in FIG. 6, the range that can be formed by the droplet fluidized bed is a favorable orifice passing wind velocity. Therefore, regardless of the orifice opening area,
It can be seen that a pressure loss of about 50 to 90 mmAq is a good operating region.

The relationship between the moving distance of the upper plate and the opening area of the orifice is grasped, and the upper plate is moved by a predetermined distance according to the exhaust gas treatment air volume to confirm the formation of the droplet fluidized bed from the sight window. After adjusting the moving distance of the upper plate of each divided perforated plate, maintain the operating conditions according to the exhaust gas treatment air volume by driving the upper plate manually or automatically so that the pressure loss of the perforated plate is within a certain range. can do.

[0037]

EFFECTS OF THE INVENTION The orifice of a double-layered perforated plate consisting of a lower plate fixed to a tower and an upper plate that moves in parallel along the lower plate is formed by combining a plurality of long holes. To
By setting the opening area when moving from the position where the orifices of each plate overlap to each other by a distance that closes at least one long hole that intersects the moving direction of the upper plate, the opening area is set to an area close to the lower limit of the adjustment range. The difference in the moving distance of the upper plate does not significantly affect the opening area of each orifice. Therefore, when simultaneously moving the divided perforated plates separately installed in the tower to adjust the orifice opening area, the opening area of each orifice can always be maintained in the optimum range. Also,
Since the residence time of exhaust gas increases in inverse proportion to the amount of treated air, when multiple perforated plates are installed in the tower, by adopting a perforated plate with adjustable orifice opening area only in the lowermost stage, Exhaust gas cleaning processing can be performed with an orifice opening in the optimum range according to the processing amount.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of a perforated plate type exhaust gas cleaning apparatus of the present invention.

FIG. 2 is a horizontal sectional view of the device.

FIG. 3 shows how the opening area of a circular orifice changes.

FIG. 4 and

FIG. 5 shows how the opening area of the cross-shaped orifice changes.

FIG. 6 shows the relationship between the exhaust gas velocity in the tower and the pressure loss.

[Explanation of symbols]

 1 ... Tower body 2 ... Perforated plate 2a ... Upper plate 2b ... Lower plate 3 ... Blower 4 ... Cleaning liquid tank 5 ... Circulation pump 7 ... Orifice 7a ... Vertical hole 7b ... Horizontal hole 8 ... Mist catcher 9 ... Exhaust port 13 ... Drive rod 14 ... Drive device 15 ... Viewing window

Claims (6)

[Claims] 1. A perforated plate, which is installed horizontally in a tower and promotes gas-liquid contact between exhaust gas rising in the tower and washing water sprayed in the tower, having an orifice of the same shape and arrangement. In an exhaust gas cleaning device having a structure in which a plate and a lower plate are superposed on each other, the lower plate is fixed to a tower body, and the upper plate is moved in parallel along the lower plate to adjust the opening area of the orifice. Is formed by combining a plurality of long holes, and the upper plate can be moved from a position where the orifices of the respective plates overlap with each other by a distance at which at least one long hole intersecting the moving direction of the upper plate is closed. Characteristic perforated plate type exhaust gas cleaning device. 2. The perforated plate type exhaust gas cleaning apparatus according to claim 1, wherein the orifice is formed by two orthogonal long holes. 3. The perforated plate type exhaust gas cleaning device according to claim 2, wherein the upper plate is movable along one elongated hole of the orifice. 4. The orifice is formed by two long holes intersecting at an arbitrary angle, and the upper plate is movable along the bisector of the two long holes. 2. The porous plate type exhaust gas cleaning device according to 2. 5. The divided perforated plates dividedly installed in the tower have a structure in which an upper plate and a lower plate are superposed on each other, and the upper plate of each divided perforated plate can be moved simultaneously along the lower plate. The perforated plate type exhaust gas cleaning device according to claim 1. 6. The porous structure according to claim 1, wherein at least the lowermost porous plate of the porous plates installed in a plurality of stages in the tower has a two-layer superposition structure in which the opening area of the orifice can be adjusted. Plate type exhaust gas cleaning device.