JPH037411B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an exhaust gas cleaning device and an exhaust gas cleaning method using this device. Conventionally, perforated plate towers have been widely used to treat exhaust gas containing harmful substances because of their relatively simple structure and stable gas cleaning performance. In chemical engineering terms, a perforated plate column is a device that aims to increase the gas-liquid contact effect by dispersing gas as bubbles in the cleaning liquid through fine pores.The larger the pore size, the larger the bubble diameter, which increases the gas-liquid contact effect. It inhibits the increase in area. Furthermore, when the porosity exceeds a certain limit, the life period (existence period) of the bubbles becomes short due to destruction of the liquid layer, and the gas-liquid contact property decreases. For this reason, this type of perforated plate generally has a hole diameter of 3 to 6.
mm, with a porosity in the range of 5 to 15%. As a related technology, in the dust removal device of JP-A No. 51-105680, the cleaning liquid supplied to the top of the tower flows down from the upper stage through a downcomer (overflow pipe) to the lower stage during operation, and only gas is produced in the hole. The cleaning liquid flows upward from the bottom and contacts the air and liquid above the holes, so that the cleaning liquid does not flow down through the holes. This dust removal equipment is often used to treat exhaust gas from etching and other manufacturing processes in semiconductor factories, but this exhaust gas contains a large amount of dust such as silica SiO ₂ in addition to hydrogen chloride and other toxic gases. Not only is there a lot of dust, but because groundwater is often used as a cleaning solution, the growth of silica crystals and the growth of large amounts of algae are often observed, and the pores of the perforated plate become clogged during operation. As a countermeasure against this blockage, a spray nozzle was placed under each perforated plate facing upward to constantly clean the bottom surface of the perforated plate. However, although it was possible to prevent adhesion to the back side of the perforated plate, it was possible to avoid adhesion to the top surface of the perforated plate. It was not effective against blockages caused by silica and algae deposits. Also,
The pressure loss in a perforated plate tower is controlled by the liquid layer on the perforated plate and the resistance when gas passes through the pores, so when the wind speed inside the tower exceeds a certain limit, the pressure loss increases rapidly, causing flattening. If the hole diameter and porosity are small, such as the above-mentioned perforated plate, the wind speed inside the tower must be suppressed to 1 to 2 m/sec due to power loss and performance, and therefore the required cross-sectional area of the tower is also large. Therefore, a large installation space was required. The present invention was completed in view of the above-mentioned problems, and has the following features: does not cause clogging of the holes in the perforated plate of a perforated plate tower type exhaust gas cleaning device, has low power loss at high wind speeds in the tower, and has a high dust removal effect. The objective is to provide an exhaust gas cleaning device that requires less installation space and an exhaust gas cleaning method using the device. Hereinafter, the configuration of the present invention will be explained with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the exhaust gas cleaning device of the present invention, and FIG. 2 is a partially cutaway plan view showing an example of an orifice plate used in the device. In the drawings, reference numeral 1 denotes a blower by which exhaust gas is forced and dispersed into the tower through a duct 2. It is desirable that the outlet of this duct faces downward so that the gas can be easily dispersed within the column. Reference numeral 3 denotes an orifice plate having a large number of cross holes 4, which are arranged in at least two stages between the upper and lower parts of the tower. Further, 5 is a pipe that allows the cleaning liquid pumped by the pump 6 to flow down onto the orifice plate in the column.
The same pipe has cleaning liquid inlets 7 at appropriate intervals.
is provided. Reference numeral 8 denotes a mist catchy for removing the mist that has passed through the cross hole of the orifice plate, and is disposed above the pipe. In addition, 9 is an exhaust hole for arranging purified gas from which mist has been removed, 10 is a gas outlet, and 1
Reference numeral 1 denotes a pipe to which a tank partition plate 12 is attached, from which the cleaning liquid is recirculated via a tank 13. Here, the hole area of each cross hole is 150
~700mm, open area ratio for orifice plate is 20~40
%, and the step spacing of the orifice plate is
150 to 300 mm, and these limitations are due to the following reasons. First of all, the reason why the hole shape of the orifice plate is made cross-shaped instead of round is that the gas flow is not rectified like a round hole, but the turbulent gas flow due to the increase in the number of Ray nozzles based on the shape. The longer length increases the gas-liquid contact area, making gas-liquid contact extremely effective, and the turbulence of liquid gas becomes more pronounced compared to round holes, so the area around the hole is strongly washed away, reducing the adhesion of dust. This is because it is possible to prevent the growth of reaction products and to maintain operation without clogging the pores. Next, the reason why the hole area per cross hole is set to 150 to 700 ^mm2 is that if the hole area is less than ^{150 mm2} , the flow of liquid will decrease, causing flattening, and stable operation will not be possible. If so, the liquid will not be retained on the orifice plate and the gas-liquid contact function will not be maintained. In addition, the opening rate for the orifice plate is 20 to 40%.
The reason for this is that 1 part of the cleaning liquid is flowed for 1 ^m2 of gas, the effective gas velocity is 2.5 m/sec, and the hole area is 500 mm2 ^.
When operating under these conditions, if the open area ratio is less than 20%, the pressure loss will increase significantly, and if it is more than 40%, it will not be possible to hold the cleaning liquid on the orifice plate. Furthermore, the reason why the orifice plate step interval is set to 150 to 300 mm is that the effective gas velocity is 2.5 m/sec, 1 part cleaning solution is poured for 1 ^m3 of gas, the pore area is 30%, and the hole area is 500 ^m2 . If the stage interval is set to 150 mm or less, the pressure loss will increase significantly.
This is because if it is 300 mm or more, the cleaning efficiency will be greatly reduced, which is not practical. By the way, in the present invention, the effective gas velocity means that when an orifice plate with a cross hole is disposed in the device, a ring-shaped receiver is attached as an auxiliary plate to support the orifice plate inside the main body, so the gas velocity in this ring-shaped receiver part is refers to the gas velocity that passes through the entire area of the orifice plate inside the ring without passing through, and this effective gas velocity affects pressure loss and cleaning efficiency. The exhaust gas cleaning device configured as described above feeds exhaust gas from the upper part of the tower body at an effective gas velocity of 2 to 3 m/sec, and the rate of exhaust gas is 0.5 to 1 m2 per ^m2 of exhaust gas from the upper part of the tower body.
The gas is supplied at a ratio of 1.5%, and the gas is brought into gas-liquid contact on the orifice plate to clean the exhaust gas. Here, the reason why the exhaust gas is introduced at an effective gas velocity of 2 to 3 m/sec is that if 1 part cleaning liquid is poured for 1 m ² of gas, the pore area is 500 mm ² , and the porosity is 30%,
If the effective gas velocity is less than 2 m/sec, the liquid flow will drop significantly and the cleaning liquid cannot be retained on the orifice plate, resulting in poor cleaning efficiency. If the effective gas velocity is more than 3 m/sec, the liquid will rise along with it, causing flattening and a large amount of cleaning liquid will remain on the orifice plate. This is because pressure loss increases. Also, the reason why cleaning liquid is supplied at a ratio of 0.5 to 1.5 to 1 m ² of exhaust gas is that if it is less than 0.5, the absolute amount of cleaning liquid retained on the orifice plate will be small and gas-liquid contact cannot be expected, and if it is more than 1.5, absolute retention will occur. This is because if the amount becomes too large, a phenomenon occurs in which the amount of liquid remaining on the orifice plate increases rather than flowing down. When the exhaust gas cleaning device of the present invention is used under specified conditions, the cleaning liquid supplied from the upper part of the column body is held on the surface of the orifice plate, but as it flows down through the cross hole, it is sent from the lower part of the column body. When the cleaning liquid passes through the cross hole of the orifice plate, it comes into contact with the exhaust gas, which becomes a super turbulent flow of around 10 m/sec, and is dispersed by violent turbulence, a principle similar to that of a ventilate scrubber. A portion of the dispersed cleaning liquid rises on the orifice plate along with the rising airflow of exhaust gas, and intense gas-liquid contact occurs in a mixed flow state. The other part falls from around the hole to the lower stage as droplets. In this case, fine dust contained in the exhaust gas, such as SiO ₂
Even if such substances are mixed together, they will be captured by the cleaning liquid before coagulating, flow down together with the cleaning liquid, and be accumulated at the bottom of the tower. Next, examples of the present invention and comparative examples will be described. Example The outer diameter of the tower body of the exhaust gas cleaning device is φ600 round, and the orifice plate with a cross hole has a porosity of 30%.
The hole area (per hole) is 500 mm, the orifice plate is arranged with a step interval of 200 mm, and the gas type listed in the table below is 1.
m ² , apply the same type of cleaning solution listed in the table below.
When the gas was supplied into the column at a ratio of 1.0 and the gas was allowed to flow at an effective gas velocity of 2.5 m/sec, the results shown in the table below were obtained.

[Table] As is clear from the above results, HCl and other harmful gases are very efficiently cleaned and removed after treatment (outlet concentration) compared to before treatment (inlet concentration). It can be seen that the effect is large. Comparative Example 1 The exhaust gas cleaning device of the present invention was made into the type shown in Fig. 1 (the outer diameter of the tower body is 600 mm), with a porosity of 20% and a pore area (per hole) of 314 mm ² Orifice plate with cross holes drilled in two stages (stage interval)
200mm) with an inlet concentration of 50ppm.
of gas (Cl ₂ gas or SO ₂ gas) is fed into the tower at an effective gas velocity of 2 m/sec, and 5% of the cleaning liquid is
Gas removal efficiency was investigated using NaOH at a cleaning liquid/gas ratio of 1.0/m ² . In addition, in place of the orifice plate with cross holes in the above-mentioned device, a perforated plate with round holes (diameter 20 mm) with the same porosity and the same hole area was used to evaluate the gas removal efficiency under the same conditions. Examined. The results are shown in the table below.

[Table] From the above results, it can be seen that when an orifice plate with cross holes is used in the apparatus of the present invention, gas removal efficiency is superior to when a perforated plate with round holes is used. Comparative Example 2 In the device of the present invention, the pore opening rate was 30%, the pore area (hole 1
Using two stages of 500 mm ² cross-hole orifice plates,
A cleaning solution of 1 was flowed per 1 m ² of gas, and changes in pressure loss across two stages of orifice plates were measured when only the effective gas velocity was varied in the range of 0 to 4 m/sec. For comparison, in the above device, instead of the cross-hole orifice plate, a hole area of 14% and a hole area of 7 m ² (hole diameter of 3
Changes in pressure loss were measured under the same conditions using a two-stage round perforated plate with a conventional overflow tube of 1.5 mm). These measurement results are graphed in FIG. In the figure, A shows changes in pressure loss when a cross-hole orifice plate is used, and B shows changes in pressure loss when a conventional perforated plate is used. As is clear from these results, the device of the present invention using a cross-hole orifice plate can operate with lower pressure loss at high wind speeds than the device using a conventional perforated plate, which means that it can be operated more quickly and efficiently. It is clear that the exhaust gas can be cleaned and removed. As described above, according to the exhaust gas cleaning apparatus and exhaust gas cleaning method of the present invention, the cleaning liquid supplied into the apparatus from the upper part of the tower naturally flows down to the lower part through the cross hole provided in the orifice plate arranged horizontally in the tower. Because of this structure, there is no need for a downcomer (overflow pipe) as in conventional devices of this type, and the structure is simple, which has great advantages in terms of manufacturing. In addition, since the area around the cross hole provided in the orifice plate is constantly washed away with cleaning liquid, it is possible to prevent dust in the gas (such as SiO ₂ ) from adhering to the area around the hole and the growth of reaction products. There will be no blockage and no hindrance to the operation of the device. Furthermore, as is clear from Comparative Example 1, when a cross-hole orifice plate is used, the harmful gas removal performance is higher than when a round-hole perforated plate is used. Furthermore, as is clear from Comparative Example 2, the pressure loss is small even when the effective gas velocity into the column is high, so a stable and high exhaust gas cleaning and removal effect can be obtained with low power consumption. It has advantages such as requiring less installation space.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of the exhaust gas cleaning device of the present invention, Fig. 2 is a partially cutaway plan view showing an example of an orifice plate used in the device, and Fig. 3 is a cross-sectional view showing an example of the exhaust gas cleaning device of the present invention. It is a graph showing changes in pressure loss. 1...Blower, 2...Duct, 3...Orifice plate, 4...Cross hole, 5...Pipe, 6...Pump, 7...Cleaning liquid inlet, 8...Mist catchy, 9...Exhaust hole , 10... gas outlet, 11...
... Pipe, 12 ... Tank partition plate, 13 ... Tank, A ... Shows the change in pressure loss in the column when two stages of cross-hole orifice plates are used. B... shows the change in pressure loss inside the column when two conventional perforated plates are used.

Claims (1)

[Claims] 1. A gas inlet and a cleaning liquid outlet are provided in the lower part of the column body, a gas outlet and a cleaning liquid inlet are provided in the upper part of the column body, and one inlet is provided between the upper part and the lower part. An exhaust gas cleaning device characterized in that two or more orifice plates having cross-shaped holes with a perforation area of 150 to 700 mm ² and an aperture ratio of 20 to 40% are arranged at a stage interval of 150 to 300 mm. 2 A gas inlet and a cleaning liquid outlet are provided at the bottom of the column body, a gas outlet and a cleaning liquid inlet are provided at the top of the column body, and a hole area of 150 pores per piece is provided between the upper and lower parts. Using an exhaust gas cleaning device with two or more stages of orifice plates with cross holes with a pore size of ~700 ^mm2 and a porosity of 20 to 40%, with a stage interval of 150 to 300 mm, the effective gas velocity is 2 to 3 m/sec from the bottom of the tower body. Inject exhaust gas with
An exhaust gas cleaning device characterized in that a cleaning liquid is supplied from the upper part of the tower body at a ratio of 0.5 to 1.5 to 1 m ³ of exhaust gas, and brought into gas-liquid contact on the orifice plate.