JPS62728B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ozone removal method, and more particularly to an ozone removal method that maintains the activity of activated carbon and efficiently removes ozone.

Recently, ozone has been shown to be extremely effective in treating various types of industrial wastewater or foul-smelling gases, and research and development of ozone treatment equipment has been actively conducted, and large-scale equipment has come into practical use. Apart from this, radiation irradiation devices such as electron beam accelerators that generate large amounts of ozone have also come to be used industrially. However, as is well known, ozone has a unique unpleasant odor even at a concentration as low as 0.1 ppm, and has various toxicities to animals and plants, causing pollution. Therefore, it is necessary to completely remove excess waste ozone discharged from ozone treatment equipment or ozone discharged from ozone generating equipment such as radiation irradiation equipment.

In general, combustion methods, chemical absorption methods, activated carbon decomposition methods, and the like are known as methods for removing ozone contained in gas. The combustion method is a method in which ozone is decomposed by heat and converted into oxygen, and the absorption method is a method in which ozone is absorbed and removed using a substance that reacts with ozone as an absorbent. The activated carbon decomposition method is a method for removing ozone from the ozone-containing gas by bringing an ozone-containing gas into contact with activated carbon and catalytically decomposing the ozone with the activated carbon.

Among these ozone removal methods, the activated carbon decomposition method has features such as high ozone removal ability and the ability to process a large volume of gas with a relatively small device. In the activated carbon decomposition method, a method for bringing an ozone-containing gas into contact with activated carbon includes a method of passing the ozone-containing gas through an activated carbon fixed bed, an activated carbon moving bed, an activated carbon fluidized bed, or the like. Among these, the fixed bed method can be said to be an excellent method compared to other methods because there is no movement of activated carbon, so there is no wear and tear due to activated carbon wear, and the equipment is simple and operation management is easy. .

By the way, ozone removal using activated carbon is as follows:
In addition to the catalytic decomposition of ozone as shown in equation (1), this is carried out by reaction with activated carbon as shown in equations (2) and (3).

O ₃ →O ₂ (1) C+O ₃ →CO ₂ +1/2O ₂ (2) C+2O ₃ →CO ₂ +2O ₂ (3) In this way, in the activated carbon decomposition method, as ozone is removed, activated carbon converts into carbon dioxide gas. Therefore, consumption of activated carbon is unavoidable. However, since it is difficult to accurately detect the amount of activated carbon consumed, in ozone removal equipment using an activated carbon fixed tank, the lifespan of the ozone removal equipment is set at 6 months or 1 year, etc.
An excessive amount of activated carbon must be filled in advance, which inevitably increases the size of the device and increases pressure loss. In addition, with the removal of ozone by activated carbon, (2)
Since the combustion reaction of activated carbon shown in equation (3) occurs, the surface of the activated carbon is covered with ash, which is the combustion residue of activated carbon.
There is a drawback that the ozone removal ability of activated carbon gradually decreases.

The purpose of the present invention is to acutely detect the consumption of activated carbon due to ozone removal and enable appropriate replenishment of activated carbon, and also to renew the surface of activated carbon, which is covered with ash and has reduced ozone removal ability. It is an object of the present invention to provide an ozone removal method that can maintain activity and efficiently remove ozone.

In order to achieve the above object, the present invention has the following configuration. That is, the ozone removal method of the present invention is a method for removing ozone by bringing an ozone-containing gas into contact with activated carbon. A gas containing ozone is aerated through the packed bed at a superficial velocity sufficient to fluidize the activated carbon particles, and when a slugging condition occurs during the aeration, replenishing activated carbon is injected into the activated carbon packed bed. It is something.

As a result of repeated research through various experiments, the present inventors have found that when ozone-containing gas is aerated through an activated carbon packed bed, combustion of the activated carbon occurs as ozone is removed and the activated carbon is consumed, and that the surface of the activated carbon It was confirmed that the ozone removal ability of the activated carbon is covered with ash generated by the combustion of activated carbon, and the ozone removal ability is reduced. As a means of removing ash from the activated carbon surface and renewing the activated carbon surface, activated carbon particles are made to flow through an activated carbon packed bed filled so that the upper surface is in contact with a perforated plate having ventilation holes smaller than the particle diameter of the activated carbon. We have completed the present invention by discovering that a method of aerating ozone-containing gas at a sufficient superficial velocity is extremely effective.

In the present invention, for example, when an ozone-containing gas is aerated through an activated carbon packed bed filled with activated carbon having a particle size of about 4 mm and its upper surface is brought into contact with a perforated plate, the activated carbon is consumed as the aeration time passes. Skyline speed approx.
Activated carbon flows from 100 cm/sec, and the speed is approximately
When the speed reaches 120 cm/sec, the activated carbon is pushed up to the perforated plate, and a space is created in the middle of the packed layer, causing a so-called slugging phenomenon. By aerating for a certain period of time, the activated carbon is covered with ash generated by the combustion of the activated carbon as ozone is removed, but this ash is peeled off by the flow of the activated carbon, and the ozone removal ability does not deteriorate even after that. Activated carbon wears out due to flow, and also loses weight due to combustion, reducing the volume of the activated carbon packed bed. Such wear can be acutely detected by observing the slugging phenomenon of the activated carbon particles. , which allows appropriate activated carbon replenishment.

According to the present invention, ozone can be removed efficiently by the above-mentioned structure and operation, which will be explained in more detail below with reference to experiments and results conducted to confirm these points.

Experiments 1 to 3 show experiments regarding consumption of activated carbon and decrease in ozone removal ability accompanying ozone removal.

Experiment 1 A gas containing 1000 ppm of ozone was aerated at 1140/hour for 10 hours into an activated carbon packed bed filled with 100 g of activated carbon with a particle size of 4 mm. After aeration, the weight of activated carbon decreased by 4.1g. In addition, the ozone concentration in the activated carbon treatment gas during the ozone-containing gas ventilation was 0.01 ppm or less and was completely removed.

Experiment 2 4000 ml of gas containing 10 ppm ozone was added to an activated carbon packed bed filled with 10 g of activated carbon (new), the same as in Experiment 1.
/ hour for 10 hours. The ozone concentration in the activated carbon treated gas was always below 0.01ppm and was completely removed.

Experiment 3 A gas containing 10 ppm of ozone was added to the activated carbon packed bed filled with 10 g of the activated carbon used in Experiment 1 at 4000/ml.
It was vented for 10 hours. The ozone concentration in the activated carbon treated gas was below 0.01ppm up to 6 hours of ventilation, but it was 0.05ppm after 8 hours of ventilation and decreased to 0.05ppm after 10 hours of ventilation.
It was 0.011ppm.

From Experiment 1 above, it is clear that activated carbon is consumed as ozone is removed. This is because the reactions of equations (2) and (3) above occur in addition to equation (1) when removing ozone with activated carbon, and it is clear that the activated carbon is inevitably consumed as ozone is removed. means. Note that the amount of activated carbon consumed in Experiment 1 was 0.17 g (activated carbon)/g (ozone).
Furthermore, from the results of Experiments 2 and 3, it can be seen that the ozone removal ability of activated carbon that has undergone ozone removal is lower than that of new activated carbon. This is because when activated carbon removes ozone, the combustion reaction of the activated carbon shown in equations (2) and (3) above occurs, and the surface of the activated carbon is covered with ash, which has no ozone removal ability, reducing the ozone removal ability of the activated carbon. This is because it decreases.

Experiments 4 and 5 show experiments in which the relationship between the superficial velocity of gas aeration and the flow and slugging phenomenon of activated carbon was investigated.

Experiment 4 When air was aerated into an activated carbon packed bed filled with activated carbon with a particle size of 4 mm and the amount of air was gradually increased, it was confirmed that the activated carbon flowed at a superficial velocity of 100 cm/sec or more.

Experiment 5 In Experiment 4, 3 cm from the top of the activated carbon packed bed.
After installing a wire mesh with 14 meshes (hole diameter 1.2 mm square) in the upper part, the amount of air to be vented was gradually increased, and a flow phenomenon of activated carbon was observed at a superficial velocity of 100 cm/sec or higher, and the flow rate increased to 120 cm/sec. In the above case, a part of the fluidized activated carbon was pushed up to the lower side of the wire mesh attached above the activated carbon packed bed and formed a layer, creating a space in the middle of the activated carbon packed bed, resulting in a so-called slugging phenomenon.

As in Experiment 4 above, when the amount of air flow to the activated carbon packed bed increases and the superficial velocity exceeds a certain value, flow of activated carbon particles occurs. This flow is expressed in Stokes' law as shown in equation (4) below: w=1/18・g・ρ−ρ ₀ /μ・d ² (4) where, w: Sedimentation velocity of particles (cm/sec) g: Acceleration of gravity (cm/ ^sec2 ) ρ: Density of particle (g/ ^cm3 ) _ρ0 : Density of fluid (g/ ^cm3 ) μ: Viscosity of fluid (g/cm・sec) d: Density of particle Diameter (cm) This is when the superficial velocity is greater than the sedimentation velocity of the particles.

In addition, in Experiment 5 above, the wire mesh that suppresses the free flow of activated carbon is located above the top surface of the activated carbon packed bed, so when the superficial velocity increases and the active carbon flows actively, some of the activated carbon The activated carbon is pushed up to the bottom of the wire mesh and forms a layer, creating a space in the middle of the activated carbon packed bed, that is, a slugging phenomenon occurs. FIG. 1 of the accompanying drawings is a schematic cross-sectional view of an activated carbon packed tower showing the slugging phenomenon of the activated carbon packed bed,
In the figure, 1 is an ozone-containing gas, 3 is an activated carbon packed tower, and 4 is an ozone-containing gas.
5 indicates activated carbon, 5 indicates a perforated plate, and 6 indicates a processing gas. This figure clearly shows the state of the space created in the middle of the activated carbon packed bed, that is, the slugging phenomenon. In this experiment, in order to clearly demonstrate the flow and slugging phenomenon of activated carbon, a perforated plate, or wire mesh, was placed 3 cm above the top surface of the activated carbon packed bed.
However, it goes without saying that this phenomenon occurs after the activated carbon has been burned and consumed to some extent even when the perforated plate is provided in contact with the upper surface of the activated carbon packed bed as in the present invention.

Experiments 6 and 7 show experiments in which it was investigated that ash covering the activated carbon surface was peeled off by the flow of activated carbon.

Experiment 6 100 g (230 ml) of activated carbon with a particle size of 4 mm was packed into a glass reaction tube with a diameter of 57 mm, and a gas containing 100 ppm of ozone was bubbled through the tube at a rate of 6350/hour (superficial velocity 70 cm/sec) for 50 hours. The ozone concentration in the activated carbon treatment gas is 30
The concentration was 0.01 ppm or less up to hourly aeration, but it was 0.5ppm after 40 hours of aeration and 1.3ppm after 50 hours of aeration. Note that the activated carbon layer was left standing during gas aeration.

Experiment 7 100g of activated carbon with a particle size of 4mm was filled in a glass reaction tube with a diameter of 40mm, and a gas containing 100ppm of ozone was added.
Aerated at 6350/hr (superficial velocity 140 cm/sec) for 50 hours. Ozone concentration in activated carbon treatment gas is always
It was below 0.01ppm. Note that the activated carbon particles were fluidized vigorously during gas ventilation.

In Experiment 6, the weight of activated carbon after treatment with ozone-containing gas was reduced by 11.1 g, but the reduction in the packed volume of activated carbon was about 5 ml at most, and the reduction in the amount of activated carbon could not be clearly discerned. On the other hand, experiment 7
, the activated carbon weight decreased by 12.8g after treatment with ozone-containing gas, and the activated carbon packed bed volume at rest was 22g.
A decrease of about ml was clearly observed.

As can be seen from this experimental result, the ozone removal ability of activated carbon decreases in a fixed bed where activated carbon does not flow, as in Experiment 6, but this is because the activated carbon burns due to the reaction with ozone, and the activated carbon surface This is because it is covered with ash, etc., which has no resolution. This is supported by the fact that although the weight of activated carbon decreased by 11.1 g, the fill volume decreased by only 5 ml. On the other hand, in the activated carbon fluidized bed as in Experiment 7, there was no decrease in the ozone removal ability of the activated carbon. This is because the surface has been updated. However, since the activated carbon particles are constantly flowing, the activated carbon wears out and the weight of the activated carbon naturally decreases more than in Experiment 6.

Based on the confirmation items described in detail above, it was possible to achieve the object of the present invention with the above structure. It is necessary to have ventilation holes smaller than the diameter of the porous plate, and the porous plate may be any porous plate through which the ozone-containing gas can pass through without the activated carbon being fluidized and pressed, and its shape, number of ventilation holes, etc. are not particularly limited. For example, a wire mesh of about 14 mesh (1.2 mm square) can be used. In addition, the superficial velocity for aerating the ozone-containing gas necessary to fluidize the activated carbon in the activated carbon packed bed, detect the consumption of activated carbon by the slugging phenomenon, and enable replenishment of supplementary activated carbon is approximately
A speed of 120 cm/sec or more is appropriate, and a speed of approximately 140 cm/sec is usually sufficient to achieve the purpose.

Next, an ozone removal device and its operating method used in carrying out the present invention will be explained with reference to the drawings.
Figure 2 is a schematic cross-sectional view of the device, in which 1 is an ozone-containing gas, 2 is a blower, 3 is an activated carbon packed tower,
Reference numeral 4 indicates activated carbon, 5 indicates a perforated plate, 6 indicates a processing gas, 7 indicates a supplementary activated carbon inlet, and 8 indicates a supplementary activated carbon storage tank. The ozone-containing gas 1 is supplied to the activated carbon 4 by a blower 2 at a superficial velocity sufficient to cause the activated carbon particles to flow.
Ventilation is carried out from the bottom of an activated carbon packed tower 3 having a bed of activated carbon packed so that its upper surface is in contact with a perforated plate 5 having small ventilation holes according to the particle size of the particles, and a post-processing gas 6 in which ozone has been decomposed and removed is obtained. On the other hand, if the activated carbon 4 is consumed due to the reaction with ozone and a slugging phenomenon of activated carbon 4 particles is observed in the activated carbon packed tower 3, the activated carbon in the replenishment activated carbon storage tank 8 is added to the activated carbon packed bed in the activated carbon packed tower 3. Replenishment activated carbon is replenished through the replenishment activated carbon inlet 7, and this replenishment is continued until the slugging phenomenon is no longer observed.

Note that the slugging phenomenon of particles of activated carbon 4 caused by consumption of activated carbon 4 is easiest to observe with the naked eye, but it can be observed by changes in electrical signals such as electrical resistance, capacitance, thermoelectromotive force, etc. (not shown). It can also be recognized. In this way, the consumption of activated carbon 4 can be acutely detected, making it possible to replenish the appropriate amount of activated carbon 4, eliminating the need to lengthen the life of the ozone removal device unnecessarily, and making it possible to downsize the device. .

Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto in any way.

Example 100 g of activated carbon with a particle size of 4 mm was filled in a glass reaction tube with a diameter of 40 mm, and a wire mesh with 14 meshes (hole diameter 1.2 mm square) was attached so as to be in contact with the top surface of the activated carbon packed bed, and then a gas containing 100 ppm of ozone was introduced. Aerated at 6350/hr (superficial velocity 140 cm/sec) for 50 hours. The ozone concentration in the activated carbon treated gas was always below 0.01ppm. During gas aeration, the activated carbon remained stationary for about 20 hours, but after that, it was observed that the activated carbon began to flow and a slugging phenomenon occurred in the activated carbon packed bed.

After treatment, the weight of the activated carbon decreased by 11.3 g, and the filling volume decreased by about 22 ml, and the ozone removal ability of the activated carbon did not decrease. This is because when the amount of activated carbon decreases due to combustion of the activated carbon due to the reaction with ozone, gas is vented at a superficial velocity that allows the activated carbon particles to flow, and the top surface of the activated carbon packed bed is in contact with the wire mesh. This is because the activated carbon flows and a slugging phenomenon occurs, whereby the ash generated on the surface of the activated carbon is removed and the surface of the activated carbon is renewed. Furthermore, the flow of activated carbon particles occurs after the amount of activated carbon has been depleted to a certain extent, and the flowed activated carbon is pushed up and fixed under the wire mesh, so that the activated carbon particles are constantly flowing as in Experiment 7. There is less wear on the activated carbon than when using the activated carbon.

In the above experiment, a replenishment activated carbon inlet was installed in the glass reaction tube, and activated carbon was replenished at the stage when the slugging phenomenon occurred (20 hours after aeration). When the activated carbon was allowed to stand still and aerated again, the process gas The ozone concentration was always below 0.01 ppm, and the volume of replenishment was below 10 ml.

As described above, according to the present invention, when removing ozone by bringing ozone-containing gas into contact with activated carbon, it is possible to acutely detect the consumption of activated carbon and replenish the activated carbon appropriately. The surface of activated carbon covered with can be renewed by the flow of activated carbon. Therefore, the present invention has the advantage of being able to reduce the size of the ozone removal device and to efficiently remove ozone.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an activated carbon packed column showing the slugging phenomenon of the activated carbon packed bed, and FIG. 2 is a schematic cross-sectional view of an apparatus used in carrying out the present invention. 1...Ozone-containing gas, 2...Blower, 3...
Activated carbon packed tower, 4...Activated carbon, 5... Perforated plate, 6
...Processing gas, 7...Activated carbon inlet for replenishment, 8...
...Activated carbon storage tank for replenishment.

Claims (1)

[Claims] 1. In a method of removing ozone by bringing an ozone-containing gas into contact with activated carbon, activated carbon particles are flowed through an activated carbon packed bed filled with a perforated plate having ventilation holes smaller than the particle diameter of the activated carbon so that its upper surface is in contact with the bed when filled. 1. A method for removing ozone, the method comprising: aerating an ozone-containing gas at a superficial velocity sufficient to remove ozone, and injecting replenishing activated carbon into an activated carbon packed bed when a slugging condition occurs during the aeration.