JPH11169655A - Absorbing method of organic material vapor by easily electrified solvent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the danger of ignition due to the electrification of a solvent by collecting and pulling out the solvent in a packed bed lower part so that the solvent flowing down in the bed does not drop drown in a space under the packed bed. SOLUTION: The generation of static electricity in a gas absorbing device 1 is divided into flow electrification generated when the solvent flows down through the packed bed 2 and drop electricity generated when the solvent drops down in the space under the packed bed 2. The former static electricity therein enables to escape by earthing a packing material in the packed bed. But static electricity generated by another drop electrification unenables to escape from the liquid drop because the liquid drop exists in the space. As a result, electrified charge cloud is formed in the space under the packed bed. Then, the formation of electrified charge cloud is avoided by eliminating the liquid drop in the space under the packed bed 2. Therefor the solvent flowing down through the packed bed 2 is controlled to be collected at the lower end of the packed bed 2 and to send to a liquid trap 5 thereunder through a flow-down pipe 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for safely absorbing hydrocarbons and the like in the air by using an easily charged solvent such as a hydrocarbon solvent.

[0002]

2. Description of the Related Art As a storage tank for an organic liquid which is liquid at room temperature,
Generally, an atmospheric pressure storage tank having a vent pipe communicating with the atmosphere is used. From this type of storage tank, a small amount of organic liquid vapor is constantly discharged due to an exhalation effect accompanying a change in temperature or the like. In addition, a large amount of organic liquid vapor is discharged when the organic liquid is sent into the storage tank.

Conventionally, these organic liquid vapors have generally been released to the atmosphere as they are. However, release to the atmosphere causes air pollution and should be avoided. In particular, emission control of substances specified as harmful air pollutants under the Air Pollution Control Law is required. However, since the concentration of the organic liquid vapor generated from the storage tank is generally low, it is considerably difficult to efficiently collect it.
In particular, in the case of aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene, and aliphatic or alicyclic hydrocarbons such as butane, octane, α-olefin, and cyclohexane, and naphtha and other petroleum products, these are used. Extreme care must be taken in the handling of gases as they can form detonation when mixed with air.

[0004] One of the methods of recovering organic vapor present at a low concentration is a method of absorbing it with a solvent. However, in order to recover the vapor discharged from the storage tank by this method, it must be easily implemented, and the equipment and the absorbing solvent are naturally limited. For example, the device has a packed bed in the middle and a liquid reservoir below it. A gas containing organic vapor is introduced into this space, and the gas is circulated by a pump from the liquid reservoir and the upper surface of the packed bed. A type in which the liquid is brought into countercurrent contact with the absorbing liquid to be sprayed is used. In addition, the absorbing liquid must have a low vapor pressure at room temperature, a low viscosity, be stable to air, and be inexpensive. Usually, hydrocarbon solvents, particularly hydrocarbons having 9 or more carbon atoms, are required. A solvent is used. Examples of such a solvent include petroleum products such as heavy gasoline, light oil, and kerosene, and aromatic fractions discharged as high-boiling components from the process of producing aromatic products such as benzene, toluene, and xylene.

[0005]

These hydrocarbon solvents generally have a high volume resistivity, and have the property of being charged with an electrostatic charge when they flow. As described above, the organic vapor, which is a component to be absorbed, forms explosive gas when mixed with air. Therefore, if the solvent has an electrostatic charge, it may be ignited by discharge, which is extremely dangerous. As a method for preventing a hydrocarbon solvent from being charged with an electrostatic charge, a method of adding an antistatic agent to the solvent to reduce the electric resistance of the solvent has conventionally been used. However, this method is expensive and requires care in controlling the concentration of the antistatic agent. An object of the present invention is to provide a method capable of avoiding the danger of ignition due to charging of a solvent without using an antistatic agent.

[0006]

According to the present invention, a gas-absorbing device having a packed bed in an intermediate portion and having a space below the packed bed serves to absorb the components to be absorbed from below the packed bed. A gas containing gas is introduced to raise the inside of the bed, and a solvent that is easily charged is introduced from above to flow down the inside of the bed, and gas-liquid contact is made in the bed to absorb the component to be absorbed with the solvent. By collecting and extracting the solvent at the lower part of the floor so that the flowing solvent does not drop into the space below the floor, the danger of ignition due to the charging of the solvent can be avoided.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in further detail. The generation of static electricity in a gas absorbing device using a solvent which is easily charged such as a hydrocarbon-based solvent is caused by flow electrification when the solvent flows down a packed bed. And drop electrification at the time of dropping from the packed bed to the space below. Of the above, the static electricity generated by the former flow electrification can be released via the filler by grounding the filler in the packed bed. However, the static electricity generated by the latter drop charging cannot escape the static electricity from the droplet because the droplet exists in the space. As a result, a charged cloud of charged droplets is formed in the space below the packed bed. According to the Ministry of Labor's Industrial Safety Research Institute's static electricity safety guidelines,
Generally, when the size of the charge cloud is 0.7 m or more in diameter and the average electric field in the charge cloud is 1 kV / cm or more, brush discharge is generated.

In the present invention, the formation of a charged charge cloud is avoided by preventing the droplets from dropping into the space below the packed bed. Therefore, the solvent flowing down the packed bed is collected at the lower end of the packed bed, and sent to the lower reservoir through the downflow pipe. Various devices can be used for collecting the solvent flowing down at the lower end of the packed bed. FIG. 1 shows an example of such an apparatus, in which a support plate for a filler at the lower end of a packed bed is
It has a structure with a gas riser with a cap.
FIG. 2 shows another example in which a collector for a solvent that falls directly below a filler support plate of a packed bed is provided.

According to the present invention, when the gas containing the component to be absorbed and the easily-charged solvent such as a hydrocarbon-based solvent are brought into countercurrent contact with each other in the packed bed to absorb the gas, the charging in the space below the packed bed is performed. Since the formation of a charge cloud can be avoided, even a gas that forms a detonation gas such as air containing hydrocarbon vapor can be safely treated.

[Brief description of the drawings]

FIG. 1 is a partial schematic view of an example of an apparatus for implementing the present invention.

FIGS. 2A and 2B are partial schematic views of another example of an apparatus for practicing the present invention, wherein a is a front view, and b is a plan view of a collector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas absorption device 2 Packing bed 3 Collector 4 Gas introduction pipe 5 Liquid reservoir 6 Circulation pump 7 Downflow pipe

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Claims (4)

[Claims] 1. A gas containing a component to be absorbed is introduced from below the packed bed into a gas absorbing device having a packed bed at an intermediate portion and having a space below the packed bed, and ascending the inside of the bed. Let
Introduce a solvent that is easily charged from above and let it flow down the floor.When absorbing the component to be absorbed with the solvent by gas-liquid contact in the bed, make sure that the solvent flowing down the packed bed does not drip into the space below the bed. Collecting and extracting the solvent at the bottom of the floor. 2. The method according to claim 1, wherein the component to be absorbed is one that forms a detonation with air. 3. The method according to claim 1, wherein the gas containing the component to be absorbed is air containing a dilute hydrocarbon generated from a liquid hydrocarbon storage tank. 4. The method according to claim 1, wherein the solvent is a hydrocarbon solvent.