Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
2000-05-15
2002-07-23
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S908000, C095S156000, C095S159000, C095S168000, C261S148000, C261SDIG004
Reexamination Certificate
active
06423235
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas-liquid contacting apparatus of a column system for bringing a gas into contact with a liquid. Furthermore, the present invention relates to a process for producing ozone water and a process for oxidizing an organic substance with ozone, each using the apparatus. Moreover, the present invention relates to a process for removing a gas dissolved in a liquid using the apparatus. Also, the present invention relates to a process for treating a volatile substance in a liquid using the apparatus.
2. Discussion of the Background
Known gas-liquid contacting apparatus include spray columns, wetted wall columns, packed columns, and plate columns (hereinafter referred to as “column gas-liquid contacting apparatus”), and further include ejectors, bubbling vessels, and static mixers (hereinafter referred to as “bubbling gas-liquid contacting apparatus”). The packed columns are representative. Conventionally, the packed columns in most cases have been used for treating gases and, hence, many of these have been used for the purpose of gas cleaning. Typical examples of the gas cleaning are air pollution control processes represented by flue gas desulfurization. In such cases, an important factor in design is how to treat a large quantity of a gas to be treated. However, since too large a gas amount results in a phenomenon in which the liquid is prevented from descending, i.e., the so-called flooding, and in an increased blower operating cost, an appropriate gas load is selected. Generally, employed values of this gas load are from 1 to 2 m/sec in terms of superficial gas velocity u obtained through a density correction.
Generally, a gas velocity U for a packed column is the velocity of a gas which is passing through the vacant column, and has no relation with the voidage which is the volume calculated by subtracting the volume occupied by the packing.
Various gases which are different in density (&rgr;) exist, ranging from light gases, such as hydrogen (molecular weight=2), and intermediate gases, such as air (molecular weight=29), to heavy gases, such as chlorine (molecular weight=71) Even air and steam, which are the most common gases for packed columns, each has considerably different densities depending on pressure and temperature Even when such various gases having different densities have the same gas velocity U, they differ in kinetic energy.
Consequently, the velocities of gases having the same kinetic energy can be expressed in terms of u which is the gas velocity corrected with density and is defined by the following equation (1), and gases having the same value of u have the same kinetic energy regardless of their densities:
u
=
U
ρ
(
kg
/
m
3
)
1.2
(
kg
/
m
3
)
(
m
/
sec
)
(
1
)
In equation (1), the numeral 1.2 indicates the density of air at normal temperature and pressure, i.e., 1.2 kg/m
3
. Using this numeral to convert the densities of gases having various densities into dimensionless numbers, velocities of these gases each can be expressed in terms of the velocity of air at normal temperature and pressure.
In the conventional column gas-liquid contacting apparatus described above, the gas velocities employed have been in the range of from 1 to 2 m/sec in terms of the density-corrected superficial gas velocity u. These apparatus are unsuitable for operations where the gas amount is smaller than the lower limit. Specifically, gas velocities in the range of 0.1<u<1 m/sec are undesirable from the standpoint of profitability, while gas velocities of u<0.1 m/sec are undesirable from the standpoint of performance.
Recently, ozone has been utilized in the various fields instead of chlorine etc. which had been used. Ozone water is used for cleaning of silicon wafers and liquid crystals in electronic industry, sterilization of production apparatus and instruments in the filed of foods, sterilization of vegetables, medical instruments, swimming pool water, and other applications. Also, gas-liquid contacting reactions with ozone gas is applicable to the oxidative decomposition of organic substances in water, oxidative decomposition of COD substances in waste water, decoloring of colored waste water, bleaching of pulps in the pulp industry, and the like. Furthermore, ozone is often used as ozone water in which ozone is dissolved in water as well as gaseous ozone.
Bubbling vessels, ejectors, packed columns and the like are known as ordinary equipment for producing ozone water. However, the efficiency of utilizing ozone is low, and the concentration of ozone water is limited.
Furthermore, the presence of dissolved oxygen in water to be fed to a boiler or in cooling water causes corrosion in the apparatus, pipings, and the like. Accordingly, techniques for chemically or physically removing the oxygen dissolved in the water have been used from long ago.
Also, with respect to cleaning water for use in semiconductor production, attempts are being made to diminish the oxygen dissolved therein due to that the dissolved oxygen produces adverse influences.
Known techniques for removing dissolved oxygen from water include addition of a reducing agent, a contacting with hydrogen in the presence of a catalyst, vacuum degassing under heating, nitrogen gas bubbling, removal with a separatory membrane, and the like.
However, according to the conventional removing processes, a large amount of a dispersion gas is required, and a complicated equipment is required for carrying out the reaction in vacuo under heating. Thus, an effective and simple apparatus using a packed column is not known.
Stripping columns according to a packed bed system or a plate system are conventionally known as means for removing a volatile substance from waste water by stripping. The conventional packed bed stripping columns necessitate a sufficient linear gas velocity for the countercurrent contact of a liquid to be treated with a purge gas and necessitate an exceedingly large stripping gas amount for the stripping of a highly volatile substance.
Therefore, the concentration of the volatile substance in the gas phase is insufficient as compared with that in the liquid phase. The resultant stripping gas containing the volatile substance is treated either with an adsorbent, such as activated carbon or the like, to recover the volatile substance or by incineration. In the latter case, the stripping gas should be burned in a large quantity. Consequently, this technique is economically disadvantageous.
Moreover, since discharged gases have no regulations concerning such volatile substances unlike waste water, there have frequently been cases where waste water is treated by mere exposure to air (air stripping) to discharge the stripped volatile substances as they are into the air.
Recently, there is a fear concerning influences on the human body of volatile substances or endocrine disrupters represented by benzene and toluene, volatile organic halogen substances represented by dichloromethane and chloroform, and analogues thereof. Despite these circumstances, no process has been obtained which is effective in recovering such substances from waste water. Consequently, for removing such substances from waste water, processes necessitating a large amount of energy have been used, such as the process comprising stripping with a large amount of air and recovery by adsorption and the process comprising stripping and decomposition by incineration. Alternatively, a process comprising subjecting waste water to air stripping and discharging the stripped volatile substance into the air has been used due to that the emission of such substances is not regulated by the law relating to air pollution control.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus in which gas-liquid contacting can be efficiently carried out at a low gas feed rate.
Another object of the present invention is to provide an apparatu
Adachi Takio
Goda Junichi
Shimoi Yoichi
Hoey Betsey Morrison
Nittetu Chemical Engineering Ltd.
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