Chemistry of inorganic compounds – Boron or compound thereof – Oxygen containing
Reexamination Certificate
2002-09-10
2004-10-05
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Boron or compound thereof
Oxygen containing
C423S210000, C423S276000, C423S277000
Reexamination Certificate
active
06800265
ABSTRACT:
The present invention relates to a method for efficiently removing a boric acid component from a gas containing the boric acid component.
Heretofore, borax or boric acid has been used as a raw material in e.g. the production of borosilicate glass, the production of a glaze or the production of enameled products, whereby a boric acid component will be contained in e.g. an exhaust gas from a glass melting furnace or in an exhaust gas from an enameling furnace and will be a cause for air pollution. Further, in a coal fired power plant, etc., a boric acid component is contained in the coal as the fuel, and accordingly, the boric acid component will be contained in the exhaust gas and will be a cause for air pollution. Such a boric acid component discharged to an environment is known to be a cause for pollution of water or soil.
For example, in a glass melting process employing borax, boric acid will be included in the exhaust gas. Boric acid is known to have a molecular structure shown by a compositional formula of H
3
BO
3
, HBO
2
, B
2
O
3
or the like (hereinafter referred to as the boric acid component), depending upon the temperature and partial pressure of water vapor.
Heretofore, there have been no effective methods capable of effectively removing such a boric acid component. It has been common to employ a wet scrubber wherein an alkali substance such as a sodium hydroxide solution is used, a method wherein calcium hydroxide powder is applied to a gas flue and then, the acid component is removed together with the calcium hydroxide powder by means of a bag filter or an electric dust collector, or a method wherein the gas containing fine particles of boric acid formed, is strictly filtered by microfiltration. However, the content of the boric acid component was not adequately reduced by such removal treatment, and none of such methods was thus adequate as a removal method.
Further, for example, in the wet scrubber or the like, if the amount of circulating the alkali solution is increased to improve the efficiency for the removal of the boric acid component, the exhaust gas temperature decreases, and if the exhaust gas temperature becomes lower than the acid dew-point, the SO
3
gas or sulfuric acid gas (hereinafter referred to as the SO
3
component) in the gas will be sulfuric acid mist, whereby corrosion is likely to be led. Further, if the alkali concentration in the circulating liquid is increased, the concentrations of sodium carbonate, sodium sulfate and sodium borate in the reaction product will increase, and crystals are likely to precipitate, which may lead to clogging of the circulating pipe line. On the other hand, in the method of injecting fine powder of calcium hydroxide into the gas to be treated, the reactivity between calcium hydroxide and the boric acid component is low, and it will be necessary to use a large amount of the fine powder of calcium hydroxide, whereby the installation will be obliged to be large-sized, and further, disposal of the reaction product and the non-reacted solid waste will be required, thus leading to a problem of large costs. Further, in the method of gas microfiltration, it is necessary to cool the gasified boric acid component to change solid phase for sufficient removal of the boric acid component, whereby the temperature will be lower than the acid dew-point such as sulfuric acid or hydrochloric acid, and accordingly, it will be necessary to install a special very expensive bag filter.
The present invention provides a method for treating a gas, which comprises contacting a gas containing a boric acid component in an amount of at least 15 mg/m
3
as converted into B
2
O
3
concentration in a standard state, with a solid alkali metal carbonate material comprising at least one member selected from the group consisting of alkali metal carbonates and alkali metal hydrogencarbonates, to remove the boric acid component from the gas.
By the present invention, the boric acid component in a gas which used to be difficult to remove, can be efficiently removed. Further, in the present invention, a conventional dry-type exhaust gas treating installation such as a powder spraying apparatus or a bag filter, can be employed as it is.
Further, the present invention provides an improved method for operation of a denitrizer or a method of effectively utilizing the boron compound in an exhaust gas, which used to be disposed.
In the accompanying drawing,
FIG. 1
is a flow chart showing the method for treating a gas containing a boric acid component, discharged from a glass melting furnace.
In the figure, reference numeral
1
indicates a melting furnace for a glass containing a boric acid component,
2
a stabilizer,
3
a bag filter,
4
an exhaust fan,
5
a denitrizer,
6
a chimney,
7
alkaline solution,
8
a sodium hydrogencarbonate powder in Example 1, or a calcium hydroxide powder in Example 2,
9
a collected dust,
10
a first gas flue,
11
a second gas flue,
12
a third gas flue,
13
a fourth gas flue, and
14
a fifth gas flue.
Now, the present invention will be described in further detail with reference to the preferred embodiments.
In the present invention, the gas containing a boric acid component (hereinafter referred to as the gas to be treated) may, for example, be a gas discharged from a heating process or a melting process of a glass or other inorganic material containing a boric acid component. For example, it may be a gas containing a boric acid component, such as an exhaust gas produced during the production of a heat resistant borosilicate glass, a glass wool heat insulation material, a glass fiber, a glass for liquid crystal displays, a frit glaze, ferroboron or a porcelain, or a gas from other manufacturing or treating process. In this specification, the boric acid component is meant for H
3
BO
3
or its dehydrates and primarily for H
3
BO
3
, HBO
2
or B
2
O
3
. The concentration of the boric acid component is one as converted into B
2
O
3
. Further, the method of the present invention is effective also for the removal of an acidic gas other than boric acid component in general, and in a case where an acidic gas such as boron trifluoride (BF
3
), boron trichloride (BCl
3
), hydrogen chloride (HCl), sulfur dioxide (SO
2
), sulfur trioxide (SO
3
), sulfur acid (H
2
SO
4
), hydrogen fluoride (HF), hydrogen bromide (HBr) or hydrogen iodide (HI) is contained in the gas to be treated, containing a boric acid component, such an acidic gas can also be removed simultaneously.
In the present invention, the amount of the boric acid component in the gas to be treated, is at least 15 mg/m
3
as converted into B
2
O
3
concentration in a standard state. However, even if the amount of the boric acid component in the gas to be treated is less than 15 mg/m
3
as converted into B
2
O
3
concentration, there will be no change in the effectiveness of the present invention.
In the present invention, the solid alkali metal carbonate material is, for example, applied in the gas to be treated and uniformly dispersed to contact and neutralize a gaseous boric acid component for removal of the boric acid component. In a case where the gas to be treated contains also an acid other than boric acid (such as sulfuric acid), the gas to be treated is preferably at a temperature higher than the dew-point of such an acid. In another embodiment, the solid alkali metal carbonate material may be granulated into pellets, spheres or aggregates, and such a granulated product may be used as a packing bed. In a case where an exhaust gas at a high temperature is treated in a large amount, it is preferred to employ a method of applying a powder of the solid alkali metal carbonate material to the exhaust gas flue.
In the present invention, as the solid alkali metal carbonate material, any such material may be employed so long as it is capable of removing the boric acid component by a neutralizing reaction. The solid alkali metal carbonate material is preferably an anhydrous salt in that the amount of the gas to be treated per mass, can be thereby increased. Howe
Hirano Hachiro
Mochizuki Itsuo
Mori Yoichi
Ohtsuka Kazutaka
Asahi Glass Company Limited
Silverman Stanley S.
Strickland Jonas N.
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