Title:
Method of electrical precipitation
United States Patent 2381879


Abstract:
This invention relates to an improved method for the removal of suspended particles from gases by electrical precipitation. In the precipitation of suspended particles from gases by subjecting the gases to an ionizing discharge and a strong electrical field as in the well-known Cottrell electrical...



Inventors:
Chittum, Joseph F.
Application Number:
US54553744A
Publication Date:
08/14/1945
Filing Date:
07/18/1944
Assignee:
WESTERN PRECIPITATION CORP
Primary Class:
Other Classes:
96/74
International Classes:
B03C3/013
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Description:

This invention relates to an improved method for the removal of suspended particles from gases by electrical precipitation.

In the precipitation of suspended particles from gases by subjecting the gases to an ionizing discharge and a strong electrical field as in the well-known Cottrell electrical precipitation process, difficulty is encountered In obtaining high efficiencies of precipitation with some types of materials, because of the occurrence of electrical ] conditions leading to increased flow of current between the electrodes of the precipitating apparatus at potentials lower than those at which the-highest efficiencies can be obtained. A typical phenomenon leading to lowered precipitation efficiency is the occurrence of. discharges, emanating from the electrode of the precipitator upon which the material is precipitated. Such discharges are known as "back discharges." A principal purpose of the invention is the provision of a method of. electrical precipitation whereby electrical disturuances tending to lower the efficiency of precipitation may be reduced or eliminated.

It has heretofore been found that disturbing Selectrical phenomena of this nature can frequently be substantially reduced or eliminated by the addition of water vapor to the gases being treated or by operating under such conditions as to increase the relative humidity of the gases, for example, by cooling the gases. However, it is frequently desirable to subject gases carrying suspended particles at a relatively high temperature at which disadvantageously large amounts of water vapor are required to obtain satisfactory operation, and with some materials it is difficult or impossible to obtain satisfactory operatipn by the addition of water vapor.

It has now been found that in the electrical precipitation of suspended particles of an acidic nature, particularly weakly acid substances, disturbing electrical phenomena can be greatly reduced and substantially increased precipitation efficiencies can be obtained by adding to the gas an organic amine volatilizable at the temperature of the precipitation operation and having an alkalinity as measured by its ionization constant substantially greater than that of ammonia.

The term "particles of an acidic nature" includes substances which in contact with water produce a pH less than 7. The method of the invention is of particular value in connection with relatively weakly acidic substances such as acidic clays or other silicates that contain silica in stoichiometrical excess over the basic constituents, boric acid, arsenous oxide, and silica or substances containing free silica.

A wide range Qf organic amino compounds may be used in the invention if they meet the requirements of being volatilizable at the temperature of operation and of having an ionization constant substantially greater than that of ammonia. In general, amines having an ionization constant greater than 5X10-5 at 25* C. are effective, although the effectiveness is, in general, greater with increasing alkalinity, and an ionization constant of at least 1X10- at 25* C. is preferable.

Amines suitable for use in the invention include primary amines such as methylamine, ethylU amine, n-propylamine, and sec-butylamine; secondary amines such as dimethylamine, diethylamine, dipropylamine, and di-isobutylamine; tertiary amines, such as trimethylamine, triethylamine, tripropylamine, and tri-isobutylamine; g polyamines, such as ethylene diamine, and cyclic amines, such as piperidine.

In general, it is necessary that the gas contain some water vapor, either already present therein or introduced into the gas stream. Some of these U amines cause a marked reduction in specific resistance even with a small proportion of water vapor, as low as 1% by volume of the gas stream.

Increased concentrations of water vapor give better results, and it is generally desirable to have from about 2% to about 10% or more water vapor present in the gas. In most cases the gases to be cleaned contain sufficient water vapor for this purpose, so that additional water need not be introduced.

A useful range of proportions of the amines is from about 0.05% to 0.3% by weight of the suspended material in the gas although in some cases improved operation can be obtained with substantially lower amounts of amine, for example, aslowas0.01%.

As an example, the effective elimination of undesirable electrical disturbances in the electrical precipitation of an acidic clay material suspended in air containing about 1% or more of water vapor may be brought about by the addition to the air of 0.2% of triethylamrie based on the weight of clay suspended in the air, or about 5.6 pounds of triethylamine per million cubic feet of air containing about 20 grains of suspended clay per cubic foot.

The amines may be introduced into the gas either in the free state or in the form of their salts, such as the hydrochlorides and sulfates of the amines named above. It is to be understood that when salts of amines are used, the ionization constant criterion described above refers to the ionization constant of the corresponding free amine and the proportion of the salt used may be such as to provide an amount of the free amine equivalent to the proportions mentioned above.

This application is a continuation-in-part of my application Serial No. 515,023, filed Decem-. ber 20, 1943.

I claim: 1. A method of removing suspended particles of acidic composition from gases which comprises adding to the gases a salt of an organic amine having an ionization constant greater than 5x10-5 at 25' C., and thereafter subjecting the gases to electrical precipitation.

2. A method of removing suspended particles of acidic composition from gases which comprises adding to the gases a salt of an organic amine having an ionization constant greater than 10-5 at 25' C. in an amount equivalent to at least about 0.01% of the amine on the weight of the suspended material, and thereafter subjecting the gases to electrical precipitation.

3. In the electrical precipitation of suspended particles of acidic composition from gases, the improvement which comprises subjecting the gases to electrical precipitation in the presence of a substance of the group consisting of organic amines volatilizable at the temperature of precipitation and having an ionization constant greater than 5x 10-5 at 25' C. and salts thereof.

4. In the electrical precipitation of suspended particles of acidic composition from gases, the improvement which comprises subjecting the gases to electrical precipitation in the presence of a substance of the group consisting of organic amines volatilizable at the temperature of precipitation and having an ionization constant greater than 5 10-5 at 25" C. and salts thereof, and water vapor.

5. In the electrical precipitation of suspended particles of acidic composition from gases, the improvement which comprises subjecting the gases to electrical precipitation in the presence of at least about 0.01% by weight of the suspended material of a substance of the group consisting of organic amines volatilizable at the temperature of precipitation and having an ionization constant greater than 5X10-5 at 25° C. and salts thereof, and water vapor.

6. In the electrical precipitation of suspended particles of acidic composition from gases, the improvement which comprises subjecting the gases to electrical precipitation in the presence of triethylamine, and water vapor.

7. In the electrical precipitation of suspended particles of acidic composition from gases, the improvement which comprises subjecting the gases to electrical precipitation in the presence of at least about 0.01% by weight of the suspended material of triethylamine, and water vapor.

8. A method of removing suspended particles of acidic composition from gases, which comprises adding to the gases a substance of the group consisting of volatilizable organic amines having an ionization constant greater than 5X10-5 at 25" C. and salts thereof, and thereafter subjecting the gases to electrical precipitation.

9. A method of removing suspended particles of acidic composition from gases, which comprises adding to the gases at least about 0.01% by weight of the suspended material of a substance of the group consisting of volatilizable organic amines having an ionization constant greater than 5X10-5 at 25* C. and salt thereof, and thereafter subjecting the gases to electrical precipitation.

10. A method of removing suspended particles of acidic composition from gases, which comprises adding to the gases triethylamine and thereafter subjecting the gases to electrical precipitation.

11. A method of removing suspended particles of acidic composition from gases, which comprises adding to the gases at least about 0.01% by weight of the suspended material of triethylamine and thereafter subjecting the gases to electrical precipitation.

JOSEPH F. CHITTUM.