US2381879A - Method of electrical precipitation - Google Patents

Description

. UNITED STA 'produceapH lesst han 7; The method-of the invention is of particular value in connection with Pn nadAc ia ms I iua'rnon or nmc'rarcsr. rnncrrrra'non Joseph F. 011mm, Whittier, Cali! assignor to Weste Precipitati Corporation, Loa, An-

geles, Calm, a corporation of California No Drawing. Application July18,19 44,"

A .SQI'MNo-545J37 4 4 I i i.

- 1i cm'ms- ((31.18-3 -114) 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'inthe well-known Cottrell electrical precipitation process, difficulty is encountered in obtaining high .eiiiciencies of precipitation with some-types; of

, materials, because of the occurrence of electrical r conditions leading to increased flow of current between the electrodes of the precipitating ap boric acid, arsenous crude, and silica or substances containing i'ree silica. A wide range of organic be used in the invention if they meet the requirements of being volatilizable at the temperature-of operation and of having an ionizationconstant.

substantially greater than that of ammonia. In general, amines having an ionization constant .7 greater than 5X10rat C. are elective, al-

,though the effectiveness is, in general, greater I with increasing alkalinity, and an ionization conparatus at potentials lower than those at which 7 thehighest eflicienciesk can be obtained. A typical phenomenon leading to lowered precipita tion efficiency is the occurrence of. discharges emanating iromthe electrode of the precipitator upon which'the material is precipitated, Such discharges are known as back'dischargesff j A principal purpose of theinvention is the pro-- the efficiency of precipitation may be reduced or eliminated.

'It-has heretofore .electrical phenomena of this nature can freguently be substantially reduced or eliminated by been found; that disturbing so vision of a method of, electrical precipitation whereby electrical disturbances tending to. lower.=

the addition ofwater 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 disadvantageouslydarge amounts of water vapor are re'qulredto obtain'satisfactory operation, and'with some materials it is difficult or impossible to obtain'satisfactory operationby the addition of water vapor;

,It has now'been-found that n the h athen precipitation of suspended particles of an'acidic nature, particularly weakly acid substances, disturbing electrical phenomena can be greatly re.-

' duced and substantially increased precipitation efficiencies can be obtained-by adding to the gas an organic amine volatilizable at'the' temperature I of the precipitation operation and having an alkalinity as measuredby its ionization constant substantially greater than that of ammonia.

The term "particles of an acidic nature? includes substances which in contact with water A useful range of stant of at least l 10- at25 C. is preferable.

Amines suitable for use in the invention include primary amines such as methylamine, ethylamine, n-propylamine', and sec-butylamine; secondary amines vsuch as dimethylamine, diethyl-' amine, dipropylamine, and di-isobutylamine tertiary amines, such as trimethylamine', triethylamine, tripropylamine', and tri-isobutylamine;

polyamines, such as ethylene diamine, and-cyclic amines, such as piperidine.

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

Increased concentrations of watervapor 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 suiiicient water vapor for this purpose, so'that additional water need not'be introduced.

from about 0.05% to 03% by weight of the's'uspended material in the gas although in some cases improved operation can be obtained with sub- 4O stantlally lower amounts of amine, for'example,

as low as 0.01

As an example, the effective elimination of un-' desirable 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 triethylamine based on the weight of clay suspended in the air, or about5.6

' pounds of triethylamine per millioncubic feet of relatively weakly acidic substances-such as acidic clays or other silicates that contain silica in stoichiometrical excess over the basic constituents,

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 amino compounds may proportionsof the amines is constant criterion described above refers to the ionization constant of the corresponding i'ree 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, iiIedJDecem-- ber 20, 1943.

I claim: a

l. A method of removing suspended particles of acidic composition from gases which comprises adding to the gases a salt of an organic amine 10- 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 5 10- at 25 C. in an amount equivalent to at least about 0.01% of the amine on the weight of having an ionization constant greater thanthe 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 com-prises subjecting the gases to electrical precipitation in the presence of a substance of the group consisting or organic amines volatilizable at the temperature of precipitation and having an ionization constant greater than 5 l0- at 25 C. and salts thereof.

4. In the electrical precipitation of suspended particles of acidic composition from gases, the

material of a substance of the group consisting of organic amines volatilizable at the temperature of precipitation and having an ionization constant greater than5 10- at 25 C. and salts thereof, and water vapor.

6. In the electrical precipitation 01' 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. Amethod of removing suspended particles of acidic composition from gases, which comprises adding tothe gases a substance of the group consisting of volatilizable organic amines having an ionization constant greater than 5x10- 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 5x 10- at 25 C. and salt thereof, and thereafter subjecting the gases to electrical precipitation. 1

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 fromgases, 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