US1962555A - Method and apparatus for electrical precipitations - Google Patents

Description

June 12, 1934. w. DEUTSCH 1,962,555

METHQD AND APPARATUS FOR ELECTRICAL PRECIPITATION Filed oct 8; 1932 A TTOR/VE J Patented June 12, 1934 UNITED STATES PATENT OFFICE MET-HOD Walther Deutsch, Frankfort- AND APPARATUS FOR ELECTRICAL PRECIPITATIONS on-theMain, Ger- Company, Los Angeles,

California 4 Claims.

This invention relates to the electrical precipitation of suspended particles from gases.

The principal object of the invention is to provide a novel and advantageous method and ap- 5 paratus for effecting such electrical precipitation.

With very few exceptions, the apparatus heretofore known for electrical, precipitation comprises two essential parts or elements, namely, discharge electrodes and collecting electrodes, which perform certain definite functions. The relatively great curvature of the surface of the discharge electrodes, which usually consist of points, thin wires or the like, causes a corona discharge to occur upon application of a. high potential difference between these electrodes and the collecting electrodes, and this corona discharge serves to produce ions in the gas, for electrically charging the suspended particles.

The collecting electrodes not only'serve as opposing electrode means whereby high potential for ionization and the, necessary for preclpita tion of the charged particles may be maintained, but also provide depositing surfaces for the precipitated material.

It has been proposed to use various materials in the discharge electrodes. For example, glass covered metal wires may be used to provide more uniform distribution of corona, or rods having surfaces covered with points or with thin threads or filaments of non-conducting material. It has also been proposed to use rods over whose surface a conducting liquid. such as water, is caused to flow. Under the action of an electric field the water film is caused to form into small droplets at whose surface an eifective corona discharge is produced. However, the known forms of discharge electrodes which are mosteffective for ionization, such as thin wires or line points, are ordinarily fragile and have relatively little strength or corrosion resistance, and for this reason larger elements such as rods, used, in spite of the fact that they less efficient as sources of corona are ordinarily are somewhat discharge. It

is also sometimes undesirable to introduce moisture into the precipitator, orsuch moisture introduction may-be impossible, as in the treatment of gases at high temperature which would cause immediate evaporation of the liquid.

A particular object of the present invention, therefore,'is to provide a source of corona dis charge or ionization, for use as discharge electrode means in electrical precip will ofier relatively sharp surface correspondingly high corona pr which is not open to objection on itators, which curvature" and oduction, an

the ground of Calif., a corporation of 11 Germany July ii, 193).

low mechanical strength or corrosion resistance,

It is known that the path of the spark constitutes a linear conductor of extremely small ra dius of curvature. If a spark is produced and maintained between two electrodes, and a strong unidirectional electric field is maintained be tween these electrodes and a third electrode which is disposed, for example, parallel to the path of said spark, a unidirectional corona will occur at or adjacent the spark itself, due to the 5 small radius of curvature of the conductive path thereof. The corona is thus produced without necessitating the provision of a thin wire or other discharging member between the two firstnamed electrodes, and the conducting path of the spark itself serves as the ionizing or discharge electrode, while the third electrode serves as a collecting electrode.

The action which takes place with such an arrangement may-be described as follows: The unidirectional field serves to displace the spark somewhat from its normal position between the two first-mentioned electrodes, toward the third electrode, thus substantially eliminating any screening effect of the electrodes between which. the spark is maintained, and permitting corona discharge to be maintained throughout substantially the entire length of the spark. Further more, the electric wind which is created after the corona discharge is started serves to further dis- $5 tort the spark path away from the screening action of the sparking electrodes and provide still more favorable conditions for corona discharge,

The spark whose conducting path is utilized as a discharge electrode may be produced by either alternating or unidirectional current, and the sparking electrodes may be placed sumciently close together so that a potential. of a few thousand volts is sufficient to produce a spark therebetween. As it is more advantageous to produce a number of fine or thread-like sparks between these two electrodes, rather than a heavier luminous arc, it is preferable to limit the current between these electrodes by insertion of a relatively high reslstance in the circuit of such current flow. This 1 a resistance may advantageously be provided over insulating potential two auxiliary or sparking electrodes is independent of the discharge produced between these auxiliary electrodes and the third or collecting electrode by the unidirectional corona produced at the surface of the spark orsparks. The corona is produced solely by the unidirectional field maintained between the auxiliary electrodes and the collecting electrode, and the ions which are utilized to charge the particles are derived exclusively from this unidirectional corona, while the discharge between the auxiliary electrodes proceeds entirely undisturbed. All electrons and ions emanating from one of the auxiliary electrodes arrive at the opposite auxiliary electrode and vice versa. If,- for example, an alternating potential is maintained between the auxiliary electrodes, the alternate emanation of electrons and ions from these two electrodes, due to the alternating field, takes place in the same manner, whether or not the unidirectional field is also maintained. The sole function of this alternating discharge is to produce a narrow conducting path which serves to replace the discharge electrodes ordinarily employed.

It will be apparent that the method of the present invention cannot be safely used in the treatment of explosive or combustible mixtures of gases,

and suspended material.

The accompanying drawing illustrates the method and apparatus of this invention, and referring thereto:

Fig. 1 is a diagrammatic representation of one type of electrodes which may be used, together with means for maintaining the necessary electrical potentials therebetween.

Figs. 2 and 3 are diagrammatic representations showing modified forms of electrodes.

-Referring to the drawing, and particularly to Fig. 1, the auxiliary spark gap electrodes are shown at 1 and 2. Said electrodes may be formed as relatively massive bodies, such as spheres or rods, and the surface of either or both of said electrodes may, if desired, be covered with suitable material, such as glass. Said electrodes are connected to a source of electrical potential sufiicient to maintain a spark discharge therebetween, as indicated at 3. An alternating may be used for this purpose, and the electrodes 1 and 2 are shown as connected by wires 4 and 5 to the opposite terminals of a transformer 6.

A collecting electrode 7 of extended area is pro-- vided, the surface of which is preferably substantially parallel to the path of the spark discharge between the electrodes 1 and 2. A unidirectional potential is maintained between the collecting electrode 7 and one of the electrodes 1 or 2. For this purpose, the electrode 7 is shown as connected by through a rectifying device 10 and wire 11 to electrode 1.

The path of the spark 3 produced between electrodes 1 and 2 is relatively thin and'serves as a discharge electrode. It will be understood, however, that the spark discharge may consistr of one or a plurality of narrow spark paths, and that wire 8 to one terminal of trans' former 9, the other terminal of which is connected rectifier 10 serves to maintain a suificiently high electrical field between this discharge electrode and the collecting electrode to cause a corona discharge or ionization to occur from the path of the spark toward the collecting electrode, as indicated for example at 12. Due to the relatively large cross-section of electrodes 1 and 2, as compared to the spark path, such corona discharge occurs substantially wholly from said spark path. If gas containing suspended particles is then passed through the space between the spark path 3 and the collecting electrode 7, the suspended particles will become electrically charged by ions produced by said corona, and the charged particles will be precipitated upon the collecting electrode by the electrical field between said spark path and collecting electrode.

As above stated, it may be advantageous to insert a relatively high resistance in series with the spark gap electrodes 1 and 2. This resistance may be provided, for example, by providing a covering or coating of insulating or high resistance material over the surface of both of said electrodes, as shown at In and 2a in Fig. 2, or over the surface of one of said electrodes as shown at 1:1 in Fig. 3.

I claim:

l. The method of electrical precipitation which comprises m'ainiaining an electric spark across a path between two oppositely charged electrode members, maintaining a unidirectional electrical potential diiference between said spark and a third electrode of exlended surface substantially parallel to the path of said spark, said potential being sufiicient to cause the narrow conducting whereby corona discharge occurs substantially wholly from said spark gap toward said third electrode, and passing gas containing suspended material through the electrical field between said spark path and said third electrode.

2. An apparatus for electrical precipitation comprising two oppositely charged electrode members, means for maintaining an electrical potential between said electrode members sufiicient to produce a spark discharge therebetween, a third electrode of extended surface positioned substantially parallel to the path of said spark discharge andat no point substantially closer to said firstnamed electrode members than to the path of said spark discharge, means for maintaining a unidirectional electrical potential between said third electrode and the circuit including said first-v named electrodes sufiicient to cause corona discharge to occur from said spark toward said third electrode, said first-named elecirodes being of relatively large cross-section compared to said spark path whereby said corona discharge occurs substantially wholly from said spark path, and means for passing gas containing suspended material between said spark path and said third electrode.

3. An apparatus as set forth in claim 2 and also comprising resistance means connected in series with said two first-named electrodes.

4. An apparatus as set forth in claim 2, in which at least one of said two first-named electrodes is covered with material of high resistance.

WALTHER DEUTSCH.

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