US1650105A

US1650105A - Apparatus for electrical separation of suspended particles from gases

Info

Publication number: US1650105A
Application number: US57011A
Authority: US
Inventors: Anderson Evald
Original assignee: International Precipitation Co
Current assignee: International Precipitation Co
Priority date: 1925-09-17
Filing date: 1925-09-17
Publication date: 1927-11-22
Anticipated expiration: 1944-11-22

Description

. Nov. 22, 1927.`

E y E. ANDERSON APPARATUS FOR ELECTRICAL SEPARATION OF SUSPENDED PARTICLES FROM GASES Filed Sept. 1'7 1925 Hg. z

INVENTOR dersbn Y, ATT' NEY n A P m 5W Y, B

Patented Nov. 22, 1927.

UNITED STATES 1,650,105 PATENT OFFICE.

EVALD ANDERSON, OF ALHAMBRA, CALIFORNIA, ASSIGNOR TO INTERNATIONAL PRE- CIPITATION COMPANY, OF LGS ANGELES, CALIFORNIA, A CORPORATION Oil?v CALI- FORN IA.

APPARATUS FOR ELECTRICAL SEPARATION OF SUSPENDED PARTICLES FROM GASES.

Application led September 17, 1925i Serial No. 57,011.

This invention relates to apparatus for separation of suspended particles from gases by electrical action and particularly to the form of such apparatus in which the gases containing the particles are passed between electrodes maintained at a high potential dierence and so constructed as to produce an electrical discharge from certain of said electrodes, resulting in charging of the suspended particles and the deposition of charged particles on the electrodes and particularly en the electrodes opposing the discharge electrodes.

The main object of thek present invention is to provide discharge electrodes of such construction as to improve the operation of the electrical precipitator, and particularly of such character as to maintain a highly" uniform distribution of the electrical discharge throughout the body of the gas being treated so as to'result in a more complete and eflicient precipitation of the suspended matter, and also to prevent arcing or disruptive discharge between the electrodes.

In electrical precipitators there is a tendency for concentration of the electrical discharge at certain portions of the electrodes leading to certain disadvantageous results. By reason of such concentration of the electricl discharge insuch portions of the-electrodes there is liable to be a large portion of the gas being treated which is not subjected to the action of such electrical discharge and consequently such portions of the gas may pass through the electrical precipitator' without being subjected effectively to the electrical precipitating action. In order to ensure contact of all portions of the gas with the electrical discharge it has generally been necessary to make the gas velocity extremely slow or to make Athe conduit or gas treating space between rthe electrodes suiciently long to ensure that all of the gas will be subjected to electrical action at some time in its passage through such space.

Furthermore, by reason of such concentral tion of electrical discharge there is liable to be breaking down of the dielectric resistance of the gas to such an extent as to cause arcing or disruptive discharge which. seriously decreases the eiiciency of the treater by limiting the potential difference which may be maintained between the electrodes,

and by otherwise interfering with the operation of the precipitator.

I have found that by covering the discharge electrodes, which generally comprise ne wires or rods of smalldiameter, with suitable semi-conducting material so as to interpose a considerable resistance to the passage of current, concentration of the electrical discharge at any one portion or at arelatively limited number of portions ofthe discharge electrodes may be prevented. This may be considered as being due to the fact that the relatively'high resistance of the semi-conducting coating on the surface of the discharge electrode prevents the passage of an excessive amount of current at any one point and particularly actsvto prevent the passage of such a large amount of current as would otherwise result upon breaking down of the dielectric resistance of the gas and thus cause arcing or disruptive discharge as above described. A discharge electrode of this character may be employed in connection with a collecting electrode of semi-conducting or high resistance material, for eXample,as described in my Patent No. 1,541,677, dated June 9, 1925,

'or in connection with collecting electrodes of metal. In the first case it will be seen that in addition to the air gaptwo layers of semiconducting material are interposed between the high tension and low tension sides of the precipitator, one surrounding the discharge electrode and the other at the collecting electrode while in the second case only the semi-conducting layer surrounding, the discharge. electrode is interposed.

The accompanying drawings illustrateembodiments of my invention and referring thereto:

Fig. 1 isa vertical'transverse section of one form of my invention.

Fig. 2 is a section on line 2-2 in Fig. 1.

Fig. 3 is a section on line 3-3 in Fig. 2.

Fig. 4 is a horizontal section of a discharge electrode on line 4-4 in Fig. 1.

Fig. 5 is a vert-ical section of a tubular or so-called pipe treater embodying my invention.

Fig. 6 is a section on line- 6-6 in Fig. 5.

Referring to Figs. 1 to 3 the embodiment of my invention shown therein comprisesa casinfr or conduit 1 having inlet 2 and outlet 3 or the gas to be treated and provided with any desired number of vertical partition Walls 4 subdividing the interior of said 'conduit into a plurality of passages. The walls of the Hue 1 and the partition 4 constitute the collecting or :so-called passive electrodes and may consist of any suitable semi-conducting or high resistance material presenting sufficient conductivity for carrying the precipitating current but presenting suiiiciently high resistance to `reduce the tendency to excessive concentration of the precipitating current at a point or points of said electrodes. For this' purpose said electrode members 1 and 4 may consist of reenforced concrete or similar material, consisting for example of concrete walls of Portland cement and suitable aggregate and having metal re-enforcing bars or rods 5y which are arranged in spaced parallelism, for example vertically, andgare connected together and to ground by wires or conductors 6. Suitable means such as hopper 7 may be provided below the flue 1 for receiving the material precipitated upon the collecting electrodes and removed therefrom by the action 'of' gravity or in any other suitable manner.

`Within the flue spaces between the walls 1 Vand theA artition means 4 are provided discharge e ectrodes 8 consisting for example of 'venting cracking of said material.

metal Wires, rods, or other conductors 8 of relatively" small cross-section and having continuous and substantially smooth-surfaced coatings or coverings 9\ of suitable semi-conducting material at all portions thereof opposite the collecting electrodes.

Said discharge electrodes may be suspended from a supporting frame 10 mounted on insulators 11: in the usual manner of electrical precipitators of this character. Said semiconducting coatings may consist for exam le of Portland cement concrete, prefera ly made up with a suitable amountof fine sand but with little or no coarse aggregate, or other suitable cementitious material with or Without asbestos or other fibrous material incorporated therein for the purpose of pre- Other semi-conducting materials may also be used for this purpose, for example, enamels containing suflicient incorporated conducting material to rendei t-he same semi-conducting, said conducting material consisting for exanple of conducting metal oxides, finely divi ed metals, carbon, etc. The term semiconducting as used herein is applied to the general classiofmaterials Whose electrical conductivity is intermediate between that of Substances which are generally considered good conductors, such as metals, carbon, etc., and thaty of materials which are generally considered nonconductors, such as glass,

- porcelain, quartz, rubber, etc. For the purpose of my invention I prefer to lform the` semi-conducting coatings or covers 9 of materials having an electrical conductivity, ,at

temperatures not exceeding 200 C., between the order of 102 and 10 reciprocal ohms er centimeter cube. Materials having an e ectrical conductivity within this range' are adapted to permit the flow of sufficient electrical current to effect electrical precipitation and at the same time to prevent excessive flow of current to any part of the precipitator. The wires or rods 8 may be of any suitable small diameter, for example 11g inchv to l@ inch or larger and the thickness of the semi-conducting' coatings 9 mayl be varied, according to the material used vand the conductance desired, for example from a` mere film in the case of enamels to a'thickness of l@ inch or more in the case of cementitious materials.

The term substantially smooth-surfaced as applied to the semi-conducting coatings is not to be understood as precluding any minor roughness or unevenness which is inherent in the material used in such coating. Such coating should, however, as shown for example in Figs. 1 and 4, be of substantially uniform thickness, with a surface as smooth as it is practicable to obtain with the material used. Any minor roughnesses or protuberences which may occur are to be considered as "merely incidental and unavoidable andare not relied upon according to this invention for facilitating electrical discharge therefrom. This construction is therefore to be distinguished from certain types of previously used discharge electrodes which comprise a conducting member with pro]ecting fragments of non-conducting material secured thereto, in which case the projecting points or edges of the non-conducting material were intentionally provided for the purpose of facilitating electrical discharge therefrom.

I prefer to arrange the discharge electrodes 8 in parallel-relation to the re-enforcements 5 in the collecting electrodes and opposite the spaces between such re-enforcements so as to equalize the electrical field intensity throughout the surface of the collecting electrodes as set forth in my patent above referred to.

The operation of this form of the'invention is as follows: V

A high potential difference, preferably unidirectional, is applied to the electrodes for example by connecting the high tension system carrying the discharge electrodes 8 through Wire 12 to any suitable source of high tension rectified alternating current for example in the manner set forth in U. S. Patent to F.,G. Cottrell, No. 895,729, dated August 11,1908. A strong electric field is thus producedtbetween the surfaces of the semi-conducting coatings 9 of the discharge vcollecting electrodes 1 and 4 with the result that an electrical discharge takes -place mainly from the discharge electrodes on account of thev relatively limited cross-section and correspondingly sharp curvature thereof. Such electrical discharge takes place from the surface of the semi-conducting coating 9 of each discharge electrode and the current must therefore pass through said semi-conducting material, which prevents undue concentration of the electrical field at any portion of such surface. This effect is further increased in this case by the semiconducting character of the collecting electrodes 1 and 4, with the result that a very uniform distribution of electrical discharge, corona, or ionization is maintained throughoutthe body of gas passing between the electrodes and a more rapid, complete, and uniform electrical charge of the suspended particles in they gas is secured with .resulting rapid and com lete electrical precipitation of such suspen edparticles. Such precipitation takes place in the usual manner of electrical precipitation operations, by translation of the electrically charged particles under the action of the electrical field'toward the collecting electrode, it being understood that the particles will be electrically charged in the same sense as the discharge electrodes and will therefore be forced by the action of the electrical field away from the discharge electrodes and towards the collecting electrodes. Due lto the uniform distribution of the electrical field, and the prevention of arcing and disruptive discharge brought about by the semi-conducting coating on the discharge electrodes and the semi-conducting nature of the collecting electrodes, a very high potential difference may be safely maintained between the \electrodes without danger of producing disruptive discharge.

The discharge electrode provided .with a semi-conducting coating according to my invention may also be used in connection with metallic or conducting collecting electrodes.

As an .example of this I have shown in igs.` -5 and 6 a precipitator of the tubular or pipe type comprising a vertical tubular casing 13 formed for example of steel, cast iron, or other suitable' metal and a discharge electrode 14 mounted so .asnto extend axially Within the tubular casing 13 and consisting of a Wire, smallrodor other conductor 14; provided with coating or covering 15 of semiconducting material 'such as a semi-conducting enamel of the type above described.

Said discharge electrode may be mounted on Vsuitable insulating means 16 and may be provided at its lower end with tensioning means such as weight 17. .The discharge and collecting electrodes are in this case provided with electrical connections similar to those shown in Figs. 1 lto 3 and the operation of this form of my invention is substantially the same as that above described. 'It will of course be understood that in practice any suitable number of vertical flues or pipes 13 may be connected in parallel arrangement in the usual manner of multiple pipe electrical precipitators, a discharge electrode 14 provided with a semi-conducting coating being arranged within each of said fines.

I claim:

1. In apparatus for electrical. precipitation of suspended particles from gases, a discharge electrode comprising a conducting member ,and a continuous coating of semiconducting material surrounding said conducting member.

2. In apparatus for electrical precipitation of suspended particles from gases a dischar e electrode comprising a conducting mem er, and a continuous coating of semiconducting material surrounding. said conducting member, said semi-conducting material having an electrical conductivity, at temperatures not exceeding 200o C., between the order of 1072 and 10@ reciprocal ohmsv trode and means for maintaining a high potential difference between said discharge andV collecting electrodes.

4. An .apparatus as set forth in claim 3, said collecting electrode being of semi-conducting material so as to present high 4resistance throughout its area.

5. In apparatus for .electrical precipita- -tion of suspended particles from gases, a

discharge electrode comprising a conducting member and a continuous coating of semiconducting cementitious material surrounding said conducting member.

6. In apparatus for electrical precipitation of suspended articles from gases, a discharge electro e. comprising-a conducting member and ac'ntinuous and substantially gli smooth-surfaced l coating of semi-conducting material surrounding said conducting mem ber.

,In testimony whereof I have hereunto sub'- scribed my name this v11th day of September, 1925.

'EVALD ANDERSON.