US2195453A

US2195453A - Electric furnace

Info

Publication number: US2195453A
Application number: US234099A
Authority: US
Inventors: Gardner Daniel
Original assignee: Mij Voor Thermo Chemie N V
Current assignee: Mij Voor Thermo Chemie N V; Voor Thermo-Chemie N V Mij
Priority date: 1937-10-14
Filing date: 1938-10-10
Publication date: 1940-04-02
Anticipated expiration: 1957-04-02

Description

Patented Apr. 2, 1940 ELEUIBIC Daniel Gardner, Bueil- FUBNACE France, as-

Malmaison, signor to Maatschappij voor Thermo-Chemie N. V., Netherlands, a company of the Netherland! Application October 1l, In Great Britain Schirm.

This invention relates to electric furnaces intended for carrying out chemical, metallurgical or heat-treatment operations at high temperatures.

In a furnace according to the present invention. generation of heat is eil'ected partly by the resistan encountered by the electric current in its ww: through the furnace, partly by small electric arcs generated between the particles of l coarse granular material, into which the electrodes project. Saidy material surrounds the furnace chamber in which the treatment is to be carricd out, in such amanner that the sise of the granules or particles decreases, from the inside towards the outside, to an exceedingly small value. 'lhat is to say, the outer layer of the granular material is formed by line powder, which, in virtue of the very high intermediate ce between its particles, actually functions as an ,o insulator, both electrically and thermally. The

granules of the inner layer of said material, however. have a relatively large size, say of 38 mm., so that electric arcs can be formed between the same.

g5 In order that the above statements may be more readily understood, reference is had to the annexed drawing, which illustrates, in a vertical sectional elevation, an electric furnace constructed in'accordance with the invention.

The furnace chamber proper is constituted by a vertical inner cylinder I of graphite, petroleum coke, Carborundum, zirconium carbide or other material suitable for the purpose. Said inner cylinder is surrounded, with'a narrow interspace, by

anoutercylinder 2ofsimilarmaterlal.

The furnace chamber i, the wall of which is provided with upwardly inclined narrow passagesl,isiittedwithanimpellerscrew4 ofrefractcry materialsuch as graphite or petroleum coke, the pitch of said screw increasing from the upper to the lower end. vThe screw impeller projectsupwardlyintoahopperiforreceivingthe materialtobetreatemforinstancesuitably ground ore with the required fluxes.

Attheupperendtheinterspacebetweithe cylinders l and 2 communicates, through a conduit C, with a condensing chamber 1.

Thelowerendofthefurnacechamber opens some distance vertically above a conical screen l,

which serves for distributing the material dischargedfromsaidchamberoveratablelsemred tothespindle lloftheimpellerl.,

The spindle I0 is driven at both ends. through themedium ofelastic couplings il, I2,byworms 66 onshafts |3.i4 adaptodtoberotated,through 1938, Serial No. 234.099 October 14, 1931 mitre wheels, by a common shaft l5 in such a manner that the speed of the impeller I is say about one revolution per minute.

'Ihe outer cylinder 2 is surrounded, with a relatively wide interspace, by a refractory jacket It 5 of asbestos, magnesia, aluminium oxide or the like, said jacket resting on a refractory slab i1, which itself is supported by a steel framework, to which also the bearings of the driving gear are secured.

Electric current is introduced by electrodes I8 10 passed through aperturesprovided, at different levels, in the Jacket I6. Said electrodes are ra dially slidable in suitably cooled bushes I9, and the inner end of each electrode is provided with a readily renewable wearing piece of reduced cross- 15 section, said piece being preferably screwed into the inner end of the main electrode.

The interspace between cylinder 2 and jacket Il is filled with granularmatcrial.4 'I'he inner layer, i; e. the layer engaging the outer wall of 20 cylinder 2, consists of relatively coarse granules 2l of coke, graphite or the like. The outer layer,

i. e. the layer contacting with the 'inner wall of Jacket I6, consists of soot (lamp black, carbon black) 2l, either or not mixed with magnesia, 25 aluminium oxide or the like, and may be suitably compressed, for instance, briquetted. The space intermediate said layers 2B and 2| is filled with granular carbon, the size of these granules' decreasing, in outward direction, from a size corre- 30 sponding to that of the granules of the layer 2l, to a size corresponding to that of the particles of layer 2|.

The modus operandi of the described furnaceis asfollcws:` A

First, the electrodes It are moved inward, until their wearing pieces directly contact with the outer cylinder 2, whereupon the current is switched on. The current will now flow principally through the cylinder 2, which is thus quickly 4o heated to the required temperature. Thereafter, the screw impeller I is rotated, whereby the material to be treated Ais caused to slowly descend from the hopper l and through the reaction chamber to the bottom opening thereof'.l ,'When the furnace 45 proper and the material therein have reached the4 desired temperatures, so that from that. moment onward the electrical energy supplied the electrodes4 I8 only serve for maintaining said temperatures, the electrodes are retracted a 50 little, whereby the current will pass for the greater part through the coarse carbon granules, which by that time have-already assumed a high temperature. As a en small eleciz'icarcswillbeformedbetwcensaidgranules, 55

and the total strength of the current will be considerably reduced.

As stated, the very ne carbon powder (soot) on the outer side of the space between cylinder 2 and jacket i6 acts as a heat insulator, so that the jacket i6 remains relatively cool. Besides, said powder also acts as an electric insulator, especially when magnesia or the like has been admixed thereto.

If desired, the electrodes can be adjusted by automatic means under the control of a suitable thermostat.

The chamber 'l serves for collecting and condensing gaseous products that may be formed in the reaction chamber, for instance zinc vapours.

The increase of the pitch of screw 4 in downward direction prevents the materials under treatment from clogging the reaction chamber.

What I claim is:-

1. An electric furnace comprising a base, a reaction chamber, an inner wall structure surrounding said chamber, said structure consisting of a double-wall jacket, inclined channels in the inner wall of said jacket and connecting the reaction chamber with the inner space of the same, a condenser connected to said jacket, an outer wall encircling said inner wall structure, a space between said two walls, means for introducing the charge into said chamber, means for dis charging the treated charge from the same, an insulating layer located adjacent to the inner surface of said outer wall and lling a section of said space, a plurality of concentric layers between said insulating layer and the outer surface of said inner wall structure, said concentric layers forming the furnace heating zone proper and Consisting of current conducting particles of which the size gradually increases in the direction from said insulating layer towards said inner Wall structure and displaceable electrodes supported by said outer wall and protruding through said heating insulating layer into said heating zone proper.

2. An electric furnace comprising a base, a reaction chamber, an inner wall structure surrounding said chamber, said structure consisting of a double-wall jacket, inclined channels in the inner wall of said jacket and connecting the reaction chamber with the inner space of the same, a condenser connected to said jacket, an outer wall encircling said inner wall structure, a space between said two walls, means for introducing the charge into said chamber, a screw conveyor transporting the charge through the same, the pitch of said conveyor increasing from its upper to its lower end and means for discharging the treated charge from said chamber, an insulating layer located adjacent to the inner surface of said outer wall and filling a section of said space, a plurality of concentric layers between said insulating layer and the outer surface of said inner wall structure, said concentric layers forming the furnace heating zone proper and consisting of current conducting particles of which the size gradually increases in the direction from said .in-

wall, a plurality of at least three concentric layers of current conducting particles between said insulating layer and said inner wall-structure forming the heating zone of the furnace, the particle size of said layers gradually increasing in the direction from said insulating layer towards said inner Wall structure and displaceable electrodes supported by said outer wall.

DANIEL GARDNER.