US1481031A - Electric furnace and method of operating the same - Google Patents

Description

G. H. sETHMAN ELECTRIC FURNACE AND METHOD 0F OPERATING THB SAME Filed Jan. 30 1922 gwuenfm Patented Jan. 15, 1924.

UNITED STATES PATENT OFFICE'.

GEORGE H. SETHMAN, OF DENVER. COLORADO, ASSIGNOR, BY DIRECT AND mNE AS1- SIGNMENTS, TO THE ELECTRIC RESEARCH COHPANY, 0F DENVER, COLORADO, A

COMMON LAW TRUST.

ELECTRIC FURNACE AND METHOD 0F OPERATING THE BAIE.

Application led January 30, 1922. Serial No. 532,787.

To ai] whom t may concern:

Be it known that I, GEORGE H. SETHMAN, a citizen of the United States, residing at the city and county of Denver and State of Colorado, have invented certain new and useit appertains to make and use the. same,

reference being had to the accompanying drawings, and to the characters of reference marked thereon, which form a part of this specication.

rThis invention relates to the art of smelting refractory ores, and has special reference to an electrically operated furnace employing single or polyphase current of a certain characteristic wave form.

It has long been recognized that an electric furnace for smelting refractory metalliferous ores would possess many advantages over the present extensively employed method of using'a blast furnace provided with colte fuel. I am aware that many types ofelectrically operated ,furnaces have been designed and patented and that some of them are successfully employed in smelting highly conductive ores, such as iron ores, but so far as I am aware, there has not been produced an electric furnace which will successfully smelt the highly refractory auriferous, auriargentiferous, plumbiferous and other highly refractor ores which have little or no electrical con uctivity as compared with the highly conductive iron ores.

Attempts to employ an electric arc furnace for smelting the above type of ores have usually been followed by disastrous resuits, owing primarily to the fact that the resistance of the arc path is subject to the most violent fluctuations, varying from a very high resistance to a dead short circuit.

.i In order to successfully operate an are under such variable conditions by means of the ordinary direct or alternating current, it is necessary to equip the furnace with complicated regulating means which will automatically vary the voltage in an attem t to keep the current strength constant. uch regulating means are not reliable in operation, with the result that troublesome surges, kick-backs, and intermittent disturbances take place, which damage the generators and transformers and make it a practical` mpossiblity to carry out the smelting succes'sfully.

I have found-that if I employ,as the source of electric current supply, a generatorwhich generates a flat top expanding wave,

due to the fact that at no time after the first part of the voltage and current waves are producedis there any dynamic action between the fields and the armature, that in a circuit supplied with current by such a generator, extreme variations in the arc resistance and. even short circuits can take place without injuring the generator, blowing fuses, opening circuit breakers, throwing off the belts on belted units, or distress- -ing the engine or generator, in the case of units of the direct connected type. It is the employment of the above type of current generator that has enabled me to ,successfully smelt highly refractory ores without employing any regulating devices whatever for thepurpose of compensating for the vanations in the arc resistance, and wi-thout a source of current supply having the above characteristics, an' electric arc furnace for smelting this class of ores is not regarded as commercially practicable.

In order to describe myinvention with the greatest degree of clearness, I shall have reference to the accompanying drawing, in which- Y Fig. l is a da ram showing the characteristic voltage an current wave produced by the generator which I employ in this smelting process;

Fig. 2 is a diagram showinghow a three- `phase Y connected source of current supply is connected to the smelter electrodes;

Fig. 3 is a vertical longitudinal section of one form of smelter employed by me;

lll

onsidering (D as the point of origin, curve E extends upwardly in a direction which corresponds somewhat to that which would be followed by an ordinary sine curve until the point D is reached when it becomes parallel to the longitudinal anis @-1- K for a short time until the point lds 1s reached. it this point all dynamic action between the armature and the fields of the generator ceases and the voltage curve extends downwardly to the axis on a line that corresponds to a logarithmic curve. Fllhe current curve C follows the general shape of the voltage curve E and attains itspzero value at the same instance as the voltage curve. ln case of a low arc resistance or dead short circuit, no serious damage can result when a generator producing a potential curve of the above described type is employed, for the reason that during the part of the curve from O to D the value of the current is limited by the counter electromotive force of self induction, while after the point l? is passed, the electromotive force is merely that which is due to the inductive kick or stored energy of the windin s,

glu `Fig. 2 l have shown a source of threephase supply G in which the phases a, h and c are connected Y fashion. The neutral point of the generator is connected by means of a conductor 2 with a plate electrode 3 which is located in the bottom of the furnace. lhe free ends of the respective phases a, b and c are connected respectively with electrodes ll, 5 and 6 by means of conductors 7, 8 and 9. l have shown a three-phase supply because this is the simplest and serves to illustrate the arrangement as well as any other number of phases, but l desire to point out that it is my intention to employ any number of phases desired` as for example,

- two, three, sin, nine and twelve, the exact number being dependent on-thc size of the lili Bil

smelter and other elements which will determine the design of the layout.

lin Fig. 3 l have shown one form of furnace which l consider well adapted for use in carrying out my method. The furnace l0 is built of lire brick or anysuitable refractory substance, and has its base portion ll enlarged to some extent; the upper part of the furnace has a cylindrical opening l2 therein which terminates at the bottom in an enlarged furnace space l, in the bottom of which is formed a pocket or depression 1li within which is placed a copper plate 3 whose upper surface is provided with a number of copper points l5. The pocket 1t is iilled with graphite so as to form a conductive protective cover for the copper electrode 3. Projecting through the inclined walls 17 of the furnace l0 are a plurality of electrodes, the exact number of which depends on the number of phases employed; these agencer electrodes are equally spaced and when three arc employed, as in the example illustrated, they are spaced 120 degrees apart. "Where the electrodes enter the furnace, they pass through stuffing boxes V18 which are preferably hollow and adapted to he cooled by the circulation of water through thc hollow interior thereof. The electrodes are slidable in the boxes 18 so as to permit of adjustment being made.

The chamber 18 is provided near the bottom thereof with two spouts 19 and 20, the former of which is located near the bottom of the chamber and serves for removingthe matte. while the spout 2O is located somewhat higher and serves for removing the slag, the separation of the slag and ina-tte being effected by the action of gravity which causes the matte, which is heavier, to sink to the bottom of the liquid mass. Near the top of the furnace l provide a hollow conduit 21 which extends to and is connected with a condenser (not shown). The top of the furnace is covered by a plate 22, whichl is provided centrally thereof with a cylindrical member 23 of considerable length, the lower end of which projects into the furnace and is provided with a closing cone 2li, which is pivotally connected to one end of pivotally mounted lever 25, on the outer end of which is a weight 26. rlhe ore is fed to the fur-- nace through the tube 23 in the well known manner. @n the sides of the furnace l have provided several hoppers 27 which can be employed for adding material to the furnace. lf it should he found desirable, fuel may be added to the ore through hoppers 27 and used to increase the preheating effect. Line V28 vindicates the proper level of ore in the furnace.

ln Fig. d l have shown a slightly modified form of furnace, which differs from the one described above. mainly, in this, that a considerable space is provided between the lower edge of the opening of the matte spout and the top of the graphite packing 16, which space is designed to con-tain the molten lead. which :may be removed from time to time through opening 29, or which may automatically overiiow over edges 30 whenever it env ceeds the level of this edge.

Although l have shown and described in detail a furnace structure, it is evidentthat `furnaces of different forms may be einployed with my particular current supply. rllhe furnace described above is, however, a satisfactory and practical device, and l reserve the right to protect the same in this or in a divisional application.

The operation of my furnace is as follows: The electrical connections are formed 'as indicated on the drawing and explained above. An electrically conducting ore or other electrically conducting material is then placed inv the furnace and about and between electrodes 4, 5, 6. and 1G, so that when the electromotive force is applied, current will begin to flow between the electrodes. Ore and fluxes are then introduced into the furnace in the proper proportions and in such amounts as desired. not extending above line 28. The current is then applied and ows through the conducting material from the several electrodes to plate 3. The current flowing through -the conductive material causes the latter to become intensely heated and very soon melts the same, after which the arc having become established continues to burn and heat the refractory ores that feed down from above. down carries a small portion of the current, as it is not an absolute non-conductor, and heat is therefore generated by the current iiowing through the mate-rial as well as by the arc. Both forms of heat are therefore generated and utilized in the reduction. lVhen the condenser is attached' and operated,-a strong fan (not shown) will be in operation and arranged to suck the gases from the furnace through pipe 21, and the hot gases from around the arc will'pass upwardly, roasting and preheating the ,ore so that by the time it reaches the arc chamber' 13 it will be heated to very near the melting point. lBy having the chamber 12 of Sullicient length, the gases may be cooled to a comparativelylow degree before they leave the furnace-,thus assuring a very thorough vutilization of all the heat genera-ted. The

spouts 19 and 20 may be leftopen so that 'the slag and matte may'flow from the furnace as fast as they are formed, thus providing for continuous operation.

My smelting furnace can be made of any desired size and capacity,'and small units can be cheaply and easily constructed. It therefore 4becomes possible for mines that are 'located far from a railroad or a fuel supply to be equippedwith electric smelters, the current for the operation of which can be supplied by an internal combustion engine driving one of my specially designed gen-k erators referred to above. As fuel for the operation of the engine can be readily transported, it is apparent that mines that heref tofore have been idle owing to the excessive cost of transporting the ore to a smelter, can be operated, and the ore smelted electrically. The matte can then be sent to a refinery where it canbe separated into the` several metals of which it is composed. Large custom smelters can also be operated as de-` scribed above, and at a cost per ton of o're greatly less than what it is with the present coke blast furnace. v Y

'As pointed out above, I do not claim to be the first one to have employed electricity for smelting ores, but I do claim that I have discovered the proper form, of potential and current wave to be employed in the suc- The ore as it comes" land. as this 1s a common specific form of current wave and an electric arc furnace, as the two cooperate to produce a result long desired and often sought but never before attained.

The voltage will be anything that may be found necessary to Iproduce the arc between the electrodes and the bottom plate 3, and ordinarily itis about 145 volts, while the amperage will run from 250 in small furnaces to several thousand amperes in the larger furnaces. The frequency is also more or less optional, but cycles is satisfactory,

' frequency, it is employed in this combination by me.

Having now described my invention, what I claim as new is 1. In an electric furnace for the'smelting 2. The method of smeltin highly refractory metalliferous ores, w ich comprises subjecting the same to the heating effect of an arc between a plurality of electrodes, supplying a multiphase electric current to said electrodes, said current having a potential whose wave form is such that its front face is comparatively steep, its top is substantially flat, and whose rear'is upwardly concave.

3. The method of smelting ores in an electric arc furnace having a plurality of electrodes adapted to be connected to and operated by a Y connected source of polyphase current, which consists in supplying said electrodes with a current whose potential wave form is such that its top is comparatively flat and whose rear is upwardly concave.

4. The method ofv smelting ores in an electric arc furnace, having a plurality of electrodes adapted to be connected to and operated by a Yeconnected source of polyphase current, which consists in supplying said electrodes with a current whose potential wave form is such that its front face is substantially sinusoidal, whose top is flat,

and whose rear face is substantially a loga l UU the neutral point of said phases, and a polyphase generator in which the interaction between the armature windings and the eld is such that duringr the first part ot" each alternative, the voltage produced follows rent, one electrode adapted to be connected to the neutral point or said phases, and a polyphase generator in `which the interaction between the arma-ture windings and the field is such that the power 'factor is Substantially one.

7. The method of smelting ores in an electric arc furnace having a electrodes, which consists in supplying said electrodes with a current Whose potential Wave form is such that its front face is substantially sinusoidal, Whose top is Hat, and Whose rear tace is substantially a logarithinetic curve.

ln testimony 'whereof l affix my si nature.

GEORGE H. SETH fl'AN.

plurality ot"

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