US1939913A - Process for electrothermic reduction - Google Patents

Description

Dec. 19, 1933. P. l.. J. MIGUET A, 1,939,913

l PROCESS FOR ELECTROTHERMVIC REDUCTION Filed July 5, 1930 FIGA www@ jhmnlo Patented Dee '19, 11933 UNITED sTATEs rnocnss Fon `:mi:o'rno'r'mnmr,c REDUCTION raul Louis .meph Minet, suman-1e- Maurienne, France appumion'ruly 3, 1930, serial No. 405,118, and in France November 4; 1925 s (c1. 'z5-zas) This invention relates to an improved process for-`reducing materials in an electric furnace. This application is in part a continuation of my co-pending application Serial No. 121,189, filed July 8, 1928.

According to the known prior processes of feeding electric furnaces having a vertical electrode, thematerials of the charge have been intimately mixed and the proportions of these materials have been only changed tocorrect the defects which result 'from the incorrect proportions. This method of charging furnaces results in local overheating of the electrode especially at the end of the electrode. Such overheating causes a loss of about in the raw materials and a loss of about 50% in the-energy input. These losses are primarily due to a concentration of the current at xthe end of the electrode which causes an excessive overheating at this point. The high temperatures there give rise to an excessive formation of gas, which rapidly escapes through the charge around the electrode, thereby causing excessive heating and decomposition of the electrode and loss of heat, and of raw materials.

According to applicants invention, the raw materials of thesfurnacecharge are divided into conductive and non-conductive batches. These batches are -fed separately into the furnace chamber so that they form alternate substantially horizontal layers of conductive and non-conductive material around Lthe vertical electrode. Theconductive layers of' raw materials extend from the electrode to the conductive portion of the furnace and the non-conductive layers may extend from the vertical electrode towards the furnace walls for only a portion of the distance which separates these elements. This arrangement of the layers of the materials provides a restricted path for the current through the con- 40 ductive layers and between the non-conductive layers. Y l

In generali the conductive batch may be composed of a mixture of carbonaceous material and an ore to which mixture a ilux may or may not be added and the non-conductive batch may be composed of a flux with which a portion of the ore may or may not be mixed as desired. The proportions of the materials in the conductive batch may be changed within certain limits to give the proper conductivity to the" conductive layers of material and to provide the correct quantities of reducing agents to react most favorable with the ores. Thus, by changing the proportions of conductive materials to the non-conductive materials in the conductive layer of the furnace charge, the density ofthe current in the layer, the spreading of the current and the sine of the reducing zone can be increased or decreased within a wide range to produce a most satisfactory condition for each product. These changes of proportions in the conductive layers may be made either by altering the proportion. of carbonaceous material to the ore in the furnace charge, or by changing the distribution of the ore or iiux, or both,l between the conductive 05 and non-conductive batches.

Specic examplesv of theY proportions of the materials contained in the batches will be given infra.

Itis preferable to use a very large electrode which carries high current at a low voltage and low density. The low voltage and low density of current aids in the spreading action of the current due to the decreased tendency of the current to form arcs and thereby open up individual conductive paths through the; charge. By the use `of a large electrode, an interval of space can be maintained more easily between the end of the electrode and the molten baths. 'I'his space resists the passage of thecurrent from the end of the electrode toi-the materials or molten bath thereunderand lfurtheraids in the spread of the current laterally from the side's of the electrode. Also by the use ofthe large' electrode the bath is better protected from the falling of the raw 05 materials, in the unreduced state, into the bath and thereby contaminating it. It is stated as anexample only, to which I do not wish to be specifically limited, that I have used electrodes varying in amperage from 50,000 to 300,000 amperes with a current density of about 2 amperes per sq. cm.)

One of the objects of my invention is to increase the zone of reduction and to causea lateral reduction of the materials as they pass downward along the electrode and tocomplete the reduction of these materials before kthey reach the molten bath. y

Another object of my invention is to more efmo fectively control the temperatures of reaction and thereby prevent the excessive formation of gases and reciprocal reactions and heat losses incident thereto.

Another object of niv invention is to eliminate 105 local overheating of the electrode and the charge.

Another object of my invention is to increase the life of the electrode'.

Another object of my invention is to reduce the ores and renne the nal product simultaneously.

electrifcagllfenergy used. 1

Another' 'object of my invention is to suppress the white flames which tend to rise aroundthe v the slag lc and final product l.

electrode at the top of the charge. v

The process of my invention is more fully disclosed in the following description, and acconti-r ts in they;y

panying drawing' in which similar different figures are referred to by the same letters, and in which:

Figure 1 is a vertical section of an electric furnace having a homogeneousfcharge .fed therein according to the prior known methods.

Figure 2 is a vertical section of an electric furnace showing alternate layers of conductive and .non-conductive materials Iwhich are fed in ac. cordance withapplicants invention. Figure 3 isa vertical section of an electric furnace similar to Fig. 2Vbut havinga central lining of a neutral non-conductive material `and having aperipheral lining of conductive materials. p In Fig. 1 isshown the path of the current a ilowing. through the homogeneous charge b, which is made uniformly conductive and is fed into a furnace which is operated inaccordance with the prior known methods. It will be noted that the lcurrent a passes froml the end of the electrode c to the conductive hearth d in a very restricted path. Due to the 'furnace charge be' ing at a higher temperature under the electrode c than it is elsewhere, this portion e of the chargeinc1uding.the molten bath, is made more conductive than the remaining portion of the charge and consequently the current a will nor-A mally follow the path as indicated unless the distance to the sides of the furnace is materially less than the distance to the bottomv or unless other abnormal conditions are introduced.

The electrical power is very poorly utilized when it passes in a more or less straight line from the end of the electrode to the`-hearth alv directly underneath'it. The flow of the current through 4this zone furnishes heat where it is least needed and causes an excessive temperature to be maintained at this point. Such conditions cause a loss of heat and a volatilization of raw materials which slide under the electrode. Aside from the loss of heat and materials due to the excessive volatilization of the materials, the carbon monoxide lformed thereby causes a very bad condition around the furnace for the workmen.

Fig. 2 illustrates the method of feeding the raw materials into the furnace chamber in` accordance with my process. It will be seen that the current a spreads out laterally through the furnace charge and traverseslthe entire charge be` fore it reaches the hearth d. The current passes through the conductive layers h and between the non-conductive layers f. An interval or space t is provided between the end f the electrode and the molten bath. The resistance resulting from this Vspacein conjunction with the low voltage and the conductive layers which are interposed between non-conductive layers causes the cur'- rent to spread out laterally through the conductive layers and flow toward carbon hearth d and ,walls y of the furnace to complete the electrical '-1 tire conductive mixture h.v e,

In Fig. 3 is another example of my process in which a larger electrode c is used than that used in the furnace illustrated, in Fig'. 2. In this case the hearth of the furnace comprises an inner central non-conductive or neutral lining 9' surrounded by another peripheralportion i made of carbonaceous material. The non-conductive lining 'i offers a resistance to the .passage of the current a from the end of the electrode c through This resistance alone and also in combination with the resistyance offered by the space t will act to cause the current to spread out laterally from the electrode y, and flow through the conductive mixture instead 'of flowing from the end of the electrode and,

'throughI the molten bath where the heat produced by the iiow of current is least required.

It will be noted that in Figs. 2 and 3 the noncarbonaceous, non-conductive layers f are fed in continuous rings around the electrode and that oneofthese layers is maintained on top of the charge which acts to suppress the white flames which tend to rise around the electrode at this point.

It has been stated that the proportion of carbonaceous material in the"conductive mixture and the thickness of the non-conductive layers as compared to the thickness of the conductive layers could be changed as may be required. By such regulation and by the use of the resistant space t at the end of the electrode, which may beused with or without the resistant central lining'y in the furnace hearth, the current may be so dispersed through the charge that practically no current will flow from the end of the electrode through the molten bath. 'Ihe heating action of the current in passing laterally through the charge will cause a complete reduction of the raw materials between the sides of the electrode and the side walls of the furnace before these materials can reach the bottom of the furnace hearth. t

Final products such as metals and their alloys may be further refined under the electrode. Sufiicient heat may be derived for this purpose from the surrounding charge, the end of the electrode and by the passage of additional current from the end ofthe electrode through the final product. The necessary fluxing or oxidizing materials as `may be required for further refining the nal product may be provided in In order to conserve the energy input andl raw materials and to utilize to the best advan tage the reducing and oxidizing materials added to the ores, it is recommended to use a large electrode and to maintain a thick charge heaped up around theelectrode. Such voperating conditions, however, should be varied in accordance with the type of ores that are being worked.

and the nal product that is to be produced. Higher power can be used on the large electrodes and at the same time the current density can b'e kept low, which contributes towards the spreadingof the current, which in turn heats v the charge more'emciently. Wherethe charge is thick it absorbs the vheat generated more effectively as the upper layers have the opportunity.

of absorbing the heat from the gases generated in the lower layers. The gases in rising are thrown out towards the walls of the furnace, due

to the bailies formed by the non-conductive layersk may be present in the charge, or are formed in thefurnace, are eliminated from the charge be-v fore it reaches the stage of the final product. Although it is not known, it is thought that the elimination of these objectionable compounds is due to the thorough and effective oxidizing action of the oxidizing materials in the charge.

In choosing a reducing carbon, it is desirable to select a carbon having a very low apparent density and a relatively high conductivity Anthracite coal and hard metallurgical coke are eliminated because of their high density and also because of their low chemical reactivity, a1`

though their conductivity may be good. Wood charcoal is also excluded because of its low conductivity as well as its high combustibility in the air, although it has an apparent low density. Therefore, practically, it is necessary to utilize almost exclusively gas coke or the like.

In determining the proportions of carbonaceous material to be used in the charge in reference to its conductivity where metal turnings are employed, such metal turnings should be ignored. It is impracticable to give any specific rule for the ratio of carbonaceous material to the remainder of the charge or to that portion of the charge in the conductive batch or mixture. Generally, it may bestated that by volume the ratio of carbon in the conductive mixture to the other materials in this mixture may l vary from two to four parts 'of carbon to one of other materials in the mixture. Irrthe case of iron ore and other ores of the heavy metal clash, the minimum amount of carbon within this limit should be used in the conductive mixture because these ores require a small' portion of reducing carbon, and, if the carbon in the mixture is increased beyond this minimum, this would require an increase in the thickness of carbon-free, non-conductive layers which would lead to poor furnace operating conditions. When possible and when the thickness of the nonconductive layers is not made too great, it is advantageous to increase the proportion of carbon in the conductive mixture in orderto obtain a better spreading of the current by the corresponding increase in the conductiveness of the mixture and maintaining a better separation of the layers. As a further limitation, the raw -materials outside of the conductive mixture should not weigh more than twice the weight of the non-carbonaceous materials of the conductive mixture in the case where two additions of the mixture are fed into the furnace every half-hour, and not more than three times in cases where three additions are fed every halfhour.

In the manufacture of such products as calcium carbide, ferro-manganese and compounds of silicon, the best practical results are obtained by distributing the weight of the raw materials, exclusive of the carbon and any metallic turning, equally between the conductive and nonconductive batches. In large furnaces employing full power it may be desirable to tap the furnace every hour instead of every hour and one-half. For the hourly tapping it is preferable to feed only two additions each half hour, whereas for one and one-half hour tapping it is preferable to feed three additions each half hour.- i The following are given as examples of the composition of charges which are used for the manufacture of some of the important electric furnace products:

First-Case of heterogeneous charges with conductive mixtures according to the minimum rule of volumes.

First 'example Iron: 10,000 kw. at 45 volts with one electrode. v

Production per hourly tap:

10000'kw. hr. 2000 kw. hr.

Corresponding raw materials:

Coke 5000X0.32=1600 kg. or 4000 liters. Ore 5000 1.8 :9000 kg. or 5000 liters. Lime 5000x0.22=1100 kg. or 1222 liters.

volumetric ratio of carbon to all raw mate. rials.

per metric ton=5000 kg.'

Coke\ 4000 .=0 64' Ore+Lime 5000+ 1222 Corresponding conductive mixture:

Coke 1600 kg. or 4000 liters. Ore 3000 kg. or 1666 liters. Lime 366 kg. or 407 liters.

volumetric ratioof carbon to raw materials in conductive mixture:

Coke 4000 192 Ore-i-Lime 1666+407 Additions each half-hour:

First{0re: 3000 kg. (Variable according to the Lime: 366 kg. slags which oulght to b Ore: 3000 kg. gray for norma iron an Seeond{Lme: 366 kg. blackish for iron halfdecarburized.)

Second example Ferro-manganese 7680%10,000 kw., 45 volts, with one electrode:

Production per hourly tap:

*lgglh' per metric ton= 2941 kg.

Corresponding rawL materials:

coke 2941 os5=1911gkgor 4W: liters. Ore 2941 2.1 :6176 kg. or 2470 liters. Lime 2941 0.65=1911 kg. or 2123 liters.

Volumetric ratio of carbon to all raw materials:-

Ore 3088 kg. or 1235 liters. Lime 955 kg. or 1061 liters.

conductive mixture:

Coke 47 77 V ore-taime nas-Hochmut8 Additions each half-hour:

Fix St{Ore: 1544 kg. (Variable according to the Lime: 477 kg. appearance of the slag.)

Orc: 1544 kg. f 5 Sed{Lim: 477 kg.

Seconds-Case of heterogeneous charges in Vwhich the weight of the material to be reduced is distributed equally between the conductive mix- K tures and the carbon-free additions.

First example Calcium carbide 285 liters-10,000 kw. at 60 volts with one electrode.

Production by hourly taps:

' 10000 kw. hr. 2900 kw. hr.

Corresponding raw materials:

coke 3448 0J5=2`5a6 kg. or 6465 liters. Lime 3448 1. :3448 kg. or 3831 liters.

Volumetric ratio of carbon to all raw materials:

=per metric ton=3448 kg.

Corresponding conductive mixture:

Coke 2586 kg. or 6465 liters. Y Lime 1724 kg. or 1915 liters.

Volumetric ratio of carbon to raw materials in conductive mixture:

Additions each half-hour:

First: Lime 862 kg. (Variable according to Second: Lime 862 kg. the appearance of the taps.)

Second example Ferro-silicon 45%-10,000 kW. at 50 volts, with one electrode. Production by hourly taps:

10000 kw. hr. n5700 kw. hr.

Corresponding raw material:

coke 1'154' 0.5= s'z'z kg. or 2192 liters. Quartz 1'I54X1. :1754 kg. 0111349 liters. Turnings 1754 0.6=1052 kg. or 2104 liters.

volumetric ratio of carbon to raw materials (the turnings b`eing ignored):

per metric ton=1754 kg.

Coke 2192 Quartz 131-9- 1'62 Corresponding conductive mixture:

Coke 877 kg. or 2192 liters. Quartz 877 kg. or 674 liters.

Turnings 1052 kg. or 2104 liters.

Volumetric ratio of carbon in conductive mixture (the turnings being ignored):

Coke ,2192" Quartz 674 3'25 Additions each halt-hour:

* /G First: Quartz 438 kg. (Varied according, to

whether slag appears or as tapping is slow.) Third- Case of heterogeneous charges with one of the materials to be reduced placed entire- .5' ly in the conductive mixture.

Second: Quartz 438kg.

- Lime Quartz Corundum :735+ 1057+ 200 First example Calcium-silicon-CaSia-10,000 kw. at 50 volts with one electrode.

Production by hourly taps:

10000 kw. hr. 12000 kw. hr.

Coke 1852 Lime* 481 3'85 Additions each half-hour:

First: Quartz 683 kg. (Varied according to wheth- Second: Quartz 683. er slag appears or as tapping is slow.) Second example Calcium aluminum silicon--CaAlSiz-15,000 kw., at 50 volts with one electrode.

Production by tapping every one and one-half 31;'

per metric ton: 833 kg.

' hours:

15000 kw. hr. 12000 kw. hr.

Corresponding raw materials:

per metric ton= 1250 kg.

Coke 1250 0.85=1062 kg. or 2655 liters. Lime 1250 0.53= 662 kg. or '735 liters. Quartz 1250 1.l=1375 kg. or 1057 liters.

Corundum 1250 0.45= 562 kg. or 200 liters. u i. Volumetric ratio of carbon to all raw materials:

Coke 2655 1.33

Corresponding conductive mixture:

Coke 1062 kg. or 2655 liters. Line 662 kg. or 735 liters.

Volumetric ratio of carbon to raw materials in the conductive mixture:

Coke 2655 3.61

Lime 735 Additions each half-hour: First: Quartz 687 kg. (Varied according as to Second: Corundum 562 kg. whether slag appears Third: Quartz 687 kg. or as tapping is slow.)

The manufacture ofthe above indicated products is not limited to the exact .proportions of the charge' as given herein, as these proportions should be varied in accordance withthe quality and kind of raw materials used.

Due to the emciency of my process described herein, ores of low recovery content may be coml mercially worked which wereimpracticable to work heretofore. This process is further enhanced invalue by the apparatus described in Patent No. 1,680,163 granted Aug. '7, 1928, on an application :tiled by me which is a division -oil application Serial No. 121,189 of which this application is a continuation in part. The apparatus referred to discloses an eiiicient means for separately feeding each batch of materials into the furnace by feeding portions of each addition simultaneously from a number of points about the electrode so that they will be thrown against the electrode.

I claim:

1. The method of operating an electric furnace having a vertical electrode, said method comprising forming the charge in alternate conducting and non-conducting strata, said conductive strata extending from the electrode to the walls of the furnace and said non-conductive strata extending for only a portion of the distance from the electrode to the walls of the furnace, connecting the electrode and a portion of the furnace at the side of the electrode in circuit with a source of power whereby the current is allowed to spread through the conductive strata above the lower end of the electrode thereby heating the charge laterally.

2. The method of operating an electric furnace comprising forming alternate conductive and nonconductive strata of materials which surround the electrode; said conductive strata extending from the electrode to the walls of the furnace and said non-conductive strata extending for only a portion of the distance from the electrode to the walls of the furnace; directing current into the electrode; intercepting the flow of current from the end of the electrode through the molten bath to the hearth by interposing a resistance in such path, and causing said current to spread laterally from the side of the electrode and spread laterally through the conductive strata to the furnace hearth.

3. The method of operating an electric furnace having a vertical electrode and a hearth having at least the outer edges connected to a power circuit, which comprises forming successively alternate conductive and non-conductive strata of materiall around the electrode, said conductive strata extending from the electrode to the walls of the furnace and said non-conducting strata extending for only a portion of the distance from the electrode to the walls of the furnace, directing current at the low voltage into the electrode, intercepting 'the flow of current from the end of the electrode through the molten bath to the hearth by interposing a resistance between the electrode and the conductive portion of the hearth and causing said current to spread laterally from the sides of the electrode through the conductive strata and thence to the conductive portion of the hearth.

4. The method of operating an electric furnace comprising forming successively, alternate conductive and non-conductive strata of material around a large electrode; said conductive strata extending from the electrode to the walls of the furnace and said non-conductive strata extending for only a portion of the distance from the electrode to the walls of the furnace; directing high current at low voltage into the electrode, and causing a current of low density to ow therein; intercepting the ow of current from the end of the electrode through the molten bath to the hearth by interposing an interval of space between the end of the electrode and the materials thereunder; and causing the current to spread laterally through the conductive strata and thereby reduce the charge between the side of the electrode and the furnace wall.

5. The method of operating an electric furnace having a vertical electrode comprising one electric terminal and a hearth having at least a portion thereof conductive and comprising the other electric terminal; said method comprising charging alternate layers of conductive and non-conductive materials into said furnace, so that said conductive layers extend to the walls of said furnace and said non-conductive layers do not extend to the walls of said furnace, whereby the current is carried laterally through the conductive layers from the electrode and downwardly to the furnace hearth.

PAUL LOUIS JOSEPH MIGUE'I.

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