US3465085A

US3465085A - Smelting electric furnace apparatus

Info

Publication number: US3465085A
Application number: US677249A
Authority: US
Inventors: Jutaro Yonemochi
Original assignee: Individual
Current assignee: Individual
Priority date: 1966-10-29
Filing date: 1967-10-23
Publication date: 1969-09-02
Anticipated expiration: 1986-09-02

Description

sepr. 2, 1969 Filed Oct.

JUTARO YoNr-:MOCHI 3,465,085

SMELTING ELECTRIC FURNACE APPARATUS 1967 I5 Sheets-Sheet 'i .-Moool- Sept. 2, 1969 JuTARo YONEMOCHI 3,465,085

SMELTING ELECTRIC FURNACE APPARATUS 3 Sheets-Sheet 2 Filed Oct. 23, 1967 Sept-2,1969 JUTARO YoNEMocHl I 3,465,085

SMELTING ELECTRIC FURNAGE APPARATUS Filed oct. 2s. 1967 s sheets-sheet s United States Patent O 3,465,085 SMELTING ELECTRIC FURNACE APPARATUS Jutaro Yonemochi, Koadachi 171, Komae-machl, Kitatama-gun, Tokyo, Japan Filed Oct. 23, 1967, Ser. No. 677,249 Claims priority, application Japan, Oct. 29, 1966, 41/71,539, 41/71,538 Int. Cl. H05b 7/ 06 U.S. Cl. 13--18 4 Claims ABSTRACT 0F THE DISCLOSURE Anelectrode structure to be utilized in an electric furnace, especially a smelting electric furnace, comprising a highly conductive metal peg, such as copper, suspended longitudinally in the center of a casing by a pair of holders connected to a power source, a plurality of steel or molded electrode rods suspended in a concentrically spaced arrangement about said peg from the same holders, and a paste filled in the space between said peg and rods in said casing, said casing being suspended from another pair of holders exclusively for holding said casing, said paste being melted and sintered gradually by the heat transmitted thereto from within the furnace to integrate the whole structure, whereby the capacity of said furnace can be substantially increased.

BACKGROUND OF THE INVENTION Field of the invention The present invention is concerned with electrodes, and more particularly it relates to an improvement in electrodes for use in electric furnaces, especially in smelting electric furnaces.

Description of the prior art The electrodes which have been conventionally used in the past with smelting electric furnaces include the following types. They are:

(a) Molded electrodes (block carbon);

(b) Continuously self-sintering and self-integrating type electrodes (Sderberg type in Germany and Fujiyama type in Japan); and

(c) `Assembled electrodes (Mget type in France).

Of the foregoing types of electrodes, those molded electrodes of (a) have a unit length which is in the range of the order from 1800 mm. to 2000 mm. When used, several of these molded electrodes are connected together by nip ples and the resulting rod of connected electrodes is further supported and fixed in place by a holding member. Such an arrangement of the electrodes of this type results, when in use, in a portion of a substantial length which extends below the holding member which is adapted to securely hold the electrodes in place.

The electrodes of this type, however, bears a disadvantage that their diameters cannot be increased indefinitely as desired. In Japan, the maximum diameter of the molded electrodes has been 610 mm.

The electric furnaces having large capacities which have been developed recently tend to require electrodes of such large diameters as are in excess of said limit.

In electrodes of molded type which are used by connecting, in series by the use of nipples, several unit electrodes each having a predetermined unit length, there frequently have occurred breakage of the connected electrodes at their joints which are connected by nipples, and moreover, because of the heavy weight of the individual unit electrodes of the molded type, there have been often encountered inconveniences in their transport as well as in the operation of connecting them together.

CII

ice

Of the continuously self-sintering integral electrodes of (b), those employing a cylinder casing made of a thin steel sheet for use as a sleeve for enclosing electrode cornponents therein, while those of Fujiyama type are of an arrangement such that arc-shape plates are combined together into a cylindrical form in which the electrode components are housed. In each of these two types of electrodes, the interior of the cylindrical sleeve is packed with a paste which is the material constituting the electrode. This paste is adapted to melt by the application of the heat which is transmitted from the inner portion of the electric furnace and the paste is caused to be spontaneously sintered to thereby form an integral electrode. This continuously self-sintering integral electrode of the type (b) is not restricted of its diameter when manufactured, unlike the molded electrode of the type (a), so that the former is suited for use in electric furnaces of large capacities. How ever, the electrode holders of the conventional type which have been used with the aforesaid self-sintezring electrodes are such that the range of the portion of the electrode which is sintered does not extend to the entire length of the electrode, `but it is limited to only a small area located below the holder.

Also, the holders of the types which have been used in general involved the inconvenience that there occurred the breakage or severing of the electrodes in portions located below the holders in case the weight of the portions of the electrodes extending below the holders is great, making the operation of the electric furnace unstable. Therefore, it has been the practice to limit the lengths of the electrodes extending below the holders to about twice or less the diameters of the electrodes used.

The assembled electrode of the type (c) is a type of electrode which has been developed pursuant to the Mgets electric furnace. This electrode of the type (c) is of a structure such that a multitude of molded electrodes having rectangular cross sections are combined together to obtain a desired effective area, and there is no limitation to the size of this area. However, this assembled electrode is a type of electrode which has 'been designed basically so as to suit for the use in an electric furnace of a special structure, and therefore, the application of electrodes of this particular type in other electric furnaces in general will cause various inconveniences.

For the foregoing reasons, the continuously self-sinterdng and self-integrating type electrodes of the type (b) are best suited for use in electric furnaces of a large capacity.

The conventional smelting electric furnaces are so constructed as to have a depth corresponding to two to three times the diameter of the electrode to be used. This is because of the consideration that the temperature within the electric furnace can be elevated by covering the heat generating portions of the electrodes immediately below their holders with a layer of the charged stock and that by this arrangement the heat is prevented from undesirably irradiating and escaping from such portions and whereby the required chemical reaction is promoted. However, when it is intended to use an electric furnace having alarger capacity and in case electrodes of the (b) type having increased lengths of portions extending below their holders are employed, there will often occur such breakage of electrodes as has been described previously, and hence the lengths of said portions of the electrodes are also subjected to a certain limitation. When the diameter of the electrodes are to be increased in accordance with an increase in the capacity of the electric furnace, the depth of the electric furnace cannot be increased to a great extent, andy moreover, the attempt t0 increase the diameter of the electrodes neither will bring forth any marked advantage.

Unlike the blast furnace, the mechanism of reaction which takes place in a smelting electric furnace is such that the amount of the indirect reduction of the charged stock effected by the C gas is relatively small. Instead, the major part of reaction is effected by the direct reduction which is performed in the deep portion of the furnace due to the contact between the solid carbons and the slagcontaining molten matter.

From the viewpoint to effectively utilize the CO gas, it would be ideal to thicken the layer of the stock charged in the furnace. This cannot be materialized, however, because of the limitation in the length of the portions of the electrodes extending below the holders, as has been discussed previously.

SUMMARY OF THE INVENTION By the employment of the improved electrodes of the present invention, which are of the continuously selfsintering and self-integrating type of (b), the capacity of the smelting electric furnaces can be increased effectively and substantially.

The basic feature of the improved electrode of the present invention is represented by an electrode of the continuously self-sintering and self-integrating type which comprises a metal peg, of copper or the like, suited to carry and transmit a greater part of the electric current supplied to the complete electrode, and which is suspended longitudinaly in the center of a thin steel sheet casing from a pair of holders connected to a power source. A plurality of molded rods such as block carbon are suspended longitudinally within the space defined by the casing disposed around said metal peg in spaced relationship to each other, and spaced apart equidistant from the metal peg, and supported by said pair of holders connected t0 the power source. The remaining space within the casing, i.e. the space remaining about the metal peg and around each of the molded electrode rods, is filled with a paste of the material utilized for forming the electrodes. The casing is suspended into a smelting electric furnace from a second pair of holders, intended exclusively for supporting the casing. In the operation of the furnace, the paste is progressively melted and sintered upwardly from the bottom portion of the resulting electrode structure by the heat transmitted to the electrode from Within the furnace when the electrode is electrically charged. In this fashion the metal peg, the molded electrode rods, and the casing are integrated together by the sintering of the paste material. The metal peg which is suspended in the center of the electrode is preferably made of copper so that it carries a greater part of the electric current supplied to the interior of the electric furnace. Thus, by the employment of this metal peg in the electrode, it becomes possible to substantially increase the current-carrying capacity of the electrodes as cornpared with an electrode of the same size or diameter which is not provided with such a metal peg.

A preferred variation of the above-described example of the electrode of the present invention comprises the electrode of the continuously self-sintering and self-integrating type having a metal peg to carry a greater part of the electric current supplied to the electrode, suspended longitudinally in the center of the space within a thin sheet steel casing, with a plurality of molded electrode rods, of a material such as block carbon which are also suspended longitudinally within the casing in a spaced relationship to each other and equidistant from said metal pag, and having a paste of the material utilized for forming the molded electrode rods filling the intervening spaces around the metal peg and molded rods within the casing, wherein the paste is melted and sintered progressively upwardly from the bottom portion of the electrode by the heat transmitted from within the furnace. In the preferred variation, the molded electrode rods and the metal peg extend upwardly beyond the casing and suspended from a pair of holders connected to the power source for the electrode. The mol-ded electrode rods extend downwardly to the lowermost open end of the casing, while the metal rod extends downwardly within the 4 casing to a point above the lowermost open end of the casing, so that there is provided a clearance therebetween. By the adoption of the electrode having the aforesaid structure, i.e. wherein the metal peg does not extend to the lowermost portion of the overall electrode structure, it becomes possible to substantially increase the currentcarrying capacity of the electrode relative to the outer diameter of the casing or the electrode as a whole, and to effect a smooth operation of lowering the electrode successively into the furnace by the required distance as the electrode wears out during utilization, while providing positive support for the electrode as a Whole. The upper portion of the electrode casing will ordinarily be assembled from curve steel sheets welded into the proper configuration.

Still another modification of the basic structure of the electrode of the present invention is represented by the replacement of the molded electrode rods With steel rods. By the adoption of steel electrode rods of this type, it becomes possible to increase the current carrying capacity of the electrode relative to the outer diameter of the casing and to effect a smooth operation of luring the electrode successively into the furnace in proportion to the amount of wear during use in an even better fashion, while positively supporting the electrode as a whole and without interrupting the supply of the electric current.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan view of the smelting electric furnace of the present invention;

FIG. 2 is a longitudinal sectional view of the same;

FIG. 3 is a schematic representation of an embodiment of the smelting electric furnace having a large capacity, showing the dimensions thereof;

FIG. 4 is a longitudinal sectional view of a part of the smelting electric furnace equipped with an improved electrode of the present invention;

FIG. 5 is a longitudinal sectional view of a part of the smelting electric furnace equipped with an improved electrode of another embodiment of the present invention;

FIG. 6 is a cross sectional view taken along the line VI-VI in FIG. 4;

FIG. 7 is a cross sectional view taken along the line VII-VII in FIG. 5.

PREFERRED EMBODIMENTS OF THE PRESENT INVENTION In FIGS. l, 2, 4 and 5 of the drawing, reference numeral 1 represents a body of an electric furnace; numeral 2 represents a lining made of a refractory material; numeral 3 represents a lining made of a carbonaceous material; numeral 4 represents a cover of the electric furnace; and numerals 5 represent a plurality of electrodes. Numeral 6 in FIGS. 1 and 2 represents a passageway provided in the central portion of the electric furnace through which a charge stock or raw material is inserted; numeral 7 represents a layer of the charged stock; numeral 8 represents a layer of melted stock containing slag; numeral 9 represents a layer of floating coke particles; numeral 10 represents a tap for draining the product; numeral 11 represents a tap for withdrawing the slag; and numeral 12 represents a molten metal.

In the deeper portion of the electric furnace, the charged ore and the slag-forming agent are gradually melted and dispersed, forming a conical shape jointly with the mass-form coke or the layer 9 of the floating coke, said conical shape is surrounded by the slag 8. Particles of coke which have been escaped from the conical shaped layer 9 of coke and the mass-form coke which descends together with the descension of the blended materials are allowed to be in the floating state while being immersed in the upper portion of the slag-containing molten mntter 8.

The electric current which flows out from the electrodes through the slag-containing molten matter 8 under the aforestated conditions is neutralized, wherein the aforesaid conical body 9 of coke serves as the neutral point of the electric current.

The amount of the electric current is determined by the depth of the electrode immersed in the layer of the slagcontaining molten matter 8, provided that the supplied voltage is constant. The molten matter 8 containing slag is extracted from the furnace at predetermined intervals of time so as to maintain constant supply of electric power, under a very small range of displacement of the position of the electrode.

Under the aforesaid conditions of the electric furnace, there is always accumulated a certain amount or more of slag-containing molten matter 8 in the furnace, and therefore, the layer of stock is retained above the layer of this molten ore 8.

In case there is provided a layer 7 of stock having an increased thickness, the CO gas which is generated in the reaction zone located in the upper portion of the layer 8 of the molten matter supplies heat to the layer 7 of stock located thereabove and preheats the stock. The heat generated from the combustion of this CO gas is further effectively utilized by the provision of the layer 7 of stock having a further substantial thickness and by the injection of oxygen (pure oxygen or air) into the layer 7 of stock or alternatively by having the stock layer 7 inhale such gas so as to combust the CO gas within the layer 7 of the stock.

In FIGS. 4 through 7 of the drawing, numeral 13 represents an electrode casing made of a cylinder of a thin steel sheet; numerals 15 represent molded electrodes (block carbon) which are disposed in an appropriate number in said electrode casing 13, each of the lowermost ends of which extends to reach the lowermost open end of the electrode casing 13, while each of the upper portions of said electrodes extends past the top open end of the electrode casing 13 and extends outwardly therefrom for an appropriate distance. Numerals 20 represent steel rod electrodes which are arranged in an appropriate number within the electrode casing 13 and are substitutes for said molded electrodes 15. Each of the bottom end of steel rod electrodes 20 extends as far as the lowermost open end of the electrode casing 13, and each of the upper portions of steel rod electrodes 20 passes outwardly through the top open end of the electrode casing 13 and protrudes for an appropriate length therefrom.

Reference numeral 14 represents a metal peg such as a copper peg which is inserted in the central portion of the electrode casing 13, and the lowermost end of the metal peg 14 does not extend up to the lowermost open end of the electrode casing 13, while the upper portion of the metal peg 14 extends outwardly for an appropriate distance past the top open end of said electrode casing `13.

Numerals 18a and 1817 represent a pair of holders for suspending the completed electrode. They grippingly hold an electrode casing 13 so as to suspend the overall weight of the completed electrode. This electrode casing 13 is capable of suspendingly holding the overall weight of the completed electrode without the fear of being broken. Numerals 19a and 19h represent a pair of holders through which the electric current is supplied. This pair of holders 19a and 191; grippingly holds the molded electrodes 15 or the steel rod electrodes 20 and also the metal peg 14. The electric current is supplied, through these holders 19a and 19h adapted for supplying electric current, to these electrodes and the metal peg.

As previously shown, in the drawing, reference numeral 1 represents the body of the electric furnace; reference numeral 2 represents a refractory lining of said furnace; and numeral 3 represents a lining made of a carbonaceous material; and numeral 4 represents a cover of the furnace.

Consideration will now be directed to an electric furnace employing the Sderbergs self-sintering integral electrodes of the prior art. The diameter of the electrode for use in a smelting electric furnace being of 3 phase and having a capacity of 7500 kva., which is operated at an internal temperature of the order of 1400 C., is in the order of from cm. to 100 cm., although there may be a slight difference in the selection by the designers or the operators. In such an electric furnace of the prior art, the adopted maximum length of the electrode extending below the holders is twice the diameter of this electrode. The adopted distance from the lowermost end edge of the electrode to the bottom of the furnace is substantially identical with the diameter of the electrode with respect to the prior art. Also, the adopted distance between the lower edge of the electrode holder and the upper face of the charged stock is in the order of 50 cm.

As a result, the electric furnace of said prior type is of a depth of the order of 250 cm., and the casing made of a thin steel sheet for use in said prior type electrode is of a thickness of the order of 2.3 mm.

In contrast to this, the embodiment of the smelting electric furnace shown in FIGS. 4 and 6 employing the continuously self-sintering integral electrodes in accordance wtih the present invention provides the following structures and functions.

Specifically, a copper peg 14 having a diameter of 12 cm. is provided in the central portion of the electrode. Six molded electrodes 15 each having a diameter of 25 cm. are disposed at spaced relationship so as to lie on the same circle, entering around said peg 14. This copper peg 14 is so structured that it is cooled internally with water and that about 42% of the electric current which is applied to the electrode is passed through this peg 14. As mentioned above, the lowermost end of the metal peg 14 is disposed in such a fashion that the distance above the lowermost edge of the electrode casing 13 is maintained substantially constant. The function of this peg 14 is to receive a considerable part (eg. 90% of the entire load current) of the current supplied to the interior of the furnace from the electric power source and to transmit the current to the vicinity of the tip of the electrodes.

The lowermost end of the peg 14 is not consumed as is the molded black carbon electrodes 15 or steel rod electrodes 20, the tip on which extends to the lowermost edge of the casing 13 and contact the slag layer where they are exposed to considerable wear and degradation. Accordingly, it is necessary to maintain the metal peg in a position sufliciently above the tip of the electrodes, i.e. from the lowermost edge of the casing, so that the foremost end of the peg does not wear out.

The electrodes are lowered to compensate for wear as the furnace operates by means of the mechanical holders 18a and 18b, maintaining the established position of the metal peg 14 by means of the holders 19a and 19b, which also serve to supply current to the electrodes.

The metal peg 14, like the molded electrodes, is embedded in the sintered portion of the paste composition 17, but since the surface area of the peg 14 making contact with the paste material is comparatively limited, it is not ditlicult to position or maintain the metal peg 14 in relationship with the other elements of the electrode. It is to be understood that the foremost end of this peg 14 1s always positioned at a level substantially upwardly away from the lowermost end edge of the electrode casing Each of said six molded electrodes 1S is adapted to pass about 10% of the total electric current which is to be applied to the complete electrode assembly. Four of the molded electrodes each having the unit length of 180 cm. are connected together with nipples. As is so within the conventional self-sintering electrodes of Sderberg type, the electrode casing 13 of a thin steel sheet for use in the present invention is of a thickness of 2.3 mm. and a diameter of cm. A paste 16 is filled in the space in the casing around the molded electrodes 15 and the copper peg 14. This paste 16 is adapted to be melted 16 and then is sintered 17 by virtue of the heat which is transmitted from the inner portion of the electric furnace. The casing 1 made of a thin steel sheet is formed into an integral body with the molded electrodes 1S and the copper peg 14 when said paste 16 is sintered at 17.

According to the result of the experiment conducted by the inventor, the cylindrical electrode casing 13 made of a thin steel sheet of a thickness of 2.3 mm. used in the sintering electrode of the present invention having the aforesaid structure is capable of suspending a weight of about 12,500 kg., which means that it is possible to suspend an electrode of an overall length of 850 cm. Accordingly, this casing 13 can be safely used to contain therein molded electrodes 15 in a number which is in the order of four, as discussed above.

Said cylindrical electrode casing 13 made of a thin steel sheet is of an overall length of 700 cm. In the upper portion of this casing 13 is provided a pair of holders 18a and 18b for suspending the complete electrodes. This pair of holders 18a and 18b for suspending electrodes s adapted so that the two holders are operated alternatively in the lowering of the position of the ele-ctrodes in accordance with the wear thereof or when the cylindrical electrode casing 13 of a thin steel sheet is connected again to the holders as the result of said lowering of the electrodes.

The molded electrodes 1S and the copper peg 14 are so arranged as to protrude for a distance of 120 cm. or more outwardly from the open top edge of the cylindrical electrode casing 13 made of a thin steel sheet. A pair of holders 19a and 19b adapted for supplying electric current is provided on said protruding portions of the molded electrodes 15 and the copper peg 14. These two holders 19a and 19b are alternately used in the lowering of the position of these electrodes 15 as a whole or in the re-connection of the electrode casing 13. Said holders 18a and 18b for suspending the electrodes 1S and said holders 19a and 19b adapted for supplying electric current are so arranged as to be mechanically coupled so that they may be moved interlockingly.

With the aforesaid structure, it will be noted that by setting the distance between the lower holder 18b for suspending the electrodes 15 and the upper face of the layer of the charged stock (meaning the open top edge of the furnace 1) to be 50 cm., and the distance between the foremost (lowermost) end edge of the molded electrodes 15 and the bottom of the electric furnace to be 100 cm., then this electric furnace will have a depth of 600 cm. Therefore, it is possible to obtain an electric furnace having a depth which is by far the greater than the depth of a conventional electric furnace described above, and it is also possible to make the thickness of the layer of the charged stock to be three times or more of the thickness obtained with the conventional electric furnaces. By this increased depth and thickness of the furnace and the layer of the charged stock, it is possible to greatly improve the conditions for the chemical reaction which takes place in said layer.

In the embodiments shown in FIGS. 4 and 6, molded electrodes 15 having respectively a diameter of 25 cm. are used to apply an electric current of 8 amp/cm.2 in density. In the embodiment of FIGS. and 7, on the other hand, steel rod electrodes 20 having respectively a diameter of 32 mm. are used to substitute these molded electrodes 15, in which case the current density adopted is 47.75 amp/cm?. In the embodiment of the latter cases, it is possible to greatly simply the structure of the holders 19a and 19b for supplying electric current as compared with the instances where molded electrodes 15 are used, and it is also possible to reduce the cost of the electrodes.

The dimensions of an embodiment of the electric furnace of a large capacity such as this are shown in FIG. 3.

These dimensions will be indicated by figures as follows:

The diameter of the electrode is in the range of 95-100 cm. Accordingly, it has a cross sectional area ranging from 7,088 cm.2 to 7,853 cm?. The current density of the normally applied current is from 5 to 5.5 amp/cm?, so that a current of about 40,000 amperes can be applied.

The voltage between the electrode and the bottom ofthe furnace is normally in the order of 58 volts, and the power factor in the furnace is almost Therefore, the power charged on the electrode will be:

58 v. 40,000 amp/ 1,000#2,300 kw.

' Withthe ordinary electric furnaces, the charged power 1s:

However, with the improved type of electric furnace, the charged power can be increased to 2.300 6=`13.800 kw.

In the case of the electric furnace employing the electrodes of the present invention, the voltage applied can be increased further. For example, in case a voltage of 65 v. is adopted as the voltage to be applied between the electrode and the neutral column, then the charged power will be:

65 v. 40,000 amp %000=l5,600 kw.

Thus, the capacity of the electrical furnace can be easily increased.

It Will be obvious to those skilled in the `art that various changes made be made without departing from the spirit of the invention, and therefore the invention is not limited to what is shown in the drawing and described in the specification, but only as indicated in the appended claims.

What is claimed is:

1. A self-sintering and self-integrating electrode for use in a smelting electric furnace, comprising a metal peg suitable to conduct a greater part of the electric current requirement of said electrode and a plurality of molded electrodes disposed Within an electrode casing of a thin steel sheet, said metal peg being suspended longitudinally in the center of the space within said casing, and said plurality of molded electrodes being suspended longitudinally within said casing in positions about equidistant from said metal peg, and a paste of an electrode-forming material in the space around said molded electrodes and said metal peg contained in said casing, said paste being successively melted and sintered by virtue of the heat transmitted from the inner portion of said electric furnace, so that said molded electrodes, said paste, said metal peg, and said electrode casing are formed into an integral body.

2. The electrode of claim 1, wherein said molded electrodes extend downwardly within said casing to the lowermost edge thereof, and wherein said metal peg extends downwardly within said casing to a point above the lowermost edge of said casing.

3. The electrode of claim 1, wherein said molded electrodes comprise a number of steel rod electrodes.

4. The electrode of claim 1, wherein a pair of holders is provided which engages said electrode casing to suspend said electrode within a smelting electric furnace, and a second pair of holders for supplying electric current engaged with said molded electrodes and said metal peg, whereby the electrode can be lowered within said furnace, and whereby said metal peg can be positioned relative to the remaining elements of sai delectrode.

References Cited UNITED STATES PATENTS 2,040,215 5/ 1936 Rava. 2,448,886 9/ 1948 Hopkins 13-9 2,599,179 6/ 1952 Hopkins 13-18 3,183,396 5/1965 Becker et al. 313-355 1,679,284 7/ 1928 Westly.

BERNARD A. GILHEANY, Primary Examiner H. B. GILSON, Assistant Examiner U.S. Cl. X.R. 13-9