US2461442A - Process of making ferro-alloys - Google Patents

Description

Feb. 8, 1949. A v L,G PR1TZ 2,461,442

` PROCESS oF MAKING FERRO-@Los 2 sheets-sheet 2 File@ Nov. 25, 1944 INVENToR Patented Feb. 8, 1949 PROCESS OF MAKING FERRO-ALLOYS Lawrence G. Fritz, North Canton, Ohio, assigner to Ohio Ferro-Alloys. Corporation, Canton, Ohio, a corporation of Ohio Application November 25, 1944, Serial No. 565,111

(Cl. 'l5-11) 2 Claims.

vThis invention relates to a process of making ferro-alloys. It is herein particularly described asapplied to the making of ferro-silicon.

Ferro-alloys have heretofore been commonly made in three Ways: (a) in the blast furnace, (b) by the thermit process, and (c) in the electric furnace',but the limitations of the two processes first mentioned are such that the electric furnace process predominates. Nevertheless, the electric furnace process of making ferro-alloys as heretofore carried out has serious disadvantages and limitations. These have been due in considerable part tc the requirements of practical production operation, rather than to theoretical process limitations, and are well known to operating men. The furnaces employed are of the open-top type. A charging floor is located at the top level of the furnace and the furnace has been manually charged. The electric current, generally threephase, is supplied through electrodes suspended vertically from a structure above the furnace. The manufacture of ferro-alloys involves maintaining a' very high temperature in the reaction zone, and since a considerable part of the furnace equipment, including the electrodes, holders, clamps and suspending chains or cables, is mounted vertically over the open-topped furnace, it is subject to intense heat.

In order to get any reasonable life out of the elements located over the furnace, they must be well protected and, insofar is as possible, watercooled. The water-cooling system is very extensive andA must kbe kept in first-class condition, frequently entailing the use of special watertreatrnent, e. g., special softening procedures. Even so, the life of many of the parts is quite limited, and the manufacturing cost is thereby burdened. This is especially so of the electrode clamps, which, for reasons of electrical efficiency, arelocated' close to the top of the furnace charge.

VIt has been proposed to minimize the effect of the intense heat on the clamps by clamping the electrodes near'their tops', but this proposal has been open to the objection thatthe electrical efciency is thereby impaired, with resultant increase in manufacturing costs. Attempts have also been made to shield' the equipment lby means of' refractory and water-cooled roofs, but such structures are costly to construct and difficult to maintain. For these reasons, amongothers, the various proposals for improvement, heretofore made, have not found acceptance.

Apart from deterioration by reason of the intense heat, the equipment above the furnace proper is subject to impairment by corrosion,y dust and` blows In the manufacture of ferroalloys, large quantities of hot gases are evolved. These gases pass upwardly and continuouslyentrain dust from the furnace charge. The gases constantly tend to channel locally throughthe charge, vtaking the paths of least resistance. lThey are evolved in such quantity that substantial pressures are generated, and it is a routine occurrence that blows result, wherein the gases open up large channels and rush out through the top of the charge at high velocity and in great local volume, instead of permeating the charge with reasonable uniformity and escaping at relatively low velocity over substantially the .whole Y area of the furnace charge. Blows are particularly prone to occur around the electrodes. Since the electrodes extend upwardly from the furnace chamber, the charge cannot extend uninterruptedly over the area of the furnace chamber, and there is inherently less resistance to the flow of gases Where the granular charge is in contact with the generally smooth andunbroken electrode surfaces thanin those portions where the gases must find their way through v serpentine paths afforded by more or less interfitting charge material. Moreover, the surface of the charge material isnot static around the electrodes-but is constantly feeding downwardly, so that the tend ency to blow around the electrodes is enhanced. It is customary under very severe heat, etc., to provide metal cases for the projecting parts of the electrodes so they will not deteriorate.

Furnaces for the manufacture of ferro-alloys are manually charged because, by reason of the l factors just stated, the workmen must closely watch the working of the furnace and distribute thecharge over the furnace as conditions may dictate. Even so, the presence'of the projecting electrodes makes their task a difficult one, and great skill and endurance are required to place the charge'material properly. .Y

The physical requirements for operating .a ferro-alloy furnace are such that only sturdy and/or youthful menV can withstand it. The

- workmen are constantly subjected to adverse heat conditions, and these conditions are greatly aggravated when, as is frequently the case, they find it necessary to shovel or rake charge material into localized spots to prevent blows or check blows which have already begun. This is particularly so when blows occur, as they are prone to do, around the surfaces of theelectrodes nearest` to the central axis of the furnace. When it is necessary to slip an'electrode, i. e., to lower it in its holder,` or to make repairs on the equipment above the furnace proper, it even becomes necessary for the workmen to stand upon a sheet of corrugated iron laid over the charge, under conditions which even the hardiest men can withstand for only a few minutes at a time.

Furnace equipment suitable for withstanding the conditions prevailing, and satisfactory from the standpoint of electrical eiciency, represents a very large item of expense in the manufacture of ferro-alloys, and at the best it is always difficult to get parts which will live under the severe operating conditions and to repair and -replace them, or to slip or replace electrodes during operation. It will be understood, of course, that the operation is a continuous one from the time that a furnace is put on heat until it is shut down for rebuilding. A

My invention greatly improves the manufacturing process and minimizes the difficulties above briefly outlined. It makes possible the use of automatic charging'machines, which to date have never been found satisfactory for this use, vastly improves the working conditions and increases the over-all emciency of the smelting operation. In the accompanying drawings, illustrating present preferred embodiments of the invention, Fig. 1` is a vertical section through a ferro-alloy furnace employing horizontal electrodes, and Fig. 2` is a similar view showing a furnace with electrodes arranged at an' angle. In each case the electrodes extend laterally into the furnace chamber and terminate at a substantially common level therein.

`Referring first to Fig. 1, there is shown a furnace having a shell 2 and a refractory body or lining 3 providing a furnace chamber 4. The furnace is of the open-topped crucible type and is provided with three equiangularly spaced horizontal electrodes 5. The electrodes project through openings 6 in the furnace Wall. A refractory ring l backed by a cooler 8 is provided in the annular space around the electrode. Each electrode is secured to a pad 9 by a clamp I0. The pads 9 carry rollers l I operating on xed ways I2, so that the electrodes may be adjusted inwardly or outwardly. The clamps i are connected to the current supply, as indicated at I3, and as the electrodes are consumed, the clamps may be loosened and re-positioned thereon.

The charge material is supplied to the top of the chamber in a loose pervious condition, pref` erably as a 'loose pervious admixture of small particles of the constituent materials, although it may be desired in some cases to agglomerato the materials into larger pieces. In the manufacture of ferro-silicon, the charge will consist of silica', iron oxide or scrap and coke or other carbonaceous reducing material. For the purposes of this specification, I designate iron oxide or iron ore, and metallic iron as iron-source material. A charging platform I4,`level with the top of the furnace, is provided and, if desired, the charge may be shoveled in manually as in present practice. In operation the furnace Will be kept substantially filled with charge material, as indicated in Fig. l. It will be noted that the charge material thus forms a deep layer over the electrodes, completely covering those parts of the electrodes lying within the furnace chamber and extending uninterruptedly over the area of the furnace chamber.

The heating of the charge in a. ferro-alloy furnace is rather markedly localized, differing in this respect, among others, from iron or steel making operations. Inthe ordinary ferro-alloy process now in use, it is difficult, if not impossible, to control the location and size of the reaction zone with the desired degree of precision, and the result is that the eiiiciency of the operation is frequently reduced and current and electrode costs are higher than they should be. This is due in part to the fact that the Apath of the current cannot always be directed or confined to the saine location, as a portion of the current may vflow from the vertical circumference of one electrode to another electrode and from electrodes to the bottom of the furnace or even around the furnace walls. In the process now being described in connection with Fig. 1 of the drawings, the reaction zone is closely confined to the central portion of the furnace between the upper and lower planes of the electrodes with the result that maximum furnace efficiency and minimum current and electrode costs result. In this process the path of the current can be more definitely controlled and the greater part of the current will ow from the end of one electrode to the end of the other electrodes, thus localizing the reaction ZOl'le.

The passage of the electric current through the charge raises the charge in the heating zone to reaction temperature, whereby the ferro-alloy is formed. It descends by gravity to the bottom of the furnace and is periodically drawn off through a 'pouring spout l5 in known manner. As the charge material is consumed by the reaction; the overlying mass which overlies the reaction zone slowly descends and fresh charge material is supplied at the top as the operation proceeds.

During the formation of the ferro-alloy gases are evolved and these pass upwardly through the loose bed of charge material overlying the reaction zone. Since this bed is in the nature of a continuous and uninterrupted mass of loose particles, the tendency of the gases to channel through the charge material, with resulting blows, is minimized, The process diers markedly in this respect from the ordinary process wherein the electrodes extend vertically upward through the descending mass of charge material providing paths of minimum resistance for the evolved gases. In my process the charge material tends to descend more uniformly, thus improving the operation of the furnace, and since there are no electrodes projecting out of the zone of moving charge material the work of charging is much less arduous and the need for raking and other,- wise locally placing the charge material is minimized.

The reasonably uniform flow of hot gases upwardly through the charge material overlying the reaction zone preheats it in a more nearly uniform manner than heretofore, thus tending further to improve the operation of the-furnace. If desired, therfurnace may be provided with an adjustable hood i6 leading to a flue l1 whereby the sensible heat-of the gases may be utilized or the dust yand gases carried loflor utilized. A n

Fig. 2 shows the practice of the invention in a furnace lhaving inclined electrodes 20 which extend laterally through the sides of the furnace into the furnace chamber and terminate at a substantially common level therein. While theoretically less efficient than the horizontal electrode arrangement of Fig. 1, the arrangement shown in Fig. 2 is nevertheless highly eicient and has the advantage that the breaking load on the electrodes is reduced. s

In Fig. 2 I have shown a mechanical charger or stocker 2l. It is feasible in my invention to use mechanical chargers whereas practical experience shows that they are impractical in present-day operations.

In order to have a full understanding of myv invention, it is important to differentiate between material which is substantially static in the furnace and material which moves downwardly in appreciable amount as the process goes on. Early in the operation of the process, a mass of fused or partially fused charge material will form around and below the reaction zone and, having formed, will be substantially static, i. e., it will move but little, if at all, in the subsequent operation of the furnace. This mass is more or less honeycombecl and does not prevent drawing oi of the formed ferro-alloy. It aids in concentrating the working of the furnace at the central portion. I have already mentioned that in the ordinary ferro-alloy process now in use the location and size of the reaction zone may change considerably, with adverse effects upon the overall operation, but, in any case, the furnace material lying within the vertical projection of the confines of the reaction zone is particularly notable for downward movement of the charge material and upward flow of a large quantity of evolved gases. In the present-day process the electrodes extend upwardly through this zone, with the adverse consequences hereinabove stated. It should therefore be recognized that while, in the practice of my invention, the configuration of the furnace and the positioning of the electrodes may be varied, even to the ex`- tent, in the case of a very wide furnace, of having the electrodes not penetrate through the furnace r wall, it is Vital that conditions be so maintained that there is no substantial material movement of the charge material and no egress of substantial quantities of evolved gases in the zones where the electrodes extend out of the charge material.

Many of the advantages of my invention have been indicated in the foregoing description. To them may be added the following: All electrical contacts between the pads and holders and between the pads and electrodes can lbe kept clean and away from the heat of the furnace (which heat is variable in present-day furnaces), and consequently a more uniform and improved electrical circuit is obtainable. Less sensible heat is lost because blows are minimized and, in any case, material heat conservation is made possible by taking off the hot gases and using them for preheating the charge or in waste heat boilers, or otherwise. In present-day operations a large amount of material is entrained by the rising gases as dust and is lost, in addition to which the dust may blight the territory adjacent the plant. The costly and intricate water-cooling systems are eliminated, greater continuity of furnace operation and greater efficiency are obtained and the working conditions of the operators are vastly improved.

I have illustrated and described two present preferred embodiments of the invention. It will be understood, however, that these are by way of illustration only and that the invention may be otherwise embodied or practiced within the scope of the following claims:

I claim:

1. The process of making ferro-alloys of iron and an alloying metal in an electric furnace having a chamber and electrodes extending laterally into the chamber and terminating at a substantially common level therein, which comprises making up a charge in loose pervious condition and consisting of the constituent materials in adrnixture, charging the furnace therewith, initially raising a portion of the charge to reaction temperature and thereafter providing substantially the entire heating energy for the process by supplying electric current to said laterally extending electrodes and passing said electric current through thefurnace chargainaintaining the reaction zone localized in andr around the Yinner ends of the electrodes whereby the ferroalloy is formed in a localized zone and gases are evolved, but without substantial volatilization of the alloying metal, drawing off the ferro-alloyV in molten state from the bottom of the furnace chamber without supplying any substantial amount of heat thereto from any other source, passing the evolved gases upwardly through the overlying charge material, supplying fresh charge material above the level of the reaction zone as the operation proceeds and at all times maintaining a layer of charge material in the furnace above the reaction zone, which layer completely covers those parts of the electrodes lying within the vertical confines of the reaction zone and extends uninterruptedly over the area defined by the vertical projection of those confines.

2. The process of making ferro-silicon in an electric furnace having'a chamber and electrodes vextending laterally intothe chamber and terminating at a substantially common level therein, which comprises making up a charge in loose pervious condition from silica, carbonaceous and iron-source material in admixture, charging the furnace therewith, initially raising a portion of the charge to reaction temperature and thereafter providing substantially the entire heating energy for the process by supplying electric current to said laterally extending electrodes and passing said electric current through the furnace charge, lmaintaining the reaction zone localized in and around the inner ends of the electrodes whereby the ferro-silicon is formed and gases are evolved, but without substantial volatilization of silicon, drawing off the ferro-silicon in molten state from the bottom of the' furnace chamber without supplying any substantial amount of heat thereto from any other source, passing the evolved gases upwardly through the overlying charge material, supplying fresh charge material above the level of the reaction zone as the operation proceeds and at all times maintaining a layer of charge material in the furnace above the reaction zone, which layer completely covers those parts of the electrodes lying within the vertical confines of the reaction vzone and extends uninterruptedly over the area defined by the vertical projection of those confines.

LAWRENCE G. FRITZ.

REFERENCES CITED The following references are of record in the le of this patent:

. UNITED STATES PATENTS Certificate of Correction Patent No. 2,461,442. February 8, 1949.

LAWRENCE G. PRITZ It is hereby certefl that errorappears in the printed specification of the above numbered patent requumg eorrectlon as follows:

Column 1, line 31, for the Words is as read as is;

and that the said Letters Patent should be read With this correction therein that the same may conform to the record of the case in the Patent Oce.

Signed and sealed this 14th day of June, D. 1949.

[IML] THOMAS F. MURPHY,

Assistant 'ommz'ssz'oner of Patents.'

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