US 3326670 A
Description (OCR text may contain errors)
June 1967 B. B. BRATTON STEYELMAKING PROCESS Filed July 16, 1965 INVENTOR Billy B. Broflon United States Patent 3,326,670 STEELMAKING PROCESS Billy B. Bratton, 314 Broadmore Ave., Pittsburgh, Pa. 15228 Filed July 16, 1965, Ser. No. 472,540
- 22 Claims. (Cl. 7528) My present invention relates broadly to processes for making steel and more particularly to continuous processes for making steel directly from any finely divided iron-containing material such as iron ore fines, iron ore concentrates, flue dust, mill scale, machine shop turnings and the like with virtually no limitation as to minimum percentages of iron, or combination or proportion of materials except as dictated by the changing economic picture. My process is especially suitable for making steel from iron, ore concentrates which are obtained from low grade iron ore by grinding the ore and separating or concentrating the iron rich fractions, and for the recovery of iron from such waste or by product materials as ore fines, flue dust, mill scale, machine shop turnings, etc. The invention also relatesto processes for making various-alloy steels directly from the corresponding ores.
This application is a continuation-in-part of my copending application entitled Steelmaking Process, Ser. No. 252,295, filed Jan. 18, 1963, and now abandoned.
My process constitutes a radically new approach to making either ordinary or alloy steels by combining reduction melting and refining into one continuous operation. My process therefore, replaces both the reduction steps, now conventionally accomplished in the blast furnace, and the refinement steps, presently provided in the open hearth or oxygen furnaces. The thermal and chem= ical energy required for my process is obtained for example from hydrocarbon gases, silicon and manganese. The-simplicity, economy, and other related advantages of my process is best illustrated by comparison'with pres ent steelmaking methods. Briefly, such conventional methods include charging sintered or pelletized forms of iron 'ore, flue dust, mill scale, and the like, together with 3,326,670 Patented June 20, 1967 "ice molten metal. The blast furnace, therefore is unable to operation, oxygen must be added to remove carbon, sili- 'fs'crap, coke and limestone into a blast furnace. In the blast furnace operation, feed stock must be'abrasion resistant to withstand passage down the furnace shaft. The stock must be no less than A" in diameter to resist entrainment in the high velocity hot gases flowing upwardly through the stock. The amount of gangue or slag-forming material present in the stock must be at aminimum because slag restricts-heat distribution in the-bottom of the furnace.
Under ideal operating conditions, iron is lost both by entrainment in the exhaust gas and in the slag while the reductant, coke is lost in the form of both soot and carbonmonoxide gas in the exhaust. The solid reductant, coke, is the source of the excess carbon and the sulfur and phosphorus which become-dissolved in the molten metal produced and which are not removed in the blast furnace. y
The physical arrangement within the furnace is such that the pool of molten metal and slag is located below the combustion zone at the tuyeres. Therefore, the formation of a slag blanket on top of the molten metal restricts the downward flow of heat; This flow is further restricted as the depth of the molten metal pool and the depth of the slag blanket increases throughout the blast furnace process, so that care must be taken to prevent cooling to the point of solidification at the bottom of the con and manganese by oxidation, while sulfur and prosph-orous are reduced with calcium or magnesium fluxes.
In the older, open hearth furnace the pig iron is similarly refined by oxygen released from rusty scrap, mill scale and ore melting in the furnace, and in some instances, gaseous oxygen blown into the furnace.
Under ideal operating conditions, metal is lost in these conventional processes by both entrainment in the exhaust gas as iron oxide, and in the slag as iron oxide. Some of the oxygen gas is trapped within the molten metal during this process which must be removed by some other process, for example vacuum degassing.
The time required for operation of the blast furnace is about 6 to 8 hours in addition to the time consumed in the sintering or pelletizing operation. The very impure pig iron extracted from the blast furnace is then sent to a holding furnace from which smaller charges are withdrawn from time to time to an oxygen furnace to further refine the pig iron into the desired steel. The oxygen furnace. requires about 1 /2 hours per charge, and in the conventional steelmaking process of more recent development, has supplanted the open hearth furnace for refining pig iron into steel. The open hearth requires approxi 'mately 8 'to 9 hours per charge and is still in use at the present time. In present-day processes, iron ore fines, flue dust, and the like, cannot be charged into the blast furnace until they have been sintered or otherwise agglomerated into inch size particles or larger, which is necessary to prevent the fines from being blown out of the blastfurnace, i.e. entrained in the exhaust gases.
j My process and apparatus eliminate the traditional blast furnace in that very pure iron or soft steel is produced directly from the ore in a converter or furnace in one reductionstep, after which the desiredsteel additive s'can be injected either into the converter or the ladle. Thus, the .usual contamination picked up by the pig iron from the blast furnace, particularly a carbon content as high as 4 percent, is avoided, in addition to effecting tremendous savings in time, equipment, space, materials, and fuel consumed for blast furnaceand holding furnace op erations. The steel made in accordance with the present invention can be essentially carbon-free, if desired, and the deleteriously high percentage of carbon added by the coke in the blast furnace, is obviated. As is well-known, the carbon content of blast furnace pig iron is lowered only with difficulty even in the case of high carbon steels employing at most 2 percent carbon. Pig iron also contains deleterious amounts of silicon and manganese, which have been unavoidably reduced from gangue or slagging materials of the ore by the caroxygen furnace. The oxidizing step is eliminated by the invention, along with the necessity of employing the open hearth or the holding and oxygen furnaces, since coke is not employed in the novel process presented herein. Moreover, the higher operating temperature of my disclosed process (3000 F. as opposed to 2450 F. in the blast furnace) causes FeO to oxidize any free Si and Mn which may be present.
The conventional blast furnace, cannot be conveniently or economically used in the processing of ores having less than 50% Fe content, inasmuch as the greater quantity of slagging materials from such ores produces a correspondingly thicker layer of slag or gangue material floating on top of the molten Fe pool at the bottom of the blast furnace. When the thickness of the molten slag layer approaches that resulting from the use of 50% ores, the thermal barrier formed thereby reduces heat transfer from the hot blast immediately above the slag pool to the extent that the molten pool of pig iron on which the slag pool is floating, may freeze before it can be poured. In my process, however, ores of any economically feasible Fe content can be employed since means are provided for heating the molten Fe pool. In most cases the temperature of the molten pool in the blast furnace is even less than the melting point of pure iron, so that the pig iron pool is maintained in a molten condition by virtue of the Fe-C eutectic. In my process, however, the temperature of the pure Fe pool is always maintained above the melting point of pure iron, and no significant quantities of carbon are added.
With my novel ore treatment, and apparatus for handling the same, it is practical to utilize ore fines, ore concentrate, flue dust, mill scale, and the like, of any degree of fineness, as long as at least 10% of the iron-containing material is below A1 in particle size. As will be pointed out below, maximum efficiency of the novel processes is attained with the smallest practical particle size.
In my process, finely divided iron-containing material, usually iron ore concentrates and proportions of such others listed previously as are economically advantageous, all of known chemical composition, are weighed and transferred to a preheat chamber of special design Where the fine materials are heated and partially reduced by exhaust gas from the furnace. This material then passes through a jet aspirator of special design to withstand high temperatures, for treatment with molten slag. The molten slag binds the iron-containing material into a cohesive, semiplastic solid which is charged into a special furnace which is both rotatable and tiltable. The furnace charge can include as much as 50% scrap. Oxygen is removed from the iron oxides in the preheat chamber by hydrocarbon gases, and in the furnace by hydrocarbon gases alone or in conjunction with silicon and manganese. Where hydrocarbon gases are used the by-products are CO and H gas, and where silicon and manganese are used, the by-products are molten SiO and molten MnO in which case the molten SiO and MnO are subjected to hydrocarbon gases for the removal of oxygen, after which the free silicon and manganese are ready for reuse. The furnace exhaust gas, containing significant amounts of hydrocarbon gases and sensible heat, is piped to the preheat chamber where both are recovered, and, at the end of each cycle, the molten slag, containing silicon and manganese where desired, is circulated through a mixer such as a jet aspirator as an ore treatment, to remove oxygen by exothermic reaction, and to recover sensible heat. In this manner, metallit: oxides are converted to pure molten metal as the oxygen is converted to CO and H 0 gas and exhausted from the furnace, with a minimum of thermal and chemical energy, material and equipment.
Slag exists in the reduction process as a result of impurities present in the ores from which metals are extracted. Silica sands comprise the most abundant impurity, followed by clays and other minerals. Slags in which silica is the principal mineral will absorb oxygen and thus are considered acidic or reducing. Slags of this type are most suitable for my process. The molten slag must be fluid at the jet aspirator and must maintain plasticity in the ore and molten slag mixture. These characteristics are stabilized in the acid slag used in my process by the addition of manganese and dolomite. One example of an acid slag is as follows:
Percent Si0 48 A1 0 2 FeO 15 MnO 18 CaO+MgO 17 In this example, the SiO and A1 0 are the sand and clay from the ore, the FeO represents the oxide in equilibrium with pure metal and the MnO, CaO and MgO are the fluxes added to stabilize the slag.
If an acidic slag having approximately the aforementioned composition is not available, as when starting up a new furnace or converter, an artificial slag can be formulated.
Alternatively, an acidic slag can be obtained by melting a corresponding quantity of low-grade iron ore and using the mixture thus obtained as the molten slag component of the charge. A larger percentage of FeO and an Fe O component would result but these would not affect the desired slag characteristics. Another alternative would be to obtain slag from another furnace of the type used herein, or from an open hearth or an oxygen furnace, if any one of these is within shipping distance.
As stated above, sulfur and phosphorus can enter the process, for example when flue dust from some other source is being recovered, and in some instances when pyrites and other sulfur or phosphorus bearing ores are used. Sulfur and phosphorus can be prevented from entering the metal by maintaining an oxidizing slag. The slag is rendered oxidizing or basic by the addition of calcium minerals in the ratio of 1.25 to 1.5 parts calcium minerals to 1 part silica.
One example of a basic slag is as follows:
Percent SiO 18 FeO 12 MnO 8 A1 0 3 CaO 43 MgO 8 P 0 8 S-Trace 100 In this example, the SiO and A1 0 are the sand and clay from the ore, the FeO represents the oxide in equilibrium with pure metal. The S and P 0 are the sulfur and phosphorus, and the MnO, CaO and MgO are the fluxes added to render the slag basic and to stabilize it.
For succeeding charges, the molten slag will be recycled and its fluidity and desired melting temperature maintained by a bleed and feed system whereby excess molten slag is discarded from the process after each charge and additional fluxing agent added to balance the materials picked up from each charge of iron ore.
In contrast to the limitations to heat transfer known to exist in a blast furnace, my process, through the use of a revolving furnace, is able to achieve direct reducing gas to charge contact throughout the entire melting period and to control the temperature of the molten steel formed without regard to the thickness of a slag layer present in the furnace.
As the mixture of finely divided iron bearing material and molten slag enters the furnace it will form a level surface due to its semi-plastic, or fluid, nature. Sufficient friction exists between the mass and the refractory lining so that when the furnace is caused to revolve the level surface of the mass will incline in the direction of rotation,
O with the angle of inclination increasing until the gravitational forces acting on the mass equal the frictional resistance between the mass and the furnace lining.
A gas lance is inserted into the space above the level of the mass to supply heat for the reaction and to prevent air from entering the furnace. Natural gas or methane is used for this purpose and the amount of air or oxygen supplied to the gas is insufi'icient to support complete combustion, so that a reducing atmosphere is maintained. The gas temperature will approach 3600 F. Reducing gases, such as carbon monoxide, or hydrogen are directed at the surface of the mass by a second lance inserted near the first. In this arrangement of my process iron bearing particles composing the surface of the mass are brought up to melting temperature while receiving maximum contact with reducing gases. Molten iron and slag will flow off the inclined surface and collect at the low point of the converter where they form a stratified pool similar to that in a stationary furnace. This exposes the next layer to the gas and this sequence is continued until all of the mass has been melted. The exposed area of the furnace lining absorbs heat from the burning gases during each revolution. This stored heat is returned by direct contact to the lowest or coolest level of the molten steel pool in a continuous flow. The operation of the process is based on chemical analysis of the iron bearing materials and the molten slag. This analysis provides the temperature and gas requirements for the desired rate of reduction. Rate of gas flow and furnace rotational speed are thus established. The progress of reduction is checked by monitoring gas flow, furnace temperature, exhaust gas temperature, exhaust gas analysis and furnace rotational speed and correlating this data with that known to yield the desired product. The gases and rotational speed are varied as required to maintain the desired correlation. Metal and slag analysis are verified at the end of refining by analysis of actual samples taken from the furnace.
In another arrangement of my process, acidic or silica slag, is further activated in accordance with one feature of theinvention. In this arrangement the silica content of the slag markedly predominates and is partially reduced, together with any MnO present, to obtain a quantity of free silicon (and manganese) after each charge, after which the molten silicon-containing slag is recycled to succeeding charges. Reduction of the silica content is continued to the extent that sufiicient free silicon, and manganese' if present, is supplied as required for exothermic reduction of the iron oxides of the next succeeding charge. Excess heat from this reaction being sufiicient to melt scrap steel amounting to 50% of the furnace charge. In this form of my process molten slag is retained for further reduction in the furnace, after the steel is poured off.
The furnace is returned to its operating position and gas lances are reinserted. The reductant gas for this reaction is natural gas (principally CH The surface temperature of the slag reaches approximately 3400 F. during this reaction. The percentage of silicon (and manganese) reduced from silica (and MnO in forming the thus activated slag canbe varied to suit the quantity of steel to be produced in the succeeding batch.
In an exemplary arrangement of my novel apparatus, the gases exhausted from the furnace or converter which contain considerable amounts of uncombusted gases are flowed through a preheater for the iron-containing material whereby a portion of the latter is partially reduced in addition to advantageously preheating the material for subsequent complete reduction steps. The preheater capacity and the volume of exhaust gases flowed thereto are controlled such that the ore particles will be suspended or fluidized in accordance with known fluidization techniques. Such fluidization facilitates reduction of the iron-containing material through greatly increased gas-solids contact. Where ordinary steels are to be produced, the furnace reduction requirement is reduced by the amount of reduction achieved in the aforementioned preheat chamber. Where chromium or other alloy component is to be reduced for alloying with steel, I prefer to employ the free silicon or activated slag as the molten slag binder for my process. The slag must be sufii ciently activated to reduce the chromium since reduction of chromium ores require higher temperatures than normally obtained with gaseous reductants. The chromium and activated slag must be mixed and their exothermic reaction allowed to take place in the furnace first, because of the higher temperatures required. The remaining activated slag is then mixed with iron ore and other alloy component ores, if used, and put in the furnace with the previously reduced chromium and slag.
It will be understood that when the charge is added to the converter, certain steel additives can be charged therewith or alternately the additives can be placed in the converter before pouring off the steel, or into the ladle thereof.
Through the ability to reduce and to refine iron-containing particles of fine particle size and relatively low Fe content, my process can be used to recover Fe as pure iron or soft steel from the waste products of other steelmaking or fabricating processes; such as ore fines and screenings from iron mines, ore fines and screenings from blast furnace stock piles, flue dust from blast furnaces or open hearths or oxygen furnaces, mill scale from rolling mills, oxide from pickle liquor disposal, and filings or punchings or trimmings from metal fabrication.
These and other objects, features, and advantages of the invention together with method steps and structural details thereof will be elaborated upon during the forth-' coming description of illustrative forms of the invention, with the description being taken in conjunction with the accompanying drawings wherein FIGURE 1 is a schematic representation of the converter or furnace used in the practice of the process together with ore, slag, and gas handling equipment associated therewith;
FIGURE 2 is a schematic representation ofv the com-. postion and the progressive partial reduction of typical iron ore particles inthe presenceof hydrogen gas; and- FIGURE 3 is a schematic representation of the com position and the progressive partial. reduction of typical iron ore particles in the presence of carbon monoxide gas.
In the following description and examples, the material comprising the charge is iron ore concentrate, the reason being that this is the most-abundant of the above-. mentioned materials and is, therefore, to be the primary material used. However, the other named materials may likewise be used separately or together with theprimary material and should not be considered as less desirable. Iron ore of a particle size less than inch is generally considered'to be and is commonly referred to as iron ore fines and will be the primary material being. considered here. Steel scrap in the amount of up to. 50% of the total charge can, if desired, be added tothe converter after addition of the molten slag charge. Because of the use. of the preheater 14 which is described in detail below and in which the ore fines are partially reduced, ore fines of the smallest available particle size are desirable to faciliate the reduction reaction, and thus the conventional sintering or other agglomerating processes are eliminated. However, as further elaborated. upon, the use of the molten slag binder prevents the fines from being blown out of the furnace.
Referring now more particularly to the drawings, the iron ore fines and the like are contained in a storage bin arrangement denoted generally by reference character 10, with the individual bins 12 thereof containing different varieties of ore or of other iron-containing fines which may be economically available at any given time. The iron ore fines and fluxes are extracted and weighed in a known. manner from their respective bins and then conveyed to a preheating chamber 14 by means of the continuous conveyor belt 16. In the lower portion of the chamber a frustoconical bafile arrangement 18 is mounted through the spaces of which exhaust converter gases are conducted from a flue stack 20. The exhaust gases are composed of gaseous reaction products, the excess gas supplied to maintain reaction rate, and the products of heating gas combustion, all of which are noted in greater detail below.
The baffies 18 also serve to direct the powdered ore and the like contained in the preheater downwardly through a centrally disposed outlet conduit 22 to a suitable mixer such as a jet aspirator 24. The velocity of the exhaust gases through the preheater varies from 40 to 80 feet per second, which is sufficient to fluidize most of the particles, and thus to provide intimate contact between the ore particles and exhaust gases for reduction purposes. A variable speed feeder 15 transfers the charge from the preheat chamber 14 to the jet aspirator 24. Here, the iron-containing fines are treated with molten slag which is dumped into the runner 26 from the ladle 28 as denoted by dashed line 31.
The hot exhaust gases passing, as aforesaid, through the preheater 14 reduce at least a portion of the Fe O to FeO thereby minimizing the quantity of gases required for reduction in the converter 30.
The reduction reactions in the preheater are as follows:
The foregoing equations show that the combustibles in the exhaust gas conducted from the preheater 14 are completely oxidized.
The reduction reactions in the preheater 14 are solid state reactions where the crystalline structure of the iron oxides is modified without melting. If the sintering temperature of any one of the iron-containing minerals composing the ore fines is reached, the individual particles can stick together and impede the flow of fines from the preheater 14 to the jet aspirator 24. The lowest liquidus temperature anticipated therefor establishes the maximum allowable temperature within the preheat chamber. A safe maximum temperature for material in the preheater 14 is therefore 1700 F., and the temperature is maintained at or slightly below this temperature by by-passing a portion of exhaust gases directly to the dust collector 50 through conduit 51 or by admitting tempering air into the exhaust stack 20 through inlet conduit 53.
As shown in FIGURES 2 and 3 of the drawings the reducing gases in the preheater 14, which gases include primarily H and CO, remove oxygen from the ore particles A, which migrates outward therefrom in the form of water vapor and CO respectively. At the same time non-liquid Fe iron migrate inwardly through gaps in the crystallizing lattices left by displacement of oxygen to form increasingly thicker shells E about the particles, until in the case of H reduction, (FIGURE 2) the pressure drop across the iron shell increases to about 9 p.s.i. to form a barrier to further escape of water vapor. On the other hand, H is the most efficient reducing gas until the aforementioned, pressure barrier is reached. H therefore, exhibits higher overall reducing efficiency with smaller sized ore particles where the shell thickness represents a larger percentage of total size. In the CO reduction, however, the pressure of internal CO builds up and cracks the iron shell (FIGURE 3) and reduction of the particles continues so long as available CO is present. As reduction continues the particle divides into zones B, C, and D consisting essentially of iron oxides having correspondingly less oxygen toward the outer periphery of the particles. The zones B, C, and D typically are comprised of wiistite (FeO less than theoretical oxygen), magnetite (FeOFe O and hematite (Fe O respectively.
The ore particles discharged from the preheat chamber 14 will be in various stages of solid state reduction. Each particle will consist of spherical layers of shells. The outer shell will be soid pure iron while each succeeding inner shell will be less reduced. The number of layers will depend on original ore and the state of reduction, for instance a particle of hematite would have a center of hematite followed by shells of magnetite, wiistite and iron. Shell thickness is a function of time, with iron increasing until the entire particle is reduced with the final stages of reduction Occurring for the most part in the converter 30.
In the furnace 30 heat is added from the hot furnace linings in addition to that added by burning a portion of the natural gas atmosphere. This is accomplished by blowing a limited quantity of air through the natural gas lance 42 described below. The added air is not sufficient for complete combustion of the natural gas so that the reducing atmosphere is maintained. The added heat melts the aforementioned iron shells surrounding the ore particles allowing diffusion inward and outward to proceed very rapidly. Due to the physical structure of the mix this takes place on the surface layer of particles only and proceeds layer by layer through the entire mix. Molten metal and slag flows off the tilted surface of the mix, which is inclined by the action of furnace rotation, to form layers of molten metal and slag. The molten metal is brought up to the refining temperature by heat from the furnace. A gas flow rate is established which is in excess of that required to maintain a steady reaction rate. The gas must have sufficient velocity to impinge on the oxide surface and entrain gaseous reaction products as they diffuse through the surface of the particles. This excess gas carries the reaction products away from the surface of the particles and into the exhaust stream to prevent vapor blanketing of the particles, while maintaining the gas volume to supply reaction requirements.
When the ore and other fines are treated with the molten slag, the rate of heat transfer from the molten slag to the partially reduced fines, the liquidus temperature of the slag, and the temperature to which the fines are preheated determine how long the mixture -will remain plastic after the fines and molten slag come into contact in the mixer 24. Heat, of course, must flow from the molten slag across the stagnant layer at the liquid-solid interface and into the cooler solid particle. The initial slag temperature is desirably in the range of 32003400 F. and the initial or preheated temperature of the fines is between 1600 and 1700 F. The equilibrium temperature of the resulting mixture therefore, will be above the liquidus temperature of at least some of the slag and iron ore minerals present so that the charge will not solidify before it can be dumped into the converter 30. Here the fluidity of the charge is increased through melting of the remainder of the slag and ore minerals by heat from the furnace linings, and by additional heat from the gas lance 42 or 44, described below.
From the preheater 14, where the hot exhaust gases partially reduce the ore and other fines contained therein, the gases pass upwardly through a frustoconical section 46 of the preheater and then through exhaust conduit 48 to a dust collector 50 which can take the form of a cyclone separator of known design, or the like. The separated fines are conducted back to the preheater 14 through downcomer 52, while the exhaust gases exit from the dust collector 50 through conduit 54 the other end of which outlets into scrubber tank 56. Any additional fines separated in the tank 56 are conveyed to a sludge filter as denoted by flow arrow 58. From the scrubber 56 the exhaust gases are conducted through conduit 60 to an exhaust fan or blower 62 which discharges to the exhaust stack 64. Because the hot exhaust gases have been conducted through the preheater 14 and thoroughly reacted with iron-containing material therein, little or no combustible gas is exhausted to the atmosphere from the exhaust stack 64. Thus, there is virtually no waste of the 9 various gases blown intothe converter 30 through lances 42 and 44 inasmuch as any uncornbusted or unoxidized portions of the natural gas, CO, and H gases, together with certain products of partial combustion thereof serve "as reducing agents which are utilized subsequently and completely for partial reduction of iron ore in the preheater 14. Moreover, a considerable portion of waste heat is recovered from the exhaust gases.
As shown previously as particle size decreases the amount of surface area per unit weight increases, and as more surface area is exposed to contact with reducing gases the rate of reduction increases and therefore the process becomes more efiicient. This has a greater effect on reduction by hydrogen as shown in FIGURE 2 than on reduction by carbon monoxide as shown in FIGURE 3. As ores of this type reach the jet aspirator or other mixing means 24 their .total volume will consist of from 65 to 50% solid with the remaining 35 to 50% void or filled with air. The function of the jet aspirator 24 is to inject molten slag into these void spaces to eliminate and exclude air and thus bind the ore particles into a cohesive, plastic, solid of the same total volume as the original ore.
The molten slag densifies the particle mixture and prevents the incoming fuel and reducing gases from blowing portions of the ore fines and other iron-containing dusts out of the converter 30. The molten slag also serves to increase substantially the heat transfer characteristics of the ore fines, in addition to applying the heat of the molten slag (from the preceding charge) directly to the charge, which heat is now wasted in conventional proces ses. As a result of recirculating the slag, as it were, through the jet aspirator 24, converter 30 and the ladle 28 during successive charges, the heat imparted to the slag from preceding charges is conserved. The use of the molten slag and ore mixtures also eliminates the relatively large volume of air present in the ore fines (and present also in the sintered or pelletized iron-containing materials of conventional processes) which slows or otherwise interferes with the reduction of iron ore to metallic iron or steel. Further, the heat of the molten slag reduces a further portion of the iron oxides to the native metal, and also serves as a self-fluxing agent for the charge.
A primary advantage to the use of a molten slag binder is that iron ore fines of very small particle size can be used. In other words, the ore fines can be used directly as received at the mill without such further treatment as the agglomeration step of conventional steelmaking processes. The use of very small particles not only aids the partial reduction thereof in the preheater 14 as discussed above in connection with FIGURE 2, but also facilitates the complete reduction thereof in the converter 30. The mix entering the furnace 30 consists of a solid volume of ore particles with the voids between and around the individual particles filled with molten slag. The exposed faces of the mix will contain the same surface area of ore as the face would have if no molten slag were presout. The important difference is that without the molten slag the voids normally existing between the individual particles of the ore volume would be filled with air or gas, and, when a reducing gas would impinge on the ore surface, a differential pressure would be established between the gas confined in the ore mass and the gas at the surface. This would cause the ore particles to become entrained in the reducing gas and carried out of the furnace, and would establish a minimum particle size for that pressure differential established by the minimum gas flo'w for reduction. This is not so when molten slag is used, and therefore, there is no lower limit for ore particle sizes that can be used.
Thus, considering as an example, one cubic foot of iron ore fines which is 60% solid and 40% air voids, it would be necessary to add 0.4 cubic feet of molten slag to fill the void and about 0.1 cubic feet of excess molten slag to produce the desired volume characteristics, making a total of 0.5 cubic feet of molten slag which with the 0.6 cubic foot of iron ore fines (solid) would yield 1.1 cubic feet of molten mixture. Accordingly, with the average solid and void relation of iron ore fines stated above, it can be determined that the final mixture of iron ore and other fines with molten slag will be from about 45 to 60% by volume of iron ore fines and 40 to 55% by volume of molten slag to produce a mixture which is essentially void-free and air free. Any free moisture and Water of hydration in the fines are, of course, driven off in the preheat chamber 14.
The jet aspirator 24, in one arrangement of the invention, can take the form of a venturi tube through which the molten slag is flowed under pressure. The outlet conduit 22 of the preheater 14 desirably feeds the ore vertically and downwardly into the most constricted portion of the venturi tube and preferably on the upper side thereof. Mixing is done after the refined metal and the slag from the preceding charge are poured out of the converter 30, which is then repositioned to reecive the discharge from the mixer 24. The slag ladle 28 is then positioned to discharge to the mixer runner 26. Slag flow is started first followed by flow of the ore from the preheat chamber 14. A variable vane-type feeder 15 or the like is provided at the chamber outlet 22 to control ore flow, while a gate 27 for controlling slag flow is mounted in the mixer runner 26. By proper control of ore and slag discharge rates, a mixer discharge of absolute volume can be achieved. The furnace 30 pivots, as denoted by reference character 32, upon a suitable support 34 and is rotatable by means of its circumferential gear 36 in a known manner.
For charging the fines and molten slag into the converter 30, the jet aspirator 24 is desirably positioned with respect to the converter so that it can discharge downwardly and directly into the converter, when the latter is pivoted such that its upper or open end 38 is moved upwardly from the position shown in FIGURE 1 of the drawings. In furtherance of this purpose, a rotating exhaust hood 4!) or known construction is employed, which normally connects the open end 38 of the converter with the lower end of the flue stack 20. After the jet aspirator 24 discharges completely into the converter 30, the latter is returned to its reduction position, and the exhaust hood 40 is revolved into position over the mouth of the converter. At this time the preheat chamber-14 is being refilled for the succeeding charge, and the slag ladle is returned to its location at the dump position of the converter. As shown above the chemical and thermal energy used by my process to convert metal oxides to steel can be provided by hydrocarbon and similar or derivative gases. Examples of such gases are hydrogen and carbon monoxide which can be obtained from natural gas as well as other sources, and methane which is the principal constituent of natural gas. In my process natural gas is assumed to be the most economical source of hydrogen and carbon monoxide and which are produced from methane and steam by catalytic reforming (not shown). Hydrogen and carbon monoxide produced in this manner have about equal total reduction potential and can be used in the process in the same proportion as formed for maximum etficiency. As shown in FIGURES 2 and 3 hydrogen is more sensitive to particle size than carbon monoxide and therefore is used more eificiently in the early stages of reduction.
With the iron ore mixture, now disposed in the cons verter 30 natural gas and hydrogen gas lances 42 and 44' are extended through the exhaust hood 40 and converter and to a limited extent:
These reactions continue during the natural gas and hydrogen blow until the proportionate part of the total reduction to be accomplished with hydrogen has been reached as indicated by gas flow measurements, gas temperature and gas analysis, temperature within the preheat chamber and temperature within the furnace, as measured by suitably placed instrumentation (not shown). The lance 44 is then switched to carbon monoxide, or alternatively is removed and replaced with a carbon monoxide lance after which the carbon monoxide blow is commenced. The natural gas blow is continued at this time but can be at a reduced rate, sufficient to maintain a reducing atmosphere.
During the second blow period with carbon monoxide and natural gas, the following reactions take place:
and to a limited extent:
During both blows pure molten iron and molten slag continue to collect at the bottom of the sloping surface of the metallic oxide. When all of the oxide has melted the furnace will contain pure molten iron or soft steel and slag. This will be indicated by its effect on furnace and gas temperatures, exhaust gas volume and chemical analysis as indicated by the instrumentation mentioned earlier. The function of the natural gas lance 42 is to maintain a reducing atmosphere within the furnace and to supply any thermal energy that may be required to maintain a' desired rate of reduction. Both the flow rate through the lance and the ratio of oxygen to natural gas are controlled to maintain desired furnace conditions. The temperature of the molten pure iron pool being formedduring these blows is maintained above 2795 F. by heat transferred from the furnace refractory lining as the furnace revolves. This is a function of furnace gas temperature, refractory temperature and speed of furnace rotation, all of which are monitored and controlled through the entire melting c cle.
After all of the metallic oxides have been melted, samples of metal and slag are taken and analyzed. The quantity of alloys to be added if desired are based on this analysis. Alloys can be added either in the furnace 30, or the ladle 28. The lances 42 and 44 are withdrawn, the hood 40 is moved and the furnace 30 is tilted to discharge steel and slag into separate ladles 28.
A more specific example of this form of the invention follows where a basic slag is utilized and in connection therewith the following typical iron ore analysis by weight is given:
Percent SiO 10.3 CaO .6 MgO .1 A1 3 .9 Mn .1 S .2 F203 FeO 1.7 Ignition loss 1.0
The aforementioined ignition losses represent the proportion of ore which is lost during handling and reduction thereof. Generally, there will be free moisture and water of crystallization on the order of 3.3% in addition to the foregoing total as indicated above will be eliminated during preheating. Ore of the above analysis, therefore, contains 58.7% by weight of Fe and accordingly 3,405 lbs. of such ore would contain one ton of Fe.
Assuming the ore weighs 210 lbs. per cubic foot and is 60% solid and 40% void (including moisture) it can then be calculated that 16.2 cubic feet of dry ore would be required per ton of Fe, which upon further calculation is 9.7 cubic feet of ore solids, if the voids could be eliminated. The molten slag requirement therefor would be 40% of 16.2 cubic feet or 6.5 cubic feet plus 1.6 cubic feet (10% excess) or 8.1 cubic feet total per ton of Fe. The total mixture therefor would be 17.8 cubic feet of ore and molten slag mixture per ton of Fe.
The amount of limestone per ton of Fe needed to react With the SiO of the analysis would be 125 pounds or about one cubic foot or 0.7 cubic foot solid. The dry materials from bins 10, including dry ore and limestone are weighed onto belt conveyor 16 which transfers them to the preheat chamber 14 where exhaust gases from the converter 30 enter the chamber 14 by way of bafiles 18 from flue stack 20. These gases preheat and partially re duce this ore. At the end of the preceeding cycle ore passes through chute 22 and feeder 15 into jet aspirator 24 where it meets and absorbs slag from ladle 28 entering through runner 26 and gate 27, to initiate the next oreslag cycle.
Assuming a furnace charge of tons Fe is desired, then according to the example a total of 1850 cubic feet of molten slag, ore, and limestone mixture would be charged into the converter 30, which has been positioned to receive the charge. The furnace is then revolved into operating position, the hood 40 is moved into place and the gas lances 42 and 44 are inserted into the converter 30, the converter is started to rotating, and the blow of hydrogen and natural gas is begun.
The converter 30 in this example is constructed such that its speed of rotation can be varied from 0-30 r.p.m. The natural gas lance 42 is used to supply the heat energy necessary to sustain the endothermic reduction reaction and to maintain a reducing atmosphere in the furnace. These objectives are accomplished by burning the natural gas with a deficient oxygen supply. Either oxygen or oxygen-enriched air is supplied through the natural gas lance 42 for this purpose. The lance 42 is positioned to supply heat to this converter lining and to the area above the surface of the charge. The converter 30 is rotated at a speed between less than one and four revolutions per minute while the mix is beginning to melt. After about half of the charge has melted, the carbon monoxide lance 44 is used to supply the reductant, while the natural gasoxygen blow from lance 42 is continued until the con verter charge is completely melted. The converter 30 is rotated during this time at a speed such that the lining temperature is above the minimum temperature to transfer sufficient heat to the molten Fe pool to keep the latter from freezing, and below the maximum permissible operating temperature of the lining. These maximum and minimum temperatures will vary with the thickness and type of furnace linings used, as known to those skilled in the art. The CO or H lance 44 is positioned so that CO gas will sweep the surface of the charge as the converter is rotated, while being heated by the natural gas from the lance 42.
After melting is complete and samples of metal and slag have been taken and analyzed, the lances 42 and 44 are withdrawn, the hood 40 is revolved and the furnace 30 is tilted to discharge metal and slag into separate ladles 28.
13 Gas requirements as outlined in this example I s.c.f 2500 s.c.f. natural gas 100 tons 250,000 5000 s.c.f. carbon monoxide 100 tons 500,000
10,000 s.c.f. hydrogenx tons 1,000, 000 The maximum blowing rates for all gases in this example are 25,000 s.c.f. per minute at 40 pounds per square inch..
Therefore, the tap to tap time required to convert metallic oxides to 100 tons of steel will be as follows:
, Minutes Charging Hydrogen lancing 1,000,000/25,000 g Change lances 10 Carbon monoxide lancing 500,000/ 25,000 20 Total 1 120 1 Or 2 hours. v
This time compares favorably with conventional processes where the blast furnace-open hearth combination could require as much as 16 hours, and the blast furnace-oxygen furnace as much as 9 hours, for the same production.
Moreover, heat requirements in this example are less than 7,000,000 B.t.u. per ton of steel as compared to over 12,000,000 B.t.u. per ton of steel by the conventional blast furnaceopen hearth combination, therefore; fuel requirements are less than that of any process known at this time. W
Since the major proportion of the molten slag issuing from the converter 30 is recycled and its sensible heat retained in the process, and since most of the exhaust gas heat is recovered in the preheater 14, it will be evident then, that most of the heat carried out of the process is in the molten iron. Therefore, the advantages and benefits resulting from the aforedescribed process will-be immediately apparent to. those skilled in the steelmaking art.
In another form of steelmaking process, in accordance with the invention, free or metallic silicon (together with metallic manganese if the oxide'thereof is present in the molten slag) is generated in the molten slag carrier after the molten iron is poured from the converter 30. In this, arrangement of the-invention,- an acidic slag is employed.
having a composition of about SiO A combination of carbon monoxide and hydrogen gases,
which may be reformed from natural gas, is blown against the remaining slag through .the lance 44. At the same time, a reducing atmosphere is maintainedwithin the converter 30 by blowing natural gas through the. otherlance 42. The CO and H together with a quantity of air of combustion supply the necessary. heat required to raise the temperature of the slag to about 3300 FL, while the natural gas serves as. reducing agent to reduce the silicon dioxide to metallic silicon. 4
During the silicon regenerating cycle,- the followingre- Similarly, where a MnOslagging component is present;
The free silicon and manganese content of -the slag-can be increased so that final reduction and refinement of the ore to pure iron is achieved by. exothermic reaction with the slag instead of with gasesLThis excess heat'ofthisr'e can be used to melt scrap added with the action thus charge.
- Completion of the foregoing reaction'is indicatied. when the proportions of natural gas in the exhaust; gases from It is known that at temperatures below'about 2822 F.
oxygen possesses a greater afiinity for metallic silicon than for carbon. However, at temperatures above this point, oxygen exhibits a greater affinity for carbon. This is proved in steelmaking practice by the obsolescent Bessemer process. In the latter process, the hot metal usually contains more carbon than silicon, but when the blowing starts, since the Bessemer process is at temperatures below 2822 F., silicon is completely oxidized before the oxidation of carbon commences.
In this form of the invention, the aforementioned change in oxygen afiinities as temperature rises is em ployed to establish a silicon reduction cycle where the greater activity of silicon is employed to reduce iron ore in accordance with the following equations:
The silicon metal, manganese metal, residual free iron, and slagging material, all of which may be termed active silicon slag, are then injected into the succeeding charge of ore'fines and the like in the jet aspirator 24. The ladle containing the active silicon slag is dumped into runner 26 of the mixer while the temperature of the active silicon slag is still above 3000" F. This temperature is high enough, of course, to commence an immediate reaction with the ore fines delivered to the jet aspirator 24 from the preheater 14. Preheating and partial reduction of the ore fines, of course, further stimulates the last-mentioned reaction. This mixture of active silicon slag and ore fines falls into the converter 30 when the latter is tilted upwardly and the aforesaid reaction between the ore fines and the active silicon slag is completed in the converter.
Inthe latter-described process, it will be apparent that the regenerated silicon metal is the intermediate in the and silicon metal. For tons of iron ore having theaforestated typical analysis 13- tons of free silicon will be required.
Where the iron-containing fines initially contain moresulfur or phosphorus than the steel specifications allow, these impurities can be reduced to acceptable values in the steel ladle 28 by the addition of soda ash, burnt lime, calcium cyanamide or calcium carbide, which react with these impurities. The aforementioned S and P can be in-- troduced' with certain varieties of iron ore, or with flue dust from the blast furnace or open hearth if used.
The active silicon slag when added to the ore and the like in the'jet aspirator 24 is absorbed into the voids in the ore as described hereinbefore.
In still another arrangement of my process, a chromesteel or chrome-nickel stainless steel can be produced directly from the corresponding ores with a modified form of the active silicon slag cycle described above. The raw materials for this process are-chrome-ore, iron ore, nickel oxide (for Cr-Ni stainless steel) and natural'gas. Dual preheaters and mixers, corresponding to the preheater 14 and the mixer 24, are required because the chrome orev must be reduced at a higher temperature and thus'main tained separately of the iron and nickel ores during initial stages of the-process.v In the first step of this process, part of a quantity active silicon slag is mixed with a charge of chrome ore and put into the converter 30, which is rotated. The reaction of chrome ore-with the free silicon is similar to that mentioned previously in connection with the'iron-sllicon reaction and is as follows:'
The reaction set forth above commences immediately as Additional heat, if required is supplied by burning a portion of natural gas at the lance 42.
After the above reaction is substantially completed, the remainder of the active silicon slag is mixed with iron ore (if a chrome-steel alloy is desired) or with combined iron ore and nickel oxide fines (for a chrome-nickel-steel alloy) in the other mixer and dumped into the converter 30 which is rotated to mix the latter charge thoroughly with the partially reduced chrome ore-molten slag charge therein. The following exothermic reactions commence immediately upon mixing due to the molten condition of the active silicon slag and preheating of the ore fines:
After completion of the aforementioned reactions, the chrome-nickel stainless steel is poured off into a ladle 28 therefor. Regeneration of the silicon slag is accomplished as in the aforedescribed active silicon slag cycle until an amount of free silicon slightly in excess of that required for the reduction of all three ores is recovered from the :silica component of the slag.
The exhaust gases from the converter 30 in this process :are divided by suitable ductwork (not shown) and conducted to the aforementioned preheaters where the chrome ore is preheated separately from the iron and nickel ores. To produce the aforementioned chrome-steel alloy, the last-described process is followed, save that the NiO is omitted.
From the foregoing, it will be apparent that novel and efficient steelmaking processes have been disclosed herein. The iron content of ore fines and the like is directly reduced into pure iron or steel to which the desired additive can be added, or alternatively, alloy steel can be directly reduced with silicon from the corresponding ores. The illustrative and descriptive material employed herein is presented for purposes of exemplifying the invention and not in limitation thereof. Therefore, nu- :merous modifications of the invention will occur to those skilled in the art without departing from the spirit and scope of the invention. Moreover, it is to be understood.
that certain features of the invention can be employed without a corresponding usage of other features thereof.
1. A process for making steel from finely divided iron- :containing material, said process comprising the steps of completely mixing a quantity of said material into a suspension thereof in molten slag, charging said material and said molten slag suspension into a furnace, blowing com bustible and reducing gases into said furnace, blowing a limited amount of oxygen into said furnace for partial combustion of the combustible gas to melt completely :said material and to maintain a reducing atmosphere, and discharging molten slag and metal separately from the furnace.
2. The process of claim 1 wherein said finely divided iron-containing material is at least one of the group consisting of iron ore fines, ore screenings, pickle oxide, iron ore concentrates, flue dust, mill scale, shavings, filings, punchings, and turnings.
3. The process of claim 1 wherein the iron-containing material and slag mixture comprises about 45 to 60% by volume of iron ore fines and 40% to 55% by volume of molten slag.
4. A process for making steel from finely divided ironcontaining material, said process comprising the steps of mixing a quantity of said material into a suspension thereof in molten slag, charging the material and molten slag mixture into a tiltable rotatable converter, blowing natural gas with insufiicient oxygen for combustion thereof and hydrogen and carbon monoxide gases into the converter to melt and to reduce completely said material, and discharging the molten slag and metal separately from the converter.
5. The process of claim 4 wherein the natural gas with insufficient oxygen and hydrogen gas are blown together into the converter until the exhaust gases from the converter indicate a significant increase in hydrogen gas content and thereafter carbon monoxide gas is blown into the converter.
6. The process of claim 5 wherein said carbon monoxide gas is blown into the converter until the exhaust gases from the converter indicate a significant increase in carbon monoxide gas content.
7. The process of claim 5 wherein natural gas is blown into said converter with said carbon monoxide to maintain a reducing atmosphere therein.
8. The process of claim 4 wherein the gases are blown each through a lance into the converter at the rate of about 25,000 cubic feet per minute at a pressure of about 40 p.s.i.
9. A process for making steel from finely divided ironcontaining material, said process comprising the steps of completely mixing a quantity of said material into a suspension thereof in molten slag, charging said material and molten slag mixture into a furnace, blowing combustible and reducing gases into said furnace, blowing a limited amount of oxygen into said furnace for partial combustion of the combustible gas to melt said material and to maintain a reducing atmosphere, conducting hot exhaust gases from said furnace to a succeeding quantity of said iron-containing material to preheat and reduce partially said last-mentioned iron-containing material, and discharging molten slag and metal separately from the converter.
10. A process for making steel from finely divided iron-containing material, said process comprising the steps of completely mixing a quantity of said material into a suspension thereof in molten slag, charging said material and slag into a furnace, blowing combustible and reducing gases into said furnace, blowing a limited amount of oxygen into said furnace for partial combustion of the combustible gas to melt said material and to maintain a reducing atmosphere, flowing exhaust gases from said furnace through a succeeding quantity of said material contained in a preheat chamber at a velocity sufiicient to fluidize said last-mentioned material for the preheating and partial reduction thereof, and discharging molten slag andmetal separately from the converter.
11. A process for making steel from finely divided iron-containing material, said process comprising the steps of completely mixing a quantity of said material into a suspension thereof in molten slag, charging the mixture into a tiltable rotatable converter, blowing natural gas with insufficient oxygen for combustion thereof and hydrogen and carbon monoxide gases into the converter to melt and to reduce completely said material, said natural gas and oxygen being directed against the converter lining, and said hydrogen and carbon monoxide gases being directed onto the surface of said mixture while rotating the converter, and discharging the molten metal and slag separately from the converter.
12. A process for making steel directly from finely divided iron-containing material, said process comprising the steps of initially mixing a quantity of said material with molten slag to drive off the moisture from said material, said sla-g being sufficient in quantity at least to fill entirely the voids among the particles in said iron-containing material and being not greater in quantity than of the void volume of said material, placing the mixture into a furnace, blowing into said furnace combustible and reducing gases to melt and reduce completely said material, and discharging the molten metal and slag separately from said furnace.
13. A process for making steel from finely divided iron-containing material, said process comprising the steps of completely mixing a quantity of said material into a suspension thereof in molten slag, charging said material and slag into a furnace, blowing combustible and reducing gases into said furnace, blowing a limited amount of oxygen into said furnace for partial combustion of the combustible gas to melt said material and to maintain a reducing atmosphere, discharging molten slag and metal separately from the converter, and recirculating at least a portion of said discharged slag while molten directly to a succeeding quantity of said iron-containing material.
14. A process for making steel from finely divided iron-containing material, said process comprising the steps of completely mixing a quantity of said material into a suspension thereof in molten slag, charging said material and slag into a furnace, blowing combustible and reducing gases into said furnace, blowing a limited amount of oxygen into said furnace for partial combustion of the com bustible gas to melt said material and to maintain a reducing atmosphere, conducting exhaust gases from said furnace to a succeeding quantity of said iron-containing material to preheat and reduce partially said last-mentioned material, discharging molten slag and metal separately from the converter, and recirculating at least a portion of said discharging slag while molten directly to said succeeding quantity of the iron-containing material.
15. A process for making steel directly from finely divided iron-containing material, said process comprising the steps of completely mixing a quantity of said material with a quantity of molten free-silicon-containing slag sufficient at least to fill completely the voids in said material, charging said mixture into a furnace, heating said mixture suificiently to react said free silicon with said material to reduce the same, discharging molten iron from said furnace, blowing the mixture remaining in said furnace with natural gas to regenerate the reacted silicon, discharging molten slag containing free silicon from said furnace, and re-circulating said silicon and at least a portion of said slag to a succeeding charge of said material.
16. A process for making steel directly from finely divided iron-containing material comprising the steps of completely mixing said material with a quantity of molten free-silicon-containing slag sufiicient at least to fill completely the voids in said material, charging said mixture into a furnace, heating said mixture sufiiciently to react said silicon with said material, discharging molten iron from said furnace, blowing the mixture in said furnace with natural gas to regenerate the reacted silicon, conveying the hot exhaust gases from said furnace to a succeeding charge of said material to preheat and to reduce partially said material, discharging molten slag containing free silicon from said furnace, and re-circulating said silicon and at least a portion of said slag to a succeeding charge of said material.
17. A process for making steel directly from finely divided iron-containing material, said process comprising the steps of initially mixing said iron-containing material with a quantity of molten slag sufficient at least to fill entirely the voids in said iron-containing materials, placing the iron-containing material and molten slag mixture into a furnace, blowing the mixture in said furnace with combustible and reducing gases to melt completely said material and to reduce the same, the combustible gas being blown with insuflicient oxygen to support complete combustion thereof whereby a reducing atmosphere is maintained in said furnace, conveying the hot exhaust gases from said furnace to a succeeding charge of said iron-containing material to preheat and to reduce partially said last-mentioned material, conducting said exhaust gases thence to a dust collector, discharging molten iron and slag separately from said furnace, and combining the dust output of said collector with said succeeding charge of material to preheat said dust output.
18. In a process for making alloy steel directly from finely divided materials containing respectively the alloy components of said steel, said process including the steps of mixing a quantity of finely divided material containing at least one of said components with a quantity of molten free-siIicon-containing slag suflicient at least to fill the voids of said material, placing said mixture into a furnace, blowing the mixture in said furnace with natural gas to increase the temperature of said mixture and to react the alloy component containing material thereof with said silicon to reduce the first-mentioned quantity of material, mixing a quantity of the remainder of said alloy component containing material with a'quantity of free silicon-containing molten slag sufficient at least to fill the voids of said last-mentioned quantity of material, placing said last-mentioned mixture in said furnace for reduction thereof, discharging molten alloy steel from said furnace, blowing the slag remaining in said furnace with natural gas to regenerate the reacted silicon, discharging the molten slag containing free silicon separately from said furnace, and re-circulating said metallic silicon and at least a portion of said molten slag to succeeding quantities of said materials.
19. A process for making steel directly from finely divided iron-containing material, said process comprising the steps of completely mixing a quantity of said material With a quantity of molten free-silicon and manganese-containing slag sufficient at least to fill completely the voids in said material, charging said mixture into a furnace, heating said mixture sufficiently to react said silicon and said manganese with said material, discharging molten iron from said furnace, blowing the mixture remaining in said furnace with natural gas to regenerate the reacted silicon and manganese, discharging molten slag containing free silicon and free manganese from said furnace, and re-circulating said silicon and manganese and at least a portion of said slag to a succeeding quantity of said material.
20. In a process for making chrome-steel alloy directly from the corresponding ores thereof, said process including the steps of mixing a quantity of chrome ore with a quantity of molten free-silicon-containing slag sufficient at least to fill completely the voids in said chrome ore, placing said chrome ore and slag mixture in a furnace, blowing said mixture with suflicient natural gas and oxygen to raise said mixture to a temperature at which said chrome ore and said silicon will react, mixing a quantity of iron ore and with an additional quantity of said free-silicon'containing slag sufficient at least to fill completely the voids in said iron ore, adding said iron ore and slag mixture to the chrome ore and slag mixture in said furnace after said chrome ore and silicon reaction has been substantially completed, mixing together said firstand said second-mentioned mixtures to react said iron ore and silicon and to mix thoroughly the resultant molten chromium and iron metals, discharging said chrome-steel alloy from said furnace, and blowing the remaining slag in said furnace with natural gas and oxygen to reduce residual amounts of chrome and iron material in said remaining slag and to regenerate said silicon.
21. The process of claim 20 characterized in that a nickel-chrome-steel alloy is produced by adding a quantity of nickel ore with said quantity of iron ore.
22. The process of claim 20 characterized in that portions of the exhaust gases from said furnace are conducted to succeeding quantities of said chrome ore and said iron ore respectively to preheat and to reduce partially the same.
References Cited UNITED STATES PATENTS 55,710 6/1866 Reese 7540 108,235 10/1870 Bird 75-30 350,574 10/1886 Wainwright 75-40 604,580 5/1898 Gesner 75-54 920,391 5/1909 Reid 7540 1,081,921 12/1913 Baggaley 7525 (Other references on following page) 1 9 UNITED STATES PATENTS Boggs 7525 Lund 754'0 Bradley 75-4-0 Lewis 7546 Le Clarick 7525 X Eulenstein et a1. 7540 Pitterer 7524 Gilliland 754'0 Rummel 7540 Johnson 7540 Moussoulos 7540 X Rummel 7540 Pfeiffer et a1 7526 DAVID L. RECK, Primary Examiner.
H. W. TARRING, Assistant Examiner.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,326 ,670 June 20 1967 Billy B Bratton It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.
Column 7 line 45 for "1700 F. read 1700 F. column 10 lines 12 and 13 for "prosphorous" read phosphorus line 20, for "reecive" read receive column 12 line 50 for "this" read the column 13 line 5 for "10" read 100 column 15 line 15 for "2Si Fe" read 2Si-- 3Fe Signed and sealed this 25th day of June 1968 (SEAL) Attest:
Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents