US3272618A - Method for making steel - Google Patents

Description

Sept. 13, 1966 J. MILLER METHOD FOR MAKING STEEL 2 Sheets-Sheet 1 Filed July 30, 1965 INVENTOR JORGE M/LLEF? ATTORNEY Sept. 13, 1966 J. MILLER METHOD FOR MAKING STEEL 2 Sheets-Sheet 2 Filed July 30, 1965 INVENTOR JORGE M/LLER wand 525mm RADIUS OF THE PARTICLE-- F/G 7 ATTORNEY United States Patent 3,272,61$ METHOD FOR MAKHNG STEEL Jorge Miller, Carrera 10 No. 1964 Of. 911 y 912, Bogota, Colombia Filed .l'uly 30, 1965, Ser. No. 477,362 1 Claim. (Cl. 75-60) This application is a continuation-in-part of my copending application Serial No. 208,293, filed July 9, 1962, which issued August 17, 1965 as US. Patent No. 3,201,105.

The present invention is directed to a method of conversion of molten metal, particularly a method for continuously converting molten cast of scrap iron into steel.

Numerous previous inventors have utilized the gaseous jetting principle for degassification and other treating of molten metal mixtures. A principal patent in this respect is Feichtinger (U.S. Pat. No. 2,997,384) who utilizes a gaseous catalyst for degassification of molten metal. Yet, in Feichtinger and in other gaseous setting method the jet is applied somewhat indiscriminately to the molten stream and without the purpose of obtaining steel as the reaction product. Heretofore, in fact,- it has been regarded as impossible to control the proportions of gaseous and liquid reaction to the extent that the stoichiometry of the reaction products could be predicted.

According to the present invention, the temperature and composition of molten metal are analyzed in order to compute the stoichiometry for the desired conversion reaction. Then, a gaseous compound including oxygen is formed so that it conforms to the stoichiometry of the desired conversion reaction, and is jetted in trough-shaped cross-section into the furnace and at a pressure sufficient to shatter the molten metal into particles having a di' ameter in the range 6 to 1000 microns. Simultaneously the molten metal is poured onto the gaseous compound being jetted so as to disperse shattered molten particles throughout the furnace.

While the particles are being dispersed in the furnace they undergo a series of highly exothermic reactions. The gaseous reaction product may be continuously analyzed as a measure of the quality of the liquid reaction product. Accordingly, the rates of introducing of both the molten metal and the gaseous composition, as well as their compositions may be regulated to insure a continuous liquid reaction of consistent quality.

Accordingly, it is an object of invention to provide a method for continuous conversion of cast iron into ste'el by air jetting.

Another object of invention is to provide a method for shattering and dispersing molten metal in a gaseous medium so as to insure a steel product of consistent quality.

Another object of invention is to provide a continuous air jetting method for converting molten metal wherein ambient air is entrained in the air jetting.

Yet additional objects of invention will become apparent from the ensuing specification and attached drawings wherein:

FIG. 1 is an enlarged schematic view of a proposed installation, constructed according to applicants method;

FIG. 2 is a sectional view taken along section line 2-2 of FIG. 1 and looking from the furnace interior to air jetting nozzle which is positioned at the furnace mouth 32;

FIG. 3 is an end elevation of the furnace looking from the gaseous product exhaust pipe with damper control;

FIG. 4 is a fragmentary perspective of a damper control means utilized in a modification of applicants method;

FIG. 5 is an enlarged end elevation of applicants two slotted nozzle which provides a combined jet of troughlike cross-section;

FIG. 6 is an enlarged cross-section of the nozzle taken along section line 66 of FIG. 5 and showing the opposed vacuum effects of the nozzle slots as overcome by a medial aperture positioned co-axially with the line of maximum vacuum;

FIG. 7 is a graph equating the rate of diffusion with the radius of the individual molten metal particle; and

FIG. 8 is an enlarged cross-section of a shattered droplet of molten metal showing the iron interior, slag outer layer and gaseous film cover.

The present method provides instantaneous mixture of the jetted gaseous compound containing oxygen and the various components of the molten metal, for example: silicon, manganese and iron, in order to effect a calculated reaction under substantially equilibrium conditions. An example of such a gaseous composition is CO such as referred to in the patent to Feichtinger (US. Pat. No. 2,997,384). This is accomplished by exact temperature control, stoichiometric propotrioning of gaseous compound With the molten metal and contacting the molten metal with gaseous compound under precise condiions of velocity and temperature so as to effect a fast and precisely predictable rate of reaction. The trough jetting of the gaseous medium affords the reaction vehicle, the rate of reaction being determined, of course, by the rate of diffusion of the gases which in turn depends on the area of contact upon the molten metal. The stoichiometric proportioning is obtained by judicious forming of the gaseous compound and its jetting against the molten metal being poured. Temperature control is maintained by balancing of heat input and output while taking into consideration the highly exothermic heat of reaction.

In practice it is found that stoichiometric proportions are best obtained by a continuous analysis of the reaction gas product and its temperature and varying, accordingly, the jetting and forming of gaseous compound and the pouring of molten metal. Since the gaseous reaction is highly exothermic, means are provided for removal and regeneration of the latent heat of gaseous reaction to insure constancy of temperature during reaction. As i].- lustrated in FIGS. 7 and 8, the atomization of the molten stream provides a high area of contact between gaseous compound and molten metal. The shape and size of every spherical particle dispersed throughout the furnace will depend on the relative velocity of the gaseous compound being jetted, the ratio between the rates of flow of gaseous compound and molten metal, the density, viscosity and surface tension of the molten metal. The rate of reaction depends on the rate at which the gaseous compound can diffuse through the stagnant gas barrier, the slag barrier and the iron barrier in order to react. FIG. 7, in which the abscissa represents the radius of each particle as seen in FIG. 8 and the ordinate represents the rate of reaction, shows graphically this phenomenon taking place. Since the rate of diffusion is proportional to the area of contact upon molten metal, it is desirable to have as large an area as possible with the limitation: that a spherical particle of molten metal will reach a free falling velocity which is a function of both its size and its density. For example, a 200 micron diameter sphere of 7.5 density the free falling velocity is 10.5 feet per second and for a 10 micron sphere of 7.5 desnity the free falling velocity is 0.08 feet per second. Thus, if the molten metal stream is atomized to an average of 10 microns and the vessel containing the reactants has an internal diameter insufficient to allow the 10 micron particles to settle they will be carried out of the reactor with the gaseous reaction products. A 200 micron diameter particle in a 3' by 3 by 3 reactor ice will fall to the bottom before the exhaust gases leave the reactor. Thus, the size of the shattered particles and effectively the velocity of the gaseous compound are to be limited by the internal geometry of the reactor. In practice it is found that particles in the range of 6 to 200 microns are most desirable. As the molten metal is shattered and spherical particles of molten metal are dispersed the following phenomena occur: diffusion of oxygen from gaseous to liquid phase; chemical reaction within the liquid phase; diffusion of carbon monoxide and carbon dioxide from liquid to gaseous phase; and diffusion of silica manganese oxide and other liquid impurities to the interphase forming practically a protecting coating about the spherical particle and thereby retarding further reaction. Since the rate of reaction is retarded by this coating of the surface of the liquid phase it is imperative that the air jetting shatter the molten metal stream as finely as possible with the aforementioned limitation. Also, it is imperative that the required amount of oxygen for the desired ovidization of impurities be present at the impact so that simultaneous shattering and oxidation take place. Air under a pressure of 30-110 p.s.i.a. has been most efiiciently employed for this purpose. It has been found that reaction temperature can be controlled not only by varying the forming and jetting of gaseous compound and entraining of inert gases, but also by means of a separate stream of water or steam, water being most effective.

A specific example of making steel by the method disclosed herein is as follows:

Wrought iron containing less than 0.08% carbon in the metal with intermingled slag of iron and manganese silicates is to be made from a molten metal stream containing iron with 2.6% carbon, 0.2% manganese and 2% silicon.

STOICHIOMETRY OF THE SYSTEM [Basisz 1 ton per hour molten metal, reaction temperature at jet. impact 1 Total required.

From the above chart. the ratio of CO: to CO in equilibrium for the reaction FeO+COFe:CO2 at 3000 F. is 0659. thus:

002:0.050 CO CO+'CO2:0.0787 Solving:

co zooms Moles O2 required:0.0876

EXHAUST AND RECIRCULATION GAS ANALYSIS Moles per Percent N2 0. 3300 80. 7 O O 0. 0474 11. 6 CO 0. 0313 7. 7

Total 0. 4087 100. 0

Pressure of air jet to be within 30 to 110 1b. p.s.i.

Particle size 10 to 1,000 microns diameter.

A suggested structure for carrying out applicants method is illustrated in the accompanying drawings wherein in FIG. 1 a front-slagging cupola is illustrated as having a non-tilting fore-hearth 12 which provides a continuous stream 14 of desulphurized molten metal. Molten metal stream 14 emerges from the fore-hearth is permitted to drop onto the air jetting stream 16 which emanates from nozzle 18 controlled by valve 48. At the point of impact air jetting stream 16 instantaneously shatters molten metal stream 14 at the reactor mouth 32 so as to disperse spherical particles of molten metal away from stream 14 and throughout reactor 28.

Nozzle 18 is more particularly illustrated in FIG. 5 as comprising slots 22 and 24 converging towards each other in their lower portions so as to provide a troughlike jet directed horizontally into reactor 28. As illustrated in FIG. 6, an auxiliary orifice 26 is positioned along the line of maximum vacuum created by the separate venturi effects of the jets directed through slots 22 and 24. This auxiliary orifice 26 overcomes the vacuum effect produced between the two jets and avoids striking of the nozzle face plate 50 by molten stream 14. The gas jet flowing through auxiliary orifice 26 should be at a pressure sufiicient to shatter molten metal to particles in the range of 10 to 1000 microns in diamter.

As will be apparent, varying ratios of air or gaseous compound jet 16 to stream 14 provide differing reactions with consequent difference in quality of the steel produced. Thus the steel may range from that having a low degree of carbon reduction to that wherein there has been complete oxidation of carbon and the other alloys as well. The appearance of the flame and sparks on the reactor, as well as analysis of the exact gaseous compound of the gaseous reaction product, enables an experienced operator to detect the carbon content of the metal being produced.

Any variation in the amount of air being jetted is noticeable by a change in flame appearance, as well as the exit gas compound. A gas analyzer 44 comprising gas sampler 42 and probe 40 may be positioned within the reactor or in gas outlet 36. Gas analyzer 44 is used to control by solenoid the valve means 48 of nozzle 18 which effects the jetting of the gaseous compound, as well as the entraining of ambient air. By entraining ambient air while jetting expensive compression equipment and the like can be eliminated. This rate of entraining can be readily controlled by damper means 38 maintained in the exhaust gas chimney 36 as shown in the FIG. 4 modification.

Also water cooling has been accomplished by injecting water or steam in mouth 32 in order to control the temperature. In one adaptation a plurality of injectors 60 as seen in FIGS. 1 and 2, were circularly arranged about mouth 32. Also a basic lining has been provided for the holding system or reactor 28 which may be used together with an injected stream of lime to continuously dephosphorize the molten metal. Since extremely high temperatures are produced as a result of the exothermic reactions a high percentage of alloying material, as well as scrap steel can be fed to the molten metal stream.

As illustrated in U.S. Patent No. 3,201,105, liquid reaction products are removed from reactor 28 in conventional manner.

As will be apparent, numerous substitutions of parts and modifications in the suggested apparatus may be accomplished without departing from the spirit and scope of invention, as defined in the subjoined claim.

Iclaim:

Method for conversion of molten metal in a furnace comprising:

(A) analyzing temperature and composition of said molten metal;

(B) forming a gaseous compound to conform to the stoichiometry of the desired conversion reaction;

(C) directing a trough-shaped jet of said gaseous compound into said furnace while forcing an auxiliary jet of said compound axially through said troughshaped jet at the line of vacuum created by the opposed walls of said trough-shaped jet, said forcing of said auxiliary jet being at a pressure suflicient to liquid reaction products respectively from the top and bottom of said furnace; and

(H) analyzing said resulting gaseous reaction products and correspondingly regulating said forming of gaseous compound in accordance with the desired quality of liquid reaction product.

References Cited by the Examiner UNITED STATES PATENTS 336,439 2/1886 Samuel. 949,474 2/ 1910 Hawkins et al. 75-52 X 1,968,851 8/1934 Mottweiler.

BENJAMIN HENKIN, Primary Examiner.

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