US2526658A - Process for smelting iron ore - Google Patents

Description

Oct. 24, 1950 E. s. HARMAN ET AL PROCESSFOR smsmmc; IRON ORE 7 Sheets-Sheet 1 Filed Nov. 25, 1945 QWN 7 Sheets-Sheet 2 Nm EZEZEE E. S. HARMAN ETAL PROCESS FOR SMELTING IRON ORE Oct. 24, 1950 Filed Nov. 25, 1943 w? m3. 151/ M i if. M /M0 Oct. 24, 1950 E. s. HARMAN ETAL PROCESS FOR SMELTING IRON ORE Filed NOV. 25, 1943 '7 Sheets-Sheet 3 INVENTORS Eugene Sfl'arman Oct. 24, 1950 E. s. HARMAN EI'AL 2,526,658

PROCESS FOR suzmmc mow ORE '7 Sheets-Sheet 4 Filed Nov. 25, 1943 INVENTORS an M,

. WWW E W J Oct. 24, 1950 E. s. HARMAN EI'AL PROCESS FOR susmmc IRON ORE' 7 Sheets-Sheet 5 Filed NOV. 25, 1943 INVENTORS Eugene 5,.Harman Ire d H. Loft'us '7 Sheets-Sheet 6 E. s. .HARMAN ETAL PROCESS FOR SMELTING IRON ORE Oct. 24, 1950 Filed Nov. 25, 1943 INVENTOiRS EUHCTZES.,HOIITLGJL fred HLoftus Ma /raw.

'7 Sheets-Sheet 7 EwS-HAR'MAN EI'WAL PROCESS Fox swsurmc'mou ORE Oct. 24, 1950 Filed Nqv. 25,; 1945 mfiww $.11 SH 8d TM u r i 0% mm m6 w an mw m mm mm m6 mm mm mm mm mm aw vm (3:5 0 v6 taunt xfl oh Patented Oct.

I PROCESS FOR SMELTING IRON ORE Eugene S. Harmanand Fred H. Loftus, Mount Lebanon, Pa.; Harman said Loftus assignor to said Application November 25, 1943, Serial No. 511,672

Claims.

Our invention relates to the reduction of iron ore and consists in improvements both in method and in apparatus.

Eugene S. Harman, one of the inventors named herein, filed on March 30, 1942, an application for United States Letters Patent, Serial No. 436,849, now abandoned, disclosing an invention in apparatus for and method of the continuous smelting of iron ore, to provide a relatively pure or refined iron, a metal superior to and more economical than the iron produced in the conventional blast furnace. Our present invention consists in certain new and useful improvements in method and apparatus which are directed to the same end. The improvements herein disclosed lend themselves particularly, though not exclusively, to the teachings of the said Harman application.

The apparatus of the invention includes arotarykiln and a stationary hearth. In the operation of the apparatus iron ore and ore-reducing materials are advanced through the kiln or shaft zone at a temperature promotive of ore reduction.

2 amount of carbon injected, to convert carbon dioxide into carbon monoxide, is suflicient to establish a CO-:CO2 ratio adequate to produce an atmosphere that is at least neutral and preferably reducing. While in electric furnace practice the ratio may be 50:50, in kiln practice a ratio of 65:35 is considered to be safely reducing. As already noted, the reaction between carbon and carbon dioxide is endothermic, with the consequence that the injection of carbon lowers the temperature of the gases at the point of injection between the melting furnace and the re-.-

ducing kiln. 1 V

The point of separation of the hearth and shaft zones is located at or near the sintering zone in which the iron turns pasty and becomesnodul- From the kiln or shaft zone thereduced metal a is delivered to the hearth or hearth zone, wherein it ismelted at a temperature that is relatively high with respect to the temperature of the kiln. The metal-melting flame in the hearth zone is preferably oxidizing in character in order to obtain the desired high temperature.

The reduction of the ore to iron is effected partly by carbon charged in limited quantity with the ore, and partly by a reducing flame and gases. Carbon in regulated quantity is introduced to the metallic iron in course of its advance from" the kiln zone to the hearth zone, this for the purpose of insuring that enough carbon is present to complete the reduction of the ore and to inhibit reoxidation of the metal.

The reducing flame is obtained either by the conversion of the high temperature oxidizing flame streaming from the hearth zone into the reducing zone, and/or by the firing of the hearth zone with a reducing flame whose combustion air has been adequately preheated.

The conversion of the flame from oxidizing to reducing characteristics is preferably effected by the injection of carbon'into the flame. 'Pulverized coke breeze or carbonized coal, preferably.

preheated to incandescence, is injected into the flaming gases leaving the melting furnace or hearth zone, in such manner as to bring about intimate contact between the coke breeze and the ture of the flame in'the melting furnace. The

; apparatus in which and in the operation of which of material therein.

the mixture of iron, carbon and slag is progre s sive1y discharged into the stationary melting furnace, and caused'to form and maintain a pile High temperature flames are played upon the sides of the piled material, and the iron and slag are progressively melted and caused to drain to the foot of pile, where a pool of molten iron is formed and maintained, with a blanket of slag floating on top of it. From the melting furnace the flames and hotprod-. ucts of combustion flow into the ore-reducing kiln, and, as above noted, into such flames and products carbon is introduced in quantities adequate to insure that the desired atmosphere shall be established and maintained in the reducing kiln.

The apparatus advantageously includes independently fired hot air stoves, or recuperators, for preheating combustion air. A vertical kiln shaft may also be included as a part of the kiln train, raw materials being charged into the kiln shaft and heated by the hot waste kiln gases of the reducing kiln. I

In the accompanying drawings, we illustrate the invention is realized:

Figure I is a fragmentary view partly in vertical section and partly inside elevation of apparatus embodying the invention; 7

Figure II is a fragmentary view in plan of the rotary kiln and melting furnace, and theparts immediately associated therewith Figure III is a view in vertical section and to larger scale of the melting furnace, on the plane III-III of Figure II;

Figure IV is a central sectional View of the melting furnace, showing partly in section and partly in elevation the equipment organized therewith, the plane of section being at right angles to the plane of Figure III;

Figure V is a View of the apparatus at the melting furnace end, showing the structure partly inside elevation and partly in section on a vertical plane extending on the axis of the kiln; Figure VI is a fragmentary plan View of the apparatus as seen from above;

Figure VII is a diagrammatic view, partly in section and partly in elevation, of one of the fuelfeeding units for the burners of the melting furnace; and

Figure VIII is a diagrammatic view, illustrating the automatic combustion controls of the apparatus.

Referring to the drawings, the apparatus in general includes a kiln ill, and a melting furnace l i. The kiln is constructed of plate steel, lined with refractory material; the kiln is mounted for rotation in bearing its (Figures I and II) a ring-gear 59b is secured upon the wall of the kiln, and a pinion c, driven by means of an electric motor iilcl through. a suitable gearbox 126, effects rotation of the kiln at desired Velocity. Thebearings and the mechanism for rotating" the kiln may be such as are commonly used for the cement kilns in the The kiln I8 is arranged in an incline-d position, as indicated in Figure I, the lower end provides the delivery end of the kiln, While the upper end of the kiln provides the charging end. The lower or deliver end of the kiln extends into a stationary housing A water-cooled ring is (Figure III) is carried by the housing !2 in encompassing position upon the end of the rotary kiln, and this water-cooled ring prevents overheating of the kiln body at the delivery end thereof, and provides a relatively close fit between the end of the kiln and the wall of the housing I2, thereb inhibiting infiltration of air into the kiln, and/ or undue egress of the gases from within the kiln. The housing 52 is extended through the floor din a passage Is? that opens centrally through the roof of the stationary melting furnace ll arranged below the floor. The melting furnace is constructed circular in horizonal section, and has a roof of semi-sph rical shape. The furnace i the uptake or passage M, and the housing 12 are lined with unburned, chrome" free magnesite brick, the furnace roof being of suspended arch construction. The walls of the uptake l4 may be cooled, after the manner that the bosh walls of a blast furnace are cooled.

' Ore, limestone, and carbon (the carbon being in the form of coal, coal coke or oil coke) are dried; crushed to about & inch size, and thoroughl mixed, in the proportions of 40:8:5, and then are fed into the kiln l9 its inlet or charging end. More specifically, bins i are pro-' vided for the storage of sup-plies of ore, limestone and coal or coke, and such bins are supplied from railway cars that are unloaded into a hopper la, whence the materials are conveyed by a skip-bucket lb to the tops of the bins. The furnace-charging materials are removed from the bins, and dried, crushed, weighed and mixed by means of suitable apparatus. The apparatus for this purpose are known in the steel industry,

and it is needless to involve this specification with an illustration and description of them. The mixed materials are delievered by means of a conveyor to a hopper 4 having a chute 5, by way of which chute the mixture is introduced to the rotating kiln ii). The mixed charge may be preheated before introduction to the kiln, and means to this end are fully disclosed in the abovenoted pending application Serial No. 436,8l9. This mixture includes, manifestly, ore-reducing and slag-formingmaterials.

The mixture thus charged is advanced through the rotating kiln. The kiln is internall heated by means of a hot reducing atmosphere, in the presence of which the ore, through reaction with the solid carbon in the charge, is reduced. As presently will appear, the atmosphere Within the kiln consists of the hot waste gases or products of combustion of the melting furnace. The kiln includes a circumferentially enlarged portion ltf adjacent to its delivery end, and between this portion l0 and the housing I2 the kiln is of reduced diameter relatively to said said portion it}, as indicated at I072. The enlarged .kiln portion lfif provides a reservoir or holding zone in which the rate or advance of the charge through the kiln is retarded before it enters the portion lflh in which, because of the'reduced diameter of such portion, theefiect of the heat upon the reduced charge is concentrated and the charge sintered.

The metallurgical reactions and calculations that occur as through the kiln are considered in minute detail in the pending application above referred to;

Suflice it herein to say that the ore in the furnace charge is for the most part reduced in the travel of the charge from the inlet end of the'kim to the kiln zone Illh Where the material is sintered or'nodulized. Upon reaching the delivery end of the kiln, the sintered or nodulized material falls by gravity into the melting furnace.

A boring bar 42 mounted on carriage 23, is provided for dislodging the nodulized and pasty iron which tends to accumulate and stick upon the kiln wall in the sintering zone. In accomplishment of this operation the carriage is moved in right-to-left direction on the floor 9, as indicated in Flgure VI, projecting the boring bar through a port (not shown) in the vertical wall of the housing l2, andinto position adjacent to the internal Wall of the kiln, whereby as the kiln rotates the bar dislodges the accumulated material.

In accordance with our invention, the nodulized iron N (Figure III) and the slag clinker included therewith are caused to cascade from the delivery end of the kiln, and, falling through the passage 14, to form a substantially conical exposed pile P upon the hearth of melting furnace H, as shown in Fig. III, the pile being maintained at such height as to prevent flotation, and to afford an extended pile surface upon which the melting flames are played. The desired pile height is maintained by controlling the rate of material fiovv from the kiln, and by regulating the amount of fuel fired for melting the material. The melting flames areplayed at high temperature upon the surface of the pile, with the effect forming upon the furnace hearth a bathM of molten metal having an overlying blanket S of the furnace charge advancesslag. Advantageously, the melting flames are generated by the combustion of fuel with a slight excess of oxygen, in order that the requisite high melting temperature shall be developed.

A reservoir of about eighteen inches of molten metal is normally maintained in the bottom of the furnace, this metal acting as a mother, liquor to promote the refinement of the newly melted metal. A tap-hole oriron-notch i5 (Figure IV) is located at the level of the top of the metal reservoir, and whernfrom time to time, the fur nace is tapped, themolten metal flows through trough [5 into a hot-metal ladle ll.

The blanket S of slag upon the bath M of molten metal operates inv known way in the protection and refinement of .the metal under the applied heat. To the.end: that the insulating effect of theslag blanket may .be: controlled.

quantities of slag are flushed. off, either intermit-v tently or continuously, through one or more slagholes 58 opening through the furnace side wall. The tapped slag is delivered by way of a trough i9 into a slag-ladle 20. The ladles i1 .and'ZD are desired points within. the steel plant on railsZl and 22.

thatthe burners are spaced at points located a substantially interval from the side of the pile P, and are distributed circumferentially thereof. The burners A fire about 90% of the fuel, and

theflames of theburners areslightly oxidizing, eight-ninths of the carbon in the fuel burning to CO2 and one ninth burning to CO. Above the burners A is provided a row of burners C which inject incandescent pulverized carbon (coke) into the flames and products of combustion for the purpose of converting the CO2 therein to CO. Additionally, a row of burners D in the wall of the uptake passage [4 is provided for the same purpose. The burners D are staggered with respect to the burners C, in order to give carbon depth or the effect of a carbon bed that insures complete impregnation of the gases flowing from the furnace into the kiln. 7 And through the end wall of housing I2 a burner E opens, this burner operating with a reducing flame at a relatively high temperature.

Through ports J in the opposite side walls of housing 12, carbon in the form of pulverized coal is added to the nodulized material in the sintering zone 5071. of the kiln, but it may be noted that, even with such introduction of carbon, a small amount of iron oxide (FeO) will be carried with the sinter into the melting furnace. This iron oxide, plus that produced in the melting furnace by reoxidation of reduced metal is present in the blanket S of slag. To facilitate the recovery of this iron oxide contained in the blanket of slag, and to screen the slag-covered 'slag containing a calcium oxide content of 40% mounted on railway trucks adapted to travel to f ormore), and by the effect of the overlying layer of reducinggases. a

While substantial quantities of the carbon in the iron are derived from the carbon in thesinter,

the actual control ofthe carbon content, or of the refinement of the metal is effected by means of carbon additions made directly into the bath M. Means for this purpose comprise nine. refractory tubes 23 that extend through pockets formedatperipherally spaced-apart points in the side wall of the furnace. Pulverized coal, or coke, or charcoal is injected through the tubes into the body of the molten metal M. The carbon thus added comprises coal that is exceptionally low in sulphur, andas presently will appear the apparatus for. supplying this so-called metal-- lurgical carbon will be distinct from the apparatusthat prepares and supplies the fuel carbon. 1 a

cf'the electric furnace art maybe followed in this particular. The energized electrodes serve to prevent the metal bath from chilling to a point below that required for the reactions between the' slag and the metal. Primarily these electrodes act as temperature boosters,and the current consumed in energizing-them" is relatively low, it" being understood. that the electrodes will be op erated only as needed to maintain the desired.

conditions within the body of the bath of metal.

It will. be understood that in certain installations the slag will, either with or without the additions of limestone, prove to be of proper composition to provide a cement clinker, which may be ground or pulverized into commercial Portland cement.

Before proceeding with a more detailed descripti on of the combustion equipment of the apis collected in a hopper Zlifat the bottom of the hood, whence it is removed at suitable intervals; and the cleansed gas is led off through a duct 21 to a suitable point of disposal. Here we show a boiler installation 28 within a boiler-house 29, and the'cleanser gas is used as fuel in firing the boilers, to provide steam for the generation of power. 'The waste products of combustion of the boiler are drafted to a stacktfi. A powerdriven fan 3| is provided to propel the fuel gas from the gas cleaner to the boilers, and a dampered by-pass 3 la (Figure II) leads from the fan outlet to the stack for any bleed-offer recirculation of gas that may be desired.

- Turning to'a detailed consideration of the com-.

bustion system:

7 Fuel preparing equipment Thecoal for fuel is transported in railroad cars over track-f22 to a skip-hoist 32, by means of whichthe coal unloaded from the car is delivered The hood 25 is designed to serve as a gas cleaner; the flue dustseparated from the gas' of the particles does not occur. is heated bywaste gases circulated through the to a storage hopper 33. In preparing the coal for firing the furnace, the coal is delivered from hopper 33 to a pulverizing machine 3 3, the delivery being effected by gravity through a duct 35. A blower 35 is organized with the pulverizer, and the pulverized coal is blown from the pulverizer through a pipe iii to a carbonizer 33 of the type which is fully illustrated and described in United States Letters Patent Nos. 1,954,350; 1,954,351 and 1,954,352. The carbonizer 33 serves, as the name indicates, to carbonize the particles of powdered coal delivered thereto, and also serves to preheat the particles to incandescence in cyclone and recuperator elements included in the carbonizer structure. The operation of the carbonizer unit briefly consists in injecting hot carbonaceous gases and air into the cyclone. Such hot gases are obtained from the kiln housing and waste .gas flue, whence by-way of pipes 39 and 3% respectively, .they are fed with a small quantity of air into the cyclone. The mixture of gas and air is introduced by a duct Bab tangentially to the cyclone, to give a whirling motion to the gases, and the pulverized coal is injected through the top of the cyclone. The particles of coal are heated in suspension to'about 650 F.

The unit 38 includes a blower 38a that is effective to recirculate the coal in such manner that the degree of exposure of the coal particles to the hot gases may be regulated. The coal particles are then passed through recuperator plates,

whereby they are heated to about 1200 F., and

the volatiles distilled off. Since the surfaces of the coal particles are oxidized, adhesion or coking plates, and the distilled volatiles from'the unit comprise a by-product coke gas including the usual recoverable substances of a by product coke plant. As said above, the unit 33 is fully described in the above-noted patents, wherefore further consideration in. this specification is not required. Suffice it herein to say that the effect of the unit is to carbonize the coal particles and to preheat them to incandescence, whereby maximum flame temperature may be obtained in the furnace fired with such fuel, and so far as possible water vapor eliminated from the combustion gases.-

The incandescent carbon particles areblown by a fan fibfrom the unit 38 through a pipe 49 into a fuel bustle-pipe or header 4! that encircles the uptake passage it, the fan 3% using exit gas from the cyclone of unit 33 as the conveying medium. From the bustle-pipe or header, fuel lines M lead severally to fuel reservoirs L that are severally organized with the burners A, B, C, D-

and E. The gas used as the conveying medium is piped back from the reservoirs L to the suction side of the fan 38b of the carbonizing or coking unit 33, the pipes for this purpose being fragmentarily indicated at Ma, Figure VII and VIII.

By-prodncts from fuel The coke gas from the carbonizing or coking unit 38' is delivered by a pipe 45 to a gas-washer and tar precipitator 46.. The recovered tar is fed by a pump 81 to a storage tank 48, while the cleansed gas is delivered: to a pipe 49, whence it is fed to the regenerators, lpresently' to: be described.

Equipment for making carbon additions The means for making carbon additions to the nodulized sinter N at the delivery end of the kiln The recuperator comprises a storage bin 50 (Figures IV and VI) from which coal is delivered to a pulverizer unit 5!. Pulverized coal is pneumatically conveyed from the pulverizer unit, through a pipe 52, to the nozzles J in the opposite side walls of housing I2. Each nozzle delivers the carbon to the sinter as indicated by the arrow 53 in Figure III.

Still another pulverizer unit 54 is provided. This latter unit is arranged to supply the carbon, in the form of powdered coal in this case, to the molten metal in the furnace H. As appears in Figures II and VI, the pulverizer unit 5 3 is supplied with coal from a hopper or bin 55, and a pipe 56, fragmentarily indicated, will be understood to be connected to the refractory tubes 23, through which the pulverized coal is introduced to the bath of molten metal.

By virtue of providing three individual pulverizer units 3 3, El and 54, the chemical and physical qualities of the coal or coke used for the three different purposes may be selected and con trolled to best advantage. For example, the pulverized coal introduced to the sinter N is coarsely ground, whilt that added to the molten metal M is advantageously ground to a fine powder. Furthermore, the coal to be coked for the fuel is pulverized to the size most suitable.

Combustion air preheating equipment 'The air for the combustion of the fuel is preheated by means of two regenerators or stoves 5? and 58. Each regenerator is fired at the top by means of burners on a manifold 66 (Figure VI). The fuel for the regenerator burners comprises the cleansed Icy-product gas of the coking unit 38, delivered from the gas washer 16 to the manifolds E56 by piping El, 62 and '19. The products of combustion are drawn off from the bottoms of the regenerators through a flue system that communicates through a draft-controlling damper Hi to a stack G l, while the air heated in the regenerator is delivered from the tops of the regenerators through a duct system 65 leading toabustle pipe 65 that supplies the combustion air for the burners A. The flue and duct systems 53 and 65, respectively, are provided with the conventional complement of reversing valves 8?, whereby, while one regenerator is being operated to deliver under the propulsion of a fan til preheated air 1 for combustion in the furnace i l, the other regenerator is being fired to heat its checkers. From time to time the positions of the valves 61- are reversed, and the regenerator which had been serving to preheat the combustion air becomes the fired regenerator,

and the regenerator which had been fired becomes the combustion-air-heating regenerator.

The air for combustion for theburners B is drawn from'a bustle pipe I! connected to the airsupply duct system by a branch pipe l2, and the air for the burners C and 1D is drawn from a bustle pipe 53- connected to the air-supply duct system by a branch pipe 75. The air for the burnwith constant air flow, the air for combustion may be held at asubstantially straight-line preheat temperature at or above 1800 F;

The burners A and B consist of large powdered coal burners. There are twelve burners A spaced circumferentially of the furnace, and these burners burn 90% of the furnace fuel. The burners B are also twelve in number, and these burners burn the remaining 10% of the furnace fuel, the incandescent carbon introduced by burners, or nozzles (J and D not being termed fuel in the strict sense of the word. The burners B supply the layer of 100% CO flame and gas over the slag covered bath, while the burners A burn the fuel so that 11.11% is burned to CO and 88.89% to C02. The average 002002 ratio in the gases of the two sets of burners is 20:80, this ratiobeing maintained by automatic control equipment, hereinafter described.

There are twelve burners or injectors in each of the two sets C and D for introducing carbon into the combustion gases leaving the furnace. These incandescent coke injectors or burners insure adequate carbon impregnation of the com bustion gases flowing from the melting furnace to the reducing kiln, to reform all CO2 into CO. The heat content of the gases from the melting furnace is insuflicient to supply all of the heat required in the kiln. To compensate for this deficiency the burner E is installed in the housing 12. This burner operates with a high CO flame. To simplify the control of the kiln atmosphere, the burner E is so adjusted that the analysis of its combustion gases is the same as that of the furnace gases after they have been reformed by the addition of carbon.

With each of the burners or injectors A, B, C, D and E means are provided for delivering powdered fuel from the associate reservoir Linto the stream of preheated air jetted through the branch pipe 16 and the burner into the furnace.

As shown in Figure VII, such means comprise a screw H driven by an electric, motor 18 to feed incandescent powdered coke from the reservoir L into the airstreaming'through pipe 16' into and through the burner A, the burner A in Figure VII being illustrative of each of the burners or injectors provided for heating the furnace and kiln, as well as those for converting the flames and hot products of combustion from oxidizing to adequate reducing characteristics.

Combustion control equipment nected by lead'wires 80. to the conventional controller-relay unit 8|, which operates to open and close electrical contacts between power supply lines 82 anda, circuit83 leadin to the electrical valve-reversing mechanismsof the regenerator system (the mechanisms being diagrammatically indicated at 61, 51 in Figure VIII). and a circuit 84 leading to an electrically operated valve 85 in the fuel supply line to the regenerators. This organization is similar to the known automatic reversal equipment of modern open hearthfurnaces, and need not be dwelt upon'herein. Sufiice it to say that when the temperature of the air delivered 10 by the one regenerator (say regenerator 51) drops to predetermined value, in this casejto 1800 F., the radiation pyrometer T9 is effective through the organization described to shift the reversing valves and the fuel valve 35, whereby the regenerator 57 which had been serving as the air-heating unit is cut off from the air fan 68 and from the ducts that deliver the heated air to the melting furnace. Also communication between the duct at the bottom of this regenerator and the stack 64 is opened, and a flow of fuel to its burner manifold 60 is established. Simultaneously, the operation of the reversingvalves effects the connection of the companion regenerator 58 to the air fan and to the air delivering ducts, and also interrupts the supply of fuel to its burner manifold 03. Thus, the latter regenerator, 58, with its highly heated checkers is caused to deliver air to the combustion air bustle pipes of the melting furnace. As in the operation of the furnace the checkers of the air heating regenerator cool to. the point at which the temperature of the delivered air drops to 1800 F., the radiation pyrometer 19 operates again to operate the reversing valves and change over the regenerators. And so the regenerator system operates automatically to afford a continuous supply of highly preheated air to the melting furnace.

The rate of combustion within the melting furnace is automatically regulated to maintain a temperature of desired valueabout (3000 F. in this case, and such regulation is effected by means of a radiation pyrometer 86 set in the roof of the furnace. The radiation pyrometer control means adjust the flow of combustion air to the burners A in accordance with variations in furnace temperature, while means function to regulate the delivery of fuel from the reservoirs L to the burners A in accordance with variations in the controlled rate of air delivery. The rate of air delivery to the burners B and injectors or burners C and D is automatically coordinated with the variations in the rate of air flow to the burners A, and as the air flow to burners B,,..C and D varies the powdered coke delivered thereto is varied.

The means for regulating the flow of air to the bustle pipe 66 that supplies the burners A com prise a butterfly valve 81 in the hot airduct, and

a M. E. C. motor drive unit 88 connected tothe operating arm of the valve. The unit 88 and other elements of the control organization here described may be purchased on the open market: for example, from Leeds and Northrup Company of Philadelphia, Pennsylvania.

The radiation pyrometer 86 is. connected through a controller-relay B9 and a circuitlllll: to the electric valve-operating unit 88, with the effeet that, when the furnace temperature to which the radiation pyrometer is exposed tends to rise or fall, the butterfly valve 8'! is correspondingly moved towards closed or open position, thus regulating the flow of combustion air to the burners A. The injection of fuel to the burners is regulated in exact proportion to the variations in the flow of combustion air, wherefore it will be understood that the radiation pyrometer system is adapted to regulate the combustion within the furnace to a predetermined temperature that melts the sinter in pile P within the furnace at desired rate.

The instrumentalities that thus regulate the injection of fuel comprise an orifice plate Si in the air duct, and from the opposite sidesof this orifice-plate tubes- 92 and 93 extend to a regulator 1. 94. The regulator may be of the well known type supplied either by Hagan Corporation of Pittsburgh, Pennsylvania, or by Askania Regulator Company of Chicago, Illinois. As the flow of air to the burners A is by the operation of the butterfiy valve 81 increased, the pressure drop between the opposite sides of the orifice plate Qi is increased; this variation in diiferential pressure is transmitted by tubes 92 and 93 to the regulator 94, and in response thereto the regulator operates in known way to vary the energizing current flowing through circuits 95 to the electric motors 18 of each or" the fuel-feeding devices "ill of the burners A, whereby the speed of the motors is regulated in accordance with the variations in the combustion air delivered to the burners, and the rate of delivery of the powdered fuel to the burners is correspondingly varied. The rate of combustion maintained by the burners A in the melting furnace is thus regulated automatically, and the temperature within the furnace held to predetermined value.

The flow of air to the bustle pipes 75 and i3 is varied in exact ratio as the flow of air to the bustle pipe 66 is varied. That is to say, a butterfly valve 85 is arranged in each of the branch air ducts I2 and I4; a motor drive unit til (similar to unit 88) is connected to each valve st, and a regulator 98, connected by air lines to the main air duct as the regulator 95 is connected, energizes both units 97 to adjust the valves $5 in the branch air ducts l2 and M in correspondence to the adjustment of the valve 8'! in the said main air duct. An orifice plate 89 and a regulator iil l are organized with each branch air duct, and by such means the current fiowing in the energizing circuits ill! of the fuel-feed motors it of each of the burners or ejectors B, C and D is modified in accordance with the variations in air delivered thereto. Thus, the firing rate of the reducingfiame burners B is increased and decreased as the rate of combustion of the metal-melting burners A is increased and decreased. And similarly the rate of injection of the incandescent coke by the burners C and D is automatically regulated in accordance with the variations in the firing rates of the burners A and B, so that the desired CO:CO2 ratio in the products of combustion leaving the melting furnace is automatically main tained.

In addition, the melting furnace and kiln may be provided with the conventional automatic draft control.

When the rate of firing within the melting furnace is automatically reduced, the temperature of the gases passing from the furnace into the kiln drops. In order to compensate for such drop in temperature, the rate of firing of the burner E is automatically increased through the instrumentality of a radiation pyrometer H32, that is located in the roof of housing l2, and arranged, in conjunction with a regulator N33, to control the speed of the fuel-feed motor 58 of the burner. The gases entering the kiln are therefore held at optimum ore-reducing temperature and quality, regardless of variations in the rate of firing in the melting furnace, and thus all of the high temperature heat required for melting and refining the metal in the melting furnace is supplied without in any way interfering with the provision of the atmosphere required in the kiln for the reduction of the ore in the charge-a feature not heretofore available in direct reduction processes By virtue of the facts that our process charges a relatively high quantity of limestone, and em ploys pulverized coke that is lower in sulphur content and less in amount than that charged in the normal blast furnace, there is only a trace of sulphur in the product.

The silica in the ore is not reduced because of absence of excess carbon in the charge. The silica combines with the calcium in the limestone to form compounds of calcium silicates. The carbon in the product is accurately controlled to a content ranging from 0.40% to 1.50%, while the silicon ranges from 0.10% to 0.20%. The phosphorus and manganese reduce with the iron, and in the product there is slightly less of these elements than is present in the ore. Needless to say, a metal of this composition provides an excellent substitute for scrap, much preferable to Bessemer synthetic scrap and to heavy melting scrap. The metal of our process requires no treatment in a Bessemer converter, and in either solid or molten state the metal provides a superior charging stock for open hearth and electric furnaces, for direct refinement into high grades of both alloy and carbon steels. Furthermore, because of its high purity, the required time for refining in either open hearth or electric furnaces is SO far reduced that the production of such furnaces may be more than doubled.

It will be understood that within the term and intent of the appended claims, many modifications and variations in structural organization and in method are permissible, and that the reference to iron ore in the claims is exemplary for purpose of defining the invention.

We claim as our invention:

1. The method herein described which comprises advancing iron ore, together with slagforming and ore-reducing materials, through a kiln zone heated to a temperature promotive of ore reduction, nodulizing the reduced ore and slag and delivering them in nodulized condition from said kiln zone into a stationary melting furnace, directing high temperature fiames into the melting furnace and converting said nodulized metal and slag to liquid condition and forming on the hearth of said furnace a bath of molten metal having an overlying blanket of slag, leading a stream of flame and hot products of combustion from said furnace into said kiln zone and by the injection of incandescent carbon into said stream establishing a non-oxidizing atmosphere in said kiln zone.

2. The method herein described which comprises reducing iron ore in a reducing zone, delivering the reduced metal into a melting zone, firing the melting zone with high temperature flames, leading the products of combustion from the melting zone into the reducing zone, introducing incandescent carbon into the products of combustion flowing from said melting zone into said reducing zone, and under the effect of varia tions in melting zone temperature varying the rate of firing.

3. The method herein described which comprises reducing iron ore in a reducing zone, delivering the reduced metal into a melting zone, firing the melting zone with high temperature flames, varying under the effect of variations in melting zone temperature the air and fuel feeding said flames to establish and maintain optimum thermal and chemical atmosphere conditions in said melting zone, leading the products of combustion from the melting zone into the reducing zone, and introducing incandescent carbon into the products of combustion flowing from the melting zone into said reducing zone.

4. The method herein described which comprises reducingiron ore in a reducing zone, delivering the reduced metal into a melting zone, firing the melting zone with high temperature flames, varying under the effect of variations in melting zone temperature the rate of feeding air and fuel to said flames to establish and maintain optimum thermal and chemical atmospheric conditions in said melting zone, leading the products of combustion from the melting zone into the reducing zone, and introducing incandescent carbon into the products of combustion flowing from the melting zone into said reducing zone, and varying the quantity of incandescent carbon introduced to said products of combustion in accordance with variations in said rate of feeding air and fuel.

5. The method herein described which comprises reducing iron ore and nodulizing the reduced ore impregnated with slag-forming and ore-reducing materials in a rotating kiln and dropping the nodules into a furnace chamber containing a pool of molten metal with a blanket of slag floating thereon and forming the nodules into a pile that extends above the surface of said slag-covered pool, directing against the top and side surfaces of the pile exposed above said slagblanketed pool high temperature flames delivered from points spaced from and distributed circumferentially of said pile, and thereby melting the iron and fluxing said slag-forming materials in the pile and causing the iron to trickle into said pool and the slag-forming materials to enter said slag blanket for protecting the pool of molten metal until it is tapped.

I I EUGENE S. HARMAN.

FRED H. LOFIUS.

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

UNITED STATES PATENTS Number Name Date 803,886 Ellis Nov. 7, 1905 809,291 Fleisher Jan. 6, 1906 839,126 Ellis Dec. 25, 1906 911,870 Ellis Feb. 9, 1909 930,764 Jones Aug. 10, 1909 983,453 Kjellin Feb. 7, 1911 1,174,729 Jones Mar. 7, 1916 1,366,383 Hillhouse Jan. 25, 1921 1,403,576 Stansfield Jan. 17, 1922 1,439,957 Garred Dec. 26, 1922 1,535,174 McGregor Apr. 28, 1925 1,574,932 Pehrson Mar. 2, 1926 1,578,280 Gibson Mar. 30, 1926 1,720,055 Peyrachon July 9, 1929 1,774,333 Laist ..1 Aug. 26, 1930 1,819,238 Greene Aug. 18, 1931 1,819,239 Greene Aug. 18, 1931 1,848,710 Gustafsson Mar. 8, 1932 1,871,848 Gustafsson Aug. 16, 1932 1,944,874 .Brassert Jan. 30, 1934 1,954,350 Dornbrook et a1. Apr. 10, 1934 1,954,351 Dornbrook et a1. Apr. 10, 1934 2,035,550 Karwat Mar. 31, 1936 2,193,845 Stevenson Mar. 19, 1940 2,195,866 Clarick Apr. 2, 1940 2,242,219 Baily May 20, 1941 FOREIGN PATENTS Number Country Date 579,804 France 0012.24, 1924

Claims (1)

1. THE METHOD HEREIN DESCRIBED WHICH COMPRISES ADVANCING IRON ORE, TOGETHER WITH SLAGFORMING AND ORE-REDUCING MATERIALS, THROUGH A KILN ZONE HEATED TO A TEMPERATURE PROMOTIVE OF ORE REDUCTION, NODULIZING THE REDUCED ORE AND SLAG AND DELIVERING THEM IN NODULIZED CONDITION FROM SAID KILN ZONE INTO A STATIONARY MELTING FURNACE, DIRECTING HIGH TEMPERATURE FLAMES INTO THE MELTING FURNACE AND CONVERTING SAID NODULIZED METAL AND SLAG TO LIQUID CONDITION AND FORMING ON THE HEARTH OF SAID FURNACE A BATH OF MOLTEN METAL HAVING AN OVERLYING BLANKET OF SLAG, LEADING A STREAM OF FLAM AND HOT PRODUCTS OF COMBUSTION FROM SAID FURNACE INTO SAID KILN ZONE AND BY THE INJECTION OF INCANDESCENT CARBON INTO SAID STREAM ESTABLISHING A NON-OXIDIZING ATMOSPHERE IN SAID KILN ZONE.

Images