US 2562813 A
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July El, 1951 v H. J. OGORZALY ET AL 2,562,813
CONTINUOUS ORE REDUCING AND MEL-TING OPERATION Filed March 11, 1948 4 Sheets-Sheet 1 VENT GASES A HOPPER C PREHEATED AIR INLET PRE HEATED FUEL GAS INLET MOLTEN FE. OUTLET PLUGGED PREHEATED AIR INLET PREHEATED FUEL GAS INLET Juiy 31, 1951 H. J. OGORZALY ETAL 2,562,813
CONTINUOUS ORE REDUCING AND MELTING OPERATION Filed Marbh 11, 1948 4 Sheets-Sheet 2 PREHEATED AIR INLET PREHEATED FUEL GAS INLET July 31, 1951 -H. J. OGORZALY ETAL 2,562,813
CONTINUOUS ORE REDUCING AND MELTING OPERATION 4 Sheets-Sheet 5 Filed March 11. 1948 IOO SLAG LAYER TURBULENT LAYTR MOLTEN METAL F GURE-4 Patented July 31, 1951 CONTINUOUS ORE REDUCING AND MELTING OPERATION Henry J. OgorzaIy, Summit. and Homer Z. Martin,
Cranford, N. .L, assignors to Standard Oil Development Company, a corporation of Delaware Application March 11, 1948, Serial No. 14.266
7 Claims. (CI. 75-34) Our invention relates to improvements in ore reduction and melting and in particular it relates to the reduction and melting of iron ore.
As is known, the conventional method for producing iron from an iron ore is to smelt the latter in a blast furnace.
We have now devised a continuous method of smelting ores of fine particle size without the use of metallurgical coke, and with the production of an iron product whose carbon content can be controlled at any desired level, which consequently has advantages over blast furnace pig iron (which normally contains 4-6% carbon by weight) for any subsequent refining process; and we are able to produce an iron of such low carbon content that it may in many cases be employed directly as steel, providing that high initial purity (substantial freedom from silicon, phosphorous,
- etc.) is a characteristic of the ore supplied. In
brief compass, our process involves, in a first or primary stage, the partial reduction of a ground iron ore in the presence of a reducing gasiform atmosphere produced by incomplete combustion .of a fuel, and while the ore is in the form of a turbulent, dilute suspension of particles in said gasiform material. In an extremely short period of time, under the conditions of operation prevailing, the ore in our process is partially reduced to the ferrous state and melted, whereupon it passes into a secondary stage, where reduction of the molten ferrous oxide to the metallic state is accomplished, all of which will appear more fully hereinafter.
In the accompanying drawings, we have shown diagrammatically in Figurei a form of apparatus in which our invention may be carried into effect; in Figure 2 we have shown a section along A-A of Figure 1; in Figure 3 we have shown a section along 3-13 of Figure 1; in Figure 4 we have shown in vertical section a preferred modification of the reducing and melting device shown in Figure 1; in Figure 5 we have shown a crosssection taken along the line A-A of Figure 4; and in Figure 6 we have shown a cross-section taken along the line 3-3 of Figure 4.
Our process will now be described in detail with reference to the reduction and melting of an iron ore concentrate.
In Figure 1 we show a vessel l, in which our operation is performed. A feed hopper 2 contains a subdivided ore concentrate of high purity, such as may be produced from magnetite ore by known magnetic concentration methods, or such as may be found in the virgin state in several deposits, notably in Brazil and Venezuela.
Preferably the ore is ground so that it has a particle size within the fluidizable range, i. e. from about $4 inch diameter, down to powdered particles which may have a size as fine as 5 microns or less. A preferable particle size of the ore is from 20 microns to approximately one-eighth of an inch in diameter. In ores concentrated by magnetic means the particle size required for effective separation of ore and gangue is lower than necessarily required for use in our reduction and melting process, and the thus separated ore concentrate may be used directly without further sizing. The ground ore is withdrawn from hopper 2 through a standpipe 4 controlled by a slide valve 5 and discharged into preheated air in line 6. Oxygen, or oxygen-enriched air, may also be employed in line 6. As usual, the standpipe is provided with one or more gas taps i into which slow currents of gas may be discharged for the purpose of maintaining the fluidity of the downflowing ore. The finely divided iron ore is then conveyed in dilute suspension in the air, through line 6 andinto vessel I, where it exists in the upper part of the vessel as a dilute suspension of small particles in hot gases of a weakly reducing nature.
The entering air which has been preheated to a high temperature, preferably of the order of 1500-2000 F., joins in the upper part of the vessel l with partially burned gases rising from below, as will be hereinafter described. These gases, which are strongly reducing in nature, contain substantial proportions of CO and H2, and undergo further combustion with the air introduced through line 6 to generate the weakly reducing gases forming the atmosphere in the upper part of vessel I, at the same time releasing a substantial quantity of heat. Generally an additional amount of heat is necessary and this is supplied by introducing through line 8 a fuel gas such as methane or natural gas, the temperature of the entering fuel gas being preferably of the order of 700 to 1300 F.
The combustion in the upper part of vessel I of the gases rising from below, and of the auxiliary fuel gas, serves to increase the temperature of the are charged and of the gaseous streams entering through lines 6 and 8 to a temperature level of approximately 2500-3000 F., preferably about 2800 F. The effect of the weakly reducing nature of the gases produced by interaction of the air with the rising gas and auxiliary fuel is to cause rapid but limited reduction of the finely-divided oxide ore to the ferrous oxide state; and as the temperature level maintained gasiform material by reason of the high density of the liquiiied ferrous oxide and the tendency, resulting from its liquid nature, to coalesce into droplets considerably larger than the originalore p r Y Partial reduction of the iron ore particles in the upper part of vessel I occurs in an extremely short period of time after they encounter the reducing atmosphere at elevated temperature. Also, the ferrous oxide is melted practically simultaneously with its formation. The average residence time of any given particle of ore in the dilutesuspension prior to reduction may be as low as a fraction of a second, and the time of residence of the gases in the upper part of vessel I is only required to be suiiicient to permit such reduction and melting to occur and to facilitate growth of the liquid droplets to readily separablesize.
As previously indicated, molten ferrous oxide after separation from gaseous suspension de- 'sce'nds into the pool ll. Therein the pool of ferrous/oxide is subjected to further reduction by into the bottom of the pool air which enters at H and fuel gas such as methane, which enters at I2. The air is preheated to a high temperature, preferably about l500-2000 1''. while the methane is also preheated to a temperature preferably in the range of 7001300 I". The ratio of air to fuel gas is limited in order to produce on interaction a gas of highly reduc ing nature. accompanied by the generation of a substantialamount of heat. This reducing gas completes the reduction of the ferrous oxide to metallic iron which is withdrawn through openin ll. I
One method of effecting the introduction into pool ll of the air and gas entering through lines Ii and I2 is illustrated in Figure l. A perforated false bottom, 22,,constructed of refractory material is disposed above the base, 2i. and also above a refractory dividing member, 22, disposed between the floor 2|, and baseIl, forming chambers 23 and 24 into which the entering air and fuel gas are discharged. The conduits, 25, of refractory nature extend from chamber 24 through dividing member 22 and floor into the molten 'pool II, and fuel gas enters through these conduits. The conduits, 25, are in registry with ports 26 in bottom 2| which are of greater diameterthan the conduitstforming annular spaces through which the air discharges into the pool of molten material. As indicated, the elements contacting the hot gases and the melt undergoing reduction are constructed of refractory material or faced therewith... The perforated floors or partitions. 2| and 22. are suitably supported by refractory or metal supports (not shown in this schematic view) resting ultimately on base 2l. The molten metal in pool III is prevented from flowing down through conduits -22 and ports 26 by the continuous flow of gas therethru, in a manner similar to the operation 'of Bessemer converters. Conduits and ports 2! are preferably constructed with an expanding cross-section in the direction of flow, in the manner of the diverging section of a Venturi nozzle.
A plan view along section A-A of Figure 1 is shown by Figure 2.
While the iron product may be withdrawn from the pool II at the bottom of the vessel l as pne component of a single stream, it should be'born'e in mind that usually the molten iron is associated with a greater or lesser quantity of slag depending on the purity of the ore charge. A separation of the iron from the slag can be -accompiished by conveying the withdrawn productinto a quiescent zone whereupon the iron will settle into a lower liquid phase and the molten slag will collect as an upper liquid phase.
The iron product then can be readily withdrawn from the quiescent zone separately from the slag.
Alternatively, however, in the case where slag is associated with the iron, these may be readily separated in pool II at the bottom of the vessel l' by causing the air and fuel gas to discharge into the said pool II at a point above the bottom through tuyeres' disposed around the periphery of the vessel so 'as to permit the formation of a quiescent zone in the bottom'of said pool II which will permit stratification between the slag and the metallic iron,'and separate withdrawal of the two products.
It may be stated that instead of'discharging the ore into the air stream 6 as shown, it may be directly charged into the dilute suspension in the vessel I, and the air added separately. It is also within the scope'of the invention to combine the auxiliary fuel gas entering through line 8 with the air stream of line 2 prior to'entering the vessel. As indicated in "the drawing, it is generally preferable to introduce the air through line 0 at a point somewhat above the top of the pool ll so'that no opportunity is provided for an oxidizing atmosphere, resulting from momentarily incomplete mixing of the air stream with the rising gas, to contact the upper surface of the pool II.
"We also indicate in the upper portion of reducing vessel i an entrainment separator I! which serves the purpose of helping to separate from the gases passing upwardly and finally exiting from the retort through line ll, entrained solids and/or liquid. Refractory brick installed in checkerwork fashion is a suitable arrangement for an entrainment separator. The gases passing therethrough are caused to flow through a tortuous path, which flow causes the entrained material to be separated from the gases and to gravitate toward the bottom of the vessel. Figure 3 represents a cross-section of Figure 1 along lines 15-18 illustrating the method of construction of entrainment separator l I.
While the diagrammatic sketch of Figure 1 shows the refractory entrainment separating equipment as located in the upper portion of the reducing and melting vessel I, it will be understood that for constructional reasons it is preferable to install such equipment adjacent to the melting and reducing vessel or in an annular zone surrounding the upper portion of vessel I. The gases containing entrained material are preferably directed downward through the entrainment separator installed in such an auxiliary location, therebycontributing to the eifectiveness with which separated liquid is collected and returned to the pool It.
With respect to the hot gases leaving through line It the same contain considerable sensible aseaars secondary burners, heat exchangers, waste heat boilers, etc. in order to recover a substantial portion of their heat content. In particular, these gases can in part be used to preheat the air and fuel gas charged to the reducing and melting vessel I.
With regard to the introduction of air and fuel gas through lines II and I2, other methods of introducing into the pool I the gases required for final reduction in the molten state may be em ployed. For example, the air and fuel gas injected into pool I0 may be introduced from separate distributing ducts surrounding the lower portion of vessel I through a number of separate lines entering vessel I around the periphery. Such points of introduction would be below the surface of pool IE! but preferably removed somewhat from the bottom of vessel I so that a quiescent zone for separation of metal and slag is provided.
It is also within the scope of our invention to carry out the final reduction step by countercurrent contact of strongly reducing gases with downwardly flowing partially processed ore in molten form. Thus we may interpose between lines 6 and 8 and pool I0 a refractory surface arranged in checker-brick fashion as in separator II, which is open to flow of both gases and liquids. Melt produced in the upper portion of vessel I and descending onto such a refractory surface is distributed thereon and flows as a thin liquii stream downward, eventually gravitating into the liquid pool l0. Fuel gas and air from lines II and I2 are preferably introduced in this type of operation at a number of peripheral points located above the liquid level of pool I0. The strongly reducing gases produced by the interaction of the two streams then rise upward past the refractory surface, countercurrently to the downflowing stream of molten incompletely reduced material (distributed on said surface). The reduction is completed by this contact, so that pool I0 in this application becomes simply a collecting and separating zone, from which the slag and product metal may be separately withdrawn. The refractory surface may for example consist of brick work forming an integral part of the structure of vessel I or it may consist simply of spheroidal lumps or nodules of refractory material floating freely on the surface, of the melt in pool I0. It will be noted that this refractory surface does not bear the weight of a solid burden, as is the case with coke in a blast furnace, and is not consumed in order to provide the reducing gases.
Further discussing our invention we wish to point out that the ratio of air to methane or other fuel discharged into the vessel I should be maintained within certain limits in order to obtain the desired atmospheres within the vessel. As is well known, the combustion of hydrocarbons with air results in the formation of carbon dioxide, carbon monoxide, water vapor and hydrogen. The ratio of carbon dioxide to monoxide and water vapor to hydrogen in the gases employed for liquid phase reduction to the metallic state should be below about 0.3 and 1.5 respectively, for the case of reducing ferrous oxide. This can be assured with a typical natural gas by employing a volume ratio of air-to-fuel-gas of between about 2/1 and 2,5/1 for the gases entering through lines II and I2. The gases passing upwardly into the dilute suspension will be strongly reducing to the higher oxides of iron discharged into the said dilute suspension. As
with a refractory brick lining I04.
previously disclosed, it will usually be necessary to add additional air and fuel gas through lines 0 and 0 respectively to'supply additional heat to the dilute suspension. In this upper dilute phase the relative quantity of air and fuel gas added should be such that the CO2 and CO ratio and the water vapor to hydrogen ratio in the gases exiting from the said dilute suspension shall be above 0.3 and below 12, and above 1.5 and below 50 respectively. This may generally be accomplished by introducing into the upper part of vessel I through line 6 from 50 to of the total air discharged into the vessel, and maintaining the air-to-fuel ratio for the gases introduced through lines 6 and 8 at between about 10/1 and 20/1.
Referring now to Figures 4-6, we have shown another form of apparatus in which our invention may be carried out. In this modification, we have provided means for air and fuel gas introduction, for the separation of molten metal and slag from each other, for the separation from' gases of entrained molten particles, and for the removal of clean, hot fuel gases, which features differ in detail from those shown in Figures 1-3, all of which will appear more fully hereinafter.
Referring, therefore, in detail to Figures 4-6, I00 represents generally an ore smelting furnace which, as shown, is cylindrical in shape and has a domed crown. The furnace is preferably set on a concrete base IN and the upper part of the furnace is supported by steel beams I02 anchored in said base. The furnaceconsists of a steel shell I03 which is gasor vapor-tight, which is lined Where, desired, water cooling of the steel shell may be employed in order to preserve the temperatures within the allowable range. Ground ironore is introduced through line I05 (steel, brick linedl in suspension in a hot stream of gases, oxidizing in nature, produced by the complete combustion of a small portion of fuel gas with an excess of air, both the air and the fuel being preheated before combustion and the temperature of the resulting suspension being in excess of 2000 F. Line I05 enters the furnace I00 tangentially, as shown in Figure 6, thus causing a cyclonic flow of gasiform material containing the ore in the vessel I00.
Preheated fuel gas entering through line I06 is distributed by means of bustle pipe I01 and injected through tuyere lines I08 discharging below the surface of the liquid pool I09 maintained in the bottom of furnace I00. Preheated air entering through line H0 is distributed by means of bustle pipe III and injected through tuyeres H2 below the surface of the liquid pool I09 at the same level as the fuel gas injected through tuyeres I00. The streams of fuel gas and air injected below the surface of the pool are directed radially toward the center of the vessel I00, as shown in Figure 6, and enter at a level somewhat above the bottom of vessel I00, as shown in Figure 4. The interaction of the fuel gas and air introduced through tuyeres I00 and H2 below the surface of the liquid pool produces a substantial amount of heat and a strongly reducing gas in intimate contact with the molten ferrous oxide undergoing reduction in the upper zone of pool I09, which is kept in a state of turbulent agitation by the jets of radially directed gases entering the zone. The hot, partially utilized reducing gases venting upwards from pool I09 are intermingled with the hot oxidizing gases introduced through line I05 and with the ore suspended therein. The
the strongly reducing gas venting oxidisin gases introduced tana large amount of heat and reducing gas which acts to reintroduced through line ill to the state. The ferrous cad: tihsrthca immediately melted by the heat rele oug the reaction of the gases. A substantial part of the molten droplets immediately descends from the gaseous suspension into the pool ill. Borne molten droplets are retained in suspension within the gases rising upwards through vessel Ill. These gases are reversed in direction upon contacting' the domed roof of the vessel and are caused to invert and how downwards through annular space Iii which is filled with refractory fire brick arranged in checkerwork fashion. By the joint action of the tortuous flow of the gases through the checkerwork and the action of gravity, essentially all of the entrained metal droplets are removed from the suspension and collect in .liquid pool ill at the bottom of annular section III. The molten liquid ferrous oxide collected at this point overflows through radially directed and upwardly sloping vents III which pass through the separatin wall lit and allow the collected molten ferrous oxide to flow back into the central zone of vessel Ill and thence into pool ill. The upward slope of openings Iii serves to insure a liquid seal between the inner zone of vessel Ill and annular zone 3. Substantially clean hot gases are removed from open zone ll'l within the annular space I II by means of radially directed lines II. which slope upwards in an outward direction. These discharge into bustle pipe lit from which the gases are withdrawn through line I".
Returning to the bottom of vessel I, the liquid pool III. in addition to the turbulent upper zone in which reduction of molten ferrous oxide to the molten metallic state is taking plact contains a' lower quiescent zone in which separation into two fractions occurs. The upper and lighter fraction consists of molten slag which is periodically withdrawn through opening Iii, ordinarily closed by means of a clay plug. The lower zone consists of molten metal which is withdrawn periodically through opening II! which is similarly closed with a clay plug when not in use.
As a specific example of our process, the following description of a typical operation on a purified m ore is submitted. All the quantities given are referred to the basis of 100 mols of natural gas containing about 95% CH4 introduced into the liquid pool of molten ferrous oxide. Five tons of the finely divided concentrate is suspended in 350 mols of air preheated to 1900 F. and is carried therein into the turbulent gas phase reduction zone. The preheated air reacts in the reduction zone with gases rising from below and with 18 mols of natural gas introduced to the gaseous reduction zone as auxiliary fuel at a preheat temperature of 1000 F. raising the temperature level of the gases and the introduced ore to 2800 F. The product gases from the combustion occurring in the gaseous phase are sufficiently reducing in nature to convert the R20: to FeO which melts into droplet form and is separated from the gas and collected in a pool. In addition to the 100 mols of natural gas 226 mols of air are also discharged into the molten mixture. The interaction of these gases raises them from their inlet temperature of 1000 and 1900' 1'. respectively to a temperature of 2900" F. and also heats the molten l'eO to this temperature level.
8 'mcgasespassingthroughthepoolarestronllr reducing and convert the molten R0 to metallic Fe. which is also molten at this temperature level. 'Ihegasesleavingthepooljoininthereaction takingplaceinthegaseoussoneoverheadand molten metal is withdrawn from the pool. The quantity of natural gas consumed is 12,750 cubic feet per ton of Fe produced. of which a proportion is devoted to supplying the large heat losses which are unavoidable in operations at this temperature level.
It will be appreciated that although our process has been described in the light of the equipment illustrated in Figures 1 through 6 and with reference to the reduction of an iron ore substantially free of gangue, other forms of apparatus achieving substantially the same ends may be devised.andtheprocesscanalsobeappiiedto iron ores containing substantial amounts of gangueaswellastoothertypmofore. Itisparticularly adapted to ores of the so-called "selffiuxing" typ such as iron ores containing lime andsilicaincloselyassociatedformsothata -fiuid and low-melting flux is readily Produced at the operating temperature level without further admixtures; but where gangue of a predominantly siliceous nature is present, ground limestone or lime may be mixed with the ore charge and added to the gaseous reduction zone in the correct proportion to produce a flux of the desired properties. In this case it is particularly advantageous to direct the entering stream of solids preferably in gaseous suspension against surfaces wetted with the molten product of primary reduction so that the interaction of the lime and silica of the gangue to produce low melting slag is facilitated.
Non-oxidic iron ores, such for example a iron pyrites, and non-ferrous ores as well. may also be processed by the means of our invention. which we conceive to be a generally applicable and economic method for converting a diflicultly-fusible compound, into another readily fusible compound, melting the latter and then reducing to the metallic state while the material undergoing reduction is in the liquid phase. It will be understood that the temperature levels employed and the ratics of the air and fuel gas fed to the melting and final metallizing zones will differ for the various substances processed, but are readily determined by calculation or empirical means.
In general the above illustrative descriptions are not to be construed as limitations to our invention, which we wish to define solely by the following claims.
What is claimed is:
1. The method of smelting an iron ore which comprises charging said ore in the subdivided state into a primary high temperature reducing and melting zone, partially reducing therein said ore in dilute suspension in a gasiform reducing agent to a lower oxide melting below the temperature level maintained within said zone, fusing said lower oxide in said zone into liquid droplets suspended in said gasiform reducing agent, separating said liquid droplets from said gaseous suspension, collecting said liquid droplets in a molten pool maintained at a temperature level above the melting point of iron, passing a gasiform reducing agent through said molten pool to reduce said lower oxide to the metallic state. and withdrawing the molten metal from said pool.
2. Method of claim 1 wherein preheated gas containing free oxygen and preheated normally gaseous or liquid hydrocarbons are separately introduced into said pool below the surface thereof, generating by their interaction the strongly reducing gasiform agent employed for the reduction of the lower oxide and releasing thereby also the heat required to maintain the pool above the melting point of the reduced metal and wherein the partially utilized gases leaving the said pool pass into the said primary reduction and melting zone, and wherein additional preheated oxygen-containing gas and preheated normally gaseous or liquid hydrocarbon fuel are introduced into said primary reduction zone, and wherein the interaction of the gaseous streams entering said primary zone serves to maintain a weakly reducing atmosphere capable of reducing the said iron ore to a lower oxide. and also to release the heat necessary to maintain said primary zone above the melting point of said lower oxide.
3. The method 01' claim 2 wherein said oxygen containing gas and the normally gaseous or liquid hydrocarbons which are employed to generate by their interaction the gases eiiecting reduction of the said ore and the heat required to melt the solid charge and to maintain the pool above the melting point of the reduced metal are preheated by means of the sensible heat contained in the gases leaving the primary reduction zone.
4. The method set forth in claim 1 in which the gasii'orm material in the primary zone, after separation therefrom of the main bulk of molten material. is caused to flow through a liquid separating zone for the purpose of separating substantially the last traces of entrained liquids.
5. The method set forth in claim 4 in which the gasiform material from which the main bulk of the liquefied material has been separated is passed through a liquid separating zone subsequent to the said primary reducing zone in the direction of the gas flow.
6. The method set forth in claim 4 in which the gasiform material from which the main bulk of the molten material has been separated is passed through a liquid separating zone adjacent to said primary zone for the purpose of separating substantially the last traces of entrained liquid material.
7. The method of smelting an iron are which comprises charging said ore in subdivided form i into a primary high temperature, partially reduc.
ing, melting zone of circular cross-section. forming said ore in said partially reducing and melting zone into a dilute suspension in weakly reducing gas and impelling the said suspension on a cyclonic type of flow within said zone by introducing at near the bottom of said zone a gaseous stream tangentially with respect to said zone, reacting a gasiform fuel with a gas containing free oxygen within said zone whereby the said weakly reducing gas is produced'which partially reduces said ore and a temperature is attained within said zone suflicient to cause melting of said partially reduced ore. collecting the molten'partially reduced ore in a pool disposed below the bottom of said primary zone, separately introducing a gasiform fuel and a gas containing free oxygen into said pool. the fuel and oxygen-containing gas being so proportioned that upon interaction they form a gas which is reducing with respect to. said molten partially reduced ore, reducing said molten partially reduced ore to the metallic state, and recovering from said zone a molten metal.
HENRY J. OGORZALY. HOIIER Z. MARTIN.
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