US2418394A - Method of and means for reducing ores - Google Patents

Description

April l, 1947. o. BROWN 2,418,394

METHOD 0F AND MEANS FOR REDUCING oREs Filed March 2O 1942 Patented Apr. 1, 1947 METHOD OF AND MEANS FOR REDUCING ORES Charles 0. Brown, Rye, N. Y., assigner to American Ore Reduction Corporation, Dover, Del., a corporation of Delaware Application March 20, 1942, Serial No. 435,543

7 Claims. 1

This invention relates to the reduction or beneiiciation of ores or other metal bearing materials, and it has for its general object to provide improved methods of and means for reducing such materials to a desired state.

Heretofore, many attempts have been made to reduce or beneciate such materials by passing them in a finely divided state through a reducing zone wherein the reducing gas atmosphere needed to bring about the desired degree of reduction was intended to be created -by the incomplete combustion of coal or other carbonaceous fuel. While from a theoretical standpoint such methods appeared sound, nevertheless, in practice all have met with little or no success, this being due primarily to the fact that the temperatures created by the incomplete combustion of the fuel failed to generate the reducing gas needed for reduction or that when higher temperatures were provided the particles of ore either became melted or the impurities in the ore were sintered to a glaze and so prevented reduction.

In accordance with one phase of the present invention improved methods are provided for reducing such materials. To these ends, coal or other carbonaceous fuel and air are fed into a furnace, but in contrast with previous methods the amount of air is sucient to support substantially complete combustion of the fuel and thus obtain combustion gases at the relatively high temperatures which accompany such combustion, In eecting this combustion, the composition of the gases from the standpoint of their reducing properties is not a material factor. Preferably, however, the fuel employed is of the sort that is high in carbon and low in hydrocarbon since under these conditions the resultant combustion gases contain a high percentage of carbon dioxide and a corresponding low percentage of Water vapor. After high temperature combustion gases have been thus created they are further conditioned as, for example, by being brought into intimate contact with a secondary supply of carbonaceous or other. reducing material which combines With the carbon dioxide content of the gases and so renders them highly reducing in nature. 'I'he secondary supply of carbonaceous material is preferably chosen with particular regard to the rapidity with which it reacts With carbon dioxide to form the highly reducing carbon monoxide gas. Thereafter, the

material to be reduced is subjected to the action of -the conditioned gases which, in being both highly reducing in nature and at elevated tem- (Cl. 'i5-26) 2 peratures, effectively reduce the material to the desired state.

From the foregoing brief outline of the method it will be seen that it contemplates first the production of high temperature combustion gases under conditions enabling the desired quantity of gases at desired high temperature to be efflciently and reliably produced without interference from extraneous factors tending to adversely affect the combustion process. The initially produced gases, unsuitable as an effective reducing agent, are then conditioned to secure the desired reducing qualities, still in the absence of the inuence of any extraneous factors adversely affecting the desired chemical reaction. Thereafter, the material to be reduced is brought into contact with the conditioned gases, which, because of the manner of their preparation may readily be `controlled both as to temperature and composition, as Will hereinafter be more fully explained, to effect the desired extent and speed of reduction.

In the preferred process, the material to be treated is `ground to a finely divided state, this being desirable since it enables the reducing operation t0 go forward with extreme rapidity or "flash reaction, by virtue of the fact that the surface areas of the particles thus exposed to the action of the reducing gases are large as compared to the Weight of the particles. In addition, the material, after being ground to a fine particle size, is preferably treated to separate the metal bearing particles `from the gangue. This treatment, of course, will depend on the characteristics of the material. For example, if the metal bearing particles are magnetic in nature, suitable separation may be effected by almagnetic separator. O-n the other hand, if the metal bearing particles are non-magnetic separation may be effected by tabling or dry flotation.

Also, in the preferred process the material is passed through the gases in counter-current fashion since in so doing the contained heat of the gases may be utilized much more effectively. In otherwords, when the material to be treated is passed counter-current through the gasespreferably by causing the material to be reduced to fall by gravity through` an upwardly flowing gas column, it is subjected to a gradually increasing temperature with the result that it is progressively brought to -the desired state as exemplified, for example,` in the treatment of FezOa which requires lower temperatures to be brought to Fe3O4 than does the Fes04 to be brought to FeO, In addition, the gases in flowing countercurrent retard the passage of particles therethrough and. so effects longer periods of reaction.

In accordance with another phase of the invention an improved furnace structure is provided to enable the above described methods to be practiced with a high degree of efficiency. in its preferred form, the furnace is provided'with a separate combustion chamber wherein the gases are created and conditioned, this being desirable since by this arrangement the conditioning yof the gases may be more accurately controlled'.` In addition, a structure of this sort enables the material to be reduced without subjecting it to objectionably high temperatures or to an oxidizing atmosphere during its travel through the furnace.

tion reference may be made to the accompanying drawing which shows, in section, the improved furnace structure in its preferred form In practicing the invention with the aid of the structure shown, a primary supply'of powdered coal or other carbonaceous fuel is delivered under the influence of air flow through a feed pipe IQ to a burner I2 carried by the upper endwall Ie of a combustion chamber` I6 which projects downwardly part way through the central part of a furnace shaft I1 dened by a vertically disposed steel drum I8 having an inner lining of suitable insulating and refractory material ZEL In addition, a secondary supply of air is delivered to the burner I2 through a secondvpipe 22'. The primary supply of air is limited in amount to that required to deliver the coal to the burner i2 and preferably is not preheated, at least to any great extent, this being desirable in order to prevent packing of the powdered coal during its delivery to the burner I2. The secondary source of air, however, is preferably delivered to the burner I2 in a highly preheated'conditiom The total volurne of air thus delivered to theV burner I 2 is sufficient in amount to support complete cornbustion of the fuel. The burner-|2 is preferably of the grid type and it is adaptedand arranged to direct the flame resulting from the combustion of the fuel downwardly through the central portion of the combustion chamber IB. By virtue of the fact that substantially complete or complete eombustionof the fuel is effected plus the fact that the major portion, of the air which is fed to the burner i2 to support combustion is highly preheated the initial temperature of the resultant combustion gases is sufficiently high to generate the necessary reducing gas if carbon or a like reducing agent were present. Inasmuch as substantially complete combustion of the fuel For a more complete description of the inven-` has been eifected, however, such reducing agent is lacking with the result that the reducing qualities of such gases haveY little or no appreciable value. In order, therefore, to secure the desired composition of these gases for reducing purposes they arel conditioned by being brought intointimate contact with va secondary supply of carbonaceous or other reducing material. In accordance with the preferred process, Vas stated heretofore, the secondary supply of reducing material is chosen primarily with regard to its abil` ity to Combine withthe carbon dioxide content of the combustion gases and it preferably consists Iof a highly reactive 1 solid carbon such as char, charcoal, Ycoal or coke and desirably in the order named. This secondary supply of reducing material is delivered in' a finely divided state through a'pipe24 in 4measured amounts to an annular chamber 26 positioned about the `burner I2 and arranged to discharge the incoming material downwardly about the downwardly flowing stream of combustion gases in the form of an envelope, this arrangement being desirable since the barrier of solid carbon thus provided acts to protect the adjacent walls of the combustion chamber I 6 against the extremely high temperature of the combustion gases. As the stream of combustion gases and added conditioning material pass downwardly they become intimately intermixed by virtue of the turbulent condition of the stream with the result that the carbon thus added combines with the carbon dioxide gas in the stream to produce a high percentage of carbon monoxide and so renders the stream highly reducing in nature.

The combustion chamber I6 is defined by heat resisting wall 28 such as may be provided by carborundum or graphite blocks or the like, and it is so proportioned as to insure that substantially no carbon dioxide or other oxidizing gases remain in the stream as the stream emerges therefrom. As a practical matter, however, it has been found desirable to add slightly more solid carbon than is theoretically required to condition the gases to insure that substantially no carbon dioxide does remain in the stream at the point of its emergence from the combustion chamberil or that if some slight amounts do remain vthey will be quickly converted to the reducing carbon monoxide.

As the gas stream emerges from the lower end of the combustion chamber I its direction of travel is reversed by the pressure in the shaft and it thereafter flows upwardly in the form of an envelope about the combustion chamber to the upper regions of the furnace shaft IT, from whence it is discharged through a port 3B, or a series of such ports.

As' the gas stream travels upwardly about the combustion chamber the material to be reduced is showered downwardly therethrough, in counter-current fashion, the powdered material being introduced into the furnace shaft I'I inV measis limited to that which enables the reduced particles to drop under the influence of gravity through the upwardly flowing gas stream. y

As the powdered material drops through the upwardly owing gases it is reduced to the desired state by virtue of thev fact that the gases are highly reducing in nature and at temperatures which insure that the reactions go forward with the degree of rapidity necessary to insure the desired rate of reduction of the material. During the'conditioning of the gasesin combustion chamber I6, the temperatures thereof drop from lthe temperatures obtained by pre,- heating the air and by effecting substantially complete combustion of the fuel, this decrease in temperature being the result of` the endo-V l ports 30. Despite this, however, the temperature attacca 1 5 of the gas streaml decreases as it travels upwardlyy due to the slight heat losses through thevvalls of the reduction shaft but, due to the fact that the material to be treated is dropped countercurrent therethrough and thus progressively.

brought to the desired degree of reduction, the

contained heat of the gases is used to the greatest possible advantage.

In the event the reduced material is to be `collected in molten form, the temperature of the gas stream as it emerges from the combustion chamber I6 should be above the melting point of the material being reduced. Under these conditions, the particles are substantially completely reduced before being subjected to such-temperatures by virtue of the fact that `they are dropped counter-current through the upwardly flowing gases which, as stated heretofore, are constantly losing heat through the walls of the furnace and which may be further cooled, if need be, by cooling means external of the furnace. Because of the conditions thus obtaining in the reduction zone, it is possible to reduce the material to a molten end product Without producing the glazing effect on the raw or partially reduced particles which interferes with or prevents further reduction.

On the other hand, if the reduced material is to be collected in powder form, the temperature of the gas stream as it emerges from the combustion chamber should be low enough to prevent the descending particles from being raised to sintering temperature. The temperature at which the gas enters the reducing zone maybe varied considerably without raising the particles to sintering temperature depending both upon the nature and the size of the particles upon which the gas acts. For example, if iron ore is the material under treatment and it is to be collected in molten form, the temperature of the gas stream as it emerges from the combustion chamber should preferably be in the range of from approximately 2900 F. to approximately 3100 F., whereas if it is to be collected in powder form the temperature of the gas stream as it emerges from the combustion chamber I6 should preferably be in the range of `from approximately 20009 F. to approximately 2300 F. Regulation of the temperature of the gases as they leave the combustion chamber I6 is advantageously effected by suitably-regulating the temperature of the preheated air supplied to the burner I2.

The structure shown is adapted for the collec` tionof the reduced material in powder form.` To

conveyer 40 is employed toregulate the level to which the collected material is retained in thebottom of the furnace. When the reduced material is to be collected in powder form it is desirably cooled from the time the reduction is complete, this being desirable to prevent back reactions. To this end, the funnel shaped end closure 36 is not protected by aninner lining of heat insulating material in order to promote the.` loss of heat byradiation, and if the lossof heat thus obtained is insufficient, the endfclosure 36 may be provided with a Water jacket 42having 6 inlet and outlet ports by means of which water maybe circulated therethrough. In addition, the screw conveyer 40 for like reasons may also be provided with a water jacket 44 having inlet and i?, outletrports by. means of which water may be circulated therethrough.

In the event the reduced material is to be collected in molten form, the lower end of the furnace would necessarily have to be changed accordingly. That is to say, instead of cooling the collected material means would have to be provided to heat insulate the molten mass and a discharge spout provided for the periodic tapping of the molten end product.

As stated heretofore, the added reducing agent is preferably addedin a finely divided state. In addition, it is desirable that the particles be substantially uniform and of such size that substantially all particles are reduced during the conditioning period to a size which enables the remaining excess (if any) to be carried upwardly about the combustion chamber in suspension in the conditioned gases. It is conceivable, however, that some of the added reducing agent may be carried to the bottom of the furnace with the reduced material whether the latter be in molten or powder form. As a matter of fact, this is not objectionable since if such active reducing agent fall with a solid end product in the lower end of the shaft it will aid in `maintaining the atmosphere reducing in nature and so aid in preventing the particles from going back to a less highly reduced form. If the collected material is in molten state, carbon falling thereto will be dissolved in the mater rial.

Ying heat may be Widely varied and a relatively close control of tained.

As stated heretofore, the waste gases are Withdrawn from the furnace shaft Il through a series the temperature of the mass obof ports 3B. rhese gases may contain some reduced particles as Well as particles of gangue released during the reduction operation. In the event the quantity of the reduced particles thus carried upwardly and out of the furnace by the gases Warrant such procedure they may be freed therefrom by directing the gases as they emerge through the ports 3! through a suitable collector.

The ratio of the total Weight of the carbone.n ceous solids to the volume of air introduced into the furnace will vary depending on the grade of the solids as Well as on the grade of the material to be reduced and the desired degree of reduction. In all cases, `a certain amount of the solids is used in maintaining the temperature of the stream at desired values and the remainder is used in creating the carbon monoxide gas needed to eifect the reduction of the particles treated plus the additional smallamount needed to in- `sure that the gases remain reducing in nature;

and the amount of air introduced into the Vfurnace, in turn, depends on the amount of. solids, enough being required to insure substantially complete combustion thereof so as to obtain said temperatures, reducing gases and excess carbon.

For example when' treating hematite ore, approxmately 1G00 cubic feet of air and approximately 22"pounds of coal (mediumvolatile bituminous coal) vwill be required to reduce approximately 47 pounds of suchore to substantially `pure 4iron powder with approximately 5% excess carbon present.

Having thus defined my invention, I claim:`

1. A method for the reduction of ores or like materials which rconsists in burninga primary supply of carbonaceous vfuel with sufficient air to support complete combustion thereof `whereby to produce high temperature combustionlgas'es, corr-y 4 support complete combustion thereof whereby to produce high temperature combustion gases, conditioning said gases to render them highly reducing lin nature by bringing them into intimate contact with a secondary supply of carbonaceous material, and thereafter bringing the conditioned gases into intimate contact with dispersed finely divided material to be reduced, characterized by the fact that said gases are produced and conditioned in Va downwardly flowing column out of contact with the material to be reduced, and the conditioned gases are thereafter caused to flow upwardly in countercurrent relations with respect to material to be reduced falling through the upwardly flowing gases by gravity.

3. A. method for thereduction of ores or like materials by the aid of a Vertical shaft furnace having a separate combustion chamber in the upper portion thereof, which consists in forming a downwardly flowing column of gases of-highly reducing nature in said combustion chamber, causing said gases to reverse their direction of flow and flow upwardly through said furnace in the form of an envelope around said combustion chamber, feeding finely divided material to be reduced into the upper portion of the furnace tov fall in counter-current relation to the upwardly flowing gases, collecting the reduced material in the bottom portion of the furnace, cooling the bottom portion of the furnace, and con-4 trolling the depth of the collected material in the furnace to regulate the temperature thereof by varying the amount of the cooled surface in the lower portion of the furnace exposed to absorb heat radiated to the lower portion of the furnace and the collected material from thecombustion and reducing zones.

4. In a furnace for the treatment of ores and likeV materials, the combination of a furnace shaft,

Y saidchamber through said-shaft, means for introducing a secondary supply of carbonaceous material to said chamber to render said high temperature gases highly reducing in nature, means forintroducing finely divided material to be reduced: into said -shaft* and in' 'such' fashion that-f it is brought into intimate contact withsaid high temperature vreducing gases to effect a reduction thereof, and means for withdrawing the reduced material from said shaft, characterized in that the furnace shaft is disposed vertically and in that the combustion chamber depends part way down through the central portion thereof from its upper end.

'5.y In a furnace for the treatment of ores" and like materials, ther combination of a furnace shaft, a combustion chamber separated from saidshaft but in communication therewith, means` for supplying fuel and air to said' chamber to produce high temperature combustion gases for" flow. from said chamber`- through said shaft,

means for introducing Ya secondary supply'of carbonaceous material to said chamber to render said high temperature gases highly reducing in nature, means for introducing nely divided maf terial to be reduced into said shaft andin such fashion that it is brought into'intimate contact Vwith said high temperature reducing gases to effect a reduction thereof, and means for with- Y drawing the reduced material from said shaft, characterized in that the means for introducing the secondary supply of carbonaceous material into the combustion chamber is arranged to discharge the same about thevcombustion gases in 6. In a furnace for the treatment of ores and like materials, the combination of a furnace shaft, a combustion chamber' separated from said shaftbut in communication therewith, means for supplying fuel and air to said chamber to produce high temperature combustion gases for flow from said chamberthrough said shaft,v

means for,V introducing a secondary supply of carbonaceous material to said chamber to render saidjhigh temperature gases highlyreducing in nature, means for introducing finely divided materialto be reduced into saidshaft and in such fashion that it is brought into intimate contact withsaid high temperature reducing'gases vto effect a reduction thereof, and means V,forjwithe drawinggthe reduced vmaterial from said shaft,

characterized in that the furnace shaft is disf posed vertically, in that the combustion chamber K' depends part way down throughthe central porhav-ingA an open ended combustion chamber `in the; upper portion thereof, which consists, in form.. l

ing adownward-lyflowing column of gases'lof highly reducing nature insaidchamber byburn-QV ingftherein to complete combustion a primary source` of carbonaceous material and adding to the ,resultant combustion gases a secondary source 'of carbona'ceous material, causing said, `gases to reverse their-direction j of flow and-,flow

upwardly through said-furnace in the -form of an"envelo.pegaround said combustion chamber, feeding :finely divided material toV be reduced intoY the upperportion of the furnace to fall in counf, iter-current relation tof the upwardly flowing gases, and collecting the reduced material in the Number Name Date bottom portion of the furnace. 1,934,082 M011 et a1 Nov. 7, 1933 CHARLES O. BROWN. 2,066,665 Baily Jan. 5, 1937 803,886 Ellis Nov. 7, 1905 REFERENCES CITED 5 290,343 Morgan et al Dec. 18, 1883 1,588,217 Winkelman June 8, 1926 The following references are of record in the 1,9837541 Christensen an 2:2, 1935 le 0f this patent! 1,888,164 Freeman Nov, 15, 1932 2,030,627 Freeman Feb. 11, 1936 UNITED STATES PATENTS 10 1,829,124c Wilson oct. 27, 1931 Number Name Date 2,321,310 Moore June 8, 1943 806,774 Brown Dec. 12,- 1905 2,184,300 Hodson et al DEC. 26, 1939

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