US3922165A

US3922165A - Method for direct reduction of iron ore using sleeve-shaped briquettes

Info

Publication number: US3922165A
Application number: US498072A
Authority: US
Inventors: Louis Meade Harker; Thomas Valle
Original assignee: Jaconvel Co
Current assignee: Jaconvel Co
Priority date: 1974-08-16
Filing date: 1974-08-16
Publication date: 1975-11-25
Anticipated expiration: 1992-11-25

Abstract

A process for the direct reduction of iron ore utilizes sleeveshaped briquettes in a direct fired rotary table furnace. The briquette is formed of a mixture of iron ore, carbonaceous reductant, and a binder, compacted into the shape of an upright prismatic sleeve such as an annular cylinder or a block shaped sleeve. Vents or openings may be cut through the vertical walls. The bottom end of the briquette is notched or formed with feet or pads to enhance circulation of reaction gases when the briquettes are placed in an upright position on the table of a direct fired reduction furnace, and to support the briquette on the furnace table with a minimum of table contact area.

Description

United States ate Harker et al.

[ 51 Nov. 25, 1975 [75] Inventors: Louis Meade Harker; Thomas Valle,

both of Carbondale, C010.

[73] Assignee: Jaconvel Company, Carbondale,

22 Filed: Aug. 16,1974

211 Appl. No.: 498,072

Howard et al. 75/28 Beggs et a1 75/36 Primary Examiner-M. J. Andrews Attorney, Agent, or Firm--Burton, Crandell & Polumbus ABSTRACT A process for the direct reduction of iron ore utilizes sleeve-shaped briquettes in a direct fired rotary table furnace. The briquette is formed of a mixture of iron ore, carbonaceous reductant, and a binder, compacted into the shape of an upright prismatic sleeve such as an annular cylinder or a block shaped sleeve. Vents or openings may be cut through the vertical walls. The bottom end of the briquette is notched or formed with feet or pads to enhance circulation of reaction gases when the briquettes are placed in an upright position on the table of a direct fired reduction furnace, and to support the briquette on the furnace table with a minimum of table contact area.

10 Claims, 11 Drawing Figures xx x x US. Patent Nov. 25, 1975 Sheet 1 of3 US. Patent Nov. 25 1975 Sheet2of3 3,922,165

US. Patent N0v.25, 19.75 Sheet3qf3 3,922,165

llill IIIHI llllll METHODFOR DIRECT REDUCTION OF IRON ORE USING SLEEVE-SHAPED BRIQUETTES BACKGROUND OF THE INVENTION The present invention relates to an improved process for the direct reduction of metallic oxides such as iron ore using sleeve-shaped briquettes in a direct fired furnace.

The term direct reduction refers to the conversion of iron ore, particularly in the oxide forms of hematite and magnetite, to free iron, at a temperature which is below the melting point of iron and, more specifically, below the temperature of which large amounts of carbon tend to go into solution in the metal which would result in the production of brittle pig iron.

Briefly outlined, the major steps in direct reduction processes comprise mixing the various ingredients, including iron ore, a carbonaceous reducing agent and a binder, and forming the mixture into pellets which are fed into a reduction furnace wherein they are heated to reaction temperature. The pellets are held in the furnace for a period of time sufficient to allow the reduction reaction to be substantially completed. The reduced pellets, now containing substantial amounts of free iron, are cooled in a reducing atmosphere to prevent surface reoxidation, and are then treated in any desired manner to place the free iron in a form suitable for further use.

The direct reduction process for making iron and steel dates from ancient times. It was the only process known from at least as early as 1400 B.C. until approximately 1350 A.D., when initial developments of the blast-type furnace began. With the advent of the hot blast furnace in England in 1819, the direct reduction process fought a losing battle with the blast furnace, although direct reduction continued to be popular in certain areas of the world, for example, in India and Switzerland. Direct reduction is still used in the United States for specialized purposes, such as for the making of powdered iron for the fabrication of sintered metal parts, but it is still generally considered to be an uneconomical process for the mass production of iron.

It is well known that direct reduction may be carried on or terminated just below the sintering temperature of the metal so that the size and shape of the ore pellets are largely preserved to form sponge iron. At a higher temperature, the reduced iron fuses to form a pasty ball or mass at the bottom of the furnace and, upon further working, becomes wrought iron.

Two types of direct reduction furnaces have been in common use through the years. The first is the hearth or bloomery type furnace used in this country until about 1901, and the other is the shaft type furnace in which the ingredients, namely ore, reducing agent, and flux, are charged in layers in a vertical shaft. In both processes, the metal is recovered at the bottom of the furnace in a pasty mass. Efforts to make the direct reduction process economically feasible have not been limited to these two types of furnaces, but have extended to most of the known types, including pot furnaces, reverberatory furnaces, regenerative furnaces, shaft furnaces, rotary kilns, retort furnaces and electric furnaces.

OBJECTS AND SUMMARY OF THE INVENTION The invention described herein is directed to a direct reduction process utilizing an improved sleeve-shaped 2 briquette. More specifically, the present invention embodies the use of an improved briquette form which has been found to substantially enhance the economic value of the direct reduction process.

The principal object of the present invention is to provide a new and improved direct reduction process for reducing iron ore to free iron utilizing an improved briquette form which increases the yield of free iron in a direct reduction process.

A related object is to provide an improved process which enhances the direct reduction reaction, provides for an optimum furnace load and increases the furnace yield.

A briquette structure for use in the direct reduction method is formed of a mixture of iron ore, carbonaceous reducing agent, and binder, is shaped or formed into a prismatic sleeve, which is generally open or tubular in cross section, and includes radial ports opening through the side walls, as well as notches in the bottom or foot end. Such shaped briquette structures can be placed in an axially upright position on the table of a reaction furnace, which is preferably of the flat bed, direct-fired, rotary type. The briquettes are blanketed with flue gas at an inlet temperature of approximately 2300 F. for a reaction period of between 30 and 45 minutes. Yields are substantially increased over the use of solid pellets, which are generally spherical or ovoid in shape.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of one form of a briquette utilized in the present invention.

FIG. 2 is a bottom plan view of the briquette shown in FIG. 1.

FIG. 3 is a section view taken substantially in the plane of line 33 on FIG. 2.

FIG. 4 is a generally diagrammatic plan view of the table of a rotary, direct-fired, reduction furnace, showing an arrangement of briquettes of the type shown in FIG. 1.

FIG. 5 is an isometric view of a modified form of briquette embodying the present invention.

FIG. 6 is an isometric view of another form of briquette embodying the present invention.

FIG. 7 is a top plan view of the briquette shown in FIG. 6.

FIG. 8 is a side elevation view, with one side wall partially cut away, of the briquette shown in FIG. 6. FIG. 9 is a bottom plan view of the briquette shown in FIG. 6.

FIG. 10 is a section view taken substantially in the plane of line 10-10 on FIG. 8.

FIG. 11 is an enlarged fragmentary section view taken substantially in the plane of line 11-11 on FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENT a. Ingredients Iron Ore Iron ore used in a direct reduction process is preferably of the type having a high iron content. Such ores are available naturally, or a relatively low-grade ore can be readily beneficiated by any known benefication processes. It has been found that an ore having an iron content of at least 60% will give satisfactory results. Among the numerous ores which have been used successfully are a low-grade Republic ore which has been 3 beneficiated to about 60% iron, such well-known ores as Silver City, Woody Creek, Mackay, Nevada Magnetite, Wilson No. l,Wilson No. 2, Wilson No. 3, Empire, and many other ores, all of which contain or have been beneficiated to contain an iron content of at least about 60% or higher.v

The selected ore is ground to a particle size of approximately 8 mesh or smaller (-8 mesh). For example, it has been found that a particle size of about 35 mesh is suitable for most ores. The particle size to which the ore is ground depends primarily upon the particular ore selected. For example, a Silver City Ore ground to a particle size of 48 mesh gave good results, whereas with a Wilson ore, a particle size of-l mesh gave somewhat better results than when a slightly coarser particle was used.

The principal component of the iron ore is iron oxide. In most instances, this oxide is the magnetic iron oxide, Magnetite, although the lesser oxide, Hematite, is not uncommon. Other ores such as Taconite, Limonite and iron pyrites and the residue known as Blue Billy from the sulfuric acid process, are useful. During the reduction process in the furnace, these oxides are reduced by reaction with a carbonaceous reductant to leave free iron.

b. Ingredients Reductant Carbonaceous reducing agents are well known in the art. These reducing agents react with the iron oxides to remove the oxygen therefrom, ordinarily in the form of carbon monoxide and carbon dioxide. Carbon monoxide, itself a reducing agent, will react further with the oxygen in the ore to produce iron and carbon dioxide. The latter serves as an inert atmosphere surrounding the briquette, and may be drawn from the furnace through a briquette cooling system to provide an inert or reducing atmosphere therein.

Petroleum coke is one carbonaceous reducing agent found to be highly advantageous for reducing iron ore. This coke material is produced in connection with the refining of crude oil. Heavy petroleum bottoms from the fractionation of crude oil are heated under such conditions as to drive off certain volatile components which are further processed into gasoline, leaving a solid residue known as petroleum coke. There are various ways of producing petroleum coke, one of which is known as a *fluid" coking process and another as a delayed coking process. Coke from both processes produces excellent results. Other types of petroleum coke, coke produced from coal, and other carbonaceous substances may also be used to advantage.

The coke should be ground to a mesh size of 100 mesh or smaller (IOO mesh) and preferably in the range of about 100 to about -l50 mesh.

The amount of reductant employed should, in most instances, be sufficient to completely reduce the iron ore. It has been observed that using 2 to 3% more than the theoretical amount required gives excellent results. Ordinarily this amount of reductant constitutes between and by weight of the iron ore.

0. Ingredients Binder An appropriate binder is utilized to bind the iron ore and coke in intimate admixture. It is desirable that a binder is selcted which enhances the reduction of iron ore to free iron. The basic ingredients of one illustrative binder for this purpose are water, a soluble starch, and a soluble salt such as sodium chloride. A binder made 4 up of these ingredients, compounded as herein described has been found not only to be effective as a physical binder but also to enhance the subsequent reduction and produce an increased yield of free iron.

One starch utilized in the suggested binder is a conventional laundry-type cooked starch. The preferable form of starch used is a type of starch which dissolves in water when boiled to form a viscous, translucent liquid. The starch is used in the ratio of about 10 to about 125 parts by weight starch to about 200 parts by weight of water.

As a further ingredient of the binder, there is preferably added a small amount of sodium chloride, or com mon table salt, preferably in an amount of about 20 to about parts by weight of salt. The binder compositions which I have found to be particularly useful are constituted as follows:

The starch in powder form, and sodium chloride in granulated crystal form, are mixed with water. The mixture is brought to a boil and cooked until all the starch and sodium chloride have dissolved, and the mixture appears as a viscous, translucent liquid. Alternatively, the starch and water may be cooked, and then the salt added and the mixture boiled until the salt has dissolved. One preferred binder composition comprises 50 parts starch, 50 parts sodium chloride and 200 parts water. This mixture is cooked until all the sodium chloride is dissolved, and the mixture is a viscous, translucent liquid. Such a binder gives excellent results when used in an amount equal to about 5% by weight of the iron ore present in the briquette composition. It imparts a high green strength to the briquettes and after drying this binder provides a hard exterior shell on the green briquette which prevents crumbling.

d. Forming the Briquettes To form the briquette, the ingredients, including iron ore and the desired amount of the binder, for example 5% by weight of the iron ore, are placed in a mixer and the mass thoroughly stirred until the iron ore is completely wetted with the binder. Next, a carbonaceous reductant, such as petroleum coke, coal, or the like is placed into the mixer in an amount equal to about 20% by weight of the iron ore, and the mixture is thoroughly stirred so that all particles of iron ore and reductant are wetted with the binder. The mixing should continue until a substantially homogeneous mixture is obtained. The mixture is then formed into briquettes of the shape herein described in any suitable briquetting machine or by any appropriate method. The briquettes should be formed promptly to prevent the mixture from drying out, preferably within A hour to 1 hour, at the maximum, after the mixture is completed. If the mixture is stored in a tightly covered container, however, it may be kept in a useable condition for a number of days.

The amount of binder employed will affect the time within which the briquettes may be formed. In general, the use of an amount of binder equal to somewhere between 3 and 8% by weight of the iron ore has been found to provide for satisfactory binding of the briquettes without unduly restricting the time limits within which briquettes must be formed.

The temperature during the mixing operation is ordinarily room temperature, that is the mixing operation is carried out at temperatures between 40 and 120 F. It is essential that during the mixing operation the temperature be kept as low as possible to avoid unduly drying the material prior to forming the briquettes.

e. The Furnace In the furnace, which may be any conventional furnace suitable for maintaining a reducing atmosphere, and a temperature in the range of 2lOO to 2400 F., the briquettes are heated to the temperature at which the reduction reaction takes place. In general, with the improved briquettes embodying the present invention as hereinafter described, a furnace time of about 24 minutes at 2280 F. is appropriate. Depending upon the temperature, the briquettes will remain in the furnace for a period of between about 20 and about 35 minutes. It will be appreciated that the higher the temperature, the less the time required for the reaction to take place. The briquettes herein described are especially suitable for use in a continuous, direct, gas-fired furnace, wherein the briquettes are placed on a circular table which slowly rotates through the furnace carrying the briquettes with it. The briquettes are placed on the table from an entrance chute, and after the required period of time in the furnace, determined by the speed of rotation or movement of the table, the briquettes are pushed off of or removed from the table and directed into an exit chute from which they are conveyed, through a cooling tunnel, to a finished product hopper. Gases from the furnace produced during the reaction may be pulled out of the furnace through the cooling tunnel by an appropriate exhaust fan. These gases are cooled in the tunnel, and, in turn, cool the exiting briquettes. At the same time, these gases serve to help maintain a nonoxidizing atmosphere in the cooling tunnel. The briquettes remain in the cooling tunnel for a period of approximately minutes, or at least for a sufficient period of time to cool them to a temperature at which they will not oxidize in air, which temperature is generally 200 F. or below.

f. Briquette Structure and Reduction The briquette structure utilized in the present invention, as shown in the drawings, comprises a generally vertically upright prismatic sleeve structure in a variety of configurations. The common features, however, to each of the modified configurations shown in the drawings are the upright structure, the approximately oneto-one ratio of compacted reductant to vertically open passages, and the minimum of foot or support area at the bottom of the sleeve structure for supporting the same on the furnace table. Additionally, transverse or radial passages may extend through the walls of the briquette for further enhancing the circulation of reducing gases.

While a variety of shapes and configurations can be provided within the spirit and scope of the invention, two forms of the invention are shown in the drawings. In FIGS. 1 through 5 there is illustrated an upright cylindrical sleeve having a single vertical passage therethrough. In FIGS. 6 through 11 inclusive, there is illustrated a generally rectangular, block shaped prismatic sleeve structure in which there is provided a plurality of vertical passages. Based on the latter configuration, a plurality of the cylindrical sleeves as shown in FIGS. 1

6 through 5 could be bonded in close juxtaposition in a variety of patterns such as shown in FIG. 4.

The material to be reduced is compacted sufficiently to provide adequate green strength for handling. The density to which the reductant is compacted must be sufficient for that purpose, and yet not so tight or dense as to inhibit the reduction reaction. A variety of binders may be utilized as described above, as may a variety of forming processes and molds.

A cylindrical sleeve from briquette embodying the present invention is shown at 10 in FIG. I of the drawing. Such a briquette comprises an upright, generally cylindrical sleeve, which is annular in cross section, as shown'in FIG. 2, being formed by a cylindrical wall 11 having an inner surface 12 and outer surface 13. The briquette sleeve 10 is formed of a mixture of iron ore, carbonaceous reducing agent and a binder, as described above, and is shaped in an appropriate press under a pressure sufficient to compact the mixture to a density which provides substantial green strength to the briquette. The briquette is then dried, and may be stored for later reduction in a direct-fired furnace as described above.

The briquettes l0 embodying the structure above described are constructed with a ratio of briquette height to outside diameter of about 5-to-3, and with a wall 11 having a thickness of between and about 1 inch, and more particularly about l to about inch. A preferred briquette sleeve structure is generally between about 4 inches and about 6 inches high, and particularly about 5% inches high, with an outside diameter of about 3 inches and a wall about 6 inch thick. In general, it has been observed that the height-to-outside diameter ratio may vary from about I-to-l to about 2-to-l except that the proportion of the briquette must be such as to insure an adequate central sleeve cavity. It is believed that it is desirable to maintain an internal diameter of the sleeve of at least about /2 inch in order that the furnace gases may reach all areas of the briquette. Accordingly, the sleeve should be formed with a minimum internal diameter of about B inch in order to accomplish this purpose.

Briquettes formed and shaped as described above have been found to be highly susceptible to direct reduction in a direct-fired rotary table furnace by arranging the briquettes in an axially upstanding postion on the furnace table 15, as shown diagrammatically in FIG. 4. The briquettes may be arranged closely together on the furnace table as shown in FIG. 4, the void spaces centrally of the sleeves and between each adjacent sleeve being sufficient to provide space for the reaction gases to substantially completely envelope the briquettes.

To further enhance the reduction reaction, and increase the circulation of gases about the briquette sleeves l0, notches 19 are desirably cut in at least the end 20 of the briquette 10 which is to be placed on the furnace table 15. Additionally, radial holes 21 or apertures may be cut through the side wall 11 of the briquettes as shown in FIG. 5. These notches and passages prevent the formation of pockets of gases within and surrounding the briquettes adjacent the furnace table. Such notches and passages are of greater importance in those briquettes having smaller internal diameters in order to insure effective contact by the furnace gases. The reduction reaction thus proceeds completely and uniformly throughout the length and thickness of the briquette cylinders 10.

The loading pattern of briquettes 10 on the furnace table depends in part on the table configuration. Where the furnace embodies a rotary table, the briquettes may be loaded either radially, or in a sectional pattern as shown in FIG. 4 to facilitate maximum table utilization. To load the furnace with an array of cylindrical briquettes 10, for example, the briquettes may be placed on a sectorshaped loading chute l6 and deposited on the furnace table in a group through an entrance door of the furnace. As the table 15 rotates through the furnace, the briquettes are reduced. Following reduction, the briquettes are removed from the table by a scraper 18 or other appropriate removal mechanism. After being cooled, the briquettes may be crushed and the iron magnetically separated from the remaining ingredients.

Another form of briquette shaped as a generally rectangular prismatic sleeve structure, is shown in FIGS. 6 through 11. Referring to these figures of the drawing, the prismatic sleeve shaped briquette, shown generally at 30, comprises a generally rectangular block having side walls 31, end walls 32 and intermediate walls, indicated generally at 34, defining a plurality of vertically extending passages 35. In the form shown in the drawings, the intermediate walls 34 include a single longitudinal wall or web 36 extending between the end walls 32 and generally parallel to the side walls 31, and a plurality of intermediate transverse walls or webs 38 extending generally parallel to the end walls 32 between the central longitudinal wall 36 and the outer side walls 31. In this manner, an array of vertically extending passages or sleeve openings 35 are defined extending between the upper surface 39 and the lower surface 40 of the prismatic block 30. The briquette 30 is supported on its bottom surface 40 on a furnace table. To facilitate the passage of gases upwardly through the passages 35 and to minimize the area of contact between the block and the furnace table, a plurality of notches 41 are defined in the outer side walls 31 and the intermediate wall 36. Additional notches may be formed in the end walls 30 and intermediate walls 38 if desired. In this manner, the area of contact between the bottom surface 40 of the briquette and the furnace table is minimized.

Referring to FIGS. 8 and 10, to facilitate molding the briquettes, the various walls of the briquette taper from the upper surface to the lower surface. The material to be reduced is compacted into a mold defining the shape of the briquette and after appropriate green cure, the briquettes are removed from the mold for use in a recuction furnace.

The prismatic briquettes, in one preferred form, are inches long, 8 inches wide and 8 inches high, with 14 core passages therethrough defined by exterior walls which taper from a width of inch at the bottom of the briquette to 5/16 inch at the top of the briquette and interior walls or webs which taper from inch at the bottom of the briquette to 1% inch at the top of the briquette. The vertical, open passages thus formed have a dimension tapering from 2 X 2 /8 inches at the bottom of the briquette to 1% X 2% inches at the top of the briquette. It can be observed that the volume of compacted reductant material to the volume of the vertical passages is approximately l-to1, and, with the dimensions given, the volume of reductant material in the briquette, as shown in the drawings, is 56% of the total volume of the briquette. Depending upon the dimensions utilized for the walls of the briquette, the percentage of reductant material by volume can be expected to run between 45 and 65percent by volume of the briquette. It must be kept in mind that the burden of actual quantity of reductant material on the furnace table must be sufficiently large to make the process an economical one, and yet the reductant material must be shaped in such a manner as to maintain open and un burdened a substantial area of the furnace table. Also, adequate provision must be made for circulation of reducing gases throughout and around the briquettes in order to insure uniform reduction of the reductant materials. This is accomplished by the notches in the bottom walls of the briquette and additionally apertures may be provided through the various walls of the briquette to further facilitate circulation of the reduction gases.

It has been observed that the use of the prismatic, sleeve-shaped briquettes aligned with the briquettes standing axially upright on a furnace table, so that the open passages extend from the top to bottom, prevents the smothering of briquettes and exclusion of certain portions thereof from the furnace gases. These gases are apparently important in the reduction reaction process, as it has been observed that when a layer of more than one thickness of pellets or ovoid briquettes is utilized on the furnace table, the briquettes adjacent the table are incompletely reduced. By utilizing the sleeveshaped briquettes 10 in an axially upright position, the load of iron ore containing mixture per unit area of the table can be substantially increased, and at the same time there results a highly efficient and complete furnace reaction throughout the entire length and thickness of each briquette.

As described above, the briquettes are heated in a direct-fired furnace and are contacted directly with the furnace gases. It is essential that the furnace gases surround and intimately contact substantially all of the briquette surfaces in order that the reduction reaction proceed uniformly throughout the briquette. Obviously, the portion of the briquette contacting the table cannot be surrounded by the flue gas; however, by utilizing briquette sleeves with notches cut in the supporting end surface, ample opportunity is given for complete circulation of the flue gas and reaction gases around the briquettes. Thus the briquettes react uni formly throughout their length and thickness.

It has been observed that briquettes of the abovedescribed proportions produce highly satisfactory results. Moreover, it has been observed that by the use of briquettes having the shape and configuration embodying the present invention furnace production is increased approximately threefold. In one operation, for example, where the furnace was capable of lbs. per hour of reduced product utilizing pellets, this produc' tion rate was increased to 240 lbs. per hour through the use of briquettes embodying this invention. It has been further observed that the use of the sleeve-like briquettes prevents the furnace hearth from being smothered and cooled.

Referring to FIG. 4, it can be seen that the entire furnace table area is not covered. Sufficient uncovered table area remains centrally of the briquettes and between adjacent briquette which is exposed to hot furnace gases to maintain the table surface at the desired temperature. In this manner, the furnace table or hearth maintains its heat, thereby resulting in a conservation of fuel energy in the process.

While illustrative embodiments of the present invention have been shown in the drawing and described above in considerable detail, it should be understood that there is no intention to limit the invention to the specific forms disclosed. On the contrary, the intention is to cover all modifications, alternative constructions, equivalents and uses falling within the spirit and scope of the invention as expressed in the appended claims.

We claim as our invention:

1. A method of producing iron by the direct reduction of iron ore, comprising the steps of forming a prismatic sleeve-shaped briquette from a mixture of iron ore having an iron content of at least about 60% and a particle size of about 8 mesh or smaller, a carbonaceous reducing agent having a particle size of 100 mesh or smaller in an amount of between about and about by weight of the iron ore, and an aqueous starch base sodium chloride containing binder in an amount of between about 3 and about 8% by weight of the iron ore, with said sleeve-shaped briquette having at least one generally vertical passage therethrough, and said briquette further having defined in at least one end thereof a plurality of notches; arranging a plurality of said sleeve-shaped briquettes on a moving table of a direct-fired furnace with said briquettes arranged in an axially upright position and with the notched ends thereof on said table and with the passage extending vertically upwardly; and subjecting said briquettes directly to furnace gases at a temperature of between about 2000 and about 2400 F. for a period of time between about 20 and 35 minutes, thereby to directly reduce a substantial portion of the metallic iron oxide to free iron; while said moving table carrying said briquettes slowly rotates through the furnace and removing said reduced briquettes from said furnace and cooling the briquettes to a temperature of about 200 F. or below in a nonoxidizing atmosphere.

2. A method as defined in claim 1 wherein the volume ratio of reducible mixture to open passage in said shaped briquette is about l-to-l.

3. A method as defined in claim 1 wherein the proportion of reducible mixture in said shaped briquette is between about 45% and about 65% by volume.

4. A method as defined in claim 1 wherein said shaped briquettes include a plurality of apertures cut radially through the walls of each briquette intermediate its ends.

5. A method as defined in claim 1 wherein each said prismatic sleeve-shaped briquette is annular in cross section.

6. A method as defined in claim 1 wherein each said prismatic sleeve-shaped briquette is generally rectangular in cross section.

7. A method as defined in claim 1 wherein each said sleeve-shaped briquette comprises a generally cylindrical member having a height-to-outside diameter ratio of between about l-to-l and about 2-to-l an inside diameter of at least about inch, and a wall thickness of between about inch and about 1 inch, and said member having defined in at least one end thereof a plurality of radially extending notches.

8. A method as defined in claim 1 wherein each said sleeve-shaped briquette comprises a generally rectangular member having a plurality of vertically extending passages extending therethrough between the top and bottom thereof, said member having a volume ratio of reducible mixture to passage volume of about l-to-l and a wall thickness of between about inch and about 1/18 inch, and said member having defined in one end thereof a plurality of notches extending through the member walls.

9. A method of producing free metal by direct reduction of a mixture containing a metallic oxide ore, comprising the steps of forming a prismatic sleeve-shaped briquette from a mixture of metallic oxide ore, a solid reducing agent and a binder, with said sleeve-shaped briquette having at least one generally vertical passage therethrough, and said briquette further having defined in at least one end thereof a plurality of notches; arranging a plurality of said briquettes on a circular table of a direct-fired furnace with said briquettes in an axially upright position, with the notched ends thereof on the furnace table, and said passage extending vertically upwardly; and subjecting said briquettes directly to the furnace gases at a temperature below the sintering temperature of the free metal for a period of time sufficient to substantially reduce the metallic oxide to free metal while said circular table carrying said briquettes slowly rotates through the furnace.

10. A method producing free metal by direct reduction of a metallic oxide ore as defined in claim 9 including the step of cooling the directly reduced briquettes in a nonoxidizing atmosphere to a temperature below that at which the free metal will be oxidized in air.

Claims

1. A METHOD OF PRODUCING IRON BY THE DIRECT REDUCTION OF IRON ORE, COMPRISING THE STEPS OF FORMING A PRISMATIC SLEEVESHAPED BRIQUETTE FROM A MIXTURE OF IRON ORE HAVING AN IRON CONTENT OF AT LEAST ABOUT 60% AND A PARTICLE SIZE OF ABOUT 8 MESH OR SMALLER, A CARBONACEOUS REDUCING AGENT HAVING A PARTICLE SIZE OF 100 MESH OR SMALLER IN AN AMOUNT OF BETWEEN ABOUT 15 AND ABOUT 20% BY WEIGHT OF THE IRON ORE, AND AN AQUEOUS STARCH BASE SODIUM CHLORIDE CONTAINING BINDER IN AN AMOUNT OF BETWEEN ABOUT 3 AND ABOUT 8% BY WEIGHT OF THE IIRON ORE, WITH SAID SLEEVE-SHAPED BRIQUETTE HAVING AT LEAST OONE GENERALLY VERTICAL PASSAGE THERETHROUGH, AND SAID BRIQUETTE FURTHER HAVING DEFINED IN AT LEAST ONE END THEREOF A PLURALITY OF NOTCHES; ARRANGING A PLURALITY OF SAID SLEEVE-SHAPED BRIQUETTES ON A MOVING TABLE OF ADI DIRECT-FIRED FURNACE WITH SAID BRIQUETTES ARRANGED IN AN AXIALLY UPRIGHT POSITION AND WITH THE NOTCHED ENDS THEREOF ON SAID TABLE AND WITH PASSAGE EXTENDING VERTICALLY UPWARDLY; AND SUBJECTING SAID BRIQUETTES DIRECTLY TO FURNACE GASES AT A TEMPERATURE OF BETWEEN ABOUT 2000* AND ABOUT 2400* F. FOR A PERIOD OF TIME BETWEEN ABOUT 20 AND 35 MINUTES, THEREBY TO DIRECTLY REDUCE A SUBSTANTIAL PORTION OF THE METALLIC IRON OXIDE TO FREE IRON; WHILE SAID MOVING TABLE CARRYING SAID BRIQUETTES SLOWLY ROTATES THROUGH THE FURNACE AND REMOVING SAID REDUCED BRIQUETTES FROM SAID FURNACE AND COOLING THE BRIQUETTES TO A TEMPERATURE OF ABOUT 200*F. OR BELOW IN A NONOXIDIZING ATMOSPHERE.

2. A method as defined in claim 1 wherein the volume ratio of reducible mixture to open passage in said shaped briquette is about 1-to-1.

7. A method as defined in claim 1 wherein each said sleeve-shaped briquette comprises a generally cylindrical member having a height-to-outside diameter ratio of between about 1-to-1 and about 2-to-1, an inside diameter of at least about 1/2 inch, and a wall thickness of between about 3/8 inch and about 1 inch, and said member having defined in at least one end thereof a plurality of radially extending notches.

8. A method as defined in claim 1 wherein each said sleeve-shaped briquette comprises a generally rectangular member having a plurality of vertically extending passages extending therethrough between the top and bottom thereof, said member having a volume ratio of reducible mixture to passage volume of about 1-to-1 and a wall thickness of between about 3/4 inch and about 1/18 inch, and said member having defined in one end thereof a plurality of notches extending through the member walls.