WO1999051783A1

WO1999051783A1 - Method and apparatus for producing molten iron from iron oxides

Info

Publication number: WO1999051783A1
Application number: PCT/US1999/006248
Authority: WO
Inventors: Larry Lehtinen
Original assignee: Iron Dynamics Inc
Current assignee: Iron Dynamics Inc
Priority date: 1998-04-03
Filing date: 1999-03-22
Publication date: 1999-10-14
Anticipated expiration: 2000-10-03
Also published as: AU3110399A

Abstract

The present invention provides improved processes for reducing iron oxides to elemental iron utilizing one or more solid carbon reducing agents and a rotary hearth furnace (600). According to a preferred aspect of the invention, there is provided a method for producing molten iron which includes quickly introducing a hot sponge iron intermediate into a submerged arc furnace (660) without significant loss of heat therefrom. In alternate aspects of the invention, there are provided methods for advantageously fracturing an iron ore starting material using a roll press (340), methods for the recovery and re-use of submerged arc furnace off-gas, methods for recuperating a substantial proportion of the heat present in a rotary hearth furnace off-gas (700) to provide processes having excellent thermal efficiency and methods for controlling slag phase compositions in a rotary hearth furnace (600) and a submerged arc furnace (660) to enable advantageous processing and handling of process materials.

Description

METHOD AND APPARATUS FOR PRODUCING MOLTEN IRON FROM IRON OXIDES

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to the direct reduction of iron oxides and the smelting reduction of hot sponge iron into liquid carbon-containing iron known as pig iron, hot metal or elemental iron. More specifically, it relates to direct iron reduction processes utilizing one or more solid carbon reducing agents and a rotary hearth furnace, followed in certain aspects of the invention, by further reduction and melting in a submerged arc furnace. Discussion of Related Art Steel producers are constantly seeking sources of low cost metallic iron that can be used to replace, if not all, at least a portion of the scrap used in a conventional steel-making furnace such as, for example, a basic oxygen furnace (BOF) or an electric arc furnace (EAF). The need for a scrap substitute is particularly important where high quality, low residual content scrap is not available or is very expensive. To supply these metallic iron units to the steel industry, a number of processes for producing direct reduced iron (DRI), or "sponge iron," have been developed. Direct reduction is a chemical reduction reaction in which iron oxides in an iron ore react with a reductant, such as natural gas, coal, pitch, or other carbon-containing material, at a temperature below the melting temperatures of the materials present, to chemically reduced the oxides to metallic iron. Some reduction processes include steps such as grinding, mixing, adding a reductant and binder, pelletizing, and heating the green pellets to a temperature to accomplish direct reduction, typically in a rotary hearth furnace (RHF) or rotary kiln. Skilled artisans in the field of refining iron are increasingly recognizing direct reduction as a useful method of converting iron oxides into elemental iron. Two general categories of direct reduction are (1) those that utilize natural gas as the reducing agent, and (2) those that utilize solid carbonaceous materials such as coal as the reducing agent (solids-based direct iron reduction). While solids-based direct iron reduction is presently being given a great deal of attention as a potentially useful reduction mechanism, it presents several difficulties. The present invention provides improved processes for achieving continuous direct iron reduction using one or more solid carbon reducing agents and a rotary hearth furnace and overcomes difficulties encountered in the prior art.

In a rotary hearth process for reducing iron ore by carbonaceous direct reduction, ground iron ore and a finely divided carbonaceous reducing agent, as well as other additives, such as binding agents, are typically first formed into agglomerates, called green balls, or into briquettes. Alternative direct reduction processes utilize a particulate mixture rather than agglomerates or briquettes. The agglomerates, briquettes or mixtures are then charged onto the hearth of a rotary hearth furnace, perhaps up to three deep in the case of agglomerates, and the hearth is caused to rotate to expose the furnace charge to a high temperature for a time sufficient to reduce a substantial proportion of the iron ore in the charge, thereby producing sponge iron. The sponge iron typically contains metallic iron, a small amount of partially reduced or unreduced iron oxide, carbon, and may also include gangue material, such as, for example, Al₂O₃, CaO, MgO, SiO₂, and sulfur. The sponge iron product of direct reduction normally is densified by briquetting or passified by dry aging, and shipped and melted in a steelmaking furnace to extract the reduced elemental iron from contaminants. The sponge iron may be used as a scrap substitute in steel-making processes, for example, using a basic oxygen furnace (BOF) or an electric arc furnace (EAF).

Known processes for performing solids-based iron reduction using a rotary hearth furnace are accompanied by high heat losses. These high heat losses are associated in part with the large proportion of the heat generated in the rotary hearth process which is lost primarily to the release of hot process gases, or "off- gases," out the flue, into off-gas treatment systems and, ultimately, to the environment. Of course, processing at very high temperatures is necessary in the recovery of elemental iron from iron oxides, and heat is needed not only to achieve reduction of the iron, but also to process the starting materials.

Another significant hindrance to direct reduction processes is the difficulty commonly encountered in removing hot sponge iron from the hearth after direct reduction and in handling hot sponge iron subsequent to its removal from the hearth. This problem is largely due to silica, which is present in many useful iron ore starting materials and is typically a significant component of the gangue materials, or "slag phase," in the sponge iron. Under conditions suitable for direct reduction, silica and iron commonly react to form silicates, such as fayalite, which has a melting point lower than optimal temperatures for direct reduction of iron oxides into elemental iron in a RHF. Thus, during the direct reduction process, the materials on the hearth commonly become sticky or tacky due to at least partial melting of the slag phase, and the sponge iron is therefore difficult to remove from the hearth using conventional discharge equipment such as, for example, discharge screws. The sponge iron may also tend to clump or stick together after removal from the hearth, thereby hindering its flow from bins or containers into which it is placed after removal from the hearth.

This "stickiness" problem could be minimized by either decreasing the temperature at which the RHF direct reduction reaction is conducted, or altering the composition of the gangue material composition in the RHF charge to increase the melting/softening temperature thereof, for example, by adding slag materials having higher melting points. Each of these techniques, however, has undesirable consequences. An undesirable consequence of the first technique is that the RHF direct reduction reaction at a lower temperature results in an undesirably low degree of metallization of the iron oxide. An undesirable consequence of the second technique is that sponge iron comprising a high melting point slag phase would have to be smelted at detrimentally high temperatures to recover molten metal therefrom. If the sponge iron is directly transported to and charged to either a BOF or an EAF process, the higher melting temperature of the gangue material in the sponge iron is of little consequence because of the high process temperatures of these two processes and the open nature of the vessels for slag and metal removal. If, however, the sponge iron is charged to a submerged arc furnace (SAF), as in preferred aspects of the present invention, to produce a hot metal with a carbon content ranging, for example, from about 1 to about 5 percent, then the composition of the gangue material in the sponge iron does become critical, because the SAF is a closed furnace where the slag phase sits on top of the metal phase, is tapped like a blast furnace and, consequently, the slag layer has a temperature gradient whereby the top of the slag layer is much cooler than the portion of the layer adjacent to the slag/metal interface. The composition of this final slag phase is critical because the operating temperature of a SAF at the top of the slag layer is substantially less than the slag temperature of either the BOF or the EAF process. Consequently, the slag phase in the SAF process must have a lower melting temperature and be sufficiently fluid to drain from the SAF at the lower slag temperature of the SAF. It is well known that in the operation of a SAF, feed material is fed from the top into the SAF while electrical power is delivered continuously through electrodes. The electrical energy supplies the energy to liquefy the feed material to form hot metal and slag. When the SAF feed material is sponge iron, the sponge iron may not have sufficient carbon to complete reduction of the remaining iron oxides therein and, therefore, it is often necessary to introduce supplemental carbon, such as, for example, coke, into the SAF with the sponge iron. As the sponge iron melts, a pool of liquid hot metal builds in the SAF and molten slag resides on top of the hot metal. The temperature of the hot metal will depend upon the carbon content of the hot metal but in general will be in the range of about 1450°C to about 1550°C. Because the cooler sponge iron pellets at about 800°C to about 1200°C are fed continuously onto the top of the slag, the temperature of the slag is generally cooler than the hot metal pool.

Periodically, a portion of the liquid hot metal pool is tapped into a ladle and the tap hole is closed with suitable equipment such as a mud gun. In a similar fashion as the slag layer on the molten hot metal pool increases in depth, a portion of the slag is drained from the SAF and the slag tap hole is closed. Because slag must be drained from the SAF at periodic intervals, it is necessary that the slag be fluid at a temperature below that of the hot metal.

Efforts to overcome the above-mentioned problems have been proposed, such as, for example, in U.S. Patent No. 5,681,367 to Hunter ("the '367 patent"), which is hereby incorporated by reference herein in its entirety. In the '367 patent, there are disclosed methods which include the preparation of two or more batches of agglomerates, each batch comprising therein slag phases having different compositional make-ups, and the slag phase in each batch having a melting point higher than processing temperatures in the RHF. The sponge iron from each batch is combined in a SAF, wherein the various slag phases mix, resulting in a combined slag phase having a lower melting point than the individual slag phases. The method disclosed in the '367 patent, however, requires an unacceptable amount of material handling and processing equipment, and associated operational complexity and costs, and therefore is not a satisfactory solution to the above problems. Also limiting the efficiency of prior art direct reduction processes is the requirement that the iron ore starting material be finely ground prior to the reduction furnace. The high degree of grinding is necessary primarily due to the limited reducibility of coarse iron ore. In a coarse ore, a significant proportion of iron oxide in the ore is unavailable for contact with reducing gases in the furnace, and the sponge iron product thereby comprises a significant proportion of unreduced iron. Prior art processes require a significant degree of grinding to achieve satisfactory levels of metallization, and the grinding requirement significantly increases operating costs. An additional reason that prior art processes for producing molten metal are inefficient relates to the waste of thermal and chemical energy of smelting furnace off-gases. For example, a submerged are furnace typically generates off gas comprising at least about 80% carbon monoxide by volume. This gas therefore comprises a significant amount of energy which prior art processes have not advantageously utilized.

The present invention overcomes inefficiencies and handling difficulties experienced in the prior art. The invention provides thermally efficient and productive processes for producing molten iron which produce a high quality iron product. Inventive processes further generate a sponge iron intermediate that is readily removed from the hearth using conventional discharge equipment and readily transferred to a SAF. A molten iron product is efficiently produced in accordance with the invention and can be used as a liquid in further iron or steelmaking processes or cast into an iron product for storage, sale or further processing. By utilizing inventive methods, problems associated with prior art processes are overcome, along with the high operating costs associated therewith.

SUMMARY

To overcome problems in the prior art relating to the high costs associated with loss of heat in, for example, off-gases, the present invention provides methods for achieving direct reduction of iron in which heat is conserved by recovering heat from the off-gases, by placing hot sponge iron directly into a submerged arc furnace (SAF), to thereby utilize the sensible heat contained within the sponge iron and also by utilizing the high carbon monoxide content SAF off gas as fuel for the RHF. According to the invention, direct reduction is preferably achieved in a continuous fashion, of agglomerated starting materials, and the resulting sponge iron may be efficiently discharged from the hearth using, for example, one or more water-cooled discharge screws or plows, and passed through sealed refractory-lined chutes directly into a submerged arc furnace or into insulated containers or skips for quick transport to a submerged arc furnace. Additionally provided are processes for the pretreatment of an iron ore starting material, to advantageously condition the ores, thereby providing an excellent iron source for direct reduction. Direct reduction using such a conditioned ore advantageously yields a highly metallized sponge iron.

According to one aspect of the invention, therefore, there is provided a method for reducing an iron oxide, comprising (1) providing a first iron ore composition; (2) grinding the first iron ore in a high pressure roll press to provide a second ground and microfractured iron ore; (3) intimately contacting the second iron ore and a particulate carbonaceous reductant to provide a furnace charge; and (4) subjecting the furnace charge to reducing conditions in a rotary hearth furnace to provide a hot sponge iron.

In another aspect of the invention, there is provided a method for reducing an iron ore, comprising (1) passing an iron ore composition through an ore drier or an ore drier/grinder to provide a dried iron ore comprising less than about 0.5% water by weight; (2) intimately contacting the iron ore and a carbonaceous reductant to provide a furnace charge; and (3) subjecting the furnace charge to reducing conditions in a rotary hearth furnace to provide a hot sponge iron; wherein the iron ore composition is dried by contacting the composition with a gaseous slip stream comprising hot off-gas from the rotary hearth furnace. In another aspect of the invention, there is provided a method for producing direct reduced iron, comprising (1) passing a carbonaceous reductant composition through a pulverizer/drier to provide a particulate carbonaceous reductant comprising less than about 0.5% water by weight; (2) intimately contacting the particulate carbonaceous reductant and a particulate iron ore composition to provide a furnace charge; and (3) subjecting the furnace charge to reducing conditions in a rotary hearth furnace to provide a hot sponge iron; wherein a gaseous slip stream comprising a portion of the hot off-gas from the rotary hearth furnace is contacted with the carbonaceous reductant in the pulverizer/drier to provide the thermal drying energy. According to another aspect of the invention, there is provided a method for producing direct reduced iron, comprising (1) providing a moist mixture of a particulate iron oxide composition, a particulate carbonaceous reductant and a binding agent; (2) forming the mixture into moist green balls; (3) drying the moist green balls by passing the green balls through a drier to produce dried green balls having a water content of less than about 0.5% by weight; (4) positioning the dried green balls onto a rotary hearth furnace; and (5) subjecting the dried green balls to reducing conditions to reduce a substantial portion of the iron oxide, thereby producing hot sponge iron; wherein said drying comprises contacting the moist green balls with a gaseous stream comprising hot off-gases from the rotary hearth furnace.

In another aspect of the invention, there is provided a method for utilizing sensible heat in a rotary hearth furnace off-gas, comprising (1) recovering off-gas from a rotary hearth furnace to provide a first gaseous stream, the first gaseous stream having a temperature of at least about 1200°C, and comprising N₂, H₂, CO₂, CO and H₂O; (2) passing the first gaseous stream through a first cooler to reduce the temperature of the first stream to between about 900°C and about 1100°C; (3) passing the first gaseous stream through an afterburner to combust the CO and the H₂, thereby providing a second gaseous stream having a temperature of from about 1100°C to about 1400°C and comprising N₂, O₂, CO₂ and H₂O; (4) passing the second stream through a second cooler to cool the gas to a temperature of from about 800°C to about 1000°C; (5) passing the second stream through a first chamber of a gas-to-gas heat exchanger to heat ambient air passing through a second chamber of the heat exchanger; (6) contacting a first portion of the second stream with an iron ore in an iron ore drier or an iron ore drier/grinder; (7) contacting a second portion of the second stream with a carbonaceous reductant in a reductant pulverizer/drier; (8) contacting a third portion of the second stream with a fluxing agent in a fluxing agent pulverizer/drier; (9) combining the first portion, the second portion and the third portion to provide a third gaseous stream; and (10) contacting the third stream with green balls in a green ball drier.

In another aspect of the invention, there is provided a method for utilizing sensible heat in a rotary hearth furnace off-gas, comprising: (1) recovering off-gas from a rotary hearth furnace to provide a gaseous stream having a temperature of at least about 1000°C and comprising N₂, H₂, CO₂, CO and H₂O; and (2) recuperating heat from the off-gas.

In an alternate aspect of the invention, there is provided a method for utilizing off-gas from a submerged arc furnace, comprising (1) recovering off-gas from a submerged arc furnace to provide a first gaseous stream having a temperature of at least about 1000°C, and comprising at least about 80% carbon monoxide by volume; (2) cooling the gas; (3) cleaning the gas; and (4) mixing the off-gas with natural gas to provide a gaseous fuel.

The invention also provides a method for making molten iron, comprising: (1) preparing a furnace charge for direct reduction thereof in a rotary hearth furnace to sponge iron, the furnace charge comprising an iron ore, a reductant and a RHF 10

fluxing agent, wherein the RHF fluxing agent, together with gangue materials in the iron ore and the reductant, comprise a first slag-forming composition having a melting point higher than the pellet temperature reached in the rotary hearth furnace; (2) reducing the furnace charge in the rotary hearth furnace to provide sponge iron; and (3) feeding the sponge iron and a SAF fluxing agent into a submerged arc furnace to form molten iron and liquid slag; wherein the liquid slag comprises a combination of the first slag-forming composition and the SAF fluxing agent; and wherein the liquid slag has a melting temperature at least 50°C lower than the melting temperature of the first slag-forming composition. In another aspect of the invention, there is provided a method for making molten iron, comprising (1) providing a mixture comprising (a) a SAF fluxing agent and (b) a sponge iron comprising from about 75% to about 85% elemental iron by weight and a first slag-forming composition having a first melting temperature; and (2) feeding the mixture into a submerged arc furnace wherein the mixture melts and further reacts to form molten iron and liquid slag; wherein the liquid slag has a melting temperature less than the first melting temperature..

In an additional aspect of the invention, there is provided an apparatus for making molten iron, comprising: (1) a roll press for grinding and conditioning an iron ore; (2) a mixer for receiving and mixing a carbonaceous reductant and the output from said roll press to provide a rotary hearth furnace charge; (3) a rotary hearth furnace for receiving the charge and converting the charge to hot sponge iron; and (4) a submerged arc furnace for receiving the hot sponge iron and converting the hot sponge iron to molten iron and slag.

Another apparatus in accordance with the invention, for continuously utilizing off-gas recovered from a rotary hearth furnace, comprises: (1) a first cooler in fluid communication with a reduction chamber of a rotary hearth furnace and configured to receive off-gas recovered from the rotary hearth furnace; (2) an afterburner in fluid communication with the first cooler for combusting carbon monoxide and hydrogen in the off-gas; (3) a second cooler in fluid communication 11

with the afterburner, for cooling the gas to a temperature of from about 900°C to about 1000°C; (4) a plurality of first conduits in fluid communication with the second cooler for passing a plurality of slip streams to one or more devices selected from the group consisting of an ore drier, an ore drier/grinder, a coal drier, a coal pulverizer/drier, a flux drier, a fluxstone pulverizer/drier and a secondary spray cooler; (5) a second conduit in fluid communication with the plurality of first conduits for receiving the slip streams and introducing the off-gas into a green ball drier; (6) a third conduit in fluid communication with the green ball drier for receiving the gas from the green ball drier; and (7) a de-SOx system in fluid communication with the third conduit.

In another aspect of the invention, there is provided an apparatus for continuously utilizing off-gas recovered from a rotary hearth furnace, comprising (1) a cooler in fluid communication with a reduction chamber of a rotary hearth furnace and configured to receive off-gas recovered from the rotary hearth furnace and to cool the gas; (2) an afterburner in fluid communication with the water cooled duct for combusting carbon monoxide and hydrogen in the off-gas; (3) a heat exchanger for transferring heat from the off-gas to ambient air; (4) a plurality of conduits in fluid communication with the heat exchanger for passing a plurality of slip streams to one or more devices selected from the group consisting of an ore drier, an ore drier/grinder, a coal drier, a coal pulverizer/drier, a flux drier, a fluxstone pulverizer/drier and a secondary spray cooler; and (5) a plurality of de- dusting devices in fluid communication with the conduits for recovering dust particles entrained in the slip streams.

In another aspect of the invention, there is provided an apparatus for continuously utilizing off-gas recovered from a submerged arc furnace, comprising (1) a system for cooling and cleaning the off-gas; and (2) a device, in fluid communication with the system, for mixing the off gas with a natural gas to provide a gaseous fuel. 12

The invention also provides a method for producing molten iron, comprising (1) preparing a furnace charge comprising an iron ore and a solid carbonaceous reductant; (2) reducing the furnace charge in a rotary hearth furnace to provide sponge iron; and (3) discharging the sponge iron from the rotary hearth furnace into a submerged arc furnace oriented below the rotary hearth furnace.

Also provided by the present invention is an apparatus for producing molten metal, comprising (1) a rotary hearth furnace; and (2) a submerged arc furnace positioned below the rotary hearth furnace.

In another aspect of the invention, there is provided a method for reducing an iron oxide, comprising (1) providing a rotary hearth furnace charge comprising an iron oxide, a solid carbonaceous reductant and a member selected from the group consisting of limestone and dolomitic limestone; and (2) subjecting the furnace charge to reducing conditions in a rotary hearth furnace to provide sponge iron. Further provided by the present invention is a rotary hearth furnace comprising a plurality of feed zones, a plurality of reduction zones and a plurality of discharge zones.

Also provided by the invention is a method for preparing a rotary hearth furnace charge, comprising (1) providing a plurality of moist green balls comprising an iron oxide, a solid carbonaceous reductant and a binder; (2) contacting the moist green balls with a powdered RHF fluxing agent to provide a plurality of dusted green balls; and (3) passing the dusted green balls through a green ball drier to provide a rotary hearth furnace charge.

It is an object of the present invention to provide a direct iron reduction process which converts a pretreated iron oxide composition into metallic iron at a high conversion efficiency.

It is another object of the invention to provide thermally efficient methods for producing elemental iron, thereby decreasing the amount of heat which is lost to the environment. 13

It is also an object of the invention to provide a direct reduction process which minimizes the comminution cost associated with grinding iron oxides to a particle size distribution suitable for agglomeration.

It is another object of the invention to provide a process for the direct reduction of iron in which an iron ore composition is advantageously dried and beneficiated or ground to provide a purified or dry ground iron ore composition, using heat in the off gas of the RHF that otherwise would be lost to the environment.

It is also an object of the invention to provide a process for the direct reduction of iron in which a carbonaceous reductant is pulverized, dried and size classified using heat in the off gas of the RHF that otherwise would be lost to the environment.

It is also an object of the invention to provide a process for the direct reduction of iron in which starting materials are formed into moist green balls and in which the moist green balls are dried before introduction thereof onto the hearth of a rotary hearth furnace using heat in the off gas of the RHF that otherwise would be lost to the environment.

Additionally, it is an object of the present invention to provide a process for the direct reduction of iron which recovers heat from off-gases exiting the rotary hearth furnace to perform drying tasks and to preheat combustion air entering the furnace.

It is another object of the invention to provide a process for directly reducing iron which utilizes the sensible heat existing in sponge iron by placing the sponge iron directly into a submerged arc furnace to complete reduction and to melt the sponge iron.

It is also an object of the invention to provide a process for recovering and reusing off-gas from a submerged arc furnace. 14

It is a further object of the invention to provide a solids-based direct reduction process in which a hot sponge iron product is readily discharged from the hearth by substantially eliminating the prior art problem of sponge iron stickiness.

It is also an object of the invention to provide a solids-based direct iron reduction process in which a non-sticky hot sponge iron product is produced at relatively high and productive reaction temperatures in a RHF and is also readily smelted to molten iron in a SAF without the prior art's problem of high melting temperature slag and non-fluid slag.

Further objects, advantages and features of the present invention will be apparent from the drawings and detailed description herein.

15

BRIEF DESCRIPTION OF THE FIGURES

Although the characteristic features of this invention will be particularly pointed out in the claims, the invention itself, and the manner in which it may be made and used, may be better understood by referring to the following descriptions taken in connection with the accompanying figures forming a part hereof.

Figure 1 provides a schematic of a process for upgrading an iron ore.

Figure 2 provides a schematic of a process for upgrading an iron ore wherein the feed stream is size classified prior to being passed through the first magnetic field.

Figure 3 provides a schematic of a process for upgrading an iron ore wherein the second nonmagnetic fraction is size classified to provide an oversized fraction and an undersized fraction.

Figure 4 provides a schematic of a process for upgrading an iron ore wherein the second magnetic fraction is passed through a second high intensity magnetic separator.

Figure 5 is a flow diagram of an inventive system for upgrading and conditioning an iron ore.

Figure 6 is a flow diagram of an inventive system for upgrading and conditioning an iron ore.

Figure 7 is a flow diagram of an inventive system for mixing starting materials to provide a rotary hearth furnace charge. Figure 8 is a flow diagram depicting the preparation of a rotary hearth furnace charge in accordance with an preferred aspect of the invention.

Figure 9 is a flow diagram depicting the preparation of a rotary hearth furnace charge in accordance with an preferred aspect of the invention.

Figure 10A is a flow diagram depicting the preparation of a rotary hearth furnace charge in accordance with an preferred aspect of the invention.

Figure 1 OB illustrates a system for producing molten metal which comprises a submerged arc furnace oriented below a rotary hearth furnace.

Figure 11 illustrates a system for recovering sponge iron from a rotary hearth furnace and introducing it into a submerged arc furnace. 16

Figure 12 depicts an arrangement for recovering sponge iron from a rotary hearth furnace.

Figure 13 provides a schematic diagram of a preferred system for recuperating heat from a rotary hearth furnace off-gas in accordance with the invention.

Figure 14 is a flow diagram of a preferred rotary hearth furnace off-gas system.

Figure 15 is a flow diagram of a preferred submerged arc furnace off-gas system.

Figure 16 is a phase diagram showing a preferred compositional area for fluxing or slag-forming materials for an advantageous submerged arc furnace charge in accordance with the invention.

17

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention pertains.

The present invention provides in certain preferred aspects methods for producing molten metal from an iron oxide, which comprise a direct reduction reaction and a subsequent smelting reduction reaction. Direct reduction is achieved utilizing a rotary hearth furnace (RHF), and features excellent thermal efficiency, making inventive methods significantly more efficient than rotary hearth direct reduction processes previously known. The invention also makes possible the efficient use of a RHF in a large-scale iron-making process by providing processes which exhibit advantageously low capital and operating costs. In certain aspects of the invention, there are provided methods comprising a solids-based rotary hearth direct reduction reaction in which the hot sponge iron, also termed direct reduced iron ("DRI"), is readily discharged from the RHF and combined with SAF fluxing agents to provide an excellent feed material for a submerged arc furnace ("SAF"). In accordance with preferred aspects of the invention, hot sponge iron is discharged from the hearth of the RHF and quickly introduced into a SAF, thereby allowing the utilization of a large proportion of the sensible heat then existing in the sponge iron for subsequent processing in the SAF. This and other features of the present invention combine to overcome the need for excessive inputs of heat in smelting reduction vessels, as is characteristic of conventional methods which charge cooled DRI thereinto. Furthermore, energy, both thermal and chemical, in RHF and SAF 18

off-gases is recovered for use in accordance with the invention to offset the large amounts of heat which must otherwise be generated at great cost in the production of elemental iron. These and other advantageous characteristics of the invention will be described in greater detail herein. In accordance with a preferred aspect of the invention, appropriate proportions of particulate starting materials, including, for example, one or more particulate iron oxides, one or more particulate carbonaceous reducing agents, one or more fluxing agents selected in accordance with the invention and one or more binders are mixed, with the addition of water if needed, and placed into a balling machine to make agglomerates, or "green balls." The green balls are introduced onto the hearth of a RHF, where they are exposed to appropriate reaction conditions to achieve direct reduction of the iron oxide into sponge iron. In alternate aspects of the invention, a non-agglomerated mixture may by charged to the RHF and reduced into sponge iron. As used herein, the term "fluxing agent" refers to a composition which is added to a RHF charge or a SAF charge and which is ultimately melted and separated from molten iron in the SAF. A fluxing agent in combination with binder materials and gangue materials already present in the iron oxide and the carbonaceous reductant constitute the portion of the RHF and SAF charge materials represented by the term "slag-forming compositions." Typically, at least about 75% of the iron in sponge iron produced in accordance with the invention is in elemental form and up to about 25% of the iron exists as an iron oxide. The sponge iron, after discharge from a RHF in certain aspects of the invention, is quickly introduced into a SAF to melt the sponge iron and to reduce the remaining unreduced iron, thereby yielding liquid metal and slag. The slag may then be separated from the liquid metallic iron, which is an excellent feed for steel-making processes. Thus, when closely coupled to steel-making furnaces, inventive reduction processes provide a ready source of hot metallic iron which may be used to improve the efficiency of a steel-making process. 19

One starting material required to practice the present invention, therefore, is a particulate iron oxide composition. The particulate iron oxide composition comprises a sufficient amount of iron oxide to make the direct reduction into metallic iron economically feasible. A preferred level of iron oxide in such a composition may be determined by a skilled artisan on a case-by-case basis for a wide variety of economic conditions and situations. A wide variety of iron ores, such as virgin ores, or concentrates thereof, may be used in inventive processes. Examples of iron oxide compositions suitable for use according to the invention include virgin iron ore, such as hematite iron ore fines, ground lump ores, iron oxide pellet fines, hematite iron ore, specular hematite concentrate, earthy hematite, magnetite iron ore, magnetite concentrate, limonite, limonite concentrate, ilmenite, ilmenite concentrate, taconite concentrate, semi-taconite concentrate, pyrolusite and pyrolusite concentrate; and steel mill waste oxides such as mill scale, EAF dust and drop out dust. It is not intended, however, that this list be limiting and it is readily understood by a skilled artisan that additional compositions or combinations thereof which have iron oxide therein may find advantageous use according to the present invention. Particularly suitable iron oxide compositions include magnetite concentrates from Minnesota and Michigan, specular hematite concentrates from Eastern Canada, hematite fines from Brazil, hematite fines from Australia, hematites from India, iron ores from Sweden and iron ores from South Africa.

Suitable iron oxide compositions may be obtained from companies which are in the business of iron ore mining, such as, for example, Cleveland Cliffs, Inc., Quebec Cartier Mining Company, Iron Ore Company of Canada, CVRD, Hamersley Iron, BHP or MBR. In certain preferred aspects of the invention, an iron ore starting material is beneficiated to remove therefrom undesirable contaminants such as, for example, silica and/or manganese. Beneficiation in accordance with the invention is particularly preferred when the iron ore being reduced is a specular hematite concentrate. For example, in accordance with a preferred aspect of the invention, 20

the iron ore is upgraded as depicted schematically in Figure 1. As shown therein, a substantially dry iron ore flow stream 10 is provided and strongly magnetic materials are recovered from the flow stream 10 using a dry low intensity magnetic separator 20 such as, for example, a drum separator. A drum magnetic separator advantageously used may be obtained from a supplier such as Eriez Magnetics

(Erie, Pennsylvania) or International Process Systems, Inc. (Lakewood, Colorado). The low intensity magnetic field preferably has a field strength of from about 500 to about 2000 gauss. The field strength is more preferably from about 500 to about 1500 gauss, more preferably from about 800 to about 1200 gauss and most preferably about 1000 gauss.

Once strongly magnetic materials such as magnetite and maghemite are recovered from the feed stream 10 into the first magnetic fraction 30, the remaining materials (i.e., the first nonmagnetic fraction 40) are subjected to high intensity magnetic separation using a high intensity magnetic separator 50, preferably a dry rare earth magnetic separator. It is preferred that substantially no strongly magnetic materials remain in the first nonmagnetic fraction 40, because such particles may interfere with subsequent high intensity processing. The high intensity magnetic separator removes weakly magnetic materials, thereby providing a second magnetic fraction 60 and a second nonmagnetic fraction 70. Where the original feed stream 10 comprises a specular hematite concentrate, the second nonmagnetic fraction 70 comprises a substantial amount (i.e., up to about 75% by weight) of the nonmagnetic contaminants (e.g., the silica and/or pyrolusite) present in the feed material 10.

It is common, however, that some magnetic materials remain in the second nonmagnetic fraction 70. A common reason for this is that large, relatively pure hematite particles may have too much inertia to be deflected into the magnetic fraction during high intensity magnetic separation, and become misplaced in the second nonmagnetic fraction 70. Therefore, to recover iron values, size classification (i.e., screening or air classifying) may preferably be performed either 21

before high intensity separation, as depicted schematically in Figure 2, or after high intensity separation, as depicted in Figure 3. In Figure 2, the first nonmagnetic fraction 40 is passed through a classifier 45 to provide an oversize fraction 46 and an undersize fraction 47. The undersize fraction 47 is then passed through the high intensity magnetic separated 50 to yield the second magnetic fraction 60 and the second nonmagnetic fraction 70. In Figure 3, the second nonmagnetic fraction 7 is passed through a size classifier 110 to provide an oversize fraction 120 and an undersize fraction 130.

The high intensity magnetic separator 50 preferably has a field strength of from about 4000 to about 30,000 gauss. The field strength is more preferably from about 5000 to about 15,000 gauss, more preferably from about 6000 to about 10,000 gauss and most preferably about 7000 gauss. As with low intensity separation, a wide variety of separators may advantageously be used; however, a dry magnetic drum separator is preferred. Magnets used in accordance with the invention are preferably of the permanent type, rare earth permanent magnets being preferred due to lower maintenance required and generally simpler design and operation.

The second nonmagnetic fraction 70 in the process set forth schematically in Figure 2 or the undersize fraction 130 in the process set forth schematically in Figure 3 comprises a substantial portion of the nonmagnetic material, such as, for example, the silica and pyrolusite, present in the iron ore starting material. For example, it is expected that at least about 50% and more preferably about at least about 60% of the silica present in the iron ore starting material ultimately resides in the nonmagnetic fraction 70 of Figure 2 or the undersize fraction 130 of Figure 3. These fractions preferably have an iron content of less than about 35% by weight, and more preferably less than about 18% by weight. These fractions may be discarded or sold as is or after further refinement as a byproduct silica sand to be used, for example, in sand blasting applications or other conventional silica sand applications. Alternatively, they may be advantageously used in accordance with 22

the invention as a SAF fluxing agent to adjust the SAF slag chemistry, as discussed in greater detail below.

In certain preferred aspects of the invention, the second magnetic fraction 60 is subjected to one or more additional "cleaner" separations by passing it through one or more high intensity separators. Therefore, in one aspect of the invention, the second magnetic fraction 60 is passed through a second high intensity magnetic separator 140, as depicted schematically in Figure 4, to provide a third magnetic fraction 150 and a third non-magnetic fraction 160, thereby further increasing the purity of the product. It is preferred in inventive beneficiation processes that the iron ore feed stream 10 be substantially dry, the term "substantially dry" being used to designate that the ore has a moisture content of less than about 1.0%, more preferably less than about 0.5%. High-intensity separators used in accordance with the invention for the separation of weakly magnetic minerals are believed to have suitable separating effect only on substantially dry materials because surface tension effects of a wet material interfere with separation. Therefore, the ores or concentrates fed to this ore upgrading process normally will need to be dewatered and dried before being magnetically beneficiated in accordance with the invention. It is an advantageous aspect of the invention that heat recuperated from the rotary hearth furnace off-gas is used to increase the efficiency of this drying task, as is described in greater detail below.

Iron ore concentrates particularly well suited for the inventive ore upgrading process are concentrates produced from ores in the "Labrador Trough," this term being used to refer generally to an iron formation in the northeastern region of Canada, e.g., in Quebec, Labrador and New Foundland. Such concentrates may be obtained from Quebec Cartier Mining Company ("QCM"), Iron Ore Company of Canada ("IOCC") and Wabush Mines ("Wabush"). Concentrates presently available from these companies typically have a silica concentration of between about 3% and about 6% by weight. While this is a suitable concentration for use of 23

the ore in a blast furnace, a silica concentration of about 2% or less is needed for advantageous use of the ore in a direct reduction process. Additionally, ores mined by Wabush Mines typically have a high manganese content (i.e., up to about 2.5%). Inventive processes are advantageously used to decrease manganese (e.g., pyrolusite) content of an ore as well as silica content. It is readily understood that ores other than those explicitly set forth above may be advantageously upgraded in accordance with the invention, the main criterion being that nonmagnetic materials are present which are desired to be separated from magnetic materials.

The "save" fractions, including the magnetic fractions and the oversize fractions (if size separation is performed), are then excellent starting materials for subsequent reduction into elemental, or metallic, iron. These fractions may advantageously be combined to provide a purified iron ore concentrate. A more detailed description of various iron ore upgrading processes is given in the inventor's copending U.S. Patent Application entitled Method For Upgrading Iron Ore Utilizing Multiple Magnetic Separators, filed November 5, 1997, which is hereby incorporated by reference herein in its entirety.

In accordance with a preferred aspect of the invention, the iron ore is pulverized using a high pressure roll press following beneficiation. When roll press pretreatment is performed, it is understood that the moisture content of the ore may preferably be increased prior to roll press pretreatment where drying and beneficiation are first conducted. It is to be understood that roll press pretreatment advantageously conditions an ore whether or not the ore has been beneficiated. Preferably, the ore has a moisture content of from about 2 to about 3% at the pulverization step to minimize the amount of dust generated by the roll press. It has been discovered by the present inventor that utilization of a roll press to condition an iron ore starting material in accordance with the invention significantly increases the degree of metallization achievable in the RHF direct reduction reaction because a roll press set at a relatively high pressure, such as, for example, from about 4.5 to about 6.5 N/mm² (Newtons per square millimeter), has 24

been found by the inventor to advantageously condition iron ores, surprisingly improving their reducibility. While it is not intended that the present invention be limited by any theory whereby it achieves its advantageous result, it is believed that the roll press introduces internal fractures into iron ore particles, thereby providing additional routes for reducing gases in the RHF to contact the iron oxides.

The inventor has further discovered that an ore material conditioned by roll press pretreatment surprisingly exhibits the synergistic characteristic of being readily agglomerated to greenballs at a coarser size distribution than is generally accepted to be the required size distribution for green ball agglomeration. Iron ore particles reduced in accordance with this aspect of the invention, therefore, on average, need not be ground to the extent previously thought necessary. Conventional grinding by ball mill, for example, generally requires a grind of at least 65% minus 325 mesh to achieve acceptable greenball quality and acceptable reducibility. Inventive methods which utilize roll press pretreatment achieve similar acceptable greenball quality and reducibility at grinds as coarse as 20% minus 200 mesh. More preferably, inventive grinds have a size distribution of at least about 30% minus 200 mesh, more preferably at least about 40% minus 200 mesh and, most preferably, at least about 60% minus 200 mesh.

A wide variety of roll press designs are known and may be used in accordance with the present invention, including for example, those taught in U.S Patent No. 4,728,044 to Duill et al; U.S Patent No. 5,054,694 to Knobloch et al; U.S Patent No. 5,417,3744 to Kranz et al; U.S Patent No. 5,372,315 to Kranz et al; and U.S Patent No. 5,114,131 to Strasser et al; each of which is incorporated herein by reference in its entirety. The pulverized ore may then be transported to one or more surge bins, from which it is metered to a mixer, such as, for example, a Littleford mixer or a pug mill, along with other materials in the preparation of agglomerates.

While a wide variety of arrangements for upgrading and/or grinding iron ore may advantageously be employed in accordance with the present invention, Figures 25

5 and 6 set forth flow diagrams which illustrate preferred ore upgrading/grinding systems. An iron ore is preferably fed into an ore feed silo 170 from, for example, an ore storage pile. Ore is fed from the silo onto a drier feed conveyor 180, which feeds the ore at a preselected rate into an ore drier 190, such as, for example, a rotary drier. From the drier 190, the dried ore is preferably transported to, and passed through, a diverter 200, which splits the ore into streams, thereby feeding multiple ore upgrading circuits. It is understood that the ore may alternatively be fed into a single upgrading circuit, depending upon the amount of upgraded ore needed. After passing through the diverter 200, the ore may be conveyed into feed bins 210 from which it is fed to one or more low intensity magnetic separators 220. The low intensity separators 220 separate the ore into first magnetic fractions 230 and first nonmagnetic fractions 240. The first nonmagnetic fractions 240 are passed through high intensity magnetic separators 250 to provide second magnetic fractions 260 and second nonmagnetic fractions 270. The first magnetic fractions 230 and the second magnetic fractions 260 are directed to a save material conveyor 280 which conveys save materials to a purified iron ore bin 290. The second nonmagnetic fractions are passed through a size classifier, such as, for example, a Derrick screen 300, from which an oversize fraction 310 is introduced into the purified iron ore bin 290, and an undersize fraction 320 is conveyed to a bin 330 for containing nonmagnetic materials. In a preferred aspect of the invention, where the iron ore starting material is specular hematite, a significant proportion of the nonmagnetic material in bin 330 is silica sand, as discussed above. The purified iron ore is transported from bin 290 to roll press 340, using, for example, conveyor 350, bucket elevator 360 and belt conveyor 370. The ore exiting the roll press 340 is advantageously of high purity and is conditioned, and may advantageously be transported to a feed bin 410, as depicted in Figure 7. Alternatively, the conditioned iron ore may be passed through a size classifier, so that particles 26

having a size greater than a preselected size may be again passed through the roll press 340.

Another starting material needed to practice the present invention is a particulate carbonaceous reductant. A particulate carbonaceous reductant suitable for use in the present invention is one having a sufficient amount of reactivity, fixed carbon and volatile matter therein to advantageously react with the iron oxide composition under suitable reaction conditions to produce highly metallized sponge iron. Examples of particulate carbonaceous reductants which are suitable for use in accordance with the invention include coal, coke, coke braize, pet coke, graphite and char. It is not intended that this list be limiting, but only that it provide examples of useful carbonaceous reductants. It is well within the purview of a skilled artisan to select additional materials having sufficient reactivities, volatile matters, and fixed carbon therein to be advantageously used in accordance with this invention. In a preferred aspect of the invention, the carbonaceous reductant preferably has a size distribution of about 50% to about 95% passing 200 mesh. More preferably, the size distribution is from about 60% to about 90% passing 200 mesh and, most preferably, about 75% to about 85% passing 200 mesh. Therefore, it is understood that, in certain aspects of the invention such as, for example, where the reductant is coal, the coal starting material will preferably be pulverized prior to being mixed with other starting materials. Therefore, in certain aspects of the invention, a carbonaceous reductant is pulverized, and is then placed into one or more surge bins, from which it is metered to a mixer.

It is readily understood that equipment preferably used to pulverize a carbonaceous reductant in accordance with the invention will not only pulverize the reductant, but will also dry the reductant. For example, a preferred pulverizer utilizes upward hot air flow elutriation for discharging particles which have attained a sufficiently small size. Thus, such a pulverizer requires the input of hot gases to dry the reductant and to remove from the pulverizer those particles that 27

have achieved the desired size reduction. A pulverizer/drier having the features set forth above is known in the art and may be readily obtained, for example, from Williams Patent Crusher and Pulverizer Co., Inc. (St. Louis, Missouri). In accordance with the invention, the hot gas utilized in the pulverizer/drier preferably at least in part comprises off-gas from the RHF, as is described more fully below. Another starting material advantageously utilized in accordance with particular preferred aspects of the invention is a fluxing agent which is intimately contacted with the iron oxide and the carbonaceous reductant to control the melting point of slag phase materials in the RHF charge ("RHF fluxing agent"), or which is contacted with sponge iron discharged from the RHF to provide a SAF charge

("SAF fluxing agent"). The use of fluxing agents in accordance with the invention advantageously overcomes difficulties encountered in the prior art associated with discharging hot sponge iron from the RHF and with tapping a high melting temperature slag phase composition from a SAF. An advantageous feature of the invention is the control of materials present in the RHF charge and the SAF charge to ensure that the slag phase compositions of each charge is optimized to have an advantageous melting temperature for the function of the respective furnace. It is readily understood that a high melting temperature slag phase composition is desired in the RHF, but a low melting temperature slag phase composition is desired in the SAF. It is also readily seen that the RHF fluxing agent or agents selected for use in accordance with the invention not only impacts the physical characteristics of the hot sponge iron produced in the RHF, but also impacts the selection of and the quantity of the SAF fluxing agent to be mixed with the hot sponge iron discharged from the RHF prior to introduction thereof into the SAF (i.e., in the preparation of the SAF charge) to provide a slag layer in the SAF having a sufficiently low melting point to exhibit adequate fluidity for removal thereof during slag tapping events.

A low melting point slag could be obtained in the SAF by originally preparing an RHF charge to include specific amounts and ratios of particulate 28

bauxite (Al₂O₃), calcite lime (CaO), dolomitic lime (CaO/MgO), and sand (SiO₂); however, this would be problematic because the temperature in the reduction zones of the RHF can be about 1350°C to about 1450°C, and may exceed the melting point of a purposefully blended, low melting point, slag even when operated at somewhat lower temperatures, i.e., 1250°C-1350°C. Therefore, when a self- fluxing mixture or green ball, designed with a slag composition to optimize melting in a SAF, is used in a RHF that is operated at an optimal operating temperature to maximize reduction of the iron oxide, portions of the pellet soften and deform, causing the particles or pellets to stick together and also to the hearth of the RHF. This premature formulation of a fluid slag would cause significant operating problems and productivity losses. If the RHF is operated at a lower temperature to avoid formation of a fluid slag on the hearth, the amount of iron ore reduction decreases, resulting in less metallic iron in the sponge iron and transferring an unnecessary portion of the reduction burden to the SAF, at higher costs and with loss of productivity.

The present invention advantageously provides a slag-phase composition in the RHF charge which has a high melting point, i.e., preferably at least about 1500°C, and a slag-phase composition in the SAF charge which has a low melting point, i.e., preferably no higher than about 1450°C, and more preferably no higher than about 1400°C. Referring to Figure 16, a triangular phase diagram 910 of common slag-forming components is provided, this basic phase diagram being reproduced from U.S. Patent No. 5,681,367 to Hunter. The ordinates are in terms of percentages by weight of CaO, SiO₂ and Al₂O₃. The isotherms represent melting points in degrees Celsius. Superimposed on the phase diagram is region 920, representing an area of the phase diagram of particular importance in certain preferred aspects of the present invention. Region 920 represents combinations of CaO, Si0₂ and Al₂O₃ having melting temperatures suitable for melting in the SAF to form liquid slag. Specifically, the perimeter of region 920 is drawn on an 29

isotherm of 1450°C and includes compositions having the SAF-acceptable eutectic melting temperatures in the phase diagram 910.

A high percentage of CaO in the slag-forming composition of a RHF charge is preferred in accordance with the invention, and a preferred region of the phase diagram 910 for a RHF charge is represented as region 925. A furnace charge having a slag phase composition, such as that represented by Region 925, with a relatively high CaO content has an advantageously high melting temperature and desirable desulfurization properties. In a preferred embodiment of the present invention, an inventive RHF charge comprises a ratio of (MgO + CaO) to (Al₂O₃+ SiO₂) of from about 0.8 to about 1.2% by weight, more preferably from about 0.9 to about 1.1 and, most preferably, from about 0.95 to about 1.05. As an iron ore starting material commonly has therein a significant amount of SiO₂, it typically advantageous to add sufficient amounts of MgO and/or CaO to the mixture to bring the ratio of (MgO + CaO) to (Al₂O₃+ SiO₂) to a preferred level. It is understood that MgO and/or CaO, in certain aspects of the invention, are preferably substituted with limestone or dolomitic limestone since the carbonate mineral does not ionically interfere with conventional binders used for agglomeration. Further, in some regions of the world, for example, where bentonite and other conventional binders are very expensive, it may be advantageous to use hydrated lime or hydrated dolomitic lime as both the binder and the RHF fluxing agent.

In view of the above, the present invention provides methods for producing molten iron in which sponge iron handling and SAF slag removal are facilitated by controlling the "slag phase composition" in the RHF charge and in the SAF charge. In accordance with the invention, therefore, it is preferred that fluxing materials are selected in the formation of a RHF charge to provide a RHF charge having slag- phase constituents featuring a high melting temperature, i.e., at least about 1450°C, more preferably at least about 1500°C and most preferably at least about 1600°C. Further, compositions are added to hot sponge iron in accordance with the invention after discharge thereof from the RHF and prior to charging the same to 30

the SAF, thereby altering the compositional makeup of the slag-forming composition of the SAF charge to provide a slag-forming composition having a melting temperature of no greater than about 1450°C, more preferably no greater than about 1400°C. A skilled artisan can determine the amounts of Al₂O₃, CaO, MgO and SiO₂ present in the iron ore starting material and, without undue experimentation, select the proper amounts and proportions of fluxing agents to include in a RHF charge and in a SAF charge in view of the present description. Preferred RHF fluxing agents also function to catalyze the direct reduction reaction. The present inventor has discovered that excellent RHF fluxing agents include caustic lime, caustic dolomitic lime, limestone, dolomitic limestone, hydrated lime and hydrated dolomitic lime, and excellent SAF fluxing agents are, for example, silica (SiO₂), lime and aluminum oxide (Al₂O₃). In aspects of the invention wherein starting materials are agglomerated prior to being introduced into a RHF, it is preferred that limestone be used as the primary RHF fluxing agent, rather than hydrated lime, because limestone does not interfere with, or

"immobilize," the binder. It is also preferred that the RHF fluxing agent not have a substantial proportion of magnesium oxide therein because magnesium oxide does not promote desulfurization of the metallized product and because magnesium oxide raises the melting temperature of the slag-forming composition to an unsatisfactory level.

It has also been surprisingly found that caustic lime, caustic dolomitic lime, limestone, dolomitic limestone, hydrated lime and/or hydrated dolomitic lime may be advantageously introduced in dust form onto the surface of moist green balls in inventive processes before the green balls are dried and introduced into the RHF. Such green ball "dusting" further minimizes the stickiness of the DRI product being removed from the hearth. While it is not intended that the present invention be limited by any theory whereby it achieves its advantageous result, it is believed that, in binding with silica present in the agglomerates, preferred RHF fluxing agents prevent silica from reacting with iron to form low melting point iron 31

silicates such as, for example, fayalite. Thus, the presence of a RHF fluxing agent in and/or on an agglomerate significantly improves the rate of reduction reactions in the RHF and the ease with which DRI is discharged from the rotary hearth furnace after reduction. The presence of a RHF fluxing agent in and/or on inventive agglomerates is especially advantageous when the resulting metallic iron is to be used for steelmaking, because this reduces the amount of lime which must be added to the metallized iron in downstream steel-making operations.

It is readily understood that slag-forming materials in a RHF charge prepared in accordance with the invention are not removed from elemental iron until after the green ball is reduced on the RHF and the resulting sponge iron is further reduced and melted in the SAF. It is also readily understood that the lower the melting point of the SAF slag, and hence the greater the temperature differential between the melting point of the slag and the operating temperature of the SAF (temperature of the hot metal), the more fluid the slag in the SAF is, and the easier it is to drain the slag.

Certain preferred SAF charge compositions, featuring a slag having a melting temperature within the area of region 920 in Figure 16, preferably comprise a slag-forming composition of from about 45 to about 65% SiO₂ by weight, from about 10 to about 20% Al₂O₃ by weight and from about 20 to about 40% CaO by weight. More preferably, the composition comprises from about 48 to about 58% SiO₂ by weight, from about 12 to about 18% Al₂O₃ by weight and from about 28 to about 36% CaO by weight; and, most preferably, from about 51 to about 55% SiO₂ by weight, from about 14 to about 16% Al₂O₃ by weight and from about 30 to about 34% CaO by weight. Therefore, it is readily understood that, after the sponge iron is discharged from the RHF, it will commonly be desired to add sufficient amounts of SiO₂, Al₂O₃ and/or CaO to bring the slag-forming composition of the SAF charge to a desired ratio while meeting the desulfurization requirements of the SAF. 32

A person skilled in the art will appreciate that one will not want to use more slag-forming ingredients than necessary, not only because of their cost, but because of the effect of excess slag on the energy requirements and productivity losses of the process. It is preferred, therefore, that the overall amount of slag-forming materials used in an inventive process be minimized to the extent possible.

Fluxing agents selected for use in accordance with the invention may be obtained in the preferred powdered form from a wide variety of commercial outlets well known to a person skilled in the art. Alternatively, RHF fluxing agents may be obtained as limestone or dolomite, and then pulverized and dried in the same manner that the carbonaceous reductant is pulverized and dried, described above. Thus, a single pulverizer/drier may be used in accordance with the invention to alternately pulverize the reductant and the RHF fluxing agent, or multiple pulverizers may be used to satisfy these requirements. A RHF fluxing agent may then also be transported to one or more surge bins, where it is held until being fed into a mixer or until it is used to dust moist green balls.

SAF fluxing agents are also preferably placed into one or more surge bins until they are metered out to prepare a SAF charge. In a preferred aspect of the invention, a significant proportion of the SAF fluxing agent is silica. Thus, where specular hematite is utilized as a raw material, it is seen that the high silica non- magnetic fraction yielded during magnetic beneficiation provides an excellent source of an advantageous SAF fluxing agent. Therefore, in particularly preferred aspects of the invention, all or a large proportion of the RHF fluxing agent is limestone, and all or a large proportion of the SAF fluxing agent is silica.

Additional starting materials needed in preferred aspects of the invention are water and a binder material. It is understood that a mixture of starting materials must have a certain degree of moisture therein prior to forming the mixture into green balls. Therefore, where an iron ore starting material is dried to less than about 0.5% water in accordance with the invention to be beneficiated and/or the carbonaceous reductant and/or the fluxing agent is pulverized and size-separated in 33

a pulverizer/drier, thereby drying the reductant and/or fluxing agent, the starting materials are preferably moistened prior to being introduced into a balling machine. The overall mixture introduced into the balling machine preferably has a water content of from about 7% to about 12% by weight, more preferably from about 8% to about 11%, and most preferably from about 9% to about 10%.

The binder material selected in accordance with the invention may be one of a variety of binders available commercially. Preferably, the binder used is a mixture of Peridur or Alcotac and Bentonite. It is well within the purview of a skilled artisan, however, to select alternate binders, such as, for example, corn starch, lignosulfonate, or fly ash, for use in accordance with the invention, all of these being readily available commercially. Binder materials may also be preferably held in a feed bin so that they may be metered into a mixer along with other starting materials prior to forming green balls.

An iron oxide, a carbonaceous reductant, a fluxing agent and binder materials are metered into a mixer, such as, for example, a Littleford mixer or a pug mill, in appropriate proportions as described herein to optimize the efficiency of the overall direct reduction process, and are mixed intensely. The iron ore starting material may alternatively be in the form of an iron ore concentrate slurry that is dewatered or filtered to produce a moist filter cake that is fed into the mixer. It is often advantageous to also feed waste oxides, such as, for example, EAF dust and/or mill scale, into the mixer along with the other starting materials. While it is well within the purview of a person skilled in the art to design a system for delivering materials into a mixer, a representative example is set forth in Figure 7. In this Figure, a mixer feed conveyor 380 is depicted, onto which the various materials are placed for transport to the mixer 390. For example, iron ore is transported from an ore source, such as, for example, an ore beneficiation unit, a roll press or a stockpile, and placed into an ore bin 410, from which it may be metered onto the mixer feed conveyor 380. Coal is transported from a coal source, such as, for example, a pulverizer/drier or a stockpile, and placed into a coal bin 430, from which it is 34

metered onto the mixer feed conveyor 380. A RHF fluxing agent is transported from a source, such as, for example, a pulverizer/drier or a stockpile, and placed into a flux bin 440, from which it is metered onto the mixer feed conveyor 380. Additionally, bentonite and Peridur are placed into a bentonite bin 450 and a Peridur bin 460 respectively, from which they are metered onto the mixer feed conveyor 380. Optionally, an EAF dust and/or mill scale bin 470 is also present, which may be fed, for example, by a pneumatic transport system as is known in the art. It is understood that the starting material feed bins 410, 430, 440, 450, 460, 470 may meter starting materials directly onto the mixer feed conveyor 380, or alternatively, each feed bin may have associated therewith a secondary conveyor 480 as depicted in Figure 7. The mixer feed conveyor 380, carrying the metered starting materials, drops its load into the mixer 390, into which water may also be added in preselected amounts if necessary to provide a mixture having a desired moisture content. While it is well known that iron oxide compositions, such as iron ores, may have widely varying concentrations of iron atoms present therein, and that carbonaceous reductants may have widely varying amounts of fixed carbon present therein, the proportions of iron oxide composition to carbonaceous reductant metered into the mixer are selected according to the invention based upon the amount of iron in the iron oxide composition and the amount of fixed carbon in the carbonaceous reductant.

According to a preferred aspect of the invention, the ratio of carbon to iron in the mixture is selected to optimize reduction of the iron oxide without wasting reductant. It is within the purview of a skilled artisan to determine the amount of fixed carbon in the reductant and the amount of iron in the iron oxide composition, and to stoichiometrically determine the weight proportions of these two components needed to achieve optimal reduction. In this regard, it is expected that about 50%-80% of the fixed carbon in a reductant according to the invention will effectively perform a reducing function on the hearth. In a preferred aspect of the 35

invention, the ratio of fixed carbon in the reductant to iron in the iron oxide composition is between about 4.0:10.0 and about 2.4:10.0 by weight. More preferably, the ratio is between about 3.4:10 and about 3.0:10 by weight. Most preferably the ratio of carbon to iron in the mixture is about 3.2:10.0 by weight. The amount of fluxing agent present in a mixture is optimized to provide a

RHF charge having a slag-forming composition that will not soften or melt in optimal RHF reducing conditions, as described above. For example, it is within the purview of a skilled artisan to determine the amount and content of gangue materials, such as silica, in the iron oxide and the carbonaceous reductant, and then to select an amount of RHF fluxing agent to provide an overall slag- forming composition having the described advantageous properties. While it is common for an iron ore or an iron ore concentrate, such as specular hematite or specular hematite concentrate, to include a significant amount of silica, it is understood that alternative ores may include a wide variety of gangue compositions and, therefore, proportions of compositions in the RHF fluxing agent are adjusted in accordance with the invention to provide the advantageous result described herein.

The amount of a binder material and water present in a mixture prepared in accordance with the invention may be optimized by a person skilled in the art, without undue experimentation, for achieving high-strength green balls while minimizing the drying burden required. In a preferred embodiment, an inventive mixture comprises from about 0.1% to about 3.0% binder by weight, more preferably from about 0.5% to about 2.0% binder and most preferably, from about 0.75% to about 1.50% binder. The mixture preferably comprises from about 2% to about 14% water by weight, more preferably from about 6 to about 12%, more preferably from about 8 to about 10% and, most preferably, about 9%.

An inventive mixture may then be fed from the mixer 380 and conveyed on, for example, a mixture belt conveyor 490, directly to a balling machine 500, as depicted in Figure 8, or to a mixture feed bin 510, from which it can be metered into a balling machine 500, as depicted in Figure 9. Preferably, a feed bin 510 used 36

in accordance with the invention to hold the moist mixture is designed to handle the optimized moisture content of the mixture without bridging. Steep wall slopes, bin vibrators, and/or live bin bottoms may preferably be used to aid in the gravity flow of a moist mixture. Materials held in feed bins may preferably be removed from the bins through, for example, a slide gate by either a drum drag feeder (optionally equipped with cleats) or a star feeder.

From the mixture feed bin 510 (in an embodiment which utilizes a mixture feed bin), the moist mixture is fed onto or conveyed to a balling machine 500 for production of green balls. Green balls are then preferably sized to a size split of from about 8mm to about 13mm using, for example, a conventional roll screen 520. The roll screen separates the green balls into an undersize fraction 530 an oversize fraction 540 and a save fraction 550. It is understood that the undersize fraction 530 and the oversize fraction 540 are preferably shredded and transported to the mixture feed conveyor 490 using, for example, conveyors 560 and 570. These fractions 530 and 540 may therefore be reintroduced onto the balling machine and reformed into green balls of preselected size.

Green balls in the save fraction 550 are then transported to a green ball drier 580 using, for example, a belt conveyor 590, where they are dried prior to introduction into the RHF 600. In certain preferred aspects of the invention, the moist green balls (i.e., the save fraction 550 being transported to the green ball drier) are thoroughly dusted with a powdered RHF fluxing agent, as depicted in Figure 10A, wherein a flux bin 610 meters a powdered RHF fluxing agent onto the moist green balls conveyed therebeneath. Subsequently, upon being dried, the powdered RHF fluxing agent adheres to the green balls and provides an anti- sticking layer. This, in addition to the RHF fluxing agent preferably present within the green balls, affects the physical characteristics of the DRI product, as discussed above, minimizing the degree that reduced agglomerates adhere to one another and thereby, making the removal of DRI from the hearth after direct reduction and post hearth handling more straightforward. As is described in more detail below, the 37

green balls are advantageously dried in accordance with a preferred aspect of the invention by contacting the moist green balls with hot off-gas from the RHF, which is continually available due to the advantageously continuous nature of the RHF reduction process. The dried green balls are then introduced onto the hearth of a rotary hearth furnace 600 using, for example, a vibratory feeder 615, in a layer preferably having a thickness of from about 1 to about 2 balls thick. One problem commonly encountered in the use of a rotary hearth furnace is that the tangential speed of the "inside" edge of the hearth is different than the tangential speed of the "outside" edge of the hearth, due to the difference in radius between the inside edge and the outside edge of the hearth. This speed differential must be taken into account in order to achieve a relatively even layer of agglomerates on the hearth across the width of the hearth. There are several generally understood and accepted solutions in the related field for distributing and feeding materials onto a rotating hearth such that the agglomerates will be placed relatively evenly across the width of the hearth, and it is within the purview of a skilled artisan to assemble a material feed system for feeding the agglomerates onto the hearth in a relatively uniform layer.

The agglomerates then move into and through one or more reaction zones of the rotary hearth furnace. In the reaction zones, as is well known in the relevant field, the green balls are subjected to reducing conditions (i.e., heat and a gaseous reducing environment) to reduce a substantial portion of the iron oxide, thereby producing hot sponge iron. Specifically, the green balls are heated to a temperature and for a period of time sufficient to achieve a high degree of reduction of the iron oxide composition to metallic iron. In a preferred aspect of the invention, the green balls are heated to a temperature of from about 1200°C to about 1500°C and for a period of time of from about 3 minutes to about 30 minutes, more preferably to a temperature of from about 1300°C to about 1400°C. Conventional rotary hearth furnaces having multiple reaction zones may be advantageously used in accordance with the present invention. After passing through the reaction zone or zones on the 38

rotary hearth furnace, the agglomerates (now sponge iron) are removed from the hearth. In a preferred aspect of the invention, at least about 70% of the iron in the sponge iron is in metallic form, more preferably, at least about 80% of the iron is in metallic form, still more preferably at least about 90% and, most preferably, at least 92%.

In accordance with the invention, one or more rotary hearth furnaces are closely coupled to a submerged arc furnace. It is preferred that the time period which elapses between the time the DRI is discharged from the hearth of the RHF and the time it is introduced into the shell of the SAF is no greater than about 60 minutes, more preferably, no greater than about 30 minutes and, most preferably, no greater than about 15 minutes. It is also preferred, in embodiments where the hot sponge iron is not discharged directly into the SAF, that the sponge iron be held in an insulated container for substantially the entire period of time between discharge from the RHF and introduction into the shell of the SAF. The SAF charge thereby retains a significant amount of the sensible heat existing when the DRI is discharged from the RHF.

The sponge iron is preferably removed from the hearth using one or more water-cooled discharge plows or screws, and may then be discharged through refractory-lined chutes into insulated containers for transport to a SAF. Alternatively, a SAF may be advantageously positioned beneath the discharge zone of a RHF so that the hot sponge iron falls directly into the shell of the SAF. In accordance with a preferred aspect of the invention, the SAF is placed such that the center of the SAF lies substantially directly beneath the center of the RHF. With this orientation, it is understood that discharge screws preferably move hot DRI toward the inner edge of the hearth, i.e., toward the center of the RHF, rather than toward the outer edge of the hearth as is done in a conventional RHF system. The DRI then advantageously falls from the hearth directly into the SAF's feed system, or shell, thereby making the DRI almost immediately available for introduction into the SAF. It is understood that preselected SAF fluxing agents in preselected amounts, as 39

described above, are preferably also metered into the SAF feed system as the DRI is discharged thereinto.

Utilizing a RHF/SAF orientation as described above, an alternate aspect of the invention is provided, in which DRI falls into the SAF feed system from the RHF at a plurality of locations around the hearth. In certain preferred aspects of the invention, therefore, an RHF is provided which is configured to pass a plurality of flow streams through reduction zones using a single hearth. Figure 10B, for example, depicts a preferred RHF/SAF orientation in accordance with the invention, in which RHF 600 comprises three distinct flow streams, each of which comprises a loading zone 604, 605, 606; a reduction zone 601, 602, 603; and a discharge zone 607, 608, 609. A single flow stream, for example, is denoted in Figure 10B by the letter "A." By utilizing the orientation of Figure 10B, therefore, a single RHF 600 advantageously produces a plurality of distinct streams of DRI, which are advantageously fed into diverse parts of the feed system of the SAF 600 with minimal material handling requirements. It is readily understood that an alternate number of flow streams, preferably ranging, for example, from 2 to about 5, may be utilized.

When utilizing multiple reduction zones of a single RHF in accordance with the invention, it is desirable that the hearth feature increased dimensions and/or that the speed at which the hearth turns be decreased. It is readily understood that dividing a hearth of a given diameter into multiple flow paths in accordance with the invention will decrease the length of a given path in which the RHF charge is exposed to reducing conditions. This effect is preferably counteracted in accordance with the invention by utilizing a larger hearth and/or by slowing the rotation of the hearth as described. Either of said alterations will advantageously increase the amount of time that the RHF charge resides in a reducing environment, by increasing the distance through which the charge must pass, or by passing the charge more slowly through the shorter distance. 40

In the case of using a hearth having an increased diameter, a hearth used in accordance with the invention may preferably have an inside diameter of, for example, from about 35 to about 50 meters and an outside diameter of from about 50 to about 70 meters. If a conventional hearth is used, such as, for example, one having an inside diameter of from about 25 to about 40 meters and an outside diameter of from about 40 to about 55 meters, the rotation of the hearth is preferably decreased from about 6 rpm (revolutions per minute) to a speed of from about 2 to about 3 rpm.

In alternate preferred aspects of the invention, the SAF is positioned to one side of a RHF and the DRI must be transported thereto. In one preferred manner of transporting DRI to a submerged arc furnace, illustrated in Figures 11 and 12, there is provided beneath the discharge zone 620 of the rotary hearth furnace 600 a rotatable platform 630 configured to support a plurality of DRI transport bottles. In an alternate aspect of the invention, the containers used to transport hot sponge iron are skips on rails, these being known in the art. Alternate methods for transporting the sponge iron may be employed, it being preferred that the method selected utilize insulated containers that prevent heat loss and prevent the ingress of air that would detrimentally cause reoxidation of the hot elemental iron in the sponge iron. It is also preferred that the sponge iron retains at least about 80% of its sensible heat between the RHF and the SAF. The DRI is preferably introduced into the container at a temperature of from about 900°C to about 1300°C adjacent the discharge zone 620, and is preferably discharged from the containers to the SAF feed bins at a temperature of from about 800°C to about 1200°C. Preferably, the containers are sufficiently large to receive a DRI charge of from about 10 to about 20 tons. Additionally, in an embodiment that utilizes bottles, it is preferred that the bottles have a top feed opening and a bottom discharge opening for ease of handling.

When bottles are used to transport sponge iron from the RHF to the SAF in accordance with the invention (in embodiments which use bottles rather than, for example, skips on rails or direct discharge of sponge iron into a SAF positioned 41

beneath the RHF), it is readily understood that the bottles may have a wide variety of configurations. Alternate configurations, however, present various difficulties with respect to prevention of heat loss and oxidation of the hot metal by ingress of air into the bottles. To prevent or minimize these occurrences in accordance with the invention, SAF fluxing agents and coke are placed into the bottles in a manner such that these compositions function as an added seal to prevent heat loss and ingress of air.

When a bottle configured to have a top opening for receiving sponge iron and a bottom opening for discharging the sponge iron (i.e., a "top entry/bottom discharge bottle") is selected for use in accordance with the invention, it is preferred that at least some, and preferably all, of the additive materials be added to the bottles before hot sponge iron is discharged from the RHF into the bottle, thereby sealing the bottom of the bottle, where air ingress is otherwise most likely to occur. In such an embodiment, the continued production of carbon monoxide by the sponge iron in the bottle will substantially prevent air from entering the bottle through the top opening in the short time the sponge iron resides in the bottle, as long as the top opening is sufficiently small (i.e., preferably no greater than about 1 meter in diameter). As an additional advantage of such a bottle configuration and process, when the additives are introduced into the substantially empty, heated bottle, the coke in the additive material will combust with oxygen present in the bottle, consuming the oxygen in the bottle and creating an advantageously inert atmosphere in the bottle prior to the introduction of the hot sponge iron thereinto. It is desirable to prevent air leakage in accordance with the invention because air promotes reoxidation of the hot sponge iron, causing bridges to form in the insulated container by "sintering" the sponge iron. Reoxidation of the sponge iron places an increased reduction burden on the SAF, and bridging makes difficult the discharge of sponge iron from the containers.

In a preferred embodiment, as shown in Figures 11 and 12, a container located at a first position 635 receives a charge of SAF fluxing agent, such as, for example, silica (SiO₂), lime (CaO) and/or bauxite (Al₂O₃), in advantageous amounts 42

and proportions, as described in detail above, and carbon-containing materials such as, for example, coke. The container is then moved by rotation of the platform 630 to a second position 640 where it receives a predetermined amount of DRI. The container is then moved by rotation of the platform to a third position 650, where the container may be sealed, for example, by placing a lid on the container, if required to prevent heat loss or ingress of air. It is readily understood by a skilled artisan that various modifications may be made to the above-described arrangement without departing from the spirit and scope of the invention. For example, where a bottle configuration makes desirable the addition of some or all of the SAF fluxing agents and coke on top of, rather than underneath, the hot sponge iron, a flux/coke bin and metering/conveyance system will be arranged to deliver the flux/coke charge while the bottle resides at position 650 rather than at position 635. This alternate configuration is preferred, for example, where a single-opening transport container is used and sponge iron is both fed into and discharged from the container through a top opening in the container. It is seen, therefore, that in various alternate aspects of the invention the additives may be introduced into a transport container before, during or after loading hot sponge iron into the container. In certain preferred aspects of the invention, coke is added to a container before introduction of sponge iron thereinto (i.e., beneath the sponge iron), and SAF fluxing agents are added to the container after the sponge iron (i.e, on top of the sponge iron).

Additional variations to the RHF discharge arrangement may include, for example, reversing the direction of the platform; using a platform having only two or, alternatively, having four or more positions for seating transport containers; and using two rotating platforms. For example, in certain aspects of the invention, a portion of the hot sponge iron on the hearth is discharged from the outer portion of the heart into containers positioned beneath the outer edge of the heart and the remaining sponge iron on the hearth is discharged from the inner portion of the hearth into containers positioned beneath the inner edge of the hearth. Therefore, 43

the present invention contemplates the use of two or more rotating platforms in such an arrangement.

A filled container is then transported to a submerged arc furnace 660, where the contents of the container are introduced into the SAF shell for subsequent introduction into the slag layer in the SAF 660. It is understood that, in the embodiment described in detail above, as a first bottle is moved to second position 650 on the rotatable platform 630, a second container is simultaneously moved by rotation of the platform 630 to position 640 to receive DRI. This process continues, and at position 650, a crane system picks up a filled container and delivers it to the SAF, where the contents of the container are discharged into SAF feed bins. Onto vacant positions on the platform 630 (i.e., those vacated by the transfer of a filled container to the SAF) the crane system places a substantially empty container whose contents have previously been charged into the SAF feed bins. Thus, a continuous process of DRI transport is provided, whereby the DRI is quickly transported to and introduced into one or more SAFs.

An advantageous feature of the invention is that the DRI may be transported to the SAF using an automated system, thereby reducing the operating costs associated with inventive processes. For example, DRI bottles are transported in one aspect of the invention using a crane system spanning the RHF, the SAF and the path therebetween. The crane system preferably includes multiple lifts and is thereby able to continuously move DRI-filled bottles from the platform 630 to one of a plurality of positions 670 above the SAF. While at these positions, the hot sponge iron is discharged from the container and into the SAF 660, or into a SAF feed system. It is understood that an automated system may alternatively feature skips on rails, such a system also exhibiting the advantageous features of the invention. Alternatively, where the SAF is oriented beneath the center of a RHF, it is readily understood that hot DRI falls directly into the SAF feed bins or SAF shell, thereby minimizing difficulties associated with material handling. 44

The amount of coke and/or SAF fluxing agents to be added to the containers, if any, will be dependent upon the composition of the DRI discharged from the RHF. As described above, a primary consideration in the selection of additives in accordance with the invention is that the overall slag-forming composition of the SAF charge must provide a SAF slag layer having the proper chemistry to feature a relatively low melting point, for example, preferably not greater than about 1500°C, in the SiO₂/Al₃O₂/Ca phase diagram 910, set forth in Figure 16. It is within the purview of a skilled artisan, armed with the present disclosure, to determine the composition of hot sponge iron discharged from the RHF, and to select amounts of SiO₂, Al₃O₂ and/or CaO which should be added to achieve an excellent slag composition. These materials advantageously mix with the DRI in the container as it is moved from the discharge zone of the rotary hearth furnace to the feed bins of the submerged arc furnace and as the contents are discharged from the container. As described above, a preferred manner of practicing the invention involves

RHF reduction of green balls which have a slag phase comprising a significant proportion of limestone and a minimal proportion of silica. It is therefore preferred that DRI produced from such green balls be mixed with an appropriate amount of silica to lower the melting temperature of the SAF slag phase to an appropriate point. Where the iron ore starting material comprises specular hematite, magnetic beneficiation of the ore in accordance with the invention produces a silica byproduct, which is an excellent source of silica for the SAF charge.

The SAF charge is preferably fed continuously to the SAF. There may be as many as six or more insulated feed bins situated above the SAF shell. Slag and metal temperatures are maintained by electrode energy input, and the slag layer preferably has a temperature gradient of from about 1500°C to about 1550°C at the metal interface to as cold as about 1400°C to about 1450°C at the top of the slag layer. The DRI drops onto previously fed DRI in the SAF reaction zone, where it sinks through gradually increasing temperature zones. As it reaches the higher 45

temperatures near the slag/metal interface, which is in the range of about 1450- 1550°C, a mixture or solution of iron and carbon melts within the DRI, and slag- forming materials are freed therefrom, then mixing with the additives to form the eutectic composition necessary to melt. Reduced metal, together with the desired amount of carbon, sinks to the liquid metal layer.

Slag is removed periodically through slag tap hole. Hot metal, typically at a temperature of about 1475°C to about 1525°C, is removed periodically through liquid metal tap hole in a conventional manner. Slag is preferably tapped at about 1500°C to about 1525°C and, therefore, must have a melting temperature below about 1500°C.

Slag tapped from the SAF is preferably transported to a slag processing center 680, where it is processed using industry-recognized processes. Additionally, hot metal is preferably removed from the SAF 660 into ladles 690, and is an excellent starting material for steel-making processes. Therefore, an inventive process is particularly advantageous when closely coupled to, for example, an EAF or BOF steel-making facility, so that the high temperatures of liquid iron made in accordance with the invention may be utilized, thereby reducing the operating cost of the steel -making facility by providing an excellent EAF or BOF feed material. In an alternate aspect of the invention, the ladle transports the molten iron to a caster, a metal granulation facility or a foundry facility where the liquid metal is solidified into various advantageous shapes and sizes.

Another important aspect of the invention is a system for recuperating heat from RHF off-gas. A significant inefficiency associated with prior art reduction processes is the large amount of heat that exits a rotary hearth furnace, and which is eventually released into the environment. The present invention, however, provides a heat recuperation system which overcomes this shortcoming of prior art processes and which greatly decreases the operating costs associated with the production of molten iron. A flow diagram illustrating an inventive system for 46

recovering heat from RHF off-gas is set forth in Figure 13, and a schematic diagram of an exemplary arrangement is depicted in Figure 14.

It is well known that RHF off-gas 700 typically comprises nitrogen (N₂), carbon dioxide (CO₂), carbon monoxide (CO), hydrogen (H₂) and water vapor (H₂O) and the temperature of this off-gas is typically from about 1200°C to about 1500°C. For example, in certain RHF reduction processes, off-gas samples have been found to comprise about 60.1% N₂, about 19.5% CO₂, about 6.6% CO, about 1.2%o H₂ and about 12.6% H₂O, all by volume. In accordance with the invention, the off-gas is preferably first passed through a cooler 710, such as a water-cooled duct, and an afterburner 720, to cool the gas to a temperature more suitable for handling using conventional equipment and to combust substantially all of the CO and the H₂ in the gas. A conventional water-cooled duct and afterburner may be used in accordance with the invention, these being known to a person skilled in the art, and in certain preferred aspects of the invention, a water-cooled duct and an afterburner are combined in one unit. The compositional make-up of gas exiting the water-cooled duct/afterburner has been found to comprise about 66.6% N₂, about 2.1% O₂, about 20.5% CO₂, 0% CO, 0% H₂ and about 10.8% H₂O, all by volume and to have a temperature of from about 1100°C to about 1400°C. The gas is then preferably passed through a second cooler 730, such as a spray cooler, and a de-NOx system 740. These are also well-known to a person skilled in the art and may be advantageously combined into one unit. After spray cooler/NOx treatment, the gas has been found to comprise about 57.9% N₂, about 1.9% O₂, about 17.8% CO₂, 0% CO, 0% H₂ and about 22.4% H₂O, all by volume and to have a temperature of from about 850°C to about 1050°C. While a preferred aspect of the invention is described as advantageously including a de-NOx system, such a system is not critical to the practice of the invention. Indeed, due to the reducing environment of the gas stream, it is believed that a de-NOx system may advantageously be omitted from inventive systems. It is also understood that the types and arrangements of coolers may be varied without 47

departing from the spirit and scope of the invention. The primary concern is that gases used for specific tasks be cooled to a point where they will not damage gas handling equipment and will not combust or volatize materials, such as, for example, coal, with which they come into contact. It is also critical that the gas pass through an afterburner to combust carbon monoxide (CO), thereby yielding an inert gas which may advantageously be used for drying coal and for drying carbonaceous green balls.

After spray cooler/NOx treatment, the gas is preferably passed through a gas- to-gas heat exchanger 750 where ambient air 760 is heated prior to being introduced into the RHF 600 as combustion air 770. The heated air 770 exiting the heat exchanger 750 preferably has a temperature of from about 350°C to about 550°C and is introduced into the RHF 600 in a manner well known to a person skilled in the art. It is understood that the heat exchanger 750 does not significantly affect the composition of the RHF off-gas, and the off-gas exiting the heat exchanger 750 has substantially the same compositional make-up as the gas entering the heat exchanger 750. The off-gas stream exiting the heat exchanger typically has a temperature of from about 500°C to about 800°C.

The RHF off-gas leaving the heat exchanger is then preferably separated into slip streams 780, 790, 810, which are advantageously used for various drying tasks in accordance with the invention. One slip stream 780 is preferably linked to an iron ore drier or drier/grinder 190, discussed above, where the high temperature gas is contacted with iron ore to dry the ore. A second slip stream 790 is preferably linked to the coal pulverizer/drier 800 and a third slip stream is preferably linked to the flux pulverizer/drier 810, discussed above. Conventional ore driers, ore drier/grinders, coal pulverizer/driers and flux pulverizer/driers contact heated air with the moist material to remover water therefrom. Air is typically heated by combusting, for example, natural gas in an air blower and passed through the drier or drier/grinder. In accordance with the invention, a slip stream is preferably used to replace or at least supplement the heated air by introducing the slip stream by 48

itself or in combination with the heated air into the drier. It is well within the purview of a person skilled in the art to select a gas-flow system which provides introduction of the slip stream into the ore drier, and which also provides the capability to supplement the slip stream with heated air as needed. It is understood that some slip streams will need to be cooled further, for example, prior to being contacted with coal. A gas temperature greater than about 270°C poses a risk of volatilizing the coal. Therefore, in a preferred aspect of the invention, a slip stream may be cooled by mixing back into the slip stream a quantity of "downstream gas," i.e., gas which has already passed through the coal pulverizer/drier and a baghouse and which, therefore, is likely to be cooler than the gas in the slip stream itself. In a preferred aspect of the invention, a gas stream used to dry coal has a temperature of from about 200° to about 270°C. It is understood that a slip stream used to dry an ore will not need to include this or other type of protection circuit because very hot gases (e.g., up to at least about 1000°C) may be used in an ore drier or drier/grinder. In a preferred aspect of the invention, a gas stream used to dry ore has a temperature of from about 550°C to about 950°C.

It is understood that the gas exiting the ore drier or drier/grinder 190, the coal pulverizer/drier 800 or the flux pulverizer/drier 820 will have a larger proportion of water vapor therein than the gas entering the drier. It has been found, for example, that the combined exiting gases comprise about 48% N₂, about 2% O₂, about 15% CO₂, 0% CO, 0% H₂ and about 36% H₂O, all by volume. Additionally, the temperature of the gas exiting these driers is typically between about 120°C and about 250°C. Upon exiting the driers, the slip streams are preferably recombined and also, in certain aspects of the invention, recombined with a gas fraction 815 which has bypassed the gas-to-gas heat exchanger and/or the ore, coal and/or flux driers. It is understood that gas streams exiting, for example, the iron ore drier or the coal drier are preferably passed through baghouses 830 in the ore drier, coal or 49

flux pulverizer/drier circuits, before being recombined with other streams or before utilizing them for subsequent heat recuperation.

The recombined gas stream 840 is then preferably temperature adjusted by a secondary cooler 845, such as, for example, a spray cooler, prior to being directed to the green ball drier 580. The maximum temperature of a gas used to dry green balls is also about 270°C; therefore, the secondary cooler preferably cools the gas to no greater than about 270°C, more preferably to a temperature of from about 170°C to about 270°C. In the green ball drier 580, heat in the relatively inert gas is used to removed moisture from the uniformly sized moist green balls recovered from the roll screen 520, described above, before the balls are introduced onto the RHF 600. It is understood that the gas may also advantageously pre-heat the green balls, which will further improve the thermal efficiency of an inventive process. The green ball drier 580 inlet gas has been found to comprise about 44% N₂, about 2% O₂, about 14% CO₂, 0% CO, 0% H₂ and about 41% H₂O, all by volume. Gas exiting the green ball drier 580 has been found to comprise about 42% N₂, about 1% O₂, about 13% CO₂, 0% CO, 0% H₂ and about 44% H₂O, all by volume. These gas compositions are particularly well suited for drying carbonaceous green balls without the risk of oxidation, volatilization or explosion of the carbonaceous material in the green balls. The gas entering the green ball drier 580 preferably has a temperature of from about 170°C to about 270°C and the gas exiting the green ball drier 580 preferably has a temperature of from about 150°C to about 200°C. The gas exiting the green ball drier is then preferably passed through a de- dusting device 850, such as, for example, a scrubber or a baghouse, preferably a reverse air type baghouse. After exiting the de-dusting device, the gas is preferably passed through a de-SOx system 860, wherein the gas is contacted with, for example, hydrated lime or magnesium. The gas may then be advantageously released into the environment, for example, through a stack 870, without the release of significant amounts of heat. It is understood that an inventive gas transport system also preferably comprises emergency pressure release valves, bypass 50

circuits and other back-up gas cleaning and gas handling equipment. Such features are not shown in the Figures, but are well within the purview of a skilled artisan.

It may be desired in certain preferred aspects of the invention to provide devices for enhancing gas flow, such as, for example, booster fans, in the gas flow circuit. These devices may preferably be placed, for example, before the green ball drier. It is understood that the flow of gas through an inventive system may be achieved primarily using one or more induced draft fans positioned near the stack (i.e., preferably between the baghouse 850 and the stack 870), which fan or fans pull gas through the system. Improved gas flow may be achieved in an inventive system, for example, by placing a booster fan between the secondary spray cooler and the green ball drier. It is understood that placement of one or more booster fans at alternate locations in the gas circuit is expected to provide a similarly advantageous result.

In another aspect of the invention, there are provided processes for utilizing SAF off-gas, as depicted schematically in Figure 15. SAF off-gas carries thermal and chemical energy, the chemical energy resulting from the high carbon monoxide content of the SAF off-gas.

Gas exiting the SAF, which typically comprises at least about 80% carbon monoxide (CO) by volume, commonly at least about 90% CO by volume, is preferably cooled and cleaned in accordance with the invention. Cooling and cleaning may advantageously be achieved using devices known in the art, including, for example, direct coolers (such as, for example, scrubbers) and indirect coolers (such as, for example, water cooled ducts). In a preferred aspect of the invention, the gas is first passed through a water-cooled duct 880. Heat may be advantageously recovered in the water cooled duct 880 to improve the thermal efficiency of the inventive process, for example, by utilizing the heated water for heating applications. The gas is then preferably passed through a direct cooler such as an evaporative cooler/scrubber 890. Examples of evaporative cooler/scrubbers include venturi scrubbers and quench Venturis. The gas then has a temperature and 51

purity suitable for storage and/or introduction to a mixing station 900 using equipment generally understood in the relevant field.

In the mixing station 900, the high CO content gas is mixed with natural gas to provide a supplemental fuel source. The mixture may preferably be used as a substitute for pure natural gas, thereby utilizing a by-product of inventive processes and reducing the amount of waste which results from prior art processes. For example, as described above, if various drying tasks in accordance with the invention require supplementation with heated air, the air may be heated by the combustion of natural gas or a natural gas/carbon monoxide mixture provided in the mixing station. Alternately, the mixture may advantageously be used as fuel in, for example, space heaters and/or ladle preheaters used in inventive or other processes. A portion of the natural gas/carbon monoxide gas mixture exiting the mixing station may also be combusted in the RHF to participate in the generation of reducing conditions (i.e., high temperature and reducing gases) in the RHF. Utilization of SAF off-gas as described provides an additional increase in the overall efficiency of inventive processes, and decreases the raw material costs associated with prior art processes.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.

Claims

52 What is claimed is:

1. A method for reducing an iron oxide, comprising: providing a first iron ore composition; grinding the first iron ore in a high pressure roll press to provide a second ground and microfractured iron ore; intimately contacting the second iron ore and a particulate carbonaceous reductant to provide a furnace charge; and subjecting the furnace charge to reducing conditions in a rotary hearth furnace to provide a hot sponge iron.

2. The method according to claim 1, further comprising, after said grinding and prior to said contacting: recycling a portion of the second ore through the roll press to provide a particulate fraction comprising at least about 30% minus 200 mesh;

3. The method according to claim 1, wherein said contacting comprises: mixing the second iron ore, a particulate carbonaceous reductant and a binder material to provide a mixture; and forming the mixture into a plurality of green balls having a size of from about inch to about 2 ^lA inches.

4. The method according to claim 3, further comprising drying the green balls.

5. The method according to claim 3, wherein the mixture further comprises a RHF fluxing agent. 53

6. The method according to claim 5, wherein the RHF fluxing agent is selected from the group consisting of caustic lime, caustic dolomitic lime, limestone, dolomitic limestone, hydrated lime, hydrated dolomitic lime and mixtures thereof.

7. The method according to claim 1 , further comprising: introducing the sponge iron into a submerged arc furnace; wherein fewer than about 60 minutes elapse between the time the sponge iron is discharged from the rotary hearth furnace and the time the sponge iron is introduced into the submerged arc furnace.

8. The method in accordance with claim 7, wherein said introducing comprises: providing an insulated container, the container defining an internal volume of at least about 10 cubic meters; providing a submerged arc furnace charge in the container by charging into the container a SAF fluxing agent and discharging hot sponge iron from the rotary hearth furnace into the container; and introducing the submerged arc furnace charge into a submerged arc furnace.

9. The method in accordance with claim 8, wherein the submerged arc furnace charge comprises from about 0 to about 8% lime, from about 0 to about 5% MgO, from about 0 to about 5% coke, from about 0 to about 5% Al₂O₃ and from about 0 to about 8% SiO₂;

10. The method according to claim 7, wherein the submerged arc furnace produces, as a byproduct, an off-gas, and wherein the method further comprises: 54

recovering off-gas from the submerged arc furnace; and mixing the off-gas with natural gas to provide a high-quality fuel source; wherein the off-gas comprises at least about 80% carbon monoxide by volume.

11. The method according to claim 10, wherein the off-gas comprises at least about 90% carbon monoxide by volume.

12. The method according to claim 1 , wherein the particulate carbonaceous reductant comprises a member selected from the group consisting of coal, coke, coke braize, pet coke, graphite and char.

13. The method according to claim 1 , wherein the particulate iron oxide composition comprises a member selected from the group consisting of virgin iron ore, such as hematite iron ore fines, ground lump ores, iron oxide pellet fines, hematite iron ore, specular hematite concentrate, earthy hematite, magnetite iron ore, magnetite concentrate, limonite, limonite concentrate, ilmenite, ilmenite concentrate, taconite concentrate, semi-taconite concentrate, pyrolusite and pyrolusite concentrate; and steel mill waste oxides such as mill scale, EAF dust and drop out dust.

14. The method according to claim 1 wherein said subjecting comprises exposing the green balls to a temperature of between about 1000°C and about 1500°C for between about 3 minutes and about 30 minutes.

15. The method according to claim 1 , wherein at least about 70% of iron in the sponge iron is in metallic form. 55

16. The method according to claim 1, wherein at least about 80% of iron in the sponge iron is in metallic form.

17. The method according to claim 1 , wherein at least about 90% of iron in the sponge iron is in metallic form.

18. The method according to claim 1 , wherein the dry weight ratio in the furnace charge of fixed carbon in the reductant to iron in the iron oxide composition is from about 4.0:10 to about 2.4:10.

19. The method according to claim 1 , wherein the dry weight ratio in the furnace charge of fixed carbon in the reductant to iron in the iron oxide composition is from about 3.4:10 to about 3.0:10.

20. The method according to claim 1 , wherein the furnace charge further comprises a fluxing agent selected from the group consisting of caustic lime, caustic dolomitic lime, limestone, dolomitic limestone, hydrated lime, hydrated dolomitic lime and mixtures thereof.

21. The method according to claim 1 , wherein the reducing conditions are provided in part by firing a gas comprising a member selected from the group consisting of natural gas, carbon monoxide gas recovered from a submerged arc furnace and combinations thereof.

22. The method according to claim 1, wherein the first iron ore is a purified iron ore provided by a method comprising: providing an impure iron ore composition having a moisture content of less than about 0.5% by weight; and 56

beneficiating the impure iron ore composition with respect to iron content to provide a purified iron ore composition having an iron content of at least about 67% by weight, on a dry weight basis.

23. The method according to claim 22, wherein said beneficiating comprises: passing the substantially dry iron ore through a magnetic field having a field strength of from about 500 gauss to about 1500 gauss to provide a first magnetic fraction and a first nonmagnetic fraction; passing the first nonmagnetic fraction through a magnetic field having a field strength of from about 6000 gauss to about 8000 gauss to provide a second magnetic fraction and a second nonmagnetic fraction; and combining the first magnetic fraction and the second magnetic fraction to provide a purified iron ore composition.

24. A method for reducing an iron ore, comprising: passing an iron ore composition through an ore drier or an ore drier/grinder to provide a dried iron ore comprising less than about 0.5% water by weight; intimately contacting the iron ore and a carbonaceous reductant to provide a furnace charge; and subjecting the furnace charge to reducing conditions in a rotary hearth furnace to provide a hot sponge iron; wherein the iron ore composition is dried by contacting the composition with a gaseous slip stream comprising hot off-gas from the rotary hearth furnace.

25. The method in accordance with claim 24, further comprising, before said contacting, beneficiating the dried iron ore. 57

26. The method in accordance with claim 24, wherein the drier is a rotary drier.

27. The method in accordance with claim 24, wherein the drier/grinder is a ball mill.

28. The method in accordance with claim 24, wherein the gaseous slip stream further comprises air heated by firing a gas comprising a member selected from the group consisting of natural gas, carbon monoxide gas recovered from a submerged arc furnace and combinations thereof.

29. The method in accordance with claim 24, wherein the gaseous stream has a temperature of from about 550°C to about 950°C.

30. A method for reducing an iron oxide, comprising: passing a carbonaceous reductant composition through a pulverizer/drier to provide a particulate carbonaceous reductant comprising less than about 0.5 % water by weight; intimately contacting the particulate carbonaceous reductant and a particulate iron ore composition to provide a furnace charge; and subjecting the furnace charge to reducing conditions in a rotary hearth furnace to provide a hot sponge iron; wherein a gaseous slip stream comprising a portion of the hot off- gas from the rotary hearth furnace is contacted with the carbonaceous reductant in the pulverizer/drier.

31. The method according to claim 30, wherein the reducing conditions are provided in part by firing a gas comprising a member selected from the group 58

consisting of natural gas, carbon monoxide gas recovered from a submerged arc furnace and combinations thereof.

32. The method according to claim 30, wherein the gaseous slip stream further comprises air heated by firing a gas comprising a member selected from the group consisting of natural gas, carbon monoxide gas recovered from a submerged arc furnace and combinations thereof.

33. The method in accordance with claim 30, wherein the gaseous stream has a temperature of from about 170° to about 270°C.

34. A method for reducing an iron oxide, comprising: providing a moist mixture of a particulate iron oxide composition, a particulate carbonaceous reductant and a binding agent; forming the mixture into moist green balls; drying the moist green balls by passing the green balls through a drier to produce dried green balls having a water content of less than about 0.5% by weight; positioning the dried green balls onto a rotary hearth furnace; and subjecting the dried green balls to reducing conditions to reduce a substantial portion of the iron oxide, thereby producing hot sponge iron; wherein said drying comprises contacting the moist green balls with a gaseous slip stream comprising hot off-gas from the rotary hearth furnace.

35. The method in accordance with claim 34, wherein the gaseous slip stream further comprises air heated by firing a gas comprising a member selected from the group consisting of natural gas, carbon monoxide gas recovered from a submerged arc furnace and combinations thereof. 59

36. The method in accordance with claim 34, wherein the gaseous stream has a temperature of from about 170°C to about 270°C.

37. A method for utilizing sensible heat in a rotary hearth furnace off- gas, comprising: recovering off-gas from a rotary hearth furnace to provide a first gaseous stream, the first gaseous stream having a temperature of at least about 1200°C, and comprising N₂, H₂, CO₂, CO and H₂O; passing the first gaseous stream through a first cooler to reduce the temperature of the first stream to between about 900°C and about 1100°C; passing the first gaseous stream through an afterburner to combust the CO and the H₂, thereby providing a second gaseous stream having a temperature of from about 1100°C to about 1400°C and comprising N₂, O₂, CO₂ and H₂O; passing the second stream through a second cooler to cool the gas to a temperature of from about 800°C to about 1000°C; passing the second stream through a first chamber of a gas-to-gas heat exchanger to heat ambient air passing through a second chamber of the heat exchanger; contacting a first portion of the second stream with an iron ore in an iron ore drier or an iron ore drier/grinder; contacting a second portion of the second stream with a carbonaceous reductant in a reductant pulverizer/drier; contacting a third portion of the second stream with a fluxing agent in a fluxing agent pulverizer/drier; combining the first portion, the second portion and the third portion to provide a third gaseous stream; and contacting the third stream with green balls in a green ball drier. 60

38. The method in accordance with claim 37, wherein the first cooler is a water cooled duct.

39. The method in accordance with claim 37, wherein the second cooler is a spray cooler.

40. A method for utilizing sensible heat in a rotary hearth furnace off- gas, comprising: recovering off-gas from a rotary hearth furnace to provide a gaseous stream having a temperature of at least about 1000°C and comprising N₂,

H₂, CO₂, CO and H₂O; and recuperating heat from the off-gas.

41. The method according to claim 40, wherein said recuperating comprises contacting the gaseous stream with green balls in a green ball drier.

42. The method according to claim 40, wherein said recuperating comprises contacting a portion of the gaseous stream with an iron ore in an iron ore drier or iron ore drier/grinder.

43. The method according to claim 40, wherein said recuperating comprises contacting a portion of the second stream with a carbonaceous reductant in a reductant drier or pulverizer/drier.

44. The method according to claim 40, wherein said recuperating comprises contacting a portion of the second stream with a fluxstone in a fluxstone drier or pulverizer/drier. 61

45. A method for utilizing off-gas from a submerged arc furnace, comprising: recovering off-gas from a submerged arc furnace to provide a first gaseous stream having a temperature of at least about 1000°C, and comprising at least about 80% carbon monoxide by volume; cooling the gas; cleaning the gas; and mixing the off-gas with natural gas to provide a gaseous fuel.

46. The method in accordance with claim 45, wherein said cooling and cleaning comprise: passing the off-gas through an indirect cooler, thereby cooling the off-gas to a temperature of from about 900°C to about 1100°C; and passing the off-gas through an evaporative cooler/scrubber to provide a gas having a temperature of from about 40°C to about 150°C.

47. The method in accordance with claim 46, wherein the evaporative cooler/scrubber comprises a device selected from the group consisting of a quench venturi and venturi scrubber.

48. The method in accordance with claim 45, wherein the cooler is a water cooled duct.

49. A method for making molten iron, comprising: preparing a furnace charge for direct reduction thereof in a rotary hearth furnace to sponge iron, the furnace charge comprising an iron ore, a reductant and a RHF fluxing agent, wherein the RHF fluxing agent, together with gangue materials in the iron ore and the reductant, comprise a first 62

slag-forming composition having a melting point higher than the pellet temperature reached in the rotary hearth furnace; reducing the furnace charge in the rotary hearth furnace to provide sponge iron; and feeding the sponge iron and a SAF fluxing agent into a submerged arc furnace to form molten iron and liquid slag; wherein the liquid slag comprises a combination of the first slag- forming composition and the SAF fluxing agent; and wherein the liquid slag has a melting temperature at least 50°C lower than the melting temperature of the first slag-forming composition.

50. The method according to claim 49, wherein the RHF fluxing agent comprises a member selected from the group consisting of caustic lime, caustic dolomitic lime, limestone, dolomitic limestone, hydrated lime, hydrated dolomitic lime and mixtures thereof.

51. The method according to claim 49, wherein the SAF fluxing agent comprises a member selected from the group consisting of silica, aluminum oxide, caustic lime, caustic dolomitic lime, limestone, dolomitic limestone, hydrated lime, hydrated dolomitic lime and mixtures thereof.

52. The method according to claim 49, wherein said feeding further comprises introducing coke into the submerged arc furnace.

53. The method according to claim 49, wherein the liquid slag has a melting temperature lower than the melting temperature of the first slag-forming composition. 63

54. The method according to claim 49, wherein the liquid slag has a melting temperature at least 25°C lower than the melting temperature of the first slag-forming composition.

55. The method according to claim 49, wherein the liquid slag has a melting temperature at least 50°C lower than the melting temperature of the first slag-forming composition.

56. The method according to claim 49, wherein the liquid slag has a melting temperature at least 100°C lower than the melting temperature of the first slag-forming composition.

57. The method according to claim 49, wherein the liquid slag has a melting temperature of at least 150°C lower than the melting temperature of the first slag-forming composition.

58. A method for making molten iron, comprising: providing a mixture comprising (1) a SAF fluxing agent and (2) a sponge iron comprising from about 75% to about 85% elemental iron by weight and a first slag-forming composition having a first melting temperature; and feeding the mixture into a submerged arc furnace wherein the mixture melts and further reacts to form molten iron and liquid slag; wherein the liquid slag has a melting temperature less than the first melting temperature.

59. The method in accordance with claim 58, wherein the sponge iron comprises from about 5% to about 15% by weight of the first slag-forming composition. 64

60. An apparatus for making molten iron, comprising: a roll press for grinding and conditioning an iron ore; a mixer for receiving and mixing a carbonaceous reductant and the output from said roll press to provide a rotary hearth furnace charge; a rotary hearth furnace for receiving the charge and converting the charge to hot sponge iron; and a submerged arc furnace for receiving the hot sponge iron and converting the hot sponge iron to molten iron and slag.

61. The apparatus of claim 60, further comprising an automated transport system for moving hot sponge iron to said submerged arc furnace.

62. The apparatus of claim 60, further comprising a transport system for moving the hot sponge iron to said submerged arc furnace; wherein the time period elapsing between the time the hot sponge iron exits the rotary hearth furnace and the time the hot sponge iron is introduced into the submerged arc furnace is less than about 60 minutes.

63. The apparatus of claim 62, wherein the said conveyance system comprises: a plurality of insulated bottles for receiving the hot sponge iron; and a crane system for moving the insulated bottles between the rotary hearth furnace and the submerged arc furnace.

64. The apparatus of claim 62, wherein the said conveyance system comprises: a rail for guiding a plurality of skips between the rotary hearth furnace and the submerged arc furnace; and 65

a plurality of skips for receiving the hot sponge iron and moving the sponge iron to the submerged arc furnace.

65. An apparatus for continuously utilizing off-gas recovered from a rotary hearth furnace, comprising: a first cooler in fluid communication with a reduction chamber of a rotary hearth furnace and configured to receive off-gas recovered from the rotary hearth furnace; an afterburner in fluid communication with the first cooler for combusting carbon monoxide and hydrogen in the off-gas; a second cooler in fluid communication with the afterburner, for cooling the gas to a temperature of from about 900°C to about 1000°C; a plurality of first conduits in fluid communication with the second cooler for passing a plurality of slip streams to one or more devices selected from the group consisting of an ore drier, an ore drier/grinder, a coal drier, a coal pulverizer/drier, a flux drier, a fluxstone pulverizer/drier and a secondary spray cooler; a second conduit in fluid communication with the plurality of first conduits for receiving the slip streams and introducing the off-gas into a green ball drier; a third conduit in fluid communication with the green ball drier for receiving the gas from the green ball drier; and a de-SOx system in fluid communication with the third conduit.

66. The apparatus in accordance with claim 65, wherein said first cooler is a water-cooled duct.

67. The apparatus in accordance with claim 65, wherein said second cooler is a spray cooler. 66

68. The apparatus in accordance with claim 65, wherein the first cooler and the afterburner comprise a single unit.

69. The apparatus in accordance with claim 65, wherein the second cooler further comprises a de-NOx system.

70. An apparatus for continuously utilizing off-gas recovered from a rotary hearth furnace, comprising: a cooler in fluid communication with a reduction chamber of a rotary hearth furnace and configured to receive off-gas recovered from the rotary hearth furnace and to cool the gas; an afterburner in fluid communication with the water cooled duct for combusting carbon monoxide and hydrogen in the off-gas; a heat exchanger for transferring heat from the off-gas to ambient air; a plurality of conduits in fluid communication with the heat exchanger for passing a plurality of slip streams to one or more devices selected from the group consisting of an ore drier, an ore drier/grinder, a coal drier, a coal pulverizer/drier, a flux drier, a fluxstone pulverizer/drier and a secondary spray cooler; and a plurality of de-dusting devices in fluid communication with the conduits for recovering dust particles entrained in the slip streams.

71. The apparatus in accordance with claim 70, wherein the de-dusting devices comprise baghouses.

72. The apparatus in accordance with claim 70, wherein the cooler is a water cooled duct. 67

73. The apparatus in accordance with claim 70, further comprising a conduit in fluid communication with the cooler and the afterburner for introducing the off-gas into a green ball drier.

74. An apparatus for continuously utilizing off-gas recovered from a submerged arc furnace, comprising: a system for cooling and cleaning the off-gas; and a device, in fluid communication with the system, for mixing the off gas with a natural gas to provide a gaseous fuel.

75. The apparatus according to claim 74, wherein the system comprises one or a plurality of devices selected from the group consisting of a water-cooled duct, a spray cooler, a quench venturi and a venturi scrubber.

76. A method for producing molten iron, comprising: preparing a furnace charge comprising an iron ore and a solid carbonaceous reductant; reducing the furnace charge in a rotary hearth furnace to provide sponge iron; and discharging the sponge iron from the rotary hearth furnace into a submerged arc furnace oriented below the rotary hearth furnace.

77. The method in accordance with claim 76, wherein the center of the submerged arc furnace is substantially directly below the center of the rotary hearth furnace. 68

78. The method in accordance with claim 76, wherein the rotary hearth furnace comprises a plurality of feed zones, a plurality of reduction zones and a plurality of discharge zones.

79. An apparatus for producing molten metal, comprising: a rotary hearth furnace; and a submerged arc furnace positioned below the rotary hearth furnace.

80. The apparatus according to claim 79, wherein the rotary hearth furnace comprises a plurality of feed zones, a plurality of reduction zones and a plurality of discharge zones.

81. A rotary hearth furnace comprising a plurality of feed zones, a plurality of reduction zones and a plurality of discharge zones.

82. The furnace in accordance with claim 81, the furnace comprising: a first feed zone for introducing a first furnace charge onto a circular hearth of the furnace; a first reduction zone substantially adjacent the first feed zone for reducing the first furnace charge, thereby producing a first sponge iron; a first discharge zone substantially adjacent the first reduction zone for discharging the first sponge iron from the hearth; a second feed zone substantially adjacent the first discharge zone for introducing a second furnace charge onto the hearth; a second reduction zone substantially adjacent the second feed zone for reducing the second furnace charge, thereby producing a second sponge iron; and a second discharge zone substantially adjacent the second reduction zone for discharging the second sponge iron from the hearth. 69

83. The furnace in accordance with claim 82, wherein the second discharge zone is substantially adjacent the first feed zone.

84. The furnace in accordance with claim 82, further comprising: a third feed zone substantially adjacent the second discharge zone for introducing a third furnace charge onto the hearth; a third reduction zone substantially adjacent the third feed zone for reducing the third furnace charge, thereby producing a third sponge iron; and a third discharge zone substantially adjacent the third reduction zone for discharging the third sponge iron from the hearth.

85. The furnace in accordance with claim 84, wherein the third discharge zone is substantially adjacent the first feed zone.

86. A method for reducing an iron oxide, comprising: providing a rotary hearth furnace charge comprising an iron oxide, a solid carbonaceous reductant and a member selected from the group consisting of limestone and dolomitic limestone; and subjecting the furnace charge to reducing conditions in a rotary hearth furnace to provide sponge iron.

87. The method according to claim 86, further comprising introducing the sponge iron into a submerged arc furnace to melt and further reduce the sponge iron, thereby producing liquid metal and a fluid slag.

88. A method for preparing a rotary hearth furnace charge, comprising: 70

providing a plurality of moist green balls comprising an iron oxide, a solid carbonaceous reductant and a binder; contacting the moist green balls with a powdered RHF fluxing agent to provide a plurality of dusted green balls; and passing the dusted green balls through a green ball drier to provide a rotary hearth furnace charge.

89. The method according to claim 88, further comprising reducing the charge to provide sponge iron.

90. The method according to claim 88, wherein the RHF fluxing agent is selected from the group consisting of caustic lime, caustic dolomitic lime, limestone, dolomitic limestone, hydrated lime, hydrated dolomitic lime and mixtures thereof.