WO1998059079A1

WO1998059079A1 - Low sulfur iron reduction process using a rotary hearth furnace

Info

Publication number: WO1998059079A1
Application number: PCT/US1998/012347
Authority: WO
Inventors: Larry J. Lehtinen
Original assignee: Iron Dynamics Inc
Current assignee: Iron Dynamics Inc
Priority date: 1997-06-20
Filing date: 1998-06-17
Publication date: 1998-12-30
Anticipated expiration: 1999-12-20
Also published as: AU8143398A

Abstract

The present invention provides methods for producing direct reduced iron having a low sulfur content in a continuous and efficient fashion, and features in one preferred aspect provided agglomerates of an iron oxide composition and an internal carbonaceous reductant composition having a relatively low sulfur content; positioning the agglomerates onto a rotary hearth furnace (1) in intimate contact with a particulate matrix comprising an external carbonaceous reductant; subjecting the mixture to reducing conditions to reduce a substantial portion of the iron oxide thereby producing sponge iron and a sulfur-containing ash byproduct; discharging the sponge iron and ash byproduct from the rotary hearth furnace (1); and beneficiating the sponge iron to separate it from the high sulfur ash byproduct, thereby yielding a purified sponge iron product.

Description

LOW SULFUR IRON REDUCTION PROCESS USING A ROTARY HEARTH FURNACE

BACKGROUND OF THE INVENTION

Field of the Invention The present invention relates to the direct reduction of iron oxides to elemental iron. More specifically, it relates to direct iron reduction processes utilizing solid carbon reducing agents and a rotary hearth furnace to achieve continuous direct iron reduction. Discussion of Related Art Skilled artisans in the field of refining iron are increasingly recognizing direct reduction, which involves a chemical reduction reaction at a temperature below the melting temperature of the materials present, as a useful method of converting iron oxides, such as, for example, iron ore, into elemental iron. The two general categories of direct reduction are (1) those that utilize natural gas as the source of reducing gases, and (2) those that utilize solid carbonaceous materials such as coal as the source of reducing gases (i.e. solid-based direct iron reduction processes).

While solid-based direct iron reduction is presently being given a great deal of attention as a potentially useful reduction process, it is hindered by several problems. Perhaps the greatest problem is the presence of relatively large amounts of sulfur and ash in suitable solid carbonaceous materials, and the resulting high sulfur and ash content of the direct reduced iron produced in such processes. For example, a preferred carbonaceous reductant, coal, commonly includes about 0.1-4% sulfur by weight and about 1-15% ash by weight as contaminants. For many uses of DRI produced using known carbonaceous direct reduction processes, the sulfur and ash must be removed from the liquid metallic iron in very costly downstream processing steps. The DRI product of prior art direct reduction processes, for instance, commonly includes therein about 5-50 times more sulfur than that which may be present in iron used for making steel. This presence of sulfur and gangue in DRI product is a major shortcoming of solid-based direct reduction processes in the prior art. The present invention addresses this problem by providing advantageous processes for achieving continuous direct iron reduction using low cost solid carbon reducing agents and a rotary hearth furnace to produce sponge iron having a relatively low sulfur and ash or gangue content. Of all direct reduced iron ("DRI") currently being produced, at least 90% worldwide is produced using natural gas-based processes rather than solid carbon- based processes. These processes which utilize natural gas as the reductant, although they produce DRI of relatively low sulfur and gangue content, typically involve expensive oxide pellets or lump ore as feed stock. It is believed that the only DRI currently being produced in any significant amount using solid-based processes is produced by the SL/RN or GRATECAR processes, which use oxide pellets or lump ore together with sized coal as the furnace charge material. In these processes, because there is no admixing of ground iron ore particles with a finely-divided particulate solid reductant, the resulting DRI is of purity similar to DRI from gas based processes. In the SL/RN process large coal and ore lumps or pellets (typically having sizes of about 1/8 inch to about 2 inches) are fed into a rotary kiln furnace, and the reduction reaction proceeds very slowly, commonly requiring kiln residence times of over 12 hours. Consequently, for a large kiln with associated equipment and high capital cost, although the resulting DRI is similar in sulfur and gangue content to DRI produced by gas based processes, the equipment only produces about 50,000 to about 150,000 tons of DRI product per year. Because of the high capital cost per ton of annual production capacity and the relatively low production rate caused by the long residence times, the SL/RN or GRATECAR processes are not cost competitive with more productive coal and gas based process. Three alternative processes for DRI production using coal as the reductant are currently under development which utilize a rotary hearth furnace. In these rotary hearth processes 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 first formed into spherical agglomerates called green balls or into briquettes. One such process, termed the "FASTMET" process herein, involves producing relatively large green balls (nominally 20mm in diameter) of iron oxide and coal, and utilizes a thermal drier prior to introduction of the balls onto a rotary hearth furnace. The second process, termed the "INMETCO" process herein, is similar to the FASTMET process, but utilizes smaller green balls (nominally 10 mm in diameter) , and does not use a green ball drier. Instead, the green balls are fed "wet" directly onto the rotary hearth furnace. The third process, termed the "MAUMEE" process herein, is similar to the INMETCO process, but utilizes wet or dry briquettes formed under high pressure without binder material. The MAUMEE process uses very expensive briquetting machines to form briquettes that, depending upon the starting material, may or may not achieve briquettes strong enough to withstand handling steps onto the hearth of a rotary hearth furnace.

A major problem associated with each of these processes, however, is that solid carbonaceous reductants containing high levels of sulfur and ash or gangue are tightly bound to the iron oxide. When these reductants are tightly bound to the iron oxides and subsequently reduced, therefore, the sulfur and ash remain tightly bound in the DRI product producing a DRI product of inferior quality and of less attractiveness to the iron and steel-making customers. For this reason, a major focus of developmental work in the field of carbonaceous direct reduction of iron is directed to the development of processes for the production of DRI having an acceptable level of sulfur and gangue therein.

An additional problem associated with these direct reduction processes currently known is that a large quantity of expensive binders typically is required in order to hold the agglomerates together during handling and furnacing thereof. In this regard, both the FASTMET process and the INMETCO process, as well as other similar processes, have the inherent problem of requiring large dosages of binders. The binders are required in such large proportions in order to make a wet or dry agglomerate of adequate strength and durability to avoid breakage during handling ahead of the drier or rotary hearth furnace, and to avoid exfoliation or explosion in the case of the INMETCO process where wet balls are introduced directly onto the hot hearth of the rotary hearth furnace.

These agglomerates, typically green balls but in some processes briquettes, are charged into a rotary hearth furnace, where the iron ore in the agglomerate is reduces to yield " sponge iron." The term "sponge iron" refers to the product of a direct reduction process and is used interchangeably herein with the term "DRI". The sponge iron, which is still in agglomerate form, is then optionally densified by briquetting, transported, melted and treated to extract the reduced elemental iron from contaminants such as sulfur, ash, silica, or slag which are tightly bound to the elemental iron in the sponge iron product.

All three processes discussed above, the FASTMET process, the INMETCO process and the MAUMEE process are accompanied by large capital and operating costs, associated in part with necessity of large quantities of binder materials and/or expensive agglomerating equipment. For example, the balling or briquetting steps require large capital costs due to the need for large quantities of binders to form balls or due to the high consumable cost associated with the wear of dies in the briquette machine. Further all these processes produce DRI with ash and sulfur content that in some instances make the product unacceptable to some steel-making customers and in other cases result in substantial cost penalties to the users of the high sulfur, high gangue DRI.

In the INMETCO process, described above, moist pellets are placed directly into a rotary hearth furnace; however, in this type of process, a precautionary measure which has been proposed to avoid green ball explosion upon rapid heat-up and expulsion of water from the green balls, is to use a relatively large dosage of one or more binders to make up the green balls. This method, however, requires a binder dosage that can be up to 200 times higher than the binder dosage required if a drier is employed in the process. Consequently, the high binder dosage becomes a very significant operating cost of the INMETCO process. Overall, the binders required for the INMETCO process, typically account for about 5 to about 20% of the total production costs for the direct reduction process.

The present invention overcomes the aforementioned problems of high levels of sulfur and ash contamination in the DRI product and the need for large quantities of binders in the formation of green balls by teaching a process for achieving direct reduction of iron which minimizes the sulfur and ash that are allowed into the agglomerate and also minimizes the binder needed in the agglomerate. The present invention overcomes these hurdles by providing a solid-based direct reduction process which involves the use of relatively small green balls comprising an iron oxide tightly bound to an internal low-sulfur, reductant, that supplies only part of the carbon required for the reduction of the iron oxide. These green balls are placed on the hearth of a rotary hearth furnace in intimate contact with a matrix comprising an external solid carbon reductant typically of lower cost and quality than the internal reductant, and preferably also one or more de-sulfurizing agents. The external reductant preferably supplies more than 10% of the carbon required for iron oxide reduction, more preferably in excess of 25% of the required carbon, more preferably in excess of 50% and most preferably more than 67% of the required carbon. The optimal amount of carbon for reduction that is supplied via external carbon would depend on the relative economics of the two sources of carbon as well as the productivity that is sacrificed as more carbon is supplied externally, and the cost penalties associated with de-sulfurizing and melting the gangue in the DRI by the end user.

SUMMARY

To overcome problems in the prior art relating to the low purity of DRI product produced and the high costs associated with forming and reducing iron ore agglomerates, the present invention provides methods for achieving direct reduction of iron by providing a relatively small agglomerate comprising an iron oxide composition and an internal carbonaceous reductant; placing the agglomerate in intimate contact with a matrix comprising an external carbonaceous reductant and, optionally, one or more de-sulfurizing agents to make a furnace charge; and introducing this furnace charge into a rotary hearth furnace for direct reduction. After reduction of this charge, metallic iron is present in the agglomerated sponge iron and a significant amount of ash and sulfur contaminants are present as a byproduct exterior to the sponge iron agglomerates. Therefore, the agglomerated sponge iron is readily beneficiated to yield a relatively pure DRI product having a sulfur content as low as about 0.01% by weight. According to a preferred aspect of the invention, direct reduction is achieved in a continuous fashion by providing relatively small green balls (preferably less than 12mm in diameter, more preferably less than 10mm and most preferably less than 5mm in diameter) comprising iron oxide and an internal, preferably low-sulfur, low- ash, finely ground reductant, and placing the green balls in intimate contact with a matrix comprising an external carbonaceous reductant in relatively coarse form to provide a furnace charge. The reduction of the furnace charge produces sponge iron which may be discharged from the hearth using, for example, one or more water- cooled discharge screws or plows. The reduced balls are then readily separated from contaminating byproducts such as ash and sulfur in post-reduction beneficiation steps. The beneficiated sponge iron may then be conveyed by insulated bottles, or other means such as an inert pneumatic conveyor or heat resistant metal conveyor, to downstream users such as a smelter, an electric arc furnace, or a hot briquetting machine where the product is densified to facilitate storage and transportation. The product may be sold as merchant sponge iron, or advantageously used as hot or cold feedstock for iron making or steel-making operations.

According to one aspect of the invention, therefore, there is provided a method for producing direct reduced iron comprising: (1) providing a plurality of agglomerates comprising an iron oxide composition, one or more binders and an internal carbonaceous reductant; (2) positioning the agglomerates onto a rotary hearth furnace in intimate contact with a particulate matrix comprising one or more external carbonaceous reductants and, optionally, one or more desulfurizing agents; (3) subjecting the agglomerates and the matrix to reducing conditions to reduce a substantial portion of the iron oxide, thereby producing sponge iron and a sulfur- containing ash byproduct; and (4) discharging the sponge iron and the byproduct from the rotary hearth furnace. When positioning the starting materials onto a rotary hearth furnace, it is preferred that they be positioned in a substantially uniform layer.

According to another aspect of the invention, there is provided a method for producing direct reduced iron, comprising: (1) providing a plurality of agglomerates comprising an iron oxide composition and an internal carbonaceous reductant; (2) placing the agglomerates in intimate contact with a particulate matrix comprising an external carbonaceous reductant to provide a furnace charge material; (3) positioning the furnace charge material onto the hearth of a rotary hearth furnace; (4) subjecting the charge to reducing conditions to reduce a substantial portion of the iron oxide, thereby producing sponge and a sulfur-containing ash byproduct; (5) discharging the sponge iron and the byproduct from the rotary hearth furnace; and (6) beneficiating the sponge iron to remove the byproduct therefrom, thereby yielding a purified sponge iron product. It is an object of the present invention to provide a direct iron reduction process which converts iron oxide compositions into metallic iron at a high conversion efficiency (i.e. metallization) and productivity (i.e. low capital cost per ton of annual capacity). It is another object of the present invention to provide a direct iron reduction process which produces a DRI product having a relatively low level of sulfur and ash contamination.

It is another object of the invention to provide a direct iron reduction process which requires less binder than prior art processes to form the starting material agglomerates due to (1) the use of less carbon reductant in the green balls; (2) the smaller green balls that are inherently more durable with less binder, (3) the use of an external reductant matrix that acts as a buffer, padding material, or cushion to the green balls during handling drops thus allowing less binder to be used since the balls see less abuse in transit, and (4) the greater density of green balls due to less internal carbon results in less binder per ton of resulting DRI since none of the external carbon requires binder.

It is also an object of the invention to provide a process for the direct reduction of iron which maximizes the utilization of hearth surface area by minimizing the void space between particles, pellets, briquettes or agglomerates on the hearth, thereby maximizing unit productivity of the hearth by placing individual green balls into close proximity and intimate contact with a particulate carbonaceous reductant matrix.

It is also an object of the invention to provide a process for the direct reduction of iron that maximizes the rate of reduction reaction by including beneficial additives in the agglomerate interior while minimizing the ash and sulfur contamination of the sponge iron product by the use of one or more de-sulfurizing agents added to the external reductant mix.

Further objects, advantages and features of the present invention will be apparent from the drawings and detailed description herein. BRIEF DESCRIPTION OF THE DRAWINGS

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 drawing forming a part hereof.

Figure 1 provides a top plan view of a portion of a rotary hearth furnace along with apparatus for introducing furnace charge material onto the hearth according to a preferred aspect of the invention, the apparatus including a green ball drier 135, a matrix feed bin 150 and weigh feeder 170, a balling machine 100, a wet green ball conveyor 1 10, a green ball drier loading zone 140, a green ball drier discharge zone

180, a furnace charge conveyor 50 and an oscillating conveyor for introducing furnace charge material onto the hearth. Also depicted are a loading zone 10 of the rotary hearth furnace, a leveling screw 20 and a discharge zone 30 of the rotary hearth furnace. The furnace charge conveyor 50 passes under the ball drier discharge zone 180 after the matrix material is introduced thereon so that dried balls fall down onto the matrix material which acts as a cushion for the fragile dry balls.

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 embodiment illustrated in the drawing 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 alternations 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 improved methods for the direct reduction of iron oxides. Specifically, the present invention involves iron reduction methods wherein the iron oxide composition charged to a rotary hearth furnace is bound together in a relatively small green ball with an internal reductant, the internal reductant preferably having a low sulfur content, and being dosed in a quantity less than the total amount of reductant needed to fully reduce the iron oxide in the small green balls. The green balls are placed on the hearth of a rotary hearth furnace 1 in intimate contact with a matrix comprising an external carbonaceous reductant preferably of lower cost than the internal reductant, typically due to, for example, higher levels of sulfur, ash and/or volatiles. An example of a material useful as the external reductant is a waste byproduct such as petroleum coke. The carbon in the reductant matrix provides a portion of the carbon needed for reduction and, therefore, the amount of reductant in the green ball need only be a fraction of the total reductant needed to achieve substantially complete reduction. The use of smaller green balls, the presence of a lesser amount of carbonaceous reductant in the agglomerate, and the padding aspect of the external reductant in the matrix during handling of the small green balls all serve to decrease the amount of binder which must be used to achieve satisfactory green ball strength and durability. Since these binders are very expensive, accounting for as much as 15%> of the total costs in prior art solid-based reduction processes, this feature of the invention increases the economic value of carbonaceous direct reduction processes. Further, since the internal reductant bound to the oxide in the green ball oxide is only a fraction of the total reductant present and the internal reductant preferably has a relatively low sulfur and ash content, the resulting sponge iron agglomerates may be readily separated from the sulfur and ash byproduct contaminants present in the matrix yielding a DRI product with purity, quality and value substantially exceeding that of DRI produced by prior art solids-based rotary hearth reduction processes. These and other advantages of the present invention will be described in greater detail herein. According to the present invention, a furnace charge is prepared using appropriate proportions of particulate starting materials, including one or more particulate iron oxides, one or more particulate carbonaceous reductants, one or more binder materials and, optionally, one or more de-sulfurizing agents, one or more beneficial catalyzing additives and water. The furnace charge is prepared using two separate compositions: (1) agglomerates of one or more iron oxides one or more binder materials, and one or more particulate carbonaceous reductants, referred to herein as "internal reductant," and also, in certain preferred embodiments, one or more beneficial catalyzing additions; and (2) a particulate matrix of an additional quantity of one or more carbonaceous reductants (may preferably be a low-cost, high- ash/sulfur reductant), referred to herein as the "external reductant." In a preferred aspect of the invention, the matrix is first fed onto a conveyor and, subsequently, the agglomerates are fed onto the matrix. In this manner, the matrix acts as a padding material to cushion the impact of the agglomerates falling down onto the conveyor belt, and the subsequent agitation, handling and conveyor transfers and discharge impacts cause less degradation of the agglomerates. On the conveyor, the agglomerates become intimately coated with and embedded into the matrix, and this combined composition constitutes an inventive furnace charge. For purposes of clarity, a mixture provided to form agglomerates is termed "balling feed mixture" herein, and a mixture prepared to be the matrix is simply referred to as the "matrix mixture." The charge is placed on the hearth of a rotary furnace where it is exposed to appropriate reaction conditions to achieve direct reduction of the iron oxide into sponge iron. As stated above, the term "sponge iron" is intended to refer to the product of a direct reduction process which includes elemental iron therein, and is used interchangeably with the term "DRI". For purposes of the invention, the agglomerates preferably remain substantially intact during the reduction reaction and, thereby, the sponge iron exists in the reduced agglomerates. The sponge iron is then discharged from the rotary hearth furnace for subsequent processing or merchant sale. One starting material required to practice the present invention, therefore, is a particulate iron oxide composition, used in the formation of agglomerates. 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 skilled artisan on a case- by-case basis for a wide variety of economic conditions and situations. It is contemplated according to the present invention that 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, lump ores, iron oxide pellet fines, hematite iron ore, specular hematite concentrate, earthy hematite, magnetite iron ore, magnetite concentrate, limonite, limonite 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 is readily understood by a skilled artisan that additional compositions or combinations of reducible oxides therein may find advantageous use according to the present invention.

The particulate iron oxide composition used in accordance with the invention is preferably ground to pelletizing particle sizes, i.e. so that he particles are fine enough to form green balls having adequate strength and durability. For example, in cases where a high pressure grinding roll press (HPGRP) is used, it is preferred that at least about 30% of the particles pass 200 mesh. Alternatively, where a ball mill is used, it is preferred that at least about 50% of the particles pass 325 mesh. Grinding may preferably be achieved using a HPGRP or a ball mill, or other suitable grinding devices. Additionally, in one aspect of the invention, the iron oxide composition is beneficiated to remove therefrom undesirable contaminants such as, for example, silica, alumina, sulfur, and/or phosphorous.

Suitable iron oxide compositions for use according to the present invention include but are not limited to magnetite concentrates from Minnesota and Michigan, semi-taconites from Minnesota, specular hematite concentrates from Eastern Canada, or Michigan, hematite lump or fines from Brazil, hematite lump or fines from Australia, hematite lump or fines from India, iron ores from Sweden, magnetite concentrates or fines from Peru or Chile, and limonite or hematite ores from 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, Hammersley Iron, BHP or MBR.

Also needed to practice the present invention is one or more carbonaceous reductant. As described above, carbonaceous reductant is used to prepare agglomerates and is also used to prepare a matrix according to the invention. For purposes of clarity herein, the former is termed "internal reductant," and the latter is termed "external reductant." While the internal reductant and the external reductant may be compositionally similar or identical, in preferred aspects of the invention, the internal reductant is a low-sulfur, low-ash, carbonaceous reductant and the external carbonaceous reductant may be a cheaper high-sulfur, high-ash reductant. The external reductant may preferably be a low cost carbon source since a wide variety of combinations of ash, sulfur, carbon and volatile content may be advantageously used including low cost carbons such as petroleum coke or coke braize.

A preferred internal reductant for use in the present invention is one relatively low in sulfur and ash content while simultaneously 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 reduce a portion of the iron oxides in the green ball. With regard to a preferred aspect of the invention the internal reductant included in the green ball is a low-sulfur, low-ash reductant preferably with a sulfur content of less than about 1.0% by weight on a dry basis. More preferably, the sulfur content is less than about 0.8% by weight on a dry basis. Most preferably the reductant has a sulfur content less than about 0.5% by weight on a dry basis. The internal reductant preferably has an ash content of less than about 12% on a dry weight basis. More preferably the ash content is less than about 10% dry weight basis and most preferably less than about 6% on a dry weight basis. Examples of particulate carbonaceous reductants which are advantageously used as the internal carbonaceous reductant in accordance with the invention include low to medium volatile subbituminous to bituminous coals, anthracite, lignite, coke, coke braize, graphite and char. The high quality (i.e. low ash and sulfur) coals of Indonesia, New Zealand, Western Canada. Colorado, Utah, West Virginia, Alabama, and

Pennsylvania are particularly well suited as internal reductants of the invention.

The external reductant can be one or more of a wide variety of coals and cokes including those described above as suitable internal reductants, and also including cheaper materials such as, for example. Powder River basin coals, petroleum cokes, lignites, Indiana and Illinois coals, and a wide variety of coals produced around the world. The most economic choice of an external reductant under a particular set of circumstances can be easily made by a skilled artisan based upon delivered economics per ton of contained carbon. A very important and significant advantage of the invention is that reductants high in sulfur and ash may be used in the matrix as the external carbonaceous reductant. Since these high-sulfur and ash reductants are commonly much less expensive than their lower-sulfur counterparts, an economic advantage is obtained without causing the sulfur content of the DRI product to increase substantially. Again, it is not intended that the above list be limiting, but only that it provide examples of useful carbonaceous reductants. The internal and external reductants used in accordance with the invention are preferably ground to particle sizes that enhance reactivity and minimize fugitive loss to the process gas stream. In the case of the internal reductant, the material is preferably ground by wet or dry means to a preferred size of at least about 50% passing a 100 mesh, more preferably to at least about 80% passing 100 mesh, more preferably to at least about 50% passing 200 mesh and most preferably to at least about 80% passing 200 mesh. In the case of the external reductant, the particle size may advantageously be coarser than the preferred ranges for the internal reductant so that particles in the matrix, once dried, are not lost to the process gas stream flowing above the charge layer on the hearth. Preferably, the external reductant is crushed, ground and sized to at least about 90% smaller than one (1) inch in particle diameter, more preferably to at least about 90% passing one-half (1/2) inch particle size, more preferably smaller than about 90% passing one-quarter inch, more preferably smaller than about 90% passing 10 mesh and most preferably smaller than about 90% passing 50 mesh.

Another starting material advantageously utilized in accordance with particular preferred embodiments of the present invention is one or more de-sulfurizing agents to decrease the amount of sulfur contamination in the DRI product. As used herein with respect to particular inventive furnace charge materials, the term "de-sulfurizing agent" is intended to refer to a composition that, when present in a particulate external reductant matrix selected according to the invention, "captures" sulfur present in the furnace charge, and thereby prevents significant accumulation of sulfur in the agglomerate during and/or after the reduction reaction. Production of agglomerated sponge iron with a relatively low sulfur content significantly reduces the cost of purifying liquid iron and/or steel in downstream refining process.

It has been discovered by the present inventor that a wide variety of compositions may advantageously be used to perform this de-sulfurizing function. Suitable de-sulfurizing agents for use in the practice of this invention include, for example, high calcium hydrated or slaked lime, dolomitic slaked lime, magnesian slaked lime, high calcium caustic lime, dolomitic caustic lime, magnesian caustic lime, high calcium limestone, dolomitic limestone, magnesian limestone, calcite and calcium carbide. According to particular aspects of the invention, a plurality of de- sulfurizing agents may be blended prior to mixing with the other starting materials. These de-sulfurizing agents may be obtained in the preferred powdered form from a wide variety of commercial outlets well known to a person skilled in the art. For example, the three above-listed varieties of limestone may advantageously be ground in a batch using the same grinding system used to grind the reductants, thereby reducing the capital cost of the DRI production facility and reducing the cost of the de-sulfurizing agents.

Some de-sulfurizing agents, including some of those described above, are detrimental to carbonaceous direct iron reduction processes taught in the prior art which utilize binders to form agglomerates or briquettes, because the de-sulfurizing agents are mixed with other starting materials prior to agglomeration thereof, and interfere with the binders' ability to give the agglomerate adequate dry strength and durability. Therefore, if a de-sulfurizing agent is used in these processes, a much greater amount of binder is typically required to achieve satisfactory agglomeration, especially in the case of the FASTMET process, which handles dry green balls between the drier and the hot hearth. Due to the high costs of binders, as discussed above, the need for increased amounts of binders would result in an additional increase in material costs of about l-3%>. An additional problem with adding de- sulfurizing agents to green balls or briquettes is that the de-sulfurizing agent used in that way functions to "trap" sulfur contaminants in the agglomerates, thus compounding the problem of sulfur contamination in the DRI product. According to preferred aspects of the present invention, the de-sulfurizing agents that interfere with binders preferably are not admixed with the starting materials to be formed into the agglomerate, and only those additives that enhance the reduction reaction without substantially interfering with the binder or binders (i.e. beneficial non-interfering catalysts) are added with the starting materials to be agglomerated (i.e., the iron oxide composition and the internal carbonaceous reductant). In inventive processes, one or more de-sulfurizing agents (interfering or not) are preferably admixed with the external carbonaceous reductant, and thereby substantially prevent sulfur in the external carbonaceous reductant from contaminating the DRI in the agglomerate. The absence of or scarcity of interfering de-sulfurizing agents in the green ball eliminates the need for excessive amounts of binder material, and therefore helps minimize the cost of binder material per ton of DRI produced.

Some non-interfering de-sulfurizing agents in small dosages also function to increase the rate of an iron reduction reaction and/or serve as a flux of silica and alumina for downstream iron and steel-making and, therefore, are beneficial additives (termed "beneficial non-interfering catalysts" herein) to the balling feed mixture. The present inventor has discovered that various forms of limestone or dolomitic limestone (termed "limestone derivations" herein), including, for example, powdered forms of hydrated or slaked lime, caustic lime, finely ground limestone, dolomite or any combination thereof, used in accordance with the invention achieve a particularly advantageous rate of the direct reduction reaction, increasing metallization of iron oxides by about 1 to about 10 percentage points for a given reaction time and reaction condition. The limestone derivations are especially advantageous in certain embodiments of the invention, i.e. those wherein the resulting metallic iron is to be used for steel-making, because the use of these de-sulfurizing agents/beneficial non- interfering catalysts reduces the amount of flux which must be added to the liquid iron in downstream iron refining or steel-making operations.

Since the iron oxide composition and internal carbonaceous reductants are agglomerated according to the invention, it is critical that binders also be mixed therewith. A number of binders suitable for use in this manner are well known in the art and may be advantageously used in accordance with the invention. Examples of acceptable binders include bentonite clay and organic compositions such as water solutions of molasses, water solutions of lignin sulfate, Peridur, Alcotac and other forms of carboxymethychloride together with soda ash.

Another material which imparts advantageous features to inventive methods is water. Perhaps the most significant attribute of water in the inventive process is that when water is mixed, optionally together with a surfactant or other wetting agent, into the external carbonaceous reductant in a sufficient amount, it allows the material to be conventionally conveyed by belt conveyors such that the material can be introduced onto a furnace charge conveyor ahead of the dry green balls and thereby act as a cushion for the arriving fragile green balls. The moist nature of the matrix also prevents or minimizes the loss of reductant matrix particles in fugitive fashion to the process gases flowing above the furnace charge layer on the heath. The moisture content of the external carbonaceous reductant also imparts the following advantageous characteristics to inventive mixtures; (1) elimination of dust problems, (2) prevention of the ignition of the furnace charge upon contact with a hot hearth, and (3) delay of coal volatization so that, if the rotary hearth furnace flue is located at the beginning of the furnace loading zone, as is common in a variety of prior art rotary hearth furnace designs, then the hydrocarbon volatiles of the coal have increased time to combust usefully in the hood to the benefit of the oxidic mixture.

In view of the above benefits, the moisture content of a given charge may be optimized according to the invention to minimize the drying load born by the hearth. Preferably the water content of the external carbonaceous reductant is less than about 15% by weight, and more preferably less than about 10% by weight, and most preferably less than about 5% by weight.

In addition to the above, water is preferably mixed with the iron oxide composition, internal carbonaceous reductant and binder material in the balling feed mixture prior to agglomeration thereof in order to achieve sufficiently strong and properly sized green balls. Preferably the water content of the balling feed mixture is less than about 15% by weight. More preferably the water content is less than about 12%. Most preferably the water content is less than about 10 all by weight. 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 in the furnace charge material are selected according to the invention based upon the amount of iron in the 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 furnace charge 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 a preferred aspect of the invention, the ratio of fixed carbon in the total reductant present in the furnace charge 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.

Of the total reductant present in a given quality of furnace charge material, it is preferred that from less than about 90% of the reductant is present in the green ball (i.e. the internal reductant) and that at least aboutl 0% of reductant is in the matrix.(i.e. the external reductant). More preferably, less than about 80% of the reductant is present in the green ball and at least about 20% of the reductant is in the matrix. Still more preferably, less than about 40% is present in the green ball and at least about 60%) is present in the matrix. One skilled in the art can determine with minimal experimentation a preferred ratio of internal to external reductant for a given situation. The optional ratio will be dependent upon such factors as the delivered cost and fixed carbon of reductants, the reactivity of each reductant, the rate of metalization achieved with various ratios of reductant and the sensitivity of the end user of the DRI to gangue and sulfur content. The relative amount of de-sulfurizing agent which is included in the matrix material according to the present invention will be dependent upon the specific agent selected for use, the amount of sulfur in the external reductant, and the amount of iron and fixed carbon in the iron oxide composition and reductant in the charge, respectively. Additionally, the amount of water present may be optimized by taking into account the factors set forth herein. An optimum amount of each of these components may readily be determined by one skilled in the art with minimal experimentation. In one preferred embodiment, the inventive matrix mixture comprises less than about 0.1% de-sulfurizing agent and from about 0.5% to about 14% water, both by weight. In another preferred embodiment, the matrix mixture according the invention comprises from about 0.1% to about 30% de-sulfurizing agent by weight; and from about 0.5% to about 14% water by weight. To increase the rate of reaction, it may also be desirable to place a beneficial non-interfering catalyst into the green ball by including it in the balling feed mixture prior to agglomerate thereof. In one preferred aspect of the invention, the balling feed mixture fed to the agglomerating circuit comprises a particulate iron oxide composition, which is a hematitic or magnetitic virgin iron ore or concentrate thereof; an internal carbonaceous reductant, which is one or a blend of more than one low or medium volatile bituminous or subbituminous coals; and a binder material, which is one or a blend of more than one of the following compositions: bentonite, molasses, lignin sulfate, Peridur, Perispray or another similar carboxyme hylchloride and soda ash composition. The matrix mixture preferably includes an external reductant and a de- sulfurzing agent that is a blend of one or more of the following: high calcium hydrated or slaked lime, dolomitic slaked lime, magnesian slaked lime, high calcium caustic lime, dolomitic caustic lime, magnesian caustic lime, high calcium limestone, dolomitic limestone, magnesian limestone, calcite and calcium carbide. In a preferred aspect of the invention, the external reductant is a blend of one or more coals, cokes, petcokes, chars, lignites, anthracites, graphites or other economically attractive sources of carbon. Preferably, the overall furnace charge comprises from about 65% to about 85% virgin ore; from about 10% to about 40% total reductants (internal and external); from about 0.5% to about 3% beneficial additive; and from about 1% to about 15% water, from about .03% to about 3% binding agents, and from about 1% to about 25% desulfurizing agents, all by weight. In this embodiment, the dry-weight- basis iron content of the iron ore is from about 64% to about 70% and the dry- weight- basis fixed carbon of the internal carbonaceous reductant is from about 60% to about 80%.

In a preferred manner of practicing the invention, starting materials used to form green balls, (i.e. an iron oxide composition, an internal carbonaceous reductant, a binder material, water and, optionally, additional additives selected by a skilled artisan) are carefully weigh-fed into a intensive mixer or plug mill to thoroughly blend the mixture. A mixture prepared or obtained as described above, i.e. the balling feed mixture, is then fed into a balling machine, these being well known in the art, to form green balls according to the invention. It is preferred that green balls produced be no larger than about 15mm in diameter, more preferably no larger than about 10mm in diameter more preferably no larger than about 6mm in diameter, and most preferably no larger than about 4mm in diameter. The green balls are then placed in intimate contact with a matrix as discussed more fully below with respect to particular preferred embodiments of the invention. Optionally, the green balls may preferably be dried before they are placed in intimate contact with the matrix.

With regard to preparation of the matrix mixture, starting materials used to form the matrix (i.e. an external carbonaceous reductant, which may be compositionally the same as or different than the internal carbonaceous reductant, a de-sulfurizing agent and, optionally, water and additional additives selected by a skilled artisan) are carefully weigh-fed into an intensive mixer or plug mill to thoroughly blend the mixture. The matrix mixture may then preferably be conveyed to a surge bin, from which it is advantageously delivered to an apparatus for contacting the mixture with agglomerates in accordance with the invention. In this regard, the matrix mixture may advantageously be delivered at a predetermined rate to 11

a conveyor and agglomerates subsequently added thereto in accordance with the invention to provide a furnace charge composition.

A matrix mixture prepared in accordance with the invention is preferably fed onto a conveyor at a rate determined by a desired weight or volumetric ratio with respect to the weight or volume component of the dry or wet green balls. As stated above, the matrix mixture may optionally be first placed in a feed bin, or surge bin, before being weigh fed onto a conveyor that subsequently also receives the wet or dry green balls. The green balls and the matrix material, having been placed in intimate contact with one another in carefully-monitored ratios to provide a furnace charge material, are then placed onto a rotary hearth furnace 1 for reduction of the iron oxide composition.

Referring more particularly to Figure 1, in a preferred manner of practicing the invention, where wet green balls are continuously provided by a green ball conveyor 110 to a loading zone 140 of a green ball drier 135, such as, for example, the rotary drier depicted in Figure 1. Simultaneously, a matrix material is provided and conveyed to a surge bin 150, from which matrix material is continuously deposited onto a furnace charge conveyor 50 and passed under a discharge zone 180 of the green ball drier 135, to receive and cushion the fall of dried green balls. The furnace charge is then deposited onto an oscillating conveyor 40 that distributes the furnace charge across the width of the hearth. The movement of the charge across conveyor idlers and transfer points and the subsequent introduction of the charge onto the hearth loading zone 10 advantageously mixes the green balls and the matrix together, causing the matrix to fill the interstitial space between the green balls, bringing the matrix material and the green balls into intimate contact with one another. The hearth loading zone 10 is optionally shrouded, sealed, and fed with nitrogen gas to purge air and eliminate the hazard of combustion of the carbon in the furnace charge material upon contact with the hot hearth and to avoid air leakage into the discharge area whereby sponge iron reoxidation could occur. 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 in account in order to achieve a relatively even layer of furnace charge material 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 furnace charge material will be placed relatively evenly across the width of the hearth, and it is within the purview of a skilled artisan to assemble a furnace charge feed system for introducing the charge onto the hearth in a relatively uniform layer. An example of a preferred feed system used in accordance with the invention is an oscillating conveyor system, as mentioned above. The oscillating conveyor from which the furnace charge drops onto the hearth may advantageously be moved back and forth repeatedly across the width of the hearth, thus introducing furnace charge material onto the hearth as the hearth steadily moves thereunder. The oscillating conveyor 40 in a preferred embodiment is oriented as shown in Figure 1, wherein the oscillating conveyor 40 oscillates under the furnace charge conveyor 50, and a relatively even layer of furnace charge material on the hearth is achieved by a movement of the oscillating conveyor 40 back and forth with greater speed at the "inside" end of the stroke. The eccentric oscillation allows the oscillating conveyor to introduce the charge material across the width of the hearth.

While measures such as those described above may be taken to achieve relative evenness, it is preferred that the layer be smoothed even more uniformly before entering the reaction zone of the rotary hearth furnace. A charge layer on the hearth may be leveled using, for example, a set of stationary or oscillating plows or a leveling screw that sweeps excess material to the inside or outside of the hearth. Excess material may preferably be swept off the hearth and recycled to the furnace charge conveyor system or optionally spread over the hearth width by the plows or screws. It is also preferred that the furnace charge layer which enters the reaction zone of the rotary hearth furnace has a thickness of less than about 50mm. More preferably, the thickness is less than about 25mm, most preferably less than about 15mm; however, it is readily understood that the most preferred thickness may be dependent upon the heat transfer conditions of the particular furnace being used. The type and arrangement of burners, the type and arrangement of secondary air used to combust the coal volatiles and carbon monoxide, and the type of combustion fuel used are examples of some of the variables that will impact heat transfer conditions of the particular furnace. Additionally, if the hearth is superheated, a thicker layer may be loaded onto the hearth since heat will be conducted from the hearth into the bottom of the layer, thereby achieving the direct reduction of material not directly exposed to the radiant heat from above the hearth. A thicker layer may also be placed on the hearth in alternative embodiments of the invention where the furnace charge layer is "plowed" or "churned" at one or more points within the reaction zone of the rotary hearth furnace. In the reaction zone, the charge material is 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 charge is heated to a temperature of from about 1000°C to about 1500°C and for a period of time of from about 5 minutes to about 50 minutes. Conventional rotary hearth furnaces having multiple reaction zones may be advantageously used in accordance with the present invention. In a preferred aspect of the invention, after the charge has passed through the reaction zone, a substantial portion of the starting materials in the charge will have been chemically converted to metallic iron (in the reduced agglomerates, or sponge iron) and sulfur-containing ash byproducts. After passing through the reaction zone or zones of the rotary hearth furnace, the reduced agglomerates (sponge iron) and sulfur-containing ash byproduct material are removed from the hearth. The sponge iron and byproduct material are preferably removed using one or more water-cooled discharge plows or screws, and may then be discharged through refractory-lined chutes into, for example, an insulated and nitrogen purged buffer bin and thence into insulated and nitrogen purged bottles, or an inert pneumatic conveyance system for transport to further processing steps, or into an inert atmosphere cooler. 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 about 92%.

It is an advantageous feature of the present invention that a portion, preferably a large fraction, of the carbonaceous reductant material is in the matrix, exterior to the green balls (i.e., the external reductant). This feature of the invention advantageously facilitates beneficiation of the agglomerated sponge iron because a large percentage of the ash and the sulfur contaminants are in the loose matrix material. Therefore, the reduced agglomerates may preferably be separated from the byproduct materials by screening, by utilization of an gaseous cyclone, by magnetic separation, or by a combination of these or other known beneficiation techniques. The resulting beneficiated sponge iron is significantly more pure than DRI produced using other solid-based rotary hearth reduction processes known in the prior art. Processes according to the invention may result in sponge iron having as low as about 0.01 to 0.10 percent sulfur and as low as 1.0% to 5.0% gangue present therein. A larger or smaller proportion of the carbonaceous reductant may be placed in the green ball, depending upon whether it is more desirous in a particular application of the invention to achieve extremely pure DRI or to achieve maximum hearth productivity. Production of DRI having such low sulfur and gangue content advantageously reduces costly downstream purifying steps otherwise required if high sulfur, high gangue DRI is used in iron-making or steel-making operations. 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. The invention will be further described with reference to the following specific Examples. It will be understood that these Examples are also illustrative and not restrictive in nature.

EXAMPLE ONE Specular hematite concentrate containing less than about 5% silica and more than about 64% elemental iron by weight is ground by either a ball mill or roll press to a nominal particle size distribution of at least about 50% passing 200 mesh. The ground iron ore concentrate is admixed with low volatile subbituminous coal containing about 77% fixed carbon by weight on a dry basis, which has been dried and ground to a size of about 80% passing 200 mesh. High calcium limestone in powder form is also admixed at a dosage of 1% of the dried mixture. Binders including .15% Peridur, .025% Perispray and .3% Bentonite are also admixed to the mixture. The entire mixture is wetted to 10% water content in an intensive mixer and fed to one or more balling disks or drums in closed circuit with roll screens. The mixture is agglomerated into green balls with a size distribution of about 90% between three (3) mm and six (6) mm in diameter. The wet green balls are conveyed to a rotary grate drier where they are dried to less than about 1% water using hot gases from the rotary hearth off gas system.

Petroleum coke with a sulfur content of 4% by weight is dry ground to about 90% minus ten mesh and admixed with high calcium limestone which has been dry ground to about 80%> minus 200 mesh. The two ingredients are admixed in an intensive mixer at a weight blend of about 70% pet coke, about 25% limestone and about 5% water. The mixture constitutes the external reductant matrix material.

The matrix material is belt conveyed to a feed bin located near the pellet drier. A feeder admixes the matrix material to the dry green balls by depositing the matrix material onto the belt conveyor that subsequently receives the dry balls from the drier discharge chute. The dry green balls fall onto the moist matrix material that softens the impact of the fragile dry balls. The composite of matrix and dry balls is conveyed and transferred onto an oscillating conveyor that distributes the furnace charge evenly across the width of a rotary hearth furnace. The furnace charge is spread into a fairly uniform layer across the width of the hearth by one or more leveling screws to a thickness of about 15mm. The charge material then enters the reaction zones of the rotary hearth. The mixture is rapidly heated by natural gas and/or coal fired burners to approximately 1300°C. Residence time in the furnace is approximately 20 minutes. Metallization in excess of 90% is achieved with a unit productivity of the hearth of more than 70kg of DRI per useful square meter of hearth area per hour. The mixture is removed from the hearth using a water cooled screw, discharged to a refractory lined buffer bin and then to insulated bottles for transfer to a water cooled rotary cooler with trommel discharge screens where the mixture is cooled in an inert atmosphere and to separate the ash, unspent coal fines calcium sulfate and unspent lime and limestone from the sponge iron pellets. The clean sponge pellets are then either further cooled for storage, transported to the EAF for melting, or pre-cooled for hot briquetting.

EXAMPLE TWO Magnetite concentrate from Minnesota or Michigan with a silica content between about 1.5% and about 6.0% is ground to at least about 80% passing 325 mesh, and filtered to a moisture content of about 10%. It is then admixed with an internal reductant comprising metallurgical coal from British Columbia that has been dry ground to about 80% passing 200 mesh, together with a dosage of about 2% dry ground limestone, about .3% bentonite, about .1% Peridur and about .025% Peridur. The balling mix recipe by weight is about 77% iron ore concentrate, about 10% reductant, about 10.575% water, about 2% limestone, and about .425% binders. The thoroughly blended mixture is conventionally conveyed and discharged to a balling drum closed with a roll screen. The balling circuit produces wet green balls with a size distribution about 90% between 8mm and 10mm in diameter. The wet balls are conveyed to an furnace charge conveyor upon which a matrix mixture has previously been deposited, the furnace charge material then depositing the charge onto an oscillating conveyor which deposits the entire furnace charge onto the hearth.

The matrix material comprises Powder River basin coal dry ground to about 80% minus 50 mesh and dry ground limestone at a size of about 80% minus 100 mesh, these ingredients being intensively mixed in a mixer at a blend ratio of about 80% coal, about 12% limestone and about 8% water all by weight.

The matrix material is weigh fed to the furnace charge conveyor such that the ratio of carbon to iron in the combined furnace charge is about 3.2 to about 10 on a dry weight basis. The matrix material is placed onto the belt conveyor that subsequently receives the green balls from the roll screen so that the balls fall onto the matrix

"padding." The entire furnace charge consisting of wet green balls imbedded in the external reductant matrix material is belt conveyed to an oscillating conveyor that spreads the charge across the full hearth width of the rotary hearth reduction furnace. Using one or more leveling screws the mixture is spread into an even layer approximately 20mm thick. The charge layer enters the reaction zones of the rotary hearth furnace where it is heated slowly at first to drive off moisture, then rapidly to about 1200^°C. The residence time on the hearth is about 35 minutes. An oscillating, water-cooled plow and screw remove the sponge iron balls and ash byproduct off the hearth in the discharge zone. The plow oscillates with an amplitude of about six inches with an out stroke velocity one half that of the return stroke so that the plow gets back to the start position before the inner 6 inch material travels behind the plow on the out stroke. The hot sponge iron and ash byproduct are processed through an inert gas cyclone which separates the byproduct ash from the DRI and cools it to briquetting temperature. The purified DRI is then transported to a hot briquetting machine where the sponge iron is densified into briquettes for merchant sales. EXAMPLE THREE

Hematite fines or magnetite concentrate at about 4% moisture from South America or Australia are grounded using a high pressure roll press to about 50% minus 200 mesh and then admixed with a coal blend of Indonesian and British

Columbia coal containing about 60% fixed carbon and about 25% volatiles, the coal blend having been dry ground to about 80% smaller than 100 microns. The moist ground ore and dry coal are mixed with dolomitic hydrated lime at a ratio of about 89% ore, about 10% coal and about 1% dolomitic hydrated lime, by dry weight. The blend is intensively mixed with water and binders in a pug mill before belt conveyance to a balling disk and roll screen circuit. The green balls with an average diameter of about 7mm are dried in a traveling grate-style drier using air heated by a heat exchanger that transfers heat from the rotary hearth off gases. Pet coke and low- cost coal are ground to about 80% minus 10 mesh and admixed with about 5% hydrated lime and water to a moisture of about 5%. The matrix material is deposited on a conveyor that subsequently receives the dried balls from the traveling grate drier. The dried balls fall from the drier discharge onto the moist matrix material. The entire charge is conveyed to an oscillating conveyer that spreads the mix across a 7.0 meter wide hearth. High temperature alloy plows level the bed to about 15mm. The entire hearth loading zone is shrouded, sealed and charged with nitrogen gas to eliminate flashing as the carbonaceous mixture cascades down onto a hearth with a surface temperature of about 1000°C. Reaction time is from about 20 minutes to about 30 minutes. The DRI bed is removed in the discharge zone by a water-cooled discharge screw with a diameter of about 36 inches. DRI with average metallization of about 93%> together with ash by-product is passed into nitrogen filled bottles lined with refractory. The bottles then dicharge to a pneumatic transport system feeding one or more cyclones where the pellets are separated from the ash and calcium sulfate. The pellets are subsequently charged hot into an EAF furnace for conversion to molten steel, or hot briquetted for sales, or storage for later uses.

Claims

WHAT IS CLAIMED IS:

1. A method for producing direct reduced iron, comprising: providing a plurality of agglomerates comprising an iron oxide composition and an internal carbonaceous reductant; positioning the agglomerates onto a rotary hearth furnace in intimate contact with a particulate matrix comprising an external carbonaceous reductant; subjecting the agglomerates and the matrix to reducing conditions to reduce a substantial portion of the iron oxide, thereby producing sponge iron and a sulfur-containing ash byproduct; and discharging the sponge iron and the byproduct from the rotary hearth furnace.

2. The method according to claim 1. further comprising beneficiating the sponge iron to remove the byproduct therefrom , thereby yielding purified sponge iron.

3. The method according to claim 1, wherein the iron oxide composition comprises particles having a particle size distribution of at least 30% passing 200 mesh.

4. The method according to claim 1 , wherein the iron oxide composition comprises particles having a particle size distribution of at least 50 % passing 325 mesh.

5. The method according to claim 1, wherein the internal carbonaceous reductant comprises particles having a particle size distribution of at least 80% passing 100 mesh.

6. The method according to claim 1 , wherein the internal carbonaceous reductant comprises particles having a particle size distribution of at least 80% passing 200 mesh.

7. The method according to claim 1, wherein the external carbonaceous reductant comprises particles having a particle size distribution of at least 90% passing one inch.

8. The method according to claim 1 , wherein the external carbonaceous reductant comprises particles having a particle size distribution of at least 90% passing !Λ inch.

9. The method according to claim 1 , wherein the external carbonaceous reductant comprises particles having a particle size distribution of at least 90% passing 10 mesh.

10. The method according to claim 1 , wherein the external carbonaceous reductant comprises particles having a particle size distribution of at least 90% passing 100 mesh.

1 1. The method according to claim 1 , wherein the internal carbonaceous reductant comprises less than about 1.0% sulfur therein by weight.

12. The method according to claim 1 , wherein the internal carbonaceous reductant comprises less than about .5% sulfur therein by weight.

13. The method according to claim 1 , wherein the internal carbonaceous reductant comprises one or more members selected from the group consisting of coal, coke, coke braize, pet coke, graphite, char and lignite.

14. The method according to claim 1, wherein the external carbonaceous reductant blend comprises one or more members selected from the group consisting of coal, coke, coke braize, pet coke, graphite, char and lignite.

15. The method according to claim 1, wherein the iron oxide composition comprises one or more members selected from the group consisting of virgin iron ore, such as hematite iron ore fines, hematite 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.

16. The method according to claim 1, wherein said positioning comprises positioning the agglomerates and the matrix onto a rotary hearth furnace in a substantially uniform layer.

17. The method according to claim 16, wherein the substantially uniform layer is less than about 50mm thick.

18. The method according to claim 16, wherein the substantially uniform layer is less than about 30mm thick.

19. The method according to claim 16, wherein the substantially uniform layer is less than about 20mm thick.

20. The method according to claim 16, wherein the substantially uniform layer is between about 10mm and about 20mm thick.

21. The method according to claim 1, wherein said subjecting comprises exposing the mixture to a temperature of between about 1000'C and about 1500 'C for between about 5 minutes and about 50 minutes.

22. The method according to claim 1 , wherein at least about 85% of iron in the sponge iron is in metallic form on a dry weight basis.

23. The method according to claim 1, wherein the dry weight ratio of fixed carbon in the internal and external reductants to iron in the iron oxide composition is from about 4.0: 10 to about 2.4: 10.

24. The method according to claim 1 , wherein the dry weight ratio of fixed carbon in the internal and external reductants to iron in the iron oxide composition is from about 3.5:10 to about 2.9: 10.

25. The method according to claim 1 , wherein the matrix further comprises one or more de-sulfurizing agents on a dry weight dosage of between about .1 % and about 30%.

26. The method according to claim 25, wherein the de-sulfurizing agent comprises one or more members selected from the group consisting of hydrated or slaked lime, dolomitic hydrated lime, magnesian hydrated lime, caustic lime, dolomitic caustic lime, magnesian caustic lime, limestone, dolomitic limestone, magnesian limestone and calcium carbide.

27. The method according to claim 25, wherein the de-sulfurizing agent comprises particles having a particle size distribution of at least about 80%> passing one inch.

28. The method according to claim 25, wherein the de-sulfurizing agent comprises particles having a particle size distribution of at least about 80% passing one quarter inch.

29. The method according to claim 25, wherein the de-sulfurizing agent comprises particles having a particle size distribution of at least about 80% passing 10 mesh.

30. The method according to claim 25, wherein the de-sulfurizing agent comprises particles having a particle size distribution of at least about 80% passing 100 mesh.

31. The method according to claim 25, wherein the de-suflurizing agent comprises particles having a particle size distribution of at least about 80% passing 200 mesh.

32. The method according to claim 1. wherein the matrix further comprises water on a total weight basis of between about .1 % and about 20%.

33. The method according to claim 1 , wherein the matrix further comprises a surfactant dosed on a dry weight basis of between about .01 and about 10%.

34. The method according to claim 1. further comprising beneficiating the sponge iron to remove a substantial portion of the byproduct therefrom.

35. The method according to claim 34, wherein said beneficiating comprises one or more unit processes selected from the group consisting of screen separation, magnetic separation, inert gaseous cycloning, inert gaseous elutriation, air separation, air elutriation, water elutriation, water separation, or combinations thereof.

36. A method for producing direct reduced iron, comprising: providing a plurality of agglomerates comprising an iron oxide composition and an internal carbonaceous reductant; 33

placing the agglomerates in intimate contact with a particulate matrix comprising an external carbonaceous reductant to provide a furnace charge material; positioning the furnace charge material onto the hearth of a rotary hearth furnace; subjecting the charge to reducing conditions to reduce a substantial portion of the iron oxide, thereby producing sponge and a sulfur-containing ash byproduct; discharging the sponge iron and the byproduct from the rotary hearth furnace; and beneficiating the sponge iron to remove the byproduct therefrom, thereby yielding a purified sponge iron product.

37. The method according to claim 36, wherein the ratio of the internal carbonaceous reductant to external carbonaceous reductant in the charge is from about 1 :9 to about 9: 1.

38. The method according to claim 36, wherein the ratio of the internal carbonaceous reductant to external carbonaceous reductant in the charge is from about 2:8 to about 8:2.

39. The method according to claim 36, wherein the ratio of the internal carbonaceous reductant to external carbonaceous reductant in the charge is from about 3:7 to about 7:3.

40. The method according to claim 36, wherein the matrix comprises from about 99.9%o to about 70% reductant by weight; and from about .1% to about 30% de- sulfurizing agent by weight.

41. The method according to claim 36, wherein the matrix comprises from about 98% to about 80% reductant by weight; and from about 2% to about 20% de- sulfurizing agent by weight.

42. The method according to claim 36, wherein said positioning comprises positioning the mixture onto a loading zone of a rotary hearth furnace, the loading zone being shrouded and protected to keep air ingress leakage to a minimum.

43. The method according to claim 36, wherein said positioning comprises: first depositing the external reductant matrix onto a belt conveyor; and then depositing the agglomerates onto the belt conveyor having matrix deposited thereon such that the agglomerates become intimately contacted with the matrix.

44. The method according to claim 36 wherein the agglomerates contain one or more beneficial catalyzing additives selected from the group consisting of hydrated or slaked lime, dolomitic hydrated lime, magnesian hydrated lime, caustic lime, dolomitic caustic lime, magnesian causitc lime, limestone, dolomitic limestone, and magnesian limestone.

45. The method according to claim 36 wherein the agglomerates contain one or more beneficial catalyzing additives dosed at a dry weight ratio to the total agglomerate mixture of between about .1% and about 10%.

46. The method according to claim 36 wherein the agglomerates contain one or more beneficial catalyzing additives comprising particles with a particle size distribution of at least about 80% passing 100 mesh.

47. The method according to claim 36 wherein the agglomerates contain one or more beneficial catalyzing additives comprising particles with a particle size distribution of at least about 80% passing 200 mesh.

48. The method according to claim 36 wherein the agglomerates consist of wet or dry balls with an average ball diameter of less than about 10mm.

49. The method according to claim 36 wherein the agglomerates consist of wet or dry balls with average ball diameter of less than about 6mm.

50. The method according to claim 36 wherein the agglomerates consist of wet or dry balls with average ball diameter of less than about 4mm.