WO2018128620A1

WO2018128620A1 - Production of direct reduced iron

Info

Publication number: WO2018128620A1
Application number: PCT/US2017/012473
Authority: WO
Inventors: Romain Joseph Nicolas FRIEDEN
Original assignee: Frieden Romain Joseph Nicolas
Priority date: 2017-01-06
Filing date: 2017-01-06
Publication date: 2018-07-12

Abstract

A method for producing direct reduced iron from iron oxide and carbonaceous material is described. The iron oxide may comprise iron ore and residues from iron and steel production. A mix of iron oxide and carbonaceous material may be continuously fed onto the hearth of a rotary hearth furnace. The material may travel less than one rotation through the furnace at a temperature to cause the reducing agent to react with the iron oxide to form direct reduced iron that may be continuously discharged. The material may be turned over, moved, and mixed when traveling through the furnace. Apparatuses and systems for producing direct reduced iron from iron oxide and carbonaceous material are also described.

Description

PRODUCTION OF DIRECT REDUCED IRON BACKGROUND

[0001] This invention generally relates to the production of direct reduced iron.

[0002] The steel industry that is operating Electric Arc Furnaces (EAF) may use scrap as feed material. For some steel grades it may be necessary or useful to replace a certain part of the charge by an iron product having fewer impurities, e.g., pig iron, direct reduced iron (DRI) or hot briquetted iron (HBI). DRI and HBI may be produced by reducing iron oxide at high temperature through the use of carbonaceous materiel or gas containing carbon monoxide (CO) and/ or hydrogen.

[0003] Many conventional metallurgical processes, such as iron and steel making, may produce natural by-products and waste materials in the form of dust and sludge that may contain a high percentage of iron oxide. Due to its high monetary value, it may be desirable to reclaim the iron in this material for reuse; however, the presence of zinc and lead oxides or, in some instances, oil and/ or grease, and other impurities, may make recycling the iron difficult and impractical. This material may not be recovered by the conventional process of iron and steel making. It may be treated separately to recover iron in the form of DRI or HBI, on the one side and zinc, lead and other metals on the other side, in a direct reduction process.

[0004] The production of DRI on the basis of iron ore and/ or by-products may be

accomplished through a reaction with carbon monoxide, hydrogen and/ or solid carbon.

Typically iron oxide and a carbonaceous material, e.g., coal, may be charged into a furnace hearth and heated. At higher temperatures (e.g., above 900°C) coal may react to produce carbon monoxide (C + CO2 = 2CO, this is known as the Boudouard reaction) which may react with the iron oxide (Fe203 + 3CO = 2Fe + 3CO2). The carbon monoxide, carbon dioxide, and/ or hydrogen gases may be referred to as process gas. A process of this kind may be carried out, for example, in a rotary hearth furnace.

[0005] DRI may provide one or more of the following advantages over other types of iron, such as steel scrap: a known composition, fewer impurities, and may be continuously charged in steel making furnaces. Also, DRI processes may use temperatures of less than 1000°C, as compared to indirectly reduced iron, produced in blast furnaces, which may use liquid iron at temperatures of about 1350°C.

[0006] The reduction process, which may require mixing of the reducing agent and iron oxide at high temperatures, may be carried out in rotary hearth furnaces ("RHF"). Conventional RHF technology may be generally described in U.S. Patent Nos. 5,186,741 and 4,701,214. The rotary hearth furnace may comprise a furnace having a rotating annular furnace bottom lined with refractory material on the top side and turns in an annular casing that may also be refractory lined.

[0007] In conventional DRI production process, the input material may be prepared before it is charged into the rotary hearth furnace. The input material preparation may include mixing, pelletizing or briquetting, and drying. The furnace may be heated to temperatures 1200-1400°C by burners installed in the roof or the side walls of the furnace. Once in the furnace, the pellets or briquettes of iron oxide may react with the reducing agent to produce direct reduced iron that may be discharged from the hearth. Because the input material may have a low thermal conductivity, the furnace temperature may be considerably higher than the temperature required for the reduction reaction to insure that the temperature in the inner core or center of the pellet or briquette achieves the temperature to cause the reduction reaction.

[0008] Accordingly, more efficient and/ or cost-effective apparatuses, systems, and methods for the production of direct reduced iron and recycling of iron and steel making by-products may be desirable.

SUMMARY

[0009] According to various aspects, more efficient and/ or cost-effective apparatuses, systems, and methods for the production of direct reduced iron are described.

[0010] A method and apparatus for producing direct reduced iron from iron oxide and carbonaceous material is described. The iron oxide may comprise iron ore and/ or residues from iron and steel production. A feed material comprising iron oxide and a carbonaceous material may be continuously fed onto the hearth of a rotary hearth furnace. The feed material may travel for a less than one rotation through the rotating furnace, where the temperature is sufficient to cause reaction of the reducing agent and the iron oxide to form direct reduced iron, which may be then discharged continuously. In order to improve the heat transfer through the material layer on the hearth, the material may be turned over and moved one or more times when the hearth is rotating.

DESCRIPTION OF THE DRAWINGS

[0011] The various embodiments described herein may be better understood by considering the following description in conjunction with the accompanying drawings.

[0012] FIG. 1 includes a schematic illustrating a rotary hearth furnace according to the present invention. [0013] FIG. 2 includes a cross-sectional view illustrating the rotary hearth furnace shown in FIG. 1.

DESCRIPTION

[0014] As generally used herein, the articles "one", "a", "an" and "the" refer to "at least one" or "one or more", unless otherwise indicated.

[0015] As generally used herein, the terms "including" and "having" mean "comprising".

[0016] All numerical quantities stated herein are approximate, unless indicated otherwise, and are to be understood as being prefaced and modified in all instances by the term "about". The numerical quantities disclosed herein are to be understood as not being strictly limited to the exact numerical values recited. Instead, unless indicated otherwise, each numerical value included in this disclosure is intended to mean both the recited value and a functionally equivalent range surrounding that value.

[0017] All numerical ranges recited herein include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10.

[0018] In the following description, certain details are set forth in order to provide a better understanding of various aspects of apparatuses, systems, and methods for the production of direct reduced iron. However, one skilled in the art will understand that these aspects may be practiced without these details and/ or in the absence of any details not described herein. In other instances, well-known structures, methods, and/ or techniques associated with methods of practicing the various aspects may not be shown or described in detail to avoid unnecessarily obscuring descriptions of other details of the various aspects.

[0019] The present invention may provide more cost-effective and/ or efficient apparatuses, systems, and methods for the production of direct reduced iron, and/ or recycling of iron and steel making by-products, and/ or treating metal oxide fines to recover elemental iron from iron-bearing materials including iron-bearing ores, steel mill waste, and other metallurgical process waste.

[0020] The present invention may provide improved energy efficiency, heat transfer, and/ or no or reduced material preparation, such as agglomeration by pelletizing or briquetting of the feed material. [0021] The present invention may provide an improved method to achieve more efficient production of direct reduced iron at moderate furnace temperatures relative to conventional methods. The present invention may provide more uniform heating of the various layers of the feed material by turning over the feed material one or more times, such that a lower furnace temperature may be used to cause the reduction reaction.

[0022] The present invention may provide continuous mixing and/ or turning over and moving of the feed material on the hearth to improve heat transfer to and heating of the feed material.

[0023] The present invention may provide counter-current travel of the feed material and process gases in the combustion chamber.

[0024] The present invention may provide a furnace having improved energy efficiency by using sensible heat and chemical energy of the process gas and other volatile matter to provide the energy/ temperature to cause the direct reduction of iron.

[0025] The present invention may comprise a furnace including a plurality of arms each having a plurality of ploughs to turn over and move the feed material in alternating directions when the hearth is rotating.

[0026] The present invention may comprise a furnace including a plurality of stationary ploughs, i.e., each plough fixed to the arm, which may be more accessible during operation for cleaning of accretions of feed material relative to conventional methods.

[0027] The present invention may provide a method to produce direct reduced iron comprising up to 5 weight percent carbon, based on the total weight of the composition, when desired for the subsequent melting and production of molten metal. For example, the present invention may produce direct reduced iron comprising carbon up to 4 weight percent, 1-5 weight percent, and 4-5 weight percent, based on the total weight of the composition.

[0028] As described in more detail below, a rotary hearth furnace comprising one combustion chamber to produce direct reduced iron is illustrated in FIGS. 1 and 2. The furnace may comprise burners, inlet(s) for feed materials and gases, and outlet(s) for reaction products and by-products. Iron oxide materials and reducing agents may be provided through the inlet(s) and interact with one another in a reduction reaction in the combustion chamber before exiting the chamber through outlet(s) as direct reduced iron and gas by-products. The iron oxide compounds, reducing agents, and other additives may be provided onto the hearth by the same or different inlet. The inside of the combustion chamber may be lined with a refractory material, and/ or the chamber walls may include an insulation material. The feed materials placed onto the hearth may include iron oxide materials, reducing agents, and other additives. The feed materials may be provided at various stages of the process, i.e., before, during, or after the reduction reaction.

[0029] The reduction of iron oxide may be achieved through a reduction reaction of the iron oxide materials and the reducing agents. The iron oxide material may comprise iron ore and impurities or residue from iron and steel making, and other metallurgical processes. The impurities may comprise zinc, lead, and cadmium oxides. The iron oxide material may comprise lumps, pellets, briquettes, or fines. The fines may have a particle size from 0.1-5 mm. The reducing agents may comprise carbon monoxide, hydrogen, natural gas, coke oven gas, a gas comprising carbon monoxide and/or hydrogen, and solid carbon, e.g., coal. For example, coal may react with air and heat from the burners in the combustion chamber to form carbon monoxide.

[0030] Referring to FIG. 1 and FIG. 2, the present invention may generally comprise a rotary hearth furnace 1 to produce direct reduced iron comprising: a rotary hearth 2 within an annular combustion chamber 3, at least one inlet 12 disposed over the hearth to provide a feed material comprising iron oxide and a reducing agent, a first set of ploughs to turn over and move a portion of the feed material towards a first direction, and a second set of ploughs to turn over and move the portion of the feed material towards a second direction. The first set of ploughs and the second set of ploughs may mix the feed material, i.e., mix the iron oxide material and reducing agent. The rotary hearth 2 may comprise a rotating circular hearth within the annular combustion chamber 3. The first direction may comprise one of towards an inner edge of the hearth and towards an outer edge of the hearth. The second direction may comprise one of towards the inner edge of the hearth and towards the outer edge of the hearth. The first direction may be opposed to the second direction. The rotary hearth furnace 1 may be limited to one circular rotating hearth 2.

[0031] The hearth 2 may comprise an annular hearth frame 7, a hearth heat insulating material arranged on the hearth frame 7, and a plurality of refractory 8 arranged on the hearth heat insulating material.

[0032] The rotary hearth furnace 1 may comprise one or more wheels 11 on tracks 10 to support the hearth 2 and enable rotation of the hearth 2. The tracks 10 may be attached to a bottom side of the hearth 2. The wheels 11 may travel on the tracks 10, and the hearth 2 may be rotated by a driving device (not shown) comprising an electric motor, a hydraulic, and/ or a pneumatic motor.

[0033] The rotary hearth furnace 1 may comprise a sealing system 9 within the combustion chamber 3 to reduce or prevent gas from inside the combustion chamber 3 from escaping and/ or gas from outside the combustion chamber 3 from entering. The sealing system 9 may comprise an annular stationary chamber filled with an impermeable material, such as water or sand, attached to the furnace chamber and an annular rotating portion attached to the rotating hearth, wherein a rotating ring is immerged into the impermeable material.

[0034] The rotary hearth furnace 1 may comprise a distribution device 13 including the at least one inlet 12. The distribution device 13 may distribute the feed material across the hearth's 2 surface. The distribution device 13 may comprise a vibrating feeder, for example. The feed material may fall into the distribution device 13 through the inlet 12. The distribution device may distribute the feed material onto the hearth's 2 surface. The distribution device may substantially evenly distribute the feed material across a width of the hearth's 2 surface. For example, iron ore may be charged into the combustion chamber 3 via a distribution device 13 and a reducing agent, such as coal, may be added to the combustion chamber 3 via the same inlet 12. The rotating direction of the hearth 2 may be clockwise or, as shown in FIG. 1, counter clockwise.

[0035] The combustion chamber 3 may comprise an outer circumference wall 4, an inner circumference wall 5, and an annular roof 6. The combustion chamber 3 may comprise an annular shape having a U-shaped cross-section. The combustion chamber 3 may be lined with a refractory lining comprising one or more layers. The layer closest to the external environment may comprise an insulating material. The layer closest to the combustion chamber 3 may comprise a high temperature resistant material. The combustion chamber may comprise an exhaust pipe to exhaust gases, e.g., process gasses, therefrom.

[0036] The rotary hearth furnace 1 may comprise one or more burners (not shown) disposed in the roof 6 and/ or in the sidewalls 4 and 5 to heat the combustion chamber 3. The burners may generate, control, and/ or maintain the temperature in the combustion chamber 3. The burners may be fired with combustible gases, liquids, and/ or solids. Additional combustion air or other gas comprising oxygen may be injected through the burners and/ or through ports (not shown) adjacent to the burners to burn the process gas from the evaporation of materials. The temperature of the combustion chamber 3 may be 800-1400°C, for example, 800-900°C, 800- 1000°C, or 800-1200°C. The burners may generate sufficient heat to cause the reduction reaction of the iron oxide and the reducing agent.

[0037] The burners may preheat the combustion chamber 3. The combustion gases may or may not be preheated. The sensible heat of the off gas from the furnace may preheat the combustion gases. The combustion of the process gas may supply energy sufficient to cause the reduction reaction process. The process gas may flow in counter-current 19 to the rotation (see arrows in FIG. 1) of the hearth 2. The counter-flowing process gas may be used throughout the furnace as necessary or useful. By regulating the amount of injected oxygen in the furnace, the temperature in the combustion chamber 3 may be adjusted to achieve the desired reaction process. This control may provide a more efficient reaction process relative to conventional methods. The off gas may leave the furnace through off gas pipes 20. The process gas funnel and pipe 20 may be cooled and/ or refractory lined.

[0038] The rotary hearth furnace 1 may comprise at least one arm 14 disposed over the hearth 2. Each arm 14 may extend across the interior of the combustion chamber 3 and across a width of the hearth's 2 surface. The outer circumference wall 4 and the inner circumference wall 5 may support one or more of arms 14. The rotary hearth furnace 1 may comprise a plurality of arms 14, such as up to 24 arms, 2-24 arms, 4-20 arms, and 6-12 arms. The arms 14 may be radially spaced around the hearth 2. The plurality of arms 14 may or may not be evenly spaced around the hearth 2. A distance between the successive arms may increase, decrease, or be substantially the same in the direction of the rotating hearth. For example, a first distance from a first arm to a second arm may be equal to and/ or less than a second distance from the second arm to a third arm.

[0039] The rotary hearth furnace 1 may comprise at least one plough 15 coupled to the arm 14 or other support within the combustion chamber 3. The rotary hearth furnace may comprise a first stationary arm disposed over the hearth 2 to support a first set of ploughs and a second stationary arm disposed over the hearth 2 to support a second set of ploughs. The plough 15 may extend towards the hearth's 2 surface. The ploughs 15 may be adjustable in height relative to the hearth's 2 surface to adjust the thickness of material resting on the hearth's 2 surface and/ or ensure that the ploughs 15 do not interfere with the rotation of the hearth 2.

[0040] The rotary hearth furnace 1 may comprise at least two first sets of ploughs and at least two second sets of ploughs alternatingly disposed over the rotating hearth. For example, the rotary hearth furnace 1 may comprise three first sets of ploughs and three second sets of ploughs alternatingly disposed over the rotating hearth. A first distance from a first of the plurality of a first set of ploughs to a first of the plurality of a second set of ploughs may be greater than, equal to, or less than a second distance from a second of the plurality of a first set of ploughs to a second of the plurality of a second set of ploughs. For example, a first distance from a first arm comprising a first of the first set of ploughs to a second arm comprising a first of the second set of ploughs may be less than or equal to a second distance from the second arm to a third arm comprising a second of the first set of ploughs, and the second distance may be less than or equal to a third distance from the third arm to a fourth arm comprising a second of the second set of ploughs. The ploughs 15 may turn over and move the material 16 on the hearth 2 from side-to-side in a wave-like motion. After less than one rotation of the hearth 2, the material may be discharged from the hearth 2 by a discharging device (not shown). [0041] The plough may be at an angle greater than 0° and less than 90° to the arm that is radial to the hearth surface to turn over and move the feed material in a sideways direction along the hearth. The angle may be 15-80°, 30-45°, 45-80°, 45-60°, 60-80°, 70-80°, 45°, 60°, 70° and 80°. The spacing between adjacent ploughs may be the same or different. The spacing between adjacent ploughs may be sufficient to increase contact between the iron oxide material and reducing agent.

[0042] The ploughs may turn over, move, and mix the feeding material when the hearth rotates. For example, the feed material may comprise an upper layer closest to the external environment and a lower layer closest to the hearth's surface. The lower layer may be adjacent to or touching the hearth's surface. The plough may turn over the feed material to expose the lower layer to the heat source and cover the upper layer with the lower layer. The lower layer may be directly exposed to the heat source. Turning over the feed material may improve the heat distribution therethrough to improve the generation of carbon monoxide, and thereby the generation of DRI. The material on the hearth may be continuously turned over, moved, and mixed when the hearth is rotating to improve heat transfer in the iron oxide material. The ploughs may be arranged to move the feed material from an inner edge towards an outer edge of the rotating hearth or from an outer edge towards an inner edge of the rotating hearth while turning over the feed material when the hearth is rotating. The feed material may travel through hearth in a wave-like motion alternating from side to side.

[0043] The arms and ploughs may be cooled by a coolant circulating therethrough. The coolant may comprise a gas or a liquid, such as water, air and nitrogen. A mechanical pump may circulate the coolant through a pipe 22 to flow from one end of the arm to the other end of the arm through a channel 23 comprising two concentric pipes 24 and 25. The coolant may return through the inner pipe 25 and exit through a pipe 26. The arm may be protected from heat and insulated with an insulting and/ or refractory material 27.

[0044] The material flow lines 21 illustrate the side to side movement of the feed material by contacting the ploughs 15. Successive ploughs may be oriented in opposite directions to neutralize the sideways movement of the feed material to reduce or prevent the feed material from falling off the hearth's surface.

[0045] For example, the displacement of a portion of the feed material from an initial position on the hearth's surface to a final position on the hearth's surface may be less than the total width of the hearth's surface. The displacement of a portion of the feed material from an initial position on the hearth's surface to a final position on the hearth's surface may be up to 300 mm, such as less than 150 mm, less than 100 mm, less than 50 mm, or less than 25 mm. The displacement of a portion of the feed material from an initial position on the hearth's surface to a final position on the hearth's surface may be 25-300 mm, 50-150 mm, 75-100 mm, 25 mm, 50 mm, 100 mm, or 150 mm. The displacement of a portion of the feed material from an initial position on the hearth's surface to a final position on the hearth's surface may be less than 50%, less than 25%, less than 10%, or less than 5% of the total width of the hearth's surface. The initial position may comprise the position of the portion of the feed material when it is distributed from the distribution device to the hearth's surface. The final position may comprise the position of the portion of the feed material immediately before it is discharged from the hearth's surface and/or substantially completes one revolution, such as, at least 50%, at least 75%, at least 90%, at least 95%, at least 97% of one revolution, or 75-90% of one revolution.

[0046] The rotary hearth furnace 1 may comprise at least one stationary scraper (not shown) disposed on an inner edge of the hearth 2 and at least one stationary scraper disposed on an outer edge of the hearth 2. The scrapers may maintain the material on the hearth's surface and/ or prevent or reduce the amount of material from falling off the hearth's surface.

[0047] The rotary hearth furnace 1 may comprise at least one cleaning lance (not shown) for each set of ploughs. The lance may clean the ploughs. The cleaning lances may comprise a cleaning fluid distribution system.

[0048] The rotary hearth furnace 1 may comprise a discharging device (not shown) to discharge the direct reduced iron from the hearth 2. The direct reduced iron may be discharged prior to completing one revolution of the rotation. The discharging device that may comprise a screw conveyor installed under a hood 17 to transport DRI from the hearth 2 into a discharge chute 18. The discharge chute 18 may directly connect to a cooling device to cool the DRI or to any other equipment to further treat the DRI. The chute may be equipped with a sluice (not shown) to isolate the furnace atmosphere from the outside to avoid gas entering or exiting the furnace.

[0049] The present invention may comprise a method for production of direct reduced iron in a rotary hearth furnace. A feed material comprising iron oxide may react with a carbonaceous material at a temperature of 800-1200°C to generate metallic iron. The carbonaceous material may comprise coal, coke, petroleum coke, oil, grease, plastic waste or wood. At the same time, volatile components in the feed material, such as zinc, lead, chlorine, and alkalis, may be vaporized and evacuated with the off gas. Turning over, moving, and/ or mixing the feed material according to the present invention may improve the generation of CO (the Boudouard reaction) in the material layer 16. As a result, the CO/ CO2 ratio in the material layer may be sufficiently elevated to cause the reduction of the iron oxide by the CO. Any CO that escapes from the material layer may be combusted in the gas room above the feed material. The combustion of the CO generated by the process may produce sufficient heat to cause the reaction process. [0050] A method to produce direct reduced iron by contacting an iron oxide material and a reducing agent in a rotary hearth furnace may generally comprise providing the iron oxide material and reducing agent to a rotary hearth furnace as described above, contacting a portion of the iron oxide material and the first set of ploughs to turn over and move the portion of the iron oxide material in the first direction and contacting the portion of the iron oxide material and the second set of ploughs to turn over and move the portion of the iron oxide material in the second direction to evenly distribute heat from an outer surface of the iron oxide material to an inner core of the iron oxide material and produce direct reduced iron. The method may comprise mixing the iron oxide material and the reducing agent by successively contacting the portion of the iron oxide material with the first set of ploughs and second set of ploughs. The process gas may flow in the combustion chamber in a direction opposed to a direction of rotation of the rotating hearth. The method may comprise discharging the direct reduced iron from the rotating hearth prior to completing one revolution of the rotating hearth. The rotary hearth furnace may be limited to one circular rotating hearth.

[0051] The reducing agent may be mixed with the iron oxide material and may be charged together with the iron oxide material onto the hearth. The reducing agent may not be mixed with the iron oxide material and may be charged through a different inlet to the combustion chamber. The feed material may travel in an opposed direction from the flow of the reducing gas.

[0052] The burners may heat the reducing agent precursor, such as coal, to produce the reducing agent, such as carbon monoxide, to react with the iron oxide material. The hearth may rotate so that the feed material contacts the ploughs causing the feed material to turn over and move side-to-side along the surface of hearth and mix with the reducing agent to produce direct reduced iron. The direct reduced iron may be discharged from the hearth.

[0053] The ploughs may extend outwardly from arms towards the hearth surface. A feed material comprising the iron oxide material may be provided onto the hearth surface and mixed with the reducing agent by the ploughs as the hearth rotates. The first set of ploughs may turn over and move a portion of the feed material in a first direction and a second set of ploughs may turn over and move a portion of the feed material in a second direction. The present invention may be more efficient relative to conventional methods by repeatedly hirning over and moving the feed material in alternating directions as the hearth rotates. The metallization degree may be at least 90%, such 95-98%. Degree of metallization of DRI may be the extent of conversion of iron oxide into metallic iron during reduction. It may be defined in percentage of the mass of metallic iron divided by the mass of total iron [0054] The method may comprise continuously introducing iron oxide containing material into the furnace; continuously rotating the hearth and having ploughs installed across the hearth to mix and turn around the material on the hearth; adding at least one reducing agent in form of a solid or liquid carbonaceous material to the iron oxide; mixing the reducing agent with the iron oxide by turning it around together with the iron oxide, forming a material mix mainly containing iron oxide with impurities and reducing agent; turning around the material mix several times in order to improve heat transfer and reaction efficiency; feeding a gas containing oxygen through the roof or the inner or outer side wall of the furnace; reacting the carbon dioxide, from by the reduction reaction of the iron oxide, with carbonaceous material to form carbon monoxide as reducing gas; reacting the reducing gas with the metal oxides to form directly reduced iron; causing the gases and feed material to travel counter currently through the furnace; evaporating volatile metals, like zinc and lead, alkalis, chlorine and other impurities; withdrawing the volatile maters with the off gas from the top of the furnace; and recovering the directly reduced iron together with residues of the reducing agents after about one rotation of the hearth.

[0055] The invention may comprise a process in a rotary hearth furnace that includes mixing devices across the hearth. The feed material may comprise a mix of mainly iron oxide and carbonaceous material. Unlike in conventional furnaces, the feed material may not need to be pelletized or briquetted. The feed material may be charged onto the hearth across the whole width of that hearth. A plurality of fixed arms across the hearth may each support a plurality of ploughs to mix the feed material while simultaneously pushing it slightly sideways. The ploughs on the other fixed arm may push the feed material in an opposite direction relative to the ploughs on the previous fixed arm, i.e., when the ploughs on the first arm push the feed material inwards, the ploughs on the second fixed arm may push the feed material outwards, then the ploughs on the third arm may again push the feed material inwards, until the feed material is discharged from the hearth. After less than one rotation, the direct reduced iron may be produced from the feed material and discharged from the hearth.

[0056] The feed material on the hearth may be continuously mixed and turned around, so that the heat transfer in the feed material is improved relative to conventional methods that do not alternate turning. The temperature in the furnace may be moderate (1000-1200°C) relative to conventional processes, or only slightly higher than the temperature required to for the process reactions. The continuous mixing and alternating turning provide the improved heat exchange to favor the process reactions, i.e., on one side the Boudouard reaction in order to generate carbon monoxide from carbon dioxide and carbon and on the other side the reaction of carbon monoxide with the metal oxide in order to generate metallic iron. Intensive mixing favors heat transfer and at the same time the intensity of the reactions through improved contact of the material with the produced gases. The result of the improved reactions is the generation of a more important amount of carbon monoxide. The extra carbon monoxide reacts with the injected oxygen containing gas and generates the required heat in the furnace. The more efficient usage of process gas reduces the external energy consumption of the process.

[0057] The apparatuses, systems, and methods of the present invention may achieve more efficient reduction of iron oxide relative to conventional techniques. The present invention may provide one or more of the following advantages: no preparation of feed material, high efficiency of energy through continuous mixing and turning of the feed material in the furnace, highly metallized iron may be produced at lower furnace temperature; improved energy efficiency by burning the process gas in the furnace and by using sensible heat to preheat combustion air.

[0058] Each of the characteristics and examples described above, and combinations thereof, may be said to be encompassed by the present invention. The present invention is thus drawn to the following non-limiting aspects:

[0059] (1) A rotary hearth furnace to produce direct reduced iron comprising: a rotary hearth within an annular combustion chamber; a distribution device disposed over the hearth to provide a feed material comprising iron oxide and a reducing agent; a plurality of a first set of ploughs to turn over and move a portion of the feed material towards a first direction; a plurality of a second set of ploughs to turn over and move the portion of the feed material towards a second direction opposed to the first direction; and wherein the first direction comprises one of towards an inner edge of the hearth and towards an outer edge of the hearth, and wherein the first set of ploughs and the second set of ploughs are alternatingly disposed around the rotary hearth.

[0060] (2) The rotary hearth furnace of aspect 1, wherein the rotary hearth furnace is limited to one rotary hearth.

[0061] (3) The rotary hearth furnace of aspects 1-2, wherein the feed material has a

displacement from an initial position to a final position of about 50-150 mm.

[0062] (4) The rotary hearth furnace of aspects 1-3, wherein the combustion chamber has a temperature from about 800°C to about 1200°C.

[0063] (5) The rotary hearth furnace of aspects 1-4, wherein the plurality of a first set of ploughs comprises 2-10 first sets of ploughs and the plurality of a second set of ploughs comprises 2-10 second sets of ploughs. [0064] (6) The rotary hearth furnace of aspects 1-5, wherein the feed material is turned over and moved towards the first direction at least 2-10 times and the feed material is turned over and moved towards the second direction at least 2-10 times when the rotary hearth is rotating.

[0065] (7) The rotary hearth furnace of aspects 1-6 characterized by a metallization degree greater than about 90%.

[0066] (8) The rotary hearth furnace of aspects 1-7, wherein the first set of ploughs and the second set of ploughs are radially and unevenly spaced around the rotary hearth.

[0067] (9) The rotary hearth furnace of aspects 1-8 comprising a first distance defined from a first of the plurality of a first set of ploughs to a first of the plurality of a second set of ploughs is less than a second distance from a second of the plurality of a first set of ploughs to a second of the plurality of a second set of ploughs.

[0068] (10) A method to produce direct reduced iron using the rotary hearth furnace of aspects 1-9, wherein the rotary hearth is rotating within the annular combustion chamber, the method comprising: providing the feed material comprising iron oxide and a reducing agent onto the rotating hearth; turning over and moving a portion of the feed material in the first direction by contacting the feed material and the first set of ploughs; and turning over and moving the portion of the feed material in the second direction by contacting the feed material and the second set of ploughs.

[0069] (11) The method of aspect 10 comprising displacing the feed material from an initial position to a final position of about 50-150 mm by contacting the feed material and one of the first set of ploughs and the second set of ploughs.

[0070] (12) The method of aspect 10-11 comprising mixing the feed material by contacting the feed material and one of the first set of ploughs and the second set of ploughs.

[0071] (13) The method of aspects 10-12 comprising discharging the direct reduced iron from the rotating hearth prior to completing one revolution of the rotating hearth.

[0072] (14) The method of aspects 10-13 comprising flowing a process gas through the rotating hearth in a direction opposed to a direction of rotation of the rotating hearth.

[0073] (15) The method of aspects 10-14, wherein the rotary hearth furnace is limited to one circular rotating hearth.

[0074] While particular embodiments of apparatuses, systems, and methods for the production of direct reduced iron have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific devices, systems, and methods described herein, including alternatives, variants, additions, deletions, modifications and substitutions. This application including the appended claims is therefore intended to cover all such changes and modifications that are within the scope of this application.

Claims

CLAIMS What is claimed is:

1. A rotary hearth furnace to produce direct reduced iron comprising: a rotary hearth within an annular combustion chamber; a distribution device disposed over the hearth to provide a feed material comprising iron oxide and a reducing agent; a plurality of a first set of ploughs to turn over and move a portion of the feed material towards a first direction; a plurality of a second set of ploughs to turn over and move the portion of the feed material towards a second direction opposed to the first direction; wherein the first direction comprises one of towards an inner edge of the hearth and towards an outer edge of the hearth, and wherein the first set of ploughs and the second set of ploughs are alternatingly disposed around the rotary hearth.

2. The rotary hearth furnace of claim 1, wherein the rotary hearth furnace is limited to one rotary hearth.

3. The rotary hearth furnace of claim 1, wherein the feed material has a displacement from an initial position to a final position of about 50-150 mm.

4. The rotary hearth furnace of claim 3, wherein the combustion chamber has a temperature from about 800°C to about 1200°C.

5. The rotary hearth furnace of claim 1, wherein the plurality of a first set of ploughs comprises 2-10 first sets of ploughs and the plurality of a second set of ploughs comprises 2-10 second sets of ploughs.

6. The rotary hearth furnace of claim 5, wherein the feed material is turned over and moved towards the first direction at least 2-10 times and the feed material is turned over and moved towards the second direction at least 2-10 times when the rotary hearth is rotating.

7. The rotary hearth furnace of claim 5 characterized by a metallization degree greater than about 90%.

8. The rotary hearth furnace of claim 1, wherein the first set of ploughs and the second set of ploughs are each supported by a stationary arm radially disposed over and unevenly spaced around the rotary hearth.

9. The rotary hearth furnace of claim 8 comprising a first distance from a first arm supporting a first of the first set of ploughs to a successive second arm supporting the second set of ploughs is less than a second distance from the second arm to a successive third arm supporting a second of the first set of ploughs.

10. A method to produce direct reduced iron using the rotary hearth furnace of claim 1, wherein the rotary hearth is rotating within the annular combustion chamber, the method comprising: providing the feed material comprising iron oxide and a reducing agent onto the rotating hearth; turning over and moving a portion of the feed material in the first direction by contacting the feed material and the first set of ploughs; and turning over and moving the portion of the feed material in the second direction by contacting the feed material and the second set of ploughs.

11. The method of claim 10 comprising displacing the feed material from an initial position to a final position of about 50-150 mm by contacting the feed material and one of the first set of ploughs and the second set of ploughs.

12. The method of claim 10 comprising mixing the feed material by contacting the feed material and one of the first set of ploughs and the second set of ploughs.

13. The method of claim 10 comprising discharging the direct reduced iron from the rotating hearth prior to completing one revolution of the rotating hearth.

14. The method of claim 10 comprising flowing a process gas through the rotating hearth in a direction opposed to a direction of rotation of the rotating hearth.

15. The method of claim 10, wherein the rotary hearth furnace is limited to one circular rotating hearth.