Title of Invention	A FURNACE FOR DIRECT REDUCTION OF IRON OXIDES AND METHOD FOR CONTROLLING TEMPERATURE UNIFORMITY OF THE BURDEN IN A DIRECT REDUCTION SHAFT DEVICE.
Abstract	A method and upparatus for increasing hydrocarbon input to a direct redution shaft furnace (13) while controlling the temp[erature uniformity of the center portiuon (26) of the burden wiihin the furnace (12) wherein the hydrocarbon gases used in the XXX reduction may be preheated, which increases the temperature of the hydrocarbon gases, and therefor increases the XXX temperature of the upflowing gas as it rises from the lower section (66) of the furnace (12) into the center (26) of the XXX of the upflowing gas may be removed before it enters the reduction zone of the furnace. The removed

Title of Invention

A FURNACE FOR DIRECT REDUCTION OF IRON OXIDES AND METHOD FOR CONTROLLING TEMPERATURE UNIFORMITY OF THE BURDEN IN A DIRECT REDUCTION SHAFT DEVICE.

Abstract

A method and upparatus for increasing hydrocarbon input to a direct redution shaft furnace (13) while controlling the temp[erature uniformity of the center portiuon (26) of the burden wiihin the furnace (12) wherein the hydrocarbon gases used in the XXX reduction may be preheated, which increases the temperature of the hydrocarbon gases, and therefor increases the XXX temperature of the upflowing gas as it rises from the lower section (66) of the furnace (12) into the center (26) of the XXX of the upflowing gas may be removed before it enters the reduction zone of the furnace. The removed

Full Text	METHOD AND APPARATUS FOR CONTROLLING TEMPERATURE UNIFORMITY OF THE BURDEN IN A DIRECT REDUCTION SHAFT FURNACE FIELD OF THE INVENTION The present invention relates to a method and apparatus for controlling the temperature during the direct reduction of iron. More particularly, the present invention relates a method and apparatus which controls the temperature uniformity of the center portion of the iron burden in a direct redaction shaft furnace thereby allowing a higher amount of hydrocarbons to be used throughout the reduction process. BACKGROUND OF THE INVENTION The production of direct reduced iron in both. hot and cold discharge plants oocure in a vertical shaft furnace and involves reduction of iron ore or iron oxide as it moves downwardly in a reduction zone of a vertical shaft furnace through which is passed a suitable hot reducing gas, known as bustle gas. Bustle gas, which is principally composed of carbon monoxide and hydrogen, is introduced to the shaft furnace at temperatures in the range of about 700°C to about 1100oC. The ore is charged at the top of the furnace and caused to flow downwardly through the reduction zone wherein it is reduced by healed reducing gas which flows upwardly through the furnace, after which the reduced ore flows into and downwardly through the transition zone to be carburized if desired. For cool discharge plants, after passing through the reduction zone, the ore is cooled in a cooling zone through which is passed a gaseous coolant at a temperature below about 200oC Typically, in a cool discharge furnace, both the reducing gas and cooling gas are re- circulated, optionally in closed loops, to which streams of fresh (i,e, "make-up") reducing gas are added and from which streams of spent gas are removed. The reducing gas being fed to the reduction zone of the furnace is typically at an elevated temperature, which is required by reaction kinetics. The reducing gas is caused to 1 WO 2004/055832 PCT/U52002/039631 contact the downwardly moving iron ore to reduce the iron oxides therein according to the following basic reactions: (1) 3Fe2O3 + H2/CO=>2Fe1O4 + H2O/CO2 (2) Fe3OH + H2/CO => 3feO + H2O/CO2 (3) FeO + H2/CO=>Fe + H2O/CO2 In the production of direct reduced iron (DRI), it is desirable to increase the product carburization and to increase in-situ reforming in the lower portion of both hot and cold direct reduction furnaces by injecting hy drocarbons. This is a proven means to increase the productivity of direct reduction furnaces without adding new equipment to increase reducing gas capacity. This is also a proven means to increase product carbon. The hydrocarbons react with the hot DRL, depositing carbon and Liberating hydrogen gas. However, the reaction of the hydrocarbons to form carbon and hydrogen is endothermic. Thus, the newly formed cool hydrogen gas flows upward through the center of the furnace (called npflow), cooling the descending iron material. Because of temperature considerations, the amount of hydrocarbons that can be added to the lower portion of the furnace is limited by either low center bed temperature or low product discharge temperature. As more hydrocarbons are added to the lower portion of the furnace, cooled hydrogen gas is produced which rises into the reduction zone and the center bed temperature decreases, thus reducing reaction kinetics. The desired temperature of the burden is above 650oC. When the temperature of the burdcn is reduced to the range of 625-650°C, the average product metallization begins to stop because the material in the center of the furnace is not properly reduced/metallited. Also, in hot discharge, furnaces, product discharge temperature must be maintained above about 700°C for proper subsequent briqueting. For hot transport applications, higher discharge temperature of the DRI makes more sensible heat available in the melter ,thus reducing the power required for melting. As hydrocarbons are added to the lower postal of a hot discharge furnace, it is possible that tha average product temoperature will bebelow 700°C before the center bed temperature reaches the point that metallization drops significantly. 2 WO 2004/055832 PCT/U52002/039631 To date, several techniques have been used to allow higher flows of hydrocarbons to the furnace lower cone, to extend the limits noted above, and to control the temperature of the burden. For cold discharge furnaces, some examples of techniques being used are cooling zone bleed and simplified center injection. However, prior, art center injection techniques lack means to control or measure hydrocarbon or reducing gas flow into the center injection system and lack means to force flow into the center injection line. Another technique for temperature and carbon control which has been employed is the injecting of cold natural gas into the direct reduction furnace. The natural gas mixes with other gases already present in the furnace and is heated by the gas and solids already present in the furnace. As the hydrocarbons in the natural gas are heated, they crack to form H2 and deposit carbon on the product or they are reformed by reaction with H2O and CO2 in the gas furnace to make additional H2 and CO, The present limitation on the injection of natural gas is temperature. As more cold natural gas is injected, the center bed temperature decreases, which decreases the rate of reaction kinetics. At low flow rates of the cold natural gas, the production benefit from additional reducing gases will outweigh the disadvantage from decreased reaction kinetics. But when the temperatures in the center bed decrease to a certain point, any further production benefit from additional reducing gases will be negated by the decrease in reaction kinetics. This limits the amount of natural gas that can be added to the furnace for in situ cracking and reforming, What is therefore needed is a means and method for increasing the amount of hydrocarbon gas supplied to the transition zone and/of cooling section of a direct reduction furnace while maintaining the temperature of the central reaction zone of the direct reduction furnace at a temperature favorable to the direct reduction of iron. SUMMARY OF THE INVENTION The present invention provides a method and apparatus which controls the temperature uniformity of the center portion of the iron burden in a direct reduction shaft furnace thereby allowing a higher amount of hydrocarbons to be used in the cooling zone. 3 WO 2004/055832 PCT/U52002/039631 The invention is an efficient improvement of existing methods, particularly, the Midrex method and apparatus for direct reduction of iron which is incorporated by reference herein. Typically, the center portion of iron bearing material in the burden of a direct reduction furnace is cooler than the rest of the burden due to upflowing gases which, is injected into the lower cooling section of the furnace and rises upwardly into the center portion of the reducing section of the furnace. By increasing the temperature of the burden in the center portion of the furnace, the iron is reduced under much more favorable conditions. Thus, the present invention is advantageous to achieve the objects stated herein. Disclosed herein are methods for heating the center region of the furnace, particularly the burdeen. In a first embodiment of the invention a hydrocarbon gas used in direct reduction may be preheated, which increases the temperature of the upflowing gas as it flows upwardly into the center of the burden. Alternatively, a portion of the upflowing gas may be removed before it enters the reduction zone of the furnace. The removed upflowing gas, known as hot bleed gas, may be ducted to a top gas scrubber of the furnace or msy be mixed with the main reducing gas stream of the furnace for reintroduction to the furnace. Alternatively, hot reducing gas may be directly injected into the center portion of the burden, offsetting the effect of the upflowing gases. The center injected hot reducing gas may be split off from the maia reducing gas stream or may be generated by a partial oxidation reactor. Finally, it will be appreciated by those skilled in the art that the above noted embodiment may be employed individually or in combination depending on the DRI plant facility, OBJECTS OF THE INVENTION The principal object of the present invention is to provide a method and apparatus for controlling temperature uniformity in the burden of a direct reduction shaft furnace. It is another object of the present invention to provide an apparatus and method which allows the use of higher quantities of hydrocarbons or other gases within the lower 4 WO 2004/055832 PCT/U52002/039631 portion of both hot and cold discharge furnaces so that product carbon and/or in-situ reforming may be increased white the temperature within the center of the direct reduction furnace is maintained at a temperature favorable to the direct reduction of iron, thereby increasing the degree of carburization of the iron product without adversely affecting the metallization of the iron burden. Another object of the present invention is 10 provide an apparatus and method for conserving energy in a direct reduction furnace by maintaining a uniform temperature throughout the burden. Another object of the invention is to provide a method and apparatus for increasing the temperature of the center burden of a direct reduction furnace in order to offset the cooking effect caused by upflowing gases into the reduction zone of the furnace, and thereby increasing metallization of the burden, Another object of the present invention is to provide control options to DR plant operators to allow significantly higher levels of hydrocarbon gas additions, while reducing the temperature variations across the burden. BRIEF DESCKIFTION OF THE DRAWINGS The foregoing and other objects will become more readily apparent by referring to the following detailed description and the appended drawings in which: Figure 1 is a schematic diagram showing an example of a typical direct reduction shaft furnace system for cool discharge product according to the Midrex process. Figure 2 is a diagram showing center injection of reducing gas split from the main reducing gas stream. 5 WO 2004/055832 PCT/U52002/039631 Figure 3 is a diagram showing center injection of reducing gas produced by a partial oxidation reactor. Figure 4 is a diagram showing the entry of preheated in situ natural gas into a direct reduction furnace. Figure 5 is a diagram showing a hot cone bleed from a furnace with the hot cone bleed gas sent to a top gas scrubber. Figure 6 is a diagram showing a hot cone bleed from a furnace with the hot cone bleed gas combined with the main reducing gas stream, DETAILED DESCRIPTION The present indention provides a method and apparatus which controls the temperature uniformity of the center portion of the iron burden in a direct reduction shaft furnace thereby allowing a higher amount of hydrocarbons to be used throughout the reduction process. The invention is an efficient improvement of existing methods, particularly, the Midrex process and apparatus for direct reduction of iron. The Midrex process and apparatus far direct reduction is disclosed in U.S. Pat No. 3,748,120 entitled "Method of Reducing Iron Oxide to Metallic Iron," U.S. Pat. No, 3,749,386 entitled "Method for reducing Iron Oxides in a Gaseous Reduction Process," U.S. Pat, No. 3,764,123 entitled "Apparatus for reducing iron Oxide to Metallic Iron," U,S. Pat. No. 3,816,101 entitled "Method for Reducing Iron Oxides in a Gaseous Reduction process," and US, Pat. No. 4,046,557 entitled "Method for producing Metallic Iron Particles." all of which are incorporated by reference herein. Referring to the drawings, and particularly FIG, 1, there is shows a schematic diagram of an example of a typical prosses and apparatus for the Midrex process direct reduction of metal oxides such as iron ore to which the present invention is applicable in 6 WO 2004/055832 PCT/U52002/039631 cool discharge plants, It is to be understood that the present, invention is applicable to both hot and cool DR plants, however, for the case of visualization, a cool discharge plant is shown. The system 10 of FIG- 1 is a typical commercially available system used in many Direct Reduction Iron (DRI) plants. The system 10 includes a shaft furnace 12 having a refractory lining and generally having a feed hopper 14 from which iron ore 16 is fed to the furnace for reduction into iron using reformed gases. The furnace 12 typically has a charging zone 108, a reduction zone 26, a transition zone 66, a cooling zone 38, and a discharge zone 110. The iron ore 16 descends by gravity into the shaft furnace 12 from the hopper 14 through a pellet feed pipe 18. The pellet feed pipe 18 also serves as a gas seal pipe. At the bottom of the furnace 12 is a pellet discharge pipe 20 which also serves as a gas seal pipe. A pellet discharge device 22 of any conventional type is located below the discharge pipe 20 and receives metallic iron, thereby establishing gravitational descent of the burden through the furnace 12, Near the upper portion of the furnace 12 is a bustle and tuyere system, indicated generally at 24, through which hot reducing gas is introduced to flow upwardly through a reduction zone 26 in counterflow relationship to the downwardly moving iron ore 16, as shown by the arrows, and after reacting with the burden exits from the furnace 12 through a gas off-take pipe 28 located at the top of the furnace 12. The hot reducing gas, flowing from the bustle system 24 to the off-take pipe 28, serves to heat the iron oxidel6 and to reduce it to metallized iron. Throughout this Specification and appended claims, the term "metallized iron" is intended to include metal such as sponge iron, pellets, lumps, briquettes, DRI or other compacted forms of reduced metal and the like which contain at least 80% of their metal in the metallic state with the balance substantially in the form of metallic oxides. Metallized in this sense does not mean coated with metal, but nearly completely reduced to the metallic state. The spent gas from off-take pipe 28 flows through a pipe 30 to a scrubber 32 which cools the spent gas and removes dust. Scrubber 32 can be of any conventional type used in live, industry. After leaving the scrubber 31, the spent gas is ducted to a reformer 44. 7 WO 2004/055832 PCT/U52002/039631 Thereafter it is recycled. In addition, cooled gas is introduced and re-circulated to a lower region of the furnace 12 via a cooling inlet pipe 34 which connects to a cooling gas introduction and distributing member 36 located within the furnace 12 and arranged to distribute The cool gas into the burden 16. Hydrocarbon gas is added to the cool gas from a fuel source112 prior to a reintroduction into the burden 16. The cool gas introduced into the burden through distributing member 36 flows upward through a cooling zone 38 in counterflow relationship with downwardly moving burden 16 and disengages from the burden. 16 at a cooling region off-take member 40 which connects to a cooling region off take pipe 42, The spent gas from the off-take pipe 42 is re-circulated and recycled. The reformer 44 which generates hot reducing gas has fuel fired burners 46, a flue pipe 48 and a plurality of catalytic reformer tubes 50, only one being shown. Combustion air from a blower 52 is fed to the burners 46 through a flow regulating valve 54. Fuel is fed to the burners 46 through a pipe 56 from a fuel source 58 and flow regulating valves 60. The reformer 44 is connected to the bustle system 24 by a pipe 62. The simplest explanation of the shaft furnace-based direct reduction plant of the Midrex method in operation starts with the entry of the hot reducing gas through the bustle system 24 at the periphery of the reduction zone 26. The iron oxide burden 16 descends through the reduction zone 26 while the reducing gas ascends from the bottom of the reducing zone 26 through the iron oxide burden 16, reducing the burden 16 in the process, and exiting the shaft furnace 12 through an off-take 23 above stockline 64 of the burden 16. The reducing gases can be externally generated or result from reactions within the shaft furnace 12. The metallized iron 16 then descends through the furnace transition zone 66 to the cooling zone 38 and to the discharge zone 110, which may result in either a hot or cold product, depending on the equipment installed. Additionally, the iron bearing material 16 can be further reacted with hydrocarbon gases in either the transition zone 66 or the cooling zone 38 to increase the carbon content of the product being discharged. This has proven to 8 WO 2004/055832 PCT/U52002/039631 be a significant issue in steel production today. Higher carbon content in the metallized product, DRI, offers the steelmaker significant savings by substituting oxidation of carbon for electric energy in melting. The hydrocarbon gases can be and typically are added at various locations in the transition zone 66 or cooling zone 38 from fuel sources 114 and 112 respectively. As a result of the addition of these, hydrocarbon, gases there is an ascending gas-flow, equal to or greater than the quantity of hydrocarbon gases added, which flow up through the center of the furnace 12 all the way to the stockline 64 if no other steps are taken. This also holds true for lower seat leg gases, but they are usually very small in relative volume. The stream of reacted hydrocarbons is colder and of different quality than the reducing gases entering at the bustle 24 and results in lower burden temperatures in the central area of the furnace 12. Since temperature and quality directly affect the kinetics of reduction, the degree nf metallization reached by the burden 16 descending in the central furnace area is different than that of the remainder of the furnace 12. limiting this variation in furnace metallization is very important to the optimization of the plant. The reaction of the hydrocarbon gases is very beneficial and efficient energy wiseT but the loss of metallization in the central furnace burden can be significant if it is ignored. Generally, normal bustle gas temperature ranges from 700-1100oC. Center bed temperature, in both not and cold discharge plants, ranges from about 600 to about 800oC. Providing a small flow of high temperature reducing gas to the center of the furnace 12 raises the center bed temperature. In typical operation of a direct reduction furnace, the bustle gas stream enters from the periphery of the furnace 12. Referring now to Figures 2 and 3, a preferred embodiment of the present invention is shown. The invented apparatus and method provides a means of injection of hot reducing gases into the center of a direct reduction furnace 12 so that temperature within the center of the burden 16 is maintained within a preferred range. In accordance with this invention, the hot reducing gas is ducted to the vertical centerline of time furnace 12 -where it is allowed to mix with the upflowing stream of hydrocarbon cooling gases from the transition zone 66 of the furnace 12. The 9 WO 2004/055832 PCT/U52002/039631 invented apparatus and method is applicable to shaft furnaces discharging either hot or cold metallized product. The source of the hot reducing gas may be from either a reformer 44 or a partial oxidation reactor 44(a) sucb as the OXY+ system as disclosed in U.S, Pal, No. 5,997,596 entitled "Oxygen Fuel Boost Reformer Process and Apparatus". In accordance with Figure 2, prior to entering the furnace 12, a portion of the high temperature bustle gas stream is split-off and injected into the center of the furnace 12. A variable or fixed restriction device 68 is used to provide adequate pressure drop to force the bustle gas to flow through the center injection line 116, The flow rate of hot bustle gas through the center injection line 116 is preferably measured using a venturi 44(b), however, other suitable measuring means may be used. In accordance with Figure 3, a partial oxidation reactor 44(a) or multiple reactors generate the hot reducing gas which is then ducted to the center of the furnace 12, eliminating the need to divert a small portion of hot bustle gas to the center of the furnace 12. In ganeral the partial oxygen reactor44(a)burns oxygen 70 and a hydrocarbon fuel 72 such as natural gas to produce a high quality, high temperature reducing gas. This gas is well suited to use for center injection into a direct reduction furnace 12. Since the quantity and ratio of oxygen and hydrocarbon fuel are tightly controlled for propey combastion in the oxidation reactor 44(a), the mechanism to vary the flow rate of center injection gas may easily be built into the partial oxidation reactor 44(a) design. In an alternative embodiment of the invention in accordance with FIG. 4, preheated natural gas 74 is added to a plurality of nozzles 76, 78, 80, respectively, which are located around the periphery of the transition zone 66 or the discharge zone 110 and which are not used for cooling so as to increase the amount of hydrocarbons used within the lower cone 82 of the furnace l2 whie maintaining an adequate center furnace temperature. This entails preheating a hydrocarbon stream and adding the preheated hydrocarbon stream to any of the plurality of nozzles 76, 78, 80 which are not used for cooling of the direct reduced iron. When preheated natural gas 74 is injected into non-cooling inlets 76, 73, 80 of the furnace 10 WO 2004/055832 PCT/U52002/039631 12, additional energy is shifted to the furnace 12 and uniformity of burden 16 temperatures is improved. The apparatus includes a heat exchanger 84 to preheat the natural gas 74 before injecting it into the direct, reduction furnace 12. Hot flue gas frorn a combustion process is supplied to the beat exchanger 84 to preheat the natural gas 74 stream. The flue gas may be from a reformer 86 or from any other source of combustion flue gases. The temperature to which the natural gas 74 is preheated is typically up to 450oC, although the temperature is only limited at the upper end by cracking of the heated gas. That is, the preheat temperature must be lower than the temperature at which cracking of the natural gas 74 would present problems with carbon deposition in the heat exchanger 84 or piping. It will be appreciated by those of skilled in the art that the preheat temperature can be as high as 550°C depending upon the composition of the preheated gas and its tendency to crack. Alternatively, the natural gas 74 is mixed with H2, H2O, CO2 or any other gas that contains H2 H2O and/or CO2 before the preheating stage. Addition of any of these gases will decrease the partial pressure of the hydrocarbons and thus, their tendency to crack during or after preheating. The addition of H 2 directly decreases the tendency of hydrocarbons to crack. H2O and/or CO2 directly decreases the tendency of any H2 and CO to form carbon. With the addition of these gases the preheat temperature limit may be raised to 700°C The invented method and apparatus allows more natural gas 74 to be injected into the furnace 12 before the furnace temperatures cool to the point where any further production benefit from additional reducing gasses will be negated by the decrease in reaction kinetics. Adding more natural gas 74, because it is hot, increasses situ reforming, and cracking, thereby increasing the amount of reducing gas in the direct reduction furnace 12, which results in a higher production rate from the direct reduction furnace 12. 11 WO 2004/055832 PCT/U52002/039631 In still another embodiment of the present invention and referring to FIGs. 5 and 6, an outlet 28 is provided for the upflowing gases that cool the center of the burden 16. This technique is known as "hot cone bleeding". The upflowing gas once collected can be contained in the collected stream. This effectively redistributes the collected gas stream in the full reducing, gas flow at the furnace bustle 24, eliminating its effect on the center bed. Limiting the quantity of upflowing gas from the discharge zone 110 to the reducing zone 26 has been used for many years to limit the temperature variation or loss in the central burden 16. With a cold discharge plant, where a recirculating stream of gas is used to cool the metallised product before discharge, a method called "Cooling Zone Bleed" has been used for over 25 years to accomplish this control. The methods of bleeding have changed to take advantage of the hydrocarbon reactions from the natural gas additions to the cooling gas stream, but the basic control objective remains keeping the temperature of the central furnace burden 16 above a certain minimum. Historically, however, if a particular furnace 12 had no coaling gas recirculating stream (i.e. hot discharge), the use of a cooling zone bleed was not available. The invented method and apparatus for providing a hot cone bleed removes upflowing gas from the transition zone 66 of the furnace 12 and reintroduces the gas, as reducing gas, to the upper section or reducing zone 26 of the furnace 12. The upflo wing gas, once collected, may be injected at one, or several location in the pieces in order to take, advantage of the reducing gases contained in the collected gas stream. Mixing the collected gas stream with the main reducing gas stream effectively redistributes the collected gas stream in the full reducing gas flow at the furnace bustle 24, Thus, the cooling effect of the gas stream is distributed throughout the furnace 12 by the main reducing gas stream, eliminating the concentrated cooling effect at the center of the furnace bed. By reducing the amount of upflowing gas in the center of the furnace 12, higher bed temperatures are maintained, thus increasing reaction kinetics. The upflowing gas that is 12 WO 2004/055832 PCT/U52002/039631 removed is rich in reducing gas and is recycled back to the process through either the top gas scrubber 88 of the furnace 12 or the main reducing gas stream leading to the furnace 12, Preferably, the invented apparatus has a plurality of gas off-take pipes 90 and 92 which extend into the furnace 12 in the trransition zone 66, The pipes 90 and 92 have slots or openings 94 which face downwards toward the discharge zone 110. Upflow gas from the discharge zone 110 is drawn through the slots 94 into the pipes 90 and 92. Once the upflow gas exite the furnace 12, it is referred to as hot cone bleed gas because it is removed from lower cone 82 of the furnace. The gas drawn into each pipe 90 and 92 is sent through a venturi 96 to provide some initial coolng and scrubbing. The gas then passes through quenched pack type scrubbers 98 and 100 for further cooling and scrubbing. Flow control valves 102 and 104, located down stream from the scrubbers 98 and 100, control the flow rate of gas exiting the scrubbers 98 and 100, and therefore control the amount of gas drawn into pipes 90 and 92 from the cooling zone 38 of the furnace 12. The cool and clean hot cone bleedgas can be returned to the furnace 12 in one of two locations. As shown in Figure 5, the hot cone bleed gas can be routed to the top gas scrubber 38 of the furnace 12 so that the gas is injected underneath the packing of the scrubbers 98 and 100, similar to process gas recycle. The hot cone bleed gas exiting the furnace 12 is at a higher pressure than the top gas scrubber 88, so the system is natural flow. Alternatively, as shown in Figure 6, the cool and clean hot cone bleed gas can be compressed by a compiessor 106 and delivered directly to a bustle gas duct 24 for injection into the furnace reduction zone 26. Since hot cone bleed can be adjusted to control the amount of gas upflow, it allows more hydrocarbons to be added to the lower cone 82 of the furnace 12. The amount of hot cone bleed can be increased as hydrocarbons to the lower cone 82 are increased. The additional amount of hydrocarbons to the lower cone 82 will increase product carbon and generate more reducing gas, mostly H2 without lowering center bed temperatures which reduces reaction kinetics. 13 WO 2004/055832 PCT/U52002/039631 Because the hydrocarbons added to the lower portion of tfis furnace 12 cools the reduced iron product, the quantity and composition of added gases will still be limited by the minimum allowable temperature of the output product, which is around 650-700°C for a furnace producing hot briquetted iron (HBI). It will be appreciated by those of ordinary skill in the art that any one of these embodiments may be employed, either individually or jointly, to accomplish the goals stated SUMMARY OF THE ACHIEVEMENT OF THE OBJECTS OF THE INVENTION From the foregoing, it is readily apparent that we have invented an improved method and apparatus for controlling the temperature of the center burden of a direct reduction furnace, that allows the use of higher quantities of hydrocabons or other gases within the lower portion of both hot and cold discharge furnaces so that product carbon and/ or in-situ reforming is increased; which conserves energy in a Direct Reduction furnace by maintaining a uaiform temperature therein; which provides control options to DRI plant operators to allow significantly higher levels of hydrocarbon gas additions, while reducing the temperature variations across the burden; that offsets the cooling effect caused by rising upflowing gas into the reduction zone of the furnace, thereby increasing metallization of the burden. It is to be understood that the foregoing description and specific embodiments are merely illustrative of the best mode of the invention and the principles thereof, and that various modifications and additions may be made to the apparatus by those skilled in the art, without departing from the spirit and scope of this invention, which is therefore understood to be limited only by the scope of the appended claims, 14 WO 2004/055832 PCT/U52002/039631 What is claimed is: 1. Apparatus for controlling temperature uniformity of the burden in a furnace for direct reduction of iron oxides to a metallized iron product, comprising: a generally vertical shaft furnace having an upper charging end, a bottom discharge end, and a vertical centerline; means for charging participate iron oxide material to the upper end of said furnace to form a burden therein, and means for removing metallized iron product from the bottom end of said furnace, whereby a continuous gravitational flow of said burden can be established through the furnace; a reacted gas outlet at tha uppet end of said furnace; a first hot reducing, gas inlet means through, which, a hot reducing gas is injected into the burden, said first hot reducing gas inlet located between the upper end of said furnace and the bottom of said furnace, wherein said hot reducing gas is injected into the burden to reduce the burden to metallized iron; and a second hot reducing gas inlet means terminatin gat or near said vertical centerline and through which a hot reducing gas is injected into the furnace at or near said vertical centerline, said second reducing gas inlet being intermediate to said first reducing gas inlet and said bottom of said furnace. 2. Apparatus according to claim 1 wherein the first hot reducing gas inlet means is a bustle and tuyere system. 3. Apparatus according to claim 1 wherein the second hot reducing gas inlet means comprises an associated gas reformer for providing reducing gas and means for conducting the second reducing gas to the furnace and injection of the second reducing gas into the furnace. 15 WO 2004/055832 PCT/U52002/039631 4. Apparatus according 10 claim 1 wherein tht second hot reducing gas inlet means comprises a partial axidation reactor for providing reducing gas and mean for conducing the second reducing gas to the furnace and injection of the second reducing gas into the furnace. 5, A method for controlling temperature uniformity of the burden in a furnace for the direct reduction of iron oxides comprising the steps of; charging partculate iron oxide material to a generally vertical shaft furnace to form a burden therein; injecting a hot reducing gas into the burden from a first hot reducing gas injection means located nitermediate the ends of said furnace, wherein the injected reducing gas reduces the charged particulate iron oxide material to metallized iron; injecting a second hot reducing gas from a second hot reducing gas injection means into the center of said burden to offset a cooling effect of upftowing gases; and removing meetallized iron product from the bottom of the furnace thereby establishing a continuous gravitational flow of said burden through the furnace, 6. A method according to claim 5 wherein said second hot reducing gas is formed in a gas reformer exterior to the furnace prior to injection of the second hot reducing gas into the furnace. 7. The method according to claim 5 whreein the second hot reducing gas is formed in a partial oxidation reactor prior to injection of the Second hot reducing gas into the furnace, 8. A method for controlling temperature uniformity of the burden in a furnace for the direct reduction of iron oxides comprising the steps of: charging particulate iron oxide material to a generally vertical shaft furnace, having upper and lower ends, to form a burden therein; 16 WO 2004/055832 PCT/U52002/039631 injecting a hot reducing gas into said burden from at least one reducing gas inlet system, said reducing gas inlet system being located intermediate the upper end and the lower end of the furnace; preheating natural gas; injecting preheated natural gas into said burden, said natural gas being injected below the hot reducing gas inlet system centrally of the furnace; and removing metallized iron product from the lower end of the furnace, thereby establishing a continuous gravitational flow of the burden through the furnace. 9. A method according to claim 8 wherein preheating of the natural gas is carried out by a heat exchanger prior 10 injection of preheated natural gas into the furnace. 10. A method according to claim 8 wherein the natural gas is mixed with H 2, H3O, or CO2 prior to the preheating step. 11. An apparatus for controlling temperature uniformity of the burden in a furnace for direct reduction of iron oxides to a metallized iron product, comprising; a generally vertical shaft furnace having an uppper end and a bottom end; means for charging paniculate iron oxide metatial to the upper end of said fumace to form a burden therein, and means for removing metallized iron product from the bottom end of said furnace, whereby a continous gravitational flow of said burden can be established through the furnace; at least one reducing gas inlet means comprising a bustle and tuyere through which reducing gas is injected into the burden about the periphery of said furnace, said reducing gas inlet means located intermediate the end of the furnace; a natural gas preheating means communicably linked to a plurality of nozzles, through which preheated natural gas is ailed to said burden for offsetting a cooling effect in the burden caused by upflowing gas; and a reacted gas outlet at the upper end of said furnace. 17 WO 2004/055832 PCT/U52002/039631 12 Apparatus according to claim 11, where in said natural gas prehearing, means comprises, a. heat exchanger exterior to said frunace, 13. Apparatus according to claim 11, further comprising means fot mixing H2, H2O, or CO2 wih the natural gas prior to said natural gas preheating means, 14. A method for the direct reductian of iron oxides comprising the steps of: charging particulate iron oxide material to a generally vertical shaft furnace to form a burden therein; injecting a reducing gas from at least one reducing gas inlet system into said burden, the reducing gas inlet system being located intermediate the upper end and the lower end of the furnace; removing upflowing gas from said burden by a gas removing means located below the reducing gas inlet system; scrubbing the removed upflowing gas to create a scrubbed gas; circulating said scrubbed gas through a plurality of pipes to the reducing gas inlet system; introducing said scrubbed gas as recycled reducing gas into the furnace through the reducing gas inlet system; and removing metallized iron products from the bottom of the furnace thereby establishing a continuous gravitational flow of said burden through the furnace. 15. The method according to claim 14, wherein the circulating step further includes the step of circulating the removed upflow gas to a top gas scrubber for further scrubbing prior to the circulation of the scrubbed gas to the reducing gas inlet system. 18 WO 2004/055832 PCT/U52002/039631 16. Apparatus for controlling temperature uniformity of the burden in a furnace for direct reduction of iron oxides to a metallized iron product, comprising; a generally vertical shaft furnace; means for charging particulate iron oxide material to an upper end of said furnace to form a burden therein, and means for removing metallized iron product from a bottom end of said furnace, whereby a continuous gravitational flow of said burden can be established through the furnace; a reducing gas inlet system through which a reducing gas is injected into the burden, said reducing gas system located intermediate said upper end and said bottom end of said furnace; a gas removal system for collecting and removing upflow gas, said gas removal system being disposed between said reducing gas inlet system and said bottom end of said furnace; at least one scrubber communicating with said removal system for scrubbing remolved upflow gas; a plurality of pipes connected to said reducing gas inlet system for re introduction of scrubbed upflow gas into said furnace; and a reacted gas outlet at the upper end of said furnace communicating with said gas removal systern, 17. Apparatus according to claim 16, further comprising a top gas scrubber disposed between said at least one scrubber and said reducing gas inlet system for further scrubbing of said upflow gas priot to reimproduction into said furnace. 18. Apparatus according to claim l6, wherein said gas removal system comprises at least one pipe disposed within said furnace having a plurality of slots therein for collecting upflowing gas and routing the upflowing gas from the furnace to said at least one scrubber. 19 A method and upparatus for increasing hydrocarbon input to a direct redution shaft furnace (13) while controlling the temp[erature uniformity of the center portiuon (26) of the burden wiihin the furnace (12) wherein the hydrocarbon gases used in the XXX reduction may be preheated, which increases the temperature of the hydrocarbon gases, and therefor increases the XXX temperature of the upflowing gas as it rises from the lower section (66) of the furnace (12) into the center (26) of the XXX of the upflowing gas may be removed before it enters the reduction zone of the furnace. The removed

Full Text

METHOD AND APPARATUS FOR CONTROLLING TEMPERATURE
UNIFORMITY OF THE BURDEN IN A DIRECT REDUCTION SHAFT FURNACE
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for controlling the
temperature during the direct reduction of iron. More particularly, the present invention
relates a method and apparatus which controls the temperature uniformity of the center
portion of the iron burden in a direct redaction shaft furnace thereby allowing a higher
amount of hydrocarbons to be used throughout the reduction process.
BACKGROUND OF THE INVENTION
The production of direct reduced iron in both. hot and cold discharge plants oocure
in a vertical shaft furnace and involves reduction of iron ore or iron oxide as it moves
downwardly in a reduction zone of a vertical shaft furnace through which is passed a
suitable hot reducing gas, known as bustle gas. Bustle gas, which is principally composed
of carbon monoxide and hydrogen, is introduced to the shaft furnace at temperatures in the
range of about 700°C to about 1100oC. The ore is charged at the top of the furnace and
caused to flow downwardly through the reduction zone wherein it is reduced by healed
reducing gas which flows upwardly through the furnace, after which the reduced ore flows
into and downwardly through the transition zone to be carburized if desired. For cool
discharge plants, after passing through the reduction zone, the ore is cooled in a cooling
zone through which is passed a gaseous coolant at a temperature below about 200oC
Typically, in a cool discharge furnace, both the reducing gas and cooling gas are re-
circulated, optionally in closed loops, to which streams of fresh (i,e, "make-up") reducing
gas are added and from which streams of spent gas are removed.
The reducing gas being fed to the reduction zone of the furnace is typically at an
elevated temperature, which is required by reaction kinetics. The reducing gas is caused to
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contact the downwardly moving iron ore to reduce the iron oxides therein according to the
following basic reactions:
(1) 3Fe2O3 + H2/CO=>2Fe1O4 + H2O/CO2
(2) Fe3OH + H2/CO => 3feO + H2O/CO2
(3) FeO + H2/CO=>Fe + H2O/CO2
In the production of direct reduced iron (DRI), it is desirable to increase the product
carburization and to increase in-situ reforming in the lower portion of both hot and cold
direct reduction furnaces by injecting hy drocarbons. This is a proven means to increase the
productivity of direct reduction furnaces without adding new equipment to increase reducing
gas capacity. This is also a proven means to increase product carbon. The hydrocarbons
react with the hot DRL, depositing carbon and Liberating hydrogen gas. However, the
reaction of the hydrocarbons to form carbon and hydrogen is endothermic. Thus, the newly
formed cool hydrogen gas flows upward through the center of the furnace (called npflow),
cooling the descending iron material. Because of temperature considerations, the amount
of hydrocarbons that can be added to the lower portion of the furnace is limited by either
low center bed temperature or low product discharge temperature.
As more hydrocarbons are added to the lower portion of the furnace, cooled
hydrogen gas is produced which rises into the reduction zone and the center bed temperature
decreases, thus reducing reaction kinetics. The desired temperature of the burden is above
650oC. When the temperature of the burdcn is reduced to the range of 625-650°C, the
average product metallization begins to stop because the material in the center of the
furnace is not properly reduced/metallited. Also, in hot discharge, furnaces, product
discharge temperature must be maintained above about 700°C for proper subsequent
briqueting. For hot transport applications, higher discharge temperature of the DRI makes
more sensible heat available in the melter ,thus reducing the power required for melting. As
hydrocarbons are added to the lower postal of a hot discharge furnace, it is possible that
tha average product temoperature will bebelow 700°C before the center bed temperature
reaches the point that metallization drops significantly.
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To date, several techniques have been used to allow higher flows of hydrocarbons
to the furnace lower cone, to extend the limits noted above, and to control the temperature
of the burden. For cold discharge furnaces, some examples of techniques being used are
cooling zone bleed and simplified center injection. However, prior, art center injection
techniques lack means to control or measure hydrocarbon or reducing gas flow into the
center injection system and lack means to force flow into the center injection line.
Another technique for temperature and carbon control which has been employed is
the injecting of cold natural gas into the direct reduction furnace. The natural gas mixes
with other gases already present in the furnace and is heated by the gas and solids already
present in the furnace. As the hydrocarbons in the natural gas are heated, they crack to form
H2 and deposit carbon on the product or they are reformed by reaction with H2O and CO2
in the gas furnace to make additional H2 and CO, The present limitation on the injection of
natural gas is temperature. As more cold natural gas is injected, the center bed temperature
decreases, which decreases the rate of reaction kinetics. At low flow rates of the cold
natural gas, the production benefit from additional reducing gases will outweigh the
disadvantage from decreased reaction kinetics. But when the temperatures in the center bed
decrease to a certain point, any further production benefit from additional reducing gases
will be negated by the decrease in reaction kinetics. This limits the amount of natural gas
that can be added to the furnace for in situ cracking and reforming,
What is therefore needed is a means and method for increasing the amount of
hydrocarbon gas supplied to the transition zone and/of cooling section of a direct reduction
furnace while maintaining the temperature of the central reaction zone of the direct
reduction furnace at a temperature favorable to the direct reduction of iron.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus which controls the
temperature uniformity of the center portion of the iron burden in a direct reduction shaft
furnace thereby allowing a higher amount of hydrocarbons to be used in the cooling zone.
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The invention is an efficient improvement of existing methods, particularly, the Midrex
method and apparatus for direct reduction of iron which is incorporated by reference herein.
Typically, the center portion of iron bearing material in the burden of a direct reduction
furnace is cooler than the rest of the burden due to upflowing gases which, is injected into
the lower cooling section of the furnace and rises upwardly into the center portion of the
reducing section of the furnace. By increasing the temperature of the burden in the center
portion of the furnace, the iron is reduced under much more favorable conditions. Thus, the
present invention is advantageous to achieve the objects stated herein.
Disclosed herein are methods for heating the center region of the furnace,
particularly the burdeen. In a first embodiment of the invention a hydrocarbon gas used in
direct reduction may be preheated, which increases the temperature of the upflowing gas as
it flows upwardly into the center of the burden. Alternatively, a portion of the upflowing
gas may be removed before it enters the reduction zone of the furnace. The removed
upflowing gas, known as hot bleed gas, may be ducted to a top gas scrubber of the furnace
or msy be mixed with the main reducing gas stream of the furnace for reintroduction to the
furnace. Alternatively, hot reducing gas may be directly injected into the center portion of
the burden, offsetting the effect of the upflowing gases. The center injected hot reducing
gas may be split off from the maia reducing gas stream or may be generated by a partial
oxidation reactor. Finally, it will be appreciated by those skilled in the art that the above
noted embodiment may be employed individually or in combination depending on the DRI
plant facility,
OBJECTS OF THE INVENTION
The principal object of the present invention is to provide a method and apparatus
for controlling temperature uniformity in the burden of a direct reduction shaft furnace.
It is another object of the present invention to provide an apparatus and method
which allows the use of higher quantities of hydrocarbons or other gases within the lower
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portion of both hot and cold discharge furnaces so that product carbon and/or in-situ
reforming may be increased white the temperature within the center of the direct reduction
furnace is maintained at a temperature favorable to the direct reduction of iron, thereby
increasing the degree of carburization of the iron product without adversely affecting the
metallization of the iron burden.
Another object of the present invention is 10 provide an apparatus and method for
conserving energy in a direct reduction furnace by maintaining a uniform temperature
throughout the burden.
Another object of the invention is to provide a method and apparatus for increasing
the temperature of the center burden of a direct reduction furnace in order to offset the
cooking effect caused by upflowing gases into the reduction zone of the furnace, and thereby
increasing metallization of the burden,
Another object of the present invention is to provide control options to DR plant
operators to allow significantly higher levels of hydrocarbon gas additions, while reducing
the temperature variations across the burden.
BRIEF DESCKIFTION OF THE DRAWINGS
The foregoing and other objects will become more readily apparent by referring to
the following detailed description and the appended drawings in which:
Figure 1 is a schematic diagram showing an example of a typical direct reduction
shaft furnace system for cool discharge product according to the Midrex process.
Figure 2 is a diagram showing center injection of reducing gas split from the main
reducing gas stream.
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Figure 3 is a diagram showing center injection of reducing gas produced by a partial
oxidation reactor.
Figure 4 is a diagram showing the entry of preheated in situ natural gas into a direct
reduction furnace.
Figure 5 is a diagram showing a hot cone bleed from a furnace with the hot cone
bleed gas sent to a top gas scrubber.
Figure 6 is a diagram showing a hot cone bleed from a furnace with the hot cone
bleed gas combined with the main reducing gas stream,
DETAILED DESCRIPTION
The present indention provides a method and apparatus which controls the
temperature uniformity of the center portion of the iron burden in a direct reduction shaft
furnace thereby allowing a higher amount of hydrocarbons to be used throughout the
reduction process. The invention is an efficient improvement of existing methods,
particularly, the Midrex process and apparatus for direct reduction of iron. The Midrex
process and apparatus far direct reduction is disclosed in U.S. Pat No. 3,748,120 entitled
"Method of Reducing Iron Oxide to Metallic Iron," U.S. Pat. No, 3,749,386 entitled
"Method for reducing Iron Oxides in a Gaseous Reduction Process," U.S. Pat, No.
3,764,123 entitled "Apparatus for reducing iron Oxide to Metallic Iron," U,S. Pat. No.
3,816,101 entitled "Method for Reducing Iron Oxides in a Gaseous Reduction process," and
US, Pat. No. 4,046,557 entitled "Method for producing Metallic Iron Particles." all of
which are incorporated by reference herein.
Referring to the drawings, and particularly FIG, 1, there is shows a schematic
diagram of an example of a typical prosses and apparatus for the Midrex process direct
reduction of metal oxides such as iron ore to which the present invention is applicable in
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cool discharge plants, It is to be understood that the present, invention is applicable to both
hot and cool DR plants, however, for the case of visualization, a cool discharge plant is
shown. The system 10 of FIG- 1 is a typical commercially available system used in many
Direct Reduction Iron (DRI) plants. The system 10 includes a shaft furnace 12 having a
refractory lining and generally having a feed hopper 14 from which iron ore 16 is fed to the
furnace for reduction into iron using reformed gases. The furnace 12 typically has a
charging zone 108, a reduction zone 26, a transition zone 66, a cooling zone 38, and a
discharge zone 110. The iron ore 16 descends by gravity into the shaft furnace 12 from the
hopper 14 through a pellet feed pipe 18. The pellet feed pipe 18 also serves as a gas seal
pipe. At the bottom of the furnace 12 is a pellet discharge pipe 20 which also serves as a gas
seal pipe. A pellet discharge device 22 of any conventional type is located below the
discharge pipe 20 and receives metallic iron, thereby establishing gravitational descent of
the burden through the furnace 12,
Near the upper portion of the furnace 12 is a bustle and tuyere system, indicated
generally at 24, through which hot reducing gas is introduced to flow upwardly through a
reduction zone 26 in counterflow relationship to the downwardly moving iron ore 16, as
shown by the arrows, and after reacting with the burden exits from the furnace 12 through
a gas off-take pipe 28 located at the top of the furnace 12. The hot reducing gas, flowing
from the bustle system 24 to the off-take pipe 28, serves to heat the iron oxidel6 and to
reduce it to metallized iron. Throughout this Specification and appended claims, the term
"metallized iron" is intended to include metal such as sponge iron, pellets, lumps, briquettes,
DRI or other compacted forms of reduced metal and the like which contain at least 80% of
their metal in the metallic state with the balance substantially in the form of metallic oxides.
Metallized in this sense does not mean coated with metal, but nearly completely reduced to
the metallic state.
The spent gas from off-take pipe 28 flows through a pipe 30 to a scrubber 32 which
cools the spent gas and removes dust. Scrubber 32 can be of any conventional type used in
live, industry. After leaving the scrubber 31, the spent gas is ducted to a reformer 44.
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Thereafter it is recycled. In addition, cooled gas is introduced and re-circulated to a lower
region of the furnace 12 via a cooling inlet pipe 34 which connects to a cooling gas
introduction and distributing member 36 located within the furnace 12 and arranged to
distribute The cool gas into the burden 16. Hydrocarbon gas is added to the cool gas from
a fuel source112 prior to a reintroduction into the burden 16. The cool gas introduced into
the burden through distributing member 36 flows upward through a cooling zone 38 in
counterflow relationship with downwardly moving burden 16 and disengages from the
burden. 16 at a cooling region off-take member 40 which connects to a cooling region off
take pipe 42, The spent gas from the off-take pipe 42 is re-circulated and recycled.
The reformer 44 which generates hot reducing gas has fuel fired burners 46, a flue
pipe 48 and a plurality of catalytic reformer tubes 50, only one being shown. Combustion
air from a blower 52 is fed to the burners 46 through a flow regulating valve 54. Fuel is fed
to the burners 46 through a pipe 56 from a fuel source 58 and flow regulating valves 60. The
reformer 44 is connected to the bustle system 24 by a pipe 62.
The simplest explanation of the shaft furnace-based direct reduction plant of the
Midrex method in operation starts with the entry of the hot reducing gas through the bustle
system 24 at the periphery of the reduction zone 26. The iron oxide burden 16 descends
through the reduction zone 26 while the reducing gas ascends from the bottom of the
reducing zone 26 through the iron oxide burden 16, reducing the burden 16 in the process,
and exiting the shaft furnace 12 through an off-take 23 above stockline 64 of the burden 16.
The reducing gases can be externally generated or result from reactions within the shaft
furnace 12.
The metallized iron 16 then descends through the furnace transition zone 66 to the
cooling zone 38 and to the discharge zone 110, which may result in either a hot or cold
product, depending on the equipment installed. Additionally, the iron bearing material 16
can be further reacted with hydrocarbon gases in either the transition zone 66 or the cooling
zone 38 to increase the carbon content of the product being discharged. This has proven to
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be a significant issue in steel production today. Higher carbon content in the metallized
product, DRI, offers the steelmaker significant savings by substituting oxidation of carbon
for electric energy in melting. The hydrocarbon gases can be and typically are added at
various locations in the transition zone 66 or cooling zone 38 from fuel sources 114 and 112
respectively.
As a result of the addition of these, hydrocarbon, gases there is an ascending gas-flow,
equal to or greater than the quantity of hydrocarbon gases added, which flow up through the
center of the furnace 12 all the way to the stockline 64 if no other steps are taken. This also
holds true for lower seat leg gases, but they are usually very small in relative volume. The
stream of reacted hydrocarbons is colder and of different quality than the reducing gases
entering at the bustle 24 and results in lower burden temperatures in the central area of the
furnace 12. Since temperature and quality directly affect the kinetics of reduction, the
degree nf metallization reached by the burden 16 descending in the central furnace area is
different than that of the remainder of the furnace 12. limiting this variation in furnace
metallization is very important to the optimization of the plant. The reaction of the
hydrocarbon gases is very beneficial and efficient energy wiseT but the loss of metallization
in the central furnace burden can be significant if it is ignored.
Generally, normal bustle gas temperature ranges from 700-1100oC. Center bed
temperature, in both not and cold discharge plants, ranges from about 600 to about 800oC.
Providing a small flow of high temperature reducing gas to the center of the furnace 12
raises the center bed temperature. In typical operation of a direct reduction furnace, the
bustle gas stream enters from the periphery of the furnace 12. Referring now to Figures 2
and 3, a preferred embodiment of the present invention is shown. The invented apparatus
and method provides a means of injection of hot reducing gases into the center of a direct
reduction furnace 12 so that temperature within the center of the burden 16 is maintained
within a preferred range. In accordance with this invention, the hot reducing gas is ducted
to the vertical centerline of time furnace 12 -where it is allowed to mix with the upflowing
stream of hydrocarbon cooling gases from the transition zone 66 of the furnace 12. The
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invented apparatus and method is applicable to shaft furnaces discharging either hot or cold
metallized product. The source of the hot reducing gas may be from either a reformer 44
or a partial oxidation reactor 44(a) sucb as the OXY+ system as disclosed in U.S, Pal, No.
5,997,596 entitled "Oxygen Fuel Boost Reformer Process and Apparatus".
In accordance with Figure 2, prior to entering the furnace 12, a portion of the high
temperature bustle gas stream is split-off and injected into the center of the furnace 12. A
variable or fixed restriction device 68 is used to provide adequate pressure drop to force the
bustle gas to flow through the center injection line 116, The flow rate of hot bustle gas
through the center injection line 116 is preferably measured using a venturi 44(b), however,
other suitable measuring means may be used.
In accordance with Figure 3, a partial oxidation reactor 44(a) or multiple reactors
generate the hot reducing gas which is then ducted to the center of the furnace 12,
eliminating the need to divert a small portion of hot bustle gas to the center of the furnace
12. In ganeral the partial oxygen reactor44(a)burns oxygen 70 and a hydrocarbon fuel 72
such as natural gas to produce a high quality, high temperature reducing gas. This gas is
well suited to use for center injection into a direct reduction furnace 12. Since the quantity
and ratio of oxygen and hydrocarbon fuel are tightly controlled for propey combastion in the
oxidation reactor 44(a), the mechanism to vary the flow rate of center injection gas may
easily be built into the partial oxidation reactor 44(a) design.
In an alternative embodiment of the invention in accordance with FIG. 4, preheated
natural gas 74 is added to a plurality of nozzles 76, 78, 80, respectively, which are located
around the periphery of the transition zone 66 or the discharge zone 110 and which are not
used for cooling so as to increase the amount of hydrocarbons used within the lower cone
82 of the furnace l2 whie maintaining an adequate center furnace temperature. This entails
preheating a hydrocarbon stream and adding the preheated hydrocarbon stream to any of the
plurality of nozzles 76, 78, 80 which are not used for cooling of the direct reduced iron.
When preheated natural gas 74 is injected into non-cooling inlets 76, 73, 80 of the furnace
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12, additional energy is shifted to the furnace 12 and uniformity of burden 16 temperatures
is improved.
The apparatus includes a heat exchanger 84 to preheat the natural gas 74 before
injecting it into the direct, reduction furnace 12. Hot flue gas frorn a combustion process is
supplied to the beat exchanger 84 to preheat the natural gas 74 stream. The flue gas may be
from a reformer 86 or from any other source of combustion flue gases. The temperature to
which the natural gas 74 is preheated is typically up to 450oC, although the temperature is
only limited at the upper end by cracking of the heated gas. That is, the preheat temperature
must be lower than the temperature at which cracking of the natural gas 74 would present
problems with carbon deposition in the heat exchanger 84 or piping. It will be appreciated
by those of skilled in the art that the preheat temperature can be as high as 550°C depending
upon the composition of the preheated gas and its tendency to crack.
Alternatively, the natural gas 74 is mixed with H2, H2O, CO2 or any other gas that
contains H2 H2O and/or CO2 before the preheating stage. Addition of any of these gases
will decrease the partial pressure of the hydrocarbons and thus, their tendency to crack
during or after preheating. The addition of H 2 directly decreases the tendency of
hydrocarbons to crack. H2O and/or CO2 directly decreases the tendency of any H2 and CO
to form carbon. With the addition of these gases the preheat temperature limit may be raised
to 700°C
The invented method and apparatus allows more natural gas 74 to be injected into
the furnace 12 before the furnace temperatures cool to the point where any further
production benefit from additional reducing gasses will be negated by the decrease in
reaction kinetics. Adding more natural gas 74, because it is hot, increasses situ reforming,
and cracking, thereby increasing the amount of reducing gas in the direct reduction furnace
12, which results in a higher production rate from the direct reduction furnace 12.

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In still another embodiment of the present invention and referring to FIGs. 5 and 6,
an outlet 28 is provided for the upflowing gases that cool the center of the burden 16. This
technique is known as "hot cone bleeding". The upflowing gas once collected can be
contained in the collected stream. This effectively redistributes the collected gas stream in
the full reducing, gas flow at the furnace bustle 24, eliminating its effect on the center bed.
Limiting the quantity of upflowing gas from the discharge zone 110 to the reducing
zone 26 has been used for many years to limit the temperature variation or loss in the central
burden 16. With a cold discharge plant, where a recirculating stream of gas is used to cool
the metallised product before discharge, a method called "Cooling Zone Bleed" has been
used for over 25 years to accomplish this control. The methods of bleeding have changed
to take advantage of the hydrocarbon reactions from the natural gas additions to the cooling
gas stream, but the basic control objective remains keeping the temperature of the central
furnace burden 16 above a certain minimum. Historically, however, if a particular furnace
12 had no coaling gas recirculating stream (i.e. hot discharge), the use of a cooling zone
bleed was not available.
The invented method and apparatus for providing a hot cone bleed removes
upflowing gas from the transition zone 66 of the furnace 12 and reintroduces the gas, as
reducing gas, to the upper section or reducing zone 26 of the furnace 12. The upflo wing gas,
once collected, may be injected at one, or several location in the pieces in order to take,
advantage of the reducing gases contained in the collected gas stream. Mixing the collected
gas stream with the main reducing gas stream effectively redistributes the collected gas
stream in the full reducing gas flow at the furnace bustle 24, Thus, the cooling effect of the
gas stream is distributed throughout the furnace 12 by the main reducing gas stream,
eliminating the concentrated cooling effect at the center of the furnace bed.
By reducing the amount of upflowing gas in the center of the furnace 12, higher bed
temperatures are maintained, thus increasing reaction kinetics. The upflowing gas that is
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removed is rich in reducing gas and is recycled back to the process through either the top
gas scrubber 88 of the furnace 12 or the main reducing gas stream leading to the furnace 12,
Preferably, the invented apparatus has a plurality of gas off-take pipes 90 and 92
which extend into the furnace 12 in the trransition zone 66, The pipes 90 and 92 have slots
or openings 94 which face downwards toward the discharge zone 110. Upflow gas from the
discharge zone 110 is drawn through the slots 94 into the pipes 90 and 92. Once the upflow
gas exite the furnace 12, it is referred to as hot cone bleed gas because it is removed from
lower cone 82 of the furnace. The gas drawn into each pipe 90 and 92 is sent through a
venturi 96 to provide some initial coolng and scrubbing. The gas then passes through
quenched pack type scrubbers 98 and 100 for further cooling and scrubbing. Flow control
valves 102 and 104, located down stream from the scrubbers 98 and 100, control the flow
rate of gas exiting the scrubbers 98 and 100, and therefore control the amount of gas drawn
into pipes 90 and 92 from the cooling zone 38 of the furnace 12.
The cool and clean hot cone bleedgas can be returned to the furnace 12 in one of two
locations. As shown in Figure 5, the hot cone bleed gas can be routed to the top gas
scrubber 38 of the furnace 12 so that the gas is injected underneath the packing of the
scrubbers 98 and 100, similar to process gas recycle. The hot cone bleed gas exiting the
furnace 12 is at a higher pressure than the top gas scrubber 88, so the system is natural flow.
Alternatively, as shown in Figure 6, the cool and clean hot cone bleed gas can be
compressed by a compiessor 106 and delivered directly to a bustle gas duct 24 for injection
into the furnace reduction zone 26.
Since hot cone bleed can be adjusted to control the amount of gas upflow, it allows
more hydrocarbons to be added to the lower cone 82 of the furnace 12. The amount of hot
cone bleed can be increased as hydrocarbons to the lower cone 82 are increased. The
additional amount of hydrocarbons to the lower cone 82 will increase product carbon and
generate more reducing gas, mostly H2 without lowering center bed temperatures which
reduces reaction kinetics.
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Because the hydrocarbons added to the lower portion of tfis furnace 12 cools the
reduced iron product, the quantity and composition of added gases will still be limited by
the minimum allowable temperature of the output product, which is around 650-700°C for
a furnace producing hot briquetted iron (HBI).
It will be appreciated by those of ordinary skill in the art that any one of these
embodiments may be employed, either individually or jointly, to accomplish the goals stated
SUMMARY OF THE ACHIEVEMENT
OF THE OBJECTS OF THE INVENTION
From the foregoing, it is readily apparent that we have invented an improved method
and apparatus for controlling the temperature of the center burden of a direct reduction
furnace, that allows the use of higher quantities of hydrocabons or other gases within the
lower portion of both hot and cold discharge furnaces so that product carbon and/ or in-situ
reforming is increased; which conserves energy in a Direct Reduction furnace by
maintaining a uaiform temperature therein; which provides control options to DRI plant
operators to allow significantly higher levels of hydrocarbon gas additions, while reducing
the temperature variations across the burden; that offsets the cooling effect caused by rising
upflowing gas into the reduction zone of the furnace, thereby increasing metallization of the
burden.
It is to be understood that the foregoing description and specific embodiments are
merely illustrative of the best mode of the invention and the principles thereof, and that
various modifications and additions may be made to the apparatus by those skilled in the art,
without departing from the spirit and scope of this invention, which is therefore understood
to be limited only by the scope of the appended claims,
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What is claimed is:
1. Apparatus for controlling temperature uniformity of the burden in a furnace for direct
reduction of iron oxides to a metallized iron product, comprising:
a generally vertical shaft furnace having an upper charging end, a bottom discharge
end, and a vertical centerline;
means for charging participate iron oxide material to the upper end of said furnace
to form a burden therein, and means for removing metallized iron product from the bottom
end of said furnace, whereby a continuous gravitational flow of said burden can be
established through the furnace;
a reacted gas outlet at tha uppet end of said furnace;
a first hot reducing, gas inlet means through, which, a hot reducing gas is injected into
the burden, said first hot reducing gas inlet located between the upper end of said furnace
and the bottom of said furnace, wherein said hot reducing gas is injected into the burden to
reduce the burden to metallized iron; and
a second hot reducing gas inlet means terminatin gat or near said vertical centerline
and through which a hot reducing gas is injected into the furnace at or near said vertical
centerline, said second reducing gas inlet being intermediate to said first reducing gas inlet
and said bottom of said furnace.
2. Apparatus according to claim 1 wherein the first hot reducing gas inlet means is a
bustle and tuyere system.
3. Apparatus according to claim 1 wherein the second hot reducing gas inlet means
comprises an associated gas reformer for providing reducing gas and means for conducting
the second reducing gas to the furnace and injection of the second reducing gas into the
furnace.
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4. Apparatus according 10 claim 1 wherein tht second hot reducing gas inlet means
comprises a partial axidation reactor for providing reducing gas and mean for conducing
the second reducing gas to the furnace and injection of the second reducing gas into the
furnace.
5, A method for controlling temperature uniformity of the burden in a furnace for the
direct reduction of iron oxides comprising the steps of;
charging partculate iron oxide material to a generally vertical shaft furnace to form
a burden therein;
injecting a hot reducing gas into the burden from a first hot reducing gas injection
means located nitermediate the ends of said furnace, wherein the injected reducing gas
reduces the charged particulate iron oxide material to metallized iron;
injecting a second hot reducing gas from a second hot reducing gas injection means
into the center of said burden to offset a cooling effect of upftowing gases; and
removing meetallized iron product from the bottom of the furnace thereby
establishing a continuous gravitational flow of said burden through the furnace,
6. A method according to claim 5 wherein said second hot reducing gas is formed in
a gas reformer exterior to the furnace prior to injection of the second hot reducing gas into
the furnace.
7. The method according to claim 5 whreein the second hot reducing gas is formed in
a partial oxidation reactor prior to injection of the Second hot reducing gas into the furnace,
8. A method for controlling temperature uniformity of the burden in a furnace for the
direct reduction of iron oxides comprising the steps of:
charging particulate iron oxide material to a generally vertical shaft furnace, having
upper and lower ends, to form a burden therein;
16

WO 2004/055832 PCT/U52002/039631
injecting a hot reducing gas into said burden from at least one reducing gas inlet
system, said reducing gas inlet system being located intermediate the upper end and the
lower end of the furnace;
preheating natural gas;
injecting preheated natural gas into said burden, said natural gas being injected
below the hot reducing gas inlet system centrally of the furnace; and
removing metallized iron product from the lower end of the furnace, thereby
establishing a continuous gravitational flow of the burden through the furnace.
9. A method according to claim 8 wherein preheating of the natural gas is carried out
by a heat exchanger prior 10 injection of preheated natural gas into the furnace.
10. A method according to claim 8 wherein the natural gas is mixed with H 2, H3O, or
CO2 prior to the preheating step.
11. An apparatus for controlling temperature uniformity of the burden in a furnace for
direct reduction of iron oxides to a metallized iron product, comprising;
a generally vertical shaft furnace having an uppper end and a bottom end;
means for charging paniculate iron oxide metatial to the upper end of said fumace
to form a burden therein, and means for removing metallized iron product from the bottom
end of said furnace, whereby a continous gravitational flow of said burden can be
established through the furnace;
at least one reducing gas inlet means comprising a bustle and tuyere through which
reducing gas is injected into the burden about the periphery of said furnace, said reducing
gas inlet means located intermediate the end of the furnace;
a natural gas preheating means communicably linked to a plurality of nozzles,
through which preheated natural gas is ailed to said burden for offsetting a cooling effect
in the burden caused by upflowing gas; and
a reacted gas outlet at the upper end of said furnace.
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WO 2004/055832 PCT/U52002/039631
12 Apparatus according to claim 11, where in said natural gas prehearing, means
comprises, a. heat exchanger exterior to said frunace,
13. Apparatus according to claim 11, further comprising means fot mixing H2, H2O, or
CO2 wih the natural gas prior to said natural gas preheating means,
14. A method for the direct reductian of iron oxides comprising the steps of:
charging particulate iron oxide material to a generally vertical shaft furnace to form
a burden therein;
injecting a reducing gas from at least one reducing gas inlet system into said burden,
the reducing gas inlet system being located intermediate the upper end and the lower end of
the furnace;
removing upflowing gas from said burden by a gas removing means located below
the reducing gas inlet system;
scrubbing the removed upflowing gas to create a scrubbed gas;
circulating said scrubbed gas through a plurality of pipes to the reducing gas inlet
system;
introducing said scrubbed gas as recycled reducing gas into the furnace through the
reducing gas inlet system; and
removing metallized iron products from the bottom of the furnace thereby
establishing a continuous gravitational flow of said burden through the furnace.
15. The method according to claim 14, wherein the circulating step further includes the
step of circulating the removed upflow gas to a top gas scrubber for further scrubbing prior
to the circulation of the scrubbed gas to the reducing gas inlet system.
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WO 2004/055832 PCT/U52002/039631
16. Apparatus for controlling temperature uniformity of the burden in a furnace for direct
reduction of iron oxides to a metallized iron product, comprising;
a generally vertical shaft furnace;
means for charging particulate iron oxide material to an upper end of said furnace
to form a burden therein, and means for removing metallized iron product from a bottom
end of said furnace, whereby a continuous gravitational flow of said burden can be
established through the furnace;
a reducing gas inlet system through which a reducing gas is injected into the burden,
said reducing gas system located intermediate said upper end and said bottom end of said
furnace;
a gas removal system for collecting and removing upflow gas, said gas removal
system being disposed between said reducing gas inlet system and said bottom end of said
furnace;
at least one scrubber communicating with said removal system for scrubbing
remolved upflow gas;
a plurality of pipes connected to said reducing gas inlet system for re introduction of
scrubbed upflow gas into said furnace; and
a reacted gas outlet at the upper end of said furnace communicating with said gas
removal systern,
17. Apparatus according to claim 16, further comprising a top gas scrubber disposed
between said at least one scrubber and said reducing gas inlet system for further scrubbing
of said upflow gas priot to reimproduction into said furnace.
18. Apparatus according to claim l6, wherein said gas removal system comprises at least
one pipe disposed within said furnace having a plurality of slots therein for collecting
upflowing gas and routing the upflowing gas from the furnace to said at least one scrubber.
19

A method and upparatus for increasing hydrocarbon input to a direct redution shaft furnace (13) while controlling
the temp[erature uniformity of the center portiuon (26) of the burden wiihin the furnace (12) wherein the hydrocarbon gases used
in the XXX reduction may be preheated, which increases the temperature of the hydrocarbon gases, and therefor increases the
XXX temperature of the upflowing gas as it rises from the lower section (66) of the furnace (12) into the center (26) of the
XXX of the upflowing gas may be removed before it enters the reduction zone of the furnace. The removed

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Patent Number

214256

Indian Patent Application Number

01114/KOLNP/2005

PG Journal Number

06/2008

Publication Date

08-Feb-2008

Grant Date

07-Feb-2008

Date of Filing

10-Jun-2005

Name of Patentee

MIDREX INTERNATIONAL B.V. ROTTERDAM ZURICH BRANCH

Applicant Address

BAHNHOFSTRASSE 94, CH-8001 ZURICH, SWITZERLAND

Inventors:

#	Inventor's Name	Inventor's Address
1	METIUS, GARY, E	6110 BRIARBERRY COURT, CHARLOTTE, NC 28270, U.S.A.
2	MONTAGUE, STEPHEN, C.	530 ALVIN HOUGH ROAD, MIDLAND, NC 28107, U.S.A.
3	BAILEY, RUSSELL	65TH STREET 14/10 KIRKONAKLAN, ANKARA, TURKEY
4	KAKALEY, RUSSELL	4614 DELLFIELD WAY, CHARLOTTE, NC 28269, U.S.A.
5	VOELKER, BRIAN, W	3504 CEDAR SPRINGS DRIVE, CONCORD NC 28027, U.S.A.

PCT International Classification Number

G21B 13/00

PCT International Application Number

PCT/US2003/039631

PCT International Filing date

2002-12-12

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	PCT/US2003/039631	2002-12-12	U.S.A.