Process for the direct production of steel

Abstract

A process for the direct production of steel from particulate iron oxides or concentrates including two major steps in which in Step (1) the iron oxides are converted to iron carbide and in Step (2) steel is produced directly from the carbide in the basic oxygen furnace or the electric furnace. In the production of the carbide the oxides are reduced and carburized in a single operation using a mixture of hydrogen as a reducing agent and carbon bearing substances such as propane primarily as carburizing agents. Iron carbide thus produced is introduced as all or part of the charge into a basic oxygen furnace to produce steel directly without the blast furnace step. In order to make the steel making process auto-thermal, heat is supplied either by using the hot iron carbide from Step (1) or preheating the iron carbide or by including sufficient fuel in the iron carbide to supply the required heat by combustion.

What is claimed is: 
     
       1. A process for the direct production of steel from iron oxides which comprises: a converting the iron in the oxides to iron carbide .Iadd.by reducing the oxides and converting the iron to iron carbide in one step in a fluidized bed with a mixture of hydrogen-bearing gas and a carbon-containing material where the hydrogen serves only as a reducing material and the carbon-containing material serves only to provide carbon for the iron carbide.Iaddend.; and   b. converting the iron in the iron carbide directly to steel in .[.the basic oxygen.]. .Iadd.a steelmaking .Iaddend.furnace.   
     
     
       2. The process of claim 1 in which in step (b) the conversion is accomplished by oxidizing the carbon in the iron carbide to carbon monoxide with the heat released thereby providing heat for operation of .[.the.]. .Iadd.a .Iaddend.basic oxygen furnace. 
     
     
       3. A process for the direct production of steel from iron oxides which comprises: a reducing the oxides and converting the iron to iron carbide in one step ion a fluidized bed with a mixture of hydrogen bearing gas and a carbon containing material which provides carbon for the iron carbide, the hydrogen being present in an amount exceeding 50% of the CO present; and   b. adding the iron carbide to a basic oxygen furnace and processing it to steel by the basic oxygen furance process without the addition of external heat .Iadd.to the furnace. .Iaddend. .[.4. The process of claim 3 in which steps (a) and (b) are performed in conjunction and the iron carbide of step (a) is added directly to the basic oxygen furnace without substantial   
     
     
        heat loss so that the process is auto-thermal..]. 5. The process of claim .[.4.]. .Iadd.3 .Iaddend.in which the iron carbide is at a temperature between about 900° F. to .Iadd.and .Iaddend.1300° F. when it 
     
     
        leaves step (a). 6. The process of .[.4.]. .Iadd.3 .Iaddend.in which 
     
     
        off-gas is cycled from step (b) to step (a). 7. The process of claim 6 in which the off-gas provides substantially all of the carbon for step (a). 
     
     
           The process of claim 3 in which in step (a) the ratio of hydrogen to formed water in the reaction medium of the fluidized bed is maintained from about 2.5 to 1 to about 8 to 1 and the CO/CO 2  -hydrogen/H 2   
     
     
        O ratios being essentially in equilibrium with methane. 9. The process of claim 3 in which the volume of hydrogen exceeds the volume of CO in said 
     
     
        fluidized bed. 10. The process of claim 3 in which the carbon containing 
     
     
        material is solid carbon. 11. The process of claim 3 in which the carbon 
     
     
        containing material is lower alkyl hydrocarbon gas. 12. The process of 
     
     
        claim 11 in which the gas is propane. 13. The process of claim 8 in which the temperature of the reaction gas mixture is between about 900° 
     
     
        F. and 1300° F. 14. The process of claim 3 in which the iron carbide of step (a) has lost heat before step (b) is performed and sufficient heat in a preheat step is added to it for step (b) to render the reactions occurring in the conversion of the iron carbide to steel in 
     
     
        the basic oxygen .[.furance.]. .Iadd.furnace .Iaddend.auto-thermal. 15. The process of claim 14 in which the iron carbide charge is preheated to a temperature .[.between about 1300° F. and.]. about 
     
     
        2000° F. 16. The process of claim 14 in which at least part of the 
     
     
        heat for the preheat step is derived from off-gases from step (b). 17. The process of claim 14 in which at least some of the heat for the preheat 
     
     
        step is derived from sensible heat in the off-gases. 18. The process of claim 14 in which at least some of the heat for the preheat step is 
     
     
        derived from combustion of CO in the off-gases. 19. The process of claim 18 in which the CO/CO 2  ratio in the gas combustion products is maintained from about 1:1 to about 2:1 when attaining preheat temperatures 
     
     
        of 900°-1300° F. 20. The process of claim 14 in which the heat for the preheat step is provided by reacting at least part of the 
     
     
        off-gas to produce Fe 2  C in the iron carbide from step (a). 21. The process of claim 20 in which the composition of the reactive medium of step (a) is adjusted to provide the required amount of Fe 2  C in the 
     
     
        iron carbide charge. 22. The process of claim 3 in which the iron carbide of step (a) has lost heat before step (b) is performed and sufficient fuel is added to it to provide additional heat upon combustion in the process to render the reactions occurring in the conversion of the iron carbide to 
     
     
        steel in the basic oxygen furnace autothermal. 23. The process of claim 22 
     
     
        in which the fuel is carbon. 24. The process of claim 23 in which the carbon is added in an amount from about 3 to 5 weight percent of the iron 
     
     
        carbide charge. 25. The process of claim 23 in which the carbon is added 
     
     
        directly to the iron carbide charge. 26. The process of claim 3 in which molten pig iron is added to the iron carbide charge in step (b) and iron 
     
     
        carbide is used to control the temperature of the melt. 27. The process of claim 26 in which the temperature controlling iron carbide is added in an amount up to about 60 weight percent of the iron carbide-pig iron charge. 
     
     
         8. A process for conversion of iron oxides to iron carbide which comprises reducing the oxides and converting the iron to iron carbide in one step in a fluidized bed with a mixture of hydrogen and a carbon containing material which provides carbon for the iron carbide, the mixture containing hydrogen in an amount over 60 percent by volume of the 
     
     
        carbon monoxide present. 29. The process of claim 28 in which the ratio of hydrogen to formed water in the reaction medium of the fluidized bed is maintained from about 2.5 to 1 to about 8 to 1 and the ratio of CO/CO 2  is maintained from about 1 to 1 to about 4 to 1, the prescribed CO/CO 2  --hydrogen/H 2  O ratios being essentially in 
     
     
        equilibrium with methane. 30. The process of claim 28 in which the carbon 
     
     
        containing material is solid carbon. 31. The process of claim 28 in which 
     
     
        the carbon containing material is a lower alkyl hydrocarbon gas. 32. The 
     
     
        process of claim 31 in which the gas is propane. 33. The process of claim 28 in which the temperature of the mixture is between about 1100° 
     
     
        F. and about 1300° F. 34. A process for converting iron carbide to steel ion the basic oxygen furnace by the basic oxygen furnace process, said process comprising the step of augmenting the heat produced in the conversion process which is produced by oxidizing the carbon in the iron carbide, with additional .Iadd.in a preheat step, .Iaddend.to make the process in the basic oxygen furnace autothermal. .[.35. The process of 
     
     
        claim 34 in which the heat is added in a preheat step..]. 36. The process of claim .[.35.]. .Iadd.34 .Iaddend.in which the temperature of the iron carbide charge is .[.between about 1300° F. and.].about 
     
     
        2000° F. before it is added to the basic oxygen furnace. 37. The process of claim .[.35.]. .Iadd.34 .Iaddend.in which the preheat step is 
     
     
        performed by directly heating the iron carbide charge. 38. The process of claim .[.35.]. .Iadd.34 .Iaddend.in which at least some of the heat for 
     
     
        the preheat step is derived from sensible heat in the off-gases. 39. The process of claim .[.35.]. .Iadd.34 .Iaddend.in which at least some of the heat for the preheat step is derived from combustion to CO in the 
     
     
        off-gases. 40. The process of claim 39 in which the CO/CO 2  ratio in the gas combustion products is maintained from about 1:1 to about 2:1 when 
     
     
        attaining preheat temperatures of 900°-1300° F. 41. The process of claim .[.35.]. .Iadd.34 .Iaddend.in which the heat for the preheat step is provided by reacting at least part of the off-gas with the 
     
     
        iron carbide from step (a) to produce Fe 2  C. 42. The process of claim 34 in which said heat is agmented by adding a fuel to the iron carbide charge for combustion during the conversion step. .[.43. The process of claim 42 in which sufficient fuel is added to the charge to provide additional heat upon combustion in the process to raise the temperature of 
     
     
        the charge to at least about 1100° F..]. 44. The process of claim 
     
     
        42 in which the fuel is carbon. 45. The process of claim 44 in which the carbon is added in an amount from about 3 to 5 weight percent of the iron 
     
     
        carbide charge. 46. A process of making steel from iron carbide in the basic oxygen furnace which comprises adding pig iron to the iron carbide charge and controlling the temperature of the charge by the addition of 
     
     
        iron carbide. 47. The process of claim 46 in which the pig iron is added in an amount up to about 40 weight percent of the charge and the temperature controlling iron carbide is added in an amount up to about 60 
     
     
        percent of the iron carbide-pig iron charge. 48. A process for concentrating non-magnetic low grade iron ores which comprises converting the iron oxide in the ores to iron carbide and separating the iron carbide 
     
     
        and gangue by subjecting the treated ores to magnetic separation. 49. The process of claim 48 in which the iron oxides are converted to iron carbide in one step in a fluidized bed with a mixture of hydrogen bearing gas and a carbon containing material which provides carbon for the iron carbide. 
     
     
          . The process of claim 49 in which hydrogen is present in an amount of over 60 percent by volume of carbon monoxide in the fluidized bed. .[.51. A process for the direct production of steel from iron oxides which comprises: a. converting the iron in the oxides to iron carbide; and   b. converting an iron in the iron carbide directly to steel in an electric   
     
     
        furnace..]. 52. .[.A.]. .Iadd.The .Iaddend.process .[.for the direct production of steel from iron oxides which comprises: a. reducing the oxides and converting the iron to iron carbide in one step in a fluidized bed with a mixture of a hydrogen bearing gas and a carbon containing material which provides carbon for the iron carbide,.]. .Iadd.of claim 1 or claim 54 wherein .Iaddend.the hydrogen .[.being.]. .Iadd.is .Iaddend.present in an amount exceeding 50% of the CO present.[.; and.]. .Iadd.. .Iaddend.   .[.b. adding the iron carbide to the electric furnace and processing it to steel in an electric furnace..]. .[.53. The process of claim 52 in which steps (a) and (b) are performed in conjunction and the iron carbide produced in step (a) is added directly to the electric furnace without   
     
     
        substantial heat loss..]. .Iadd.54.  In a process for the production of steel in which iron oxide is first converted to iron carbide in a fluidized bed utilizing carbon monoxide as a reducing agent, and the formed iron carbide is then converted to steel in a steelmaking furnace, the improvement comprising: utilizing hydrogen as the reducing agent and restricting the carbon monoxide to a carburizing function. .Iaddend. .Iadd.55. The process of claim 1 or claim 54 in which hydrogen- and carbon-containing gases are in equilibrium with methane in the fluidized bed. .Iaddend. .Iadd.56. The process of claim 1 in which water is withdrawn from the fluidized bed and carbon-containing gases are reused therein. .Iaddend. .Iadd.57. The process of claim 1 or claim 54 in which the volume of hydrogen in the fluidized bed exceeds the volume of carbon monoxide. .Iaddend. .Iadd.58. The process of claim 1 or claim 54 in which the reducing reaction in the fluidized bed is conducted at a temperature below that at which transient metallic iron would cause sticking. .Iaddend. .Iadd.59. The process of claim 1 or claim 54 in which the reducing reaction in the fluidized bed is conducted at a temperature below about 1300° F. .Iaddend. .Iadd.60. The process of claim 1 or claim 54 in which the reducing reaction in the fluidized bed is conducted at a temperature of at least about 900° F. .Iaddend. .Iadd.61. The process of claim 1 or claim 54 in which off-gas is cycled from the steelmaking furnace to the fluidized bed. .Iaddend. .Iadd.62. The process of claim 61 in which said off-gas contains about 90%carbon monoxide. .Iaddend. .Iadd.63. The process of claim 62 in which substantially all the carbon necessary for providing carbon for the formation of iron carbide in the fluidized bed is supplied by the carbon   
     
     
        monoxide in said off-i gas. .Iaddend. .Iadd.64.  The process of claim 1 or claim 54 in which the iron carbide produced in the fluidized bed comprises a mixture of Fe 2  C and Fe 3  C. .Iaddend. .Iadd.65. The process of claim 64 in which Fe 3  C is predominant. .Iaddend. .Iadd.66. The process of claim 1 or claim 54 conducted in a basic oxygen furnace. .Iaddend. .Iadd.67. The process of claim 66 wherein the iron carbide charge added to the furnace contains a sufficiently high Fe 2  C. to Fe 3  C ratio and is at a temperature sufficient to make the process in the furnace autothermal. .Iaddend. .Iadd.68. The process of claim 1 or claim 54 conducted in an electric furnace. .Iaddend. .Iadd.69. The process of claim 1 or claim 54 in which carbon for the formation of iron carbide is added to the fluidized bed in the form of solid carbon. .Iaddend. .Iadd.70. The process of claim 1 or claim 54 in which carbon for the formation of iron carbide is added to the fluidized bed inthe form of carbon monoxide. .Iaddend. .Iadd.71. The process of claim 1 or claim 54 in which carbon for the formation of iron carbide is added to the fluidized bed in the form of a lower alkyl hydrocarbon gas. .Iaddend. .Iadd.72. The process of claim 1 or claim 54 in which carbon for the formation of iron carbide is added to the fluidized bed in the form of propane. .Iaddend. .Iadd.73. The process of claim 1 or claim 54 in which the hydrogen to water vapor ratio in the fluidized bed is maintained from about 5 to 1 to about 8 to 1. .Iaddend. .Iadd.74. The process of claim 1 or claim 54 in which the hydrogen to water vapor ratio in the fluidized bed is maintained from about 2.5 to 1 to about 8 to 1. .Iaddend. .Iadd.75. The process of claim 1 or claim 54 in which the CO to CO 2  ratio in the fluidized bed 
     
     
        is maintained from about 1 to 1 to about 5 to 1. .Iaddend. .Iadd.76.  The process of claim 1 or claim 54 in which the CO to CO 2  ratio in the fluidized bed is maintained from about 1 to 1 to about 4 to 1. .Iaddend. .Iadd.77. The process of claim or claim 54 in which in the fluidized bed the ratio of hydrogen to formed water in the fluidized bed is maintained from about 2.5 to 1 to about 8 to 1 and the CO to CO 2  ratio is maintained from about 1 to 1 to about 4 to 1, the prescribed CO to CO 2  and hydrogen to H 2  ratios being essentially in equilibrium with methane. .Iaddend. .Iadd.78. The process of claim 55 in which the concentration of methane in the fluidized bed is maintained between about 1 and about 70 volume percent. .Iaddend. .Iadd.79. The process for the direct production of steel from iron oxides which comprises: (a( contacting the iron oxides in a fluidized bed at a temperature between about 900° F. and about 1300° F. with hydrogen gas and carbon-containing materials present in sufficient relative quantities to ensure that the hydrogen reduces the iron oxides to carbon carbides with concomitant formation of water, and the carbon of the carbon-containing materials is used only to provide carbon to the iron carbide and not to extract oxygen from the iron oxide; wherein water is withdrawn from the system and the balance of the gases are reused; and wherein the hydrogen- and carbon-containing gases in the fluidized bed are in equilibrium with methane; and   (b) converting the iron carbide directly to steel in a steel making furnace. .Iaddend. .Iadd.80. The process of claim 79 in which in step (a) the volume of hydrogen exceeds 50% of the volume of carbon monoxide in the fluidized bed. .Iaddend. .Iadd.81. The process of claim 79 in which in step (a) the volume of hydrogen exceeds the volume of carbon monozide in   
     
     
        the fluidized bed. .Iaddend. .Iadd.82.  The process of claim 79 in which off-gas is cycled from step (b) to step (a). .Iaddend. .Iadd.83. The process of claim 79 in which the steel making furnace is a basic oxygen furnace contains sufficient Fe 2  C. and is at a temperature sufficient to make the process in the basic oxygen furnace autothermal. .Iaddend. .Iadd.84. The process of claim 79 in which in the fluidized bed the hydrogen to water vapor ratio is maintained from about 5 to 1 to about 8 to 1 and the CO to CO 2  ratio is maintained from about 1 to 1 to about 5 to 1. .Iaddend. .Iadd.85. A steel making process utilizing an iron oxide feed comprising: (a) reducing the iron oxide to be converted to steel to iron carbide in a fluidized bed, at a temperature below that which would cause transiently-formed metallic iron to be sticky, with a reducing agent consisting essentially of hydrogen, in the presence of a carbon-containing material which supplies carbon for the formation of the iron carbide; wherein the hydrogen is present in an amount in excess of 50% of the CO present, the ratio of hydrogen to formed water in the reaction medium of the fluidized bed is maintained from about 2.5 to 1 to about 8 to 1 and the CO to CO 2  ratio is maintained from about 1 to 1 to about 4 to 1, the prescribed CO to CO 2  and H 2  to H 2  O ratios being essentially in equilibrium with methane;   (b) withdrawing H 2  O from step (a);   (c) feeding the formed iron carbide to a steelmaking furnace to produce steel; and   (d) recycling carbon monoxide off-gases from step (c) to step (a) to supply carbon necessary for the formation of the iron carbide. .Iaddend.   
     
     
        .Iadd.     The process of claim 85 in which the steelmaking furnace is a basic oxygen furnace or an electric furnace. .Iaddend. .Iadd.87. The process of claim 85 or claim 86 in which the temperature in the fluidized bed is maintained between about 1020° F. and about 1170° F. .Iaddend. .Iadd.88. The process of claim 85 or 86 in which carbon for the formation of iron carbide is supplied to the fluidized bed in the form of propane. .Iaddend. .Iadd.89. The process of claim 28 in which water and iron carbide are the only products withdrawn from the system. .Iaddend. .Iadd.90. The process of claim 28 in which the temperature of the fluidized bed is maintained at a temperature below that at which transient metallic iron would cause sticking. .Iaddend. .Iadd.91. The process of claim 90 in which the temperature in the fluidized bed is maintained at at least about 900° F. .Iaddend. .Iadd.92. The process of claim 28 in which the iron carbide produced comprises a mixture of Fe 2  C and Fe 3  C. .Iaddend. .Iadd.93. The process of claim 92 in which the major proportion of the iron carbide is Fe 3  C. .Iaddend. .Iadd.94. The process of claim 28 or claim 49 in which the carbon of the carbon-containing is restricted to the function of supplying carbon to the iron carbide and does not act to reduce the iron oxides. .Iaddend.