Carbon composite agglomerate for producing reduced iron and method for producing reduced iron using the same

Abstract

Provided is a carbon composite briquette which is used as the raw material of a movable hearth furnace for producing reduced iron having a sufficient carbon content and a higher crushing strength, and also provided is a method for producing reduced iron using the carbon composite briquette. The carbon composite briquette for producing reduced iron has a total SiO 2 +Al 2 O 3 +CaO+MgO content that is between 7 and 15 mass %; an MgO content that is between 0.1 and 6 mass %; an Al 2 O 3 /SiO 2 mass ratio that is between 0.34 and 0.52; a CaO/SiO 2 mass ratio that is between 0.25 and 2.0; and a C content such that between 1 and 9 mass % of C is retained in the resulting reduced iron.

1 : A carbon composite agglomerate comprising C, Fe, SiO 2 , Al 2 O 3 , CaO, and MgO,
 wherein:   a total content of SiO 2 , Al 2 O 3 , CaO, and MgO is 7 to 15 mass %,   a MgO content is 0.1 to 6 mass %,   a mass ratio range of Al 2 O 3 /SiO 2  is 0.34 to 0.52,   a mass ratio range of CaO/SiO 2  is 0.25 to 2.0, and   wherein the C content is such that 1 to 9 mass % of C remains in reduced iron produced from the carbon composite agglomerate after the agglomerate has been reduced in a moving hearth furnace.   
     
     
         2 : The agglomerate of  claim 1  having a porosity of 37.5% or less. 
     
     
         3 : The agglomerate of  claim 1 , wherein an average grain size d50 of a carbonaceous material in the agglomerate measured by a laser diffraction scattering grain size distribution measurement method is 30 μm or less. 
     
     
         4 : The agglomerate of  claim 1 , further comprising an ironmaking dust. 
     
     
         5 : A method for producing reduced iron by reducing the agglomerate of  claim 1 , the method comprising heating the agglomerate with a moving hearth furnace, wherein the moving hearth furnace is divided into a plurality of zones in a moving direction of a hearth, and a final zone of the plurality of zones has an oxidizing atmosphere, to obtain reduced iron comprising 1 to 9 mass % C. 
     
     
         6 : The method of  claim 5 , wherein the oxidizing atmosphere of the final zone has a gas oxidation degree OD of 1.0 or more, wherein
   OD=(CO 2 +H 2 O+2O 2 )/(CO 2 +H 2 O+O 2 +CO+H 2 )   [where a unit of CO 2 , H 2 O, O 2 , CO, and H 2  is vol %].   
     
     
         7 : The agglomerate of  claim 1 , wherein a mass ratio range of CaO/SiO 2  is 0.25 to 1.5. 
     
     
         8 : The agglomerate of  claim 1 , wherein a mass ratio range of CaO/SiO 2  is 0.25 to 1.0. 
     
     
         9 : The agglomerate of  claim 1 , wherein the C content is such that 4 to 9 mass % of C remains in reduced iron produced from the carbon composite agglomerate after the agglomerate has been reduced in a moving hearth furnace. 
     
     
         10 : The agglomerate of  claim 9  having a porosity of 37.5% or less. 
     
     
         11 : The agglomerate of  claim 1  having a porosity of 25% to 37.5%. 
     
     
         12 : The agglomerate of  claim 9  having a porosity of 25% to 37.5%. 
     
     
         13 : The agglomerate of  claim 1 , wherein an average grain size d50 of a carbonaceous material in the agglomerate measured by a laser diffraction scattering grain size distribution measurement method is 10 μm or less. 
     
     
         14 : The agglomerate of  claim 1 , in briquette form. 
     
     
         15 : The agglomerate of  claim 1 , in pellet form. 
     
     
         16 : The method of  claim 5 , wherein the moving hearth furnace is a rotary hearth furnace. 
     
     
         17 : The method of  claim 5 , wherein the moving hearth furnace is a straight hearth furnace. 
     
     
         18 : The agglomerate of  claim 14 , wherein a crushing strength of the reduced iron is at least 180 kgf/briquette. 
     
     
         19 : The agglomerate of  claim 14 , wherein a crushing strength of the reduced iron is at least 300 kgf/briquette. 
     
     
         20 : The agglomerate of  claim 14 , wherein a crushing strength of the reduced iron is at least 600 kgf/briquette.