Molten pig iron manufacturing method

Abstract

A molten pig iron manufacturing method using a fixed-type DC electric furnace, wherein an auxiliary raw material is supplied to the fixed-type DC electric furnace and molten pig iron having a C concentration of 2 to 4 mass % at a temperature of 1400° C. to 1550° C. is tapped from a tap hole in a state in which a solid iron source is present in the furnace inner peripheral wall space and in a state in which the solid iron source is not present in the upper electrode facing space.

1 . A molten pig iron manufacturing method using a fixed-type DC electric furnace, wherein
 if, in a furnace, a space in which a horizontal separation distance from an outer periphery of an upper electrode at a height position between a slag bath surface and a lower end of the upper electrode inserted from a furnace lid is 0.5 times or less a diameter of the upper electrode is defined as an upper electrode facing space, and   if, in the furnace, a space in which a horizontal separation distance from an inner wall surface of a furnace wall at a height position above a height position of the slag bath surface is within the shortest distance between the furnace wall and the upper electrode facing space is defined as a furnace inner peripheral wall space,   an auxiliary raw material is supplied to the fixed-type DC electric furnace and molten pig iron having a C concentration of 2 to 4 mass % at a temperature of 1400° C. to 1550° C. is tapped from a tap hole in a state in which a solid iron source is present in the furnace inner peripheral wall space and in a state in which the solid iron source is not present in the upper electrode facing space.   
     
     
         2 . The molten pig iron manufacturing method according to  claim 1 , wherein
 a top portion of the solid iron source in the furnace inner peripheral wall space is present at a position higher than the lower end of the upper electrode.   
     
     
         3 . The molten pig iron manufacturing method according to  claim 1 , wherein
 the solid iron source is present along a whole circumference of the furnace inner peripheral wall space.   
     
     
         4 . The molten pig iron manufacturing method according to  claim 1 , wherein
 the fixed-type DC electric furnace includes:   two or more of the upper electrodes; and   two or more lower electrodes provided in a refractory at a bottom portion of the fixed-type DC electric furnace; and   the two or more lower electrodes are provided at positions corresponding to the two or more upper electrodes in a plane view of the fixed-type DC electric furnace.   
     
     
         5 . The molten pig iron manufacturing method according to  claim 1 , wherein
 a supply port or a solid iron source supply pipe for supplying the solid iron source is disposed above the furnace inner peripheral wall space.   
     
     
         6 . The molten pig iron manufacturing method according to  claim 5 , wherein
 a supply port for supplying the solid iron source is disposed above the furnace inner peripheral wall space, and   the solid iron source is supplied from the supply port using a solid iron source charging implement on which the solid iron source is loaded.   
     
     
         7 . The molten pig iron manufacturing method according to  claim 1 , wherein
 the solid iron source is at least one of iron-containing scrap, reduced iron, and iron-containing dust.   
     
     
         8 . The molten pig iron manufacturing method according to  claim 1 , wherein
 the solid iron source contains at least reduced iron,   the reduced iron is reduced iron having a C concentration of 0 to 4 mass % by reducing iron ore using at least one of hydrogen gas, natural gas, and CO gas, and   the reduced iron is DRI or HBI.   
     
     
         9 . The molten pig iron manufacturing method according to  claim 1 , wherein
 the auxiliary raw material is at least one of a carbon material and a flux for composition adjustment.   
     
     
         10 . The molten pig iron manufacturing method according to  claim 9 , wherein
 the auxiliary raw material is a carbon material having a particle size of 0.5 mm to 10 mm, and   the carbon material is supplied from a plurality of locations around the upper electrodes to the slag bath surface formed in the upper electrode facing space.   
     
     
         11 . The molten pig iron manufacturing method according to  claim 1 , wherein
 steelmaking slag is supplied to the fixed-type DC electric furnace.   
     
     
         12 . The molten pig iron manufacturing method according to  claim 11 , wherein
 at least one type of slag selected from converter slag, molten pig iron desulfurization slag, secondary refining slag, and dephosphorization slag is used as the steelmaking slag, and   the steelmaking slag is supplied in a molten state to the solid iron source present in the furnace inner peripheral wall space.   
     
     
         13 . The molten pig iron manufacturing method according to  claim 1 , wherein
 one or a plurality of bottom-blown tuyeres having a flow rate variable small diameter circle or a flat gas flow path are provided at positions separated by a horizontal distance of  1  m or more from immediately below the upper electrode at a bottom portion of the fixed-type DC electric furnace, and   from the one or the plurality of bottom-blown tuyeres, a maximum of 200 Nm 3 /h of an inert gas per one bottom-blown tuyere is blown into the fixed-type DC electric furnace.   
     
     
         14 . The molten pig iron manufacturing method according to  claim 1 , wherein
 an electric furnace slag having a T·Fe concentration of 5 mass % or less, a CaO/SiO 2  concentration ratio of 1.0 to 1.3, and an Al 2 O 3  concentration of 8 to 20 mass % is discharged from a slag hole.   
     
     
         15 . The molten pig iron manufacturing method according to  claim 1 , wherein
 when the molten pig iron has a P concentration of higher than 0.15%, dephosphorization treatment by ladle dephosphorization refining is performed until the P concentration of the molten pig iron becomes 0.15% or less.