Refining Molten Metal

Abstract

A method of refining molten metal in a vessel by the reaction of oxygen with impurities in the molten metal comprises the steps of: a) ejecting at least one primary jet of oxygen from a lance positioned above the molten metal into the molten metal to react with impurities therein and to form a layer of molten slag; b) continuing to eject the primary jet of oxygen from the lance and thereby causing the primary bet of oxygen to pass through the slag layer into the molten metal; c) ejecting a plurality of secondary jets of oxygen from the lance, the secondary jet of oxygen travelling for a distance separately from the primary jet of oxygen; and d) entraining the secondary jets of oxygen into the primary jet of oxygen upstream of the entry of the primary jet of oxygen into the molten metal. A lance head for use in the method has at least one primary oxygen port and a plurality of secondary oxygen ports, the axis of the second oxygen port diverging in the direction of flow from the primary oxygen port at an angle of up to 45°. The method and lance head are particularly of use in the Basic Oxygen Steelmaking (BOS) process. If desired, a stirring gas such as argon may be mixed with the primary oxygen.

1 . A method of refining molten metal in a vessel by the reaction of oxygen with impurities in the molten metal, wherein the vessel contains a volume of the molten metal, comprising the steps of:
 (a) ejecting at least one primary jet of oxygen from a lance positioned above the molten metal into the molten metal to react with impurities therein and to form a layer of molten slag;   (b) continuing to eject the primary jet of oxygen from the lance and thereby causing the primary jet of oxygen to pass through the slag layer into the molten metal;   (c) ejecting a plurality of secondary jets of oxygen from the lance, the secondary jet of oxygen traveling for a distance separately from the primary jet of oxygen; and   (d) entraining the secondary jets of oxygen into the primary jet of oxygen upstream of the entry of the primary jet of oxygen into the volume of the molten metal.   
   
   
       2 . The method according to  claim 1 , wherein in step (b) the said primary jet of oxygen is ejected at a supersonic axial velocity is in the range of Mach1.5 to Mach 3. 
   
   
       3 . The method according to  claim 1 , wherein the longitudinal axis of each secondary jet diverges from the longitudinal axis of its associated primary jet in the direction of travel at an angle of up to 45°. 
   
   
       4 .- 6 . (canceled) 
   
   
       7 . A The method according to  claim 1 , wherein the head of the lance is immersed in the slag layer during the said step (b). 
   
   
       8 .- 13 . (canceled) 
   
   
       14 . The method according to  claim 1 , in which the secondary oxygen flow is from 5-50% of the primary oxygen flow. 
   
   
       15 . The method according to  claim 1 , additionally including the step of mixing with at least one stirring gas upstream of ejection the oxygen from which the primary jet and/or secondary jet is formed. 
   
   
       16 .- 19 . (canceled) 
   
   
       20 . A lance head for use in a method according to  claim 1 , the lance head having at least one primary oxygen port and a plurality of secondary oxygen ports, each secondary oxygen port being associated with the primary oxygen port or one of the primary oxygen ports and having an axis diverging in the direction of flow from its associated primary oxygen port at an angle of up to 45°. 
   
   
       21 - 22 . (canceled) 
   
   
       23 . The lance head according to  claim 20 , wherein there is a plurality of primary oxygen ports and a group of from one to eight secondary oxygen ports associated with each primary oxygen port. 
   
   
       24 . The lance head according to  claim 23 , wherein each group of secondary oxygen ports are arranged on an arc of a circle that is concentric with the primary oxygen port with which said group is associated. 
   
   
       25 . (canceled) 
   
   
       26 . The lance head according to  claim 20 , wherein the linear separation of each secondary oxygen port from the primary oxygen port is less than twice the diameter of the primary oxygen port. 
   
   
       27 . The lance head according to  claim 20 , wherein the primary oxygen port and each secondary oxygen port are situated at the tip of the lance head. 
   
   
       28 .- 29 . (canceled) 
   
   
       30 . The lance head according to  claim 20 , in which the primary oxygen ports are located in a sloping annular face of the lance head which has a leading inner circumferential edge, such that the longitudinal axes of the primary oxygen ports all diverge from one another in the direction of oxygen flow. 
   
   
       31 . The lance head according to  claim 20 , in which all the primary and secondary oxygen ports communicate with a common chamber in the lance head. 
   
   
       32 . The lance head according to  claim 20 , in which the or each primary oxygen port communicates with a chamber in the lance head that does not communicate with the secondary oxygen ports.