Foamy slag process using multi-circuit lance

Abstract

A method of improving post-combustion heat recovery in a vessel containing a charge of molten ferrous metal and slag includes the use of a lance for the introduction of oxygen gas into the charge. The method includes blowing oxygen into the charge through at least one first nozzle of the lance for refining the molten metal into steel. Oxygen is blown through at least one second nozzle of the lance from at least one location spaced above the first nozzle at an oxygen flow rate effective to produce foamy slag in an amount for obtaining a post-combustion heat transfer efficiency of at least about 40% without appreciable overflow of the slag from the vessel. The oxygen flow rate from the second nozzle is at a minimum at about a starting point of a peak decarburization period of the charge. Iron oxide containing pellets may also be added to the charge. In this case, the oxygen flow rate from the first nozzle may be reduced while the iron oxide containing material is being added, and the reduced oxygen flow may be replenished with an inert gas.