Patent ID: 7959708

Claim:
A method of injecting inert gas into melt located within a metallurgical furnace having a heated furnace atmosphere, said method comprising: (a) introducing an inert gas stream into a nozzle having a passageway of converging-diverging configuration; (b) forming a combined fuel, inert gas and oxygen-containing stream by (b.1) injecting an oxygen stream into the inert gas stream at inner circumferential locations of the passageway that are situated entirely within the passageway so that a combined inert gas and oxygen-containing stream is formed with the passageway, and injecting a fuel containing a hydrogen species into the inert gas stream at inner circumferential locations of the passageway that are situated entirely within the passageway, or (b.2) injecting a pre-mixed stream of oxygen and a fuel containing a hydrogen species into the inert gas stream at inner circumferential locations of the passageway that are situated entirely within the passageway; (c) so that a combined fuel, inert gas and oxygen-containing stream is formed within the passageway having a structure composed of an outer circumferential region containing a mixture of the inert gas, the oxygen and the fuel and an inner central region surrounded by the outer circumferential region and containing the inert gas and essentially no fuel or oxygen; (d) the inert gas stream being introduced into an inlet section of the passageway at or above a critical pressure, thereby to produce: a choked flow condition within the central throat section of the passageway; acceleration of the combined fuel, inert gas and oxygen-containing stream to a supersonic velocity within a diverging section of the passageway; and discharge of the combined fuel, inert gas and oxygen-containing stream as a structured jet from the nozzle into the furnace atmosphere, the structured jet having the structure of the combined fuel, inert gas and oxygen-containing stream and the supersonic velocity upon discharge from the nozzle; (e) preventing ignition and combustion of the fuel within the passageway by providing the passageway with an inner surface uninterrupted by any discontinuity within which the outer circumferential region could otherwise decelerate and provide a site for stable combustion of the fuel; (f) producing a flame envelope surrounding a jet of inert gas formed from the inner central region of the structured jet and initially having the supersonic velocity to inhibit velocity decay and concentration decay of the jet of inert gas, the flame envelope being produced entirely outside of the nozzle through contact of the outer circumferential region of the structured jet with the heated furnace atmosphere so as to create a shear-mixing zone containing a flammable mixture composed of the fuel, the inert gas, the oxygen and the heated furnace atmosphere and auto-ignition of the flammable mixture through heat supplied by the heated furnace atmosphere; and (g) directing the jet of inert gas into the melt, while surrounded by the flame envelope.