1. Field of the Invention
This invention relates to a method of refining a metal by blowing a refining gas surrounded by a cooling gas into the melt of the metal to be refined using a concentric multi-tube system nozzle, e.g., a concentric double tube system nozzle, situated beneath the surface of the melt in a metal refining vessel, and more particularly, the invention relates to a method of protecting the concentric multi-tube system nozzle.
2. Description of the Prior Art
In a conventional concentric double tube system nozzle (hereinafter, referred to as simply a double tube nozzle) of a metal refining vessel, mainly oxygen gas is blown into the melt to be refined from the inner tube and a cooling gas is blown into it from the outer tube of the double tube nozzle. As the cooling gas, a hydrocarbon gas such as methane or propane is mainly used in the metal refining system and as one of the improvements of such a method, there has been proposed a method which gives much better cooling effect than is attainable using CO.sub.2 or steam as the cooling gas. In this improved method hydrocarbon gas is used in an amount of slightly less than 10% by weight of the amount of blowing oxygen gas as disclosed in, for example, U.S. Pat. No. 3,706,549. The technical gist of the proposed method is thus to control the amount of the cooling gas according to the amount of blowing oxygen.
However, in this method, the cooling gas used is limited to a hydrocarbon gas and it has been confirmed that when the kind of cooling gas is changed or when the dimensions of the nozzle are changed, the desired cooling effect cannot always be attained even when the amount of the cooling gas employed is adjusted to an amount of less than 10% by weight of the amount of the blowing oxygen gas.