Appeal 2007-0200
Application 10/445,466
DISCUSSION
The invention of Watkins "relates to cleaning and maintaining a
steelmaking furnace and, in particular, to a multipurpose lance assembly and
gas flow control apparatus for cleaning and maintaining a basic oxygen
furnace" (Watkins, col. 1, ll. 13-16). Violent agitation of the melt during
refining of molten metal into steel causes a material commonly known as
skull, a mixture of molten metal and oxides, to be deposited on the working
surface of the furnace. The formation of skull at the cone of the furnace is
undesirable because it restricts the ability to lower lances and charge scrap
into the cone. (Watkins, col. 1, ll. 31-37.)
One way the problem of skulling has been addressed is to blow
oxygen gas from a deskulling lance to melt the skull at the furnace cone by
moving the lance vertically up and down near the location of the skull
(Watkins, col. 1, ll. 38-42). On the other hand, factors including wear, high
temperature, and the combustion of high velocity oxygen gas in the furnace
cause the refractory walls to deteriorate, requiring repair or replacement
(Watkins, col. 1, ll. 44-46). One way to maintain the refractory walls of the
furnace is through a process known as slag splashing, in which a lance is
used to blow an inert gas toward the slag layer causing the slag to be
splashed upwardly onto the refractory walls to coat portions of the walls that
have been worn. The slag cools on the walls, thereby effectively repairing
worn portions of the walls, but slag splashing may increase the problem of
skull build-up at the furnace cone. (Watkins, col. 1, ll. 47-55.)
Watkins approaches the tasks of deskulling and slag splashing by
providing a single multipurpose lance for carrying out both operations
(Watkins, col. 2, ll. 6-9). Watkins discloses a double circuit lance
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