METHOD OF IMPROVING THE PERFORMANCE OF SUBMERGED OXYGEN INJECTORS

METHODE POUR AMELIORER LA PERFORMANCE D'INJECTEURS D'OXYGENE SUBMERGES

English Abstract

ABSTRACT OF THE DISCLOSURE
In the injection of oxygen through a refractory
lined wall into a molten metal, for example, pig iron,
the injected oxygen is surrounded by a stream of a pro-
tective fluid to diminish erosion of the refractory lining:
the velocities of the oxygen and protective fluid are
selected to minimize eddying of the oxygen into the pro-
tective fluid so that the protective fluid retains its
effectiveness for a greater distance from the injector
whereby greater protection is provided to the injector
and the refractory.

Claims

WE CLAIM:
1. In a method of injecting oxygen into a bath of
molten metal, in the refining of said metal, in which the
oxygen is injected in a stream into the molten metal
from below the upper surface thereof and in which the
injected oxygen is surrounded by a simultaneously
injected stream of protective fluid, the improvement
wherein the relative velocities of injection of the
oxygen and protective fluid are selected to substantially
minimize turbulence between the streams.
2. A method according to claim 1, wherein the
velocity of the stream of protective fluid is about
0.5 to 1.5 the velocity of the oxygen stream at the
point of injection.
3. A method according to claim 1, wherein said
metal is pig iron and said fluid is N2, SO2, H2O, Ar or
a hydrocarbon.
4. A method according to claim 1, wherein said
metal is pig iron and said fluid is a hydrocarbon.
5. A method according to claim 2, wherein said
metal is pig iron and said fluid is a hydrocarbon.
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6. In a method of injecting oxygen into a bath of
molten metal, in the refining of said metal, in which the
oxygen is injected in a stream into the molten metal from
below the upper surface thereof and in which the injected
oxygen is surrounded by a simultaneously injected stream of
protective fluid, the improvement wherein the velocity of
the stream of protective fluid is controlled at about 0.5
to 1.5 times the velocity of the oxygen stream at the
point of injection, whereby turbulence between the streams
is substantially minimized.
7. In a method of injecting oxygen into a bath of
molten metal, in the refining of the metal, in which the
oxygen is injected in a stream into the molten metal from
below the upper surface thereof and in which the stream of
oxygen is surrounded by a stream of a hydrocarbon, the
improvement wherein the velocity of the stream of hydro-
carbon is controlled at about 0.5 to 1.5 times the
velocity of the oxygen stream at the point of injection,
and said hydrocarbon stream scavenges oxygen which eddys
into the hydrocarbon stream to prevent the oxygen and
molten metal reacting, with a minimum of turbulence
between the streams.

Description

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BACKGROUND OF THE INVENTION
i) Field of the Invention
This invention relates to metal ~fining in a
molten metal bath into which oxyqen is injected.
ii) Description of the Prior Art
- U.S. Patent 3,706,549, the teaching of which
is hereby incorporated herein by reference, describes
the injection of oxygen into a bath of molten metal from
below the bath surface ln the refining of pig iron -to
steel, such that accelerated erosion of the refractory
used to line the container of the bath, is prevented.
The oxygen injector which e~tends through the
refractory wall lining of the container, comprises two
concentric tubes. The inner tube is used for injection
of oxygen gas and the annular space between the inner
tube and the outer tube is for applying a protective
fluid. The fluid, which is usually a hydrocarbon, is
employed to shield the oxygen from the reactive molten
metal at the interface of the refractory wall and the
molten metal and ensures that the vigorous reaction with
the molten metal takes place away from the refractory wall.
The resultant delay in the e~othermic reaction
between the oxygen and the molten metal is sufficient to
maintain the integrity of the refractory wall.
The prior art teaches that the effectiveness of
the hydrocarbon protective fluid shield is due to its endo-
thermic decomposition under the high temperature conditions
existing in the molten metal bath.
Although use of the method,of the U.S~ Patent
results in an overall improvement, particularly in the life
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of the refractory, the injector is s-till subject to erosion
and it is desirable to further improve the life of the
refractory lining.
It ls an object of this invention to improve
the life of an injector and of the refractory lining
employed in a method of the kind described in U.S. Patent
3,706,549.
SUMMARY OF THE I~VENTION
According to the invention there is provided in
a method of injecting oxygen into a bath of molten metal,
in the refining of said metal, in which the oxygen is
injected in a stream into -the molten metal from below
the upper surface thereof and in which the injected
oxygen is surrounded by a simultaneously injected stream
of protective fluid, the improvement wherein the relative
velocities of injection of the oxygen and protective fluid
are selected t~ substantially minimize turbulence between
the streams.
DESCRIPTION OF THE PREFERRED EMBODIME~TS
It has now been found that an important feature of
the protactive fluid, for example, the hydrocarbon, is
its scavanging capability for oxygen. By scavanging
the oxygen from the central stream which eddies into the
protective annular fluid envelope, the protective fluid
; 25 is effective in preventing the oxygen and molten metal
reaction from taking place at the refractory/molten metal
interface and at the molten metal/injector interface.
Since the scavanging effect is important for
extending the life of the injector and reractory surround-
~ 30 ing the injector, is has now been found that it is
- ~ important to design the injector so that the turbulent
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conditions between the central oxygen stream and the
annular protective stream are minimized, thereby minimiziny
the oxygen eddying and the migration of oxygen into the
protective stxeam with mixing of oxygen and the protective
stream. In this way it is possible to retain the
effectiveness of the protective stream for a significant
distance from the injector outlet and hence to provide
greater protection of the injector and refractory, and
thus longer life in these parts.
It has been found that a major factor assisting
in retaining the integrity of the protective annular
stream and thereby reducing the eddying or turbulence
between the streams is their relative velocities at the
exit of the injector.
In order to obtain the maximum protection with
the minimum amount of protective fluid, the relative
velocity of the central oxygen stream must be as low as
possible. For the most efficient range the velocity
of the protective fluid stream should be about 0.5 to 1.5
of the velocity of the oxygen stream as the streams leave
the injector and enter the molten metal.
The velocity difference parameter is more
critical in the case of a non-oxygen scavanging protective
fluids, such as N2, SO2, H20 and argon. The larger the
deviation from the condition where minimum eddies are
formed, the larger the amount of protective fluid required
to maintain the integrity of the injector and the surround-
ing refractory.
.
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