METHODE DE PROTECTION DES BUSES ET DE LA GARNITURE REFRACTAIRE D'UNE CUVE D'AFFINAGE

PROCESS FOR PROTECTION OF NOZZLES AND REFRACTORY LINING OF A VESSEL FOR REFINING MOLTEN METAL

Abrégé anglais

ABSTRACT
A process for protecting oxygen injection nozzles and the
surrounding refractory lining of a molten metal refining vessel
having such oxygen injection nozzles beneath the bath surface.
The injection nozzle comprises at least three concentric pipes,
the central conduit thereof being connected to a source of oxygen,
the outer annular conduits thereof each being supplied with a
protective fluid, said protective fluid containing at least one
hydroxyl compound or water or a mixture thereof. The protective
hydroxyl compounds are selected from the gaseous or liquid alcohol
group and preferably from the aliphatic alcohol group. Methanol,
ethanol, propanol and butanol are preferred alcohols.
Apparatus for carrying out the process is also disclosed.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Process for protection of underbath blowing nozzles and
refractory lining of a vessel for refing a bath of molten metal
therein, wherein an injection device projects through the vessel wall
below the bath surface, said injection device being composed of at
least three concentric pipes with annular gas passageways therebet-
ween, said process comprising:
injecting oxygen through the central conduit of said
device and injecting a protective fluid through the annu-
lar passageways thereof, said protective fluid containing
at least one of the group comprising an hydroxyl compound,
water, and a blend of the two.
2. Process according to claim 1, characterized in that the
hydroxyl compound is selected from the gaseous and liquid alcohol
group.
3. Process according to claim 2, characterized in that the
hydroxyl compound is selected from the aliphatic alcohol group.
4. Process according to claim 3, characterized in that the
hydroxyl compound is selected from the methanol, ethanol, propanol
and butanol group.
5. Process according to claim 1, characterized in that the
blend of hydroxyl compounds and water contains at least 40% water by
weight.
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6. Process according to claim 1, characterized in that at
least one hydroxyl compound is supplied through the inner annular
passageway (18) and a blend of at least one hydroxyl compound and
carbon dioxide is supplied through the outer annular passageway (19).
7. Process according to claim 1, characterized in that at
least one hydroxyl compound is supplied through the inner annular
passageway (18) and a blend of at least one hydroxyl compound and an
inert gas is supplied through the outer annular passageway (19).
8. Process according to claim 6, characterized in that the
proportion of the carbon dioxide is increased during the course of
the refining process.
9. Process according to claim 1 wherein said protective fluid
is water in atomized form.
10. Process according to claim 1 wherein said protective fluid
is water in vaporized form.
11. Apparatus for injecting treating gas into a molten metal
containing vessel beneath the surface of the molten metal therein,
comprising:
a central pipe connected to a source of treating gas;
an annular jacketing pipe surrounding said central pipe
and spaced therefrom to form an annular gas passageway
therebetween, said jacketing pipe being connected to a
source of protective gas;
an outer pipe surrounding said jacketing pipe and spaced
therefrom to form an annular space therebetween, said outer
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pipe being connected to a source of protective gas; and
a pair of spaced discs mounted external to and concentric
with said outer pipe.
12. Apparatus according to claim 11 further comprising a
tubular chamber surrounding said outer pipe.
13. Apparatus according to claim 12 wherein said discs are
mounted on said chamber.
14. Apparatus according to claim 12 further comprising an
inlet for a gaseous medium to maintain a positive pressure within
said tubular chamber.
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Description

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This ii~vent ion relates to a method ~or reiinir.g
molten met~l:l, arl(~ more particu].arly to t~le refining of iron
to steel.
Whell refining molten metal, particularly liquid pig
iron, in an open hearth furnace, an electric arc furnace or in
a converter by introducing an oxygen-containing gas into the
molten metal below the surface of the bath, there is a problem
involving the protection of the nozzle and the refractory
lining of the vessel surrounding the nozzle fromtoo rapid wear.
In general, gaseous or liquid hydrocarbon compounds are used
as a.protective fluid for this purpose.
OBJECT OF THE INVENTION
The principal object of the invention is to reduce the
nozzle and refractory lining consumption in a process for
refining molten metal, thus attaining a longer service li.fe of
the device for injection of the oxygen-containing gas~
..~ ,...
SUMMARY OF INV~NTION
The present invention is a process for protecting
oxygen injection nozzles and the surrounding refractory
lining of a molten metal :refining vessel having such oxygen
injection nozzles beneath the bat}l surface. The injection
nozzle comprises at least three concentric pipes, the
central conduit thereof being connected to a source of
o~ygen, the outer annular conduits thereof each being supplied
with a protective fluid, said protective fluid containing at
east one of the group comprising a hydroxyl compound, water
and a mixture thereof. The protective fluids can be the same
in each annular passageway or they can be different compounds
or mixtures.
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It has become possible through the process of the invention
to attain a service life of the nozzles and the refractory lining
surrounding the nozzles of 400 operating hours. The extended
service life of the nozzles compared to that in known processes
is attributed to the increased heat of dissociation of hydroxyl
compounds compared to hydrocarbon compounds. It has been deter-
mined that 0.38 kg of alcohol exhibits the same heat of dissocia-
tion when used for local cooling as 1 kg of propane (C3H8). It is
also possible to blend the hydroxyl compounds with water or to use
only water for cooling. Water must be atomized or vaporized to
be effective.
Particularly suitable hydroxyl compounds are liquid ones that
are miscible with water and remove as much heat as possible from
the surroundings through an endothermic dissociation reaction.
Monovalent or polyvalent aliphatic or aromatic alcohols are
particularly suitable for this purpose.
DESCRIPTION OF THE DRAWINGS
-
The present invention will be more readily understood by
referring to the following detailed description and the appended
drawings, in which Figure 1 is a sectional view of an injection
device according to the invention in a hearth-type furnace.
Figure 2 is an enlarged sectional view of a portion of Figure
1 showing the injection device with greater clarity.
DETAILED DESCRIPTION
Referring now to Figure 1, a hearth-type furnace 1 such as an
open hearth furnace, has an injection device 2 installed in the
sidewall thereof at at least one location, the device opening into
the vessel under the bath level 3. Two burners 4 are directed
downwardly toward the bath above the bath level.
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As can be seen in Figure 2, the injection nozzle consists of
three concentric pipes 11, 12, 13 held apart by spacers (not
shown3, each of which is provided with a respective gas inlet 14,
15, 16 for gases or gas mixtures. These pipes form a central
S conduit 17 and a first annular conduit 18 and a second annular,
conduit 19. The opening of the pipes into the furnace interior
can, as depicted, be designed in the form of annular conduits but
also with annular discs covering the annular conduits with outlet
openings along the circumference. The outer pipe 13 is anchored
in the brickwork 6. In the outer region of the furnace wall,
outer pipe 13 is surrounded by a closed pipe section 20 having an
inlet 21 for a gaseous medium to maintain a positive pressure
within chamber 22. Two concentric discs 23 are mounted on the
outer surface of this pipe section 20. The pipe section 20,
including the associated discs 23, serves to prevent the
combustible gases flowing back between the refractory material
and the outer jacket pipe. Pipe section 20 is optional.
Alternatively, discs 23 may be mounted on the outer jacket pipe
13.
Oxygen is injected during the refining process through the
central conduit 17. Alcohol is supplied through the first annular
conduit 18, which changes to a gaseous state at the tip of the
nozzle because of the temperatures prevailing there. A mixture
of 50% alconol and 50% carbon dioxide is injected through the
second annular conduit 19. Nitrogen is supplied to the pipe
section 20 through inlet 21.
The following indicates the process conditions for a preferred
embodiment.
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The concentrically arranged pipes of the injection device
have the following dimensions:
Inner pipe 11 Inner Diameter 13 mm
Outer Diameter 16 mm
First jacket pipe 12 Inner Diameter 20 mm
Outer Diameter 26 mm
Second jacket pipe 13 Inner Diameter 32 mm
Outer Diameter 48 mm
Pipe section 20 Inner Diameter 60 mm
Outer Diameter 72 mm
Concentric discs 23 Outer Diameter 150 mm
Pressure and throughput of the gases/gas mixtures measured
in the supply lines to the individual pipes 11, 12, 13:
Pipe 11 and central conduit 17: 3.5 bar
3 m3/min
First jacket pipe 12 and first
annular conduit 18: 2.5 bar
0.3 m3/min
Second jacket pipe 13 and second
annular conduit 19: 2.5 bar
0.3 m3/min
The values indicated apply to a 25 ton open hearth furnace.
The indicated gas pressure values increase by about 0.5 to 1 bar
for larger furnaces and with application of the injection device
in a converter.
If a mixture of alcohol and water is supplied through the
first conduit instead of alcohol alone, the pressure is increased
as well. A pressure of 3.5 bar has shown itself to be suitable
with a mixture of 60% alcohol and 40% water.
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Table I shows the acceptable broad ranges of fluid pressures
and flow rates through the three gas passageways.
Table I
Conduit Fluid Pressure (Bar) Flow (Nm3/min)
17 Oxygen 2.5 to 4.5 2.0 to 5.0
18,19 Carrier Gas 2.0 to 3.5 0.2 to 0.6
Protective Fluid 4.0 to 6.0 0.3 to 0.7 l/min
Table II shows the preferred ranges of fluid pressures and
flow rates through the three gas conduits.
Table II
Conduit Fluid Pressure (Bar) Flow (Nm3/min)
17 Oxygen 3.0 to 4.0 3.0 to 4.0
18,19 Carrier Gas 3.0 to 3.5 0.3 to 0.5
Protective Fluid 4.5 to 5.5 0.4 to 0.6 l/min
The carrier gas in the examples of Tables I and II is
preferably nitrogen. The gas indicated as oxygen can be any
oxidizing gas or oxygen-containing gas.
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