Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
21281~7
~ Process for treating molten metals, in particular molten
steel, with a refining agent.
The invention relates to a process for treating molten
metals, in particular molten steel, with a refining agent.
It is known to use oxidizing gases or gas mixtures, in
particular gaseous oxygen, for the refining of steels.
Usually, the refining process is carried out in converters
by top-blowing or blowing-in of the gases or a combination
of the two. A number of process designations are derived
from the type of the introduction of oxygen, such as, for
example the LD process, LDAC process or OBM process. The
gaseous oxygen is here fed to the crude iron for reaction
through a lance or a bottom bubble brick.
The refining of steels with gaseous oxygen requires a
blowing time of 15 to 18 minutes in order to oxidize the
elements carbon, silicon, phosphorus and manganese, present
in the crude iron bath and to reduce the iron.
The invention provides a process for increasing the
refining rate.
Starting from the state of the art, this is achieved,
according to the invention, by a process for treating
molten metals, in particular molten steel, with a refining
agent, which comprises using liquid oxygen or a two-phase
mixture of liquid and gaseous oxygen as the refining agent.
There is also provided in accordance with the invention
apparatus for treating molten metals, having an oxygen
supply device and a blow nozzle connected to the supply
device, wherein the supply device is an insulated stock
vessel for liquid oxygen and the blow nozzle is designed
as a liquid-oxygen blow nozzle or as a combined
liquid/gaseous oxygen blow nozzle which is connected via
at least one insulated feedline and a liquid-oxygen pump
to the liquid-oxygen stock vessel.
212818~
Advantageous further developments of the invention are
indicated below.
For the refining of steels, the invention uses liquid
oxygen which is in the sub-cooled state as a single-phase
liquid at the boiling point or below the boiling point, or
is present as a two-phase mixture of liquid and gas. The
density of liquid oxygen is 855 times greater than that of
gaseous oxygen under st~n~d conditions. As a result,
oxygen is provided in a concentrated form to the reaction
zone and the reaction rate is thu~ increased. The oxygen
introduced in the liquid state results in a larger total
quantity, whose influence advantageously controls the
refining process with respect to a higher refining rate,
a shortening of the blowing time by up to 75% resulting
from the invention. The refining procesR can then also be
controlled with respect to a higher refining rate by the
influence on the gaseous/liquid oxygen ratio and/or by the
influence on the oxygen pressure and the geometry of the
blow nozzle. The impingement energy can be influenced by
varying the liquid oxyye~pressure and the nozzle geometry.
In æome ca~es, it can be increased to such an extent that
the jet penetrates into the molten bath. A further point
is that the yield of alloy elements and the blowing
behaviour are improved and the dust ejection is reduced
since, on the one hand, the solubility, and on the other
hand, the mixing of the crude iron are improved by the
introduction of high-momentum liquid oxygen.
An exemplary embodiment of the invention is Rhown in the
drawing and described in more detail below. In the
drawing:
Fig. 1 shows a diagrammatic repre~entation of the
equipment with a 3-hole liquid-ox~yc.. blow lance
and a heat e~ch~nger;
Fig. 2 shows a diagrammatic representation of a 3-hole
2128187
_ - 3 -
blow nozzle with a li~uid-oxygen core jet;
Fig. 3 shows a diagrammatic representation of the equip-
ment with a shower head and a gas-phase sepa-
rator.
Figure 1 diagrammatically shows a blow nozzle 1 from
which a jet 2 of liquid oxygen emerges at high ~elocity
of up to 90 m/s and impinges onto the molten steel bath
of the converter 3. The liquid oxygen is supplied
through an insulated line 4 from an insulated stock
vessel 5 for liquid oxygen.
This stock vessel 5 has the conventional piping and
valves, not designated in more detail, for taking off
liquid and gaseous oxygen. The liquid oxygen required
for the process according to the invention is taken from
the insulated stock vessel S through the line 6 and - if
the pressure of the stock vessel S alone is -not suffi-
cient - pressurized to a pressure of up to 50 bar down-
stream of the isolation valve 7 by means of the liquid-
oxygen pump 8. The line 4 can additionally be provided
with a jacket of a cryogenic medium, in order-to avoid-
premature vaporization of the oxygen. The sub-cooling of
the oxygen is effected with liquid nitrogen or liquid
oxygen. Liquid nitrogen has, at ambient pressure, a
boiling point which is 13C lower than that of oxygen and
is therefore very suitable as a cooling medium.
Liquid oxygen as a suitable cryogenic medium for cooling
and sub-cooling has an equilibrium temperature which
depends on the ambient pressure. At an ambient pressure
of 1 bar, it is -183C and falls when the pressure is
lowered. As shown in Fig. 1, the pressurized oxygen-is
therefore cooled to the required extent by heat exchange
with oxygen under low pressure. The liquid oxygen
intended for cooling is branched off from the insulated
line 4 downstream of the isolation valve 7 through the
line 20 and passed via the level detection system 22 into
2128187
_ - 4 -
the heat exchanger 21.
In the interior of the heat exchanger 21, a vacuum of
down to 0.1 bar absolute is generated by means of the
pump 24. This lowers the boiling point of the_liquid
oxygen in the heat exchanger 21 by up to 17C, so that it
can be used as a cooling medium for the refining oxygen.
The temperature difference between the cooling oxygen and
the refining oxygen and hence the size of the heat
exchanger can be determined by the choice of the vacuum.
The oxygen which is intended for refining and is under 3
to 6 bar tank pressure (corresponding to an equilibrium
temperature of -167 to -159C) is passed into copper
coils 25 through the heat exchanger 21 and thus cooled by
the surrounding cooling oxygen by 16 to 41C, depending
on the existing pressure ratio, to a temperature below
its boiling point. This sub-cooling can be carried out,
as described above with or else without use of a vacuum.
The refining oxygen then passes through the insulated
line 4 into the blow nozzle 1 which is surrounded by
insulation and a water cooling jac~et 16 (Fig. 2) in
order to protect it from the high radiant heat of the
molten metal 3. The refining oxygen leaves the blow
nozzle 1 by being let down.
The gaseous oxygen arising during the self-cooling of the
2S medium can be used for refining in the conventional
manner or in combination with liquid-oxygen refining. A
blow nozzle 1 designed as a 3-hole liquid-oxygen blow
lance for this purpose is shown in Fig. 2. The blow
nozzle 1 has a central inflow channel 10, connected to an
outflow nozzle 11, for liquid oxygen. In the outflow
nozzle 11, an outflow channel constricting the liquid
oxygen is provided, wherein the liquid oxygen is formed
into a jet before it emerges. Concentrically to the
inflow channel lO, a feed 13 for gaseous oxygen is
provided, which preferably emerges from three outflow
orifices 14 which surround the outflow channel 12. The
2128187
_ - 5
outflow orifices 14 are arranged in a nozzle block 15
which is connected to a jacket pipe 17 having cooling
channels 16. The coolant, preferably water, flows in the
form of circulation cooling, corresponding to the arrows
18, 19.
According to another embodiment variant, the blow nozzle
1 (Fig. 1) can be designed as a pure li~uid-oxygen blow
lance.
Fig. 3 shows equipment for refining with liquid oxygen,
by means of which the liquid oxygen is taken from the
stock vessel 5. Liquid oxygen passes through the take-
off line 6, the level detection system 31 and the insu-
lated line 4 into the gas-phase separator 30. The level
detection system 31 automatically keeps the liquid
oxygen, used for refining, in the gas-phase separator 30
at the desired level, for which purpose the level is
detected by means of the sensor 32.
In the gas-phase separator 30, the gaseous oxygen is
separated from the liquid oxygen. The liquid oxygen is
fed via line 4 to a blow nozzle which is designed as a
multi-jet shower head. The liquid oxygen in an almost
unpressurized state is distributed by the shower head
with many jets 2 to the surface of the molten metal, and
a large reaction area is thereby produced without any
hazard.
The gaseous oxygen portion formed by the ingress of
exterior heat is separated off by the gas-phase separator
30 upstream of the pump or blow nozzle 1 and returned via
a line 34 connected to the orifice 33 into the stock
vessel 5 or into an 2 ring line.
As described in connection with Fig. 1, line 4 can
additionally be provided with a jacket of a cryogenic
medium, in order to avoid premature vaporization.
2128187
_ - 6 -
If required, other media such as, for example, argon or
solids can also be added to the oxygen.
