Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS FOR THE METALLURGICAL TREATMENT OF MOLTEN STEEL IN A CONVERTER WITH
OXYGEN
TOP BLOWN
For the metallurgical treatment of molten steel in
a converter, oxygen is blown onto the top of the molten
steel under the control of a blowing lance. The oxygen
lance is subjected to a high thermal load during this top
blowing, particularly on its front end. It is therefore
typical to cool the lance down intensively. The most
effective way to cool an oxygen blowing lance is to
thoroughly flush die head of the lance with a large
volume of cool water under high pressure. The head of the
lance is made of a material with good thermal
conductivity, such as copper. High temperature peaks up
to 3000 degrees C, particularly at the front end of the
lance head which is the focus of heat radiating from the
surface of the bath as well as wear and tear lead over
time to a reduction in the thickness of the cooling
chamber walls found in the head of the lance. If there is
not enough distance between the head of the lance and the
molten metal, the walls can weaken rapidly and suddenly
rupture because they have been weakened. Any release of
water vaporizes explosively and damages more than just
the metallurgical process. If the lance head ruptures,
the treatment of the enamel must also be terminated
immediately.
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To avoid the danger of a water release while
simultaneously cooling the lance even when the lance is
plunged into the molten steel melt, there is a process
(DE 35 43 836 C2), which employs two blowing lances used
in rotation. These two lances arc cooled alternately and
intensively with cool air and then with cool water. The
lance in the blow position which is being plunged into
the molten steel is cooled with cool air while the other
lance outside of the molten steel is cooled intensively
with cool water. By repeatedly switching as needed
between cool air cooling and cool water cooling the
overheating of either lance can be avoided, the advantage
of effectively avoiding a water release is the cost of
purchasing a second lance.
Starting at this point in the state of technology
the invention concerns a process for the refinement of
molten steel in a converter with top blown oxygen on the
molten steel surface with a water cooled blowing lance
made up of a 'shafted' lance body and a lance head.
Furthermore, the invention concerns a water cooled
oxygen blowing lance made up of a shafted lance body and
lance head, for implementation of this process more
specifically, with an oxygen supply that runs through the
lance body and flows to blowing nozzles distributed in
the lance head and with outlet and inlet passageways for
water running through the lance body to the cooling
chambers in the lance head.
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The invention is based on the task of achieving a
process as above with which the metallurgical blowing
process is monitored and controlled. The invention is
also based on the task of creating an oxygen blowing
lance that to a great extent is protected from the
release of water.
According to the process, the problem is solved in
that the temperature in the lance head of the blowing
lance. which is transferred from the molten steel to the
lance head is monitored using at least one of the
temperature probes which are integrated into the lance
head and regulated by cooling off with water and/or with
an oxygen supply and/or the addition of aggregates and/or
the distance of the lance head from the molten metal
bath, In the process, the abrasion on the front end of
the lance head as a function of the tool life and the
temperature curve as a function of the tool life can be
primarily considered as correction sizes. With the
addition of aggregates it can be assumed that the rate
and the time of the addition influence temperature
regulation. In particular, scrap for cooling. briquettes,
ores, lime and other similar things arc considered as
aggregates.
In the invention the temperature of the melting bath
surface radiating directly onto the front end of the
lance head is detected through the temperature in the
lance head. Using this measurement of the temperature the
metallurgical process of the refinement can be
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controlled. At the same time the head of the blowing
lance can be protected from the release of water through
the various individual steps or through a combination of
measures.
It is true that it is already known how to determine
temperature for water cooled blowing lances (JP 62-278217
A) in the treatment of enamels but such a blowing lance
is used in another process and with other objectives. In
this process the blowing lance is actually submerged in
the enamel and the level of the slag of the molten metal
relative to the blowing lance is determined by
temperature probes which are staggered inside the lance
body. In this known process though, protection from
overheating by detecting the temperature of the lance and
controlling the~treatment process are not dealt with.
With the oxygen top blowing lance the above task is
solved by integrating at least one temperature probe in
the lance head behind its front end and between the
cooling chambers, the signal. lines of which are ducted
through the lance body.
With the invention the temperature of the local area
in the lance head can be determined, and from experience
used as an indicator of the danger of rupturing. Thus
there is a requirement for an immediate reaction to
imminent collapse whether it be due to the outside wall
of the lance head being too thin or becoming too weak.
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In order to be able to mount the signal lines of
(lie temperature probes simply and to be able to protect
them they are in a central, protective pipe. This pipe
should not have any connection to the process medium
5 oxygen or to the cooling medium water. This is thus
particularly advantageous and contributes to the
reliability of operation if the head of the lance is
burned down to the temperature probes integrated within
it and is therefore open. In this situation it is
therefore impossible for there to be a leak of oxygen
andlor cooling water. In a preferred set tip the oxygen
piping is situated in the middle of the lance head and
surrounded with inlet and outlet channels for the cooling
water through the formation of coaxial ring channels,
where the outermost ring channel is the outlet channel
and the center ring channel is the inlet channel.
In order to make the assembly work required when
switching out a deteriorated lance head for a new one as
easy as possible the temperature probe can be put in a
bore hole of a nose saddle of the lance head using a
disconnectable adapter which is secured inside the lance
head. To ensure an error free measurement of temperature
it is advantageous for the temperature probe to be kept
in contact with the floor of the bore hole by a spring so
that it can conduct heat.
For technical assembly reasons as well as for length
compensation with various thermal linear expansions of
the protective tube and the oxygen pipe, the protective
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pipe should overlap and seal the adapter like a
telescopic sleeve.
In the blowing process the most extreme thermal
damage to the oxygen blowing lance is sustained by the
lance head. As a result the head of the oxygen lance is
subjected to the most wear and tear and should be
interchangeable . In order to make it easier to change out
the lance head one of the set ups of the invention
provides for there being coaxial fittings oil the cooling
chambers of the lance heads for continuing coaxial inlet
and outlet cool water channels. These fittings may then
be welded on to the continuing coaxial inlets and outlet
channels.
The invention is explained more clearly in the
following with the help of an illustration that shows an
example of an implementation. In detail the figures show:
Figure 1 the axial section of an oxygen blowing lance,
Figure 2 an axial section of the lower part of the
oxygen blowing lance in accordance with Figure
1 as an enlarged drawing,
Figure 3 an axial section of the lower part of the
oxygen blowing lance in accordance with Figure
1 without the lance head and as an enlarged
drawing,
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Figure 4 an axial section of the upper part of the
oxygen blowing lance in accordance with Figure
1 and as an enlarged drawing,
Figure 5 the cross section of die oxygen blowing lance
along the line B-B in Figure 4, a n d
Figure 6 cross section of the oxygen blowing lance along
the line C-C in Figure 4.
The oxygen blowing lance shown in Figure 1 is made
up of a shafted lance body 1 and a lance head 2 which is
welded onto the body. For safety reasons, with awareness
of the oxygen processing gas that is flowed through die
lance, the lowest part of the lance head 2 is made from
copper. Another reason for making the decision to use
copper as the material for the lance head 2 is the good
thermal conductivity of copper which makes it possible to
effectively cool the lance head 2 with cooling water
during blowing.
The lance head 2 comprises a nozzle head 2a, made of
copper, with a crown of a total of six evenly spaced
nozzles 3 and 4 in a circle and simply directed outwards,
cooling chambers 5, 6, 7, 8, 9 and 10 as well as a
central, axial strut 11. Coaxial, tubular fittings 2b,
2c, and 2d, are connected to the outermost cooling
chambers which together with the nozzle body 2a form an
interchangeable modular unit.
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The lance body 1 consists of three coaxial tubes 12,
13 and 14 made from steel. Together with the
incoming/feed connection piece 12a the inside tube 12
forms a central supply line 15 for the oxygen to be
supplied to the blowing nozzles 3 and 4. A close sliding
fit for 12a is provided in the upper area between the
inside pipe 12 on the inside and the middle and outside
tubes 13 and 14 which together form a single unit, on the
outside. This close sliding fit at 12a serves for
adjustment of the relative linear expansions between the
tubes 22, 13 and 14 and the assembly of the lance body 2.
Conduits 16 and 17 are developed between the inside tube
~12 and the outside tube 14 as well as tube 13 that lies
in between them. Of these conduits, the inside conduit 16
is the supply conduit and the outside conduit 17 forms
the outlet conduit for the cooling water that is to be
forced through the channels under high pressure. The
cooling water is brought in and let out via laterally
placed fittings 18 and 19.
In the central strut 11 of the nozzle head 2a there
is a bore hole 20 into which an engaging and disengaging,
rod-shaped thermoelectric couple is plugged in as the
temperature probe 21. The temperature probe 21 is
centered by an adapter 22 and held with its end in
contact with die floor of the bore hole 20, which is
recessed just a few millimeters opposite the front end
11a of the nozzle body. The adapter 22 is fastened with
screws to the inside of the nozzle body. The temperature
probe 21 is movable and stored in the adapter 22 and
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'forced towards the floor of the bore hole 20 by a spring
23 that is supported on a regulating screw 25 screwed
into the adapter 22. Signal lines 26, which are installed
in a central protective pipe 27, go out from the
temperature probe 21. The lower end 27a of this
protective pipe and the upper end 22a of the adapter 22
form a sealed, telescopic sleeve which makes it easier to
switch out the lance head 2 and allows for various linear
expansions of the approximately 20 meter long pipes 27
and 12.
The protective pipe 27 is kept centered oil several
axially distributed places on the inside walling of the
inside tube 12 using springed, radial supporting elements
29 which allow for relative axial motion of the
protective pipe 27 compared with this tube 12. The
protective pipe 27 is attached directly to the tube 12
only at the top with radial struts 30 and scaled free
from tube 12 and open to the atmosphere.
Because of the close sliding fit 12a with potential
axial movement of the inside tube 12 and the middle as
well as the outside tubes 13 and 14, to fit the lance
body 1 with a new lance head 2, the regulating screw 25
is first screwed into the adapter 22 with the rod-shaped
temperature probe 21. By doing this the adapter 22 is
already preassembled on the inside of the nozzle body 2a
so that the temperature probe 21 sits -securely in the
bore hole 20 after the regulating screw 25 is screwed in.
. The nozzle body 2a is then connected with its fitting 2d
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to the inside tube 12 on the point of separation 31 and
welded on. Tn this way the middle and the outside tubes
13 and 14 are pushed back on to the inside tube 12 and
the middle tube 13 respectively. Finally, the middle tube
5 13 and the outside tube 14 are brought close to the
fittings 2b and 2c, where the middle tube 13 overlaps the
fitting 2c with a close sliding fit and the outside tube
14 is welded on. The removal of a worn out lance head 2
is done in reverse sequence.
The special advantages of the invention are that the
temperature is monitored at the places of an oxygen
blowing lance which are critical with regard to a release
of water, that is the front end 11a of the nozzle head
that lies opposite the sensor focal point. In this way
counteractive steps can be taken with as little delay as
possible when there is the threat of a rupture, whether
it be due to the mechanical wear and tear of the
remaining wall thickness of the cooling chamber, or due
to weakening of die chamber walls because of high thermal
peaks when there is insufficient cooling during
dismantling. Because of the practically immediate
determination of the actual temperature is also possible
to consider die march of temperature over time when
choosing what measures to take, using which a rupture can
be counteracted. Finally, it is an advantage that it is
not only possible to protect the actual oxygen blowing
lance from ruptures but that it is also possible to
influence the factors which have an effect on temperature
determination and on the regulation of the metallurgical
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treatment such as the inflow of oxygen, the distance of
the lance head from the surface of the molten metal bath
etc. to positively influence the refinement process. If
for example a temperature is taken that falls far below
the critical limit for a lance to rupture, a targeted
reduction in the distance between the lance head and the
surface of the molten metal bath is possible, through
which the refinement process is accelerated and made more
efficient.
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