Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
It is known to melt solid materials bearing iron,
such as scrap metal, with a flame produced by the combustion
of a fuel and essentially pure oxygen. It has been found that
the resultant product is of a steel making composition having
a very low carbon content and is often highly oxidized. It is
also known to add xeagents to the melt as it is discharged
from the melter into a collection vessel.
It is further known to melt solid'materials bearing
iron with an oxy-fuel flame and for continuous feeding of
the melt to the receiving vessel of further refining means.
It is a purpose of the present invention to improve
the efficiency of the above disclosed processes and to provide
improved methods for controlling the oxygen and carbon contents
of the melt from the oxy-fue,l flame melter.
This invention relates generally to a process for
; melting of iron or steel bearing material in which melting
the charge ~ay be partly or entirely'scrap metal; the melt is
then further treated in a number of different steps in a number
of different apparatus having different functions.
In one aspect the invention provides a process for
producing refined steel which comprises: providing a supply
of molten iron bearing material, having a carbon content of at
least 2%, by weight; adding, ko said molten iron, molten steel
, having a carbon content less than 2~, by weight, to provide a
molten mix; adding, to said molten mix, unmolten iron bearing
material`in an amount where the unmolten material comprises
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`approximately 5 - 15%, by weight, of the resultant mixture comprised of said
molten mix and the added unmolten material; and blowing essentially pure
oxygen through the resultant mixture to refine the same.
In another aspect the present invention provides a process for producing
refined steel, comprising: (a) melting a supply of iron bearing material,
in a melting chamber, said material being in solid form, with a reducing
flame produced by the combustion oE fuel with essentially pure oxygen in a
lower position of said chamber; (b) completing combustion of the reducing
gases, resulting from said flame, by providing a supplementary source of
combustion supporting gas at an elevated position of said chamber, in respect
to said lower position; (c) adding the molten composition having a carbon
content of at least 2%, by weight, resulting from step (a) to another iron
bearing molten composition having a carbon content less than 2%, by weight,
to produce a molten mix; (d) combining said molten mix with unmolten ferrous
bearing material in an amount comprising approximately 5 - 15%, by weight
of the resultant mixture and (e) refining the combination of step (d) by
in~ecting essentially pure oxygen into the molten mix.
In a further aspect the present invention provides a process for the
refining of steel-making composition, which comprises: (a) providing a
supply of molten iron at a temperature oE about 2400F and having a
composition comprising, in percent by weight:
.5 - 2.0 Silicon
2.0 min. Carbon
.4 - 1.5 Manganese
and the balance being essentially iron
(b) adding to said molten iron, low carbon molten steel scrap to provide a
- molten mixture being comprised of approximately 60% of
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said molten scrap and approximately 40~ of said molten iron
composition; said mixture being at a temperature of about 2600F
and being of a composition comprising:
.5 - .6 Silicon
2.0 Carbon
.3 - .~ Manganese
td) adding to said molten mixture unmolten iron bearing material
ln an amount where said unmolten lron bearing material comprises
approximately 5 - 15% of the resultant mixture; and (e) refining
said resultant mixture by blowing oxygen therethrough with a
nozzle having its discharge opening positioned beneath the
surface of the molten charge.
The objects of this invention are attainable through the
provision of method and means for oxy-fuel melting a charge of
splid material, bearing iron, which melting produces a relatively
low carbon containing composition; the low carbon composition is
added to another molten composition of relatively higher carbon
content, such as that produced by conventional blast furnace
practice, to provide a molten mix; unmolten iron bearing material
is added to said molten mix in a refining vessel having means for
introducing essentially pure oxygen beneath the surface of the
melt in said refining vessel.
; DESCRIPTION OF THE DR~WING
The single figure in the drawing is a schematic representation
of the melting, mixing, and refining vessels used in conducting
the basic steps comprising the process of this invention.
DESCRIPTION OF PREFERRED E~IBODIMENTS
In the drawing, there is disclosed method and means of the
type which may be employed in the process of this invention for
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melting solid materials bearing iron, e.g. scrap metal. For
convenience the melting apparatus is schematically illustrated
and is generally designated by the numeral 10.
In a preferred embodiment, a plurality of oxy-fuel burners 12
are disposed about the melting vessel 10 and positioned to direct
their flames at a bottom portion oE the feed charge
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column 14. As portions of the bottom of column 14 are rendered molten, the
melt flows toward and through a tap hole 16. Optionally, auxiliary heat may
be directed at the tap hole 16 to deter "freezing" o~ the metal. Trough 18
is provided to direct the melt to positionable mixing vessel 20. The melting
of the solid charge with oxy-fuel produces a melt which is of very low carbon
content, generally less than 0.1%, and which is highly oxidized. For the
purpose of definition in this patent application, a "low carbon" containing
composition is considered to be one having less than 2% carbon, and a "high
carbon" containing composition is one which includes at least 2% carbon. All
% composition igures herein given are "by weight".
; Preferably, the low carbon composition melt from the malter 10
is directed to a mixing vessel 20 into which a high carbon molten composition
- has been previously charged. Suitably, the high carbon melt may be blast fur-
nace iron at a temperature generally around 2400 - 2500 F and having a typical
composition comprising, by weight: .5 - 2.0% silicon; at least 2% carbon;
.40 - 1.5% manganese; and the balance being essentially iron. In a more
preferred embodiment, the high carbon molten composition comprises: about
1~ eilicon, about 4% carbon, .5 - 1.0% manganese; and the balance essentially
iron. Also preferably, a composite molten mix is provided which is compr sed
of 40 - 75% low carbon composition and 60 - 25~ of the high carbon composition.
The mix will usually result in a composition being at a temperature of about
2600 F and comprising: .5 - .6% silicon; 1.8 - 2.0 carbon; .3 - .~ manganese;
and the balance essentially iron.
It is also preferred to provide agitating means for the mixing
vessel 20 for stirring and enhancing intermixing of the "low carbon" and "high
carbon" compositions. Such agitating means may be in any suitable form,
mechanical, electrical, or by
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injection of a gaseous stream discharged below the surface of
the molten mix through separate tuyeres 22.
By the addition of the low carbon composition from the
melter to the high carbon composition (blast furnace iron) and
the refinement of the res~lltant mix, it is expected that any QX-
idized metal from the melter will be reduced by the carbon in
the high carbon composition.
The molten composite mix metal is preferably charged,
for ease in processing, to a separate refining vessel. However,
it will be understood that the further refinement may be con~
ducted in the same vessel, where the mixing of the low carbon and
the high carbon compositions takes place through the-provision
of suitable means for introducing the refining medium.
The separate refining vessel~ referred to above, is
desi~nated by the numeral 30 and is illustrated to be generally
in the form of an open hearth t~pe furnace; h,owever, modified
to omit the usual burners and/or oxygen lances employed in the
typical open hearths. Instead, one o~ more tuyeres 32 are
provided as refinement medium means for introducing a refinin~
gas, such as essentially pure ox~gen (at least 80%)~ beneath the
surface of, into, and for refinement of the molten metal bath
mix charged from mixing vessel 20.
- Alternatively, the refinement medium means may be
incorporated in those refining vessels commonly referred to as
"bottom" blown conyerters or to "side" blown converters~ As
another alternative, as indicated above, the refinement medium
means may be incorporated into the mixing vessel 20. It will
be apparent from this disclosure that a single mixing vessel
may be used to serYice more than one refining vessel.
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In a t~pical and preferred process, sufficient molten
mix metal is provided to the vessel, where refining is to take
place without the addition of more heat~ to constitute approximatel~
85 - 95% of the total anticipated work charge. The approximately
remaining 5 - 15~ of the charge ma~ be advantageously comprised
o cold unmolten scrap, and~or iron ore pellets, and/or other
iron bearing materials in solid fo~m~ After the charge is com-
pleted, refining is conducted by introducing substantially pure
oxygen beneath the surface and blowing through the molten chargeO
Of ~ourse, if additional heat is provided~ such as b~ burners in
the refining vessel, then the amount of unmolten scrap may be
- increased.
It will be noted that the total "hot metal" (relatively
high carbon content composition) imput to the refining vessel
is in the order of 22 - 54%~ i.e., 25 to 60% total charge to
mixing ~essel x 90% total charge to refining vessel. In con-
trast, conventional open hearth and BOF practices utilize 55 -
60% and 70% "hot metal"~ respectivel~
It is also anticipated that higher yields of usakle
steel are attainable through the use of the introduction of the
refining medium below the surface of the molten bath, as opposed
to blowing unto the surface. One of the contributing factors
is better utilization of the refining medium attained by virtue
of the more intimate contact with the bath. Another factor is
that there is less iron oxide emission loss than that encount-
ered with the use of ox~gen lances and the resultant fumingO
The process of this invention provides several advan-
tages in steel refinement as compared with conventional steel-
making practices. Some of these advantages are:
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lo Improved yields of usable steel;
2. Unprepared scrap may be used;
3. No additional heat imput required in the refining
; vessel or furnace;
4. The refining furnace charge may be comprised of
as little as 22 - 54% hot metal (relatively high
carbon content, e.g. blast furnace iron), in con-
trast, 55 - 60% hot metal is required in conven-
tional open hearth practice and 70% is required in
conventional BOF practicei
5. Faster refining times are attainable through the
introduction of refining oxygen beneath the surface
and through the molten bath, i~e., the rate of
oxygen that can be introduced is not limited to
the extent as in the case of vertically supported
oxygen lances in conyentional open hearths;
6. Higher fuel efficiencies are attainable, i.e~, 70%
or better, compared with usual 15~ in open hearth;
7~ LmproYed ~essel roof life because of reduced dust
emissions and decreased fuel consumption;
8. Flexibility of batch sizes which can be produced
in refining vessel; and
9. Ease of process control through selectable adjust
ment of oxygen injection in scrap melter and/or
refining vessel.
~he present inYention proYides improye~ents in the
melting practice as pre~iously known. In the melter of this
in~ention, the burners are operated to provide a reducing fl~me,
i.e., less oxygen .~s supplied directly to the burners than that
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required to provlde a stoichometric mixture. Such operation
minimizes oxidation of the molten charge produced in the melter.
Also, supplementary combustion supporting gas supply means,
illustrated in the form of nozzle 15, is provided. Air,
oxygen enriched air, or additional essentially pure oxygen is
introduced through the nozzle means 15, positioned at an elevated
position in relation to the burner 12 and the work charge column 14.
The provision of such supplementary combustion supporting gas
facilitates "burning" of the carbon monoxide, produced by the
reducing flame of burner 12, and conversion to carbon dioxide
for optimum fuel efficiency.
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