Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a steelmaking process using
solid sources of iron, in particular scrap, in a convertor,
into which oxidizing gases or oxygen surrounded by a protective
medium are blown by means of tuyeres through the refractory
brickwork.
A number of convertor processes are known in which
pig iron is refined by top or through blowing. Appreciable
heat is generated from the oxidation of the elements present
in the pig iron and this heat is used for melting cold scrap.
~or instance when making one ton of steel, 800 kg of a con-
ventional pig iron containing 4.2% carbon, 1.0% silicon and
0.8% manganese and 300 kg of scrap are loaded into the con-
vertor. Since scrap is generally available in large amounts
and at favourable prices, while the winning of pig iron in
the bla.st furnace is expensive and relatively costly, the
attempt is made to use as much scrap as possible ~hen making
steel. A higher proportion of scrap is more economical and
avoids a corresponding enlargement of blast furnace capacity.
In addition to scrap, suitable solid sources of iron
20 applicable to the convertor process and available at fairly
favorable prices include pre-reduced pellets, sponge iron or
solid pig iron. Their use, as is true for scrap, leads to
increasing the steelmaking capacity without entailing an en-
largement of the blast furnace capaclty.
The upper limit o~ the proportion of scrap which
can be use~ is limited by the exothermal oxidation of the
elements present in the pig iron, that is, by the heat released
by the burning of the silicon, carbon and other oxidizable
elements usually present in the pig iron~ To use more scrap,
the attempt has been made for instance to melt the scrap using
a burner with a saucer-like flame in a special scrap melting
apparatus, and to subsequently refine the melt in a convertor
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together with liquid pig iron to obtain steel. This process,
however, is complicated because it requires a special scrap
melting apparatus and because much time is required to melt
the scrap using the saucer-like burner flame. Furthermore,
there is some risk in loading the scrap melt, even when already
partly pre-refined, into a pig iron melt already present in the
convertor, considering the high potential of oxidation of a
scrap melt of low carbon content in the presence of a pig
iron melt with a high carbon content.
10Again the preheating of scrap in a convertor using
a natural gas or oil/oxygen lance burner is resorted to only
occasionally because the approximate thermal efficiency of
30% of the fuels is low and because of the appreciable wear
~ suffered in the refractory lining due to the relatively lon~
; preheating time, the convertor furthel~more being unavailable
for refining during this preheating period. If there is a
ratio of preheating time to refining time of 2:3, the pre-
heating of the scrap is then at the cost of convertor output~
The invention tl~erefore addresses the task of pro-
viding a steelmaking process using higher than usual propor-
tions, of solid sources of iron such as scrap, pre-reduced
pellets, sponge iron and solid pig iron, and which provides
a relatively fast heating of the solid sources of iron
accompanied by high thermal efficiency and low iron losses
due to oxidation, plus a relatively low temperature of the
exhaust gases and therefore an improved life of the refractory
brickwork. Depending on the economics a charge of even 100%
of scrap may be used.
This problem is solved according to the present in-
vention (1) by blowing an oxidiæing gas, i.e. oxygen, air or
mixtures thereof, through tuyeres mounted in the lower region
of the convertor and burning therewith carbon carriers in an
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arrangement such that the resultirlg hot cornbustion gases flow
through the pile of solid sources oE iron by said combustion
yases, (2) subsequently melting the solicl sources of iron,
ancl ( 3 ) then ref :ining the rnel-t in the sarne convertor by the
use of oxygen as -the ref ining means .
'I'he process of the invention oEfers high thermal
ef:ficiency and a very brlef time of preheating b~3cause the
hot cornbustion gases flow through the pile of the solid
sources o iron and transfer an appreciab] e part of their
1(:) heat due to the intimate contact and the surfaces of contact.
The exhaust yas temperatu.re in the upper part of the convertor is
relatively low and therefore the wear in -the refractory lining is
also slight~ The use of carriers using several tuyeres in the
corlvertor bottom or at the lower part of the s ide wall for the
combustion of carbon furthermore provides a very uniform dis-
tribution of the hot combustion gases across the pile of the
solid sources o: iron.
The sequences taking place in the process of the
invention may be divided approximately into three phases: a
irst phase, hereafter designated as the preheating phase,
in which the scrap is heated to an average temperature of about
1100C, without there being a substantial orrnation of liquid
steel, and in which the oxidizing combustion gases are pre-
dominantly present, a second phase, denoted as the premelting
phase, in which a large part or the entire mass o the scrap
is melted and :i.n which the composi-tion of the exhaust gases
becornes much less oxidizing than the composition of the ex-
haust c3ases duri.ncJ the preheating phase, and finally -the re-
i:ini.ng phase proper, in which the amount of ca:rbon and other
e.l.ements present in the melt i.s decreased by rneans o:f oxygen
in the known manner.
Gaseous or liquid carbon carriers such as natural
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gas or methane, propane, butane, benzol, crude oil, fuel oil,
crude tar and refinery residues are especially suitable for
preheating. These materials may be fed through the annular
gaps of tuyeres made of concentric pipes, in which an ox-
dizing gas, such as air, oxygen or mixtures thereof is blown
into the convertor through the center pipe. In this case
the proportion of refining gas to the gaseous or liquid
carbon carriers acting as protective media is changed with
successive phases of the process of the invention. For in-
stance, at the beginning of the preheating phase, liquid orgaseous carbon carriers are introduced in proportions required
for about a stoichiometric combustion with the oxidizing gases
to form CO2 and ~2' while in the refining phase hydrocarbons
are introduced only in such amounts as are needed to protect
the tuyeres. It may be appropriate to switch once or more
` often from liquid to gaseous carbon carriers.
In addition to being introduced through the tuyeres
also serving for the refining, the gaseous or liquid carbon
carriers may be introduced through special supply systems, for
instance through a pipe in the taphole of the convertor.
Li~uid carbon ~arriers such as petroleum, fuel oil or light oil
then flow down along the convertor wall to burn with the oxygen
issuing from the tuyeres in the convertor bottom or at the
lower part of the convertor wall.
It is essential in all cases that the combustion
of the carbon carriers take place as close to the convertor
bottom as possible and especially below the solid sources of
iron, so that the hot combustion gases when flowing upward
follow a relatively long path through the solid sources of
iron.
One impor-tant aspect of the invention consists in
using the described, short-term preheating of the solid sources
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of iron, in particular scrap, for the increase of the scrap
proportion, in the conventional convertor refining processes,
The OBM/Q-BOP convertors, described for example in United
States Patent 3,706,549 issued December 19, 1972 and which
comprise tuyeres for introducing oxygen surrounded by a
protective medium below the bath surface, have been found to
be particularly suitable,
Preferably liquid carbon carriers are introduced into
the convertor through the annular gaps in the multiple pipe
tuyeres during preheating and gaseous carbon carriers, for
instance 1% by volume of propane or 5-10% by volume of natural
gas referred to the oxygen are introduced into the convertor
through the annular gaps during refining. The switch over
from the liquid to gaseous carbon carriers takes place during
the premelting phase, or at the beginning of the refining
phase.
Liquid carbon carriers, in particular oil, are fed
through the annular gap of the tuyere into the convertor at
a rate of 1-10 liters a minute per ton of solid source of
iron, Simultaneously an oxidizing gas flows through the in-
side pipe of the tuyere at a rate of 1~5-2.5 Nm3 of o~ygen
per liter of liquid carbon carrier. The tuyeres are operated
according to the invention as burners during the preheating
time, One advantageous tuyere design useful in the invention
comprises the u,se of conventional tuyeres consisting of con-
centric round pipes, the tuyere annular gap being ordinarily
1 mm wide or tuyeres consisting of individual channels of
approximately square cross section with the sides 2-3 r~n long.
Gaseous protective media are passed through the annular gap
following the preheating period and during the prernelting of
the solid sources of iron and the refining of the melt, for
instance 1% by volume of propane, referred to the oxygen.
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In practical operation, the protective media were found to be
problem ~ree and very reliabl0 for the refining phase.
During the refining phase, from 15,000 to 18,000
~m per hour of oxygen are made to pass through the inner
pipes of ten tuyeres of a 60 ton convertor, for instance, and
simultaneously about 300 Nm3 per hour of propane are blown
through the annular gaps of these tuyeres. According to the
invention, the switch over from a liquid to a gaseous medium
; in the tuyere annular gap and vice-versa can take place at any 10 selected time, without thereby interrupting the convertor
process.
Again, when liquid hydrocarbons are used as the
tuyere protective media during the premelting and the refining
phases, for instance when the rates in the above convertor of
60 tons are about 1000 liters per hour of fuel oil for a chosen
oxygen rate of about 16,000 Nm3 per hour, the tuyeres are op-
erated with nitrogen or an inert gas in the inside pipe and-in
the annular gap at least during tilting and erecting the con-
vertor. Accordingly the sense of the invention also includes
the switching to and frorn gaseous media when using liquid
tuyere protective media~
According to the invention, the proportion of scrap,
defined as the weight ratio of cold scrap to liquid steell
may be increased by about 10%, for instance from about 30% to
40%, when the solid sources of iron in the convertor are heated
in the manner described. The addition of solid carbon carriers,
for instance coke, during the preheating phase is not re-
quired. For instance in a 60 ton convertor, for which the
tapping weight of the finished steel melt was 60 tons, the
scrap proportion could be increased from the conventional value
of 28% to 38%, namely from 17 tons to 23 tons. To preheat
this amount of solid sources of iron, 450 liters of fuel oil
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were blown into the convertor through the annular gaps of
the ten tuyeres for five minutes in conjunction with 1000 Nm3
of oxygen. These figures show a thermal oil efficiency of
about 70%. Therefore it was possible to trans~er about
170,000 kcalories per ton of solid source of iron. rrhis is
equivalent to an average effective preheating ternperature of
about 1050C for the solid sources of iron. Following the
preheating period of five minutes, 43 tons of pig iron are
poured into the 60 ton convertor and the melt is refined to
completion in about eight minutes.
When using gaseous carbon carriers, mostly natural
gas, for the preheating, no design changes for the tuyere
supplies to these convertors are required. It is advantageous
however to use liquid carbon carriers during the preheating
period and to switch subsequently to gaseous tuyere protective
media~
This preheating technique of the invention can be
carried out in less than ten minutes and preferably is perforrned
with 2-5 minutes; it allows increasing the use of solid
sources of iron in steelmaking by up to 10% and ordinarily
up to a scrap proportion of about 40% without sensible losses
in production time. This entails appreciable economic
advantages in steelmaking.
~ further increase in the proportion of solid
sources of iron, mainly scrap, exceeding an increase in scrap
of 10% is possible, since steelmaking from scrap without
using any liquid pig iron can be accomplished by melting of
the solid sources of iron. Solid carbon carriers, mainly coke,
graphite, coals such as anthracite and mixtures thereof, are
preferably loaded into the convertor for this premelting phase.
After this time the proportion of CO in the convertor exhaust
gas also increases.
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The gaseous and liquid carbon carriers flowing
through the annular gaps of the tuyeres may be diminished to
the proportion of less than 10% by weight, re~erred to the
oxygen, which is required to protect the tuyeres.
It is within the scope of the in~ention to charge
solid carbon carriers together with the solid sources of iron.
However it is particularly advantageous to introduce the solid
carbon carriers following the preheating phase onto the
preheated solid sources of iron in the convertor. It is
advantageous for the purpose of increasing thermal efficiency
to preheat the solid carbon carriers, for instance coke, before
loading the same.
The amount of solid carbon carriers loaded into the
convertor increases in the process of the invention as the
amo~mt of solid sources of iron and the length of the pre-
heating increase. Thus 20 kg of coke per ton of scrap suffice
to increase the scrap proportion by another 10% beyond the
increase in scrap proportion achieved by preheating, for in-
stance from 40% to 50% scrap. To increase the scrap proportion
by another 60%, that is, for a steel melt of 100% scrap, the
amount of solid carbon carriers increases approximately lin
early to 120 kg of coke per ton of scrap.
~len at least some coke is initially charged with
the solid sources of iron the consumption of solid carbon
carriers is relatively small in the preheating phase because
the coke reacts differently with the exhaust gases presumably
consisting of carbon dioxide and water vapor, possibly of
nitrogen too, than with free oxygen gas. Thus the coke es-
sentially is merely heated during the preheating phase, while
in the prernelting phase, during which the proportion of
oxygen to fluid carbon carriers increases, it reacts with
free oxygen or oxygen bound to oxides in an overall
0`.;~
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exothermal process to become CO. Thus the exhaust gas in the
region of the convertor above the charge of solid sources of
iron contains CO only beyond approximately 1000-1200C, that
is, in the premelting phase, and from this time the melting
heat is obtained principally from the combustion of solid
carbon carriers/ e.g. coke or anthracite coal. Therefore it
is not necessary to introduce the solid carbon carriers until
that time. A small 'oody of liquid melt is present in con-
vertor by this time so that part of the carbon will be dis-
solved in the melt and later refined out of the liquid iron.
As soon as a melt has been formed, the solid carbon
carriers may also be blown through the tuyeres into the con-
vertor in the form of powders with carrier gases, for instance
nitrogen or argon, during the premelting phase. ~his allows
a particularly fast combustion and an extremely effective
heat transfer to the sources of iron which remain in part
solid and are already in part liquid.
Other solids, especially slag forming agents, for
instance lime dust, preferably are blown in during the refining
phase entrained in the oxygen gas, as described in United
States Patent 3,771,g98 issued November 13, 1973.
Carbon carriers in powder form and other powders,
and combustible or inert gases also may be fed centrally to
the stream of oxygen ~as for instance by a special feed pipe
located inside of the oxygen pipe. It is also practical to
use several concentr1c pipes and an annular gas as the oxygen
supply channel. Tuyeres as shown in German Patent 24 38 ]42
have also been found suitable for carrying out the process of
the invention.
The process of the invention additionally may be
practiced by blowing oxygen surrounded by hydrocarbons
through tuyeres made of concentric pipes and located above
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the bath surface, below the pivot of the convertor and passing
through the refractory bric~work of the convertor vessel. The
ratio of hydrocarbon to oxygen during the refining phase
preferably is less than 10% and for instance may be between
0.5 and 5% by weight, preferably between 1 and 2% hy weight.
This oxygen is used primarily to burn the carbon monoxide
generated in increasing amounts from the beginning of the
premelting phase as it leaves the solid sources of iron or
the melt so as to at least partly form carbon dioxide~ The
oxygen may be blown in during the preheating phase as air
and during the premelting phase as industrially pure oxygen.
In some instances, it may be found to be desirable to feed
more than 10% by weight of hydrocarbons during the preheating
phase.
This group of tuyeres may be mounted at the cylin-
drical center of the convertor, for instance at a height of
about 1 to 1-1/2 meters, preferably 1.2 meters above the
bottom for a newly prepared convertor. The elevation of these
tuyeres allows continuing the operation of the burner beyond
the time the refining tuyeres, which are mounted in the con-
vertor bottom or slightly above the convertor bottom for ex-
ample, from 20 to 80 cm, preferably 50 cm above the convertor
bottom in the side wall, are switched over to pure refining
operation, that is to a proportion of hydrocarbons less than
10% with respect to the oxygen. In this manner, it is possible
to extend burner operation of the tuyeres mounted above the
bath surface to the beginning of the re~ining phase. Only
then is the amount of oxygen raised with respect to that of the
hydrocarbons ko obtain as extensive as possible combustion of
the carbon monoxide above the melt.
The duration of the preheating and premelting phases
of the solid sources of iron depends on the particular amount
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596;Z
of scrap charged into the convertor vessel and varies between
2 and 20 minutes. Following preheating, unless a 100% scrap
charge is involved, li~uid pig iron is charged into the con-
vertor. The liquid pig iron together with the melt obtained
from the scrap upon further heat from the refining action en-
sures rapid fusion of the remaining solid scrap. Thus for
instance up to 800 kg of scrap per ton of steel may be pre-
heated and premelted and subsequently at least 300 kg of liquid
pig iron per ton of steel may be charged into the same con-
vertor. In this case the preheating period lasts five minutes,
, the premelting period fifteen minutes and the refining time
proper is only four minutes. For smaller proportions of scrap
per ton of steel and greater amounts of pig iron, the pre-
~; heating and premelting periods are correspondingly shortened
. ~ .
~ ~ and the refining time for instance is prolonged to eight to
.. ~: .
ten minutes.
For small proportions of pig iron of 200 to 300 kg
per ton of steeL, there would be a danger of explosive re-
actions due to the large difference in oxidation potential
between the melt obtained from the scrap and the subsequently
charged pig iron. However this danger does not arise in the
case of the process of the present invention because the melt
obtained from melting the scrap continuously absorbs carbon
from the solid carbon carriers which are present.
The process of the invention is carried out in a
convertor with tuyeres consisting of at least two concentric
pipes installed in the refractory lining of the convertor.
These tuyeres may be mounted in a convertor bottom, e.g. as
shown in United States Patents 3,706,549 issued December 19,
1972 or as shown in 4,047,707 issued September 13j 1977 they
may be mounted in the side wall of the convertor below andJor
above the bath surface, and also in the region of the convertor
59~Z
hood. The tuyeres mounted below the bath surface, and also in
the region of the convertor hood. The tuyeres mounted below
the bath surface may consist of four concentric pipes, whereby
they form three annular gaps between the convertor pipes. A gas-
eous protective medium, for instance, propane, may be blown in
through the outermost annular gap while liquid carbon carriers
such as oils of different viscoslties and preheating temperatures
are fed through the other annular gaps, the oxygen required
for heating and refining being supplied through the central
pipe. During the preheating phase air or oxygen-enriched air
is blown through the central pipe. During the premelting and
refining phases it is preferred that oxygen gas is blown in,
said oxygen being at least part of the time loaded with lime
dust and other slag forming agents.
It is important tbat the tuyeres be connected out-
side the convertor through switch over valves to at least
two individual lines in each case, one for gaseous and the
other for liquid protective media or carbon carriers, so as to
be able to switch from one medium to the other as a function
of the individual phases of the process of the invention, for
instance from nitrogen to oil and again to nitrogen and then
to propane for the refining phase.
The switching from one fluid medium to arlother pre-
ferably takes place using a three way valve directly mounted
on the assembly flange of the tuyere, the exhaust aperture of
said valve beiny connected to the annular gap of the tuyere,
while one of the two intake orifices communicates with a feed
line for a liquid carbon carrier or a liquid protective me-
dium, the other input orifice communicating with a feed line
for a gaseous carbon carrier or a gaseous protective medium.
By means of this device one obtains rapid switch over from
one medium to another.
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Individual tuyeres also may be provided entirel~
with fluid carbon carriers during the preheating and/or pre-
melting phases, when the convertor is in a vertical position.
In one aspect of the present invention there is
provided a process for steelmaking using scrap and/or other
solid sources of iron, in a convertor into which an oxidizing
gas selected from the group consisting of air, oxygen or
mixtures thereof are blown into the convertor through the
refractory lining of the convertor by means of tuyeres, which
process comprises: charging said solid source of iron into
said convertor, blowing said oxidizing gas through tuyeres
mounted in the lower region of the convertor; burning with
said oxidizing gas carriers of carbon thereby forming hot
gaseous combustion products; flowing said hot combustion
gases upwardly from bottom to top through the pile of the
solid sources of iron, thereby preheating said pile and then
melting said solid sources of iron and thereafter refining
the resulting melt in the same convertor by means of oxygen
blown into said melt.
In a further aspect of the present invention there
is provided a convertor, for carrying out a process for steel-
making using scrap and/or other solid sources of iron, in a
convertor into which an oxidizing gas selected from the group
consistlng of air, oxygen or mixtures thereof are blown into
the convertor through the refractory lining of the convertor
by means of tuyeres, said convertor .including si.de walls,
which process comprises: charging said solid source of iron
into said convertor, blowing said oxidizing gas through
tuyeres mounted in the lower region of the convertor; burning
with said oxidizing gas carr:iers of carbon thereby forming
hot gaseous combustion products, and flowing said hot com-
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bustion gases upwardly from bottom to top through the pile of
the solid sources of iron, thereby preheating said pile and
then melting said solid sources of iron, to thus provide a
bath having a surface, and thereafter refining the resulting
melt in the same convertor by means of oxygen blown into
~ said melt, and wherein, in said convertor some tuyeres are
; mounted above the bath surface and other tuyeres are mounted
below the bath surface in said convertor.
In a further aspect of the present invention there
is provided a convertor for carrying out a process for steel-
making using scrap and/or other solid sources of iron, in a
convertor into which an oxidizing gas selected from the group
consisting of air, oxygen or rnixt~lres thereof are blown into
; the convertor through the refractory lining of the convertor
~::;. by means of tuyeres, said convertor including side walls,
which process comprises: charging said solid source of iron
into said convertor, blowing said oxidizing gas throu~h
tuyeres mounted in the lower region of the convertor~; burning
with said oxidizin~ gas carriers of carbon thereby forming
hot gaseous combustion products, and flowing said hot com-
bustion gases upwardly from bottom to top through the pile
of the solid sources of iron, thereby preheating said pile
and then melting said solid sources o~ iron, to thus provirle
a bath having a surface, and thereafter refining the result-
ing melt in the same convertor by means of o~ygen blown into
said melt, and wherein in said convertor said tuyeres are
mounted below the surface of the bath in a side wall of s~id
convertor.
The process aspect of the invention is described
below in further detail in relation to vario~s embodiments
which are not intended to limit the invention and the oxygen
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blow through convertor comprising the invention is shown in
the drawings forming a part of the present application, in
which:
Figure 1 is a schematic vertical longitudinal
section through an OBM convertor equipped with several sets
of tuyeres; and
Figure 2 is an axial lengthwise section through one
of the bottom tuyeres with a switch over valve for the media
supply to the tuyere annular gaps between the concentric
tuyere pipes.
As shown in Figure 1, convertor 1 comprises a re-
fractory lining 2 with side wall tuyeres 4' and an exchangeable
bottom 3 with bottom tuyeres 4. Each tuyere is connected
to a feed line 5 for an oxidizing gas which may be charged with
powder. This is implemented by a powder distributor 12. The
annular gap 6 of each tuyere 4 having a width of about 1 mm
is connected by an assembly piece 7 both to a gas supply line
8 and to a liquid supply line 9. Lines 8, 9 pass through
a multiple swivel joint 10 installed in the convertor trunnion
11 and are connected with supply lines in which are mounted
control valves (not shown).
A feed tube 14 for liquid carbon carriers projects
through tap hole 13. Additional tuyeres 4" are located in
a side wall of the convertor above the bath surface. Oxygen
preferably surrounded by a protective medium for the after
burning of carbon monoxide is blown into the convertor through
these tuyeres 4".
Each bottom tuyere 4 is secured to the convertor
bottom plate 15 (Figure 2) by means of a welded guide piece
16. Tuyeres 4 project through a bore 17 in bottom pla~e 15
and extend through a bore 18 in convertor bottom 19. Tuyere
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4 is clamped betw~en a tuyere flange 20 and a mating flange
21 on the guide piece 16 by means of bolts 22 and seals 23.
The innermost pipe 24 of tuyere 4 is connected with a feed
line 25 for a refining gas or for a suspension of powder in
a refining gas. Annular gap 6 is connected by means of a
switch over valve 26 selectively with the feed line 8 for a
gaseous medium such as argon, nitrogen and/or gase~us hydro-
carbons or with a feed line 9 for liquid media such as oil.
A valve body 27 in switch over valve 26 connects the exhaust
orifice 28 with the annular gap 6 of tuyere 4 to either the
liquid medium supplied through line 9 or the gaseous medium
supplied through line 8.
The side wall tuyeres are similarly secured to the
steel casing of the convertor and connected to feed lines,
there being no connection to the powder distributor 12 for the
tuyeres 4" which are located in the side wall abave the bath
surface.
The following is a specific example of the present
invention.
22 tons of scrap were loaded into a 60 ton convertor
of the kind shown in Figures 1 and 2 of approximately spherical
cross section equipped with ten bottom tuyeres and having a
volume of 0.8 ~m per ton of steel. The scrap consisted of
2 tons of bales of sheets or plates, of 10 tons of mill scrap
Erom the rolling mill and of 10 tons of r~ixed scrap. After
the scrap was loaded into the convertor, during turnup of the
convertor, the bottom tuyeres were supplied with nitrogen at
rates of 8000 Nm3 for the inside pipe and 600 Nm3 for the
annular gaps, per hour. After rotating the convertor back into
its vertical (upright) position the nitrogen supply was changed
over so that the inside pipes of the tuyeres were provided with
13,000 ~m3 an hour of oxygen and the annular gaps were su~plied
with 6000 liters of oil an hour. Following a preheating time
of five minutes with oxygen and oil, there was a switch over
to nitrogen again, and the convertor was pivoted into the
horlzontal position and charged with 44 tons of molten pig
iron containing 3.6% carbon, 0.7% silicon, 1.1% manganese and
1.6% phosphorus. This took two minutes, whereupon the con-
vertor was pivoted back into the vertical blowing position
while introducing nitrogen through the tuyeres to prevent
inflow of metal into the tuyeres. Once the convertor was up-
right, there was a switch over to 18,000 Nm3 an hour of oxygen
and 350 ~m3 an hour of propane for ten minutes. After a pause
of three minutes for steel analysis, further refining was
carried out for two minutes under the same conditions. The
overall consumption of oxygen amounted to 4200 Nm3, that of
the blown in lime dust was 5 tons and that of propane was
70 Nm . The amount of steel tapped was 60 tons and analysis
showed 0.02% of carbon and 0.2% of manganese.
For a comparative charge with the same pig iron
analysis, only 16 tons of scrap and correspondingly 50 tons
of pig iron could be charged when following the prior art
procedureO Accordingly the addltional amount of scrap which
could be processed in the heat made according to the present
invention amounts to 6 tons, requiring for its preheating a
heat of 4.35 Gcal which was provided by burning with oxygen
the oil fed through the annular gaps. This heat also includes
a part corresponding to the heat gain obtained from that
quantity of pig iron from the oxidation of the iron companion
elements which is replaced by addi,tional scrap. Overall the
t,hermal efficiency of the supplied oil is 64%.
As regards further heats about 100 ,in number, each
with an additional quantity of 6 tons of scrap or a scrap
proportion of 36%, the preheat;ng periods on the average
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amounted to five minutes and resulted in an average thermal
efficiency of 65%.
In all cases a two slag operation was followed,
which is preferred when refining phosphorus rich pig iron.
There remains in such a case the entire slag, on the average
about 7 tons, at the end of refining, for the following charge
in the convertor. The cold scrap loaded into the slag was
heated by the slag to a temperature of 700C and subsequently
preheated to 1100C. When refining without changing the
slag, the additional scrap may be raised to 25 tons, which
corresponds to an increase in the scrap proportion from 26% in
conventional refining in the OBM convertor to 41%, that is,
an increase of 15%. This further increase in scrap proportion
is predicated on cold scrap being raised in temperature with
higher thermal efficiency than scrap preheated by the final
slag remaining in the convertor.
In a further comparative example, 19 tons of scrap
and 47 tons of pig iron containing 3.5% carbon, 1.0% silicon,
1.0% manyanese and 2% phosphorus were first charged into the
60 ton convertor of Figures 1 and 2 and then conventionally
refined by means of bottom tuyeres 4, using oxygen surrounded
with propane, latter present at 3% by volume with respect to
the oxygen, for ten minutes, corresponding to a total heat
time of thirty-five minutes, into 60 tons of steel containing
0.03% carbon, 0.10% manganese and 0.025% phosphorus.
When operating the same convertor in accordance with
the present invention it was possible to load 33 tons of scrap
and 1.6 tons of coke into the convertor and to preheat these
for six minutes with an oil consumption of 600 liters and
an oxygen consumption of 3000 Nm3. After preheatin~ the cold
charge, 33 tons of molten pig iron containing 3.5% carbon,
1~0% silicon, 1.0% manganese and 2% phosphorus were poured into
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the convertor and the melt was terminally refined for a total
heat time of forty-one minutes under the same conditions. The
time of preheating was increased by si~ minutes. ~owever, the
advantage obtained was in using 33 tons of scrap in lieu of
19 tons.
For a heat made without liquid pig iron in the 60
ton convertor with ten bottom tuyeres, a total of 40 tons of
scrap of varying nature and with an iron content of 93%, corre-
sponding to 38 tons of iron, was charged into the convertor
together with 6 tons of blast furnace coke. The tuyeres were
loaded with nitrogen during the tilting of the convertor to
an upright position, whereafter the tuyere supply was switched
over to 10,000 Nm3 an hour of oxygen and 3% by volume of propane.
When the convertor was in the vertical position, a pipe 14
projecting through the tap hole was fed with 150 liters of light
fuel oil and at a flow rate of 50 kg a minute, for the purpose
of increasing the supply of carbon carriers and to simultan-
eously achieve large surface ignition of the coke~ The oxygen
rate during the preheating of coke was gradually increased
to 15,000 Nm /hr. After a total consumption of oxygen of 7000
~m3, the generation of gases dropped marXedly, indicaiing the
complete combustion of the coke. After a total of 20 minutes,
the bath temperature was 1620C and the bath analysis showed
0.10% carbon, 0.10% manganese, 0.03% phosphorus and 0.15% sulfur.
Thereupon an after blowing was conducted for 1-1/2 minutes
with 300 Nm3 of oxygen loaded with a total of 2000 kg of lime
and the same amount (3% by volume) of propane. The final
analysis of the steel showed 0.02% carbon, 0.05% man~anese, 0.10%
phosphorus and 0.0~% sulfur for a time of treatment of forty
minutes and a quantity of steel of 35 tons and a tap temperature
of 16~0C.
In another batch with the same input materials but
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15~
lacking coke, a total of 750 liters of oil at a flow rate
of 75 liters a minute was fed into the convertor following
its rotation to an upright blowing position; and the tuyeres
were simultaneously supplied with a stoichiometric amount
of oxygen of about 150 Nm a minute. After ten minutes the
scrap temperature was 1100C and 3.5 tons of coke were loaded.
After another twenty minutes of blowing at a rate of about
200 Nm of oxygen a minute and with 2% by volume of propane
to protect the tuyeres, the entire batch was liquified and
could be tapped after a total time of blowing of thirty-eight
minutes to obtain 36 tons of steel of the previously stated
; analysis.
Another heat was made without pig iron, as follows:
66 tons of scrap and 6.5 tons of blast ~urnace coke were loaded
into the 60 ton convertor. During the preheating phase of
twelve minutes, 220 ~m3 per minute of oxygen were passed
through the ten bottom tuyeres each consisting of two con-
centric pipes and 100 liters a minute of oil were passed
through the annular gaps. Subsequently the oxygen rate was
raised to 340 Nm3 per minute and the oil rate lowered to 20
liters a minute during the premelting phase. After another
eighteen minutesj the scrap had completely melted, the bath
temperature was 1600C and the steel analysis was 0.05% carbon,
0.5% manganese, 0.03% phosphorus and 0.09% sulfur. The steel
was tapped and desulfurized conventionally in a ladle. For a
ferrous oxide content of the slag of 7% the yield was a very
~ good 91%.
; In another heat in a convertor in which there were
; two additional tuyeres in the side wall of the convertor located
over the trunnions and 50 cm above the convertor bottom, con-
sisting each of one central pipe 50 mm in diameter for oxygen
and of a concentric pipe 54 mm in diameter. The same amount ~;
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~,
of scrap as in the previous example but only 4 tons of coke
were loaded into the convertor and 300 Nm3 per minute of
oxygen were fed through the inside pipes o~ the tuyeres and
100 liters of oil a minute through the annular gap during the
fifteen minute long preheating In the second phase, the ox-
ygen rate was raised to 340 ~m per minute and th~ oil flow
rate lowered to 20 liters a minute. The second phase lasted
for twelve minutes. Thereupon a steel of similar analysis
and temperature was tapped.
A further heat was refined in similar manner, except
that no coke was loaded initially with the cold scrap; instead
3 tons of coke preheated to 900C were loaded after ten
minutes of preheating, that is, at approximately the end of the
scrap preheating phase. After the loading of the hot coke,
the batch was terminally refined for ten minutes and resulted
in a steel of approximately the same analysis as in the two
previous examples.
I~ pig iron i5 loaded in the process of the invention
after preheating the solid sources of iron, then there results
an increase of 10% in the proportion of scrap to about a
proportion of 40% scrap. This involves practically no ex-
tension of the batch sequence time (tap-to~tap). The addition-
al amount of scrap which utllized therefore results in higher
productivity. This is a particularly advantageous application
of the process of the invention.
A further increase in scrap proportion is achieved
if the preheating is followed by a premelting phase in the
presence of solid carbon carriers prior to the addition of the
pi~ iron. I'his procedure offers the possibility of practically
increasing the scrap proportion arbitrarily, for instance 50
to 60%. Therefore the process of the invention can replace
the open hearth process, since it can utilize the same pro-
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~ .. ,~
portions of scrap and consequently open hearth plants may beconverted to the more economical oxygen blow through con-
vertors (OBM or Q-BOP convertors) without requiring any in-
crease in the pig iron capacity. If it should happen, that
due to an operational breakdown of the b:Last furnace, no
liquid pig iron at all is available for a time, then the pro-
cess of the invention may be carried out entirely with solid
sources of iron, in particular scrap.
In al] three variations of the process of the in-
vention, the intensive motion of the bath of the melt and theconsequently possible good heat transfer between melt and
scrap contribute significantly to problem free and rapid
liquifaction of the solid sources of iron.
In the above the symbol Nm3 represents normal cubic
meters at standard temperature (273K) and pressure (760 mm Hg).
Having now described preferred embodiments of the
process and apparatws of this invention it is not intended
that it ~e limited except as may be required by the appended
claims.
,:
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