Note: Descriptions are shown in the official language in which they were submitted.
56~
PRODUCTION OF CARBON ~TEEL AND LOW-ALLOY ST~EL
~ITH BOTTOM BLOWING BASIC OXYGEN FURNACE
This invention rela~es to the production o~` carbon
steels and low-alloy steels with a bo-ttom blowing basic oxygen
furnace ~hereinafter sometimes referred to as "bot-tom blowing
BOF"~. More particularly9 this in~ention relates to a steel
making process in which a blow of gas is injected into a melt
so as to promote the agitation of the melt during top-blowing
of pure oxygen through a lance.
In the oxygen top-blowing steel making process9 molten
iron, scrap and other starting materials are charged into a
converter and then refining of steel is carried out while
blowing pure oxygen onto the charge melt through an oxygen
lance. In the early or intermediate stage of the blowing, the
oxygen vigorously reacts to the melt still containing a sub-
stantial level of carbon so that the generation of carbon
monoxide is sufficien-t to bring about thorough agitation of
the melt.
However, since the amount of carbon in the melt
decreases at the end stage of the blowing, the generation of
carbon monoxide rapidly diminishes and the reaction between
the molten steel and slag rapidly goes down. Due to such
decrease in decarburizing efficiency of oxygen9 i.e. decrease
in the proportion of oxygen which has been used to effect
decarburization to the total amount of oxygen blown into
the melt, the presence of excess oxygen is unavoidable
resulting in oxidation of iron far beyond the equilibrium
level. In addition, due to insufficient agitation of the
,~
56~
-- 2 --
molten s-teel and slag, there will be a temperature di~ference
be-tween them9 resulting in a dephosphorizing reaction proceed-
ing in an adverse direction. This is caused by less agitation
of the molten metal. Therefore, it has been proposed to
provide an oxygen converter with an electromagnetic agitator.
It has also been proposed to add scrap iron to the melt at
the last stage of blowing to generate a turbulence of the melt
due to a temperature difference between the scrap and melt.
However, these proposals have never been practiced because
they require a high construction cost and their effect is
supposed not so large as expected.
Furthermore, it has been proposed to rotate or swing
the oxygen blowing lance to provide additional agitation of
molten metal and slag. But this promotes the agitation of
slag, not of the molten steel.
In order to eliminate these prior art disadvantages,
it has also been proposed to inject a blow of gas into a
molten metal through the bottom while pure oxygen is blown
onto the melt through a lance. Examples of the gases to be
injected into the melt are limited to an inert gas such as
argon and a neutral gas such as ni-trogen. However, since
argon is very expensive, and a relatively large amount must
be blown into the melt in the bottom blowing so as to thorough-
ly agitate the melt, a sharp increase in cost is unavoidable.
The introduction of pure ni-trogen or a gas predominantly
comprised of nitrogen, such as a compressed air will increase
the nitrogen content of the melt. Thus, the blowing of
nitrogen is not practical) either.
~15~560
-- 3 --
French Patent 1,151,05~ and U.S. Patent 3,~54,9~2
disclose the bottom blowing of various kinds of gases, includ-
ing argon, steam, air, carbon oxide, etc. However, U.S.
Patent 3,854,g32, for example, is directed to the production
of stainless steel, so that the main purpose is to suppress
the oxidation of chromium. Thus, it is necessary to carry
out the process of this invention under subatmospheric
conditions. In addition, it treats these gases as being
equivalent. Furthermore, since the French patent teaches
the bottom blowing of a relatively large amount of gas into
the melt, the process disclosed therein is less economical.
In addition, the oxygen is blown through the convention-
al lance into the steel melt as a supersonic oxygen jet.
Therefore, the temperature at the impinging surface between
the oxygen and molten steel, goes up to 2,000C or more.
Therefore, iron loss due to evaporation (hereinafter referred
to as "fume-loss") is significant. Furthermore, the problems
of spitting of fine iron particles after firing and the slGp-
ping of slag and molten steel still remain unsolved. There-
fore, even in this combined blowing process, a remarkableincrease in tapping yield cannot be expected. This is because,
according to the conventional oxygen steel process, the Lavel-
type nozzle is used as a lance and the oxygen jet is injected
at a supersonic rate of Mach 2 - 2.5 so that the disadvantages
mentioned above are inevitable. In order to avoid such
disadvantages controlling the decarburization rate and the
slag conditions during blowing has been tried. However, it
is difficult to control these factors during operation and9
56~)
in fact, such improved results as expected could not be
obtained.
A recent development in this field is the "Q-Bop"
process, in which instead of top-blowing of pure oxygen, the
oxygen is blown into the molten metal through nozzles provided
at the bottom of the converter. Since the "Q-Bop" process
employs the pure oxygen gas for bottom-blowing instead of for
top~blowing, it is necessary to blow another gas such as
propane for protecting the nozzles. Consequently, in this
case,, too, a relatively large amount of blowing gas must be
injected into the molten metal. The "uniform mixing time"
hereinafter described in detail is about 10 seconds.
The primary object of this invention is to provide a
method of producing carbon steel and low-alloy steel with a
basic oxygen furnace.
Another object of this invention is to provide an
economical method of thoroughly agitating a melt in an oxygen
steel converter.
Still another object of this invention is to provide
a method of producing carbon steel and low-alloy steel with
a basic oxygen furnace, in which a waste gas discharged from
the furnace is circulated and used as the only source of the
gas to be blown through the bottom of the furnace.
Still another object of this invention is to provide
a method of producing carbon steel and low-alloy steel with
improved tapping yield.
This invention resides in a method of producing carbon
steels and low-alloy steels in a basic oxygen furnace,
560
-- 5 --
characterized in that a blow of gas predominantly comprised
of carbon dioxide is introduced into the molten metal through
at least one nozzle provided in the bottom or side wall of
said basic oxygen furnace at least partly during the period
of time from the beginning of blowing to the tapping of the
melt) the flow rate of the bottom blowing gas being 1/200 -
9/100 the rate of oxygen impinged upon the melt through a
lance.
The blowing gas predominantly comprised of carbon
dioxide may comprise more than 50% by volume of carbon dioxide,
including the exhaust gas from a metal refining furnace such
as a steel converter and a purified or concentrated gas derived
from a combustion gas of a heating furnace. Other components
of the blowing gas may be nitrogen, oxygen, etc. The more
nitrogen there is in the blowing gas, the greater the nitrogen
content of the melt. In case of producing the usual rimmed
steels, nitrogen in an amount of less than 50% by volume may
be present in -the blowing gas without bringing in any troubles.
But it is preferable to use a gas containing less than 20%
by volume of nitrogen if it is intended to produce a low-
nitrogen steel. It is to be noted, however, that if a rela-
tively large amount of nitrogen is blown into the melt, the
nitrogen will be almost completely removed until the carbon
content reduces to 0.5%. This is because the denitrifying
reaction takes place vigorously when the carbon content is
more than 0.5%. Thus, nitrogen gas may be blown into the
melt instead of carbon dioxide gas until the carbon content
reduces to 0.5%. After the carbon content reduces to Q.5%
s~
~ 6 --
or less, the bottom blowing should be carried out in accordance
with this invention.
In addition, mushroom deposition about 5 - 15 cm thick
will sometimes be formed at the tip of the nozzle in practicing
the method of this invention because of the temperature dif-
ference found between the nozzle cooled with the blown gas
and the melt surrounding it. It is supposed that the deposi-
tion is formed at the beginning of operation and is mainly
comprised of slag. The formation of such a deposition at the
tip of a nozzle makes difficult the blowing of gas in a pre-
determined amount. In order to avoid such a difficulty, it
is advisable to increase the pressure or flow rate of the
blowing gas to such a level that the deposition is made porous
due to the passing of the gas through the nozzle. It is also
advisable to incorporate a small amount of oxygen in the blow-
ing gas so as to utilize its generation of heat in accordance
with the equationo
2C0 + 2 = 2C2
According to thls invention, the bottom blowing i5
applied at least partly during the period of time from the
beginning of the blowing of oxygen through a lance to the
ta~ping of the refined molten steel. The bottom blowing rate
may be varied during the process, e.g. depending on the proceed-
ing of -the steel making reaction in the converter. For example,
it is preferable to increase the blowing rate at a final stage
of the top-blowing so as to compensa-te for the decrease in
agitation due to the going down of the decarburizing reaction.
Therefore, an effective refining reaction can be con-tinued
~l3 S~5
-- 7 --
successfully to the end, resulting in a remarkable reduction
in the amount of gas used.
The blowing of carbon dioxide is preferably carried
out by way of at least one nozzle provided in the bottom or
in the side wall of the oxygen steel converter.
The advantages obtained by using carbon dioxide as a
blowing gas is not only that it is less expensive than an
inert gas such as argon, but also that carbon dioxide increases
twice in volume when it is added to the melt in accordance
with the equation~ C + C02 = 2CO, bringing about violent
agitation of the melt. In other words, less gas is required
to achieve the same effect of agitation in comparison with
argon or nitrogen. This reduction in amount of gas used
means that it is possible to simplify the equipment includ-
ing piping required to blow gas into the molten steel inaccordance with this invention. This is very advantageous
from a practical viewpoint.
According to this invention the flow rate of the bottom
blowing gas is limited to less than 9/100, preferably less
than 5/100 the rate of oxygen impinged upon the melt through
a lance. This means that a relatively small amount of gas
is injected into the melt through the bottom blowing. If
the bottom blowing gas is injected into the melt in an amount
of more than 9/100 the rate of oxygen blown through a lance,
the agitation takes place so vigorously that reduction in
tapping yield is substantial due to much slopping of the
melt. On the other hand, if the amount of the bottom blowing
gas is less than 1/200 the top-blowing gas, the necessary
35~)
agitation of the melt canno-t be obtained.
In addition, the amount of the bottom-blowing gas may
preferably be res-tricted on the basis of the amount of molten
metal to be treated, independently from the blowing rate of
pure oxygen through a lance. According to this embodiment,
the amount of gas to be injected into the melt is precisely
regulated or adjusted such that the uniform mixing time is
20 seconds or more.
The uniform mixing time means the time which is required
to uniformly mix the molten steel and molten slag ~nly by the
bottom-blowing. The uniform mixing time is a factor introduced
by K. Nakanishi et al ("Ironmaking and Steelmaking" (1975)
3, 193) and is defined as follows.
Uniform Mixing Time T = 800 x ~ 0 4 (sec.)
~ - 28.5 WQ x T x log (1 + z/148) (Watt/ton)
wherein
Q = gas flow rate (Nm3/min)
Wg - amount of molten steel (ton~
T = bath temperature (~)
Z = depth of the bath (cm)
In a preferred embodiment9 the uniform mixing time is
more than 30 seconds. If the amount of gas falls within the
limitation defined above, then thorough agitation will be
obtained. If the uniform mixing time is less than 20 seconds,
the agitation between molten steel and molten slag occurs so
vigorously that the reduction of iron oxide in the molten slag
proceeds excessively, reducing the content of the iron oxide,
whic~ is effective for dephosphorization of the molten steel.
~5~5~
g
Furthermore, if the uniform mixing time is less than 15
seconds, there is much leakage of the molten steel from the
nozzles~ resulting in less -tapping ~ield of steel.
If the uniform mixing time is longer than 70 seconds,
i.e. the amount of the bot-tom blowing gas is much reduced,
no agitation is expected, and the blowing process is substan-
tially the same as the conventional oxygen steel making process
with top-blowing. This results in a remarkable increase in
the total amount of iron in the molten slag, and a decrease
in the tapping yield. Thus, it is desirable to adjust the
uniform mixing time to 20 - 70 seconds.
It can be said on the basis of experiments that, for
example 9 when the bath depth is 250 cm the uniform mixing
time of 20 seconds corresponds to bottom blowing at a rate
of 0.5 Nm3/min per ton of molten steel, and uniform mixing
-time of 70 seconds to 0.02 Nm3/min per ton of molten metal.
Noting the fact that oxygen gas is discharged primarily
as carbon monoxide gas after the decarburizing operation in
such oxygen top-blowing refining furnace, this in~ention, in
one aspect, provides a steel refining process that utilizes
said waste gas as the only source of the gas to be blown
from below the melt bath to stir it. In so doing, the process
supplies i-ts own gas for stirring the molten steel.
This invention, therefore, also resides in a process
for making steel in a basic oxygen furnace by the top-blowing
of pure oxygen and the bottom-blowing of a gas mainly composed
of carbon dioxide, characterized in that a waste gas discharged
and collected from said furnace is combined with additional
-- 10 --
oxygen and/or steam9 the mixture thereof is burned, and the
resulting combustion gas mainly composed of carbon dioxide
is used as at least a part of the bottom-blowing gas.
Since the combustion gas sometimes contains a rela-
tively large amount of nitrogen gas, it i9 preferable toremove the nitrogen gas, or to collect carbon dioxide from
the combustion gas and then the gas rich in carbon dioxide
is used as the bottom-blowing gas. The removal of nitrogen
gas from the combustion gas is preferably carried out when
low-nitrogen steel is intended to produce.
For carrying out the process above9 a steel making
apparatus having a gas circulation system, has been provided,
which comprises, in combination, a basic oxygen furnace permit-
ting both top-blowing of oxygen and bottom-blowing of carbon
dioxide-rich gas, a device for collecting the waste gas
generated from the furnace, a device for burning said gas
with oxygen and/or steaml an optional device for separating
the combustion gas into carbon dioxide and nitrogen, and a
piping system for supplying the molten steel in the furnace
with carbon dioxide generated from said burner and separator.
This invention also resides in a method characterized
in that the top-blowing oxygen is injected through a lance
onto the molten metal at an outlet velocity of Mach 0.8
2.0, preferably Mach 0.8 - 1.5.
The oxygen top-blowing steelmaking process of this
invention, in another aspect, resides in a method characterized
in that a powder of a slag-forming agent (flux) comprising
quick lime, limestone, fluorite, dolomite, iron ore or
mixtures thereof is supplied together with a top-blowing
oxygen jet, and at the same time, carbon dioxide is blo~
from below the molten steel throughout the period of oxygen
top-blowing or even up -to the time of the start of tapping,
i.e. at least partly during the period of time fro~ the
beginning of blowing to the tapping of the melt.
In the case of using the conventional oxygen top-
blowing converter, the oxygen jet may be supplied wit~ a
powder from a conventional oxygen top-blowing lance. However,
the supply of a powder into a high-pressure oxygen piping
inevitably results in a high equipment cost. Therefore, a
separate path is provided for directing the powder on a car~
rier gas up to the tip of the oxygen blowing lance and for
mixing the powder with an oxygen jet being delivered from the
nozzle of the lance. By so doing, the defects mentioned above
of the LD-AC process can be eliminated without abrasion of
the Lavel-type oxygen blowing nozzle. More specifically, a
three-sheathed lance (four coaxial tubes) used in one embodi-
ment of this invention (see Figs. 6 and 7 referred to herein-
after) is one example of such method. The carrier gas forthe flux powder is not specified, and a suitable gas can be
selected depending upon the composition and particle size of
the flux, the inside diameter of the piping, the type and
flow rate of the carrier gas or the type of the furnace used.
But it is desired that the total amount of a given flux powder
be supplied within about three quarters of the blowing period.
This is in order to dissolve the flux within the period of
refining operation and rapidly form a reactive slag for
5~
- 12 -
effective refining operation.
According to -the process of this inven-tion9 a gas is
blown from below the molten steel together with -the supply of
a flux through a lance, and the bottom blowing gas is prefer~
ably blown at a rate of 0.02 to 0.50 Nm3/min per ton of the
molten steel in case the bath dep-th is 250 cm. Within this
range, less oxidation of iron and manganese takes place as
the gas flow rate increases. Therefore, by choosing a suit-
able pattern for blowing the flux and for blowing the gas
from below the melt bath depending upon the type of the steel
to be produced, a steel of a desired final composition can
be produced with high accuracy, in high yield and with great
ease.
The features of this invention have been described
hereinbefore in detail.
This invention is particularly applicable -to produce
carbon steel9 such as rimmed steel, killed steel etc.9 and
low-alloy steel. More particularly, this invention provides
a satisfac-tory method of producing low-carbon steel, such as
carbon steel con-taining less -than 0.3D/D C.
Comparing the col~ven-tional process with this inven-tion
method, the following advan-tages of this inven-tlon are no-tedO
Since -the oxidation of iron, manganese etc. is signifi-
cantly inhibited, the yield of iron is markedly improved and
the amount of ferro-alloys used may be decreasedO In addi-
tion, since the temperature difference between the molten
steei and the slag diminishes, the dephosphorizing is promoted.
Another advantage of this inven-tion is that the blowing gas,
- 13 -
i.e. carbon dioxide9 is ab~dan-t in a s-teel making plant and
is available at low cost. This is an economicaL aspect o~
this invention. Thus, this invention has also a practical
value in the light of the present day demand for saving energy
and preventing the discharge of pollutants into the
environment.
As hereinbefore mentioned9 the method of this l~vention
can easily be practiced in the usual steel making process by
installing at least one nozzle in the conventional basic
oxygen furnace. Of course, the application of this invention
is not limited to the existing oxygen converters. As far as
the combination of the top-blowing and the bottom-blowing is
possible, this inven-tion is applicable to any type of metal
refining furnace.
Fig. 1 is an elevational side view diagrammatically
showing the bottom-blowing BOF utilized in this invention,
Fig. 2 is a graph showing -the blowing patterns of this
invention,
Fig. 3 is a schematic diagram illustrating -the arrange-
ment of the steel making apparatus according to -this invention,
Figs. 4 and 5 are graphs showing the effect of this
invention,
Fig. 6 is a bot-tom view of the three~sheathed lance -to
be used in one embodiment of this inven-tion, and
Fig~ 7 is a longi-tudinal cross section of said lance
taken on -the line a-a of Fig. 6.
According -to this invention, molten iron, iron scrap
and other starting materials are charged into a bottom-
~5356~)
-- 14 --
blowing BOF, i.e. converter 1, as shown in Fig. 1. Two to
ten concentric nozzles 2 are provided at the bottom of this
oxygen converter. During operation of the converter pure
oxygen is impinged onto the surface or into the molten metal
3 through a lance 4 while the bottom-blowing gas pr~dominantly
comprised of carbon dioxide is blown into the molten metal
by way of the nozzles 2. The nozzles are arranged in two
rows in this example. It is to be noted, however, that the
structure, arrangement and number of the nozzle are not
limited to particular ones.
In a preferred embodiment of this invention, a blow
of gas predominantly comprised of carbon dioxide and supplied
by way of conduits 5 is introduced into the molten metal 3
through concentric nozzles Z provided in the bottom of said
basic oxygen furnace at least partly during the period of time
from the beginning of blowing to the tapping of the melt and
the M ow rate of the bottom blowing gas is less than 9/100
the rate of oxygen blown onto the melt through lance 4.
In one embodiment of this invention, the uniform mixing
time is adjusted to 20 seconds or more.
Another embodiment of this invention is now described
by reference to Fig. 3, an oxygen steel furnace 31 has an
oxygen top-blowing lance 32 and a series of gas bottom-blowing
nozzles 33. Oxygen gas is blown from the top-blowing lance
32 into the furnace 31 to perform decarburization and is
discharged primarily as carbon monoxide gas. A gas primarily
consisting of carbon dioxide is jetted from the bottom-
blowing nozzles 33 into the furnace 31 where it is decomposed
.535~i~
-- 15 --
following the course C + C02 ~ 2C0 and discharged from -the
furrlace. These two supplies of carbon monoxide gas are
caught in a hood 34 on top of the furnace 31. They contain
less than 20 vol% of nitrogen gas since they entail a-tmosphere
as they are being caught in the hood.
The gas caught in the hood 34 is first freed of dust
through a dust collector 35 and transferred to a gas holder
36 where it is stored temporarily before proceeding to sub
sequent treatments. The gas in the holders 36 is mixed with
oxygen and/or steam prior to entering into a burner 37. The
gas in the holder 36 may be burnt with oxygen coming from an
oxygen holder 41 for supplying oxygen to the oxygen top-
blowing lance 329 and is optionally dehumidified before i~
is transferred to a carbon dioxide holder 399 or after the
burning, the gas may be denitrified in a C02/N2 separator 38
to increase the C02 content before it is transferred to the
carbon dioxide holder 39.
The carbon dioxide transferred to its holder 39 is
supplied to the gas bottom-blowing nozzle 33 through the flow
regulator 40. Alternatively, it may be combined with
untreated gas from the gas holder 36 before it is supplied
to the nozzle 33.
The gas Jetted from the bottom-blowing nozzle 33 into
the bath is again caught in the hood 34 together with the
carbon monoxide resulting from decarburization. Thus, each
supply of carbon monoxide gas and carbon dioxide gas keeps
recycling through the path described above.
Another embodiment of this invention is now described
~ 16 -
by reference to Figs. 6 and 7. A 2~ton pure oxygen -top-blow
ing converter is provided wi-th -two bo-ttom nozzles (I~D~ 8rnm)
-through which a gas is -to be blown f`rom below the rnelr bath.
The oxygen top-blowing lance used is a three-sheathed lance
(four coaxial tubes) 61 as shown in the bottom view and
longitudinal cross section of Fi~s. 6 and 79 wherein -the
center of the disc 63 of i-ts tip 62 is provided with a single
nozzle opening 659 10 mm in diameter serving as a passage 64
for the supply of a flux powder and said opening is surrounded
by -three nozzle openings 67 each 4.2 mm in diameter serving
as a passage 66 for the supply of oxygen. This lance permits
the powder to be blown against the surface of the mel-t 68
as it is mixed with oxygen being jetted from the three
surrounding points.
This invention will be further described in conjunction
with the working examples.
Example 1
A conventional oxygen conver-ter wi-th the capacity of
250 -tons was used to carry out this invention. Four nozzles
10 mm in diame-ter were ins-tallecl at -the bot-tom of the conver-ter~
Into this converter, as main s-tarting materials, 215 tons of
mol-ten iron and 35 tons of scrap iron, and, as other starting
material, 3 -tons of quick lime were charged. The composi-
tion of the molten iron was9 by weight percent, 4.63% C~
0.48% Si, 0.45% Mn9 0.123% P, 0.0018% S, 0.0038~ N and the
balance iron and incidental impurities. The temperature
thereof was 1385C.
The gas blowing from the top and from the bottom was
s~t ~
~ 17 -
carried out as in the following.
The top~blowing of oxygen was carried out at a flow
rate of 409000 Nm3/hr in accordance with the flow pattern
shown in Fig. 2. The bottom blowing was also carried out
following the flow pattern shown in Fig. 2. As shown in
Fig, 2, the bottom blowing was initiated at a flow rate of
50 Nm3/hr and the rate was încreased to 100 Nm3/hr when the
top-blowing of oxygen was initiated. At the end stage of the
blowing, the rate of the bottom blowing was increased to
200 Nm3/hr and was then reduced to 50 Nm3/hr after the top-
blowing was finished. The bottom blowing gas was an exhaust
gas obtained from an oxygen converter and comprised, by
weight percent, 18% C0, 63% C02, 16% N2 and 3% H2.
For the purpose of comparisonJ a conventional oxygen
steel making process was also carried out using the same
oxygen converter. The composition of the starting material
charged into the converter and the manner of top-blowing were
the same as in the above. In this case, however, the bottom
blowing was not applied. The intended product steel was low-
carbon rimmed steel. Table 1 below summarizes the finalcomposition of -the molten steel.
Table _
Composition (% by weight) Tem. in Tapp ng
~ c-- ~ -n-T--P~ r---- (c,l s17)g (%)
Ths l l l ( _ _
invention 0.063 0.16¦0.017 0.012 0.0025 1625 11 13.8 96.3
. I _ _ . ~ _,
tional 0.065 0.12¦0.021 0.015 0.0011 1618l 19.5 95 8
18 ~
As ls apparent from the data show~ in Table ] above 9
the produc-t steel o:E the me-thod of this invention has -the
composition falling within that of low carbon rimmed steel
and also shows a remarkably efficierlt dephosphorization and
tapping yield.
In this example 9 Example 1 was repeated except that
various kinds of gases were used as the bottom blowing gas.
As hereinbefore mentioned, the bottom blowing gas of
this invention may be an exhaust gas discharged from an iron
making plan-t, or a s-teel making plant. In this example,
therefore, such kind of exhaust gas was used as the bottom
blowing gas. Gas No. 1 was derived from an exhaust gas
discharged from an oxygen converter and was made rich in
carbon dioxide. Gas No. 2 was derived from an exhaust gas
discharged from a hot stove and was made rich in carbon
dioxide.
The final composition of the molten s-teel in each run
is summarized in Table 2 be]ow.
Table 2
___ _ Gas composition (% by volume)
Gas No. C2 CO N2 2 2
1 9~ O 5 O
2 ~2.6 O 4~ 3.2
~ ~; ?~ .3~
~ 19 -
Table 3
Final composition ~ _ ~ 1
Gas~ by ~:gl:l~ T Fe Ten~lp. ¦
No. C Mn j N (%)
__ _ .
1 0.058 0.15~.0019 14~2 1632
2 '~r, 1 = o, ODC5 1~.5 1619
According to this invention, an exhaus-t gas discharged
from the oxygen converter may be used as the bo-ttom blowing
gas. If the nitrogen content of the exhaust gas is below 5C%
by volume, the nitrogen content of the resulting steel product
is accep-table. In addition, according to this inven-tion, the
agita-tion of the melt was effected thoroughly, resulting in
sufficient degree of decarburization and dephosphorization
to make the method of -this invention practical.
Example 3
The following star-ting materials were charged lnto an
oxygen converter shown in Fig. 1. The capacity of the conver-
-ter was 250 -tons and the bath depth was 250 cm. Two concen-
tric nozzle were provided at the bottom (the inner nozzle was
12.7 mm in inner diameter and 15.4 mm in outer diameter, -the
slit width was 1.15 mm9 and the ou-ter nozzle was 17.7 mm in
inner diame-ter and 19.1 mm in outer diameter.
Mo]-ten iron. 220 tons
The [Mn] is about 0.40% and ~p] is about 0.150%
in molten iron.
Scrap irono 30 tons
- 20
Other materials:
quick llme 9 tons
iron ore 4.5 tons
light dolomite 3~0 tons
fluorite 0.2 ton
converter slag 1.8 tons
According to the method of this invention, various
kinds of bottom blowing gas were injected into the melt while
top-klowing pure oxygen through a lance. The blowing condi-
tions and the resulting uniform mixing time are summarizedin the following Table 4.
r-
-- 2
. _ . .. _ _ _ . .. . . _ . _ . _ .. _ .. _ . ... . .
hO O
.~ ~ ~ ~ o 1-~ ~
P~r-l~ . . . O
P~ a) ~~) ~) Lt~
0 ~ I c~ ,
~ :~ a) ~1
_... _ .. _ _... .. _._ _ .. ~ . .
~1 o a~ _~LO L~ L~`\
t~ `o~ O O O a~ OC)
~ h ~_ . . .
1 0 o O o o ~ ~ P
tH C.) t) r-l
o ~a~
.. ___ -- __ __ ~ h h
0 ~ r-l ~ O
S~ r~ 1--l r~ J r-lrl
E-- ~l tn a) t~
. _ _ __ . ~a~
h ~0 ~ ~ ~ +' ~i:~
O s: O . ~ tn ~cu
tH ~ O ~ r-l a) u~ .
. ~ ~ ~ a~ ~ L~ tn ~r-l
n ~ ~r-l
~ e ~ h ~
_ ___ .________.___ ___
Pr~ O O O rJ O
+' ~ V O O O C~ ~
a)O ~ ~ ~o ~ ~~1
,D ~_, r-lr~l ~1 a~ ~3
a>___~ ___ _______._ ~ ll
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- 22 -
In this example, an oxygen top-blowing converter with
the capacity of 2 tons was usèd. Two nozzles 6 mm in diameter
were provided in the bottom of the converter.
Carbon dioxide gas was injected into the mol-ten metal
through the nozzles. The top-blowing oxygen was supplied
through the straight type nozzles and Laver-type nozzles.
In one series of experiments, the flow rate of the
bottom blowing carbon dioxide gas was varied. In another
series of experiments, the outlet velocity of the top-blowing
oxygen was varied.
Other experimental conditions were:
molten iron: 2000 kg, 1380C,
4.20% C, 0.52% Si, 0.61% Mn,
0.121% P, 0.020% S
scrap : 360 kg
oxygen flow rate: 6 Nm3/min
oxygen pressure before passing into the lance:
5 kg/mm
distance between the lance tip
and the bath surface: 300 mm
carbon dioxide flow rate: 0.1 - 2.3 Nm3/min. ton
oxygen jet velocity: Mach 0.3 - 2.3
blowing period: 18.6 minutes
Under these conditions, the tapping yield and the
oxygen effect were determined. The results are summarised
in Figs. 4 and 5. Fig. 4 shows the results obtained when the
flow rate of carbon dioxide was varied as indicated with an
- 2~ -
outlet velocity of oxygen of Mach 1. Fig. 5 shows the resulls
obtained when the outlet velocity of oxygen was varied as
indicated at a carbon dioxide ~low rate of 1 Nm3/min. ton.
The data plotted in Figs. 4 and 5 are shown in com-
parison with those obtained in the conventional oxygen top-
blowing process9 and no bottom-blowing is employed.
From the results shown in Fig. 4 it is noted that
improved tapping yield (shown by graph A) and oxygen effect
(shown by graph B) in comparison with those of the conven-
tional process were obtained when an flow rate of carbondioxide of 0.3 - 2.0 Nm3/min. ton was employed at an outlet
velocity of oxygen of Mach 1. It is also noted from Fig. 5
that improved tapping yield (shown by graph A) and oxygen
e~fect (shown by graph B) in comparison with those obtained
15 in the conventional process were obtained when an outlet
velocity of oxygen of Mach 0.8 - 2.0, preferably Mach 0.8 -
1. 5 was employed at a carbon dioxide flow rate of 1 Nm3/min.
ton.
Example 5
The steel making apparatus comprised a 2~0-ton oxygen
top-blowing converter provided with four bottom-blowing
nozzles and the gas circulation system comprising the com-
ponents described above in conjunction with Fig. 3. The
refining conditions were as followso the molten iron consisted
f 4.63% C, 0.51% Si, 0.43% Mn, 0.115% P, 0.023% S and the
remainder Fe9 the melt temperature was 1358C, the hot metal
ratio was 87%, and 3.5 tons of iron ore was charged together
with auxiliary materials composed of 11 tons of quick lime
-- 24 _
and 8 tons of dolomi-te. The supply ra-te of:-top-blowr-l oxygen
was 40,000 Nm3/hr. The was-te gas recovered -through the abo~Je
circulation sys-tem was burnt, denitrified, and supplied at a
1OW rate of 1,500 Nm3/hr as a bottom-blown gas that consisted
of 98.5 vol~o C0~ and 1.5 vol% N2. The refining pattern was
adapted for the production of low-carbon rimmed steelo oxygen
was blown in the same marmer as in the conventional me-thod
whereas a constan-t flow of bottom-blown gas was supplied up
to the time of start of tapping.
The results of the refining were- a waste gas con-
sisting of 71.1 vol% C0, 15.2 vol% C029 10.5 vol% N2 and
3.2 vol% H20 could be recovered from the furnace in a quan-tity
of 108,000 Nm3/hr. The steel obtained had a final analysis
of 0.0058% C, 0.01% Si, 0.11% Mn, 0.018% P, 0.020/~ S,
0.0011% N and -the remainder Fe, and its temperature was
1628C. This indicates the fact that refining operations
such as decarburization and denitrification were adequate
for the making of the desired s-teel.
Example 6
The converter equipped with such sys-tem was opera-ted
by four differen-t me-thods: the process of this invention (I)9
the LD-AC process (II), the process wherein oxygen was blown
from above and a gas was blown from below and a flux was
supplied as a mass (III), and the conventional oxygen -top-
blowing process (IV). In each case, the following conditions
were employed, and the resul-ts shown in Table 5 below were
obtained. Composi-tion of molten iron 4.3/0 C, 0.50% Si,
0.58% Mn, 0~125% P and 0.023% S.
- 25 -
Temperature 1380C
Charge ~ 2000 kg of molten iron and
370 kg of scrap
Flow rate of top-
blown oxygen o 6 Nm3/min. ton
Powder carrier gas : argon gas at 1 Nm3/min
Bottom-blown gas o carbon dioxide gas at 1 Nm3/min
Distance (h) between
lance and molten
metal surface : 300 mm
Blowing period : 17.3 min
Table 5
T Fe
Chemical analysis (%) I Tem in
C Si ~ - ~ (C) Slopping slag Yie d
I 0.38 _ 0.30 0.012 0.019 1680 no 6.3 ~0.5
II 0.~9 _ 0.15 0.013 0.021 1685 much 21.8 -0.7
III 0.38 _ 0.27 0.035 0.021 1680 no 6.5 +O.h
IV 0.41 _ 0.14 0,044 O.OZ3 1690 no 7.3 0
As is apparent from the foregoing, the method of this
invention is very practical, since the existing oxygen conver-
ter may be utilized merely by installing a nozzle at the bot-
tom or at the side wall of i-t. In addition, the gas to be
used as the bottom blowing gas may be an exhaust gas obtained
from the converter with or without further treatment of
increasing -the concentration of carbon dioxide. Thus, the
method of this invention is easily applicable to the existing
oxygen converter and will bring about practical advantages.
