Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~o~ ~
BACXGROUND OF T~E I~ENTION
~ his invention relates generally to steelmaking
processes and apparatus and more particularly to a
steelmaking process and apparatus wherein an (electric)
arc furnace with assisted combustion is used.
More specifically, this invention relates to a
rapid steel melting process in an arc furnace for prc-
ducing ordinary carbon steels and alloy steels from a
cold charge of steel scrap as raw material and to relat-
ed apparatus comprising an integrated combination of
the arc ~urnace, special oxygen-fuel oil burners instal-
led in the furnace for effecting assisted melting, and
a fume evacuation system and incorporating a number of
innovations in various parts o~ this apparatus.
By the provisions of this invention, the steelmak-
ing apparatus can be operated continuously and efficient-
ly over a long period with remarkably reduced time for
maintenance shutdowns.
In recent years there has been widespread use of ~,
the so-called ultra-high-powered process (U. HoPo process)
and, in some instances, auxiliary or assisted combustion
systems, for the purpose of increasing the efficiency
of (electric) arc furnaces for steelmaking in which a
cold charge such as steel scrap is used as raw material. ~ -
In this U. H~Po process, which has in one bound be- ~` -
come the focus of intense attention through the proposals
and disclosures by W.E. Schwabe and others, use is made - -
of a transformer of a capacity which is 1.5 to 2.0 times
that of a conventional furnace of the same operational
- 2 - 5
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~0~ 4~f~
capacity, and the operation is conducted with a short arc.
This process, however, is still accompanied by ~everal
problems, among which are high investment cost or ini-
tial cost for equipment and the limitation of location
to one where a large power supply is available. Further-
more, in actual operation, the following difficulties
are encountered because the operation is carried out with
a low power factor of low voltage and high current.
1). In the U.~.P. process, since the operation is
generally carried out with high current, much Joule's
heat and electromagnetic force are generated and accele- -
rate damage to the electrode holders and oxidation and
wear of the electrodes. Furthermore, thermal stresses
due to temperature difference between the exterior and
interior of the electrode tend to produce damage such - -`-
as breaking, splitting, and spalling of the electrodes.
2). In general, as the electrical capacity is in-
creased, the melting time for steel scrap is reduced,
and the ratio of the total power-on time A from start
to tap (i.e., the time during which steelmaking work is
actually carried out) and the power-off time B from tap ~
to start (i.e., the time from tap to the succeeding `
power-on and the time such as that spend in charging of
scrap steel and repair of parts such as furnace wall
refractories), that is, the effective operational rate
or practice ratio A/(A+B) x 100 % of the furnace, tends
to become low, and the effectiveness of equipment invest- -
ment decrease in some cases. -
3~. Since the distance between the steel scrap and ;
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~4~
the electrodes fluctuates, in the melting period wherein
the bulk density of the steel scrap in the furnace is
low, operation with a short arc is more disadvantageous
than that with a long arc in order to shorten the melt-
ing time.
4). Concentrated local damage due to melting of
the re~ractorles of the furnace walls and roof caused
by powerful electric arcs generated between the elec-
trodes and the steel scrap is severe.
Because of the above enumerated difficulties, the
practice ratio of the furnace as a whole is lowered,
and, when considered from the viewpoint of long-period
and continuous operation, the process entails several
features which are not advantageous improving produc~
tivity and economy.
On one hand, the so-called "Shell Toroidal" burner
used in the ~uel, Oxygen, and Scrap (~.O.S.) process
developed in England is at present a representative
example of an auxiliary burner for an assisted melting
process. ~he advantages afforded by the installation
of this system in an arc furnace for steel-making are
as follows.
1. ~his system can be installed with relative ease
in an already existing arc furnace.
2. A tremendous equipment investment is not re~
quired as in the UoH~Po process. -
In actual practice, however, several problems are
encounter~d, the principal being as follows, whereby
there is a limit to the effectiveness of this system.
. ~ .
_ 4 _
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66
: . .
An ordinary burner of the type representable by the "Shell
Toroidal" burner is used for the purpose of preheating and melting steel
scrap by means of a high-temperature flame. In a closed furnace such as
an arc furnace, however, there is no combustion chamber, and it is diffi-
cult to use a large quantity of fuel. Furthermore, as a natural consequence,
it is necessary to generate a flame of short frame. Provisions have been
devised for thisnecessity but give rise to the following problems.
1. Low thermal efficiency
In the case of a "Shell Toroidal" burner in which the fuel
` 10 is atomized with pure oxygen, the theoretical combustion temperature be-
comes approximately 2,800C. On one hand, in a high-temperature region,
the dissociation coefficients of CO2 and H2O increase, and the latent heats
become even higher than 50 percent.
The average temperature of the steel scrap is very low, of course,
and when the combustion gases contact this material to be heated, combustion
takes place on the outer surface, whereby recombination occurs. Consequent-
ly, heat of reaction is generated. By advantageously utilizing this cha-
racteristic, rapid heating becomes possible. However, if an error is made ~;
in the use of the burner, the latent heat in the exhaust gases will increase
and give rise to a great drop in thermal efficiency. It can be seen from
this that during the initial period when the cold charge has been placed in
the fur~ace, the process is relatively effèctive, but
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1~)4~46~
the thermal efficiency decreases with increase in the
temperature of the material being heated.
2. ~imit to period of use
While the steel scrap oxists with an appro-
pirate bulk density in the furnace, the flame issuing
from the burner disperses suitably within the body of
steel scrap pieces, but as the quantity of molten steel
increases, and the material being heated becomes dense,
its surface area becomes small. For this reason, the
coefficient of heat absorption decreases, and, at the
same time, the temperature of the exhaust gas increases.
As a consequence, in general, effectiveness is afforded
in only the first part, excluding the last period of
the melting.
3~ Much damage to the furnace facilities
Severe local melting damage occurs at each
burner orifice and frame contact parts, and, at the same
time, excessive rise in the tempercature of the atmosphere -
within the furnace generally hastens melting damage of
the furnace wall bricks, increases the brick consumption,
and entails economic disadvantage. On one hand, the
rise in the waste gas temperature is accompanied by a
rise in the temperature of the cooling water of the
furnace body, c~nd problems associated with the cooling
water piping readily arise. ~urthermore,in the dust ~
collector, also, trouble such as breakage of the bag ~ -
filter and deficient suction performance occur and give
rise to an increase in the damage to the accessory facili-
ties thereof~ - -
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10~66
4. Difficulty in maintenance because of complexity
of the mechanism of the burner and entire
apparatus
In the case of a burner in which the fuel is
caused to undergo combustion by atomizing it dlrectly
with pure oxygen, damage to its working end is caused by
back firing of the flame at a high temperature.
Furthermore, because of special provisions such as a
safety device for holding any back fire within the bur- . `
ner cylinder, a complicated structure at the burner tip
for causing a toroidal curve to be defined, and a ratio
setter for proportional control of the fuel-air ratio,
the entire burner device becomes complicated and expen-
sive in production and difficult to maintain.
Because of the above enumerated problems 1 and 2,
the limit to the output produced in this process is
generally considered to be of the order of 20 percent
of the total input energy of the arc furnace from the
operational and economic viewpoint, although this depends ; ,
on the factors of the efficiency of the burners and the
prices of electric power, oxygen, and fuel oil. By the
practice of this invention, the output is increased by
the unique mechanism of melt cutting and melting of the
cold charge of scrap and the like by the burners.
, . . .
Furthermore, because of the above problems ~ and 4, .~
. difficulties in maintenance are encountered, but by the ..
improvements in construction of the burners for injection
of oxygen and fuel oil and in the burner mounting parts . .
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lf~)~4466
and other novel innovations according to the invention,
these difficulties are overcome and remarkable improve-
` ments are attained as described below.
SUMMARY 0~ THE INVENTIO~
. ..
It is an object of this invention to solve theabove described problems accompanying the high-powered
process (H.P. process) carried out in conjunction with
an arc furnace and the assisted combustion process using
"~hell Toroidal" burners and to provide a process and
series of devices for and organization of an arc furnace
; by which the above mentioned problems can be solved, and
a continuous and highly efficient operation can be carried :
out over a long period with high stability and produc-
tivity.
While this invention provides special oxygen-fuel .
oil burners (hereinafter referred to as oxygen-fuel
~` burners) in an arc furnace designed to produce ordinary
carbon steels and alloy steels with a cold charge of
steel scrap as raw material, its principal feature is
not merely the introduction of high energy by means of - -
special burners in additon to electric energy but the .~-
provision of a comprehensive technique including features .~ :
such as the use of furnace walls having carbonaceous ~:~
bricks and water cooling means for preventing melting
damage to furnace wall refractories of the electric arc.-.
furnace, il furnace roof having a water cooling ring for
. .
incre~sing the durability, thereof, and a fume evacua-
tion system for sustaining high-efficiency operation and
of an integrnted organization of devices therefor. ;-~
" ",~ .. .
~ 8 ~
104446~
According to this invention in one aspect thereof,
briefly summarized, there is provided a steelm~king
process in which use is made of an arc furnace for pro-
ducing ordinary steels and alloy steels from a cold
charge of steel scrap as raw material in the arc furnace,
and which comprises injecting an oil fuel and oxygen
into the furnace interior through oxygen-fuel burners
installed with specific mounting angle in the furnace
wall and thus carrying out combustion of the fuel there-
by to assist the arc in r~pid melting of the raw material
and, at the same time, drawing off exhaust gas from the
furnace interior by fume evacuation means to place the
furnace interior under negative pressure thereby to draw
secondary air from outside the furnace into the interior
thereof and thereby to increase the furnace combustion
efficiency.
According to this invention in another aspect
thereof, there is provided steelmaking apparatus com-
prising an arc furnace for producing ordinary steels,
alloy steels, and the like from a cold charge of steel : ~
scrap as raw material and fume evacuation means for ~-.
drawing exhaust ~as and dust out of the furnace interior '
and, at the same time, creating a negative pressure in --
the furnace interior, the arc furnace being characterized -- -
by: 1) a furn~ce wall formed of carbonaceous brick up- ~ :
ward from a point slightly above the slag line within
the furnace and cooled by water-cooled boxes imbedded
therewith; 2) a furnace roof having an outer peripheral
part made of steel-cased, magnesite-chrome bricks, a .
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1~4~66
central part around electrode insertion holes provided
with hi~h-alumina rc~nming mass, and a p~rt around an
exhaust port provided with a water-cooled ring and high-
alumina rc~nming mass disposed therearound; and 3) a
plurality of oxygen-fuel burners each mounted in inserted
state with specific orientation in the furnace wall and
provided with means for ejecting oxygen and a fuel to
cause a combustion flame to be injected into the furnace
interior and with water-cooling means at the p.q~t of the
burner inserted through the furnace wall, the part of
the furnace wall around the water cooling menns being
provided with burner tiles. ~- :
The nature, utility, and further features of this
invention will be apparent from the following detailed
description with respect to one example of preferred
embodiment of the invention when read in conjunction with : -
the accompanying drawings, throughout which like parts
are designated by like reference numerals.
BRIE~ DESCRIPTION OF THE DRAWINGS
In the drawings: ~ :
FIG. 1 is a layout diagram showing the essential ~-
components and arrangement thereof of one example of -~
steelmaking apparatus accorcing to this invention;
FIG. 2 is a side view, in longitudinal section, of t~
an oxygen-oil burner according to the invention;
FOG. ~ is a relatively enlarged side view, in - ~:
longitudinal section, showing an example of a nozzle body
part of the burner shown in ~IG. 2; .
FIGo 4 is a simplified plan view showing the -~
,-,~' ' .
- 10 - ,.~
'''`"'-
~, , ,, , ;, .... ... . ..... .
10~ ;6
positionsand orientations of installation of the oxygen-
oil burners in an arc furnace according to the invenion;
FIG. 5 is a simplified elevation, in vertical sec-
tion, showing the angle of installation of a burner
relative to the horizontal plane;
~ IG. 6 is a relatively enlarged elevation, for the
most part in vertical section, showing details of the
part of an oxygen-oil burner where it is fitted into and
secured to the furnace;
FIG. 7 is a simplified elevation, in vertical sec-
; tion, showing the furnace wall construction;
FIG. 8 is an elevation, in vertical section of thefurnace roof;
~ IG~ 9 is a plan view showing one half of the fur-
nace roof shown in FIG. ~;
; FIG. 10 is a relatively enlarged, fragmentary plan
view showing an exhaust outlet of the furnace roof;
FIG. 11 is a relatively enlarged, fragmentary ele- -.
vation, in vertical section, of the exhaust outlet shown
in FIG. 10; and
FIG. 12 is a time chart or diagram indicating one
example of operation pattern in carrying out the process
of the invention.
DE~AILED DESCRIPIION
General Organization of Apparatus
The example of steelmaking apparatus according to
this invention, as shown in FIG. 1, comprises essential- --
ly an arc furnace 1 having a furnace wall Z and a furnace ;
roof 4, a plurality of oxygen-oil burners ~ provided in
-- 11 --
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- the furnace wall 2, and a fume evacuation system compris- -
ing a water-cooled suction elbow 6 connected to the fur-
nace roof 4, a water-cooled duct 7 connected to the
outer end of the elbow 6, a combustion column 8 to the
upper part of which the other end of the duct 7 is con-
nected, a gas cooling tower 10, a water-cooled, jacket
connecting the upper part of the gas cooling column 10
to the lower part of the combustion chamber 8, an flow
pipe 11 for exhaust gas connected at one end to the lower
part of the tower 10, an exhaust fan 5 connected to the
other end of the air jacket 11 and operating to draw
exhaust gases through the furnace roof 4 and through ~-
the above named parts of the fume evacuation s~stem, and -~
a bag filter 12 through which the exhaust gases thus
drawn are passed for filtration and then discharged into
the atmosphere.
The various components constituting this steelmaking
apparatus will now be successively described in detail. , ~-;
1. ~ ~en-Fuel Burners
In accordance with this invention, special oxygen-
fuel burners ~ ~re mounted in the arc furnace 1 and ~-
accomplish rapid melting of steel scrap. ~he function
of these special burners with respect to the melting of
steel scrap differs fundamentally from that of conven- - -
tional burners of assisted melting equipment which, with -
a high-temperature flame, heat and melt cold charges
such as steel scrap.
The function of the special burners of the inven- i-
tion is 1) first, to heat the cold charge such as steel -
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6t~
scrap to red heat by the combustion of the fuel and to
eject a large quantity of still unreacted ox~gen as a
B jet stream o~ high velocity (approximately ~rmeters/
sec.) thereby to melt cut and melt directly the steel
scrap or the like and 2) to cause ef~ective oxidation
reaction with combustible matter (e.g., oil adhering to
the steel scrap) charged simultaneously with the steel
scrap into the ~urnace and to apply the resulting heat
to the cold charge such as steel scrap.
1-1. Burner mechanism
Each of these special oxygen-fuel burners has a
structural arrangement, as described more fully herein-
after, wherein a mixture gas stream resulting from atomi-
zation of a fuel oil with air is ejected through the
center of the working end of a burner cylinder, and, a -
large quantity of oxygen is ejected at high velocity
;
from around the center stream in a form to encompass the -
same. During this operation, the air for atomizing the
fuel oil is caused to undergo spiral movement by a heli-
cal vane provided within a burner cylinder, and, further-
more, thorough mixing of the fuel oil and air is carried -
out by an agitating impeller of a mixing chamber. A
rotational movement is imparted to this mixture stream.
This mixture stream is caused by a conical constriction
to assume a high velocity and be ejected through an
injection orifice to become a jet stream of rod shape,
which does not diffuse into the surrounding region until
it has traveled through a certain distance, being en-
compassed during this interval by oxygen ejected at high
,
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~044466
velocity from at least three other injection orifices.
~or this reason, these streams assume a long focus shape
of high velocity and concentrate ~t a single point, there-
by promoting the cutting and melting of the steel scrapO
1-2. Burner construction
One specific example of a burner as illustrated
in FIGS. 2 and 3 will now be described.
; Referring to FIG. 2, the oxygen-fuel burner 3
has a cooling cylinder 15 constituting an outer casing
to which a cooling water supply pipe 13 and a cooling ~
water discharge pipe 14 are connected. ~hrough this ~ -
cooling cylinder 15 and along the longitudinal center-
line thereof, there is inserted a burner cylinder 16 -'
adapted to mix a fuel oil and air and eject the mixture. -
A plurality (three in instant example) of oxygen supply
pipes 17 are disposed within the cooling cylinder 15 and -
around the burner cylinder 160
The burner cylinder 16 has therewithin a bulkhead -~ ;
wall 18 at its rear part, and through this wall 18 and
along the centerline of the burner cylinder 16, a rela- --
tively thin fuel oil supply pipe 19 is disposed to extend ; -
from the wall 18 toward the front or working end of the
burner cylinder, or toward the right as viewed in FIGSo 2
and 3. ~he space thus formed between the burner cylinder
16 and the fuel supply pipe 19 constitutes a passageway ~-
for air, which is supplied with air by an air supply
pipe 20 connected to the burner cylinder 16 at the rear
part of the air passa~eway. A helical vane 21 is provid-
ed around the fuel supply pipe 19 from the connection of
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1~ 66
the air supply pipe 20 to the front end of the fuel
supply pipe.
In front of and in a position to confront the for-
ward open end of the fuel supply pipe 19, there is
provided an agitating vane structure 22 for mixing the
fuel and air. ~his a~itating vc~ne structure 22 is
mounted on a sha.ft 25 coaxially alined with the fuel
supply pipe 19 and rotatably supported on bearin~ support
members 23 and 24 fixed to the inner wall surface of the
burner cylinder 16 and is rotated by the stream of fuel
oil and air.
~ he front ejection end of the burner cylinder 16 is
convergently tapered to an ejection orifice 26. The
discharging nozzles of the above mentioned oxygen supply
pipes 17 are so directed that their flow axes interset
the flow axis of the ejection orifice 26 at a point in
front of or downstream from the ejection orifice 26. :
By the above described structural arrangement of
the burner 3, the fuel oil supplied through the fuel
supply pipe 19 and the air supplied through the air sup-
ply pipe 20 and caused by the helical vane 21 within the
burner cylinder 16 to advance as a twisting flow merge
in front of the forward end of the fuel supply pipe 19.
As a result of this combined flow of the fuel and air, ~ -
the agitating vane structure 22 rotates, whereby the fuel
and air are thoroughly mixed and are ejected out in a
straight-line form through the ejection orifice 26. At
the same time, oxygen from the oxygen supply pipes 17 -~
is ejected in a manner to encompass the fuel-air mixture
- 15 -
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10~66
jet until it intersects this mixture jet in a region
where combustion t~kes place with the generation of
maximum temperature.
1-3. Nl~ber and positions of burners
The special oxygen-fuel burners ~ used in the
apparatus of this invention are installed in cold spot
parts of the furnace wall 2 of the arc furnace, as shown ~, -
in FIGS. 4 and 5, with due consideration of the burner
installation height and dip angle (relative to the hori-
zontal) so as to attain maximum melt cutting and melting
of the cold charge of steel scrap and the like charged
into the furnace. Each burner is thus inserted into the
furnace in a direction such that the extension of ~he
centerline of its burner cylinder will be clear of any -
of the electrodes 27 and will intersect the plane of the
slag line at a point short of the vertical centerline
of the furnace. ;
In the example 50-ton arc furnace, these burners 3
are installed in the furnace wall at positions approxi-
mately 600 to 1,000 mm. above the slag line, with a dip
angle of approximately 20 degrees, and in directions not
passing through the electrodes. ~urthermore, the number
of these burners is selected on the basis of factors such ;
as the size of the furnace. FIGS. 4 and 5 shown the
positions and number of the special oxygen-fuel burners -~ -
installed in a 50-ton arc furnace. In this ex~mple,
the extensions of the centerline of each burner inter-
sects the slag line at a point somewhat short of the
vertical centerline of the furnace.
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466
In general, in -the case where burners of this
character are installed in an arc furnace, the forward
end of each burner is exposed to not only heating by
its own hi~h-temperature flame but also to heat due to
reflected flame from the combustion materials within
the furnace and heat radiated from the molten steel and
is severely oxidized and damaged.
~ his damage is not limited to the front end of each
high-temperature burner but is similarly to be found in
the furnace wall in the neighborhood of each burner, and
the frequency of such damage it very high.
The use of a burner must be stopped not only when
the front end of its burner cylinder is damaged but also
when the furnace wall is damaged. Intermittent stoppage
with considerable frequency of the furnace operation for
this reason gives rise to a drop in the steelmaking ef-
ficiency and an accompanying rise in production cost.
~ urthermore, while a damaged burner cylinder can be
readily replaced, the furnace wall must be repaired each
time a portion thereof is damaged. For this repair,
moreover, because of the requirements for forming the
burner insertion aperture, it is necessary to use special,
expensive materials such as refractory materials of
special shape and burner tiles filled with a refractory -
material of indeterminate form such as castable refrac-
tories~ whereby the production cost is further increased.
A further problem in a conventional apparatus of
this character is the ejection of heat and noise from
the furnace interior to the outside through gaps formed
,;~
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~9(~4~66
between the peripheral part of each burner and the inner
surface of the burner insertion aperture, whereby the
work environment is greatly impaired.
1-4. Burner mounting parts
This invention contemplates overcoming these
difficulties by providing novel improvements also for
the mounting parts of the burners. ~or forming the
structure around the apertures through which the burners
are inserted into the furnace, which structure, being -
exposed to strongly oxidizing flame at high temperature, - -
is most apt to be damaged by heat, burner tiles made of ;
a metal having excellent resistance to oxidation and -
high thermal conductivity, such as pure copper, and
havin~ a melting point above 1,000C are provided in
place of refra~tories. In addition, burner boxes made --
of a metal such as steel, which has good thermal conduc-
tivity and resistance to oxidation and suitable strength ~ -~
at high temperatures, and which, moreover, is relatively -~
inexpensive are provided around the burner tiles. Still -
another novel innovation is a sealing device comprising,
essentially, a steel plate and spring for pressing on
the plate and installed between each burner body and the -
corresponding burner tile for completely sealing the gap
therebetween. A specific example of this device will
now be described with reference to ~IGo 6~ :
The furnace wall 2 at its part for insertion there-
through of each oxygen-oil burner 3 is provided with ~
inner and outer, double (cooling) water frames 30 and ~- -
31. The inner water frame 30 has a hollow cylidrical ~ -
' '' -
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".'
.", . - . ,, , ,, , ,, ~ , " ~ ., ,,,, ., . , , ,:.
1~)4~466
shape with a central bore 32 for insertion thereinto of
the forward or working end of the burner 3 and is made
of a metal, such as pure copper, having resistance
against oxidation, high thermal conductivity, and a
melting point above l,000C. ~his inner water frame 30
is provided with cooling water inlet and outlet 34 and
33.
The outer water frame 31 is made of readily workable
iron and supports the inner water fr~e 30 in the furnace
wall 2. This outer water frame 31 is provided with cool-
ing water inlet and outlet 36 and 35 and functions to
cool the inner end of the inner water frame 30 and the
region of the furnace wall 2 around the burner insertion
bore 32~
Although not shown in the drawings, such oxygen-fuel
burner 3 is provided with a movable frame which can be
freely moved forward (advanced) and rearward (retracted),
a mechanism adapted to drive the movable frame and driven ~ -
in advancing and retracting movements by a motor, and ~ -
related parts. The burner 3 has a fixed flange 37 at a
specific position of its rear part and a movable, ring- -
shape sealing plate 38 slidably fitted around the burner
and forward of the fixed flange 37. This sealing plate
38 is connected to the fixed flange 37 by way of a com-
pression coil spring 39 disposed therebetween and around `-
the burner 3 and can thereby retract while still retain- -
ing an elastic force for forward sliding movement when
it is pushed from the front.
The oxygen-fuel burner 3 with its accessory parts
',''' ''' '-
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466
of the above described construction is mounted into
operative position as follows. ~he burner is advanced,
` and its for~ard end is inserted into the burner insertion
bore 32. ~hen, as the distance of this insertion of the
burner increases, the sealing plate 3~, which has con-
tacted and been stopped by the outer end of the inner
water frame 30, is pressed with increasing force against
the outer end face of the water frame 30 and thereby
tightly seals the gap between the burner 3 and the inner
water frame 30. The resulting state of these parts is ~.
indicated by two-dot chain line in ~IG. 6. ~
With the above described parts in the stated state,
. a flame is injected from the front end of the burner 3. -:
i Consequently, the front end of the burner 3 is subjected
to great heat due not only to the heating of the burner
itself but also the reflected heat of the combustion
. materials, the heat of radiation from the molten steel,
and other sources, but it is cooled by the cooling water
flowing through the inner water frame 30. ~urthermore,
the inner water frame 30 and the furnace wall 2 in its
part surrounding the burner mounting parts are cooled by
~ the cooling water flowing through the outer water frame : ~ .
31. Accordingly, the parts of the burner 3 and the fur- .
nace wall 2 sub~ected to great heat are amply cooled and - .
maintained in a safe condition. `.
Still another safety feature of the above described ~ -.
burner mounting is that, since the gap between the inner .~
water frame 30 and the burner 3 at the bore 32 is tight- :
ly closed by the sealing plate 38, blowing out of the
"~ ~
_ ~o - - . .
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';' .
, ~ . . . .. . ... . . . ... . . .. .
10~466
fire and heat within the furnace is, of course, prevent-
ed, and there is no leakage out of noise generated in
the furnace.
1-5. Burner performance and other paxticulars
When the special oxygen-fuel burners 3 are in- - -
stalled in an arc furnace, the standard and maximum
quantities of consumption of fuel oil, oxygen, and air
for producing one ton of molten steel with high effective-
ness are as set forth in TABLE 1.
~ABLE I. Consumption of oil, oxygen, and air in
arc furnace operation with special oxygen-
fuel burners
fl 'Standard consumptlon Maximum
. uld consumption
, , __
Oil 600 l/t 8.0 l/t ~ :
Oxygen35 Nm3/t 55 Nm3/t
(28 Nm3/t for burner) (42 Nm3/t for
burner)
Air 2~0 Nm3/t 2.5 Nm3/t
. ., . . __ . . _ . - - ., ,:
- . -:
As one example, the particulars of an example of
our experimental operation with high efficiency of an .- ~
arc furnace of 50-ton nominal capacity in which the ~: :-
instant special oxygen-fuel burners are used set forth ~- -
in TABLE 2. The particulars of a special oxygen-fuel ~-
burner are shown in TABLE 3. :-
..~
-.: -
, . ''''-' ~
- 21 -
'' -
~
~4 6tj
TABLE 2
h ~ ~ ~ ~ ~ o ~ ~G i~
E E E I E ~ o ~; E o E , ~ ~ ~ E 1,
1 2398 614145 14 8 107' 52,300 49,260 291 5.9 2040 41.4 17,700 3592 2399 72ll46 13 6 105 52,580 49,460 268 5.4 2020 40.8 16,000 335
3 2400 826 48 13 6 107 53,200 48,280 272 5.6 2180 45.o 16,300 337
4 2401 933 50 12 7 109 52,640 47,020 287 6.1 2080 44.2 15,900 338
5 2402 1042 47 11 8 106 53,460 47,920 278 5.8 1850 38.6 16,400 344
6 2403 1148 50 13 6 109 52,935 49,460 273 5.5 2130 43.1 17,100 346
7 2404 1257 48 12 6 106 52,820 47,130 277 5.9 2110 44.8 16,600 352
8 2405 1403 48 14 811lo 53,100 49,180 291 5.9 2290 46.6 16,600 337
i~9 2406 1513 51 lo 6 107 52,5&0 49,o80 311 6.3 ~270 46.3 17,200 350
o 2407 1620 43 12 7 102 52,510 48,130 310 6.4 ~280 47.4 15,100 314
1 2408 1722 48 12 5 105 52,660 47,500 308 6.5 2210 46.5 16,200 341
`12 2409 1827 46 13 7 106 52,760 50,o80 338 6.8 2300 45.9 16,300 326
13 2410 1933 43 lo 7 1oo 51,180 48,100 312 6.5 2020 42.0 14,700 306
14 2411 2033 47 11 6 104 52,540 49,520 312 6.3 2250 45.4 15,500 313
15 2412 2137 52 13 6 1ll 52,120 49,390 295 6.o 2270 46.o 16,400 332
16 2413 2248 47 15 6 108 52,580 49,790 252 5.1 2200 44.2 16,600 333
17 2414 23O55149 12 6 107 52,640 49,480 296 6.o 2350 47.5 16,100 325
1812415 104~50 13 6 109 51,960 47,490 265 5.6 2260 47.6 16,200 3419 2416 212 48 14 6 108 52,200 48,580 277 5.7 2380 49.o 16,200 334
20 2417 317 47 12 6 105 51,940 47,350 280 5.9 2300 48.6 16,200 343
21 2418 426 51 12 6 109 52,420 48,680 295 6.1 2360 48.~ 15,400 338
22 2419 5 36 52 11 7 1 lo~ 4B,670 296 6.1 2320 47.7 15,300 315
Average 48 12 6 1 07 52,520 48,616 290 6.o 2191 45.1 16,250 335
. .... _ ......... _ _ _ .................. .. _ .. _ .
- 22 -
lQ~66
TABLE 3~ Particul~rs of oxygen-fuel burner
. ._ . . . _ j i
Particular Numerical
. . _ .. . .~
Dimenslons of burner bod~
Burner cylinder length 650 mm.
" " outer di~mo 665 mm.
Oil supply pipe diam. 10 mm~
Oxygen " " " 5 mm.
. _ ...
Fluid suppl~ capacities
Fuel oil 1 Max. 500 l/hr.(at 2kg/cm2)
Oxygen -i Mc~x.l,OOONm3/hrO
l (at 7kg/cm2)2
Air Max.150 Nm/hr.(at 4kg/cm )
. _ . . . ----_ ,;
t Burner bod~ stroke
~ength inserted in furnace 250 mmO
~ength retracted out of 600 mm.
furnace _
_ - -
'' .''' '
2. Furnace Wall and Roof
In the operation of the steelmaking apparatus of the -~ -
invention, the above described special oxygen-fuel bur-
ners are used to inaect high energy generated by the
combustion of the fuel oil into the arc furnace thereby -
to cause the steel scrap to melt rapidly. For carrying
out this operation over a long period in a stable manner,
the wall 2 and roof 4 of the arc furnace 1 must have
ample resistance to withstand the high heat. This inven- ;
tion provides a solution to this problem by the use of
- 23 -
, , ,
~Q~4~66
, . .. .
special innovations in the furnace wall and roof refrac-
tories, themselves, and in their construction as describ-
ed below.
2-1. Furnace wall refractories
~ he furnace wall 2 of the arc furnace in the
apparatus of the invention has a construction in which,
essentially, special carbonaceous bricks and water-
cooling means are combined and assembled in a sandwiched
state of several tiers.
In general, the furnace wall of a furnace which has
the object of melting metals must have excellent resis- -
tance to fire and to erosion, heat insulative property,
and high strength at high temperatures. While this is
true in other reheating furnaces, in a steelmaking fur- -
.. , ~
;~ nace intended for producing steels from steel scrap as
~ raw material, there is a particular necessity for excel-
.... . . .
?` lent resistance to damage such as spalling of the furnace --
~ brick faces.
, .... .. .
For meeting these requirements, the use of carbo~
~` naceous bricks formed as matrixes by applying carbon to
~` a refractory material such as magnesite as an aggregate
and having a softening temperature of 1,500 to 1,900C,
~i resistance to heat and spalling, and strength at high -~
~c temperatures which a~e all for superior to those of
`,"?~, other furnace wall bricks is known to be effective. -
; Carbonaceous bricks, however, are accompanied by certain -
difficulties such as a lowering of resistance to slag
attack at high temperatures and a high value of thermal
conductivity which is nearly 10 times that of an ordinary
.~ .
- 2~ -
'~,'
, f
,: ,.. . . . . . . . .
10~6~
firebrick.
In accordance with this invention, the arc furnace
wall comp~ises furnace wall refractories in which the
characteristic of high thermal conductivity of carbonace-
ous brick, conversely, is utilized to good advantage to
provide superior shall refractories of the arc furnace
for steelmaking having the combination of excellent
resistance to heat, resistance to slag attack, and high
strength at high temperatures. More specifically, the
furnace wall rising from a point slightly above the slag
line in the arc furnace is formed from carbonaceous
brick, and, moreover, a number of tiers of water cooling
means are arranged in a state wherein the carbonaceous
bricks are interposed and sandwiched therebetween. By ~
this construction, excessive temperature rise of the ;
carbonaceous bricks themselves is prevented, whereby
the resistance of the carbonaceous bricks to slag attack
is increased, and only the other desirable characteris-
tics of these bricks are effectively utilized.
These carbonaceous bricks used in the practice of
this invention have a carbon content higher than 99 per-
cent, a porosity of 28 to 29 percent, a bulk density of
1.5 to 1.6, and a thermal conductivity of 120 to 150 -
kcal./m.h.C.
Referring to FIG. 7, the arc furnace l shown there-
in has an upper furnace wal1 2 rising from a level ap-
proximately 200 mm~ above the slag line 40 and made of
carbonaceous bricks. This furnace wall 2 contains a
plurality of tiers (three in the illustrated example)
- 25 -
,; , , -, , . . , , :
66 :`:
of built-in water-cooled boxes 41, the lowest tier being
disposed 300 to ~00 mm. above the slag line 40 and the
other tiers being successively distributed upwardly
therefrom with spacing intervals of the order of 300 mmO
In the case where the -thickness of the furnace wall
2 is of the order of 350 mmO, for example, each water-
cooled box 41 is formed with a dimension parallel to the ~ ` `
thickness direction of the furnace wall 2 of the order - `
of 200 mm. and a height of approximately 130 mm. and is
disposed nearer to the outside surface of the furnace ` `
wall. In one example of this water-cooled box 41 in-
stalled in a furnace wall of a thickness of the order
of 350 ~m~l. (thickness of -the carbonaceous bricks) and
having a cross sectional dimensions of approximately
130 x 200 mm., cooling water was supplied under a pres- `~
sure of 2 kg/cm2, and its flow velocity withln the box
was from 9.5 to 10 mO/min~ The reason for this is that,
by using n lar~o ~re~l of contact with the carbonaceous
bricks to increase tho cooling effect and thereby to
reduce the ef~ect on the atmosphere within the furnace,
~md by constantly maintaining the cross-sectional area
of the box 41 less than 0.03 m in order to facilitate ~
brick breaking and dressing in the brick laying work "
and the flow velocity within the box above 8m./minO,
the objec-ts of this invention can be achieved.
Furthermore, in each tier, the water-cooled box 41
may be in the form o~ ~ single, ring-shaped, con-tinuous
structure or it may be divided along the circumferential
direc-tion into 3 or 4 blocks, each of which is supplied
~ "'`
- 26 -
.
:. ~
66
therethrough with cooling water circulnted through cool-
ing water inlet and outlet pipes connected thereto. ~y
thus dividing the water-cooled box 41 in each tier as
in the latter arrangement, it is possible to facilitate
the work of maintenance and replacement in cases when
defects such as water leakage occur.
While, in the ex~mple illustrated in ~IG. 7, three
tiers of the water-cooled boxes 41 are used, and the box
41 in each block is divided into 3 blocks, the number
of tiers (e.g., 2 or 4) and the number of divisions
(eOg., 2,3, or ~) of the water-cooled box in each tier
can be suitably selected according to factors such as
the size of the arc furnace.
By passing cooling water through the water-cooled
boxes 41 within the furnace wall 2 of the above describ-
ed construction, the furnace wall is cooled because of
the high thermal conductivity of the carbonaceous bricks.
Accordingly, heating of the carbonaceous bricks to a
high temperature is prevented, and damage accompanying
the adherence of metal oxides such as iron oxide cannot -~-
readily occur. At the same time, the furnace wall 2
retains and can fully exhibit high resistance to heat,
high resistance to spalling, and high strength at high
temperatures which are the adv~ntageous characteristics
of carbonaceous bricks. Thus, this steel-making arc
furnace has high overall performance.
As one example, we have carried out a series of ex-
periments with an arc furnace of a nominal heat size of
50 tons in which carbonaceous bricks and water cooling
' ~: ,-
27 - ~
... . . .. . .
10~ 6
means are combined in the furnace wall, and which ~as
operated with high efficienc~ with the use of three
special oxygen burners. As a result, the furnace wall
was found to have a serviceable life of 240 heats at
the part of the furnace wall hot spot where the distance
between an electrode and the furnace wall is the short-
est, and a total life of 1,440 heats when this part was
repairedO It was also found that the brick unit con-
sumption of the furnace wall over the last six months
by this process was less than 1.8 kgO/ton. This is an
excellent result, which is 1/2 to 1/3 of the brick unit
consumption in the case of bricks used conventionally. -
2-2. Furnace roof refractories
~ he furnace roof of the arc furnace used in the
practice of this invention must be made up of furnace
roof refractories which can withstand high temperatures
and have long serviceable life in order to make possible
stable and efficient operation of the arc furnace over
a long period. For this purpose: steel-cased, magnesite-
chro~e bricks are used for the refractory material in the
outer peripheral part of the furnace roof; high-alumina
(A1203) ramming mass is used in the central part of the
furnace roof around the electrode insertion holes; and
a water-cooled ring is provided at the exhaust hole where
the damage and loss of the refractories are the most
severe in furnace roofs of this class, high-alumina ram-
ming mass being formed around this ring. -
In ~eneral, for the furnace roof refractories of an
arc furnace for steelmaking, silica bricks (more than
- 28 -
104~ 6
96 % silica) and bauxite bricks, which have excellent
heat resistance and stren~th at high temperatures and
are relatively inexpensive, have heretofore been used.
However, as the aforementioned U.H.P. process and as-
sisted combustion process were developed, ~nd high energy
c~e to be injected into the furnace, the durability of
the conve~tional silica brick bec~me deficient, and, ac-
cordingly, it has become the practice to increase the
alumina content in the brick or to adopt magnesite-chrome
brick. In spite of these measures, however, when a dust
collector of direct evacuation type is additionally used
for improving the environment of the steel mill and its
surro~mdings, it has not been possible to avoid a drop in
the life of the furnace roof refractories due to melt
damage to the peripheral region of the exhaust hole in
the furnace roof in the prior art. ~-
In accordance with this invention, it is possible
to increase the durability of the furnace roof and achieve
the original objects of the invention by providing a new-
ly devised water-cooled ring as described below at the
exhaust hole in the furnace roofO
More specifically, as shown in ~IG~o 8 through 11,
the above mentioned novel water-cooled ring in the furnace ~
roof 4 has a water-cooled ring body 42 installed by a ~ -
method which, differing from the conventional method of
installing on the furnace roof refractories after com-
pletion of their assembly, comprises installing the ring -
body 42 in imbedded state in the refractories and fixing ~ ~ -
the same with a bolt 45 by way of a bracket 44 to a
- 29 ~
66
furnace water-cooled roof ring frame ~3, the structure
surrounding this water-coolcd ring body 42 being formed
with high-alumina ramming mass 460 The water-cooled
ring 42 is provided with a cooling water supply pipc 47
end a water discharge pipe 48 connected thereto.
Heretofore, the refractories of the furnace exhaust
hole have been subject to damage and expansion of the
hole due to the passage of high-temperature gas from the
furnace interior until they become unable to withstand
further use, where the serviceable life of the entire
furnace roof also is reduced. According to this inven-
tion, however, the use of the water-cooled ring 42 makes
it possible to prevent a reduction in the furnace roof
life due to expansion of the exhaust hole and thereby
to prolong the life of the entire furnace roof.
In one instance of testing, in which a furnace roof
4 according to this invention was mounted on a 50-ton -~-
arc furnace, and high-efficiency operation of the furnace
was carried out, the life of the high-alumina ramming
mass at the central part of the furnace roof was found
to be from 120 to 130 heats, and the life of the part
of the steel-cased, magnesite-chrome brick at the outer
peripheral part and the exhaust hole provided with the -
water-cooled ring 42 was found to be from 240 to 250
heats. ,
Accordingly, if the central part of the furnace -~
roof 4 is rebuilt after 120 to 130 heats, the life of
the entire furnace roof will be from 240 to 250 heats.
In comparison with this, when a water-cooled ring is
- 30 -
. .
lQ~66
installed on fire-bricks after the bricks have been laid,
as in the convention procedure, the life of the exhaust
hole is from 100 to 120 heats. If the refractories of
this part are removed together with the central part,
the other magnesite-chrome brick parts will also fall
off, and the life of the entire furnace roof will be no
different from those of the central part and the part
of the exhaust hole.
3. me ~
In order to elevate the combustion efficiency of
the special oxygen-fuel burners, ~he re~llation of the
pressure within the arc furnace during its melting oper-
ation is indispensable. As a result of our stud~, we
have found that this combustion efficiency is elevated ` -
by maintaining the furnace interior at a negative pres-
sure in the range of from -0.5 to -2.5 mm. H20.
We have found that if this pressure is higher than
-0.5mm. H20, the quantity of air drawn into the fu~nace
from the outside will be small, whereby the combustibles --
charged together with the cold charge of scrap and the
like will not be sufficiently combusted, and the thermal
..
efficiency of the burners will drop remarkably. If the
pressure within the furnace is above atmospheric pres-
sure, flames will be ejected from openings in the furnace. - -
On the other hand, if the pressure is less than -2.5 mm.
H20, the quantity of infiltrating air will be large,
whereby the erosion of the electrodes and the furnace
wall will become severe, and, at the same time, since
high-temperature gas is discharged through the exhaust
" ~
- 31 -
:.
~.
~~4Y~
hole, there will be increased possibility of pro~lems
relating to the exhaust hole and the fume evacuation
systemc Accordingly, for the above stated reasons, the
fume evacuation system of the invention is of a direct-
suction type capable of maintainin~ the pressure within
the furnace of from -0.5 to -2.5 mm. H20.
In order to increase the combustion efficiency of
the special oxygen-fuel burners 3, the pressure within
the arc furnace at the time of steel meltin~ is always
caused to be nega~ive, and air is drawn through openings
such as the slag door into the furnace. Accordin~ly,
the fume evacuation system used in the practice of this
invention, in this sense, must be a fume evacuation
system of direct suction type. -
As one example, an example of determination of the
capacity (volume of treated gas) of a fume evacuation
system installed in conjunction with an arc furnace of ~ -
50-ton nominal capacity rating will be considered. This
furnace was provided with the special oxygen-fuel bur-
ners, furnace wall lining, water-cooling devices, and - -~
other unique features for long life as described above,
and which was operated with high efficiency as the -
principal component of an integrated steelmaking appa-
ratus and with the operational technique of the
invention. -
This arc furnace had a shell of an inner diameter
of 5.1 meters and a transformer capacity of 22,000 kVA. -
and was provided with three special oxygen-fuel burners.
The basic operational specifications of this furnace --
- 32 -
~ , . . .
66
designed for an oil unit consumption of 6 liters/ton
(of steel), an oxygen unit consumption of 35 Nm3/ton
(28 Nm3/ton ~or burners only), an (electric) power unit
consumption of 360 k~H/ton, and a tap-to-tap time of 1
hour lO minutes.
It will now be assumed that the other combustibles
(e.g., oil, grease, and other combustible matter adher-
ing to the steel scrap) introduced into the furnace at
the same time as the fuel oil injected thereinto through
the burners and the steel scrap, coke for blending and
recarburizing, and other matter are completely burned ~ -
with the oxygen injected at the same time through the
burners during the steel melting period to become C02,
H20, and other products, any lack of oxygen being sup~
plied by the oxygen in the infiltrating air introduced
into the furnace interior through openings such as the
slagging door thereb~ to effect complete combustion. ~-
r~hen, the total quantity or flow rate of the exhaust
gas from the furnace becomes approximate]y 375 Nm3/min.,
and the temperature thereof is estimated at approximately i~;
1,300C. This high-temperature gas is permitted to mix
with air drawn in through gaps between the water-cooled
suction elbow and water-cooled duct and air drawn in
through other openings in the water-cooled ductso r~o
obtain a ~sulting mixed gas of a temperature of 600C,
an infiltration rate of air of approximately 600 Nm3/min. -
is required. r~herefore, the total required suction rate
becomes 975 Nm3/min. ~or a processing temperature of ~ ;
250C, this total rate becomes approximately 1,870 m3/min.
- 3~ -
,
Furthermore, a gas cleaning system comprising bag
filters is used in the instant fume evacuation system.
~he fil-ter bags are of silicone-treated fiber and are
cleaned periodically by reverse flow of cleaning air of
approximately 300 m3/min. This flow rate added to the
above total results in a total flow rate of approximately
2,170 m3/min. as the total vol~etric flow rate of ex-
haust gas to be treated, i.e., the processing capacity
of the fume evacuation system. ~rom this result, and
with some allowance for increase in required capacity,
the design capacity was selected at 2,200 m3/min (at
250C).
4. Example of Practice
A specific exam~le of practice will now be described ~ -
in detail with respect to an example of a steelmaking ~
apparatus according to the invention including a 50-ton ~ -
arc furnace of the following particulars.
4-1. High-efficiency melting
~ he particulars of the instant arc furnace are
set forth in ~ABLE 4. In this furnace, three special
oxygen-oil burners each of the character indicated in -
~ABLE 3 were used. ~he constructional features of this
furnace and related parts were as set forth hereinabove,
and a fume evacuation system of the particulars set forth ; -~
in TAB~ 5 was used.
- 34 -
~ ;
.. . . . ....
4~6
TABLE 4. Particulars of 50-ton arc furnace
¦ Component Item j Specification
j
Furnace structure --
Nominal capacity50 tons
Charge quantity (actual) 54 tons
¦ Shell inner diameter5,100 mm.
Shell height 3,635 ~m.
Depth of molten bath850 mm.
Furnace internal volume 40 m3.
- ._ .-
Transformer --
Capacity 22,000 kVA.
Primary voltage 22 kV ,~
Secondary voltage145 - 400 V
Rated secondary voltage 366 V
Rated current 31,700 A
_ : .
Electrodes -- -
Diamter18 in.(457.2 mm)l
_ __._ .... . _ . ! : :.
TABLE 5. Particulars of fume evacuation system
.
Item ~pecification , -
~ . .. .-
Type of suction Top-of-furnace, direc-
suction type
Type of filter Bag filter type
Gas quantity to be 22,000 m3/ min (at 250C) -
treated
Filtration area 3,000 m2 (approx~)
Fan motor 450 kW, 1,200 rpm.
- 35 ~
lO~
The arc furnace specified in Table 4, as jud~ed
from its transformer capacity, falls within the range
of high-powered processes but, as a furnace of this
character at the present time, is on the lower side of
this range. ~Iowever, by the high-efficiency operation
and the apparatus according to this invention the steel-
making time (tap-to-tap) can be shortened to one hour.
With two of these arc furnaces the production per year
of continuousl~ cast billet is approximately 600,000 tons.
In general, the productive capacity of an arc fur- -
nace can be expressed by the number of heats per day
(24 hours). However, the capacity of an arc furnace of
a nominal rating of the order of 50 tons is ordinarily
8 to 10 heats per day, and even in the case where a
high-efficiency measure such as the use of a U.H.P. pro-
cess or the ~.O.S. process is resorted to, it is estimat-
ed to be from 12 to 14 heats per day. We have found that -~ -
by the process and apparatus of this invention, however,
this performance is from 20 to 22 heats per day of conti-
nuous operation over a long period.
While Table 2 indicates the performance resulbis of
operation through one day, many unique characteristics
can be observed from this table. For example, the steel-
making time (tap-to-tap) is a minimum of 1 hour, a maximum -;
of 1 hour 11 minutes, and an average of 1 hour 07 ~inutes,
which are very short. In addition, it is to be observed ~1
that the quantity of oxygen consumed is 45.1 Nm3/ton,
which is very large, that the quantity of fuel conisumed
is leiss than that of o~ygen, and that the electric power
;
- 36 -
- ~
66
consumption is 335 KWH/ton, which is very low.
~ hree special oxygen-oil burners are installed in
this arc furnace as described hereinbefore, and a unique
characteristic of their operation is that the quantity
of oxygen is very large in comparison with the consump-
tion of the fuel. More specifically, the theoretical
quantity of pure oxygen required for complete combustion
of one liter of fuel oil is approximately 2.2 Nm3. How-
ever, according to the actual performance results, 36.5
Nm3/ton, which corresponds to approximately 80 percent
of the total oxygen quantity of 45.1 Nm3/ton, is used in
the burnersO This means that oxygen of a quqntity which
is approximately 2.8 times the theoretically required
oxygen quantity is used in the burners. From the de- -~
scription set forth hereinbefore, it can be seen that ~
this excess oxygen is ~eing consumed for melt cutting of `
the steel scrap due to oxidation reaction directly with
the steel scrap and for causing combustion of combustibles
(e.g., oil adhering to the steel scrap) introduced to- -
gether with the steel scrap into the furnace. The remain-
der 20 percent of oxygen of the total oxygen quantity is
consumed for lancing carried out at the time of cutting
and oxidizing refining of the steel scrap by means of ~ -
lancing pipes through slagging and inspection doors as
is carried out also in the operation of an ordinary arc ~ .
furnace.
While the power supply unit in the operation of an
ordinary arc furnace, in general, is from 500 to 550 KWH/
ton, that in the instant performance result is 335 KWH/ton,
- 37 -
~04446~
which is very low. ~he only explanation for this is that
the heat of combustion of the fuel oil and the heat of
oxidation due to the excess oxygen of and the afore- ;
mentioned combustibles introduced together with the
steel scrap are contributing to the melting of the ~teel
scrap, the excess oxygen also contributing to the melt
cutting of the steel scrap.
4-2. Example of heat balance analysis
In general, the power unit consumption in the case
where an arc furnace is operated in a very ordinary state
is from 500 to 550 KWH/ton. Of this, the power consumed
for only the melting of the steel scrap during the melt-
ing period is of the order of from 410 to 440 EWH/ton,
and the remainder power of 90 to 110 KWH/ton is the power
consumed subsequent to melting, that is, in the refining
period.
However, in the example of actual performance in
~able 2, this power unit consumption is set forth as
335 kWH/ton. In this case, the power consumed for only -
the melting of the steel scrap is 278 kWH/ton, and a
power of 57 KWH/ton is consumed in the refining period. ~t
When the quantity of power consumed in the melting period
is considered, the difference, 132 to 162 KWH/ton, bet-
ween the above quantity and that consumed in the melting
period in an arc furnace operated in an ordinary state
is comparable to the total of the heat of combustion of ;
the fuel oil, the heat generated when the steel scrap is
melt cut by excess oxygen, and the heat of combustion of
the other combustibles introduced simultaneously with
- 3~ ~
.:
1~4~466
the steel scrap into the furnace.
More specifically, the oxygen consumption for ac~
B complishing complete combustion ~ ~liters/ton of oil is ~ ;
approximately 13 Nm /ton, and the heat thus generated is
59,400 Kcal/tonO ~urthermore, the total oxygen quantity
used in the burners is 36.5 Nm3/ton, and ~hen the oxygen
quantity required for combustion of the fuel oil is sub-
tracted from this, an oxygen quantity of 23.3 Nm3/ton
remains. When 40 percent or 9 Nm3/ton of this remainder
is assumed to be consumed for melt cutting of the steel
scrap, while 60 percent or 14.3 Nm3/ton thereof is as- --
sumed to be consumed for the combustion of the other
combustibles introduced together with the steel scrap
into the furnace, the generated heat quantity of the
former becomes 51,813 Kcal/ton, while that of the latter
becomes 16,874 Kcal/ton.
~ he total of these generated heat quantities due
to the fuel oil and the excess oxygen then, becomes
128~087 Kcal/ton, which becomes 149 KWH/ton when convert-
ed into electric energy. Accordingly, it is observable
that there is a substantial agreement between this and ~ -
the difference of 132 to 162 KWH/ton in the power unit -
consumptions of the actual performance result shown in
Table 3 and the arc furnace operated in the ordinary --
state. Thus, it is apparent that the special oxygen-
fuel burners of this invention accomplish a great func-
tion in promoting the melting of the steel scrap.
~ urthermore, in the refining period an oxygen quan-
tity of 8.6 Nm3/ton, which results from the subtraction
_ ~9 -
. :.
.. .. ... . ..
466
of the oxygen quantit of 36.5 Nm3/ton used in only the
burners from the total oxygen quantity of 45.1 Nm3/ton
in Table 2, is blown into the molten steel bath, there-
by serving to promote agitation and decarburization of
the molten steel. However, in the operation according
to this invention, the carbon content in the molten
steel bath in the initial part of the refining period
is of the order of 0.2Q percent, and the greater part
of the oxygen blown into the molten steel is used in
its oxidation reaction with ~e.
A characteristic feature of this invention, however,
is that, since high power is charged into the process
as oxygen is blown into the molten steel bath thereby
to force a temperature rise, the heat of oxidation of
Fe contributes directly, as it is, to the rise of temper-
ature. The heat of oxidation of ~e by 8.6 Nm~/ton of
oxygen becomes 49,540 Kcal/ton, which corresponds to
57.6 k~H/ton. Therefore, the contradiction of the power
unit consumption for the refining period being a low --
value of 57 EWH/ton can be accounted for.
4-3. ~urnace wall refractories ~ -
As mentioned hereinbefore, when a large quantity ~-
of thermal energy is introduced in a short time into an
arc furnace, heat damage becomes rapid in furnace wall -
bricks made of magnesite or magnesite-chrome material -~
which were heretofore used, and the furnace wall bricks
c~nnot withstand this kind of operation. ~ecause of the ;~
need for repairs, the practice ratio of the furnace - -~
drops. This has been considered to be problem
_ 40 -
", , , . , - " . ~ . . ~. , ~ , . . - ~ -
.
1044466
accompanying the aforementioned U.H.P. process and the
FoO~S~ process, and this is problem encountered also in
the practice of this invention.
According to this invention, however, this problem
has been solved by the use of a furnace wall lining
developed on the basis of a totally new concept of com-
bining carbonaceous bricks and water-cooled means as
described hereinbefore. In the aforedescribed arc fur-
nace of 50-ton nominal capacity, in which high-efficiency
operation is carried out with three special oxygen-fuel
burners, the improved lining is used over the entire
furnace wall between a line approximately 300mm. above
the slag line and a line approximately 700mm. below the
upper end of the furnace wall. As a result of an ex-
periment carried out recently over 6 months, the unit
consumption of all furnace wall ~ricks was 1.8 kg~/ton,
and the unit consumption of only the carbonaceous bricks -
was 1.2 k~./ton. In this case, the serviceable life of ~ -
parts of the carbonaceous bricks varied with location,
and repairs were carried out by partially interchanging
the carbonaceous bricks, whereupon a life of 1,440 heats
was obtained as a whole. - -
4-4. Furnace roof refractories -
The furnace roof refractories have been de~e-
loped in exactly the same manner as the furnace wall
refractories. When silica bricks (more than 97 percent
silica) or bauxite bricks of known character were used, --
they could not withstand the introduction of high energy
into the furnace and c~me to be replaced by basic bricks
- 41 ~
1~)4~466
or high-alumina bricks. However, in an arc furnace
provided with a fume evacuation system of the direct
suction type, a fume exhaust hole for drawin~ off ex-
haust fumes out of the furnace must be installed as
a fourth openin~ in addition to the holes for three
electrodes.
The refractories in the re~ion surrounding this
fourth opening are subjected to severe mechanical and
physical damage due to the high-temperat~re exhaust
fumes flowing past these refractories, and the life of r;
furnace roof refractories have been extremely short
even in the conventional arc furnaces.
Accordingly, in accordance with the present inven-
tion, this problem is solved by installing a metal water-
cooled ring as described hereinbefore around this fourth
opening and arranging xefractories of the character
previously described, whereby we h~ve succeeded in great-
ly prolonging the furnace roof life. In the aforede- ~-
scribed arc furnace of 50-ton nominal capacity having
a furnace roof provided with a water-cooled ring, per-
formance results as described hereinbefore were obtained. ~
That is, the life of the furnace roof as a whole was --
found to be from 240 to 250 heats, which is more than
twice that obtainable by the prior art.
4-5. Fume evacuation system
In the practice of this invention with the object
of accomplishing efficient operation of an arc furnace
provided with the special oxygen-fuel burners, the fume
evacuation system has an extremely important and
' ''
- 42 -
. .
104~4Y;6
indispensable function. More specifically, in order for
the special oxygen-fuel burners to accomplish combustion
in an effective manner, it has been found necessary to
maintain the interior of thc furnace continually under
negative pressure throughout the scrap melting period
during which these burners are used and thereby to lead
the air infiltrating through gaps in the slagging door
and the like into the furnace interior. This uni~ue
feature constitutes a vital point of know-how in the
technology of this invention.
In one example of efficient operational of the afore-
described arc furnace of 50-ton nominal capacity provided
with the special oxygen-fuel burners, the steelmaking
apparatus according to the invention included a fume
evacuation system of the specifications set forth in
~able 5. ~he v~lue of 2,200 m3/minO (at 250C) of the
quantity of exaust gases to be treated, determined in
the manner described hereinbefore, is greater than that
in the case of a general type of 50-ton arc furnace.
In this direct evacuation t~pe dust collector, exaust `- -
fumes are drawn out of the arc furnaoe through the fourth h - -
opening, that is, the opening for evacuation in the fur~
nace roof, pass through a double-pipe type, water-cooled
suction elbow made of steel, and arc conduc-ted through ~
a water-cooled duct to a double-pipe type, water-cooled -
combustion chamber. A sliding type double-pipe water-
cooling pipe is interposed between the suction elbow -
and water-cooled duct. By causing this pipe to slide,
the infiltration of secondary air through the gap between
;
- 43 -
1044466
the suction elbow ~nd the duct is held at a minimum.
~ or this reason, o~ the incompletely burned gases
drawn out of the furnace, incompletely combusted CO gas
under-goes combustion with air drawn in through the top
of the vertical combustion chamber, and, at the same
time, with an even greater quantity of cool air, the
temperature of the exhaust gases is lowered. ~he gases
which have passed through the combustion chamber are
further passed through a double-pipe, water-cooled duct
and cooled to approximately 300C by a gas cooling tower
of vertical, indirect water-cooled type installed out-
side of the melt shop. Thereafter, the gases thus cool-
ed are passed through air-cooled ducts, continuing to
discharge heat until they reach the fan, and, upon reach-
ing a predetermined gas temperature, are sent into a
bag filterO
One example of actual measures of various numerical
values in the flowpath in this fume evacuation system
is set forth below.
The first important item is the velocity of the air
infiltrating through the slag door. ~his velocity was -
measured and found to be 4.8 to 5.5 m/sec. When this is
used in the following Eq. (1), the pressure within the
furnace is indicated as being from -1.0 to -2.0 mm. II20
v2 '.'
p = p , _ _ _ _ _ -- (1) "', ~'
.:
where: v is the gas velocity, m/sec.;
g is acceleration, m/sec .;
- 44 - -
.
,. , ., ,, . ~, . .. . .
p is air density; and
PP is pressure (mm. H20)
The results of analysis of the exhaust gases in the
vicinity of the outlet of the suction, constituting a
second important item, are shown in ~able 6. The sampl-
ing time was 6 minutes after the second charge.
~able 6 Composition of exhaust gas
Constituent Content (%)
.
2 0.
C2 25
CO 11 .',
Others 63.7
'" '" . '
At this time, the flow rate and temperature of the
exaust gas ;mmediately in front of exhaust fan, consti- -
tuting a third important item, were 1,180 m3/min. and ~ -
180C., respectively. The operation pattern of the time -
of measurement of the instant perfo~mance is indicated
in Fig. 12. That is, this pattern is that of Heat No.
2,400 indicated in Table 2.
As set forth in Table 2, the particulars of this
heat are: an oil consumption of 5.4 l/ton; an oxygen -~
consumption of 45.0 Nm3/ton (of which the quantity of -
oxygen used in the burners was 36 Nm3/ton); a melting
period of 48 minutes (during which the burners we~e used
three separate times for a total of 36 minutes); a refin-
ing period of 13 minutes; a tap-to-tap time of 67 minutes - -
- 45 -
, :, , . ^ . , , , , ~
.
66
(1 hr. 07 min.); and a power unit consumption of 3~7
k~H/ton~
When, from these results of performance, consider-
ation is added to this direct suction type dust collector,
the carbon of the fuel oil blown into the furnace through
the burners, of the combustibles introduced together with
the scrap into the furnace (on the assumption that 1.5
percent of oil is adhering to turning scrap blended in
a quantity of 25 percent), of the electrodes, of the
carbonaceous bricks, of a recarburizing agent, and of
like materials is transformed into CO and CO2 by the
oxygen injected from the burners. Any deficient 2 is
made up by the oxygen in air infiltrating through open-
ings such as the slagging door, whereupon CO and CO2 -
gases are similarly formed, the ratio thereof being 11
versus 25. -
Furthermore, the quantity of 63.7 percent of "Others"
in Table 6 may be considered to be N2 gas. ~hen, a
balance is established between the total quantity of
exhaust gas, the quantity of the oxygen blown in, and
the quantity of air which has infiltrated. ~he quantity
of the 2 in the gas immediately after being discharged
from the furnace is very low, being 0.3 percent below the
actual performance result. ~his indicates that the
introduction into the furnace of air infiltrating through
the slagging door in order to elevate the combustion :~
efficiency of the burners as emphasized in this invention
does not rise to an excessively oxidizing atmosphere
within the furnace. Moreover, it is apparent that a
,, .
- 46 -
66
steelmaking process according to this invention fully
exhibits high effectiveness in elevating the efficiency
of an arc furnace.
The determination of the performance capacity of
the fume evacuation system in the steelmc~king apparatus
of this invention can be calculated as described herein-
before, but we have discovered that there exists a speci-
fic relationship between the melting capacity (tons/hr.)
only during the melting period and the flow rate of the ~
exhaust gas (~m3/min.) of the arc furnace. More specifi- -
cally, in terms of the exhaust has flowrate A and the ~-,
melting capacity B, the following Eq. (2) is always
constant.
- = K , - - - - - - (2)
In this case, K is a constant. When the value of this -
constant K is substituted into the following E~. (3),
the resulting value V becomes the capacity (flow rate of
gas to be treated) of the fume evacuation system.
TK = V , - - - - - - (3)
here: V is the capacity (Nm3/min.) of the fume evacua-
tion system;
T is the steelmaking capacity (tons/hr.). -
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