Note: Descriptions are shown in the official language in which they were submitted.
5~
METHOD AND APPARATUS FOR MEASURING
SLAG-FORMING CONDITIONS WITHIN CONVERTER
,
- BACKGROUND OF THB INVENTION
(1) Field of the Invention
The present invention relates to a method and
apparatus for directly observing slag-forming conditions
within a converter used for steel refining.
(2) Description of the Prior Art
In refining molten pig iron and steel in a con-
verter, pure oxygen is ejected from a lance inserted
through the mouth of the converter into the converter
body (below "vessel"). The oxygen is blown onto the molten
steel to both effect decarburization and stir the molten
steel. In addition, flux is charged into the converter
to form molten slag, thereby effecting dephosphorization,
desulfurization, or the like due to the reactions
between the molten slag and steel.
Slag foaming occurs due to several slag conditions,
such as the slag composition, viscosity, the total
amount of oxygen in the slag, etc. ~oo extensive slag
foaming causes the slag and even molten steel to overflow
the converter mouth, which overflow is referred to as
"slopping". Of course, the composition of the molten
steel and the steel yield are greatly influenced by
slopping. Also, various problems are caused, such as
reduction in the operational efficiency and in the
calorific content of the recovered gases, impairment of
the operational environment, e.g., generation of brown
smoke, and damage to the steelmaking devices. Slopping
~ therefore must be suppressed as much as possible.
Various proposals have been made on how to enable
prompt prediction of the slag conditions within a
converter and hence realize optional converter operation
without slopping.
Japanese Unexamined Patent Publication (Xokai)
- 2 _ ~25~35~
No. 52-101618 discloses a method for estimating the
amount of slag by calculating the oxygen balance based
on information on the waste gases during blowing and
then estimating the amount of oxides formed in the
converter, i.e., the molten slag. In this method,
however, there is an unavoidable time delay due to the
gas analysis and mathematical analysis. In addition,
since slopping is not dependent upon just the amount of
molten slag alone, the accuracy of prediction of slopping
is not very high.
Various attempts have also been made on detecting
the slag level by physical means. These include an
acoustic measuring method (Japanese Unexamined Patent
Publication No. 54-33790), a vibration measuring method
(Japanese Unexamined Patent Publication No. 54-114,414),
a method for measuring the inner pressure of a converter
(Japanese Unexamined Patent Publication No. 55-104,417),
a method using a microwave gauge (Japanese Unexamined
Patent Publication No. 57-140812), and a method for
measuring the surface temperature of the converter body
(Japanese Unexamined Patent Publication No. 58-48615).
In the acoustic measuring method, changes in the
frequency and magnitude of the acoustics generated in
the converter are monitored to estimate the slag level
and to predict slopping.
In the vibration measuring method, changes in the
magnitude of lance vibration and the wave transition
of the lance vibration are monitored during blowing
to estimate the slag level or conditions and then to
predict slopping.
In the method for measuring the inner pressure of
a converter, variations in the ejecting pressure of the
waste gases through the converter mouth are monitored to
predict slopping.
In the method using a microwave gauge, a microwave
is directly projected into the converter interior to
directly measure the slag level based on the FM radar
~L2~ 6
-- 3
technique and to predict slopping.
In the method for measuring the surface temperature
of a converter body, the energy emission from the upper
and lower parts of the converter body in detected as
temperature, and the occurrence and magnitude of slopping
are predicted based on the temperature magnitude and
peak values.
The acoustic measuring method, vibration measuring
method, method for measuring the inner pressure of a
converter, and method for measuring the surface tempera-
ture of the converter body are all indirect measuring
methods and suffer from low accuracies of prediction of
slopping due to the inability to quantitatively measure
the slag level or conditions. The method using a micro-
wave gauge enables direct measurement of the slag level,but suffer from the fact that it is not easy to detect
or estimate abnormalities by microwave measurement,
since the melt, slag, gases, and the like effect
considerably complicated movement in the converter
during blowing. In addition, this method requires
sophisticated signal processing, which increases the
cost of the measuring device.
SUMMARY OF THE INVENTION
The present inventors recognized, as a result of
various studies concerning abnormal reactions in a
converter, that the occurrence of such abnormal reactions
is closely related to the slag-forming conditions, i.e.,
the foaming behavior of slag. The present inventors
studied the foaming behavior of slag and discovered that
the light intensity of the gaseous atmosphere and the
wavelength characteristics of light emitted from the
gaseous atmosphere considerably differ from those of
the slag. The present inventors discovered that they
could positively utilize such differences to detect the
foaming behavior.
The present invention provides a method and appa-
ratus for directly observing slag-forming conditions,
`` ~2~3~;~
i.e., the slag-foaming conditions, in a converter during
blowing, thereby allowing more precise and speedy
observation than in the prior art and contributing to
a highly accurate converter operation.
The method according to the present invention is
characterized in that at least one observation device of
the vessel-interior light is disposed in at least one
throughhole of the side wall of a converter so as to
face the vessel interior and observe the slag-forming
conditions.
The apparatus according to the present invention
comprises a light-detecting device including a receptor,
which receptor is disposed in a throughhole of the side
wall of a converter so as to face the vessel interior,
and a device for detecting the intensity and/or wave-
length of a light signal input from the light-detecting
device.
BRIEF DESCRIPTION OF DRAWINGS
In the drawings, Fig. 1 is a cross-sectional view
of a top-blowing converter, schematically showing an
embodiment of mounting a device for observing the
vessel-interior light on the converter;
Figs. 2A through 2C are cross-sectional views of
a converter, showing non-immersion portions of the
converter side wall;
Figs. 3A through 3C, Fig. 4, and Fig. 5 illustrate
the principle of the present invention, Figs. 3A through
3C showing the position of mounting the devices for
observing vessel-interior light and Figs. 4 and 5
showing time charts on the level of detected light
signals;
Figs. 6 and 7 are partial cross-sectional views of
a converter, showing different mounting structures of a
device for observing the vessel-interior light;
Fig. 8 is a schematic drawing of the arrangement
of the device for observing the vessel-interior light,
relative to the converter;
_ 5 _ ~2~3~;
Fig. 9 is a partial cross-sectional view of a
converter and a cross-sectional view of the device for
observing the vessel-interior light, which device is
gas-tightly inserted into a throughhole of the converter;
Fig. lOA is an overall view of a supporting platform
with a displacement mechanism;
Figs. lOB through lOE are partial views of the
supporting platform shown in Fig. lOA;
Figs. 11 (I), (I'), (II), (II'), (III), and (III')
illustrate the blowing conditions of a converter and the
operation of the device for observing vessel-interior
light according to the present invention;
Fig. 12 graphically illustrates the relationship
between the wavelength and intensity of light emitted
from the slag and gaseous atmosphere above the slag;
Fig. 13 illustrates an example of a vessel-interior
display, showing the variation in the surface-area
proportion with the lapse of blowing time;
Fig. 14 illustrates an example of the piping of
purge gas;
Fig. 15 is a partial cross-sectional view of an
example of a probe according to the present invention;
Fig. 16 illustrates the relationship between the
slag level and blowing time;
Fig. 17 is a block diagram of another example of
the device for observing the vessel-interior light;
Fig. 18 shows the mounting position of devices for
observing the vessel-interior light mounted on a top-
and bottom-blowing converter;
Fig. 19 is a time chart of light signals detected
by the devices shown in Fig. 18 and of the slag level
detected by using a sublance;
Fig. 20 is a block diagram of method of detecting
the slag-forming conditions according to the present
invention; and
Figs. 21 through 23 illustrate the slag level
during blowing and a method for controlling it.
- 6 - ~2~35~
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 is a cross-sectional view of a to~-blowing
converter, schematically showing an embodiment of
mounting a device for observing the vessel-interior
light. Referring to Fig. 1, a converter 1 is provided,
on its side wall 2, with at least one throughhole 4
opening into the vessel interior 3. At least one
vessel-interior observation device 5 is disposed in the
throughhole 4 to face the vessel interior 3 and observe
the intensity or the wavelength of the light emitted
from the slag and gaseous atmosphere within the con-
verter 1. This observation device 5 may be a photometer
and is hereinafter referred to as the photometer 5. In
Fig. 1, only one throughhole and observation device are
shown.
It is possible, based on the measurement of inten-
sity and/or wavelength of the light, to monitor whether
slag-foaming occurs above or beneath a processing level
X of the photometer 5.
Figures 2A to 2C show non-immersion portions 8
of the converter side wall 20, i.e., in the converter
upright position, tilting position for tapping, and
tilting position for charging the pig iron from the
ladle, respectively. In each of the positions shown
in Figs. 2A, 2B, and 2C, the portion of the converter
wall 20 where a trunnion shaft 6 is rigidly secured and
the region around that portion are not immersed within a
melt 7. This portion and region, shown by the hatching
are the non-immersion portion 8. The throughholes 4 can
be formed through the non-immersion portion 8 to prevent
the melt 7 from entering the throughholes 4.
- As is described below, the photometers 5 can also
be removably inserted into the tapping hole. When the
molten steel is tapped through the tapping holes, the
photometers 5 are removed therefrom.
Figures 3A through 3C, Fig. 4, and Fig. 5 illus-
trate the principle of the present invention, Figs. 3A
_ 7 ~ 5~356
through 3C showing the portions of mounting the devices
for observing vessel-interior light and Figs. 4 and 5
showing time charts on the level of detected light
signals. Referring to Figs. 3A through 3C, three
photometers 5a, 5b, and 5c are arranged as seen in the
vertical direction of the converter, so as to measure
the vessel-interior light at the levels xa, xb, and Xc,
respectively. The position of the throughholes 4,
i.e., their distance from the bottom or mouth of the
converter 1, must be empirically determined by the size
and capacity of the converter 1. In the case of a
single throughhole 4, the throughhole 4 must be located
at the highest target slag level. In the case of
plurality of throughholes 4, the highest and lowest
lS throughholes 4 must be located straddling the highest
target slag level.
Figure 4 shows the light signal tordinate) detected
by any one of the photometers Sa, 5b, and 5c and then
subjected to signal processing with the aid of an
appropriate filter. The abscissa of Fig. 4 indicates
the blowing time periods, the former period when the
gaseous atmosphere is present beneath the level Xa, Xb,
or Xc and the latter being when foaming slag is present
beneath the levels Xa, Xb, or Xc.
Figure 5 illustrates the results of continuous
measurement of the vessel-interior light by the photo-
meters Sa through Sc. Under the slag-foamin~ conditions
shown in Fig. 3A, all of the photometers 5a through 5c
face or are exposed to the gaseous atmosphere, which
indicates that the slag-foaming level y is located
beneath the level Xc.
Under the slag-foaming conditions shown in Fig. 3B,
the photometers Sa and 5b face or are exposed to the
gaseous atmosphere and the photometer 5c faces or is
exposed to the foaming slag. The slag-foaming level y
is therefore located beneath the level of the converter
mouth 9 and between the levels Xb and Xc.
~a2~3356
-- 8 --
Under the slag-foaming conditions shown in Fig. 3C,
all of the photometers Sa through 5c face or are exposed
to the slag. The slag-foaming level y is therefore
located between the level of the converter mouth 9 and
S the level Xa of the photometer 5a.
The complicated foaming behavior of slag can
therefore be accurately monitored by means of mounting a
plurality of the photometers in the vertical direction
and continuously measuring the vessel-interior light
during the operation of the converter 1. If necessary,
photometers may also be mounted along the width of the
converter 1.
As described above, the intensity of light of the
gaseous atmosphere and the wavelength characteristics of
light emitted from the gaseous atmosphere considerably
differ from those of the slag. Therefore, by direct
observation of the vessel-interior light, it is possible
to distinguish, without signal processing of the light,
the light upon facing or exposure to the slag from the
light upon facing or exposure to the gaseous atmosphere.
However, if the vessel-interior light is subjected to
signal processing with regard to the intensity or wave-
length of the light, a clearer image of the slag-forming
conditions can be obtained. Also as is described in
detail hereinbelow, the obtained signals can be advan-
tageously utilized for controlling various blowing
operations.
Using the slag-foaming behavior, one can prelimi-
narily determine slag-forming criteria specifying the
relationship between such behavior and slag-forming
conditions. Therefore, according to an embodiment of
the present invention, it is possible to compare the
detected intensity and/or wavelength of the vessel-
interior light with the slag-forming criteria determined
for specific slag-forming conditions, such as formation
of dephosphorizing and/or non-slopping slag. The
slag-forming criteria are determined for each converter
- 9 -
having a specified structure and vessel volume and for
each blowing condition. The value detected by the
photometers Sa through 5c (Figs. 3A through 3C) is
comp~red with the slag-forming criteria, thereby
achieving detection of slag-forming conditions.
An example of the slag-forming criteria is as
follows. When the slag-forming level y arrives at the
level Xa of the highest photometer 5a, this means there
is excessive slag formation and a high possibility of
slopping. The level Xa can therefore be established as
the slag-forming criterion indicating excessive formation
of slag.
The slag-forming criteria are determined for each
type of slaq formation. That is, dephosphorization
requires formation of a dephosphorizing slag having an
appropriate total amount of iron oxide for normal dephos-
phorization reaction and also having a sufficient volume.
The formation of the dephosphorizing slag can be verified
by monitoring the slag-forming level y, e.g., at the
lowest level Xc of the photometer 5c. If the level of
slag is beneath the lowest level Xc during the dephospho-
rizing period, abnormality in slag formation occurs.
Although the above explanation was made with
reference to a plurality of photometers 5a through Sc
arranged in the converter 1, it is possible to satis-
factorily observe the slag-forming conditions even by a
single photometer, as shown in Fig. 1 and as described
hereinbelow.
Figures 6 and 7 are partial cross-sec~ional views
of a converter, showing different mounting structures of
a photometer. Referring to Fig. 6, a photometer 5 is
mounted in the throughhole 4 via a protective tube 11
having an inner cylinder 110. A cooling-water circu-
lating channel 111 is formed in the protective tube 11.
Cooling water w is supplied into the cooling-water
circulating channel 111 via one of conduits 112. The
water w is withdrawn via the other conduit 112. The
3~;~
-- 10 --
photometer 5 is installed within the inner cylinder 110
in such a manner that its active side faces the vessel
interior. Purge gas, such as N2 ~ Ar, CO2 , or another
inert gas g, is supplied to and passed through the inner
cylinder 110 and then ejected through the aperture 113
into the vessel. During its passage and ejection, the
purge gas cools the photometer 5 and prevents gases
including dust, slag, or the like from entering the
inner cylinder 110.
The signal detected by the photometer 5 is input
via a cable 12 into a signal processing device 13, such
as a transmission filter, a computing device 14, and a
display device 15.
The converter operation may be controlled either
automatically or by a human operator. In automatic
control, the signal detected by the photometer 5 is
compared with the slag-forming criteria preliminarily
input into the computing device 14 so as to automati-
cally detect the slag-forming conditions. A warning
signal or operating command is thereupon generated from
the computing device 14 to various controlling devices
(not shown). In control by a human operator, the
operator watches detected values indicated on the
display device 15 and compares them with predetermined
slag-forming criteria, to control the converter
operation.
Figure 7 shows another examples of the photometer
in Fig. 7, the same reference numerals and symbols as
those of Fig. 6 indicate identical members. An optical
conductor 51, i.e., a body capable of transmitting at a
low loss the light emitted from a high temperature body,
e.g., a quartz-based optical fiber, is located in the
inner cylinder 110 of the protective tube 11. The
optical conductor 51 is connected to the body of a
photometer 52, which is disposed at an appropriate
position outside the converter. The structure shown in
Fig. 7 is particularly advantageous, since the body of
~25;~
-- 11 --
photometer 52, which is expensive, can be located a safe
distance from the high-temperature wall 2.
The photometer 5 is not limited to any particular
form provided that it can measure the intensity and/or
wavelength of the vessel-interior light. The photometer
5 includes various assemblies; a MOS or CCD device
assembled with an optical filter, and a lens; a spectro-
meter and a photomultiplier; and an optical thermometer
and a detector of the temperature profile.
Figures 8, 9, and 10 show still another structure
for mounting a photometer on a displacement mechanism
disposed in the neighborhood of the converter and
provided with means for retractably inserting the
photometer into the throughhole.
Referring to Fig. 8, a supporting stand 21 located
at the neighborhood of the converter 1 is equipped with
a photometer 22. The photometer 22 includes an optical
conductor and a receptor 23 at the front end thereof.
The receptor 23 can be retractably advanced into the
throughhole 4 by means of the displacement mechanism 24
which is secured to the supporting stand 21. The
receptor 23 can therefore be timely inserted into the
throughhole 4 when the vessel interior is to be observed
and can be kept protected from such detrimental environ-
ments as thermal load and dusts during the operationperiod, e.g., the tapping period, in which the vessel
interior is not to be observed. The tapping hole can
therefore be utilized as the throughhole 4. The vessel-
interior light received by the receptor 23 is trans-
mitted via connector 25 into a photoelectric converter26 for generating an electric signal. The electric
- signal is input into an image processor 27 for detecting
the intensity and/or wavelength of the vessel-interior
light. The detected signal is shown on a display 28 of
the vessel-interior conditions or a display 29 of the
slag level.
Referring to Fig. 9, showing a detailed structure
- 12 _ ~2~356
of the photometer as well as an example of the seal
mechanism of the throughhole 4, an inner brickwork
lining 2a and steel mantle 2b have an aperture of, e.g.,
500 mm diameter. A cylindrical body 4a has an inner
refractory lining for defining the throughhole 4 and is
welded to the steel mantle 2b. A flange 4c having an
aperture is secured to the cylindrical body 4a. A seal
cap 4d is attached to the flange 4c by bolts and has a
conical-shaped seal surface spread toward the vessel
exterior. A probe 22a provided with a photoconductor
therein (not shown) is equipped with a conical seal
body 22b, the conical shape of which body allowing
gas-tight contact with the seal cap 4d. The length of
the probe tip end 23 is adjustable by an adjusting bar
22c and adjusting nut 22d, so that the probe tip end 23
can be positioned at an appropriate position to receive
the vessel-interior light. The probe 22a is displace
toward and locked to the seal cap 4d by displacement
mechanism 24 (Fig. 8). The spring 22e, which is guided
along the spring guide 22f, is not indispensable but is
preferable to further displace or and thus compress the
probe 22a against the seal cap 4d.
Referring to Figs. lOA, lOB, and lOC, showing an
example of the displacement mechanism 24, a supporting
platform 30 having wheels 30a and 30b is displaced along
a pair of rails 21a. The wheels 30a are attached to the
supporting platform 30 so that they are engaged to the
upper and lower surfaces of the rails 21a, while the
wheels 30b are attached to the supporting platform 30
so that they are engaged to the inner surfaces of the
rails 21a. The probe 22a is provided, at its rear end
as seen from the throughhole (not shown), metallic
fittings 22g and is loosely connected to the displacing
platform 30c via the metallic fittings 22g and a
bolt 30c. The displacing platform 30c is provided with
a probe-supporting base 30d on which the probe 22a is
freely placed.
5~351~
- 13 -
The displacement mechanism 24 described above
with reference to Figs. lOA, lOB, and lOC, retractably
displaces the receptor included in the probe tip end 23
into the throughhole 4 by means of carrying the dis-
placing platform 30 along the rails 21a. The displacingplatform 30 can be an automotive one directly equipped
with a driving mechanism or one which is driven via a
rod, gear, wire, or the like by means of an electric
motor, pneumatic means, or hydraulic means installed
separate from the displacing platform 30.
The driven mechanism shown in Figs. lOA through lOC
are hydraulic. The hydraulic cylinder 24a is connected
via the rod 24b to the metallic fittings 22h, thereby
transmitting the force of the hydraulic cylinder 24a
to the probe 22a. As shown in Figs. lOD and lOE, the
metallic fitting 22h the rod 24b are loosely connected
with one another. Since the probe 22a is loosely
connected to both the displacement mechanism 30 and the
rod 24b as is described above and, further, since a
clearance can be formed between the wheels 30b and one
of the rails 21a, the probe 22a is somewhat displaceable
in any direction, thereby making it possible to realiæe
a further highly gas-tight contact between the conical
seal body 22b and the conical seal surface of the seal
cap 4d.
The probe 22a, including the photo-conductor
therein, is generally a dual tube. Therefore, the
annular space between the inner and outer tubes can be
used as the passage for an inert gas blown toward the
end of the probe so as to cool it or clean the receptor
located at its end.
In an embodiment of the method according to the
present invention, described with reference to Figs. 11,
; 12, and 13, the photoelectrically conducted signal of
the vessel-interior light is divided into a plurality
of ranges of wavelength. The proportion of area of the
light to the total image area of the receptor is computed
- 14 - ~ ~5~
with regard to each wavelength range, and the computed
area proportion compared with predetermined slag-forming
criteria.
Referring to Figs. 11 (I, I') through (III, III')
the melt 7 is charged in the converter 1. A photometer
22 is displaced until it is inserted into the through-
hole. Oxygen begins to be blown through a lance 16, and
then refining is initiated. The flux materials are
charged into the converter 1 and form molten slag.
The amount of slag 31 is still relatively small in
Fig. 1 (I), and the circular field of the receptor 22
gives a white image of the high-temperature gaseous
atmosphere 32 of converter, as shown in Fig. 11 ~I').
When the slag formation further advances, the surface
of the slag 31 (Fig.ll (II)) is vigorously stirred by
the oxygen blown through the lance 16 and by the CO gas
or the like formed due to the blowing reactions. The
slag 31, which is in an emulsion state and which has
a lower temperature than the high-temperature gaseous
atmosphere 32, is detected by the circular field of
the receptor 22 as yellow waves. When the slag 31
(Fig. 11 (III)) overflows the converter mouth and
slopping occurs, the circular field of the receptor 22
is entirely yellow. The above changes in the conditions
of slag formation can be continuously observed by
television with the naked eye or can be recorded as
is explained with reference to Figs. 12 and 13.
The intensity-wavelength relationship of slag
becomes clearly different from that of the gaseous
atmosphere above the slag, as shown in Fig. 12, when
the slag forming proceeds to an appreciable extent and
- the temperature of the gaseous atmosphere is higher than
that of the slag. Therefore, the vessel-interior light
can be subjected to wavelength separation by means of,
for example, a blue-transmitting filter, so as to pass
through the filter light having the wavelength range
where the intensity of light emitted from the slag is
~25i~ i6
-- 15 --
dominant. The filtered light is subjected to a computing
process so as to obtain the proportion of the filtered
light to the entire area of the circular field of the
receptor. The obtained surface-area proportion is
plotted, as shown in Fig. 13, with time.
Referring to Fig. 13, A indicates the pseudo slag
signal generated during the blowing start period, in
which the temperature of the gaseous atmosphere is low,
and B indicates an abrupt increase of the surface-area
ratio and thus occurrence of slopping. Prior to the
occurrence of slopping, the surface-area ratio intensely
varies. The slopping can therefore be predicted on the
basis of such intense change.
When a throughhole is exposed to the gaseous
atmosphere, the vessel's contents progressively deposit
on the throughhole, resulting in clogging. In an embodi-
ment of the method of the present invention, described
in with reference to Figs. 14 and 15, observation of the
vessel interior is carried out while blowing through the
probe an oxygen-containing purge gas to prevent clogging
of the throughhole. Clogging of throughhole is one of
the most serious problems impeding the observation of
the vessel interior. The situation is not so serious
when using the tapping hole as the throughhole for
observation. Since the tapping hole is brought into
contact with molten steel at each tapping, the tapping
hole can be maintained at an extremely high temperature
even during the blowing period. The deposits on the
tapping hole, composed of contents of the vessel,
therefore cannot solidify that much and can be blown out
even by inert purge gas blown through the probe tip end.
Contrary to this, a throughhole formed at the non-
immersing portion 8 (Figs. 2A, 2~, and 2C) cools due to
non-contact with the molten steel and further cools if
the inert purge gas is blown to it through the probe tip
end. Still, deposits on the throughhole can be melted
due to the latent heat of the slag when the end of the
il2r~35
- 16 -
throughhole is exposed to the foaming slag. In this
case, the deposits can be blown out by inert purge gas,
thus preventing accumulation of deposits.
Oxygen-containing purge gas is preferred purge gas
discovered after various investigations of the assignee
of the present application. In this regard, while the
coolant gas of the probe can be blown at an almost
constant rate to attain the intended cooling, the flow
rate of the oxygen-containing purge gas for attaining
the intended purge greatly varies depending upon the
position of the throughhole, quality and quantity of
the vessel's content, temperature, and vessel interior
conditions. Control of the flow-rate for the purge is
therefore difficult. It is more desirable and convenient
to control and to vary the oxygen content of the purge
gas.
Referring to Fig. 14, inert gas is fed from a
source A and is separately blown into conduit systems 34
and 40. The conduit system 34 includes a stop valve 35
and a reducing valve 36, a flow-rate adjusting device 37
with an orifice and flow-control valve, and a stop
valve 38 successively arranged in the flow direction.
The inert gas blown through the conduit system 34 flows
via a flexible hose 39 into an inner cylinder 62
(Fig. 15) which is connected via an inlet port 63
(Fig. 15) to the flexible hose 39. The inert gas is
further blown through a small aperture 42 of a front
tip 41 screwed into a probe 61. The inert gas is then
released from a tip aperture 43 into the vessel interior
while preventing fogging or contamination of a front
glass 67 of the probe 61.
The inert gas flowing through the conduit system 40
is mixed with oxygen fed from a source B into the conduit
system 44. The mixture gas flows via a flexible hose 45
and inlet port 65 into an outer cylinder 64 to cool the
outer surface of the inner cylinder 62 and the front
tip 41. The mixture gas is released into the vessel
- 1 7 ~ 35~
interior from the outer cylinder 64. The flow rate
ratio of oxygen to inert gas is adjusted by a flow-rate
controller 33 connected to the conduit systems 40
and 44. The reverse Z (S) symbol indicates the check
valves located upstream of the joining point of the
conduit systems 40 and 44. The probe 61 includes a
photo conductor therein. The symbols 26, 27, 28, and 29
indicate a photoelectric converter, image processor,
display device of the vessel-interior condition, and
slag level-display device, respectively.
In an embodiment of the method according to the
present invention, the amount of slag is controlled on
the basis of the detected slag-forming conditions so as
to maintain the amount of slag within an appropriate
range at a high accuracy. This embodiment aims not
only to predict the occurrence of slopping but also to
enhance operational efficiency and improve the steel
quality by means of observing the slag level at a high
accuracy, monitoring the variation tendencies in the
slag level, and suppressing detrimental tendencies.
A typical example of this embodiment is described with
reference to Fig. 16.
Referring to Fig. 16, the level of slag at which
slopping is likely to occur is denoted by 72. Reference
numeral 74 indicates the change of the slag level with
time, allowing one to maintain the level of slag lower
than the level 72 over the entire blowing period. The
level of slag at which the slag formation is poor is
denoted by 73. Reference numeral 75 indicates the
change of the slag level with time, allowing one to
ensure, at a certain initial preparatory blowing period,
a slag level higher than 75. In this example, target
slag-level control is effected to control the level of
slag between the levels 74 and 75 during the entire
blowing period. The symbols I, II, and III indicate
that slag-level control actions.
In an embodiment of the present invention,
~25~ 56
- 18 -
information is extracted from the signal obtained by the
photometer so as to monitor the surface-area proportion
of yellow base color to the entire color signal and
variation in that proportion. The proportion and
variation are compared with predetermined color criteria.
This embodiment enables very accurate detection of the
slag-forming conditions, as described with reference to
Fig. 17.
Figure 17 is a block diagram for computing and
outputting the proportion described above. The probe 61,
more specifically the photo-conductor, is provided with
a connector 25 and photoelectric converter 26. The
light detected by the probe 61 is electrically converted
to an image signal 77 which is transmitted to the
wavelength-range divider 78. Analog signals 79, i.e.,
one (B-blue) having a wavelength range of from approxi-
mately 0.3 to 0.4 ~m, another (G-green) having a wave-
length range of from approximately 0.4 to 0.6 ~m, and
the other (R-red) having a wavelength range of from
approximately 0.6 to 0.8 ~m, are generated by the
wavelength range-divider 78. The analog signals are
converted at an appropriate threshold level to binary
signals 80 which are input into an area-computing
device 81. In the area-computing device 81, the binary R
signal, the binary G signal, and the binary B signal are
multiplied by a count pulse of, for example, 0.134 ~sec
(7 MHz) in a reset cycle of 16.7 msec, and the number of
pulses of R-G on and B off is counted. Thus, the area
proportion of yellow base color is counted for each
16.7 msec cycle and is generated as the output signal
of yellow 82, which is observed with a area-proportion
display device 91.
In an embodiment of the method according to the
present invention, in accordance with the observed
slag-forming conditions, at least one of the following
control operations: controlling the oxygen-blowing
rate; controlling the lance height; charging the
- 19 _ ~2~ 6
auxiliary raw materials, such as lime or iron ore; and
controlling the bottom-blowing gas rate are carried out.
This allows stabilization of the slag composition to
drastically reduce the occurrence of slopping and to
improve the slag quality.
In another embodiment of the method of the present
invention, one or more of dolomite powder, quick lime
powder, coal powder, and cokes powder is blown, into the
vessel preferably through an additional throughhole of
the side wall, upon the prediction of occurrence of
slopping so as to stabilize the blowing. The present
invention will be further clarified by the ensuing
examples, which, however, by no means limit the
invention.
Example 1
Figure 18 shows a 170 ton top- and bottom-blowing
converter which has a top lance 16 for blowing 2 and
a bottom nozzle 17 for blowing CO2.
Throughholes 4 were formed at levels 1.5 m, 2.5 m,
and 3.5 m beneath the converter mouth 9. Protective
tubes 11 having an inner cylinder 110 (Fig. 7) were
inserted into the throughholes 4. An optical conductor
51, having a diameter of 12 mm, was stationarily located
in each inner cylinder 110 and was connected to each
body of photometers 52. The photometers 52 were ITV
cameras equipped with short wavelength-transmitting
filters. Signals from the ITV cameras were transmitted
into signal processing units 13 including digital
memories to store the signals in the digital memories.
The digital information was subjected to signal process-
ing for generating an image. The difference in the
intensity of light between the gaseous atmosphere and
the foaming slag was more distinct than by conventional
photometers.
In addition to the observation of the slag-forming
conditions as described above, observation using a
sublance, hithertofor believed to be the most reliable,
- 20 ~ 35~;
was carried out. The temperature of the foaming level
of slag was intermittently measured by lowering the
sublance equipped with a consumable thermometer at the
tip end thereof.
The results are shown in Fig. 9. As is apparent
from Fig. 9, there is no appreciable difference between
the value measured by the sublance method and the value
detected by the method according to the present inven-
tion. Thus, the present invention attains measurement
of the slag level y at a high accuracy. The present
invention attains, furthermore, continuous measuremsnt,
which makes it possible to successfully detect or
predict the dynamic slag-foaming behavior within the
converter.
Table 1 shows the relationship between the total
number of heats in which the foaming level of slag y
arrived at the respective ;evels of the photometers and
the occurrence of slopping, the relationship being
determined by investigations of the assignee.
Table 1
Level of Total Occurrence
photometers number of of sloppinq
heats
Times Percentage
1.5 m (5a) 28 15 54
2.5 m (5b) 35 6 17%
3.5 m (5c) 52 0 0%
In the present example, the slag-forming criterion
was defined as the time when the photometer Sa detected
the foaming slag, i.e., the slag-foaming criterion
indicated abnormal or excessive formation of slag. The
intensity of vessel-interior light was continuously
~ ~S~3~;6
- 21 -
measured during blowing by the photometers 5a, 5b,
and 5c. When the photometers 5a, 5b, and 5c detected
the above-mentioned slag-forming criterion, the warning
signal shown by Z in Fig. 19 was generated to warn of
abnormal or excessive formation of slag. On the basis
of the warning signal, control actions, such as reduction
in the O2-flow rate, through the top-blowing lance 16,
and charging of unburnt dolomite into the converter 1,
were carried out. Due to such control actions, the
occurrence of slopping could be reduced to as low as
0.5% or less.
Example 2
A converter having an outer diameter of approxi-
mately 7 m and a height from the bottom to mouth of 8 m
was pierced by a throughhole 150 mm in diameter through
the side wall. A probe having an outer diameter of
80 mm and a photoconductor having an outer diameter of
40 mm were used.
The type of probe and also the type of purge-gas
blowing conduit systems were as described with reference
to Figs. 14 and 15. As the inert gas, CO2 was used.
By means of varying the flow rate ratio of the
oxygen to inert gas, the influence of oxygen upon the
burning out of deposits was investigated. The results
are shown in Table 2.
25~3~6
- 22 -
Table 2
I
Gas rate 2 Eje ~ ng State of ~valua-
(Nm /Hr) Vol% rate ~nughholes tion
* **
o2 C2 2 (Nm3/s)
100100 0 0 11 Clogging, 3 minutes x
aft~r blowing ini-
tiation
100200 0 0 17 Clogging, 7 minutes x
after blowing ini-
tiation
100300 0 0 22 Clogging, 15 minutes x
after blowing ini-
tiation
100250 50 12.5 22 Clogging at 4 heats x
100100 70 25.9 15 Clogging at 4 heats x
100200 140 31.8 24.2 No clogging o
100150 150 37.5 22 No clogging o
10070 110 39.3 15.4 No clogging o
100100 200 50.0 22 Bricks of vessel x
eroded greatly
* Conduit system 34 ** Conduit system 40
As understood from Table 2, when the purge gas is
free of oxygen, clogging of the throughhole cannot be
sometimes prevented even by blowing a large amount of
inert gas. In addition, when the purge gas contains too
high a concentration of oxygen, the bricks around the
throughhole greatly erode due to oxidizing. An appropri-
ate oxygen concentration is from 30 to 45% by volume.
In this case, repeated observation of the vessel interior
is possible without trouble such as clogging of the
throughhole and erosion of the bricks.
356
- 23 -
The purge gas blowing exe~ted no detrimental
influence upon the blowing operation and quality of
tapped steels.
Example 3
A 170 ton top- and bottom-blowing converter 8 m in
height was charged with melt 1.5 m in depth. A through-
hole was formed at the converter wall 2.5 m perpendicu-
larly under the mouth. An optical fiber 12 mm in
diameter was used as a photoconductor and inserted into
a cooling protective tube. A CCD color-camera was used
as a photoelectric converter. The slag level was
detected by the method as described with reference to
Fig. 17 of computing the area ratio of yellow base color.
The relationship between the area ratio of yellow base
color and the position of the optical fiber was so
established that the area ratio was 50% when the slag
level coincided at the center of field of the optical
fiber. The area ratio 100% and 0% corresponded to the
slag levels above and below the throughhole, respec-
tively. The threshold levels in the binary circuit wereK 35%, G 35%, and B 25~. Slopping was detected by the following method,
described in reference to Fig. 20. The area ratio
signal of yellow base color 82 from a circuit 81 was
divided and transmitted into two circuits. In one of
the circuits, the area ratio signal was converted in the
binary circuit 83 having appropriate threshold level
(10%), into a binary signal 84. In the other circuit,
the area-ratio signal of yellow base color 82 was passed
through a high-pass filter 85 (cut frequency of 5 Hz)
and then converted to a positive value at a circuit 86.
The positive signal was converted to a binary signal 88
in the binary circuit 87 having an appropriate threshold
level (50~), which binary signal 88 indicated the changes
in the area ratio. The two binary signals 84 and 88 were
input into a decision circuit 89. The possibility of
occurrence of slopping was decided as shown in Table 3.
~25;~3~;6
- 24 -
Table 3
: ~
Possibility
of occurrence Yes No No No
of slopping
_ _ _
Binary signal 84 1 1 0 0
(Area ratio of
yellow base color)
Binary signal 88 1 0 1 0
(Change in the
area ratio of
yellow base color)
The control actions to attain the target slag level
were as shown in Table 4.
Table 4
. Controlling method or amLunt
Operatlng ob~ect
_ SuPpression of foaminq Promotion of foaminq
No. 1 Bottcnrblowing increase by 50 Nm3/H decrease by 50 Mm3/H flow rate
(oO2)
¦ No. 2 Lance height decrease by 100 mm increase by 100 mm
I No. 3 Top blo~ increase by 1000 Nm3/H decrease by 1000 Nm3/H
flow rate
No. 4 Auxiliary raw Continuous charging of Charging of agent
materials coolant (fluorite) to promote
slag formation
One or more of the operating objects were manipu-
lated as described with reference to Figs. 21 through 23.Referring to Fig. 21, when the slag level varies during
operation as shown by a curve 71 and exceeds the target
~ 2~ [33~
- 25 -
slag level 76 at the points 92 and 93 and when there is
no possibility of occurrence of slopping, an increase
in the bottom-blowing flow rate (No. 1~ is effective to
attain the target slag level 76.
Referring to Fig. 22, when the slag level varies
during operation as shown by the curve 71 and falls
under the target slag level 76 at the points 9~ and 95,
a decrease in the bottom-blowing flow rate (No. 1) is
first employed. If the slag level seemingly will not
reach the target level 76 approximately 2 minutes after
than the decrease in bottom-blowing flow rate, the lance
is lifted (No. 2) or the oxygen-flow rate is decreased
(No. 3) to promote the foaming of slag.
Referring to Fig. 23, when the slag level varies
during operation as shown by the curve 71 and exceeds
the target slag level 76 at the point 97 and when there
is a possibility of occurrence of slopping, continuous
addition of ore and dolomite is effective to attain the
target slag level 76 and to prevent slopping.
It was found that the operations are preferably
carried out in the order of Nos. 1, 2, 3, and 4. It was
also found that, for action I in Fig. 16, increasing the
bottom blowing rate was effective and, for action II,
either decreasing the bottom blowing rate or lifting the
lance (increasing the lance height) was effective.
The operations as described above were carried out
for 50 heats. The results are shown in Table 5.
- 26 _ ~2 ~ ~35 6
Table 5
[P~(xlO ~ Blcwn heats Failure in
(T-Fe)% at blowin~end with [P] outside Remarks
slopping standard (%~
X a X o (%)
_ _
Inven-15 1.1 20 2.2 2 0.5 Low-carbon
tion steel
Conven-16 2.3 17 5.3 28 4.2 [P]_25xlO 3%
tional
Example 4
Blowing was carried out as in Example 3 except for
the following: In addition to the throughhole (for
observing the vessel interior), another throughhole was
formed in a non-immersing portion of the side wall of
the converter to charge the auxiliary raw materials
therethrough. The additional throughhole was equipped
with a nozzle for blowing auxiliary raw materials, purge
gas and carrier gas. Purge gas consisting of 75% CO2
and 25~ 2 was blown without interruption at a rate of
120 Nm3/hr to prevent clogging of the additional
aperture. When the occurrence of slopping was predicted,
the CO2 gas was blown with flow rate by 500 Nm3/hr as
carrier gas, and coke powder (5 mm or less) was blown
into the vessel interior. Alternatively, instead of the
coke-powder injection, lump dolomite was charged.
The results of blowing were as shown in Table 6.
- 27 - ~ 3~6
Table 6
ALxiliary Total number Successful Success
raw materials of heats heats percenta~e
Lump dolomite 32 11 34%
Powder coke 43 42 98%
When the prediction signal of slopping disappeared
1 minute or less after the blowing of the auxiliary
materials to suppress the slopping, the heats were
deemed to be successfully blown. This was used as the
criterion for effective suppression of slopping.
As is understood from Table 6, the coke-powder
injection is more effective than the lump dolomite
charging.
Since the auxiliary material was directly injected
through the additional throughhole into the foaming
slag, blowing could be initiated immediately after the
prediction of occurrence of slopping.
Example 5
Blowing was carried out as in Example 4 except
for the following: Instead of addition of another
throughhole for injection of pulverized auxiliary raw
- materials using purge gas to the throughhole for
observation of the vessel interior, an assembled probe
was equipped, which had an observation device and
injection mechanism. This kind of probe is a modified
one shown in Fig. 15 in the following points. Inlet
port 65 into an outer cylinder 64 is connected to the
powder injection unit. The injected powder in carrier
gas is released into the vessel interior from the outer
cylinder 64. The probe 61 includes a photoconductor
therein. The purge gas is released from an inlet port 63
and blown through a small aperture 42 of a front tip 41
- 28 - ~ 3~6
screwed into a probe 61. The purge gas is mixed with
oxygen concentration with 30 to 40% by volume.
