INFRA RED IMAGERY BASED SLAG DETECTION SYSTEM FOR
BASIC OXYGEN FURNACE (BOF) CONVERTER
FIELD OF THE INVENTION
The present invention, in general, relates to a slag detection system for a
metallurgical furnace and in particular, to a technology for detection of slag for its
removal, applying its higher emissivity, from a pouring stream of liquid, coming out
of a converter such as but not limited to a Basic Oxygen Furnace (hereinafter
referred to as BOF) converter, in a steel furnace.
BACKGROUND OF THE INVENTION
It has been the priority of metallurgical industry in general and steel industry in
particular, to lower the recurring cost and improve the quality of steel for present
and future customers. It is also traditionally known that, slag generation is a
permanent hindrance, which deteriorates the quality and yield of the final product,
often leading to high cost of production.
The problems of slag carry over at the heart of the steel making process i.e. from
Basic Oxygen Furnace (BOF) to caster are many folds. For example, slag layer
hinders addition of alloys and conditioners. Slag constituents (higher level of FeO and
MnO) result in higher oxygen content of steel. This in turn, leads to increased
processing time and treatment cost. High inclusion formation leads to steel
cleanliness problems and caster nozzle clogging, poor ladle desulphurization,
phosphorus reversion, high cost of slag modifier and so on.
Research and development is on over the years to minimize the aforesaid problems
caused by slag generation, by the tapping of liquid steel from BOF so that the steel
removal form BOF is maximized, while the amount of slag deposited into the holding
vessel or ladle is consequently, minimized. In brief, the ongoing research in this
area, is primarily focused on detection and removal of slag from the pouring stream
of liquid from a converter to the holding vessel or ladle, so that the deposit on the
ladle, comprises minimum amount of slag and maximum amount of steel.
The conventional practices of slag detection for its removal, mainly depends on two
methods namely human vision and dart method.
Human vision technique, applies a furnace glass filter. Now having regard to the fact
that the visual contrast of the scene is quite small, the detection is often not
satisfactory, so far as the degree of precision is concerned. Furthermore, it requires
considerable training for an observer to distinguish slag from steel and there is
always a substantial degree of subjectivity, involved with such detections.
The dart method applied for slag stopping produces erroneous results due to short of
reaching slag- metal interface, when the slag is heavy.
Accordingly, there was a long felt need for a slag detection system in metallurgical
industry, such as but not limited to steel industry , for its removal whereby the
quantity of slag deposited on the holding vessel such as ladle from the converter, is
substantially minimized and the quantity of steel/final product on such holding vessel
is substantially maximized.
The present invention meets the aforesaid long felt need.
All through out the specification including the claims, the words "slag", "ladle",
"converter", "digital controlling means", "Personal Computer", "card", "camera",
"relay", "thermal imaging", "emissivity" are to be interpreted in the broadest sense
of the respective terms and includes all similar items in the field known by other
terms, as may be clear to persons skilled in the art. Restriction/limitation, if any,
referred to in the specification, is solely by way of example and understanding the
present invention.
In the above context it is hereby clarified, that simply by way of example and for
understanding the present invention and not by way of any limitation, the slag detection
system, in accordance with the present invention, has been explained with reference to
steel furnace, steel and BOF converters. It should be understood to persons skilled in the
art that, the present invention is equally applicable to other metallurgical furnaces, alloys
and other converters and will be equally effective, in achieving the objects of the present
invention.
OBJECTS OF THE INVENTION
It is the principal object of the present invention to provide a slag detection system
for a metallurgical furnace for its removal applying its higher emissivity, whereby the
amount of slag deposited on the holding vessel from a converter, is substantially
minimized.
It is a further object of the present invention to provide a slag detection system for a
metallurgical furnace, whereby the quality and yield of final product is substantially
ameliorated.
It is yet another object of the present invention to provide a slag detection system
for a metallurgical furnace, whereby the cost of production of the final product is
substantially minimized.
It is yet another object of the present invention to provide a slag detection system
for a metallurgical furnace, whereby processing time and treatment cost is
substantially minimized.
It is a further object of the present invention to provide a slag detection system for a
steel furnace, for its removal applying its higher emissivity, whereby the amount of
slag deposited on the ladle, from a Basic Oxygen Furnace (BOF) converter, is
substantially minimized.
It is yet another object of the present invention to provide a slag detection system
for a steel furnace, which applies real time thermal imaging system, in discriminating
liquid steel from liquid slag.
It is another prime object of the present invention to provide a method for detecting
and removing slag in a metallurgical furnace by applying real time thermal imaging
system for identifying liquid slag in a liquid stream, poured from a converter such as
but not limited to a BOF converter in a steel furnace, to a holding vessel.
How the foregoing objects are achieved and the other aspects of the present
invention, will be clear from the following description which is purely by way of
understanding and not by way of any sort of limitation.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a slag detection system for a
metallurgical furnace including an infra red (IR) camera operatively connected to a
converter means, to an industrial grade digital controlling means and to a holding
means, wherein said infrared camera is adapted to transmit signal to said digital
controlling means, in the event of detection of slag in said converter means and said
digital controlling means is adapted to trigger an alarm on receiving said signal from
said infrared camera, in the event of which, the converter means is adapted to be
tilted back to stop the pouring stream of liquid , from said converter means to said
holding means.
In accordance with preferred embodiments of the present invention:
-said furnace is a steel furnace, said converter means is a Basic Oxygen
Furnace(BOF) converter, said holding means is a ladle said IR camera is a long wave
camera with upper temperature measurement limit in the vicinity of 2000°C ( for 8
to 14pm wavelength range).
-said industrial grade digital controlling means is an industrial grade Personal
Computer (PC), operatively connected to said IR camera through a frame grabber
card for image acquisition.
-said PC is adapted to generate an audio visual alarm in the event of detection of
slag by said IR camera, through a relay card installed in said PC.
-said IR camera is housed inside an environmental enclosure for dust and heat
protection.
-a vortex air cooling system is located inside said environmental enclosure for
cooling said IR camera.
-a stand alone air-compressor unit is operatively connected to said enclosure to
supply dry and filtered air at 5 bar.
-temperature and pressure data inside said enclosure and converter tilt angle are
adapted to be fed to said PC, through a data acquisition card.
-camera control signals are adapted to be fed to said PC through a serial card.
The present invention also provides a slag detection system for a steel furnace,
including an infra red (IR) camera, operatively connected to a Basic Oxygen Furnace
(BOF) converter, to an industrial grade Personal Computer (PC) and to a ladle,
wherein said infra camera is adapted to transmit signal to said PC, in the event of
detection of slag in said converter and said PC is adapted to trigger an audio visual
alarm on receiving said signal from said infra red camera, in the event of which, said
converter is adapted to be tilted back to stop the pouring stream of liquid from said
converter to said ladle.
The present invention also provides a method for detecting and removing slag in a
metallurgical furnace including :-
-operatively connecting an infrared (IR) camera to a Basic Oxygen Furnace (BOF)
converter, to an industrial grade digital controlling means and to a holding means,
-putting on said camera and said industrial grade digital controlling means,
-initiating flow of pouring stream of liquid from said converter means into said
holding means,
-detecting slag in said pouring stream by said IR camera by virtue of high emissivity
of said slag,
-transmitting signal to that effect by said camera to said industrial grade controlling
means instantaneously,
-generating audio visual alarm by said industrial grade controlling means in that
event,
- utilizing the tilt angle of said converter means to stop flow of said pouring stream
into said holding means.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The nature and scope of the present invention will be better understood from the
accompanying drawings, which are by way of illustration of some preferred
embodiments and not by way of any sort of limitation. In the accompanying
drawings,
Figure 1 illustrates a graphical representation of Emissivity against Wave Length of
steel and slag.
Figure 2 illustrates a general layout of a preferred embodiment of the slag detection
system, in accordance with the present invention.
Figure 3 illustrates a preferred embodiment of the IR Camera enclosed in an
environment enclosure and industrial grade computer and cards housed inside the
central panel in the BOF central room, in accordance with the present invention.
Figure 4(a) illustrates a screen shot generated by the slag detection system in
accordance with the present invention.
Figure 4(b) illustrates the screen shot showing processing window.
Figure 5 illustrates imagery of a slag portion detected by the slag detection system in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
As described under the heading, background of the invention, slag generation is a
permanent hindrance in the metallurgical industry, which deteriorates the quality and
yield of the final product, often leading to high cost of production.
The present invention relates to detection and removal of slag from the pouring
stream of liquid from a converter to the holding vessel or ladle, so that the deposit
on the ladle, comprises minimum amount of slag and maximum amount of steel.
Conventional techniques, for such detection and removal, involved some vital
drawbacks as stated hereinbefore, under the heading background of the invention.
The present invention advocates a new technology for overcoming such drawbacks.
The present invention applies real time thermal imaging system for discriminating
liquid steel from liquid slag. For that purpose, the present invention advocates a slag
detection system, which includes an Infra Red Camera (IR) for locating the higher
emissivity of slag, as compared to liquid steel. Because of higher emissivity than
steel, the slag appears hotter (brighter), even if it is at the same temperature as the
steel. This will be particularly clear from the graphical representation, in the
accompanying figure 1. The IR based slag detection system, in accordance with the
present invention effectively minimizes the slag carry over, with judicious tuning.
As illustrated in the accompanying figure 2, the slag detection system in accordance
with a preferred embodiment of the present invention, includes an Infra Red(IR)
camera(l), which is preferably a long wave camera, operatively connected to a Basic
Oxygen Furnace (BOF) converter(3), to an industrial grade Personal Computer(2)
and to a ladle(4). Now, the liquid (5), that is poured from the BOF converter (3) to
the ladle(4) comprises liquid steel as well as liquid slag. As soon as the infra red
camera (1) detects slag, by virtue of its higher emissivity as compared to liquid
steel, it transmits an instantaneous signal to the Personal Computer (PC). The PC in
turn, instantaneously triggers an audio visual alarm, so that the converter (3) is
tilted back to stop the pouring stream (5) of liquid from the converter (3) to the
ladle(4). Thus, minimization of slag and maximization of liquid steel is ensured in the
liquid, deposited on the ladle (4).
Based on thermal imaging principle, the system is developed to detect the onset of
slag during pouring from BOF converter to ladle. Advances in infrared technology and
development of long wave infrared focal plane array (FPA) facilitate the development
of cost effective, low maintenance, compact IR imaging system for obtaining higher
resolution imagery of metal and slag. An example of screen shot of the slag
detection in BOF control, room has been illustrated in the accompanying figure 4.
The accompanying figure 5, illustrates an imagery of slag, as detected by the IR
camera. The long wave infrared camera acquires the images of the pouring stream of
molten metal at around 1600° C in real time. The steel and slag principally have
different radiance, because of their difference in emissivities. Because of higher
emissivity than steel, the slag appears hotter (brighter) even if it is at the same
temperature as the steel. Thus, higher the emissivity difference better is the
discrimination between steel and slag. A long wave camera (8.0 um - 14um) is thus
applied, where the difference between slag and steel emissivity is highest as shown
in the accompanying Fig. 1. Further the long wavelength region (8um-14um) of IR
spectrum offers widest window, with least atmospheric interference, mainly due to
water vapor and carbon dioxide. The sight path attenuation due to scattering from
micron sized particles is also very small in long IR region.
The long wave IR Camera (1) is aimed to grab the full view of the pouring stream(5).
Preferably, a camera model Thermovision A40M from FLIR is applied. The camera
consists of uncooled focal plane array microbolometers with upper temperature
measurement limit in the vicinity of 2000°C (for 8 to 14pm wavelength range). To
protect the camera from harsh environment of converter zone, preferably, it is
housed inside an environmental enclosure as illustrated in the accompanying figure
3. The long wave IR Camera continuously, acquires the image of the pouring stream
and differentiates between metal and slag with the help of digital image processing.
Slag being lighter than steel floats on the liquid steel and starts coming out at the
end of pouring. At the onset of slag, the image processing software generates visual
and audio alarm for the operator to tilt back the converter. The IR Camera is
connected to an industrial grade personal computer (PC) through frame grabber card
for image acquisition. For controlling the camera parameters such as focusing, level
and span selection, isothermal range selection, emissivity selection and so on
through PC, the camera controls signals are fed to the PC through a data acquisition
card. The camera is cooled with the help of a vortex air cooling system housed inside
the environmental enclosure. The temperature and pressure data inside the camera
enclosure are fed to the PC through a data acquisition card. The converter tilt angle
is measured by a rotational position encoder and fed to the PC through data
acquisition card. The process parameters such as temperature, pressure, tilt angle of
converter and images are used to design a custom software for generating slag
alarm. The visual and audio slag alarm signals are generated through a relay card
installed inside the PC. The system is computer controlled where the slag appears in
different colour (pseudo colour can be changed by the user) than the background
colour of steel in computer monitor. The operator is also alerted preferably with
buzzer and flush light during the onset of slag.
It should be understood to persons skilled in the art that a PC has been adopted in
the aforesaid exemplary description, by way of understanding only and any other
digital controlling means can be effectively applied, to achieve the desired objectives.
The software applied in the system in accordance with the present invention, in
combination with the hardware, is developed on LabView platform. The image
grabber card acquire HSL(Hue saturation and luminance) image with the help of an
onboard RGB(Red, Green, Blue) to HSL conversion since luminance(Brightness)
information can be easily decoupled. However, for the display purpose the image is
automatically converted back to RGB colour space. The luminance image is then
threshholded to extract the bright part of the stream that represents slag. The
thresholded binary image is shown in the processing window located behind the
display window of the accompanying figure 4(b) where the white region indicates
onset of slag. The black regions represent the steel and the body of the converter
which are at lower apparent temperatures. The area of the white region inside the
region of interest (ROI)(green rectangle of the processing window) is computed and
the ratio of the slag area to the area of ROI is displayed as "Slag%". The ROI can be
changed by the user. The tapping angle is considered in the logical operation since a
small amount of slag comes out during the start of the tapping process and it is
required to detect the onset of slag at the end of the tapping. The black regions
represent the steel and the body of the converter which are at low apparent
temperatures. The area of the white region inside the region of interest (ROI)(green
rectangle of the processing window) is computed and the ratio of the slag area to the
area of ROI is displayed as "Slag%". If the slag% is greater than the user defined
slag% setting (shown in Figure 4) and tapping angle is within the final angle range,
then alarm is generated and otherwise the process of image grabbing again starts.
The dart method applied for slag stopping produces erroneous results. The slag darts
consists of a refractory attached to a pipe. The geometry is designed in such a way
that when the dart is dropped (through the mouth of the converter) over the tap-
hole, the pipe helps prevent the dart from drifting away from the tap-hole. The dart
shaped floating elements produce unsatisfactory results because accurate placement
of dart over tap-hole is difficult and critical. Further, the dart produces unsatisfactory
result when the slag is viscous and thick and where the floating elements can not
reach the slag-metal interface. Sometimes the dart closes the tap-hole too early
which results in the leaving of steel in the converter affecting yield.
The protective environmental enclosure is applied as stated hereinbefore, where the
camera is cooled by a vortex cooler. The environmental enclosure used is completely
dust proof with protective window (made of zinc selenide) for the passage of IR
radiation from the pouring stream. A stand alone air-compressor unit is used to
supply dry and filtered air to the environmental enclosure at 5 bar. The dust
deposition on the surface of the protective window is prevented with the help of air
curtain where compressed air flows through the holes of the environmental enclosure
located at the periphery of the protective window. Temperature probe and pressure
sensor are mounted inside the camera enclosure to measure temperature and
pressure.
Preferably, PCI slots of standard industrial computer are used for inserting PCI based
control cards. The advantage of PCI based control card is that the card is not
manufacturer specific and may be replaced, depending upon the requirement and the
desired choice of the user, pursuant thereto.
The system in accordance with the present invention is adapted to run 24x7 and the
software is activated automatically when the tap angle(tilt angle of converter) is
within a certain angle range indicating the end phase of tapping. Further the camera
is positioned such that the initial slag is not likely to appear in the region of interest
(ROI) during the start of tapping. In addition the slag is not likely to appear in the
region of interest(ROI) during deslagging (the pouring of residual slag in the
converter to the slag pot after completion of tapping).The temperature and pressure
inside the camera enclosure is considered in the software design where the software
generates warning in the display monitor when temperature and pressure crosses
predefined limits. The processing software is designed in a simple way with the help
of a single region-of-internet(ROI) and with the aim of detecting the slag that
appears during the end of tapping.
Preferably in the system in accordance with the present invention, the slag counter
to estimate total amount of slag flowed in a single heat is not incorporated since it is
likely to give false value due to the invisibility of slag through IR Camera when
additives are poured in to the converter. The invisibility occurs due to the formation
of fumes during the time of addition.
The method for detecting and removing slag in a metallurgical furnace, in accordance
with the present invention first of all comprises operatively connecting an infrared
(IR) camera to a Basic Oxygen Furnace (BOF) converter, to an industrial grade
digital controlling means and to a holding means and putting on said camera and
said industrial grade digital controlling means.
Thereafter, flow of pouring stream of liquid is initiated from the converter means into
the holding means. On detecting slag in the pouring stream by the IR camera by
virtue of the higher emissivity of slag, signal to that effect is transmitted by the
camera to the industrial grade controlling means instantaneously, followed by
generation of audio visual alarm by the industrial grade controlling means in that
event and consequently, utilization of the tilt angle of the converter means to stop
flow of the pouring stream into the holding means.
Some of the salient advantages, achieved by the present invention may be
summarized as follows:
(i) Slag carry over consistency.
(ii)Reduction in slag layer thickness (around 50 %) in the holding vessel i.e. ladle.
(iii)Reduction in rephosphorization in ladle.
(iv)Reduction in aluminum consumption for deoxidizing.
(v) Continuous 24 x 7 operation.
(vi)Very low maintenance.
(vii)High camera life of around 10,000 hour (MTBF mean time between failure).
(viii)Automatic triggering of alarm at the end of tapping independently of operator.
(viii)Totally non-contract operation.
(ix) Minimum interference with existing tapping operation.
(vii) Cost saving for replacement materials such as slag stoppers and so on.
The present invention has been described with reference to some drawings and
preferred embodiments, purely for the sake of understanding and not by way of any
limitation and the present invention includes all legitimate developments within the
scope of what has been described hereinbefore and claimed in the appended claims.
WE CLAIM:
1.A slag detection system for a metallurgical furnace including an infra red (IR)
camera operatively connected to a converter means, to an industrial grade digital
controlling means and to a holding means, wherein said infrared camera is adapted
to transmit signal to said digital controlling means, in the event of detection of slag
in said converter means and said digital controlling means is adapted to trigger an
alarm on receiving said signal from said infrared camera, in the event of which, the
converter means is adapted to be tilted back to stop the pouring stream of liquid ,
from said converter means to said holding means.
2.The slag detection system as claimed in claim 1 wherein said furnace is a steel
furnace, said converter means is a Basic Oxygen Furnace(BOF) converter, said
holding means is a ladle and said IR camera is a long wave camera with upper
temperature measurement limit in the vicinity of 2000°C ( for 8 to 14µm wavelength
range).
3.The slag detection system as claimed in claim 1, wherein said industrial grade
digital controlling means is an industrial grade Personal Computer (PC), operatively
connected to said IR camera through a frame grabber card for image acquisition.
4.The slag detection system as claimed in claim 3 wherein said PC is adapted to
generate an audio visual alarm in the event of detection of slag by said IR camera,
through a relay card installed in said PC.
5.The slag detection system as claimed in any preceding claim, wherein said IR
camera is housed inside an environmental enclosure for dust and heat protection.
6.The slag detection system as claimed in claim 5, wherein a vortex air cooling
system is located inside said environmental enclosure for cooling said IR camera.
7. The slag detection system as claimed in claim 5 wherein a stand alone air-
compressor unit is operatively connected to said enclosure to supply dry and filtered
air at 5 bar.
8.The slag detection system as claimed in claims 6 and 7, wherein temperature and
pressure data inside said enclosure and converter tilt angle are adapted to be fed to
said PC, through a data acquisition card.
9.The slag detection system as claimed in claims 2 to 8, wherein camera control
signals are adapted to be fed to said PC through a serial card.
10.A slag detection system for a steel furnace, including an infra red (IR) camera,
operatively connected to a Basic Oxygen Furnace (BOF) converter, to an industrial
grade Personal Computer (PC) and to a ladle, wherein said infra camera is adapted
to transmit signal to said PC, in the event of detection of slag in said converter and
said PC is adapted to trigger an audio visual alarm on receiving said signal from said
infra red camera, in the event of which, said converter is adapted to be tilted back to
stop the pouring stream of liquid from said converter to said ladle.
11. A method for detecting and removing slag in a metallurgical furnace including:-
-operatively connecting an infrared (IR) camera to a Basic Oxygen Furnace(BOF)
converter, to an industrial grade digital controlling means and to a holding means,
-putting on said camera and said industrial grade digital controlling means,
-initiating flow of pouring stream of liquid from said converter means into said
holding means,
-detecting slag in said pouring stream by said IR camera by virtue of high emissivity
of said slag,
-transmitting signal to that effect by said camera to said industrial grade controlling
means instantaneously,
-generating audio visual alarm by said industrial grade controlling means in that
event,
- utilization of the tilt angle of said converter means to stop flow of said pouring
stream into said holding means.

A slag detection system for a metallurgical furnace including an infra red (IR)
camera(2) operatively connected to a converter means(3), to an industrial grade
digital controlling means(2) and to a holding means(4), wherein said infrared camera
is adapted to transmit signal to said digital controlling means, in the event of
detection of slag in said converter means and said digital controlling means is
adapted to trigger an alarm on receiving said signal from said infrared camera, in the
event of which, the converter means is adapted to be tilted back to stop the pouring
stream of liquid (5), from said converter means to said holding means.