FIELD OF THE INVENTION
The present invention relates to an improved Lance Position Indication (LPI) system for
accurate and precise measurement of oxygen lance positioning in BOF converters for steel
making process in SMS. More particularly, the invention is directed to a system for lance
positioning and measurement in BOF converters using multi-turn absolute encoder as
position sensor and display means for both right and left lances at lance platform of the BOF
converters in SMS shop, adapted to locate anyone of the lance with respect to the center of
any converter with an accuracy of ± 1 cm with facility for instant calibration and the position
is indicated on 4-digit display panel for either of the lances so that the tip leakage due to
blowing of oxygen at wrong position is reduced/eliminated. The LPI system of the invention
having interconnectivity with a processing unit with electronic maintenance console via
Ethernet network for easy and faster fault diagnosis. The system is further adapted to share
same digital display panels for lance position as well as blowing time on either lance. The
system of the invention ensure lance position with respect to selective vertical disposition
for oxygen blowing that occur at different height for a fixed interval of time as per
operational requirements during steel melting in BOF converter involving encoders. The
system further takes care of the large distance of position signal data transmission by
selectively involving Synchronous Serial Interface (SSI) for reliable transmission. The
present system of lance positioning is thus adapted to minimize lance tip leakage by about
60% as compared to conventional practice, reduce down-time of converters, simplifying
calibration method/means, prompt fault diagnosis and maintenance, increased converter
availability and thus improving the overall productivity in SMS plants.
BACKGROUND ART
It is well known in the field of steel melting that oxygen blowing Lances plays an important
equipment in steel making process in BOF. In this steel making process, converter vessel is
charged with basic raw material comprising 70-80% liquid hot metal from the blast furnace,
and 20-30% steel scrap, which is used here as a coolant for controlling very high
temperatures produced by violently exothermic reactions in the converter. Oxygen (>99.5%
pure) is "blown" into the metallic charge at supersonic velocity through a lance. The
converter needs no external heating because the oxygen combines exothermically with the
impurity elements such as carbon, silicon, manganese and phosphorus. The oxidation
reactions inside converter produce high volume of gas and finally leads to formation of slag
that floats on molten steel.
After blowing of oxygen for pre-determined duration the metal is sampled and converter is
ready for tapping. Slag is lighter and it floats on liquid metal surface. It is separated first
into a separate vessel known as slag pot. Slag is ultimately treated as waste and disposed
of as skull. Liquid steel is poured in a separate vessel known as ladle for transfer to next
processing/casting shop.
The oxidation of carbon and silicon liberates voluminous quantity of gas out of the
converter, which is to be used in waste heat boiler for steam generation as by-product.
Thereafter, gas passes through gas cleaning system and dried further. Finally, this is sucked
out by exhauster and discharged through the chimney to atmosphere.
Conventionally, two lances provided for blowing oxygen in BOF converters. One lance is
used at a time for blowing oxygen while the other is kept as stand-by. These lances are
designated as either as Lance#l and Lance#2 or as Left Lance and Right Lance. Both these
lances are mounted on lance platform. For selecting one of the lances to put into service,
the platform is moved either left or right direction to position the lance at the center of the
converter. Thereafter, the selected lance is lowered into the converter at desired height for
blowing oxygen.
In the existing lance blowing practice in BOF converter, analog Lance Position Indication
(LPI) system with dial type indicator is used that leads to poor measuring accuracy. There
also occur erroneous reading of lance position due to parallax error. One of the reasons for
tip leakage is due to blowing of oxygen at wrong position and such tip leakage was high
with prior art.
There has thus been a persistent need in the art to developing a Lance position Indication
(LPI) system that would overcome the limitations of the existing LPI systems and be able
to ensure desired accuracy of measurement avoiding any parallax or other errors and
means for display of such measured data for on-line position/location indication on digital
display panels. The system on one hand provide digital display for both lance positions
through the active lance display panel and on the other hand provides for a running timer to
indicate oxygen blowing time on a separate digital display panel of the dormant lance, which
provision was not available in the prior art. A further object of the invention is
implementation of new networked PLC system, that facilitate faster diagnosis of fault on
maintenance console. An Ethernet network is used for connecting of PLC panel with PC
based maintenance console. A redundant off-line Ethernet connection facility is also
provided near to panel in addition to existing network connection. Advantageously, the
present invention is directed to ensure precise lance positioning adapted to minimize lance
tip leakage by about 60% as compared to conventional practice and thus making the
invention suitable for operation in SMS plant of Integrated Steel manufacturing Units with
significant economic advantage.
OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to provide an improved on-line lance
position measurement/indication (LPI) system for steel making in converters adapted to
ensure precise positioning of lance as per requirement of process to thereby reducing the tip
leakage by about 60% and providing digital display panel for position display for both left
and right lance in a converter at operator's pulpit, thus improving energy efficiency and
productivity in converter operation.
A further object of the present invention is directed to providing an improved on-line lance
position measurement/indication (LPI) system for steel making in converters adapted to
display lance position continuously on a display panel having 4-digit display means for both
left and right lances.
A further object of the present invention is directed to providing an improved on-line lance
position measurement/indication (LPI) system for steel making in converters wherein
instantaneous calibration of lance position is performed by pressing a single push button.
A still further object of the present invention is directed to providing an improved on-line
lance position measurement/indication (LPI) system for steel making in converters wherein
the lance position is displayed on the panel for the live lance through which oxygen is blown
at any instant and the time for oxygen blowing is displayed on panel attached to the other
lance not engaged in blowing operation such that the blowing time is displayed on right
lance display panel for left lance operation or blowing time on left lance is displayed on right
lance display panel for right lance operation.
A still further object of the present invention is directed to providing an improved on-line
lance position measurement/indication (LPI) system for steel making in converters wherein
separate cables are used to connect the digital display means for lance position indication as
well as the time for blowing on two separate display panels for easy traceability of signals
and favoring faster fault diagnosis and maintainability reducing down-time and increased
converter availability.
A still further object of the present invention is directed to providing an improved on-line
lance position measurement/indication (LPI) system for steel making in converters wherein
interconnectivity is provided between the processing unit and electronic maintenance
console on Ethernet network.
A further object of the present invention is directed to providing an improved on-line lance
position measurement/indication (LPI) system for steel making in converters wherein
synchronous serial interface(SSI) is introduced for reliable transmission of position signal
over long distances.
A further object of the present invention is directed to providing an improved on-line lance
position measurement/indication (LPI) system for steel making in converters wherein the
existing equipments on lance trolley is suitably modified to accommodate mounting of
position sensors for both lances.
A still further object of the present invention is directed to providing an improved on-line
lance position measurement/indication (LPI) system for steel making in converters wherein
improved accuracy and precise measurement is ensured for lance position measurement
and indication and retain the position details even after power failure.
A still further object of the present invention is directed to providing an improved on-line
lance position measurement/indication (LPI) system for steel making in converters wherein
the position sensors used for lance position detection/measurement are protected from
dust, heat, water spray etc. with shaft sealing facility and providing a dust-proof enclosure.
A still further object of the present invention is directed to providing an improved on-line
lance position measurement/indication (LPI) system for steel making in converters wherein
the signal carrying cables are protected from heat with asbestos clothing and termination of
cables from lance trolley to junction boxes is maintained with appropriate sagging enabling
desired trolley movement from, left to right and vice versa.
A still further object of the present invention is directed to providing an improved on-line
lance position measurement/indication (LPI) system for steel making in converters wherein
supply power to the control system is tapped from two alternate sources, so that in the
event of failure of one source, automatic switching over to other source is ensured.
A still further object of the present invention is directed to providing an improved on-line
lance position measurement/indication (LPI) system for steel making in converters wherein
parallax error in reading the lance position as usually occur in the conventional analog read
out, has been eliminated by providing the digital display based measurement/indication of
lance position.
A still further object of the present invention is directed to providing an improved on-line
lance position measurement/indication (LPI) system for steel making in converters wherein
sharing of same digital display panel on either lance is achieved with advantage for
displaying the lance position or the blowing time.
A further object of the present invention is directed to providing an improved on-line lance
position measurement/indication (LPI) system for steel making in converters wherein power
distribution facility with redundant power sourcing to provide un-interrupted supply to the
system.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to a system for on-line digital
position measurement of lance position for converter operation comprising:
(a) lance position sensors on lance trolley;
(b) PLC based position measurement unit; and
(c ) display unit for on-line digital indication of the lance position.
Another aspect of the present invention is directed to a system for on-line digital position
measurement of lance position for converter operation wherein the said lance position
measurement sensor comprise for both left and right lances multi-turn absolute encoder at
lance platform which is located at a greater height and said PLC based display is located at
control room at a lower height.
A further aspect of the present invention is directed to a system for on-line digital position
measurement of lance position for converter operation comprising elimination of parallax
error in reading lance position wherein the lance position measurement and display for both
left and right lances of a converter are provided in two separate panel/enclosures and
involve separate cables for easy traceability of signals and maintainability.
A still further aspect of the present invention is directed to a system for on-line digital
position measurement of lance position for converter operation comprising:
Ethernet network providing interconnectivity of processing unit with electronic maintenance
console;
sensor means protected from dust, heat, water spray with shaft sealing facility and
enclosed in dust-proof enclosure;
said sensor cables protected from heat with asbestos clothing and termination of cables
from lance trolley to junction boxes with appropriate sagging for trolley movement from left
to right and vice versa;
means for sharing same digital display for lance position or blowing time; and
power sourced from two sources such that in the event of failure of one source, automatic
switching over to other source .
A still further aspect of the present invention is directed to a system for on-line digital
position measurement of lance position for converter operation comprising:
lance position indication means with an accuracy of ± 1 cm;
press-button switching adapted for instantaneous calibration of lance position by pressing
single push-button;
synchronous Serial Interface (SSI) for reliable transmission of position signal over long
distance.
A still further aspect of the present invention is directed to a system for on-line digital
position measurement of lance position for converter operation comprising :
(a) said lance position sensors comprising two lances in one converter, said lances
mounted on a movable trolley, the Lance platform adapted to move either in left or right
direction for positioning of one of the lances with said lance adapted for moving upward or
downward as per requirement at desired height from metal level for a predetermined time
during blowing, said sensor means comprising multi-turn absolute encoder which is
mounted on extended shaft of non driving end of worm reducer, the input shaft of worm
reducer connected to motor and output shaft connected to driving sprocket, which controls
the upward and downward movement of lance vertically, means for converting position
data into serial data and transmitting for receiving at processing unit and converted back
parallel data by binary converter;
(b) said PLC based measurement unit comprises two position sensors for said left and right
lances, the position signals converted back to binary signals by binary converter, said
binary converter output interfacing directly with digital input module of PLC, the position
signals being processed by CPU of PLC and adapted to generate 4-digit Binary Coded
output at 24 VDC level for display of lance position in separate unit;
(c) said display unit for lance position comprising preferably 24 VDC Binary Coded Digit
(BCD) output generated by PLC directly connected to 4-digit display, said display unit
having facility to reference lance position measurement system manually by keeping lance
tip at pre-determined position and pressing the push-button displays lance position of pre-
determined position, single push-button adapted for referencing both lances by Blower
(Operator) for referencing the lance position as required.
A still further aspect of the present invention is directed to a system for on-line digital
position measurement of lance position for converter operation comprising:
means interfacing the encoder with PLC comprising SSI to binary converter for converting
serial signal to parallel signal, the output of binary converter being directly interfaced with
PLC, a maintenance/ programming console being interfaced with PLC on Ethernet adapted
to diagnose any fault in PLC system.
The present invention and its objects and advantages are described in greater details with
reference to the following non limiting illustrative examples.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: is the schematic illustration of the conventional system for lance operation.
Figure 2: is the schematic illustration of the conventional lance positioning sensing system.
Figure 3: is the schematic illustration of the encoder based lance positioning system
according to the present invention.
Figure 4: is the schematic illustration of the encoder interface scheme as of the present
invention.
Figure 5: is the schematic diagram of the complete system for encoder based on-line lance
position sensing/measuring system for converter according to the present invention, clearly
showing the different elements and their functional interconnectivity.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
The present invention is directed to a system for lance position measurement and display
for two lances of a BOF converter. This position sensing and control is implemented on
Programmable Logic Controller (PLC) interfaced with PC based maintenance console through
an Ethernet network favoring easy and quick diagnosis of fault. The position of left and right
lances is obtained from absolute encoders, which are mounted on respective lance driving
units. These position signals are transmitted by multi-core cables over approximately a
length of 100 meters. The transmitted signals are converted into serial data with transmitter
on encoder and receiver in SSI to binary converter located in PLC panel.
Reference is first invited to the accompanying Figure 1 that illustrates the over view of
traditional lance operations for steel making in BOF converters. The lance has interlocking
outputs for platform movement, converter tilting, oxygen start, oxygen stop,
acceleration/deceleration of lance movement in upward/ downward direction which are
obtained from multi-point cam switch. This cam switch also provides both lower and upper
limits.
Reference is now invited to the accompanying Figure 2 that illustrates the conventional
lance positioning system for converters. Said Figure 2 describes the location of Selsyn on
lance platform. Kinematic gear unit has been appropriately configured and used for getting
multiple shafts for connecting selsyn and 3 nos. of rotary switches known as command
apparatus. In the existing art, selsyn is used as position sensor and it generates current
according to its position. The transmitted current is receiver at distant end to rotate another
equipment in synchronism to show position of lance.
Accompanying Figure 3 shows the encoder based lance positioning system involving multi-
turn absolute encoder according to the present invention, wherein the arrangement is same
as in Figure 2 additionally illustrating the shaft extension of worm reducer for connecting
absolute encoder for position measurement. This arrangement has advantage with respect
to previous art in terms of less mechanical mis-alignment and slippages.
The implemented system has digital display for both lance positions and in addition to that a
running timer is also provided through digital display, which was not available in
conventional systems. The new networked PLC system is capable of easy and quick
diagnosis/ fault detection mostly on maintenance console. An Ethernet network is used for
connecting of PLC panel with PC based maintenance console. A redundant off-line Ethernet
connection facility is also provided near to panel in addition to existing network connection.
The maintenance console can be hooked-up at centralized location or near to panel as per
requirement.
The new Lance Position Indication (LPI) system consists of position measurement sensors
i.e. multi-turn absolute encoder at lance platform, located at a greater height and PLC with
display at control room at a lower height for viewing by the operator. Mechanical
modification is carried out on existing worm reducers and lance platform extension to install
position measurement sensors for both left and right lances without disturbing other major
equipments on lance trolley.
Reference is next invited to the accompanying Figure 4 that schematically illustrates the
schemes for interfacing the absolute encoder with PLC. Synchronous Serial Interface (SSI)
is used to favour transmission of lance position signals over a large distance and for
converting serial signal to parallel signal. The output of SSI to binary converter is directly
interfaced with PLC.
The accompanying Figure 5 schematically illustrates the total system for lance position
measurement/sensing and display as of the present invention. It is clearly apparent from
Figure 5 that a maintenance/ programming console is interfaced with PLC through Ethernet
network. Any fault in PLC system is advantageously diagnosed with the help of this console.
The present invention also provides stable power supply to processor unit through Constant
Voltage Transformer (CVT), which takes care of ± 10 - 15 % input voltage fluctuations on
power line.
The present invention has been successfully implemented in SMS of steel plant, where more
than one converter, such as in SMS of a steel plant where 5 nos. of 130 Ton converters are
operated are used for steel making. This system shall be upwardly connected to other
systems through networking. The position measurement according to the invented system
involves display of lance position continuously during upward and downward movement.
The implementation of such a system has resulted in about 60% reduction in tip leakage
and enabling precise lance positioning accurately within a tolerance of ± 1 cm.
The system of the present invention consisting mainly of three parts: (a) Lance position
sensors on lance trolley; (b) PLC based position measurement unit; and (c) Display unit for
lance positions.
The details of the features of the subsystems are as follows:
(a) Lance position sensors :
There are normally two lances located in one converter. During blowing of oxygen in
converter, one of the lances is put to service at a particular instant while the other one
remains unused. On a next occasion, the order of use of the lances are reversed. These
lances are mounted on a movable trolley. Lance platform moves either in left or right
direction for positioning of one of the lances. Lance also moves upward or downward as per
requirement. However, its position is extremely important at the time of oxygen blowing.
Operator positions the lance at desired height from metal level for a predetermined time
during blowing. The blowing is required at different heights for a fixed interval of time as
per operational requirement. The accuracy of lance position is important in this respect. The
calibration of position measurement is done at fixed height and operator checks
measurement accuracy periodically. In the LPI system of the present invention multi-turn
absolute encoder has been used as position sensor. This encoder is mounted on extended
shaft of non-driving end of worm reducer. The input shaft of worm reducer is connected to
motor and output shaft is connected to the driving sprocket, which operatively controls the
upward and downward movement of lance vertically inside the converter. As the distance
between the position measurement and that of processing unit is large enough, position
data is converted into serial data and transmitted over SSI link, as already described. This
data is received at processing unit and converted back to parallel data by SSI to binary
converter.
(b) PLC based position measurement unit:
Two position sensors are used separately for left and right lances. The position signals
converted back to binary signals by SSI to binary converter. The voltage level of binary
converter output is 24VDC for interfacing directly with digital input module of PLC. The
position signals are processed by CPU of PLC and generates 4-digit Binary Coded output at
24 VDC level for display of lance position in separate unit. In previous art, electro-
mechanical system was used to achieve synchronous rotation of receiving unit with respect
to transmitting unit.
(c) Display unit for lance positions :
The 24 VDC Binary Coded Digit (BCD) output generated by PLC is directly connected to 4-
digit display. This display unit has a facility to reference lance position measurement system
manually by keeping lance tip at pre-determined position and pressing the push-button
displays lance position of pre-determined position. Single push-button is used for
referencing both lances. Operator (Blower) is capable of referencing the lance position as
required. In the previous art, adjusting gear mechanism of analog measuring unit does
referencing the lances at pre-determined position and this requires intervention from
instrument personnel and requires more time.
It is thus possible by way of the present invention to developing an online system for
precise measurement and digital display of lance position in converter operation adapted to
precisely determine and position the lances to an accuracy of ± 1 cm. The system is
provided with facility of instant calibration using push button switch and avoids
requirements of frequent calibration. An Ethernet networking interface of the processing
unit with maintenance console favor easy and quick fault diagnosis and maintenance and
thus reducing the converter down time improving the productivity. The system adopted the
multi-turn absolute encoder as position sensor for the present LPI and introduced SSI based
signal transmission for processing and display at distant location of the operator's pulpit
with reliability and free of any error. Moreover, a scheme for redundant power sourcing for
the system ensure reliable un-interrupted sensing and display service even in the event of
power failure. Importantly, the precise lance positioning and display facility of the present
system enable control the lance position to ensure reducing the tip leakage to an extent of
about 60% than convention. The sensor and signal cables are protected from harsh
operating conditions of shop floor. Advantageously, the lance position as well as the
blowing time is displayed on the digital display on either of right lance or left lance, favoring
accurate process control in converter operation and achieving improved productivity and
quality of steel products. The present online Lance Position Indicator system thus having
potential for wide industrial application in SMS shop in steel plants with significant economic
advantage.
WE CLAIM:
1. A system for on-line digital position measurement of lance position for converter
operation comprising:
(a) lance position sensors on lance trolley;
(b) PLC based position measurement unit; and
(c ) display unit for on-line digital indication of the lance position.
2. A system for on-line digital position measurement of lance position for converter
operation as claimed in claim 1 wherein the said lance position measurement sensor
comprise for both left and right lances multi-turn absolute encoder at lance platform which
is located at a greater height and said PLC based display is located at control room at a
lower height.
3. A system for on-line digital position measurement of lance position for converter
operation as claimed in anyone of claims 1 or 2 comprising elimination of parallax error in
reading lance position wherein the lance position measurement and display for both left and
right lances of a converter are provided in two separate panel/enclosures and involve
separate cables for easy traceability of signals and maintainability.
4. A system for on-line digital position measurement of lance position for converter
operation as claimed in anyone of claims 1 to 3 comprising:
Ethernet network providing interconnectivity of processing unit with electronic maintenance
console;
sensor means protected from dust, heat, water spray with shaft sealing facility and
enclosed in dust-proof enclosure;
said sensor cables protected from heat with asbestos clothing and termination of cables
from lance trolley to junction boxes with appropriate sagging for trolley movement from left
to right and vice versa;
means for sharing same digital display for lance position or blowing time; and
power sourced from two sources such that in the event of failure of one source, automatic
switching over to other source .
5. A system for on-line digital position measurement of lance position for converter
operation as claimed in anyone of claims 1 to 4 comprising:
lance position indication means with an accuracy of + 1 cm
press-button switching adapted for instantaneous calibration of lance position by pressing
single push-button
synchronous Serial Interface (SSI) for reliable transmission of position signal over long
distance .
6. A system for on-line digital position measurement of lance position for converter
operation as claimed in anyone of claims 1 to 5 comprising :
(a) said lance position sensors comprising two lances in one converter, said lances
mounted on a movable trolley, the Lance platform adapted to move either in left or right
direction for positioning of one of the lances with said lance adapted for moving upward or
downward as per requirement at desired height from metal level for a predetermined time
during blowing, said sensor means comprising multi-turn absolute encoder which is
mounted on extended shaft of non driving end of worm reducer, the input shaft of worm
reducer connected to motor and output shaft connected to driving sprocket, which controls
the upward and downward movement of lance vertically, means for converting position
data into serial data and transmitting for receiving at processing unit and converted back
to parallel data by binary converter;
(b) said PLC based measurement unit comprises two position sensors for said left and right
lances, the position signals converted back to binary signals by binary converter, said
binary converter output interfacing directly with digital input module of PLC, the position
signals being processed by CPU of PLC and adapted to generate 4-digit Binary Coded
output at 24 VDC level for display of lance position in separate unit;
(c ) said display unit for lance position comprising preferably 24 VDC Binary Coded Digit
(BCD) output generated by PLC directly connected to 4-digit display, said display unit
having facility to reference lance position measurement system manually by keeping lance
tip at pre-determined position and pressing the push-button displays lance position of pre-
determined position, single push-button adapted for referencing both lances by Blower
(Operator) for referencing the lance position as required.
7. A system for on-line digital position measurement of lance position for converter
operation as claimed in anyone of claims 1 to 6 comprising:
means interfacing the encoder with PLC comprising SSI to binary converter for converting
serial signal to parallel signal, the output of binary converter being directly interfaced with
PLC. , a maintenance/ programming console being interfaced with PLC on Ethernet adapted
to diagnose any fault in PLC system.
8. A system for on-line digital position measurement of lance position for converter
operation substantially as hereindescribed and illustrated with reference to the
accompanying figures.

A system for Lance Position Indication (LPI) for accurate and precise on-line measurement
of oxygen lance positioning in BOF converters for steel making process in SMS comprising
(i) Lance position sensors on lance trolley; (ii) PLC based position measurement; and (iii)
Display unit for Lance positions. More particularly, the present system uses multi-turn
absolute encoder as position sensor and digital display means for lance position both right
and left lances with an accuracy of ± 1 cm with respect to center of converter and level of
liquid metal, with the facility for instant calibration and the digital display of lance position as well as blowing time indicated on 4-digit display panel of the lances, so as to reduce tip leakage for lance positioning error. The system employs multi-turn absolute encoders to operatively control the precise vertical up and down positioning of lances in converter. The
processing unit of the system is interconnected with electronic maintenance console via Ethernet network favoring easy and faster fault diagnosis. The system reduces tip leakage by about 60%.