CLIAMS:WE CLAIM
1. A process of optimizing steel making, comprising the steps of:
providing slag analysis from source database;
providing the other parameters including lime and dolo composition;
inputting the hot metal composition, for recording the basicity and % MgO;
calculating typical slag composition based on the avg. %CaO+%SiO2+%MgO in
the slag and the basicity using the lime and dolo correction factors from the source
database;
calculating the required amount of lime and dolo which is to be added on the basis
of basicity and %MgO, weight and composition of hot metal and scrap using the
oxygen correction factors from the source database;
calculating oxygen required from the hot metal, scrap composition and amount
oflime and dolo using the temperature correction factors from the source database;
calculating heat balance based on heating effect of different elements and cooling
effect of different additions in the hot metal scrap;
calculating the waiting time and its temp loss effect;
predicting the steel temperature at the end of blow and amount of oxygen required.
determining slag carry-over weight and steel weight; and their predicted
composition; and
refining of the hot metal including stages of de-oxidizing said steel and slag,
alloying and refining the steel to bring flux C, Ca, Si, and Mn elements contained
therein within predetermined limits as per the source database.
2. The process as claimed in claim 1, further including the steps of:
executing a feedback module to update correction factors based on actual
measurements recorded during steel making;
recording updated factors in the source database which is used in next heat ; and
recording the heat details in the source database.
3. The process as claimed in claim 1, wherein some of the said fluxing agents are
added in hot metal scrap.
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4. The process as set forth in claim 11, wherein the slag chemistry includes
%CaO+%SiO2+%MgO=75 and %FeO=20 alloys based on requirements for
product specifications.
5. The process as claimed in claim 1, wherein the volume of oxygen required is
calculated as 1 kg of oxygen corresponds to 0.7m3 of oxygen at STP.
6. A process for controlling and determining the amount of slag carryover in steel
making during tapping, using the process as claimed in claim 1 further comprising
steps of:
providing an algorithm for the quantitative relationship between slag formed and
thermal balance;
providing level detection means for detecting the level of liquid steel within said
ladle; and
determining required mass of tapped steel for a mass of metallic charge and
thermal balance from said algorithm.
7. The process as claimed in claim 6, wherein the flux balance, oxygen and
temperature balance modules depend on the accuracy of the measured input
parameters
8. The process as claimed in claim 10, wherein the detected value and determined
value is calculated feedback and correction module which measures this deviation
from the determined values oflime, dolomite, oxygen balance and temperature
factors and are calculated based on the formula : Correction Factor = (Actual
Value - Predicted Value)/Predicted Value
9. The process as claimed in claim 8, wherein the calculation further includes a
weighted average running factor is calculated in order to reduce the noise from
heat to heat, which is calculated by the following formula:
Factor for current heat = (1xF1 + 2 x F2 + 3 x F3 + 4 x F4 + 5 x F5) / 16 where F1,
F2, F3, F4, F5 are the factors for last 5 heats with F5 being the factor for last heat.
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10. The process as claimed in any of the preceding claims, wherein the different
modules of the BOF model are flux balance module, oxygen balance module,
thermal balance module, data logging module, feedback and correction module,
lance movement modules are all integrated together.
11. The process as claimed in claim 8, wherein the correction parameter of
temperature is also stored which is used for offline analysis of the performance of
the model.
Dated: this 26th day of May, 2015.
(N. K. Gupta)
Patent Agent, ,TagSPECI:2
AN IMPROVED BOF PROCESS MODEL FOR STEEL MAKING
FIELD OF THE INVENTION
The present invention relates to an improved process model for Basic Oxygen
Furnace (BOF) Steelmaking. The present invention relates to calculation of static
charge balance of materials to be input during steelmaking to achieve the desired
output of steel in terms of chemistry and temperature.
BACKGROUND AND PRIOR ART OF THE INVENTION
Research & Development Centre for Iron and Steel (RDCIS), Ranchi and Rourkela
Steel Plant (RSP), Rourkela have designed, installed and commissioned “An
improved BOF Process Model for Steelmaking.” This system is being utilized
successfully since commissioning at Steel Melting Shop - II (SMS-II), Rourkela
Steel Plant. Steel Melting Shop- II has 3 converters of 150 t each. The present
invention is installed in Converter-1 and Converter-2 in the Steel Melting Shop- II
(SMS-II). The Basic Oxygen Furnace (BOF) Steelmaking process is autogenous,
or self-sufficient in energy. The primary raw materials for the BOF are 70-80%
liquid hot metal from the blast furnace and the balance as steel scrap. These are
charged into the Basic Oxygen Furnace (BOF) vessel. Oxygen (>99.5% pure) is
"blown" into the Basic Oxygen Furnace (BOF) at supersonic velocities. It oxidizes
the carbon and silicon contained in the hot metal liberating great quantities of heat
which melts the scrap. There are lesser energy contributions from the oxidation of
iron, manganese, and phosphorus. The post combustion of carbon monoxide, as it
exits the vessel, also transmits heat back to the bath. The product of the BOF is
molten steel with a specified chemical analysis at 1600 to 1700°C. The operation
of BOF starts with charging of scrap, and then hot metal into the vessel. A multihole
lance for top-blowing pure oxygen is inserted from the throat and lowered
near the surface of hot metal. Blowing starts with a supersonic jet of pure oxygen
gas impinging on the metal bath. The oxygen jet contacts the metal bath directly
and is picked up by the molten iron. The dissolved oxygen reacts with other
3
elements dissolved in the molten metal at the interfaces between metal and gas,
and between metal and slag. Meanwhile, metal droplets are ejected through the
slag phase and metal droplets are simultaneously in contact with FeO in the slag.
Gas bubbles are generated due to a decarburization of metal droplets via FeO
reduction. Slag-metal-gas emulsion is formed due to refining reactions. Silicon is
oxidized in first few minutes, transfer of P, Mn and Carbon takes place over entire
blow period. The solid oxides formed due to this oxidation are then fluxed with
calcined lime and dolomite to form a slag of desired composition which aids in
removal of sulphur and phosphorus from steel. At the end of blowing period, all the
residual elements are oxidised and captured in slag or ejected as gaseous oxides.
The temperature of the steel rises due to generation of heat during oxidation. The
slag is removed from the steel and then samples for chemistry and temperature
(First Turn Down) are taken. Once the temperature and chemistry conform to the
desired output the steel tapped into ladle for further processing.
The blowing regimes i.e. oxygen flow rate and lance height have a significant effect
on the path followed during slag formation and each plant eventually standardizes
its own blowing regime depending upon many operating factors viz., hot metal
quality, hot metal scrap ratio, lime quality and size, converter size, lining material,
use of fluxing agents, cost of raw materials, metallic yield, thermal losses etc.
Owing to its very fast and multi-phase nature of the process, the control of BOF in
terms of lance height control, oxygen flow control, timely addition of fluxes and
coolants etc., to reach the target window of chemistry and temperature have
always been a challenging task. Process control based on visual observation and
operator’s reflexes or based on few simple measurements for such a complex,
multiphase, transient high temperature process is a daunting task. These
difficulties can be addressed by employing mathematical process control models
which make it possible to describe the complicated nature of the process and
provide fairly accurate predictions. Mathematical model have been developed to
describe the complicated nature of the process and be used as a predictive tool to
control the process.
4
The earlier model system installed in Converter-1 and Converter-2 was based on
stoichiometric calculations of various metallurgical equations related to
steelmaking. However, the balances performed had a number of closing
parameters which are difficult to measure. With a large number of input
parameters, whose data is missing or difficult to measure, it was difficult to fine
tune the model. The model also had no provision for the changes that has been
incorporated in BOF steelmaking practice such as slag splashing.
The present inventors have designed, installed and commissioned a model system
for calculation of static balances for BOF and for better and scientific way of
controlling the process of Steelmaking. The present invention takes into account
the statistical variation of slag chemistry of the Steel Melting Shop-II for making the
slag balance and calculation of flux requirement. The improved system takes into
account all the major parameters that need to be monitored by the operator and
providing the same through a single window. Lance movement for the blowing can
be predefined and can be controlled by the model system in computer mode. The
model also has been equipped with feedback and correction routines which
dynamically keeps adjusting the factors to reduce the variance between predicted
and actual output.
OBJECTS OF THE INVENTION
One object of the present invention is to overcome the disadvantages / drawbacks
of the prior art.
A basic object of the present invention is to provide a method for calculation of flux
and oxygen requirement for steelmaking, prediction of end temperature through a
mathematical model.
Therefore such as herein described there is provided a process of optimizing steel
making, comprising the steps of: providing slag analysis from source database;
providing the other parameters including lime and dolo composition; inputting the
hot metal composition, for recording the basicity and % MgO; calculating typical
5
slag composition based on the avg. %CaO+%SiO2+%MgO in the slag and the
basicity using the lime and dolo correction factors from the source database;
calculating the required amount of lime and dolo which is to be added on the basis
of basicity and% MgO, weight and composition of hotmetal and scrap using the
oxygen correction factors from the source database;calculating oxygen required
from the hot metal, scrap composition and amount of lime and dolo using the
temperature correction factors from the source database;calculating heat balance
based on heating effect of different elements and cooling effect of different
additions in the hot metal scrap; calculating the waiting time and its temp loss
effect; predicting the steel temperature at the end of blow and amount of oxygen
required; determining slag carry-over weight and steel weight; and their predicted
composition; andrefining of the hot metal including stages of de-oxidizing said steel
and slag, alloying and refining the steel to bring flux C, Ca, Si, and Mn elements
contained therein within predetermined limits as per the source database.
As per another exemplary embodiment, the said process for controlling and
determining the amount of slag carryover in steel making during tapping, further
comprising steps of: providing an algorithm for the quantitative relationship
between slag formedcarryover and thermal balance;providing level detection
means for detecting the level of liquid steel within said ladle;anddetermining
required mass of tapped steel and for a mass of metallic charge and thermal
balance from said algorithm.
Another object of the present invention is to provide an improved method for
monitoring and automatic control of lance movement according to standard
blowing pattern.
Yet another object of the present invention is to providea method for setting the
correction factors in a scientific manner through a mathematical model.
Yet another object of the present invention is to provide a method for logging all
the relevant heat making data and generating daily heat reports automatically.
6
These and other advantages of the present invention will become readily apparent
from the following detailed description taken in conjunction with the accompanying
drawings.
SUMMARY OF THE INVENTION
According to one of the aspect of the present invention there is provided an
improved mathematical model for calculation of flux (lime and dolomite) for
formation of slag of desired chemistry. Improved mathematical model for
calculation of oxygen requirement and an improved logic for calculation of the
temperature at First Turn Down at the end of steelmaking. The invention has a
mathematical model for adjustment of correction factors based on outcomes of
past heat. It also has an improved logic for automatic control of lance movement
during auto control mode of blowing. The overall BOF model system is based on
improved mathematical models for prediction of flux, oxygen, temperature,
feedback and correction, data logging.
Therefore such as herein described there is provided a process of optimizing steel
fabrication, comprising the steps of: providing a carrier vessel for retaining liquid
steel; geometrically determining the volume of said carrier vessel; determining,
while tapping, a steel weight and slag weight for a given height of slag and steel in
said carrier vessel; profiling said carrier vessel using slag line, barrel and ladle
bottom life information; providing steel treatment in the ladle including adding
alloying agents to said steel in said ladle; determining the height of steel in said
carrier vessel; determining slag carry-over weight and steel weight; and a refining
stage including: de-oxidizing said steel and slag, alloying and refining the steel to
bring Ca, Si and Mg elements contained therein within predetermined limits.
As per another exemplary embodiment, also described herein a process for
controlling and determining the amount of slag carryover in steel fabrication during
tapping, comprising: providing an algorithm for the quantitative relationship
between slag carryover and thermal balance; determining required mass of tapped
steel and level within a ladle for a mass of metallic charge and thermal balance
7
from said algorithm; providing level detection means for detecting the level of liquid
steel within said ladle; comparing determined level of steel within said level with a
detected value; and ceasing tapping when said detected value and determined
value for said steel level in said ladle are equivalent, whereby slag carryover is
minimized.
BREIF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates the flowchart of the mathematical logic followed for the BOF
model system
Figure 2 illustrates the new GUI of the BOF model system in accordance with the
present invention;
Figure 3 illustrates the GUI of the operator’s interface i.e. single window in the
operator’s pulpit running in computer mode for automatic lance movement during
steelmaking in accordance with the present invention;
Figure 4 illustrates a graph showing the variation in the predicted temperature
against measured temperature in sample heats in accordance with the present
invention;
Figure 5 illustrates a graph showing the variation in the predicted lime against
actual lime consumption in sample heats in accordance with the present invention;
Figure 6 illustrates a graph showing the variation in the predicted dolo against
actual dolo consumption in sample heats in accordance with the present invention;
Figure 7 illustrates a graph showing the variation in the predicted oxygen against
actual oxygen consumption in sample heats in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to an improved model for calculation of lime and
dolomite required for slag making, oxygen required for removing residual elements
and prediction of temperature during steelmaking. Automatic control of lance
movement is based on the standard blowing schemes designed and stored in the
8
model. Blowing during steelmaking is based on the results of the calculation of the
model.
Major variables and their descriptions in the model system are listed in Table 1
The present model is a mathematical logic as detailed in the flow chart in Figure
1.that has been soft coded in programmable software.
The earlier model system developed had many screens where data entry was
repetitive. A number of important parameters were distributed on different screens.
Operators needed to switch between different screens to see important blowing
parameters. Parameters which were important for blowing like, total oxygen blown,
lance height, oxygen flow rate, blow start time, blowing time etc. were all brought
on single redesigned screen and called the “Main Blowing Screen” (Figure 1). This
screen provides all the necessary information to the blower and is being used
regularly by the operator during blowing.
Figure 2 shows the Main Blowing Screen for BOF model. The left portion of the
screen details about lance and lance related parameters. Bottom left section
shows the waste gas details during blowing, blowing time, blow start time etc. The
top central section depicts the flux addition details. Below that, in the tapping
section, the system currently displays the tap start time, tap duration, tap additions
through ferroalloy bunker. The bottom central section shows the lance control
mode, blow pattern details etc. It also has control button to shift from manual mode
to auto lance movement mode. The right bottom corner of the screen provides two
tabbed windows for charge calculation, and graphical representation of waste gas
CO, CO2, lance movement in the graph. The charge calculation screen is the
window in which inputs are to be provided. Bottom of the charge window shows the
flux and oxygen advice. It also shows the predicted temperature of the blow.
9
Model for Slag Balance
Analysis of a number of first turn down slag samples of suggest that
(%CaO+%SiO2+%MgO) in slag vary within a narrow range. Thus assumption for a
fixed amount of (%CaO+%SiO2+%MgO) in slag can considered for creating a flux
balance. In any steelmaking shop, to ensure proper dephosphorisation of steel, an
optimum slag basicity is fixed. This slag basicity varies from 2.8 to 3.5. This is one
of the desired parameters. In order to ensure minimum erosion from the converter
lining the slag should be saturated with MgO. For steelmaking slags, MgO around
8-10% is considered to be the saturation level. The MgO content of slag is also
one of the desired parameters in steelmaking. Fluidity of slag is an important
parameter that has to be kept in consideration during steelmaking. For ease of
operation the slag should be fluid enough to be easily removed. Too viscous slag
will lead to dry blow and poor dephosphorisation. On the other hand, too fluid slag
will have slopping tendency. Very fluid slags are also unable to hold phosphorous
and so there is a tendency of phosphorus reversal. It is seen that when FeO is
around 18-20% in slag, maximum dephosphorisation is achieved.
Thus we have an optimum slag chemistry where Basicity is 3; MgO content is 9%,
FeO content of 20%. When the total content of CaO, SiO2, and MgO in slag is fixed
based on plant measurements, we can calculate percentage of all the major oxides
of slag. The equation (%CaO+%SiO2+%MgO=75) suggests that typical slag
composition for such assumption will be % SiO2 =16.5, CaO = 49.5 %, % MgO = 9,
% FeO=20 %, Rest oxides = 5 %.
From the above calculation, a desired slag chemistry can be achieved by making
assumptions of %CaO+%SiO2+%MgO = 75 and %FeO=20 in slag. Together with
required basicity and aim MgO, the assumptions help in calculating the weight of
fluxing agents required and the weight of slag formed. By carrying out balance of
SiO2, CaO and MgO the required weights of calcined lime, dolomite and the weight
of slag can be known.
10
The slag balance can be performed by solving three equations for SiO2, CaO and
MgO for the unknown weights of lime, dolo and slag formed.
Oxygen Balance
Oxygen is required in steel to oxidise the known impurities to its oxidise. In order to
simplify the model, oxygen required for oxidation of Carbon, Silicon and
Manganese is considered. Oxygen required for oxidation of Fe to FeO to the tune
of 20% in slag is taken into account. A stoichiometric equation for oxidation of
Carbon, Manganese and Silicon is taken into consideration for calculation. Once
the weight of oxygen is required, the volume of oxygen required is calculated as 1
kg of oxygen corresponds to 0.7m3 of oxygen at STP. The list below shows the
oxygen consumption coefficient of various elements of interest in steelmaking
Oxygen = 933 m3/t
Oxygen = 203 m3/t
Oxygen = 903 m3/t
Oxygen = 797 m3/t
Oxygen = 467 m3/t
Oxygen = 622 m3/t
The uncertain terms which cannot be measured directly has been considered in
the closing terms and taken care through the factor K which is updated in the
Feedback and Correction Routine.
Lance Movement Module
The Lance Movement Module consists of scripts which change the lance height
during the blow based on Standard Blowing Patterns. The standard blowing
pattern is saved as a comma separated text file and saved under filename such as
11
‘BP#.txt’. The # is replaced with number such as 0,1,2,3 and likewise to generate
different kinds of lance pattern based on different set of input parameters. A typical
lance blow pattern file is shown here: -
0,2.65
501,2.55
1001,2.45
1501,2.30
2000,2.10
2500,1.90
2650,1.80
2800,1.70
2900,1.60
5000,2.00
5060,1.50
6000,2.50
6100,1.50
7000,2.50
7100,1.50
7500,2.50
7600,1.50
8000,2.50
8100,1.50
8200,2.50
8300,1.50
50000,10.50
In each row, the first data corresponds to total oxygen and the second data shows
the lance height. The bath height correction factor is added to the lance height at
that oxygen and information is accordingly downloaded to PLC setting the lance
height. For example, if total oxygen is 1600, then from above mentioned data we
find lance height between 1501-2000 of oxygen is 2.30 meters. If the bath
correction factor is 0.9. The actual lance height becomes 3.2 meters. Once total
oxygen reaches 2000 Nm3, lance will move to its new position of 3.0 meters. The
12
lance movement module has capability to take control of the lance movement in
Computer Mode and make blow according to the pattern set. The module has
provision to read the next set of data and load it into a set of variables. Moment the
total oxygen of that set of data is read, the new lance height is immediately sent to
PLC and lance height is set accordingly. This has led to standardisation of blow for
different levels of hot metal silicon and temperature. The lance movement module
has provision for the blower to change the blow patterns. However, the pattern
currently being used during blow is locked and cannot be changed. This has been
done to take safety precautions. Also it has a number of checks to prevent unsafe
lance movements. Figure 3 is screenshot of operator’s desk taken during
steelmaking when the lance control was in computer mode. The operator can take
control in manual mode whenever there is some abnormality. Manual override has
the highest priority.
Heat Balance
The heat balance or the thermal balance routine takes into account the effect of
heating due to oxidation of the input elements, the cooling factor of additions like
lime, calcined dolo, iron ore and scrap. Losses in terms of temperature is
considered for the converter waiting time, i.e. the time between last heat tap end to
current heat blow start. A heat loss from the converter during this waiting time
follows a parabolic path. However, in the current implementation, this temperature
loss is linearized for different waiting period.
Pseudo code below shows the logic for implementation of the waiting loss
If Waiting Time < 20 min then
Temp Loss = 20oC
else if 20 min < Waiting Time < 30 min then
Temp Loss = Waiting Time x 1.0
else if 30 min < Waiting Time < 60 min then
Temp Loss = 30 + (Waiting Time - 30 ) x 0.5 then
else
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Temp Loss = 45 + (waiting Time - 60) x 0.25
If Temp Loss > 75oC then
Temp Loss = 75oC
The heat of oxidation of all the major elements (C, Mn, and Si) is taken into
account. It is initially assumed that each kilogram of oxidation element raises the
temperature of the bath by 0.1oC. Thus if hot metal analysis contains 4.2 % C, 0.05
% Mn, 0.95% Si, then the total weight of all these oxidation elements for a 150t hot
metal input will be
Oxidation Elements (kg) = (4.2%+0.05%+0.95%) x 150 t = 7800 kg.
So according to the above assumption the expected increase in steel temperature
will be 780oC. However, such rise in temperature of the bath is not seen in reality,
because a portion of this heat is lost in waste gases, to the converter lining etc.
This rise in temperature is corrected by multiplying with a correction factor which is
adjusted through the feedback and correction routine.
Additions made during steelmaking like lime, dolo, iron ore takes away a part of
heat to go into solution at steelmaking temperature. Losses in terms of
temperature for each ton of scrap, lime and dolo added is predefined. Similarly loss
on account of formation of slag is also defined. The total heat loss in terms of
temperature for these additions is calculated.
The predicted bath temperature is corrected with the help of temperature
correction factor
Feedback & Correction Module
The flux balance, oxygen and temperature balance modules depend on the
accuracy of the measured input parameters. Inaccuracies in the measured values
of inputs, missing measurements or lack of certain measurements make it
14
impossible to accurately predict the output. Hence a deviation in the predicted
value from the actual output will be observed. The feedback and correction module
measures this deviation from the predicted values. Lime, dolomite, oxygen balance
and temperature factors are calculated based on the following principle.
Correction Factor = (Actual Value - Predicted Value)/Predicted Value
Correction factors are calculated at the end of heat when all the additions made,
oxygen consumed and bath temperature are known. The values of these factors
are logged for last five heats. A weighted running average of the correction factors
are then calculated in order to arrive at correction factors for next heat. A weighted
average running factor is calculated in order to reduce the noise from heat to heat.
The weighted average is calculated by the following formula:
Factor for current heat = (1xF1 + 2 x F2 + 3 x F3 + 4 x F4 + 5 x F5) / 16 where F1,
F2, F3, F4, F5 are the factors for last 5 heats with F5 being the factor for last heat.
Different modules of the BOF model such as flux balance module, oxygen balance
module, thermal balance module, data logging module, feedback and correction
module, lance movement modules are all integrated together with the HMI. The
data logging modules creates a link with Oracle Database to create a daily log of
all the heats from each converter. The log file generates an excel report which
provides information on the converter input parameters such as hot metal and
scrap weight, chemistry and temperature of hot metal. It also generates report on
the predicted and actual values of flux, oxygen consumption. It also stores
information on the predicted and actual temperature during heat making. The
correction parameter of temperature is also stored which is used for offline analysis
of the performance of the model.
Figure 4 represents the results from the model indicating that temperature
predictions are quite reasonable for a majority of heats. There have been very few
instances where there is a substantial deviation between the predicted and actual
15
temperature. The plot also indicates that a majority of heats are being opened
around First Turn Down of 1640 to 1690oC.
Figure 5, 6 and 7 shows the relationship between the predicted amount of lime,
dolo and oxygen and the actual amount of lime, dolo or oxygen consumed. There
is an improvement in the hit rate. Most of the data points lie around the 1:1
diagonal line signifying a strong correlation between predicted and actual values.
Table 1. List of major variables and their description
Variable Name Unit of
variable
Description
HM_Wt T Weight of input hot metal in weight (User input)
HM_C % Percentage composition of hot metal carbon (User input)
HM_Mn % Percentage composition of hot metal manganese (User input)
HM_Si % Percentage composition of hot metal silicon (User input)
HM_Temp 0C Temperature of the hot metal in Celsius (User input)
Scr_Wt T Weight of input scrap metal in weight (User input)
Scr_C % Percentage composition of scrap carbon (Read from file)
Scr_Mn % Percentage composition of scrap manganese (Read from file)
Scr_Si % Percentage composition of scrap silicon (Read from file)
Scr_Temp 0C Temperature of the scrap (Read from file)
Aim_Bas -- Aim Basicity of the slag (User input)
Aim_MgO -- Aim % MgO of the slag (User input)
Pr_Lime T Predicted amount of lime that has to be added (Output)
Pr_Dolo T Predicted amount of calcined dolo that has to be added (Output)
Pr_Oxygen Nm3 Predicted amount of oxygen that has to be blown (Output)
Pr_Temp 0C Predicted temperature of the steel formed (Output)
Act_Lime T Actual amount of lime added (Measured variable)
Act_Dolo T Actual amount of calcined dolo added (Measured variable)
Act_Oxygen Nm3 Actual amount of oxygen added (Measured variable)
Reblow_Oxygen Nm3 Amount of oxygen reblown (Measured variable)
Act_Temp 0C Actual temperature measured at the end of heat making
(Measured variable)
Corr_Fact_Lime -- Correction factor for lime flux calculation ( Read/Write in File)
Corr_Fact_Dolo -- Correction factor for dolo flux calculation ( Read/Write in File)
Corr_Fact_Oxy -- Correction factor for predicted oxygen calculation ( Read/Write in
File)
Corr_Fact_Temp -- Correction factor for temperature calculation ( Read/Write in File)
Slag_CaO % Typical composition of % CaO in slag (internal variable)
Slag_SiO2 % Typical composition of %SiO2 in slag (internal variable)
Slag_MgO % Typical composition of %MgO in slag (internal variable)
Slag_FeO % Typical composition of %FeO in slag (internal variable)
16
Although the foregoing description of the present invention has been shown and
described with reference to particular embodiments and applications thereof, it has
been presented for purposes of illustration and description and is not intended to
be exhaustive or to limit the invention to the particular embodiments and
applications disclosed. It will be apparent to those having ordinary skill in the art
that a number of changes, modifications, variations, or alterations to the invention
as described herein may be made, none of which depart from the spirit or scope of
the present invention. The particular embodiments and applications were chosen
and described to provide the best illustration of the principles of the invention and
its practical application to thereby enable one of ordinary skill in the art to utilize the
invention in various embodiments and with various modifications as are suited to
the particular use contemplated. All such changes, modifications, variations, and
alterations should therefore be seen as being within the scope of the present
invention as determined by the appended claims when interpreted in accordance
with the breadth to which they are fairly, legally, and equitably entitled.
17

To,
The Controller of Patents,
The Patent Office, Kolkata.