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Blast Furnace Simulation User Guide
1 Introduction and Disclaimer
This document has been prepared as a user guide to the blast furnace simulation,
available at http://www.steeluniversity.org/. The interactive simulation has been
designed as an educational and training tool for both students of ferrous metallurgy andfor steel industry employees.
The information contained both in this document and within the associated website is
provided in good faith but no warranty, representation, statement or undertaking is given
either regarding such information or regarding any information in any other website
connected with this website through any hypertext or other links (including any warranty,
representation, statement or undertaking that any information or the use of any suchinformation either in this website or any other website complies with any local or national
laws or the requirements of any regulatory or statutory bodies) and warranty, representation,
statement or undertaking whatsoever that may be implied by statute, custom or otherwise is
hereby expressly excluded. The use of any information in this document is entirely at the risk
of the user. Under no circumstances shall the World Steel Association or their partners be
liable for any costs, losses, expenses or damages (whether direct or indirect, consequential,
special, economic or financial including any losses of profits) whatsoever that may be incurred
through the use of any information contained in this document. Nothing contained in this
document shall be deemed to be either any advice of a technical or financial nature to act or
not to act in any way.
2. Introduction to Blast Furnace Ironmaking
The blast furnace process is the dominating ironmaking route to provide the raw materials for
steelmaking industry. Blast furnace uses iron ore as the iron-bearing raw materials, and coke
and pulverised coal as reducing agents, lime or limestone as the fluxing agents. The main
objective of blast furnace ironmaking is to produce hot metal with consistent quality for BOS
steelmaking process. Typically the specification of steel works requires a hot metal with 0.3
0.7% Si, 0.2-0.4% Mn, and 0.06-0.13% P, and a temperature as high as possible (1480
1520oC when tapping). A modern large blast furnace has a hearth diameter of 14-15 m, and a
height of 35 m with an internal volume of about 4500 m. One such large blast furnace can
produce 10,000 metric tonnes hot metal per day.
Iron ore concentrates are first sintered or pelletised before charged into the blast furnace in
order to provide sufficient permeability of the feed in the furnace. Metallurgical grade coke is
prepared in a coking plant. Then the sinter, pellets, sometimes lumpy ore, as well as coke are
charged to the blast furnace in a layered structure through the furnace top. The pre-heated
hot blast is blown into the furnace from tuyeres, and combustion of coke and/or pulverized
coal generates heat and CO reducing gas in the raceway of the blast furnace. The reducing gasmixture of CO and N2 ascends in the furnace while exchanging heat and reacting with the raw
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materials descending from the furnace top. The gas is eventually discharged from the furnace
top and recovered as the primary fuel to heat up the hot blast stoves which are used to preheat
the blast.
During this process, the layer-thickness ratio of iron-bearing materials to coke charged from
the furnace top and their radial distribution are controlled so that the hot blast can pass withappropriate radial distribution. During the descent of the burden in the furnace, the
iron-bearing materials are indirectly reduced by carbon monoxide gas in the low-temperature
zone of the upper furnace. In the lower part of the furnace, carbon dioxide, produced by the
reduction of the remaining iron ore by carbon monoxide is instantaneously reduced by coke
(C) into carbon monoxide which again reduces the iron oxide, via the so called Boudouard
reaction.
The overall sequence can be regarded as direct reduction of iron ore by solid carbon in the
high-temperature zone of the lower furnace. The reduced iron simultaneously melts, drips,
and collects as hot metal at the hearth. The hot metal and molten slag are then discharged atfixed intervals (usually 2-5 hours) by opening the tap-hole. A high productivity furnace is
almost continuously casting as each cast typically lasts for about 3 hours.
The hot metal is then transported to the BOS steelmaking plant by torpedo cars, and is
pretreated with desulphurisation and dephosphorisation sometimes before charging to the
BOS converters.
3. Simulation objective
This simulation aims to select the raw materials (ore, fuels and fluxes) for the blast furnaceand give a proper charging ratio of the raw materials to get the target pig iron, and then to
evaluate mass and heat balance and other indexes of the process. It is also expected to
minimize the cost of pig iron.
In the simulation you can produce two different kinds of pig iron; either foundry pig iron or
steel pig iron:
Foundry pig
Intended for foundries, the Si content is usually high, from 1.25% to 3.6%, and the C content
is higher than 3.3%. The high Si content requires a high operating temperature in the blast
furnace; therefore, the price of foundry pig iron is usually higher than steel pig iron.
Steel pig
This product is produced for steel refining process, for example, the BOS process to produce
different grades of steel. The Si content is lower than that in foundry pig iron, ranging from
0.45% to 1.25%, while the C content exceeds 3.5% up to 5%.
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4. Simulation interfaces
The simulation offers four interfaces to input data about the blast furnace production
conditions.
1. Raw material composition2. Production settings3. Charging rates4. Production environment parameters
When these have been successfully reviewed and corrected, a green tick will appear next to the
label. This means that it is safe to move on and review the next position. After completing all
six settings dialogues, the results can be reviewed by clicking on the torpedo car.
4.1 Raw Materials Composition
You need to review the input for the composition of all the raw materials that are used in the
simulation. Raw materials include three categories: ores, fuels and fluxes.
Figure 1 - Main simulation screen. Raw m aterials icons are highlighted.
Click on any of the three raw materials icons to bring up a selection of available raw material
beds. Click on either of these beds to review and adjust the composition data of available
materials in that material group. To be able to continue you will need to ensure that all
compositions in a material are close to 100%, so make sure to check each of the material beds
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in a raw material group before continuing. The accepted range for the total composition is 98
to 102%.
If a particular ore will not be used, simply set this raw material bed to empty. A bed that is
set to empty will not affect any calculations so feel free to experiment by using many or only a
few raw materials.
4.1.1 ORES
There are several types of ores that can be selected.
Agglomera ted Ores
Two types of sinter and two types of pellets can be selected. These are produced by sintering
or pelletizing processes during which a basic flux (limestone or dolomite) has been added into
the ores to get a high basicity product.
Lumpy Ores
Three types of lumpy ores can be selected. Usually, these original ores are acid ores and the Fe
content is higher than 50% which can be charged into the blast furnace directly. With a
suitable charging ratio of manmade ores and original ores, blast furnace can run more
smoothly and can achieve higher efficiency.
Manganese Ore
For the production of ferromanganese or foundry pig which contains a certain amount of Mn.
It is described as Mn ore in the simulation.
Illmen ite Ore
To protect the bottom and wall of the blast furnace, sometimes, schreyerite is charged into the
blast furnace. It is described as V-Ti ore in the simulation.
4.1.2 FUELS
For the production in a blast furnace, coke and pulverised coal are the common fuels. To
lower the cost, a small proportion of small coke or lump coal is added into the blast furnace
within the charge. The pulverised coal is usually injected into the blast furnace from tuyeres,
and usually called PCI (Pulverized Coal Injection). Since the price of coke is extremely high,
you need to think about cutting your cost by reducing the coke rate of the blast furnace. To doso, you can raise your PCI rate and improve the temperature of hot blast, but you cannot
reduce the coke rate lower than its minimum level. There are three types of coke for selection,
Please note that the total composition in the ash also should be 100%.
4.1.3 FLUXES
There are four types of fluxes available. Among them, limestone (CaO) and dolomite (MgO)
are basic; silicate (SiO2) is acid, while fluorite (CaF2) can improve the fluidity of slag greatly.
In the simulation, you should decide which types of fluxes you need according to your target
slag basicity and the iron ores you selected.
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Figure 2 - Input window for iron ore composition.
4.2 Production Settings
After setting raw material compositions the next step is to consider production settings. To
change these settings, please click on the house. The following sections will describe each of
production settings.
Figure 3 - Main simulation screen. Pro duction settings area is highlighted.
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Figure 4 - Production settings dialogue sho wing default values.
To ensure a working model, each of the settings in the simulation has a validity range. For the
productions settings, the following limitations apply:
Item Range Comment
Working volume 100-10000 m
Charging speed 6-10 batches/hour
Silicon content in pig iron 0.45-1.25% Steel pig iron
1.25-3.6% Foundry pig iron
Binary basicity 1.0-1.2 Producing steel pig
0.95-1.1 Producing foundry pig
4.2.1 WORKING VOLUME OF BLAST FURNACE
In this simulation, the size of blast furnace is described by its working volume. And some of
the production indexes are also evaluated according to the size of blast furnace, e.g. the coke
rate, the utilization coefficient of blast furnace, etc.
The utilization coefficient of blast furnace is a very important index, defined as follows:
iron
BF
WUtilization coefficient=
V
Wiron: the output of iron of blast furnace per day, metric tonne/d;
VBF: the working volume of blast furnace, m
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Therefore, the utilization coefficient is the output of iron per day per m of blast furnace.
According to the production conditions, this index is evaluated in the heat and mass balance
results.
4.2.2 TARGET SI CONTENT
For steel pig iron, the Si content ranges from 0.45 to 1.25%. Usually, the average data is
around 0.7%. For foundry pig iron, the Si content is from 1.25 to 3.6%.
4.2.3 CHARGING SPEED
Since the raw materials (including ore, coke and flux) are charged into the blast furnace by
batch, the charging speed is defined as the number of batches charged every hour. Usually,
this value ranges from 6 to 10 in ordinary operation. This value can also be used to recalculate
the PCI injection ratio (coal rate). Coal injection rate is input as kg/batch, but can sometimes
be found in literature as kg/hour. To convert between kg/batch to kg/hour, the following
formula should be used:
PCI (Kg/hour)PCI (Kg/batch)=
Charging speed(batch/hour)
4.2.4 TYPE OF CHARGE CALCULATIONS
There are four different options for performing charge calculations based on the selected
options. The easiest option is fixed weights, where weights for all used raw materials of
different kinds are directly input in order to obtain correct furnace operation conditions. Inthis case, amounts of ores, fluxes and fuels need to be input using the Charging rates
dialogue reachable by clicking on the skip ramp. When all necessary data has been input,
please check the results screen to make sure that the slag properties are in the proper range.
The charging calculation is based on the element balance. For example, the CaO balance and
SiO2 balance. To ensure a smooth operation of blast furnace and good quality of iron, a proper
slag is expected in the operation. The property of slag is also very important for extending the
campaign of blast furnace. The ratio of basic oxide and acid oxide in slag, a very important
parameter for slag, is usually defined as R (slag basicity) and exists in several forms:
R2 = CaO / SiO2
R3 = (CaO+MgO) / SiO2 (High MgO content)
R4 = (CaO+MgO) / (SiO2 + Al2O3) (High contents of MgO and Al2O3)
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Generally, a suitable slag with properties in the following table is satisfying the production.
Iron
Grade
R2 R3 Melting
Temper ature, C
Fusibility
Temper ature, C
Viscosity*
PaS
Steel pig 1.0-1.2 1.2-1.4 1300-1600 1300-1450 0.2-0.6
Foundry
pig
0.95-1.10 1.15-1.3 1300-1600 1350-1500 0.2-0.6
*Viscosity of CaO-SiO2-MgO-Al2O3 at 1500 C.
In the simulation, slag basicity can be either a fixed value, or it can be calculated. By choosing
to use a calculated value, slag basicity is determined by using data of raw materials charged
into the blast furnace. In this case, target basicity is uneditable.
4.2.5 FIXED SLAG BASICITY
To be able to choose target slag basicity, please select either of the options with variableweights and then input target basicity. When one of these options is activated, the weight of
the variable raw material(s) will be dynamically calculated so that the target basicity is
reached. Raw materials proportions (including iron ores and fluxes) are then calculated per
metric tonne of hot metal, aiming at the target slag basicity, a suitable slag with proper
melting point, viscosity and at the lowest possible raw materials cost.
Using a dynamic charge calculation of raw material additions requires the use of 1 or 2
variables in ores or fluxes. This means that the amount charged into the blast furnace is
unknown, but to get a proper slag composition, you need to give the target slag basicity.
Except for the 2 variable amounts, the remaining ores and fluxes will still need to be set byusing the Charging rates dialogue. The same dialogue is in this case used to choose which
materials that will have their amounts dynamically calculated.
When this calculation model is used, there is a choice between three different methods to
calculate necessary raw materials additions:
2 ore variables 1 flux variable 2 flux variables
When using the first option, two ore additions are calculated dynamically. The second and
third option calculates one or two flux addition amounts dynamically.
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4.3 Charging rates
The charging rates dialogue is used to input the weights of all raw materials that should be
used to charge the blast furnace. In the case of Fixed weights charge calculations, you will
only need to input weights all materials that are used.
But, when dynamic charge calculations are chosen, additional fields will appear and needs to
be filled out. In addition to the regular weights, Total ore weight or Total flux weight must
also be input. In Figure 5 the user has chosen dynamic calculations using two variable ore
weights. If Sinter 2 and Lump ore 2 are to be used as variable weights, the respective
checkboxes next to the labels must be clicked once. After that the Total ore weight should be
input, taking into consideration that the fixed weights of Sinter 1 and Lump ore 1 are
included in the total amount. In this case, a reasonable total weight could be about 90,000
tonnes.
Figure 5 - Dialogue for setting material cha rging rates.
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4.4 Production Environment Settings
This dialogue is reached by clicking on the blast furnace body. The settings that can be
changed here includes temperatures, gas additions, hot blast properties and which type of
heat loss model that is used in the mass and heat balance calculations.
Figure 6 - Production environment parameters.
Valid ranges for these parameters are as follows:
Item Range
Hot metal 1430-1530 C
Slag 1450-1560 C
Top gas 100-400 C
Ore 0-300 C
Ambient 0-50 C
Blast temperature 900-1250 C
Blast temperature drop 20-150 CBlast pressure 0-1000 kPa
Blast humidity 0-20 g/Nm
Oxygen enrichment 0-20 %
H2 utilization 25-45 %
C-CH4 rate 0-20 %
Direct reduction rate (Rd) 38-48 %
Heat loss 0-15 %
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4.4.1 TEMPERATURES
All temperatures in this section are added in degrees centigrade (C). Hot metal and slag
temperature indicate the temperature inside the furnace, while top gas and ore temperature
means the temperature when being charged into the furnace. The ambient temperature
should indicate the temperature of the air surrounding the blast furnace.
4.4.2 HOT BLAST PROPERTIES
Hot blast temperature is measured on the outside of the furnace body. The associated
temperature drop is the difference between the measurement point and the blast pipe before
the tuyeres.
4.4.3 GAS ADDITIONS
Oxygen enrichment: In blast furnace operations, the oxygen enrichment means the
increase of oxygen (%) in the hot blast. Therefore, the amount of oxygen added into the hot
blast is calculated by:
3 30 /( 0.21)
fw m m
w : volume of oxygen in m added to 1 m hot blast
:oxygen enrichment
: oxygen purity, set to 99.5% in the simulation
C-CH4-ratio: The percentage of C that reacts with H2 to produce CH4 is called C-CH4-ratio.
The default value of carbon is 1% in the blast furnace.
4.4.4 HEAT LOSS MODEL
Measuring the heat loss of a blast furnace is very complicated. Therefore, to fulfill the heat
balance evaluation, this simulation offers two different ways to estimate the heat loss:
Free heat loss model
In this method, heat loss is calculated as the difference between incoming and outgoing heat.
In order to evaluate the energy utilization, the heat loss percentage needs to be within a
reasonable range, for instance, between 5 and 7%. Otherwise the calculation parameters will
need to be changed.
Fixed heat loss mo del
Using this method means that the heat loss is fixated to an assumed value, for example, 7% of
the incoming heat. In order to balance incoming and outgoing heat, the raw materials weight
or other operation parameters needs to be adjusted to minimize the heat error.
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5. Underlying Relationships
This section presents some underlying scientific relationships that are included in the
simulation. The different sections include important information about areas where no
interaction is needed but knowledge about these relationships are still deemed important tobe able to successfully complete the simulation.
5.1 Raw Materials Loss Ratio During Charging
Ores, coke and flux usually lose some of the original weight during charging due to dust
emission and mechanical loss. Therefore, it is necessary to compensate for the lost material
when predicting the added raw material amount. The loss ratios used in the simulation are as
follows:
Ore Coke Flux
0.03 0.02 0.01
Therefore, the weight charged into the blast furnace is calculated by:
Wafter loss = Wbefore loss (1loss fraction)
5.2 Free Water Content in Raw Materials
Together with for example lump ores, coke and fluxes, moisture (free water) will be charged
into the blast furnace. The moisture will vaporize before any reaction takes place. Therefore,the weight of all the raw materials in the calculation refers to the dry weight (total weight
minus the weight of free water).
Free water added to the furnace system in this way will affect the energy balance in a
detrimental way. Furthermore, raw material amounts need to be compensated for the free
water content to obtain the correct dry weight of the added material.
5.3 Element Distribution Factors
The following element distribution factors between hot metal and slag are used in thesimulation:
Elements Fe Mn P S V Ti K Na
Molten iron 0.997 0.5 1 0.075 0.7 0.3 0.7 0.7
Slag 0.003 0.5 0 0.9 0.3 0.7 0.3 0.3
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6 Mass and Heat Balance Evaluation
The heat and mass balance evaluation is a very important process calculation for the blast
furnace. Via balance evaluation, it is possible to analyze the production performance of blast
furnace.
6.1 Mass Balance
The mass balance is done by comparing the amount of incoming and outgoing materials, e.g.
blast air volume, injected coal weight, iron ore weight etc. Once performed it is then used as
the base for a heat balance. Establishing an accurate mass balance is always the crucial first
step to guarantee the validity of the energy balance.
m
1j 1t
jtjij
n
1i
k
1j
i YMXM
The mass balance is usually done in one of two different ways.
6.1.1 BLAST FURNACE PRODUCTION
The composition of top gas can be analyzed by gas sample; therefore, the direct reduction
degree of iron (Rd) is calculated by these data. The aim of mass balance in this aspect is to
calculate blast and gas volume and to check the raw materials weight during production. Care
must be taken to accurately quantify the weight of materials; otherwise there will be a
significant error in the heat balance.
6.1.2 BLAST FURNACE DESIGN
Here, the direct reduction degree of iron (Rd) is assumed according to the ore properties,
operating conditions and experiences. The value of Rd has a great influence on the mass
balance and heat balance. The compositions of top gas are also calculated by this datum.
Both of these methods use a similar principle of mass balance calculations. In this simulation,
the second way is adopted, which means, the value of Rd is set by the user within a proper
range.
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The calculation of mass balance (per metric tonne molten iron) concerns:
Mass in Mass out
Weight of mixed ore 1000 kg Molten iron
Coke weight and small coke weight Slag weight
Coal powder and lumpy coal Weight of top gas and its composition
Flux weight Moisture weight in top gas
Blast weight1) Dust weight
Free water
Total incoming Min Total outgoing mass Mout
1) Blast volume is calculated on the basis of oxygen content in blast and the weight of carbon
burnt in the combustion area, and then with density of blast, the blast weight is obtained.
The error of mass between input and output is calculated by:
100%in out mass
in
M ME
M
The value of Emass should be less than 2% in practice.
6.2 Heat Balance
The heat balance is used to evaluate energy utilization in the blast furnace, and on the basis of
the evaluation, to reduce costs and achieve high energy utilization.
Heat in Heat out
Carbon oxidation Oxide decomposition
Hot blast Carbonate decomposition
Hydrogen oxidation Moisture decomposition
Slag forming heat Free water evaporation
Heat provided by materials Coal decompositionMolten iron
Slag
Top gas
Heat loss
Total incoming heat Hin Total outgoing heat Hout
The error of heat between incoming and outgoing is determined by:
100%in out massin
H HH
H
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The heat loss value should be maintained in a proper range for smooth operation of the blast
furnace. For different blast furnaces or the same blast furnace producing different grades of
iron, this value varies. Generally, Hmass should be in the range of 3-8% for steel iron
production and 6-10% for foundry iron production. The heat loss value can also be used to
identify whether the coke rate or fuel rate is in a proper range. A high heat loss means the
coke rate or fuel rate exceeds what it is needed or vice versa that the blast furnace need more
coke or fuels.
The enthalpy of slag is calculated by slag composition and its heat capacity within a ternary
system of CS, C2S and C2AS. Some heat capacity data used in the heat balance calculations are
listed below.
Table 1 - The heat capacity of gas: C p = 4.18 (a+bT+cT2) Jmol-1k-1
a b10 -3 c10-5 Temperature/C
O2 7.16 1.00 -0.4 25-2700N2 6.66 1.02 - 25-2200
H2 6.52 0.78 0.12 25-2700
CO 6.79 0.98 -0.11 25-2200
CO2 10.55 2.16 -2.04 25-2200
CH4 5.65 11.44 -0.46 25-1200
H2O(g) 7.17 2.56 0.08 25-2500
Table 2 - The heat capacity of m olten iron : Cp=4.18 (a+bT+cT2) Jmol-1k-1
a b10 -3 c10-5 Temperature/CFe 4.18 5.92 0 0-760
10.5 0 0 1400-1536
Fe3C 19.64 20 0 0-190
29 0 0 1227-1727
Table 3 - The heat capacity and e nthalpy of slag: Cp=4.18 (a+bT+cT2) Jmol-1k-1
a b10 -3 c10-5 Temperature/K
CS 26.64 3.6 -6.52 298-1463
25.85 3.94 -5.65 1463-1813
C3S2 64 9.05 -16.6
C2 AS 53.73 17.68 -0.89
C2S 27.16 19.6 0 298-948
34.87 9.74 6.26 948-1693
32.17 11.02 0 1693-2403
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7 Evaluation of Operation Efficiency
When the mass and heat balance is finished, the energy efficiency of blast furnace can be
evaluated by some indexes, for example, utilization coefficient of available energy and
utilization coefficient of carbon energy.
7.1 Utilization Coefficient of Available Energy
Utilization coefficient of available energy (Kt) means the ratio of heat outgoing minus the heat
taken by top gas and heat loss in the total heat incoming. It is given by:
100%out gas loss
t
in
H H H K
H
A higher value of Kt indicates better energy utilization. Generally it is in the range of 75% to
85%, but for some blast furnaces it can be as high as 90%.
7.2 Utilization Coefficient of Carbon Energy
Utilization coefficient of carbon energy (Kc) is the ratio between heat released from carbon
oxidization, in which CO and CO2 are produced, and heat emitted when carbon is completely
oxidized to CO2. It can be expressed as:
2
2
1 2
( 1 2)
100%C CO C CO
C C CO
H HKcH
Usually, Kc varies from 48% to 56%, but in some rare cases it can reach 60%.
7.3 Evaluation of Production Efficiency
To compare and to evaluate the production efficiency of different blast furnaces and their
costs, some useful parameters are used in steel industry, such as volume utilization coefficient,
coke rate, PCI, blast temperature, as well as the utilisation coefficient of available energy and
carbon energy (Kt, Kc) as described above. In this simulation, these parameters are evaluated
and classified into three levels: normal, good and very good according to the indexes
published by some steel producers.
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Table 4 - Standard indexe s for pro duction efficiency evaluation
Item Volume /
m
Normal Good Very good
Utilization coefficient, t/md < 1000 2-3 3-4 4-4.5
>= 1000 2-2.3 2.3-2.8 2.8-3.2
Coke rate, kg/t 550-450 350-450 250-350
Coal rate, kg/t =160
Fuel rate, kg/t 650-570 500-570 440-500
Limestone, kg/t
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In the dialogue that appears you will be able to review how the blast furnace operates with the
currently set conditions. Figure 7 shows an example of how the feedback can look like in an
unsuccessful attempt.
Any item in the feedback that is in red requires attention. In this example, the fuel rates are all
too low. This means that to get a successful attempt both the coke rate and the coal rateshould be increased so that these are within the limits detailed in Table 4.
When this has been corrected, attention should then be given to the iron ore compositions
since the overall Fe content is too low. Again, guidelines for an acceptable Fe content can be
found in Table 4.
After these two last items have been corrected, results can be generated again by pressing the
torpedo car once more.
Figure 8 - An examp le of results feedback from a succe ssful attempt.
Now when all the feedback is positive, you have successfully finished the simulation.
At this point compositions and the heat and mass balance can be reviewed. Note that it is still
possible to continue refining the inputs to further improve the results.