BF Simulation User Guide 1.00

8/6/2019 BF Simulation User Guide 1.00

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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.

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