BF Simulation User Guide 1.00

Blast Furnace Simulation User Guide 1

Introduction and Disclaimer

This document has been prepared as a user guide to the blast furnace simulation, simulation, available at http://www.steeluniversity.org/. http://www.steeluniversity.org/. The interactive simulation has been designed as an educational and training tool for both students of ferrous metallurgy and for 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 such information 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 m³. 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 gas mixture of CO and N2 ascends in the furnace while exchanging heat and reacting with the raw

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Blast Furnace Simulation User Guide

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 with appropriate 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 at fixed 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 furnace and 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 composition

2. Production settings 3. Charging rates 4. Production environment parameters When these have been successfully reviewed and corrected, a green tick will appear next to t he 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 i n 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 do so, 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

Working volume

Range

Comment

100-10000 m³

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

1.0-1.2

Producing steel pig

0.95-1.1

Producing foundry pig

Binary basicity

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 importa nt index, defined as follows:

Utilization coefficient=

Wiron VBF

W iron: the output of iron of blast furnace per day, metric tonne/d; V BF: the working volume of blast furnace, m³

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Therefore, the utilization coefficient is the output of iron per day per m³ 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/batch)=

PCI (Kg/hour) 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. In this 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

R2

R3

Grade

Melting

Fusibility

Viscosity*

Temper ature, °C

Temper ature, °C

Pa·S

Steel pig

1.0-1.2

1.2-1.4

1300-1600

1300-1450

0.2-0.6

Foundry

0.95-1.10

1.15-1.3

1300-1600

1350-1500

0.2-0.6

pig *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 variable weights 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 by using 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 °C

Blast pressure

0-1000 kPa

Blast humidity

0-20 g/Nm³

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:

w

f 0

(  0.21)

m3 / m3

w : volume of oxygen in m³ added to 1 m³ 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 to be able to successfully complete the simulation.

5.1 Raw M aterials 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: W after loss = W before loss × (1－loss fraction)

5.2 Free Water Content in Raw M aterials 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 the simulation: 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. n

k

m

 M i X ij   M jY jt i 1 j1

j1 t 1

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 1)

Total outgoing mass Mout

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:

E mass 

M in  M out 100% M in

The value of E mass 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 decomposition Molten 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:

H mass 

H in  H out H in

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100%


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 C2 AS. 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+cT 2 ) J•mol -1 •k -1

a

b×10 -3

c×10 -5

Temperature/°C

O2

7.16

1.00

-0.4

25-2700

N2

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+cT 2 ) J·mol -1·k -1

Fe Fe3C

a

b×10 -3

c×10 -5

Temperature/°C

4.18

5.92

0

0-760

10.5

0

0

1400-1536

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+cT 2 ) J·mol -1 ·k -1

CS C3S2 C2 C2S

a

b×10 -3

c×10 -5

Temperature/K

26.64

3.6

-6.52

298-1463

25.85

3.94

-5.65

1463-1813

64

9.05

-16.6

AS

53.73

17.68

-0.89

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 A vailable Energy Utilization coefficient of available energy (K t) 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:

K t 

Hout  Hgas  Hloss H in

100%

A higher value of K t indicates better energy utilization. Generally it is in the range of 75% to 85%, but for some blast furnaces it can be a s high as 90%.

7.2 Utilization Coefficient of Carbon Energy Utilization coefficient of carbon energy (K c) 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:

Kc 

H C1CO  H C 2 CO2 H (C1C 2)CO2

100%

Usually, K c varies from 48% to 56%, but in some rare cases it can reach 60%.

7.3 Evaluation of P roduction 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 /

Normal

Good

Very good

< 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

<100

100-160

>=160

Fuel rate, kg/t

650-570

500-570

440-500

Limestone, kg/t

<= 80

Dolomite, kg/t

<= 80

Silica, kg/t

<= 80

Fluorite, kg/t

<= 30

Fe content in ores,%

52-55

55-58

>=58

Blast temperature, °C

900-1050

1050-1200

1200-1250

K t, %

75-85

85-90

>=90

K c, %

48-56

56-60

>=60

m³ Utilization coefficient, t/m³d

7.4 Results Summary Having completed all required input dialogues, the torpedo car will become activated. This indicates that clicking on it will bring up the results screen for the simulation. Each time the torpedo car is clicked, the results are calculated once again. This ensures that any changes that have been made are included in the results.

Figure 7 - An examp le of results feedback from an u nsuccessful attempt.

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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 rate should 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 th e results.

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BF Simulation User Guide 1.00

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