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Model studies on the effects of compositiondifferences of direct reduction pellets and anadaptive addition of slag formers for the EAF

process

Björn KeskitaloMaster of Science Thesis

Version 0.94292015-04-29

SupervisorsMagnus Tottie, LKABNiloofar Arzpeyma, Kobolde & Partners

Examiner Pär Jönsson, KTH

Abstract

This work has been conducted to study the effect of different types of iron ore pellets on an EAFbased steel production. The study has focused on how the chemical composition of the raw materialsinfluences the slag amount and as a result the EAF operation. It is also shown that the raw materialselection can be optimized for a better slag practice. The advantage of slag former additions that arestrictly adapted to the EAF charge composition is also demonstrated.

This work is based on a MgO-saturation model for slag, developed by Dr Roger Selin. The model hasbeen implemented in RAWMATMIX®, a software developed by Kobolde & Partners AB in Stockholm.

In this report I discuss the following studies: i) A study and comparison between different basicityindices and MgO-saturation for EAF slags, ii) a comparison between different DR-pellets and mixesbetween them and their corresponding DRI, iii) a parameter study on how different properties for theDR-pellet and DRI influence the EAF process, and iv) a case study of two hypothetical steel plants toillustrate the value of an adaptive slag former addition based on the raw material input. Overall,these studies describe the value of using DRI based on DR-pellets, containing low amount of acidicoxides and balanced amounts of MgO, for an EAF based steel production.

Table of Content

1. Introduction

1.1 Introduction Page 1

1.2 Purpose Page 1

2 Background

2.1 Direct Reduced Iron Page 2

2.2 EAF Process Page 4

2.3 EAF Slag Page 5

2.4 MgO-saturation model Page 6

2.5 Calculation tool Page 7

3. Execution, Limitations and Input

3.1 Setup and work order Page 8

3.2 Limitations Page 11

3.3 Input Page 11

4. Results and Discussion

4.1 Basicity and MgO-saturation Page 17

4.2 Basicity and slag forming fractions Page 18

4.3 DR/DRI Comparison Page 20

4.4 Parameter study Page 23

4.5 Value-in-use Page 26

5. Conclusions 0

6 Acknowledgment Page 32

7. References Page 33

Appendix 1 – DR/DRI Page 34

Appendix 2 – EAF slag Page 45

Appendix 3 – Input Page 52

1.1 Introduction

The market for iron and steel produced using direct reduction (DR) of iron ore has been estimated togrow and is becoming of more importance for the iron and steel industry. Today, LKAB develops andproduces iron ore pellets for DR. The pellets produced contain low amounts of silicon and aluminum,which results in smaller slag amounts when melted in an electric arc furnace (EAF). In order toimprove the properties during DR and melting, dolomite is added to the pellets.

Dr Roger Selin has developed a model to calculate the MgO solubility and equilibrium distributionsfor phosphorous and vanadium for slag compositions from direct reduced iron (DRI). This model hasbeen implemented in a web-based optimization program, RAWMATMIX® by Kobolde & Partners AB.

1.2 Purpose

1. Model Focus: Study the chemistry of pellets for DR by using RAWMATMIX® and identify theadvantages and disadvantages of using different DR pellets as raw materials in electric arc furnaces.

2. Customer Focus: How the model and results could be presented to LKAB's customers and be usedby them, in order to achieve an efficient pellet selection and EAF operation.

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2. Background

2.1 Direct Reduced Iron

Direct reduced iron (DRI) is a raw material used in steel production. DRI is primarily used in EAF whenthere is a demand for low amounts of metallic impurities, such as copper and tin. It is also used whenthere is a shortage of suitable scrap. Direct reduction (DR) is a solid state type of reduction of iron oreto metallic iron by the use of a reducing atmosphere or environment [1,2,3].

The most common way to produce DRI for EAF based steel production is by DR of a certain grade ofpellets, direct reduction pellets (DR-pellets). These are typically produced in vertical direct reductionshaft furnaces (DR-furnaces). The DR-pellet, compared to pellets designed for a blast-furnace use,must have lower amounts of silica, sulfur and other impurities to be used in an EAF [1,2,3].

In a DR-furnace, the reduction takes place as the DR-pellets flow downwards from the top to thebottom of the furnace. This is done as the reduction gas at a high temperature flow upwards from theinlet of the reduction zone to the top of the DR-furnace. The reduction gas is injected at the middle ofthe furnace just above the cooling zone for the DRI at the bottom end of the DR-furnace. In thecooling zone, a carbon rich gas is injected to increase the carbon content of the DRI inside the furnaceand also to cool down the DRI to a desired temperature. This means that it is possible to control boththe carbon content of the DRI and the metallization, which is the ratio of metallic iron to the totalmass of iron. This is done by changing the process conditions, such as the production rate for the DR-furnace. An overview of the process can be seen in Figure 1, which illustrates a Midrex process[1,2,3,4]. Another common process is the Energiron process (HYL) [5].

The reduction gas consists primarily of carbon-monoxide (CO) and hydrogen-gas (H2). The reductiongas is normally produced by a reformation of natural gas. The way that the natural gas is reformed isone major difference between different types of DR processes [2,3,6,7].

The following reactions take place within a DR-furnace [2,3,4,6,7]:

1: 3Fe2O3 + H2 = 2Fe3O4 + H2O

2: 3Fe2O3 + CO = 2Fe3O4 + CO2

3: Fe3O4 + H2 = 3FeO + H20

4: Fe3O4 + CO = 3FeO + CO2

5: FeO + H2 = Fe + H2O

6: FeO + CO = Fe + CO2

2

Figure 1. An illustration of a DR-furnace of a Midrex type. It shows an overview of the zones and thereactions within a DR-furnace [1].

DRI is produced in the following three major categories: 1) Cold DRI is the most common DRI productand is charged into an EAF at ambient temperature, 2) hot DRI is designed to be used in a nearby EAFto utilize the latent-heat in hot fresh DRI, and 3) hot briquetted iron, which is a compressed DRI typewith the purpose to reduce the surface area, and thereby the reactivity, of the DRI. Also, it isproduced to enable longer transportation and storage time [1,2,3].

A problem that might occur during DR of DR-pellets in a DR-furnace is that the DR-pellets start tostick to each other, which will form clusters. This happens in the reduction zone in the DR-furnacewhere the temperature and metallization of the DRI is high. To avoid this type of behavior it iscommon to coat the DR-pellets with an oxide which has a high melting temperature, such as CaO orMgO[2,3].

Another important aspect of the DR of DR-pellets is that all the slag elements remain and follows thepellet on its transition from iron ore to metallic iron. This is due to the fact that the DR is a solid statereaction during which primarily the iron oxide is reduced while almost all the other elements and

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compounds are kept intact. Therefore, the slag components can either be removed before the pelletis produced or follow the pellet until it is melted, which for most DRI types are in an EAF [1,2,3].

2.2 EAF Process

The electric arc furnace (EAF) is primarily a melting furnace, which produces liquid steel by meltingscrap and DRI. Today, the typical tap-to-tap time is around 40-60 min. In 2011, EAFs produced over25% of the world's total crude steel production. A typical layout of an EAF can be seen in Figure 2.The charge is melted by powerful electric arcs, which are formed between the electrodes and thecharge. As these arcs radiate a lot of heat against the furnace walls and roof, the walls and roof oftencontain cooling elements to increase the durability. Foaming slag is also an important tool which isused to protect the walls and roof [8,9,10].

Figure 2. Standard design of a three-phase AC EAF. And the number shows the following parts of theEAF: 1) transformer, 2) cable connection, 3) electrodes, 4) electrode clamps, 5) arms, 6) off-gas duct,7) cooled wall panels, 8) structure, 9) basculating structure, 10) rack, 11) cooled roof, 12) basculatingdevice, 13) hydraulic group [8].

Although most of the energy in an EAF comes from electric power, it is also important to use chemicalenergy to minimize the tap-to-tap times and the consumption of electrical energy. The chemicalenergy is often based on oxidation of carbon. The carbon comes from either the raw material, i.e. DRIor is injected into the furnace during the melting. Injection of carbon and oxygen into the slag alsocontribute to a foaming of the slag [8,9,10].

2.3 EAF Slag

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The EAF slag is an ionic solution that floats on top of the steel. The viscosity of the slag may vary fromwatery to crusty depending on the temperature and composition [8,9,10,11].

The primary functions of an EAF slag are to:

1. Protect the liquid steel from oxidation.

2. Prevent the liquid steel from absorbing hydrogen and nitrogen.

3. Improve the steel quality by dephosphorization of the melt and absorption of gangue oxides andinclusions.

4. Insulate, to minimize the heat loss.

5. Be compatible with the refractory to minimize the refractory wear.

6. Protect the walls from radiation load by foaming.

The slag consists primarily of oxides. The composition is also often divided into two differentcategories, acidic oxides and basic oxides. The most common acidic oxides in the EAF slag are Al2O3,Cr2O3, P2O5, SiO2, TiO2, VO2* which are assumed to form anions by receiving O2- ions from the basicoxides. The basic oxides primarily consist of CaO, MgO and MnO, which on melting into the ionic slagare assumed to form free cations, i.e. Ca2+, Mg2+, Mn2+ by giving off O2- ions. The majority of the acidicoxides originate from the scrap, DRI, coal/coke ash or dirt and residual elements from transportationand storage. They are often unwanted and of negative effect for the steel production. The basicoxides, CaO and MgO, are often called slag formers and are added to the melt both to facilitate theformation slag and to neutralize the corrosive effect from the acidic oxides on the furnacerefractories. For practical reasons, the iron oxide in a MgO-saturated EAF slag is often referred to asFeO, although in reality it consists of both Fe(II) and Fe(III) oxides. The latter however, constituting aminor part. Fe(II) is a basic oxide assumed to form Fe2+ cations, whereas Fe(III) oxides to some extentare acidic in this context. The FeO content can have a negative effect on the basic lining as the FeOlowers the viscosity of the slag and therefore, increases the wear of the basic lining if conditions fordissolution of MgO exist [8,9,10,11].

A number of models have been developed to predict the behavior of EAF slags. The most commonlyused is a group of models called basicity models. These models have been developed to be used inthe same way as the pH value is used for aqueous solutions. Also, these models are mostly based onthe weight fraction of basic oxides over acidic oxides. For instance, the basicity model B3, is shown inequation 10 [9,10].

The slag is also important because it is one of the factors that affect the yield of the EAF process. Ifthe amount of slag increases, it causes more iron units to go to slag. Therefore, the amount of steelformed per charge is reduced. An increased slag amount also leads to an increased energyrequirement per ton of steel. This is due to the use of more raw materials, that has to be heated.Also, the increased amount of slag requires an energy contribution. This also affects the yield andprocess time for the EAF process [8,9,10].

If an EAF process is primarily based on DRI as a raw material, it is important to take intoconsideration the composition of the DR-pellet. This is because most of the slag elements that exist in

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the DR-pellet will remain and follow the DR-pellet during the DR and finally end up in the EAF slag[2,8,9,10,11].

2.4 MgO-saturation model

Compared to the more commonly used slag models, such as the basicities, Roger Seilin's MgO-saturation model considers all gangue oxides for the slag, such as the Al2O3, P2o5,VO2* and TiO2 [11].According to Selin, it is more appropriate to use the wt%CaO and wt%FeO* as a basis for slag designfocused on the MgO-saturation of the slag compared to any basicity index. This would be possiblebecause the concentrations of the components are more connected to the activities than the fractionbetween different components [11].

To calculate the slag composition it is required to have an analysis of the raw material. Also, there arethree important variables that have to be set for the desired slag composition. The variables areCaO20, FeO* and λ-MgO. CaO20 is a reference state for the concentration of CaO when the slagcontains 20wt% FeO* and is calculated as follows [11]:

7:CaO20=

(%wt CaOactual)×80(100−(%wt FeOactual))

Since this calculation is based on wt%, the number 80 comes from the relationship 100wt% - 20wt%FeO*. Also, the number 100 comes from the total amount of 100wt% [11].

FeO* describes the total concentration of the different ferrous oxides that exist in the slag calculatedas FeO. FeO* is thus easily obtained from %Fetot in a metal free slag sample [11].

λ-MgO is the actual concentration of MgO in the slag, MgO-actual, divided by the calculated MgO-saturation, as is shown in equation 8. This ratio indicates the saturation level of the MgO content inthe slag [11].

8:λ−MgO=

(wt %MgO−accutal)(wt %MgO−saturation )

λ-MgO = 1, indicates that the slag is saturated with MgO.

λ-MgO > 1, indicates that the slag is over saturated with respect to MgO. It is often desired to have aλ-MgO value a bit larger than 1, as it ensures MgO-saturation.

λ-MgO < 1, indicates that the slag is under saturated with respect to MgO, which results indissolution of the MgO containing lining of the furnace.

By using the CaO and FeO* content, Selin [11] was able to set up a model for how the MgO-saturationvaried with the concentrations of CaO and FeO* for the reference system CaO-FeO*-MgO sat-SiO2. Theamount of MgO required to achieve a MgO-saturation decreases with increasing CaO and FeOcontent, as it can be seen in figure 3. If the slag contains a lower content of MgO than the MgO-saturation level, for a certain CaO and FeO* concentration, then the slag will dissolve MgO from the

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lining inside the furnace [11]. Also, by using the %CaO and %FeO* as main parameters the effect onthe MgOsat is quite small if SiO2 from the reference system of CaO-FeO*-MgOsat-SiO2 is replaced bysome of the oxides Al2O3, P2o5,VO2*, TiO2 and can even be expressed in linear equations [11]

Figure 3. Illustration of MgO saturation concentrations created by Roger Selin [11]. The graph showhow the MgO saturation is dependent on the FeO and CaO20 content of the slag for the reference

system CaO-FeO*-MgOsat-SiO2.

2.5 Calculation tool

Most of the work for this report has been done using RAWMATMIX®, a web based software for thesteel industry [12]. RAWMATMIX® focuses on raw material optimization to find the minimumoperation cost possible per ton of liquid steel for the EAF process.

RAWMATMIX® contains many functions, and one of the most important used in this project is thepossibility to calculate the value-in-use of different raw materials for an EAF process [12]. Theprogram works by defining specific target products. Both the desired steel and slag analysis areconsidered. For the steel, the target concentrations of elements are set. For the slag, the targetconcentration of CaO, FeO and λ-MgO are set to be used for calculating the required minimumamount of slag, which is based on Roger Selins MgO-saturation model [11,12]. Based on thesesettings, the minimum amount of required raw materials, basic slag forming additions, and costs forthe steel production can be calculated [12].

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3. Execution, Limitations and Input

Based on the literature study, which is summarized in Appendix 1 and 2, the following aspects aretaken into account. Most of the work is based on calculations done in RAWMATMIX® and RogerSelin's MgO-saturation model [11,12]. The raw materials used are based on KPRS and two othercompeting DR-pellet grades, namely Competitor 1 (Com 1) and Competitor 2 (Com 2). Thecomposition of the DR-pellets and corresponding DRI can be seen in Table 2.

3.1 Setup and work order

3.1.1 Basicity and MgO-saturation

The aim is to investigate how slag basicity changes when the proportion of the slag former additionsvaries. The proportion of dolomitic limestone to burnt limestone varies from 100%/0% (dolomiticlimestone/burnt lime) to 10%/90%. The composition used for dolomitic limestone and limestone canbe seen in Table 3.

Two types of charges are made and calculated using RAWMATMIX®. The charges simulate theproduction of 80 tons of the steel type A2, by melting 32 tons of DRI based on 100% KPRS or 100%Com 2 together with 54.5 tons of scrap. The analysis of both the steel and slag for the two steeltypes, A1 and A2, can be seen in Table 4 and Table 5.

Based on the optimization of the slag former addition for the two charges the addition of slagformers used for the KPRS case is set to 3.5 ton. For the Com 2 case, the addition of slag former is setto 5.5 ton.

The basicity is calculated according to the following equations [2,9,13]:

9:B2=

(wt%CaO)

(wt%SiO2)

10:B3=

(wt%CaO)

(wt %Al2O3+wt %SiO2)

11:B3=

(wt %CaO+wt %MgO)

(wt %Al2O3+wt %SiO2)

12: Bells Ratio=

(wt %CaO+0.69∗wt %MgO)

(0.93∗wt %SiO2+018wt%Al2O3)

The optical basicity is calculated by using the following table and equations [9].

13: OpticalBasicity =X AOx∧AOAOx+X AOy∧AOAOy+.. .

Where XAOx is calculated using equation 14 [9].

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14: X AOx=(NOAOx∗X Ao)

(Σ(NOYOx∗X Yo))

NOAOx is the number of oxygen atoms in the oxide molecule. XAO is the mole fraction of the molecule.And the Σ (NOYOx * XYO) is the sum of all the different oxygen molecules times their oxygen content forthe system.

Table 1. Pauling’s electronegativity data for glasses [9].

3.1.2 Basicity and varying slag forming fractions

This part is done to show how basicity varies when the raw material is changed, including a change ofboth the raw material input and the fraction of slag former. The basicity used is the B2, B3, B4 andBells Ratio expressions, shown in equations 9-12. In this case, the charge is optimized for a DRI basedon Com 2. It means that the amount of slag former addition is set to 5.5 ton. Then the raw material ischanged, in this case to a DRI material based on KPRS. At the same time, the amount of slag formeraddition is kept to the same amount which was used for Com 2.

The produced steel amount is 80 tons of an A2 grade. The amount and grade is produced by melting32 tons of DRI based on KPRS or Com 2 together with 54.5 tons of scrap. The composition of thescrap can be seen in Table 6.

3.1.3 DR/DRI Comparison

This part of the study is based on smelting of 100% DRI, and is done to see how three different DR-pellets, KPRS, Com 1 and Com 2 influence some important properties for EAF based steel production,such as the slag amount per ton steel and tap-to-tap times. The steel production is based on anoptimized amount of slag former addition for the material mix. This is done for both the A1 and A2steel type. Different combinations of charged raw materials are taken into account which are: Com 2-

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Oxide Optical Basicity (Λ)Na2O 1.15CaO 1.0MgO 0.78CaF2 0.67TiO2 0.61

Al2O3 0.61MnO 0.59

Cr2O3 0.55FeO 0.51

Fe2O3 0.48SiO2 0.48

KPRS, Com 2-Com 1 and Com 1-KPRS. The mixtures are made based on the weight fraction of thematerial types. Because of restrictions on the target composition in the A1 and A2 steel typestogether with the type of slag, it was impossible to use larger fractions of Com 1 in the raw materialmixes.

3.1.4 Parameter Study

This part is meant to give a more in depth analysis of how individual properties of a DR-pellet andcorresponding DRI affect the EAF steel production. Thus, a parameter study was conducted. This wasdone for an A2 steel by melting 100% DRI based on KPRS. The chemical properties for the DRI waschanged one at a time while the others was set to have the same values as the KPRS pellet andcorresponding DRI. The properties which were studied were the carbon content, metallization, Al2O3

content, SiO2 content and the combined (Al2O3 +SiO2) content. These properties can be changedeither by the DR-pellet material, such as the Al2O3 and SiO2 content, or by the DR process, such as thecarbon content and metallization degree.

The properties used for the DR-pellet and DRI and setup were as follows:

The carbon content was set to 1wt%, 2wt%, 3wt% of the DRI.

The metallization degree was set to 92%, 95%, 98% of the DRI

The SiO2 content was set to 0.50wt%, 1.00wt%, 1.50wt% of the DR-pellet.

The Al2O3 content was set to 0.25wt%, 0.50wt%, 0.75wt% of the DR-pellet.

The combined Al2O3 + SiO2 content was set to 0.75 wt%, 1.50wt%, 2.25wt% of the DR-pellet.

The compositions for the combined (Al2O3 +SiO2) contents were as follows:

0.75 wt% Al2O3 +SiO2 : (0.25 wt% Al2O3 + 0.50 wt% SiO2)

1.50 wt% Al2O3 +SiO2 : (0.50 wt% Al2O3 +1.00 wt% SiO2)

2.25 wt% Al2O3 +SiO2 : (0.75 wt% Al2O3+ 1.50 wt% SiO2)

3.1.5 Value-in-use of DRI and adaptive addition of slag formers

To illustrate the value-in-use of the KPRS material and adaptive addition of slag formers two casestudies were performed. They were based on two fictitious steel plants, that produce 80 ton of A2grade steel per charge. One is located in the Middle East and one in North America. These two plantsdiffer primarily with respect to the production cost and the charge mixture. The plant located in theMiddle East only charges DRI, while the North American charges scrap and DRI in two differentcombinations. More specifically, one high scrap charge which charges 50 tons of scrap and 36 tons ofDRI as raw materials and a low scrap charge which charges 25 tons of scrap and 63 tons of DRI as rawmaterials.

To illustrate the value-in-use of KPRS for the EAF process, KPRS is mixed with a normal mixture of DRIfrom 0% to 50% of the total amount of DRI. The normal mixture consists of 50% Com 1 and 50% Com2.

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To illustrate the value-in-use of adaptive addition of slag formers, two different setups wereconducted for each of the steel plats settings. One setting has a fixed slag former amount andfraction based on the normal mixture of 50% Com 1 and 50% Com 2 and the other utilizes adaptiveaddition of slag formers.

The Middle East plant has a slag former addition of 1250 kg lime and 2250 kg dolomitic limestone percharge. For the North American plant the high scrap setup has a fixed slag former addition of 1500 kglime and 1750 kg dolomitic limestone, and the low scrap setup has a fixed slag former addition of1250 kg lime and 2000 kg dolomitic limestone.

3.2 Limitations

The MgO-saturation model used for the slag is valid for low alloy steels and for the final slagcomposition. In addition, the slag and heat are considered to be homogeneous both with respect tocomposition and temperature [11]. The slag composition has to meet the following conditions [11]:

Temperature: 1550 - 1700 C

CaO: 18 - 45 wt%

FeO: 7 – 48 wt%

MgO: 5 – 25 wt%

For RAWMATMIX®, the most important limitation is the model for the heat loss which is set to aspecific value per time unit [12].

3.3 Input

Most of the calculations are based on the three different DR-pellet types and their corresponding DRIcomposition is presented in Table 2 to Table 5. For more input details see appendix 3, “Input”.

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Table 2. The composition for the three DR pellets and their corresponding DRI that most of thecalculations are based on in this work. The DRI are set to have 2% carbon content and 95%

metallization.

The table shows the composition for the DR-pellets used and the corresponding composition for theDRI. By comparing KPRS to competitor 1 and 2 it becomes apparent that the KPRS contains higheramounts of basic oxides CaO and MgO, while also smaller amounts of acidic oxides such as Al 2O3 andSiO2.

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DR-Pellet compostionKPRS

wt% wt% wt%

0.7489 1.2299 1.3294

0.1598 0.4899 0.6397

MnO 0.0773 0.0684 0.0549

CaO 0.8848 0.6882 0.6666

MgO 0.649 0.087 0.2099

0.0573 0.0094 0.0744

0.1962 0.007 0.03

0.1798 0.039 0.06

0.0029 0.0023 0.0184

0 0 0

0 0.0003 0.0003

NiO 0.0382 0.0052 0.005

0.0123 0 0

0 0 0

0 0 0

CuO 0.0013 0.0038 0.0005

0 0 0

NbO 0 0 0

0.0399 0.04 0.004

0.3 0.008 0.0055

0.0085 0.1741 0.0076

0 0.0001 0.0001

ZnO 0.0037 0.0025 0

0.0031 0 0

0 0 0

FeOOH 0 0 0

0 0 0

FeO 0 0 0

95.9416 96.5005 95.6051

0.9654 0.6445 1.2885

C om petitor 1 C om petitor 2

SiO2

Al2O

3

P2O

5

V2O

5

TiO2

Cr2O

3

MoO2

MoO3

CaF2

CaCO3

MgCO3

WO3

Na2O

K2O

CaSO4

SnO2

CaCl2

Ca(OH)2

FeCO3

Fe2O

3

Fe3O

4

DRI compostion

KPRS

Metallic Components

wt% wt% wt%

C 2 2 2

S 0.0027 0.056 0.0025

Fe 87.8535 88.216 87.8236

Ni 0.0409 0.0056 0.0053

Cu 0.0014 0.0041 0.0005

Mo 0 0.0003 0.0003

Oxidic Components

1.0215 1.6804 1.8127

0.2179 0.6694 0.8723

FeO 5.9486 5.9732 5.9466

MnO 0.1055 0.0935 0.0748

CaO 1.2115 1.0383 0.9131

MgO 0.8852 0.1189 0.2862

0.0781 0.0128 0.1015

0.2676 0.0095 0.0409

0.2452 0.0533 0.0818

0.004 0.0032 0.0251

0 0 0

0.0168 0 0

C om petitor 1 C om petitor 2

SiO2

Al2O

3

P2O

5

V2O

5

TiO2

Cr2O3

MoO3

CaF2

Table 3. The composition for the two types of slag former. Dolomitic limestone and burnt lime.

The table shows the composition for the two types of slag formers that is used in this study. The mostimportant to notice is that the dolomitic limestone contains both CaCO3 and MgCO3 as a source forbasic oxides as opposed to burnt lime which contains CaO and CaCO3.

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Slag formersBurnt Lime

wt% wt%

2.5 1.7

0.5 0.3FeO 0.67 84

0.09 MgO 4.9

58.2 9.1

38.04

Dolomitic Limestone

SiO2

SiO2

Al2O

3Al

2O

3

CaOP

2O

5

CaCO3

CaCO3

MgCO3

Table 4: A1 steel and slag analysis.

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Steel and Slag analysis

A1 Slag Model1.2

L-LP 0.5L-LV 0.5

Desired FeO 32.50%Desired CaO20 40.00%Refractory wear 2.0kg /ton nominal furnace capacity

MgO material Dolomitic limestoneLime material Lime

Distribution from L-factors slag quantity 0.12 kg slag / kg steelSi inf Mn 100 P 40 S 1Cr inf Ni 0 Mo 1 Nb InfTi inf Cu 0 Al inf V 600W inf Fe 0.2 Co 1 As 1B 1 Bi 1 Pb 1 Ca infTa 1 Sn 1 Zn 1

A1 Steel Analysis

Element min target maxAl 0 0 1Si 0 0 0.1P 0 0 0.05Si 0 0 0.05Ti 0 0 0.1V 0 0 0.05Cr 0 0 0.3Mn 0 0 1Fe 0 99.85 100Co 0 0 0.3Ni 0 0 0.3Cu 0 0 0.3Nb 0 0 0.1Mo 0 0 0.3As 0 0 0.1W 0 0 0.1B 0 0 0.1Bi 0 0 0.15Pb 0 0 0.05Ca 0 0 0.01Ta 0 0 0.01Sn 0 0 0.05Zn 0 0 0.01O 0 0 0.01N 0 0 0.01

Carbon 0.1 0.15 5

λ-MgO

Table 5: A2 Steel and slag analysis.

Table 4 and 5 shows the analysis for the two steel grades A1 and A2 together with the corresponding slag composition and distribution factors. The most important difference between the two steel grades are the values for CaO20, FeO* and λ-MgO.

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A2 Slag Model1.1

L-LP 0.5L-LV 0.5

Desired FeO 30.00%Desired CaO20 35.00%Refractory wear 3 kg /ton nominal furnace capacity

Lime material Lime


A2 Steel Analysis

Element min target maxAl 0 0 1Si 0 0 0.1P 0 0 0.05Si 0 0 0.05Ti 0 0 0.1V 0 0 0.02Cr 0 0 0.03Mn 0 0 1Fe 0 100 100Co 0 0 0.3Ni 0 0 0.3Cu 0 0 0.3Nb 0 0 0.1Mo 0 0 0.3As 0 0 0.1W 0 0 0.1B 0 0 0.1Bi 0 0 0.1Pb 0 0 0.05Ca 0 0 0.01Ta 0 0 0.01Sn 0 0 0.05Zn 0 0 0.01O 0 0 0.01N 0 0 0.01

Carbon 0.1 0 5

λ-MgO

MgO material Dolomitic limestone

Table 6. Scrap analysis

The table shows the composition of the scrap used. It should be noted that the composition containsboth pure elements and oxides.

16

Scrap AnalysisC 0.4 SiO2 0.5Al 0 Al2O3 0Si 0.3 FeO 2P 0.1 MnO 0S 0.05 CaO 0Ti 0 MgO 0V 0 P2O5 0Cr 0.1 V2O5 0Mn 0.64 TiO2 0Fe 95.84 CrO 0Co 0 Cr2O3 0Ni 0.01 Fe2O3 0Cu 0.01 Fe3O4 0Nb 0 MoO2 0Mo 0 MoO3 0As 0 NiO 0W 0 CaF2 0B 0 CaCO3 0Bi 0 MgCO3 0Pb 0Ca 0Ta 0Sn 0.05Zn 0O 0N 0H 0

4. Results and Discussion

4.1 Basicity and MgO-saturation

The steel is produced by melting 32 tons of DRI based on KPRS or Com 2 pellets together with 54.5tons of scrap to produce 80 tons of steel of grade A2. The two figures below, 4 and 5, show howdifferent mixtures of slag forming additions influence the basicity values for two different rawmaterial inputs.

Figure 4. Basicity versus lime / dolomitic limestone fraction in the slag former addition for a slagbased on Com 2 DRI.

Figure 5. Basicity versus lime / dolomitic limestone fraction in the slag former addition for a slagbased on KPRS DRI.

17

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

B2 KPRS

B3 KPRS

B4 KPRS

Bells ratio KPRS

Optic Bas KPRS

MgOsat KPRS

Ratio Burnt Lime / (Burnt Lime + Dolomitic limestone)

Ba

sic

ity V

alu

e

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

B2 Com 2

B3 Com 2

B4 Com 2

Bells ratio Com 2

Optic Bas Com 2

MgOsat Com 2


Ba

sic

ity V

alu

e

Figure 4 and 5 shows how different mixtures of slag former additions affect the basicity and whereMgO-saturation is reached for the slag when producing either KPRS or Com 2 based steel.

The vertical line represents at what slag former fraction the slag will be saturated with MgO. A higherfraction of lime/dolomitic limestone over the MgO-saturation fraction leads to a dissolution of MgOfrom the furnace lining. This results in an undesired wear on the furnace. In this case the usage ofKPRS results in a wider interval of possible fractions between burnt lime and dolomitic limestone thatmaintains a MgO saturated slag.

From these figures it can be seen that the basicity values have the same behavior for both rawmaterials, the basicity increases with the fraction of lime in the slag former. One difference betweenthe two cases is that the MgO-saturation occurs at different fractions of slag former additions. Thisindicates that the composition of the raw material has an effect on the slag composition and in thiscase specifically the MgO content. Furthermore the raw material composition also affects the amountof slag, where a charge based on Com 2 pellets produces a larger slag amount than a charge based onKPRS pellets.

Another important thing to notice is that there are no indications from the basicity values if andwhen MgO-saturation occurs. Also, a certain basicity value is no guarantee of MgO-saturation.

4.2 Basicity and slag forming fractions

It was also studied how different basicity models behave when the raw material is changed from Com2 to KPRS pellets while the amount of slag former addition is 5.5 ton, and the fraction between theslag formers, lime and dolomitic limestone varies. Figure 6 to 9 are based on 80 tons of A2 steel thatis produced by melting 32 tons of DRI based on KPRS or Com 2 together with 54.5 tons of scrap.

Figure 6. Basicity values (B2) versus lime/dolomitic limestone ratio for Com 2 and KPRS.

18

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

1

2

3

4

5

6

B2 KPRS

B2 Com 2


B2

Va

lue



19

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

1

2

3

4

5

6

B3 KPRS

B3 Com 2


B3

Va

lue

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

1

2

3

4

5

6

B4 KPRS

B4 Com 2


B4

Va

lue

Figure 9. Basicity values (Bells ratio) versus lime/dolomitic limestone ratio for Com 2 and KPRS.

Figure 6 to 9 show how different basicity models behave for two raw material types while theproduction uses a fixed amount of slag formers but the ratio between lime and dolomitic lime varies.

These results show that the different basicity measures have the same behavior for both of the rawmaterial types with the basicity value increasing with more lime in the slag forming addition. There isalso a difference between using a raw material based on KPRS-pellets and Com 2-pellets. Were theKPRS material leads to higher basicity values compared to Com 2 material with the same slag formermix. Furthermore, as in figure 4 and 5, there is no indication in the basicity values in figure 6 to 9when MgO-saturation occurs.

4.3 DR/DRI Comparison

A DR/DRI comparison between the mixes Com 2-KPRS, Com 2- Com 1 and Com 1-KPRS was done tosee how the DR types affect some of the important properties in an EAF based steel production.Properties such as, slag amounts, electric energy consumption and tap-to-tap time were studied. Thiswas done for both A1 and A2 steel types. However, a high amount of DRI based on competitor 1could not be used, since it was not possible to reach the target composition for the two steel types.Furthermore, it should be noted that there is a change of slope in all of the curves containing KPRS ataround 60-70% KPRS. This change of slope originates from the slag getting over saturated with theregards to MgO. Therefore, the effects that occur after the slope change depends primarily on thelesser amounts of acidic oxides in KPRS compared to Com 1 and Com 2.

20

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

1

2

3

4

5

6

Bells ratio KPRS

Bells ratio Com 2


Be

lls V

alu

e

Slag amounts (kg slag / ton liquid steel)

Figure 10 and 11. Slag amounts generated per ton liquid steel versus the DR-pellet mixes betweencompetitor 2-KPRS, competitor 1-KPRS and competitor 2-competitor 1.

Figure 10 and 11 shows how the amount of slag that is generated per ton steel for the two steelgrades A1 and A2 when the raw material mixture varies. It can be seen that the slag amountdecreases for all of the mixtures. This is due to the fact that Com 1 contains a lower amount of acidicoxides compared to Com 2, and KPRS contains less of acidic oxides than both Com 1 and Com 2.

It can also be noted that there is a slope change for the curves containing KPRS pellets , around 4:6 -3:7, for the A1 and A2 steel types for Com 1-KPRS and Com 2-KPRS. This indicates that the slagbecomes over saturated with MgO. Before the slope change, the decrease in slag amount is thanks toboth smaller dolomitic limestone additions and to smaller amounts of acidic oxides in the DR-pellet.

21

10;0 9;1 8;2 7;3 6;4 5;5 4;6 3;7 2;8 1;9 0;100

20

40

60

80

100

120

140

160

A1 Com 2-KPRSA1 Com 1-KPRSA1 Com 2-Com 1

Weight fraction of DR-pellets

Sla

g a

mo

un

t (kg

/ to

n s

tee

l)

10;0 9;1 8;2 7;3 6;4 5;5 4;6 3;7 2;8 1;9 0;100

20

40

60

80

100

120

140

A2 Com 2- KPRSA2 Com 1-KPRSA2 Com 2-Com 1


Sla

g a

mo

un

t (kg

/ to

n s

tee

l)

After this point, it is just the smaller amount of acidic oxides that contributes to the lower slagamounts.

Electric consumption (kWh / ton liquid steel)

Figure 12 and 13. Required electric energy amount for the EAF versus the DR-pellet mixes betweenCom 2-KPRS, Com 1-KPRS and Com 2- Com 1.

Figure 12 and 13 show how the consumption of electricity varies for the two different steel grades A1and A2, when the raw material mixture varies. The electricity consumption has the same behavior asthe slag amount. This is due to two reasons that are connected to the slag amounts. First, larger slagamounts require more energy per ton steel. Second, larger slag amounts require the use of more rawmaterials, especially iron, per ton steel in order to form the slag. Thus, if an increased amount of irongoes to the slag, this will result in increased iron loss, which has to be compensated for by addition ofmore DRI pellets to the furnace. This all leads to an increased energy demand. Therefore, the DR-pellet mixture which results in the lowest amount of slag is also the mixture with the lowestelectricity requirement. In this case it is the 100% KPRS mixture, as the KPRS pellets contains thelowest amount of acidic oxides.

Tap-to-tap time (hours)

22

10;0 9;1 8;2 7;3 6;4 5;5 4;6 3;7 2;8 1;9 0;100

100

200

300

400

500

600

700

800



Ele

ctri

c co

ns

um

ptio

n (

kWh

/ to

n s

tee

l)

10;0 9;1 8;2 7;3 6;4 5;5 4;6 3;7 2;8 1;9 0;100

100

200

300

400

500

600

700



Ele

ctri

c co

ns

um

ptio

n (

kWh

/ to

n s

tee

l)

Figure 14 and 15. Tap-to-tap time versus the DR-pellet mixes consisting of Com 2-KPRS, Com 1-KPRSand Com 2-Com 1.

Figure 14 and 15 show how the tap-to-tap time changes for the two steel types A1 and A2 when theraw material mixture varies. The tap-to-tap time is observed to have the same behavior as theelectricity consumption. This is because tap-to-tap times is calculated based on the electricityconsumption in RAWMATMIX®. This results in that the raw material mixture that requires thesmallest energy consumption is also the raw material mixture that generates the shortest tap-to-taptime. And in this case it was the 100% KPRS mixture that generated the shortest tap-to-tap times forboth the A1 and A2 steel grades.

4.4 Parameter study

23

10;0 9;1 8;2 7;3 6;4 5;5 4;6 3;7 2;8 1;9 0;100

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1



Ta

p-t

o-t

ap

tim

e (

ho

urs

)

10;0 9;1 8;2 7;3 6;4 5;5 4;6 3;7 2;8 1;9 0;100

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1



Ta

p-t

o-t

ap

tim

e (

ho

urs

)

A parameter study is done based on smelting 100% KPRS DRI while individual properties for the KPRSand its corresponding DRI is varied. This is done to study what effect the individual properties have onthe EAF production of an A2 steel grade. The composition for KPRS and its corresponding DRI with 2%carbon and 95% metallization can be seen in table 2.

The parameters setup for the KPRS can be seen below:

The carbon content was set to 1wt%, 2wt%, 3wt% in the DRI.

The metallization degree was set to 92%, 95%, 98% in the DRI

The SiO2 content was set to 0.50wt%, 1.00wt%, 1.50wt% in the DR-pellet.

The Al2O3 content was set to 0.25wt%, 0.50wt%, 0.75wt% in the DR-pellet.

The combined Al2O3 + SiO2 was set to 0.75 wt%, 1.50wt%, 2.25wt% in the DR-pellet.

Slag amount kg per ton liquid steel.

Figure 16. Graph of how individual parameters for a DR-pellet and DRI affect the slag amount in theEAF process.

In figure 16, which shows how the slag amount per ton steel varies when the individual parametersare changed, it can be observed that the carbon content and metallization degree hardly affect theamount of slag at all. This is expected due to the fact that neither the carbon content nor the FeOcontent, which is an equivalent to the metallization degree, should have an effect on the slag amount.However, the acidic oxides have an effect on the slag amount. More specifically, larger amounts ofacidic oxides result in larger amounts of slag. This can be seen in the combined effect of the (Al 2O3 +SiO2) content.

Electricity consumption per ton liquid steel

24

Carbon content Metallization SiO2 content Al2O3 content Al2O3+SiO20

20406080

100120140160180

[1.00% 2.00% 3.00%] [92.0% 95.0% 98.0%] [0.5% 1.0% 1.5%] [0.25% 0.50% 0.75%] [0.75% 1.50% 2.25%]

Sla

g a

mo

un

t kg

/ton

ste

el

Figure 17. Graph of how individual parameters for a DR-pellet and DRI affect the electricityconsumption in the EAF process.

Figure 17 shows how the consumption of electricity varies with the individual parameters per tonsteel. It can be seen that the electricity consumption decreases when the carbon content andmetallization increases. For the carbon content, the decrease in electrical energy consumption withincreasing carbon content are due to that the carbon is used to produce chemical energy whichreduce the need for electricity. An increased metallization degree means that the DRI contains lessFeO. Larger amounts of FeO than the required amount for the slag are unnecessary and need to bereduced by carbon to form CO which is an endothermic process. Thus, higher metallization reducethe electricity consumption.

For the acidic oxides, it can be seen that an increased amount of acidic oxides leads to an increasedslag amount. This generates a larger need for electricity for slag melting.

Yield required amount of DRI per ton liquid steel

Figure 18. Graph of how individual parameters for a DR-pellet and DRI affect the amount of DRIrequired per ton steel in the EAF process.

Figure 18 shows how the amount of DRI, which is required to produce one ton of liquid steel, varieswhen individual properties for the KPRS pellet and corresponding DRI is varied. For the carboncontent of the DRI it can be seen that for each amount of carbon added to the DRI, an equal amountof iron has to be added to compensate the “non-iron” in the DRI. Therefore, the DRI consumption

25


100

200

300

400

500

600

700

[1.00% 2.00% 3.00%] [92.0% 95.0% 98.0%] [0.5% 1.0% 1.5%] [0.25% 0.50% 0.75%] [0.75% 1.50% 2.25%]

Ele

ctri

c co

ns

um

ptio

n k

Wh

/ to

n s

tee

l

Carbon content Metallization SiO2 content Al2O3 content Al2O3+SiO21.071.081.09

1.11.111.121.131.141.151.16

[1.00% 2.00% 3.00%] [92.0% 95.0% 98.0%] [0.5% 1.0% 1.5%] [0.25% 0.50% 0.75%] [0.75% 1.50% 2.25%]

Yie

ld (

ton

s o

f DR

I / to

n o

f ste

el)

increases with increasing carbon content. Moreover, it is also natural that the DRI consumptiondecreases when the metallization degree increases since the DRI contains less amount of FeO. Alsothe DRI consumption increases with increasing content of acidic oxides. Therefore, for the requiredDRI amount per ton steel, it can be seen that with increasing purity of the DRI the required amount ofDRI per ton steel decreases.

The Cost per ton liquid steel.

Figure 19. Graph of how individual parameters for a DR-pellet and DRI effects the total productioncost in the EAF process.

Figure 19 shows how the production cost varies when individual properties for the KPRS pellet arechanged. The cost for steel production includes the EAF process costs, raw material costs and cost forproduction of DRI from DR pellets. Thus, the cost contains the total effect from the previousparameters and their effect on the final product. In this case that leads to an decreasing cost withincreasing carbon content and metallization degree, although it requires a more expensive treatmentin the DR shaft. Furthermore, the acidic oxides especially the combined Al2O3+SiO2 content are ofimportance for the EAF production, as increasing amounts leads to a higher production cost due tothe process would generate more slag, higher energy consumption and larger consumption of rawmaterials per ton steel. And in this case, an increase in the content of Al 2O3 + SiO2 within the DR pelletfrom 1.5wt% to 2.25wt% resulted in an increased production cost of 3%. An increase of just the SiO2

content of the DR pellet from 1.0wt% to 1.5wt% resulted in an increased production cost of 1.7%.

4.5 Value-in-use

The setup is as stated before, two different plants that produce the A2 steel type. One is charging100% DRI and the other plant is assumed to charge varying amount of scrap. The base composition ofDRI consists of 50% Com 1 and 50% Com 2. This is done to study the value-in-use of adding KPRS tothe base mixture, between 0-50%, together with the value of adaptive addition of slag formerscompared to a fixed amount and composition of the slag forming addition.

26


335

340

345

350

355

360

365

[1.00% 2.00% 3.00%] [92.0% 95.0% 98.0%] [0.5% 1.0% 1.5%] [0.25% 0.50% 0.75%] [0.75% 1.50% 2.25%]

Co

st u

sd

/ to

n s

tee

l

Middle East

The charged materials consist only of DRI. The fixed slag former addition consists of 1250kg burntlimestone and 2250 kg dolomitic limestone. Moreover, as stated before, adaptive addition of slagformers mean that the slag former addition composition and amount is based on the composition onthe raw material input.

Figure 20. Production cost for an A2 steel grade as a function of the amount of KPRS in DRI mixturewith adaptive addition of slag formers and fixed slag former addition.

Figure 20 shows how the production cost varies with increasing amount of KPRS in the raw materialmixture. This is done for two settings one with adaptive addition of slag formers and one with a fixedamount and mixture of the slag forming addition. Besides the reduced production cost of using KPRSpellets in the raw material mixture adaptive addition of slag formers would also reduce the tap-to-taptimes to 0.79-0.76 hours, when the amount of KPRS goes from 0% to 50%. This should be comparedto 0.8 h if a fixed slag former addition is used.

27

0% 10% 20% 30% 40% 50%28200

28400

28600

28800

29000

29200

29400

Fixed MEAdaptive ME

Percent KPRS

Co

st U

SD

/ C

ha

rge

North-America

Two different setups are used for charging the raw materials, one with a large scrap amount and onewith a smaller scrap amount. The setup is described as follows:

1. Large scrap amounts:

The charge consists of 50 ton scrap and 36 ton DRI. Fixed slag former addition consists of 1500kgburnt limestone and 1750 kg dolomitic limestone. Moreover, as stated before, adaptive addition ofslag formers mean that the slag former addition composition and amount based on the compositionon the raw material input.


Figure 21 show how the production cost varies with increasing amount of KPRS in the raw materialmixture. This is done for two settings one with adaptive addition of slag formers and one with a fixedamount and mixture of the slag forming addition. Besides the reduced production cost of using KPRSpellets in the raw material mixture adaptive addition of slag formers would also reduce the tap-to-taptimes to 0.69-0.67 hours, when the amount of KPRS goes from 0% to 50%. This should be comparedto 0.7 h if a fixed slag former addition is used.

2. Small scrap amount:

The charge consists of 25 ton scrap and 63 ton DRI.

Fixed slag former addition consists of 1250kg burnt limestone and 2000 kg dolomitic Limestone.Moreover, as stated before, adaptive addition of slag formers mean that the slag former additioncomposition and amount based on the composition on the raw material input.

28

0% 10% 20% 30% 40% 50%34300

34400

34500

34600

34700

34800

34900

35000

35100

Fixed NA 50Adaptive NA 50

Percent KPRS

Co

st U

SD

/ C

ha

rge


Figure 22 show how the production cost varies with increasing amount of KPRS in the raw materialmixture. This is done for two settings one with adaptive addition of slag formers and one with a fixedamount and mixture of the slag forming addition. Besides the reduced production cost of using KPRSpellets in the raw material mixture adaptive addition of slag formers would also reduce the tap-to-taptimes to 0.74-0.72 hours, when the amount of KPRS goes from 0% to 50%. This should be comparedto 0.75 h if a fixed slag former addition is used.

The following behaviors can be seen in Figures 20 to 22. The production costs decreases withincreasing amount of KPRS in the DRI mixture. This is due to the smaller amount of acidic oxides andlarger amount of basic oxides in the KPRS. The production cost will also decrease with adaptiveaddition of slag formers. Due to that the composition of the raw material is considered to minimizethe superfluous amount of slag and slag former, which also decreases the tap-to-tap times for theprocess.

All cases show the same type of behavior, namely that a high amount of KPRS and adaptive additionof slag formers is better compared to using no KPRS at all as well as a fixed slag amount and mixture.

29

0% 10% 20% 30% 40% 50%3630036400365003660036700368003690037000371003720037300

Fixed NA 25Adaptive NA 25

Percent KPRS

Co

st U

SD

/ C

ha

rge

5 Conclusions

As the primary focus of this project has been on how the composition of DR-pellets affect the EAFprocess and the chemical composition of the slag, the following conclusions can be made.

Basicity and MgO-saturation

The results show that the MgO-saturation and the conventional basicity values have no connection toeach other. Also the use of basicity values for process optimization focused on low refractory wearcan be misleading as they are not focused on the refractory compatibility. This is seen in the resultsshown in the chapter “Basicity and MgO-saturation”.

Acidic oxides

For the EAF process one of the most important aspects of the raw material inputs is the amount ofacidic oxides in the raw material. This is because the acidic oxides influence a lot of parameters in theEAF process. Besides an increasing amount of acidic oxides results in negative effects such asincreasing slag amounts and increasing costs.

In this study, it has been shown that increased amounts of acidic oxides lead to following results:

A higher slag amount: the acidic oxides are unwanted and are removed from the meltthrough the slag layer.

A lower yield between the amount of charged DRI and produced steel: more iron is oxidizedinto the slag, which results in larger amounts of raw material being required for each ton ofproduced steel.

A larger slag former addition: larger CaO and MgO additions are needed to keep the slagMgO saturated in order to avoid unnecessary wear on the furnace refractory.

Larger energy consumption: more slag and more raw materials which require more meltingenergy.

In this study, it has been shown that an increase in the content of Al2O3 + SiO2 in the DR pellet from1.5wt% to 2.25wt% results in an increased production cost of 3%. And an increase of just the SiO 2

content in the DR pellet from 1.0wt% to 1.5wt% result in an increased production cost of 1.7%.

Basic oxides and slag former additions

The amount of slag former addition is connected to the content of acidic oxides in the DRI and laterthe amount of acidic oxides in the charge. Larger amounts of acidic oxides result in a demand forlarger additions of slag formers to counteract the effect from the acidic oxides.

The ratio between limestone/dolomitic limestone depend on the content of MgO in the DRI. Largeramounts of MgO in the DRI result in that the MgO-saturation can be obtained at a higher ratio oflimestone/dolomitic limestone compared to a DRI with lower MgO contents.

30

By utilizing an adaptive addition of slag formers and taking the constituent components in the rawmaterials into account, it should be possible to make large reductions in production costs comparedto a fixed addition of slag formers.

Carbon and Metallization

The carbon content and the metallization degree have little to no effect on the slag amount or slagcomposition. However, they both effect the energy requirement for the EAF and through that theprocess time. In this case, higher carbon content and metallization degree results in shorter processtime for the EAF. However, as both higher carbon content and metallization degree requires longerprocess time in the DR-furnace. So the carbon content and metallization degree should be balancedwith regards to both the DR-furnace and EAF processes.

KPRS

KPRS contains both low amounts of acidic oxides and balanced amounts of MgO. These are excellenttraits for a DRI raw material. Therefore, these properties should be valued highly if steel plants woulduse KPRS together with adaptive addition of slag formers. As it can be seen from this study, usage ofadaptive addition of slag formers additions together with a large quantity of KPRS in the chargemixture could reduce the production cost by 2% and the tap-to-tap times by 5%.

31

6 Acknowledgment

I would like to thank Niloofar Arzpeyma, Magnus Tottie and Pär Jönsson.

Niloofar Arzpeyma, at Kobolde & Partners for her understanding and patience

Magnus Tottie, at LKAB for his wise comments and discussions.

Pär Jönsson, at KTH for this time.

32

7. References

[1] A.E Morris, 2001, Iron Resources and Direct Iron Production, Encyclopedia of Materials: Science and Technology

[2] Battle T, Srivastava U, Kopfle J, Hunter and R, McClelland J, 2013, TheDirect Reduction of Iron Chapter 1.2, Treatise on Process Metallurgy, Vol 3 Process Metallurgy

[3] Zervas, T., McMullan, J. T. and Williams, B, 1996, Gas-Based Direct Reduction Processes for Iron and Steel Prodcution, Internationaljournal of Energy Research, Vol 20

[4] The MIDREX Process Brochure, 2013, Technocal Paper, Company Brochures http://www.midrex.com/downloads_detail.cfmdown_cat_id=9&cat_id=154

[5] Energiron Direct Reduction Technology Overview

[6] Basak Anameric, S. Komar Kawatra, 2007,Properties and Features of Direct Reduced Iron, Mineral Processing and Extractive Metallurgy Review, Vol 28 Issue 1

[7] L. Kolbeinsen, 2010, Modelling of DRI Processes with Two Simultaneously Active Reducing Gases, Steel Research International, Vol 81 Issue 10

[8] Madias J, 2013, Electric Furnace Steelmaking, Chapter 1.5, Treatise on Process Metallurgy, Vol 3 Process Metallurgy

[9] Pretorius E, 1998, Fundamentals of EAF and Ladele Slags and Ladle Refining Principles

[10] Pretorius E, Carlise R.C, 1998 Foamy slag fundamentals and their practical application to electric furnace steelmaking

[11] Selin, R (1987) Dissertation, The Role of Phosphorous, Vanadium and Slag Forming Oxides in Direct Reduction Based Steelmaking

[12] RAWMATMIX system-documentation, Kobolde and Partners AB, Stockholm

[13] Sikström P, Sundqvist Ökvist, L, Wikström, J 2002, Injectrion of BOF slag throught Blast Furnace Tuyers – Trials in an Experimental Blast Furnace, LKAB

33

Appendix 1

Direct Reduced Iron (DRI)

Direct reduced iron is a raw material used in steel production. It is primarily used in EAF when there isa shortage of scrap or when there is a demand of low amounts of metallic impurities, such as copperand tin, in the steel [1,2,3].

In 2013, the total production of DRI was just over 75.2 M ton. This included Cold Direct Reduced Iron(CDRI) which represents the majority of the produced DRI, around 62.8 Mt. It also included the HotDirect Reduced Iron (HDRI) production at 6.2 Mt and the Hot Briquetted Iron (HBI) production at 6.2Mt [4].

Direct reduction (DR) of iron oxide is a process in which iron ore is reduced to metallic iron in a solidstate, and the only phases involved are in solid or gas state. Solid state reduction of iron ore tometallic iron requires less energy compared to the blast furnace, because there is no need for energyto melt the material [1,2,3].

The primary chemical compounds involved during DR of iron ore are iron and iron oxides, carbon andcarbon oxides, oxygen, hydrogen and water. The remaining chemical components are more or lessinert during the process. This means that any trace elements and impurities, such as gangue from themineral, remain inside the pellet throughout the DR process. Therefore, they end up in the DRI, whichthen follows the DRI to the melting process [2,5].

The raw material for DR of iron ore is often in the form of pellet. Typical compositions for both DRpellets and resulting DRI are presented in Table 1.

The reduction of iron ore is a stepwise process. First, hematite is reduced to magnetite which has ahigh reaction rate [6]. Then, the reduction of magnetite to wüstite takes place which also has a ratherhigh reaction rate compared to the final reduction. Finally, the reduction of wüstite to iron occurs,which has the lowest reaction rate and requires the highest reducing gas potential, which is describedas (H2+ CO)/(H2O+ CO2) [2,3,5,6].

34

Table 1. Range of composition for DR pellets and the resulting DRI after DR process. [2]

One of the important aspects to take in consideration during DRI production is the degree ofmetallization. This is the amount of iron within the pellet in the form of metallic iron and carbide(Fe3C) over total amount of iron within the pellet. The degree of metallization is important becausebesides the pure iron and iron carbide, there is often some amounts of unreduced iron oxide residuesand the degree of metallization describes that. Today, DRI is normally produced with a metallizationdegree of 90-97%. The DRI is rarely produced with a 100% metallization since it severely increases gasconsumption and deceases production compared to a DRI which contains a small percentageremaining iron oxides.

Another important aspect is the carbon content in DRI production. The DRI is sent for smelting and itis rarely reduced completely, and it contains a few percent of iron oxide. To reduce the amount ofrequired energy during the final reduction at melting stage, it has become common practice tocarburize the DRI which also contributes to the cooling of the DRI.

35

The content of gangue is also important, since the DR process is a solid state reduction process. Allthe gangue that comes with the iron ore stays within the DR pellet. Later it ends up in the meltingprocess, where most of it ends up in the slag. Thus, the slag in the melting stage is affected by thegangue content from the DRI. Depending on the melting process and the amount of the DRI, theimportance of the gangue can vary [1,2,3,5,7,8].

Reactions

The following temperature dependent reactions take place during the DRI process. At temperaturesbelow 1000 C, the reduction reactions are dominating in DR furnaces. These reactions are theprimary reduction reactions of iron ore. According to reaction 7 and 8, pure iron is carburized by thereducing gas. Also, at temperatures over 1000 C reactions 10 and 11 becomes important for thereducing gas because if carbon is accumulated somewhere in the process then off-gas can be used togenerate more reducing gas [2,3,5,8,10].

The gas reformation reactions and gas balance reactions show that if a high reducing gas potential isrequired, the reducing gas must be balanced between H2 and CO according to the water-gas shiftreaction 18 [2,3,5,9]

Reduction reactions

1: 3Fe2O3 + H2 = 2Fe3O4 + H2O

2: 3Fe2O3 + CO = 2Fe3O4 + CO2

3: Fe3O4 + H2 = 3FeO + H20

4: Fe3O4 + CO = 3FeO + CO2

5: FeO + H2 = Fe + H2O

6: FeO + CO = Fe + CO2

Carburization reactions

7: 3Fe + CO + H2 = Fe3C + H2O

8: 3Fe + 2CO = Fe3C + CO2

9: 3Fe + CH4 = Fe3C + 2H2

10: CO2 + C = 2CO

11: H2O + C = CO +H2

12: FeO + C = Fe + CO

36

13: 3Fe + C = Fe3C

Gas reforming reactions

Catalytic reforming

14: CH4 + H2O = CO + 3H2

15: CH4 + CO2 = 2 CO + 2H2

Partial oxidation

16: CH4 + ½O2 = CO +2H2

Gas balance reactions

17: 2H2 + O2 = 2H2O

18: CO + H2O = CO2+ H2

Carbon deposition on catalyst

19: CH4 = C+ 2H2

20: CO2 + C = 2CO

Types of DRI

Cold Direct Reduced Iron (CDRI) is the most commonly produced DRI product and it accounts for over80% of the total DRI produced. Since the DRI is produced through a solid state process, it keeps itsshape and volume. Due to its typical “sponge like” structure with a very high inner surface area andhigh metallization degree (92-97%) it is highly reactive with the atmosphere so it can be reoxidized.Thus, CDRI is not recommended to be transported by ship without special precautions, since it canreact with water leading to a hydrogen formation during reoxidation [2,4,5,10].

Hot Direct Reduced Iron (HDRI) is designed to be used in nearby EAF plants. The HDRI is not cooledcompared to CDRI and HDRI has a temperature of 600-700 C. Normally, it is charged into EAF attemperatures around 400-600 C. The advantage of using HDRI compared to CDRI in an EAF is that itrequires less energy to melt compared to CDRI [2,4,5,10].

Hot Briquetted Iron (HBI) is designed for longer transport and storage times compared to CDRI. Dueto its much smaller surface area it is less reactive with the atmosphere. HBI is produced by pressingfresh DRI into larger briquettes, at a temperature around 700 C, in a way to reduce the surface area

37

compared to CDRI. HBI is used as a supplement to scrap in EAF, BF and basic oxygen furnaces[2,4,5,10].

Natural gas reforming

The DRI production based on DR via reformed natural gas stands for almost 80% of the total DRIproduction. Natural gas (CH4) in itself cannot be used for a reduction of iron ore to metallic iron. It isrequired to be reformed to a reducing gas, which mostly consists of H2 and CO. Today, the reformingof natural gas for DR is primarily done by catalytic steam reforming, partial oxidation and reductionreactor off gas reforming which are described as follows [3,4,5,8,9].

Catalytic steam reforming of natural gas to reducing gas takes place in a reformer outside the furnaceas it can be seen in Figure 1. The reformer is equipped with a catalyst of nickel. Natural gas is injectedtogether with steam. These two gases react in the reformer and form a reducing gas consisting of H 2

and CO according to the following endothermic reaction 14 [3,5,8,9].

Because of the endothermic nature of the reaction the reducing gas needs to be heated before it canbe used within a DR furnace. This is done by both recirculation of off gases and adding more externalheat. Also it is important to use a natural gas with a low content of sulfur to avoid sulfur poisoning ofthe nickel catalyst which would lead to a lower efficiency and even its failure [3,5,8,9].

Figure 1. Steam reforming. Flowchart of natural gas and reducing gases for natural gas based DR witha steam reformer [5].

38

Partial oxidation of natural gas to reducing gas can replace part of the external reformer. A partialoxidation of natural gas can be achieved by injecting small amounts oxygen together with the naturalgas so that no total combustion of the natural gas occurs, the flow scheme and were the oxygen isinjected can be seen in Figure 2. Then reforming of natural gas can take place according to equation16 [3,5,8,9].

Moreover, an in situ reforming of the natural gas within the DR furnace is possible by using a partialoxidation, to totally replace the reformer. In situ reforming within the DR furnace is done by using thehot direct reduced iron as a catalyst within the furnace. The lack of a nickel catalyst for the reformingmakes the process less sensitive to sulfur, which makes it possible to use natural gas with a highersulfur content compared with the process based on a nickel catalyst [3,5,8,9].

For a shaft furnace, it is also possible to make some reformation of natural gas during thecarburization process of the DRI at the cooling stage of the process. It is based on the endothermicreaction 9. Since the reaction is endothermic, it can contribute to cooling of the DRI at the end of theprocess [3,5,8,9].

Figure 2. Partial oxidation/in situ. Flowchart of natural and reducing gases for natural gas based DRwith partial oxidation and in situ reforming of natural gas [5].

Reduction reactor off gas reforming of natural gas to reducing gas. By recirculating the off gas fromthe reduction process it is possible to reform natural gas to reducing gas. The reforming of natural gastakes place in a nickel based catalyst outside the furnace, similar to the steam reformer, but thisprocess utilizes carbon dioxide instead of steam. The reaction between CO2 and natural gas formsreducing gases according to the endothermic reaction 15. Because of the endothermic nature of the

39

reaction, the reformer needs to be heated during the reformation process. The heat normally comesform combustion of natural gas and part of the off gases. As the gas is recirculated, which can be seenin Figure 3, it is important to use a natural gas with low amounts of sulfur to avoid poisoning of thecatalyst [3,5,8,9].

Figure 3. Flowchart for a off gas reforming furnace [5].

DR in Vertical Shaft Furnaces

Around 80% of the world’s total production of DRI comes from the two leading technologies based onshaft furnaces, namely MIDREX and Energiron (previously known as HYL III). Both types of furnacesuses a counter current flow, which means that iron ore is charged from the top and flows down whilebeing reduced by the reducing gas. The latter is injected at the bottom of the reduction zone in theshaft and flows upwards. The reducing gas consists of H2 and CO. Reduction reactions which takesplace can be seen in reactions 1-6 [2,3].

MIDREX

The MIDREX process consists of three primary parts. These are the reduction shaft, the gas systemwith reformer and the cooling gas system, the latter if cold DRI is produced. In the reduction zone of

40

the shaft, the iron ore is reduced from iron oxide to metallic iron by using a reducing gas. The gasreformer reforms natural gas and off gas to a reducing gas that is used within the reduction shaft. Thecooling gas system is used in the cooling zone at the below the reduction zone in the shaft to bothcool and carburize the DRI.

Fig4. An illustration of a MIDREX furnace together with furnace zones and reactions.[10].

In the MIDREX process the reducing gas is formed by reforming natural gas with recycled off gas fromthe reduction shaft. The natural gas and off gas, primarily CO2, are preheated before it is injected intoa heated reformer. The reformer has to be heated due to the endothermic reaction of reformingnatural gas and off gas to reducing gas. After the reforming the reducing gas has a temperature over900 C. Then it is injected into the bottom region of the reduction zone in the reduction shaft. Thereducing gas has it highest reduction potential just as it is injected into the furnace [2,3,5,8,10,12].

41

Iron ore is charged from the top and the reducing gas moves in a counter current flow to the top ofthe furnace. The reduction of iron ore occur in a stepwise manner, while the ore flows downwards inthe furnace, according to reaction (1) and (2) during which magnetite is formed from hematite, andthen as shown in reaction, (3) and (4), wustite is generated from magnetite and finally in reactions (5)and (6), metallic iron is formed wustite. The process is designed so that at the bottom of thereduction zone, the DRI should be reduced to a desired grade, which normally corresponds to adegree of 94-96% metallization. After the reduction stage ends, the cooling stage starts if cold DRI isproduced. The cooling stage is designed to cool, carburize and also produce an amount of reducinggas. This is done by injecting a cooling gas similar to the reducing gas, but with a quite high rate ofnatural gas. The carburization occurs according to reactions (7), (8) and (9). If no cooling, the DRIcould be sent either to a briquetting machine to produce HBI, or directly as HDRI to a nerby EAF[2,3,5,8,10,12].

Energiron

The Energiron ZR process (Zero Reforming) has a lot of similarities with the MIDREX process.However, unlike the MIDREX, the Energiron process does not use any outside reformer to producethe reducing gas from natural gas. The Energiron process relies on in situ transformation of thenatural gas to a reducing gas inside the reduction shaft. The reforming of natural gas is done by usingfresh DRI within the furnace as a catalyst. Also, depending on where in the furnace the gas is injected,the natural gas is used for reforming (at the reduction zone) or carburization (in the cooling zone). Inthe reduction zone, the primary reactions for gas reforming are reactions (14) and (15). In the coolingzone the carburization reactions (7), (8) and (9) are the main reactions.

Because of the in situ reforming, the Energiron process has no need for a separate reforming module.This means that the Energiron process can handle a natural gas and iron ore with higher amounts ofsulfur compared to the MIDREX process. This is due to the fact that there is no risk for catalystpoisoning, because the catalyst is always refreshed in the Energiron process in the form of new DRI.This in contrast to the processes which utilize a stationary nickel catalyst. Another thing that differsbetween the Energiron and MIDREX processes is the pressure within the furnace. In the MIDREXfurnace, the reducing gases are only injected into the furnace to reduce and carburize the iron. Thisgives a possibility to operate the process at ambient pressure combined with a high gas speed toensure an even distribution of reducing gas. In contrast to the MIDREX the Energiron process isworking at a high pressure, 6-8 bar and lower gas speed to insure that the reforming of natural gas toreducing gas occurs at the desired zone [2,3,5,8,10,12,13].

Sticking between DR pellets during DR in a shaft furnace

One common problem in DR of iron ore pellets in a vertical shaft furnace is that the pellets have atendency to stick to each other. Thereby, they form clusters, which is not desirable because it disruptsboth the gas and mass flow and decreases the productivity of the furnace. This is primarily due to thefact that the clusters decrease the permeability of the reducing gasses and this leads to an unevendistribution of temperature and concentration gradients within the furnace.

42

Today, this problem can be avoided by having a good process control so that the conditions for clusterformation are kept to minimum within the furnace. There is also the possibility to decrease thesticking behavior by coating the pellets with mineral oxides that are stable at the prevailing reductiontemperatures. This is a suitable way to reduce the sticking behavior because the DR process is a solidstate reduction where the active components are the iron ore and reducing gases. Examples of oxidesthat are commonly used are lime (CaO) and dolomite (MgO) [2,3,11,12].

43

[1] A.E Morris, 2001, Iron Resources and Direct Iron Production, Encyclopedia of Materials: Science and Technology

[2] Battle T, Srivastava U, Kopfle J, Hunter and R, McClelland J, 2013, TheDirect Reduction of Iron Chapter 1.2, Treatise on Process Metallurgy, Vol 3 Process Metallurgy

[3] Zervas, T., McMullan, J. T. and Williams, B, 1996, Gas-Based Direct Reduction Processes for Iron and Steel Prodcution, Internationaljournal of Energy Research, Vol 20

[4] World Direct Reduction Statistics, 2013, http://www.midrex.com/handler.cfm/cat_id/153/section/company

[5] Basak Anameric, S. Komar Kawatra, 2007,Properties and Features of Direct Reduced Iron, Mineral Processing and Extractive Metallurgy Review, Vol 28 Issue 1

[6] L. Kolbeinsen, 2010, Modelling of DRI Processes with Two Simultaneously Active Reducing Gases, Steel Research International, Vol 81 Issue 10

[7] Zervas, T., McMullan, J. T. and Williams, B, 1996, Developments in Iron and Steel Making, Internationaljournal of Energy Research, Vol 20

[8] J. Feinman, 1999, Direct Reduction and Smelting Preocesses, Direct reduction and smelting processes, Iron Making Volume, AISE Steel Foundation

[9] Reimert, R., Marschner, F., Renner, H.-J., Boll, W., Supp, E., Brejc, M., Liebner, W. And Schaub, G. 2011. Gas Production, 2. Processes. Ullmann's Encyclopedia of Industrial Chemistry

[10] The MIDREX Process Brochure, 2013, Technocal Paper, Company Brochures http://www.midrex.com/ http://www.midrex.com/downloads_detail.cfmdown_cat_id=9&cat_id=154

[11] Lingyun Yi, Zhucheng Huang, (2013) Sticking of iron ore pellets during reduction with hydrogen and carbon monoxide mixtures: Behavior and mechanism, Powder Technology Vol 235

[12] Oeters, F., Ottow, M., Senk, D., Beyzavi, A., Güntner, J., Lüngen, H. B., Koltermann, M. and Buhr, A. 2011. Iron, 1. Fundamentals and Principles of Reduction Processes. Ullmann's Encyclopedia of Industrial Chemistry

[13] Energiron Direct Reduction Technology Overview

44

Appendix 2

EAF Slag

EAF slag is an ionic solution that floats on top of the steel. The main components in the EAF slag forcarbon steel are CaO, MgO, FeO and SiO2. It is also common practice to use a foaming slag which isdesigned to expands in volume by the formation and capture of gas bubbles within the slag to reducethe refractory wear and increase the heat exchange [1,2,3,4].

The primary functions of an EAF slag are to:1. Protect the liquid steel from oxidation.2. Prevent the liquid steel from absorbing hydrogen hand nitrogen.3. Improve the steel quality by dephosphoring the melt and absorb oxides and inclusions. 4. Insulate, to minimize the heat loss.5. Be compatible with the refractory to minimize the refractory wearing.

Common oxides in EAF slag and their melting point are presented in Table 1 [3].

Table 1. Common oxides in EAF slag and corresponding melting point.

Slag composition

The major components for slag can often be divided into two different categories, acidic oxides andbasic oxides. Some of the common acidic oxides are Al2O3, Cr2O3, FeO, MnO and SiO2. The basic oxidesprimarily consists of CaO and MgO. The majority of the acidic oxides originates from the scrap, DRI ordirt and residual elements from transportation and storage. The basic oxides are often called slagformers and are added to the melt to both form slag and balance the corrosive effect from the acidicoxides on the furnace refractories [1,3].

The origin of the oxides differs depending on the oxide type and its metallurgical value [2].

Al2O3 - Oxidation of aluminum that comes as an impurity from the scrap, 2Al + 3½O2 = Al2O3 - Already oxidized aluminum scrap - Steel deoxidation, 2Al + 3O = Al2O3

- Dissolution of refractories containing aluminum

Cr2O3 - Oxidation of chromium that comes as an impurity from the scrap, 2Cr + 3½O2 = Cr2O3

45

Oxide Melting point (C°)SiO2 1720CaO 2600MgO 2800Al2O3 2030FeO 1370MnO 1850Cr2O3 2260

FeO - Oxidized iron scrap - Unmetalized DRI and rust. - Carbon balance for the steel, Fe + CO (g) = FeO + C- Oxygen balance for the steel, Fe + O = FeO

MnO - Steel deoxidation, Mn + O = MnO- Oxidation of manganese that comes as an impurity from the scrap, 2Mn + O2 =

2MnO

SiO2 - Oxidation of silicon that comes as an impurity from the scrap, Si + O2 = SiO2

- Steel deoxidation, Si + 2O = SiO2 - Sand

CaO - Addition to the melt as a slag former - Dissolution of refractories containing CaO

MgO - Addition to the melt as a slag former- Dissolution of refractories containing MgO

Viscosity

An important physical factor for the slag is its viscosity. This is because it has an influence on both thewear of the refractory and the kinetics of the reactions taking place in the slag and steel-slag-interface. To have a long lasting refractory it is favorable to have a slag with a high viscosity, since theslag penetration into the refractory will be minimized. From the metallurgical point of view, a lowviscosity is of interest because it will give favorable kinetics and faster reaction rates for the reactionstaking place in the slag and slag-steel-interface compared to slag with high viscosity. Therefore, it isimportant to balance the viscosity in such a way that the wear of the refractory is kept to a minimumvalue while also providing required conditions for the steel-slag reactions to take place [1,2,3].

Classification of slag

The slag is often classified into four categories depending on its viscosity which are from lowest tohighest viscosity: Watery, creamy, fluffy, crusty[ 3].

Watery slag having low viscosity are often undesirable because it contains to little refractory oxides,which makes it incompatible with the refractory. This results in a high refractory wear and poorfoaming properties. Has a high amount of acidic oxides compared with basic oxides [1,2,3].

A creamy slag is often the desired consistency for the EAF slags. This is due to the fact that itrepresents a balance between the metallurgical properties and a low wear on furnace refractoriesand a good ability for slag foaming [1,2,3].

A fluffy slag is often a sign of too high amounts of refractory oxides in the slag which gives a higherviscosity and less foaming properties. This results in lower amounts of wear compared to a creamyslag but also a less effective cleaning effect. In a fluffy slag there are higher amounts of basic oxidescompared to acidic oxides [1,2,3].

46

Crusty slag is a slag with a high amount of solid slag compared to the amount of liquid slag. A crustyslag is rarely desirable because it has poor foaming properties and also poor metallurgical propertiesto clean the steel from unwanted elements and particles [1,2,3].

The slag classifications can be visualized by using a simplified phase diagram of the CaO-Al 2O3 system,which is shown in Figure 1 [3].

Figure 1. CaO-Al2O3-phase diagram that show and describes how the viscosity classification can belinked with the fraction of liquid and solid phases in a slag [3].

Basicity slag models

Today the most common way to predict the metallurgical behavior and compatibility with the furnacerefractory are through basicity models. These models are often the ratio of basic oxides over theacidic oxides in the slag. The basicity is used as a single compositional parameter for slags whichcould be applied in similar ways as the pH-value are used for aqueous solutions [2].

The name of basicity models are depending on what oxides is considered and if the fractions areassigned certain values such as the B2 or V ratio, or Bells ratio or even optical basicity.

The B2 or V ratio is given by

B2=(wt%CaO)

(wt%SiO2)

Bells ratio is given by

47

Bells Ratio=(wt %CaO+0.69∗wt%MgO)

(0.93∗wt %SiO2+018wt%Al2O3) [5].

Another model that has been developed for slags is the optical basicity model. It has been created byusing spectrographic data of glasses together with Pauling’s electronegativity data, which can be seenin table 2 [2].

Table 2. Table of Optical basicity values for some typical slag components.

The average optical basicity for a slag is calculated as follows:

OpticalBasicity =X AOx∧AOAOx+X AOy∧AOAOy+.. .

Where XAOx is calculated by using the equation.

X AOx=(NOAOx∗X Ao)

(Σ(NOYOx∗X Yo))

Where NOAOx is the number of oxygen atoms in the oxide molecule. XAO is the mole fraction of themolecule. And the Σ (NOYOx * XYO) is the sum of all the different oxygen molecules times their oxygencontent for the system.

So for SiO2 in CaO-FeO-MgO-SiO2 slag, X is calculated by

X SiO2=

(2NSiO2)

(2NSiO 2+NCaO+NFeO+N MgO)

48

Oxide Optical Basicity (Λ)Na2O 1.15CaO 1.0MgO 0.78CaF2 0.67TiO2 0.61Al2O3 0.61MnO 0.59Cr2O3 0.55FeO 0.51

Fe2O3 0.48SiO2 0.48

Where 2NSiO2 results from the two oxygen atoms in the molecule and the mole fraction of thecompound. The same apply for the other molecules in the CaO-FeO-MgO-SiO2 slag.

MgO Slag model

Instead of using basicity to define the slag Roger Selin suggested that EAF slag should be construedbased on MgO saturation (MgOsat) of the slag. This comes from the idea that the slag closest to therefractory should be saturated with MgO, either by addition of slag former or by dissolving MgO fromthe furnace wall. So according to Roger Selin an EAF slag should be designed according to thecomplex slag composition of the weight percent of CaO-FeO-MgOsat-SiO2. This mean that the MgOsatcan be found by the CaO and FeO content. In this slag definition Roger Selin has also investigated andlinked the phosphorus and vanadium distribution between the slag and steel bath [4].

.

Diagram 1. Diagram of Roger Selins solubility calculations of MgO saturation in a complex slag of CaO-FeO-MgOsat-SiO2 at 1600°C. According to Selin the saturation of MgO is dependent on the

composition of CaO and FeO [4].

FoamingSlag foaming is the function of the generation of gas bubbles and slag that can sustain gas bubbles.Together they will create a foaming slag. The process of slag foaming is primarily dependent on threethings. The surface tension which is the controlling factor for the energy requirement for the creationof gas bubbles. So the surface tension controls the amount and size of the gas bubbles. The viscosity

49

controls the residence time for the gas bubbles in the slag. A higher slag viscosity results in longerresidence time compared to a slag with lower viscosity. Suspended second phase particles within theslag. According to Kimihisa Ito, Freuehan R.J [6,7] the amount of suspended second phase particles,such as CaO and MgO, in the slag has a greater impact on the foaming properties compared to thesurface tension and the viscosity [1,3,6,7].

That second phase particles has a greater impact on the foaming properties derives from that thesecond phase particles act as a nucleation site for gas bubble generation. This gives better foamingproperties. However, this is true to a certain point where the fraction of solid/liquid in the slagincreases which is negative for the foaming properties [3,6,7].

The generated bubbling gas in the foaming slag is primarily CO gas that is formed through reductionof FeO to Fe by the following reaction [3].

(I) FeO + C = Fe + CO

Furthermore, it can be produced by oxygen reacting with carbon inside the steel bath or by carboninjection into the slag and melt according to reaction (II) [3].

(II) C + ½O2 = CO

It is important to notice that if only oxygen is injected into the steel and slag it results in a higher slagtemperature. This, in turn results in a lower viscosity of the slag. This is due to the two exothermicreactions, (III) and (IV) [3].

(III) C+ ½O2 = CO

(IV) Fe + O = FeO

Besides, increasing the temperature of the slag reaction (IV) also contributes to an increased amountof FeO in the slag which also contributes to a lower viscosity [3].

50

[1] Madias J, 2013, Electric Furnace Steelmaking, Chapter 1.5, Treatise on Process Metallurgy, Vol 3 Process Metallurgy

[2] Pretorius E, 1998, Fundamentals of EAF and Ladele Slags and Ladle Refining Principles

[3] Pretorius E, Carlise R.C, 1998 Foamy slag fundamentals and their practical application to electric furnace steelmaking

[4] Selin, R (1987) Dissertation, The Role of Phosphorous, Vanadium and Slag Forming Oxides in DirectReduction Based Steelmaking

[5] Sikström P, Sundqvist Ökvist, L, Wikström, J 2002, Injectrion of BOF slag throught Blast Furnace Tuyers – Trials in an Experimental Blast Furnace, LKAB

[6] Kimihisa Ito, Freuehan R.J, 1989 Study on the Foaming of CaO-SiO2-FeO Slags: Part I. Foaming Parameters and Experimental Results, Metallurgical Transactions B Volume 20 Issue 4

[7] Kimihisa Ito, Freuehan R.J, 1989 Study on the foaming of CaO-SiO2-FeO slags: Part II. Dimensional analysis and foaming in iron and steelmaking processes, Metallurgical Transactions B Volume 20 Issue4

51

Appendix 3

Input

DR-Pellets compositions

DR Pellets mixes and corresponding DRI

Com 2-Com 1

Com 1-KPRS

Com 2-KPRS

Carbon

Metallization

SiO2

(Al2O3 + SiO2).

Steel and Slag constraints

Plant Data - DR Furnace

Plant Data – EAF

Scrap analysis

Slag formers

52

DR-Pellets compositions

Table 1. Composition of the three different DR-pellets used in this work.

53

DR Pellets Types

KPRS Com 1 Com 2

wt% wt% wt%

0.7489 1.2299 1.3294

0.1598 0.4899 0.6397MnO 0.0773 0.0684 0.0549CaO 0.8848 0.6882 0.6666MgO 0.649 0.087 0.2099

0.0573 0.0094 0.0744

0.1962 0.007 0.03

0.1798 0.039 0.06

0.0029 0.0023 0.0184

0 0 0

0 0.0003 0.0003NiO 0.0382 0.0052 0.005

0.0123 0 0

0 0 0

0 0 0CuO 0.0013 0.0038 0.0005

0 0 0NbO 0 0 0

0.0399 0.04 0.004

0.3 0.008 0.0055

0.0085 0.1741 0.0076

0 0.0001 0.0001ZnO 0.0037 0.0025 0

0.0031 0 0

0 0 0FeOOH 0 0 0

0 0 0FeO 0 0 0

95.9416 96.5005 95.6051

0.9654 0.6445 1.2885

Moisture 1.6 1.6 1.6Fines 3.00% 3.00% 3.00%Dust loss 3.00% 3.00% 3.00%

SiO2

Al2O

3

P2O

5

V2O

5

TiO2

Cr2O

3

MoO2

MoO3

CaF2

CaCO3

MgCO3

WO3

Na2O

K2O

CaSO4

SnO2

CaCl2

Ca(OH)2

FeCO3

Fe2O

3

Fe3O4

DR-pellets mixes and corresponding DRI

Table 2. Composition of mixture between Com 2 and Com 1 and its corresponding DRI.

54

DR Pellets MixFraction

Com 2-Com 110-0 9-1 8-2 7-3 6-4 5-5 4-6 3-7 2-8 1-9 0-10

wt% wt% wt% wt% wt% wt% wt% wt% wt% wt% wt%

1.3294 1.31945 1.3095 1.29955 1.2896 1.27965 1.2697 1.25975 1.2498 1.23985 1.2299

0.6397 0.62472 0.60974 0.59476 0.57978 0.5648 0.54982 0.53484 0.51986 0.50488 0.4899

MnO 0.0549 0.05625 0.0576 0.05895 0.0603 0.06165 0.063 0.06435 0.0657 0.06705 0.0684

CaO 0.6666 0.66876 0.67092 0.67308 0.67524 0.6774 0.67956 0.68172 0.68388 0.68604 0.6882

MgO 0.2099 0.19761 0.18532 0.17303 0.16074 0.14845 0.13616 0.12387 0.11158 0.09929 0.087

0.0744 0.0679 0.0614 0.0549 0.0484 0.0419 0.0354 0.0289 0.0224 0.0159 0.0094

0.03 0.0277 0.0254 0.0231 0.0208 0.0185 0.0162 0.0139 0.0116 0.0093 0.007

0.06 0.0579 0.0558 0.0537 0.0516 0.0495 0.0474 0.0453 0.0432 0.0411 0.039

0.0184 0.01679 0.01518 0.01357 0.01196 0.01035 0.00874 0.00713 0.00552 0.00391 0.0023

0 0 0 0 0 0 0 0 0 0 0

0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003

NiO 0.005 0.00502 0.00504 0.00506 0.00508 0.0051 0.00512 0.00514 0.00516 0.00518 0.0052

0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

CuO 0.0005 0.00083 0.00116 0.00149 0.00182 0.00215 0.00248 0.00281 0.00314 0.00347 0.0038

0 0 0 0 0 0 0 0 0 0 0

NbO 0 0 0 0 0 0 0 0 0 0 0

0.004 0.0076 0.0112 0.0148 0.0184 0.022 0.0256 0.0292 0.0328 0.0364 0.04

0.0055 0.00575 0.006 0.00625 0.0065 0.00675 0.007 0.00725 0.0075 0.00775 0.008

0.0076 0.02425 0.0409 0.05755 0.0742 0.09085 0.1075 0.12415 0.1408 0.15745 0.1741

0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001

ZnO 0 0.00025 0.0005 0.00075 0.001 0.00125 0.0015 0.00175 0.002 0.00225 0.0025

0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

FeOOH 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

FeO 0 0 0 0 0 0 0 0 0 0 0

95.6051 95.69464 95.78418 95.87372 95.96326 96.0528 96.14234 96.23188 96.32142 96.41096 96.5005

1.2885 1.2241 1.1597 1.0953 1.0309 0.9665 0.9021 0.8377 0.7733 0.7089 0.6445

DRI composition

10-0 9-1 8-2 7-3 6-4 5-5 4-6 3-7 2-8 1-9 0-10

Metallic Components


C 2 2 2 2 2 2 2 2 2 2 2

S 0.0025 0.0078 0.0131 0.0185 0.0239 0.0292 0.0346 0.0399 0.0453 0.0506 0.056

Fe 87.8236 87.8627 87.9019 87.9411 87.9803 88.0196 88.0588 88.0981 88.1374 88.1767 88.216

Ni 0.0053 0.0053 0.0054 0.0054 0.0054 0.0055 0.0055 0.0055 0.0055 0.0056 0.0056

Cu 0.0005 0.0009 0.0013 0.0016 0.002 0.0023 0.0027 0.003 0.0034 0.0037 0.0041

Mo 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003

Oxidic Components

1.8127 1.7995 1.7863 1.773 1.7598 1.7466 1.7334 1.7201 1.7069 1.6963 1.9804

0.8723 0.852 0.8318 0.8115 0.7912 0.7709 0.7507 0.7304 0.7101 0.6897 0.6694

FeO 5.9466 5.9492 5.9519 5.9545 5.9572 5.9599 5.9625 5.9652 5.9678 5.9705 5.9732

MnO 0.0748 0.0767 0.0785 0.0804 0.0823 0.0841 0.086 0.0879 0.0897 0.0916 0.0935

CaO 0.9131 0.9256 0.9381 0.9506 0.9631 0.9757 0.9882 1.007 1.0132 1.0258 1.0383

MgO 0.2862 0.2695 0.2528 0.2351 0.2194 0.2026 0.1859 0.1691 0.1524 0.1356 0.1189

0.1015 0.0926 0.0838 0.0749 0.0661 0.0572 0.0483 0.0395 0.0306 0.0217 0.0128

0.0409 0.0377 0.0346 0.0315 0.0283 0.0252 0.0221 0.0189 0.0158 0.0127 0.0095

0.0818 0.0789 0.0761 0.0732 0.0704 0.0675 0.0647 0.0618 0.059 0.0561 0.0533

0.0251 0.0229 0.0207 0.0185 0.0163 0.0142 0.012 0.0098 0.0076 0.0054 0.0032

0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

SiO2

Al2O

3

P2O

5

V2O

5

TiO2

Cr2O

3

MoO2

MoO3

CaF2

CaCO3

MgCO3

WO3

Na2O

K2O

CaSO4

SnO2

CaCl2

Ca(OH)2

FeCO3

Fe2O

3

Fe3O

4

SiO2

Al2O

3

P2O

5

V2O

5

TiO2

Cr2O

3

MoO3

CaF2

Table 3. Composition of mixture between Com 1 and KPRS and its corresponding DRI.

55


Com 1-KPRS10-0 9-1 8-2 7-3 6-4 5-5 4-6 3-7 2-8 1-9 0-10


1.2299 1.1818 1.1337 1.0856 1.0375 0.9894 0.9413 0.8932 0.8451 0.797 0.7489

0.4899 0.45689 0.42388 0.39087 0.35786 0.32485 0.29184 0.25883 0.22582 0.19281 0.1598

MnO 0.0684 0.06929 0.07018 0.07107 0.07196 0.07285 0.07374 0.07463 0.07552 0.07641 0.0773

CaO 0.6882 0.70786 0.72752 0.74718 0.76684 0.7865 0.80616 0.82582 0.84548 0.86514 0.8848

MgO 0.087 0.1432 0.1994 0.2556 0.3118 0.368 0.4242 0.4804 0.5366 0.5928 0.649

0.0094 0.01419 0.01898 0.02377 0.02856 0.03335 0.03814 0.04293 0.04772 0.05251 0.0573

0.007 0.02592 0.04484 0.06376 0.08268 0.1016 0.12052 0.13944 0.15836 0.17728 0.1962

0.039 0.05308 0.06716 0.08124 0.09532 0.1094 0.12348 0.13756 0.15164 0.16572 0.1798

0.0023 0.00236 0.00242 0.00248 0.00254 0.0026 0.00266 0.00272 0.00278 0.00284 0.0029

0 0 0 0 0 0 0 0 0 0 0

0.0003 0.00027 0.00024 0.00021 0.00018 0.00015 0.00012 0.00009 0.00006 0.00003 0

NiO 0.0052 0.0085 0.0118 0.0151 0.0184 0.0217 0.025 0.0283 0.0316 0.0349 0.0382

0 0.00123 0.00246 0.00369 0.00492 0.00615 0.00738 0.00861 0.00984 0.01107 0.0123

0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

CuO 0.0038 0.00355 0.0033 0.00305 0.0028 0.00255 0.0023 0.00205 0.0018 0.00155 0.0013

0 0 0 0 0 0 0 0 0 0 0

NbO 0 0 0 0 0 0 0 0 0 0 0

0.04 0.03999 0.03998 0.03997 0.03996 0.03995 0.03994 0.03993 0.03992 0.03991 0.0399

0.008 0.0372 0.0664 0.0956 0.1248 0.154 0.1832 0.2124 0.2416 0.2708 0.3

0.1741 0.15754 0.14098 0.12442 0.10786 0.0913 0.07474 0.05818 0.04162 0.02506 0.0085

0.0001 0.00009 0.00008 0.00007 0.00006 0.00005 0.00004 0.00003 0.00002 0.00001 0

ZnO 0.0025 0.00262 0.00274 0.00286 0.00298 0.0031 0.00322 0.00334 0.00346 0.00358 0.0037

0 0.00031 0.00062 0.00093 0.00124 0.00155 0.00186 0.00217 0.00248 0.00279 0.0031

0 0 0 0 0 0 0 0 0 0 0

FeOOH 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

FeO 0 0 0 0 0 0 0 0 0 0 0

96.5005 96.44461 96.38872 96.33283 96.27694 96.22105 96.16516 96.10927 96.05338 95.99749 95.9416

0.6445 0.67659 0.70868 0.74077 0.77286 0.80495 0.83704 0.86913 0.90122 0.93331 0.9654

DRI composition

10-0 9-1 8-2 7-3 6-4 5-5 4-6 3-7 2-8 1-9 0-10

Metallic Components


C 2 2 2 2 2 2 2 2 2 2 2

S 0.056 0.0507 0.0453 0.04 0.0347 0.0293 0.024 0.0187 0.0134 0.008 0.0027

Fe 88.216 88.1797 88.1434 88.1071 88.0708 88.0346 87.9983 87.9621 87.9259 87.8897 87.8535

Ni 0.0056 0.0091 0.0127 0.0162 0.0197 0.0233 0.0268 0.0303 0.0339 0.0374 0.0409

Cu 0.0041 0.0038 0.0036 0.0033 0.003 0.0027 0.0025 0.0022 0.0019 0.0016 0.0014

Mo 0.0003 0.0002 0.0002 0.0002 0.0002 0.0001 0.0001 0.0001 0.0001 0 0

Oxidic Components

1.6804 1.6144 1.5484 1.4825 1.4165 1.3506 1.2848 1.2189 1.1531 1.0872 1.0215

0.6694 0.6242 0.579 0.5338 0.4886 0.4435 0.3983 0.3532 0.3081 0.263 0.2179

FeO 5.9732 5.9707 5.9682 5.9658 5.9633 5.9609 5.9584 5.956 5.9535 5.9511 5.9486

MnO 0.0935 0.0947 0.0959 0.0971 0.0983 0.0995 0.1007 0.1019 0.1031 0.1043 0.1055

CaO 1.0383 1.0556 1.073 1.0903 1.1077 1.125 1.1426 1.1596 1.1769 1.1942 1.2115

MgO 0.1189 0.1956 0.2723 0.03491 0.4257 0.5024 0.579 0.6556 0.7322 0.8087 0.8852

0.0128 0.0194 0.0259 0.0324 0.039 0.0455 0.052 0.0586 0.0651 0.0716 0.0781

0.0095 0.0354 0.0612 0.087 0.1128 0.1386 0.1644 0.1902 0.216 0.2418 0.2676

0.0533 0.0725 0.0917 0.1109 0.1301 0.1493 0.1685 0.1877 0.2065 0.226 0.2452

0.0032 0.0033 0.0034 0.0034 0.0035 0.0036 0.0037 0.0037 0.0038 0.0039 0.004

0 0 0 0 0 0 0 0 0 0 0

0 0.0017 0.0034 0.0051 0.0067 0.0084 0.0101 0.0118 0.0135 0.01515 0.0168

SiO2

Al2O

3

P2O

5

V2O

5

TiO2

Cr2O

3

MoO2

MoO3

CaF2

CaCO3

MgCO3

WO3

Na2O

K2O

CaSO4

SnO2

CaCl2

Ca(OH)2

FeCO3

Fe2O

3

Fe3O

4

SiO2

Al2O3

P2O

5

V2O

5

TiO2

Cr2O

3

MoO3

CaF2

Table 4. Composition of mixture between Com 2 and KPRS and its corresponding DRI.

56


Com 2-KPRS10-0 9-1 8-2 7-3 6-4 5-5 4-6 3-7 2-8 1-9 0-10


1.3294 1.27135 1.2133 1.15525 1.0972 1.03915 0.9811 0.92305 0.865 0.80695 0.7489

0.6397 0.59171 0.54372 0.49573 0.44774 0.39975 0.35176 0.30377 0.25578 0.20779 0.1598

MnO 0.0549 0.05714 0.05938 0.06162 0.06386 0.0661 0.06834 0.07058 0.07282 0.07506 0.0773

CaO 0.6666 0.68842 0.71024 0.73206 0.75388 0.7757 0.79752 0.81934 0.84116 0.86298 0.8848

MgO 0.2099 0.25381 0.29772 0.34163 0.38554 0.42945 0.47336 0.51727 0.56118 0.60509 0.649

0.0744 0.07269 0.07098 0.06927 0.06756 0.06585 0.06414 0.06243 0.06072 0.05901 0.0573

0.03 0.04662 0.06324 0.07986 0.09648 0.1131 0.12972 0.14634 0.16296 0.17958 0.1962

0.06 0.07198 0.08396 0.09594 0.10792 0.1199 0.13188 0.14386 0.15584 0.16782 0.1798

0.0184 0.01685 0.0153 0.01375 0.0122 0.01065 0.0091 0.00755 0.006 0.00445 0.0029

0 0 0 0 0 0 0 0 0 0 0

0.0003 0.00027 0.00024 0.00021 0.00018 0.00015 0.00012 0.00009 0.00006 0.00003 0

NiO 0.005 0.00832 0.01164 0.01496 0.01828 0.0216 0.02492 0.02824 0.03156 0.03488 0.0382

0 0.00123 0.00246 0.00369 0.00492 0.00615 0.00738 0.00861 0.00984 0.01107 0.0123

0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

CuO 0.0005 0.00058 0.00066 0.00074 0.00082 0.0009 0.00098 0.00106 0.00114 0.00122 0.0013

0 0 0 0 0 0 0 0 0 0 0

NbO 0 0 0 0 0 0 0 0 0 0 0

0.004 0.00759 0.01118 0.01477 0.01836 0.02195 0.02554 0.02913 0.03272 0.03631 0.0399

0.0055 0.03495 0.0644 0.09385 0.1233 0.15275 0.1822 0.21165 0.2411 0.27055 0.3

0.0076 0.00769 0.00778 0.00787 0.00796 0.00805 0.00814 0.00823 0.00832 0.00841 0.0085

0.0001 0.00009 0.00008 0.00007 0.00006 0.00005 0.00004 0.00003 0.00002 0.00001 0

ZnO 0 0.00037 0.00074 0.00111 0.00148 0.00185 0.00222 0.00259 0.00296 0.00333 0.0037

0 0.00031 0.00062 0.00093 0.00124 0.00155 0.00186 0.00217 0.00248 0.00279 0.0031

0 0 0 0 0 0 0 0 0 0 0

FeOOH 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

FeO 0 0 0 0 0 0 0 0 0 0 0

95.6051 95.63875 95.6724 95.70605 95.7397 95.77335 95.807 95.84065 95.8743 95.90795 95.9416

1.2885 1.25619 1.22388 1.19157 1.15926 1.12695 1.09464 1.06233 1.03002 0.99771 0.9654

DRI composition

10-0 9-1 8-2 7-3 6-4 5-5 4-6 3-7 2-8 1-9 0-10

Metallic Components


C 2 2 2 2 2 2 2 2 2 2 2

S 0.0025 0.0025 0.0025 0.0025 0.0026 0.0026 0.0026 0.0026 0.0027 0.0027 0.0027

Fe 87.8236 87.8266 87.8296 87.8325 87.8355 87.8385 87.8415 87.8445 87.8475 87.8505 87.8535

Ni 0.0053 0.0089 0.0124 0.016 0.0196 0.0231 0.0267 0.0302 0.0338 0.0374 0.0409

Cu 0.0005 0.0006 0.0007 0.0008 0.0009 0.001 0.001 0.0011 0.0012 0.0013 0.0014

Mo 0.0003 0.0002 0.0002 0.0002 0.0002 0.0001 0.0001 0.0001 0.0001 0 0

Oxidic Components

1.8127 1.7336 1.6545 1.5754 1.4962 1.4171 1.338 1.2589 1.1797 1.1006 1.0215

0.8723 0.8068 0.7414 0.676 0.6106 0.5451 0.4794 0.4143 0.3488 0.2834 0.2179

FeO 5.9466 5.9468 5.947 5.8472 5.9474 5.9476 5.9478 5.948 5.9482 5.9484 5.9486

MnO 0.0748 0.0779 0.0809 0.084 0.0871 0.0901 0.0932 0.0963 0.0993 0.1024 0.1055

CaO 0.9131 0.943 0.9728 1.0026 1.0325 1.0623 1.0921 1.122 1.1518 1.1817 1.2115

MgO 0.2862 0.3461 0.406 0.4659 0.528 0.5857 0.6456 0.7055 0.7654 0.8253 0.8852

0.1015 0.0992 0.0968 0.0945 0.0921 0.0898 0.0875 0.0851 0.0828 0.0805 0.0781

0.0409 0.0635 0.0862 0.1089 0.1315 0.1542 0.1769 0.1995 0.2222 0.2449 0.2676

0.0818 0.0981 0.1145 0.1308 0.1471 0.1935 0.1798 0.1962 0.2125 0.2289 0.2452

0.0251 0.023 0.0209 0.0188 0.0167 0.0145 0.0124 0.0103 0.0082 0.0061 0.004

0 0 0 0 0 0 0 0 0 0 0

0 0.0017 0.0034 0.005 0.0067 0.0084 0.0101 0.0118 0.0134 0.0151 0.0168

SiO2

Al2O3

P2O

5

V2O

5

TiO2

Cr2O

3

MoO2

MoO3

CaF2

CaCO3

MgCO3

WO3

Na2O

K2O

CaSO4

SnO2

CaCl2

Ca(OH)2

FeCO3

Fe2O

3

Fe3O

4

SiO2

Al2O

3

P2O

5

V2O

5

TiO2

Cr2O

3

MoO3

CaF2

Table 5. Composition of KPRS and its corresponding DRI when the carbon content or metallization is varied.

57

Varying the DRI MetallizationBased on KPRS Pellets

92.00% 95.00% 98.00%

wt% wt% wt%

0.7489 0.7489 0.7489

0.1598 0.1598 0.1598MnO 0.0773 0.0773 0.0773CaO 0.8848 0.8848 0.8848MgO 0.649 0.649 0.649

0.0573 0.0573 0.0573

0.1962 0.1962 0.1962

0.1798 0.1798 0.1798

0.0029 0.0029 0.0029

0 0 0

0 0 0NiO 0.0382 0.0382 0.0382

0.0123 0.0123 0.0123

0 0 0

0 0 0CuO 0.0013 0.0013 0.0013

0 0 0NbO 0 0 0

0.0399 0.0399 0.0399

0.3 0.3 0.3

0.0085 0.0085 0.0085

0 0 0ZnO 0.0037 0.0037 0.0037

0.0031 0.0031 0.0031

0 0 0FeOOH 0 0 0

0 0 0FeO 0 0 0

95.9416 95.9416 95.9416

0.9654 0.9654 0.9654

Moisture 1.6 1.6 1.6Fines 3.00% 3.00% 3.00%Dustloss 3.00% 3.00% 3.00%

DRI composition

Metallization92.00% 95.00% 98.00%

wt% wt% wt%Metallic ComponentsC 2 2 2S 0.0027 0.0027 0.0027Fe 84.3947 87.8535 91.3689Ni 0.0406 0.0409 0.0412Cu 0.0014 0.0014 0.0014Mo 0 0 0

Oxidic Components

1.0132 1.0215 1.0298

0.2162 0.2179 0.2197FeO 9.4412 5.9486 2.3989MnO 0.1046 0.1055 0.1063CaO 1.2018 1.2115 1.2214MgO 0.8781 0.8852 0.8925

0.0775 0.0781 0.0788

0.2654 0.2676 0.2697

0.2432 0.2452 0.2474

0.0004 0.0004 0.004

0 0 0

0.0167 0.0168 0.017

SiO2

Al2O

3

P2O

5

V2O5

TiO2

Cr2O3

MoO2

MoO3

CaF2

CaCO3

MgCO3

WO3

Na2O

K2O

CaSO4

SnO2

CaCl2Ca(OH)

2

FeCO3

Fe2O3

Fe3O

4

SiO2

Al2O

3

P2O

5

V2O

5

TiO2

Cr2O

3

MoO3

CaF2

Varying Carbon content in DRIBased on KPRS Pellets

1.00% 2.00% 3.00%

wt% wt% wt%

0.7489 0.7489 0.7489

0.1598 0.1598 0.1598MnO 0.0773 0.0773 0.0773CaO 0.8848 0.8848 0.8848MgO 0.649 0.649 0.649

0.0573 0.0573 0.0573

0.1962 0.1962 0.1962

0.1798 0.1798 0.1798

0.0029 0.0029 0.0029

0 0 0

0 0 0NiO 0.0382 0.0382 0.0382

0.0123 0.0123 0.0123

0 0 0

0 0 0CuO 0.0013 0.0013 0.0013

0 0 0NbO 0 0 0

0.0399 0.0399 0.0399

0.3 0.3 0.3

0.0085 0.0085 0.0085

0 0 0ZnO 0.0037 0.0037 0.0037

0.0031 0.0031 0.0031

0 0 0FeOOH 0 0 0

0 0 0FeO 0 0 0

95.9416 95.9416 95.9416

0.9654 0.9654 0.9654

Moisture 1.6 1.6 1.6Fines 3.00% 3.00% 3.00%Dustloss 3.00% 3.00% 3.00%

DRI composition

Carbon DRI1.00% 2.00% 3.00%


Oxidic Components

1.0319 1.0215 1.011

0.2202 0.2179 0.2157FeO 6.0093 5.9486 5.8879MnO 0.1066 0.1055 0.1044CaO 1.2239 1.2115 1.1992MgO 0.8943 0.8852 0.8762

0.0789 0.0781 0.0773

0.2703 0.2676 0.2648

0.2477 0.2452 0.2427

0.004 0.004 0.0039

0 0 0

0.017 0.0168 0.0166

SiO2

Al2O

3

P2O

5

V2O5

TiO2

Cr2O3

MoO2

MoO3

CaF2

CaCO3

MgCO3

WO3

Na2O

K2O

CaSO4

SnO2

CaCl2Ca(OH)

2

FeCO3

Fe2O3

Fe3O

4

SiO2

Al2O

3

P2O

5

V2O

5

TiO2

Cr2O

3

MoO3

CaF2

Table 6. Composition of KPRS and its corresponding DRI when the SiO2 content or Al2O3 is varied.

58

Based on KPRS Pellets

0.25% 0.50% 0.75%

wt% wt% wt%

0.748225 0.74635 0.744475

0.25 0.5 0.75MnO 0.0773 0.0771 0.0769CaO 0.883975 0.88175 0.879525MgO 0.64855 0.647 0.64545

0.05725 0.0571 0.05695

0.196 0.1955 0.195

0.17965 0.1792 0.17875

0.0029 0.0029 0.0029

0 0 0

0 0 0NiO 0.038125 0.03805 0.037975

0.012275 0.01225 0.012225

0 0 0

0 0 0CuO 0.001275 0.00125 0.001225

0 0 0NbO 0 0 0

0.0399 0.0398 0.0397

0.029925 0.02985 0.029775

0.008475 0.00845 0.008425

0 0 0ZnO 0.0037 0.0037 0.0037

0.0031 0.0031 0.0031

0 0 0FeOOH 0 0 0

0 0 0FeO 0 0 0

95.854875 95.61465 95.374425

0.964575 0.96215 0.9597250 0 0

Moisture 1.6 1.6 1.6Fines 0.03 0.03 0.03Dustloss 0.03 0.03 0.03

DRI composition

Al2O3 Content0.25% 0.50% 0.75%


Oxidic Components

1.0202 1.0166 1.0131

0.3408 0.681 1.0205FeO 5.94115 5.9204 5.8998MnO 0.5792 0.105 0.1046CaO 1.21 1.2058 1.20155MgO 0.8841 0.881 0.87795

0.07805 0.0778 0.07745

0.2672 0.2663 0.26535

0.2449 0.244 0.2432

0.004 0.0004 0.004

0 0 0

0.0168 0.0167 0.0167

Varying the Al2O3 Content

SiO2

Al2O3

P2O

5

V2O5

TiO2

Cr2O

3

MoO2

MoO3

CaF2

CaCO3

MgCO3

WO3

Na2O

K2O

CaSO4

SnO2

CaCl2

Ca(OH)2

FeCO3

Fe2O

3

Fe3O

4

SiO2

Al2O3

P2O5

V2O

5

TiO2

Cr2O

3

MoO3

CaF2


0.50% 1.00% 1.50%

wt% wt% wt%

0.5 1 1.5

0.1602 0.1594 0.1586MnO 0.077525 0.07715 0.076775CaO 0.88695 0.8825 0.87805MgO 0.65065 0.6474 0.64415

0.057425 0.05715 0.056875

0.196625 0.19565 0.194675

0.1802 0.1793 0.1784

0.0029 0.0029 0.0029

0 0 0

0 0 0NiO 0.03885 0.0392 0.03955

0.01235 0.0123 0.01225

0 0 0

0 0 0CuO 0.001275 0.00125 0.001225

0 0 0NbO 0 0 0

0.04 0.0398 0.0396

0.03005 0.0299 0.02975

0.00855 0.0085 0.00845

0 0 0ZnO 0.003775 0.00375 0.003725

0.003175 0.00315 0.003125

0 0 0FeOOH 0 0 0

0 0 0FeO 0 0 0

75.9322 82.1989 88.4656

0.967825 0.96295 0.9580750 0 0


DRI composition

SIO2 content0.50% 1.00% 1.50%


Oxidic Components

0.6826 1.3625 2.0398

0.2187 0.2172 0.2156FeO 5.9694 5.9277 5.8861MnO 0.1058 0.1051 0.1044CaO 1.2158 1.2073 1.1988MgO 0.8883 0.8821 0.8759

0.0784 0.0778 0.0773

0.2685 0.2666 0.2647

0.2461 0.2443 0.2426

0.0004 0.004 0.0039

0 0 0

0.0169 0.0168 0.0166

Varying the SIO2 content

SiO2

Al2O3

P2O

5

V2O

5

TiO2

Cr2O

3

MoO2

MoO3

CaF2

CaCO3

MgCO3

WO3

Na2O

K2O

CaSO4

SnO2

CaCl2

Ca(OH)2

FeCO3

Fe2O3

Fe3O

4

SiO2

Al2O

3

P2O

5

V2O5

TiO2

Cr2O

3

MoO3

CaF2

Table 7. Composition of KPRS and its corresponding DRI when the combined SiO2 + Al2O3 content is varied.

59


0.75% 1.50% 2.25%

wt% wt% wt%

0.5 1 1.5

0.25 0.5 0.75MnO 0.077425 0.07685 0.076275CaO 0.8862 0.8795 0.8728MgO 0.6500875 0.645175 0.6402625

0.0574375 0.056975 0.0565125

0.1965 0.195 0.1935

0.18005 0.1787 0.17735

0.0028875 0.002875 0.0028625

0 0 0

0 0 0NiO 0.038225 0.03795 0.037675

0.0123125 0.012225 0.0121375

0 0 0

0 0 0CuO 0.001275 0.00125 0.001225

0 0 0NbO 0 0 0

0.04 0.0397 0.0394

0.030075 0.02985 0.029625

0.008525 0.00845 0.008375

0 0 0ZnO 0.0037625 0.003725 0.0036875

0.0031625 0.003125 0.0030875

0 0 0FeOOH 0 0 0

0 0 0FeO 0 0 0

96.09525 95.3691 94.64295

0.86176625 0.7492325 0.636698750 0 0


DRI composition

SiO2 + Al2O3 Content0.75% 1.50% 2.25%


Oxidic Components

0.6824 1.3607 2.0351

0.3412 0.6804 1.0175FeO 5.9619 5.8993 5.8371MnO 0.1057 0.1046 0.1035CaO 1.2142 1.2015 1.1888MgO 0.8872 0.8779 0.8686

0.0783 0.0775 0.0767

0.2682 0.2653 0.2625

0.2458 0.2432 0.2406

0.004 0.004 0.0039

0 0 0

0.0169 0.0167 0.165

Varying the SiO2 + Al

2O

3 Content

SiO2

Al2O3

P2O

5

V2O

5

TiO2

Cr2O3

MoO2

MoO3

CaF2

CaCO3

MgCO3

WO3

Na2O

K2O

CaSO4

SnO2

CaCl2

Ca(OH)2

FeCO3

Fe2O

3

Fe3O

4

SiO2

Al2O3

P2O

5

V2O

5

TiO2

Cr2O3

MoO3

CaF2

Steel and Slag constraints

Table 8. A1 steel and slag analysis.

60

Steel and Slag analysis

A1 Slag Modelλ-MgO 1.2L-LP 0.5L-LV 0.5

Desired FeO 32.50%Desired CaO20 40.00%Refractory wear 2.0kg /ton nominal furnace capacity



A1 Steel Analysis

Element min target maxAl 0 0 1Si 0 0 0.1P 0 0 0.05Si 0 0 0.05Ti 0 0 0.1V 0 0 0.05Cr 0 0 0.3Mn 0 0 1Fe 0 99.85 100Co 0 0 0.3Ni 0 0 0.3Cu 0 0 0.3Nb 0 0 0.1Mo 0 0 0.3As 0 0 0.1W 0 0 0.1B 0 0 0.1Bi 0 0 0.15Pb 0 0 0.05Ca 0 0 0.01Ta 0 0 0.01Sn 0 0 0.05Zn 0 0 0.01O 0 0 0.01

Table 9. A2 Steel and slag analysis.

61

A2 Slag Modelλ-MgO 1.1L-LP 0.5L-LV 0.5

Desired FeO 30.00%Desired CaO20 35.00%Refractory wear 3 kg /ton nominal furnace capacity



A2 Steel Analysis

Element min target maxAl 0 0 1Si 0 0 0.1P 0 0 0.05Si 0 0 0.05Ti 0 0 0.1V 0 0 0.02Cr 0 0 0.03Mn 0 0 1Fe 0 100 100Co 0 0 0.3Ni 0 0 0.3Cu 0 0 0.3Nb 0 0 0.1Mo 0 0 0.3As 0 0 0.1W 0 0 0.1B 0 0 0.1Bi 0 0 0.1Pb 0 0 0.05Ca 0 0 0.01Ta 0 0 0.01Sn 0 0 0.05Zn 0 0 0.01O 0 0 0.01N 0 0 0.01

Carbon 0.1 0 5

Plant data

Table 10. ME DR-furnace.

Table 11. NA DR-furnace.

62

DR Furnace MEEnergy Type Consumption

Natural gas ME NG 10 GJ/Ton DRI typicalElectricity ME NG-based electricity 100 kWh/Ton DRIWater source Process water 10 Nm3/Ton DRISource of Oxygen ME Oxygen 10 Nm3/Ton DRI

DR Furnace Data typicalMetallization 95.00%Carbon content 2.00%

Briquetting cost 4 USD/ton

Average specific heat DRI 0.17 kWh/ton DRI CHot Discharge temperature 25 CHot Discharge temperature 0 kWh/ ton DRI

Capital Cost: 13.147 M USD/ yearAnnual Production: 814680 Tonnes

DR Furnace NAEnergy Type Consumption

Natural gas NA NG 10 GJ/Ton DRI typicalElectricity NA 100 kWh/Ton DRIWater source Process water 10 Nm3/Ton DRISource of Oxygen NA_Oxygen 10 Nm3/Ton DRI

DR Furnace Data typicalMetallization 95.00%Carbon content 2.00%

Briquetting cost 4 USD/ton

Average specific heat DRI 0.17 kWh/ton DRI CHot Discharge temperature 25 CHot Discharge temperature 0 kWh/ ton DRI

Capital Cost: 13.147 M USD/ yearAnnual Production: 814680 Tonnes

Table 12. ME EAF.

Table 13. NA EAF.

63

EAF ME Type ConsumptionEnergy Source of Energy1 ME NG-based electricity Calculated

Carbon source Coke fines CalculatedSource of oxygen ME Oxygen 2800 Nm3/ ChargeElectrode material Graphite electrode 2.65 kg/MWhWater source Process water 0 m3/min

EAF Furnace DataStandard tapping temperature 1600 CStandard tapping weight 80 tonnesAverage Idle time 3 minAverage power off time 3 minPower on Heat loss 5 MWIdle/power off heat loss 1 MWAverage power on 65 MWAverage idle 5 MWPost combustion 20 %Inner diameter 6.1 mNo of furnaces 1Slag carry over to ladle 0 kg/ton steel

Capital Cost 19.721 M USD/year

Additional Cost AdjustmentsSteel production 5 USD/ ton steelSlag Disposal 25 USD/ ton slagDust Disposal 50 USD/ ton dust

EAF NA Type ConsumptionEnergy Source of Energy1 NA Calculated

Carbon source Coke fines CalculatedSource of oxygen NA_Oxygen 2800 Nm3/ ChargeElectrode material Graphite electrode 2.65 kg/MWhWater source Process water 0 m3/min

EAF Furnace DataStandard tapping temperature 1600 CStandard tapping weight 80 tonnesAverage Idle time 3 minAverage power off time 3 minPower on Heat loss 5 MWIdle/power off heat loss 1 MWAverage power on 65 MWAverage idle 5 MWPost combustion 20 %Inner diameter 6.1 mNo of furnaces 1Slag carry over to ladle 0 kg/ton steel

Capital Cost 19.721 M USD/year

Additional Cost AdjustmentsSteel production 5 USD/ ton steelSlag Disposal 25 USD/ ton slagDust Disposal 50 USD/ ton dust

Table 14. Scrap analysis.

64

Scrap Analysis

Elements wt% Oxides wt%

C 0.4 0.5

Al 0 0

Si 0.3 FeO 2

P 0.1 MnO 0

S 0.05 CaO 0

Ti 0 MgO 0

V 0 0

Cr 0.1 0

Mn 0.64 0

Fe 95.84 CrO 0

Co 0 0

Ni 0.01 0

Cu 0.01 0

Nb 0 0

Mo 0 0

As 0 NiO 0

W 0 0

B 0 0

Bi 0 0

Pb 0

Ca 0

Ta 0

Sn 0.05

Zn 0

O 0

N 0

H 0

SiO2

Al2O3

P2O

5

V2O

5

TiO2

Cr2O

3

Fe2O

3

Fe3O

4

MoO2

MoO3

CaF2

CaCO3

MgCO3

Table 15. Slag former analysis.

65

Slag formersBurnt Lime

wt% wt%

2.5 1.7

0.5 0.3FeO 0.67 84

0.09 MgO 4.9

58.2 9.1

38.04

Dolomitic Limestone

SiO2

SiO2

Al2O

3Al

2O

3

CaOP

2O

5

CaCO3

CaCO3

MgCO3

model studies on the effects of composition differences of …815530/fulltext01.pdf · another...

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