Model studies on the effects of composition differences of direct reduction pellets and an adaptive addition of slag formers for the EAF process

Björn Keskitalo Master of Science Thesis Version 0.9429 2015-04-29

Supervisors Magnus Tottie, LKAB Niloofar 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 EAF based steel production. The study has focused on how the chemical composition of the raw materials influences the slag amount and as a result the EAF operation. It is also shown that the raw material selection can be optimized for a better slag practice. The advantage of slag former additions that are strictly 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 has been 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 basicity indices and MgO-saturation for EAF slags, ii) a comparison between different DR-pellets and mixes between them and their corresponding DRI, iii) a parameter study on how different properties for the DR-pellet and DRI influence the EAF process, and iv) a case study of two hypothetical steel plants to illustrate 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 acidic oxides 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 Page 30

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 to grow and is becoming of more importance for the iron and steel industry. Today, LKAB develops and produces 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 to improve 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 distributions for phosphorous and vanadium for slag compositions from direct reduced iron (DRI). This model has been 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 the advantages 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 used by them, in order to achieve an efficient pellet selection and EAF operation.

1 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 when there is a demand for low amounts of metallic impurities, such as copper and tin. It is also used when there is a shortage of suitable scrap. Direct reduction (DR) is a solid state type of reduction of iron ore to 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 of pellets, direct reduction pellets (DR-pellets). These are typically produced in vertical direct reduction shaft 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 the bottom of the furnace. This is done as the reduction gas at a high temperature flow upwards from the inlet of the reduction zone to the top of the DR-furnace. The reduction gas is injected at the middle of the furnace just above the cooling zone for the DRI at the bottom end of the DR-furnace. In the cooling zone, a carbon rich gas is injected to increase the carbon content of the DRI inside the furnace and also to cool down the DRI to a desired temperature. This means that it is possible to control both the carbon content of the DRI and the metallization, which is the ratio of metallic iron to the total mass 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 reduction gas is normally produced by a reformation of natural gas. The way that the natural gas is reformed is one 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 the reactions within a DR-furnace [1].

DRI is produced in the following three major categories: 1) Cold DRI is the most common DRI product and is charged into an EAF at ambient temperature, 2) hot DRI is designed to be used in a nearby EAF to utilize the latent-heat in hot fresh DRI, and 3) hot briquetted iron, which is a compressed DRI type with the purpose to reduce the surface area, and thereby the reactivity, of the DRI. Also, it is produced 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 to stick to each other, which will form clusters. This happens in the reduction zone in the DR-furnace where the temperature and metallization of the DRI is high. To avoid this type of behavior it is common to coat the DR-pellets with an oxide which has a high melting temperature, such as CaO or MgO[2,3].

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

3 compounds are kept intact. Therefore, the slag components can either be removed before the pellet is 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 melting scrap and DRI. Today, the typical tap-to-tap time is around 40-60 min. In 2011, EAFs produced over 25% 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 the charge. As these arcs radiate a lot of heat against the furnace walls and roof, the walls and roof often contain cooling elements to increase the durability. Foaming slag is also an important tool which is used 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 the EAF: 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) basculating device, 13) hydraulic group [8].

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

2.3 EAF Slag

4 The EAF slag is an ionic solution that floats on top of the steel. The viscosity of the slag may vary from watery 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 and inclusions.

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 different categories, acidic oxides and basic oxides. The most common acidic oxides in the EAF slag are Al2O3, 2- Cr2O3, P2O5, SiO2, TiO2, VO2* which are assumed to form anions by receiving O ions from the basic oxides. The basic oxides primarily consist of CaO, MgO and MnO, which on melting into the ionic slag are assumed to form free cations, i.e. Ca2+, Mg2+, Mn2+ by giving off O2- ions. The majority of the acidic oxides originate from the scrap, DRI, coal/coke ash or dirt and residual elements from transportation and storage. They are often unwanted and of negative effect for the steel production. The basic oxides, CaO and MgO, are often called slag formers and are added to the melt both to facilitate the formation slag and to neutralize the corrosive effect from the acidic oxides on the furnace refractories. For practical reasons, the iron oxide in a MgO-saturated EAF slag is often referred to as FeO, although in reality it consists of both Fe(II) and Fe(III) oxides. The latter however, constituting a minor part. Fe(II) is a basic oxide assumed to form Fe2+ cations, whereas Fe(III) oxides to some extent are acidic in this context. The FeO content can have a negative effect on the basic lining as the FeO lowers the viscosity of the slag and therefore, increases the wear of the basic lining if conditions for dissolution of MgO exist [8,9,10,11].

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

The slag is also important because it is one of the factors that affect the yield of the EAF process. If the amount of slag increases, it causes more iron units to go to slag. Therefore, the amount of steel formed per charge is reduced. An increased slag amount also leads to an increased energy requirement 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 and process 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 into consideration the composition of the DR-pellet. This is because most of the slag elements that exist in

5 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 design focused on the MgO-saturation of the slag compared to any basicity index. This would be possible because the concentrations of the components are more connected to the activities than the fraction between different components [11].

To calculate the slag composition it is required to have an analysis of the raw material. Also, there are three important variables that have to be set for the desired slag composition. The variables are

CaO20, FeO* and λ-MgO. CaO20 is a reference state for the concentration of CaO when the slag contains 20wt% FeO* and is calculated as follows [11]:

(%wt CaO )×80 CaO = actual 20 (100−(%wt FeO )) 7: actual

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 calculated as 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 in the slag [11].

(wt %MgO−accutal) λ− MgO= ( wt %MgO−saturation ) 8:

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 a λ-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 in dissolution 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-saturation varied with the concentrations of CaO and FeO* for the reference system CaO-FeO*-MgO sat-SiO2. The amount of MgO required to achieve a MgO-saturation decreases with increasing CaO and FeO content, 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

6 lining inside the furnace [11]. Also, by using the %CaO and %FeO* as main parameters the effect on the MgOsat is quite small if SiO2 from the reference system of CaO-FeO*-MgOsat-SiO2 is replaced by some 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 show

how 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 the steel industry [12]. RAWMATMIX® focuses on raw material optimization to find the minimum operation 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 the possibility to calculate the value-in-use of different raw materials for an EAF process [12]. The program works by defining specific target products. Both the desired steel and slag analysis are considered. For the steel, the target concentrations of elements are set. For the slag, the target concentration of CaO, FeO and λ-MgO are set to be used for calculating the required minimum amount of slag, which is based on Roger Selins MgO-saturation model [11,12]. Based on these settings, the minimum amount of required raw materials, basic slag forming additions, and costs for the steel production can be calculated [12].

7 3. Execution, Limitations and Input

Based on the literature study, which is summarized in Appendix 1 and 2, the following aspects are taken into account. Most of the work is based on calculations done in RAWMATMIX® and Roger Selin's MgO-saturation model [11,12]. The raw materials used are based on KPRS and two other competing DR-pellet grades, namely Competitor 1 (Com 1) and Competitor 2 (Com 2). The composition 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 additions varies. The proportion of dolomitic limestone to burnt limestone varies from 100%/0% (dolomitic limestone/burnt lime) to 10%/90%. The composition used for dolomitic limestone and limestone can be seen in Table 3.

Two types of charges are made and calculated using RAWMATMIX®. The charges simulate the production 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 steel types, 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 slag formers used for the KPRS case is set to 3.5 ton. For the Com 2 case, the addition of slag former is set to 5.5 ton.

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

(wt%CaO) B2= ( ) 9: wt %SiO2

(wt %CaO) B3= ( + ) 10: wt %Al2 O3 wt %SiO2

(wt %CaO+wt %MgO) B3= ( + ) 11: wt %Al2 O3 wt %SiO2

(wt %CaO+0.69∗wt %MgO) Bells Ratio= ( ∗ + ) 12: 0.93 wt %SiO2 018wt %Al2O3

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

13: Optical Basicity =X AOx∧AO AOx +X AOy∧ AOAOy +...

Where XAOx is calculated using equation 14 [9].

8 (NOAOx∗X Ao) 14: X AOx= (Σ(NOYOx∗X Yo))

NOAOx is the number of oxygen atoms in the oxide molecule. X AO 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 for the system.

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

Oxide Optical Basicity (Λ) Na2O 1.15 CaO 1.0 MgO 0.78 CaF2 0.67 TiO2 0.61 Al2O3 0.61 MnO 0.59 Cr2O3 0.55 FeO 0.51 Fe2O3 0.48 SiO2 0.48

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 of both the raw material input and the fraction of slag former. The basicity used is the B2, B3, B4 and Bells Ratio expressions, shown in equations 9-12. In this case, the charge is optimized for a DRI based on Com 2. It means that the amount of slag former addition is set to 5.5 ton. Then the raw material is changed, in this case to a DRI material based on KPRS. At the same time, the amount of slag former addition 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 melting 32 tons of DRI based on KPRS or Com 2 together with 54.5 tons of scrap. The composition of the scrap 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 an optimized amount of slag former addition for the material mix. This is done for both the A1 and A2 steel type. Different combinations of charged raw materials are taken into account which are: Com 2-

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

3.1.4 Parameter Study

This part is meant to give a more in depth analysis of how individual properties of a DR-pellet and corresponding DRI affect the EAF steel production. Thus, a parameter study was conducted. This was done for an A2 steel by melting 100% DRI based on KPRS. The chemical properties for the DRI was changed one at a time while the others was set to have the same values as the KPRS pellet and corresponding DRI. The properties which were studied were the carbon content, metallization, Al 2O3 content, SiO2 content and the combined (Al2O3 +SiO2) content. These properties can be changed either by the DR-pellet material, such as the Al2O3 and SiO2 content, or by the DR process, such as the carbon 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 case studies were performed. They were based on two fictitious steel plants, that produce 80 ton of A2 grade steel per charge. One is located in the Middle East and one in North America. These two plants differ primarily with respect to the production cost and the charge mixture. The plant located in the Middle East only charges DRI, while the North American charges scrap and DRI in two different combinations. More specifically, one high scrap charge which charges 50 tons of scrap and 36 tons of DRI as raw materials and a low scrap charge which charges 25 tons of scrap and 63 tons of DRI as raw materials.

To illustrate the value-in-use of KPRS for the EAF process, KPRS is mixed with a normal mixture of DRI from 0% to 50% of the total amount of DRI. The normal mixture consists of 50% Com 1 and 50% Com 2.

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

The Middle East plant has a slag former addition of 1250 kg lime and 2250 kg dolomitic limestone per charge. For the North American plant the high scrap setup has a fixed slag former addition of 1500 kg lime and 1750 kg dolomitic limestone, and the low scrap setup has a fixed slag former addition of 1250 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 slag composition. In addition, the slag and heat are considered to be homogeneous both with respect to composition 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 a specific value per time unit [12].

3.3 Input

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

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

DR-Pellet compostion DRI compostion KPRS Competitor 1 Competitor 2 KPRS Competitor 1 Competitor 2 wt% wt% wt% Metallic Components SiO 0.7489 1.2299 1.3294 2 wt% wt% wt% Al2O3 0.1598 0.4899 0.6397 C 2 2 2 MnO 0.0773 0.0684 0.0549 S 0.0027 0.056 0.0025 CaO 0.8848 0.6882 0.6666 Fe 87.8535 88.216 87.8236 MgO 0.649 0.087 0.2099 Ni 0.0409 0.0056 0.0053 P2O5 0.0573 0.0094 0.0744 Cu 0.0014 0.0041 0.0005 V2O5 0.1962 0.007 0.03 Mo 0 0.0003 0.0003 TiO2 0.1798 0.039 0.06 Oxidic Components Cr2O3 0.0029 0.0023 0.0184 SiO2 1.0215 1.6804 1.8127 MoO2 0 0 0 Al2O3 0.2179 0.6694 0.8723 MoO3 0 0.0003 0.0003 NiO 0.0382 0.0052 0.005 FeO 5.9486 5.9732 5.9466 MnO 0.1055 0.0935 0.0748 CaF2 0.0123 0 0 CaO 1.2115 1.0383 0.9131 CaCO3 0 0 0 MgO 0.8852 0.1189 0.2862 MgCO3 0 0 0 P O CuO 0.0013 0.0038 0.0005 2 5 0.0781 0.0128 0.1015 V2O5 0.2676 0.0095 0.0409 WO3 0 0 0 TiO NbO 0 0 0 2 0.2452 0.0533 0.0818 Cr O Na2O 0.0399 0.04 0.004 2 3 0.004 0.0032 0.0251 MoO K2O 0.3 0.008 0.0055 3 0 0 0 CaF CaSO4 0.0085 0.1741 0.0076 2 0.0168 0 0

SnO2 0 0.0001 0.0001 ZnO 0.0037 0.0025 0

CaCl2 0.0031 0 0

Ca(OH)2 0 0 0 FeOOH 0 0 0

FeCO3 0 0 0 FeO 0 0 0

Fe2O3 95.9416 96.5005 95.6051

Fe3O4 0.9654 0.6445 1.2885

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

SiO2.

12 Table 3. The composition for the two types of slag former. Dolomitic limestone and burnt lime. Slag formers Dolomitic Limestone Burnt Lime

wt% wt%

SiO2 2.5 SiO2 1.7

Al2O3 0.5 Al2O3 0.3 FeO 0.67 CaO 84

P2O5 0.09 MgO 4.9

CaCO3 58.2 CaCO3 9.1

MgCO3 38.04

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

13 Table 4: A1 steel and slag analysis.

Steel and Slag analysis

A1 Slag Model λ-MgO 1.2 L-LP 0.5 L-LV 0.5

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

MgO material Dolomitic limestone Lime material Lime

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

A1 Steel Analysis

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

Carbon 0.1 0.15 5

14 Table 5: A2 Steel and slag analysis.

A2 Slag Model λ-MgO 1.1 L-LP 0.5 L-LV 0.5

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

MgO material Dolomitic limestone Lime material Lime

Distribution from L-factors slag quantity 0.12 kg slag / kg steel Si inf Mn 100 P 30 S 1 Cr inf Ni 0 Mo 1 Nb Inf Ti inf Cu 0 Al inf V 500 W inf Fe 0.2 Co 1 As 1 B 1 Bi 1 Pb 1 Ca inf Ta 1 Sn 1 Zn 1

A2 Steel Analysis

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

Carbon 0.1 0 5

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.

15 Table 6. Scrap analysis

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

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

16 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 54.5 tons of scrap to produce 80 tons of steel of grade A2. The two figures below, 4 and 5, show how different mixtures of slag forming additions influence the basicity values for two different raw material inputs.

5 4.5 4 3.5

e 3 u B2 Com 2 l a V

2.5 B3 Com 2 y t i c i 2 B4 Com 2 s

a Bells ratio Com 2 B 1.5 Optic Bas Com 2 1 MgOsat Com 2 0.5 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Ratio Burnt Lime / (Burnt Lime + Dolomitic limestone)

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

5 4.5 4 3.5 e

u 3 B2 KPRS l a V

2.5 B3 KPRS y t i c i 2 B4 KPRS s

a Bells ratio KPRS B 1.5 Optic Bas KPRS 1 MgOsat KPRS 0.5 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Ratio Burnt Lime / (Burnt Lime + Dolomitic limestone)

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

17 Figure 4 and 5 shows how different mixtures of slag former additions affect the basicity and where MgO-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 higher fraction of lime/dolomitic limestone over the MgO-saturation fraction leads to a dissolution of MgO from the furnace lining. This results in an undesired wear on the furnace. In this case the usage of KPRS results in a wider interval of possible fractions between burnt lime and dolomitic limestone that maintains a MgO saturated slag.

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

Another important thing to notice is that there are no indications from the basicity values if and when 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 Com 2 to KPRS pellets while the amount of slag former addition is 5.5 ton, and the fraction between the slag formers, lime and dolomitic limestone varies. Figure 6 to 9 are based on 80 tons of A2 steel that is produced by melting 32 tons of DRI based on KPRS or Com 2 together with 54.5 tons of scrap.

6

5

4 e u l 3 a V B2 KPRS 2 B 2 B2 Com 2

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Ratio Burnt Lime / (Burnt Lime + Dolomitic limestone)

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

18 6

5

4 e u l 3 a V B3 KPRS 3 B 2 B3 Com 2

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Ratio Burnt Lime / (Burnt Lime + Dolomitic limestone)

Figure 7. Basicity values (B3) versus lime/dolomitic limestone ratio for Com 2 and KPRS.

6

5

4 e u l 3 a V

4 B4 KPRS B 2 B4 Com 2

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Ratio Burnt Lime / (Burnt Lime + Dolomitic limestone)

Figure 8. Basicity values (B4) versus lime/dolomitic limestone ratio for Com 2 and KPRS.

19 6

5

4 e u l

a 3 V

s l

l Bells ratio KPRS e

B 2 Bells ratio Com 2

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Ratio Burnt Lime / (Burnt Lime + Dolomitic limestone)

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 the production 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 raw material types with the basicity value increasing with more lime in the slag forming addition. There is also a difference between using a raw material based on KPRS-pellets and Com 2-pellets. Were the KPRS material leads to higher basicity values compared to Com 2 material with the same slag former mix. Furthermore, as in figure 4 and 5, there is no indication in the basicity values in figure 6 to 9 when 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 to see 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. This was done for both A1 and A2 steel types. However, a high amount of DRI based on competitor 1 could 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 at around 60-70% KPRS. This change of slope originates from the slag getting over saturated with the regards to MgO. Therefore, the effects that occur after the slope change depends primarily on the lesser amounts of acidic oxides in KPRS compared to Com 1 and Com 2.

20 Slag amounts (kg slag / ton liquid steel)

160 140 ) l e

e 120 t s

n

o 100 t

/

g

k 80 (

A1 Com 2-KPRS t n

u 60 A1 Com 1-KPRS o

m A1 Com 2-Com 1 a

40 g a l

S 20 0 10;0 9;1 8;2 7;3 6;4 5;5 4;6 3;7 2;8 1;9 0;10 Weight fraction of DR-pellets

140

120 ) l e e t 100 s

n o t

/ 80

g k (

A2 Com 2- KPRS t 60 n

u A2 Com 1-KPRS o

m 40 A2 Com 2-Com 1 a

g a l 20 S

0 10;0 9;1 8;2 7;3 6;4 5;5 4;6 3;7 2;8 1;9 0;10 Weight fraction of DR-pellets

Figure 10 and 11. Slag amounts generated per ton liquid steel versus the DR-pellet mixes between competitor 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 steel grades A1 and A2 when the raw material mixture varies. It can be seen that the slag amount decreases for all of the mixtures. This is due to the fact that Com 1 contains a lower amount of acidic oxides 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 slag becomes over saturated with MgO. Before the slope change, the decrease in slag amount is thanks to both smaller dolomitic limestone additions and to smaller amounts of acidic oxides in the DR-pellet.

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

Electric consumption (kWh / ton liquid steel)

800 ) l e e t 700 s

n o

t 600

/

h 500 W k (

n 400 o

i A1 Com 2-KPRS t p 300

m A1 Com 1-KPRS u

s A1 Com 2-Com 1 n 200 o c

c i 100 r t c e l 0 E 10;0 9;1 8;2 7;3 6;4 5;5 4;6 3;7 2;8 1;9 0;10 700 Weight fraction of DR-pellets ) l e e t 600 s

n o t

/ 500

h W k

( 400

n o

i A2 Com 2- KPRS t 300 p

m A2 Com 1-KPRS u

s 200 A2 Com 2-Com 1 n o c

c

i 100 r t c e l 0 E 10;0 9;1 8;2 7;3 6;4 5;5 4;6 3;7 2;8 1;9 0;10 Weight fraction of DR-pellets

Figure 12 and 13. Required electric energy amount for the EAF versus the DR-pellet mixes between Com 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 A1 and A2, when the raw material mixture varies. The electricity consumption has the same behavior as the slag amount. This is due to two reasons that are connected to the slag amounts. First, larger slag amounts require more energy per ton steel. Second, larger slag amounts require the use of more raw materials, especially iron, per ton steel in order to form the slag. Thus, if an increased amount of iron goes to the slag, this will result in increased iron loss, which has to be compensated for by addition of more 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 lowest electricity requirement. In this case it is the 100% KPRS mixture, as the KPRS pellets contains the lowest amount of acidic oxides.

Tap-to-tap time (hours)

22 1 0.9 0.8 ) s r 0.7 u o h

( 0.6

e

m 0.5 i t

A1 Com 2-KPRS p 0.4 a

t A1 Com 1-KPRS - o t 0.3 - A1 Com 2-Com 1 p

a 0.2 T 0.1 0 10;0 9;1 8;2 7;3 6;4 5;5 4;6 3;7 2;8 1;9 0;10 Weight fraction of DR-pellets

1 0.9 0.8 ) s r 0.7 u o h

( 0.6

e

m 0.5 i t

A2 Com 2- KPRS p 0.4 a

t A2 Com 1-KPRS - o t 0.3 - A2 Com 2-Com 1 p

a 0.2 T 0.1 0 10;0 9;1 8;2 7;3 6;4 5;5 4;6 3;7 2;8 1;9 0;10 Weight fraction of DR-pellets

Figure 14 and 15. Tap-to-tap time versus the DR-pellet mixes consisting of Com 2-KPRS, Com 1-KPRS and 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 the raw material mixture varies. The tap-to-tap time is observed to have the same behavior as the electricity consumption. This is because tap-to-tap times is calculated based on the electricity consumption in RAWMATMIX®. This results in that the raw material mixture that requires the smallest energy consumption is also the raw material mixture that generates the shortest tap-to-tap time. And in this case it was the 100% KPRS mixture that generated the shortest tap-to-tap times for both the A1 and A2 steel grades.

4.4 Parameter study

23 A parameter study is done based on smelting 100% KPRS DRI while individual properties for the KPRS and its corresponding DRI is varied. This is done to study what effect the individual properties have on the 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. 180 160 l e

e 140 t s

n 120 o t /

g 100 k

t

n 80 u

o 60 m a 40 g a l 20 S 0 Carbon content Metallization SiO2 content Al2O3 content Al2O3+SiO2 [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%]

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

In figure 16, which shows how the slag amount per ton steel varies when the individual parameters are changed, it can be observed that the carbon content and metallization degree hardly affect the amount of slag at all. This is expected due to the fact that neither the carbon content nor the FeO content, 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 of acidic 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 l

e 700 e t s 600 n o t

/ 500 h W k 400 n o i t

p 300 m u

s 200 n o c

100 c i r t

c 0 e l

E Carbon content Metallization SiO2 content Al2O3 content Al2O3+SiO2 [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%]

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

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

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

Yield required amount of DRI per ton liquid steel

) 1.16 l e

e 1.15 t s

f 1.14 o

n 1.13 o t

/

1.12 I

R 1.11 D

f

o 1.1

s

n 1.09 o t ( 1.08 d l e

i 1.07 Y Carbon content Metallization SiO2 content Al2O3 content Al2O3+SiO2 [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%]

Figure 18. Graph of how individual parameters for a DR-pellet and DRI affect the amount of DRI required 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, varies when individual properties for the KPRS pellet and corresponding DRI is varied. For the carbon content of the DRI it can be seen that for each amount of carbon added to the DRI, an equal amount of iron has to be added to compensate the “non-iron” in the DRI. Therefore, the DRI consumption

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

The Cost per ton liquid steel.

365 360 l

e 355 e t s

n 350 o t

/

d 345 s u

t 340 s o

C 335 330 Carbon content Metallization SiO2 content Al2O3 content Al2O3+SiO2 [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%]

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

Figure 19 shows how the production cost varies when individual properties for the KPRS pellet are changed. The cost for steel production includes the EAF process costs, raw material costs and cost for production of DRI from DR pellets. Thus, the cost contains the total effect from the previous parameters and their effect on the final product. In this case that leads to an decreasing cost with increasing carbon content and metallization degree, although it requires a more expensive treatment in the DR shaft. Furthermore, the acidic oxides especially the combined Al2O3+SiO2 content are of importance for the EAF production, as increasing amounts leads to a higher production cost due to the process would generate more slag, higher energy consumption and larger consumption of raw materials per ton steel. And in this case, an increase in the content of Al 2O3 + SiO2 within the DR pellet from 1.5wt% to 2.25wt% resulted in an increased production cost of 3%. An increase of just the SiO 2 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 charging 100% DRI and the other plant is assumed to charge varying amount of scrap. The base composition of DRI consists of 50% Com 1 and 50% Com 2. This is done to study the value-in-use of adding KPRS to the base mixture, between 0-50%, together with the value of adaptive addition of slag formers compared to a fixed amount and composition of the slag forming addition.

26 Middle East

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

29400

29200 e

g 29000 r a h C

/

28800 D

S Fixed ME U

t 28600 Adaptive ME s o C 28400

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

Figure 20. Production cost for an A2 steel grade as a function of the amount of KPRS in DRI mixture with 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 material mixture. This is done for two settings one with adaptive addition of slag formers and one with a fixed amount and mixture of the slag forming addition. Besides the reduced production cost of using KPRS pellets in the raw material mixture adaptive addition of slag formers would also reduce the tap-to-tap times to 0.79-0.76 hours, when the amount of KPRS goes from 0% to 50%. This should be compared to 0.8 h if a fixed slag former addition is used.

27 North-America

Two different setups are used for charging the raw materials, one with a large scrap amount and one with 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 1500kg burnt limestone and 1750 kg dolomitic limestone. Moreover, as stated before, adaptive addition of slag formers mean that the slag former addition composition and amount based on the composition on the raw material input.

35100 35000 34900 e g

r 34800 a h C

34700 /

D

S 34600 Fixed NA 50 U

t Adaptive NA 50 s 34500 o C 34400 34300 0% 10% 20% 30% 40% 50%

Percent KPRS

Figure 21. Production cost for an A2 steel grade as a function of the amount of KPRS in DRI mixture with adaptive addition of slag formers and fixed slag former addition.

Figure 21 show how the production cost varies with increasing amount of KPRS in the raw material mixture. This is done for two settings one with adaptive addition of slag formers and one with a fixed amount and mixture of the slag forming addition. Besides the reduced production cost of using KPRS pellets in the raw material mixture adaptive addition of slag formers would also reduce the tap-to-tap times to 0.69-0.67 hours, when the amount of KPRS goes from 0% to 50%. This should be compared to 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 addition composition and amount based on the composition on the raw material input.

28 37300 37200 37100 e

g 37000 r a

h 36900 C

/

36800 D

S 36700 Fixed NA 25 U

t Adaptive NA 25 s 36600 o

C 36500 36400 36300 0% 10% 20% 30% 40% 50% Percent KPRS

Figure 22. Production cost for an A2 steel grade as a function of the amount of KPRS in DRI mixture with adaptive addition of slag formers and fixed slag former addition.

Figure 22 show how the production cost varies with increasing amount of KPRS in the raw material mixture. This is done for two settings one with adaptive addition of slag formers and one with a fixed amount and mixture of the slag forming addition. Besides the reduced production cost of using KPRS pellets in the raw material mixture adaptive addition of slag formers would also reduce the tap-to-tap times to 0.74-0.72 hours, when the amount of KPRS goes from 0% to 50%. This should be compared to 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 with increasing amount of KPRS in the DRI mixture. This is due to the smaller amount of acidic oxides and larger amount of basic oxides in the KPRS. The production cost will also decrease with adaptive addition of slag formers. Due to that the composition of the raw material is considered to minimize the superfluous amount of slag and slag former, which also decreases the tap-to-tap times for the process.

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

29 5 Conclusions

As the primary focus of this project has been on how the composition of DR-pellets affect the EAF process 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 to each other. Also the use of basicity values for process optimization focused on low refractory wear can be misleading as they are not focused on the refractory compatibility. This is seen in the results shown 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 of acidic oxides in the raw material. This is because the acidic oxides influence a lot of parameters in the EAF process. Besides an increasing amount of acidic oxides results in negative effects such as increasing 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 melt through the slag layer.

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

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

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

In this study, it has been shown that an increase in the content of Al 2O3 + SiO2 in the DR pellet from

1.5wt% 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 later the amount of acidic oxides in the charge. Larger amounts of acidic oxides result in a demand for larger 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. Larger amounts of MgO in the DRI result in that the MgO-saturation can be obtained at a higher ratio of limestone/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 raw materials into account, it should be possible to make large reductions in production costs compared to 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 slag composition. However, they both effect the energy requirement for the EAF and through that the process time. In this case, higher carbon content and metallization degree results in shorter process time for the EAF. However, as both higher carbon content and metallization degree requires longer process time in the DR-furnace. So the carbon content and metallization degree should be balanced with 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 excellent traits for a DRI raw material. Therefore, these properties should be valued highly if steel plants would use KPRS together with adaptive addition of slag formers. As it can be seen from this study, usage of adaptive addition of slag formers additions together with a large quantity of KPRS in the charge mixture 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 is a shortage of scrap or when there is a demand of low amounts of metallic impurities, such as copper and 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 Hot Direct Reduced Iron (HDRI) production at 6.2 Mt and the Hot Briquetted Iron (HBI) production at 6.2 Mt [4].

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

The primary chemical compounds involved during DR of iron ore are iron and iron oxides, carbon and carbon oxides, oxygen, hydrogen and water. The remaining chemical components are more or less inert during the process. This means that any trace elements and impurities, such as gangue from the mineral, remain inside the pellet throughout the DR process. Therefore, they end up in the DRI, which then 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 DR pellets 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 a high reaction rate [6]. Then, the reduction of magnetite to wüstite takes place which also has a rather high 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 described as (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 of metallization. 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 because besides the pure iron and iron carbide, there is often some amounts of unreduced iron oxide residues and the degree of metallization describes that. Today, DRI is normally produced with a metallization degree of 90-97%. The DRI is rarely produced with a 100% metallization since it severely increases gas consumption and deceases production compared to a DRI which contains a small percentage remaining iron oxides.

Another important aspect is the carbon content in DRI production. The DRI is sent for smelting and it is rarely reduced completely, and it contains a few percent of iron oxide. To reduce the amount of required energy during the final reduction at melting stage, it has become common practice to carburize 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. All the gangue that comes with the iron ore stays within the DR pellet. Later it ends up in the melting process, where most of it ends up in the slag. Thus, the slag in the melting stage is affected by the gangue content from the DRI. Depending on the melting process and the amount of the DRI, the importance of the gangue can vary [1,2,3,5,7,8].

Reactions

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

The gas reformation reactions and gas balance reactions show that if a high reducing gas potential is required, the reducing gas must be balanced between H2 and CO according to the water-gas shift reaction 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 over 80% of the total DRI produced. Since the DRI is produced through a solid state process, it keeps its shape and volume. Due to its typical “sponge like” structure with a very high inner surface area and high 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 can react 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 cooled compared to CDRI and HDRI has a temperature of 600-700 C. Normally, it is charged into EAF at temperatures around 400-600 C. The advantage of using HDRI compared to CDRI in an EAF is that it requires 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. Due to its much smaller surface area it is less reactive with the atmosphere. HBI is produced by pressing fresh 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 DRI production. Natural gas (CH4) in itself cannot be used for a reduction of iron ore to metallic iron. It is required to be reformed to a reducing gas, which mostly consists of H2 and CO. Today, the reforming of natural gas for DR is primarily done by catalytic steam reforming, partial oxidation and reduction reactor 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 furnace as it can be seen in Figure 1. The reformer is equipped with a catalyst of nickel. Natural gas is injected together 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 can be used within a DR furnace. This is done by both recirculation of off gases and adding more external heat. Also it is important to use a natural gas with a low content of sulfur to avoid sulfur poisoning of the 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 with a steam reformer [5].

38 Partial oxidation of natural gas to reducing gas can replace part of the external reformer. A partial oxidation of natural gas can be achieved by injecting small amounts oxygen together with the natural gas so that no total combustion of the natural gas occurs, the flow scheme and were the oxygen is injected can be seen in Figure 2. Then reforming of natural gas can take place according to equation 16 [3,5,8,9].

Moreover, an in situ reforming of the natural gas within the DR furnace is possible by using a partial oxidation, to totally replace the reformer. In situ reforming within the DR furnace is done by using the hot direct reduced iron as a catalyst within the furnace. The lack of a nickel catalyst for the reforming makes the process less sensitive to sulfur, which makes it possible to use natural gas with a higher sulfur 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 the carburization process of the DRI at the cooling stage of the process. It is based on the endothermic reaction 9. Since the reaction is endothermic, it can contribute to cooling of the DRI at the end of the process [3,5,8,9].

Figure 2. Partial oxidation/in situ. Flowchart of natural and reducing gases for natural gas based DR with 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 from the reduction process it is possible to reform natural gas to reducing gas. The reforming of natural gas takes place in a nickel based catalyst outside the furnace, similar to the steam reformer, but this process utilizes carbon dioxide instead of steam. The reaction between CO2 and natural gas forms reducing 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 comes form combustion of natural gas and part of the off gases. As the gas is recirculated, which can be seen in Figure 3, it is important to use a natural gas with low amounts of sulfur to avoid poisoning of the catalyst [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 on shaft furnaces, namely MIDREX and Energiron (previously known as HYL III). Both types of furnaces uses a counter current flow, which means that iron ore is charged from the top and flows down while being reduced by the reducing gas. The latter is injected at the bottom of the reduction zone in the shaft and flows upwards. The reducing gas consists of H2 and CO. Reduction reactions which takes place 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 system with 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 gas reformer reforms natural gas and off gas to a reducing gas that is used within the reduction shaft. The cooling gas system is used in the cooling zone at the below the reduction zone in the shaft to both cool 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 from the reduction shaft. The natural gas and off gas, primarily CO2, are preheated before it is injected into a heated reformer. The reformer has to be heated due to the endothermic reaction of reforming natural gas and off gas to reducing gas. After the reforming the reducing gas has a temperature over 900 C. Then it is injected into the bottom region of the reduction zone in the reduction shaft. The reducing 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 of the furnace. The reduction of iron ore occur in a stepwise manner, while the ore flows downwards in the furnace, according to reaction (1) and (2) during which magnetite is formed from hematite, and then 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 the reduction zone, the DRI should be reduced to a desired grade, which normally corresponds to a degree of 94-96% metallization. After the reduction stage ends, the cooling stage starts if cold DRI is produced. The cooling stage is designed to cool, carburize and also produce an amount of reducing gas. This is done by injecting a cooling gas similar to the reducing gas, but with a quite high rate of natural gas. The carburization occurs according to reactions (7), (8) and (9). If no cooling, the DRI could 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 produce the reducing gas from natural gas. The Energiron process relies on in situ transformation of the natural gas to a reducing gas inside the reduction shaft. The reforming of natural gas is done by using fresh 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). In the reduction zone, the primary reactions for gas reforming are reactions (14) and (15). In the cooling zone 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 of sulfur compared to the MIDREX process. This is due to the fact that there is no risk for catalyst poisoning, 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 differs between the Energiron and MIDREX processes is the pressure within the furnace. In the MIDREX furnace, the reducing gases are only injected into the furnace to reduce and carburize the iron. This gives a possibility to operate the process at ambient pressure combined with a high gas speed to ensure an even distribution of reducing gas. In contrast to the MIDREX the Energiron process is working at a high pressure, 6-8 bar and lower gas speed to insure that the reforming of natural gas to reducing 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 a tendency to stick to each other. Thereby, they form clusters, which is not desirable because it disrupts both the gas and mass flow and decreases the productivity of the furnace. This is primarily due to the fact that the clusters decrease the permeability of the reducing gasses and this leads to an uneven distribution 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 cluster formation are kept to minimum within the furnace. There is also the possibility to decrease the sticking behavior by coating the pellets with mineral oxides that are stable at the prevailing reduction temperatures. This is a suitable way to reduce the sticking behavior because the DR process is a solid state reduction where the active components are the iron ore and reducing gases. Examples of oxides that 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 for carbon steel are CaO, MgO, FeO and SiO2. It is also common practice to use a foaming slag which is designed to expands in volume by the formation and capture of gas bubbles within the slag to reduce the 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.

Oxide Melting point (C°)

SiO2 1720 CaO 2600 MgO 2800

Al2O3 2030 FeO 1370 MnO 1850

Cr2O3 2260

Slag composition

The major components for slag can often be divided into two different categories, acidic oxides and basic oxides. Some of the common acidic oxides are Al2O3, Cr2O3, FeO, MnO and SiO2. The basic oxides primarily consists of CaO and MgO. The majority of the acidic oxides originates from the scrap, DRI or dirt and residual elements from transportation and storage. The basic oxides are often called slag formers and are added to the melt to both form slag and balance the corrosive effect from the acidic oxides 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 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 the wear 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 the slag penetration into the refractory will be minimized. From the metallurgical point of view, a low viscosity is of interest because it will give favorable kinetics and faster reaction rates for the reactions taking place in the slag and slag-steel-interface compared to slag with high viscosity. Therefore, it is important to balance the viscosity in such a way that the wear of the refractory is kept to a minimum value 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 to highest 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 poor foaming 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 it represents a balance between the metallurgical properties and a low wear on furnace refractories and 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 higher viscosity and less foaming properties. This results in lower amounts of wear compared to a creamy slag but also a less effective cleaning effect. In a fluffy slag there are higher amounts of basic oxides compared 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 crusty slag is rarely desirable because it has poor foaming properties and also poor metallurgical properties to 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 be linked 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 furnace refractory are through basicity models. These models are often the ratio of basic oxides over the acidic oxides in the slag. The basicity is used as a single compositional parameter for slags which could 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 are assigned certain values such as the B2 or V ratio, or Bells ratio or even optical basicity.

The B2 or V ratio is given by

(wt%CaO) B2= (wt %SiO2)

Bells ratio is given by

47 (wt %CaO+0.69∗wt %MgO) Bells Ratio= ( ∗ + ) 0.93 wt %SiO2 018wt %Al2O3 [5].

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

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

Oxide Optical Basicity (Λ)

Na2O 1.15 CaO 1.0 MgO 0.78

CaF2 0.67

TiO2 0.61

Al2O3 0.61 MnO 0.59

Cr2O3 0.55 FeO 0.51

Fe2O3 0.48

SiO2 0.48

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

Optical Basicity =X AOx∧AO AOx +X AOy∧ AOAOy +...

Where XAOx is calculated by using the equation.

(NOAOx∗X Ao) X AOx= (Σ(NOYOx∗X Yo))

Where 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 for the system.

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

2N ( SiO2 ) X SiO = 2 2N +N +N +N ( SiO 2 CaO FeO MgO)

48 Where 2NSiO2 results from the two oxygen atoms in the molecule and the mole fraction of the compound. 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 construed based on MgO saturation (MgOsat) of the slag. This comes from the idea that the slag closest to the refractory should be saturated with MgO, either by addition of slag former or by dissolving MgO from the furnace wall. So according to Roger Selin an EAF slag should be designed according to the complex slag composition of the weight percent of CaO-FeO-MgOsat-SiO2. This mean that the MgOsat can be found by the CaO and FeO content. In this slag definition Roger Selin has also investigated and linked 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].

Foaming Slag 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 three things. The surface tension which is the controlling factor for the energy requirement for the creation of 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 longer residence time compared to a slag with lower viscosity. Suspended second phase particles within the slag. 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 the surface tension and the viscosity [1,3,6,7].

That second phase particles has a greater impact on the foaming properties derives from that the second phase particles act as a nucleation site for gas bubble generation. This gives better foaming properties. However, this is true to a certain point where the fraction of solid/liquid in the slag increases 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 reduction of 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 carbon injection 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 slag temperature. This, in turn results in a lower viscosity of the slag. This is due to the two exothermic reactions, (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 amount of 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 Direct Reduction 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 Issue 4

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.

DR Pellets Types

KPRS Com 1 Com 2

wt% wt% wt%

SiO2 0.7489 1.2299 1.3294

Al2O3 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

P2O5 0.0573 0.0094 0.0744

V2O5 0.1962 0.007 0.03

TiO2 0.1798 0.039 0.06

Cr2O3 0.0029 0.0023 0.0184

MoO2 0 0 0

MoO3 0 0.0003 0.0003 NiO 0.0382 0.0052 0.005

CaF2 0.0123 0 0

CaCO3 0 0 0

MgCO3 0 0 0 CuO 0.0013 0.0038 0.0005

WO3 0 0 0 NbO 0 0 0

Na2O 0.0399 0.04 0.004

K2O 0.3 0.008 0.0055

CaSO4 0.0085 0.1741 0.0076

SnO2 0 0.0001 0.0001 ZnO 0.0037 0.0025 0

CaCl2 0.0031 0 0

Ca(OH)2 0 0 0 FeOOH 0 0 0

FeCO3 0 0 0 FeO 0 0 0

Fe2O3 95.9416 96.5005 95.6051

Fe3O4 0.9654 0.6445 1.2885

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

53 DR-pellets mixes and corresponding DRI

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

DR Pellets Mix Fraction Com 2-Com 1 10-0 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%

SiO2 1.3294 1.31945 1.3095 1.29955 1.2896 1.27965 1.2697 1.25975 1.2498 1.23985 1.2299

Al2O3 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

P2O5 0.0744 0.0679 0.0614 0.0549 0.0484 0.0419 0.0354 0.0289 0.0224 0.0159 0.0094

V2O5 0.03 0.0277 0.0254 0.0231 0.0208 0.0185 0.0162 0.0139 0.0116 0.0093 0.007

TiO2 0.06 0.0579 0.0558 0.0537 0.0516 0.0495 0.0474 0.0453 0.0432 0.0411 0.039

Cr2O3 0.0184 0.01679 0.01518 0.01357 0.01196 0.01035 0.00874 0.00713 0.00552 0.00391 0.0023

MoO2 0 0 0 0 0 0 0 0 0 0 0

MoO3 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

CaF2 0 0 0 0 0 0 0 0 0 0 0

CaCO3 0 0 0 0 0 0 0 0 0 0 0

MgCO3 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

WO3 0 0 0 0 0 0 0 0 0 0 0 NbO 0 0 0 0 0 0 0 0 0 0 0

Na2O 0.004 0.0076 0.0112 0.0148 0.0184 0.022 0.0256 0.0292 0.0328 0.0364 0.04

K2O 0.0055 0.00575 0.006 0.00625 0.0065 0.00675 0.007 0.00725 0.0075 0.00775 0.008

CaSO4 0.0076 0.02425 0.0409 0.05755 0.0742 0.09085 0.1075 0.12415 0.1408 0.15745 0.1741

SnO2 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

CaCl2 0 0 0 0 0 0 0 0 0 0 0

Ca(OH)2 0 0 0 0 0 0 0 0 0 0 0 FeOOH 0 0 0 0 0 0 0 0 0 0 0

FeCO3 0 0 0 0 0 0 0 0 0 0 0 FeO 0 0 0 0 0 0 0 0 0 0 0

Fe2O3 95.6051 95.69464 95.78418 95.87372 95.96326 96.0528 96.14234 96.23188 96.32142 96.41096 96.5005

Fe3O4 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 wt% wt% wt% wt% wt% wt% wt% wt% wt% wt% wt% 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

SiO2 1.8127 1.7995 1.7863 1.773 1.7598 1.7466 1.7334 1.7201 1.7069 1.6963 1.9804

Al2O3 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

P2O5 0.1015 0.0926 0.0838 0.0749 0.0661 0.0572 0.0483 0.0395 0.0306 0.0217 0.0128

V2O5 0.0409 0.0377 0.0346 0.0315 0.0283 0.0252 0.0221 0.0189 0.0158 0.0127 0.0095

TiO2 0.0818 0.0789 0.0761 0.0732 0.0704 0.0675 0.0647 0.0618 0.059 0.0561 0.0533

Cr2O3 0.0251 0.0229 0.0207 0.0185 0.0163 0.0142 0.012 0.0098 0.0076 0.0054 0.0032

MoO3 0 0 0 0 0 0 0 0 0 0 0

CaF2 0 0 0 0 0 0 0 0 0 0 0

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

DR Pellets Mix Fraction Com 1-KPRS 10-0 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%

SiO2 1.2299 1.1818 1.1337 1.0856 1.0375 0.9894 0.9413 0.8932 0.8451 0.797 0.7489

Al2O3 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

P2O5 0.0094 0.01419 0.01898 0.02377 0.02856 0.03335 0.03814 0.04293 0.04772 0.05251 0.0573

V2O5 0.007 0.02592 0.04484 0.06376 0.08268 0.1016 0.12052 0.13944 0.15836 0.17728 0.1962

TiO2 0.039 0.05308 0.06716 0.08124 0.09532 0.1094 0.12348 0.13756 0.15164 0.16572 0.1798

Cr2O3 0.0023 0.00236 0.00242 0.00248 0.00254 0.0026 0.00266 0.00272 0.00278 0.00284 0.0029

MoO2 0 0 0 0 0 0 0 0 0 0 0

MoO3 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

CaF2 0 0.00123 0.00246 0.00369 0.00492 0.00615 0.00738 0.00861 0.00984 0.01107 0.0123

CaCO3 0 0 0 0 0 0 0 0 0 0 0

MgCO3 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

WO3 0 0 0 0 0 0 0 0 0 0 0 NbO 0 0 0 0 0 0 0 0 0 0 0

Na2O 0.04 0.03999 0.03998 0.03997 0.03996 0.03995 0.03994 0.03993 0.03992 0.03991 0.0399

K2O 0.008 0.0372 0.0664 0.0956 0.1248 0.154 0.1832 0.2124 0.2416 0.2708 0.3

CaSO4 0.1741 0.15754 0.14098 0.12442 0.10786 0.0913 0.07474 0.05818 0.04162 0.02506 0.0085

SnO2 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

CaCl2 0 0.00031 0.00062 0.00093 0.00124 0.00155 0.00186 0.00217 0.00248 0.00279 0.0031

Ca(OH)2 0 0 0 0 0 0 0 0 0 0 0 FeOOH 0 0 0 0 0 0 0 0 0 0 0

FeCO3 0 0 0 0 0 0 0 0 0 0 0 FeO 0 0 0 0 0 0 0 0 0 0 0

Fe2O3 96.5005 96.44461 96.38872 96.33283 96.27694 96.22105 96.16516 96.10927 96.05338 95.99749 95.9416

Fe3O4 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 wt% wt% wt% wt% wt% wt% wt% wt% wt% wt% wt% 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

SiO2 1.6804 1.6144 1.5484 1.4825 1.4165 1.3506 1.2848 1.2189 1.1531 1.0872 1.0215

Al2O3 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

P2O5 0.0128 0.0194 0.0259 0.0324 0.039 0.0455 0.052 0.0586 0.0651 0.0716 0.0781

V2O5 0.0095 0.0354 0.0612 0.087 0.1128 0.1386 0.1644 0.1902 0.216 0.2418 0.2676

TiO2 0.0533 0.0725 0.0917 0.1109 0.1301 0.1493 0.1685 0.1877 0.2065 0.226 0.2452

Cr2O3 0.0032 0.0033 0.0034 0.0034 0.0035 0.0036 0.0037 0.0037 0.0038 0.0039 0.004

MoO3 0 0 0 0 0 0 0 0 0 0 0

CaF2 0 0.0017 0.0034 0.0051 0.0067 0.0084 0.0101 0.0118 0.0135 0.01515 0.0168

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

DR Pellets Mix Fraction Com 2-KPRS 10-0 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%

SiO2 1.3294 1.27135 1.2133 1.15525 1.0972 1.03915 0.9811 0.92305 0.865 0.80695 0.7489

Al2O3 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

P2O5 0.0744 0.07269 0.07098 0.06927 0.06756 0.06585 0.06414 0.06243 0.06072 0.05901 0.0573

V2O5 0.03 0.04662 0.06324 0.07986 0.09648 0.1131 0.12972 0.14634 0.16296 0.17958 0.1962

TiO2 0.06 0.07198 0.08396 0.09594 0.10792 0.1199 0.13188 0.14386 0.15584 0.16782 0.1798

Cr2O3 0.0184 0.01685 0.0153 0.01375 0.0122 0.01065 0.0091 0.00755 0.006 0.00445 0.0029

MoO2 0 0 0 0 0 0 0 0 0 0 0

MoO3 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

CaF2 0 0.00123 0.00246 0.00369 0.00492 0.00615 0.00738 0.00861 0.00984 0.01107 0.0123

CaCO3 0 0 0 0 0 0 0 0 0 0 0

MgCO3 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

WO3 0 0 0 0 0 0 0 0 0 0 0 NbO 0 0 0 0 0 0 0 0 0 0 0

Na2O 0.004 0.00759 0.01118 0.01477 0.01836 0.02195 0.02554 0.02913 0.03272 0.03631 0.0399

K2O 0.0055 0.03495 0.0644 0.09385 0.1233 0.15275 0.1822 0.21165 0.2411 0.27055 0.3

CaSO4 0.0076 0.00769 0.00778 0.00787 0.00796 0.00805 0.00814 0.00823 0.00832 0.00841 0.0085

SnO2 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

CaCl2 0 0.00031 0.00062 0.00093 0.00124 0.00155 0.00186 0.00217 0.00248 0.00279 0.0031

Ca(OH)2 0 0 0 0 0 0 0 0 0 0 0 FeOOH 0 0 0 0 0 0 0 0 0 0 0

FeCO3 0 0 0 0 0 0 0 0 0 0 0 FeO 0 0 0 0 0 0 0 0 0 0 0

Fe2O3 95.6051 95.63875 95.6724 95.70605 95.7397 95.77335 95.807 95.84065 95.8743 95.90795 95.9416

Fe3O4 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 wt% wt% wt% wt% wt% wt% wt% wt% wt% wt% wt% 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

SiO2 1.8127 1.7336 1.6545 1.5754 1.4962 1.4171 1.338 1.2589 1.1797 1.1006 1.0215

Al2O3 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

P2O5 0.1015 0.0992 0.0968 0.0945 0.0921 0.0898 0.0875 0.0851 0.0828 0.0805 0.0781

V2O5 0.0409 0.0635 0.0862 0.1089 0.1315 0.1542 0.1769 0.1995 0.2222 0.2449 0.2676

TiO2 0.0818 0.0981 0.1145 0.1308 0.1471 0.1935 0.1798 0.1962 0.2125 0.2289 0.2452

Cr2O3 0.0251 0.023 0.0209 0.0188 0.0167 0.0145 0.0124 0.0103 0.0082 0.0061 0.004

MoO3 0 0 0 0 0 0 0 0 0 0 0

CaF2 0 0.0017 0.0034 0.005 0.0067 0.0084 0.0101 0.0118 0.0134 0.0151 0.0168

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

Varying Carbon content in DRI Varying the DRI Metallization Based on KPRS Pellets Based on KPRS Pellets

1.00% 2.00% 3.00% 92.00% 95.00% 98.00%

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

SiO2 0.7489 0.7489 0.7489 SiO2 0.7489 0.7489 0.7489

Al2O3 0.1598 0.1598 0.1598 Al2O3 0.1598 0.1598 0.1598 MnO 0.0773 0.0773 0.0773 MnO 0.0773 0.0773 0.0773 CaO 0.8848 0.8848 0.8848 CaO 0.8848 0.8848 0.8848 MgO 0.649 0.649 0.649 MgO 0.649 0.649 0.649

P2O5 0.0573 0.0573 0.0573 P2O5 0.0573 0.0573 0.0573

V2O5 0.1962 0.1962 0.1962 V2O5 0.1962 0.1962 0.1962

TiO2 0.1798 0.1798 0.1798 TiO2 0.1798 0.1798 0.1798

Cr2O3 0.0029 0.0029 0.0029 Cr2O3 0.0029 0.0029 0.0029

MoO2 0 0 0 MoO2 0 0 0

MoO3 0 0 0 MoO3 0 0 0 NiO 0.0382 0.0382 0.0382 NiO 0.0382 0.0382 0.0382

CaF2 0.0123 0.0123 0.0123 CaF2 0.0123 0.0123 0.0123

CaCO3 0 0 0 CaCO3 0 0 0

MgCO3 0 0 0 MgCO3 0 0 0 CuO 0.0013 0.0013 0.0013 CuO 0.0013 0.0013 0.0013

WO3 0 0 0 WO3 0 0 0 NbO 0 0 0 NbO 0 0 0

Na2O 0.0399 0.0399 0.0399 Na2O 0.0399 0.0399 0.0399

K2O 0.3 0.3 0.3 K2O 0.3 0.3 0.3

CaSO4 0.0085 0.0085 0.0085 CaSO4 0.0085 0.0085 0.0085

SnO2 0 0 0 SnO2 0 0 0 ZnO 0.0037 0.0037 0.0037 ZnO 0.0037 0.0037 0.0037

CaCl2 0.0031 0.0031 0.0031 CaCl2 0.0031 0.0031 0.0031

Ca(OH)2 0 0 0 Ca(OH)2 0 0 0 FeOOH 0 0 0 FeOOH 0 0 0

FeCO3 0 0 0 FeCO3 0 0 0 FeO 0 0 0 FeO 0 0 0

Fe2O3 95.9416 95.9416 95.9416 Fe2O3 95.9416 95.9416 95.9416

Fe3O4 0.9654 0.9654 0.9654 Fe3O4 0.9654 0.9654 0.9654

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

DRI composition DRI composition

Carbon DRI Metallization 1.00% 2.00% 3.00% 92.00% 95.00% 98.00%

wt% wt% wt% wt% wt% wt% Metallic Components Metallic Components C 1 2 3 C 2 2 2 S 0.0028 0.0027 0.0027 S 0.0027 0.0027 0.0027 Fe 88.75 87.8535 86.957 Fe 84.3947 87.8535 91.3689 Ni 0.0413 0.0409 0.0405 Ni 0.0406 0.0409 0.0412 Cu 0.0014 0.0014 0.0013 Cu 0.0014 0.0014 0.0014 Mo 0 0 0 Mo 0 0 0

Oxidic Components Oxidic Components

SiO2 1.0319 1.0215 1.011 SiO2 1.0132 1.0215 1.0298

Al2O3 0.2202 0.2179 0.2157 Al2O3 0.2162 0.2179 0.2197 FeO 6.0093 5.9486 5.8879 FeO 9.4412 5.9486 2.3989 MnO 0.1066 0.1055 0.1044 MnO 0.1046 0.1055 0.1063 CaO 1.2239 1.2115 1.1992 CaO 1.2018 1.2115 1.2214 MgO 0.8943 0.8852 0.8762 MgO 0.8781 0.8852 0.8925

P2O5 0.0789 0.0781 0.0773 P2O5 0.0775 0.0781 0.0788

V2O5 0.2703 0.2676 0.2648 V2O5 0.2654 0.2676 0.2697

TiO2 0.2477 0.2452 0.2427 TiO2 0.2432 0.2452 0.2474

Cr2O3 0.004 0.004 0.0039 Cr2O3 0.0004 0.0004 0.004

MoO3 0 0 0 MoO3 0 0 0

CaF2 0.017 0.0168 0.0166 CaF2 0.0167 0.0168 0.017

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

Varying the SIO2 content Varying the Al2O3 Content Based on KPRS Pellets Based on KPRS Pellets

0.50% 1.00% 1.50% 0.25% 0.50% 0.75%

wt% wt% wt% wt% wt% wt% SiO 2 0.5 1 1.5 SiO2 0.748225 0.74635 0.744475

Al2O3 0.1602 0.1594 0.1586 Al2O3 0.25 0.5 0.75 MnO 0.077525 0.07715 0.076775 MnO 0.0773 0.0771 0.0769 CaO 0.88695 0.8825 0.87805 CaO 0.883975 0.88175 0.879525 MgO 0.65065 0.6474 0.64415 MgO 0.64855 0.647 0.64545 P O 2 5 0.057425 0.05715 0.056875 P2O5 0.05725 0.0571 0.05695 V O 2 5 0.196625 0.19565 0.194675 V2O5 0.196 0.1955 0.195 TiO 2 0.1802 0.1793 0.1784 TiO2 0.17965 0.1792 0.17875 Cr O 2 3 0.0029 0.0029 0.0029 Cr2O3 0.0029 0.0029 0.0029 MoO 2 0 0 0 MoO2 0 0 0 MoO 3 0 0 0 MoO3 0 0 0 NiO 0.03885 0.0392 0.03955 NiO 0.038125 0.03805 0.037975

CaF2 0.01235 0.0123 0.01225 CaF2 0.012275 0.01225 0.012225

CaCO3 0 0 0 CaCO3 0 0 0

MgCO3 0 0 0 MgCO3 0 0 0 CuO 0.001275 0.00125 0.001225 CuO 0.001275 0.00125 0.001225

WO3 0 0 0 WO3 0 0 0 NbO 0 0 0 NbO 0 0 0

Na2O 0.04 0.0398 0.0396 Na2O 0.0399 0.0398 0.0397

K2O 0.03005 0.0299 0.02975 K2O 0.029925 0.02985 0.029775 CaSO 4 0.00855 0.0085 0.00845 CaSO4 0.008475 0.00845 0.008425

SnO2 0 0 0 SnO2 0 0 0 ZnO 0.003775 0.00375 0.003725 ZnO 0.0037 0.0037 0.0037 CaCl 2 0.003175 0.00315 0.003125 CaCl2 0.0031 0.0031 0.0031

Ca(OH)2 0 0 0 Ca(OH)2 0 0 0 FeOOH 0 0 0 FeOOH 0 0 0

FeCO3 0 0 0 FeCO3 0 0 0 FeO 0 0 0 FeO 0 0 0

Fe2O3 75.9322 82.1989 88.4656 Fe2O3 95.854875 95.61465 95.374425

Fe3O4 0.967825 0.96295 0.958075 Fe3O4 0.964575 0.96215 0.959725 0 0 0 0 0 0 Moisture 1.6 1.6 1.6 Moisture 1.6 1.6 1.6 Fines 0.03 0.03 0.03 Fines 0.03 0.03 0.03 Dustloss 0.03 0.03 0.03 Dustloss 0.03 0.03 0.03

DRI composition DRI composition

SIO2 content Al2O3 Content 0.50% 1.00% 1.50% 0.25% 0.50% 0.75%

wt% wt% wt% wt% wt% wt% Metallic Components Metallic Components C 2 2 2 C 2 2 2 S 0.0027 0.0027 0.0027 S 0.0027 0.0027 0.0027 Fe 88.1605 87.5445 86.931 Fe 87.7431 87.4374 87.13245 Ni 0.0411 0.0408 0.0405 Ni 0.04085 0.0407 0.04055 Cu 0.0014 0.0014 0.0013 Cu 0.0014 0.0014 0.0014 Mo 0 0 0 Mo 0 0 0

Oxidic Components Oxidic Components

SiO2 0.6826 1.3625 2.0398 SiO2 1.0202 1.0166 1.0131

Al2O3 0.2187 0.2172 0.2156 Al2O3 0.3408 0.681 1.0205 FeO 5.9694 5.9277 5.8861 FeO 5.94115 5.9204 5.8998 MnO 0.1058 0.1051 0.1044 MnO 0.5792 0.105 0.1046 CaO 1.2158 1.2073 1.1988 CaO 1.21 1.2058 1.20155 MgO 0.8883 0.8821 0.8759 MgO 0.8841 0.881 0.87795

P2O5 0.0784 0.0778 0.0773 P2O5 0.07805 0.0778 0.07745

V2O5 0.2685 0.2666 0.2647 V2O5 0.2672 0.2663 0.26535

TiO2 0.2461 0.2443 0.2426 TiO2 0.2449 0.244 0.2432

Cr2O3 0.0004 0.004 0.0039 Cr2O3 0.004 0.0004 0.004

MoO3 0 0 0 MoO3 0 0 0

CaF2 0.0169 0.0168 0.0166 CaF2 0.0168 0.0167 0.0167

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

Varying the SiO2 + Al2O3 Content Based on KPRS Pellets

0.75% 1.50% 2.25%

wt% wt% wt%

SiO2 0.5 1 1.5

Al2O3 0.25 0.5 0.75 MnO 0.077425 0.07685 0.076275 CaO 0.8862 0.8795 0.8728 MgO 0.6500875 0.645175 0.6402625

P2O5 0.0574375 0.056975 0.0565125

V2O5 0.1965 0.195 0.1935

TiO2 0.18005 0.1787 0.17735

Cr2O3 0.0028875 0.002875 0.0028625

MoO2 0 0 0

MoO3 0 0 0 NiO 0.038225 0.03795 0.037675

CaF2 0.0123125 0.012225 0.0121375

CaCO3 0 0 0

MgCO3 0 0 0 CuO 0.001275 0.00125 0.001225

WO3 0 0 0 NbO 0 0 0

Na2O 0.04 0.0397 0.0394

K2O 0.030075 0.02985 0.029625

CaSO4 0.008525 0.00845 0.008375

SnO2 0 0 0 ZnO 0.0037625 0.003725 0.0036875

CaCl2 0.0031625 0.003125 0.0030875

Ca(OH)2 0 0 0 FeOOH 0 0 0

FeCO3 0 0 0 FeO 0 0 0

Fe2O3 96.09525 95.3691 94.64295

Fe3O4 0.86176625 0.7492325 0.63669875 0 0 0 Moisture 1.6 1.6 1.6 Fines 0.03 0.03 0.03 Dustloss 0.03 0.03 0.03

DRI composition

SiO2 + Al2O3 Content 0.75% 1.50% 2.25%

wt% wt% wt% Metallic Components C 2 2 2 S 0.0027 0.0027 0.0027 Fe 88.0494 87.1256 89.2072 Ni 0.041 0.0406 0.0401 Cu 0.0014 0.0014 0.0013 Mo 0 0 0

Oxidic Components

SiO2 0.6824 1.3607 2.0351

Al2O3 0.3412 0.6804 1.0175 FeO 5.9619 5.8993 5.8371 MnO 0.1057 0.1046 0.1035 CaO 1.2142 1.2015 1.1888 MgO 0.8872 0.8779 0.8686

P2O5 0.0783 0.0775 0.0767

V2O5 0.2682 0.2653 0.2625

TiO2 0.2458 0.2432 0.2406

Cr2O3 0.004 0.004 0.0039

MoO3 0 0 0

CaF2 0.0169 0.0167 0.165

59 Steel and Slag constraints

Table 8. A1 steel and slag analysis.

Steel and Slag analysis

A1 Slag Model λ-MgO 1.2 L-LP 0.5 L-LV 0.5

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

MgO material Dolomitic limestone Lime material Lime

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

A1 Steel Analysis

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

60 Table 9. A2 Steel and slag analysis.

A2 Slag Model λ-MgO 1.1 L-LP 0.5 L-LV 0.5

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

MgO material Dolomitic limestone Lime material Lime

Distribution from L-factors slag quantity 0.12 kg slag / kg steel Si inf Mn 100 P 30 S 1 Cr inf Ni 0 Mo 1 Nb Inf Ti inf Cu 0 Al inf V 500 W inf Fe 0.2 Co 1 As 1 B 1 Bi 1 Pb 1 Ca inf Ta 1 Sn 1 Zn 1

A2 Steel Analysis

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

Carbon 0.1 0 5

61 Plant data

Table 10. ME DR-furnace.

DR Furnace ME Energy Type Consumption Natural gas ME NG 10 GJ/Ton DRI typical Electricity ME NG-based electricity 100 kWh/Ton DRI Water source Process water 10 Nm3/Ton DRI Source of Oxygen ME Oxygen 10 Nm3/Ton DRI

DR Furnace Data typical Metallization 95.00% Carbon content 2.00%

Briquetting cost 4 USD/ton

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

Capital Cost: 13.147 M USD/ year Annual Production: 814680 Tonnes

Table 11. NA DR-furnace.

DR Furnace NA Energy Type Consumption Natural gas NA NG 10 GJ/Ton DRI typical Electricity NA 100 kWh/Ton DRI Water source Process water 10 Nm3/Ton DRI Source of Oxygen NA_Oxygen 10 Nm3/Ton DRI

DR Furnace Data typical Metallization 95.00% Carbon content 2.00%

Briquetting cost 4 USD/ton

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

Capital Cost: 13.147 M USD/ year Annual Production: 814680 Tonnes

62 Table 12. ME EAF.

EAF ME Type Consumption Energy Source of Energy1 ME NG-based electricity Calculated Carbon source Coke fines Calculated Source of oxygen ME Oxygen 2800 Nm3/ Charge Electrode material Graphite electrode 2.65 kg/MWh Water source Process water 0 m3/min

EAF Furnace Data Standard tapping temperature 1600 C Standard tapping weight 80 tonnes Average Idle time 3 min Average power off time 3 min Power on Heat loss 5 MW Idle/power off heat loss 1 MW Average power on 65 MW Average idle 5 MW Post combustion 20 % Inner diameter 6.1 m No of furnaces 1 Slag carry over to ladle 0 kg/ton steel

Capital Cost 19.721 M USD/year

Additional Cost Adjustments Steel production 5 USD/ ton steel Slag Disposal 25 USD/ ton slag Dust Disposal 50 USD/ ton dust

Table 13. NA EAF.

EAF NA Type Consumption Energy Source of Energy1 NA Calculated Carbon source Coke fines Calculated Source of oxygen NA_Oxygen 2800 Nm3/ Charge Electrode material Graphite electrode 2.65 kg/MWh Water source Process water 0 m3/min

EAF Furnace Data Standard tapping temperature 1600 C Standard tapping weight 80 tonnes Average Idle time 3 min Average power off time 3 min Power on Heat loss 5 MW Idle/power off heat loss 1 MW Average power on 65 MW Average idle 5 MW Post combustion 20 % Inner diameter 6.1 m No of furnaces 1 Slag carry over to ladle 0 kg/ton steel

Capital Cost 19.721 M USD/year

Additional Cost Adjustments Steel production 5 USD/ ton steel Slag Disposal 25 USD/ ton slag Dust Disposal 50 USD/ ton dust

63 Table 14. Scrap analysis.

Scrap Analysis

Elements wt% Oxides wt%

C 0.4 SiO2 0.5

Al 0 Al2O3 0 Si 0.3 FeO 2 P 0.1 MnO 0 S 0.05 CaO 0 Ti 0 MgO 0

V 0 P2O5 0

Cr 0.1 V2O5 0

Mn 0.64 TiO2 0 Fe 95.84 CrO 0

Co 0 Cr2O3 0

Ni 0.01 Fe2O3 0

Cu 0.01 Fe3O4 0

Nb 0 MoO2 0

Mo 0 MoO3 0 As 0 NiO 0

W 0 CaF2 0

B 0 CaCO3 0

Bi 0 MgCO3 0 Pb 0 Ca 0 Ta 0 Sn 0.05 Zn 0 O 0 N 0 H 0

64 Table 15. Slag former analysis.

Slag formers Dolomitic Limestone Burnt Lime

wt% wt%

SiO2 2.5 SiO2 1.7

Al2O3 0.5 Al2O3 0.3 FeO 0.67 CaO 84

P2O5 0.09 MgO 4.9

CaCO3 58.2 CaCO3 9.1

MgCO3 38.04

65